texts: What all computing knowledge should a computational chemist traditionally have?

texts:
If I want to develop algorithms or computer programs for studying chemical systems, where should I start? Is learning one or two programming languages like FORTRAN enough? And if I do it, then how do I proceed further?
I would be grateful if someone can tell me about a book or any other learning resource.

Edit:
I am 3rd year undergraduate in chemistry. I am interested in pursuing computational chemistry for my master's as well as PhD. I am mostly interested in electronic structure theory and ab initio calculations.
Regarding the theory, I think I have got that part covered as I am taking courses and learning stuff on my own as well (QM, Linear Algebra, Quantum Chemistry etc.). What I want to know is the fields in computer science that I should have a knowledge of so that I can start learning it and be prepared with it if I encounter it in my grad school.


texts: How to make pyramid-shaped NaCl salt crystals

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I'm attempting to make sea salt pyramids like the one below.

I understand this needs to be evaporated at a reasonable speed to stop the crystals forming a cube, as the when formed quickly, the edges grow faster than the faces, creating the inverted pyramid shape.

When evaporating the saturated water at around 75 degrees celsius, I start with what look like great pyramids forming (like the below image). However, the crystals then begin to join together forming a large flat 'crust', with the individual small pyramids losing their unique shape.

I've attempted reducing the temperature of evaporation to a point where this mass of crust does not form, however at that point, the crystals which now form are cubic instead of pyramids.

Any help would be great!


texts: What is the relative rate of diffusion of ammonia to hydrogen chloride, both in gaseous states?

texts:
I encountered this problem during an assignment:

I answered it as C, but the assignment grader marked it as wrong and indicated that A is correct.

I asked another instructor about it and gave me a different answer: D.

I am confused on how to approach this problem given that I have received different answers from what I consider reputable sources. How do I proceed to solve this?


texts:
note: @Mithron's proposed duplicate Why can't rust form without water? does not have anything about the conditions on the Moon, so no, it's not a duplicate.

Several popular news articles mention that "rust" has been found on the Moon, and this is surprising because rust requires the presence of both oxygen and liquid water.

nasaspaceflight.com: Rust on the Moon. How is that possible without oxygen and liquid water? "But how can rust form far from water ice deposits on a barren oasis devoid of oxygen?"
Axios: Researchers find rust on the Moon "Scientists were surprised by the findings because rust requires oxygen and water to form on Earth."

When I open a plastic-wrapped cake or muffin there is often an "O-buster" packet with finely powdered iron. When I open the packet (chemistry is more interesting than cake) and watch the powder, indeed it rusts. Of course air has plenty of both oxygen and water, so this is no surprise.
Question: But why and how is rust forming on moon? Why does it need both oxygen and water there, and more importantly, how is it getting them?


texts: Why is ionisation energy of bismuth lower than lead?

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Why is ionisation enthalpy of Bismuth less than that of Lead for it just comes after the latter in periodic table?
First ionisation energy of bismuth is 703 kg/mol while that of lead is 715 kg/mol.

I also found that the covalent radius of Bismuth was more than that of lead, though both try to show me the same cause but I couldn't figure this out.
Let me give out some reason why Bi should have higher first ionisation energy than bismuth:-
* Bi falls after Pb in the periodic table so it should be more non metallic in nature than Pb.(as from the general trend)
*  Bi have half filled p orbitals contributing to its extra stability(as from the general trend).
* Bi falling down the the group 15 elements show metallic nature but still it should be less metallic than lead as it falls just after it.
* Even if we consider d/f orbitals,it would have same effect on lead and bismuth as both falls after elements occupying 5d orbitals and much after lanthanoid series.In fact the only effect I could see would be of increase in 1 electron thus there should be decrease in size of the atom and hence increase in ionisation energy.
* I tried to find out whether there might be any relativistic corrections but I was only able to reach to the conclusion that as the nuclear charge increases for atoms the size gets shorter somewhat like in the case of radium so ionisation energy should have increased.


texts: how to calculate the initial concentration of NaOH in a mixture?

texts:
I have doubts about how to find the equation for the calculation of the initial concentration of $\ce{NaOH}$. I have the following information:
 in the kinetic study of a reaction,

We measure $\ce{20.00 ml}$ of $\ce{CH_3COOC_2H_5}$ solution of 0.0400 $\ce{mol/L}$ and also $\ce{20.00 ml}$ of $\ce{NaOH}$ solution of 0.0400 $\ce{mol/L}$

We mix both substances in one Erlenmeyer.

The question is:  find the equation to calculate the concentration of $\ce{NaOH}$ at $\ce{t=0}$.

It is a bit weird to me because a concentration of the $\ce{NaOH}$ solution is already given.

The best (and the only) that I can think is this:
if the concentrations of the reactives are equal, then:
$$\ce{C_iV_i = C_fV_f}$$

then we have,
$$\ce{C_i=C_fV_f/V_i}$$

$\ce{C_i}$ is the initial concentration of $\ce{NaOH}$, $\ce{V_i}$ is the initial volume of $\ce{NaOH}$, $\ce{C_f}$ is the final concentration of the whole mixture ( which I don't know how to find), and $\ce{V_f}$ is the final volume of the whole mixture

Probably this is wrong but I don't have any other ideas.
 any clues?

Thanks.

(Note: apologies for my poor English)


texts:
Let's say I have carrot juice, standard kitchen and access to grocery store. How do I extract pigment from Orange juice? Sugars need to be separated out.

What's the fastest option? I thought about filtering, sedimentation, heating.


texts:
The best explanation I found so far is this:

  These salts (magnesium, potassium, sodium, etc.) are responsible for the "greasy" feel of the water.

But it doesn’t say which salts exactly are responsible, and why it feels so different from seawater.


texts: Nucleophilic substitution of trifluoroiodomethane

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Will $\ce{CF3I}$ show nucleophilic substitution? In other words, is the following reaction feasible?
$$\ce{CF3I + NaOH -> CF3OH + NaI}$$

I know that $\ce{I-}$ is a pretty good leaving group. Also due to inductive effects, the carbon already has a $\delta+$ charge. So I think it should react, yet the answer in my textbook is telling me otherwise.
Are there any other effects that I am not considering?


texts: Deciding locants of double bonds vs. other substituents

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After having decided that the keto-group is the highest priority, this is a ketone. However, does the double bond become C2, or does the amino become C3?
In locant placement, do we prioritize double bonds over substituents, or other substituents over double bonds? (Or is it just a matter of having the smallest starting number?)

5-aminocyclohex-2-enone
3-aminocyclohex-5-enone


texts: During acid catalyzed hydrolysis of ester why does the carbonyl oxygen attack the $\ce{H^{+}}$ ? Why doesn't the alkoxy oxygen which is more electron rich and less electronegative not attack the $\ce{H^{+}}$ with its lone pair? Any ideas?


texts: Effects of Ka on the Half-Equivalence Point

texts:
I'm new to studying chemistry at a university level and am currently reviewing acid-base titrations. I am wondering about the relationship between your ionization constant for a weak acid ($K_\mathrm{a}$) and both the volume of strong base needed to reach the half equivalence point and the $\mathrm{pH}$ at the half-equivalence point.

Assuming these two weak acids are of the same concentration, if you had a higher $K_\mathrm{a}$ value for one of them, my reasoning is that your $\mathrm{pH}$ at the half equivalence would be lower than that of the weak acid with a lower $K_\mathrm{a}$ value because given the equation

$$\mathrm{pH} = -\log[\ce{H3O+}],$$

a greater hydronium ion concentration (from being present in larger amounts as a product given the larger $K_\mathrm{a}$ value) would result in a lower $\mathrm{pH}$ overall.

However, I am not entirely sure if this is correct, and I am also unsure as to how the volume of strong base titrant needed to reach the half equivalence point would be affected.


texts: Why do some salt ions in solution conduct electricity better than others?

texts:
My experiment involves a potentiometric titration, and I have used $\ce{AgNO3}$ as a titrant and KCl/KI/deionised water only as an analyte.

In the image below of my data, the potential difference as recorded by a multimeter drops from 0.6V to 0.15V.

What causes the drop in potential difference when the silver nitrate and whatever analyte (all exhibited the same pattern of a sudden drop in PD) reaches its endpoint in the titration?

Why is there a higher potential difference when using KI as analyte than KCl?


texts: Effect of removing the product from equilibrium

texts:
For the reaction

$\ce{PCl3 + Cl2 <=> PCl5 }$

Upon removing some $\ce{PCl5}$ from the equilibrium, the equilibrium position will shift right and the forward reaction is favored, increasing the yield of $\ce{PCl5}$.

Is the information suggested by the attached graph true? (Do $\ce{PCl3}$ and $\ce{Cl2}$ decrease by the same extent?)

For an arbitrary reaction $\ce{2A + B -> 3C}$, how will the concentrations of each substance change accordingly when say, some $\ce{C}$ is removed from the system? Will $\ce{A}$ and $\ce{B}$ still decrease by the same amount, and why?


texts: How to identify whether an electrophile will attack benzene ring when a deactivating group is attached to it?

texts:
I was asked to find out the major product formed when this molecule is subjected to nitration using $\ce{HNO3/H2SO4}$ mixture

Here $\ce{NO2+}$ will be the electrophile. Lets call the benzene ring which is directly attached to the carbonyl group as ring 1 (benzylic ring) and the other as ring 2 (phenolic ring). Now ring 2 is attached to an activating group as $\ce O$ will show +M and will increase the relative electron density at o-p positions. But the electrophile will preferably attack para position due to steric hindrance at ortho position.

Benzene ring 1 is attached to a carbon atom which in turn is connected to a more electronegative atom. So it is partially positively charged and will show -M effect thereby deactivating the ring. But it is also meta directing group. So will the electrophile attack meta position of ring 1?

The answer to this question says, ring 1 won't be attacked by the electrophile as it is attached to a deactivating group. The the molecule after nitration is

Then how to identify whether an electrophile will attack benzene ring when a deactivating group is attached to it?


texts: Difficulties understanding how salt bridge works

texts:
A picture for reference:

Difficulty 1: I don't get why a salt bridge is needed. People say it's to maintain the overall neutrality. But in both cases where  salt bridge is a tube of solution and a membrane, two half cells can be seen as one. So as long as no thing leaves either of the two half cells, the whole is always neutral.

Difficulty 2: as in the picture, cations go to the right cell, and anions go to the left. I can understand that anions go the left because the number of zinc ions increase as the reaction proceed. But in the right half cell, the electrons are being absorbed, its charge cancelled by that of the copper ion; I don't see any need for sodium ions to move to the right.


texts: Difference between Lindlar and Rosenmund catalysts

texts: Is there any difference between the Lindlar and Rosenmund catalysts? I've checked around, and it seems the same compounds are used to make both. Is there a difference in their reactivities or are they essentially the same?


texts: What is the relation between surface tension and initial molecular harmonic?

texts:
Initial harmonic is measured as Hartree/Bohr^2 ( like IHarmonic=n in Gaussian Software ). As I am from physics background I am used to look at features from their dimension point of view:

Actually surface tension is the only physical feature that I know is compatible with Force / Distance. I was wondering if there is any relation between the surface tension and initial harmonic.
Update: Another physical feature is spring constant which is not irrelevant also !


texts: Is there such a thing as an acid without a hydrogen?

texts: I'm in AP Chemistry and we are learning about the Brønsted-Lowry model and my teacher mentioned that "for the most part" acids have hydrogen, could there be such a thing as an acid that has no hydrogen in it?


texts:
Water has an unusually high specific heat capacity due to it's hydrogen bonds.

Why is it that the change in isotope causes a 10% difference in the heat capacity? How does the added neutron in the nucleus make any difference to the bonds?


texts:
I was wondering whether there is a trick in the following problem:

Since both carbons are equally substituted, shouldn't the products be the same with or without the use
of peroxides?


texts: Effect of impurities on enthalpy of fusion of ice

texts:
When I freeze water with some impurities (1% NaCl by mass), the mixture seems to have a much lower enthalpy of fusion that pure water. The impurities cause the freezing point to depress to 0.6°C. I only have a simple calorimeter available but it looks like the enthalpy of fusion is dropping by 25%+ compared to pure water (tested by melting the ice into water and measuring the temperature drop).

Additionally, the ice does not have a nice crystal structure. It is "mushy" and easily deformed.

This effect is surprising to me since colligative theory tells us that most properties changes in a pretty small linear way at low concentrations (like the freezing point).

Am I observing a real phenomenon or is there some problem with my testing?

If its a real phenomenon, is there a way to calculate/estimate the effect?


texts: How does simulation software work at a fundamental level?

texts:
There are lots of software packages like Schrödinger Maestro or Argus Lab, which are used for simulations of docking.

I have always been fascinated as to how such software works. What is the fundamental principle working "under the hood" of this kind of sofware?

Let's say I wanted to make a simple piece of software which, when I input the atoms and atom number (e.g., C1H4) can be used for finding different energy levels (or other properties) in a molecule such as methane ($\small\ce{CH4}$).

Where does one have to start in attempting to make such a package, given a considerable knowledge of programming? What theory is applicable?


texts: Calorimetry Question - determine temperature change without knowing enthalpy change?

texts:
I have a lab that I honestly cannot figure out.
Basically, we have a video where we watch 200 ml of NaOH (2M) and HCl (1M) combined in a calorimeter with a magnetic mixer. Pretty standard. This video starts off when they are both at 20C and then ends off when they're at about 27 C and says that the reaction is incomplete (there are two parts to the video - the rest of the reaction is in a video that I can only unlock when I have finished the first part).
The first question is:

Determine the expected change in temperature.
Hint:
Remember to take into account the limiting reagent.

And I'm honestly not sure what that means, especially since the question is out of 10 full points, which I assume means calculations are involved. I put it through this simulator (https://media.pearsoncmg.com/bc/bc_0media_chem/chem_sim/calorimetry/Calor.php), though I could only make them both 100ml instead of 200, and it also ended off at 26.8 C. I doubt this ten point question is just a "27-20" = 7, but it very specifically is asking for the change in temperature, not heat or enthalpy change or anything else. Also, we do not have the delta H rxn provided.  Also, I have no idea why the hint is asking me to mind limiting reagent specifically. I know there's that one equation that's like delta H rxn = q rxn / mol of limiting reactant, but I can't know q without the temperature change??
Basically, I'm super confused about what this question is asking. For reference, the next question:

The table below tells the concentration of the solutions in the videos. In each video, the HCl is in the beaker on the left, and NaOH is in the beaker on the right: [img lol] Choose a trial. Record the volume and molarity of both the acid and the base.  Determine which substance will be the limiting reagent. Describe your reasoning in the space below.

... is only worth five points


texts: Does benzene structure stand for a single resonance form or the whole molecule?

texts:
It is known that benzene has two main resonance forms

Often we still draw benzene molecule as one of them

My question is, actually when we draw the lower figure, do we refer to the whole benzene molecule or one of the resonance structure or depend on the context?


texts: Do IUPAC names for haloalkanes require numerals?

texts:
I'm new one of chemistry. I want to know the IUPAC nomenclature rules. That is if we write alkane with halogen must be indicate the numerals? Are the following names right or wrong?

chloropentane
trichloropentane


texts: Why can't element with paired electron have colour

texts: I know that elements with unpaired electrons are coloured especially the d-block element which can be explained by crystal field theory. But, why can't element with paired electrons give colour, is it because the energy gap is too large ?


texts: Could the loss of mass in the kilogram be due to oxidation?

texts:
I was wondering about this. I have heard, and known for a while, that the famous and celebrated Prototype Kilogram - the lump of metal whose mass is used to define the standard mass scale worldwide - is slowly changing, degrading in some fashion, and this has prompted the search for a new and better definition of the kilogram mass unit on something more stable (the lead is now Planck's constant, but the change has not yet been adopted by the BIPM and looks like it won't be until at least next year.).

However what I'm curious about is the reason for the mass change. Apparently it's said it's not clear as to what exactly could be causing it, but I was wondering: is it chemically possible that this mass change could be due to oxidation - tarnishing - of the kilogram and removal of the oxide? I would imagine that the scientists who have studied this must have thought of this, so I'd be more interested in why it's dismissed as an explanation. In particular, it's said that the material it's made of - mostly platinum - has a very low oxidation rate, but "very low" need not equal "zero", and the mass change is reported as up to (unclear, because it's the measuring standard itself!) 50 micrograms over 100 years - which is nonetheless a very slow rate of loss - about $10^{-16}$ mol Pt/s, so that it would take $10^{16}$ s (10 Ps) to oxidize just one mole, or about 300 million years. Could this be within range of the very-slow-but-not-zero range of oxidization of platinum in air? In particular I find this:

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0ahUKEwjTsN2bleLWAhWB5YMKHf7_A14QFggyMAI&url=http%3A%2F%2Fwww.technology.matthey.com%2Fpdf%2Fpmr-v19-i4-135-140.pdf&usg=AOvVaw2D87XQhqSGonkmrjf0kD_a

talking about platinum oxidizing in air upon mild heating, and even losing mass. Now it seems that a rule of physics is "whatever isn't forbidden is compulsory", that is, whatever isn't absolutely impossible will eventually happen given a suitably long time period, and so if the oxidation is possible could it still be going on at very reduced rates at room temperature that nonetheless might still be sufficient to degrade the kilogram? Or is the rate then so low as to not contribute at all? (I'd think about Arrhenius rate law, but no idea what the relevant constants would be. Nonetheless exponentials are pretty steep, so this might rule it out.)


texts: Calculating the density of a magnesium sulphate solution

texts:
I am trying to calculate the density of a magnesium sulphate solution and came across this paper which determines an equation from experiment to do that. However, I am having trouble understanding the paper, as parameters A, B, C and D are mentioned but I don't understand how to calculate these from Table 2 in the paper. Can someone please explain how this works?
EDIT:
I am adding the data from the above paper:

The paper mentions the equation
to calculate the relative density where the parameters A, B, C and D are said to come from the table. m stands for the molality (I assume mol/kg) t is temperature (°C) and d is in g/cm^3. As you can see there is no mention of A, B, C or D in the table, leading to the confusion.


texts:
The reaction between p-methylbenzaldehyde and $\ce{NaOH}$ is an example of:
  A) Cannizzaro reaction
  B) Aldol condensation
  C) Hydrolysis
  D) Haloform reaction

I selected B, aldol condensation, as the given compound is an aldehyde and it reacts with $\ce{NaOH}$. But the given answer is A. Why is it so? The $\ce{NaOH}$ is not mentioned to be concentrated.


texts: determine at which v and J the rotational and vibrational energy differences are equal

texts:
I was presented with this question and I started working on it but I ran into a problem.
We've got $\Delta E_{rot} = 2B_e(J+1) $  and $\Delta E_{vib} = \hbar \omega$

We get to the point that we've got  $J= \hbar\omega/(2B_e)-1$ but we know that J should be a lot larger than 1 so we don't quite know what we've done wrong. Can anyone help us?

We are given that $\omega _e =4400$ and $B_e = 60.9$


texts: Can F2/HF be separated using acid/base solutions in series?

texts:
I am trying to verify the results of EPA method 26A (http://www.epa.gov/ttnemc01/promgate/m-26a.pdf). The Method claims to be able to separate and quantify a mixed halogen/halide gas stream. Although I believe the chemistry holds true for Cl₂/HCl and Br₂/HBr, I'm not so sure about F₂/HF. Despite the Method not mentioning F₂, it commonly produces data for both HF and F₂. I am dubious that the F₂ results are real and am trying to develop a chemistry argument to support that position, if possible.

In summary, the Method takes a mixed gas stream (F₂/HF) and passes it through a 0.1 N H₂SO₄ solution, then a 0.1 NaOH solution; sodium thiosulfate is later added to the alkaline potion. The theory is that the HF is captured in the acid solution, while the F₂ passes through unreacted. In the alkaline solution, the F₂ reacts to form HF and the hypohalous acid (HOF, I assume). The thiosulfate converts the HOF to another HF. When the acid and alkaline solutions are analyzed for fluoride ion, the quantity is assumed to be the HF and F₂ in the original sample, respectively.

Considering that F₂ is so reactive, I would think that any F₂ in the gas stream would react with the water in the acid solution and that theoretically no F₂ would make it to the alkaline solution. Is this a reasonable assumption?

If any F₂ did get to the alkaline solution, I am not sure that the conditions are favorable for the creation of HOF; F₂ reacting with water to produce HF seems more probable. Unless the acid solution is ignored by the F₂, I don't think that a true separation is taking place and any fluoride detected in the alkaline solution would represent blow through or some other error. Does this seem like a reasonable conclusion?

Thanks in advance for any input!


texts:
My son and daughter got given gifts where you place a plastic egg in water, and the (rubber?) toy inside expands (over three days) and breaks the shell of the egg so it 'hatches'.

I also observed that three weeks later the toys shrank again, but grew once placed in water.

I found the chemical reaction fascinating.

My question is: What is the reaction in a child's 'add water and watch the egg hatch' toy?


texts:
Lets say we have an nitrogen atom - it should have 7 protons and 7 electrons.

How can an nitrogen anion - lets say $\mathrm{N^{\,1\mathbf{-}}}$- even exist - shouldn't the 7 electrons in valence shell repell the extra one?

What force does hold the extra one electron in the valence shell? There isn't an extra proton in the $\mathrm{N^{\,1\mathbf{-}}}$ that would hold the extra electron.


texts:
Is it possible to synthesize L-lysine acetate in the following steps? First, mix L-lysine HCl with an excess of NaOH and just enough water so that the total water in the product is enough to solve all NaCl. Decant the water to obtain L-lysine free base. Then either mix with excess (concentrated) acetic acid and dry the product in a hermetic environment with silica gel, or pour acetic acid in a pot, wrap a cheesecloth on the top, spread l-lysine over it and let the acetic acid steam gently without cooking the lysine.

Aside: According to an article from 2015, L-lysine is usually available in hydrochloride and acetate forms because the free base form is unstable. However, L-lysine acetate seems to have gone out of the market. Is there a reason for that? Is l-lysine citrate also stable and could it be made by simply mixing l-lysine free base with citric acid?


texts: N-heterocyclic carbene metal complexes. Question about the delocalization of the nitrogen lone pairs

texts:
I am wondering why nitrogen lone pairs are delocalized in NHC metal complexes. What I can think of is, when complex is formed, plus charge is formed on the carbon atom and therefore delocalization from the nitrogen atoms. But there should be then "plus" sign like in the picture below.

But these kind of carbene complexes are always depicted without the plus sign. Can anyone please tell me what I am missing out?


texts: What are the units of 85000 Molecular Weight of a polymer

texts:
I have a PVA bottle, which says that the molecular weight (Mw) of PVA is between 85000 - 124000.

I know that this means that there are repeated chains of the PVA monomer, but what are the units to the molecular weight (of PVA). Is it $\frac{\mathrm{g}}{\mathrm{mol}}$? I am having trouble grasping this concept. Or does 85000 - 124000 mean the number of monomers in the chain of this PVA?


texts: How can 30 ml of water be heated in less than 10 seconds?

texts:
How is it possible to heat a tiny amount (30 ml)[1] of water to a high enough temperature to make a coffee, in less than 10 seconds and possibly instantly?

Most heaters that I know of heat water in no less than 90 seconds (induction heater) or 3 minutes which is way too much for my purposes, and a microwave oven takes me one minute and a half to heat.

[1] A single coffee is between 20 - 30 ml and my coffee machine makes 30 ml for each cup.


texts: Why is benzoic acid less soluble in water than acetanilide?

texts: Why should acetanilide be more soluble in water than benzoic acid when benzoic acid has the same number of h-bonding sites and has an ionizable site, allowing it to form ion-dipole forces while acetanilide can't be ionized? I don't see how the dipoles would be significantly different as to make acetanilide more soluble. They are of the approximately same size so dispersion can't be a factor either.


texts: Potential energy versus reaction coordinate (graph of Gibbs free energy)

texts:
Does the potential energy scale in the above mentioned graph measure the Gibbs free energy of the system?

As the system always tries to achieve a minimum of free energy and chemical reactions are taking place can be considered a non-mechanical work (I'm not sure of it, as the system isn't in a state of chemical equilibrium if a reaction is taking place), potential energy should represent Gibbs free energy.

If not, how should I understand the potential energy of a reaction mixture?


texts: When naming alcohols based on alkanes, when do you keep the "e" at the end of the alkane's name?

texts: For example, you would write pentane-1,2-diol but pentan-2-ol, correct? Is the difference simply the number of hydroxyl groups?


texts:
Carbon with 6 protons, the first of its group, is a solid, while the very next elements, nitrogen and oxygen, are gaseous in their elemental form.

Why carbon is a solid? If it's not the molar mass that defines carbon phase (carbon's molar mass is lesser)

In pnictogen and chalcogen group only the second element, phosphorus and sulfur, is solid.


texts: Is there a way to tell what the coordination of a complex ion will be without knowing the ligand?

texts: Do complex ions tend to form a certain number of coordinate bonds, or does it completely depend on the ligand molecule?


texts: How does the size of a molecule affect acidity?

texts:
Today I learned that $\ce{H2S}$ is more acidic than $\ce{H2O}$ because $\ce{H2S}$ has a larger molecule size. But $\ce{Fe^3+}$ is more acidic than $\ce{Fe^2+}$ and $\ce{Fe^3+}$ is smaller than $\ce{Fe^2+}$.
Likewise, formic acid is more acidic than acetic acid but formic acid is smaller than acetic acid.

How does this go together?


texts: Relative stability of cis and trans cycloalkenes

texts:
Why is the stability of (Z)-cyclodecene 2 greater than that of (E)-cyclodecene 1?

I'd think that since 1 contains a trans double bond instead of a cis double bond, it should experience less steric repulsion and hence be more stable.

However, I've read that the cis isomer 2 is more stable than the trans isomer 1 if the ring size is 11 or smaller. For ring sizes larger than 11, the opposite is true.

Why is this so? Also, what would happen if there were more double bonds?


texts: Sensitivity vs. Limit of Detection of rapid antigen tests

texts:
I'm comparing a bunch of SARS-CoV2 rapid antigen tests:

Columns 4 and 6 list the values for sensitivity and limit of detection (LOD). How come that a test with a several times lower limit of detection can have a worse sensitivity?
As an example, consider tests #2 and #4:
#2 - Sensitivity: 97.7% - Limit of detection: 2.0*10^2.4 = 502 TCID50/ml
#4 - Sensitivity: 91.4% - Limit of detection: 2.5*10^1.8 = 158 TCID50/ml
Shouldn't these values correlate, i.e. the more sensitive a test is the smaller the amount it is still able to detect?


texts:
What will be the order of reactivity towards electrophilic substitution in case of the following compounds:

benzene, ethyl benzene, isopropyl benzene, tert-butyl benzene

The answer at the end of the book says that ethyl benzene will be most reactive (the book doesn't explain the cause though it's a MCQ) but as according to inductive effect I think the tert-butyl group will have more +I effect on the ring. Doesn't it?


texts: Does the field of organic chemistry cover all group 14 elements or only carbon?

texts: Does the field of organic chemistry cover all the other group 14 elements or does it strictly deal with Carbon chemistry?  Since the other group 14 elements have similar chemical properties, such as silicon, wouldn't they fall under the same discipline? Why or why not?


texts: How can I tell if a certain carbon/hydrogen molecule can actually exist?

texts: My 11 year old daughter asked me if the following compound exists in real life, and if so, what is it called. Not only do I not know, I have no idea how to find the answer to such questions. Any ideas?


texts: Would ionic compounds dissolve in methanol?

texts:
Question:

  Determine whether liquid hexane ($\ce{C6H14}$) or liquid methanol ($\ce{CH3OH}$) is the more appropriate solvent for the substances grease ($\ce{C20H42}$) and potassium iodide ($\ce{KI}$).

It seems logical that $\Delta H$ to dissociate $\ce{C6H14}$ would be small, since it's non-polar, that $\Delta H$ to dissociate $\ce{C20H42}$ would also be small, since it's non-polar, which would be conducive to a solution forming between those two.

The question that I'm stuck on is if the $\Delta H$ of formation of a solution between $\ce{K+}$, $\ce{I-}$, and the mildly polar $\ce{CH3OH}$ would be greater than the amount of energy it would take to dissociate potassium iodide. How can I estimate how much energy will be released by the attraction of the $\ce{I-}$ to the slightly positive hydrogen on the hydroxide group is greater than energy required to dissociate $\ce{KI}$?

Am I missing something?


texts: Determine stable oxidation state from Ionization energy

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Question:
Given the first, second and third ionization energies of an element (7 eV, 12.5 eV and 42.5 eV respectively), find the most stable oxidation state (or charge on the resultant ion) of that element.

I think that the element has to ionize with oxygen to reach a certain oxidation state, since oxygen has a 6 valence electrons, the element has to lose 2 electrons to attain stability. So the second ionization energy will the give the most stable oxidation state. So my answer is +2.
Now that happens to be the correct answer but can someone verify my reasoning?


texts: There's an absolute zero, is there an "absolute hot"?

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This might be more of a physics question, but is there a ceiling on how hot things can get?

What happens at this temperature?


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What type of reaction is the following?

$\ce{ 10Na(l) + 2KNO3 (s) -> K2O(s) + 5Na2O(s) + N2 (g)}$

So far my best guess has been that it's a double replacement reactions with evolution of gas. Is this correct or am I totally lost?

Edit: It's not a double replacement reactions with evolution of gas (don't know why I thought it was), but what is it then?


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I know that aromatic rings exhibit diamagnetic ring currents which causes the protons outside the ring to go downfield in H-NMR. Antiaromatic compounds exhibit paramagnetic ring currents which have the opposite effect. How does the difference in two electrons between aromatic and antiaromatic systems cause such a dramatic shift in the properties of the ring current? Why does diamagnetic current induce a downfield while the paramagnetic current induces an upfield shift?

I've found this question: Ring currents of anti-aromatic and aromatic systems but the answer doesn't address how the different currents give rise to different effects in H-NMR.


texts: Why are some organic reactions run at elevated temperatures?

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We are using a water bath at $70\ ^\circ\mathrm{C}$ for different reactions to identify oxygen-containing organic compounds, such as the Tollens reaction, the iodoform test and hydroxamic acid test.

What is the function of heat in these reactions? Does the heat act as a catalyst?


texts: In what approximations, if any, can we assume a constant temperature in a Bomb calorimeter?

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In most, if not all, general chemistry books, you will find that in from constant volume calorimeters, $\Delta H = \Delta U + RT \Delta n_\mathrm{g}$, which is, of course derived from $H = U + PV$.

My question is, given that the measured quantity is the change of temperature of the calorimeter, how can we assume that $T$ is constant to get to $\Delta H = \Delta U + RT\Delta n_\mathrm{g}$?

Edit:

As said in the comments, I found this link where it says that this approximation is valid for a small $\Delta T$ value. But if we have the values, why not just use them to get a more accurate number? Furthermore, for example, let's assume an experiment we measure a $\pu{10 kJ mol-1}$ heat from a $T_\mathrm{i} = \pu{298 K}$ to $T_\mathrm{f} = \pu{303 K}$, and a $n_\mathrm{i} = 0$, $n_\mathrm{f} = 2$. Then the approximation gives:

$$\Delta H = \pu{-10 kJ mol-1} + (\pu{8.314 J mol-1 K-1})(2)(\pu{298 K}) = \pu{-5.04 kJ mol-1}$$

$$\Delta H = -\pu{10 kJ mol-1} + (\pu{8.314 J mol-1 K-1})\left[(2)(\pu{303 K}) - (0)(\pu 298 K)\right] = \pu{-4.96 kJ mol-1}$$

And the error is, indeed, small ($\pu{80 J}$) (side question, isn't $\Delta n$ supposed to be in moles? my dimensional analysis doesn't match if it does). However, if the reaction was from $n_\mathrm{i} = 2$ to $n_\mathrm{f} = 4$, and we keep the other values, we get:

$$\Delta H = \pu{-10 kJ mol-1} + (\pu{8.314 J mol-1 K-1})(2)(\pu{298 K}) = \pu{-5.04 kJ mol-1}$$

$$\Delta H = -\pu{10 kJ mol-1} + (\pu{8.314 J mol-1 K-1})\left[(4)(\pu{303 K}) - (2)(\pu 298 K)\right] = \pu{-4.88 kJ mol-1}$$

And the error is, yes, still small but it doubled (of course). So I'm guessing the $\Delta T \approx 0$ to be valid only for small values of $\Delta T$, but also dependent on the actual values for $n_\mathrm{i}$ and $n_\mathrm{f}$. Is there a rule I'm missing?


texts: Skeletal formula for carbon with two double bonds

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How do I depict an sp-hybridised carbon with two double bonds?

$$\ce{R=C=R}$$

If I just leave it out, like I would for a normal $\mathrm{sp^3}$ or $\mathrm{sp}$ carbon, it's difficult to see that it's there.


texts: Relative stability of keto- enol form of acetyl chloride

texts: Why is the keto form of acetyl chloride more stable even though the enol form is stabilized by the hydrogen bonding?


texts: Does NaOH react with K to form NaOK or KOH?

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I realized that the $\ce{-OH}$ group when it reacts with some metal like $\ce{Na}$ or $\ce{K}$ will replace the $\ce{H}$ element to form $\ce{-OK}$ or $\ce{-ONa}$:

\begin{align}
    \ce{H2O + Na &-> NaOH + H2}\\
    \ce{CH3OH + Na &-> CH3ONa + H2}\\
    \ce{H2O + K &-> KOH + H2}\\
\end{align}

So I am just wondering is that always true? Will $\ce{NaOH + K}$ form $\ce{NaOK}$ or $\ce{KOH}$? Does $\ce{NaOH + Na}$ form $\ce{Na2O}$?


texts: Why do osmium and iridium have the most oxidation states of all the elements?

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Both osmium and iridium have 12 oxidation states.  Indeed, iridium has the highest oxidation state of all elements at +9.  see https://en.wikipedia.org/wiki/List_of_oxidation_states_of_the_elements

I'm just curious as to why these elements have the most oxidation states and whether this confers on them special properties or different reactivities or any special uses.  Thank you!


texts: How to specify a different isotope in the ORCA quantum chemistry program?


texts: Reaction of Seretonin with aqueous Bromine

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I have a question that I am stuck with. Serotonin (figure below) reacts with $\ce{Br2 (aq)}$ to give a compound. The marking scheme I am following says that Bromine only reacts in the ortho position of the phenol group. But I think it should also react with the double bond. Shouldn't the bromine react with the double bonded carbon?

Additionally when I react serotonin with $\ce{CH3COCl}$, shouldn't phenol and both the $\ce{NH}$ react? My marking scheme says it won't react with the double substituted $\ce{NH}$ group but does with the $\ce{NH2}$ group? Who is wrong here?


texts: Calculating change in enthalpy of combustion of 1.12g of hexane

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I will calculate the change in enthalpy of combustion of 1.12g of hexane.

1) Calculate the energy transferred to 200g of water using the equation: J = mass of water in grams (200g) x specific heat capacity of water (4.18 J/gK) x temperature increase in Kelvin (24C = 297.15K). This results in the amount of energy transferred to the water of a total of 248,417.4J or 248.4kJ.

2) Calculate number of moles of hexane burnt using n=m/M. Weight of hexane before experiment = 222.07g. Weight of hexane after experiment = 220.92g. Therefore 1.15g of hexane was burnt during the experiment. 1.15g of hexane = 0.013mol of hexane.

3) Find enthalpy change of reaction. Combustion of 1mol of hexane produces (by my calculations) -4194 kJ/mol.  Therefore, 0.013mol will produce (0.013/-4194) -3.1x10-6 kJ/mol.

So this is the procedure that I used to find out the answer! Was it correct?
Because, apparently, you can use the values of steps 1 and 2 to find out the enthalpy change?


texts: What is the IUPAC Name of [Cr(NH3)5Cl]Cl2.NH3?

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What is the IUPAC Name for the complex $\ce{[Cr(NH3)5Cl]Cl2.NH3}$?
I can't even find it through the internet and also by employing a find in "IUPAC's Red Book".


texts:
I am doing some chemistry problems with given answers, and supposedly the $107^{\circ}$ and $92^{\circ}$ bond angles in $\ce{H_2O}$ and $\ce{H_2S}$, respectively, is due to the fact that"$\ce{O}$ uses $\ce{sp^3}$ hybrid orbitals for bonding, $S$ uses its $\ce{3p}$ orbitals."

There is quite a lot of stuff on the Internet pertaining to this exact problem. For example, the first answer on this page says that sulfur doesn't have as much electron repulsion because it's bigger, so it doesn't need to hybridize to lower its nergy. That answer assumes that hybridization in oxygen and sulfur atoms requires energy like it does in oft-used carbon, but I think that is wrong: since oxygen and sulfur don't need to promote any $ns$ electrons to $np$ orbitals (they already have filled $p$ orbitals), they can simply "mix" what they already have. Thus, why doesn't S just hybridize anyway to save a little bit of energy, and consequently have tetrahedral bond angles?

Another answer involves lone pair repulsion: perhaps both atoms hybridize, but the lone pairs on $S$ repel the $H-S-H$ bond more. I simply don't think this can have such a large effect. Even more, the other $H-X-H$ bond angles for Group 6 elements (selenium and tellurium) are around $90^{\circ}$, so it cannot be due to increased lone-pair size, as Se and Te have even bigger ones.

Because of the anomaly in $\ce{H_2O}$'s angle ($107^{\circ}$) versus the other ones (all around $90^{\circ}$), I think that the non-hybridization is more likely to be correct, so why don't sulfur atoms hybridize?


texts:
I am trying to look for healthy options for 5 gallon water jugs. The problem is all the plastic 5 gallon water jugs on the market are either made of #1 PETE (BPA free) or #7 (which contains BPA). It seems #1 PETE is healthier option but it turns out #1 PETE is known to leach a bit of antimony oxide ($\ce{Sb2O3}$ catalyst, used in its synthesis) into water.

So my question is if I bathe the jug in water, so that the antimony oxide can leach into the water and wash the jug one more time, can all the antimony be removed that way?


texts: Can anyone explain why at a conical intersection the wavefunction changes sign? My understanding is that it is a test to see if the crossing IS indeed a conical intersection or just a coincidence of potential energy surfaces, which do not exhibit such phase changes upon periodic cycling. If this is correct ... why? Further what can we gain from knowing that?


texts: Why are atoms with eight electrons in the outer shell extremely stable?

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Atoms that have eight electrons in their outer shell are extremely stable. It can't be because both the $s$ and the $p$ orbitals are full, because then an atom with 13 or 18 valence electrons would be extremely stable. ($d$ has 10, and 5 is also stable).

Why is it that atoms with eight electrons in the outer shell are extremely stable?


texts: What are the active ingredients of shampoo, and how do they work?

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After seeing one too many TV commercial about the fantastical properties of different high-profile shampoo products all "with documented effect" it suddenly struck me that I never actually researched what the active ingredients of a shampoo really is.

So what are the active ingredients of most shampoos, and how do they work?

Is there is any significant difference between popular brands?

Is there any significant difference between cheap and expensive brands?

Will they actually heal your hair?


texts: Difference in color between the chromate and permanganate ions

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As the title states, I'm wondering why the $\ce{[CrO4]^2-}$ and $\ce{[MnO4]-}$ ions display different colors in solution. Both of the metal ions have a $\mathrm{d}^0$ electron configuration, have the same ligands, yet their respective absorption spectra max out about $100\mathrm{~nm}$ apart, with the chromium complex absorbing at the shorter wavelength of $420\mathrm{~nm}$, and the manganese absorbing at $526\mathrm{~nm}$.

What causes this difference?


texts:
I have been recently studying chemical kinetics. I've understood what the rate law and the rate constant mean, and also that, kinetics depends completely on experimental observations, due to which we have zero order reactions as well as fractional order reactions.

Take for example, this: $$\text{Rate of a certain chemical reaction} = k [A]^p [B]^q [C]^r $$

Here, $[A]$, $[B]$ and $[C]$ are the molar concentrations of the three reactants involved, while $p$, $q$ and $r$ are the number of molecules of each respectively taking part in the reaction.

So, $\text{the order of the reaction} =p+q+r $.

Now, this $p$, $q$ and $r$ are completely determined experimentally, and cannot be determined theoretically.

How are these values determined experimentally? How does one find out how many molecules of each reactant are taking part in the reaction? Is there any special instrument to do this? If not, then how do scientists find the order of a reaction?

As an attempt to shorten out the answering area, consider this reaction: $$\ce {NO2 +CO -> NO +CO2} $$ Now, experimentally it has been determined that $\text {the rate of this reaction} = k[\ce{NO2}]^2$.  I want to know how have scientists determined that the rate depends on the square of the concentration of $\ce {NO2} $ and not on the other reactant.

N.B.: My question is how it can be experimentally determined, and not why it has to be experimentally determined.


texts: Why is the electrode with the lower reduction potential the cathode?

texts: Wouldn't it make sense that the electrode with the higher reduction potential be the cathode, since reduction occurs at the cathode?


texts: Is it possible to use the school supplied algorithm to build the Lewis diagram of the iodate ion?

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I am upgrading the grade 12 chemistry credit and have to use the school supplied algorithm to build the Lewis diagram of $\ce{IO3-}$ ion. It seems to me that iodine oxidation state in this ion should be 5, therefore it would have one single and two double bonds with oxygen. When I follow the steps below, I am arriving at a different formula.

I do not need to answer whether the ion is polar or not and what is its shape.

  Step 1: Count all of the valence electrons in the molecule or ion. In the case of an ion, add or subtract electrons to account for the ionic charge.

$$\ce{I = 7e^-, O = 18e^-}; \text{ionic charge} = \ce{1e^-}; \text{total} = \ce{26e^-}$$

  Step 2: Arrange the peripheral atoms symmetrically around the central atom. Use a pair oil electrons to form a bond that links these atoms to the central atom.

6 electrons placed on $\ce{I}$, $\ce{26e^- - 6e^- = 20e^-}$ remain

  Step 3: Add pairs of electrons to complete the octet of the peripheral atoms.

$3\cdot 6$ electrons placed on $\ce{O}$, $\ce{20e^- - 18e^- = 2e^-}$ remain

  Step 4: Place any unassigned electrons on the central atom.

2 electrons placed on $\ce{I}$, $\ce{2e^- - 2e^- = 0e^-}$ remain

  Step 5: If the octet of the central atom is incomplete, move a lone pair of electrons from a peripheral atom to a new position between the central and peripheral atom.

After completing step 4 of the rules above I am arriving at $\ce{I}$ having 8 electron dots. At this point all electrons have been used up, the octet of $\ce{I}$ is complete, and I can only create a structural diagram with two single and one double bonds.

In the course I have taken previously we were taught that $\ce{I}$ was an exception to the octet rule, but when I asked this teacher, I was told that I was not allowed to use the exceptions and had to apply the octets only.

Am I missing anything? Is it possible to comply with the algorithm above and come up with the correct answer?


texts: How to draw chair-form for trans-decalin (with slight variation)?

texts: I understand how to draw chair form for trans-decalin (figure 1) for the usual structure, but I am having difficulty if taken as shown in figure 2 wherein the hydrogens at bridge-head carbons are in opposite orientation. Please help me with relevant chair form diagram.


texts: Why is there an orbital angular momentum if the electron isn't properly revolving around the nucleus?

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I'm a tenth grader who's just been introduced to this subject of atomic structure, so please help.

I recently read that an electron doesn't have circular motion around a nucleus, its motion is kind of bizzare, buzzing and basically all over the place. (As long as it's around the nucleus) But we use the azimuthal quantum number to talk about an electrons orbital angular momentum.

Now, to be sure I didn't know what that meant, so I looked it up. I can't figure out why is there a question of orbital angular momentum if the electron isn't revolving around the nucleus.

Also, is the azimuthal number somehow related to the energy an electron has? I can't figure out if it's the radius that matters or the energy of the electron, so can someone please explain that?


texts: Using the method of differential absorption to determine the ethanol content of an unknown sample

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I have completed a whole set of FITR-ATR spectra analysing 6 solutions of ethanol-water mixtures, all at different concentrations of each.
I have now been instructed to use the method of differential absorption to determine the concentration of ethanol. I am subtracting the absorbance at the base of the C-H stretch of ethanol from the maximum absorbance of the same stretch so now I have a difference in absorbance value. At this stage, I am a little confused as to how I use this value to obtain the concentration of ethanol. All I know is that the Beer-Lambert law is involved somehow.
Any help with this would be appreciated. Thanks.


texts: Why does magnesium prefer to insert into C–Br bonds over C–Cl bonds?

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In the formation of a Grignard reagent from a compound possessing both bromine and chlorine, magnesium preferentially inserts into the C–Br bond over the C–Cl bond. For example, the formation of a Grignard reagent from 1-bromo-2-chloroethane proceeds with good selectivity:[1]

How can this be explained? Can it be rationalised using a reaction mechanism?

Simon, P. Y.-R.; Oreal, H.; Audran, G.; Schulz, M.; Joly, J.-P.; Siri, D.; Siri, A. Proteasome Inhibiting β-Lactam Prodrugs Useful for the Treatment of Cancer and Neurodegenerative Disorders. World Patent WO 2018/115497 A1, June 28, 2018.


texts: Calculating the pH of a solution of sodium carbonate

texts:
I've seen similar questions on this site, but I'm having trouble as my book said something else. For a $\pu{0.09989 M}$ solution of $\ce{Na2CO3}$, my book said:

$$\ce{Na2CO3 + 2H2O -> H2CO3 + 2Na+ + 2OH-}$$

So , $\mathrm{pH} = 14 + \log(2 \times 0.09989) = 13.3006$ .

The problem is that I haven't been given a value of $K_\mathrm b$ as I saw in other questions on the site. We usually don't use any of them if they're not supplied in the question. What should I do?


texts:
Is it possible that strong acids like $\ce{H2SO4}$ behave as weaker ones like $\ce{CH3COOH}$ when the concentration is really high and vice versa for weak acid? And the same question for bases.
By this I am generally referring to pH values.

Why do concentrated acids react more than dilute ones? The degree of ionization of concentrated acids are lower than diluted acids, so they are supposed to react less. Where am I wrong?


texts:
So again in Chapter 4 David Klein book, we have this organic molecule with a t-butyl group (just as an aside, this is t-butyl ethane, right?

Now how is it that the correct Newman projection must be the following?

What I glean from the Lewis structure is that because there are no wedges or dashed lines, the methyl groups ought to be in the same plane. How can there be a methyl group jutting out upwards and to the right, and another methyl group jutting out upwards and to the left in the t-butyl group and not be illustrated as such with dashed lines and wedges? Thanks in advance!


texts: What are the different types of van der Waals forces?

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As per different websites on internet van der Waals force are of

Three types (Keesom force, Debye force and London dispersion force) @ Wikipedia
Two types (Dipole-dipole force/Keesome force and London dispersion force) @chemguide and chemwiki

While an expert website  also explained H-bonds to be a van der Waals force.

I'm confused. What is originally correct?


texts: Reaction mechanism of glycerol with hydrogen iodide acid

texts:
I was watching a chemistry video lecture today and I came across this:-

Basically the lecturer was illustrating the mechanism of reaction glycerol with $\ce{HI}$.See from right to left(follow the arrows :-P) in the screen shot.I have a doubt in the fourth step where it is shown by an arrow that the $\ce{I^-}$ ion shifts from terminal position to the central position therby forming a positive charge at the terminal position where another $\ce{I-}$ attacks.He says something like "The $\ce{I-}$ shifts to central position due to areal resonance(or something like that..hope I heard that word correctly) which increases stability".

Now that's my doubt!Why should the iodine ion shift its position at all?Isn't the positive charge more stabilized by hyper conjugation in the central position?And what on earth is areal resonance(I searched google too but no use)?
Can someone help me out ?Thanks in advance!


texts: cooling/refrigeration essentiality for carbonated softdrinks

texts: How does cooling/refrigeration help in maintaining the taste and shelf life of food products, especially CSD (Carbonated Soft Drinks)? For example, chilled drinks have a nicer taste than a normal drink and may have longer shelf life. Why is that?


texts: Can ionic compounds can ever "dissolve" as molecular compounds do?

texts:
Here's an example. Say you take a 25˚C solution of NaCl, and lower the temperature suddenly. The equilibrium constant (solubility product) is immediately decreased, so ions start to join together into ionic compounds that float freely in the solvent before settling to the bottom. (In some cases they may be visible as precipitate.)

Can we refer to these free-floating ionic compounds as "dissolved" solute?
Does "XY(aq)" (the aqueous solution of an ionic compound) seem like a good description of this state?


texts: Extracting elemental ratios from X-ray photoelectron spectroscopy (XPS)

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Is it possible to extract information on elemental ratios from X-ray photoelectron spectroscopy (XPS)?  For example, I am reading a paper and in it they say that the carbon to oxygen (C:O) ratios of the four samples are 2.8, 2.9, 5.1, and 23.3.  However, the authors do not provide the actual XPS spectra, not even in a Supporting Information-type addendum.

I am a computational chemist and have no experience with XPS.  I do know that elements, and even particular hybridizations, give characteristic peaks at characteristic binding energies (in units of eV, for example).  This, I know, enables qualitative analysis of compounds.  But is there a way to extract quantitative information from XPS?  Suppose I want to determine the C:O ratio in a compound containing only C, O, and H.  Do I take the ratio of the C and O peak heights, or do I take the ratio of the area under the peaks corresponding to C and O?

Do you know of any good review articles that would help me to understand the basics of XPS?


texts: How do I determine the absolute configuration experimentally?

texts:
Let's say I synthesized or isolated a chiral molecule and want to know the absolute configuration (R or S) of that molecule. I could obviously solve the structure by X-Ray crystallography, but that's a lot of work and I might not want to do that or might not have access to the necessary equipment.

What other ways exist to determine the absolute configuration of a molecule experimentally?


texts: $\ce{NO}$ can't dimerize and that is explained because the free electron is in an antibonding orbital. The same is true for $\ce{NO2}$, but it can dimerize, how?


texts: How do I synthesise this tertiary amide from these 5 compounds?

texts: So basically I'm at a loss as to how to proceed. I started with the idea of converting the primary alcohol into an aldehyde and that is where I stoped. I understand that each substituent of the Nitrogen is somehow made from B, C and D and that the cynaonitrile is supposed to help you make the amide and the Gringnard Reagent is for adding a methyl group somewhere, maybe to C. Im completely at a loss and I'm just getting frustrated now :(


texts: Is a person warmed by fire an example of endothermic reaction?

texts: My chemistry textbook gives the example of a man being warmed by a fire as an endothermic reaction. If the man's body is the system and it is increasing in temperature, how can this be endothermic?


texts: Why does NaCl act as a catalyst for the reaction of CuSO4 + H2O + Al?

texts:
I am analyzing a reaction between water sulfate copper and aluminum. A chunk of $\ce{Al}$, e.g., aluminum foil. I realize that a layer of $\ce{Al2O3}$ forms on the surface of the $\ce{Al}$, passivizing it, and I realize that the $\ce{NaCl}$ (or rather just the $\ce{Cl^-}$) cleans the aluminum oxide off the surface of the chunk of aluminum, but I don't understand why. I'd appreciate greatly if somebody could offer me an explanation.

Furthermore, (I didn't exactly include this in the topic of my question,) why is it that the reaction looks like this:

$$\ce{6H2O + 3CuSO4 + 5Al \rightarrow 3H2 + Al2(SO4)3 + 3Al(OH)2 + 3Cu}$$

(or something along the lines of that) rather than:

$$\ce{3CuSO4 + 2Al -> Al2(SO4)3 + 3Cu}$$ ?

Something along these lines has to be the case, because the reaction yields gas..


texts: Chemical reaction to create a delayed mark on skin

texts:
I'm looking for a dye or chemical reaction that can create a mark on the hand.

Substance A is placed on hand in advance.  When substance B is added, the reaction creates a black mark or stain on the hand.

Ideally, after a delay of a few seconds, a stain or mark appears on the hand. It could possibly be two clear substances that when mixed together create the reaction.

Does anyone have experience with anything that might achieve this effect?  I'm working on this for a visual experiment.


texts: Can someone explain me the difference in boiling point of water when I add: KBr; CaCl2; AlCl3?

texts:
I have noticed (during an experiment) that the boiling point of the solutions created by H2O+KBr; H2O+CaCl2 and H2O+AlCl3 see their boiling point increase.

During the experiment, I thought that, since every time the number of Ions dissociated in each solution increases, the boiling point of each solution should increase with the number of Ions formed: BP(H2O+AlCl3)>BP(H2O+CaCl2)>BP(H2O+KBr)

But apparently this is true only when the concentration of the salt in the water is small: in fact, with high concentrations, the solution formed by CaCl2 reaches much higher boiling points than the one formed by AlCl3.

Is there someone who can help me to understand?


texts: Why do we use nCv∆T=∆U almost universally(for ideal gases)

texts:
In my understanding $C_V$ which is defined when the volume is constant is written as
$$C_V=\frac{q_V}{\Delta T}$$
Thus,
$$q_V={nC_V\,\Delta T}$$
since for an isochoric process work done is zero
$$\Delta U=q+w$$
(which is zero)
$$\Delta U=nC_V\,\Delta T$$


texts: X-ray fluorescence: where do expelled electrons go?

texts:
I'm studying the XRF method cause I'm about to use a WDXRF spectrometer at college so I'm getting all the information about the physics and chemistry behind it.

I'm just curious about one thing, as you know when a beam of x-ray hits the electron of an inner shell if the energy is just about lower than the electron binding energy, that electron is expelled and the hole is filled with an electron from an outer shell and a photon (fluorescence) is emitted with the same energy as the difference between the shells.

What about the electron that has been expelled from the atom, where does it go and what happens to it?


texts: Is glycine strong or weak field ligand? If yes, how?

texts: The fact that it contains both oxygen and nitrogen atoms is confusing me since N is generally strong ligand field while O has a weak ligand field


texts: Temperature dependence of molarity and molality

texts:
My textbook says

  Molarity is dependent on temperature, whereas molality is not.

I'm aware of the definitions of both molarity and molality, but consider this scenario:

A solution of $\ce{NaCl}$ in $\ce{H2O}$ is heated. Eventually, all the water will escape and I will be left with only $\ce{NaCl}$ crystals. At the end, there is no solvent to even measure the concentration of what was once a solution. In this case, how does the argument "molality is independent of temperature" still hold true?


texts: Is PCl5 really trigonal bipyramidal in shape?

texts:
We know that the structure of $\ce{CH4}$ is tetrahedral, and not planar tetragonal, as a tetrahedron enables maximum distribution of $\ce{H}$-atoms in space, as they repulse from each other. This is proved by the fact that each $\ce{H-C-H}$ bond angle is equal in magnitude.

In the case of $\ce{PCl5}$, why should the shape be trigonal bipyramidal? Obviously the top and bottom $\ce{Cl}$-atoms, above and below the plane subtend $90^\circ$ with each of the $3$ planar $\ce{Cl}$-atoms; whilst planar ones subtend $120^\circ$ in between each other. This means all bond angles aren't equal. Why so? Shouldn't there be regular distribution of $\ce{Cl}$-atoms in space?

To my opinion, the XY-plane distribution of $\ce{Cl}$-atoms should be such that each $\ce{Cl-P}$ is $72^\circ$ apart from the other $\ce{Cl-P}$ bond (atoms would not be in the same plane at all. But we should see that the orthogonal projection of each on XY-plane subtends equal angles, i.e. $72^\circ$). Same for YZ-plane. Hence there is regular distribution of atoms along all planes. Now it is to be calculated what the ultimate structure results in.

Sorry, I don't have the necessary tools/knowledge to represent my hypothesis. Else could've just modelled this figure and shown a representative model.


texts: The rate of change in pH v.s Temperature

texts:
I have somewhat established that there is a linear relationship between change in pH of carbonic fizzy drinks over time. I also realise that the pH increases linearly faster for the same carbonated fizzy drink when the temperature of the drink is changed (increased).

Now the problem is, when I graph the relationship between the rate of pH increase (y-axis) and the temperature (x- axis), I get an exponentially increasing relationship. I do not know if this relationship is true, but even if it was true I do not know how to explain why this is true.

Are there any equations I can manipulate to show a mathematical relationship between rate of pH increase and temperature of the same carbonated fizzy drink?


texts: What is a suitable material for a cathode in electroplating experiment?

texts:
I am going to do an electroplating experiment, whereby I will be using a Cu(NO3)2 solution to plate onto a cathode.
What is an easily accessible cathode which I can use for this? Would a strip of Ag (s) be sufficient, since it is a weaker reducing agent than Cu(s), and should therefore not react with any of the solution? And furthermore, using a strip maximises surface area and there will be a more noticeable change in mass of the cathode?
I am performing these at standard conditions.


texts:
I came across a question where $\ce{R-CH2-NH2}$ and $\ce{R-NH-CH3}$ are considered as functional group isomers but not as metamers.

If I'm not wrong, metamers compounds which have same molecular formula but different number of carbon atoms on a functional group (for example, $\ce{CH3-CH2-O-CH2-CH3}$ and $\ce{CH3-O-CH2-CH2-CH3}).$

So, shouldn't the compounds given in start of the question be metamers considering the fact that the '$\ce{NH}$' has different number of carbon atoms on either side in the two compounds, and if not, why so?


texts: Chemistry of Walter Mitty's negative developer/stop bath/fixer?

texts:
I asked a question here How can Walter Mitty examine the negatives of photos in the bright sunny day?

Commonly known, there are three steps using chemical baths to bring out the images of negatives:

developer to bring out the image,
"stop bath" to halt the process,
"fixer" to make the image permanent.

So in details what are the Chemical procedure/compounds/reaction for the negative's developer/stop bath/fixer?

Wish the answer is in depth.


texts: Why is moist hydrogen made to react with chlorine to give hydrogen chloride?

texts: Moist hydrogen reacts with chlorine in diffused sunlight to give out hydrogen chloride. Why is moist hydrogen used? Why not dry hydrogen?


texts:
How did the first chemists know that a sample contained so and so elements?
If they tried to find through reactions,they should know what elements make up the other reactant(s), and how it reacts beforehand (which is absurd as elements weren't discovered & studied before that)


texts: Why is boiling point of carbon tetrachloride greater than silicon tetrachloride?

texts:
$\ce{CCl4}$ and $\ce{SiCl4}$ both are non polar molecules thus London forces must be the only forces of interaction.

Then London forces are supposed to be greater in $\ce{SiCl4}$ due to its larger size and its boiling point should be higher than comparatively smaller $\ce{CCl4},$ but $\ce{CCl4}$ has higher boiling point.

The only explanation I got is the greater polarity of the $\ce{Si-Cl}$ bond. I don't understand how polarity of individual bonds in a non-polar molecules increases its boiling point.


texts: How can transition metals form so many bonds with ligands?

texts: For instance, copper can form $\ce{[Cu(H2O)6]^2+}$ so it accepts 6 electron pairs from $\ce{H2O}$ molecules to form dative covalent bonds. However it has one electron in the 4s subshell and 10 in the 3d subshell. To which shell does it accept these electrons? Is it to the 4d subshell? And how are these accepted electrons arranged?


texts: Why is carbon monoxide a "weak" lewis base?

texts:
A lewis base is substance that donates an unshared pair of electron.

In CO, a lone pair is present on both carbon and oxygen each. Moreover, lone pair of electron on carbon is localised so CO will act as lewis base.
What causes the CO to become weak lewis base?

Also tell, what "Lewis acidity of CO" would mean? Actually , I read that lewis acidity of CO is very small? But I am not able to understand it.


texts: What is causing the buffer region in a weak acid - strong base titration?

texts:
For the buffer region in this, why does it stop the pH from increasing?

At the start:

$$\ce{CH3COOH + NaOH -> CH3COONa + H2O}$$

Which means there will be a high amount of salt in the solution, but why is this stopping the pH from rising? I thought it would actually make it rise further as the disassociated salt it reacts with water to form $\ce{OH-}$?

What's reacting with the $\ce{OH-}$ in solution, that isn't there anyway? Seeing as, with a buffer solution, the acid is needed ($\ce{CH3COOH + OH- -> CH3COO- + H2O}$).

The acid concentration hasn't been increased?

Or is the presence of the dissasocated salt:
$\ce{CH3COONa(aq) -> CH3COO- + Na+}$

Causing the acid to reform:
$\ce{CH3COO- + H2O -> CH3COOH + OH-}$ <<< but there's more $\ce{OH-}$!!

Surely the $\ce{Na+}$ isn't going to react with the $\ce{OH-}$, as it will dissociate in the water.


texts:
The following is from my teacher's notes:

  The reaction (where the reaction mixture is thermodynamically unstable but kinetically inert) tends to go as indicated by a positive total entropy change, yet nothing happens because the rate of the reaction is too slow to be noticeable due to a high $E_\mathrm a$.

Does that mean that the reaction is taking place but we don't see it because of how slow it is, or that the reaction will not take place in the first place?

This is A2 chemistry.


texts: Why are thioethers not better leaving groups than ethers?

texts: Why are thioethers ($\ce{RSR}$) not better leaving groups than ethers ($\ce{ROR}$)? I learnt that better bases are poorer leaving groups. Here, clearly   the poorer base is thioether, as the lone pair is on a larger atom.


texts: How can weaker nucleophiles kick out stronger ones in the reaction of chloroalkanes with sodium iodide in acetone?

texts:
I have the following SN2 reaction, in an acetone:
1,4-dichlorohexane (1 mol) reacting with NaI (1 mol) to form 4-chloro-1-iodohexane and NaCl.

However, chloride ions are stronger nucleophiles than iodide ions in an aprotic solvent and iodide ions are weaker bases than chloride ions. Reactions generally form weaker bases, why does this reaction occur? My text shows it does, but I don't understand why. What am I missing?


texts: Can I use a digital multimeter as substitute for a zero resistance ammeter?

texts: I am testing the galvanic corrosion between two metals, following ASTM G71. In this method, a zero resistance ammeter was the material presented to determine the galvanic current measurements. Unfortunately, we don't have access with it. So can I use a digital multimeter instead?


texts: Major product in Reimer-Tiemann Carbonylation

texts:
Attempt:

This is Reimer-Tiemann Carbonylation reaction in which the ortho product is major when phenol is the substrate. Hence, here I expected the ortho product to be major as well as it would also make hydrogen bonding possible, which stabilizes the compound. Besides, $\ce{-OH}$ is a better activator than $\ce{-OCH3}$.

But the answer given in the module is $C$ and not $A$. Where is my thought process wrong?


texts: Can sodium bicarbonate be considered an acid?

texts:
I was reading about acids and bases today and finally decided to question the statement that "baking soda is a base."

Let's start with the dissolving of baking soda, $\ce{NaHCO3}$.  The equation to represent its dissolution in water is $\ce{NaHCO3 + H2O <=> Na+ + H3O+ + CO3^{-2}}$.

In this "reaction," baking soda is a proton donor, creating hydronium ions and a conjugate base, $\ce{CO3^{-2}}$.  Doesn't this make baking soda an acid?

If what I have written here is correct, then baking soda will create a base when dissolved, but baking soda itself is not the base.  Is this accurate?


texts: Does changing EDTA concentrations affect the amount of calcium ions in milk?

texts: For my chemistry experiment I am titrating EDTA against milk to find out the concentration of calcium ions in milk. I will be using EriochromeT as the indicator. The lab tech said that if I use temperature as my independent variable the end-point of titration will fluctuate. She suggested that I should change the concentration of EDTA instead. Is it a good suggestion? What is a better independent variable to use?


texts: Why is H2O a weaker acid than acetylacetone? Shouldn't a hydrogen connected to an oxygen be more acidic than a hydrogen connected to a carbon atom?

texts:
I recently started studying chemistry after a long pause in my education so pardon me if it is a simple question.
In the organic chemistry course I am taking, the professor told us that the first factor defining the stability of the conjugate base (and thereby the acidity of the compound) is the atom that is connected to the acidic hydrogen. By this definition, the hydrogen in $\ce{H2O}$ should be more acidic than the hydrogen in acetylacetone as the first one is connected to oxygen but the second one is connected to carbon (as oxygen is more electronegative than carbon).
My professor mentioned other factors such as the existence of resonance structures, inductive polarity, and the effect of side chains, but she mentioned these factors come next and only if both hydrogens in our comparison are bound to the same element.


texts:
In Gibbs energy equation:

$$\Delta G=\Delta H-T\,\Delta S$$

At constant pressure,

$$Q=\Delta H\tag{1}$$

and we know that $T \Delta S=Q$ (reversible)
so finally

$$T\,\Delta S=Q\tag 2$$

Putting values of Equation $\text{(1)}$ and $\text{(2)}$ in Gibbs energy equation ,
we should always get $\Delta G=0$ for a reversible reaction. ..

Why isn't it so?

I don't know how to search it on Google; if anyone could give me a link or otherwise explain it?


texts: If you can smell something does that mean that this thing loses molecules?

texts:
When you can smell something there must be some molecules in your nose which signalize the smell in your nose. Does that mean, that e.g. a cheese is losing molecules which fly into your nose?
And does that effect the weight or amount significantly?


texts: What is the main contributor of the color of honey?

texts: I was told that the color of honey contains so much chemistry and that was interesting to me and after doing a couple of research I found that the color of honey depends on the presence of plant pigments including carotene, xanthophylls, anthocyanins, flavonoids, polyphenols, as well as amino acids and mineral salts. So as we can see there are many factors to the color of honey but my question is which out of all of the listed above is the main contributor and is the most affected by the increase in temperature (for example for acidity the main contributor is gluconic acid).


texts: Boiling and melting point of trans- and cis-but-2-ene

texts: The boiling point of trans-but-2-ene is lower than that of its cis isomer but the melting point of the former is higher than the later. Why is it not following the same order? Is there any factor of structural symmetry coming playing a role here?


texts: Why do we measure the initial rate of a reaction?

texts: Why do scientists usually measure the initial rate of a reaction, instead of measuring the rate some time into the reaction?


texts:
In class, we learned about the Lewis structure of some elements such as carbon, but we didn't learn how to do the Lewis structure of cations and anions.

Do we just draw the number of electrons in the ion, or do we do something different?

So for example, what would be the Lewis structure of $\ce{Li+}$ and $\ce{Li-}$? How would you draw it out?


texts:
How can acetic acid be distilled by freezing when its freezing point is above the freezing point of water.

Examples on the web show the water portion of the vinegar as ice and the acid as a liquid but Wikipedia shows that freezing point of acetic acid is 16.6°C.


texts: Determining the oxidation state of a bridging platinum complex

texts:
I want to ask a question about determining the oxidation state of a Platinum complex.

I was presented today with the following complex and asked to comment on the oxidation state and hence the d-orbital configuration of the central metal ion:

My working was as follows:

The $\ce{Me}$ groups do not contribute to any charge.

The $\ce{SMe2}$ ligands are neutral similar to $\ce{H2O}$ and don't contribute to any charge either.

However, if I take this into account, this would therefore mean that each Platinum central metal ion has the same magnitude of charge, but in opposite magnitudes i.e. $-2$ or $+2$ and this is not valid chemistry.

My other thought was whether the electronegativity of the $\ce{SMe2}$ ligand central S atom compared to the $\ce{Pt}$ meant that the bonding pair of electrons is electronegatively attracted to the S atom, meaning that for each $\ce{Pt}$ atom, the $\ce{Pt}$ atom would lose two of its own electrons, one in each opposite direction giving a +2 oxidation state.

The answer given is +2 for both metal centres but I was unsure using the approaches above whether this was valid.

What other steps am I missing to reach the final oxidation states of the $\ce{Pt}$ centres?


texts: What type of sensor technologies exist to determine the chemical composition of a polymer?

texts:
Let's say I have several pieces of trash and each is made with a different type of material like:

Plastic bottle : High Density Polyethylene (HDPE)
Cereal box : Paperboard & Epichlorohydrin
Shrink Wrap : Polyolefin
Kitchen utensil : Melamine-resin
Textiles : Urea-formaldehyde
Crown Cork Bottle Cap : Metal and Plastisol lining
Rock
Plasterboard
Coffee cup : Ceramic and Glaze (silica + metal oxides)

My objective is to build a system complete with sensors that automatically determines the material (chemical makeup) of each object. Are there material sensors currently on the market that can identify all of the materials that make up these objects?


texts: Addition of Methyl Grignard and use of HClO4 in this question

texts: Okay so the first step is the use of Grignard. I know that Grignard does a 1,2 addition(generally) and the attack happens directly on the carbonyl,and I think HClO4 basically does protonation.Not sure about the role of NaOH. Also the final answer given is 3,5 dimethylphenol. The final product is devoid of the oxygen which is present in the ring. How should I approach this question?


texts: In a galvanic cell where the two electrodes are in the same electrolyte solution, why do reduction and oxidation occur separately?

texts:
In a certain book, I was presented with the following solution:

An iron nail is attached by a piece of wire to a magnesium ribbon, and the iron and magnesium are placed into the same container, with dilute sulfuric acid.

My understanding is that due to the difference in reduction potential of the iron and magnesium, the magnesium ribbon will oxidise in preference to the iron, so the Mg metal will oxidise and lose its electrons to form Mg2+ ions, and the electrons will travel to the iron electrode and react with the H+ ions in the electrolyte solution, and H2 gas will be evolved at the iron electrode.

My question, is why must oxidation and reduction occur at the two different electrodes? If the magnesium isn't connected to the iron, it will just react with the H+ ions there, and the same overall redox reaction will occur. Why is it, that if there is a wire attached from the magnesium to the other electrode, the electrons from the oxidation of magnesium would prefer to follow the path of the wire, rather than just react with the H+ ions already present at the magnesium strip?


texts: What source of error in an acid-base titration could lead to a higher reading of the acid concentration?

texts:
Methanoic acid ($\ce{HCOOH}$) is found in stinging nettles. In an analysis of the concentration of methanoic acid in a solution extracted from nettles, the solution was titrated with a standard solution of potassium hydroxide. Aliquots of the methanoic acid were transferred to a conical flask and titrated against the potassium hydroxide solution in a burette.
Which one of the following would cause the calculated concentration of methanoic acid to be higher than it actually is?
A Rinsing the conical flask with deionised water
B Rinsing the burette with deionised water
C Rinsing the pipette with deionised water
D Rinsing the conical flask with potassium hydroxide solution

For this question, im not sure if A and B are correct answers. The book only has B.
For A: if you rinse the conical flask, would this mean that there would be a greater volume in the flask after the titration than expected? Therefore when you have a lower concentration?
For B: if you rinse the burette with deionised water, this would dilute the $\ce{KOH}$, therefore causing a greater titre required. This means a greater mole of $\ce{KOH}$ and hence acid. Would this then lead to a greater concentration?
So B is the only correct answer, is my reasoning correct?


texts: Does the Clemmensen reduction reduce the C=C bond of α,β-unsaturated ketones?

texts:
The Clemmensen reduction is a chemical reaction which reduce aldehydes and ketones to alkanes.

In my book, it is written that under such conditions, double and triple bonds are not reduced, but my teacher told me of one exception:

  α,β-unsaturated carbonyl compounds undergo reduction of both the olefinic and carbonyl group.

But according to my book, when this compound undergoes Clemmensen reduction, the product is pent-2-ene.

Who is correct?


texts: Theoretical Calculation of Lattice Parameter from Space Group

texts: If I am given a compound which belongs to, say the cubic $\text{Ia}\bar 3\text{d}$ space group, is there a known way to calculate the lattice parameter of the compound? In general, can lattice parameters be calculate from knowing what space group the compound belongs to?


texts: Propanoic acid reaction with potassium permanganate

texts:
I was conducting a lab where we have to identify/justify how functional groups affect the oxidation of a molecule.

I used propene, propanone, and propanoic acid for this reaction. From what I have learned in class, ketones and carboxylic acids cannot get oxidized. However, in my experiment the ketone somehow is not getting oxidized while the propanoic acid is. I tried using butanoic acid just to be sure but it turns out that it gets oxidized as well. I have also made sure that there are no contaminants. I used 4 ml of 100% propanoic acid with 0.003 mol of $\ce{KMnO4}$.


texts: What is the oxidation state of oxygen in Na2O2?

texts:
I am asked to determine what is the O.S. of oxygen in $\ce{Na2O2}$

I was under the impression that oxygen had a charge of -2 and I multiplied that charge by 2 giving me a total of -4.

However, the computer program I am using, states that I am wrong. Can someone clarify why?


texts:
Why doesn't the carbocation form on the carbon that is attached to the ethyl group in this reaction?

Subsequently, why doesn't the $\ce{Cl-}$ attack the carbon that is attached to the ethyl group? Is a tertiary carbocation less stable than a secondary allylic carbocation?

Reaction:


texts:
So I wanted to know what the reaction between sodium hydroxide and carbon dioxide can be, and upon research I got 2 answers. The first one is

$$\ce{CO2 + NaOH(aq) -> NaHCO3(aq)}$$

and the second one is a two-step reaction, first with water then sodium hydroxide:

$$\ce{CO2 + H2O(l) -> H2CO3(aq)}, \\
\ce{H2CO3(aq) + NaOH(aq) -> NaHCO3(aq) + H2O(l)}$$

So my question is which one of these answers is right?

To me, I do not understand why the 2nd option takes into account water because really concentrated $\ce{NaOH}$ would/should be written just as $\ce{NaOH}$, which to me makes the 1st option the right one. Am I wrong?


texts: Does a smell imply particles or chemicals in the air?

texts:
(I know little science so please help me if I'm in the wrong place or if my question needs editing. I could use help with tagging, for example.)

If I can smell something then does that mean there are particles or chemicals in the air?

My question is motivated by some new window blinds that have been installed in my home. The blinds have a smell, which is most noticeable when the sun is shining on them. I am trying to work out if the blinds are emitting some chemical into the air. This question is my first step.

[This question is not the same as "How does the smell of a compound come about, and is it possible to define a smell?". This is clear from the title.]


texts: When disolving a iron pill for titration, why do I use sulfuric acid instead of nitric or hydrochloric acid?

texts: In a titration to decide the iron content of a pill we dissolved the iron in sulfuric acid and then titrated it with cerium(IV) sulfate. But I just wondered what's wrong with using nitric and hydrochloric acid in this scenario?


texts:
I'm currently reading through Clayden's Organic Chemistry, and in chapter 30 an assertion is made that

Halo aldehydes are unstable and should be avoided.

I should be clear that the context of this situation is under treatment with an enolate, so basic conditions are being employed. I believe the most likely hypothesis is that the instability has to do with the increased electrophilicity of the α-haloaldehyde's carbonyl group. The increased electrophilicity is supported by the equilibrium constant for the hydrate formation from acetaldehyde and chloroacetaldehyde, which is 1 and 37 respectively. This means that the rate of nucleophilic attack on the carbonyl group will be faster. Is it possible that the rate of nucleophilic attack is fast enough for O-attack on the carbonyl (hard-hard) as opposed to the expected C-C attack at the halogen center (soft-soft)? I have also proposed that α-haloaldehyde could eliminate H-Br to yield the ketene. I am less confident in my second proposal, as I have not seen any literature reporting this, and if so, I would expect equilibrium to lie on the side of the α-haloaldehyde.


texts: Spin orbital coupling and total angular momentum

texts:
The Sodium emission spectrum has 2 bright yellow lines called the Na-D lines. Superficially I understand the cause; there's spin-orbit coupling and the 3p orbital is split into 3p(3/2) and 3p(1/2).
But I don't understand why those numbers (3/2 and 1/2)?
Are these the total angular momentum values or the orbital angular momentum values?
And how does one work them out?


texts: What makes selectivity other than activation energy?

texts:
Selectivity and kinetics of reactions are somehow linked to the activation energies of reactions. However, there's something not totally clear in my mind about the selectivity. I will get a general example as many systems can fit to this.
Let's consider a reaction between A and B. The reaction between A and B can proceed through different pathways (1 & 2). A selectivity of 100% is observed for pathway 1 and it is demonstrated that the activation energy for this pathway is slightly lower than pathway 2.
Let's consider than a system of C and D. The reaction between C and D can also proceed through 2 pathways, let's name them 3 & 4. In this scenario, a selectivity of 75% for example is observed for pathway 3. The activation energy for pathway 3 is lower than pathway 4 in a more marked way than when we considered the reaction of A and B.
My question is then. Why are sometimes observed a total selectivity when the difference in activation is low, while sometimes the products result from different selectivities when the difference in activation energies between the pathways is rather high.


texts: Why does greater orbital overlap mean a stronger bond?

texts: According to valence bond theory, orbital overlap produces a bond. However, I don’t understand why having greater orbital overlap renders a bond stronger. It’s intuitive, I suppose, but I haven’t been able to find an actual explanation as to why that is. Are there quantum mechanical effects behind this?


texts: Why is this reaction spontaneous in standard conditions?

texts:
To study if this reaction is spontaneous I proceed in this way:
$$\ce{2H_{3}O^{+} +Fe ->H_{2} +Fe^{2+} + 2H_{2}O}$$
First I write the two semireaction:
$$reduction: \ \ \ce{2H_{3}O^{+} +2e^{-} -> H_{2}} $$
$$oxidation: \ \ \ce{Fe -> 2e^{-} +Fe^{+}} $$
Then I write the scheme of the cell:
$$\ce{Fe|Fe^{2+}||H_{3}O^{+}|H_{2}}$$
I know that:
$$E^{0}_{cell}=E^{0}_{right}-E^{0}_{left}$$
$$E^{0}_{cell}=E^{0}_{H_{3}O^{+}|H_{2}}-E^{0}_{Fe|Fe^{2+}}=-E^{0}_{Fe|Fe^{2+}}=-0.44$$
But also:
$$\Delta G^{0}=-nFE^{0}_{cell}$$
So $$\Delta G^{0}>0$$
And the reaction is not spontaneous, while my textbook says it is, so I must be wrong. Someone could find my error?


texts: Mathematical proof of ΔQ=ΔH at constant external pressure

texts:
Consider a system with an ideal gas. A process is being carried out in which the gas is being compressed at a constant external pressure ($P_{ext}$). For this process ΔQ should be equal to ΔH, but this is where I am stuck.

Work done by the system will be: $$ΔW= -P_{ext}ΔV$$ and
$$ΔH=ΔU+Δ(P_{sys}V)$$Now we can write: $$ΔQ=ΔU-ΔW = ΔH-Δ(P_{sys}V)-(-P_{ext}ΔV)$$ In this expression $Δ(P_{sys}V)$ and ($P_{ext}$ΔV) are not equal as the process is irreversible and the so the external pressure will remain constant throughout the process but the internal pressure varies. I know that at the initial and final stage the external and internal pressure will be equal as the system will be then at equilibrium with the surrounding but the magnitude of the internal pressure will be equal to the constant external pressure($P_{ext}$) only at the final stage. So how will ΔQ be equal to ΔH when the process is carried out at constant external pressure?


texts:
A piece of electronic equipment originally contained $\pu{1.250 g}$ of a valuable metal. Corrosion over time has given a compound of formula $\ce{M(OH)3}$, which is isolated but not weighed. This compound is treated with sulfuric acid to give a compound that has beautiful red crystals and is found to have a molecular formula of $\ce{M2(SO4)2}$ and a mass of $\pu{1.860 g}$. What is this valuable metal?

My attempt:
$$ 1.860 ~\mathrm{g} - 1.250~\mathrm{g}= 0.61~\mathrm{g}\, \ce{SO4} $$

I took the $\pu{0.61 g}$ and converted them to moles of $\ce{SO4}$, then I converted 2 moles $\ce{SO4}$ to 2 moles $\ce{M}$ and got $0.0064~\mathrm{M}$.
Then I divided that by $\pu{1.250 g}$.

I got 195.31, so is platinum the correct answer?


texts: Test for diethylether or tertiary alcohol?

texts:
What is a simple chemical test to tell the difference between a tertiary alcohol (e.g. 2-methylpropan-2-ol) and an ether (specifically diethylether/ethoxyethane)?

Neither of them can be oxidised by reagents such as potassium dichromate, Tollens reagent or fehlings reagent.

I came up with a test in which a less than stoichiometric amount of ethanoic acid is added and left to react, then some sodium carbonate is added and if there is no effervescence that means an ester has formed hence it must have been the alcohol, otherwise it was probably the ether. However I am unsure about the extent to which this reaction completes and it's simplicity.


texts: What will be the order of acidity in the following compounds?

texts: What will be the order of acidity in the following compounds ? From My point of view it should be 3>1>2>4. But the answer given is 3>2>1>4. Can anyone explain how ?


texts: Enthalpy, heat of solution test: Calcium chloride vs magnesium chloride in water

texts:
I did a school experiment to measure the heat of solution (enthalpy) of various salts dissolved in water.
My results are completely different to the teacher's answer.
Specifically my test showed Calcium Chloride increasing the temperature of the cup of water by 6 degrees Celcius, while the Magnesium Chloride only increased the temperature of the same volume of water by 1 degree Celcius.
The teacher's answer shows Magnesium Chloride with an enthalpy more than double (twice as negative) as that of Calcium Chloride.
I'm happy to be wrong about this but could someone point me to an "official" answer so I can conclude that the experiment was done incorrectly.


texts:
There is Lugol's 5 % solution with 5 g of pure iodine and 7.5 g of potassium iodide.
In one ml there should be 12.5 mg of iodine in sum.

But there are suggestions telling that two drops of this solution contains 12.5 mg of iodine and the drops I seen used there are no way 1 ml.
Is it a mistake? Why they don't use measurement in ml rather than drops to be precise?


texts:
Suppose I have a group of organic compounds say A, B, C, D, E, F, G, H. I know their chemical formula and their names. Now there exists a reaction among these compounds but we do not know which compounds would react to give which products. It may be that A and B react to give C and D or B and D react to give F and H. If we are given these compounds, is it possible to identify a reaction that will occur among any number of these compounds to give the product which would belong to this set of compounds?

Note: If you have not understood any part of this question, please ask me before down-voting, I will edit the question and try to re-explain. Thank you. ALso I am a computer science student, so I dont have too deep knowledge in chemistry, so do help me.


texts: What would happen if you burned paper with a laser, in a vacuum?

texts:
If you hit a piece of paper with a powerful laser inside a vacuum, what would happen? It sounds like it should not "burn" and have a flame spread over the paper, as there is, of course, no oxygen.

Would it perhaps turn the paper into a thin sheet of charcoal where the laser makes contact? If so, perhaps one could make a cnc-type machine within a vacuum chamber that automatically cuts out stencils.


texts: Gas concentrations along the gradient from sea level to deep-sea

texts:
Studying scuba diving-related phenomenas I thought about how to estimate gases concentration down the sea.

Of course, solubility of gases at, for example, $5$ atm of pressure, can be estimated with Henry's law, i.e

$$S=k\,P_g$$

But this is not the case down the sea, cause there is no gas in equilibrium with sea-water. There should be a way to relate solubility on the deep with the surface pressure, but can't find how.

So, is there any way to estimate gases concentration deep into the sea?


texts: How does Potassium Hexfluoronickelate(IV) exist in a stable state?

texts:
Nickel generally does not exist in a $+4$ Oxidation state. Wikipedia has the following to say regarding Nickel(IV):

  Ni(IV) is present in the mixed oxide $\ce{BaNiO3}$. ....... Ni(IV) remains a rare oxidation state of nickel and very few compounds are known to date.

This article directly contradicts the first statement, as it says:

  the photoelectron spectroscopy data suggest the description of $\ce{BaNiO3}$ in terms of trivalent Ni and oxygen anion holes.In terms of a local ionic model the idealized description of this high-valent oxometalate would correspond to $\ce{Ba^2+Ni^3+(O2)^2O^•-}$

Now, we end up coming to the curious case of Potassium Hexfluoronickelate(IV), which decomposes at 350°C, meaning that it is relatively stable. Not much literature is available on this compound online, except this article, which is unfortunately behind a paywall.

Could someone explain how nickel exists in a (IV) state in this compound instead of degenerating to $\ce{K4[NiF6]^2-}$? Also, are there any more Nickel compounds exhibiting the (IV) state? Explanations regarding the formation and stability of this compound are also welcome!


texts: Confusion about Ethinyl estradiol IUPAC name

texts:
According to Wikipedia, the IUPAC name of ethinyl estradiol is:

  17α-Ethynylestra-1,3,5(10)-triene-3,17β-diol

However, in PubChem, its IUPAC name is:

  (8R,9S,13S,14S,17R)-17-ethynyl-13-
  methyl-7,8,9,11,12,14,15,16-octahydro-6H-cyclopenta[a]phenanthrene-3,17-diol

My questions:

Which one is correct by latest IUPAC blue book?
How are the locants assigned for this molecule? Specifically, which carbon was assigned the locant "10", since it does not appear in the locants of "octahydro"?


texts: Product of primary amine and acid anhydride

texts:
How does an acid anhydride react with a primary amine? I thought it'll be some sort of condensation reaction, so I made the product by removing a water molecule and got a cyclic product. However, the product given is an open chain molecule (major).

How does the reaction occur? How does the ring open? Could someone please give a detailed mechanism?

P. S. What is the general reaction for primary amines and acid anhydrides?


texts: Size of dispersed phase particles in colloid?

texts: I am really confused about what the size of particles of dispersed phase in a colloid is: one of my textbook says its between $1 - 100nm$, another says its between $1-1000nm$, and Wikipedia says its between $2-500nm$. Is there any reliable source giving the exact information?


texts: What is the reaction mechanism for the polymerisation of formaldehyde?

texts:
Clayden et al. (2012) mention that formaldehyde is rather prone to polymerisation. In an aqueous solution containing formaldehyde, it is known that the polymeric "paraformaldehyde" is formed. However, the book does not did not display any information regarding the mechanism of polymerisation. Upon searching the Internet, I was only able to find this image which shows a plausible mechanism for polymerisation:

However, this mechanism seems to be for polymerisation under acidic conditions. I was wondering if there is a general scheme for the polymerisation of formaldehyde.

Reference

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


texts: Does spectrochemical series trend depend on the metal center?

texts:
Can the trend of spectrochemical series vary/fluctuate according to the central metal atom (CMA) that is being used?
For example, for the CMA $\ce{Ni^2+}$ the ligand $\ce{H2O}$ will have more CFSE than $\ce{NH3}$ because $\ce{NH3}$ acts as a weak field ligand (WFL) for $\ce{M^2+},$ even worse then $\ce{H2O},$ though $\ce{NH3}$ is placed higher then $\ce{H2O}$ in the spectrochemical series.


texts: We're going to conduct a study to make corn husk fiber into a paper. Soda Ash is always used to extract the fibers from the husks, First question is there any chemical we can use aside from soda ash to extract fibers? Second, we want the fibers to paper white is there a chemical that could turn the yellow-greenish fiber into white? I don't have the means to do the experiment just yet so it would be helpful to have answers.


texts: What is the sense of electronic configuration of an atom if an electron can be in any superposition of energy eigenfunctions?

texts: I recently started learning abou the quantum mechanical explanation of hydrogen atom. In the derivation of the wave functions of hydrogen atom we find its energy eigenfunctions. But according to the Schrödinger equation, the electron can exist in any linear combination of the energy eigenfunctions. So what I don’t understand is that why do we say that the electrons in an atom belong to specific orbitals? Why do we always treat electrons in an atom as if their energy is fixed?


texts: How to calculate the equivalent weight of a metal in a metal sulphate?

texts:
The question is:

$\pu{2g}$ of a metal is present in$\pu{4.6g}$ of its metal sulphate. Find the equivalent weight of the metal.

I understand the concept that equivalent weight of an element is the molecular weight divided by the n-factor (in this case it's the valency), but I couldn't arrive at a conclusion.
Could you also help me understand how equivalent weight of a metal is related to the equivalent weight of the sulphate? In my textbook, it's written like this:
$$\textrm{eq. wt. of metal} = \textrm{eq. wt. of metal sulphate(2-)}$$
and then they carried on with the calculations.
PS I know the answer, I need to know how one should conceptually arrive at it!


texts: Nanocellulose suspension in water being dialysed in ethanol

texts: I am working on nanocellulose. To prepare the sample for silanization, the first step is to dialyse the preparation in ethanol overnight. I wonder why this is a necessary step. Sorry, I am a physicist working on something which involves a lot of chemistry. I am alone in my lab so I don't know who else to ask. Thank you very much!