texts: Finding the number of orbitals on a central atom

texts:
In $\ce{BeCl2}$ the number of orbitals on central atom, i.e. on beryllium, are 2. In $\ce{BF3}$, the number of orbitals on central atom , i.e. on boron, are 3.

Similarly in $\ce{NH3}$ there are 4, on $\ce{PCl5}$, $\ce{SF4}$, and $\ce{ClF3}$ there are 5. But how?


texts: Why does the phosphate ion have resonance structures?

texts:
My first-year chemistry teacher depicted $ \mathrm{PO_{4}^{3-}}$ as exhibiting the resonance structure inset below this question.

However, I can't figure out what diagramming rules (which is what she was teaching) she used to deduce her answer. I thought that the double bonded oxygen would be single bonded and that it would have six unbonded electrons like the other oxygens.

Why should one oxygen be different than any of the others?
What diagramming rules imply that  $ \mathrm{PO_{4}^{3-}}$ should be depicted as my teacher did?


texts: What repulsion keeps non-hydrogen atoms at a distance: between inner shells or between nuclei?

texts:
Bonded or not, when two atoms or ions come closer than the bond distance or the van der Waals distance, the energy increases drastically. What is the underlying cause of that repulsion?

The repulsion of the negatively-charged inner-shell electrons
The repulsion of the positively-charged nuclei (or the effective positive charge of nuclei plus inner-shell electrons)
Any classical explanation solely based on electrostatics falls short, and the increase in energy is related to the Pauli exclusion principle.
There is no single underlying cause, it depends on the specific case. Sometimes repulsion of positive charges is the problem, sometimes repulsion of negative charges.


texts: What happens when an ionic compound is boiled?

texts: Do ionic compounds such as NaCl become individual ions such as one Na ion and one Cl ion or are they hold together by ionic bonds even when they are boiled. Thanks in advance.


texts: Is there any danger of forming explosive reaction products during the electrodeposition in Diethylene glycol?

texts:
I know that perchloric acid could be potentially explosive and some organic solvents could form dangerous peroxides.

I am going to do an electrodeposition in diethyleneglycol solution containing $\ce{NH4Cl}$, $\ce{ZnCl2}$ and $\ce{FeCl2}$. Since in my case there are all elements to form $\ce{HClO4}$ and I am going to heat everything up to 60 degrees I want to be sure that it is safe.

Is there any danger of forming explosive reaction products during the electrodeposition?


texts: What types of ultraviolet light will ignite hydrogen?

texts: I saw a reaction between hydrogen and chlorine ignite in the presence of UV light. I was wondering if the same thing would happen with something like near-ultraviolet light (around 400 nm). What kinds of UV light (if any) would start a reaction of stoichiometric amounts of hydrogen and oxygen gas in something like a balloon?


texts: How many atoms can be reduced in a single redox reaction?

texts:
I am doing high school chemistry and I am busy working with redox reactions.

The explanation in my text book, of how a redox reaction works, left me a bit confused as to how many atoms can be reduced/oxidized in a single reaction equation.

Can only one atom (species) be reduced/oxidized in a single equation or can there be more than one reduced/oxidized in the same chemical equation?

All of the reaction equations I have come across so far have just one atom reduced and one atom oxidized, for example:

$$ \ce {Mg(s) + 2HCl(aq) -> H_2(g) + MgCl_2(aq)} $$

In this reaction only Mg is oxidized and only H is reduced. Is there a reaction in which more than one species of atom it reduced or oxidized?


texts: Calcium Nitrate - Why only 18.8% Calcium for fertiliser?

texts:
I brought a kilo of Calcium Nitrate for my hydroponic setup.

The chemical formula for Calium Nitrate is Ca(NO3)2. I did a quick calculation of its weight:

Ca = 1*40.078

N  = 2*14.006 = 28.012

O  = 6*15.999 = 95.999

Total = 164.085

Hence the % in weight of calcium is ~24.42%.

BUT I see on the fertilizer pack that Calcium is only 18.8% and Nitrogen is 15.5%

Eg: https://www.fertinagroindia.com/calcium-nitrate.html

Why is this?


texts: In Thomson's atomic model, why did he not assume that there are positively charged particles embedded in a negatively charged sphere?

texts: Why did Thomson assume that electrons are embedded in a positively charged sphere? Why did he not assume that they are positively charged particles embedded in a negatively charged sphere?


texts: Isotope pairs in different states at room temperature?

texts: Does any pair of isotopes exist which are in different states at room temperature—either in isolation or as part of an otherwise-identical compound?


texts: TKN: Why are they called Missouri tablets?

texts:
When analyzing for Total Kjeldahl Nitrogen (TKN), you can make a copper sulfate digestion solution in the lab or purchase a variety of pre-prepared digesting tablets for example on VWR. My question is, why are some formulations called Missouri tablets?
As far as I can tell, the state of Missouri does not specifically require this formulation, and I haven't seen any digestion tablets named after any other states. Were they perhaps invented in Missouri?


texts: Would a melted crystal recrystallize back into the same lattice structure when frozen?

texts:
Two things that I'm not sure about melted crystals:

For a material that has only one possible crystal structure, would freezing cause it to recrystallize, or could it become amorphous upon freezing?
What would happen upon freezing to a material with more than one possible crystal structure?


texts: Precipitate Sodium Hypochlorite from tap water before distillation

texts: Is there a fairly simple way to precipitate Sodium Hypochlorite from tap water before I distill it? Or, second best, a way to neutralize it?


texts: Plastic membrane that lets water in from the outside only?

texts:
I'm looking for a type of plastic membrane that would let water through it from the outside, but wouldn't allow water to escape once it's inside the membrane.

Ideally available in a roll.

Does such a plastic membrane exist?


texts: Will Calcium Carbonate react with Sodium Chloride?

texts:
After reading through my school chemistry notes and the answer to the question here at Chem S.E of how do we know whether an $\ce{A + B}$ reaction will occur, I find myself stuck on this very basic question.
I understand that $\ce{CaCO3 + HCl}$ will react as it is an acid + base reaction and that the reverse reaction $\ce{Na2CO3 + CaCl2}$ to $\ce{CaCO3}$ and $\ce{HCl}$ is possible.
I don't think I can use bond enthalpy to figure out if the reaction is spontaneous or non-spontaneous, because the reactants and products are ionic rather than molecular compounds.
I believe that I might need to use some sort of enthalpy calculation to figure this reaction out, but I'm not sure which specific one in particular.
On a whim, I believe that this reaction will not occur but I'm still very uncertain.


texts: What does a comma signify in inorganic chemistry?

texts:
$\ce{(Ca{,}Co)CO3}$

I have never ever seen this before. What does this mean exactly?


texts:
Carbon has 4 valence electrons, so it means that it can have a total of four (covalent) bonds, correct?

If that's the case, why can't carbon share four bonds, such as with another carbon atom (to form $\ce{C2}$, for example)?


texts: How to verify if a rate law fits the experimental data?

texts:
A student after doing an experiment on chemical kinetics, decided that the rate law of the reaction is $u = k[\ce{IO3-}]$ which is correct, but do the data below match with this? Or does he have to repeat the experiments?
   $$\ce{IO3- + 8I- + 6H+ → 3I3- + 3H2O}$$

  In order to decide the rate law he took into consideration the data below:

  experiment: $\pu{1 mL}~\ce{IO3-}$; time: $\pu{11 min}$
  experiment: $\pu{0.75 mL}~\ce{IO3-}$; time: $\pu{8 min}$
  experiment: $\pu{0.5 mL}~\ce{IO3-}$; time : $\pu{5.7 min}$

Looking at the rate law, the order is supposed to be one.
I know that in order to conclude if the data matches the rate law I have to find out if the concentration is linear combination of time. But I'm confused, because I don't know anything about the concentration and thinking about it I guess I should at least talk about relative concentration? But still I don't know how.


texts: Do alkyl halides with an alpha nitrogen atom undergo SN1 reaction?

texts:
Today, in my organic chemistry class, I learnt about the nucleophilic substitution reaction. The notes have stated that:

  Alkyl halides with $\alpha$ oxygen atom can also undergo SN1 reaction because of the heteroatom stabilised cation (oxonium ion)

An example was then given of a bromide leaving from a bromoether to give a resonance-stabilised carbocation.

I was wondering if alkyl halides with an $\alpha$ nitrogen atom can undergo SN1  reaction as well. When asked, the teacher responded by saying that with $\alpha$ nitrogen atoms, the carbocation would experience greater stabilisation and result in a faster rate of SN1 reaction for such alkyl halides.


texts: I was reading a book and it was mentioned that $\ce{Co[Hg(SCN)4]}$ is diamagnetic. I know that it is made up of $\ce{Hg^2+}$ and $\ce{Co^2+}$. $\ce{Co^2+}$ has 7 electrons which means that it should always have an unpaired electron but then why is this compound diamagnetic? Am I missing something?


texts: Why do ionisations from non-bonding orbitals result in little/no vibrational structure in a photoelectron spectrum?

texts:
I understand that ionisations from bonding and antibonding orbitals create vibrational structure from the Franck-Condon principle, resulting in a greater overlap integral between different vibrational levels, but surely if a non bonding orbital is ionised the equilibrium bond length will not change (much), resulting in a good overlap integral between the vibrational levels?

If someone could explain the principle to me in this context I would be very grateful.


texts: Calculating partial pressure equilibrium constant Kₚ given initial pressure and equilibrium pressure

texts:
A reaction
$$\ce{A(g) <=> B(g) + C(g)}$$
happens in constant volume and constant temperature. The reaction starts only with gas $\ce{A}$ (no $\ce{B}$ or $\ce{C}$) with given pressure $P_1 = \pu{6 atm}$, in equilibrium the pressure of all three gases is $P_2 = \pu{10 atm}$. Calculate $K_p.$

It seems to me like a very simple question, however it seems that I don't understand a basic concept regarding gas equilibrium. As for my understanding it is suppose to be
$$K_p = \frac{P_2 \cdot P_2}{P_2} = P_2 = \pu{10 atm}$$
But the given solution is $\pu{8 atm}$ and I really don't get what miss.


texts: Simple experiment to do at home that involves acids and bases?

texts:
so long story short I am in the IB Diploma and I am required to come up with an experiment to investigate pretty much anything to do with chemistry. I'm thinking about doing mine on investigating how temperature affects the pH value of a solution, but my teacher said it was too simple.

Basically, is there any reaction I can make at home with simple chemicals(vinegar, baking soda, salt, juice, etc.) that would produce a meaningful experiment and involves me measuring the pH level? Thank you guys so much.


texts: Comparison of basic strengths of hydroxides of alkali metal group

texts:
I have read that $\ce{LiOH}$ is less basic than $\ce{KOH}$. But I don't know its reason. I have tried to frame a possible explanation.

My explaination:

I think that as $\ce{Li}$ undergoes more hydration than $\ce{K}$, $\ce{OH-}$ group will stick stronger to $\ce{Li+}$ ion. Due to this $\ce{Li+}$ will be reluctant to loose $\ce{OH-}$ and thus will be less basic. Is my explanation correct?
And, is this explanation correct for any other pair of hydroxides, eg, $\ce{Sr(OH)2}$ & $\ce{Ba(OH)2}$?


texts: Mathematical explanation of blank titration in Mohr method for argentometry

texts:
In my book it is written that in order to minimize systematic error in Mohr method for argentometry it is a common procedure to conduct a blank titration with $ \mathrm{Ag^+} $ against a $\mathrm{CrO_{4}^{2-}}$ solution (with the same concentration of the original solution).

The book then suggests to subtract the $ \mathrm{Ag^+} $ volume needed to observe precipitation (in the blank solution) from the volume obtained as a result of the 'standard' titration.

I don't understand why I have to subtract that number, specifically I do understand that there is a systematic error but I don't get why it is the volume of $ \mathrm{Ag^+} $ obtained by the blank titration.


texts:
In thermodynamics many definition has been made from partial derivatives at constant conditions for instance:
Let $U$ be $U:f(S,V,m_)$ then:
$$T = \left( \frac{\partial U}{\partial S} \right)_{V, m_{k}};  p = \left( \frac{\partial U}{\partial V} \right)_{S, m_{k}}; \mu_k = \left( \frac{\partial U}{\partial m_k} \right)_{V, S}$$
In a particular case, heat of reaction and van 't Hoff relation
Being $H:H(T,p,\xi)$
$$\mathrm dH= \left( \frac{\partial H}{\partial T} \right)_{p, \xi}\,\mathrm dT + \left( \frac{\partial H}{\partial p} \right)_{T, \xi}\,\mathrm dp + \left( \frac{\partial H}{\partial \xi} \right)_{T, p}\,\mathrm d\xi$$
Where $C_p$ is the specific heat at constant pressure, $h_T$ is the heat compressibility and $r_{T,p}$ is the heat of reaction at constant temperature and pressure:
$$C_p = \left( \frac{\partial H}{\partial T} \right)_{p, \xi} ; h_T = \left( \frac{\partial H}{\partial p} \right)_{T, \xi}; r_{T,p} = \left( \frac{\partial H}{\partial \xi} \right)_{T, p}$$
In terms of variation of affinity with temperature, the heat of reaction is given by (where $K$ is the equilibrium constant of a chemical reaction):
$$r_{T,p} = -RT^{2}\frac{\partial }{\partial T} \ln K(T,p)$$
So the question is: How can I define an equation where the left side needs constant temperature, but the right side implies the derivative of temperature?


texts: How do you name a bicyclo compound with a fused benzene ring?

texts:
What is the IUPAC rule for naming a bicyclo compound with a fused benzene ring? Are you required to state the number of double bonds by adding something like 2,4,6-ene to the name or do benzene rings have a specific name ?
For example:

What will this compound be named? Will it be bicyclo[4.3.0]non 1,2,4 triene or is there some specific rule for fused benzene rings, as I stated before?


texts:
Why does coupling of α-naphthol take place at δ-position (para to $\ce{-OH}$) rather than the β-position (ortho to $\ce{-OH}$)?
In the case of β-naphthol, we consider the aromaticity of the entire compound to decide the position.
Aromaticity is not disturbed even when the attack takes place at the ortho position. So I don't find any reason for the diazo compound to not attack there.


texts: Which base pair is more stable, U:G or I:C?

texts: As a result of damage (usually deamination), DNA will sometimes contain uracil and inosine bases. I am trying to determine which unnatural base pairing combo would be more stable: uracil paired with guanine or inosine paired with cytosine. See the images below.


texts: How many tetrahedral and octahedral holes are there in a bcc unit cell?

texts:
When I tried to count, I found 24 tetrahedral holes (each formed by 2 body centers of 2 unit cells sharing a face and 2 vertices of the same edge of that face). As each hole is being shared by 2 unit cells, there are 12 holes per unit cell.

Also,I found 6 octahedral holes (6 at face centers being shard by 2 unit cells each and 12 at every edge center being shared by 4 unit cells each).

Generally I was taught that for $n$ packed spheres, there should be $2n$ tetrahedral holes. Does the analysis above mean that this rule doesn't apply here?


texts:
According to Wikipedia, for the $\ce{AH2}$ Walsh diagram:

and the Walsh diagram in Shriver and Atkins Inorganic Chemistry, the $a_1$ orbital sinks in energy going from 90 to 180°. Furthermore, the $b_2$ orbital at 90° is higher in energy than the $a_1$ (lone pair).

However according to the second, newer diagram for a AH2 molecule on the same page:

the $a_1$ is rises in energy and the $b_2$ is definitely lower in energy than  the $a_2$ (or $a_1$ lone pair). This matches also my own self-made diagram, using Hartree-Fock 6-31G*, calculated through Spartan. Other pages use the same Walsh diagram.

What is going on here?

Shrivers textbook explains the rise of the $a_1$ orbital through decreased H-H overlap and reduced involvement of the $\ce{X~2_{pz}}$.


texts: Explicit differential equation based model of protein folding

texts:
I am an applied mathematician interested in the dynamics of potential systems - i.e., systems with multiple unique energy minima. One of the best examples of such systems are protein folding potentials. From sources like This one I know that the potential,
$$
V(x)
$$ exists and is a function of the positions of each residue in space and their interactions with each other. Since such a function exists, there should (mathematically) be a set of ordinary differential equations that capture the dynamics described by the potential.

However, although I have seen definitions of $V(x)$ in the literature, for the life of me I can't figure out exactly what the set of differential equations associated with this system is - i.e., the system is usually written out in a generalized form that applies to all proteins, but the exact information required to build such a potential for one such protein is unclear.

Does anyone have an example of of a particular $V(x)$ (for a particular, short, set of amino acids, say) where all the parameters are known and the system can be solved numerically as a set of ordinary differential equations?


texts: Which are the differences between resonance Raman and fluorescence?

texts: If the fluorescence is the re-emitting of a photon with a larger wavelenght due to the transition from a higher energy state to a lower energy state the case of resonance Raman (where there aren't any virtual states involved) seems be equal to the fluorescence. Which differences are there?


texts:
Question:

  Given the subshells $\ce{1s, 2s, 2p, 3s, 3p}$ and $\ce{3d}$, identify those
  that meet the following descriptions:
  a) has $l=2$
  b) Can contain two electrons with spin $m_{s}=\pm\frac{1}{2}$.

For a): from my understanding $l=n-1$. Therefore $\ce{3s, 3p}$ and $\ce{3d}$ should be correct but according to my solutions manual, the answer is only $\ce{3d}$. Why is this so?

For b) The answer is $\ce{2p, 3p}$ and $\ce{3d}$. Why are these the answers?


texts: treatment of alkyl chloride with aqueous KOH and alcoholic KOH

texts: The treatment of alkyl chloride with aqueous KOH leads to the formation of alcohol but in the presence of alcoholic KOH alkenes are major product. Why?


texts: Why is my solution for the partial pressures of two different gases incorrect?

texts:
I have the chemical equation: $\ce{NH4NO3(s) -> 2H2O (g) + N2O (g)}$. There are $12.8$ g of ammonium nitrate, and it decomposes completely in an empty container at $25.00\ ^\circ\pu{C}$ until the total pressure is $3.70$ atm.

This is what I tried:

Because there are 2 more $\ce{H2O}$ than $\ce{N2O}$ I said that there are $\pu{9.06g}$ of $\ce{H2O}$ and $\pu{3.02g}$ of $\ce{N2O}$.

$$\pu{9.06g}\times \frac{\pu{mol}}{\pu{18.016 g}} = \pu{0.503 mol}\  \ce{H2O}$$
$$\pu{3.02g}\times \frac{\pu{mol}}{\pu{44.02g}}= \pu{0.0686 mol}\ \ce{N_2O}$$

I then found the mole ratio of both compounds:
$$X_{H_{2}O}={0.503\over 0.572}=0.879 $$
$$X_{N_{2}O}={0.0686\over 0.572}=0.1199$$

Then I used the relationship between mole ratios and partial pressure $X_i={P_i \over P_{tot}}$, where $P_{tot}=\pu{3.70atm} $:

$$P_\ce{H2O}=(0.879)(\pu{3.70atm})=\pu{3.25atm}$$
$$P_\ce{N2O}=(0.1199)(\pu{3.70atm})=\pu{0.444atm}$$

According to the answer solution for this problem $P_\ce{H2O}=\pu{2.47atm}$ and $P_\ce{N2O}=\pu{1.23atm}$. What am I doing wrong? I can't figure out how to get the correct solution.


texts: What's the most trusted source for bond lengths?

texts:
I'm doing some computational work and am manually inputting Z-matrices for the molecule (no GUI support for my program). For this, I need bond lengths:

I tried Herzberg's book
I tried a basic optimize in Avogadro and then asked it to generate a Z matrix.
I checked Scifinder for structural properties

However, bond lengths vary quite a bit from these sources (upto 0.4 Angstroms). I understand that these sources are a few decades apart from each other.

Should I just stick to the newest source? Or should I stick to Herzberg because he's like the established standard?

(I'm not sure what are the best tags for this question, please feel free to suggest more/edit them)

Thanks!


texts: Applying Ligand Field Theory, How Can The Color Of Transition Complex Ions Be Explained/Represented?

texts:
1.

To my understanding, Crystal Field Theory allows for an explanation for the colors of transition metal complex ions due to the d-d transitions which occur. This transition ∆o, is from the t2g orbitals to the eg.

Now looking at Ligand Field Theory. Is it right to say that this is equivalent to/same as the transition from the t2g orbitals to the eg* or t2g* to eg* orbitals depicted in the diagrams below?

2.

(Assuming octahedral complex with sigma bonding only)

Moreover, I was also initially confused due to the issue that if two of the d-orbitals of the transition metal ion is used for bonding with ligands e.g in a hexaaquachromium(III), [Cr(H20)6]3+, how would the d-d transitions occur if these eg orbitals are involved in sigma bonding with 6 of the ligands.

Is it right to say that the d-d transitions occur from the t2g non-bonding orbitals to the eg* anti-bonding orbitals and that the bonding with the ligands involve eg bonding orbitals which is separate to the anti-bonding eg orbitals?

In summary, I have the impression that CFT provides an explanation for the colors of complex ions and LFT provides an explanation for the bonding of transition metal ions with ligands as well as the colors. Hence, is that fact that there are bonding and anti bonding orbitals which allows for the both the colors and the bonding with ligands?


texts:
Why some acid/alkali can react with some salt, forming another acid/alkali? For example:

$\ce{2NaCl +H2SO4->Na2SO4 + 2HCl}$

$\ce{Ca(OH)2 +Na2CO3->CaCO3 +2NaOH}$

but not the reverse.
What determines this? I heard someone said the weaker acid/alkali produced is favourable, but HCl is stronger than $\ce{H2SO4}$. I also heard that only if the products are insoluble or lost from the solution, the reaction happens. Someone suggested that the problem is concentration, as sulfuric acid is 98% while HCl is 38% Is that true?


texts: Which Lewis Structure for BeCl2 is more commonly seen?

texts: One is more stable according to its charge. The other one does not satisfy as much as the first does the formal charge rule but has a complete octet.


texts: Is there a least reactive chemical species?

texts:
As a total chemistry layman I enjoyed reading "Why doesn't $\ce{H2O}$ burn?", but it prompted another question in my mind. One of the answers there was that $\ce{H2O}$ can burn in the presence of a stronger oxidizer like fluorine, so burning stable compounds is just a question of using a stronger oxidizers.

Or is it? Is there a chemical species, or a "least reactive compound" that, once made, is difficult or impossible to chemically transform into something else? A chemical black hole, if you will.

Does the above answer change if we allow high temperatures and pressures versus restricting ourselves to roughly standard temperature and pressure?


texts: What is the dipole moment direction of an aliphatic amine, i.e., R-NH2?

texts:
Since the electron donating property of $\ce{N}$ and $\ce{C}$ is different, there is partial charge transfer between $\ce{N}$ and $\ce{C}$ atoms in aliphatic amines, namely $\ce{R-NH2}$. What is the charge transfer direction? Can the following be true? And how large is this dipole moment?

More generally, how can one determine both the direction and quantity of the charge transfer dipole moment given two common organic groups? Or what is the order of electron donating property of common groups?


texts: Are there chemicals that absorb and release upon heating oxygen more efficiently than potassium oxide?

texts: $\ce{K2O}$ absorbs oxygen forming $\ce{K2O2},$ which decomposes to $\ce{K2O}$ and $\ce{O2}$ at 500 °C. This means that $\ce{K2O}$ can absorb up to 17% its mass of oxygen. Are there other substances that exceed this ratio and release oxygen below 1000 °C?


texts:
I am slightly confused by what the spectrum would show for carbon-13 NMR of $\ce{CHCl3}$.

My initial guess would be that the peak would be split by coupling to both the proton and the 3 chlorines, as both nuclei have a net spin.

If the peak were split by the chlorine only, then as there are three chlorine atoms we would get a quartet peak. However this cannot be correct because the spectrum for CDCl3 shown here has only three peaks:

I also don't understand here why the areas of the three peaks are the same. Should they not be in some other ratio (for the four peaks I expected it would be $1:3:3:1$ are ratio)?

Then I would expect that the presence of the proton would split every one of the four peaks from $\ce{C-Cl}$ coupling further into a doublet, giving a quartet of doublets.

I didn't find any spectra showing this, only showing very tiny peaks for $\ce{CHCl3}$ compared with $\ce{CDCl3}$ which I don't understand:

To make it more confusing, my lecture notes say that for chloroform, $\ce{CHCl3}$,

  each $\ce{^13C}$ is attached to a spin $1/2$ proton so unless we applied broadband proton decoupling, coupling to the proton would mean that the $\ce{^13C}$ signal would appear as a doublet.

And it makes no mention of the effect of the chlorine atoms on the spectrum.

I would be very grateful is someone could expalin what the spectrum for carbon-13 NMR of chloroform, $\ce{CHCl3}$, would actually look like!


texts: Is there a possible effect of mechanical vibration on the stability of organic molecules?

texts:
Is there a possible theoretical effect of mechanical vibration on the stability of
organic molecules.  E.g. some medicines degrade if they are not stored in a fridge, is there a theoretical foundation that suggests that low frequency vibrations might have the same effect?


texts:
when I add $\ce{RCl + H2O -> ROH + HCl}$

but it's also true in reverse $\ce{ROH + HCl -> RCl +H2O}$

however this is not in case of $\ce{FeSO4 +Zn -> Zn + FeSO4}$

$\ce{ZnSO4 + Fe -> no rxn}$

How can a reaction be true both ways ?


texts: does aluminum oxide float on molten aluminum and by what mechanism?

texts:
Not really a chemistry question since no reactions happening, but couldn't find a more appropriate stack exchange site.

Considering recycling aluminum cans for scrap metal using induction heating. I've seen people do it with very unsophisticated equipment, but what I don't get is Al2O3 is denser (3.95g/mL) than molten aluminum (2.38 g/mL).

I suppose surface tension can stop any oxide that forms at the surface of the melt from sinking, but how strong is that? Is it resistant to mild stirring (e.g. when you skim off the dross)? Are there other examples of denser materials floating?


texts: Radioactivity and Kinetics of disintegration

texts:
Well I've just started on kinetics and there are a few things I am absolutely confused about!

First of all, is a neutron actually made up of a proton and electron? If yes, then how is this possible?
In K-electron capture where the electron of the K-Shell is captured by the nucleus, doesn't the species become positively charged or ionized as it is losing an electron?
When metastable technetium disintegrates into normal technetium and a gamma particle, what is the change brought about? Isn't the technetium on both sides of the equation basically the same?


texts: Why HF plus H2O is not a buffer solution?

texts: I think $\ce{HF}$ can be hydrolysis and get $\ce{F-}$ as a conjugate base, so this solution should be a buffer solution. But the correct answer is that this solution is not a buffer. Please explain it to me. I'm very confused.


texts: Is there a definition of rotatable bond?

texts:
Some intramolecular bonds are rotatable in the sense that the torsion angle around this bond is flexible (for example, $\psi$ and $\phi$ angles in a protein backbone). Others are essentially fixed (for example, the $\omega$ angle in the peptide bond in a protein backbone).

Is there an operational definition, or a published study where a general definition is given, which would allow me to recognize in a generic molecule (or at least an organic molecule) whether a given bond is rotatable or not?

If there is no general theory for this, what are the most common indicators of whether a bond can or cannot be rotated? Are there some rules of thumb?


texts: Determining the most stable enolic form of 1-phenylbutane-1,3-dione?

texts:
Question

Which form of 1-phenylbutane-1,3-dione is more stable?

Answer

3-hydroxy-1-phenylbut-2-en-1-one

My question
I've been told that between the above two, 3-hydroxy-1-phenylbut-2-en-1-one is more stable because the double bond is in the middle which is unclear to me.
Could someone explain the above statement?


texts:
How would Dalton's law be affected when there are two ideal gases in a
  container at different temperatures?

Let the gas with higher temperature be gas A and the gas with lower temperature be gas B. Then heat will be transferred from gas A to gas B due to which kinetic energy of the molecules of gas A will decrease and kinetic energy of molecules of gas B will increase. Hence, molecules of gas B should make more collisions to the walls of the container because of the increased kinetic energy and hence the total pressure exerted by gas B should increase and using the same argument, pressure exerted by gas A should decrease.

Now, we can no longer use P(A) + P(B)= P(T)

; P(A) is the partial pressure of gas A,

P(B) is the partial pressure of gas B

and P(T) is the total pressure exerted by the mixture of gas A and gas B

Am I correct with this logic?

  A glass bulb of volume 400 ml is connected to another bulb of volume
  200 mL by means of a tube of negligible volume. The bulbs contain dry
  air and are both at a common temperature and pressure of 293 K and
  1.00 atm. The larger bulb is immersed in steam at 373 K ; the smaller, in melting ice at 273 K. Find the final common pressure.

In the above problem, we cannot simply use PV= nRT to calculate final pressure because we don't know the final common temperature. So, we have to individually calculate the partial pressure of both the gases and then sum them up to get the total pressure. But according to me, as stated above, that should not be correct.

Is my reasoning correct or I am missing out on something? Also, how should I solve using my logic and please tell if there are other ways to go about solving this problem.


texts: Can acid-base reactions occur in a non-aqueous medium?

texts:
To better illustrate my question, allow me to refer to the case of ammonium chloride, formed through a classic acid-base reaction.

The reaction between ammonia and hydrogen chloride to give ammonium chloride is a neutralization reaction, since ammonia acts as a base and hydrogen chloride acts as an acid.

The reaction is usually written as:

$$\ce{NH3 + HCl -> NH4Cl }\tag{1}$$

Usually, in the synthesis of ammonium chloride, the reagents in aqueous solution (ammonium hydroxide and hydrochloric acid) are used. In aqueous solution, they behave differently than when they are in anhydrous form.

On the one hand, when ammonia dissolves in water, the ammonium cation, its conjugate acid, is formed:

$$\ce{NH3 + H2O <=> NH4+ +OH-}\tag{2}$$

On the other hand, a similar, but opposite, reaction occurs when hydrogen chloride dissolves in water, forming the chloride anion, its conjugate base:

$$\ce{HCl + H2O <=> H3O+ + Cl-}\tag{3}$$

Then, when mixing both solutions, the following reactions occur:

$$\begin{align}\ce{NH4+ +Cl- &-> NH4Cl}\tag{4.1}\\[0.5em]
\ce{H3O+ +OH- &-> 2H2O}\tag{4.2}\end{align}$$

However, apparently, it is not necessary to mix the solutions to obtain ammonium chloride, just by mixing the vapors of the solutions, it is enough to give the expected product.

But when the ammonium hydroxide evaporates, the ammonia ceases to be in the form of ammonium and returns to its anhydrous form. The same goes for hydrochloric acid. Then, the vapors would be ammonia and hydrogen chloride, but wouldn't this affect the reaction since they are not in the form of conjugate acid or conjugate base now?

I still don't understand acid-base chemistry very well and I would like to know if such reactions, such as that of ammonia with hydrogen chloride, can occur without the reagents being in the form of ions in aqueous solution.


texts: How does an irreversible process maintain internal energy while dissipating excess heat?

texts:
From my understanding, if you were to look at a pressure-volume graph of a reversible, isothermal expansion, the area under it would represent reversible work. Similarly, if you were to graph an irreversible, isothermal expansion on top of this graph, you’d see a smaller rectangular area representing the irreversible work.

What I have been told is that the area between these areas, irreversible and reversible, is wasted energy dissipated as heat. This confuses me, however. If the work the irreversible system does is less, then it should draw less heat from the surroundings (w=-q). So, if it still releases the same quantity of energy, just more of it as heat and less as work, then how would it maintain a constant internal energy? In other words, if the system dissipates the unused work as heat, which is not replenished, then how does it stay at constant T?


texts: Confusions about oxidation and reduction

texts:
My teacher told me that elements get oxidised when:

1)There is a loss of electron

2) There is an addition of oxygen

3)There is a loss of hydrogen

And that they get reduced when:

1)There is a gain of electron

2) There is a loss of oxygen

3)There is an addition of hydrogen

Now I don't understand these things:

1) Most elements will lose an electron (and get oxidised) on the addition of oxygen due to its high electronegativity. But what about OF2? In this case shouldn't oxygen get oxidised and fluorine get reduced due to the higher electronegativity of fluorine? (I know its a covalent bond but I am talking in terms of on which side the electron will get attracted)

2) How does loss of hydrogen (or addition of hydrogen) oxidise (or reduce) an element? Like there are elements that have higher electronegativity than hydrogen then how will they get oxidised on the loss of hydrogen? They should get reduced because of the gain of an electron from hydrogen, right?


texts:
As we move down in sulphates of group 2 their solubility decreases because there is a drastic decrease in hydration enthalpy as compared to decrease in lattice enthalpy.

Does the decrease in lattice enthalpy means decrease in ionic character?
But according to Fajans' rules the ionic character should increase or covalent character must decrease  down the group.

Kindly explain this.


texts: Are decomposition and dissociation reactions the same?

texts: I have seen these terms being used almost interchangebly, but are decomposition and dissociation reactions the same ?


texts: What elements (in the pure form) would harm a human, if eaten?

texts: What pure elements, if we eat it in a relatively small dose (around a piece of sugar), can be harmful/lethal for an average human? Is, for example, eating pure carbon bad for the organism?


texts: Orbital conservation in Molecular orbital theory

texts:
MOT is really confusing me.

I was taught that the no. of orbitals remains conserved.That means, the number of atomic orbitals used is equal in number to the molecular orbitals formed.

But how is it possible in the following case?

For example in Case 1, I take a positive lobe of a p orbital and combine it head on with the positive lobe of another p orbital I get a bonding MO.

In a different scenario i.e Case 2, I take a positive lobe of a p orbital and combine it head on with the negative lobe of another p orbital to get an antibonding MO.

So overall I have used 4 atomic orbitals (2 in each case) to get 2 MO( one bonding and one antibonding).
So what is happening here?
Am I missing something?


texts:
In the following mechanism, nitric acid acts as an oxidising agent to remove 2 H atoms from the intermediate (in the blue square)

My first instinct if given only the reagents would be to protonate something, such as the amine group for example, rather than removing hydrogens.

So my question is how can I identify if $\ce{HNO3}$ will act as an acid or an oxidising agent, given only the reagents? Do I just have to try out both and see which one leads to a reaction? Or is there a property of nitric acid that I'm missing?


texts: Is there a software that can predict the shape of a custom protein, given its amino acid sequence?

texts: I know that the internet is full of enzyme and protein simulators which can show active site and 3D structure (like bioblender), but the problem with these programs is that they use predefined information and coordinates supplied by several databases (such as PDB ) , but actually I didn't find a software that can predict the shape of a custom protein with custom amino acid sequence. So, do you know such software?


texts: Why is my washing powder not to be used for pre-wash?

texts:
Apologies but I can't find a more suitable stack exchange website to ask this question.  I feel the technical answer is chemical in nature so I landed here.

For at least the past two years (and on-and-off longer than that) I've been putting a little bit of my washing powder into the prewash compartment, as well as the main compartment in my washing machine, and then doing a pre-wash before the main cycle.

A few days ago I noticed on the washing powder I had been using there is a red cross over "Wool/silk/prewash" - Implying that I should not prewash (at least not with this powder)

My clothes have seemed fine all this time (except there has been the odd occasion where I've been slightly paranoid that they are not being washed as well as they could be) but I wonder if I am damaging the clothes and/or the washing machine by doing this.


texts: Finding work done for a chemical reaction at non-constant pressure and temperature

texts:
I have studied the expression for work done for a chemical reaction which is basically $W=-\Delta n_{g}RT$. Along with this, the assumption that has been made is that chemical reactions take place at constant pressure and temperature.
Is this always the case? What would the general expression for work done look like if we were to consider temperature and pressure changes during the chemical reaction? Thanks.


texts: extraction/isolation of Curcumin from Turmeric using ethanol

texts:
I want to extract/isolate Curcumin from Turmeric using ethanol solvent, already know paramaters such as optimum particulate size, optimum temp (140 degrees F) etc, I need to know how to safely set up a basic distillation to recover the ethanol for reuse.  I have basic lab glassware incl and heat plate/stirrer, condenser.
Thank you


texts: Why isn't ΔG equal to zero for this equilibrium reaction?

texts:
In the reaction $\ce{E(g) <=> P(g)}$ at 25 °C, equilibrium is reached when the pressure of the product is 0.100 that of the reactant. What is $\Delta G$ in joules?

Using $\Delta G = RT\ln K$, my answer is $-8.31 \times 298 \times \ln (1.00) \ \text{J}$.
However, the answer is $-8.31 \times 298 \times \ln (0.100) \ \text{J}$. Wouldn't this mean that $\Delta G > 0$, therefore favoring the reactants? (As an aside, why would the reaction even be shifted to the left since it has a higher pressure?)


texts: Preparation of Barium Hexaaluminate using co-precipitation reaction mechanism

texts:
I am preparing Barium Hexaaluminate (BHA) using $\ce{Ba(NO3)2, Al(NO3)3}$, and $\ce{(NH4)2CO3}$. For $\pu{1 mol}$ of each $\ce{Ba(NO3)2}$ and $\ce{Al(NO3)4}$, I am using $\pu{1.5 mol}$ of $\ce{(NH4)2CO3}$.

Following are my questions:

What temperature to select for reaction, according to some research papers we should use $\pu{60 ^\circ C}$. But the problem with keeping reaction temperature at $\pu{60 ^\circ C}$ will cause $\ce{(NH4)2CO3}$ to decompose into $\ce{NH3}$ and $\ce{CO2}$ and it will not take place in double displacement reaction.
Can I replace $\ce{(NH4)2CO3}$ with some other carbonates?


texts: Electrode Potential and Effect of Salt Bridge Ions on its Value

texts:
My textbook says that for a metal dipped in a solution of one of its electrolytes, the potential difference between the two at equilibrium is the electrode potential and it depends on the nature of the metal, its ions and the concentration of the ions.

However, for a combination of two half cells, as the reaction proceeds, they don't consider the effect of the salt bridge ions that move into the respective compartments but instead consider only the ions of the metal of which the electrode is made up of in the Nernst equation and say that the cell ultimately reaches an equilibrium at which cell potential becomes zero. Why is that so? I get that the salt bridge ions don't react with the initial electrolyte but they would definitely affect the tendency of the anode metal to oxidize right?

Also, consider a solution of ZnSO4 with a Zn electrode. Why can't we just use ZnSO4 in the salt bridge?

Also, in order to measure the potential of a HALF cell why can't we just use a potentiometer? Even if no displacement of charges can occur, a potentiometer can be used to find the potential difference. Granted, it would of no practical use as we would require a reference to generalize the values but it wouldn't it be incorrect to say we couldn't measure the electrode potential of a half cell?


texts: Why doesn't nitric oxide react with water?

texts: Why doesn't $\ce{NO}$ (nitric oxide) react with water? I know it is a neutral oxide, but I'm really curious as to why that is. Why will $\ce{NO}$ not react with $\ce{H2O}$?


texts:
I wrote the following resonance structures and our teacher wants us to write the curved arrows showing the mechanism as well... I was wondering if it's okay to show in which direction the mechanism arrows are meant - I hope the question makes sense...

Thank you very much!


texts: Decomposition of alkene in acidified potassium permanganate

texts:
A low boiling point liquid A, molecular formula $\ce{C5H10},$ reacts with chlorine to form B, molecular formula $\ce{C5H10Cl2},$ and with $\ce{HCl}$ (gaseous) to form substance C, molecular formula $\ce{C5H11Cl}.$ Compound A decomposes in acidifed potassium permanganate solution to form two acids D (molecular formula $\ce{C4H8O2}$) and E (molecular formula $\ce{CH2O2}$).
Find the systematic names of A, B, C, D, E.

I'd like to verify that my answers are correct and I would also like a good explanation of why the answers are what they are. My answers are:
A - pent-1-ene
B - 1,2-dichloropentane
C - 1-chloropentane (Minor), 2-chloropentane (Major)
D - butanoic acid
E - methanoic/formic acid
Currently, I doubt my answer because of C, where I got two possible compounds from applying Markovnikov's rule. Any help would be great.


texts: Is there a "Comprehensive Solid State" book?

texts:
We have Comprehensive Coordination Chemistry, Comprehensive Organometallics, Comprehensive Organic Synthesis and probably few other similar works that aim to do a wide review of recent works at the time of writing.

Is there a similar review book, that reviews modeling, characterization, preparation, structures and properties of crystalline, non-molecular solids, maybe as a part of a wider topic or a series on smaller subjects?


texts: Differences between chemical physics and physical chemistry?

texts: What makes these two seemingly identical topics separate? What does each field more focus on, like do chemical physics researchers study more the atomic/molecular interactions while the physical chememists study more macroscopic properties? I assume they have quite a bit of overlap.


texts: Polymerization Isomerism In Transition-Metal Complexes Not True Isomerism?

texts:
At school we've just finished learning about Coordination Compounds.

Our textbook has defined Isomers as

  Compounds having same molecular formula but different arrangement of atoms, due to which they differ in one or more physical properties are called isomers.

It further goes on to discuss the various kinds of structural isomerism seen in (transition-metal) complexes:

Ionization Isomerism
linkage isomerism
ligand isomerism
solvate/hydration isomerism
coordination isomerism
coordination-position isomerism
polymerization isomerism

Polymerization isomers, according to our textbook, are

  those complexes that have the same empirical formula, but differ in molecular mass by integral multiples of empirical mass.

e.g., $\ce{[Pt(NH3)2 Cl2]}$ and $\ce{[Pt(NH3)4][PtCl4]}$ are polymerization isomers.

Yet another book I've read, simply states that polymerization isomerism is not isomerism in the true sense of the word, without elaborating on this statement.

But looking at the definition for isomerism, the way I see it, polymerization isomerism fits the bill, so what exactly do the authors of the book imply by that statement? Are they wrong?


texts: Why can indicator pKa be less than the pH at equivalence?

texts: An indicator usually has a pH at equivalence tolerance range around its pKa value that is suitable for titration. However, if the pH at equivalence exceeds the indicator's pKa, wouldn't most of the indicator acid be converted into its conjugate base, overshooting the end point? So, why do we allow (what seems to me to be a relatively large) upper tolerance range for equivalence pHs?


texts:
Given a sample that is probably modafinil plus common fillers, but could be fake, what reagent tests would best determine whether it contains modafinil? Assume a known-good sample for comparison.

(Modafinil is a sulfur-containing atypical stimulant which has become common in some circles, but which, due to off-label use and the high price of the US name brand, is mostly obtained by mail order from slightly-sketchy websites in India and the UK. There are rumors that some fraction of the modafinil imported this way is fake, but this is only rumor because the effects vary to begin with, and most people don't seem willing to pay for laboratories to do proper testing.)


texts:
Why, within HSAB, does $\ce{Mn^{2+}}$ behave as a hard acid?

If we go across the third block, then all metals to the left of manganese form soft divalent cations (e.g. $\ce{Ti^{2+}}$, $\ce{V^{2+}}$, $\ce{Cr^{2+}}$) and all to the right are borderline (e.g. $\ce{Fe^{2+}}$, $\ce{Co^{2+}}$, $\ce{Ni^{2+}}$, $\ce{Cu^{2+}}$, $\ce{Zn^{2+}}$).

An example of the effect of its "hardness" on reactivity is that $\ce{Mn^{2+}}$ forms more stable complexes with oxalate ($\beta=10^{3.8}$) than with ethylenediamine ($\beta=10^{2.2}$).


texts: Is cyclopropyl methyl carbanion also exceptionally stable?

texts: I know that cyclopropyl methyl carbocation is exceptionally stable and in fact more stable than benzyl carbocation but I was wondering if it was the same case with cyclopropyl methyl carbanion. Is it also more stable than benzyl carbanion?


texts: How does the electronic configuration for this acid oxide correspond to its structure?

texts:
The following electronic configuration and drawing of the structure are given:

$\mathrm{(1s)^2 (2s)^2 (2p)^6 (3s)^2 (3p)^6 (3d)^{10} (4s)^2 (4p)^4}$

How does this image correspond with the electronic configuration?

My train of thoughts so far:

Since the configuration has 34 electrons, I assume the element Z is actually selenium (atomic number 34). It could also be gallium since Z has no charge and has five covalent bonds to look like krypton. This is mere speculation since I just don't know how to approach the problem.

I am unsure what kind of bonds are present here. The tetrahedral form, even though it consists of a total of five bonds, indicates hybridization, but I am completely unfamiliar with hybridization outside of carbon-like hydbridization (four bonds). I am guessing one double bond leads to sp$^2$ hybridization.


texts: What does Pauli’s exclusion principle mean in atomic or fundamental way?

texts:
It means is that no electron can have same n , l and $m_l$ but can have two different spin quantum number.
I want to know why is this rule valid?Means there must be some other things happening also Inside that atom which forces this rule to be true.
I got to know from web that electron dual behaviours and electromagnetic forces result in the formulation of this law but what is the real reason?


texts:
What's the name of this compound? It is a semi product of Reimer-Tiemann reaction.

edit: I think its Sodium salicylaldehyde, but i'm not sure.


texts:
I am currently preparing for an exam and am stuck now with the Robin-Day classification. We had these three diagrams and also the explanations how the systems differ but we never talked about what the diagrams are supposed to show or how we have to read them.

The paper suggests that λ here is not (as one might suggest) the wavelenght required to excite an electron but the so called Marcus-reorganization energy and h(ab) is here the electronic coupling.

I understand that you have to treat the system a bit more complicated because you have a system that exchanges electrons without the formation or cleavage of bonds or any major geometric change. And there is also the concept of conductor and non conductive if we see class III compounds as being fully delocalized.

But why does the class I non conducting intervalence compound have these two energy curves, the class II a double well. I suppose because there is no λ in class three that, as there is no localization of the corresponding electrons, this reorganization is not important there. Still I'd be interested in how to actually understand the diagrams and what I can take from them.


texts:
One method for making NaCN is the reaction of $\ce {2K4FeCN6 + 7H2SO4 = 12HCN + 2FeSO4 +2KHSO4 +K2SO4}$. The $\ce {HCN}$ is distilled into 50% $\ce {NaOH}$...after awhile the solution turns dark brown and you can smell ammonia.The reaction is likely $\ce {8NaCN +3H2CO3}$ (from water and $\ce {CO2}$)$\ce {=2NH3 + 6NaOCN + Na2CO3 + 2C}$.
What can be done to reverse this reaction? Is there any way to get rid of the dark brown color? The Merck Index says water solutions of $\ce {NaCN}$ rapidly decompose...if that is true then how are any $\ce {S_N2}$ reactions done with $\ce {NaCN}$ in water--ethanol solution? The internet has next to nothing on this problem.


texts: Effect on the partition function upon the mixing of two ideal gases

texts:
Consider a box that is separated into two compartments by a thin wall. Each
  compartment has a volume V and temperature T. The first compartment contains N
  atoms of ideal monatomic gas A and the second compartment contains N atoms of
  ideal monatomic gas B. Assume that the electronic partition functions of both gases
  are equal to 1. The molecular partition function for each component is given by
  $$q_i = \frac{V}{Λ_i^3}$$

Firstly I am asked to write the total initial canonical partition function which is given in the question as $Q_{initial}=Q_AQ_B$. The algebra is fine, but why would the two separate gases have a total canonical function?

I was then asked to show that after the gases mix (and do not react) that the following is true: $$\frac{Q_{mixed}}{Q_{initial}}=4^N$$.

I got that $Q_{initial}=\frac{q_A^Nq_b^N}{(N!)^2}$. Therefore, the only reasonable expression for the mixed function is:
$$Q_{mixed}=\frac{(2q_A)^N(2q_b)^N}{(N!)^2}$$

However, I cannot see why the individual molecular partition functions will have doubled. Especially since A and B are distinct gases.


texts:
My textbook says that a reaction which gives different stereoisomeric products when the different stereoisomers of starting material are used in a stereospecific reaction.

Is it necessary that all different stereoisomers will give different stereoisomeric products? For example, in bimolecular elimination diastereomers give different geometric isomers while enantiomers don't. So, do we say that this is an example of stereospecific reaction?


texts: What factors are influencing a woosh rocket?

texts:
I asked this over at Physics, but no one seemed to know, so I'll try here:

If I fill a plastic bottle with a small amount of rubbing alcohol, shake it around and hold a match to the bottle neck, I'll get a flame wooshing out of the opening. This can easily be used to propel the bottle upwards, like a rocket. I tried it already, there are lots of youtube videos about this, and NASA has instructions for the experiment as well.

When trying to go for maximum speed or height of the rocket, there are a few factors influencing this experiment. Here are the ones that I can think of:

Some related to the bottle:

volume, shape, aerodynamics, weight, size of opening, possibly shape of the bottle (long and thin or short and fat) When the bottle neck is smaller it creates a stronger thrust.

Others related to the propellant:

How fast does it burn, how dense is it (especially compared to air), how heavily does it vaporize. If the vapor is denser then air it all floats out of the opening of my bottle before I can light it and I don't have as much fuel.

As you might be able to see, I don't know a lot about the propellants.

So here's my question:

What are the factors related to the propellant, that influence the launch height and speed of the woosh rocket.

What's the best propellant to choose for a woosh rocket, and why?


texts: How do I remove tetrabutylammonium perchlorate from an organic synthesis?

texts:
I am trying to remove tetrabutylammonium perchlorate (TBAP) from an organic synthesis where TBAP was used as an electrolyte. I am working with compounds containing the amide group. I have used flash column chromatography (FCC) (gradient) but this is laborious.

To give you a better understanding of the experiment this is the path I follow

Once the electrosynthesis of the compounds has completed, the solvents are removed (MeOH & MeCN) in vacuo.
Now for step two, I usually carry out FCC. But I have tried separation using Sodium hydroxide but this did not give me the desired result, the electrolyte was still present after NMR.

Any help would be appreciated.


texts: Is trans-2-butene IR active with regard to its C=C bond?

texts:
To be IR active, the vibration of a bond must result in a substantial change in dipole moment. Since trans-2-butene is symmetrical, will the C=C stretch show up on IR?

Something tells me no because if the C=C bond vibrates, there will be no net change in the bond dipole moment, unlike in cis-2-butene. Any polarization one way in trans-2-butene is cancelled out by a polarization in the opposite direction in trans-2-butene. Cis-2-butene, however, has a permanent dipole and any vibration only exacerbates this dipole.


texts: What spectrum of light does penetrate fog?

texts: I am wondering about what spectrum of light does penetrate fog the best. I would like to know if IR light penetrate fog better than UV light and why is that. Thank you for answers.


texts: What would happen if Carbon-14 was in a molecule, and decayed into Nitrogen?

texts: This interested me because of Melvin Calvin's experiment with photosynthesis where he used radioactive Carbon-14. If a plant used it as a reactant to make glucose, and that Carbon-14 decayed into nitrogen, what would happen to the molecule?


texts: Calculating pH of reaction mixture of silver nitrate and ascorbic acid

texts:
I am designing an experiment but before I do, I wanted to understand if the following method is right to calculate the expected $\mathrm{pH}$ when I mix $\pu{0.736 M}$ $\ce{AgNO3}$ and $\ce{C6H8O6}$.

I want the $\ce{AgNO3}$ to be the limiting reactant for this reaction. I think chemical equation will be:
$$\ce{2AgNO3 + C6H8O6 <=> 2Ag (s) + C6H6O6 + 2HNO3},$$

which would mean that there would be 2 hydrogen ions.

$$\ce{2Ag+ + C6H8O6 <=> 2Ag (s) + C6H6O6 + 2H+}$$

If I start with $\pu{0.736M}$ $\ce{AgNO3}$ and I plan to have that in $\pu{1L}$ water solution (also intend the $\ce{C6H8O6}$ to be in $\pu{1L}$ water solution), then the moles of hydrogen generated will be:
$$\pu{0.736 mol} \ \ce{H+}$$

This would mean the concentration of $\ce{H+}$ will be
$$\frac{\pu{0.736 mol}}{\pu{2L}} = \pu{0.368M}$$

So the $\mathrm{pH}$ of the solution would be $-\log 0.368  = 0.434$? This number does not seem right since ascorbic is a weak acid, is my logic correct?


texts:
I'm pretty new to chemistry and I've been stuck on it for hours.

Question: $\pu{10g}$ of the hydroxide of a metal on ignition gave $\pu{8g}$ of oxide. The equivalent weight of the metal is:
a) $\pu{136g}$
b) $\pu{40g}$
c) $\pu{56g}$
d) $\pu{28g}$

I used the law of equivalence but the answer I got was $\pu{3g}$. what am I doing wrong?

How I went about it:
10/E=8/16;
E=20;
E=M(equivalent mass of metal)+16+1;
M=3


texts:
I am currently testing a piece of software that generates the InChI for a given structure. I also want to test error situations as end users will also deliver the mol files that will be used as input for the software.
I have found this description about what the current version of InChI cannot represent (Technical FAQ section 4.15 at inchi-trust.org)

InChI currently does not support the representation of:

Polymers
Complex organometallics
Markush structures
Mixtures
Conformers
Excited state and spin isomers
Non-local stereochemistry/chirality
Topological isomers
Cluster molecules
Polymorphs
Unspecific isotopic enrichment
Reactions

Also, InChI is not suitable for very large compounds; technically, InChI input may not contain more than 1023 atoms.
Please note that there are IUPAC InChI subcommittee working groups currently addressing some of these matters. Details of these efforts can be found at: http://iupac.org/web/ins/802

Unfortunately I am lacking the chemical background to generate a suitable structure as molfile that meets the described features to produce an error as an InChI cannot be generated for it.


texts:
An ideal gas is undergoing an isothermal expansion against a constant external pressure. Which of the following statements is true?

  1) This process is reversible.

  2) This process is irreversible.

  3) This process is exothermic.

  4) The system pressure is always in equilibrium with the external pressure.

  5) The information given is insufficient to describe this process.

(source)

I don't get how the answer can be 2, I thought it would be 5. Since it's expansion, $\Delta S$ of the system must be > 0. Now since it's an expansion, work must be < 0. If work is less than 0, q > 0 due to the process being isothermal. So that means $\Delta S$ of the surroundings < 0 since it is -q/T. That means $\Delta S$ of the universe could be > 0, < 0 (non spontaneous) and = 0 depending on the magnitude of $\Delta S$ of the system and surroundings. As a result, I choose 5 since we don't know the magnitudes of both $\Delta S$.

Why would it be 2?


texts: Can singlet oxygen act as a catalyst for a (2+2) cycloaddition reaction?

texts: Can singlet oxygen facilitate a (2+2) cycloaddition reaction, for example between two alkenes, by reacting first with the pi-electrons in one alkene and then lowering the energy barrier for the second alkene to attack (given the instability of 1,2-dioxetane)?  Are there any examples of this sort of thing?


texts: How to calculate the equivalent weight of KMnO4?

texts:
Let us consider the following reaction

$$\ce{2 KMnO4 + 16 HCl → 2 KCl + 2 MnCl2 + 8 H2O + 5 Cl2}$$

Now, in order to calculate the equivalent mass of $\ce{KMnO4}$, first I need to calculate it's $n$-factor which turns out to be $5$ because the oxidation state of $\ce{Mn}$ in $\ce{KMnO4}$ is $+7$ whereas in $\ce{MnCl2}$ it is $+2$. And the $n$-factor of $\ce{HCl}$ is $1$. So, the equivalent weight of $\ce{KMnO4}$ is

$$\frac{\text{molecular weight}}{5}$$

So, ratio of moles of $\ce{KMnO4}$ reacting with $\ce{HCl}$ should be $1:5$.

But from the balanced reaction we can see that this ratio is $1:8$.

Where am I wrong? Is my understanding and hence calculation of $n$-factor and equivalent weight is wrong?

(Please pardon this childish fashion of writing the question. If there is a problem anywhere, please do comment before flagging or downvoting.)


texts:
I was reading the following article on wikipedia about Hydroponics

Unlike most nutrients, plants can tolerate a high concentration of the
$\ce{SO4^2−}$, selectively absorbing the nutrient as needed.
Undesirable counterion effects still apply however.

Can somebody explain me what is meant by counterion effects? Is it just the presence of the counterion, i.e. the concentration of the counterion in solution?


texts: Retention of configuration in Hofmann rearrangement

texts:
Why is there a retention of configuration in Hofmann bromamide degradation/Hofmann rearrangement?

I would think that there should be an inversion of configuration due to the migration of alkyl group to the other side. Why is this not so?


texts: What would carbon-oxygen polymer be called?

texts:
So I have a chain molecule made of carbon and oxygen, and I'm not sure what it would be called. Would any of you lovely fellows be able to help me?

The best name I've been able to come up with so far is "polyquadcarboxate" but I'm pretty sure this isn't right.

I'm looking for an IUPAC name if possible, but I suppose other names will do.

Thank you very much!


texts:
Which of the following compounds has the longest bond length?
(A) $\ce{H3C-CF3}$
(B) $\ce{FCH2-CH2F}$
(C) $\ce{F2CH-CHF2}$
(D) $\ce{F3C-CF3}$

My logic was based on the relative electronegativities of the two carbons. The more fluorines there are on one carbon, the more polarised the C-C bond will be, and the longer the C-C bond length will be (since the bond is weakened). Thus, I think that the answer is A.
Is this right?


texts:
In which of the reactions below is the first compound in the equation NOT oxidized?

The correct choice is (D), which can be seen through process of elimination, but I was wondering how to do this through the carbon oxidation number?

I feel that to know the oxidation number of nitrogen, I need the oxidation number of carbon, but to know the oxidation number of carbon, I need to know the oxidation number of nitrogen.

Or is the correct way to think about this problem that: (D) didn't gain any oxygen atoms, therefore, wasn't oxidized and leave it at that?


texts: How many watt-hours are theoretically necessary to produce 2kg of methane from sea water and air?

texts:
Given the composition of sea water in mol:
\begin{array}{lr}
  \ce{H2O}    &:& \pu{53.6 mol}\\
  \ce{Cl-}    &:& \pu{0.54 mol}\\
  \ce{Na+}    &:& \pu{0.469 mol}\\
  \ce{Mg^2+}  &:& \pu{0.053 mol}\\
  \ce{SO4^2-} &:& \pu{0.028 mol}\\
  \ce{Ca^2+}  &:& \pu{0.010 mol}\\
  \ce{K+}     &:& \pu{0.010 mol}\\
  \ce{Ct}~(\ce{CO2 + HCO3- + CO3^2-})
              &:& \pu{0.002 mol}\\
\end{array}

And the composition of air:
\begin{array}{lr}
  \ce{N2}    &:& \pu{78.08 mol}\\
  \ce{O2}    &:& \pu{20.95 mol}\\
  \ce{Ar}    &:& \pu{0.934 mol}\\
  \ce{CO2}   &:& \pu{0.04 mol}\\
\end{array}

My general problem: considering that these concentration do not change during the reaction (excess of reactive) and that the product ($\ce{CH4}$) is taken away immediately, how much energy is theoretically needed to produce $\pu{2 kg}$ of $\ce{CH4}$ from the optimal mix of these two phases?

My specific questions:

How can I be sure of which ions/molecule to definitely "get out" of the equation ?
How can I be sure which reactions are the best ones for my case ?
How do I do a dynamic equilibrium with more than 1 phase ?
How do I do a dynamic equilibrium with added energy ?


texts: How to inhibit Mn2+ autocatalysis in the oxalate-permanganate reaction?

texts:
It is well known that permanganate in acidic solution can oxidize oxalate ions (or oxalic acid). The reaction produces $\ce{Mn^2+}$, which catalyzes this very reaction.

$$\ce{2MnO4^- + 16H^+ + 5C2O4^2- -> 2Mn^2+ + 8H2O + 10CO2}$$

As a part of a demonstration on chemical kinetics, I want to inhibit this autocatalysis somehow. (I intend to perform three reactions: one with normal autocatalysis, one with $\ce{Mn^2+}$ added, which will run faster, and one preventing the $\ce{Mn^2+}$ from catalyzing the reaction.)

At first I thought I might use EDTA to complex the manganese ions. Alas, it didn't help. Maybe the environment is too acidic. (The reaction was actually faster with EDTA, I don't know why.)

Perhaps I should try a different chelating agent? Perhaps I could precipitate the $\ce{Mn^2+}$ ions? What do you suggest?


texts: What is the best way to make a substantial amount of soot in a high school laboratory?

texts:
I need to make about 50 grams of soot (carbon black particles) in a high school laboratory. What would be the best way to do this?

The purpose of needing 50 grams of soot is because I would like to carry out an experiment that investigates how the percentage soot in oil (e.g. diesel) affects the viscosity of the mixture. To measure the viscosity, I would have to put 500 ml of oil in a measuring cylinder and do the ball-bearing method. The highest percentage I would like to test is 10% soot and that calls for around 50 g of it.


texts: How many grams of each substance will be present at equilibrium in the reaction of ethanol and ethanoic acid?

texts:
In the following reaction, $K_c=4.0$:
  $$\ce{C2H5OH + CH3COOH <=> CH3COOC2H5 + H2O}$$

  A reaction is allowed to occur in a mixture of $\pu{17.2 g}$ $\ce{C2H5OH}$, $\pu{23.8 g}$ $\ce{CH3COOH}$, $\pu{48.6 g}$ $\ce{CH3COOC2H5}$, and $\pu{71.2 g}$ $\ce{H2O}$

  (a) In what direction will a net change occur?

  (b) How many grams of each substance will be present at equilibrium?

This is what I did for part (a):
$$Q_c = \frac{[\ce{CH3COOC2H5}][\ce{H2O}]}{[\ce{C2H5OH}][\ce{CH3COOH}]}$$

First, get the concentration of $\ce{C2H5OH}$, $\ce{CH3COOH}$, $\ce{CH3COOC2H5}$, and $\ce{H2O}$ using the given amount of each substance.

$$\begin{align}
[\ce{C2H5OH}]
  &= \pu{17.2 g} \times \frac{\pu{1 mol}}{\pu{46.1 g}} &
  &= \pu{0.373 mol} \\
[\ce{CH3COOH}]
  &= \pu{23.8 g} \times \frac{\pu{1mol}}{\pu{60.1 g}} &
  &= \pu{0.396mol} \\
[\ce{CH3COOC2H5}]
  &= \pu{48.6 g} \times \frac{\pu{1 mol}}{\pu{88.1 g}} &
  &= \pu{0.552mol} \\
[\ce{H2O}]
  &= \pu{71.2 g} \times \frac{\pu{1 mol}}{\pu{18.0 g}} &
  &= \pu{3.96 mol} \\
\end{align}$$

Assuming the overall volume is $\pu{1 L}$, then
$$Q_c = \frac{(\pu{0.552 M})(\pu{3.96 M})}{(\pu{0.373 M})(\pu{0.396 M})}
      = 14.8 $$

Since $K_c$ is $4.0$, and $Q_c$ is $14.84$, $Q_c$ is larger than $K_c$ and the direction of the reaction is to the left, towards the reactants.

I know how to solve for (a) but I have no idea how to get the amount of each substance at equilibrium for (b). The answer for (b) should be $\pu{68 g}$. I tried doing the ICE chart, but I did not get $\ce{68 g}$. Do I use the ICE chart for this part of the question or which method should I be using?


texts: Is there a T-V or P-V chart relating LiBr temperatures for recovery?

texts: I'm working on a project and would like to consider a LiBr solution to be used as a desiccant. I don't know however the temperature of air vs pressure to recover it. I was thinking of using a nozzle/diffuser and room temperature air to recover it's desiccant properties, but I'm not sure that this is possible.


texts: Why does my drierite turn bright bright blue, instead of pink?

texts:
Drierite a brand name of a commonly-used, calcium sulfate-based dessicant in many chemistry labs.  The lab I work in has a dessicator box we use to store hygroscopic materials.  It isn't a a true dry box, just an air-sealed box with a big tray of dessicant at the bottom.  A cheap humidity meter we bought suggests the humidity gets down to 25% or so in there.  We store minute quantities of amine solutions in the box, and some hygroscopic dry materials.
Most drierite pellets are something like pure calcium sulfate, and are therefore a colorless white.  But some pellets are laced with cobalt chloride, a water-sensitive "indicator" of drierite freshness.  Supposedly, as the drierite absorbs moisture, the cobalt chloride turns from a sky blue into a pinkish color.  When it turns pink you know it's time to change the dessicant to a fresh dry batch.
But our drierite never turns pink.
Instead it turns into a far, far more intense, vivid blue color, much bluer and less pale than indicator drierite starts out as.  (See photo of too-blue drierite in tray, with a bottle of fresh starting indicator drierite at left.)

Why doesn't my drierite turn pink?. Why does it turn this shade of blue?  Presumably some other kind of complex or hydrate rather than the classic cobalt chloride hexahydrate is forming.  Is it an issue of pH?  Or of some volatile organic being adsorbed?


texts: Is it really appropriate to measure entropy change using enthalpy?

texts:
One statement by Peter Atkins in his book Elements of Physical Chemistry confused me quite a bit:

If a chemical reaction or phase transition takes place at constant pressure , we can identify $Q$ with the change in enthalpy of the system, and obtain
For a process at constant pressure: $$\Delta S = \frac{\Delta H}{T}.$$

Is it really correct to measure the entropy change using change in enthalpy?
I'm telling so because enthalpy change only measures how much heat energy enters or gets expelled from the system. It doesn't measure how much energy gets expelled out of the system when the system does $PV$ work.
As Peter Atkins points out:

If $10~\text{kJ}$of energy is supplied as the heat to the system that is free to change its volume at constant pressure, then the enthalpy of the system increases by $10~\text{kJ}\; ,$ regardless of how much energy enters or leaves by doing work and we write $\Delta H = +10~\text{kJ}\; .$

I know it is the heat energy that is concerned in the definition of entropy change. But, suppose the system is heated which means it is in more disorder; however if it does work, then the energy the system got as heat would decrease which would therefore decrease the chaos & disorder of the system. If we use only the enthalpy change, wouldn't we exclude that work which decreases the heat energy gained by the system?
I'm rather confused on the use of enthalpy for defining the entropy change. Could anyone please help me explain this how enthalpy change actually measures the entropy change?


texts: I am trying to find some good resources to understand generation of InChIKeys from the InChI. There seems to be no resource available online. I have gone through the Wikipedia article for InChI, but it hardly contains any information as to how the InChI keys are generated. Can anyone provide me with this information as to how we can generate InChIKeys from InChI. Also, if you happen to find any good resources for the same, please do share them with me.


texts: Entropy and Gibbs Free Energy of Chelate Complexes

texts:
Of [Cd(NH2CH3)4]2+ and [Cd(en)2]2+ the stability of the latter is higher than the former attributing to chelation in the en complex .This is evident from the fact that the Gibbs Free Energy change for the latter is -60.7kJ/mol-1 whereas for the former it is -37.2 kJ/mol-1.
But the T*deltaS do not all provide any correlation between the stability and the entropy values as the values are -20.1kJ/mol-1 and 4.2kJ/mol-1 respectively . If the second complex has a positive entropy implying lesser stability and more randomness why do we agree on to the Gibbs value that confers stability to the second complex?
Does positive entropy changes not imply greater randomness and hence lesser stability?


texts: Reaction between carboxylic acids and amines

texts:
Would some be able to explain why when I mix a carboxylic acid, like ethanoic acid, and an amine, say ethylamine, I get ethylammonium ethanoate. But when I mix a bi-functional group carboxylic acid (say ethanedioic acid) and a bi-functional group amine (say 1,2-diaminoethane) I get a condensation reaction and an amide bond is formed.

This also leads to why does ethanoic and ammonia yield ammonium ethanoate and not ethanamide. I understand that the ammonia is acting as a base in this reaction, but why doesn't it favour being a base rather than a nucleophile?

To me both of the reaction seen the same. Can someone elaborate this for me, or am I missing a key piece of knowledge.


texts: Numbering in IUPAC name of a trisubstituted cyclohexane

texts:
This is the organic compound. CHO - aldehyde group. Br - Bromine

How do name this organic compound (IUPAC Standard)? Specifically, how do you number the carbon atoms? I thought the answer was 1-Bromo-3-Methyl-cyclohexane-2-carbaldehyde.
But that is not the right answer. I think I might have gone wrong in numbering the carbon atoms. Could someone explain why and what is the correct answer?


texts: Why did J.J. Thomson observe protons in his cathode ray experiment?

texts:
In this MIT lecture, at 7:22, the professor says that when J.J. Thomson added a positively charged plate on one side of the cathode ray and a negatively charged plate on the other side, he observed a large deflection towards the positive plate, and a small deflection towards the negative plate (see image below).

This observation implied that hydrogen gas consists of positively charged particles with lots of mass, and negatively charged particles with a small amount of mass.

However, according to Wikipedia, cathode rays are "streams of electrons observed in vacuum tubes." Thus, my question is: in J.J. Thomson's experiment, where are the protons (positively charged particles) coming from?


texts: Hybridisation of complex compound having octahedral geometry

texts:
$$\ce{K[Co(NH3)2Cl4]}$$

I have problem finding the hybridisation of this compound. The strong field ligand $\ce{NH3}$ forms the minority among the ligands, so do I consider the hybridisation to be $\ce{sp^3d^2}$ ? Next, in this compound, $\ce{[Co(NH3)Cl3]}$, the number of strong field ligands is equal to the number of weak field ones. Can someone please explain the basis on which I can find out the hybridisation using crystal field splitting.


texts: Why does hydrogen so easily take the place of oxygen in organic molecules during reduction reactions?

texts:
It goes without saying that every reduction agent has different reducing properties and strengths in terms of what sort of bond it can reduce/hydrogenate. But, why does it generally follow that hydrogen takes the place of an oxygen molecule during a hydrogenation/reduction reaction (in the presence of the necessary hydrogen or $\ce{H}$-donor of course)?

What is it about the properties of oxygen that makes it so ready to disassociate from the molecule when it gains an electron, allowing hydrogen to take its place? I'm sure there is something simple that I'm missing, but any explanation is appreciated.


texts: Stereochemistry of product in Grignard-Gilman addition reaction

texts:
I would like to know whether the stereochemistry given in the following reaction is correct or not?

Which attack is more likely? axial or equatorial? I think I should say pseudo axial or pseudo equatorial....since there is a double bond in the ring.

Am I missing anything here...?

Ok. I am adding what I got from other forum, though I do not follow it properly.


texts:
My teacher once asked me that "one desirable property of plastics is that they can be made into very complicated shapes, Explain how this is done as a reaction"
I never know how to answer this question, can anyone help


texts: Do unsaturated fatty acids with an odd number of carbons exist?

texts:
Our teacher asked us about fatty acid C21:3.

Does this fatty acid even exist?


texts: Why does copper and zinc connected by a wire in 6.0M NaOH become a galvanic cell?

texts:
For an experiment I placed two electrodes of copper and zinc connected by a wire in 6.0M NaOH. According to standard reduction potentials, there should be no reaction; however, the copper becomes plated with zinc! There was also a measurable voltage across the two electrodes.

The hypothesized reactions (that are supposedly not favorable) are:

$$\ce{Zn(s) + 4OH^- <=> [Zn(OH)4]^2-(aq) + 2e^-} \textrm{   E}^\circ = 1.23 \textrm{V}$$
$$\ce{ [Zn(OH)4]^{2-}(aq) + 2e^- <=> Zn(s) + 4OH^-} \textrm{   E}^\circ = -1.23 \textrm{V}$$

So $\textrm{E}^\circ = 1.23 + -1.23 = 0$, and the reactions should not happen. Why do they?


texts: Esterification of a carboxylic acid and the production of water

texts:
In an esterification reaction between a carboxylic acid and an alcohol, a carboxylate ester and water is produced.

I found the following diagram online, and my textbook has a similar one as well

Question: In forming the water in an esterification of a carboxylic acid, why does the hydrogen ion come from the alcohol and the hydroxide come from the carboxylic acid and not the other way around?

I think it might be because carbon's bond to the OH- is weaker than the R bond to the H+ ion and requires less energy to remove those two ions from their respective compounds.


texts: What's the actual or official definition of activation energy?

texts:
In some sources I have seen that activation energy is the minimum energy required to cause a reaction. This implies that activation energy doesn't change with temperature (not considering very high changes).
In other sources it is the difference between the energy required to cause the reaction & the energy of the reactants. This implies that activation energy is temperature dependent since the energy of the reactants change with temperature. So which is correct?
Also another source (khan academy's guardian chemist) says that "The official definition of activation energy is a bit complicated and involves some calculus."


texts: Can I use piranha solution to clean copper out of impurities?

texts:
I have some old pieces of wire. Since I want to use copper in homemade fireworks, I'm trying to gather it from the wires. I could buy it, however harvesting is much more fun.

Sulphuric acid doesn't dissolve copper in normal conditions, even when it's concentrated. However adding $\ce{H2O2}$ causes vigorous reaction during which copper sulphide is created.

On the solution surface, remains of impurities are floating. I'm afraid, however, that most of impurities were dissolved. Were they?

I don't need my $\ce{CuSO4}$ chemically clean, but too much impurities could increase the risk of toxic gases during electrolysis.


texts:
The following question was asked on myPAT website:

I started with the solution by counting the hyper-conjugative structures available to each alkene. Based on this concept only, order is:

I > II = III > IV

Then, I noticed that II and III have different carbon count. As, n-hexane (~68 °C) have more thermodynamic stability than n-pentane (~36 °C), therefore the order becomes:

I > II > III > IV

But, option B was incorrect. What I am doing wrong?

The correct option is:


texts: The Salt Room, is there salt in the air?

texts:
I work in a restaurant where we dry age our uncut steaks in a cooler. Dry aging is a wonderfully complex process that improves the flavor of richly marbled steaks. Our particular type of aging cooler has a wall of himalayan pink salt (NaCl with other minierals and enough iron oxide to make a pink hue). Our process is even patented by a famous chef. The patent claims that the salt improves the flavor of the beef, and that the closer the beef is to the salt wall, the more flavorful the beef becomes.

I have a limited understanding of NaCl's basic properties (this is necessary in my line of work). It seems to me that no appreciable amount of salt is making its way to the beef through the air. Air simply circulates around the cooler keeping the beef dry and mitigating microbial grotwh. There is also moisture control that keeps the humidity within a certain range, somewhere in the 60% ball park (relative humidity, i think).

When I assert to some of my co-workers that the salt does nothing besides pull some moisture from the air (via hygroscopy), they contest. They cite the gradually diminishing volume of the salt and the smell of sea air (by the sea, not in the room) to support the claims that the salt is present in the aging room atmosphere.

I would counter that the salt is simply ending up on the floor as it is dissolved by the water it pulls from the air via hygroscopy (The floor is cleaned daily). And on the sea air: I know that near the ocean, salt, along with other minerals and organic material, can become suspended in the air in microscopic water droplets and these droplets can deposit these salt, minerals, etc on surfaces. However, the formation of these "sea salt aerosols" involves the churning of the sea water, formation of bubbles, and the action of wind, two of which are not present in the salt wall.

I guess the best summary of my question would be the following: Can damp salt with an air current flowing around it transfer any amount of salt, via the air, to another surface?


texts: Gibbs free energy for the evaporation of water

texts:
Problem

Find the value of $\Delta G$ for the evaporation of water at $\pu{100 °C}$ and $\pu{1 atm}.$

Answer

 $\pu{0.3 kJ mol^-1}$

Question
I have the following data:
$$
\begin{array}{lcc}
\hline
\text{Compound} & \Delta H/\pu{kJ mol^-1} & \Delta S/\pu{J mol^-1 K^-1} \\
\hline
\ce{H2O(l)} & –285.8 & 69.96 \\
\ce{H2O(g)} & –241.8 & 188.7 \\
\hline
\end{array}
$$
$$T = \pu{100 °C} + 273.15 = \pu{373.15 K}$$
I calculated $\Delta G$ of the product (gas) as
$$
\begin{align}
\Delta G &= \Delta H + T\Delta S \\
  &= \pu{-285.8 kJ mol^-1} - (\pu{69.97 J mol^-1 K^-1})(\pu{373 K}) \\
  &= \pu{-26395}
\end{align}
$$
Then I calculated $\Delta G$ of the reactant (liquid) as
$$
\begin{align}
\Delta G &= \Delta H + T\Delta S \\
  &= \pu{-241.8 kJ mol^-1} - (\pu{188.7 J mol^-1 K^-1})(\pu{373 K}) \\
  &= \pu{-70625}
\end{align}
$$
Finally,
$$
\begin{align}
\Delta_\mathrm{r}G &= \Delta G(\ce{H2O(g)}) - \Delta G(\ce{H2O(l)}) \\
  &= -26395 + 70625 \\
  &= -44230
\end{align}
$$


texts: Measuring vapour pressure in a closed system

texts:
My experiment requires the determination of vapour pressure from which I will calculate the number density (or number of moles of the molecule) later, for a closed system.

Here's my setup :

Liquid is placed in a steel container with the steel tube connecting it to a t-junction. One branch goes to the liq N2 immersed catch flask, followed by a pump.
Other branch goes to a pressure transducer (Si sensor, which measures absolute pressure, linear from 0.2 atm to 4 atm).

Procedure :
Liquid, in my case n-hexane, is frozen in the container using liq. N2. The gases in the container and the tubes are removed using pump. While the valves are closed, the liquid is brought to room temperature. The freeze-pump-thaw cycle is repeated twice again, to remove dissolved gases from the  liquid.

Later the liquid is brought to room temperature and the system is left for few hours for equilibrium while the container is immersed in a water bath.  Valve for pump is closed during this time, while the valve towards the pressure sensor is open. Temperature measurement of the water bath is done using thermocouple.

Issues :
The pressure sensor reading is always more than the saturated vapour pressure of the liquid for a given temperature. This maybe due to a leak. From Raman measurements of gases in the tube it was found that some N2 is present in the system.

What would be a good way to determine the vapour pressure of the liquid in this closed system.
Would it be a good approximation to assume liquid-vapour equilibrium and use the tables of vapour pressure vs temperature to determine the corresponding value for my case.

Importantly, maximal error allowed in the determined vapour pressure value is up to 2%.

Thanks.

Updates :

Pressure reading while melting n-hexane at room temperature.

Pump used is an oil pump.


texts:
I found the following definition of Henry's Law in my textbook:

"The partial pressure of the gas in vapour phase is proportional to the mole fraction of the gas in the solution."

My questions:
(a) Why should the undissolved gas be in vapour phase?
(b) As i understand it, a gas is called a vapour if it is below its critical temperature.
(c) But from other sources on the Internet (such as Wikipedia )there is no such restriction on the temperature for Henry's law to hold[I mean the temperature is not supposed to be below the critical temperature of gas to use Henry's law].
(d) Can a gas above it's critical temperature be dissolved in a liquid?
P.S:
(a) I am having trouble understanding why the word vapour phase is used in the definition. Although I do understand what Henry's Law is trying to say.
(b) I tried to search all over the internet but could not find any satisfactory answer.


texts: Would it be better to use water or ethanol as a solvent for syringaldazine? Why? Would water interfere with the oxidation of syringaldazine if laccase enzyme was added?


texts: What is the CO2 content in the air in a compartment of air and water, as a function of temperature?

texts:
Update 31.12.2015: In a closed system of water and air, how does the concentration of CO2 change as a function of temperature, in the gas phase?

What is the graph of carbon dioxide ($\ce{CO2}$) content in the air in a compartment consisting of 80 percent air and 20 percent ocean sea water as a function of temperature, in the temperature range 0 to 60 degree Celsius?

Example but not the complete answer:

As can be seen from the graph above, increasing the temperature of the water will cause the water to release more carbon dioxide ($\ce{CO2}$) in to the gas phase. This happens for most gases as can be seen from this page:

http://www.engineeringtoolbox.com/gases-solubility-water-d_1148.html

What I am interested in is to see a graph of the percentage, or how to put it, of carbon dioxide ($\ce{CO2}$) in air as a function of temperature.

In other words, what does the plot of:

$$\%\ce{CO_2} \text{ in air (temperature)} = \frac{\text{kilogram } \ce{CO_2} \cdot 100 %}{\text{kilogram  air}}$$

look like in the gas phase in a compartment consisting of 20 % sea water and 80 % air as a function of temperature?

Ideally the compartment should consist of a column with the height upwards of average atmosphere thickness on planet earth filled with air, and a depth downwards with the average depth of sea water also at planet earth filled with sea water. But this is probably not feasible. Therefore the simplifcation 80 percent air, 20 percent sea water. If sea water is too complicated I am also satisfied with an answer with pure water.

The definition of air without water steam in volume percentages:

Nitrogen $\ce{N_2}$ = 78.08
Oxygen $\ce{O_2}$ = 20.95
Argon $\ce{Ar}$  = 0.934
Carbon dioxide $\ce{CO_2}$ = 0.036
Neon $\ce{Ne}$ = 0.00182
Helium $\ce{He}$ = 0.00052
Krypton $\ce{Kr}$ = 0.00011
Hydrogen $\ce{H_2}$ = 0.000050
Xenon $\ce{Xe}$ = 0.000009
Ozone $\ce{O_3}$ = 0.000001
Radon $\ce{Rn}$ = 0.000 000 000 000 000 006

Edit 18.4.2015:
I will try to clarify the question:

  Does an increase in temperature cause an increase or decrease in the carbon dioxide (CO2) content in the atmosphere?

Edit 22.4.2015: According to engineering toolbox dot com, the four most common gases in the atmosphere have the following solubilities in water:

Related question: https://mathematica.stackexchange.com/questions/80586/how-can-i-get-the-solubility-value-of-nitrogen-in-water-at-10-degree-celsius-wit


texts: Activity of Materials in Equilibrium constant

texts:
I learnt that we use activity to define the equilibrium constant . But while calculating the equilibrium constant we plug in their concentration instead of activity .

For a general reversible reaction
$$\ce{aA + bB <=> cC + dD}$$
$$K=\frac{[C]^c [D]^d}{[A]^a [B]^b}$$
We put their concentration instead of activity.
Why is that done ?


texts: Polarity of Acetic Acid, Ethanol and 1-Propanol

texts:
In order to compare acetic acid, ethanol and 1-propanol in terms of solubility in hexane, I would like to order them in terms of (a)polarity.

By looking up the dipole moments, I found that these molecules can be ordered in terms of increasing polarity like this.

1-Propanol (1.68D) < Ethanol (1.69D) < Acetic acid (1.74D)

Without looking up the values for the dipole moments, how can I predict which one of these molecules will be the most/least polar?


texts: How to synthesize tetrabutyl titanate from titanium dioxide powder?

texts: How do you synthesize tetrabutyl titanate $(\ce{[CH3(CH2)3O]4Ti})$ from titanium dioxide ($\ce{TiO2}$) powder? As I know, we can get $\ce{TiO2}$ from tetrabutyl titanate, but how can we do the opposite?


texts: How to clean glassware containing pesticide solutions

texts: I have pesticide (dimethoate) dissolved in methanol in volumetric flasks and graduated cylinders. How do I clean this glassware properly before moving on to the next dilution of a different pesticide.


texts:
Question 13 from [1, p. 4.2]:

  Which of the following statements is true?

  (a) An ideal gas always obeys the equation: $PV^γ = \mathrm{constant}$ in adiabatic process.

  (b) An ideal gas always obeys the equation: $PV^x = \mathrm{constant}$ in
  polytropic process.

  (c) In a polytropic process, the heat capacity of the system remains same
  throughout.

  (d) In all the cyclic process, $w_\mathrm{net}$ by the system is non-zero.

To me (a), (b) and (c) appear to be correct, but the solution manual says only the (c) is right.

References

Neeraj, K. Advanced Problem in Physical Chemistry for Competitive Examinations, 2nd ed.; Pearson India Education Services Pvt. Ltd: Dehli, Chennai, 2015. ISBN 978-93-325-4373-7.


texts:
I tried to parameterize a particular x-y-z-t dihedral angle of novel molecule using a Quantum Mechanical scan, but I got the strange result below.

The energy changes sharply around 130° and $E_\text{dihedral}(0°) \neq E_{dihedral}(360°)$.
I performed PES scan in gaussian09 and psi4 and I got the same results in different softwares.

I'm uncertain what approach to take to fix the scan. I saw some parameterization articles which didn't perform PES scan 0-360 degree. Other authors performed scan in the range of 0-60 degree or 0-120 degree and I didn't predict I will face a result like this. What is going wrong with my scan and how can I fix the issue? Would performing single point energy for each angle instead of PES scan help?


texts: number of optical isomers of a cyclic molecule

texts:
What is the number of optical isomers for this compound?

Also, there seems to be no clear-cut boundary between geometrical isomers and optical isomers. Referring to a post in StackExchange,

is (RS)- and (RR)-form of 1,2-dichlorocyclohexane considered optical isomers or geometrical isomers? The isomers exist due to restriction of rotation caused by the ring, you can also called the two geometrical isomers, can't you?


texts:
A friend is trying to understand a paper which discusses the diffusion of proteins through milk. Rather than listing a diffusivity (with units [Length]^2/[Time]), the paper lists the 'diffusion rate' of the proteins through the liquid, in units of mm/hr (i.e. [Length]/[Time]).

We can't make heads or tails of this. I was wondering about some sort of 'average front propagation velocity', but I'm not sure how that would be defined, as a diffusion front's velocity can change over time, and depends on the geometry, concentrations, etc.

Has anyone run into this terminology before?

Thanks


texts: How to calculate the activation energy of diffusion of carbon in iron?

texts:
At room temperature, $298~\mathrm{K}$, the diffusivity of carbon in iron is
  $9.06\cdot 10^{-26}\frac{m^2}{s}$.
  At $573~\mathrm{K}$ the diffusivity is $1.66\cdot 10^{-15}\frac{m^2}{s}$. What is the activation energy, $Q$?

I am wondering if my solution is correct:

$D=D_0\exp\left\{\frac{-Q}{RT}\right\}$ and $D_0$ is constant (is this correct), thus

$\displaystyle \frac{D_{298}}{\exp\left\{-Q/(RT_{298})\right\}}=\frac{D_{573}}{\exp\left\{-Q/(RT_{573})\right\}} \implies Q\approx 122~\mathrm{\frac{kJ}{mol}}$

I would be very greatful if someone could check my math here as well, if the logic is correct, since this was a test problem.


texts: In attachment I have tried to derive Raoult's law by using the concept of equilibrium constant. There is nothing mentioned in my text book about how this equation comes about, so I decided to do it myself. I may like to know whether there is some mistake in what I have done.


texts: Derivation of formula used in calculating molecular mass from a mixture

texts:
In a solution to a problem, to calculate Molecular mass of unknown gas from a mixture containing $\ce{O2}$ in $80~\%$, the author used the formula :

  $\frac{1}{\sqrt{M_\text{mix}}}=\frac{X_{\ce{O2}}}{\sqrt{M_{\ce{O2}}}}+\frac{X_\text{gas}}{\sqrt{M_\text{gas}}}$.

The exact problem is:

  Pure $\ce{O_2}$ diffuses through an aperture in $224\mathrm{s}$, where as mixture of $\ce{O_2}$ and another gas containing $80~\%\ \ce{O_2}$ diffuses from the same in $234\mathrm{s}$. The molecular mass of gas will be?

Solution by author:

  $$\begin{align}\frac{t_\text{mix}}{t_{\ce{O2}}} &= \frac{r_{\ce{O2}}}{r_\text{mix}} = \sqrt{\frac{M_\text{mix}}{32}}\\[1em]
\frac{234}{224} &= \sqrt{\frac{M_\text{mix}}{32}}\\[0.5em]
M_\text{mix} &= 34.92\\[1em]
\Longrightarrow \qquad \frac{1}{\sqrt{M_\text{mix}}} &= \frac{X_\text{gas}}{\sqrt{M_\text{gas}}} + \frac{X_{\ce{O2}}}{\sqrt{M_{\ce{O2}}}}\\[1em]
\Longrightarrow \qquad \frac{1}{\sqrt{34.92}} &= \frac{0.2}{\sqrt{M_\text{gas}}} + \frac{0.8}{\sqrt{32}}\\[0.5em]
M_\text{gas} &= 51.5\end{align}$$

I wish to know why this works here?


texts: Creating Molecular Orbital and Walsh Diagrams

texts:
Does anyone know of a good website to create your own MO and Walsh diagrams? Could you potentially make them on a software package such as excel?

Any advice on this would be greatly appreciated.


texts:
Consider glycosidic linkages in disaccharides.

I know a condensation reaction occurs, with the loss of water.

But which OH is lost? The O in the linkage belongs to which monosaccharide?

Example: take sucrose, the O in the linkage belongs to fructose or glucose?

I couldn't find any literature regarding this. Any help is appreciated .


texts: What is the boiling point and density of LSD?

texts: I have tried to do a lot of research and didn't succeed to find the boiling point and density of LSD. I would want to know this information. In addition, I can't use Clausius–Clapeyron equation because I don't have the data that I would need to use that equation.


texts: Variation of battery potential with current density

texts:
It is found experimentally that the potential of an electrochemical cell with applied current density varies as follows:

To produce the passage of current through a cell it is necessary to apply a potential difference that exceeds the equilibrium f.e.m by at least the overpotential of the cell. Furthermore, the potential of the cell will decrease as it generates current, because under such conditions it no longer works reversibly and therefore does less work than the maximum. When the current is high and close to the limiting value of one of the electrodes, a sharp drop in the work potential is observed.
I know this is what is observed, but I can't explain why. Why does this happen?


texts: Multidimensional potential energy scans - picking the ideal dimensions to scan

texts:
I am relatively new to electronic structure calculations, and I am trying to figure out the most appropriate way of scanning a potential energy surface (PES) to locate an appropriate transition state.

The proposed reactants and products can be found at the bottom of this post (only the relevant fragments are shown).

What is the most appropriate PES scan to perform? It seems logical to scan through possible values of the bond length between atoms 9 (blue) and 6 (red). But should I actually be doing a two-dimensional scan, the other dimension being the bond length between atoms 9 (blue) and 4 (orange)? Or perhaps the bond angle between atoms 9-6-5 is better? I read that doing a two-dimensional scan over two parameters that are related to the same structural parameter may not be ideal.

Any suggestions would be greatly appreciated!

Reactant:

Product: Note that N2 is also the product but is infinitely separated.


texts:
Given that $\ce{CO2}$ is comprised of carbon and oxygen, why
isn't it a flammable gas?


texts: What is the difference between chiral molecule and chiral carbon?

texts: I read in my book, that substituted allenes do not have chiral carbons, but actually the molecule is chiral, so they show optical isomerism. But what is the difference between them( chiral carbon and chiral molecule)?


texts: What is the physical state of a single atom?

texts: Can a single atom on its own be either a solid, liquid, or a gas? Or is it none of them?


texts: E1 and E2 elimination reactions of isotopically labeled bromocyclohexanes

texts:
Question
  a) What would the product of the reaction be for an E2 mechanism

  b) What would the products be for an E1 mechanism

  The Br coming out of the page is the 79 isotope while the Br going into the page is the 81 isotope.

There is no mention of reaction conditions.

I am not totally sure what the effect of the isotope will have on bromine's ability to leave. I am guessing that the bromine-81 will leave since it is bigger and can stabilise the negative charge better.

I am also not sure how the products for the E1 and E2 mechanism will be different. Won't they be the same?