texts: Correct Rate Equation for a Reversible Reaction

texts:
I'm helping my son with Matlab as he is having trouble learning differential equations as they apply to chemical kinetics.   His task is to solve for the equilibrium concentrations for a reaction
$$\ce{A + B <=>[$k_{\mathrm{f}}$][$k_{\mathrm{b}}$] C}.$$
We are given the forward and backward rates and the initial concentrations of the reactants and products.   I helped him to set up the required equations and ran them through the ode integrator in R and Matlab but the results don't look right.   I'm pretty sure the integration process is working so I think maybe the actual formulae are wrong:
\begin{align}
\frac{\mathrm{d[A]}}{\mathrm{d}t} &= {k}_\mathrm{b}[C]-{k}_\mathrm{f}[A][B]\\
\frac{\mathrm{d[B]}}{\mathrm{d}t} &= {k}_\mathrm{b}[C]-{k}_\mathrm{f}[A][B]\\
\frac{\mathrm{d[C]}}{\mathrm{d}t} &= {k}_\mathrm{f}[A][B] -{k}_\mathrm{b}[C]
\end{align}
When I run this through the integrator with $k_\mathrm{f}=3$, $k_\mathrm{b}=1.5$,
$[A]=\pu{1M}$, $[B]=\pu{1M}$, and $[C]=0$,
the concentrations all reach equilibrium at the same level of $\pu{0.5M}$.  Is that correct?  I would have expected them to be different with the forward rate being bigger.
Really sorry for the basic question but as I said, I'm a programmer not a chemist.  I got the formulae from this How to set up an equation to solve a rate law computationally? but assumed that I didn't need to square any of the concentrations since the reaction is $\ce{1+1<=>1}$.


texts: Ionization isomerism in coordination compounds

texts:
Ionization isomerism is defined as complexes which have same empirical formula but ionize to different ions in solution.

Consider the complex $\ce{[Pt(NH3)4Cl2]I2}$. The other possible ionization isomers are:
$\ce{[Pt(NH3)4I2]Cl2}$ and $\ce{[Pt(NH3)4ICl]ICl}$.

But I have not come across the complexes similar to the last one with two different anions outside the coordination sphere.
So, do these sort of complexes exist?

Moreover, what can be the IUPAC name for this compound?

tetraamminechloridoiodoplatinum(IV) chlorineiodine seems wrong.


texts: Does it make sense to differentiate the Arrhenius equation with respect to temperature?

texts:
I am trying to answer the question: "between concentration and temperature, which has a greater significance on the rate of reaction"
Hence, I'm trying to find a method to systematically compare the impact/significance of concentration and temperature on rate. This is where I ended up trying to differentiate the Arrhenius equation:
$$k = A\mathrm e^{-E_\mathrm a/(RT)}$$
I thought that deriving rate constant $k$ with respect to temperature is finding the rate of change of $k$ with respect to temperature. Is it conventionally and mathematically correct to do this?
If it is, then continuing the thought process:
I differentiated the equation assuming that the Arrhenius constant...is...constant... But is that true? Does $A$ change when temperature change (since my variable here is temperature)?
If everything was not non-sense until this point, I ended up with the derivative:
$$\frac{\mathrm dk}{\mathrm dT}=A\mathrm e^{-E_\mathrm a/(RT)}\times E_\mathrm a/(RT^2)$$
Is this correct chemistry/maths?
EDIT
Is there a better way to compare the significance of concentration with that of temperature on the rate of reaction? Maybe using percentage increase of each factor with the percentage increase of rate?


texts: What is a "tri-salt polymer" as described by this product that eliminates and prevents mold?

texts:
This answer mentions an anti-mold product called Concrobium Mold Control. The FAQ linked on their website says:

Q: I see Sodium Carbonate listed on the label. Is Concrobium Mold Control just Sodium Carbonate (washing soda) and water?
A: No. Sodium Carbonate is the listed “active ingredient” on the Concrobium Mold Control label, but in fact there are two other ingredients in the solution which, when combined with the sodium carbonate and the water, result in this patented tri-salt polymer that eliminates and prevents mold. (Sodium Carbonate and water alone are not effective against mold.) The solution contains no bleach, ammonia or VOCs. Our Material Safety Data Sheet is posted on our website.

The MSDS lists two particular ingredients:
Chemical Name            CAS #          % by Wt

Trisodium phosphate   7601-54-9           1-5
Sodium Carbonate       497-19-8           < 1

I'm guessing the third might be water.
Question: What might the term "tri-salt polymer" refer to in general, and if possible to answer, what might it be in this particular case?
I did find a patent in a google search but I'm not sure of it's relevance and I don't understand it.

CA2504014C, Non-toxic water soluble inorganic anti-microbial polymer and related methods


texts: Why does water volume decrease when salt is added? Our teacher asks us in the class but I don't find any strong reason.


texts: Functionalizing CTAC stabilized nanoparticles

texts:
I am working on functionalizing silver-gold bimetallic nanoparticles. My nanoparticles are stabilized by CTAC(cetyltrimethylammonium chloride).The most articles which I found, are about the functionalizing of citrate stabilized nanoparticles.
Is functionalizing CTAC stabilized nanoparticles more difficult than citrate stabilized nanoparticles?


texts: Why don't water molecules react alongside aqueous reactions?

texts:
To explain my question I'll use an example: We all know that sodium displaces copper in a solution of its sulfate in the reaction:

$$\ce{2Na (s) + CuSO4 (aq) \rightarrow Na2SO4 (aq) + Cu (s)}$$

My question is why don't some of the water molecules present in the aqueous solution of $\ce{CuSO4}$ also react with the sodium (Na) to form sodium hydroxide and hydrogen ($\ce{NaOH + H2}$) along side this displacement reaction. Shouldn't at least a bit of NaOH be formed?

I would appreciate a comprehensive response that a high school sophomore (me) would understand. Thanks in advance.


texts:
My textbook has a question which says what would happen to the pH of a weak acid if it is diluted with water. The answer is its pH would decrease.
My teacher’s argument is that it would indeed decrease because water ionizes to hydronium ions which would increase the concentration of H+ ions and therefore, decrease the pH.
My argument is that it would increase because when the acid is diluted, the concentration of H+ ions will decrease and hence, the pH will increase. Further details in the attached photo.
My father, who is a chemist, argues that it would decrease then increase. He says that it varies upon the amount of water added and that it is not a direct relation. Instead, it would form a graph similar to the letter V.
I am honestly lost. What would exactly happen?


texts: How to create the equivalent of luminol for a compound?

texts:
How would you go about creating a compound, like luminol, that would visibly react with monomorine I (5-methyl-3-butyloctahydroindolizine) on a household surface (like a kitchen floor)?

It is ok if the compund reacts with other similar compounds as well, as long as they aren't common to a household.

Background:

Luminol is the chemical used by forensic investigators (like those on CSI) to detect trace amounts of blood at crime scenes. The luminol is sprayed over an area and when it comes into contact with blood (specifically, the iron), it exhibits a blue glow.
Monomorine I is an ant trail pheromone (a trail guiding other ants to food).

Objective:

I'd like to be able to apply a compound on a surface and see the trails left by ants.


texts: What acid can remove Calcium in Ca2SiO4 to leave SiO2 (mostly)

texts:
What acid can remove calcium in $\ce{Ca2SiO4}$ to leave $\ce{SiO2}$ (mostly)?

It seems that calcium silicate is stable in most acids, but I need to etch it and leave only silica (mostly).


texts: Why should the salt being used in salting out process be neutral?

texts:
When doing salting out it's been said that the salt being used should be neutral, meaning both acid and base which make the salt should be categorized as strong acids or bases. Why is that?

For example, $\ce{NaCl}$ could be used as a salting out salt in principle, because $\ce{NaOH}$ is a strong base and $\ce{HCl}$ is a strong acid but using $\ce{NaCH3COO}$ is not right because $\ce{CH3COOH}$ is not a strong acid.


texts: Could density be defined as the measure of matter per unit volume instead of mass per unit volume because mass is a measurement of matter?


texts: How do you find the enthalpy change for a given reaction?

texts:
$0.500\,\mathrm g$ of magnesium chips are placed in a coffee-cup calorimeter and $100.0\,\mathrm{mL}$ of $1.00\,\mathrm M$ $\ce{HCl}$ is added to it. The reaction is:
$$\ce{Mg(s) + 2HCl(aq) -> H2(g) + MgCl2(aq)}$$
The temperature of the solution increases from $22.2\,^{\circ}\mathrm{C}$ to $44.8\,^{\circ}\mathrm{C}$. What’s the enthalpy change for the reaction, per mole of $\ce{Mg}$? Assume specific heat capacity of solution is $4.20\,\mathrm {J\,g^{-1}K^{-1}}$ and density of the $\ce{HCl}$ solution is $1.00\,\mathrm {g/mL}$.

I don't understand how to solve this; does this have to do with heat capacity equation? (Or is that just a completely different thing).
$$q = mc\Delta T$$
(Also note this is not a homework problem. The answer should be $\Delta H = -4.64 \cdot 10^{5}\,\mathrm{J\,mol^{-1}}$ $\ce{Mg}$, but I don't know how to get there and would like to understand.)


texts: Why does a reduced compound become a better electron donor?

texts: When a compound gains an electron, why are they more likely to give them up (i.e. become stronger reducing agents)?


texts:
How many different organic structures (from the pure theoretical viewpoint) can be drawed with only 4 (exact) carbon atoms and with/without hydrogen? Polycyclic compounds and bridged compounds are also allowed. Please, name them all as well! :)

Remark: I have drawed the chemical graphs in a piece of paper (the skeletons) and I get 37 graphs (including linear with simple, double and triple bonds, and planar and nonplanar compounds), without geometric isomerism (cis/trans). Is that OK?


texts: How to handle CO2 being evolved during vacuum distillation?

texts:
Setup: vacuum aspirator pump, distillation apparatus with stirring (instead of a bubbler). Partial vacuum around 5" Hg.

What would you suggest to hold the vacuum set-point?


texts: Are HPLC and GC comparable in term to size exclusion, ion exchange, sequential injection chromatography? Or they are two different terms, HPLC and GC refers to the equipment and phase of the analyte, while IEC, HIC, SEC are the principles that would refer more to the column itself?


texts: Is there an efficient and effective way to clean oil from floor?

texts:
I've recently had several jerry-cans of oil (awaiting disposal) topple over in the attached garage, and several rooms following influx of water following heavy rain. After the water level receded the floor is left with a thin layer of burnt oil.

Various sites on the net recommend using sawdust, baking soda etc. I'm talking close to 800sq.ft of area split into several levels with a step between different levels.

The question I have to ask, therefore, must be obvious now. How does one clean large volumes of burnt oil spilt distributed by water over cement, and stone floors?

EDIT: Nature giveth, and Nature taketh away. Another cloudburst, this time over 100mm of rain in a couple of hours, and muddy waters found their way indoors again. Now the waters have receded, and almost all the oil is replaced with a thin layer of mud. Hopefully washing with water will get rid of the most of it.


texts: Understanding the bond dissociation energy of poly-atomic molecules

texts:
Now I have a breaker which is containing $\ce{CH4}$ of some amount at standard conditions and then I put it on a burner.

In Thermodynamics we are taught about how to find the bond enthalpy of poly-atomic atoms. They say that such molecules (here in this case methane) all four $C-H$ bonds are identical. However, the energies required to break the individual $C-H$ bond in each successive step differs
$$\begin{alignat}{2}
\ce{CH4(g) &-> CH3(g) + H(g)}\qquad &&\Delta_\text{bond}H^\circ=+427\ \mathrm{kJ\cdot mol^{-1}}\\
\ce{CH3(g) &-> CH2(g) + H(g)}\qquad &&\Delta_\text{bond}H^\circ=+439\ \mathrm{kJ\cdot mol^{-1}}\\
\ce{CH4(g) &-> CH(g) + H(g)}\qquad &&\Delta_\text{bond}H^\circ=+452\ \mathrm{kJ\cdot mol^{-1}}\\
\ce{CH(g) &-> C(g) + H(g)}\qquad &&\Delta_\text{bond}H^\circ=+347\ \mathrm{kJ\cdot mol^{-1}}
\end{alignat}$$

and now their bond enthalpy is the mean of all those numbers.

now going back to the diagram we heat up the beaker containing methane then the energy that is absorbed by any one of the $\ce{C-H}$ bond should be equal to the energy absorbed by the other $\ce{C-H}$ bond because all the bond in a molecule should absorb equal amount of energy at the same time because at time $t$ the temperature is same all over the beaker and  all bonds are equal. so it should be like that while calculating the bond dissociation energy of a poly-atomic molecule (take the example of methane) calculate it like $4\times 427\ \mathrm{kJ\cdot mol^{-1}}$. (is this a common sense?)

  all bonds Should broke up at once!

but we know that this does not happen, which means that all the bonds in a molecule does not absorb heat of equal amount at the same time or are they unequal? And fairly speaking it is painful to me to visualize this thing maybe because I am not able to understand this reality.

How do I comprehend this thing?

In Short

all bonds of $CH_4$ are equal
The temperature of beaker is same all over its volume
energy that is absorbed by any one of the $\ce{C-H}$ bond should be equal to the energy absorbed by the other $\ce{C-H}$ bond
bonds should absorb equal energy at time t
the should all break at once at same time t

this do not happen so how to understand this thing?


texts: Why is nitromethane not especially reactive? $\ce{NO2}$ is stable by itself, so why does it stay attached to $\ce{CH3}$?


texts: galvanic corrosion in the wild: where is the reduction?

texts:
Galvanic corrosion occurs of an active metal (i.e. iron or zinc) in contact with a passive metal (i.e. copper) in a conductive solution. A famous example is the corrosion of iron girders in contact with copper in the statue of liberty.

Although the difference in potential can account for the protection of copper, it does not explain the girders in had a greatly accelerated corrosion rate. In a zinc/copper battery there is a solution of copper sulfate that gets reduced at the copper electrode. However, if all the copper is in metallic form in the first place, no galvanic reaction can occur.

It seems galvanic corrosion in real-life, does not increase total corrosion, but rather concentrates it (at lest for pairs of metals with similar non-galvanic corrosion rates). Copper sheets have a large surface area that initially reacted non-galvanically to form the green color we see. Some of these ions are then reduced at the expense of the oxidizing the girders. The statue of liberty and other infamous examples of corrosion involve large amounts of inactive metals connected to small amounts of active (iron/steel) girders/fasteners/etc.

This logic predicts that the attaching a copper bar to an iron bar of equal surface area will only double it's corrosion rate. That being said, predicting the corrosion rate is not easy so there could be some other effect I am overlooking. Is the surface area logic correct or would there a large increase in the total corrosion?


texts: Which of the following is most likely to undergo hydride shift?

texts: For the following question the answer is given as option (a) . However both,option (a) and (c) has alpha H atoms and both will form 3° carbocations after rearrangement. So what makes (a) more favorable than (c)?


texts: Is kinetic energy proportional to temperature for non-gases?

texts:
If the molecules in a sample of ice at $\pu{-15 °C}$ and $\pu{1 bar}$ all have their kinetic energy doubled, then what is the final phase?

The answer is gas, but I am not sure how to get this answer.

I was wondering if the equation $\displaystyle k = \frac{3}{2}RT$ still holds in this case, even though the molecules are not a gas. It seems as though it does (it gives the right answer because $2 \times \pu{258.25 K} = \pu{516.3 K},$ which is a gas), but I am not too sure why.


texts: Why is the ionic radius of hydride so large?

texts:
The order of ionic radii for halides and hydride is apparently as follows:
$$\ce{F-} < \ce{Cl-} < \ce{Br-} < \ce{H-} < \ce{I-}$$
Why is the hydride ion so large, even larger than bromide which has filled 3d and 4p subshells? Some claim that it is because the ratio of positive to negative charge is 0.5, which is an unusually small ratio. But this explanation doesn't fully convince me.
Nat. Commun. 2014, 5 (1), No. 3515 also makes mention of the unusually large size:

The ionic radius of an $\ce{H-}$ ion is $\pu{134\pm 2 pm}$, which is slightly larger than the radius of $\ce{F-}$(II) ($\pu{128.5 pm}$) and almost the same as the radius of $\ce{O^2-}$(II) ($\pu{135 pm}$). This evaluation agrees with the generally accepted trend that the radius of an H− ion is nearly the same or slightly larger than that of an $\ce{F-}$ ion and increases with increasing electropositivity of the coordinating cation.


texts: Also, why can some elements such as $\ce{Fe}$ have different ionic forms such as $\ce{Fe^{2+}}$ and $\ce{Fe^{3+}}$? What determines each form?


texts: Stability of half and fully filled orbitals

texts:
1) My textbook tells me that chromium's electronic configuration is $\ce{[Ar]}\space 3d^5 4s^1$ instead of $\ce{[Ar]} \space 3d^4 4s^2$, as fully filled and half filled orbitals have more stability. But how does that happen? Why is the fully or half filled orbital more stable?

2) Following this method as we go down group 6 we would expect tungsten's last two orbitals to be filled as $5d^5 6s^1$ to attain more stability. But the actual configuration turns out to be $5d^4 6s^2$. Isn't this supposed to be "unstable"?


texts: Can a piece be electroplated without being connected by wire to the cathode?

texts:
I had this great idea for making electronic circuits that would have made me rich and famous by printing them on a surface with an inkjet spraying custom-made graphite conductive ink, then copper-electroplating the circuit to get perfect conductivity until realizing that not all the tracks from the PCB are connected, thus not all the parts connected to the cathode so not being plated and rendering the idea unfeasible (not to mention the difficulties of making a proper conductive ink and getting it printed by a modified printer and so on...).
I wonder if there is some technique that could be used to overcome this problem, not involving having to interconnect all the PCB tracks with little wires. For instance, maybe something like physically attaching a sheet of aluminum or copper foil to the track's side could work? So current would get into the tracks but, as long as there is some "space" between the foil and the tracks, some copper atoms could get in there and create s thin layer of copper between the layers of the "sandwich"?
I know it was too good to be true and a bit suspicious that there weren't a single reference to such a great idea on the whole internet when searching for it on Google, but maybe the great minds on here can think of some alternative before definitively abandoning my great invention, lol.


texts:
I want to make aspirin. Normal method is to react salicylic acid with acetic anhydride, but it is extremely hard to find acetic anhydride. How may I synthesize aspirin with acetic acid and salicylic acid only?

I have watched a video where someone makes it with sulphuric acid, salicylic acid and acetic acid. Can I use phosphoric acid insted of sulphuric acid as a catalyst?


texts: How do fuel/oxidizer combustion mechanics change when the constituents are supercritical?

texts:
The problem to solve is this: I want to create a heat generator [or heat absorber] that functions at atmospheric pressure to the pressure at the bottom of the sea. It will be used to drive a Stirling engine.

As such, I'm worried that a simple burner with adjustable flow rates won't act predictably at extreme pressures.

Givens:

1 atm - 1000 atm ambient pressure
I can maintain a constant differential pressure between fuel/oxidizer bottles and the reactor
1 kW output power (small in scale)
Nitrous oxide/hydrocarbon (probably propane) constituents [edit: not set in stone]

Will the combustion chemistry work out? Is the reaction so fast that stable combustion is impossible at low flow rates?

I am also reading up on supercritical hydrothermal combustion as an alternate solution. I have contemplated using liquid nitrogen as a heat absorber, but it is appx 1/100 mass-efficient in terms of energy input/output. Alternate solutions that avoid the problem entirely are also welcome. <3


texts:
Im thinking specifically of N2 + 3 H2 ⇌ 2 NH3. Its an exothermic reaction, therefore heat is generated. Im trying to understand how Chateliers principle interacts with this reaction. I understand that if you remove heat, Chateliers principle dictates that the equilibrium shifts to the product-side. I cant quite understand why though, do the reactants kind of know how warm it is and then decide, if its too warm "No, its too warm, lets not react and make it too warm"?

A followup on that question too, these reactions happen in enclosed places where temperature and pressure can be manipulated.Is it just efficiency of these containers that prevent the containers to not get as hot as the sun? If temperature wasnt manipulated, would the temperature keep rising?


texts:
Question

Attempt

I thought the products would be from simple darzens reaction. So   I replaced the OH by Cl. But the answer of mine seems way wrong. Do give some tips on what might be happening in the reacton.
Please help


texts: At what amount is digesting soap unhealthy?

texts:
Several of my friends, when they do the dishes manually, do not rinse the dishes after cleaning but merely dip them in the dishwater and then dry them (using a towel or a dish rack). I myself on the other hand always rinse the dishes with fresh (hot) water from the tap before drying them, mostly because the idea of having a dose of soap with my next meal freaks me out.

But is there some guideline as to how much of the soap you can ingest until something goes wrong, be it the taste of the next meal or some poisonous reaction? The soap used for doing the dishes manually doesn't have any warning labels on it... I've found this describing poisonous effects of automatic dishwater soap, and this pertaining to a dish soap that is used for manual dishwashing.


texts: Does the plastic cup PETE 1 material leak toxic material if subject to boiling water even for part of a minute?

texts:
Sometimes a cafe may pour boiling tea into a plastic cup made of PETE 1 and then add lemon and cold water / ice to it.  When the cup is handed to the customer, the cup looks ok.  And I suppose even if a person drinks such drinks for a few years, and gets cancer, what proof do you have that it is due to the cup?   The cafe doesn't really care, because money, profits, and speed is of the utmost importance in the country.

For PETE 1 plastic, when it is subject to boiling, 100°C, water or tea for 30 seconds or 1-2 minutes, will it already leak out toxic chemicals?


texts:
Should Formaldehyde (37%) be stored at 5 degrees C or lower?
Will it damage the Formaldehyde?


texts: Discrepancy between preparation of yttrium aluminum garnet powder in a nonpreheated and preheated oven

texts:
I've made yttrium aluminum garnet (YAG) precursor powder and in my last batch, I placed one half of the powder to be annealed in a non-preheated oven (letting the powder heat up with the oven) and the other half of the powder, I placed it in the oven once the temperature reached my final desired annealing temperature, 1020ºC. Aside from this difference, everything about the annealing process was the same; Annealing for both were performed in air and in the oven for 2 hours.
The curious thing is, the XRD results showed that the sample placed in the preheated oven still showed traces of secondary phases (YAH and YAM), but sample that was placed in non-preheated oven (the one that was heated up as the oven was being heat up) showed phase pure YAG, which to me is counterintuitive. How can this be? Does it have to do with some sort of kinetic steps in the formation of YAG?


texts: What is the difference between enthalpy of formation and Gibbs free energy of formation?

texts:
I'm having trouble (not alone, apparently) understanding the concept of Gibbs free energy, but I'm beginning to. What I still don't understand, however, is how Gibbs free energy of formation differs from heat- or enthalpy of formation. Is it more precise, somehow? given that entropy is accounted for in Gibbs free energy?

Thanks in advance


texts: What is the effect of the surface area of an electrode on the emf of a cell?

texts:
I've read that a platinum electrode has no effect in a hydrogen fuel cell - why is this?
Also, what is the effect of the surface area of an electrode such as zinc in a zinc copper cell?


texts: Is the given statement regarding Radial Probability Distribution Function correct or not?

texts:
Radial Distribution Function $(4πr^2R^2(r))$ gives the probability of the electron being present at a distance $r$ from the nucleus.

Answer: The given statement is correct.
My Query:
According to me, isn't the Radial Probability Distribution Function ($RPDF$) used for finding the probability of an electron being present at a distance $r$ from the nucleus within a region of thickness  $dr$?
Therefore, shouldn't the above statement be wrong?


texts: What does the reaction of chromium with ozone form?

texts: I know almost nothing beyond 10th grade chemistry. I'm trying to name a web application, and was wondering what the products are of a reaction between the element Chromium and the gas Ozone (ozonolysis of chromium?).


texts: Enthalpy of formation and bond energies of CH2(OH)2?

texts:
I was wondering if I could have the bond energy and enthalpy of formation in kJ/mol for $\ce{CH2(OH)2}$?

I honestly searched the Internet and my textbook and I couldn't find it.  I'm sure I could have missed it somewhere but nevertheless I need to calculate the energy produced by the reaction of $\ce{CH2O}$ and $\ce{H2O}$.

If someone could give me that info that would be exceedingly helpful.


texts: What chemicals are mixed together to cause chemoluminescence?

texts:
My brother is supposed to do a science experiment at school for an open house. We found an interesting experiment in which you pour several chemicals together, causing the resulting concoction to glow brightly. You can make several colors in this way. Then you can dump them together, to demonstrate how white light is made up of several colors mixed together. Several questions.
1. Which chemicals are used?
2. How do you get the colors?
3. Where can you buy the chemicals you need?


texts: Ligand exchange reactions... are they one way or reversible?

texts:
Are ligand exchange reactions one-way  reactions or reversible? I know this is a very silly question but its not said outright in any place...

For example, in my high school chemistry book, these two ligand exchange reactions are shown:

$$\ce{[Cu(H2O)6]^{2+} (aq) + 4Cl- (aq) <=> [CuCl_4]^{2-} (aq) + 6H2O (l)}$$

$$\ce{[Cu(H2O)6]^{2+} (aq) + 4NH3 (aq)-> [Cu(NH3)4(H2O)2]^{2+} (aq) + 4H2O (l)}$$

The first is reversible but the second is one-way

Also, my teacher stated that ligand exchange reactions are irreversible... this confused me further

Can someone please tell me what is right...


texts: Why is coulomb integral is called local while the corresponding exchange integral is called non-local

texts: In the book "A chemist's guide to DFT" page 27-29 they said that coulomb integral is local interaction term while exchange integral is non-local. I can visualize, to some extent, that repulsion between two orbital/wave function at two different position (say x1 and x2) is called coulomb integral and that is why it's local. But I am having problem with the exchange term. It is also local, I feel, just the difference is two orbital can interchange their position between them. Can anyone please shed light on these concepts?


texts:
If I have an iron-platinum alloy, can I put this into a solution of $\ce{HCl}$ to dissolve the iron, leaving a $\ce{Pt}$ precipitate?

I know that Fe dissolves in $\ce{HCl}$ to form $\ce{FeCl2}$ and $\ce{H2}$, and I know that $\ce{Pt}$ does not dissolve in $\ce{HCl}$.

But will the $\ce{Fe-Pt}$ bonding affect the Fe dissolution?


texts: What happens if hydrogen peroxide is added to silver oxides?

texts:
I have some powders that contain $\ce{Ag2O}$ and $\ce{AgO}$.

What happens if I add $\ce{H2O2}$ and some water to these silver oxides?


texts: Equilibrium composition of methane–water system under given conditions

texts:
Calculate the equilibrium composition of a reactive system consisting of an equimolecular mixture of $\ce{CH4}$ and $\ce{H2O}$ at $\pu{900 K}$ and $\pu{1 atm},$ considered to be an ideal mixture of ideal gases. Under these conditions, the equilibrium constants of the two possible reactions are
$$
\begin{align}
\ce{CH4 + H2O &<=> CO + 3 H2} &\quad K_{p,1} &= 1.307 \tag{R1}\\
\ce{CO + H2O &<=> CO2 + H2}&\quad K_{p,2} &= 2.210 \tag{R2}
\end{align}
$$

I have tried to solve it by expressing each $K_{p,i}$ independently, considering there are five constituents in this ideal mixture and that $\ce{CH4}$ and $\ce{H2O}$ are the starting compounds, with $n^0 = 1.$ I associated a different degree of advance, $\xi_i,$ to each of the reactions and solved the two-equation system, but it seems that this is not the proper solution because the reactions are not independent.
Can anybody figure out a solution?


texts: What is the world's finest powder substance?

texts: What is the world's finest powder substance that has the smallest granules but remains solid?


texts: Why is sodium sulfate neutral while its conjugate acid is weak?

texts:
It is commonly taught in chemistry class that the conjugate base of a weak acid (well, at least if it's not weaker than water) is a weak base, as shown by the relation

$$\mathrm{p}K_\mathrm{a} = 14 - \mathrm{p}K_\mathrm{b}  \iff K_\mathrm{a}=\frac{K_\mathrm{w}}{K_\mathrm{b}}$$

where the $K_\mathrm{a}$ is of the conjugate acid, and $K_\mathrm{b}$ of the base. For weak monoprotic acids this means that their conjugate bases are weak, e.g. various carboxylic acids, phenol and hydrofluoric acid. For polyprotic acids, if the conjugate base's next $K_\mathrm{a}$ is smaller than its $K_\mathrm{b}$, then it would also form an alkaline solution but not fully dissociate, e.g. bicarbonate ion (carbonic acid), bisulfide ion (hydrogen sulfide), ammonia (ammonium ion).

However, according to Wikipedia as well as my teacher, sodium sulfate $\ce{Na2SO4}$ is neutral, but Wikipedia also says the acidic hydrogen on the bisulfate ion has $\mathrm{p}K_\mathrm{a} \approx 2$, so sulfate would have $\mathrm{p}K_\mathrm{a} \approx 12$ and a $1\ \mathrm{M}$ solution of sulfate with a perfectly non-acidic counterion would have $\mathrm{pH} \approx 8$. Is sodium sulfate in fact neutral? If so, what would be the reason? Could it be that $\ce{Na+}$ is slightly acidic? Or is the formula for conjugate basicity inapplicable here?


texts: Are fossil fuels and petroleum the same thing?

texts: I've been reading articles about renewable energy, and in comments people talk about fossil fuels and petroleum as examples of non-renewable types of fuel. Sometimes they are used interchangeably, or even mentioned as different things. I couldn't find explicit explanation for which is which, and if one is a subset of the other. Can someone clarify this for me?


texts: qualitatively: Why are thioesters more reactive than regular esters?

texts:
In ochem students are taught that shorter bonds (like alkynes) have more energy than longer bonds such as alkanes. However in biochem we are taught that thioesters are very energetic bonds and release alot of energy upon breaking.

Is there a specific mechanism that explains the relationships between bond energy and length?

background: a university student with a chem minor


texts:
Doing a first year chem class.
Just read through the molecular naming of compounds and now I'm confused as to why $\ce{CaCl2}$ is called calcium chloride and not calcium dichloride?


texts: How does sulfuric acid dehydrate sugars?

texts:
I know sugars have $\ce{-OH}$ groups, and that sulfuric acid is a strong acid. What I'm failing to see is how exactly sulfuric acid dehydrates sugars. Does it protonate the hydroxyl groups, making them good leaving groups? What about the case of sucrose?

For example, how are the oxygens "taken care of" by the sulfuric acid? Are they doubly protonated? Is there some established mechanism for the dehydration of sugars by sulfuric acid, because I can't find any - I just find general equations and I've looked on Google and through textbooks.

After some further research I learned that the gas, sulfur dioxide, is evolved. This suggests to me that this reaction is also redox in nature. So is this reaction both an acid-base reaction and a redox reaction? Sulfur in sulfuric acid has an oxidation state of +6; sulfur in sulfur dioxide has an oxidation state of +4. Plus the elemental carbon formed has an oxidation state of 0 while in sucrose, carbon has various oxidation states.


texts: Alcohol (ethanol) distillation: mystery congener

texts:
I regularly home-distil small amounts of potable alcohol (ethanol), mainly from fermented sugar(s) solutions (the 'wash').
My still is a box standard, $4.5\mathrm{L}$ electrically heated (safety!), air-cooled pot still, which produces exactly $1$ single stage distillation ('one Theoretical Plate') Starting from a wash of about $17\text{ %}$ ABV, I can distil that to (initial ABV) about $65\text{ %}$ ABV.
About $1.0\mathrm{L}$ is distilled off from $1$ gallon that way and the distillate then diluted with water to about $37\text{ %}$ ABV.
Distillers (home, pro, moonshiners) use a system to get the most and the best out of their distilled washes and it goes as follows:

The "Heads": the first part ($5 - 10\text{ %}$) of the distillate is often discarded because it contains non-ethanol low boiling congeners like methanol, ethanal, acetone and low boiling esters (it's a commonly held but erroneous belief that methanol and ethanol can be separated by means of a single distillation - see the $\text{MeOH/EtOH}$ VLE). These congeners give the distillate a 'synthetic' and undesired taste profile.
The "Heart": this is the good tasting part of the distillate, that is kept as an alcoholic beverage.
The 'Tails' (or 'faints'): the last part of the distillate contains very little alcohol, as well as higher boiling compounds like higher alcohols and $\text{C8 - C12}$-based esters. The high boiling congeners are also referred to as "fusel oils".

Apologies for the lengthy preamble.

Due to the pandemic and restrictions on the hospitality sector I obtained several gallon of out-of-date $4.5\text{ %}$ ABV apple cider of a very well known brand, from a friendly publican.
I first consumed a couple of liters as such and it tasted fine and caused no adverse effects. The product was indistinguishable from 'in date' virgin cider. But my purpose was always to distill the ethanol of out it.
So, using my standard procedure I distilled several gallon of the out of date cider, obtaining about $2\mathrm{L}$ of distillate at about $35\text{ %}$ ABV. Heads were discarded and the distillate was run over activated carbon (a practice highly recommended by home distillers and moonshiners, even though I'm not sure it serves a real purpose)
And here's the rub: the 'heart' smelled and tasted awful. The taste is hard to describe but keywords would be 'spicy', 'hot', 'sharp', 'solvent-like'.
I then took the step of redistilling the $2\mathrm{L}$ of product, discarding the first $300\mathrm{ml}$ and keeping a 'heart' of about $1.1\mathrm{L}$. Alas it changed very little, if anything: the redistilled alcohol was still basically undrinkable!
The contrast between the redistilled alcohol and cheap commercial gin is quite stark.
I measured the paper $\text{pH}$ of both and they were both essentially neutral.
That redistilling didn't remove the offending compound(s?) suggests that  its BP is close to that of ethanol or that it forms an azeotrope with it.
The smell and taste of the mystery congener(s?) doesn't really comply with what is usually suspected to be in the 'heads':

$\text{MeOH}$ smells and tastes very much like alcohol (and in any case should only be present in very small amounts)
acetone and ethanal probably are too low boiling to remain partly in the 'heart'. Ethanal has a pleasant odour anyway.
all the low boiling esters have pleasant, fruity flavours.

My questions are:

What could be the problem congener{s)?
How to further investigate to find out what might be the problem congener{s)? I don't have access to modern analytical techniques like IR, GC, GC-MS etc.

I do have access to $\text{TLC}$ and a $1\mathrm{L}$ lab still with an $800\mathrm{mm}$ Vigreux column.


texts: Why copper wires submerged in salt (or fresh) water oxidize much faster while they conduct electrical current?

texts:
On a lot of flooded vehicles (salt/fresh water), I've noticed that wire that carries more current is always the one with most destruction (at the connector/splice), in comparison with lower current carrying wire. Wire turns black on the outer layer, accumulating green/white oxidation(?) on top of it.

How does electricity affect the rate of oxidation?


texts: How to write a wave function for infinite potential well with different width than from 0 to a?

texts:
I am working on the perturbation theory problem with the infinite potential well. However, I am not sure how to write a wavefunction for different than the infinite potential well from $0$ to $a$ and in my problem the well is from $0$ to $2a$.

Is it necessary to solve the potential well all over again? Maybe it is possible just to apply the transformation as $a\rightarrow2a$, for the initial wavefunction

$$\psi(x)=\sqrt\frac{2}{a}\sin\left(\frac{n \pi x}{a}\right)$$ ?


texts:
First order phase changes occur when one local minima of the Gibbs Free Energy becomes deeper than another. Thus at 1 atm and 99 °C, the Gibbs Free Energy of liquid water is less than the Gibbs Free Energy of steam at those conditions (though both states form local minima). As the temperature increases, the relative depths of the two minima change: at 100 °C they are the same depth, and above 100 °C the vapour-phase minimum is lower.

I'm wondering if similar first-order changes can occur in chemically reacting systems? It seems to me that equilibrium constants always change continuously with temperature: are there any situations in which this isn't the case, and there exist discrete jumps in chemical compositions? And if these jumps in the deepest minima of the Gibbs Free Energy never occur in chemically reacting systems, do we know why not? Of course, situations in which a chemical reaction is accompanied by a phase change don't count!


texts: Effect of impurities on melting and boiling points

texts:
I am tutoring my nephew for his science GCSEs; and his chemistry textbook states that you can tell how pure any compound is by how close its melting and boiling points are to the "official" mp and bp for that compound. It says that impurities will always lower the melting point of any compound, but - paradoxically (intuitively speaking) - will always raise the boiling point. But it just states this as a fact and offers no explanation!
I found a simple explanation for why the melting point is reduced in the case of crystalline solids:

Foreign substances in a crystalline solid disrupt the repeating pattern of forces that holds the solid together. Therefore, a smaller amount of energy is required to melt the part of the solid surrounding the impurity. This explains the melting point depression (lowering) observed from impure solids.

... although this doesn't explain why impurities in solids that are not crystalline also lower the melting point.
But I can't find any easy to understand explanation anywhere for why impurities would always increase the boiling point of any compound. I've found explanations that are specific to water (and even then, the explanations I've seen only make sense if the impurity binds more strongly to water molecules than water molecules bond to each other, which isn't always the case); and I found one explanation that says it's because of increased solution phase enthalpy, without explaining what on earth that means!
So I emailed a Professor of Physical Chemistry about this and she replied

The reason for impurities lowering the melting point yet increasing the boiling point is because the impurities stabilise the liquid phase, making it more energetically favourable. This extends the liquid range to lower temperatures (lowering the melting point) and to higher temperatures (raising the boiling point). The liquid phase is stabilised due to the entropy increase when you have the impurity (or any solute) in the liquid.  Normally solids do not dissolve the impurities, so the melting point involves transition to pure solid (with impurity separating out or staying in the liquid state).

She made it clear she didn't have time to answer any follow-up questions, and I can't make full sense of her answer, so I am hoping someone here can understand her explanation and elucidate it.
I think I understand why impurities increase the entropy of a substance in its liquid phase by more than they increase the entropy of the same substance in its solid or gasseous phases - I presume impurities don't significantly affect the entropy of a solid because the solid can't rearrange itself into different configurations without absorbing a lot of energy; and they don't affect the entropy of a gas because the gas can disperse over an almost infinite distance to all intents and purposes, so it will be almost infinitely disordered even when pure; but they do increase the entropy of a liquid because there are many more ways of arranging the molecules within a liquid if there is more than type of molecule in that liquid, and the molecules in a liquid can rearrange themselves in all those different configurations without any input of energy.
First of all, have I got that much right?
But even if I have, I don't understand why increasing the entropy of the liquid by adding an impurity to it would make it energetically more stable - and therefore both more difficult to freeze and more difficult to vapourise.
Can anyone help to explain this?
Dave


texts: Are there any STP liquids not containing large amounts of hydrogen and oxygen that are safe for human contact?

texts:
I'm working on a science fiction short story and was wondering if there were any liquids that would be safe to bathe in while traveling on a space craft with artificial (spin-based) gravity.  In such a context hydrogen and oxygen are valuable resources not to be wasted.  While bath water could be recycled, it is not available for other uses while someone is sitting in it, so I was wondering if there are other liquids at Standard Temperature Pressure that would be safe to bathe in (potentially ingesting small amounts).

I thought of using carbon bucky-ball fullerenes in a fluid but the viscosity looks to be much too high (essentially tar-like).  I know there are waterless chemicals that can be used for cleaning (e.g. DryBath), the purpose of this is more to have a hot-tub to relax in than to disinfect and clean.  If the addition of some hydrogen and oxygen (either as H2O or in other compounds) can improve the viscosity or is necessary to form the liquid, that is acceptable as long as less than 10% of the liquid is comprised of hydrogen and oxygen.  The purpose is to save water and oxygen for air while still being able to soak in a hot-tub.

Unfortunately most oils contain a substantial amount of hydrogen and some oxygen, so they don't qualify unless the amount of carbon offers substantial savings in volume.  I'd prefer something without any hydrogen or oxygen if such a chemical exists.

This is my first post here and I'm unfamiliar with the tags, so feel free to edit or add any you feel are appropriate.


texts: Does hyperconjugation into sigma-star explain methylamine's increased basicity relative to ammonia?

texts:
The inductive effect with the polarisation of the C-N bond obviously plays a role in stabilising the positive charge of the conjugate acid. But given the similar electronegativities for C and H, CH3 group should donate as much electron density to N as H does (roughly), if only the bonding atoms are considered. And if we're considering atoms other than the two bonding atoms in their contribution to stability, is it not a question then of hyperconjugation?

This question seems to deny hyperconjugation plays a role in stabilising ammonium derivatives. However, it takes a very narrow view of hyperconjugation and focuses only on electron density donation into bonding orbitals. But if more substituted double bonds are more stable because of the donation of alkyl groups into pi-star orbitals, antibonding orbitals must be viable recipients. And similarly in methylammonium, we have sigma-star orbitals on the positive nitrogen which the C-H bonds of the methyl should be able to donate into, destabilising the N-H bond in methylammonium but overall stabilising the system.

So, my question is does hyperconjugation from sigma C-H bonds into sigma-star orbitals of sp3 centres occur, and then from that - does hyperconjugation explain methylammonia's strength (or alkylammonias' strength, more generally) relative to ammonia?


texts:
According to this video:

http://www.youtube.com/watch?v=ns4Py96Bkn8&NR=1

1) Is this true? (You might recall I asked a similar question about $\ce{sp^2}$ hybridization implying $\ce{sp^2}$ hybridization for all directly linked atoms a while back, but I couldn't remember my prof's exact wording). I think this YouTube video is saying the same thing my prof said.

2) Does this rule imply that both the oxygens in the below diagram are $\ce{sp^2}$ hybridized? Each is connected to an $\ce{sp^2}$ carbon atom. Each has lone pair(s).

3) Even if we didn't know that the rule existed, we should still know that both oxygens are $\ce{sp^2}$ hybridized because of the following resonance possibility, correct?

ETA:

If the above is true then this doesn't make sense:


texts: Why is the A-value of methoxy group lower than that of the hydroxyl group?

texts:
I am studying conformational analysis of monosubstituted cyclohexane. "A-value" refers to the energy difference between conformers with substitutent in equatorial (more favored) and axial positions. A higher A-value means that the axial conformer will more readily convert to equatorial.
According to Wikipedia, methoxy has A-value of $0.6 \text{ kcal/mol}$ while that of hydroxyl is $0.87 \text{ kcal/mol}$. Why does methoxy, a bulkier group, have a lower A-value than hydroxyl?
I think that in both cases the group attached to the oxygen faces away from the axial hydrogens, so the size of those groups shouldn't matter very much. That is to say, the A-value of methoxy may be the same as or at the most only slightly larger than that of hydroxyl. This explanation does not suffice as its A-value is in fact smaller.
A possible reason could be that the $\text{C-O}$ bond is shorter in methoxy than in hydroxyl. However, I don't understand why this should be true. Hints would be appreciated.


texts: Is there geometrical isomerism in case of 2-methylcyclopentanone?

texts:
How can 2-methylcyclopentanone show geometrical isomerism?
A ring and a double bond are in different planes, so even after having restricted rotation there will be no change in areal distance.


texts: What makes trans fats more harmful than saturated ones?

texts:
Why are by many trans fats considered to be worse for you than fully saturated fats?

I am asking specifically which of their structural features accounts for this condemnation. They won't form clumps any larger nor will their melting temperature be higher than that of saturated fats, unless I'm mistaken, so it must be due to the double bonds' reactivity in trans configuration. But is it different from that in cis one?

It's sometimes suggested that trans fats increase low-density lipoprotein (LDL) and decrease high-density lipoprotein (HDL) - could that solely result from the properties of the trans configuration of the molecules?


texts: Why does formaldehyde exist primarily as the gem-diol in aqueous solution?

texts:
From Wikipedia,

Methanediol is the product of the hydration of formaldehyde $\ce{H2C=O}$, and predominates in water solution: the equilibrium constant being about $10^3$ and in a 5% by weight solution of formaldehyde in water, 80% is in the methanediol form.

As far as I know, carbonyl compounds usually don't exist in their gem-diol form, unless there's a stabilizing effect (like H-bonding, release of angle strain, inductive effect etc.), which we observe in ninhydrin, chloral, hexafluoroacetone, etc. (relevant image) But such effects don't seem to be the case for formaldehyde.
My question: What is the stabilizing factor in the case of hydration of formaldehyde?


texts: Liquid nitrogen is approximately -330 degrees Fahrenheit. Liquid neon is approximately -413 degrees Fahrenheit. I want to know about if this type of freezer is easily possible in practice and if such a freezer actually exists. The idea is to keep the matter as cold as possible and combine it with a noble element that doesn’t react with anything that we know of due to electron configuration. The idea of liquid neon is to stop effectively all biological activity and chemical reactions, because liquid nitrogen is both hotter and not a noble gas, though liquid neon is not a noble gas though neon usually is.


texts: Bond formations in doping of semiconductors

texts:
I was reading about semiconductors and found out that semiconductors are doped with either 13th group or 15th group elements which are named p-type and n-type semiconductors, respectively. In n-type semiconductors I found out about the following:

Why does antimony form four bonds with silicon when it could just bond with three silicon atoms and have a lone pair instead of having an electron excited and have a free electron?


texts: Ingredients for cleaning optical elements

texts:
I have recently purchased a cleaning solution for precision optics which has the following ingredients (amounts were not specified):

Ethyl Alcohol
Methylethylketon
Aqua
Diethyl Ether
Isopropyl

Typically reagent grade isopropyl alcohol alone is used for cleaning optical elements. So, does the mixture above provide any advantages over using pure isopropyl? (Possible advantages may include a faster dry time, better removal of oils/smudges, and less toxicity)

Any explanations would be greatly appreciated.


texts: Why is  cis-1,2-cyclohexadiol less polar than trans-1,2-cyclohexadiol?  I know it has something to do with stability and chair conformations, but I'm not sure how it relates to polarity.  I know cis-1,2-cyclohexadiol has a more stable chair conformation than trans.


texts: How can an inexperienced chemist determine the chemical structure of a molecule?

texts:
I'm a fairly inexperienced, but nonetheless interested chemist, currently planning a small project for the coming summer: I want to isolate an unknown chemical from a plant and determine it's chemical structure.

I have ample access to Carex grayi, a sedge plant, and have chosen this plant for a few reasons.

Of the plants growing near where I live, I can definitively identify Carex grayi. I am relatively inexperienced in taxonomy and plant identification, and I want to know which species I am working with.
As far as I can tell, the plant is relatively unresearched, and may or may not contain alkaloids.

This brings me to my next point. I know it may seem immature or disheartening, but my interest in chemistry stemmed from my interest in neuroscience and neurotransmitters. From countless hours of reading, I have learned much about the pharmacological (and sometimes psychoactive) tendencies of alkaloids. I realize that ingesting unknown alkaloids is extremely dangerous, and I do not intend to ingest anything. However, due to their numerous applications in medicine and recreational use, there is a massive amount of information on the internet regarding their extraction and isolation. I am entirely open to the idea of isolating a chemical from another group, but as I am inexperienced and my interest stems from neuroscience, I only really know about alkaloids. I am only somewhat familiar with terpenoids, and know little about any other group.

So, assuming I am able to extract an unknown chemical of some specified group from a plant, is there any way for me to determine the chemical's structure? The Chemical structure Wikipedia page lists the following methods for determing chemical structure:

X-ray diffraction
Proton NMR
Carbon-13 NMR
Mass spectrometry
Infrared spectroscopy

I don't really have access to these tools as student over the summer. I am willing to spend a small amount of money on this project, but no more than about one hundred dollars. Is it too much or too difficult for a student to determine a chemical's structure over the summer? Should I do anything differently (as in, is there a certain group of chemicals that would make this project possible or easier)?

Also, is there a "classical" chemical extraction similar to this that most fledgling chemistry students would conduct? This is obviously a ridiculous made-up example: extract dandylionine from a dandy lion flower.


texts: Cis and trans substituents on rings different stereodescriptors

texts:
The attached two compounds are diastereomers. They can be differentiated by cis/trans descriptors. Is there another way of describing them as cis/trans seems to be outdated?

EDIT: How to determine the r/s configuration of the pseudochiral C atoms in this case? The usual rule is that R precedes S, but here two identical groups are bounded to the same pseudochiral atom. How to assign r/s in this case?


texts: Why is there a z² label for d orbitals, but no x² and y² labels with corresponding shapes?

texts: I know that the $\mathrm{d}_{z^2}$ orbitals are named as a result from the conversion of the angular component of the hydrogen-like wave function in terms of Cartesian coordinates, but how come we lack analogous orbitals along other axes, such as $\mathrm{d}_{x^2}$ or $\mathrm{d}_{y^2}$? My naive assumption would be due to the fact that $z$ axis is considered the principle axis in regards to chemical bonds, but I don't feel that this is the best answer, nor can I seem to come across anything in textbooks or articles online.


texts:
My friend and I are trying to synthesize mercury thiocyanate, however the only reagents we have access to are mercuric acetate and ammonium thiocyanate.
We figured that we could possibly force a substitution reaction with these reagents in alcohol over heat with stirring.
It worked, but after a few moments the solution turned yellow and after diluting with water (since mercury thiocyanate is insoluble in water and ammonium acetate is the opposite) the precipitate was yellow.
Was there a possible side reaction that occurred? If so what was it? And why is it yellow? I am accrediting that to the sulfur, but I could be wrong as I am a novice chemist.
I don’t have many peers to ask and would appreciate some input!


texts:
Please bear with my long winded description.

It is classical to model radioactive decay of some particles $A \rightarrow A^\ast$ by the differential equation
 \begin{align}
 \frac{\mathrm dN_A}{\mathrm dt}=-\lambda N_A
 \end{align}
where $N_A$ refers to the number of particles in state $A$ and $\lambda$ is the rate of decay. If we initially start with
$N_0$ number of particles in state $A$ then by solving the above differential equation we see that
\begin{align}
N_A(t) = N_0\mathrm e^{-\lambda t}
\end{align}
gives us an explicit number of particles in state $A$ as a function of time $t$. In particular, we also see that
\begin{align}
\lambda = \frac{\ln 2}{t_{1/2}}
\end{align}
where $t_{1/2}$ is the half-life. However, the model is completely deterministic, meaning no probability required.

However, quoting Wikipedia

  Radioactive decay is a stochastic (i.e. random) process at the level of single atoms, in that, according to quantum theory, it is impossible to predict when a particular atom will decay, regardless of how long the atom has existed.

But collectively, the mean number of particles in state $A$ is well modeled by the above deterministic model. However, the
difficulty here is to articulate the connection between the deterministic model and the stochastic model in a rigorous manner.

Let $T$ be a continuous positive random variable (RV) that denotes the lifetime of a single (microscopic) particle in state $A$. It is natural to make the assumption that in the stochastic model the decay of a particle in state $A$ is independent of the time that the particle spends in state $A$. With this assumption and a little bit of math (which is not important for the discussion), one can show that $T$ has an exponential distribution with a parameter $\lambda$, i.e. the
  PDF of $T$ is given by
  \begin{align}
  p_\lambda (t) =
  \begin{cases}
  \lambda\mathrm e^{-\lambda t} & \text{ if } t \geq 0,\\
  0 & \text{ if } t<0.
  \end{cases}
  \end{align}
  and the cumulative distribution function (CDF) is given by
  \begin{align}
  P(t\geq T) = 1-\mathrm e^{-\lambda t}
  \end{align}
  for $t \geq 0$ and 0 otherwise. In particular, we see that the probability of the particle in the decayed state $A^\ast$ at time $t$
  is precisely $1-\mathrm e^{-\lambda t}$ and the probability in of the particle in the state $A$ is $\mathrm e^{-\lambda t}$. Hence at each fixed time
  $t$ we have a Bernoulli distribution. If we make another assumption that a collection of the radioactive particles decay independently, then we see that given $N_0$ particles at time $t$ the probability that $N$ particles survives and $N_0-N$ particles decay is given by
  the binomial distribution
  \begin{align}
  P(N_t=N) = \frac{N_0!}{N!(N_0-N)!}(1-\mathrm e^{-\lambda t})^{N_0-N}\mathrm e^{- \lambda N t}
  \end{align}
  By standard computations, we also see that the mean of the binomial distribution is $\operatorname{E}[N_t]= N_0\mathrm e^{-\lambda t}$ and the variance is $\operatorname{Var}[N_t]= N_0\mathrm e^{-\lambda t}(1-\mathrm e^{-\lambda t})$ which leads to the relative standard deviation
  \begin{align}
 \frac{\sqrt{\operatorname{Var}[N_t]}}{\operatorname{E}[N_t]} = \frac{1}{\sqrt{N_0}}\left(\mathrm e^{\lambda t}- 1\right)^{1/2}.
  \end{align}

I have two questions.

  Question 1: Looking at the relative standard deviation, it seems to me that for very large time $t$ the deterministic model seems to be a poor approximation of the stochastic model since the relative standard deviation grows exponentially in time. Is my assertion valid?

I actually disagree with the above calculation but have no valid argument against it.

  Question 2: My interest in the above analysis comes from my desired to give a rigorous justification for using Monte-Carlo simulation of radioactive decay to arrive at the above deterministic model. However, I'm stuck after the above analysis. Could someone provide me with some reference or explanation to rigorous justify the connection?


texts: Do atoms form either a positive or a negative charge, but not both?

texts:
I do not mean at the same time, of course, but I mean it appears from an overview of the common charges formed from ionizing various elements that each element forms one or more of either positive or negative ions, but they never have the opposite charge. For example Fe may have +4 or +3, but never -anything.
However, I am aware that this is from a common ion chart. Perhaps an atom can be a cation and an anion under specific circumstances?


texts: Expected accuracy of experimental IR spectra compared to literature reference

texts: I have a table from a journal which indicated signals of an alpha chitin that I used as theoretical values. I did my own analysis to identify a chitin sample and it had signals that slightly varied from the theoretical (ex. $3106\ \mathrm{cm}^{-1}$ symmetrical N-H vibration and I got $3103\ \mathrm{cm}^{-1}$). Should I consider this? And what caused the variation?


texts: What reagents or series of reactions would allow for selective hydroxylation of an allylic methyl group outside of a ring?

texts: Sample transformation for selective hydroxylation of an allylic methyl group outside of a ring. Selenium dioxide would not work since hydroxylation would be favored inside the ring.


texts: Effect of passing hydrogen sulfide gas on electrode potential

texts:
Consider the cell reaction
$$\ce{2Ag+ + Pb <=> 2Ag + Pb^2+}$$
If $\ce{H2S}$ gas is passed through the solution, what will be the effect on the EMF of the cell?

My attempt:
The Nernst equation for the EMF of a cell results in
$$\mathcal{E}=\mathcal{E}^\circ-\frac{RT}{nF}\ln{\frac{[\ce{Pb^2+}_{(aq)}]}{[\ce{Ag+_{(aq)}}]^2}}$$
Now, I assumed that $\ce{Ag2S}$ was more covalent and hence less soluble in water than $\ce{PbS}$, by Fajan's rule, due to smaller size of cation and pseudo-inert gas configuration  and hence it would precipitate out more. hence the ratio
$${\frac{[\ce{Pb^2+}_{(aq)}]}{[\ce{Ag+_{(aq)}}]^2}}$$
would decrease and hence the EMF of the cell would decrease.
Is my reasoning correct? I do not have the answer with me.


texts: How do you figure out the positional and chain isomer possibilities of a compound?

texts:
I need to figure out the chain and positional isomers of C4H7Cl. I am not looking for someone to directly give me the answer, I just want to know what steps are needed to be able to figure them out for a given compound.

This is different to my prior question. Here I am asking for the technique, not the direct answer. Thanks.


texts: Can anions be reduced at the cathode in an electrochemical cell?

texts:
Two related questions:

(1) It's my understanding that for a galvanic cell, as electrons flow from the anode to the cathode, the cathode (+) becomes negatively charged due to the accumulation of electrons. If I have a sodium chloride electrolyte, the sodium ions will move toward the cathode. However, does that mean chloride will not be reduced at the cathode?

(2) Is the same true for an electrolytic cell? The cathode is (-), so I assume it stays negative. But, what if I wanted to force the reduction of an anion like perchlorate - is it possible or will there be too great of an electrostatic barrier?

I see people reporting on the electrocatalytic reduction of anions, but I don't understand how this is possible if the ionic current is the opposite direction.


texts:
In the textbook "Molecular Quantum Mechanics" by Atkins and Friedman [1, p. 11], it says in chapter 1:

  … a general function can be expanded in terms of all the eigenfunctions of an operator, a so-called complete set of functions.

Can ANY function be written as a linear combination of eigenfunctions of ANY operator? I think not.

What are the criteria here for which functions can be written as linear combinations of which operators?

References

Atkins, P. W.; Friedman, R. Molecular Quantum Mechanics, 5th ed.; Oxford University Press: Oxford ; New York, 2011. ISBN 978-0-19-954142-3.


texts: Effective nuclear charge of oxygen atom (O) vs oxygen anion (O2-)

texts:
The size of an anion is greater compared to its parent atom because former's effective nuclear charge is lesser than that of latter.

I found on wikipedia that the effective nuclear charge can be calculated by the formula:

Zeffective = No. of protons in the nucleus - No. of non-valence electrons

For oxygen atom, the electronic config is: 1s2 2s2 2p4

For oxygen anion, the electronic config would be: 1s2 2s2 2p6

Zeffective for oxygen atom = 8 - 2 = 6

Zeffective for oxygen anion = 8 - 2 = 6

If the effective nuclear charge is staying the same, then how it can be said that the size of an anion is greater than that of its parent atom?


texts:
If you can use precipitate colours to determine an anion, what makes the precipitate have that particular colour?

Like for example what in sodium sulfate or barium chloride makes a white precipitate when these two combine?


texts: Why plastic sheets contract when heated?

texts:
Why do thin plastic sheets contract when heated, contradictory to the behavior of most other materials ?

What are the things going on at the molecular level ?


texts: Are the best buffers those that are in a 1:1 ratio with its conjugate acid/base?

texts:
I wanted to comment this, but I don't have enough reputation, so I just made this a question. I know that buffers and their conjugate base/acid must exist in similar amounts for the buffer to be effective, so would the buffer be most effective when the ratio is close to 1:1 (of the buffer and its conjugate acid/base)?

Also I'm confused about how much of a weak base/acid buffers should be. If you have a very weak acid, then wouldn't you have a very strong base. In this case will the buffer be ineffective? So the upshot of this paragraph is asking will buffers still work if you have a very weak acid?


texts: Will dioxygen difluoride set fire to sand?

texts: I've heard that dioxygen difluoride (a.k.a FOOF) would set fire or react with nearly everything including sand ,bricks or even ice. Is this true?


texts:
I'am working on this exercice, Is my answer correct? and can you please help me to solve the second part?

exercice:

1/Calculate the ionization coefficient and pH (with two methods) of a 0.1M ammonia solution of pkb = 4.7

2/ to one liter of the previous solution, an equal volume of water is added. Calculate the new ionization coefficient and deduce the pH of this new solution

1/ For the first part my answer is :

$\ce{NH3  +  H2O = NH4+   +  OH^-}\tag{1}$

$Ka = \dfrac{\ce{[NH4+][OH^-]}}{\ce{[NH3+]}}\tag{2}$

The coefficient of ionization $\alpha$

$\alpha = \sqrt{Ka/C°}\tag{3}$

$Pkb = \log{kb}\tag{4}$

$Kb= 10-pkb\tag{5}$

$\alpha =0,014\tag{6}$

Two methods:

First one:

$pH= \frac{1}{2} (pka + 14 + \log{C°})\tag{7} $

$pka + pkb=14\tag{8}$

$pH = 11,15\tag{9}$

second method:

$14 + \log (\alpha C°) = 11,15\tag{10}$

for the second part, i am lost

Thank you


texts: Would molybdenyl chloride or tungstenyl chloride work as an alternative to chromyl chloride test?

texts:
(This is a follow up of this question)

Chromyl chloride test is by far the best test to determine the presence of chloride ions in a salt because no analogous compounds are formed with fluorides, bromides, iodides and cyanides, so this test is therefore specific for chlorides. This test is considered selective for $\ce{Cl−}$.

But can molybdenyl chloride work similar to that of chromyl chloride?.  I couldn't find enough information in the internet about the feasibility of the compounds as a replacement to chromyl chloride. What about tungstenyl chloride?

In this link, I found a preparation process of molybdenyl chloride but that doesn't follow the same reaction used to make chromyl chloride. It uses common salt, sulfuric acid and molydenum trioxide. This made me curious. Common salt contains chloride that ultimately reacts with other reagent to form molydenum chloride. If I use another chloride containing compound and react with the other reactants, will molydenyl chloride form?. I am aware of thermodynamic or kinetic aspect of the reaction for its feasibility but still will the reaction count as a form of 'molybdenyl chloride test'?


texts:
Suppose you have the following equation:

$$\ce{2NH4SCN(s) + Ba(OH)2(s) ->Ba(SCN)2(s) + 2H2O(l) + 2NH3(g)}$$

You initiate this reaction using 15.22g of the $\ce{NH4SCN}$ (and excess of the barium hydroxide) in a boiling tube resting in 50g of water. The temperature rises by 11 degrees. Therefore energy = $4.2 \times 11 \times 50 = 2.31kJ$ and moles = $\frac{15.22}{76.1} = 0.2mol$

I would then assume that it would just be $\frac{2.31}{0.2} = 11.55kJmol^{-1}$

But the actual answer is 23.1 (double my answer) which I am guessing is because there are 2 moles of $\ce{2NH4SCN}$. I do not understand why this is the case, because you are using 0.2 moles and the energy raised is 2.31 so why the multiplication by 2?


texts: Change in pH when boiling off acidic water

texts: Assume 1 L of deionized water at pH 2 at ambient pressure open to atmosphere. I boil off 500 mL. I believe the pH will not change because to the same extend as water boils off it will also boil off H+ ions. Correct?


texts: Why can copper have both four and six bonds?

texts:
I'm trying to understand the Biuret test by first understanding how copper dissolves in the aqueous solution. We first have added the $\ce{CuSO_{4}}$ to a substance than the $\ce{OH^{-}}$.

I've read the following page on the reaction, but I still confused: http://www.docbrown.info/page07/transition09Cu.htm

How is it possible to have tetraaquacopper(II) and hexaaquacopper(II) ions in the solution? How could this configuration be explained using electron configuration? $[\ce{Ar}]\mathrm{3d^{10}4s^{1}}$


texts: How to develop a Reactive Force Field (ReaxFF)? (Molecular simulation)

texts:
Currently, I am working on CO2 capture on Hydrotalcites as solid adsorbents. I want to run molecular simulations to analyse the behaviour of the material under different temperatures, pressures and CO2 concentrations.

In order to do so, I am working in ADF, with the ReaxFF method. Nevertheless, there are no force fields generated specially for this kind of material. That is why I am building one by comparing data from existing force fields and selecting the data from the most similar to my project. However, I am not sure this approach is the best. I have read the ReaxFF manual (https://www.scm.com/wp-content/uploads/ReaxFF_training.pdf) but could not make a lot of sense of it. The ReaxFF manual of van Duin (https://www.scm.com/wp-content/uploads/ReaxFF-users-manual-2002.pdf) explains better but fails to say how to manipulate the data.

Does anyone know how to develop a Force Field input file for ReaxFF?


texts: What is the difference between ''1 C atom and 1 mole of C atoms?''

texts:
Does 1 C atom mean 1 single C atom out of Avogadro's number of C atoms = 1 single C atom out of 6.023 X 10^23 numbers of C atoms?
Does 1 mole of C atoms mean Avogadro's number of C atoms = 6.023 X 10^23 numbers of C atoms?

I am confused. Could you clarify it, please?


texts:
The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at $T = \pu{298 K}$ are $\pu{0 kJ mol-1}$ and $\pu{2.9 kJ mol-1}$, respectively.
The conversion of graphite [C(graphite)] to diamond [C(diamond)] reduces its volume by $\pu{2e-6 m3 mol-1}$.
If C(graphite) is converted to C(diamond) isothermally at $\pu{T = 298 K}$, the pressure at which C(graphite) is in equilibrium with C(diamond), is
(A) $\pu{14501 bar}$
(B) $\pu{58001 bar}$
(C) $\pu{1450 bar}$
(D) $\pu{29001 bar}$

We know that
$$\mathrm{d}G = V\mathrm{d}P - S\mathrm{d}T$$
At constant temperature, $\mathrm{d}T = 0$ and we are left with
$$\mathrm{d}G = V\mathrm{d}P$$
But as the volume is also changing in conversion of graphite to diamond and the pressure has also to be increased, how do I integrate this equation? Please tell me if I'm going wrong.


texts: Is there a non-violent, practical way of making hydrochloride with only Hydrogen and Chlorine?

texts:
A way of making HCl gas is to put Chlorine and Hydrogen into a test tube and expose it to UV light.

This reaction is however fast and strong and I would like to store the Hydrochloride from it.

Another way would be to dissolve Chlorine in water, which would make Hydrochloride, but most of it would go in water and make dilute hydrochloric acid. I could however store the HCl fumes from the dilute acid. I do not know about the practicality of this.

What is the best, and exceptionally practical way of making Hydrochloride when the only resources I have are Hydrogen and Chlorine?


texts: Does 11.2 dm3 of nitrogen consist of 0.5 moles at STP?

texts:
Which of the following statements is true?
$\pu{11.2 dm^3}$ of nitrogen at STP-
A: has a mass of $\pu{14 g}$.
B: consists of $\pu{0.5 mol}$ atoms.

My instinct was that the answer is B because any gas has a volume of $22.4$ liters regardless of what the gas is. If $\pu{0.5 mol}$ of nitrogen has a volume of $\pu{11.2 dm^3}$ at STP, then $\pu{1 mol}$ of nitrogen has a volume of $22.4$ liters at STP (if I am correct).
It turned out the answer was A. Why is B not the correct answer?


texts: I was taught that Avogadro's number was $6.023 \cdot 10^{23}$. Now, the accepted value is allegedly $6.022 \cdot 10^{23}$. Has there been a change? If so, when and why? There are still some sites that use $6.023 \cdot 10^{23}$, so if this is wrong, why have those sites not been corrected?


texts: Is exposure to amyloid beta proteins dangerous?

texts:
Recently, I began working in a lab in which our main area of study is Aβ peptides. My concern is whether or not exposure to high levels of Aβ proteins is hazardous.

I suspect that the peptides cannot pass through one's dermis, but this is just speculation. Also, if one were to accidentally ingest Aβ, it would likely be broken down into its monomers by your digestive system before it could cause any harm.

I've tried to find resources covering my concerns but to no avail.


texts: What is a possible side reaction during the oxidation of fluorene? 9-fluorenone is synthesized, but what else?


texts:
The textbooks I have read introduce LCAO by considering the H2 molecule. In this example, there are only two possible combinations of the two 1s orbitals (in phase and out of phase).

When there are more than two valence orbitals, however, a greater amount of combinations arise. A common description of the pi-MOs in butadiene is shown below:
There are two (and I think only these two, assuming all combining p-orbitals are identical) possible combinations of the p-orbitals which (apparently) do not contribute to the bonding in butadiene. These are shown at the bottom of the illustration above.

Why is it that n AOs only form n MOs, even when more than n LCAO are possible? You would think that all possible combinations would contribute a possible electron energy state to the molecule.


texts: Enthalpy change defined at constant pressure only?

texts:
Is change in enthalpy defined only at constant pressure?

I know Q-W=del(U)
And Q at constant pressure equals del(H) (enthalpy change).

Can Q (heat given to the system) be used interchangeably with del(H) in the first equation?

Is del(H) =nCp del(T)?
How?


texts:
Critical points are defined (by wikipedia) as the "end-point of the phase equilibrium curve".

I would say this diagram therefore has three critical points. But this is unnatural. I doubt its true.

Other curves are different from the ones with critical points because "they can run to infinity". But I think thats ridiculous because its physically impossible.

I don't know if I'm interpreting PDs correctly but I think that what defines that you are on a phase in these diagrams is that if you travel along a horizontal line you meet with a phase equilibrium curve.

If you don't then you were either on a single phase the whole time or on a sort of "critical phase".

I don't like it though. For example if you travel along a horizontal line that wont intersect the L-V curve, how would you know when the LV critical phase is present? Regions are not clearly defined here, except for monoclinic.

Whats wrong with my ideas?

How many critical points does this diagram really have and why?

Thanks.


texts:
We say that a homogeneous sample consists of the chemically same type of molecules whereas heterogeneous ones vary chemically, i.e. the molecules throughout are not same and also not uniform.
Why do we treat a (water + water vapour) system as heterogeneous in spite of the presence of the same kind of molecules? Also if there exists an equilibrium in the two phases would we still not call them homogeneous?
Does heterogeneity have a chemical basis or physical basis?
I do not seem to get a clear idea as to what defines heterogeneity. The definition has kept on changing since my high school and later on.


texts:
What is the hybridization and angle (in degrees) with respect to the y-axis for the following hybrid orbital $ψ=\frac{1}{√3}c×(s-\frac{1}{√3}×p_x+\frac{√3}{√2}×p_y)$
The answer given is 30 degrees but I couldn't figure out how.I was able to figure out that it is an $sp^2$ hybrid orbital wavefunction.Any help is appreciated.


texts: Electron configuration of non-hybridized carbon

texts:
I'm currently learning about orbital hybridization in carbon.
I see that carbon has an electron configuration of 1s2 2s2 2p2.
However, there are actually three p-orbitals in the second shell, namely px, py and pz, which could each hold two electrons. However, there are only two electrons to be distributed on these three orbitals. Which orbitals do they occupy? Since their energy levels are identical, is it random?
I also learned that the three p orbitals can be combined with the 2s orbital (sp3 hybridization) to form four new hybrid orbitals. It then makes sense that the four electrons available each occupy one of the four new orbitals (so that each of them holds one electron), because this way, they can have the greatest spatial distance to each other (I assume they "want" this as they repel each other).
However, how are the second shell electrons distributed in a non-hybridized carbon atom? Does such an atom even naturally occur or does it always hybridize?

Update: I found this question and this answer which both state that non-hybridized carbon has the configuration 1s2 2s2 2px1 2py1.
Why is this the case, and not, for example, 1s2 2s2 2py1 2pz1?


texts: Why the energies of orbitals in the same subshell decrease with increase of atomic number? For eg., energy of 2s orbital of hydrogen atom is greater than energy of 2s orbital of lithium atom. What is the reason?


texts: Calculating the pH of a buffer made by a diprotic acid and its double salt

texts:
The concentration of the diprotic acid (tartaric acid) will be constant at $\pu{ 0.1 M}$. I want to find the concentration of its double salt (potassium sodium tartrate) needed to create a buffer of $\pu{ pH }$=x (for example,x= 4.0). How would I do this? Do I have to use the Henderson-Hasselbalch equation? Make certain assumptions?

I tried to set up two equilibrium expressions with $K_\mathrm{a1}$ and $K_\mathrm{a2}$ as follows:

$$K_\mathrm{a1} =\frac{[\ce{C4H5O6-}][\ce{H+}]}{[\ce{C4H6O6}]}$$
and

$$K_\mathrm{a2} =\frac{[\ce{C4H4O6^{2-}}][\ce{H+}]}{[\ce{C4H5O6-}]}$$

Can I multiply $K_\mathrm{a1}$ and $K_\mathrm{a1}$ to eliminate$[\ce{C4H5O6-}]$, and then get the concentration of $\ce{C4H4O6^{2-}}$ necessary by plugging in $\pu{0.1M}$ for$[\ce{C4H6O6}]$ and the target $\pu{pH}$ in the appropriate form in $[\ce{H+}$]? I feel like I'm making some big assumptions here, though.

(Also, please forgive me; I don't know how to use LaTeX or Tex.)

If I try to make the assumption that the second dissociation does not occur as it is too weak (which it isn't) I wouldn't have the concentration of $\ce{C4H4O6^{2-}}$ in my equation, which is what I'm trying to find.


texts: What does it mean to say that a strong base is only slightly soluble?

texts:
I've often seen the hydroxides of Calcium, Strontium and Barium described as "strong bases that are only slightly soluble," or similar.  But strong bases dissociate completely in solution, so I would guess this means that such hydroxides dissolve only a small amount, but the dissolved portion dissociates completely.

But the problem with this interpretation is that these hydroxides are ionic compounds, and my understanding is that "dissolve" is essentially equivalent to "dissociate" for ionic compounds, i.e. ionic compounds dissolve by dissociating.

If there's no distinction between dissolving and dissociating for ionic compounds, what does the description "strong base that is only slightly soluble" mean?  How does it differ from the term "weak base?"

If there is a distinction, and it is possible for ionic compounds to dissolve without dissociating, how does such dissolution work?  I have a model for the distinction between dissolution and dissociation of covalent compounds: first the compound dissolves into separate molecules, then each molecule dissociates into two or more ions.  If ionic compounds can dissolve without dissociating, into what sort of particles do they dissolve? Formula units? Small clusters of ions?  Something else?


texts: Could XY crystal be a special case of X2YZ crystal?

texts:
There are some types of crystals we call them XY type (i.e. NaCl) or X2YZ type?
Could XY type be a special case of X2YZ type by assigning Y=Z?


texts: Sodium percarbonate and sulfuric acid reaction

texts:
If an excess sulfuric acid is added to a detergent containing sodium percarbonate, would it be possible for the excess acid to react with hydrogen peroxide?

I believe that the hydrogen peroxide will be released from the reaction with sulfuric acid given by this reaction

$$\ce{2Na2CO3·3H2O2 + 3H2SO4 -> 3H2O2 + 2NaSO4 + 2CO2 + 2H2O}$$

So if an excess acid is added will it react with hydrogen peroxide to yield peroxymonosulfuric acid?


texts: What does the subscript n on methylene groups in a cyclic alkene mean?

texts: I've recently come across an unfamiliar notation on a cyclic alkane. One carbon had parentheses around it with a subscript $n$. Does this refer to rings of variable sizes (i.e.  one or more $\ce{CH2}$ groups are located in this position)? If not, what does this refer to?


texts:
Usually maximum time we see then after cooking by gas there is no black spot on the pot. But continually burning can affect the pot surface and makes black powder.

My question is:

  What is the most acceptable reason that black powder(carbon) take places on the pot surface. Is it related to the burning temperature? or fuel reacts with the pot surface?


texts: Which cup of tea cools down more quickly?

texts:
There are 2 cups (both cups are identical) of tea which are served at the same temperature. Assume that the walls of the cup to be non-heat conducting. Which cup of tea cools down faster, a full-filled glass or a half-filled glass?

According to what I think, The walls of the cup don't make a difference and neither do the top and bottom surfaces. The only determining factor would be the volume of the tea. So what I came up with is that, somehow the cooling process by convection will be affected by the volume of the tea in the cup but I'm not sure about my above assumption and even if it's true how will the volume of the tea affect the cooling process by convection within the volume of the liquid?

Taking the initial temperature higher than the room temperature.


texts: 1H NMR of p-methoxy phenol, 32 possible lines?

texts:
This is a follow-up question, emerging from answering this one.

The Silverstein book 1 aims to rise awareness that not every 1H NMR signal that on first inspection may look like a doublet actually is a doublet.  Triggered by counting possible number of lines of signals for p-methoxy phenol

-- which would yield just 16 (two ddd) I came across this part of the book about p-chloro nitrobenzene:

(loc. cit., p. 175)

Question: For the sake of understanding this part I leave out a potential simplification of the 1H NMR spectrum if some of the centres of the signals of the aryl H's accidentally may coincide, or some parts of the multiplets overlap.  For a moment, I assume each aryl H's multiplet may be recorded without disturbance of the signals by any other aryl H.

Is my understanding of this section correct, in theory there were up to 32 (thirty-two) lines observable, as each of the aryl H's couples with the other three H's relatively in ortho, meta, para position, hence four ddd?

On the next page, the book actually displays an experimental 1H NMR spectrum of p-chloro nitrobenzene

and assuming the more intense peaks could be a partial overlap of two lines (not all of them are smooth), I "count" only 16 lines. As if -- a speculation follows -- obviously the p-coupling, as the one with the lowest coupling constant, was not-at-all resolved in this acquisition.

1 Spectroscopic Identification of Organic Compounds, Wiley, 6th edition, 1998, ISBN 0-471-13457-0


texts:
In Sodium Nitroprusside and related compounds (eg. brown ring complex) why is the oxidation state of NO +1 and not zero? It seems pretty unusual without any explanation.

Could anyone please explain this, and maybe provide a satisfactory theoretical explanation for the exhibition of 'unusual oxidation state'?


texts: Electron promotion in hybridisation: A misconception

texts:
Recently, I read through a short article on Nature Chemistry, written by Michelle Francl, titled "Talking to Pauling's ghost". The article talks about how electron promotion was never something that was conceived by Pauling when he devised the theory of hybridisation. Instead, it likely arose from misinterpretations and mistranslations over the years.

It has been established very well on this site that hybridisation does not refer to a physical process and is merely a mathematical construct. This is consistent with the view presented by Francl. However, what I do not seem to understand is why the alternative view of seeing hybridisation as electron promotion and orbital "mixing" has become so prevalent, if it is so inaccurate. Clearly, there must be some truth in the alternative view. Is there?

Reference: Francl, M. Talking to Pauling’s ghost. Nature Chem 2018, 10 (7), 688–689. DOI: 10.1038/s41557-018-0099-3.


texts: What is the nature of interstitial hydrides?

texts:
In my Chemistry book(NCERT Chemistry,Part 2, textbook for class 11, Pg 281). I found the mention of interstitial hydrides:

  Unlike saline hydrides these compounds are nonstoichiometric, for
  example $\ce{LaH_n, TiH_n}$ and $\ce{PdH_n}$, where the chemical composition is variable. Typical formulae are $\ce{LaH_{2.87}, YbH_{2.55} , TiH_{1.8}, ZrH_{1.9}, VH_{1.6}, NbH_{0.7}}$ and $\ce{PdH_{0.7}}$.

The book also said:

  Earlier it was thought that in these hydrides hydrogen occupies the
  interstices in the metal lattice producing distortion without any
  change in it's type. However recent studies have shown that except for
  hydrides of $\ce{Ni, Pd, Ce,  Ac}$ other hydrides of this class have
  lattice different from the lattice of the parent metal.

What does this mean? Please explain the nature of these compounds and type of bond present in them.


texts: What kind of compound absorption the 365nm UV light on TLC

texts:
What kind of compound absorption the 365nm UV light?

compounds that has benzene ring or conjugated pi bond, make a fluorescence on 254 nm UV on TLC.
what kind of moiety(functional group) make fluorescence on 365nm UV on TLC


texts: How can you build a model of tetrahedral coordination from objects found at home?

texts:
Our college is switching to teaching online mid-semester in hopes of slowing the spread of Covid-19. All the molecular model kits are still on campus. How could you build a model of tetrahedral coordination (say methane) from materials found at home?

I'm aware of computer visualizations (and will make those available), but I think having a physical model when first encountering three-dimensional structures adds value. I made a model from lawn toys (see below), but these are not common household items.


texts: Is atmospheric pressure acting only on the contents or also on the container?

texts:
$22~\mathrm{g}$ of dry ice is placed in an an empty $600~\mathrm{ml}$ closed vessel at $298~\mathrm{K}$. Find the final pressure inside the vessel, if all $\ce{CO2}$ gets evaporated?

Now by applying $pV = n\mathcal{R}T$, the value of $p$ comes out to be $20.4~\mathrm{atm}$, but in the solution shown, it adds $1~\mathrm{atm}$ i.e atmospheric pressure pressure, so the answer comes out be $21.4~\mathrm{atm}$. Now why do we need to add atm pressure, the question tells us to find the total pressure inside the vessel, isn't the atmospheric pressure acting only on the container, and not on its contents?


texts: Does electroplating fall off if I disconnect electrolytic cell?

texts:
So I understand the basic mechanism of electroplating. I want to ask is there any chance that the electroplating may fall off if I disconnect the electricity supply? As a consequence, should I recommend the plated object to be taken out of the electrolytic solution before disconnecting the electricity supply?

Specifically I want to know if disconnecting electrolytic cell can be the sole reason why the plating on an electrode may fall off.


texts: Which ideal gas law does a constant volume thermometer work on?

texts: I searches online for my question and found mixed answers. I think the Ans. Should be Gay Lussac's Law as we are dealing with a case of constant volume but variable pressure and temperature. In many books the answer is given to be Charles Law. Would appreciate if someone gave me the ans. Thanks.


texts:
Is the caffeine from green tea that is extracted acidic?
This goes for powder and liquid form.

If I add Alkaline water (pH: 7 or higher) will it change?


texts: When you carry out iodometric titration for determining the Peroxide value of a phospholipid mixture, the end point is the solution turning colourless. But, after some time the colour reappears. Do you stop at the first discoloration or continue titrating with sodium thiosulphate?


texts: Is there fire suppression in some phone batteries, and if so, how does it work?

texts:
I recently saw a rugged smartphone, three or four years old, with a ~5000 mAh battery, suffer a major impact to its back.  This wasn't a fall, it was a fast impact with a heavy object.  Immediately there was this loud hissing sound, and clouds of what looked like white and very-light-brown smoke came out of every aperture in the sides of the phone.  The "smoke" was not acrid, did not disturb my (quite sensitive) lungs, and smelled only like slightly peculiar burning, not even strongly plasticine.  There were absolutely no flames visible at all, the phone was warm and not hot to the touch within 30 minutes, and although the back of the phone had meltage visible, much of it was intact.
To me the above looked a lot like some sort of fire suppression system I had never heard of, which perhaps released a whole lot of CO2 or perhaps something else, to prevent anything more dangerous from happening.  Anyone know if this is true, and if so, how it works?


texts: Thermodynamic model of inclusion process of alpha-cyclodextrin

texts: I have a question about thermodynamic model of inclusion process of CD, published by Tabushi (DOI: 10.1021/ja00471a043). Here, in 3rd step, action is described as: "An apolar solute (guest molecule) is transferred from water to the ideal gaseous state leaving a structured cavity behind. The cavity then collapses with redistribution of the water molecules." I don´t understand this part where guest molecule is transferred to the gaseous state (why this state). Can somebody try to explain this in some simple way if it is possible, please? Thanks for all the answers!


texts: The toxicity of carbon monoxide in terms of its interaction with haemoglobin

texts:
On the basis of its interaction with haemoglobin, explain the toxicity of carbon monoxide.

I understand that ligand substitution is involved and carboxyhaemoglobin is formed meaning that the haem group in the haemoglobin molecule cannot form a ligand with the oxygen molecule, but i would like to know more in depth in terms of its chemistry, why this is the case.


texts: Why is the square of the wavefunction a probability density?

texts: Can anyone explain it in simple words? I tried to read about the Born rule on Wikipedia but it seems it is just describing the rule. Is there any proof that is suitable for person with no solid math background?


texts: How to increase the conversion of a reaction between an ammonium salt and ethylenediamine?

texts: I've been trying this reaction in my lab and there is the formation of the substituted ethylene diamine but along with that, I am obtaining some amount of RCH2N(CH3)2. The reaction is done under solvent-free condition using only excess of ethylenediamine. After the reaction, it is washed with water and the compound is extracted with DCM. Can anyone suggest me a method to ensure complete conversion of the ammonium salt? Increasing reaction time or temperature isn't showing any effect.


texts: What actually happens when 'energy is released'?

texts:
Thermodynamics classes and equations always discuss a chemical reaction in the form of energy being released or absorbed. This is always hand-waved as just 'energy' from the surroundings.

What's actually happening at a molecular level? When a bond is broken and 'energy is absorbed' to accomplish this, is the kinetic motion of the resulting species lower than the total kinetic motion of the species before it broke? Does something else happen?

When 'energy is released' on a bond being formed, does the new species then have a greater kinetic motion than the combination of the two species alone? Does this energy somehow translate to a change in energy level of an electron and a release of a photon at the subsequent decay?

Thanks in advance.


texts: Which electronic effects are responsible for the reduction of nucleophilicity of a hydroxy group orthogonal to an ester?

texts:
I am facing a similar synthetic problem as Boekman Jr. et al noted in their synthesis of Tetronolide.[1] I will quote their’s rather than disclosing my actual synthetic problem, but note that the key element — an α-hydroxy-γ-lactone is identical.

The authors’ intended convergent synthesis involves coupling the two compounds 1 and 2 shown in scheme 1 in a ‘tandem ketene-trapping/[4+2] cycloaddition’, which requires the free hydroxy group in 1 to nucleophilicly attack the ketene.

Scheme 1: Tandem reaction attempted by Boekman Jr. et al; would include a nucleophilic attack of 1’s hydroxide onto 2’s ketene motif.

However, as indicated this reaction did not produce 3. The authors note:

  However, despite considerable experimentation, all attempts to couple lactone [1] with [2] to afford β-ketoester lactone [3] failed. We surmised that the failure stemmed from impaired nucleophilicity of the tertiary OH group owing to a stereoelectronic effect resulting from the enforced alignment of the lactone carbonyl π-orbitals and the adjacent CO bond. (Compound numbers adapted to fit this scheme.)

Instead, the authors used alcohol 4, which readily reacted with the masked ketene 2 to give the ester 5 as shown in scheme 2.

Scheme 2: Successful tandem reaction attempted by Boekman Jr. et al; included a nucleophilic attack of 4’s hydroxide onto 2’s ketene motif.

My experimental findings have confirmed a similar effect for my compound. However, I have a bit of trouble discerning which electronic effects exactly cause this unreactivity. My first assumption is that the conformation of the five-membered ring forces the hydroxy group into an angle of approximately $90^\circ$ with respect to the carbonyl-π system. This should allow mixing of σ and π orbitals of whichever kind.

My second assumption was tracing the problem back to the anomeric effect. In that effect, a nonbonding electron pair interacts with an adjacent σ* orbital, lowering its own energy but reducing the σ bond strength. The required electrons could be supplied by the π system, resulting in the effect being π and σ*. However, I do not quite see yet, how this kind of mixing would reduce the nucleophilicity of the oxygen atom.

Thus, the questions are:

Which electronic interactions exactly are responsible for this effect?
Has this been the topic of a research paper?

Reference:

R. K. Boekman Jr., P. Shao, S. T. Wrobleski, D. J. Boehmler, G. R. Heintzelman, A. J. Barbosa, J. Am. Chem. Soc. 2006, 128, 10572. DOI: 10.1021/ja0581346.


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