texts: Is water acidic enough for an redox reaction involving H+?

texts:
If you stored $\ce{Pb(NO3)2(aq)}$ in a $\ce{Cu(s)}$ container, would any reaction occur? Lead(II) ions will not react spontaneously with the copper solid as the $E^0_\mathrm{net}$ of the reaction would be negative. However, the $E^0_\mathrm{net}$ of the reaction between nitrate ions and copper solid is positive. The reduction reaction for nitrate ions is
$$\ce{2 NO3- (aq) + 4 H+(aq) + 2 e- -> N2O4(g) + 2 H2O(l)}\qquad{E^0=\mathrm{+0.80\ V}}$$

As is obvious, the reaction requires not only nitrate but hydrogen ions. However, water (the solvent) does have hydrogen/hydronium ions. Would this be enough to furnish the reaction? If not, why?


texts: Has anyone even taken a picture of a molecule to confirm the geometry predicted by theory?

texts: Have the geometries of molecules been proven, or are we operating strictly on mathematical theory? To put it over-simplistically: has anyone ever taken a picture of a molecule to compare against their math?


texts: Why does the electron affinity increase become more exothermic down group 2 and group 5?

texts:
It is generally true that the electron affinity becomes less exothermic down a group, because of the increase in atomic radius.

There is a well-known exception that the electron affinity of Cl is more exothermic than that of F, because fluorine has a high electron density; adding electrons would be unfavorable because of the electron-electron repulsions.

In Group 2 and Group 5, this is more extreme: the electron affinity becomes more exothermic down the group. Why is this so?


texts: In the reaction between salicylic acid and acetic anhydride to produce aspirin, why is it necessary to quench the reaction?

texts: I understand that water is added to hydrolyse acetic anhydride into acetic acid, but what is the point of this?


texts:
Why is an aqueous solution of $\ce{NH3}$ (ammonia) often referred to as $\ce{NH4OH}$?
I know that dissolved ammonia gas reacts with water in the following equilibrium:

$$\ce{NH3 + H2O <=> NH4+ + OH-}$$

However, $K_\mathrm b = 1.8\times10^{-5}$. Since only a small amount of $\ce{NH3}$ dissociates, why is the whole solution called "ammonium hydroxide"?

Is ammonium hydroxide soluble, or is it an actual aqueous species?


texts: Is carbon–sodium bond mainly ionic or covalent?

texts: We all know that carbon mostly forms covalent bonds (almost always) and sodium mostly forms ionic bonds (almost always). But if $\ce{NaOH}$ reacts with ethyne, then $\ce{HC#CNa}$ and $\ce{H2O}$ are formed. Then what type of bond will $\ce{C-Na}$ be: mostly ionic or covalent?


texts:
Inspired by this question, I'm wondering why arsenous acid is frequently denoted $\ce{H3AsO3}$, as opposed to $\ce{As(OH)3}$, which would appear to more accurately reflect its connectivity?

[edit]

I feel like such a doofus, forgetting about sulfuric acid ($\ce{H2SO4}$), phosphoric acid ($\ce{H3PO4}$), and boric acid ($\ce{B(OH)3}$), etc. Great discussion, people!


texts: difference between glyceraldehyde-3-phosphate and 3-phosphoglycerate

texts: In the photosynthetic dark reaction there are two types of reactions: light-dependent and light-independent.  In the light-independent reactions during reduction 3-phosphoglycerate is converted to glyceraldehyde-3-phosphate.  I don't find any difference between them because both have a 3 carbon chain attached to a phosphate group. Can you please clear it up for me because my book says that the latter one is a sugar.  Why isn't the first one sugar too?


texts: Concentrations appearing in the Ka of buffer solutions

texts:
I've just finished studying buffer solutions and I think I understood more or less how they work, but there's something I can't make sense of:

In the $K_a$ of equilibrium of a buffer solution made from Sodium acetate and acetic acid, we just have the concentrations of acid, $\ce{H+}$ and acetate ion. So, why isn't the concentration of $\ce{Na+}$ taken into consideration in the $K_a$? Why just the others?

Moreover as $[\ce{Na+}] = [\ce{CH3COO-}]$ (the acetate ion in solution is almost only the one dissociated from the salt) shouldn't in the Henderson-Hasselbach solution occur a $a^2$ factor? So in the numerator having $[\ce{CH3COO-}]^2$ and no just a single one?

Thank you


texts: How does C−Br bond obtain energy through solvation?

texts:
I came across a question related to SN1 mechanism. In an example of SN1 reaction, i.e. hydrolysis of tert-butyl bromide to form tert-butyl alcohol, the following was given in NCERT Chemistry: Textbook for class XII, Part II [1, p. 304]:

Step I is the slowest and reversible. It involves the C—Br bond breaking for which the energy is obtained through solvation of halide ion with the proton of protic solvent. Since the rate of reaction depends upon the slowest step, the rate of reaction depends only on the concentration of alkyl halide and not on the concentration of hydroxide ion.
Further, greater the stability of carbocation, greater will be its ease of formation from alkyl halide and faster will be the rate of reaction. In case of alkyl halides, 3° alkyl halides undergo SN1 reaction very fast because of the high stability of 3° carbocations. We can sum up the order of reactivity of alkyl halides towards SN1 and SN2 reactions as follows:
$$
\def\CL{{\large\text{Tertiary halide; Secondary halide; Primary halide;}~\ce{CH3X}}}
\ce{->[\text{For}~\mathrm{S_N2}~\text{reaction}][\CL]} \\
\ce{<-[\hphantom{[\CL}][\text{For}~\mathrm{S_N1}~\text{reaction}]}
$$

How does C-Br bond obtain energy through Solvation of bromide ion ?
References

NCERT. Chemistry: Textbook for Class XII. Part II, Reprint: August 2019 Bhadrapada 1941; M. Siraj Anwar, Shveta Uppal, Arun Chitkara, Bibash Kumar Das, R.N. Bhardwaj, Mukesh Gaur, Series Eds.; National Council of Educational Research and Training: New Delhi, 2007. ISBN 978-81-7450-716-7. (PDF)


texts:
I am unable to understand how to decide reactivity of alkyl halides based on inductive effect in a nucleophilic substitution reaction. I have 2 explanation for deciding. Consider 2 alkyl halides:

(A) 2-chloro-2-methylbutane
(B) 2-chloro-3-methylbutane

First explanation:

In (A) we have a $3^\circ$ carbon so if we break the $\ce{C--Cl}$ bond a $3^\circ$ carbocation will be formed, which is stabilized by +Inductive effect of surrounding  groups. Therefore we can say that as  breaking of $\ce{C--X}$ bond in (A) leads to the formation of a more stable carbocation than that formed in (B){$2^\circ$ carbocation}. And due to this the reactivity will be more of (A).

Second explanation:

As in (A) $3^\circ$ carbocation is formed, it will get more stabilized than $2^\circ$ carbocation formed in (B). So this means that $2^\circ$ carbocation in (B) becomes more positive than $3^\circ$ carbocation in (A), making it easier for a nucleophile to attack on (B)'s carbocation. This would make (B) more reactive.

Which one of them is correct?


texts: Is pyrene aromatic despite failing Hückel's rule?

texts:
Pyrene doesn't seem to be aromatic. However, sources claim that it is aromatic.

Considerations:

Pyrene is cyclic. ✓
Pyrene is flat (planar). ✓
Pyrene has 16 π electrons.
Every atom in the ring structure of pyrene is $\ce{sp^2}$ hybridized. ✓

The problem is that pyrene fails the $4n+2$ rule. $4n + 2 \neq 16$ where $n$ is an integer.

Something leads me to suspect that Hückel's rule is an oversimplification here. Or is pyrene indeed non-aromatic?


texts: Nomenclature of cycloalkane with substituent having the same number of carbons

texts:
What is the IUPAC name of the following molecule? More importantly, what is the rule for cycloalkanes having a substituent with the same number of carbons.

The undergraduate organic chemistry texts that I use when teaching tend to hide from complex nomenclature issues that cannot be addressed by the more common rules. Most texts clearly state that the parent chain in cases like these is the one with the larger number of carbon atoms.

For example, the following is butylcyclopentane.

The following is 1-cyclopentylhexane.

The addition of another substituent also makes it clearer, since we choose parent chains to maximize the number of substituents. The following is 1-cyclopentyl-3-methylpentane.


texts: Does a covalent bond constitute of 1 or 2 electrons?

texts:
A covalent bond is pictured as two electrons shared by two different atomic nuclei, which means that each of the two nuclei has two electrons. The problem I see with it is that it implies that if a hydrogen atom is neutral then a hydrogen nucleus in a covalent bond must be negatively charged since it has one more electron than a hydrogen atom. Which implies that a hydrogen molecule is negatively charged which is a contradiction (molecules are neutral).

Alternatively, one can say that the covalent bond is composed out of a single electron, which acts as a negative potential for both hydrogen nuclei hence it exerts negative potential of two in the molecule. But then the question is, where does the second electron go when two hydrogen atoms form a covalent bond?

My question does not relate only to this specific example, it's about covalent bonds in general.


texts:
I’d like to ask a question and clear my misunderstanding.

  Which of the following 0.01 M solutions have the highest osmotic pressure?
  -$\ce{NaCl}$
  -$\ce{C12H22O11}$
  -$\ce{BaCl2}$
  -$\ce{CO(NH2)2}$
  -$\ce{[Cr(NH3)4Cl2]Cl}$

I know that the equation for osmotic pressure is
$$\Pi = cRTi$$
I have eliminated sucrose, sodium chloride, and urea from my answer, because sucrose and urea are non-electrolyte. And sodium chloride has smaller van ’t Hoff factor than barium chloride. I ended up in barium chloride and the complex compound. I’m not really sure with the complex compound since from what I learnt, a complex compound is easier to dissolved in water (my teacher in solubility chapter taught me that $\ce{AgI + NH3 -> [Ag(NH3)2]I}$ have a high solubility because it is a complex compound). However I’m not sure if it has a high van ’t Hoff factor as well.


texts:
Is there any way to generate fake smoke that could be used in a fire drill on boat? Basically the idea is that the captain would set the "fire" and it would start smoking. The crew then has to find it and put it out.

Ideally it needs to smell, if not like real smoke, at least like something.

Also, it needs to billow out and obscure vision the way real smoke does.

I seem to remember a reaction that billows out black smoke but I cannot remember what it was.


texts: Most stable conformation of aldehydes and ketones

texts:
Why is the most favorable conformation of ketones and aldehydes the one where the alkyl group is anti to the other alkyl group (or hydrogen atom in an aldehyde) as attached? Why isn't more stable the conformation where the bond between the alpha and beta carbon atoms can participate in hyperconjugation with the carbonyl pi antibonding MO?

By contrast, the slightly more favorable conformation for butene is the right one:


texts: How does changing the concentrations of intermediate products/reactants change the rate law?

texts:
A = CH2(CN)2
B = CH(CN)2-
C = BrCH(CN)2
The rate law above is derived from applying the steady state approximation.

I am trying to work out how to modify the rate law to accomodate the following conditions:

1) [Br2] is low relative to [H+]

2) [Br2] is high relative to [H+]

And in the 2nd case how this affects the RDS and order of reaction.

It seems to me like these conditions would just affect the rate coefficient, not actually change the rate law.

EDIT:

$$
\frac{d [CH(CN)_{2}^{-}]}{dt} = k_{1}[CH_{2}(CN)_{2}] - k2[CH(CN)_{2}^{-}][Br_{2}] - K_{-1}[CH(CN)_{2}^{-}][H^{+}]
$$

$$
Applying\ Steady\ State\ Approximation:
$$
$$
k_{1}[CH_{2}(CN)_{2}] - k2[CH(CN)_{2}^{-}][Br_{2}] - K_{-1}[CH(CN)_{2}^{-}][H^{+}] = 0
$$

$$
k2[CH(CN)_{2}^{-}][Br_{2}] + K_{-1}[CH(CN)_{2}^{-}][H^{+}] = k_{1}[CH_{2}(CN)_{2}]
$$
$$
Dividing\ by\ [CH(CN)_{2}^{-}]:
$$

$$
k2[Br_{2}] + K_{-1}[H^{+}] = \frac{k_{1}[CH_{2}(CN)_{2}]}{[CH(CN)_{2}^{-}]}
$$

$$
[CH(CN)_{2}^{-}](k2[Br_{2}] + K_{-1}[H^{+}]) = k_{1}[CH_{2}(CN)_{2}]
$$

$$
[CH(CN)_{2}^{-}] = \frac{k_{1}[CH_{2}(CN)_{2}]}{(k2[Br_{2}] + K_{-1}[H^{+}])}
$$

$$
\frac{d [BrCH(CN)_{2}]}{dt} = {k_{2}[Br_{2}][CH(CN)_{2}^{-}]}{}
$$

$$Rate\ Equation:$$

$$
\frac{d [BrCH(CN)_{2}]}{dt} = \frac{k_{2}[Br_{2}]k_{1}[CH_{2}(CN)_{2}]}{{k_{2}[Br_{2}]}+k_{-1}[H^{+}]}
$$

So if $ [Br_{2}]$ is low compared to $ [H^{+}]$ then I would remove $ [Br_{2}]$ from the rate equation giving:

$$
\frac{d [BrCH(CN)_{2}]}{dt} = \frac{k_{1}[CH_{2}(CN)_{2}]}{k_{-1}[H^{+}]}
$$

If $ [H^{+}]$ is low compared to $ [Br_{2}]$ then I would remove $ [H^{+}]$ from the rate equation giving:

$$
\frac{d [BrCH(CN)_{2}]}{dt} = k_{1}[CH_{2}(CN)_{2}]
$$

So in this case the reaction is 1st order and the RDS no longer proceeds backwards with rate coefficient $k_{-1}$.

Is this right or have I made a mistake somewhere?


texts: Is there a piece of software that can help me see the (hkl) planes in a crystal lattice?

texts:
I am doing research with calcium carbonate structures. I need a way in which I can familiarize myself with the lattice structure of calcium carbonate polymorphs, especially calcite.

I really struggle to see things in three dimensions. I borrowed an atomic model kit from my professor and that worked out OK, but I still wouldn't be able to tell which is the $(101)$ plane, for example.

I tried downloading software such as BallVIEW, but I found it quite confusing. I need something in which, I can load the structure, and then it can tell me where each $(hkl)$ plane lies. I don't know how to program so I would really appreciate it if anyone can direct me to something user-friendly.


texts: Determining pH of immunoprecipitation buffer recipe

texts:
I'm following a protocol for extraction of proteins from yeast, and I came across this recipe for immunoprecipitation buffer:

  $\pu{50 mM}$ HEPES-$\ce{KOH}$, pH 6.8, $\pu{150 mM}$ $\ce{KOAc}$, $\pu{2 mM}$ $\ce{MgOAc}$, $\pu{1 mM}$ $\ce{CaCl2}$, $15\%$ glycerol.

Does this mean I bring the whole solution to pH 6.8, or do I make the HEPES at pH 6.8, and then add the remaining reagents?


texts: What is the CNC bond angle in methyl isothiocyanate?

texts: According to VSEPR theory, for $\mathrm{sp^2}$ hybridisation the bond angle is approximately $120^\circ$. In $\ce{H3CNCS}$, the nitrogen has one lone pair. As lone-pair-bond-pair repulsion is greater than bond-pair-bond-pair repulsion, the bond angle of $\ce{CNC}$ should be less than $120^\circ$,  but it is actually greater. How can this be rationalised?


texts: Equivalence point pH derivation of a tribasic acid

texts:
Considering $\pu{100 mL} \ \pu{0.1 M} \ \ce{H3A}$ and $\pu{0.1 M} \ \ce{NaOH}$ titration curve:

I understood the half equivalence points, but couldn't understand the reason why $\mathrm{pH} = \frac{1}{2}[\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2}]$ at equivalence points.
So I tried to derive this and for that I did following:
$$\ce{H3A  -> H2A- + H+}  \quad \mathrm{}K_\mathrm{a1}$$
$$\ce{H2A-  -> HA^2- + H+}  \quad \mathrm{}K_\mathrm{a2}$$
$$\therefore \ \ce{H3A -> HA^2- + 2H+} \quad  K = \mathrm{}K_\mathrm{a1} \cdot \mathrm{}K_\mathrm{a2}$$
So, $\mathrm{}K_\mathrm{a1} \cdot \mathrm{}K_\mathrm{a2} = \frac{[\ce{HA^2-}][\ce{H+}]^2 }{[\ce{H3A}]}$.
This would give $\mathrm{pH} = \frac{1}{2}[\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2}]$ but I don't know how $\ce{[H3A]}$ gets cancelled with $\ce{[HA^2-]}$.


texts: Dependence of Heat Capacity on Temperature

texts:
I was studying about the graph of dependence of heat capacity on temperature.

As you can see in this picture, heat capacity with constant volume increases near 0K.
As the temperature keeps rising, it converges to 3R.
I was finding out why these changes happen. In the textbook, the author explained like this.
For the increasing part,

This corresponds to an increased ability of the lattice waves to enhance their average energy with increasing temperature.

And, for the converging part,

The quantity of energy required to produce a 1-degree temperature change is constant.

However, I could not understand about the reason of converging part.
I think the energy required to produce a 1-degree temperature change can be constant, but how this can be only applied only for converging part?


texts: Why is crystallography still used in some cases for small molecule structure determination?

texts: I was wondering for some time why in some cases x-ray crystallography and not NMR is used for structure determination of small molecules? Does crystallization maybe require a smaller amount of the compound than NMR?


texts: If a chiral molecule reacts with an achiral molecule will the product be chiral or achiral?

texts:
My book says that a pair of enantiomers will react the same way with an achiral substance.

How is this possible? Does this imply that the product is achiral, even though the enantiomers are chiral? If so, why?


texts: Why does chlorine gas have a higher boiling point than hydrogen iodide

texts:
Hydrogen iodide, $\ce{HI}$, is a dipolar molecule much larger than chlorine, $\ce{Cl2}$.

The melting point of $\ce{HI}$ $(222.35\ \mathrm K)$ is definitely higher than that of $\ce{Cl2}$ $(171.6\ \mathrm K)$. However, the boiling point of $\ce{HI}$ $(237.79\ \mathrm K)$ is less than that of $\ce{Cl2}$ $(239.11\ \mathrm K)$.

This is very confusing since $\ce{HI}$ has more London dispersion forces than $\ce{Cl2}$. It also has a dipole, which chlorine does not.

A similar question to this looked at how silicon tetrafluoride $(\ce{SiF4})$ had a higher melting point than sulfur tetrafluoride $(\ce{SF4})$, and the answer concluded that the exception happened because symmetrical molecules fit into lattices better than asymmetrical molecules. However, I am not sure if this applies to the situation between $\ce{Cl2}$ and $\ce{HI}$ because they both only contain two atoms. This situation is also in the opposite order, where the molecule with greater London dispersion forces and a dipole has a higher melting point but a lower boiling point.

With this in mind, can anyone explain why this exception between $\ce{Cl2}$ and $\ce{HI}$ exists?


texts: What is the exact nomenclature of ionization?

texts:
I'm a little confused as to what reactions are considered ionizations. Is there any requirement for the educts, for example?

Some references suggest that it's only considered an ionization if you produce additional charged atoms/molecules from the educts (and some processes are dubbed detachment, which intuitively look like ionizations to me). Then "double ionization" wouldn't be possible, strictly speaking. To what extend have electrons to be produced. At the moment I think that it's legal to call most processes that look like ionization ionization.

There is a remark in the wikipedia article regarding the distiction from dissociation, but I don't really understand it.


texts: Proton NMR spectrum of aminocaproic acid

texts: I have completely unpacked the NMR spectrum for the drug aminocaproic acid (structure below) and have found a peak that I myself can not explain. The signals for the drug are simple to understand what corresponds to what but the reason behind one of the peaks having six peaks is unknown to me. I had made the assumption that the furthermost up-field signal would have 5 peaks and be a multiplet, due to it having four nonequivalent neighbors and N+1 rule. If there is a reason behind this can some one please explain.


texts: CHARMM parameter files for NBD (nitrobenzoxadiazole)

texts:
I have been looking all over the internet for forcefield parameters for a fluorescent probe called NBD (nitrobenzoxadiazole). Here is an example of an NBD labeled fatty.

I have so far only found parameters for AMBER or GROMACS. Also when following the articles from these two reviews, there seem to be no CHARMM parameters anywhere.

My questions are:

What CHARMM forcefield parameters would you use for NBD?
How could I transfer the AMBER or GROMACS parameters for use in CHARMM?


texts: How to relate a reaction barrier to the time the reaction needs to proceed?

texts:
As I am writing this I am at a conference and one of the participants just asked a question where he linked reaction barriers to durations for the reaction to complete. To paraphrase:

  From our experience a reaction with an activation barrier of 15 kcal/mol should occur instantaneous at room temperature. An activation barrier of 20 kcal/mol takes about one to two minutes and an activation barrier of 25 kcal/mol needs about 10 hours.

I would like to rationalise this statement as it seems quite hand-weaving to me. How can I judge from (a possibly also computed) activation barrier how long a reaction will need to complete? For the the sake of the argument, let's only consider reactions that proceed in one step; generalisations may also be implied, but may be too complex.

In the comments (and the already existing answer) the Eyring equation is mentioned. If the connection between the energy values and the duration can be made with that, an illustrative example would be nice.


texts: We have to clean substrates, often made of STO or MgO, before PLD for thin film growth. Previously we would use ethanol for sonication to clean the substrates. We recently ran out of ethanol but have a lot a methanol. In looking on the web I have only found conflicting viewpoints on which to use, or how corrosive methanol is. Are the two interchangeable for cleaning substrates? From where do you know?


texts: How does the entropic force arise within the hydrophobic effect?

texts:
I know that the hydrophobic effect is usually explained by the entropic effect originating from the disruption of hydrogen bonds between molecules of water and the nonpolar substance. The hydrogen bonds are reoriented to minimize the disruption of the hydrogen bond network of water molecules.
What I don't understand here is how this explains the tendency of non-polar substances to aggregate in water? Supposedly they disrupt the hydrogen bond network, but what forces them to clump together?
Then how does the above explain the tendency of water to decrease its surface area toward the nonpolar substance? Yes, the molecules of water around the nonpolar surface have lower entropy, but how does a decrease in entropy (in sense of a higher structural order) force them to minimize their exposure towards the nonpolar substance?


texts: I already know that thymolphthalein is soluble in alcohols, very alkaline aqueous solutions, acetone, and propylene glycol methyl ether.  My questions are what other solvents dissolve thymolphthalein, and what additives increase solubility (for example, specific surfactants)?


texts: Reversible and irreversible processes of thermodynamics

texts:
My text book states the following:

(Edit:It should be p1/p2, sorry.)

My understanding of a reversible process is that it us a process that is executed so slowly that no energy would be dissipated at all and it is possible to bring it back to the original state again due to this.
(The classic jar and piston example)
An irreversible process is every other process.

I understood the derivation for work for reversible processes but for the irreversible process I am unable to relate to the formula.
Take the example of the jar again.
If we suddenly compress the gas, we are changing the external pressure, right? What would we substitute for p ext ?
Also, how did this formula come and how does it accommodate the extra work we had to do that gets dissipated to get to the same state?

Please correct my understating if it
Is wrong.


texts: Why is the auto ignition temperature of petrol higher than that of diesel?

texts: I can't find any reasonable explanation please help.


texts: Diluting a sodium chloride solution with specific glassware

texts:
I have a $\pu{0.3 M}$ $\ce{NaCl}$ stock solution and need to create a $\pu{0.01 M}$ $\ce{NaCl}$ solution that is $\pu{50 mL}$. The only tools I am given are volumetric pipettes that are $10.0, 5.0, 1.0 \text{ and }\pu{0.5 mL}$ and $\pu{50.0 mL}$ volumetric flasks. I understand the physical process where I would measure out a specific amount and place it in the flask using the pipette(s) and then add the required amount of water.

I need to use the dilution equation $M_1\times V_1 = M_2\times V_2$ which I did and I got $\pu{1.666667 mL}$ of solution that needs to be taken from the $\pu{0.3 M}$ stock solution to create the $\pu{0.01 M}$ solution. The only problem is that I can't do that since the materials I have do not allow me to measure out that amount.

I tried to "convert" the $\pu{0.3 M}$ to various other concentrations that would hopefully get me down to $\pu{0.01 M}$ but have failed so far. I tried to find concentrations that would result in a whole number or a value with $.5$ at the end after dividing by the product from $M_1\times V_1$ but failed every time. In addition, I combined the two concentrations and found the midpoints between them and tried to use those values, but they did not work either. Where is a good place for me to start?


texts: What's the difference between a tetrahedron and a trigonal pyramid?

texts: The shapes respectively denoted by 'tetrahedron' and 'trigonal pyramid' seem to be the same. Is there a difference between the two? If not, why are the two presented as different concepts in introductory chemistry courses?


texts:
A lab presented me with an elemental composition (mainly metals in char) derived from an XPS analyzer and mentioned that binding energies suggested a list of compounds (various oxides, sulfides and silicates etc). Is there a way to show the composition in terms of these compounds instead of just the elements? Only familiar in bucket chemistry (aka chem eng), these analyzers are a bit of a black box to me even after reading up on them.

Also, is analyzing the surface of a batch of tiny particles <<1 micron somewhat tricky to get reliable results?


texts: Interplanar distance given Miller indice of the planes

texts:
Say we've a cubic crystal of unity edge length.
A set of planes in such a crystal is specified by their miller indice as $(3 2 0)$. One of these planes then has intercepts on the axes as $(2 ,3 ,\infty)$.
It's well known that the interplanar distance between two adjacent planes in a cubic lattice is given
$d_{hkl} = \frac{a}{\sqrt{h^2+k^2+l^2}}$,in our case this gives us
$d_{320} = 1/\sqrt13$.
Now if I look at the planes which form the Miller indices of $ 3 2 0$ I find that apart from a plane having intercepts as $(2 ,3,0)$ an adjacent parallel plane to this plane having the same indices will pass via origin $0,0,0$ and the distance between them is
$d_{320} = 6/\sqrt13$
Which contradicts the above result!
Can anyone please point out what's wrong in my reasoning?


texts: Hydroxide as leaving group in Aldol Condensation in base

texts: My professor said that in the base-catalyzed aldol condensation, because there is a lot of hydroxide already in solution, hydroxide on the beta position on a ketone can act as a leaving group. What's the logic/reasoning behind this?


texts: Role of amalgamated zinc in Clemmensen reduction

texts: What is the role of amalgamated zinc in the Clemmensen reduction mechanism?


texts: Reactants in high temperature chemical vapour deposition

texts:
I'm setting up a high-temperature electrolysis rig for the purpose of chemical vapour distribution.

The molten carbonate (750 degrees Celsius) will be lithium carbonate. The cathode will be galvanised steel with the anode being nickel. Nitrogen, carbon dioxide and water vapour will be fed in with the intention of splitting the carbon dioxide as a low voltage, high current is passed through the electrodes.

I'm anticipating that the carbon dioxide splits, but I am not sure how the nitrogen and water vapour will react under those conditions. I'm guessing the nitrogen won't react, but how would the water vapour react? Ideally, I'd rather not have to go to the trouble of using pure/near-pure carbon dioxide.

Thanks in advance!


texts: Is this mechanism for the formation of a tosylate correct?

texts: I've been given this mechanism by my lecturer for the formation of a tosylate. It claims that NEt3 is needed to remove the hydrogen from the O+ in the second step. However surely the Cl- from TsCl would remove the H and no NEt3 is needed?


texts: Given a forward reaction with positive enthalpy, is its reverse reaction be endothermic or exothermic?

texts:
I'm pretty sure the sign changes.

But, I want to be sure if it becomes endothermic or exothermic.


texts: Why are amino acids least soluble at isoelectric point?

texts:
At isoelectric point amino acids exist as zwitterions. As a molecule it is electrically neutral, but still has a positive and a negative charge. Then why are amino acids still least soluble at isoelectric point?
The positive and the negative charges of the amino acid can interact with the negative and the positive charges of water and can dissolve, right? Where am I going wrong?


texts: Why is tetrachlorocuprate (II) yellow if it is high-spin?

texts:
From my knowledge of transition metal complexes, tetrahedral complexes generally have less splitting (compared to octahedral complexes) because they only involve four ligands are they aren't placed directly near any d-orbitals (unlike octahedral complexes). Furthermore, chloride is a weak-field ligand and therefore forms high-spin complexes. Both of these facts point to tetrachlorocuprate absorbing light of low energy (red to orange) and therefore being blue in colour (as blue is complementary to red in the colour wheel).
However, it is a yellow complex, suggesting that it absorbs high energy purple or violet light. I can't make any sense of this. Even if I factor in Jahn-Teller distortion, it shouldn't surpass that of hexaaquacuprate (II) which is blue in colour. Does this have to do with de-excitation? If so, what makes tetrachlorocuprate different from all other complexes?


texts: Electorchemical Systems (Newman 3rd edition) problem solving

texts:
I am trying to solve the very first problem (Problem 1.1) of Newman 3rd edition book. The book problem goes as follows:
'Starting with the following equation for the concentration overpotential:
$\eta_c = U_{c} + \int_0^b (\frac{1}{\kappa(y)} - \frac{1}{\kappa_b}) \ i_y \ dy \ \ (1)$
Where the limits of the integration go from $y=0$ (region near the electrode) to $y = b$ (bulk electrolyte), and $b$ is the width of the diffuse layer. $i$ is the applied current density and $\kappa$ is the ionic conductivity, which depends on the salt concentration.
The objective is to arrive at the following formula:
$\eta_c = \frac{RT}{F} [\ \ln{\frac{c_o}{c_b}}+t_+(1-\frac{c_o}{c_b}) \ ] \ \ (2)$
For this we hace to assume that the concentration profile between the electrode and the bulk electrolyte is linear.'
First, we define the equilibrium concentration potential as function of the concentration at the electrode surface $c_0$ and the bulk $c_b$:
$U_c = (1 - t_+) \frac{RT}{F} \ln{\frac{c_o}{c_b}}$
Then ionic conductivity is defined with the contributions of anionic and cationic species in solution:
$\kappa_b = F^2 (z_+^2 u_+ c_{+,b} + z_-^2 u_- c_{-,b})$
$\kappa(y) = F^2 (z_+^2 u_+ c_+(y) + z_-^2 u_- c_-(y))$
Due to electroneutrality, we define salt concentration as $c = \frac{c_+}{\nu_+} = \frac{c_-}{\nu_-}$. Where $\nu_+$ and $\nu_-$ are the stoichometric coefficients of the salt. Therefore:
$\kappa_b = F^2 (z_+^2 u_+ \nu_+ + z_-^2 u_- \nu_-) \ c_b$
$\kappa(y) = F^2 (z_+^2 u_+ \nu_+ + z_-^2 u_- \nu_-) \ c(y)$
So, substituting these expressions in $(1)$, and considering that in plane electrodes the ionic current density $i_y$ is independent of $y$, we arrive at:
$\int_0^b (\frac{1}{\kappa(y)} - \frac{1}{\kappa_b}) \ i_y \ dy = \frac{i_y}{ F^2 (z_+^2 u_+ \nu_+ + z_-^2 u_- \nu_-)} \int_0^b (\frac{1}{c(y)} - \frac{1}{c_b}) \ dy \ \ (3)$
For $y < b$ we approximate the concentration profile to be linear:
$c(y) = c_0 - \frac{c_0 - c_b}{b} y$
Therefore:
$\int_0^b (\frac{1}{c(y)} - \frac{1}{c_b}) \ dy = -\frac{b}{c_b - c_0} \ln{\frac{c_0}{c_b}} - \frac{b}{c_b} = \frac{b}{c_b - c_0} (-\ln{\frac{c_0}{c_b}} - 1 + \frac{c_0}{c_b})$
Knowing that $\partial_y \ c = \frac{c_b - c_0}{b}$ using the Nerst-Einstein relation $D_i = RT \ u_i$, we substitute in $(3)$:
$\frac{i_y}{ F^2 (z_+^2 u_+ \nu_+ + z_-^2 u_- \nu_-)} \int_0^b (\frac{1}{c(y)} - \frac{1}{c_b}) \ dy = \frac{i_y RT}{ F^2 (z_+^2 \nu_+ D_+ + z_-^2 \nu_- D_-) \ \partial_y} (-\ln{\frac{c_0}{c_b}} - 1 + \frac{c_0}{c_b}) \ \ (4)$
If I have not done any mistake, I am stuck at this place. The objective formula $(2)$ expresses the concentration overpotential $\eta_c$ with a term proportional to the cation transference number $t_+$. But no matter what I will always arrive at an expression which contains a inversely proportional relation with $t_+$.
By using the Fick's first law $N_i = - D_i \nabla c_i$ we can write Equation $(4)$ as
$\frac{i_y RT}{ F^2 (z_+^2 \nu_+ D_+ + z_-^2 \nu_- D_-) \ \partial_y \ c} (-\ln{\frac{c_0}{c_b}} - 1 + \frac{c_0}{c_b}) = \frac{i_y RT}{ F^2 (z_+^2 N_+ + z_-^2 N_-)} (\ln{\frac{c_0}{c_b}} + 1 - \frac{c_0}{c_b})$
The ionic current density is defined as $i = \sum_i F z_i N_i$, and defining transference number as $t_i = \frac{z_i F N_i}{i}$ so:
$\frac{i_y RT}{ F^2 (z_+^2 N_+ + z_-^2 N_-)} (\ln{\frac{c_0}{c_b}} + 1 - \frac{c_0}{c_b}) = \frac{RT}{F (z_+ t_+ + z_- t_-)} (\ln{\frac{c_0}{c_b}} + 1 - \frac{c_0}{c_b})$
Knowing that $t_+ + t_- = 1$, assuming that z_+ = 1 and z_- = -1 and substituting everything in equation $(1)$:
$\eta_c = (1 - t_+) \frac{RT}{F} \ln{\frac{c_o}{c_b}} + \frac{RT}{F (2t_+ - 1)}(\ln{\frac{c_0}{c_b}} + 1 - \frac{c_0}{c_b})$
I cannot find a way of deriving $(2)$ from this equation. I must have done a mistake somewhere, but my eyes are blind already. Any help would be much appreciated.


texts: What materials are resistant to hot chlorine?

texts: I'm looking to do an experiment involving hot chlorine gas (900 Celsius), however at the moment the only material I'm aware of that could cope with this is Hastelloy's C-22 alloy. What other alternatives exist?


texts: Why is dialysis tubing impermeable to sucrose when it should retain >12,000 Da?

texts:
While writing up a lab for biology, I realized that the dialysis tubing for sale online seemed to retain large molecules (12-14,000 Da) but didn't specify an upper bound. I learned that the tubing is impermeable to Sucrose, molecular weight 342 Da, because it's too big. This doesn't make sense to me; the site says the tubing "retains >12,000 Da molecules", but Sucrose is clearly smaller than that.

So either A) Sucrose does indeed pass through dialysis tubing and I misheard/mis-learned or B) my class used tubing with much smaller pores.


texts: How to calculate initial and final temperatures during supercritical steam expansion?

texts:
Ten $\mathrm{kg}$ of steam at $500~\mathrm{bar}$ is expanded at constant pressure until its volume increases to seven times its initial value of $0.01~\mathrm{m^3}$.
  (a) Calculate the initial and final temperature of the steam
  (b) Calculate the heat that must be supplied to carry out the process

An attempt at solving this problem:
$$\Delta H + \Delta E_k + \Delta E_p = Q - W_S\ \ \text{(open system)}$$

Taking out unnecessary terms leaves us with
\begin{aligned}
\Delta H &= Q\\
500~\mathrm{bar} &= 5\cdot10^7~\mathrm{Pa}\\
\Delta H &= H_f - H_i\\
H_i &= (5\cdot10^7~\mathrm{Pa})\cdot(0.01~\mathrm{m^3}) = 5\cdot10^5~\mathrm{J}\\
H_f &= (5\cdot10^7~\mathrm{Pa})\cdot(0.07~\mathrm{m^3}) = 3.5\cdot10^6~\mathrm{J}\\
\end{aligned}

Converting to kJ/kg (10 kg of steam)
\begin{aligned}
\hat{H}_i &= 50~\mathrm{kJ/kg}\\
\hat{H}_f &= 350~\mathrm{kJ/kg}\\
\end{aligned}

And that's where I stopped. I tried looking up the values of $\hat{H}_i$ and $\hat{H}_f$ in steam tables to interpolate the temperatures, but the values are too low. Since the pressure is too high, I also know the ideal gas law $(PV=nRT)$ won't apply to this scenario. Can someone point me in the right direction?


texts: How to capture the gas produced by combusting alcohols

texts: I am burning various alcohols and am attempting to capture the carbon dioxide produced. I could burn the alcohols in a conical flask with a cork on the top, with a tube directing the gas into a gas jar. However, due to the small volume of a conical flask, there would be almost no oxygen to burn and the flame would extinguish quickly. Is there any experimental setup I might have access to with high-school lab equipment that allows me to burn alcohols in an environment with plenty of oxygen, while capturing the gas produced? Thanks


texts: How can I best achieve a stable solution of Pt-Nanowires in water

texts:
I am synthesizing platinum nanowires ($50nm×20\mu m$) in aqueous solution. Unfortunately they start to aggregate rapidly, which is not desired.

How can I keep them dispersed?


texts: How do we get g and E values for various levels to calculate electronic partition function

texts:
When we calculate electronic partition function using the formula:
$$q_\mathrm{elec}=\sum^\infty_{n=1}g_ne^{-E_n/k_BT}$$
How can I get the $g_n$ value and $E_n$ values for $n=0,1,2,3...$ levels?
I need to calculate the $q_\mathrm{elec}$ for various species like $\ce{H, H2, OH, H2O, O2, O, O+, H+}$.


texts: How does Le Chatelier's principle apply to a gas phase reaction at constant volume?

texts:
This reaction is given in my book and the direction of shift of reaction on addition of $\ce{CO}$ and removal of $\ce{CO2}$ at constant volume is asked.
$$\ce{2CO(g) + O2(g) ⇌ 2CO2(g) + \Delta H}$$
If "at constant volume" was not specified, I understand that the forward reaction would occur since the reactant is added and the product is removed, but I do not know if this will vary with constant volume. What will happen in the case of constant volume? Does it matter that there is a change in the number of particles comparing reactants and products? Which direction will the equilibrium shift?


texts: Can we separate positive ions from negative ions in a solution?

texts: Can we make a solution containing only positive ions by using electrodialysis but instead of using 2 kinds of membrane (one blocks the positive ions and one blocks the negative ions) we can use only one kind (the one which blocks the positive ions) so the positive ions wont reach the electrode and wont be electrolysed while the negative ions will be electrolysed leaving the positive ions in the solution


texts: What type of hybridization does phosphorus have in P2O5?

texts: I'm inclined to think that P has a $dsp$ hybridization in that compound, because it makes 5 bonds and 2 of them are $\pi$ bonds - with oxygen. However, I found in some websites that it may have $sp^2$ hybridization, although I have no idea how could it be possible - since it has to make two $\pi$ and 3 sigma bonds.


texts: Comparing SN2 reaction rate for phenacyl chloride and methyl chloride

texts:
KI in acetone undergoes $\mathrm{S_N2}$ reaction with (1) and (2). Compare the rates of the reactions.

Like many kinds of these questions there are many factors involved. One is the steric effect, and, since steric effects plays a central role in inversion of reactant and there is a very bulky group attached to (2), I think (1) should be more reactive. Also, (2) will serve as a better $\mathrm{S_N1}$ substrate as the carbocation generated will be resonance stabilised.
And so using these two reasons I thought (1) is more reactive than (2), but, according to the answer, (2) is almost 500 times more reactive than (1), and I am not able to see the reason for this mammoth difference.


texts: How to tell whether lone pairs in heterocycles contribute to aromaticity?

texts:
How can I decide whether lone pair electrons take part in the continuous overlap of electron or not?

For example, the lone pair in pyridine is not a part of the conjugated system, whereas the lone pair in pyrrole is.

I had read that this was due to the lone pair in pyridine being localised in an sp2 orbital, while the lone pair in pyrrole is delocalised.

How do we identify this?


texts: How to proceed when percentage "exchange" is given in a reaction?

texts:
If $3.7~\mathrm{mol}$ of $\ce{Cu}$ reacts with an excess of $\ce{Cl2}$ and the exchange is $45\,\%$, how many moles of $\ce{CuCl2}$ can at maximum be created?

So I start with write the reaction formula
$$\ce{Cu + Cl2 -> CuCl2}$$
and then balance it.
$$\ce{2Cu + 2Cl2 -> 2CuCl2}$$
I know that I have $3.7\ \mathrm{mol}$ of $\ce{Cu}$, which is $235.1202\ \mathrm{g}$ of $\ce{Cu}$.
I assume that $\ce{Cu}$ is limiting reagent and $\ce{Cl2}$ is an excess reagent.

This is where I get stuck, I don’t know how I’m supposed to proceed with the only information that the exchange is $45\,\%$.


texts: How can I eliminate the harmful gas produced from the heating/manipulation of galvanized steel?

texts: When welding on steel with a galvanized coating, hexavalent chromium is yielded from the chemical reaction. This gas is something that I would like to eliminate before I begin welding, possibly with some liquid or mixture. Any ideas?


texts: Why is the methyl group electron-donating via the inductive effect?

texts: I have been reading mechanisms recently, and I find that $\ce{-CH3}$ is a $+I$ effect group. I understand the mechanisms that require this, but can someone explain at the molecular level why is $\ce{-CH3}$ a $+I$ effect group?


texts: Which is most reliable excitation energy: LUMO-HOMO energy or TD-DFT excitation energies?

texts:
After running a TD-DFT , we can calculate the HOMO-LUMO difference and then calculate the the excitation energy.

Another approach is just simply pick the energies calculated in the TD-DFT and use them.

For me the latter makes more sense as that's the reason we do TD-DFT , otherwise we could access the HOMO-LUMO difference by any other methods but I have seen papers using the first concept. I also have noticed that the energies in second concept are closer to the experimental values.

Also when I run TD-DFT, I can see Oscillator Strength. Should I pick the energy that has the largest Oscillator Strength for calculation of the maximum wavelength ?
Here is an example. Should I pick number 8 for maximum wavelength calculation?


texts: What determines how much water of crystallisation a salt has?

texts:
Is there any reason behind the number of water of crystallisation?

For example, $\ce{LiCl.2H2O}$ has two waters of crystallisation, and $\ce{MgCl2.8H2O}$ has 8 waters of crystallisation. Why does $\ce{LiCl}$ have only 2 waters of crystallisation and not 8?


texts: How to remove Ethanethiol from household natural gas?

texts:
Household natural gas is injected with a little bit of Ethanethiol to make it a distinctive odor for safety purposes.

But, if it is used to drive cars (*), its odor is sensible and it is annoying.

Is there a way to remove this from the household gas (which is mainly the mix of 90% methane and 10% ethane) on a home budget scale?

My first idea is to have some type of chemicaly which could be inserted into the empty bottle.

(*) In most countries, this can be done legally, although it has to follow relatively strict safety and tax regulations.


texts: What does 'preconcentration techniques' mean?

texts:
In the scope of the analysis of organic compounds in column-switching liquid chromatography, what does the following statement mean?

  sample preconcentration techniques with high enrichment factor(EFs)

The word  preconcentration is not understandable for me.
Is it a technique for extracting the components?


texts: Can you experimentally determine activation energy if the rate expression and rate constant are unknown?

texts:
When drawing a graph to find the activation energy of a reaction, is it possible to use ln(1/time taken to reach certain point) instead of ln(k), as k is proportional to 1/time?

For example, if an experiment I'm doing has a specific end point, can I use ln(1/time taken to reach that endpoint) instead of ln(k), and do this for a range of temperatures in order to work out the activation energy? Or would I have to use the rate equation and determine the rate constant for each temperature, as I am not sure of the rate equation for the reaction.

Thank you:)


texts:
I am told by Dr. Klein that in the nitration of benzene, hydrogen sulfate anion acts as the base and deprotonates the sigma complex.

My question is why would the hydrogen sulfate anion be doing the deprotonation? We've just established that sulfuric acid is a stronger acid than nitric acid; hence sulfuric acid is able to protonate nitric acid to some extent. Now are we expected to believe that the conjugate base of a stronger acid is stronger than the conjugate base of a weaker acid? Why not have nitrate anion do the deprotonation? It is a stronger base than hydrogen sulfate anion.


texts:
what are the systems of recording atomic masses and their units?

I know that the nucleon number is the number of protons and neutrons

I also know that the mass number on the periodic table is the masses of all the isotopes and their relative abundance (I believe this is called relative atomic mass and is equal in numerical value to the molar mass of that element)

I am not sure what units relative atomic mass is measured in. some say there is no units as it is a relative scale, others say that it is measured in atomic mass units (AMU), unified mass units (u) or daltons (Da).

I believe (but would like it to be confirmed) that the atomic mass unit (AMU) is an obsolete unit based on the mass relative to oxygen.

I also believe (but would like it to be confirmed) that the unified mass units (u) and dalton (Da) are equivalent units (u=Da=1/12 mass of a carbon-12 atom)

what is the difference between isotopic mass, relative atomic mass and atomic mass and what units do they all have?


texts: What's the difference between "extent of reaction" and "position of equilibrium"?

texts:
My chemistry textbook defines the terms in question as follows:

  Extent of reaction: the relative amounts of products compared with reactants. The extent of reaction is indicated by the value of the equilibrium constant.

  Position of equilibrium: the relative amounts of products and reactants at equilibrium. The position of equilibrium varies depending on the extent of the reaction.

I don't understand the difference between these two concepts and would appreciate it if someone could explain both how they are different and how they are linked/influence each other.

Thanks.


texts: How much lactose is there in milk (mechanism)?

texts:
Iodometric titration is sometimes used to find out how much lactose there is in milk. The overall oxidation reaction is written as follows.

$$\ce{C12H22O11 + I2 + 3NaOH ->[\ce{CuSO4}]C12H21O12Na + 2NaI + H2O}$$

How does this reaction proceed? What is the role of $\ce{CuSO4}$?

The solution is then acidified with $\ce{HCl}$. Excess $\ce{I2}$ is determined via

$$\ce{2Na2S2O3 + I2 ->2NaI + Na2S4O6}.$$

What I think might be going on (with references)

Using basics of inorganic chemistry, iodine reacts with cold sodium hydroxide to give sodium hypoiodate.

$$\ce{I2 + 2NaOH <=>NaIO + NaI + H2O}$$

$\ce{NaIO}$ is the main oxidiser of lactose.$^{[1]\ [a]}$

$$\ce{C12H22O11 +NaIO + NaOH ->C12H21O12Na + NaI + H2O }$$

I have no clue as to what the complete mechanism might be here.

Alternatively, $\ce{Cu^{2}^+}$can be reduced. The following picture$^{[2]}$ shows the general transitions for (semi)linear lactose.

Sadly, neither reference mentions the other option, nor are there arrow-pushing mechanisms which is what I am after.

Sodium iodate is prone to decomposition even under room temperature, but the reaction is vigorous from $80 \ ^\circ \text{C}\ ^{[3]}$:

$$\ce{3NaIO->NaIO3 +2NaI}.$$

This is partly why the acid is added. To get an accurate reading of "unreacted" iodine we must somehow re-release $\ce{I2}$ from the ions $\ce{IO^-}$ and $\ce{IO_3^-}$.$^{[1]}$

$$\ce{NaIO + NaI + 2HCl -> I2 + 2NaCl + H2O\\ NaIO3 + 5NaI + 6HCl -> 3I2 + 6NaCl + 3H2O}$$

Thiosulphate is a widespread reagent that is subject to inaccuracies$^{[4]\ [5]}$ due to

$$\ce{Na2S2O3 + 4I2 + 10NaOH -> 2Na2SO4 + 8NaI + 5H2O}.$$

This reaction is less favoured in acidic conditions.$^{[1]}$

Clarification

I am asking for

arrow-pushing mechanisms that show the role of $\ce{NaIO}$ and/or $\ce{CuSO4}$ with cyclic lactose (if possible).

$^{[1]}$ A Study of the Method for Titrating Aldose Sugars with Standard Iodine and Alkali.  G. M. Kline, S. F. Acree. Bureau of Standards Journal of Research. Link [Comment: the study actually deals with aldose sugars. The equation for cyclic lactose might thus be a stretch.]

$^{[a]}$ Agu-Tõnis Talvik. Organic chemistry. (1996). page 490 (as far as I know, not available in English)

$^{[2]}$ Dairy Chemistry and Biochemistry. Second Edition. P. F. Fox, T. Uniacke-Lowe, P. L. H. McSweeney, J. A. O'Malhony. page 62. Link

$^{[3]}$ Иодат натрия. Russian Wikipedia. Link

$^{[4]}$ (G. Topf). Zeit. anal. Chem., 26, p. 137; 1887

$^{[5]}$ (Bougault). Compt. rend., 164, p.; 949; 1917


texts: Given Kd find equilibrium concentrations of the reactants

texts:
$$\ce{Biotin + Avidin → Complex}$$
Biotin is a vitamin derivative that binds extremely tightly to avidin (a protein found in egg white) with a $K_\mathrm{d}$ of $\pu{1e-15 M}$.
If you make a $\pu{2 mL}$ solution of $\pu{10 μL}$ biotin and $\pu{2 μL}$ avidin, what fraction of biotin molecules will remain free at equilibrium?

Answer Key
The TA found the
$$K_\mathrm{d,new} = \frac{[\text{Biotin}][\text{Avidin}]}{[\text{Complex}]}$$
using the given initial reactant concentration values and making an ICE table to find the equilibrium concentrations and found $K_\mathrm{d,new} = \pu{1e-9}.$
$$K_\mathrm{d} = \frac{(10 - δ)(2 - δ)}{δ} = 10^{-9}$$
Where does the TA get that $K_\mathrm{d} = \pu{1e-9 μL}$? Don't you need to either know the delta term or have the value of $ΔG$ of reaction? Neither of which was given in the problem statement. Also, why did TA find another $K_\mathrm{d,new}$? Doesn't the provided $K_\mathrm{d}$ already describe the dissociation, which gives the concentration of reactants on top?
I understand that $K_\mathrm{d}$ is the equilibrium constant which describes dissociation.
My solution
My solution was to find
$$f_\mathrm{empty} = \frac{[\ce{RL}]}{[\ce{R}] + [\ce{RL}]}$$
I rewrote the $f_\mathrm{empty}$ relation to be in terms of the known values, the provided $K_\mathrm{d}$ and the concentration values.
I found $f_\mathrm{empty}$ to be $0.0009999$ which is also essentially zero, meaning that $f_\mathrm{bound}$ is essentially $1$, which is also what the TA found.
The TA's approach wasn't intuitive for me, so if someone could help clarify it?


texts: Creation and Combustion of Nitrocellulose

texts:
I am intending to demonstrate the formation and combustion of nitrocellulose with my high school students, however I am concerned about the potential products of the combustion equation. I have been able to satisfy the safety requirements for the creation which I believe follows this equation:

$$\ce{3HNO3 + C6H10O5 → C6H7(NO2)3O5 + 3H2O}$$

The only equation for the combustion I have found is this one:

$$\ce{2C6H7N3O11 + 9/2 O2→12CO2 + 3N2 + 7H2O}$$

I am concerned about the possibility of $\ce{NO2}$ gas being created instead of or in addition to $\ce{N2}$ gas, my understanding of chemistry if fairly basic so I was hoping someone could confirm whether or not the production of $\ce{NO2}$ is likely.


texts:
What is the difference between D and L configuration, and + and −?

My textbook says they are two different things.
It also says that the correct way to name glucose is D(+)-glucose.

Could someone please explain what D, L and +, − represent, and why they are different?


texts: Why are carbocations with sp3 hybridisation highly unstable?

texts:
Why is it that sp3 hybridized carbonium ions do not exist? Or why are they very difficult to form?

For instance, nucleophilic substitution in bicyclo compounds at the bridge head carbon is not very easy. I don't understand the explanation given in the book. Thanks for any help.


texts: Why does d/l-2,3-dibromobutane on reaction with NaI/acetone give cis-2-butene?

texts:
This is what I have read/know about the dehalogenation of vicinal dihalides by NaI/acetone:
The two halides which are leaving must be on opposite sides (from the mechanism).
In case they are present in the same side, we must rotate the C-C bond first and then proceed with the reaction.
In both cases we end by with a trans alkene.
But now I came across this:

meso-2,3-dibromobutane on reaction with NaI/acetone gives trans-2-butene.
d/l-2,3-dibromobutane on reaction with NaI/acetone gives
cis-2-butene.

I have no problem regarding the first statement. But regarding the second, from what I have learnt, the product again must be trans-2-butene.
I drew the Fisher projection and tried to figure out the reaction. For the 1st reaction, meso-2,3-dibromobutane must undergo C-C bond rotation, (performing two "swaps") and then we would end up with d/l-2,3-dibromobutane leading both 1st and 2nd reactions to trans-2-butene.
Where is my mistake? Is my understanding of the mechanism of the dehalogenation of NaI/acetone wrong? Any good sources to read regarding the same (I couldn't find it in any of my books) are appreciated, too.


texts: Why is water taken in calculating K, equilibrium constant

texts:
For the given question,

I was trying to solve it but I was not considering the concentration of water in the calculation (because water is a pure liquid and its concentration is supposed to be taken as 1), but then I needed the volume to be able to calculate the answer. I saw the solution,

Is it taken here because the reactants are organic and thus water would probably not be the solvent?


texts: Compare rate of hydrohalogenation between 1,2-diphenylethene and 1-phenylpropene

texts:
Consider the compounds, (I) - 1,2-diphenylethene and (II) - 1-phenylpropene. Compare their rate of hydrohalogenation (HX addition)

I feel that the answer should be (II) > (I), but to my surprise it's given to be (I) > (II).

My thoughts:

In (I), phenyl group consists of sp2 carbons, operates -I effect and destabilises the carbocation intermediate.
In (II), protonation should occur at the carbon directly attached to the phenyl group. The methyl group (instead of phenyl, as in (I)) operates +I effect and stabilises the carbocation.
In both cases, the carbocation formed enjoys resonance stabilisation from a phenyl group - so it's not a factor we need to compare.

So, what is the real order of rates of $\ce{HX}$ addition? Is my reasoning correct, or have I missed something?


texts: Why acidity of p-methoxybenzoic acid is more acidic than p-hydroxybenzoic acid?

texts:
I know +M effect of $\ce{OCH3}$ is more than $\ce{OH}$, but in my book (ALLEN General organic chemistry), it is given that $\mathrm{p}K_\mathrm{a}$ of para-substituted benzoic acid containing $\ce{OCH3}$ is less than that of para-substituted benzoic acid containing $\ce{OH}$:

$\mathrm{p}K_\mathrm{a}$/Benzoic acid → $4.20$
$$
\begin{array}{lcccc}
\hline
\text{Substituent} & \mathrm{p}K_\mathrm{a} & \textit{o-} & \textit{m-} & \textit{p-} \\
\hline
\cdots \\
\ce{OMe} & - & 4.09 & 4.09 & 4.47 \\
\ce{OH} & - & 2.98 & 4.08 & 4.58 \\
\cdots \\
\hline
\end{array}
$$

I am in doubt whether these data wrong or correct. If correct, what can be an explanation?


texts: My teacher said that on the periodic table there is a "nose" formed by Al, Zn, Ag, and Cd. She said that they are all fixed charged (+3, +2, +1, and +2 respectively), and said that if I write them in ionic equations, I just say Silver Nitrate instead of Silver (I) Nitrate. She also said to put all Al as +3 charge in all cases, etc. But I did some research and found out that you do say Silver (I) Nitrate (actually both are fine, but my teacher specifically said never put the (I) in such cases). So is my teacher wrong? And are there cases where the charges of the elements are not what my teacher says?


texts:
Which of the following reactions doesn't represent an oxidation-reduction?
$$
  \begin{align*}
    \ce{2 P + 5 HClO + 3 H2O &-> 2 H3PO4 + 5 HCl} \\
    \ce{Zn + 2 HCl &-> ZnCl2 + H2} \\
    \ce{Mg + CuSO4 &-> MgSO4 + Cu} \\
    \ce{NaOH + HNO3 &-> NaNO3 + H2O}
  \end{align*}
$$

I want to find which of those reactions is not an oxidation-reduction reaction, but I'm not sure how to do this and how to find the oxidation numbers, should I memorize them?
Is there some rules like when bases and acids react this can't be an oxidation-reduction reaction — the last reaction implies this — so I can know if the reaction is an oxidation-reduction reaction or not when I look at it without searching for every oxidation number?


texts: Why do the alkali metals form different products upon combustion in air?

texts:
From Wikipedia's article on sodium:

  When burned in dry air, it forms primarily sodium peroxide with some sodium oxide.

We know that sodium has a strong reducing capacity, so why does it produce a compound in which the oxygen atom is not reduced to the fullest possible extent?

After posting the question, I read up some more and found this, on Chemguide's page describing the oxidation properties of Group 1 elements:

  So why do any of the metals form the more complicated oxides? It is a matter of energetics.

  In the presence of sufficient oxygen, they produce the compound whose formation gives out most energy. That gives the most stable compound.

  The amount of heat evolved per mole of rubidium in forming its various oxides is:

  $$\begin{array}{|c|c|}
\hline
 & \text{enthalpy change (kJ / mol of Rb)} \\ \hline
\ce{Rb2O} & -169.5 \\
\ce{Rb2O2} & -236 \\
\ce{RbO2} & -278.7 \\
\hline
\end{array}$$

This is hardly an explanation, because it just says in a circular way that it's energetically profitable to form such compounds. Why is this energetically profitable?

Can part of the explanation be "because in Group 1, starting from $\ce{Na}$, ion charge densities are low enough to allow peroxides and superoxides to exist"?

I wonder if the following behaviour is related to this: lithium nitrate decomposes to lithium oxide (again the other participant has the oxidation -2), while the rest of the group's elements have their nitrates decompose to a nitrite (again the other participant's oxidation is -1):

  From Chemguide:

  $$\ce{4 LiNO3 (s) -> 2 Li2O (s) + 4 NO2 (g) + O2 (g)}$$

  $$\ce{2 MNO3 (s) -> 2 MNO2 (s) + O2 (g)}$$


texts: Would 2 C₂ be 2 moles of diatomic carbon, or 4 moles of carbon?

texts: Would molecules like $\ce{C2, H2}$, etc., be considered 1 mole of diatomic [element] or 2 moles of [element]?


texts: How to pronounce "potassium manganate(VII)"?

texts: The formal names for such inorganic compounds having metals showing of variable oxidation states involve use of Roman numerals, for example "copper(II) sulphate" or "potassium manganate(VII)" or "hexaaquacopper(II)". Of course, common names like "copper sulphate" or "potassium permanganate" do exist, but if I wanted to use the formal ones, how do I correctly pronounce them?


texts: Computational Chemistry (Ab Initio), what should I study?

texts:
I'm interested in ab initio computational chemistry. I'm trying to figure out what I should study. I know that I should study physical chemistry, mathematics, and programming.

However, I am not sure in what I should be focusing on. It seems to be a fairly new field and books on the topic are rather specific.

Can anyone working in computational chemistry research provide me with a list of (math, computational chemistry, physical chemistry) textbooks they studied or any additional resources to get me started?


texts: Is Al2O3 (aluminum oxide) diamagnetic or paramagnetic?

texts:
The title about covers it, I am an amateur and I have found that checking 'molecule orbitals' can reveal the answer here but I cannot locate such an orbital. The reason for this question is I am trying to sort aluminum oxide beads from aluminum oxide beads coated in palladium with a magnet via the Lenz Effect.
I have researched magnetic properties. It appears that I can determine them by seeing how many unpaired valence electrons there are. I have no idea how to figure out what the valence orbital of a molecule is, even though such information is widely available for individual elements. For molecules, this information is referred to as molecule orbitals. I expect that it is diamagnetic because both Oxygen and Aluminum are not noble, but this sentence should reveal my level of chemistry knowledge.


texts:
I was doing my Science Fair Project and I tried to burn Calcium Carbonate. But the match went out as soon as it touched the Carbonate. I am wondering why the Carbonate isn't burning. I later tried to use a torch and a lighter but nothing worked. My science fair project is due tomorrow and I've looked everywhere on the internet but nothing really explained why the calcium carbonate didn't ignite.
Do I need HEAT or something like that to make it burn?
(I'm a 5th grader so please take it easy on me)


texts: Why is the Lucas test not recommended to differentiate higher alcohols?

texts: I read about the Lucas test for alcohols in which a cloudy precipitate is produced with a tertiary or secondary alcohol. However, on a side note it was mentioned that this test is useful only for compounds having less than six carbon atoms. Why is this so?


texts: Nonflammable epoxy remover that won't chip paint

texts: I was wondering if anyone knew of a nonflammable epoxy remover that also won't chip paint. My professor wants to use it in our lab to remove dried epoxy from the floors and the fume hood.


texts:
Can someone guide me through step by step how amitriptyline is named by IUPAC?
I know the name per se, but it is very confusing to me, and I'd like someone to explain it to me. The systematic name is

  3-(10,11-Dihydro-5H-dibenzo[a,d]cycloheptene-5-ylidene)-N,N-dimethylpropan-1-amine.


texts: Is there a mistake in diagramatic representation of RS perturbation theory described in Szabo and Ostlund textbook?

texts:
I'm trying to understand rules of the diagrammatic representation of the many body perturbation theory that described in Szabo and Ostlund "Modern Quantum Chemistry" textbook. One of the first rules they introduced is the following:
"Each pair of adjacent dots contributes the denominator $$\sum E_{hole}^{(0)} - \sum E_{particle}^{(0)}$$ where sums run over the labels of all hole and particle lines crossing an imaginary horizontal line separating the two adjacent dots."
According to that rule and other rules described in this book, the sum of the following diagrams:

can be translated as follows:
$$-\sum_{n,m\neq i}\frac{2|V_{ni}|^2|V_{mi}|^2}{(E^0_{i}-E^0_{m})(2E^0_{i}-E^0_{n}-E^0_{m})(E^0_{i}-E^0_{n})}$$
The idea of authors was that if we sum all possible n-dots diagrams we will get the exact expression for nth-order correction to energy. However, for the fourth-order perturbation theory there are no terms with such a denominator factor:
$$(2E^0_{i}-E^0_{n}-E^0_{m})$$
Am I right that in the case of 4th-order perturbation theory there is no direct mapping between those diagrams and strict algebraic formulations?


texts: Why can't the conjugate base of benzoic acid be stabilized by conjugation with the aromatic ring?

texts: All the carbon and oxygen atoms are sp2 hybridised and can have a p orbital in the correct plane yet only conjugation of the COO- group occurs. I can't think why. I can't draw resonance structures for the negative charge being delocalised around the ring but if you look at it from the orbital perspective (sp2 hybridisation) it seems clear that this conjugation should occur.


texts: Electronegativity comparison of group 13 elements

texts: Why is electronegativity of indium slightly  greater than gallium?


texts: For cubic materials, there are equations in which to calculate nearest neighbor (NN), second nearest neighbor, etc. Can this be done with tetragonal crystal structures? I want to calculate NN, 2NN, and 3NN of $\ce{TiO2}$ rutile with a tetragonal crystal structure but am unsure how to do it. Any suggestions/help would be appreciated!


texts: Using Avogadro's law to find gas volumes

texts:
An important step in the preparation of sulfuric acid involves the production of sulfur trioxide ($\ce{SO3}$) from sulfur dioxide ($\ce{SO2}$) and oxygen.
$$\ce{2 SO2 (g) + O2 (g) -> 2 SO3 (g)}$$
If all volumes are measured at the same temperature and pressure, calculate the volume of sulfur trioxide produced when $\pu{25 mL}$ of sulfur dioxide is placed in a container with $\pu{8 mL}$ of oxygen. What will be the total volume of all gases remaining in the container?

I seem to keep getting the wrong answer for the question, and I'm not totally sure why. I assumed I needed to use Avogadro's law, given that temperature and pressure are constant. So I used:
$$\frac{V_1}{n_1} = \frac{V_2}{n_2}$$
I determined $V_1$, $n_1$ the following way:
$$V_1 = \pu{8 mL} + \pu{25 mL} = \pu{33 mL}$$
$$n_1 = \pu{2 mol} + \pu{1 mol} = \pu{3 mol}$$
From the equation I assumed $n_2 = \pu{2 mol}$. This gave me
$$\frac{\pu{33 mL}}{\pu{3 mol}} = \frac{V_2}{\pu{2 mol}} \implies V_2 = \pu{22 mL}$$
The provided answer says $\pu{16 mL}$, and I am just unsure of how to alter the method.


texts: Why is -OCH3 more strongly activating than -CH3 in electrophilic aromatic substitution?

texts:
Facts I know:
1) More the electron density in benzene ring, the faster the reaction.
2) Lone pair on -OCH3 group undergoes resonance and makes ortho-para positions electron rich, and so does -CH3 by hyperconjugation.
3) -OCH3 group shows -I (electron withdrawing) and -CH3 shows +I (electron releasing).

Now, -OCH3 and -CH3 both undergo resonance and hyperconjugation respectively and both make ortho/para positions equally electron rich.

So the factor that should come in play is I effect. As the -CH3 group releases electron into benzene ring by +I effect, and -OCH3 withdraws electron by -I, what should be more activating is the -CH3 group.

Where am i wrong?


texts: Does all fire only emit light on its outermost shell?

texts:
This question is about light emission, which may overlap with physics, but I am most interested in combustion and types of flame (incandescence, petrochemical fuel flames, nuclear ractions).
Consider this article about candle flames. In it they describe how a candle flame only emits light where it has contact with oxygen (emphasis mine):

However the reaction can only occur where the air meets the wax vapour.  This cannot happen all the way though the flame, just around the outside.  So all flames are hollow.

How accurate is this? What parts of a flame emit light?
If flames have complex scattering and absorption properties distinct from the burning substance, does this only apply to the outside regions, with the interior being goverened by whatever fuel is burning?
I suppose "fire" is many different phenomena, so are the following flames also hollow?
A: Campfire
B: Rocket exhaust
C: Oil platform explosion
D: The Sun


texts: Contact lenses come in two polymer classes, ionic or non-ionic. Whats the significance of having both?

texts: As a contact lenses user, I was looking for information about why manufacturers produce soft contacts using polymers from both classes. Common knowledge would suggest that something placed in contact over the eyes for corrective vision should be inert. Ionic usually means more reactive. So why do they even make ionic contacts?


texts: Why does a weak acid and a salt containing its conjugate base form an acidic buffer?

texts:
I read this today:

  If you mix equal amounts of $1 M$ $\ce{H_3PO_4}$ and $1 M$ $\ce{NaH_2PO_4}$ you get a buffer at $pH<6$.

The reason given is that a weak acid plus a salt containing the conjugate base forms a acidic buffer.

  If you mix equal amounts of $1 M$ $\ce{NH_3}$ and $1 M$ $\ce{NH_4Cl}$, you get a buffer at $pH>8$.

The reason given is that a weak base plus a salt containing the conjugate acid forms a basic buffer.

I don't understand why this is true. Let's take the first statement for example. If you have equal amounts of a weak acid and its conjugate base, then by definition you have a buffer. Whether the buffer is acidic or basic shouldn't depend on whether the salt contains the conjugate acid or the conjugate base, right?


texts: Determine the concentration of the original NaOH solution

texts:
This was a question on the mt exam two days ago :

A chemist added 40.0 mL of an $NaOH$ solution to 90.0 mL of 0.400 M $HCl$.

The solution was then treated with an excess of $\text {nickel(II) nitrate}$, resulting in the formation of 1.06 of $Ni(OH)_2$ precipitate. Determine the concentration of the original $NaOH$ solution.

I didn't know what to do with this question

I knew that I should get the number of mol of NaOH to get the solution's concentration

Then I  wrote first the equation that describes the first part of the reaction :

$NaOH +  HCl \rightarrow NaCl + H2O $

After that I wrote the second part of the reaction :

$NaCl + H_2O + Ni(NO_3)_2 \rightarrow Ni(OH)_2 + ? + ?$

I don't know what will be the the other products ?

I stopped here and I guessed an answer.


texts: Why are stable ionic charges so strongly related to the group number?

texts: Why do lighter elements have ionic charges so strongly related to the group number? For example, why does $\ce{Al}$ only show +3 ionic charge? The basic concept of stability in an ionic compound is that lattice energy is greater than the sum of ionisation energy and electron gain enthalpy. Why can't $\ce{Al}$ show +1 or +2 states? I understand that the +3 state is in a 'sweet spot' since going from +3 to +4 requires a large amount of energy whereas going from +2 to +3 doesn't require much. Besides, a higher charge results in more lattice energy. Hence, it makes sense that the element would want to have the highest charge possible. This explains the abundance of ions in those states but not the absence of others. Why is it that the energy calculations always work out for lighter elements so that they only have the highest charge possible? Is it just chance or am I missing some deeper principle here?


texts: What reagents are used to selectively reduce 2,2,3‐trimethyloxirane to secondary and tertiary alcohols?

texts:
Problem

Answer

 (c) $x = \ce{LiAlH4},~y = \ce{LiAlH4}/\ce{AlCl3}$

Questions
I know $\ce {LiAlH4}$ is a reducing agent because it gives four $\ce{H-}$ and will attack on our reactant on carbon with less substituents, i.e. in this case on $\ce{-CH-}$ and on attack the $\ce{-O-}$ will go to other carbon and on protonation we get 3° alcohol.
But what about 2° alcohol? How can we get that?
What does $\ce{AlCl3}$ do such that we get 2° alcohol?
I thought maybe the oxygen is giving its lone pair to $\ce{Al}$ being deficient in $\ce{e-}.$ Then what happens if it does so? Will now $\ce{H-}$ attack 3° carbon? Does that mean it's following SN1 mechanism? Why?


texts: Liquid storage of transition metal oxides?

texts:
Transition metal oxides (TMOs) have a lot of interesting properties, from ferroelectricity to battery applications. Often times you can change the properties with only slight changes of oxygen stoichiometry. For example, SrTiO$_3$ is an insulating paramagnet, but becomes ferroelectric and then metallic with slight changes in oxygen stoichiometry in SrTiO$_{3+\delta}$. Another example is La$_2$CuO$_4$ which is an insulator, but with increasing oxygen content La$_2$CuO$_{4+\delta}$ becomes a superconducting metal.
One downside of this functionality is that transition metal oxides are notoriously finicky, and tend to change properties upon exposure to air, moisture, etc. In many cases, bulk polycrystals of TMOs have to stored under inert gases or vacuum to maintain their properties. Needless to say, that is quite annoying with regards to transportation.
My question is: is it possible to store transition metal oxides in liquids without significant deterioration? If so, which ones are the most practical? I'm sure the answer is "it depends", but even general suggestions and publication references would be useful.


texts: Which functional groups are not reduced by DIBAL.H?

texts:
According to the table here, diisobutyl aluminium hydride can reduce amides to aldehydes but according to the data given to me by my teacher DIBAL.H cannot reduce:  amides, acids, isocyanides and nitro groups.

It's I also given in my notes that DIBAL.H is  parallel to $\ce{LiAlH4}$ as a reducing agent but it is more selective.

I would like to know if DIBAL.H is able to reduce these functional groups or not.


texts: How would you draw the Newman projections of 3-methylpentane, sighting along the C3-C4 bond? I am unsure as to how to position the $\ce{-CH3}$ and $\ce{-CH2CH3}$ groups on the C3.


texts: Titration to determine the amount of hydrogen peroxide

texts: I have a mixture of sodium carbonate, sodium bicarbonate, ammonium carbonate, copper (II) sulfate, hydrogen peroxide, and sulfuric acid. I'm titrating potassium permanganate against this mixture to find out the amount of hydrogen peroxide in it. Will anything else in this mixture react with potassium permanganate? If so, is there another better way of determining the amount of hydrogen peroxide in it? Thank you.


texts: What is the mechanism of saccharification by H2SO4?

texts:
We have been estimating total carbohydrate by Umbreit method/ Anthrone method in college. The website I have been reading says that $\ce{H_2SO_4}$ and heat is used to treat a polysaccharide solution yield hexoses and pentoses which further undergo dehydration to form hydroxymethylfurfural and furfural respectively. These compounds when react with Anthrone form coloured compounds.

I have been wondering what the mechanism of hydrolysis of polysaccharide is?


texts: On what factors does the true reaction Stoichiometry depend when there are multiple valid options?

texts:
Consider the following unbalanced reaction:

$$\ce{XeF4 + H2O -> Xe + XeO2 + HF + O2}$$

There are six variables to be solved, but only four equations linking them. I solved the set of equations using Gauss elimination and arbitrarily set the stoichiometric coefficient of $\ce{XeF4}$ as $3$:

$$\ce{3XeF4 + 6H2O -> $(4k)$Xe + $(3-4k)$XeO2 + 12HF + $(4k)$O2}$$

where $k$ is the free variable, the parameter, with $0<k<\frac 34$ (since coefficients must be positive).

Clearly, for different values of $k$, it gives radically different yet balanced equations. The very yields are different for fixed amount of $\ce{XeF4}$ and $\ce{H2O}$. This issue has been noted in a previous question.

My textbook, however, gives the balanced equation:

$$\ce{6XeF4 + 12H2O -> 4Xe + 2XeO2 + 24HF + 4O2}$$

clearly setting $k=\frac 12$. The linked question above does not offer any explanation for why a particular value of $k$ should be favoured. So, my exact question is: Why set $k=\frac 12$? Why was $\frac 12$ preferred over any other value for $k$:

Is it determined by experimentally measuring the stoichiometry?
Is there a theoretical explanation for it?


texts: Calculating dew point and bubble point of gas mixtures

texts:
How do you calculate approximately the triple point and critical point of any given CH-based gas mixture?

I have developed a software which uses iterations to find bubble point and dew point of any CH-based gas mixture. It uses Peng-Robinsson EOS and Van Der Vaals mixing algorithm.

When calculating the dew point pressure for a certain temperature, it's difficult to know the starting range for the iteration. First I used False-Position method in finding the root, but now I have switched to Bisection. Although it's slower, it's more safe as it's not affected by function derivatives.

What would be needed is as approximation of the range where the liquid/vapour phases are found. Setting the iteration's range to start below triple point pressure, or above critical point pressure will cause the iteration to diverge and never find a root.


texts: Oxidation state of hydrogen in the LaNi5H intermetallic

texts:
This question is from an introductory chemistry course:

  What is the oxidation state of $\ce{H}$ in $\ce{NaH}$, $\ce{HCl}$, and $\ce{LaNi5H}$?

I've looked in the textbook to no avail.

Google doesn't help me much either. It does tell me that $\ce{LaNi5H}$ is an "intermetallic" compound.

The best I've found is this:

  Allen electronegativities also yield zero for the oxidation state of all such $\eta^2$ hydrogen atoms.

What is the justification? Preferably, is there an "intro to chem" level explanation for this?


texts:
I am attempting the 2016 Canadian Chemistry Contest Part A, and one of the questions concerns the WHMIS symbols and whether a compound is an oxidizer or not.

The correct answer is that ethanol would not require a WHMIS oxidizer symbol. However, I am confused as to why ethanol is not an oxidizer when compounds such as potassium permanganate and nitric acid are when all of them contain oxygen.


texts: Plasma, Fourth State of Matter, and Magnetic Fields and Electric Fields

texts: Plasma is the fourth state of matter consisting of positive atoms, and freed negative electrons.  Does plasma have an electric field, and magnetic field?


texts: Does the reaction become more or less favorable as temperature increases?

texts:
Suppose a reaction has $\Delta S > 0$ and $\Delta H < 0$.

The equation $\Delta G = \Delta H - T\Delta S$ predicts that as the temperature increases, the reaction becomes more favorable because the $T\Delta S$ term becomes larger and $\Delta G$ becomes more negative.

However, the equation $$\ln(\frac{K_2}{K_1}) = -\frac{\Delta H}{R}(\frac{1}{T_2}-\frac{1}{T_1})$$ as well as Le Châtelier's principle, predict that as the temperature increases, K will decrease (and the reaction shift to the left, thereby becoming less favorable and $\Delta G$ becomes more positive).

These two claims seem to be inconsistent, but I can't identify the error in my reasoning.


texts:
In Peter Sykes' A Guidebook to Mechanism in Organic Chemistry, it says that sp3 orbitals have greater relative overlap compared to sp bonds.
We know that the $\ce{C-H}$  bond is shorter in ethyne compared to ethane. So the intuitive idea that more overlap would lead to stronger bond formation is obviously incorrect.
So what is the relation between relative overlap of two orbitals and their bond strength? Is there any use that we can get from this overlap?


texts:
What is the rationalization for calling reactions with rates independent of pH but dependent on the concentration of a particular acid catalyst under "general" acid catalysis, and pH dependent reactions under "specific" acid catalysis ?

It would seem to me that the pH-independent reactions would be better considered to be under "specific" acid catalysis given as they are catalysed by a specific species.


texts: Why methoxy group acts similar to trifluoromethyl in nucleophilic aromatic substitution

texts:
In an online test, the following question was asked:

The answer to this question was:

I totally agree with the answer, as $\ce{OCH_3}$ is an EDG, hence it will tend to form meta product in this reaction.

While reading NAS on Master Organic Chemistry, I came up to this article:

This article says that $\ce{OCH_3}$ behaves similar to $\ce{CF_3}$, but I can't figure out the possible reason. Any help is appreciated!

Related (unanswered) question: Nucleophilic substitution in aromatic compounds


texts: Why does sulfonation of alcohols even work?

texts: I am now near the end of organic chemistry 2, and I'm trying to understand the patterns of reactions so that I can predict them rather than brute force memorizing all of them. Looking at the sulfonation of alcohols using mesyl chloride, I don't think I would ever predict that. I don't understand why the oxygen should attack the sulfur in mesyl chloride. To me it looks like a nucleophilic substitution reaction, but alcohols aren't even powerful nucleophiles. Not to mention that the end of this reaction creates HCl a very powerful acid. I thought when reactions occur they like to create relatively weaker acids and bases? What is driving the reaction, and what patterns should I be noticing here for future predictions?


texts: I was reading recently about environmental remediation being done, using an esterase to break down / neutralize cocaine that had contaminated waterways in Europe. Are there similar enzymes that can be used to safely break down pharmaceutical drugs, like surplus SSRIs and neuroleptics, that medical staff might otherwise just flush down the toilet thus causing more pollution? A way to neutralize them into safe inert ingredients first would seem beneficial to educate people about.


texts: metal salt solutions g/l means hydrate or anhydrous

texts:
I want to redo an experiment. They've used

Nickel chloride: 40 g/L

Nickel chloride can be bought in two forms: anhydrous ($\ce{NiCl2}$) and hydrate ($\ce{NiCl2.6H2O}$). The paper doesn't say which one they've used. Which one did they mean in the paper? In one liter of water should I dissolve 40 grams of $\ce{NiCl2}$ or 40 grams of $\ce{NiCl2.6H2O}$? Is there a convention?


texts: On the periodic table: Why are groups of elements organized by 'letter'

texts:
Why are the groups of elements on the periodic table organized into areas represented by the letters s,p,d,f,g, and h?
What does this mean?


texts: Vapour pressure of a liquid subjected to pressure

texts:
I am following the derivation by Atkins in section 4B(c) (Physical transformations of pure substances; thermodynamic aspects of phase transitions), in which the authors derive the equation ${p = p_* * exp[V_m(liquid)* ΔP/RT]}$. The derivation starts by noting that chemical potentials of vapour and liquid are equal at equilibrium, $μ_{liquid} = μ_{gas}$, and follows by integration over the pressure to calculate the change in chemical potentials due to the added external pressure.

What is unclear to me is why the integration for the liquid phase is taken over the ambient pressure while the integration for the gas phase is taken over the vapour (NOT ambient) pressure. It seems counterintuitive to me because I would expect that $μ_{gas}$ is a function of the ambient pressure and therefore should be integrated over the ambient pressure. Am I missing something?

EDIT: I guess the question could be rephrased: in the definition of molar volume for gas, $V_m=(\frac{\partial \mu} {\partial P})_{T,n}$, is $P$ the partial or ambient pressure? More generally, does $\mu_{gas}(T,P)$ depend on the partial or ambient pressure?


texts: Combustion of non-hydrocarbon organic compounds

texts: When we learned about combustion, we learned about the combustion of hydrocarbons and compounds with only hydrogen, oxygen, and carbon. However, how would combustion work with compounds that contained nitrogen or other compounds? For instance, what would the combustion of an amino acid look like in a formula?


texts: How can it be determined that a liquid is saturated with a gas?

texts:
How can it be determined if a liquid is saturated with a gas?

For example, if I am introducing carbon dioxide to water at 40 PSI at 35F in a sealed container, how would I know at what point the water is saturated with the gas?


texts: Activities of Solutes - especially acids and bases

texts:
What is the concentration of hydrochloric acid needed to have a solution with the activity of the hydrogen proton = 1? I read 1.18 M somewhere but I am unable to find a corroborating source. Also, how can the activity of the hydrogen proton = 1 when it doesn't exist by itself, suggesting that its activity should = 0 (since it can't act as an independent particle)?

Also how would one get to this result? Does one use a high-grade pH meter? Don't analytical-level pH meters measure activities rather than concentrations of hydronium ion?


texts: Energy cost of C−N rotation in hydroxamate group

texts: I am looking for a literature reference on the energetic cost of C−N rotation in hydroxamate group such in LC5 in water. I have been googling for a while.


texts: Miller indices: How does one translates the orientation to the origin of the unit cell?

texts:
In a section discussing Miller indices, my textbook says the following:

  The rules for determining the Miller indices of a direction or an orientation in a crystal are as follows: translate the orientation to the origin of the unit cell, and take the normalized coordinates of its other vertex.

What I'm confused about is how one translates the orientation to the origin of the unit cell?

Since the textbook just mentions this without elaboration or illustration, it is not clear precisely what this means or how one would go about it. I would appreciate it if people could please take the time to explain and demonstrate how this is (mathematically) done. Sources would be appreciated, if you have them.


texts: Why is zinc deposited on copper when boiling an aqueous zinc sulfate solution?

texts:
I did an experiment where I dissolved 30 grams of zinc sulfate in water and boiled it with strips of solid zinc metal and strips of copper metal and a layer of zinc was deposited on the copper.

I know that if you place solid copper in zinc sulfate aqueous without the solid zinc nothing would happen because zinc is more reactive than copper.  Why does the addition of zinc sulfate cause the zinc to coat the copper?  What is happening?


texts: in hybridization, can bond angles be different

texts: Is there a concept of mixed hybridization where bond angles in a hybridized molecule are different angles?


texts: Why is the water solubility of CO worse than that of CO2?

texts:
I tried my best to ask SciFinder, Google, and Google Scholar the wrong questions ...
I found many paper on the fitting of the solubility to some equations to be able to calculate the amount of $\ce{CO}$ in water, but I could hardly find any explanation on the low solubility. Only one paper [1] dealt with it.
Why is $\ce{CO}$ way less soluble in water than $\ce{CO2}$, despite, e.g., the first having a dipole moment and the latter doesn't? What am I missing?

[1] H. Sato, N. Matubayasi, M. Nakahara, F. Hirata, "Which carbon oxide is more soluble? Ab initio study on carbon monoxide and dioxide in aqueous solution," Chemical Physics Letters 2000, 323(3-4), 257–262 (https://doi.org/10.1016/S0009-2614(00)00508-X).


texts: A slightly bruised apple will rot extensively in about 3.5 days at room temperature (22.0 degrees Celsius). If it is kept in the refrigerator at 0.5 degrees Celsius, the same extent of rotting takes about 12 days. What is the activation energy for the rotting reaction?


texts: How do we know the number of atoms in an inorganic compound? If there's a question like 'Write the chemical formula for sulfur dioxide', the only thing I managed to do is answer '$\ce{SO}$'. I don't know how to find out the number of sulfur atoms or oxygen atoms.


texts: In which condition CO uses the oxygen end for bonding?

texts:
Generally Metal Carbonyl complex are formed from Carbon end. Is it possible under some specific condition that the Oxygen end is used?
(PS -I know about the structures of M-CO bonding)


texts: For azeotropic mixtures, is the total vapour pressure at equilibrium equal to the partial pressure of one of the components?

texts:
I know, a ridiculous statement. But here's how I reached at it .
Say we have a solution of two components liquids A and B.

By Raoults law,

$$p_A= p_A^o \times x_A \tag1$$

Also by Dalton's law,

$$p_A= P_T\times x^V_A \tag2$$

Now if the solution is azeotropic,

$$x_A= x_A^V$$

So that implies the total pressure equals the partial pressure of A.

Which is absurd.
Please tell me where I am going wrong.


texts: How do I go about either finding or calculating Aluminum-Oxalate salt solubility values in aqueous medium?

texts: Water would contain other salts which may complicate things a bit. But finding out the Aluminum-Oxalate salts solubility values in pure water would be a good indicator already. It's for temperatures from 10-50C. Wikipedia doesn't have a page for Al-Oxalate but it has a page here: https://pubchem.ncbi.nlm.nih.gov/compound/Aluminum_oxalate


texts: What reaction could rubidium undergo in a vacuumed chamber with Macor ceramic and glass?

texts:
In the center of the chamber on the photo below you can see the hexagonally-shaped Macor  glass-ceramic consisting of

Silicon dioxide $\ce{SiO2}~46\%$
Magnesium dioxide $\ce{MgO}~17\%$
Aluminum oxide $\ce{Al2O3}~16\%$
Potassium oxide $\ce{K2O}~10\%$
Boron oxide $\ce{B2O}~7\%$
Fluorine $\ce{F}~4\%$

The original color of Macor is white as you can see on the second picture on the side. I insert the rubidium into the chamber. It all became black at the temperature of approx. $\pu{150–200 °C}.$ What could rubidium possibly react with?

It was in the vacuum $\pu{E-8 Torr}.$ I have heard that the window material can also react with rubidium. Rubidium is in vapor state (according to optical spectrum at temperature $~\pu{100 °C}$ and $\pu{E-4 Torr}).$ Rubidium tends to condense on the cold part of the chamber, so it is possible to touch the ceramic.

I heat the chamber outside, so rubidium should be in vapor state inside of the chamber, and Macor is connected to the chamber, so it should be close but lower than the chamber temperature.


texts: Why does reducing the pressure in an equilibrium reaction favour the side with more moles of gas?

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I was trying to explain it in terms of reaction rates and such; more than just 'Le Chatelier's principle states ...', but I can't figure out the underlying reason as to why. I can explain why for increasing the pressure, temperature changes and such, but not for this specific one. If there is more space for the particles to move without collided, this reduces the frequency of successful collisions, reducing the reaction rate of both forward and reverse reactions. But, in $$\ce{A + B<=>3C}$$
there is initially more moles of C than A and B combined. So, isn't it reasonable to think C will collide more frequently than A and B, meaning the reaction rate of the reverse is quicker, rather than the reaction rate of the forward being quicker?


texts: Effect of direct exposure to sunlight on various drugs

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Today, we were discussing optical activity in class and our teacher said that some drugs are kept in dark coloured bottles to avoid direct exposure to sunlight. Same is the case with some other drugs in which it's written that the direct exposure to sunlight should be avoided.

The reason he gave for the above was that the one form of isomer can get converted to other form in direct sunlight.
But as far as i know, photolytic decomposition can happen. Is the conversion of d to l isomer and vice versa possible in sunlight?


texts: Does the process of chemically strengthening glass change its volume?

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The process of chemically strengthening glass replaces sodium ions in the glass's surface with potassium ions through a process that uses a potassium nitrate bath solution. These potassium ions are larger than the sodium ions and therefore wedge into the gaps and create pressure on the surface of the glass which can make it 6-8 times stronger than glass that is untreated. My question is whether this process would be expected to cause the glass to swell or change volume.
I have conducted experiments with chemically strengthening blown glass globes and have measured a consistent volumetric increase in the diameter of the globes post process. I am trying to determine how to predict and estimate this change. I can't determine if this is the result of the added mass from the potassium ions or if the surface pressures themselves are stretching the material.
I have talked to a few chemical engineers and looked through textbooks and online journals but much of the research done on this topic seems to be proprietary. I am posting my question here in hopes of finding someone who can point me in the right direction with my research.
This is my first question asked in this Stack Exchange Chemistry Site. Please let me know if there is anyway I can improve my question.


texts: A Curious (definitely wrong) result of Absolute Entropy

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The Gibbs free energy is defined as
$$G=H-TS$$
Differentiating both sides
$$dG=dH-TdS-SdT$$
For an adiabatic reversible expansion of an ideal gas, we would have $dG=0$, and $dS=0$.
Thus we can write, $dH=SdT$
Also, $dH=n C_p dT$.
Finally I reach the strange result that $S=nC_p$. How can I define absolute entropy so simply. Something is definitely very wrong here. Please correct me.


texts: Nucleophillic addition reaction in the presence of an acid catalyst on a molecule with an alkene

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This is a solution for a question in my textbook.

In the presence of an acid catalyst, am I wrong in my understanding that the acid will protonate the alcohol, and then do an electrophillic addition reaction onto the alkene (in addition to the nucleophillic addition reaction from the alcohol)? If so, was it omitted from the solution because it is not a major product (if it's not a major product, why)?


texts:
Question

In which of the aqueous solutions of the following, dissociation of $\ce{NH4OH}$ will be minimum?
A) $\ce{NaOH}$
B) $\ce{H2O}$
C) $\ce{NH4Cl}$
D) $\ce{NaCl}$

My Thoughts
My book says that the answer is option C '$\ce{NH4Cl}$' giving the reason as common ion effect.
But I think that option A '$\ce{NaOH}$' also has a common ion as $\ce{OH-}$.
What should be the right answer and how do we compare which will cause more suppression by common ion effect?
I get why $\ce{H2O}$ will not suppress dissociation of $\ce{NH4OH}$ that much since its equilibrium constant is very low (of the order of $10^{-14}$). But then why not $\ce{NaOH}$ (which is a very strong base and thus will almost completely dissociate into constituent ions)? Which one out of $\ce{NaOH}$ and $\ce{NH4Cl}$ is a more stronger electrolyte?
Is it because $\ce{NH4Cl}$ will form a buffer with $\ce{NH4OH}$?
I am feeling really confused about this. Any help will be highly appreciated!
Final Question
I now understand that both $\ce{NaOH}$ and $\ce{NH4Cl}$ will cause decrease in dissociation of $\ce{NH4OH}$. Hence my final question is this: Which will cause more decrease in dissociation and why?


texts: How to determine steady state of multi-step reaction with both reversible and irreversible steps?

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I am trying to determine the relative concentrations of $\ce{U1}$, $\ce{U2}$, and $\ce{E}$ when the following reaction is at steady state. Note that $k_t$ is the zero order rate constant of new $\ce{U1}$ entering the system and $k_d$ is the first order rate constant of substances leaving the system.

$k_1$ and $k_2$ are the first order rate constant for the forward and reverse reaction, respectively, of $\ce{U1}$ turning into $\ce{U2}$, and $k_e$ is the first order rate constant for $\ce{U2}$ reacting to $\ce{E}$. First order reactions are all first order in the respective reactant.

All the individual rate constants are known but the concentrations are not.

Can anyone point me in the right direction for how to determine the relative concentrations at steady state? I'm imagining an equation or set of equations such that when values for each rate constant are plugged in, the concentrations of the products are determined.


texts: Why has the mole been redefined for 2019?

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The mole is still defined as an SI unit representing the number of constituent particles (whether they be atoms, molecules etc.) in 12 grams of carbon isotope 12 (carbon-12).

Effective from May 20 this year the definition of the mole will change to a unit representing Avogadro constant number of particles.

Since the Avogadro constant was and will be still tied to the mole (number of particles in a mole), I think this also changed the definition of the Avogadro constant, though I'm not sure. Although the old and new definitions define the constant as the number of particles contained in the mole, it seems that the definition of the mole has changed from the earlier carbon-12 definition to simply the Avogadro constant.

First of all I would like to know if anyone knows why this redefinition happened now (it was decided at the end of the last year).

Also, please correct anything wrong I've said. This is rather confusing for me and the definitions seems rather circular. The new definitions are that Avogadro's constant is the amount of particles in a mole, and a mole is defined by the Avogadro constant.

  Previous definition:
  The mole is the amount of substance of a system that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.
  2019 definition:
  The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.02214076 × 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol−1 and is called the Avogadro number.
  Avogadro constant - Wikipedia


texts: Which is more stable chemically: DNA or peptide

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Assuming enzyme-free environment, and the DNA and peptide are lyophillized, and then stored in vials under the same conditions (temperature and humidity).

On average, which would be more chemically stable,

in terms of backbone cleavage?
in terms of loss of side chain?


texts: Why quaternary nitrogen but not tertiary oxygen?

texts: Why do quaternary ammonium ions with a partially positive nitrogen form fairly readily and are often stable but tertiary oxygens, apparently called oxonium ions, are more rare/less stable? The trend seems to continue down the periodic table, too, with phosphonium and sulfonium.


texts: How do we number the carbon atoms in symmetrical molecules while giving R and S notation. For instance, in 2,3-Dibromobutane, there is an ambiguity over which is carbon C2 and carbon C3. Will we call it (2R,3S) or (2S,3R)?


texts: What non-poisonous chemicals can get rid of SLS effectively?

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Whenever I brush teeth, there are some kind of bubbles sticking inside the cavity and that's uncomfortable, it should be SLS as found on the internet. Does anyone know how do I get rid of those bubbles things easily?
Eat/Drink sth? Tell me if anything is wrong.

Any help would be appreciated, thanks.

Addition: SLS represents sodium lauryl sulfate, chemical exist in our cleaning product: toothpaste, shampoo,   etc. I don't know what it is for but seems it produce bubbles as long as the product is used.


texts: Oxidation number looks all but a convenient accounting tool for balancing chem equations. Or does it? Why would a molecule care about its oxidation state? Is a different oxidation state sort of a different chem specie with specific properties, reactions, etcetera... Does an oxidation state tend to maintain itself through "weak" exchange processes till some "strong" electron pushing/withdrawing agent gets into? Is it sort of dividing species into carnivores and herbivores?