texts: Why is vapor pressure constant at boiling point?

texts:
At non-boiling point, I understand that when you add heat, temperature increases and also the amount of gas increases, so by using $PV=nRT$ at constant volume, the increase in $n$ and $T$ would increase $P$.
Thus, vapour pressure increases with temperature.
However, at boiling point, if you add heat, temperature does not increase and the energy is used to generate more gas molecules.
So if you are at a equilibrium where there is $\pu{1 mol}$ of $\ce{A(l)}$ and $\pu{1 mol}$ of $\ce{A(g)}$, after you add heat and shift equilibrium to $\pu{0.5 mol}$ of $\ce{A(l)}$ and $\pu{1.5 mol}$ of $\ce{A(g)}$ wouldn’t the vapour pressure increase even though temperature is the same by the ideal gas law– $PV=nRT$, where increase in $n$ increases $P$?
So why is vapour pressure is constant at boiling point?


texts: Why enzyme-catalyzed reactions mostly go one way?

texts:
I listened to the lecture about enzymes. Professor downplayed the question in the subject. He said that enzymes are able to work both ways, but practically speaking reactions with overwhelming probability flow in only one direction. He said that a variety of factors cause this, and there is nothing interesting there beyond this.

I am not clear what the reasons are. There is the reaction rate constant. Does this mean that rate constants are very different in value depending on direction? Or the reason is that reaction product molecules are always quickly consumed by the next step, and as a result the concentration of the product is always low?


texts: Do catalysts shift equilibrium constant towards 1?

texts:
I want to be able to understand shifts in equilibrium from the maxwell boltzmann distribution. One thing I cannot get my head around is the effect of catalysts on the equilibrium position - supposedly it's none at all.

But consider these diagrams of the M.B distribution of both reactants and products of a reversible reaction.

The top diagram shows the distribution of the products of the reaction which equilibrium favours. It has a bigger concentration of particles. The line dividing the shaded region on these diagrams represents activation energy and the $dE$ represents the shift in activation energy due to the catalyst. We can see that the shaded regions, $A_1=A_2$ because forward and backward rates are the same at eqm. But clearly, the rate of the top reaction increases more as a greater fraction of particles have above activation energy. So adding a catalyst should shift equilibrium to the middle?

Basically, catalysts work better on reactants with higher concentration. So shouldn't the side with the lower concentration be favoured?


texts: Aluminum Monoacetate Solubility in Aqueous Medium?

texts:
Does anyone have access to the aqueous solubility value of  aluminum monoacetate?
I would expect it to be slightly soluble but I've searched the internet and haven't found any solubility values. : /


texts: Calculate limiting molar conductivity of BaCl2

texts:
How can I calculate limiting molar conductivity of BaCl2 in water at 25 degree Celsius?
I have got a formula for calculating limiting molar conductivity .

limiting molar conductivity  =  V+ A+ +
V- A-
V+  =  number of cations per formula unit of the
electrolyte
V-  =  number of anions per formula unit of the
electrolyte
A+ = molar conductivity of the cations
A- = molar conductivity of the anions

Here I figured out, V+ = 1 and V- = 2
How can I solve the question and tell me  if there is any information that is not present above to solve the question.


texts: How can I draw alpha helices in ChemDraw?

texts:
I am trying to draw a polyisocyanopeptide with different kinds of monomeric units that intramolecularly interact with one another. However, I wanted to show these connections with its carbon backbone in the helix configuration.
An example of what I mean is shown below, taken from Kouwer et al (Nature 2013, 493 (7434), 651–655). How can I draw the alpha-helix as shown in red in ChemDraw (or any other program)?


texts: Calculating pH of a saturated weak acid/base solution

texts:
How can you calculate the $\mathrm{pH}$ if you know for example the $\mathrm{p}K_\mathrm{a}$ or $\mathrm{p}K_\mathrm{b}$ value of a weak acid/base and how much acid/base can dilute in water. Let's take an example:

Quinoline has $\mathrm{p}K_\mathrm{a} = 4.5$ and $\pu{0.6 g}/\pu{100 ml}$ can dilute in water. I can easily calculate that the concentration of the saturated solution is $\pu{0.0465 M}$. So if the reaction is

$$
\ce{C9H7N + H2O -> C9H7NH+ + OH-},
$$

why $[\ce{OH-}]\neq \pu{0.0465 M}$? I know that I can get the correct answer by making an ICE-table and use that given $\mathrm{p}K_\mathrm{a}$ value but why is it necessary? It seems weird as after making the ICE-table it seems that all quinoline isn't diluted…


texts:
Carboxylic acid is much more acidic than phenol ($\mathrm{pK}_\mathrm{a}$  difference of ~6). I wonder why? In terms of resonance, there are 5 resonance structures for phenol, and only 2 in carboxyl group.
My thought is 4 out of 5 structures in phenol are minor (lone pair electrons at carbon, less stable), compared to the equivalent resonance in carboxyl group. Is that really the sole answer to the large $\mathrm{pK}_\mathrm{a}$ difference? I am not so convinced.
Although these resonance (4/5) structures are minor in phenol, I think the combined delocalization effect should make it more acidic than a carboxylic acid.


texts: Is ammonium a strong or weak conjugate acid?

texts:
Ammonium, $\ce{NH_4^+}$, is the conjugate acid of ammonia, $\ce{NH_3}$. I have searched the Internet and so many different answers pop up. The rule of thumb that I read was that a strong acid has a weak conjugate counterpart.

For example, a strong acid has a weak conjugate base. Is ammonium a strong or weak acid? Is ammonia a strong or weak base? Is there something to the rule of thumb that I mentioned?


texts:
Is there a decent way to test for solvable manganese in water without purchasing a 150USD test kit? I have a fair chemistry set available (I use it to teach my kids chemistry), and would rather pay 50USD for something to add to it that can also be used for other things later than pay for some test that may not be that accurate anyway.

Our city water supply to our house produces a black slime that is likely from bacteria that feeds on iron or manganese. I’d like to start getting to the bottom of it. This is a first step.


texts: Will the temperature of a faucet actually be lower than the countertop or will it only feel cooler due to specific heat?

texts: Due to specific heat capacity of metals, they feel cooler because they don't retain  as well as other materials. But is their temperature actually lower if it could be measured?


texts: Is it possible to melt potassium nitrate without it decomposing into potassium nitrite and oxygen? If so when it solidifies does it keep its oxidizing properties?


texts: Why is sugar used in low-cost homemade rockets?

texts:
I was thinking about making a "rocket candy". It's relatively inexpensive rocket based on sugar and some oxidiser, mostly $\ce{KNO3}$.

The fuel is usually formed by heating the mix of both compounds so that the sugar sticks onto the potassium nitrate. They can also stick together by being dissolved and dried.

My question is, what makes sugar the best fuel? Paraffin or resin can be melted more easily and the oxidizer could be poured on them while they are hot. To me, that seems like a much better idea.

But there were many people before me and they have surely tried many things. So, what is the reason the sugar is more advised than paraffin or resin?


texts: If NO3- were to get oxidised to some compound in the way SO4 2- gets oxidised to S2O8 2-, what would be that compound?

texts: In electrochemistry, we learn of the sulphate ion getting oxidised to peroxydisulphate ion. If this was to occur in the case of the nitrate ion which has a larger discharge potential, what would be formed?


texts:
An organic compound A $(\ce{C10H14O})$ exhibits following characteristics.
A) It reacts with metallic sodium to give a colorless odorless gas.
B) It is oxidized by $\ce{KMnO4}$ to benzoic acid.
C) It can be resolved.
D) It does not give precipitate with iodine in presence of $\ce{NaOH}.$
E) It changes the color of acidified potassium dichromate from orange to bluish
green, and gives a chiral compound.
How many of the following compounds satisfy all the five criteria from A to E?

The given answer is the compounds 4, 5, 10 satisfy the criteria but I think the compounds 5, 6, 12 satisfy the criteria.
From statement A, we come to know it's an alcohol (which is common to every compound).
From statement B, we come to know that it has a benzylic hydrogen (which rules out the compound 11).
From statement C, we come to know that it has a chiral carbon. (which rules out options 4, 7, 9).
From statement D, we come to know that $\ce{OH}$ group is not attached to a methyl group (which rules out options 3, 10).
For statement E, I guess potassium dichromate will oxidise 2° alcohol to ketone and 1° alcohol to carboxylic acid and the compound still remains chiral (which rules out options 1, 2, 8).
So where's the mistake?


texts: Efficiency of H production from FeOOH catalyst?

texts:
Research has recently found that FeOOH is 25 times better at hydrogen production than titanium dioxide.

Today, a new electrolysis plant delivers energy efficiency of around 80%. Is 25x the Honda-Fujishima reaction, using FeOOH higher efficiency than that?

ref:
https://www.tus.ac.jp/en/mediarelations/archive/20200227001.html


texts: Calculating Redox Potential; Coupled Reactions

texts:
For the reaction of silver and hydrochloric acid to form silver chloride: would the following be the correct way to couple the below two half reactions?

$\ce{2Ag(s) + 2Cl^- ->2AgCl(s) + 2e^-} ~~E^0 =-0.222 ~V$

$\ce{2e^- + 2H_3^+O -> H_2 + H_2O}{ ~~E^0 =0.000~ V}$

Add the above:

$\ce{2H_3^+O +2Ag(s) + 2Cl^- -> 2AgCl(s) + H_2 + H_2O}{ ~~E^0 =-0.222~ V}$

Implying that the reaction is non-spontaneous as we have a "negative potential"?


texts: What units do I use for energy in the Boltzmann distribution?

texts:
I am a mathematics student doing a course in thermodynamics and am working on the basics now. The question I am asked is:

  Suppose two states differ in energy by one electronvolt. What can be said about the ratio of the population at $T = \pu{300 K}$?

Now it is clear that I will use the formula:

$$\frac{N_i}{N_j} = \exp\left(-\frac{E_i-E_j}{kT}\right)$$

where $k = \pu{1.381 \times 10^−23 J K-1}$. Now if let $E_i$ be the higher energy state, then am I right in saying that $E_i-E_j = \pu{1 eV}$, or should I convert this to some other unit?


texts: References to draw 3D molecules with directionality of non-bonding electron pairs and p-orbitals

texts:
My instructor has been drawing 3D molecules that show the directionality of non-bonding electron pairs and p-orbitals. I've been trying to find references online that show this process, but I'm having a hard time finding anything useful.

Can someone please explain the process or link to a source that does? I've included two pictures of molecules that show what I'm looking for.


texts: Why does multipying a scalar in both sides of a balanced chemical equation, change related quantities?

texts:
Stoichiometric coefficients appearing in a balanced chemical equation are unrelated to the actual concentration of reactant/products at any stage of a chemical reaction. They give information only about the ratio in which the reactants and products are consumed and produced. Multiplying by a scalar on both sides of the equation doesn't change that ratio.

Then, why does doing so result in changes in physical quantities related to the reaction, like equilibrium constant or Gibbs energy?


texts: Regioselectivity in the aldolcondensation towards (Z)-Jasmon

texts:
In the synthesis of (Z)-Jasmone via aldol-condensation as shown below,
how can the observed regioselectivity be explained?
After all, it is also possible to form the side product shown below. I thought that at least with LDA, the sideproduct should be favored, while I assume that for milder bases such as KOH, the thermodynamic enolate is formed, finally leading to the desired (Z)-Jasmone. Are there any other reasons for the regioselectivity?


texts: Intensity of “surface plasmon resonance “ absorption peaks for a nano-rod

texts: The SPR absorption spectrum of a nano-rod is seen to have two peaks with the longer wavelength peak corresponding to the absorption by the longitudinal plasmons and the other to the transverse plasmons. When the intensities are compared.. longitudinal plasmon peaks are almost always more intense than transverse ones. Why?


texts: Can molecular structure be determined without modern characterization methods?

texts:
Molecular composition can be determined in some "primitive" ways (1, 2). What about the molecular structure? Is there a way to know what's bonded to what without spectroscopy etc.?

By "modern" I mean any method that emits and detects particles (photons, electrons, etc.).


texts: I've read that alkali metals form ionic bonds; $\ce{Li}$ is an exception which majorly forms covalent bonds. Wikipedia says dilithium exists. This makes me wonder why $\ce{Li_8}$ doesn't exist. It seems having all 8 electrons shared produces a low energy state (because the valence shell in each of the 8 atoms will be completely filled) ?


texts: What is the safe level of energy output for hydrogen combustion at home?

texts:
With confinement, my son would like to do some home experiments for a class. So far, he has a good setup that seems sound for the electrolysis of water. A later part of the experiment would combine back the $\ce{O2}$ and $\ce{H2}$ to get back water vapour.

What amount of atmospheric pressure $\ce{H2}$ and $\ce{O2}$ can be safely combined, at home, without it turning to a fireball and/or a news event?  From Googling, I found 12,749 joules per litre of hydrogen. What I'm asking is:

How does dissipating 12K joules look like in a plastic bucket? Is this a case of needing only gloves and eye protection, or does it need further protection? Will it be just some heat, just a small flame, or a McGyver-type explosion?

Also, will $\ce{H2}$ and $\ce{O2}$ at atmospheric conditions instantly react, or would this be a progressive reaction?


texts: Deuterium depleted water through fractional distilation

texts: Could a packed fractional still of the same type used to distill ethanol to 95% be used to produce deuterium depleted drinking water? The still has a 1000 watt electric heating element and has a fractioning column that is 120cm long which is packed with stainless steel wool. If it is feasible what kind of performance might I expect?


texts: Why is the equilibrium constant defined that way intuitively?

texts:
Suppose we have chemical equation: $$\ce{ aA + bB  <=>   cC + dD }$$

then equilibrium constant is defined: $$K=\frac{[C]^c[D]^d}{[A]^a[B]^b}$$

but why don't we define it as: $$K=\frac{cd[C][D]}{ab[A][B]}$$

or even as: $$K=\frac{c[C]+d[D]}{a[A]+b[B]}$$

As adding concentrations is additive and not multiplicative. And because: $$\ce{ aA + bB <=> cC + dD }$$
is the same as: $$\ce{ cC + dD <=> aA + bB }$$
then we should have: $$K=\frac{[A]^a[B]^b}{[C]^c[D]^d}$$
and specifically: $$\frac{[A]^a[B]^b}{[C]^c[D]^d}=\frac{[C]^c[D]^d}{[A]^a[B]^b}$$
but trying some examples shows that this isn't the case.


texts: Why do charges result on atoms when coordinate bonds are formed?

texts:
I have not been able to get my head around it yet.

For instance in the reaction between ammonia and borontrifloride why is it that a positive and a negative charge results? Is it that ammonia donates is lone pair completely? If not so, if sharing of lone pair donated by ammonia occurs why then should charges result?


texts: Acids / Bases - Need some clarity for final exam

texts:
I'm studying for my final exam, and these are the questions I got wrong on the mid term, could anyone help correct me? I know people are against giving answers for homework, so I must add that is now exam period for Universities, so this is only for my further understanding!
Thanks so much!

My attempts will be in this format

1)The pH of a 0.2M unknown base X OH is 8.15

a)Calculate [OH-]

10^(-8.15) = 7E-9M

b)What is the % disassociation

(7E-9/0.2M) x 100 = 3.5E-6%

c)What is the Kb of the base?

This one I don't even know where to begin..

2)Calculate the pH of the following solutions

a) 0.10M KCN, Ka (HCN) = 6.2E-10 (Hint: KCN is the salt of a weak acid and a strong base)

x = sqrt(Ka*c)
x = sqrt(6.2E-10 * 0.1) = 7.8E-6
-log(7.8E-6) = pH = 5.1


texts: I was wondering what the difference between $c_n$ and $c_{jn}$ is? In the context of molecular orbital construction, for example, if $c_{jn}$ is the coefficient of the basis functions $\phi_j$ (contribution of the constituting atomic orbitals), what would $c_n$ be?


texts:
I have seen $\ce{P4O_{10}}$ and $\ce{HSO3Cl}$ being used to dehydrate carboxylic acids giving an anhydride and a ketene respectively.

Can  we use them to dehydrate $\ce{-OH}$ (of aliphatic alcohol) group from an organic compound? I have never seen anyone do that. If we can, then please specify the appropriate conditions for the reaction  to be carried out.


texts: Why is % yield in a purification table measured using activity instead of total protein?

texts:
I'm trying to understand why % yield is measured with activity instead of total protein in mg. According to my biochemistry notes, activity is "1.0 units of enzyme activity = 1.0 μmol of substrate catalyzed to product under optimum conditions."

Then, yield is defined as "% of total starting protein/enzyme in final purified protein fraction."

With this definition of yield, it would make sense to say that you get 30% yield in the second step since you have 3,000 mg / 10,000 mg of the original protein amount. The definition of yield in my notes mentions nothing of activity.


texts: Hydrogen peroxide and carbon as hybrid rocket propellant?

texts:
I was thinking that a hybrid rocket could be made using hydrogen peroxide and activated charcoal or some other carbon source.

Step 1: Decompose hydrogen peroxide to steam and oxygen, as in a monopropellant H₂O₂ rocket. This step is exothermic.

2H₂O₂ → 2H₂O + O₂

Step 2: Have the superheated steam flow over the finely divided carbon, which is the "water gas" reaction and is endothermic:

H₂O + C → H₂ + CO

Step 3: The oxygen produced by the hydrogen peroxide incompletely burns the water gas, which should be exothermic.

2H₂ + 2CO + O₂ → x(H₂O + CO) + y(H₂ + CO₂), where x + y = 2

Total reaction: 2H₂O₂ + 2C → x(H₂O + CO) + y(H₂ + CO₂). This is certainly exothermic in total, and also favored entropically.

Depending on the kinetics, either reaction x or reaction y would dominate; I'm hoping y will, as having lots of diatomic hydrogen would be good for specific impulse.

According to the article on water gas, the carbon bed has to be heated red-hot. I'm hoping that having the steam be hot and the carbon be porous would be sufficient. I'm also wondering if the oxygen would react right there in the chamber, or if it'd flow out the back and need to be ignited. Small amounts of catalysts might be mixed in with the carbon as well. You might even be able to just coat the carbon with silver catalyst so the decomposition of hydrogen peroxide heats the coal bed, but replacing the catalyst every time would probably be expensive.

The primary advantage of such a rocket would be that the oxidizer is relatively nontoxic and nonreactive; the fuel is safe enough you could eat it like a biscuit; any fire caused by an oxidizer tank leak or rupture could be far more easily contained; and design of the rocket should be fairly simple, involving just placing a fuel biscuit in the exhaust of a H₂O₂ monoprop rocket; this could theoretically supercharge the peroxide-using USAF Astronaut Maneuvering Unit.

Has this idea been tried before by serious rocketers? What are the numbers (enthalpy, Gibbs free energy, calculated specific impulse, and so on)? How can I make sure the carbon biscuit is porous enough that it reacts easily and completely with the steam and oxygen, yet not so porous that it just gets shredded and blasted through the exhaust by the pressure?


texts: Is there a connection between UV-degradation and the photoelectric effect

texts:
Recently I've been learning about the photoelectric effect in my physics classes.

I only have a rudimentary understanding of chemistry, but I've been wondering what the connection is between the photoelectric effect and UV degredation.

For the sake of simplicity let's focus on the degredation of polypropylene.

My hypothesis is, that the UV light frees some electrons from the material. These will either weaken or break the bond between two molecules or atoms in the molecule itself.
I would ultimately except the molecule chains to be broken into smaller pieces due to this.

Is that a reasonable assumption or does the process work completely different?


texts: What is a quick and easy way to find an alternative axis of symmetry?

texts: According to a question in my book (1R,3R)-1,3-dichloro-2,2-bis[(S)-chloro(2H1)methyl](1,3-2H2)propane has an S4 alternative axis symmetry. I tried trial-and-error method using an axis that passes through only the top group straight down, one that is a horizontal line across the screen and some others but couldn't find it. How exactly do I do this?And also this is a JEE practice question and I need to do it in at the most a minute or two.


texts: Wedge Dash Diagram of 1,2-Dichloroethane

texts: I'm in class right now and my teacher put this up on the board as a representation of 1,2-dichloroethane. He also projected a model. I'm thinking ... his board drawing is wrong. Shouldn't the chlorines also be on dashes too? There's no way the chlorines can be in the same plane as the carbon atoms; the model makes it too obvious.


texts:
In potentiometric titration between ascorbic acid and iodine, when we plot the graph of EMF with volume of iodine consumed, we get a sudden decrease in EMF at equivalance point--why? It is also negative--why?

Using Nernst equation at equivalence point we get
$$E_{cell}=E_{STP}~~~(voltage ~at ~STP)$$

What is its physical meaning?


texts: Difference between chiral and stereogenic centre?

texts:
I've seen in some books where they state all chiral centres are stereogenic centres, but not the other way around.

Is "chiral centre" related to only to optical isomerism and "stereogenic centre" related to stereoisomer in a broader sense?


texts: Radiationless energy transfer: how to arrive at the equation that give R0 between two chromophores?

texts:
I have a homework question where I should calculate  $R_0$ of an energy transfer between two chromophores. However, I don't understand how my professor arrived at the equation that we should apply (which is important to understand for the exam).

  In a radiationless energy transfer experiment (RET) it was observed that the efficiency of transfer was $0.0185$ at $\pu{5 nm}$ distance between the two chromophores. Estimate $R_0$ for the two chromophores, assuming the energy transfer efficiency is $0.7$ at short distances.

In our lecture we are given the formula:
$$[E_\mathrm{eff}] = \frac{R_0^6}{r^6 + R_0^6}$$

I understand that $E_\mathrm{eff}$ is the efficiency of the transfer, and $r$ is the non-variable distance between the two chromophores. However, I am not able to solve for $R_0$. I tried to ask my professor but he thinks faster than I do and skips steps. So I was not able to follow completely, but he somehow mathematically solved the equation to (where $Eff_\mathrm{max}$ is maximum efficiency of energy transfer):
$$r = R_0 \sqrt[6]{\frac{E_\mathrm{eff}}{E_\mathrm{eff,max}}}$$

When I apply his formula I "plug in" the given numbers and solve for $R_0$ as following:
\begin{align}
R_0 &= \frac{r}{\sqrt[6]{\frac{E_\mathrm{eff}}{E_\mathrm{eff,max}}}}\\
R_0 &= \frac{\pu{5 nm}}{\sqrt[6]{\frac{0.0185}{1}}}\\
R_0 &= \pu{9.72 nm}
\end{align}

I would like to understand how he arrived at the final formula that I apply. Is it correct to solve for $R_0$ like I have shown above?


texts: What happens if I increase the amount of water on water based epoxies?

texts:
I am using a water based epoxy coating that is composed of a resin and a hardener. There is a specific amount of proportion to use to obtain the optimum cured coating. But I am trying to introduce some dry pigments into the resin then I add the hardener. However adding the pigment increases the viscosity of the mixture and the obtained coating is thicker.

Since I cannot increase the amount of resin or hardener without influencing the optimum condition, I was thinking since it is a water based coating, I could still have the same amount of functional reacting groups and just increase the amount of water in the resin to make the mixing of pigment with the resin easier ?!

But I am afraid during the drying process, the evaporation of the extra added water might influence my coating !

Do you know what could happen in this case ?


texts: Required temperature for the reduction of iron oxide using carbon

texts: When reducing iron oxide with carbon, must the substances be set alight or do they only need to be heated. Also, when the iron is formed will it immediately oxidise in the air?


texts:
I was trying to do an investigation on the variation of caffeine content with temperature. I used 6 Lipton yellow label tea bags (black tea) to brew the tea solution.
Next, I perform the extraction of caffeine using standard procedures (separate by dichloromethane and evaporate). I was able to extract ~80mg of caffeine in 70-degree celsius water. I redissolve the powder into water to a 100 mL volumetric flask. I then pipette 25mL of the caffeine and added excess $\ce{I2}$ and $\ce{H2SO4}$. The chemical equation is given by:

$$\ce{C8H10N4O2 + 2 I2 + KI + H2SO4 → C8H10N4O2 .HI .I4 + KHSO4~~~(1)}$$

$$\ce{I2 + 2 Na2S2O3 → 2NaI + Na2S4O6 ~~~(2)}$$

Yet, I was unable to get any precipitation. I carried on with the titration and found that some Iodine did react in the (1). In fact, I did get a value of caffeine close to my theoretic result. So why didn't I get any precipitation?


texts: Unusual hydrolysis of methyl 2,4,6‐trimethylbenzoate

texts:
Problem 223 from Conceptual Problems in Organic Chemsitry by Singh [1, p. 367]:

The given answer is b and I don't get why.
Usual ester hydrolysis would've given a.
I somehow managed to know that the mechanism is SN2, but why?
Also, if someone could provide the reaction mechanism, it would be wonderful.
Reference

Singh, D. K. Conceptual Problems in Organic Chemistry: For Engineering and Medical Entrance Examinations, 3rd ed.; Pearson India, 2013. ISBN 978-93-325-8207-1.


texts:
While discussing magma in class with my students, I showed a video of a man throwing water onto molten, running lava.  A large flame ensued.  I realize that the water is being converted into steam and expanding extremely rapidly, but why does this create a small "explosion," if you will?

Surely none of the lava is being "atomized" into the air in small droplets, is it?  But even so, they would not light aflame.


texts: What chemicals would make lime sulfur dip to produce a green colored smoke?

texts: I work at an animal shelter that uses lime sulfur dip to treat ringworm. We had an accident where someone mixed bleach instead of water with the lime sulfur dip which caused us to go through decontamination with Hazmat. Are there any other chemicals or acids that could cause this to happen?


texts: 1,4-addition vs 1,2-addition aldol/aldol type reactions

texts:
In the aldol/cross aldol reaction, of $α,β$-unsaturated carbonyl compound, under what circumstances does a 1,2-addition i.e. aldol condensation (carbanion formed directly attacking carbon of carbonyl group) and 1,4-addition i.e. Michael condensation (carbanion formed attacking $β$ carbon)?

These are the following points I considered:

Stability of resulting product.
The amount of conjugation in the compound. What I feel, extended conjugation ($γ,δ$-unsaturated double bond as well) would always lead to 1,4-addition.
The group attached to the $β$ carbon. For example, an electronic withdrawing group would increase the probability of 1,4-addition and an electronic donating group would reduce the probability, favoring a 1,2-addition.
The steric crowding around the carbonyl or the unsaturated carbon system.

Are these arguments valid?

I have added a few examples (I have just written the final product and not the mechanism as my question lies in the very step after generating carbanion). In examples 1, 2, and 4, aldol condensation (1,2) has taken place but in example 3, Michael condensation (1,4) has taken place.

Is there a way we can account for this?


texts: Find the pH of a sodium chloride solution using the extended Debye-Huckel equation

texts:
Question
  Use activities to calculate the pH of each of the following solutions, being sure to use $\mathrm{\alpha}$ values and the extended Debye-Huckel equation.

  The first one the concentration is $0.020 \mathrm{M}$ $\ce{NaCl}$
  with the answer being : $\mathrm{pH}$ = $6.99$

  The second one the concentration is $0.10 \mathrm{M}$ $\ce{NaCl}$
  with the answer being : $\mathrm{pH}$ = $6.98$

The thing is i have no idea how to find the activity coefficient of $[\ce{H}^+]$

I know ionic strength $u$ is calculated as
$\mathrm{\frac{1}{2}\left(\sum C_iZ_i^2\right)}$

but how does $[\ce{H+}]$ work into the charge balance?

I also know that the activity coefficient is calculated as

$$\log\gamma=\frac{-0.51(z^2)(\sqrt{u})}{1+(\alpha(\frac{\sqrt{u}}{305})}$$

The best I have is:
$$\ce{Na+ + Cl- + H+ + OH-}$$

and that raises the question of how do I know what $[\ce{H+}]$ is and $[\ce{OH-}]$ for calculating the ionic strength? Am I approaching this wrong? Where do I start?


texts:
Is the order of a complex reaction determined by the slowest step always? Is it so that order of a reaction is determined by rate determining step and since in a complex mechanism, we write elementary steps hence the order should be the molecularity of the rds?

I am slightly confused in this since I saw that in E1CB the molecularity of the rds is 1 but the order of E1CB is 2.

Basically I know order is determined experimentally but for elementary reactions, don't we write order as the sum of stoichiometric coefficients (here I am assuming that it is not a pseudo order reaction and no products are there in the rate expression.)


texts:
In amateur perfumery, raw chemicals are usually stored in sealed bottles in refrigerators/freezers to reduce decomposition rates. However, aldehydes are tricky to store for long periods of time because they tend to be reactive. The two biggest decomposition routes are oxidation (which can be prevented by having a good seal on containers) and oligo/polymerization.

Folk knowledge (1, Pell Wall Perfume blog and 2, Perfumery and Flavoring Synthetics by Bedoukian page 24) claims aldehydes polymerize more quickly in the cold, and so unlike most chemicals, perfumers are warned to store aldehydes at room temperature, rather than frozen.

Why do aldehydes polymerize faster in the cold?

From thermodynamics, it makes sense polymerization occurs to greater completion in the cold, since polymerization is usually exothermic, so Le Châtelier's implies the cold will drive the reaction to the right. Likewise, since polymerization has $\Delta S <0$, cooling below the polymer ceiling temperature $T_c=\Delta H/\Delta S$ causes polymerization to be spontaneously possible.

However, I can't find any mechanistic explanation of why the rate increases in the cold, or even any other sources besides an online blog and a perfumery textbook which back up this claim. Can any polymer fans explain why cold is bad for aldehydes?


texts: Magnesium powder + sodium carbonate solution: what happens?

texts:
I put magnesium powder into a sodium carbonate solution and it fizzed very slowly. The gas produced put out a lit splint immediately, which implies that carbon dioxide was released, but I cannot work out the equation for this reaction.

I'm fine with an acid plus a carbonate or a metal salt displacing another but this was just metal powder plus a carbonate.


texts: Why is F2 (fluorine) colourful despite being diamagnetic?

texts:
According to Molecular Orbital Theory, $\ce{F2}$ must be diamagnetic, then why is it colourful?

Also, $\ce{O2}$ is paramagnetic but it is colourless in gas phase. Why?


texts: Is the compressibility factor smaller or greater than 1 at low temperature and high pressure?

texts:
The compressibility factor of a gas is defined as $Z = pV/(nRT)$. If attractive intermolecular forces dominate then $Z$ tends to be smaller than 1, and vice versa if repulsive forces dominate.

In the case where temperature is low, attractive forces increase due to less kinetic energy, but at the same time repulsive forces also increase due to high pressure. How can I determine which force will dominate?


texts: How do I know the valence number by looking at the groups?

texts:
Groups say the valence number. For example Hydrogen is on group 1, has 1 electron on it's last and only level. So we can know the valence number on that are on the groups 1-2 and 13-18. But how am I supposed to know the valence number on transition metals(3-12)?

PD: You could tell me to use the oxidation number but that is completely wrong since they are not the same.


texts: Which of the following is a secondary alkyl halide

texts:
a $\ce{(CH3)2CHCH2CCl(CH3)2}$

b $\ce{(CH3)2CHCHClCH3}$

c $\ce{(CH3)2CClCH3}$

d $\ce{(CH3)2CHCH2Cl}$

This is just to check that I'm understanding the material correctly.

I'm thinking it's c because when drawing the line structure the alpha carbon is connected to two other carbons.


texts: What is the difference between a desiccant and a deliquescent?

texts:
I understand that both a desiccating solid and a deliquescent solid are "hygroscopic" in the sense that they bind to water.

But what is the difference? And what are the applications of a desiccant vs a deliquescent?


texts: What exactly is a potential energy surface?

texts:
I first learned about potential energy surface (PES) when I was studying Born-Oppenheimer approximation. In the approximation, the PES is essentially electronic PES which is defined as follows:

Given the Hamiltonian of a molecule
$$\hat H = \hat T_{\text{nucleus}} + \hat T_{\text{electrons}}+\hat U_{\text{electron-nucleus}}+\hat U_{\text{electron-electron}}+\hat U_{\text{nucleus-nucleus}}$$
Under Born-Oppenheimer approximation, $\hat T_{\text{nucleus}} = 0$. So the equation about to be solved is:
$$(\hat T_{\text{electrons}}+\hat U_{\text{electron-nucleus}}+\hat U_{\text{electron-electron}}+\hat U_{\text{nucleus-nucleus}}) \psi_{\text{electron}} = E(\{ R_{\text{nucleus}}\}) \psi_{\text{electron}}$$
Clearly, $E(\{ R_{\text{nucleus}}\})$ gives a PES, and this PES is the relation:
$$\{ R_{\text{nucleus}} \} \rightarrow E_{\text{ground state electronic energy}}$$

However, when I learned about molecular dynamics (also in wikipedia), a PES is defined to be the relation
$$\{ R_{\text{nucleus}} \} \rightarrow E_{\text{energy of the system}}$$
How do we find this map in practice? The only way I can think of is:

We solve the electronic eigenequation for several $\{ R_{\text{nucleus}} \}$.
For each calculated $E(R_{\text{nucleus}})$ of electrons, we solve the equation
$$(\hat T_{\text{nucleus}} + E(R_{\text{nucleus}})) \phi_{\text{nucleus}} = E_{\text{nucleus}}\phi_{\text{nucleus}}$$
to find the energy of the nucleus. (I have never learned how to solve an eigenequation of a nucleus in quantum chemistry)

Is this the way that we find the 'generalized' PES? When we say PES, which is the PES that we are referring to?


texts: Delta G in an equilbrium reaction(forward and backward)

texts:
Consider a reaction say

$$\ce{A + B <=> C + D}$$

Now $\Delta G$ for the forward reaction is:
$$\Delta H - T\Delta S$$
For the backward reaction $\Delta H$ and $\Delta S$ are clearly the same in magnitude but opposite in sign. Therefore,

$$ \Delta G_\text{forward} =-\Delta G_\text{backward}$$
Which implies that if the forward reaction is feasible then the backward isn’t or vice versa.

But both the reactions occur simultaneously in an equilibrium reaction.
Can anyone please help me sort this discrepancy?


texts: Can a tertiary enamine tautomerize to an imine?

texts:
Which of the following compounds does not show tautomerism?

The correct answer is (a), and I'm curious if this is because to show tautomerism, there can't be any net charge.

For instance, ketones can tautomerize to enols, and more importantly, enamines can tautomerize to imines.  In (a), we would get an imine-like thing, but the nitrogen would be positively charged.  Does this still count as tautomerization?

EDIT: Thank you everyone for your helpful clarifications, but I'm still a bit confused as to why, mechanistically, we need a hydrogen on the nitrogen.

When I Google the mechanism for imine tautomerization, what if find is this:

Where the nitrogen lone pair pushes down and the double bond reaches out to pick up a proton.  There isn't a transfer of hydrogen from the nitrogen to the solvent in the case shown below, yet the molecule still tautomerizes.


texts: Why hydrofluoric acid (HF) has two Raman bands?

texts:
Hydrofluoric acid ($\ce{HF}$) is a diatomic molecule with only one vibrational coordinate. Therefore I would expect only one Raman band, however there are two. Why?

(source)


texts: Why don’t we have a list of all compounds yet?

texts: With only three basic particles making up atoms, and their interaction fairly well understood (we can even predict the chemical properties of elements we have not yet discovered) atoms seem to be like Lego bricks: only fitting together in a limited number of ways. So how come, in the age of super computers, we have not yet invented a program that can predict every single possible chemical compound (lets start modestly: of around fifty atoms or less)? Would a “super version” of such a computer program- one that would create a “master list” of all possible compounds and their reactions - theoretically make the field of experimental chemistry obsolete? I realize the vast number of possibilities, but just as with a chess game, the number of actual possible boards is far less than the theoretical number of all possible chess pieces and positions. Many simple compounds could be ruled out as “impossible” and a dead end, thereby considerably shortening the list of possible compounds. Am I missing something obvious here?


texts: Can aluminium hydroxide be split into Al 3+ and OH-?

texts: When writing a net ionic equation containing aluminum hydroxide, can the aluminum hydroxide be split into ions of $\ce{Al^3+}$ and $\ce{OH-}$, or does it stay as $\ce{Al(OH)3}$?


texts: Delocalised electrons and stability of benzene

texts: In most high school chemistry books, it is said that the delocalised electrons in benzene makes it particularly stable. However, how does it contribute to stability? Is there any simple way of understanding this?


texts: Can redox reactions involve only non metals?

texts: When non metal react they form molecule, and whether the bond is polar or not, the elements in the molecular compound will not have charges what so ever, because they are not ionic. But can non metals be the only that is involved Ina redox reaction ?


texts: Conversion process of lanolin to 7-Dehydrocholestrol

texts:
What is the Chemical process to convert lanolin to 7-Dehydrocholestrol?
I don't know about the chemcial reaction, if I get the process I can try in lab scale.


texts: Any open-source to animate 2D materials in 3D. (e.g. van der Waals heterostructures, 2D crystal layers etc.)

texts: I want to model different 2D nano-structures, layered materials in 3D (animated version). Is there any open source where I can build these structures. Like this:


texts: How to account for solvation of a molecule explicitly in quantum calculation?

texts:
I'm looking for a way to account for hydrogen bonds formed with my molecule in aqueous solution explicitly in DFT calculation. I'll do it in order to compare stability of two structures in water. As far as I understand, it can be done by molecular dynamics calculation of the structure surrounded by molecules of water or by multiple random choice of H2O molecules around the structure with subsequent optimization.

Any suggestions, references to articles or programs are appreciated.


texts: Reaction of grignard with beta Keto ester

texts: A reaction takes place between $\ce {CH3COCH2COOC2H5}$ with 4-chlorophenyl magnesium bromide, followed by acidic work-up. What will be major product of the reaction? Would the product be the same as the original $\beta$-keto ester due to the active methylene group, at which the acidic doubly-$\alpha$ $\ce {H}$ gets deprotonated?


texts:
My chemical bonding professor says that the $\ce{O-S-O}$ bond angles in $\ce{SO4^2-}$ are ideal (109.5°).

Why? Is this because all bonds are equivalent, and electron distribution is shared among all oxygens?


texts: I have been looking for a paper that by using spectrophotometry method, we can determine rate of reaction of colourant. I could not find any paper. I was wondering if any body could help me.


texts: Is it possible to generate electricity by using two inert electrodes in a galvanic cell?

texts: The Daniell cell has two active electrodes, meaning that both the copper and the zink electrodes participate in the redox reaction. However, in a lemon battery for example, the copper electrode is inert - it doesn't participate in the redox reaction. When is it possible to only have one active electrode? Is it possible to generate electricity by using two inert electrodes?


texts: finding cation of unknown salt in solution from precipitate

texts:
I should probably add that I was originally given an unknown solid mixture of 2 salts. I separated the insoluble salt out by centrifuging and then decanting. I found that the insoluble salt is $\ce{MgCO_3}$ by adding $\ce{HCl}$ (bubbles) and $\ce{NaOH}$ into the solution (jelly like white ppt). The decanted liquid was then what I observed as having 1 soluble salt. The soluble salt I know by testing for $\ce{SO4^{2-}}$ with $\ce{BaCl_2}$ and observing a violet flame in a flame test. Then I had a second bottle with 3 unknown, 2 of which I discovered above. I know that the 3rd one has 2 soluble and then my original question follows.

I have 2 soluble salts in aqueous distilled water solution. I know that one of the salts is potassium sulfate ($\ce{K_2SO_4}$) and I know that the anion of the second salt is chloride ($\ce{Cl^{-}}$). I know that the second salt is either magnesium, sodium, calcium or potassium chloride ($\ce{MgCl_2}$, $\ce{NaCl}$, $\ce{CaCl_2}$, or $\ce{KCl}$).

I tested for the anion for the second salt by adding silver nitrate ($\ce{AgNO_3}$) into the solution and observing a white precipitate. When I added sodium hydroxide ($\ce{NaOH}$) to it, I observed that the cloudy white precipitate disappeared and turned into small black precipitate which then settled to the bottom of the tube. Is there any way to get the cation of the second salt with this information, and are there any other test(s) I can do to find what is the cation for the second salt?


texts: Convention in electrochemical cell notation

texts:
While writing the cell notation for a cell, doesn't one have to write the two states in which a species exists in a sequence appropriate to the reaction in which they participate?
For example, in the Daniell cell reaction, shouldn't it always be written $\ce{Zn}|\ce{Zn^2+}$, and never, $\ce{Zn^2+}|\ce{Zn}$?
I didn't see anything in the definitions, and I saw a question asking for the cell reactions for this;
$$\ce{Pt,Cl2}|\ce{Cl^-(aq)}||\ce{Ag^+(aq)}|\ce{Ag}$$
Obviouly, chlorine doesn't react in that direction, but gets oxidised.


texts: Intuitive explanation for depression of freezing point

texts:
Why does depression of freezing point takes place if a non-volatile solute is added to the solution?

For more details about the question checkout this link below

Depression of freezing point


texts: How does hydrogen bonding affect the boiling points of chemical compounds?

texts:
My main question is why is the boiling point of methanol so much different from that of water?

I understand that both compound are able to develop hydrogen bonding, and obviously water can develop one more hydrogen bond than methanol.

But on the other hand:

  Due to presence of an electron-releasing alkyl group, the oxygen atom of an alcohol molecule is less-electron withdrawing on the remaining hydrogen atom. Therefore the electron deficiency of the hydrogen atom is less than that of a water molecule resulting in the formation of a weaker hydrogen bond.

What does this actually mean?

Both hydrogen, in methanol and water, are connected to oxygen, which has the same electronegativity and takes electrons off the hydrogen making it have a partial positive charge.

Why does a "less electron withdrawing oxygen atom" lead to a weaker hydrogen bond?

I thought that a less electron withdrawing oxygen atom would mean that the H is more negatively charged, meaning it would be stronger for hydrogen bonding, since F, O, N want more electrons as they are more electronegative?


texts: Why thermal decomposition of iron(II) nitrate and sodium nitrate yields different products?

texts:
\begin{align}
\ce{4Fe(NO3)2 &-> 2Fe2O3 + 8NO2 + O2}\tag{1} \\
\ce{2NaNO3 &-> 2NaNO2 + O2}\tag{2}
\end{align}

Why do nitrates of different metals decompose in different ways?

Why do we get a nitrite with sodium, but an oxide with iron(II)?


texts:
Consider the differential $$\mathrm dp=\frac RV\,\mathrm dT+\left(\frac{2a}{V^2}-\frac{RT}{V^2}\right)\,\mathrm dV$$ (where $a$ is a constant value)
(a) Determine whether the above differential, i.e. $\mathrm dp$, is exact or not. Show all your steps and evaluation of the appropriate partial differentials!

I have no idea on how to even start this. As far as I can tell the differential is exact, but I don't know how to prove or show it. I'm really struggling to show the steps involved. I would appreciate any advice and thank you very much in advance.


texts: crystalline structure of Si wafers used for MEMS

texts: When they say that we have a {1 0 0} single crystal wafer, I know that the surface normal to the wafer is oriented in the <1 0 0> family direction, but if I draw a line on the wafer, parallel to my primary flat, does it indicate a crystallographic direction family too? Like <1 0 0> or <1 0 1>. I mean it's obvious that it cannot be <1 1 1> due to the FCC lattice of Si(I am making the assumption that the thin plane of the primary flat is at exact right angles to the wafer surface, if that angle is allowed to be 54 degrees, it can also be a <1 1 1> ), but it can surely be directed at none of the crystallographic directions at all, so the question is, if I draw a line on the wafer surface parallel to the primary flat, will it be directed towards the <1 0 0> or the <1 0 1> family, or does the manufacturing process just slice an arbitrary flat out of the Si ingot before slicing it into wafers?


texts: Why does 1,2-dimethylcyclohexane only possess three stereoisomers?

texts:
Why does 1,2-dimethylcyclohexane in chair form have only three stereoisomers?

I understand that the trans isomer doesn't possess plane of symmetry and thus it has two stereoisomers. But my book says that the cis isomer has does not have two  stereoisomers. Why is this so?

The structure of cis-1,2-dimethylcyclohexane is shown above. Its mirror image is non-superimposable and cannot be obtained by rotation about single single bonds or by a ring flip. Can anyone explain?Thanks


texts: What explains the stark white colour of my iodometric titration analyte solution?

texts:
During my Advanced Higher (secondary school) investigation, I reacted pure copper with concentrated nitric acid to acquire a copper nitrate solution. This was neutralised with excess sodium carbonate and brought back to a clear solution with ethanoic acid.

I then reacted the solution with potassium iodide in a conical flask before titrating it with sodium thiosulfate.:

$\ce{2Cu^2+(aq) + 4I^-(aq) → 2CuI(s) + I_2(aq)}$

$\ce{I_2(aq) + I^-(aq) ⇌ I_3^-(aq)}$

$\ce{I_3^-(aq) + 2S_2O_3^2-(aq) → S_4O_6^2-(aq) + 3I^-(aq)}$

This analyte solution was at first brown, but when titrated it turned a pale coffee colour. When starch was added just before the end point, it turned a dark grey-brown colour, as expected - the iodine forming a complex with starch. https://en.wikipedia.org/wiki/Iodine_test

But when all of the iodine had reacted with the sodium thiosulfate, I was left with a stark white solution. I tested to make sure no iodine was left over by adding in another drop of starch - no reaction. So, this seems to be the endpoint.

Copper iodide seems the likely explanation, but the wikipedia page shows that it is mostly insoluble in water. It is soluble in iodine solutions but all the iodine is gone, presumably.

Does it take time for the copper iodide to precipitate? I quickly rinsed out the conical flask. There was some white staining on the sides which I think is copper iodide.


texts: Why does cotton dissolve in a dilute solution (1/2) of fuming sulfuric and nitric acids?

texts:
A nitration experiment carried out showed that a solution of half diluted sulfuric and nitric acids would turn the submerged cottons into a gooey substance. The remnants of the cotton balls did not flash as nitrocellulose would have.

On the other hand, cotton balls submerged in a mixture of fuming nitric acid and fuming sulfuric acid remained intact and were nitrated, producing nitrocellulose.

What I'm really curious and confused about is how the dilution not only interferes with the nitration itself, but also affects its dissolution.

Any guidance is appreciated.


texts: Configuration change at chiral carbon in SN2 reaction

texts:
Consider $\ce{A}=\ce{CH(CH3)(C2H5)(C3H7)}$ in R configuration. Suppose somehow in a $\mathrm{S_N2}$ reaction, $\ce{Br-}$ attacks and replaces $\ce{-H}$ (this compound we call $\ce{C}$). Now we expect change of configuration (Walden inversion), i.e. it to become S. If the structure was inverted without replacing $\ce{-H}$, we would have got the S-stereoisomer of $\ce{A}$, call this $\ce{B}$. Replace the $\ce{-H}$ in $\ce{B}$ with $\ce{Br}$, we obviously get $\ce{C}$. Now since $\ce{H}<\ce{C}<\ce{Br}$ in the Cahn-Ingold-Prelog rules, $\ce{C}$ is R. But $\ce{C}$ should have been S.

Where is my logic wrong?

EDIT: As noted by A.K. below, there is no problem in this case, and $\ce{C}$ is in-fact S. But everything depends on the atomic number of $\ce{Br}$. Is there a general proof of correctness for the scheme?


texts: Why is fabrication of ordered graphite substrates difficult?

texts:
While reading this paper (suggested by @Janice here), I came across the following line:

  Surface reconstruction is known to be extremely important for Si, the material of  20th century electronics. However, surface reconstruction has been much less studied for graphite. One of the reasons might be graphite's limited use in electronics because fabrication of ordered graphite substrates is difficult.

(emphasis mine)

I've always believed that graphite isn't much used in semiconductor tech since it isn't a metalloid and conducts in an entirely different manner, probably making doping not work. This reason is new to me, but quite interesting.

I can sort of guess why "fabrication of ordered graphite substrates is difficult" — I'm not too sure though.

At any rate, I'd like to know more about it. Exactly why is such fabrication difficult?


texts: Mechanism for Ce(IV) Oxidation of Naphthalene

texts:
S. Cotton's Lanthanide and Actinide Chemistry reports that naphthalene can be oxidized to naphthalene-1,4-dione using cerric ammonium sulfate (CAS), $\ce{MeCN, H2SO4},$ and $\ce{H2O}$.1 No mechanism was provided, and I was unable to find a complete mechanism for this transformation in the literature. From what I did find, Love et al.2 have reported the first step of this mechanism is the formation of the radical cation while the second step is the attack of a water molecule. After these two steps, the authors of the paper do not give any further information. I proposed a mechanism below, but I have a few concerns. To start, why is sulfuric acid used when protons seem to be lost during the transformation? I assume this is to prevent the cerium from reacting with the water to form hydroxides as it can be quite basic, but it is nonetheless unsettling.

References:
1Simon Cotton, In Lanthanide and Actinide Chemistry;  Inorganic Chemistry, A Wiley Textbook Series, John Wiley & Sons, Ltd: Chichester, England, 2006 (ISBN-13: 978-0-470-01005-1).
2Brian E. Love, Alexander L. Simmons, "Substituent Effects in the Oxidation of 2-Alkyl-1,4-dialkoxybenzenes with Ceric Ammonium Nitrate," Tetrahedron Lett. 2016, 57(50), 5712-5715 (DOI: https://doi.org/10.1016/j.tetlet.2016.11.042).


texts: Whilst the Bohr model is incomplete and incorrect, it had limited usage in predicting spectral lines. In the same way, could it possibly with limited accuracy, be used to predict the outcome of chemical interactions to within "an order of magnitude" for which it was so famously known to do for many physical phenomena?


texts: Major product monochlorination of 2-methylpropane

texts:
What is the major product of monochlorination of 2-methylpropane and for 2-methylbutane?

My attempt: as in 3 degree position, monochlorination is favoured (due to free radical formation), so according to me, it should be 2-chloro-2-methylpropane and same as in other 2-chloro-2-methylbutane.

But, it is stated to be incorrect. The correct answer is 1-chloro-2-methylbutane. Why's that the correct answer instead?


texts: Heaviest atom with which chemistry has been performed?

texts:
The nucleosynthesis of superheavy atoms such as transactinides is an exciting area of nuclear physics, but not much of a playground for chemistry because

My question is: what is the heaviest atom ever used in chemistry? For this I define chemistry as “making a compound with the atom (molecule or material) and characterizing it to some extent”.

The one source I found on the topic is “Critical evaluation of the chemical properties of the transactinide elements (IUPAC Technical Report)”, dated 2003, but it seems quite old for such a rapidly developing field. Also, despite being title “chemical properties” it mostly reports on physical properties.


texts: What are some incapabilities that the early spectroscopy have when compared to the more modern method?

texts: What are some incapabilities that the earlier spectroscopy (Visible, Ultraviolet and Infra-red) have when compared to the more modern method?


texts: How to recognise the significant figures in given input values for the calculated output value?

texts: If the transfer of $1~\mathrm{kJ}$ of energy to a quantity of water causes its temperature to rise $10~^\circ\mathrm{C}$, what is the mass of the water?  I know how to do the math and everything but I'm so confused with significant figures. If $1~\mathrm{kJ}$ or $100~\mathrm{J}$ only has 1 significant figure, then would I write $\pu{23.90 g}$ as $\pu{20 g}$?


texts:
The Law of mass action has 2 parts - the equilibrium rate part & the reaction rate part.
The "reaction rate part" states that rate of a reaction is directly proportional to the product of active masses of the reactants with each reactant term raised to it's stoichiometric coefficient. The rate law states that rate of a reaction is directly proportional to the product of active masses of the reactants with each  reactant term raised to some power which may or may not be equal to stoichiometric coefficient of the reactant.

Why are the two laws different when in fact we are talking about the powers to which active masses of reactants should be raised in both the cases ? And which law is correct?


texts: p-nitrophenol and sodium bicarbonate test

texts:
I was doing an experiment in lab and found that about one-third of p-nitrophenol dissolved in $\ce{NaHCO3}$ solution with liberation of $\ce{CO2}$ in small amount. This is contradictory to what most textbooks say. I was surprised as p-nitrophenol is less acidic than carbonic acid yet it gave positive $\ce{NaHCO3}$ test.

Can anyone give any possible explanation? I thought that one reason maybe that since their $\mathrm{pK}_\mathrm a$ differ by about $1$, the reaction maybe in equilibrium to a significant extent, but this kind of thing isn't mentioned anywhere.


texts: Is there a mnemonic to study the spectrochemical series?

texts:
Mnemonics help to by-heart things which are difficult to do so and which are important. I found mnemonics for studying the periodic table, electromagnetic series etc which were of great help. So, is there a mnemonic to study the spectrochemical series since knowing it will be of great help to find the geometry of a given co-ordination compound?

The spectrochemical series is a list of common ligands for transition metals in order of increasing ligand-field splitting parameter $\Delta$, which is the energy difference between the sets of $\ce{d}$ orbitals:

$$\ce{I-} < \ce{Br-} < \ce{S^2-} < \ce{SCN-} < \ce{Cl-} < \ce{NO3-} < \ce{N3-} < \ce{F-} < \ce{OH-} < \ce{H2O} \approx \ce{C2O4^2-} \text{ (oxalate)} < \ce{NCS-} < \ce{CH3CN} < \ce{py}\text{ (pyridine)} < \ce{NH3} < \ce{en}\text{ (ethylenediamine)} < \ce{bpy}\text{ (2,2'-bipydiridyl)} < \ce{phen}\text{ (1,10-phenanthroline)} < \ce{NO2-} < \ce{PPh3} < \ce{CN-} \approx \ce{CO}$$

  Is there a mnemonic device for remembering this series?


texts: Is a sequence of two Wagner-Meerwein rearrangements possible?

texts:
We've just studied about the Wagner-Meerwein rearrangement in carbocations.
Our teacher told us that it occurs in order to stabilize the carbocation intermediate.

Knowing the carbocation stability order,

  $\mathrm{Tertiary > Secondary > Primary} > \ce{CH3+}$

I decided to test the "limits" of this particular rearrangement reaction.

I drew a primary carbocation (A):

Upon subjecting it to a Wagner-Meerwein hydrogen-shift (in my head), I obtained the secondary carbocation (B):

Which was all fine and dandy; well within what I've been taught.

But seeing the potential for additional stability another Wagner-Meerwein rearrangement could provide, I conducted a Wagner-Meerwein alky(methyl)-shift and ended up with the following tertiary carbocation (C):

I started with a primary carbocation, changed it to a secondary carbocation and finally ended up with a tertiary carbocation.

Now I showed this to my teacher, but he said that in this particular case the carbocation (B) won't convert to carbocation (C); i.e- carbocation (A) isn't going to undergo two Wagner-Meerwein rearrangements (1,2-anionotropic shifts), because in effect it'd be a 1,3-shift and not the 1,2-shift as the Wagner-Meerwein rearrangement calls for.

A few days later, I took a different sheet with carbocations (B) drawn on it and carried out a Wagner Meerwein alkyl(methyl)-shift to obtain carbocation (C) just as before [except that this time around, my starting molecule was B not A]. I showed this to my teacher again, but the rearrangement I carried out in this case doesn't seem to perturb him at all. His argument is that, since my starting intermediate is carbocation (B), to reach carbocation (C), it undergoes only one Wagner-Meerwein rearrangement which is perfectly fine, unlike my first case which involved two rearrangements.

Now my question is, if he's right, then how would carbocation (B) "know" whether it already underwent a Wagner-Meerwein rearrangement [from carbocation (A)] before considering rearranging itself to become the more stable, carbocation (C)? How does it "know" if it's the starting intermediate or not.


texts: Why are isotopes of hydrogen the only ones with special names?

texts: Why does no other element but hydrogen get special names for its isotopes?


texts: How can organocuprates generated with catalytic Cu(I) be competitive in 1,4-addition to an enone?

texts:
Organocopper compounds (e.g. $\ce{LiCuR_2}$) are often prepared from an organolithium or Grignard reagent when a soften nucleophile is needed, such as for a conjugate addition to an $\alpha,\beta$-unsaturated carbonyl. Clayden et al. (p.499) recommend generating it in situ catalytically via transmetallation with 1% $\ce{CuI}$.

My question: if at the start, there is 1% of organocopper reagent and 99% Grignard reagent, why don't those 99% do direct addition? Why is the organocopper reagent so much more reactive that conjugate addition is the main outcome of the reaction?


texts: Regarding rate dependence on redox potential

texts:
I am stuck with an equation wherein chloroauric acid reacts with oxalic acid to form Au(s). Even though one of both are enough for the reaction:

How does the rate change with increased oxalic acid?
Does it have anything to do with low reduction potential of oxalic acid?


texts: What is the actual mechanism of Fenton reaction?

texts:
Fenton reaction was supposedly discovered by Fenton as Tartaric Acid oxidation by hydrogen peroxide in presence of ferrous cation in 1894. Research Paper link.

I have worked on this reaction for years, not an exaggeration. Whenever I mixed $\ce{H2O2}$ with $\ce{Fe^2+}$ solution, or directly solid ferrous sulphate hepta hydrate, I instantaneously got a dark beer-like color, and a vigorously reacting mixture without adjusting $\mathrm{pH}$. $\pu{10 ml}$ of 35% $\ce{H2O2}$ and $\pu{150 mg}$ of $\ce{Fe2SO4.7H2O}$ is mostly what I used. This much peroxide generally defined the reaction as Catalyzed Hydrogen Peroxide Propagations by RJ Watts group. When mixing with 1g soil in first 12 seconds temperature escalated to $\pu{84^\circ C}$, then slowly calmed. Overall bubbling ceased in 60 seconds, what kind of soil did not make any difference. And for $\mathrm{pH}$ measurement, it is very problematic for many reasons so I simply could not get any meaningful results. This just increased my curiosity.

There are experimental and computational studies over its mechanism of reactive oxygen species generation and organic matter degradation. The second one is a bit easier since somehow catching the end products gives the idea, especially with spin trap compounds.

I have lost all of references so I can only give the categories I have encountered.

Majority went for radical species mechanisms and chain reaction, involving hydroxyl, perhydroxyl, superoxide radicals and uses as a base Haber & Weiss,
Haber, F. & Weiss, J. J. (1934) Proc. R. Soc. London Ser. A 147, 332-351.
Yet these reactions are inherently fast, they are just proposed mechanisms.
There is a considerable number of people stand for ferryl ion pathway, which mostly does not involve radicals but unstable iron (IV) oxidation state compound.
Usually computational studies propose this idea, as hydroxyl radicals lifetime is very short for making it as an efficient reactant.

The reaction of Fenton I am asking is reaction between aqueous hydrogen peroxide and $\ce{Fe^2+}$ ion without any ligand other than water. If it does not help for explanation you may very well ignore more than 30 variations like sonofenton.


texts: I think my prof made a mistake. Shouldn't the answer be 1, 4 and 5 instead of 2 and 3?


texts: Implication of completely non relativistic Hamiltonian

texts:
I am studying the
Application of perturbation theory to hydrogenic atoms subject to internal or external electromagnetic fields.

The very first equation it uses is the hamiltonian of hydrogenic atoms
$$H_0=\frac{p^2}{2\mu}-\frac{Ze^2}{r}$$
This equation is said to have no spin and is completely non-relativistic.

What does completely non-relativistic mean?


texts: Why is OH group activating towards electrophilic aromatic substitution?

texts:
In phenol, the OH group has -I effect due to electronegative oxygen. So, OH group should deactivate the benzene ring towards electrophilic substitution.

[P.S.: I am not talking about the o,p-directing ability of OH, which appears due to lone pair. Also please do not suggest me the question at the link Why is a hydroxyl group more activating than a methoxy group in electrophilic aromatic substitution?, because that is not what I am looking for.]


texts: Is this ancient explosive mixture mentioned in the Apocrypha plausible?

texts:
I understand that religious discussion is not wanted here, but it's just the pretext to my question. I recently decided to read the Apocrypha. Sounded interesting. Anyway, when I got to The Book of Bel and The Dragon, there was this verse, which struck me as particularly interesting:

1:27 Then Daniel took pitch, and fat, and hair, and did seethe them together, and made lumps thereof: this he put in the dragon's mouth, and so the dragon burst in sunder and Daniel said, Lo, these are the gods ye worship.

Now, what I'm wondering (and the only reason I'm bringing this up here), is what would this do? It seems to be an extremely early reference to use of explosives, which is fascinating in a purely historical sense, but what sort of material would actually be formed by boiling a mixture of pitch, fat, and hair? Would this have some explosive tendency, as can be interpreted from the passage? I'm a chemistry major, but I haven't even gone through Organic yet, so if any of you know anything about the properties this would (or would not) have, I would greatly appreciate the knowledge.


texts: Calculating with Method of Equal-area differentiation

texts:
I have been trying to understand this method although I admit, don’t have a very good calculus background just yet.
For a given reaction where $x$ is time, $f(x)$ is cell concentration and assuming it to be first order (autocatalytic), we obtain the table:
\begin{array}{rrrrr}\hline
x  &
f(x)  &
\frac{\Delta f}{\Delta x}  &
\frac{\mathrm{d}f}{\mathrm{d}x}  &
\text{actual}\frac{\mathrm{d}f}{\mathrm{d}x}\\\hline
0    &    0    &    -    &    1010    &    1000    \\
0.2  &  182    &    910  &     805    &     818    \\
0.4  &  332    &    740  &     670    &     670    \\
0.6  &  451    &    605  &     550    &     548    \\\hline
\end{array}

For this data: Is it possible to calculate the $\mathrm{d}f/\mathrm{d}x$ column with the rate formula? Or maybe $\mathrm{d}f/\mathrm{d}x$ can only be calculated by using the equal areas given in the plot?


texts: Relative fraction of population of different enzyme conformations, knowing the rate constants

texts:
Say we have an enzyme that has multiple structural conformations, say A, B, C and D. Additionally, we say that the enzyme must go through all conformations, to get to one end to the other, i.e.

$$\large \ce{A <=>[k_{A-B}][k_{B-A}] B <=>[k_{B-C}][k_{C-B}] C <=>[k_{C-D}][k_{D-C}] D}$$

So there's no skipping any of these steps to go from A to D.

Given all the rate constants derived experimentally, and thus knowing the equilibrium constants for every step, is it possible to derive an overall equilibrium constant that describes which conformation the enzyme is most likely to be found, and perhaps more importantly, the relative fractions for every conformation?


texts:
Does chilling drinking water in copper bottle result in any chemical reaction that turns it dangerous for consumption in any way?

Few days back, in summer, I carried kokum juice in copper bottle. I had a sip of it after some time when I reached office and I felt super dizzy. I felt that traveling might have an effect on me, so I stopped. I had another sip of juice after some hours I had a strong dizzy feeling. At first, the juice tasted ok but then it started tasting very very weird. When I reached home and poured the juice back out of the bottle, to my surprise, its green! The normal color of kokum juice is pinkish-reddish. So somehow copper reacted with the juice and possible resulted in some acid, even though it was at normal room temperature (or in fact cold one as the juice was prepared from cold water). I believe there shouldn't be an issue with cooling water in a copper bottle in the fridge, I just want to know if there is any slight drawback, maybe from Ayurveda point of view? Also, I hope you get the chemistry angle to this question.


texts: Travelling wave ion mobility spectrometry: determination of size?

texts:
I performed an ESI / travelling wave ion mobility spectrometry / MS experiment and observe $\ce{M + H+}$ at $m/z ~701$ and $\ce{M + K+}$ ions with $m/z ~740$. The drift times are 6.75 ms for $\ce{M + H+}$ and 7.0 ms for $\ce{M + K+}$. My first instinct was that this means that the proton adduct is smaller than the potassium adduct. However, if the mass is taken into account as well, i.e.
$$
   7.0 ~\mathrm{ms} ~/ ~740 = 0.0095 ~\mathrm{ms}
$$
for the potassium adduct, and for the proton adduct
$$
   6.75 ~ \mathrm{ms} ~/~ 701 = 0.0096 ~\mathrm{ms}
$$
which would indicate that the two are very similar in size, the proton adduct being slightly larger. For a linear drift tube it would be very easy for me to calculate the relationship (i.e. Mason-Schamp equation), but for travelling wave IMS I am pretty unsure. Which of the two reasonings is correct?


texts: Chemical interaction between Pterostilbene and Nicotinamide Riboside

texts: Some supplement companies are putting a combinations of nicotinamide riboside and pterostilbene into the same capsule. Considering the stomach acid, water, body temperature, etc. I am wondering if there is any likelihood of undesired chemical/pharmacological interaction when those two are ingested at the same time.


texts: Finding region of electromagnetic spectrum with wavenumber

texts:
A line with wave number $\pu{1.028\times10^{-2} nm^{-1}}$ is emitted in the spectrum of atomic hydrogen. In what region of the electromagnetic spectrum does this line occur?

Do we find this by referring to the range of wavelength for UV, IR, etc., or is there a method for knowing which series (Lyman, Balmer, Paschen, Bracket, Pfund) this wavelength belongs to?


texts: Why are acetylene and air commonly used for AAS?

texts: I see that this fuel/oxidant combination is most commonly used, but it's never stated why.


texts: Balancing molecular and net ionic equations for reactions

texts:
Source:'Chemistry: The Central Science 11th edition' by Brown. Ch.4, 4.53:
Question:

Write balanced molecular and net ionic equations for the reactions of:

chromium with hydrobromic acid;
tin with hydrochloric acid.

My attempts:

$\ce{ Cr(s) + 2HBr(aq) →CrBr2(aq)~ or~ CrBr3(aq)? + H2(g)}$
I got the left part of the reaction correct, but I can't figure out what charge chromium should have because it can have either $\ce{+2}$ charge or $\ce{+3}$ charge when it ionizes.  The answer says that it should be $\ce{CrBr2}$, but why can't it be $\ce{CrBr3}$?

same thing for this option. Why can't $\ce{SnCl4}$ can be an answer?


texts: Energy Levels of Molecular Orbitals formed by combination of Atomic Orbitals

texts:
In general when we talk about chemical bonding, we say that it is "nature's way to stabilize the systems" and the energy of the molecule formed by atoms will be lower than that of the individual atoms; hence leading to stabilization.

However, while reading about the Molecular Orbital Theory in my NCERT Chemistry Textbook, I came across a statement -

  The total energy of the molecular orbitals formed remains same as that of the original atomic orbitals.

How can we then justify through the Molecular Orbital Theory that the process of chemical bonding leads to stabilization, if no energy is released?


texts: Relevance of strain energy, total energy and stability of molecule?

texts: Would anybody please highlight the difference between total strain energy of a molecule, total energy of a molecule and what we can infer about the stability of the molecule using the total strain energy of the molecule as well as the scope of using such inferences made.


texts: How to merge PDB-files to build trimer from monomers

texts:
Problem

Using WinCoot or SWISS PDB viewer, how would one merge monomeric structures that should be in dimer formation?

What I have done:

I have downloaded the PDB-file which shows the monomer with a bound drug (Infliximab Fab fragments), but it should be a trimetric structure as whole -although you only get the monomer when you download the file (TNFa) .
I have opened the file in both coot and SWISS-PDB viewer, and opened three copies of the monomer, but they just overlap and I am not able to combine them to the proper structure

I also know that it is possible to download the "biological assembly" PDB-file that has the entire trimetric structure, but the point here is to be able to do that on my own (which should be easy for those who know it?).

I am very new to all of this modeling, so there might be something basic I don’t understand. But I though that you can somehow "merge" the monomers by using some "layer" function? I am really unsure.


texts: Conductivity and Molar Conductivity of Equimolar Solutions of LiCl and KCl

texts:
If one took equimolar solutions of $\ce{Li}$ and $\ce{K}$, which would have higher conductivity? Is it the same for molar conductivity?

Say, $\ce{LiCl}$ and $\ce{KCl}$, of a litre each. Also, as Molar Conductivity = Conductivity / Molarity, are molar conductivity and conductivity directly proportional? Why or why not?


texts: Effect of chloromethyl substituent vs methyl substituent on yields of nitration

texts:
The effects of $\ce {-CH3}$ and $\ce {-CCl3}$ substituents on the product distribution of an electrophilic aromatic substitution reaction are unambiguous. The $\ce {-CH3}$ group exhibits a clear electron-donating effect and directs electrophiles to the 2- and 4- positions. Similarly, the $\ce {-CCl3}$ group exhibits a clear electron-withdrawing effect and directs to the 3- position. Additionally, due to the steric bulk of the three chlorine atoms, there is significant steric hindrance that electrophiles would face when they attack the 2- position. Hence, the proportion of ortho nitration products would be very low.

Some data on the production distributions for nitrations of particular substituted benzenes, taken from Carey & Sundberg (2007), p. 786, is shown below. Observe that the ratios given are consistent with what we have discussed above.

\begin{array}{|c|c|c|c|} \hline
\text{Substituent } & ortho & meta & para \\ \hline
\ce{$\ce {-CH3}$} & 56-63 & 2-4 & 34-41 \\ \hline
\ce{$\ce {-CCl3}$} & 7 & 64 & 29\\ \hline
\end{array}

However, we are interested in the $\ce {-CH2Cl}$ substituent, not the $\ce {-CCl3}$ substituent. We would, of course, expect the steric effect to be lesser than that of the $\ce {-CCl3}$ substituent and we would also expect different electronic effects exerted on the ring. If we were to look at more data from p. 786, as shown below, we would observe that for a substituent like $\ce {-CHCl2}$, it still remains as an electron-donating group as the proportion of meta nitration is still lower than that of ortho and para nitration. It seems that even with one $\ce {C-H}$ bond, there is still sufficient hyperconjugation with the benzene ring to outweigh the inductive pull of the two electronegative chlorine atoms.

I have no data for the $\ce {-CH2Cl}$ substituent but I believe that based on the above analysis, we predict that $\ce {-CH2Cl}$ would also be an electron-donating group that is more electron-donating than $\ce {-CHCl2}$ but less so than $\ce {-CH3}$. Additionally, we would expect to also display directing effects to the 2- and 4- positions However, I have great uncertainty regarding the steric effect of this substituent. How would the ratio of ortho to para nitration be like?

Reference

Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry Part A. Structure and Mechanisms (5th ed.). Springer, 2007.


texts:
I was looking for some help on understanding this practice question from my text book, I know how to figure out enthalpy, but this is my first temperature change question and I am stumped. Any guidance would be greatly appreciated.

Nitric acid is neutralized with potassium hydroxide in the following reaction:
$$\ce{NHO3(aq) + KOH3(aq) -> KNO3(aq) + H2O(l)}$$
$$\Delta_\mathrm rH= -53.4\ \mathrm{kJ/mol}\ \ce{HNO3}$$.
$55.0\ \mathrm{mL}$ of a $1.30\ \mathrm{mol/L}$ solutions of both reactants, at $21.40\ \mathrm{^\circ C}$, are mixed in a calorimeter. What is the final temperature of the mixture? Assume that the density of both solutions is $1.00\ \mathrm{g/mL}$. Also assume that the specific heat capacity of both solutions is the same as the specific heat capacity of water. No heat is lost to the calorimeter itself.

I know the answer is 29.7 degrees Celsius, I'm just not sure how to get there. I tried juggling around my equation "delta t r H= m c delta t" but since I don't know the final temperature i don't think the delta t works in this case. I've tried omitting the delta t but I get no where near 29.7 degrees Celsius.
So I took my formula Q=mc delta t and rearranged it, I now have delta t= Q / mc. Delta t= -53.4 kJ/mol / (55.0g)(4.19 J/g C) I changed the 55mL to g as the question says to assume the density is 1.00 g/mL. I also used the heat capacity as water given in my course data booklet). And I get -0.2317. I tried doubling the mass as there is two solutions but that doesn't work either


texts: Does the Bohr model violate the uncertainty principle?

texts: In a book, it is stated that one reason for the failure of Bohr's theory was the fact that it violates the uncertainty principle. Is this fact true? How so?


texts: Can we have an adiabatic process in a sealed metal container?

texts: Let us consider a non-isothermal process inside a metal container. If we somehow are able to make the temperatures on the inside and outside the system remain same throughout the process, can it be called an adiabatic process?


texts: We've learnt that the electropositive element is written first. Then why is ammonia written as $\ce{NH3}$ ?


texts: Calculating pH of an unknown base, and the pKb

texts:
The percent dissociation of a base $\ce{X}$ in a $0.002\ \mathrm{M}$ solution is $4.7 \cdot 10^{-3}\ \%$. What is the pH of the solution and what is the $\mathrm{p}K_\text{b}$ of base $\ce{X}$? The autoionization of water may not be neglected.

Attempt at solution: We have the following reactions: $$ \ce{X + H2O(l) <=> XH+ + OH-} \\ \ce{H2O(l) <=> H+ + OH-}$$

Since the percent dissociation is $4.7 \times 10^{-3}\ \%$, this enables us to find the concentration dissociated: $$ \frac{x}{0.002\ \mathrm{M}} \cdot 100 = 4.7 \times 10^{-3},$$ so $x = 9.4 \times 10^{-8}$. Now I did: $$ K_\text{a} = \frac{x^2}{0.002 - x}$$ and I let $(0.002 - x) \approx 0.002$ since $x$ is so small. But this gives me the wrong answer, and it seems I haven't taken the autoionization of water into account yet. How should I solve this problem then?


texts: What does [O] denote in organic redox reactions?

texts:
I've seen a few examples in the lectures we've been having and I wasn't able to find any sources talking about it. I think I remember a previous teacher saying it was a symbol for oxidation itself, but I doubt this is true.

Said examples from the lectures:


texts: Where does the beta notation come from in the alpha 1,2 beta glycosidic bond (in sucrose)?

texts:
I am confused as to where the beta is coming from (in the alpha-1,2-beta glycosidic bond in sucrose). I understand that the alpha is from the anomeric carbon of the glucose, but I don't see how the beta is part of this

To me it seems as though the hydroxyl on the anomeric carbon of fructose (i.e. th OH below the plane of C-2 in fructose) causes it to be an alpha form, correct? If so, then why is it called a beta linkage?


texts: Quantifying reactivity in substrates and electrophiles

texts:
What is "quantitative treatment of reactivity in substrates and electrophiles"?
I read about it in Jerry March's Advanced Organic Chemistry textbook, but I'm finding it difficult to comprehend.


texts: Are these statements about change in enthalpy contradictory?

texts:
Just going through my thermodynamics chapter I came across 2 contrasting statements:

Change in enthalpy=enthalpy of (products-reactants) at constant pressure and temperature.

Change in enthalpy=Energy required to break bonds in molecules of reactants -energy
released in the formation of bonds in molecules of products.

So, if I consider these statements individually then these sound correct to me but they are different in the sense that in the first one it is (products-reactants) and in the second one (reactant -products)?
Is the book wrong or am I mistaken in my fundamentals  ?


texts:
I'm trying to name the following compound:

I believe the carboxyl group has priority and should make up the parent name. I'm not sure how to name the alcohol derivative portion. My first thought is:

  potassium ethyl 2-oxyacetate

or

  potassium ethyl oxyacetate

I've seen that there is a compound without the alcohol derivative and ester side chain called glycolic acid, but I have seen no examples of this common name being used as part of an alkoxide salt.

What is the correct way of naming a compound like this?


texts: Failed esterification of 1-butanol and ethanoic acid

texts:
I did an esterification experiment of 1-butanol and ethanoic acid.

30 mL of 1-butanol was added followed by 30 mL of ethanoic acid, and then 1.5 mL of concentrated sulphuric acid and some boiling chips.

The mixture was colorless at first. However, it turned brown during the reflux of esterification immediately after heating the solution, and the solution had a burnt fruity smell.

I suspect this is because I didn't swirl the mixture before heating. Also, before heating, the bottom of the round bottom-flask felt warm, and I suspect this could be the reaction between the concentrated sulphuric acid and ethanoic acid.

One thing that I can't seem to understand is, how did the color of the solution turn brown? Could it be that the product of the reaction between sulphuric acid and ethanoic acid reacted with the 1-butanol to produce a colored solution?

P.s: I couldn't obtain any pure ester after the distillation of the ester as the temperature didn't rise above 100 °C.


texts: Is Chemical Engineering a good pathway to Biomedical Engineering for graduate school?

texts: I have been thinking about my future goals and I have recently decided to go for Biomedical Engineering. sites recommend to start in Chemical Engineering because its a good pathway for biomedical engineering. is this true? please share what you think and from your perspective, thanks


texts: Which resonance structure would be favorably contributed to the actual structure?

texts:
Total number of pairs of resonating structure in which second is more favorable than first:

I know  (d) and (e) have second structure more stable.

(f) has both same.

According me to, (a) and (c) should have second structure unstable as oxygen has positive charge.
I don't have a clue about (b) and (g).
Please help me out.


texts: How to determine the concentration of oxygen in a nitrogen/oxygen mixture?

texts:
I need to prepare a 10% oxygen in nitrogen mixture for an aerobic reaction I'm developing in lab and I found an old instrument in someone else's lab that controls the flow of two gases. So I am able to control the "percentage" of both gases in the mixture using this manifold.
However, I want to test whether or not that thing is calibrated and how exact/precise it is since I don't want to report in a paper that I'm using 10% oxygen when it is actually 20 or 30 or 50%. What is the easiest way to determine the percentage/partial pressure of this gas mixture that will give me reliable results?
I thought about physical-chemical methods such as weighing the mixture and based on basic thermodynamic equations determine its partial pressures but I think a chemical method would be more interesting, such as reacting a known volume of gas with something that would consume the oxygen in a known stoichiometry. Any ideas?


texts: Minimizing Catalyst Residue in Vegetable Oil Hydrogenation

texts:
We are using a nickel catalyst in our hydrogenation process to help convert vegetable oil to vegetable wax. The issue is ensuring all additives are successfully removed once hydrogenation is complete.

There are numerous catalysts that can be used to assist this process.

The question is: what catalyst is effective for hydrogenation but also extremely efficient to filter back out of the finished wax? Or, is there a cleaner way to hydrogenate oil such that almost no residue remains?


texts: Why should I care about the highly radioactive elements after fermium?

texts: After element 100, fermium, there are a bunch of highly radioactive elements like fermium, tennessine, and oganesson, and others. These elements are to radioactive to store, they will instantly disappear, so we cannot use them in any way. If they are to radioactive to use, why should I care about them? I by NO means am saying that we should not care about them, I am asking what kind of potential they have?


texts: Is reforming and isomerization the same thing?

texts:
Okay, just to give an idea of my current understanding. Reforming is a step one can do after one has cracked some hydrocarbons. As such, the process of reforming is dependent on a separate process, cracking. What it involves is cracking the hydrocarbons, then putting them together in new ways, whilst still having the same chemical formula. In a sense, one is reversing the work done by the cracking, since that is a process that changes the chemical formula, however, when one puts the molecules back together, one changes them structurally. Basically, one is making isomers.
However, I do wonder if reformation also includes the saturation of hydrocarbons; as in, making alkenes and alkynes into alkanes. This obviously requires cracking, since double and triple bonds must be broken down into single bonds. If this is a part of reformation, that would mean the term applies to a wider process than just making isomers, since an alkane cannot be an isomer of an alkene/alkyne.
Perhaps isomerization is the creation of isomers, but within any field of chemistry, whereas reforming applies specifically to petrochemistry?


texts: What are the physical properties affected in ZnO when there is a sulfur impurity?

texts: I have a question. I work at a brass metal foundry where one of our waste products is $\ce{ZnO}$, which we sell. Because we have been making new alloys which contain sulfur, our $\ce{ZnO}$ has a very small sulfur impurity level and the people that we sell our $\ce{ZnO}$ to have been complaining that our $\ce{ZnO}$ makes their product yellow. Do you think this is due to the sulfur? What are the effects of very little sulfur on tons of $\ce{ZnO}$ dust? thanks!


texts: Can Henderson-Hasselbalch equation be used to determine the pH of a solution when a strong base and a strong salt of that base stay together?

texts:
The following problem I have stated was not given to me as a homework. I have found this one in my textbook. I have solved it in my own way, but I'm not sure about the correctness of my procedure. I have posted to be sure about the procedure that I want to follow to solve such kind of problem.

  A $5~\mathrm{ml}$ sample of $0.2~\mathrm{M}\ \ce{CH3COOH}$ is titrated with $0.2~\mathrm{M}\ \ce{NaOH}$. Calculate the $\mathrm{pH}$ after adding $25~\mathrm{ml}$ volume of base has been added. Where $K_\mathrm{a} = 1.8 \times 10^{-5}$

By applying $v_1s_1=v_2s_2$ formula, I got the concentration of weak acid and it is $0.0333~\mathrm{M}$. Again by applying same formula, for the total volume of $30~\mathrm{ml}$, I got the concentration of base and it is $0.1667~\mathrm{M}$.

Since the concentration of base is more than that of acid, $0.0333~\mathrm{M}$ base will neutralize the $0.0333~\mathrm{M}$ weak acid and the concentration of remaining base will be $0.1334\ \mathrm{M}$.

Then I used this concentration to evaluate the $\mathrm{pOH}$ of this solution and it was $0.875$. So $\mathrm{pH}$ will be $13.125$.

Do you think that my procedure to solve this problem is correct? I am confused. Because my textbook says that $\mathrm{pH}$ will be $8.87$. Has the author of this book made an error in this case? I cannot use Henderson-Hasselbalch equation in this case because it is not a buffer solution. If weak acid ($\ce{CH3COOH}$) and a strong salt of that weak acid ($\ce{CH3COONa}$) stay together in a solution, we can say it to be a buffer solution. But in the problem I stated above we can see that no weak acid exists after reaction takes place, and strong base ($\ce{NaOH}$) and strong salt ($\ce{CH3COONa}$) stay together. We also know that strong base and strong salt of that base cannot form buffer solution.

Now I want suggestion from the experts of this forum. Is my procedure correct? If it is not, which procedure should be followed to solve this problem?


texts: Does cyclobutanol undergo acidic catalysed dehydration?

texts:
In an exam I had to find a substance X for the following reaction to be correct:
$$\ce{X <=>[\ce{H2SO4}] Y + H2O}$$
I picked cyclobutanol. My teacher said cyclobutanol is wrong . Why?


texts: How is bismuth(III) able to form 3 bonds with hydroxide molecules in bismuth(III) hydroxide?

texts:
Bismuth(III), if I am not mistaken, has only two valence electrons in the 6s orbital. However it is able to form 3 bonds with hydroxide. This goes against my intuition. How is it able to form 3 bonds with 3 hydroxide molecules with only 2 valence electrons?

my best guess is that i am mistaken in thinking that the bismuth(III) is forming 3 covalent bonds when in actually it is forming ionic bonds. As a result, bismuth does not need to offer/share 3 electrons to each hydroxide, but simply take 3. Is this correct?


texts: What is the size of the rate constant dependent on?

texts:
In the rate equation, consider k:

I know that $k$ is fixed unless temperature changes, but what else besides temperature is $k$ dependent on?


texts:
I know that the ferromagnetism of iron is because of its unpaired d electrons, but I also know that there are other metals with unpaired electrons like aluminum that are not ferromagnetic.  Is the difference due to the molecular orbitals or whatever the name is for the orbitals in a solid metal?  I have a suspicion but I'm not sure that in bulk aluminum, the lone unpaired electron of one aluminum somehow shares a molecular(?) orbital with another aluminum atom with a lone electron of the opposite spin so that the net result is that there are no unpaired electrons.

I think this based on a calculation I read in a very well-regarded physics book by Purcell.  In the book he calculates the magnetic dipole moment of a magnet that he doesn't identify except to say that it is a new type of magnet that can be formed into a disc, and since Purcell came out in the 1960's, I suspect he is referring to the ferrite ceramic magnets.  In his calculation, he seems to use one unpaired electron per "molecule".

If the ferrite magnets do have one unpaired electron per "molecule", in contrast to the iron atom in textbooks having 4 unpaired electrons, I'm suspecting that some of the spins are being cancelled out in the actual magnet, and thus I suspect that something similar is happening in aluminum.  Is this correct?

Thanks


texts: What is the balanced chemical equation for a redox reaction between a lithium-cobalt battery and a graphite electrode?

texts:
I'm doing a project for my last year of secondary school on lithium cobalt batteries and got confused about the equation.

This is the only equation I can find (source: www.science.org.au):

\begin{align}
\ce{LiC6 &→ $x$ Li+ + $x$ e- + C6}\tag{anode}\\
\ce{Li_{(1−x)}CoO2 + $x$ Li+ + $x$ e- &→ LiCoO2}\tag{cathode}\\
\hline
\ce{C6 + LiCoO2 &→ Li_xC6 + Li_{(1−x)}CoO2}\\
\end{align}

But I don't understand it at all! I figured it must be balanced, but the '$x$' part of the equation is beyond my level of understanding. Is there a simpler way of writing this formula for someone at my level? If not, can someone please explain what this equation means?


texts: Why is there an exponent 4 after the brackets in sp3?

texts:
My professor wrote an electron configuration for carbon as: 1s2 (sp3)4

I thought it was just 1s2 sp3 where did the 4 come from?


texts: How to find out the energy gained from hydrolysis of Dimethylsulfoniopropionate?

texts:
I am trying to find out what the energy gain from hydrolysis of DMSP (Dimethylsulfoniopropionate) is, versus the energy gain from oxidation of a sugar or carb (e.g. glucose) in a terrestrial atmosphere.

To be clear, I am talking about the 'cleavage of chemical bonds by the addition of water' to DMSP.

This question is motivated by the issue of whether heterotrophic animals living in a reducing atmosphere of an exoplanet which has no free atmospheric oxygen might use DMSP or some similar compound for energy storage in preference to carbohydrates.

DMSP was mentioned by the paper linked below, which suggests that ocean algae get energy from this process and so could alien metabolisms which don't have access to O2. The author states that the energy available from hydrolysis of DMSP is the same in a reducing or oxidising atmosphere but doesn't state what that energy gain actually is in j/mol.

I realise the actual energy storage molecular species used by an actual organism on such a planet is probably going to be something else, but this seems like a good proxy.

"Photosynthesis in Hydrogen-Dominated Atmospheres", William Bains, Sara Seager and Andras Zsom


texts: Is the rate of a zero order reaction always independent of the concentration of its reactants?

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Consider the following reaction :
$\ce{A + B}$ $\rightarrow$ $\ce{Products}$
where order of the reaction w.r.t. $\ce{A}$ is $-1$ and order of the reaction w.r.t. $\ce{B}$ is $+1$. So, overall order of the reaction $=(-1)+(1) = 0$. So, it is a zero order reaction. My teachers told me that in a zero order reaction, the rate of the reaction is independant of concentration of the reactants. Below I have derived the integrated rate law for the above reaction. You can clearly see that in the integrated rate law there are terms of concentration of $\ce{A}$ and
$\ce{B}$. Obviously, the integrated rate law is telling us that the rate of the reaction depends on the concentration of the reactants. Then why does everyone say that in a zero order reaction the rate of the reaction is independant of concentration of the reactants. Why?


texts: What is responsible for making the bonds identical?

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Here is an MO diagram of methane found on the internet:

There are 4 bonds here, one involving the 2s of carbon, three involving the 2p of carbon, and they have different energies.

However, I am told that the four bonds are actually equal.

Then what made them equal? Also, I am told that hybridisation does not exist.


texts: What are solvents that can dissolve sebum that is safe for topical use?

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I do not know much about these properties and I need some feedback regarding these.

Sebum is a semi-fluid that in humans contains a mixture of triglyerides, cholesterol, ester waxes, and squalene. 57.5% of sebum is triglycerides and fatty acids. The next most abundant molecules are ester waxes, which comprise 26% of sebum. Squalene makes up 12%, and cholesterol is the least abundant lipid in sebum.


texts: Burning different isotope combinations of hydrogen and oxygen, how much does the energy vary?

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In this comment I suggested that there would be a (very) small difference in energy released from burning a stoichiometric mixture of hydrogen and oxygen, depending on the isotopes, due to a slight difference in bond energy. The differences can be simply related to different masses of the nuclei, or to other quantum mechanical effects due to the large differences in nuclear spin and moments.

I'd like to repeat the calculation in this answer just to see the sensitivity to the isotopic shifts.

Approximately how large are these small differences in bond energies? Are the differences mostly due to the mass difference or due to the other nuclear properties?

Isotopes in question: $\ce{{}^1H, {}^2H, {}^3H$,  ${}^{16}O$, ${}^{17}O$, ${}^{18}O}$

Either the bond energies themselves, or just a link to a source where I can look it up myself would be fine.


texts: What do the brackets mean in this inline structure representation?

texts: Based on the way the molecular formula is written — $\ce{Br(CH2)4Br}$ — I'm assuming this means that there are $4\ \ce{-CH2}$ groups attached to $\ce{Br}$.  Am I correct? I've always thought that $\ce{Br}$ can't accept so many groups though.


texts: Why is it important that glucose’s third OH group points to the left?

texts: My question pertains to the location of the OH group on the 3rd carbon in a glucose molecule. If atoms can rotate freely around single bonds, then why is this important? Why can't glucose be drawn with 'all H on the left'?


texts: What is the carbon footprint of a diamond?

texts: I think it would be interesting and illuminating to calculate the carbon footprint (per carat) of diamond. The answer would undoubtedly be different for artificial (industrial grade) diamonds vs. natural ones. Is anyone out there familiar enough with either natural diamond mining and processing or the high-pressure process for making artificial diamonds to venture an answer to this question? Both surely involve expenditure of a considerable amount of energy.


texts: Difference between Coupled Cluster and Full CI

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I'm looking at some high precision quantum chemistry methods like Coupled Cluster (CC) and FULL CI (FCI).

It seems both CC and FCI start from Hartree-Fock and then excite the electron to higher states.

If I understand correctly, CC uses an exponential operator to raise the states of the electron while FCI explicitly calculates the coefficients of each determinants.

What makes the difference between CC and FCI? Can someone give an intuitive explanation? Thanks.


texts: I am having trouble calculating the value of $\Delta H_\mathrm r$ for the reaction: $$\ce{Mg + HCl}$$ The total heat capacity ($C_\text{cal} + C_\mathrm r$) is $6.88\ \mathrm{kJ/{^\circ C}}$, and the $\Delta T$ is $10.5\ \mathrm{^\circ C}$. When I multiply the two I get $72.24$ which is $Q_\mathrm r$ (Total heat produced). Finally when I divide $72.24$ and $0.005$ moles of $\ce{Mg}$ I get $14\,448\ \mathrm{kJ}$. This seems to me to be inaccurate. Can anyone help me solve $\Delta H_\mathrm r$