texts: Distinguishing between different geometries of bromochlorobis(triphenylphosphine)platinum(II) using ¹⁹⁵Pt NMR

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Question

The question off which I am basing my question assumes that $\ce{[PtClBr(PPh3)2]}$ can exist in either the square-planar or tetrahedral geometry. If one would use $\ce{^{195}Pt}$ NMR spectroscopy, how would the spectra of the possible molecules differ from each other? The effect of the $\ce{Cl}$ and $\ce{Br}$ can be disregarded.

My reasoning

For the square planar geometry, either the cis or trans isomer is possible. I am assuming that you won't be able to distinguish between the square planar trans molecule and the tetrahedral molecule since the $\ce{PPh3}$ ligands in each molecule are equivalent. The $\ce{^{195}Pt}$ NMR spectra for these two orientations will thus be the same, a single triplet.

Will the square planar cis molecule also produce the same spectrum or will there be second-order coupling present since the $\ce{PPh3}$ ligands are non-equivalent? How would the $\ce{^{195}Pt}$ NMR spectra then look for the cis isomer?


texts: Graphite: Thermal and electrical conductivity

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I recently encounter this question:

Compare, while providing an explanation, the thermal and electrical conductivity of graphite to that of diamond.

Provided answer:
Graphite conducts electricity(only across a layer) where as diamond does not.

Diamond is better at transferring heat than graphite.

Explanation:
Diamond is covalent network solid of carbon atoms which are linked to each other through sigma bonds.

Graphite has a layered structure where each layer is bonded to the other later through vanderwall forces only. Each layer consists of hexagonal rings which have a delocalized pi electron network just above and below the plane.

These delocalized pi electrons are the reason why graphite can conduct electricity along the planes, where as diamond cannot due to the lack of delocalized electrons.

Diamond is a better conductor of heat because the transfer of heat takes place through adjacent atoms transferring their vibrational energy and diamond has a very close knit network of atoms where as graphite does not.

My doubt:
In metals it is accepted that both electrical and thermal conductance is due the the free electrons present in the metal body.

Graphite too has delocalized free electrons so according the same logic graphite should be both a good conductor of heat and electricity.

So where am I or the answer provided going wrong?

P. S. I'm writing from a mobile device due to the lack of access computers so there might be some errors.

Edit:

J. D. Lee: Concise inorganic chemistry, fifth edition :

This would mean that the electrons are truley free since they can interact with other species nearby not preventing them from being bound to a system.


texts: Fractional index in a chemical formula of metal oxide

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I have just read an article in which they used $\ce{WO3}$ and $\ce{WO_{2.9}}$ as precursors, whose objective was to form $\ce{WS2}$, in an atmosphere of argon by CVD. In one boat there is the powder of $\ce{S}$ and in another boat there is $\ce{WO3}$ or $\ce{WO_{2.9}}$, in an oven with a double temperature zone. In the article they conclude that $\ce{WO_{2.9}}$ forms larger layers of $\ce{WS2}$ in the substrate giving the following justification:

  They found that $\ce{W^6+}$ cannot be directly sulfated by $\ce{S},$ unless some intermediates are formed due to the high energy of the $\ce{W-O}$ bond. The reduction from $\ce{W^6+}$ to $\ce{W^5+}$ is mandatory for the incorporation of sulfur in the $\ce{WO3}$ network. For $\ce{WO_{2.9}}$ in our case, its partial $\ce{W^6+}$ ions have been reduced to $\ce{W^5+}$ or $\ce{W^4+}$ ions. Therefore, we find that replacing $\ce{W^5+}$ or $\ce{W^4+}$ with $\ce{W^6+}$ in the initial stage facilitates the growth of the single crystal $\ce{WS2}$ film.

I didn't realize what the difference is between $\ce{WO3}$ and $\ce{WO_{2.9}}$ and where these ions come from that they talk about in this part of the article. I also don't understand what a fractional index means in a chemical formula. Could you help me to interpret that part of the article and explain these doubts that I have please?


texts: Why are potentials of cells with magnesium electrode always lower than expected?

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I have prepared the 1M water solution of magnesium acetate. Then I placed $\ce{Mg}$ and $\ce{Cu}$ electrodes in it. I predict there such reactions take place: $$\ce{Mg-2e^- \rightarrow Mg^{2+}}$$ $$\ce{H_3^+O + e^- \rightarrow\frac12 H_2 + H_2O}$$
The gas bubbles emitting on both electrodes probably confirm my prediction (I did not check is it hydrogen or not).
So I expect to obtain the potential difference about 2.3 V. But really I observe something like 1.62 V.

Then I changed the acetate solution to a water (simple water which we drink) and observed almost same value of 1.60 V. Adding there many crystals of $\ce{Mg}$ acetate (I added them till they could not dissolve more) almost did not change the voltage!

When I added much acid to the solution the potential difference became larger - up to 1.9 V.

So, I have two questions: 1) why the real voltage is so different from the expected value? 2) Why changing the $\ce{Mg^{2+}}$ concentration almost does not change the voltage?

You may say I have dirty magnesium electrode etc. But if you search e.g. experiments with potatoes (when one puts $\ce{Mg}$ and $\ce{Cu}$ strips in potato) you can observe that everywhere it is mentioned that such $\ce{Mg-Cu}$ cell gives 1.7 V.

I have several ideas why can it happen: a)some story with overpotentials, b)oxide film on magnesium surface.
What is the real reason?


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I read that ammonia can be used to clean scratches of certain materials, for example from wedding rings. I was thinking about how this would work but I actually don't know. I suspect that the question I might have to ask is "what is a scratch" and that thus the reason for my misunderstanding comes from some ambiguity in what a scratch might be in the English language.

This is how I would phrase my understanding of a scratch: A scratch on a material is a place on which parts of the surface are removed, creating a "cut" in the surface. Thus there are less particles in one place than the surrounding.

Either way, that is pretty much how I imagine it. If this is the case, why does ammonia "remove" the scratch? Does the ammonia-water solution fill the crevice left and attach itself to the surrounding material, for example the gold. If the ammonia-water solution is transparent you would just see the gold underlying the scratch and it would seem to have "filled" the scratch. But for that to happen the ammonia would have to become solid, which does not happen at room temperatures.

Perhaps the reason why a deep cut can not be "cleaned" with the solution, whilst the small cuts can, is that the word "scratch" is used for two different physical phenomena.

I'm hoping to get a deeper understanding of what is actually happening to the material being cleaned by the water-ammonia solution. Or, perhaps, a link to a paper or other resource explaining what happens.

Links:

https://www.leaf.tv/articles/how-to-get-scratches-out-of-a-gold-ring/
http://www.wikihow.com/Remove-Scratches-from-Glass


texts: Finding the percent of calcium carbonate in commercial antacid by using back titration

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I'm an IB Chemistry student and I had to do a back titration lab where 1g of a powdered antacid tablet were mixed with 50mL 1M HCl, and the mixture was titrated using 0.2 M NaOH; the NaOH was to neutralize the leftover HCl that hadn't reacted with the antacid. The active ingredient in the antacid is CaCO3.

It took me about 40mL of NaOH to titrate the leftover HCl to endpoint; 40 mL at 0.2 mol/L translate to 0.008 moles of NaOH. In the equation for reaction between NaOH and HCl the ratio of the two reactants is 1:1; therefore there were 0.008 mol of unreacted HCl in the mixture.

There were 50mL of HCl (1 mol/L) in the mixture originally; 50mL * 1 mol/1000mL = 0.05 mol HCl total. Subtracting from this the molar quantity of unreacted (leftover) HCl yields: 0.05 - 0.008 = 0.042 mol HCl that did react with the CaCO3 in the antacid.

The reaction between CaCO3 and HCl is as follows:CaCO3 + 2HCl --> CaCl2 + CO2 +H2O
Therefore, molar ratio between CaCO3 and HCl is 1:2. 0.042 moles HCl reacted, therefore 0.021 mol CaCO3 were present in the sample. Multiplying this by the molar mass yields 0.021mol * (40+12+48)g/mol = 2.1 grams CaCO3.

That's a problem - i can't be having 210% composition by mass (the sample was 1g; I calculated 2.1 g CaCO3 present). So somewhere along the line i made a mistake, but I've checked my math so I don't know if it was a calculation error or if my method is dead wrong? Can anyone help me with this?


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I am using a rotary evaporator ('rotovap') in my lab mainly with dichloromethane as a solvent.

Usually between experiments I clean the receiving and boiling flasks with a brush using soap and water and finally rinse with alcohol.
For the condenser I try to do the same, but it is next to impossible to brush the water serpentine.

I want to try and distil some coffee and tea for consumption, but I am afraid of any possible contaminants.

What is an efficient and safe method to clean the glassware?


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In the Friedel - Crafts acetylation of bromobenzene, how is it possible to obtain a black-coloured product?

When the acetic anhydride was slowly added to the reactants - $\ce{AlCl3}$, DCM, bromobenzene - a small, hard, yellow lump formed.

Would this be $\ce{AlCl3}$?

When the acetic anhydride was added, the reflux was initiated. The lump appeared to disappear, leaving behind a dark red solution.

However, when the reflux was turned off, the solution appeared black. I'm trying to think of potential products, such as ortho and para bromobenzene or acetic acid or $\ce{Al(OH)3}$ but why so black?

Does anyone have any ideas?


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$\pu{5 mL}$ of $\pu{0.012 M}\,\ce{Pb(NO3)2}$ is mixed with $\pu{5 mL}$ of $\pu{0.030 M}\,\ce{KI}$. $\ce{PbI2}$ forms. Calculate the diluted concentrations of $\ce{Pb^{2+}}$ and $\ce{I-}$ ions.

I couldn't figure out whether it is an equilibrium question, or something else entirely.

I have currently tried using the moles of the limiting reactant (Pb(NO3)2) to obtain the moles of PbI2 formed and using the molar ratio to get concentration of each ion. However I have no idea whether I have done the correct calculation for ion concentration. The values I am getting are 0.003M Pb2+ and 0.012M I-

update: I have looked at the questions that follow and am able to say for certain this is not an equilibrium question.


texts: How to neutralise path weeder contamination

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I strongly suspect my aquarium has been contaminated by a rock sprayed with a path weeder containing Simazine, Amitrole & Ammonium Thiocyanate.

I removed all rock and made several large water changes but fish continued to die one or two a day. When the surviving fish were removed to separate tanks with identical water conditions fish are fine and not one has died for about a week. So it seems to me the chemicals have permeated the crushed coral substrate and filter media and is still leaching into the water.

I have emptied the tank completely & easily can replace the filter media but the substrate, resin decorative pieces, and plastic plants are expensive to replace and I would like to be sure I remove any residue in the tanks and piping etc. Is there anything I can wash the tank, substrate, and decor with to neutralize any remaining toxicity that would not leave a toxic residue in itself?

Would washing everything with vinegar be of any help?

Any advice from those understanding the chemical structure of these toxins and how I might rescue my prized aquarium would be greatly appreciated!


texts: Using baking powder to make baked food crispy

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The recipe I use for chicken wings achieves a fried texture by dusting the wings with baking powder and then baking at $220^\circ\pu C$ ($425^\circ \pu F$). The chicken is also dusted with salt and other seasonings, but I assume they're not chemically relevant.  What chemical process is going on, here?

I'd assumed it was some kind of reaction between the baking powder and the skin of the chicken, though I had no idea what. Then, one time, there was a stray boneless, skinless chicken thigh in with the wings I bought, and that also became crispy on the outside when cooked this way. I've also heard of people using the same technique on oven fries.


texts: Can I perform electrolysis without electrolyte? (with distilled water)

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When performing electrolysis at home, I usually used salt water as electrolyte. The problem is, that this method also produces chlorine and chlorine is aggressive to both humans and electrical equipment.

I was thinking of creating pure hydrogen and oxygen by using distilled water. I was taught that water is not conductive.

But since water has "positive" and "negative" part (which allows for it to dissolve polar bonds, doesn't it?). Couldn't I just tear the molecules apart if I use electrical field strong enough? If I can, how high the voltage must be?


texts: Why does my eudiometer have this excess volume at the top?

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It looks like this:

The measurements start at 2 mL and the volume remaining in the top seems to be greater than 1 mL. What is the purpose? I am trying to measure hydrogen gas.


texts: How do the def2-SV, def2-SV(P), and def2-SVP basis sets differ?

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I am trying to calculate the energy of complex molecules with DFT and have a question about the Ahlrichs (Karlsruhe) def2 basis sets.

What is the difference  between the def2-SV, def2-SV(P), and def2-SVP?
Do they only differ in whether the basis set includes split valence polarization or not?


texts: How is N to C ratio measured in forming austenitic stainless steel?

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Nitrogen is the future hope of stainless steel industry; since in the production of austenitic steel it can even completely replace Nickel (which is relatively very expensive) in some cases and for another reason: It decreases the temperature at which carbides should form.
As a result, there is always an optimum Carbon to Nitrogen ratio.My problems are:

How is N decreasing the temperature of the formation of carbides? Is it a catalyst or something?
Resources, however, didn't mention how the N to C ratio is measured? How? Am I missing something very easy in here?

Update: I just found this paper in which almost all of the info above can be found; but it's not my main reference.


texts: Is the surface of glass a fine layer of silanol?

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Today we learned in class through a vivid demonstration that water sticks to glass. We were then taught that water sticks to glass because while glass is mainly composed of silicon dioxide, the surface of glass is actually silanol. Hydrogen bonds form between molecules of water and silanol, which is why water sticks to glass.

Is this correct?


texts: Order of Reactivity of Halogens in Electrophilic Addition

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What is the order of reactivity of halogens in electrophilic addition reaction via formation of cyclohalonium intermediate?
(A) $\ce{F2}$> $\ce{Cl2}$> $\ce{Br2}$> $\ce{I2}$
(B) $\ce{I2}$> $\ce{Br2}$> $\ce{Cl2}$> $\ce{F2}$
(C) $\ce{I2}$> $\ce{Br2}$> $\ce{F2}$> $\ce{Cl2}$
(D) $\ce{Br2}$> $\ce{Cl2}$> $\ce{I2}$> $\ce{F2}$

I tried to predict it using the mechanism, but couldn't reach a conclusion. Is this based on thermodynamic and kinetic data?
Here's the mechanism involving bromine, for reference:

Could someone provide a detailed explanation for the above problem, with data if possible?


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In my textbook (Olmsted and Williams 4th ed) it is given that pH of pure water is 7, pH of unpolluted rain water is between 5-6 and pH of acid rain is between 4-5.

It is obvious that pH for acid rain would be low. But how is it acidic, even slightly, for unpolluted rain water? Shouldn't unpolluted mean without any solutes or dust in water? Shouldn't it be similar to pH of pure water (7)?


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I was faced with a question where the skeletal structure of of D(+)-glucose was given and I was asked to give the right structure of L(-)glucose. I noticed that the correct answer was the one where all the stereocenters had opposite absolute configuration of those of D(+)glucose.

But my question is: Will the dextrorotatory and laevorotatory enantiomers always have a set of stereocenters with opposite absolute configuration?


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Why is the electron configuration of $\ce{Y^2+}$ $\mathrm{[Kr]5s^1}$ rather than $\mathrm{[Kr]4d^1}$? It seems as though there are numerous anomalies from the typical electron configuration rules, but can one predict these exceptions (and if so, how)?

What causes one electron to be removed from the $\mathrm{5s}$ orbital and one from the $\mathrm{4d}$ orbital, is it simply due to the $\mathrm{5s}$ energy decreasing below the $\mathrm{4d}$ energy after the first ionization?


texts: What is the reason for the exceptional stability of the cyclopropylmethyl carbocation?

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Can someone explain this to me by drawing resonance structures for the cyclopropylmethyl carbocation please?

Also one more question, is the tricyclopropylmethyl carbocation more stable than tropylium ion?


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Does kosher salt has a different structure than regular table salt or it is an issue of crystals size?
Why some recipes want us to use one instead of another?


texts: Comparison of acidity of aqueous solutions of Lewis Acids

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What can be the order of acidity of aqueous solutions of following Lewis acids: $\ce{FeCl3, AlCl3, BeCl2, NiCl2}$

The simplified reactions are:

$\ce{FeCl3}$:

$\ce{FeCl3 + 6H2O -> [Fe(H2O)6]^3+(aq) + 3Cl-(aq)}$

$\ce{[Fe(H2O)6]^3+(aq) -> [Fe(H2O)5(OH)]^2+(aq) + H+(aq)}$

$\ce{AlCl3}$:

$\ce{AlCl3 + 6H2O -> [Al(H2O)6]^3+(aq) + 3Cl-(aq)}$

$\ce{[Al(H2O)6]^3+(aq) -> [Al(H2O)5(OH)]^2+(aq) + H+(aq)}$

$\ce{BeCl2}$:

$\ce{BeCl2 + 4H2O -> [Be(H2O)4]^2+(aq) + 2Cl-(aq)}$

$\ce{[Be(H2O)4]^2+(aq) -> [Be(H2O)3(OH)]^+(aq) + H+(aq)}$

$\ce{NiCl2}$:

$\ce{NiCl2 + 4H2O -> [Ni(H2O)4]^2+(aq) + 2Cl-(aq)}$

$\ce{[Ni(H2O)4]^2+(aq) -> [Ni(H2O)3(OH)]^+(aq) + H+(aq)}$

For first step of reaction, the octet of $\ce{Al}$ and $\ce{Be}$ are not complete. Thus, reaction will be faster in case of $\ce{AlCl3}$ and $\ce{BeCl2}$.

For second step of reaction, the charge density of $\ce{Al}$ and $\ce{Fe}$ are more than that in others. Thus, it can break one $\ce{OH}$ bond and the reaction will be faster in case of $\ce{AlCl3}$ and $\ce{FeCl3}$.

But what will be the overall acidity order of these four compounds?


texts: Why is pickle salty? How does salt get into pickle?

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I know this may look like some question easily answered with common sense, but please read.

If water is the solvent wouldn't the only thing that moves be water? (Osmosis)

Edit: this is basically what I think. If you imagine the skin of whatever you are pickling as a membrane that prohibit the flow of electrolytes but allows that if water. Then salt, NaCl, cannot move anywhere.


texts: Near IR spectroscopy vs. IR spectroscopy

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I am a backer of this Kickstarter: SCiO Near IR Spectroscopy

Here is a link to their technology: SCiO Technology

Question: How short of full IR spectroscopy do you think this device is? I have asked them whether we could program the SCiO to act as an IR spectrometer, and they have said this would require additional programming (which I am not qualified to do). But I am wondering if there would still be limitations. Conversely, Consumer Physics seems to imply that our taking more observations with the SCiO will make the device smarter and more useful.

This is obviously a question directed at experts in IR spectroscopy, which I am most definitely not.


texts: Calculate the number of atoms of oxygen present in 1.3 mol of sulfuric acid

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Calculate the number of atoms of oxygen present in $\pu{1.3 mol}$ of $\ce{H_2SO_4}$

1 mol has $6.02\times 10^{23}$ atoms

So $\pu{1.3 mol}$ must have $1.3 \times 6.02 \times 10^{23} = 7.826 \times 10^{23}$ atoms

Since there are 4 oxygen atoms  out of 7 atoms in total in $\ce{H_2SO_4}$,

${4 \over 7} \times 7.826 \times10^{23}$

So there are $4.472 \times 10^{23}$ oxygen atoms present.

However the answer key says that $3.1 \times 10^{24}$ atoms is the answer.

What went wrong?


texts: Why does plastic tear easier when you pull it quickly?

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If you've ever taken the plastic from a plastic bag and pulled on it, you might know what I mean. If you pull quickly, the plastic tears relatively easily, but if you pull it slowly, it gets stretched out into an indestructible plastic string. Once stretched, pulling the plastic as hard as you did to tear it before yields no results.

Similarly, adhesive bandages are pulled off the skin (almost) painlessly if pulled quickly, but seem to stick even under the same level of force if it is applied more gradually.

What explains this phenomenon?


texts:
Which of the following is the best description of the arragement of fluorine atoms around the arsenic atom in a molecule of $\ce{AsF5}$?
  (a) trigonal bipyramid
  (b) octahedron
  (c) tetrahedron
  (d) square pyramid
  (e) planar pentagon

The correct answer is (a).

I know that the answer can't be (b), (c), or (e) since octahedron requires 6 ligands and tetrahedron requires 4 ligand, and planar pentagon is only observed in $\ce{[IF5]-}$ and $\ce{[XeF5]-}$. I recall that first row transition metals prefer trigonal bipyramidal configurations, thus trigonal bipyramidal is the more likely geometry, but I'm not sure why this is true?

Any help would be greatly appreciated.


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Follow this paper,

Structural analysis of humins formed in the Brønsted acid catalyzed dehydration of fructose

They explained "humins are spatially and chemically heterogeneous materials."

I found "spatial" means "about space" but I think this meaning doesn't correlate with this context"

In summary,
What is spatially and chemically heterogeneous materials? and How did they know humins are spatially and chemically heterogeneous materials?


texts: Can thiols be created using a Grignard reagent?

texts: I'm trying to find information on the synthesis of thiols via Grignard reagents. While looking at the synthesis routes on Wikipedia, it said that a Grignard reagent will react with sulphur to form thiolates which will hydrolyse easily to the thiol; however, I'm struggling to find any references for this. Has anyone ever heard of this before or maybe tried it themselves?


texts: What's the difference between "conversion" in condensation polymerization and in radical polymerization?

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The conversion in condensation polymerization is defined as the fraction of functional groups reacted,

$$p=\frac{[M]_0-M}{[M]_0}$$

while in radical polymerization it's defined as the fraction of monomer that has reacted.

Why is it not the same thing?


texts: Why does a 57.15% ABV spirit (ethanol+water) have a density of 923 kg per cubic meter?

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According to the UK proof standard, a 100 proof spirit was defined as a spirit with gravity of $\frac{12}{13}$ that of water or $\pu{923 kg m-3}$, which is equivalent to $\mathrm{57.15\% \ ABV}$.

One liter of $\mathrm{57.15\% \ ABV}$ spirit contains $\pu{571.5 cm3}$ ethanol and $\pu{428.5 cm3}$ water. If the densities of ethanol and water at $\pu{20 ^\circ C}$ are $\pu{0.789 g cm-3}$ and $\pu{0.998 g cm-3}$, respectively, then the density  of spirit should be $\pu{0.8785 g cm-3}$ or $\pu{878.5 kg m-3}$.
Where did I go wrong with that? How can a $\mathrm{57.15\% \ ABV}$ spirit have a density of $\pu{923 kg m-3}$?


texts: How does sulfuric acid catalyze the reaction of potassium chlorate and sucrose?

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Part of the total reaction is mentioned here:

http://chemistry.about.com/od/demonstrationsexperiments/ht/instantfire.htm

$\ce{2KClO3(s)} + \text{heat} \rightarrow 2\ce{KCl(s)} + 3\ce{O2(g)}$

The rest is a mystery. (And where does the heat come from?)

I regret to say that I have delayed acquisition of organic chemistry principles that might have answered this question already but can't help but wonder why, right now.

I feel that once the role of sulfuric acid is cleared up, the reaction with sucrose not described above will explain itself.

(And no I am going to run around burning things down with this knowledge.)


texts: Making a non-CN dissolved gold solution ideal for electroplating

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I've had success electroplating $\ce{Ni}$ and $\ce{Cu}$, but interestingly never $\ce{Al}$. My focus here is on plating with $\ce{Au}$, specifically onto an $\ce{Ni}$ surface.

In general from my own work and others' suggestions, I have found applying a voltage (direct current) of 5 V through a relatively dilute solution of relevant metal, e.g. 2.53 g $\ce{Ni(NH4)2(SO4)2*6H2O}$ dissolved in 81.9 mL 0.42 % acetic acid at ~60 °C makes a very nice, lustrous plating of $\ce{Ni}$ on a clean $\ce{Cu}$ surface after ~90 s of submersion.

I have been able to dissolve $\ce{Au}$ in warm, concentrated $\ce{HCl}$ and minimal $\ce{HNO3}$, and have heard that you can dissolve it in $\ce{HCl}$ and $\ce{H2O2}$, which makes sense because $\ce{Cu}$ does the same.

I'm looking for an ideal solution here, starting with pure metallic gold. I want to avoid any mistakes because I only have 1 g to work with. By default I'm going to try a comparable concentration of dissolved $\ce{Au}$ to what I mentioned with $\ce{Ni}$, but any advice is appreciated – especially a specific method for making an "ideal" solution.

I've found that several commercial solutions contain $\ce{(CN)4AuK}$, but I really want to avoid using cyanide.

This paper by Paul A. Kohl is immensely helpful and interesting, but I'm wondering if anyone has had any success with something simple.
It makes mention of using sulphide, thiosulfite, thallium, etc.


texts: How to calculate the dissociation constant of a weak acid from the titration with a strong base?

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Problem:
  A solution of an unknown weak acid of unknown concentration was titrated with a solution of a strong base of unknown concentration. During the titration, the pH after adding $\pu{2.00 mL}$ of the base was 6.912. An additional $\pu{14.00 mL}$ of the base was required to reach the equivalence point. Calculate the Ka of the weak acid.

I have decimated six sheets of paper trying different equations. Combining the two ICE tables you can make for each equation, I can still get no fewer than three unknowns. I'm sure I'm overlooking a super-simple solution but I cannot  think of it.

These images are what I have done so far.


texts: Non-trivial cases where the frozen core approximation is bad?

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In computational chemistry, it is extremely common to freeze the core electrons after an initial Hartree-Fock calculation, meaning that the core electrons are left out of any treatment of the electron correlation. Which orbitals are considered core depends on the atom, but for the second row, it usually just means the 1s electrons are not correlated.

This is an intuitive approximation, as one would expect that correlation of the valence electrons would have the greatest effect on any actual chemistry.

Now, clearly one can imagine situations where freezing the core electrons is a very bad idea. One such case is if you were interested in modelling x-ray spectroscopy. I am less interested in this type of example as this is almost just a user error, and hence I would consider this a somewhat trivial example.

So, to be concrete, are there any known examples in which treatment of correlation of the core electrons results in a qualitative change in the modelling of a process which is primarily mediated by the valence electrons?

My guess is if there is an example it occurs in the third row and beyond.


texts: What would be the major products of this reaction?

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Obviously, A would be 3-Bromoo 3-methyl cyclo hexene:

as the stable free radical intermediate would be formed.
But B is what I am having problems with. I read that $\ce{LiAlH4}$ forms alkenes with three degree halides. So my guess was
2-Methyl-1,3-cyclohexadiene:

But when I checked my book, it said B would just be the Bromine getting substituted by Deuterium in (A)
(I'm sorry I don't know any site that allows making chemical structures with isotopes included so I had to describe it like this.)
Can someone please help me out with this?


texts: Is there a single word antonym for dissociate?

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Teaching ionic and covalent compounds, and one of the differences is that some ionic compounds will dissociate when dissolved but covalent compounds usually do not (salt water vs. sugar water, just basic stuff).

Although I'm taking a very basic approach, I would still like to use proper scientific language with my students. Is there a single-word synonym for "stay bonded" or a single-word antonym for "dissociate"? My own searches either come up with only 2-word terms or with synonyms for "come together" which aren't appropriate since the atoms are already together before dissolution.

Example sentence: Some ionic compounds dissociate when dissolved, but covalent compounds __ (stay together/don't dissociate) __.


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Common saying. Diamond possesses:

ultra hardness, (10 on the Mohs scale; 10000 HV on Vicker's Hard Test (iron merely 30-80))
hyper thermal conductivity, ($2320~\mathrm{W\, m^{-1}\, K^{-1}}$, or over ten times better than the heatsink in your computer!)
extreme pressure resistance, (withstands a crushing 600 gigapascals; or around 2 times the pressure at the center of the earth, enough to snap carbon nano-tubes and graphene or create metallic oxygen or overcome copper's electron degeneracy pressure, making the maximum chamber pressure of a firing pistol seem literally like popping popcorn... I digress)
and excellent luster (what do you expect, it's a diamond) combine to make the gemstone coveted by all.

Diamonds are the stuff of awesome.

But do they really exist forever?

Wikipedia notes that,

  Diamond is less stable than graphite, but the conversion rate from diamond
   to graphite is negligible at standard conditions.

Huh. But Wikipedia doesn't mention how long. So how long would it take for this super-material to convert to the stuff I scribble with?

(If you doubt the claims about diamond's seemingly unbelievable properties, check out the link on Wikipedia about diamond and this and this.)

Great point Joe made, that $10^{80}$ is just forever to us puny humans. Being a geek I can't resist the urge to compare the time length $10^{80}$:

Makes the entire lifespan of a red dwarf star seem like the Planck second.
Enough time for you to sift through all the atoms in the entire UNIVERSE at a rate of one atom per second.
Getting $67 worth of US quarters and flipping them, one per second, to get all heads-up.
Chance of macroscopic quantum tunneling!! (I don't know precisely how much, but quite large)

...and this is $10^{80}$ seconds I'm talking about...


texts: For the solubility of AB2, Ksp=[A][B]^2=x*(2x)^2. Why is (2x)^2 not considered double dipping?

texts:
For $$\ce{AB_2<=> A + 2B} $$

$$K_{\text{sp}}=\ce{[A]*[B]^2} $$

$$K_{\text{sp}}=\ce{[x]*[2x]^2} $$

For the term $$\ce{[2x]^2} $$

Why isn't this considered double dipping on B's behalf?

I.e. why isn't it just $$K_{\text{sp}}=\ce{[x]*[x]^2} $$ or $$K_{\text{sp}}=\ce{[x]*[2x]} $$

Why is B both multiplied by 2 and squared?


texts: Formation of O₂, Water, and Electricity from Hydroxide?

texts:
The Clark Type Oxygen Electrode converts water, oxygen, and electrons into hydroxide via a hydrogen peroxide intermediate:

\[\ce{O2 + 4e^{−} + 2 H_2O -> 4 OH^{−}}\]

Which is the sum of:
\[
\begin{align*}
\ce{2H2O +O2 + 2e- &-> H2O2 + OH- \\
H2O2 + 2e- &-> 2 OH-}
\end{align*}
\]
Can this be reversed?


texts: Color difference among oxovanadium species

texts:
Why dioxovanadium $\ce{[VO2]+}$ is pale yellow, whereas orthovanadate $\ce{[VO4]^3-}$ is colorless?

Both of them should be colorless if we ignore charge transfer for a moment, because in both cases vanadium is at +5 oxidation state.

Now considering the charge transfer is the reason for the pale yellow color of dioxovanadium species, why orthovanadate does not show charge transfer band?


texts: Why is it aqueous and ethanolic conditions for nucleophillc substitution of cyanide ion with benzyl chloride?

texts:
I was doing an exam question where benzyl chloride was undergoing a nucleophilic substitution with cyanide ion to form benzyl cyanide.

Please can someone enlighten me as I have never seen both conditions before just one or the other. I have Googled it but no sites talk about the conditions of nucleophilic substitution with a cyanide ion in a benzene context. Does the benzene alter the conditions?


texts: Looking for a Solvent for Fragrance Oils

texts: Hi I am looking for a solvent for fragrance oils, that has low evaporation and high diffusivity (low molecular weight and hence spreads well in the air). The solvent should also be soluble in water and should have a low evaporation rate (I tried methanol, it diffuses well but it evaporates very fast, thus not serving the purpose)


texts: Why do different substances containing saturated hydrocarbons burns with different flame?

texts:
LPG and Candle wax both contain saturated hydrocarbon, yet LPG gives a clean white flame but a candle gives yellow flame with lots of smoke. Why so?
I have read some answers on web which says that it is due to the insufficient supply of oxygen, so I tried burning candle beside LPG ( so there is no difference in supply of oxygen for both candle and LPG ) , but  still candle gives a yellow flame. Why?


texts: Role of 10-camphor sulfonic acid as a catalyst in protecting group chemistry

texts:
I recently did a reaction in the lab where 10-camphor sulfonic acid was used as the catalyst instead of something more conventional like hydrochloric acid or sulfuric acid. Dry acetontrile was used as a solvent. The scheme is shown below:

I'm not too sure why it is used. My initial thoughts are it's due to the solubility of 10-CSA in water/organic solvents. Alongside this using a conventional acid such as hydrochloric acid, the water content of the acid may affect the equilibrium. Although 10-CSA still has water in it, it would not be comparable to hydrochloric or sulfuric acid. 10-CSA also is quite bulky, which could provide some selectivity on which positions are deprotonated, although I don't see this as being likely due to its conjugate base having such a high pKa. Aside from this what else could be plausible explanation for the usage of 10-CSA?


texts: Chemical writing: the term "synthesis route"

texts:
Can someone tell me, which of the following terms should be used or avoided? (Google shows the presence of all the candidate terms.)

synthesis route
synthetic route
route of synthesis
synthesis pathway
synthetic pathway

Imagine for example a sentence such as "A new ... was developed."


texts: knowing that a strong base is a strong electrolyte, when we add a weak acid in water, will its conjugate strong base be a strong electrolyte too?

texts: I am not sure if the questions makes sense. What i am trying to say is that, if weak acids form strong conjugate bases, why aren't they strong electrolytes?  Thank you in advance.


texts: What is the isomer distribution in monosubstituted fluorobullvalene?

texts:
Bullvalene (tricyclo[3.3.2.02,8]deca-3,6,9-triene) is a fluxional molecule able to interconvert any two carbon atoms through a series of degenerate Cope rearrangements (for more information, see the Wikipedia article on bullvalene).  At slightly above room temperature bullvalene produces a single line in its 1H-NMR spectrum.  Considering fluorobullvalene, there are 4 possible isomers:

1-fluorotricyclo[3.3.2.02,8]deca-3,6,9-triene, i.e. the fluorine could be attached to any of the 3 equivalent cyclopropyl carbons
3-fluorotricyclo[3.3.2.02,8]deca-3,6,9-triene, i.e. the fluorine could be attached to any of the 3 equivalent olefinic carbons alpha to the cyclopropane ring
4-fluorotricyclo[3.3.2.02,8]deca-3,6,9-triene, i.e. the fluorine could be attached to any of the 3 equivalent olefinic carbons beta to the cyclopropane ring
5-fluorotricyclo[3.3.2.02,8]deca-3,6,9-triene, i.e. the fluorine could be attached to the unique tris-allylic carbon

Again, at room temperature or thereabouts, only a single line is observed in the 1H, 13C and 19F-NMR spectra.  I remember once reading that about 80% of the fluorine is in the tris-allylic position (4), most of the remainder is attached to the two olefinic carbons (2 and 3) and a very small amount is attached at the cyclopropyl position (1). This was often cited as an example to support the argument that fluorine prefers to form bonds to carbon when the involved carbon orbital has high p-content (low s-content).

Does anyone know what the isomer distribution is?  Those 4 numbers and a reference would be very helpful.


texts: What component of the human DNA reacts with 4,5-benzo[a]pyrene oxide and 7,8-benzo[a]pyrene oxide to produce cancerous tumors

texts:
I read in an article that we have this enzyme called P450 that converts aromatic compounds into water soluble compounds that can be eliminated. This enzyme converts aromatic compounds into arene oxides. For example, benzene can be oxidized into benzene oxide.

In the same article it talked about nucleophilic arene oxides being carcinogenic. The nucleophilic $\ce{NH2}$ group of 2'-deoxyguanosine is known to react with certain arene oxides. Once a molecule of this type becomes covalently bonded to an arene oxide the 2'-deoxyguanosine can no longer fit into the DNA double helix. Since the genetic code can't be transcribed it will lead to mutations that can lead to cancer.

Benzo[a]pyrene is found in cigarette smoke and automobile exhaust. It was the culprit behind the scrotum cancer epidemic among Victorian chimney sweepers in the late 1770s to 1800s. The two most harmful are the 4,5-oxide and 7,8-oxide, but I was wondering do these same oxides react with 2'-deoxyguanosine?


texts: Find the major products when these cyclohexenone bromides react with caustic potash in alcoholic medium:

texts:
Question:

Also find the order of the rates of the given reactions.

Answer: The answer of this question is given as option 'D' ie. all products are identical, however I am getting the answer as option 'C'.

My approach: I figured out that the under the presence of the given reagent the substrates will undergo elimination reaction via the E2 mechanism, in reactions (2) and (3), the same alkenes will be formed and the ketone will tautomerise to form a highly stable phenol, but in the first reaction I made Cyclohex-2,5-dien-one as the product, I am not able to understand how will this covert to phenol?

For the comparison of the rates I figured out that reaction (2) will have the fastest rate due to a highly acidic hydrogen present (the anion formed is in extended resonance with the double bond and the ketone), however I am not able to compare between the rates of the first and the third reactions.

Am I thinking in the right direction or is there some mistake? Please help.


texts: Pople Basis Set Abnormality: 3rd row 6-311G


texts: How do proton exchange membrane electrolysers work?

texts:
I've seen lots of videos, animations, and a few Wikipedia pages, but I'm still trying to figure out a few things.

Is an electrolyte needed to make the water conductive like an alkaline electrolyser?
Does the cathode remain dry? If so, how do the protons get across the gap from the membrane to the cathode?
Are platinum cathode and iridium anode catalysts required for the reaction, or just needed to speed it up a small amount? Why are these specific materials used?


texts: More stable carbocation, tertiary or benzylic?

texts:
This is a very confusing question that which is more stable, benzylic or tertiary butyl carbocation?
Some sources say benzylic due to resonance some say tertiary due to +i effect and 9 hyperconjugative structures.
I also found that benzylic has almost 3 kcal/mol more energy than the other making it less stable. But some very good examinations has approved benzylic.
So finally whats the concrete answer?


texts:
During the combustion of hydrocarbons, there is a difference between the amounts of carbon or hydrogen that results in incomplete or complete combustion of the material.

My question is, besides from an insufficient amount of oxygen, what can cause incomplete combustion?

What are the physical or chemical properties of the hydrocarbon responsible for incomplete combustion, such as the hydrogen to carbon ratio (mass, volume, number of atoms, etc.) or the saturation.

Please keep the reply suitable for a student studying high school to early university chemistry.


texts:
I need help identifying the following 5 substances; G, Y, T, L and J

G is a white solid which is insoluble in water. Consider the following reactions carried out on solid G.
Step 1:
Excess dilute nitric acid is added to a small amount of G in a test-tube. A colourless and odourless gas Y is given off and it is noticed that Y extinguishes a lighted splint.
The solution remaining in the test tube is divided into two different test tubes, sample A and sample B.
Step 2:
A few drops of potassium iodide solution are added to a sample A and a bright yellow precipitate L is observed.
Step 3:
Sodium hydroxide solution is added drop wise to sample B. A dense white precipitate, T, is immediately observed. Precipitate T dissolves when excess sodium hydroxide solution is added to it.
Step 4:
When some G is heated in a hard glass tube, gas Y which is colourless and odourless is given off. The solid J remaining in the hard glass tube changes colour on cooling from red-brown to yellow.

These are my solutions:

G = $\ce{PbCO3}$ because
Y = $\ce{CO2}$ - colourless and odourless gas
L = $\ce{PbI2}$
T = $\ce{Pb(OH)2}$
J = $\ce{PbO2}$

Are they correct or not?


texts: I was preparing $\ce{Mn3O4}$ but it was when characterized by XRD, a $\ce{Mn2O3}$ phase existed. Now how can I convert $\ce{Mn2O3}$ to $\ce{Mn3O4}$?


texts:
here's what I wrote from lecture,

what i'm confused about is, if two magnetic moment(B0 and the one of red H) have the same direction. wouldn't the magnetic field by red H cancel out the external magnetic field? I tried to visualized it in picture below.

2.1  if the directions of the two magnetic moment are different, is it because aromatic compound can flip upside down?

2.2 If the spin state is always same whether or not compound flip upside down, is it because of E from NMR machine?

Why do protons interact only with themselves? there are also O,C and Cl

hope someone would answer me~~


texts: Variation in atomic radii of elements in different blocks?

texts:
If we look at the values for the atomic radii (look at the table here), we can see that they rapidly decrease across the period initially. Looking at the second period,

The graph is pretty steep early on. But further down the period, as we enter the p-block elements, the graph levels out. This trend is repeated across the third and higher periods as well. Why is that?

The variation of atomic radii across the d-block and f-block elements is even more gradual. Why is that again?


texts: In aminobenzoic acid, do we have three different pKa's?

texts:
In para-aminobenzoic acid, how can I know whether the amino group loses a proton or not when $\mathrm{pH}$ exceeds $8.5$? I have only found two values for $\mathrm{p}K_\mathrm{a}$ but I never found info about the pKa (in this case it would be the third $\mathrm{p}K_\mathrm{a}$ at $\mathrm{pH}>8.5$) of the amino group.

In any case I guess at basic $\mathrm{pH}$, negative charge over $\ce{NH2}$ would be stabilized by aromatic ring and $\ce{COO-}$.


texts:
As part of intern work I am running simulations on a group of compounds, but as it is I have little in the way of O-Chem experience and I wanted to be able to at least get some direction on naming these compounds (maybe some examples).

I think I've got the names of the functional groups down right, and I've recognized a few of the reaction types, but after that what do I do?

What are the other 2 reaction types?

How should I take the names of the products/reactants and the functional group names and stick em together.

What about when the functional group listed is bigger than the main group. (example R8 and ring opening)?

I should have written F1-F8 but R1-R8 represent functional groups if I'm not mistakened.
Here are my best guesses

R1:alkane

R2:alkene

R3:alkyne

R4:amine

R5:alcohol

R6:ketone

R7:amide

R8:benzene


texts: Hydrogenation of imines to amines by $\ce{H2}$ on $\ce{Pd/C}$ has been used e.g. in the synthesis of Pumiliotoxin. By contrast, carbonyl groups are rarely reduced in this way, which I though was due to the fact that if a carbonyl is adsorbed, the interaction is through O’s lone pairs, rather than C=O $\pi$. However, the lone pair on the imine N should be of an even higher energy than in carbonyl and so should adsorb more easily. Why then does the hydrogenation of imines happen successfully?


texts: What kind of system is required for dynamic equilibrium to be set up?

texts: Most websites and books mention a closed system, but technically isn't an isolated system required? If energy can be transferred, then the position of of the equilibrium will continuously change and no equilibrium will be set up, right?


texts:
Are enones resistant to hydrogenation? My solutions manual thinks so.

I don't recall discussion regarding enones in my text. Nonetheless, could the resonance stabilization of the enone be preventing its hydrogenation? In that case, why is the alkene hydrogenated; both the carbonyl and the alkene are resonance-stabilized to some extent!


texts:
Determine the pH and pOH of pure water at 50 °C.

I’m not sure what formulas to use on this problem.


texts: Why neglecting Bradford Solution Volume in the assay?

texts:
I would like to know why do we not need to take account of Bradford agent solution in dilution calculation?
For example, $\pu{2.5 \mu g mL-1}$ BSA will calculate from $\pu{0.4 \mu L}$ of $\pu{1 mg mL-1} \ \text{BSA} + \pu{159.6 \mu L}$ of distill water. The additional Bradford reagent ($\pu{40 \mu L}$ in my experiment) does not count in the dilution calculation. This seems mysterious to me since the total volume is $\pu{200 \mu L}$. If the volume of Bradford reagent counted, the concentration should have been $\pu{2 \mu g mL-1}$.
I try to search for publications regarding to the protocol and most of them said just ignore the Bradford volume with no explanation. Could someone kindly explain the mechanism behind this?
Edited: I aim to determine protein concentration via Bradford assay. The standard curve is prepared by serial dilution of BSA + distill water + Bradford
serial diluion was as below:

I understand completely how to calculate the unknown concentration. However, I just want to know that why 'Bradford solution' volume can be ignored during the calculation.
Regards


texts: The difference between elementary and concerted reactions

texts:
In the IUPAC Gold Book:

elementary reactionA  reaction  for  which  no  reaction  intermediates  have  been  detected  or  need  to  be  postulated  in  order to  describe  the  chemical  reaction  on  a  molecular  scale.  An  elementary  reaction  is  assumed  to  occur in a single step and to pass through a single  transition state.
concerted reaction A  single-step  reaction  through  which  reactants  are  directly  transformed  into  products,  i.e.,  without involvement of any intermediates.

What is the difference between them?


texts: How to apply the $parvo/amplo$ akamptisomeric stereodescriptors to this bicyclic system?

texts:
I'm looking for examples of akamptisomerism[1].
I'm try to find simple molecules able to (theoretically) show this kind of isomerism.
I thought about the isomers of (2R)-2-methyl-9-oxabicyclo[3.3.1]nonane.
Considering only the $\ce{(HC)O(CH)}$ group, I found the eight akamptisomers.

$\hspace{5em} \ce{(1$R$_p,2$S$,5$R$_a)} \hspace{7em} \ce{(1$R$_a,2$S$,5$R$_p)}$

$\hspace{5em} \ce{(1$R$_p,2$S$,5$S$_p)} \hspace{7em} \ce{(1$R$_a,2$S$,5$S$_a)}$

$\hspace{5em} \ce{(1$S$_p,2$S$,5$R$_p)} \hspace{7em} \ce{(1$S$_a,2$S$,5$R$_a)}$

$\hspace{5em} \ce{(1$S$_p,2$S$,5$S$_a)} \hspace{7em} \ce{(1$S$_a,2$S$,5$S$_p)}$

Could the (3S)-3-methyl-11,12-dioxabicyclo[4.4.2]dodecane show akamptisomerism too?
What descriptor to use? Is this also akamptisomerism or will be another (new?) kind of isomerism?

$\hspace{5em} \ce{(1$R$_?,3$S$,6$R$_?)} \hspace{7em} \ce{(1$R$_?,3$S$,6$R$_?)}$

$$\ce{(1$R$_?,3$S$,6$R$_?)}$$

Reference

Canfield, P. J.; Blake, I. M.; Cai, Z.-L.; Luck, I. J.; Krausz, E.; Kobayashi, R.; Reimers, J. R.; Crossley, M. J., A new fundamental type of conformational isomerism. Nature Chemistry 2018, 10, 615–624.


texts: Ensuring constant ionisation of transition metals using plasma ionisation for accurate mass spec

texts:
Mass spectrometry depends on separation of the analyte based on mass to charge (m/z). ICP-MS is used to detect metals, but under the plasma conditions many of these metals could be ionised multiple times, giving them a variety of (m/z) ratios making a difficult to identify peak for any particular metal. Additionally some metals would have m/z ratios that overlap with others. Then it is conceivable that depending on your solution the quantitation of some elements is impracticable. For example if you want to quanitate aluminium (mass ~27) then a solution high in manganese (mass ~54) would make this impracticable, if manganese were twice ionised to give the same mass to charge ratio as a single ionised aluminium ion. How does the ICP-MS ensure atoms are ionised only once, or that only singly ionised species are detected?

This is further complicated if you consider that the elements rarely exist in solution at oxidation states of 0, but rather aqueous ions with varying oxidation states.


texts: How long does it take for nitric oxide to turn into dinitrogen and dioxygen?

texts:
I'm new to chemistry and am studying nitric oxide as a combustion accelerant. Nitric oxide is said to be a free radical.

People say that nitric oxide, by itself, is pretty stable. But I saw that $$\ce{2NO -> N2 + O2}$$ so in a room of nitric oxide, will it decompose to nitrogen and oxygen?


texts: What are the main axis of research in Chemistry?

texts:
I would like to know what are the main problems currently studied in Chemistry.

For some reason, it seems that there is far less vulgarisation in chemistry than the other fields, and it's hard to find an overview of the field accessible to a layman (compared to math or physics for instance).

I only found this wikipedia page, but I have no idea how relevant it is.


texts:
I have an object made of what I assume to be brass, i.e. an alloy of copper and zinc.
The curved parts have both a black layer and a white layer (also note the verdigris (I guess) on the left top, but this is the only spot on the whole piece) :

If I understand correctly, the black layer is tarnish, or patina, and due to oxidation from sulfur dioxide in the air.
But I can't find reliable reports of white corrosion on brass.  Could it be wet storage stain, a.k.a. "white rust" ?
Hints on how to remove it are welcome.


texts: How can I calculate the percentage of dissociated dinitrogen tetroxide?

texts:
When $\pu{36.8 g}$ $\ce{N2O4(g)}$ is introduced into a 1.0-litre flask at $\pu{27 °C}$ the following equilibrium reaction occurs: $\ce{N2O4(g) <=> 2NO2(g)}$; $K_p = 0.1642~\mathrm{atm}$.
Find the percentage dissociation.

I tried the following:
Let $x$ be the degree of dissociation and $P$ be the initial pressure of $\ce{N2O4}$  that is $\approx 9\ \mathrm{atm}$.
Then, $$\frac{9Px^2}{1-x} = 0.1642$$
Neglecting $x$ in $(1-x)$, I got $x$ as $\displaystyle \frac{0.4}{3}$ [approx]
But the answer given as $6.44~\%$.


texts: What could be causing my bath salts containing baking soda to explode out of their containers?

texts: I run a small herbal wellness business and one of the products i sell are bath salts containing baking soda. The base ingredients are Epsom salts, Dead Sea salts, magnesium chloride, baking soda, coconut milk powder, and fractionated coconut oil. I’ve made and sold this recipe for over a year and because i buy my ingredients in bulk i haven’t bought new ingredients recently. All of a sudden, some kind of chemical reaction is happening (which i assume is coming from the baking soda), and after i seal the bags they blow up like a balloon and then eventually explode. I cannot for the life of me figure out what is causing the baking soda to react. I’ve noticed when I’m mixing up batches that there is a fizzing sound that has never been there before, and I’ve wondered if the salts have somehow absorbed water. But water doesn’t really cause baking soda to react like this. Thanks for the help!


texts: How to esterify phenol with oxalic acid?

texts: Is it possible to fully esterify phenol with oxalic acid in order to get diphenyl oxalate? What catalyst should I use and is the synthesis possible to perform at home with hobby equipment?


texts: How can I know the composition of a gas pocket entrapped in a plastic sheet?

texts:
I have a 1 mm thick plastic sheet, the plastic is not opaque.

Some gas pockets, I would say some bubbles, are inside the sheet; the size of the bubbles is about 1 mm.

What methods are available to know the composition of the gas that is inside the pockets?

Methods can destroy the sample.


texts: Does fluorescein decompose from long term exposure to light?

texts:
I've had about one liter of fluorescein solution setting on the shelf for at least several years and one day noticed that it suddenly lost its characteristic green color. It's now a light yellowish-green solution that seems to have lost the property of fluorescence altogether.

The container is a reagent bottle with a leak-proof cap so I doubt that the solution reacted with anything in the atmosphere other than maybe 100 mL of air that was in the bottle to begin with.

The bottle was exposed to direct and indirect sunlight on a daily basis.

Does it have to do with the decomposition of the fluorescein, and if so, what are the expected decomposition products?


texts: Expansion of ideal gas in isothermic conditions

texts:
I'm doing this problem and I get a different value than the answer in a book. I'm not sure if the book is wrong or me.

  At a constant temperature of $298~\mathrm{K}$, calculate $\Delta S_{\mathrm{sys}}$ and $\Delta S_{\mathrm{univ}}$ for the free expansion of $3.0~\mathrm{L}$ of an ideal gas at $1.0~\mathrm{atm}$ to $11.0~\mathrm{L}$.

My solution

Firstly, I calculated the moles of gas $n$:

$$\begin{align}
n &= \frac{PV}{RT} \\
&= \frac{(1~\mathrm{atm}) \cdot (3.0~\mathrm{L})}{(0.0821~\mathrm{L~atm~mol^{-1}~K^{-1}})\cdot(298~\mathrm{K})} \\
&= 0.1226~\mathrm{mol}
\end{align}$$

Secondly, I used this to calculate $\Delta S$:

$$\begin{align}
\Delta S &= nR \ln{\frac{V_2}{V_1}} \\
&= (0.1226~\mathrm{mol}) \cdot (0.0821~\mathrm{L~atm~mol^{-1}~K^{-1}}) \cdot \ln{\left(\frac{11.0~\mathrm{L}}{3.0~\mathrm{L}}\right)} \\
&= 0.0130~\mathrm{L~atm~K^{-1}}
\end{align}$$

However, the answer in the book is $0.027~\mathrm{L~atm~K^{-1}}$. I'm not sure if that's an error.


texts: What is the chemical reaction between coins (copper and nickel) and polyvinyl chloride?

texts:
I often carry coins in a cheap plastic sandwich bag. A green solid soon appears.  Is it copper oxide? How is the polyvinyl chloride (or polyethylene or polypropylene) greatly accelerating the reaction? Or are they?  Are there other chemicals being formed?
Coin collector websites all say vinyl-containing compounds, and maybe other plastics, damage coins. But they don't say how....
P.S.:  Coins are made of copper, nickel and zinc, right?


texts: Exception in trend of increasing ionisation energy across a period

texts:
One exception to the trend of increasing ionisation energy across a period in e.g. period 2 is going from N to O. There is no loss of exchange energy in I1 of O, but there is 2K lost in I1 of N, hence more energy is required to remove the valence electron of N.

If Zeff increases from N to O, and n stays constant, then

$$E=-R_H \frac{{Z_{eff}}^2}{n^2} $$
must become more negative, and I = -E, which implies that I increases, when in actual fact it decreases.

Is this equation therefore flawed?


texts: Why does the reaction between Na (s) and Cl2 (g) occur spontaneously if the entropy of the system decreases?

texts:
1- The reaction is exothermic.
2- My book says that it is because the total entropy change is very positive.
Here is my book's explanation and it is the highlighted part which i dont understand :
"Despite the fact that there is a decrease in the entropy of the system, the energy leaving the system produces a substantial increase in the entropy of the surroundings, because there are more ways of arranging the energy quanta in the rest of the universe than there are of arranging them in the system alone.


texts: How can I interpolate between two densities at different temperatures?

texts:
I'm trying to find the temperature of methanol ($\ce{CH3OH}$) when its density is equal to $\pu{780 kg m-3}$.

I know that when $T = \pu{30^\circ C}$ the density is equal to $\pu{783 kg m-3}$, and when $T = \pu{40^\circ C}$ the density is equal to $\pu{774  kg m-3}$.

Is there any formula or a trick to find the temperature corresponding to an intermediate density? Likewise is it possible to find the density at a temperature intermediate between the two?


texts: Why does microwave heat up things so much more quickly than visible light?

texts:
I wonder why microwave has more "energy" to heat things up than visible light does. Microwave has a much longer wavelength, therefore should supposedly has less energy than visible light.

But does wavelength and frequency really have to do with how fast a certain type of electromagnetic radiations give an object heat, or it is something to do with how a microwave oven is built?


texts: How diphenylcarbazide is used to detect Mercury II ions?

texts:
Diphenylcarbazide is used in test strips for heavy metals detection in drinking water but I can't find much info on this reagent, apart from it's MSDS and a preparation for detecting Chromium VI ions, in which diphenylcarbazide 250 mg is dissolved in 50ml acetone and few drops added to test sol which is then mixed with sulfuric acid. Also, "Vogel's qualitative inorganic analysis" references this reagent but it is very vague explanation.

If you can elaborate on how the reagent works to detect mercury, and possibly how it is stored and synthesized, that would be really appreciated.

Also, how are the test strips for heavy metals in drinking water made from this compound, I'm curious?


texts: Expansion under isobaric adiabatic condition

texts:
A 3 mole sample of a triatomic gas at $\pu{300 K}$ is allowed to expand under isobaric adiabatic condition from $\pu{5L}$ to $\pu{40L}$. The value of change in enthalpy is:

  $\pu{12.46 KJ}$
  $\pu{-14.965 KJ}$
  $\pu{-24.62 KJ}$
  $\pu{-10.24 KJ}$

In case of adiabatic process, there is no transfer of heat so $Q=0$. Again for an isobaric process, pressure is constant that is $\Delta P=0$.
So, change in enthalpy:

$$\Delta H = \Delta U + \Delta(PV) = Q + W + P\Delta V + V\Delta P = W + P\Delta V = -P\Delta V + P\Delta V = 0$$

Thus, we see that change in enthalpy is zero. But the answer matches with none of the options. What is incorrect in my solution?


texts: Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?

texts:
Quoting from this site:

  As conjugated pi systems become larger, the  energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes longer.   The absorbance due to the π - π* transition in 1,3,5-hexatriene, for example, occurs at 258 nm, corresponding to a ΔE of 111 kcal/mol.

It's also quite easy to see that this is true glancing at various dye absorption tables.

But why is this true?  I can understand why the optical cross-section would increase, implying a higher quantum efficiency at some maximum absorbance wavelength (is this generally true?), but why would the energy gap between the ground state and the excited state correspondingly shrink?


texts: I saw this picture on a teacher's wall and I noticed the C single bonded to the N on the right side. How is it possible that carbon has four bonding sites but is only using one in the picture? Is this stable?


texts:
I have found out how to make silica aerogel.

Currently, the solution that I need to create to make the gel requires tetramethyl orthosilicate or TMOS. Furthermore, the procedure requires me to make two solutions, one being a catalyst and mix the two.

What is the chemistry that goes on to form the ultra-light gel? How does the TMOS, methanol, and ammonium hydroxide interact with one another? What are possible substitutes for TMOS, that are less expensive?


texts: Balancing ionic equations and determining number of ions

texts:
There were two questions that I've listed below that I've had troubles on. I got an answer in both, but both of them weren't correct.

For the first question, they list the answer to be D and then for the second they list the answer as A.

  Determine the net ionic equation for the reaction between $\ce{HNO3}$ and $\ce{Mg(OH)2}$.
   a. $\ce{2H+(aq) + (OH)2^{2-}(aq) -> H2(OH)2(aq) }$

  b. $\ce{2HNO3(aq) + Mg(OH)2(aq) -> Mg(NO3)2(aq) + 2H2O(l) }$

  c. $\ce{Mg2+(aq) + 2NO3 (aq) -> Mg(NO3)2(s) }$

  d. $\ce{H+(aq) + OH(aq) -> H2O(l) }$

  e. $\ce{Mg+(aq) + NO3 (aq) -> MgNO3(s) }$
  Determine the number of ions that are present in $38.8~\mathrm{mL}$ of $0.113~\mathrm{M}$ $\ce{(NH4)2CO3. }$

  a. $7.92\cdot 10^{21}~\text{ions }$

  b. $2.64\cdot 10^{21}~\text{ions }$

  c. $2.07\cdot 10^{23}~\text{ions }$

  d. $6.20\cdot 10^{23}~\text{ions }$

  e. $1.32\cdot 10^{23}~\text{ions }$

For the first question, the work that I did was $\ce{2 H+ + 2NO3- +Mg(OH)2 -> 2H2O + Mg+2 + 2NO3-}$. The problem that I have in this problem is why the $\ce{Mg(OH)2}$ splits up. I don't get it because the things you split up are the things that are aqueous or soluble. $\ce{Mg(OH)2}$ isn't soluble so I listed it as a solid and thought that you wouldn't break it down. All I need to know is why I have to break the $\ce{Mg}$ and the $\ce{OH2}$ down because it isn't soluble.

For the second, I got an answer of $2.64\cdot 10^{21}~\text{ions}$ but the review said it was A. I set it up as $.113~\mathrm{M} = \text{moles} / 0.0388~\mathrm{L}$ and then multiplied $.113$ by $0.0388$ and then multiplied that amount by $6.022\cdot 10^{23}~\text{ions}$ which got me the answer B.


texts: Colligative properties: why does the size of solute not matter?

texts:
Colligative properties are defined as the "properties of solutions that depend on the ratio of the number of solute particles to the number of solvent molecules in a solution, and not on the nature of the chemical species present (wikipedia)."
When a solute is dissolved in a solvent, the number of solvent molecules near the surface decreases, and the vapor pressure of the solvent decreases. That's why boiling-point elevation, freezing-point depression etc correspondingly occurs.
If the reason of elevated boiling points is due to decreased surface area of volatile solvent molecules, then why does the size of the solute not matter? Won't larger solutes occupy more space in the solution?


texts: Stacking two square (2D) layers to make a 3D close packed structure

texts:
My textbook states these ways of stacking 2D layers to make 3D close packed structures:

Square close packing layer over Square close packing layer (though not written explicitly, the illustration imply stacking done in a non staggering manner), generating Simple primitive cubic unit cell lattice.
Hexagonal (2D) close packing layer over Hexagonal (2D) close packing layer (here, again not stated explicitly, but the illustrations imply it is done in staggering manner so that one layer just fits right in the depressions of other layer) giving two different close packed structures: hcp and ccp

However, they did not mention the two cases arising naturally (out of curiosity  maybe):

a) Square close packing layer over Square close packing layer done so that the second layer fits just right in the depressions of the first layer, i.e. in a staggering manner so the layer pattern is of 'ABAB...' type.

b) Hexagonal close packing layer over Hexagonal close packing layer in a non-staggered manner, which might generate a lattice with the primitive hexagonal unit cell, layer put in the pattern 'AA...' type.

The case (b) was easier to work out its unit cell's type, however I am unable to comprehend the 3D structure of what type of unit cell case (a) can generate.

My question is, are these cases of lattice arrangements possible? If yes, then what are their respective unit cells?


texts: How can the formal charge of the B in the Lewis structure of BF4(-) ion be minus one?

texts:
How can the formal charge of the $\ce{B}$ in the lewis structure of
  $\ce{BF4-}$ ion be minus one ?

I draw the lewis structure of $\ce{BF4-}$ ion such like the following:
I put $\ce{B}$ in the central position and make single bonds between $\ce{B}$ and $\ce{F}$s, then completed the octet of $\ce{F}$s.

But in such a structure, the formal charge of $\ce{B}$ is $-1$, and the FC of $\ce{F}$s is 0.However, we know that if someone is going to get a minus FC, it should be the one whose electronegativity is the highest, and in this example this rule is not followed, so what is the reason for that ?


texts: What is the order of acidity for hydrogens in primary, secondary and tertiary alkanes, alkenes, and cycloalkanes

texts:
The bond dissociation energies of C-H bonds in alkanes, alkenes and aromatic compounds decrease in the following order: primary > secondary > tertiary > allylic > benzylic.
The weaker the bond, the lower the bond dissociation energies. Does the acidity of primary, secondary, tertiary, allylic and benzylic hydrogens follow the same order?


texts: Rate the following ions in increasing ionization energy

texts:
Sr2+, Rb1+, S2-, P3-

I believe it is P3- < S2- < Rb1+ < Sr2+ because it should be easier to take an electron away from the negatively charged ions, but I'm not sure about the Rb and Sr because they both have their electrons taken out of their outer shell.


texts:
Tom Lehrer’s The Elements song (listen) mentions all elements up to Nobelium, and ends with the appology

  These are the only ones of which the news has come to Harvard,
  And there may be many others, but they haven't been discovered.

Now that’s a bit dated. We can’t ignore trans-uranic elements when every bedroom in developed countries contains Americium-241, and now that official names have been ratified for all elements through period 7, I can hope that an updated song will be available.

Are there any such songs, whether a revision of the original or based on a new melody, or any known efforts underway to complete one?


texts: IUPAC nomenclature: "Smallest sum of locants"?

texts:
While naming any compound, the numbering should be done such that position of substituted groups gives smallest sum.

I'm struggling with the IUPAC naming for cyclic compounds. How exactly does this rule work?


texts: Influence of sodium cyanoborohydride on C=N bonds in DNA bases

texts:
I would like to crosslink an amino-modified DNA strand with an APTES monolayer (which also has a $\ce{NH2}$ end group) using a glutaraldehyde linker. After the formation of Schiff base linkages between the aldehyde and the amino groups, I would like to reduce the bonds using sodium cyanoborohydride to form secondary amine bonds.

Does the cyanoborohydride also affect the $\ce{C=N}$ bonds in the DNA bases or not?


texts: Cis and Trans Isomerism in Resonance-Stabilized Compounds

texts:
Would it be valid to describe $N_2O_5$ isomers as cis or trans? As a matter of fact, does this molecule even have isomers, given that all its outer N-O bonds are resonance stabilized and therefore equal in length and strength?

Also for non-resonance stabilized compounds, would it be okay to describe say the N to O double bonds as cis or trans with respect to each other? I've just never heard of cis/trans being used this way.


texts: Why do we have surface charges on a polymer sheet immerged in water ?

texts:
I am working with a conductive polymer sheet where I have dropped off a drop of water (with ions). I have plugged the polymer with a conductive wire and an other wire is on the drop. With a voltmeter I measure a voltage (open circuit) between these two points the drop and the polymer (around 300 mV)
And when I use a resistor in my circuit, I can measure an intensity. So What happens on my polymer ? Where come from the electrons crossing my resistor ?


texts: How to calculate the energy of a single proton?

texts:
Using e.g. the VWN5 functional, what is a simple way to calculate the energy of a single proton? Of course, it is not possible to perform a calculation of a proton in isolation, as it bears no electrons. So I first attempted to use the experimentally determined value (see e.g. M. Dewar and K. Dieter, J. Am. Chem. Soc. 1986, 108, 8075.), but this leads to highly erratic proton affinities.

Could it be that I need to determine the proton affinity for any given functional + basis set (e.g. VWN5, 6-31+G** in my case)? What would be an effective way to get a good rough estimate of the energy of a proton?


texts: Calculation of Bond/Angle/Dihedral force constant

texts:
I am a big fan of Mopac (Though I have a very little knowledge about the tool). I have some queries regarding some calculations in Mopac2016:

Problem:

How to calculate Bond or Angle or Dihedral force constant for Vanadium (V) (with other elements: Oxygen and Chlorine)?

My compound (smiliar to): CN(OV(=O)ON(C)C(C)=O)C(C)=O

Structure:


texts: Length of NaH bond from the edge length of unit cell

texts: If the edge length of $\ce{NaH}$ unit cell is $\pu{488 pm}$, what is the length in $\pu{pm}$ of an $\ce{NaH}$ bond? The answer is $\pu{244 pm}$, I thought that $d = 2 \sqrt{2}\times r$ , do you not need to know the radius for this?


texts:
I have studied that as electronegativity increases nucleophilicity decreases. But in the aprotic solvent the order of nucleophilicty is: $$\ce{F- > Cl- > Br- > I-}$$ but how is this possible as $\ce{F-}$ is strongly electronegative as well as a strong nucleophile Isn't this contradictory? There is no effect of the aprotic solvent on anions.

Information given : This causes the most confusion, because it is solvent-dependent. In polar protic solvents (e.g. water and alcohols, any solvent with OH) nucleophilicity increases as you go down the periodic table (F- < Cl- < Br- < I – ). In polar aprotic solvents (e.g. DMSO, acetone) the order is reversed, and the most basic nucleophiles are also the most nucleophilic. (F- > Cl – > Br – > I – ).

On https://www.masterorganicchemistry.com/tips/what-makes-a-good-nucleophile/

I want to know why my concept is wrong.


texts:
I am trying to solve an exercise, where a block of 605.5g calcium carbonate should be completely dissolved in 30% hydrochloric acid (w/w) and the concentration of the acid should be 3% in the end. The question is: How many g of 30% HCl-acid is needed in the beginning.

$$\ce{CaCO3 + 2 HCl -> CaCl2 + H2O + CO2}$$

So for each dissolved molecule of $\ce{CaCO3}$:

2 molecules of $\ce{HCl}$ are used
1 molecule of $\ce{H2O}$ is produced
1 molecule of $\ce{CaCl2}$ is produced
1 molecule of $\ce{CO2}$ is produced, but leaves the solution

I got a result (about $\pu{1671.524g}$ 30% hydrochloric acid), which I verified this way:

Let $p$ be the number of dissolved $\ce{CaCO3}$ moles, which is about $\mathrm{605.5/100.0869 = 6.05}$

$\ce{HCl = 1671.524g * 0.3}$

$\ce{H_2O = 1671.524g * 0.7}$

$\ce{HCl_{end} = HCl - 2 * (p * M(HCl)}$)

$\ce{H2O_{end} = H2O + p * M(H2O)}$

$\ce{CaCl_{2end} = p * M(CaCl2)}$

$c_{end}$ = $\ce{\frac{HCl_{end}}{HCl_{end} + H2O_{end} + CaCl_{2end}} = 0.03}$

But my solution is claimed to be incorrect. Am I missing something here?


texts:
I know that $\ce{NaHCO3}$ is sodium bicarbonate, but According to Wikipedia:

  In chemistry, a carbonate is a salt of carbonic acid, characterized by the presence of the carbonate ion, $\ce{CO3^{2-}}$.

$\ce{NaHCO3}$ also has the $\ce{CO3^{2-}}$ group, but is it a carbonate?

That is, are bicarbonates a subset of carbonates?


texts: Why is temperature regulation an important factor for producing explosives?

texts: I was wondering why temperature regulation is an important factor for producing explosives. I know many are exothermic reactions but what would happen if you did not use an ice bath and allow the temperature to go too high (Considering the explosive substance has not already been formed in the reaction)? Would it explode? For example when mixing acetone with sulfuric acid and hydrogen peroxide to make TATP.


texts: What is the difference between bond disassociation energy and lattice energy?

texts:
Bond disassociation energy refers to amount of energy required to break bonds of one mole of atom of particular type whereas lattice energy is the energy required to separate a crystal lattice containing one mole ions into their respective gaseous states.

What i can understand from the above information is that bond dissociation energy has to be a broader classification and lattice energy must be a subset of it.

Is it true or am i wrong. Please correct me, i am a bit confused.
Any help would be appreciated.


texts: Is is possible to add NO2X, AlX3 to achieve nitration of benzene?

texts:
According to Organic Chemistry as Secondary Language (2nd semester), for nitration of benzene, the general way is to add $\ce{HNO3}$ and $\ce{H2SO4}$ and it said to make $\ce{NO2+}$. $\ce{(AlBr3 + NO2Br)}$ is impossible since it is a 'nasty' stuff? Why is it 'nasty'?
I searched online, there is no info about $\ce{NO2Br}$. Is it too unstable? If yes, may I ask why? However, there is $\ce{NO2Cl}$ present, so is it possible for it to react with benzene ($\ce{+AlCl3}$) to achieve nitration?


texts: What are the factors affecting osmosis (bio)?

texts: Asking from the blood barrier angle. The wikipedia states that glucose, urea, and $\ce{Na/K}$ count. Can there be any other factors, like $\mathrm{pH}$, temperature, hydraulic pressure on the cell walls? Why do minerals not play a role? Because there are only traces of them?


texts: How to determine the boiling point of substances?

texts:
Which of the substances has the lowest boiling point?
a) $\ce{H2O}$ b) $\ce{H2S}$ c) $\ce{H2Se}$ d) $\ce{H2Te}$

I've been searching for any formula or rule to determine this, but I read that it didn't exist.
Do I have to remember some boiling points by heart?


texts:
Tollen's test is an important test to distinguish between aldehyde and ketone.

$$\ce{2 [Ag(NH3)2]+ + RCHO + H2O → 2 Ag(s) + 4 NH3 + RCO2H + 2 H+}$$

But is this reaction safe? Is there any threat in the formation of silver nitride (fulminating silver)? It is formed when the products of most of the reaction of silver($\ce{I}$) salts are kept aside undisturbed. It act as a potential explosive or a  contact explosive. If there is any threat in the formation of silver nitride, what precaution must be taken to prevent it?


texts: I am interested in preparing an anhydrous sample of sodium tungstate (Na2WO4), which is normally found as the dihydrate.  Finding an example of this in literature is proving difficult, I am interested if someone can suggest a preparation method based on prior experience or difficulties I should encounter.


texts: How to be able to tell if a molecule will react via SN1 or SN2?

texts:
I've been having a lot of issues with a question.

2 compounds, (1-chloro-2,2-dimethylpropyl)benzene and (1-chloro-2-methylpropyl)benzene react with EtOH in water.

It asks to classify the reaction mechanism for each and to then go on and explain why (1-chloro-2-methylpropyl)benzene has a much faster relative rate.

I am having major issues with the question, because I just cannot tell where there are any major differences between molecules which could make a difference. Both of them have a benzene ring, but this stabilises both the transition state and the carbocation intermediate so will favour both SN1 and SN2. Both reactions are done in the exact same solvent with the same nucleophile.

The only differences I can spot is that in (1-chloro-2,2-dimethylpropyl)benzene, there will be more stabilisation due to the inductive effect and hence it will favour SN1. But this does not help with determining the mechanism for (1-chloro-2-methylpropyl)benzene.

Any help will be much appreciated. Many thanks :)


texts: Why does thermodynamics only apply to macroscopic systems at equilibrium?

texts:
A text says:

  The laws of thermodynamics deal with energy changes of macroscopic systems involving a large number of molecules rather than microscopic systems containing a few molecules. Thermodynamics is not concerned about how and at what rates these energy transformations are carried out but is based on initial and final states of system undergoing the change. Laws of thermodynamics apply only when a system is in equilibrium or it moves from one equilibrium state to another equilibrium state. Macroscopic properties like pressure and temperature fo not change with time for a system in equilibrium state.

Why do the laws of thermodynamics not apply when the system is microscopic or not at equilibrium but in intermediate stage? How can we say that thermodynamics cannot tell anything about rate and method of energy transformations?


texts: How to compare the boiling point of water, ammonia and hydrogen fluoride?

texts:
According to the values of boiling points that I found on internet the order is as follows:

  $\ce{H2O}$ >  $\ce{HF}$ >  $\ce{NH3}$

I was expecting $\ce{HF}$ to have highest boiling point because F is the most electronegative atom hence should form stronger H Bonds.

Now, I think the factor here might be number of H Bond rather than strength of H Bond.

$\ce{H2O}$ have 2 lone pair and 2 H atoms, hence it can form 4 H Bonds with surrounding molecules.
Similarly  $\ce{NH3}$  is also capable of forming 4 H Bonds with surrounding molecules.
$\ce{HF}$ on the other hand is only capable of forming 2 H Bonds with surrounding molecules.

Still the above hypothesis doesn’t explain why the boiling point of $\ce{HF}$ is greater than $\ce{NH3}$. I’m not sure what am I missing here.


texts:
Every reasonably effective method of electroplating $\ce{Au}$ onto another metal's surface (e.g. $\ce{Cu}$,$\ce{Ni}$,$\ce{Ag}$, etc.) involves use of $\ce{KAu(CN)2}$ or in some cases $\ce{KAu(CN)4}$ in acidic, neutral, or (in almost all cases less effective) basic solution. Ideally it should be $60$ to $80~\mathrm{^\circ C}$ with a certain current density applied (c. $0.5~\mathrm{A/dm^2}$). In the past I have tried a direct route of dissolving the gold in warm $\ce{HCl / HNO3}$ as the deposition solution to little effect (a brownish/blackish tint is left on the receiving surface with very little tint of gold). The short story is that I have found the use of cyanide unavoidable.

$\ce{KAu(CN)2}$ runs $157/g from Sigma-Aldrich so I would like to synthesize it, if possible.

I have:

1g solid $\ce{Au}$
Excess $\ce{KNO3}$, $\ce{KI}$
Various $\ce{C-N}$ organic compounds, e.g. urea, uric acid, etc.

I think my best route is indirect — to first synthesize $\ce{KCN}$ and then form the product:

$$\ce{4 Au + 8 KCN + O2 + 2 H2O → 4 K[Au(CN)2] + 4 KOH}$$

...and follow by vacuum filtration on the solid precipitate. Which begs the question of the best method for safe synthesis of $\ce{KCN}$.

Much of my information comes from this difficult-to-find and expensive book, "Properties of Electrodeposited Metals and Alloys: A Handbook" by Safranek. It's got quite a lot of proprietary data. Also Kohl's chapter on gold electrodeposition.


texts: Number of nodes in Hartree-Fock solution

texts:
The Hartree-Fock equation for atoms  is of the form

$\left(\frac{d}{dr^2}+f(r)-\epsilon\right)P(r)=g(r) \tag1$

Usually algorithms to solve this equation assumes that the number of nodes of $P(r)$, $n_r$, is of the form
$$n_r=n-l-1 \tag2$$

where $l$ is the orbital quantum number and $n$ the principal quantum number.
For closed shell $(1)$ is spherical symmetric so $(2)$ is justified.

What about non closed shell, what is the theoretical justification for $(2)$?


texts: What kinetic model does the hydrogenation reaction of dibenzyltoluene follow?

texts:
So during the course of my research, I've read countless papers related to the hydrogenation of dibenzyltoluenen and the dehydrogenation of perhydro-dibenzyltoluene. Now what I've noticed, is the fact that I could not find any data concerning the kinetic models linked to this hydrogenation process (I did find kinetic data concerning dehydrogenation of perhydro-dibenzyltoluene).
Is there a specific reason for this?
Many thanks in advance.


texts: Can silver metal be used to electrochemically reduce copper?

texts: I have a solution of copper(II) ions and several cations.  I am trying to reduce the copper ions to copper metal with electricity.  My Ideas was to use silver as the anode and a copper wire as the cathode.  I have seen people say to do this using platinum as the anode, however this is expensive.  I was wondering if silver could be used as an alternative anode because it has a higher reduction potential than copper.  If not, could any metals besides gold and platinum work.  I have attached a picture of my proposed cell.  I have tried the cell, but the silver began to corrode and form a silvery deposit, probably a silver salt.


texts: Inductive effect and hyperconjugation - one elephant, different parts?

texts:
Are the inductive effect and hyperconjugation both different ways of looking at the same phenomenon - i.e. methyl groups donate negative charge for example. Inductively we can argue that carbon is of greater electronegativity than hydrogen, and so carbon withdraws negative charge from hydrogen, and thus negative charge is "donated" to whatever that the methyl is attached to.

From a hyperconjugative effect we can argue that there is some interaction between the C-H orbitals and some antibonding orbital ... how is this supposed to be stabilizing if it involves an antibonding orbital?


texts: What does "/2" in the structure of calcium benzoate mean?

texts:
Please see the following figure. This is from the high school chemistry book of my son. He wants to know what does that /2 after $\ce{-COOCa}$ mean.

The book is a non English one. And I have changed the relevant caption to English.

Primary searches over Google have not revealed anything usable. And my major not being Chemistry might have to do something with this.


texts: Can lead(II) oxidize tin metal in aqueous solution?

texts:
According to my textbook, element $\ce{X}$ can oxidize element $\ce{Y}$ if $\ce{X}$ was lower in the activity series.
Lead is lower than Tin in the activity series table in the textbook, but the following question contradict that rule and I can't figure out why:

  Will the reaction $\ce{Sn(s) + Pb(NO3)2(aq) -> Sn(NO3)2(aq) + Pb(s)}$ occur?

The book reveals at the end that the answer is no, but doesn't explain why.


texts:
Recently I've been going through an exercise of Chemical Kinetics and Nuclear Chemistry and right now I am stuck on one question that was previously asked in JEE(Advanced)-2013. The question says,

In the reaction,
$\ce{P + Q -> R + S}$
The time taken for $75\%$ reaction of $\ce{P}$ is twice that time taken for $50\%$ reaction of $\ce{P}$. The concentration of $\ce{Q}$ varies with reaction time as shown in the figure. What is the overall order of the reaction?

And here was my approach to the question,
In the question different data have been given for different reactants (i.e. $\ce{P}$ and $\ce{Q}$). For $\ce{P}$ it has been given that it take $\ce{P}$ double the time to react $75\%$ than that from $50\%$. So assuming the time taken for $50\%$ reaction to be $t$ and that of $75\%$ to be $2t$, we can easily find that order of reaction w.r.t P is $1$. As,

$$\frac{t_{\frac12}}{t_{\frac34}}=\frac{\log 2}{\log 4}=\frac12$$

Further w.r.t $Q$ there is a graph given which is something like in form $\ce{[Q]=[Q_o]-mt}$. So comparing with the equation of zero order reaction which is like $\ce{[A]=[A_o]-kt}$ (where $\ce{[A]}$ is the concentration of reactant and $k$ is rate constant), we can conclude that order of reaction w.r.t to $Q$ is $0$.
So I concluded that overall order of reaction will be

order of reaction of $P +$ order of reaction of $Q$
$\implies 1+0=1$

So was this the right approach from my side or there is any kind of error in any step?


texts:
Why is Ammonia stronger than Phosphine in terms of basic strength?
I am confused as Nitrogen is more electronegative than Phosphorous.


texts: What is the best hydrogen bond acceptor in 2-amino-N-(3-hydroxyphenyl)acetamide?

texts:
I was preparing for my first exam in organic chemistry and came across this question.

  Draw a water molecule that is hydrogen bonded to the best anticipated hydrogen bond acceptor.

  2-amino-N-(3-hydroxyphenyl)acetamide, PubChem CID: 20238693

I was thinking that it would be one of the oxygens, because of its greater electronegativity compared to nitrogen. However, I'm having a little trouble distinguishing which oxygen.

I'm leaning towards the alcohol group. My reasoning is that there is less steric hindrance preventing solvation, but I am not sure.


texts: reaction coordinate, kinetics, equilibrium in example

texts:
In this special reaction coordinate diagram with two reaction mechanisms, I tried to analyze it in two other ways, one with kinetics, another with equilibrium.

A. kinetics, I tried to find reaction rate of forward, and reverse. By the diagram, rate determining step of forward reaction is the first one (because activation energy is the highest and let's say it is one and only factor for RDS in this case). so Vf=k1[A][B].
RDS in reverse reaction is second step of the reaction judging by the diagram activation energy (M->A+B). So I used pre-equilibrium approximation for that. That's Vr in the picture.

B. equilibrium, I wrote all the equilibrium constant and simply added the reactions.

now here is the question. Expression of the rate of forward and reverse reaction in dynamic equilibrium is quite different from each case, analyzing in a way of kinetics and equilibrium constant, as you see in the picture below. Why is it different? What's right expression? What am I missing here?


texts:
How can I find the oxidation state of sulfur in $\ce{H2S2O5}$ using its structure?

This is the structure of $\ce{H2S2O5}$:


texts: Finding mathematically the ground state density in DFT

texts:
To find the ground state density in DFT, you set the following Lagrangian:

$$L = E[\rho(\vec r)] - \mu\left(\int \rho(\vec r) \mathrm{d}\vec r - N\right)$$

While minimising with respect to the density, we get:

$$\frac{\partial L}{\partial \rho} = \frac{\partial E[\rho(\vec r)]}{\partial \rho} - \mu = 0$$

My problem is with the explicit derivation of the energy functional. Let's consider the Thomas-Fermi-Weizsacker kinetic energy functional:

$$T_s(\rho) = C_F \int \rho^{5/3}(\vec r)\mathrm{d}\vec r + C\int \frac{| \nabla \rho (\vec r)|^2}{\rho (\vec r)}\mathrm{d}\vec r$$

For example, how do you derive this with respect to the density?

$$\frac{\partial T_s(\rho)}{\partial \rho} = C_F \frac{\partial}{\partial \rho}\int \rho^{5/3}(\vec r)\mathrm{d}\vec r + C\frac{\partial}{\partial \rho}\int \frac{| \nabla \rho (\vec r)|^2}{\rho (\vec r)}\mathrm{d}\vec r$$

For the first term, you could use Leibniz integral rule, since the density very far away from the nucleus is zero. However, I really have no idea how to tackle the second term. Moreover, what is the algorithm afterwards to find the ground state density? How does one figure out this density from the equation?


texts: Does washing soda (sodium carbonate) turn into baking soda (sodium bicarbonate) over time?

texts:
I have some sodium carbonate. But it's over 20 years old and was not kept in tight bottle. I wonder if this compound absorbs $\ce{H2O}$ and $\ce{CO2}$ from air.

I guess I'd need to burn it a little to turn it back in case the answer was yes.


texts: Why is the viscosity of water and ethanol lower than that of a water-ethanol mixture?

texts:
We found in an experiment using Ostwalds method that
ethanol is more viscous than water, which
is already surprising as water has stronger intermolecular bonds than ethanol as @MaxW pointed out.

The mixture
of both substances furthermore is significantly more viscous than both individual substances. This
is interesting. We did not come up with a
satisfying explanation for this behaviour.

I know that one shouldn't expect that a mixture behaves the same way or proportional to the concentration of the components, but I would appreciate an explanation of this effect on a molecular level.


texts: Formation of halohydrin vs alkyl dihalide

texts:
For the electrophilic addition of $\ce{X2}$ to alkene in $\ce{CCl4}$ solvent, a dihaloalkane is formed. This is a halogen addition reaction, with the intermediate being a halonium ion.

However, if instead of $\ce{CCl4}$, $\ce{H2O}$ is used instead, a halohydrin would be formed.

However, in the second case (halohydrin formation reaction), the $\ce{X-}$ ion is still present in the reaction. Furthermore, $\ce{X-}$ is a stronger nucleophile than $\ce{H2O}$. Why is it then that it is $\ce{H2O}$ that reacts with the halonium rather than $\ce{X-}$, the stronger nucleophile?


texts: Configurations of Reactants in Second Order Nucleophilic Substitutions

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The question asks me to draw the product for the reactions. However, I am stuck and do not understand how to draw the reactants with configurations correctly.

(a) (S)-2-Chloropentane and NaSH

I thought the reactant I drew was in S configuration. Also, I thought since it was a chirality center, inversion of configuration will occur. Can someone please explain this in detail?


texts: Diketone intramolecular reaction question

texts: I realize that one of the methyl groups on either carbonyl compound will become deprotonated and then it will attack the other carbonyl to form a pentane ring. However, with the methyl group in the picture below there should be an OH group. There is no heat in the reaction at all that would make this reaction an aldol condensation, thus how does the double bond form?


texts: Why does CO2 lowers the pH of water below 7?

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Ok so I understand that having a pH below 7 is considered to be acidic and I also understand that part of the definition of an acid is that it gives off H+ when dissolved in water(even though not all acids necessarily need to give off H+ when dissolved in water)

But I was the rather confused when I came upon this ( when they refer to the 2 gases they are talking about CO and CO2)

What I dont understand is how the equation came to be ? ( the product side of the equation)

And how would It have looked if CO was dissolved in H2O, would it have still lowered the pH??


texts: Are there any ways to figure out if the copper foil and mesh I have are pure, as-close-to 100% copper as possible (and as advertised)?


texts: Hyperpolarization of molecules via the SABRE-SHEATH technique is a fairly new idea. Does anybody know if hyperpolarizing aliphatic nitrogens is possible? The articles I've read mostly use N-heterocyclic compounds like pyridine or imidazole as substrates. If not, why?


texts: Is it possible to prevent saponification by modifying free fatty acids?

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Not big on chemistry so this question might be a bit out there. It is my understanding that a soap molecule is made up of a free fatty acid and lets say a sodium ion. Correct? Would it be possible to modify the free fatty acid (with a solid or liquid substance) in such a way that when it comes in contact with the sodium ion it wouldn't be able to form a soap molecule?

Thanks


texts: Generate fit of virial expansion to osmotic pressure data and obtain second virial coefficient

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So I have some osmotic pressure data that I would like to obtain the second virial coefficient ($B_{22}$) for, but I am getting increasingly more confused on how the theory works. I know you can rewrite the expansion in the following manner:
$\Pi (T, c) = RT(c + B_{22}c^{2} + B_{23}c^{3} + ...)$
where $\Pi$ is the osmotic pressure, $T$ the temperature in K, $c$ the concentration and $R$ the gas constant. I would like to do (presumably) a least-squares fit but my maths is a little rusty. Can you do this in Mathematica or Python and if so, is there any literature on this that I can reference? Apologize if this is a stupid question.


texts: When soap is made from triglycerides and NaOH reacting, is saponification the only reaction that occurs or are there other side reactions. Information concerning this issue seems slim online


texts: Does fractionation use enough heat to destroy nutrients in Coconut Oils when seperating the MCT oils?

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We have recently been giving MCT (medium-chain triglyceride) oil to our dogs in place of Coconut Oil as from what I understand the majority of the benefits of Coconut Oil comes from the MCT's themselves and by doing this you can avoid Lauric Acid, which has 12 carbon atoms and can behave like both classes of fatty acids (MCT's and LCT's (long chain triglycerides)).
Apparently only 10% of the saturated fat in Coconut Oil has MCT's:

A small percentage of the saturated fat in coconut oil, about 10%, is made up of these less harmful saturated fatty acids, but virtually all the rest of coconut oil’s saturated fat is made up of the long-chain varieties that send LDL soaring.

However I have heard claims as well that Coconut Oil is 2/3 MCT, but I would assume this comes down to Lauric Acid and whether or not it is classified as an MCT or an LCT; the aforementioned articles states it is an LCT but others state it is an MCT.
I am getting off track here, so I digress.
Based on the information I have found it is best to avoid Coconut Oil and instead give straight MCT oil to avoid LCT's (including Lauric Acid), however after speaking with the manufacturer of the MCT oil we are using, I asked them if the oil was "cold-pressed" and was told whilst they did cold-press it they also have to use fractionation to separate the oils.

To get MCT the process is a little different from other oils. First it starts with organic coconut oil which is cold pressed. Then the oil goes through  the process of fractionation, which is done by steam. There are no solvents used in this process, it's just heat. It needs to be heat because whole coconut oil needs to have its fatty acids broken to extract the medium chains (the MCT part). Coconut oil is a mix of long chains and medium, and you can't separate them using a cold press, as it won't be enough to break the fatty acids bonds. Once the fractionation is done we are left with the long chain fats (which we use in our soaps and personal care ranges) and the MCT.

The heat from the fractionation isn't enough to change the structure of the fats, it's just enough to split the long chains away from the medium. I hope that's clear! It's always a little tricky to understand first go - it's almost like separating the milk solids from melted butter, or curds from whey, if you can imagine that?

Now, obviously the reason you want a cold-pressed oil is because you don't want to destroy the nutrients in it - apparently using too much heat can destroy things such as antioxidants, vitamin E and oleic acid.

Cold pressed retain healthy antioxidants that are otherwise damaged by being exposed to heat. Antioxidants help combat free radicals that cause cell damage in the body. Most cold pressed oils are rich in vitamin E, which has anti-inflammatory and healing properties. They are also rich sources of oleic acid that help boost your immune system. All these oils when cooked on low heat are excellent oils; however, they lose all the nutrients once exposed to too much heat.

Based on the response from the manufacturer and the statement above that "low heat" should be fine, generally, does the process of fractionation retain all the nutrients in the oil?


texts: The most acidic hydrogen of 4‐hydroxybutanenitrile

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Identify the most acidic hydrogen atom in the compound below:
$$\ce{NC-CH2-CH2-CH2-OH}$$

My teacher said that the $\ce{H}$ connected to $\ce{O}$ is the most acidic since $\ce{O}$ is more electronegative than carbon.
However, I see that the $\ce{H}$ connected to the carbon adjacent to cyanide must be more acidic since the conjugate base is stabilized by resonance, contrarily to that connected to $\ce{O}$.
Isn't resonance the most significant criterion in determining the stability of a conjugate base? Or does the electronegativity of the donor atom matter more?


texts: Why are NBr3 and NI3 unstable, but NF3 is stable? Is there any reasoning behind the stability? I found that one nitrogen can accommodate fluorine easily, but not the others. Also, I don't understand what is meant by "accommodate."


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So I'm trying to figure out if nitrobenzene is an overall polar or non-polar molecule. I calculated the electronegativity difference of each bond, and according to the ranges I learned in class all of the bonds are non-polar covalent bonds. I'd assume that this would then be a non-polar molecule since there aren't any slightly positive or negative points to create a dipole. However, searching up online nitrobenzene appears to be a polar molecule.
Am confused. Is there something to do with that this is an organic molecule with NO2 or something? I'm in my 11th year in highschool in Ontario so I have no background at all with organic chemistry, if this question has anything to do with it.


texts: What's unique about the most commonly used hetero-cyclic elements?

texts: I have question about hetero-cycles: Why do we use (the most common hetero-cyclic elements) nitrogen, oxygen, sulfur as hetero compounds most of time?


texts: What is the relationship between enthalpy of atomisation and enthalpy of sublimation?

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The $E^θ(\ce{M^{2+}}/\ce{M})$ value for copper is positive ($\pu{+0.34 V}$). What is possibly the reason for this? (Hint: consider its high $Δ_aH_V$ and low $Δ_{hyd}H_V$)

We know that we have to first break the metallic lattice to turn the metal into gas and hence there should be some sort of relation between the two.
My confusion is that when we split the lattice, aren't we technically subliming the substance as well?