texts: Can dissolved salts (or any soluble chemicals, for that matter) 'bump' each other out of solubility?

texts:
Will a more soluble substance dissociate, causing a less soluble substance to precipitate out?

in equation:

AB(s)+ C(aq)+ D(aq)--> A(aq)+ B(aq)+ CD(s)

Does that equation go through, under the assumptions that AB, as a whole, is more soluble than CD, and saturation point is achieved with both substances?

Thanks in advance! This question has been bothering me for a while...


texts: Removing Tungsten Trioxide from Tungsten Electrode

texts:
I need a very sharp tungsten electrode, and I think radial electrochemical etching with sodium hydroxide is the way to go. The problem therein (I think) is that the etching will cause an oxide layer to form deeper than the native oxide layer, ruining the electrode.

Are there any reactions close to STP that will get rid of a few layers of $\ce{WO3}$? I found one recommendation that involves using ammonia as a reducing agent at 80 °C, but I can't determine its validity.

$$\ce{WO3 + 2 NH3 -> 3 H2O + W + N2}$$


texts: There is a higher energy 2Σ+ state with a bond length of 1.15 Å for CN molecule, explain this

texts: How can there be an excited state for CN where the bond length is lower (stronger bond) than the actual ground state? The molecular orbital diagram suggests that the single electron in the sigma orbital gets excited, but to which orbital? This was a question asked by one of my professors and I don't know where to start, I think that the ground state X 2Σ+ goes to the B 2Σ+ excited state and maybe the electron could go to the 3S orbital? but then how would this affect the bond long is beyond me. In addition, would the vibrational fine structure go from V'=0 to V'=2? Can anyone help?


texts:
Why is it that a specific order is followed while performing qualitative inorganic analysis? I mean, why are we told to first test for the anion in the given salt (and there is an order to be followed for which anion to test for first, which second and so on) and then for the cation?

Does it really matter which way we do it?
How does it affect the analysis if we don't follow the order of cations/anions?


texts: How does mesh size of Barium Chloride affect sulfate results via turbidimetric method?

texts:
I am analyzing sulfate using Standard Methods 4500 $\ce{SO4 ^2-}$ E (turbidimetric method) using $\ce{BaCl2}$ and measuring %T at 420 nm. In the past, we used an appropriate 20-30 mesh size for the $\ce{BaCl2}$; however, it appears that it only is sold in mesh size 10 now.

This smaller mesh size is causing higher %T in the standards (less turbidity), but a check standard will still give accurate results ($r^2$ = 0.98). The main issue is sample results being anywhere from 3-10 mg/L too high  (e.g., routine samples of 7-8 mg/L now give 10-11 mg/L, and 5-6 mg/L now is 15 mg/L). How does the size of the crystals affect the sample results? Is there any way to correct the results or in some way account for the smaller mesh size?


texts: Density and concentration of hydroiodic acid

texts:
I weighted my hydroiodic acid sample: 25 ml weight 34.1 g, so the density is about 1.364 g/ml.

I want to know its concentration based on density. Does anyone have the corresponding density chart?


texts: Statistical thermodynamics question. Can somebody explain the low temperature Schottky anomaly for two level systems? Why is this anomaly not seen in all materials?


texts: Helium superfluid-3 has got at around 2K a special liquid state with 0 viscosity with interesting properties. I am really interested in what would happen at 0K. With no kinetic energy in the particles of the compound, would it be solid? Do elements with no solid state at all exist?


texts: How to solve constants out of the internal energy equation?

texts:
Imagine we deal with a new kind of matter, whose state is described by:
$$PV = AT^3$$
Its internal energy is given by
$$U = BT^n \ln\left(\frac{V}{V_0}\right) + f(T)$$
where $A$, $B$ and $V_0$ is a constant and $f(T)$ is a polynomial function.
Find $B$ and $n$.

What I know
The given expressions remind me of adiabatic compression/expansion. If we assume quasistatic adiabatic compression/expansion we know that heat won't get out/in the system.
$$\Delta U = -W$$
And work is:
$$W = -P\Delta V$$
Some thoughts on how to solve the problem
We notice here that we are dealing with a non-ideal gas. Assuming that the above equations are correct and using first thermodynamics law one gets:
$$\mathrm{d}U = \left[nBT^{n-1}\ln\left(\frac{V}{V_0}\right) + f'(T)\right]\mathrm{d}T$$
$$\left[nBT^{n-1} \ln\left(\frac{V}{V_0}\right) + f'(T)\right]\mathrm{d}T = \frac{AT^3}{V}\mathrm{d}V$$
I do not see a solution to this differential equation. There has to be a easier way to get both $B$ and $n$, but how?


texts: Why we don't get sharp point at equivalence points in case of acid base titration other than the case of strong acid and strong base titration?


texts: Literature value for the activation energy of the reaction between hydrochloric acid and sodium bicarbonate

texts:
Does anybody have the literature value for the activation energy of the reaction between hydrochloric acid and sodium bicarbonate? If yes, could you please cite the source for it and the value?

I searched through the internet for hours, but the closest I could find was the activation energy between sodium carbonate and HCl, nothing for bicarbonate. I tried the NIST database and could not find anything, and other databases too.


texts: Can aniline be made with the method described in Dr Stone?

texts: In Dr Stone, the main character makes aniline by rinsing coal tar with HCl, then mixing in ethyl acetate. See the image below. Is a method like this possible? What is occurring here?


texts:
I get that $G=H-TS$ because then: $$\begin{align}\mathrm dG&=\mathrm dH-T\,\mathrm dS-S\mathrm dT\\&=T\,\mathrm dS+V\,\mathrm dp-T\,\mathrm dS-S\,\mathrm dT\end{align}$$
Therefore, by cancelling: $\mathrm dG=V\,\mathrm dp-S\,\mathrm dT$ which is the equations for $\mathrm dG$. However, I can’t get this result from using $\mathrm dG=\mathrm dH-T\,\mathrm dS$.
$$\mathrm dH=S\,\mathrm dT+V\,\mathrm dp$$
$$\mathrm dG=\left(S\,\mathrm dT+V\,\mathrm dp\right)-T\,\mathrm dS$$
This does not give me the right equation. Where am I going wrong?


texts:
Does the hyponitrite molecule exist? I know the hyponitrite ion exists (http://en.wikipedia.org/wiki/Hyponitrite) but what about the molecule?

I have found no reference to the molecular form on Wikipedia. But it does seem that such a molecule could at least come together through the dimerization of nitric oxide.


texts:
As part of a synthesis I was considering the following reaction:

How selective is the Clemmensen reduction? I know that this reduction favours ketones adjacent to benzene rings but will it also reduce the other ketone, and/or affect any other parts of the molecule. Are there any other methods that would achieve this transformation more effectively.


texts: it is possible for the hydrogen bond to form between the hydrogen chloride molecule, HCl?

texts: Recently I'm doing my work, and I can't find what it is the answer. Can you guys help me?


texts:
A full FAQ post has been written on meta.chem.SE, explaining the premise of synthesis golf and the 'rules'. Please take a look at this if you haven't already.

This round of synthesis golf concerns the Corey synthesis of Erythronolide B (J. Am. Chem. Soc. 1978, 100 (14), 4620–4622).

In order to narrow the scope of the challenge, only a small fragment of the natural product will be considered. Fragment 2 was an intermediate on the Corey route, and provided C10-C13 of Erythronolide B.

Crucially, 2 was needed as a single enantiomer and diastereomer. In the original Corey report, 13 steps were needed to accomplish the synthesis of the fragment, a length which prevented significant amounts of material from being made.

The challenge is to propose a synthesis of 2 which sets up the required 1,2-stereochemistry with absolute configuration. You may start from anything commercially available in the Sigma–Aldrich catalogue, including chiral building blocks.


texts: Why starch (amylose) and cotton (cellulose) are so different?

texts: Both amylose and cellulose have the same "monomer" structure (glucose), so what makes them look/form so differently?


texts:
Two substances undergo a reaction that gives off propylthiouracil and another compound as products.

Is there an additional compound I could throw into that sludgy product to strain off the $\ce{C9H17O6}$ such as that used in the Miller Process, but instead would leave a clear propylthiouracil for my use? The chemical reaction is given below:

$\ce{2 C11H19NO6 + C3H6OS -> C7H10N2O6 + 2 C9H17O6}$


texts: Find the pH of an amphiprotic salt dissolved in water at room temperature

texts:
Let's say I have a polyprotic acid $\ce{H2A}$ with the following properties:

$$
\begin{align}
\ce{H2A &<=> HA- + H+} & K_1 &= 1\cdot 10^{-1}\\
\ce{HA- &<=> A^2-+ H+} &  K_2 &= 1\cdot 10^{-4}
\end{align}
$$

Now a 0.5 M solution of $\ce{HA-}$ is prepared; what will be the $\mathrm{pH}$ of the solution?

My textbook (and many other sources) says it should be

$$\frac{\mathrm{p}K_1 + \mathrm{p}K_2}{2}$$

which sounds a little counterintuitive to me.

First of all, it implies that the $\mathrm{pH}$ is independent of the concentration of $\ce{HA-}$ present.

Also, if $1/\mathrm{p}K_1 > \mathrm{p}K_2$, then $\ce{HA-}$ should have the tendency to accept a $\ce{H+}$ more than it has of losing one, then why is the $\mathrm{pH}$ exactly partway between $\mathrm{p}K_1$ and $\mathrm{p}K_2$?


texts: Substitution reaction rate for tertiary halide substrate with adjacent carbonyl

texts:
In the book "Organic Chemistry" by Clayden et al. p 343 it is stated that this substrate reacts very slowly through both the SN1 and SN2 pathways. It is shown side by side with neopentyl chloride as an example of notoriously unreactive compounds.

I get that being tertiary might slow down SN2 to counteract the effect of the adjacent carbonyl. But why would SN1 not still be good?

My question is: why does this substrate react slowly through both SN1 and SN2?


texts: Can you make deuterium-depleted water through a freezing method?

texts:
Deuterium-depleted water (DDW) is sold commercially by some companies. It is apparently manufactured by fractional distillation, which leverages differences in boiling points of heavy and light water.

My question is this: can DDW be manufactured through a freezing method? Heavy water has a freezing point of 38.8 °F and normal water of 32 °F. If a jar of water were kept in a water bath of say a constant 35 °F, wouldn't the heavy water freeze and sink to the bottom of jar, allowing the DDW to be siphoned off of the top? I am surprised there appears to be no discussion of the merits or demerits of this idea anywhere on the internet.


texts: Relation between various bond angles of Nitrogen compounds

texts:
I was thinking what could be order of bond angles of NH3, NF3, N(CH3)3 and N(C2H5)3.

Considering  NF3 and NH3:

Since there is backbonding between 2p-2p orbitals of N and F, there will be a partial double bond character between N and F and therefore, since repulsion between lone pair and double bond is more than that between lone pair and single bond and thus bond angle in  NF3 will be less than NH3

But, the size of F is very small, and F has lone pairs while H does not. If the N-F bond acquires partial double bond character, the lone pair of other F atoms should repel the bond making the F-N-F angle larger? Would the two effects cancel each other making the bond angle of  NF3 equal to  NH3

It is known that bond angle of  NF3 is less than NH3. Why? How do I decide which factor will dominate over other?

Now since N(CH3)3 and N(C2H5)3 have bulky groups, the groups will repel each other making the bond angle greater than NH3.

But between N(CH3)3 and N(C2H5)3 , which will have greater bond angle? I suppose C2H5 will repel other C2H5 groups more than CH3 groups.

Again there is another factor to be considered here. There are more numbers of bonds in C2H5 and shape is tetrahedral which might (there is a possibility) bring the CH3 connected to the C (which is connected to N) closer to N hence increasing repulsion between the group and N and thus decreasing C2H5-N-C2H5 bond angle.

Again, why does this not happen?

Can anyone explain the correct order between these molecules?


texts: onset of oxidation for cyclic voltammetry

texts:
I have plotted a cyclic voltagram for my different polymer blends and I am trying to work out the onset of oxidation. picture below is my graph

from this website: https://www.ossila.com/pages/cyclic-voltammetry
There is a diagram which shows how the straight line should be placed so that it intersects the horizontal line, and thus the onset of oxidation can be found

However I am being told to draw my lines like this:

The procedure I am being told to do, doesnt make sense to me, I dont think the data from that would be useful. I would only get values for the Eonset that are very similar if I were to do it the way I'm being told. From my data, theres a clear difference in oxidation slope, so wouldn't it make sense to plot the diagonal line against that slope, rather than a small section near the beginning? From my 5 cyclic voltagrams, it would make much more sense if I were to do it as the website has told me to. There are more pictures on google which do it that way too


texts: Why is the product of $\ce{Al(OH)3 + NaOH -> Na[Al(OH)4]}$ and not $\ce{NaAlO3H2 + H2O}$? Is this an acid-base reaction?


texts: Decomposition products of magnesium ethanoate

texts:
What does magnesium ethanoate decompose to? The Wikipedia page states that one of the products is magnesium oxide. What's the other product? I can come up with some guesses:

Ethanoic anhydride ($\ce{MgC4H6O4(s) -> C4H6O3(g) + MgO(s)}$)
Propanone and carbon dioxide ($\ce{MgC4H6O4(s) -> C3H6O(g) + CO2(g) + MgO(s)}$)


texts:
Electrolytes are ionic compounds that conduct electricity, or the flow of charged particles, when dissolved in water. This occurs via the separated ions acting as those charged particles, or charge carriers, when a voltage is applied. Which compound would not create an electrolyte solution when dissolved in water?

A) ammonium acetate, $\ce{NH4C2H3O2}$

B) sucrose, $\ce{C12H22O11}$

c) sodium hydroxide, $\ce{NaOH}$

D) potassium nitrate, $\ce{KNO3}$


texts: What are dipole moments in a molecule supposed to act upon?

texts:
In a $\ce{CO_2}$ molecule, a total of four electron pairs are shared between the carbon and oxygen atoms, such that 2 pairs are shared between the carbon atom and each oxygen atom. Oxygen has a greater electronegativity hence the atoms of oxygen will spend greater time with shared pairs and are partially negative. Since both oxygen atoms will exhibit this same behavior, the carbon atom will become partially positive.

I was reading about the dipole moment of $\ce{CO2}$ (e.g., as here), in which it said that the net polarity of the $\ce{CO_2}$ molecule is zero because if we add the individual dipole moment vectors directed from the positive pole (carbon) to the negative poles (the oxygen atoms), the resultant will be zero which implies the polarity of the molecule is zero.

My problem is this:

If these individual dipole moments (vectors) are showing the opposite and equal pull of shared pairs of electrons toward more electronegative atoms (oxygen atoms), then the carbon atom should stay partially positive with the oxygens remaining partially negative.

Given this, though, it seems that the molecule should remain polar on whole.  This is because these dipole moment vectors are acting on different shared pairs: the first vector acts on the two shared electron pairs between the carbon atom and one of the oxygen atoms, and the other acts on the two shared electron pairs between the carbon atom and the other oxygen atom. According to the following law, then, these vectors cannot cancel each other and thus $\vec u \neq\vec 0$:

  Two equal and opposite vectors do not cancel each other out when acting on different bodies.

My best attempt to resolve this contradiction:

Since in reality it is the case that the net polarity of $\ce{CO_2}$ is null, I think that both vectors (viz., the 'pull' from both oxygen atoms) must be acting individually on all electrons of carbon atom and therefore they cancel each other out resulting in molecule to be non-polar on whole. This explanation isn't all that satisfying to me, however.


texts: What happens to acids/bases left out overnight?

texts:
I conducted a titration experiment a few days back and was unable to neutralize the solution in time, so I had to leave the solutions of HCl and NaOH out overnight in order to use them the next day. Also, one of my partners blew into the buret to get a drop of NaOH out. At the end of the experiment, we found that we required 6-7 mL more base to neutralize the HCl solution; another group who was forced to leave their solutions overnight used 3 mL more even than we did.

My hypothesis is that CO2 from the air formed carbonic acid in both solutions, mainly due to the instance where my partner blew into the buret, and thus the acidity of both solutions required that we use more base than we would have originally. As far as I've researched, this seems to be the case. Just to be sure, though: is this a correct assumption? If not, what could be the cause of this discrepancy?


texts: Is bamboo based plastic less likely to leak chemicals?

texts:
Some plastics have been known to leak plasticizers (bisphenol and phthalates) into the food they contain, especially when heated.
Because such compounds are suspected of being endocrine disruptors it seems best to avoid eating hot food from a plastic container.

Recently bamboo bowls, cups and plates have become available. As far as I can tell these are made from some kind of composite material which contains bamboo fibers and something that glues these together.
The only information  is that it's: renewable, dishwasher safe, bio-degradable (the last two claims seem contradictory), food safe, but not suited to be microwaved.

Is it possible that these kitchen-wares are safer than other plastic bowls, plates and so on? Is it possible to even assess the risks?


texts: Can I make Cobalt Violet with these materials?

texts:
I'm given $\ce{CoCl2*6H2O}$ as well as $\ce{Na3PO4*12 H2O}$

The chemical formula for Cobalt Violet is $\ce{Co3(PO4)2}$. I haven't done stoichiometry in a long time but I think that's creatable, right?

Some website says that I need $\ce{NaH2PO4·10H2O}$, instead of the Sodium phosphate dodecahydrate which is what I have.


texts: Is it possible to have electric field in water without having electrolysis?

texts: Is it possible to have electric field in water (using electrodes with voltage difference) without having electrolysis in the water (or any other reaction)?


texts: Liquid nitrogen superheating with a layer of oil?

texts:
edit: Thanks Ivan, also further research.

Pure water can be superheated to a few degrees above 100 degrees. However I remember reading reading that water can be superheated to even higher temperatures by covering it in a thin layer of oil that more effectively prevented the water from boiling. When disturbed the water can then suddenly boil and vaporise at a very fast rate. Apparently a microwave is an effective way to heat the water for this purpose.

However this can easily become very dangerous.

As liquid nitrogen boils at -196 degrees C, would using liquid nitrogen instead, with a thin layer of oil allow the same suppression of boiling, superheating, and sudden vaporisation to be observed but at much safer temperatures, as well as keeping the liquid nitrogen in it's liquid state at higher temperatures?

See also: physics.stackexchange.com/questions/29392/why-droplets-of-water-under-oil-explode-when-heated


texts: When do lone pairs affect dipole moments?

texts:
My textbook says that NH3 has more dipole moment than NF3 despite F being more electronegative than H, because the dipole moment due to the lone pair on N points in the same direction as the ones due to the H atoms, but not the F atoms. But this is the only time it talks about a dipole moment being caused by a lone pair.
In multiple examples and questions involving calculating dipoles with H20, HF, etc (that contain lone pairs), they are just ignored. It's the same with other websites. Are lone pairs negligible when calculating dipoles if they are on O, F, etc atoms?


texts: Thermal properties of 301 stainless steel

texts:
So I know that 301 stainless steel was chosen for the SpaceX Starship rocket as it can handle high temperature differences.
What about this alloy makes the steel harden when it gets colder?


texts: Determining the direction of chemical reactions based on the activity series

texts:
Based on the activity series (table of standard reduction potentials), indicate whether or not the following reactions would occur in the direction written.

Don't worry about what the activity series is, I don't even know what it is so it isn't important. I'm more confused on the procedure and how to find the answer. Would you just find the oxidation states, then find the half reactions according to what the oxidation states are and find the voltage according to the reduction potentials sheet, then be able to tell whether it was spontaneous therefore whether it would run in the direction it was written?

Here are a few of the first questions, the easy ones.

$$\ce{Ag + KNO3 → AgNO3 + K}$$
$$\ce{Zn + AgNO3 → Ag + Zn(NO3)2}$$
$$\ce{Li + H2O → LiOH + H2}$$
$$\ce{Cu + FeSO4 → Fe + CuSO4}$$


texts: The pH of a drop of water containing ammonia

texts:
Presented with the following equations: What would the $\mathrm{pH}$ of a drop of water be, while in equilibrium with $\ce{NH3(g)}$ at a concentration of $\pu{150 ppb}$?

$$\ce{NH3_{(g)} + H2O_{(l)} <=> NH3_{(aq)} + H2O} \qquad K_\mathrm{H} = \pu{1.76 \cdot 10^{-2} M/atm}$$

$$\ce{NH4+_{(aq)} <=> NH3_{(aq)} + H+}  \qquad K_\mathrm{a} = 5.62 \cdot 10^{-10}$$

So my issue is that I don't know how to express the concentration of $\ce{[NH4+]}$.

Calculating the concentration of $\ce{NH3_{(aq)}}$ is simple: $K_\mathrm{H} \cdot P_\ce{NH3}$, while $P_\ce{NH3} = C \cdot P_\mathrm{air} = 150 \cdot 10^{-9} \cdot \pu{1atm}$, yields $\ce{NH3_{(aq)}} = \pu{2.64 \cdot 10^{-9} M}$.

If we are to tally up all contributions of $\ce{H+}$ then we get:
$\ce{[H+]} = K_\mathrm{w}/\ce{[H+]}$ (from water dissociation) + $K_\mathrm{a} \ce{[NH4+]}/\ce{[H+]}$.

Then $\ce{[H+]} = (K_\mathrm{w} + K_\mathrm{a}\ce{[NH4]})^{0.5}$ and we'd get the $\mathrm{pH}$.

I'm stuck unsure how to express $\ce{[NH4]}$.


texts: How to remove a stuck stopper from a flask?

texts: How do I remove a stopper that has been stuck in the neck of a 100 mL round bottom flask since I forgot to wipe the neck of the flask. A salt was formed in the 100 mL flask and the stopper is just stuck like cement. Is there anyway to remove it without breaking the flask, breaking the stopper, or heating the flask (since I don't want to interfere with the product)?


texts: Why do alkyl bromides and iodides develop colour when exposed to light?

texts: My book says alkyl halides are colourless when pure. However, bromides and iodides develop colour when exposed to light. Why do they develop colour when exposed to light? It is important to note that alkyl fluorides, and alkyl chlorides are not said to develop colour.


texts: Why the use of MD simulations is less popular for the study of carbohydrates?

texts: In classical all-atom MD simulations, the force fields for proteins, nucleic acids and lipids seem to be more well developed than carbohydrates. It seems to me that the use of MD simulations is not so popular for the study of carbohydrates. Is there any reason for this?


texts: Why is water a poor solvent for organic molecules?

texts: Few organic molecules dissolve in water but why is this the case?


texts: What is insoluble in drinking alcohol, but edible?

texts:
What substances are edible for human consumption, but will not mix with alcohol? What is a substance that would block alcohol from mixing with its counterparts in a product?
For example: You make a cupcake and want an alcohol shot in that cupcake. What substance could the alcohol shot be contained in so it wouldn't disperse into the cupcake, but still be edible?


texts: Can hydrocarbons undergo combustion without oxygen present?

texts:
Most of us are familiar with the standard reaction of methane gas combustion:

$$\ce{CH4 + 2O2 -> CO2 + 2 H2O}$$

In standard combustion, oxygen is generally used as the oxidant. Would it be possible for hydrocarbons to undergo combustion using alternative oxidants? If so, under what conditions could this be reproduced?

For example, could we achieve anoxic combustion by replacing oxygen in the atmosphere with another highly electronegative element such as chlorine or fluorine? Or perhaps compounds in high oxidation states such as permanganate or dichromate under different pressure/temperature conditions such that they were gaseous?


texts: Why is $^3P_1$ an atomic term symbol for carbon?

texts: I'm using these rules, $^{2S+1}L_J$ with $J=L+S$ and it seems to imply that $^3P_1$ means $S=1$, $L=1$, and $J=1$ but clearly $1+1 \ne 1$ so according to me this shouldn't be an atomic term symbol but it is. Why?


texts:
I am taking the instrumental methods of analysis course. Our job is to find the unknown  mass of $\ce{Fe}$ which is added, by measuring the absorbance of different solutions with ortho-fenantroline.

Is there any way I can know if my calculated mass of $\ce{Fe}$ is correct or not?   Is there any way I can prove it, since I know the absorbances?


texts: Iodine color change in different complexes

texts: Why does the color of iodine differ when it forms a charge transfer complex with benzene (pi donor) - pink and ethanol (electron pair donor) - brown? Does the HOMO-LUMO energy differ, if so how?


texts: Odd color reaction with Marquis and MDMA

texts:
The textbook colour reaction of Marquis reagent (mixture cc. $\ce{H2SO4}$ + formaldehyde, optionally with some methanol to slow down polymerization) with MDMA (3,4-methylenedioxy-methamphetamine, the party drug "ecstasy") is a gradually appearing dark purple/blue colour.

Recently three different samples were examined with marquis. The samples were taken in different countries, at different times. They looked a bit different too, one was light brown, the other two were clear.

TLC results suggested they are the same compound with $R_f$ values that of MDMA.

Reaction with Mecke reagent was also MDMA-like.

Reaction with Marquis started OK, with fizzing (a sign of a HCL salt) a light and then dark purple colour appeared.

After maybe a minute or two, the dark colour started to fade, it turned into light purple. As the colour faded even more, it turned green, and then to light yellow.

The test was repeated with two different reagents and all three samples, the results were the same.

I found no documented nor anecdotal record of marquis turning green/yellow in the presence of MDMA after a few minutes.

Is this normal? Should Marquis turn green/yellow after a few minutes in the presence of MDMA?
If this is really unusual, then what could possible cause fading & color change?


texts: Three-membered ring pathway bromination of alkene

texts:
Bromination of alkene occurs by the mechanism as shown (source: Master Organic Chemistry — Bromination of Alkenes: The Mechanism):

Here $\ce{Br^-}$ attacks bromonium ion from a side which is more hindered to form Markovnikov product. But shouldn't it attack on the less hindered carbon as we do in case of reaction following SN2 mechanism to form anti-Markovnikov product?
For example, in ring opening of epoxide in basic medium attack by $\ce{CH3O^-}$ occurs on the less hindered carbon (source: Lumen's Organic Chemistry 1: An open textbook — 9.6. Epoxide reactions):

Why does the same doesn't happen in case of bromination of alkenes and oxymecuration of alkenes?


texts: How does base size affect the ratio of kinetic/thermodynamic enolate?

texts:
One of the factors that favor kinetic products is bulky bases. So, I'd expect that, for a certain substrate, the use of a more bulky base to favor even more the kinetic product.

However, in the table below we see that as the base becomes even more sterically hindered, the thermodynamic product is formed. It's never the main product but it does get produced a little bit more (1% to 10%).

Why is that? Why in the case of Ph3CLi we get more B than in the case of LDA?


texts:
In thermodynamics work is defined as $~-p_{ex}\Delta V~$ for an ideal gas. If the total work is a negative value, that is in case of expansion of gas, we say that the work is done by the system and is negative.

I don't understand that why we use the pressure exerted on the gas in expression of work that is the external pressure and say that the work is done by the system ? If work is done by the system we should use internal pressure and if we use that in case of expansion the work done by the system will be positive which is contradicting. Please provide an explanation


texts: What is the hybridization of the central carbon in buta‐1,2‐diene?

texts:
State the hybridisation of asterisked carbon in $\ce{CH3-CH=\overset{\ast}{C}=CH2}.$

I am not sure between $\mathrm{sp^2}$ and $\mathrm{sp}$ hybridization. Because of the presence of double bonds I think it should be $\mathrm{sp^2},$ but because of the two π-bonds I think $\mathrm{sp}$.
Which one is correct?


texts: Why does copper react only with nitric acid?

texts:
When we are entering the chapter for acid and base, one of the reactions is about reacting metal with acid to form a salt and hydrogen gas. My teacher also informed us that a metal which is at a lower position than hydrogen in the electrochemical series, such as copper, cannot react with acid. It is because copper cannot displace the hydrogen atom from the acid.

However, I have seen several videos from YouTube which show copper can react with nitric acid as follows:

$$\ce{Cu + 4HNO_3 -> Cu(NO_3)_2 + 2H_2O + 2NO_2}$$

My question does why nitric acid react with copper, unlike the other acids? And are there any other acids which can react with copper?


texts: Carbocation formation in electrophilic addition of hydrogen halides to alkenes

texts:
Question:

My attempt:

I made the carbocation on the carbon labelled $1$ because I think that the positive charge would be slightly more stable on $1$ compared to $2$ due to the inductive effect of $\ce{Cl}$.

But my teacher made the carbocation on $2$ giving the explanation that after rearrangement, the positive charge will be stabilised by resonance with $\ce{Cl}$.
His approach:

Now, my question is, comparing the stabilities of the carbocation intermediates without rearrangement, the positive charge will be stable on $1$ compared to $2$. After rearrangement too, I think that the tertiary carbocation will be more stable than compared to the one stabilized by resonance with $\ce{Cl}$.

So, what is wrong in my reasoning?

Or as suggested by Mithoron, will there be intramolecular attack by $\ce{Cl}$?


texts:
I bought a pressurized liquid chlorine ampoule online and I was surprised how thick it was.  It was more like oil than water.  Here's a YouTube video showing someone else with a very similar sample.

I trust my seller but I’m wondering why is it so thick? It doesn’t flow easily.


texts: Why does Mg react vigorously in NaCl solution and less so in water?

texts: When you put $\ce{Mg}$ into water a few $\ce{H2}$ bubbles appear. But when you put $\ce{Mg}$ into a $\ce{NaCl}$ solution there is a vigorous release of $\ce{H2}$, why is this and what reactions are taking place?


texts: Why is the amu of chlorine-35 less than 35?

texts:
My book says that a proton weighs 1.0073u, a neutron weighs 1.0087u, and an electron weighs 0.00055u.

Now, why is the mass of chlorine-35 equal to 34.969? Are there not 17 protons, 18 neutrons, and 17 electrons? I calculated it and it sums to around 35.29. Where did I go wrong?


texts: Does phenol undergo Friedel–Crafts reactions or does it react with Lewis acids like aniline does?


texts: Why Freundlich adsorption isotherms fails at high pressure conditions?

texts:
Experimentally it was determined that extent of gas adsorption varies directly with pressure, and then it directly varies with pressure raised to the power 1/n until saturation pressure Ps is reached. Beyond that point, the rate of adsorption saturates even after applying higher pressure. Thus, the Freundlich adsorption isotherm fails at higher pressure.

This is an extract taken from Wikipedia explaining limitation of Freundlich isotherm.But analyzing the freundlich adsorption equation we can reach the same conclusions

The Freundlich adsorption isotherm is mathematically expressed as:
         $$X/M=KP^{1/n}$$

Giving whole number values to 'n' we can explain adsorption at various pressure conditions.If so why then it is said that Freundlich adsorption isotherm fails at high pressure?

Edit

  It cannot be used for a straight linear isotherm part occurring either at low pressures as the
  value n =1 should be then assumed, or at high pressures as the curve increases
  unreservedly, whereas a surface has a limited value and it must be in the condition of
  saturation.

Why is it given here that it's not possible to assume a value of 1 for n?


texts:
I want to perform a reaction which needs the temperature to be maintained between 400–430 °C. Since it's the only practical solution, I opted for a heated bath.

I'm looking for a hydrocarbon fraction/blend with the boiling point in this range, however, I keep finding conflicting information. If anyone knows such a hydrocarbon product please, let me know.


texts: Looking for a non-toxic substance that evaporates very quickly

texts:
Firstly I am not a chemist so please be kind. I am a creative technologist working on a large art installation. The challenge is to make people perceive rain without it raining. I am looking for something we can very occasionally drop from above that will feel like a rain drop but almost instantly evaporate leaving the person completely dry when they leave (they will only experience a few drops whilst in the room — the rest of the effect uses lights and sound).

My initial thought was liquid nitrogen but I assume that whilst a tiny occasional drop on the back of the hand would be fine, one in the eye for example would probably be dangerous. Plus the room would need to be heavily ventilated to prevent the risk of asphyxiation.

I'm assuming the answer is nope but if anyone has a genius idea for some way i could achieve this effect I would love to hear it. Over to you.


texts:
Since glass is a mix of silicates of sodium and calcium produced by heating or fusing together $\ce{Na2O}$ (Lewis base) with sand or $\ce{SiO2}$ (Lewis acid). Since $\ce{Na2O/NaOH(aq)}$ is a strong base and is used to create water glass(es)$(\ce{Na2SiO3},$ $\ce{Na_xSiO_y}$ etc.).

Is there some procedure in place to create glass by mixing (a base rich) water glass at room temperature with calculated amounts of $\ce{CaO}$ in mould to prepare float glass of definite shape without heating or mild heating?


texts: What would be the correct mechanism for hydration of ethene?

texts:
Given above is the mechanism that I drew but my textbook puts it a bit differently. It says that the ethene is dissovled in the concentrated $\ce{H2SO4}$ to form ethyl hydrogen sulphate $\ce{CH3-CH2OSO3H}$ which when diluted with water reacts to form ethanol and the acid
$$\ce{CH3CH2OSO3H + H-OH -> CH3CH2OH + H2SO4}$$
So which mechanism is true?


texts: What makes a ligand stronger than another?

texts:
A ligand is a neutral molecule or negative ion with at least one lone pair of electrons which forms a dative covalent bond with a complex ion that has a vacant, energetically accessible orbital.

It is said that in terms of ligand strength, or 'binding power', the cyanide ion is stronger than ammonia, which is in turn stronger than water, which is in turn stronger than the chloride ion.

What determines the strength of a ligand?


texts: Is chloronitrobenzene and nitrochlorobenzene same?

texts:
Is it 2-chloronitrobenzene or 2-nitrochlorobenzene?

If we take nitro group as the substituent, it will be 2-chloronitrobenzene. But if we take chloro group as the substituent, it is 2-nitrochlorobenzene.

What if we start numbering the carbon atom from the carbon to which the nitro group is attached, it should be o-chloronitrobenzene. But no, carbon atom numbering starts from the group to which chloro group is attached.

Is it the fact that chlorobenzene forms ortho-para substituted product and it is named accordingly or according to some IUPAC rules?


texts: Why does bond length decrease with increased basis set quality for SCF methods?

texts:
From Reviews in Computational Chemistry Vol. 5, for $\ce{H2O}$ using HF, MP2, CCSD, and CCSD(T), all lengths in angstroms:

$$
\small
\begin{array}{rcccc}
\text{Basis}  & \text{HF} & \text{MP2} & \text{CCSD} & \text{CCSD(T)} \\
\hline
\text{STO-3G} & 0.989 & 1.013 & 1.028 & 1.028   \\
\text{3-21G}  & 0.967 & 0.989 & 0.993 & 0.994   \\
\text{DZ}     & 0.951 & 0.979 & 0.979 & 0.980   \\
\text{6-31G*} & 0.947 & 0.969 & 0.969 & 0.971   \\
\text{DZP}    & 0.944 & 0.963 & 0.961 & 0.962   \\
\text{TZ2P}   & 0.941 & 0.958 & 0.956 & 0.959   \\
\text{Experimental} & 0.957
\end{array}
$$

In case one is skeptical due to effects from the lone pairs and the changing bond angle, here are results for $\ce{BH}$ using Hartree-Fock:

$$
\small
\begin{array}{rc}
\text{Basis}  & r_{e} \\
\hline
\text{cc-pVDZ} & 1.235950 \\
\text{cc-pVTZ} & 1.222062 \\
\text{cc-pVQZ} & 1.220306 \\
\text{cc-pV5Z} & 1.220010 \\
\text{cc-pV6Z} & 1.219877
\end{array}
$$

and for $\ce{LiH}$ using Hartree-Fock:

$$
\small
\begin{array}{rc}
\text{Basis}  & r_{e} \\
\hline
\text{cc-pVDZ} & 1.619017 \\
\text{cc-pVTZ} & 1.607865 \\
\text{cc-pVQZ} & 1.605530 \\
\text{cc-pV5Z} & 1.605519
\end{array}
$$

Going on the NIST CCCBDB and looking at calculated geometries, I cannot find a counterexample, at least when considering only HF, as adding dynamic correlation introduces an effect to counterbalance this bond shortening, since electrons can then properly repel each other to levels beyond the mean-field approximation, and DFT offers no insight beyond HF here.

One potential reason that doesn't receive much attention is intramolecular BSSE, where one part of a molecule borrows the basis functions from another. However, in the case of my calculations, I would argue that only cc-pVDZ could be considered a "deficient" basis, and the trend is still seen when leaving it out. I also believe that this is more plausible for molecules with distinct "domains" that can interact with each other, like one amino acid in a peptide forming a hydrogen bond with another AA, etc.

The current rationale I have is that as the basis set becomes more complete, and functions with higher angular momentum (polarization functions) are included, the overlap between the atomic wave functions is increased. This increased overlap results in higher electron density in the bonding region, which strengthens it, causing it to become shorter, like going from ethane to ethene to ethylene.

Specifically, I'm looking for a literature reference where an explanation is given for the phenomenon, not just examples with or without comparison to experiment.


texts: Is the analyte included in the ionic strength equation?

texts:
I don't quite understand the calculation for ionic strength of a solution. The formula includes the concentration and charges of the ions in solution, however, is the analyte (whatever we're trying to analyze) also supposed to be incorperated into the ionic strength equation?

If so, how would we include it if the analyte has an unknown concentration (which we have to figure out, using equilibrium and ion activity)?


texts: Why are Grignard reagents nucleophiles and not ambiphiles?

texts: The way I see it, the -R (alkyl part) obtains a negative charge and the MgX obtains a net positive charge on bond dissociation. So a nucleophile and an electrophile both are obtained simultaneously. So why is Grignard reagent a nucleophile and not an ambiphile? Where am I wrong?


texts: Hydrogen bonding relating to molecular orbital theory

texts:
In [1, p. 232] here is an explanation of how alcohols hydrogen bond to each other and I do understand how the alcohols form hydrogen bonds to each other:

FIGURE 6.15 Water and alcohols are both Brønsted acids and Brønsted
bases. This figure shows hydrogen bonding between molecules of water $(\ce{R=H})$ and alcohols.

Is it possible to think of hydrogen bonding as a Lewis Acid-Base reaction rather than just a Brønsted Acid-Base reaction, and, by extension, think of this whole scheme as a HOMO-LUMO interaction?
Like, can I think of hydrogen bonding as a HOMO-LUMO interaction in general, arising from the idea that it can be classified as a Lewis Acid-Base reaction?
References

Jones, M.; Gingrich, H. L.; Fleming, S. A. Organic Chemistry, 4th ed.; W.W. Norton: New York, 2010. ISBN 978-0-393-93149-5.


texts:
Why is the $\ce{F-F}$ bond relatively weak? And why does bond strength decrease from $\ce{Cl-Cl}$ to $\ce{I-I}$?

Does this have anything to do with "lone-pair" repulsion on the rather small $\ce{F-F}$ molecule? I haven't asked my professor but I'm suspecting this is going to the first thing on his mind. I'm sure that many of you here will have rebuttals to this argument.

On the other hand does $\ce{F2}$ even have lone pairs? There are no non-bonding orbitals populated on the molecular orbital diagram of fluorine. I wouldn't expect there to be any non-bonding orbitals populated either, as this is a simple diatomic we're dealing with and the atoms involved are identical ... so each atom's orbital should be able to interact with the other atom's orbital effectively.


texts: How does one optimize the molar concentration of electrolyte in terms of the rate of electrolysis?

texts:
There are many textbooks/recipes for various electrolyte solutions in the electrolysis of water. I know there is a minimum voltage to kick off electrolysis, and I'm supposing a minimum concentration of electrolyte like $Na_2SO_4$.

But isn't there an optimum concentration of electrolyte that maximizes the rate of electrolysis? Are these recipes based on that optimum, and if so how can one calculate what that would be for any given salt or liquid electrolyte?


texts: Can heteroatoms with lone pairs be chiral centres?

texts:
If a compound has a carbon atom with four different groups covalently bonded to it, it is called asymmetric and enantiomers of the compound can exist.

But imagine if one has a different central atom, such as a nitrogen or a sulfur where one of the four "groups" is an electron pair (see examples below).

Would such a thing still behave like a "normal" asymmetric carbon? If not, how else does it behave, i.e. are there enantiomers? Is my assumption that those will still have $\mathrm{sp^3}$ hybrid orbitals wrong? I would also enjoy pointers to literature, I was unable to find any.


texts: Problem in the calculation of ionic strength of a solution

texts:
Recently I've been trying to answer the question 10-13 (c) of 9th edition of  Fundamentals of Analytical Chemistry of Skoog et al. Comparing my answers with the student manual , I realized that my numbers didn't agree to the amount of $\mu$ of solution calculated by the book.
Here's the full question:

Use activities to calculate the molar solubility of $Zn(OH)_2$ in the solution that results when you mix 40.0 mL of 0.250M $KOH$ with 60.0 mL of 0.0250M $ZnCl_2$.
(Available information : $K_{sp}$ $Zn(OH)_2$ = $ 3\times 10^{-16}$ , $\alpha_{Zn^{+2}}$ = 0.6 nm , $\alpha_{OH^{-}}$=0.35 nm , $-\log\gamma_x=\frac{0.51{Z_x}^2 \sqrt{\mu}}{1+3.3\alpha_x \sqrt{\mu}}$)

I'm not looking for the full answer. I'm okay with the whole provided answer except with $\mu$.  To be brief the final solution should contain $[K^+]=0.1M$ , $[OH^-]=0.07M $ , $[Cl^-]=0.03M $ , $[Zn^{+2}] \approx 0 M$.
Then
the manual says : $\mu = {1\over 2 }{(0.1 \times 1^2 +0.07 \times 1^2 + (2) \times 0.03 \times 1^2) }$ which means $\mu = 0.115$  . From that, the solubility is found to be 2.8 $\times$ $10^{-13}$ M
From my point of view:
$\mu={1\over 2 }{(0.1 \times 1^2 +0.07 \times 1^2 + 0.03 \times 1^2) }$
Therefore $\mu=0.1M$ and finally Solubility = 2.6302 $\times$ $10^{-13}$M.
I can not understand why we have to multiply the corresponding portion of $Cl^-$ by two (In the parenthesis). Is the book making an error or am I missing something ?
According to the ending pages of the book the answer is 2.8 $\times$ $10^{-13}$ M and not 2.6302 $\times$ $10^{-13}$M. Please be aware that the differences do not result from approximations.


texts: How to calculate the concentration of conjugate acid from given pH and pKa values?

texts:
Preface: Buffer solution (acid-base buffer). I am provided with a weak base, which I will designate B. $\mathrm{p}K_\mathrm{a}$ for $\ce{B}$'s conjugate acid, which I will designate $\ce{BH}$, is $8.1$, and its mole weight (sic) is $121.1$. I'm assuming the latter is the molar mass, though I don't know how that helps me solve this problem.

  Problem: $\pu{0.1 M}$ ($\pu{mol/L}$) of $\ce{B}$ was dissolved in $\pu{1.0 L}$ water, then titrated to $\mathrm{pH}$ $8.1$ and $7.5$. I am to assume no change in volume.

The last statement sounds like an odd assumption to me, how do you titrate something without [significantly] altering the volume? I always assumed titration is only done by adding a liquid to another liquid, is this not correct?

I am to find the concentration of $\ce{BH}$ at $\mathrm{pH}$ $8.1$ and $7.5$.

This question looked really easy to me at the first glance, but after a few hours I realized I had no idea on how to go about this.

I've tried calculating the equilibrium concentrations and going from there. This just ends up in $x \neq x$ in my calculations (where $x$ is the concentration of some substance), which obviously doesn't hold.

I've used the acid dissociation-, base dissociation- and Henderson–Hasselbalch equations, but nothing seems to do the trick. I might not be the brightest person to have grazed the surface of the planet, but I'm confident that I've got a firm grasp on elementary arithmetic.

The answer is provided, and should be $\pu{0.05 M}$ at $\mathrm{pH} = 8.1$.

I would highly appreciate somebody showing or explaining the thought process to me.


texts: Stability of the alkenyl and phenyl cations

texts:
One reason often cited for why alkenyl and phenyl halides do not undergo nucleophilic substitution by the $\ce {S_N1}$ mechanism is that the formation of the alkenyl and phenyl cations involve a prohibitively large activation energy since they are rather unstable. In fact, this reason has been discussed in various posts on this site; see for example, here and here. Recently, I chanced upon some calculated energies for these cations in the gas phase and it seems to suggest that they are not as unstable as various textbooks and educators claim. The following table is taken from p. 300 of Carey and Sundberg (2007):

From the data above, we clearly see that the alkenyl carbocation is more stable than the primary carbocation although still significantly less stable than the secondary carbocation. Perhaps, we should be cautious when we discuss the stabilities of these carbocations because some sources seem to suggest that these alkenyl carbocations are so unstable that they are even less stable than primary carbocations. One thing that is consistent with most sources that the phenyl carbocation is the least stable of the lot.

There seems to be a cut-off point of stability, after which the $\ce {S_N1}$ reaction proceeds with much difficulty. This "cut-off point" seems to be between the stability of the alkenyl carbocation and the secondary carbocation. Is my interpretation correct?

Reference

Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry Part A. Structure and Mechanisms (5th ed.). Springer, 2007.


texts: Heat transfer with surroundings: why considered reversible?

texts:
I do not understand how the fact that the surroundings are large makes heat transfer with them reversible? I understand that the temperature of the surroundings is not going to change in the limit, but what about processes in which there is a definite temperature gradient with the system, such as a highly exothermic reaction?

I was sure that this question had already been asked somewhere on Stack, but I can't find anything similar – if you know of one, I would really appreciate if you could refer me to it.


texts: Is it possible for halogens to show oxidation states less than -1?

texts:
Halogens like $\ce{Cl,Br,I}$ generally show oxidation states between $-1$ and $+7$. However, is it possible that they can show an oxidation state beyond $-1$ (e.g. $-3$)?

I was thinking of some compound in which chlorine is bonded with a less electronegative element and forms more than one bond with such element(s).

Is it theoretically possible?


texts: Why are chlorides, sulfates, and bicarbonates of Ca and Mg solely responsible for the hardness of water?

texts: When soap is dissolved in water - irrespective of the anion - $\ce{Ca^2+}$ and $\ce{Mg^2+}$ form precipitates. Why are just chlorides, sulfates, and bicarbonates the only specie considered as "hardness" in water?


texts: Direction of electron density in p orbitals

texts:
$\mathrm{s}$ orbitals are spherically symmetric while $\mathrm{p}$ orbitals are not. For Boron, the electronic configuration is $\mathrm{1s^2 2s^2 2p^1}$.

In which p orbital does the most energetic electron lie? Is it $\mathrm{p}_x$, $\mathrm{p}_y$ or $\mathrm{p}_z$? Since all the three are degenerate, how does the electron decide which orbital to occupy? If it occupies any of the one orbitals, is a neutral atom not spherically symmetric? Or does the electron keep changing between $\mathrm{p}_x$, $\mathrm{p}$ and $\mathrm{p}_z$ rapidly (or in a superposition of occupying all the three orbitals at once with the probability of finding in any one of the orbitals equal to $1/3$)? The same question can be asked for $\mathrm{d}$ and $\mathrm{f}$ orbitals.


texts: Can diamond undergo a self sustaining combustion reaction all the way to carbon dioxide?

texts: I know charcoal can smoulder in an incomplete combustion to produce carbon monoxide so I assume diamond also can. If it's heated to a sufficiently high temperature, will the reaction produce enough heat to sustain the full combustion reaction all the way to carbon dioxide even in air that's only 21 °C. If so, does the reaction of carbon monoxide with oxygen occur fast enough to be perceived as smouldering or does it occur slowly enough to be perceived as flaming combustion?


texts: Is there a similar characteristic of the lanthanide contraction in the other transition metal groups?

texts:
Basically, does the lanthanide contraction also occur with the 4d, 6d groups as well? I am at a lack of understanding in this topic, I am just wondering what specific elements does this jump in a lower atomic radii occur. It seems to happen due to the d orbitals being occupied? I am making that judgement based on this graph.
I am hoping someone can explain, as one orbital seems to make all the difference.


texts: Is the carbanion formed in benzyne mechanism non-planar?

texts: I was told by my chemistry teacher that the carbanion formed in the picture above is non-planar. I don't understand why. It looks like benzene with an extra electron pair at one of the carbons so shouldn't it be planar?


texts: Is the term "heteroatom" reserved for exclusive elements?

texts:
From my experience, typically in organic chemistry, the implication of "hetero-atom" in some molecule is understood as B, N, O, S, P or a halogen -- or any nonmetallic element, perhaps.

If one describes a nanostructure that contains inorganic and organic ligands (like metal-organic frameworks), is it safe to describe the metals as heteroatoms? Or should the term be reserved for covalent-type atoms only?

For example, is this an acceptable statement?

  Snurr and co-workers showed results for simulated H$_2$ sorption in a
  variety of rht-MOFs containing only carbon and hydrogen in the
  linkers, as originally these MOFs did not contain heteroatoms
  other than oxygen and the metal.


texts:
We have an evaporative cooling system here at the power plant that uses city water.  The water is pumped up and cascades down across a filter media cooling the intake air to the gas turbine.  This is a recirculating system but a certain amount of the water is blown down continuously to a floor drain.  The water goes through the floor drain system to an oil-water separator then to a collection sump.  The water is then pumped out to the city sewer system.  There are pH monitors in the discharge to the city sewer.

When ever the evaporative cooling system is in operation we have a problem with the discharge pH meters going low on pH causing alarms.  It only happens when the pumps are off and the water is sitting stagnant in the wet loop where the pH meter probes are located.  Over time the pH will drop from around 7.5 down to a reading of around 6 which brings in the alarm.  If we recirculate the sump water through the line the pH will go back up to match the sump pH but once the pumps are turned off the pH will start to slowly drop again till the alarm comes back in.  Again, this only happens when the evaporative cooling systems are in service.

My question is could the drop of pH be caused by CO2 being dissolved into the water as the air is being draw across it in the filter media then coming out of solution and turning to carbonic acid as the water sits stagnant in the pipe where the pH probes are located?  It is definitely not an instrumentation error but we are at a loss to explain why this happens.

Thank you for your help.


texts: Atomic orbitals: how is bond strength related to stability, energy, bond length?

texts:
I have a lot of confusion regarding atomic orbitals and I don't know if what I am having in mind is even correct or not.

The bond dissociation energy of H-H is greater than that of Cl-Cl and as far as I can make out, it is because in H-H, there is an s-s overlap whereas in Cl-Cl, there is a p-p overlap. Because s-s is more compact, therefore more energy is required to break the bond.

Assuming what I wrote above to be correct, this means an s-s bond is stronger than p-p bond. But then, bond strength of p-p is more than that of s-s because of greater extent of overlap.

So there is definitely something/everything wrong in what I am thinking.

In short, how is the bond strength related to other things like stability, energy, bond length (bond length of s-s < s-p < p-p?).

Kindly help because I cannot find any of my queries anywhere else.


texts: Approximating entropy change in a reaction using Arrhenius equation

texts:
Recently my teacher finished teaching the chapter Chemical kinetics in which I have gone through Arrhenius equation.Can we estimate the change in entropy using it? I have done my calculation, considering the reversible reaction, $\ce{A <=> B}$ which has forward and backward rate constants $\mathrm{k_f}$ and $\mathrm{k_b}$ with pre-exponential factors $\mathrm{A_f}$ , $\mathrm{A_b}$ with activation energies of $\mathrm{E_f}$ and $\mathrm{E_b}$ respectively.
According to Arrhenius Equation,
$\mathrm{k_f= A_f.e^{-E_f/RT}}$ and
$\mathrm{k_b=A_b.e^{-E_b/RT}}$
$\mathrm{ k_f/k_b = {A_f/A_b}.e^{{-E_f+E_b}/RT}}$
and $\mathrm{k_f/k_b}$ = $\mathrm{{A_f/A_b}.e^{-\Delta H^0/RT}} $
$\mathrm{k_f/k_b}$=$\mathrm{k_{eq}}$=$\mathrm{e^{-\Delta G^0/RT}}$
but, $\mathrm{\Delta G^0 = \Delta H^0 - T \Delta S^0}$
which gives $\mathrm{\Delta S^0 = Rln(A_f/A_b)}$
Will the final expression give an approximate value of change in entropy of reaction?


texts:
I have read that Latimer diagrams can be represented both in an acidic medium (pH = 0) and in a basic medium (pH = 14).

I would like to know how to calculate the reduction potentials as a function of pH. That is, if I know the reduction potential for the pair $X^{+}/X$ at pH = 0, calculate it for another pH.

I thought the Nerst equation could be applied, but I'm not sure about that.


texts: How can I convert lidocaine HCL to lidocaine base

texts:
So I'm a hobbiest, no pro.  I've got a formulation for a topical anesthetic I'm trying to mimic.  It calls for lidocaine, ethoxydiglycol (aka. diethylene glycol monethyl ether) and a couple of oils.  I've got Lidcaine HCL, and I've read that Lidocaine HCL is soluble in water, but not soluble in ether.  Based on that, I'm concerned I won't be able to mix my Lidocaine HCL with the ethoxydiglycol. Similarly, I've read that Lidocaine base is soluble in ether, but not water.  Since the formulation calls for ethoxydiglycol (aka. diethylene glycol monethyl ether), I assume what I need is Lidocaine base instead of the Lidocaine HCL I've got on hand.

To get around this.  I'm planning to dissolve the Lidocaine HCL in distilled water, then add baking soda to it until the PH drops low enough for Lidocaine base to precipitate.  After that, I plan to filter the whole thing through a coffee filter, rinse with more distilled water, then evaporate the water off.  I'm hoping this will yield pure Lidocaine base that I can work with.

So, here are my questions:

Will it work?
Are their any caveats I should know about?

Thanks for your help!


texts: Do 2-hexyne and hexa-2-yne mean exactly the same thing? If so, what is the purpose of having two naming conventions?


texts: Why does lattice enthalpy decrease with increasing ionic size?

texts:
Lattice enthalpy decreases as ions get larger, but I have found two explanations:

The charge density is greater in smaller ions, so greater attraction
The ions are themselves able to get closer together, so greater attraction

Do these two explanations relate in any way? What would be the best explanation?


texts: Which molecule is more acidic: CHF3 or CHBr3?

texts:
I know that fluorine is more electronegative than bromine. However, because of the size of bromine, it is more stable with a negative charge. In the case of $\ce{HF}$ vs. $\ce{HBr}$, to me, $\ce{HBr}$ is without a doubt the stronger acid. When it comes to comparing $\ce{CHF3}$ with $\ce{CHBr3}$, we are supposed to compare the stability of their conjugate bases.

In $\ce{CF3^-}$, the fluorine can hold the electronegative charge quite well. It also exerts a strong inductive effect.

In $\ce{CBr3^-}$, the bromine is less electronegative than the fluorine but is more polarizable, so I think it can hold the negative charge more efficiently.

With this understanding, I am concluding that $\ce{CBr3^-}$ is more stable which would mean $\ce{CHBr3}$ is the stronger acid. However, I've been told otherwise.

I'm aware that the $\ce{C-Br}$ bond length is longer than the $\ce{C-F}$ bond length. I'm wondering if that short bond length causes $\ce{CF3^-}$ to be more stable than $\ce{CBr3^-}$. If this is true, is it okay for me to think about $\ce{CF3^-}$ dissociating vs. $\ce{CBr3^-}$ dissociating? In that scenario, I believe $\ce{CBr3^-}$ dissociates more easily than $\ce{CF3^-}$, meaning $\ce{CF3-}$ is more stable.

Note: This logic wouldn't apply to the instance of $\ce{HO-}$ vs. $\ce{HS-}$ because $\ce{HS-}$ is more stable than $\ce{HO-}$ (even though $\ce{H-O}$ bond length is shorter than $\ce{H-S}$ bond length).


texts: Can rate constant depend upon the concentration of reactants (or other species involved in the reaction)?

texts:
Transition state theory tells us that the rate constant of an elementary step is $$k_\mathrm{r} = \frac{\kappa k_\mathrm{B}T}{h}\exp\left\{\frac{- \Delta G^\ddagger}{RT}\right\},$$
where $\Delta G^\ddagger$ is the activation free energy of the step, i.e. the difference between the Gibbs free energy of the transition state and the reactant state.
Then the rate law would be $$r = k_\mathrm{r}[A]^a[B]^b[C]^c\dots,$$
where $A$, $B$, $C$, ... are all the reactants that come together in that elementary step. So far so good.
But I have come across reactions where changing the concentration of a reactant (by a large amount) in a multi-step reaction seems to change the rate determining step of the whole reaction.
The explanation offered was that changing concentration changed the Gibbs free energy of the reactant or intermediate states (as Gibbs free energy depends on the concentration in solution). The states which contain the species (whose concentration  is changed) are affected whereas others are not, so the Gibbs free energies of activation are changed, which means the rate constants are changed, which can change the rate determining step.
But if concentrations can affect $k_\mathrm{r}$ then it seems like the rate law cannot be written like that.
Does this sound right, or am I overthinking this?


texts: Will an acyl chloride be attacked by water molecule to form carboxylic acid?

texts: $\ce{H2O}$ molecules can act as a nucleophile. So it should attack the carbonyl carbon. However, I think that that when the $\ce{O-}$ "kicks back" it will once again remove the water molecule keeping the $\ce{Cl}$ intact as water is definitely a better leaving group. But in my book they showed a reaction intermediate, which involved an acyl chloride and they used water molecule as a nucleophile to convert acyl chloride to carboxylic acid. I'm confused as to how that is possible? Isn't water a better leaving group than $\ce{Cl-}$ ?


texts: Effect of solvent polarity on SN1 reactions of different charge types

texts:
On the topic of the ionisation mechanism (i.e. $\mathrm{S_N1}$), Carey & Sundberg (2007) discuss the effect of polarity of solvent on the rate of $\mathrm{S_N1}$ reactions of different charge types (p. 392). It is well-known that the rate of $\mathrm{S_N1}$ reactions are increased by the use of polar, protic solvents. Hence, the energy profile diagram shown in a is no surprise. This is type of $\mathrm{S_N1}$ involves the initial ionisation step $\ce{RX -> R^+ + X^-}$ and it is typically seen.

However, the energy profile diagram shown in b is less straightforward. The reaction that it describes has the first ionisation step as $\ce{RX^+ -> R^+ + X}$. In the caption, it is written:

  Polar solvents decrease the rate because stabilisation of the [transition state] is less than for the more polar reactant.

Firstly, I would like to ask if "decrease the rate" here means that this type of $\mathrm{S_N1}$ reactions occur more slowly in polar solvents compared to in nonpolar solvents. If we look at the activation energy $E_\mathrm a$ and assuming they are relatively drawn to scale, then we can conclude that for such reaction type, the rate would be faster in nonpolar solvents since it has a comparatively smaller $E_\mathrm a$.

Actually, we do notice that the TS is still lower in energy for the polar solvent, which is logical since although it may be less charged overall, the TS is nevertheless charged and would obviously be stabilised by a polar solvent.

Finally, I would like to ask if the reason why this type of $\mathrm{S_N1}$ reactions proceed faster in nonpolar solvents because, the charged reactants $\ce{RX^+}$ are in fact stabilised in polar solvents to a much greater extent compared to in nonpolar solvents. Thus, the $E_\mathrm a$ in polar solvents is thus much larger. This point was not discussed in the text and it is purely my deduction. Could I confirm that it is a correct interpretation?

Reference

Carey, F. A., & Sundberg, R. J. (2007). Advanced Organic Chemistry Part A. Structure and Mechanisms (5th ed.). Springer.


texts: Chemical Composition of NMC cathode in lithium ion battery

texts:
I am working with lithium ion batteries having the cathode material as NMC i.e. LiNixMnyCozO2, wherein x + y + z = 1. The proportion of Nickel, Manganese and Cobalt in the cathode varies, but mostly Nickel is either equal to or greater than the amount of Manganese and Cobalt in the cathode (for example NMC-111, NMC-532, NMC-622, NMC-811 are the commonly reported chemistries in literature).

I tried doing Energy dispersive X-ray spectroscopy on the surface of my battery cathode to find out the proportion of Nickel, Manganese and Cathode. The results I obtained were: Ni - 20%, Mn - 20%, Co - 60%. I repeated the EDXS procedure at ten different locations on the battery cathode and still got the same results with 1% error in the values. This result is far from what I expected and I suspect the reason for this is that I am scanning only the surface of the cathode.

So I have two questions regarding this:

1) Should I expect the EDXS results to be different and correct if I perform it on the cross-section of my battery cathode?

2) What are other cheap techniques which can get me the elemental composition of the cathode? One of my friends suggested me ICP-MS (inductively coupled plasma mass spectrometry), which is way too expensive for me.


texts:
This question is not very mighty. But I'm having a problem wrapping my head around the Bohr's atomic structure. The textbook says electrons revolve around the nucleus in fixed energy shells, with each shell having its different value for energy. What I want to know is, what does it mean for a shell to have an energy level? Where does the electron get the energy to revolve around the nucleus from? And when the electron jumps from a ground state to other shell, after gaining energy, why does it have to return to its original shell? I mean it has satisfied the criteria of going into the next shell, so why does it return.

And my main concern is the energy part. Where does electron get the energy to revolve in a shell.

If possible, please refer me a source to study this in depth.


texts: What does the symbol ϕ mean in skeletal formulae?

texts: I was given this formula by my A-level teacher and was curious as to what it means. It seems to be the Greek letter phi. I have searched online and have not been successful. Any help would be greatly appreciated.


texts:
I am a student of grade 11. I am learning about resonance phenomena. I am a beginner with this and I am a bit confused about this. I wished to know whether atoms in resonance hybrid (not resonating structure) have complete octet or not. For eg in the resonance hybrid of the following resonating structure:-

If not, then does it gain stability by resonance or something else?
I request you to please help me.


texts: Do I need to include calcium chloride in this reaction equation?

texts:
Yesterday I titrated a solution of calcium hydroxide in aqueous calcium chloride with $16.7~\mathrm{mL}$ of $\ce{HCl}$. More specifically, I took $25\ \mathrm{mL}$ of the calcium hydroxide in aq calcium chloride and mixed it with $25~\mathrm{mL}$ of deionized water and 3 drops of an appropriate indicator. I wrote the reaction equation as

$$\ce{Ca(OH)_2 + 2HCl -> CaCl_2 + 2H_2O}$$

But do I need to somehow take into account the aqueous calcium chloride in this equation? I know that it affects the molar solubility of the calcium hydroxide during titration but I'm not sure if this should also change my reaction equation.


texts: Decomposition through thermolysis, electrolysis, photolysis

texts:
What decides whether a compound will dissociate (break-up) under thermal decomposition or photolysis or electrolysis i.e if I am provided with a compound and I'm asked to dissociate it then how will I get to know that it would dissociate under thermal decomposition or photolysis or electrolysis.

Please try to provide an easy-to-understand as I'm in just 10th grade


texts: How does dehydration of an alcohol occur in alkaline medium?

texts:
During aldol condensation reaction the aldol formed reacts further to give alkene (which is probably called enone)

I am really struggling with this part of the reaction as my textbook says nothing about the mechanism of this particular step
the medium during aldol condensation reaction is alkaline but the end product is a dehydrated product and the conversion of alcohol into alkene is dehydration. Do we need to make the medium acidic at later stage of reaction, or does some mechanism causes dehydration in alkaline medium?

Also please suggest if there is some other reaction, or examples depicting similar phenomenon that I could go through for better understanding

(I am really new to chemistry as well as to asking questions. thank you)


texts:
From a description of my experiment:

  Potassium iodide crystals are place in the middle of filter paper soaked with potassium sulphate and phenolphthalein. Two electrodes are placed on the filter on two opposite sides. The electrodes are connected to a battery. The objective of this experiment is to see the movement of ions.

Why soak the filter paper in potassium sulphate and not just soak it in potassium iodide?


texts: Role of pH in azo C-coupling reaction, continued

texts:
In the question, "What is the role of pH in azo coupling reaction of diazonium with phenol and aniline?" asked by @DhrubaBanerjee and answered by @Klaus-DieterWarzecha, I find several ends untied. I considered starting a bounty on the previous question, but since my question is looking for slightly more specificity than just looking at the whole picture, I decided to ask a separate question.
That post discusses why azo coupling of aniline is conducted in acidic medium. However, I am not convinced of a few things.
My query is twofold:

The $\ce{-^+NH3}$ group is inductively deactivating (as mentioned here). That is a turn-off for attacks on electrophiles (like a diazonium cation). But why is the protonation of aniline preferred?

In the case of aniline, the lone pair on the nitrogen atom is the preferred centre for the reaction with the diazonium cation:

This isn't what we want! Protonation of aniline avoids this side reaction.

I do agree with Klaus-Dieter Warzecha that an alkaline $\mathrm{pH}$ would lead to azo N-coupling, but if we were concerned about the electrophilic attack occurring from the nitrogen atom, in my opinion, it should have been acylated at $\ce{N}$, leaving no room for side reactions but also keeping the ring activated (although less than before). I believe the yield would be higher.

If an equimolar mixture of Aniline and Phenol was added to a reaction vessel containing benzenediazonium chloride in acidic medium, would the major product be phenol's couple product or aniline's couple product?

This Wikipedia article states that phenol's coupling is base-catalyzed. I assume it accelerates the reaction by assisting the formation of phenolate ion. Going by that, the aforementioned conditions will be less favorable for phenol's coupling.
But I find it hard to take in that a protonated aniline could couple faster than phenol. Phenol would still be capable of coupling (only unaccelerated), while aniline should have been weakened by the deactivation.
Hence I would choose phenol to form the major product. I wish to know if my reasoning is correct or not, and if not, an explanation.
I would greatly appreciate any constructive discussion/specific answers.


texts: In many sites I see that they take $\ce{C}$ with valence 4, bur our teacher takes it with valence 2. With what valence should I take $\ce{C}$?


texts: why we can use the equipartition theorem for translational motion of molecules at room temperature and above because quantization is unimportant

texts:
From the book Chemical Principles The Quest for Insight, 5th Edition by Peter Atkins, Loretta Jones

The equipartition theorem is a result from classical mechanics; so we can use it for
translational and rotational motion of molecules at room temperature and above, where
quantization is unimportant.

I know quantization describes that photons, separate "packets,"are what energy is thought to happen in a subatomic level. However, I don't how quantization is related here: because quantization is unimportant, we can use it for translational and rotational motion of molecules at room temperature and above? and also why quantization is unimportant here? I believe translational and rotational motion of molecules happen in a subatomic level. Moreover, why can't we use the equipartition theorem for vibrational motion?


texts: A dataset of drugs or molecules that failed the FDA approval process

texts:
I am looking for a dataset of bad drugs, the opposite of FDA approved drugs.
There is this database of withdrawn drugs, but these drugs were withdrawn after making it into the market.
Is there any such dataset of drugs that failed the FDA approval process because of their toxicity or poor pharmacokinetics properties?


texts: How to identify whether a molecule is planar

texts:
While solving for plane of symmetry of molecules I came across 1,3-dichlorocyclobutane (1) and I realized it does not have any plane of symmetry because we don't know whether hydrogen and chlorine are in same plane. How to judge which plane do the substituents belong to?
Similarly for compound 2, but in compound 3 it is known that both the planes of the rings are perpendicular. Is there some kind of rule for it?
<img src="https://i.stack.imgur.com/4iFNg.png" alt="1: 1,3-dichlorocyclobutane; 2: 2‐[(2E)‐1,3‐oxathietan‐2‐ylidene]‐1,3‐oxathietane; 3: 2‐[(P)‐1,3‐oxathietan‐2‐ylidenemethylidene]‐1,3‐
oxathietane" />


texts: What happens to chromium (as Cr2O7-) in the plasma of the ICP?

texts:
I have recently been analyzing some biological samples for chromium using a standard Cr(VI) solution for external calibration.

Cr standards are typically supplied in a 2% nitric acid matrix. That concentration corresponds to a pH of 0.44. Under that pH, most species of Cr would have oxidized into the form of $\ce{Cr2O7-}$ or $\ce{CrO4-}$; yet in literature, all measurements carried out on ICP-MS for Cr have been in the +1 oxidation state.

Could this be from the rapid reduction from the free electrons in the argon plasma?


texts: Why would a solution of FeCl2 appear brown/yellow sort of like FeCl3?

texts: If we prepare a solution of $\ce{FeCl2}$ by dissolving solid $\ce{FeCl2}$ powder in water, supposing the bottle of $\ce{FeCl2}$ was left open for sufficient time, is it possible for $\ce{FeCl2}$ to have oxidised to $\ce{FeCl3}$? I can't find a suitable reaction for this excecpt one which includes $\ce{HCl}$ which was definitely not present when preparing the mixture.


texts: Computing i0 in the Butler-Volmer equation: How to interpret Wikipedia and Wolfram Alpha

texts:
So far, when using the Butler-Volmer equation, I had j0 given and could then just use I = A * j0 * [exp(...) - exp(...)], with A the electrode surface area.

Now I have a material from which I don't know j0 but just the rate constant. According to Wikipedia on exchange current density I can compute j0 as

Wolfram-Alpha on Butler-Volmer equation however says:

In this equation, the expression F * k0 would correspond to the above j0. k0 is explicitly defined as the rate constant in m/s on that same page.

Is Wolfram-Alpha wrong by missing out the concentration? The F * k0 does not even result in the units of a current density, and the whole expression will not evaluate as a current.


texts: How can endothermic reactions be spontaneous?

texts: If endothermic reactions absorb heat from the surroundings, how can they be spontaneous, if heat only flows from high temp to low temp objects?


texts: Is it possible to have anions of metals?

texts: I've been wondering if it is possible to have negatively charged metal ions. Most ions tend to have electron configuratons of noble gases. So then is it possible to obtain metal ions from metal atoms by changing their electron configuration to that of the next noble gas in the periodic table? (e.g. something like Be(6-))


texts: Spectrochemical series of TMs: why does the field-splitting parameter NOT steadily increase along a period?

texts:
Why doesn't the field splitting parameter increase steadily along the period for 3rd-row transition metals, as one would expect due to a better energy match between ligands and the metal as $Z_\mathrm{eff}$ increases?

The series is (in the order of increasing $\Delta$: $\ce{Mn^2+}, \ce{Ni^2+}, \ce{Co^2+}, \ce{Fe^2+}, \ce{V^2+}$ etc. Source: Spectrochemical series – Wikipedia, confirmed by Shriver and Atkins.

I would guess that this is to do with $\mathrm{3d}$ orbitals getting too contracted on the right of the period and, and hence, having a poorer size match, but I couldn't find this explanation mentioned anywhere.


texts: Please explain the shapes of the orbitals

texts:
For a lot of years, I had been believing that sphere was the most stable 3-dimensional shape. But after coming across the p,d and f-orbitals, I am unable to comprehend the fact that these orbitals have such crude shapes. Can we prove that these shapes(dumb bell and crossed dumb bell) are the regions in which the electrons would be most stable (No wave functions please. I am only in high school)?

P.S.: An intuitive answer would be much appreciated than a mathematical one.

P.S.S: This is not a duplicate question. I don't want to know how the shapes are like that. I know it is due to the probability functions, I want to know if it is just the rule of nature, or can we show it is because of stability.


texts: Why did Dalton assume that atoms are spherical?

texts: One of the primary components of Dalton's theory is to "express" an atom as an unbreakable spherical shape filled with whatever. The question is, why didn't he suggest any other shape, like for example, cubes?


texts:
Does "Mole of Iodine" or any other element that normally appears as diatomic molecules refer to a mole of single atoms ($6.02\times 10^{23}$ iodine atoms) or a mole of the molecules ($6.02\times 10^{23}$ molecules of $I_2$)?
EDIT: If there is no specification of moles of atoms or moles of molecules, what do I do? Do I default to one of them?
e.g. in this question

For the combustion of sucrose:
$\ce{C12H22O11 + 12O2 -> 12CO2 + 11H2O}$
there are 10.0 g of sucrose and 10.0 g of oxygen reacting. Which is the limiting reagent?


texts:
I was told that an atom's atomic number is defined as follows:

  The number of electrons or protons present in a neutral atom is called atomic number. It is represented by Z.

What does neutral mean here? Why isn't it just "..present in an atom..."?


texts: What do the subscripts 1/2 and 3/2 for the p-orbitals refer to?

texts:
What does $p_{1/2}$ and $p_{3/2}$ mean when referring to electron configuration?

I've seen sub shells and I'm assuming it has something to do with spin. I am asking this in regard to the  $8p_{1/2}$ and  $8p_{3/2}$ shells and the way they get filled at different energy levels?


texts: Are there ways to predict which chemicals will kill certain bacteria?

texts:
Are there ways to compute what chemicals kill a give bacteria but not another given bacteria ?
Does that help much to make medication ?


texts: Will washing child seat belt straps with baking soda and hydrogen peroxide make them unsafe to use?

texts: My friend is afraid to use the child seat for her next child.  She was told washing them with the solution weakened the fabric,  The straps weren't submerged, but they did get throughly wet.


texts: Reaction of a cyclic tertiary alcohol with chromic acid

texts:
We know that $\ce{H2CrO4}$ cannot oxidize tertiary alcohols. The mechanism is:

Now the ${\alpha}$ carbon does not have any hydrogen to proceed to next step. Therefore, this reaction would not occur.
Is there any possibility of dehydration due to acidic medium?


texts: Why do reactions of sodium halides with sulfuric acid produce sodium hydrogen sulfate instead of sodium sulfate?

texts:
In the reaction of sodium halides with sulfuric acid, sodium hydrogen sulfate is produced \eqref{NaHSO4}. Why would this be produced instead of sodium sulfate \eqref{Na2SO4}?
\begin{align}
\ce{NaX + H2SO4 &-> NaHSO4 + HX}\tag1\label{NaHSO4}\\
\ce{2 NaX + H2SO4 &-> Na2SO4 + 2 HX}\tag2\label{Na2SO4}
\end{align}

Is this because of lower energy requirement for this reaction compared to forming sodium sulfate?


texts: Raise the pH of a solution and prevent build up of carbonates

texts: I need to raise the pH of a solution so the easiest approach is to add alkali hydroxides (NaOH, KOH, etc). But as most of you know, the CO$\ce{_2}$ in the air can react with these hydroxides to form carbonates which usually  precipitate out the other metal ion dissolved in the original solution. So what else are my options?


texts: Radical Bromination of a 1-isopropyl-4-methylcyclohexane

texts:
I'm considering a problem whereby 1-isopropyl-4-methylcyclohexane with the indicated stereochemistry shown undergoes radical bromination at the indicated position. I understand there are other products produced. However, if the radical initiator (not shown) extracts the hydrogen at the 4 position, then the bromine radical attacks, there will be two distinct products. However, I am having trouble determining if these molecules are chiral? Are they diastereomers to each other?

Also, as a follow up, how would you name these (reagent + two products) to indicate their stereochemistry?


texts: Determining cation-to-anion radius ratio for "ideal" Anti-fluorite structure

texts:
My book under the heading of Anti-fluorite structure makes the following remark, about the radius ratio of an ideal Anti-fluorite:

  The ideal antifluorite would have a cation-to-anion radius ratio of $0.228$. However, the ideal ratio is not observed in the antifluorite structure, the observed ratio is higher than the ideal.

I do not understand why the ideal radius ratio should be $0.228$. It is clear that since the antifluorite structure has the smaller ion filled into the tetrahedral voids, radius ratio can range from $0.225-0.414$, with $0.225$ being the best fit for this type of void. It is however unclear as to why there is a difference in the ideal radius ratio for antifluorite structure and for the best fit of the tetrahedral void. It would be great if this is clarified. Thanks.


texts: What substances do humans consume that are caloric but neither protein, carb, nor fat?

texts:
On the Medical Sciences StackExchange site I asked Can a calorie be neither protein, carb, nor fat?
 and got a very helpful answer, which was that ethanol (in alcoholic drinks) is caloric but neither a protein, nor a carb, nor a fat.  I then asked a follow-up question as a comment: Where can I find a list of all such substances?  That is, substances that are caloric but neither protein, nor carb, nor fat.  The person who answered my question recommended I post the question to this SE site.


texts: Are there types of glue that are designed to be dissolved easily?

texts:
I've heard that some types of glue are easily dissolved.  For example, wood glue dissolves in vinegar and super glue dissolves in acetone.  This doesn't mean that wood glue or super glue were necessarily intended to be dissolved.

Are there types of glue/adhesive that are pretty strong and have a cheap solvent that is intended to remove the glue/adhesive later?


texts: Why does a protein crystallize with a specific salt but not with another?

texts:
So I am conducting an experiment and I do not understand this super fundamental part.
I know salting out works via solubility, and I know crystallization works via ordered structures. But could someone explain to my why one salt allows a crystal to form, but another salt doesn't. A component of one of my salts (Mg) has been found to be important to my protein in optimization and activity, but why would another cation with the same anion (I know the anion is not the problem) discourage the formation of crystals. If this is a clearly stupid question I apologize.

EDIT:looking for theory. I have already crystallized everything, and have CRYSTALS. Will be performing x-ray crystallography.This post was more to get me on the right track in thinking.


texts: Does pressure affect non-gaseous reactions?

texts:
Pressure holds a great significance when it comes to reactions involving gaseous species. Changing pressure can affect the kinetics and even mechanisms of such reactions.
However, does pressure hold any significance in reactions involving solid and liquid reactants only?

Examples, if any, would be appreciated.


texts: Gibbs Free Energy : What is it trying to say actually?

texts:
"Gibbs Energy is the useful work that can be extracted from the heat of a reaction or a thermodynamic process." I understand how it predicts the feasibility of a chemical reaction , considering the Entropy statement of the Second Law. But how does it relate with the useful work that can be extracted? (This definition is implicitly used in my textbook in deriving from Nernst Equation, the useful work that can be extracted from an electrochemical cell and I am missing the point why this actually works.) Is there an intuitive explanation? Also if this much of energy is "free", what happens to the energy that is "not free"? Why can't we extract the whole energy that is released?

Also I am interested to know if there is any direct relation between Gibbs Function and Kelvin-Planck Statement, which apparently expresses the inherent inability to convert the whole heat to useful work, or am I mixing up two very different aspects?
Thanks.


texts: Reaction of secondary alcohol with ammoniacal silver nitrate (Tollens' reagent)

texts:
What are the products of the reaction of 2-butanol with silver nitrate?

For the moment, I am a bit stumped as I only have $\ce{AgNO3}$ as an oxidizing agent to form a carboxylic acid from an aldehyde. Additionally, the lack of $\ce{H2O}$ indicates that this is not the reaction I should be looking for. The only reaction that seems feasible to me is an SN2 mechanism where the nitrate anion acts a nucleophile and the hydroxide ion as the leaving group.

Here is my proposed mechanism much in the style of Tollen's reaction with an aldehyde.


texts:
Consider an exothermic reaction. If we double the temperature at which the reaction is run, will the reaction quotient increase?

I know that an increase in Q relative to K causes the reaction to favor the reactants as the system tries to return to equilibrium.

If a reaction is exothermic, and we take heat to be a product, wouldn't an excess of heat cause the reaction to favor reactants?

The question I'm having trouble with is this one; apparently the answer is choice 2. I wonder if this is a typo or am I fundamentally misunderstanding something.


texts: What's the most complete basis set for calculating chemical shifts with DFT?

texts: I'm trying to benchmark some NMR chemical shifts. The literature suggests that the pcS-4 basis set will be the most accurate. I was wondering if there were any basis sets that are more complete than the Jensen basis sets? Even for just general basis sets. I'm looking for something similar to the Partridge basis sets, except for DFT.


texts: Why do we use dG < 0 to describe a spontaneous process?

texts:
With something like a reaction or phase change, all sources use the criterion that $dG < 0$ for the reaction to be spontaneous and then substitute an appropriate expression for $dG$ to the specific application. For phase change my book stats $(\mu'-\mu'')dn' < 0$ where $'$ is phase A and $''$ is phase B, $\mu$ is the chemical potential and $dn' > 0$ means gaining of molecules in phase A.

However, reactions require activation energy and phase change require nucleation (I think this is kind of like an activation energy); both of these processes require an increase in $G$ before a larger decrease. Why do we not use $\Delta G$ (between initial and final equilibrium states) instead?

Edit:

I am confused by the use of dG (a rate differential) as opposed to $\Delta G$ (a net change between end states) because I'm not sure how one would integrate this for say, a phase change, since it must pass through a potential barrier where G must increase. Is the integral just $G_2-G_1$ between the end states and thermodynamically the process ignores the barrier (since thermodynamics deals with equilibrium only)? A typical thermodynamic process I'm imagining is quasistatic compression, where we can get work from the integral of PdV and P is defined as it goes through an infinite number of equilibrium states; I'm not sure if it's possible to draw a parallel here for free energy and phase change/reacting systems.

Edit 2:

From this graph it looks like G increases then decreases to stable equilibrium after phase change. If we find dG/dr from this graph and integrate dG(r), should we get the same $\Delta G$ as from thermodynamics (before and after phase equilibrium)? If so, this seems to me like finding work of a rapid piston-cylinder compression of an insulated system; PdV is undefined since we are not passing through a set of equilibrium states but we can still find work from $\Delta U$. Difference is that in this case, our initial state is technically not in equilibrium/stable since the system favours a phase change, so we are beginning from a state that technically does not exist on the phase diagram (like if we have a supercooled/superheated liquid).


texts: Does the 3D conformation of rings affect chirality?

texts:
During the chirality analysis of various molecules containing rings, we assume for convenience that the rings are completely flat/planar and if the molecule has a plane of symmetry, it is achiral. However, does the fact that say, 6-membered rings actually exist in a chair or boat conformation have any effect on our final answer (it has a plane of symmetry if it is completely planar, but does not if it is in its 3D conformation)?
I'm a little confused because the odd, puckered conformation of various rings don't seem like they would have a plane of symmetry. Take for example, the molecule below. In the 2D drawing, we see 1 plane of symmetry, it goes through $\ce {Br}$ and cuts through the ring in a perpendicular fashion. However, in the 3D drawing, the plane we identified earlier doesn't seem like a plane of symmetry anymore.

Of course, in the 2D picture, the molecules would seem to be equivalent no matter if the bond were wedged or dashed, but why do they appear to be different if they are drawn in 3D?


texts: comparision between basic nature of CH3O- and -OH

texts:
when comparing the basic nature of $CH_3O^-$ and that of $OH^-$. I found two arguments. one favoring the more basic nature of $CH_3O^-$ and the other favoring the basic nature of $OH^-$. so which of them is true. and why isn't the other condition correct.
the conditions are as follows.

since $CH_3OH$ is a stronger acid when compared to $H_2O$, its corresponding conjugate base should be weaker. that is $CH_3O^-$ is a weaker base when compared to $OH^-$
since there exists a methyl group on the $O^-$ the electron density on $O^-$ increases hence it is a better base when compared to $OH^-$ since H doesn't have any +I effect /


texts: How would one correct for a blank in a potentiometric titration?

texts:
I want to do a potentiometric titration with perchloric acid of a sample consisting of active drug (weak base) and two other components. Based on theory, I already know that these two other components should not interfere with my titration.

However, I still want to do a blank titration with just these two components to make sure. What I would expect with this blank titration is just an exponentially decreasing curve. If this is indeed what I observe, would I have to correct my sample for this blank titration? If so, how would one do this?


texts: Why does delocalization lead to stability?

texts: If the electrons are relatively more stable when they are delocalized than when they are localized between two atoms, then why do we have bonds formed in the first place? Forming of bonds between two atoms means that electrons localized between the two atoms, if electrons tend to delocalize then why not all electrons (including the sigma bond electrons) are just delocalized? What is the driving force for delocalisation ? How does delocalisation the energy of the system?


texts: when do we consider the samples in a calorimeter as a solution in calculation?

texts:
I noticed some problems consider the samples in a calorimeter as a solution thereby calculating the mass of the combining samples, whereas in others I found that they separate the samples into different calculations by using the distinct mass and specific heat for each.

could you explain why?

Thanks|!


texts: Why do the names of most chemical elements end with -um or -ium?

texts: Why do the names of most chemical elements end with -um or -ium for both primordial and synthetic elements?


texts:
I have looked around and most of the sites suggest that bond angle of $\ce{OBr2}$ is greater than $\ce{OCl2}$ and it is explained by stating the electronegativity difference and looking at electron repulsion (VSEPR). However none of the websites actually give any experimental data so i am unsatisfied. I think that extent of back bonding would be more for $\ce{OCl2}$ and hence its bond angle should be greater.

Can someone please explain why i may be wrong and give experimental data on bond angle along with it?


texts:
According to the chemical formula $\ce{H−(O−CH2−CH2)_n−OH}$ of polyethylene glycol, or PEG, I assume that this organic compound has a long chain structure when it is dry and in powder form. (This is also what guys in the chemistry field say.)
But when PEG is dissolved in water, would it form some structure like a cluster or would it remain a long chain?
Can we somehow calculate the diameter of a dissolved PEG molecule when $n$ is given? Or the dissolved PEG molecules band randomly so there are no calculations for an average diameter statistically at all?


texts: Affinity to mobile or stationary phase during column chromatography

texts: I have carried a column chromatography and obtained two compounds. The first one is liquid (ester) and the second one is solid (nitro) yet I know that the second compound is less polar than the first one. Why does the result differ from the knowledge about polarity (the more polar the molecule is, the slower the compound)?


texts: Keeping the electronic configuration in the ground state is expensive in Ab-initio MD?

texts:
In E. Sandré & A. Pasturel's An Introduction to Ab-Initio Molecular Dynamics Schemes

  If using small time steps (typically in the order of a few tenth of femto-second), the changes in the electronic configuration is small enough so that convergence of the electronic configuration is easily achieved using a few conjugate gradient steps. However, the computational cost of dynamical simulation appears to be mostly due to keeping the electronic configuration in the ground state.

I don't understand this. DFT and HF are methods that can only give electron ground state. Since it is either DFT or HF that is used in Ab-initio MD simulations, then what does this excited state is referring to?

My understanding:

First of all, the number of electron orbitals calculated by either DFT or HF approach equals the number of electrons in the system, so we get no electronic excited state.

Under Born-Oppenheimer approximation, while varying the atomic configuration, the electrons are expected to stay in their ground state.
Since the validity of BO approximation dictates no abrupt change in electronic energy.

So, the reason of 'Keeping the electronic configuration in the ground state is expensive' is that when the atomic configuration changes in MD simulation, it is hard to make the electronic energy difference small.

Is my understanding correct?


texts:
I'm currently learning about corrosion prevention, and have a question regarding galvanising.

Say that you have an iron nail. You galvanise it (coat it in zinc), so that is doesn't rust by preventing water and Oxygen from reaching its surface. But then wouldn't the Zinc coating rust? What would be the point of galvanising an object when its coating is going to rust anyway?


texts: What is the accuracy of scf=qc when convergence criteria is lowered?

texts:
I am trying to run single point calculations with Gaussian 09 for a Mulliken population analysis on large graphene/graphite (940-1411 atoms) sheets/clusters.

I was having difficulty with memory issues (single CPU license) running DFTBA for single point calculations. I have stepped my convergence (beginning with conver=1, and increasing by reading in my previous checkpoint files).  I found my results oscillating and failing.

I decided to try scf=(qc,conver=5,maxcycle=500).  This worked, which concerned me.

It not only worked, but it worked much faster than my failed sp calculations.  I know Gaussian's old default convergence for single point calculations was N=4.  As my calculation was done in less than two hours compared to the days it was taking for DIIS, I have become concerned at the accuracy of the QC using conver=5.  I cannot find anything indicating my approach is bad, but also I cannot find anything syaing my approach should yield reasonable results.

Can anyone please tell me if this approach is reasonably accurate?


texts:
I did some undergraduate level Chemistry as part of my degree. It left me with the distinct impression that the polarity of water is responsible for its unusual phase properties: it's the only everyday substance that can exist in all three states under easily replicable conditions.

My daughter is learning about states of matter at school, and I thought this might be a fun "extra" for her homework, so I sat down to explain it to her. At which point I realised that I couldn't explain it myself. Polarity explains why water solidifies relatively easily, and why ice floats/expands - but I couldn't see/remember why it might have anything to do with transition into a gas.

So I taught her about phase diagrams instead, as a nice visual thing to take to class.

But it left me with the question: does water's polarity help explain its unusual phase properties? Or is it something else? Or are those phase properties perhaps not as unusual as I seem to remember?