texts: Creating a 10% saturated sodium triphosphate and 2.7% sodium hypochlorite solution for tomato seed sterilization

texts:
For tomato seed extraction/sterilization a standard procedure involves the treatment of tomato seed pulp with 6M HCl for 15 min and then one of the two following:

15 min in 10% saturated sodium triphosphate

or

15 min in 2.7% sodium hypochlorite solution

Is it possible to create a solution that has both without any cross-reactivity or decrease in properties? Each solution appears to better destroy different types of pathogens, so combining them would save time if that would be an option.
Thank you.


texts: Rotational Barriers - Amide and Hydroxamic Acid

texts: Why the barrier to rotation about the $\ce{C-N}$ bond higher in an amide than it is in a hydroxamic acid? (MO-based explanation preferred)


texts: Why does acidity increase going from sulfide to sulfoxide to sulfone?

texts:
It is fairly well-known that the acidity of a proton alpha to a sulfide/sulfoxide/sulfone increases in that order. Some pKa values (in DMSO), courtesy of the Evans pKa table:

Traditionally this has been explained by resonance, or delocalisation of the carbon-based negative charge onto oxygen (left, below). But this necessarily invokes hypervalency and a S=O double bond. The major resonance form in a sulfoxide should be the charge-separated, octet-compliant form (right, below).

What is the proper explanation for the acidity trend above, then?


texts:
Polypropylene glycol is produced by ring-opening polymerization of
propylene oxide. The initiator is an alcohol and the catalyst a base,
usually potassium hydroxide. When the initiator is ethylene glycol or
water the polymer is linear. With a multifunctional initiator like
glycerine, pentaerythritol or sorbitol the polymer branches out.
Source: https://en.wikipedia.org/wiki/Polypropylene_glycol
Polypropylene glycols ... are formed by action of base on propylene oxide in the presence of 1,2-propanediol as an initiator.

I don't understand the meaning of an initiator here. My mechanism is the first the OH- adds to the propylene oxide giving $\ce{HOCH2CH2O-}$ which again adds to another molecule of the oxide and the chain continue and the polymer is formed.
My mechanism requires no role of the "initiator". I want to know what is the requirement of the diol in initiating the polymerisation, whether my mechanism is correct and if wrong, what is the actual mechanism?


texts: Can I convert from an emission amount (in tonnes per area) to a concentration (in ppbv)?

texts:
Hi, I was wondering if it is possible to estimate the concentration of SO2 given the total mass of SO2 emissions?

Europa's EDGAR has a resource called "Global Emissions EDGAR v4.2" (see http://edgar.jrc.ec.europa.eu/overview.php?v=42). A database of SO2 emissions in Metric Tons per Area is provided, but I need concentration instead.

Currently I am determining the volume of the gas by assuming it's at STP, then I am dividing this by the estimated total containing volume, which I tried to estimate as follows.

  Total Containing Volume = (11120 m*11120 m)*altitude

or

  Total Containing Volume = (apprx. area of 1° latitude by 1° longitude "square")*altitude

I calculated an altitude that makes the calculation match another database of SO2 concentrations that I have. Unfortunately the other database of SO2 concentrations is limited in the area that it covers, so it is not suitable.

Is this estimation attempt misguided or is there a better way to do it? If there is another database that contains global or continental SO2 concentration grids that would also fix the problem.


texts: How can the size of atom be the cause of octet expansion?

texts:
Lately, I was reading The Lewis Theory of Covalent Bonding by Peter Atkins in Appendix 4 of 'Elements of Physical Chemistry'. There he was talking about expansion of octet . As he wrote:

  Many molecules cannot be written in a way that conforms to the octet rule. Those classified as hypervalent molecules requires an expansion of octet. Although it is often stated that octet expansion requires the involvement of d-orbitals, and is therefore confined to Period 3 and subsequent elements, there is good evidence to suggest that octet expansion is a consequence of an atom's size, not its intrinsic orbital structure. [...]

I had always bore in mind that octet expansion was always due to d orbitals.

But size of atoms? How can it be related to octet expansion?


texts: What is the difference between a Chemical Formula and Formula Unit?

texts:
In my textbook, a chemical formula is described as :

  "A formula that shows the kinds and numbers of atoms in the smallest representative unit of a substance"

While a formula unit is described as :

  The lowest whole number ratio of ions in an ionic compound.  Thus the formula unit for sodium chloride is NaCl.

Though the definitions seem to differ, the written formulas appear identical.  A chemical formula appears to be another way to represent a formula unit. For example, NaCl is both the chemical formula and formula unit for Sodium Chloride.
Is there ever a difference between the written terms?


texts:
In all the chemistry books and eBooks it says that "like dissolves like"... but when it comes to some molecules like ether, cellulose, vitamin A and $\ce{CO_2}$, it confuses me.

If we take ether, it is true that it will not form hydrogen bonds with water when it dissolves, but they have polar bonds between $\ce{O}$ and $\ce{C}$ and it's not in a linear form like $\ce{CO_2}$ where the dipoles cancel out.

Vitamin A also has $\ce{-OH}$ group but it still is hydrophobic. In some book, I read that this is because it has more hydrophobic molecules or that they have more $\ce{C-H}$ bonds than $\ce{-OH}$. If it is so, octadecanol and nonadecanol also have way more $\ce{C-H}$ bonds than $\ce{-OH}$ groups, so  why is it still soluble? $\ce{CO_2}$ is dipolar — the dipoles cancel out, so why is it still soluble? Cellulose also has a bunch of $\ce{-OH}$ but still it is soluble. I am very confused by this.


texts: Is solubility coefficient affected if ion data is given in Ksp?

texts:
Recently I've been looking at this website, which says:

The $K_{\mathrm{sp}}$ of $\ce{Cr(OH)3}$ is $6.70 \times 10^{-31}$
Problem 1: What is the minimum $\mathrm{pH}$ at which $\ce{Cr(OH)3}$ will precipitate?
$$\ce{Cr(OH)3\rightleftharpoons {Cr^{3+}}+3OH-}$$
$$K_{\mathrm{\mathrm{sp}}}=[\ce{Cr^{3+}}][\ce{OH-}]^{3}$$
$$[\ce{Cr^{3+}}]=s$$
$$[\ce{OH^{-}}]=3s$$
Problem 2: What is the minimum $\mathrm{pH}$ at which $\ce{Cr(OH)3}$ will precipitate if the solution has $[\ce{Cr^{3+}}] = 0.0670~\mathrm{M}$?
$$\ce{Cr(OH)3\rightleftharpoons {Cr^{3+}}+3OH-}$$
$$K_{\mathrm{sp}}=[\ce{Cr^{3+}}][\ce{OH-}]^{3}$$
$$6.70 \times 10^{-31}=[0.0670~\mathrm{M}][s^{3}]$$

I don't understand why the site wrote this:

Note that $3s$ is not necessary. In example one, $s$ was assigned to the chromium ion and we knew the hydroxide to be three times greater than that value. Here, the hydroxide is simply an unknown value and it is not expressed in terms of some other unknown value (as it was in Problem 1).

Can anyone tell me why?
Also is also used to other equilibrium constant equation? What did I miss?


texts: Is there a way to calculate bond energies using computational chemistry?

texts:
I'm currently trying to see if a particular set of ligands will react with a metal ion to form a complex. While I'm waiting for the wet lab results to arrive, my adviser suggested we look into computational chemistry to see if we can model the proposed structures theoretically.

Neither of us (or anyone in the department for that matter) have any experience in computational chemistry. I got my hands on a copy of Avogadro and GAMESS-US and have optimized the geometries of the complexes we think might arise. Is there a way to determine if the complexes would form? Thanks.


texts: Is the correlation energy of a system always negative?

texts: The correlation energy of a system is defined as the difference between the exactly energy and the energy in the Hartree-Fock method: $E_\mathrm{cor} = E - E_\mathrm{HF}$. In the case of an atom or a molecule, is it possible say that $E_\mathrm{cor} < 0$, since the interaction between the electrons is positive?


texts: Is cyclohexane saturated or unsaturated?

texts: I have this confusion that cyclohexane is of form $\ce{C_{n}H_{2n}}$ and so it must be an unsaturated compound, but also it does not have a double or triple bond so it must be saturated.


texts:
In the reduction of an aldehyde (e.g. ethanal) to a primary alcohol, a reducing agent is needed:
$$\ce{CH3CHO + 2[H] -> CH3CH2OH}$$
My book states that one hydrogen (the $\ce{H-}$ ion) is from the reducing agent, and the other hydrogen (the $\ce{H+}$ ion) is from the solvent.

However, elsewhere it more generally notes that "$\ce{[H]}$ denotes a hydrogen from a reducing agent".

Does the $\ce{[H]}$ notation refer only to hydrogen atoms from the reducing agent, or, as this example implies, can it also refer to hydrogen atoms from other sources (such as the solvent)?


texts: Stability of meta ethyl and meta methyl benzene carbocations respectively

texts: It is known that Methyl has a greater +I effect than Ethyl, but here, in this case, the condition is satisfied in the para benzene carbocations whereas, in the meta forms, it is the opposite. Shouldn't meta methyl benzene carbocation be more stable than meta ethyl benzene carbocation? Please, Can anyone explain?


texts: Is aromaticity of the 4 aromatic amino acids affected by pH?

texts:
During a discussion of NMR, my lecturer told me to think about which amino acids contain protons in an aromatic ring, and whether any are likely to be affected by changes in pH.

The 4 aromatic amino acids are His, Phe, Tyr and Trp. I've marked Histidine as such in my notes, but can't remember why I thought this at the time. Contrary to this, Wikipedia states explicitly that “the imidazole ring of histidine is aromatic at all pH values”.

I also marked Histidine as "+ve" (as in, positive) but I'm stumped as to what I meant by it

I can't find any information on the others, but am guessing perhaps the fact that these have phenyl (rather than imidazole) rings means it's possible they respond differently to changing pH?

Any advice or hints would be appreciated, as I can't find any further information online and nothing in the structures jumps out at me to suggest an answer.


texts: Why does water become less dense when it cools

texts: Most materials become more dense as they cool, but ice floats in water, meaning that it's less dense. Why is this?


texts:
My textbook had this question:

  Hydrogenation of napthalene with excess hydrogen gas stops cleanly at 1,2,3,4-tetrahydronapthalene. What conclusion can be drawn from this experiment?

I observed that only one of the two rings was reduced. I did expect both the rings to reduce though, because the hydrogen gas was in excess.

In the solution manual, it is given that this is the "annelation effect", which isn't given in my textbook. I checked the internet, and could only find two research papers, which only detailed some typical aspect of annelation, not annelation itself. Wikipedia instead has no article on the "annelation effect" (but annulation instead, they definitely don't seem to be related though)

So, what is the annelation effect? I am not asking for the mechanism (unless it is as simple as catalytic reduction of alkenes, which I guess it isn't) nor the internal details of its procedure, but a simple overview of what it is and where it is applicable, with an example or two so I can easily identify it. And, how does the "annelation effect" help the fact that the above hydrogenation "stops cleanly" at one ring, even with excess hydrogen?


texts: Can someone please explain buffers to me?

texts:
This is what I understand so far:

The concept of a buffer is to minimize any swings in pH. In order to do this you need to create a solution with both acidic and basic compounds.

To create one, you start with an acid:
$\ce{HA + H2O -> A- + H3O+}$

[My first question is why for buffers the acid needs to be weak.]

The buffer is then created by adding in a salt containing the anion of the base which allows for both the acid and its conjugate base to exist in the solution.

Here, why doesn't the conjugate base react with the acid? Second, why does this help minimize pH changes. I see that since that you have a weak acid the conjugate base will be strong and can react with any acid added. However, if you add base what is going to react with it? Isn't the acid too weak to do so? Third, what happens to the $\ce{H3O+}$ that exists in the solution?


texts: Reaction between 1-methylcyclopentanol and potassium permanganate

texts:
In my basic organic chemistry class, I learned that only primary and secondary alcohols undergo oxidation (using $\ce{KMnO4}$).

However, what is the outcome of reacting tertiary alcohol (1-methylcyclopentanol) with a strong oxidant like $\ce{KMnO4}$ with no heat?

P.S. I am specifically interested to know what happens with no heat, because according to my minimal knowledge I know if heat was added then it is dehydration.


texts: Vanishing integral rule for two-electron integrals

texts:
I understand the vanishing integral rule for a one-electron integral to be:

$$\langle i | \hat{O} | j \rangle = 0 \hspace{1cm} \mathrm{if} \hspace{0.2cm} \Gamma_O \neq \Gamma_i \otimes \Gamma_j$$

For electronic repulsion integrals, the Coulomb operator is totally symmetry, so the product must contain the totally symmetric irrep (TSIR). However, I am not sure what form the vanishing integral rule will have. Is it simply

$$\langle ij | kl \rangle = 0 \hspace{1cm} \mathrm{if} \hspace{0.2cm} \Gamma_\mathrm{TSIR} \neq \Gamma_i \otimes \Gamma_j \otimes \Gamma_k \otimes \Gamma_l$$

or does it have a different form? Additionally, will a Schwarz-inequality matrix composed of:

$$Q_{ij} = \sqrt{\langle ii | jj \rangle}$$

have an identical block-diagonal structure to the one-electron matrices constructed in this fashion?


texts: Why are calorimeters often made of materials with low specific heats?

texts:
When building calorimeters, a material with a low specific heat is often used (such as Styrofoam, aluminum, etc.). However, why would a material with a low specific heat be preferred? My thought process is below:

Scenario: An exothermic reaction occurs in a calorimeter.

Principle: In calorimetry, we are always trying to minimize the amount of heat transfer from the calorimeter to the surroundings. The amount of heat transferred from the reaction to the calorimeter doesn't really matter because we can calculate this quantity of heat using the calorimeter's calorimeter constant, which we can derive experimentally.

Case 1: Calorimeter made of material with low specific heat

If the calorimeter had a low specific heat, it would absorb less heat, but its temperature would increase more. Differences in temperature cause heat transfer, so a larger difference in temperature between the calorimeter and the surrounding air would mean more heat transfer from the calorimeter to the surroundings.

Case 2: Calorimeter made of material with high specific heat

If the calorimeter had a high specific heat, it would absorb more heat, but its temperature would not increase much. Differences in temperature cause heat transfer, so a smaller difference in temperature between the calorimeter and the surrounding air would mean less heat transfer from the calorimeter to the surroundings.

Therefore, a calorimeter with a high specific heat would be more effective because it would minimize heat transfer between the calorimeter and the surroundings.

Where is the flaw in my logic?

Additionally, according to http://www.greenspec.co.uk/building-design/insulation-materials-thermal-properties/,

  A good insulator has a higher specific heat capacity because it takes time to absorb more heat before it actually heats up (temperature rising) to transfer the heat.


texts: Salt Bridge for Microbial Fuel Cell: Full or Partly Full?

texts: I'm making a microbial fuel cell out of benthic mud and salt water in containers. My salt bridge will be made of agar and table salt solidified in PVC pipes. Does the salt bridge connecting the anode (benthic mud) and cathode (salt water) have to be full of the agar-salt solution, or can it be partly full?


texts: Does reduction/ oxidation take place separately at a half cell electrode?

texts:
In the redox reaction chapter, we learn that oxidation and reduction go hand in hand.  The oxidising  agent oxidises by accepting the electron released by the reducing agent and gets reduced in the process.

However, in the half cell electrode (say, $\ce{Zn}$/$\ce{Zn^{2+}}$) only oxidation is  taking place and no simultaneous reduction is happening in the scene. Also, in a $\ce{Cu}$/$\ce{Cu^{2+}}$ half cell electrode, only reduction is taking place. Until  the half cells are joined by a  saltbridge, oxidation and reduction go on violating the basic  principle of  redox reactions.


texts: Reference for UV/Vis Spectroscopic Data request

texts:
I am looking for a complete reference of UV/Vis spectroscopic data for organic materials ( mostly interested in λmax ) .

I have the CRC handbook but it only has data about some organic solvents in water and very limited data on dyes.

Can anyone suggest a comprehensive reference that includes the λmax of a wide variety of molecules in different solvents ?


texts:
I've been taught that to make esters, the carboxylic acid has to be activated — for instance as the acid chloride or using DCC.

But, when I read papers on total synthesis, always they use more complex reactions such as a Yamaguchi in order to do a ring closing esterification.

Why are standard esterificaton conditions not suitable for complex molecules?   One though I had was that acid chlorides are so reactive that they're easily quenched by water, but this would just give back a carboxylic acid which could be reacted again (no damage done overall).


texts: Why only a specific pressure for the Haber's process?

texts:
This question, in my opinion is different from Why is the Haber process carried out at such high temperatures?

Referring to the above link, I understand that why high temperature of 700 K is chosen, i.e, to overcome the activation energy barrier as well as kinetic considerations. However, why is the pressure 200 atm only. Why not 300?

According to Le Chatelier's principle, there larger the pressure, more ammonia will be formed.


texts: How was it possible to accurately measure the mass of gases in the 19th century?

texts: I have seen periodic tables of Mendeleev (1834-1907) and Newland (1837-1898) in which masses of gases such as oxygen and nitrogen were shown. I don't think there were instruments to measure mass of gases at that time. So how were they able to predict the mass of gases at that time accurately?


texts: Why can Bi not achieve its 4+ oxidation state?

texts: Bi can reach its 3+ and 5+ oxidation state. Why not 4+? Can you use the inert pair effect here to explain this?


texts:
Smoke alarms are a necessary part of many modern day buildings, especially in laboratories and of course, the family home.

According to the World Nuclear Association page Smoke Detectors and Americium (2014), a major part of the operation of a smoke detector is when the Americium-241 emits alpha particles collide with atmospheric oxygen and nitrogen, ionising them - which form part of an electric current between two electrodes.

When there is smoke (from the article) - bolding mine:

  When smoke enters the space between the electrodes, the smoke particles attach to the charged ions, neutralizing them. This causes the number of ions present – and therefore the electric current – to fall, which sets off an alarm.

What is the chemical process that causes smoke to neutralise the charged oxygen and nitrogen ions in smoke alarms?


texts:
I have a few small bottles of 0.5M $\ce{SnCl2}$ solution, however solution was prepared about 4 months ago, and there is a yellow precipitate on the bottom of each bottle. Working hypothesis is that this yellow precipitate is $\ce{Sn(OH)Cl}$, and reaction is:

$$\ce{SnCl2 (aq) + H2O (l) ⇌ Sn(OH)Cl (s) + HCl (aq)}$$

(from Wikipedia)

I added a few drops of $\ce{HCl}$ to push the equilibrium towards left-hand side, but so far only small part of yellow precipitate is dissolved. Should I add plenty of $\ce{HCl}$ then? If you have any idea on how much, please let me know.

Wikipedia says:

  Therefore, if clear solutions of tin(II) chloride are to be used, it
  must be dissolved in hydrochloric acid (typically of the same or
  greater molarity as the stannous chloride) to maintain the equilibrium
  towards the left-hand side (using Le Chatelier's principle).

do I read it right that I have to add the same volume of $\ce{HCl}$ (0.5M) to my 0.5M $\ce{SnCl2}$? (well, they didn't say that, but sort of hinted)

Thank you very much in advance!

UPDATE: I added decent amount of $\ce{HCl}$, and I still have some yellow precipitate (I think less, than before, but still a rather large amount), and my solution is not transparent, it is whitish-opaque. $\ce{SnCl2}$ solution has to be transparent.


texts: Adiabatic flame temperature of hydrogen peroxide calculation

texts:
I will first demonstrate my cursory method for evaluating the adiabatic flame temperature of H2O2 at atmospheric pressure.

$$\ce{H2O2 -> H2O + 0.5O2}$$

At $\pu{1200 K}$,

\begin{align}
h_\ce{H2O}^\pu{1200 K} - h_\ce{H2O}^\pu{298 K} &= \pu{34.506 kJ/mol}\\
h_\ce{O2}^\pu{1200 K} - h_\ce{O2}^\pu{298 K} &= \pu{29.761 kJ/mol}\\
\Delta_f H^\pu{298 K} &= \pu{-241.826 kJ/mol}
\end{align}
Sources: $\ce{H2O}$: https://janaf.nist.gov/tables/H-064.html;  $\ce{O2}$: https://janaf.nist.gov/tables/O-029.html

At this temperature,

$$\text{Energy released} = 241.826 - 34.506 - 0.5 \times 29.761 = \pu{192.44 kJ/mol}$$

For Adiabatic flame temperature, the energy released should be equal to zero which is not so in this case (I am aware that the process is iterative). However, multiple sources indicate the flame temperature to be around $\pu{1000 K}$. A screenshot from RPA (a rocket propulsion software) is one such source.

The software obviously takes into account other products but, even as a first estimate my calculation shouldn't have been so off from the software calculation. I would appreciate any help in pointing out the mistake in my calculation.


texts: Can liquids be made a lot purer than by fractional distilation?

texts: Suppose you have a fused quartz tube with one closed end coiled into a spiral with a diameter of more than 10 m and you submerge it into a mixture of water and ethanol in a way that gets rid of all air then reposition it in such a way that it's partly submerged with the axis of the coil going nearly horizontally and slightly up in the direction from open end to closed end. Furthermore, suppose that the coil then starts moving and spinning along its length in the direction from open end to closed end and once the closed end passes the height where cavitation occurs, the closed end is cooled to recondense liquid there and after cavitation occurrs again on the next loop, liquid is condensed again in the same way? Is it true that if the concentration of water is above a critical concentration, it will become more concentrated after it cavitates and is recondensed because a smaller fraction of ethanol vapour will condense than water and if the concentration of water is below that amount, the water will become less concentrated after it cavitates and then is recondensed because a smaller fraction of water will evaporate than ethanol? Could really pure water be gotten in that way because fused quartz is extremely insoluble in water?


texts: What is the temperature of heat generated from LPG gas?

texts:
I'm working on a project and I require around 300-400 degree Celsius of temperature. As of now I'm taking the normal LPG gas that is available in our house for cooking purposes for my project, but I'm not sure whether it can reach 300-400 degree Celsius or not? I can definitely use multiple burners but how much heat/temperature does 1 burner generate?

Maybe I'm wrong because heat is counted in calorific value, but then how do we know the temperature of that calorific value? Or is there some relation which says that x amount of LPG would give x degree Celsius or maybe x calorific value? But yet again, how can I know the temperature?


texts: What is the major product of the reaction of 2-methylbuta-1,3-diene with HBr?

texts:
What is the product of the reaction of 2-methylbuta-1,3-diene (isoprene) with HBr?

What I understand is that carbon (2) will get a positive charge after protonation.
But after this, which should be the major product?

3-bromo-3-methylbut-1-ene – because in this case the carbocation would be stable because of being tertiary, but the double bond would have less number of hyperconjugated structures and will be less stable

1-bromo-3-methylbut-2-ene –  as the carbocation would be less stable because it would be primary but the double bond would be much more stable because of 8 $\alpha$ hydrogen available


texts: Reaction mechanism of a terminal alkene with an anhydride

texts:
In a reaction (as given in my textbook),

$$\ce{R-CH=CH2 + (CH3-CO)2O  -> R-CH2=CH-COCH3}$$

an alkene reacts with acetic anhydride to give methyl alkenyl ketone.

I am not sure of how this proceeds, a search on google displays no links to any relevant matter, and I have not successfully found this reaction in any of the other books I possess.

According to me, it should have been an addition reaction (characteristic of alkenes) across the double bond. But this isn't the case here. So, what exactly is the reaction mechanism?


texts: Calculating equilibrium concentrations of silver and halide ions

texts:
$\pu{500 ml}$ of $\pu{0.01 M}$ $\ce{AgNO3}$ is mixed with $\pu{500 ml}$ of solution containing $\pu{0.1 M}$ $\ce{NaCl}$ and $\pu{0.1 M}$ $\ce{NaBr}$. $K_\mathrm{sp}$ of $\ce{AgCl}$ is $10^{-10}$ and $K_\mathrm{sp}$ of $\ce{AgBr}$ is $5×10^{-13}$. Find $[\ce{Ag+}],$ $[\ce{Cl-}],$ $[\ce{Br-}]$ in equilibrium solution.

After adding all of these molarities will get halved. At equilibrium condition, both $\ce{AgCl}$ and $\ce{AgBr}$ would have precipitated out. So, using the $K_\mathrm{sp}$ expression, we can find maximum amount of $\ce{Ag+}$ required to precipitate both the salts, and this becomes the equilibrium concentration of $\ce{Ag+}$.

Plugging these values in $K_\mathrm{sp}$ of respective salts, we can get the equilibrium concentration of remaining anions.

The $[\ce{Ag+}]$ for precipitation of $\ce{AgCl}$ is $\pu{2E-9},$ and for precipitation of $\ce{AgBr}$ is $\pu{E-11}.$

So, $\ce{AgCl}$ gets precipitated at last.

$$K_\mathrm{sp}(\ce{AgCl}) = [\ce{Ag+}][\ce{Cl-}]$$

Therefore, $[\ce{Cl-}]$ at equilibrium is $\pu{5E-2}.$

$$K_\mathrm{sp}(\ce{AgBr}) = [\ce{Ag+}][\ce{Br-}]$$

Therefore, $[\ce{Br-}]$ at equilibrium is $\pu{2.5E-4}.$
$[\ce{Ag+}]$ at equilibrium is $\pu{2E-9},$ which is already calculated in first step.

However, this doesn't match the answer key. Where am I wrong?


texts: How did Noe et al. derive $k_{AB}$ in their PNAS 2009 paper?

texts:
This question is regarding Constructing the equilibrium ensemble of folding pathways from short off-equilibrium simulations which uses Markov State Model to find the equilibrium protein folding pathways from off-equilibrium simulations.
I find the notation a bit hard to follow. How does Frank Noe and others derived equation 1?

In the supplementary information they don't really explain and aren’t careful with the math notations:

I do see how a rate equals $k_{AB} = P(A^C|A)/P(B^C \cap A^C)$, but I don’t see how $\sum_{i=1}^m \pi_i q_i^{-}$ gives $P(B^C \cap A^C)$ which is the probability to be outside of $A$ and not in $B$.


texts: Chromium from electrode not oxidizing in electrolysis

texts:
I performed an electrolysis of an aqueous sodium carbonate solution with a platinum electrode and a chromium-vanadium-steel-alloy electrode. The solution turned yellow at the chromium-vanadium-alloy electrode (I suspect that it is sodium metavanadate (NaVO3))

Then I also performed an electrolysis in an aqueous sodium carbonate solution with a platinum electrode and an inox electrode (the inox electrode is composed of iron, chromium,...) . A green compound (insoluble) was formed and when I later added acetic acid, a brown compound (I think Iron(III) acetate ) was formed.

But in both cases there were no chromium compounds formed (at least of what I know) So why didn't the chromium react (why didn't the chromium get oxidized)?

More information:
Voltage was around 13 Volts, the inox electrode was stainless steel (see http://en.wikipedia.org/wiki/Stainless_steel) and has according to wikipedia a minimum of 10.5% chromium content by mass. I read online that a regular chromium-vanadium-steel-alloy has a vanadium  content  of approximately  0.181%  and a chromium  content  approximately  1.00%. (however, I'm not sure about these last two figures) What is true is that there wasn't a lot of yellow sodium metavanadate after an electrolysis of around 20 minutes. ) The electrolysis solution contained sodium carbonate(Na2CO3) and water(H2O) the electrolysis was performed at normal conditions (1atm - 25°C)


texts: Finding formula of reduced scandium oxide using its mass and mass of obtained metal

texts:
An oxide of scandium, with a mass of $\pu{1.423 g},$ is chemically reduced with $\ce{H2}$ to give $\ce{H2O}$ and $\pu{0.929 g}$ of $\ce{Sc}$ metal. What is the formula of scandium oxide? How much water is formed?

I know that the reaction is of the form:
$$\ce{Sc_xO_y + H2 -> H2O + Sc},$$
where $x$ and $y$ are the units to define scandium oxide molecular formula (not empirical).
I don’t know how to get the constants using the info given, and what the info given tells me. I typically use a linear system of equations to solve for the reactants and products. In this case, we’d have:
$$
\begin{align}
\ce{Sc}&: &\quad  Ax - D &= 0;\\
\ce{O}&: &\quad   Ay - C &= 0;\\
\ce{H}&: &\quad   2B - 2C &= 0.
\end{align}
$$
Usually, we would have an equation where $x$ and $y$ aren’t present and you can solve the system of equations. Here, it prevents you from doing the balancing. Instead, you’re just guessing. Any suggestions when linear algebra doesn’t work?


texts: Why does the fructose monomer in sucrose appear different from isolated fructose?

texts:
I understood that the representation of fructose is:

But during the formation of sucrose:

How did fructose, whose representation is given in the first picture, turn out to be different in the second. I tried to visualize myself rotating the molecule but the position of oxygen changes and it doesn't match with the one in sucrose.


texts: when drawing the chair conformation for beta-L-fructose, I got the structure above (in the picture). The answer said that the conformation above had a ring flip. Why does a ring flip occur and how can we tell when it occurs?


texts: Thermodynamic vs kinetic reaction control with radical substitution

texts:
Doing a revision for a chemistry class test tomorrow, I stumbled upon thermodynamic and kinetic reaction control in the context of radical substitution.

Here, my chemistry teacher said, that thermodynamic reaction control would basically be about favoring stabilized (originally instable) transition states, e.g. by increasing temperatures. According to him, this would "thermodynamically prefer" the substitution of tertiary hydrogen atoms relative to primary ones.

However, he also told us that kinetic reaction control would, instead, prefer the substitution of primary hydrogen atoms. More precisely, the fastest reaction (which would result in the substitution of primary hydrogen atoms due to less steric hindrance) would be favored under certain conditions.

The question is, under which conditions a certain type of reaction control would be prefered.


texts: How does pressure influence the dehydration of salts?

texts:
It's well known that the boiling point of a substance increases with pressure. I was wondering if something similar happens with hydrated salts and the temperature at which they dehydrate.

I mean, if the pressure is increased, does the temperature at which a salt dehydrates rise or is it not affected by the pressure?


texts:
Recently I have tried to perform an experiment with luminol and hydrogen peroxide (with potassium ferricyanide as the catalyst). Upon googling, I found two ways to conduct this experiment and was wondering which way is more suitable (because I have limited amounts of luminol and do not want to fail the experiment and waste luminol).

1st way: Preparing an alkaline stock solution of luminol and potassium ferricyanide and another stock solution consisting of hydrogen peroxide only.

2nd way: Preparing an alkaline stock solution of luminol  and another stock solution consisting of hydrogen peroxide and potassium ferricyanide.


texts: Synthesis of Almotritpane - mechanism for educational purpose

texts:
I purposed a full mechanism of the almotriptane synthesis.
I wanted to help my fellow students and myself.
Could you give me any tips? Are there any mistakes? I posted the SnCl2 reduction already, but I proposed a second mechanism and cant decide which one is right.


texts: What are possible side reactions for the generation of hydrogen via electrolysis?

texts:
I recently completed making a simple water electrolysis setup to generate hydrogen which uses two graphite rods from a standard AA battery. The power source is a $24~\mathrm{V}$ $6~\mathrm{A}$ adapter. I am using salt water as electrolyte (The salt is iodized). Strangely, a minute or so after running, a black precipitate starts to form on the negative terminal.
Also, besides the hydrogen, another gas is generated which smells sour, not very sour, but somewhat like lemonade. I have no idea what is causing this.
I thoroughly cleaned the graphite rods before using them. Has anybody an idea about what reaction might be happening here?


texts: Which is more effective at raising pH, Tums or baking soda?

texts:
Chemical buffers like Tums (calcium carbonate) and bases like baking soda (sodium bicarbonate) are both used medically to reduce acidity in the stomach to ease heartburn symptoms. I'm curious which is more effective in vitro.

I'm interested specifically in the comparison in effectiveness of bases and buffers, which act in slightly different ways to raise pH. I'd also love to learn the math behind figuring this out so next time I can answer such a question myself :)


texts: What is the reaction between NaOH and urea?

texts:
In this video it is mentioned that urea and sodium hydroxide will react to produce ammonia. However, I can't seem to find a clear explanation of the reaction and the other products generated.

One explanation I found says that the NaOH causes the urea to hydrolyze, yielding sodium carbamate, which will then further hydrolyze to sodium carbonate.

Another says that the urea tautomerizes to ammonium cyanate, which preforms a substitution with the NaOH to yield ammonium hydroxide and sodium cyanate.

Which of the two reactions occurs? Do they both occur? Neither?


texts: Surface Chemistry - Dipole Moment of Surfactant with Water and Phases of a Monomolecular Layer

texts:
Recently, I have been trying to study surface chemistry and I have come across questions that I do not understand how to answer. I understand what a dipole moment is, defined as a charge separation over a defined distance, and I have a fair understanding of surfactants and other areas of surface chemistry such as Langmuir Isotherms. But I am struggling to answer such questions:

How would surfactants with a dipole moment in contact with water be characterised?

Would this mean that most likely the ionic head of a surfactant interacts with either the partially-positive hydrogen or partially-negative oxygen moiety of a water molecule? If so, what would be the proper way to characterise this phenomenon?

In what phase of the monomolecular layer are the sizes of surfactants determined?

I am puzzled by this question, as I do not understand what exactly is meant by phase. I have spent relentless time trying to search for monomolecular layers and their phases but I have come out empty-handed. I see that phase can refer to distinct boundaries of physical states, such as those between gasses and liquids, but I do not know how this could be used to find the size of molecules. I know that in order to find the area that each surfactant molecule covers at an interface the Gibbs Adsorption Equation is utilised, however it uses concentration of surfactant molecules plotted against surface tension.

I would be much obliged if anyone could provide assistance to aid me in understanding this subject of surface chemistry better.


texts: What reactions does this steel cold-bluing solution undergo?

texts:
Bluing steel generally refers to the process of forming a protective layer of $\ce{Fe_3O_4}$ ("black iron oxide") that prevents normal rust from forming. The chemistry behind the traditional industrial process for bluing steel involving multiple baths in hot alkalis and acids ("hot bluing") is reasonably well documented (and is not the focus of this question).

My question is about a different procedure referred to as "cold bluing" in which steel parts are treated with a solution at room temperature and blacken instantly without heat. The ingredients from the MSDS of a popular cold bluing product are:

Phosphoric Acid
Copper (II) Sulfate
Nickel (II) Sulfate
Selenous Acid

(The compounds are listed in descending order by percentage.)

Phosphoric acid seems like a reasonable ingredient. It's well known as a rust remover and iron phosphate protects some steels from oxidation. Unfortunately, from there the ingredients seem to become increasingly perplexing.

Copper sulfate isn't itself an unusual compound, but I'm not sure what it's doing here. Nickel sulfate is even more confusing, but nickel salts are toxic so it must be there for a pretty good reason.

The relevance of selenous acid escapes me. All I really know about it is that it's an oxidizing acid and is basically selenium dioxide dissolved in water.

Treatment of steel with this solution causes a black coating to form almost instantly. I've been starting to wonder if cold-bluing is actually "plating" the similarly colored copper (II) oxide onto the steel rather than forming black iron oxide.

If this is the case, I would expect the reaction to be something vaguely like:

$\ce{Fe + CuSO_4 +\ ?-> FeSO_4 + Cu +\ ?}$ (copper is more noble)

$\ce{Cu + H_2SeO_3\ +\ ?\ -> CuO + Se +\ ?}$ (is selenous acid really strong enough to oxidize copper?)

...but this doesn't involve the nickel sulfate at all and just generally feels wrong.

So, overall my question is:

What is the black compound that forms on the outside of steel when treating it with the solution described above, and how does it form?

edit: Additional thoughts:
While there is very little information on this compound online, copper selenide is described by Sigma-Aldrich as being a black powder. I can't find any discussion of its synthesis outside of some articles about nanoparticles, but I wonder if it's a more reasonable outcome than copper oxide.


texts: Reaction rate coefficient constant multiplier for equation with multiple atoms consumed?

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For the elementary reaction $\ce{2O -> O2}$, when calculating the rate of concentration change of atomic oxygen as $\frac{d[O]}{dt}$, would I use the standard rate coefficient $k_f$ or would I have to multiply by 2 since 2 oxygen molecules are being consumed?

$\ce{O + O -> O2}$ with $\frac{d[O]}{dt} = -2 \cdot k_f \cdot [O] \cdot [O]$

or

$\ce{O + O -> O2}$ with $\frac{d[O]}{dt} = -k_f \cdot [O] \cdot [O]$

Or would the rate constant define the dependency on atomic oxygen?


texts: Stoichiometry based on addition of simultaneous equilibria

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I read on another equilibrium question that if two equilibria occur at the same time, then it is not accurate with actual stoichiometry to add the two equations and multiply the equilibrium constants $K_1$ and $K_2$ in order to get an equation with stoichiometric consistency. In , multiple ICE tables are used to get around the problem. This makes the most sense to me.

However, when dealing with solubility of compounds with complex formation, many textbooks (Atkins) and websites (libretexts Oxtoby) show that you just add the two equations together and calculate solubility from there. From the libretexts site, Example 16.5.2, Equation 16.5.15 - 17 does the same operation as what I thought was forbidden/not accurate above. Here, the website says $\ce{{AgCl} + Cl^- <=> [AgCl_2^{-}]}$, which I do not think is correct.
edit: I understand that this equilibrium is correct in the way that $\frac{\ce{[AgCl_{2}^{-}]}}{\ce{[Cl^-]}}$ is constant, but using the new equilibrium to solve based on stoichiometry (when the website says that

$K=\dfrac{[\mathrm{AgCl_2^-}]}{[\mathrm{Cl^-}]}=\dfrac{x}{1.0 - x}\approx1.9\times10^{-5}=x$

can be used to solve for $x = \ce{[AgCl_{2}^{-}]}$) is off to me.

Which one is right? Can you actually add two simultaneous equilibria together to simplify the problem with easier stoichiometry? Or is this some sort of approximation that works because of the specific conditions that most solubility problems have?
I feel like I have a big misunderstanding here.

EDIT: I figured it out. For solubility-complex reactions, the above is an approximation based on the relative magnitudes of the equilibrium constants. Because complex formation is so favorable the majority of the time, we can assume that almost every mol of solid dissolving into solution will be consumed to form complex ions. I didn't see this anywhere I looked so I figure I might as well post it here.


texts: Why does CO2 have higher boiling point than CO?

texts: The intermolecular forces between $\ce{CO2}$ molecules are dispersion forces, while the forces between $\ce{CO}$ molecules are mostly dipole-dipole attraction forces. So, why does $\ce{CO2}$ have a higher boiling point than that of $\ce{CO}$?


texts: Behavior of π-conjugated chromophores in the presence of light

texts: In the presence of light, I have read that, structures comprising π conjugated systems like retinol, straighten out from their curled positions, what phenomenon drives this behavior and why does this need to happen? I do understand that for proper π-orbital delocalization in the conjugated system, I would need the p orbitals of all the carbon atoms to be in the same plane, so staying straight would be an assistance, but what I fail to understand is that how does the absorption of light have anything to do with this?


texts: What is the difference between a 500W high pressure mercury lamp and a 400W high pressure mercury lamp

texts: I know that the Wattage of a UV lamp is only one factor in the UV output of a light, and therefore cannot be used as a measure of how powerful a light is. Also it doesnt have any effect on the produced wavelength. Is it like this that a lamp with higher wattage can cause higher temperature on substrates that are being irradiated ?


texts: I know the that it(Resonance) is the delocalisation of pi electrons but how and why are those electrons delocalised? What is the driving force that causes the effect?


texts: XRD-Shorter distance between planes than actual radius of atoms/or cell parameter

texts:
I'm solving problems related to X-ray diffraction, and I get these results which apparently are correct. My question may be dumb, but I just can't see how the interplanar distance might be shorter than the atoms radius.

What's up with this?

I think it might make sense that its shorter than the cells parameter, but it's not immediately obvious to me, so if someone could prove it to me, i'd be quite glad.

Edit:

For example:

The atomic radius of chromium is 124pm. THe distance between (310) planes is .0912nm.
See problem 6


texts: What do (2S,3S) and similar notations mean?

texts: When my textbook is discussing stereoisomers with more than one chiral centers, it's using notation like (2S,3S) being an enantiomer with (2R,3R) and so forth. I understand R and S configuration, and I'm guessing there are two items in each brackets to represent the two chiral centers (so 2S, 3S would at least mean that both chiral centers have an S configuration), but I don't understand what the numbers preceding the configuration mean. What does the 2 in 2S mean and what does the 3 in 3R mean? I was unable to find an explanation in the text and it seems that their meaning is assumed. Can I get some help?


texts: Why there were changes in molar mass of lithium?

texts:
I am curious why there were changes in molar mass of lithium in the past.

The values were like 9 to 10 before 1830. But suddenly after 1830, the range of molar masses seems similar to the molar mass that is used now.
I thought there might be some technical issues in the past. But, from 1830, the values were consistent and stable. So, I cannot assume there were lack of development in equipments and technics.

So, my questions are:

1. why the values were around 9-10 before 1830, not around 6.941?

2. why the values suddenly became similar to the molar mass which is used now?


texts: What is the difference between hand wash and body wash soap?

texts:
I do not like body wash always with strong favor. I like hand wash soap to wash my body. Are they difference at all?

Thanks for the comments, so that I add the following information
I am really sorry that I posted the question using my phone at my office parking lot right before I went to work this morning, so not much detail was added

To my limited knowledge, Body wash and hard wash soaps are detergent, they both are OK to use on skin. If that is the case, why body wash soap is body wash soap? What I mean is that from the chemistry point of view, what makes body wash soap difference from hand wash soap?


texts:
What's wrong with ionic resonance structures? I asked one professor about them once and all he commented was "I've seen them too, and I think they're wrong."

Another professor rejected an ionic resonance structure showing the "H+" ion and asked me what phase the experiment was run in, in an attempt to figure out why the authors reported a resonance contributor with a H+ proton. He specifically asked if the experiment was run in the gas phase.

I think this guy forgot what resonance structures are because I know that he emphasizes that bare protons do not exist in solution, and he was probably thinking about how there could be a bare proton shown in a resonance structure if the molecule is in solution. The resonance structure I showed him was this (which I could see him picturing in solution, given that it is nitrous acid.

However, resonance structures are not discrete forms of the molecule in question - they're just contributors and show that there is partial ionic character; that there is a highly electronegative atom that is withdrawing electron density.

So I ask:

1) Are ionic resonance structures valid?

2) If so, why might they be valid, or what counterarguments might you present to someone who argues they are invalid?


texts: The real structure of difluoro(dioxo)xenon (XeO2F2)

texts:
I have a problem regarding structure of difluoro(dioxo)xenon ($\ce{XeO2F2}$). I have posted a image above. my teacher is saying that the structure B is correct as there is very less repulsion in structure B that is what I too think but many of the sources and books have written the structure A to be correct and me as well as my teacher is in a doubt that why structure A is correct not structure B as there is an angle of 180° between oxygen atoms. If I am wrong please guide me and also please tell me what are factors should I look at for judging a correct shape for a compound.
Any hint will be very very helpful to me .


texts: Does borax do anything more for "boosting" detergent than adding active oxygen would?

texts:
Borax, $\ce{Na2B4O7}$, is often marketed as a "laundry booster" under the brand "20 Mule Team Borax".  The unit crystal of borax can be seen below.

Other laundry products in the past have added sodium perborate (which can be produced from borax, hydrogen peroxide, and sodium hydroxide) as a bleaching additive.  The "peroxide" portion can readily be seen below.

Through what mechanism does the plain borax "boost" the detergent?  Would it be more effective to throw some weak peroxide and a small amount of base into the laundry to form the perborate instead of using plain borax?


texts: Optical isomerism regarding diastereomers

texts:
Are diasteriomers always optically active?
If not then why?
Though they are chiral then also.


texts: Why laboratory glassware shatter in big pieces?

texts: What are laboratory glassware made up of? This question came up in mind because once I accidentally dropped a test tube and it shattered into big pieces. I observed that it didn't broke into pieces on first impact to the floor rather it bounced and broke into pieces on second impact. Any ordinary glass would shatter into small pieces On the very first impact to the floor. Does this type of glass possess elasticity?


texts:
Is there any logical reasoning behind the migratory aptitude for different groups in Baeyer-Villiger Oxidation?
Like in pinacol-pinacolone rearrangement, hydride ion is a better migrating group than an aryl which is better than an alkyl group. But why isn't this kind of order in Baeyer-Villiger Oxidation?


texts:
From Russian test problem 4301:

$$\ce{3NaNO3 + 8Al + 5NaOH + 18H2O -> 8Na[Al(OH)4] + 3NH3(g)}$$

How does ammonia evolve here? Is it that we get hydrogen gas evolving in the reaction between Al and NaOH, and this gas reacts with the NO3 anion?

I there a logical way to deduce this, or should one just memorize that "Al and Zn reduce $\ce{NO3-}$ to ammonia in basic solutions"?

P.S.

I learned that the reaction is called "a nitrate test using Devarda's alloy", but there is no specific description of the process in Wikipedia. All I learned is that the reason is certainly not the freshly-minted hydrogen:

  Nascent hydrogen was supposed to be responsible for the reduction of arsenate or nitrate in arsine or ammonia respectively. Nowadays, isotopic evidence[8] has closed the nascent hydrogen debate, presently considered to be a Gedanken artifact of romanticism.

And I wonder why NaOH is needed. Probably to activate the aluminium (to break the oxide layer).

Related question: testing for nitrate ions with NaNO3


texts: What is Meant by "Eluting with 1-2% EtOAc/pentane" in Terms of Flash Chromatography?

texts:
I am reading the experimental section of a paper, and it states

  [compound of interest] Isolated as a pale yellow oil after flash chromatography on silica gel, eluting with 1-2% EtOAc/pentane...

This is all this paper states in regards to the work-up procedure. I fully understand everything in this section except what is meant by 1-2% EtOAc/pentane. Does this mean that in total only 1-2% by volume of ethyl acetate is used compared to the amount of pentane used in the flash chromatography? This could also mean that a solution of 1-2% ethyl acetate in pentane was used throughout the entire run (which I find most likely). Which of these interpretations is most likely? Would this mean the author of the paper did not change the polarity of the solvent during chromatography and only use a 1-2% EtOAc in pentane solution?

Here is the DOI to the paper: 10.1039/c6ob01026a


texts: Defining enantiomer of morphine by R/S designation

texts:
How to know if the following chemical structure of morphine is an R or S? What I basically need to know is: which chirality center do we use to make the decision?

$\hskip2in$


texts: What is the order of the reaction with respect to NO?

texts:
The following reaction mechanism has been proposed for the reaction of $\ce{NO}$ with $\ce{Br2}$ to form $\ce{NOBr}$
  $$\begin{align}
\ce{NO(g) + Br2(g)&<=>NOBr2(g)}\\
\ce{NOBr2(g) + NO(g) &-> 2NOBr(g)}
\end{align}$$
  If the second step is the rate determining step, what is the order of the reaction with respect to $\ce{NO}$?

Since the 2nd step is the rate determining, shouldn't the order with respect to $\ce{NO}$ be 1? According to my book though, the correct answer is 2. What am I missing here?


texts: What does chemical bonding look like at the quantum level?

texts: How does chemical bonding look like on the quantum scale per se since the electron is a wave, and a particle?


texts: Why does diamond have no molecular formula?

texts: Why does diamond have no molecular formula, while buckminsterfullerene does have it, despite both being allotropes of the same element?


texts: Oxidation of alkyl side chain of a benzene ring

texts:
We do know that the side alkyl chain of benzene ring is oxidized by hot KMnO4 to benzoic acids. But how exactly it happens. I couldn't get a proper mechanism for this reaction.
Please help me out


texts:
I have heard of of a special system which specially deals with naming of organic compounds.

How do we get names such as 2-methylpropan-1-ol.
I have tried googling it and found few links but their explanation was way above my head. I also asked my teacher about the same question and he said this is not required in your standard, but I really want to know about naming.

Few Links that I found on Google were

http://en.wikipedia.org/wiki/IUPAC_nomenclature_of_organic_chemistry
Another is wikihow very difficult, I need a simple explanation.


texts: Why do pregnant women turn toilet seats blue?

texts:
My partner is pregnant, and thought perhaps she was going mad when one day she found our toilet seat had turned blue. After some investigation, it seems this is a real phenomena, see here for a nice example, with the image from this link shown below.

One explanation suggested is dye transfer from new maternity jeans, however we find this unlikely for a variety of reasons:

This is late pregnancy and the jeans have been worn for some time without this effect.
My partner assures me she takes her trousers off to go to the toilet, and even her underwear, and there is not a white patch where the underwear would have been (and therefore no dye transfer)

The phenomenon is also described as possibly relating to taking certain pharmaceuticals for Crohn's disease. My partner happens to take (Sulfasalazine) which is used for this (although it's not what she's taking it for) and she's never encountered this before, despite taking them for some time. Another suggestion we've seen is that it is from the dye in a batch of pregnancy vitamin tablets she's started taking, which are indeed blue, although, she's also been taking these daily for a month or so.

However, we don't know the answer, and these are just ideas, so why has our toilet seat turned blue?!


texts: Contradiction of general rules of bond character

texts:
The rules the ionic character of metal halides of halogens is given in order $\ce{MF > MCl > MBr > MI}$.

While judging polarisability we say that a compound that has large cation and small anion will have more covalent nature. So here for same cation, anion with small size should have more covalent character but the trend is totally reverse. Is there any explanation to this?


texts: Why is proton coupling through bonds and how does this affect identical protons?

texts:
I had the opportunity to work with a NMR spectrometer and decided to learn some of the theory behind it. After finishing Clayden's chapter on $^{1}\textrm{H}$ NMR (Ch. 11) I'm still left with some questions, mostly concerning coupling.

Proton coupling is described as the interaction between neighboring (2-4 bonds away) protons magnetic field. This can split the signals by a constant amount (the coupling constant), which depend on the environment of the protons but not on the strength of the magnetic field. Ideally creating a binomial distribution when the neighboring protons have the same shift.

How does a proton create a magnetic field that influences the neighboring protons (mainly) through bonding and not through space?
Why do identical protons not influence each other? Or more generally: why is it that the more identical the influencing protons are with the influenced proton (i.e. $\Delta\delta$ getting equal to/lower than $J$), the more their "outer" signals vanish? Especially since $J$ is a constant, I would expect that for example two doublets would just merge into one doublet and not into only a singlet.


texts: How do we check octet rule in resonance structures?

texts:
For example, this carbon has an incomplete octet:

Can we say this is because C has configuration $\mathrm{1s^2 2s^2 2p^2}$ and hence here its just forming 3 bonds whereas it should form 4 to make it $\mathrm{2p^6}$ and complete its octet? Or do we say that it's forming 3 bonds and hence has 6 electrons and therefore it's octet isn't complete?


texts: Enthalpy change of chromate-dichromate reaction

texts:
I am a uni study doing chemistry. I have taken a little bit in highschool before, but not in a while.

In a (nonassessed) practical, we have to predict how heating a chromate/dichromate solution:

$$\ce{2CrO4^2- + 2H+ <=> Cr2O7^2- + H2O}$$

will affect its equilibrium position. However we have not been given its enthalpy, and I can't find it online anywhere.

I remember from highschool that when you don't know an enthalpy you can estimate it by using heats of formation, heats of combustion, or bond energies. However I have never had to do this with an equilibrium of ions in solution before. Can the same approaches still be taken?

Please provide an explanation of how I can estimate the enthalpy change. Quantitative data would be greatly appreciated.


texts: What is pure oxygen (gas) density as a function of T or P?

texts:
I'm looking for a set of data (ideally graphed) of $\ce{O2}$ density as a function of $T$ or $p$ (with constant $p$ or $T$, respectively).

The best I've found is this 1948 paper which provides an empirical model but (1) it's not as recent as I'd like and (2) I want solid experimental data, not empirical fits. One can calculate ideal-gas densities by $$\frac{pM}{RT}$$ but I'm looking for real values.

A recent empirical model would also be very useful!

Something like this, which is $\rho(T)$ for air:


texts: Why does a bonding molecular orbtial increase stability?

texts:
When two atomic orbitals come together, they fuse to form a molecular orbital. There is a large probability that the electrons will spend time between the nuclei. This will reduce the nuclei - nuclei repulsion and hence increase stability.

The part that I do not get is how do the electrons reduce nuclei-nuclei repulsion? Is it because the electrons in the middle attract the positive nuclei. This creates an opposing force to the electrostatic repulsion? Is this the case and if not what is actually causing the stability?


texts: Why are larger alicyclic rings more flexible?

texts:
My lecturer said that the increasing flexibility of an alicyclic ring is an inherent property. I'm not entirely sure what they mean by flexibility. Number of feasible conformations? How far the bond angles can be away from non-ideal?

Is there an actual explanation for the increasing flexibility?


texts: Strong exothermic mixing of two 'safe' liquids

texts:
I have read (thanks to Stack Exchange) that mixing water and sulfuric acid is exothermic, as is NaOH and HCl.

Are there two 'safe' liquids that can be mixed and produce anywhere near the same amount of heat? By 'safe' I mean they don't come with the same heavy warnings as sulfuric acid or lye. I would like them to be safe enough to be stored in a home and that a spill would probably cause some damage but clean up could be performed by the home owner safely.

I understand that the actual mixing might not be considered safe if they do release a lot of energy.

I'm only considering liquids because they can be kept separate and pumped together.


texts: How do you draw nitrogen in a newman projection?

texts:
I have to draw a Newman projection for a molecule, sighting along the bond between a carbon and nitrogen. Given that the nitrogen is behind the carbon from this viewing angle, how would I depict the nitrogen? I know that I cannot draw it as a circle, as that represents carbon, so I am assuming that it is not possible to draw a Newman projection of this molecule from this particular angle. Is that a valid assumption?

And, if that is true, what would be considered an acceptable answer to that question? Should I just draw a standard 3D structure from the proposed viewing angle?


texts: Balancing a reaction where dichromate ion reacts with ethanol to give Cr(III) and carbon dioxide

texts:
I have only started to learn balancing redox reactions, and a recent question has me confused.
The question is :

Balance in both acidic medium and basic medium:
$$\ce{Cr2O7^2- + C2H5OH -> Cr^3+ + CO2}$$

I usually look for symmetries between the reactant and product sides of a reaction to pair reactants with the corresponding products to form the half reactions, as per the first steps of balancing a redox reaction. I'm having a difficult time doing that here; what am I supposed to pair Cr with? I would personally pair it with the $\ce{Cr2O7^2-}$ molecule but that's just by process of elimination because I would naturally pair $\ce{C2H5OH}$ with $\ce{CO2}$ due to the stronger resemblance they have with each other.
Another matter of concern is the answer in the answer key; the answer in acidic solution is, apparently:
$$\ce{2Cr2O7^2- + 16H+ + C2H5OH -> 4Cr^3+ + 2CO2 + 11H2O}$$
In a basic solution:
$$\ce{2Cr2O7^2- + 5H2O + C2H5OH -> 4Cr^3+ + 2CO2 + 16OH-}$$
It seems like in the answer for the reaction in acidic medium, the left side of the reaction has a charge of +14 and the right side has a charge of +12.
However,  in the basic medium the answer has the left side with a total charge of -2 and the right side -4. How can these answers be correct if the charge isn't balanced?
How do you balance a redox reaction lacking a molecular reactant on the product side? I am referring to the atom or molecule that changes oxidation state when I say molecular reactant.


texts:
If we can have liquid - vapour equilibrium at any temperature what is the 'point' behind boiling point.Boiling point is just a special case of liquid - vapour equilibrium where partial pressure equals atmospheric pressure.Why is it told in my textbook that boiling point is where the liquid and vapour coexist. At any temperature we can have liquid and vapour in equilibrium.

During boiling process when vapourisation take place from the bulk of the liquid does that increase the vapour composition which alters the equilibrium constant without the change in temperature?..

If we look at the phase diagram boiling point lies on phase boundary between liquid and gas ...so does that mean boiling point is when liquid and gas coexist..


texts: How to derive the rate laws for three consecutive reactions?

texts:
Given the following three consecutive unimolecular reactions $$\ce{A ->[$k_1$] I_1 ->[$k_2$] I_2 ->[$k_3$] P}$$ write the rate of change for each.

I have gotten the following:$\newcommand{\diff}{\mathrm{d}}$
\begin{align}
  \frac{\diff [A]}{\diff t}   &=-k_1[A]\\
  \frac{\diff [I_1]}{\diff t} &=k_1[A]-k_2[I_1]\\
  \frac{\diff [I_2]}{\diff t} &=-k_3[I_2]+k_2[I_1]\\
  \frac{\diff [P]}{\diff t}   &=k_3[I_2]\\
\end{align}
Is this correct? If it is, then why cant we write
\begin{align}
  \frac{\diff [A]}{\diff t}   &=-k_1[A]\\
  \frac{\diff [I_1]}{\diff t} &=k_1[A]-k_2[I_1]\\
  \frac{\diff [I_2]}{\diff t} &=k_3[I_2]+k_2[I_1]+k_1[A]\\
  \frac{\diff [P]}{\diff t}   &=k_3[I_2]\\
\end{align}


texts:
A friend of mine who thinks that she is under influence of black magic met an astrologer. The astrologer asked her to wear a t-shirt for three nights and then bring that to him. The astrologer then cut some lemons and rubbed them throughout the t-shirt. Then he poured some water on her hands and face; and asked her to keep the t-shirt on her palm. After about 15 minutes, the y-shirt caught fire and the astrologer dropped the rest of water to put the fire down.

I'm now wondering what chemical could cause this fire. I know that the water looked muddy. Would you please help me to find out what material was potentially used by the astrologer? I'm suspicious of the acid in the lemons and water which has been used, as well as body fat or sweat perhaps was on the t-shirt too. She was telling me that at first, smoke color was white but then it turned to black after the t-shirt caught fire. The smell of the fire was as bad as rotten meat.


texts: Explain the difference in stability of permanganate ions in acidic/ alkaline solutions?

texts:
The question is such:

  Use the data to comment on the stability of $\ce{MnO4-}$ in acidic and basic solution. Suggest a reason for this difference.

  $$\begin{align}
&\text{acidic solution:}&\ \ce{MnO4- + 4H+ + 3e- &-> MnO2 + 2H2O}\qquad &E^\circ&=+1.70\ \mathrm V\\[6pt]
&\text{basic solution}:&\ \ce{MnO4- + 2H2O + 3e- &-> MnO2 + 4OH-}\qquad &E^\circ&=+0.59\ \mathrm V
\end{align}$$

I know that the permanganate ion is more stable in alkaline solution than in acidic solution, as the more positive electrode potential in acidic solution means more negative Gibbs free energy, therefore the reaction is more feasible in acidic solution, therefore less stable...

However, is there a chemical reason for this?


texts:
I am referring to rocks in this instance. Individual crystals grow together in an igneous rock as it solidifies. I know that the $\ce{SiO4}$ tetrahedron is the basic building unit of silicate minerals, and metal cations attach to ensure electroneutrality.

What I am wondering, however, is what force keeps the crystals together (as in bound to one another) in the solid? For comparison, sediment grains are held in place by a silica or calcite cement in fragmental rocks, but what stops individual crystals from breaking free in crystalline solids?


texts: How the Nernst equation is applied for electrodeposition?

texts:
For using the Nernst equation

$$E = E_0 - \frac{RT}{nF}\ln\frac{[\ce{Red}]}{[\ce{Ox}]}$$

the concentrations of $\ce{Red}$ and $\ce{Ox}$ species are required. For the reaction

$$\ce{Cu+ + e- <=> Cu}$$

in which the $\ce{Red}$ part leaves the solution and has no concentration in the electrolyte. How is the Nernst equation used to calculate the potential at different stages when the reaction proceeds?


texts:
Would equal masses of gold and copper result in the same volume change if added to water?
  Density of gold: $19.3~\mathrm{g/mL}$
  Density of copper: $8.96~\mathrm{g/mL}$

I was thinking the answer would be no since the density is different between gold and copper but was unsure if this was a trick question since it maybe has to do with the mass of the substance that is placed into the water.


texts:
I take potassium as a supplement in the form of potassium citrate. I dissolve a small amount in tap water and I drink it. Usually, I need to stir a lot, and sometimes I warm the water a little to make it easier to dissolve the potassium.

Recently, I bought some sparkling water (San Pellegrino, but I don't think that makes a difference) and when I put the potassium in it, it reacted making it bubble a little and it dissolved immediately.

Why is that? Did the potassium react with the CO2 or something else in the sparkling water?


texts: Valency of each atom in a molecule with python

texts:
Consider ethanol, where each carbon atom has a valency of 4 and oxygen a valency of -2. I would like to determine these values for many compounds given their SMILES or InChI keys. (For the purpose of computing the degree of reduction, which in the case of ethanol is 6)

I would like to find a systematic method to calculate this for many molecules. I attempted to use Open Babel as described below, but I am open to any other programmatic solution.

Attempt with Open Babel on Python:

I attempted the following with openbabel.pybel (after installing the appropriate packages):

from openbabel import pybel

ethanol = 'CCO'  # SMILES

mol = pybel.readstring('smi', ethanol)

for atom in mol.atoms:
     print(f"type={atom.type} charge={atom.formalcharge} \
     degree(valence)={atom.degree} implicitvalence={atom.implicitvalence}")

This returns the error:

AttributeError: 'OBAtom' object has no attribute 'GetImplicitValence'

If I understand correctly the implicit valence is the value I am after. I am stuck and the documentation is not helping (is not even consistent with the behavior of the module)
openbabel.__version__ returns 3.0.0.
This is based on a 6 year old question


texts: Distance requirement for hydrogen bonding to occur

texts: I am trying to understand the distance requirement for hydrogen bonding to occur (more specifically in the context of protein folding). There needs to be a donor and acceptor atom for bonding to occur. What is the range of distances between these atoms where one can say that a hydrogen bonding is likely to occur when the polypeptide is in an aqueous environment? Is it element pair specific?


texts: Not sure why, but I can't modify/balance this equation

texts:
I'm working on modeling a few reactions for my research. For example:

$$\ce{CO2 + H2S + CH4 <=> CH3SH + H2O}$$

was one I grabbed from the literature. However, this reaction is taking place in the aqueous phase around neutral pH, so most of the $\ce{CO2}$ will actually be $\ce{HCO3-}$. So in an attempt to model modified versions, I swap out the $\ce{CO2}$:

$$\ce{HCO3- + H2S + CH4 <=> CH3SH}$$

I've tried a redox-equation balancing approach but this hasn't really gotten me anywhere- sulfur doesn't change oxidation states.

I think my brain might just be fried, but can anyone lend any insight on this?


texts: Collisonally induced intersystem crossing

texts:
What makes a molecule a good initiator of collisionally induced ISC? $\ce{N2}$, $\ce{O2}$ and $\ce{CH4}$ have been mentioned as examples.

I imagine the most important factor is the ability to quench vibrational excitation so that the Franck-Condon factors for non-radiative decay are optimized.


texts: Why was the definition of chiral carbon changed?

texts:
Before 1984, the definition of chiral carbon was,

  carbon atom that is attached to four different types of atoms or
  groups of atoms

In 1984, the definition was changed to

  Any carbon molecule that is not superimposable on its mirror image.

Why was this change made? Don't both definitions mean the same or is/are there cases where the former is false. Preferably, please provide an example


texts: Do Grignard reagents deprotonate amines?

texts:
Can I add Mg/dry ether to 2,4,6-tribromoaniline followed by $\ce{D2O}$ in order to replace the bromines with deuterium?

The reaction I'm proposing is part of a synthetic route as shown below.


texts: Comparison of organic and inorganic acid strengths

texts:
So I know how different factors affect acid/base strength, but I am not sure when they are all in the same question, which affects acid/base strength more.

So, for example this question:

How do I know that $\ce{HBr}$ is the strongest acid...because I also have the inductive electron withdrawal from Fluorine in answer choice B.


texts:
I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance.

This seems to disobey Pauli's exclusion principle.

Let's take benzene for example. It has a delocalized cloud of electrons. These all had the "original" (as in, if resonance didn't occur) quantum numbers $n=2,l=1,m=\text{(1,0,or -1; but it must be the same for all)},m_s=\pm\frac12$. But, due to delocalization, they're now all in one extra-large orbital-like region (by orbital-like, I mean that the pi cloud is similar to an orbital in the sense that it is also a probability cloud which defines the probabilities of finding one or more electrons at different coordinates).

Now, it's obvious that the original quantum numbers are insufficient here due to Pauli's exclusion principle. They may not even exist for these electrons.

The easiest thing to do would be to "propose" (not exactly propose, since I guess the Dirac equation can prove their existence) an extra quantum number, which can take twelve values. Or a combination of a few extra quantum numbers that have the same effect.

But this raises the question: do the electrons belonging to the pi cloud "retain" their "original" quantum numbers as well?

Basically I want to know how benzene and other resonating compounds are described quantum mechanically, with focus on quantum numbers. (links to papers are fine, probably necessary here--but please explain the gist of the link)

I'd prefer the answer in terms of simpler quantum mechanics, though I'm not averse to the idea of some extra reading.


texts: Canonical Restricted Open-shell Hartree–Fock equation

texts:
In Frank Jensen's Introduction to Computational Chemistry ($\mathrm{2^{nd}}$ edition), on page 99, it says:

  For an ROHF wave function, it is not possible to choose a unitary
  transformation that makes the matrix of Lagrange multipliers in eq.
  (3.41) diagonal, and orbital energies from an ROHF (Restricted
  Open-shell Hartree–Fock) wave function are consequently not uniquely
  defined and cannot be equated to ionization potentials by a
  Koopmans-type argument.

Here ROHF eq. (3.41) is the non canonical Hartree-Fock equation:

$$F_i\phi_i=\sum\lambda_{ij}\phi_j$$

But in ATTILA SZABO, NEIL S. OSTLUND's Modern Quantum Chemestry, they prove that the Hartree-Fock equation can always be put into the canonical form:

$$F_i\phi_i=\lambda_{i}\phi_i$$

What am I misunderstanding here?


texts: What safety measures should I take when operating a backyard aluminum furnace

texts:
I have made a DIY furnaces out of cement. Before I do any smelting, I would just like to take any suggestions in regards to any safety measures I should take.

I plan to only melt aluminum cans and small parts. I then plan to pour them onto a flat plane to make aluminum plates. Later I plan to make casts.

My furnace is very similar to the one pictured below.

I plan to connect a hair drier to the hole (with an extension metal rod) in order to increase air flow. It will operate by burning charcoal brickets.


texts: How do I find the moles of NaOH required to reach the equivalence point?

texts:
For each trial with the unknown acid, calculate the following:
  a) Moles of $\ce{NaOH}$ required to reach the equivalence point.

I need help with part A. I have already solved and figured out the concentration of $\ce{NaOH}$ ($.125$M). I've been reading my notes and it says moles of acid will equal moles of base. I've tried solving for both using the volumes and molarity and using the $M_1V_1 = M_2V_2$
I think that's wrong and I'm not sure how else to solve it.

Do I even have the correct equation?


texts: References for Transition State Theory and Quantum Transtion State Theory

texts:
Having asked recently this, I started to look for good references and notes on Transition State Theory and, also, modern versions of it including things like tunneling (which isn't taken into account in Eyring's equation).

Unfortunately, I haven't been able to find any satisfactory reference. I have downloaded a bunch of lecture notes and gained conceptual understanding of TST, but nowhere do I find a explanation with all the mathematical details.

What could you recommend for a thorough and detailed exposition of the TST?

Also, I would like to find stuff about how the theory has been improved over the years (the theory is mainly classical). I guess there are more accurate quantum mechanical versions of the theory.

Thanks a lot.


texts:
If I have the reaction
$$\ce{2HI (g) ⇌ H2(g) + I2(g)}$$
and know that at $T = \pu{448 °C}$ the dissociation degree $α = 0.2198,$ how do I calculate $K_c?$
I thought that it would be something like this:
$$
\begin{array}{cccCc}
\ce{&2HI &<=> &H2(g) &+ &I2(g)} \\
&2n && 0 && 0 \\
&2n(1 - α) && αn && αn \\
\end{array}
$$
Then
$$n_\mathrm{tot} = 2n(1 - α) + 2nα = 2n$$
$$p(\ce{HI}) = \frac{2nα}{2n} = (1 - α)p_\mathrm{tot}$$
$$p\ce{I2} = p(\ce{H2}) = αp_\mathrm{tot}$$
$$K_p = \frac{(αp_\mathrm{tot})^2}{((1 - α)p_\mathrm{tot})^2} = \frac{α^2}{(1-α)^2} = \frac{0.2198^2}{(1 - 0.2198)^2} = 0.0794$$
and then from $K_p$ I could calculate $K_c:$
$$K_c = \frac{0.0794}{(8.314 \times 721)^0}$$
I think the last step is where I'm going wrong since it shouldn't be raised to zero. The correct answer is $K_c = 0.01984.$


texts: What is the largest, noncrystalline, non-polymer inorganic molecule?

texts:
A question came up in class from one of my chemistry students. He asked what the largest, non-crystal, non carbon-based, molecule is. We ruled out complex proteins, DNA, and other polymers, as well as crystalline structures and metals from the list. I didn't have an answer for him, so I looked it up but could not find a definite answer. I found two threads on Reddit, listed below. Polyoxometalates come up, but without any specifics. I know "largest" can be subjective, so please specify if the molecule is "largest" because of its physical size or because of its mass.

https://www.reddit.com/r/chemistry/comments/2phl4s/whats_the_largest_inorganic_molecule_you_know/

https://www.reddit.com/r/askscience/comments/i6v07/what_is_the_biggest_noncrystalline_inorganic/


texts:
This is part of my homework. Given the chemical equation :
$$\ce{Sb2S3_{(s)} + 3H2_{(g)} <=>2Sb_{(s)} + 3H2S_{(g)}}\text{        }K_{p}=0,429\text{ at }713\text{K}$$
What is the value of $K_c$ for the reaction?

I used the formula : $K_p = K_c(RT)^{\Delta n}$, but I know that $\Delta n$  considers only the coefficients of the reactants and the products of gas forms, so $\Delta n = 3-3=0 \Rightarrow K_c=K_p$?

Am I right? Thanks for any help!


texts: Derivation of relationship between Gibbs free energy and electrochemical cell potential

texts:
Why is $\Delta G = -nFE$?

I don't understand what the motivation is behind this definition. Was it derived or just given? The textbook provides no justification for this equation. In fact, much of the book associated with the Gibbs free energy provides no justification and just says, 'This is how it is. Now go and solve some problems.'


texts: Can naphthenic acid be ionized in n-dodecane?

texts:
I am not very clear about the difference between ionization and dissolution. I know that naphthenic acid can dissolve in n-dodecane, but I do not know if it is ionized in n-dodecane.
Thank you!


texts: What is the functional difference between a radical anion and a nucleophile?

texts:
Radical Anions are hundreds if not thousands of times more reactive than nucleophiles (right?). A radical anion is just a molecule with an unpaired electron. Where as a normal radical is missing an electron and an atom. If an acidic organic compound is deprotonated to form a nucleophile by removing a proton, then is there not an unpaired electron availible? (which makes the compound nucleophilic)

Why aren't nucleophiles as reactive as radical anions, since they both have "free electrons"? What is the functional difference?


texts: I made an ant poison using boric acid and peanut butter for grease eating ants.  They eat the peanut butter (mixed with some olive oil to get it closer to a liquid), but I see a white residue (crystals?) left behind.  How can I get the boric acid dissolved in an oil or grease?


texts: Powdered Dipropylene Glycol Monomethyl Ether

texts:
Entrepreneur here, background in electronics, so thank you in advance for your patience with me.

Question:
Is Dipropylene Glycol Monomethyl Ether available as a powder? If not, is there a powdered alternative?
Application:
My invention, for everyday people to use inside their homes on steel, plastic and aluminum, requires two liters of diluted liquid degreaser used at room temperature. On lay assumptions pertaining to design, logistics and safety, I am intent on offering this as powdered "just add water" degreaser. Dishwasher detergent does work, but a liquid degreaser sold by Harbor Freight Tools, diluted 50:1 works significantly better -and- it's MSDS describes overall threats on par with dishwasher detergent. It contains:

Sodium MetaSilicate Pentahydrate - readily available in powder form

Tetrasodium EDTA readily available in powder form

Dipropylene Glycol Monomethyl Ether Unable to find in powder form

I could not determine the constituent percentages. (sub-question: is there a way find this out?)


texts: How does a redox reaction between NaClO and KBr take place? will bromide be oxidised to bromine?

texts:
How does a redox reaction between $\ce{NaClO}$ and $\ce{KBr}$ take place?

will bromide be oxidised to bromine?

$\ce{2Br^{−} + ClO^{−} + H2O ⟶ Cl^{−} + 2 OH^{−} + Br2}$

or will bromide be oxidised to $\ce{BrO^{−}}$?

$\ce{Br^{−} + ClO^{−} ⟶ BrO^{−} + Cl^{−}}$


texts: When dealing with electrons and the electromagnetic spectrum, why are there only four visible transitions in the hydrogen atom?


texts: How to control the optimization step size in Gaussian?

texts:
I would like to perform a geometry optimization for a weakly bound methane dimer structure with Gaussian 16. During this process, the Newton-Raphson step should be controlled such that its length should not exceed 0.01 bohr. For this purpose, I created the following input (strictly for testing purposes):
%nprocs=120
%chk=test
%mem=100GB
#hf/sto-3g opt=(trustupdate,nrscale,maxstep=1,maxcycles=100,tight)

test

0 1
C        0.000000000      0.000000000     -1.821797542
H        0.000000000      0.000000000     -2.931818538
H       -0.906328348      0.523268916     -1.451790544
H        0.906328348      0.523268916     -1.451790544
H        0.000000000     -1.046537831     -1.451790544
C        0.000000000      0.000000000      1.821797542
H        0.000000000      0.000000000      2.931818538
H       -0.906328348     -0.523268916      1.451790544
H        0.906328348     -0.523268916      1.451790544
H        0.000000000      1.046537831      1.451790544

Here maxstep=1 should restrict the NR step below 0.01 bohr. Nevertheless, in the 9th step, I received the following report on convergence:
         Item               Value     Threshold  Converged?
 Maximum Force            0.001795     0.000015     NO
 RMS     Force            0.000287     0.000010     NO
 Maximum Displacement     0.079485     0.000060     NO
 RMS     Displacement     0.024807     0.000040     NO

It seems to me that the 0.01 bohr criterion is not fulfilled for the optimization displacement. Is there any way to really constrain the step length during optimization?


texts:
https://pubchem.ncbi.nlm.nih.gov/compound/hexane
Another name for hexane is skellysolve-B, is that just to be silly?


texts:
The packing fractions of hexagonal close packed unit cell and face centred cubic unit cell come out to be same when calculated geometrically.

Is it just a coincidence? Differently put, could it be predicted that the packing fractions of HCP and FCC will be same without calculating them geometrically?


texts: What will happen if ligand orientation is changed?

texts:
How we came to know ligand should approach from t2g orbitals in d5 configuration for tetrahedral complexes? What will be the difference in energy if ligand approach from eg?

As far as I can think, The major driving force for formation complex is the Nucleus-Ligand interaction and the opposing minor force is ligand's e-- Metal's e- but important for determining the coordination no. and orientation.  The field of nucleus should be spherically symmetrical so It can't be the reason.
So we've left with only one reason which is Ligand's e- - Metal's e- interaction, but how ?

Does CFT have any answer to it?

A similar question can be asked for Octahedral, but we know it is associated with CFSE, so it plays an important role for orientation.

But what difference will it make in the octahedral complex if we assume that ligand will approach from x', y' and z' (particularly in the case of d4 configuration)?

Let's assume it is a weak ligand
in this case, the CFSE should be -Δ'2/5, as eg orbitals, will be in lower energy state, but if ligand approaches from x,y and z then CFSE will be -Δ3/5.
Is this the reason, that ligand will always approach from x,y and z.
what if Δ3/5 < 2/5Δ' ?


texts: Why does silver (I) have a larger lattice enthalpy and hydration enthalpy than sodium?

texts:
The ionic radius of the $\ce{Ag^+}$ ion is $129$ pm, and that of the $\ce{Na^+}$ ion is $116$ pm.

Since the sodium ion is smaller than the silver ion, it makes sense that it has a stronger polarizing power than the silver ion. Due to the higher charge density, the lattice energy of $\ce{NaX}$ compounds is predicted to be larger than those of $\ce{AgX}$ compounds. However, that is not the case, as shown here:

Furthermore, the enthalpy of hydration of $\ce{Na^+}$ is expected to be more exothermic than that of $\ce{Ag^+}$, because $\ce{Na^+}$ is more polarizing than $\ce{Ag^+}$. However, that is not the case:

Why are the lattice enthalpies of silver compounds larger than those of sodium compounds, and why are hydration enthalpies of silver compounds more exothermic than those of sodium compounds, despite the silver ion being larger than the sodium ion?

Sources:

R. D. Shannon (1976). "Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides". Acta Crystallogr A. 32: 751–767. Bibcode:1976AcCrA..32..751S. doi:10.1107/S0567739476001551.

Atkin's Physical Chemistry


texts:
When solving the lewis structure for the $\ce{ClO2-}$ ion, taking into consideration formal charges, the structure is represented as:

A lewis model with 2 double bonds also fits the formal charge and lewis model requirements, however this time the negative formal charge would be on the chlorine atom. Is there a reason this form is not favoured?


texts: Prevention of Electrophilic Aromatic Substitution

texts: Actually, I want to prevent unwanted electrophilic aromatic substitution in the reaction without deactivating the phenyl ring. Is there  any way through which I can prevent E.A.S. I am thinking about certain solvents or other approaches.


texts: Boltzmann Transport equation: Is df/dt=o for collisionless only?

texts:
$$\frac{\mathrm df}{\mathrm dt} = \left(\frac{\partial f}{\partial t}\right)_\text{force}+\left(\frac{\partial f}{\partial t}\right)_\text{diff}+\left(\frac{\partial f}{\partial t}\right)_\text{coll}$$

where the "force" term is the external force, the "diff" term represents the diffusion of particles, and "coll" is the collision term.
Source: https://en.wikipedia.org/wiki/Boltzmann_equation

So shouldn't $\frac{\mathrm df}{\mathrm dt}$ be 0 when it is not just collisionless but also force and diffusion must go to zero too?


texts:
All metals form basic oxides. Metallic oxides are basic in character.

Polonium is a metal, so it should form basic oxides but it forms acidic oxides. Why are its oxides acidic in character?


texts:
The Lucas test for alcohols is based on the way primary, secondary and tertiary alcohols react with Lucas reagent. If on adding Lucas reagent to an alcohol, the mixture immediately becomes turbid, then it is a tertiary alcohol.

I am aware that alcohols get converted to alkyl chlorides on reaction  with concentrated HCl, and that it the alkyl chloride that is insoluble and hence responsible for the turbidity.

But why do tertiary alcohols react the fastest with HCl?


texts:
Vinylic carbocation is unstable as the carbocation is bonded to a $\mathrm{sp^2}$ carbon that has high electron density, and pulls the electrons from the carbocation, which is already electron-deficient (empty $\mathrm{p}$ orbital)
However, the mechanism for the addition of $\ce{H-X (X = Cl/Br/I)}$ to alkynes involves the formation of vinylic carbocation, which to me, should not be plausible due to extremely high activation energy (the cation is very unstable).
Is the mechanism wrong or my concept on the stability of vinylic cation is wrong?


texts:
Question: What might serve as an initial starting photocatalyst for this large water-splitting solar simulator? Surely there must have been some planned experiments!

The Gizmodo article Insane Light System Blasts the Energy of 10,000 Suns and Phys.org's Let there be light: German scientists test 'artificial sun' both describe the large, powerful concentrated light source called Synlight which has been built by the German Aerospace Center (DLR).

This large (~350 kW!) solar simulator - built from 149 high intensity xenon arc lamps, all collimated/focused to a single 20x20cm area - will be used to test and develop materials and catalysts that will allow photochemical splitting of water to yield hydrogen gas, to be scaled up later and used with a solar concentrator instead of electrically powered lamps. Hydrogen could be used as fuel directly, or to synthesize hydrocarbon fuels when combined with carbon dioxide or monoxide.

Water is transparent over most of the sun's useful spectrum, and this is for the obvious reason that the wavelengths reaching the ground are those not already absorbed in the atmosphere. Thus a photocatalyst will be necessary for a high yield of hydrogen gas from concentrated solar light.

From the Gizmodo article:

  When the array is focused onto a single spot, it heats metal to 1,475 degrees Fahrenheit (800 degrees Celsius), which is then sprayed with water vapor. The metal reacts with the oxygen in water, and hydrogen remains. With further heating, the oxygen is once again separated from the metal.

There are certainly easier ways to heat a metal plate than building a giant solar simulator, so I assume the point is to provide an intense source of photons with a somewhat similar spectrum to sunlight as a test platform for various catalysts. But the quote suggests the surface will react with the oxygen released, and need to then be cycled to higher temperature to release it. This does not sound like a very practical photocatalytic process.

So far I have not found anything clearer about what kinds of catalysts are likely to be investigated, but there must be some potential candidates. Based on known photocatalytic water splitting mechanisms, or if someone can find a discussion by DLR, what would be a starting point, or proof-of-concept photocatalyst that might work here?

below: Images from here, photo credit: DLR (top), DPA (bottom). The shape of each reflector is likely to be close to an ellipsoid with the xenon arc at one focus and the sample near the other. This way a ~100 cm diameter reflector can illuminate a much smaller 20x20cm sample.

[


texts:
Would this be proper resonance structures? I know there's a lone pair on the top carbon. Having a carboanion isn't favorable as opposed to a negative formal charge on the more electronegative carbon so I flipped a bonding pair to oxygen's valence. I then proceeded to move the pi electrons inside the ring as well. This seems to satisfy all octet requirements.

For the second resonance diagram I saw the negative charge on the oxygen and decided to take one of its lone pairs and make it a bonding pair so that oxygen has 0 formal charge. This in turn necessitates pushing around a few pi electron pairs inside the ring. Same thing for the third one; I tried giving nitrogen a positive formal charge.


texts: Are food calorie values really integers?

texts:
According to what I've seen, fat has a listed caloric value of 9 Cal/g, while carbs and protein have listed caloric values of 4 Cal/g.* Are these numbers exact, or have they been rounded? And if they have been rounded what are the exact numbers? One hit said that the numbers are rounded, but not by how much.
*These are "food calories" (aka "large calories" or "Calories" with a capital "C").
1 food calorie = 1000 "small calories" or "gram calories" = 1 kcal = 4.184 kJ
See: https://en.wikipedia.org/wiki/Calorie


texts:
Let's say I have a double bond between carbons 6 and 1 on a 6 carbon cycle (the numbering is imposed because of the positions of the suffix functional groups), is the bond numbered 1 or 6?

6 seems logical because it is not ambiguous (clearly if it starts on 6 it ends on 1), but usually you must minimize numbers (however numbering the bond 1 means there's ambiguity between it being between 1 and 2 and between 1 and 6).

I've tried finding the official rule but haven't managed to.


texts: Reaction of hydrogen peroxide and catalase

texts:
All Google searches have simply returned more info on catalase. I'm looking for a catalyst that isn't found inside living organisms which can break down $\ce{H2O2}$. Looking for any resources to look at, or just examples of other catalysts.

Side question: Can catalase be used for anything other than the decomposition of  $\ce{H2O2}$?


texts: What are quantifier and qualifier ions in mass spectrometry data for GC-MS or LC-MS?

texts: I've read that one should pick an ion peak that is unique to an analyte for quantification purposes and then pick at least 2 qualifier peaks and use their ratios to identify the analyte (or avoid misidentification thereof). How exactly does this work?


texts:
Consider the 4 cis-trans isomers for the above compound. In what way
  would the cis-trans isomers affect their heat of combustion.

I think that if the substituents are on alternating sides of the ring, then there will be minimum steric crowding. But is there anything else that would affect their heat of combustions?

UPDATE: Here is as far as I have gotten. Now I think for the methyl group on carbon 4, either conformation would be stable. I am guessing that an axial methyl group would be more stable, because the axial position is free from all types of steric repulsion (This is just a guess). Is this correct?


texts: Why do Organolithium or Grignard reagents act as nucleophiles and not as bases with aldehydes and ketones

texts:
I've read entire Chapter 14: Organometallic Compounds of  Francis Carey's "Organic Chemistry" but I still didn't get an answer to my question.

Quote from the book:

  Because of their basicity organolithium compounds and Grignard reagents cannot be prepared or used in the presence of any material that bears a $\ce{-OH}$ hydroxyl group. Nor are these reagents compatible with $\ce{-NH}$ or $\ce{-SH}$ groups, which can also convert an organolithium or organomagnesium compound to a hydrocarbon by proton transfer.

Fine. No arguments with that.

  Terminal alkynes also give alkanes with Organolithium and Organomagnesium compounds.

Must be true if he says so. Now coming to the point,

  Ammonia and Amines have $\mathrm{p}K_\mathrm{a}$ around 36.
  Terminal alkynes have $\mathrm{p}K_\mathrm{a}$ of 25.
  Aldehyde $\mathrm{p}K_\mathrm{a} = 17$, Ketone $\mathrm{p}K_\mathrm{a} = 19$ and an Ester $\mathrm{p}K_\mathrm{a} = 25$.
  Water & Alcohols have $\mathrm{p}K_\mathrm{a}$ of 15–18.

If organolithium compounds and Grignard reagents act like bases with alcohols, terminal alkynes, and amines/ammonia, why do they act like nucleophlies and give addition reaction with carbonyl compounds? Why don't they act as bases and give alkanes instead? What am I missing here?


texts: Why did roasting of copper(II) sulfate pentahydrate hurt my nose?

texts:
I want to use copper(II) sulfate as rocket propellant additive in hope that it will alter the flame colour. Because water is not welcome in rocket fuel, I decided to dehydrate the crystals.

First I tried stainless steel mess tin, but that produced some smoke warning me that it's reacting. So I switched to aluminium mess tin, that one didn't smoke.

But still some fumes, presumably steam was produced. I continued roasting. Almost at the end, I noticed that my nose hurts in the inside a little.

I suppose copper sulfate has got in there. Do you think I risked badly, or is it just weak irritation? How can I avoid it next time, apart of using fumehood?


texts: Why does a carbonyl reform in ester reactions

texts:
I have noticed that frequently whenever esters react with a nucleophile, the nucleophile will attack the carbonyl carbon and eventually in order for the carbonyl to reform the other oxygen will leave for example the first addition of the grignard reagent to an ester:
$\ce{PhMgBr + Ph-(C=O)-O-R}$
will result in
$\ce{(Ph)2-(C-O^{-})-O-R}$
as an intermediate, and then rather than the
$\ce{O^{-}}$ simply getting protonated with water for example, its favorable for the $\ce{O-R}$ to leave and the $\ce{C-O^{-}}$ to become $\ce{C=O}$. Why is the carbonyl reforming more favorable, isn't $\ce{O-R}$ a bad leaving group?


texts: Why does rearrangement not take place in Wurtz reaction?

texts: The Wurtz reaction is $$\ce{R-X + Na ->[ether] R-R}$$ where $\ce{R}$ is alkyl. But if we take butylchloride with $\ce{Na}$, the product is n-octane and not 3,4-dimethylhexane. I am unable to understand the fact that rearrangement does not happen even when it's a free radical mechanism.


texts: How many d-electrons are in the outer shell of metals like Cadmium (this is counting the 4d electrons)?

texts:
First I know similar questions have been asked about counting d-electrons.

However, my question is about the electrons in the 4d orbital. For example if I have CdS. The cadmium has a charge of +2. So does this affect the number of d-electrons?

Would it be 10 d-electrons as the 2 extra have been removed from the 5s orbital?

Also is the electron configuration of Cd in CdS:

[Kr] 5s2 4d10

or is it:

[Kr] 4d10


texts: Considering the sign of orbital and assuming the $z$-axis as a principal axis, for me, it looks like that it has two perpendicular $C_2$ axes that penetrate the lobes, so I think it is $C_\mathrm{2v}$. But the book (Inorganic chemistry by Miessler and Tarr) says it is $D_\mathrm{2h}$.


texts:
As an exercise I have to predict the formula of the compounds that fluorine and tellurium can build using group properties.

My idea was to use the octet rule and therefore the formula would be $\ce{TeF2}$ so both atoms have eight valence electrons.

However, the correct solution given by the exercise is $\ce{TeF4}$ and $\ce{TeF6},$ and I have literally no clue how to get these solutions. Can you give me some advice on how to retrieve these solutions?


texts:
Why does ligand exchange happen?
Are there specific factors that determine when a ligand can replace another ligand?
When ligand exchange takes place, does that mean that the "previous" ligand is not bonded to the complex ion at all, or both ligands are bonded?