texts: White powder observed after boiling water in electric kettle for many weeks

texts:
I used my water kettle (metal ones, not the plastic ones) to boil my water. Usually, if I did not consume all the water in the kettle and the water was cold, I usually topup extra water to the kettle and turn it on to boil.

So, after many weeks of boiling in this way, I notice that there are white powder outside the kettle. (I notice that when the water is boil, some water was splashed to the outside of the kettle and I left those water splashed out to dry as time goes)

Is the white powder actually called fluoride? How do I tested it to verify if the white powder chemical is safe or not?


texts:
Let's say we have a mixture of different ideal gases. I found that the chemical potential of a single component of the mixture is
$$\mu_{i}=g_{i}^{0}+Ln(\frac{f_{i}}{P_{ref}})$$

where $f_{i}$ is the fugacity of the component. I also found somewhere else that the chemical potential of pure substances is the molar gibbs property. Would it be safe to then say..

$$\mu_{i}(T,P)=g_{i}(T,P)$$


texts: What is the correct approach to obtain PES using CASSCF?

texts:
I am new to CASSCF. I want to draw a PES for the ground state and the first excited sate of methyl amine for learning purpose. I want to verify if I am correct using the correct approach.

Do a RHF/STO-3G opt pop=full ... orbital calculation.
Use the checkpoint file obtained in step 1 and use CASSCF (provided I know the active space) to optimize the structure again and then use the scan keyword to map the PES by increasing the N-H bond distance in a different Gaussian job.
Take the optimized geometry of ground state obtained using CASCF and then use NROOT=2 and opt to get the the optimized geometry of 1st excited state and then scan to get the PES, similar to what was done in step 3.

Any correction would be greatly appreciated.


texts: How can FeS2 be the formula of iron sulphide and CaC2 be the formula of calcium carbide?

texts:
I know that the valency of iron can either be 2 or 3 and so the formulae of the possible sulphides of iron should be $\ce{FeS}$ and $\ce{Fe2S3}$. But I have recently seen the formula $\ce{FeS2}$ used for iron sulphide. How is this possible.

Similarly the formula for Calcium carbide is supposed to be $\ce{Ca2C}$ and not $\ce{CaC2}$. Why do we write $\ce{CaC2}$ for it?


texts: Why don't gases escape Earth's atmosphere?

texts: Some gases are lighter than others and rise. Why don't they continue going up, leave the atmosphere, and then enter outer space?


texts:
While studying about Mendeleev's periodic table in my textbook( class 11 NCERT chemistry), I have studied that Mendeleev has predicted some elements like Eka-boron(scandium), Eka-Aluminium(Gallium),Eka-Silicon(Germanium)etc. He also predicted their physical properties which were most accurate. One such element about germanium is given in the below link.

How could he predict such accurate values of such physical properties?


texts: What happens to a quaternary ammonium cation at a pH above its pKa?

texts:
I am working with a lipid and I have firm reasons to believe that its pKa is around 8. This lipid is a cationic lipid where the nitrogen is a quaternary amine with two lipid chains and two methyl groups.

Now, my question is that at a pH above the pKa of this lipid, the quaternary ammonium ion should get deprotonated, or basically act as an acid. But the quaternary ammonium cation doesn't have any protons to lose, so what would happen to it? My guess would be it accepts a lone pair and becomes negatively charged.


texts: What is the cause of decrease in volume of gaseous mixture in the following problem?

texts:
I am studying Gaseous State.

The problem says: A mixture of gas contains $\ce{N2}$ and $\ce{C2H2}$. $\pu{20 \\mL}$ of this mixture is added to $\pu{70\\mL}$ of $\ce{O2}$ and combustion is allowed to take place over mercury. After cooling the volume of gas was found to be $\pu{68.5\\mL}$. When the resultant gas mixture is passed through a $\ce{KOH}$ solution, the volume of residual gas is $\pu{38.5\\mL}$. Then the percentage composition of $\ce{N2}$ is:

In the solution to the question there is this following step which I am not getting:

:Volume of $\ce{CO2} = \pu{68.5\\mL} - \pu{38.5\\mL}$.         How come?
Also please clarify why nitrogen does not undergo combustion.

Please help.


texts:
Different internet sources say different things.

If possible, can someone explain why it is (or isn't) chemically reactive?


texts: How can a methyl cation exist without 8 valence electrons

texts:
So far I have been taught that everything wants to achieve noble gas configuration - 8 electrons in the outer shell.

I came across a methyl cation. Which contains a positive carbon, no lone pairs and 3 bonding pairs of electrons so 6 electrons in total. 6 electrons are obviously less than 8 electrons so how can it exist as it defies apparently the rules I have been taught.

Thanks,

Daniel


texts: Is there a particular name for a Hill formula or sum formula omitting hydrogen?

texts:
Often, single-crystal X-ray diffraction analysis determines the non-H atoms first, and eventually puts hydrogen atoms "as riding" on idealized positions in respect to heavier atoms (e.g., C, O, N), because the latters are easier to localize in the Fourier maps.  This then considers both distance and geometry (e.g., 0.93 Å for an H attached to a sp-hybridized C) and temperature during the experiment, determined by other experiments (e.g., neutron diffraction).

Is there a particular name for a sum / Hill formula where the hydrogens are omitted, for example, when stating glucose as $\ce{C6O6}$ instead of a complete $\ce{C6H12O6}$ to describe just the backbone of the molecule?


texts: Does a non-terminal alkyne react with sodamide?

texts:
Hydrocarbon (A), $\ce{C6H10}$, on treatment with $\ce{H2/Ni}$, $\ce{H2}$/Lindlar catalyst and $\ce{Na}$/liquid $\ce{NH3}$ forms three different reduction products (B),(C) and (D) respectively. (A) does not form any salt with ammoniacal $\ce{AgNO3}$ solution but forms a salt (E) on heating with $\ce{NaNH2}$  in an inert solvent. Compund (E) reacts with $\ce{CH3I}$ to give (F). Compound (D) on oxidative ozonolysis gives n-butanoic acid along with other other products. Give structures of (A) to (F) with proper reasoning.

From the formula of (A) and the details given, it is clear that (A) is an alkyne. I could make out that (B) would be an alkane while (C) and (D) would be cis and trans alkene respectively. Now, as (A) does not react with ammoniacal $\ce{AgNO3}$ solution, it is not a terminal alkyne. But, then I got confused as the question told, (A) reacts with $\ce{NaNH2}$ to give a salt. Till now, I knew that only terminal alkynes react with $\ce{NaNH2}$. What is it that am I missing?


texts: Why do nitrogen-containing organic compounds give N2 as the combustion product?

texts:
My teacher gave the explanation stating that consider that first the nitrogen in lower state is oxidised to $\ce{N2}$ and then the further oxidation would stop as the $\ce{N-N}$ bond energy of $\ce{N2}$ is very high and can't be overcome under normal conditions.
But my doubt is can't the nascent nitrogen (formed during the formation of $\ce{N2})$ react further with $\ce{O2}$ and get oxidised to some higher oxides like $\ce{NO2}$ or $\ce{N2O}?$
The Latimer diagram shows that it is possible for oxygen to oxidise the nitrogen to higher states:


texts: How to find the atomic packing factor of Sodium Chloride (and other FCC ionic compounds in general)?

texts:
For a piece of coursework I am doing, I need to calculate the atomic packing factor of some ionic compounds. I have had no formal teaching in this area, so what I know comes from information I have found on the internet.
I take that the atomic packing factor is given by:
$$
APF = \frac{V_{atoms}}{V_{unit cell}}
$$
Taking a unit cell of NaCl, we get:
$$
APF = \frac{2\pi(r_{Cl}^3+r_{Na}^3)}{3(r_{Cl}+r_{Na})^3}
$$
Is this right? I took the side length of the unit cell to be $r_{Cl} + r_{Na}$, and reasoned that 1/8 of each ion is actually "inside" the unit cell, so there is essentially 1/2 of a chlorine ion and 1/2 of a sodium ion "within" the cell. $r_{Cl}$ is the ionic radius of chlorine, and $r_{Na}$ is that of sodium.
Would this also hold for all alkali metal-halides with a FCC crystal structure? i.e for a compound with anion A and cation C:
$$
APF = \frac{2\pi(r_{A}^3+r_{C}^3)}{3(r_{A}+r_{C})^3}
$$
Finally, is this a good measure of packing efficiency? As I mentioned, I have little experience in this topic, so I would be grateful if anyone knew of a better measure.


texts: 1,2-dibromopropane reaction with OH and NaNH2

texts:
We have the reaction of the alkyl halide $\ce{CH3-CHBr-CH2Br}$ with 1) $\ce{OH-}$ 2) $\ce{NaNH2}$ The answer is propyne.

I am unable to understand why we have performed an elimination reaction here. Why can't it be a substitution reaction instead? Also, how do we decide which two carbon atoms would lose their hydrogen atoms? (as in elimination, there are two choices for losing the $\ce{H}$ atom - from left and right carbon respectively)


texts: Which element has the highest binding energy per nucleon

texts: The graph of binding energy per nucleon (Hyperphysics) seems to peak at Iron-56. However, Wikipedia says that Nickel-62 has the highest binding energy per nucleon of any known nuclide (8.7945 MeV). Isn't this a direct contradiction? Why does the binding energy per nucleon peak at Iron-56, but then Wikipedia says Nickel-62 has the highest binding energy per nucleon?


texts: Confusion between electronegativity and electron affinity

texts:
Electronegativity is a chemical property that says how well an atom can attract electrons towards itself.

The electron affinity of an atom or molecule is defined as the amount of energy released when an electron is added to a neutral atom or molecule in the gaseous state to form a negative ion.

However,fluorine is taken as the most electronegative element but chlorine is accepted as the element with most electron affinity.

But shouldn't the atom which attracts the electron the strongest also release the most energy?


texts: What is the largest coupled cluster calculation that has ever been done (as of March 2019)?

texts:
I am doing some research and trying to make sure the numbers I am reporting are accurate.

I found that the paper by Sylvetsky et. al. says:[1]

  We  were,  however,  able  to  complete  a CCSDT(Q)/cc-pVTZ  calculation  on  benzene,  which entailed  2.2 trillion (Q)  contributions  and  3.1  billion  iterative  CCSDT  amplitudes

But there is no indication that this was the largest number of amplitudes (3.1 billion), or largest number of perturbative contributions (2.2 trillion). Furthermore, the paper was done in 2016 so surely larger might have been possible since then.

Does anyone know what the largest couples cluster calculation done as of March 2019 was? By "largest" I mean containing the largest number of cluster amplitudes (of any excitation level).

Nitai Sylvetsky; Kirk A. Peterson; Amir Karton; Jan M.L. Martin; Toward a W4-F12 approach: Can explicitly correlated and orbital-based ab initio CCSD(T) limits be reconciled? J. Chem. Phys. 2016, 144, 214101. DOI: 10.1063/1.4952410 arXiv:1605.03398 [physics.chem-ph]


texts: What is the use of chloroform in the procedure of determining peroxide value?

texts:
In this procedure of determining peroxide value, the oil sample is dissolved in acetic acid chloroform solution. I understand that the acid is added so that the following reaction occurs

$\ce{2ROOH + 2H^+ + 2I^- -> 2ROH + I2 + H2O}$.

But what is the point of the added chloroform?


texts:
Why are alkyl halides more soluble in alcohol water solution rather than pure water?

I could not find any satisfactory explanation using Google.


texts: If dS ≥ dq/T for a spontaneous change is dS ≤ dq/T for a non-spontaneous change and is that even possible?

texts: I am struggling with the concept of entropy but might be on the verge of understanding it. The Clausius inequality, $$\mathrm{d}S \geq \mathrm{d}q/T,$$ is true for all spontaneous changes with the equality for reversible changes. But what if a change is not spontaneous or is that impossible i.e a change cannot be forced. Any help with answering this question or to help conceptualize and understand the entropy would be greatly appreciated.


texts:
I encountered a question where the type of bonding for various oxides are prompted. Two of which are $\ce{Al2Cl6}$ and $\ce{Al2O3}$.

I thought that chlorine atoms are more electronegative than oxygen atoms, so if one of them is ionic and the other is covalent, surely chlorine would be ionic, because it may be able to "tear off" the electrons from aluminium atoms.

This is evidently not the case according to the answer key of this question. I would like to know an explanation for the ionic/covalent properties of these bonds.


texts: SN2 on compound containing halogen and carbonyl

texts:
I was given the following question on a sample exam for my organic chemistry course:

I am quite certain that it would happen in a SN2-type reaction considering that

the nucleophile is $\ce{CN-};$
the solvent is DMF.

However, I'm not sure what electrophilic center would be attacked first. I'd appreciate any explanation about why the nucleophile would choose one carbon over the other (if that were the case). The question also states that there are 2 product formed, so could it be possible that an elimination reaction is happening as well?


texts:
I am reading the contents of the oatstraw:

  .. high in vitamins A, C, B complex, LE, G..

I am unable to find on the Internet what LE refers to.


texts: How explosive is benzene compared to TNT?

texts:
Benzene is explosive within the explosive limits of minimum $\pu{1.2 \%}$ and maximum of $\pu{7.8 \%}$ in air. Source: Wikipedia More accurate, benzene itself is not explosive, but the fuel-air mixer or, fuel–air explosive (FAE), is. This fuel-air explosive is used, because of its power in Thermobaric weapons https://en.wikipedia.org/wiki/Thermobaric_weapon Benzene does burn and could be a fuel in a fuel-air explosive. So it would be, more specific, a benzene-air explosion.
I would like to know what is the explosive power of benzene measured in TNT-equivalent. Benzene can explode like in China in 2005 which was 'only' 100 ton benzene.
The reason why I want to know is that there was a huge explosion in Beirut on August 4th 2020, with the equivalent of 1.1 kiloton TNT. In my country, the Netherlands, benzene is transported in huge ships of 2000 ton. This could explode, spreading the benzene gas over the area, which is heaver than air. Benzene is highly carcinogen. I would like to know how a possible explosion could be compare with the explosion in Beirut. Benzene burns very easy, so may be only a fraction of benzene would explode, the rest would burn. I just want to know what we, as citizens, might expect when things goes seriously wrong.
An approach could be a list with the relative effectiveness of benzene compared to TNT. All kind of benzene derivatives are mentioned in that list but not benzene itself. I could not find  a list in which benzene itself is mentioned.
So my (much to simple) calculation is:

1 ton TNT: $\pu{4184 \times 10^{12} J}$ see: TNT equivalent
Energy [(Heat of combustion) / mol]: $\pu{3267.6 kJ/mol}$ see: Benzene
Energy / kg:   $\pu{41831 \times 10^{6}J/kg}$ ($\pu{\frac{3267.6 ~ kJ/mol}{78114 ~ g/mol} \times 1000 g/kg}$)
Mass: $\pu{2000 kg}$
Total energy: $\pu{83662 \times 10^{12} J}$ ($\pu{41831 \times 10^6 J/kg \times 2000 kg}$)
TNT-equivalent: $\pu{~ 20 kiloton}$ TNT ($\pu{\frac{83662 \times 10^{12}~  J}{4182 \times 10^{12}~  J/ton}}$ TNT)

My questions are:

Could all benzene explode at once? Because benzene might be mixid in
air within the explosive limits range, but this will be only for a
limited ammount of benzene. But because the explosion the rest of the
benzene will be blown into the air and possible then be again be
within the explosive limites ranges. So causing a chain-reaction. The
explosion in Jilin in China took 1 hour so that seems to be the case.
If not is it possible to calculate what is the maximum of benzene that
could explode?

Note: I have very limited chemical knowledge. I can passive read chemical formulae and make very simple calculations like above.


texts: Why is Tyrian purple called 6,6′-dibromoindigo?

texts:
If the two bromines are attached at opposite ends of the molecule, why are they both labelled with a 6?
Also, why is 6,6′-dibromoindigo not called 1,1′-dibromoindigo if carbons in a ring are numbered according to their substituents, and bromine is the substituent, therefore the carbon it is attached to should be called 1, not 6?


texts: Thermal and photochemical excitation of electron in photochemistry

texts:
One of the basic rules of photochemistry is that the electronic configuration of a conjugated polyene does not change when excited thermally, but changes when photochemically excited, i.e. an electron moves from HOMO to LUMO.

Can anyone please explain this to me in terms of quantum mechanics?

I have done some calculations, which I am enclosing here.

(P.S.: Please do not provide explanation like thermal energy is very less to excite than photochemical, since it would imply that at very high temp (~1,00,00,000 C) the reaction is possible, which is not really the case).


texts:
We will be buying methanol by a about 200 liters at a time, I was wondering what I should consider when storing it.

So far I know that it should be

in the shade
earthed with a copper stake
in a secondary plastic container
wash empty containers and drain them

But I am wondering what else should be considered? How far should it be away from a house?


texts: Molecular dynamics after modeling a protein loop. Necessary?

texts:
Firstly, I am postign this question to both chemistry and physics stacks exchange as I am not sure to which it belongs and to use the benefits from both sites.

I have modeled missing loops in a PDB structure using chimera. Should I run MD or energy minimization on the output file?

Thank you in advance.


texts: In a monomolecular reaction, how can a reactant experience collision to react?

texts: Monomolecularity means no molecules which experience collision with each other taking part in reaction. So how it is possible that in monomolecular reaction only one reactant experiences collision?


texts: Need help finding equilibrium constant for equilibrium system

texts:
The reaction between iron (III) ions and thiocyanate ions, SCN$^-$, is an equilibrium reaction:
Fe$^{3+}$ (aq) $+$ SCN$^-$ (aq) $\ce{<=>}$ FeSCN$^{2+}$ (aq)
When $20$cm$^3$ of $1.0\times10^{-3}$ mol dm$^{-3}$ Fe(NO$_3$)$_3$ (aq) is mixed with $20$cm$^3$ of $1.0\times10^{-3}$ mol dm$^{-3}$ KSCN (aq), the concentration of FeSCN$^{2+}$ (aq) at equilibrium is $8.0 \times 10^{-3}$ mol dm$^{-3}$. What is $K_{c}$ for the equilibrium system?

The question also includes a hint, saying that,

After mixing, the concentration of each reactant is half, because the
volume of solution is doubled.

My attempts to solve this question are as follows:
The initial number of moles of Fe$^{3+}$ and SCN$^- $$= 1\times 10^{-3}\times20\times10^{-3}=2\times10^{-5}$mol
At equilibrium, the concentration of Fe$^{3+}$ and SCN$^-$$ = \displaystyle\frac{2\times10^{-5}}{20\times10^{-3}} - (8\times10^{-3})=1\times10^{-3} - (8\times10^{-3}) $mol dm$^{-3}$
I have obtained a negative value for the concentration Fe$^{3+}$ and SCN$^-$, so I think I have made some wrong calculations somewhere. I am confused about the volume and concentrations of Fe$^{3+}$ and SCN$^-$.
Could you tell me where I made a  mistake?


texts: Racemization of ketones in presence of catalytic acid

texts:
Question:
Which of the following ketones racemise in aqueous solution containing acidic or basic impurities?

My answer:
A and B should racemise in aqueous solution, for the carbonyl groups in A and B contain alpha-hydrogens, leading to the possibility of enolisation, hence racemization. Compound C can't form an enol, hence shouldn't racemise.

It's very clear that compound C doesn't racemise, my confusion is about A and B.

My logic (stability of carbanion) says that A and B should both racemise, however, the answer I have is only B.

I agree that the carbanion formed by A would be less stable than that formed by B, but not so much so to ignore the possibility of enolisation and racemization.

Could someone please help? Is there anything obvious that I'm missing? or is it related to data? A good explanation would help. Thanks a lot.


texts: How do water molecules overcome the van der waals distance and form hydrogen bonds?

texts:
I read in Voet & Voet that the hydrogen bonds are at least 0.5 angstrom shorter than the calculated van der waals distance. As I understand, van der waals distance is the distance of closest approach between two atoms/molecules. How are two water molecules able to break this to get closer to each other and form hydrogen bonds?

We also know that ice is less dense than liquid water. In ice, water molecules are hydrogen bonded to each other and the distance between them is shorter than van der waals distance. but it liquid water not all of them is hydrogen bonded and it should be ideally at a minimum distance of van der waals and the density should be less. What is making the water molecules to interact closer to make liquid water more dense than ice?


texts: Calculating relative molecular mass given mass of solute and solvent, as well as freezing point depression, but no cryoscopic constant?

texts: Find RMM of anthracene given that when 0.813g is dissolved in 45g of benzene. freezing point of depression is 0.51 degrees celsius.


texts: A lot of biological reactions need photons to work, like photosynthesis and making vitamin D in our skin. But are there any chemical reactions where photons are really just a catalyst so they are absorbed and emitted the same as the came? Or is there always a change in frequency/wavelength involved which implies perhaps that the photon is 'used'. Or is perhaps the use of the word catalyst in case of photons not very appropriate?


texts: What is the mechanism of addition of glycine into 5-chloro-N-methylisatoic anhydride?

texts:
The following transformation is involved in a step in the synthesis of diazepam:

(†)

What is the mechanism of the transformation from the second to the third intermediate (N-methylisatoic anhydride to 1 via glycine in triethylamine)?

There are a few possible electrophiles and nucleophiles that could be involved here. Either the aniline could attack the glycine carboxyllic acid, or the glycine could attack either of the anhydride carbonyls. The paper, however, says that the glycinate is formed, so I don't think the former option is viable. Based on the pKa's involved, what might be the most reasonable proposal?

(†) J. Org. Chem., Vol. 45, No. 9, 1980, 1679


texts:
What is the property of a water molecule that allows it to split into $\ce{OH-}$ and $\ce{H+}$ ions?

And subsequently, why - when these ions are attracted towards each other in a neutralisation reaction, for example - can these ions then become a single covalently bonded molecule?


texts: This was asked in a school exam of mine, GCSE curriculum, exactly as it was worded on the title. I found this question a bit vague, and answered it francium, however of course francium is just an estimation. I couldn't be sure what the answer to the question would be, so can anyone give me some insight?


texts: Clarification required on whether to use $C_v$ or $C_p$ in this question on finding entropy change

texts:
$1 \text{ mol}$ of an ideal monoatomic gas at $300 \text{ K}$ is subjected to a reversible isentropic compression process until final temperature reaches $600 \text{ K}$. If initial pressure is $1 \text{ atm}$. Then find $\ln (\text{P}_2)$.

My Attempt

$$\begin{aligned}\Delta S &=nC\ln\left(\dfrac{T_2}{T_1}\right)+nR\ln\left(\dfrac{P_1}{P_2}\right)=0 \\ & \boxed{\ln(P_2)= \ln(P_1)+C\ln\left(\dfrac{T_2}{T_1}\right)}\end{aligned}$$

Now if I take $C=C_v$, I get the answer $\ln(P_2)=1.5\ln(2)$, but the answer is given to be $2.5\ln(2)$ which will be obtained when we take $C=C_p$. So how to decide which one to take?


texts: Why is sodium potassium tartarate used in Fehling's solution?

texts: Why is this salt used specifically in Fehling's solution, instead of a simple disodium or dipotassium salt of tartaric acid?


texts: Procedure to assign the irreducible representation of a derivative operator

texts:
How can we assign an irreducible representation to a derivative operator like
$\displaystyle\frac{\mathrm d}{\mathrm dx}$ or the whole gradient operator $\nabla$ in a given point group?

Since the Hamilton operator can be assigned to the totally symmetric representation, it seems like there is a way to to do so for derivatives or operators in general, but I have no clue how to do so. I am well aware how to determine the representation for normal functions, but I have never seen it done for operators.


texts: Is the ionic solution of a half-cell part of the electrode in a electrochemical cell?

texts:
A simple electrochemical cell consists of two half-cells, that is: a metal solid submerged in a solution. Additionally, there is salt bridge connecting the half-cells.

Ex: $\ce{Cu(s)}$ in $\ce{CuSO4(aq)}$ and $\ce{Zn(s)}$ in $\ce{ZnSO4(aq)}$

According to my text-book (Chemistry: Collins 3rd Edition, pg.506), the 'electrode' in a electrochemical cell is the whole half-cell.

"In work on electrochemical cells, however, the term electrode is extended to include what is known as a half-cell. So it refers not only to the conductor, but also to the conducting solution in which it is placed."

From other sources, I get the idea that the electrode is the metal solid (ex. $\ce{Zn}$), while the $\ce{ZnSO4}$ is an electrolyte (a solvent that seperates the cations and anions). Even when they are talking in the context of an electrochemical cell.

However, would not the saltbridge be considered the electrolyte as that is the compound that actually neutralizes the half-cells, through a seperation of cations and anions that travel to respective half-cells. While the redox reactions is actually happening between the $\ce{Zn(s)}$ and the $\ce{Cu^2+(aq)}$, which includes the metal solid and the ionic solution. As they are both conducting electrons.

Or are both the ionic solution and the saltbridge made of an electrolyte. Both consists of polar solvents, that seperate cations and anions. Therefore the electrode would be a metal solid in an electrolyte.

I guess the essence of my question, comes to down how to define electrode and electrolyte in the context of an electrochemical cell.


texts:
Consider the initial boundary value problem

$$u_t=a(t)u_{xx},\,\,\,0<x<1,\,\,\,t>0$$
$$-ku_x(0,t)=hu(0,t),\,\,\,t>0$$
$$u(1,t)=u_0,\,\,\,t>0$$
$$u(x,0)=f(x),\,\,\,t>0$$
where $a(t)>0$ is time-dependent thermal diffusivity, $k>0$ constant thermal conductivity and $h>0$ constant heat transfer coefficient.

-I wonder that is there any chemical process that can be modelled by the above equation ?
-Is it possible for a physical process that the thermal diffusivity is time dependent but thermal conductivity and heat transfer coefficient are constant ?


texts: leaving a spoon in a cup of tap water for about 12 hours makes a pattern of bubbles, why?

texts: I left the spoon in the water after showing the cup from the tea that I was drinking last night makes a spoon like the pattern of bubbles


texts:
Here is how my textbook proves that dissolution of solid in liquid is dynamic in nature. It considers the example of a saturated solution of sugar. It says that,

  Though the solution is in equilibrium, the process of dissolution of sugar and crystallization of sugar takes place continuously and also at the same rate. This can be confirmed with the help of radioactive sugar. If we drop some radioactive sugar into saturated solution of non-radioactive sugar, then after some time radioactivity is observed both in the solution and in the solid sugar. Initially there were no radioactive sugar molecules in the solution but due to dynamic nature of equilibrium, there is exchange between the radioactive and non-radioactive sugar molecules between the two phases.

It also proves the dynamic nature of chemical equilibrium in a similar way.

From this proof, my argument is that dynamic nature of equilibrium is proved only by adding another substance. This disturbs the equilibrium. It is possible that the saturated solution was in static equilibrium but addition of this substance has led to the dynamic nature.
I do not find it logical to prove that it is dynamic by the process of disturbing it.

Is this proof invalid or am I going wrong in my arguments?


texts: Help me understand electrochemistry and batteries

texts:
I have a brief understanding of how batteries work, but there are still some things that I can't put together. Therefore I would like to ask for help in understanding how batteries work. Every time I try to learn about batteries, I end up seeing the Zinc and Copper cell, but I can't connect with any of these materials. Therefore I would like to ask what would happen if instead of Zinc and Copper, one would make a battery made out of... Steel and Aluminum, for example. Or any materials that are randomly or wrongly chosen.

I have chosen a random example because I think I can understand better if a system doesn't work rather than having a system that works. So now the questions:

Would such a system work if the electrolyte would be a solution that would allow the transfer of ions?
If not, why would this not work?
What can one do/change to make such a system work?
What would happen at an atomic level with both electrodes?

By work, I mean store energy. Numbers such as electrode potential and cell potentials would also be useful.


texts: Our teacher told us that a carbocation connected to 3 cyclopropane rings is among the most stable carbocations. But I am unable to understand how, as resonance (the most important factor governing stability) is absent. How did other factors bring so much stability?


texts: Relationship between surface area of electrode and reaction rate of hydrogen in fuel cells

texts:
I am looking at the effects of increasing the surface area of which the flowing hydrogen fuel is in contact with the anode in a fuel cell.

At the anode the hydrogen is catalytically split into protons and electrons. The catalyst used is most commonly platinum. So, for a fixed flow rate of hydrogen, increasing the contact surface area with the anode will increase the number of hydrogen atoms in contact with the catalyst, and the duration that they are in contact with it. Therefore the number of oxidization half cell reactions will increase. But what is the mathematical relationship that governs the number of reactions that will occur? Is it just a linear relationship, i.e doubling the surface area doubles the number of reactions, or is it more complex?

If it is impossible to get an exact mathematical relationship, what is a good approximation on how these variables will scale with each other? Also, how do chemist usually predict the number of reactions/reaction rate, and could this be applied to my example?


texts: Can we use phosphorous triiodide in Hell-Volhard-Zelinsky reaction?

texts:
With the help of HVZ reaction, we can get alpha-chloro or alpha-bromo carboxylic acid.

But can we make alpha-iodocarboxylic acid  with the help of HVZ reaction? I could not find any reference of HVZ reaction forming alpha-iodocarboxylic acid.
Though $\ce{PI3}$ is much less stable than $\ce{PBr3}$ and $\ce{PCl3}$, it has a decent shelf life of few months and is actually widely available reagent. But still,  $\ce{PBr3}$ and $\ce{PCl3}$ is seemed to be used in HVZ reaction. Why not $\ce{PI3}$? Is the reaction thermodynamically unfavourable? Is so, what is the reason?
If $\ce{PI3}$ is used instead of $\ce{PBr3}$ or $\ce{PCl3}$, will the reaction proceed to form alpha-iodocarboxylic acid? If so, why?

Update (I was visiting some of my older questions and encountered this question and thought of providing a little more information)
I found this information from a handbook:

Carboxylic acid can react with iodine without any intermediate enolate ion to produce alpha-iodocarboxylic acid. alpha-iodocarboxylic acid chlorides can be produced when hexanoic acid reacts with iodine and thionyl chloride at 85°C to give 80% yield of 2-iodohexanoyl chloride. Similarly, butanoic acid reacts with chlorosulfonic acid and iodine to give 94% of 2-iodobutanoyl chloride. These examples are nothing more than iodine analog of Hell-Volhard-Zelinsky reaction.

Why are these reaction considered as iodine analog of HVZ reaction? Doesn't HVZ reactions strictly uses phosphorus halides?
If these examples are iodine analog of HVZ reaction, why are they producing 2-iodoacyl chloride? They should be producing 2-iodocarboxylic acid.
If it is producing 2-iodoacyl chloride, how to get rid of the chloride atom to get 2-iodocarboxylic acid?

In this site, it is mentioned that only iodine cannot simply iodinate carboxyl acid due to thermodynamic reasons and alternative and noble ways were discovered to overcome this problem. The reactions mentioned were with carboxylic acid dianions, acyl chlorides with iodine in thionyl chloride and iodination with iodine in the presence of cupric salts. There is no mention of phosphorus triiodide where I later found that with phosphorus diiodide, $\ce{P2I4}$, it can produce 1-iodopropanoic acid and not 2-iodopropanoic acid). Is it considered HVZ reaction?


texts: Multiplicity of orbitals in a magnetic field

texts: Solving past questions preparing for a test, I am stuck at number 11. Is multiplicity the ml value


texts:
I've been quite stunned during the last Winter Olympics in Sochi by the following fact.

Temperatures were quite high, sometimes 10° Celsius, and the organizers had to do something to prevent the snow from melting. I heard on the TV the commentators saying that they were discharging salt on the tracks.

However where I live (France), we have occasionnally snow in the winter, and to keep the roads clear for the vehicles or the sidewalks clear for the pedestrians, city services also discharge salt !

How is it possible to have these two different effects with the (seemingly) same component ?


texts: Migratory aptitude of substituents for carbonation rearrangement in Pinnacol Pinnacolone rearrangment

texts:
Generally, the observed migratory aptitude for carbocation rearrangement is (as given in various books)  :

$$\ce{H- > Ph- >CH_3-}$$

But the fact is that the carbocation at the benzylic carbon is more stable.

This is counter-intuitive, so what is a reasonable explanation for this?


texts: How to model the Belousov-Zhabotinsky (BZ) (in Maple)

texts:
I need to model the Belousov-Zhabotinsky reaction (or a different oscillating one). I found out about the Oregonator and the Brusselator reaction and now I want to model them in Maple (or similar software). In this post the rate equations are given. On Scholarpedia the rate equations are scaled (I do not know what that means), but I still don't have clue how to model this. I have very basic knowledge of rate equations and modelling reactions (it is a project at the end of secondary school). I do know how to differentiate and find primitives of a lot of functions if that's needed.

I would be very grateful if someone could explain to me how scientists use rate equations and if someone could show me how to enter the Oregonator (and/or Brusselator) in Maple of similar software. Preferably also that I can change the starting concentrations (and the temperature if that's possible).

Many thanks!


texts: Why does zinc sulfide have to be doped with silver to phosphoresce?

texts: $\ce{ZnS}$ is a boring white powder and it doesnt glow in the dark, but if its doped with silver it starts to show some phosphorescent properties.How does silver force zinc sulfide to do that?


texts: Does increasing the pressure in hydrogen fuel cells make them convert faster?

texts: In particular Alkaline fuel cells. I saw that increased temperature increases efficiency and was hoping pressure would increase production so that I could keep the alkaline fuel cell small and just increase the pressure. Is that how it works?


texts: Total number of carbon atoms in buckminsterfullerene

texts: From what I read, buckminsterfullerene is composed of 60 carbon atoms, $\ce{C_{60}}$ and it is made up of 20 hexagons and 12 pentagons. So, I decided to do a back of the hand calculation with the knowledge that each of these were tri-atomic junctions. Since one hexagonal tri-atomic site would comprise a $\ce{C-C}$ bond angle of $\frac{2\pi}{3}$, thus just $\frac{1}{3}$rd of an atom and hence two atoms in a hexagon. Since there are 20 hexagons, this gives me 40 atoms. Now the $\ce{C-C}$ bond angle at the pentagon site is $\frac{3\pi}{5}$ which makes it $\frac{3}{10}$ atoms per site and hence $\frac{3}{2}$ atoms per pentagon. With 12 pentagons, it results in 18 atoms. So the total number of atoms according to this calculation amounts to 40+18=58. Where did I go wrong?


texts:
I think most have heard the advise that you should put flour (or baking soda) on a grease fire to absorb the oil before. While this is certainly better than using water, I'm skeptical.

For starters it is know that flour is excellent at demolishing flour mills,  but in these instances it is a dust explosion (actually a deflagration) in a confined space versus a splash of mostly unaerated powder onto a fire. Even the fine particles that fall off should only cause mild flames compared to the on going grease fire. The main cause of skepticism is the potential charring of the flour releasing water and causing splattering (i.e. bigger fire).

Alternatively baking soda has been suggested, but this also seems dodgy as it starts to decompose at 50 °C releasing carbon dioxide and water, and how many people have enough baking soda to fill a pan in their kitchen ready to go? It seems that a lid would be the most appropriate response and of course would not recommend someone to do their own fire fighting if not prepared to do so, but when seconds count help is only minutes away.

I suppose that decomposition would be less of an issue if sufficiently slow kinetically. But debating physical sciences is a fools errand so I ask: Is flour or baking soda really suitable for extinguishing grease fires?


texts: If a gas always occupies the volume of its container, will its volume always be 22.4L at STP?

texts:
According to the Avogadro's law, an equal volume of gases have a equal number  of moles (with constant pressure and temperature), therefore STP molar volume is $\pu{22.414 dm3 mol-1}$.

Think this: There is a container of volume $\pu{40 dm3}$ without any gases. I fill it with 1 mole of $\ce{O2}$ gas ($\pu{32 g}$), therefore according to the STP molar volume, the volume should be $\pu{22.414 dm3}$.

But we know that a gas always take the volume of its container. In above problem, the container volume is $\pu{40 dm3}$. So the volume of the gas should be $\pu{40 dm3}$. But why $\pu{22.414 dm3}$? I am confused with it.


texts: How is the Activation Energy of the Arrhenius equation related to the exponents in rate laws?

texts:
I know that activation energy for a particular reaction does not depend on the stoichiometry of the reaction.But how can that be justified from Arrhenius Equation ?Doesnt 'k' change with stoichiometry?Or am I going wrong?

Because we know that in all the kinetics equations, when  the reaction stoichiometry changes the rate constant in the equations have to be altered accordingly.


texts: What are the rate laws for each elementary step?

texts:
Overall reaction

$$\ce{2NO + H2 -> N2O + H2O}$$

Mechanism

\begin{align}
\ce{NO + NO &-> NO2}\\
\ce{NO2 + H2 &-> NO + H2O}\\
\ce{N + NO &-> N2O}\\
\end{align}

I am aware that this is not a valid mechanism for the overall reaction however I am still supposed to find the rate law for each elementary step. I am having trouble determining what this rate law would be in step 3 of the mechanism.


texts: Boiling points of Butan-2-ol and Butan-1-ol

texts:
Butan-1-ol has a boiling point of approx. 117.7 celsius, and Butan-2-ol has a boiling point of approx. 99.5 celsius. What causes this difference in boiling points?

My initial idea would be that Butan-2-ol essentially has a side-branch (the OH-group), whereas Butan-1-ol does not. This should disrupt the London dispersion forces and thereby reduce the strength. Another idea would be that the position of the OH-group being in the middle for Butan-2-ol creates fewer Hydrogen bonds than Butan-1-ol does. My third idea is that the position reduces the strength of the regular dipole-dipole bonds (when I mean regular I mean not hydrogen bonds), because the polarisation is weakened.

Am I correct in any of my assumptions? Is there something else to it?


texts: Trying to understand the chemistry in an iron carbon battery

texts:
I am trying to understand the chemistry that occurs in an iron carbon battery during charging.

The negative electrode is iron, the positive electrode is carbon. The electrolyte is iron(II) chloride. I understand that ferrous chloride dissociates in water to $\ce{Fe^2+}$ and $\ce{Cl-}$ ions. During charge the $\ce{Fe^2+}$ ions are attracted to to the negative iron electrode and the $\ce{Cl-}$ ions are attracted to the positive carbon electrode. The $\ce{Fe^2+}$ ions combine with electrons from the power supply to form metallic iron that plates on to the iron electrode.

My problem is understanding what happens at the positive carbon electrode. I'm told that iron(II) chloride loses electrons to the positive electrode and becomes iron(III) chloride. Fine, but how does this happen if all the $\ce{Fe^2+}$ ions are at the negative electrode? How does this happen if the iron(II) chloride has dissociated in to ions, there is no iron(II) chloride anymore?

If the power supply drives all the $\ce{Fe^2+}$ ions to the negative electrode and $\ce{Cl-}$ ions to the positive electrode how can any $\ce{Fe^2+}$ ions even be at the positive electrode to somehow recombine with $\ce{Cl-}$ ions back into iron(II) chloride that then loses electrons to the positive electrode and becomes iron(III) chloride?


texts: What is required to achieve 999.9999 or finer gold?

texts:
After doing some research on gold purity, I found that the current record of gold fineness is at an astounding 999.999 fine achieved by the Perth Mint, Australia 1957. However, I could not find any other attempts to break this record.

I have also read the other related answers like this one: Obtaining 100% pure metal

I was hoping that perhaps some insight could be given as to how the current fineness record was achieved, and what refinement or fineness verification barriers may need to be overcome to achieve finer purities.


texts:
The Boring Stuff
I'm well acquainted with various fields of science & engineering, but my foray into the world of chemistry is relatively recent.
I'm in a location (probably most of us are to some degree) where many chemical reagents are highly scrutinized and difficult to legally obtain from legitimate supply houses in any appreciable quantity. To do so is considered highly suspicious, requires a business account, legal documents, and so on. In short, it's a headache and it's very uncomfortable for amateur chemists/experimentalists.
And possibly rightfully so. While googling chemical (i.e. red phosphorus) purification methods, it quickly becomes apparent why. Most of the information available is in the form of poorly written (often dubious) discussions between amateur illicit drugs manufacturers.
But I digress. Despite all this, I'm determined to continue my exploration and extraction of phosphorus in it's various allotropes.

The Interesting Stuff
The only readibly available consumer class product (that im aware of) which contains red phosphorus is the humble safety-match striker pad. Here they're only something like $2 for twenty, so it seemed like a good place to start.
The sample can be collected in a bowl with the use of a solvent and/or sufficient agitation. Pretty easy. Although naturally it contains some undesired impurities, particularly including fine particles of glass frit, an unknown adhesive, the odd stray paper/cardboard fibres, and probably traces of a few various other things.
Washing with solvents and decanting seems to work to a degree, however on drying it cakes and adheres to its container almost like a paint. It's not the pulverulent powder described in the literature. In suspension with various solvents, fine particles can be seen while agitating, yet a somewhat viscous milky yellow substance rapidly adheres to the sediment upon settling.
Some sources recommend alkaline and acidic solutions (e.g. HCl, H2SO4, H2O2, NaOH, etc.) for removing various impurities. While other sources claim acids and bases like these will react with the desired red phosphorus, creating undesired molecules such as phosphorus pentoxide and ortho-phosphoric acid.
Furthermore if the desired effect is to reduce the organic compounds to a fine black elemental carbon powder, the challenge of separation still remains.
However, in my experience, when mixing with H2SO4, it seems no phosphorus is left in the beaker at the end.
It will apparently crystalize when heated under pressure, so that seemed like a possible solution, but supposedly the black allotrope posseses different properties, is highly unreactive, and can't be converted back to the red allotrope, so might not be viable.
Does anyone have a solution or suggestion for how to purify the red phosphorus? Thanks in advance.

References

Liquid-Liquid Techniques in Phosphorus Chemistry by
H Harnisch

Process for Stabilizing Red Phosphorus Against Oxidation by G Nordblom & M Silverstein

Purification of Red Phosphorus by P Miller


texts: What type of gloves should be used while diluting sulfuric and hydrochloric acids?

texts:
What type of gloves should we use on hands while diluting sulfuric and hydrochloric acid?

Can we use these gloves in chemistry lab to handle other acids?


texts:
This concerns ongoing work to find a plausible approach to large-scale production of clear glass on the Moon. It's for an ultra-hard science fiction project and I really want to get it right.

Olivine of good purity can be gotten from deposits of dunite in the lunar highlands. You need to get to the bedrock, but it's there. If you melt the dunite you can use fractional crystallization to improve its purity - I have asked about that on Earth Sciences but it seems to be true. If that works it would also suggest you can do the same thing again to separate the olivine into forsterite ($\ce{Mg2SiO4}$) and fayalite ($\ce{Fe2SiO4}$).

If the forsterite is pure enough, could that be used to make decent clear glass?

Could the fayalite be processed into iron, water, and silicon dioxide with something like the reaction below?

$\ce{Fe2SiO4 + 2H2 -> 2H2O + 2Fe + SiO2}$


texts:
In German problems olympiad 2014, the solution says that decomposition of arsine is not a redox reaction. Why would that be? Shouldn't H turn from -1 to 0 and As from 3+ to 0?

$$\ce{2AsH3 -> 2As + 3H2}$$


texts: At equilibrium are the rates of the forward and backward reactions equal to zero?

texts: At equilibrium, the concentrations do not change with time. So, is it true that the rates of the chemical reactions are zero at equilibrium? Wikipedia says that they are not zero. Why is this?


texts: Best way to prepare reference crystal structure with a given force field

texts: I was wondering if somebody could give me some insight into best ways to produce crystal structures, with a given force field, at 0 K. I am interested specifically in glycine, and have obtained the experimental structure from the CSD. I have seen in the literature people refer to annealing, where I equilibrate my crystal at a large temperature, and then anneal. However, I am concerned about the effects of such things as annealing rate here. I have also seen people mention performing energy minimization. However, my concern is typical energy minimization routines, at least to my knowledge, do not adjust the simulation volume according to a specified pressure. Thus, if my virial is positive for my experimental atomic coordinates using my force field, I don't think the minimizer would expand the volume to bring the pressure back to 1 atm. Could anyone give me some guidance. I am trying to prepare glycine crystal structures, at 0 K, using the GAFF force field with the CNDO charges.


texts:
I'm completely stuck on this one - I was doing an experiment in a lab and now I cannot find the molarity of an ion in a solution. I've looked everywhere on the web but after 2 hours of searching I couldn't find anything. Maybe I am looking in the wrong direction.

I mixed three solutions: 1mL of $\ce{0.1M ~CuSO4}$,  $\ce{0.28 M ~~NH3}$ and  water.
This solution turned into

$$\ce{Cu(H2O)4^{2+} + 4NH3 = Cu(NH3)4^{2+} + 4H2O}$$

This turned the solution from light blue to dark blue-ish purple. The final mL of the mixed solutions was 25 mL.
Now I am supposed to calculate the molarity of the $\ce{Cu(NH3)4^{2+}}$ ion. I am pretty sure that I only have to calculate the molarity of $\ce{Cu^{2+}}$ but I am not entirely sure. If you guys could give me some help on this I would be very grateful.


texts: How much KMnO4 is required for the complete oxidation of ferric/ferrous oxalate in acidic medium?

texts:
Find out the amount of $\ce{KMnO4}$ required for the complete oxidation of $\pu{5 mol}$ of an equimolar mixture of ferric oxalate and ferrous oxalate.

I understand that $\ce{MnO4-}$ will be oxidised to $\ce{Mn^{2+}}$ and ferrous ions to ferric ions. I wrote the following reaction:
$$\ce{FeC2O4 + Fe2(C2O4)3 + MnO4^- + 8H+ + e- -> 2Fe^3+ + 4CO2 + Mn^2+ + 4H2O}$$

Then, I applied equivalence concept but could not get a correct answer. Any ideas?


texts: Calculating the electronegativity of an element from bond dissociation energies

texts:
Calculate the electronegativity of fluorine from the following data:
$$\begin{align}
\text{BDE}(\ce{H-H}) &= \pu{104.2 kcal/mol} \\
\text{BDE}(\ce{F-F}) &= \pu{36.6 kcal/mol} \\
\text{BDE}(\ce{H-F}) &= \pu{134.6 kcal/mol} \\
\chi_\ce{H} &= 2.1
\end{align}$$

I thought that electronegativity should be related to effective nuclear charge, as it is a measure of how strongly atoms "pull" on bond pairs.
Is there a formula to calculate the electronegativity from bond dissociation energies, and what is the rationale behind it?


texts: Is the atom the smallest particle, which takes part in chemical reactions?

texts: According to modern atomic theory, the atom is the smallest particle which can take part in a chemical reaction. But during the formation of hydronium ion, $\ce{H+}$ ion reacts with $\ce{H2O}$ to form $\ce{H3O+}$ ion. Here the $\ce{H+}$ ion, which is smaller than hydrogen atom, takes part in a chemical reaction. So is that postulate invalid?


texts: Do I have to systematically show the protons in my reaction equation to find the Pourbaix diagram's line equations?

texts:
I was trying to get the line equation for the Pourbaix diagram for the couple $\ce{Ni(OH)2}/\ce{Ni}.$ I can write two chemical equations for basic and acidic conditions, respectively:
$$
\begin{align}
\ce{Ni(OH)2 + 2 e- &-> Ni + 2 OH-}\tag{R1}\\
\ce{Ni(OH)2 + 2 H+ + 2e- &-> Ni + 2 H2O}\tag{R2}
\end{align}
$$
Now I can determine the line equation for both chemical equations using Nernst equation:
$$
\begin{align}
E^\circ + \frac{0.06}{2}\log\left([\ce{H+}]^2\right) &= E^\circ - 0.06\,\mathrm{pH};\tag{1}\\
E^\circ - \frac{0.06}{2}\log\left([\ce{OH-}]^2\right) &= E^\circ + 0.06\,\mathrm{pOH}.\tag{2}
\end{align}
$$
I need to make the $\mathrm{pH}$ appear in the previous equation. To do so, I use the relation
$$\mathrm{pH} + \mathrm{pOH} = 14 \quad\Leftrightarrow\quad \mathrm{pOH} = 14 - \mathrm{pH},\tag{3}$$
which gives
$$E^\circ + 0.06(14 - \mathrm{pH}) = E^\circ + 0.84 - 0.06\,\mathrm{pH}.\tag{4}$$
I've found two slightly different expressions depending on whether I choose basic or acidic conditions. I've spend quite a few hours trying to figured out what is wrong here, and I've found a PDF Diagrammes E-pH = Diagrammes de Pourbaix (courtesy of Académie de Clermont-Ferrand) stating on page 4 that even if the species only exists in basic conditions I need to make the $\ce{H+}$ appear in the half-reaction.
Is there a convention when writing chemical equation prior to the determination of the line's equation for Pourbaix diagram? Or did I make a mistake somewhere? If yes, could help me please?


texts: Hybrid functional calculations using different approach

texts: In hybrid functional such as B3LYP, PBE0, HSE etc, some part of HF exchange and/or correlation is added to some part of DFT X/C part in order to get better results. My question is if I am adding 1/4 th of HF exchange part that means I already calculated HF exchange part and HF is undoubtedly better than DFT, then why don't we just use the full HF solution that we already have in our hand?


texts: Reactivity of unsaturated organolithium compounds

texts:
I'm particularly looking in the context of alkyl lithiums compared to vinyl-lithiums and alkynyl-lithiums.
Why is it that shifting from sp3 to sp2, and even further to sp carbanions, reduces the basicity and allows for nucleophilic attack to occur preferably?
I understand that a greater s-character means the negative charge is held closer to the nucleus and therefore further stabilised, decreasing its drive to obtain a proton, but wouldn't this also decrease its drive to attack an electrophile?


texts: Determining the purity of commercial NaCl

texts:
I am trying to figure out how to determine the percentage of NaCl in salt. My purpose is to be able to test the purity of salt that I received before washing so that I can determine the quality of the salt and how much I should pay for it. I also want to be able to determine how good a salt washing machine works by comparing the before and after purity of the salt.

My basic understanding is that there is a standard minimum percentage of NaCl in after wash salt (usually above 99% depending on where you are), the percentage is lower for a pre-wash salt.

Is there any test to know the purity of Salt?

Thank you..


texts: How to decide whether to pick 4-bromo-2-methoxyphenol or 4-bromo-6-methoxyphenol as the name for the compound?

texts:
Why is the following compound named as 4-bromo-2-methoxyphenol and not 4-bromo-6-methoxyphenol?
Shouldn't the substituents be numbered according to their alphabetical order?


texts: How to determine the greatest d orbital splitting?

texts:
This question comes specifically from an IB Chemistry HL Paper 1 in May 2018 TZ1, namely question 8.

Which complex has the greatest d orbital splitting?

It gives 4 Complexes $\ce{[Fe(H_2O)_6]^{2+}}$, $\ce{[Fe(H_2O)_6]^{3+}}$, $\ce{[Co(H_2O)_6]^{3+}}$, $\ce{[Cr(NH_3)_6]^{3+}}$ and it says that they give the colours green, orange, blue and violet respectively.

Initially I thought that the answer would be $\ce{[Cr(NH_3)_6]^{3+}}$ because it gives the highest energy light, being violet. However, the answer is given as $\ce{[Fe(H_2O)_6]^{3+}}$, why is this?


texts: Using enthalpies of formation and combustion to find formation enthalpy of Acetylene (Hess' Law)

texts:
I understand this is a simple question (I’m in high school), but for some reason the numbers just are not working for me.

Given:
$$\Delta H^\circ_\text{c} = -1301\ \mathrm{kJ}\ \text{for}\ \ce{C2H2(g)}$$
$$\Delta H^\circ_\text{f} = -394\ \mathrm{kJ}\ \text{for}\ \ce{CO2(g)}$$
$$\Delta H^\circ_\text{f} = -242\ \mathrm{kJ}\ \text{for}\ \ce{H2O(g)}$$
Calculate $\Delta H_\text{f}$ for $\ce{C2H2(g)}$.

My process:
$$(1) : \ce{C2H2(g) + 5/2 O2(g) -> 2CO2(g) + H2O(g) }\quad \Delta H^\circ_\text{r} = -1301\ \mathrm{kJ}$$
$$(2) : \ce{C(s) + O2(g) -> CO2(g)} \quad \Delta H^\circ_\text{r} = -394\ \mathrm{kJ}$$
$$(3) : \ce{H2(g) + 1/2O2(g) -> H2O(g)} \quad \Delta H^\circ_\text{r} = -242\ \mathrm{kJ}$$

$$\text{Target:}\ \ce{2C(s) + H2(g) -> C2H2(g)}$$

After some experimentation I arrive at:

$$-1\times(1) + 2\times(2) + (3) = \text{Target}$$

As shown through:
$$-1\times(1){:}\ \ce{2CO2(g) + H2O(g) -> C2H2(g) + 5/2 O2(g)} \quad \Delta H^\circ_\text{r} = 1301\ \mathrm{kJ}$$
$$2\times(2){:}\ \ce{2C(s) + 2O2(g) -> 2CO2(g)} \quad \Delta H^\circ_\text{r} = -788\ \mathrm{kJ}$$
$$(3){:}\ \ce{H2(g) + 1/2O2(g) -> H2O(g)} \quad \Delta H^\circ_\text{r} = -242\ \mathrm{kJ}$$
$$\text{Sum:}\ \ce{2C(s) + H2(g) -> C2H2(g)} \quad \Delta H^\circ_\text{f} = 271\ \mathrm{kJ}$$

Now as far as I know, all the givens are accurate empirical values. But the empirical value for $\Delta H^\circ_\text{f}$ for $\ce{C2H2(g)}$ is $227\ \mathrm{kJ}$.

What’s even weirder is that this disparity $(271-227=44)$ is equal to the difference between standard enthalpies of formation for water in gas and liquid states $(-242 - -286 = 44)$.

Have I made an error somewhere, or is water formed in the liquid state during the combustion of acetylene?


texts: Activation energy in physical adsorption

texts:
Physical adsorption of molecules on surface requires activation energy, because bonds of the adsorbed molecules are broken.

Is this a valid statement?

I have been under the assumption that physical adsorption does not involve any energy of activation as there is no chemical bond formation between the adsorbed molecules and the surface (and hence there is no necessity for bonds of adsorbed molecules to be broken).


texts: Why can't the strength of superacids be measured in water?

texts:
I learned about acid strength, that the strength of an acid increases with it's degree of ionization when solvated. So, in water, a strong acid is one where $\ce{[H_3O^+]}$ is large, which is equal to a low pH: $\mathrm{pH=-log[H_3O^+]}$.

Considering extreme cases, such as superacids, I have found out that other methods are used to measure their acidity (methods I don't really understand). My question is why is it impossible to simply get super high concentrations of $\ce{[H_3O^+]}$ in aqueous solutions of superacids, and use this to determine the acid strength. Also, is pH used as a measure of acidity outside of aqueous solutions?

I have come over the leveling effect, but I don't think I fully understand it. The way I understand it (for the case with water as solvent) is that basically any acid in water will protolyze $\ce{H2O}$ to $\ce{H3O+}$, making this the effective acid. I don't understand why this would affect the measured pH, as it is $\ce{[H_3O^+]}$ you are measuring.


texts: Name for H2O- radical? (H2O+ radical is Oxoniumyl)

texts: Radical are atoms with unpaired electrons, and they have short lifetimes because the unpaired electrons are highly chemically reactive. The $\ce{H2O^{.+}}$ radical is named oxoniumyl. Is there a name for a hypothetical $\ce{H2O^{.-}}$ radical?


texts: The reasoning behind predominance diagrams

texts:
Consider a one dimensional predominance diagram for a simple acid-base reaction:

$$\ce{AH <=> A^- + H^+}$$

With equilibrium constant:

$$K_a = \frac{[A^-]_{eq}[H^+]_{eq}}{[AH]_{eq}}$$

If I understand correctly, $[H^+] > K_a$, then $[AH]>[A^-]$. At first I thought I understood why this was so: the $[H^+]$ cancels out on both sides of the inequality, and then you bring $[AH]$ to the other side. Only now I realized that you can't actually cancel $[H^+]$ because on one side of the inequality it's actually $[H^+]_{eq}$, not the current amount of protons but the amount at equilibrium. So now I'm lost. What justifies this rule for determining predominance?


texts: Determination of timescales using characterization methods

texts:
There are 4 different timescales in material characterization (as classified in the Atkins textbook):
a. Time during which a quantum of radiation or a particle can interact with a molecule.
b. Lifetime of excited state of a molecule.
c. Minimum lifetime species must have to be seen as a distinct species.
d. Total time of experiment in which the species is observed.
Now the question is how to determine each of these? Say I have a certain compound and want to know what is the time of interaction of a photon with the molecule (part a). Is there an experimental method or instrument to determine these timescales?


texts: How does a Pt and reference electrode measure the cell potential in a potentiometric titration?

texts:
I'm trying to perform a potentiometric titration to determine the redox potential of a $\ce{Fe^3+|Fe^2+}$ couple. To do this, I am using an $\ce{Ag|AgCl}$ electrode connected to an inert $\ce{Pt}$ electrode, which is submerged in a solution containing $\ce{Fe^3+}$ ions. I then titrate it with $\ce{Co^2+}$, which reduces it to $\ce{Fe^2+}$. The reference and inert electrode are connected with a standard voltmeter.

What I don't understand is why the inert electrode measures the redox potential of the $\ce{Fe^3+|Fe^2+}$ couple. As per my understanding, there is an electron flow from the reference electrode into the inert electrode, which would get accepted into the Fe solution, but now, the transfer of electrons is only between the $\ce{Co^2+}$ and $\ce{Fe^3+}$ ions, so what happens to that electron? Can someone explain exactly how the redox potential of the $\ce{Fe^3+|Fe^2+}$ couple gets measured, with reference to electron transfer between the reference and inert electrodes?


texts: How can I calculate molality from molarity?

texts: How can we determine the boiling point of 1 molar aqueous solution (density 1.06 g per ml) of KBr? If I use the colligative property formula than I require molality instead of molarity. Here the density given is the one of the solution not the solvent.


texts: Is there a way to find the kinetics data for the strong acid weak base reaction?

texts:
I am layman of chemistry. Latterly, I am asked to do an mathematical optimization task for a bio-chemical process, which contains a conditioning step to neutralize the sulfuric acid using ammonia hydroxide. I am trying to use the mathematical model of the reaction (kinetic model) to optimize the reaction time/energy/efficiency (target not determined yet). However, I could not find the kinetics data. Is there a way I could find the kinetic model of the reaction?

Another question is that: Should I treated this reaction as an element reaction and use third-order reaction rate formula?

I am confused by a former post (Finding rate of acid - base reaction). In that post, the accepted answer says "Typical acid - base reactions that occur in solution are diffusion controlled reactions. Such reactions do not follow second order kinetics because at virtually every encounter of the acid and base, rapid proton transfer occurs and the reaction is complete. " Should I use the diffusion control model instead of the reaction rate model?

Any suggestion is welcomed.


texts: In electrolysis, why is hydroxide oxidised in preference to anything(?) but halides?

texts:
In electrolysis of aqueous solutions, I can loosely explain what happens at the cathode in terms of reactivity - any metal more reactive than hydrogen stays in solution, effectively because they're more attracted to water molecules. I could also explain this in terms of redox potential if I had to (I'm teaching this at GCSE level right now - to 16-year-olds - and we don't bring in redox potential or the electrochemical series until later).

But what happens at the anode is currently puzzling to me. We're told that the only anions which get oxidised in preference to hydroxide are the halides, but I can't explain that in terms of reactivity, and so far I'm not sure how to explain it in terms of standard reduction potential, either.

So - why the halides? And are they really the only anions oxidised in preference to hydroxide?


texts:
I recently realised that the STO-nG basis functions were fit to 1s/2s/3d STOs of various exponents, instead of being fit to STOs of higher principal quantum numbers (such as 2s/3p orbitals etc.).

Has a Gaussian expansion of STOs of higher quantum numbers (for example, 2s or 3p STOs) been performed, and are there any GTO integration schemes for Cartesian GTOs of higher principal quantum numbers?


texts: I was wondering if the above mentioned reaction has any uses? I looked up applications and significance and couldnt find anything. I came across Saponification but that involves a base and is a completely different reaction. Then I thought the products maybe useful but i realised that ethanol and acetic acid are used to produce said ester. then what exactly is the point of this reaction?


texts:
I am really confused about how reducing partial pressure of a gas by a certain percentage would impact the behavior of an equilibrium system.

e.g $\ce{POCl3_{(g)} <=> POCl_{(g)} + Cl2_{(g)}}$ is at equilibrium.  How would this system behave if the partial pressure of $\ce{Cl2}$ is reduced by 75%?

I understand the partial pressure is related to moles but having a hard time applying it here.  My guess is that the reactant would be consumed to produce more of the $\ce{Cl2}$ since its pressure and thus moles are decreasing.  However, my instructor said the system would react by consuming $\ce{POCl}$, the reason for which was not explained too well.

If I could get an explanation, it would be much appreciated.


texts: Why does only a single azeotropic composition exist for a mixture of two given substances?

texts: In the image below, which represents a generic composition vs. temperature plot for a mixture, there is a single intersection point between the vapor and liquid curves. This is due to the fact that the composition corresponding to this intersection point has an extremely low boiling point due to negative deviation from Raoult's law. If this is the case, why is it not possible for the vapor curve to "hug" the liquid curve along an entire section, rather than just at one point? Similarly, why does the vapor curve have to intersect liquid curve at all? Would it be possible for the minimum point of the vapor curve to be located just above the minimum point of the liquid curve?


texts: What are the components of a labware setup for short-path distillation?

texts:
I've recently become interested in short-path distillation and have found that most kits are in the thousands of dollars. So I thought that I would compile the labware myself.

I understand the theory behind short path distillation, but do not know the actual names of the components. I do know I will be using a digital hotplate and labware grade pyrex labware.

So what is the (cheapest) "shopping list" needed to compile and assemble all the labware necessary to construct a short-path distillation apparatus?


texts: Why would phosphorus pentoxide be called 'phosphorus(v) oxide'?

texts:
There's a question in the chemistry textbook I use with my GCSE class which asks pupils to identify which of various compounds feature ionic bonding. One of the compounds is phosphorus(V) oxide, which I gather is an accepted name of phosphorus pentoxide (or tetraphosphorus decoxide, if you prefer). But why? One of my pupils reasoned that it must have ionic bonding, because I'd just explained to them how Roman numerals in brackets indicate the number of electrons lost. This is evidently an exception, but none of the guides to chemical naming I've found explain why!

I figure the explanation must lie in subtleties of the oxidation state that I haven't yet got my head round - Wikipedia's page on oxidation state lists phosphorus pentoxide as having oxidation state +5, and phosphorus trioxide as +3, but I'm not entirely following why.

Any clarification much appreciated!


texts: Simulation of Pyridin attached to gold atom

texts:
I would like to simulate to get the influence of a gold atom on the oscillation modes of pyridine. I have already carried out simulations in which there is a coordinative bond between nitrogen and gold atom.
now I would like to simulate the effect when the gold atom is next to the ring system. So that a kind of pi complex from the ring system can attack the gold atom.
In the literature, I have found that apparently the gold atom is only positioned next to it and the calculation starts. with me, however, the gold atom is only moved away.
Does someone have a tip for me? I use gaussian with the oniom option and the pwb6b95d3 functionally. basic set organic: aug-cc-pvtz and for gold lan2dz.


texts: Removing sulfur in Barton-Kellogg reaction without triphenylphosphine

texts:
I'm trying to understand how the sulfur was removed in the following reaction, taken from a paper by Ben Feringa:1

After some research I found out that this is a Barton-Kellogg reaction. Based on this I went through the mechanism as follows:

I'm stuck on the final step of how to remove the sulfur. I looked over multiple papers and all of them used $\ce{PPh3}$ to open the episulfide but the reaction from the paper I'm considering does not have $\ce{PPh3}$. I looked at all the sources and supporting information the paper had linked but couldn't find anything to explain how the double bond forms. My only guess is that something happens when they purify it using $\ce{SiO2}$ flash column chromatography. Here is the excerpt from the SI (L2 is the alkene product):

  Freshly prepared diazafluorene 1 ($\pu{350 mg}$, $\pu{1.80 mmol}$) and thioketone (±)-2 ($\pu{383 mg}$, $\pu{1.80 mmol}$) in THF ($\pu{10 mL}$) were heated at reflux for 14 h under a $\ce{N2}$ atmosphere. The solution was cooled to rt, concentrated and purified by FC ($\ce{SiO2; EtOAc}$) to afford (±)-L2 ($\pu{327 mg}$, $52\%$) as yellow solid [...]

I would like any suggestions on what people think may be happening.

Reference

Wezenberg, S. J.; Chen, K.-Y.; Feringa, B. L. Visible-Light-Driven Photoisomerization and Increased Rotation Speed of a Molecular Motor Acting as a Ligand in a Ruthenium(II) Complex. Angew. Chem. Int. Ed. 2015, 54 (39), 11457–11461. DOI: 10.1002/anie.201505781.


texts: What is the explanation of the changes in stability going down a group for carbonates, bicarbonates, fluorides, and chlorides?

texts:
For carbonates and bicarbonates, I know that stability increases down the group, and for chlorides and fluorides, stability decreases down the group. Why does this happen?  Can someone explain this in detail?

(I am talking about S block alkali metals)


texts: Was nitroglycerin invented as an explosive?

texts: Although I have researched this as carefully as the web allows, it is not clear to me if the inventor was planning to make an explosive and if so, why he thought the process he undertook would yield one. Were there similar compounds created with acids that were also explosive? I understand that in the early 1800s, there was a lot of apparently random experimentation.


texts: Why total heat of hydrogenation of 1,3-cyclohexadiene is more than that of benzene?

texts:
I'm told that heat of hydrogenation (HOH) is directly proportional to number of π bonds and inversely proportional to stability. So, is the aromaticity responsible for this?

Also, what is the general approach to the problems like this? Say, I encountered napthalene and some hydrocarbon which contains about 2 rings and have π bonds less than naphthalene, just like stated above – then how shall I decide?

Is there any specific rule like if a compound will be aromatic then it's HOH will be reduced by this amount or something like that?


texts: Why is potassium ferrocyanide considered safe for consumption, when it is just one reaction away from the highly toxic potassium cyanide?

texts:
According to this answer, heating potassium ferrocyanide will decompose it into potassium cyanide.

Now, potassium ferrocyanide is an approved anti-caking agent, and hence used in table salt, for example.

Table salt is often heated as part of cooking. So, isn't there a chance for trace quantities of potassium cyanide entering the body?

NB: I understand that the dosage here, if any, might not be lethal; am more concerned about trace amounts causing inefficiencies in bodily functions.


texts: Removing potassium chloride crystals from a mineral composed of manganese dioxides

texts:
How can I remove crystals of potassium chloride from a mineral composed of manganese dioxides?
Hey, i'm a high school student trying to do a good cryptomelane sample to use in my scientific project.
I was able to develop the cryptomelane, but after some necessary processes, the mineral was crusted with crystals of potassium chloride, what would be the best process to remove this salt?


texts: Which of the following isomers of 2,3‐dihydroxy‐4‐methoxy‐4‐oxobutanoic acid are identical?

texts:
Which of the following are identical?

A and B are identical
A and B are diastereomers
A and C are enantiomers
A and B are enantiomers

What I know is that when we rotate a Fisher projection by 180°, then we get identical compounds (I might be wrong). But how to tell if the compounds are enantiomers of each other or not?
For that how to get the same group, i.e. $\ce{-COOH}$ in this case at the top to compare the compounds?
Also, is there any trick to tell that if they are diastereomers, enantiomers or identical by the hydroxyl group positions in Fisher projections?


texts: Is there a point at which Ethanol (E10) fuel becomes harmful to gas tanks or engines if not used?

texts:
This is not the typical chemistry question on this website, but I think it's an important practical question.

When I got a gas string trimmer, the woman who worked at the gardening shop told me that E10 (fuel commonly sold in the USA - 10% Ethanol, 90% gas) left sitting in a gas tank for months would be harmful. So I wonder, is this true? And if so, what about for cars and other engines (boats, tractors, etc).

This effects my life because I was considering at some point getting a plug-in hybrid car because during most weeks I would never have to use or buy fuel. However, could I be damaging this car by leaving the same fuel inside the tank for months?

There are various claims about ethanol either helping or hurting things, but I have not seen any supported by science. What is the chemical basis of these claims? A layman translation is appreciated.


texts: How would I make a basic protein folding algorithm?

texts:
On the face of it it doesn't seem especially difficult.
Model the amino acids as solid objects linked together. Approximate the 3D force fields around them using a coarse approximation, then set the simulation going in a computer and see what happens.
Why is this such a difficult problem that it has taken decades to crack? Are there subtle difficulties not apparent in the above model?


texts:
How would you find the pH of an acid dissolved in water? Would you need to take the fact that the pH of water is already 7 into account and go on from there?

Say, for example, that you add 0.0500 mL of 0.00100 M HCl into 50 L of pure water, what will be the pH of the new solution?

I made the mistake of just finding the moles of the HCl placed into the pure water, and finding the new concentration by dividing by the litres of water present. This gave me a pH of 9, which does not seem to make any sense as acids are meant to lower pH!

Some help would be wonderful!


texts:
I've been learning to use Gaussian recently and I found a question here that seemed like a good opportunity for me to practice. I know that I can obtain $K_a$ from $$\Delta G=-RT\ln(K_a)$$ using the general reaction $$\ce{HA(aq) + H_2O(aq)->A-(aq) +H_3O+(aq)}$$ and taking the sum of thermal and electronic free energy for each compound as their value of $G$ However, I'm not confident that the method I'm using in Gaussian is correct.

I performed an optimization/frequency calculations on all these molecules using the APFD functional, with basis set 6-311G+(2d,p) and SMD solvation using water.

After working out my calculation, I obtained $pK_a=26.10$. My main question comes down to: did I use a sufficient level of theory, at least approximately, to capture the effect of solvation? I've looked at the Gaussian white book for thermochemistry as well as a few journal articles (1  2) and couldn't get a clear sense of if I had the right level of theory or if my calculations were completely off-base.

Another finer point might be: are there any fairly similar experimental values to which I could compare my calculation to see if I'm in the right ballpark?


texts: Why do liquids vaporise spontaneously at temperatures below boiling point despite ∆G being positive?

texts:
We say that for the equilibrium
$$\ce{A(l)<=>A(g)}$$ the ∆G is zero at its boiling point (the thermodynamic definition of boiling point), and becomes positive at temperatures below the boiling point. However every liquid has a characteristic vapour pressure at all temperatures. How does this happen even though the ∆G has become positive thus the reaction has lost spontaneity?


texts:
(source: sigmaaldrich.com)

I'm trying to analyse the proton NMR of this, and there's one singlet for the H on the non-substituted Cp ring and a singlet for the methyl group, as expected.

However, while I was expecting to see a dd signal from $\ce{H_2}$ and $\ce{H_3}$ and a doublet from $\ce{H_1}$ and $\ce{H_2}$, there is only one doublet that accounts for all the protons according to integration.

Can someone help me explain this?


texts:
I have two crystal structures, one in R3m and one in Cm symmetry. Both structures also differ in stoichiometric ratios, $ABC_4$ and $A_2B_2C_8$, respectively. Both structures look nigh on identical, with the exception of double the amount of atoms in one than the other.
How would I go about manually changing the symmetry of the Cm structure to R3m symmetry? I normally use VESTA as a visualization tool, and Avogadro as a tool for imposing symmetry.


texts: How to identify if it is a buffer solution

texts:
Aqueous solutions of $\ce{HNO3}$, $\ce{KOH}$, $\ce{CH3COOH}$, and $\ce{CH3COONa}$ of identical concentrations are provided. The pair (s) of solutions which form a buffer upon mixing is(are)?
A. $\ce{HNO3}$ and $\ce{CH3COOH}$
B. $\ce{KOH}$ and $\ce{CH3COONa}$
C. $\ce{HNO3}$ and $\ce{CH3COONa}$
D. $\ce{CH3COOH}$ and $\ce{CH3COONa}$

I think that option D is correct as it a solution of a weak base and its a salt; that's why it is a buffer solution. But how do I check the other options?


texts: Changing the spectroscopy type to infrared in GC-MS

texts: I know you can use GC-MS for the analysis of gaseous molecules, but would you be able to instead use an infrared spectroscopy method to analyse gaseous molecules, or does it need to be mass spectroscopy?


texts: What exactly does a "system" include in chemistry?

texts:
If we have reactants $\ce A$ and $\ce B$ and the reaction(s) between them haven't started yet, are those reactants our "system"?

After the reaction takes place, are products then also included in the "system"?

Basically, is it the case that the term "system" refers to all the chemicals we have in a reaction?


texts: How can an electron being a wave have such property as spin?

texts:
Here's what I know about electrons.
Electrons have wave-like properties and the number of wavelengths in the $n^\text{th}$ shell is equal to $n(\lambda).$ Also, I read in my book that they have another property called spin.
But I couldn't imagine how a wave can have a property of spin. If this property is just a mathematical model, then is this property compatible for a wave i.e.  Is it appropriate to use this property of spin with waves ?


texts:
Will oxalic acid, in a saturated solution in ethanol, be able to undergo an esterification reaction with the ethanol? This is assuming no acidifying agents (or anything else, for that matter) are added, and room temperature is also assumed.

I tried to find an equilibrium constant to predict the extent of such a reaction, but I couldn't seem to find anything. This suggests either that the reaction does not take place, or that it is so obscure that nobody has bothered to examine it.


texts:
I was wondering what the product will be in the following reaction:
$$\ce{H3COOCH3 ->[\ce{H+}]} \:?$$

I was thinking about $\ce{CH3COOH}$  being a product but I do not know the mechanism.


texts: Net direction of dipole moment in oxygen difluoride

texts:
What is the net direction of dipole moment in $\ce{F2O}$ molecule?
In the case of $\ce{NH3}$ and $\ce{NF3}$ molecules both have net dipole moment with direction reversed due to strong electronegativity of fluorine atoms, whereas in the case of $\ce{H2O}$ the direction of net dipole moment is from oxygen atom towards lone pair with a value $\mu(\ce{H_2O}) = \pu{1.84 D}.$
But in my textbook the value of net dipole moment of $\ce{F_2O}$ molecule is given $(\mu(\ce{F2O}) = \pu{0.3 D}),$ but not its direction.
I have done a lot of research on google but I could not find any related information.


texts:
Calculate the change in pH of a buffer made by combining $\pu{500 ml}$ of $\pu{0.1 M}$ $\ce{CH_3CH_2COOH}$ and $\pu{500 ml}$ of $\ce{CH_3CH_2COONa}$, when $0.04$ moles of $\ce{NaOH}$ is added to the solution. Assume the addition of sodium hydroxide has no effect on volume.
  ($\pu{\mathit{K_a} = 1.3 \times 10^{-4}}$)

My solution:

$$\pu{0.10 M \times ~ 500 ml = 0.05 mol} \ \ce{CH3CH2COOH}$$
$$\pu{0.12 M \times ~ 500 ml = 0.06 mol} \ \ce{CH3CH2COO-}$$

$$\pu{pH = p\mathit{K_a} + \log \left(\frac{0.06}{0.05}\right) = 3.965}$$

Using the equation again where the salt is $\pu{0.1M}$ and the acid is $\pu{0.01M}$ due to the addition of $\ce{NaOH}$ yields a wrong result equal to $1$.

I honestly find the wrong answer to be logical, however I can't think of a way to find the right one.


texts:
$$\ce{A -> B -> C -> A}$$

In Alberty's Physical Chemistry (7th ed.), the author says that this reaction mechanism is not possible. The reason given is:

  Although this mechanism at first sight appears reasonable, no actual process follows this mechanism because it violates the principle of detailed balance. According to this principle, at equilibrium the forward rate of each step is equal to the reverse rate of that step. Thus equilibrium cannot be maintained by this mechanism.

I understand the statement of the principle ("at equilibrium the forward rate of each step is equal to the reverse rate of that step"), but I don't get how it implies that equilibrium cannot be maintained, or that this reaction is not possible.


texts: How does the human body deal with free radicals it creates itself?

texts:
I know that free radicals are created all over your body all the time as a byproduct of its chemical processes, (or maybe I do not and that is false). However I am confused about the distinction between free radicals formed from UV photons that will affect DNA base pairings, and the ones that the human body creates on a consistent basis.

How does the body deal with the free radicals it created by itself?

And how are those free radicals different from the ones that cause oxidative damage (e.g., from UV rays)?


texts: Approximated formula of acid dissociation constant

texts:
$K_\mathrm{a}$ can be expressed as $K_{\mathrm{a}} = \frac{[\ce{H^{+}}] [\ce{A^-}]} {[\ce{HA}]}$, however, it can be approximated that $K_{\mathrm{a}} = \frac{[\ce{H^{+}}]^{2}} {[\ce{HA}]}$.

I usually use the approximated equation when I'm dealing with questions that don't provide [$\ce{A-}$]. What I don't understand is why/how can we approximate it to this?

To approximate to $\ce{[H+]^2}$, then $\ce{[H+]}$ and $\ce{[A-]}$ must be pretty much equal, and so this must assume that the acid completely dissociates. However, in practice, do acids dissociate to the point that $\ce{[H+]}$ and $\ce{[A-]}$ are equal? If not, then how can we approximate to $\ce{[H+]}^2$, and are there any mathematics that demonstrate this approximation?


texts: How can t2g orbital account for extra stability in absence of ligands?

texts:
I have read in a book that t2g orbitals sometimes account for stability in 3d block transition elements. For example,

Chromium in 2+ oxidation state shows reducing properties because Chromium in 3+ oxidation state will have half-filled t2g orbitals which will account for extra stability.
Vanadium has a low value of M+3/M+2 standard electrode potential because of half-filled t2g orbital.

What I have read is that the d orbitals in the absence of ligands have equal energy, and the orbitals split up into eg and t2g due to the presence of ligands. Then how can the half-filled t2g orbitals account for stability, even in absence of ligands?


texts: Problem in Colour in Cerium (IV)Sulphate due to charge transfer

texts:
My text says that $\ce{Ce(SO4)2}$ is coloured due to charge transfer spectra.
It also gives other examples such as $\ce{KMnO_4}$ and $\ce{K_2Cr_2O_7}$, to which I agree but when I read the conditions for charge transfer spectra to take place it says

+6;+7;+8 show it more
if the central metal atom is diamagnetic but still if compound is showing colour.

I see $\ce{Ce}$ in its +2 state and configuration
$\ce{[Xe] 4f^1 5d^1 6s^0}$
doesn't show 1st  the conditions then where am I going wrong?


texts: Gibbs free energy describes the maximum of useful work that can be done by a chemical reaction. My question is(Sorry I am not into chemistry and biochemistry) : during a chemical reaction that creates ATP, we say that ATP stores energy between its chemical bonds . For exemple this is the equation of creating ATP: ADP + Pi + energy ----> ATP and of course this reaction has DG. What is the relation of DG with the stored energy? Is it the same?


texts: Why does naphthalene have a higher melting point than both water and diphenylamine?

texts:
We learn that polar compounds have higher melting and boiling points than nonpolar compounds due to strong intermolecular forces such as hydrogen bonds and dipole-dipole interactions.

Naphthalene is an extremely simple and nonpolar compound, yet it has a significantly higher melting point than diphenylamine (a similar enough structure that is not only heavier, but has a dipole-inducing amine) and water (famously super polar).

What's going on here?


texts: Why does adding salt to water reduce the pH?

texts:
I recently heard someone claim that adding table salt to vinegar caused HCl to form which helped them clean coins - clearly not the case - however I thought I'd disprove it by doing an experiment.

So I added NaCl to ethanoic acid and measured a 0.5 reduction (3 to 2.5) in pH using a pH probe. This seemed a bit weird so I repeated using tap water and the same happened (7 to 6.5).

The pH of water when NaCl is added should not change from 7!

The probe measures by detecting a change in voltage through the solution so it could be that, but you'd think that salts shouldn't have such an effect or be adjusted for. Can anyone repeat please?

What's going on?


texts: Chemistry underlying blacks spots in banana bread

texts:
I've noticed that when I bake banana bread with certain brands of self-raising flour, the finished product looks more or less like any other cake.

However, when I use flour with sodium bicarbonate as the leavening agent, black spots appear peppered throughout the cooked cake.

What is the chemistry behind this phenomenon?


texts:
I have several questions about the rusting of metals (take iron as a specific case if you wish) that I have not found clear answers to:

1) Does water act as a catalyst in prototypical rusting reactions, or is it actually consumed? (keeping in mind that $H_2$ gas produced may be oxidized back to water by ambient $O_2$.)

2) Is dry rusting possible with just $O_2$ and metal? Am I correct that it is thermodynamically favored but kinetically discouraged?

3) Is it realistic to rust a metal using oxygen and a dry polar solvent? If so, what solvents would be suitable?


texts: Silver-promoted reaction of alkyl halide with diphenyl sulfide

texts:
What is the major product formed when 1-chloro-3-iodopropane reacts with diphenyl sulfide in the presence of one equivalent of $\ce{AgBF4}$?

I know that sulfur is nucleophilic and that it can displace a halide in a SN2 reaction, but the resulting molecule will have a positive charge. Is that okay? What possible use does the product have?


texts: Doesn't the isothermal irreversible expansion/compression of an ideal gas law violate the ideal gas law?

texts:
Let's say a cylinder has some ideal gas. We use a piston to suddenly expand the gas in isothermal condition from $1\ \mathrm{atm}$, $20\ \mathrm L$ to $0.5\ \mathrm{atm}$, $50\ \mathrm L$.

Since the gas is ideal, $pV = nRT$ implying that $nRT = 20\ \mathrm{L\ atm}$ initially. Later $pV$ changes to $25\ \mathrm{L\ atm}$. However, $nRT$ has to continue to be $20\ \mathrm{L\ atm}$ as the number of moles and the temperature remain constant.

Doesn't this violate the ideal gas equation, as $pV$ and $nRT$ are no longer equal. Does this mean that the irreversible expansion or compression of an ideal gas can not be isothermal unless the number of moles change (through some chemical reaction)?


texts:
As I understand, if a molecule is cyclic and planar, then every atom in the ring must be $\ce{sp^2}$-hybridized and the molecule must have [4n+2] π electrons, where n∈N (Hückel’s rule).

An article in Chemistry World by Sam Howell ("New rule predicts stabilising aromaticity in open-shell metal clusters", 21 MAY 2019), talks about jellium aromaticity.

image source : https://www.chemistryworld.com/news/new-rule-predicts-stabilising-aromaticity-in-open-shell-metal-clusters/3010515.article

My  question is what is jellium aromaticity?

Does it have anything to do with Hückel's rule?


texts:
If you have $\ce{CH3-\color{\red}{CH2}-CH2Br}$

Then the $\ce{CH2}$ (in red) would have a peak splitting of $12$ because $(n+1)(m+1)$
where $n$ for the $\ce{CH3}$ is $(3+1=4)$ and m for $\ce{CH2}$ is $(2+1=3)$ so its $4\times3=12$

source:

  In the general case, a signal will be split into $(n + 1) \times (m + 1)$
  peaks for an $\ce{H}$ atom that is coupled to a set of $n~\ce{H}$ atoms with one
  coupling constant, and to a set of $m~\ce{H}$ atoms with another coupling
  constant.

How can we determine differences in the coupling constant by just looking at the structure? Otherwise how do I know when to apply $n+1$ OR $(n+1)(m+1)$?

But in the other textbook it says:

$\ce{CH3-\color{\red}{CH2}-CH2-COOH}$

The $\ce{CH2}$ (in red) has a peak splitting of $6$ because $(n+1)$ where $n=5$, $(5+1=6)$ and the $n$ is the $3~\ce{H}$ on $\ce{CH3}$ plus the $2~\ce{H}$ on $\ce{CH2}$.

Source:

Which is the correct method? Or are both right? and why?

Alternatively symmetric adjacent hydrogen groups:

$\ce{CH3–\color{\red}{CH2}–CH3}$

Is the $\ce{CH2}$ split to 4 peaks due to symmetric adjacent hydrogen environments? Due to $n+1$, where $n=3$ so $(3+1=4)$.  I read that it should be split into 7 peaks - but where are they getting 7 from - is it $n+1$, where $n=6$ so $(6+1=7)$. For symmetric adjacent groups do you allow $n$ to be the sum of all hydrogens adjacent/or not?


texts: ASTM D2270 Viscosity Index Formula/Table derivation

texts:
How was the formula (3) for viscosity index $\mathrm{VI}$ derived in section 5. Procedure A—Oils of Viscosity Index Up to and Including 100 [1]?
Specifically with reference to the reference oils considered and the table for it.

$$\mathrm{VI} = \frac{L - U}{L - H} \times 100$$

References

D02 Committee. ASTM D2270 - 04 Practice for Calculating Viscosity Index from Kinematic Viscosity at 40 and 100 °C; ASTM International. DOI: 10.1520/D2270-04. (PDF)


texts:
I saw online that the radius for each level is defined by the formula:

$$r_n=n^2 r_1$$

Where $r_1$ is approximately $53\ \mathrm{pm}$.

However, on the Barron's AP chemistry book 7th edition, it says "The radii of the other orbits are whole-number multiples of the Bohr radius" (Page 89). It even gives an example of when $n=2$ that the radius is $106\ \mathrm{pm}$.

But that's different from what the formula above says, which when $n=2$ radius should be $212\ \mathrm{pm}$. Is this an error in the book? I'm quite confused by the discrepancy.


texts: Why is the ionic radius of Al(3+) smaller than that of Li+?

texts:
I was examining the ionic radii of some ions from this site for a school assignment. I noticed a weird anomaly in the ionic radius of $\ce{Li+}$  as compared to that of $\ce{Al}^{3+}$.

The ionic radius of $\ce{Li+}$ is about 2/3 as large of that of $\ce{Al}^{3+}$. How is this possible, since the electronic configuration of $\ce{Al}^{3+}$ is $[1s^2, 2s^2 2p^6]$ whereas that of $\ce{Li+}$ is $[1s^2]$? It appears that despite the presence of an extra shell in $\ce{Al}^{3+}$, it has a smaller ionic radius than $\ce{Li+}$.

The answers in this post suggests an exactly opposite outcome. All the answers says that $\ce{Mg^{2+}}$ is above $\ce{Ca^{2+}}$, thus it has a smaller radius. By applying  the exactly same logic i can say $\ce{Li+}$ is above $\ce{Al^{3+}}$ so it must have less ionic radius but that is not the case.

As the below picture suggests,(taken from the same post).

I think it is because of diagonal relationship. As $\ce{Mg^{2+}} = \ce{Li+}$ because of diagonal relationship and $\ce{Mg^{2+}} \gt \ce{Al^{3+}}$ because ionic radius decreases for cations along the period by going left to right.

Am I correct?


texts: Why is zinc blende not directly reduced in smelting furnaces?

texts: My question can also be generalized as, why are some sulfide ores (like $\ce{ZnS}$) roasted first to generate oxides, and only then reduced in a blast furnace or similar furnace?


texts: What product is formed in the Wurtz reaction of 1-bromo-3-chlorocyclobutane?

texts:
I want to do Wurtz reaction of 1-bromo-3-chlorocyclobutane:

Wikipedia suggests to do an intramolecular reaction. Instead, I remember reading somewhere that bromine is more reactive and hence we should do an intermolecular reaction, and attach two carbons to where $\ce{Br}$ was attached.

So, what product is formed in the Wurtz reaction of 1-bromo-3-chlorocyclobutane?


texts: If dark surfaces absorb/store more light/energy than light surfaces, then does dark skin, on average, store energy from light most efficiently?

texts: If darker surfaces absorb/store more light/energy per square inch than light surfaces, then does dark skin, on average, store energy more efficiently than light skin? (edited).


texts:
The acid catalysed hydrolysis of an compound $\ce{A}$ at $\pu{303K}$:
$$\ce {A ->[$k$] B}$$ has a half-life of $\pu{100 min}$ when carried out in a buffer solution of $\mathrm{pH=5}$ and $\pu{10 min}$ when carried out at $\mathrm{pH=4}$. Both the times the half-life are independent of the initial concentration of $\ce{A}$. Find its Rate Law.

I am planning something like this:
Let $$\text{Rate} = k [\ce{A}][\ce{H+}]^x\tag1$$
Now let:
$$k'=k[\ce{H+}]^x\tag{constant}$$
And then:
$$k' t_\frac 12 = \ln2$$

Is it conceptually correct?

Note:

I have found tons of solutions over the internet all with different answers.

The answer given in my book is x=1 (x is same as is used in eq(1)) and I found the same myself but some sites give answer of the same question as x=2.


texts: Synthesis of phenethyl alcohol from benzene

texts:
How can I make phenethyl alcohol $(\ce{C6H5CH2CH2OH})$ from benzene?

I have got information that phenethyl alcohol is made from benzene by Friedel-Crafts reaction between benzene and ethylene oxide in the presence of aluminium trichloride as follows:

$$\ce{C6H6 + CH2CH2O + AlCl3 → C6H5CH2CH2OAlCl2 + HCl}$$

But I have no idea how it reacts and proceeds to work.

Can anyone help me understanding the mechanism of synthesis and reaction of making phenethyl alcohol from benzene?


texts:
The key tells me these are enantiomers.

I however don't think they are; their chiral carbons' configurations aren't inverted - i.e. only one chiral carbon's R/S configuration changes! This suggests diastereomers to me! Plus the Sawhorse projections I draw don't seem to be mirror images.


texts: What is the intuition behind 'mol' as a unit 'symbol'

texts: Why are moles written with 'mol' as opposed to something which is easier to write with one character, or even two?


texts: Why negative charge delocalises away from electronegative atoms

texts:
In the mechanism for the Wolff-Kishner reduction, after the $\ce{OH-}$ abstracts a proton, the resulting negative charge delocalises away from the nitrogen atom to the carbon, and the subsequent protonation occurs to the carbon.

Why does the negative charge delocalise away from the more electronegative nitrogen to carbon, for ostensibly a longer time period (for the chances of the proton settling with the carbon to be high)?

How does this happen, when the molecule that results from protonation here doesn't have resonance stabilisation, but there is resonance if it was on Nitrogen that the proton attached?

A similar question arises in Aldol condensation; why is the carbanion the molecule that moves the reaction forward and not the enolate? Since the enolate has the negative charge on the oxygen, I would have assumed it would be the prevalent species in the reaction mixture.


texts:
Consider the relation:
$$E_{Activation}=E_{Threshold} - E_{Avg}$$
Here the $E_{Avg}$ refers to the Potential Energy of the reactants. Now in order of meet $E_{Threshold}$ , the molecules must have sufficient Kinetic Energy which is measured in terms of $E_{Activation}$.
Hence when we write Arrhenius equation:
$$k=Ae^{-\frac {E_{activation}}{RT}}$$
The term $exp(-E_{activation}/RT)$ means the number of molecules having Kinetic Energy greater than Activation Energy which coherently measures the minimum Kinetic Energy reactants need to have for reaction

Do my arguments make sense?


texts: What dictates the lifetime of a solvated electron in a given solvent?

texts:
Solvated electrons have a long lifetime in ammonia solutions, but their counterparts in water (called hydrated electrons) have a much smaller lifetime, of the order of microseconds in very pure water.

(image from: Boero et al, Phys Rev Lett 2003, 90, 226403)

What properties of the solvent account for these very different lifetimes? Both are polar protic solvents, so what other(s) factor(s) could be involved here?


texts: When a solution is diluted, the number of moles of the solute decreases. what would happen to the molarity?

texts: When a solution is diluted, the number of moles of the solute decreases, so the molarity decreases??