texts:
I have a Chemistry lab in which I must design and carry out an experiment to determine the compound in each of eight numbered vials. Each vial contains one of these ionic compounds:

BaCl2
CaCO3
Ca(OH)2
KI
NaCl
NaHCO3
Na2SO4
Pb(NO3)2

Materials:

Distilled water
Several microwell reaction plates
Tooth picks (to stir)
8x 1mL Beral style pipets
The contents of the lab drawer (beakers, test tubes, etc.)

In addition to the materials above, one of the following four additional reagents may be used:

6M H2SO4
6M HCl
6M NaOH
phenolphthalein indicator solution

I know how to identify a couple of them. For instance, CaCO3 can be identified by its insolubility in water, but as for the rest, I'm not completely sure. I know some can be identified by how and if they react with other compounds, but I don't know exactly how to go about that.


texts: I don't get the CBS reduction of ketones in organic chemistry. I can draw two ''chair'' structures for the reduction of phenyl,methyl ketone and each gives a different enantiomer. Both have the phenyl equatorial, I don't know what I'm doing wrong. Please, help.


texts: Why is it considered acid rain with pH <5.6?

texts:
I recently read in a book that rain is considered acid rain if the pH falls below 5.6. However a substance is acidic when the pH is below 7; so why is the boundary for acid rain 5.6?

I was thinking pH between 5.6-7 would be too diluted to have an effect on limestone and other materials, and that's why the pH has to be under 5.6. But I wasn't sure if this is true so I wanted to find out.


texts: Does burning plastic completely disintegrate it? Accidentally melted some plastic in a BBQ, wondering if pyrolytic cleaning is an option

texts:
I accidentally barbecued some plastic today, making quite a mess. It's a cushion for a lawn chair, so I imagine probably some sort of plastic or polyurethane.
Rather than cleaning melted plastic manually, I'm wondering if its a good idea to just burn it off? The BBQ is a Kamado oven, so it can reach about $\pu{350 ^\circ C}$ or $\pu{700 ^\circ F}$ for a sustained period of time.
It's a well ventilated area, so smoke isn't a concern. I am somewhat concerned that it may not burn completely and contaminate future cooks.
Can anybody offer some insights on if $\pu{350 ^\circ C}$ is hot enough or if this is a good idea at all?


texts: Ratio of uncharged to charged side chains

texts:
The $\mathrm{p}K_\mathrm{a}$ of the side chain imidazole group of histidine is $6.0.$ What is the ratio of uncharged to charged side chains at $\mathrm{pH}~7?$

Here's my attempt to the solution:

$$7 = 6 + \log\frac{[\ce{A-}]}{[\ce{HA}]}$$

$$1 = \log\frac{[\ce{A-}]}{[\ce{HA}]}$$

$$10[\ce{HA}] = [\ce{A-}]$$

$$\underset{\text{uncharged}}{1} : \underset{\text{charged}}{10}$$

I've used the Henderson-Hasselbalch equation to the solve this, considering imidazole group to be the acid $\ce{HA}$. However, the correct answer appears to be 10:1 uncharged to charged ratio. If I use $\ce{HA^+}$ to be the acid, the answer turns out correct.

Can anyone tell me what have I done wrong? If I was wrong in assuming $\ce{HA}$ please tell me why. Let me know if some clarification is needed.


texts: Would the change in enthalpy change of chemical reaction in space be considered as change in internel enrgy?

texts:
The formula of enthalpy change is

change in H = U + P*(change in V)

In space since there is no air, thus atmospheric pressure = 0 , P= 0 , Pv = 0 ,

So will H = U  ?


texts: Water purification procedure that does not involve a flocculant of any kind?

texts: I have read about "electroflocculation" that uses less flocculant/alum, but is there a method – no matter how expensive or impractical – that uses no flocculant at all?


texts: How to calculate "accurate" surface area of a microporous material using Micromeritics equipment?

texts:
How do I get an accurate surface area from a nitrogen isotherm?

I've been doing some surface areas on MOFs and upon showing my boss the isotherms he asked me to convert them to show the "range", which will give the most accurate surface area.

I'm using Micromeritics ASAP-2020 software and I believe that you measure this BET range by using points from relative pressures between 0.05 and 0.3. However, this seems to be unsuitable for some microporous compounds?


texts: Precision Balance (1mg) vs. Analytical Balance (0.1mg)

texts:
I'm in the lucky position to building my own home lab and I'm looking to get a nice balance, but I don't want to waste money on something I won't use though.

I'm currently about to start second year chemistry (Organic) and I plan to take at least a few courses beyond this as time allows (I already have my Comp Sci degree and a full time job and I've been in and out of grad school for Mathematics and Computer Science). So this is just a hobby.  As far as what I'll be doing I honestly don't know chemistry well enough to say exactly, but I think it'd be fun to synthesize various molecules you come across and see what kind of purity I could get after running the experiment a few times.

I probably won't ever get much past 4th year undergrad or 1st year graduate level knowledge since I can only take one night class at a time.

I understand that analysis and p chem have a decent amount of use for sub-mg level accuracy, but how often do these situations come up in practice?

Should I spend the extra on a 0.1mg balance or just go for a 1mg balance?  This decision won't affect future lab purchases much more likely just the timeline of the purchases. Eventually I'd like to get additional useful instruments as I start needing them like a centrifuge and/or autoclave. But I probably won't ever get a FT-IR for example.


texts:
Most of the common organic solvents are regarded as noncorrosive, but  stainless steel can be attacked by formic, acetic, and propanoic acids.
Corrosion of stainless steel by organic solvent mixtures, Alice Y. Ku , David H. Freeman, Anal. Chem., 1977, 49 (11), pp 1637–1638
DOI: 10.1021/ac50019a044
Are there some aromatic hydrocarbon that attack stainless steel? Which organic solvents can corrode copper and aluminium?


texts: Isobaric entropy relation from isothermal Gibbs free energy relation

texts:
I have been given a problem to derive a relation for change in entropy from change in Gibbs free energy:

Starting with the isothermal equation
$$G(p_2) = G(p_1) + nRT\ln\frac{p_2}{p_1}\label{eqn:1}\tag{1}$$
derive
$$S(V_2) = S(V_1) + nR\ln\frac{V_2}{V_1}\label{eqn:2}\tag{2}$$
using the relation
$$\mathrm dG = V\,\mathrm dp - S\,\mathrm dT.\label{eqn:3}\tag{3}$$

The derivation wants you to assume that pressure is constant and thus $\mathrm dp = 0,$ and \eqref{eqn:3} can be arranged to
$$\left(\frac{\partial G}{\partial T}\right)_p = -S.\label{eqn:4}\tag{4}$$
Now I understand that then differentiating \eqref{eqn:1} w.r.t $T$ and using the fact $p_1 V_1 = p_2 V_2$ (for constant $T)$ can produce the required equation \eqref{eqn:2}.
However, I don't understand quite how we can justify the derivation of an isobaric equation from an isothermal one as this method appears to. Equation \eqref{eqn:1} describes isothermal processes and is a function of pressure, $p_2.$ How is it valid then to suddenly say now pressure is constant and therefore use \eqref{eqn:4} when in equation \eqref{eqn:1} the pressure is clearly not constant?
Might it have something to do with Gibbs free energy being a state function meaning, once there is a relationship for it, constraints (for different state variables) can be changed to derive new relationships using a different constraint?


texts: Why is the maximum % for a gold alloy 92%?

texts:
The assignment question is asking us to explain why you can't get more than 92% gold in a gold alloy, and I can't seem to find out why it's specifically 92% in either the textbook or online.

Any help is appreciated. Thank you.


texts: Why concentrated sulfuric acid for dehydration and dilute for hydration?

texts:
To dehydrate ethanol one uses concentrated sulfuric acid:

$$\ce{C2H5OH ->[\text{conc.} H2SO4] C2H4 + H2O}$$

but to go in the reverse direction, dilute sulfuric acid is used:

$$\ce{C2H4 + H2O ->[\text{dil.} H2SO4] C2H5OH}$$

Why is one concentrated, and one dilute? For that matter, how does the sulfuric acid even help in the first place?


texts: Calculating excitation energies of a molecule

texts:
I am trying to calculate the excitation energies for the first three transitions of a molecule which is made up by a chain of k phenyl rings, where k shall be between 1 and 8. The angle between each rings shall be $\pm 30^\circ$. You can see a picture of the molecule with $k=8$ rings below.

I have calculated the first three transistion energies using Gaussian. You can see them in the table below.

Now I want to calculate them by hand using a very simplified model. Since there is a linear correlation of $E(\frac{1}{k})$ a good model would be the particle in a box. Therefore I tried to use such a model, but unfortunately the difference between my energies is way to high. I used $$E_{n+1}-E_n = (2n+1)\frac{h^2}{8m(kl)^2}$$ as formula where k shall be the number of phenyl rings and l ($\simeq 2.1\mathring{A}$) shall be the diameter of one ring.
You can see my results I obtained by using this formula in the table below.

How could I improve my calculations?


texts: Comparing the pKb of piperazine and methylpiperazine

texts:
In comparison to piperazine, the inductive effect will cause the $\mathrm{p}K_\mathrm{b}$ of methylpiperazine to be:

The answer given is that the $\mathrm{p}K_\mathrm{b}$ will be lower due to electron donation by the methyl substituent. I understand that the methyl group stabilizes through the inductive effect by releasing electron density. However, wouldn't this make the $\mathrm{p}K_\mathrm{b}$ higher (a weaker base) since it's more stable and less likely to react?


texts: Is is possible to do mass spectrometry without coupled liquid chromatography?

texts:
It's possible to identify a solution with several compounds* without the coupled liquid chromatography (LC) before to isolate the compounds?

On the university where I study, the LC is broken, so all we can do is inject the solution directly on the mass spectrometer. I wonder if I will be able to identify the metabolites? I don't need quantitative analysis, I just want to know what's in there.

(*) To be precise: A bacterial culture, that has gone under organic solid phase extraction, freeze dried and resuspended in methanol.


texts: How to proceed pyrene fluorescence probe for CMC determination?

texts:
Pyrene fluorescent probe is the most common method to determine the critical micelles concentration in researches. However, there is no obvious protocol for that method.
Please I need a guidance from experienced researcher in nanomicelles.
What I understand is that series of concentrations of monomeric form of micelles can be dissolved in pyrene-saturated water then fluorescence intensity can be measured. Is that right?


texts:
Why is the reverse electron demand Diels-Alder reaction much rarer than the normal one? By reverse electron demand, I mean one with an electron-rich dienophile and an electron deficient diene.

In the book by Clayden they have drawn a diagram with the electron deficient dienophile lower in energy and saying that it would prefer to give its LUMO to the reaction.

But, I don't get what's wrong with an electron-rich dienophile lending its HOMO.


texts: White organic solid that forms CO2 with NaHCO3, forms a diazo dye withe beta-naphthol, and reacts with bromine water

texts:
A white crystalline solid "X" gives the following chemical tests:

It liberates $\ce{CO2}$ with $\ce{NaHCO3}$
It forms a coloured dye in diazotisation and coupling with $\beta$-naphthol
With $\ce{Br2}$/$\ce{H2O}$, it forms a white precipitate of 2,4,6-tribomoaniline.

"X" can be identified as:

I thought that (d) could be the answer as COOH releases $\ce{CO2}$ from $\ce{NaHCO3}$, but can sulphonyl group release $\ce{CO2}$ from $\ce{NaHCO3}$?


texts: Why did my vinegar not create the traditional volcano?

texts:
At the weekend, my son and I tried the volcano experiment. You know the one: vinegar introduced to sodium bicarb (and a little red dye) within a conical "volcano".

Not actually ours; photo borrowed from here.
So, after assiduously funnelling some (slightly clumpy) bicarb into the volcano and meticulously counting drops of red food colouring... nothing happened? You can imagine our disappointment.
As luck would have it, we have two types of vinegar in the house. So I went about swapping the "non-brewed condiment" (more on this below) that we had used previously for some fancy balsamic vinegar. Lo and behold, this time we were treated to an eruption to rival Vesuvius!
I'm left to conclude that the first vinegar we tried must have gone bad somehow. It still looked, smelled and tasted like malt vinegar, but why else would it have failed us when we needed it most?
So, my question: Why would our vinegar have failed to react with sodium bicarb?

Note 1: In the UK, "non-brewed condiment" is the glamorous name for the cheap type of vinegar that is very common in fish & chip takeaway shops. It's basically identical to malt vinegar. (In fact, I only realised mine wasn't malt vinegar when preparing this question!) It's a brown, semi-transparent liquid with a sharp taste and smell. The principle ingredients are water, acetic acid, and caramel for colouring. Since acetic acid is the same acid found in real (i.e. brewed) vinegar, surely it shouldn't matter whether it's real vinegar or not?
Note 2: For completeness, it's worth mentioning that traditional (in the UK at least) vinegar bottles aren't really very air-tight. It has occurred to me that the acetic acid has been subject to some sort of chemical/physical reaction with the air. (Perhaps oxidation? Or even just evaporation?)


texts: Do amines or alcohols have stronger intermolecular hydrogen bonds?

texts:
Which has stronger hydrogen bonding, $\ce{CH3OH}$ or $\ce{CH3NH2}$

I think it comes down to which has more dominance; number of hydrogens, number of lone pairs, or electronegativity.


texts:
In a calculation of for example a Li-Atom in a DZ basis we have 4 MO.

For the alpha string (containing two electrons), that means we have for a FCI calculation the determinants:
|12>, |13>, |14>, |23>, |24>, |34> (electrons in MO 1 and 2, 1 and 3 and so on).

If I wanted to do a truncated CI calculation (CIS for example) only singly excited wavefunctions would contribute.

My (maybe extremely dumb) question now is: Are the determinants |23> and |24> singly excited or doubly excited? Is it the excitation
$$a^\dagger_3a_1|12> = |32> = -|23>$$
 or is it
$$a^\dagger_2a_1 a^\dagger_3a_2|12> = |23>$$
 Or is it both? And the coupling (1,-1) so to say determines whether this in used as a single or doubly excited determinant?

EDIT: From the "Molecular Electronic Structure Theory" book by Helgaker, Jorgensen and Olsen, from the chapter 11.8.5 (Direct CI algorithms for RAS Calculations) I read "In CISD theory, there are three such classes (string classes): class 0, with no electrons in virtual space; class 1, with one electron in virtual space; and class 2, with two electrons in virtual space".

This for me reads as if |23> would count as a class 1 string and not a class 2.


texts: What is the fate of sulfur in cysteine when it participates in gluconeogenesis?

texts:
Amino acids can be broken down to yield pyruvate, which in turn can be used to construct glucose molecule in the process of gluconeogenesis.  What happens to the sulfur atom in the amino acid cysteine when it is processed into pyruvate?

Image source: NCBI Bookshelf


texts: Why is Aluminum's 2nd ionization energy higher than Silicon's?

texts: According to the periodic table trend for I.E. Silicon should have a higher 2nd ionization energy than Aluminum so I'm confused.


texts: Synthesis of Potassium Trioxalatoaluminate (III) Trihydrate

texts:
We mixed $\ce{Al}$ powder and hot water. Then we added $\ce{KOH}$ to the $\ce{Al}$ solution and it bubbled heavily (producing $\ce{H2}$). When that was over we added oxalic acid dihydrate to the boiling aluminate solution. We filtered and added cold ethanol. How do write these reactions?

I was thinking:

$$\ce{Al + KOH + 2H2O -> K[Al(OH)3] + H2}$$

and when oxalic acid comes in:

$$\ce{K[Al(OH)3] + C2H2O4.2H2O ->K3[Al(COO)3].3H2O}$$

The problem is this site says that the reaction is wrong and What is the reaction between oxalic acid and potassium permanganate?  is a similar question but has a completely different looking answer. I'm lost.


texts: What is an example of an isopropyl alcohol resistant caulk?

texts:
What is a caulk (or bonding adhesive) that can be exposed permanently submerged in an isopropyl alcohol (>91%) bath?

The idea came from this previous question:
Silicone vs Alcohol

It seems from one of the answers there the alcohol would be resistant but the adhesion properties may be compromised.

The more readily available the product, the better.


texts: Determining covalent bond strengths without hybridisation

texts:
Assuming pure $\ce{2s}$ and $\ce{2p}$ orbitals of carbon are used in forming $\ce{CH4}$ molecule, which of the following statements is false? (single choice question)

  Three $\ce{C-H}$ bonds will be at right angles
  One $\ce{C-H}$ bond will be weaker than the other three $\ce{C-H}$ bonds
  The shape of the molecule will be tetrahedral
  The angle of $\ce{C-H}$ bond formed by $\ce{s-s}$ overlapping will be uncertain with respect to other three bonds.

According to me, the second option is false because $\ce{1s-2s}$ overlapping is stronger than $\ce{1s-2p}$. I just randomly found this question and I don't know the correct answer.


texts: How can reversible reactions be exothermic or endothermic?

texts: So this may be a dumb question, but because the forward reaction of a reversible reaction releases the sane amount of energy as the backwards reaction absorbs (because the bonds that are formed from the forwards reaction are broken by the backwards reaction and vice versa) and at equilibrium both reactions occur at the same rate, surely in a reversible reaction the rate of energy release to the environment is equal to the energy absorbed by the environment. So how can there be any net loss/gain of energy to the environment like what is needed for an exothermic/endothermic reaction? I don't understand.


texts:
By free expansion, I am referring to gas kept in a piston-cylinder arrangement freely allowed to expand against vacuum.
It is clear to me that free expansion is an irreversible process because if it were not then it could get compressed as well at equilibrium, but we know it doesn't as it would be violating the 2nd law of thermodynamics.
I know that all the parameters work 'W', Change in Internal Energy '∆U', and Heat transfer '∆Q' would all be zero in the case of an ideal gas.
But, what I want to know is how will all the parameters vary if gas is real?
Also, I wanted to ask whether the answer will change if the surface between the piston and cylinder is not frictionless?


texts: Why does hot steam produce MgO instead of Mg(OH)2?

texts:
Background research

Magnesium hydroxide exists naturally as brucite (source: wiki)
Passing hot steam over magnesium produces magnesium oxide (source: Edexcel's June 2014 Unit 2 exam (CH02_01): question 18)

Question

Why doesn't magnesium hydroxide form when treated with hot steam, instead of magnesium oxide?


texts: Approximate time for pure water pH to equilibrate in open air?

texts:
I'm a complete non-chemist, so I don't know how to calculate this,  or even what to google for (my searches yielded esoteric research papers).
I'm doing some hobby experiments, and I'd  like to know what approximate timeframe to expect for relatively pure (distilled or double distilled) water left in open air at around 24 °C/75F to reach whatever the pH equilibrium point is (I read around 5.5 somewhere).

I'm not looking for a giant equation please,  just a quick approximate number.
Thanks


texts: How to balance the equation for the reaction of aluminum bicarbonate and hydrochloric acid?

texts:
Here's what I have to balance:

  Solid aluminum bicarbonate and hydrochloric  acid combine to form an aluminum chloride solution and carbonic acid.

Or in an equation form:

$$\ce{\text{__ } Al(HCO3)3 + \text{__ } HCl -> \text{__ } AlCl3 + \text{__ } H2CO3}$$

Side Note:

$\ce{Al}$ has a charge of $3+$ and $\ce{(HCO3)}$ has a charge of $1-$. To balance the ionic compound we have to change it to: $\ce{Al(HCO3)3}$.

The underscores before each compound in the chemical equation are just there for number values we can input in order to balance the equation.

My question is: what would be the reactants and products in this chemical equation? Would $\ce{HCO3}$ as a whole compound be a reactant itself?


texts: In all oxidation reactions of glucose, it seems that the aldehyde group alone gets oxidised and none of the hydroxyl groups. In one reaction with nitric acid, the aldehyde group and the terminal hydroxyl group get oxidised but none of the remaining hydroxyl groups. I was wondering why this happens. Are the hydroxyl groups less susceptible to oxidation for any reason? If so why would that be? And also is there a difference is ease of oxidation of the terminal hydroxyl and remaining hydroxyl groups?


texts: Are there any significant uses of the compound formed by magnesium and anthracene?

texts:
In an unusual reaction, magnesium reacts with anthracene in THF to form a grignard-like compound called, prosaically, magnesium anthracene:

I remember using it briefly in the 1980s. At the time there was speculation about its potential use in both synthesis and as a starting material for hydrogen-storage systems.

Are there any significant current uses of the the unusual complex?


texts: What is the structure of $\ce{FeSO4 \cdot NO}$ that is formed when $\ce{NO}$ is passed through ferrous sulfate solution? If it is a brown ring complex then why does the complex sphere break upon heating to yield $\ce{NO}$? In general, when do the complex spheres break?


texts: How do we explain NMR shielding in filled valence shells?

texts:
It is universally recognized that NMR measures the shielding of nuclei from magnetic fields by electrons.  The electrons move, producing an eddy current that produces an opposing magnetic field.
It is also fairly widely said that a filled valence shell contains electrons making every possible motion within a certain range of energy.  For example the p orbitals are added up using +1 and -1 values for angular momentum, and the electron spins are paired.  MO theory seems, in most cases, to have the same paradox.
Now I know you can look into it and find more detailed math for NMR tensors, but at the intuitive level: what is going on here?  (Are the filled orbitals being hybridized, slightly, with ordinarily unfilled complex-valued higher-energy orbitals to permit the electrons to take on some degree of net overall angular momentum in relation to the axis of the magnetic field, or is it something else?)


texts: How to remove nitrate from water sample?

texts:
Are there any simple methods to completely remove nitrate ions from few ml of impure water sample?

One method I am curious about is the following process:

Add one or more reagents to water in test tube, which would crystallize nitrate ions into some solids
Then filter out the solids from water such that the water is now nitrate free.

Is the above process possible? If so, what are some reagents that can be used?


texts:
How did the tablet become like this?

There was a gap in the packet, so I'm guessing it reacted with moisture but is it so?

Edit: Composition of 'Tendocare'- Chondroitin Sulfate and Vitamin C tablets.
Ingredients- Lactose, Chondroitin Sulfate sodium, Binder(468), Collagen peptides type 1, Sodium Hyaluronate, Binder(462) Stabilizer(1202),(1205)and(464), Silicon Dioxide, Magnesium Stearate, Sorbic Acid, Emulsifier.
Contains permitted natural colors and flavor. Appropriate overages added.
NUTRACEUTICAL, NOT FOR MEDICINAL USE.


texts: Mechanism for the formation of butanoic acid from ethylacetoacetate

texts:
My problem sheet asks me: "Draw a mechanism for the formation of $\ce{EtCH2COOH}$ from the reaction of $\ce{MeCOCH(Et)COOEt}$ with $\ce{NaOH}$ in $\ce{EtOH}$"

This has got me stumped. The mechanisms that I have attempted use the hydroxide ion as the base/nucleophile, is this right? My initial thoughts were to make the enolate by deprotonating between the caronyl groups then doing and aldol into the ketone part of another molecule of ethylacetoacetate but this just gives me a complicated molecule that I can't see reacting further.

I simply cannot find a way to make the product using only the reactants in the question.


texts: Hellmann-Feynman Forces with Hartree-Fock

texts:
The energy in the Hartree-Fock approximation is given as:

$$E_{HF}=\left<\psi_{HF} \left| \hat{H} \right| \psi_{HF} \right>=\sum_{i,j}P_{i,j}H_{i,j}^{core}+\frac{1}{2}\sum_{i,j,k,l}P_{i,j}P_{l,k}(ij||kl)+V_{NN} \tag{1}$$

The geometrical derivative of the Hartree-Fock energy can be shown to be [1]:

$$\frac{\partial E_{HF}}{\partial X_A}=\sum_{i,j}P_{i,j}\frac{\partial H_{i,j}^{core}}{\partial X_A}+\frac{1}{2}\sum_{i,j,k,l}P_{i,j}P_{l,k}\frac{\partial (ij||kl)}{\partial X_A}-\sum_{i,j}Q_{i,j}\frac{\partial S_{i,j}}{\partial X_A}+\frac{\partial V_{NN}}{\partial X_A} \tag{2}$$

The Hellmann-Feynman Theorem states:

$$\frac{dE}{d X_A}=\left<\psi \left| \frac{d\hat{H}}{d X_A} \right| \psi \right>$$

The Hellmann-Feynman Theorem implies that the energy derivative only depends on the parts of the Hamiltonian that have a dependency on the derivative. This leads to the geometrical derivative being equal to:

$$\frac{dE}{d X_A}=\left<\psi \left| \frac{d\hat{V}_{NN}}{d X_A} + \frac{d\hat{V}_{Ne}}{d X_A} \right| \psi \right> = \left<\psi \left| \frac{d\hat{V}_{NN}}{d X_A} \right| \psi \right> + \left<\psi \left| \frac{d\hat{V}_{Ne}}{d X_A} \right| \psi \right>=\left<\psi \left| Z_A\sum_B\frac{Z_B(X_B-X_A)}{R^3_{AB}} \right| \psi \right> + \left<\psi \left| -Z_A\sum_i\frac{X_i-X_A}{r^3_{iA}} \right| \psi \right>$$

Now the Hellmann-Feynman theorem can be applied to find the derivative geometrical of the Hartree-Fock energy:

$$\frac{\partial E_{HF,\ce{Hellmann-Feynman}}}{\partial X_A}=\left<\psi_{HF} \left| \frac{\partial\hat{H}}{\partial X_A} \right| \psi_{HF} \right>=\sum_{i,j}P_{i,j}\frac{\partial V_{Ne,ij}}{\partial X_A}+\frac{\partial V_{NN}}{\partial X_A} \tag{3}$$

I tried to implement equation $(2)$ and equation $(3)$, and used them to calculate, the force between H and Li for different distances, with cc-pVDZ and cc-pVTZ. and got the following:

Hartree-Fock refers to equation $(2)$ and Hellmann-Feynman refers to equation $(3)$. I have read that the Hellmann-Feynman theorem is only valid for exact solutions, but should become a better and better approximation, when going towards the Hartree-Fock limit. As can be seen in the picture, equation $(3)$ performs worse with the larger basisset cc-pVTZ. This now leads me to my question, were am I wrong in my understanding of the application of the Hellmann-Feynman theorem to the Hartree-Fock approximation?

[1] Attila Szabo, Neil S. Ostlund; Modern Quantum Chemistry: Introduction to Advanced Electronic Structure Theory; equation C. 12


texts:
What is the Lewis acid on the reactants side?

$$\ce{HNO2(aq) + HPO4^{2-}(aq) <=> NO2-(aq) + H2PO4-(aq)}$$

The book says it is the $\ce{H+}$ only, not the whole molecule of the nitrous acid, how so?


texts:
Will it be correct to make a general statement that all compounds having odour are volatile?

My reasoning: if a compound has odour then to smell that it must evaporate ( ie. some molecules must diffuse in the surrounding) . So I conclude that for smelling the compound must be volatile.

Am I right?


texts: Energetic stability in relation to α-hydrogens

texts:
I am new to organic chemistry and was asked to rank the following materials according to energetic stability. I think I have understood that the way to do this is to count the amount of α-hydrogens: the more α-hydrogens, the more stable the molecule. However, the definition of an α-hydrogen is "a hydrogen that is attached to an α-carbon", where the α-carbon is the first carbon next to a functional group. In this case, it is not clear to me where the α-carbon is located: the only candidate for a functional group is the CH2/CH3 (depending on the case) at the very end of the chain, but then would the α-carbon be the very first one or the one next to it?

Any further general insight into the ranking of molecules according to energetic stability would also be very much appreciated… Many thanks!


texts: What can I use to remove print from hard surfaces?

texts:
I have a lot of profile products with the logotype of the company handing them out printed on them. In some situations I don't like to show these logos. However, it is stupid to bin working products for this reason so I would like to remove the print on them.

What solvent can be used for this purpose? What solvent is used in this type of colours?

Currently there are two items I want to remove the printing from:

A clear plastic bottle in BPA free tritan.
A tool in, I think, aluminium (metal anyway) with a surface similar to a Macbook Pro.


texts:
Why is the N-N bond length greater in dinitrogen trioxide than in dinitrogen tetroxide?

If the lone pair on $\ce{N}$ in $\ce{N2O3}$ delocalises, then the $\ce{N-N}$ bond will have a double bond character, so it should be shorter.

From data on Wikipedia, the $\ce{N-N}$ bond length in dinitrogen trioxide is  $\pu{186.4pm}$ while that of dinitrogen tetroxide is $\pu{178pm}$.


texts: NMR spectrum of 3-hexylthiophene: why is the methyl group not a triplet?

texts:
I have an example spectrum, and it shows which peaks correspond to which H, but I don't understand why the spectrum looks like that

e.g. I would expect the peak at 0.88 to be a triplet based on the (n+1) rule, why is it such a large multiplet?


texts: How many isotopologues of water are there?

texts:
If ordinary water molecules can contain any of the three hydrogen isotopes, $\ce{^1H}$, $\ce{^2H}$, $\ce{^3H}$, and any of the three oxygen isotopes, $\ce{^{16}O}$, $\ce{^{17}O}$, $\ce{^{18}O}$,  how many kinds of water molecules $\ce{H2O}$ are there?

I'm a little confused because since there are $\binom{3}{2}$ ways of choosing two hydrogen atoms and 3 ways of choosing oxygen atoms, shouldn't there be 9 different kinds of water molecule? Why would it be 18 (as the answer says)? In other words, why would the order of hydrogen atoms matter here?


texts: Heat lost in evaporation at constant temperature

texts:
I ran an experiment evaporating salt water at different temperatures and concentrations. I’m trying to figure out how much energy is needed to maintain water at a specific temperature even when its evaporating. I have tried a calculating the heat loss by evaporation but since the mass is decreasing during evaporation, both mass and heat would change, but temperature would have to remain constant. I am going crazy trying to figure this out.
Using the equation here would give me watts
https://www.google.ca/amp/s/www.engineeringtoolbox.com/amp/evaporation-water-surface-d_690.html
but it doesnt account for change in mass or temperature of the water.


texts: Use of significant figures in addition and subtraction

texts:
My book mentions:

  The proper use of significant figures in addition and subtraction involves a comparison of only the absolute uncertainties of numbers. This means that only as many digits are retained to the right of the decimal point in the answer as the number with the fewest digits to right of the decimal

But I don't understand that why must the answer be rounded off after addition? Is the answer not accurate enough to be retained as it is ?


texts: Can one relate the frequencies of vibrational modes within a molecule to the molecule's HOMO/LUMO energies?


texts: Why are hollow cathode lamps used for atomic absorption spectroscopy?

texts: In 1955, it was proposed that hollow cathode lamps are good emission sources for monochromatic radiation, and thus for atomic absorption spectroscopy (AAS).  In looking into the topic, I've read that "continuum radiation is not preferred in AAS." Why not?


texts:
Which of the following has highest solubility in water?

A. $ Ca(OH)_2 $

B. $ Fe(OH)_3 $

C. $ Cr(OH)_3 $

D. $ Zn(OH)_2 $

And also please explain how can we predict their solubilities when we are not provided with their solubility products.

I know that calcium hydroxide is sparingly soluble. So it cannot be the right option. I think Iron hydroxide is also soluble to a good extent. I haven't got any idea about option C. I think D may be the right answer.


texts: What makes protons give the property of acidity?

texts:
Brønsted Lowry definition of an acid says that an acid gives away protons.

What I don't understand is what makes dissolved protons grant the property of acidity? Like, why would dissolved protons eat up materials?

My question applies to bases too, I suppose. And I guess you could include Lewis-acids and bases in your argumentation...

It's a question that has been bothering me for long. By the way I am not chemist(nor do I study chemistry).


texts:
Why is phenol more polar than alcohol. I mean the benzene ring seems to be extremely unpolar. Furthermore, is the hydrogen bonding stronger in phenol than in alcohol? Are polarity and hydrogen bonding related (in hydroxy compounds)?

I am doing TLC and I was taught that hydrogen bonding can occur with the alcohol/phenol and that alcohol has stronger hydrogen bonding to the silica gel than it would have despite the lower polarity a lower Rf value than phenol.

But to be honest I am very unsure about those teachings.


texts: What is the amount of UV light required to make fluorophores glow and what is the minimum amount of electricity needed to achieve this?

texts:
So I have heard that fluorophores glow under UV light, so I was wondering what is the minimum amount of UV light needed to make the fluorophores glow and what would be the minimum amount of electricity required to make that much amount of UV light.
Also, is there any other type of light that makes fluorophores glow but requires a lesser amount of electricity?


texts: Stereoisomers of octahedral co-ordination compounds of the form [Ma3b3]

texts:
Does $\ce{[Co(H2O)3Br3]}$ show geometrical and optical isomerism?
According to me $\ce{Co}$ should be $\mathrm{sp^3d^2}$ hybridised giving an octahedral geometry. It is of the form $\ce{[Ma3b3]}$ type. I know it can show geometrical isomerism, namely fac and mer isomers. But can it show optical isomerism?


texts: Hydroboration/oxidation vs acid-catalyzed hydration of 1-phenylpropene

texts:
I am trying to predict the products of both the hydroboration/oxidation and acid-catalyzed hydration of 1-phenylpropene:

Both C1 and C2 of the double bond are secondary carbons. However, I have the feeling that there are slight differences in the electron density on each carbon, which will affect the addition of the boron electrophile and the stability of the carbocation for the two reactions respectively.

Which regioisomers are predominantly formed from both reactions?


texts:
For the reaction:
$$\ce{F
+ Br_2 -> FBr + Br}$$
The gas concentrations as a function of time are given by:
$$kt=\ce{\frac{1}{[Br2]_0-[F]_0}}\ce{\ln(\frac{[Br2][F]_0}{[F][Br_2]_0})}$$
Given that $\ce{[F]_0=4 x 10^{-9}}$ and $\ce{[Br2]=1x 10^{-10}}$ I am meant to show that the rate constant is first order with respect to $\ce{Br2}$. How do I do this?

Fluorine atoms are in excess but is it a large enough excess to assume that the isolation method is valid? I could then cancel terms but would I the have to differentiate to find the rate law?


texts: What are the assumption of Gibbs free energy equation referring to the system and the surrounding?

texts:
The system for

$\mathrm dG=\mathrm dH-T\,\mathrm dS$

is a constant temperature and pressure throughout the process, only volume work is possible and it is in thermal equilibrium with the surrounding. Is that right? Are there any other constraints?


texts: Why doesn't tetrachloridotitanate(II) obey the 18-electron rule?

texts: I have worked out that the complex comes to 10 electrons, however I do not understand why it does not obey the 18-electron rule? What are the factors that account for this?


texts: Comprehensive resource on diazo coupling?

texts:
I am starting to do research on diazo coupling reactions and am looking for a book or literature review that is a comprehensive exploration of everything diazo coupling.

I found one book which is pretty amazing: https://ia802302.us.archive.org/8/items/aromaticdiazocom031270mbp/aromaticdiazocom031270mbp.pdf

It has a whole chapter devoted just to diazo coupling with various classes of compounds like phenols, amines, phenolic ethers, hydrocarbons, etc (which is exactly what I am looking for).  BUT, it's from the 1930's! It is quite challenging to read because it mostly describes reactions rather than showing them pictorially. Also, some of the theory is a bit dated!

My question: Does anyone know of a more modern resource?


texts: Why doesn't a temperature and pressure gradient exist in a container of real gas?

texts:
In the Kinetic theory of gases, it is assumed that there are no intermolecular forces between the atoms/molecules. But real gases, have intermolecular attractive and repulsive forces.

Suppose a container filled with a real gas.

The molecules well inside that container will feel no net force of attraction/repulsion on any side. But considering molecules near the boundaries of the container, a net inward force will be felt. I think this will make velocities of atoms less than that of the atoms well inside the container.

So, is the pressure at the centre of the container more than that of the pressure at the boundary(measured actual pressure)?

My book says that the slowing down does not mean that the gas is cooler close to the walls. The relation of $\sqrt{T} \propto v_{\mathrm{rms}}$ is valid only in the absence of intermolecular forces. Temperature is defined by the Zeroth Law. Will net energy/heat transfer take place between the atoms of the gas and the metal bar if I keep a metal of temperature $T$ inside the container near the boundary? Here, $T$ is the temperature at the centre of the container such the no heat transfer takes place if a metal bar is kept at temperature $T$ at the centre of the container.


texts: Resonance in carbocation derived from allenes

texts:
During a reaction if addition on one of the $\pi$ bonds of an allene (containing even number of $\pi$ bonds like $\ce {H2C=C=CH2}$) takes place then a carbocation is formed. To decide the position of the positive charge, we look at the stability of the carbocation. Example:
$$\ce {H2C=C=CH2 ->[\ce{H3O+}]} \quad?$$

In the above reaction the proton ($\small{\ce{H+}}$) attacks the electron rich $\pi$ bond (say the left one) and can form one of the following carbocation:
$$\ce{H2C+\bond{-}CH=CH2}\quad\quad \text{or }\quad\quad \ce{CH3\bond{-}C+=CH2}$$
$$ (\text{I})\quad\qquad\qquad\qquad (\text{II})$$

Now the major product (acetone) is formed as a result of the carbocation on the right (II), which apparently is less stable than the one on the left (I) as the positive charge in I is in resonance/conjugation with the $\pi$ bond. But our teacher said that since in allenes the overlapping p-orbitals (say $\ce{p_z}$) of one $\pi$ bond are perpendicular to the overlapping p-orbitals of the other (say $\ce{p_y}$; which makes $\ce{p_x}$ in the direction of internuclear axis $x$) and hence the positive charge cannot resonate with the $\pi$ bond (formed by overlap of $\ce{p_z}$) as the positive charge is effectively an empty p-orbital (the $\ce{p_y}$) and hence the carbocation (II) is relatively more stable.

But once addition has taken place the $\ce{C_1-C_2}$ $\pi$ bond no longer exists and the $\sigma$ bond is free to rotate so the empty p-orbital/positive charge can freely rotate and become coplanar with the p-orbitals of the $\pi$ bond. But why does this not happen?
The reason cannot be steric hindrance as the two groups on $\ce{C_1}$ are the smallest, $\ce{H}$.


texts: Elimination vs reduction reactions - how to tell

texts:
Here are two compounds:
Compound H:

and compound I:

Compound H reactions with the reagent shown below to form compound I and two other products.
How would you clarify this reaction? I thought it was a reduction, because we are losing the oxygen bonded on the left hand side of the molecule. The actual answer is elimination Any advice for tell-tale signs for this type of reaction, and why my answer was wrong?


texts: What does “at%” mean and how it differs from “mol%”?

texts:
Sorry if my question is a bit obvious, but for some reason I'm getting confused with the percentages in this question:

  Concentration of $\ce{A}$ is $\pu{80 at\%}$ and concentration of $\ce{B}$ is $\pu{19.8 at\%}$ for $\ce{AB2}.$ What would be the mass for $\ce{A}$ and $\ce{B}$ individually, if the atomic weight of $\ce{A}$ is $\pu{5 g/mol}$ and $\ce{B}$ is $\pu{10 g/mol}?$

I understand that the molecular weight $M$ for my compound would be:

$$M(\ce{AB2}) = (5 + 2\cdot 10)~\pu{g/mol} = \pu{25 g/mol}$$

How do I include the atomic percentage to get the mass of $\ce{A}$ and $\ce{B}?$

I am just not sure how to use $\pu{at\%}.$ My understanding is that if I assume $\pu{1 mol}$ of $\ce{AB2},$ then I can calculate the mass of $\ce{A}$ by assuming that $\pu{80 at\%}$ is $\pu{0.80 mol}?$

I have another problem where they specify $\pu{mol\%}$ (mole percentage) instead.
So I am getting confused as to how to use $\pu{at\%}$ and $\pu{mol\%}.$


texts: Why isn't chlorine reduced or nitrogen oxidised in the reaction between ammonium perchlorate and aluminium?

texts:
A space shuttle’s upward thrust came from the following reaction between aluminium and ammonium perchlorate.
$$\ce{10 Al + 6 NH4ClO4 → 4 Al2O3 + 2 AlCl3 + 12 H2O + 3 N2}$$
Which statements about this reaction are correct?

Aluminium is oxidised.
Chlorine is reduced.
Nitrogen is oxidised.

I understand why aluminium is oxidized, but why are 2 and 3 wrong?


texts: It is possible to make radical Chlorination on the α-position of ketones?

texts: I need examples of radical α-Chlorination of ketones. It is possible to make radical chlorination happen in the alpha position?


texts: Is it possible for a liquid chemical to have a pH value lower than its aqueous solution?

texts:
During the QC check of one of the products that we make as a company, the product had a $\mathrm{pH}$ of $10.44$ on one $\mathrm{pH}$ meter and $10.20$ on the other. (The product is a liquid, so it's straightforward to immerse $\mathrm{pH}$ probes to take the measurements.)

For QC of the product, it is required to make a $1\%$ solution using demineralised water and to take a $\mathrm{pH}$ reading.

The first $\mathrm{pH}$ meter read $11.72$ for this $1\%$ solution, and the second meter read $11.41$.

How is it possible for the raw product's $\mathrm{pH}$ to be lower than the $1\%$ solution's $\mathrm{pH}$? The product is supposed to be basic and not acidic at all.


texts:
I've bought pewter at the thrift store and I want to try casting metal. This pewter may contain toxic metals. A ready-made testing kit I've found cost €25 for each sample.

In comparison pewter of know origin (98% tin/2% antimony) costs €40 per kg,
pewter from the thrift store is €4 per kg. If possible I want to test the pewter before buying.

Is there an easy way to measure the lead content of a pewter sample?

I'm not a chemist but do have a basic understanding of chemistry.
I've calculated the density of the sample to be: $8.55~g~cm^{3} ± 0.5~g~cm^{3}$.


texts: Are the breaking of bonds simultaneously endothermic and exothermic?

texts:
I understand that energy is NEEDED to BREAK bonds. But don't chemical bonds already have some form of potential energy in them already? So wouldn't it make sense that even though energy is required to break them, their potential energy is also RELEASED once they are broken?

In other words, shouldn't the bond breaking process be considered simultaneously endothermic AND exothermic?

Side note: I'm studying grade 12 level chemistry right now, so I don't have too much knowledge on the nitty gritty details of this concept. That being said, It would be greatly appreciated if anyone could explain this in very simple terms.


texts:
Here is what I think I know: The entropy of dissolution reactions increases as methylene groups are added (i.e. butanol has higher entropy of dissolution than propanol). Also, acyclic saturated hydrocarbons become more hydrophobic as the number of methylene groups increases.
Here is where I get confused:
Larger hydrocarbons have a higher enthalpy of dissolution because they are composed of a greater number of bonds. BUT why does the CHANGE in entropy of dissolution become more negative as the number of carbons increases? Doesn't the dissolution of a larger hydrophobic compound yield a more positive entropy value/become less negative because the initial entropy of the solvent is very low (many large, ordered solvent cages) and then solvent entropy increases after the molecules aggregate by the hydrophobic effect?
Super confused...thank you.


texts:
I think it has something to do with the fact that at high temperature it interconverts and so all the coupling constants are the same hence quintet but at lower temperatures the frequency of the rotation is less than the sample rate and so there are different coupling constants for the planar and axial fluorine atoms. We have two structures to consider; 3 planar-1 axial and 2 planar-2 axial. If my line of thought it correct the P-31 NMR spectra for each of these should superimpose to give the spectrum shown.

But I'm lost because when I draw my diagrams they don't match the spectrum shown, I end up with a much more complicated splitting pattern.


texts: Anhydrous magnesium sulfate to replace epsom salt?

texts: Can anhydrous magnesium sulfate be used instead of epsom salt for feeding plants? Do hydrates and anhydrous salts become the same when dissolved in water?


texts: Obtaining mercury from mercury(II) nitrate

texts:
I was thinking about obtaining mercury from mercury(II) nitrate. Is it possible?
I've tried putting chunks of Fe into it, I've got the logic from the voltaic table (where Fe is on the left side of Hg, so I think it would get it out of the compound). Can anyone please correct me and show me the right way? I've tried searching on Google, but found nothing.

I'm just a rookie in chemistry, and was interested in it when my teacher announced about a talent show which I'll perform some cool chemistry there (I'm going to perform using fires, I've tried the colored fires and the alcohol carboy). I'm also planning to make a mirror, if anybody has some ideas please comment below.


texts:
My teacher gave me a shortcut to calculate the resultant pH if 2 or 3 solutions are mixed, which are relevant only if the difference between the pH of individual solutions is 1.

If there are two solutions, the pH of the mixture $\approx$ (the mean pH − 0.24).
If there are three solutions, the pH of the mixture $\approx$ (the mean pH + 0.56).

What is the logic behind this approximation?


texts:
Which of the following complex is diamagnetic?

  $\ce{[Cr(Cl3)(NMe3)]}$
  $\ce{[Co(EDTA)]-}$
  $\ce{[Cu(CN)(NO2)(NH3)(Py)]}$
  $\ce{[Fe(NH3)6]^2+}$

For (4) I found that since $\ce{NH3}$ is a weak field ligand it cannot pair the electrons of $\ce{Fe^2+}$. Thus, (4) will remain paramagnetic.

But, for the rest of the options, I'm unable to clearly understand if they are paramagnetic or diamagnetic. I need help here.


texts: Would solar panels produce energy if uniform temperature in the universe?

texts: If the temperature on the surface of the sun and on the surface on the earth were the same, and the temperature of the universe were uniform, would the solar panels produce energy?


texts:
We know the basic Thermodynamic equations are:
$$ dU=-PdV+ TdS + \mu dN$$
$$ dH=dU+d(PV)= TdS+ \mu dN + VdP$$
we typically assume constant Pressure for a reaction carried out in air and neglect the dP term
$$dG=dH-d(TS)=  \mu dN - SdT+ VdP$$
once again we neglect the dT and dP terms
but for heat of reaction we use the enthalpy not just the TdS term. When we have a battery though the electrical energy is the Gibbs free energy with the heat of reaction being TdS and other energy losses also contributing to the heat. When the reaction is not separated (not an electrochemical cell) then the Gibbs is part of the heat.
For a typical reaction where the chemicals are in contact why do they use the enthalpy to determine the heat of the reaction produced?


texts: I have $\ce{CO2}$, $\ce{CO}$, $\ce{O2}$ sensors and need to calibrate them. Can anybody help me to produce the $\ce{CO2}$, $\ce{CO}$, $\ce{O2}$ in laboratory for calibrating the sensors (the gas should be produced in known in $\mathrm{ppm}$)


texts: Electrophilic attack of X+ on double bond

texts:
Is it the double bond attacking the $\ce{X+}$ ion or the other way around?

Also, does it form a cyclic transition state if it isn't bromine or chlorine?

Eg. cyclohexene $+ \,\ce{Cl+ ->}$ cyclic transition state

But would the same thing happen if I put any other electrophile?


texts: What property of zinc chromate makes it a good anticorrosion paint

texts: What properties of zinc chromate make it a good anticorrosion paint?  I know that stainless steel is protected by a layer of chromium oxide.  Is it because the zinc chromate doesn't flake off the metal it is protecting?


texts: Keto-Enol tautomerism acidity of α Hydrogen vs stability of double bond

texts: If I consider a ketone that has an ethyl group and a methyl group attached to it. The α-Hydrogen of the methyl group would be more acidic than that of the ethyl group due to -I effect of the adjacent carbon in ethyl group. However the double bond formed in the enol form would be more stable in case it is formed using the α-carbon on ethyl since it's more substituted. In this case which enol form should I choose to be the more stable form ?


texts:
Consider a strong acid $\ce{HA}$. In a $\pu{1000 mL}$ of hexane (assume it is unable to accept a proton) we "dissolve" (this can mean forming a suspension with vigorous stirring - otherwise we can use a polar solvent which cannot accept a proton) $\pu{1e-30 mol}$ of the acid along with enough water to remove all the protons.

Now we have extremely dilute solution of $\ce{H+}$ where autoprotolysis is insignificant compared to the volume of solvent, so according to $\mathrm{pH} = -\log[\ce{H+}]$, pH should be extremely high. However, we are still using an acid, so pH should not be too high. What accounts for the difference?


texts: How do amino acids look like at the isoelectric point?

texts:
At the isoelectric point amino-acids are neutral to the outside. It is however not known to my knowledge if the molecules are indeed in a zwitterionic form or just in its "normal" totally uncharged form, i.e. the dissociation constant for this reaction:

is not known. Does anyone know how they actually look like? What form is more probable, how realistic is the zwitterionic form?

Edit: I did a test calculation for cysteine with DFT, using a PBE functional and implicit water and found that the zwitterionic form is about 7 kcal/mol more stable, which would rather strongly indicate that the zwitterionic form is indeed dominating a lot and you would not at all find the structure on the left as the bars from wikipedia indicate (supposing that I found low lying minima in both calculations and not only local ones). Are there some other studies proving this?

Edit2: Ok the zwitterionic form is definitely more stable, that one can somehow reason from chemical knowledge or pKa's. But how much more stable, can one somehow get a dissociation constant for the reaction above?

Edit3: Since there is much confusion about my question. I want a dissociation constant for the reaction (COOH)(NH2) -> (COO-)(NH3+). Until now I think only the dissociation constants for (COOH)(NH3+) -> (COO-)(NH3+) and (COO-)(NH3+) -> (COO-)(NH2) are known if I am right and I cannot tell how these would help to calculate the constant I want...

Edit4: To clear up my question even a bit more, here is a diagram:

The red arrow and question mark is what I want to know about. The pks1 and pks2 are known, that was clear to me, but how to get any information about the equilibrium in the middle?


texts:
I am searching a long time now. I have a question about the Folin–Ciocalteu formula for quantification of polyphenol. How is the $62.5$ in the equation explained? Where does it come from?
This is the protocol [1, p. 38]:

$\pu{5.0 mL}$ of extract were placed in calibrated flask and filled up to $\pu{25 mL}$ by distilled water. $\pu{1.0 mL}$ of Folin-Ciocalteu reagent, $\pu{10.0 mL}$ of distilled water were added to $\pu{2.0 mL}$ of diluted extract (from $\pu{25 mL}$ calibrated flask) and filled up to $\pu{25 mL}$ by sodium carbonate solution ($\pu{290 g/L}$). An absorbance of prepared sample was measured by means of UV spectrophotometer at $\pu{760 nm}$ after $\pu{30 min}$ of incubation in darkness. The same liquid (with pure water instead of plant extract) was used as a blind test. All determinations were performed in triplicate. The content of polyphenols was calculated from the formula:
$$X = 62.5 \cdot \frac{A_1 \cdot m_2}{A_2 \cdot m_1}$$
where $A_1$ - absorbance of pyrogallol solution, $A_2$ - absorbance of investigated samples, $m_1$ - mass of investigated sample [$\pu{g}$], $m_2$ - mass of pyrogallol [$\pu{g}$].

Reference

Modnicki, D.; Balcerek, M. Herba Polonica 2009, 55 (1), 35–42.


texts: Does conjugation increase λmax of n to π* transitions as well as π to π* transitions?

texts: I would presume yes if the lone pair is on an atom involved in the conjugated system, but no if the lone pair is not on an atom involved in the conjugated system.


texts: How to study (by heart) all the equations in inorganic chemistry?

texts:
Physical chemistry is easy to study as I have to just understand the concepts (like in physics) and apply some equations for calculations. In organic chemistry, reaction mechanisms helpsin remembering a lot of reactions and also doing conversion problems help a lot.

But, in the case of inorganic chemistry it is very difficult for me to remember those equations. My high school syllabus includes a lot of preparation methods of different compounds and reactions showing their chemical properties. But, unlike organic chemistry there is no problems based on it for deep understanding. So, what is actually needed is a good memory power. But, I'm not able to remember all those equations. So, how should I study them?


texts: Why is Lithium Fluoride much safer than Sodium Fluoride

texts: I've looked at the MSDS of Lithium Fluoride and Sodium Fluoride. It really seems that Lithium Fluoride is much safer to work with. Why is that, if both are in the Alkali Group?


texts:
I have a quick question in Stoich and Gasses, I however could not get any far, any answer will be appreciated. Thank You.

  A sample of $\ce{Pb(NO3)2}$ is heated, yielding $\ce{O2, NO2\ gas,\ and\ solid\ PbO}$. A
  $\ce{293 \ ml}$ gas sample, measured at $\ce{200C}$ and $\ce{1\ atm}$, is collected. What
  was the mass of the $\ce{Pb(NO3)2}$ sample?

I feel like in this situation I need to have only one gas so I can apply the Ideal Gas Law to solve and find the mass of $\ce{Pb(NO3)2}$. What should I do there are two gasses and I don't know the volumes or the masses?

$$\ce{2Pb(NO3)2 -> O2 + 4NO2 + 4PbO}$$


texts: Why opposite of electrophilic is not Protophilic

texts:
In organic chemistry , considering definitions of  electrophilic and nucleophilic:

Electrophilic:having an affinity for electrons : being an electron acceptor.
nucleophilic : having an affinity for atomic neuclei (also can we say proton?) : being an electron donor.

So both being opposite to each, why dont we say nucleophilic as protophilic?


texts:
I was trying to use $\ce{HCl}$ (muriatic acid) to remove chrome plating from plastic chrome plated shower parts (shower head holder) in order to make chromium chloride.  I understand that in chrome plating, the order of plating is generally, copper, then nickel, then chrome.  I also know that chrome and nickel dissolve in $\ce{HCl}$, copper doesn't.  Or isn't supposed to very quickly at least.  I let the parts set for several days to a week. and the parts were white, so everything was removed.

The chrome came off, but much off it came off in little flakes.  Apparently the nickel is removed also. But also the copper.  I filtered the solution to remove the black residue and save the chrome flakes and put them in a beaker of fresh $\ce{HCl}$.

Doesn't seem to do much. Why?


texts: How can a chemical structure be stored in a matrix?

texts:
How do I represent a chemical structure in a matrix format in Matlab? Can I input a chemical structure into Matlab using the S.M.I.L.E.S notation?

I have to specify the connectivity of different atoms with others and type of bonds between them. I have to write the structure in matrix form, so that it can be utilized in some linear programming. For example, if one atom is connected to another atom I have to store 1 in matrix otherwise 0 (binary variables).
I need to develop back end code for my purpose to design some molecules using this approach. As of now I am dealing with 2D structures.


texts: I can not find a mechanism online. I understand that some poisoning effect causes the catalyst to be unable to reduce an alkene to alkane; however, if the catalyst is poisoned, how does it continue to reduce alkynes to alkenes?


texts:
So I casted a zinc ingot around a week ago and I also casted 2 zinc ingots yesterday. After observing the two side by side I noticed that the older zinc ingot was darker colored, then I went and looked at all of my old ingots containing zinc. They where all dark. Here is a picture of the old one and the new one side by side

The old ingot is on the left and the new one is on the right.

Here is another photo

Is this oxidation possibly? What causes this? Any answers are appreciated.


texts: What does "the natural bond angle" mean in the context of Universal Force Field (UFF) potential energy calculation and how are bond angles calculated?

texts:
As the title says, what does "the natural bond angle θ0" mean in the context of Universal Force Field (UFF) potential energy calculation? The reference appears in section D. Angular Distortions, 1. Angle Bend). The article also talks about "natural bond length" (Section C. Bond Stretch).
I am curious about how molecular dynamics (MD) simulations estimate/calculate bond angles using the Universal Force Field.
At several points in the original UFF paper they mention a "natural angle" but it is not overwhelmingly clear to me what this means. Is it the empirically observed bond angle(s) in particular molecules? How do MD simulations, then, produce bond angles for molecules that there is no published data for?
I understand that the UFF potential energy calculation contains several terms that account for various properties like hybridization, van der Waals interactions, etc. Which of the terms, which are outlined in the first pages, account(s) for steric interactions between molecules and determine the final bond angles?
I am admittedly not very well versed in the types of maths that are involved, but I would appreciate any explanation possible.
Thank you very much in advance!


texts: Magnetic non-equivalence of acetal protons

texts:
I have been using bromoacetaldehyde diethyl acetal recently and noticed something interesting about the 1H NMR. The methylene protons of the ethyl acetal are magnetically non equivalent. You see two quartets integrating for two protons with different shifts.

You can see this in the spectra here.

I have found a short description, however it is a little unclear:

  Diethyl acetals such as (1 6) and triglycerides such as triacetin (1 7) have a molecular symmetry plane and consequently are optically
  inactive. However, this plane does not bisect the connecting line of
  the geminal protons, which are magnetically non equivalent. This is
  manifested by the relative complexity of the AA'BB'X type proton
  spectrum of the glyceryl moiety of triacetin (Figure). Similar
  magnetic non-equivalence can be induced across an ester bond; e.g.,
  the two methyl groups of the isopropyl ester (18) area non-equivalent.

I don't really understand as there is no restriction of rotation. And does this mean that this would disappear using high temperature NMR?


texts: Are there natural or artificial enzymes that break down metals?

texts:
Do natural or human engineered enzymes exist that can speed up the break down metals (element, compounds & alloys)?

If no, then what biological or chemical construct can break down metals in the same way that enzymes break down food in a person's stomach?


texts: Is the fact that table salt is composed of Na & Cl a chemical or physical property?

texts:
So I came across this question asking whether something is physical or chemical.

  Table salt is composed of $\ce{Na}$ & $\ce{Cl}$. Is it a physical property or a
  chemical property?

I really don't understand why the answer says its a chemical property. I asked the others and they did not give me an understandable answer.

Edit: Now as I think about it, I really don't think there is an accurate answer, even if the book said it was chemical. Bad question from the book.


texts: What are the basic conditions for a carbocation to rearrange into a stable carbocation?

texts:
While rearranging,every rearrangement has to increase the stability of carbocation, other than this is there any other thing that we have to keep in mind while rearrangements?

Is there any limit to the number of rearrangement to the carbocation given in the first step?


texts: How was the diatomic nature of many common gaseous elements originally determined?

texts: How did scientists find out that  $\ce{Cl2, H2, O2}$ atoms have a two-atomic molecular structure ?


texts: Arrange the following compounds in the increasing order of equilibrium constant for hydration

texts:
Arrange in their increasing order of equilibrium constants for hydration:

(a) A < B < C < D < E
(b) A < C < B < E < D
(c) A < C < E < B < D
(d) C < A < B < E < D

How to compare figures E and D? Formaldehyde (figure D) doesn't have steric repulsion. Figure E has steric repulsion along with an electron withdrawing group. Given answer is (b). Does this mean steric hindrance is dominant over inductive effect while comparing? Please explain!


texts: GOC allylic,vinylic, benzylic positions, carbocation stability

texts:
Carbo-cations may be stabilized by:
(a) π-bonds only at allylic position

(b) π-bonds only at vinylic position

(c) π-bonds at allylic and benzylic position also
(d) -I effect

While the answer is obviously not (d), I am really confused about what 'allylic', 'vinylic' and 'benzylic' positions actually mean. I have heard about allylic/vinylic/benzylic carbons, but positions..?
Please, help.
Thank-you.

The question has been taken from ADVANCED PROBLEMS IN ORGANIC CHEMISTRY by HIMANSHU PANDEY


texts: Sulfur trioxide violates the octet rule. Upon drawing the Lewis dot structure for sulfur trioxide, we see that the central sulfur atom is bonded to three other oxygen atoms by double covalent bonds. Therefore, sulfur is in fact surrouded by 12 electrons and not 8 as per the octet rule. This is explained by the fact that the excited state of sulfur has the following electronic configuration: $1s^22s^22p^63s^13p^34s^03d^2$. As there are 3 oxygen atoms, $sp^2$ hybridised orbitals take part in single $\sigma$ covalent bonds with the unpaired $p_y$ orbitals of the oxygen atoms. In sulfur, there still exist one unpaired $p$ orbital and 2 unpaired $d$ orbitals. These remaining unpaired orbitals take part in $\pi$ covalent bonds with the unpaired $p_z$ orbitals of the oxygen atoms. My question is, why do the electrons in sulfur from the $3s$ and $3p$ orbitals in the ground state promote themselves to the $d$ orbitals rather than one electron going into the intermediate $4s$ orbital and the next electron going into the first $3d$ orbital? After all, according to the Aufbau Principle, $4s$ is less energetic when compared to $3d$.


texts: Obviously, it really would be $\ce{O=P-O-F}$.  Since $\ce{F-O-O-F}$ exists the $\ce{-O-F}$  part is obviously possible and the rest of it doesn't strike me as unreasonable, but whether it can actually hold together is way beyond my knowledge.  That $\ce{-O-F}$ says it would be some nasty stuff if it exists at all.


texts: Electrode/solution interface : What's the difference between the electrochemical Peltier heat and the heat caused from the overpotential?

texts: In principle heat effects caused by the passage of an electric current might arise from: electronic peltier effect at the junction of electrode/solution level, Joule effect due to solution resistance, electrochemical Petier effect at the interface level and the thermal effect due overpotential. What is the difference between the last two ones?


texts:
I'm taking my first chemistry class with a laboratory component this quarter. My first laboratory session was earlier this evening (observing simple metathesis reactions). While I found the lab work to be fairly straightforward, the fact that the interior surface of my safety goggles accumulated a considerable amount of condensation proved to be a moderate hinderance.

I'm wondering if anybody has recommendations for lab goggles? Particularly ones which may avoid this problem?

Note: it is school policy that we wear lab goggles with side shields, not lab glasses.

Any insights here would be appreciated!


texts: Bredt's rule applied to fused bicyclic systems

texts:
Ultimate question: Is Bredt's rule equally valid for fused bicyclic system (no bridgehead alkenes without a ring 8 carbons or more), but for other reasons (historical?) it is only defined as applying to bridged systems? Or am I missing something else fundamental about bridged vs fused bicyclic systems?

--Background--

Everywhere I can look (online, reference texts), Bredt's rule is specifically in reference to bridged bicyclic systems. However, shouldn't the rationale behind Bredt's rule -- that by having a bicyclic alkene with the double bond at the bridgehead means it has to have a trans alkene and therefore needs 8 carbons or more -- also apply to a fused bicyclic alkene as well?

The only example my book gives students is a bicyclo[4.4.0]dec-1-ene. It says "well this doesn't need Bredt's rule, because it's not a bridged system, but it's still stable because the largest ring has 10 carbons to accommodate the trans bond". That answer is unsatisfying to me, because the basis for them recognizing that the molecule has a trans alkene in it, comes from the discussion about Bredt's rule in the first place.

It never gives an example of something like bicyclo[3.1.0]hex-1-ene (above)...but I assume based upon a trans-alkene with less than 8 carbons this should also not be stable? Would this just be an application of the idea that trans-alkenes need to be in rings 8 or larger to be stable (without being part of Bredt's rule specifically)?


texts: Where does the charge on an electrode, responsible for the formation of a double layer once submerged in an electrolyte, come from?

texts:
I've started exploring electrical double layers and electrode-tissue interfaces whilst dealing with deep brain stimulation and stimulus artefact. I've heard many times that what causes the double layer to form is a net charge at the surface of the submerged electrode that then quickly attracts ions (cations or anions depending on the surface charge sign).

I always thought that in general, objects are neutral and don't carry charge around, where then, does the surface charge on electrodes come from?


texts:
How the Gibbs free energy of a chemical compound is theoretically calculated from scratch?

When saying that the Gibbs free energy of NaCl is -384.1 kJ/mol, this value is related to the chemical bonds of Na-Cl.

We should be able to calculate this value from the sum of energies in chemical bonds of one mole of NaCl? Right? How?


texts: Estimation of ground state energy from wave function

texts:
Given the wave functions of a particle in a 1D box below determine (for each pair) if the left or right function gives a better estimation of the ground state energy if the variational method is used. No calculaltions are needed.

I am having some problem understand how to solve this question. We are not allowed to use any graphing calculators and the tip says "try to plot some points and compare it with the exact wave function", which I don't find helpful.
All help is truly appreciated!


texts: Can PBE (and LDA) actually be a better choice sometimes?

texts:
Part of my work as an inorganic chemist is to investigate the magnetic coupling between metallic centers in coordination compounds. After some time, I've noticed that the classic PBE functional is the one giving me the best results (better than B3LYP, PBE0 or even M06) and, at first, I was convinced that this was a mere coincidence.

The cases in which PBE keeps giving me better results are adding up, so, I've decided to perform a quick test using the well known $\ce{[Mn(III)2O2(NH3)8]^{2+}}$ that have a reported experimental $J_{AB} = -186.5~cm^{-1}$.

My benchmark showed this:

To me, the results are that the Local and Gradient Corrected Functionals like PBE and LDA are, actually, better for this kind of properties in which orbital superposition and spin delocalization are important.

My point here, I think, is that I struggle to believe that such simple and "old" functionals like PBE and LDA are actually better describing a complicated phenomenon like magnetic coupling.

I'd love to hear what you, guys, think.

P. S. 1: I'm using ORCA, that gives me J calculated using 3 different formulas, that's why I have 3 J values.

P. S. 2: Sometimes I'm using 2 basis sets, a bigger one for Mn and a smaller for O, N and H.


texts: Is there a scientific database where one can find all the H and P statements for all chemicals? I would like to avoid using wikipedia but I can't find a database from a trusted source.


texts: Steady-state approximation for the destruction of ozone

texts:
As a personal problem, I am trying to find a rate law for the reaction $\ce{3 O2 -> 2 O3}$ using the steady-state approximation.

The elementary reactions are, \eqref{eq:equilib} (forward rate constant $k_1$, reverse rate constant $k_{-1}$), and \eqref{eq:destroy} (forward rate constant $k_2$):
\begin{align}
\ce{O3 &<=> O2 + O} \tag1\label{eq:equilib}\\
\ce{O + O3 &-> 2 O2} \tag2\label{eq:destroy}
\end{align}

I go about by setting the total rate of disappearance of $\ce{O}$ equal to that of its formation. Thus,

$$k_1[\ce{O3}] = k_{-1}[\ce{O2}][\ce{O}] + k_2[\ce{O}][\ce{O3}]$$

and rearranging gives
$$[\ce{O}] = \frac{k_1[\ce{O3}]}{k_{-1}[\ce{O2}] + k_2[\ce{O3}]}$$

Next, I express the overall rate in terms of the disappearance of $\ce{O3}$. This means that

$$\text{Rate} = -\frac{\mathrm{d}[\ce{O3}]}{\mathrm{d}t} = k_2[\ce{O}][\ce{O3}].$$

Then I can substitute the expression for $\ce{[O]}$ to get an expression for the overall rate, and I get

$$\text{Rate} = \frac{k_1 k_2[\ce{O3}]^2}{k_{-1}[\ce{O2}] + k_2[\ce{O3}]}$$

With the step above lies my question. Is $-\frac{\mathrm{d}[\ce{O3}]}{\mathrm{d}t}$ equal to what I have above, or does it also include the rate of disappearance of $\ce{[O3]}$ from the first elementary reaction?

$$\text{Rate} = -\frac{\mathrm{d}[\ce{O3}]}{\mathrm{d}t} = k_1[\ce{O3}] + k_2[\ce{O}][\ce{O3}],$$
as opposed to just
$$\text{Rate} = k_2[\ce{O}][\ce{O3}]?$$

I suppose the former is correct, because when $k_2$ is small, the expression reduces to one obtained by simpler methods ($\text{Rate} = \frac{k_1k_2[\ce{O3}]^2}{k_{-1}[\ce{O2}]}$). However, it seems that I do need to include the first elementary step, since that is involved in consuming $\ce{[O3]}$.


texts: How does sulbutiamine work in the same way as thiamine, even if it doesn't have a thiazole ring?

texts:
So sulbutiamine is said to be a thiamine substitute.

Yet - it doesn't contain the thiazole ring that's so important for many of thiamine's functions (highlighted in red).

How does it function as a thiamine substitute?


texts: Where to buy/How to build a Devanathan-Stachurski cell?

texts:
I'm preparing to do some hydrogen permeation tests to calculate the diffusivity of some iron samples. I would like to do this using the Devanathan-Stachurski cell, which consists of two cells, one where the hydrogen is charged and the other where it is oxidized (each containing an electrolyte solution), with the sample in the middle. The current produced by the diffusing hydrogen can be used to calculate diffusivity.

Does anyone have experience using this cell and know where to purchase one? So far I've only been able to find one company that sells it, but I would like to know about more options. If anyone has built it from scratch, can you provide some specifications on dimensions and materials used and how it worked for you?


texts: Why does the light catalyzed radical addition of tetrachloromethane to an alkene produce only a single regioisomer?

texts:
This reaction always occurs in the following, regiospecific way:

$$\ce{CCl4 + R-CH=CH2 ->[$h\nu$]  R-CHCl-CH2-CCl3}$$

The same should apparently also happen when there is a carbon that has two substituents (e.g. methyl groups) and yield only one major product:

$$\ce{CCl4 + (CH3)2C=CH2 ->[$h\nu$]  (CH3)2CCl-CH2-CCl3}$$

I believe the initiation step goes like this:

$$\ce{CCl4 ->[$h\nu$] CCl3^. + Cl^.}$$

Can't both of these radicals, that form in the initiation step, react with the double bond and form a secondary or tertiary radical carbon? Why does only $\ce{CCl3^.}$ apparently attack the double bond?


texts: Calculating PPM of colloidal material in solution produced by electrolysis

texts:
I am running an electrolysis between two silver electrodes.
The “electrolyte” is deionized water.
Ions are still formed as the CO2 of the air generates enough ions for a few µA of current.
During the electrolysis the ions are converted to metallic silver nanoparticles due to strong ultraviolet radiation.
I have the following variables:

Current in Ampere [A]
Time passed in seconds [s]
Coulomb [C or As]
Quantity of deionized water [l (liter)]
I want to know:
On the anode dissolved silver in milligrams [mg]
PPM of silver in the deionized water [PPM]

In practice there will be some silver ions that make it from the anode to the cathode without “colliding” with an photon – so they will be depleted on the cathode.
However for the calculation I assume that all ions will get reduced to metallic nanoparticles and nothing will be depleted on the cathode.
How do I calculate the dissolved silver in mg and the PPM of the solution?
Thanks in advance!


texts:
What is the pH of a $\pu{0.050 M}$ solution of $\ce{NaH2PO3}$? I am given that $\mathrm{p}K_\mathrm{a1} = 2.0$ and $\mathrm{p}K_\mathrm{a2} = 6.58$.

I am getting two different answers, $3.94$ and $4.30$, using two different methods that I have learned:

Method 1

$\ce{H2PO3-}$ can either be protonated or deprotonated. The protonation reaction has

$$K = \frac{10^{-14}}{10^{-2}} = 10^{-12},$$

while the deprotonation reaction has

$$K = 10^{-6.58} = 2.63\times 10^{-7}.$$

Since the protonation reaction is significantly less favorable than the deprotonation ($K$ ratio is less than $1000$), we can ignore the protonation and only focus on the deprotonation. This yields:

$$10^{-6.58} = \frac{x^2}{0.05-x} \to x = [\ce{H+}] = \pu{1.15e-4 M},$$

$$\mathrm{pH} = -\log(x) = 3.94.$$

Method 2

With a diprotic acid that can either be protonated or deprotonated, the $\mathrm{pH}$ is given by the following approximation:

$$pH = 1/2(\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a1}),$$

$$\mathrm{pH} = 1/2 \times (2.0 + 6.58) = 4.29.$$

This is the correct answer as presented in the text. Why is the first method invalid?


texts:
Why is $\ce{OH-}$ more basic than $\ce{F-}$?

From what I understand, $\ce{O}$ has larger radius so it should be more stable (meaning less basic) than $\ce{F}$. When they form anions, since $\ce{O^{2-}}$ is larger, it can distribute its electrons over larger volume than $\ce{F-}$, meaning $\ce{OH-}$ should be less basic. Is this because of partial negtaive charge on oxygen?

  In a polar aprotic solution, why is $\ce{F-}$ a stronger nucleophile than $\ce{I-}$?

I learned that basicity (not nucleophilicity) is about stability. So can this be explained by electron density? Is explaining it with polarizability right?

  In a lecture, my teacher said $\ce{RO-}$ is relatively stable because of the high electronegativity of $\ce{O}$.

I think it should be unstable because of high electron density caused by high electronegativity. What's right?

  When people say something is stable, are they referring to its acid/base characteristics, or can stability also be referring to nucleophilicity/electrophilicity?


texts: What is this brown liquid that I got when I boiled glycerol and water solution?

texts:
I boiled a solution of glycerol and water at about 160 degree Celsius and got a brown liquid much less in volume (boiled off the entire water I think; also not so sure about the accurate temperature).

Before mixing glycerol with water it was a colourless liquid, now it is golden brown! Why would that be? Also, I smelled burnt sugar during the last couple of minutes of boiling. So I'd like to know what that gas was. So, do I have glycerin in my hand or any other byproducts?


texts: Hassium is predicted to be the densest element at 41 g/cm ^3, but how do you predict something like that? Wikipedia says there have only been 100 hassium atoms made to date and it's half life is less than ten seconds, so I have no idea how a scientist came up with that figure... any insight?


texts: Why does entropy increase in reactions that make more molecules?

texts:
I used to understand this (more molecules ⇒ more degrees of freedom), but do no longer, because the total number of atoms is conserved, so translational d.o.f. should just be turned into internal d.o.f.
(at least considering only those reactions in which that is the case, no particle creation or annihilation).
Example:
Two separate H atoms have 3 translational d.o.f. each (x,y,z), for 6 d.o.f. total. I bring them together to form $\ce H_2$ and now have 3 net translational d.o.f. for the whole molecule, as well as 2 rotations, and a vibration.
In fact, the vibration has 2 d.o.f. for kinetic and potential energy giving heat capacity $\frac{7}{2}RT$ for a diatomic molecule.
So why does entropy decrease in the type of reaction with a form something like
$$\ce{ nA + mB -> A_nB_m }$$
Is it perhaps related to certain internal degrees of freedom only being “unlocked” at higher temperatures because of high minimum quanta of energy per d.o.f.?  If so, that would mean that at higher temperatures, entropy no longer increases for reactions that produce more molecules.


texts: How can I know if there is a phospholipid (phosphatidylcholine) in a solution?

texts:
I have a solution which probably contains a phospholipid (phosphatydylcholine), I would like to know if there is an easy method to show the presence of the phospholipid.

I came across TLC, but I couldn't perform it since it's too difficult and expensive to buy chloroform.
So, If you guys know an easy method to show the presence of phospholipids please reply.


texts: Alternative to mercury bubbler for increasing boiling temp?

texts:
A common reaction for forming the octachlorodirhenate(III) anion is to heat tert-n-butylammonium perrhenate in benzoyl chloride at 209 ºC. If you look up the info for benzoyl chloride, one sees that the boiling point is only 197 ºC. To increase the boiling point, publications suggest closing off the system with a mercury bubbler, which increases the pressure enough to bump the boiling point of the liquid to 209 ºC.

In the teaching lab, use of mercury is highly frowned upon… are there any reasonable alternatives to a mercury bubbler to increase the boiling point (and thus, the reaction temperature) for this reaction? Publications report a 30-40% decrease in yield if the reaction temperature is lowered to 196 ºC, so there's a lot of motivation to keep the temperature up.


texts:
I know that the “$\mathrm{g}$” stands for symmetry of octahedral shape, but how are labels “1” and “2” given in $\mathrm{A_{1g}}$ and $\mathrm{A_{2g}}$ representations too…

Is it related to group theory? If so, then please elaborate.


texts: electrolysis - selection of what is going to be on anode and cathode

texts: I have a question about electrolysis. How do we know what will be on anode and cathode if we have for example NaCl diluted in water. How do we know if it's gonna be Na+ or H+??


texts: What is the complete reaction for Cyanide ions reacting with Thiosulfate?

texts:
I was recently studying about the properties of Sodium Thiosulfate, where I came across the fact that $\ce{S2O3^2-}$ reacts with $\ce{CN-}$ ions to produce $\ce{SCN-}$ ions. This was quite useful in treating cyanide poisoning.

I have tried to find the complete reaction, but with no success. I believe this must be a redox reaction, since $\ce{S2O3^2-}$ has an average oxidation state of $+2$, while $\ce{SCN-}$ has a state of $-2$ (correct me if this is wrong). Can someone give me the complete reaction?


texts: Show the acid nature of hydrogen sulfide

texts:
We are studying the chalcogens at school. I should prove (show) the acid nature of $\ce{H2S}$ by writing two chemical interactions.

I am really sorry if the terms I am using aren't the right ones. It's the first time I've ever used this part of the language. Which reactions should I write, and why? I think the first one must be neutralization:

$$\ce{H2S + 2 NaOH -> Na2S + 2 H2O}$$


texts: Why does $\ce{FeF6}$ not exist? There are hexavalent iron compounds, so that is not the problem. There is the $\ce{[Fe(CN)6]^3-}$ ion, so there doesn't seem to be a steric problem.


texts: Can carbon dioxide be used as oxidant for iron?

texts:
Determine whether it is possible for $\ce{CO2}$ to be an oxidant for $\ce{Fe}$. Justify your choice by comparing the corresponding half reactions.

I found the following half-reactions, both on reduction form:

\begin{align}
\tag{I}\label{I}
 \ce{Fe^2+ + 2e^- &<=> Fe(s)} & E^\circ &= \pu{-0.44 V}\\
\tag{II}\label{II}
 \ce{CO2(g) + 2H^+ + 2e^- &<<=> CO(g) + H2O}& E^\circ &= \pu{-0.1 V}
\end{align}

As iron should be oxidized, we turn \eqref{I} the other way and change the sign:

\begin{align}
\ce{Fe(s) &<=> Fe^2+ + 2e^-}& E^\circ &= \pu{0.44V}\\
&&E^\circ(\text{total}) &= \pu{0.44 V} - \pu{0.1 V} = \pu{0.34V}
\end{align}

$E^\circ(\text{total}) > 0$, and the reaction is spontaneous. But according to the solution manual $E^\circ(\text{total})$ should be less than $0$. Have I misinterpreted the task?


texts: How does a group 15 oxide react with water?

texts:
Given the following reactants:

  $\ce{P2O5}$ and $\ce{H2O}$

How does one determine what product the two will form in a reaction?

I instantly tried to treat the problem as a double displacement reaction. However, the compounds that I got by doing so were absurd. Do double replacement reactions only occur with ionic compounds (e.g., the cations of two ions switch)?

The two elements listed above form $\ce{H3PO4}$. How do I even go about determining that? What indicates that such a product forms from those two reactants?


texts:
I am learning about electron configurations and I came across the "exceptions" of $\ce{Cr}$ and $\ce{Cu}$ where electrons actually half fill the $\mathrm d$ orbitals instead of the expected $\mathrm s$ orbitals. I thought maybe vanadium would do the same, but my textbook gives the answer of an electron configuration exactly following the Aufbau principle.

I've attached a picture of my drawing for the textbook answer and what I had thought might happen — could someone explain why vanadium is not an "exception" like chromium or copper?


texts: It is said that covalent bonds are directional, while ionic bonds are not. Why? Is it because of the orientation/directional properties of the overlapping orbitals?


texts: If we count the total number of π electrons, there are 10. But to apply Hückel's rule to this molecule, we should count only the electrons of the outer periphery and there are 8 of these. How can the molecule be aromatic?


texts: What is the difference between balancing a redox reaction in acidic solution vs basic solution?

texts:
I'm asked to balance the potassium permanganate and hydrogen peroxide reaction. I misread the problem and thought that the reaction was in acidic solution. This is the result that I've got:

$$\ce{2MnO4 + 5H2O2 + 6H+ -> 2Mn^2+ +5O2 +8H2O}$$
What do I have to change to balance the equation in a basic solution?.


texts: How is mercury in drinking water detected?

texts:
A document I've been reading states that:

  Both the Maximum Contaminant Level Goal and the Maximum Contaminant Level were set at 2 parts per billion because current technology allows public water suppliers to detect and remove mercury levels that low.

But I know of drinking water test strips that detect 0, 50, 100, ... 1000 ppb and are 1,5-Diphenylcarbazide based.

On a chem supplier catalog I've found that 1,5-Diphenylcarbazide can detect up to 0,000002 g/ml, which is 2000 ppb. But I know from a question on this website that the above reagent can detect up to 250 ppb.

And as per urine and blood concentrations we are looking at 10 ng/ml they detect.

So what is the threshold for 1,5-Diphenylcarbazide test and how they detect those minute amounts anyway?

Is there a DIY method of detecting something like 2 ppb at home?

P.S. I am talking about Hg2+ ions, if it is not clear


texts:
There are two possible structures for Nitrosonium :

In the first structure, there is a +1 Formal charge on Oxygen, whereas,
In the second structure, there is a +1 Formal charge on Nitrogen.

Q. Which is a better lewis structure?

Q. Are they resonating structures of NO+?

Wikipedia gives the first structure only, so i think that is the only correct structure.

I think structure in which less electronegative atom has a positive formal charge is better, so the first structure is better.

Q. Is the above reasoning correct?


texts: Why is the orbital angular momentum of a pi electron along the axis of two atoms' molecule one?

texts:
I'm reading quantum chemistry. The book says that the orbital angular momentum of a $\pi$ electron along the symmetry axis of a molecule made up of two atoms is $\pm 1$. I think this is a primary question, but I do not know why (I'm a student studying physics)

I currently have a preliminary understanding of this:

In a molecule inculding two atoms, potential energy axisymmetric about z' axis(the line connecting the two atoms). So, the angular momentum along z axis is quantized. That is to say $m_z$ is good quantum number. Let's consider $\pi$ orbit made up of two $p_z$. The orbital angular momentum along z axis(the symmetry axis of $p_z$) of an electron in $p_z$ is 0. So considering orbital angular momentum along z' axis of this electron, the electron is in $\frac 1 {\sqrt 2}(|+>-|->)$. So the orbital angular momentum along z' axis is either 1 or -1. So the orbital angular momentum along z' axis of a $\pi$ electron is either 1 or -1.

Is my understanding correct?


texts: Is an iron (II) sulphate solution supposed to turn cloudy when silver nitrate is added?

texts:
$\ce{AgNO3}$ is not suppose to cause a precipitation when mixed with $\ce{FeSO4}$, but the acidified solution turns slightly cloudy when $\ce{AgNO3}$ is added.

Is this suppose to happen? solutions are all prepared fresh. Any reason as to why? This also happens when silver nitrate is added to magnesium sulphate.

Picture is as attached, the left one has the $\ce{AgNO3}$ added (labelled Ag) while the one on the right has $\ce{Ba(NO3)2}$ added to show the comparison


texts: Why does my filtered water turn thick and almost slimy when refrigerated?

texts:
I just started using a water filter.

I have 2 containers to store the filtered water; one goes in the fridge and the other stays out on the filter.

The water that stays out is fine and stays good for days.  The water that is stored in the fridge gets thick and almost tastes gluey.

Why is this happening?


texts:
I am currently studying the textbook Mass Spectrometry, third edition, by Jürgen H. Gross. Chapter 2.4.3 Bond Dissociation Energies and Heats of Formation says the following:

  The heat of formation of organic radicals and positive ions decreases with their size and even more importantly with their degree of branching at the radical or ionic site. A lower heat of formation is equivalent to a higher thermodynamic stability of the respective ion or radical. The corresponding trends are clearly expressed by the values given in Tables 2.2 and 2.3, This causes the fragmentation pathways of molecular ions proceeding by formation of secondary or tertiary radicals and/or ions to become dominant over those leading to smaller and/or primary radical and ionic fragments, respectively (Sect. 6.2).

Why does the heat of formation of organic radicals and positive ions decrease with their size and degree of branching at the radical or ionic site?

I would greatly appreciate it if people would please take the time to explain this.


texts: If you owned old kitchen appliances or old computer you might notice that they the once cream white plastic become increasingly yellow, old and disgusting. I have read that UV lighting can damage plastics as they disrupt the structure of plastics but what really is at play here? What chemical reactions are happening? Are such damages reversible?


texts:
As I know, chlorophyll is green as it absorbs all wavelengths but green. It absorbs red, yellow, blue, purple, etc. Thus, the plant does not utilize green light.

i] Why is chlorophyll green? Is there 'chlorophyll' of other colors?

ii] Is the green chlorophyll an 'evolutionary mistake'?

iii] If chlorophyll was black, what effects would there be?

iv] What is the effect on non-visible electromagnetic-radiation?

Thanks!


texts: Why is methoxide strong base? In case of halogens, I get why one is weak base, and one is strong base, but in the case of ones with oxygen, this seems to be hard to figure out.


texts: Thermal decomposition of calcium propionate

texts:
What are the decomposition products?

For example:

Calcium formate decomposes into formaldehyde and calcium carbonate.

$$\ce{Ca(HCOO)2 -> CaCO3 + HCHO}$$

Calcium acetate decomposes into acetone and calcium carbonate.

$$\ce{Ca(CH3COO)2 -> CaCO3 + (CH3)2CO}$$

How does calcium propionate decompose?


texts: Mechanism for reaction of Tollens' reagent with aldehydes

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Upon treatment with Tollens' reagent (ammoniacal silver(I) nitrate), aldehydes are oxidised to carboxylic acid, and silver(I) is reduced to silver metal.

I am trying to find a mechanism for the this reaction online, but the only thing I can find is the balanced equation. Can someone propose or help me find the mechanism?


texts: Is there any difference between geometrical and cis-trans isomerism in coordination complexes, because in my book it is given that complexes of the form [Ma4bc] does not show cis-trans isomerism but shows geometrical isomerism


texts: anionic surfactants as salt water induced rust inhibitors

texts: There are a multitude of product that purport to protect boat engines from the adverse effects of salt water.  These anionic surfactants claim to rinse away salt buildup.  I do not understand how a surfactant would improve water's ability to dissolve NaCl.


texts: Safest and easiest method to neutralize nitric acid

texts: I would like to know the safest method for neutralizing 70% ACS Reagent Nitric Acid that is used in small amounts of 1-5 ml, for an electronics process in which there will be small traces of silicone and other similar trace materials dissolved into it, to safely contain for proper disposal to not be a risk for acid accidents or fire/explosion risks. Should a calcium carbonate-water mixture be used to increase $\mathrm{pH}$ slowly or is this method still unstable from higher purity of $\ce{HNO3}$ being involved or?


texts: What's the chemical formula of "Everitt's salt"?

texts:
According to my school textbook (which is notorious, for being in possession of several errors), a certain "Everitt's salt" is a complex that results from the reduction of Prussian Blue.

Everitt's salt (according to our inglorious textbook)  has the chemical formula $\ce{K2[Fe(CN)6]}$... which I straightaway dismissed as nonsense, because it would mean it's got $\ce{Fe^{4+}}$ (ferryl ion). From my (very limited) knowledge of the subject, the ferryl ion doesn't look like something that would occur in any reasonably stable compound; since Everitt's salt is, well, a "salt" (and since salts can usually be crystallized into stable solids).

Google wasn't much help in this regard,

  I've no idea how to interpret the formula that is supposedly that of Everitt's salt

Questions:

1) Is there really something called "Everitt's salt"? Is it produced by the reduction of Prussian Blue?

2) What's its chemical formula?


texts: Sodium metal from electrolysis of molten sodium bisulfate?

texts:
My question is relatively straightforward. Can sodium metal be extracted from molten sodium bisulfate via electrolysis?
I have done it before with molten sodium hydroxide, but there is such a small temperature range to keep the salt molten and prevent the extracted sodium from dissolving back into the melt.
I then find out that sodium bisulfate melts at a much lower temperature than sodium hydroxide. This gives me much more wiggle room for error.


texts: Meaning of Cu1.5Al in Cu-Al phase diagram (I understand all other indexes incl. fractions like Cu0.75Al0.25)

texts:
I understand Cu0.75Al0.25 - that's just 75% Cu, 25% Al. I understand integer indexes - that's a normal chemical formula after all.

However, I have no idea how to interpret Cu1.5Al, I've never seen a fraction in a chemical formula, and if it was a composition-percentage it should be like in the 0.75-0.25 example?

Look at between 50% and 60%, below 630°C in the diagram below.

I read this page but still don't understand it.


texts:
I know that graphite and boron nitride are aromatic in nature.

In a similar way, can black phosphorous too exhibit aromaticity? Since it is essentially the same having 6 membered rings with lone pair of electrons and vacant d orbitals.

If not, then it would show some double bond character also, right?


texts: Derivation of the Heisenberg uncertainty principle

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The Heisenberg uncertainty principle states that

$$\Delta x \Delta p \geq \frac{\hbar}{2}$$

where
$\Delta x$ is the uncertainty in the position,
$\Delta p$ is the uncertainty in linear momentum, and
$\hbar = 1.054571800(13) \times 10^{-34}\ \mathrm{J\ s}$[source] is the reduced Planck constant

This means that, regardless of what quantum mechanical state the particle is in, we cannot simultaneously measure its position and momentum with perfect precision. I read that this is intrinsically linked to the fact that the position and momentum operators do not commute: $[\hat{x},\hat{p}] = \mathrm{i}\hbar$.

How can I derive the uncertainty principle, as given above?


texts:
(Almost) Everyone is familiar with making simple syrup from table sugar and water.

I was wondering if pure sucralose is also capable of forming a syrup.

I wanted to do an experiment myself, but to my consternation,

Splenda is not pure sucralose.
pure sucralose is not readily available to me

So, I would like to hear if anyone has tried this experiment, or reasons why sucralose would not form a syrup if such is the case. Pointers to references would be nice.

P.S. I do not have a deep chemistry background, so simple explanations (or even pictures) will be very much appreciated.


texts: Need to dissolve glue placed intentionally in a lock

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Someone intentionally sabotaged the lock on the front door of my house by putting glue inside it apparently, I have no idea what type of glue it is. Is there any chemical substance I can use to dissolve the glue instead of having to replace the entire lock?

Also, would heating the lock work?

I took a look at this, the heating option wasn't possible since they're talking about paper, but I was wondering if it'll work before trying any of the chemicals mentioned.

Please consider that I don't have much experience in Chemistry while answering, thank you for your time.


texts: Is the d-block ever part of the valence electrons?

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The d-block sub-shell is always one shell lower than the s-block and p-block sub-shells. Assuming only the electrons in the highest energy shells count toward the set of valence electrons (is that correct?), d-block is never in the highest energy shell, and so none of the electrons in the d subshells would ever count toward the valence electrons.

I suspect I'm mistaken. Am I? If so, where have gone wrong?


texts: What prevents inner-sphere electron transfer from oxalato-iron(II) to chloro-platinum(II)?

texts:
In this book (p. 237), when talking about the reduction of $\ce{[PtCl4]^{2-}}$ by $[\ce{(C2O4)2Fe]^{2-}}$, the author states that

  There is no easy route for imparting electrons onto the $\ce{PtCl4}^{2-}$ ion, but it may proceed more readily via the aqua-complexes $\ce{(H2O)PtCl3-}$

and

  The pathway for the electron transfer from iron(II) to platinum(II) has not been elucidated, but in view of the labile nature of iron complexes with respect to ligand substitution it is unlikely to proceed via an 'inner sphere' mechanism, whereby the two coordination shells share a common bridging ligand.

What prevents the inner-sphere mechanism in this case?

In Taube's original example, the metal with the bridging ligand is low-spin before, and the other metal, which takes the bridging ligand, is low-spin after. Can inner-sphere transfer only occur in those kinds of cases? Here, both the Fe(III) and Fe(II) are high-spin.


texts: Why are neutralisations involving weak acids and bases less exothermic than those involving only strong acids and bases.?

texts: I read somewhere that for example the neutralisation reaction between sodium hydroxide and acetic acid is less exothermic than those of sodium hydroxide with hydrochloric and nitric acid because some energy is needed to cause the weak acid (acetic acid) to completely ionise. Is this true?