texts: Why is sulfuric acid used in crystallization

texts:
I read that:

  Take a cupful of water in a beaker and add a few drops of dilute
  sulfuric acid. Heat the water. When it starts boiling add copper
  sulfate powder slowly while stirring continuously.
  Continue adding copper sulfate powder till no more powder can be
  dissolved. Filter the solution. Allow it to cool. Do not disturb the
  solution when it is cooling. Look at the solution after some time. Can
  you see the crystals of copper sulfate? If not, wait for some more
  time.

So why is sulfuric acid required in this experiment?


texts: What is the relationship between migration and the potential of double layer theory?

texts:
Double layer theories like that of Gouy-Chapman give the electrostatic potential $\ \phi\ $ in solution. For a symmetrical electrolyte and small potential drops $\ \phi\left(x=0\right)-\phi\left(x\rightarrow\infty\right)=\phi_0-0\ \text V=\phi_0$, the theory gives
$$
\phi=\phi_0\exp\left(-\kappa x\right)
$$
where $x$ is measured from the electrode/solution interface into the bulk solution.
As $\kappa$ is very large $\left(\sim10^{-9}\frac{1}{\text m}\right)$, the electric field
$$
E=-\frac{\text{d}\phi}{\text{d}x}=-\kappa\phi_0\exp\left(-\kappa x\right)
$$
falls to a constant value (0  V in this example) very quickly.

In the equations for the transport of ions in diluted solutions, the migration flux of species $j$ is
$$
J_{\text {j,migr}}=-z_ju_jFc_j\frac{\text{d}\phi}{\text{d}x}
$$

As the flux is proportional to $E$ it must be zero everywhere in solution according to Gouy-Chapman. But in every book about electrochemistry migration is said to contribute to the flux $J_j$ of species $j$ except when $c_j$ is much more smaller than the concentrations of other species. But why should there be migration in a macroscopic cell at all? In double layer theories ions gather near the electrode surface and compensate the charge on the metal, so there should be no electric field in solution. Isn't this what the equation for $\phi$ above says?

Or are there two different types of "electrostatic potentials" in solution: One associated with the double layer theories and one associated with transport?
$$
\phi_{\text{Gouy-Chapman}}\neq\phi_{\text{Migration}}
$$

If this is the case: How are both potentials related to each other (and why do books always use the same symbol for both)?


texts: How to convert glucose to fructose? Moreover, can there be direct conversion(not necessarily in a single step), or we have to use indirect means, such as from sucrose, or other higher carbohydrates, and then separating fructose from the products?


texts: Taste same but why not LiCl a substitute for NaCl (common salt)?

texts:
A clinical paper from 1949 [1] observes the toxicity of LiCl, at very low concentrations. That just went over my head... Is toxicity the only reason to avoid LiCl as a substitute for NaCl (specially for those who were on a salt restricted diet)? Why did they even consider it to be a substitute in the first place?

What physical and chemical property of Li behaves differently than Na (e.g. being toxic)?

P. S.: not sure what tag to put in.

Bibliography

Hanlon, L. W. Journal of the American Medical Association 1949, 139 (11), 688. DOI 10.1001/jama.1949.02900280004002.


texts: Why do we need PBr to help enolize a carboxylic acid. My textbook doesn't give a reason for this at all. Does it have to do something with the acidity of carboxylic acid. Thanks.


texts: How much energy does it cost to have electron configurations that are not in accordance with Hund's rules?

texts: What is a ballpark figure for the difference in energy for an atom that follows Hund's rule vs one that has two electrons with opposite spins?  I'd be interested to know carbon and nitrogen.  Is there a bigger difference when there are two electrons with one spin and one electron with the opposite spin vs two electrons with opposite spins?


texts: Electrophilicities of carboxylic acid derivatives

texts:
I would like to ask about the rate of hydrolysis for 4-hydroxyphenyl acetate (A), N-(4-hydroxyphenyl)acetamide (B), 4-hydroxyphenyl chloroacetate (C), and methyl 4-hydroxybenzoate (D). I know that hydrolysis depends on the positive charge of the carbonyl carbon and also the substituent around it (e.g. electron withdrawing).

Therefore, from the picture above I can see that compound C is the most reactive since it has a phenol and a chlorine as its substituents. Compound B is the least reactive due to nitrogen being the weakest electronegatively as compared to oxygen (I think?).

I am confused between compounds A and D because they are isomers of each other. The oxygen and phenol group are on the same substituent in compound A and are in two different substituent in compound D. Does this affect anything? or can I say that the strength of the electron withdrawing groups are additive, meaning compound A and D are similar in terms of reactivity?


texts: Reconciling Flory-Huggins Theory with Le Chatelier's Principle

texts:
(I discuss the Flory-Huggins parameter as chi from here onward). So I had learned in class that when discussing polymers the Flory-Huggins Theory helps us figure out whether mixing is thermodynamically favorable. We had also discussed UCST and LCST behavior. Now from what I understood (and where there might be a misconception), with a chi value less than 0 the solution always mixes, chi value equal to 0 the solution is ideal (with no preferable interactions) and a chi value greater than 0 the solution may or may not mix depending on the entropy related terms in the Flory-Huggins equation.

Looking at the case where the chi values is greater than 0 the reaction (solvation reaction) is endothermic based on the equation in terms of internal energies ((z/2kbT)(2*uAB-(uAA+uBB)) where u represents the energy of interaction between molecules A and B). However, we also know that if I model chi as A+B/T then, as temperature is increased, the chi value can change giving rise to either UCST or LCST behavior. Which means a reaction (of solvation) that is endothermic (chi greater than 0) could either increase or decrease in terms of Gibbs (or Helmoltz's) free energy with rising temperature. However, this cannot be reconciled then with Le Chatelier's Principle which would tell me that for an endothermic reaction of solvation, rising temperature would always push the reaction to be more thermodynamically favorable to the products. Could someone please point out my error in logic?

In advance, thank you!


texts: How can I make something like fire which is safe?

texts:
I want to know a magic trick that helps me put  my hand on fire without burning. My teacher told me you can use acetone but I should fire it fast in my hand because of volatility. Also I want to have fire that doesn't get put out fast; can I fire acetone for 5 minutes?!

If I fire acetone in my hand it may burn my hand. Are there any safe materials for my experiment?
Is there anyway to convert this heat into cold or Protectival material from burning?

I am looking for cold fire(fake fire)!

I read an article about cool flame;can I use it for solving my problem?


texts: How does one calculate the pH of an aqueous solution of a weak acid and a weak base?

texts:
In order to create a simple program which calculates titration curves (also to provide some closure in the comments here) I am trying to come up with all the equations so I can calculate the equilibrium proton concentration for any given concentrations of any two given weak acids/bases.

This is a collection of what I've come up with so far and what I assume I still need. If someone could help me back on track I'd kindly appreciate it.

We're looking at the following reactions:
$$\begin{align}
\ce{HA &<=>[$K$_{\text{a, 1}}][$K$_{\text{b, 1}}] H+ + A- && (1) }\\
\ce{H+ + B- &<=>[$K$_{\text{b, 2}}][$K$_{\text{a, 2}}] HB && (2)}
\end{align}$$
A is the weak acid and B the weak base with the according equilibrium constants (the indices 1 and 2 refer to the acid and base respectively).

For the total masses I've got the following:
$$\begin{align}
\ce{[A]_{tot} &= [HA] + [A- ] && (3) }\\
\ce{[B]_{tot} &= [HB] + [B- ] && (4) }
\end{align}$$

The equilibrium constants are linked via
$$ K_\text{a, 1} \times K_\text{b, 2} = \frac{\ce{[A- ][HB]}}{\ce{[HA][B- ]}} $$

Furthermore:
$$
\ce{[H+ ]_{eq}} = \frac{\ce{[A]_{tot}} K_\text{a, 1}}{\ce{[A- ]}} - K_\text{a, 1}
 = \frac{\ce{[HB]}}{K_\text{b, 2} (\ce{[B]_{tot} - [HB]})}
$$

For the equilibrium proton concentration I've derived
$$ \ce{[H+ ]_{eq}} = K_\text{a, 1} \ce{[HA]} + K_\text{a, 2} \ce{[HB]} + K_\text{w} \ce{[H2O]}$$
where I neglect the influence of the water (the additional term $[\dots] + K_\text{w} \ce{[H2O]}$) since it is so small.

Now, I'm struggling with the following:
$$ \ce{[H+ ]_{tot}} = ? $$

I believe that with the last equation I will be able to solve for $\ce{[H+ ]_{eq}}$. But maybe I'm wrong there as well.

Thanks for any pointers.


texts: The detergent 'Positive 170' and what exactly makes it so corrosive?

texts:
So in season 5, episode 7 of Dirty Jobs, we're shown how a locomotive engine block is degreased using the detergent 'Positive 170' and we're told that it is extremely dangerous.

Just how 'dangerous' are we talking about here and why?

Thanks.


texts: Has there been any independent verification of the results from this Chinese nanotube study?

texts:
Watts up referred to the South China Morning Post in reporting that a Tsinghua University team led by Wei Fei claimed in 2018 to have manufactured carbon nanotube fibre has tensile strength of 80 gigapascals.

Has this result been verified or reproduced independently?

The study was published in Nature and is available in ResearchGate, and a pretty nice plain language summary came out of ArsTechnica.


texts: We were just wondering in our chemistry class: is there any reaction which is neither exothermic nor endothermic?


texts: Dispersal of pyrethroid insecticide by vaporization - role of petroleum distillate in distribution in air

texts:
I live in Indonesia where there are many mosquitoes and products sold for their control.
One such product is this one:

The product contains 22ml of liquid, the contents of which likely vary slightly by jursidiction
https://www.whatsinsidescjohnson.com/ph/en/brands/Baygon/baygon__liquid_starter

Prallethrin - 1.316% (Wikipedia indicates 1.6% in typical products in India https://en.wikipedia.org/wiki/Prallethrin)
Petroleum Distillate (carrier) - Enables the delivery of a product to a surface.
Butylated hydroxytoluene (BHT) - preservative
Fragrances

They sell a liquid for use in a sprayer like this:

Unlike the plug-in which releases very small amounts of insecticide continuously, a sprayer would be sprayed manually perhaps once or twice a day. The product is sold in quantities of around 300-700ml.
Active ingredients vary by jurisdiction: in the Philippines
https://www.whatsinsidescjohnson.com/ph/en/brands/Baygon/baygon__multi_insect_spray_waterbased_refill

Water
Transfluthrin / Cyfluthrin
Isopropanol "wetting agent" - Helps a formula spread across a surface.
Benzyl Alcohol - anti microbial preservative
Sodium Lauryl Sulfate - detergent
Acetyl Tributyl Citrate - Helps ensure even distribution of a product's ingredients.

The Indonesian version is:
https://www.whatsinsidescjohnson.com/id/id/brands/baygon/baygon__liquid_spray_floral

Water
Cybermethrin, imiprothrin, prallethrin
Propylene Glycol Butyl Ether and PEG-60 Hydrogenated Castor Oil instead of the Acetyl Tributyl Citrate
Methylisothiazolinone & Benzisothiazolinone instead of the benzyl alcohol
Ethoxylated Alcohol in place of the SLS

Another company sells a similar liquid product to the Baygon liquid

This is sold in two formulations, the regular and the water-based which notes

'tanpa minyak tanah' (literally 'without ground oil', i.e. paraffin - this is not a very technical term and obviously means that the alternative product contains some kind of petroleum distillate)
Both regular and water-based formulations contain the same active ingredients: 1.14% prallethrin, 0.29% cyfluthrin.
I presume that there are particular properties of prallethrin that make it better for vaporization with an electric plug-in device (which I guess is not close to boiling - this should be evaporation) than certain other pyrethroids, but the question is:

if one were to refill the plug-in device with the 'spray'-type 1.14% prallethrin, 0.29% cyfluthrin petroleum-based product, would it be reasonable to expect it to have similar dispersal effectiveness to the 1.32% prallethrin petroleum-based 'vaporizer' product
given the existence of 'water-based' and 'petroleum-based' products with the same insecticides, is the 'water-based' less effective at dispersal, and does it have any advantage beyond presumably some sort of antipathy towards hydrocarbon vapours for health reasons.


texts: Investigating the effect of solvents on the alkaline hydrolysis of ethyl acetate

texts:
In the following reaction, I believe a polar aprotic solvent like propanone will be more favorable since the partial negative charge on the oxygen atom in propanone will attract the sodium ion from sodium hydroxide leaving the nucleophile, $\ce{OH-}$ to freely attack the carbonyl group:

$$\ce{CH3COOC2H5 + NaOH → CH3COONa + C2H5OH}$$

On the other hand, a polar protic solvent like ethanol will be less favorable because the partial charges on the oxygen and hydrogen atoms (created due to a difference in electronegativities) in the ethanol will surround the nucleophile, $\ce{OH-}$ and would prevent the attack on the carbonyl group slowing down the reaction.

However, while performing the experiment and obtaining conductances of the solutions at different time intervals using a conductivity probe to calculate rates and $E_\mathrm{a},$ it was observed that the rate of reaction was faster in ethanol and the activation energy in ethanol was also lower proving my argument incorrect.

Can someone help?


texts: How to calculate the percentage dissociation of phosgene using the pressure equilibrium constant?

texts:
In phosgene gas reaction at $\pu{400 ^\circ C}$, the initial pressure $p_{\ce{CO}}= \pu{342 mmHg}$ and $p_{\ce{Cl2}}= \pu{352 mmHg}$ and the the total pressure at equlibirum is $\pu{440 mmHg}$.
  $$\ce{CO + Cl_2 = COCl_2}$$
  Calculate the percentage dissociation of phosgene at $\pu{400^\circ C}$ at $\pu{1 atm}$.

Let $x$ be the decrease in pressure of both $\ce{CO}$ and $\ce{Cl_2}$
\begin{array}{lcccc}
 & \ce{CO &+& Cl_2 &<=> &COCl_2}\\\hline
\text{Initial pressure of substance} & 342 && 352 && 0\\
\text{Final pressure of substance}   & 342-x && 352-x && x\\\hline
\end{array}

$$342 - x + 352 - x + x = 440 \implies x = 254$$

Using the formula for $K_p$ I found it to be $\approx 13$.
For the dissociation at $\pu{760 mmHg}$,
$$\ce{COCl2 <=> CO + Cl2} \implies K_p= \frac{1}{13}$$

Let $y$  be the decrease in pressure of phosgene which is proportional to the amount of substance of it lost or it's degree of dissociation.
$$\frac{1}{13} = \frac{y^2}{760-y} \implies y \approx 7.6$$

The value of $y$, that I have obtained, must be proportional to percentage dissociation, so percentage dissociation should be $7.6 \%$. But the answer given is $20.6 \%$.

I am not looking for the entire solution but would like to know where have I misapplied the concepts. I am doubtful about my second step, but can't figure out how it's wrong.


texts: If given a question to compare stability of free radicals, can we always check it by same parameters that we use for stability of cations (since both are electron deficient) or is there any exception to this? By parameters I mean hyperconjugation, mesomeric, resonance, inductive effects. Is there any other effect that can be added to this list?


texts: Reaction between RCH2=CH2 and CCl4 -- Why does it form RCHClCH2CH(R)CH2CCl3 along with RCHClCH2CCl3?

texts:
I am reading Organic Chemistry from Morrison & Boyd and there is this problem in it:

  Problem 6.8 From the addition of $\ce{CCl4}$ to alkenes (in presence of peroxides), $\ce{RCH2=CH2}$, there is obtained not only $\ce{RCHClCH2CCl3}$ but also $\ce{RCHClCH2CH(R)CH2CCl3}.$ Using only the kind of reactions you have already encountered, suggest a mechanism for formation of this second product.

I know that the addition of CCl4 to alkenes in presence of peroxides is a free radical reaction. So what I have thought is, while the reaction is going on, there are the following species present: RCH=CH2 (reactant), RC^HCH2CCl3 (^ represents the electron on the free radical) and the product $\ce{RCHClCH2CCl3}$.

When the free radical reacts with $\ce{RCH=CH2}$ it gives the main product $\ce{RCHClCH2CCl3}$ and $\ce{.CCl3}$. So probably the second product is formed by reaction of $\ce{.CH(R)CH2CCl3}$ with $\ce{RCHClCH2CCl3}$?

$$\ce{RCHClCH2-CCl3 + .CH(R)CH2CCl3 ->[???] RCHClCH2CH(R)CH2CCl3 + .CCl3}$$

However this reaction I have never encountered while the question explicitly states that I have to use only the kind of reactions I have already encountered. I don't think anyway that this reaction is possible.

There must be something big that I am missing here ... Can someone give me a little hint?


texts: Reaction between barium peroxide and hypochlorous acid

texts:
When $\ce{BaO2}$ reacts with $\ce{HClO},$ the question tells us that that oxygen, barium chloride and one other product is formed.
The equation I came up with is
$$\ce{BaO2 + 2 HClO -> BaCl2 + 2 O2 + 2 H2}\tag{R1}$$
The equation given, however, is
$$\ce{BaO2 + 2 HClO -> BaCl2 + 1 1/2 O2 + H2O}\tag{R2}$$
Why is $\ce{H2O}$ produced and not $\ce{H2}?$ More importantly, what clues/rules are there that would have helped me to predict these products?


texts: Is suckback possible after removing stopper?

texts:
I am making hydrogen gas to fill a balloon. I will run the gas to a washing bottle with $\ce{NaOH}$ and then connect the balloon. I was wondering what would happen if I removed the stopper of my main reaction flask (e.g. to change wasted reagents) when the balloon is already half inflated.

Would $\ce{NaOH}$ get sucked out of the washing bottle somehow?
Would gas that's already in the balloon come out? Or the washing solution would prevent it?


texts: How can I turn mercury metal into mercury oxide? I know that many metals will react with oxygen if enough heat is supplied in the presence of oxygen. If I heated up mercury enough and also supplied oxygen from my oxygen tank, would that result in mercury oxide? Also how about lead? Thank you


texts:
When an ion is adsorbed from an aqueous solution onto a solid, what happens to its counterion? Obviously, the solution does not become charged - does this mean that it too is adsorbed?

(Example: $
\ce{NaF}$ with activated alumina as the adsorbent)

I suppose an alternate explanation would be that the remaining cation hydrolyses , but this does not seem likely in the example above as $\ce{Na^+}$, being the salt of a strong base, will not hydrolyse.


texts: What is the easiest way to concentrate a solution without causing it to hydrolyze?

texts: I’ve been working with iron acetate solutions in dilute acetic acid (vinegar) and I’ve been running into a problem. Every time I try to boil off the solvent the solution hydrolyzes to form iron oxides. I’ve given up trying to dry it completely because supposedly iron acetates can’t exist outside of solution, but is there a way of concentrating the solution?


texts: Calcium chloride + starch desiccant packs inside PPE for ebola workers?

texts:
(First question on stackexchange, apologies for any faux pas)

Ebola workers get drenched in sweat while working inside their personal protective equipment.  There's a discussion happening over on OpenIdeo about whether the desiccant packs used in shipping containers might help reduce humidity:
https://openideo.com/challenge/fighting-ebola/ideas/desiccant-embedded-ppe-suit-to-keep-ppe-dry-and-bearable

Questions for the chemists:

What are the reaction products of a calcium chloride + starch desiccant pack with humid air?  In particular, would it generate any gases?  (That'd obviously be a problem inside an impermeable suit)
The worker sweats to carry away heat evaporatively.  Presumably most of that body heat would need to pass through the desiccant pack as the sweat gets absorbed, and would need to be transmitted outside the suit in order to be worthwhile.  It looks like the reaction is also exothermic.  How much total heat would need to be removed from the pack, and is this going to be too much to dissipate?
Any other risks to be aware of with this idea?


texts: How to remove nitrose gasses from ozone gas mixture?

texts:
I produce ozone gas with an ozone generator based on corona discharge principle.
These kind of ozone generators have the disadvantage that if $\ce{N2}$ is present, a bit of $\ce{NO}$ and $\ce{NO2}$ will be produced too.
To produce oxygen I use a oxygen concentrator, with an output of about $90\%$ $\ce{O2}$ and about $10\%$ $\ce{N2}$.
For that reason I have a little quantity of $\ce{N2}$ entering the ozone generator, which subsequently lead to unwanted side reactions like $$\ce{N2 -> NO -> NO2}.$$

The $\ce{NO2}$, even in that small quantity as it is, does influence the following processes in an negative way.

The easiest way to circumnavigate this issue would be to take pure oxygen – however for cost reasons I cant use LOX, so I have to stay with the concentrator.
I am searching for an reagent or an catalyst, which is not effected by the ozone but does absorb or disintegrate the $\ce{NO}$, and especially the $\ce{NO2}$.

To stripe $\ce{NO2}$ from a normal gas is not so difficult, but the ozone does make trouble.
I thought about dry $\ce{NaOH}$, soda lime, or dry $\ce{KOH}$, but I have the feeling that these chemicals will react with $\ce{O3}$.

Any suggestions?


texts: Why is vapour pressure not dependent on shape and size of the container?

texts:
In my textbook, it's written that vapour pressure of a liquid does not depend on shape and size of a container but won't a container that provides less surface area to the liquid will have lower vapour pressure?

for example, consider 2 containers give in the diagram below, the volume of container and liquid is same in both the diagram just the shape is changed.

wouldn't the vapor pressure be lower in the diagram on the left side? and how does changing size not affect vapor pressure?


texts: Creating a chemical solution with water and chlorine

texts:
I bought a swimming pool for my kids and also a measurement instrument for measuring the amount of chlorid in the pool in mg/l. The problem is now that you have to calibrate the instrument before using it. This means you have to know the current amount of chlorine in the pool.

Since the test strips are quite inaccurate and hard to read an exact value. My idea was to just create a perfect solution in a one liter water container.

Now I am not really sure how much of the given pool chlorine I have to put into the 1 liter water to get a 1.5 mg/l solution of chlorine. With that I would be able to calibrate the instrument perfectly.

What I am using is chlorine granules.
The instruction leaflet says it contains "CAS 51580-86-0 Troclosenatrium, Dihydrat (100g/100g)"
Registration: BAuA N-23822.

Would I just have to add 1,5 mg to 1 liter of water to get 1,5mg/l?
Is it maybe that easy?


texts: What is the term for the amount of volume change at a phase boundary?

texts:
Apologies for the extremely basic question, but I would like to look up the amount by which the volume (or equivalently, density) of various substances changes when they freeze. However, I don't know the correct term for this, and Google isn't helping much.

To clarify, I'm asking about the vertical line segment on the plot below (from Wikipedia). If the $y$ axis was internal energy then the height of this line segment would be called "latent heat of fusion", and I could easily look it up for any given substance. I would like to know the equivalent term for the discontinuous volume (or density) change, in whichever units are most standard.

I realise that unlike latent heat, this will depend quite a bit on the pressure. However, I would hope that it would be tabulated for atmospheric pressure at least.


texts: What's the difference between aqueous NaOH and dilute NaOH?

texts:
Dilute $\ce{NaOH}$ can be prepared by adding a suitable amount of concentrated $\ce{NaOH}$.

What's the difference between "dilute $\ce{NaOH}$" and "aqueous $\ce{NaOH}$"?


texts: What is distorted square pyramidal structure of a compound?

texts: I have recently being studying structures of different types of compounds, when I came across the structure of $\ce{[XeF5]+}$ which have a structure distorted square pyramidal. I could not understand what "distorted" square pyramidal is and how it is different from square pyramidal.


texts:
The starch and iodide test is to detect amylose, a polysaccharide. We add an iodide solution to a sample and observe a color change with the starch; it turns dark blue.

While researching information online, I understood that $\ce{I_{2}}$ is not soluble in water, hence it needs to react with iodide ions present to at least create $\ce{I_{3}}$, which is soluble in water, and also forms polyiodide complex, as research shows. I also understood that this linear molecule of iodide migrates to the center of the helicoid polysaccharide structure. Then, with some electronic interactions, there is a modification in the electron configuration which produces the dark blue color.

My questions are as follows. What are the electron's movements? Which atoms are implicated in this transfer of electrons? What is the electron configuration change that results in the color change? In other words, I don't understand the electron's interactions between iodide and amylose that are creates the color change.


texts: Ionic compound having highest solubility in water

texts:
Which ionic compound has highest solubility in water? I can find CsBr having highest solubility with 1230 g/L at 25 °C.

Note: compounds like ethanol are soluble to any extent in water, but they are covalent, not ionic.


texts: Prepare 1 liter of 28% NH3(aq) solution from 1 gal of %10 NH3(aq)

texts:
I have one gallon of commercial, surfactant free, ammonium hydroxide solution that I would like to use to prepare a concentrated solution.

I have two options as I see it, and I am still getting into the chemistry side (amateur chemistry), but am pushing ahead and want to do this even without the understanding. I am hoping the solutions will provide adequate explanation as to what is being done, and why, which will help me learn to solve problems like this in the future. Chemistry newbie, here.

Solubility at room temperature is to be assumed.

I see that I have two options.

1) Prepare a receiving flask with cold distilled water (likely in an ice bath) and then prepare a distillation flask with the %10 ammonium hydroxide solution. Slightly heat the distillation flask to the point where the ammonia gas begins to off-gas, which is funneled into the receiving flask and dissolve.

2) Prepare a receiving flask and distillation flask both with an amount of the 10% ammonium hydroxide solution. As above, gently heat the distillation flask to off-gas the ammonia into the receiving flask where it should dissolve, and increase the concentration beyond 10%.

Since I would like a 1 liter solution containing 28% NH3(aq), what volume of cold distilled water should be placed in the receiving flask, which I ask because I assume the solvation of NH3 into water will cause the volume to increase. If I placed 1 liter of water into the flask initially, then this would result in more than 1 liter of solution. This also depends on the amount of ammonia that needs to be dissolved to reach my desired concentration, which varies from option #1 to #2.

So what I want to know is,

Q1) How to determine the volume of a solution given a specific concentration of NH3(aq). This will allow me to account for the increase in volume when adding ammonia to an existing solution, in order to reach a desired concentration.

Q2) How do I know when I have reach %28 NH3(aq) concentration?

Q3) A procedure leading from 10% to 28%, and any advice on more technically correct approaches to this problem. Is it a problem that should be considering molarity, etc.?

Q4) Any quick background info that I can look up to help me understand this problem would be welcome!

Bottom line: Prepare a 1 liter solution of 28% NH3(aq) from 1 gallon of 10% NH3(aq), and please provide an explanation.

Thank you for any help. I am a software programmer, and have delved into he world of chemistry as a hobby, and am getting confused by terms like molarity, normality, and both of those versus concentration, etc. It's maddening to say the least.


texts: why is molybdenum a much stronger magnet than chromium

texts: Molybdenum is well known for its strong magnetic properties. Why is Chromium with an identical set of unpaired electrons not nearly as strong?


texts: What causes the smell of something being "musty"?

texts: You know the smell that arises when you leave a wet sponge out for too long? Does anybody know the chemical structure of the molecule that causes that smell? Similarly, what chemical process might be underpinnig that smell from occuring in the first place?


texts: Electroplating copper yields rough surface?

texts:
I am attempting to electro-plate vias in a home brew printed circuit board. The medium I am attempting to electroplate is fiberglass bound together with epoxy. This is an intentional insulator.

I drilled a few holes in this medium using a regular electric drill and covered the holes with a graphite based conductive paint by covering the board in the paint and drawing it through the holes using a vacuum. I repeated this in both directions in an attempt to cover the holes evenly. I then cured the paint at about 100C for 20 minutes. In my experiments, this was far sufficient to dry the paint.

I then created a solution of 1000ml distilled water, 250ml of 38% sulfuric acid (battery acid to improve conductivity) 160g of copper sulphate pentahydrate, and 2 ml of polysorbate 20.

I prepared this solution by adding the sulfuric acid to the water slowly (to avoid rapid exothermic reaction between acid and water) then adding the polysorbate and the  the copper sulfate pentahydrate. I then mechanically agitated the copper sulfate pentahydrate crystals until the solution was homogenous.

I ran .8A of constant current through the solution with the board as the cathode and an anode consisting of two electrically common (14ish guage) copper wire on either side of the board. After about 90 minutes this was my result...

I'm wondering why the copper clad had "beads" on it...the entire surface was sanded with 1500 grit sandpaper directly preceding the electroplating.

I'm also wondering why the holes are so "rough". In my testing, every via has come up as 0.0Oohms...or electrically common to the clad. Aesthetically though, this is not pleasing and makes me wonder if my method is truly reliable.


texts: Nomenclature priorities with ethers, acyl groups and ketones

texts:
$\hspace{6cm}$

(2-oxopropionyl)oxy butanoic acid

$\hspace{6.5cm}$

3,4-dioxo 4-methoxy butanoic acid

$\hspace{6.3cm}$

3-(2-oxopropyl),6-oxo heptanoic acid

$\hspace{6.25cm}$

3-propionyl,6-oxo heptanoic acid

$\hspace{6.3cm}$

3-(3-oxobutyl),6-oxo hexanoic acid

Aldehyde takes priority over ketone, yes?

Have I got these right?

PS: With the third molecule, wouldn't it be convenient if we could have a ketonyl group so that instead of 2-oxopropyl , one could say propanonyl?


texts: Is the width of a Soxhlet Condenser Inherent to its Function?

texts:
Soxhlet extractors are often coupled to a specifically designed condenser with a very large lower joint.
Is this inherent to it's function as a condenser in the apparatus or only because the Soxhlet Extractor part underneath it needs a big upper joint to get stuff in and out? In other words, is there any drawback to using an adaptor and replacing the condenser by a longer (but thinner) graham condenser?
Preventing flooding might be another reason (for high boiling solvents mainly?).


texts: Why does Fe(II) have electrons in the 3d subshell?

texts:
The electron configuration for $\ce{Fe^2+}$ in my coursebook is given as:
$$ 1\mathrm s^2\, 2\mathrm s^2\, 2\mathrm p^6\, 3\mathrm s^2\, 3\mathrm p^6\,3\mathrm d^6$$
But shouldn't the $4\mathrm s$ subshell take precedent over the $3\mathrm d$ subshell according to Aufbaus principle?


texts: The definition of peptide, peptide bond and protein

texts: According to what I understand the difference between peptide and peptide bond is that peptide is two or more amino acids (up to 19 -inc.) which linked together, while the term "peptide bond" refers to the bond between each two amino acids. Is that true? If it is, the definition of protein is that it contains at least 20 amino acids which are linked together. Isn't it?


texts: Are the total number of electrons present in the central atom of triiodide equal to 10?

texts:
My book states that

  the total number of electrons present in the central atom of $\ce{I_3^-}$ is equal to 10.

What if I put a negative charge on the central iodine atom such that it gains a noble configuration and then I say that it is coordinatively bonded with other two iodine atoms? Then the number of electrons which the central atom will have would be 8. Wouldn't it?

Am I wrong somewhere in my analogy?


texts: In pig iron, from where does carbon in it comes from?

texts:
I've read that:

  "During extraction of iron another impurity appear which is carbon from coke in furnace."

However, I don't understand how there will be enough unreacted carbon that would blend with iron. As reaction of carbon and oxygen is very exothermic so there must be enough energy for all carbon atoms to react with oxygen.


texts: Since PPh₃ is strong field ligand and, the famous Wilkinson's catalyst, which also possess this ligand is square planar, then what makes the above complex tetrahedral?


texts: What causes that foul taste with combination of toothpaste and orange juice?

texts:
Ugh, I drank orange juice too soon after brushing my teeth and my mouth feels awful!

What causes that foul taste with this combination of toothpaste and orange juice? Is it a reaction between the oil of wintergreen in the toothpaste and the citric acid in the OJ? Is it something else? What's the explanation for this?

As a second part to this question, is there a way to stop this reaction from happening, aside from not drinking orange juice after brushing?


texts: Assigning R/S configurations to Fischer projections of 3‐chloro‐2‐hydroxybutanoic acid

texts:
A question requires you to assign the R/S configuration for 3‐chloro‐2‐hydroxybutanoic acid:

In the answer, while assigning the configuration to carbon #1, apparently the group below is given the third priority, lower than the COOH group above.
Using the CIP rules, doesn't the Cl atom in the bulky group give it a higher priority than the COOH group?


texts: 8 moles of so2 and 4 moles of O2 are mixed in a closed vessel.the reaction proceeds at constant temperature. By the moment when equilibrium sets in,80% of the initial amount of so2 enters into the reaction. The equilibrium pressure would be?    My attempt: reaction will be 2so2+O2---->2so3. There will be 1.6mole of so2,0.8 mole of O2 remaining and 6.4 mole of so3 will be formed. Now how to find the equilibrium pressure?


texts: How to control and vanish termiticide/pesticide fumes from room

texts:
I had some wood work done in my room and termiticide (UNIBAN-20 (Chlorpyriphos-20% EC) was used so that there is no termites attack in future. The stupid carpenter was using this product for the first time and it had to be diluted 10 times in kerosene oil before use which he didn't do. He poured the concentrated solution of this termiticide.

Now we have very strong smell and poisonous fumes (the head starts spinning within seconds) in the room.

How can I neutralize the smell and get rid of the poisonous fumes? It has been 13 days now.

I have exhaust fan switched on but the smell is still there in the room.


texts: Solving for H+ given dissociation of weak acid, c and Ka Can the quadratic equation yield two nontrivial solutions?

texts:
For example, if a question asks for $[\ce{H+}]$ of a $0.100~\mathrm{M}$ solution of picric acid (monoprotic), given that its $K_\mathrm{a}$ at the system temperature is $4.2 \times 10^{-1},$ following my teacher's instructions I would use the ICE table, which looks like this (for a different example).

$$\begin{array}{cccccccc}
 & \ce{CO (g)} & + & \ce{H2O (g)} & \ce{<=>} & \ce{CO2 (g)} & + & \ce{H2 (g)} \\
\text{Initial} & 0.100~\mathrm{M} & & 0.100~\mathrm{M} & & 0 & & 0 \\
\text{Change} & -x~\mathrm{M} & & -x~\mathrm{M} & & x~\mathrm{M} & & x~\mathrm{M} \\
\text{Equilibrium} & (0.100-x)~\mathrm{M} & & (0.100-x)~\mathrm{M} & & x~\mathrm{M} & & x~\mathrm{M} \\
\end{array}$$

I would then solve for $x$ by using the expression for $K_\mathrm{a}$. However, since $0.100/K_\mathrm{a} < 100$ (lowest initial concentration divided by $K_\mathrm{a}$ is less than 100), $x$ is significant and cannot be omitted from the $0.100-x$. Thus, you need to use the quadratic equation, which yields two solutions for my example above: $x=0.0834, 0.503$. The latter is obviously incorrect because it is greater than the initial concentration of the undissociated compound.

However, my question is: Is it possible that both solutions to a given reaction will be nontrivial, that is, is it possible that both answers appear to work at a glance? (No conflicts with the initial concentration, etc.) This question refers not specifically to the example in question, but rather looks at if it is possible at all (is there a reaction and starting concentration for which both answers would seem correct). In addition, if it is possible, how would one determine which answer is nontrivially impossible?

Whenever I get into a new subject I'm not able to "do" it until I work out some small details that stick with me.  It would be best if the answer had some logical explanation, or even a proof as to why the two answers will never be both possible at a glance, or if the answer shows a way to determine without fail which answer is correct. I don't see an obvious reason why both solutions resulting from the quadratic equation will always have one blatantly incorrect result.

Please ask for clarifications if necessary.


texts:
I am a little bit confused trying to name the compound fulvene:

I'm not sure whether its name is 5-methylene-1,3-cyclopentadiene or                        3-methylene-1,4-cyclopentadiene.


texts:
How should the water flow in your condenser? From the flask to the top of the condenser, or from the top of the condenser back to the flask? I could imagine both: flask to top will fill the entire condenser with water, because of the resistance of gravity, enlarging cooling area, or top to flask, because this will generate counter current exchange increasing heat flow, but then it is almost impossible to get a decent cooling surface without extreme water pressure.

This picture suggests the first.


texts: Where do we report yields in a research report?

texts:
I'm in an integrated laboratory course at university that combines all the disciplines of chemistry that we have here. I was instructed to place the yield in the methods section of the report by my professor, but found that to be odd.
Is reporting the yield in the methods section a standard protocol in some paper formats?


texts: Acid titration of sodium acetate in the presence of sodium ethoxide, is it possible?

texts:
I have an aqueous solution of ethanol of $30 - 40\text{ V%}$ that contains a few (unknown) $\text{%}$ ethyl acetate (ethyl ethanoate - $\ce{EtOAc}$).
I wonder if I can quantitatively determine the $\ce{EtOAc}$ content by back titration of a small excess of strong $\ce{NaOH}$.
The idea is to add a stoichiometric excess of $\ce{NaOH}$ to a known volume of sample solution, then reflux this mixture to achieve saponification of the $\ce{EtAc}$, acc.:
$$\ce{EtOAc}+\ce{NaOH} \to \ce{NaOAc}+\ce{EtOH}$$
The excess $\ce{NaOH}$ would form sodium ethoxide with the ethanol, acc.:
$$\ce{NaOH}+\ce{EtOH} \to \ce{NaOEt}+\ce{H2O}$$
Since as $\ce{NaOEt}$ is a strong base and $\ce{NaOAc}$ a weak one, I think it should be possible to titrate them sequentially.
Any thoughts would be appreciated.


texts: Why are real orbitals used to define the orbital of hydrogenic atoms instead of complex orbitals?

texts:
On the physics site, I asked the difference between real & complex orbital. Real orbitals are the superposition of complex orbitals having definite magnetic quantum number states.

\begin{align}
p_z &= p_0 \\
p_x &= \frac{1}{\sqrt{2}} \left(p_1 + p_{-1} \right) \\
p_y &= \frac{1}{i\sqrt{2}} \left( p_1 - p_{-1} \right)\\
\end{align}
where $p_0 = R_{n1} Y_{10}$, $p_1 = R_{n1} Y_{11}$, and $p_{−1} = R_{n1} Y_{1−1}$, are the complex orbitals corresponding to $\ell = 1$.

My question is:

Why aren't the orbitals of hydrogenic atoms taken as complex orbitals instead of the real ones? They are valid states for an electron, aren't they? So, what is the problem in having complex atomic orbitals?


texts: How is the structure of triiodide ion (I3-) possible?

texts:
I have seen the structure of triiodide ion ($\ce{I3-}$) but I cannot understand why this structure is even possible. I have seen in my textbook that

  $\ce{I_3^-}$ is formed by combination of $\ce{I2}$ and $\ce{I^-}$ ion in which $\ce{I^-}$ ion acts as a donor and $\ce{I2}$ molecule act as acceptor. It accommodates electrons in empty d orbitals:

But I think $\ce{I-}$ is stable due to its complete octet. Then why it should combine with $\ce{I2}$ molecule to form another new compound? I am confused because the Lewis structure of $\ce{I3-}$ would not make any sense if we consider the octet of central iodine atom.


texts: Is lithium L-threonate a potential brain medicine?

texts:
Lithium ions have known neuroprotective qualities. That would explain its therapeutic benefit in some mental disorders. It is also well known that lithium carbonate must be taken in toxic doses to get even small amounts into the brain. This makes lithium carbonate a very non-optimal medicine. On the other hand, lithium orotate promises to reach the brain much more efficiently and therefore require smaller doses. Unfortunately it contains orotic acid, which is a known carcinogen.

Magnesium L-threonate is a form of magnesium that easily penetrates the blood-brain barrier and therefore confers therapeutic effects on the brain. Is it then conceivable that lithium L-threonate is both safe and effective as a medicine for brain disorders?


texts:
I read the book an it said when $\ce{NH4Cl}$ dissolves in the water, the reaction  of $\ce{NH4+}$ will be

$$\ce{NH4+ <=> NH3 + H+},$$

but instead, the first reaction came to my mind was

$$\ce{NH4+ + H2O <=> NH4OH + H+}$$

Are these two reaction the same? And if they are the same, does that means that $\ce{NH3} = \ce{NH4OH}$ in the water?


texts: What happens when Isopropyl alcohol expires?

texts: My isopropyl alcohol is expired. What happens when it expires? Does it break down into something else? Can I still use it to clean or sanitize?


texts: Nomenclature of unusual nitrogen functional group

texts:
I am trying to create a proflavine derivative containing a 1,2,4-oxadiazole-5-one functional group, the first step produces an interesting functional group that I have no idea how to name:
$$\ce{[Pro]-NH-CH=N-OH}$$
I am trying to find literature on the above functional group so I can analyze proton NMR to see if I have actual created the above molecule.


texts: What does the salt actually do during electrolysis?

texts:
Pure water does not conduct electricity.
When you dissolve a salt like $\ce{Na2SO4}$ in water the solution becomes a better conductor.
If electrolysis is done on this solution, oxygen and hydrogen gases form at the electrodes.
The ions $\ce{Na+}$ and $\ce{SO^{2-}4}$ don't seem to be doing anything further.
The electrons from the cathode don't involve the ions:
$$
\begin{align}
\ce{4 H+ + 4 e- &-> 2 H2} \\
\ce{4 OH- &-> 2 H2O + O2 + 4 e-}
\end{align}
$$
How are the salt ions helping here or what are they doing?


texts: How does the purification until analytical grade work?

texts: What are some industrial methods used for puryfing organic solutions, like toluen, until it is analytical grade? Im not looking for details just some names and somewhere to keep reading


texts: Am I correctly showing a hydride shift on the alkyl halide?

texts:
I did this quiz and I forgot the hydride shift.

With the hydride shift, would these be the right answer?


texts: Work can be extracted from galvanic cell which has a negative Gibb's free energy. I was wondering what is the driving force of it: I would naturally think its the Gibb's free energy, but the gaps between two fermi levels of the two electrodes also seem to pay a role in the potential difference. Could someone correct me or maybe tell me the connection between these two concepts?


texts: Sulfur hexafluoride creation process and risks/safety

texts: I would like to create sulfur hexafluoride and test floating things in it but I am a "chemistry noob" and from what I've read it's non-toxic and generally quite safe but first of all I do not know how to make it (other than that it involves sulfur and fluoride which are both definitely not safe) and the precautions for doing this. Basically: Safe way to make sulfur hexafluoride and how safe is sulfur hexafluoride?


texts: How does the 1.5 bond order of ozone contribute to its instability?

texts: I'm confused as to why ozone is so unstable? I've been told it's because it has a fractional bond order. However, this doesn't make sense to me. Don't fractional bond orders mean resonance and doesn't resonance stabilize ozone?


texts: How would this reaction look like in a potential energy diagram? (SN1 Reaction)

texts:
My task is to explain, why molecule A reacts in a SN1-reaction faster than molecule B. (I would do this by comparing their potential energy diagrams)

My idea is to have a closer look at the reaction mechanism at first:

TS1 is here the intermediate with the carbo-cation. That's the step, where the reaction is slow, where one needs a lot of energy to remove the Bromine.
Maybe I guess one does not need this lot of energy in molecule A compared to B because the Bromine is in the background (trans- isomer) there and not in the foreground? Furthermore, in SN1 reactions the reaction rate is determined by the substrate (the first step).
So, the activation energy of molecule A is smaller then the activation energy needed in B and that's the reason, why the reaction ist faster?


texts: Derive expression for heat flow from oil bath to metal sphere

texts:
A spherical ball of iron is put into a hot bath of oil. The iron ball is initially at a low temperature and heat transfer from the oil to the iron will increase the temperature of the iron ball.
Use the concept of heat transfer coefficients to express the heat flow (i.e. the quantity with units J/s) from the oil to the ball. Denote your variables according to the notation in Table 1. Notice that not all variables in Tab. 1 might show up in your expression. Variables not listed in Table 1 must not be used in your final expression.
Table 1: Notations
$$
\begin{array}{ll}
\hline
c_{p, f} & \text{ heat capacity oil} \\
c_{p, s} & \text{heat capacity iron} \\
D & \text{diameter iron ball} \\
h & \text{heat transfer coefﬁcient} \\
k_f & \text{thermal conductivity oil} \\
k_s & \text{thermal conductivity iron} \\
Q & \text{heat ﬂow oil to iron (J/s)} \\
R & \text{radius of the iron ball} \\
T_s & \text{temperature iron ball} \\
  & \text{(can be assumed homogeneous)} \\
T_0 & \text{bulk temperature oil} \\
ρ_s & \text{density iron} \\
ρ_f & \text{density oil} \\
\hline
\end{array}
$$

I'm really unsure of how to solve this problem. I know that the heat flow for a sphere with an inner and outer radius is
$$Q = \frac{4πkR_o}{1 - R_o/R_a}(T_0 - T_a),$$
but here I only have the radius of the whole sphere. So, how do I write the expression for the heat flow then?


texts: How to compare stability of following two alkenes

texts:
How to find which alkene is more stable ?. As same number of hydrogens are added across the double bond so I am not able to use the fact that more substituted alkene is more stable.

I was initially thinking in terms of steric effect (Repulsion Between the two methyl groups) which led me to believe the second alkene should be less stable but in answer given the second alkene is shown more stable .

Can somebody explain on what basis this result is deduced. Any help is appreciated.


texts: Is there safe chemicals for making voice pitch or bass?

texts:
I'm looking for safe experiment that can pitch and bass my voice.finally I find a video that do it but he said "not try in home,ok..?".Is there safe tool or chemicals for Manipulation of the larynx is used to generate a source sound with a particular fundamental frequency.

other my question is about below viedo link:How these chemicals make voice pitch or bass!(Helium and Sulfur Hexafluoride)

Pitch is a perceptual property of sounds that allows their ordering on a frequency-related scale,1 or more commonly, pitch is the quality that makes it possible to judge sounds as "higher" and "lower" in the sense associated with musical melodies.

video link


texts: Energetic Placement of Atomic Orbitals in the HCl Molecular Orbital Diagram

texts: How are the 3p orbitals of chlorine lower in energy than the 1s orbital of hydrogen?


texts: Theoretical yields and determining the number of moles in a reaction

texts:
I'm working on a question which asks me to do two things. I've balanced the related equation as:

$$\ce{6H2O + 6CO2 -> C6H12O6 + 6O2}$$

Now, if I have $44$ grams of $\ce{CO2}$ and $36$ grams of $\ce{H2O}$, how many moles of glucose will I have? The molecular mass of $\ce{CO2}$ is $44\mathrm{~g/mole}$, and that of $\ce{H2O}$ is $18\mathrm{~g/mole}$. Do I need to determine how many moles of each element are in the certain amount of grams for each compound, and then use that to determine how many moles are in the glucose?

Secondly, for the same amounts of $\ce{CO2}$ and $\ce{H2O}$, I need to figure the theoretical yield. Am I correct in saying since for ever 6 molecules of $\ce{H2O}$ and $\ce{CO2}$ I get 1 molecule of glucose, I would do

$$36\text{ grams of } \ce{H2O} \times \left( \frac{1~\mathrm{mol}~\ce{H2O}}{18\mathrm{g}~\ce{H2O}} \right) \times \left(\frac{1~\mathrm{mol}~\ce{C6H12O6}}{6~\mathrm{mol}~\ce{H2O}}\right)$$

Then take the same for $\ce{CO2}$? I'm unsure of what to do with the values after that.


texts: Reorganization during ionisation for d block elements

texts:
This is a quote from my textbook:

  The irregular trend in the first ionisation enthalpy of 3d lmetals,can be accounted for by considering that the removal of one electron alters the relative energies of 4s and 3d orbitals. So the unipositive ions have dn configuration with no 4s electrons.There is thus a reorganization energy accompanying ionisation with some gains in exchange energy as number of electrons increases and from transference of s electrons into d orbitals.However the value of Cr is lower because of the absence of any change in d configuration.

What I basically understand from this is that during first ionisation, electron is lost from $\mathrm{4s}$ orbital because it have higher energy and forms uni-positive ion and the remaining one electron is transferred back into $\mathrm{3d}$ lower energy orbital as energy gap between $\mathrm{3d}$ and $\mathrm{4s}$ lowers. This transition of electrons into lower orbital gives a net decrease in ionisation enthalpy (where energy is released as reorganization energy). But I don't understand what they mentioned about $\ce{Cr}$.

https://www.chemguide.co.uk/atoms/properties/3d4sproblem.html

In this site when they explain about Vanadium electronic configuration it has been mentioned that Vanadium in its unipositive ion state have 4 electrons in $\mathrm{3d}$ rather than 3 electrons in $\mathrm{3d}$ and 1 electron in $\mathrm{4s}$ which supports the idea that electrons is transferred from $\mathrm{4s}$ to $\mathrm{3d}$.

Is it true that during ionisation there is a transference of electron from $\mathrm{4s}$ to $\mathrm{3d}$ orbital?Why the text mention reorganization and exchange enthalpy when talking about ionisation?

Text source:NCERT textbook ($\mathrm{d}$- and $\mathrm{f}$-blocks, page 215)


texts: How to derive this temperature-pressure-specific volume relationship?

texts:
(for isentropic, adiabatic, ideal gas flow)
 $$\frac{T_x}{T_y} = \left(\frac{p_x}{p_y}\right)^{\frac{(\gamma-1)}{\gamma}} = \left(\frac{V_y}{V_x}\right)^{\gamma-1}$$ where $V$ is the specific volume, $x$ and $y$ are any 2 rocket nozzle axial sections (though I presume this relation holds true for many other things as well), and $\gamma$ is the specific heat capacity ratio $c_p/c_v$, numerically equivalent to the molar heat capacity ratio $(\bar{C}_p/\bar{C}_v)$.

Thanks!
p.s. I may have just learnt the hard way that it is probably not the best idea to write a markdown-dense blurb on a phone ;)


texts: Determine the geometry of each nitrogen atom in formamidinium ion

texts:
The geometry at A seems to be straightforward: $\ce{N}$ is surrounded by $\ce{C}$ and two $\ce{H}$'s. By VSEPR, this is trigonal planar.

For the geometry at B: $\ce{N}$ is surrounded by $\ce{C}$, two $\ce{H}$'s, as well as a lone pair. Once again by VSEPR, I determined this was trigonal pyramidal.

However, the answer was given as A, which means that my process for the geometry at B was incorrect. What mistake did I make and how should I fix it?


texts: Does a Na2SO3 solution oxidize to Na2SO4 in an oxygen rich atmosphere?

texts:
Let's assume I have a pure solution of water and $\ce{NaOH}$. When this solution comes in contact with an atmoshpere containing inert gases and $\ce{SO2}$, then $\ce{NaHSO3}$ and $\ce{Na2SO3}$ will be formed into the solution.

The question is, if the atmosphere now contains also $\ce{O2}$, would these reactions happen?

$$\ce{2Na2SO3 + O2 <=> 2Na2SO4 + 2e-}\\
  \ce{2NaHSO3 + O2 <=> 2NaHSO4 + 2e-}$$

What would happen to the freed electrons?


texts:
Where I'm from, most paper you find/get at stores has this yellowish tinge. Why is it yellow and not white?

In my chemistry book it's mentioned that paper manufacturers "refine" paper from wood pulp, and that this involves treating the pulp with $\ce{CaCO3, TiO3}$, etc and this is what makes paper white.

But the paper that's commonly available here is yellow(ish). Is it because the manufacturers don't carry out the required treatment with $\ce{CaCO3}$ and $\ce{TiO3}$ (why would they do that anyway?), or could it be due to some other reason?

Also, if treatment with $\ce{CaCO3}$ and $\ce{TiO3}$ is what's used to color paper white, can someone tell me how the color change to white (from what would've otherwise been yellow paper), actually works?

My question is different from the proposed duplicate. In my question, I'd like to know why (relatively fresh) paper is yellow, straight out of the press. I'm not asking for why paper yellows over time.


texts: What do the numbers in the preferred IUPAC name for ascorbic acid mean?

texts:
If I look up the IUPAC name of ascorbic acid, I find this: (5R)-[(1S)-1,2-Dihydroxyethyl]-3,4-dihydroxyfuran-2(5H)-one.

I am used to numbering of molecules in a way like the 3,4-dihydroxyfuran part in this molecule name. But now what I want to know is: what do the 5R, 1S and 5H parts signify?

For the 5H I came up with this: furan has two double bonds, so the H might signify that this is not the case any more, because if there is an extra H at the fifth position, this would be impossible. This can be seen in the IUPAC name of 2-furanone: 5H-furan-2-one. I don't know though if this assumption is correct, also because in 5H-furan-2-one the 5H is before the furan part and in 3,4-dihydroxyfuran-2(5H)-one it is after (shouldn't it be 2(3,4-dihydroxy-5H)-furanone anyway?)

Fact is that I can't find an explanation for the 5R, nor the 1S (as I see no sulfur). Could anyone explain me these weird molecule numberings?


texts: Why carbonyl groups are strong benzene deactivating group for electrophillic aromatic substitution?

texts:
In carbonyl group there is a resonance avaibility and also due to inductive effect it can also withdraw electron from benzene ring . As, resonance(e- donating chracter) dominates than Inductive effect , it must be a Benzene activating group.
but accorting to  L.G Wade carbony groups are strong benzene deactivating group for Electrophillic Aromatic substitution
Where am I wrong ? Explain.


texts:
All the chemical compounds can be categorized as acids, bases, and neutral compounds.
There are different theories, namely Arrhenius Theory, Brønsted-Lowry Theory, Lewis Theory, which define the acids and bases. Each successive theory becoming more general; Lewis Theory is the most generalized one of the three.
Neutral compounds could be salts, hydrocarbons like ethanol, oxides, and many more. A salt is always a result of a reaction between an acid and base.
The difference between a base and an alkali is that an alkali is a base which are soluble in water. In other words, all alkalies are bases but not all bases are alkalies.
I'm sure like bases there would be many acidic compounds which are not soluble in water. Please correct me if I'm wrong.
Q1:
Is litmus test really a defining criterion for classification of a compound as an acid or base? I believe that to perform litmus test, the compound should be soluble in water, and we have already agreed that not all bases and acids form aqueous solution. It means that litmus test is not a main criterion for the classification. It is something of secondary importance. Do I make sense?
Q2:
Likewise, general properties given in school chemistry books are also not primary criteria. Stated differently, an acid doesn't always need to taste sour, turn litmus red, and a base doesn't have to feel slippery or turn litmus blue. Is what I'm saying correct?
Boron trifluoride is classified an acid. Boron has three electrons in its outer shell and it forms three covalent bonds with three fluorine atoms which give it total sum of six electrons. It's still deficient of two electrons and therefore it can accept an electron pair so it's Lewis acid.


texts: Is work done by a system negative delta G or positive delta G?

texts:
My textbook states that a process is spontaneous and can perform work only when it is moving toward equilibrium. Since the process is spontaneous, wouldn't that mean that the work done is attributed to negative free energy?

Another way of considering it is the question of what should the sign of the amount of work done on objects outside the system (or heat released from the system) should be when the reaction is exothermic or endothermic.


texts: Material Properties Dealing with "Wetting"

texts:
I am designing a rain device, and I am interested in a set of common metrics / standards for determining how something gets "wet".
(1) Is there a "water absorbance" metric for materials (ie will the water be deflected or actually penetrate the surface)
(2) Ability for the material to dry (I know this is measured in time, but is there a standard for the drying conditions)
If you know of any other standards that may be of interest please let me know.


texts: Why are negatively charged ligands behind the neutral ligands in spectrochemical series?

texts: I had doubt that shouldn't negatively charged ligands be better electron pair donors than neutral ligands like $\ce{CO}$ or $\ce{PPh3}$. But its not so. Why?


texts:
Is it possible to make crepe rubber from
combining a synthetic rubber emulsion (Styrene Butadiene Emulsion)
and a strong acid?


texts: Why can't NAD+ undergo single-electron reduction?

texts:
$\ce{FAD}$ can undergo single-electron reduction to form a stable radical, which can then be reduced again to $\ce{FADH2}$. This is supposedly possible due to resonance stability, where the unpaired electron is delocalised amongst the molecule. In $\ce{NAD+}$ however, the free radical formed is very unstable, so it can only undergo hydride-mediated (or two-electron) reduction.
This sounds simple by itself, but the diagram I found (shown below), in my opinion, contradicts this claim.

It seems to me that $\ce{NAD+}$ is just as capable in forming resonance structures as $\ce{FAD}$; the double bonds are adjacent to the unpaired electron and the lone pair on the carbon (in $\ce{NAD+}$) should be in a p-orbital, which also allows it to be delocalised. It is true that $\ce{FAD}$ is larger and has more aromatic rings, which makes it a better candidate to undergo single-electron reduction; however, $\ce{NAD+}$ should ALSO be able to form radicals, albeit not as often. Contrary to that, it is said that the $\ce{NAD}$ radical is very rare or even non-existent.
The source I mainly used (due to lack of others) is this Chemistry LibreTexts site. If anyone can point out the reasoning behind this oddity, I would appreciate it very much.


texts: In the conversion shown below I need to find B . Initially I thought of protecting the carbonyl group using ethylene glycol and then carry out reduction of double bonds using hydrogenation but it is required to be a single reagent and cannot be multi step. What are the other ways in which it can be done?


texts: How to store molecule data using SMILES when building a toy chemistry model

texts:
I'm currently building a toy chemistry model based around Gillespie's algorithm. Starting from a food set of {H,O,N,C} I let my system evolve, I have been storing my molecules as strings in SMILES format.

For instance:

[O] reacts with [H] --> [O] ([H])

[O] ([H]) reacts with [H] --> [O] ([H]) ([H])

Using square brackets I've been able to keep the molecules in my system consistent with their SMILES interpretation.

However this system of storage is only allowing me to construct linear molecules.

How can I create, for instance, a carbon ring, so that it is interpreted in SMILES as only a ring of carbon atoms, without hydrogen atoms?

For instance C1CCCCC1 gives http://www.chemicalize.org/structure/#!mol=C1CCCCC1&source=calculate
How would I generate 6 carbon atoms in a ring without the 12 hydrogen?


texts: If a temperature of a reaction is raised from 300 to 320K, what factor will the reaction rate increase by

texts:
In general, if the temperature of a reaction is raised from 300k to 320k, the reaction rate will increase by how much?

So the first thing I do is try out the Arrhenius equation:

$k=Ae^{\frac{-E_a}{RT}}$

so I ignore the activation energy and A because they will cancel out to get the following:

$k=e^{\frac{-1}{300}}$

$k=e^{\frac{-1}{320}}$

and I divide the two k's to get 1.000208

but that can't be right.

It seems to me that I do not know how to answer this question and would like some assistance

I do not want to know a proof of anything but rather to know how to execute methods in solving this problem.


texts: Calculating Commutator of Differential Angular Momentum

texts:
I have tried for hours to calculate the commutator of angular momentum in the differential form, but I cannot get the correct answer. This is my first experience with actually checking if two operators commutes, so there may be some beginner's misunderstandings that causes the problem.

I know from my textbook the correct answer is:

$$
[\hat{L}_x,\hat{L}_y] = \frac{\hbar}{\mathrm{i}}\hat{L}_z = \frac{\hbar}{\mathrm{i}} \left( x \frac{\partial}{\partial y} - y \frac{\partial}{\partial x} \right)
$$

The angular momenta are defined as

$$
\hat{L}_x = y \frac{\partial}{\partial z} - z \frac{\partial}{\partial y} \\
\hat{L}_y = z \frac{\partial}{\partial x} - x \frac{\partial}{\partial z} \\
\hat{L}_z = x \frac{\partial}{\partial y} - y \frac{\partial}{\partial x}
$$

Sets up the commutator expression, and writes it out:

$$
[\hat{L}_x,\hat{L}_y] = \left[ y \frac{\partial}{\partial z} - z \frac{\partial}{\partial y} , z \frac{\partial}{\partial x} - x \frac{\partial}{\partial z} \right]
$$

From what I assume is a well-known algebraic rule for handling commutators, I get the following:

$$
\left[y \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}, z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial x}   \right] - \left[y \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}, x \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}   \right]
- \left[z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial y}, z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial x}   \right]
+ \left[z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial y}, x \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}   \right]
$$

It was straight forward to find that the two middle terms commute, i.e. they equal zero. Hence, we are left with:

$$
\left[y \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}, z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial x}   \right]
+ \left[z \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial y}, x \frac{\hbar}{\mathrm{i}} \frac{\partial}{\partial z}   \right] \tag{1}
$$

Upon evaluating these terms, I let them act on a function $ \psi $. Looking at the first term:
First I factored the complex fraction out. Then I wrote out the commutator and let each differential fraction act on $ \psi $:

$$
\frac{\hbar}{\mathrm{i}} \left(y \frac{\partial \psi z}{\partial z} \frac{\partial \psi}{\partial x} - yz  \frac{\partial \psi }{\partial x}  \frac{\partial \psi}{\partial z}     \right)
$$

The y in the second term above can be factored out from the differentials, because the differential is not done with respect to y. In the first term, however, the z must be differentiated along with psi by using the product rule. Doing this, and cancelling equal terms of opposite sign, yields:

$$
\frac{\hbar}{\mathrm{i}} y \psi \frac{\partial \psi}{\partial x}
$$

Repeating this calculation for the second term in equation $(1)$ yields

$$
-\frac{\hbar}{\mathrm{i}} x \psi \frac{\partial \psi}{\partial y}
$$

Substituting into $(1)$ yields

$$
[\hat{L}_x,\hat{L}_y] \psi = \frac{\hbar}{\mathrm{i}} \left(  y \frac{\partial \psi}{\partial x} - x \frac{\partial \psi}{\partial y}  \right) \psi
$$

Now, comparing with the correct answer:

i) My signs are opposite of what they should be

ii) More importantly, I have a $ \psi $ in the differentials which should not be there. My question is, "why, and how do I rid my answer of it?".

I hope I have sufficiently showed what I have done. I have checked my notes several times, and I cannot get rid of those extra psi's in my answer.


texts:
$$\ce{2NaIO3 + 5NaHSO3 -> 3NaHSO4 + H2O + I2 + Na2SO4}$$
  $\mathrm{20ml}$ of $\ce{NaIO3}$ solution reacted with excess $\ce{NaHSO3}$ releasing $\ce{I2}$ that can oxidize $\mathrm{20ml}$ of $\mathrm{0.1M}$ hypo. What is the molarity of $\ce{NaIO3}$

The reaction of iodine with hypo is
$$\ce{I2 + 2Na2S2O3 -> 2NaI + Na2S4O6}$$
moles of hypo used is $\mathrm{20\times 10^{-3}\times 0.1=20\times 10^{-4}}$

Therefore moles of $\ce{I2}$ reacted is $\mathrm{10\times 10^{-4}}$

Hence, moles of $\ce{NaIO3}$ reacted is $\mathrm{20\times 10^{-4}}$

Therefore concentration of $\ce{NaIO3}$ is $\mathrm{\frac{20\times 10^{-4}}{20\times 10^{-3}}}=\mathrm{0.1M}$

But answer given is $\mathrm{0.02M}$


texts: Here it says that the hydrocarbon tail is non-polar. I understand that the $\ce{H}$ on top of the $\ce{C}$ and on the bottom have dipoles that cancel, but at the very end, with the $\ce{CH3}$ group, there is no opposing vector to cancel with that dipole. Why then is the hydrocarbon tail still non-polar?


texts: Is Km the concentration needed to keep the enzyme running at max speed?

texts:
$K_m$ is the Michaelis constant, which is the concentration of substrate needed to achieve a rate of $\frac{V_{max}}{2}$. $V_{max}$ is the maximum number of molecules that can be reacted per second.

My lecturer has said that $K_m$ is the lowest concentration of substrate needed to ensure that the system runs at $V_{max}$.
I do not understand why. To me, I would have assumed that it would need to be at a concentration that would produce $V_{max}$ or something close to it.
I can understand that at a concentration that is too low, then the enzyme will make quick work of the backlog. However, I cannot see why exactly Km should be the point at which this happens. It all feels quite arbitrary to me.
Could someone explain, preferably intuitively, why this is true?


texts: 1-Methyl-4-nitrobenzene proton NMR spectrum confusion

texts:
I wanted to analyse and suggest the peaks for the NMR spectrum and ran into a problem.

I knew that the methyl $\ce{CH3}$ produces a singlet peak with integration $3$ but when I ran into the benzene protons, I thought that the two equivalent protons (one on each side) would split into a doublet (considering if coupling occurs through 3 bonds or fewer only).

So this was my solution to the problem:

s, $\ce{3H}$, integrated $3$, ppm $2.0$ due to $\ce{CH3}$ group.
d, $\ce{3H}$, integrated $2$, ppm $7.2$ due to $\ce{H}$ on benzene furthest from $\ce{NO2}$.
d, $\ce{3H}$, integrated $2$, ppm $7.9$ due to $\ce{H}$ on benzene closest to $\ce{NO2}$.

However, the spectrum answer given by the mark scheme was as such:

Where have I made a mistake?


texts: Cadmium Selenide, Cadmium Sulfide, Cinnabar and Lead Oxide toxicity

texts:
I have a question about the toxicity of the pigments Cadmium Selenide (Cadmium Red), Cadmium Sulfide (Cadmium Yellow), Mercury Sulfide (Cinnabar or Vermillion) and Lead Oxide (Lead White).

Not long ago the EU banned lead-white pigments from use, even for art. It is now generally impossible to get hold of lead-white oil paint on the internet. However, the cadmium pigments were spared a ban recently. And it is quite easy to find Cinnabar and Vermillion oil paint online even of European production. For example, the dutch company Royal Talens supplies Vermillion paint online, without even warning that it contains mercury: https://www.royaltalens.com/en/catalog/rembrandt-oil-colour/oil-colour-paint-vermillion-311-40ml-tube/

I am not a chemist but my limited knowledge tells me that mercury is a lot more poisonous than lead. How come Cinnabar wasn't banned and what is the relative toxicity of the four pigments I listed, given that they are suspended in oil?

Thank you very much.


texts: How to estimate the enrichment of U-234 from the enrichment of U-235?

texts:
Fresh nuclear fuel made from naturally occurring uranium (i.e. neither MOX nor ERU fuel) is mainly characterised by the enrichment of $\ce{^235U}$. The mass and activity concentrations of $\ce{^235U}$ and $\ce{^238U}$ can be directly calculated from the given level of enrichment. If necessary, the mass and activity concentrations of relevant decay products can also be calculated easily.

However, the gas diffusion or gas centrifuge processes for $\ce{^235U}$ enrichment do not only lead to an increase in the $\ce{^235U}$ concentration in the fuel, but also to a more than proportional increase in the $\ce{^234U}$ concentration. This can be seen from the following table where the mass concentrations of uranium isotopes in natural uranium and typical fresh nuclear fuel (with $3.5\ \%\ \ce{^235U}$) are compared.

$$
\textbf{Mass concentration of uranium isotopes (in g/kg HM) in fresh nuclear fuel} \\
\begin{array}{lll}
\hline
 & \text{Natural U} & 3.5\ \%\ \ce{^235U} \\
\hline
\ce{^234U} & \hphantom{00}0.06 & \hphantom{00}0.4 \\
\ce{^235U} & \hphantom{00}7.2 & \hphantom{0}35.0 \\
\ce{^238U} & 992.8 & 965.0 \\
\hline
\end{array}$$

The corresponding activity concentrations are shown in the second table.

$$
\textbf{Activity concentration of uranium isotopes (in MBq/kg HM) in fresh nuclear fuel} \\
\begin{array}{lll}
\hline
 & \text{Natural U} & 3.5\ \%\ \ce{^235U} \\
\hline
\ce{^234U} & 13 & 93 \\
\ce{^235U} & \hphantom{0}0.58 & \hphantom{0}2.8 \\
\ce{^238U} & 13 & 12 \\
\hline
\end{array}$$

Is there a simple  and reliable calculation method or model that can be used to estimate the enrichment of $\ce{^234U}$ from a given enrichment level of $\ce{^235U}$?


texts: Calculation of fluorescence quantum yield

texts:
The fluorescence quantum yield of a sample $\Phi$ is defined as the fraction of photons emitted per number of photons absorbed. The quantum yield is often calculated by comparing a sample with a reference substance of known quantum yield $\Phi_\mathrm{r}$ such that
$$
\Phi=\Phi_\mathrm{r}\times\frac{n^2}{n_\mathrm{r}^2}\times\frac{I}{I_\mathrm{r}}\times\frac{A_\mathrm{r}}{A},
$$
where $n$ ($n_\mathrm{r}$) is the refractive index of the sample (reference), $I$ ($I_\mathrm{r}$) is the integrated emission of the sample (reference), and $A$ ($A_\mathrm{r}$) is the absorbance of the sample (reference) at the excitation wavelength (see here or here for details).

It seems odd to use the integrated emission because it is not proportional to the number of photons emitted unless the emission peak is extremely narrow. In particular, the integrated emission is
$$
I=\int_{\lambda_1}^{\lambda_2}\mathrm{d}\lambda\,I_\lambda,
$$
where $I_\lambda$ is the spectral intensity. Because the number of photons for a given energy changes with wavelength ($E=hc/\lambda$) using a quantity that is proportional to the number of photons seems more sensible. In particular,
$$
I_\lambda= n_\lambda \frac{hc}{\lambda},
$$
where $n_\lambda$ is the photon density at wavelength $\lambda$. Consider the quantity
$$
N=\int_{\lambda_1}^{\lambda_2}\mathrm{d}\lambda\, \frac{I_\lambda \lambda}{hc}.
$$
It is directly proportional to the number of photons even if the emission peak is broad. Why is $I$ used instead of $N$?


texts: Acidic conditions, high heat, and return to carboxylic acids

texts: Apparently carboxylic acid derivatives such as cyanohydrins can be taken back to "daddy" - a carboxylic acid - under the right conditions. This involves acid, water, and "high heat." What, however, is the mechanism of a cyanohydrin going back to daddy?


texts: Is there a drug that can encapsulate benzene in the liver?

texts:
I'm doing a project on the prevention of leukemia and upon researching on the metabolism of benzene in the liver (since high levels of benzene can lead to leukemia), I thought of a question that was puzzling to me:

Is there a drug that can encapsulate benzene in the liver until the benzene is released through urination or defecation(pooping)?

Thanks


texts: Can entropy increase during bond formation?

texts: Recently the question was asked, "Is bond formation “strictly” exothermic?"  As a corollary to that question, what is the relationship between entropy and bond formation?  Does the entropy of the bond formation reaction always decrease when a chemical bond is formed?


texts: Laws of electrolysis and quantisation of charge relation

texts:
The quantisation of charge was first suggested by the experimental laws of electrolysis discovered by Faraday

I think about it a lot but could not find any relation, as the number of electrons involved is too large in electrolysis that the charge can be assumed to be continuous and discrete nature is negligible.

How did Faraday first suggested quantisation by this non microscopic process (electrolysis)?


texts: Energy of electrons in the same subshell

texts:
So I have this quote from wikia (it's similar to my lecture pdf file) but I don't fully understand the statement

  Although it is commonly stated that all the electrons in a shell have the same energy, this is an approximation. However, the electrons in one subshell do have exactly the same level of energy,[6] with later subshells having more energy per electron than earlier ones. This effect is great enough that the energy ranges associated with shells can overlap

In this statement, does it mean for example:

1) "Each" electron in the subshell 1s and "each" electron in subshell 2s have the same amount of kinetic energy.

Or

2) It means :"All electrons 1s have the amount of Kinetic Energy & All electrons 2s have the same amount of Kinetic Energy. However each electron in 1s doesn't have the same amount of Kinetic Energy compared to one electron in 2s" ?


texts: Is the index 1 in the substituent name "1-methylethyl" a redundant index?

texts:
I want to identify the correct IUPAC name for this compound:

I would say this is 2-methyl-5-(methylethyl)-5-(1-methylpropyl)-nonane. However, the solution manual says that it is 2-methyl-5-(1-methylethyl)-5-(1-methylpropyl)-nonane.

I don't understand why the first "1-" index is necessary. It doesn't add any information, as "(2-methylethyl)" would actually be just a propyl.

Am I missing something?


texts: Why is the carboxyl proton in salicylic acid more acidic than the phenol proton?

texts:
I know I'm just wrong about this but I'd appreciate some help seeing why.  It seems to me like the phenol proton in salicylic acid should be more acidic than the carboxyl proton.  When I try to draw resonance structures for the conjugate base, it looks to me like the charge gets distributed over two oxygen atoms and the whole ring (if anyone can tell me what software makes the nice pictures in some answers here I'd take it):

Then when I try to draw the conjugate base when the carboxyl group is deprotonated, as far as I can tell only the oxygens take the charge, and trying to distribute over the ring results in invalid resonance structures because you aren't supposed to add formal charges to already charged species.

What am I doing wrong?


texts: Will silicon dioxide react with hydrochloric acid?

texts:
I have the following equation, based on the reaction of $\ce{SiO2}$ with $\ce{HF}:$

$$\ce{SiO2 + HCl -> SiCl4 + 2 H2O}$$

I want to know if this reaction is indeed feasible, what conditions may be needed to induce it, or if it isn't possible why that's the case.


texts:
Since region 1 is closer to the source, I presume it to be the hottest as complete combustion takes place there. Also, this is the part where the gas mixture(responsible for flame) reacts with oxygen first(as soon as valve is open). So, the reaction should take place much quicker and more heat should be released. But in my book, the answer is given as region 2. Where am I wrong?

I know there exists as question similar to this in our community : Bunsen burner and hottest part but the answers don’t answer my question.


texts: Can ionic compounds dissolved in organic solvent conduct electricity?

texts:
Ionic compounds dissolved in water, as an aqueous solution, can conduct electricity.

Can they conduct electricity if they are dissolved in organic solvent?


texts: How energy is released when chemical bond is formed?

texts:
In books it is commonly written that whenever a chemical bond is formed the energy of the molecules/atoms gets lowered and hence energy is released. This is generally explained by diagrams like this

But I'm really unable to understand this process, I accept that before bonding the potential energy of the molecules were more and after bonding the potential is less and hence this difference of energy must be released but how does this lowering of potential energy happens? Let's just take an example of electrostatic situation (and as far as I know its the electric potential energy only that get's lowered and hence some energy gets released), say I have an electron at the origin and a proton at $x=x_1$ and then somehow it is moved to $x=x_2$ like this

   We know from equation of electrostatics that potential energy of proton at $x=x_1$ is $$ U_1 = \frac{1}{4\pi \epsilon_0}~\frac{-e^2}{x_1} \\
\\
\textrm{and at} ~x=x_2 \\
U_2 = \frac{1}{4\pi \epsilon_0}~\frac{-e^2}{x_2}$$
Since, $x_1$ is greater than $x_2$ (from figure) therefore $U_1 \gt U_2$. So, we energy at $x_2$ is less therefore there must be some release of energy, but how? If we let the field to do the work then no energy will be released because our proton gonna get the kinetic energy, if we do the work to move it from $x_1$ to $x_2$ then according the to the laws of physics I will do the negative work and hence energy will transfer from the proton to me. So, how does energy ever get released?

How in chemistry the energy gets released by the formation of bonds? I know that we can say without intricacies that potential energy gets lowered and hence the difference of energy is the energy that we get, but how does this happens? If we have some cation and then we put some anion in the reaction mixture then, of course, cations will get attracted towards the anion and hence will gain kinetic energy and according to me that's the only possible way to lower the potential energy. Is that kinetic energy that we measure as heat and say that the reaction is exothermic?

Any help or clarification will be much appreciated.


texts: Is the salt of a weak acid and a weak base also a weak electrolyte?

texts:
I'm able to find a lot of information on acids and bases, as well as strong-strong, weak-strong, and strong-weak salts. However all the introductory materials on electrolytes just stop there and say "we won't bother to cover weak-weak salts here". I have also heard blunt statements that all salts are strong electrolytes, but never with satisfactory explanation or even some weak-weak examples.
So are there any salts that are weak electrolytes?

My interest in the subject is mainly directed at finding the van 't Hoff factor, for osmotic effects and tonicity.


texts: What is the purpose of balancing a redox half equation using H+ and H2O and electrons?

texts:
Is it possible to say that:

H+ is used due to the provision of an acidic medium?

H2O used as it is an aqueous medium and products have oxygen, so logically oxygen must come from H2O?

Electrons added to conserve charge?


texts: Shape of Weak-Strong Acid-Base Titration

texts:
I can understand why in any titration, the pH changes really quickly near the equivalent point.

However, in a titration of either weak base-strong acid or weak acid-strong base, the weak acid/base first has a steep rate of change in pH in the beginning, then slows down at the midpoint, then becomes steep again closer to the equivalence point. Why is this the case? (See picture below). Also, it seems that the weaker the acid/base, the more pronounced the initial quick rate of change.
Also, why is the "midpoint" (not the equivalence point) so special anyways?
You can refer to this picture. The steep drop portion is from 0-10 mL.


texts: Coupling patter for a methyl-butyl ether

texts: What would the high resolution H-NMR spectroscopy coupling pattern look like for the hydrogen attached to the carbon the arrow is pointing at? I am confused because there is a CH2 connected to either side of the carbon, but the hydrogens on each carbon are in different chemical environments since the one on the left is next to the oxygen in the ketone, so would it coupling pattern be a doublet of doublets? or just a doublet?


texts: Can the presence of radon (Rn-222) be determined by testing dust?

texts: If a relatively unventilated area, like a basement, were to be exposed to radon gas (Rn-222), would the dust in the area possess a detectable amount of lead? Considering lead 214 is a decay product of radon 222, will a room exposed to radon gas possess dust with a detectable and differentiable amount of lead relative to a room that is unexposed?


texts:
I have a mixture with 1 part of gas A, and 7 parts gas B. This ratio is in terms of mass.

Gas   Molar Mass (kg/mol)
A     0.17034
B     0.034

I'm trying to find the specific gas constant of the mixture.

$$
R_{\text{sp}} = \frac{R}{M}
$$

I thought it might be
$$
M = 0.17034\frac{1}{8} + 0.034\frac{7}{8}
$$
but I can't work out if that makes sense given the units, or whether I should be using atomic mass or something.


texts:
I am a little bit confused about what an isobar is. Its online definition is that it's an element with the same number of neutrons but a different number of protons from an element $\ce{X}$.

To me, it doesn't make sense from the get-go, because once you change the number of protons the element changes as well so why exactly is it defined as the same element $\ce{X}$ with the same number of neutrons and a different number of protons.
Definition of an isotope: An isotope is an element $\ce{X}$ with the same number of protons and a different number of neutrons.

So to the actual question now. Isn't an isobar just an isotope? Here is an example to clarify what I mean.
If we take for example carbon $\ce{^12C(p:6, n:6)}$ and turn it into an isotope it will be $\ce{^13C(p:6, n:7)}$, and that makes sense, but if we turn it into an isobar it would be $\ce{^13C(p:7, n:6)}$, which doesn't make sense, because it looks exactly like an isotope of nitrogen $\ce{^13N(p:7, n:6)}$.

If the atomic number changes than the element changes as well. So isn't an isobar just an isotope of the following element with a smaller neutron number?


texts: Why the bond length of $\ce{I-I}$ bond in $\ce{I3-}$ greater than $\ce{I3+}$ . Is that because the former has more p character than s


texts: Chemical reactions as exponential functions

texts:
Are all graphs of molar concentration vs. time, for the reactants, exponential decay functions? (Until equilibrium is reached, if it goes to equilibrium at all.)

If so, intuitively, why is that the case?

EDIT: @ShankRam has brought it to my attention that zero-order reactions do not entail exponential decay functions. However, I would still like to know if first-order and second-order reactions do, and why they do.


texts: What is resonance, and are resonance structures real?

texts: My teacher told me about resonance and explained it as different structures which are flipping back and forth and that we only observe a sort of average structure. How does this work? Why do the different structures not exist on their own?


texts: The standard state for a gas is defined at 1 bar of ideal gas.  Why isn't there a corresponding standard state temperature?


texts: Probability density of a particle in a 2D box with given coordinates

texts:
Wavefunction of particle in a $2$D box with sides $L$ in the $x$ and $y$-axis:
  $$φ = \sqrt{\frac {4}{L^2}} \sin\frac{n_1πx}{L}\sin\frac{n_2πy}{L}$$

  For the different states ($n_1=1$, $n_2=2$), ($n_1=2$, $n_2=2$) and ($n_1=1$, $n_2=3$), which has the highest probability density at the coordinate ($0.25L$, $0.25L$)

I know that the probability density is the integral of $φ^2$ but I don't know the interval for the integral. I would assume that it is $0<x<L$ but when I do this I get something completely different from the given answers. The given answers are:

  For ($n_1=2$, $n_2=2$) $=>$ the value of the wavefunction is $\frac{4}{L^2}$

  For ($n_1=1$, $n_2=2$) $=>$ the value of the wavefunction is $\frac{2}{L^2}$

  For ($n_1=1$, $n_2=3$) $=>$ the value of the wavefunction is $\frac{1}{L^2}$

  The dimension of the probability density must be $\frac{1}{length^2}$, so ($n_1=2$, $n_2=2$) is the correct answer.

I don't understand how they have gotten this and why ($n_1=2$, $n_2=2$) is the correct answer. Could someone please explain this to me. Thank you!


texts: What are some materials that expand a lot proportionally to heat?

texts:
There's never any source on the internet that can simply give me a list of materials that have the kinds of properties I'm looking for. I'm wondering what materials, like for a solid block of something, in general expand either a lot or at least very quickly when exposed to heat. I also can't remember what property this is exactly, but I think it's the coefficient of thermal expansion.

Am I looking for something with a high coefficient or low coefficient to achieve this?


texts: I am trying to name the molecule pictured below. I thought it would be 5-bromo-4-isopropyl-2-methylhex-2-ene, but googling that name does not show any results, which makes me think it is not right. Can anyone suggest what I might be doing wrong?


texts: Using significant figures when measuring with an instrument with marks other than powers of ten

texts:
If an instrument does have markings that are powers of ten, then finding the precision of the instrument is easy. For example, if a graduated cylinder had markings for every $\pu{0.1 mL}$, or every $\pu{mL}$, or every $\pu{L}$, then it is easy to tell that those measurements will be to the hundredth mL, to the tenth of a $\pu{mL}$, and to the tenth of a $\pu{L}$, respectively. These would be valid measurements with the correct number of significant figures.
See this image, for example:

These markings are to the tenths and ones. This is simple.
However, what if that graduated cylinder went up by something like $\pu{5 mL}$? Would its precision be to the tens or to the ones (in other words, will the measurements be to the $\pu{0.1 mL}$ or to the $\pu{1 mL}$)? What would be the valid measurement?


texts: How to show/represent an ionic bond visually?

texts:
How to represent/ show an ionic bond visually?
For example in NaCl


texts: How to extract pure potassium carbonate from ash?

texts:
In our village, lots of ash is produced which is thrown off. I want to extract pure potassium carbonate from that ash. I am able to extract the potassium compound and a soluble compound by recrystallizing and evaporating but I found impurities. The first test I performed is electrolysis. This test confirmed the presence of chlorine gas which is able to change the litmus paper to white. The second test I performed is flame test. During the flame test, I got a yellowish orange color while my expectation was bluish violet. So, I assume there is sodium. How can I extract the pure compound?
To conclude, there is a small amount of potassium chloride, sodium chloride, sodium carbonate which are the impurities.


texts: Balancing a redox equation with only one product

texts:
Is it possible to balance this equation using the half reaction method?

$$\ce{Au + Cl2 + HCl⟶HAuCl4}$$

I know that the equation balanced would be:
$$\ce{2Au + 3Cl2 + 2HCl⟶2HAuCl4}$$

However, how would the half reactions end up?


texts:
In deriving the expression for $K_\mathrm w$, we often start with the equilibrium equation of water
$$\ce{H2O <=> H+ + OH-}$$

The $ \rm K_c$ expression is quoted as $$K_\mathrm c = \frac{[\ce{H+}][\ce{OH-}]}{[\ce{H2O}]} $$ followed on by multiplying the $[\ce{H2O}]$ by $K_\mathrm c$.

The problem I face is I have been taught that the pure liquids aren't included in the expression of $K_\mathrm c$ since they have a concentration of 1. So why are we including in the above example?


texts: Measuring the colloidal nanoparticles stability by dynamic light scattering

texts:
In this article the ligand exchange reaction is done for thiol coating of gold nanoparticles.In the first step dicholoromethane (DCM) is used as a extraction solvent to remove CTAC(Cetyl trimethylammonium chloride) from the gold nanoparticle's surface.CTAC acts as a stabilizer for gold nanoparticles.However,only incomplete CTAC removal occurs to ensure that there is still enough CTAC present to maintain colloidal stability.The optimum of solvent extraction is determined by dynamic light scattering.
My question is "How can be measured the the optimum solvent extraction by dynamic light scattering?"


texts: Why is the E2 protein important for protein degradation?

texts:
In the ubiquitination process, the E2 protein transfers ubiquitin from E1 to E3. Why can't E1 work with E3 directly to tag some protein with ubiquitin? Going further, why can't one of the E(1-3) proteins just do it all by itself?

E1: ubiquitin-activating enzyme

E2: ubiquitin-conjugating enzyme

E3: ubiquitin-protein ligase


texts: How do we get the wave function of Ligand Group Orbitals with the same symmetry as that of the corresponding metal orbitals

texts:
In the book Principles of Structure and Reactivity by Huheey, Chapter 14, the author has taken linear combination of ligand orbitals to form ligand group orbitals and then further combination of LGOs(Ligand Group Orbital) with corresponding orbital of metal which has the same symmetry as that of the LGO.

I do not understand how they calculated the wave function for the Ligand Group Orbitals.


texts: Calculate quantity of ions eliminated by acids

texts:
I have limescale $(\ce{CaCO3})$ and a solution of hydrochloric acid at 30% concentration of hydrogen chloride $(\ce{HCl}).$
This acid-base equation
$$\ce{HCl + H2O -> H3O^+ + Cl^-}$$
with the following data:
$m_\mathrm{solution} = \pu{1180 g},$ $m_\ce{HCl} = \pu{354 g},$ $M_\ce{HCl} = \pu{36.5 g mol-1},$ $n_\ce{HCl} = \pu{9.70 mol}.$
But now I need to calculate how much of $ \ce{CO3^{2-}} $ is eliminated by the $\ce{H3O^+}.$ I've written the molar concentration of $\ce{H3O^+}$ which is $\pu{9.70 mol L-1}$ and I calculated the $\mathrm{pH}$ of the solution:
$$\mathrm{pH} = -\log_{10}9.70 = 0.986$$
But I have no idea how to go from there.


texts: What is the explanation of the energy gap law in radiationless transitions?

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The rate of radiationless transitions such as internal conversion and intersystem crossing decrease with the size of the energy gap between the states, according to

$$k\propto \exp\left(\frac{-\gamma\Delta E}{\hbar\omega_M}\right)$$

The papers by Jortner[1] that I have found which derive this expression involve taking steepest descent integrals of the flux autocorrelation function, but this is not a very intuitive explanation. (And in particular is not suitable for undergraduate chemists.)

How can this expression be understood qualitatively from the perspective of the sum over Franck-Condon factors:

$$k_{sl} = \sum_j \frac{2\pi}{\hbar} |V_{s0,lj}|^2\delta(E_{s0}-E_{lj})$$

References:

Jortner, J. Radiationless transitions. Pure Appl. Chem. 1971, 27 (3), 389–420. Section IX, weak coupling. DOI: 10.1351/pac197127030389. Mirror: pdf via publications.iupac.org, pdf via the Internet Archive


texts: Is the Ebullioscopic constant temperature-dependent?

texts:
In tables, the ebullioscopic constant is usually written as a single value.

But, when the value is not available, it can be calculated by applying the formula: $$K_{\mathrm b} = RT_{\mathrm b}^2/\Delta h_\text{vap}$$

I was wondering: since in this last definition the ebullioscopic constant does depend on temperature, being the value of $\Delta h_\text{vap}$ temperature-dependent (its value is different if calculated at room temperature or at the boiling point @1 atm) what is, in real life, the best approximation of the behaviour of $K_b$?

In other words, does it behave like a constant or its value changes at two different temperatures? (eg: boiling point elevation for a solution @atmospheric pressure vs boiling point elevation for the same solution @reduced pressure)


texts: In elementary school, there was an experiment  to show that water has dissolved air, which involved boiling some water and observing the drops at the surface of the container,  and this proved that water has air. Now, in senior high school, I was thinking about the same,  and I think this conclusion is wrong. Aren't the drops formed by the conversion of liquid water to steam due to evaporation? Or is it really the dissolved air that is escaping? What are your thoughts?


texts: Relative reactivity of alkyl and aryl halides in nucleophilic-substitution reactions

texts:
In case of alkyl halides, the order for relative rates of reactions is $\ce{RI > RBr > RCl}$.
The reason is clear that $\ce{I-}$ is a better lg because of negative charge stabilisation and also $\ce{C-I}$ bond is weaker than $\ce{C-Br}$ bond which in turn is weaker than $\ce{C-Cl}$ because of overlap of orbitals.
But why is it the reverse order in case of aryl halides, $\ce{ArF > ArCl > ArBr > ArI}$?
Why is it so even though $\ce{C-F}$ bond strength is higher and $\ce{F}$ is also not able to stabilise negative charge?


texts: Trouble with Converting from Structural Formulas into Newman Projections

texts:
I have the following question from my Organic Chemistry textbook:

I'm asked to convert the following line diagram into a Newman Projection.

The arrow pointing to the carbon signifies "looking down the carbon".

My logic was the following:

At the carbon that is being pointed at by the arrow, there are 3 bonds to other carbons, all of which are in the same plane due to the absence of any 'dashed lines' or 'solid wedges' that would indicate otherwise.

I then concluded that the geometry of that carbon is trigonal planar and that it has a lone pair, since all the bonds to other carbons are in the same plane.

However, drawing a Newman Projection for an atom with trigonal planar geometry proves to be impossible.

I'm not sure how to go about converting this line diagram into a Newman projection.

How can I do so?

Thank you.


texts: which starting material on heating with concentrated sulfuric acid generate cyclic ester

texts: I have just learned esterification of normal reactions with aliphatic compounds, but this one is a cyclic compound. Is it different? There are both a hydroxyl group and a carboxyl group in choice B and D, but why the correct answer is B, not D?


texts: Potential energy curve for dissociation of cation of carbon dioxide

texts: Can anyone suggest me some literature where I can find the potential energy curve or the electronic states for singly ionized $\ce{CO2}$ ($\ce{CO2+}$) dissociating into singly charged oxygen ($\ce{O+}$) and carbon monoxide ($\ce{CO}$).


texts: HDEHP and complexes formed in extraction

texts:
I did an solvent extraction of $\ce{Eu(III)}$ using $\ce{HDEHP}$ from nitric and hydrochloric acid solutions to determine which acid, and which concentration, will yield the highest distribution coefficient.

My results were interesting, I got that the hydrochloric acid extractions had much lower distribution coefficients, and less dependence on acid concentration (the max distribution coefficient was at 0.3 M).  The nitric acid extractions were far more dependent on acid concentration with the global max at 0.01 M and another local max at 0.6 M, as well as being higher in general than the $\ce{HCl}$ distribution coefficients.

I did a literature review, and based on this paper, I think I know the structure of the $\ce{HDEPE/Eu}$ complex.  My original complexes were $\ce{EuCl3}$ and $\ce{Eu(NO3)3}$ dissolved in the acid solution, and extracted with 0.8 M HDEHP in dodecane.  I know the melting point of solid $\ce{EuCl3}$ is about $\sim\pu{600°C}$ which is far higher than $\ce{Eu(NO3)3}$ ($\sim\pu{85°C}$) so I'm wondering if the stronger bonds in the $\ce{EuCl3}$ complex are preventing the $\ce{HDEHP}$ complex from forming, or if the conjugate bases are somehow participating in the complex formation between $\ce{HDEHP}$ and $\ce{Eu(III)}$.

Does anyone have any insight into my results?