texts: Decreasing rate of reaction between I2(s) and H2(g)?

texts:
Which change will decrease the rate of the reaction  between
  $\ce{I2(s)}$ and $\ce{H2(g)}$?

  (A) Increasing the partial pressure of $\ce{H2(g)}$

  (B) Adding the $\ce{I2(s)}$ as one piece rather than as several small ones

  (C) Heating the reaction mixture

  (D) Adding a catalyst for the reaction

I can eliminate D as a catalyst would speed up the reaction.

I am not sure about the others though. I could look up the enthalpy for this reaction and eliminate C, but this is from the Chemistry Olympiad and I can't look up enthalpies during the test. Is there any other way to determine that this reaction is endothermic?

Once you eliminate C, you are left with A and B. How would you go about finding the right answer?


texts: Does Reverse Osmosis remove elemental ions from water?

texts:
From what I understand, RO is able to remove (or at least considerably reduce) the salts dissolved in water.

But thinking about it just doesn't make sense. RO works by filtering the solution using a membrane with pores so fine that only water can go through them. But elemental ions are WAY smaller than molecules of water.

So how does RO prevents salts from going to the other side?


texts: Ways of bringing a small peptide to gas-phase

texts: I have a tripeptide molecule with an unnatural amino acid unit. I want to do the gas phase study of the molecule, hoping to understand the intrinsic interactions in detail. I need to bring the peptide to the gas phase for that. I don't think heating the sample will be a good idea, as I am worried about the denaturation of the peptide. Is there any other way to bring my sample to the gas phase. I want to know if there are any methods by which I can measure the melting point of the peptide without denaturing it.


texts:
I want to ask a question about the varying sizes in the LUMO of acrolein during a 1,2- or 1,4-addition.

Today in our introductory lesson to Organic Synthesis with 1,2- and 1,4-addition we were listening to the reason why some nucleophiles may attack one functional group compared to another.

The following picture was discussed:

Now, as shown here, the far orbital on the alkene is far larger than the orbital on the $\ce{C}$ of the $\ce{C=O} $ bond. This implies that for a larger orbital, a nucleophile finds it is easier to attack the alkene than the carbonyl.

This makes sense.

However, when finding an explanation for these varying sizes in orbitals, I couldn't find anything to explain this.

This question was the closest which explained the effects of varying orbital sizes but did not differentiate between $\ce{C1}$ of the alkene and $\ce{C3}$ of the carbonyl.

Why are there two different orbital sizes?


texts: How is the hydrolysis of amides done in a lab?

texts:
I have seen this video about the hydrolysis of amides in order to convert them to a carboxylic acid. I understood how it works but I want to know how would someone physically do it in a lab.

I need to know the temperature needed, the time required for the reaction to happen, the reactants ratio and the process itself.


texts:
Chloral consists of two OH bonds on the same carbon, which is usually unstable, and leads to the evolution of a water molecule, and converts into an aldehyde. However, this is not observed in chloral, and there must be a reason for this.
I have come up with 2 possibilities:

hydrogen bonding in chloral, although it is quite weak
high EN of the chlorines, which results in a huge partial positive charge on C

Which reasoning, if any, is correct, and why does it dominate over the other?


texts: I have been taught that oxygen is a chemical element, in other words a certain type of atom that has 8 protons in its nucleus. So why is O2 called oxygen? It is not a type of atom but rather a molecule.


texts: p-Nitroaniline reaction with sulfuric acid

texts:
An alternative version of the well-known demonstration carbon snake (the dehydration reaction of sugar by concentrated sulfuric acid forming a column of graphite) consists in mixing  paranitroaniline and sulfuric acid.
This reaction is very vigorous and occurs suddenly, forming a similar column of black solid. However, except from the article "Studies on nitroaniline–sulfuric acid compositions: Aphrogenic pyrostats" (https://onlinelibrary.wiley.com/doi/abs/10.1002/app.1970.070140813), I could not find any relevant information about it. I would like to know if the products of this reaction or its mechanism have already been studied.


texts:
I know that when adding carbonated water with Yerba Mate leaves there is a reaction that removes the carbonation. (Empirical results)

I wonder what actually causes such reaction but looking in Scholar even for similar reaction such as soda + mate wasn't very productive.

What is the reaction that undergoes there? Is mate just a catalyst ?


texts:
In the book "Foundations of Materials Science and Engineering" (Smith and Hashemi) the following is written:

For cases of non-steady state diffusion in which diffusivity is independent of time, Fick's second law of diffusion applies, which is

$$\frac{\partial c_{x}}{\partial t}=\frac\partial{\partial x}\left(D\frac{\partial c_{x}}{\partial x}\right)$$

In what cases are materials' diffusivity dependent on time, and in what cases are they not?


texts: Interaction of the oscillating magnetic field of electromagnetic radiation with a molecule or atom

texts:
Whenever we read rotational, vibrational and electronic spectroscopy, we find details on the interaction of the electric dipole moment of the molecule with the oscillating electric field of electromagnetic radiation. The selection rules are also derived on the basis of transition dipole moment operator on wavefunctions. I was talking to spectroscopists today and asked that why do spectroscopy textbooks (and authors) do not mention anything about oscillating magnetic field of light waves. The magnetic field also carries the same energy as the oscillating electric field. Doesn't that interact with electrons as well?* They said that interaction of the magnetic field with a molecule's electric dipole is very weak and hence nobody mentions about it. Does anyone have a good reference or an equation which shows that the oscillating magnetic field interacts very weakly with the molecule's electric dipole moment? They were mentioning Fermi's golden rule and at this stage I lost them.

__
* Electron spin resonance is an example.


texts: Solubility experiment of different organic compounds

texts: Chemistry lab note says that:1) Aromatic acids like benzoic acid and salicylic acid are NOT soluble in water. But they are soluble in 5% NaOH,  and 5% NaHCO3.  Due to having a large hydrcarbon part (which is hydrophobic), it is understandable that aromatic acids won't dissolve in water. But why would they dissolve in base solvents.2) aromatic carbonyl compounds like benzaldehyde and acetophenone are NOT soluble in H2O, 5%NaOH, 5% NaHCO3, 5% HCl. But they are soluble in highly concentrated H2SO4. Got no idea about the reason behind it. Can somebody clarify?


texts: How do I calculate the color of a compound?

texts: I know this is complicated, but I'll ask. How do you calculate the color of a compound with pen and paper? Everyone knows that iron(II) sulfate is yellowish. How do I know without looking at it?


texts: What is the number of unpaired electrons in cobalt(II) tetrathiocyanate?

texts:
Find the number of unpaired electrons present in the d orbital (whose lobes are present along the axis) for the complex $\ce{[Co(SCN)4]^{2-}}$.

Since $\ce{{SCN}^{-}}$ is a weak ligand I did not pair the electrons, but still I got the wrong answer. The correct answer is 0. But how?


texts: Equilibrium constant calculation from concentrations

texts:
Consider the following equilibrium: $\ce{A2\ _{(g)} + 2B_{(g)} <=> 2AB_{(g)}}$

A chemist puts 8.0 moles of $\ce{A2}$ and 10.0 moles of $\ce{B}$ into an evacuated 1.0 L container. The system reaches equilibrium at a certain temp according to the process outlined above. When the system is at equilibrium the chemist determines $\ce{[AB]}$ is 8.0 M. What is the $K_c$ for this process at this temperature (278 K). I set up a nice chart and everything and I cant figure this out. My answer choices are 10, 3.0, 1.0, 4.0, and .50

Initially I thought that The Kc was [AB]^2/([A2][B^2]) but I put in the values and didn't get any of the answers...

Then i set up an ice chart

It's hard to show on here but I then ended up with [8+2x]^2/([8-x][10-2x]^2) but that didn't really get me anywhere


texts: Does changing the stoichiometric coefficients affect the Nernst equation?

texts:
If I take the electrodes as nickel and silver, I've according to the nernst equation that

$\ce{Ni(s) + 2Ag+(aq) -> Ni^2+(aq) + Ag(s)}$

Now $E=E_{0} - \frac{RT}{2F} \ln\left(\frac{[\ce{Ni^{2+}}]}{[\ce{Ag+}]^2} \right)$

But if I double the stoichiometric coefficients, the value inside the logarithm would square up. So if I write the same reaction but with different coefficients, I'll get different values of potential of the cell?


texts: Oxidation of metals/halogens by oxygen gas in acidic aqueous solution

texts:
I had some confusion about the correct answer to the following question:

  Which substance can be oxidized by $\ce{O2(g)}$ in acidic aqueous solution?

Two of the answer choices were metal cations (usually not oxidized further). The remaining three choices were:

  $\ce{Br2(l)}$, $\ce{Ag(s)}$ and $\ce{Br-(aq)}$.

The standard reduction potentials were given:

  $$
\begin{align}
\ce{O2(g) + 4 H+(aq) + 4 e- &→ 2 H2O(l)} &\quad E^\circ &= \pu{+1.23 V} \\
\ce{Ag+ + e- &→ Ag(s)} &\quad E^\circ &= \pu{+0.799 V} \\
\ce{Br2(l) + 2 e- &→ 2 Br-(aq)} &\quad E^\circ &= \pu{+1.065 V}
\end{align}
$$

The correct answer given was $\ce{Br2(l)}$, however, this did not make sense to me as the oxidation of bromine would result in a positively charged bromine ion. Am I reasoning correctly that $\ce{O2(g)}$ can oxidize both $\ce{Ag}$ and $\ce{Br-}$ in acidic solution?

Since the value of $E^\circ$ for $\ce{O2(g)}$ is greater than both of the other values, more energy is released when $\ce{O2}$ gains the electrons, and this will result in the oxidation of both $\ce{Ag}$ and $\ce{Br-}$, correct?


texts: transpiration of trees and the cooling of the air

texts:
The change from the liquid state of water to the water vapor requires a large latent heat to loosen the hydrogen bonds. The process of transpiration in the plant involves exactly this change of state. Here, the water evaporates from the lower leaf surface and the leaf gives up some of its heat. In this way, the leaf is prevented from overheating that would result from exposure to sunlight. Sweating in animals involves this same latent heat aspect of water.

If trees use transpiration to decrease their temperature, shouldn't the air around them  be warmer? The leaves are cooled as water evaporates, and the air should be warmer.

I always experience the opposite as I approach a forest. I'm not sure if the effect could be attributed to the reduced irradiation due to foliage.


texts: Treatment of copper (0) with sodium hydroxide

texts:
I recently made self-assembled monolayers (SAMs) of alkanethiols on a copper substrate. After scrubbing off the $\ce{Cu2O}$ top layer and rubbing the surface with ether and ethanol, I let my copper plates stand in a 5% (w/w) $\ce{NaOH}$ solution for 5 minutes, which I then throughly rinsed off with deionized water.

I'm wondering if I could skip this step. I'm not sure what it is needed for. My knowledge of chemistry tells me that $\ce{Cu(0)}$ should not react with sodium hydroxide. I'm also positive that any grease or other contaminants were washed off in the previous steps.

What do you think?


texts:
I'm slightly confused by a common situation in thermochemistry.

Consider a container with gas inside and a movable, massless piston. The pressure of the gas inside is 6 atm and the external pressure is 5 atm. Thus the gas will expand. However since the piston is massless, the two forces on the piston must be equal by Newton's 2nd Law. But the pressure from the gas and the pressure from the outside atmosphere are clearly unequal, so what's the problem here?


texts: Is there any notion of pH out of solution?

texts: For example, could one define a $\mathrm{pH}$ for pure acetic acid? It's a weak acid in water, but if someone handed you $1~\mathrm L$ of pure acetic acid, what would its $\mathrm{pH}$ be?


texts: Is the bond dissociation enthalpy of Cl-F greater than that of Cl-Cl?

texts: In my book, it is mentioned that $\ce{Cl-F}$ has greater bond dissociation enthalpy than $\ce{Cl-Cl}$. Is it true? I know that interhalogen molecules usually have weaker bonds than dihalogen molecules except $\ce{F-F}$ molecule due to high electron-electron repulsion.


texts: Looking for color changing reaction to track snow layer depth

texts:
I'm trying to find a chemical to mark the position of a snow layer with for detection in future seasons.

The substance has to be:
1. Colorless
2. Not water soluble/solid
3. Stable for multiple years
4. Easily detectable in the field

I'm aware of pH tracers, but I am wondering if there are other reactions with one colorless solid/insoluble component that would produce a dramatic color change.


texts: How one can calculate Si-O-Ca/Mg valence angle energy?

texts:
I want to perform the relaxed scan (or relaxed surface scan) for the valence angle energy of Si–O–Ca, Si–O–Mg, Al–O–Ca, and Al–O–Mg. I will use DFT (ORCA), probably B3LYP and triple zeta basis set (Def2-TZVP or 6-311++G(2df,2pd)) I'm making reference data to parameterize an emperical force field.

But the problem is metal ions, Mg²⁺ and Ca²⁺, because their coordination chemistry is very different from Si or Al. More precisely, I'm not sure how can I 'terminate' the Mg or Ca atoms.

I was thinking of making simple molecules, like (OH)₃–Si–O–Mg–OH or (OH)₂–Al–O–Mg–OH, just giving one OH to Mg or Ca. In this case, Mg or Ca have 2 oxygen neighbors. I can perform geometry optimization, but not sure if that geometry is proper one to perform valence angle scan or not.

I'm not considering aqueous environment (because this is for condensed phase material), so I'm not planning to use water molecules at current stage. But maybe I need to if there are no other way...


texts: I am looking for a chemical test for the presence of gluten: however, having looked online for such a thing, all the results seem to be about 'home testing kits' (presumably for people with a gluten intolerance). Is there a simple chemical test which can be used for a school science project (meaning that the chemicals involved should be easily available), something similar to how iodine can be used to detect starch?


texts:
The degradation of hydrogen peroxide in water $\ce{(2 H2O2 (aq) → 2 H2O +O2 (g))}$ can be catalyzed by $\ce{Br-}$ and $\ce{H3O+}$. Derive an expression for the production rate for the following reactions:

  $\ce{H2O2 + H3O^+ <-> H3O2+ + H2O}$ , where the reaction constants are $k_1$ and $k_{-1}$

  $\ce{H3O2+ +Br- -> HOBr + H2O}$ , where the reaction constant is $k_2$

  $\ce{HOBr + H2O2-> O2 + H3O+ + Br-}$, where the reaction constant is $k_3$

I known that $\ce{H3O2+}$ and $\ce{HOBr}$ are intermediates and so I can use the steady-state approximation and set these rates to zero. From this I get that:

$$\frac{d[O_2]}{dt} = \frac{k_1k_2k_3 [\ce{Br-}][\ce{H3O2+}][\ce{H3O+}]}{k_1k_3[\ce{H2O}] + k_2k_3[\ce{Br-}]}$$

Which I hope is correct.

Then they ask:

  Under what conditions does: $$\frac{d[O_2]}{dt} = k [\ce{Br-}][\ce{H3O2+}][\ce{H3O+}]$$

Here I am unsure if the conditions are that we could suppose that $\ce{H2O}$ is in excess and thus not include it in our rate expression, and that $\ce{Br-}$ also can be excluded since it is a spectator ion.

I would appreciate if someone could confirm that my expression for the rate of production is correct and that my conditions are valid. Thank you!


texts: Why do nonmetal oxides react with water to form acidic compounds?

texts:
I am confused about the molecular basis by which nonmetal oxides react with water to form acidic compounds. For example, I understand that sulfur trioxide reacts with water to form sulfuric acid as shown in the following reaction:

SO3 (g) + H2O (l) --> H2SO4 (aq)

I recognize that the polarized nature of the O-H bond in sulfuric acid makes it thermodynamically favorable for H2O to abstract a proton and subsequently form an acidic solution with the formation of H3O+. However, I fail to recognize how reactions like this with a nonmetal oxide proceeds to form an acidic oxide. Namely, I fail to understand the role of the covalent bond in the nonmetal oxide for the mechanism of this reaction. I recognize that metal oxides dissolve in water to form the highly polarizing, high charge density ion O2-, which polarizes the O-H bond in H2O to form hydroxide. Can someone give a similar explanation for nonmetal oxides and their dominant acidic nature in water?


texts: How does a cyclization occur with a carboxylic acid and (CF3CO)2O?

texts: The product of the reaction below is unsaturated, bicyclic ketone, but I'm confused as to how (CF3CO)2O reacts with it to cause the cyclization. There is no base involved so I don't know how the carbon delta to the carboxylic acid attacks it. What is the mechanism?


texts: Standardization of sodium thiosulfate using potassium dichromate

texts:
In this process first we need to liberate iodine to react with sodium thiosulfate.

First, sodium bicarbonate is added to a iodate-free solution of potassium iodide. The mixture is shaken until the salts dissolve, then conc. hydrochloric acid is added. The solution is shaken again, then covered and keept in a dark place. I have two questions here:

What is the role of sodium bicarbonate here?
Can conc. sulfuric acid be used to provide the acidic media instead of conc. hydrochloric acid?


texts: Why lowering of vapour pressure is not a colligative property?

texts:
In my textbook, it is written that lowering of vapour pressure is not a colligative property but relative lowering of vapour pressure is a colligative property. But why is that? There is literally no explanation given in my textbook as to why this is true. Please someone explain. I am so confused. Please help.
(By lowering of vapour pressure I mean $P_{0} - P_{S}$ where $P_{0}$ is the vapour pressure of pure solvent and $P_{S}$ is the vapour pressure of the solvent containing non-volative solute. Relative Lowering in Vapour Pressure means $\frac{P_{0} - P_{S}}{P_{0}}$).


texts: Can someone recommend me a book ( preferably written long ago) that includes all the details of high school chemistry?

texts:
The textbook I got from my teacher is shown to be too general. Part of the fun of learning chemistry, for me, comes from knowing the derivation of equations. But most of the derivations are missing out from the textbook, like the derivation of kinetic molecular equation and real gas equations.

It will be fine to recommend a college level textbook as long as it does not include calculus.


texts: Bromination of ethyl substituted benzaldehydes

texts:
In a material that I use to study High School Organic Chemistry, the bromination of ethyl substituted benzaldehydes is given as follows:

Source: FIITJEE Grand Masters Package - Chemistry (JEE Preparatory Material)

$\ce{-CHO}$ is a meta directing group, and $\ce{-C2H5}$ is an ortho, para directing group. So isn't some of the products given wrong?

For example, let's take the bromination of ortho ethyl benzaldehyde. Shouldn't the 2nd product's bromine be in a way that is in position 4 wrt $\ce{-C2H5}$ and position 3 wrt $\ce{-CHO}$?

In the meta ethyl benzaldehyde case, why is the $\ce{-CHO}$ group not affecting the position of $\ce{Br}$? Even though it is meta directing, $\ce{Br}$ doesn't seem to substitute the $\ce{H}$ in the meta position of $\ce{-CHO}$

I searched the internet for more information regarding such reactions, and could not find any helpful results for this case.


texts: Glucose and related aldohexoses are interconvertible with a little base. Does anybody know how much of each sugar is present at equilibrium?

texts:
If you add NaOH to D-glucose in water, a mixture of almost all aldohexoses will arise over time, including mannose and fructose. I wonder how much of each will be present and what could explain the distribution. My assumption is that the amount will match stability and that the most stable D-beta-glucose will be most abundant. I'd love to see better quantitative data on this. Do you know how much of each aldohexose is produced?
I found a paper using sodium titanate nanotubes as catalyst but not sodium hydroxide. There, Kumar et al. show in figure 3a(CC-by) that glucose is converted to mostly fructose (blue) and to a lesser extent mannose (red).

The paper does not really answer my question as it only touches upon 2 aldohexoses and doesn't give a molar % (or I didn't find it). I do wonder how much of each sugar would be present in the basic reaction of glucose described above. Does anybody know of experiments to answer that?


texts: Does liquids that emit light when vibrated exist?

texts:
I am looking for a liquid that illuminates when vibrations are added.

It does not have to be strictly chemical, it might as well be something else as well.

Maybe a crystal in powder form mixed with some kind of oil, or even algae in a thick:ish liquid.

Does such a liquid exist?


texts: How does work from other sources affect Gibbs free energy of the system?

texts:
In most physical chemistry textbooks, Gibbs free energy is given like this:
$$\Delta_\mathrm rG = \Delta_\mathrm rG^\circ + RT\ln Q\tag{1}$$
and Gibbs free energy is part of this three-way relationship:
$$\Delta_\mathrm rG^\circ = -RT\ln K = -nFE^\circ\tag{2}$$
which gives rise to the Nernst equation.
However, in many cases, $\Delta_\mathrm rG > 0,$ so it is not thermodynamically favourable. In these cases, there would be an external source of work.
First Question: In the case of an electrolytic cell, in the system, there is also a power source. How would this external voltage source affect the Gibbs free energy equation? Would it just be an extra $-VIt$ term or something else which would cause $\Delta_\mathrm rG < 0?$
Second Question: In the case of a biological cell, the work usually comes from the hydrolysis of ATP. How would this alter the equation and cause $\Delta_\mathrm rG < 0?$


texts: Reverse Cannizzaro reaction to make aldehydes?

texts:
Is it possible (and practicable) to reverse Cannizzaro reaction (disproportionation of aldehydes to carboxylic acids and alcohols) to produce aldehydes from carboxylic acid and alcohol without need to use neither chromate or $\ce{LiAlH4}$?
For example: 1,4 butanediol + 1,4 butanodioic acid - > 1,4 butanedial


texts: Bond dissociation energy of the trihydrogen cation

texts:
Recently, in one of the questions in an assignment on the topic of energetics, we were asked to explain why the bond dissociation energy for the trihydrogen cation is much larger than what we would expect it to be. The value given was +849 kJ/mol. To clarify, the bond dissociation process refers to the conversion of the molecular cation into 2 individual hydrogen atoms and a proton.

My proposed explanation is that the additional interaction with the proton lowers the bonding MO of the molecular ion overall. Essentially, I viewed the interaction of the $\sigma$ bonding MO of $\ce {H2}$ with the low-energy 1s atomic orbital of the proton, giving a bonding MO which would be even lower in energy.

The answer given by the teacher is that this molecular ion is particularly stable due to the $\sigma$ aromaticity present in the ion. This results in a very large bond dissociation energy since by breaking up the molecular ion, we destroy the aromaticity of the ion.

I acknowledge that the teacher's explanation is correct but is my explanation also a valid way of looking at the problem?


texts: Is a hue indistinguishable from its equivalent frequency of light?

texts:
A hue is the color characteristic of a pigment, a particular chemical molecule, when illuminated by sunlight.

Of course such a molecule will not emit a single frequency of light, but will emit a spectrum of light at different frequencies and intensities. This depends on the absorption characteristics of the molecule and its emission characteristics. In some cases, for example, light energy can be absorbed at one frequency and re-emitted at different frequency. In any case, what results is a spectrum of color.

The eye perceives this spectrum as being of a single color, called the pigment's hue.
https://physics.stackexchange.com/questions/ask
My question is whether this hue is truly indistinguishable from energy emitted purely at that frequency. For example, the pigment vermillion, mercuric sulfide, has a nominal wavelength of 607nm. If we create a pure light source of that frequency only, is it indistinguishable from the light of the pigment to the eye?


texts: Is it correct to say that “some degree of pollution is an inescapable consequence of the Second Law of Thermodynamics”?

texts:
The quote above is from ‘Enlightenment Now’ by Steven Pinker, I was just wondering if this was true or if it misrepresented the Second Law.

The full quote below...

  ...some degree of pollution is an inescapable consequence of the Second Law of Thermodynamics. When people use energy to create a zone of structure in their bodies and homes, they must create entropy elsewhere in the environment in the form of waste, pollution, and other forms of disorder

(Page 123)


texts: What would be the typical DRY ingredients in moisture absorbing and odor eliminating materials that work especially well on perspiration/organic odors?


texts: Can an element have a third energy shell without completely filling the second energy shell?

texts:
I came across an electronic configuration diagram, it had three shells. The first shell had only one electron, the second had six and the third energy shell had five. An electron was also present outside all the shells.
Is this configuration possible?


texts: Simultaneous solubility of CaF2 and SrF2

texts:
Solubility of two electrolytes having common ion when they are dissolved in solution is called simultaneous solubility.

How do I calculate the simultaneous solubility of the above mentioned salts given that:

  $\mathrm {K_{sp}(\ce CaF_2)= 3.9 \times 10^{-11}}$ and $\mathrm {K_{sp}(\ce SrF_2)= 2.9 \times 10^{-9}}$

My attempt:

Let the solubility of $\ce {CaF_2}$ be $x$ and that of $\ce {SrF_2}$ be $y$.

Two equations are obtained:

$3.9\times10^{-11} = x(2(x+y))^2$
$2.9 \times 10^{-9} = y(2(x+y))^2$

Dividing the two we get, $x=0.013y$
Substituting this value of $x$ in equation $1$, I got $y= 5.2\times 10^{-3}$ which should be the solubility of $\ce {SrF_2}$. However, answer given is $\pu{9\times 10^{-4}M}$.

How do I solve this problem then?


texts: Any references for adsorption of ions to metal surfaces?

texts:
I'm specifically interested in ions that would adsorb to gold surfaces, however I would be incredibly appreciative if someone could direct me to a textbook reference or something more expansive, that i could use to reference in the future.
I've been doing some reading and found the following regarding Silver:
Silver Adsorbing
Chloride, Bromide, Iodide, Urea, thiocyanate
Silver Nonadsorbing
Fluoride, Perchlorate, Sulfate
I know Gold leeches with cyanide and I think bisulfide.
 I actually found a good set of lecture slides that discusses chemisorption an Oxygen atom across a series of Transition metals. Also I'm also looking for something about physiorption not chemi...
 The slides reference a book called "Surface Science:Foundations of Catalysis and Nanoscience" by Kurt Kolasinski"...I guess I'll start there, but would love to hear about other references anyone else may have.


texts: Solubility of gases in water in comparison to their liquefiability

texts:
My textbook of physical chemistry says

...The following factors affect the solubilities of gases in liquids:
(i) Nature of the gas and solvent: Generally, the gases which
can be easily liquefied are more soluble in common solvents. For example, $CO_2$ is more soluble in water than oxygen or hydrogen. The gases which react with the solvent posses higher solubility. For example, $HCl$ and $NH_3$ are highly soluble in water.
Oxygen, nitrogen and carbon dioxide are much more soluble
in ethyl alcohol than in water at the same temperature and
pressure.
(ii) Temperature: The solubility of most of the gases in
liquids decreases with increase...

Why is it so that the gases which can be easily liquefied are more soluble?
I mean, more liquefiable gases would have a stronger attractive forces amongst the molecule. This would mean that it would become increasingly tougher to dissolve them as their ability to be liquified increase. Then why the opposite is true?

Edit
I found a similar question on Chemistry.SE here asking Why does physisorption (physical adsorption) increase with ease of liquefaction?. I know the above question (and answers) are aimed at adsorption and mine is about solubility, but I think there must be an explanation like that for the aforementioned one.


texts: Is there any book as Landau's for Physics but for Chemistry?

texts:
Landau's series of books are a collection of books that describe briefly but very deeply the core part of the main fields of Physics. He wrote them rigorously and they are very very abstract. He gave Physics new approaches in those books. If you want to understand them, your starting point should be knowing all those main fields of Physics previously.

Is there any book like it but in Chemistry?

Thank you all!


texts: How to calculate bond enthalpies from first principles?

texts: Is it possible to calculate bond enthalpies using the periodic table and the molecule's geometric structure? I am interested in a way of calculating this without getting the answer from measurements or pre-existing bond enthalpies.


texts: Is it possible for a substance to absorb a longer wavelength of EM wave and emit a shorter wavelength?

texts: I know a fluorescent lamp works by emitting UV first and then the specific substance inside absorbs UV and finally emits visible light. An object may emit infrared under sunlight due to heating. But those examples are absorbing short wavelength of EM and then reemitting a longer one. Is there a substance that can do the opposite (e.g.: absorb visible light and then emit UV)?


texts: Is Changing between Allotropic forms a Physical or Chemical Process?

texts:
When a substance changes its alloptropic form, is this considered a physical change or a chemical change?

Right now, I am thinking that it would depend on what the change was. For example, if graphite was changed to diamond under high pressure, I would say it is a chemical change since new bonds are formed. However the change of iron from a body-centred cubic structure (ferrite) to a face-centred cubic structure (austenite) at high temperatures would be a physical change because only the arrangement of the atoms are changed.

Am I correct?


texts:
Can coal (carbon) be "burned" in a hydrogen atmosphere? I know it would not match the definition of "combustion".

But is the reaction $$\ce{C +2H2 ->CH4}$$ exothermic?

(I'm fairly convinced this is a duplicate, but I didn't find any question like that.)


texts: Can grignard reagent contain secondary amino group?

texts: Is there any reason why this grignard reagent wouldn't work? My best guess is that perhaps the nitrogen could act as a second nucleophilic "head", thereby not giving a good yield on the intended product. Or maybe this isn't stable enough?


texts: "Hamiltonian operator has no effect on the spin function" what does it mean?

texts:
I have read the Levine Quantum Chemistry book and it says "Hamiltonian operator has no effect on the spin function" in chapter 10 (Electron Spin and the Spin-Statistics Theorem)  and does the Hamiltonian operation like the following. Why the g(ms) state is taken out of the Hamiltonian?? Why is it constant with respect to the Hamiltonian?

$$\hat H[\psi(x,y,z)g(m_s)] = g(m_s)\hat H\psi(x,y,z) = E[\psi(x,y,z)g(m_s)]$$


texts: Is hydrogen (on its own) considered an acid?

texts:
An acid is:

  A molecule or other species which can donate a proton

So when hydrogen appears by itself on one side of a dissociation reaction e.g. $\ce{HOCl  ->   H+ + OCl-}$ is the hydrogen an acid? As the hydrogen can donate itself?


texts:
Can ionic and atomic radii be compared?  For example, this is a common problem in some intro chem courses:

Rank the following from smallest to largest:  sodium ion, magnesium ion, neon, fluoride, oxide.

Any student who has been trained in trends should be able to get the "answer", but if one looks at the actual figures, there are data that show that sodium ion is larger than neon atom.

I am of the opinion that it is comparing apples to oranges and that the problem can be rescued by removing neon from the list.


texts: Considering the hyperconjucation effects with C-T,C-D and C-H bonds, the maximum efficiency is given by C-H bond.This should mean that C-H must be the weakest bond and must hve the least bond energy compared to others.While all are isotopes of the same element with completely identical outer electronic configuration,then with is the difference in the bond energy?


texts: Rate of solvolysis of allyl and alkyl halides

texts:
Suppose I have 2 compounds, 3-chloropropene and 1-bromo-1-methylcyclohexane. Without knowing the values, how can we compare the rate of solvolysis?

My attempt: Resonance is quite dominant character thus alkyl chloride resonance I think should dominate over hyperconjugation but then we have an exception that 3 degree carbocation is more stable than benzyl carbocation hence there might be some disparity in orders.


texts: What is the effect of pressure upon the melting and boiling points of a substance?

texts: I want to know about the inter-relation between the effect of pressure upon the melting and boiling points of a substance. Can anyone help?


texts:
I believe the first reaction would be a substitution of $\ce{SiMe3}$ for $\ce{I}$ and creating $\ce{SiMe3Cl}$.
The second process I think would involve the $\ce{Mg}$ removing the two $\ce{Cl}$ and forming diphenylsilane, which would likely be a repeating unit in a silicone polymer.
Could any explain the mechanism for these reactions?


texts:
I am working on analyzing the mass spectrum of pentabromophenol but am struggling to determine the fragment at 60 m/z. It could possibly be 5 carbons however that is too much positive charge to exist at high abundance.

Below are the mass spec retrieved experimentally and from literature.

Literature Mass spec: NIST WebBook

Experimentally determined mass spectrum:


texts: How can alkali metals form covalent bonds?

texts:
Alkali metals have spherical outer s orbitals unlike elements like carbon which have protruding p orbitals that can "attach" onto other orbitals to form covalent compounds. Even in cases like methane elements like carbon can form hybrid orbitals that still have a protruding p like character.

So how can covalent alkali metals form covalent bonds given that their orbitals are spherical and not protruding?

Does the s orbital distort to be more p like in covalent compounds?

Can the s orbital hybridize and steal a more protruding like character from internal orbitals or from the orbitals of another atom?


texts: Detection limit of selective ion electrodes

texts:
I've been studying about the selective ion electrodes and I came across a question which I seem to not be able to answer. It has to do with why the detection limit for iodide ions is lower than the one for chloride ions.

I know that the detection limit depends on the type of the electrode, temperature, pH, the interfering ions etc., but how can I understand the difference between the detection limit of I- and Cl- ions?


texts: How to calculate the equilibration time of two connected chambers of salt solution, initially at different concentrations?

texts:
I am trying to build a system of two connected chambers, one of which is also connected to a cuvette, so I can perform a spectrometry experiment with different concentrations of $\ce{KNO3}$ solution. In its simplest form, the cuvette and the first chamber would hold solution at the same concentration, while the second chamber would hold solution of higher concentration. I would perform one experiment, open a valve between the chambers, and wait for the concentration to equilibrate before performing the next experiment.

My advisor suggested this system and said that the equilibration time would likely be on the order of minutes.

I used this equation to calculate equilibration time between two chambers:

$$
t = \frac{\Delta m \cdot  l_{v}}{A_{v} \cdot D \cdot 10^6 \cdot \Delta c}
$$

where $t$ = equilibration time in s
$\Delta m$ = the difference in mass of $\ce{KNO3}$ between the chambers in g
$l_{v}$ = the length of the valve in m
$A_{v}$ = the orifice area of the valve in m^2
$D$ = the mutual diffusion constant of $\ce{KNO3}$ and $\ce{H2O}$, which is on the order of 10^-9 m^2/s
$\Delta c$ = the difference in concentration between the chambers in g/cm^3
the factor of 10^6 is to convert between g/cm^3 and g/m^3

For a cylindrical valve 1 cm long and 2 cm in radius (improbably short and wide) and chamber volumes 95 cm^3 and 400 cm^3, this gives an equilibration time of 4.7 days!

This is much more than I was expecting. I can reduce the sizes of the chambers to decrease the time demand, but I would prefer to keep them as large as I can, to increase the final concentration that can be achieved in the cuvette.

Is there something obvious that I'm missing in this calculation? Is there a better way to do it?

Edit:

The equation above was derived by equating the mass flux $j_{m}$ with its definition from Fick's first law (using $c$ as mass/volume rather than amount/volume):

$$
j_{m}=\frac{\Delta m}{A_{v}\cdot \Delta t}=D\cdot\frac{\Delta c}{\Delta x}
$$

I know that strictly the RHS should contain $\frac{\delta c}{\delta x}$ rather than $\frac{\Delta c}{\Delta x}$. Does this approximation make much difference? For now, I am also making the fairly large assumptions that the volumes of solution in each chamber do not change, and that the density of the solution is independent of concentration. I think I can include these considerations later on.

This is an actual system that I need to build (well, ask our machine shop to build for me) and I need to have a good idea of the best valve sizes to use as they have a significant effect on the overall structure.


texts: How to access implicit bond angles that don't appear in Gaussian's z-matrix input?


texts: Is the change of the Gibbs free energy always zero at constant pressure?

texts:
At constant pressure, which is the usual condition for chemical reactions, heat absorbed/released by the system is the same thing as enthalpy change. According to the Gibbs equation,
$$\mathrm dG = \mathrm dH - T\,\mathrm dS = \mathrm dH - đq$$But, $\mathrm dH=\mathrm đq$ at constant a pressure. So is the Gibbs energy change $\mathrm{d}G$ simply zero for any reaction?


texts: Nucleophile vs base and Electrophile vs acid

texts:
How we will figure out that a given compound will behave as nucleophile or base ? Same problem for electrophile and acid.

By the way I have already seen a similar question though I didn't find it helpful but if someone could correct the answer posted by Vikas Avasthi then I think (no sure) that it might become part of answer to my question.


texts: Comparison of basicity of Aniline, p-Anisidine, and o-Anisidine

texts:
I have a question where I am required to compare the basicity of Aniline, o-Anisidine, and p-Anisidine.

Now here's what I do know:-

In ortho substituted aniline, an ortho effect acts which reduces the basicity of the ortho-substituted aniline. But, my text book (Solomons and Fryhle) states that this effect doesn't act if the ortho substituent is $\ce{-OH}$ or $\ce{-OCH3}$. So I should be able to do the comparison here without taking into account this ortho effect.

Now here's my try:

In Aniline, clearly the lone pair is quite a bit delocalised in the benzene ring which reduces its availability. Now, $\ce{-OCH3}$ is a group that has both $\ce{-I}$ and $\ce{+M}$.

Taking a look at the para variant, clearly there is $\ce{+M}$ acting which reduces the extent of delocalization of the Nitrogen lone pair, thus making it more available. Also, the $\ce{-I}$ effect in the para is lesser than that in the ortho variant, so in the para variant, much more of the electron density of the Nitrogen lone pair is available which helps in easier donation, and thus I find the para variant to be the most basic which is all well and good.

The problem arises in the next part of the comparison, between Aniline, and o-Anisidine.

If the ortho effect isn't acting, due to the $\ce{+M}$ effect of the $\ce{-OCH3}$ group,  the lone pair of the Nitrogen should be more available for donation than that of Aniline, (but less than the availability in the para case, due to stronger $\ce{-I}$ in the ortho case), and thus the Ortho variant should be more basic.

But my book states that the basicity order is : p-Anisidine>Aniline>o-Anisidine

I cannot really understand why the basicity order of the last two (Aniline>o-Anisidine) is the way that it is, if no ortho effect is acting and $\ce{-OCH3}$ has a $\ce{+M}$ effect.

PS: Just took a look at Peter Sykes and the order given is same as that in my book. This this due to the fact that in ortho, the molecule goes slightly out of plane, so $\ce{+M}$ effect may not be as effective?


texts: What is the Difference between Menthol Crystal and Menthol Powder?

texts: I want to buy menthol powder from a chemical supplier but he is selling menthol crystal at half price of menthol powder (he says manufacturing process is the difference) so I am really confused what should I do. Can I buy menthol crystal and just powder them to get the powder form I want it or are crystal and powder menthol totally different things altogether?


texts: What is the energy package released to the outside world?

texts:
Consider a chemical reaction where two different particles form another one

$$\ce{O + O_2 -> O_3}$$

I find it confusing how this can be an exothermic process. How to picture the release of $+\Delta H$ to the surroundings.

And am I right in viewing this energy value only as the net energy coming from an integration of the particle potentials as they get closer along the reaction coordinate?


texts: How can I recognize aromatic rings in a connection table?

texts:
Given a connection table (that is, a list of atoms, their connectivities/bonds, and the type of bonds), how can I detect the presence of an aromatic ring?

For reference, the aromatic rings in the structure will always be depicted in Kekule form (alternating single and double bonds).

It is simple enough for me to use a cycle finding algorithm on the graph representing the bonds to find candidates. The problem is now recognizing which of those rings can be aromatic.

A naive approach for at least six-membered carbocyclic rings would be to check if the ring bonds alternate between single and double bonds. But, the structures below would be problematic:

where the center ring in phenanthrene and the six-membered ring in 2H-indene are decidedly aromatic, even if there is no complete alternation of single and double bonds. If you try to check exocyclic double bonds, the leftmost structure could be a false positive.

Pointers to algorithms would be very much appreciated. I am ignoring heterocyclics like thiophene or imidazole, or cations like tropylium for now, but if you know how to handle them too, it would be a nice bonus.

I haven't gotten an adequate explanation of why people thought the question was "too broad"; thus, to restrict the question, here is a drastically short reformulation:

  Given a connection table for a molecule that contains any number of six-membered rings (possibly fused, spiro, etc.) and is represented in Kekule form, can one write an algorithm to determine which rings are aromatic and which are not? Atomic coordinates are available if necessary.


texts:
I've recently conducted a viscosity experiment to find the relationship between alkali metal ions, the concetration of the solution, and the viscosity of the solution. We used the Oswald viscometer to determine the viscosities of $(\pu{0.5 M}, \pu{0.25M}, \pu{0.125M}, \pu{0.0625M})$ solutions of $(\ce{LiNO3}, \ce{NaNO3}, \ce{KNO3})$, and found that the while the viscosities of the $\ce{LiNO3}$ and $\ce{NaNO3}$ solutions increased as the concentrations of their solutions increased, the viscosity of the $\ce{KNO3}$ solution would instead decrease.

And so we ask:

What is the relationship between the viscosity of a alkali-metal nitrate solution and the variant of the alkali metal ions within?
Why would the viscosity of the $\ce{KNO3}$ solution decrease with concentration?


texts: Alphanumeric preference between hexyl and heptyl

texts:
Our chemistry teacher taught us that hexyl (five letters) is preferred to heptyl (six letters) as hexyl has lesser number of letters. After searching many sources I could not find any such rule.
Which one would be preferred while writing IUPAC names?
For example, will it be 8-heptyl-10-hexylheptadecane or 10-heptyl-8-hexylheptadecane?


texts: Approaches to cap/modify the terminal 3' OH of DNA polymer

texts:
I am looking for a procedure that would cap/protect the 3' hydroxyl of DNA molecules with high efficiency. I have tried to perform a similar step enzymatically using dideoxynucelotide triphosphates but have found the efficiency to be unacceptable for my application, so I am exploring non-enzymatic approaches.

If this process also has side reactions that modify other hydroxyls (including 2' hydroxyls on RNA and/or other moieties on proteins), that would also be OK as long as the internals of the DNA backbone or the bases are not modified.

There is a standard part of some in-situ nucleic acid hybridization protocols that reacts tissue sections with acetic anhydride in a triethanolamine solution. The stated purpose of this step is to acetylate the 2' OH on RNA, and to acetylate some amino groups on proteins, and reduce background in subsequent hybridization steps.

1) Is there any reason to think that these conditions would NOT efficiently acetylate at the 3' hydroxyl of DNA (and RNA)?

2) Would this approach (acetic anhydride in basic conditions) cause any modifications to the standard DNA bases? I am specifically concerned that the primary amines critical for base pairing would be acetylated, which would be undesirable.


texts: I've read in a book that a catalyst may be included in the rate equation even though it is never used up. It was written as having zero order kinetics however I thought catalyst concentration will always have an effect on the rate, especially since in a lot of biological enzyme-controlled reactions, enzyme concentration is a key element of the rate of a reaction. Is this only the case if the catalyst is above a certain concentration such that adding more will have no effect?


texts: Significance & applications of polarizability for nucleophiles

texts:
One of the reasons given for the greater nucleophilicity of iodine ion compared to fluorine ion is the greater polarizability of the large electron cloud of iodine. The other reason given is that it is less crowded by polar protic solvent molecules.

However, when the solvent is changed to a polar aprotic solvent the nucleophilicity order is reversed.

If polarizability had any significant role to play, the order would've not been completely reversed. It seems to me that the only reason iodine ion is more nucleophilic than the fluoride ion is because it is less crowded by the solvent.

Now, this leads me to believe that polarizability is not a very important factor and should only be used when comparing nucleophiles of the same basicity, but of different size (and hence polarizability) in a polar aprotic spent.

But why then, for uncharged nucleophiles does polarizability dominate over basicity in determining the order of nucleophilicity (regardless of the solvent used)?


texts:
I'm looking into anodization, and all the people doing it seem to have sulfuric acid as their first choice electrolyte, while others use sodium metabisulfate. Having simple access to exactly neither of these, I was wondering.

Why is sulfuric acid important?
Can I use more accessable (and safer) electrolytes such as vinegar or sodium bicarbonate instead?
How much of a difference would it make?


texts: Why does HNO3 not give off H2 when reacting with Cu?

texts:
A dilute solution of which acid is most likely to produce a  reduction
product other than $\ce{H_{2}}$ when it reacts with a  metal?
(A) $\ce{HF}$
(B) $\ce{HCl}$
(C) $\ce{HNO3} $
(D) $\ce{H2SO4}$
$\tiny{\text{Question from 2012 local chemistry olympiad}}$

The given answer is (C), $\ce{HNO3} $ but I don't understand why.
First off, what does it mean by reduction product -- is it the product that is formed when the acid is reduced in the redox reaction between the metal and the acid?
Second, why is the answer $\ce{HNO3} $?


texts:
What are the criteria for a molecule to be chiral?
(We frequently get questions of this type, so this is an attempt to construct a suitable general answer for duping.)


texts: Contradictory Properties of Mercuric Cyanide

texts:
It is said that mercuric cyanide [$\ce{Hg(CN)_2}$]  is water soluble and also is a non-electrolyte.

How is this possible?


texts: Calculating Sensitivity in Mass Spectrometry

texts:
My mass spectrometry textbook gives the following example:

  Calculating sensitivity Magnetic sector instruments are specified to have a sensitivity of about $4 \times 10^{-7} C \ \mu g^{-1}$ for the molecular ion of methylstearate, $m/z \ 298$, at $R = 1000$ in $70 \ eV$ EI mode. One microgram of methylstearate is equivalent to $3.4 \times 10^{-9}  mol$ or $2.0 \times 10^{15}$ molecules. The charge of $4 \times 10^{-7} C$ corresponds to $2.5 \times 10^{12}$ electron charges of $1.6 \times 10^{-19} C$ each. Vice versa, in dividing the number of molecules per microgram by the number of charges at the detector we may conclude that only one out of $800$ molecules is finally detected.

I have three questions:

What is $R = 1000$ supposed to be? The author never mentioned such a quantity at any previous point in the textbook.
How did the author calculate that the charge of $4 \times 10^{-7} C$ corresponds to $2.5 \times 10^{12}$ electron charges of $1.6 \times 10^{-19} C$ each? Or is this just a fact that he has knowledge of?
How did the author calculate the last part:

  Vice versa, in dividing the number of molecules per microgram by the number of charges at the detector we may conclude that only one out of $800$ molecules is finally detected.

?

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


texts: Preventing the gas when Hydrogen peroxide is added to a detergent

texts:
In organic detergents, when I add Hydrogen peroxide to increase the stain removing feature a gas is produced.

How should I prevent the gas production process?


texts: In a battery, what happens to LiCoO2 when the lithium leaves? It becomes CoO2?

texts:
What chemical compound exists at the cathode of a lithium-ion battery when the lithium is not there?

The cathode is usually described as $\ce{LiCoO2}$, so does it become $\ce{CoO2}$?

$\ce{CoO2}$ puts cobalt in an oxidation state of +4, which is possible but rare and unstable. I think $\ce{CoO2}$ doesn't even have a Wikipedia page.


texts:
As I know, $\ce{MnO2}$ is called manganese(IV) oxide.

Why can't we name it manganese peroxide since manganese(II) exists too?

In other words, how do we know that the oxidation number of manganese in $\ce{MnO2}$ is $4$ and not $2$?


texts: Validity of the leveling effect of water in nitration reactions

texts:
Wikipedia gives this as the levelling effect of water

  Any acid that is stronger than $\ce{H3O+}$ reacts with $\ce{H2O}$ to form $\ce{H3O+}$. Therefore, no acid stronger than $\ce{H3O+}$ exists in $\ce{H2O}$. For example, aqueous perchloric acid ($\ce{HClO4}$), aqueous hydrochloric acid ($\ce{HCl}$) and aqueous nitric acid ($\ce{HNO3}$) are all completely ionized and are all equally strong acids.

So from what I can understand, if I take an aqueous medium, then $\ce{H2SO4}$ and $\ce{HNO3}$ both should be equally strong.

But then comes the nitration reaction, where the nitronium cation acts as the real attacking electrophile, which means that in this reaction, $\ce{HNO3}$ acted as a base and $\ce{H2SO4}$ acted as an acid.

I am also aware concentrated acids are taken in the nitration reactions, but even the most concentrated acids have some amount of water.

How are these two concepts contradicting, where am I going wrong?
What are the limitations of the levelling effect and where all is it applicable? Is it not applicable to concentrated solutions, and if so, how concentrated?


texts: Accessible statement on the intuition and usefulness of group theory to chemistry

texts:
I am writing a lesson plan for high school students who are studying group theory,
and I am having difficulty in relating the subject matter to the real world.
I have quite a few examples using the Rubik's cube, but I would like to use
some statement that might provide some intuition to students of how group theory
is useful for chemists.
I understand that group theory is used with spectroscopy, but I am not sure how to
relate this back to the theory.

I have seen some good reasonable non rigorous attempts to relate group theory to
the insolubility of quintic polynomials, but I think it would great to have a second
more concrete example, such as chemistry.

I understand this may be a big thing to ask, and would be happy with just a broad brush strokes answer without being too technical or trivial.


texts: Boiling point of alkynes from n = 2 to 10

texts:
From a video on organic chemistry, I found this table that shows the boiling point temperatures of alkynes $\ce{C_{n}H_{2n-2}}$ with $\,n=2...10$.

$$\begin{array}{|c|c|c|c|}
\hline n & t_\mathrm{boil}/^\circ\mathrm{C} & m & T_\mathrm{boil}/\mathrm{K}\\
\hline 2 & -83.6 & 26 & 189.6\\
\hline 3 & -23.2 & 40 & 250.0\\
\hline 4 & 8.1 & 54 & 281.3\\
\hline 5 & 39.7 & 68 & 312.9\\
\hline 6 & 71 & 82 & 344.2\\
\hline 7 & 99.7 & 96 & 372.9\\
\hline 8 & 125.2 & 110 & 398.4\\
\hline 9 & 150.8 & 124 & 424.0\\
\hline 10 & 174 & 138 & 447.2\\
\hline\end{array}$$

Here $\,m=14n-2\,$ is the molecular mass and $\,T_\mathrm{boil}\,$ is the boiling point temperature converted to kelvins. Surprisingly, when I plot $T_\mathrm{boil}$ v.s. $m$, I find a power law $T_\mathrm{boil}\propto \sqrt{m}$. The melting point temperatures were also shown in the video but were not so regular. Can someone explain why the boiling point satisfies such a simple power law?


texts: Cyclobutylamine with sodium nitrite in dilute HCl

texts:
What are the products formed in the reaction of cyclobutylamine with $\ce{NaNO2}$ and $\ce{HCl}$?

I thought the answer was only cyclobutanol. But the answer given says the product contains cyclopropyl carbinol as well. How does the second product form?

This is basically a diazotization reaction which results in  the conversion of $\ce{- NH2}$ to $\ce{- N2^+Cl-}$ which is a good leaving group. Then water molecules will attack the carbon containing the leaving group. Is the reaction $\rm{S_N1}$ or $\rm{S_N2}$?


texts: What determines the maximum size of salt crystals as grown in flux growth?

texts:
Like many other children, I grew single crystal salt crystals in a salt solution. This is a common and fun experiment for children.

However, with both this experiment, and with flux growth methods for single crystals in general, is there a limit on the size of the grown crystal?

That is, if I was to keep dumping in more salt so as to replenish the solute, would the crystal grow forever? And if not, what limits the size of these crystals?


texts: How do you Synthesise Glycosides of flavonoids and stilbenoids?

texts: I would like to know how you go about synthesising glycosides of flavonoids and stilbenoids from their respective sugars and flavonoids/stilbenoids. I read http://www.netsci-journal.com/97v1/97005/005p20.htm but I found it too specific (as it only applied to aliphatic compounds) and required an enzymatic catalyst that is impossible to predict. I would like a general formula that if it does contain an enzymatic catalyst the enzyme is either constant or at least usually predictable.


texts: Liquification of gas to liquid at critical temperature

texts:
The gas that liquifies first, when cooled from 500 K to its critical temperature given in parenthesis is

  a) $\ce{CO2}$ (304.1 K)

  b) $\ce{NH3}$ (405.5 K)

  c) $\ce{O2}$ (154.3 K)

  d) $\ce{N2}$ (126.0 K)

Answer=b

I know that the critical temperature is the highest temperature at which the gas can be liquified and above which the gas can not be liquified whatever high pressures are used.

$\frac{p_\mathrm c V_\mathrm c}{T_\mathrm c} =nR =\frac{m}{M}R$

i.e.,  $T_\mathrm c$ is directly proportional to $M$, when all the other quantities are constant.

So, based on $M$ $\ce{NH3}\lt\ce{N2}\lt\ce{O2}\lt\ce{CO2}$
So, b should be the answer.

This is how I have solved this problem, please tell me if I am wrong and if so, then please tell me the correct way to answer this too.


texts: Hypothetical: What happens to water as pressure increases to infinity?

texts:
I've asked a similar question here but the answer given shows the behaviour of water under general conditions.

I'd like to know what the behaviour of water is like as pressures increase towards infinity without being able to escape it's confinement.. i.e. a ball of water at the core of a galactic mass.. maybe this question is more for theoretical physics since we can't really measure or experiment?


texts: What household substances could be distilled

texts:
I'm looking to experiment with distillation to have a basis for understanding the theory slightly better, and get a better feel for it.

I'm hoping for some suggestions as to what I could try distilling, such as purifying drinking alcohol. Any single idea would be appreciated, best answer would be awarded to an idea where:

The resulting purity would be straight forward to approximately test
No part of the distillation presents a significant hazard (e.g. toxic fumes, high volatility)
No particularly specialist or expensive equipment is required (e.g. extreme temperatures)

I think that pretty much covers it. I'm just looking for one or two ideas which I can experiment with besides alcohol.

Thanks


texts: Equilibrium constant for a multi-step reaction

texts: If a reaction proceeds in steps, is the equilibrium constant of every step taken into account to arrive at the final constant? Or can we just calculate equilibrium constant for the overall reaction with reactants on one side and the products on the other?


texts: Why does the reaction of chlorosulfonic acid (colorless) and 1-dodecanol (colorless) produces a deep dark-red-colored solution?

texts:
I was wondering if anyone had any insight as to why the reaction of chlorosulfonic acid (colorless) and 1-dodecanol (colorless) produces a deep dark-red-colored solution? The reaction should give hydrogen lauryl sulfate, which according to this website, is a white solid.

I have also tried adding $\ce{NaCl}$ to the chlorosulfonic first, and then adding the 1-dodecanol, which surprisingly gives the sodium dodecyl sulfate soap as expected.

Is this color from over sulfonating the hydrocarbon chain on the hydrogen lauryl sulfate?  If so, what would this side product be called, and why isn't it seen much in industry if it is created along with sodium dodecyl sulfate?


texts: Do acids and bases have the same coefficients if they neutralize one another?

texts:
The questions states: Ammonia has the formula $\ce{NH3}$. Household ammonia is a dilute aqueous solution of $\ce{NH3}$. Aqueous ammonia is a base that can neutralize acids.
If 18.2 mL of 0.800 M $\ce{HCl}$ solution are needed to neutralize 5.00 mL of a household ammonia solution, what is the molar concentration of the ammonia?
Express your answer with the appropriate units.
I used the values I was given; converted the $\ce{HCl}$ to moles; divided the moles of $\ce{HCl}$ by the liters of ammonia solution. However, I do not understand why this is correct.
$\ce{HCl}$ is an acid and $\ce{NH3}$ is a base. How does finding the molar mass of $\ce{HCl}$ help one calculate the molarity of $\ce{NH3}$?


texts:
I have a question regarding whether argon or nitrogen is to prefer when it comes to preserving wine.

Specifically, I am interested in knowing if there is a difference in preservation periods.

Also, if there is a risk of them reacting with the wine, which might affect taste and smell?


texts:
I conducted an experiment on electrolysis of concentrated solution of NaCl. Hoffman Electrolysis Apparatus was used for this experiment. I observed a formation of gas bubbles on both anode and cathode. It was expected to obtain hydrogen gas on negative electrode (cathode) and chlorine gas on positive electrode (anode). I also hoped to test these gases: (1) as hydrogen should ‘pop’ with a lighted splint, and chlorine should bleach damp litmus paper. I was unable to demonstrate these tests for gases, as I suppose there was not enough gas formed for test to go efficiently. I wonder, if someone knows what apparatus is better for this goal. I used 9V battery for this electrolysis experiment.
Even though I had no direct proof of hydrogen formation, solution near anode smelled as a chlorine gas, and smell was very strong. I am not sure why wet blue litmus paper didn't get bleached by this chlorine. Blue litmus paper got bleached very fast in another experiment (not related to electrolysis) where chlorine was released, within 30 sec of exposure.
The most interesting part of experiment was formation of brownish chemical species on anode. At times, I didn't see any chlorine bubbles at all, but I could see formation of this brown chemical species. At first, I thought it is an iodine. I tested it with starch and found, that it was not iodine. Today I tested it with alkene and alkane, and I found it was a bromine (decoloration of bromine water was observed with alkene, but not alkane). Yes, I know, that brine is main source of bromine, but is there any way I can buy NaCl without bromine, just for demonstration purposes?


texts: What is the pH of a solution of HCOONa and HNO3?

texts:
Calculate the pH of an aqueous solution obtained by mixing
  20 ml of $\ce{HCOONa}$ 0,1 M and 5 ml of $\ce{HNO_3}$ 0.2 M.
  ($K_\mathrm a$ of $\ce{HCOOH}$ $= 10^{-4}$)

My try:

The number of the moles involved are: $n_{\ce{HCOONa}}=0.002~\mathrm{mol}$, $n_{\ce{HNO3}} = 0.001~\mathrm{mol}$.
We have the reaction:

$$\ce{HCOONa + HNO3 -> HCOOH + NaNO3}$$

Where 0.001 moles of $\ce{HNO3}$ si is consumed by reacting with 0.001 moles of $\ce{HCOONa}$ giving 0.001 moles of $\ce{HCOOH}$. Because remains $0.002\ \mathrm{mol}-0.001\ \mathrm{mol}=0.001~\mathrm{mol}$ of $\ce{HCOONa}$, we'll have a buffer solution with the acid $\ce{HCOOH}$.

It'll start the reaction:

$$\ce{HCOOH + H2O <=> HCOO- + H3O+}$$

Where the initial concentration of $\ce{HCOO-}$ is equal to $\ce{HCOONa}$ and is $\frac{0.001~\mathrm{mol}}{(0.02+0.005)~\mathrm l} = 0.04~\mathrm{mol~l^{-1}}$. So we have,

$$[\ce{H3O+}]=K_\mathrm a \frac{[\ce{HCOO-}]}{[\ce{HCOOH}]} \Rightarrow \mathrm{pH} = \mathrm pK_\mathrm a - \log_{10}{\frac{[\ce{HCOO-}]}{[\ce{HCOOH}]}} = \mathrm pK_\mathrm a = 4$$

Is it correct?


texts: Determine the position of an equilibrium process

texts:
For the exothermic reaction of nitrogen gas with iodine solid to produce nitrogen triodide gas. Write the balanced equation including heat and select the overall direction of shift in the reaction.

I have balanced the equation: $\ce{N2 (g) + 3 I2 (g) <=> 2 NI3}$
Is this equation correct?

I am confused on how to find the overall direction of shift. Should I use the Le Chatelier's principle? If so, then I think the overall shift is a "shift to the left"/reverse reaction. Am I correct?


texts: Are entries ever removed from the Merck Index?

texts:
I was re-sorting books the other day, and thought about how many years it has been since I bought my Merck Index. I'm sure there are new entries in the more recent additions, but I do not have such a need to stay that up-to-date.

At first thought, it seemed to me that a book of this nature only adds entries, and does not remove any entries. But is this the case? Are compounds de-listed because they are bad science? Other reasons?

Iit would be great to know other details about the editorial process, as well, if relevant.


texts: How do the silicon-hydrogen bonds in polydimethylsiloxane react with a H2PtCl6 catalyst

texts:
How does $\ce{H2PtCl6}$ react with $\ce{Si-H}$ to give $\ce{[PtCl4]2-}$?

I know $\ce{H2PtCl6 -> 2H+ + [PtCl6]2-}$ but I'm not sure what is next.

This question comes from this laboratory assignment (PDF link), in which I am asked to write the redox reaction between the silicon-hydrogen bonds in polydimethylsiloxane and the metal compound $\ce{H2PtCl6}$.

I found a source which confirms that $\ce{H2PtCl6}$ reacts with $\ce{Si-H}$ to give $\ce{[PtCl4]2-}$, but I don't understand how the $\ce{Si-H}$ interacts with the $\ce{H2PtCl6}$.


texts: I was introduced with an exercise which asks to find $K_\mathrm{b}$ of $\ce{NH3}$ when the $\mathrm{pH}$ of $\ce{NH3}$ solution with concentration $M_1$. Well, in order to solve it, I used the fact that $\mathrm{pOH} = 14 - \mathrm{pH}$ and the dissociation $\ce{NH3 + H2O <=> NH4+ + OH-}$ to compute $\ce{[OH-]}$ and then $K_\mathrm{b}$. However I don't fully understand what does $\mathrm{pH}$ mean, since in this dissociation there aren't any $\ce{H3O+}$ molecules. I think it relates to the conjugate dissociation of the $\ce{NH4+}$, i.e.: $\ce{NH4+ + H2O <=> NH3 + H3O+}$, so the $\mathrm{pH}$ of the $\ce{NH3}$ solution is in fact related to the concentration of $\ce{H3O+}$ which is formed from the $\ce{NH4+}$ dissociation. Is it indeed the case? I would really appreciate any explanation.


texts: Why is isobutane more thermodynamically stable than n-butane?

texts:
I would like to understand the term stability in organic chemistry. We know empirically that isobutane (2-methylpropane) is more stable than n-butane. For example, their heats of formation (taken from the NIST WebBook) are $\pu{-134.2 kJ/mol}$ and $\pu{-125.6 kJ/mol}$ respectively, putting isobutane at ca. $\pu{10 kJ/mol}$ lower in energy.

But why is this so? Is there a physical or chemical explanation for this?


texts: NIR spectrometer on smartphone. Are any such products available or companies working in this area?

texts:
Are there any successful products commercially available? If not, what are the technical challenges which make it currently infeasible? For example, are the sensors too big? Is illumination a challenge? etc.
Suppose I wish to miniaturize this spectrometer and embed that into a phone, what would be the challenges?


texts:
Would the formal charge of terminal atoms differ from the FC of the non-terminal atoms?

Say you had a sheet of graphite; inside the network covalent solid all the carbons are bound to one another, but the terminal atoms are obviously missing some C-C bonds since they are terminal.

Their formal charges would differ, correct?

What is the consequence of the differing charges?


texts: How to calculate an enthalpy change for this reaction

texts:
I've got an assignment to solve problem number 4 in this worksheet, that is to calculate change in enthalpy for reaction:
$$\ce{CHCl3 + O -> COCl2 + HCl}$$

How do I solve it? Why is oxygen $\ce{O}$, and not $\ce{O2}$?

I figured out that, it is not a combustion reaction, as combustion of any hydrocarbon will lead to formation of $\ce{CO2}$ and $\ce{H2O}$, as per this page.

Well, what I have at the beginning is not exactly a hydrocarbon, but rather, a halogenated hydrocarbon. Yet, no water and no carbon dioxide is produced. So as I mentioned above, I consider it is not a combustion. Any thoughts on this? Could it still be a combustion? Why or why not?

When I calculate $\Delta H$ of this reaction, the total outcome depends on using reaction as it is shown in the worksheet, or correcting $\ce{O}$ to $\ce{O2}$ and balancing it. Which option, do you think, is preferable, and why?


texts: For isomers, what does the term "connectivity" mean?

texts: I would like an explanation for the term "connectivity" in the question "Do the compounds have the same connectivity? I do not understand what "connectivity", a vague term, means.


texts: I know of 3 different definitions for acids and bases including Arrhenius, Brønsted–Lowry and Lewis. Can anyone tell me what is the common feature among these 3, that we have to label the compounds under those definitions as acids or bases? Is there any defining physical or chemical feature that guides this?


texts: Unusual oxidation numbers for alkaline earth metals?

texts: Are there compound of alkaline earth elements showing unusual oxidation numbers? For the sake of the question, every oxidation number different from +2 counts as unusual, most exciting would be oxidation numbers greater than +2.


texts: How do we obtain the expressions for integrated rate laws ?!? What are the limits we integrate it under and with respect to what do we integrate it?


texts:
I understand that starch will precipitate from an aqueous solution in the presence of alcohol. I also understand that molar mass effects solubility and starch has a relatively high molar mass. There is also an issue regarding the polarity of the solute and solvent.

Is the insolubility of starch (which has the form $\ce{(C6H10O5)$_n$}$) in ethanol only due to the fact that starch is polar and ethanol is only slightly polar?


texts: Definition of early vs. late transition metal

texts: Is there an accepted definition of an early or late transition metal? I think the late transition metals start at Group 8 (including Fe), but others have said Fe is not a late transition metal. I'm just curious if this is a matter of preference based on one's field of study or if there is a generally accepted definition.


texts:
The idea of water potential still confuses me. I understand the general idea: water moves from an area of higher water potential to an area of lower water potential. However, I still do not understand the mechanism by which this occurs.

Take the example of putting salt on a slug. Putting salt on a slug lowers the dilute potential which in turn lowers the water potential on the outside of the slug. This lower water potential on the outside then draws water from the higher water potential of the inside of the slug.

I do not understand how this occurs. All the answers I find is that this just “occurs” because “nature wants to find equilibrium” (such as the second response on this Quora question). That makes sense in theory, but how does the cells of the slug “know” that there is now a lower water potential? What has changed?


texts: Why does dipole must lie parallel to a rotation symmetry axis?

texts:
While studying group theory, I've got confused by the following statement:

  For a molecule to have a permanent dipole moment, it must have an asymmetric charge distribution. The point group of the molecule not only determines whether the molecule may have a dipole moment but also in which direction(s) it may point. If a molecule has a $C_n$ axis with $n > 1,$ it cannot have a dipole moment perpendicular to the axis of rotation (for example, a $C_2$ rotation would interchange the ends of such a dipole moment and reverse the polarity, which is not allowed — rotations with higher values of $n$ would also change the direction in which the dipole points). Any dipole must lie parallel to a $C_n$ axis.

why does the dipole need to be parallel to the $C_n$ axis? If I put a fluorine atom in just one of the light gray atoms of the following molecule, wouldn't it have a molecular dipole that isn't parallel to the main axis?


texts:
I am just reading what a double  replacement  reaction is and what are the examples.

So I came up with  this  question : what is a reaction actually?

For example when we add $\ce{Fe(NO3)3}$ and NaOH to water we see $\ce{Fe(OH)3}$ forms as a precipitate. So hay! A reaction  has occurred!

But the reaction in the title doesn't form any precipitate depending on solubility rules. So does any reaction really takes place or the substances just dissociate into separate ions?


texts: H-NMR Equivalent Protons and Coupling of Glycerol

texts:
I've been searching for explanations to understand why the labeled protons on carbons 1 and 3 are not equivalent in the below figure.

Another figure that shows the same results:

SDBS confirms the same, although the assignments of the signals show that all 3 hydroxyl Hs are equivalent, which I don't understand.

I would think that all 4 hydrogens on C1 and C2 would be in identical environments but it seems this is incorrect. In fact, the figures show that the two hydrogens on C1 (and C2) are not equivalent to each other. Why is it that the hydrogens on the terminal carbons are not equivalent, but rather each hydrogen on one terminal carbon has an equivalent hydrogen partner on the other?

Also, what is the explanation for why SDBS shows all 3 hydroxyl protons as equivalent? Why would the -OH on C2 be equivalent to the ones on the terminal carbons?

Edit: As for my first question, I think I found the correct explanation. I believe it's because the hydrogens pairs are either diastereotopic or enantiotopic.


texts: Intutive understanding of internal energy

texts:
Our high school teacher told us that once we calculate the formula of internal energy, it is valid everywhere. I cannot understand how? I asked him, he simply answered because it is state function. It made me even more confused.

From first law, $\mathrm dU=\mathrm dq+\mathrm dW$

In constant volume process, volume differntial $\mathrm dV=0$, hence $\mathrm dW=0$, so

$(\mathrm dU)_V=(\mathrm dq)_V$ and $(\mathrm dq)_V=C_V\mathrm dT$

  So, $(\mathrm dU)_V=C_V\mathrm dT$

Why we use this formula everywhere even when volume is changing (since we derived this relation for a constant volume process), at least for ideal gas?


texts: How can we calculate enthalpy change in a closed tank containing methanol adsorbed by activated carbon?

texts:
Here's the problem in the simplest way:

I have a closed box containing methanol adsorbed by activated carbon. The box is made from copper. A pipe is connected to that box, which has condenser on the other end to return the methanol back to the liquid state.

The box is painted black and put in the sun to absorb heat.

The data I have collected are:

initial and final pressure
initial and final temperature
0.26 kg of methanol was condensed in the other end
0.3744 kg of methanol remained in the tank

How can we calculate enthalpy change in the box (heat absorbed by the box from the sun)?


texts: Confusion regarding calculating the pH of a salt of weak acid and weak base

texts:
I need to calculate the $\mathrm{pH}$ of a salt of weak acid and weak base in an aqueous solution.

Method I used for calculation

For a salt of weak acid and weak base (assuming complete dissociation of salt) both cation and anion part of salt undergo hydrolysis. When cation part undergo hydrolysis, since they are the conjugate base of weak acid, they grab $\ce{H+}$ from water and releases $\ce{OH-}$ ions. Similarly, when anion part undergo hydrolysis they release $\ce{H3O+}$ ions.

This $\ce{H+}$ and $\ce{OH-}$ may react to give water. If we have same concentrations of these ions the solution will have a $\mathrm{pH}~7.$ If there is any excess of any of these ions after reaction, then the $\mathrm{pH}$ of the solution may be greater than or less than $7.$ But my answer didn't match up with what is given in my text.

Textbook answer

Formula given in my textbook is

$$\mathrm{pH} = \frac{1}{2}\left(\log K_\mathrm{b} - \log K_\mathrm{a} - \log K_\mathrm{w}\right)$$

where $K_\mathrm{b}$ is dissociation constant of base, $K_\mathrm{a}$ is dissociation constant of acid and $K_\mathrm{w}$ is ionic product of water.

When I try to derive this formula I need to make some assumptions like degree of hydrolysis of both anionic and cationic part of salt is equal. And the $\ce{H+}$ in the solution is contributed by the dissociation of weak acid how can this be possible. The dissociation of the weak acid formed from salt hydrolysis is been suppressed by already available concentration of its conjugate base (anion part of salt).


texts: Thermal decomposition of group 2 permanganates

texts: Do group 2 permanganates produce manganates via thermal decomposition?


texts: Is the existence of chirality center equivalent to chiral?

texts:
To make my question more clear, I want to ask two questions:

Is it possible for molecule to be achiral even though molecule has chirality center?

Is it possible for molecule to be chiral even though molecule doesn't have chirality center?

I thought of these questions because the definitions of chiral center and chiral do not have a one to one correspondence.
A chiral center is defined by carbon having four different ligands around it and chiral is defined by a compound being non-superimposable with its mirror image. They are quite related, but I think there will be counterexamples that satisfy one condition but not satisfy the other one.


texts: Can ring inversion in Cis-Decalin allow the E2 reaction?

texts:
This is a tutorial question I need to do, I initially thought the question was testing whether students properly understand (1) chair conformations of decalin, and (2) that the leaving group and the breaking bond should be 'anti-periplanar'.
However, the third molecule also turned out to have undergone the elimination reaction when the first didn't, so I am very confounded. I have drawn all possible conformations of cis-Decalins, but no single conformation seems to allow $\ce{C-OTs}$ bond and $\ce{C-OH}$ bond to be anti-periplanar. Am I missing out something?


texts: What is special about the molecule luciferin that it can emit light?

texts:
A classic example of bioluminescence; the protein luciferin is oxidized by the enzyme luciferase, releasing energy as light.
What is it that gives luciferin this ability? Why can't just about any protein display bioluminescence?

Are there more chemical reactions where electromagnetic waves are produced? Also, are there any chemical reactions which produce high energy electromagnetic waves, such as X-Rays?


texts:
Consider the following reaction at equilibrium.
$$\ce{A->B}, \Delta H < 0 $$

Suppose I increase the temperature. Now, quite a few people would invoke Le Châtelier's Principle and say that since "heat" is a product of this reaction, the equilibrium should shift backwards. This is clearly wrong because "heat" is not a species you can have in a reaction. You can't incorporate it into the reaction quotient.

If you take
$$\Delta G = \Delta H - T\Delta S$$
for $\Delta S < 0$, you could make a claim of the equilibrium shifting backwards at higher $T$. This doesn't have anything to do with the sign of $\Delta H$ however.

Is there an actual theoretical basis for the following claim that does not invoke a principle that does not apply:

  For an exothermic reaction at equilibrium, increasing the temperature
  will cause the equilibrium to shift towards reactants.


texts: Hybridization of Cu2+ in tetraamminecopper(II) sulfate complex

texts:
$\ce{Cu^2+} $ has 9 electrons and the $\mathrm d$-orbital is almost completely filled (except for 1 electron vacancy), eventually forming $\mathrm{sp^3}$ hybrid orbitals, where each $\ce{NH3}$ donates a lone pair of electrons.
But it has been found to have a square planar geometry, hence completely contradicting the above reasoning. So, please explain what is the hybridization of the $\ce{Cu^2+}$ in the given complex?


texts: Why is the Vitamin B complex, a "complex"?

texts:
I often come across the term "Vitamin B Complex" in my biology classes and innumerable times on the back of multivitamin packets, but what does the term "complex" here, even mean?

I'm still in high-school, and the only times we ever come across the term "Complex" in our Chemistry classes is when we're dealing with Coordination Compounds, but I don't think that's what our textbook is getting at when it says "Vitamin B Complex". I compared the structures of a few B-vitamins, but they don't appear to have anything to do with the coordination Chemistry kind of "Complexes".

My teacher tells me, that the term "Complex" here is supposed to indicate the existence of a wide range of B-Vitamins (Like $\ce{B1, B2, B3,}$ etc.). But I didn't find that 'explanation' satisfying, since there are all sorts of other vitamin categories (such as D and K) that have quite a few subtypes ( $\ce{D1, D2, D3, K1, K1, K3,}$ etc) but I've never heard of a Vitamin D Complex or a Vitamin K Complex for that matter.

So my question stands:-

What does the term "Complex" mean, with regard to the Vitamin B Complex? Do  Vitamin D Complexes and Vitamin K Complexes exist as well?


texts: Harmonic frequencies (IR) and basis set size

texts:
Usually vibrations (harmonic), derived from harmonic approximations are bigger than for experimental values. The question is, how does this depend on the size of the basis set. Many papers give that as a statement in their introduction without any explanation.

My idea would be that, if I use variational methods like DFT, then my energy will always be bigger than the real energy, as long as I use a finite basis set. And also increasing the set gives better results in DFT. The harmonic frequencies I determine computationally are derived from the Hessian matrix (or better the force constants for the harmonic oscillator) and this matrix is the second derivative of the energy, which is much too big for small basis sets.

So can I say that, because a smaller basis set will give me a bigger energy, the derived frequency will have to be bigger as well?


texts: How does the Hammett acidity function work and how to calculate it for [H2SO4] = 1,830? Any references?

texts:
I'm modelling the concentrations in the Belousov Zhabotinsky reaction. For this model, I need to convert [BrO3-] to [HBrO3]. I discovered in several papers that the following correlation applies:
$$ [\ce{HBrO3}] = \frac{h0}{h_0+0.2} * [\ce{BrO3^-}]_0 $$
See for example this dissertation on page 28 or this paper on page 2.
I have a solution which has $[\ce{H2SO4}]$ = 0.915M (I assume $[\ce{H+}]$ = 1,830 M).
My $[\ce{BrO3^-}]$ was 0,2411 M.
I researched the Hammett Acidity function, but I still don't completely understand the concept. What I do know is that $h_0$ substitutes for $[H+]$ and that $h_0$ has the unit of M.
Can anyone explain the concept of this function in a bit more detail and explain in what way it exactly relates to pH (and therefore to H+)?
On the internet I found this paper, which says that $h_0$ = 3 when $[\ce{H2SO4}]$ = 1.5M. Are there any other tables or references with $h_0$ related to the concentration of $\ce{H+}$ or $\ce{H2SO4}$? There is one more question on SE about Hammett acidity. This question links to tables with $h_0$ for certain % of H2SO4. Can I perhaps use that? How does $[\ce{H2SO4}]$ relate to a % of H2SO4?
Is there a way to calculate the $h_0$ when $[\ce{H2SO4}]=1.830 M$?


texts: How can water with a very low hardness have substantial buffer capacity?

texts:
My freshwater fish tank has a pH of 5.8 and a KH value in excess of 40 or 720+ppm while still maintaining a water hardness of 20 ppm or GH< 1 now I am a math/phsyics student but I have taken both first year chem class at university so I expect to follow most basic ideas pertaining to chemistry but this doesn't make a lot of sense. Most water with a high alkalinity also has a basic pH around 8-8.5 normally I'd say that a high KH value is simply saying I have an acidic solution that is very resistant to a pH change i.e. a large buffering capacity but my water is very soft to the point of almost not having anything in it ( GH<1) or less than 20ppm of minerals how can water be so acidic have such a large buffering capacity and have nothing in it?

(the reason why I am asking here is all the aquarium forums i have tried can't seem to figure out what's going on in my tank)

EDIT:

This answer poseing an intresting possibility my tank has Turtles in who obviously are advanced enough to excreet urea instead of amonium i Titrated out a reaction and Got KH value of 28 and GH value of 4.5 i also added several air stones ( my buddie has a bio chem degree and figured it could of been too much $CO_{2}$ we managed to get the Ph up to ~6.4 and drop the KH value ot be more closely in line with accpetable parameters ( a value of 8 still oddly high compared to the GH value of 4.5)


texts: I know it is covalent because there are covalent bonds between atoms of carbon in the same plane. But there are Van der Waals interactions between different planes. Isn't this a feature of molecular solids?


texts: Reactor mass balance with solid feed and overflow

texts:
I am modeling a lime slaker which is basically a stirred tank reactor with two separate feeds:
1. CaO feed screw (powder)
2. H2O binary valve (liquid)

These react according to the reaction:
$\ce{CaO(s) + H2O(l) -> Ca(OH)2(s)}$

The slaker is operated on a semibatch fashion where water and lime are fed until the desired amounts have been added and when the reaction has finished a new batch can be started. Water is added in excess with a mass ratio of approximately 1:4. The addition of the reactants takes about six minutes and after that some minutes are required for the temperature to rise due to the reaction. The reactor is not emptied between the batches but the contents exit to a secondary tank through internal piping on an overflow basis. An example of the development of the reactor temperature is given below.

Because of the overflow the volume of the reactor (and the contents) stays constant. The output feed is not measured. In general, the material balance of a model is:

the rate of accumulation of mass in the system = rate of mass entering the system - rate of mass leaving the system

or

$\frac{dM}{dt}=\dot{m}_{in}-\dot{m}_{out}$

or

$\frac{dV\rho}{dt}=\dot{F}_{in}\rho_{in}-\dot{F}_{out}\rho$.

For the lime addition weighing data is available to determine the mass of the added quicklime. The lime feed screw is operated at a constant speed so the feed rate can be determined. The water feed has a flow measurement.

What would be the best way to form the material balances as the reaction happens between a liquid and a solid? How to determine how much material is displaced by the addition of lime? How does the formation of calcium hydroxide affect the balance?


texts: When and why do hot material take heat from cold material?

texts:
This is what I read on Chemwiki:

  Rudolf Clausius was a German physicist, and he developed the Clausius statement, which says "Heat generally cannot flow spontaneously from a material at a lower temperature to a material at a higher temperature." However, there is one exception to this statement and that is sometimes a hot material will take heat from the cold material, making the hot material warmer and the cold material colder.

Chemwiki does not provide a reference for the exception about heat transfer from cold material to hot material. How is this possible? What is an example of this happening?


texts: Which is the cheapest plastic that retains its structure at 85 °C or higher temperature?

texts:
In an academic project, I need to protect some electronics components from heat (around 85 °C). I am searching for both a cheap plastic film and a cheap plastic to be used in a injection molding process.

As matt_black referred, the main criteria of the selection is "the point where structural integrity is reduced by repeated use at that temperature or the point where the polymer starts to creep".

By now I am using cork, but I would like to use a more robust material.

Those materials should be both thermal and electrical insulators and should not absorb water. They should also be resistant to the external environment: rain, sun (UV radiation), dust, etc.

Which materials are the best option in this case? From what I have searched, these are the main options in terms of thermal requirements:

PPO/PPE based
Polypropylene
Polyurethane
Vinyls
Polybutylene
Acetals
ABS and SAN
Polystyrene
ABS/Polycarbonate alloy
Acrylics
Cellulosics
Polyethylene and copolymers


texts: NH2- and Primary Alkyl Halides: Sn2 vs E2

texts:
When we mix 1-bromopropane and $\ce{NaNH2}$, what happens? Which reactions wins out to make the major product?

My textbook says that primary alkyl halides give mainly SN2 products unless the base is hindered ($\ce{t-BuO-}$) (where E2 would win out).

But it contradicts itself when you have for example 1,2-dichlorobutane and you add three molar equivalents of $\ce{NaNH2}$ and then $\ce{NH4Cl}$ to have an alkyne. Why is there no SN2 going on in that case?


texts:
According to your experience, in terms of durability and longevity of the tools, which one of these types of pipette pumps is better and why?

Tri-valve pipette bulb
Syringe pipette pump
Electronic pipette pump

These pipette pumps are mentioned in the YouTube video Bio-Rad Laboratories — Using Serological Pipets.


texts: Surface Tension of Water and Breaking through that surface tension

texts: I know that the high surface tension of water makes it relatively more difficult for light objects to break through the surface (i.e. it's why insects can "walk" on water).  So that seems to work when an object moves from the air into the water (submerged).  But what about from the other direction?  By that I mean, an object trying to break through the surface of the water but moving from a submerged location to one above the water (in air).  In this scenario, is it also relatively more difficult to break through water than if an object was trying to break through ethanol, for example, from a submerged location?


texts: Accuracy benchmarks for atomic multipole moments

texts:
Thermochemical accuracy is regularly quoted as 1 kcal mol$^{-1}$, or 4.2 kJ mol$^{-1}$. I'm expressing some data and I want to use benchmarks like this to validate them, however, they are not all in units of energy. My analyses involve various ranks of a multipole expansion.

I have found a reference when benchmarks dipole moments$^{1}$, but I can't find anything in the literature which similarly benchmarks higher rank multipole moments. Any pointers to the literature or comments from experience would be greatly appreciated.

[1]: J. Phys. Chem. A, 2014, 118 (20), pp 3678–3687.


texts: Why isn't 4-hydroxybenzoic acid formed along with salicylic acid in Kolbe's reaction?

texts:
I've read that in Kolbe's reaction of phenol, i.e. reaction of phenol $(\ce {C6H5OH})$ with $\ce{NaOH}$ forming sodium phenoxide $(\ce {C6H5O^{-}Na^{+}})$, followed by reaction with $\ce{CO_2}$ and acidification; salicylic acid (2-hydroxybenzoic acid ) is formed, but when $\ce{KOH}$ is used instead of $\ce{NaOH}$, 4-hydroxybenzoic acid is formed.

I don't understand why two different products are formed in the same reaction using very similar bases. Moreover, there is electrophilic aromatic substitution on the phenoxide ion in both reactions and  $\ce{O^{-}}$ being an ortho-para directing group must form both products in both the reactions.


texts: Why doesn't the enthalpy change of a reaction affect the rate of reaction?

texts: For example, an exothermic reaction will release energy to provide energy to overcome the activation energy. So, why doesn't the enthalpy change affect the rate of reaction?


texts: I taught chemistry for 30 years and never encountered the unit until I saw it on a juice bottle!


texts: Which has greater +R strength - toluene or anisole?

texts: I read that resonance in toluene is initiated with the help of hyper-conjugation. Also hyper-conjugation is weaker than resonance/mesomeric effect. But, in toluene, its resonance is taking place with the help of hyper-conjugation, am I right? I am confused which has greater +R strength - toluene or anisole?


texts: The difference between bonding and unpaired single electron radicals

texts: I was wondering as to why would two unpaired single electron radicals form a bond. So, I tried to compute the added ground state energies of two particles in two distinct, yet identical boxes, The energy of ground states would be $E_1=\frac{\hbar^2\pi^2}{2mL^2}$ each, so the total energy of the system would be $E=\frac{\hbar^2\pi^2}{mL^2}$. But when I compute the ground state energies of putting both the particles in the same box. (I am keeping the box length the same, just trying to look at it like an approximate model). Then I have a ground state energy of $E=\frac{5\hbar^2\pi^2}{2mL^2}$. So, the ground state energy of having two electrons in a box is higher than the combined energy of the system having one electron each in a separate but identical box. How does one explain bonding to himself. Is there any literature on it, or am I going wrong somewhere? I would appreciate if I was directed towards some literature on it.


texts: If temperature and volume are same, the pressure of gas obeying van der Waal's equation is smaller than that of an ideal gas"

texts: Can you state the reasons for it. I think " It is smaller because mutual forces of attraction would resist the collision of particle and container".


texts: How to measure the content of sugar, proteins and fat in meat?

texts: I do a research project for Science Symposium and I need to measure a content of proteins, sugar and fat in a meat. Unfortunately, I have found only the methods that require specials apparatus/device that I do not have in my school. I'm a student of secondary school, so I need a simple method. Could you please recommend me one?


texts: Comparing van der Waals constant for gases

texts:
How can I compare the van der Waals constant $a$ (the liquefication constant) for different compounds based on my knowledge of bonding in the compound? Let's pick the following sample set:
$$
\newcommand{\d}[2]{#1.&\hspace{-1em}#2}
\begin{array}{lrl}
\hline
\text{Compound} & &\hspace{-1em}a \\
\hline
\text{Helium} & \d{0}{0346} \\
\text{Argon} & \d{1}{355} \\
\text{Xenon} & \d{4}{25} \\
\text{Water} & \d{5}{526} \\
\text{Ethanol} & \d{12}{18} \\
\text{Acetone} & \d{16}{02} \\
\text{Acetic acid} & \d{17}{71} \\
\text{Benzene} & \d{18}{24} \\
\text{Toluene} & \d{24}{38} \\
\hline
\end{array}
$$
A general trend that I can see is $a$ is proportional to molecular mass. Am I wrong to compare on the basis of intermolecular forces like hydrogen bonding, which is clearly very good in the water but the $a$ value isn't so promising?
Is it my misconception that $a$ depends on intermolecular forces? As far as I know, the stronger the forces, the more easily it will be liquefied, and greater should be $a.$


texts: What are the half-equations of manganese and oxygen in the following redox reaction?

texts:
The equation is $$\ce{2Mn^2+(aq) + 4OH^-(aq) + O2(aq) -> 2MnO2(s) + 2H2O(l)}$$
I know that the Manganese (II) gets oxidized to Manganese (IV), but I'm not sure about the other half. I know oxygen gets reduced, but using simply $\ce{O2 +2e^-->2O-}$ doesn't work because the equations won't balance out then.

By the way, this chemical equaltion is used in the Winkler titration.


texts: Term symbol for atomic nitrogen: why can't S be -1/2?

texts:
The spectroscopic notation for an element is given by $^{2S+1}L_{J}$. I want to use this notation for nitrogen with configuration

$$\mathrm{[1s^22s^22p^3]}$$

This is what I did. $l=1$ for p orbital. There are three electrons in p orbital, two electrons: spin up and spin down, and the remaining electron in spin up position, so that my $$S = \frac 12 + \left(-\frac{1}{2}\right) + \frac12 = \frac12$$ which gives

$$J=l+s=1+1/2=3/2$$

My query is can't the remaining electron in p orbital be in spin down position so that my $S$ becomes $-1/2$ and so that $J=l+s=1/2$.


texts: Matching a Slater-type wavefunction with a minimal (STO-nG) Gaussian basis set

texts:
I have on hand a high-precision wavefunction expressed in Slater orbitals.  I need to express it as accurately as possible in a minimal Gaussian basis set.

For background: I am currently working with STO-6G, but it is not good enough to describe the cusp condition with the accuracy I need. How can I get to a basis like STO-7G, or even beyond to something like STO-10G, preferably in a form that is compatible with QChem?


texts: Why might the yield of my synthesis of triphenylmethanol be so poor?

texts:
I performed the classic Grignard reagent formation leading into the preparation and purification of triphenylmethanol using phenylmagnesium bromide as my Grignard, and benzophenone as the reagent for the subsequent reaction.

In the formation of the Grignard reagent, I used Mg turnings to react with bromobenzene to produce phenylmagnesium bromide with excess bromobenzene as Mg was my limiting reagent.

In the second reaction, I reacted the Grignard reagent with benzophenone, my limiting reagent, to form an alkoxide intermediate, to which I added excess 6M HCl to protonate the intermediate to form crude triphenylmethanol.

I then performed a recrystallization of the crude triphenylmethanol (with biphenyl as a by-product) with isopropyl alcohol.

Aside from poor technique with the laboratory procedures, what can contribute to a poor yield of purified, recrystallized triphenylmethanol?

I did some searching online, and found that certain individuals mentioned a low yield being attributed to "competing side reactions", but with no further details. Is this referring to the biphenyl side-reaction between the phenylmagnesium bromide and bromobenzene, or another external factor?


texts: Imagine a compound such as 1,3-dibromo-1,2,3-trichloropropane. Since the first and third carbons are attached to four different groups, they are both chiral centers. Assuming that both of these stereocenters are mirror images of one another (as in (1$S$-3$R$)-1,3-dibromo-1,2,3-trichloropropane), would the second carbon also be considered a stereocenter? If so, how would you differentiate the two enantiomers around that carbon using IUPAC nomenclature? Also, would such a carbon be optically active?


texts: What gas is released during dissolving NaOH

texts: What gas is released during dissolving solid $\ce{NaOH}$ in a high purity water? Water more than 10 M$\Omega$/cm and standard quality $\ce{NaOH}$.