texts:
I need to dilute a face cream with 10 % active ingredient to 2.5 % and 5 % but I am confused as to how. I looked into the $$c_1V_1=c_2V_2$$ and $$\text{concentration of a solution}=(\text{amount of solute}/\text{amount of solvent})\times100$$ but not sure which would work.

Would I have to make a standard solution first and place 10 g of the cream into 100 ml of water?


texts:
$\ce C$ is a good reducing agent and hence it can remove oxygen from $\ce{CaO}$. But instead of forming $\ce{Ca}$ and $\ce{CO}$, the products are $\ce{CaC2}$ and $\ce{CO}$.
Why does this happen?


texts:
What will be the reaction for producing benzene from toluene?

My attempt:

Toluene→Benzoic acid→Sodium benzoate→Benzene(decarboxylation) ...

Is there any other ways, like a direct reaction?


texts: Boiling point elevation and liquid solutions

texts:
$\pu{1 L}$ of an aqueous solution of urea having density $\pu{1.06 g mL-1}$ is found to have elevation in boiling point $\Delta T_\mathrm{b} = \pu{0.5 °C}.$ If the temperature of this solution is increased to $\pu{101.5 °C},$ then calculate the amount of water which must have vaporized by doing so. Ebullioscopic constant of water is $K_\mathrm{b} = \pu{0.5 K kg mol-1}.$

I tried solving this question using the Clausius-Clapeyron equation and the basic ideal gas equation. I calculated the change in the number of (gaseous) moles of water that would occur by raising the solution's temperature to $\pu{101.5 °C},$ and then multiplied it by its molar mass, hoping to get the mass of water thus evaporated.

Am I doing something incorrectly? My answer does not seem to match the answer given in my book at all. If yes, please help me out here.


texts:
While I was doing experiments in my school days, they gave me different substances with the combination of base and acid radicals, for example ammonium nitrate and zinc chloride and they seldom called it a salt.

But actually a salt is a NaCl as far as I know.

So My Question is: Actually, what is called a salt?
Why do they call the acid and basic radical a salt?


texts: Why does the electrolyte used in Lechlanché cell turn blue?

texts: In my school there are jars which are turned into Lechlanché cells. Basically the cell has aqueous ammonium chloride solution as the electrolyte which is obviously transparent in the beginning. The electrodes used are zinc and the second electrode is a porous pot which has a carbon rod and crushed manganese(IV) Oxide. The electrolytes in cells which have been used for a long time have turned blue. I want to know where this colour is coming from. Because ammonium salts are colourless, zinc complexes cannot show colour due to d-d transition and I have never seen a blue coloured manganese compound. So what is it that is forming due to which the solution is turning blue?


texts:
$\ce{H2C=C=O}$ what is the group of the  molecule? How to characterize it and how  is this dissimilar to ketone?

If we add $\ce{O2}$ with it then will we get $\ce{CO2}$?


texts: Does the relationship equation between standard cell potential and equilibrium constant violate potential's intensive properties?

texts:
The equation:

$$E^{。}_{cell}= \frac{RT}{nF}\ln K_{eq}$$

We all know cell potential is intensive, not affected by the amount, Because: $volt=\frac{joule}{coulomb}$. Both joule and coulomb will be doubled altogether.

But as seen from the equation, cell potential is affected by the number of electrons transferred.


texts: offset in measuring decomposition potentials

texts:
as far as I've understood to measure the decomposition potential of an electrolyte using a galvanic cell we just put two electrodes, connect them to a battery, and vary the external potential till when we observe a current. The potential at which the current starts to grow linearly is the decomposition potential of the electrolyte. There is not appreciable current before the decompositon potential because the electrodes are supposed to be inert and do not provide the ionic charges needed to "close the circuit". Is it right?
An other question. How the role of the electrodes is taken into consideration in the experimental setup? Is it considered an offset due to an eventual nonzero cell potential? I made this question because I'd like to be sure that I'm understanding the experimental setup.

Tirrel


texts: Which complexes are stable: ammine complexes or carbonyl complexes?

texts:
According to Wikipedia,

A spectrochemical series is a list of ligands ordered on ligand
strength and a list of metal ions based on oxidation number, group and
its identity.
$$\ce{I- < Br- < SCN- < Cl- < S^2- < F- < OH- < C2O4^2- < H2O < NCS- < edta^4- < NH3 < en < CN- < CO}$$
Ligands arranged on the left end of this spectrochemical series are generally regarded as weaker ligands and cannot cause forcible pairing of electrons within 3d level and thus form outer orbital octahedral complexes. On the other hand ligands lying at the right end are stronger ligands and form inner orbital octahedral complexes after forcible pairing of electrons within 3d level.

According to above passage $\ce{CO}$ is a stronger ligand than $\ce{NH3}$. So, carbonyl complexes are more stable than ammine complexes.
Now, there are many other factors which determine the stability of complex:

Nature of central metal atom
Nature of ligand
Crystal field effects

Nature of ligand has further classification:

Basic character of ligands
Charge on ligands
Chelate effects

Classification source: see here and here
Basic character of ligands states that the more basic a ligand is, the greater the ease of ligation with the central metal atom is and the more stable the complex is. Now, $\ce{NH3}$ is more or less a basic compound and $\ce{CO}$ is a neutral molecule.
So, according to above assumption, $\ce{NH3}$ is a stronger ligand than $\ce{CO}$. So, ammine complexes are more stable than complex complexes.
So, which one is the stronger ligand: $\ce{CO}$ or $\ce{NH3}$? or which complexes are stable: ammine complexes or carbonyl complexes?


texts: Question based on finding impurity of a sample of Sodium bicarbonate

texts:
12.5g of commercial  sodium bicarbonate gives 3 g of carbon dioxide. What is the percentage in purity in the sample?
$$\ce{2NaHCO_3 -> Na_2CO_3 + CO_2 + H_2O}$$
I have solved this question, but I just need my solution verified, as it’s not given. I have solved it as follows

Molar mass of sodium bicarbonate=84

Molar mass of carbon dioxide=44

expected yield of carbon dioxide=3.27g, obtained using stoichiometric calculations.

But obtained product=3g

%yield =$\frac{obtained product}{expected product}.100$

Therefore %yield =91.74%

The answer given is 8(I don’t know how that’s possible), so I would appreciate if someone would let me know if my solution was right. Thanks!


texts:
When mixing two fluids of different composition at constant pressure when no heat can escape, is the enthalpy additive?

If not, how to compute the enthalpy of the mixture resulting from mixing two fluids with given composition after equilibrium is re-established?


texts: Carbonate + acid reactions - How to recognize these type of reactions?

texts:
So I've got $$\ce{CaCO_3 + HCl \rightarrow CO_2 + H_2 O + CaCl_2}$$

I'm wondering how I can recognize these types of reactions? I know that when I mix an acid and a base I get salt and water but in this reaction there is also some $\ce{CO2}$ which is confusing me. When can I expect this type of salt base reaction and should I expect more like these with other by products other than $\ce{CO2}$?


texts:
What does it mean when a substance (powder) is 'dissolved in DMSO and used at $\mathrm{5~\%}$'

Does is mean that the substance is first dissolved in DMSO and then added to another solution where it makes up $\mathrm{5~\%}$ of that total solution?
Or does it mean something else?


texts: Does evaporation reverse salt hydrolysis?

texts:
It has been a long time since I studied organic chemistry, but one thing I do remember is that when we needed cyanide salts we were told not to bother keeping any remaining solution because the salts hydrolyze very quickly.

But can't hydrolyzed salts be fully recovered by simply evaporating the water?

E.g., we don't worry about evaporating NaCl from a distilled water solution and finding anything other than NaCl.  So I'm wondering if the lab instructions to neutralize and dispose of cyanide salt solution was just based on expediency.  Or: can something unsafe happen during the evaporation of a hydrolyzed salt solution?


texts: Why does the equilibrium law work mathematically and what does it really mean

texts:
For example consider:

$$aA + bB \rightarrow pP + nN$$ where $a, b, p$ and $n$ are moles.

The equilibrium constant is $$ \frac{[P]^p [N]^n }{[A]^a [B]^b}$$ Where does this come from? I don't understand why anyone would multiply the concentrations of the products together and then divide it by the product of the reactants together. There doesn't seem to be anything in my prior experience to justify that. And why are the exponents the number of moles? What is the physical meaning of an equilibrium constant?


texts: My initial thought was that the stronger acid will act as an acid and the weaker acid as base like the reaction between $\ce{H2SO4}$ and $\ce{HNO3}$ but in this reaction there is a lone pair available for protonation, what if the lone pair was not present , will the reaction still occur? Is the answer dependent on what the acids exactly are?


texts: Filling up a table about a chemical reaction

texts:
I am filling up this table but I'm not sure about what it means in the mass row, amount of substance, molecule quantity.
In mass do I just have to repeat 16 in the second column or do I need to put the mass of a single molecule?
Amount of substance 1 mole of the molecule or 5 moles of each atom?
I'm confused.


texts: Why do liquids freeze into a polycrystal solid when they freeze fast?

texts: I don't see any possible explanation. If there's a crystallite at one orientation, why would a crystallite at another orientation start growing instead of more molecules just building onto the surface that's already there in the same orientation? Does the size of the crystallites vary as the reciprocal of the speed of movement of the boundary between the solid state and the liquid state?


texts: what are some books and research papers that an aspiring theoretical chemist must read?

texts: Can anybody suggest books that must be read by someone who wants to work in the field of theoretical and computational chemistry?


texts: Newer ionic radii data than Shannon's 1976 compilation?

texts:
Shannon, R. D., 1976, Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides: Acta Crystallographica Section A, v. 32, p. 751–767. DOI: 10.1107/S0567739476001551 provides a very detailed list of ionic radii for just about any element, for various oxidation states and coordination numbers.

This paper was published in 1976. Is there a newer compilation with new data?


texts: I have some confusion about perturbation theory, and just how it fits into the hard-hard/soft-soft interactions within organic reactions. I have come across a formula for perturbation that is proportional to an overlap constant squared but is inversely proportional to the energy difference of the orbitals in question. This suggests that for orbitals of poor energy match, there is least perturbation, and vice versa for good orbital energy matching. How does this translate into a hard/hard and soft/soft interpretation? I am not looking for a quantitative answer because my chemistry is not advanced enough!


texts: Clarification about Frost diagram y-axis conventions?

texts:
I was looking at the Frost diagram of Manganese, and on the UC Davis ChemWiki, I see this one:

However, the one straight from my textbook, "Descriptive Inorganic Chemistry" (Overton), looks like this:

In the first image, the y-axis is $\mathbf{nE^o}$ and the x-axis goes from 0 to +7 from left to right, but in the second image, the y-axis is $\mathbf{-nE^o}$ and the x-axis goes from +7 to 0 from left to right.

I'm wondering if reversing the oxidation state ordering changes the y-axis definition between $nE^o$ and $-nE^o$.

It seems like a silly question to me, but I still want to be sure.


texts: What is the correct temperature probe for a wet etch solution?

texts:
What type of probe or probe coating should one use to measure the temperature of a roughly 100c aqueous solution of cupric chloride?

A stainless steel probe seems incorrect. Is a Teflon coated probe sufficient or is something else more appropriate?

Is there a standard way of protecting metal probes in corrosive liquids?


texts:
I dissolved aluminum sulfate in DI water and expected to see just a clear water solution with aluminum sulfate dissolved as ions. However, a precipitate was visible. I addd only 0.6g of Aluminum sulfate so there is no way that the precipitated is saturated aluminum sulfate. Furthermore, it does not seen to be aluminum hydroxide, so then what is the precipitate? Aluminum sulfate has the property of filtering out impurities in water, however, I am using DI water so then what is the precipitate?

Also, the precipitate is not aluminum hydroxide because aluminum hydroxide is dissolvable in sulfuric acid; however, when I added sulfuric acid to the precipitate solution, the precipitate did not disappear.


texts: Steps in mechanism of pyruvate dehydrogenase

texts:
I am having some trouble with certain steps in the mechanism below (from Mike Lu on Proteopedia) detailing the mechanism of action of pyruvate dehydrogenase converting pyruvate to acetyl-CoA. This reaction happens under the physiological conditions present in the human body ($\mathrm{p}H = 7.4, 37^{\circ}C$, 1 atm, various intracellular ionic concentrations: http://www.ld99.com/reference/old/text/2878909-566.html).

In the first step, how does the ylide of TPP form?
Why is the deprotonation of the hydroxyl group to form a ketone in the 6th step favoured, especially given that the $\ce{-OH}$ group normally has a very high $\mathrm{p}K_\mathrm{a}$?


texts: How to calculate the abundances of certain gases from the peak areas, GC-MS

texts:
In an experiment we had a series of air samples which were analysed through GC-MS, before using TargetLynx software to integrate the mass spectrum obtained.

So I now have the specific peak areas for a number of compounds (for example CFC-12 has an area of 28335299.35m^2) and a calibration standard for each specific gas investigated. For example CFC-12 has a mixing ratio (ppt) of 539.894.

With this information how could I determine the actual abundance of CFC-12 from the air sample?

Apologies for any confusion!
Thanks!


texts: How to determine the strongest oxyacid of chlorine without being given the acid dissociation constant data?

texts: I was told to find the strongest and weakest acids out of $\ce{HCl, HClO, HClO2, HClO3}$, and $\ce{HClO4}$. I knew that $\ce{HClO}$ was the weakest but was stuck between $\ce{HCl}$ and $\ce{HClO4}$ for the strongest (as these are both strong acids). Is there a way to find the relative strength of strong acids without being given the $K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{a}$? Or would I just have to have memorized that $\ce{HClO4}$ is generally stronger than $\ce{HCl}$?


texts: Any home made tricks to fill up a baloon that floats?

texts:
These days there are a number of fancy balloons available, some of them are very beautiful. As always, they loose their gas overtime and don't rise anymore.

Some of those new type balloons appear to have been made of plastic and are quite easily re-usable but then you can't be going to the balloon guy every time you want a refill.

Are there any home made techniques that can let you fill those up (so they float again) and which generate a gas which is safe to handle at home without any protective gear?

P.S: This question is not motivated by any urge to save extra money, it's just that I find so many of them lying at home useless when they can be filled up again. Looking for something that's simple to make if possible.


texts: Are we wrong about Bakelite formation mechanism?

texts: In the reaction of phenol with acetyl chloride the oxygen of the phenol attacks the acetyl chloride. In Bakelite formation we know that pi electrons attack the carbonyl carbon of formaldehyde.My question is shouldn't the oxygen atom of phenol attack the formalaldehyde just as in the reaction of phenol with acetyl chloride?


texts: Why does a pickled gherkin glow only at one end when a current is passed through it?

texts:
I recently saw this Periodic Video.

The Professor (Martin Polyakoff) notes that,

The Gherkin normally glows only at one end due to excitation of $\ce{Na+}$ ions.
The end which glows can either be the neutral end or the positive end. It is impossible to predict which one will glow.
During the video, both ends glowed together only for a few seconds.

Even the Professor admitted that probably glowing at one end happens due to pure chance.

  Why should the gherkin glow only at one end? Is there any reason? Normally one would expect it to glow symmetrically around the center, that is, at both ends.

The question has been quite well received. However no one has commented or answered. Does the question need to be re-worded or better explained?

Do let me know in the comments.


texts: How does sodium in ethanol reduce carbonyl compounds?

texts: According to my teacher, Na in ethanol reduces carbonyl compounds (e.g. aldehydes and ketones) to alcohols. However, I can't see where the hydrogen needed for reduction comes from. How does the reduction take place? (or is my teacher wrong?)


texts: Where can I find the total enthalpy and heat of dissolution in water of a given components?

texts:
I don't really have a background in chemistry but I'm actually studying in aerospace engineering, sorry if this question may seem trivial.

I am interested in the decomposition process of the hydrogen peroxide ($\ce{H2O2}$) and I need to find the total enthalpies of $\ce{H2O2}$, $\ce{H2O (l)}$, $\ce{H2O (g)}$ and $\ce{O2 (g)}$ and the heat of dissolution ($\Delta H_{\text{dis}}$)of $\ce{H2O2}$ in water, as a function of the solution concentration of $\ce{H2O2}$.

Firstly, I tried to find the values of the total enthalpies, but I couldn't find them. However, I found a lot of values about the $\Delta H^0$ and $h^o_f$. I can't understand if I can retrieve the value of $H$ with the $\Delta H^0$ and/or $h^o_f$.

Secondly, I can't find a good answer to another question. Does the $H$ is a function of the pressure or not? If so, how can I find the value of $H$ at a given pressure and a given temperature?


texts: How right is defining elements with the number of protons?

texts:
Atomic number is the number of protons a certain atom has. It's the defining attribute of a certain element. But, How right is that?

From the viewpoint of chemistry, the definition is right. Because, for a certain chemical reaction, isotopes of a certain element will react in the same way.

For example, $\ce{H2 + 1/2O2 -> H2O}$
$\ce{ ^2H2 + 1/2O2-> ^2H2O}$

So, it's useful to define elements in terms of their number of protons.

But, other than reactivity in chemical reactions, many properties of an atom differ wildly due to difference of  number of neutrons and electrons eg. half life of radioactive decay, type of radioactive decay, magnetic moment, stability, nuclear quantum states etc. So, even having the same number of protons can't ensure much similarity in some aspects.

I think to a rational perspective, the similarity of reactivity of isotopes in chemical reactions should weigh more than the other nuclear difference between isotopes. So, in that logic, the definition is right.

But, difference in nuclear properties should do matter. So, how right is defining elements with atomic number i.e. number of protons?


texts: What does gases at constant pressure mean?

texts:
My teacher told me that if we keep some weight on a piston containing 2 different gases, both gases will be at constant pressure, and hence the volume occupied by each gas will be proportional to number of moles of each gas according to the ideal gas law ($pV=nRT$)

My doubt is that won't the 2 gases exert different pressures and the sum of the two different pressures will be equal and opposite to the pressure exerted by the weight? Also, if the two gases exert different pressures, then how can we say that both gases are at constant pressure? Do gases at constant pressure exert equal pressure?


texts:
I'm all bent out of shape trying to figure out what Bent's rule means. I have several formulations of it, and the most common formulation is also the hardest to understand.

  Atomic s character concentrates in orbitals directed toward electropositive substituents

Why would this be true? Consider $\ce{H3CF}$.

Both the carbon and the fluorine are roughly $\ce{sp^3}$ hybridized. Given that carbon is more electropositive than fluorine, am I supposed to make the conclusion that because carbon is more electropositive than fluorine, there is a great deal of s-character in the $\ce{C-F}$ bond and most of this s-character is around the carbon?

Or is this a misunderstanding of "orbitals directed toward electropositive substituents"? The fluorine is $\ce{sp^3}$ hybridized and these orbitals are "directed" toward the carbon in that the big lobe of the hybrid orbital is pointing toward the carbon. So does electron density concentrate near the fluorine? Because that would make more sense.

And this s-character concentrated toward the fluorine has the effect of what on the bond angle? I understand that the more s-character a bond has, the bigger the bond angle - consider $\ce{sp}$ vs $\ce{sp^2}$. But since the $\ce{C-F}$ bond now has less s-character around the carbon, the $\ce{H-C-F}$ bond angle can shrink, correct?


texts: Function of water and the need of two barrels in a biogas Generator

texts:
For my chemistry assignment, I have to build a biogas generator. I found the following diagram,

This is the website that the image is from: http://www.motherearthnews.com/renewable-energy/other-renewables/biogas-generator-zm0z14aszrob
(Manure goes through the feeding tube, then anaerobic bacteria produces methane. The methane then goes to the second tub and is collected)

On the right side of the diagram,

why does the barrel need to be immersed in water? Does it do something to the methane?
why does the methane not immediately go from the first tank through the tube out to the burner but instead goes into the second tank?
Once the methane is inside the second tank, what's stopping it from rising and going out?


texts: I am a high school student so please apologise if I say something very dumb or irrelevant. I am conducting an experiment in which I want to find UV index at different points. Such as under shade, inside house, near beach etc. Anything will be greatly appreciated, also even if there is a device thats very expensive please tell me about that as well.


texts: First order differential equation for transmembrane diffusion

texts:
I want to model transmembrane diffusion using a first order reversible differential equation. The diffusion rate is known from literature. There are two volumes $V_{\mathrm{intra}}$ and $V_{\mathrm{extra}}$. The former is $10^{12}$ times smaller than the latter. $c_{\mathrm{intra0}}=0~\mathrm{mol~L^{-1}}$, and $c_{\mathrm{extra0}}=x~\mathrm{mol~L^{-1}}$, with $x>0$.

Thus far I am using this:
$$\frac{\mathrm{d}c_{\mathrm{intra}}}{\mathrm{d}t}=k_{\mathrm{diff}}\cdot c_{\mathrm{extra}} - k_{\mathrm{diff}} \cdot c_{\mathrm{intra}}$$

However, this does not account for the fact, that $V_{\mathrm{extra}}$ is much larger than $V_{\mathrm{intra}}$. I expect $c_{\mathrm{extra}}$ to be virtually constant. So far the the simulation results in the equilibrium being at $c_{\mathrm{extra0}}/2$.

Can someone suggest a method to account for the volume discrepancy?

Edit:

From the outlined scenario above, I expect in REALITY, my $c_{\mathrm{extra}}$ to not noticeably change from its initial value due to the large difference between $V_{\mathrm{intra}}$ and $V_{\mathrm{extra}}$.

However, in the simulation I don't want to set $c_{\mathrm{extra}}$ as constant, because I want to apply a 'extracellular' decay rate later on. Basically, I want to be able to modulate the extracellular concentration over time and see how the concentration within the cell changes.

This is why I want to account for the volume. Maybe, one needs an entirely different approach for that?


texts: Can I use the Henderson–Hasselbalch for calculating the pH of non-buffer systems?

texts:
Can I use the Henderson–Hasselbalch equation on reactions that are not buffers? When I read up on the derivation of the equation, I noticed that there is absolutely no assumption on the relative concentrations of the acid and conjugate base at least for a monoprotic acid.

Here's a quick derivation of the Henderson Hasselbalch equation:
The reaction:

$$\ce{HA(aq) + H2O(l) <=> A-(aq) + H3O+(aq)}$$

$$K_\mathrm{a} = \frac{[\ce{A-}][\ce{H3O+}]}{[\ce{HA}]}$$

Then I take the logarithm of each side, resulting in

$$\log K_\mathrm{a} = \log\frac{[\ce{A-}][\ce{H3O+}]}{[\ce{HA}]} = \log\frac{[\ce{A-}]}{[\ce{HA}]} + \log [\ce{H3O+}]$$

Consequently,

$$-\mathrm{p}K_\mathrm{a} = -\mathrm{pH} + \log\frac{[\ce{A-}]}{[\ce{HA}]}$$

$$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log\frac{[\ce{A-}]}{[\ce{HA}]}$$


texts: Extracting metallic magnesium from cholorphyll

texts:
My understanding is that when chlorophyll is exposed to an increased concentration of hydrogen ions (or rather the pH is lowered), the magnesium is displaced by a hydrogen ion and chlorophyll is converted to pheophytin.

My question relates to the Mg2+ ion that is released in this process. Is it possible, naturally depending on the acid used to convert the chlorophyll to pheophytin, to isolate the Mg released?

Note my background in chemistry is rather limited. My guess is that the Mg will react to whatever acid (say sulfuric acid) to create a compound like magnesium sulfate which in turn can be processed to extract Mg in metallic form (electrolysis?).

Any clarity would be much appreciated as this has tickled my curiosity for a while now.


texts: Cis/trans Proline vs. Double bond character

texts:
I am learning about proteins and we have learned that the C-N bond is rigid because of it's partial double-bond character. We have also learned that proline is commonly found in beta turns (type 1) because it can isomerize from trans to cis (which helps make the 180 degree turn).

I don't understand how these 2 things fit together--how can it change from trans to cis if it can't rotate around the C-N bond?

I found this which talks about the double bond being broken (in this case, it would be the partial double-bond, I guess) and then reforming...is that what is going on here?


texts: How to explain covalent bonds with Bohr's atom model?

texts: I was reading about covalent bonding and got to know that in this type of bonding, the atoms of elements "share" electrons with each other to have an octet or duplet. But, I also have been taught that electrons keep on revolving around the nucleus of the atom, much like the planets around the sun. But, if this is true, how are the able to easily share electrons if these electrons keep on moving around their respective nuclei? I hope I have made myself clear. If not, then please tell in the comments.


texts:
I've been reading about freeze drying and how it increases the shelf life of certain foods and is overall a good preserving technique.

My question is with regard to the actual process. I understand that freeze-drying involves freezing the actual material and then proceeding to dry it by placing it in a vacuum. This way the ice is turned into vapour without going into any liquid phase. My question is why is avoiding the liquid phase necessary and beneficial? When it comes to vaccines, foods, and polymer storage for example, why is it advantageous? I don't intuitively understand the reasoning behind why lyophilization is so favourable.


texts: Combustion of saturated hydrocarbons vs combustion of unsaturated hydrocarbons

texts:
I read in my science book that saturated hydrocarbons burn with a blue flame (indicates complete combustion) and unsaturated hydrocarbons burn with a yellow flame (indicates incomplete combustion) due to the highier percentage of carbon in unsaturated hydrocarbons as compared to saturated hydrocarbons. So I think the reason why unsaturated hydrocarbons don't burn completely is the presence of double and triple bonds in unsaturated hydrocarbons which are more stronger than single bonds because of which they are difficult to break.  There was a question that :-

Why is a mixture of ethyne and oxygen used for welding?

And the answer was(as written in the book) :

So that ethyne burns completely without producing soot but according to me the issue is not about availability of oxygen.
As I saw in the reactions of combustion, unsaturated hydrocarbons require less oxygen to burn than saturated ones. For example :-
$$\ce{C2H6 + 7/2 O2 = 2CO2 + 3H2O}$$
And
$$\ce{C2H2 + 5/2 O2 = 2 CO2 + H2O}$$
Here we can see that unsaturated hydrocarbons require less oxygen as compared to saturated hydrocarbons.
So my queation is :-

Is the answer given in the book correct. If yes, why?
$$Thank you$$


texts:
I searched for copperas on google and it says ferrous sulphate. My dictionary shows that the word copperas is derived from copper.

I was just wondering what has ferrous sulphate to do with copper


texts: Proton attached to N or O in HNMR spectroscopy

texts: I was wondering why a hydrogen attached to a nitrogen or oxygen is not able to couple with p+ on adjacent carbon atoms and hence why it always appeats as a singlet in HNMR spectroscopy?


texts: Sodium azide to Nitrogen ratio in airbags

texts:
I've been given this question and I don't know how to solve it.

Airbags are designed to protect the occupants of a car during a collision. They use the decomposition of sodium azide, $\ce{NaN3}$. Three chemical reactions occur rapidly after impact and produce nitrogen gas ($\ce{N2}$) to fill the airbag.
The equations summarise the overall process that takes place.

$\ce{2 NaN3 -> 2 Na + 3 N_2}$
$\ce{10 Na + 2 KNO3 -> K2O + 5 Na2O + N2}$
$\ce{K2O + Na2O + 2 SiO2 -> K2O3Si + Na2O3Si}$

What is the ratio between the number of sodium azide ($\ce{NaN3}$) molecules used and the number of nitrogen ($\ce{N2}$) molecules produced in the overall process?

I initially just used the first equation to get a ratio of 2:3, but obviously that's not right. I have no clue where to start. How do you do this? (How this can be considered a Year 10 question baffles me)


texts: Having trouble understanding the iron-carbon phase diagram

texts:
At room temperature, alpha and alpha+$\ce{Fe3C}$ are present (depending on carbon content), which is ferrite and pearlite. In the lab we polished and etched samples of carbon steel to observe the microstructure, and saw both ferrite grains AND pearlite grains. Not unlike the following:

However, from my understanding of the phase diagram, only one phase should be present. For any steel with less than 0.02% carbon we should see only ferrite, and for steel with >0.02% carbon we should see only pearlite. Though this was not the case, and rather there was a mix of pearlite and ferrite, with the higher carbon content steel having a higher proportion of pearlite.

It would be much appreciated if someone could explain to me what is happening here. Links to further reading would be helpful but not required.


texts: Doubt's regarding inputting surface reaction for Chemkin Pro

texts:
I want to simulate the reaction of a mixture of ethanol and Hydrogen Peroxide on $\ce{Pt}$ using Chemkin Pro. I want to create a surface input files which will include surface reaction mechanism of Decomposition of $\ce{H2O2}$ on $\ce{Pt}$.
So I have 3-4 different reaction mechanism's for the decomposition of $\ce{H2O2}$ on $\ce{Pt}$ each with its own elementary steps.
I have 2 doubts:

Do I include all possible proposed reaction mechanism's each with
their own elementary steps or only one mechanism which I think is
the best match for fitting?
Also I am having trouble getting kinetic data for the reactions
which containing adsorbed species, I tried finding in various
catalysis databases but couldn't data for reactions I was looking
for.

I tried catalysis-hub and other popular catalysis databases.


texts:
I have been given a formula on the topic of alloys and temperature, however am unsure specifically what this equation calculates. The equation is as follows:

$xC_{1} + (1 - x) C_{2} = C_{3}$

I am assuming that the C's will be given (and possibly represent Specific Heat?) - however exactly what is this equation to represent? What does solving for $x$ achieve?

I know that the letters used may vary, however our teacher has provided no more information due to sickness. I have provided all the information I know.


texts: Why is sulfuric acid used in the Jones oxidation of alcohols?

texts:
When oxidising primary alcohols, $\ce{K2Cr2O7}$ is used because it's a useful & readily available oxidising agent.

Why does the sulfuric acid need to be added?
Does it have to do with the acidity of the resulting dichromate solution? How would this facilitate the oxidation?


texts: How can the Bonding in IF7 be explained using LCAO method?

texts:
I know that the VSEPR theory explains $\ce{IF_7}$ (iodine heptafluoride)'s structure as a pentagonal bi-pyramidal one. The valence bond theory can be used to say that it has $\mathrm{sp^3d^3}$ hybridisation (I think). How can the bonding in it be explained using the LCAO (Linear Combination of atomic orbitals) method in molecular orbital theory?

I got this doubt because there are only two "axial" d-orbitals ($\mathrm{d}_{z^2}$ and $\mathrm{d}_{x^2-y^2}$) among the 5 present, which can have head-on overlap with p-orbitals (non-axial orbitals can only have sideways overlap). In the excited state, the iodine atom has 7 half filled atomic orbitals (an s-orbital, three p-orbitals, and 3 d-orbitals) and according to LCAO each of them has to combine with one p-orbital of each fluorine atom to form molecular orbitals by σ and π bonds. But, the formation of only 6 σ bonds can happen between an iodine and 6 fluorine atoms, as σ bonds involve head-on overlap of orbitals, and there are only 6 orbitals capable of doing that (the s and p orbitals, and the two 'axial' d-orbitals). Therefore, the seventh fluorine atom must be in pπ-dπ bond with fluorine.

This doesn't explain "five equivalent bonds and two bonds of equal length (all σ bonds)" as predicted by VSEPR theory. How many σ bonds does it really have?


texts: Keep two Mica Powders separate in oil and water mixture

texts:
First off, apologies if this isn't the appropriate place to ask this, let me know and I'll remove immediately.

I recently acquired some Mica Powder Pigments, and they are fun the play with.  I mixed some with mineral oil, and some with water.  On there own, that's neat.  However, if I mix the oil and water (with powder suspended), the pigments tend to mix in the oil, reducing the contrast between the oil and water.

Is there some process I can do that will make one of the pigments hydrophobic and the other oleophobic?

Preferably with "household" items, or easily attainable items, in a DIY/hobbyist environment.


texts:
During my organic chemistry lesson, I was told that the reason why alkenes are low in reactivity is that their sigma bonds have very low polarity.
Why is this the case?
Thanks, Dave


texts: Why is entropy change in an irreversible adiabatic process positive?

texts:
I've read this in a book

During irreversible compression, large quantity of heat is produced due to friction, while the decrease in volume is less. Thus, increase in entropy due to rise in temperature exceeds the decrease in entropy due to decrease in volume.

I don't get this at all. Is the friction they're talking about the one between pistion and container? What if we consider an ideal condition with no dissipation?
I also want to know the physical interpretation of increase in entropy in adiabatic (irreversible) process. Shouldn't it be zero? This book tried to explain it but it was confusing and I'd love to get further insight on this.


texts: Computing reaction mechanisms using solvation effects

texts:
I am about to compute reaction steps for a series of compounds using DFT.
A key point in our discussion is the dependency of the experimental rate of reaction w.r.t. solvent used, so it is very important that we incorporate solvation effects in our computational models.

I am aware of the best practices in choosing functionals, dispersion corrections, basis sets, etc..
By reading a little I decided on using the SMD model for implicit solvation.
I may use either ORCA or NWChem.

My questions are:

a. Should geometries be optimised in solvent, in the gas phase or both?
b. In case I use only gas phase geometries, should I calculate frequencies using implicit solvation (I doubt) or can I use the calculated free energy of solvation (done in a single point calculation) to correct the gas phase free energy?
a. In case I decide on using (one or two) explicit solvent molecules to better model the system, are there best practices on using them together with an implicit solvation model (in terms of calculating free energy of solvation and in deciding when it has converged/is adequate)?
b. What about the points addressed in 1. (gas phase versus condensed optimisation and frequency calculations) for this case?

References from literature are greatly appreciated.
I am looking forward to hear from you!


texts: Frost diagram and acidic/basic conditions.

texts: The Frost diagram for sulfur shows the relative stability (in terms of cell potentials) of the possible aqueous oxidation states. What is the reason for the instability of higher oxidation states in the acidic regime and their stability in the basic regime ? Something I have always noticed but never been able to apply chemical intuition to.


texts:
In my book it says that aluminium can react with water as a base when it's in the form $\ce{[Al(OH)2(OH2)4]^+}$.

And this way as an acid: $\ce{[Al(OH2)_6]^3+}$.

So ... does it depend on with which ion it's accompanied by? Let's say, $\ce{AlCl_3}$ will react as an acid?


texts: Equilibrium constant and reaction Quotient

texts:
does reaction quotient After equilibrium has been achieved make any sense?
At equilibrium point rates of forward and backward reaction are same and the system is in dynamic equilibrium.The graph of concentration vs time shows a straight line parallel to x axis after equilibrium point.
Reaction quotient refers to ratio of concentration at any stage.This means that after equilibrium point reaction Quotient value will same as equilibrium constant as no more products are formed.So how can it have a value more than that of K ?!
I have been thinking about this for hours but I get more confused with time.


texts: How to predict the color of a pH indicator using Le Chatelier's principle

texts:
The question I have is above. Could someone explain why the answer is (A)?

What I think so far:

Does the sodium hydroxide turn the indicator blue because it is a strong base and hence it will react completely to form water,
shifting equilibrium really far to the right?
Does the HCl turn the indicator red for a similar reason?
I am unsure of the sodium acetate effect


texts: Why does using NaI as a nucleophile and acetone as solvent lead to an SN2 reaction mechanism instead of SN1? Is I- not considered a weak nucleophile?

texts: In a reaction with a secondary leaving group, why does using $\ce{NaI}$ with acetone as a solvent lead to an $\mathrm{S_N2}$ reaction mechanism instead of $\mathrm{S_N1}$? I thought that halogens were weak nucleophiles, and only really led to $\mathrm{S_N1}$ reactions?


texts: Effect of pressure on gas solubility in liquids

texts:
By Henry's Law ($K=\frac{x}{p}$), we know that increasing the partial pressure of a gas also increases its solubility on liquids.
Now a lot of sources (this, for instance) illustrate this by presenting "the bends", a condition that divers may experience when ascending too quickly due to the rapid decrease of the N$_2$ solubility on the blood.
So, my question is: why is the N$_2$ solubility greater deep on the ocean than on the surface?
Henry's Law says nothing about the total pressure, only about the partial pressure of the gas in question. When deep in the ocean, the pressure rises thanks to the water above, not due to a increase in N$_2$ partial pressure.
Bonus: does this video illustrate a greater CO$_2$ solubility in coke because of the greater total pressure? I feel like this is the same situation. Why would the CO$_2$ partial pressure be greater?


texts: Can classification techniques used for identifying solids be used to identify precipitates?

texts:
I am preparing for an assessed practical experiment where an unknown precipitate must be identified. I know that precipitates are insoluble, and my textbook says they are considered to be solid with reference to the aqueous solution.

I want to test for carbonate, halide, sulfate, and nitrate anions in the precipitate and understand that if it were a normal solid I would be able to test for carbonates by using a nitric acid solution, and test for halides by dissolving in nitric acid and testing with silver nitrate, and test for sulfates by dissolving the unknown solid in nitric acid and adding barium sulfate solution. I also know that I would normally be able to test for nitrates by heating the unknown solid with copper and then treating with H2SO4.

Are these classification techniques applicable to precipates as well?


texts: Is greater relative AA battery capacity at high currents indicative of greater capacity at low currents?

texts:
I originally posted this on EE.SE but might be better here:

Battery showdown compared the mAh and mWh capacity of different AA batteries discharged at 200mA.

Would the relative capacities of each battery type (within the same chemistry type) be the same at much lower current draw, e.g. 1mA? If not, why not? Are there things battery manufacturers do to 'tune' batteries to a certain discharge range?

Furthermore, I've noted that as current goes down alkaline batteries approach lithium batteries in capacity. Is there a current below which alkaline batteries have more than lithium?

Image from battery showdown:


texts: Bridged ring system reduction through Wolf Kisher: Is it possible?

texts: Is it possible for  a ketone like this to undergo the Wolf Kishner mechanism? If so, what would be the product? It seems unlikely to me as disrupting the stable equitorial carbonyl seems unfavorable...


texts: Theory behind Experiment: Extraction and Identification of DNA

texts:
A few days ago, in my chemistry lab class, I performed an experiment aimed at extracting and identifying DNA. The class is mostly practical oriented, so I thought of asking my theoretical doubts on ChemSE.

First of all, let me explain the experiment:

We used onion extract, sodium dodecyl sulfate (SDS) solution, 4% $\ce{NaCl}$ solution, papain extract, ethanol, TE buffer solution, and diphenylamine reagent. I shall ask my questions while explaining the procedure followed-

I took $\pu{10ml}$ of the onion extract in a boiling tube, and added $\pu{1.5 ml}$ of SDS solution to it, following which the mixture was allowed to stand in ice for nearly $\pu{10 minutes}$.
What does onion extract + SDS do? What's the chemical reaction if any? Why is low temperature (ice bath) important?
I added 5-6 drops of papain extract to the mixture, and stirred gently. A quick Google search says Papain, also known as papaya proteinase I, is a cysteine protease enzyme present in papaya. I wonder how it 'reacts' with the mixture prepared in step 1?
Next, I slowly poured nearly $\pu{25ml}$ of ice cold ethanol down the wall of the test-tube, so that ethanol formed a separate layer on top of the mixture. Note that this won't happen if ethanol is poured in rapidly, as that disturbs the mixture at the bottom of the tube. Why so, though? Difference in densities should make sure separate layers are formed, even if so after a long time? What's wrong here?
After allowing the tube to stand straight in a test-tube holder for ten minutes, I noticed some stringy white substance collect in the alcohol layer. We were told that that substance was DNA! How did this happen?
Using a hooked glass rod, I spooled out whatever DNA I could from the top of the test-tube, very carefully. This was used to carry out the following confirmation tests:

Diphenylamine Test:

Some crude DNA was collected in a test-tube, to which $\pu{2ml}$ of 4% sodium chloride solution was added. Next, $\pu{2ml}$ of diphenylamine reagent was added and the mixture was placed in a boiling water bath for an hour. The colour of the mixture changed to pale blue. How does this work? What are the reactions involved? Why the colour change?

UV Absorption:

DNA was dissolved in $\pu{2-3ml}$ of TE buffer solution (why?), and ratio of absorbances was determined at $\pu{260nm}$ and $\pu{280nm}$. Furthermore, our instructor told us that this ratio should be less than 2 (I guess?), for a confirmation. I wonder how that number was determined. (Also, some of my classmates got the ratio slightly greater than 2, due to some error. What error could they possibly have made?)

I'm trying to make sense of what I did practically, with the help of theoretical inputs, and would appreciate any help with the same. No doubt, the experiment was really fun to do!


texts: How can sulfur dioxide and nitric oxide be filtered out from a waste incinerator's smokestacks?

texts:
How can sulphur dioxide and nitric oxide be filtered out from a waste incinerator's smokestacks?
I also want to know what it looks like after it is filtered out.


texts: Balancing reaction between copper and nitric acid given the ratio of formed nitrogen oxides

texts:
Problem

$\ce{Cu}$ reacts with $\ce{HNO3}$ according to the equation
$$\ce{Cu + HNO3 -> Cu(NO3)2 + NO + NO2 + H2O}$$
If $\ce{NO}$ and $\ce{NO2}$ are formed in 2:3 ratio, what is coefficient of $\ce{Cu}$ when equation is balanced with simplest whole numbers?

Answer

 9

Question
I am getting the coefficient of $\ce{Cu}$ as $2,$ which contradicts the answer:
$$\ce{2 Cu + 9 HNO3 + 5 H+ -> 2 Cu(NO3)2 + 2 NO + 3 NO2 + 7 H2O}$$


texts: Reaction of fumaric acid and performic acid

texts: Performic acid ($\ce{CH2O3}$) has strong oxidizing properties. So when it reacts with fumaric acid, is this the product (2,3-dihydroxybutanedioic acid) that I should expect?


texts: How does partial reduction of esters to aldehydes occur?

texts: Wikipedia says that esters can be reduced to aldehydes using DIBAl-H. Can anyone please explain how this reaction occurs?


texts: Molar Conductivities of H+ and OH- V/S other Ionic Electrolytes

texts:
The following table gives the Ionic Molar Conductivities of a few electrolytes in water. What are the reasons for the unusually high values for both H$^+$ and OH$^-$ even though both undergo solvation in water? Why do they retain their mobility in water even after solvation?

\begin{array}{lr}
\text{Electrolyte} & \text{Ionic Molar Conductivity (mS m$^2$ mol$^{-1})$} \\
\hline
\text{H$^+$} & 34.96 \\
\text{Li$^+$} & 3.87\\
\text{Mg$^{+2}$} & 10.60 \\
\text{[N(CH$_3$)$_4$]$^+$} & 4.49 \\
\end{array}

\begin{array}{lr}
\text{Electrolyte}&\text{ Ionic Molar Conductivity (mS m$^2$ mol$^{-1})$} \\
\hline
\text{OH$^-$} & 19.91\\
\text{F$^-$} & 5.54\\
\text{CO$_3$$^{2-}$} & 13.86\\
\text{HCO$_2$$^-$} & 5.46\\
\end{array}


texts: Is Sweetwater, Missouri, named due to water contamination with lead compounds?

texts: The town of Sweetwater, Missouri is known for its mineral resources, particularly rich lead sulfide (galena) deposits. I am curious to find the origin of the name "Sweetwater" and if it has any connection with lead compounds that at one time or another leached into the local water resources (I believe lead acetate tastes sweet). In any event, I can't seem to find any history or such a connection through internet research.


texts: Work done when P,V, and T are changing simultaneously

texts:
I am given the following P-V graph for an ideal gas:

I have been asked to find the work done in the process from C to A, for which $P$ is directly proportional to $V$. This may be calculated in two ways:

Work done= Area under the line CA, which is the area of the trapezium, given by

$$w = -\frac{1}{2}(P_0+2P_0)V_0 = -\frac{3P_0V_0}{2}$$

(where the negative sign has been introduced since the work done is negative due to decrease in volume.)

Work done = $\int -P\,\mathrm{d}v$. However, in this case, since $P$ is directly proportional to $V$, how to integrate this?

How to calculate the work done in a process where all 3 variables, $P$, $V$, and $T$ are changing simultaneously and $P$ is directly proportional to $V$?


texts: How to acetylate a thiol group in general?

texts:
I wonder (and have tried to find the answer by searching in synthetic chemistry resources) how do you acetylate thiol (R-SH) groups in general? For example the cysteine-SH group either alone to make S-acetyl-cysteine or, in the glutathione tri-peptide to make S-acetyl-glutathione.

Below I am using SMILES notation, here completely protonated. I am new to the chemistry section of stackexchange, so not sure how y'all draw structural formulas here.

So this is the reaction in general:

R-SH + X --> R-S-C(=O)-CH3

I am thinking that the best reactant should be acetic anhydride:

H3C-C(=O)-O-C(=O)-CH3

And so, I suppose the reaction is this:

R-SH + H3C-C(=O)-O-C(=O)-CH3 --> R-S-C(=O)-CH3 + H3C-C(=O)-OH

Now specifically for cysteine:

HOC(=C)-C(NH)-C(H2)-SH

We would want:

HOC(=C)-C(NH)-C(H2)-SH + H3C-C(=O)-O-C(=O)-CH3 --> HOC(=C)-C(NH)-C(H2)-S-C(=O)-CH3 + H3C-C(=O)-OH

However, how would I direct the reaction toward the thiol group and not the amino group? Difference between N-acetyl-cysteine and S-acetyl-cysteine.

Next step of the question is how this would apply to glutathione, when we try to make S-acetyl-glutathione? So glutathione

gamma-glutamyl - cysteine - glycine

where we have an available amino-group on the glutamyl part:

OC(=O)-C(H)(NH2)C(H2)C(H2)C(=O)-N(H)-C(C(H2)SH)C(=O)-N(H)-CC(=O)OH
            ^not here                       ^but here

I know people also use catalysts such as simply potassium carbonate or more complex things. Finally, I wonder, how do you get rid of the remaining acetic acid and the potassium carbonate or other catalysts from the reaction to purify the synthesized thio-ester?

I apologize, I have studied medicine not synthetic organic chemistry or pharmaceutical engineering. So, I am asking a lot in one question. I did some research but since I am no longer in academia, I don't have access to journals, such as for A simple acylation of thiols with anhydrides


texts: Cs Point Group's "Horizontal" Reflection Plane

texts:
Why is it that $C_s$ character tables always list a $\sigma_h$ operation despite the definition of $C_s$ not necessitating the reflection plane be horizontal?

In fact, how can the reflection plane even be characterised without a principal rotation axis to base it on?


texts: Representing conformers using SMILES and Graph representations

texts:
I was wondering if either of SMILES or graph representations (in their vanilla form) can distinguish between two conformers of the same molecule.

Can this be enhanced by adding additional metadata on Graph nodes?
what info are necessary then?
Can this be enhanced for SMILES representations?


texts: Searching for a solvate that changes its solvation property

texts:
I'm looking for a solvate that changes its solvation property when being dried.
One example of such a material is gypsum:

at temperatures up to 250°C it becomes γ-anhydrite which will slowly
hydrate to a hemihydrate.
at temperatures above 250°C it becomes
β-anhydrite which will not hydrate again.

However the temperature range is too high to use it as example in my thesis.


texts: Arrhenius equation - Proper Interpretation of Activation Energy term

texts:
Consider the normal form of Arrhenius Equation:$$k=Ae^{-\frac {E_a}{RT}}$$
The term, $e^{-\frac {E_a}{RT}}$, is interpreted as the fraction of molecules having energy greater than Activation Energy.
My question: Isn't the term threshold energy better than activation energy?

Please provide a suitable interpretation of the terms involved.


texts:
The molar heat of fusion of ice is 6.01 kJ/mol.
Can you explain what this means? What I think it means is that it requires 6.01 kJ to melt a mole of ice. I'm not positive though..


texts: Is common ion effect applicable on two strong electrolytes

texts:
Consider the nitration of benzene using mixed conc. $\ce{H2SO4}$
and $\ce{HNO3}$.If a large amount of $\ce{KHSO4}$ is added to the
mixture the rate of nitration will be :

Faster
Slower
Unchanged
doubled

The answer given in my textbook is option 2 , i.e. the reaction will become slow. my teacher told me that it is due to common ion effect.
But in common ion effect, a strong electrolyte decrease the dissociation of weak electrolyte. So,how can common ion effect possibly be the reason here($\ce{KHSO4}$ and $\ce{H2SO4}$ both are strong electrolytes). In my view the answer should be no effect and I'd love to have my concepts about Ionic Equilibrium be corrected if I'm wrong.


texts: Why do isomeric complexes often have different colors?

texts:
For example, $\ce{[Cr(NH3)2Cl2]+}$

One isomer is green and the other is violet. Why is this so? The ligands are the same, the oxidation state is the same, and so is the coordination number. The only reason I can think of is that if two $\ce{NH3}$ ligands are trans to each other, they repel the 3d orbitals differently than if they were cis. But I don't know why this would occur.

The explanation given in the other question involves anti-bonding orbitals, and I simply have no idea what these are. I'd like an answer which uses highschool chemistry so that I can understand (albeit perhaps in a flawed way ) whats going on.


texts: Woodward Fieser rules for dienes - non conjugated double bond as exocyclic?

texts:
When looking for exocyclic double bonds in a diene, should a double bond not connected to the conjugated system be considered?

For example, in this compound, should the marked double bond considered as an exocyclic double bond?


texts:
I read a problem which was as follows:

Equal volumes of $\pu{1M} \ \ce{H3PO4}$ and $\pu{1M} \ \ce{Na3PO4}$ are mixed. The $\mathrm{pH}$ of the resultant mixture is (along with this $K_\mathrm{a1}, K_\mathrm{a2}, K_\mathrm{a3}$ of the acid were mentioned)

The way I approached this problem was as follows:
$K_\mathrm{a1} = \frac{[\ce{H2PO4^-}][\ce{H^+}]}{[\ce{H3PO4}]}$, similarly $K_\mathrm{a2} = \frac{[\ce{HPO4^{2-}}][\ce{H^+}]}{[\ce{H2PO4^-}]}$ and so on...
Which gives me $K_\mathrm{a1}\cdot K_\mathrm{a2}\cdot K_\mathrm{a3} = \frac{[\ce{PO4^{3-}}][\ce{H^+}]^3}{[\ce{H3PO4}]} = [\ce{H^+}]^3$ (since $\ce{[H3PO4] = [Na3PO4]}$). Using this, I calculate the $[\ce{H^+}]$ and so the ph which comes out to be $-\log{\sqrt[3]{K_\mathrm{a1}\cdot K_\mathrm{a2}\cdot K_\mathrm{a3}}}$ which is $\frac{\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2} + \mathrm{p}K_\mathrm{a3}}{3}$.
However, it seems from the answer that the system is forming a buffer and $\mathrm{pH}$ is $\mathrm{p}K_\mathrm{a2}$
What am I doing wrong here and how does the $\mathrm{pH}$ come out to be $\mathrm{p}K_\mathrm{a2}$. Is there any such general result or theory for polyprotic acids?
EDIT: I understand now why my solution is wrong. Any help as to how to proceed further will be appreciated.


texts: Adding pure solid/liquid in heterogeneous equilibrium

texts:
If I have the heterogeneous equilibrium

$$\ce{aA(s) + bB(g) <=> cC(g) + dD(g)}$$

I understand that the equilibrium expression is

$$K_c = \frac{[\ce{C}]^c[\ce{D}]^d}{[\ce{B}]^b}$$

and that $\ce{A}$ is left out of the equilibrium expression since it is a pure solid and pure solids/liquids are left out of the equilibrium expression in heterogeneous equilibria.

However, does this mean that adding or removing substance $\ce{A}$ has no effect on the reaction at all? For instance, is it true that adding $\ce{A}$ does not produce more products and removing $\ce{A}$ does not produce more reactants (as Le Chatelier's principle would predict for a reactant included in the equilibrium expression, such as $\ce{B}$)?

On a side note, adding/removing the other substances could potentially affect $[\ce{A}],$ right? For example, adding $\ce{C}$ or $\ce{D}$ would cause $[\ce{A}]$ to increase (because more $\ce{B}$ would be formed and with that more $\ce{A}$ would be formed as well) and adding more of substance $\ce{B}$ would cause $[\ce{A}]$ to decrease (because $\ce{B}$ would be consumed and with it $\ce{A}$ would be consumed as well), correct?


texts: I'm trying to find the product of the oxidation of iso-butane using KMnO4, i know that alkanes undergo step wise oxidation with strong oxidising agents to finally give carboxylic acids.. With straight chain carbons, its very straightforward - ethane becomes acetic acid etc. But with branched chain alkanes I don't know how to proceed. Can someone tell me if there's a general rule for oxidation of alkanes- to get the product?


texts:
I know that water is 2 parts hydrogen and 1 part oxygen. Hydrogen and oxygen are quite light gasses, they don't weigh very much compared to water. Water is very heavy and it made me wonder exactly how much oxygen I'd need to make a cup of water.

Please answer in terms of cubic meters of air, assuming the air is 21 % oxygen, and that my small cup contains only 100 ml. I suppose the exact question is: How many cubic meters of air contains the same amount of oxygen as found in 100 ml of water?


texts: Defining and testing custom made DFT functionals?

texts:
What is a good and free software for this endeavor? Any recommended articles on the subject?
I want to design dft functionals, trying out different parametrizations and optimizing mixing constants for exchange and correlation contributions for specific data sets. Even add PT2 perturbation energy into the mix if possible.

I am aware of Gaussian's user-defined functional options, but would like to have a bit more control in the parameters and contributions, instead of just 6 parameters.


texts: Why is it experimentally difficult to accurately find the critical volume of a real gas?

texts:
I was reading up on the derivation of the values of various critical state functions( $\ce{Vc}$, $\ce{pc}$ and $\ce{Tc}$) from the Van der Waals equation (Physical Chemistry by G.W. Castellan). There, he was about to express a and b in terms of these critical state functions, when I came across this line:

  Since experimentally it is hard to determine $\ce{Vc}$ accurately, it would be better if a and b
  could be obtained from $\ce{pc}$ and $\ce{Tc}$ only.

What is exactly the difficulty in finding $\ce{Vc}$ accurately?
I found this source stating that:

  Of the three constants, measurement of critical temperature and critical pressure is very easy. The measurement of critical volume is very difficult because it varies considerably for slightest variation of temperature and pressure near the critical region; hence for the measurement of critical volume, the substance must be kept in perfectly critical temperature and pressure.

My two cents

If $\ce{Vc}$ is so short-lived and unstable, then any variation in the same would almost instantly affect the vapour pressure of the gas phase above it, and thereby $\ce{pc}$ would also not be a very reliably measured quantity. Then maybe we would end up with two variables(a and b) and one equation($\ce{Tc}$).

Can somebody explain the procedure of measurement of critical state function here, and why only $\ce{Vc}$ causes problems,and the other two remain appreciably accurate?


texts: How do electronegativity and lone pairs affect bond angles?

texts:
How do bond angles vary in molecules with a lone pair and central atom of different electronegativity, but in the same period so that electronegativity matters more than orbital size? Let's assume that the molecules I am comparing have the same substituents and one lone pair.

Will the molecule with the more electronegative atom in the middle have the lone pair electrons closer to the nucleus, so they take up more bonding space and the angles for the other substituents will be smaller?


texts:
In the synthesis of DMAD, we eliminate two bromides from dibromosuccinic acid in basic environment to get acetylenedicarboxlyic acid (Step 2).

However, this reaction could also happen:

The reaction in Organic Syntheses (http://www.orgsyn.org/demo.aspx?prep=cv2p0010) went with a yield of 72-88 %, which means that these pathways probably do happen, but only in a minority of cases.

Why is that so, given that the elimination of CO2 is entropically favoured?


texts:
Consider a solution of $\text{HCl}$ with a concentration of $10^{-10}$ $\text{M}$. Now, if I find it's pH:
$$\begin{aligned}\text{pH} &= -\log([\text{H}^+])\\
\text{pH} &= -\log(10^{-10}) = 10\end{aligned}$$
At room temperature, $\text{pH} + \text{pOH} = 14 \implies \text{pOH}$ of the given acid is $4$. This means that the $[\text{OH}^-]$ ions is $10^{-4}$ $\text{M}$. But from where do these $\text{OH}^-$ ions come?


texts: Which acid/base does a strong base/acid react when added to a buffer solution?

texts:
I'm in high school chemistry and just learning about buffer solutions. For example, given a buffered solution of $\ce{CH3COOH}$ and $\ce{NaCH3COO}$ with $K_a = 1.8 \times 10^{-5}$, we might want to find what the pH will become if $\ce{0.010 M KOH}$ is added. Given the dissociation of acetic acid:

$$\ce{CH3COOH + H2O <=> H3O+ + CH3COO-}$$

My question is, which acid ($\ce{CH3COOH}$ or the conjugate $\ce{H3O+}$) will the base $\ce{KOH}$ react with? My teacher said that the base will react with $\ce{H3O+}$ to shift equilibrium in the forward direction, but why wouldn't it react with $\ce{CH3COOH}$ since it also is an acid?

Is there a specific rule that an added acid/base will react only with the base/acid in the product side of the reaction?


texts: Have there been no advances in the determination of effective nuclear charges since Clementi and Raimondi in the 60s?

texts:
Effective nuclear charge is a very important concept in chemistry, and is the basis for the qualitative explanation of many observed chemical and physical properties, including several periodic trends. Hence it seems to me to be of significant importance that these values are accurately determined (not only for neutral atoms, but for monoatomic ions too). Slater's rules for the calculation of effective nuclear charges, from the 1930s, are in practically any university-level general or inorganic chemistry book, though they are heavily outdated and inaccurate, being mostly of interest due to their simplicity and their historical value. Many books go on to mention updated values for atomic screening constants, calculated by Clementi and Raimondi in 1963 and 1967. This updated table of effective nuclear charges is significantly more interesting, but not used as often probably because all the values for each orbital in each atom must be looked up individually.

However, it's been 50 years since Clementi and Raimondi's first publication on the topic, and I have seen no clear reference to a more recent improved calculation. Surely it is not because the values they found are not without flaws. For example:

Screening constants have only been calculated up to $Z = 86$, leaving out a portion of the table, in particular the actinides which have interesting electronic properties
No relativistic terms whatsoever were considered in the calculation of the screening constants, which is deleterious especially for atoms beyond about $Z \simeq 70$
The calculations are not completely reliable as they are, having not converged well especially some lanthanides, creating odd kinks in screening capacities for electrons in the $4f$ subshell
The calculations converged to inaccurate electron distributions in several atoms, such as $[\ce{Kr}]4d^85s^2$ for $\ce{Pd}$ instead of the actual $[\ce{Kr}]4d^{10}$

By now we should be able to do their calculations again with much more accuracy and much more speed, both due to the development of physical and mathematical theory behind the calculations, and due to the stupendous increase in affordable computational capacity. So why has there been no improvement to effective nuclear charge calculations? Has no one bothered? Or have there been several attempts, none of which have gained wide acceptance since then (sort of like what happens with electronegativity)?


texts: Formation of symmetrical ether or dehydration of primary alcohol?

texts:
My textbook gives the formation of diethyl ether from dehydration of ethyl alcohol:

  $\ce{\underset{\text{ethyl alcohol}}{2C2H5-OH} ->[\text{conc.} H2SO4][413~K] \underset{\text{diethyl ether}}{C2H5-O-C2H5} + H2O}$

In the reaction where it is said that concentrated $\ce{H2SO4}$ at temperature $413~\mathrm K$ is used as a catalyst, will the primary alcohol not dehydrate to form alkene?

Concentrated sulfuric acid is a strong dehydrating agent, and is used as $95~\%$ concentrated when dehydrating primary alcohol. So will the alcohol dehydrate or will the diethyl ether be formed?


texts: Why do sulfur and oxygen form sulfur dioxide?

texts: Both sulfur and oxygen have 6 electrons in their outermost shell. Since both only need two electrons to stabilize, why doesn't just one atom of oxygen react with one sulfur atom, forming sulfur monoxide SO instead of sulfur dioxide $\ce{SO2}$?


texts: Reaction of one mole of (PO4)3- with one mole of H2CrO4

texts:
I am looking for the endproducts of a reaction of one mole of $\ce{PO4^3-}$ with one mole of $\ce{H2CrO4}$ in one litre of water.

First, the following reaction can happen:

$$\ce{PO4^3- + H2CrO4 <=> HPO4^2- + HCrO4-}$$

Then the following reactions may happen:

\begin{align}
\ce{PO4^3- + HCrO4- &<=> HPO4^2- + CrO4^2-} \\
\ce{HPO4^2- + HCrO4- &<=> H2PO4^- + CrO4^2-} \\
\ce{HPO4^2- + H2CrO4 &<=> H2PO4^- + HCrO4^-} \\
\ce{H2PO4^- + H2CrO4 &<=> H3PO4 + HCrO4^-}
\end{align}

Is there a way to determine how many moles there will be of each end product?

Note: this is not homework, rather just a thing I'm interested in. However, I have barely an idea where to start.


texts: Making sense of J coupling data for Hydronium

texts: I found J coupling data for hydronium using DFT and GIAO but I need help making sense of the data. Can someone with help?


texts: Reference request: review paper / overview of chemical oscillators

texts:
I know about the Belousov-Zhabotinskii reaction as an example of "chemical oscillator", e.g. a reaction that can produce repeating patterns over time as it exhausts its reagents. I also know about the Briggs-Rauscher reaction but I wonder how many such chemical oscillators are possible? Can somebody provide me with a good review paper and/or book reference written specifically to survey the range of all possible chemical oscillator systems?

To note, I know there are a lot of people outside of chemistry (particularly people interested in chaos theory and non-equilibrium thermodynamics) who do detailed research on modeling the detailed behavior of such oscillating systems, and I've found several such papers/reviews. But, what I'm looking for is a resource focusing on the chemical properties of oscillator systems, not the mathematics or dynamics modeling.


texts: Examples of non-volatile, but flammable liquids?

texts: As far as I know, most flammable liquids are volatile. Are there flammable liquids that are non-volatile?


texts: Given the concentration and density of a sample, calculate moles of bleach?

texts: Given the concentration of bleach ($6\%\,\mathrm{m/m}$), density of bleach ($1.07\,\mathrm{g\,mL^{-1}}$), and molar mass of bleach ($74.44\,\mathrm{g\,mol^{-1}}$) how many moles of bleach are in a $4.0\,\mathrm{mL}$ sample? I don't understand where the concentration factors in, but the problem says to use it.


texts: How does an electron identify whether to absorb a photon of a certain wavelength or not in absorption spectrum?

texts:
How would an electron identify the specific photons of a certain wavelength which are to be absorbed in a Hydrogen atom while creating an absorption spectrum? Well, I was thinking of it like this-
Way-01: The electron will absorb any photon coming towards it regardless of its wavelength and jump. Then if the wavelength is the exact amount required to jump from one shell to another, then the electron simply jumps to the higher shell. Otherwise, it cannot find a shell and since electrons cannot exist in between shells, they simply re-emit that photon and we perceive the incident as if the photon weren't absorbed at all.
Way-02: The explanation given above is false and electrons choose the photons via some other mechanism
Now, my question is- is the "Way-01" correct? Or do electrons identify the photons via some other way? If so, then what is it?
Note: I'm only a high-schooler, so any relatively simple qualitative explanation will be greatly appreciated.


texts:
What is the meaning of "free" $\ce{SO3}$ and "combined" $\ce{SO3}$ in the oleum sample concentration description?

Also what are these maximum and minimum values of % labelling in oleum sample?


texts: Why exactly does high pressure (72 bar) nitrous oxide's pseudocritical¹ temperature drop so far when oxygen is added to make 50%v/v mixture? (Entonox)

texts:
This answer to Can precipitation occur in states of matter other than liquids? mentions the unusual case of Entonox.
The effects of temperature on nitrous oxide and oxygen mixture homogeneity and stability (Litwin P. D. 2010 BMC Anesthesiol. 2010; 10: 19. doi: 10.1186/1471-2253-10-19) says:

Poynting found that the critical temperature and pressure of a vapour may be affected when it is mixed with another gas. The critical point of a substance is the temperature at above which a gas cannot be liquefied, no matter how much pressure is applied. Conversely, it is the temperature and pressure point at which condensation of the gas into liquid will commence. For nitrous oxide this critical point occurs at a temperature of +36.4°C and at a pressure of 72.45 bar (1050 psi) [12]. For a cylinder of a 50% nitrous oxide and 50% oxygen v/v mixture filled to 138 bar (2000 psi), the new critical temperature of the nitrous oxide (known as the pseudocritical temperature) decreases from +36.4°C to -6°C.

Answers to Can precipitation occur in states of matter other than liquids? tend to guide us away from thinking of the Poyting effect as being related to dissolution or solubility but my concern is that "Poynting effect" is simply a name for an observation, and by itself not a well developed scientific concept or explanation.
That Wikipedia article says:

In thermodynamics, the Poynting effect generally refers to the change in the fugacity of a liquid when a non-condensable gas is mixed with the vapor at saturated conditions.

and that linked subsection ends with:

This equation allows the fugacity to be calculated using tabulated values for saturated vapor pressure. Often the pressure is low enough for the vapor phase to be considered an ideal gas, so the fugacity coefficient is approximately equal to 1.

So if we start with tabulated basic measurements of vapor pressure and calculating fugacity f and then see an unexpected, significant increase in vapor pressure of A when introducing gas B to the vapor, we say "Oh, that's the Poynting effect!"
We might then quickly change the subject or excuse ourselves before "What's that?" or "Why does that happen exactly?" gets ask.
Question: This change has a name, but what is happening? Why does the high pressure (~72 bar) nitrous oxide's pseudocritical1 temperature drop so far below it's pure substance critical temperature (from +36.4°C to -6°C) when oxygen is add to achieve a 50% v/v mixture at ~138 bar? Is the mechanism at least analogous to dissolution in some ways? Or could it be considered a "liquification point depression" analogous to a freezing point depression?
The citation of a readily available reference or published work explaining "exactly why" this is thought to happen will be most helpful, and if in what ways the process is and is not like dissolution can be added, then that's a complete answer.

1As pointed out in comments, critical temperature is defined for a pure substance so "pseudocritical temperature" is used in the block quoted work accordingly. See Real gases; Real gas law or Interaction Parameters for Kay's Pseudocritical Temperature for some examples of the term in use.


texts: What would the name of this organic compound be?

texts:
I am a little lost in naming this compound.

I think it would be something like 2 bromo 4 methylene pentene??

Is that close?

It is a five carbon chain, so pentane, with a Br on carbon two, a methylene substituent on carbon 4, and a alkene on carbon 1.


texts: If a metal's solvent extraction process is exothermic, then the stripping is necessarily endothermic?

texts: I checked some articles, including Hydrometallurgy 2012, 133-144, 185-191 and Hydrometallurgy 2000, 57, 269-275. In all research papers I checked, an exothermic stripping process followed an endothermic solvent extraction process and vise versa. First, what reasons can be behind such phenomena? Second, is such a claim necessarily right in all cases?


texts: Calculating ionic strength and pH of a buffer solution

texts:
Im trying to calculate ion strength and pH of solution.

Components of the solution:
47 ul of 1000 pmol DNA in Elution Buffer (10 mM Tris-HCl pH 8.5) was bound to 3 ul of 10 µM YoYo1 (flourescent dye) in DMSO and was mixed with 50 ul of Tris-EDTA buffer (100 mM Tris-HCl, 0.01 M EDTA pH 8.0).

About calculation of ion strength, Im confused what Ions are in the solution too.
Tris-HCl => Tris-H + Cl- ?
EDTA => Mg2+ + Ca2+??
DMSO => ??

Furthermore, how can I calculate it?

I think the pH range is about 8.0~8.5, because of two buffers.
Is there any method for calculating more exact pH value?

Thank you so much for your answers!


texts: Soil conductivity: How do I get a near equivalent between meq/100 g to mS/cm?

texts:
I have two soil reports, one that reports CEC as 45 meq/100 g and another that reports 6 mS/cm using 1:1 water soil.

I can see that the two are, if not apples and oranges, they are at best tangerines and grapefruit — the meq/100 g is the source for the ions in a water extract, but an equilibrium solution may not contain all the ions.

Can a meaningful conversion between meq/100 g and mS/cm be made?

E.g: few plants will grow in soil that has conductivity greater than 2.5 mS/cm and generally you start getting concerned at 1.  What is the equivalent measure in meq/100 g?

FWIW main ions of concern are $\ce{K+},$ $\ce{PO4^3-},$ $\ce{Mg^2+},$ $\ce{Ca^2+},$ $\ce{CO3^2-},$ $\ce{HCO2-}.$


texts: Separating NaClO from its aqueous form in bleach

texts:
I was wondering, can I separate the $\ce{NaClO}$ from the $\ce{H2O}$ in bleach. The decomposition point for $\ce{NaClO}$ is $374.14\ \mathrm{K}$, so I'm risking decomposing the compound if I do simple distillation.

What should I do?

PS: I don't have a vacuum pump.


texts: We have seen that $\ce{HBr}$ shows an anti-Markovnikov effect when it reacts with alkenes in the presence of peroxides. Why does only $\ce{HBr}$ shows this effect? How about the other hydrogen halides $\ce{HX}~(\ce{X} = \ce{F}, \ce{Cl}, \ce{I})$?


texts: Are pi electrons in 1,3 cyclobutadiene delocalised?

texts:
The original question in my test was whether all bonds in the aforementioned molecule are of same length. According to the solution booklet, it is not because pi electrons are not delocalised due to anti-aromatic character.

This seems a bit weird...


texts:
I wonder, what are the exact IUPAC organic chemistry nomenclature rules that give the preference to the chain length over number of unsaturated bonds, i.e. that justify, or prefer following names:

4-ethenyl-4-ethynylheptane over
3,3-dipropylpent-1-en-4-yne

3,5-dimethylideneheptane over
2,4-diethylpenta-1,4-diene

?


texts: Which hydrogen does the nucleophile attack in E2 reaction?

texts: This reaction will be both an E2 and SN2, where the E2 will be major and the SN2 minor (If I have done it correctly). I was drawing out the mechanism as I noticed that I was making my nucleophile attack the wrong hydrogen, the one attached to the alpha-carbon. I know that the nucleophile is supposed to attack the hydrogen on the beta-carbons however how do I determine if the $MeO^-$ attacks the hydrogen on the second carbon to the left or to the right of the alpha-carbon? Or does it attack both and since the sturcture of the compound formed is the same either way, it doesn´t matter which hydrogen it removes?


texts: Calculating the pH of a ammonium hydrogen sulfate solution

texts:
I am attempting to complete a question in which I need to use an ICE table to calculate the pH of a $\pu{2.61 mol L-1}$ $\ce{NH4HSO4}$ (ammonium hydrogen sulfate) solution.

When $\ce{NH4HSO4}$ dissociates I know that it splits into $\ce{NH4+}$ and $\ce{HSO4-}$ ions.

According to my textbook, $\ce{HSO4-}$ is actually an acid and not a base, so I set up my equilibrium expression like such:

$$\ce{NH4+ + HSO4- + 2 H2O <=> 2 H3O+ + SO4^2- + NH3}$$

$\ce{NH4+}$ has a $K_\mathrm{a}$ of $\pu{5.56e-10}$. $\ce{HSO4-}$ has a $K_\mathrm{a}$ of $\pu{1.2e-2}$.

According to my ICE table:

$\ce{NH4+}$ and $\ce{HSO4-}$ have starting concentrations of $\pu{2.61 mol L-1}$.

Both lose $x~\pu{mol L-1}$, and have equilibrium concentrations of $2.61 - x$.

$\ce{H3O+}$ has a concentration of $2x$ at equilibrium. $\ce{SO4^2-}$ and $\ce{NH3}$ each have a equilibrium concentrations of $x$.

To calculate the final answer I am using the $K_\mathrm{a}$ of $\ce{NH4+}$ and plugging in the values from my ICE table for the equilibrium concentrations of the products and reactant.

Since $K_\mathrm{a}$ of $\ce{NH4+}$ is so small, I am disregarding the changes and substituting $2.61$ instead of $2.61 - x$.

The final answer I am getting is not the same as the answer in the back of the book which is approximately $\mathrm{pH} = 0.76$.

What is wrong with my process?


texts: I'am not familier with chemisty,& trying electroplating on brass, by using C4 H6 CUO4.H2O.But the result is unsatisfied,am I using right chemical or I have to choose another one.I yes,anyone may guide me the right one.


texts: What is the solid crud that appears inside my kettle?

texts:
Almost every share-house I've lived in has had some nasty looking solids collecting inside.  I always regret looking inside the kettle because a cup of tea never tastes quite as good after you've seen this:

What is that stuff?  What's the physical process that causes it to collect and why is it usually concentrated around the heating element?  Is it related to calcium in tap water, or is there any trick to prevent it appearing in your kettle?  Is it dangerous to ingest and should be removed, or is it harmless?


texts:
Which system at equilibrium will not be influenced by a change in pressure?
$$
\begin{align}
\ce{3 O2(g) &<=> 2 O3(g)}\tag{A}\\
\ce{N2(g) + 3 H2(g) &<=> 2 NH3(g)}\tag{B}\\
\ce{2 NO2(g) &<=> N2O4(g)}\tag{C}\\
\ce{H2(g) + I2(g) &<=> 2 HI(g)}\tag{D}\\
\ce{2 W(g) + X(g) &<=> 3 Y(g) + 2 Z(s)}\tag{E}
\end{align}
$$

My attempt: Equilibrium will be influenced if the number of moles on one side of the equation is different than the other side. Thus, I can eliminate option A,B, and C. But how to differentiate between options D and E? They both look right to me, because there are the same amount of moles of gases on both sides, and solids do not play a factor in determining equilibrium.
For reference, the answer given in the book is D.


texts: Why cyclohexane-1,4-dicarbaldehyde does not give aldol condensation?

texts:
I was recently came to know as a fact that cyclohexane-1,4-dicarbaldehyde does not give the aldol condensation reaction in spite of possessing α-hydrogens. I was told that this is due to steric reasons, but I am trying to come up with a more specific reason, which does not require prior knowledge of this fact. Can anyone guide me towards a better explanation?

Edit 1: I am able to understand that there is absolutely no scope for an intramolecular aldol condensation. But what I am asking is whether even the aldol REACTION would take place, as basically the exact wording of the book is " cyclohexane-1,4-dicarbaldehyde gives zero aldol reaction products". So I am confused that what part is aldol reaction and/or condensation


texts: Making elemental phosphorus from phosphoric acid

texts: What is the most efficient way for making pure or semi-pure elemental phosphorus, by using phosphoric acid as an source of phosphorus?


texts: Where did the INN name of fentanyl come from?

texts:
Fentanyl is a potent anilidopiperidine opioid. Where did its INN name come from?

Figure 1: Fentanyl

I know that the INN name of paracetamol came from its chemical name para-acetylaminophenol (par-acet-am-ol). Is there a meaningful origin of the INN name of fentanyl?


texts: What is the actual reason behind PCl₅ existing as an ionic solid?

texts: Why does $\ce{PCl_5}$ exists in the solid state as $\ce{[PCl_6]^{-}[PCl_4]^{+}}$? What is the problem with it that it doesn't exist in its original form in solid state? Like why isn't it just $\ce{PCl_5}$ in solid state as well?


texts: How does equalizing voltage for lead acid battery depend on the temperature?

texts:
I am using advanced lead-carbon batteries (these ones) in an off-grid solar system. The spec specifies equalizing voltage 14.1 V for 12 V block @ 25 °C (77 °F). I keep the batteries in an outdoor shed, and the temperature where I live tends to hang around 0 °C (32 °F) these days.

So, for lead acid chemistry, would the equalizing voltage go up or down with temperature going down? I feel like it would go up (more voltage needed to do the same job at lower temperatures). How does this reasoning stand? What are the underlying scientific considerations?


texts: Are electron orbitals in a helium atom degenerate?

texts:
In a hydrogen atom, the presence of only one electron allows various orbitals' energy states to be dependent only on the principal quantum number and not on angular momentum. Orbital degeneracy and all that fun stuff. (This has been answered many times on SE)

In helium, would this still be true? How come? I can't seem to find a satisfactory explanation.


texts: Is there a specific historical figure or era that is most responsible for our current definitions of "physical change" and "chemical change"?

texts:
I understand that there is a very blurred distinction between the idea of a physical and a chemical change at advanced levels of chemistry, so I'm referring mainly to the definitions provided in most introductory texts and websites:

physical change - processes that change the form of a substance and not its chemical composition.
chemical change - processes in which new substances are created through changes to a substance's chemical composition.

The closest thing I found to an answer is the formation of Dalton's atomic theory in the early 19th century, which defines a chemical reaction as a rearrangement of atoms in the reactant and product compounds. I am hoping to confirm that this is the earliest definition closest to our modern perception of physical and chemical change, and that I am not missing anybody important.


texts: Are there any reasonably obtainable supercritical fluids that I could, say, run my hand through? Wikipedia makes it sound like there are plenty of room-temperature ones, but no room-pressure fluids.


texts: Protecting elemental Li from the atmosphere

texts:
I would like to make a small decorative object out of lithium, and keep it in an ordinary household (indoors) atmosphere.

The making itself aside, what can I do to protect it long-term from reacting with the atmospheric water and gases? Is there something that could react with it to form a protective outer layer, like oxides do on some other metals? Is it perhaps possible to electroplate it with Mg or Al? Are there other solutions?
To be clear, I don't want to just keep it submerged in oil; I want it to stand on a shelf and hopefully even get handled occasionally by curious hands.

I have no access to advanced equipment or supplies - I'm only armed with a high-school level of chemical understanding, access to ordinary hardware/paint shops, and patience.

I do understand that the question is unusual and has little broad practical utility, but it's still a proper chemistry problem to which I would like to see a proper chemistry solution (or an exhaustive explanation why a search for a solution is futile). Please don't answer along the lines of "your idea is stupid and you should feel stupid".


texts:
I am trying to figure out which tautomer of creatinine:

is more stable.

We see that the enol tautomer is more highly conjugated: the $\pi$ electrons from the alcohol to the double bond to the $\pi$ electrons of the Nitrogen to the imine to the final $\pi$ electrons of the amine.

In the keto form, we have the $\pi$ electrons from the carbonyl to the imine to the two amines.

I know the enol form is more conjugated, but in general I also know that the keto form is more stable. How do I reconcile this?


texts:
From what I understand, the Bradford reagent contains Coomassie Brilliant Blue in an acidic solution so both of the (sulfonic acid groups? I'm not sure if this is the correct name- I can't seem to find an answer) are protonated. In this form the dye colour is red. The theory is that in the presence of basic R-groups like in arginine residues, the acidic groups react with the basic groups. I don't understand why this is so? Why do the acidic groups react with the basic groups as opposed to just binding with the free $\ce{H+}$ ions in the solution. I suppose this is a fundamental question about acid base reactions.

Also, why does the colour change when the $\ce{SO3-}$ group is bound to a basic R group residue as opposed to a H+ ion? It is still essentially bound to a positive charge? With the basic residue now being protonated e.g. -$\ce{NH3+}$


texts: Equilibrium Constant in terms of Molar Concentration of Gases versus Equilibrium Constant

texts:
Suppose the gases involved in a reaction behave as real gases with
significant intermolecular attractions.

I just learned that $$K_c(RT)^{\Delta n_r} = K$$

Would the value of Kc calculated
from the equation above be too high, too low, or the same as the actual value?

I thought that it would be the same, but I don't think that's right because deviation from ideal behavior should deviate from equilibrium.


texts: Trends in conductivity in groups 1 and 2

texts: I have read that the trend for conductivity in groups 1 and 2 is a decrease down the groups (generally). Apparently this is because the atoms of each element get larger, so while the number of electrons per atom stays the same, the number of electrons per unit volume decreases. But the amount of shielding between the outer electrons and the nucleus increases, so surely the outer electrons become easier to donate to the delocalised sea, and will experience less attraction to the positive ions around them. Which I would have thought made them more mobile and therefore made the metal a better conductor. Obviously I'm wrong but can someone please explain why?


texts:
Vitamin $\ce{B_7}$ or Biotin is a member of the vitamin B complex. Members of the vitamin B complex are usually known to be water soluble. However, this webpage mentions that biotin is water soluble. Again, according to another webpage, biotin is neither fat soluble, nor water soluble.

So, is biotin soluble in fat or water? As different sources are contradictory, please provide a reference.


texts: Number of possible microscopic states and their probabilities

texts:
I'm having trouble with the following problem:

Boltzmann defined entropy as a measure of the number of possible microscopic states of a system, $W$,
as:
${S = k_BlnW}$
Here, $k_B$ is the Boltzmann constant. Hereafter, it is assumed that neither energy nor particles are
exchanged between the system of interest and the surrounding environment, and that the system is in
equilibrium at a constant temperature. In addition, the gas atoms and molecules (henceforth referred
to as ‘molecules’) are assumed to behave as an ideal gas.

Figure 1. Example of a microscopic state (4,6) in which ten molecules are distributed in two chambers separated by a wall.
Removing the boundary wall that separates the two chambers in Figure 1 allows the molecules to move
throughout the entire container. Assume that it is possible to measure the arrangement of the molecules
instantly after the removal of the wall. If this measurement is performed a sufficiently high number of
times, the probability that a state with an arrangement (n,m) will be found can be calculated.
1) Calculate the arrangement ($n^*$, $N$ − $n^*$) with the highest probability of occurrence for $N = 10$ and $N = 100$, as well as the corresponding probability of occurrence for each state.
2) Calculate the probability of observing a state in which $n^*$ is in the range $n^* – 0.02 N ≤ n^* ≤ n^* + 0.02 N$ for
$N = 10$ and $N = 100$. Here both $N$ and $n^*$ are integers.

I was able to calculate the first part and got the following results using a spreadsheet.
For $N = 10$:

$W(5,5) = 252$ and $P(5,5) = 0.226$
For $N = 100$:

$\ce{W(50,50) = 1.0*10^{29}}$ and $P(50,50) = 0.0788$
On the other hand, I don't understand what the mentioned range in the second part of the problem means and I'm therefore unable to solve it:

$n^*$ is in the range $n^* – 0.02 N ≤ n^* ≤ n^* + 0.02 N$


texts: Coloured compounds on reacting with oxygen

texts:
In the reaction of chlorine gas with water, Hydrogen chloride and nascent oxygen is produced.The reaction of any coloured substance with this nascent oxygen makes it colourless.

Is it true?if yes, how?


texts: Can a flame start on water (video included)?

texts:
Can a flame a start on a wet piece of paper immersed in water?

The video is shown below (not the full video):

https://youtu.be/Ey3z8z4Hxtc?t=1h27m29s

This is not in English so you might not understand anything. In the video they simply say it is demons or whatever that starts the fire, which is silly to me, of course.

My questions:

What kind of compounds can we use (or the fraud used in the video)?
What do they do in movies, tv shows, magic shows, or even the olympics, to start flames on water?
What changes the color of flame. For example it was pink in the video?


texts:
What is the refractive index of barium respectively where do I find it? I only find values for alpha, beta and x-ray radiation like on https://pubchem.ncbi.nlm.nih.gov/compound/barium_sulfate#section=Decomposition

I need it for all wavelengths or at least at 455 nm. Thank you in advance!


texts: The Workings of Pulse-Height Discrimination

texts:
Pulse-height discrimination is a common technique to filter out unwanted background signals from the analytical signals. But how exactly does it work?

The analytical signals are not continuously detected, but detected rather in pulses. This is because the detector has a "dead time", and there is a pile-up of ion-pairs (or whatever the principle of detection is) in this dead-time. The intensity of the built up signal - the pulse - is then detected.

Pulse-height discrimination is just that; a discrimination of the detected pulse-heights. However, to be able to discriminate the pulse-heights, surely the system must know what a "desirable" pulse-height is, or, in other words, when a detected pulse deviates from the desirable? How exactly is this done?

In the context of X-ray diffraction, we know the desirable energy of the detected radiation: in theory, this energy should be equal to the K$\alpha_1$ of the X-ray tube's anode material (since diffraction is an elastic interaction, and hence no energy lose occurs). However, the intensity of the signal has nothing to do with the energy. How do we (that is, the ones developing the analytical system) know which pulse-heights are relevant and which are irrelevant to our analysis?

I hope have presented my question clearly, and I appreciate all help. Finding free references online was not very easy, in my experience.


texts:
While going through some questions on chirality and optical isomerism, I came across this compound:

Note that I have marked 3 carbons as $C_1,C_2,C_3$
Its obvious that $C_1,C_3$ are chiral carbons.
$C_2$ is not a chiral carbon as it has the same group above and below it( With respect to the picture)
However a thought struck me that chiral carbon meant that 4 different groups are attached to it.
But what exactly does same group mean?
Does it mean that even the spatial arrangement of the groups should be different?
Or does it not matter?
So if spatial arrangement mattered, then the compound I have mentioned would have a chiral $C_2$ carbon for specific configurations around $C_1$ and $C_3$ carbons.


texts: Do I really need to wear protective clothing while using isopropyl alcohol?

texts:
I recently purchased a 500ml bottle of 99% isopropyl alcohol (aka isopropanol aka rubbing alcohol) for everyday use at home. The label for the bottle worryingly states:

  Wear protective gloves/protective clothing/eye protection/face protection

I'm surprised by this particular warning because I've always known of isopropanol being used for such everyday household appliances as cleaning and sterilising wounds, and have never known even the experts to wear or recommend wearing any sort of protective clothing while doing so.

The most I expect to handle the isopropanol is when pouring the solution from the 500ml bottle into smaller dropper bottles, and after that either using the 500ml bottle to wet cleaning cloths, or the dropper bottle pipettes to apply the solution directly to electronics.

Do I need to wear protective clothing for such applications? If not, at what volumes/for what applications would it be necessary to start wearing protective clothing?


texts: Polyethylene terephthalate reaction with tap water

texts:
I have searched the internet and I found that reusing PET no.1 is dangerous. Why it is dangerous and what is the equation of the reaction between it and water tap ? And why it is not danger to when it is used for the first time in water bottles but it is danger when reusing it ?

Thanks!

Links I have found useful:

http://greenliving.nationalgeographic.com/plastic-drink-bottles-safe-reuse-drinking-water-3110.html

http://www.plasticsinfo.org/Main-Menu/MicrowaveFood/Need-to-Know/Plastic-Bev-Bottles/The-Safety-of-Polyethylene-Terephthalate-PET.html


texts: Analytical Organic Chemistry - Do you agree with my answer to this C-13 NMR question?

texts:
Question 2b:

Because of the 184.7 signal, I think it's either an ester or carboxylic acid. There isn't a DEPT signal based on 184.7 because the carbon is not bonded to any hydrogens. Since there are some carbons not being shown, I figure there is probably some symmetry going on. From what I know, the DEPT (+) signs indicate the presence of either a CH or CH3.  Since it's kind of hard to make a symmetric ester, I settled on the molecule: methylpropanoic acid. The 2 methyl groups at the end of the chain are symmetric, being represented by 1 peak.

Do you agree with this reasoning?


texts: Is there a mathematical formula for electronegativity?

texts: If we lost all the numerical values we have for the electronegativity of elements, is there any mathematical formula that can be used to re-calculate them based on proton (and neutron) numbers alone? For example, if I had no way to look up the electronegativity of Carbon, could I use some existing formula to calculate it from scratch? Or would I have to go actually measure it?


texts: The Boiling or Evaporation of Diethyl Ether

texts:
When we heat water, we see bubbles appear as the boiling point approaches. The water then "boils" vigorously as it is converted from the liquid phase to a gas.

I realised recently that during an ether extraction of a product, a lot of ether had evaporated, as was evident from the mass balance. The ether vapours were visible, but no "boiling", or fluid motion that we tend to associate with boiling, was observed. The boiling point of ether is $34.6\ \mathrm{^\circ C}$. The ambient temperature then was around $35\ \mathrm{^\circ C}$.

Question: Why do we not see ether "boiling" near its boiling point?

Let me also put forth my thought process: The most apparent difference between the two cases of boiling water and boiling/evaporating ether is the location of the heat source. The ether was kept in a beaker on a stable platform, so it could exchange heat through the upper surface and the walls of the beaker. Heating water from below might create pockets of 'hotter' and hence less dense water that might lead to the "boiling". In the case of ether, the only possible explanation I found believable was that the walls of the beaker were really bad conductors of heat, as we would have seen some fluid flow in the ether case as well.

We also see puddles of water evaporating off. In that case, the heat exchange is possible only from above. Considering no disturbances, there is no visible fluid motion in the puddle. I felt this was because the rate of evaporation was too low. In the case of ether, it is already at its boiling point. This leads me to believe that in a restricted environment as a beaker, when the ether changes phase, the vapour accumulates near the surface as it is denser than air (almost 2.5 times as much). This further slows down the transfer of heat. Taking this into account, I find it very hard to believe that about 5 g of ether was lost in a mere span of a bit less than 10 minutes.

Is my reasoning right, or is it flawed? Please do tell.

Notes & References:

Diethyl Ether - Wikipedia
weather.com and personal experience
Modified Ideal Gas Law: $\rho=\frac{pM}{RT}$, i.e. $\rho\propto M$, taking $M_\text{air}\approx 28.84\ \mathrm{\frac{g}{mol}}$