texts: Calculate the concentration of the deprotonated adipic acid anion

texts:
Adipic acid is a diprotic acid having $K_\mathrm {a1}=3.9\times10−5$ and $K_\mathrm {a2}=3.9\times10−6$. A saturated solution of adipic acid is about $\pu{0.10 M}~\ce{HOOC(CH2)4COOH}$. Calculate the concentration of the $\ce{−OOC(CH2)4COO−}$ in this solution. Express your answer to two significant figures and include the appropriate units

Lets represent adipic acid as $\ce{H2A}$ for the sake of simplicity.

$$\ce{H2A <=> H+ + HA-}\qquad   K_{\mathrm a1} = 3.9 \times 10^{-5}$$

$$\begin{array}{lccc}
\text{Initial}\quad &0.1 \quad &&0 \quad &&0\\
\text{Change}\quad &0.1-x \quad &&+x \quad &&+x\\
\text{Eq}\quad &0.1-x \quad &&x \quad &&x
\end{array}$$

$$3.9 \times 10^{-5} = x\times x/0.1-x$$

$x^2 = 3.9 \times 10^{-5} \times 0.1$ (neglecting $x$ in nominator because $x\ll0.1$)

$x = x_1 = 0.00197\ \mathrm M$

Let's designate $x$ as $x_1$. $\ce{HA-}$ dissociates again as

$$\ce{HA- <=> H+ + A-}\qquad K_{\mathrm a2} = 3.9 \times 10^{-6}$$

$$\begin{array}{lccc}
\text{Initial}\quad &0.00197 \quad &&0 \quad &&0\\
\text{Change}\quad &0.00197 -x \quad &&+x \quad &&+x\\
\text{Eq}\quad &0.00197 -x \quad &&x \quad &&x
\end{array}$$

$$3.9 \times 10^{-6} = x^2/0.00197$$

$x^2 = 0.00197 \times 3.9 \times 10^{-6}$ as shown above

$x = x_2 = 8.77 \times 10^{-5}$   (designate $x$ as $x_2$)

Concentration of $\ce{HOOC(CH2)4COOH}$ ($\ce{H2A}$) $= 0.1 - x_1 = 0.098\ \mathrm M$

But that was wrong. I then  $x_1 - x_2 = 0.00197 - 8.77 \times 10^{-5} = 0.00188\ \mathrm M$ but that answer is wrong.


texts: Reduction with NH2-NH2 , OH-, and glycol

texts:
this question was asked in my exam and I have done it properly until the very third step but unfortunately, although the last step looked like wolfkishner reduction to me I could not do it.
My approach:
At first, via ozonolysis aldehyde groups will come and then aldol reaction would take place and by heating alpha-beta unsaturated aldehyde product will be formed.
But then what if I reduce it in the last step my answer is not matching with any of the options given. Any help will be highly appreciated.


texts: What is the basis of naming the various isomers of hexachlorocyclohexane $\alpha$, $\beta$, $\gamma$, etc.? Here is a list of these isomers. Is it just random naming, or is it according to some convention?


texts: Eigenvalues of Hessian matrix when the molecule is not at its equilibrium configuration

texts:
Given the potential energy surface (PES) of a system, we can calculate the Hessian matrix $H$ of each point $x$ on the PES.
$$H_{ij}(x) = \frac{\partial^2 E}{\partial R_i \partial R_j}|_{R = x}$$

When the structure of a molecule is optimized, the eigenvectors of $H$ are displacement vectors, the corresponding eigenvalues are the 'force constants' and they are all positive. On the other hand, when the structure corresponds to a transition state, some of the eigenvalues will be negative.

When a structure is neither the optimized one nor a transition state, the first derivate of the PES is not zero. However, we can still calculate the Hessian matrix for this structure. Moreover, as long as the PES has continuous second partial derivatives, the Hessian matrix is symmetric and thus diagonalizable (the proof). Can we interpret the eigenvalues here?


texts: In preparing sulphonilamide, why is aniline acylated if the acyl group has to be removed later?

texts:
Our professor talked about the six stages of the synthesis of sulfa-drugs, which are:

nitration of benzene
reduction of nitrobenzene
acylation of aniline
reacting acetanilide with chlorosulfonic acid
treating the product with a primary amine
subsequent hydrolysis of acetyl groups

If we skip step 3, and let aniline react with chlorosulfonic acid, and then go till step 5, could sulfonamide be synthesized? Why do we perform acylation of aniline if we just have to remove the acyl group by subsequent hydrolysis later?


texts:
I am currently attempting to generate an arrow pushing mechanism for the oxidation of glucose to gluconic acid using Fehling's solution. My original thought was to go the route of alcohol oxidation using acidified dichromate where the alcohol attacks in and loses the H using a E2 mechanism.

In the aldehyde oxidation, I would have a hydroxide ion attack prior to the H bond collapse leaving an extra electron on the Cu from the $\ce{C-\mathbf{O-Cu}}$ bond resulting in reduction of $\ce{Cu^2+ -> Cu+}$. Which would satisfy the observed empirical data. After an attempt I googled the mechanism finding very little real information.

A post on this very site suggested the mechanism proceeds via enolate formation followed by single electron transfer with $\ce{Cu^2+}$. Unfortunately, there is no elaboration on this or a source, I also can't find a source online which corroborates this mechanism. Does anyone have a good source for this?


texts: Why Molecular Solids can be treated as Monoatomic in Reactions

texts:
I'm trying to figure out what is the precise rule for the formula of elemental substances in reactions. I'm afraid I can't word the question properly, so I'll try to give some examples.

1)Oxidation of some metal, e.g. Calcium

$2Ca+O_2 \rightarrow 2CaO$

Since Calcium is a metal I understand that each atom reacts independently and the formula is plain $Ca$

2)Oxidation of some molecular gas, e.g. Hydrogen

$2H_2+O_2 \rightarrow 2H_2O$

Now atomic hydrogen in gas form is not what one usually expects, but rather the diatomic gas, so the formula must be $H_2$.

3)Oxidation of Sulfur

$S+O_2\rightarrow SO_2$

Now, here I get confused. I just copied the reaction from a textbook, but everywhere I looked in the internet says that this is the correct formula. On the other hand the textbook says that the most common allotrope of sulfur has formula $S_8$. And now I wonder why the reaction should not involve molecular sulfur and be

$S_8 +8O_2\rightarrow 8SO_2$.

I do understand that either way one would get the correct mass proportions, but I'm sot sure if that wold be the case in other reactions or with other substances.

So, I get that for metals the formula for the elemental substance that appears in reactions is just the atom. I get that for carbon and other network covalent materials the same applies. And I get that for molecular gases you need the diatomic formula, because each molecule participates as a whole. What puzzles me is what is the rationale beyond plain atoms appearing in molecular solids like sulfur, phosphorous, etc.

I apologize for not being able to state the problem in a more succinct fashion, feel free to edit the question or ask for further clarifications.


texts:
Ammonium nitrate is one of the classic examples of an endothermic dissolution.  People will usually explain why it's soluble by stating that the spontaneous dissolution process of ammonium nitrate is what drives the reaction, meaning that the obvious answer is it's soluble because ΔG of dissolving it is negative.  Here is an example.

However, after thinking a bit more about it, this explanation seems very vague and doesn't explain it well.  Enthalpy usually has a stronger role in determining the solubility of salts, since their ΔH values are usually much larger than the TΔS values they would have, especially at room temperature.

Both calcium and aluminum fluoride are also salts that have an endothermic dissolution, but by the number of ions dissociated, one would think that ΔS of dissolving both of these salts would be much higher than that of ammonium nitrate.  Ammonium nitrate is still several times more soluble though.

My question is, what mechanisms allow ammonium nitrate to have such a high ΔS when dissolving in solution that allow it to still be very soluble, despite having an endothermic dissolution?


texts:
According to Hückel's rule a compound is aromatic if it has conjugation throughout the compound and the number of conjugated electrons is $4n+2$. This compound does not satisfy both:

The benzene ring itself is aromatic, though. Is the compound considered aromatic because of this?


texts: When Ammonium chloride is in an aqueous medium its cation part ammonium undergo hydrolysis. Since ammonium is conjugate acid of a weak base it readily release one $\ce{H+}$ and converts back to $\ce{NH3}$. But its given in my textbook that hydrolysis of Ammonium chloride gives ammonium hydroxide. Why Ammonium hydroxide is formed instead of staying as ammonia? Because according to my understanding ammonium hydroxide is formed when ammonium ion and hydroxide ion attract each other to have an ionic bond, and since ammonium ion converts back to ammonia how is this possible?


texts: Does isopropyl chloride undergo SN1 or SN2 with sodium acetate?

texts:
What's the reaction of isopropyl chloride with sodium acetate? (The solvent is acetic acid)
Is it SN1 or SN2?

My thoughts:

It's not that difficult to approach isopropyl chloride's carbon, for there isn't much steric crowding. It's just a 2 degree alkyl halide with two methyl groups. This favours SN2.
The carbocation formed by the 2 degree alkyl halide, here in this case, is stabilised by the +I effect of two methyl groups and also six hyperconjugative structures. This should favour carbocation formation, hence SN1.
Acetic acid is a polar protic solvent, and can solvate sodium acetate.
Acetate ion isn't a great nucleophile (or is it?). I'm not sure, here. I know that acetic acid is a weak acid, so acetate ion is a strong base but I believe its nucleophilicity is suppressed by solvation.
Chlorine isn't an amazing leaving group.

So, does SN1 take place or SN2? Could someone also give some experimental data to support their reasoning?

Here's something I found, it says that both SN1 and SN2 can occur. Now which one occurs here, is probably decided by the nucleophile? I'm not sure. Anyway, thought I'd put this table up here for reference:

Source:
Organic Chemistry - Clayden - Oxford University Press - 1st edition - Page 424

Edit: Someone in the comments section said that you can't predict which mechanism is major, and have to look for experimental facts. So, for the sake of the completeness, where are the facts? Could someone please post the relevant details as an answer?


texts: Would sodium carbonate from carbon dioxide plus hydroxide be formed in solution or as a solid?

texts:
If normal breathable atmosphere were to be reacted with aqueous sodium hydroxide, what form would the resulting sodium carbonate take, would it be dissolved in the solution or solid?

Note:

I'm defining air here as the atmosphere of earth at between sea level and 200m.

(Not a homework question, just interested.)


texts: In such a setup, the copper anode is known to dissolve. My question is, why? Does it not receive electrons from the $ \ce{OH^-}$ ions. And if you say that those electrons just flow to the battery, let me provide the counterargument: the electrons flowing to the cathode do not prevent the copper cathode from dissolving because copper ions in solution accept the ions, so there is actually nothing stopping the cathode from dissolving as well. So, very simply, my question is this:  Why does the copper anode dissolve?


texts: In reaction equations, why are j and k sometimes capitalized to J and K?

texts:
From 'Leighton relationship' on Wikipedia:
through the following mechanism:[2]
($J_1$) $$\ce{NO2 + h\nu (\lambda < 420 nm) → NO + O (^3P)}$$
($k_2$) $$\ce{O (^3P) + O2 + M → O3 + M}$$
($k_3$) $$\ce{NO + O3 → NO2 + O2}$$
This series of reactions creates a null cycle, in which there is no net production or loss of any species involved.
And here:
Since $\ce{O (3P)}$ is very reactive and $\ce{O2}$ is abundant, $\ce{O (3P)}$ can be assumed to be in steady state, and thus an equation linking the concentrations of the species involved can be derived:
$$\ce{[O_3]} = {J_1\ce{[NO2]} \over k_3\ce{[NO]}}$$
$${\displaystyle [{\ce {O3}}]={\frac {J_{1}[{\ce {NO2}}]}{k_{3}[{\ce {NO}}]}}}$$
$${\displaystyle [{\ce {O3}}]={\frac {J_{1}[{\ce {NO2}}]}{k_{3}[{\ce {NO}}]}}}$$
The ${J}$ is capitalized, but the $k$ (or $k$s) are not....
Does this signify anything?


texts: Why does the structure of haemoglobin change when the ferrous ion changes to ferric ion?

texts: It is said that $\ce{Fe^2+}$ can bind oxygen while $\ce{Fe^3+}$ cannot. Why is that so? $\ce{Fe^3+}$ has an extra electron, it could bind more easily to the oxygen. And how and why does the structure of heme protein change with the ferric ion?


texts:
I plan on creating 100 mL of 100mg/L aspirin solution by dissolving 10 mg of pure aspirin powder in 100 mL of buffer solution (of different pHs). Problematically, aspirin doesn’t tend towards dissolving in polar solution easily, so I thought about dissolving the 10 mg of aspirin in 1 mL of ethanol first, and then taking that ethanol-aspirin solution and adding it to 99 mL of the buffer solution.
I was wondering if this method seems reasonable/feasible. If not, are there any better suggestions?


texts: How does a Brunauer–Emmett–Teller device function?

texts:
The Brunauer–Emmett–Teller (BET) theory is comprehensible.

My question is more geared towards what is physically and chemically happening within a BET device to get a reading?  How does a BET device actually go about measuring the physisorption or chemisorption of a material?  Why does this process tend to take multiple hours?


texts: Where should I publish my formula related to Aufbau Principle?

texts: I have made a formula for determining the sequence of orbitals which is currently obtained using the Aufbau diagram. So, I wanted to know where should I publish it (if it is new). I searched the same on internet but did not get any such formula.


texts: What is the more stable conjugate base of cyclohex-2-en-1-one?

texts:
We have to identify the structure of its more stable conjugate base obtained by proton transfer of cyclohex-2-en-1-one.

In the following question, there are two possibilities:
We can either remove a hydrogen nearest to carbonyl group or remove a hydrogen next to carbon carbon double bond.
I think the later should be correct as it involves higher conjugation, but the answer is the opposite, they have removed hydrogen which is nearest to carbonyl group. Why is this position preferred?


texts: Is the polarisation of halogens of higher atomic number easier because the electrons are further away from its core?

texts:
This question concerns the dihalo addition reactions. I've learned that a halogen molecule (which, of course, consists of two atoms of the respective halogen) is more easily polarised by the double bond present in an alkene if it has a larger atomic number.
My question is this: Is this because the electrons of the halogens of higher atomic number are, on average, further away from its nucleus, so that they are easier to dislocate because the force that the protons exert on them is weaker?
A follow-up question would be: Is it, for the same reason, easier (in terms of energy requirement) to ionise elements of higher atomic number?


texts: Is a compound aromatic if it also has anti-aromatic rings?

texts:
Is 5,6,11,12-tetradehydrodibenzo[a,e][8]annulene aromatic?

If I use Hückel's rule for the whole molecule, I get the answer as anti-aromatic. But the compound has two benzene rings which are individually aromatic.


texts: Direct connection in a zinc copper battery

texts: Why can't you just hook up a piece of wire between a piece of zinc and  copper and get an electric current? What is it about the electrolyte that makes zinc give up electrons?  Also, why will the lack of a salt bridge stop the electric current from moving?   Why  does balancing out the positivity and negativity at the cathode and anode matter?


texts: Smallest nearest neighbor distance among elements

texts:
Of all the elements in periodic table, which one has smallest nearest neighbor distance? I tried searching on net, but could not find any reference. My earlier guess was one which goes into FCC with smallest unit cell dimension should be one. But I am not sure.

In an FCC, if unit cell dimension is a, then nearest neighbor distance will be a/sqrt(2) because nearest atom to an atom on the edge of the cube will be face atom. But this is for FCC. For SC of size a, nearest atom will be at a distance of a. So, for different elements, there will be different nearest neighbor distance based on its unit cell geometry and unit cell length. I want to know which combination of these result in shortest nearest neighbor distance.


texts: Why is ice cubical in structure at very low temperature?

texts:
My book says that at atmospheric pressure ice crystallises in the hexagonal form but at very low temperatures it condenses to cubic form.

Why and how does this happen?


texts: Why do molecules of a body exhibit vibrational motion? Is it due to interaction between various molecules of the body, or interatomic interactions between atoms in the same molecule? If it is because of any of them, how can these interaction cause the molecules to vibrate?


texts: Comb and hair, is that an example for ionic boding?

texts:
As i understand, when brushing hair, some electron transfer from hair to the comb. Thus, make the comb have different charged from hair and they attract each other.
It's look likely what i have learn from school about ionic bond. One electron from Na is transfer to F and so we have NaF . Isn't it ???


texts: Does higher Oxidation/ reduction potential translate to higher energy storage in battery?

texts:
Some articles refer to the fact that Lithium is preferred metal of choice for batteries because their half cell voltage is high (slightly above 3V)

If that is the case why can't we use other metals like Mn which can have higher oxidation potential (Mn can have +7 oxidation state which translates to higher oxidation potential)?


texts:
Can we chemically characterize a flame ?

Recently, while I was lighting a candle, I came across this question; can we find out the chemical composition of a particular flame? If yes then how? In other words, can we know which elements are present in flame, and not just the salts we test using the flame tests?


texts: Organic Nomenclature: But-1-en-3-yne or But-3-yne-1-en

texts: Just wondering whether "but-1-en-3-yne" or "but-3-yne-1-en" follows the correct IUPAC naming convention for organic molecules. I'm going through a text book that uses the former in an example, but in the answer to one of the questions it uses the latter, so is it interchangeable or is one just wrong?


texts:
One of our customers used a very high dose of formaldehyde 37% solution (60 liter formaldehyde  in 40 liter water) for disinfection in  his chicken farm (saloon). Now he says the odor of formaldehyde is very strong and can`t start breeding  season.  How can I help her?

Can he  neutralize  formaldehyde odor with some chemical treatment? Maybe he can use sodium hypochlorite (bleach). Do you think chlorine can oxidize formaldehyde?


texts: Gibbs free energy as a difference of irreversible and reversible heats

texts:
I read in a book that ∆G=∆H-T∆S and then ∆H and T∆S were substituted with Q and Qrev respectively(where Q and Qrev are heats added to the system in any process and reversible process respectively) and then there were two cases,

Case 1:irreversible process
Q was replaced with Qirr(heat added to system irreversibly)so ∆G=Qirr-Qrev
Case 2:reversible process
Q was replaced with Qrev and so ∆G=0

What I don't understand is that replacing T∆S with Qrev in both the cases implies that the state change in both cases is same(∆H,∆S and ∆G are state functions) but the values of ∆H and ∆G imply otherwise.Is the book wrong or am I thinking wrong?


texts: Getting the wrong pH value, according to data and online calculator

texts:
I'm doing a titration problem with a week acid and strong base, I used experiment data and an online calculator to check my answer, but my pH I calculated is a bit off. Can anyone see where I messed up? I can't figure out where...

AcOH
0.0984M
0.02500L
0.00246mol
Ka 1.8x10^-5

NaOH
0.096M
0.02580L
0.00025mol

After rxn:

0mol AcOH left

0.0025mol - 0.00246mol = 4.0x10^-5 mol OH excess

0.00246mol AcO-

4.0x10^-5mol OH / 0.0508 L total soln = 7.87x10^-4 M OH-

-log([OH-]) = pOH = 3.104

pH = 10.90

The pH should be 10.52 according to my data and the online calculator.


texts: Ortho vs para alkylation of chlorobenzene

texts: I have a question to the solution regarding the product formed in a reaction with chlorobenzene with the use of (i) $\ce{CH3CH2Cl}$ and (ii)$ \ce{AlCl3}$. Since the -Cl substituent is ortho- para-directing shouldn't the answer then be a mixture of 1-chloro-4-ethylbenzene and 1-chloro-2-ethylbenzene? - I suppose that the para-orientation is the major product. But how is that determined?


texts: Looking for a two step first-order reaction with a useful intermediate

texts:
I am working on a mathematical model for my homework, and would like to do some tests to see if it is accurate in real life as well. The model involves a two step chemical reaction in the form of the following:
\begin{align}
\ce{A + B &-> C + D} \tag{1}\\
\ce{C + D &-> products} \tag{2}
\end{align}

Is anyone aware of such processes where either $\ce{C}$ and $\ce{D}$ are:

measurable (not necessarily continuously, could be done by say, quenching the reaction at intervals);
are also useful in real life in some way or another;
where the order of reaction with respect to the chemicals are first order?

Any ideas are welcome!


texts: Why don't alkaline earth metals lose only one electron when they are ionized?

texts: Why doesn't alkaline earth metals lose only one electron when they are ionized ? I know that magnesium atoms like to have the electronic configuration of neon but I don't understand the reason that we can't find $\ce{Mg+}$ atoms .


texts:
Just beginning to grasp this. Betaphenylethylamine to n-methyl-b-pea. Can I use water instead of DMSOesque solvent in regards to cesium carbonate/hydroxide monohydrate? Also are molecular sieves necessary? As well as 1-bromobutane?

Bottle + water + pea + cesium carbonate/hydroxide = NMPEA?


texts:
I found this reaction over here:

which illustrates the carbonyl test but looks fuzzy.

Assuming that the R in the product is a typo for H, I couldn't conserve the number of Nitrogen atoms.

What is the correct reaction?
Is this correct?
Is there a possibility of a methyl substitution on the ring in a variant of this test?


texts: Chemical processes and chemical reactions difference

texts:
Whats the difference between chemical processes and chemical reactions?
Ive heard that the chemical industries only uses chemical processes to produce new substances, but isnt that also what happens when a chemical reaction occurs? I couldn't find a lot on this topic online except for the wikipedia aricles that only made me more confused.


texts: Differentiation between zinc, aluminium, and magnesium ions in solution

texts:
If I have three aqueous ionic solutions in which I know that the cation is $\ce{Al^3+}$, $\ce{Mg^2+}$, or $\ce{Zn^2+}$, how do I find out which is which?

I was thinking to add $\ce{OH-}$ in the form of $\ce{NaOH}$, or something else to produce a precipitate, and testing these precipitates in other liquids, but I'm not sure what other liquids to try.


texts: MO diagram when three orbitals of the same symmetry is allowed to mix

texts:
How exactly should we combine three orbitals when we have three orbitals that are of correct symmetry to interact?
Take $\ce{H2O}$ for example. $\mathrm{2s},$ $\mathrm{2p}_z$ and the $A_1$ group $(\ce{H2})$ orbitals can interact. It would seem trivial that the lowest bonding orbital is $\mathrm{2s}$ in phase with $A_1,$ but what about the anti binding orbital? Most resources suggest $\mathrm{2p}_z-A_1$ out-of-phase interaction, but is $\mathrm{2s}$ with $A_1$ out of phase not correct?
Could this be due to we try to construct the anti bonding orbital with least overlap possible?


texts: For what is reaction enthalpy more relevant than reaction free energy?

texts:
I know enthalpy is a component of the Gibb's Free Energy (along with entropy). For practical purposes, though, isn't Gibb's Free Energy what a chemist is actually interested in, as that determines the overall equilibrium of a reaction? What important detail does enthalpy inform us of and what applicable function does that detail serve?

I am asking this because I have a DFT calculation that yields both the enthalpy and free energy, and I see a paper citing the enthalpy, so I am wondering why it is being preferred over the free energy.


texts: Where do the electrons not in the S1 orbital get this "extra energy" from?

texts: In this video, Sal Khan says that an electron reaches a higher energy state if the electron possesses more energy. So I assume that, say in the case of carbon, the electrons not in the S1 orbital have more energy. Where does this energy come from?


texts: Why does technetium not exist in nature?

texts: Why does technetium not occur in nature? It is the only element before bismuth to net exist in nature. What's the reason for that?


texts: Relative acidity of acetic acid derivatives with strongly withdrawing substituents

texts:
What would be the order of $\mathrm{p}K_\mathrm{a}$ values of the following:

$\ce{O2N-CH2-CO2H},$
$\ce{Me3\overset{+}{N}-CH2-CO2H},$
$\ce{NC-CH2-CO2H},$
$\ce{HO-CH2-CO2H}?$

Since only the groups attached to $\ce{-CH2-CO2H}$ are changing, we must look at the point of difference in each group and I was able to figure out that since there is no conjugation, we cannot compare these groups on the basis of the mesomeric effect.
So, we must compare them on the basis of negative inductive effect as the more stable the conjugate base will be, the more acidic our compound is and hence the lesser is its $\mathrm{p}K_\mathrm{a}$ value. But I am not able to come to a final conclusion which matches with what's given in my book.
Is there some other factor playing role in this as well? Because if we just look at it on the basis of inductive effect, the order for increasing values of $pK_a$ should be
$$\ce{Me3\overset{+}{N}-CH2-CO2H} < \ce{O2N-CH2-CO2H} < \ce{NC-CH2-CO2H} < \ce{HO-CH2-CO2H},$$
which seems to be wrong.

The order for the increasing $pK_a$ values given in my book is:
$$\ce{O2N-CH2-CO2H} < \ce{Me3\overset{+}{N}-CH2-CO2H} < \ce{NC-CH2-CO2H} < \ce{HO-CH2-CO2H},$$
Note that the order given in my book may be subject to errors.

EDIT:
After pondering over this for a lot of time and with no convincing answers or explanations, I finally came to a potential explanation for this. Could Hydrogen bonding be the reason for the compound with $-NO_2$ to be more acidic than the one with $-Me_3\overset{+}{N}$ group ?

EDIT-2:
Thanks to Buck, it's now clear that my book's answer is right. Could someone please give a possible explanation to this from organic point of view?


texts:
Lithium chloride is soluble in pyridine while other lithium halides are not. Why?

I know that lithium chloride is deliquescent like magnesium chloride. Lithium halides are covalent and thus are soluble in organic solvents. Then, why is it that only lithium chloride is soluble in pyridine?


texts: Does fumaric acid form maleic anhydride upon heating?

texts:
Maleic acid (the cis isomer of the dicarboxylic acid $\ce{C4H4O4}$) readily forms its anhydride on heating. Clayden's organic chemistry textbook mentions this as a point of distinction between it and fumaric acid (the trans isomer), which fails to dehydrate to its anhydride upon heating. However, I have discovered that at temperatures above 200 $^{\circ}\mathrm{C}$, fumaric acid forms maleic anhydride as well.

Which is the correct answer? I don't think it is likely that fumaric acid can form the anhydride - even at higher temperatures - given the trans configuration and restricted rotation.


texts: Can the properties in a tomato help make hair curl?

texts: Is it possible for the active properties of a tomato to turn your hair from straight to curly? And what are the active ones that do this and why?


texts: I have read about grain boundary etching. They use acid to make grain boundary visible for light microscope. I know that grain boundary is reactive to acid, but why? Thanks.


texts: Solving a quadratic equation for pressure of real gas with unknown volume

texts:
Question

  Calculate the pressure exerted (in atm) by 1 mole of $\ce{CH4}$ gas at a temperature of $\displaystyle\pu{\frac{24}{0.0821} K}$ if volume occupied by $\ce{CH4}$ molecules is negligible. Given $a = \pu{2 L^2 atm mol^{-2}}$.

Solution:

  $$
\begin{align}
\left(p + \frac{a}{V_\mathrm{m}^2}\right)V_\mathrm{m} &= RT\\
pV_\mathrm{m} + \frac{a}{V_\mathrm{m}} &= RT\\
pV_\mathrm{m}^2 - RTV_\mathrm{m} + a &= 0\\
pV_\mathrm{m}^2 -24V_\mathrm{m} + 2 &= 0\\
\end{align}
$$

  For real gas this equation must have only one root:

  $$D = 0\quad\implies\quad b^2 - 4ac = 0$$
  $$24^2 - 4×p×2 = 0$$
  $$p = \pu{72 atm}$$

My thoughts

I had a doubt whether this solution was really true or not. When I first encountered it, I was convinced that it was true. But, now, I doubt it. I don't have any appropriate reason why and that's what I seek to ask. Is this approach correct? Why?


texts: Explain the voltage drop curve of a set of lead acid batteries

texts:
Living on a boat and using batteries to power things over night, I've noticed that the battery discharge pattern seems to be a bit like a pyramid or the point of a sharpened pencil.

The batteries quickly fall back from 13.2 -> 12.7, and 12.7 -> 12.6 is faster than 12.6 -> 12.5 and by the time you get to 12.5 you seem to have hit the meat of the battery and further voltage drop is much slower, much like a pencil without a sharp point doesn't degrade as quickly as a freshly sharpened pencil.

We've never gone below 12.2, but I'm assuming at some point voltage starts falling faster, or maybe it doesn't.

99% of the load on these batteries comes from 2 refrigerators and 1 freezer and can range from 50Watts to 200Watts depending on temperature and how many are running simultaneously.

I'm curious about WHY the battery bank displays this voltage drop that isn't very uniform.  What is going on inside the cells that cause this kind of voltage drop.  What causes the battery to begin shouldering the load with less voltage drop around 12.5v?  I'm sure there is some chemistry behind the reason, but I don't know what that is.

Charging voltage runs as high as 14.4 during the day when the solar panels are refilling them batteries, and we are adding 3.3-5.2KWh/day to the batteries, depending on sun and clouds.


texts: Interpretation of H as T goes to absolute zero

texts:
Euler's identity for the enthalpy states that (for a single component and phase)

$ H = TS + \mu N$

What are the implications of this expression in the context of the third law of thermodynamics (consider a "a perfect crystalline substance")? My textbooks describe the behaviour of $\Delta S$, $S$ and $\Delta G - \Delta H$ but not of $\Delta H$ or $H$.

Is it safe to assume that as $C_p$ and $S$ go to zero, so too does $\Delta H$ for any process at 0 K?


texts: How does haloform reaction take place if the reactants NaOH and X2 react with each other?

texts: If $\ce{NaOH}$ reacts with halogen to produce $\ce{NaX}$ and $\ce{NaXO3}$, then how does haloform reaction take place?


texts:
I have a protein that I purified in PBS buffer, pH 7. I will do dialysis to remove salt and will then further purify the protein with ion exchange chromatography.

I will need to use another buffer (Tris-HCl) with pH 8 in the chromatography, and so my question is:
Can I change the buffer system for my protein in the dialysis step? Or would you recommend me to use the Tris-HCl buffer from the very start and then just adjust the pH for the chromatography?

Thanks in advance!


texts: Connection between irreducible representations and electronic states in diatomic molecules

texts:
I am trying to understand the connection between irreducible representations and molecular electronic states.
To explain the problem: I found some potential energy curves (PECs) for $\ce{N2+}$ in the form of irreducible representations such as $\mathrm{A_g}$, $\mathrm{A_u}$, $\mathrm{B_{2g}}$, ...

However, in the literature, I normally find the PECs in the form of $\Sigma$, $\Pi$, $\Delta$... states. How do we connect these two pictures? I am not an expert in quantum chemistry calculations. A simple explanation will be highly helpful.


texts:
Do radial nodes exist in molecular orbitals?
Radial nodes exist in atomic orbitals and the number of radial nodes for an atomic orbital can be determined by the general formula $n-l-1$ where $n$ is principal quantum number and $l$  is azimuthal quantum number.
But do radial nodes exist in molecular orbitals, and if they exist, is there a general formula for determining number of them present?


texts: How do I determine whether it is the *ferrous* or *ferric* ion that is implied in this displacement reaction?

texts:
I'm supposed to write a balanced equation for:

$$\ce{Iron(s) + copper(II) sulfate(aq) -> ?}$$

If I use Iron(II)/ferrous I get

$$\ce{Fe + CuSO4 -> FeSO4 + Cu}$$

and if I use Iron(III)/ferric,

$$\ce{Fe + CuSO4 -> Fe2(SO4)3 + Cu}$$

(Before balancing).

Is there a way to determine which one I am supposed to use?


texts: Can a substance donate a proton without the proton getting accepted by another substance?

texts:
I have read that the concept of Brønsted and Lowry is based on the fact that acid-base reactions involve the transfer of $\ce{H+}$ ions from one substance to another, and that an acid is a substance that donates a proton to another substance, but:

can a substance donate a proton without the proton getting accepted by another substance? So for example:
$$\ce{AH -> A- + H+}$$
without reacting with another substance?

If yes: Is this a Brønsted-Lowry acid?


texts: How would you order alkyl groups of this compound numerically?

texts: If akyl groups are ordered alphabetically and ethyl comes before methyl, would this compound be called 2-ethyl-3,4 dimethyl pentane? Since that would be less than 4-ethyl-2,3 dimethyl pentane, correct?


texts:
This patent notes in passing:

  It may be necessary to add $\ce{NaOH}$ to stabilize aqueous $\ce{NaCN}$. Anyone
  skilled in the art would know the amount of $\ce{NaOH}$ to add.

Obviously I'm not skilled in the art.  I assume the stabilization is against hydrolysis.  What is the mechanism by which $\ce{NaOH}$ would stabilize aqueous $\ce{NaCN}$, and how would one determine the correct amount of $\ce{NaOH}$ to add?

(I'm expecting it's some target pH level, but I'm too far along my "assumption" chain to know what the issues are.)


texts: Understanding the difference between physical and chemical changes

texts:
Which of the following is a chemical change?
A. Hydrolysis of a dipeptide.
B. Stretching of a balloon.
C. Freezing of water.
D. Breaking a stick.

I'm pretty sure that the answer is (A), but I'm not 100% positive.
I know that, for (C), you can freeze water, and then you can melt it back to liquid water.
For (D), you can break a stick, and the stick is still now two sticks.
For (B), however, I think that it is a physical change, but I'm not entirely certain.
Can someone please explain this for me?


texts: What are the height and width of the large and small nodes of the sp3 hybridized orbitals of carbon and silicon?

texts:
I will make an effort to interpret answers based on wave functions, but I am a senior pursuing a bachelor's degree in Biology, so I don't have the background in quantum physics for a purely mathematical answer to make intuitive sense.

I would appreciate any partial answers which cover only carbon or only silicon, as well as partial answers that give the height and width of only the small node or only the large node of the sp3 orbital. I am asking about the width of the large and small nodes at their widest points, not at their center of electron density.

I am aware the sp3 hybrid orbitals only form when these atoms are bonded to four other atoms, so there are no empirical observations showing the height of sp3 orbitals from isolated atoms (for this question, assume a tetrahedral lattice composed purely of carbon or silicon). That said, any estimates based on halving bond lengths should account for orbital overlap in these bonds so that the height of the orbital from each bonding atom is not underestimated.

Pieces of information that I would find very useful as an addendum to answering my main question are estimates of the electric potential energy, kinetic energy, and total energy (constant) of an electron as it travels in the largest ellipse contained within the sp3 orbital of either a carbon or silicon atom in a lattice – including the large and small nodes, and assuming this ellipse does not move from one bonded atom to another.

Thank you!

EDIT to update: Having taken organic chemistry I and II, I am also aware that orbitals are simply the 95% confidence interval for finding an electron. I am also aware that the common understanding of electron movement in orbitals is that they can move between states of equal energy without occupying all of the states in between. In my question about an electron moving in an elliptical path, I am asking for answers to assume that the electron is following such a path, and that this path is a planar ellipse which corresponds to a cross-section of the outer edge of the 95% confidence interval. Smaller elliptical paths would have lower energy, and I'm asking this because it is the highest energy path an electron would take in the orbital if it were following a planar elliptical path.


texts:
Why is proton transfer always kinetically favored? In other words, why are Brønsted acid-base reactions so quick?

Is it because protons are generally unhindered, sterically? This seems plausible; consider an alcohol. The proton isn't blocked by any bulky groups. It's on the end of a oxygen atom.

What else could contribute to the kinetic favorability of a proton transfer? Reasoning backwards - given that protons transfers are very fast - this implies that the activation energy of a proton transfer reaction is small. And as outlined above - the activation energy is small in part because most of the time, protons are unhindered. What else might contribute to the small activation energy of a proton transfer/kinetic favorability of a proton transfer?


texts: How to designate the position of an amine substituent in an alkyl-chain?

texts:
Why is 1-phenylethanamine named like it is using IUPAC rules? Why isn't it 1-phenylethan-1-amine?

I thought you had to designate where the amine group would be? I.e. the first position on the ethane-chain.


texts: What is the adverb for a "hydrogen bond"?

texts:
I am looking for some opinions concerning the terminology around hydrogen bonds. Other types of bonds can be expressed as an adjective: "The atoms are bonded covalently." or (though less common) "(...) are bonded ionically.". Sometimes the sentence can be made clearer, and its length reduced, by using the adverb form rather than the noun. In the case of hydrogen bonds, I often end up with awkward and longer-than-they-need-to-be formulations, because I feel I need to use the noun form.

However, I have come across the term "(...) are hydrogen-bonded" or "(...) are H-bonded". This is inventing a new verb, and some people do not like (I have gotten feedback on reports). "The two water molecules are bonded hydrogenly" seems odd, and no results are found in Google. So, what do you do?

My own opinion is to use "H-bonded", as I feel this gets the message across without ambiguity in a concise way.


texts:
At the moment I am cleaning crucibels in aqua regia. I was wondering, whether I could stir it with a standard PTFE stirring bar or not?
I am not sure if it is needed or if the normal flactuation in the liquid is enought but usally stirring makes things better.
There is no doublebond in it to be attacked by Cl-radicals and C-F is one of the strongest bonds so I could not think of any reaction that could occur. But maybe there is some crazy side reaction I am not aware of.


texts: Polarisation of electron clouds by partially positively-charged hydrogen atoms

texts:
Premise of my question:
I was just wondering about this as I was writing a response to the question (linked here: Bicarbonate decomposition and pKa): Is it possible for partially positively-charged atoms participating in covalent bonds to polarise the electron cloud of the electron-rich part of the molecule to the extent that it becomes unstable. FYI My response explained the instability of the carbonic acid molecule by the polarisation of the "carbonate ion" by the "hydrogen ions". The reason I have placed quotation marks on the two ions is that they are no longer ions, but rather just partially positively-charged atoms in a neutral molecule. But I am calling them "ions" so as to emphasise the magnitude of the partial charges on them.

Point of contention: I believe this is contentious because we always describe the polarisation of an anion by a cation, not the polarisation of the rest of a molecule by one atom of the molecule. By the former, I am referring to cases aluminium carbonate, iron (III) carbonate etc. To clarify, polarisation here refers to the distortion of the electron cloud of molecules/ions. (This post over here discusses polarisation of anions by cations in greater detail: Polarising power.)

Rationale for my argument: But I don't see why the partially positively-charged hydrogen atom cannot polarise the electron cloud of the rest of the "very polarisable" molecule because it has been established that hydrogens bonded to electronegative atoms, such as F, O and N, tend to behave like a "bare protons", stripped of a lot of electron density. This also makes hydrogen bonding a particularly strong type of an intermolecular force of attraction.

My stand: Thus, the partial positive charge on the hydrogen atom is of quite a large magnitude, such that it is capable of strong polarisation of electron clouds.

Question to users: Firstly, I want to know if covalently-bonded hydrogen atoms can polarise (i.e. distort the electron cloud) the rest of the molecule. Based on my line of reasoning above, it should. Secondly, I would also like to know if this distortion of the electron cloud by the hydrogen atom would lead to instability of species of molecules. In particular, for the question at least, I would like to know if the polarisation of the molecule affects the stability of the carbonic acid species. However, it would be great if we could generalise this relationship between stability and extent of polarisation of the electron cloud, for all molecular species.

Further clarification: "Instability" in this case refers to the ease of decomposition of carbonic acid into carbon dioxide and water.


texts: Why does a Fluoride ion only have a -1 charge and not a -2 charge or more?

texts: Transition elements can form ions with different charges. Why can't elements other than transition elements form ions with different charges? If it is a Fluoride ion, why does it have to be an anion of charge -1? Why can't it have a -2 charge, or more?


texts: Is it possible to make a disaccharide from two fructose monomers? If so, what is its name?

texts:
Maltose is a disaccharide made from two molecules of glucose; and sucrose (table sugar) is made from glucose and fructose. Is it possible to combine two fructose molecules to make a disaccharide?

If so, what is that called? Or if not, what prevents the glycosidic bond from forming?


texts: Comparison between Boron Nitride and Graphite: Interlayer distance

texts:
Boron-nitrogen chemistry has attracted significant attention, partly because a B–N unit is isoelectronic with C–C. Furthermore, the radius of carbon and its electronegativity are roughly the
average of those properties for B and N.

I was going through the structures of BN and Graphite, and here's what I found:
In graphite the C atoms in the C6 rings of one layer lie over the middle of a C6 ring in the layer below. In BN, a boron atom in one layer is directly over an N atom in the layer below.

My question: How do we compare the interlayer distance in boron nitride and graphite?

Attached are the structures for reference:

I looked up some data, and found out that the interlayer distance in graphite is greater than that in boron nitride. I'm not sure why it is so.

Data for interlayer distance:

Graphite: $\pu{335.4 pm}$
Boron nitride: $\pu{333 pm}$


texts: when Al2O3 melts which bonds are broken?

texts:
Previously, I was trying to understand why $\ce{Al2O3}$ has a lower melting point than MgO. An answer on quora said

  Do not confuse the character of the bond between the metal and oxygen with the bonds between molecules in the compound. The polar character of the bonds between aluminum and oxygen is indeed less than between magnesium and oxygen but this describes the energy needed to separate the metal from oxygen. When a solid melts it doesn’t break down the bonds between oxygen and aluminum or magnesium. The intermolecular bonds (that is bonds between one $\ce{Al2O3}$ and another $\ce{Al2O3}$) are in fact weaker than the bonds between two magnesium oxide molecules. This results in the greater melting point of magnesium oxide in spite of the less covalent character of the bonds within the molecule.

But if $\ce{Al2O3}$ is ionic and forms a giant lattice, which bonds that are "between one $\ce{Al2O3}$ and another $\ce{Al2O3}$" are broken?


texts: Easy method of analysing iodine content in supplements?

texts:
Most health-food stores carry supplements supposedly containing iodine for people with iodine deficiency. I recently bought some kelp tablets that are supposed to have iodine but as a consumer how can I be sure that there is any iodine in them at all, let alone the claimed minimum daily requirement.

How do I know that I'm not just taking green-colored sawdust? Is there a cheap way to test a kelp tablet for its iodine content? If not are there testing labs that I could send some kelp to for testing that isn't going to cost me thousands of dollars?


texts: How to determine the speed of GLUT1 transporter using Michaelis-Menten kinetics?

texts:
I am reviewing a passage in my Lehninger Biochemistry Textbook (6th Edition), and the following passage has me very confused.

How can one sentence from this passage claim that when [S]out = Kt, the rate of uptake is 1/2 Vmax, but then go on to say that when the concentration in the blood is close to Kt that GLUT1 operates near Vmax?


texts:
Why is cis-1,2-dichloroethene more stable than trans-1,2-dichloroethene?

Usually, trans compunds are more stable than cis ones, due to less strain and its non-polarity. But, in this case it's quite the opposite. I tried to search the reason behind it, and found that it's supposedly due to the cis effect?


texts: Is there any relation between resonance and smell of a hydrocarbon?

texts: I came across several examples (such as many benzene derivatives) of hydrocarbons having resonance that also seem to have a sharp odour. So, does resonance have an effect on smell?


texts: Finding initial amount of ammonia using equilibrium constant and amount of nitrogen gas

texts:
Question

When an amount ammonia is added at $\pu{600 K}$ in a $\pu{1 L}$ container the following reaction takes place:
$$\ce{N2(g) + 3 H2(g) <=> 2 NH3(g)}$$
The equilibrium constant $K_c = 4.20$ at $\pu{600 K}.$
At equilibrium, it is known that $\pu{0.200 mol}$ of $\ce{N2}$ gas exist in the container. What amount of ammonia was added at the start of the reaction? Choose from the answers below:
$\pu{0.826 mol};$ $\pu{0.482 mol};$ $\pu{1.226 mol};$ $\pu{0.400 mol};$ $\pu{0.800 mol}.$

My attempt
I created an ICE table, but I think it's wrong:
$$
\begin{array}{lccc}
\ce{&N2(g) &+ &3 H2(g) &<=> &2 NH3(g)} \\
\text{I} & 0 && 0 && y \\
\text{C} & +x && +3x && -4x \\
\text{E} & 0.2 && 0.6 && y-0.8 \\
\end{array}
$$
$$K_c = \frac{(y - 0.8)^2}{0.200\times 0.6^3}$$
Solving the equation with Maple gives me none of the answers above. I must have messed up on the table. Can anyone tell me where I messed up?


texts: Why is the number of carbonyl stretches in the IR spectrum different for solid state samples compared to samples in solution?

texts:
I am comparing two IR spectrums of the same molecule, one in the solid state and one in $\ce{CH2Cl2}$ solution. There is only one CO group in the molecule.

Why does the solid state spectrum show two carbonyl stretches, while the solution spectrum has only one carbonyl stretch?


texts: Is there a structured data source containing information on the World Health Organisation's Stability Testing Policies?

texts:
Hoping to automate some product testing guidance software, I've been attempting to find a (hopefully live, up-to-date) Database, Web-service, or other structured data source containing the pharmaceutical Stability Testing policies (zones/countries/conditions) held by the World Health Organization.  But so far, the only format that I can find these policies in is PDF (http://apps.who.int/medicinedocs/documents/s19133en/s19133en.pdf) which is difficult to interpret for my purposes (even more so to automate).

Could anyone confirm the existence or non-existence of a structured data source containing information regarding WHO policy Stability Testing Conditions, Zones and countries within each zone?


texts: In the nitration of compounds such as naphthalene and anthracene, how can you determine which would be the major product? I tried drawing resonance structures for the intermediate formed because stability of intermediate determines which product will be major, but this became too hard for me as there were too many resonance structures and I couldn't really compare them. Can someone please help?


texts: How to correctly prepare a standard solution?

texts:
Having just spoken to my teacher about the creation of a standard solution, and she suggested one way of doing it, however a previous chemistry teacher had told us a different way of doing it. My question is, (of the below methods) which is the "correct" way of doing it, and what are the pros/cons of doing one over the other? If you're interested in the full procedure of making this/any other standard solution (with the names of compounds, it is page 24 here).

Method 1:

The solid was weighed accurately in a weighing bottle, and then transferred to the volumetric flask, and then the bottle is re-weighed to calculate the amount of solid transferred to the flask.

Method 2:

Rather than re-weighing the solid in the weighing bottle, the weighing bottle is rinsed with DI water, and then poured into the volumetric flask. (this is repeated a few times).

If I'm not including enough detail in the above methods please let me know and I'll try to expand. For reference the 2 methods are Part 1, step 3 of the above link.


texts: With a partition coefficient how do you decide which solute concentration is the numerator?

texts:
Kpc = [X(in solvent A)]/[X(in solvent B)]

I realise that Kpc is actuallly a ratio but when you need the numerical value it has to be treated as a fraction.

When it has to be treated as a fraction how do you decide which solvent is A and which is B?


texts: What causes polarization in noble gases?

texts:
According to my knowledge, polarization occurs when in a compound there is a difference of polarity its constituents.

But in the case of noble gases, there is a single component. What exactly is polarization of noble gases and how does it occur?


texts: Why is the molozonide adduct thermally unstable?

texts:
In the mechanism of alkene-ozonolysis, the intermediate molozonide adduct, which is a cyclical but symmetric molecule (shouldn't symmetry about the C-C single bond bring stability?), decomposes thermally into a ketone and a peroxy-zwitter ion via cleavage of the O−O and C−C bonds.
However, it seems unlikely, and is against the symmetry argument. Is there some better explanation? Or we don't know the correct mechanism? Please add some references.
Knowing that there are two symmetrically placed O−O bond in the adduct, the cleavage of the only one bond is weird.


texts: Standard electrode potential for electrolytic vs galvanic cells

texts:
Whys is the standard electrode potential (-) for electrolytic cells but positive for (+)  galvanic cells.

  If E°cell > 0, then the process is spontaneous (galvanic cell)
  If E°cell < 0, then the process is non-spontaneous (electrolytic cell)

  Thus in order to have a spontaneous reaction, E°cell must be positive,
  where:

  E°cell = E°cathode − E°anode

^ above taken form wiki.

Also can someone please explain the follow:

In both cells is the electron flow from

anode -> cathode ??

For electrolytic cells isn't the electron flow from the battery (-) anode to cathode (-) of the cell.

Do we then show this by electron flow as cathode (-) ------> anode (+) [in the actual cell itself]??


texts: Why does sulfur dichloride have a lower boiling point than phosphorus trichloride? Is it to do with the higher number of electrons causing stronger id-id interactions in PCl3, or do we need to compare pd-pd interactions also?


texts: Phase subscript for supercritical reagent?

texts: When writing a chemical reaction, one can use subscripts to denote the phase of a reagent, e.g. $\ce{SiO2 (s)}$, $\ce{H2O (l)}$, $\ce{F2 (g)}$ or $\ce{Na^+ (aq)}$. However, I need to write a reaction involving a reagent that is above its critical point. What is the subscript for a supercritical reagent?


texts:
I'm working on a science project which involves the production of methane. I would like to be able to use the methane as fuel in (e.g.) cars (using octane) or gas tanks (using butane and propane) etc. I have found that there are a variety of coupling reactions out there, but a lot of them seem to involve 'aryl Grignard reagents' which are not relevant to me.

So, I'm looking for a relatively simple method to lengthen an alkane. Preferably the reaction should occur below 100 degrees Celsius.


texts: Why enthalpy changes in phase transition when there is no change of temperature?

texts:
Why there is a change in enthalpy in phase transition?

I'm asking because enthalpy depends only on temperature:

$$\mathrm dH = C_p\,\mathrm dT,$$

and the change in temperature is $\mathrm dT = 0.$


texts: When to include the mass of the dissolved substance in calorimetry problems?

texts:
In some calorimetry problems, in which a substance is dissolved in water and we want the heat of the reaction, the mass of the dissolved substance is included in the mass plugged into mcat but other times it isn't. When should I include the mass of the substance?
For example, in this problem the mass of $\ce{NH4NO3}$ is not added to the mass of water to find the enthalpy:

$\pu{5.44 g}$ of ammonium nitrate was added to $\pu{150.0 mL}$ of water in a coffee-cup calorimeter. The temperature changed from $\pu{18.6 °C}$ to $\ce{16.2 °C}.$ Calculate the enthalpy change for dissolving $\ce{NH4NO3(s)}$ in water in $\pu{kJ mol^-1}.$ Assume the solution has a specific heat capacity of $\pu{4.18 J g^-1 K^-1}.$

But in this problem the mass of $\ce{CaCl2}$ is added to the mass of water:

In a coffee cup calorimeter, $\pu{2.6 g}$ $\ce{CaCl2(s)}$ was dissolved in $\pu{260 g}$ of water at a combined initial temperature of $\pu{23 °C}.$ The final temperature was $\pu{26.4 °C}.$ Calculate the enthalpy change of the reaction.

I would really appreciate if someone could explain to me when to include the mass of the dissolved substance.


texts: Is a spectrophotometric method of measuring the rate of a complex reaction valid?

texts:
A few months back I designed and carried out an experiment to measure the rate of the reaction between ferric chloride and copper.The dependent variable was the rate of the reaction; the independent variable was the the concentration of ferric chloride.

I searched up the reaction and got it from chemiday. There, it stated it as the following:

$$\ce{2FeCl3 + Cu -> 2FeCl2 + CuCl2}$$

So the method I used to measure the rate of this reaction was to use a spectrometer to find a rising absorbance peak for one of the reactants, which I selected to be: $\ce{CuCl2}$.

Then I got some anhydrous $\ce{CuCl2}$ and made a standard curve (Absorbance vs Concentration) for it, so that I could use that to convert the absorbance at it's $\lambda_\mathrm{max}$ to a concentration value.

I carried out the experiment taking the readings at that $\lambda_\mathrm{max}$ at set time intervals, and I reached the conclusion that the relationship between the concentration of ferric chloride and the rate of the reaction between it and copper was a linear one, at least for the concentrations I tested ($\pu{0.1 .. 0.6 M}$).

But now I'm doing more reading to write my report and I found out that this was a complex reaction, meaning that there were several steps to the reaction. After searching up some papers, the consensus seems to be:

\begin{align}
\ce{FeCl3 + Cu &-> FeCl2 + CuCl}\tag{1}\\
\ce{FeCl3 + CuCl &-> FeCl2 + CuCl2}\tag{2}\\
\ce{CuCl2 + Cu &-> 2CuCl}\tag{3}
\end{align}

As seen from above, it isn't as simple as the original single reaction that I mentioned earlier. First, $\ce{CuCl}$ is produced, then it becomes a reactant in the second reaction to produce $\ce{CuCl2}$, and lastly $\ce{CuCl2}$ becomes a reactant to produce $\ce{CuCl}$.

I'm seriously questioning my method after finding out that a series of reactions takes place, not a just single one. Although the data that I got and the conclusion that I reached matched nicely with other papers that I've read, I'm not sure if the explanation behing my method is correct.

Any input would be greatly appreciated. Thank you.


texts:
If Electronegativity of Cl is greater than H2 then why is the bond angle of Cl2O greater than H2O?
Cl2 has more EN than H2 and size of Cl2 is more than H2 but if we go according to EN then more angle should be of H2O as electrons in H2O would more nearer to O2 than the electrons in Cl2O near to O2?


texts: How to get the SMILES of all compounds on PubChem?

texts:
I would like to download all the compounds from ChEMBL and PubChem. For ChEMBL this is easy using their webUI. Nevertheless, for PubChem, it isn't clear how to download all the compounds on the database including their SMILES representations.

I am also not sure how pubchem has 33,000,000 compounds where ChEMBL has "only"  2,000,000.


texts: Migratory aptitude in Baeyer-Villiger reaction

texts:
In short, I do not understand how or why the migratory aptitude is as listed in every textbook I've read.

Firstly, they talk about a positive charge being built up that is stabilised by the movement of the most substituted group.

I cannot fathom such a build up in my mechanisms.

Please help me understand this in a mechanistic fashion.


texts:
A friend recently sent me the following chemistry joke:

As a lover of puns, I'd like to enjoy it, but I think that it is actually false the way it is phrased.

A solution is defined as: "a homogeneous mixture composed of two or more substances" Alcohol alone would not constitute a mixture of multiple substances and would therefore not be a solution.

But in English the word "alcohol" is also commonly used to refer to many recreational drinks containing ethyl alcohol in addition to other types of molecules. Are there any common examples of alcoholic beverages which are solutions in the scientific sense that would make the pun valid, such as liquor, wine, or beer?


texts:
I need to find in which of the following complexes the M-CO bond is stonger:
[WO3(CO)3] and [W(CH3)3(CO)3].

According to my knowledge this is chiefly determined by the π-backbonding and how good donors or acceptors the present ligands are. CO is a great σ-donor as well as a decent π-acceptor while CH3- functions as a donor. Now apart from the final answer, I'm not sure about the oxygens. Is there a dioxygen ligand alongside with an oxo ligand? If that's the case I think the second compound would present a stronger M-CO bond since only the CO ligands can receive charge from the metallic centre. Is this approach correct?


texts:
in RDKit, there is this nice function to decompose a chemical compound into its scaffolds.
Is there a way to automatically name the scaffolds?
I usually search names in PubChem but this may not be practical for a large dataaset.


texts: How to understand this form of writing the solution: (some salt • n H₂O)?

texts: For example — "high purity chloride salt of Zinc $(\ce{ZnCl2.2H2O})$" or "various concentrations of $\ce{FeCl2.4H2O}$". What does the number before $\ce{H2O}$ mean?


texts: Final product when sp2 oxygen of acid is O18 in fischer esterification

texts: In the question above, i was curious about option 3. If the carbonyl oxygen is O18, shouldn't half of the product we obtain contain O18 on the carbonyl since we have two possible leaving groups with equal probability of leaving?


texts: How and why can more volatile acids be made with sulfuric acid?

texts:
I have read that sulfuric acid has low volatility. Then it states that more volatile acids can be made using sufuric acid and their corresponding salts, because of the low volatility.

Can you help me understand the chemistry behind the second statement?


texts: How do you melt metals with super high melting points?

texts:
At the Renaissance fair a few years back I was watching a smith forge metal into shapes. During this time a very odd question came to me. I was wondering what the furnace was made of. My logic stated that whatever the furnace was made of must have a higher melting point than the materials he was melting. This quickly turned into an elemental arms race resulting in an odd question of how do we melt stuff like refractory metals (more specifically the one with the highest melting point) so we can melt other things inside of it.

Now I know that (for some odd reason I don't understand) rapid cooling can manipulate the strength of an item. Is there a similar property to manipulate the melting point?

Note: My current best guess (like can be done to make weapons harder) is that we take two elements, melt them, and the resulting compound has a higher melting point.


texts:
Can something be both a nucleophile and a brønsted base?
Also , I'm actually quite confused about the difference between these two terms.


texts: Identifying the dependence of various time-independent wavefunctions

texts:
I'm tasked with finding the variables that each of the following wavefunctions depends on: (1) a free particle in 2 space (2) a free particle in 3 space (3) a hydrogen atom (4) a lithium atom.

for situations (1) and (2) I get $\psi(x,y)$ and $\psi(x,y,z)$. However, regarding situations (3) and (4), I'm unsure how to proceed - advice?


texts: Conflict Between Organic and Physical Chemists--explaining the intensities of IR absorptions

texts:
I am currently a Chemistry undergrad and I love to fact check everything my O Chem professor says against my research advisor, a physical/computational chemist. Well, my O Chem professor, when discussing IR absorptions, said something which was a simplification for teaching purposes but which seemed rather unusual to me. He said that high intensity peaks are due to a large change in dipole (clealy true) which often corresponds to more electronegative bonds and then gave the example of carbonyl absorptions which are intense, or nitrile absorptions, or $\ce{CO}$ single bond absorptions, etc.

What he then said, and says he has no good explanation for, is the following:

The absorption of an $sp^3$ hybridized $\ce{CH}$ stretch is high-medium intensity.

The absorption of an $sp^2$ hybridized $\ce{CH}$ stretch is medium intensity.

The absorption of an $sp$ hybridized $\ce{CH}$ stretch is medium-low intensity.

Of course the hybridizations given refer to the hybridization state of the carbon to which the hydrogen is attached.

The reason he has no good explanation for this phenomenon is that in most other situations, an $sp$ hybridized carbon will behave as if it is more electronegative than an $sp^2$ or $sp^3$ hybridized carbon.

An example of this would be that $pK_a$ of an $sp < sp^2 < sp^3$. That is a characteristic of how electronegative they are in an acid-base sense.

Here, however, we see the opposite trend. That is, when the more electronegative stretch should have a higher intensity peak, it is weaker, and the less electronegative stretch has a high intensity peak.

For the record, the arbitrary assignment of more and less electronegative based on behavior isn't super satisfactory to me, and is probably why I'm digging deeper on this.

So, my advisor essentially said all that matters is this equation: $$f=\left\langle\psi_0\right| \mu\left| \psi_v\right\rangle^2$$
Basically, he said I can ignore the wavefunction details of the equation because the wavefunctions of the three stretches are not going to differ by much because they all have identical reduced masses and some other stuff I can't remember.

So, all that matters is the dipole moment change as the bond is displaced from its equilibrium position.

His physical explanation of the intensities described above is that there is a smaller dipole moment change for $sp^2$ and $sp$ hybrid carbons because the electron density is trapped in the double and triple bonds more so than in the single bond. That seems reasonable to me.

The Organic Chemist fires back, however. He says that he would expect intensity to increase with the double and triple bonds because the electron in pi bonds are in a higher energy state than the sigma bond electrons and are thus more easily displaced which ought to result in a larger dipole moment change. That also makes a lot of sense I think.

So, is my advisor correct or is there a more complicated explanation?

Sorry for being so long-winded, I just wanted to get past the simple explanations so that we can have a deeper, better answer.

Edit: A very good answer would also explain why $sp$ hybridized C-H stretches are sometimes very high intensity. Even as high as $sp^3$ stretches at times.


texts: Why strong bases only give elimination products as major while they could give substitution products too being good nucleophiles? (I am excluding those non nucleophilic bases)


texts: If aqueous $\ce{NaCl}$ and $\ce{NaClO}$ are added together no reaction occurs, but if you add dilute acid to the solution $\ce{Cl2}$ gas is formed. Why does this reaction only happen in acidic media? I know that there's something to do with the reduction potentials but I couldn't formulate a full explanation for this effect.


texts: What is this wave function in Chemical bonding?

texts: Was studying chemical bonding(Valence bond theory) but there came this topic called wave equation but  have not studied quantum mechanics,so finding hard to understand these terms.Please help!!!


texts: Identification of solutions by solubility when mixed with each other

texts:
$\ce{Pb^{2+} (aq), Cl- (aq), Ag+ (aq), (SO4)^{2-} (aq)}$.  You number the four bottles, 1,2,3,4and while numbering them, you notice that bottles 1 and 3 have the word "cation" on their lids while bottles 2 and 4 have "anion" on their lids. You decide to test them by mixing them together in pairs, but you have only three empty beakers. When the solutions are mixed in pairs.
Three combination give white precipitates;
Bottle 1 + bottle 2. bottle 1 + bottle 4, bottle 2 + bottle 3. ive done each combination and theyre all insoluble? but my chart says there has to be 1 combination thats soluble and 3 that arent ?


texts: Is atom-clean aluminum active enough to react with alkali salts?

texts:
Thermally evaportated $\ce{Al}$ under high vacuum is free of oxidized species and highly active. But is it active enough to even substitute the alkali cationic metal in alkali salts, like $\ce{LiOH, NaOH, Cs2CO3}$.
Here $\ce{Al}$ is directly depositely onto the salt substrate.


texts: How can I find the parent chains in these two compounds?

texts:
We recently started organic chemistry in school and I decided to make a computer program that names the compounds, so far it works with alkanes that do not have branched branches and I want to make it work with compounds with double and triple bonds. I know that if there is only one double/triple bond, the answer is just the same rules as with alkanes, but it must include the 2 atoms that are bonded in that way. Also, I would appreciate it if you tell me how I decide from which side to number them.

Compound 1:

Compound 2:


texts:
Assume I have kept a single molecule in vacuum and in absolute zero (0 K) temperature. There is no energy left in the particle, and hence any type of motion is absent.
Now, what happens when I increase the temperature of that system? Does the molecule start to move? Does the energy increase?
What does temperature even mean in vacuum?
I don't know I'm asking a good question, but this troubles me a lot.


texts:
For hydrogen atom, L^2 and Lz can be obtained as eigenvalues for a particular wave function. But that does not completely specify the angular momentum vector. How to get about this problem?

Also, in the orbital approximation (ie the solutions obtained after ignoring electronic repulsions in the Hamiltonian) of the many electron atom( say helium) how does one go about finding total orbital angular momentum?


texts: Electronic spectra of transition metal complexes

texts:
I have been studying about the UV-Vis spectroscopy. Sometimes we are given a graph which shows the absorbance and the wavelength,the appropriate Tanabe-Sugano diagram and we are asked to assign the transitions to the bands.
I know that the bands can be d-d transitions, Ligand To Metal Charge Transfer or Metal To Ligand Charge Transfer or π→π* etc.Out of the things that I have studied, d-d transitions have low intensity whereas the LMCT phenomenon is extremely intense.

The part which gets confusing for me is I have seen some exercises for the complex [Co(H20)6]2+ for example, and there was a question that said why there is a small intensity band at ~640nm and the answer was because there is a two electron transition. Also, in another example of the complex [Ni(H2O)6]2+ where there was a question about why there is a shoulder, the answer was that it is spin forbidden and it has to do with borrowing energy from a close band.

Is there a way in order to understand if a small band is because of d-d transition or borrowing energy from another band or of a two electron transition etc?


texts: Different solder composition affects the connection strength?

texts:
I was wondering if the tin/lead/other metals bond with the metal parts that are low-temperature soldered. I know that the flux in the solder is used to remove the oxide layer, leaving a clean metal surface ready to form metallic bonds (I think).

So for example, should I use a tin/silver/copper eutectic to bond a silver surface and copper wire? Will that make a difference or can I use tin/lead with the same result? For example, do we get a different connection strength? In every case the solder material is mostly made of tin, which is why I was wondering what's the real impact of the other components.


texts: Why is potassium permanganate paramagnetic?

texts: $\ce{KMnO4}$ is coloured due to charge transfer spectra. As Mn doesn't have any electrons, it shouldn't be magnetic. But, according to the magnetic susceptibility value given on Wikipedia, it comes out to be paramagnetic. How is it possible?


texts: Carbon dioxide concentration from pressure changes

texts: Is there a way of determining the concentration of CO2 if we know the pressure in the container before the addition of CO2 and the pressure in the container after the addition of CO2 if we have no way of measuring the amount of CO2 delivered to the container (like with a CO2 controller with a CO2 monitor)? For instance, if we have a sealed container with air in it at 298 K, whose pressure is measured at 1 atm, and we introduce carbon dioxide gas causing the pressure to increase to 1.2 atm... can we use the ideal gas equation and assume that the 0.2 atm increase is due to addition of CO2 and is the partial pressure of CO2 and just use 0.2 atm/(0.0821 × 298) = 0.008 m/L (approx. 352 ppm) as the concentration of the CO2 in the chamber? Or, is there more to it?


texts: The intermolecular distance between the molecules are much greater than the diameter of the gas molecules so we neglect their volume compared to the volume of container. "The rapidly moving particles constantly collide among themselves and with the walls of the container. All these collisions are perfectly elastic. This means, the molecules are considered to be perfectly spherical in shape, and elastic in nature". How then are molecules thought to be perfectly spherical in shape although its volume is neglected.


texts:
I am investigating ways to reliably decontaminate instrumentation that has come into contact with mammalian prions. Chaotropic salts and extreme pH are good at inactivating prions by disaggregating the assemblies of PrP.

Also phenol is among the most effective "prionicidal" agents. I presume that this is because it flips hydrophobic side chains of proteins towards the solvent, thereby denaturing/disaggregating PrPSc. My questions are:

is this true?
if so, might other phenolic scaffolds/derivatives be even more effective for prion disinfection?
and if so, which scaffolds might be most promising?


texts: Derivation of the Temperature Dependence of the Boltzmann Distribution

texts:
In lecture notes, Atkin's Physical Chemistry, etc. the Boltzmann Distribution is derived by first claiming that the system takes on properties of its weightiest configuration. The weight is therefore maximised, utilising Lagrange multipliers.

\begin{align}
\nabla \ln{W} - \alpha \ \nabla \sum_i n_i - \beta \ \nabla \sum_i n_i\epsilon_i &= 0
\\
\to \frac{\partial{\ln{W}}}{\partial{n_i}} - \alpha - \beta \epsilon_i &= 0
\end{align}

The Stirling Approximation transforms the derivative to something we can work with, and the Boltzmann distribution is eventually derived.

\begin{align}
\frac{\partial \ln{W}}{\partial n_i} &= -\ln{\frac{n_i}{N}} \\
&\vdots \\
\frac{n_i}{N} &= \frac{e^{-\beta\epsilon_i}}{\displaystyle \sum_i e^{-\beta\epsilon_i}} \hfill
\end{align}

The derivation is left there with no mention of the value of $\beta$, though it is later claimed $\beta = \frac{1}{kT}$. How is the value of $\beta$ ascertained?


texts:
While studying particle on a sphere, I read that boundary condition on $\theta$ and $\phi$ results in quantization.
I understand boundary condition for $\phi$ part which varies from 0 to 2$\pi$. As $\psi(0)$ should be equal to $\psi(2\pi)$ otherwise in standing wave the wave function can have more than one value and can interfere destructively.

But I am not able to figure out boundary condition for $\theta$ part which varies from 0 to $\pi$. In books,the result is directly quoted as "Boundary condition in $\theta$ part resulted in quantization which restricts the quantization in $\phi$ part". Quantization in $\theta$ part is called as azimuthal quantum number$(l)$ and $\phi$ part is called magnetic quantum number($m$) which varies from $-l$ to $l$.

Please tell what would be the boundary condition for $\theta$ part. I am not able to figure out and visualize it.


texts:
This component is mentioned in an article called "Novel geopolymer materials containing borate and phosphate structural units".
I've never heard about this before, and a google search didn't really give an answer it seems.


texts:
I am facing a challenge, and this is my first question in this stack exchange. I have worked out the following problem but the answer I got (number of shots) is ridiculous. Could any of the chemist here please advise me where I went wrong?

Question: Assume that you are on vacation in Florida and enjoying the company of friends at a bar. Using the information in Table 80-1 in your text, calculate the number of shots of Captain Morgan’s rum required to take your blood ethanol concentration above twice the legal limit to drive. [Note: The legal limit in Florida is 80 mg/dL]. Assume that the shots are consumed in rapid succession (the wisdom of which you were later unable to explain). Show your complete calculation, including all inputs and assumptions.

My calculation:

Table reference

Let us assume that my binge-drinking has led to a blood alcohol concentration (BAC) of 162 mg/dL.

The formula for BAC is as follows:

`BAC = A/(R x W) – (0.15 x H)` where

A = weight of pure ethanol consumed (g)
R = Widmark’s rho factor (0.68 and 0.55 L/kg for men and women, respectively)
W = body weight (kg)
0.15 = average ethanol elimination rate in humans
H = drinking period (hr)

Inserting the values of 162 mg/dL for BAC, R = 0.55 L/kg, W =  50 kg, and H = 1 hr, the equation becomes:

162 = A/(0.55 x 50) – (0.15 x 1)
162 = A/27.5 – 0.15

Therefore,

A = 27.5(162 + 0.15)
    = 4459.125 g

According to table 80-1 in the book, one shot is 30 mL and contains 40% ethanol.
So one shot contains 12 mL ethanol.
Density of ethanol = 0.789 g/cm3
The volume of pure ethanol which I consumed = 4459.125/0.789                                                                       = 5651.62 mL
So, no. of shots consumed = 5651.62/12 = 471, over the course of 1 hour

Conculsion: 471 shots of Captain Morgan Rum is absurd for any person. So I think I am missing something in my calculation. I'm not able to figure out what it is.


texts:
Why does methane have two different ionization potentials? How does this work? I understand that MO theory predicts C-H bonds of differing strength, while hybridization predicts C-H bonds of varying strength.

http://books.google.com/books?id=gY-Sxijk_tMC&pg=PA827&dq=methane+ionization&hl=en&sa=X&ei=VrMVVN3JLI-vogTv8IGABw&ved=0CCgQ6AEwAA#v=onepage&q=methane%20ionization&f=false

Is methane ionized successively and is are there two different ionization energies found? Doesn't this make intuitive sense; by ionizing methane we end up with a fundamentally different molecule which would more than likely have different ionization energies.

Also, how are these ionizations performed? The reference given above makes no mention of whether the bonds are broken homolytically or heterolytically (although ionization implies heterolytic bond cleavage). Even then, there are two ways bonds can be cleaved heterolytically.


texts: What does the phase diagram mean by "liquid" at NTP? (The liquid and vapor coexist even when the situation is not on the curve)

texts:
[Solved. For anyone who is also confused, see the comments under Poutnik's answer. As Poutnik reminds me, remember there is no air involved. I successfully picture that with the piston experiment in Karl's answer.]

When I read the phase diagram, I think it suggests that "at certain temperature and pressure, the phase of water would be (solid, liquid, gas) or two/three of them coexisting."
But when I look up NTP on the diagram, it says "liquid", while the saturation pressure of water at 25°C is 0.03atm. So the situation can't exist since the vapor is going to condense until the pressure drops to 0.03atm.

Then what actually is the phase diagram suggesting by "liquid"?
What am I missing here?

Edited: Poutnik reminds me that the pressure is the total pressure, not the vapor pressure. Then my question should be "If the vapor and liquid coexist not only at the curve, then what is the meaning of 'liquid' on the diagram?"


texts:
I came across a problem which stated that borole isn't aromatic. I thought that borole is similar to pyrrole so it should be aromatic, but that isn't the case. Can I know why isn't it aromatic?
I was also wondering if we replace the nitrogen in pyridine with boron then will the compound remain aromatic?


texts: Potassium sulfate as a byproduct of manganese heptoxide synthesis?

texts:
Manganese heptoxide may be  formed by the action of concentrated sulfuric acid on potassium permanganate (ref):

$$ \ce{2KMnO4 + 2H2SO4 -> Mn2O7 + H2O + 2KHSO4} $$

Could the amount of potassium permaganate as a reactant in the reaction be increased to yield potassium sulfate as a product instead of potassium bisulfate as shown?


texts:
I've heard that the kinetic energy of any different gases are the same

  All gases at a given temperature have the same average kinetic energy.

But if we have 2 moles of hydrogen and 4 moles of helium in a container at a specific temperature will the kinetic energies become the same?
I think it cannot be as the n is different..

As the kinetic energy is
3nrt/2

This might be a small question but this has been a conflict between my friends..


texts: Dosing leaves with Zinc Nitrate for pollution experiment - Need specific concentration

texts:
I am trying to assess the pollution tolerance of an insect using Zn as a proxy. I have a supply of Zinc Nitrate Hexahydrate that I want to use to contaminate dried leaves (the insect's food). The LD50 for my insect is around 2000 micrograms g^-1.

I was thinking I could achieve this by using 0.1 g squares of dried leaf that I would contaminate by topically applying 1 ml of Zn solution. To get my desired concentration, I am thinking that I would dissolve 200 micrograms of Zn into 1 ml of distilled water, so that when I apply 1 ml of this solution to a 0.1 g square of leaf I would have a final concentration of 2000 micrograms/gram of food. But if I wanted to apply only 0.5 ml of Zn solution to 0.1 g of leaf but still have the same final concentration of 2000 microg/g food, I would create a solution of 400 micrograms/ml. And if I wanted to use 1.0 gram of leaf and have a concentration of 2000 micrograms/g, I would make a solution of 2000 micrograms/ml. Is all of this correct?

I am also open to suggestions of how to better contaminate the food in a more consistent way. I thought about soaking leaves in a defined concentration, but then I am worried that some leaves will absorb more or less liquid than others, making the final Zn/g food concentrations unequal across different leaves.

Thank you for any solutions (pun intended) anyone might provide.


texts:
How does one recognize lipophilic points, hydrogen bond acceptors and hydrogen bond donors in organic molecules? For example, provided this SMILES instance

O=C1NC(=O)SC1Cc3ccc(OCCN(c2ncccc2)C)cc3

I know it contains 2 lipophilic points, 5 hydrogen bond acceptors and 1 hydrogen bond donor. How can I determine them?


texts: Does symmetry lower the energy of molecules?

texts:
Why does nature "prefer" symmetry? Why is symmetry energy-lowering? I keep hearing statements along the lines of this tossed around by chemists. Here are some examples:

https://physics.stackexchange.com/questions/135671/nature-favours-symmetry

https://books.google.com/books?id=WkRy8b0F2HwC&pg=PA153&dq=nature+favors+symmetry&hl=en&sa=X&ei=V__fVPvpGsuxggSptIG4AQ&ved=0CDAQ6AEwAw

IBrF2 - van der Waals repulsions - and number of unique bond angles (The more symmetric conformation of the molecule is probably preferred).

So:

1) Are any of the above statements true? If so, can you provide example(s)?

2) I think the statement is false at least to some extent. Consider cyclobutadiene ... it's not a square; it's a rectangle.


texts: Why does NO2 react with HCl ? What is the mechanism of the reaction?

texts:
I found the following reaction given in a certain book:
 $$\ce{2NO2 + 4HCl -> 2NOCl + Cl2 + H2O}$$

I cannot think of any reason why an acidic oxide like $\ce{NO2}$ will react with an acid like $\ce{HCl}$.

So, why will they react? And, what will be the mechanism of the reaction?


texts: Why does hydrogen bonding require a lone pair?

texts: Why does hydrogen bonding require a lone pair of electrons on the partially negative atom? They would still be partially negative even without the lone pair right? Or does a bond exist, but is much more negligible compared to when a lone pair is there?


texts:
I am pretty confused by some principles of resonance. Well by my study of electrostatics I know that potential energy of a system of  charges of same nature decreases as we increase the separation between them but same doesn't goes with a system of charges with different nature because their potential energy decreases as we decrease their separation as internal conservative forces do positive work.

I am a newcomer in chemistry so I have a doubt that my book says that energy of a molecule is minimum when they are separated by large distance (under the heading of application of resonance) without caring for nature of charges.This fact goes well for charges of same nature but contradicts the fact for system having different nature of charges.

Please tell me  that why this contradiction exists.


texts: I have been thinking about energy levels of an atom. When we study line spectra of hydrogen atom we say that when electrons jumps back from a higher shell to a lower shell it emits photons of certain frequency, but in that example we say that hydrogen has infinite energy levels and electron can jump back from any level. But when we study bonding we say that some atoms lack in d orbitals and for example say Nitrogen has no d orbitals, but when doing line spectra it has infinite energy level. How these two statements hold up with each other?


texts: Why is the pressure correction constant 'a' independent of temperature?

texts:
In the van der Waals equation of state, 'a' which is the correction value is based on inter-molecular forces of attraction? Then should inter-molecular forces decrease when temperature increases, and thereby cause a change in value of 'a'?

Then why is 'a' independent of temperature?


texts: What chemical available in 18th century would explosively react with phosphorus?

texts:
For fictional use, I'd like to "construct" a clockwork device featuring phosphorus which could reasonably be expected to:

A) glow consistently.

B) explode upon some trigger (e.g., influx of air, mixture with another chemical, a spark), with enough explosive force or incendiary strength to kill someone standing very close.

Constraints:

1) this takes place in the early 18th century, so phosphorus has been discovered, but most of the modern types of phosphorus used in weaponry have not.

2) the quantity is no larger than a couple of liters.

Progress:

I've read the relevant chapters in Emsley's 13th Element, and then moved on to the primary sources for the time – mostly records of demonstrations held for the Royal Society and Boyle's Aerial Noctiluca.
It's hard to tell exactly what sort of phosphorus any of these early chemists were working with, but it looks like I can achieve goal (A) by just letting in a bit of air now and then (based on Boyle's description / Wikipedia on oxidation).

Goal (B) is more difficult. Is just oxygen enough?

Slare added sulfuric acid ("oil of vitriol") and achieved something, but it doesn't seem to have been an explosion exactly:

  being well shiken together did first heat, and then throw up such fiery Balls, which like so many stars will adhere to the sides of the Glass and continue to burn for some time


texts: How to find the concentration of an of ammonia solution by titration with nitric acid?

texts:
I am stuck with this question I am doing:

To determine the ammonia ($\ce{NH3}$) concentration in a cleaning product, a chemist diluted 20 mL of the product to 500 mL. Of the 500 mL solution, 25 mL was titrated with 0.151 M $\ce{HNO3}$. The endpoint occurred at 26.2 mL. Calculate the concentration of the cleaning fluid.

[Ans: 3.956 M]

What I have done so far:

I worked out the moles of $\ce{HNO3}$ that the $\ce{NH3}$ must have reacted with, using the concentration and volume they gave me. I got 0.0039562 moles.
I then wrote the balanced equation and worked out that the stoichiometric ratio of $\ce{HNO3:NH3}$ must be 1:1. Therefore, I worked out that the amount of moles of $\ce{NH3}$ reacting with the $\ce{HNO3}$, must also be 0.0039562 moles.
From here, I initially worked out the concentration of $\ce{NH3}$ reacting with $\ce{HCl}$ and got 0.158 M, but then I realised this wasn't what the question was asking. I tried using 0.02 mL as the volume instead (as this was the very initial volume of $\ce{NH3}$) but still got the wrong answer.

Can someone please tell me what I have done wrong/ guide me in the right direction.

Edit: I have just tried it again, and this time I used the concentration I previously found (0.158 M) and a volume of 0.5 L to work out the number of moles in the 500 mL dilution of the product. I used this value which was 0.079 moles and a volume of 0.02 mL which was the original volume of cleaning liquid, to work out the concentration. I seem to be getting the right answer, but is my working correct?


texts: Why are fluoride ions (and ions in general) reactive?

texts:
Please bear with me—-I have a pretty meager background in chemistry but am trying to learn some!

My question is about ion reactivity—-specifically of the reactivity of $\ce{F-}$.
I often hear that the main reason the “weak” acid $\ce{HF}$ is so dangerous is because of the fluoride ion rather than the $\ce{H+}$. The impression I’ve gotten is that fluoride is the real hit man in this situation, with the $\ce{H+}$ only really serving to corrode barriers to entry.

A search for “fluoride ion reactive” yields the following sentence: (source)

  Unlike other hydrogen halide acids, the anion (fluoride ion) is quite reactive, and can form fairly insoluble salts with alkaline earth metals such as calcium and magnesium.

However, I think I’m fundamentally failing to grasp something. Why is this insoluble salt effect specific to fluoride? It’s obvious why fluorine is reactive, but why is the octet-satisfied fluoride reactive as well? And how does fluoride reactivity compare with the other halides?

I have also heard people say that fluoride is a bad nucleophile, which makes sense given how tightly it holds on to its electrons. So I can’t quite wrap my brain around why fluoride would want to react with anything at all. Wouldn’t that just force it to share its extra electron with another atom? (Is there such a thing as “electronegativity” but for ions rather than atoms?)

After thinking about it, I realized my confusion extends to all ions in general. Why would “fully dressed” ions with full octets do anything but sit around on the couch eating Cheetoes?

There’s definitely something stupidly fundamental that I’m missing — hopefully someone can point me in the right direction!


texts: I have bought a zinc sheet and with SEM I can see a ZnO layer, which is a passivity layer. But when I connect this sheet to a conductive wire, le zn sheet is conductive too. Is that normal ?  the ZnO layer should prevent the Zn/wire connection from, isn't it ?


texts: Tools to draw molecular structure (wireframe) along with atom numbering

texts:
I am looking for open-source tools which can generate 2d molecular structure from the MOL or SMILES file. Further, it SHOULD number the atoms in the order of occurrence of atoms in the connection table of MOL file or SMILE string. I used MarvinSketch 6.1.2 but the position of numbering is not very good, as it get cluttered with the bonds.
Please refer some tools with which I can draw molecule similar to the one shown in figure but numbering is also clear. In the figure, all numbering except 1-7 are ok.


texts: Why does gaseous HCl not change dry blue litmus paper to red?

texts: I am doing a practical in lab, in which HCl is to be evolved. I found that when blue litmus is near the evolved gas, it doesn't turn red. But, when litmus is dipped in water and then brought near the HCl gas it does change to red. Why is this happening?


texts: How come we can't use the equivalence point equation of NV=NV in this problem?

texts:
So, the problem is you prepare to standardize a $\ce{Na2S2O3}$ solution. $\pu{32 mL}$ of $\ce{Na2S2O3}$ solution is titrated into $\pu{50 mL}$ of a $\pu{0.01 M} \ \ce{KIO3}$ solution to reach the equivalence point. They first titrate the $\ce{KIO3}$ solution until it loses color, then add a starch indicator until the reaction is complete. The reaction proceeds in these two steps:

$$\ce{IO3- + I- + H+ <=> I3- + H2O} \tag{1}$$
$$\ce{I3- + S2O3^2- <=> I- + S4O6^2-} \tag{2}$$

Determine the concentration of $\ce{Na2S2O3}$ solution at the beginning of the experiment.

The answer is $\pu{0.094 M}$, and basically you need to first balance out the two formulas to create a net ionic equation for the two reactions, and then you use the moles of $\ce{KIO3}$ (it's molarity times it's volume) and then the balanced stoichiometric ratio ($\pu{6 mol}$ of $\ce{S2O3^2-}$/$\pu{1 mol}$ of $\ce{IO3-}$) to get the moles of $\ce{S2O3^2-}$, which is the dissociated version of $\ce{Na2S2O3}$ in a $1:1$ ratio (dissolved $\ce{Na2S2O3- -> 2Na+ + S2O3^2-}$). Then you just divide the moles of $\ce{S2O3^2-}$ by it's volume converted to liters to get $\pu{0.094 M}$.

My question is, since we are looking at the equivalence point in a titration, why can't we use $N_\mathrm{acid} \times \pu{Volume_{acid}} = N_\mathrm{base} \times \pu{Volume_{base}}$, since equivalents of acids and bases are the same at the equivalence point? If we can, how would we do it?


texts: Why so differance in alkali halide's crystal forms?

texts: I always wonder that though Both $\ce{NaCl}$ and $\ce{CsCl}$ are alkali halides, why they adopt different crystal forms, FCC and BCC respectively? and I have a doubt about $\ce{CsCl}$ structure that Why the $\ce{Cs+}$ or $\ce{Cl-}$ ions are not located at voids/lattice points as like as $\ce{NaCl}$ structure?


texts: Stability of complexes based on number of rings

texts:
$\ce{[Co(edta)]^-}$ has 5 rings in total and in $\ce{[Co(en)_3]^{3+}}$, there are 3 rings. The stability of the former is more than that of the latter. The reason I was told was that a complex with more number of rings is more stable.
Why is this so?


texts: Is there any paper making alternative? What is there in trees that makes it the only thing from which paper can be made? Do we even need paper anymore with all electronic devices and stylus', etc


texts: Is there a chemical that will etch antimony but not stainless steel?

texts:
I am working with ultra high vacuum equipment made out of stainless steel that has been contaminated with a number of metals, but in particular Antimony.  We'd like to do some machining of the equipment but this requires cleaning prior.  The amount of contamination is only a few hundred nanometers, but needs to be removed.  Is there a wet chemical etch that would selectively etch antimony (and antimonides) but not stainless steel?

I had initially considered $\ce{HNO3}$ as a possibility, but it appears without $\ce{HCl}$ or $\ce{HF}$ (which will make the solution etch Stainless) its etch rate of antimony is either slow/negligible or unreported.  I'm currently trying an experiment etching a small antimony pellet, but the initial results are not promising.

Any possible solutions would be preferably easy to mix and not require overly strict ventilation.  The etch will be contained and ventilated to an exhaust; however, doing it in a fume hood is not practical due to the size of the equipment.  Additionally, this means that highly toxic/corrosive chemicals are undesirable (e.g. $\ce{HF}$).


texts: Why is the melting point of iodine so high compared to ammonia? What about Zn and C(diamond)?

texts:
Increasing order of melting point by searching the temperature on the web:

  $$\ce{NH3} <\ce{I2} <\ce{Zn}<\ce{C_{diamond}}.$$

The idea I have read on "Chemistry: The Central Science" by Theodore L. Brown, H. Eugene LeMay Jr., Bruce E. Bursten on Chapter 11 says something related:

We need more energy to break intramolecular bonds than overcame an intermolecular bond. So, as much stronger is the bond, most energy is required to overcome it.

I want to know why $I_2$ has a higher melting point than $NH_3$. I suspect that $I_2$ has the strongest bond (so a bigger melting point). $I_2$ has intermolecular bonds such as dispersion force (It has big polarizability because of its larger size so his intermolecular bond is strong) and $NH_3$ it has Hydrogen bonding force (the strongest intermolecular force) and also dispersion force. So, I think, but I am not very sure that iodine's force is bigger than NH3 force because of its size (and polarizability).

Is it correct? Must I have into account covalent force in $I_2$?

And why Zinc has an upper melting point in relation with C? Is it because Zn has a covalent bond and Zinc metallic bond or it does not matter?


texts: Why is the first ionization enthalpy of molecular O2 less than atomic O?

texts:
A cousin of mine asked for my help to answer one of his homework questions. It stated-

Explain why- The first ionization energy of molecular oxygen $\ce{O2}$ ($\pu{1175 kJ mol-1}$), is lesser than the first ionization energy of $\ce{O}$ ($\pu{1314 kJ mol-1}$)?

It took me some time trying to find out perfect reasons for it, because generally, bonded electrons are harder to remove than valence electrons in atoms. But indeed, not just with $\ce{O2}$, but $\ce{F2}$ ($\pu{1515 kJ mol-1}$) also has a first ionization enthalpy lesser than atomic $\ce{F}$ which is $\pu{1681 kJ mol-1}$. (I wonder why there aren't any more talked of!). So I ended up taking a "class" on the basics of MOT, trying to reason that "the energy required to remove an HOMO electron from an ABMO in $\ce{O2}$ is lesser than removing an electron from a bonding orbital. That could probably lead to this anomaly."
But this wasn't convincing enough for me. I could sense a lack of conviction, a whole list of factors that could go wrong, also with the possibility of a much simpler explanation. But what made me post it up here, despite its dubious look, is the lack of convincing information addressing this issue even on the internet. Hence, a proper answer would be helpful for the community at large.


texts: PTFE coating - how? Alternatively, lowering surface energy

texts:
Another part of our experimental setup requires me to lower the surface energy of a small sealed hollow glass sphere (30mm dia) in order to minimize adsorption.
Any idea how I can do this? There seem to be some PTFE sprays, but how well do they adhere to (fragile) glass? Any alternatives ideas?


texts: How did Williard Gibbs come up with the Gibbs equation?

texts:
The equation I am referring to is

$$\Delta G = \Delta H - T\Delta S$$

I understand that this Gibbs free energy determines if a process is spontaneous or not. My question is how did Williard Gibbs, presumably, come up with this equation? Did he do a bunch of experiments and guessed the answer, or did he define this thing called Gibbs free energy because of well motivated theory?


texts: How to calculate the 15 geometrical isomers of an octahedral complex with all ligands different?

texts:
Suppose we have a complex of type $\ce{[Mabcdef]}$ then we know it’ll show geometrical isomerism. According to my textbook (Cengage Inorganic Chemistry II, Page 7.37) there are 15 geometrical isomers possible.

I tried calculating it but ended up with different answers every time.

I think we have to use the knowledge of permutations and combinations for this calculation.