texts:
An ionic compound has a solubility of $1\ \mathrm M$ in water at $25\ ^\circ \mathrm C$ and its solubility increases as the temperature is raised. What are the signs of $\Delta H^\circ$ and $\Delta S^\circ$ for the dissolving process?

Since the the solubility increases as the temperature is raised ($\Delta G^\circ$ becomes more negative), I know that $\Delta S^\circ$ is positive. However, I am unsure of how to determine the sign of $\Delta H^\circ$. The answer is $\Delta H^\circ > 0$.


texts: Can a system of 2 consecutive biphenyl systems be optically active , even if any adjacent biphenyl systems aren't optically active?

texts:
This question came in an online test, where they asked whether or not 22,26-dibromo-12,32-dichloro-23,25-diiodo-16,36-dimethyl-11,21:24,31-terphenyl was optically active.

The answer is that, it is optically active.

According to Solomon and Fryhle:

  "Biphenyl is an asymmetric compound so it must not have a plane of symmetry or center of symmetry to be optically active".
  Hence compounds which have 2 same adjacent groups on a single phenyl in any biphenyl system cant be considered optically active .

Applying that concept above as same groups (Br and I) are attached to the middle phenyl system, the individual biphenyl systems on both sides are optically inactive, hence the compound should be optically inactive.

Please tell me where I am going wrong in my interpretation.


texts: Do various soaps work better when dissolved/used in different water temperatures?

texts:
My wife and I have had an ongoing argument about various cleaning agents, and I wanted to get a Chemists' view on it.

When we are doing laundry, she will generally clean using the cold water setting and a standard amount of detergent.

If I do laundry, I will use the warm water setting with a standard amount of detergent.

Either way, the clothes come out (seemingly) clean. Using cold water saves energy from the heating process, which has been her excuse for doing such a dastardly thing. Her argument against using warm water is that it will damage/shrink the cotton. While I don't disagree on that point, I am curious if the use of warm water causes the detergent to work better or not.

In addition, there are various soaps that work best in cold water.

What is the actual mechanism at work here? Why do some soaps work better in cold (or hot) temperatures?

To make things a bit better, let's remove some more variables. We use this detergent:

Tide Pods

Unfortunately I can't find information on the normal temperatures those machines operate at.

Also who is right? (I bet it's her)


texts: What is the cost of 1.00 g of calcium ions as provided by this brand of dry milk?

texts:
A student determined the $\ce{Ca^{2+}}$ ion content in a sample of nonfat dry milk. For complete titration of the $\ce{Ca^{2+}}$ ion present, a sample weighting $1.483 ~\mathrm{g}$ required $41.33 ~\mathrm{mL}$ of $1.183 \times 10^{-2} ~\mathrm{M}$ EDTA solution. Calculate the mass of the $\ce{Ca^{2+}}$ ions in the titrated sample.

So I did:

$41.33 ~\mathrm{mL} = 0.04133 \mathrm{L}$

$(1.183 \times 10^{-2}~\mathrm{mol\, L^{-1}})\times (0.04133 \mathrm{L}) = 4.89 \times 10^{-4} ~\mathrm{mol}\, \ce{Ca^{2+}}$

$(4.89 \times 10^{-4} ~\mathrm{mol}\, \ce{Ca^{2+}}) \times 40.078 ~\mathrm{g\, (mol\, \ce{Ca^{2+}})^{-1}} = 0.0196 ~\mathrm{g}\, \ce{Ca^{2+}}$

My question is:

A $25.06$ oz box of the powdered milk analyzed above costs $5.46$.

  Calculate the cost of $\pu{1.00 g}$ of $\ce{Ca^{2+}}$ ion as provided by this brand of dry milk.

How do I do that?


texts: Procedure for laboratory synthesis of tertiary amines

texts: I am having difficulty finding a procedure for making tertiary amines in the lab, any is fine but I am specifically interested in tributylamine.


texts: tap water and distilled water for electrolysis

texts:
my water electrolyzer which I've built using this pdf, produces less gas than I expected. In that file the author insists on using distilled water instead of tap water and I have used tap water. would it be the reason?

Why is it so important to use distilled water since it has high resistance for electricity?


texts: What is the hybridization state of the carbon atoms in [10]annulene?

texts:
I know that one of the more stable structures of [10]annulene or cyclodecapentaene is planar boat-shaped. But that means the hybridization state of the carbons must have changed to suit the geometry. What does it change to? And how are the hybridized orbitals distributed such that the double bonds remain intact?

Edit: I have encountered this molecule only once and am not familiar with the naming convention. For much the same reason, I don't know the exact structure of the most stable isomer of the compound. So even though I was more interested in the boat-shaped isomer of the compound, I think to do away with the ambiguity of the question, I should mainly ask for the most stable isomer of the molecule, viz., trans,cis,cis,cis,cis-isomer.


texts: How are reactants ad-/ -desorbed during Haber process?

texts:
Collecting information for a presentation [academic high-school] about catalysts, I stumbled upon the terms desorption and adsorption as important parts of the Haber process.

However, I could neither find a good explanation for these processes (why and how do they occur?) nor the difference between ad- / desorption and the process
of the reactants "diffusing through the phase boundary to the active site", as it's stated on German Wikipedia.


texts:
We have to find the order of rate of exchange of O with H2O of the following compounds

$\ce{CCl3CHO}$
$\ce{CH3CHO}$
$\ce{CH3COCH3}$
$\ce{CF3CHO}$

According to me, higher rates of exchange would be when electron density is be less on the carbonyl carbon

But how we will compare 1. & 2.? In first compound there is hydrogen bonding (chloral hydrate)


texts: Free Radical Reaction of Methane and Chlorine

texts:
The problem statement:

  Lets say you have $1 L$ of $2 M$ methane and the same amount of chlorine. Lets also say that both are liquids since those are most likely to react. Now the only way they can both be liquids at STP is if the temperature is as cold as an antarctic winter so this is not aqueous. Gases more often bump the wrong way and solids don't react unless it is oxidization or dissolving.

  Now the initiation step is forming the first molecule of $\ce{HCl}$ and Methyl.

  Now the methyl and chlorine atom really want to react and form chloromethane

  Relevant equations

  $\ce{CH4 + Cl2 -> HCl + CH3Cl}$
  (this continues up to tetrachloromethane)

  $\ce{2 CH3Cl -> Cl2 + C2H6}$
  (this can continue for much longer than the previous one can)

The attempt at a solution

$\ce{2 CH4 + 2 Cl2 -> 2 HCL + 2 CH3 + 2 Cl}$

$\ce{2 Cl + 2 CH3 -> 2 CH3Cl}$

$\ce{2 CH3Cl + 2 CH3Cl -> 1 C2H6 + 1 Cl2}$

$\ce{2 HCl -> 2 H2 + 2 Cl2}$

This obviously can't happen because then we have more chlorine than we started out with. Why? Well that $1 M\; \ce{Cl2}$ from ethane plus $2 M\; \ce{Cl2}$ from $\ce{HCl}$ is $ 3 M\; $$\ce{Cl2}$ and we started with $2 M \ce{Cl2}$. Just like the number of each element the molarity has to be balanced. What I find confusing is figuring out the molarity of each compound at each step of the process not the compounds per se.


texts: Reason for Optical Isomerism (at electronic level)

texts:
I have been studying Optical Isomerism recently, and I have got one question, answer to which was not in the books that I have.

I have understood what the phenomenon is, and that, how one can determine whether the plane of polarised light is rotated, and how to tell from the structure whether the molecule will rotate the plane of polarised light or not.

However why does the phenomenon occur? If I go to the atomic level or the quantum mechanical level, it is surely a result of interaction of the polarised light with the electrons in the atomic orbitals and the molecular orbitals. Can anyone explain how this interaction occurs? That is, how is the plane of polarised light bent by the electron - photon interaction (if any)?


texts: Can all species that undergo aldol reactions also undergo Cannizzaro reactions? Ater all, the nucleophile can always attack the carbonyl group.


texts: What Is The Heat Of Combustion Of Diesel And How Do I Find It?

texts: I need help in finding the heat of combustion of diesel, no where online can i find it, and my chemistry teacher does not know how to find it....


texts: How to condense a melted wax in to small aggregate forms like stones of different sizes?

texts:
I am an Architect trying to do some experiments with wax. Normally when the wax is melted and poured on to a surface and it takes the shape of the surface with some strings formed . But instead I would like to condense the wax before it hits the surface so it becomes a small aggregate of varying sizes in the form of a stone . How can this be achieved ?

I want it to condense quickly before it hits the surface once its relieved from the melting point and gets in contact with the room temperature of 12-14 Degrees celcius.Should any solvent be added to the melted wax to achieve this state I wanted?

Your suggestions are most welcomed.


texts: What is the most accepted explanation of aurophilicity?

texts: Gold has a special property called aurophilicity. Inorganic chemistry by Huheey has some explanation, but that was not enough to clear the conception.


texts: Order of Lewis acid character among sulfur hexafluoride, sulfur tetrafluoride and tetrachloromethane

texts:
Problem

Compare the order of Lewis acid character of $\ce{SF6},$ $\ce{SF4}$ and $\ce{CCl4}.$

My attempt
Oxidation state of $\ce{S}$ in $\ce{SF6}$ is $+6,$ so it is very electrophilic.
$\ce{S}$ has a lone pair on it in $\ce{SF4},$ but can expand its octet if attacked by a donor.
$\ce{C}$ cannot accept lone pair from donor.
So, the order should be $\ce{SF6} > \ce{SF4} > \ce{CCl4},$ but that is a wrong answer.


texts:
I'm really confused over how to weigh the molecular mass with intermolecular forces such as hydrogen bonding in HF in terms of figuring out the melting points in relation to each other.

I know that HF has the highest melting point out of HCl and HI, but then HCl and HI both have significantly larger molecular mass.

So how does one properly explain why HF has the higher melting point out of HCl and HI? (Not just saying that generally hydrogen bonds out weigh the molecular mass when considering boiling point)

Is there any mathematical basis?


texts: Reactivity of carbonyl adjacent to cyclopropyl group

texts:
We know that cyclopropyl, because of $\ce{sp^{\sim 5}}$,  hybrid orbitals behaves much like a double bond. It even takes part in conjugation to stabilise positive charge on carbons adjacent to it. I would like to know if it conjugates with the carbonyl carbon too?

Are there cases of 1,4 addition and 1,2 addition with such compounds analogous to that observed in alpha-beta unsaturated carbonyl compounds?


texts: Final temperature of a adiabatic process

texts:
One molar of a perfect gas of $C_v = \pu{20.18 J/K}$ at $\pu{3.25atm}$ and $\pu{310 K}$ undergoes adiabatic expansion to reach a final state of $\pu{2.50atm}$. Calculate final volume and temperature.

Since $PV^{\gamma} = const$ and $\displaystyle T^{C_v/R}V = const$,

$$V_f = V_i\left(P_i\over P_f \right)^{1\over \gamma}$$

Which I got as $\pu{0.0113m^3}$ and $V_i = \pu{0.00782 m^3}$ .

To get final temperature I used
$$T_f = T_i\left(V_i\over V_f \right)^{R\over C_v} = 310\left(0.00782\over 0.0113 \right)^{8.314\over 20.8} = \pu{267K}$$

But when I use equation of state to get final temperature I get $\pu{344K}$ which is the correct answer.

Why did not equation of state and $\displaystyle T^{C_v/R}V= const$ match in this case ?


texts: Why is nucleus charge squared in Rydbergs formula?

texts:
According to coulumbs law, the energy changes linearly with charge. So why is the nucleus charge squared in this formula? Is there a way to derive it?

I was suspecting it might be because it pulls the electron closer too.


texts: What is the difference between ψ, |ψ|², radial probability, and radial distribution of electrons?

texts:
I am very confused regarding these four terms- ψ,|ψ|², radial probability and radial distribution

I know that ψ is called the wave function but is it the same as radial probability?

I also know that |ψ|² is called the probability density of finding an electron inside an atom but is it the same as radial distribution—which is the probability of finding an electron in a volume $\mathrm dV$ inside a nucleus?


texts: Regiochemistry and stereochemistry in synthesis of alcohols from cycloalkenes through oxymercuration and hydroboration

texts:
I have been posting several practice final questions for my organic exam next Tuesday. I have worked through all the questions, but my prof does not post the answers. I would greatly appreciate your feedback.

Draw full structures, including any relevant stereochemistry of the organic products expected in each of the following reactions:

One reaction uses a syn addition, and the other uses oxymercuration. Question: for the oxymercuration, this is anti-Markovnikov because the hydrogen doesn't end up on the most substituted carbon, right?


texts: I have tried to understand what the oxidation state for Mn in $\ce{MnO4^-}$ is. So far i have understood that O have the oxidation state of -2 so because there is 4 O the number turns to -8. What happens to the minus at O? and what is the oxidation state for Mn?


texts:
here,should I prefer hydride shift or a product with more $\alpha$ hydrogens?
my doubt is...as hydride shift is easier than methyl shift,the answer should be $a$ or $c$.if methyl shift takes place the alkene formed has more $\alpha$ hydrogens than $a$ and $c$.what should I prefer? The question is to find major product.also,irrespective of the answer I would like to know which is more stable $a$ or $c$?


texts: How can we produce gasoline from electricity without fossil fuels?

texts:
The other day, I was wondering, if cheap and easy nuclear fusion were developed tomorrow and fossil fuels disappeared, would there be a way to fuel all the gas-powered cars out there? After all, we have the Haber-Bosch process for producing ammonia. But then gasoline is not a chemical but a mixture of different organic compounds. So, let me structure a question to get at the heart of my curiosity:

How might we produce gasoline from electricity on an industrial scale without the use of fossil fuels as input?

Assume the electrical power came from an unlimited source, such as nuclear fusion, solar arrays in space, or very specific magic.

You may also assume that the gasoline doesn't need to be replicated perfectly -- that which can fuel anything that uses gasoline, or which satisfies an industry definition of gasoline, is sufficient. Ethanol does not count, since most cars cannot use it solely.

Feel free to comment on the environmental friendliness of the solution, excepting the electricity generation itself.

This basic question was originally asked here, and where it was suggested to migrate to chemistry SE.


texts: Can we do combustion caused by limited supply of air in a lab? How?

texts:
For example Ethyne in combustion by limited supply of air

$$     \ce{ 2C2H2 + 3O2 ->[\Delta] 2CO2 + 2H2O + 2C } $$ vs.

$$     \ce{ 2C2H2 + 5O2 -> 4CO2 + 2H2O + Energy } $$

What are the limits of air availability to make these combustions?
How to do these experiments in lab?


texts: Why is the electronegativity of hydrogen 2.20?

texts: Well, I was doing research about the ways we can measure electronegativity and I just realized there must be an arbitrary electronegativity set for an specific element to give us the relative amounts of the other ones. Pauling used hydrogen and suggested 2.1 for its electronegativity which later was altered to 2.20. Now, the question is, why was the electronegativity of hydrogen suggested as 2.1 and why is it 2.20 right now? What are the secrets in those numbers?


texts: Elephant Toothpaste demo: How to concentrate hydrogen peroxide (freezer?)

texts:
I would love to do an 'elephant toothpaste' demo in my Chemistry classes this week, but I do not have enough time to order 30% $\ce{H2O2}$ from a supply company.  I have been reading (and seeing on YouTube), however, that some people choose to create their own concentrated $\ce{H2O2}$ (concentration allegedly in the vicinity of 20-35%) by putting 3% $\ce{H2O2}$ in the freezer overnight, then separating the concentrated $\ce{H2O2}$ from the then-frozen water.

My ideal plan would be to use all of the $\ce{H2O2}$ that I produce during my classes throughout the day.  I've never worked with concentrated $\ce{H2O2}$ and so would like to ask.

Would anyone here actually recommend this method to me, given that I would be using this in class for the Elephant Toothpaste demo?  Are there any safety-related deal-breakers that I should be aware of?
What is the highest possible concentration of $\ce{H2O2}$ I could feasibly achieve by storing a bottle in a school's lunch-room freezer overnight?  I don't need anything above ~30% and would just love to know if this method has the potential to make >35% concentrations.
If I do happen to have extra $\ce{H2O2}$, what is the simplest way for me to dispose of it responsibly?  I know that $\ce{H2O2}$ will eventually decompose into $\ce{H2O}$ and $\ce{O2}$, and would rather not have to find a way to store home-made $\ce{H2O2}$ of an unknown concentration, but want to be safe and responsible with any disposal methods I use.


texts: Up to which temperature and pressure can dendrimers (PAMAM) be stable?

texts: I am preparing PAMAM (poly amido-amine) dendrimer and I want to know up to which temperature and pressure can it be stable?


texts: Why does formic acid smell like getting hit in the head?

texts:
I was cleaning up a concentrated formic acid spill and when I was close enough to the hood to get a whiff it smelled exactly like the smell sensation from hitting my head.

We know that olfactory memory is very keen.  While many people identify a vaguely metallic odor when hit in the head, I doubt many non-chemists have had occasion to smell pure formic acid.  Do chemists familiar with the chemical generally agree that formic acid matches the olfactory sensation of head concussion?

If so: Is there a physiological effect of head concussion that would mimic the effects of formic acid vapor on the olfactory system?  (Or maybe even produce formic acid that could be picked up by olfactory nerves?)


texts: What type of chemical reaction is sulfuric acid with calcium carbonate?

texts:
$$\ce{H2SO4 + CaCO3 -> H2CO3 + CaSO4}$$

I thought it would be a double replacement and also a decomposition reaction because $\ce{H2CO3}$ immediately breaks down to $\ce{H2O}$ and $\ce{CO2}$.


texts: Can a molecule be neither gerade nor ungerade?

texts: Or can any molecular orbit always be written a linear combination of gerade and ungerade basis states?


texts: How much electricity could be generated by a person's stomach acid?

texts: Motorola has a device that is powered by stomach acid. Given that a battery consumes the electrolyte as it generates a charge, how much power could be generated using a device such as this? Let's assume the electrodes are large enough that the electrolyte is the limiting factor in this reaction. Would the body just generate more acid to compensate? Would there be any physiological side-effects from using such a battery?


texts:
In a true muniom(muon-antimuon atom) do the energy levels match with that of the hydrogen's?

The core is lighter for about 100 times but the muon is 100 times heavier than the electron so it would make sense the energy levels of a true muonium and a hydrogen atom to match?

Or is this wrong?


texts: Selection of parent carbon chain for IUPAC naming

texts:
How to select the parent carbon chain for IUPAC naming of following compound?

I think the red numbering is correct, but in the answer key, they have used the blue numbering.
Which is correct?
My question is regarding selection of parent chain in an alcohol. While selecting the parent carbon chain (base name) to write the IUPAC name of an alcohol, do we have to give preference to the one which gives the lowest locant to the $\ce{–OH}$ group (viz. primary functional group here), or the one which has the maximum number of carbon atoms?


texts:
I could not think of this reaction fitting into any of the reactions I know except the aryne mechanism. And hence I came up with the following mechanism after seeing the answer (which I've written in the picture next to question). Please tell if my proposed mechanism is correct.

Also, I am highly unsure of the fact that the last species formed will be able to extract a hydrogen atom from somewhere in the solution.

Question:

This is my proposed mechanism:

Source: Joint Entrance Exam (JEE) 1997 India


texts:
How can I find the crystal lattice vectors, given the crystal parameters?
For example, consider a crystal of rhombohedral symmetry, where a=b and c are known, and alpha=beta=90, gamma=120. How can the lattice vectors be found?


texts: What is the form of the Hamiltonian for solids?

texts: For atoms, and even molecules, I can  understand how the Hamiltonian would be constructed, but what of solids (as in, for electronic structure calculations)? Thank you for any help.


texts: Comparing basic strength of nitrogen heterocycles

texts:
Compare the basic strength of the following compounds:

  d > b > c > a
  c > b > a > d
  c > a > b > d
  a > d > c > b

I know that in compound (c), the π-bond between nitrogen and cyclopropenyl will polarize (due to aromatic stability) such that it increases electron density of the nitrogenous ring. Whereas, in compound (d), the π-bond will polarize reducing the electron density of nitrogenous ring. Hence, comparing compounds with similar nitrogenous rings, I get that the basic strength of (c)>(b)and that of (d)<(a). But I thought the ring containing more number of nitrogen atoms will be more basic as there will be more lone pair donors, so I thought the answer to be option (4), but the correct answer happens to be option (2). I would like to know that how is basic strength of the nitrogenous rings being compared?


texts: What is known about the phase of matter at very high temperature and enough pressure?

texts:
Are there theoretical reasons for or against the existence of materials that will not become solid at some fixed, sufficiently large temperature when enough pressure is applied? Or is this even the normal state of affairs?

The usual phase diagrams typically only give a finite portion of the thermodynamical state space, probably as more cannot be experimentally tested.

But theory might tell us what happens, one way or another.


texts: Entropy as "extent of energy dispersal" vs. entropy as defined by the Clausius equation

texts:
Currently, the concept of entropy as "energy dispersal" has been proved to be more easy to understand than the concept of "disorder". While the first can be applied successfully to explain the expansion of a gas through vacuum, I don't get how the temperature influences the "energy spreading" according to the Clausius equation (although this is simple to understand with the concept of "disorder"):
$$dS = \frac{dq_{rev}}{T}$$
If the temperature is low, the energy added to the system ($dq_{rev}$) increase its entropy ($dS$) more than if the temperature is high. How this can be explained applying the "energy dispersal" interpretation?


texts: How to get the reducible representations of the B-B and the B-Cl bond of B2Cl4

texts:
I just can't seem to get the correct answer to this symmetry question in my book. "Introduction to molecular symmetry J.S.Ogden."

I am trying to find the reducible representations of both the $\ce{B-Cl}$ bond and the $\ce{B-B}$ bonds in $\ce{B_2Cl_4}$ in the point group of $D_\mathrm{2d}$.
The correct answer for both is $\Gamma_{\ce{B-Cl}}=A_1+B_1+E$ and $\Gamma_{\ce{B-B}}=A_1$.
My reducible representations are:

$\Gamma_{\ce{B-Cl}}=4,0,0,0,2$ for the $\ce{B-Cl}$ bond in the order $E, 2S_4, C_2, 2C', 2\sigma_\mathrm{d}$.
$\Gamma_{\ce{B-B}}= 1,0,1,0,1$.

Clearly either of these are not correct but honestly I can't see why! Your help is much appreciated! (I worked them out based on the number of bonds that remain unshifted during the respective symmetry operation. I have also made a little model for myself in Gaussian but it didn't really help.


texts: Why can't a thermosetting plastic be stretched like an elastomer?

texts:
So far I've learnt that there are 2 'types' of thermosets: thermosetting plastics and thermosetting elastomers. Both of them consists of crosslinks that when stretched, allows for the material to spring back into its original shape. So why can't a thermosetting plastic be stretched like an elastomer? Is it something to do  with the degree of crystallinity and elastomers being amorphous?

Sorry if my question is a bit messy, I'm quite new to this topic.


texts: Purity of calcium carbonate in limestone

texts:
$\mathrm{150~mL}$ of $\mathrm{0.1~N}$ $\ce{HCl}$ is required to react with $\mathrm{1~g}$ of a sample of limestone. Calculate percentage purity of calcium carbonate.

Reaction: $$\ce{CaCO3 + 2HCl -> CaCl2 + H2O + CO2}$$

Number of milli equivalence of $\ce{HCl}$ used initially is $\mathrm{15}$

Number of milli moles of $\ce{HCl}$ used initially is $\mathrm{\frac{15}{2}}$

$\mathrm{2}$ moles of $\ce{HCl}$ reacts with $\mathrm{1}$ mole of $\ce{CaCO3}$.

So amount of calcium carbonate is $\mathrm{\frac{15}{4}\times 10^{-3}~mol}=\mathrm{\frac{3}{8}~g}$

But answer given is $\mathrm{75\%}$


texts:
If the following gasses are to mix, what is the partial pressure of neon?

The correct answer is 0.1. I cannot figure out how my professor derived this equation. From the ideal gas law, all I can arrive to is this:

$P_x = \frac{P_tV_t}{V_x}$

This gives me an answer of 4.4, which is obviously incorrect.

I've determined the equation he used is as follows:

$P_x = \frac{P_xV_x}{V_t}$

which gives the correct answer of 0.1. How did he arrive to this answer?


texts: Recently, I read the definition of  oxidation state on Wikipedia. It read that a 100% ionic bond is impossible. So what does a 75% ionic and 25% covalent bond mean at all?


texts: I was reading about the p-block elements and found that the inert pair effect is mentioned everywhere in this topic. However, the book does not explain it very well. So, what is the inert pair effect? Please give a full explanation (and an example would be great!).


texts: Reduction of potassium ion and hydrogen ion

texts:
I am studying a galvanic cell, and the cathode uses potassium hydroxide as its electrolyte. I am getting confused as to what gets reduced when electrons come from the anode.

I believe it would be the hydrogen ions (because the solvent is water) as potassium ion would never want to accept an electron (because it has a configuration of a noble gas as an ion and is therefore very stable). However, the pH of the solution would be very basic because KOH is the electrolyte; thus, the reduction potential value of hydrogen ion should also decrease.

Can someone please tell me what the right answer is?


texts: How can I safely handle a concentrated (fuming) nitric acid spill?

texts:
I will shortly be using $90~\%$ or higher concentration nitric acid in a home environment for the purpose of decapping ICs. I understand the corrosive dangers of nitric acid, and most of the important dangers of its reactivity (e.g. exothermic with water, don't make nitrobenzene, explosive nitrations are bad) and will be performing the decapping in a well-ventilated clean area. I'll also be wearing the best thick acid-resistant gloves I could find, since it seems nothing is really rated for RFNA handling.

My primary concern is handling a spillage. I know a common disposal technique for liquid waste is to feed the $\ce{HNO3}$ very slowly into water to dilute it, then add a base such as sodium bicarbonate to level out the pH, using an indicator mixture to monitor it. However, that's not so easy if the spillage is a few splashes on the workbench — I need a reasonably safe way of wiping it up and disposing of it. Someone told me that acetone wipes are an option for cleanup, but they couldn't remember where they'd read it, so I'm wary of accepting that advice without having it verified.

So, what're my options? How can I clean up a splash of RFNA off a work surface without doing myself (or the environment) any real harm?


texts:
I am trying to figure out the shape of the iodate ion or $\ce{IO3^-}$. No matter how many times I draw it, I keep getting iodine in the centre, and 3 oxygen atoms surrounding it, 2 with single bonds, and 1 with a double bond. This would make it a trigonal planar shape. It would mean that it is not a "bent" shape.

I went to double check on the internet, and I am now confused. On Wikipedia it says it is in fact polar and a pyramidal shape.

Why does iodine have a pair of lone electrons in its shell? Why would it not combine with one of the oxygen atoms to make a double bond?


texts: How does the mass composition affect the empirical formula?

texts:
I have to do an assignment of empirical formula, and how different percentage mass compositions affect the formula obtained, from experimental data.

We did three trials and 2 of which of the same compounds (copper chloride hydrate), has different mass compositions.

I can't find any information about how mass composition affect the empirical formula, although I do understand i need extra proof to explain all the little detail behind it all.

I would really appreciate it if someone could help me thank you so much !!!


texts: Free chemical database to search for physical properties?

texts: I am looking for an Open-access tool that can search "backwards", eg. give me all the structures corresponding to a given heat of formation, critical pressure, etc. It would be even better if the database canbe automatically searched by API or by downloading it. Currently my best go is ChemExper, where I can search for some of the properties, but it is challenging to make it automatic. Is there anything similar in the field?


texts: Very elementary question about valence electrons of ionic compound

texts:
In a university entrance question, I found this question:

  What is the number of valence electrons of $\ce{Mg(OH)2}$? Answer = 24

I know that Mg has 2 valence electrons and O has 6. But I don't know what I must do for a complete ionic compound. If I add them up I get 2+6+6+1+1 = 16, but the answer of this question was 24. Is the answer right? If yes, then how to get it?


texts: I was studying the types of stereo-isomerism E-Z, Cis-Trans and then I come across syn-anti stereo-isomerism this one is giving me a bit of fight in understanding, especially where lone pairs are taken into consideration.How do classify the molecules with lone pairs in consideration as syn and anti Please help me out here!


texts:
I was trying to calculate the resonance energy of benzene by using Argus Lab. These values are weird and very different from the experimental data. I have two questions regarding them.

What is the difference between Final SCF Energy and heat of formation?

When I tried to calculate the energy, It gave me two kinds of energy - Final SCF Energy and Heat of Formation. I know the definition of heat of formation. But what I found weird is that Heat of Formation of $\ce{H2}$ molecule was $\pu{-13.3564 kcal/mol}$. It should be zero instead.
Is there any mistake in following procedure:

a. I calculated the energy of cyclohexane($x$), cyclohexene($y$), and benzene ($z$).
b. Energy change while converting cyclohexane to cyclohexene ($a$) $= y-x$
c. Expected energy for benzene ($b$) $= x+3a$
d. Resonance energy of benzene = $z-b$
(Answer should be negative, implying that resonance energy is stabilizing in nature)

By using the SCF Energy data, I got  resonance energy $\pu{415 Kcal/mol}$ and while using the heat of formation data I got $\pu{-41.8 Kcal/mol}$.

Here is the data (in $\pu{Kcal/mol}$) -:
$$
\begin{array}{|l|c|c|c|} \hline
\text{Energy type} & \mathrm x & \mathrm y & \mathrm z\\
\hline
\text{SCF Energy using PM3} & {-21556.7995} & {-20680.6471} & -18512.6189 \\
\text{Heat Of Formation} & {-37.43} & {-3.0101
} & 23.96 \\ \hline
\end{array}
$$

Is this a reliable software for calculating the resonance energy as there is a difference about $\pu{5 Kcal/mol}$ or I am doing some mistake by overlooking any concept?


texts: Change in Gibbs free energy vs. change in enthalpy

texts:
When learning about other thermodynamic quantities, like $\Delta H$, I was taught that this represents the energy absorbed or released by a system after the reaction has gone 100% to completion. For example, if a reaction has $\Delta H = -100 \text{kJ}$, it means that the final state of the system after the reaction is complete has $100 \text{kJ}$ less energy than it did before the reaction began. As such, $\Delta H$ is a statement about the overall reaction, and is not dependent on where the reaction is at the present moment. (Is this understanding correct? Or does $\Delta H$ change throughout a reaction like $\Delta G$?)

However, when learning about Gibbs Free Energy, I have read that $\Delta G$ changes throughout a reaction, as can be seen from $\Delta G = \Delta G^\circ + RT\ln Q$, because Q varies through the course of a chemical reaction. If $\Delta G$ gives information about a specific point in the reaction, then why is there a "$\Delta$" at all? In other words, $\Delta G$ is the difference between what two values?

Thanks for the help.


texts: What chemical is responsible for the distinictive odor of Scotch tape?

texts:
Scotch Tape has a distinctive odor which is noticeable if you hold a piece close enough to smell. What chemical is responsible for this odor? The wikipedia page doesn't seem to mention composition.

Is the odor due to the the kind of plastic used in the strip of tape itself? Or is it due to the adhesive?


texts: Surface energy for different crystallographic planes

texts:
For a given crystal structure, say body centred cubic, on what factors does surface energy of each plane depend?
A basic approach considers the atomic density on each crystallographic plane, the number of bonds broken if the surface is cleaved along that plane and combines these two.

Is this a realistic and reasonable approach if I want to compare the surface energies of two crystallographic planes, say (100) and (111)? What are the other factors, if any, that should be included in the comparison?

Edit : Background : My problem related to the wettability of a crystal surface by a liquid. The contact angle that the liquid makes with the crystal surface is determined by the interfacial energies between solid-liquid, liquid-vapour and solid-vapour. Keeping all other factors, I only change the nature of the solid crystal surface, by presenting a different crystallographic plane. I would like to theoretically estimate which crystallographic plane would have the highest energy, and which would have the lowest, so that a prediction can be made about the extent of wettability of the surface.

Thank you!


texts: What type of bonding occurs in isolated silicon?

texts:
Would isolated silicon engage in network covalent bonding as quartz does or would it engage in a different kind of bonding? Would germanium display similar qualities?

I am asking what is the bonding of silicon, not why silicon is different from carbon.
I am interested in isolated silicon, not silicon as a "hydrosilicon".

I believe it is network covalent, but I am not sure.


texts: What does "gamma" in gamma-oryzanol mean?

texts:
The structure of gamma-oryzanol is:

What does the "gamma" in its name mean?


texts: Interference of Ca-EDTA with fluoride delivery in mouthwash

texts:
The goal of fluoride mouthwash is to deliver $\ce{F-}$ to the surface of the teeth to turn hydroxyapatite in the dental enamel into fluorapatite.
Typically sodium fluoride or stannous fluoride are used.

ACT fluoride mouthwash also contains $\ce{Ca}$ in the form of $\ce{Ca-EDTA}$.

$\ce{CaF2}$ has a very low solubiliy product of $3.9 × 10^{−11}$, I would expect the $\ce{F-}$ to precipitate as $\ce{CaF2}$ and become unavailable.
This is in agreement with the literature where $\ce{EDTA}$ has been used in the determination of $\ce{F-}$ through backtitration of $\ce{Ca^2+}$. This shows that the complex is less stable than the fluoride.
http://www.sciencedirect.com/science/article/pii/S0003267000876369

Note:

It was suggested in the comments to use 10x the concentration of $\ce{Ca-EDTA}$. I don't see how this could work, all it would do is depress the concentration of available fluoride even more.

I suspect $\ce{EDTA}$ is used as an anti biofilm agent or preservative, and the $\ce{Ca}$ is used so it doesn't chelate dental $\ce{Ca}$. I assume this use is unrelated to the process of fluoride delivery.


texts: If CO2 is nonpolar how come much more dissolves in water than O2?

texts:
Why is it that $\ce{CO2}$ is considerably more soluble in water than $\ce{O2}$ is?

$\ce{CO2}$ is nonpolar but dissolves in water which like $\ce{CO2}$ being nonpolar, doesn't make any sense.

Is it the bond polarity and that the bond polarity is more important in solubility?

If not than why is $\ce{CO2}$ more soluble in water than $\ce{O2}$.


texts: I have a clear liquid with a faint sweet smell. I know this compound contains an aromatic group and an ester. However, something strange happens when I try to distill it - it forms a white solid. I believe this solid to be the result of thermal decomposition of the ester - the ester reacting with oxygen in the air. I have searched around, but can't find much written about thermal decompositions of esters. What reaction is this? What is the product? Could it be a carboxylic acid?


texts: In the addition of HBr to isoprene why does the less stable carbocation form?

texts:
According to me, the answer is B as the tertiary allylic carbocation should be more stable. But the answer given is D and in the given solution, the tertiary allylic carbocation rearranges to primary allylic carbocation to yield Option D.

My question is why does rearrangement from tertiary allylic carbocation to primary allylic carbocation take place?

Source: JEE Advanced 2015 Paper 1 Q31


texts: Balancing a REDOX reaction using the oxidation number method, in acidic solution

texts:
I am trying to balance the REDOX equation shown below, but I got stuck after balancing the major atoms. Where can I go from here? I know I need to balance the H and O atoms, and make sure the charges are balanced.

Second Attempt (Answer Only)

Is this correct?


texts: In this specific case is the proton considered product or catalyst?

texts:
Assuming we have a reaction of

$$\ce{CO2 + H2O ->  HCO3- + \color{red}{H+}}$$

then is the proton (in red) is considered a product or a catalyst?

I read the Wikipedia article titled Product (chemistry), but the issue is still not clear to me. The article gives the following illustration:

In my original example above, I assume that the proton is considered a product since the hydrogen was originally part of the water molecule.

But in this case (see here, at 6:45) the hydrogen proton of the product of the reaction goes to the hemoglobin and kicks off an oxygen molecule.


texts: Respect to other chemicals in reduction/oxidation potentials

texts:
From what I understand, the standard reduction/oxidation potential table is based on the hydrogen half reaction which makes a reduction and oxidation potential of 0 respectfully.

In a research internship I'm in now, we are looking for more efficient batteries, they are basing potential candidates in respect with magnesium.

My problem is seeing how the 'in respect' part works and how it affects the system. Maybe it's just hard for me to relate to it in my mind so maybe a more common analogy would help?


texts: How is Humic substance destroyed in nature?

texts: Humic substance consists of many, to my knowledge poorly understood, species of organic matter, mostly carbohydrates chained in intersting (and also poorly understood) ways. Humic substance is an endproduct of digestion of other organic matter, and is in itself known to be hardly biodegradable. Industrial processes to destroy humic substance or humic acid in wastewater involve UV and strong oxidizers. But how is humic substance destroyed in nature? Given that at least part of the carbon embedded in life ends up as humic substance at one point or other, there must be a natural pathway to destroy it, or several. What is it?


texts: Pubchem: list all compounds for which Kovats retention indices are available

texts:
Pubchem recently started listing Kovats retention indices, e.g. for
alpha ionone:
https://pubchem.ncbi.nlm.nih.gov/compound/5282108

I was wondering though if there is a way to get a list of all Pubchem compound ids which have this info available? Ideally via a PUG REST query, and a JSON or XML export option?

Note:
doing a search

https://www.ncbi.nlm.nih.gov/sites/myncbi/searches/save?db=pccompound&qk=14

https://www.ncbi.nlm.nih.gov/sites/myncbi/searches/save?db=pccompound&qk=12

will get me all records uploaded by NIST and NIST Chemistry Webbook - this will already get me close. But how can I get the list of all these pubchem IDs, ideally using some PUG REST query? (it has to be used programmatically from R)


texts: Le Chatelier's Principle and Rate constants

texts:
Consider the reaction: $$\ce{H2O2(g) <=> 2OH^.(g)}\label{a}\tag{1}$$ to be at at equilibrium ($\ce{OH^.}$ is a radical). As the pressure is increased, the reaction moves towards forming $\ce{H2O2}$ as this direction reduces the amount of substance in the system.

However, it is well-established that the forward rate constant of $\ref{a}$ increases with increase in pressure, meaning forming more $\ce{OH}$. This seems to be in conflict to what the Le Chatelier's principle suggests. Could someone help me get my head around this?


texts: How to calculate the pH of a sodium bicarbonate-sodium hydroxide buffer solution?

texts:
This website claims that if you add $\pu{50 mL}$ of $\pu{0.05 M}$ sodium bicarbonate, and $\pu{5 mL}$ of $\pu{0.1 M}$ sodium hydroxide (and dilute to $\pu{100 mL}$), you should create a solution with $\mathrm{pH }= 9.6$.

I'm struggling a bit getting this result.

My attempt:

The sodium bicarbonate reaction would be:

$$\ce{NaHCO3 + H2O -> H2CO3 + OH- + Na+}$$

We know the $\mathrm{p}K_\mathrm a$ of $\ce{H2CO3}$ is 6.4, so the $\mathrm{p}K_\mathrm{b}$ of $\ce{HCO3-}$ is:

$$14 - 6.4 = 7.6$$

Furthermore, $\ce{pOH} = \mathrm{p}K_\mathrm b + \log\frac{[\ce{B+}]}{[\ce{BOH}]} = 7.6 + \log\frac{[\ce{H2CO3}]}{[\ce{HCO3-}]}$

However, how do we find $[\ce{H2CO3}]$ ?

I'm not entirely sure this is the right approach, but none of the other resources I've used to determine this have helped.


texts: What is the difference between statistical mechanics and quantum mechanics in terms of accuracy?

texts: It is my impression that everything relevant to 'quantum' is the truth and others is just a simplification. Is this the case in those two kinds of mechanics?


texts: How to explain Born repulsion between ions in gas phase?

texts:
In simple terms, the collision of two atoms $\ce{A}$ and $\ce{B}$ will result in ions $\ce{A^+}$ and $\ce{B^-}$ if $$I_a(\ce{A})+E_a(\ce{A})<I_a(\ce{B})+E_a(\ce{B})$$ where $I_a$ and $E_a$ are the ionisation energies and electron affinities, respectively. Let us view $\ce{A^+B^-}$ as a molecule of sorts, having ions of rigid, non-polarisable spheres. Say $r$ is the sum of the radii of such spheres. The potential energy $E_p$ of such a system would then be $$E_p=I_a(\ce{A})-E_a(\ce{B})-\frac{e^2}{r}+\frac{b}{r^n}.$$

It is intuitive that

the term $I_a(\ce{A})-E_a(\ce{B})$ characterises the energy required to form isolated ions $\ce{A^+}$ and $\ce{B^-}$ in the gas phase;
$-e^2/r$ takes into account culonic attraction between two ions.

It is not intuitive for me why ${b}/{r^n}$ is  how it is.

  The final term, introduced by Max Born, encompasses the repulsion generated by shells of electrons at either ion.

Of course, such effects cannot be ignored. But I am interested in why is it $b/r^n$. What is the justification? Feel free to provide the rigorous approach, even though it will probably$^{[1]}$ be above my abilities of comprehension.

Browsing on Wikipedia, the information might be given in the book Advanced Inorganic Chemistry by F. Albert Cotton, Geoffrey Wilkinson, Carlos A. Murillo, and Manfred Bochmann.

The pertinent section “1-6. Energetics of Ionic Crystals” starts at page 18$^{[2]}$, however I cannot find the derivation. There is only that the value of $n$ relies on a compressibility measurement, given as fractional change in volume per unit change in pressure, or

$$\frac{\Delta V}{V\Delta P}.$$

Also, this is seems somewhat contradictory to the earlier assumption of rigid spheres as written in another book$^{[3]}$. So, if anything, the linked book confused me further.

$^{[1]}$ Most certainly.

$^{[2]}$ Page 28 in the PDF.

$^{[3]}$ U. Palm, V. Past. Physical Chemistry. (1974) [To my knowledge, not available in English.]


texts: Work done in irreversible isothermal expansion against vacuum

texts: Why is the work done in an irreversible isothermal expansion against vacuum equal to zero?


texts: How can dish-soap make glass less misty?

texts:
Warm glass that face a cold temperature becomes misty - but becomes less misty if sprayed with dish-soap. Moreover, dish-soap sprayed on glass makes the glass less misty, if it face a drastic change in temperature - at least makes it harder for the glass to become misty.

Why is it so?


texts: Clausius–Clapeyron equation: shape of phase diagrams makes no sense

texts:
I am trying to model the melting point of a substance at varying pressures (ranging from very small to very very large). All I am trying to do is make an equation that relates melting temperature to pressure, so $T(P)$ is some function. To do this, I am trying to use the Clausius–Clapeyron equation (CC), which states that

$$\frac{\mathrm dP}{\mathrm dT} = \frac{L}{TΔV}.$$

In other words, the slope of the equilibrium line on the phase diagram should decrease as temperature is increased.

However, this is not the case; the curve of the equilibrium line is exponential and the slope $\mathrm dP/\mathrm dT$ increases as $T$ increases. Integrating CC we arrive at a logarithmic function, which again is not what empirical measurements reflect.

As I see it, the empirical results and the equation that is supposed to describe them are mutually exclusive. There is no way to arrive at an exponential curve from a slope that varies with $1/x.$ The CC equation and phase diagrams cannot be both be true at once and it is driving me mad.

Why is this the case? Is the CC equation valid at all because it seems to be totally false? What function do I use to model melting points at different temperatures?

The results that are so stupefying are these:

The shape of the curve is exponential. But, the supposed derivative is $1/T$, in which case the slope of each curve (red and blue here) should flatten as $T$ increases, but it steepens. Also, integrating that supposed derivative gives us $\ln (T)$ which is definitely not the shape of the phase diagram. This discrepancy is true for both the liquid/solid and liquid/gas curves.
I hope this clarifies the question!


texts: Reuse 20 litre plastic drums for drinking water?

texts: Would you consider it safe to clean and reuse a 20 litre plastic drum that contained 36% Hydrochloric Acid for drinking water? If so how would you recommend cleaning it?


texts: Is organic carbon the same thing as organic compounds?

texts:
Are they the same thing or is there some minute difference? I have looked all over the web and you would think this would be a common question but I can't find any answer. If they are different then what is the difference?

Thanks


texts: Mechanism of action for Citric Acid as a cleaning agent for limescale?

texts:
This may be a silly question, but I am not that certain I understand this process because of the low solubility of Calcium Citrate.

How does citric acid actually clean limescale? How much limescale can be cleaned (dissolved in water) in a container with 1 liter of water and limescale under room temperature?

Thanks!


texts:
Balance the following equation using oxidation number method:
  $\ce{PbS + H2O2 -> PbSO4 + H2O}$

Attempt:

I have written down the oxidation states of all atoms and we can observe reduction of peroxide and oxidation of sulphur.

$\ce{Pb^{II}S^{II-} + H^{I}_2O^{-I}2 ->Pb^{II}S^{VI}O^{-II}_4 + H^{I}2O^{-II}  }$

The specific problem I am facing with this question is that oxygen is going from $-1$ to $-2$ in both the reaction products. How do I handle that?


texts:
In chemistry, it is agreed in general that the octet is extremely stable, through experiments except in some cases. But is there any specific theoretical reasoning for that?

According to me, if:

The $\ce{s}$ and $\ce{p}$ orbitals are full, they should repel in every orbital, causing destabilization.
There is no exchange of energy in fully-filled orbitals as it occurs in half filled orbitals.

So, shouldn't these two reasons make an octet filled atom unstable? Then, why is the octet stable and how does it counter the above arguments?


texts: What is the physical interpretation of "internal pressure"?

texts:
$$ \require{begingroup}
\begingroup
\newcommand{\md}[0]{\mathrm{d}} \md U = \pi_T\,\md V + C_V \,\md T$$
  where  $\pi_T$ is the internal pressure and is given by $\displaystyle {\left(\partial U \over \partial V\right)_T}$.

What does the internal pressure actually physically mean? I can see it is the slope of the $U$-$V$ graph at constant temperature but that does not clear things up.
Also why is this quantity called the internal pressure and not something else? $\endgroup$


texts: Is a weak deactivator considered a stronger activator than a strong deactivator for the purposes of directing effects

texts: A nitro group is a strong deactivator whereas a halogen is a weak deactivator. The directing effects of these groups oppose each other: Nitro is meta directing whereas halogens are ortho/para directing. It is said that the strongest activator determines the directing effects in a disubstituted benzene ring. In a ring with no activators, such as one containing a halogen and a nitro group, is the weakest deactivator considered the "strongest activator", so that in the example I have just given the halogen would control the directing effects and said ring would be ortho/para directed?


texts: On the assignment of axial and equatorial to substiuents of polyhexacyclics

texts:
Must the assignment of axial and equatorial substituents of polyhexacyclics always be with respect to each six-membered ring or is there a shorthand?

For example, how would X, Y, and Z be assigned axial/equatorial in the following substituted adamantane?


texts: If a reactant appears on both sides of an elementary equation, can it be cancelled?

texts:
Me and a friend were debating the following. For the elementary reaction

$$\ce{A + B -> A + C}$$

my friend says that it is unimolecular because $\ce{A}$ does not "participate" in the reaction. So, he says that the rate law is

$$\text{rate} = k[\ce{B}].$$

But, I think that that since it is an elementary reaction step, you cannot cancel $\ce{A}$ from both sides. I think that it is a bimolecular reaction with

$$\text{rate} = k[\ce{A}][\ce{B}].$$

Who is correct?


texts:
In one of my chem classes I had to do a lab that involved finding the mass and volume of a substance.  I did three trials and for my mass I got 9.3g, 9.3g, and 9.4 g.  For my volume, I got 9.7ml, 9.9ml, and 9.9 ml.

I am being asked to find the inherent instrument error calculation.

For volume, I used a graduate cylinder which has 1 % vol/reading as an inherent error.

For mass I used a one place electronic balance which has error of 0.1g/reading

How would I find the error in mass and the percent error in mass?


texts: So basically I have a graph of Absorbance on y-axis against Time on x-axis and it is a negative curve. So this will give me a negative slope gradient. My question is how to reason the negative gradient. Do I write down the rate of concentration as a negative value and just reason it by saying that by being negative it means that the concentration is decreasing?


texts: I am new to nano-sized particles and conducting a very simple experiment using nano particles. In my experiment I have nanomagnetic particles inside water and they are moving due to applied magnetic field. I am looking for a method to track or detect the motion of nano particles. Is there any easy way?


texts: How to determine Langmuir adsorption isotherm constants and use the models

texts:
I am doing some adsorption tests on bio materials and would like to test the data with Langmuir and Freundlich adsorption isotherm models. Assume these values:

adsorbent(g).   initial con (µg/L)  final con.(µg/L)
0.1                   1                0.65
0.1                   5                2.1

(Sample volume is 20ml. In both cases the dose of adsorbent was the same (0.1g) and in the first initial concentration is 1ppb and, after adsorption, is 0.65ppb.  In the second initial concentration is 5ppb and, after adsorption, is 2.1ppb.)

Using these data how can I use Langmuir and Freundlich isotherms models to get the constants and check whether my adsorption data fit the model or not.  (If any other parameter is needed you can assume some reasonable value.)


texts: Finding the thermodynamics of protein unfolding from temperature and absorbance using fluorescence spectroscopy?

texts:
I recently did an experiment on protein unfolding using a Perkin Elmer fluorescence spectrometer. The protein was $\alpha$-chymotrypsin. I was given this paper for my procedure. I am now trying to make sense of the data.

Increasing temperature was used as the denaturant. Temperature and absorbance were plotted, resulting in an essentially sigmoidal curve describing unfolding. The paper gives the following equation for determining an equilibrium constant for the experiment.
$$K_u=\frac {X_N-X}{X-X_D}=\frac {[P_D]_{eq}}{[P_N]_{eq}}$$ Where $K_u$ is the equilibrium constant, $X_N$ is the absorbance for the native state, $X_D$ is the absorbance for the denatured state, and $X$ is any given absorbance. $P_D$ is the denatured protein and $P_N$ is the native protein.

The paper says that the free energy of unfolding can be described by the familiar equation: $$\Delta G = -RT\ln(K_u)$$
I'm fairly sure that I've calculated $K_u$ at each temperature recorded, but I'm not quite sure whether I use each $K_u$ as a point for another plot, or average them, or something else. If I use a Van't Hoff plot to graph each point of $\ln(K_u)$ vs. $\frac {1}{T}$, will the slope and intercept be $\frac{-\Delta H}{R}$ and $\frac{\Delta S}{R}$ respectively? I think so due to the rearrangement described here, and perhaps I've answered my own question as I attempted to ask it. Nevertheless, I would appreciate having my understanding of this calculation confirmed.

Update:
I've plotted $\ln(K_u)$ vs. $\frac {1}{T}$ and the slope of $\ln(K_u)$  vs. $\frac{1}{T}$ is not linear as had been expected. Linear regression analysis gives a trendline with an $R^2$ value of 0.87. Should I separate the data so as to graph $\ln(K_u)$ vs. $\frac {1}{T}$ for points leading up to the sudden unfolding and also for points once unfolding becomes dramatic? This would give me two values for the enthalpy of unfolding--one before it unfolds much and the other for when unfolding is happening quickly. If I do so, will the difference between those enthalpies be the overall enthalpy of unfolding? I'm not sure what the significance of those two values would be.


texts: How to rationalise with MO theory that CO is a two-electron donor through carbon?

texts:
A question I am looking at is as follows:

  $\ce{CO}$ is isoelectronic with $\ce{N2}$. Sketch MO diagrams for $\ce{CO}$ and $\ce{N2}$. Point out key differences between the diagrams and use the diagram to explain why $\ce{CO}$ acts as a two-electron donor through carbon rather than through oxygen.

Understandably, the key difference between these molecules is that $\ce{CO}$ is heteronuclear, and thus will have differences in energy between the molecular orbital and the atoms.

But I can't explain why $\ce{CO}$ is a two-electron donor using MO theory, even though I can with Lewis?

Does anyone have any thoughts?

In the above MO diagram, the 5σ is the HOMO. But it is closest in energy to oxygen's 2p orbitals, so why is it centered on carbon?


texts: Does the free energy of the universe decrease for every process?

texts:
The second law of thermodynamics states that $dS_{universe}>0$ for all processes.

In addition to the second law, gibbs free energy is used to consider the feasibility of a reaction. $dG=dH_{syst}-T*dS_{syst}$. If $dG_{syst}<0$, this means that the reaction is spontaneous, but a reaction with $dG_{syst}$ can also occur if energy is input into the system (for example electrolysis).

Therefore, $dS_{univ}>0$ does not imply $dG_{syst}<0$.

However, is there such a quantity as $dG_{univ}$, and if so is the relationship $dG_{univ}<=>dS_{univ}$ true?


texts: Is there any way to carry out voltammetry without a potentiostat?

texts:
I'm trying to do a voltammetry experiment, but my high school doesn't want to have to buy a potentiostat (understandably, I know they are very expensive). Is there any way to carry out a voltammetry experiment, either linear sweep or cyclic, without a potentiostat? Or am I doomed to have to go back to the drawing board...

I should mention that the physics lab has some equipment like variable power sources, but not much--my school kind of under-appreciates science--and I was planning on creating a cruddy makeshift three-electrode cell.


texts: Rate constant units for gravimetric measurements

texts:
For gravimetric measurements, why is the reaction rate constant $k$ represented change in mass per time?

  Evaporation Rate and Activation Energy

  Evaporation changed the slag chemical composition and as a result affected the evaporation rate in the process of measurements. To mitigate this effect, the evaporation rates were analyzed in the first 10 minutes of the TGA measurements. Evaporation rate $k$, $\pu{s^{-1}}$, was calculated as:

  $$
\begin{align}
k &= - \frac{\Delta m_i / m_0}{t_i} \\
\Delta m_i &= m_i - m_0
\end{align}
$$

  where $\Delta m_i / m_0$ is the flux mass change, and $m_i$, $\pu{g}$, is the flux mass at time $t_i$, $\pu{s}$.


texts: What is the E/Z configuration of cyclic compounds?

texts:
What are the configurations of 1-bromo-3-methylcyclopent-1-ene and 1-nitro-2-(propan-2-yl)benzene? Are they E or Z? Are they cis or trans?

What are the rules for these types of isomerism?


texts:
Question

Attempt

I thought that the bromine atom farther from the ring would be substituted because of less hindrance, but the book says opposite, why?


texts: Is there a household method to decolorize potentially contaminated water?

texts:
I am living in my dorms at the moment and apparently it is an accepted thing that the water in the building is brown and yellow. According to my RA, this is a characteristic of the town I live in.

The only "clean" water we get is a water filter at the zeroth floor of our building where transparent water comes out.

Other than that the water that comes out of the tap, the kitchen, the shower, and the toilet bowl is light yellowish-brown water. I haven't done enough research as the cause of this problem.

Boiling water doesn't seem to change the colour either (is this even possible?). I for one cannot live like this, so I am asking the community here if they know a household method to remove the discoloration from the water.


texts: Something denser than lead but with lead like properties?

texts: I read that tungsten is 1.8 times more dense than lead. What other elements are denser than lead but safe to handle.  I want something that will fit under the keys of my computer keyboard so my pinky doesn't have to press so hard on the key.


texts:
I know when electrolysis on a concentration aqeuous solution which contains halide ions($Cl^-$ , $Br^-$ , $I^-$). The halide ions is discharged although $OH^-$ is more easily to discharged.

For example, electrolysis of concentration aqueous sodium chloride. The cation $Cl^-$ and $OH^-$ will attract to the anode. The $Cl^-$ ions will be discharged although according to the electrochemical series that the $OH^-$ will be more easily discharged.

Why do that happen?


texts: What are good representatives for the concepts of endergonic and exergonic?

texts:
We must demonstrate two reactions: endergonic and exergonic. I'm wondering if thefollowing reactions are accurate.

Exergonic: I have sodium bicarbonate and vinegar. Would it be catabolic, spontaneous, and $-\Delta G$ as well?
Sodium bicarbonate and vinegar is your basic science-fair volcano reaction. You have the baking soda in a container of some sort and pour the vinegar. The formula would be something like
$$\ce{Bicarbonate of soda + vinegar -> Carbonic acid + Water + Carbon dioxide gas}.$$

Endergonic: I have ammonium chloride and water. Would it be anabolic, nonspontaneous, and $+\Delta G$?
Ammonium chloride would be dissolved into the water. The formula would be something like
$$\ce{NH4Cl + water -> NH4+ + Cl-}$$

I've just barely touched on the $G$ value thing. I don't exactly know what's going on there. What I mean I guess is that if it's $+\Delta G$, the enthalpy increases, and if it's $-\Delta G$, the enthalpy decreases. To be more precise, we're on the Gibbs free energy lesson at the moment.
Endergonic means energy is absorbed during the reaction. Exergonic means that energy is released during the reaction. Is energy released or absorbed during a vinegar and baking soda reaction? Is energy released or absorbed when dissolving ammonium chloride and water?


texts: As methanol is both a lewis acid and a lewis base, the lewis base part suggests that it can act as a ligand as many bases are. So, is methanol a ligand? And what is the reason behind it?


texts:
I came across a protocol saying:

  Homogenize 50 g powdered plant material (accurately weighed and recorded) in 2
  vol (w/v) acidified methanol.

What does 2 vol (w/v) mean?


texts: What is a food-safe level of exposure of plastic containers to heat?

texts:
There are many articles about how heat can trigger the release of potentially harmful carcinogens from plastic containers into the food or liquid they contain.  Specifics they fail to mention, though, are 1) the safe level of exposure and 2) the rate of BPA release per measurement of time at a constant level of heat.  While I will never drink from a water bottle that has been in my car exposed to summer heat over the course of days or weeks, I have been known to forget my water in my car as I head into work where I'll only end up retrieving it hours later when I go to lunch.  I also store bottled water in my garage which may reach temps of 90 degrees Fahrenheit or slightly higher in the summer.

So I am basically inquiring not only about the safe level of exposure to chemicals by quantity, but also the rate of chemical release over time based on heat level.  This would allow me to produce a practical ballpark idea as to whether or not the water is safe to drink.


texts: Conductivity as a function of acid concentration

texts:
I have conducted an experiment measuring the conductivity of both hydrochloric acid and sulfuric acid in solution respectively, with varying concentration. Wikipedia as well as a question on the site suggests a $\sqrt{c}$ relationship is viable. However, my data resembles this:

Clearly not a simple $\sqrt{c}$. It reminds me of the inverse gamma distribution. I have tried looking at papers by Onsager on his conductivity theory, but they're unclear, and he doesn't propose a function. Are there any papers that look at accurately modelling conductivity as a function of concentration which exhibit this form? Obviously for low concentrations (e.g. 1-2 molar), a linear or $\sqrt{c}$ would suffice.


texts:
In the above reaction, I do know that $\ce{SnCl2/HCl}$ reduces $\ce{-NO2}$ group to $\ce{-NH2}$ but which one of the two $\ce{-NO2}$ will be reduced first by $\ce{SnCl2/HCl}$? Why so?

And how does $\ce{NH4HS}$ react and again which one of the two $\ce{-NO2}$ will be reduced first by $\ce{NH4HS}$ and why so?

NOTE: 1eq represents 1 equivalent.


texts: Transparency and partially deuterated polymers

texts:
I've been skimming over the literature and have come into some conflicting information about the optical properties of partially deuterated polymers.  From what I've seen, in general deuterated polymers have less attenuation of visible and IR than their non-deuterated equivalents.  But I've seen some papers remarking that partially deuterated polymers also have improved optical properties while others reporting that partial deuteration increases opacity versus non-deuterated equivalents.

Is there some sort of general rule, or does it depend on the polymer in question?  The underlying mechanisms governing transparency in polymers, beyond the basics such as crystallinity, are something I haven't studied in depth.


texts: Should the tip of the burette of an automatic titrator be immersed in the analyte?

texts:
In all the tutorials I found online, the tip of the burette (containing the titrant - NaOH) was immersed into the analyte solution. My question is: shouldn't the tip be out of the solution? Isn't there a possibility for the analyte to crawl up the tip and react with the NaOH inside the burette that hasn't been dispensed yet?.

Everyone does that... Even in the official tutorials of the company


texts: how to calculate mols Ag from AgNO3 solution

texts:
Sorry for the very basic question but its been a very long time since I've taken chemistry and I'm having difficulty solving this problem.

If I titrate something with 1 molar AgNO3, adding 50 ml of AgNO3 solution... How would I calculate how many mols of Ag that equates to?

What I have so far is that 1 M means that there is 0.05 mol of AgNO3 in that 50 ml sample (M = mols/L). So then how many mols of Ag are there in 0.05 mol of AgNO3? Is there just 0.05 mols of Ag in AGNO3 or do I need to somehow take into consideration the proportion of the rest of the elements?

Thank you!!!


texts:
Hydride ion, as I know is a pretty powerful base, much stronger than hydroxide ion and cannot exist in an aqueous phase.

Can it act as a ligand in coordination compounds? Hydride ion has its electronic configuration as $\mathrm{1s^2}$ in a symmetrical s orbital so the tendency to donate a lone pair into a metal atom would be less. But can its high nucleophilicity allow it to bind to the metal atom despite the symmetry of its orbital?


texts: Forms of carbon in incomplete combustion

texts:
When hydrocarbons burn with little oxygen, carbon is produced. What form do these particulates of carbon come in?

Is it a simple molecule like $\ce{S8}$, or a small fragment of a larger structure, like graphite?

Why is this form more stable than others?


texts: Are there any free pharmacophore modelling software?

texts: I would like to know if there is any free and relatively updated software to getting started in pharmacophore modelling.


texts: The production of what substances has a similar environmental impact to Chlorinated paraffins?

texts:
I am currently conducting a Life Cycle Assessment (LCA) study in which the final product consists to a large part of Chlorinated paraffins. However, I cannot find Chlorinated paraffins as a process in available LCA background data.

Therefore, I am asking what other substances are likely to have a similar environmental impact during the production compared to Chlorinated paraffins (and are maybe even more commonly used so that the likelihood to find them as an existing LCA data set is high)?


texts: What is the difference between distilled water and rainwater?

texts:
I am studying different means of collecting water for consumption. From resources available on Internet, I understand that distilled water is not advised for regular consumption because of the lack of minerals and salts, while rainwater can be consumed if not overloaded with unwanted chemicals.

What confuses me is that I know water to be pouring down from clouds, which is water vapor turning into droplets through condensation. To me, this looks to be exactly the same as the process of distillation, i.e. evaporation and condensation of water.

So is my assumption about rainwater formation wrong? What is the difference between rainwater and distilled water? What causes this difference to happen?


texts: Is there a database which give reaction constant?

texts:
For instance, I have a chemical reaction like :
$$\ce{Fe^{2+} + $0.5$O2 + H^{+} ->Fe^{3+} + $0.5$ H2O}$$

And I would like to use Action-Mass law, but I need to have equilibrium constant for this reaction. And this for many other reaction.
That's why I'm wondering if there exist a nice database with this information ?


texts:
I want to find a lower limit of the Michaelis constant for some evaluations of Michaelis-Menten enzyme kinetics.
What is the lowest $K_m$ you ever encountered? Is there a theoretical limit?


texts:
What is the theoretical quantum ground state energy of helium hydride positive ion?

I am speaking of the usual assumptions such as the approximate modeling of the two nuclei here - one being a proton, the other being 2 protons plus 2 neutrons - as two infinitely massive particles alone in the universe at some equilibrium distance, in the non-relativistic simple case alone considering no spin dependent terms etc.

So actually only the charge of the nuclei is relevant in this approximation unless the vibrational energy - perhaps modeled in first approximation as a simple harmonic oscillator with some force constant - is also taken into account - which would be the positive 'zero' point value of harmonic oscillator.

I would assume that it would have to be lower (that is greater bonding magnitude or absolute value of the negative energy) than that of the neutral helium atom, but I am not sure. But one place on internet gives $\pu{3600 cm^-1}$ as a fundamental frequency (but of what?) which - if I am not mistaken comes - to $\pu{1.64E-2}$ Hartrees or atomic units - so that cannot be correct or the value i am looking for as the helium atom is about -2.904 Hartrees or atomic units. I suppose it would be almost impossible to practically devise any experiment to arrive at any experimental value? Though, if so, what is that value?


texts:
Interaction between atom or molecule is neglected
The transformation to liquid or solid is observed under appropriate condition
The volume of constituent atom or molecule is neglected
The compressibility, PV/RT is independent of pressure

Why is 2 wrong? In formula there is P,V,T which means under certain condition?

Why is 3 true? Then what volume of gas do we calculate if it is not from atom or molecules?

Why are 1 and 4 true? Do atoms in gas interact? Why is the compressibility independent of pressure?


texts: "HBr is donating a proton to LiOH": Why doesn't it produce LiOH2?

texts:
In the section Brønsted-Lowry acid and base theory from Khan Academy:

In the reaction $\ce{LiOH(aq) + HBr(aq) -> H2O(l) + LiBr(aq)}$, $\ce{HBr}$ is donating a proton to $\ce{LiOH}$, thus acting as a Brønsted-Lowry acid. Since $\ce{LiOH}$ accepts the proton, it is acting as a Brønsted-Lowry base.
Image source: https://i.stack.imgur.com/fjV8R.png

I don't understand how $\ce{HBr}$ is donating a proton to $\ce{LiOH}$, because I think it would produce something like "$\ce{LiOH2}$", but the reaction gives $\ce{LiBr}$.
So where is my misunderstanding?


texts: Are d electrons ever delocalized in metallic bonding

texts:
It has been my understanding that delocalized electrons that participate in metallic bonds come from the highest primary energy level, specifically from the s and p sublevels and that electrons in d orbitals (from one level lower) do not delocalize.

Palladium however, has its $5d^{10}$ electrons IN its highest energy level because it has no 6s electrons, and yet Palladium clearly has electron delocalization.  So do d sublevel electrons delocalize in general?  In any metal elements? (such as in Palladium).


texts: Separation of Methanol-water in a plate distillation column

texts:
I conducted an experiment to separate methanol and water. I am trying to determine the mole fraction of the distillate collected but having a little trouble with the calculation.

So i had a flow rate of 55ml/min. When i collected my sample i got a specific density of 0.815 and  a volume of 334ml. I tried to work out the mass but i cant seem to use specific density as its a ratio so has no units.

Would i just assume the specific density is the density and set units to g/cm3 so i can get the mass of the distillate , the concentration and then determine the mole fraction from there or does that not make sense
?


texts: Is there anything that can react with molecular gaseous nitrogen?

texts: I am looking for something to react with nitrogen in the air. Is there any substance that can react fast with molecular nitrogen at room temperature?


texts: What is the difference between λ and Λ with regard to molar conductivity?

texts:
I came across these equations (boxed in red) in a book:

  $$
\begin{align}
&\therefore & t_\mathrm{c} &= \frac{u_\mathrm{c}}{u_\mathrm{c} + u_\mathrm{a}}\\
&\text{and} & t_\mathrm{a} &= \frac{u_\mathrm{a}}{u_\mathrm{c} + u_\mathrm{a}}
\end{align}
$$
  At infinite dilution,
  $$\text{Also,} \quad t_\mathrm{c}^\infty = \frac{u_\mathrm{c}^\infty}{u_\mathrm{c}^\infty + u_\mathrm{a}^\infty}$$
  Since, $\lambda_\mathrm{c}^\infty = u_\mathrm{c}^\infty\times F$ and $\lambda_\mathrm{a}^\infty = u_\mathrm{a}^\infty\times F$
  $$
\bbox[3px,border:1px solid red]{
\begin{align}
&\therefore & t_\mathrm{c}^\infty \times \Lambda_\mathrm{elecrolyte}^\infty &= \lambda_\mathrm{c}^\infty\\
&\text{and} & t_\mathrm{a}^\infty \times \Lambda_\mathrm{elecrolyte}^\infty &= \lambda_\mathrm{a}^\infty
\end{align}
}
$$

Where $t$ refers to the transport number of an ion, and the subscripts $\mathrm{a}$ and $\mathrm{c}$ refer to an anion and cation, respectively.

From what I've learnt, the uppercase lambda $\Lambda$ refers to molar conductivity. But then what does the lowercase lambda $\lambda$ stand for?

Different sections within the same book give different definitions for $\lambda$, one being 'ionic conductance' and another being 'ionic conductivity', and I'm pretty sure 'conductance' and 'conductivity' are not the same thing.

I did try looking it up online, but Wikipedia wasn't much help.


texts: Is elastomeric better with more polymer, or with added calcium carbonate?

texts: While comparing elastomeric roof coatings, I notice that one brand is 60% polymer, while the the other is 40% polymer along with 30% calcium carbonate.  Polymer is flexible.  Calcium carbonate is brittle.  With that consideration it would seem more polymer is better, since weather conditions challenge the membrane integrity for water resistance.  However, polymer degrades far more than calcium carbonate.  Perhaps inclusion of calcium carbonate provides some protection against degradation.  So is it better to have more polymer, or some of that replaced with calcium?  (Since polymer is more expensive than calcium carbonate, my instinct suggests there would be no reason to maximize polymer at its higher cost, if it did not improve performance.)


texts: Help to understand the fundamental equation of thermodynamics

texts:
The fundamental equation of thermodynamics states that $\mathrm dG = V\,\mathrm dp-S\,\mathrm dT$. I am having difficulty understanding this equation. The Wikipedia page for Gibbs free energy says:

… is a thermodynamic potential that can be used to calculate the maximum of reversible work that may be performed by a thermodynamic system at a constant temperature and pressure (isothermal, isobaric).

Isn't this in direct contradiction to the fundamental equation of thermodynamics? If you have constant pressure and constant temperature, then $\mathrm dp$ and $\mathrm dT $ are both equal to $0$, so $\mathrm dG = 0$?
What am I not understanding?


texts: Why does an increase in alkyl group substitution cause downfield shift H'NMR?

texts: Since alkyl groups are electron donating, wouldn't an increase in alkyl group subsitution mean the protons would feel a lower magnetic field? Because they feel a lower magnetic field, wouldn't this cause an upfield shift? Is it just that alkyl groups are less electron donating than a hydrogen bound to the carbon?


texts: Dependency of Standard Gibbs free energy (using electrode potential) on stoichiometric moles of electron exchanged

texts:
I have a question regarding the definition of the number of moles $n$ when using the equation-
$$\Delta G=-nF\Delta E$$
I understand that $n$ is the number of moles transferred in the overall redox reaction, however, it seems to depend on how you write the equation.
If I write an equation as-
$$\ce{Ag+ + e- -> Ag}$$ $$\ce{\frac{1}{2} Cl2 + e- -> Cl-}$$
Then, we have $n$=1.
But if I wanted one mole of chlorine and I write:
$$\ce{Cl2 + 2e- -> 2Cl-}$$
then I get $n$=2.
Which one is preferred and why?


texts:
Enantiomeric excess is defined as

$$ee = \frac{[R]-[S]}{[R]+[S]}$$

I found this problem in an IChO paper:

"When using the enantiomerically pure (BINOL)Al(OiPr) as a catalyst for reduction of αbromoacetophenone, the ee of the product equals 81%. What is the ee of the product if the catalyst ee equals 50%?"

The problem as stated is not that difficult: if given the ee of the product mixture ($ee_{p1}$) when the catalyst is enantiomerically pure ($ee_{c1}=1$) then (after noting that mole fraction of [R] and [S] are simply $f_R=\frac{1}{2}(1+ee)$ and $f_S=\frac{1}{2}(1-ee)$ respectively) we say that $f_{Rp2} = f_{Rc2}f_{Rp1} + f_{Sc2}f_{Sp1}$ from which we can calculate $ee_{p2}$, which after a little algebra reduces to $ee_{p2} = ee_{c2} ee_{p1}$. In the above case, then, we'd get $ee_{p2} = 0.5*0.81$.

It's quickly possible based on this formula ($ee_{p2} = ee_{c2} ee_{p1}$) to show that, if given one value $ee_{p1}$ for the product mixture's enantiomeric excess when the catalyst is of a certain enantiomeric excess $ee_{c1}$, we can calculate the product's predicted enantiomeric excess $ee_{p2}$ for any other catalyst enantiomeric excess we try $ee_{c2}$ through the equation

$$ee_{p2} = ee_{p1} \frac{ee_{c2}}{ee_{c1}}$$

What I am wondering is, is there a way to derive this latter formula from the beginning without going through the step of first considering an enantiomerically pure catalyst case? I would not have thought of that case had the contest writers not specifically mentioned it. But not being able to derive the formula from first principles makes me feel I don't really understand the way the various mole fractions would contribute etc.


texts: References for learning about acid and bases in organic chemistry

texts:
I was wondering if someone could help me find references available that will help me solve the following problems. These are not homework problems, but are suggested problems that were given to me by my instructor.

I'm specifically interested in learning how to solve question A. (b). How can I know whether a reaction will occur between the two products and further, how can I predict what the product will be if a reaction does occur (what atoms bond together, and how can I know which atoms bond together in any organic reaction)?


texts: What decides -1/2 and +1/2 spin values of subatomic particles?

texts: This question is in context of nmr. I know that prior to application of magnetic field and RF energy, protons are found in -1/2 and 1/2 spin values. What decides whethere a particular proton has positive or negative values. I know these values are not intrinsic to a proton since applying energy can cause them to change their spins so what decides whether proton has one value over other in first place.


texts: How does the steric effect affects the electronic density of the central atom?

texts: For example, if you have Nitrogen attached to some methyl groups, and other attached to some ethyl groups. Why the electron releasing effect on the ethyl will be lower than for the methyl?


texts: How many valence electrons does a copper atom have?

texts: The valence electron configuration of $\ce{Cu}$ is $\ce{4s^1 3d^{10}}$. According to this the answer is $11$, but shouldn't it be $1$ since the d shell is already filled up?


texts:
$$\ce{Cu^2+ + Ni -> Cu + Ni^2+}$$

The standard potential of this redox reaction is 0.57 volts (which was obtained by 0.23 + 0.34)

$$E = E_0 - \frac{RT}{nF}\ln Q$$

I used 0.1 M nickel sulphate and 0.5 M copper sulphate in my galvanic cell.

$$E_{25} = 0.57 - \frac{8.31 \cdot 298}{2 \cdot 96485}\ln(0.2)=0.59065\ldots$$

$$E_{45} = 0.57 - \frac{8.31 \cdot 318}{2 \cdot 96485}\ln(0.2)=0.59204\ldots$$

Shouldn't the two be inversely proportional? Is the effect of temperature really this minuscule?


texts: Recently the sugar glycoaldehyde was detected in a star system 400 light years from Earth. How exactly are molecules detected in space? I am aware that spectroscopy is used to detect them, but I don't know the details.


texts:
I am building a greywater harvesting system. It is a 3-stage system:

The 1st stage breaks down soap and detergents.
The 2nd stage filters the water.
The 3rd stage pumps water out of system.

What is the best way to break down soap and detergents in a timely manner with as few mechanical parts as possible?


texts:
This question was in my book. According to me CO should be polar as it should have a dipole moment.

But I found that the $\sigma$-electron drift from C to O is almost nullified by the $\pi$-electron drift from O to C. What is about the $\pi$-electron drift towards the Carbon atom?

In Google it is given CO is polar, but my book says it is practically nonpolar ... now I am confused.


texts: Mass of monomer needed to obtain a polymer of a given molecular weight

texts:
In a condensation polymerization between two different monomers, the average molecular weight of the product depends on the ratio of the monomers used. This question illustrates the effect of using different ratios of ethylenediamine ($\ce{A}$) and 1,4-butanoic acid chloride ($\ce{B}$):

The reaction of $\ce{A}$ ($\pu{2 mol}$) with $\ce{B}$ ($\pu{1 mol}$) gives a compound with molecular weight $\pu{202.3 g mol-1}$ as the major product.
The reaction of $\ce{A}$ ($\pu{1 mol}$) with $\ce{B}$ ($\pu{2 mol}$) gives a compound with molecular weight $\pu{297.1 g mol-1}$ as the major product.
What mass of $\ce{B}$ (in grams) should be combined with $\pu{400 g}$ of pure $\ce{A}$ in order to obtain a high molecular weight polymer?

This question is part of a sample test for my course. I calculated the answer as follows.
For the higher molecular weight polymer, we'll need a $1 : 2$ molar ratio between $\ce{A}$ and $\ce{B}$.
That means we'll need $\pu{2067 g}$ of $\ce{B}$. However, this doesn't seem to be the right answer, which is given as $\pu{1032 g}$.
I'm really not sure what I'm doing wrong at this point.


texts: What is the difference between Cyclic Process and Reversible Process?

texts:
I want to ask the difference between Cyclic Process and Reversible Process.
Consider this graph:

If we have a process that goes from A to B then go back to A through the same path, then will it be called a Cyclic Process or Reversible Process or Both?


texts:
Does vibrating an NMR sample produce the same benefits and artifacts as spinning an NMR sample?  Are there "vibration sidebands" above the C13 satellites and is there a line thinning effect on the sample spectrum?  Please list any references that you may have read or seen.

Thank You


texts: How exactly do Copper salts help in Sandmeyer Reaction (Halogenation)?

texts: I have searched a quite few sources on mechanism for Sandmeyer's reaction, but couldn't find (and understand) how CuCl for example helps in replacement of N2 from Benzene diazonium chloride and gives Chlorobenzene? In Solomon-Fryhle-Snyder's regarding the mechanism its been given that "the mechanisms of these replacement reactions are not full undertstood", is this true and the reason most sources don't have mechanisms for Sandmeyers Halogenation reaction?


texts: Is there a way to theoretically estimate the overpotential losses in a battery?

texts:
Me and my team are currently designing a battery and are looking to do some pre-experimental analysis of different battery chemistries based on their overpotential losses.
I am aware of the Butler Volmer equation, which relates current and overpotential loss, however there are terms like the exchange current density and the charge transfer coefficients that we can't seem to calculate.
Tldr; We would like to find a way to find the overpotential (maybe as a function of current like in the Butler Volmer eqn) related with a particular battery chemistry


texts:
Can E2 reactions be reversible?

A lot of E2 reactions I have seen are irreversible. Is this true in general?

(Image source: Organic Chemistry 11e by Solomons)
I tried to reason this using the following argument; The transition state requires the base, the $\beta$-hydrogen, $\alpha,\beta$-carbons, and the leaving group to be simultaneously co-planar. In the forward direction, it is usually possible due to the stability of the staggered conformation. In the reverse, we would require both the leaving group and the conjugate acid of the base to become simultaneously co-planar with the double bond, which would have nearly $0$ probability.
Is this reasoning correct? Or is there an example of a reversible E2 reaction?


texts: What makes a compound a dehydrating agent?

texts:
When a carboxylic acid with low molecular weight is heated with $\ce{P2O5}$ we get the corresponding anhydride. My book says that this reaction happens with dehydrating agents such as $\ce{P2O5}$. I have also learned from my teacher that $\ce{H2SO4}$ is also a good dehydrating agent.

My question is what makes a molecule a good dehydrating agent? How can I identify one (or maybe what are the common dehydrating agents?) while solving questions?

Also, I have seen the use of $\ce{P4O10}$, but do $\ce{P2O5}$ and $\ce{P4O10}$ play the same role as a reagent?


texts: The Chemistry behind creating Polylactic Acid (PLA)

texts:
I've seen a few videos of persons creating plastics from starch by adding an acid, glycerol, and water, however no explanation of the chemistry.
Does anyone know what $\ce{(C6H10O5)_{n} + C3H8O3 + C2H4O2 + H2O -> (C3H4O2)_{n} + (what)}$?
or does it?

I only have a basic understanding of organic chemistry, so sorry if the equations don't make sense.


texts: Can you steam clean your range hood, by adding dishwashing liquid to boiling distilled water?

texts:
My grandparents physically can't remove their Sakura R-727II range hood that lacks any filter. Because of COVID-19, no handyperson can visit their house. But their range hood is now clogged and failing to suck out fumes, so they must de-grease their range hood's interior that hasn't been cleaned in 4 years.
Please see the pictures below. They wonder if they can de-oil their range hood by adding dishwashing liquid to boiling distilled water, then boil this mixture to evaporate the dishwashing liquid that will rise into and de-grease their range hood.

Does the dishwashing liquid vaporize as they think? Or does it remain in the saucier?

Can the resultant evaporated dishwashing liquid + steam combination de-grease their range hood? I wonder if this dishwashing liquid + steam will have enough pressure.

The two pictures above are like their range hood. Theirs isn't a Samsung range hood pictured below, but I used it to devise my collage for it shows steam.


texts: What does fractional notation represent in molecular formulas such as SiO4/2 or H2SiO2/2?

texts:
I'm going through some papers about HSQ (hydrogen silsesquioxane) and keep seeing this fractional notation being used:
HSiO3/2 , SiO4/2 , H2SiO2/2 , H3SiO1/2.
Example paper.
I understand that the proper formula for HSQ is [HSiO3/2]2n. Because we can't have fractional atoms, it's always multiplied by an even number and as such the fraction is never a consideration. But then why are the fractions maintained in the other compounds, and not reduced to SiO2 and H2SiO ?
Does keeping the fraction confer some structural information ? I've tried to find out what this notation means, but could not find a proper explanation.
Edit: What do the numerator and denominators mean, formally, in those formulas ? If it's that the oxigen atoms share outside bonds, why not write the compound as SiO4−4 ? If the numerator is the number of atoms, what does the denominator represent ? And is it always /2 ? Can we have /x , where x is a different integer ? I've never seen this type of notation before. Does the denominator mean that the valence electrons are halved ?


texts: How does caesium’s density change with temperature?

texts: According to Wikipedia caesium’s density is $1.90\ \mathrm{g/cm^3}$ at $\Theta =20\ \mathrm{^\circ C}$. How does this change when $T$ changes? E.g. will it expand when melting?


texts: I want to keep a medical-grade 3% H2O2 solution in a glass vial as the container for medicinal applications. It was claimed that inside of the vial should be covered with a thin layer of silicone to prevent H2O2 decomposition. Is there any need for this?


texts:
lets say we increased the excitation wavelength higher than it should be, what effect would this have on the sensitivity on our analysis, or changing the emission wavelength to a higher value than it would be.
My guess is that the higher wavelength leads to a lower frequency and so lowers the sensitivity but I have no idea what changing the emission wavelength would do?


texts: What's the reaction between H2SO4 and NaH2PO4?

texts:
I'm guessing it's going to be

$$\ce{H2SO4 + 2 NaH2PO4 -> 2 H3PO4 + Na2SO4}$$

Could anyone please let me know what the actual reaction is?

Thank you


texts: How to create a buffer solution from NaOH and CH₃COOH?

texts:
In my chemistry book, they say that an approach to making a buffer solution of $\mathrm{pH}=5.09$ is by adding an appropriate amount of strong base $(0.052\ \mathrm{mol}\ \ce{NaOH})$ to $0.300\ \mathrm{l}$ of $0.025\ \mathrm{mol/l}\ \ce{CH3COOH}$. But, I haven’t been able to figure out how they got those numbers. If I am not mistaken the relevant equation is,

$$\ce{CH3COOH +OH- <=>CH3COO^- + H_2O}$$

where the weak acid and conjugate base are respectively $\ce{CH3COOH}$ and $\ce{CH3COO^-}$. My concern is that this equation above goes nearly to completion $(K=1.8\times10^9)$ so I don’t see how this can even be a buffer solution. If not, how do they get the values? I would appreciate any help.


texts:
My following questions are related to $\mathrm{pH}$ values in irrigation water in plants.
I got a $\mathrm{pH}$ meter and I am measuring the tap water and I get an value about 8.
My first question: Why it is that high?
To get the $\mathrm{pH}$ down, I am using a $\mathrm{pH}$ regulator of phosphoric acid.
My second question: I now have some tap water with $\mathrm{pH}$ of about 6.5 but when this water sits for about 1-2 days, the $\mathrm{pH}$ increases back to 8. Why is it increasing?
Edit: the water with $\mathrm{pH}$ 6.5  tap water adjusted with small amounts of phosphoric acid. This then increases back to 8 when it sits for some time.


texts: Numbering and naming a disubstituted cyclohexene

texts:
I saw this cyclohexene in my textbook and wonder why it’s like that. I searched the internet and it’s correct but why?
As I know we try to keep the numbers low, so instead of 1,6-dichlorocyclohexene we can tell 2,3-dichlorocyclohexene and the numbers are lower. I appreciate your help.


texts: Understanding Equivalent Wyckoff positions

texts:
I'm somewhat confused by the concept of Wyckoff positions in crystal structures. From Quantum Chemistry of Solids by Robert Evarestov, the definition of a Wyckoff position is "all the crystallographic orbits which have the same (not only isomorphic, but the same) site-symmetry group". I was okay with this, but he then went on to define equivalent Wyckoff positions as positions such that "equivalent sites have the same point-group symmetry and the same orientations of symmetry elements with respect to the lattice".

What I fail to understand is how the equivalent Wyckoff positions don't collapse to a single Wyckoff position, as they seem to meet the criteria of having the same site-symmetry. Is there a clear explanation of what distinguishes two Wyckoff positions enough to be equivalent, but not just a single position?

To clarify my question a little more, here is the specific example given in the text for the space group 136, also called P42/mnm or $D_{4h}^{14}$.

  Pairs of Wyckoff positions a-b, f-g, and i-j have isomorphic site-symmetry groups
  ($D_{2h},C_{2v},\text{ and } C_s$ respectively). As is seen from the table, the pairs of points a-b and f-g not only have isomorphic, but also equivalent Wyckoff positions. The equivalent sites have the same point group symmetry and the same orientations of symmetry elements with respect to the lattice.


texts: What's the effect of temperature on buffering capacity?

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I did some research online but I still couldn't get any conclusion. Some said that the buffering capacity decreases when temperature increases because of the increase in ionisation of the weak acid molecules and therefore, some of the conjugate base ion will be used to neutralised the $\ce{H+}$ ion from the ionization of the weak acid molecules. Hence, only a small amount of strong acid is needed to complete remove the conjugate base ion and to break the buffering capacity. But, the problem is that the acid molecules ionise into both $\ce{H+}$ and the conjugate base so doesn't it mean that the number of conjugate base ion will remain the same since the $\ce{H+}$ ion is just reacting with the same conjugate base ion which they were initially bonded together ?

The other assumption is that temperature has no effect on buffering capacity since buffering capacity apparently only depends on two factors: concentration of the buffer solution and the ratio of pH to pKa. So even if the pKa changes due to the change in temperature, the pH also changes accordingly whereby pH increases when pkA increases and vice versa. So the ratio will remain the same no matter what.

So could anyone please give me a solution?


texts: Mechanisms for Reimer-Tiemann and Kolbe-Schmidt reaction on deuterium labelled phenol

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I was solving a bunch of reactions when I encountered the following:

So for the first question:

This is a Reimer-Tiemann reaction. I felt that the tautomerism would result in the deuterium getting attached to the phenolic $\ce{O^-}$. As it turns out, that was wrong. Oh well. Then I proceeded with the second question. Now this one is a Kolbe-Schmidt reaction, where the $\ce{CO2}$ liberated will react with the phenol. Going by the previous reaction, this time I decided not to add the $\ce{D}$ atom to the phenolic $\ce{O-}$. Consequently, this is how it panned out:

All of this has left me quite confused. So here's my question:

Why is it that the $\ce{D}$ atom during tautomerism adds on to the phenolic $\ce{O-}$ in the Kolbe-Schmidt reaction, but does not proceed to do so in the Reimer-Tiemann reaction?

Image credit: Created using Marvin JS


texts: Why are aqueous solutions included in the equillibrium constant but liquids are not?

texts:
I understand solids are insoluble and will just sit at the bottom of the vessel so we don't include them.

But I am confused as to why aqueous solutions are used in the equilibrium equation but liquids are not.

E.g. for the reaction:

The equilibrium constant is:

Why isn't H20 (liquid) included in the equilibrium constant yet KCl (aq) is?

Thank you


texts: Can molten sugar also rotate polarized light as sugar water does?

texts: It is well know that the sugar water can rotate the plane of linearly polarized light, so light bends when travelling in sugar water. However, do the liquid state of sugar but not the sugar solution also have this property?


texts: Inert cyanide groups in polyacrylonitrile(PAN)

texts: Cyanide group undergoes hydrolysis and gets converted to Carboxylic acid. However, the cyanide groups in polyacrylonitrile(PAN) are inert. Why?


texts: Determining stoichiometry of an unsaturated hydrocarbon via combustion

texts:
$60\ \mathrm{cm^3}$ of oxygen was added to $10\ \mathrm{cm^3}$ of a gaseous unsaturated hydrocarbon. After explosion and cooling to room temperature, the residual gases occupied $45\ \mathrm{cm^3}$. What volume of carbon dioxide was formed in the reaction?

I’ve tried to make an unbalanced equation out of it:

$$\ce{(CH2)$_n$ + O2 -> CO2 + H2O}$$

My problem now is I don’t know how to proceed to the next step. How do I even find the moles? Is the equation correct? How do I balance this equation?


texts: Why is change in gibbs energy not zero through the gibbs free energy equation?

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Change in enthalpy of the system is equal to its temperature multiplied by its change in entropy (as change in enthalpy is equal to heat absorbed /given out at constant pressure and change in entropy is heat absorbed/given out divided by its temperature). So, through the Gibbs free energy equation, the change in Gibbs free energy should be zero?

This question might seem messy, as I don't know how to write equations on Stack Exchange.

Please help. The problem is in the elementary concepts, I think.