texts: How can I define alkenes using graph theory?

texts:
I want to represent alkenes in a mathematical fashion but I want to make sure of what I'm writing. Here is what I tried by defining "alkenic" graphs:

Alkenic graphs are connected non-looped multigraphs where:

nodes are of degree less than 5 (octet rule);
there is at least a double edge and no triple or quadruple ones (edges like in bonds);
cyclic submultigraphs with conjugated single-double edges given in any conjugation order are to be considered isomorphic (anti aromatic or aromatic isomorphism).
For example, the graphs representing "1,4-dimethylcyclobuta-1,3-diene" and "1,2-dimethylcyclobuta-1,3-diene" are isomorphic.

In this case I'm not taking stereoisomers into account.


texts: Why are van der Waals' forces between gas molecules strong near its critical temperature?

texts:
My textbook says

  …easily liquefiable gases i.e. with higher critical temperatures are readily adsorbed as van der Waals' forces are stronger near the critical temperatures.

What I do understand is that at a temperature higher than the critical temperature $(T_\mathrm c)$ the gas molecules have higher kinetic energy which is why they're unable to form strong bonds.

But, what if the temperature is lower than the critical temperature? Or is my reasoning incorrect?


texts: How to determine a Reynolds number for mixture of 2 liquids

texts:
I'm experimenting with synthesis in microreactors and I'm using 2 reactants. I'd like to estimate the Reynolds number of the flow containing two miscible fluids. I have the values of their properties (density, viscosity, flowrate).

Do I just average both property values for both liquids or is there a more intricate relation?

Thank you very much in advance for your solutions and suggestions!


texts: Best ways to compress and store tons of CO2?

texts: We are looking at doing planet changing work, and removing CO2 from the atmosphere. The issue is storing the CO2. Please let us know the best ways to compress millions of tons of CO2, as we have limited storage space. For example, how much could we compress a ton of CO2 gas? What size container would a ton of CO2 fit in, when fully compressed? Also, would turning tons of CO2 into liquid be more space effective? How much space would a ton of CO2 gas that has been turned into liquid take up?


texts: Computer killed by insecticide; what compounds are likely?

texts:
A friend of mine sprayed "Black Flag Home Defense" insecticide under her
computer. It died immediately. I'm trying to figure out why, and how
fixable it might be.

I found an MSDS, but it only says what the active ingredient is,
deltamethrin, 0.02%. Apparently everything else is proprietary and/or
non-hazardous.

Deltamethrin is not water-soluble, so I'm thinking that this probably
doesn't contain any water; more like nonpolar hydrocarbon sorts of
compounds. I'm thinking there's some particular nonpolar solvent that
makes up the bulk of it.

So, my questions:

Information or informed speculation as to the likely solvent
involved.
For those with knowledge of electronics, information or informed
speculation about the effect of such solvents on PC boards and
electronic components.

Answers to 1 alone are also useful, as I can then ask on
electronics.se what those compounds would do.

UPDATE: I don't have access to the computer myself. I passed on some of
the suggestions to my friend, and she will bring it in to a shop and see
how repairable the damage seems to be. Thanks for all your thoughts.

UPDATE 2: I spoke with the tech who looked at it. Apparently the
computer was very dirty inside; years of dust, cigarette smoke residue,
and insects. She's not sure exactly what happened, but there seems to be
a short somewhere on the motherboard, and that may have fried the power
supply as well. Given the dirt, it was probably not in good shape even
before the incident; the heat sinks were thoroughly clogged.

Overall conclusion: keep your computer clean! Keeping unknown chemicals
away from it is a good idea too.


texts: Does the frequency of incident light change in Beer-Lambert Law?

texts:
The Beer-Lambert law is meant to describe the interaction between a solute and incident light.

But, does the frequency of the light here change due to the interaction with molecules?

I think there is a change in the intensity of light, not in the frequency. But this seems counter-intuitive.

Is there no change, or is it so small that it's just neglected?


texts: Why does reduction using sodium borohydride require a protic solvent?

texts:
Recently, I was looking at the chapter on chemoselectivity in Clayden et al.'s Organic Chemistry (2nd ed.). On p. 530, it is mentioned that sodium borohydride reduction only occurs in protic solvents or in the presence of electrophilic metal ions, such as $\ce {Li+}$ and $\ce {Mg^2+}$ while the more powerful reducing agent lithium aluminium hydride does not require protic solvents. Why is that the case?

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: What is the coordination number for BeCl2?

texts:
I am confused, should it be 2 or 4?

If I consider $\ce{BeCl2}$ as a chain structure the coordination number is 4, and in the gas phase it is 2.


texts: What is the name of the amine shown above? Is it N,N dimethyl (1-methyl-1-ethyl propane amine)?


texts: What is the difference between the reactivity of Lead subacetate and Lead II acetate undergoing a hydrothermal process?

texts:
I am attempting to adapt a hydrothermal method for synthesizing $\ce{PbS}$ nanocrystals to my school that contains a mixture of cationic and anionic surfactants sodium dodecyl sulfate (.05 mmol, SDS) and cetyltrimethylammonium bromide (.05 mmol, CTAB) and ethylenediaminetetraacetic acid (.2 mmol, EDTA) as a chelating agent that diminishes the reactivity of lead ions in solution. The lead source within the method is Lead II Acetate and the sulfur source is an organosulfur compound with the formula $\ce{SC(NH2)2}$.

The company that we bought our chemicals from sent us Lead subacetate and while I wait for them to send us the right one back I am wondering if using the appropriate ratio of moles of Lead subacetate which has 3 moles of lead per 1 mole of lead subacetate to the documented lead II acetate which contains 1 mole of lead would lead to lead sulfide $\ce{PbS}$ nanocrystals.

The structure of subacetate contains two crystalline basic acetates containing hydroxide ions in addition to acetate ions. Does the subacetate create a conjugate acid that lowers the pH?


texts: Degradation of carbon anode in electrolysis of copper sulfate

texts: I'm electrolysing a copper sulfate solution with a 12 volt DC supply using two carbon electrodes. The anode is reducing in mass and becoming thinner. Is there any way I can overcome this problem?


texts: Brown color at end point during titration with phenolphthalein as indicator

texts:
We did a titration experiment at school and I did not understand one part of it.

The scenario:

Titrate : White wine (ethanoic acid)
Titrant: $\ce{NaOH}$
Indicator:  Phenolphthalein

What happened: We carried out the titration and the end point was a brown colour!

How does that happen? Why is the color brown and not pink?


texts: How to attach a liebig condenser to a flask for reflux heating?

texts:
I know it's probably a stupid question, but I can not figure this out. I have a liebig condenser that I usually use for distillation with a Kjeldahl bulb, which makes it easy to attach to a flask because the bulb has a stopper on both ends?

Now I have an experiment that calls for reflux heating, where the condenser needs to be held vertically over the flask. One end of the condenser is a cork-fit opening, and the other end is a spout. The flask also has a cork-fit opening.


texts: Purpose of electrolyte in a galvanic cell

texts:
I am confused as to why galvanic cells have electrolytes. For example, a zinc-hydrogen galvanic cell has a zinc sulfate anode electrolyte and hydrochloric acid cathode electrolyte. The overall reaction of this may be written as:

$$ \ce{ZnSO4 + 2HCl -> ZnCl2 + H2SO4} $$

But rather, it is written as:

$$ \ce{Zn(s) + 2H+(aq) -> Zn^2+(aq) + H2(g)} $$

Why is this the overall reaction? What is then the purpose of an electrolyte, if only the anodes and cathodes are written in the overall equation?


texts: How many valence electrons do elements in the d block have?

texts:
I just noticed that on the periodic table it doesn't say how many valence electrons there are for each column in the d block.

How do I find out how many valence electrons elements in the d block have?


texts:
I am really struggling with this question we have been set in class:

Metal-carbonyl bonding: Conceptionally, one can build up $[Fe(CO)_5]$ from the $Fe(CO)_4$ fragment plus free CO in order to analyse the bonding between the two moieties. Consider first the HOMO and LUMO of free CO: Describe both MOs with respect to their C-O bonding character (bonding/anti-bonding). Note the type of bond that would be formed if CO bonded to another moiety through the HOMO and LUMO respectively.

Predict how the C-O bond itself would be affected
(i) if electrons were donated into the LUMO (e.g., from a metal centre);
(ii) if electrons were withdrawn from the HOMO (e.g., by a metal centre).

Next consider the $Fe(CO)_4$ complex fragment: Does its LUMO possess significant amplitude at the location where the additional CO will bind? Does the LUMO’S shape and symmetry (by visual inspection) match the symmetry of the HOMO of CO? Conversely, does the HOMO of the complex fragment match the LUMO of CO?

Based on these considerations, describe the bonding and orbital interactions between the $Fe(CO)_4$  fragment and CO. Predict how binding to the metal centre would affect the structure and vibrational frequency of CO.

Compare your prediction with the structural and vibrational data obtained for CO. $[Fe(CO)_5]$ and $[Fe(CO)_4)^{2-}$and rationalise the observed trends.

I know that the HOMO of CO is 3σ which is primarily carbon in character and the LUMO is $2π^*$ which is also more carbon in character.

Symmetry is one of my worst topics so if someone could give me a hand on this and could even suggest some further reading material it would be awesome :)


texts: Which element is undergoing oxidation in the combustion of methane?

texts:
Chemical reaction:

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

The example in our textbook for this type of problem involves the following reaction:

$$\ce{C + 2S -> CS2}
$$

Here, I can clearly see that $\ce{C}$ starts off with an oxidation state of zero and ends with an oxidation state of +4, meaning that it underwent oxidation.

In my given reaction, I see how the $\ce{C}$ in $\ce{CO2}$ has an oxidation state of +4, but I don't quite understand why it doesn't also have an oxidation state of +4 in $\ce{CH4}$. My assumption here is that, in the case of $\ce{CO_2}$, $\ce{C}$ has an oxidation state of +4 and $\ce{O2}$ has an oxidation state of -4; and in the case of $\ce{CH4}$, $\ce{C}$ has an oxidation state of +4 and $\ce{H4}$ has an oxidation state of -4. If that is incorrect, could someone explain why?

Edit: I just realized I overlooked a table that says that hydrogen has an oxidation state of +1, which would mean that in $\ce{CH_4}$, $\ce{C}$ would have an oxidation state of -4. I gather that this means that $\ce{C}$ loses 8 electrons in the reaction, which is why it is considered to undergo oxidation.


texts: Production of Succinic Acid from Crude Glycerol using Fermentation

texts:
So I am writing a short paper on how one can produce Succinic acid from glycerol. I have to find a microorganism which can do that. I have found the following microorganism, which are traditionally being used for fermentation: Anaerobiospirillum succiniciproducens, Actinobacillus succinogenes, Mannheimia succiniciproducens and recombinant Escherichia coli strains. But the problem is that whatever article I find, they are written with respect to Glucose.

Does anyone know any article/paper/hints or some information they can share?

I just need to understand which organism can be used to do the fermentation, and how much succinic acid can be made from it.


texts: Computational heat of reation vs. using literature values

texts:
My question is I don't understand how to explain why or what I did wrong to have such large differences between my computational heat of reaction and heat of reaction using enthalpies of formation from literature, and my experimental heat of reaction.

I performed a lab in which three methods were used to compute the heat of reaction for the reaction:

$$
\ce{Na2CO3 (s) + 2 HCl (aq) -> 2 NaCl (aq) + H2O (l) + CO2 (g)}
$$

First method I used was using experimental data from solution calorimetry and from my results I got that the average heat of reaction was $\textbf{-89.835 kJ/mol}$.

For my second method I found the heat of reaction computationally with Orca. I was instructed to use this equation instead of the original equation to calculate heat of reaction for the above reaction.

$$
\Delta U = U \left[ \ce{CO2 (g)} \right] + 3U \left[ \ce{H2O (l)} \right] - 2U \left[ \ce{H3O+ (aq)} \right] - U \left[ \ce{CO3^{2-} (aq)} \right]
$$

So basically I used Orca to find the energy for each of the molecules, and I plugged those values into their proper U(molecule) in the above formula and I calculated delta U and then I used the approximation of $\Delta H = \Delta U + R \Delta T$ to transform it into heat. My overall answer ended up being $\textbf{-378 kJ/mol}$. My work (data from Orca optimization is listed first):

\begin{align*}
\ce{CO3^{2-} (aq)} &= -264.0667 \, \text{Ha} \\
    \ce{H3O+ (aq)} &= -76.8491 \, \text{Ha} \\
      \ce{H2O (l)} &= -76.4409 \, \text{Ha} \\
      \ce{CO2 (g)} &= -188.5873 \, \text{Ha} \\
    1 \, \text{Ha} &= 627.503 \, \text{kcal/mol} \\
          \Delta H &= \Delta U + R \Delta T \\
          \Delta U &= \left[ -188.5873 + (3*-76.4409) \right] - \left[ (2*-76.8491) + -264.0667 \right] = -0.1451 \, \text{Ha} \\
-0.1451 \, \text{Ha} &\rightarrow 627.503 \, \frac{\text{kcal/mol}}{\text{Ha}} * -0.1451 \, \text{Ha} = -91.0507 \, \frac{\text{kcal}}{\text{mol}} \\
-91.0507 \, \frac{\text{kcal}}{\text{mol}} &* 1000 \, \frac{\text{cal}}{\text{kcal}} * 4.184 \, \frac{\text{J}}{\text{cal}} * \frac{1}{1000} \frac{\text{kJ}}{\text{J}} = -380.956 \, \frac{\text{kcal}}{\text{mol}} \\
\Delta H_{\text{rxn}} &= -380.956 \frac{\text{kJ}}{\text{mol}} + \left[ 8.314 \frac{\text{J}}{\text{mol K}} * (273.15 + 25.27) \, \text{K} * \frac{1}{1000} \frac{\text{kJ}}{\text{J}} \right] = -378.475 \, \text{kJ/mol}
\end{align*}

My third method I used enthalpies of formation (values for looked up from various sources) and my work is shown below.

\begin{align*}
\ce{Na2CO3 (s)} &= -1130.7 \, \text{kJ/mol} \\
       \ce{HCl (aq)} &= -167.2 \, \text{kJ/mol} \\
 \ce{NaCl (aq)} &= -407.27 \, \text{kJ/mol} \\
   \ce{H2O (l)} &= -285.8 \, \text{kJ/mol} \\
   \ce{CO2 (g)} &= -393.5 \, \text{kJ/mol} \\
\Delta H_{\text{rxn}} &= \left[ (2*-407.27) + (-285.8) + (-393.5) \right] - \left[ (2*-167.2) + (-1130.7) \right] = \mathbf{-28.74 \, \textbf{kJ/mol}}
\end{align*}

I'm not really sure how to say why the computational method did so poorly, I would have thought the computer would have done a decent job. Please let me know if something looks wrong in my calculations! Thanks for all the help! Even just a little advice will help this non-chemistry nerd!


texts:
Why is the energy of an electron in an orbit is always negative?
What does it mean?
Why isn't it positive?
Does it mean that energy is released by revolving electron?


texts:
Can someone explain why boric acid prevents zinc from vapourizing out of the brass alloy when it is being melted?  What is the actual chemistry occurring and why?
Thanks


texts:
Would the acidity of the aluminium trihalides be the same as that for the boron trihalides?

The interesting thing about the acidity of the boron trihalides is that they actually increase in acidity from fluorine to iodine. This is due to the presence of stronger pi bonding in boron trifluoride compared to the other boron trihalides, which means that stronger partial pi bonds would have to be broken when boron accepts an electron pair from a base.

Would we observe this trend in acidity in the aluminium trihalides as well?
Based on the same reasoning, we should be able to right?


texts: Formic Acid vs Formica - Which came first?

texts:
Source: Google(Oxford)

So, we know that 'Formic Acid' was derived in formic acid in the late 18th century from the Latin word 'formica'. From Wikipedia:

  Formica is a genus of ants of the family Formicidae, commonly known as wood ants, mound ants, thatching ants, and field ants. Formica is the type genus of the Formicidae, and of the subfamily Formicinae.

I think I've read in some junior classes that the biological name 'Formica' was given to ant because of the secretion of 'Formic Acid' by it which is the cause of the irritation at the stung area.

So, I want to know - Is formic acid derived from 'Formica' (ants) or are ants' (biological name) derived from the presence of 'formic acid' in them?


texts: HNMR spectroscopy mono-carboxylated acid

texts:
During lab, I have done following reaction:

I did HNMR of the product, to be certain if the product really was formed.

The HNMR gave following results:

And looked like this:

So my question is: has the reaction succesfully taken place?
I know that the peaks between 6.5 and 8 ppm represent protons, attached to an aromatic molecule. But there are only four peaks between 6.5 and 8 ppm, instead of 5 (the amount that I expected). At 3.89 ppm, there is a singlet with 5 protons present, which is weird because I expected only 1 singlet with 3 protons. The 7 protons at 1.53 ppm I don't understand at all.

Please help me out.

Thanks.


texts: The chemical structure of a diamond is defined as an endless lattice in which each carbon atom is covalently bonded to four other carbon atoms situated at the four ends of a tetrahedron.  But of course they aren't endless; diamonds have edges and faces.  So what happens when the lattice reaches the edge and there aren't any other carbon atoms to bond to?  What is the "surface layer" of a diamond composed of?


texts: What was the process that created a plastic-looking material from the jam leftovers?

texts:
I was making apricot jam using fresh apricots and gelling sugar. All went well except I burnt it. Some of the solid parts sank to the bottom and stuck there. After putting the good stuff in jars, I then soaked the pot.

About five hours later I went to scrub it and the whole bottom layer came free in a perfect circle. The under side is shiny — looks like plastic. The upper side is matt and almost furry. As it dries out it is curling up and is brittle.

What happened?


texts: Beer Lambert law when complex is tetragonal (Jahn-Teller elongated)

texts: I wondered what modifications there would be to the Beer Lambert law to find the molar extinction coefficients for the solution if the solvent contained the ligands which bind to the metal centre of a metal compound (ie 2 ligands add along the z axis only) and the complex was tetragonal?


texts:
Is it necessary that the valency of an element must have the same valency?

For eg. If 2 elements A and B combine with the same mass of C, is it necessary that they will have the same valency as they would have when combining AB?


texts: Drawing bonds and delocalised electrons in condensed formulae

texts:
The $\LaTeX$ mhchem package provides commands for drawing bonds within condensed chemical formulae. Some of them have a clear allocation to covalent bonds while others have not. Single, double, and triple bonds can be drawn in a very easy and convenient way and, of course, delocalised $\pi$-electrons in condensed formulae like $\text{H}_2\text{C}=\text{CH}-\text{CH}=\text{CH}_2\;\;$of 1,3-butadiene can easily be drawn by dashed lines, too (see image below). However, the following four general formulae remain incomprehensible with respect to their application.

Does anyone know semi-structural (condensed) formulae of chemical compounds in which such chemical bonds (dashed lines/arrows) are drawn? Or are they just a "nice to have feature" provided by the package?


texts: Production of ozone from oxygen and Le Chatelier's principle

texts:
My NCERT textbooks says as follows:

  Since the formation of ozone from oxygen is an endothermic process, it is necessary to use a silent electrical discharge in its preparation to prevent its decomposition.

Reaction is:

$3\ce{O2}\ce{->}2\ce{O3}$ $\triangle H$=+142 kJ mol $^{-1}$

And somewhere on the net, I have learnt that silent sparkless discharge is needed as sparks may increase the temperature of the vessel/setup environment.

My question is, isn't the text contradicting the very principle of le Chatelier for endothermic processes, i.e the temperature should be as high as reasonably viable and allowable (for kinetics reason)?


texts:
Recently I did an experiment on isolating casein and now that I am processing the results, I feel my method of uncertainty calculation is not feasible. The casein was isolated 3 times and the results are as follows: 2.386, 2.628 and 2.164 grams. The scale had an uncertainty of 3 decimal places. Furthermore, the casein was isolated from 100 mL of milk, measured using a measuring cylinder with an uncertainty of 1 mL. The mean uncertainty was found using the following formula:

$$Δx_\mathrm{avg} = \frac{Δx}{\sqrt{N}} = \frac{R}{2\sqrt{N}}$$

Hence, my calculations were:

$$\mathrm{Range} = 2.628 - 2.164 = 0.464$$

Thus the uncertainty for the average would be:

$$\frac{0.464}{2\sqrt{3}} = 0.133945262 = 0.2$$

This would result in a final value for the average amount of casein in the isolated milk of $\pu{2.4 ± 0.2 g}$.

However, this error seems unreasonable considering that my measurements were to 3 decimal places. Furthermore, how would I add the uncertainty of the 100 mL of milk to this value? Would I simply add the uncertainties?


texts: Freezing point lowering for a mixture of many liquids

texts:
I have been taught that if I have a solute of molality $m$ mixed with a liquid, the freezing point in lowered by an amount $K_\mathrm{f}\cdot m$ where $K_\mathrm{f}$ is the molal freezing depression constant.

But if I have a solution containing three liquids, and if all the $K_\mathrm{f}$ values are known, what would be the lowering of freezing point of such a solution?


texts:
When I took high school chemistry many years ago, considerable effort was spent on teaching us to compute oxidation states of atoms in various compounds, following a set of rules that looked somewhat arbitrary to me at the time. As far as I remember, we were never told what benefits (other than passing tests) knowledge of oxidation states would give us.

They were used as part of a convoluted procedure for "balancing redox reactions", but I never saw an example of that where it wouldn't give the same results simply to require that the number of nuclei of each element, as well as the total charge, must be the same on both sides of the reaction, and solve the resulting linear Diophantine equations.

Nevertheless, the concept must be useful other than for setting homework exercises -- I see encyclopedias and other sources use much space on classifying compounds based on the oxidation state of this atom or that. Still I don't recall seeing any case where the oxidation states are used for anything (other than computing other oxidation states).

What is this concept actually used for? Just a basic example or two where knowing the oxidation states helps produce a meaningful prediction.

It doesn't seem that "oxidation state" actually encodes any particular configuration change inside the atom that tends to be preserved across reactions. Or does it somehow require effort (energy?) to change an atom from
one oxidation state to another? In which case, what actually changes?

Sorry if this is too basic a question. It may be something "everybody knows". I've tried looking e.g. at the Wikipedia article, but that too seems to be entirely focused on how to determine oxidation states and doesn't explain why one would desire to know them. And all the oxidation-state questions here seems similarly to be about determining the oxidation states, and it is left unsaid why the asker wants to know ...

Edit: I'm looking for applications of oxidation numbers, by which I mean rules, laws, tendencies, rules-of-thumb or the like of the general form:

  When you have (condition that involves oxidation numbers) then (prediction that can be verified without knowing what oxidation numbers are).


texts:
My teacher in college says that bonds between metals and nonmetals are ionic.

$ \ce{Metal - Metal} $ $\Rightarrow$ Metalic bond

$\ce{Non metal - Non metal}$ $\Rightarrow$ Covalent bond

I have to write about $\ce{CuCl2}$, and found in Wikipedia that if you subtract electronegativity you get what bond it is:

$$\chi (\ce{Cl}) = 3.16, \quad \chi (\ce{Cu}) = 1.90$$

$$\chi = 3.16 - 1.90 = 1.26$$

$\chi < 0.4 \Rightarrow$ covalent non-polar

$0.4 < \chi < 1.7 \Rightarrow$ covalent polar

$\chi > 1.7 \Rightarrow$ ionic

So it should be really a covalent bond. Which one is correct?


texts: What are the limits of size differences in a host–guest complex?

texts:
We learn in my chemistry course that there must be a snug fit for a host-guest complex to form. So, something like benzene (0.6 nm in diameter) can form a host-guest complex with a β-cyclodextrin host (0.7 nm cavity).
Other than this vaguely-worded ‘snug-fit’ rule, we are not given a lot of information of what molecules would fit.
Would something like methane (0.38 nm diameter, according to Wikipedia) form a stable host–guest complex with β-cyclodextrin, or would it be too small?
I know that methyl red fits in a β-cyclodextrin cavity, but what about something slightly larger like anthracene?
These questions are a small part of something that contributes a small amount towards my overall course grade. Please, if you are able to, give me some kind of guidance so that I can work out answers on my own. I've tried to look independently online but I come up with nothing.


texts: Application of Nernst Equation in Potentiometric titration of Fe2+ with Ce4+

texts:
It is well Known that to find $E_{cell}$ during titration of  $Fe^{2+}$ with $Ce^{4+}$ we consider 3 domains:

Before Equivalance point ,  $E_+ = E_{Fe^{3+}/Fe^{2+}}^o+\frac{RT}{nF}log\frac{[Fe^{3+}]}{[Fe^{2+}]} \tag{1}$

At Equivalance point , $E_+=\frac{E_{Fe^{3+}/Fe^{2+}}+E_{Ce^{4+}/Ce^{3+}}}{2} \tag{2}$

After  Equivalance point ,$E_+ = E_{Ce^{4+}/Ce^{3+}}^o+\frac{RT}{nF}log\frac{[Ce^{4+}]}{[Ce^{3+}]} \tag{3}$

$E_+$ is the electrode potential of the positive electrode where the negative electrode is a fixed reference electrode.

In the book Quantitative Chemical Analysis by Daniel C Harris, Chapter 15 says that both equation 1 and 3 can be used either of the two domains and the reason why one is used instead of the other is due to the fact that the ratio of the concentration of a particular metal ion in different oxidation state is much easily found in that domain while the other ratio usually requires a complicted equilibrium equation to be solved to obtain the solution.

my questions:

Does this mean that if by some means I knew the ratio of concentrations of both metals I could substitute it in eqn 1 and eqn 3 and end up getting the same value for $E_+$.
If not does it only hold near the Equivalance point?
If one is True , The only explanation I have is that both $Fe^{2+}$ and $Ce ^{4+}$ are in equilibrium with the same electrode. But this still doesn't make sense as usually when 2 reactions are occurring at the same container the $\Delta G_{net}=\Delta G_{1}+\Delta G_{2} $ So in some sense shouldn't $ E_+ =E_{due-to-Fe}+E_{due-to-Ce}$ be the equation we require?

If I'm missing some essential concept it would be Great if someone could point it out and probably provide some links for me to look up.


texts: Reaction of cyclopropane with hot potassium permanganate

texts:
Hot potassium permanganate is usually used as an oxidising agent, and cyclopropane being an unstable three membered ring undergoes reaction with several reagents such as bromine, $\ce{HBr}$, metal adsorbed with hydrogen, etc.

However, I don't know for a fact if cyclopropane undergoes oxidation with hot permanganate – and I couldn't really find much data online.

If at all cyclopropane doesn't react, what happens with its methyl derivative? Does it get oxidised to the corresponding acid?


texts: Reaction of sulfate ion in copper sulfate electrolysis

texts: I am planning to try copper plating a piece of metal by performing electrolysis on an aqueous solution of copper sulfate. I plan run an electrical current with the metal I want to plate as the cathode and a platinum anode. I understand that the copper ions will become reduced when they plate the metal, but I am curious what will happen to the sulfate ions. Will it oxidize to form sulfur trioxide with the produced oxygen from the electrolysis?


texts: Why can we not hydrogenate or brominate etc. on cycloalkanes to convert into linear molecule? And are there any exceptions to this?


texts:
Is there chemical that can break down the red blood cells/hemoglobin into smaller protein sub units/globins?

I would like to extract the heme molecules from the blood but not necessarily purify it,or separate it.I would like to get solution containing liberated heme units,its not problem if other stuff,like proteins and globins are floating in that solution,I just want to detach the heme part from the protein.Heme is iron containing coordination complex that binds to oxygen and give blood its red color.


texts:
From section 'Nitrogen Containing Compounds'

I spent quite a lot of time here but could not figure out the answer. It's not mentioned in my school text book either. The solution given in my book is:

I'd like to know:

Is the answer provided (c) correct?
How do I know that heating that compound in the presence of a base results in the formation of that product? We've got plenty of cases in our textbook (Tollen's Test, Fehling's Test and the aldol reaction, to name a few) where we heat organic compounds in the presence of a base, but none of them go by what happened in this question.


texts: Why is the formation of lead (II) iodide precipitate favoured over that of the tetraiodo plumbate (II) complex ion in low concentrations of iodide?

texts:
I was wondering why

$$\ce{Pb2+ + 2I- <=> PbI2}$$

occurs in low $[\ce{I-}]$, however when $[\ce{I-}]$ is in excess, $\ce{PbI4^2-}$ is produced with

$$\ce{Pb2+ + 4I- <=> [PbI4]^2-}$$

Why is the formation of complex ion "favoured"? Furthermore, since the formation of insoluble precipitate will reduce entropy, wouldn't the formation of insoluble precipitate be favoured?


texts:
I'm learning electrolysis and we learned that the positive ions go to the cathode which is where reduction takes place.
However, I got confused because when you learn about ionic bonding, the positive ions are the ones that lose electrons. And we learned that reduction is the GAIN of electrons. These two things clash. Can somebody please explain this to me?


texts: Change in pressure or volume of molten salt

texts:
I am doing a project in which I fill a cylinder with a volume of $636cm^2$ (made of stainless steel) with molten salt: 60% Sodium Nitrate ($NaNO_3$) and 40% Potassium Nitrate($KNO_3$).

The container might reach (worst case scenario) -35 degrees Celsius in a cold winter night and in the summer (with ideal conditions) up to 700 degrees Celsius.

I'm trying to find out if I should add a relief valve (like in old water boilers) or just seal it tight. This of course depends o how much the pressure increases between those 2 states.

I know that molten salt  melts at 221 degrees Celcius and starts  freezing when it reaches 238 degrees Celcius.

I can't find any relevant data, so I don't know how I could find the result for this. Any ideas or suggestions?

EDIT: My worry is that it would blow up due to pressure or the lid would blow open...


texts: Ozone is heavier than nitrogen. Then why is ozone in stratosphere and nitrogen in troposphere?


texts:
I know that technically two or more gases in one container should have different volumes. But when you imagine the gas molecules being mixed together, it look sorta like the two gases have the exact same volume, that is the volume of the container.

Also, in one of the questions I did on gas laws, wet hydrogen and hydrogen are shown to have the same volume in a container. Given the barometric pressure, I subs tract the vapor pressure at the certain temperature from it. Then I sub the pressure of dry hydrogen gas into the ideal gas law along with the volume of the container to find the number of mole of hydrogen gas.

This is the part in my textbook that I am confused about. It shows how partial pressure fraction is equal to the corresponding mole fraction. But this is all under the assumption that the volume and other things are constant. I am lost right here, because Avogadro's theory states the volume and mole number of a gas are directly proportional.
( wait...wouldn't this mean that pressure, mole and volume are all directly proportional to one another???)

Can anyone give a answer, along with a proof/ a source?


texts: Do Biuret test always means proteins presence in a substance?

texts:
I am a student and I got this answer I cant really say for sure if I understood correctly :

"A substance reacts positively to Biuret's test. ¿ Can you say with 100% accuracy that such substance is a protein? Justify"

Is this correct to say that the substance is a protein?
Is there a chance that the test reacts but the substance is NOT a protein?

Additionally, I am being asked why we are using whole milk instead of skim milk in this test.


texts: How can I determine the activation energy of a reaction if the reaction rate constant is unknown?

texts:
I am trying to conduct an experiment to determine the activation energy of the following chemical reaction:

$$\ce{IO3- (aq) + 3HSO3- (aq) -> I- (aq) + 3SO4^2- (aq) + 3H+ (aq)}$$
$$\ce{5I- (aq) + 6H+ (aq) + IO3- (aq) -> 3I2 (aq) + 3H2O (l)}$$

The Arrhenius Equation can be rewritten as $$\ln k = \frac{-Ea}{{\rm R}T} + \ln A$$ Therefore, if ln k and 1/T were plotted on a graph, the slope of the line should be equal to -Ea/R.

I can use temperature as my independent variable and the reaction time as my dependent variable. However, I am unsure as to how to determine the reaction rate constant (k) of the reaction experimentally from the reaction time.


texts: Relation between molar mass and van der Waals force

texts:
In the book that I'm reading it is mentioned higher molar mass results in stronger van der Waals force, but didn't continued why.

I wonder why is that so? molar mass is actually dependable on the number of protons and neutrons, how can it be effective on the van der Waals force?


texts: How can I attempt to inhibit the hydrolysis/degeneration of aspartame?

texts:
I've surfed the internet, looking for some possible inhibitors for the hydrolysis process of aspartame, but couldn't find any. I'm wondering if such a thing is possible and if yes, how should I proceed?

I'm writing an essay about how the rate of degradation of aspartame could be slowed down and wanted to attempt using some compounds to inhibit the reaction.


texts: Do chemical compounds have spectral lines, or only elements?

texts: I know that elements (ex. Ag) have spectral/emission/absorption lines, but do chemical compounds (ex. NaCl) have spectral lines as well? Ones that when seen you can tell that that compound (NaCl) is made up of certain elements (Na and Cl).


texts:
I am reading about NMR, and from what I'm understanding it should give information on the transition energies in the spectrum of the nuclear spin in a magnetic field.

What I don't understand is how this information is accessed during the experiment.

The NMR measurement is usually described as: a magnetic field $H_0$ polarizes the sample along a certain direction; then a short pulse of an auxiliary magnetic field alters the direction of the magnetization, which then starts to precess around $H_0$. The changing magnetization induces a current the coils of the NMR machine which is measured and gives the precession frequency. The magnetization gradually aligns with $H_0$, leading to a diminishing current intensity. The decrease in intensity gives the nuclear relaxation rate.

A first question is: is the above description of the measurement correct?

A second question is: How do we extract the information on the energy levels $E_m$, or their separation, from the precession frequency? If not from the precession, how is the energy spectrum obtained?


texts: Analytical gradient of the Hartree-Fock nuclear-electronic repulsion term

texts:
The analytical gradient of the Hartree-Fock energy is given by (Szabo & Ostlund eq. C.16):

$$ \frac{\partial E}{\partial X_{A}} = \sum_{ij}{P_{ji} \frac{\partial H_{ij}}{\partial X_{A}}} + \frac{1}{2} \sum_{ijkl}{P_{ji}P_{kl} \frac{\partial (ij|kl)}{\partial X_{A}}} - \sum_{ij}{Q_{ji} \frac{\partial S_{ij}}{\partial X_{A}}} + \frac{\partial V_{NN}}{\partial X_{A}} $$

Of course, the Born-Oppenheimer approximation means that the nuclear repulsion term is easy to handle, and the derivative is given as:

$$ \frac{\partial V_{NN}}{\partial X_{A}} = Z_{A} \sum_{B} \frac{Z_{B} (X_{B} - X_{A})}{R_{AB}^{3}}$$

The remaining terms require computing the derivatives of the Gaussian functions (depending upon the molecular integral evaluation scheme used). However, in Szabo & Ostlund the nuclear-electronic attraction term is provided as:

$$ \frac{\partial V_{Ne}}{\partial X_{A}} = -Z_{A} \sum_{i} \frac{X_{i} - X_{A}}{r_{iA}^{3}}$$

In the Hartree-Fock equations, the molecular Hamiltonian is formed as $H = T + V_{Ne}$. Presuming that the gradient of the molecular Hamiltonian is formed the same way, how can I treat this formulation of the analytical gradient with only a scalar value for the nuclear attraction term, when I must take into account the density matrix? Is this solution to the nuclear attraction gradient of no use in calculating the gradient of the energy?

  [1] A. Szabo and N. S. Ostlund, Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory, Dover Publications Inc., New York, pp. 441-442.


texts: How can scientists be certain that there are no undiscovered elements missing from the periodic table from hydrogen to lawrencium?

texts: Scientists are certain that there are no undiscovered elements missing from the periodic table from hydrogen to lawrencium. How? and why?


texts:
What is the reason behind the following statement:

  The $Δ_fH^\circ$ for the fluorides become less negative as we go down the group while the reverse is true for chlorides, bromides and iodides.


texts: Melting point of unsymmetrical dimethylhydrazine vs 1,2-dimethylhydrazine

texts:
Unsymmetrical dimethylhydrazine ($\ce{H2NN(CH3)2}$) has a melting point of −57 °C, but its isomer, 1,2-dimethylhydrazine ($\ce{(CH3NH)2}$) has a melting point of −9 °C. That looks to me like a significant difference, so there must be some mechanism which makes these two compounds extremely different in this respect. However, I'm unable to figure out why that difference exists; could you please explain that?

These are the structures of the compounds (from wikimedia commons):

Unsymmetrical dimethylhydrazine:

1,2-dimethylhydrazine:

Here're some of the arguments which I considered:

The packing in crystal structures could be 'different' in a significant way. This could potentially be supported by the fact that the difference between their boiling points is much lower: unsymmetrical dimethylhydrazine has a boiling point of 64 °C while 1,2-dimethylhydrazine's is 87 °C. However, this is an extremely vague argument; it could be strengthened by some details regarding how the different packings contribute to the melting points.
Hydrogen bonding should be a pretty significant factor to consider while analyzing these compounds. I suspected that steric hindrance may allow only one $\ce{N}$ atom for hydrogen bonding in unsymmetrical dimethylhydrazine. However, this would suggest that 1,2-dimethylhydrazine should have a lower melting point, which is clearly not the case.

We had a discussion about these two compounds' melting points in the Physics SE chat a while back, so I thought I'd pop over here and ask.


texts: Why does viscosity decrease when divalent cations are dissolved into aqueous solutions of sodium carboxymethylcellulose?

texts:
Sodium Carboxymethylcellulose (CMC/NaCMC/Aqualon) is a common product used in many instances for its unique properties, especially its ability to make solutions viscous. It is well known that the charge of metal ions directly affects CMC's viscosity.

According to the pdf: AQUALON Sodium Carboxymethylcellulose (ResearchGate), it states that:

  Compatibility of CMC with inorganic salt solutions depends largely on
  the ability of the added cation to form a soluble salt of
  carboxymethylcellulose.

Then it proceeds with:

  As a general rule, monovalent cations from soluble salts of
  carboxymethylcellulose, divalent cations are borderline, and trivalent
  cations form insoluble salts.

It then continues on to discuss the effect of this on the viscosity of aqueous solutions with these cations mixed with CMC, but doesn't explain why.

It says that divalent cations (which are "borderline" yet still soluble into CMC solutions) decrease the viscosity of CMC solutions, yet monovalent cations (which fully dissolve) do not decease the solution's viscosity (or not to the same extent). Why is this?


texts: How to purify volatile haloalkanes prepared by Darzens halogenation?

texts: We know that the Darzens method of substitution works on $S_n i$ and is considered the best method in terms of yield of product. Also the side products are $\ce{SO_2}$ and $\ce{HCl}$ so the equilibrium shifts in the forward direction. But we know the lower haloalkanes are gases so if the molecular masses of the halides are comparable with that of the side products then how can we purify them since we cannot use Grahm's Law of Diffuson.


texts: How to quantify caffeine content in coffee?

texts:
How do I titrate caffeine from coffee to estimate the percentage of caffeine in coffee?

I have tried using iodine solution, sulfuric acid, and sodium thiosulfate to no avail.


texts: Why is the Gaussian Window Function used to enhance resolution in 1D NMR spectra?

texts: In a recent question it was explained that Gaussian window functions are not used in 2D NMR spectra as they can introduce artifacts into the spectrum baseline by truncating the FID. Why then are they used with 1D spectra instead of sin or cosine functions?


texts: Hybridisation of hexaamminecobalt(III) complex

texts:
Does $\ce{[Cr(NH3)6]^3+}$ have $sp^3d^2$ or $d^2sp^3$ hybridisation?

Oxidation state of $\ce{Cr}$ is $+3$. The electronic configuration is $3d^3$ and the $d$ electrons occupy $t_{2g}$ orbitals. If the electrons from the ligands were to occupy the $e_g$ orbitals the stability of the complex decreases. So shouldn't the hybridisation be $sp^3d^2$?


texts: Why does stannous chloride occur despite the octet rule?

texts:
Shouldn't reaching an octet be any atom's "goal"?

However, I've recently learned about cases that are either expanding octets, or have lesser than "enough" electrons for an octet abiding. e.g.:

S in sulfur hexafluoride (Expanding octet into $\text{3d}$)

Source

B in boron trifluoride (It's "hextet", instead of octet)

Source

However, both $\ce{SnCl2}$ and $\ce{SnCl4}$ are existent. The latter is explainable with octet, but not the former. Surprisingly, $\ce{SnCl2}$ is more stable!

How?
Why is the phenomenon happening?

Dave pointed out that the octet nonabidingness is happening in the vapor phase. So I redirect the question to ask about the vapor phase; since that's what I'm looking for.


texts: Why does the electron configuration for some elements not follow the diagonal rule?

texts:
I'm doing a high-school assignment, and I came across a question that I didn't quite understand.

  Explain how the electron configurations for the following elements do not follow the diagonal rule:

  Gold
  Curium
  Thorium
  Molybdenum
  Palladium

From what I understand, all of these elements do follow the diagonal rule. How exactly do they not follow this rule?


texts: What are some ways to measure sugar concentration of fruits?

texts: I've tried to do titrations using the quantitative Benedict's Solution and it was difficult to use as I do not have a way of keeping a constant temperature. I am currently using a Polarimeter to find the angle of the various concentrations of sugar in my solutions but it does not seem very clear or efficient.


texts: (Why) is it difficult to liquidize the polluting exhaust of a vehicle?

texts:
Considering the hazardous effects of car and other vehicle exhaust when released into the atmosphere, I began wondering why we are not dominantly preventing the exhaust from entering into the atmosphere, for example by liquidizing it and storing it either in the driving vehicle or elsewhere?

My question is: why is it so difficult to liquidize the exhaust, in order to prevent it from entering the atmosphere? Or isn't it difficult at all perhaps?

Please note that it is not forbidden to theorize about adding any equipment and or chemical reactants to the vehicle.

P.S.: I would be equally interested in just storing the exhaust of a vehicle inside the vehicle by means of compression, rather than liquidization.


texts:
I have a C++ code which calculates the combustion thermodynamic variables (temperature, density) and the mass fractions of Dimethyl Ether for different equivalence ratio. I would like to check my results but I couldn't find anything on google. Most of the papers about DME that I've found show the laminar flame speed.

Please refer me to some paper or book if you know any. A graph showing the adiabatic flame temperature vs equivalence ratio would be ideal.


texts: Calculate mass concentration of Ca(OH)2 solution

texts:
Can anyone help me calculate the mass concentration of $\ce{Ca(OH)2}$ solution with molar mass $\pu{74.1 g/mol}$ at the $\pu{pH of 12.8}$.

My work so far:

From the pH I get the molar concentration of $\pu{0.063 mol/L}$.   Assuming we have $\pu{1L}$ of substance we have $\ce{n(OH-) = 2 \times n(CaOH2) = 0.126 mol/L}$

I put the results in $m = M \times n$ to get 9.35 g which is incorrect. Where did I go wrong?


texts:
I understand that this is an elementary question, but I tried to find answers which I could not get.

I am trying to understand why Nitrogen in Ammonia is a proton acceptor.

Now as I can see from the structure the octet is complete hence should be stable as it is.

But couple of points here:

1) Nitrogen is more electronegative than hydrogen hence $N$ will pull electrons towards itself. Hence not a good candidate to donate electrons! In addition, the lone pair is in 2s orbital.

2) The other point is the presence of lone pair, it is claimed that this lone pair is more stable if its part of some bond, hence it accepts proton. But if this is the case then lets take the case of Oxygen $O=O$, here each Oxygen atom has 2 lone pairs, and going by the above logic these lone pairs should also participate in bond formation and create an Oxygen polymer(!!), but they do not and Oxygen is quite stable.

Hence with the above points I still could not see why Nitrogen has to accept proton.

The only explanation that I can think of is the lone pair is in 2s orbital and the spread of this electron cloud is larger than electrons participating in bonds. Hence to be stabilized further it accepts a proton $(H_+)$ to form a bond!!


texts: What inference can be made from the fact that there is no reversal in how three components eluate?

texts:
I gave an answer this question about TLC. I now realize that I am blundering my way through this question.

The problem statement doesn't specify if the compounds to be eluted are polar or non-polar. So this seems to leave a door open.

Question 1 - Could compounds be either relatively polar or relatively non-polar?

Question 2 - If an absolutely non-polar solvent like hexane were used, and some other more polar solvent, wouldn't a reversal of the order of the elution of the compounds happen?

Question 3 - Have I in fact, like a blind squirrel, finally found the nut?

EDIT 1

The problem specifies that "normal phase TLC" is being used so the stationary phase is polar.

The problem only states that the elutants have different polarity and not that any is actually non-polar like hexane.

EDIT 2

With Question 3 I was trying to be funny and ask if my two answers to the original question are right.


texts: Number of electrons transferred & Gibbs free energy

texts:
To determine the number of electrons transferred for the following reaction:

$$\ce{CH3OH + \frac{3}{2} O2 -> CO2 + 2 H2O}$$

I found the half reactions to be:

$$\text{Anode: } \ce{CH3OH + H2O -> 6H+ + 6e- + CO2}$$
$$\text{Cathode: } \ce{\frac{3}{2}O2 + 6 H+ + 6 e- -> 3 H2O}$$

The number of electrons transferred is therefore 6. If I was given the following overall reaction:
$$\ce{2 CH3OH + 3 O2 -> 2 CO2 + 4 H2O}$$

Which is just multiplying everything by 2 for the original reaction, would I say 12 electrons have been transferred or still 6? Since the Gibbs free energy change = nFE where n is the number of electrons transferred should surely be the same?


texts: working with ratios and RMS to find variables

texts:
question
consider separate 1.0L samples of helium and $UF_6$ both at 1.00atm and containing the same number of moles. what will the ratio of the separate temperature need to be in order to have the same root-mean-square speed?

my steps
So i set up an equation
$\sqrt{\frac{3(8.314T)}{0.004}}$=$\sqrt{\frac{3(8.314T)}{0.352008}}$
but i soon realized that that would be impossible
and that is where i got stuck


texts: Energy profile of cyclohexene conformations

texts:
The energy profile for cyclohexane flipping looks like this:

How does the corresponding diagram for cyclohexene look like?


texts: Reaction quotient and Gibbs free energy at the start of a reaction

texts: According to the equation 33 above, shouldn't be all the reactions be spontaneous initially? Because the reaction quotient Q, is zero at the start of the reaction and logarithm of Q makes it a very large negative value and ultimately we'll have ∆G to be a large, negative value which makes the reaction spontaneous?


texts: How should I identify my leaving group in SN1 reactions if there might be more than one option?

texts:
Before I can even begin to contemplate the products of a given SN1 reaction, I need to be able to determine what my leaving group will be, which should be a species with a strong conjugate acid, and as I understand it the species should be relatively stable once it has left the substrate. Please correct me if I am making any mistakes in my understanding.

A hydroxide ion will be a terrible leaving group, since its conjugate acid is water, and hydroxide is not very stable by itself.

So when I am asked this question "Draw the major organic product(s) for this SN1 reaction:

How do I know what will be the best leaving group? Hydroxide is not very good, so perhaps $\ce{CH_3OH}$ will work better? How do I know it is not $\ce{CH_3CH_2OH}$ instead?

Is this only one decent option, and I am over thinking this?


texts: Wieland's method for triphenylamine bromination

texts:
I'm looking for a Wieland's paper on triphenylamine bromination. I've found other papers referencing it like this but I don't find the actual paper.

Does someone know where could I find it? Or whats Wieland's method all about?


texts:
What can cause the biuret test to produce an orange colored solution?

I did the biuret test to a few number of foods in a school lab assignment. The test with tofu turned orange. I wonder why, since the biuret test is supposed to give violet as positive. I tried looking it up on google with no success.

An explanation I came up with is this: during my search, I found out the composition of the biuret and Fehling reagent is quite similar (Fehling reagent and biuret test). Maybe the orange result has something to do with this similarity, as the Fehling test gives orange as the positive result. But the thing is, the Fehling test I did on the tofu showed a negative result. At first, I suspect I took the test tube with Fehling for the biuret. But this is not the case since my classmates got the same orange result with the biuret.


texts: What happens if you superheat timber in a zero oxygen environment?

texts: I was thinking to myself, what would happen if you were to put a lump of wood in a zero oxygen environment and superheat it? It couldn’t burn because fire needs fuel, heat and oxygen however because wood is a mixture of cellulose + other things, it can’t really just melt... If this were done, what would really happen?


texts: How to determine the value for n in the Gibbs free energy and redox potential equation?

texts:
I am having a problem with this equation for redox potentials

$$\Delta G = -nFE_\mathrm{cell}$$

In this equation I never am totally sure about what the value of $n$ should be, for example for the reaction shown below, would the $n$ be 2 electrons or 1 electron? Personally, I think it should be 2 electrons because that is the number of mol of electron under the simplest whole number ratio.

\begin{align}
\ce{cyt $c$(Fe^3+) + e- &-> cyt $c$(Fe^2+)}\\
\ce{NADH &-> NAD+ + H+ + 2e- }\\
\end{align}

I think this is a different matter than in the already answered question "Does the relationship equation between standard cell potential and equilibrium constant violate potential's intensive properties?" Because in that Nernst equation the change in $n$ would be balanced by the change in the equilibrium constant. I assume that you are insinuating that there is one of the variables here which will correct for the increase in $n$. I don't see which would, as $E_\mathrm{cell}$ should be independent of quantity and $F$ is a constant.


texts: Does PubChem have stereocenter location data?

texts:
I have spent the last couple of days learning to navigate, find useful information and use the download service on the PubChem website. One of the pieces of information you can find is a stereocenter count, but I can't seem to find anything about the stereocenter location.
This might just be something that isn't available, but since I find parts of the PubChem website (specifically the download services), a bit unintuitive it might just be that I missed it. Therefore my question is this: is information about the stereocenters' location available in PubChem? Also, if it's just something that is not available in PubChem, are there any similar websites where it is available?
Note: the format doesn't really matter - it can be in terms of coordinates of the 2D-image or the number of the carbon counted from the highest priority functional group or whatever.


texts: Can an interaction be considered both hard-hard and soft-soft?

texts:
The $\ce {B-F}$ bond can be described as having both a large ionic and a large covalent character$\ce {^1}$, with the AIM charges on $\ce {F}$ and $\ce {B}$ being $\ce {-0.81}$ and $\ce {+2.43}$, respectively, and the bond critical point density being only slightly smaller than that for the $\ce {C-C}$ bond. In a similar vein of thought, can interactions between Lewis acids and Lewis bases be both rather hard and soft at the same time?

The Klopman-Salem equation can be used to quantify the degree of hardness and softness in a Lewis acid-base interaction$\ce {^2}$. The second term is a Coulombic attraction term and the third term is a HOMO-LUMO interaction term. Are there cases where both the 2nd and 3rd terms are large in magnitude?

References

Matta, C. F.; Gillespie, R. J. Understanding and Interpreting Molecular Electron Density. J. Chem. Educ. 2002, 79(9), 1141 - 1152
Fleming, I. Molecular Orbitals and Organic Chemical Reactions. John Wiley & Sons, Ltd. United Kingdom, 2009.


texts: What is thermal plasma in-flight oxidation technique?

texts:
From Vijay, M.; Ramachandran, K.; Ananthapadmanabhan, P. V.; Nalini, B.; Pillai, B. C.; Bondioli, F.; Manivannan, A.; Narendhirakannan, R. T. Current Applied Physics 2013, 13 (3), 510–516. DOI 10.1016/j.cap.2012.09.014:

  Since large quantity of energy is consumed to vaporize the solvent in liquid precursors, a novel method that involves thermal plasma in-flight oxidation of $\ce{TiH2}$ has been developed to synthesize nanocrystalline $\ce{TiO2}$."

What does in-flight mean in this context? Obviously it doesn't have anything to do with actual flying, but everywhere I look it says that it is used for something that occurrs or is provided during an aircraft flight.

The article is about photocatalytic inactivation of bacteria by reactive plasma nanocrystalline $\ce{TiO2}$ powder. It suggests a new method for the physical preparation of $\ce{TiO2}$ for a novel reactor.


texts: Why is the suffix carbaldehyde valid here?

texts:
The compound in question, and the name generated by ChemSketch:

I think this compound should be named as "cyclopentylmethanal" because the principal functional group (carbonyl) lies in the methane chain and not in the ring. So, the ring should be treated as a substituent for methanal, but apparently this is not the right answer.

I also noted that the following compounds validate my logic (ring is being treated as a substituent):

So, what is the exceptional rule with the first compound?


texts: Volume of nitrogen gas produced during taking off

texts:
The fuel in the buster rockets of the Space Shuttle is constituted of a mixture of ammonium perchlorate, $\ce{NH4ClO4}$, and aluminum powder. One of the reactions taking place during taking off is given by
  $$\ce{6 NH4ClO4(s) + 10 Al(s) -> 5 Al2O3(s) + 3 N2(g) + 6 HCl(g) + 9 H2O(g)}$$
  The indication (s) and (g) signify solid and gaseous phase. Suppose that these rockets are loaded with $\pu{11.75 ton}$ of ammonium perchlorate and $\pu{2.70 ton}$ of aluminum.

  Calculate the volume of nitrogen gas produced during taking off under normal
  conditions ($\pu{0^\circ C}$ and atmospheric pressure, so that $\pu{1 mol}$ corresponds to $\pu{22.4 L}$ of gas).

I got to the point where it's $\pu{10^5 mol}$ for each of the compounds.
How do you get to the answer $\pu{6.72e5 L}$?


texts:
The entropy change of a system is given by
$$\mathrm dS=\frac{\mathrm dq_\text{rev}}{T}$$
which at constant temperature is
$$\Delta S=\frac{q_\text{rev}}{T}$$
I also learned that the entropy change of the surroundings is
$$\Delta S_\text{surr}=-\frac{q_\text{actual}}{T}$$
Why do we use $q_\text{rev}$ for the system but $q_\text{actual}$ for the surroundings? How do we derive
$$\Delta S_\text{surr}=-\frac{q_\text{actual}}{T}$$


texts: What could cause a peak to split into 2 resonances as temperature increases in NMR spectroscopy

texts:
I understand that some peaks may coalesce upon an increase in temperature due to an increase in free rotation, this does occur with some peaks in my data. Why might you see a peak split into two other peaks? I have thought it may be to do with an equilibrium shift in a rapid conversion between species but really I would expect that to show as one peak shrinking and another one growing. The observed effect is one peak clearly splitting into two. Any ideas why this could happen?

Edit:
The sample is a diamagnetic complex with aromatic ligands with t-Bu groups in the meta and para positions. It is hard to assign peaks as I believe there may be an equilibrium between different conformations in solution. The peak that splits is in the alkyl region of the NMR (around 1.5 ppm) and probably corresponds to some part of the t-Bu groups. The 2 peaks produced do appear to get sharper with temperature and the two peaks are the same size, however the difference in chemical shift (between the 2 peaks) at higher temperature is much greater than the linewidth at the lower temperature (where it is one peak), so I'm not sure if this could be J-coupling being resolved.

If it was the case of 2 conformers being present, would you not expect the single peak to reduce in intensity as another separate peak appears and increases in temperature? Rather than a splitting into 2 new peaks?


texts: What is the major product obtained on acidification of substituted epoxide?

texts:
The problem

Source : MS Couhan (problems in organic chemistry . Chapter: Alcohols , phenols and ethers).
My Thoughts

If I proceed along $\ce{path 1}$ , $\ce1a$ is formed . It is unstable due to inductive withdrawing effect of $\ce{C=O}$ neighboring to it. Eventually $\ce2$ is obtained.
However, along $\ce{path 2}$ relatively more stable $\ce{3a}$ (compared to $\ce{1a}$) is formed. $\ce3a$ on ring expansion gives $\ce{3b}$ , leading to $\ce{4}$  ($\ce{3b}$ is relatively unstable compared to $\ce{1b}$).
My question
Which of the two paths should I choose that would lead to a major product ?


texts:
So, regarding a generic reaction (for the sake of argument, let us assume that it is completely gas phase), we have Le Chatelier's Principle. Let us use this example:

$$\ce{2SO2(g) + O2(g) <=> 2SO3(g)} \quad\quad \Delta H < 0$$

Now, we have the questions: oxygen gas is added, heat is added, a noble gas is added, etc.

For the addition of oxygen gas, we obviously shift right, and for heat, we shift left.

For a noble gas, I would expect no shift to happen. Indeed, this is what the SAT's seem to say, and I completely agree. However, my teacher seems to have the conception that when one adds a noble gas to a reaction such as above, you decreases molecular space, and the reaction does shift/speed up.

I have a test tomorrow, and if she gives me a question like this, I am planning to write that there is no shift or rate change. Now, if she marks this wrong, I need a formal argument to support my claim.

Am I correct in saying that with the addition of a noble gas, there is no change in either equilibrium shift or rate change? Why?


texts: Why should we use platinum wire or loop in flame test, can we use any other material ? Why can't we use glass it something?


texts: I had a bunch of old military trioxane fuel tablets.  I decided to open all of the packets, maybe a dozen, and place the contents in an empty tin coffee can with a plastic lid.  I put the can in a dark closet.  I let it sit undisturbed for several months.  Upon opening the can, I saw crystal structures growing off of the sides of the tin can.  They appear to be of a lightweight somewhat flexible plastic composition and are flammable in the same way that the rest of the fuel is.  If I disturb them by damaging them or removing them, more will grow over time, if I let the container sit.  What is this reaction?  Has anyone witnessed this before?


texts: Why are the vinylic bonds in alkenes slightly polar?

texts: when searching in the internet about why are alkenes more polar than alkanes (but still they are non-polar), they are always saying that the double bond is more polarizable , i understood the whole story about how the sp2 attract electrons from the sp3 and forming london forces, but they always said that vinylic bonds are slightly polar but i never understood why.


texts: Curious precipitate from substitution reaction

texts:
Two solutions were prepared.
'Solution A' being $\ce {Na2S4}$ prepared from aqueous $\ce {NaOH}$ and elemental sulfur, the mixture heated and additional sulfur added until sulfur remained as a precipitate.
'Solution B' being a solution of  $\ce {FeSO4}$ and $\ce {Fe2(SO4)2}$ prepared from reacting steel wool with $\ce{H2SO4}$, adding steel wool until reaction ceased. The liquid portion drained off and collected for use.
Solution A was added to Solution B via squeeze pipette in intervals allowing precipitate to settle between additions. This was continued until the net solution began to turn yellow from a rising conventration of  $\ce{Na2S4}$.
The solution was washed drained and the precipitate collected, however its character is not as expected from micro particulate $\ce{FeS2}$ but rather a black oily colloidal mass was the collected product. Did I somehow manage to acquire $\ce{Fe2S4}$?


texts: Why is the solution of (NH4)2[Ce(NO3)6] used as an oxidizing agent?

texts:
In an MCQ, the correct statement regarding the abovementioned compound is that its solution is used as an oxidizing agent.
I do not understand why that is so.


texts: Acidity of cyclopentadiene when fused to benzene rings

texts:
Why does fusion to a benzene ring reduce the acidity of a cyclopentadiene ring?

For example, acidity decreases going from cyclopenta-1,3-diene to indene and to fluorene:


texts: Which ligands would be exchanged in this reaction?

texts:
I have this reaction and need to state what the products would be:

$\ce{(CF3)2PH + [W(CO)5(THF)] -> }$

THF stands for Tetrahydrofuran.

Would this just be a simple ligand exchange, and if so which ones would be exchanged? How would you know?


texts: Why does Carbon-13 NMR not have splitting patterns?

texts:
I read about splitting patterns in proton NMR and found that this is due to spin-spin coupling, where reference to Pascal's triangle can explain the splitting patterns found in doublet, triplet and quartet.

My book mentions this later:

  There are also no splitting patterns caused by the spin-spin coupling, i.e. interaction of neighbouring protons in the 1-H atoms within molecules.

Advanced Chemistry for You, Third Edition (Ryan)

Why do you not find splitting patterns in Carbon-13 NMR?


texts: Resonance structures of 4‐aminobut‐3‐en‐2‐ylium

texts:
Problem

How many resonance structures can be drawn for the following molecule?

(a) 1
(b) 4
(c) 3
(d) 2

Answer

 (d) 2

Question
I think that the molecule can be drawn in three ways, which contradicts the book's answer. Can anyone explain?


texts:
Does "easily hydrated" imply highly soluble in water too?

Small ions like $\ce{Li^+}$ and $\ce{Be^{2+}}$ are said to be easily hydrated but does it also imply they are highly soluble?

I looked up some books and they say that compounds of Lithium like $\ce{Li_2O}$
and $\ce{LiF}$ are sparingly soluble.Why?


texts: Are there natural conditions that could enable the formation of noble gas compounds?

texts:
Noble gases were considered to be inert until compounds that include them, such as xenon trioxide (as an example) were found.

My question is, what natural conditions allow the formation of noble gas compounds?


texts: What is the viscosity of menstruation blood?

texts: I am writing my bachelor thesis about alternative materials for feminine hygiene products and for testing I need to know what the viscosity is of menstruation blood. Can I use water as replacement for menstruation blood because this kind of blood exists out of a big part of water? And what is the composition of menstruation blood in percentages?


texts: Does Potassium Superoxide also absorb Carbon Monoxide?

texts:
Potassium Superoxide ($\ce{KO2}$) is used as an oxygen provider and carbon dioxide scrubber in life support systems
$$\ce{2KO2 + H2O -> 2KOH + O2} \\
\ce{2KOH + CO2 -> K2CO3 + H2O}$$
I encountered a question that asked if Potassium superoxide can also serve as a scrubber for $\ce{CO}$. I thought of a reaction where $\ce{KO2}$ oxidized $\ce{CO}$ to $\ce{CO2}$ and the $\ce{CO2}$ was absorbed as previously mentioned
$$\ce{2KO2 + 2CO -> K2O2 + 2CO2}$$
Another possible reaction would be reduction of $\ce{KO2}$ to $\ce{K2O}$
$$\ce{2KO2 + 3CO -> K2O + 3CO2}$$
I could not find these reactions or similar ones mentioned in any literature online. This article describes the working of $\ce{KO2}$ in detail but I could not find a mention of carbon monoxide in there.
Can $\ce{KO2}$ also be used to scrub $\ce{CO}$? If so, how?


texts: how to remove acetone free nail polish remover from a thinkpad laptop keyboard?

texts:
I had dried spraypaint on my laptop keyboard and I tried my oxx studio brand nail polish wipes
(ingredients; propylene glycol, dimethyl adipate, dimethyl glutarate, dimethyl succinate, caprylic/capric triglyceride, parfum, propylene, glycol propyl ether, phenoxyethanol, benzyl alcohol, ethylhexylglycerine)
the wipes did get off the spray paint but it left the keys being sticky...
How do I get rid of the stickiness?


texts: What does the term "simple" in the phrase "simple whole number ratio" mean in Gay Lussac's law?

texts:
What does the term "simple" mean in the phrase "simple whole number ratio" in Gay Lussac's law?
I have searched this site as well as different sites on the internet. The answer to one question on this site states that it indicates that the numbers are small whole numbers. Another site stated that the terms of the ratio are not decimal numbers while another site states that the terms of the ratio are in simplest terms that is reduced form.


texts: Identifying luminescent transitions for lanthanides

texts:
Using the ground-state of Eu(III), how can I identify the possible (number of) luminescent transitions from the $^{5}D_{0}$ excited state?

I identified the ground-state term symbol for Eu(III) using Russel-Saunders coupling as $^{7}F_{0}$. I understand the selection rules and allowed transitions, but I'm not sure where to start on listing all of the possible transitions. I know that using RS coupling the $J$ states are $J=6,5,4,3,2,1,0$ but the transition from the $^{5}D_{0}$ state to the $^{7}F_{0}$ ground-state has $0\rightarrow 0$ with respect to $J$.

The only thing I could think of was to take the possible combinations of $\Delta S = 0,1$ and $\Delta L = 0,1$ and identify which of these transitions were allowed; is this along the right lines?


texts: Explanation of Lemon Juice-Invisible Ink

texts:
A cute homegrown spy-trick we all know: lemon juice invisible ink. But there is no scholary article available in the internet about this phenomenon.

A rough explanation I found in Scientific American:

  Lemon juice—and the juice of most fruits, for that matter—contains carbon compounds. These compounds are pretty much colorless at room temperature. But heat can break down these compounds, releasing the carbon. If the carbon comes in contact with the air, a process called oxidation occurs, and the substance turns light or dark brown.

But, this is not the type of explanation to be content with.

Question: What is the mechanism going on here? Please, support your answer with sufficient information and references, don't give a rough explanation.

Edit: I don't think my question is duplicate as I am asking for a well-referenced and informative answer which the other question doesn't have.


texts: Why do some reactions require specific pressures to happen?

texts:
For example, carbon monoxide reacts with hydrogen to synthesize methanol in the presence of some catalysts, but the pressure needs to be $\pu{50 atm}$ and the temperature needs to be $\pu{523 K}$.

Why the pressure? What does the pressure adds to the reaction?


texts: Why is lemon mixed with water considered alkalizing water?

texts: The benefits and facts of alkaline water are often skewed due to the marketing of companies and uneducated hype for the innocent idea of unlimited potential. I wanted to know the specific reactions occurring when mixing water and fresh lemon slices that lead to water becoming alkalized (higher in pH).


texts: Charge consistency in fragment qm/mm methods

texts: I'm calculating the multipole moments on several fragments of a molecule. What are some procedures to ensure that the charges etc are representative of the complete molecule? How do I ensure I'm not getting an overall charge in a neutral molecule?


texts: “Good” properties of transparent conducting oxides

texts:
I'm a computer scientist and I'm trying to figure out which are the key properties that define a “good” acting transparent conducting oxide (TCO) in order to consider several possible features to create machine-learning models for eventually discovering new TCOs.
I've already read that a “good” TCO should have a high electrical conductivity with a low absorption of visible light (which, in fact, makes it transparent), so a good measure of the TCO behavior could be defined as
$$\frac{\sigma}{\alpha} = -\frac{1}{R_\mathrm{s}\ln(T + R)},$$
where $R_\mathrm{s}$ is the sheet resistance in ohms per square, $T$ is the total visible transmission, and $R$ the total visible reflectance. By my understanding, also films thickness plays some role and it influences the values of $\sigma$ and $\alpha$. In particular, the more thickness I have, the more figure of merit $\sigma/\alpha$ increases and it results in a better behaving TCO.
Since I'm diving into chemistry for the first time, I wanted to ask you some suggestions about the topic, as well as eventually where to find interesting data about it.


texts: Common etchant for Stainless Steel 304L and Titanium Grade 2

texts:
I have Stainless Steel welded to Titanium. I need a common etchant to etch both S.S. and $\ce{Ti}$ so that I can do further analysis (like SEM etc). Right now I'm etching Ti Side separately and S.S. side separately and doing analysis twice, once for each metal. The etchants I'm using are mentioned below:

$\ce{HNO3 + 3HCl}$ - for S.S. 304L
$5\%~\ce{HCl} + 6\%~\ce{HNO3} + 16\%~\ce{HF} + 74\%~\ce{H2O}$ - for $\ce{Ti}$

Is it possible to combine these two etchants to form a common etchant, or are there any standard etchants available to etch both S.S. and $\ce{Ti}$?


texts: Charged nucleophile and SN1/E1/SN2/E2 reactions

texts: How can we say that if a charged nucleophile/base is present we can safely rule out the possibility that the reaction can take place via SN1/E1 mechanism? I have been trying to figure this out since hours. Help would be appreciated. Thank you. Source


texts: Using drip extraction, how much caffeine is extracted from coffee as a function of the amount of water used?

texts:
When using a drip coffee maker, there are basically two choices we make: the amount of water and the amount of coffee grounds.

If we use the same amount of coffee grounds but double the water, how much extra caffeine is in the resulting brew? Does all the available caffeine in the grounds get quickly liberated, so that there's not much of a difference between brewing with more water and diluting the brew with water afterwards? Or is it closer to the other extreme, where twice the water means twice the caffeine?

I saw on wikipedia that only about 20% of the caffeine is extracted for an 'optimal brew,' but I wasn't sure if that means we can extrapolate and say that the remaining 80% can be extracted just as easily.

I have the same question about the amount of coffee grounds. I only care to consider the 'normal brewing regime', that is with water at ~80-90C, 3-6 cups of water, and 1/4-1/2 a cup of grounds.

Thanks!


texts: Good sources to understand Stat Mech with concepts

texts:
I never had a proper course on Statistical Mechanics during my undergrad. I've tried picking up the subject by reading books, but I find that many focus on the mathematical derivations and I get easily lost in the details.

I was wondering if someone could point me to some useful reference materials where I could better understand concepts that are confusing to me. For example, why do chemical systems overcome energy barriers? I know that when a molecule samples a potential energy surface, the different states are occupied with probabilities relating to their energy difference according to the Boltzmann law. But, in classical physics, a ball rolling down a hill would eventually get stuck in the energy minima? I fail to see where do chemical systems get the energy from to be constantly in motion.

Sorry if this is a vague question or ill-posed, but as you can see I have some confusion of concepts in my mind which is not allowing me to develop a more accurate question.


texts: How to find the empirical formula for an nitrogen oxygen compound from the given mass of nitrogen and the product?

texts:
$5.00~\mathrm{g}$ of nitrogen is completely converted into an oxide of nitrogen. The mass of the oxide formed is $19.3~\mathrm{g}$.
  The empirical formula of the oxide would be?

My working:

$$\ce{N2 + O_2 ->  N$_x$O$_y$}$$

$m(\ce{N2}) = 5~\mathrm{g}$
$n(\ce{N2}) = 5/28~\mathrm{mol}$
$n(\ce{N$_x$O$_y$}) = 19.3~\mathrm{g}$

How do I approach this?


texts: Describe the electrons defined by the following quantum numbers?

texts:
n=3, l=1, ml=2; and
n=4, l=2, ml=-1

I know that the first one is in the third energy shell and the second one is in the fourth energy shell because n=3 and n=4 respectively. I also know that when l=1 it should be in the p orbital and l=2 should be in the d orbital. The next part I am a bit confused about!
In the third energy shell, my textbook shows there is no ml=2. Am I missing something?
In the fourth energy shell, where ml=-1 in which of the three p orbitals should the electron be, that is the x, y, or z one?


texts: How does the splitting in this molecule take place?

texts:
Consider the following molecule and data:

  $$
\begin{align}
\mathrm{H_a} &= \pu{1.0 ppm} &\quad J_\mathrm{ab} &= \pu{5.0 Hz}\\
\mathrm{H_b} &= \pu{3.0 ppm} &\quad J_\mathrm{bc} &= \pu{8.0 Hz}\\
\mathrm{H_c} &= \pu{6.0 ppm} &\quad J_\mathrm{ac} &= \pu{1.0 Hz}\\
\end{align}
$$

  Draw a splitting diagram for $\mathrm{H_b}.$ $(\pu{1 box} = \pu{1 Hz})$

Tried to draw the splitting diagram and ended up with this diagram:

I am also stuck as to how to draw the spectrum of the whole molecule as I feel $\mathrm{H_a}$ would be triplet of triplet. Am I on the right track and how to draw the sketch of the spectrum?


texts:
In class, the other day, we were discussing pH curves. Assume that I have HCl and NaOH of concentration 1 mol/mL. Now, consider that I have 50mL of HCl, and begin adding small quantities of NaOH. I observe that the pH increases, and once the volume added of NaOH reaches 50mL, the pH of the resulting solution becomes 7.

However, when mathematically calculating, if I added 49.99999 mL of NaOH, I find that the pH is way over 7 (the concentration of H+ becomes 50-49.99999 divided by 99.99999), which seems to be an anomaly. In essence, when finding the limit of - log (H+) as [H+] approaches 0, it needs to equal 7, but it doesn't. Does this mean that there should be a horizontal asymptote at pH = 7? Can somebody please explain this?


texts: I've heard from a few sources that over-voltage in a electrolysis cell for water will cause a greater heat buildup with no yield. Is this true, and if it is, why is it true? From my electronics background, voltage can be though of as electric potential, or thinking of it as water in a pipe for an analogy it is the strength of the substance flowing through the pipe, or as the strength of each electron, so why does it cause extra heating with no appreciable/no yield?


texts: I am trying to perform the demonstration of a strongly endothermic reaction reacting barium hydroxide with ammonium nitrate.  I have been scouring the web for ways to get barium hydroxide, but none have showed any promise.  The only way I have seen to obtain it is by heating the nitrate to decomposition and reacting the oxide with water.  I would rather avoid this as I have no way to deal with the nitrogen dioxide gas that would result.


texts:
I'm having a hard time finding data about an experiment that I know has been done a bunch of times:

I have a sheet of single crystal rutile $\ce{TiO_{2}}$ (110) that I want to reduce to various $\ce{TiO_{2-x}}$ forms where the x is what I want to vary. I want to try to avoid conversion to the other Magnéli phases if possible $(\ce{Ti_{n}O_{2n-1}})$. To do this reduction, I have a high temp oven that I can flow with 95% $\ce{N_2}$ and 5% $\ce{H_2}$ or simply evacuate. I can set the flow rate to cubic centimeters per second. I need a chart that will tell me what temperature, flow rate, and duration I need to convert my sheets surface to a desired reduced value (i.e., I want a specific x).

I then want to reoxidize the surface by using lower temperatures in a furnace that I can fill with oxygen at different pressures. I need a chart that will tell me what temp, partial pressure of $\ce{O_2}$, and duration I need to re-Oxidize the surface.

The goal here is not to simply get the surface, but to test other properties. I was hoping this step (finding the proper charts) would have been fairly straightforward, but my literature searches haven't turned up quite what I need. I was hoping someone here can point me to a resource that has this data.


texts: Does chromium oxide form on Stainless-steel in 'deoxygenated' water?

texts: Will a passive layer form on stainless-steel in pure (0.055 μS/cm) water with an oxygen concentration < 50 ppb. If so, why is this type of water generally called 'deoxygenated'? If a passive layer (chromium oxide) does not form with such low oxygen concentration why is this, since there IS still oxygen in the water.


texts:
While reading about the size of atoms and ions of the Group 1 elements in the textbook "Concise Inorganic Chemistry" by JD Lee, I came across this line:

  The Li+ is much smaller than the other ions. For this reason, Li only mixes with Na and above 380 Celsius, and it is immiscible with the metals K, Rb and Cs, even when molten; nor will Li form sunstitutional alloys with them. In contrast the other metals Na, K, Rb, Cs are miscible with each other in all proportions.

I am unable to understand why the elements cannot form alloys with Li and what makes the other elements miscible with each other in all proportions.

I observed that the metallic radius of Li is 1.52 $\unicode{xC5}$ and that the difference between its radius and that of Na is about 0.34 $\unicode{xC5}$. But the difference between the radii of the other successive elements in this group is also about the same, so it doesn't help explain miscibility.

I would really appreciate some insight and clarification.


texts:
In the aldol condensation reaction of a ketone with an aldehyde, both having acidic alpha hydrogens present; what is the major product?

Is it formed from enol of the ketone, or of the aldehyde? Is it from the enol of the ketone, because aldehydes are more reactive towards nucleophilic addition? Confirming, just to be sure.

Furthermore, which aldol condensation products are usually neglected?


texts: What's the purpose of stirring the mixture at 0 degree and dding NaOH to the organic reaction mixture?

texts:
I used to follow the lab protocol without thinking, but I now hope to understand why certain procedures are done.
I am synthesizing dimethoxyacetic acid from methyl dimethoxy acetate(so hydrolysis from ester to COOH).

Add lithium hydroxide monohydrate (89.5 mmol, 3.75 g,1.2 equiv) to a solution of methyl dimethoxyacetate (74.6 mmol, 10 g, 1 equiv) in dioxane (45 mL) and water (45 mL) at 0 °C.
Stir the mixture for 1 h at 0 °C and one additional hour at room temperature.
Add sodium hydroxide (1M aq soln, 75 mL) to the mixture.
Extract the mixture with diethyl ether (375 mL).
Acidify the recovered aqueous layer with hydrogen chloride (6N aq soln) until a pH of 1-2.
Extract the organics with diethyl ether (375 mL).
Dry the combined organic layers with magnesium sulfate and filter.
Evaporate the solvent slowly under reduced pressure to obtain 2,2-dimethoxyacetic acid.

I thought the reason why you acidify the aq. layer was to convert -COONa or -COOLi (ester salts) in the layer to acid (-COOH). Then doesn't it mean that the product I want ( dimethoxyacetic acid ) will be in the aqueous layer? Why do I need to care about the organic layer?

Would appreciate any insight&help!


texts: Identifying Name/Purpose of piece of ellipsoid glassware with internal tube?

texts:
I recently went to a market in Southern France and found this little piece of equipment for sale along with a whole bunch of other chemistry things. the guy had no idea what it was for or where he'd gotten it from, but for €1 I decided I had to have it because I've never seen anything quite like it (and I'm mildly infatuated with old chemistry equipment...). I'm wondering if anyone here would be able to identify it?

An image with a 10 pence coin for size comparison.

My first thought was some sort of condenser, because the design is a quite similar due to the external jacket with an internal tube. However on closer inspection the internal tube has a cut out section which would mean any coolant would mix with the substance being condensed.

this diagram shows a little bit more detail about the internal construction of the piece (cross-section):

There is also some text on the body of the tube which says:

  EX 2ml COLD E - MIL LINE

Thanks for any information someone could give me about what this piece of equipment is and/or what it was used for.


texts:
I mix and develop glaze recipes for midfire stoneware (fired to 1220°C). The colorants in pottery are mostly iron, copper, cobalt, tin, titanium, chrome, and a few other transition metals. Many of these materials are somewhat toxic in the raw form but safe in the finished work. These colors usually make up less than 3% of a glaze recipe.

Vanadium is a colorant that potters seem to fear without good reason. I find resources such as MSDS sheets to be very unhelpful on this subject.

The heart of my question is: in your humble-I-am-not-going-to-sue-you opinion, is vanadium (specifically tin-vanadium) safe enough? How about relative to cobalt?


texts: What should be the name of the given compound?

texts:
Following compound is named as

(1) 6-Mercaptocyclohex-4-ene-1,3-diol
(2) 1-Mercaptocyclohex-2-ene-4,6-diol
(3) 1-Mercaptocyclohex-5-ene-2,4-diol
(4) 4-Mercaptocyclohex-2-ene-1,5-diol

As per my knowledge if I start numbering the compound from the alcohol then to mercapto group, then alkene group.
So, according to me, the numbering should be from bottom alcohol as number 1 and making the way to the top alcohol as number 3. Then mercapto will come at number 4 and alkene at 5.
So as per me the name should be 4-mercaptocyclohex-5-ene-1,3-diol, but according to the answer key the answer should be (1). Is there any rule which I am missing out on?


texts: Why can DAP be used to elute a protein in affinity chromatography?

texts:
A little background: as part of my bioinformatics degree I have to take Protein Chemistry course, but I miss chemistry basics (have CS background), so that's why I'm asking the following question.

We performed protein (Galanthus Nivalis L. agglutinin) purification in class, using affinity chromatography.
The mannose column was loaded with protein (mixed with ammonium sulphate), washed with ammonium sulfate and then the protein was eluted using 20 mM DAP. While I understand the principle of affinity chromatography, I can't really figure out the chemistry of using DAP to elute the protein.

Would appreciate any help.


texts: How does LC50 translate to "real world" exposure for paint thinner?

texts:
Last year I started oil painting, which means (in part) that I use paint thinner for working with and/or cleaning brushes. I recently became concerned about my exposure to the vapor from the paint thinner I use, so I requested a toxicology report from the manufacturer. In the document it specifies that the summated $\mathrm{LC}_{50}$ for the product is 21400 mg$\cdot$ m$^{-3}$.

My (basic) understanding of this is that 50% of test subjects will die with a single exposure at the above level; however, I've really no idea how that translates to "real life" and wonder if someone can shed some light on it.

I'm painting in a reasonably small room (around 3 m x 5 m) with windows open, so I'm essentially trying to determine if this is safe or not, or whether I should be using breathing apparatus and/or move to a different room.

This is a link to the whole document which I received from the manufacturer which contains the substance and other information.


texts: Relationship between Van der Waals forces and the boiling point

texts:
Choose the right answers in the following statement:

The boiling point of a liquid substance is higher as the Van der Waals forces (in/between) the molecules of the substance are (lower/higher).

I don't understand why the Van der Waals forces are lower when the boiling point is lower. Second, do you say: the forces in the molecules of a substance or the forces between the molecules of a substance?


texts: Using Le Chatelier's Principle to explain why percent dissociation of acids/bases increase with dilution

texts:
$$\ce{HA(aq) +H2O(l) <=>H3O+(aq) +A- (aq)}$$

Say the acid solution is currently in equilibrium. How would diluting the acid by adding water change the equilibrium position? Le Chatelier's Principle says pure liquids like water do not affect the equilibrium position. Using the equilibrium constant, it is easy to show the reaction should shift towards the right, but how can we show that with Le Chatelier's Principle?


texts: Sign of the work done during a reversible compression

texts:
The work done during a reversible compression - if $V_\mathrm{i} = V_1$ (initial) and $V_\mathrm{f} = \frac{1}{6}V_1$ (final) - of an ideal gas is?

I chose $1.8 p_1 V_1$. Is it right or should it be $-1.8 p_1 V_1$?


texts: Equlibrium for a non-spontaneous reaction

texts: Consider a reversible reaction $\ce{A -> B}$, at standard state wher $\ce{A}$ and $\ce{B}$ are at $\pu{1 atm}$. If the free energy of products is greater than the free energy of reactants, $\Delta_{\text{R}} G^\circ > 0$, and since $Q = 1$, the overall free energy for this reaction is $\Delta_{\text{R}} G^\circ > 0$ and this tells me the reaction is non-spontaneous. Yet, being at standard state does not mean that the reaction is at equilibrium, in fact $Q = 1$ could be greater or less than $K$, the products are not at equilibrium, and hence amount of $\ce{A}$ and $\ce{B}$ will adjust to a point where $Q = K$. Wouldn't that have just mean that the reaction is not at equilibrium and hence would spontaneously adjust to reach equilibrium. But yet $\Delta_{\text{R}} G^\circ$ tells me that it would not be spontaneous. Wouldn't this two concepts be conflicting against each other?


texts: I have been looking for a physical explanation for entropy and enthalpy variations. An example would be the air system of a vehicle, where people say we have a strong enthalpy and entropy variations along the exhaust line, which is not the case in the fresh air line. How could that be possible?


texts: Free Web-Based Orbital Solver to look into the Walsh orbitals of a perturbed cyclopropane

texts:
There exists a free online orbital calculator.

When I draw cyclopropane it plots three molecular orbitals, but unfortunately it doesn't use the Walsh orbitals.

Are there any free online tools which can solve such the problem?

(It would be very nice if it would also be an android app. Please let me know if you know one.)

The section below is for interested chemists:

The reason why I want to do that:

Cyclopropane can, to a good approximation, be described with the following orbitals:

The question was how the molecule orbitals behave if we add an electron withdrawing group (a $\pi$ acceptor because some people call it the "CXZ model")

The solution says:

  In the substituted case all energy levels are lying more down in energy.

I don't agree because I only see overlap with the Walsh Möbius set of $sp$ orbitals in the following sketch:

The Hückel set (a simpler way to put it: the energy lowest orbital in the scheme of cyclorpropane; used above) gives no overlap with the $p$ orbitals of an electron withdrawing group, e.g. X=COOH.

As I see from the orbitals' interaction, I believe the solution is wrong, I don't agree that all orbitals are lowered.

EDIT:

Sorry for the mistake in the sketch, there is of course only one of the two degenerate Möbius orbitals lowered.
I guess COOH not only has a $\pi$ acceptor effect but also a $\sigma$ acceptor effect which could lower all orbitals.


texts: Why does cationic charge density affect metallic bonding?

texts: Group II metals have a smaller cationic size but one more valence electron than Group I metals. Why would the higher charge density of a metal cation affect the strength of the bonding of it in its elemental state?


texts: Oxidation of water — what is the half reaction for water?

texts:
During the electrolysis of a solution of copper sulfate, copper is reduced to form a solid on the inert electrode while water is oxidised at the anode. What is the half equation for water?

\begin{align}
\text{Is it}&&
\ce{4 OH−(aq) &-> O2(g) + 2 H2O(l) + 4 e−}\\
\text{or}&&
\ce{2H2O(l) &-> 4H+(aq) + O2(g) + 4e–}?
\end{align}

What is the difference? And what is the standard reduction potential in an electrolytic cell?


texts: Cr(II) and Mn(III) - their oxidizing and reducing properties?

texts:
My textbook states that $\ce{Cr^2+}$ is a reducing agent while $\ce{Mn^3+}$ is an oxidizing agent in spite of both having $\ce{d^4}$ configuration. The explanation states that when $\ce{Cr^2+}$ gets oxidized to $\ce{Cr^3+}$, it attains a stable half-filled $\mathrm{t_{2g}}$ orbitals but when $\ce{Mn^3+}$ gets reduced to $\ce{Mn^2+}$, it attains a stable half-filled $\mathrm{d}$ orbitals.

First, is it a reasonable explanation? If this is the case, why can't $\ce{Cr^2+}$ get reduced to $\ce{Cr+}$ to attain a stable half-filled $\mathrm{d}$ orbitals and $\ce{Mn^3+}$ get oxidized to $\ce{Mn^4+}$ to attain a stable half-filled $\mathrm{t_{2g}}$ orbitals, i.e. in-short is the vice-versa true?


texts: Why can't beryllium react with hydrogen gas directly to give hydride?

texts: I read in a textbook that all alkali metal and alkaline earth metal can react with hydrogen directly to give hydride except for beryllium. I want to know the reason why because I know that $\ce{BeH2}$ exists in a polymeric state.


texts: Quantifying a racemic mixture by combining signal-to-noise measurements

texts:
I'm working with chromatographic data for the measurement of a chemical that takes two separable forms in equal proportions (a racemic mixture). This produces two adjacent signals (peaks) which are nearly identical, notwithstanding some minor analytical measurement variation. I need to make a judgement call on whether the compound is "detected" or not across many hundreds of samples, so I'm looking specifically at the signal-to-noise ($s/n$) ratios of each peak (using the root-mean-square measurement of baseline noise). I'm using $s/n = 3$ as a threshold for detection (LOD), but some peak pairs close to the threshold of detection will have one peak with s/n barely above and the other barely below.

How can I most appropriately combine these two largely-redundant measurements?  Can I average the two s/n measurements for one single easy-to-interpret value?


texts: Can you differentiate between Kc and Kp in this problem?

texts:
I know how to do this problem. We must find the value of K to compare to the value of Q, which can easily be calculated.

I know that the equation we use to get a K out of delta G is as follows:

However, does this equation give us a Kp or a Kc value? What would it give me in this problem if I plugged in the provided delta G standard value?

I calculated the value of this K (whatever it is) to be 1.00, and I also calculated the Qc and Qp for this problem to be 0.00005 and 0.36, respectively. So clearly, Qc and Qp are both less than K. But how can we determine of Qc is really < Kc in this problem?


texts: Difference in work done by a gas in reversible and irreversible isothermal expansion

texts: Why there is difference in work done by gas in isothermal expansion when gas expands through reversible and irreversible process?


texts:
Is it possible, in principle, for a second row homonuclear diatomic system to show a bond order of 4 in an excited state?  If so show the energy level diagram for such a system?

I am confused about this problem, mainly because I don't understand what it would mean for a diatomic system to be in an excited state.  Could I just move an arbitrary number of electrons from the n=2 energy level to the n=3 level?


texts: Why do electron-rich aryl groups have greater migratory aptitudes?

texts:
In the following reaction there are three possible aryl groups that can migrate: an unsubstituted phenyl group, a p-methoxyphenyl group, and a p-nitrophenyl group:

Why does the electron-rich p-methoxyphenyl group migrate instead of the phenyl or p-nitrophenyl group, especially when it leads to a carbocation that is less stabilised (since it will no longer be conjugated with the stabilising p-methoxyphenyl group, cf. the crossed-out arrow)?


texts: Mechanism for the synthesis of 2-pyridone from pyridine N-oxide

texts:
I'm specifically interested in the pathway from pyridine N-oxide, where there is some kind of reaction and rearrangement with acetic anhydride.

I'm assuming there is first a substitution (by the negative oxygen) at the carbonyl. The -OAc group can then attack at the alpha-position on the ring.

We could continue and say that the loss of H and the -OAc group on nitrogen happens next to restore aromaticity, but then we're stuck with that OAc group instead of the carbonyl.

From what I could find, it doesn't seem that there's a radical mechanism here, but if there is some intramolecular rearrangement, I cannot seem to find it.


texts: How can I make my yeast experiment more chemistry-oriented?

texts:
For a school chemistry design lab I tried to find the optimal sugar concentration for fastest yeast fermentation. I put the same amount of yeast and sugar water solutions with different concentrations of sugar together and measured the carbon dioxide produced using a water displacement apparatus. My teacher approved the topic, which is why I went along with it, but our teachers are often too lenient with approving topics, and this will be moderated so I can't just squeak through.

My main problem is that I feel it is too biology-oriented. There is very little chemistry in it. What can I do (preferably with yeast because I still have quite a bit and it wouldn't seem like a complete change of topic to my teacher)


texts: What is the name of the compound Sc(HCO2)3?

texts: I would like to know what the name of the compound $\ce{Sc(HCO2)3}$ is. I've been told that it is not scandium hydrogen carbonite and that it is not scandium formate. Any hints or suggestions about how I can solve this problem?