texts: What are the units that measure free energy?

texts: Is it $\pu{kJ/mol}$? I have done problems and I always end up with these units, but is this correct?


texts: What is the difference of molar volume between dissolved 35Cl- and 37Cl-?

texts:
Im am geochemist, dealing with isotopes such as 35Cl and 37Cl.

For some model I'm trying to make I need to be able to estimate what is the difference of partial molar volume between dissolved 35Cl and 37Cl in water (as chloride Cl-).

Huge literature exists concerning the partial molar volume of Cl- and other ions, but I can't find anything on specific studies on variations of volume on different isotopes. As in isotopes geochemistry we're often looking a permil variations of ratios, any tiny difference in molar volume of 35Cl and 37Cl would have an importance for me.


texts: How can I permanently write on HDPE plastic?

texts:
So I just spent the better part of an hour graduating a food grade HDPE 5 gallon bucket with permanent marker so I can easily fill it with water of a certain amount for homebrewing.

I'm all done. The only problem is that permanent marker wipes off of HDPE quite easily. I guess I should have tested that first...

Anyways... what CAN I use to write on HDPE plastic? Or will I be forced to etch the markings in with a nail or something?

I tried a Google search for "How to write on HDPE plastic?" and came up empty.


texts: How to calculate concentration from reaction quotient and initial concentration?

texts:
Say I know that the reaction quotient $\left(Q = \dfrac{[B]}{[A]}\right)$ for a simple reaction $\ce{A\to B}$, at $t = 0$, $[A] = 1$ and $[B] = 0$, at some time in the future is $Q = 1$ (or any number really).

Is there a way to calculate the concentrations of A and B, or is more information required?


texts: What do you call different formations of polycyclic molecules, such as the 'bent' phenanthrene vs. the 'linear' anthracene?

texts:
Are there terms, IUPAC or not, that describe multiple carbon rings fused in different shapes, like the aforementioned anthracene and phenanthrene?
Also, I thought I read about a term describing carbon rings that only attach at one carbon, as opposed to two....


texts: What is the difference between the units 'torr' and 'mm of Hg'?

texts:
According to present definition torr and mm of Hg differ though slightly.
I am still confused over it. Can someone write an explicit answer differentiating between them and the reason for differentiation as earlier they were considered same. The explanation is probably related to the changes is pressure at different heights so I want the exact definitions of these units that was used earlier and what modifications have been made?


texts: Acetophenone reacted with LDA and diethyl carbonate. Why do I need HCl?

texts: I'm working on a practice problem that asks for the product of acetophenone and LDA reacted with diethyl carbonate. After this, it says step 2 is HCl. After I react the first step, I get the correct answer to the problem - ethyl benzoylacetate. I'm asking why the problem says that HCl is added even when everything is neutral in the product I got and it's correct.


texts: Whether the entropy change of the system is positive or negative

texts:
$$\ce{N2(g) + O2(g) → 2NO(g)}$$

My thinking: since gases are combined together, so there randomness or disorder gets decreased. Hence the sign of entropy change of the system should be negative.

Book Solution: the sign of entropy change is impossible to predict.

Why can't we predict the sign of entropy change for the given system?


texts: How can we tell the particle size of solutes in solutions?

texts:
This is a general question in regard to solutes dissolving into solvents. I am interested in the reality of the particle size of the solute during dissolution.

For example, take $\ce{NaCl}$ and dissolve it into water. Are the salt particles, which are now invisible to the eye, truly dissolved? Meaning have they turned into single atom particles of $\ce{Na+}$ and $\ce{Cl-}$ clinging to $\ce{H2O}$ water structures?

Chemical equations seem to imply this. However, when you look at colloids, then particle size matters and can vary. Do ionic salts still have large clusters of their cations/anions upon dissolution?

I am really interested in this topic and would love someone to give me a good explanation.


texts: Why is distillation not a viable way to separate ammonia from water?

texts:
Since the steam pressure of ammonia is higher than that of water, I would expect distillation to be a reasonable way of separating a mixture of both.

However, in industrial applications known to me there's always a step of stripping the ammonia chemically from the vapor. Why is this necessary?


texts:
The following table is showing the solubility of CO2 at different pressures.

However, I cannot figure out how to read this graph. The y-axis is molar fraction so that should mean that its value = mol CO$_2$/(mol CO$_2$ + mol H$_2$O). The journal that I got this graph from does not specify how many moles/what mass of water is used. Can I assume that it's 1 and that the y-axis is actually just the moles of CO$_2$


texts: Is the ring or the chain chosen as the parent structure in octan-2-ylbenzene?

texts: How would you name the above compound according to IUPAC rules? I see some sources say it is 2-phenyloctane, but ChemDraw and a few other sources say it is 2-octanylbenzene.


texts: Why does hybridization produce a more stable structure?

texts:
I am aware of the fact that hybridization does not ALWAYS produce a stable structure (example: PH3)
However, my question is, what makes hybrid orbitals so effective in forming stable bonds? Although exceptions like PH3 do exist, what makes hybridization the best option for stability most of the time?
Is it due to the fact that the unequal lobes formed ensure greater overlapping and hence more stability?


texts: Does granite become soft as modelling clay at 2000 °C?

texts: As Wikipedia tells us, it consists of $\ce{Al2O3}$ ($14.42\%$) (alumina) whose melting point is $\pu{2072^\circ C}$, and $\ce{SiO2}$ ($72.04\%$) (silica) whose melting point is $\pu{1713^\circ C}$. So does it soften to modelling clay (or at least partially soft, modelable via tools structure) at $\sim\pu{2000^\circ C}$, or does it stay hard and why?


texts: Can gold cause tin or other metals to corrode?

texts:
I stumbled upon the following article while trying to identify some old RAM modules:

https://www.techrepublic.com/article/quickly-identify-ram-chips-with-these-tips/

In the article, it mentions the following about gold contacts:

  A note about contact metals

  Chip contacts are either gold- or tin-plated. I recommend chips with
  gold contacts because they don’t corrode. Also, never insert
  tin-plated chips into gold-plated sockets. Different metals will
  increase the likelihood of corrosion.

I don't understand how gold cannot corrode on it's own, yet cause another dissimilar metal such as tin to corrode.  Is this article correct?


texts: Why do 3d orbitals have lesser energy than 4s orbitals in transition metals?

texts:
This is quoted from Jim Clark's Chemguide

  For reasons which are too complicated to go into at this level, once you get to scandium, the energy of the 3d orbitals becomes slightly less than that of the 4s, and that remains true across the rest of the transition series.

What is the reason stated above? Why does in only transition series, 4s has more energy than 3d & not in the preceeding elements?


texts:
In the following reaction, why does ring expansion not take place?

Mechanism that was the correct one:

In the second step when there is a protonated carbon the ring should expand to become 6 membered as that is more stable. This should be followed by a methyl shift from Quaternary to tertiary and then the $\ce{Cl}$ should get attached. But this doesn't happen. Why is that? According to my textbook's theory, what I described should occur but the mock test says otherwise. Are there some more criteria-besides.

protonated carbon next to ring,

forming of a more stable 6 number ring

for ring expansion that my text book is missing?
Any help would be appreciated.


texts:
Attempt:

I did aldol condensation in acidic medium followed by $\ce{E1cB}$ to get 1,3-diphenylbut-2-enone but the answer given is:

I am unable to devise a mechanism to reach the above product from the reactant. Could someone please suggest the mechanism?


texts: Which has a lower boiling point, Ozone or CO2? Why?

texts:
Ozone is a bent molecule, and therefore, Ozone is a polar molecule.
Polar molecules have dipole-dipole intermolecular forces.
CO2 is a linear molecule, and therefore, CO2 is a nonpolar molecule.
Nonpolar molecules have london dispersion intermolecular forces.

Having dipole-dipole intermolecular forces means you have greater intermolecular forces than London dispersion forces, and therefore means that you have a higher boiling point. Therefore, Ozone should have a higher boiling point than CO2.

However, after looking at multiple sources across the internet, Ozone has a lower boiling point than CO2.
Could someone provide an explanation as to why this is true?


texts: Why does HCN boil at a higher temperature than NH3?

texts:
The boiling point of ammonia is −33 °C while that of $\ce{HCN}$ is 25 °C. In a recent AP (Advanced Placement) Chemistry test, a free response question asked why this is the case. Can someone shine light on this?

Based on Jan's answer:

Although the $\ce{C-H}$ bond does not usually exhibit good hydrogen bond, $\ce{H-CN}$ is a special case in which the bond is polar enough to provide better hydrogen bonding than $\ce{NH3}$. I agree with Jan on this point.
However, Jan's explanation is for the polarity of the $\ce{H-CN}$ bond is based on $\mathrm pK_\mathrm a$ (lower $\mathrm pK_\mathrm a$ suggests higher acidity and good hydrogen bonding). As one user pointed out, $\mathrm pK_\mathrm a$ is only defined in aqueous solution, so stating pK$_a$ as an evidence is not suitable for the system I have which is a pure $\ce{HCN}$ liquid. In such system, $\ce{HCN}$ does not significantly dissociate. A suggestion was made on using proton affinity as the evidence for the acidity of $\ce{HCN}$.

I perceive that the answers (reasons and evidence) are mostly targeted at the chemical process of dissociation of $\ce{HCN}$. Should this question be addressed more in terms of a physical process? I mean there is little dissociation of pure-liquid $\ce{HCN}$.

What I have been thinking about is a MO picture in which the cyano group withdraws electron density from the hydrogen atom, in a similar way to how acetate group withdraws electron from the hydrogen in acetic acid. What is your thought on this?


texts: When calculating the distance between molecules in a solution, is it reasonable to approximate a sphere around each molecule?

texts: I am attempting to calculate the average distance between molecules in a particular concentration of a solution. My first instinct was to treat the solution as a system of spheres surrounding the solute molecules, the size of which would be dictated by the concentration. Obviously such a calculation of the distance between molecules is primarily dimensional analysis, but is it a realistic treatment of the system, or is there a more appropriate way to arrive at the distance? A spherical treatment, in my mind, has the drawback of not accurately reflecting the distribution of solvent in the solution: a matrix of identically-sized spheres has vacant space, which a solution clearly would not have.


texts: In sourdough bread baking what do the wild yeast and bacteria not eat during dough fermentation and why?

texts: I bake bread using a sourdough starter. The starter is a culture of lactobacillus and some kind of yeast. They apparently eat the sugars or carbohydrates in the dough during fermentation but when I look at the nutritional info for fully baked sourdough bread I see 56gm of carbohydrates per 100gm and my question is, why do these organisms stop eating and what is it exactly that they leave behind? They seem to consume something in the dough then they stop as if they have run out of food at which point you need to bake the bread else it becomes "over-proved". Why do they stop eating and what is actually left over when the fully fermented dough goes in the oven?


texts: What is the number of stereoisomers for hex-4-en-2-ol?

texts:
For the following compound, find

  Total number of stereoisomers
  Number of optically active stereoisomers
  Total number of fractions on fractional distillation of all stereoisomers

There is a chiral carbon marked with "*" in the compound. The compound is thus chiral and is optically active. The configuration at the chirality centre can either be R or S. There is also a double bond in the compound and cis-trans (geometrical isomerism) is possible here. So using basic permutations there are totally $2\times2=4$ stereoisomers (optical and geometrical).

Since there is a chirality centre the compound exists in right-handed and left handed systems and thus is optically active. Thus all the 4 stereoisomers are optically active.

Out of R-cis, R-trans, S-cis, S-trans isomers there are two pairs of diastereomers - R-cis, S-trans and R-trans, S-cis - so there are 2 fractions obtained due to fractional distillation.

Final Answer

Total number of stereoisomers = 4
Number of optically active stereoisomers = 4
Total number of fractions on fractional distillation of all stereoisomers = 2

Are my approach and my answers right?


texts: Why do certain mixtures foam and others don't? How to predict if a mixture will yield a foam?

texts:
I recently acquainted myself with the skill of whipping a mixture of sugar, fresh brewed/ hydrated instant coffee into a pale, fluffy, stiff and stable foam. This, as some might know, is known as Café Cubano or Whipped Coffee in some of parts of the world (gives you a foamy and light textured espresso).

The other day, I tried whipping the mixture, just with the addition of some peanut butter in the start (I had tried it with peanut butter before, but had added it at a later stage) and it failed to stiffen and hold up any air.

I am familiar with how whipping cream works: the mechanism is easily available to be read on several sources over the internet, but am unable to figure out the mechanism for the above mentioned mixture.

Also, I want to know why an impurity (peanut butter, as I've yet explored) inhibits the foaming process. What decides if a mixture can be whipped and how can it be predicted if a given mixture will foam?

All insights are welcome. .)


texts: Calculating partial pressure of carbon monoxide

texts:
$\ce{ZnO}$ is exposed to pure $\ce{CO}$ at $\pu{1300 K}$ and the equilibrium
$$\ce{ZnO(s) + CO(g) <=> Zn(g) + CO2(g)}$$
is then established at $\pu{1 atm}$ pressure. The density of the gas mixture is $\pu{0.344 g L-1}$ at the same temperature. Calculate the partial pressure of $\ce{CO(g)}$ at equilibrium (atomic weight of $\ce{Zn}$ is $65.4).$

My attempt
Since at equilibrium the amounts of $\ce{CO}$, $\ce{Zn}$ and $\ce{CO2}$ are equal (as no information about initial amounts are given), mole fraction of $\ce{CO}$ is 1/3.
Since pressure is given as $\pu{1 atm},$ the partial pressure of $\ce{CO}$ is 1/3 atm. Where I am wrong?


texts:
I was trying to assign weights to each state in a CASSCF PES scan using nroot=2 in Gaussian. I specified 0.500000 0.500000 at the end of .com file. But it caused the program to assign the weight for the first calculation only. All the rest points of the scan had weights 0 and 0, which I don't want to have. I referred to the Gaussian manual which states

  StateAverage: Used to specify a state-averaged CASSCF calculation. All states up to NRoot are averaged. This option requires the weighting of the various states to be input in format $n$F10.8 (no trailing blank line).

But I don't understand what is this nF10.8 format means and if it could help me solve the problem to assign the weight in each step of the scan. I tried writing 0.500000 0.500000 one after the another for say 50 points and I could see the required weight has been assigned. Can someone clarify the meaning of the nF10.8 format? I searched on internet but I couldn't find any helpful material.


texts:
Which among these hydrocarbons is more acidic?

Here, I thought about hyperconjugation. For this, I counted the alpha H i.e. the number of hydrogens attached to the carbon attached to a sp2 hybridized carbon. What I get is, (C) has most no. of those Hydrogens. So, my assumption is that  it should be more acidic. But that's not the case. Where am I going wrong?


texts: Equilibrium constant for heterogeneous equilibria having aqueous as well as gaseous reactants

texts:
Suppose we have a heterogenous equilibrium :
$$\ce{A(aq) +B(aq) <=>  C(g) +D(aq)}$$
Which equilibrium constant is used here?
Both pressure and concentration terms are there. So, according to me, both $K_\mathrm{p}$ and $K_\mathrm{c}$ can be written separately. If that is the case, can we relate both of them by $K_\mathrm{p} = K_\mathrm{c} (RT)^{\Delta n}$?


texts: Equivalent weight in case of disproportionation reaction

texts:
We all know that

$\text{Equivalent weight} = \frac{\text{Molecular weight}}{\text{n-factor}}$

However consider a reaction like:

$\ce{Br2 + OH- -> Br- + BrO3- + H2O}$
where oxidation numbers of $\ce{Br}$ are $0, -1, +5$ respectively.

  What should here be the equivalent weight of $\ce{Br2}$?

PS: I understand that I should also show what I've attempted. But, this is just a question that came up into my head
and I've made it as descriptive as possible. I don't really see anything else that I must add to make this question complete.

Thank you!

UPDATE: I just came across a formula for calculating the n-factor for a dispropportionation reaction $n_f=\frac{n_1\cdot n_2}{n_1+n_2}$ (sources, 1 and 2), for $n_1$ the magnitude of n-factor in oxidation reaction and $n_2$ the magnitude of n-factor in reduction reaction. Can anyone prove how to arrive at this formula?


texts: I am running a proton NMR on a liquid organic product. I understand that we wouldn't want to use anything that contains hydrogen atoms as a solvent, but I'm not sure why we need a solvent at all.


texts:
According to my notes, octahedral site stabilization energy (OSSE), sterical effects and electronic effects in stability create a confusion in this theory. However, we are able to solve this problem with few rules:

Tetrahedral splitting energy is nearly equal to 4/9 octahedral splitting energy.
As the OSSE increases, the $O_\mathrm{h}$ geometries will be more favored.
These are useful to decide to whether the structure is spinel or inverse spinel.

I got $\ce{ZnCr2O4}$ ($\ce{Zn^2+}$, $\ce{2Cr^3+}$, $\ce{4O^2-}$):

$\ce{Zn^2+}$; $\mathrm{d^{10}}$ ion with CFSE = $0$ and thus, there will be no effect on $O_\mathrm{h}$ holes.
$\ce{Cr^3+}$; $\mathrm{d^3}$ ion with CFSE = $\pu{-8 Dq}$ and OSSE = $\pu{8.45 Dq}$ so, this is thought to occupy $O_\mathrm{h}$ holes.

Since $\ce{Zn^2+}$ can only occupy $T_\mathrm{d}$ holes, then it suits the rules for being normal spinel.

On the other hand, if we got a group II metal with a non-zero CFSE, then what would the result be?


texts: Complexation of hydroxy chalcone oxime with metal

texts: Does the complexation of 2-hydroxy chalcone oxime (below) with a metal require any catalyst? Is the complexation pH sensitive?


texts: Determination of +/- reflections in sigma molecular term symbols

texts:
This page, which depicts the molecular term symbols for the $\ce{O2}$ and $\ce{O2-}$ (Edit: Mistaken on $\ce{O2-}$) molecules, perhaps best summarizes the full scope of my questions. In general, I don't understand how a specific electron configuration relates to either +,- or both reflections.

Why does the linked page switch reflections for different spin multiplicities, ie. why does $^3\Sigma^-$ have a minus reflection but $^1\Sigma^+$ a positive reflection?
For $\ce{O2-}$, the left configuration leads to $^3\Sigma^- + ^1\Sigma^+$. Why are two sigma terms needed to describe this configuration?
As a more general question, how accurate is it to use the molecular orbital representation for deriving term symbols? Most sources I have seen describe electron configurations as three degenerate p-orbitals or 5 degenerate d-orbitals and never invoke MO diagrams. However, it seems necessary for deriving both parity and reflections. Is the MO approach always correct? Can the term symbols be derived without using MO diagrams, specifically for the parity and reflections?

Thank you for any advice.


texts: What chemical reactions take place when mixing baking soda with citric acid and epsom salt and putting it into a microwave oven?

texts:
When I mixed in a bowl baking soda, citric acid and Epsom salt, then put it in the microwave between 30-60 seconds, the mixture will start to fizz and puff up, kind of like dough rising. What is happening here?

I've done test with all of the ingredients individually in the microwave and nothing happens. I've tried various combinations of any two of the three ingredients and nothing happens. Only when all three are mixed together does the mixture fizz and puff up. It seems like the catalyst is the Epsom salt. What is in the Epsom salt that is setting off the other two ingredients?

I know that baking soda plus citric acid together with water will also fizz, as $\ce{CO2}$ is released. I was wondering when I have the three ingredients in the microwave and it is puffing up, is $\ce{CO2}$ also being released?

Furthermore, the resulting mixture that had puffed up, if I put it in water it will still fizz and create $\ce{CO2}$, just as if had I never put the mixture in the microwave and just put it straight in the water. What I'm also wondering about if the microwave had hurt the ability of the mixture to create fizz in the water later, i.e., would there have been more fizz in the water otherwise?

After asking my question I found this YouTube video that said heating up Epsom salt releases $\ce{H2O}$ gas. Which would make sense why my mixture is puffing up. Still I'd love to hear anyone else's opinion on this.


texts: Why doesn't CaO decompose into Ca and O2?

texts:
Many metal oxides decompose into the free metal and oxygen gas at high temperatures, but why doesn't $\ce{CaO}$ do that? What happens to $\ce{CaO}$ at high temperatures?

This is from problem 2 of the 2011 USNCO local exam:

  Oxygen gas can be produced by the decomposition of all
  of the following substances EXCEPT

  (A) calcium oxide. (B) hydrogen peroxide.
  (C) mercury(II) oxide. (D) ozone.

The correct answer to this question was (A).


texts: Given solubility of sodium carbonate, find mass of hydrate sodium carbonate dissolved?

texts:
I am working on a problem from my scholarship exam practice (MEXT). I am not quite sure if I got it right. The question was provided with multiple choices (a) to (f) below:

  The solubility of sodium carbonate in $\pu{100 g}$ water is $\pu{25.0 g}$ at $\pu{22 ^{\circ}C}$. How many grams of the hydrate $\ce{Na2CO3∙10H2O}$ can be dissolved in $\pu{100 g}$ of water at $\pu{22 ^{\circ}C}$? (a) $\pu{0.556g}$; (b) $\pu{0.762g}$; (c) $\pu{9.27g}$; (d) $\pu{67.5g}$; (e) $\pu{81.7g}$; (f) $\pu{117g}$

I honestly do not know how to solve this problem. My best guess is to find the moles of sodium carbonate that can be dissolved in water first (from $\pu{25.0 g}$). And use that moles equate to the moles of hydrate form (1:1). Then find the mass of hydrate form by multiplying its molecular weight and my answer would be $\pu{67.5g}$. There is no answer key provided so I would like to hear other opinions and get some advice.


texts: I'm trying to generate a figure for a physics textbook to show examples of the vector addition of dipole moments in small molecules. For this purpose, I would like to render pictures of a bunch of small molecules, such as CS2, formaldehyde, benzene, SF6, and chloroform. I've got avogadro running on my linux box, but I'm finding it very time-consuming and confusing to construct the molecules using the GUI. Is there anywhere that I could find pre-made CML files for small molecules like these?


texts: I observed a sharp decrease in the current when I carried out the electrolysis of water. Just to set the context, I used a voltage of $\pu{12V}$ and the concentration of my electrolytes were $\pu{0.15 mol dm^{-3}}$ for $\ce{Ca(NO3)2}$ and I used graphite rods which were flaking but I am not sure whether that might cause such a significant dip in the current. I did also notice some white material forming on the cathode. So I want to know why there is such a dip?


texts: Why does increasing the pressure cause ice to melt more?

texts:
This question was given under chemical equilibrium.

  Why does increasing the pressure on this system cause ice to melt more?
  $$\ce{H2O(s) <=> H2O(l)}$$

I'm pretty sure this has to be solved using Le Chatelier's principle; the hint given is that The molar volume of water is more that of ice.

My understanding of Le Chatelier's principle is that a system tries to oppose any change.

So the equilibrium must shift towards the side where the pressure decreases.

Given this hint, I fail to see the correlation between molar volumes and pressure.


texts: Is there a method to separate iron from mercury?

texts: The mercury is contaminated with iron. Is there any way to remove iron from mercury?


texts: Correct Electron Pushing with HCl and Water

texts:
My book indicates that the following electron pushing is wrong:

So what would the right electron pushing diagram be?

I have the following in mind. My rationale is:

1) Electrons attack protons, not the other way around. This is just convention right? Is this just a conceit in chemistry; just a standardization? On a related note is this why one person described organic chemistry as:

"The foundation of every reaction in organic chemistry can be found in one statement: Nucleophile Attacks Electrophile."

Rather than electrophile attacks nucleophile?

2) Water is the base here; water is the Lewis Base (nucleophile) so water will attack the hydrogen cation (which is a bare nucleus).
3) HCl is the acid here; H+ is the Lewis Acid (electrophile, so it's going to go toward the lone pairs on the water).

So:

Would this be right?


texts: Reaction between phosphorus pentachloride and sulfuric acid?

texts: I am a novice in chemistry. While reading a magazine, I stumbled on some information about phosphorus pentachloride and sulfuric acid. Phosphorous pentachloride and sulfuric acid are both good dehydrating agents. What is the reaction between them (at standard temperature and pressure).


texts: Why does sulfur, but not oxygen, catenate?

texts:
Oxygen is a rather boring element. It has only two allotropes, dioxygen and ozone. Dioxygen has a double bond, and ozone has a delocalised cloud, giving rise to two "1.5 bonds".

On the other hand, sulfur has many stable allotropes, and a bunch of unstable ones as well. The variety of allotropes, is mainly due to the ability of sulfur to catenate.

But, sulfur does not have a stable diatomic allotrope at room temperature. I, personally would expect disulfur to be more stable than dioxygen, due to the possibility of $\mathrm{p}\pi\text{-}\mathrm{d}\pi$ back-bonding.

So, why do sulfur and oxygen have such opposite properties with respect to their ability to catenate?


texts: Why is the first ionization enthalpy of zinc higher than expected?

texts:
The following sentence is stated in my current chemistry book:

  The first ionization enthalpy of zinc is higher because it represents an ionization from the $\rm 4s$ level.

Now zinc does have an ionization enthalpy of $\pu{906 kJ/mol}$, which is higher than copper's $\pu{745 kJ/mol}$ or nickel's $\pu{736 kJ/mol}$ in the same series. But I am not sure that the reason for this increase stated in the book is correct. For example, even copper has an ionization from the $\rm 4s$ level, but it does not have anywhere near as high ionization enthalpy as zinc. Is the book correct, or is there some other reason for this?


texts: Where to find a comprehensive list of chemical/biochemical etymologies?

texts:
I've found lists like this, which explain what different root words mean. But I'm looking for explanations of why those roots mean those things.
For example, why does carbonyl refer to a carbon double bonded to an oxygen? What is the historical rational behind why the -yl implies the oxygen double bond?
I'm hoping this gives me a little more intuition to remember what different chemical terminology means without brute-force memorization.


texts: How can we measure the rate of reaction of EDTA chelation with zinc carbonate?

texts: I am performing an experiment in order to find the activation energy of EDTA chelation. Consequently, I need to measure the rate of reaction of the process. I am high school student, and so I do not have access to sophisticated equipment, although they might be unnecessary. However, I have been attempting to measure the volume of gas produced, but I am not achieving any result. So, can you suggest any other method to measure the rate of reaction? I would greatly appreciate the help since there is not a sufficient amount of information on the internet to help me get a clear answer, I have been working on the reaction for more than a month and a half.


texts: Why sugar solution/sugarcane juice becomes sour when kept for certain time?

texts:
I stir-dissolve some sugar in a cup of water and then keep it open for certain time (say a few hours), when I taste it I feel that it has became sour.
I have observed the same thing many times when I went to juice shop(s) and asked especially for sugarcane juice when I drank it, it tasted a bit sour (sometimes too sour to drink) and I just realized that the sugarcane (or other fruits) juice was extracted some hour(s) ago because I know that a fresh juice doesn't taste sour until kept (open) for a certain time.
From all this experience one thing I know is that the sugar solution or sugarcane (or other fruits) juice becomes more or less sour when kept for a certain time after extraction. It's most probably due to acid (which usually tastes sour) formation but I don't know what chemical changes turn a sugar solution or (sugarcane) juice sour (acidic) when kept for a certain time?
Any explanation will be greatly appreciated. Thanks.


texts:
What are the IUPAC rules when naming a coordination complex like:

  $$\ce{[Pt(NH3)4][Pt(NH3)Cl3]}$$

Now according to my textbook, it is named as tetraammineplatinum(II) amminetrichloridoplatinate(II). Both the $\ce{Pt}$ atoms have the oxidation state +2 .There are no charges assigned to the two complex ions in the formula, so, my assumption is that the entire complex is neutral and thus the oxidation states for $\ce{Pt}$ should be assigned accordingly. However, on assigning the oxidation states as mentioned in the answer the assumption is proven wrong. I'm confused about the mentioned oxidation numbers.

How do you calculate the oxidation numbers of the metal atoms in such a complex?
Shouldn't the charge on each complex ion be mentioned in the formula if the oxidation states given in the answer are correct?


texts: Are any other orthonormalizations schemes besides Lowdin normally used when solving SCF equations?

texts:
When solving equations of the form:

$$F(C)C = SC\epsilon$$

(e.g. Hartree-Fock-Roothan or Kohn-Sham-Roothan) where $F$ is the fock matrix, $C$ is the coefficient matrix and $S$ the overlap matrix, the usual way to proceed is to first perform a change of basis and orthonormalize the AOs (atomic orbitals) by performing a Lowdin (Symmetric) orthogonalization. I know at least one case (The Psi4 program) where a different orthogonalization scheme is used (Canonical) but I haven't been able to find any information of other alternative orthogonalization schemes implemented in any programs. Are any other schemes used? If so, where and why?


texts: How may the water from rain be tested to determine it is natural, or from cloud seeding?

texts:
This article lists several mechanisms that may be used to control the weather and/or induce rainfall. Apparently many states, other than the one listed in the headline, have experimented with such techniques. The article also lists concerns over contamination from such artificial rainfall.

Say I, a layman without access to a laboratory, collect the rain in a glass. What test/tests may I apply to determine whether it is natural rainfall, or the outcome of cloud seeding?


texts: Is there an easy way to detect methanol in spirits (which may have been adulterated)?

texts: Is there an easy way to detect methanol in spirits, which, you suspect, may have been adulterated?


texts:
I am attempting to isolate pure iodine from kelp using the method described here
but I do not have any way of possibly obtaining cyclohexane.  I was wondering if any easier to obtain solvents would work as well to isolate the iodine from the rest of the mixture.  I was hoping to use a solvent that is easy to obtain in a grocery or hardware store.


texts: Why do significant figure rules contradict each other?

texts:
So I came across a problem in my chemistry textbook that brought up another question. The problem had to do with calculating the mass% composition of chlorine in a certain molecule.

So to go about solving this, you could calculate the mass in grams of 1 mole of the molecule and divide the mass in grams of the corresponding amount of moles of chlorine by that number and multiply that by 100 to get a percent.

The molecule had 3 Cl molecules, so I would look and see that the molar mass of 1 mole of Cl is 35.45g. So I would multiply that by 3 to get 106.35g of Cl, but I would have to round that to 4 significant figures since 3 has infinite significant figures, and the mass of Cl was given in 4. Which means the mass of 3 moles of Cl is 106.4g.

Which poses my question... Isn’t multiplying the molar mass of Cl by 3 the same as adding the molar mass of Cl 3 times? And if so, wouldn’t that mean that if you were to add the mass 3 times, then the significant figure rules for adding would tell us to round to the number in the problem with the least decimal places, which is 2 decimal places? So when you add the mass of Cl 3 times you get 106.35g so then you round to 2 decimal places and get 106.35g.

Why does this give a different answer? How come when you multiply by a number with infinite significant figures, the number of significant figures in your rounded answer can be different than if you were to add that something to itself that same amount of times?

Can’t you be certain to the tenths place in this example, and have the hundredths place by your uncertain digit since when you add, you don’t have to round any numbers off? If not, why not?


texts: How to Protect one -OH group in 1,4-benzenedimethanol using TBDMS

texts:
Actually i want to protect one -OH group using using 1.1Eq of TBDMSCl and 1.5 Eq of Imidazole. Is is possible to protect one OH group using these condition. Even if i get mixture of Products ( one protected OH and Both OH protected compounds), separation by column would be easy and what would be approximate yield of both products.

any suggestions.?


texts: How to model CRISPR/Cas9 binding and cleavage using a generalized Kittel's zipper model?

texts:
I am thinking about how to model the binding of a CRISPR/Cas9+guide-RNA complex to a double-stranded DNA that cause its cleavage.
This post describes four steps at which a CRISPR/Cas9 system binds and cuts a target DNA strand:

PAM Binding:
Phosphate Lock Loop
Guide RNA binding
Cleavage

I believe it is possible to develop a fairly simple model based on Kittel's zipper model or its generalization to estimate the propensity of a Cas9 and gRNA to cleave the DNA.
Thus, I would appreciate some advice how to develop such a zipper-like model (e.g., maybe by having a double zipper).
Ultimately, I would like to compute the free energy of the different states based on the sgRNA sequence: $\Delta G_\text{bind}$, $\Delta G_\text{melt}$, $\Delta G_\text{cut}$.
Here is another schematic illustration by Addgene (in this illustration, the binding step includes the DNA melting and the binding of the RNA with the DNA):


texts:
We did an experiment where copper iodide 4-methylpyridine and copper iodide imidazole was formed and now we are asked what orbital the electron is excited from and to.

After much research we still struggle to answer this question. We came to the conclusion that the structure of our two products are tetrahedral and thus the electron should be excited from $\mathrm{e_g}$ to $\mathrm{t_{2g}}$. However, since copper is a $\mathrm{d^{10}}$ metal, isn't the $\mathrm{t_{2g}}$ orbital full? So, to which orbital would the electron be excited? Have we misunderstood anything?

All help as well as links to helpful information is much appreciated!


texts: Why is the effect of beta-branching neglected in this comparison of SN2 reaction rates?

texts:
Which compound would give a faster SN2 reaction?

  2-bromobutane
  1-bromo-2-methylpropane

The answer is given (2).

While I agree that the primary position is preferred as compared to the secondary position (for an SN2 attack), but won't beta branching hinder the nucleophile's attack, hence, reducing the reactivity for SN2?


texts:
Question:

  Calculate the potential of hydrogen electrode in contact with a solution of pH 10.

My attempt:

Cell reaction: $\ce{ H^+ + e^- -> \frac{1}{2}H_2 }$

I've attempted to solve this myself by using Nernst equation which yielded the answer -0.591 V. But I believe that Nernst equation is used when there are two electrodes, but my friends are saying that

"how will you make a cell from one electrode?".

So guys, please rectify the problem.


texts: Does 1-ethylidene-2-(propan-2-ylidene)cyclobutane show geometrical isomerism?

texts:
I think it should be yes, but my book says no.
I think the two geometrical isomers are

Z-isomer

E-isomer


texts: Are there any amphoteric substances other than water and ammonia?

texts: I have read about the Brønsted-Lowry and Arrhenius concepts to define a substance as an acid or a base. Our teacher told us that there are substances which behave both as an acid and a base, using water and ammonia as examples. He also asked us to find other substances with the same behavior. Does anyone know any more substances which are amphoteric in nature?


texts: What is the difference in the effect of DTT (Dithiotreitol) and SDS (sodium dodecyl sulfate) for PAGE?

texts:
In class, we have studied that when running a polyacrylamide gel with our protein sample to separate the proteins by molecular size, we can use several techniques, among which we have denaturing PAGE and SDS-PAGE. Basically, we focused on the latter, in which SDS is a detergent added to negatively charge all proteins in the sample (at a constant mass:charge ratio), as well as denature them. Then, the professor mentioned that we also add reagents such as DTT or beta-mercaptoethanol to reduce the disulphide bonds in between proteins.

My question is: if SDS already denatures proteins (so we have primary structure only), why would we be interested in adding DTT?


texts: The most variant groups of periodic table

texts: Is it okay to call group 11 (formerly 1B) a "group"? I meant that according to my knowledge "A group is a horizontal column consisting of elements with similar valencies and a continuous gradation in physical and chemical properties" but there is no gradual trend or we don't obtain similar reactions for same circumstances. Members do not show similar oxidation states and do not form analogous compounds. Electronegativity values and other bonding characteristics also deviate badly from one another. Are they in a group just because their atomic numbers allot their positions in same vertical column? Shouldn't 1B and other d-block "groups" (which show such variant properties) treated as "ungrouped region" or something like that?


texts: Why are group 1 elements so low in density?

texts: I was studying the s-block elements and found that they extremely low in density. Lithium is said to be the least dense solid in the entire periodic table and their Cohesive Energies are also very low. Could anyone please explain in detail the reason for this?


texts: Why are protons in the same position in 1-chloro-4-nitrobenzene magnetically different?

texts: Protons in ortho positions towards the nitro group are said to be magnetically different, even though they're chemically equivalent. Same goes for protons ortho towards the chlorine. Why is that so?


texts: What is a laboratory set-up for the synthesis of ethanol from ethene?

texts:
I am doing a chemistry investigation and one component of that requires me to synthesize ethanol from ethene. Ethene itself is gaseous at room temperature and pressure so I was wondering if someone could suggest how I can carry out this synthesis with the use of acids to obtain ethanol.

To give you an idea of what I am actually doing for this investigation, I am trying to find the yield of ethanol when ethene is hydrated using different acid catalysts. However, because ethene is gaseous, I don't know how I am going to actually do this experiment.

To further clarify, I know what reagents I need to use and I know the mechanism of the reaction, I just don't know how to do it practically within a laboratory setting.


texts: Distinguishing among SN2/SN1/E1/E2 for a secondary bromide

texts:
a. 2-Bromo-3-phenylbutane reacts with $\ce{NaOMe}$ in methanol. What is the mechanism?
b. This compound then reacted with $\ce{CN-}$ in DMSO. What is the mechanism?

My Attempt
a. I am debating between $\mathrm{E1}$ and $\mathrm{S_N1}$ since it is a polar protic solvent and the carbocation can be stabilized by the tertiary carbon and phenyl group. I am leaning towards $\mathrm{E1}$ since $\ce{OMe-}$ is a strong base. Am I correct?
b. If the answer to the first question was $\mathrm{E1}$, then 2-phenylbut-2-ene would be the product. I don't see how that would react with $\ce{CN-}$ in DMSO. So, would no reaction occur?


texts: Additional example determining Marcus parameters searched

texts:
Background / theory: The electron transfer in organic materials was formalized by the Marcus theory, introducing $|H_{ab}|$ to describe the how molecules (or more generally: sites) are coupled with each other, and reorganization energy $\lambda$, about how costly it is to to accommodate a charge after the carrier moved.  Especially if the atomic coordinates of the material already are known, it is possible to access these parameters by quantum chemical calculations.

Background / software: NWChem seems to be one of the freely available programs allowing such an additional characterization.  New to this program, I found both the standard entry in the manual (here), as well as a post in the user forum (here) by 2012, comparing the result to a literature reference in Phys Rev B 2007 as "work[ing] pretty well".  It is possible for me to to replicate the computation filed there under "Sep 19th 2012", too.

The feeling: It seems dangerously simple to use this script for an other structure, just replacing the first / second / third block of coordinates by the $(x,y,z)$ extracted from X-ray diffraction analyses about molecule A, hoovering neighbor B, and the close couple / dimer (AB).  Indeed, my first tests (again, as a beginner) failed; the program launched, yet eventually shut down -- likely because I do not know well enough how to proceed.

The question: Does one of you know about an additional tutorial, starting from accessible atom coordinates of molecular materials, concluding with the Marcus parameters of the electron hopping?


texts: R or S configuration of propane-1,2-diol

texts:
What is the specific configuration (R or S) of this compound?

My answer is R, because $\ce{H}$ is not in the back so I flipped the compound. Is my answer right?

My teacher is telling me it is S, though I'm pretty sure that it is R. That made me very confused.

What I did is that I got S at the beginning, but because $\ce{H}$ is not in the back, I flipped the compound and got the answer R. My teacher flipped the compound in a way that the answer was still S.

$\ce{OH}$ (1), $\ce{CH2OH}$ (2), $\ce{CH3}$ (3), $\ce{H}$ (4) from 1 to 3, anticlockwise which means it is S configuration. But $\ce{H}$ is not in the back, Therefore rotate the compound and the answer should be the opposite to S which means it is R.


texts: A transition element is one which forms one or more stable ions which have partially filled d-orbitals. Manganese (Mn) could have an oxidation state of 7+, which means that it will lose all of the $\ce{3d^5}$ and $\ce{4s^2}$ electrons. So how could it make a 7+ ion in that case (which means that it will lose all of the $\ce{4s^2}$ and $\ce{3d^5}$ electrons) and still be defined as a transition element?


texts: Are these two space groups in a group–subgroup relationship?

texts: Given two crystal space groups, how can one determine if they are in a group-subgroup relationship? The specific case at hand is P 21/m 2/m 2/a (aka P m m a, #51) and P m m 2 (#25), but knowing how to solve this question in a general manner will sure prove helpful in the future as well…


texts: What drives vibrational cooling in an excited stated?

texts: As we excite a molecule from its ground state, $S_{0,v=0}$, to some excited state in a higher vibrational state, i.e. $S_{1,v'=3}$, what drives vibrational cooling within that excited state manifold (such as $S_{1,v'=0} \leftarrow S_{1,v'=3} $?) This is a fast process, typically on the order of hundreds of femtoseconds, and it occurs prior to any photorelaxation (as per Kasha's rule). Due to the vibrational density of states being quite high near the first excited state, is it the anharmonic coupling to these states that drives vibrational cooling? Furthermore, is there a quantum mechanistic/mathematical way of depicting the probability/rate of this process (as in, what would the relevant perturbation term $\hat{H}{'}$ for dealing with this problem in the context of Fermi's golden rule)?


texts: Potassium carbonate and water/alcohol/toluene?

texts:
Recently I did a distillation. At a certain point an azeotropic mixture of alcohol, water and toluene evaporated and was caught in a beaker with anhydrous potassium carbonate. I had to shake it and then pour it back into the reaction mixture (while filtering out the solid).

Why did I have to catch it in a $\ce{K2CO3}$-mixture?

(The product was diethyladipate)


texts: Which compound reacts faster in the Cannizzaro Reaction?

texts:
Which reacts faster in the Cannizzaro Reaction?
  a) $\ce{OHC-C6H4-NO2}$
  b) $\ce{OHC-C6H4-OCH3}$

Obviously, a better hydride releasing group will react faster. Therefore my answer was b, as $\ce{-OCH3}$ shows -I (inductive) effect as well as +R (resonance) effect, as it's in the para position. This increases the electron concentration in the $\ce{C}$ atom of $\ce{CHO}$ and due to the excess electrons, it is a better donor of an electron to the $\ce{H}$ attached to it. Thus, leaving a  $\ce{H-}$.

But the answer given is a. The answer states that $\ce{C}$ can only give electron to $\ce{H}$ when it accepts an electron from the $\ce{O}$ attached to it. For that the $\ce{C}$ should be electorn deficient. Therefore an electron withdrawing group (in this case $\ce{NO2}$, which shows -R effect at ortho and para positions) better releases hydride.

But I don't think that happens. That's because if $\ce{C}$ is electron deficient, then it wouldn't give an electron to $\ce{H}$ (less electronegative) in the first place, even if it takes an electron from oxygen (which is also tough).

Can anyone give a proper explanation to the whole problem?


texts:
I have been told that with the help of crystal field theory, we can decide the electronic configuration ($\mathrm{t_{{2g}}}$ $\mathrm{e_g}$ configuration) of the metal ion in a complex.
For example, in octahedral complexes, if the ligand is a strong field ligand, pairing of electron in $\mathrm{t_{{2g}}}$ will be favorable, rather than the electron occupying an $\mathrm{e_g}$ orbital. The opposite is true for a weak field ligand.

The spectrochemical series which helps us relatively identify which ligand is a strong field ligand, and which is a weak field one.

I have two questions:

I understand that the ligands towards left side are strong field, and the ligands towards right side are weak field. But let’s say we take a ligand in the middle. Is it strong field or weak field? Which ligand from the left side is the last strong field ligand? Is it even possible to determine that?
Let’s say we have the following compound:
$\ce{[CoCl2(en)2]Cl}$. Now, as $\ce{Cl}$ is a weak field ligand and en is a strong field ligand, how exactly do we decide the electronic configuration? Is there any general method which considers cases like this?

Please bear in mind that I am a high school student, and I might not be able to understand any  advanced theory involved.


texts: Recrystallization of two unknown compounds?

texts:
I managed to separate a binary mixture(in solid form) of two unknown substances into two individual solid compounds. For the separation, I used an acid-base extraction with dichloromethane, NaOH, and after separation HCl.  My next step is to purify the two separated solids using recrystallization(this is the technique mandated by my instructor for solid purification) but I am not sure which solvents to use. Can anyone suggest how I should proceed ? Thanks a lot !

Edit: I was thinking since I used NaOH and HCl on my aqueous layer, NaCl would have formed. Since compound doesn't dissolve in water, is it okay to just put the compound in water, let NaCl dissolve and vacuum filter the solid(which presumably should be pure solid) ?


texts:
Is it possible to say water vapour and dew is the same? I know that the water vapour is the gaseous phase of water. But what is the dew? I just wonder how can I categorised it. Is it the liquid  or the gas phase of the water.

Figure below shows dew formed in grass. It seems as a liquid. But is it actually  exhibit in liquid phase or gas phase?


texts: How can I calculate the molar conductivity of a solution with multiple solutes?

texts:
I'm running an experiment mixing 2 different solutions, $\pu{5 mL}$ of $\pu{0.1 M}$ $\ce{NaCl}$ with $\pu{5 mL}$ of  $\pu{0.1 M}$ $\ce{KCl}$. I am measuring the conductivity of the total solution in $\pu{mS/cm}$, and also measuring concentration of the electrolytes with electrolyte analyzer, so I will get the individual concentrations of $\ce{Na+, K+, Cl-}$ in the mixed solution.

How do I calculate this mixed solution total molar conductivity given these settings? The literature only shows the calculation for a single solution, and I couldn't find any reference on how to calculate this kind of combination.


texts: DFT Calculations, Atomic Ionization Potentials -- Which Exchange-Correlation Functional to Use, to Preserve Koopmans Theorem?

texts:
I have a program which can perform density-functional calculations for atoms, given a density functional.

Of course the simplest form of exchange potential to use is one relevant for a uniform electron gas (i.e. the original Kohn-Sham exchange, proportional to $n_e^{1/3}$). A good correlation functional is also available. However when I performed calculations for some atoms the energy of the highest occupied orbital differs greatly from the ionization potential (off by a few eVs!).

That the energy of the highest occupied orbital equals the ionisation potential of the neutral atom is known as Koopmans' Theorem. I get a feeling from the literature that DFT can be quite accurate. So what's wrong?

Interestingly when I use the Slater exchange functional, coupled with a correction suggested by Skillman (i.e. replacing the potential by $1/r$ when the overall potential drops below that value), the results improve significantly. (See the book "Atomic Structure Calculations" by Herman Skillman). Well, maybe I should follow this recipe, but it seems the procedure is quite ad-hoc.

My question is, are there any functionals which will give reasonable values for the atomic ionisation potentials? I do not want to implement methods like the optimised effective potential method since the latter is not readily generalised to a finite-temperature scenario. Thanks.


texts: How do you determine the hybridisation state of a coordinate complex?

texts:
If an exercise asks for the hybridisation state of a coordinate complex (ion in solution) consisting of a central cobalt atom surrounded by $\ce{NH_3}$ ligands, and neither coordination number or complex ion is given, how do you decide which configuration will occur?
The answer is that in a solution this will form a $\ce{[Co(NH_3)_6]^{3+}}$ complex ion. I know that this means the hybridisation is $\mathrm{d^2sp^3}$ but can't figure out how to get there since cobalt is found in different oxidation states.


texts:
For hydrogen, other than in the 1s state, the electron wavefunctions have radial and/or angular nodes where the electron probability density is zero.

In helium or further atoms with more than one electron, considering correlation of electrons, what happens to these nodes?  Are there still radial and angular nodes where electron probability density is zero?

For example, if helium is in a 2s2s state, is there anywhere that an electron cannot be?


texts: How is the yellow colour of nitric acid removed?

texts:
Nitric acid obtained in laboratory is slightly yellow due to the dissolution of nitrogen dioxide which is produced due to thermal decomposition of a portion of $\ce{HNO3}$.

$$ \ce {4HNO3  -> 2H2O + 4NO2 + O2}$$

Its says here that if $\ce{CO2}$ is bubbled through the acid, it turns colourless- because it drives out $\ce{NO2}$ from warm acid which is further oxidized to nitric acid.

What does it mean by drives out ? How can carbon dioxide drive out nitrogen dioxide that's dissolved in the acid? And also, the oxidation of 'what' is being talked about here?


texts: Why can't primary alcohols react with sodium bromide via an SN2 mechanism?

texts:
I was told that a primary alcohol reacts with $\ce{HBr}$ for example, but not with $\ce{NaBr}$ through the $\mathrm{S_N2}$ mechanism in the same reaction environment. Why?

This reaction can occur:

$$\ce{R-OH + HBr -> R-OH2+ + Br- -> R-Br + H2O}$$

But this reaction does not occur:
$$\ce{R-OH + NaBr -> R-OHNa+ + Br- -> R-Br + NaOH}$$


texts: Different shapes of fluorescence spectra in Raman

texts:
Note: I haven't owned any of these spectrometers. I'm asking so I can decide whether to buy 532nm or 785nm wavelength raman to probe molecular structure (especially solutions) and I'm concerned about fluorescence versus signal intensity. The first picture is from 16:00 minute time of this video https://www.youtube.com/watch?v=VHjmlQdzpW4&t=1099s

Why is the shape of fluorescence spectrum different between systems using 532nm and 785nm wavelength laser in Raman Spectroscopy? In the following using the 785nm RMX, the fluorescence is maximum at the left (starting at 100 cm-1) and minimum at the right (ending at 2750 cm-1).

While in the following where the sample is the coke itself using 532nm raman spectrometer, the fluorescence has the peak at center with each side at minimum (also started a 100 cm-)?

This is with the coke removed and spectra saved. The peak is at 2400 cm-1.

My question is that both started a 100 cm-1. But in the case of the 785nm raman, the fluorescence spectrum started at maximum already compared to the 532nm raman which has the peak at higher cm-1. Why?


texts: In a liquid crystal cell used for LCD the conductive substrates, usually made of ITO, are in contact with the liquid crystal. The question is: when a voltage is applied to the electrodes to reorient the molecules is there any current flowing through the liquid? The answer should be positive because LCs are conductive materials. But I know that the molecules should reorient themselves under an applied electric field for example between two plates like a capacitor even without being in contact with the LC. So why the electrodes are placed in contact with the LC and why LCDs consume electricity?


texts:
Is the bridged ion intermediate aromatic or not?
What is the way to quickly identify aromaticity?


texts:
Which alkene reacts faster with HCl?

The logic tells me the most stable alkene 2 which is the most substituted would react the slowest.
On the other hand, it would form the most stable tertiary carbocation which would mean it's best for this specific reaction which would make it react faster. Also, one could think about rearrangements because these could take time too. How should I answer this question?


texts: Heat produced when magnesium is reacted with acid

texts:
Calculate the heat produced when a strip of $\ce{Mg}$ metal with a mass of $\pu{0.0801 g}$ is reacted with $\pu{50.0 ml}$ of $\pu{1.0 M}$ $\ce{HCl}$ to raise the temperature of the water by $\pu{7.6 °C}$ (change in temperature is $\pu{7.6 °C})$ Calculate the heat produced when a mole of this metal is used.

I have this so far:
$$q = mc\,\Delta T$$
$m =\pu{0.0801 g}$ and the change in temperature is
$$\Delta T = T_2 - T_1 = \pu{7.6 °C} - \pu{4.184 K} = \pu{3.416 K}.$$
Is that right? I have no idea what the specific heat $c$ is. Is it the specific heat of $\ce{Mg}?$
What do I do with the $\pu{50.0 ml}$ of $\pu{1.0 M}$ $\ce{HCl}?$


texts: Why can't sodium salts be produced through a reaction between a metal and an acid?

texts:
I am writing a lab report for the preparation of sodium sulfate crystals. This question came up: Why can the reaction between a metal and an acid not be used to make sodium salts?

In this case, could one not use sodium metal and sulfuric acid to make sodium sulfate, as in the following:

$$\ce{2Na + H2SO4 -> H2 + Na2SO4}?$$


texts: Why are ions much more efficient than electrons at beam-induced deposition?

texts:
I have recently been reading about electron beam induced deposition and ion beam deposition. The idea is to send a high energy (5-30 kV) beam of electrons/ions focused down to a spot on a material and open a gas precursor source. The beam somehow breaks down the bonds of the precursor gas, and some of the components of the gas get deposited on the sample. (e.g. carbon, silver,  platinum,...)

My question is, why does this deposition process work more quickly with ions than electrons with the same kinetic energy? From what I've seen in the literature, ions like Gallium can be 10-1000 tines faster at deposition than electrons at the same energy.


texts: Is there a chemical or chemicals that can be infused in fabric that will react when exposed to blood that would produce a bright or glowing color other than red?


texts: Method for regioselective hydroalkylation of terminal alkyne

texts:
I'm trying to figure out a method to add a linear alkyl chain R and a hydrogen atom H across the triple bond of a terminal alkyne. The alkyl chain should end up on the internal carbon (C-2):

My attempt :
First, we can hydrolyse the alkyne to produce a methyl ketone. Addition of a Grignard reagent produces the tertiary alcohol. But, now I'm stuck as I can't treat it with $\ce{H2SO4}$, because then ring-expansion will ruin the whole matter.

How to move on?


texts:
When the electrons that are excited by the energy of burning drop back into lower energy levels they emit light at the wavelength of colour.

When metals are burnt, metal oxides(some coloured) are formed.

When metals are burnt under high temperature, will they turn to plasma state? If so, should the metal ions be responsible for the colours and sparks?

Which one is the reason for the beautiful colours of fireworks?


texts: Does anyone know what this piece of glassware is?

texts: I recently found this piece of lab glass with a jacket and spout. It says eubilicmeter but I cannot find any information about it online and I do not know what it is supposed to do.  It is hollow in the middle, sort of bell shaped. What is its name and what is it for?


texts: Can the colour change in litmus paper be explained by conjugated systems?

texts:
I have been trying to understand the colour change in litmus paper on a more detailed level than "the chemical identity changes, and therefore also physical properties". I have knowledge of the particle in a box model of quantum mechanics, and i would like to apply this to the conjugated system in the active indicator-component of litmus dye.
In other indicators I have looked at, you can clearly see that when the dye molecule dissociates or is protonated, there is change to the length of the conjugated system (number of alternating double bonds in a row), which explains the colour change. An example is given below for BTB (bromo thymol blue)

However, i can't find any explanation like this as to why the indicator dye in litmus paper (7-hydroxyphenoxazone) changes colour when protonated/deprotonated. From what I can see, the length of the conjugated system is the same in both versions of the molecule.

Edit: If someone knows of a model that more easily explains this colour change than conjugation, feel free to share that as well.


texts:
Thermal decomposition of calcium carbonate.

In general, we heat $\ce{CaCO3}$ to temperature of approximately 825°C it decomposes into calcium oxide and liberates carbon dioxide gas:*

$$\ce{CaCO3} \overset{825\ ^\circ \text{C}}{\ce{ ->}}\ce{CaO + CO2}$$

Is it possible to heat the calcium carbonate at temperatures below 825 degrees Celsius.


texts: Mechanism for reaction of aryl diazonium with potassium iodide

texts: I’m working on a synthesis problem that requires me to draw the arrow mechanism for the second half of the Sandmeyer reaction. Basically it’s the halogenation of an aryl diazonium compound. Typically it’s done using a copper catalyst, but it can also be done using just potassium or sodium iodide. Problem is, I can’t find any reference showing how this works in an arrow pushing mechanism. Does anyone know where I could find an example to show me how it works?


texts:
Grignards don't add to alkyl halides to create linear carbon extensions because Grignards do transmetallation rather than SN2 displacement of halide.

Is this correct?

I thought transmetallation a) involved two metals and b) involved ligand exchange between the two metals … correct me if I'm wrong, but if I have a Grignard and an alkyl halide, I only have one metal.


texts: Why do bubbles form when a reactive metal is placed in a less reactive metal's salt solution?

texts:
What is the gas that if formed when a reactive metal is placed in a salt solution of a less reactive metal? Theoretically, it should just be a simple displacement.
I know that this question has been asked on a different page, but there Hydrogen formation was the accepted answer, which I don't think is the case (see observations).
Observations:
When a strip of magnesium ribbon was placed in a concentrated copper sulfate solution, the magnesium ribbon piece started bubbling.
Magnesium didn't bubble as violently when placed in plain water of the same temperature.
The gas was bubbled through a soap solution and the bubble was passed near a candle flame. It just popped and nothing happened.
Pure hydrogen gas was obtained by placing a Mg ribbon in acid, and bubbles were obtained. These exploded with a bang when passed over a flame (learnt the hard way not to do this!).
Regular distilled water was used everywhere.
Thanks a lot in advance for any help.


texts: Why is the spin magnetic moment for nickel(II) given as 1.7 Bohr magnetons in some references?

texts: I read some theoretical articles concerning $\ce{Ni-O}$ system, where $\ce{Ni}$ sits at the center of the octahedron formed by $\ce{O}$. The calculated magnetic moment on the $\ce{Ni}$ sites is about $1.7$. And these articles said that this is the typical magnetic moment of $\mathrm d^8\ \ce{Ni^2+}$. I think according to $\mu=\sqrt{n(n+2)}$ where $n$ is the number of unpaired electrons, $\mathrm d^8\ \ce{Ni^2+}$ should have 2 unpaired electrons and $\mu=2.8$.


texts:
In kinetics, zero order reactions are those reactions who are independent from the concentration of the reactant or the product. So their rate is equal to the constant k. But still we build the diagram where we find the correlation between concentration and time, where the slope is negative.
Why do we even write a diagram to find the correlation between concentration and time, since these reactions are completely independent from concentration ?


texts:
I'm doing an oxidation of an alcohol with Dess–Martin periodinane which works really well but having trouble with the work up. Doing this reaction with about 5 g of alcohol so the reaction ends up using about 17 g of DMP. As the reaction progresses the DMP byproduct crashes out. And working up turns it into a gun that is quite difficult to remove

Running reaction in DCM and work up with bicarb. Even after filtration DMP is still present. Separates fine on a column but with how much there is it seems to be trappings some of my product.  I've read that a thiosulphate wash is also used in these reactions, but I don't think this will be useful to get rid of the gum.

Any suggestions?


texts: What is the nature and character of fire?

texts: What is fire? Is it a material or energy or something else? Please explain it to me. My friend asked me this. I am stuck with this problem.


texts: Reactivity of alkaline earth metals towards water

texts:
In general, it seems to be a trend regarding the reactivity of alkaline metals with water which says that as you go down the group, they become more reactive towards water. But I'm curious about which factors explain this trend.

When Group 2 metals react to form oxides or hydroxides, metal ions are formed.So this must be explained by the atomization energy of the metal and also the first and second ionization energies?(Ionization energies fall down the group, it gets easier to form the ions, the reactions will happen more quickly.)

But apart from these two factors, should we also take into consideration the atomic radius, the hydration energy, the ionic radius or something else in order to fully understand why the reactivity towards water increases as we go down the group?  Also,  do the standard potential value has to do with it?


texts: How to measure a distance along the surface of a protein in a PDB

texts:
I would like to measure the distance between two active sites in a protein complex (pdb), but I do not find a straightforward way to do it.

To be more precise I need the distance along the surface of the protein and not the linear distance that would go through the protein, and which the distance wizard will give.

I have access to Pymol and would prefer a solution using that software although I would consider other as well. Thanks.


texts: is it possible to break the bonds of diatomic elements such as fluorine or iodine and create positive and negative ions by electron bombardment?

texts: If I had a container in vacuum filled with $\ce{I2}$ gas and then I bombarded it with high speed electrons using an electron gun, would  be able to get both $\ce{I+}$ and $\ce{I-}$ ions or would I only get $\ce{I2+}$ plus an ejected electron?


texts: Why is fluorine more reactive than iodine despite the weaker I-I bond?

texts:
The atomic radius of halogens increases as we go down the group due to the addition of new shells. As a result, the bond length of halogen $\ce{X-X}$  increases down the group. So, less energy is required to break the bond (bond dissociation enthalpy decreases). So, as per this assumption, iodine should be the most reactive halogen. But this is not true. Rather,  fluorine is the most reactive halogen. It reacts violently with almost all chemicals. Bond cleavage of fluorine is much easier that that of other halogens, which may be due to the repulsive force of the lone pairs of electrons.

$$\ce{2F2(g) + 2H2O(g) → O2(g) + 4HF(g) + heat}$$

So, what about iodine? This source gives the values of bond dissociation enthalpy. It shows that the B.D.E value of iodine ($\pu{151 kJ/mol}$) is less than that of fluorine ($\pu{158 kJ/mol}$). So, iodine should be the most reactive halogen and not halogen. But this does not happen. In most of the reactions of iodine, equilibrium is maintained. To push the reaction forward, a catalyst is used.

$$\ce{I2(l) + H2O(l) <=> OI-(aq) + 2H+(aq) + I-(aq)}$$

Another similar phenomenon is that acidity of hydrohalic acid increases on going the group. $\ce{H-X}$ bond length increases on going down the group. Bond dissociation enthalpy decreases. Bond breaks into corresponding ions. So, $\ce{HI}$ is able to furnish $\ce{H+}$ ion faster than $\ce{HF}$. So, $\ce{HI}$ is more acidic than $\ce{HF}$. But, the reverse is observed. $\ce{HF}$ is so reactive that it reacts with glass and has to be stored in wax bottles.

$$\ce{SiO2 + 4 HF -> SiF4(g) + 2 H2O}$$

$$\ce{SiO2 + 6 HF -> H2SiF6 + 2 H2O}$$

In most of the reactions of hydroiodic acid, equilibrium is maintained. To push the reaction forward, a catalyst is used.

$$\ce{H2(g) + I2(g) <=> 2 HI(g)}$$

My question: Why is it so?


texts:
This question first popped up in my head when I learnt that $d_{z^2}$ orbital is used in $sp^3d$ hybridization and $d_{x^2-y^2}$ and  $d_{z^2}$  orbitals are used in $sp^3d^2$ hybridization. If all the $d$ orbitals are said to be degenerated orbitals (i.e. they are said to have equal energy) then why these two orbitals are used in $sp^3d$ and $sp^3d^2$ hybridization?

Some said that $d_{z^2}$  is used because it is closer to the nucleus because of the ring of electron density surrounding the nucleus, but if that is the reason then why do we call the $d$ orbitals as degenerated in the first place when clearly two orbitals are closer to nucleus.

Here's what I want to know:

A) Why $d$ orbitals have same energy when its clearly apparent from their shape that two orbitals have lower energy than other three?

B) Why $d_{z^2}$ orbital is used in $sp^3d$ hybridization and $d_{x^2-y^2}$ and  $d_{z^2}$  orbitals are used in $sp^3d^2$ hybridization?


texts: Electrolytic cell to remove soft solder from silver?

texts:
Hi my chemistry is pretty dire but have vague idea that an electrochemical cell could be used to remove soft solder (lead/tin probably) from a piece of sterling silver in need of a repair.

The correct electro cell arrangement could be a good method of removing contaminants without damaging the silver / copper of the piece since lead and tin are less noble...

Opt 1 (reverse electroplating): Cell with something like a weak sulphuric acid solution as electrolyte, the contaminated silver as cathode, and possibly a stainless/carbon anode. Current should cause oxidation of the soft solder to lead/tin sulphate in solution. I'm guessing lead/tin may build up on the anode where would also be a release of... er, oxygen???

Opt 2 (Conversion to lead/tin chloride): Cell with something like H2O / NaCl solution as electrolyte, the contaminated silver as the anode and carbon / stainless cathode. Current should cause Cl to liberate at the anode and bond with lead / tin which hopefully will dissolve in the solution or can be scraped off easily. (not sure this is any better than just pouring HCl onto piece though!)

Opt 3 (conversion to lead/tin oxide): Cell with pure water or weak NaOH solution as electrolyte, the contaminated silver as the anode, and a carbon/stainless cathode. Current should generate oxygen at anode which might also cause lead/tin to convert to oxides which can hopefully be scraped off easily.

Are any of these methods viable/preferable? Opt 1 seems to be best as i dont think the electrolyte will react with the silver/copper if not too strong. Not sure if the sulphates will go into solution though or just build up / precipitate out from cathode.

Are any of these methods likely to be preferable to just pickling the piece in acid such as HCl?


texts: Justification for Freezing Point Depression & Boiling Point Elevation in Solutions?

texts:
I was wondering if the following justification for freezing point depression and boiling point elevation are conceptually correct. The reason why I ask this question is because I have been self studying chemistry for a course I will be taking this fall, and I don't have a human reference to check with. My book is also very confusing on this subject, and I don't have a world renowned memory (meaning I'd rather understand than memorize the equation), so I tried to think about it and came with the following conclusions:

-Freezing Point Depression: When a solvent is not pure and has particles dissolved in it, there are constituents (be it molecules, ions, etc.) that take up volume in the solution. For freezing to occur, these constituents need to aggregate to form a lattice, bonds, etc. Say we have a pure solvent X. This process occurs at a temperature Y. However, when this solvent is not pure and has dissolved solutes, there is "blockage" impeding these constituents from aggregating and bonding. Therefore, the temperature Y needs to be reduced further to slow down the kinetic energy of all constituents in solution (solvent and solute), which gives a greater statistical probability of intermolecular forces getting an opportunity to bind solvent-solvent constituents.

-Boiling Point Elevation: Boiling, if I'm not mistaken, occurs when the partial pressure of a vapor exceeds atmospheric pressure. For a gas to enter the vapor phase, molecules in solution need to have a certain kinetic energy (as specified by a Boltzmann distribution) to free themselves of the intermolecular forces in the solution phase and become a vapor. When a pure solvent is now diluted with other particles, the new solute-solvent bonding energy needs to be overcome to allow a solvent molecule to exist as a vapor. One way to overcome this energy is to increase the average kinetic energy of all molecules, and this is done through a temperature increase.

This is for an introductory chemistry course, and I'm not sure if my explanations are sound. I just want a yay or a nay in terms of my logic, because I don't have the most intimate background in chemistry and I'm trying to conceptually understand things.


texts: Why convert benzoate in soda to benzoic acid for spectroscopy experiment?

texts:
I did an experiment where I analyzed the amount of caffeine and benzoate in soda via spectroscopy. I've got the absorbances and did all the math for everything, but I'm having a hard time figuring out why we had to add an acid to protonate the benzoate to form benzoic acid before running the spec.

I've been able to find many similar procedures and many with various pre-lab questions, but none seem to address the reason for the conversion from benzoate to benzoic acid. Here is one such procedure: UV Spectroscopic Analysis of Caffeine & Benzoic Acid in Soft Drinks

The only thing I can think of is that it was in an aqueous solution (soda), so perhaps some benzoate will be in the form of benzoic acid and some will still be in the form of benzoate. By adding $\ce{HCl}$, we can force all the benzoate to be in the form of benzoic acid for better quantification.

Is this the correct line of thinking or am I missing something?


texts: What makes an X-ray machine's white photographic film go black?

texts:
I read on a   bbc gcse bitesize webpage "In older X-ray machines, white photographic film" [edit- I now know that bbc webpage is wrong, and it's not a white film. I'll leave the rest of the post after the next sentence, as is, but note that from the next paragraph, the rest of the post is based on the misunderstanding from that bbc link that there is white film  (And I guess it's talking of any pre digital when it says 'older' - and anyhow prior to film they used photographic plates - glass rather than plastic/film ).]

I understand that X-ray images are black and white. You have the X-rays themselves, the white film, and an object/person in-between.

The white parts of the image are bones and/or things the X-rays couldn't get through, the white film remains white, and the black part is where the X-rays did pass through, and it blackens the white film.

I've also heard that they have a cassette/casing, and in that is fluorescent material or coating and film.  The X-rays hit the fluorescent material and (I guess by absorption and reflection, or absorption and emission) converts it into regular light, and there is a phosphorescent material/coating there, too, so the light remains for a while, and the light, I guess, blackens the film.

I understand they don't work like that anymore and now you can have other types of X-ray detection mechanisms. But I want to understand at least how the traditional ones are black and white.

I understand that X-ray machines used to use a white photographic film.

What is the white photographic film made from that distinguishes it from a black photographic film? Can I buy white photographic film?

I have seen old-fashioned camera film before.

In black and white photography, was it a black photographic film that went white when exposed to light?


texts:
In mass spectrometry, 1-pentanol can be observed to have no peak at $m/z = 59$, whilst 3-pentanol can be observed to have a peak at $m/z = 59$.

Clearly the 3-pentanol peak at $m/z = 59$ is due to the cleavage creating $\ce{CH3CH2CHOH | CH2CH3}$

Why is this the case, as isn't 1-pentanol able to form the fragment $\ce{CH2CH2CH2OH}$ by cleaving at the third carbon?

i.e. fragmenting into $\ce{CH3CH2}$ and $\ce{CH2CH2CH2OH}$ (this should have $m/z = 59$?).


texts: Chirality of carbon and R/S naming when enatiomeric groups attached

texts:
when checking chirality for a tetrahedral, let's take carbon as an example, will two enantiomers or diastereomes of a group attached to same carbon cause chirality at that carbon, I mean are they considered different for comparing valencies and what about r/s naming , in cis trans and r/s, which enantiomer or geometrical isomer have more priority(supposing one chirality centre each) have more priority in cip?

I am not clear on how to apply method of plane of symmetry here


texts: Oxidation of ethanol upon heating in a test tube

texts:
The diagram shows an experimental set-up which can be used in several different experiments.

Which processes could be demonstrate by using the above apparatus?
1. Oxidation of ethanol (liquid X)
2. Dehydration of ethanol (liquid X)
3. Cracking of paraffin (liquid X)

The answer is 2 and 3. I understand that for 2, ethene is produced which is a gas and for 3, cracking of paraffin will produce short-chained hydrocarbons which have low boiling points.
However, I expected 1 to be an answer as well because oxidation of ethanol will produce ethanal which has a boiling point of 21 °C. So shouldn't 1 be an answer as well?


texts:
Furfural $(\ce{C5H4O2})$ has been used as a feedstock for synthesis. Furfurylamine $(\ce{C5H7NO})$ is made from furfural.
Given that industrial manufacturing ammonia is matured, how about combining furfural, ammonia and hydrogen to directly synthesize pyridine? Is the following reaction realizable?
$$\ce{C5H4O2 + NH3 + H2 -> C5H5N + 2 H2O}$$
Both furfural and pyridine are significant organic compounds. If one compound can be made from the other, the cost of the other can drop. So far is how pyridine itself is being manufactured remained an industrial secret? Substituted pyridines are covered in many articles and online information.
Wikipedia pyridines production indicates that

Chichibabin synthesis makes dihydropyridine, a pyridine derivative from acrolein, acetaldehyde and ammonia and byproducts are observed.
Bönnemann cyclization of acetonitrile and two molecules of acetylene gives 2-methylpyridine, a substituted pyridine. Following dealkylation gives pyridine.

In essence, substituted or derived pyridines were first made in multisteps and they are further processed to the parent pyridine.
Another possible route would be using the aza variety of the Achmatowicz reaction on furan.

Hydrogen replaces Ts() and removing of hydroxyl and alkyl make the parent pyridine.
( removing the hydroxyl makes the parent pyridine.

Still, substituted furfurylamines $(\ce{C5H7NO})$ is needed at the beginning. In other words, my question was about if as few steps as possible making the parent pyridine from a prevalent starting material such as furfural is realizable.


texts: Is there an adhesive that is not dissolved by acetone?

texts:
I am trying to glue glass sheets together to make a sealed 13" x 13" x 13" box. Inside this box there would be acetone gas used to melt 3D printed parts to make them more durable. Acetone will remove just about any type of adhesive I know and I was wondering if there is anything out there that would not react to acetone?

If you are going to send me the questions that was posted on this website titled "Is there a paper glue that is NOT dissolved by acetone?" don't send it, because I've seen it and the thing he suggested was to use tape, which wouldn't work because not only would it be very difficult to cover all the inside corners with tape to seal off the acetone gas from escaping, the acetone gas would either way slowly remove the tape away from the glass because it would seep under the edges of the tape.


texts: Friedel–Crafts alkylation of benzene with propyl chloride

texts:
This is a question from my textbook:

  Why does the alkylation of benzene with 1-chloropropane give (propan-2-yl)benzene and not (propan-1-yl)benzene?

The book shows the reaction with chloromethane and chloroethane, and there is no such ambiguity in the two cases as the obvious products are methylbenzene and ethylbenzene respectively.

Is there a rule which I need to know in order to figure out which substituted benzene of the two would be more stable? Up till now I've only encountered Markovnikov's rule, Kharash/peroxide effect, Zaitsev's rule and Popoff's rule in the book; none of these seem to be applicable in this case.


texts: Less maintenance-dependent continuous pH testing

texts:
I am creating an automated chemical component mixing system (DIY project). One of the features required is continuous monitoring of pH value in my main solution. I do not need it to be very precise, precision of 0.2 would be enough. Also, I want it to be as low maintenance as possible (cleaning the probe once a month would be great). pH of the solution will vary from $pH = 4$ to $pH = 7$.

So, the question is, which of this testing ways will require less maintenance of pH probe:

Constant submersion in the solution.
Once per hour dipping in the solution.


texts:
Where can one find examples of raw data for an 1H-NMR spectrum?

This may sound as an odd request, so I'll give some context.

I have found lots of images of spectra such as this:

where you can see an image of the peaks. What I am interested is a spreadsheet
of the $(x,y)$-values used to draw the spectre. The data is needed for a student mathematics/chemistry project (high school). The mathematics section will be on calculating the area under a curve using numerical methods. To get a connection to the chemistry part, I'd like the student to use realistic data.

(I am aware that it is the ratio of the areas of the peaks that are interesting, so the actual scaling of the y-axis is unimportant.)


texts: I came across the formula for enthalpy of solution, which is equal to the sum of lattice enthalpy and hydration enthalpy. Therefore, for salts that have endothermic dissolution, the lattice enthalpy has to be greater than hydration enthalpy. But if that is true, then how will the salt dissolve in water in the first place?


texts: Photochemical rearrangement of 4,4‐diphenylcyclohexa‐2,5‐dien‐1‐one

texts:
I can see how the option A and B are correct as it is just a standard dienone–phenol type reaction which involves a phenyl shift. However, the given answer is A, B, C and D.

I do not see how C and D are formed. Does the presence of light affect the reaction? If so, how?


texts: How do you all remember the name of chenical formula of Glucose, Lime, Vinegar ... etc. becasue these substances have big big chemical formula. So, How do I remember their chemical formula?


texts: Elastic scattering of x rays in 3D: the principle for XRD analysis

texts:
I have some trouble visualising scattering of x-rays in 3D, since all textbooks and examples present it in 2D. Under I will share some reflections (no pun intended) about the elastic scattering of x rays, and the diffraction effects observed, which is the basis of XRD analysis.

Here you see a figure of two crystal planes, separated by the distance d. Two parallel and in-phase x-rays hit an atom in the planes. The scattering cones are drawn. The darker area represents those scattering directions going into the crystal itself, and thus not detectable and uninteresting for XRD analysis. The light area are those scattered rays exiting the crystal.

Thinking in three dimensions is different from thinking in one dimension. To achieve constructive interference, the rays must travel in the same direction and also be superimposed on each other. Even though the scattered rays ' angle is, say, 45 degrees, they may not travel in the same direction.

However, if Bragg's law is valid for 45 degrees, all rays of 45 degrees scattering angle will interfere constructively. So we would get a diffraction cone of increased intensity. However, we cannot detect the whole diffraction cone, partly because some of the rays travel into the crystal, and partly because the detector surface area only covers parts of the diffraction cone; we would measure a curved segment of the diffraction cone. This is called the Debye-Scherrer ring, yes?

Though we get constructive interference in all directions of 45 degrees scattering angle, the scattering angle itself is random. This means there are scattered rays which do not undergo constructive interference in all directions, regardless of angle (though smaller angles are more probable). So, in an ocean of random scattering, we have diffraction cones of much greater intensity, since Bragg's law is fulfilled.

Is this a correct assessment of the XRD situation?


texts: Relation between First Law of Thermodynamics and Ideal Gas Law

texts:
Thermodynamics has always been a tough thing for me. There are lots of assumptions in this subject (those assumptions, I know, are necessary, I know the science of thermodynamics is a very practical science).
First Law of Thermodynamics states mathematically:
$$\Delta U=Q+W$$
(with proper sign conventions must be used). This is just a law of conservation of energy and a very straightforward equation, but when we come to chemical thermodynamics this equation changes its form and becomes:
$$\Delta U=Q+p\,\Delta V$$
My intuition says as soon as pressure and volume comes in any equation it becomes specifically for gases. So, my first question is:

Why thermodynamical equations are just for gases?

Let's imagine an isothermal expansion of a gas (that simple piston and gas experiment) under a constant pressure, now work $W$ is
$$W=p\,\Delta V$$
but if use ideal gas Law equation i.e.
$$pV=nRT$$
$$p\,\Delta V = \Delta nRT + nR\,\Delta T\tag1$$

since the expansion is isothermal therefore $\Delta T = 0$ and I can think that during expansion no atom or molecule has been annihilated therefore $\Delta n = 0$, so after all we get
$$p\,\Delta V = 0$$
$$W=0$$

I want to know my mistakes in above consideration.

There is a question in my book:

  A swimmer coming out of a pool is covered with a film of water weighing $18\ mathrm g$. How much heat must be supplied to evaporate this water at $298\ \mathrm K$? Calculate the internal energy change of vaporization at $100\ \mathrm{^\circ C}$. $\Delta_\mathrm{vap}H^\circ = 40.66\ \mathrm{kJ\ mol^{-1}}$ for water at $373\ \mathrm K$

My book give its solution like this
$$\ce{H2O(l) -> H2O(g)}$$
Amount of substance of $18\ \mathrm g$ of $\ce{H2O(l)}$ is just $1\ \mathrm{mol}$. Since, $\Delta U=Q-p\,\Delta V$, therefore,
$$\Delta U=\Delta H-p\,\Delta V $$.
$$\Delta U=\Delta H-\Delta nRT$$
$$\Delta U=40.66 \times 10^3\ \mathrm{J\ mol^{-1}}-1\ \mathrm{mol}\times8.314\ \mathrm{J\ K^{-1}mol^{-1}}\times373\ \mathrm K$$
$$ \Delta U=37.56\ \mathrm{kJ\ mol^{-1}}$$

I have a lot of problems with this solution which goes directly to the foundations of science of thermodynamics. (I must say it's because of these books that science becomes a rotten subject, these books destroy the real essence of science).
How is $\Delta n=1\ \mathrm{mol}$?
Why temperature is taken as $373\ \mathrm K$ and not $298\ \mathrm K$, since the process starts at $298\ \mathrm K$ we should use it?
At $373\ \mathrm K$ the process becomes an isothermal one (latent heat) so $\Delta U$ ought to be zero, if we think the process of vaporization starts from $373\ \mathrm K$.

Any help will be much appreciated. Thank you.


texts: Can the electrophile attack at the position of the NH2 group in nitration of aniline?

texts:
In the nitration of aniline, we observe the formation of a meta-substituted product (47%) almost as much as a para (52%).

However, can't the electrophile attack at the position where $\ce{-NH2}$ is already attached, so that after the attack, it will be stabilised by the mesomeric (+) effect of $\ce{-NH2}$? Maybe just after some time, the $\ce{-NH2}$ group will become $\ce{-NH3+}$ (acidic medium) and $\ce{NH3}$ would depart as a leaving group?


texts: Calculating the change in pH upon diluting an acid

texts:
What volume of water is added to $\pu{400 ml}$ of $\ce{HCL}$ solution so that the pH of the solution increases by 1 unit

This is how far i went but the answer says $\pu{1000 ml }$ where am I wrong is there any simplet alternative  to this question?


texts: Why flame color of salts is determined by metal

texts:
If a pure metal is heated up in a flame, we see it giving the flame a characteristic color, e.g. $\ce{Na}$ burns yellow.

If a salt, e.g. $\ce{NaCl}$ or $\ce{Na2SO4}$, is heated up, resulting color to a greater degree still is that of the pure metal. Although the color does change depending on the anion, this effect is usually not much pronounced.

Why is that the case? Shouldn't ionization happen to anions as well, causing electrons (including those pulled from the cation) to "fall back" and give off photons? In other words shouldn't we see a mix of two characteristic colors?


texts: Do molecules change shape when they become vibrationally excited?

texts:
In quantum mechanics we learn the the classical picture of a vibrational excitation is wrong. The atoms will 'vibrate' only while the molecule is in a coherent superposition of two vibrational states, and will find itself in a stationary state once this coherence is broken.

Let's say I have a carbon monoxide in vacuum, and I excite it from v = 0 to v = 1. In order to describe the electron distribution of the molecule, I would expect the electron distribution to be given by the sum of the electron distributions for the CO at each bond distance, weighted by the nuclear wave function.

So... An excited CO in vacuum would look similar to a stationary molecule of C-o-o, where the little o's indicate that the electron density is smaller than that of a regular oxygen. Is this interpretation correct?


texts: Relationship between Hartree-Fock and Hückel coefficients

texts:
I am new in computational chemistry. I'm studying the Hartree–Fock–Roothaan (HFR) method and have some of questions about the HFR basis function coefficients.

Do we have the condition on HFR coefficients like in the Hückel method?

In the Hückel method, we have a normalization condition on the coefficients $\{c_i\}$:

$$c_1^2 + c_2^2 + \dots + c_i^2 = 1 \tag{1}\label{1}$$

In the HF literature I didn't see that condition, so my guess is that we don't have it.

Do we have similar to Hückel method condition on HFR coefficients of bf?

I'm wondering because going deeper in understanding HF I find out that we have certain conditions that looks like $\eqref{1}$. For example, a normalization condition for the Gaussian primitives that are not normalized:

$$
S = \left< \Phi_{\textrm{1s}}^{\text{STO-3G}} | \Phi_{\textrm{1s}}^{\text{STO-3G}} \right> = 1
$$
$$
\Phi_{\textrm{1s}}^{\text{STO-3G}} = N_1C_1e^{-a_1r^2} + N_2C_2e^{-a_3r^2} + N_3C_3e^{-a_3r^2}
$$

This is not the same as $\eqref{1}$ but we can represent it as

$$f_1(c_1^2) + f_2(c_2^2) + \dots + f_i(c_i^2) = 1 \tag{2}\label{2}$$

Because HF is more complex than Hückel, $\eqref{2}$ can make a sense. So can I think about $\eqref{2}$ as complex version of $\eqref{1}$? I was hoping to find $\eqref{2}$ or similar equation in HF literature intro part, but those sources that I have do not mention $\eqref{2}$ in intro part. Maybe my attention was scattered or it is just a mess in my head, anyway I will be grateful for any help.

What are the conditions imposed on the coefficients of the basis functions that use in the calculation of the HFR equations?

For example, the electronic charge distribution is

$$
\sum_{mn} P_{mn}S_{mn} = N =\sum_{mn} 2\sum_{a}^{N/2} c_{ma}c_{na}^*\int{f_m(r)f_n^*(r)\mathop{dr}},
$$

where

$$
S_{mn} =\int{f_m(r)f_n^*(r)\mathop{dr}} = \delta_{mn},
$$

and N is the total number of electrons. Can we consider this as a condition?


texts: How to calculate the required concentration for sodium sulfite to remove oxygen as an oxygen scavenger from a solution?

texts: If I know the amount of oxygen in such a solution, how can I know the required concentration of sodium sulfite to be used and react as oxygen scavenger?


texts:
In the extraction of $\ce{Sn}$ from $\ce{SnO2}$ by carbon reduction method, why is  $\ce{CO}$ formed instead of $\ce{CO2}$ as per the following reaction?

$\ce{SnO2 + C -> Sn + CO}$


texts:
When a polyatomic ion reacts with another atom to create an ionic compound, often, we know the charge of the polyatomic ion. But how can we infer the charge of the atom it is reacting with?

For example, the question states, 'What is the correct formula for Calcium Phosphate?'

I know that the charge of the polyatomic ion named Phosphate is 3-. But does that mean the charge of Calcium, in this case, must be 3+ in order for it to react with Phosphate? If not, how can we figure out the charge of the Calcium ion in this ionic bond?


texts: How to calculate the vapour density of a mixture?

texts:
I have a gaseous mixture of $\ce{H2}$ and $\ce{CO2}$ which contains $66\%$ by mass of $\ce{CO2}$. I have to figure out the vapour density of the mixture (defined as mass of a certain volume of a substance divided by mass of same volume of hydrogen).

My approach: let's assume $\pu{100 g}$ of mixture contains $\pu{66 g}$ of $\ce{CO2}$ and $\pu{34 g}$ of $\ce{H2}$. Hence, the amount of substance of $\ce{CO2} = \pu{1.5 mol}$ and the amount of substance of $\ce{H2} = \pu{17 mol}$. The total amount of substance $= \pu{18.5 mol}$.

The mass of $\pu{1 mol}$ of mixture is 5.4 g (mass of 18.5 mol is 100 g), and the vapour density $\text{VD} = 2.7$.

I got my answer right, but now I am doubtful of my approach. Was it safe to assume that the amount of substance of mixture equals that of the amount of substance of both the gases?


texts: What is the meaning of the prefix "per-"?

texts: The prefix "per-" appears in the names of many compounds, such as in perchlorate, persulfate, peroxide. What does it mean?


texts: Why does hydrazine have a higher boiling point than water?

texts:
$\ce{N2H4}$ has a boiling point of 114 °C, which is higher than the boiling point of water. Why is this so?

Both $\ce{N2H4}$ and $\ce{H2O}$ have two lone pairs, so the number of hydrogen bonds per molecule seems to be the same. Also, the $\ce{O...H}$ hydrogen bond (21 kJ/mol) is stronger than the $\ce{N...H}$ hydrogen bond (13 kJ/mol). So, given this information, why is it that $\ce{N2H4}$ has a higher boiling point?


texts: How to write equations for dissociation of ionic compounds in water?

texts:
Please write a dissociation-in-water equation for the compounds $\ce{BeI2}$ and $\ce{LiI}$. Make sure to add the states of matter after each compound.

Currently, for $\ce{BeI2}$ I have the equation $$\ce{BeI2 (s) -> Be^2+ (s) + I2^2- (g)}.$$ I have yet to attempt the second one.


texts: Will this reaction form magnesium carbonate?

texts:
I have magnesium oxide pills I take. I know if I dissolve them they'll form magnesium hydroxide, and I'm trying to make pure magnesium from my pills. I've come up with a double replacement reaction, will it do what I think it will?

$$\ce{Na2CO3(aq) + Mg(OH)2(aq) -> MgCO3(s) + 2NaOH(aq)}$$

Will this precipitate out magnesium carbonate?

Another thing: I was planning on using electrolysis to separate the magnesium, but if it's insoluble then I'm not sure what to do. How can I separate the magnesium from the carbonate?


texts: Preparation of ammonium acetate buffer for HPLC

texts:
Buffer solutions are typically prepared by dissolving an appropriate salt in water and then adjusting the $\mathrm{pH}$ to the desired position by addition of the conjugate acid or base.
For example, to prepare a $\pu{100 mM}$ ammonium acetate solution at $\mathrm{pH}~9,$ you’d first prepare a $\pu{100 mM}$ ammonium acetate, and then add ammonium hydroxide dropwise until the desired $\mathrm{pH}$ was achieved (a titration, using a pH meter to determine endpoint).
I’d like to work out (roughly—I understand that what I’m about to describe is nothing more than an approximation, but it’s a reproducible approximation at least which is good enough for our needs) directly how much ammonium hydroxide and acetic acid I would need to make up the same solution.
I understand the fundamental Henderson–Hasselbalch equation:
$$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log\frac{[\ce{A}]}{[\ce{HA}]}$$
But as I see $\ce{A}$ is ammonium and $\ce{HA}$ is ammonium acetate. Thus, in my example I don’t really simplify things that much.
Additionally the majority of examples I’ve found look at acidic buffers rather than alkali ones. Does my equation therefore need to be rearranged further to take account of this?


texts: Grignard Reagent in THF vs in Diethyl ether

texts:
While learning about the Grignard reagent I was taught this by my teacher, but I couldn’t justify why it was so..
I cannot see how Grignard reagent would react differently in basically an ethereal solvent..
So i needed a justification as in why this was happening.
Thanks


texts: I have found a gif photo on the internet and I am very curious what is happening there? What reaction is the reason for that?