texts: Role of acetate ion in formation of hydrogen sulfide ion from thioacetamide

texts:
We are using TAA to form metal sulfides. What is the effect of sodium acetate on sulfide ion concentration?

The procedures instruct me to add sodium acetate and to heat the test tube with the metal ion if no precipitate forms after the initial addition of TAA.

From the equilibrium given below, it seems that addition of sodium acetate would actually reduce sulfide ion concentration by driving the equilibrium to the left! That would be antithetical to sulfide salt formation.

However, this cannot be the case; the instructions clearly tell me to add sodium acetate if no precipitate has formed; the instructions are clearly suggesting that sodium acetate helps a precipitate form.

Thinking about it some more, could it be that the addition of sodium acetate basicifies the system by forming hydroxide ion, thereby driving the equilibirum to the right? This seems to make sense, because the addition of sodium acetate is to be accompanied by heating, and wouldn't heating drive the formation of acetic acid and hydroxide ion from acetate ion? And acetic acid is rather volatile, so it'll just leave the solution and not interfere by making the solution too acidic. Am I correct in my thinking? How can I predict the effect of heat on an acid-base reaction? I know heating ammonium chloride causes the ammonium ion to lose its proton. Will heating acetate ion in the presence of water cause it to gain a proton?


texts: Hoffman's Isocyanide test: How does addition of concentrated HCl degrade the isocyanide formed?

texts:
This question is regarding a laboratory procedure followed for Hoffman's Isocyanide test (also known as the "Carbylamine test")

I've been taught that the isocyanide formed in this reaction is highly toxic and must therefore be destroyed in situ.

I'm told that one method of carrying this out is to cool the test tube and carefully add an excess of concentrated $HCl$.

Though it wasn't mentioned, I'd like to know how exactly the addition of "excess concentrated $HCl$" results in the degradation of the isocyanide formed.

I've provided the reaction-mechanism for a primary amine subjected to the Hoffman Isocyanide test below;


texts: Mechanism for the conversion of 4-bromobenzyl bromide to 4-bromobenzoic acid using Oxone (potassium peroxymonosulfate)?

texts:
Oxone is a mild, inexpensive and easy to handle and environmentally benign oxidation agent that has many application in organic synthesis.

4-Bromobenzyl bromide can be converted to 4-bromobenzoic acid using Oxone. I am curious what would be the mechanism for the oxidation.

The proposed mechanism seems like that, but how the carbocation is formed in the first step?


texts: Why does the black powder that comes off aluminum pans behave the way it does?

texts: When I wet an aluminum pot or cookie sheet and then dry it with a towel, it creates dark gray marks on the towel. This happens more if the aluminum is a little rough. It seems that there's a fine black powder coming off the aluminum. I would guess that's aluminum oxide, but I was under the impression that aluminum oxide forms a hard coating that protects it from corrosion. So is that stuff really aluminum oxide? Why does it come off that way? Does it mean the aluminum isn't protected from corrosion?


texts: How to get rid of calcium carbonate and other salts formed by calcium hydroxide in air?

texts:
My basic question comes from the idea that in olden days people used lime to paint houses, so after it is dried out it becomes white paint which sticks to the walls. So, how to get rid of it? The reaction is

$$\ce{Ca(OH)2 + CO2 -> CaCO3 + H2O}.$$


texts:
Enthalpy of a reaction $$\ce{2H2 (g) + O2 (g)-> 2H2O(g)} \Delta H_1$$

$$\ce{2H2 (g) + O2 (g)-> 2H2O(l)} \Delta H_2$$

Now I was asked to compare the enthalpy.

If I subtract reaction 2 from 1, I get $$\ce{2H2O(g)-> 2H2O(l)} \Delta H_2 - \Delta H_1$$

Since this is exothermic enthalpy is negative and $$ \Delta H_2 - \Delta H_1 < 0 $$ or $$ \Delta H_2 < \Delta H_1 $$

But if I consider

Enthalpy of $\ce{2H2O(l)}$ is less than enthalpy of $\ce{2H2O(g)}$ therefore more energy will be released in the formation of $\ce{2H2O(l)}$ and thus $$ \Delta H_2 > \Delta H_1 $$

So which one is it, where am I going wrong ??


texts:
In my book it talks about amino acids. It says the general structure of an amino acid is as follows:

However, on the next page it lists specific amino acids such as glycine shown here:

My question is when comparing the first image to glycine, why does glycine or any of the other specific amino acids have an extra H atom as in "H3N+"?

Where does the extra H come from and why is it positively charged?

Also, on the general structure it shows the an amino should have a COOH but on glycine it is just C double bonded to an O and then another O- negative charge.

Does this have to do with the pH and ionization?


texts:
I am wondering how to use the Gompertz model in modelling drug diffusion:
$$x(t) = x_\mathrm{max}\exp(-a\exp(b\log t)).$$
$x_\mathrm{max}$ is to be taken as $100,$ $a$ is the undissolved proportion at time $t = 1.$ But what is $b?$ I've seen it variously described as half of the max asymptote, the $m$ of the linear portion of the graph, or the $m$ divided by $\mathrm e.$


texts: Why are the majority of cleaning solutions basic?

texts: When testing for pH for common household cleaning products, such as dishwasher fluid, I noticed that majority of them tend to be basic? Why is that? Do acid make good cleaning solutions as well?


texts: Are there any increment systems for guessing the heat of formation for organic compounds that have C, H, O in them?

texts: In the link, you can find two methods of approximation which can help one calculate the heat of formation for Alkanes. I do realize that with the addition of O, the position of the functional group starts to play a significant role, so significant that Pentan-1-ol has the heat of formation of 298. kJ/mol compared to Pentan-2-ol with 312.7 kJ/mol. Though, I thought there might still be a systematic way of theoretically determining the heat of formation of organic compounds -that takes the position of the functional group into account, possibly- like ketone bodies.


texts: What is the Mechanism of hydrogenation of alkenes by Wilkinson's catalyst?

texts: I've learnt that the Wilkinson's catalyst $[\ce{Rh(PPh3)3}]$ is used for hydrogenation of alkenes into alkanes. But I'm curious to know the mechanism. Could someone help me?


texts: Is this a viable method for graphene production?

texts:
In a cup of warm water add sugar until it no longer dissolves then add a few spoonfuls more of sugar.

Drop in a small amount of graphite powder into the sugar water mixture. Stir it up well. There should be a thin black film on top of the liquid.

Let it set for a few days.

The sugar crystals will grow on the graphene surface similar to how rock candy grows.

The sugar crystals grow on the bottom of the floating film of graphite and once heavy enough the graphene and sugar crystal wafer will sink. And then the process repeats.

Is this possible with graphite powder in water as a film or is a thin solid piece of graphite necessary for sugar crystal growth?


texts: If atoms are mostly empty space then how are we able to interact with things?

texts:
Note: This question has come out of curiosity

Q: We all have read that atoms are mostly empty, they are generally compared to a football stadium in which a pea is kept in the center (nucleus) and flies buzzing in stands (electrons). Then why is it that we can interact with things?
It would be of great help if anyone can provide me with any article because I can't find any.


texts: From what I have read about fullerenes, the lower fullerenes like $\ce{C60}$ or $\ce{C70}$ have higher bandgaps around 3.5 eV or such, while the higher fullerenes have much smaller bandgaps of the order of 0.5 eV. Initially I thought that this could be explained using electron delocalization on the surface area of the sphere, but later I read that the fullerenes were not necessarily super-aromatic. What could be the reason behind such a dip of the HOMO-LUMO gap?


texts: Can Cellulose Molecules be Synthesized from Glucose?

texts:
I am reading that cellulose may be broken down into glucose. This is usually done with some sort of solvent.

Is there any way to 'rebuild' these cellulose molecules from glucose?


texts: Can ionic and covalent bond be explained in terms of orbitals?

texts:
Covalent bonding is stated as overlap of atomic orbitals .In ionic bonding the composite ions are held together by their electrostatic charges that result from the transfer of electrons from one atom to the other. What is exactly meant by "transfer"
in terms of orbitals?


texts: Why is time-dependent density-functional theory (TD-DFT) used to describe excited states?

texts: It seems that TD-DFT is a common choice for a computationally efficient method to describe excited states. But if DFT is a single-configurational method, and hence a ground state method, how does the TD-DFT method treat the excited states?


texts: Do bulky bases participate in substitution reactions?

texts:
I see how bulky bases influence the regioselectivity of E2 and E1 reactions. I do not see very much content on the involvement of bulky bases in substitution reactions.

I know that bulky bases like t-BuOK are generally not involved in substitution reactions because the t-BuO− ion would prefer to take a β-hydrogen instead. Are any  substitution reactions possible, and if so, what mechanism would be seen in substitution reactions involving bulky bases?


texts: Are there any datasets containing molecules with more than 38 heavy atoms?

texts:
I have been testing a machine learning approach for molecular energy prediction. The current dataset that I have is QM9, which is consist of molecules with up to 9 heavy atoms.

I was wondering if anyone knows of available datasets that contain molecules with large numbers of heavy atoms. I will be testing ZINC, which has up to 38 atoms. Anyone knows of a larger dataset available?


texts: Change in current in an electrolytic cell over time

texts:
Why does the current increase over time in an electrolytic cell with a $\ce{CuNO3}$ electrolyte. The current increased about $2~\mathrm{A}$, and the temperature increased during the experiment to around $55\ \mathrm{^\circ C}$.

I’m not sure whether the formation of hydrogen and oxygen gas at the electrodes would decrease the internal cell resistance causing the current to increase. Or is there something else causing this?


texts: Any free tool for Calculating Gasteiger-Hückel charges for ligands?

texts:
I want to know if there is any free open source tool available for Gasteiger-Hückel charge calculation? I know it is available on Sylbyl but is there any other(free) way to calculate these charges for small molecules?

I was actually trying this paper, if any one is interested,

How to improve docking accuracy of AutoDock4.2: a case study using different electrostatic potentials.

Hou X1, Du J, Zhang J, Du L, Fang H, Li M.X et al.


texts:
Quite a self-explanatory question I guess. I wonder whether there is any information or theory on this. I seem to like remember there is such an element with positron in center and electron rotating around but nothing else.

Can there be any use if we somehow get these? Don't think like immediate destruction, the electrostatic force between "normal" elements electron and the other types can still repel each other and prevent immediate annihilation, in my view.

Can there be any spot in universe with mostly antimatter?


texts: Why does the US not manufacture sodium thiopental themselves?

texts:
A shortage of a given chemical (sodium thiopendal) has prompted Utah to allow firing squads for executions. This shortage is due to mostly European chemical factories refusing to export the drug to the US.

I am against the death penalty, but can't help wondering why USA, arguably the most powerful nation in the world, can not manufacture this chemical themselves. Is it difficult to produce ?


texts: How does a chemical "know" which other species are present and where equilibrium is?

texts:
Please forgive me if this is a vague question. I have always wondered how a chemical reaction "knows" where its equilibrium should be. For example, using a basic example of Le Chatelier's principle, for some theoretical reaction
$$\ce{A + B <-> C + D}$$
 If I were to add extra A and B to the tube, the reaction would proceed to the right until a new equilibrium was established. How do the chemicals "know" that I have added extra A and B?

Am I thinking about this incorrectly? Is it not actually a matter of the chemicals "sensing/knowing" which other species are present, but rather their own individual properties and how likely they are to exist in one form or another?

Related to this quandary, I learned in my metabolism course that NADH and NADPH are used to regulate different reactions because the NAD+/NADH and NADP+/NADPH ratios need to be different, and that merely adding the phosphate allows these separate species to have different equilibria. Can NAD+ really distinguish NADH from NADPH?


texts: Are there still "prairie dog refineries"?

texts:
In the old days (meaning the 1940s) there still many small "prairie dog" oil refineries, that were little more than a bunch of hooch stills soldered together, but from what I understand these are all gone now and there are only a handful of oil refineries in the United States.

Are there still small refineries in the United States or have they been regulated out of existence?


texts: How to convert isopropanol to acetone and hydrogen

texts:
From Wikipedia:

  Isopropyl alcohol can be oxidized to acetone, which is the corresponding ketone. This can be achieved using oxidizing agents such as chromic acid, or  by dehydrogenation of isopropyl alcohol over a heated copper catalyst: $$\ce{C3H8O -> C3H6O + H2}$$

However, how exactly do I do this? Is it possible to do this by simply mixing isopropanol with an oxidizer (e.g. sodium chlorate)? Also, if the copper catalyst is actually required, what temperature is needed to drive the reaction? Neither the Wikipedia article nor the cited source provide much information on this. I want acetone as opposed to isopropanol, as a fuel, because its flash point is lower and it is much easier to ignite.

This is just an experiment, and if this method of producing acetone is impractical, I will just make/obtain it in other ways.


texts: Reaction mechanism with benzylchloride (KMnO4 and Soda lime)

texts:
So I know that $\ce{KMnO4}$ converts any side chain irrespective of chain length to -$\ce{COOH}$ group and Soda lime converts that into the respective alkane. But in benzyl chloride, the alkyl group side chain also has a chlorine atom attached. How would the mechanism proceed?

It is given that Benzene is the product.


texts: Compounds that Liberate Hydrogen from Water, Reversibly

texts:
I'm working on a paper which provides an overview of all the current methods for storing hydrogen gas as part of a renewable energy system, and I understand compressed gas and metal hydride storage well enough. I am struggling, however, to find a table, paper, database, etc.  which compares all the compounds that could be used to liberate hydrogen gas from water.

I’m looking for a compound(s) that can be stored indefinitely at ~STP and would yield hydrogen gas in a reversible reaction with water? By reversible, I mean that with the addition of electrical or heat energy, it could be transformed back to the state it was in before it reacted with the water (and thus used to generate more hydrogen gas). Ideally, all the reagents would be low cost and abundant, but this is less important provided that the reaction is reversible.
I am aware that this process is likely to be wildly inefficient, and that the round trip efficiency of any commercially available battery chemistry would make it a superior option for storing electrical energy. In the context of a broader application, however, this system could afford to have huge energetic losses in exchange for providing what is in effect a "stockpile" of hydrogen with virtually no storage cost.

If this information does not exist in an aggregated form(s), how would I go about hiring an individual or institution to compile it? Very grateful for any thoughts the community has on this subject.


texts: Which method can be used to determine the pKa of an acid-base indicator like bromothymol blue?

texts:
I have a question about how one would determine the pKa of an acid-base indicator such as bromothymol blue.

I know that spectrophotometric analysis is one option, but is it possible to perform an acid-base titration to find the pKa (7.1)? How would one set up this experiment?

I was thinking I would use a pH meter/titrant curve and treat the indicator like a weak base, but what titrant would I use? Would I use a strong acid like HCl?


texts: why lattice energy have to be greater than IE and EA?

texts: Why is lowering effect of the lattice energy not able to be greater than the combined net energy raising effects of the IE &EA?


texts: Why is the carbon monoxide triple bond stronger than the nitrogen-nitrogen triple bond?

texts:
The $\ce{CO}$ triple bond has a bond enthalpy of 1072 kJ/mol while the $\ce{N2}$ triple bond has a bond enthalpy of 945 kJ/mol, at least according to my source. The molecules are isoelectronic, so I couldn't think of any way to explain it using MO theory. I've read many explanations that did not make much sense, including

Of course because they are different elements and nitrogen nitrogen bond is balanced and oxygen is more electronegative than nitrogen so it will have a greater bond strength

So my question is why is the $\ce{CO}$ triple bond stronger than the $\ce{N2}$ triple bond?


texts: What is the right way to express pH and concentrations?

texts:
Which of the following expressions are used in English to express the pH of solutions and the concentration of solutions?  I think they are all clear to someone with knowledge of chemistry, but I want to avoid awkwardness in my English.

A. I prepared a solution such as below:

a solution of pH 3
a solution with pH 3
a solution with a pH of 3
a solution of a pH of 3

And

B. I prepared a solution such as below:

a 3 nM buffer solution
a buffer solution of 3 nM
a buffer solution of 3 nM concentration
a buffer solution with a concentration of 3 nM
a buffer solution of a concentration of 3 nM

I'm not a native speaker and confused. Especially, can I use A-1, B-2 or 3 expressions?


texts: Influence of rotational degrees of freedom on gas phase stability of ions in CID

texts:
In mass spectrometry it is possible to determine the stability of an ion in the gas phase using e.g. collision induced dissociation (CID). In CID, we fragment an ion by colliding it with a neutral buffer gas. By gradually increasing the collision energy, it is thereby possible to get a relative measurement of the stability of the ion in the gas phase (so called survival yield analysis).

Now, I have the following question:

The picture below illustrates an effect that is commonly observed in CID namely that bigger ions tend to be more stable as they have more rotational degrees of freedom available to handle the collision energy transferred using CID. This can lead to counterintuitive effects, as for example in this case, one would expect acetic acid to be more acidic (and thus a more stable anion), than propanoic and decanoic acid, but it is the least stable.

In my work, I wanted to show that increasing chain lengths of the ligand increase the stability of a complex by weak interactions but I don't know how to factor in the effect that the increasing chain length has on the stabilization by the increased rotational freedom. Obviously I want to rule out that the increase in stability is due to the longer chains absorbing the collision energy better. How large could that effect be? Is there any systematic approach to take this effect into account? Is there any literature on the subject?


texts: A cylinder contains 2 kg of steam at 200 kPa and 200 $^\circ$C. Now steam is compressed at constant pressure until its temperature rises to 250 $^\circ$C. What is the work done during this compression process?


texts: I've read that Tropylium carbocation is formed by the ring expansion of benzyl carbocation. But in benzyl carbocation, the $\ce{C}$ atoms in the benzene ring are $sp^2$ hybridized i.e. $120^\circ$  is the required angle for stability. And in the benzene ring of the benzyl carbocation, the angle is already 120 degrees. Therefore benzyl ring need not expand for stability. Therefore why does benzyl rearrange to give tropylium?


texts: How do valence shell configurations affect attraction and repulsion forces between atoms?

texts: It seems clear that the electrons of one atom are attracted to the protons of another and that this is the source of attractive forces between atoms. However, it is not clear why an atom with a full valence shell such as a noble gas or covalently bonded atom is incapable of bonding or being attracted to other atoms. Are the electrons not attracted to protons in the same way? Is it because the repulsion between the electrons wins out over the electron-proton attractive forces. Furthermore, why do valence shell arrangements with few electrons bring about attractive forces?


texts: Reaction of diamines with carboxylic acids to form imidazole

texts: I've recently came across this reaction and my guess is that firstly an amide forms that later reacts with the second amine group. Is this a general reaction? Does it matter if the compounds used are aromatic?


texts: Kb values of N,N-dimethylaniline derivatives

texts:
I need the $K_\mathrm{b}$ values for ortho-, meta- and para- positions of the following compounds:

I've looked and couldn't find them anywhere.


texts: Why methanoic acid is more acidic than phenol?

texts: If you draw the resonatic structure, obviously, the conjugate base of phenol seems to be more stabilized than methanoic acid's. Then why this anomaly?


texts: Why does 2+ oxidation state become more stable relative to 3+ oxidation state for first row of transition metals?

texts:
I viewed an image showing all the possible oxidation states of each element in the first row of transition metals, and the main oxidation states highlighted in a different colour.

I noticed all elements Sc to Cr had in common a   3+ main oxidation state,
and from Mn to  Zn 2+ was the common main oxidation state.

The reason stated for this in my good textbook was 2+ oxidation state become more stable relative to 3+ oxidation state, I can't quite understand why.

So  Q : why does 2+ oxidation state become more stable relative to 3+ oxidation state  for first row of transition metals?

I had drawn the electron - in -boxes configuartion for all elements in the first row, and looked at Hund's rule and partially and fully filled orbtals, but I have not really seen a clear, fundamental explanation of why, for this question.


texts: Why is fermentation of cellulose to produce biofuel and nutrients so difficult?

texts:
The formula for glucose is $\ce{C6H12O6}$ and that of cellulose is very similar $\ce{C6H10O5}$.  Glucose can be readily fermented by yeast and other micro-organisms to produce carbon dioxide and ethanol. Whereas cellulose is not ferment-able by yeast and only very specific anaerobic Archae bacteria can digest it, but the end product being methane, water, sugars (primarily lactose), and volatile fatty acids (acetate, proprionate, butyrate); not ethanol.  These bacteria reside in the guts of termites that allow them to digest wood, and in the intestines of cattle and other ruminants.  The termites and ruminants use the sugars and fatty acids as food.

The enzymes used by the host anaerobic bacteria in the gut of termites are of particular interest because:

termites produce very little solid waste as feces
termites can digest wood, leaves, and broader variety of plant fodder than ruminants, which mainly feed on grasses

We are not really interested in the termites, nor the anaerobic bacteria, but rather specifically the enzymes and chemical processes used by the bacteria that break down the cellulose into the lactose and fatty acids.  Can this be accomplished synthetically in an anaerobic lab setting outside of said bacteria?

This article describes a company that tried to use cellulose raw material to produce ethanol on a commercial level, but recently went bankrupt.  This company apparently was not getting ethanol directly from fermentation of cellulose but rather the result of a multiple step process of generating syngas from the cellulose, then creating alcohol from the syngas; a much less efficient process than direct fermentation of cellulose into alcohol.

Obviously, such a process if achievable would relieve the need to use food crops to generate ethanol and put to use otherwise inedible cellulose plant waste. What is the main challenge here.  Cellulose is just one water molecule different from glucose.


texts: Is it true that un-dissociated HCl exists in dilute hydrochloric acid?

texts: My book says that the equilibrium constant for $\ce{HCl + H_2O}$ is so high that the reaction goes to completion. But that does not make sense since the existence of an equilibrium constant for this reaction means that there is some reactant in the equilibrium mixture. I think there is only a very small amount of reactants in the mixture. What is the truth?


texts: Find molar concentration of sodium carbonate dissolved in water

texts:
The question is

  A solution of $\ce{Na2CO3}$ is made by dissolving $5.3~\mathrm{g}$ of the powder in enough water to make $250~\mathrm{mL}$ of solution. Find the molar concentration.

I have done the following but I don't know why it's not working.

  Molar mass: $106~\mathrm{g}$

  $5.3~\mathrm{g} / 106 = 0.05\ \mathrm{mol}$

  $0.05\ \mathrm{mol} / 250\ \mathrm{mL} = 0.0002\ \mathrm{mL}$

However, the answer is $0.2\ \mathrm{mol/L}$ but I got $0.0002$. It does become $0.2$ when I multiply by $1000$ but the answer is already in $\mathrm{mL}$. How do I arrive at the correct answer?


texts: Isothermal vs adiabatic compression of an ideal gas

texts:
Could someone please explain these specific questions physically (especially the first question!)? I understand the corresponding mathematical proofs, but not the physical reasoning? I have looked online and can only find answers to what I believe correspond with my second question.

Why is isothermal work larger than adiabatic work for the compression of an ideal gas for the same change in pressure?
Why is isothermal work less than adiabatic work for the compression of
an ideal gas for the same change in volume?


texts: Will ferric nitrate or nitric acid dissolve polylactic acid?

texts: Will ferric nitrate dissolve 3D printed items? I wish to etch some sterling silver, for which we use either ferric nitrate or nitric acid, and wonder about 3d printing the design straight onto the silver to form the block against the acid.


texts:
I have seen various different contradicting statements about oxoacids of chlorine regarding oxidising strength & reducing strength of these.

I understand the trend for acidity that HClO4 is strongest and HClO is weakest , but what about oxidisind and reducing character,

Some day that HClO4 is strong reducing as well as strongest oxidising agent as well,

I understand that it will perform reduction of itself and oxidise other element but what about reducing strength?


texts: What is the structure of the hypothetical xenon octafluoride?

texts:
According to Frlec et al.,[1] theoretical studies indicated that there is a possibility (albeit slim) that neutral xenon octafluoride ($\ce{XeF8}$) might exist.

I am curious as to what structure this molecule might possibly have. In terms of hybridisation theory, I have only learnt cases up to seven-coordination ($\mathrm{d^3sp^3}$ or $\mathrm{sp^3d^3}$), where the molecular geometry is pentagonal bipyramidal. However, answers based on other frameworks (e.g. molecular orbital theory) would also be welcome.

My conjecture: could its structure possibly be hexagonal bipyramidal?

Frlec, B.; Holloway, J. H.; Slivnik, J.; Šmalc, A.; Volavšek, B.; Zemljič, A. An examination of the possibility of the existence of xenon octafluoride. J. Inorg. Nucl. Chem. 1970, 32 (8), 2521–2527. DOI: 10.1016/0022-1902(70)80296-2.


texts:
Here is the reaction of $\ce{HCl}$ with $\ce{H_{2}O}$ I found on a website

$$\ce{HCl  + H_{2}O -> H^{+}(aq) + Cl^{-}}(aq)$$
However, in my text-book, the reaction is given as

$$\ce{HCl + H_{2}O -> H_{3}O^{+} + Cl^{-}}$$
Can anyone tell me what's going on here ? Which one is correct ?


texts:
How do I determine if a process is reversible without numeric information?

It would be nice to know how to determine whether a process is reversible in order to solve problems LIKE this one:

A weather balloon is filled with Helium gas and released from the ground. It goes up 18km and achieves a diameter of 15m. Determine if the following values are greater than zero, less than zero, or equal to zero: ΔV, ΔP, ΔT, ΔU, ΔH, S_sys, S_surr, S_tot.

Here is my attempt at solving this problem. I believe at least half of my error comes from not knowing how to determine if this process, or any other process merely described, is reversible.

Obviously, ΔV increases because the balloon expands as the diameter gets to be large compared to what it presumably was at the time of release, even though the diameter at that time isn't mentioned.
ΔV > 0

ΔP < 0 because pressure decreases as altitude increases.

ΔT < 0 because temperature increases as altitude increases.

ΔU < 0 because ΔT < 0
ΔH < 0 because ΔT < 0

It seems that I have assumed that the external properties of T and P apply to the inside of the balloon, so I guess the system is reversible.
Stot = 0

Ssys = -Ssurr

I don't really know where to go from here...

I want to argue that because the balloon actually does manage to overcome gravity, it's change in volume must be pretty substantial (making the w = -PdV be what causes the balloon to go up). Maybe it's more substantial than the change in temperature, giving a large positive term due to volume in the entropy state equation listed above.
Ssys > 0

However, if the system is being looked at as the balloon itself rather than the air inside the balloon, then when the balloon isn't inflated, it has more freedom of movement than after it's fully inflated and therefore more entropy, meaning that the final entropy change of the system would be negative.

If I am correct in guessing that this process is reversible AND in guessing that Ssys > 0, then Ssurr < 0.

I would rather not have all of my answers to physical chemistry problems be guesses. How can I solve this problem without guessing? How can I know if my guesses are correct or not? How can I better approach this problem? It's possible that the correct answer to this problem is due to something that I have completely overlooked. How do I not overlook considerations while doing these types of problems?


texts: In Statistical Transition State Theory, why is the concentration of the transition state for the forward and reverse reaction identical?

texts:
For example on Wikipedia, and also in my lecture notes, it is assumed that for a reaction
$$\ce{A + B<=> AB^{\ddagger} <=> P}$$
at equilibrium,
$$[\ce{AB^{\ddagger}_f}] = [\ce{AB^{\ddagger}_r}],$$
but I don't see how the equation follows from the assumption, since there is no direct relation between transition state concentration and total reaction rate. And if it is, how can they simply be equal instead of depending on some constants?


texts: How to activate polystyrene with carboxyl group?

texts:
Is there a simple (that is one that requires few and not very exotic reagents) chemical reaction to "activate" or "functionalize" the polystyrene of a simple microtitre plate?
In other words, I would like to add carboxyl groups to the surface of a common ELISA plate to then use ethyl-carbodiimide hydrochloride and N-hydroxysuccinimide to immobilize a target on the bottom of the well.


texts:
Is there any relationship between q at constant volume and q at constant pressure that I could derive with just the reaction equation, and the enthalpy of formation and Cp of the products and reactants?
I am aware that q at constant pressure is enthalpy of formation of products - enthalpy of formation of reactants.


texts: Why does oxymercuration-demercuration always result in H2O attacking at the more substitued side but protonated epoxides don't?

texts:
In my organic chemistry textbook it states that protonated epoxides are usually attacked at the more substituted side due to more positive charge and carbocation character on that carbon. But, if one side of a protonated epoxide is primary and the other secondary, SN2 is very fast for the primary side and gives the major product (see image).
Wikipedia says that "Oxymercuration is very regioselective and ... the water nucleophile will always preferentially attack the more substituted carbon." So, I'm wondering why something like this doesn't happen for the intermediate with a similar three-membered ring during oxymercuration-demercuration.


texts: Interatomic spacing vs electric conductivity

texts:
I have a theory which may be wrong but I will write it down.If 2 elements at the same group (in solids)have the same crystal structure then the one with the biggest interatomic spacing has better electric conductivity.I don't know if anyone else has found this but I will give you 2 examples:
The crystal structure of diamond,silicon and germanium is face-centered cubic.We know that the order in conductivity of Ge>Si>Diam.
The order in interatomic spacing is Diam<Si<Ge.
Is this a coincidence or not?


texts: Why do we say "approximation" in the dipole approximation in spectroscopy?

texts:
In the dipole approximation, the following relation holds:

$$
\hat{V} = -\hat{\mu} \cdot \vec{E}.
$$

When we say "approximation", I guess we want to point out that we are dealing with linear spectroscopy, where we have the polarizability of the molecule proportional to the electric susceptibility of a molecule:

$$
\vec{p}(\omega) = k\chi \vec{E}.
$$

If the wavelength of the light is not larger than the atom size, the dipole approximation is no longer a good approximation. This is probably also true for large molecules. I'm not sure if this has to do with large molecules no longer having symmetry, so transitions might be allowed which otherwise should be forbidden.

Is this correct?


texts: How is it possible to draw a radial wave function for the 2p orbital?

texts:
Below is a picture of the radial component of the wave function distribution for the 1 through 3s orbitals. It makes sense to me that there are points where the wave function is 0, since by definition, a radial node is where the wave function = 0.

What confuses me is the following graph of the 2p orbital wave function distribution. Since the 2p orbital is shaped like a tear drop, if you went a certain distance r from the nucleus, there would be areas that the tear drop doesn't cover (since a tear drop isn't spherical). Wouldn't the probability of finding an electron in those empty space areas be 0? How can you draw a radial wave function when the 2p orbital depends on angles as well?

Source of images: http://faculty.uml.edu/ndeluca/84.334/topics/topic1.htm


texts: Carbocation rearrangement in alkene addition reaction

texts:
This is a question from my textbook:

  Determine a step-wise $S_N1$ mechanism for the overall reaction:

The solution shows the following carbocation rearrangement after Bromine leaves in the first step:

Why does the carbocation rearrange like this, going from a tertiary allylic carbocation to a secondary allylic carbocation? I thought tertiary carbocations are more stable and thus favored to be the major product? I considered Zaitsev's Rule in which the more substituted alkene is the major product, but I thought that only applies in elimination reactions.

Any clarification is appreciated!


texts: Where does the molar mass difference between N₂ and CO come from?

texts:
The molar masses of $\ce{N2}$ is 28.0134 g/mol, for $\ce{CO}$ it's 28.0101 g/mol (WolframAlpha computation).

Of course, they do have the same mass in atomic units (28). My question is, where does this small discrepancy come from? Different binding energies in the respective nuclei? I know that oxygen is a "double-magic" nucleus from an atomic physics POV, that is, it's binding energy per nucleon is higher than what would be expected. But since normally, you equate mass with energy, shouldn't $\ce{CO}$ be heavier then?


texts: Pseudo-asymmetry-like situation in alkenes

texts:
We have pseudo-asymmetric carbons in optical isomerism which dictates that if 2 groups on the carbon atom are different in terms in configuration then the carbon is chiral. In alkenes can the same thing happen with respect to geometrical isomerism? For example consider
If both the alkenes on the left were E or both Z, then certainly there wouldn't be any chance of geometrical isomerism. But as in this case if the configurations are different ,i.e, E and Z, can the alkene be contended for geometrical isomerism ,i.e., whether the compound is a Z or E isomer in terms of the middle alkene (to which a methyl group is attached)?
While giving the answer to this question, it would be extremely helpful if you cite the source of your information for me to look it up.


texts: As we go down a fluoride-alkali metal series, why doesn't the boiling point decrease?

texts:
As you can see from the graph below, as we go down the blue fluoride-alkali metal series (alkali metal ion is varied from Lithium to Rubidium, which is represented by an increase in ionic mass on the graph), the boiling point increases then decreases.  This is contrary to my expectation that the boiling point should continuously decrease due to an increase in ionic radius.  The charge is obviously not a factor because it is consistent throughout.  What could be the factor that causes this deviation?

Thanks!


texts: Explaining redox reactions to a 6 year old?

texts: In a similar vein and for pretty much the same reason as I post this question on the Physics.SE site, what would be a an effective means to promote understanding about redox reactions to a 6 year old?  In particular, what (if any) simulations are available?


texts: Why is there a bulge at the top of my volumetric flask?

texts: Sometimes volumetric flasks are designed with a bulge in the neck right below the stopper opening. What is the design intent of that bulge?


texts: The reaction of iron with sulfur to produce Iron(II) sulfide is inconvenient (for me)

texts:
I am taking a lot of iron properties this semester, but I have found some contradicting piece of information about the reaction of iron with nonmetals illustrated with two cases
\begin{align}\ce{ **First Case** }\\\end{align}
If we react the iron with chlorine, only FeCl3 will result as following:

$$\begin{align}\ce{2Fe +3Cl2 &->[\space \Delta ]2FeCl3}\tag{1}\\\end{align}$$

No FeCl2 has produced because iron prefers to have oxidation state at +3 as sublevel 3d will be half-filled.

One case that FeCl2 will result when H2 exists as
$$\begin{align}\ce{Fe +2HCl &->FeCl2 +H2}\tag{2}\\\end{align}$$
In this situatuon if any Fe2Cl3 formed, H2 will reduce it to FeCl2
\begin{align}\ce{ **Second Case** }\\\end{align}
Although, Iron favor +3 oxidation state (as illustrated in 1), If we react iron with sulfur; it will actually favor +2 oxidation state as follows:
$$\begin{align}\ce{Fe +S &->[\space \Delta ]FeS}\tag{3}\\\end{align}$$
I tried to find a convenient way that explains how this happen (as the way illustrated at 2), but

I failed to do so. I am really confused:

Does the iron actually favor +3 state or not?

If yes, Why 3 happens? Why there isn't any Fe2S3 in the products?

If no, Why 1 happens?

Is this has to do anything with some hidden conditions or unobvious reaction mechanism?


texts: Why does HCO₂⁻ exhibit delocalized bonding while CO₂ does not?

texts:
$\ce{HCO_2^-}$ exhibits delocalized bonding and $\ce{CO2}$ does not?

What I am confused about is, that both of them have resonance structures. Therefore, why doesn't $\ce{CO2}$ exhibit delocalized bonding?


texts: For homogeneous equilibrium, why are liquids and solids included in the equilibrium constant (when they aren't in heterogeneous equilibria)?

texts:
In a heterogeneous reaction (where the states are varied) we do not include liquids and solids in the equilibrium equation because their concentrations do not change.

E.g. Chemguide.co.uk

However, when it is a homogenous equation we DO include solids and liquids.

E.g. Chemguide.co.uk

1) Why do we include liquids and solids in the Kc equation in homogeneous equilibrium equations? I get that if we didn't there would be nothing on the right hand side of Kc=.... , but why is it physically different to the case where there are varied phases?

2) What if there was an equation that involved only liquids and solids  (if this is possible)? As this is a heterogeneous equation would we still not include solids and liquids? If so how would you write the Kc equation where there is nothing but solids and liquids?


texts: So a beam of white-light photons passes through a gas and various photons, having exactly the same energy as the gas's molecular energy transition state deltas, get absorbed. We then get a characteristic absorption pattern. But wait a minute, don't the energised electrons fall back to their ground states within a nanosecond and create photons of precisely the same energy as those that caused the disturbance? How come we still see the absorption band?


texts: Does precipitated copper carbonate contain impurities

texts:
I recently performed a double replacement reaction between copper sulfate and sodium carbonate to yield copper carbonate as a precipitate. I then filtered the precipitate, but I noticed that the precipitate still contained a large amount of water.

Would there be a significant amount of sodium sulfate dissolved in this water, making the copper carbonate impure? If so, how would I separate the remaining sodium sulfate from the copper carbonate?


texts: How can I generate 250 GPa to create metallic hydrogen?

texts:
In the preparation of metallic hydrogen, how does one conjure up such immense pressures?

I mean, I read that something like diamond anvils were used to contain the hydrogen, but now, in accordance with Newton's 3rd law, shouldn't the diamond also face the same extreme forces?

I mean a 10 on the Mohs scale is very high, but how does that suffice to withstand the immense force applied back by the compressed gas?


texts: How to determine the correct InChI for a certain compound?

texts:
Let's say I have a compound L-xylulose 1-phosphate and I want to know its correct InChI, how to do this? The reason I ask is because when I go to different databases I get different results:

ChEBI:

$\ce{C5H11O8P}$

InChI=1S/C5H11O8P/c6-1-3(7)5(9)4(8)2-13-14(10,11)12/h3,5-7,9H,1-2H2,(H2,10,11,12)/t3-,5+/m0/s1

NIKKAJI; link taken from KEGG:

$\ce{C5H11O8P}$

InChI=1S/C5H11O8P/c6-3-1-12-5(8,4(3)7)2-13-14(9,10)11/h3-4,6-8H,1-2H2,(H2,9,10,11)/t3-,4+,5?/m0/s1

ModelSeed:

$\ce{C5H10O8P}$

InChI=1S/C5H11O8P/c6-3-1-12-5(8,4(3)7)2-13-14(9,10)11/h3-4,6-8H,1-2H2,(H2,9,10,11)/t3-,4+,5?/m0/s1

So, ChEBI and NIKKAJI do show the same chemical formula but different InChI expressions, while NIKKAJI and ModelSeed differ regarding their chemical formula but have the same InChI (which seems wrong, as ModelSeed's InChI suggests that it also als 11 Hs). But this would still not explain the differences for the first two...

That all looks quite fishy to me; how can I now decide which of the databases show me the correct information? Is it possible that one gets the same InChI for compounds that differ in their chemical formula (I thought this wouldn't be possible)?


texts: Finding the wavelength of maximum absorption and Crystal Field Splitting of [Ni(H2O)6]2+

texts:
(I haven't been here for a long time, so tell me if my formatting is fine)

Given

  The $\ce{[Ni(H2O)6]^2+}$ complex appears green in solution from the transmitted light. Estimate the wavelength of maximum absorption, and also the crystal field splitting $Δ_0$.

I got 1.59ev for the CFS, but I want to verify if I'm doing this right.

I wasn't sure if I also need to know the wavelengths of light and spin pairing energy for this problem. So I just looked up the average wavelength of red light (650nm) and plugged it in (and ignored spin pairing energy since my prof never talked about it)

My Method

Since H20 isn't charged, so Ni is 2+ to make this complex 2+.
Since $\ce{Ni^2+}$ is $[Ar]3d^8$, and water makes a weak ligand field, I basically did Crystal Field method and filled the bottom row (t2g) with 6 electrons and put the remaining 2 electrons in eg.

I then used stablization energy: $ΔE = -6(2/5)Δ_0+2(3/5)Δ_0=-6/5Δ_0$

And then $ΔE = hv = hc/λ= 6/5Δ_0$ (I think I can exclude that negative sign since I'm just finding the splitting)

to get $Δ_0 = 5hc/(6(650nm)) = 1.59ev $


texts: Why are copper, iron and lead so common in everyday use?

texts:
Copper, iron and lead are commonly used around the world in construction,
for pipes and in electrical wiring. Why are these used instead of zinc and magnesium?


texts: What is the "‡" symbol meaning in a reaction mechanism?

texts:
I was studying hydroboration from Clayden's Organic Chemistry [1, p. 1281] and the transition state had “‡” symbol in the upper right corner of the activated complex:

  We know that this is not the whole story because of the stereochemistry. Hydroboration is a syn addition across the alkene. As the addition of the empty p orbital to the less substituted end of the alkene gets under way, a hydrogen atom from the boron adds, with its pair of electrons, to the carbon
  atom, which is becoming positively charged. The two steps shown above are concerted, but formation of the C–B bond goes ahead of formation of the C–H bond so that boron and carbon are partially charged in the four-centred transition state.

What does this symbol mean? I have seen it before as a superscript at the Gibbs energy symbol.

References

Organic Chemistry; Clayden, J., Ed.; Oxford University Press: Oxford; New York, 2001. ISBN 978-0-19-850347-7.


texts: What's the point of solubility products?

texts:
What is the advantage of solubility products, e.g.

LiF(s) ⇄ Li+(aq) + F-(aq)  |  K = [Li+(aq)] * [F-(aq)] = 0.00184 M2 at 25°C (source)

compared to just stating that

Solubility in water = 0.134 g/100 mL (25 °C) (source)

(There's a little difference between (0.00184 M2)½ = 1.11 g/L and the solubility of 1.34 g/L above; I take it that's because of the difference between activity and concentration?)

It seems to me that solubility products are just a roundabout, complicated way of expressing the concentration of a saturated solution. I suspect that I'm missing something though: otherwise why would people publish long lists of solubility products?

What I read: Wikipedia; all my high school textbooks.


texts:
Setup

Consider a closed binary mixture of known total molar composition $n_i$, held at volume $V$ and temperature $T$.  The equilibrium phase composition is determined by $\mu_i^{vap} = \mu_i^{liq}$. Assume the vapor is an ideal gas mixture, the liquid is an ideal mixture, Poynting's correction is negligible, and $V_{liq} \ll V$. Then Raoult's law holds:

$$y_i P = x_i P_i^{sat}(T)\quad \tag{1}\label{1}$$

Simplify

For convenience, denote vapor quantity = $v_i$, liquid quantity = $l_i$, total quantity = $n_i=v_i+l_i$, and "saturation quantity" = $s_i=\frac{P_i^{sat}(T)\,V}{R T}$.  A closed system means $n_i$ are constant, and $s_i$ are constant at constant $T$.  For simplicity, choose units such that $R T = V = \sum_i n_i=1$, so that Raoult's law becomes

$$ n_i - l_i = s_i \frac {l_i}{\sum_i l_i} \tag{2}\label{2}$$

where $l_i$ are the only independent variables.  (The solution/result is independent of these choices. It holds for any Raoult's law system at constant $N, V, T$. It generalizes to infinite systems with fixed $\sum n_i/V$.)

Question

Eq. ($\ref{2}$) can be algebraically solved.  But it has no solution when $s_1>1$ and $s_1 - n_1 ≥ n_2 \frac{s_1}{s_2}$.  For example, if $s_1=2$ and $s_2=1/2$, then no solution exists when $n_2≤1/3$ ($x_2=y_1$ and $y_2=x_1$ at $\lim n_2\to \frac{1}{3}^+$).

This seems to predict that any generic species can form an uncondensable mixture if one is uncondensable (as a pure component), and there are few enough of the condensable species.  Is this correct?


texts: The increasing order of reactivity of substituted benz0yl chlorides towards nucleophilic substitution

texts:
Arrange the following compounds in the order of their increasing reactivity towards nucleophilic substitution:

The answer to this question is $[3<2<1<4]$. We have to compare the positive charge density on the carbons to which leaving group is connected. In $(1)$, the phenyl ring shows negative inductive effect but my teacher did not mention anything for that. In $(3)$ and $(4)$ the connected groups ($\ce{OCH3}$ and $\ce{NO2}$) show +M and -M respectively. But, they also show -I effect. Why are we ignoring the inductive effect?


texts: How to determine the valence electrons of D-block elements in their mono atomic form?

texts: For s and p block we can determine the valence electrons easily,but what about d-block elements. How to determine their valence electrons?


texts: Show which group the element with Z=31 belongs

texts: and I understand it belongs to the 13 th group, but my teacher wants to express it as IIIA, so how should I convert it in my mind?


texts: Nomenclature and bonding of the complexes ions

texts: Why the nitrogen and not the sulphur in the SCN is bonded to the chromium?


texts: Strength of nucleophiles among SN1 and SN2 reactions

texts:
As per the theory of chemistry, we say that unstable carbocations undergo SN2 reactions as it involves strong nucleophile. As a consequence, it does not lead to the formation of reaction intermediate, i.e. a carbocation.
Similarly, in stable carbocations undergo SN1 reaction by substitution of a weak nucleophile.
Why necessarily weak nucleophiles are involved? In case of SN2, since the carbocation is unstable, a strong nucleophile which prevents the formation of carbocation. But in SN1, since stable carbocation is involved, why shouldn't both strong and weak nucleophiles be involved?


texts: Why is the amino acid cysteine classified as polar?

texts: Cysteine amino acid has an embedded sulfur group in its side chain. Looking at the electronegativity difference of hydrogen and sulfur, it can be considered a non-polar side chain because the electronegativity difference is less than 0.5. This makes it non-polar but still we put it in polar category, why?


texts: Geminal diols or triols are very unstable and are easily converted into keto or carboxylic compounds. Triethyl orthoformate is a triether of similar structure. I want to know why the former is so unstable and the latter stable.


texts: How to determine which of two similar compounds has the larger dipole moment?

texts:
I am solving some problems involving the order of dipole moments of some compounds. I could solve most of them but the following:

Which has greater dipole moment?

$\ce{CH3F}, \ce{CH_3Cl}$

Since fluorine is more electronegative my assumption was that $\ce{CH3F}$ should have a larger dipole moment.
On the other hand since the angle between the dipole moments is less in 3-nitro phenol than in 4-nitrophenol, my assumption was that 3-nitro phenol has a greater dipole moment. But this contradicts the answer given.


texts: How do catalysts provide alternative routes for reactions?

texts:
According to collision theory, a reaction will take place between, say, two molecules, if the collision between the atoms has a sufficiently high kinetic energy (to meet the activation energy threshold) and have the correct orientation. If these two conditions are not met, the collision will not result in a reaction.

However, there is one way to make a reaction easier, and that's with the use of a catalyst. Catalysts do not lower the activation energy or increase the kinetic energy, as I've just learned trying to figure out this question, but they provide an alternative activation energy, lower than the initial one, that, if met, will allow the reaction to take place.

My question is this: what is the actual chemistry behind how catalysts provide this alternative route? What's happening with the molecules or atoms? How does it work?

For example, if I wrap zinc in oxidized copper wire and mix it with some hydrochloric acid, the oxidized copper will act as a catalyst for the reaction between zinc and hydrochloric acid. I'm not sure how this takes place, though.

Thanks.


texts:
Sometimes we say that electron has volume, as in orbital we can define it's volume (at least for some fraction, as orbital itself has no limit, it is spread all over the space expect nodes).

On other hand in general chemistry books often spin quantum no. is referred as electron spinning on its axis. But this is absurd, because this magnetic angular momentum is an intrinsic property of the electron. Also that an electron is an elementary particle, it is 1-D (no volume), so it's not possible for an electron to spin on it's own axis.

So what's the matter, do electron has volume or not?

What I think that it's a particle, but we can't describe it's position what we can do is probabilistic approach, we can only describe some region where we can find it more likely or less likely. We defined it's volume, otherwise electron themselves has no volume. Even it is more weird that electron is everywhere in the orbital ;D

Can somebody explain it?


texts: Low solubility of propanal compared to propanol, propanone, propanoic acid and methyl ethanoate

texts: I found on the internet that propanol, propanone, propanoic acid and methyl ethanoate where all completely soluble in water at room temperature. (23 degrees Celsius) But I found that propanal was, comparatively, was not completely soluble in water (Wikipedia said it was 20g/100ml). I was wondering why it was not completely soluble like all the others as small aldehydes can interact with hydrogen bonds and dipole-dipole forces with water (like all the others). Is there some other intermolecular force that influences solubility that I'm missing?


texts: Is it possible that in a water soluble polamerization, by injecting some additional initiator, the monomer concentration increases?

texts:
I have a simple polymerization process with the following kinetic mechanism:

$$I_2 \stackrel{k_d}{\rightarrow}2\dot{I}$$
$$\dot{I}+M\stackrel{k_p}{\rightarrow}\dot{P_1}$$
$$\dot{P}_i + M\stackrel{k_p}{\rightarrow}~~\dot{P}_{i+1}$$
$$\dot{P}_i + \dot{P}_j\stackrel{\frac{1}{2}k_{tc}}{\rightarrow} D_{i+j}$$

This polymerization is taking place in a tubular reactor.

By default, the initiator is injected at the inlet of the reactor. Now, in addition to this injection, I have added another injection of the initiator at the middle of the reactor. I am expecting that the monomer concentration at the reactor outlet reduces, but this does not happen. Indeed, the monomer concentration at the reactor outlet increases.

I wanted to ask you guys, if such a behaviour is possible?


texts: What method do I use to synthesize propyl-2-(2-methylpropyl)-ether and why?

texts:
I need to know which method to use to synthesize propyl-2-(2-methylpropyl)-ether.

I considered electrophilic addition of alcohols to alkenes, but I'm not really sure how the method works, and anything I found on it was hard to understand. From my understanding I need to "add" electrophilically activated alkenes to alcohol.

I don't really know what that means. I was thinking of using t-butanol and propylene, but the whole part of electrophilically activated alkenes threw me off. Any advice or help is greatly appreciated!


texts: Can oxidizing agents be used to increase the combustion efficiency of waste oil?

texts:
Waste oil is atomized and combined with air to produce a very high temperature flame capable of melting iron. I was wondering if it's possible to further increase its combustion efficiency by mixing it with an oxidizing agent such as Sodium Perchlorate, Hydrogen Peroxide or some other oxidizer in mixable form.
Conceivably, it could enhance the combustion since it adds more oxygen to the fuel, especially at higher temperatures. At the same time, it could also inhibit the combustion since the additive may absorb energy from the reaction than it produces, since it's already an oxide.


texts: Can a table salt + vinegar mixture be explosive?

texts:
I remember having read in a book, Ask Me Anything (Dorling Kindersley), that a combination of copious amounts of table salt and vinegar is explosive.

Now this was a really long while back, and I can't even find my copy of the book anymore. But I'm quite sure there was a mention of salt+vinegar being explosive.

Simply knowing the composition of table salt and vinegar doesn't seem to help in any way. I really don't see any reason for some sodium, chlorine, acetate and hydrogen ions floating around in a bowl to simply react in some godforsaken way and explode. Heck, all salt+vinegar seems like is a good Pringles flavor. I did take into consideration possible impurities in table salt, like other sodium, potassium, calcium and magnesium salts, but even then, I don't see why the explosion would occur at all. I though of iodized salt too, but still, an explosion seems a little far-fetched.

Now the book did mention 'large' quantities of salt and vinegar, maybe there could be something to that?

Is the book correct? If so, what concentration of salt and vinegar have to be used?

I did conduct an internet search, but nothing really turned up.

[ I suspect, the book might've meant baking soda instead of table-salt. Baking soda combined with vinegar in a closed plastic bottle could pass for an 'explosion'. ]


texts: Graph theory, isomer enumeration and chemical graph theory

texts: Where could we find a good description of graph theory applied to the general problem of isomer enumeration and chemical graph theory?


texts: Is heat a form of energy or is it just a transport of energy, not energy itself?

texts:
In every textbook I read, it says that heat is a form/type of energy... but in lecture, my professor said, that there is no such energy as heat and that heat is just a method by which we can transport energy to another system. Do these 2 statements say the same and I'm just reinterpreting the first one badly. If I were to say in my own words what heat is just based on the textbook's definition, I'd say that heat is energy, that... But if I were to say it by the lecturer words, I'd say that heat is a disordered transfer of energy, not energy itself.
What's more correct?


texts: Obtain chemical insight from neural network results

texts: I have recently read many papers where neural networks (NNs) are trained to predict chemical properties (starting from the structure of small chemical compounds) for compounds rather close to the ones with which they were trained. In some cases the predictions are rather good. But I see that apart from the predictive capability, people use NNs as "black boxes" in the sense that they do not tell you or give you chemical insight about why that compound has that value for that predicted property. At least that is my impression now. So my question here is, do you know cases where useful chemical information can be extracted from NN predictions?


texts: How long did the most difficult compound to synthesize last?

texts: I heard that the most difficult compound to produce was a molecule that included Argon because it is a noble gas. I was wondering how long it was stable for.


texts: What do the horizontal lines in a P-V phase diagram mean?

texts:
I have been studying phase diagrams of pure substances, and for a substance such as carbon dioxide for example, it's diagram looks something like this:

The horizontal lines in the liquid phase puzzle me. It seems if we shrink the specific volume by a certain amount, the pressure change is much much less. This doesnt seem to be what is observed in reality (liquids have a very high bulk moduli and are generally considered incompressible), which would require a large pressure change for a less change in specific volume. The solid phase has vertical lines, which seems to be true, but the liquid portion baffles me.

Can someone please help me understand what I'm missing here?


texts: With respect to chemical bonding does the $\ce{I2-}$ ion exist?


texts: Why Li can't make it's Peroxide when heated with more O2?

texts:
Every first group metal reacts with $\ce{O2}$ and makes there monoxide at room temperature.

But it says that $\ce{Li}$ does not make peroxide when heated with more $\ce{O2}$. But other metals in that group do.

Why $\ce{Li}$ can't make it's Peroxide when heated with more $\ce{O2}$?

And if we give the heat continuously with more $\ce{O2, K, Rb, Cs}$ give there Super-oxides. In that time Both $\ce{Li}$ and $\ce{Na}$ do not gives there Super-oxides. What is the reason for it?


texts: Is there a better equation than the Nernst equation for low concentrations?

texts:
The Nernst equation can be applied to the whole cell reaction or a half-cell reaction. Consider the half cell reaction:
$$\ce{Cu^{2+} + 2e^- -> Cu(s) \quad \quad E^0 = +0.337~\rm{V}}$$

The Nernst equation expressed in base 10 log at 25 °C is:

$$E = E^0 - \frac{0.1596}{2}\log_{10} \frac{a_{\ce{Cu^2+}}}{a_{\ce{Cu}}}$$

But $a_{\ce{Cu}} = 1$ by definition, and for low concentrations of $\ce{Cu^2+}$ where $a_{\ce{Cu^{2+}}} \ll 1$ then: $\ce{[Cu^2+]} \approx a_{\ce{Cu^2+}}$.

But when $\ce{[Cu^2+]} < 1$ then the log will be negative so:

$$\lim_{\ce{Cu^2+}\to 0} (0.337 - 0.0798 \times \log_{10} [\ce{Cu^2+}]) = \infty $$

This doesn't seem realistic. For instance $\ce{[Cu^2+] = 1.0\times 10^{-1,000,000}}$ is fine mathematically, but that sort of concentration doesn't make any sense chemically.

Thus what is the limit of the half cell potential as the $\ce{[Cu^2+] -> 0}$?

Edit-1 - My gut reaction to this is that you can't really measure the activity of a single ion. If the ion of interest is low in concentration compared to the ionic strength in general, then it would seem that the activity of that ion should go to zero as its effect on the total overall ionic strength goes to zero.


texts: What is the simplest approach to balance a complex reaction equation?

texts:
Consider the redox reaction:

  $$\begin{multline}
\ce{ a K4Fe(CN)6 + b Ce(NO3)4 + c KOH ->\\ d Ce(OH)3 + e Fe(OH)3 + f H2O + g K2CO3 + h KNO3}
\end{multline}$$

The book's answer for the coefficients $a, b, c, d, e, f, g,$ and $h$ is $1, 61, 258, 61, 1, 36, 6$, and $250$. The final answer for the problem is the sum of the coefficients which is $674$.

I have tried balancing it by using the general methods such as oxidation number method, ion-electron method, etc. However, they seem to be giving me incorrect equations. The answer given by the book is perfectly correct. I am sure of it, as I multiplied and checked each atom on both the sides, and they checked out completely. Also, the coefficients don't have a common factor other than 1.

What is the simplest way to solve this problem?


texts: Determining reaction formula from optical absorption graphs

texts:
The rate of a reaction between A + B was followed spectroscopically at three different wavelengths, and the percent absorption at each wavelength was plotted as a function of time.  Which of the following mechanisms is consistent with the spectral data?

  (a) $\ce{A + B -> C}$
  (b) $\ce{A + B -> D, D -> E}$
  (c) $\ce{A + B -> F, A + B -> G}$
  (d) $\ce{A + B -> H, H + A -> I}$
  (e) none of the above

The correct answer is (b), which I can believe, but not sure why.

So, it can't be (a), because in $\lambda_2$, the curve went up then down, indicating the presence of an intermediate. However, I'm not sure why this can't be (d) or (c) as well. As long as F, G, and H are active at $\lambda_2$, then wouldn't all of the reactions show a similar curve?

I'm not sure what to do with $\lambda_1$ and $\lambda_3$, as I think they just tell me that A + B is consumed, and that the product and/or intermediates aren't active at either $\lambda_1$ or $\lambda_3$.


texts:
The ionization constant of benzoic acid is $6.46 \times 10^{-5}$ and solubility product for silver benzoate is $2.5 \times 10^{-13}$. How many times silver benzoate is more soluble in a buffer of $\mathrm{pH}$ 3.19 compared to its solubility in pure water?

Equation used to calculate solubility of silver benzoate in water:

$$\ce{C6H5COOAg <=> C6H5COO- + Ag+}$$

I've calculated the solubility of silver benzoate in water , it is $5 \times 10^{-7} \pu{mol/L}$ (since that is all I calculated, this is the only equilibrium equation I know).

But I cannot understand what to do next.


texts:
'application of the BET equation should be restricted to the range where the term n(1 – p/p0) continuously increases with p/p0'see 5.2.2 in the reference
This is one of the criterias IUPAC proposes for BET to be applied to micropores.
What is the physical meanning of n(1 – p/p0) and why does it need to increase?


texts: Can you in reality give neon a charge of +8?

texts:
First off, I am currently confused about why neon can even be ionized at all. But since it can be ionized, this is the energy required to give a mole of neon a charge of +8: 207,390,000 joules!! Or ~0.5 GJ! Giving one-fifth of a kilogram of neon the maximum charge would be like the energy from 50 armor-piercing rounds of the ISU-150 assault tank, or approximately one Tour-de-France! Charging up one kilo of neon would be basically either throwing a lightning bolt or melting a tonne of steel.

My question is, what insidious chemical or procedure could rip away all of neon's electrons like that? Or is it just simply impossible to do?

I suspect that it is possible to do (otherwise how would they be able to calculate the energy expenditure), but how is the question.


texts: Why does solvent particles move towards solution when semi permeable membrane is added?

texts: When a SPM is added in between solute and solution the water molecules move towards salt water even though the concentration is same both sides. Why does this happen? According to SPM's perspective, concentration (of water) at salt water side is lower than that at fresh water side but how does that change the fact that the overall concentration is same both sides? My book says it depends on vapour pressure. If that's the case then osmosis should take place without SPM because it depends only on vapour pressure?


texts: Formation of Hydrogen - from a proton and an electron

texts:
If I place a proton and an electron close to each other, can they form an atom of hydrogen? Why or why not? Please explain the scenarios where this is not likely/unlikely.

Personally I doubt it, since the electron would have to spin around the proton to call it an atom.

Can it be well-explained by classical mechanics?

How does quantum mechanics explain this sort of a possible bonding? I mean,an electron and a proton can't collide with each other because they would have had infinite attraction between them (that is they would act like magnets), and we know that this does not happen.

Is there something in QM that defines a minimum distance of some sort that is relevant to the proton-electron forming hydrogen?


texts:
I am trying to determine two of the theoretical values for the enthalpy of the combustion of methanol.

I have calculated (using Hess' law) that the $ \Delta H_{\mathrm {reaction}}\; = -1453.418~\mathrm{kJ~mol^{-1}} $, which is correct according to several sources. However, when I tried to calculate the $ \Delta H_{\mathrm{reaction}} $ using the bond dissociation and formation method: $ \Delta H_{\mathrm{reaction}}\; =\; \sum{\Delta H_{\mathrm{bonds\; broken}}}\;-\; \sum{\Delta H_{\mathrm{bonds\; formed}}} $

I got a value of $\mathrm{-464.9~kJ~mol^{-1}}$. I am just wondering if this is correct, or if I have made a mistake somewhere?

Ps: My balanced equation looks like this: $$\ce{2CH3OH + 3O2 -> 4H2O + 2CO2}$$

I used this table to get the known values for the various bond energies.

Thanks


texts: Crystal structure in function of pressure

texts: If you were to investigate crystal structure changes as a function of pressure, which metals would you study first? Last? Why?


texts: Why are powder XRD axes sometimes plotted in reverse?

texts: Just plotting some powder XRD data and I wanted to know why the axes in some of the literature that I'm looking at is plotted in reverse. Is there a reason it starts at 60 Degrees (2 theta) and then goes down toward zero?


texts: Effect of solvent in the reaction of alkyl halide with nitrite ion

texts:
$$\ce{RX + NaNO2 -> ?}$$

Is there a difference in the outcome of the reaction if the solvent is changed from an alcohol (e.g. EtOH) to a polar aprotic solvent such as DMSO or DMF?

I have two books - one book mentions an alcoholic solvent gives $\ce{RONO}$ as product; the other mentions $\ce{RNO_2}$ is the product in DMSO/DMF. Can anyone please confirm?


texts: Why is chromate coloured but tungstate colourless?

texts: I have to try and work this out using the tetrahedral molecular orbital diagram for $\ce{[WO4]^2-}$ but I am confused as both are $\mathrm d^0$ right?


texts:
I've done a very similar reaction to the one below but by TLC I observe only starting materials. It's super clear that nothing else is going on. Conditions: K3PO4, Pd(dppf)Cl2, dioxane/water, heat to 100 deg.C.

What thoughts do you have on why this doesn't work?

I imagine the alkyne chelating to the Pd and potentially 'poisoning' it? I currently lack the words and technical lingo to put this into a formal explanation.
A competing Sonogashira perhaps? Unlikely given the aqueous conditions.
Any other issues?


texts: How to verify that ethanol is infinitely soluble in water?

texts:
My textbook [Chemistry Live, Declan Kennedy] states that ''Ethanol is said to be infinitely soluble in water''. It then says ''verify this for yourself by mixing some ethanol with water in a test tube''.
Both water and ethanol are colourless. How can I observe that they are infinitely soluble ?


texts: Why is the titratable acidity of my wine going down as it ages and oxidises?

texts:
I am currently studying chemistry in grade 12 studies and I have come across a halt in my investigation.

The experiment was to see how the increase in ethanol would lead to a more acidic wine, because ethanol oxidises to ethanal and then to acetic acid. However, the inverse has appeared to happen throughout the 15 days of the test. Inbetween the tests, the wines were stored in an airtight bottle however they had a chance to oxidise while we opened them to test them.

Why is the acidity of the wine decreasing when the increase in reactants should also result in the bias towards the product side? My tests have yielded the opposite to what I expected (titratable acidity going down by almost half of what it was initially by the end of the 15 days) and I cannot explain it in my discussion.


texts: What is the heat energy required to perform electrolysis equivalent?

texts:
The question may be off-topic here. If my concept is flawed, please poke me in the rib (+:

Sources on the internet indicate a minimum 1.2Volts is adequate for electrolysis of water; nominally 6V. Applying a DC source to water provides adequate energy to break the hydrogen bond. Apparently some heat is also released in the process..

Say, one were to collect 100ml (an arbitrary figure) oxygen by electrolysis applying 6V DC to 1 Litre of water.

Can the energy to break the hydrogen bond be provided by applying heat to water? All other things being identical, how many calories would be required to collect the same amount of oxygen from the same volume of water?


texts: Is this a plausible reaction mechanism? (H2SO4 cyclization after Friedel-Crafts)

texts:
in my undergraduate chemistry lab we synthesized the substituted benzene on the left in a Friedel-Crafts reaction.
As a next step we're supposed to reflux for 1.5h at 90°C with concentrated sulfuric acid and obtain the product on the right. A bicyclical product.

We have to come up with a plausible mechanism for the ring closure reaction and I am unsure that what I came up with makes sense or not.

Thank you!

edit: this is the FC reaction we did in the first step:

The Steps for this reaction are as follows:
To a Solution of AlCl3 in abs. DCM the following reagents were added:
-3-chloropropionic chloride.
-p-xylene.
The reaction mixture was stirred at rt for 1h.
Then added to a mixture of 1:1 conc. HCl and ice water.
Then extracted with DCM in a separatory funnel.
Washed twice with a sat. NaCl solution.
The organic phases were dried with MgSO4.
The DCM was then removed in the rotary evaporator.
A yellow-orange Solution was left at the end.
It was left to crystallize over night.

Now this is where the second part happens, the H2SO4-cyclisation reaction.
.......
Some comments suggested that there might be a hydrolyzed intermediate with a displaced chloride. Here is my take on how that would look like:


texts: Figuring out the concentration of weak polyprotic acids in presence of strong acid

texts:
We have a $\pu{0.1 M}$ solution of $\ce{H2S}$ with a $\pu{0.1 M}$ solution of $\ce{HCl}$. We need to figure out the concentration of $\ce{S^2-}$ ions at equilibrium.
$$\ce{H2S <=> HS- + H+}$$
$$\ce{HS- <=> S^2- + H+}$$
Given $K_{\mathrm a_1} = 9.1 \times 10^{-8}, K_{\mathrm a_2} = 1.2\times 10^{-13}$.
I have no idea how to do this problem. I can't relate the $\ce{S^2-}$ concentration to the first equation. I first tried determining the $\rm{HS^-}$ concentration from the first equation, then putting that into the second one to obtain the required concentration, but then I realized that as the second reaction approaches equilibrium, the concentrations of the $\ce{HS-}$ ions will change, which will then throw the first reaction out of whack.
I tried taking the required concentration as $\pu{y M}$ and then tried to establish a relationship, but the only thing I could get was that the concentration of the hydrogen ions will go up by $y$, which is of no use at all.


texts: Periodic Trends of Zeff and Electronegativity

texts:
The effective nuclear charge $Z_\mathrm{eff}$ increases from left to right and from top to bottom. Can you explain why it increases from top to bottom?

Also can we explain the periodic trend of electronegativity using the shielding effect?

EDIT:
The calculation of $Z_\mathrm{eff}$ for Li would be 1 (3 protons − 2 core electrons). For Na is 1 (11 protons − 10 core electrons). So far it doesn't seem to me that $Z_\mathrm{eff}$ should increase from top to bottom. Considering the fact though that for Na there are more electrons shielding the only valence electron than Li as well as Na's electron is relatively more distant than that of Li, the first should be experiencing less $Z_\mathrm{eff}$. This is not true however. As far electronegativity is concerned I can't come up with a neat explanation.


texts: Why does ice water get colder when salt is added?

texts:
It is well known that when you add salt to ice, the ice not only melts but will actually get colder. From chemistry books, I've learned that salt will lower the freezing point of water. But I’m a little confused as to why it results in a drop in temperature instead of just ending up with water at 0 °C.

What is occurring when salt melts the ice to make the temperature lower?


texts: Chemical in (s) mixed with chemical in (aq) vs. chemical in (aq) mixed with chemical in (aq)

texts:
Hopefully the title is comprehensive enough.

But I am wondering, does it make a difference if you take a powder and mix it with an aqueous solution or take a solution with the very same chemical formula as the powder and mix it with the same aqueous solution?


texts: What is the stability order for these octahydrobiphenylene structures?

texts:
According to me most stable is Z because it has maximum alpha hydrogen,
Between X and Y both have same alpha hydrogen, but X has conjugation. So it is more stable than Y.

So Order is Z>X>Y.
Is my explanation correct?


texts: charge transfer between layers of graphite with stacking fault

texts: As a general rule, we only expect two parts of a system to have the exact same amount of charge if they are symmetry-related to each other. How much charge transfer would occur in graphite with a stacking fault (e.g., with stacking ABABABCBCBC...), due to the layers no longer being all symmetry-equivalent as in pure Bernal graphite?


texts: Reaction of aluminum hydroxide and nitric acid

texts: I've been focusing a lot on aluminum hydroxide recently, or specifically breaking it down into its base components. I know that when aluminum hydroxide dissolves in nitric acid it forms aluminum nitrate ($\ce{Al(NO3)3}$), which decomposes when it boils into aluminum and nitrogen dioxide. The end goal of this process is to recover the aluminum from the aluminum hydroxide, but that can't be done until the aluminum hydroxide dissolves into the nitric acid. I don't know if aluminum hydroxide readily reacts with nitric acid or not. Can aluminum hydroxide react with nitric acid readily? Or does it need to be catalyzed, or should I use a different reaction to isolate the aluminum?


texts: Mechanism for bromoetherification of olefinic alcohol

texts:
Propose a mechanism for the following reaction showing the relevant stereochemistry of intermediates and the final product.

I am confused as to what is going on here. I guess there's some sort of neighboring group participation after the formation of the bromonium intermediate. From the molecular formula of the product, I deduce the mechanism seems to proceed via an addition and subsequent elimination. But then again I'm not very sure.


texts: A Tool to atomize liquid in the milliliter range

texts:
for some graduate project I'm trying to create a mist from some water based solution to apply it to a surface, basically the surface is solid but very gentle and I need to spray it with this solution as evenly as possible, I cannot apply the solution with a syringe and then spread it around since this will pattern the surface, also the volume applied to the surface is important, I need to spray 2ml+-0.5ml, spraying 4ml for example would be too much

I've looked into an air brush but I couldn't find a way to control the volume and I've looked into a spray bottle but the volume there is too big.
any advice or suggestion would be welcome for a tool that can do this would be great!


texts: Fischer to Haworth projection: which carbon connects to the oxygen?

texts:
For D-erythose, carbon 4, (the last carbon), connects to the O which connects to Carbon 1.

However, for D-glucose, carbon 5 (the 2nd last carbon) attaches to the O which attaches to carbon 1.

Why is it the last carbon for D-erythose but the second last carbon for D-glucose that is connected to the oxygen in the Haworth projection? How do I decide which one gets connected when trying to convert Fischer to  Haworth projections?


texts:
In amine inversion, there is a planar $sp^2$ intermediate.

The electron pair transferred from the blue lobe to the red one during the inversion. It is natural to assume, for a layman like me, that in the planar intermediate the electron pair is present in both lobes- one electron in each. That would impart paramagnetic character to the molecule. Does this really happen? I couldn't find any such phenomenon on internet.

Picture: http://chemistryjee.blogspot.in/2015/02/amines.html


texts: Analytical Chemistry Textbook Recommendation

texts:
Could anyone recommend a good book for self-learning that provide a clear, step by step guide on solving such chemical equilibria questions.

It should cover the following topics: weak acid and strong base titration, buffers, redox reactions, electrochemical reactions, complexation reactions, potentiometric titrations.

Preferably, I would like it if the textbook also provide work solutions to the practice questions it gives. I heard that Fundamentals of Analytical Chemistry by Skoog is good and covers the topics that I have listed above but I don't think it provides any worked solutions to its questions.

Any help will be much appreciated.


texts: I was wondering that like whenever I boil milk I just have to keep standing in front of it to make sure that I don't waste any milk but then I was wondering like Why does it even overflow ? In case of water it doesn't happen. What makes it to behave like this ?


texts:
After looking for proper reasons for boiling point orders, nobody could even explain why $\ce{CCl4}$ has a higher boiling point than $\ce{SiCl4}$, but after looking for patterns, in lots and cases of $\ce{CH2X2}$, $\ce{CH3X}$, $\ce{CHX3}$ has more boiling point than similar silicon derivatives.

In some places some explanation related to electronegativity difference is given, but how is that relevant and since Si is less electronegative hence there's more partial charge on Cl which results in more polarisability and stronger London forces; which are quite powerful as evident from various examples like $\ce{HCl < HBr < HI}$.

Order of boiling point (leaving HF due to Hydrogen bonding) London forces even dominate dipole-dipole , which I observed in various cases like the above one and they increase rapidly with polarisability and number of polarisable electrons.

Now, in comparing $\ce{CH2F2,CH3F,CHF3,CHF4}$ we can see that it follows dipole's magnitude order as polarization is negligible.

So my questions are

Is there a good way with no real calculation to compare polarisability/effectiveness of polarisable electrons of molecule to compare magnitude of vanderwall forces or any other way to do it?
And does polarising power of central atom play a role?
Why do halomethanes have more boiling point than their respective silicon derivatives?
While comparing the boiling points of $\ce{CH4}$ and $\ce{CF4}$, as fluorine is less polarisable, methane should have more boiling point as both are non-polar (my reasoning works for higher homologous for $n\geq 2$ in $\ce{C_{n}H_{2n +2}}$ and $\ce{C_{n}F_{2n + 2}}$)

If somebody could include nitrogen family too, that would be great.


texts: Precaution steps on qualitative analysis (inorganic salts)

texts: I will carry out the experiment on determine the cation and anions of inorganic substances (magnesium thiosulphate, aluminium ion and ammonium ion) on Wednesday. I am looking for the precaution steps for this experiment. Anybody can answer my question?


texts: Is the resonance depiction of benzene typically portrayed incorrectly?

texts:
I can understand that the carbon atoms in benzene have delocalized p electrons that are shared amongst all 6 of the carbons in a cloud on either side of the ring. I also understand why this could be represented as resonance structures like so:

I can also understand representing it in this form:

What I cannot understand, however, is why only one of the first form appears so often in depictions of organic molecules. For example, this:

Since this is a "resonance structure," is this not incorrect to list only one of the structures?

One might argue that the reader understands what is being portrayed or that this is done in aims of saving time, but that doesn't sit right with me. The entire point of nomenclature, drawing a chemical, or anything scientific is that it can be interpreted by anyone in exactly the same way. I feel that if someone is deciding to draw a chemical using the resonance structures of benzene, then they should draw both resonance structures, lest it be mistaken for 1,3,5-cyclohexatriene.


texts: As phase transitions are considered reversible processes, shouldn't they be non-spontaneous?

texts:
On the one hand it is stated that reversible processes cannot occur, as they are infinitely slow.

On the other hand phase transitions are said to be reversible processes?


texts: Is the deprotonation of phenol exothermic?

texts:
I just wanted to confirm that deprotonation reaction of weak acids are exothermic?
I know that strong acids deprotonate exothermically (e.g. adding liquid $\ce{H2SO4}$ to water releases a lot of heat), but is this true for weak acids?


texts:
In my book there is a reaction that is

  $\ce{HCCl2-CH2F}$ in presence of $\ce{RO^- ROH}$ gives $\ce{CCl2=CH2}$

I could not understand my type of reaction it is?

And why does $\ce{F-}$ leave whe $\ce{Cl-}$ should leave as it is a better leaving group?


texts:
Upon reading the given question, I realized that:

The first reaction is an aldol condensation reaction between the given compound and formaldehyde.

So the product after 1st step is:

Now, the second part has thrown me off. The current ketone has no $\alpha$ hydrogen left. Condensation reactions are out of the question.
Cannizzaro reaction can not take place as this is a ketone (and not an aldehyde) also the medium is now acidic.
However, I saw one possibility of formation of hemi-acetals.
(I did not think about full acetals, as such a structure was not present in the given options to this question)

Which gave me the following product:

However, the answer provided seems to be not this.
The given answer is this:

Can someone give a suggestion that where I want wrong and/or how could I reach the answer and also what was wrong in my thinking as well?

This question is taken from the JEE(A)-2016 [Paper - 2]


texts: Nucleophilic Addition of Hydrohalic Acids

texts: Hydrogen cyanide shows nucleophilic addition at carbonyl compounds' carbon to form a cyanohydrin. Alcohols, similarly, form acetals or ketals. Will hydrogen chloride - or hydrohalic acids in general - show a similar reaction to form alpha halohydrins?


texts: Why in aromatic nucleophilic substitution the Nucleophile attacks carbon and not the halogen?

texts:
In nucleophilic aromatic substitution of halobenzene why does Nucleophile attack the carbon atom bonded to halide X not the halide.

The carbon atom atom has partial positive charge whereas the halide has positive charge due to resonance as its lone pair is delocalised in the benzene ring doesn't resonance always dominate so why does Nucleophile behave so?

I can think of because of lone pair repulsions between electron rich Nucleophile and halogen but I'm not sure. May someone help ?
(Ofcourse Here the benzene ring has electron withdrawing groups at o p position)


texts: In a jet or internal combustion engine that burns hydrogen as a fuel, what would happen if you replaced the hydrogen with deuterium?

texts:
Would it increase the power of the jet engine due to heavier atoms being exhausted out the back?

For the same reason would it slow down an internal combustion engine?


texts: Birch reduction- 1,4-cyclohexadiene over 1,3-cyclohexadiene

texts:
While reading of birch reduction I was confused as of why  1,4-cyclohexadiene is prefered over 1,3-cyclohexadiene,  the latter which ought to have been the major product due to conjugation.
One of the reason I felt could be of this outcome was "symmetry".
The symmetry produced by the product could cancel the dipole forces acting on the cis- bonds, making the molecule stable. But is this sole reason sufficient to overpower the conjugation? Please explain.
Edit: another possible reason I feel could be is the stereochemistry of the product. The product could facilitate more efficient structure in space about it's double bond (again symmetry), where as 1,3-cyclohexadiene formation could face issues of rotational barriers and might increase torsional strain on it.


texts:
Why are the axial bond lengths greater than those of the equatorial bonds in a trigonal bi-pyramid (TBP) geometry molecule; but the opposite is true for pentagonal bi-pyramid (PBP) geometry molecules? I think that it might have something to do with the angles between the bonds, so I thought of a possible explanation.

In a TBP molecule, the equatorial bonds are spaced apart from each other by 120 degrees, resulting in lesser repulsion; compared to the axial bonds at 90 degrees. The reduced repulsion leads to greater stability of the equatorial bonds.

In contrast, the equatorial bonds in a PBP molecule are separated by 72 degrees which results in them being less stable when compared to the axial bonds.

To what extent is this reasoning correct? Please provide a more detailed and accurate explanation, if there is one. Thanks!!


texts: Do covalent salts produce sodium carbonate extract?

texts:
In case of qualitative analysis of anions, sodium carbonate extract is prepared for insoluble salts.

It is done by heating (for 10 minutes) an aqueous solution of a mixture of the solid salt and sodium carbonate in 1:4 ratio (by mass). As far as I understand, the principle behind preparing sodium carbonate extract is to prepare a clear solution containing the anion by precipitating the cation as insoluble oxide or carbonate.

But is this process applicable for salts that do not ionize at all in water, or covalent salts like $\ce{SnCl2}$, $\ce{SbCl3}$ etc.? I have never tried this myself.


texts: Why do electrocatalysts based on polyoxometalates and carbon materials have a weaker activity/performance in acidic media?

texts:
I am testing now some doped N and S doped carbon nanomaterials alone and immobilized in POM for the purpose of developing a nanocomposite that can serve as an electrocatalyst for energy-related reactions in order to replace Pt.

The purpose in this work is for the reaction to proceed in 1 step, which means to have a 4 electron transfer.

In KOH 0.1 M they are giving better results (3.0 - 3.6 e), while in H2SO4 0.1 M the number of transferred electrons goes down to 1.5-2.

I was wondering what might be the specific reason of the acidic media (hydrogen cations) to lead to this ?

Thank you!


texts: Why does iodine sublime? I have researched it myself and I have got the same answer; it sublimes because it directly converts from solid to gas. But why don't bromine or chlorine also sublime?


texts: What is the range of values of n in [Cu(NH3)4(H2O)n]SO4?

texts:
My textbook represents the copper ion as "tetraaminecopper(II) sulfate-1-water", so I assumed that this complex ion has only 1 water of crystallization.

Then, in the Wikipedia article, they represent the ion as $\ce{[Cu(NH3)4(H2O)_n]SO4}$. The same formula is used but the number of water of crystallization is variable, denoted by $n$. So $n$ must have a range of values.

My question is what determines the value of $n$? What condition would cause $n$ to be larger or lower?


texts: Calcium ion and sulfate did not form precipitate

texts:
I was in the chemistry lab earlier this week. We were doing a qualitative experiment (no concentration given for any solution).

I added an unknown solution that contains $\ce{Ba^2+},$ $\ce{Ca^2+},$ and $\ce{Mg^2+}$ with $\ce{(NH4)2SO4},$ I got barium precipitate and added $\ce{(NH4)2C2O4}$ and another precipitate appeared. I was told the second precipitate is $\ce{Ca^2+}.$

But I recall from solubility mnemonic rule, I should be able to see precipitate from both $\ce{Ca^2+}$ and $\ce{Ba^2+}$ after adding ammonium sulfate. Why didn't I? What are the mechanics behind this? How did calcium just sit there as a spectator ion?


texts: How to calculate n factor for O2 and H2 in this reaction?

texts: How do I find n factor of $\ce{O2}$ and $\ce{H2}$ if I want to use equivalence principal on a reaction like $\ce{O_2 +2 H_2 -> 2 H2O}$?


texts:
I am a second year mathematics student. I am mostly interested in statistics. Right now my curriculum doesn't offer me much choice (all second year courses are mandatory) but next semester I will be able to select the courses I want. Among the ones that are offered is a course called Biochemistry. It is actually a second year class for those how study chemistry and chemical engineering but I guess there must be applications of statistics in this field since it is also offered to third year math students.

My problem is that I am a math student: I have no knowledge or whatsoever in chemistry or biology. Granted that I had some in high school but back then I just learned everything by heart in order to pass.

My questions are the following:

With no knowledge of chemistry, is it realistic to undertake a biochemistry class?
The course description lists the following prerequisites: "Basic knowledge in general and organic chemistry". How important are these subjects in biochemistry? What are some good references (books) for self-learning these subjects?
Is Stryer's Biochemistry a good book for self-learning?
Are biochemistry and biostatistics related at all?
Are there many applications of statistics in biochemistry?

I have already searched for some information on the internet but I'd like to have some specific answers.

If it helps here is the information page of this class.

Finally I hope this kind of question is accepted here, if not please point me to a better place. Thanks in advance!


texts:
I need help on identifying precipitation, acid-base, and redox reactions. I know what each one is in theory:

Precipitation: Creating a solid
Acid-Base: neutralization
Redox: exchange of electrons

But given a chemical reaction like:
HCl (aq) + NaOH (aq) → H2O (l) + NaCl (aq)

I need to understand how to classify them. Are there any tell-tale signs to look out for when determining. For example, does a precipitation reaction ALWAYS produce a (s) as a product and therefore any reaction with a (s) on the product side is a precipitation reaction?


texts: What is the variation of atmospheric pressure at large heights?

texts:
In an approximation (though not a very accurate one), temperature can be assumed constant throughout the atmosphere. The Earth's gravitational field can also be assumed constant (a better assumption).

For these approximations, what is the calculated pressure at the top of Mt. Everest ($8848\ \mathrm m$), given that the pressure at the top of Mont Blanc ($4807\ \mathrm m$) is $4.32\times10^4\ \mathrm{Pa}$?

  $T = 0.0\ \mathrm{^\circ C}$

  $\rm g = 9.81\ \mathrm{m\ s^{-2}}$

  $\ce{O2}$: $M = 32\ \mathrm{g/mol}$, percentage composition of atmosphere =
  $21\ \%$

  $\ce{N2}$: $M = 28\ \mathrm{g/mol}$, percentage composition of atmosphere =
  $79\ \%$

I thought about using $pV=n\mathbb{R}T$ for this question – perhaps using the difference in the volume of air above the different heights, but I couldn't come to an answer.


texts: Does sodium form complexes like transition metal ions?

texts: I realise that there is a similar question here Difference between sodium ion and a transition metal ion dissolving in water? and it seems to answer my question, however I was reading about how aluminion ions form complexes in water, and aluminium is not a transition metal. So how can aluminium form complexes like transition metal ions, but sodium does not?


texts: The covalent bond in HCl and the Lewis model

texts:
Can the formation of the covalent bond in HCl be explained through the hybridization model?
We know for sure that it can be explained by the theory of molecular orbitals. In this way, it would be normal for the atomic orbital $s$ of the hydrogen to mix with one of the chlorine's atomic orbitals which has the same form or energy. Neither the symmetry of the form nor that of the energy can be preserved (totally), because the energy levels of the atomic orbitals of chlorine are much lower than that of the $s$ orbital of the hydrogen. Thus, the $s$ orbital of the hydrogen mixes with the $pz$ orbital of the chlorine and forms $2$ molecular orbitals (a bonding one and an antibonding one). The atomic orbitals $s$, $px$ and $py$ of the chlorine are nonbonding and remain at the initial energy.
According to the Lewis structure, between H and Cl we have a simple sigma bond and around the chlorine atom we are left with $3$ pairs of nonbonding electrons. The charges on H and Cl are null. With this in mind, we notice that $4$ hybrid orbitals would be needed to host the sigma bond and the $3$ pairs of nonbonding electrons of the chlorine, thus getting an $sp^3$ hybridization (the real geometry of the molecule is linear and the one in which are also involved the orbitals with pairs of nonbonding electrons is tetrahedral.
Considering the energy diffrence between the $s$ orbital of $H$ and the $s$ and $p$ orbitals of Cl (as we saw in the theory of molecular orbitals), is it possible to create hybrid orbitals in the HCl molecule?


texts: Why does dissolving a salt in water get a high pH?

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I dissolved some sodium carbonate in water and I measured the $\mathrm{pH}$. It turned out to be 11. I don't really understand why dissolving it in water increased the $\mathrm{pH}$. I mean, I know that $\mathrm{pH}$ of water was 7, so it must have something to do with the $\ce{H+}$ ions. We just covered acid and bases today so please bear with me.

Here are my thoughts. My salt had some $\ce{OH-}$ salt and this combined with the $\ce{H+}$ to produce $\ce{H2O}$ thereby decreasing the amount of $\ce{H+}$ ion. Or maybe one of my salt ions combine with the dissolved $\ce{H+}$, again thereby decreasing the $\ce{H+}$ concentration and increasing the $\mathrm{pH}$, so I'd have something like this could have something like:

$$\ce{Na+ + H+ -> NaH2+}$$

or maybe

$$\ce{CO3^2- + H+ -> HCO3-}$$

Which one do you think happened?


texts: Why does Bismuth only create a +3 ion instead of a +5 ion?

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It has 5 valence electrons, but only loses 3 of them to make a +3 ion. Why does this occur?

I believe it may have something to do with how losing 3 electrons leaves you with the p sublevel full, but I do not understand why Bismuth is okay with that.


texts: What are disadvantages of having an impurity?

texts: I thought about this while thinking about alloys and why they are better than pure metals, even though they are technically impurities. It got me wondering, are there actually any good real-life applications where having an impure substance is completely disadvantageous?


texts:
Can $\ce{SiO2}$ melt at $\pu{20 ^\circ C}$?

I have searched the web for $\ce{SiO2}$ phase diagram, but it seems to me that almost all the graph I can find have the temperature axis where the minimum temperature is in the hundreds degrees Celsius.
Is it theoretically possible that with an high enough pressure I can melt $\ce{SiO2}$ in a temperature range like $\pu{-30 ^\circ C}$ to $\pu{50 ^\circ C}$? Or is it something theoretically simply impossible?