texts: Is cobalt (II) chloride in silica gel dangerous when heated?

texts:
Today I decided to reheat 3 x 40 gram silica gel canisters with the blue/pink silica gel for the first time, and after I decided to order some more. While shopping, I noticed people say how it is a carcinogen, and that my family and I could now be at risk for cancer. Is this true?

It was in the toaster oven of the kitchen for 5 minutes, 2x each since by the time the canisters cooled off they became pink again before I put them where I needed to.

So am I looking at a risk, or is what I have done too minimal to worry about?


texts: Why isn't formation of benzyne a 1-step process?

texts:
According to "Organic Chemistry as a secondary language", during elimination-addition, formation of benzyne involves 2 steps (as shown in the bottom photo). I wonder during 2nd step, it is just electron transfer and 'kick out' the Cl as leaving group.
Can the 2 step process be simplified as 1 step? (as shown in the upper photo) The only difference is that I used the electrons from C-H bond to form the 3rd C-C bond, where the book suggest a deprotonated anion is first formed then C-C is subsequently formed. I wonder what causes the difference? Thank you.


texts: Differentiating between Prins reaction / ene reaction experimentally

texts:
The Prins reaction – stepwise addition of an alkene to a carbonyl compound – leads to the same product as a concerted ene reaction. This is illustrated here with tin tetrachloride as a Lewis acid, which (as far as I know) lowers the activation energy of both pathways:

How can these two mechanistic pathways be differentiated experimentally?

One thing that I can think of right now would be the stereochemistry of the alkene formed - presumably in a concerted pathway, the cyclic transition state (envelope-like, if I remember correctly?) the substituent R' would be positioned equatorial or pseudo-equatorial. However, I'm not confident enough to undertake an analysis of the stepwise reaction.

I'm open to hearing about other possibilities, e.g. kinetic studies or spectroscopic studies. I suppose the free carbocation in the Prins reaction could lead to a more negative coefficient $\rho$ in a Hammett analysis, compared with a stepwise mechanism?

I'd also be glad if somebody could provide an example in the literature, if it exists. (I confess to not having looked this up - been very busy.)


texts:
How can I prepare $\ce{Cu2S}$ powder?

I have some idea about preparing the ternary composition containing copper, but copper sulfides are difficult due to the large difference between their melting points (Cu: 1084°C, S: 119°C).


texts: Difference in application between Standard Type Bulb Pipette Filler and Universal Type?

texts: I want to ask what is the difference in terms of application between the HHH (Heinz Herenz Hamburg) Bulb Pipette Filler Standard Type (1081801) and the HHH Bulb Pipette Filler Universal Type (1081802)?


texts:
I'm having a hard time understanding the use of coagulation wastewater treatment. I have read in literature that ferric chloride is used as a coagulant to remove COD, TSS and ammonia from landfill leakage. Their dose was $\pu{10 g/L}$ at a $\mathrm{pH}$ of 8. Since there is so much ferric chloride, it will neutralize all of the alkalinity in the leakage and then start decreasing the $\mathrm{pH}$. To maintain the current $\mathrm{pH}$ of 8 lime, $\ce{Ca(OH)2}$, is added so that the ferric chloride will neutralize that instead.

$$\ce{2 FeCl3 + 3 Ca(OH)2 -> 2 Fe(OH)3 + 3 CaCl2}$$

What I don't understand is what exactly is going on in this reaction? What do the products do in the leakage? What will happen to the reaction at higher or lower $\mathrm{pH}$?


texts: Does resonance affect the polarity of the molecule?

texts:
Ozone is a resonating structure, is it because of its resonance and bent structure that it is a polar molecule? Or Is it because of the formal charges whereby the formal charges determine the direction of the dipole moment. If yes, how does this work with resonating structures. Initially, I thought that resonating structures automatically are polar, however, the azide ion is a clear counter-example. I am curious, how one deals with such a case, should we take each resonating structure by itself and consider the superposition in the end.

Edit:
Ultimately, my question is how can you explain ozone's polarity without formal charges because on a wikipedia page, they explain it using formal charges. If that's the case, shouldn't resonance be considered. If yes, how?


texts: Iodometric Titration - Iodine Crystal formation

texts:
During an iodometric titration iodide is oxidised to iodine by an oxidiser, and then titrated using standardised sodium thiosulfate. I have had no problems using iodate as the oxidiser, however, using sodium hypochlorite (bleach) causes trouble for some reason. Instead of the iodine dissolving in the solution upon addition of acid/KI, the iodine forms black crystals which fail to dissolve even upon addition of sufficient sodium thiosulphate (even when excess is added). The solution is still black, but the crystals become readily apparent during titration.

I suspected this to be due to insufficient KI, and have used both solid and aqueous KI, however I have tested this and this is not true.

Does anyone know what is causing the crystals to form?


texts: What are the fundamental parameter by which lubricants are graded?

texts:
I am into hobby machining using an old beaten CNC mill in my garage. Being novice my confidence is rather low and I have genuine fear of breaking something (even ancient CNC machines like mine cost a fortune), so when I got to the part of the users manual that listed recommended lubricants for the different parts of the machine I felt out of my league completely (especially since I just basically submerged the whole machine in a bath of general purpose lubricant spray).

So I would like to know, how are lubricants usually classified/graded?

Which classification/grade matters to which kind of use?

What are the risks of using the wrong lubricants?


texts: Is this the correct relative Brønsted acidity in these four acids?

texts:
We are asked to sort these four acids by increasing Brønsted acidity:

The problem is, I am confused why $\ce{H2F+}$ is the strongest acid of them all. I understand that stronger acids will have weaker bonds, and the $\ce{F-H}$ bonds should be the most electronegative of them all, leading me to believe that they are the strongest bonds. So then why are these bonds the most easily broken? What have I forgotten here? Is the correct order really from weakest to strongest acid as follows? $\ce{CH3OH}$, $\ce{(CH3)2OH+}$, $\ce{CH3SH2+}$, $\ce{H2F+}$


texts:
Question:

  A conductivity cell containing distilled water has a resistance of $\pu{454 k \Omega},$ while the same cell containing $\ce{KCl}$ solution prepared in the same sample of water shows resistance of $\pu{2150 \Omega}.$ If the plates of the conductivity cell have area $\pu{0.5 cm^2}$ each and are separated by $\pu{1 cm},$ find the cell constant and also calculate the specific conductance of $\ce{KCl}.$

My Attempt

First things first. I found out the cell constant, that is, $G^*:$

$$G^* = \frac{l}{A},$$

where $l$ is the distance between the square plates and $A$ is the surface area of the square plates — hence, $G^* = \pu{200 m^-1}.$ Now I also know that,

$$\frac{1}{R} = \frac{\kappa}{G^*},$$

where $\kappa$ is the conductivity, and $R$ is the resistance of the solution.

Plugging in $R = \pu{2150 \Omega}$ and $G^* = \pu{200 m^-1}$ yields the answer $\kappa \approx 0.093.$ [Which is incorrect.]

Note

I did not use the value of resistance of distilled water that is provided in the question. What am I doing wrong? I also feel that the sentence "…also calculate the specific conductance of $\ce{KCl}$" is a bit weird? Shouldn't be referred to as "$\ce{KCl}$ solution"?


texts:
In many cultures, human dead bodies are burnt to ashes, which is then thrown in rivers and some time buried in earth.
Are human ashes after burning dead bodies biodegradable?

Note: Earlier I posted this question here
But I was suggested to post it here.


texts: Database for molecular dipole transition moments?

texts:
I'm looking for the dipole transition matrix elements for electronic transitions between the ground and excited states of the carbon dioxide cation, $\text{CO}_2^+$, that is, objects like
$$\langle\text{CO}_2^+ \,\tilde{\text{A}}\,\Pi_\text{u}|\mathbf{r}|\text{CO}_2^+ \,\tilde{\text{X}}\,\Pi_\text{g}\rangle.$$
I feel this is a standard enough quantity that it ought to be easy to find in some appropriate database of chemical data. However, I've searched for quite some time and I can't even find something similar.

Where should I be looking?


texts:
This is a question that had me puzzled for quite a while.  I feel that information is missing.

A weak acid, $\ce{HA}$, $K_\textrm{a} = \pu{1.0E-4 M}$, is titrated with $\ce{NaOH}$.  The concentration of $\ce{NaA}$ at the equivalence point is $\pu{0.010 M}$.  What is the $\mathrm{pH}$ at the equivalence point?
a) 4.0
b) 6.0
c) 7.0
d) 8.0
e) 11.0

The correct answer is :

 d) 8.0

The answer is fairly easy to guess, as the $\mathrm{pH}$ needs to be greater than 7, but 11 is much too basic.  However, I'm not sure how I would be able to figure that out from the information given?  I've tried using the Henderson-Hasselbalch equation, but I can't figure out the relationship between $\ce{[NaA]}$ or $\ce{[A-]}$ and $\ce{[HA]}$.


texts: Calcium based Corrosion-Inhibitors used in Ethanol fuel, and their effect on the organic-solvent abilities of that alcohol?

texts: Ethanol is a good organic solvent, often the preferred non-toxic choice for the processing of plant extracts. One of the cheapest sources of Ethanol is the kind used in fireplaces and racing fuel, but this has the corrosion inhibitor DCI-11 added. DCI-11 is added to the Ethanol at a rate of 86mg/litre and is made from Calcium Nitrate (max 1-10%) and Calcium Nitrite (max 25-50%). DCI-11 "reduces the corrosion and solvent effects of the alcohol, also buffering/stabilising the pH". My question is - to what extent if any, will this reduce its use as an organic solvent for the processing of plant extracts?


texts: Placing oxygen molecule into electric field

texts:
I am trying to understand what happens inside various types of air ionisers.

Some of them are sold for their purported health effects (which I do not want to discuss here), another type are used in industry to control electrostatic charges on surface of materials. Also there are some natural processes where oxygen form is modified by electric current namely thunderstorms.

  Can an oxygen molecule be broken by placing it into a strong external electric field?

If yes how is it possible because as we know the oxygen atoms in molecules are bonded by a non-polar bond?

What are possible by products of this process (even temporary one)?

I assume that air is composed only from oxygen (no nitrogen, argon, carbon dioxide etc.).


texts: how to destroy excess iodomethane in reaction mixture?

texts: I have used iodomethane to make a phenolic $\ce{OH}$ group to $\ce{OMe}$ group in Aq+Methanol medium. I have added water to precipitate the product of mine and will evaporate the solvents but I cant use rotavap until I am sure that any residual iodomethane is not contaminating the condenser of rotavap. How shall I destroy excess iodomethane? will aq. solution of $\ce{KOH}$ work?


texts:
What is its structure? I found an image of $\ce{B6O11}$ unit, but it looks incorrect:

 The top left corner one.

The oxygen can make max 2 bonds but atom $\mathrm{O8}$ has three!
There are six oxygen with only one bond, that is the unit has $-6$ net charge, but $\ce{2Ca^2+} = +4$ positive charge.


texts: Spontaneity of an exothermic chemical reaction

texts:
When the process is exothermic (ΔHsystem<0), and the entropy of the system increases (ΔSsystem>0), the sign of ΔGsystem is negative at all temperatures. Thus, the process is always spontaneous.

It is easy to prove this using the formula of Gibbs free energy, but how can we prove it by logical reasoning?

I was thinking that in an exothermic process, the system loses heat. Shouldn't "the loss in heat" normally cause more ordering of the system and eventually a decrease in entropy? Might be a stupid question, but what am I missing here?


texts: Would the line structure of formaldehyde, H2COH, simply be a straight line with a OH on the end of the line?


texts: How to obtain sodium oxide from sodium chloride?

texts:
Under what conditions can $\ce{Na2O}$ be made from $\ce{NaCl}?$

I know $\ce{NaCl}$ doesn't oxidise under normal ambient conditions, but in the presence of what temperature and pressure ranges is this reaction possible?


texts: Calculating entropy change: reversible vs irreversible process

texts:
Since the change in internal energy and enthalpy, which are equal to the heats for a constant-volume and constant-pressure process, respectively, are state functions, the heats for a reversible v.s. irreversible process should be equal. Thus, the entropy change of the surroundings which equals the quotient of the heat and temperature are equal for reversible v.s. irreversible processes.

As Engel's Physical Chemistry states it:

  Because H and U are state functions, the amount of heat entering the surroundings is independent of the path; q is the same whether the transfer occurs reversibly or irreversibly.

However, when the book proceeds to evaluating the change in entropy for the surroundings for a reversible vs irreersible process, the q used for evaluating the change in entropy of surroundings are not equal for the reversible v.s. irreversible process, which contradicts what the textbook previously stated.

The question:

  One mole of an ideal gas at 300. K is reversibly and isothermally compressed from a volume of 25.0 L to a volume of 10.0 L. Because the water bath thermal reservoir in the surroundings is very large, T remains essentially constant at 300. K during the process.

Calculation of change in entropy for reversible path:

Calculation for irreversible path:

It seems that the book used the actual heat for the irreversible process. However, I don't understand why the entropy's from the two calculations are not equal. Also, I fail to understand why the change in entropy for the surroundings are not equal for the two process for which the final and initial states are equal --> change in entropy is a state function and should be the same regardless of path.

References

Engel, Thomas, and Philip Reid. Physical Chemistry. San Francisco: Pearson Benjamin Cummings, 2006.


texts: Is there an alternative wet chemical method or electrochemical method to obtain precipitation of iron, nickel and silicon powder?

texts: There are many methods available to obtain powdered metals and alloys. Wikipedia show some of them. Another form is grinding with posterior removal of wheel particles. All these methods produce metal powder with the help of specific machinery. I am asking for an alternative wet chemical method (water solution) or electrochemical method (water or ionic liquid electrolyte) to obtain metal powder (specifically iron, nickel and silicon, in pure or controlled alloy form).


texts: How to assign priorities around the asymmetric carbon with its substituents having multiple bonds?

texts:
How do I assign priorities to substituents with triple bonds?

If we take a look at the molecule above, the atom directly bonded to the asymmetric center is carbon for all three substituent.
Moving on to the atoms connected to those carbons, benzene side has carbons attached by a double bond and a single bond. The double bond is counted twice and the atoms count as $\ce{C, C, C}$.
For the sp carbon on the lower right, it is triple bonded to its neighboring sp carbon, so it counts as $\ce{C, C, C}$ as well.
The tert-butyl group is bonded to three carbons from methyl groups, so this gives another $\ce{C, C, C}$ making it a tie again.
If we look at the next set of atoms, the tert-butyl group has methyl groups so it's $\ce{H, H, H}$, giving it the lowest priority.
However, I'm not sure how to count the next set of atoms for benzene and the triple bond containing group. Judging from the R, S configuration the benzene group should have a higher priority, but I'm not sure how to figure that out. What should be my next step?


texts: I read a technical German book that refers to "ölsaurem Alkali" which apparently means "oleic acid alkali". How could it be both an acid and an alkali?


texts: Reaction of hydrogen peroxide with sodium carbonate

texts:
In my book the following acid base reaction is written:

$$\ce{H2O2 + Na2CO3 -> Na2O2 + H2O + CO2}$$

But I found that the $\mathrm{p}K_\mathrm{a}$ value of $\ce{H2CO3}$ is less than the one for $\ce{H2O2},$ which means $\ce{H2CO3}$ is more acidic than $\ce{H2O2}.$

As $\ce{H2CO3}$ is getting formed as the product (and then decomposing to give $\ce{CO2}$), shouldn't the reverse reaction be more favourable due to greater acidity of $\ce{H2CO3}$ and the above reaction not happen significantly?

Is $\ce{H2CO3}$ maybe getting decomposed as soon as it forms allowing this reaction to occur?


texts: Is melting of Tar for road construction a reversible change?

texts:
In India roads are made up of a black liquid which is prepared by melting a black material(probably coal tar). After cooling the liquid becomes very rigid. Can this solid be converted back to its previous liquid state by heating?

P.S: This is a question in my book. I think that after getting solidified the chemical composition of Tar may change so it can't be converted back to its original state.


texts: what is the product of reaction of Traut's reagent with aliphatic hydroxyl called? I am reacting Traut's reagent with Fmoc protected Doxorubicin and I just need to know the name of the product after Traut's regent reacts with the hydroxyl group. What is $\ce{OCNH2}$ called? I am looking for a name for $\ce{OCNH2}$ circled in red.


texts: Understanding the setup of a chemistry lab about redox

texts:
In chemistry lab we were looking at oxidation and reduction reactions. To determine the relative activity of several metals we observed reactions between the metals and aqueous solutions of dissolved metals. We mixed metals like $\ce{Fe}$ with solution like $\ce{Cu(NO3)2}$ to see if a reaction occurred.

I'm wondering why is it not necessary to mix a metal like $\ce{Fe}$ into its own solution $\ce{Fe(NO3)2}$ (like you would do when setting up an electrochemical cell)? We mixed $\ce{Fe}$ with $\ce{Zn(NO3)2}$, $\ce{Cu(NO3)2}$, and $\ce{Ni(NO3)2}$.


texts: Comparison of the rate of SN1 and SN2 reaction

texts:
It is known that $\mathrm{S_N1}$ (Substitution Nucleophilic Unimolecular) follows the order of rate of reaction:

  Tertiary ($3^\circ$) > Secondary ($2^\circ$) > Primary ($1^\circ$)

For $\mathrm{S_N2}$ (Substitution Nucleophilic Bimolecular) the order of rate:

  Tertiary ($3^\circ$) < Secondary ($2^\circ$) < Primary ($1^\circ$)

But what is the effective rate of reaction, if we consider that both $\mathrm{S_N1}$ and $\mathrm{S_N2}$ may occur?

Let us assume that we are using $\ce{NaOH(aq)}$ as the reagent, and using n-butyl chloride ($1^\circ$), isobutyl chloride ($2^\circ$), and tert-butyl chloride ($3^\circ$). As water is used, substitution will be favoured, and for this discussion, let us neglect any elimination reaction occurring. In this case, what would be the effective rates of reaction for these cases?


texts:
Q:
You have 10 g NaCl (s) and 90 g Lactose (s) (both easily soluble in water.) You want to achieve a 100 g mixture of these two compounds in solid form where they are completely evenly mixed. (A 1 mg sample of this mixture will always have 0.1 mg NaCl and 0.9 mg Lactose no matter from where in the mixture the sample is taken.)

Attempted A:
Boil a litre of distilled water in a clean container. In a sterile container put the pulverized NaCl and Lactose. Wait until boiled water cools to at least 50 C because high temperature increases risk of hydrolyzing lactose. While stirring with a sterile glass stir rod add the hot water step-wise until just enough water has been added to completely dissolve all the powder. Leave the solution on a warm plate (temperature shouldn't exceed 40-50 Celsius) and use a fan or similar device for airflow to speed up evaporation. Once most of water has evaporated put in a dessicator chamber to finish drying.

What I'm not sure about:
Would this actually create a completely even mixture because lactose and NaCl have slightly different solubilities so as the amount of water drops wouldn't one start precipitating earlier? If this is true how could you prevent that and are there any other issues?


texts: How to find the number of valence electrons?

texts:
I need to understand the following:

Considering an element Sulfur - S which has 16 electrons.

How do we calculate the number of valence electrons of S?

Please correct me if I am wrong:2+2+6+2+4=16. So, the valence electron = 4+2=6

Is it that always valence electron is the addition of the last two shells? In that case for Na, sodium, if we take 11 and arrange it as 2+2+6+1, then the valence electron is 1 or 6+1?

Now, considering the fact valence electron is 1, if we go by, up down up down rule, then as it is 1, hence the spin is up?

For 6: is it up(1) down(2) up(3) down(4) up(5) down(6) as it is both up/down hence it would be +-1/2 spin?

For Phosphorous 2,8,5, what would be the valence electron? 5 or 13?

If 5 then up down up down up, will it have an up spin?

Is it that for even numbers like 4,6 the spin will be both up/down i.e. +-1/2?


texts: Which are the appropriate washing solvents for gas chromatography equipment?

texts:
I work in a laboratory where gas chromatography is used extensively. We handle terpenes and terpenoids (alcohols, ketones, and acetates derived from terpenes), organic solvents (acetone, acetonitrile, ethyl acetate, hexane, and toluene), acetic acid, and water.

I want to know which are the most appropriate solvents to use for washing the equipment or which criteria should I use to decide among the existing solvents. Now, we are using acetone and ethanol, but sometimes it seems that they do not work for some terpenoids (the syringe sticks and sometimes the equipment crashes). Any suggestions about this?


texts: Directionality of ring current-induced magnetic fields in purines

texts:
What would be the directions of ring current-induced magnetic fields in purine-like heterocycles in a strong magnetic field?
Would be the antiparallel state be a default state for these substances in the absence of strong magnetic field at warm temperatures due to heat motion?


texts: Why do some solid chemicals dissolve better in colder water?

texts: I just discovered that some solid chemicals, such as $\ce{Na2SO4}$, dissolve better in cold water than hot water from here and would like to know if there is any particular reason as to why. Is it their structure, their charge, etc.?


texts: I’ve seen the video etc of sodium being put into freshwater and the reaction of flames/small explosion but I wonder if the same reaction would occur if conducted in salt water such as the ocean.


texts: If I mix carbon dioxide and sodium hydroxide in the right amounts in water, do I get baking soda?

texts:
Suppose I need a sodium bicarbonate solution (for non-food related reasons). Can I get something resembling it by mixing $\ce{NaOH}$ and $\ce{CO2}$ in water?

Of course one should not attempt to make food in a chemistry lab, so lets rule out the food safety requirements for food-grade baking soda.


texts:
Antioxidants are free radical scavengers and are able to reduce free radicals to make them stable. What I am interested in is why some molecules make for superb free radical scavengers and why others don't. For example why Vitamin E is a better scavenger then say methane (I know the comparison is silly but for arguments sake).

If its possible could the answer be as simplified as possible as I have not yet reached an advanced enough level in chemistry. I would also like to stay away from the biological aspect of free radicals would like the answer to be in purely chemistry terms.


texts: Miller Indices of Goldnanoparticles from Turkevich and Frens method

texts:
I need the miller indices of gold nanoparticles that were synthesized after the route of Turkevich and Frens. I during my research I found a lot of publications, but it looks like no one measured it before.
Has someone an idea of what the miller indices can be? Or better a source or paper where I can found them?


texts:
We have these nomenclatures of the same family :

4H-chromene
2H-chromene
Why do we use 2H and 4H to name them? And how ?


texts: Is cis dipole moment is always greater than trans dipole moment?

texts: In trans compound the dipole moment always cancels each other!  Then how can it's dipole moment be greater than cis compound's dipole moment?


texts:
As in other posts I have seen and learnt that, if one is given four compounds, namely para-nitrophenol, ortho-nitrophenol, meta-nitrophenol and phenol and is told to arrange them in order of acidity, then one has to take into account the $\text{-R}$ and $\text{-I}$ effect.

Now, for the inductive effect, the greatest intensity is observed at the ortho-position, followed by meta-, and then para-.

For the resonating effect, the intensity is greatest for para and lowest for ortho, while meta has no such effect. Now keeping in mind, that $\text{-R}$ and $\text{-I}$ both tend to withdraw electrons away from the phenol group (and thus increases the acidity), and the $\text{R}$ effect has more contribution than the $\text{I}$ effect, we can thus deduce that para-nitrophenol is most acidic, followed by ortho-nitrophenol, then meta-nitrophenol and since phenol has no ring activating group, it comes out to be least acidic in the given compounds.

The facts are the proof of my theory, where the $\mathrm{p}K_\mathrm{a}$ for:
$$
\begin{array}{c|c}
\text{Compound} & \mathrm{p}K_\mathrm{a} \\
\hline
para\text{-nitrophenol} & 7.16\\
ortho\text{-nitrophenol} &7.2\\
meta\text{-nitrophenol} & 9.3\\
 \text{phenol}   & 9.95
\end{array}
$$

So far so good.

But one of my colleagues, when I asked the problem, tried to give the theory in different way. He said, in para-nitrophenol, hydrogen bonding is strongest, so it can't be most acidic, which in his view port should be least. I knew this is not the case, but I just can't explain or point out where he's been wrong. Can anyone of you make it little easy for me to understand it?


texts: Does boiling water really treat it to make it safer than filtered/chlorinated water?

texts: It doesn't seem like it would, but some folks I know are adamant about boiling their water before ingesting it and the online articles I've found on this seem very subjective.


texts: I was doing an experiment on boiling-point of water and I was supposed to measure the temperature of the water when it boils, but I saw the there were droplets of water on the lid of the pot, and I was confused if I should take the temperature of the droplets too ,then record the average temperature.


texts: Finding ionic radii from solubility data and density

texts:
$\pu{5.35 g}$ of a salt $\ce{ACl}$ is dissolved in $\pu{250 ml}$ of solution. The $\mathrm{pH}$ of the resultant solution was found to be $4.85.$ Find the ionic radius of $\ce{A+}$ and $\ce{Cl-}$ if density of $\ce{ACl}$ is $\pu{2.2 g cm-3}.$  Given
$$\frac{r_+}{r_-} = 0.73 \qquad K_\mathrm{b} = \pu{2E-5}$$

So first we can find $\log C$ by using the formula
$$\mathrm{pH} = \frac{1}{2}(\mathrm{p}K_\mathrm{w} - \mathrm{p}K_\mathrm{b} - \log C),$$
which gives $\log C = 4.3.$ Now for the density $ρ$
$$ρ = \frac{ZM}{N_0V},$$
which will give relation in $M$ and $V,$ which are lacking. But how to proceed further?


texts: Choosing the right wavelength for calibration curve and for analysis of actual results

texts:
Introduction:
I am currently conducting a series of experiments in which I am studying the transport of polystyrene nanoparticles (PNPs) through sand and soil. This is done in sand/soil columns, into which I am injecting the PNPs solution using a peristaltic pump.
The PNPs are fluorescent, so I am using a fluorimeter for detection. During the experiment, I am collecting the fluid that is leaving the column in a fraction collector, and as a result I am constructing a breakthrough curve that is supposed to show me the behavior of the PNPs compared to an inert tracer (bromide) that is also found in the inlet solution.
In order to construct the breakthrough curve, I need to prepare a calibration curve that will allow me to convert the intensity of the collected fractions into concentrations. For the calibration curve I am preparing several samples with known concentrations.
Question:
For preparation of the calibration curve, I am choosing the wavelength that gives me the max intensity in each sample's emission spectrum, and then for the breakthrough curve I am taking the intensities in that same wavelength from each fraction for the breakthrough curve. In the example below it is 635 nm.

Then, when I came to take the appropriate intensities of my actual results, I obtained this graph:

The X-axis range is the same: 575-700 nm. I need to choose a certain wavelength and take the data pertaining to it.
Can I actually use these intensities, or would it be wrong because at 635 nm I don't have a max point?


texts:
Recently I have studied Huckel-theory and I appreciated how this approach is suitable to provide simple models to understand chemical behaviour.

However, it is highly approximate and qualitative at best.

According to Huckel's theory, for example, the homo-lumo gap decreases going on to add carbon atoms to the chain. And so, I could wrongly suppose that polyacetylene is a metal (the band gap shall be very small).

Why is not so? Which is the 'approximate' assumption in this theory that predicts an incorrect result?


texts: Degeneracy of second excited state of H-?

texts:
This is a question presented in a IIT-JEE 2015 paper I exam. It says,

  . Not considering the electronic spin, the degeneracy of the second excited state (n = 3) of H atom is 9, while the degeneracy of the second excited state of H- is-

I saw a solution which says it's 3.

I think by 9 degenerate energy levels the question meant 9 possible orbitals for M shell. But I am not sure how's that 3 for for H-.

Please don't delete this question as I haven't found it anywhere.


texts: How to tell which species has the highest ionization energy?

texts:
I am preparing for my final exam, and I am very confused about ionization energy. An example question would be:

  Between the species $\ce{Ne, Na+, Mg^2+, Ar, K+, $\&$~Ca^2+}$, which one has the highest ionization energy?

I thought that ionization energy increased from left to right in a period and from down to up in a group in the periodic table, so I thought that $\ce{Ne}$ would be the one with the highest ionization energy. But the right answer is $\ce{Mg^2+}$. I assume that this has something to do with the electrons, but I don't know what.


texts: I did not know there are products such as a magnetic stirrer with a hot plate, enabling one to apply heat and stirring to a solution with relative ease. Did I understand correctly, that device needs a magnetic bar to be added to the solution the device to work? Does that pose any limits when it can be used (if the magnet would react with something..) How much do these devices increase productivity?


texts:
I learnt about how ocean acidification can be described in terms of equilibrium. This is summarized in the textbook diagram below:

However, this diagram doesn't explain to me why the shells should be softening. As more CO2 is put into the atmosphere, this will increase $\ce{CO2_{(aq)}}$. By the second equation this should create more H+ and HCO3-.
People say that the increase in H+ concentration will eat up the CO3 ions in solution and thus the loss of CO3 will shift the dissolution equilibrium right and make shells soft. However, although there is an increase in H+ which eats up the CO3, there is also an increase in the amount of HCO3 so shouldn't that prevent a shift in equilibrium?


texts: I know nothing about chemistry, I managed not to take it in correspondence high school. I don’t know how to read or make sense of this: $\ce{CuAl6(PO4)4(OH)8.4H2O}$ the chemical formula of turquoise. From looking at a children’s periodic table I figured out some of the letters like Copper and aluminum, but I don’t know what the parenthesis or numbers mean. Also, is the PO polonium?


texts: What angle limits should apply to Graham condensers?

texts:
I have seen Graham condensers set at an angle (perhaps as low as 30 degrees from horizontal).  I guessed this wouldn't be a problem because siphoning would clear the condensate.  But I recently saw an argument that Graham condensers should only be used at near-vertical angles.  Thinking harder this makes sense to me, because as soon as enough liquid condenses in the first loop to form a trap the condenser can't work on any other vapor.  Absent some vacuum on the receiving end the only way it could clear itself is if there happened to be enough vapor to eventually close a loop and start the siphon effect, or if enough pressure built up on the boiling end to push the liquid through which would be bad!

But I still see diagrams and photos of Graham condensers set at shallow angles.  Here's an example from the first few Google image results:

So when and why, if ever, is it considered a good practice to run a Graham condenser in a non-vertical orientation?


texts: Chemical tests given by glucose (biomolecule)

texts:
We know that glucose gives Tollen's test because it's a reducing sugar, and having a hemiacetal group, on hydrolysis can be converted into an aldehyde group, giving the positive test.

But, when we come to tests like the Schiff's test or with sodium bisulphite, it does not show any reaction which are shown by aldehydes. Why? Is the answer that hemiacetal group cannot be converted into aldehyde or anything else? Probably there shouldn't be any water used in these reactions, so no hydrolysis, no conversion from hemiacetal to aldehyde. Is there any water present in Tollen's reagent?


texts: Mixing cobalt(III) hydroxide and thallium(III) hydroxide

texts:
A simple question on solutions is driving me crazy. At this point, I think the textbook's wrong. Here's the question:

  A saturated solution of cobalt(III) hydroxide $(K_\mathrm{sp} = \pu{1.6e-44})$ is added to a saturated solution of thallium(III) hydroxide $(K_\mathrm{sp} = \pu{6.3e-46}).$ What is likely to occur?

The answer given is that $[\ce{OH-}]$ is above saturation levels for both the cobalt and thallium in the solution, so that both will precipitate (thallium(III) hydroxide first, since it has a smaller $K_\mathrm{sp}).$

What I don't understand is how they can make such a statement. We don't know the amounts of each solution originally. Furthermore, wouldn't $[\ce{OH-}]$ be somewhere between the two original $[\ce{OH-}]$ depending on amount of each solution? And if so, wouldn't it not trigger precipitation of the cobalt (III) hydroxide (larger $K_\mathrm{sp},$ larger $[\ce{OH-}]$ at full saturation than $[\ce{OH-}]$ of the mixed solutions)?

Because of this, my answer would be that thallium(III) hydroxide precipitates, but cobalt(III) hydroxide remains dissolved.


texts: Why does the 31P{1H} NMR spectrum of cis-[Mo(CO)2(dppe)2] show two signals?

texts: I've tried searching for literature references that explain this, finding only a single reference which refers to the two signals as originating from phosphine environments cis/trans to carbonyls, however I'm having trouble rationalising why this occurs.


texts:
I understand the basics of carbonic acid + 1 kcal breaking down into water and carbon dioxide.

However, my professor wants me to draw an energy map showing the catalyst in human blood reducing the activation energy from 21 kcal to 12 kcal. I've never run into an energy map nor have we discussed this catalyst in class yet.

Anyone have a resource I can look at?


texts: Why do strong polyprotic acids not dissociate completely, whereas strong bases with multiple (OH)- groups do?

texts:
$\ce{H2SO4}$ is a strong acid, which follows the reaction
$$\ce{H2SO4 -> HSO4- + H+}$$
Not
$$\ce{H2SO4 -> SO4^2- + 2 H+}$$

However,

$$\ce{Ba(OH)2 -> Ba^2+ + 2OH-}$$

Is there a reason why these "polyprotic analogs" in bases completely dissociate but polyprotic acids do not?

Note: This is in context to titrations, where $\pu{0.10M}$ of $.\ce{Ba(OH)2}$ is $\pu{0.20M}$ of $\ce{OH-}$, and leads to different values of titrant needed.


texts: Are we advanced enough to calculate the abundance of an element throughout the universe or is our atomic weight only based on the occurrence of an element in our planet alone?


texts: What does a higher half cell potential mean?

texts:
I was taught in class that a positive large half cell potential generally meant that the reaction was more favorable.  What exactly does this mean?  Doesn't a reaction with potential 4V need a greater input of energy to occur? Meaning that a lower electron cell potential would occur first and is therefore more favorable?

Also how why does Zn(II) +2e- ---> Zn favor the left side of the reaction?  Shouldn't Zinc naturally tend towards being neutral?


texts:
Quick question:  Any one knows a resource for Cohesive Energy Density of some organic materials ?

I am not looking for any specific molecule, actually I want to plan my project based on available data. I have found some tables for internal cohesive pressure but could not find any thing for CED.

Anything including tables/papers and books are fine.


texts: Competitive protonation between alkene and carbonyl

texts:
Given this compound in an acidic medium, what would get protonated first?
Would the double bond not get protonated preferentially, since oxygen is more electronegative than carbon and less willing to donate an electron pair for protonation?

I checked the $\mathrm{p}K_\mathrm{a}$ value for the conjugate acid of an  aldehyde, and it was around -10, which is pretty low; this suggests that the aldehyde would have a very low basicity.

Also carbocation had a $\mathrm{p}K_\mathrm{a}$ value of around -3.

Going by this information does it not make sense for a double bond to get protonated first?

On the other hand, the oxonium ion is resonance stabilised, which would indicate that it is protonated in preference to the double bonds.

Which reasoning is correct? And more importantly, in these situations how are we supposed to predict which factor dominates?


texts: Can visible light or infrared radiation excite electrons?

texts:
So the limit of ionizing radiation seems to be UV light.

I'm wondering if IR light or Visible light can excite the electrons in an atom.

It has to do with the difference in energy level right?
So the closer two energy levels the lower the frequency/energy.

And that is why coordination complexes and/or transition metals are usually colored because once coordinated, the d orbitals lose their degeneracy?

I also just wanted to clarify that this excitation is different from the color we see for conjugated systems. That is because these systems when conjugated can absorb light? And so we see what is not absorbed and reflected back to us?


texts: Is there a theoretical way to predict the coordination number a metal can have in a complex?

texts:
We know that metals can form complexes with different coordination numbers, but I was told that certain metals have a greater probability to have a certain coordination number.

But I was not able to find any such list that correlates a metal with its most favorable coordination number.

As an example, I guess $\ce{Fe^3+}$ forms complexes with coordination number 6, but can I actually predict the coordination number in a reaction or not?


texts:
I am not a chemist.  But I am curious...

This evening I was making ingredients for a "lemonade bar", where people mix various flavors into a lemonade base to create custom flavors (mint + cucumber is a favorite, strawberry + ginger is another).

I wanted to offer "really sour" as one of the mix-ins, so I put about an ounce of food-grade powdered citric acid in a jar and added enough apple juice to make it dissolve [see note].  I shook it vigorously, and as the citric acid dissolved, I noticed that the jar got fairly cold.

That's neat! So what's the process that makes apple juice + citric acid get cold?

(For extra credit: are there other kitchen counter endo- or exo-thermic reactions I should try with my six year old son?)

update

I just repeated the experiment mixing tap plain water and citric acid. It was also endothermic, dropping the water temperature from 21.5 to 11.5 celsius.

[note] And yessir, it's really sour!  :)


texts: How to determine the bond order using the Lewis structure?

texts: What are the steps to follow in order to determine which molecule has a higher bond order by drawing the Lewis structure? For example, with $\ce{CO}$ and $\ce{CO3^{2-}}$?


texts: pH of an aqueous solution with acetic acid and sodium acetate

texts:
An aqueous solution of $\pu{1L}$ contains $\pu{0.2 mol}$ of acetic acid and $\pu{0.2 mol}$ of sodium acetate ($K_\mathrm{a} = 1.8 \times 10^{-5}$). Compute the $\mathrm{pH}$ .

I'm trying to help my little sister in solving this exercise... however, a lot of years passed away since the time I attended the school...
Our (unsuccessful) attempt:
$\ce{CH3COOH <=> H+ + CH3COO-}$
$K_\mathrm{a} = \frac{[\ce{H+}][\ce{CH3COO-}]}{[\ce{CH3COOH}]} = \frac{x\cdot x}{0.2} = 1.8 \cdot 10^{-5} \rightarrow \mathrm{pH} = 2.72$
Then
$\ce{CH3COONa -> Na+ + CH_3COO-}$
$\ce{CH3COO- + H2O <=> CH3COOH + OH-}$
\begin{align}
K_\mathrm{b} = \frac {K_\mathrm{w}}{K_\mathrm{a}} &= 5.56 \cdot 10^{-10} \\
 &= \frac{[\ce{OH-}][\ce{CH3COOH}]}{[\ce{CH3COO-}]}  = \frac{x^2}{0.2} \\
 \implies \mathrm{pOH} &= 4.97 \\
\implies \mathrm{pH} &= 9.02
\end{align}
Hence, $\mathrm{pH}_\text{solution}= (9.02+2.72)/2 = 5.87$
However, the result should be $4.74$.


texts: Will the addition of salt further cool down ice that is already at -30 °C?

texts:
I know that ice gets colder when salt is added. But how big is the effect if it is already −30 °C?

Can it cool it down more or does it just work with −1 °C cold ice?

Another question: If I have a water cooling circuit, does adding salt help it cool down?


texts: How can I get a hand sanitizer solution to form a gel?

texts: I am trying to formulate a gel hand sanitizer for a thesis project. The sanitizer that I have right now is watery and will not gel.  My teacher told me to change our formulation because it is not good. Our ingredients are ethyl alcohol, aloe vera gel, and lavender scent. What else could we add to this mixture to really "gel" the hand sanitizer?


texts: Mechanism of photochemical hydroamination with LDA

texts:
I've recently come across a couple examples of intramolecular alkene hydroamination accomplished by treatment with LDA followed by visible light irradiation (tungsten light bulb):[1,2]

I'd assume that this proceeds via some kind of radical mechanism, with the initially formed amide ion losing one electron to form an aminyl radical which then adds into the alkene. Trost[2] also suggests that the addition is facilitated by an SET:

My question is – what species is taking the electron away, and how is that species generated? There doesn't seem to be any decent electron acceptor in this system, unlike, for example, Ru(II) in a photoredox mechanism. If one is aware of any mechanistic studies which have been carried out, it would be an added bonus.

References

Kou, K. G. M.; Pflueger, J. J.; Kiho, T.; Morrill, L. C.; Fisher, E. L.; Clagg, K.; Lebold, T. P.; Kisunzu, J. K.; Sarpong, R. A Benzyne Insertion Approach to Hetisine-Type Diterpenoid Alkaloids: Synthesis of Cossonidine (Davisine). J. Am. Chem. Soc. 2018, 140 (26), 8105–8109. DOI: 10.1021/jacs.8b05043.
Trost, B. M.; Tang, W. Enantioselective Synthesis of (−)-Codeine and (−)-Morphine. J. Am. Chem. Soc. 2002, 124 (49), 14542–14543. DOI: 10.1021/ja0283394.


texts: The synthesis of 1-phenylprop-1-ene from propiophenone

texts:
I would like to know how to make 1-phenylprop-1-ene ($\ce{C6H5-CH=CH-CH3}$) from propiophenone ($\ce{C6H5-CO-CH2-CH3}$)?

I think carbonyl group ($\ce{C=O}$) of propiophenone is electron-withdrawing group because of Oxygen of carbonyl group.
So the carbonyl group of propiophenone will be attacked by nucleophile. And this will be oxidized to make double bonds.

But I don’t know the detail reaction mechanism to make phenylprop-1-ene from propiophenone.
Can anyone help me understand this reaction mechanism?


texts:
I have understood the basic mechanism of cannizzaro reaction. But I am unable to understand the products formed in case of a crossed Cannizzaro reaction.

Suppose Benzaldehyde and Formaldehyde are heated in presence of $\ce{NaOH}$ to carry out Cannizzaro transformation. I have read that it is Benzyl Alcohol and Formic Acid formed in the greatest proportion and not Benzoic acid and Methyl alcohol.

Why is this so? How can we understand this in terms of the stability
 of Cannnizzaro intermediates?


texts:
As we all know ammonium chloride is a acid. And what explains this is its salt hydrolysis. It breaks down into ammonium and chloride ions. Ammonium react with water to produce hydronium or hydrogen ions.

But then why can't chlorine ions react with water to produce hydroxide ions?
Is there any way other than using an indicator to know, whether a compound is acidic or basic? We know the second reaction can't happen, because we can tell the compound is acidic by using an indicator.

What really stops the second reaction from happening?


texts: Why is it important to remove the used up electrons in oxidative phosphorylation?

texts:
I get that oxygen is the terminal electron acceptor in oxidative phosphorylation.  But why is it essential to accept these electrons and remove them as $\ce{H2O}?$

Oxygen is essential for cellular respiration, but after learning about cellular respiration it seems oddly unimportant.  Why is having an efficient garbage collector (oxygen picking up the used electrons) so crucial to cellular respiration, and to ATP production?


texts: Do most chemical reactions happen at constant pressure?

texts:
While studying enthalpy $H=U+PV$ and its changes, I realized I am not clear on the following: chemical reactions happen with the external pressure being constant and equal to the atmospheric pressure $P_{atmos}$. But, in general, the system's internal pressure $P_{gas}$ would seem to be different from $P_{atmos}$ and variable during a reaction...
The change in enthalpy $\Delta H= Q$, where $Q$ is thermal energy, only when the gas internal pressure matches the environment external pressure: $P_{gas}=P_{external}=constant$ Under those circumstances, the emitted or absorbed thermal energy $Q$ goes into change #H# while the gas expands/contracts. The work $PV$ done by the gas is perfectly matched by the $PV$ work done on it by the environment.
How common is for the gas internal pressure to be constant and equal to $P_{atmos}$ during chemical reactions to justify $\Delta H = Q$?


texts: How is traditional thermite powder stored such that it doesn’t corrode?

texts: I watched some guy talk about redox reactions. Then he was going to do the good old thermite demonstration. He just had a bottle of thermite mixture. I’m wondering, why didn’t it have a chance to corrode before the demonstration? I’ve always thought that aluminum metal gets a thin layer of corrosion in air.


texts:
I heard a friend say:

  You have to watch out for coffee, the caffeine is an oxidation agent.

Now I remember carbon Chemistry from year 12.

You can oxidise ethanol to ethanal, and then to ethanoic acid.

But I don't understand how this would apply to caffeine.

My question is: Is the caffeine in coffee an oxidation agent?


texts: Octan-1-ol is polar due to the presence of the $\ce{-OH}$ group, but it is immiscible with water. How is it possible?


texts: Differences between LIBS over LA-ICP-MS?

texts:
Which differences should I consider between the techniques Laser-Induced Breakdown Spectroscopy and Laser Ablation Inductively Coupled Plasma Mass Spectrometry for a geochemistry fingerprint focused research?

Both use Laser Ablation for particle generation and analysis, so the sample preparation step is minimal in both instruments, but I would like to know about the instrument costs, the cuantification limits if apply and the advantages that offer each one.


texts: Do crown ethers have to have two carbons between the oxygens? If so, why?

texts: I just began learning about ethers and I have noticed that pictures of crown ethers, no matter what size they are, always have two carbon atoms left and right of each oxygen atom before you reach another oxygen atom in the ring. It's almost like it is a poly-ethyl ether. So my question is can you have crown ethers with more than 2 carbon atoms between the oxygen atoms?


texts: Should rates and rate constants be expressed in terms of pressure or concentration?

texts: If an elementary reaction was conducted in the gaseous phase, say $$\ce{X (g) -> Y(g)},$$ would the formal definition of the rate law be $\mathrm{rate} = kP_\ce{X}$ or $\mathrm{rate} = k[\ce{X}]$?


texts: Rutherford's Alpha Ray Scattering Experiment

texts:
I understood the result of this experiment that the nucleus is nearly empty and things like that.
 But what I have on mind is that when an alpha particle goes nearer to the thin gold foil why couldn't it capture electrons from gold and convert to very stable helium gas? It could also happen right?
All the textbooks only mention the deviation of alpha particles. Why couldn't the above happen or is there anything wrong about my question?


texts: electronic configuration of lanthinide series

texts:
Why does the 57th electron enter the $5d$ subshell in lanthanum, shouldn't it should enter the $4f$ subshell according to the Aufbau rule?
Also in thorium, the 89th and 90th electrons enter the $6d$ subshell while they should enter the $5f$ subshell?


texts:
Why does intramolecular hydrogen bonding make an organic (or possibly inorganic as well(?)) compound volatile.

What I think is that it might be due to decrease in the solubility of the compound as intermolecular hydrogen bonding cannot be done after that.


texts: How could you distinguish between an irreversible electron transfer couple and a chemically irreversible couple using cyclic voltammetry?

texts:
What is the difference between an irreversible electron transfer couple and a chemically irreversible couple?

How could you distinguish between these two processes using cyclic voltammetry?


texts: The feasibility of the electrochemical cell.

texts:
This is the question extracted from my country high school level' exam.
So it asks to discuss the feasibility of the electrochemical cell to carry out electrolysis of an aqueous solution of sodium chloride at standard condition.

Al(s)/Al(aq)//Cu(aq)/Cu

My question is how I should start to answer this question?


texts: How do you find the bond enthalpy from an equation?

texts:
Which equation represents the $\ce{N-H}$ bond enthalpy in $\ce{NH3}?$
$$
\begin{align}
&\textbf{A.} &\ce{NH3(g) &-> N(g) + 3 H(g)}\\
&\textbf{B.} &\ce{1/3 NH3(g) &-> 1/3 N2(g) + H(g)}\\
&\textbf{C.} &\ce{NH3(g) &-> 1/2 N2(g) + 3/2 H(g)}\\
&\textbf{D.} &\ce{NH3(g) &-> .NH2(g) + .H(g)}
\end{align}
$$

From what I've learnt, I understand that the bond enthalpy is defined as the energy required to break one mole of a specific bond.
In the question above, I opted for answer C as it was the only one with the products in the form of $\ce{N2}$ and $\ce{H2}.$ But since there are three $\ce{N-H}$ bonds in $\ce{NH3},$ I am unsure about answer B.
Can you clarify this?


texts: Different direction of dipole moment in physics and chemistry

texts:
In chemistry, we learn that dipole moment tells us about measure of polarity in a molecule. In books, it is written that "conventionlly the direction of dipole moment is from electropositive to electronegative element or less electronegative to more electronegative element"

My question is that in physics we are taught that the direction of dipole moment is from negative charge to positive charge as convention, so what is the basis behind the conventions of dipole moment in the two subjects which leads to different signs of dipole moment?


texts: How does boric acid behave as an acid? Is it a Lewis acid or a Brønsted-Lowry acid?


texts:
I am sorry if this question is too vague, but what is peak identification? I am working with a chemistry professor to program an autosampler and he says he would like to "program the robot for a peak identification feature that he would use on his project." Can someone please explain in detail what peak identification is?
Many thanks in advance for any help


texts: How would you separate sugar from water?

texts: I'm a student and I've been getting interested in chemistry. I really like experiments and was brainstorming of possible things to try out, one of them was separating a homogeneous mixture. I thought of sugar water and tried looking it up online but couldn't find anything like I wanted. Everything says to use crystallization but I don't understand why you can't just boil away water and be left with sugar like you can with salt water. Anyways, what methods/ways can I separate sugar from water?


texts: How can benzaldehyde have a pKa of 14.9?

texts:
There are numerous websites out there which claim that the pKa of benzaldehyde – C6H5CHO – is 14.90. (Just do a Google search for benzaldehyde pka to see what I mean.) This doesn't make sense chemically, as there are no protons in benzaldehyde which would be so acidic.

However, it doesn't seem to have been made up. The CRC Handbook of Chemistry and Physics lists the same value of 14.90 for the pKa of benzaldehyde, at $\pu{25 ^\circ C}$ in aqueous solution. But I can't find this information in the primary literature.

If this value refers to the acidity of the hydrate, does it include the equilibrium constant for hydrate formation? i.e. is this Ka the equilibrium constant for the reaction:

$$\ce{PhCHO + 2H2O <=> H3O+ + PhCH(OH)O-}$$

or is it just

$$\ce{PhCH(OH)2 + H2O <=> H3O+ + PhCH(OH)O-}?$$

I would appreciate some kind of definitive evidence. Using chemical reasoning and intuition is great, but if this value is to be of any use to anybody, then we need to know exactly what it describes.


texts: Derivation of time probability distributions for single molecule kinetics

texts:
If we have a protein $\ce{A}$ that can bind to protein $\ce{B}$:

$$\ce{A + B <=>[$k_\mathrm{fwd,1}$][$k_\mathrm{rev,1}$] AB}$$

and the bound complex $\ce{AB}$ can be converted into $\ce{C}$:

$$\ce{AB <=>[$k_\mathrm{fwd,2}$][$k_\mathrm{rev,2}$] C}$$

Assume we have a volume of 1 and some initial amount of $\ce{A}$ and $\ce{B}$ (which are $A_0,$ $B_0$) and that $C_0 = 0.$ We then measure the amount of time elapsed before the first molecule of $C$ is formed. The experiment is repeated many times, and the frequency of occurence of first $C$ during each time interval 0 to $t_1$, $t_1$ to $t_2$, $t_2$ to $t_3$, etc. is plotted, so that the result is a probability distribution of the time elapsed before the first molecule of $C$ is formed.

I would like to know what is the mathematical function that describes this distribution and how is it derived?

UPDATE: this is not a homework question and the point is not a specific answer. I would like references to literature/textbooks that derives these distributions analytically for simple examples like the above would be helpful. Have not seen a setup where distribution of duration is derived. Commenters say it's standard. Please give references.


texts: How to read TINKER's force field parameters

texts:
I'm going to parameterize AMBER force field for the simulation of some small molecules. I have found the parameter sets provided by TINKER at here.

I'm stuck here because I couldn't find any explanations about the parameter values. They should be the parameters that appear in the formula of AMBER force field. However, I have no idea which numbers mean $k_b$, $l_0$, $k_a$, $θ_0$, or the rest parameters.


texts: Finding compounds with B, Si, Ca, and Mg in differing amounts

texts:
Not sure if my question is better suited to a software related group, but here goes:

Is there a software program that lets you add differing amounts of elements, minerals, etc., then tells you what the items added might make?  Specifically, I am looking for information about what boron, silicon, calcium and magnesium together (no idea about amounts for each) would make.


texts: How to make a primary alcohol from an alkane?

texts: Alcohols can be made from alkyl halides, which can be made from alkanes. However $3° > 2° > 1° > 0°$ for alkyl halides synthesis from alkanes. What approach could make an alkane with primary and secondary carbons into only primary alcohols?


texts: Hydrogen Fluoride, Hydrogen Monofluoride?

texts:
I had a student ask why this is not referred to as hydrogen monofluoride. Similar, we call H2S hydrogen sulfide, not dihydrogen monosulfide.

Could we just call those common names, but that by IUPAC naming, it is actually hydrogen monofluoride? Or is it really just hydrogen fluoride. I have seen various answers on other websites, but curious if anyone knows the official answer.

The most common reason I've seen is that because both H and F has a single site open for bonding that there is no other combination possible (so no need for numerical prefixes).


texts: How are electrons in conjugated molecules excited?

texts: I have recently started reading about colour in organic molecules and come across conjugation of pi bonds. My question is pretty short... In transition metal ions I understand colour is caused by molecules jumping between the d sub orbitals as a result of ligand splitting them. The concept of excitation easily applies here. So what I want to know is. How do electrons get excited in a conjugated molecule?


texts: Why does dimethyl sulfoxide have higher boiling point than acetone?

texts:
They have very similar structure except for a central atom, but the difference in boiling points is very large $(\pu{186 ^\circ C}$ for DMSO and $\pu{56 ^\circ C}$ for acetone).
How is central atom impacting the boiling point?


texts: Major product from allylic halogenation of alkenes

texts:
Allylic halogenation of butene happens in the following way:

The RDS of this radical chain mechanism is allylic hydrogen abstraction ($\ce{H_a}$) from the allylic position to give a 1° allylic radical$^1$. This radical is stabilized by resonance to give a 2° allylic radical (which is more stable). Reaction of the radical at carbon 1 gives the major product. Reaction at carbon 3 gives the minor product. The more substituted (and more stable) alkene isomer predominates. The reason for this regioselectivity seems to be that the resonance contributor of the allylic radical with the more substituted double bond dominates.
Now, my question is that if the RDS is the formation of allylic radical then why the formation of major product is decided exclusively by the stability of final product? Can we generalize the statement that the major product will always decided by the stability of final product?
Reference
1: Organic Chemistry- Brown, Iverson, Anslyn, Foote (8E); Page 352


texts: Proton NMR chemical shift of water peak in different solvents

texts:
Why does the water peak appear at different chemical shift values (ppm) in different solvents in proton NMR spectra? For example, the water peak in DMSO-d6 appears at nearly 3.33 ppm, but the same moisture peak in $\ce{CDCl3}$ appears at 1.56 ppm.

What is the reason behind it? Why should the same species ($\ce{H2O}$) give rise to two different chemical shift values?


texts:
Symptoms of mercury poisoning become apparent after a person has accumulated $\pu{20 mg}$ of mercury. If a person ingested $\pu{30 mg}$ of mercury, what concentration of mercury in parts per million, are in his body? Assume the person has a mass of $\pu{63.5 kg}$."

My thought process, using dimensional analysis, was to convert the amount of $\pu{mg}$ the person ingested into $\pu{g}$. Then I took it ($\pu{0.03 g}\ \ce{Hg}$) and divided by the molar mass of mercury to find the number of moles of mercury there are.

I then divided the amount of mercury by $\pu{63500 mL}$ because I assumed $\pu{1 g} = \pu{1 mL}$. I did not use the $\pu{20 mg}$ information that it got me at all. Thus what I got was:

$$\pu{0.03 g} \cdot \frac{\pu{1 mol}}{\pu{200.59 g}} \cdot \frac{1}{\pu{63500 mL}} = \pu{2.3e-9 mol L-1}$$

However, I completely messed up, because first, my answer was in $\pu{mol L-1}$, and I'm not sure if you're supposed to use the molar mass of mercury here. The answer was $\pu{0.47 ppm}$, but I don't know how to get to here. Could someone explain the thought process for this?


texts: Pressure at which graphite and diamond are in equilibrium

texts:
I came across this problem :

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

I applied : $$\Delta G_{(P,T)} =\Delta_f G^{\circ}+\int_{p_1}^{p_2}Vdp$$.
Since the system is at equilibrium,$$ \Delta_f G^{\circ}= -\int_{p_1}^{p_2}Vdp$$
Now I am stuck. I have not been given any relation between Pressure and Volume. Is there any assumption i have to make to solve this integral ?


texts: How to convert CO2 ppm volume to ppm weight?

texts:
I'm using a sensor that measures $\ce{CO2}$ in ppm by volume aka atmosphere.
What I'm using it for is to measure $\ce{CO2}$ concentration in water which is measured in ppm by weight.

This is what I have so far

$$\text{Ppmwco2} = \text{ppmvco2} \times 0.8317 \times 44.01 / 10000;$$

This is quicker than $\text{co2}/1000000 \times 0.8317 \times 44.01 / 1000000$. 0.8317 accounts for Henry's Law and max ppmw will be 36.6 with 10,000 ppmv.

The sensor floats on the waterline detecting any $\ce{CO2}$ bouncing out of the water. Do I even need to account for Henry's law? Is the math right?


texts: Vibration motion at the imaginary frequency for TS of the Claisen rearrangment

texts:
I understand that the vibration along the reaction coordinate is different for the transition state , as the motion of the atoms takes TS towards products/reactants.

However, what would be the vibrational motion corresponding to the imaginary frequency of the Claisen rearrangement?


texts:
Is eicosapentaenoic acid (EPA) omega 3 or that's just a acid that comes with a omega 3? Same question for docosahexaenoic acid (DHA).

Just want to know are both of those two acid omega 3 despite being different acids.


texts: Is the reaction involving a proton transfer a redox reaction?

texts:
$$
\begin{align}
\ce{H2S (aq) + NH3 (aq) &→ NH4+ (aq) + HS- (aq)}\tag{1}\\
\ce{Pb(s) + 2 FeCl3 (aq) &→ 2FeCl2 (aq) + PbCl2 (aq)}\tag{2}
\end{align}
$$

  Which of the following statements correctly describes both of the equations above?

  A. Both equations represent redox reactions.
  B. Equation 1 represents a redox reaction but equation 2 does not.
  C. Equation 2 represents a redox reaction but equation 1 does not.
  D. Neither equation represents a redox reaction.

The answer key says that the correct answer is C. I picked A. But in equation 1, $\ce{H2S}$ donates a hydrogen to the $\ce{NH3}$ which would mean it's a redox as well. Both equations had donations and acceptances so I really don't understand why equation 1 is not a redox reaction.


texts: Modeling perturbations of a quantum mechanical system

texts:
I'm wondering how to properly perturb a quantum mechanical system.

I'm looking for a way to express the return to equilibrium of such a perturbed state, where the perturbation is in the Hamiltonian. The unperturbed Hamiltonian is $H_{\text{u}}$ and the perturbed Hamiltonian is $H_{\text{p}}$.

I can compute the eigensystem for both $H$ and thus find the relevant energy spectra and eigenfunctions, and can add the time-dependence factor $e^{-iEt}$, but I do not know how to generate the final system from its component, isolated systems. I would guess an inner product to be of use here, but...

What theory/mathematical methods do I need to learn to perform such simulations?

Something I want to model is a molecule in a polarized state, that is, with an asymmetric electron distribution.


texts: What kind of compounds are very basic and mildly volatile at room conditions?

texts:
We have a liquid seeping up into our concrete.  It is dissolving our epoxy floors and we can't stop it with any sort of sealant.

I tested it with pH strips and it seems to be very basic.  It's likely not got much water content either because it evaporates fairly quickly on a mild day.

What am I dealing with here?  I am going to send it out to get tested, but I was wondering if any chemists could help me out with classifying it.


texts: Regarding units of water potential and chemical potential

texts:
If water potential is nothing but the chemical potential of a given solution, then why do their units differ?

If the unit for the latter is taken as 'Energy per molecule' (which makes sense to me mathematically), then why is the former measured is 'Pressure'(Pascal)?


texts: Entropy change upon mixing cold and hot water

texts:
A closed, well-insulated container is filled with $\pu{454 g}$ of water at $\pu{94.4 ^\circ C}$. To the hot water, $\pu{200 g}$ of water ice at exactly $\pu{0 ^\circ C}$ is added. The mixture reaches an equilibrium temperature of $\pu{41.1 ^\circ C}$. Assume the molar heat capacity is constant and all the processes are at constant pressure. The standard enthalpy of fusion for water at $\pu{0^\circ C}$ is $\pu{6.008 kJmol–1}$. The constant-pressure heat capacity for water is $\pu{75.291 JK–1mol–1}$. Water has a molecular weight of $\pu{18.015 gmol^-1}$.
Calculate the entropy change (in $\pu{JK–1}$ ) for the system that happened because of this mixing.

I know the entropy change equals to $q/T$ because $q$ equals to the enthalpy exchange in the system as it is constant pressure, so what I did was:
$$q=(454/18.015)\times 75.291\times (41.1-94.4)+(200/18.015)\times 75.291\times(41.1)+(200/18.015)\times6008 = \pu{172.2 J}$$
Change in entropy = $172.2/(41.4+273) = \pu{0.55 JK-1}$
That is apparently incorrect, what have I done wrong?


texts: How many different possible structures (isomers) are there for the complex, [Mn(OH2)3(NH3)3] 3+?

texts:
How many different possible structures (isomers) are there for the complex,
$\ce{[Mn(OH2)3(NH3)3]^{3+}}$?

I really don't know how to begin with this. I know the answer is 2, but i don't have the faintest idea how this is the case. Since $\ce{Mn}$ has a charge of $3+$, I know that its valence electron configuration is $3d^4$. I also know that $\ce{NH3}$ and $\ce{H2O}$ are monodentate, which means they contribute 1 lone pair.


texts: Why is exothermic reactions are favoured by low temperature while endothermic reactions are favoured by high temperature?


texts:
I am using a (1,1,1) gold electrode for electron transport experiments using Transiesta. I have never used it before. I am wondering if when I do the electrode run, do I build a system where it is the left and right electrodes connected to each other? or do I use the entire device (molecule AND electrodes) and just set a flag in the file?

(In response to andselisk's request for more information about Transiesta: it is a computational chemistry program that is a part of the Siesta Suite. It is used mainly for electron transport calculations.)


texts: Selectivity of diazo-coupling with p-amino phenol

texts:
I came across this question and I've been thinking about it since, without being able to find a convincing major product. This question is related to one I found on this site, Diazo Coupling reaction with para-substituted phenol?, but it doesn't totally clear my doubt, and hence I specifically posted this reaction.

My thoughts were, since benzene diazonium is a weak electrophile, it would prefer to attack the most nucleophilic or electron rich site, and $\ce{-NH2}$ being better nucleophile than $\ce{-OH}$, I feel that would be more preferred site of coupling. Also I found out that aniline reacts with diazonium in basic medium to form diazo-aminobenzene which later rearranges to form more stable amino azobenzene; only to support my opinion. Thus my product was:

But the actual answer given was ortho coupling w.r.t. to $\ce{-OH}$, and it supports the product shown in the previously mentioned question, and @orthocresol commented that it occurs due to formation of phenoxide in basic medium:

But still it wasn't very convincing for me, as no one posted a solid answer to the question, neither are their any suitable articles I found on the internet that compare the reactivities of different functional groups towards diazonium.
I would be very obliged if someone could provide a deeper insight to the matter, and clear my misconceptions(if any), and a critical view about the barriers or aids in formation of the products.


texts: Why is pressure or external force needed for combination of electron and proton in plasma phase?

texts: I have studied that after rising temperature matter is converted into plasma. I want to  know that whether in plasma phase nucleon coexist with electron but do not combine until pressure is applied. Why?


texts: Intuitive understanding of standard electrode potential

texts:
I have read many books on standard electrode potential and they define the term in various ways but I just can’t seem to get an intuitive idea of it.

$$\ce{Cu^2+ + 2e- <=> Cu}$$

Standard electrode potential, $E= 0.34\ \mathrm{V}$

Does this mean that when $1\ \mathrm{C}$ of charge passes from the hydrogen half cell to copper half cell, $0.34\ \mathrm{J}$ of energy is released?

$$\ce{Zn^2+ + 2e- <=> Zn}$$

Standard electrode potential, $E= -0.76\ \mathrm{V}$

Does this mean that when $1\ \mathrm{C}$ of charge passes from the hydrogen half cell to zinc half cell, $0.76\ \mathrm{J}$ is absorbed?


texts:
When cooking in the kitchen you usually use some oil or butter to bake your meat and potatoes in. After some weeks without cleaning (which happens every now and then) the surroundings of the stove will get a greasy, sticky layer. Since this only happens relatively close to the stove, say a 1-2 meter radius, I'm assuming that it is caused by my cooking.

My question is: how does the grease get so far away from the stove?

I know that sometimes oil will spray a bit when you add something water-containing to it, but the grease is actually also in places that are not in the 'line of fire' (on top of the ventilation hood for example). Therefore, the grease must be getting airborne somehow, but I don't understand how, because evaporation of the vegetable oil or butter seems highly unlikely to me. Does anyone know what is going on?


texts: How do you change the cis-trans isomerism of compounds?

texts: I would like to know a general procedure for the synthesising cis isomers from their trans counterparts and vice versa.


texts: Diazo Coupling reaction with para-substituted phenol?

texts:
Usually Diazo coupling occurs at para-position unless the para-position is occupied, in which case coupling occurs at ortho-position.

While solving questions I found in both the cases as shown, the coupling occurred at ortho-position of the $\ce{-OH}$ group:

So in case of phenol, is it possible that in all cases the coupling will occur at ortho-position with respect to the $\ce{-OH}$ group in phenol, irrespective of whether the other group has stronger +M Effect than $\ce{-OH}$?

I am not sure but I think this is happening because of Hydrogen bonding as shown below. But in that case it should also happen with the $\ce{-NH2}$ group. Is this the reason or there is some other?


texts:
I'm looking at purchase orders and I see purchases for chemicals like the following.

Glutaraldehyde, EM Grade, 25%

What does the "EM Grade" mean in this text? It says that it's recommended for histological or immunological techniques, but how?


texts:
My question concerns the relative stability of a radical next to an ester oxygen compared to a radical next to an ester carbonyl carbon.

The stabilizing effect of the electron pairs of ether oxygen is known, but the situation may be different for an ester oxygen, which donates fewer electron density.
On the other hand, can the pi electrons of the carbonyl contribute to the stabilization of the radical next to it?
What is the preferred point for a radical attack on such a (poly)ester structure and, in your opinion, is there a clear preference? References are welcome.


texts: How does ammonium chloride increase the solubility of magnesium hydroxide in water?

texts:
In my textbook it is written that $\ce{Mg(OH)2}$ is slightly soluble in water, and it forms a milky solution which is called "milk of magnesia".

Its solubility can be increased by the addition of $\ce{NH4Cl}.$ But how? There seems to be no reason.


texts: How addition of a soluble salt affects equilibrium involving precipitation with a base sharing the same cation?

texts:
I have the following reaction at equilibrium:

$$\ce{Ba(NO3)2(aq) + KOH(aq) <=> Ba(OH)2(s) + 2 KNO3(aq)}$$

Will there be a change in the equilibrium if the salt $\ce{KCl}$ is added? Will the reaction shift in a certain direction to restore equilibrium?

I know that with adding $\ce{KCl}$, $\ce{K+}$ ions are added, but I am not sure if that is related to the answer.


texts: What will be the form of coulomb and exchange operators for electron m in an n-electron molecule?

texts:
I know that the Fock operator for electron $m$ in $n$-electron molecule would be:

$$\hat{f}\!(m)u_i(m) = \varepsilon_iu_i(m)$$

$$\hat{f}\!(m) \equiv -\frac 1 2 ∇_m^2 - \sum_α\frac{Z_α}{r_{ma}} + \sum_{j = 1}^n\left[\hat{j}_j(m) - \hat{k}_j(m)\right]$$

And the Coulomb operator according to Wikipedia is given by:

$$\hat{J}_{\!j}(1)f(1) = f(1)\int\left|\varphi_j(2)\right|^2\frac{1}{r_{12}}\mathrm dr_2$$

My understanding of this equation is that we are finding the interaction of $f(1)$ with the electrons of $j$-th orbital (we take interaction with electron 2 and twice that result, hence $2J$ is used in the expression for Fock operator), and $r_{12}$ is the separation between our electron in $f(1)$ and 2nd electron in $j$-th orbital.

This is the expression for exchange operator for electron $1$ in $j$-th orbital with an arbitrary function '$f$'. What would be the expression of Coulomb and exchange operators for electron $m$? Will we consider the $1$st electron of $(m/2)$-th orbital? Or will we simply put $m$ in place of $1$?

Or have I understood the whole thing incorrectly?


texts: Why does Tyndall scaterring produce conical shape?

texts:
When light is passed through a collidal solution, due to Tyndall scattering, the path of light appears to be a bright cone. Why does it have to form only a conical shape?
The conditions for Tyndall effect are that the diameter of dispersed particles should not be much smaller than wavelength of light used and refractive index of dispersed phase and dispersed medium should differ greatly.
This is perhaps because colloidal particles scatter light in all directions. Normal refraction shouldn't cause such a shape.
Is there any logical reson for the conical shape?

Source: NCERT class 12


texts: Why do only chiral molecules rotate the plane of polarized light and how do they rotate it?

texts:
I have learnt that only chiral or unsymmetrical molecules can rotate the plane of linearly polarized light. But, why is it so?

And how can molecules rotate the plane or what does it actually mean by 'rotating'?
Does it mean that the electric field vectors are tilted or turned left or right depending on the type of isomer?


texts:
Sorry I understand this looks like a "homework question", (I'm actually a 46yr old dentist looking to see what amount of calcium phosphate should be effective in a proprietary toothpaste!). However, if the actual question below can not be worked out can you let me know what the process of the calculation would be to determine mass of a salt to add to gain a mmol/L concentration?

Original Question:
I wonder if you can help on this? I want to calculate how much calcium phosphate to add to 1g of toothpaste to have between 18mmol/L to 1.5mmol/L of calcium and phosphate on the tooth surface? Also if you are able to work this out can you let me know what assumptions you have made in this calculation?


texts: Which one is nitric Acid, HNO3 by itself, or when it is included in H2O?

texts:
This is a quote from my Chemistry textbook:

  Nitric acid ionises according to the following equation:
  $$\ce{HNO3(l) + H2O(l) -> H3O+(aq) + NO3- (aq)}$$

I know that the formula for nitric acid is $\ce{HNO3}$. But I cannot understand what is the product of this equation. What is $\ce{H3O+(aq) + NO3- (aq)}$? Is it a diluted acid with less concentration?

This is another quote (from my textbook) that confuses me:

  Nitric acid and sulfuric acid are not quite as strong as hydrochloric acid. Chemical and spectroscopic studies have shown that concentrated solutions of both these acids do contain some unionised molecules. For our purpose, however, their ionisation is effectively complete. This is particularly true in dilute solutions.

I cannot understand the part that is in the bold. What are these unionised molecules? I know that these acids are considered strong acids which completely ionise in water solution. If that is the case, then why does the text indicate that there are some unionised molecules?


texts:
Solomon and Fryhle $11^{th}$ edition says :

Order of reactivity of HX in the acid catalyzed conversion of alcohols to alkyl halides follows the order : HI>HBr>HCl

We can account for this by saying that the acidity order is also HI>HBr>HCl
and hence the $-OH$ is easily protonated by the more acidic halide but the reaction is already acid catalyzed by a strong acid and the conversion of $-OH$ to  $-H_2O^+$ is fast so the acidity of $HX$ should make a negligible difference.

The slow step of the reaction is the formation of the carbocation and that does not seem to involve the halide so how can we explain this order ?


texts: In an ionic bond, are electrons actually transferred from one atom to the other to form a positive and a negative ion OR are ionic bonds just extremely polar covalent bonds? Sorry if this seems like a simple question but I've heard this somewhere so just wanted to make sure.


texts: Photochemistry of beta, gamma-unsaturated ketones

texts:
Is there a Norrish reaction for beta, gamma-unsaturated ketones?
I know that Norrish reaction is used for saturated ketones, but in my homework I found this question. I have looked a lot in books and websites but I haven't found anything


texts: How to unify all the subunits in a PDB file?

texts:
A PDB may contain a TER token. For example, hemoglobin has 4 subunits separated by a TER identifier.

If we take hemoglobin's biological assembly pdb file we see:

ATOM   1067  NH1 ARG A 141      26.176   8.362  17.810  1.00 11.11           N
ATOM   1068  NH2 ARG A 141      24.650   9.068  16.200  1.00 13.86           N
ATOM   1069  OXT ARG A 141      26.697  14.784  20.720  1.00 10.99           O
TER    1070      ARG A 141
ATOM   1071  N   HIS B   2       3.670 -13.643  19.447  1.00 38.58           N
ATOM   1072  CA  HIS B   2       2.695 -14.734  19.744  1.00 32.83           C
ATOM   1073  C   HIS B   2       1.379 -14.140  20.199  1.00 30.79           C

Is there an easy way to merge all the subunits into a single VMD frame?


texts: How to specify atomic carbon terms in the coupled and uncoupled representation?

texts:
So, we know, that the atomic carbon in the electronic configuration $1s^22s^22p^2$ has the following terms

$${}^1S, {}^1D, {}^3P$$

My question is - how can I correctly specify these terms in the terms of coupled and uncoupled representations?

My attempt

So, in the case of terms, we're only considering the orbital angular momentum, not the spin. Because of that, we can describe the single terms in the coupled representation $\left|L, M_L\right>$ which correspond with the linear combination of microstates, i.e. the uncoupled representations $\left|m_{l1}, m_{l2}\right>$ using Clebsch-Gordan coefficients.

For ${}^1S$ term it's pretty easy, as $L=0$ and $M_L=0$ (as described in this answer):

$$\begin{align}{}^1S: |L = 0, M_L = 0\rangle &= \frac{1}{\sqrt 3} |m_{l1}= 1, m_{l2} = -1\rangle + \frac{1}{\sqrt 3} |-1, 1\rangle - \frac{1}{\sqrt 3} |0, 0\rangle\\ &= \frac{1}{\sqrt{3}} \left| 8 \right> + \frac{1}{\sqrt{3}} \left| 11 \right> - \frac{1}{\sqrt{3}}\left| 14 \right >\end{align}$$

In the last expression there are wavefunctions specified with indices from the microstate table below.

But further it gets somewhat more tricky - both ${}^3P$ and ${}^1D$ will contain multiple states.
$P$ corresponds with $L=1$ and so $M_L \in \left\{ -1, 0, 1 \right\}$. I suppose, that its coupled representations are $\left| L=1, M_L=-1\right>, \left| L=1, M_L=0\right>, \left| L=1, M_L=1\right>$.

$$\begin{align}
{}^3P: \left| L=1, M_L=-1\right> &= \frac{1}{\sqrt{2}}\left| -1, 0 \right> + \frac{1}{\sqrt{2}}\left| 0, -1 \right>\\
&= \frac{1}{\sqrt{2}}\left| 2 \right> + \frac{1}{\sqrt{2}}\left|5 \right>\\
\left| L=1, M_L=0\right> &= \frac{1}{\sqrt{2}}\left| 1, -1 \right> - \frac{1}{\sqrt{2}}\left| -1, 1 \right>\\
&= \frac{1}{\sqrt{2}}\left| 3 \right> - \frac{1}{\sqrt{2}}\left|6 \right>\\
\left| L=1, M_L=1\right> &= \frac{1}{\sqrt{2}}\left| 1, 0 \right> - \frac{1}{\sqrt{2}}\left| 0, 1 \right>\\
&= \frac{1}{\sqrt{2}}\left| 1 \right> - \frac{1}{\sqrt{2}}\left|4 \right>
\end{align}
$$

${}^1D$ corresponds with $L=2$ and $M_L \in \left\{ -2,-1,0,1,2 \right\}$.

$$\begin{align}
{}^1D:\left| L = 2, M_L = -2 \right> &= \left| -1, -1 \right> = \left| 15\right>\\
\left| L = 2, M_L = -1 \right> &= \frac{1}{\sqrt{2}}\left| 0, -1 \right> + \frac{1}{\sqrt{2}}\left|-1, 0 \right> \\
&= \frac{1}{\sqrt{2}}\left| 10 \right> + \frac{1}{\sqrt{2}}\left| 12 \right>\\
\left| L = 2, M_L = 0 \right> &= \frac{1}{\sqrt{6}}\left|1, -1 \right> + \sqrt{\frac{2}{3}}\left| 0, 0 \right> + \frac{1}{\sqrt{6}}\left| -1, 1 \right> \\
&= \frac{1}{\sqrt{6}}\left| 8 \right> + \sqrt{\frac{2}{3}}\left|14 \right> + \frac{1}{\sqrt{6}}\left| 11 \right> \\
\left| L = 2, M_L = 1 \right> &= \frac{1}{\sqrt{2}}\left| 1, 0 \right> + \frac{1}{\sqrt{2}}\left| 0, 1 \right>\\
&= \frac{1}{\sqrt{2}}\left|7 \right> + \frac{1}{\sqrt{2}}\left|9 \right> \\
\left| L = 2, M_L = 2 \right> &= \left| 1, 1 \right> = \left| 13 \right>
\end{align}
$$

Is this the right approach or do I understand it incorrectly?

Table of microstates


texts:
Can anyone explain to me the chemical process of bronze tarnishing? According to Wikipedia:

Bronzes are typically ductile alloys, considerably less brittle than
cast iron. Typically bronze oxidizes only superficially; once a copper
oxide (eventually becoming copper carbonate) layer is formed, the
underlying metal is protected from further corrosion.

Does this mean the tarnish that we see in the picture below is created by copper oxide turning into copper carbonate? If so, how do you write out that equation? What is being oxidized and what is being reduced?


texts:
Consider two liquids with vapour pressures in pure form being ${P^o}_A$ and ${P^o}_B$. ${P^o}_B >{P^o}_A$ which implies liquid B is more volatile. If the liquids formed an ideal solution, then a straight line (drawn with red in the diagram) will be obtained for the vapour pressure of the solution. However, if they formed a non ideal solution with positive deviation, the red curve would have been obtained.

Now, we get a maxima on that curve. At that composition, the solution would be called a minimum boiling point azeotrope. I understand why minimum boiling point. It's because of the maximum vapour pressure but what I don't understand at all are these points:

The azeotrope boils at a constant temperature.
The composition of the azeotrope remains fixed while boiling.
The azeotropic mixture cannot be separated by fractional
distillation.

These points are really not explicit from the graph. I am not able to figure out the reasons for those points. Can someone please provide a mathematical/ intuitive view of azeotropes relating to these 3 properties?

Also, "in an azeotrope or constant temperature boiling mixture, the vapour has the same composition as the liquid." How can we confidently claim that the point of maxima is the point where the vapour has same composition as liquid?


texts: Choice of solvent during thin layer chromatography

texts:
I understand most of the theory behind TLC and that different volatile solvents have different polarities and cause the 'spotted' substances to move at different rates, but what is the point of creating mixtures and then using them in different ratios? How could the results change if I changed the ratios?

For example, during our lab, we synthesized acetylglycine and made three spots on our TLC plates, one spot was pure glycine, one spot was glycine + acetylglycine, and the third spot was just acetylglycine. the chamber was equilibriated with Dichloromethane & Hexane in an 8:2 ratio.

Glycine didn't move, and the other two spots did move up.
How would the results have changed if I used only dichloromethane? only hexane?

What if I used a 7:3 ratio? 5:5 (1:1) ratio?
I have a feeling the answer is really obvious and i'm overthinking this but it's really not hitting me right now.
Thank you for reading!


texts:
What is the ratio of copper(II) ions to EDTA in a $\ce{[Cu(EDTA)]^{2-}}$ complex?

I know that EDTA forms up to 6 coordinate bonds with the central atom, but is that what they are asking for with "ratio"?
According to this website, it seems that copper actually bonds with all 6 free electron pairs.


texts: How to tell if a molecule will participate in hydrogen bonding with water?

texts:
I was recently doing some organic chemistry work and came across a set of problems.

"Which of the following compounds will participate in hydrogen bonding with water? For each compound, indicate whether it will be a hydrogen bond donor, hydrogen bond acceptor, or both."

I do not have an idea of how to approach the first part of the question. Can someone help me with the first molecule: (a) $\ce{CH3CH2OCH3}$ in order of connectivity.


texts: How is the tetrachloridocobaltate(II) anion stable if its crystal field stabilization energy comes to be positive?

texts: I tried to calculate the ligand field stabilisation enthalpy of $\ce{[CoCl4]^2-}$ (as shown in the image) but found it to be positive. What could be the reason behind this? How is it stable with positive crystal field stabilization energy?


texts:
at first I wondered why 2 H are added to opposite side of benzene like reaction below. because I could imagine 2 H added right next to each other or 1 C away from each other.

so, looking for explanation I saw a molecular orbital of benzene.

It's one of LUMO from benzene and from this I just guessed that maybe hydrogen could be added to 2 unpaired p orbitals in the opposite direction.

but when I learned another Birch reduction I got confused again.

since the E level of LUMO above would get high, I assumed another LUMO maybe come into play.

so from MO right above, I can under stand e- from Na would go to ortho- or meta- position of substituted group.

And here's my question. why does hydrogen go to ortho position first?
additionally, why second Hydrogen goes to the opposite side of first-added hydrogen? and I'd really appreciated any correction about my educated guess above.


texts: Order of the reaction between hemoglobin and oxygen

texts:
I have the reaction:

$$\ce{Hb + O2 <=>[$k$][$k'$] HbO2}$$

where $\ce{Hb}$ is hemoglobin, $k$ is the rate constant of the forward reaction, $k'$ is the rate constant of the inverse reaction. On my book there is the rate law:

$$W = kP(\ce{O2})[\ce{Hb}] - k'[\ce{HbO2}]$$

where $W$ is in $\pu{mol m-3 s-1}$, $P(\ce{O2})$ is a partial pressure in Pascal ($\pu{kg m m-2 s-2 = kg m-1 s-2}$).

The inverse reaction is a first order reaction because:

$$\pu{mol m-3 s-1} = [k'] (\pu{mol m-3})$$

thus $[k'] = \pu{s-1}$.

I am in trouble with the forward reaction because I got a strange unit of measurement:

$$\frac{\pu{mol}}{\pu{m3 s}} = [k] \frac{\pu{kg}}{\pu{m s2}} \frac{\pu{mol}}{\pu{m3}}$$

$$[k] = \frac{\pu{m s}}{\pu{kg}}$$

Which is the order of the forward reaction?


texts: Do volumes and pressures calculated from Boyle's Law depend on the temperature?

texts:
As the title suggests, i have a question regarding Boyle's law.

As Boyle's law states that "The volume $V$ of a given mass of a gas, is inversely proportional to the pressure $p$ applied to it when the temperature $T$ is constant."

So if we had a gas at say a pressure $p_1$, and a volume $V_1$, corresponding to this pressure at a constant temperature $T_1$.

Now if i were to increase the the temperature of this gas to a new temperature $T_2$ and make it constant. And then apply the same pressure $p_1$ on the gas would the volume still be $V_1$?

Considering the fact that volume and pressure are inversely proportional for a constant temperature, and hence they dont depend on the temperature?? Am i right?

Thanks


texts:
In Peter Sykes' A Guidebook to Mechanism in Organic Chemistry  regarding the retention of configuration of reaction of alcohols with $\ce{SOCl2}$:

  The rate at which the alkyl chlorosulphite intermediate breaks down to $\ce{RCl}$ is found to increase with increasing polarity of the solvent and also with the increasing stability of the carbocation $\ce{R+}$: an ion pair $\ce{R+SOClO-}$ is almost certainly involved.

But it is nowhere mentioned whether a carbocation rearrangement is possible or not.

In "NCERT Chemsitry Class 12" in the section of Preparation of Alkyl halides from Alcohols:

  The hydroxyl group of an alcohol is replace by halogen on reaction with concentrated halogen acids, phosphorous halides or thionyl chloride. Thionyl chloride is preferred because the other two products are escapable gases.

If that method is preferred, then I assume rearrangement does not occur.

So, why does not a carbocation rearrangement (like Wagner–Meerwein rearrangement) occur in the $\mathrm{S_Ni}$ pathway eventhough the intermediate is involved? Is it because the intermediate breaks down too quickly before any rearrangement is possible?


texts: What is the highest the boiling point of water can be raised?

texts: As I understand it, the boiling point elevation in a particular solvent (in this case water) is a function of a particular constant of that solvent, and the molality of a dissolved substance. In turn, the maximum molality is a function of the solubility of the compound, as well as the van 't' Hoff factor. Thus it would follow that the highest possible elevation of water's boiling point would be the compound with the greatest ratio of solubility to van 't' Hoff factor. So the question remains: which compound is that?


texts: What do these mineral classification symbols mean?

texts:
For my birthday I got an awesome mineral specimen case, as pictured below. What piqued my interest was the notations in the lid where the minerals are described with 5 specifications: C (obviously for Colour) then S, H/SG (I'm guessing specific gravity), L and CL.

Can anyone shed any light on what these abbreviations mean? Additionally, do the coloured squares mean anything or are they just for identification (they match colours painted on some of the samples).


texts: When does hydrogen peroxide act as a reducing and when as an oxidising agent?

texts:
My chemistry books details out both, the oxidizing and reducing properties of hydrogen peroxide, $\ce{H2O2}$.

  Its reducing properties:

  It reduces $\ce{Cl}$ to $\ce{HCl}$
  It reduces $\ce{Ag2O}$ to $\ce{Ag}$
  It reduces $\ce{K3[Fe(CN)6]}$ (potassium ferricyanide) to $\ce{K4[Fe(CN)6]}$ (potassium ferrocyanide)
  Etc.

  Half equations for reduction:

  In acidic medium: $\ce{H2O2 -> 2H+ + O2 + 2e-}$
  In basic medium: $\ce{H2O2 + 2OH- -> 2H2O + O2 + 2e-}$

  Its oxidizing properties:

  It oxidizes sulphites to sulphates
  It oxidizes arsenites to arsenates
  It oxidizes nitrites to nitrates
  It oxidizes potassium ferricyanide to potassium ferrocyanide
  Etc.

  Half equations for oxidation:

  In acidic medium: $\ce{H2O2 + 2H+ + 2e- -> 2H2O}$
  In basic medium: $\ce{H2O2 + 2e- -> 2OH-}$

I was unable to find any pattern in all of the reactions I studied above (except for potassium ferrocyanide, for which the medium triggers the electron addition/removal) to recognize when hydrogen peroxide behaves as an oxidising agent and when it behaves as a reducing agent.


texts:
In reactions that go until the end the stoichiometric number indicates the exact amounts of reactants and products you will get. However, this is not the case in equilibrium reactions and you will get a different amounts (concentrations) than what exhibits the stoichiometric numbers.
$$\ce{Na + Cl -> NaCl}$$
You will get in the end 1 mole of NaCl from 1 mole of Na and one mole of Cl.
$$\ce{2SO3<=>2SO2 + O2}$$
In equilibrium you will not get 1 molar of $\ce{O2}$ and 2 molar of $\ce{SO2}$ from 2 molar of $\ce{SO3}$.
Then what do the stoichiometric numbers indicate in equilibrium?


texts: Best Method To Make Large Graphene Oxide Sheets?

texts:
There are so many methods to make graphene oxide now, I'm not exactly experienced enough to know which is ideal. I want to know what the best method is for making large graphene oxide membranes. The goal is to have a surface area of a square meter.

Graphene oxide is usually made by filtration so the two requirements I have are:

that it can be made by filtration over porous aluminum oxide (for stability in water as revealed here: bit.ly/1HExnui)...well any method really, as long as Al^3+ cations can be incorporated into the graphene oxide in some way
that the method is known for success with the helium permeation test (as in essentially only water can pass through the graphene oxide).

I've asked a few questions already here on stackexchange and it always feels strange to simply ...demand or extract information. Thank you all.


texts: How to formulate the 1 dimensional time-dependent Schrodinger’s equation from a given function?

texts:
Assuming $f(t) =e^{−iωt}$, formulate the 1 dimensional time-dependent Schrodinger’s equation.

I started solving the problem as
\begin{align}
  E &= hf, \tag1\label{eq:1}\\
  E &= ħw, \tag2\label{eq:2}\\
  \frac{\partial f(t)}{\partial t}
    &=-iωf(t). \tag3\label{eq:3}
\end{align}

Then I solved \eqref{eq:2} and \eqref{eq:3} to get
$$\frac{-iE}{ħ}f(t)=\frac{\partial f(t)}{\partial t}. \tag4 $$

Now I am not sure how to continue from here to get the time-dependent Schrodinger’s equation.


texts:
I want to use silicon nitride ball bearings with a reciprocating piston that will be powered by $\ce{CO2}$ liquid heated to  $\mathrm{288^oC}$ becoming super critical. That temperature is the maximum and the cylinder will not exceed that staying well below the $\mathrm{768^oC}$ rating of the bearings.

I can not use lubrication and the 1/4 bearings will be stacked 3 high with 4 of them surrounding the rod for a total of 12 bearings in direct contact with the rod that could have traces of supercritical $\ce{CO2}$ upon it. The bearings will be in contact with each other to provide both a seal and to align the piston and if there is any contamination it will spread.

Can I expect any type of reaction between the supercritical $\ce{CO2}$ and silicon nitride bearings?


texts: What is the favoured geometry of chlorine trifluoride?

texts:
Why is the first structure on the left more stable than the second one on the right?

In the first one the angle between the two pair of nonbonding electrons is about 120° which is a lot less than that in the second structure. And it is also very well known that lone pair-lone pair repulsions are worse than bonding pair-bonding pair repulsions. So why is the first structure more stable?


texts: Are Organic Solvents used in Addition Reactions catalysts?

texts:
Say for example you are performing a halogenation reaction with dichloromethane (DCM) as the solvent:

ethylene + chlorine $\stackrel{DCM}\longrightarrow$ 1,2-dichloroethane

I have 2 questions:

Is the DCM acting as a catalyst to the reaction, or just a solvent? And if just a solvent, why do we have to use an organic solvent, why not water?
Are solvents like DCM necessary if the reactants are liquids already, or only for gaseous or solid reactions?

Thank you


texts: Why are styrene acrylate copolymers used for toner?

texts:
I have been scratching my head lately, after learning that laser printer toners are often made from styrene-acrylate copolymers. As of yet, I have not found information on these polymers in reference texts or papers/research outside of the realm of xerography, electrophotography, and other printing technologies. What properties make these polymers particularly interesting for toners, but completely uninteresting to other fields? At risk of overreaching, I'm also curious how these copolymers came to be used in toner in the first place, given the lack of convenient information?

References:

Reactive Polymers Fundamentals and Applications, chapter 20 "Toners"
Production of carbon black acrylic composite as an electrophotographic toner using emulsion aggregation method:
Investigation the effect of agitation rate, paper by Maryam
Ataeefard
Production of black toner through emulsion aggregation of magnetite, carbon black, and styrene-acrylic co-polymer:
Investigation on the effect of variation in components, paper by
Maryam Ataeefard
Various MSDS pages from toner and laser printer manufacturers


texts: Reactivity of Ni Vs. Pd - available oxidation states

texts:
I'm hoping someone can help me tighten up my understanding of the origins of the differences between Ni and Pd catalysis.

I understand that Ni has higher charge density and this is the reason for it's larger capacity for oxidative addition for say an aryl halide. It also has access to the oxidtaion states (0), (I), (II), (III) and sometimes (IV). Palladium conversely only shuttles between (0) and (II) in a standard cross-coupling reaction. I believe the lower first ionisation energy can account for the increased tendency of Ni to do SET but I don't know how best to explain why all the additional oxidation states are available to Ni and not for Pd.

thanks in advance, Cat