texts: Effect of redefining Avogadro's constant and kilogram on molar mass

texts:
Avogadro's constant $N_\mathrm A$ is defined as the number of constituent particles (usually atoms or molecules) contained in the amount of substance given by one mole.

The value of Avogadro's constant $N_\mathrm A$ is going to be set to exactly $6.02214076\times 10^{23}\ \mathrm{mol}^{-1}$ in 2019.

I might add that the kilogram is also going to be redefined in 2019 based on Planck's constant.

Will these changes result in the molar mass of a substance no longer being exactly equal to the molecular mass expressed in grams?


texts: What is the reaction between Magnesium chloride and Sodium bicarbonate?

texts:
For some reason it has been very difficult to find the right answer for this question as there's so much conflicting information to be found online. Some mention a reaction where carbonic acid is made, others mention carbonates and hydroxide end product but nothing seems to be precise.

But can the reaction be as simple as this (a double displacement reaction) where magnesium bicarbonate and sodium chloride are the end products:
$$
\ce{2NaHCO3 + MgCl2 ->  2NaCl + Mg(HCO3)2}
$$


texts: Reaction of Diazonium salt with Grignard reagent?

texts: Why doesn't Grignard Reagent undergo Nucleophilic Substitution with a Diazonium Salt? for example if we want to convert phenol to p-cresol. Then first nitrating it, then convert it to a diazonium salt and treating with a methyl grignard reagent. But the reaction dos not happen. Instead we have to use Gilmann Reagent for this process. Why?


texts: Help understanding Electrochemistry diagram

texts:
I was reading some literature when i came across the following figure and was wondering if someone could help explain it to me. I see on the vertical axis it is potential vs Li/Li+ and see that Oxides are at ~1.2V since the potential of lithium ion batteries are ~4V and it is a transition metal oxide are they talking about other oxides? I am assuming by potential they mean Reduction potential? Graphite is at ~0.2V Silicon at~0.3V and TiO2~1.5V but they are all used as anodes in lithium ion batteries why are they not reduced as
$$
\Delta G = -zFE
 $$
and E is positive so dG is negative?


texts:
A $52\ \mathrm{g}$ piece of iron at $250\ \mathrm{^\circ C}$ is added to a mixture of $100\ \mathrm{g}$ of ice and $100\ \mathrm{g}$ of liquid water at thermal equilibrium $(0\ \mathrm{^\circ C})$. Calculate the mass of ice that melts (not all of the ice will melt, so you know the final temp of everything mixed together).

I think that the temperature of the mixture should stay same, if is at thermal equilibrium. Because then it less willing to accept change in temperature. But I am not sure how to use heat of fusion and heat capacity of liquid water to solve this.

My attempt:

$Q$ lost from iron = $Q$ gained by water + ice mixture

$(0.93\ \mathrm{mol}\ \ce{Fe})(25.1\ \mathrm{J\ mol^{-1}\ K^{-1}})(T_\text{f}-250\ \mathrm{^\circ C}) = -(200\ \mathrm{g}\ \text{mixture})(\text{what is }C\text{?})(T_\text{f}-0\ \mathrm{^\circ C})$


texts: Physical intuition behind negative values for wave function?

texts:
So a positive and a positive wave function create a bonding orbital where the probability of finding an electron is summed while a positive and a negative create an anti-bonding orbital with a lower electron probability in the region between them leading to a repulsion. My confusion stems from not having any idea as to what a negative wave function is representing - can anyone give me some physical intuition on how this negative wave function could be correlated to something in reality?

(I tried asking this question on physics.SE but it would seem that in physics you just don't talk about or use the wave function until after you square it)


texts: Ligand strength - Coulombic effect and/or Electronegativities?

texts:
According to my teacher, these three Lewis bases generally decrease in strength in the following order:

Ammonia
Water
Hydroxide ion

I agree. However, he argues that their ability to act as Lewis bases stems from Coulombic repulsions. For example, nitrogen has only one lone pair. Water however has two lone pairs, and when water uses one of its lone pairs in a Lewis base fashion, the other lone pair weakens the resulting Lewis adduct through exerting a repulsive force on the lone pair used in forming the Lewis adduct. Same with hydroxide, except that the repulsions are even greater in hydroxide since it has three lone pairs.

I say that in addition to this effect, there is also the effect of the Lewis base being able to stabilize its valence electron density. Nitrogen is less electronegative than oxygen. Thus, any valence electron density on nitrogen will be more reactive than that on oxygen. On the other hand, oxygen in hydroxide ion has a greater valence electron density than that of oxygen in water, and hydroxide ion is a poorer Lewis base than hydroxide ion.


texts: Reaction between copper(II) iodate and iodide

texts:
I was attempting the following question from IChO 1989, which involved balancing of redox equations. One may just expect this to be a typical iodate-iodide redox reaction, usually employed in iodometry. However, the presence of $\ce{Cu(II)}$ makes things a bit more complicated since it can also be reduced to give $\ce{CuI}$.

To determine the solubility product of copper(II) iodate, $\ce{Cu(IO3)2}$, by iodometric titration in an acidic solution ($\pu{25 ^\circ C}$), $\pu{30.00 cm3}$ of a $0.100$ molar sodium thiosulfate solution are needed to titrate $\pu{20.00 cm3}$ of a saturated aqueous solution of $\ce{Cu(IO3)2}$.
1.1 Write the sequence of balanced equations for the above described reactions. [...]

After realising that $\ce {Cu^2+}$ is reduced as well, I wrote the following overall equation :
$$\ce{2Cu^2+ + 2IO3^- + 12H^+ + 14I^- -> 7I2 + 2 CuI + 6H2O} \tag{1}$$
which is based on
$$\begin{align}
\ce{2Cu^2+ + 4I^- &-> 2CuI + I2} \tag{2} \label{eq:cuii} \\
\ce{2IO3^- + 12H^+ + 10I^- &-> 6I2 + 6H2O} \tag{3} \label{eq:iodate}
\end{align}$$
However, it turns out that the equation given in the answer scheme seems to have multiplied eq. $(\ref{eq:iodate})$ by $2$ and the overall equation given is:
$$\ce{2Cu^2+ + 4IO3^- + 24H^+ + 24I^- -> 13I2 + 2CuI + 12H2O} \tag{4}$$
Usually, this is a trivial thing and does not matter. But in this case, it does since the reaction stiochiometry is completely different based on the equation given. Have I gone wrong somewhere?


texts: Platinum Orbitals in Cisplatin Forming Bonds with LCAOs of Chlorine

texts:
My inorganic chemistry professor placed two questions on the exam review that he did not cover in class; I haven't been able to figure out how to answer them and could really use some help in learning how to think about this problem.

The two questions are:

  Which orbitals of $\ce{Pt}$ can form a $\sigma$ bond with the LCAO $\left[\Psi((\ce{Cl}')_{\mathrm p_z})+\Psi((\ce{Cl}'')_{\mathrm p_z})\right]$ of the two $\ce{Cl}$ atoms in cisplatin?

  Which $\mathrm d$ orbital of $\ce{Pt}$ can form a $\pi$ bond with the LCAO $\left[\Psi((\mathrm{Cl}')_{\mathrm p_z})-\Psi((\mathrm{Cl}'')_{\mathrm p_z})\right]$ of the $\mathrm p_{z}$ orbitals of the two $\ce{Cl}$ atoms in cisplatin?

How do I arrive at the corresponding oritals?


texts:
I have a number of toy balls filled with a liquid-presumably water or something else non-toxic. Over about a year, the balls have gone from firm to indented as shown. The water level in one is visibly low but four others have become indented as if some water were removed without allowing air to take its place. There are no indications of any leaks, balls have all been maintained at room temperature.

I posted this to chemistry because my hypothesis is that there is some sort of diffusion through the ball surface or in to the floating toy contained within. In the case of the ball on the right, the toy inside appears to have a hole so maybe it was originally full of air but the liquid has migrated inside pushing the air out and appearing to lower the water level. Explanation doesn't work for the other balls.

Thoughts?

-Engineer Dad


texts: Relative magnitudes of intermolecular forces from phase diagrams

texts:
Is it possible to say whether or not a system A or B has stronger intermolecular forces from a phase diagram according to which:

The $T_{\text{b}}$ of A is lower than the $T_{\text{b}}$ of B.
The $T_{\text{melting}}$ of A is higher than the $T_{\text{m}}$ of B.
The triple points of A and B are the same.

Or is it not possible to compare A and B's intermolecular forces from a phase diagram?

I was sure that B has stronger intermolecular forces, as its boiling point is higher than for A at the same pressure.


texts: Why does Azo coupling of β-naphthol takes place at alpha position and not at gamma position

texts:
I have searched for coupling reaction of $\beta$-naphthol with benzene diazonium salt at quite a few places. But everywhere the coupling has been shown at alpha position. Why doesn't it take place at gamma position to minimise steric hindrance.

Chemistry LibreTexts

Chemguide

My book


texts: Exceptions to motif: nucleophile attacks electrophile

texts:
I hear this motif - nucleophile attacks electrophile - all the time with regard to organic chemistry. Are there any exceptions?

I think this statement is always true in general because it's a restatement of Coulomb's law. But then are there any organic reactions that cannot be characterized as nucleophile attacking electrophile?

What I learned: Radical termination does not involve nucleophiles attacking electrophiles.


texts: extract cellulose from CMC using cuoxam reagent (schweizer's reagent)

texts:
Good day, I am new in the field of chemestry. My question is, if it is possible to reverse or extract (I am not very sure how to say it), cellulose from carboxymethyl cellulose (CMC) by the use of schweizer's reagent. I read that this reagent is capable to "regenerate" cellulose from a different sources, but unfortunately I havent found any paper that can support this idea.
I want to thank in advance for your time and help.


texts: Is there an energy cost associated with flipping the spin of an electron?

texts:
THE STORY:

A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves.  RHF enforces electrons to be paired into spin orbitals, $\chi$, or two spatial orbitals $\phi$ with the same set of spatial coordinates $\mathbf{r}$ but a different spin function (i.e. $\alpha$ or $\beta$ for spin-up $\uparrow$ and spin-down $\downarrow$, respectively).  Unrestricted Hartree-Fock theory gives each spatial orbital its own set of coordinates, allowing for $\phi_1(\alpha$) to have a different energy than $\phi_1(\beta)$, giving rise to a proper description of the H$_2$ dissociation energy (see the graph below).  I didn't include units in this graph but the energy is in kcal mol$^{-1}$.  The red curve gives the appropriate (and approximate) $D_e$.  The RHF formalism (blue curve) gives a $D_e$ that is three-times greater than the 'right answer'.

A corresponding electron configuration picture is shown below.  Here we clearly see RHF forcing the electrons to be paired at infinite distances, giving rise to an H$^-$H$^+$ description of the system which is clearly wrong.  (Note that this is a 'state' that included into the wave function by RHF).  UHF allows the electrons to reside in their own spatial orbitals giving rise to two doublets at infinite separation.

Now here is where things get interesting.  In terms of the actual computations implemented to generate the curves in Figure 1, the electrons adopt opposite spins.  However, let us imagine a theoretical scenario where two lone hydrogen atoms are floating around in space at infinite distance.  The corresponding electrons (which we will assume is not interacting with each other) can adopt any spin they want so both electrons can have a spin-up configuration.  Now imagine these two hydrogen atoms approaching each other.  For a covalent bond to form, the electrons will be paired into a spin-orbital which means that one electron must flip its spin according to the Pauli-Exclusion principle.  (We should note at this point that orbitals are merely mathematical functions whereas spin is an actual physical property).  This now leads us to...

THE QUESTION:

Is there an energy cost associated with flipping the spin of an electron such as in the scenario I've described?

The obvious follow up question (if the answer is yes to the first piece), would the H$_2$ dissociation energy curves be different for two H atoms each with spin up electrons and two H atoms with electrons of opposite spin (and how different would they be)?


texts: Continuous flow mass spectrometer for isotope analysis

texts:
If i took thousands of discrete samples of mineral fragments in a field study using a specialized drill, what mass-spectrometry techniques/equipment would allow me to analyse the samples as fast as possible?

Some machines can take 5000 readings per second, how can that be applied to a continuous flow of mineral fragments?

The premise is a feasibility-study of a robot archaeology tool:
Cartesian Axis Robots have an accuracy of about 0.01mm, so it would be possible to excavate sensitive sites to sample submillimeter 3d slices of the soil.
The technical challenge of the machine would be how to prepare and record tens of thousands of chemistry results every hour.


texts: Reasoning retention factor of benzoic acid

texts:
In my organic chemistry lab, we ran a TLC plate on silica to determine the identity of an unknown compound. The two possibilities were benzoic acid and acetanilide. I know that the general rule is, the more polar the compound is, the more it absorbs onto the silica and slower and lower it would travel (corresponding to a lower $\mathrm{R_f}$ value). However, one question on my lab report asks:

  In practice, benzoic acid tends to have larger $\mathrm{R_f}$ values than acetanilide. Attempt to find an explanation why this is. And note that spots from more concentrated benzoic acid leas to larger $\mathrm{R_f}$ values.

My professor said the answer has something to do with the $\ce{-OH}$ group on benzoic acid.


texts: Why we don't talk about unit cells in hcp/fcc structures?

texts:
I'm studying basics of Solid State Chemistry from this source.

So there are 14 types of Bravais crystal lattices (Primitive + Centered) in 3D. Every solid in this universe is made by the unit cells of these lattices. OK so far so good.

Later on there was the topic of Close packing and Structure of Metallic Crystals and we are told about hcp /fcc types of structures.

Problems:

Why do we remain silent about the unit cells and crystal system in this context? It seems like a huge disconnect.
Is there any relation between the Hexagonal Unit cell and hexagonal close packing?


texts: How is alcohol different from water as a solvent

texts: Since both are polar and protic, they both should give similar reaction mechanisms and intermediates


texts: A semi-transparent material that is a solid

texts: I am trying to find something I can get the ingredients for and make that starts out a liquid and sets into a solid. My end goal is to create a simple 8bit art figure so I want to pour it into a mold and have it harden. Also I would really like something fully or partly transparent (I was looking at aerogel because of the nice blue translucency but it seems too brittle to work with). So my question is what would be the best compound to try to create this figure out of?


texts:
I read that, and was wondering that in the first reaction shown they have used a tertiary butoxide where ether is formed because there is a primary alkyl halide but in the second reaction, they have used a methoxide. The Alkene formed is due to the tertiary alkyl halide my doubt here, is that is there any reason for taking a tertiary butoxide in one and methoxide in the other? Does the product also depend on the attacking species carrying the O-?

Update:

What I am trying to say, is that in the book, they first gave 4th reaction and if they were to follow the similar reaction then they should have mentioned something like 2nd reaction but they rather changed the tert-butoxide to a methoxide. Is there a reason behind it? And what would be the products for the other two reactions? Would it be a mixed product with no component in a majority?


texts: Field Keyword and Molecular Orbitals--Gaussian 09

texts:
I am using Gaussian 09 to run calculations. I am applying a 0.1 eV field in the positive Z direction to a molecule. I am also using the %chk keyword so that I may analyze the Molecular Orbitals after I apply the field. Only the HOMO and LUMO show absolutely no change. Am I doing something wrong? Should I use a higher value for the field? I am using #Field=z+36 (did the conversion to hartrees)

Theory wise there should be a change in the orbitals, correct?

To add, I aligned the molecule along the Z axis using a script I wrote.


texts:
I am looking for a heat-resistant odor neutralizer that can be released into the air at 200 degrees Fahrenheit and still be effective.

Does anyone have any ideas?


texts: Predicting changes in pH of water when chlorinating using two different methods

texts: Two methods for chlorinating water are using chlorine gas $(\ce{Cl2})$ or calcium hypochlorite $(\ce{Ca(OCl)2}).$ By using chemical equations how can you predict the pH of the water brought about by the chlorinating process?


texts: How easy is it to make animal horns transparent?

texts:
I never knew that HORN in HORNbook refers to animal horns, or animal horns can be made transparent? If Medievalists can make it transparent, the transparency process must've been cheap easy and quick, right?
The Horn Book | Why is it called "The Horn Book"?

Back in the sixteenth century, English monks began to make hornbooks to help their pupils learn to read. Usually a wooden paddle with an alphabet and a verse glued to the surface, hornbooks derived their name from the piece of transparent horn protecting the verse. The picture to the right shows a modern replica of a hornbook.

Hornbook - Wikipedia

A hornbook is a book that serves as primer for study. The hornbook originated in England as long ago as 1450,[1] or earlier.[2] The term has been applied to a few different study materials in different fields. In children's education, in the years before modern educational materials were used, it referred to a leaf or page displaying the alphabet, religious materials, etc., covered with a transparent sheet of horn (or mica) and attached to a frame provided with a handle.[3]


texts: What techniques can determine the concentration of ethyl acetate in a solution containing ethyl acetate, acetic acid, ethanol and water?

texts: I need to monitor the concentration of ethyl acetate in an Fischer esterification reaction. What techniques or spectroscopies can detect the concentration of the compound? And which one do you recommend based on precision and less sample preparation?


texts: How are solubilities of hydrate salts determined when competing equilibria are unavoidable?

texts:
When you calculate the solubility product constant for a salt and one of its hydrates, you sometimes get drastically different numbers! I don't know how this can be because they both dissociate into the same ions. For example, sodium sulfate heptahydrate $\ce{Na2SO4.(H2O)7}$ is more soluble than anhydrous sodium sulfate $\ce{Na2SO4}$. If you work through the math, the discrepancy in solubility is not completely explained by the larger mass of the heptahydrate (see calculations below).

I can explain the differences in solubility by assuming that the water molecules within the crystal structure of sodium sulfate heptahydrate lower the enthalpy of crystallization, which makes solvation energetically more favorable than the anhydrous salt.

What confuses me is the logical series of events that would happen when you add the solid hydrate into solution. The hydrate will dissolve into $\ce{Na+}$ and $\ce{SO4^2-}$ions. The concentration of those ions will increase until the solution is saturated (with respect to the anhydrous salt). Anhydrous $\ce{Na2SO4}$ will begin to precipitate out, keeping the ion concentrations below $K_\mathrm{sp}(\ce{Na2SO4})$ The hydrate will dissolve completely, because the solution will never reach saturation (with respect to the heptahydrate). How, then, was the solubility of the hydrate ever experimentally determined?

Using $\ce{Na2SO4}$ as an example:

Solubility of anhydrous $\ce{Na2SO4}$ = $\frac{4.76\ \mathrm g}{100\ \mathrm{mL}}$ (water, $0\ \mathrm{^\circ C}$)
Solubility of $\ce{Na2SO4.(H2O)7}$ = $\frac{19.5\ \mathrm g}{100\ \mathrm{mL}}$ (water, $0\ \mathrm{^\circ C}$)

Calculating saturated concentration:

Solubility of anhydrous $\ce{Na2SO4}$ = $$\frac{4.76\ \mathrm g\ \ce{Na2SO4}}{100\ \mathrm{mL}}\times\frac{1\ \mathrm{mol}\ \ce{Na2SO4}}{142.04\ \mathrm g\ \ce{Na2SO4}}\times\frac{1000\ \mathrm{mL}}{1\ \mathrm L}=0.335\ \mathrm M\ \ce{Na2SO4}$$

Solubility of $\ce{Na2SO4.(H2O)7}$ = $$\frac{19.5\ \mathrm g\ \ce{Na2SO4.(H2O)7}}{100\ \mathrm{mL}}\times\frac{1\ \mathrm{mol}\ \ce{Na2SO4.(H2O)7}}{268.1491\ \mathrm g\ \ce{Na2SO4.(H2O)7}}\times\frac{1000\ \mathrm{mL}}{1\ \mathrm L}=0.727\ \mathrm M\ \ce{Na2SO4.(H2O)7}$$

Calculating $K_\mathrm{sp}$:

Anhydrous $\ce{Na2SO4}$: $$\ce{Na2SO4 <=>2Na+ + SO4^2-}$$  $$K_\mathrm{sp}(\ce{Na2SO4})=\left[\ce{Na+}\right]^2\left[\ce{SO4^2-}\right]=\left(0.335\times 2\right)^2\times\left(0.335\right)=0.150$$

$\ce{Na2SO4.(H2O)7}$: $$\ce{Na2SO4.(H2O)7 <=>2Na+ + SO4^2- +7H2O}$$  $$K_\mathrm{sp}\left(\ce{Na2SO4.(H2O)7}\right)=\left[\ce{Na+}\right]^2\left[\ce{SO4^2-}\right]=\left(0.666\times 2\right)^2\times\left(0.666\right)=1.18$$


texts: Reaction between phenol and nitrous acid

texts:
My question is about the products formed when phenol reacts with nitrous acid. I googled it and reached this PubChem paper (DOI: 10.1016/S0045-6535(02)00857-3), which states:

  It was found that phenol reacts with nitrous acid to produce cyanide ions. Cyanide ion generation is attributed to the conversion of phenol to nitrosophenol through the well-known nitrosation reaction, and decomposition of benzoquinonoxim to form cyanide and aliphatic compound.

Is this correct? If not, then what is the actual reaction?


texts: Most dense hydrogen containing composition

texts: I am searching for a composition which could host the most hydrogen atoms in a specific volume. Note that this density is sought for justifiable conditions in terms of pressure, temperature, ... and should be realizable in a reasonably equipped lab in quantities of a few kilograms. As for hydrogen itself, besides its very low melting point (which is a problem in certain respects), the density itself is 0.086 g.cm-3 which is lower that water (nearly 0.110 g.cm-3), so that it is evident that a composition should be sought after. Any help would be appreciated.


texts: What is the product of the reaction of diol with tosyl chloride followed by lithium aluminum hydride?

texts:
This question is about the structure of products X and Y.
According to me, the answer should be only A (as OTs will substitute on benzylic carbon).

But in the answer key, they have given B and D.

Please help.


texts: Thermodynamic vs Kinetic Sulphonation of Naphthalene

texts: The left hand isomer is clearly the kinetically favoured product and the right hand isomer is the thermodynamically favoured product. However, I have no idea why. Can you explain?


texts: Does adding lemon juice to water chemically alter its nutrients and thereby negating any of its health benefits?

texts:
An acquaintance who apparently has some chemistry understanding told me that eating lemon juice freshly squeezed to drinking water negates all of its health benefits because the water chemically alters the vitamins minerals and enzymes. I am very dubious because a lemon is 82% water and a human body is 75% water and of course lemon juice must be to a very great extent just water.
Also lemon juice is renowned as being a great morning drink because of its health benefits.
My acquaintance however emphatically stands by his statement.
Please clarify this situation for me.
Does water really chemically alter the nutrients in lemon juice rendering a lemon drink of no health benefit whatsoever other than the obvious water base?


texts: Mechanism of substitution for disubstituted benzene

texts:
Here,  I count the individual effects of the two oppositely directing groups.  I assume that the deactivation of $\ce{NO_2}$ group at ortho and meta positions is higher.  While bromination,  I get the product as mentioned above. My query :

If OH group is more powerful than nitro group,  then why doesn't bromination occur at ortho position on between and para position ?

If I apply the same logic in the following compounds' bromination,  will the points marked red be the permissible position for substitution (separately)  ?


texts: What happens when you put a battery in saltwater?

texts: If somebody puts a battery in a salt solution, what path do the electrons take?


texts: In the awwa notebook for $\ce{Na2SiF6}$ determination, why it is required to wash the product sample in an alcoholised $\ce{KCl}$ solution before titration?


texts: Moles of chlorine gas needed to make up an equivalent amount of saturated salt solution

texts:
I’m trying to solve a question about a saturated salt solution but am unsure of how to answer one of the parts or what it’s asking for.
The Problem
The maximum solubility of table salt (NaCl) in water at 25 degrees Celsius is approximately 359 g/L. Assume the volume of the solution does not change with the addition of salt.
a) What is the molar concentration of the mixture in mol/L?
b) What is the molal concentration of the mixture in mol/kg? Assume that the density of water is 980 kg/m3.
c) How many moles of Cl2 gas would need to be present in order to make up an equivalent amount of saturated salt solution?
d) What is the density of the mixture?
My Attempt
a) molar concentration
359 g NaCl * 1 mol NaCl / 58.44 g NaCl = 6.14 mol => 6.14 mol/L
b) molal concentration
(1 L H2O * 1 m3 H2O * 980 kg) / (1000 L H2O * 1 m3) = 6.14 mol / 0.980 kg = 6.26 mol/kg
c) moles of Cl2 gas
I thought it was asking how many moles of chlorine gas is equivalent to the amount of salt in the 1 L solution (359 g NaCl). There are 70.9 g in 1 mole of Cl2, so that gives me an answer of 5.06 mol Cl2 gas (359 g NaCl / 70.9 g Cl2).
But the answer key states the correct solution as 3.07 mol Cl2 gas. How should I go about this part?
d) density of the mixture
density of water = 980 kg/m3
density of salt = 359 g/L => 359 kg/m3
density of mixture = (980 + 359) kg/m3 = 1339 kg/m3


texts: Freezing point depression to find molecular weight

texts:
0.845g of the unknown dissolved in 4.250 grams of camphor had a freezing point of 1.36C. The freezing point depression constant for camphor is 40C*kg/Mol and the melting point of pure camphor is 129C.

Calculate the freezing temperature depression, T? Tf=Kf*m

Calulate the molality? Which i know is mol/kg solvent

Calculate the number of moles present of the unknown compound?

Calculate the molar mass of the unknown compound?

Thank you in advance and please lists steps if possible. I really want to understand and to get this!! :)


texts: Does dihydroimidazole show geometrical isomerism?

texts:
Does dihydroimidazole (above) exhibit geometrical isomerism? Does the fact that the lone pair is involved in conjugation with a double bond affect anything?

As far as I know, it does not exhibit geometrical isomerism. However, one of my colleagues pointed out that the two nitrogens' lone pairs and hydrogens can adopt cis and trans configuration with respect to each other.

Please provide a detailed explanation. If possible, please also cite your sources.


texts:
I have heard that the dianion of carbon dioxide, $\ce{CO2^{2-}}$ was named carbonite.

Does such a species really exist? Basically, is it stable enough to be a plausible molecule? If so, under what conditions is this true?

This question is very confusing to me, I understand the concept somewhat but I don't know what information I need in order to figure out the answer.


texts: empty 30 Gal. barrel of Potassium Hydroxide and Sodium Hypochlorite - safe for collecting Maple syrup?

texts: I bought an empty 30 Gal. barrel of Potassium Hydroxide and Sodium Hypochlorite - CIP 150 - Wondering if it is SAFE to use for the collection of Maple Tree Syrup?  (Label say the white plastic barrel had been rinsed 3 times - however it does say that the previous contents (above) were corrosive. - AND, I plan on rinsing it a few more times) Answers? Suggestions?


texts: Which has higher rate of hydrogenation - methyl propene or trans-2-butene?

texts:
Which has higher rate of hydrogenation- methyl propene or trans-2-butene?

I know that cis-2-butene has a higher rate of hydrogenation than both of these due to steric reasons, but here, both of these compounds have the same steric hindrance.

So, when they come in contact with the hydrogen adsorbed catalyst, they both should behave in a similar manner. Is this correct?


texts: Can I extract water from diethyl ether to get anhydrous diethyl ether?

texts: I am trying to get anhydrous diethyl ether. So, I am considering using a condensor to heat up diethyl ether and extract water. Would this method work?


texts: Is paper aging(oxidation) and paper burning(rapid oxidation) the same thing?

texts:
I woke up today with a question of what is fire; looked up the definition and the first response was that fire was rapid oxidation.

I was curious what the difference was between rapid oxidation and regular oxidation that we have all around us as seen with metals rusting, book pages yellowing, artificial aging, paint drying, apples browning due to air exposure.

I cannot find an answer to what the difference between rapid and regular oxidation is, other than the speed of the reaction, and the visibility of the reaction when it becomes fast enough.

I am curious whether there is any difference at all between metals "rusting", paper "burning"/"aging", paint "drying", or if these are all different names for the same process at different rates.

Is it reasonable to say that there is fire everywhere there is oxidation occuring, but it's invisible until the reaction is fast enough?


texts: Which C-C bond would break first, the one in ethane, or 2,2-dimethylpropane?

texts:
I have drawn the figures and determined intuitively that the larger molecule's $\ce{C-C}$ would break first. I made this assumption that ethane has the stronger $\ce{C-C}$ bond and I am correct, however I do not understand the underlying reasons why.

In both molecules we have single bonds, but in ethane we have more space for the hydrogen atoms to fill. This was my initial reasoning, that the larger molecule is less compact and will have longer $\ce{C-C}$ bonds. Am I correct in my reasoning, or does it have something to do with the radical stabilities? My book is saying "radical stability increases along the series from primary to secondary to tertiary; consequently, the energy required to create them decreases."

In ethane we would have primary carbons because they bond to only one other carbon. In 2,2-dimethylpropane the central carbon is bonded to four other carbons, making it quaternary. Is this the underlying reason, and if so then what is the reason for this trend?


texts: Why is the formation free energy of carbon dioxide almost constant in Ellingham diagrams?

texts:
While reading about Ellingham diagram in my textbook, I noticed that for:
$\ce{C_(_s_) + O2_(_g_) -> CO2_(_g_)}$,
the standard Gibbs free energy ($\ce{\Delta_fG^\circ}$) doesn't seem to vary with temperature (I even compared the line's inclination with a horizontal line and they coincided completely!).
Going through the Wikipedia page for Ellingham diagram, I was able to find the following information:

The formation free energy of carbon dioxide ($\ce{CO2}$) is almost
independent of temperature, while that of carbon monoxide (CO) has
negative slope and crosses the $\ce{CO2}$ line near $\mathrm{700 ^\circ C}$.

I agree with this more as I believe that $\ce{\Delta_fG^\circ}$ should vary with the temperature. Upon comparing the $\ce{CO_2}$ line (in the Ellingham diagram in Wikipedia) with a horizontal line, this time the $\ce{CO_2}$ line is inclined slightly upwards.
I still have a doubt as to why the inclination of the $\ce{CO2}$ line is so less. One reason that I am able to think of is:
As there are equal number of gases on each side of the reaction, the entropy of the reaction is going to be less (as there is no net increase of decrease in the number of gases). As $\ce{\Delta G^\circ = \Delta H^\circ -T\Delta S^\circ}$, if $\ce{\Delta S^\circ}$ (whose negative value is also the slope of the lines) is really very less as compared to $\ce{\Delta H^\circ}$, then we can conclude that $\ce{\Delta G^\circ}$ is going to be almost constant. But I seem to have a doubt (more specific to thermodynamics). We know that the entropy of reaction is "less", but "less" as compared to what?, i.e., how are we able to tell that this magnitude of entropy is lesser than the magnitude of entropies of all the metal oxidation reactions?
I think there must be a better way to explain the less magnitude of entropy of formation of  $\ce{CO2}$.
Could anyone please provide a concrete method / reason to prove this?
Also, are there any other factors (other than the entropy factor) governing this?


texts: Why does ice melt slower at higher altitudes?

texts:
Why does ice melt slower at higher altitudes and how does Le Chatelier's principle play a role in this?

This question appeared right after this chapter in my text book and I've also read a very rough explanation from another source which cited this principle.


texts: This compound of uranium called uranium hexoxide or uranium (XII) oxide is a theoretical chemical compound. The uranium should have  an oxidation state of +12 ,the highest of any known chemical. The closest is the $\ce{[IrO4]+}$ cation with iridium having an oxidation state of +9 so this is obviously mind blowing. Does this compound exist or has it been synthesized yet,without it spontaneously decomposing?


texts: Hydration Isomerism in Cr(III) and Co(III)

texts:
Cr(III) and according to a paper I found also Co(III) are famous for the property called hydration isomerism. I already asked about how changes in the environment of a complex, for example temperature causes a ligand substitution but Cr(III) seems to be treated differently here. I guess it's somehow basically the same reaction but Cr(III) often adapts to changes quite slowly.

I once made a Cr(III) salt, which was green in solution and it took a week till the color suddenly changed to purple. On the other hand if I dissolve some anhydrous CrCl3 and wait for a day the purple color will change to green. This exchange of ligands and counter-ions or solvent seems to be a bit slower for Cr(III) and of course some reactions don't even happen for other metals. The chlorocuprate(II) would only form at elevated temperatures when in equilibrium with the aqua-complex.

But perhaps this temperature is just lowered for Cr(III) and room temperature is enough to cause the change here. Because according to a paper I found is this property of hydration isomerism something very unique in Cr(III) and Co(III) or d3 and d6 ions.

But then I again I don't see that much of a difference to other changes in ligands. Most anhydrous compounds will change from a situation where the counter-ions are coordinated to the metal to an aqua-complex. They do it faster than Cr(III) and they do the opposite reaction but still I don't see that much difference here.

The problem is that I cannot find any good explanation about what makes Cr(III) so special. Does this have to do with the d6 configuration? I know Cr(III) tends to act as an acid as well forming polynuclear compounds, so perhaps the Cr-OH2 bond is weaker than the Cr-Cl bond or something like that?

To summarize it and formulate is as a question, because it doesn't really matter if we give this property a name or not, what makes Cr(III) so special, that it will exchange its aqua ligands for chloride ligands when dissolved in water? Or the other way around? Because there are also reports where, if you dissolve the aqueous CrCl3 in water the green solution will turn purple and in my case the purple solution turned green. And with other Cr(III) complexes I watched transitions in both directions as well.


texts: Differing number average molecular weight results for 1HNMR, MALDI and GPC of a polymer

texts:
I have been given 1HNMR, MALDI-ToF-MS and GPC spectra for a laboratory synthesized sample of polycaprolactone.
The number average molecular weight (Mn) obtained from their analysis differed significantly though:
Mn(1HNMR) = 3186,41 g/mol
Mn(MALDI) = 4751,64 g/mol
Mn(GPC) = 6750,81 g/mol
I tried to find in the literature an explanation for that pattern but found only that 1HNMR is the more reliable one for being quantitative source, while MALDI can present inconsistencies due to chain breakage during ionization and that GPC might present wrong molecular masses if the calibration is not done correctly (in this case, calibration was done with PS). I am also considering that the analysts made no mistakes in the generation of these spectra, as it was performed by a professor in laboratory course on the subject.
So, I wanted to ask, does anyone have an insight as to why those three techniques are presenting such inconsistent results for this sample?
(Also, this is my first question here, so any remarks on question posing are also welcome)
Thanks for the help!


texts: How to get a protein's dihedral angles ordered by variance?

texts:
The setting: I want to simulate protein docking and let some dihedral angles vary, but in order to keep it low-dimensional I have to select those which are most likely to change.

What I've thought of so far:

The easiest solution would be some tool/database that simply returns a list of dihedral angles ordered by their variance (something like http://www.ifm.liu.se/compchem/msi/doc/life/cerius46/qsar/theory_descriptors.html#515786, but that only returns the number of "meaningful" rotamers)
Take a set of different conformations and use principal component analysis on the phase space consisting of the dihedral angles.
Take Ramachandran plots and try to combine all those conditional variances (if φ is …, then ψ has some amount of freedom) into a more "holistic" statement.

The problems I encountered:

I couldn't find such a list.
Searching rcsb.org, I only found about ~100 conformations (for albumin), but if I'm not mistaken the format isn't the exactly the same, so it'd be kinda hard to compare. Besides, ~100 samples won't yield good results for >100 dimensions (=angles).
The only approach for which data seems to be available, but it just looks like a real pain.


texts:
In AlMg3, magnesium atoms outnumber aluminum atoms by a factor of three. In terms of mass, the ratio of aluminium to magnesium is a mere $27.0 / (3\times24.3) = 0.37$.

Shouldn't AlMg3 be better called magnesium alloy?


texts: Deciding the order of heat of combustion of isomeric alkanes

texts:
I'm asked which one of the alkane has the lowest heat of combustion (note: the question says heat, not enthalpy) and according to the answers, the right one is d.

I'm trying to understand why d is the right answer but with no success.
Please help me understand the concept behind it for future problems.


texts: Terminology of atomic spectroscopy: Difference Among Term, States and Level

texts:
In A Primer on
Quantum Numbers and Spectroscopic Notation
Contents, the concept of a term and level is described as

  a) The level is the set of 2J+1 states with specific values of L, S,
  and J. The difference in the energy between two levels gives the
  wavelength or frequency of an atomic transition.

  b) The term is the set of levels characterized by a specific S and L.

1) Is there a better way to understand the subtle difference among the concept of a level, a state, and a term. A example would be helpful.

2) A side question is what are the German equivalents of term, state and level. What do they call it in atomic spectroscopy literature?
Thanks.


texts: C14 Nuclear Diamond to AA Battery Apples-to-Apples Engery output

texts:
I was reading an article about nuclear diamonds and they made an apples-to-oranges comparison of a 1 gram C14 nuclear diamond to a single AA battery. Here is the part I'm referencing:

  "An alkaline AA battery weighs about 20 grams, has an energy density
  storage rating of 700 Joules/gram, and [uses] up this energy if
  operated continuously for about 24 hours." Meanwhile, "A diamond
  beta-battery containing 1 gram of C14 will deliver 15 Joules per day,
  and will continue to produce this level of output for 5,730 years — so
  its total energy storage rating is 2.7 TeraJ."

I'm far from a chemist or any other applicable type of scientist otherwise I'd take a crack at the answer myself. The question simply is this: according to the data provided how many Joules per gram would a C14 nuclear diamond produce if it weighed 20 grams (to compare it to the quoted AA battery that weighs 20 grams)?

To visualize the desired apples-to-apples answer:

Conventional 20 gram battery: 700 Joules/gram, for 24 hours.

Nuclear ?? gram battery: ??? Joules/gram, for 5,730 years.


texts: why the terminal Br/Cl is an electrophile in AlBr5/AlCl5 complex?

texts:
In halogenation of benzene, e.g. bromination, $\ce{AlBr3}$ and $\ce{Br2}$ is added in order to make $\ce{Br+}$ by forming delivery agent $\ce{AlBr5}$ (step 2 of picture).
Why is the terminal (outermost) Br atom serve as an electrophile instead of bromine with positive formal charge? I don't get it because the terminal Br atom has an octet and should be stable and not as electron-deficient, why is it bears a partial positive charge?
another question related is that can use the combination of $\ce{AlCl3}$, $\ce{Br2}$ to achieve bromination? Is the mechanism the same as adding $\ce{AlBr3, Br2}$ if it is possible? Will the electrophilicity of terminal halogen be altered and prevent the reaction?


texts: Is it possible for a bicyclo compound to have three bridges of equal length?

texts:
My teacher told me that the value of $x$ is always greater than or equal to $y$ and that y is always greater than $z$ in a bicyclo compound, where $(x,y,z)$ are the lengths of the bridges.

But in this compound $x = y = z$.
Can someone clarify?


texts: Computed partial charges for protonated amine: discrepencies between Gasteiger and other methods

texts:
Consider the following molecule:

SMILES: COC(=O)[C@@H](c1ccccc1)[C@@H]1CCCC[NH2+]1

I would expect the computed partial chage on the amine to be positive, due to its protonation state.

When using Gasteiger charges calculator, it is affected a positive charge of 0.2422.

However, when using more sophisticated methods (AtomicChargCalculator or Antechamber's AM1-BCC implementation) it is affected a negative charge (-0.649), in  these results for example.

It seems the charges computed for the other atoms are roughly similar, as shown in this graph (x-axis: AtomicChargCalculator charge, y-axis: Gasteiger)

Does this amine really have a negative partial charge ? Why the discrepency ? Is there something I am missing ?


texts: What exactly does κ stand for in this equation connecting solubility and molar conductivity?

texts:
I came across the following equation while studying electrochemistry ("Physical Chemistry" by Wallwork and Grant):

  The solubility $s$ of a sparingly soluble salt can be determined from conductivity measurements, provided that the molar conductivities of the ions at the temperature of these measurements are known to enable $\Lambda_0$ to be calculated. Since the saturated solution is dilute, $\Lambda_0 \approx \Lambda = \kappa/c$, where $c = s~(\pu{mol m-3})$. The conductivity $\kappa$ is the conductivity of a saturated solution of the salt in conductance water minus that of the water alone. The solubility $s$ is calculated from:
  $$s = \kappa/\Lambda_0 \tag{8.36}$$

It's mentioned that κ is the conductivity of the saturated solution of the salt in conductance water, minus that of the water alone. Now the thing is, from what I've read, conductance water has NO (or negligible) conductivity.

In that case, what's the point of having to subtract the conductivity of conductance water? Or is there something I've misunderstood here?


texts: Derivation of an equality in Michaelis–Menten kinetics

texts:
Enzymatic action may be described as follows:

$$\ce{Enzyme + Substrate <=>[k_1] ES complex ->[k_\mathrm{2}] Enzyme + Product}$$

The initial rate of enzyme-catalyzed reactions can be described by the Michaelis-Menten equation:

$$\mathrm{rate} = \frac{V_\mathrm{max}[\ce{S}]}{K_\mathrm{M} + [\ce{S}]} = \frac{k_\mathrm{cat}[\ce{E}][\ce{S}]}{K_\mathrm{M} + [\ce{S}]}$$

where $V_\mathrm{max}$ is the maximum rate, $[\ce{S}]$ the substrate concentration, $[\ce{E}]$ is the enzyme concentration, $K_\mathrm{M}$ is the Michaelis constant and $k_\mathrm{cat}$ is the number of catalytic cycles per second.

It is known that

$$V_\mathrm{max} = k_2[E]_0$$

and by inspecting the equation above we can deduce that

\begin{align}
V_\mathrm{max} &= k_\mathrm{cat}[\ce{E}]\\
\implies k_2[\ce{E}]_0 &= k_\mathrm{cat}[\ce{E}]
\end{align}

How, and why, does this equality hold?

How do we know when to use ${[\ce{E}]_0}$ and $[\ce{E}]$ in rate equations, and what are the implications of using either?

${[\ce{E}]_0}$ refers to the enzyme concentration at the start of the reaction, and [E] refers to the concentration of enzyme at any point in time during the course of the reaction.


texts: Relationship between surface area and rate of reaction

texts:
Say I add a whole piece of calcium carbonate to some $\ce{HCl}$ and then measure the reaction rate by measuring how quickly the mass changes (how quickly $\ce{CO2}$ is being evolved).

Then, I repeat the experiment for the same size calcium carbonate piece but broken into 2 pieces, then 4 pieces and finally, 6 pieces. If I plot the rate of reaction vs. the surface area of the calcium carbonate, would I get a linear relationship?


texts:
How to calculate the heat released when sodium hydroxide is dissolved in hydrochloric acid solution? Here is the data I gathered from a lab experiment:

$50\ \mathrm{mL}$ of hydrochloric acid solution
$2.00\ \mathrm g$ of sodium hydroxide (in solid form)
Initial temperature is $24\ \mathrm{^\circ C}$
Final temperature is $44\ \mathrm{^\circ C}$

The chemical equation of the reaction is:

$$\ce{NaOH(s) +H+(aq) + Cl- (aq) -> Na+(aq) +Cl- (aq) + H2O(l)}$$

This is the ONLY information I can use and I cannot search up anything online.

I calculated:

$$
\begin{align}
q&=mc\Delta T\\
q&=\left(50\ \mathrm g\right)\left(4.18\ \mathrm{J/(g\ ^\circ C)}\right)\left(20\ \mathrm{^\circ C}\right)\\
q&=4180\ \mathrm J
\end{align}
$$

So calculating the heat released by the reaction, I assumed that the mass is $50\ \mathrm g$ since hydrochloric acid is a solution of hydrogen chloride in WATER and the reaction produces water as well. Therefore, since the density of water is $1\ \mathrm{g/mL}$, $50\ \mathrm{mL}$ must be approximately $50\ \mathrm g$. Also, the specific heat capacity must be similar to water as well which would be about $4.18\ \mathrm{J/(g\ ^\circ C)}$.

So my question is: Is my assumption correct? If not, why?


texts: Detecting impurities in polyethylene glycol 3350

texts:
I would like to test samples of polyethylene glycol 3350 ($\ce{H−(O−CH2−CH2)_n−OH}$ with an average molecular weight of 3350, so n is around 75) to determine if there are any impurities and if so the rough concentration of them. Some likely impurities that may be present are:

ethylene oxide
diethylene glycol
ethylene glycol

My goal is to test samples from different sources to find out which one has the lowest level of impurities.
If there happens to be an easy way for me to test this at home using supplies that I would be able to buy online for < $1000 that would be great. More likely, I am interested in finding out what equipment would be used to test this so that I can try to find a lab that would do this testing for me.
Level of detection:
In a sample of 10 grams, I would want to detect levels at least as low as the following (though detecting even lower levels would be preferable):

ethylene oxide: 0.07 mg
diethylene glycol: 1 mg
ethylene glycol: 4 mg

If there is a way of detecting arbitrary impurities rather than just these specific ones I'd be interested in knowing that too (mass spectrometer? $\mathrm{^{13}C \; NMR}$? these are things I've heard of but am not sure what would be applicable here).


texts: Isothermal vs. adiabatic compression of gas in terms of required energy

texts:
I am working on an instruction manual of sorts to be used with an introductory course in thermodynamics. As an example of problem solving, I attempt to answer the following question:

  If you have little energy available, would you rather use an
  isothermal or an adiabatic process to compress a gas?

My analysis is as follows:

The work required to compress a gas from volume $V_0$ to volume $V$ is $$W=-\int_{V_0}^{V}PdV$$
For the isothermal compression, the ideal gas law, $P=\frac{nRT}{V}$, is used and inserted into the equation above:
$$W=-\int_{V_0}^{V}\frac{nRT}{V}dV=-nRT\int_{V_0}^{V}\frac{dV}{V}=nRT\ln\left(\frac{V_0}{V}\right)$$
For the adiabatic compression, $PV^\gamma=P_0V_0^\gamma \iff P=P_0\left(\frac{V_0}{V}\right)^\gamma$ is valid. Thus, the required work is $$W=-\int_{V_0}^{V}P_0\left(\frac{V_0}{V}\right)^\gamma dV=-\frac{P_0V_0^\gamma}{-\gamma+1}\left(V^{-\gamma+1}-V_0^{-\gamma+1}\right)=\frac{PV-P_0V_0}{\gamma-1}$$
       $$W=-\frac{P_0V_0-PV}{\gamma-1}$$

This result indicates that the magnitude of the required work depends on the properties of the gas in question. Thus, it may vary which of the two compression processes requires the lowest amount of energy.

Now, finally, to my question:

Intuitively I would assume that the isothermal work is usually lower than the adiabatic work, as compression lowers the volume of the system and therefore usually increases the temperature if heat exchange with the surroundings is not allowed. Isothermal compression requires heat transfer to the surroundings to maintain constant temperature, lowering the pressure of the system and thus lowering the resistance to compression compared to the adiabatic compression (where heat exchange is not allowed).

Is the isothermal work actually smaller than the adiabatic one in most cases or is my argument flawed?


texts: Is this representation correct although it seems to show a pentavalent carbon?

texts:
While I was trying to draw a possible representation of $\ce{(CH3O)2CH=CHCH(OCH3)2}$ I was perplexed  by the fact that from left to right the second carbon atom has a double bound with the third one, while at the same time it is connected to two methyl groups, plus the H element.  That makes five bounds.
I found this as an answer:

$\hspace{25ex}$

But in my opinion, in the image, the double bound is misplaced as it should be on the from the first carbon atom after O.
I am stuck here.


texts: Why is the enthalpy change not zero in an adiabatic process?

texts:
Which of the following must be true for adiabatic processes?

  $C_V = C_p$
  $\Delta H = 0$
  $\Delta U = 0$
  $\Delta S = 0$
  $q = 0$

(Source: Chemistry GRE)

The answer is $q = 0$. From what I can find, an adiabatic process is when there is no transfer of heat, but then why is the enthalpy change not zero?


texts: Covalent Bonding in odd electron sharing molecules

texts: Why in odd electron sharing molecules (like NO ) the bond containing 3 electrons is considired to be half covalent bond?


texts: How does VB theory explain the Si-O-Si bond angles in SiO2?

texts:
Silicon dioxide has a huge variety of structures. Most of them are built up from connected $\ce{SiO4}$ units — the $\ce{O–Si–O}$ angle is $109.5°$, accordingly. The VB/hybridization approach to this tetrahedron would consequently assign $4\text{ }\mathrm{sp^3}$  orbitals to the silicon atom.
Now, the interesting part about silicon dioxide is the flexibility of its $\ce{Si–O–Si}$ angles, i.e. the bond angle of the bridging oxygen atoms; they vary from $100$ to $180$ degrees (the latter occurs in hexagonal tridymite, see e.g. here), depending on the polymorph. In vitreous samples, these angles show a distribution centered around $145$ degrees or so (source). In common forms of crystalline $\ce{SiO2}$, the angle also is close to $145$ degrees (e.g. this source). How is this possible? Since the oxygen bonds to two silicon atoms, one would expect a $\mathrm{sp^3}$ hybridization, with two orbitals filled with lone pairs — hence, a $104°$ angle like in water, or a slightly bigger one (since silicon is less electronegative than hydrogen — thus, the $\ce{Si–O}$ bond is more polar than the H–O bond and the angle bigger). But never an angle as large as $170°$: that would almost point at an $\mathrm{sp}$ hybridization of the oxygen atoms. How is such an angle energetically more convenient than the typical bent one?


texts: Acidity comparison between 4-hydroxybenzaldehyde and methanoic acid

texts:
Acidity is dependent on charge dispersal. Greater the charge dispersal in conjugate base greater the acidity (assuming that both acids being compared have similar stablities).

So in the case of 4-Hydroxybenzaldehyde, in the conjugate base the charge would delocalise over two oxygen atoms as well as the benzene ring.

Whereas in formic acid charge would only delocalise over two oxygen atoms and hence charge would be concentrated. So the predicted order of acidity according to this logic should be formic acid < 4-hydroxybenzaldehyde.

This is contrary to actual data:

$\mathrm{p}K_\mathrm{a}(\text{4-hydroxybenzaldehyde}) = 7.61$ (Source),

$\mathrm{p}K_\mathrm{a}(\text{formic acid}) = 3.7$

Please put forth the correct logic.


texts: At which temperature does carbon monoxide explode?

texts:
I had doubt whether carbon monoxide explodes or not. I checked out this resource and found out that carbon monoxide explodes when heated. But they didn't mention the temperature at which it explodes. So my question is that at which temperature does carbon monoxide explode and also at which pressure ?

Thanks in advance!


texts: Approximation of electron density of a small molecule

texts:
Starting point for Quantum Theory of Atoms in Molecules (AIM) is the electron density $\rho(r)$. It could be determined experimentally (X-ray diffractions). I want to know how can we estimate them ab initio. In AIM
it is often emphasized that the focus is on density rather than a wave function for the later is just a mathematical function while the former is experimentally observable. Are there ways to estimate electron density without first calculating wave function (which will obviously lead to density function).

My interest is to use AIM in quantitative structure-activity relationship. I will typically deal with molecules of around 50 atoms. Usually I will already have the graph (connectivity) of the molecule (eg .SDF file, smile notation etc), how can we incorporate this to speed up electron density calculation?

It would be helpful if brief comment on the computational cost is also included in the answer.


texts: Is there a catalyst for the decomposition for hydrogen peroxide that speeds it up but still makes the reaction light dependent?

texts:
I am building a Rube Goldberg machine for Science Olympiad, and one of the scoring steps is to use light to trigger a chemical reaction, which made me immediately think of the decomposition of hydrogen peroxide, but the only problem is that it doesn't occur fast enough. After doing some research, I realized that manganese oxide, the only catalyst for this reaction that I am aware of, will make the reaction occur without light. So, I am now looking for a catalyst that will speed up the reaction fast enough (to produce enough gas to inflate a balloon), but not lower the activation energy so much that it will occur without light.

Just to clarify, the competition does allow people to ask online, and there is in fact a whole community where people discuss this stuff.


texts: How does Rosuvastatin 5 S-lactone form in human body?

texts:
I've searched lots of free resources online but cannot find the answer.

the top compound is Rosuvastatin.
Some websites say it is metabolized by the enzyme CYP2C9,
but I can't figure out how a CYP450 mediated reaction will produce Rosuvastatin 5 S-lactone. And I tried thinking about an intramolecular esterification, but it does not look like the answer. Perhaps I missed something?


texts: Supplement weight by element or compound

texts:
When a vitamin or supplement claims, for example, that it contains

  600 mg of calcium (as calcium carbonate)

what does that mean? Does each tablet contain 600 milligrams of the element calcium?

Or does a tablet contain 600 milligrams of the compound calcium carbonate? In that case, using the molar masses of Ca and CaCO3, each tablet would contain only

600 * (40.1 / 100.1) = 240.4 milligrams of the element calcium.


texts: I read that the heavier alkali metals, like K, Rb, and Cs all prefer to form superoxides. Since Fr is the heaviest alkali metal, I assumed it would follow the same trend as the previous alkali metals, forming $\ce{FrO2}$. However, I was told that the most stable oxide of Fr is $\ce{Fr2O}$. Why would this be the case?


texts: How do Chiral centers determine the number of isomers?

texts: I think I read somewhere that if an organic compound has n number of chiral centers, there must exist 2^n number of isomers. Is that true? And why?


texts:
I was trying to look-up the mechanism of reaction of organic compounds with SeO2, but I am not able to understand it. I would really appreciate if someone can predict the end product with the mechanism.

I am getting 2-oxo-propan-1-al (I hope the nomenclature is correct), as a product. But I have a doubt, will it react further, because it could still exist as a enol (2-Hydroxy-prop-2-en-1-al), which can further undergo the reaction with SeO2.


texts: During the formation of a molecule of water ($\ce{H2O}$), what kind of bond occurs between the elements? I'm studying this subject on my own and from some sources I saw that there is a covalent bond and others showed an hydrogen bond, responsible for the non-evaporation of water at $-90\ ^{\circ} \rm{C}$. Can you guys explain to me exactly how this bonds behave? Both of them occurs to the molecules of water?


texts: Prediction of surface atoms in molecule from its graph

texts:
If we are given a molecular graph i.e. al the atoms involved and their connectivity, how can we make reasonable prediction if the atom would lie in the surface or in the inner part. On way might be check it degree (how many atoms it is bonded to), higher the valency higher it surface accessibility.

I will most of the time have small molecules (drug molecules) which have in average 50 atoms.
My broader interest is to find out which atoms directly affect the activity of the molecule more than the other. Probably, atoms lying at surface have more role to play. Any other suggestions aimed at this identification would be helpful.


texts: Is Sodium metal more reactive towards an alkyl halide or an alcohol in a protic polar solvent?

texts:
Will Sodium metal donate its electrons to bromine in 1,3-dibromopropane or to the hydroxyl group in ethanol in a polar protic solvent?

This question comes from a problem:

'What is the major product formed when 1,3-dibromopropane is added to Na(sodium)/EtOH(ethanol)?
(a)cyclopropane

(b)3-bromoprop-1-ene

(c)propyne

(d)prop-1,2-diene'

The answer was (a)cyclopropane but I was not convinced as then it would have to follow Wurtz reaction- where sodium donates its electron to bromine forming a alkyl radical. But, Wurtz reaction takes place in an ether solvent and here ethanol is used as solvent.

ethanol is shown to readily react with Na to form a sodium ethoxide and liberate hydrogen. The ethoxide ion would react with 1,3-dibromopropane in either Sn1 or E2 mechanism and so it would not form cyclopropane.

If sodium donates electron to bromine however, then it would follow Wurtz reaction mechanism and form (a)cyclopropane.

So, I want to know whether an alkyl halide or alcohol reacts more readily with sodium metal and what your reasoning is to assert your statement.


texts: Does the boiling boint of miscible liquids follow a linear relationship?

texts:
I want to create a steam bath for a reaction the proceeds well at 105℃.  I cannot use pure (demineralized, anyway) water for this, since it would boil at 100℃ at STP.

As such I figured that maybe I could get the required temperature by mixing water with another liquid (with which water is miscible) which has a higher boiling point (e.g. vinegar at BP around 118.5℃ or vegetable glycerin with BP at 190℃).

Does the boiling point of the mixture of liquids proceed in a linear manner between the two temperatures?  E.G. would a volume of 50% water & 50% VG boil at 145℃?

As it is being done right on the boiling point of the combined liquids, I expect to lose some of the liquid to steam and need to add more. Will the lower temperature liquid boil out first?


texts:
Consider this typical 1,2 methanide shift in a carbocation:

Which isotopic form of methanide ($\ce{CH3, CD3, or CT3}$) would migrate from secondary carbocation to form more stable tertiary carbocation?
This link explains the mechanism but I could not understand the abstract.
Assuming that the migration of $\ce{CH3-}$ takes place, the following facts can be considered:

The electronegativity of $\ce{CH3}$ is highest, thus, the formation of $\ce{CH3->CH3-}$ (methanide) is easiest. Consequently, the migration would be fastest in this case.

The transition state would be most unstable in this case due to highest electronegativity of $\ce{CH3}$.

The tertiary carbocation would be most stable in this case due to order of $\mathrm{+I}$ effect: $\ce{CT3 > CD3 > CH3}$

There are few exchanged comments below the second answer of this question and the proper explanation can be found in this link, which I can't access.


texts: anode and cathode in lithium ion battery?

texts:
By definition, the anode is the electrode where oxidation takes place, the cathode is the electrode where reduction takes place.

When I am charging the Li-ion battery, positive electrode undergoes oxidation and hence I may call it the anode. When I am discharging the Li-ion battery, negative electrode undergoes oxidation and I may call it the anode. Is this correct?

Do the anode and cathode interchange for charging and discharging?


texts:
What is the correct structure for the $\ce{NO2}$ compound (not ion)? I always thought it was like:

since the negative charge would be residing the on the highly electronegative oxygen, but was reading this blogpost by the guys at WolframAlpha, who state that contrary to popular belief, the correct structure is actually:

They explain that it has to do with molecular orbital theory, but don't explain in depth.

Can someone please explain why this occurs?


texts: the chemical mechanism for deviations from Raoult's law

texts:
Mixtures of ethanol and acetone have vapor pressures that are higher than predicted by Raoult's law, while mixtures of acetone and water have lower vapor pressures than predicted by Raoult's law.  Why is this?

That is, why is there a "positive deviation" from Raoult's law for acetone/ethanol solutions but a "negative deviation" for acetone/water?

Isn't an acetone-ethanol hydrogen bond stronger than an acetone-acetone hydrogen bond? If the reason for the positive deviation of the ethanol/acetone solution is that the H bonds there are weaker than ethanol-ethanol H bonds, then there wouldn't that imply that acetone/water solutions would also have a positive deviation, as water-water H bonds must be much stronger than water-acetone, right?

So is there some other explanation?


texts: Acidified sodium sulfite in the reduction of iron(III) to iron(II)

texts:
Why does sodium sulfite have to be acidified in the reduction of $\ce{Fe^{3+}}$ to $\ce{Fe^{2+}}$?

Does the acid act simply as a catalyst or is it necessary for the reduction process?


texts: Why does soup turn purple when lemon juice and salt are added?

texts:
Well you have probably heard about salpeter. I don't know if it is a myth or not that it is used to reduce men's libido by adding to food especially in boarding schools and remote military campuses.

I didn't know that before but because I studied at boarding school, this topic and its alleged test intrigued me. According to the test, when you add lemon juice and salt to food and if the salt in the food turns to purple/blue, it means salpeter is added to the food. I don't know if it is scientifically proven.

Now I live with my parents but just for fun I wanted to try to test on my homemade food and I shocked because the salt I added to the soup, which was made by mom, turned to be  purple /blue. I've become really baffled and I checked if there is any salpeter in cupboards I found a bottle of white like flour thing. I presumed it was powdered salpeter and tested it with the same method, which I added lemon juice and salt and it turned blue/purple.

But when I asked what that white thing is, she said it was "powdered sugar".
and I tried the same test on new powdered sugar yeah it turned to be blue too.

I hope you are not confused. So far what I am sure about is that when I add salt and lemon juice to powdered sugar it turns to be blue.

My mom said there is neither salpeter nor powered sugar in the soup she made.

Buy how come does soup turn to be blue /purple when I added some lemon juice and a lot of salt?

Here is a picture.The soup is made of lentil, some spices and salt, some potato and carrot.


texts: Intuition for why catalyst affects both forward and reverse reactions equally?

texts:
I have looked for quite a long time on the site however all the answers involve mathematical explanations involving Arrhenius's equation. I would really like an intuitive reason (or one using collision theory?) as to why adding a catalyst should increase both reactions equally.

It seems that if you add a catalyst it should decrease the activation energy by a constant for both forward and reverse reactions. Thus it should decrease the forward activation energy proportionately more than the reverse reaction then the forward reaction should go forward, and shift equilibrium. But it doesn't. Why not?


texts: Balanced equation for neutralisation reaction betweeen potassium carbonate and hydrochloric acid

texts:
They seem all correct to me, is there any reason why one reaction would happen over the other(s)?

$$\begin{align}
\ce{K2CO3 + 2 HCl &-> 2 KCl + H2CO3}\\[6pt]
\ce{K2CO3 + 2 HCl &-> 2 KCl + H2O + CO2}\\[6pt]
\ce{K2CO3 +   HCl &-> KHCO3 + H2O}
\end{align}$$


texts: Does carbonated water change over the course of several days, or was my container leaky?

texts:
I have a Klean Kanteen flip-top growler, allegedly leakproof at up to 35psi of pressure, that I filled with some freshly-carbonated water 4 days ago — just to see how long it would last. I used a Soda Stream for carbonation. The bottle was filled to the brim.
When fresh, the carbonated water fizzed and sparkled. You could see the bubbles constantly rising to the surface. It felt like pop rocks when you put it in your mouth.
Now, 4 days later, the water is still clearly carbonated, but it's a lot more subdued. You can taste the fizz when you drink it, but there's no more surface bubbling. When you pour it into a cup, you see bubbles for about a second before the water clears up.
The obvious theory is that some CO2 escaped over the course of the week, but I'm fairly certain there were no liquid leaks. I also couldn't hear any hissing. The bottle was stored on its side in the fridge.
Is it possible for a container to be liquid leak-proof, but not gas leak-proof?
If not, does the nature of carbonated water change over time? Does the water, perhaps, absorb more of the CO2 the longer it sits? If so, why does this not happen with soda cans and such?

Update 2015-11-3:
I repeated the experiment with a 20oz screw-top Klean Kanteen I had lying around, ensuring that the water was as close to the cap as possible and that the lid was screwed on as tightly as possible. The results after 4 days were more carbonated than my initial trial with the flip-top Kanteen, though still not as much as fresh. Currently repeating the experiment once again with the flip-top, this time making 100% sure that the water is touching the lid.


texts: What is the difference between configuration and conformation in stereochemistry?

texts: I understand conformation to be any spacial arrangement of atoms that can be achieved through rotation of a single bond. I understand configuration to be the disposition of atoms/groups in space. However, would a conformational isomer also be a configurational isomer since the groups are arranged differently in space?


texts: What is entropy change in electrochemistry?

texts:
I keep seeing entropy change (or reversible effects) and irreversible effects (Joule heating) when reading about charging and discharging of Li-ion batteries. I understand the Joule heating part (the irreversible), but I have troubles understanding the reversible effects. What's going on in the structure of the electrodes that the process is reversible? As far as I know, reversiblities come from the fact that there is no friction or other losses. If one isolates a single ion, the charging or discharging, in my interpretation, would look roughly like in the figure below:

What happens inside the battery during this charge and discharge that would make one think of reversibility? And why is entropy important in this case? And why would a reversible process release heat?


texts: What is the type of orbital depicted in this diagram?

texts:
The following image is from this answer for the question Why is one lobe of an sp3 hybridized orbital smaller than its other half?:

I understood everything from that answer, but couldn't identify what is the type of orbital marked by the red circle. It could not be a $d_{z^2}$ orbital with $x$ axis as it's $z$ axis, as it has a big spherical node and not a circular ring? I haven't encountered such an orbital till now.


texts: How can one find products when one knows the reagents?

texts:
I'm going to use an example (I could have used a different one);
On the document it is about the study of the chemical balance of an acid-basic solution.
The chemists have written the chemical reaction equation to make a table of the evolution of pH during the reaction.
If I understand with this equation I'll be able to understand others.
$\ce{CH3COOH + H2O ->CH3COO- + H3O+}$

Here is what I already understand:

This is the equation of methanoic acid with water
I understood why the general formula of methanoic acid is $\ce{CH3COOH}$

What I want to know is how do we know that

$\ce{CH3COOH}$ changes into $\ce{CH3COO-}$ ?
$\ce{H2O}$ changes into $\ce{H3O+}$?

In general, how does one find the products when one knows the reagents?
Does reagents molecules always correspond the same ions?


texts: How can it be proved that (S)-bis-[2-(t-butylsulfinyl)phenyl] diselenide is a chiral non-racemic product?

texts:
I read in paper that:

  The aim of this part of the work was to synthesise new aromatic diselenides with chiral phosphorous or sulfoxide centres in coordinative distance to the selenium as precursors for new chiral selenenylating reagents.

How can it be proved that (S)-bis-[2-(t-butylsulfinyl)phenyl]diselenide is a chiral non-racemic product?


texts:
I know that a strong electron withdrawing group reduces electron density and makes a molecule more acidic. Also, a meta substituent will have less effect than ortho and para substituence and the para isomer will be more acidic than the ortho one.
The point that I wonder: Does the acidity always increase with the number of withdrawing group as well?

Some group, let's say, phenol has one strong electron withdrawing group like nitro, carboxyl, chloro etc. If phenol would have two more of that same withdrawing group attached, would it be simply more acidic? Or, should another factors be considered to determine the acidity? I thought that maybe it would be more reliable to look $\mathrm{p}K_\mathrm{a}$ values but couldn't find any molecule that fits that situation.


texts: How can you tell how much actually reacted in an acid base reaction

texts: If you facilitate a weak acid base reaction. i.e. $\ce{NaOH + H2SO4}$. All of it may not react and the solutions will not neutralize. How can you determine how much actually reacted?


texts: We are looking to design flexible substrates with electroless plated silver on them (for use in sensor applications).  We need convert the surface of the silver to silver-chloride (AgCl) for conduction to hydrogel/hydrocolloid.  What are simple ways to do this.  The material will be on rolls and we need a simple production method that can be applied to the rolls.  Thank you.


texts: One of the uses of the Tollens' reagent is to confirm the presence of a terminal triple bond in a compound. Does acetylene give a positive Tollens' test? If not, why is this so?


texts: I figured that it is probably having to do with the wavelengths of visible light that are absorbed and transmitted by the ions, but I'm not entirely sure.


texts: Applying salt to roads to melt ice--is it special?

texts:
Most everyone is familiar with applying salt to the roads during winter to melt ice.
I'm wondering if there's anything special about placing salt on the roads or would any other substance, sand for example, work equally well in melting the ice.


texts: In Flame Emission Spectroscopy, what part of the flame is used to measure the concentration of the analyte?

texts:
Flame Emission Spectroscopy is an analytical measuring device that relates the intensity of the emitted light relative to to the concentration of the sample.

As I am reading an article about FES, I noticed how the author purposely inserted the different parts of the flame and their activity.

The above image was from an article in Chemistry LibreTexts about FES.

The author said "The Primary Combustion Zone is where the initial decomposition occurs and molecular fragments are observed. The Interzonal Region is the hottest part of the flame and atomic fragment are observed. The Secondary Combustion Zone is cooler overall and a conversion is seen from atoms back to stable molecules and oxides."

I have read the article but it was never mentioned what part of the flame does the transducer or sensor was placed on.


texts: Why are so many ionic compounds brittle?

texts: Even when ionic compounds are strong (e.g. rubies and sapphires), they are neither malleable nor ductile in the slightest, and if sufficient stress is put on them, they will shatter, not bend. Why is that?


texts: Can I compare DFT calculations with different grids?

texts:
When doing DFT calculations, some integrations are commonly done numerically on grids. [In fact, more than a single grid may be used at the same time for different integrals, e.g. approximations such as the resolution of identity (RIJCOSX, RIJK, etc., see e.g.  J. Chem. Phys. 118, 9136 (2003)) use grid schemes too (I believe some programs call this approximation density fitting).]

There's the downside that those grid schemes introduce a source of error. In fact, I find that only by increasing the quality of the grid I can remove some imaginary frequencies. Can I rigorously compare energy values among calculations that used slightly different grid schemes?

I think yes and I reasoned as follows. Since I'm interested in energy differences, let's imagine two structures with true energies $E^*_1$ and $E^*_2$. Both energies are approximated by the calculated energies $E_i = E^*_i + \epsilon_i$, where $\epsilon_i$ is the error introduced by calculations (including grids, etc.). Now the energy difference $\Delta E^* = E^*_2 - E^*_1$ is approximated by $\Delta E = E_2 - E_1 = \Delta E^* + \Delta \epsilon$, where $\Delta \epsilon = \epsilon_2 - \epsilon_1$. Since grid schemes introduce errors that are smaller than other sources of error (e.g. implicit solvation), everything should be fine as long as $\Delta \epsilon$ is acceptably small for the particular application at hand.

Does this seem reasonable? If not, what's wrong with the above?


texts: How to obtain pure alcohol from mixture of alcohol & carbonyl? (Grignard experiment)

texts:
If one discovers that after finishing up a Grignard reaction that their alcohol product has been contaminated with the carbonyl starting material, how could they separate the alcohol from the carbonyl compound to obtain a purified alcohol product?

I was thinking that they could recrystallize the contaminated product using an alcohol as a solvent, but is there a better option for separating these two compounds?


texts: What is the significance of the "Standard Temperature" in Standard Enthalpies of Formation tables?

texts:
In my data book, there's a list of common compounds and their molar enthalpies of formation -- at 298.15 K. What's the meaning of this given temperature value (is it the final temperature of the compound in question?) and how does it affect the molar enthalpy of formation of a substance?

What, for example, does it mean when the molar enthalpy of formation of H2O(g) at 298.15 K is given as -241.8 kJ/mol, even though water should be in a liquid state at 298.15 K? And what would the molar enthalpy of formation of H2O(g) be at, for instance, 500 K?


texts: Effect on acidity of benzene due to electron withdrawing groups

texts:
With respect to the compounds I–V, choose the correct statement(s).

Compound II becomes more acidic when it has a $\ce{-NO2}$ substituent.
The acidity of compounds follows the order I > IV > V > II > III.
The conjugate base of compound IV is aromatic.
The acidity of compound I is due to delocalization in the conjugate base.

I am not able to decide about the first statement properly. I compared the acidity by considering the conjugate base, which is the same (benzyne) even if $\ce{NO2}$ group is added.
However, the solution says that it will increase acidity because of being an electron withdrawing group.


texts: Work done by an expanding gas, how to solve this particular example?

texts:
I just need help with one of these types of questions and I can handle the rest.  It is from a practice quiz on Coursera, Physical Chemistry.

  How much expansion work is done on the system when exactly 1 mol of solid ammonium chloride, $\ce{NH4Cl}$, decomposes completely
  to yield gaseous ammonia, $\ce{NH3}$, and hydrogen chloride, $\ce{HCl}$, at
  a temperature of 1280 K. Treat the expansion as
  irreversible and the gases formed as perfect.

I'm not sure how to compute the two volumes required to use the formula:

$$W = n R T \int\limits_{V_\mathrm i}^{V_\mathrm f}\frac{\mathrm dV}{V}$$

Do I assume $1\text{ atm} = 101.325 \text{ kPa}$.  I did that and was able to use the ideal gas law: $V = \frac{nRT}{P}$ to get the final volume of the 1 mole of gas, but I'm unsure how to choose the initial volume (0 won't work here as it leads to $-\infty$).

Is this the correct approach?
If 1., then how do I also get the initial volume.
If not 1., then how should I approach it?


texts:
I'm not interested in a simple telling of what the properties of the equilibrium constant are and how to use them. I'm more hoping for an explanation of where it came from/how it might be possible to derive it.

My current guess is that it is a probability equation:

The numerator in the equation is proportional to the probability reactants meet and form products in the volume and the denominator is proportional to the probability products meet and form reactants in the volume. This ratio clearly must stay constant (unless the proportionality constants are changed via temperature or such).

Would anyone help?


texts: Why are the equilibrium exponents stoichiometric when the rate law's are not?

texts:
I'm learning about rate law and equilibrium, and the textbook really hammers in that the exponents for the rate law must be determined experimentally - you can't just use the coefficients from the balanced equation. In a generic reaction aA + bB -> cC + dD:

rf = kf[A]w[B]x

rr = kr[C]y[D]z

It is not always the case that w = a, x = b etc.

Equilibrium is then described as the point that the forward reaction is occurring at the same rate as the reverse reaction. For the same reaction as above, we set the two rates to equal each other.

rf = rr

kf[A]w[B]x = kr[C]y[D]z

Kc = kf / kr = [C]y[D]z / [A]w[B]x

I'm told that the exponents here are based on the coefficients of the balanced equation, such that w = a, x = b, y = c, and z = d. This seems to be in direct opposition to what I read earlier about the rate law, as equilibrium is just built from two rates.

Why is this?


texts: in the picture, the product is a neutral material, but in the illustration of the molecular structure, the compound is shown in its ions, why we can't show it in its ions even in the equation or if we can't, why in this molecular structure it is shown as ionic although it is neutral?


texts: How important is tin for a bronze age society when there's many copper alloys including arsenical bronze. If you're out of tin whats the next best copper alloy(s) for making shortswords and axe blades and is it such a downgrade. This is a chemistry and history question.


texts: Separate less volatile component from distilling a mixture

texts:
Is it a strict rule that when we boil a mixture of two liquids, with one being less volatile than the other, the more volatile vapour has to form the greater portion of the total vapours?

If it is so, how are we able to obtain a pure liquid of less volatility in the distillate and an azeotropic mixture by distilling a certain composition of a non-ideal mixture? Shouldn't we be getting ALWAYS the more volatile component in the higher plates and thus in the distillate?

And if it is not so, please enlighten me with a valid explanation. Thank you.


texts: Why is the y intercept of a G vs X curve treated as chemical potential?

texts:
Whenever I am to prove the fact that the $y$ intercept to the $G$ vs $X$ curve is basically my chemical potential, there are two equations that need to be assumed. One is
$$G=\mu _{A}X_{A}+\mu _{B}X_{B},$$
and the other is the total differential expression of $\mathrm{d}G'$. However they are treated as two independent equations. However, are they not related? What is the  intuition to the geometrical interpretation of the chemical potential?


texts: How does potassium nitrate work as an oxidiser?

texts:
Potassium nitrate is very popular compound in pyrotechnics, used as an oxidiser. It can be mixed with sugar to make a "rocket candy", with coal and sulphur to form black powder. You can stick it on rope to create functional fuse.

The saltpeter releases oxygen in all these reactions. But what are the results of reaction? I learned that $\ce{KNO2}$ is also oxidiser. So does the nitrate turn tu nitrite and then reacts again? Or does it form something else?

I have noticed that some strange bubbles come from my homemade fuse (photo will follow). Since potassium nitrate has melting point at 334°C (according to Google) it's likely the saltpeter melting.

And what about fumes? Does potassium nitrate or nitrite evaporate to turn the air poisonous or irritating?


texts: Total number of octahedral void(s) per atom in a cubic closed pack structure

texts:
The total number of octahedral void(s) per atom present in a cubic closed pack structure is
(a) 1
(b) 2
(c) 3
(d) 4

I answered with (d), but the key on internet says it is (a). Please clarify the dispute.


texts: Why does Mg(HCO₃)₂ on heating gives Mg(OH)₂?

texts:
Normally, bicarbonates on heating forms carbonates.
Why does Mg not give this too?

In a reference book I am referring to, it is given that it is due to high solubility  product of Mg(OH)₂ compared to Mg(CO₃) .

Then shouldn't the latter form? As even small amounts of it will lead to precipitation, driving the equilibrium  forward?

Edit: This is related to removing temporary hardness of water.


texts: How to form 6-31G basis set; specific instructions


texts:
Consider this picture of an $\ce{NaCl}$ unit cell:

It appears to show 14 $\ce{Cl-}$ ions and only 13 $\ce{Na+}$ ions.  Given that discrepancy, how is table salt balanced for charge?  Why isn't there a charge excess?


texts: Why can't Grignard reagents react like Organolithium does (with acids)?

texts:
I'd read yesterday that Grignard reagents can't give ketones on reaction with carboxylic acids. It is because of the fact that Grignard reagent is a "super-base", and it will deprotonate the acid to form a carboxylate salt, rather than doing a $\ce{Nu-}$ attack.
However, after watching a video on Youtube, on the reaction of organolithium with acids (example reaction below),

I wondered,

After the acid-base reaction, why couldn't Grignard reagent (when taken in excess) do a $\ce{Nu-}$ attack on the carboxylate salt, just like organolithium does and then form ketone? Just like it does with an ester, acid chloride, etc.


texts:
When talking about gaseous fuel / oxidizer mixture what does one mean by oxidizer if there is no oxygen involved?

Is it correct to think of oxidizer as the more electronegative specie, because it is pulling the electron? Or is this definition only valid for solutions?
The Wikipedia article is not clear whether the definition applies to gaseous reactants or only valid for solutions.


texts: Term for compound of carbon, hydrogen, and oxygen

texts:
Is there a term for a compound of carbon, hydrogen, and oxygen?

There is hydrocarbon for a compound of carbon and hydrogen.  There is also carbohydrate but that requires the ratio of hydrogen to oxygen to be 2:1.

As well as the carbohydrates, there are many other compounds of these three elements: alcohols, aldehydes, ketones, esters, etc.  Yet, I cannot find a term for the whole group.  Have I missed something or just no need is felt for such a term?


texts: Way to establish the acid/base properties of a compound from its chemical formula?

texts: Is there a way to figure out the acid/base properties of a compound just by looking at the chemical formula?


texts: Calcium chloride hexahydrate has separated in jar - is it beyond saving?

texts:
I work in a lab where I'm in charge of ordering new supplies. A graduate student brought up a $500~\mathrm{g}$ amber jar of $\ce{CaCl2.6H2O}$ and pointed out that it had separated into a clear liquid (on top) and a white crystal (on bottom). The cap seemed to be on normally and there is no expiration date on the jar.

Before I decide if I need to order more, I am wondering:

What happened to the $\ce{CaCl2}$?
Can it be saved?


texts:
When mixing HCl with K2CO3, the reaction that is usually given is the following:

K2CO3 + 2HCl → 2KCl + CO2 + H2O

I am wondering, however, if I could produce KHCO3 from K2CO3, by using half as many moles HCl. The reaction I imagine could happen would be expressed as follows:

K2CO3 + HCl → KHCO3 + KCl

I've gathered the solubility data for this reaction hereafter:

K2CO3: 112 g/100 mL  (20°C)
HCl: 72,5 g/100ml (20°C)
KHCO3: 22.4 g/100 mL (20°C)
KCl: 34.2 g/100ml (20°C)

From solubility data I see that it wouldn't be extremely practical to conduct as both KHCO3 and KCl are fairly soluble, but I'm wondering if the reaction would occur, or if it would just produce half the amount of KCl + CO2 + H2O through the first reaction (which is generally attributed to these reagents).

If the reaction occurs, can I assume that the first reaction is strongly dominant until I get close to have added as many moles of HCl as the initial moles of K2CO3?

And if it doesn't occur, why does it not?

Note that this question had been asked already, but had received no satisfying answer.


texts: Why are hydrogen ions always associated with another molecule?

texts:
I was reading N.C.E.R.T. class XI part 2 book and chapter Hydrogen,when I came across this statement:

  Loss of the electron from hydrogen atom
  results in nucleus ($\ce{H+}$) of ~1.510–3 pm size.
  This is extremely small as compared to normal
  atomic and ionic sizes of 50 to 200pm. As a
  consequence, H+ does not exist freely and is
  always associated with other atoms or
  molecules.

So a question arose in my mind that why it is a consequence of small size of hydrogen nucleus that $\ce{H+}$ does not exist freely and is always associated with other atoms and molecules?


texts: Writing a electrochemical cell representation in correct way

texts:
The answers to following question seem wrong to me. The books has plainly told correct answer is (3), but it seems incorrect to me. Please help.

The chemical reaction $\ce{2AgCl(s) + H2(g) -> 2 HCl(aq) + 2 Ag(s)}$ taking place in a galvanic cell (under standard condition) is represented by the notation
$$\ce{Pt(s) | H2(g), \pu{1 bar} |  1 M KCl(aq) | AgCl(s) | Ag(s)}\tag{1}$$
$$\ce{Pt(s) | H2(g), \pu{1 bar} |  1 M HCl(aq) | 1 M Ag+(aq) | Ag(s)}\tag{2}$$
$$\ce{Pt(s) | H2(g), \pu{1 bar} ||  1 M HCl(aq) | AgCl(s) | Ag(s)}\tag{3}$$
$$\ce{Pt(s) | H2(g), \pu{1 bar} |  1 M HCl(aq)  | Ag(s) | AgCl(s)}\tag{4}$$

Photo of problem: https://i.stack.imgur.com/Oflyg.jpg


texts: Can anyone tell me the difference of aggregates and clusters from the molecular point of view? Thank you so much.


texts: thinking about osmotic pressure when liquid is replaced by gas

texts:
An option in my test says:

  "The osmotic pressure of a dilute solution is the same as it would exert if it exists as a gas in the same volume of the solution and at same temperature."

I'm not able to think how should I relate between a solution and a gaseous mixture. Am I missing something?


texts: How to convert benzene to N,N-dimethylbenzamide?

texts: This is my solution to convert benzene to N,N-dimethylbenzamide. If you think is the right way, even just saying the equations are correct would help me! Thanks in advance.


texts:
I'm having a hard time trying to figure out n factor of $\ce{SO2}$ in the reaction

$$\ce{FeS2 + O2 → Fe2O3 + SO2}\qquad \text{(unbalanced)}$$

To balance it, I saw that in 1 mole of $\ce{FeS2}$, it looses a net total of 11 moles of electrons, while $\ce{O2}$ gains 4 moles of electrons per mole of it. That means they will have to react in a $4:11$ ratio, from this, the equation balances out to

$$\ce{4 FeS2 + 11 O2 → 2 Fe2O3 + 8 SO2}$$

The question was (wrt to this equation), what will be the equivalent weight of $\ce{SO2}$, if the molecular weight of $\ce{SO2}$ is $M$?

This means I will need the $n$ factor of it to divide by $M$,

I tried to reverse this reaction

$$\ce{2 Fe2O3 + 8 SO2 → 4 FeS2 + 11 O2}$$

But the problem is that now it's hard to tell from which $\ce{O}$ atoms (of the now-products), the oxidation state is getting changed to $\pm0$ (zero). It's now confusing me.

The answer is given as $M/5$. I don't know why, according to the solution they only concidered the oxidation number change of $\ce S$ while ignoring the others, I don't think it's right.


texts: Software recommendations for overlaying molecular structures

texts:
I am looking for a program to overlay the structure of small molecules as an aid for my students in comparing the results of optimization geometries using different optimization methods.

At this stage, we are thinking of atomic coodinates and a visual comparison. However, if it can be complemented with a quantitative comparison that would a welcomed extra.

We work with the Windows versions of Gaussian 09 and GaussView 5.


texts: Finding reactants in a azo-coupling reaction whose product is given

texts:
Find the reactants of the following azo-coupling reaction:

My solution would look like this:

My reason for the above answer
The amino Group is more activating than the nitro group and therefore the diazonium salt had to be on the left ring.
Is this correct? If not, what is the correct explanation?
Edit: To get to the azo-coupling product shown above I should use a high temperature, or? So, the reaction has to be thermodynamically controlled because the azo-group is localized on the  carbon.


texts:
Is methyl free radical a polar molecule?
According to Advanced Organic Chemistry by Jerry March, it is given as non-polar.
But then wat about the moment of the single electron?


texts: Cyanotype photography with potassium ferrocyanide

texts:
Some years ago, due to a translation error that I only discovered later, I made cyanotypes using a mixture of ammonium ferric citrate and potassium ferrocyanide instead of ferricyanide. This worked, although they seemed to be less sensitive (reacted slower to sunlight) than the guide I was trying to follow, but I didn't have a way to measure.

Is it safe to make this substitution? (I have lots left over and it would be good if I could use them up)

Is the resulting blue pigment the same Prussian blue as would result from using potassium ferricyanide? (some of the pigment seemed to wash away, whereas the guide said that only the unreacted reagents would do so)

Is there really a difference in sensitivity between this mixture and the ferricyanide mixture?


texts:
Could someone please help me with the following question.

Due to the perspective of voids in the MgO structure, what is the maximal amount of Sr that can substitute with Mg.
And why is it unlikely that it will happen?

Since the quota between the radiis is 0.84 and the size of the octahedral void is 0.414 the atom should substitute all of the Mg atoms. But is it unlikely because of the size of the Sr ion or is it some other factors involved?


texts: Molecular orbitals used with CCSD(T) geometries

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Suppose I am given some geometry data (say, of a water dimer) from CCSD(T).  If I were to do a single-point energy calculation to generate orbitals for the system, wouldn't CCSD give something more representative of the correlation in the system than DFT?

I see "CCSD(T) orbitals don't exist - used DFT orbitals instead" kind of statements in papers (quotations below), and wasn't sure why they don't even mention CCSD.  Perhaps it's just due to speed/availability, but that would lead to another question "why is it not worth it to use CCSD orbitals with CCSD(T) geometry".

The same question can be asked for DFT orbitals being used with MP2 geometries, but MP2 perturbs about HF ... so clearly DFT is needed to capture correlation.

[edit: more context]
What I'm trying to do is "export" these orbitals to a diffusion quantum Monte Carlo (DMC) calculation which doesn't do geometry optimization by itself but augments the imported orbitals with explicit correlations (eg. something that depends directly on electron pair distances).  Usually the final DMC energy is not very sensitive to whether the orbitals are from CC or DFT (I have outputs from both), but I was checking here to make sure I wasn't missing any "deeper" reason.

From ChemPhysChem 2018, 19 (15), 1886–1894:

  Since MP2 orbitals are nonexistent, the charge-transfer interactions were computed using the B3LYP functional with the aug'-cc-pVTZ basis set at the MP2/aug'-cc-pVTZ geometries, so that at least some electron correlation effects could be included.

and J. Phys. Chem. A 2017, 121 (49), 9544–9556:

  Due to the nonexistence of CCSD(T) orbitals, ΔE(del) was calculated with ωB97XD/aug-cc-pVTZ.


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What is occuring on the quantum level when a molecule rotates plane polarized light?

Also, why do enantiomers then rotate light in opposite directions? I would think that the electromagnetic waves would interact with the transient electric and magnetic fields within the molecule itself as it propagates and therefore the light changes direction as it passes through the molecule. However with this idea there seems to be a problem with the fact that all the molecules wouldn't be oriented in the same directions and thus scatter the light in all directions rather than a net rotation in one direction of the light. I am looking for an explanation using electromagnetism if it can be explained at that level or if it cannot, the quantum mechanical answer would be fine as well.


texts: How do metals split the oxygen double bond during corrosion?

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For a metal like $\ce{Mg}$ to corrode into $\ce{MgO}$, the double bond in $\ce{O2}$ must break. Since the dissociation energy of $\ce{O2}$ is 500 kJ/mol, using estimates from the Boltzmann distribution, it looks like there would not be any $\ce{O2}$ molecules in the entire atmosphere  with enough energy to break this bond at room temperature:
$$\text{Fraction of $\ce{O2}$ with at least $\pu{500 kJ}$ energy} \approx \mathrm e^\left(\dfrac{-500\,000\ \mathrm{J/mol}}{298\ \mathrm K(8.3145\ \mathrm{J/(mol\ K)})}\right) \lt 10^{-261}.$$

But my understanding is that $\ce{MgO}$ does form at room temperature. In fact, it seems that even stable $\ce{Pt}$ can break the $\ce{O2}$ bond at room temperature (for example in the context of catalyzing the ignition of hydrogen).

It seems that something like this must be happening: an $\ce{O2}$ molecule collides with $\ce{Mg}$ metal and gets stuck onto the surface, temporarily forming $\ce{MgO2}$. And once this bond is formed, the remaining bond between the two oxygen atoms suddenly becomes easy to break, and one of the oxygen atoms falls off and bonds with a different $\ce{Mg}$ atom. Is this the case?

I'd like to understand this mechanism better. How weak does the $\ce{O2}$ bond become after latching onto magnesium, and why does it become weaker? Why are metals able to split the $\ce{O2}$ bond this way, compared to other materials like hydrocarbons?