texts: Why do electrophillic addition reactions (between hydrogen halides and alkenes) happen?

texts:
I understand that the type of solvent (protic or aprotic) may impact the rate of the reaction, but why doesn't the hydrogen just stick with the halide in the first place?

I'm not sure if the reason is just that the hydrogen's electrophilic attraction to the π orbital electrons are just stronger than the hydrogen's electrostatic attraction to the electrons it shared with the halide.

Am I missing something?


texts: What is the relationship between the values of n and ml?

texts:
Example question: ml=+5 what is the lowest value of n?
I can't seem to remember the easy trick to finding the relationship if someone could explain that would be great. -Thank you in advance.


texts: During a Gaussian scan calculation, I got a high negative frequency for a transition state candidate, but it doesn't matter what I do (Berry algorithm, qst methods) I cannot get a stable TS, I always get a really low frequency that's clear a rotation in a methyl group.


texts: If you put two blocks of an element together, why don't they bond?

texts:
Say you have two lumps or blocks of an element, like lithium for example, say in the form of two bars.

Why, when you bring the two bars together so that they touch each other, do they not instantly bond with each other forming one larger bar or block? We can weld elements together so they 'stick' to each other, but what is the process that actually causes two like elements to bond together? Why do we need to 'weld' two bars together - why don't they just bond on their own?


texts: Which is more basic: 1,2‐dihydropyridine or 1,4‐dihydropyridine?

texts:
Which compound is more basic of the two?

My thinking: In compound A, the lone pair of nitrogen are in resonance with two other double bonds. The resonance chain here seems to be longer as compared to in compound B. However, in compound B, the lone pairs of nitrogen seem to be more 'busy' because of the two double bonds on its either side,when compared to compound A (@YUSUFHASAN provided this second logic).
So, which of the two compounds should be more basic? (The main idea is that, the lesser 'busy' lone pair electrons of nitrogen means more 'free' electrons to pick up $\ce{H^+},$ which is what bases do.)
Do note that this question is supposed to be answered qualitatively. (By this I mean, not looking at tabular data from research papers or books!)


texts: Why does tomato soup "explode" when boiled?

texts:
When you boil tomato soup it very easily "explodes" when reaching the boiling point. Why is that?

A related question has been answered here before: Why do some solutions eventually stop boiling and start "popping" as they get more concentrated?
However, the answer to that question does not fully answer the current question since it does not address what properties in a solution causes superheating/bumping. That answer describes what we see but does not describe WHY it happens (except for the words "heated too rapidly", but many solutions can be heated with the same speed as tomato soup without "exploding").

For example, to my knowledge tomato soup only suffers the risk of "exploding" THE FIRST TIME it reaches the boiling point. Therefore I have thought the reason for the explosion could be that it contains gases that leave the solution violently. (I have read this is the reason that milk also may "explode" at the boiling point.)

Friends if mine suggest that the reason for the explosive boiling is the viscosity of tomato soup. But this answer would not explain why tomato soup only risks "exploding" the FIRST time it boils. (Without extensive experience I would also say that NOT ALL viscous solutions boil explosively.)

Tha tomatoes are naturally peeled so their elastic peel/membrane does not come into account.

The previous question also relates to gradual concentration which is not the issue of the current question. The current question relates to reaching the boiling point.

So this question is not answered. To rephrase it slightly:
What properties in tomato soup causes it to boil "explosively"?


texts: Why lithium salts crystallize in octahedral lattice , although radius ratio values are much below than expected ratio?


texts:
I'm totally confused about the relationship between the polarity and acid strength of a given compoud.

Take the case of alcohols itself, it's said that primary alcohols have greater acid strength compared to secondary alcohols as the electron-releasing group in secondary alcohol decreases the polarity of $\ce{O-H}$ bond.

But why is this so?
I mean, less polarity will help in liberating $\ce{H+}$ ions more easily so acidity is meant to be increased.

That means secondary alcohols are meant to have more acid strength.

Some help to solve this dilemme is appreciated.


texts: Which reactions are more temperature sensitive: the ones with higher Ea or the ones with lower Ea? And why?

texts:
Which reactions are more temperature sensitive: the ones with higher $E_\mathrm{a}$ or the ones with lower $E_\mathrm{a}$? And why?

I wasn't able to find much useful content on googling it, however on doing the math I came to a conclusion that the ones with higher $E_\mathrm{a}$ are more sensitive to increase in temperature. But why is it so? I mean math proves it, but why exactly does it happen?

Here are my calculations:


texts: Mechanism for basic hydrolysis of α-chloronitrile to ketone?

texts:
In Corey's 1969 prostaglandin synthesis,1 compound 2 is formed from compound 1 by:

  [...] treatment with 2.5 equiv of potassium hydroxide (added as a hot saturated aqueous solution) in dimethyl sulfoxide for 14 hr at 25-30°.

Can anybody explain the mechanism of this reaction? I thought of an $\mathrm{S_N2}$ reaction, followed by nitrile hydrolysis and elimination of $\ce{CO2}$. But $\mathrm{S_N2}$ there seems impossible, and the elimination of HCl should be more reasonable than decarboxylation.

Reference

(1) Corey, E. J.; Weinshenker, N. M.; Schaaf, T. K.; Huber, W. Stereo-controlled synthesis of dl-prostaglandins F2α and E2. J. Am. Chem. Soc. 1969, 91 (20), 5675–5677. DOI: 10.1021/ja01048a062.


texts: Benzyne formation with Grignard reagents

texts: Nucleophilic substitution through an elimination-addition mechanism (involving benzyne formation) occurs with a strong base. $\ce{NH2-}$ can show this reaction. Can Grignard reagents $\ce{RMgX}$, which form $\ce{R-}$ - an even stronger base - show this reaction?


texts: When I first heard about buckminsterfullerene, I thought it was a very fascinating molecule, with its interesting complex ring structure and pseudo-symmetry.  I wonder though, can you get similar structures with other atoms?  Maybe neighbors of similar size, like boron, nitrogen or oxygen?  Or maybe silicon, one row down?   What would their chemistry be like?


texts: Why does pasta become sticky after being cooked?

texts:
This question was posed by my biochemistry professor at the end of a class and then never answered.

What I've gathered is that:

It has something to do with the denaturing of a protein, since we were on the subject of denaturing that lecture.
It most likely involves gluten, because that's the main protein in wheat. And, from personal experience of making glue, gluten is very sticky.
The answer might involve hydrophilic/hydrophobic interactions, because those interactions are disturbed during the denaturing process.

Any ideas?


texts: Formation of water vapour during combustion

texts: When we burn fuel, water vapour is produced because hydrogen is burnt as well. But since the vapour is in gaseous state already, it shouldn't steal any heat from fuel gases, should it?


texts: How to find the molecular formula for a hydrocarbon compound from known combustion products?

texts:
What is the molecular formula of a compound containing only carbon and hydrogen if combustion of $1.05~\mathrm{g}$ of the compound produces $3.30~\mathrm{g}~\ce{CO2}$ and $1.35~\mathrm{g}~\ce{H2O}$ and its molar mass is about $70~\mathrm{g}$?

Here is my work:

$$
\begin{array}{cccccc}
                  & \ce{C_{a}H_{b}} & \ce{->} & \ce{CO2} & + & \ce{H2O} \\
\text{masses (g)} & 1.05            &         & 3.30     &   & 1.35
\end{array}
$$

\begin{align*}
\ce{CO2} &\rightarrow \ce{C} \\
44~\mathrm{g} &\rightarrow 12~\mathrm{g} \\
3.30~\mathrm{g} &\rightarrow x
\end{align*}

$$
x = 0.9~\mathrm{g},~\text{moles of C} = \frac{0.9}{12} = 0.075
$$

\begin{align*}
\ce{H2O} &\rightarrow \ce{2H} \\
18~\mathrm{g} &\rightarrow 2~\mathrm{g} \\
1.35~\mathrm{g} &\rightarrow y
\end{align*}

$$
y = 0.15~\mathrm{g},~\text{moles of H} = \frac{0.15}{1} = 0.15
$$

$$
\text{empirical formula}~\ce{C_{0.075/0.075}H_{0.15/0.075} -> CH2}
$$

$$
\frac{70}{14} = 5
$$

$$
\text{molecular formula is}~\ce{C5H10}
$$


texts: I ask this b/c I know the NMR deal with magnetic fields (MF) and it can change energy of proton’s magnetic energy. But my question is that electrons also have a spin and M F. Just like how IR and Mass deal with electrons, why don’t NMR also talk about electrons? Why just focus in the nucleus.


texts: Why are protein hydrophobic cores denatured by heat when entropic forces should be favoured at high temperature

texts: The hydrophobic interaction is thought to be driven by an entropic force. If it is, shouldn't hydrophobic interactions be stronger at higher temperatures, where states of higher entropy are favoured? Why, then, are protein hydrophobic cores denatured by heat?


texts: Does syn-dihydroxylation form racemic mixture?

texts:
I have been asked to determine the nature of the product for the following reaction:

And as I recognized this reaction to be a case of syn-dihydroxylation, my obvious response was that the product formed will be meso.
But, in the solution to the problem, it says it makes a racemic mixture.

Shouldn't both the $\ce{-OH}$ be on the same side and form a meso-compound? And what does the $(sym)$ stand for?


texts: Confusion in calculating $\Delta U$ from a bomb calorimeter

texts:
In the book, it is mentioned the formula for $\Delta U$ in a bomb calorimeter without any derivation:

$$\Delta U = q_v = \frac{Q\times M\times \Delta T}{m}$$
where
$$Q=\textrm{heat capacity of calorimeter,}$$
$$M=\textrm{molecular mass of sample,}$$
$$m=\textrm{mass of sample used, and}$$
$$\Delta T=\textrm{change in temperature of water in the bath}$$

I am confused regarding this formula. Can anyone give me the derivation of this formula (or a corrected formula)?
[I am 11-grader and am studying chemical thermodynamics. I can distinguish between $C$ as an extensive property and $c$ and $C_m$ as intensive properties.]
Any help would be appreciated :)
NOTE: I know that a formula is $q_v=cm\Delta T$, I want to know how the book got to the formula mentioned previously.


texts: How does the application of Schrödinger equation to model a particle in a box explain the origin of degeneracy of atomic orbitals?

texts:
Is the particle in a box concept analogous to an electron in an orbital? If so, can we apply the equation for the allowed energies of a particle in a box
$$E = \frac{h^2n^2}{8mL^2}$$
to the allowed energies of electrons in orbitals? Are the orbitals degenerate because this equation only includes the quantum number $n$ and not the others and therefore all orbitals in a subshell will roughly be degenerate?
Finally, if this equation can be used to explain the allowed energies of orbitals/electrons, what would $L$ be in this instance?


texts: Does rice protein have a high concentration of arsenic?

texts:
According to recent reports rice is high in arsenic. What about rice protein?

I am taking a protein powder that has "yellow pea protein isolate, sprouted whole-grain rice protein concentrate, organic instantized quinoa seed protein, organic Chia Sprout protein".

Would protein concentrate from Rice have high levels of arsenic?

http://www.consumerreports.org/cro/magazine/2015/01/how-much-arsenic-is-in-your-rice/index.htm


texts: pH level of fabric with regard to inhibiting fungal growth

texts:
Someone on another forum made the point that doing laundry with sodium hypochlorite (bleach) will kill any fungus such as athlete's foot fungus, but that after the fabric dries, the pH level of the fabric is conducive to more fungal growth, since bleach is a base.  The person made the point to substitute bleach with an acid like lemon juice, or to first do the laundry with bleach and then a second time with lemon juice.  Exact quote below:

  "Bleach removes fungus and mold but also promotes it’s later development. I had jock itch on and off for years until I stopped using bleach in my wash. Once I stopped using bleach it never returned. Fungus thrives in high PH environments caused by Bases like bleach. My jock itch returned for a short time when my wife used bleach again. If you must use bleach you should neutralize it with a post acid rinse like vinegar or lemon juice."

Is there any scientific rationale to backup this statement?  Is lowering the pH of fabric with an acidic substance a workable means of preventing fungal growth?  Or does it not matter- in other words, washing your clothes with bleach should neither promote nor inhibit future fungal growth (emphasis: athlete's foot fungus)


texts:
What is the $\mathrm{pH}$ when you dissolve equal amounts of $\ce{NaHCO3}$ and $\ce{Na2CO3}$ in water?

When both of the compounds are dissolved, we will have equal amounts of $\ce{HCO3-}$ and $\ce{CO3^2-}.$ But how do we go from this to actually calculating the $\mathrm{pH}$?

In the solution manual, it is given that $\mathrm{pH} = \mathrm pK_\mathrm{a2} = 10.33$ (It seems like the $\mathrm pK_\mathrm{a2}$ value of $\ce{CO2}$ has been used here — why?), but I don't understand how they can just conclude with that.

My attempt

So, we will start with equal amounts of $\ce{HCO3-}$ and $\ce{CO3^2-}$. We have the following equilibrium:
$$\ce{HCO3- <=> H+ + CO3^2-}$$
We can set up an equilibrium expression (and cancel) until we are left with $K_\mathrm{a2} = [\ce{H+}]$ and $-\log K_\mathrm{a2} = \mathrm pK_\mathrm{a2} = \mathrm{pH} = -\log[\ce{H+}]$.

Now, what I don't understand is why are we using the $\mathrm pK_\mathrm{a2}$ of $\ce{CO2}$? Why that value?


texts: Force Constants for Angles From Gaussian To AMBER: which value should I put in the matrix equation?

texts:
I am trying to make a new force field in AMBER for a novel compound including boron (which does not exist in GAFF). For this, I calculated freq and I found bond force constants but I couldn't find force constants for angles.

For example I tested $\ce{H2O}$: I calculated $\ce{H2O}$ frequencies in Gaussian and I got force constants from the log file. In the log file, the $\ce{O-H}$ stretching force constant was $\pu{9.1465 mDyne/\require{mediawiki-texvc}\AA{}}$ and I converted this to approximately $\pu{1315.65 kcal mol^{-1} \AA{}^{-2}}$. In AMBER, $v = 0.5k(l-l_{o})$, so I multiplied this by 0.5 and I found

ow-hw 657.825

which is very close to the GAFF2 forcefield:

ow-hw  612.98

which can be found on line 87. However, I couldn't find a way to calculate force constants from Gaussian for angles. In GAFF2 for $\ce{H2O}$, the values are

hw-ow-hw   43.276     104.520       AMBER              1    TIP3P_water

I searched and I found a lot of answer like this, but in this answer, for the Seminario approach I do not know what value to put in the matrix equation. Could you provide an example on a Gaussian log file?


texts: Relationship between thermodynamic reversibility and reactions

texts:
Often we're concerned with changes in thermodynamic properties during reactions, like $\Delta H_p = Q_{reaction}$ (change in enthalpy for an isobaric process). What seems odd to me is that in the derivation of this relationship,

$\Delta H_p = \Delta U + P\Delta V=Q-W+P\Delta V$

we assume the work is given by $W=P\Delta V$, which requires that the process is reversible in the thermodynamic sense. Then the change in enthalpy simplifies to

$\Delta H_p=Q - P\Delta V + P\Delta V=Q$.

Supposedly, measuring the heat transfer during a reaction at constant pressure will give the enthalpy. Even though enthalpy is a state function in general, our case requires that the process is reversible.

To what extent does the restriction of thermodynamic reversibility apply to the reaction? Do we have to assume the reaction happens slowly and can be undone, leaving only an infinitesimal change in the universe? Or does it not matter?

Please correct me if any of my points are wrong. Classical thermodynamics usually doesn't mention kinds of matter, so I'm a bit confused when chemistry comes into it.


texts: On eating powdered glucose I felt a cold sensation in my mouth. Then I thought it would be a result of the reaction between saliva and glucose. Then I thought that this would imply that the reaction would be endothermic. I don't find myself to be pretty sure and need to know whether I am right or not. Why would the reaction be endothermic in spite of the fact that glucose is readily soluble in saliva?


texts: Baking Soda + Citric Acid + Water = CO2, how much though?

texts: Baking soda (sodium bicarbonate) + citric acid react when mixed with water to form some amount of carbon dioxide gas ($\ce{CO2}$). I am trying to determine what percentage of the products is carbon dioxide: in other words, how much does reaction make?


texts: How do I calculate the concentration of sulphuric acid by a titration experiment with sodium hydroxide?

texts:
In my latest chem lab the objective was to create a primary standard of $\ce{NaOH}$ and use it to determine the concentration of sulfuric acid.

The first part of the lab was determine the molarity of the $\ce{NaOH}$ solution through a series of titrations.

A sample of KHP (abbreviated form of $\ce{KHC8H4O4}$) was placed into a flask with approximately $\pu{25 ml}$ of water.
Phenolphthalein was added to the flask as the indicator. $\ce{NaOH}$ was then titrated into the flask with a burette. From multiple titrations of this sort I was able to calculate the molarity of $\ce{NaOH}$.

Below I have included part of my table and calculations (Note: $\pu{1 mol}$ of KHP is equal to $\pu{1 mol}$ of $\ce{NaOH}$ in this experiment. If I have made any mistakes please tell me).

Trial 1:
Mass of KHP in flask $= \pu{0.5108 g}$
Volume of $\ce{NaOH}$ added to flask $ = \pu{21.73 ml}$
Calculation of molarity of $\ce{NaOH}$ for trial 1:
Molar mass of KHP $ =  \pu{204.23 g/mol}$
$\pu{0.5108 g}/\pu{204.23 g/mol} = \pu{0.002501 mol}$ of KHP, which is equal to $\pu{0.002501 mol}$ of $\ce{NaOH}$.
Molarity of $\ce{NaOH} = \pu{0.002501 mol}/\pu{0.02173 L} = \pu{0.1151 M}$

I did 3 other trials like this (in total 4) and calculated the average molarity of $\ce{NaOH}$ to be $\pu{0.1159 M}$.

The second half of the lab is the part I had trouble with.
We were given a sample of $\ce{H2SO4}$ with an unknown concentration. I took $\pu{10 ml}$ of this $\ce{H2SO4}$ and mixed it with $\pu{100 ml}$ of distilled water. This new diluted solution of $\ce{H2SO4}$ (I will refer to it as solution 2 now) was the solution used in the trials to determine the molarity. So $\pu{25 ml}$ of solution 2 was added to a flask with a few drops of phenolphthalein. A titration using $\ce{NaOH}$ (the same $\ce{NaOH}$ as used in the previous section) was performed.

My task is to now figure out the concentration of the original $\ce{H2SO4}$ solution. I have tried 2 different methods. The first method I attempted seems so flawed I didn't bother to put it on (it didn't even make sense to me). Each method seems incorrect and have yielded drastically different results. Below I have provided a sample of my table and one of my attempts to solve for the molarity of $\ce{H2SO4}$.

The net ionic equation of this procedure is:
$$\ce{H2SO4 +2NaOH <=> Na2SO4 + 2H2O}$$

Trial 1:
Volume of diluted acid (solution 2) in flask: $\pu{25.00 ml}$
Volume of $\ce{NaOH}$ added to flask: $\pu{23.81 ml}$

Attempt 1 at finding molarity:
Moles of $\ce{NaOH}$ added to flask: $\pu{0.02381 L} \cdot \pu{0.1159 M} = \pu{0.0027596 mol}$ $\ce{NaOH}$

Amount of of $\ce{H2SO4}$: $0.0027596/2 = \pu{0.0013798 mol}$ $\ce{H2SO4}$ (The 2 came from the net ionic equation above)
Molarity of diluted $\ce{H2SO4}$ (solution 2): $\pu{0.0013798 mol}/ \pu{0.025 L}= \pu{0.054172 M}$
(I may be using the wrong volume, is it possible that I have to add the $\pu{25 ml}$ to the $\pu{23.81 ml}$ and divide by $\pu{0.04881 L}$?)

\begin{align}
C_1V_1 &= C_2V_2\\
C_1&=?\\
V_1&= \pu{0.01 L}\\
C_2&= \pu{0.054172 M}\\
V_2&=\pu{0.1 L}\\
\text{Therefore:}\\
C_1&=(\pu{0.054172 M})\cdot(\pu{0.1 L})/(\pu{0.01 L})\\
C_1&=\pu{0.54172 M}\\
\end{align}
Molarity of original/stock $\ce{H2SO4}$.


texts: How to optimise battery usage on modern electronics?

texts:
What is the best way to use an external power bank with a modern smart phone or similar device if the goal is to get as much usage out of the combination?

Premises:

The devices has a battery of 2 Ah and the power bank's capacity is 10 Ah
As I understand it, a rule of thumb is that the thermal efficiency η when charging a battery is about 50 %. That is, charging the power bank from (1) requires 20 Ah.

With 1 and 2 in mind, the power bank could charge the phone from 0 to 100 % 2.5 times.

Therefore, my question is: wouldn't it be better to keep the power bank attached to the phone all the time to keep the phone at 100 % as long as possible rather than using it to charge the phone when the battery is half empty or so? My idea is that keeping the power bank attached all the time would make η ≈ 100 % since the phone's battery would just "pass by" the current from the power bank. Am I right?


texts: Are there proteins with permanently bound magnesium?

texts: Do you know something about the existence of a magnesium containing protein/enzyme in which magnesium is coordinated in the structure and the structure is stable? (like iron in haemoglobin or zinc in zinc fingers)


texts: How to check percentage yields in a given reaction?

texts:
For a general reaction , if it is asked to predict and not given by theoretically, how would we determine the percentage yield of the products based on their mechanism , stability , path taken for the reaction etc. ?
For example , where my main problem lies is  :

According to Solomon and Frhyle it is said that chlorine is highly unselective. But in a problem I was asked percentage yields of the two products:

So how do I go about determining the percentage yields in this reaction ?


texts: What can I do if I don't get a phase separation between my organic and water phases?

texts:
Solvent extraction in a separation funnel is a very common method in preparative organic chemistry. But sometimes you don't get a nice phase separation between the organic and the water phase.

What are the possible causes that can prevent the formation of two distinct phases, and how can you force a phase separation when you encounter such situations?


texts: Competing half reactions in electrolysis of aqueous solution of sodium hydroxide

texts:
If you run a direct current using pure nickel electrodes through a solution of NaOH in distilled water, you will separate the water into hydrogen and oxygen.

Are there any other reactions that could possibly take place that would release anything other than hydrogen and oxygen?


texts:
The given compound is: $\ce{CH3-CH2-CH2-CH(CH3)-CH(CH2CH3)-CH2-CH2-CH3}$

The IUPAC name I came up with was 4-ethyl-5-methyloctane but the given answer states 5-ethyl-4-methyloctane.

Are both acceptable? Is there any rule I'm missing out on? I went through the rules but couldn't find the appropriate rule.


texts: Why is triatomic hydrogen relatively short-lasting?

texts:
The first chapter of Fleming's "Molecular  Orbitals and Organic Interactions," describes the formation of triatomic hydrogen. In summary, the sigma MO of diatomic hydrogen interacts in phase with the third hydrogen's AO. In consequence, a new bonding and antibonding MO are formed. The antibonding MO of diatomic hydrogen does not interact due to antisymmetry.

Since two electrons will fill the bonding MO and one will fill the antibonding MO, there is a overall bonding interaction. This raises my question as to why triatomic hydrogen is relatively short-lived,  a duration of one millionth of a second prior to decomposition.


texts: Why are the total energies of transition states so commonly corrected for zero-point vibrational energy?

texts:
So often I see total energies of transition states corrected for zero-point vibrational energy which always confuses me.  Zero point energy is the lowest energy that a ground state minimum energy configuration can have at 0K in a vacuum.  Transition states are indeed not minima, can never be isolated, have one imaginary mode of vibration, etc.

So why do people constantly factor in zero-point vibrational energy to the total energy for a transition state?  Obviously this is done to have 'comparable' minima and TS energetics (if you are applying ZPE to the minima) but is this even physical?  If zero-point correcting the TS, should the zero-point energy of the imaginary mode be included in the summation or excluded (or should both quantities be provided)?


texts:
How to determine whether the face of the attached alkene is re or si?
If assigning priorities in regard to the left C atom it is re, but for the right C atom it is si. How is it actually determined?


texts: Why do we neglect the zero point energy in statistical mechanics?

texts:
Quantisation associated with translational modes can be modelled like a particle in a box (PiB).

$$E_n = \frac{n^2h^2}{8mL^2} \qquad n \in \mathbb{Z} \, | \, n \ge 1$$

By the equation above, the zero point energy associated with a PiB is $E_1 = \frac{h^2}{8mL^2}$. However, in my statistical mechanics lectures, we set this to zero by modifying the equation as below:

$$E_n = \frac{(n^2-1)h^2}{8mL^2}$$

Atkins does this too in Physical Chemistry, claiming to do so "for reasons that will soon become clear". But, alas, I'm still not sure why this is done.

Could somebody enlighten me?


texts: How to find the volume of oxygen release by the decomposition if potassium chlorate?

texts:
In the reaction:
     $$\ce {2KClO3 -> 2KCl + 3O2}$$
What is the volume of oxygen released under NTP conditions when $36.75~\mathrm{g}$ of $\ce {KClO3}$ is heated?

I tried to find the answer this way:

$2~\mathrm{mol}$ $\ce{KClO3}$ form $3~\mathrm{mol}$ $\ce{O2}$
$0.3~\mathrm{mol}$ $\ce{KClO3}$ form $0.45~\mathrm{mol}$ $\ce {O2}$, i.e. $36.75~\mathrm{g}~\ce{KClO3} = 0.3~\mathrm{mol}~\ce{KClO3}$

I don't know how to convert moles into litre. Can we convert mass directly to volume in $\mathrm{L}$. I read somewhere that $1~\mathrm{L} = 1~\mathrm{kg}$.


texts: What will be the product of this reaction?

texts: We have an alpha beta unsaturated ether, along with a keto group in the same compound, which is being treated with a grignard reagent shown (assume the grignard reagent is in excess). Will it only attack the carbonyl group, or are things different here?


texts: René alloys are nickel-based super alloys (René 41, René 88, René N5 etc. etc.). But how did it get the name René? Is it an acronym or contraction of other terms? It was created by Earl Ross and the General Electric Materials Science group, so it doesn't seem to be the name of the discoverer.


texts: Computing initial reaction speed given reaction constant

texts:
Problem: $\ce{N2O}$ falls apart in oxygen gas and nitrogen gas according to a first order reaction rate. If you know that the rate constant is $0.38\ \mathrm{s^{-1}}$ at $760\ \mathrm{^\circ C}$, compute then the initial rate for the decomposition of $3.00\ \mathrm{g}$ $\ce{N2O}$ in a barrel of $5.0\ \mathrm{L}$. When the initial concentration doubles, what happens with the rate?

Attempt at solution: I set up the reaction as $$\ce{2 N2O -> O2 + 2 N2}$$ The molar mass of $\ce{N2O}$ is $44.019\ \mathrm{mol/g}$, and since we got $3.00\ \mathrm{g}$, this is $132.057\ \mathrm{mol}$. Then I computed $[\ce{N2O}] = 27.01\ \mathrm{M}$ since we had to divide by $5$ because the barrel has a volume of $5.0\ \mathrm{L}$. Then we have $$v = k [\ce{N2O}] = 10.26\ \mathrm{M/s}$$ But I’m not sure if this is the correct approach. Any help please?


texts:
My friend spilt a "level 4 carcinogen" on their lap.  What is it and how dangerous is it?

They had washed if off after.


texts:
I'm working on ceramic glaze chemistry. One ingredient I don't have, but want to substitute is ulexite:

$$\ce{NaCaB5O6(OH)6.5H2O}$$

I  have borax, calcium borate, and calcium silicate:

$$\ce{NaB4O7 . 10H2O, Ca3(BO3)2, CaSiO3}$$

Since the hydroxides and waters will burn off at firing temperature, it is safe to ignore them. I have already worked out that I can use a mix of the three to supply the needed mount of calcium, boron, and sodium, but I am uncertain of the silicate ions I would be introducing to the mix. I don't know how silicate decomposes at 2200 degrees Fahrenheit. This is important because if it does decompose into silica, it will throw off the balance of silica in the glaze. At such temperatures, iron oxide decomposes to $\ce{FeO}$, so it could make sense that this is possible, but I have no evidence. There isn't much about the decomposition of silicate online, any help?


texts: This is a legitamate question.  If one atom wants to lose an electron and another wants to gain an electron why don't they just transfer the electrons and just part ways?


texts:
Are there any solids that undergo diffusion?

Introduction:

In school, my teacher is only talking about diffusion happening in liquids and I though that it may be able to happen to solids also.

Though I did think about how the concentration of the molecules in a solid was too concentrated for the molecules to pass through a cell membrane. What I am mainly wondering and would answer my question, is there a way that the molecules of a solid would break up into less concentration, in which they can undergo the process of diffusion.


texts: Why does increasing the concentration of oxidizing agent decrease the E° in a galvanic cell?

texts:
In a galvanic cell, when we add ions of the oxidation agent (in this example, Zn2+) to the anode solution, it decreases the cell potential.

However, if the Zn2+ ions aren't involved in the redox reaction, then why does the extra concentration affect the cell potential? I know the Le-Chatelier and Nerst equation arguments, but I wanted a conceptual explanation.

I hypothesized that the higher Zn2+ concentration decreased the anode's affinity for solubilization, therefore decreasing the anode's desire to release electrons, thereby decreasing the cell potential, as less electrons will flow per unit of time.


texts: the particle in 1-D box momentum and total energy(P.E + K.E (x))

texts: Employing the particle in 1-D box can momentum and total energy(P.E + K.E (x)) can be measured simultaneously?


texts: Is optical activity of a given compound a statistical picture?

texts: When optical activity is taught it is done in terms of single molecules. But when it is actually measured it is done on a large collection of such molecules. So, how does the asymmetry manifest itself as the rotation of plane polarised light. Is it a collective effect of all the molecules put together in a sample or does each molecule play a role?


texts:
I searched for this onsite already, and also found the following answer on Quora:

In aqueous environment, iron(III) is bound by water molecules and exists as $\ce{[Fe(H2O)6]^3+}$. Due to strong interaction between Fe(III) and some of the aqua ligands, the complex can dissociate into $\ce{[Fe(OH)_n(H2O)6^{n-}]3^{n-}}$ and $\ce{H+}$. Carbonate is a base, so it will capture proton and further facilitate the formation of hydroxyl complexes so much that it will produce $\ce{H2CO3}$ and $\ce{Fe(OH)3}$, the former eventually decomposes into water and $\ce{CO2}$. Therefore, iron(III) carbonate cannot exist in water.
In solid state, most of iron(III) compounds are hygroscopic, which means that they have strong affinity for moisture. And of course, when water gets involved, the above processes start happening, which eventually decomposes iron(III) carbonate, if it could ever be formed as solid.
Therefore, the compound itself is not stable in solutions or in solid states.

Is this correct?  What happens in the following equation then:
$$\ce{2 FeCl3(aq) + 3 Na2CO3(aq) -> Fe2(CO3)3 + 6 NaCl}$$
Will we get different end products?  What will be solid?  Hydroxides or oxides?  Will there be carbon dioxide evolved?  Are any of the products going to be hydrates?


texts:
I have 20mL gas samples and I need to determine the [CO2] in ppm. I have a Li-Cor 6200 with a closed loop, so essentially I will inject a volume of gas into the loop and the change in the output is how to determine the concentration of CO2.

To calibrate I'm using a standard of gas that is 5020ppm CO2, and injecting volumes of 50, 75, & 100 uL then recording the change in [CO2] in the closed loop.
After calibration I will inject 50uL of sample and record the change of CO2 in the closed loop.

But how do I set up the conversion? It is spring break and I am having trouble finding help around campus.

This is what I have done.

Taking the average change in CO2 output from 3 different volumes of standard injected, the output changes 0.114 per uL of standard gas injected (5020ppm CO2). So, (5020/.114)=44035.0877. Then, I just multiply the change in output per uL of sample injected by 44035.0877 to get the CO2 ppm of the sample.
My first sample I inject 50uL and the output changes by 20.2, so I divide to get the change per uL; (20.2/50=0.404). Then multiply, (0.404 * 44035.0877 = 17790.18 ppm CO2)

Is it really this simple, or is my thinking to simple?

Thanks. This is my first post, I hope I have followed the rules.


texts: Are these reaction equations for the formation of the brown ring complex correct?

texts:
\begin{align}
\ce{NO3- + 3Fe^2+ + 4H+ &-> NO + 3Fe^3+ + 2H2O}\tag{1}\\
\ce{[Fe(H2O)6]^2+ + NO &-> \underset{\text{(brown)}}{[Fe(H2O)5(NO)]^2+} + H2O}\tag{2}
\end{align}

The above are the reactions given in my book [1] for the qualitative analysis of nitrate ion (formation of the brown ring complex). I think that the reactions above are incorrect. The first one shows formation of $\ce{Fe^3+}$, which should be attacked by excess of $\ce{H2O}$ to give ferrum(III) hexaaquasulphate, not ferrum(II) hexaaquasulphate. Now that should be attacked by $\ce{NO}$ as a ligand and give $\ce{[Fe(H2O)6NO]SO4}$, where the oxidation number of $\ce{Fe}$ is being $3+$.

Here the reactions show that the $\ce{Fe}$ already present gives $\ce{[Fe(H2O)6]^2+}$ and then $\ce{NO}$ acts as a neutral ligand to form the complex. But by the reactions shown in the book, even after formation of the brown ring complex $\ce{Fe^3+}$ is still present in the solution, which according to me shouldn't be because if $\ce{Fe^3+}$ still remains in the solution then water should also have attacked it as a ligand to give $\ce{[Fe(H2O)6NO]SO4}$.

I need some clarity on this. Are the reactions given in the book correct?

Edit: After reading the answers, I do get that the hexaaqua iron(II) will be formed and the $\ce{Fe^3+}$ will be attacked by water to give $\ce{[Fe(H_2O)_6]^3+}$ but why won't $\ce{NO}$ take electrons from the oxidation of iron ($\ce{Fe^2+ -> Fe^3+ + e- }$), make $\ce{NO-}$ and attack the above and substitute one water molecule and give more of the brown ring complex?

NCERT. Chemistry: Textbook for class XII; National Council of Educational Research and Training: New Delhi, 2007. ISBN 978-81-7450-648-1.


texts: Stereochemistry of epoxide hydrolysis under acidic conditions

texts: The epoxide on the top of the picture, in aqueous acid hydrolyzes to the compound below. What is the mechanism of this reaction? Standard epoxide opening in acidic conditions would happen at the more substituted end, therefore the secondary -OH group would end up below the plane of the paper, and the tertiary center would racemize to a significant extent. What is happening here?


texts:
When I add dish soap to a sponge it is able to foam up. But if I leave the sponge alone for an hour, it doesn't foam up, not even if it is wetted.

Why? The sponge should still contain dish soap an hour later.


texts: Is silicon-oxygen bond length non-uniform in quartz glass?

texts:
In many pictures depicting the molecular structure of quartz glass(In fact, almost every picture that represents amorphous state of any solid that I have seen), the bond lengths are non-uniform (I do not refer to bond angles).

Are the bond lengths really non uniform?

If yes, why is it so?

Because, as far as my knowledge goes, the bond length between the nuclei of two specific atoms with a particular bond order should be uniform at a given constant temperature and external conditions such as pressure etc.( at least in a particular compound it makes). So, the silicon-oxygen bond length ( Not bond angle) in quartz glass should be uniform, shouldn't it? Please correct me if I'm wrong anywhere.

Thanks for any answer in advance!


texts: Does everything exist as a gas at p = 0?

texts:
Attached is a phase diagram for carbon dioxide. At $p = 0$, it appears that the substance will exist as a gas regardless of temperature.
My questions are:

For any liquid at a fixed temperature, is it possible to vaporize it completely by simply reducing its pressure isothermally?

For any solid at a fixed temperature, is it possible to sublime it completely by simply reducing its pressure isothermally?

What if the solid is at $T \approx0\ \mathrm K$?


texts: Why does oxidation of the electrode take place in a solution?

texts:
What makes the electrode atoms start to ionize? Perhaps because of the solutes in the solvent?

So probably if you place it in distilled water it will not ionize, right?

Follow up question: If the solutes in the water are the reason of ionizing the electrode, Do they rip off the electrons from the electrodes atoms? (Most of websites illustrate that both electrons (on the electrode) and ions (in solution) contribute to the voltage of the electrode).

So why do I use electrode potentials if I have lets say a bowl made purely of $\ce{Zn}$ atoms and it contains lets say Copper ions. Even though I only have positive ions of copper. Does the copper ions generate the same voltage by their own without electrons?


texts: Can hydrogen on platinum reduce carboxylic acids and esters?

texts:
Can $\ce{H2/Pt}$ reduce carboxylic acids and esters?

I am confused about the reducing nature of hydrogen in presence of platinum. In some books, it reduces carboxylic acid and ester while in others, not. I have checked Finar and Boyd books for it.


texts: Can benzene ring be the part of a acyl group

texts: Can benzene ring attached to c=o i.e carbonyl group be considered as a acyl group?


texts: Is ZnO still diamagnetic after you dope it with aluminium?

texts:
There are no unpaired electrons in $\ce{ZnO}$, making $\ce{ZnO}$ diamagnetic.

Aluminium has an unpaired electron, which would mean it is paramagnetic.

Will $\ce{ZnO}$ become paramagnetic after it is doped with aluminium?


texts: Question regarding $Z$ (Compressibility factor)

texts:
Oh! This problem has been bugging me for a long time. According to Wikipedia, the Compressibility factor $Z$ is defined as the ratio of the volume occupied by a real gas to the volume occupied by an ideal gas at the same temperature and pressure.
$$Z=\frac{V_{real}}{V_{ideal}} \text{              ........(1)} $$
Now the Ideal Gas Equation is
$$P_{ideal}V_{ideal}=nRT   \text{        ....(2)}$$
Now from here we can substitute the value of $V_{ideal}$ into the above expression $(1 )$ to get
$Z=\frac{PV_m}{RT}$
Where $V_m$ is the molar volume of the gas and $P$ is the value of $P_{ideal}$ that was in the ideal gas equation $(2)$.
OK, So far so good!
Deriving the compressibility factor value from the van der Waals' gas equation:
We know for real gases the pressure exerted by them is always less than the pressure exerted by an ideal gas so we correct the pressure by the term $a\frac{n^{2}}{V^{2}}$, we get
$$P_{ideal}=P_{real}+a\frac{n^{2}}{V^{2}}$$
And the volume occupied by the gas molecules can be written as
$$V_{ideal}=V_{real}−nb$$
On substituting the above values of $P_{ideal}$ and $V_{ideal}$ in the ideal gas equation, we get our van der Waals' Gas Equation
$$(P+a\frac{n^{2}}{V^{2}})(V−nb)=nRT$$
Please note that in the above equation $P$ is $P_{real}$ and not $P_{ideal}$. Now I'm going a step further to calculate the value of Z from this equation by shifting the terms and I got this
$$Z=\frac{PV_m}{RT}=\frac{V_m}{V_m−b}−\frac{a}{RTV_m}$$
Now here's the problem that I'm facing: In the above expression the value of $P$ is not the $P_{ideal}$ but it is the value of $P_{real}$ that we had in the van der Waals' gas equation.
Doesn't that contradict the whole definition of Compressibility factor that we had learned in the first place? How this expression for $Z$ can be correct?
Thanks for reading.


texts: Which is the most reactive metal: Caesium or Francium?

texts:
I searched on Wikipedia for reactivity series but it showed me Caesium as the most reactive metal. I know and have studied that reactivity increases as we go down the first group. Then shouldn’t it be Francium more reactive than Caesium than the other way around.

PS: I study in class 10 so please explain in that way only.


texts: Why does dimethyl dichlorosilane undergo hydrolysis to form siloxane polymers, but its carbon analog does not?

texts:
Dimethyl dichlorosilane will undergo hydrolysis to form siloxane polymers. But why would its carbon analog dimethyl dichlorocarbon not be able to undergo a similar hydrolysis reaction to form polymers?

My guess is that $\ce{Si-Cl}$ bond being much weaker than $\ce{C-Cl}$ bond would be easier to break and undergo hydrolysis, and that the geminal diol is unstable, hence it is less likely to form.

I'm unsure of my answer though. Could anyone please explain and elaborate?


texts: Does SN2 favor strong nucleophile and SN1 favor weak nucleophile? Does E2 favor a strong base, and E1 favor a weak base?

texts:
I understand if you have a protic solvent, it will stabilize the strong base (to form weak acid) or the strong nucleophile. The protons would react with them. To have an SN2 or an E2, so you need an aprotic solvent. I also know that in general, a tertiary substrate will favor SN1/E1 reactions, because a tertiary carbocation is more stable. A primary substrate will SN2/E2 reactions, because of less stereo-hinderance.

But why does SN2 favor strong nucleophile and SN1 favor weak nucleophile from the first place? Besides, does E2 favor a strong base, and E1 favor a weak base? I also don't get the reason.


texts: Why does electrolysis of aqueous concentrated sodium bromide produce bromine at the anode?

texts:
It is often stated that electrolysis of any aqueous concentrated halogen compound will produce the halogen at the anode, despite it having a more postitive standard electrode potential than the oxidation of hydroxide, while when it is dilute oxygen will be produced, but what is the reason for this?

Why does the principle of concentrated solutions during electrolysis only apply for halogens and not any other element. For example, why isn’t sodium produced at the cathode when concentrated sodium chloride is electrolysed?


texts:
I am trying to find out if there are any non-toxic organic bases that could be given orally on a non-empty stomach to treat acidosis. From my research, histidine and diluted choline hydroxide were the best candidates. Some phosphazenes, including polyphosphazenes, could make the cut, but I don't know which ones exactly.

Wikipedia [1] lists the following compounds as organic bases: pyridine, alkanamines (such as methylamine), imidazole, benzimidazole, histidine, guanidine, phosphazene bases, hydroxides of quaternary ammonium cations or some other organic cations.

The LDLO of guanidine given orally to rabbits is 500 mg/kg [2]. The LD50 of imidazole (rabbits, oral) is 950 mg/kg. Pyridine seems to be in the same range [3]. Benzimidazoles are also toxic.

Histidine, which is considered the most toxic amino acid, can be therapeutic in doses of up to 4.5 g/d, but is toxic in the range 24–64 [4].

The last ones from this list are choline hydroxide and phosphazenes. The UTL of choline is 3.5 g/d; in the 10-16 g/d range it causes fishy smell so it probably overloads us with TMA, which is a carcinogen. Polyphosphazenes are being studied for drug delivery; apparently their metabolism generates low-toxicity products such as urea and phosphates. [5].


texts: Why are lactate and lactic acid used synonymously in biochemistry?

texts:
In science there's always a misuse of the two terms. I know that lactate is the conjugate base of lactic acid.

Why are they used like is the same thing? For exemple: in lactic acid bacteria (LAB) fermentation it's often said that anaerobic glycolysis produces lactic acid, but if you actually look at the reaction it produces lactate.

Is this relevant? Because lactate is a negative compound while lactic acid is a neutral one.


texts: Does light absorption result in a momentarily weaker bond?

texts:
I may have just misunderstood the topic, but light absorption by a molecule is a result of a promotion of an electron into an empty antibonding orbital; hence, does that mean that the strength of the bond is momentarily weakened by absorption of light? What processes account for the actual radiation part (release of heat) associated with the absorption of light?

http://www.chemguide.co.uk/analysis/uvvisible/bonding.html


texts: Nernst equations for the reduction of sulfate(IV) and nitrate(V) anions

texts:
Write a Nernst equation $(\pu{25 °C})$ for system:
$$\ce{SO3^2- + 3 H2O + 6 e- -> S^2- + 6 OH-}\tag{R1}$$
and system:
$$\ce{NO3- + 3 H+ + 2 e- -> HNO2 + H2O}\tag{R2}$$

I am not really sure if these are correct:
$$
\begin{align}
E_1 &= E^\circ(\ce{SO3^2-}/\ce{S^2-}) - \frac{0.059}{6}\log\frac{[\ce{S^2-}]\cdot \left(\frac{10^{-14}}{[\ce{OH-}]}\right)^6}{[\ce{SO3^2-}]}\tag{1}\\
E_2 &= E^\circ(\ce{NO3^-}/\ce{HNO2}) - \frac{0.059}{2}\log\frac{[\ce{HNO2}]}{[\ce{NO3^-}]\cdot[\ce{H+}]^3}\tag{2}
\end{align}
$$
I don't know how to deal with the $\ce{OH-}$ in the equation. Am I supposed to consider $\ce{OH-}$ at all? Or should I count with it in form of $[\ce{H+}]$—in that case, can I use $K_\mathrm{w} = [\ce{H+}]\cdot[\ce{OH-}]$ (as written above in my solving attempt)?


texts: Hybridization - Mixing one atomic s orbital with 2p orbitals

texts: Explain why three ${sp^2}$ hybrid orbitals result when one s atomic orbital is blended with two p atomic orbitals.


texts: Orbital and state correlation diagram for ring-closure of pentadienyl to a cyclic allyl

texts:
This is an exam question. I am to construct the orbital and state correlation diagram for one of the reaction below (disrotation or conratation). Also, I should explain whether the reaction is thermally or photochemically allowed.

I know the procedure to these kinds of problems:

Draw (Hückel) π orbitals of the reactant
Draw relevant orbitals of the product. Here: π and newly formed σ orbitals
Identify the symmetry element that is preserved through the reaction (common for reactant and product)
Assign symmetry labels to orbitals
Correlate orbitals of same symmetry

I know what the molecular orbitals of the reactant looks like, but I am unsure about those of the product. Here's what I have

Using the vertical reflection plane perpendicular the screen, I get the MO's of both reactant and product (in the order from bottom to top) to have the following symmetries: S, A, S, A, S. However, the orbital correlation diagram will be very boring if this is correct, and the reaction will be allowed both thermally and photochemically.

So are the product orbitals correct? I just assumed that an in-phase and out-of-phase combination of the π orbitals on C1 and C5 lead to the desired σ orbitals. Or perhaps my ordering is incorrect?

Final orbital correlation diagram:

Concerning the state correlation diagram, I look at the electron configurations of the states of interest, which I take to be $S_0$, $S_1$, and $S_2$. I find the symmetry of each state by multiplying the symmetry of each electron in every MO. However, should I just draw straight lines between each state? The corresponding states are of the same symmetry, so no avoided crossings occur. I don't see whether the reaction is thermally or photochemically allowed from the state correlation diagram. Or did I do something wrong?

Electron configurations:

Non-finished state correlation diagram:


texts: Analysis of a mixture of carbonate salts

texts:
We've got a mixture of carbonate salts. It's a buffer, used in fish tanks. How might we go about identifying the components and their concentrations?

I suspect it'd be hard to separate some of this. Is this correct? If so, why?


texts: Hammett plot shape: dependent on substituent or mechanism?

texts:
So, we were shown a Hammett plot that, on the left was linear, but on the right was concave up.  How would I explain the shape of the Hammett plot?  Does it depend on whether the substituent is an EDG or an EWG?  Is it based on the mechanism of the reaction/rds?

Also, a hypothetical question was proposed to us regarding the generation of Hammett plots: how would you generate a Hammet plot for a ring with multiple substituents? The sigma value, sigma+ value, etc. are based on a single substituent, right? So, if you were to have multiple substituents, then what would you do? Would the plot be 3D with two axes for sigma or would you just compare the groups and see which one has the larger effect?


texts: Relative O-O bond lengths in O2X2 molecules (X = H, F, Cl)

texts:
I am facing problem in the following question:

  What is the order of bond length of $\ce{O-O}$ in the following
  compounds:

  $\ce{H2O2, O2F2, O2Cl2}$

In my view since fluorine is more electronegative than oxygen it will attract the bonded electrons towards itself resulting in low bond length in case of $\ce{O2F2}$ than in case of $\ce{O2Cl2}$. However if the same concept is applied to $\ce{H2O2}$ it should have the greatest $\ce{O-O}$ bond length however my book states it otherwise.


texts: How would I determine the relative acidity of substances?

texts:
Which of the following salt will produce a neutral solution (If any)? A) $\ce{KI}$ (Potassium Iodine) or B) $\ce{SrS}$ (Strontium Sulfur)

I tried to solve this problem by using the "Relative Strengths of Brønsted-Lowry Acids and Base in aq solution at room temp table". From what I know each of those two substance will dissociate into ions. Having the ions $\ce{K^+, I^-,Sr^{2+}, S^{2-}}$

Since K does not hydrolyze and I is a product of HI which is a strong acid it won't hydrolyze either. I also know that the only cations that hydrolyze are Al,Fe and Cr hence Sr will not hydrolyze. However how do I know weather S will hydrolyze? The other question I had difficulties was "Order the following from most acidic to least. SO3, CO3 and CO2".


texts: Why Fe(OH)2 and some precipitates do not dissolve in excess ammonia?

texts: I understand that Cu(OH)2 can dissolve in excess ammonia because ligand exchange reaction occurs. But why ligand exchange reaction does not occur for Fe(OH)2?


texts: Reaction of phoshorus pentasulfide with ethers

texts:
Why does phosphorous pentasulfide on reaction with ethers give dialkyl sulfides?

I searched for this reaction in my organic chemistry reference books and the internet but couldn't find it.

What is the mechanism of the reaction? I expected the oxygen as nucleophile to attack P atom but am not sure of the steps that follow.


texts: Explaining the result of experiment---Aluminum foil heated in boiling KMnO4 solution

texts:
I've recently been thinking back to an impromptu "experiment" I performed almost exactly 3 years ago. The setup was as follows:

  A concentrated solution of KMnO$_4$ was produced by dissolving 2 grams of
  Condy's crystals in 250 ml of water. This was subsequently poured into
  an Erlenmyer flask containing a strip of aluminum foil, and the entire
  system was then heated at high on a stove until the water came to a boil. As the water evaporated, the solution lost the intensity of its violet
  hue, turning a light pink-violet instead. The stove was then turned off, and the aluminum strip was removed, having turned a golden color.

My questions are two:

What, precisely, was the chemical reaction(s) that occurred?
How much of a risk did the steam from the boiling solution pose in
   terms of potential acute manganese inhalation toxicity---and what are the potential long-term effects? Unfortunately, this
   experiment was performed on an ordinary kitchen stove and not in a
   fume hood (I'm kicking myself to this day).

My guess as to the former is that MnO$_2$ was produced, hence the observed color changes of the solution and foil. I am not sure whether this occurred via heat decomposition of the MNO$_4^-$ (which seems to occur at temperatures of >240$^\circ$C, and thus should not have been able to take place in boiling water) or oxidization of the aluminum (having somehow penetrated the surface layer of aluminum oxide). As for the latter, welp.

Thanks in advance!


texts:
I recently learned that aqua regia can dissolve less reactive or noble metals like gold. Aqua regia is a mixture of $\ce{HCl}$ and $\ce{HNO3}$, but separately, neither of these acids dissolve gold.

So why don't concentrated $\ce{HCl}$ or $\ce{HNO3}$ dissolve gold, though combined in aqua regia they can?


texts: Is UV-Vis absorption polarization dependent ? Why?

texts:
Consider molecule of interest be dissolved in a solvent (and this molecule has absorption in the visible region). We are using a broadband visible light source say tungsten lamp.  This light passed through a polarizer and then split into two beams, one passing through sample cell, and other through reference cell having solvent.

Would there be difference in the electronic absorption spectra when measured keeping the polarizer parallel or perpendicular with respect to the incident polarization ?  Also, no external electric field is present and we have randomly oriented molecules.

(Consider the transmission of optics and detector are corrected for this polarization difference)


texts: Reactivity of meta- and para-bromo-nitrobenzene towards nucleophilic substitution

texts:
Among 1-bromo-3-nitrobenzene and 1-bromo-4-nitrobenzene, which would be more reactive towards nucleophilic substitution?

From what I can infer, the answer should have been 1-bromo-3-nitrobenzene. Nitro is a −M/−R group, so it would create regions of high positive charge in the ortho and para positions with respect to the nitro group.

Now in 1-bromo-4-nitrobenzene, Br is in the para position with respect to the nitro group. Hence the positive charge would be created only in the ortho position, as the para position is blocked. On the other hand, in 1-bromo-3-nitrobenzene, there would be regions of positive charge in the both the ortho and para positions wrt to the nitro group.

But the answer given in my book is 1-bromo-4-nitrobenzene. Am I missing something here?


texts: DIY spectrometers limits as a water quality sensor

texts:
What pathogens or harmful stuff IN WATER can you detect with these homemade video spectrometers (webcam) + UV light?

https://www.youtube.com/watch?v=IA5BTD-aelo

I'm trying to do a cheap spectral analysis to analyze water quality, something electronic, so I can do continues monitoring remotely.


texts: Is palladium on carbon acting as an oxidising or reducing agent?

texts:
In the conversion of piperidine to pyridine, palladium on carbon (Pd/C) is used. But it is reducing agent.

Clear the confusion, please.


texts: How is 2D spectroscopy able to show quantum coherent transport through networks?

texts: For wave-like (quantum coherent) energy transfer in networks (eg. propagation of excitation in photosynthetic protein complexes of algae or FMO complex in plants) 2D electronic (photon echo?) spectroscopy is used (eg. in this article). I have read an article (unfortunately I can't cite it here) about how it works, but I didn't understand it. I know that the off-diagonal peaks in the spectrum mean some kind of coherence in the network but I don't know why. I also don't know what kind of coherence it means. What are meant by electronic eigenstates? What are the so called 'quantum beatings'? It would be very much appreciated if somebody would be so kind as to make these thing clear.


texts: Stereoisomers of compounds named tribromocyclobutane

texts:
Here is the link to the page in which I don't understand the answer to the last question (Question 13). The question states:

  Draw all of the constitutional isomers and stereoisomers of compounds named
  tribromocyclobutane (all structures must contain a cyclobutane ring).

The following image exists as a part of the answer.

But why is the following image not part of the answer?

Are the above two images not diastereomers (hence stereoisomers)?


texts: Return time after perturbation in a chemostat

texts:
I'm wondering how I can derive the return time of the culture cell concentration back to a steady-state in a chemostat after a small perturbation of the bulk culture cell concentration.

More specific, I have the following situation. I have a very small chemostat with a working volume of about 200 µL. Influx is achieved via a very small needle which drops fluid in the reactor. At this small scale, the influx cannot be seen as a continuous stream, but rather as points in time when the next drop is added. Consequently, when a new droplet is added, the culture concentration in he chemostat drops slightly, which is seen as a perturbation from the steady-state situation. Now, I want to determine how long it takes for the system to recover and again arrive at the steady-state situation.

The chemostat is assumed to be perfectly mixed, and the working volume of the reactor is constant over time (efflux is removed by overflow at a certain level in the reactor).

Any answers or suggestions how to calculate this are very welcome!


texts: Zwitterion (amino acid) equilibrium and the equilibrium constant

texts:
I just had my biology test paper back from my teacher, and my teacher insisted that when functioning as a buffer in an alkaline solution, the amino acid deprotonates by the ammonium group instead of the carboxyl group, because amino acids in solution are mostly zwitterionic. I thought zwitterions only consist a small portion of the mixture, but checking Wikipedia only further confirms what my teacher said.

In an attempt to find mathematical proof, I tried to derive the equilibrium constant between zwitterionic and completely neutral forms of amino acids, with the assumption that the solution is pure and only constitutes the said acid(and its zwitterionic isomer) and water. This was my working:

Using $K_\mathrm{a}$ for carboxyl group and $K_\mathrm{b}$ for amine group.
$$\ce{H2N-CHR-COOH <=> H3N+ -CHR-COO-}$$
\begin{align}
[\ce{H2N-CHR-COOH}]   &=  [\ce{H2N\bond{-}}] = [\ce{-COOH}]\\
[\ce{H3N+ -CHR-COO-}] &=  [\ce{H3N+\bond{-}}] = [\ce{-COO^-}]
\end{align}

\begin{align}
K_c &= \frac{[\ce{H3N+ -CHR-COO-}]}{[\ce{H2N-CHR-COOH}]}\\
    &=\sqrt{\frac{[\ce{H3N+-CHR-COO^-}][\ce{H3N+-CHR-COO^-}]}{[\ce{H2N-CHR-COOH}][\ce{H2N-CHR-COOH}]}}\\
    &=\sqrt{\frac{[\ce{H3N+\bond{-}}][\ce{-COO^-}]}{[\ce{H2N\bond{-}}] [\ce{-COOH}]}}\\
    &=\sqrt{\frac{[\ce{H3N+\bond{-}}]}{[\ce{H2N-}][\ce{H+}]} \times
      \frac{[\ce{-COO^-}][\ce{H+}]}{[\ce{-COOH}]}}\\
    &=\sqrt{\frac{[\ce{H3N+\bond{-}}][\ce{OH-}]}{[\ce{H2N\bond{-}}][\ce{H+}][\ce{OH-}]} \times \frac{[\ce{-COO^-}][\ce{H+}]}{[\ce{-COOH}]}}\\
&\text{(now assuming $[\ce{H2N\bond{-}}] = [\ce{H2O.H2N\bond{-}}]$)}\\
    &=\sqrt{\frac{[\ce{H3N+\bond{-}}][\ce{OH-}]}{[\ce{H2O.H2N\bond{-}}][\ce{H+}][\ce{OH-}]} \times \frac{[\ce{-COO^-}][\ce{H+}]}{[\ce{-COOH}]}}\\
    &=\sqrt{\frac{K_\mathrm{b}}{K_\mathrm{w}} \times K_\mathrm{a}}\\
    &=\sqrt{\frac{K_\mathrm{a} K_\mathrm{b}}{K_\mathrm{w}}}
\end{align}
With $K_\mathrm{w}$ being the denominator, it is easy to see that $K_c$ would be sufficiently large that nearly all amino acids in aqueous solution exists in the zwitterionic form, that is contrary to my initial belief; bringing in the $K_\mathrm{a}$ and $K_\mathrm{b}$ values further confirms that.

However, I am not content with just that. I'd like to ask:

What are the faults (calculation errors, false/inappropriate assumptions, etc) in my working, if any?
What is the main reaction mechanism that mediates this equilibrium? Is it an intramolecular transition or is it brought about by the solvent, or something else?
Can this be considered as a form of tautomerization? If so, is it prototropy? Hence, is the $K_c$ above the so-called tautomeric ratio?


texts: How to disarm and correctly dispose of tear gas spray?

texts:
I have a can of spray for self-protection which has expired way back in 2008. It hasn't been used at all, and it doesn't seem a good idea to just throw it away without disabling it somehow first. I'm looking for ways to disarm it with minimum risk to myself and others. Obviously, I can just spray it away, but I'd rather not if I can avoid it.

The active ingredient is 2-chlorobenzalmalononitrile.

It's not water-soluble, but I was thinking of some combination of cooking oil and alkaline agent (baking soda, for example) to neutralize it. I'm still doing research on it, and I won't be doing anything rash just yet :-)

Any particular advice how to neutralize this spray?

If jurisdiction is somehow important, assume European Union.


texts: Can protons be swapped in a chemical reaction?

texts: Can the protons of two elements be swapped in a chemical reaction?


texts:
Theoretically speaking,  beryllium and magnesium does not give flame test because their atoms are comparatively smaller and the valance electrons are strongly attached to the nucleus. Therefore their ionisation energies are high, so they need large amount of energy for the excitation of their valence electrons to higher energy level which is usually not available in the Bunsen flame. So they do not impart any colour to the flame.

Now, comparing the atomic radius of lithium and magnesium, both have nearly same atomic radius due to diagonal relationship.($\ce{152}$ pm and $\ce{160}$ pm respectively). Since both of them nearly have same atomic radius, why is lithium imparting flame coloration(crimson red) while magnesium is not? Both of the metals has to be supplied equal amount of energy to excite the electron which the burner is not able to supply and thus flame test should fail in this case but this is not happening.

I don't understand despite the reasoning for beryllium not giving flame coloration is quite correct, wikipedia claims beryllium  to give flame coloration(white).


texts: Are there any silicone like substances that cure far faster?

texts: I was wondering if there are any silicone like substances that cure far faster. Are there any substances that you can mix together to create a fast curing elastic like substance like silicone? Are there any substances of that same description that will cure under room temperature, or just by coming in contact with air? This substance would have to be able to cure In under a minute hopefully a minute the longest. Also by cure I just mean seal it can still be elastic or rubber like, preferably not a hard substance.


texts: Is there a material that turns from being electrically conductive to non-conductive irreversably upon exposure to some form of radiation?

texts: For my project I am looking for a material which can turn from being electrically conductive to nonconductive (has to be irreversible) upon exposure to electromagnetic radiation (say UV). I tried googling for my question but found no relevant answer. A short explanation or a link would be greatly appreciated.


texts: How to determine the Bravais lattice and atom basis vectors from a CIF file?

texts:
Say I have a CIF file describing some material in terms of its symmetry space group, lattice parameters and in-cell atom positions. A simple example might be,

data_global
_chemical_name 'Graphene'
_cell_length_a                 2.46
_cell_length_b                 2.46
_cell_length_c                 1
_cell_angle_alpha              90
_cell_angle_beta               90
_cell_angle_gamma              120
_symmetry_space_group_name_H-M 'P 3 m 1'
loop_
_atom_site_label
_atom_site_fract_x
_atom_site_fract_y
_atom_site_fract_z
C  0.00000   0.00000   0.00000
C  0.33333   0.66667   0.00000

I would like to extract from this Bravais lattice vectors and atom basis vectors. For this specific example, this might look like,

 2.456   0.0     0.0
-1.228   2.126   0.0
C
 0.0      0.0      0.0
 0.0      1.418    0.0

where the first two lines give the two lattice vectors (in some basis), while the next two give the positions of the atoms in the unit cell.

I have tried using Open Babel for this, converting from the CIF format to a VASP one.  This works well for the example above, but fails for a material such as tin sulfide (SnS), which has a structure similar to black phosphorus---four atoms in a unit cell, only two of which are explicitly listed in the CIF file.  The positions of the other two are implied by the symmetry group, and programs such as Mercury correctly visualize the structure based on the CIF file.  However, converting the CIF into VASP only gives you two of the four unit cell atoms.  I tried all other formats in Open Babel, with no success.

Is there a reliable way to convert a CIF file into a description in terms of a Bravais lattice plus atom basis vectors?


texts: Viability of proposed carbon-carbon bond-forming reaction

texts:
Here is my proposed synthetic pathway to make propanoic acid from bromoethane:

  $\ce{CH3-CH2Br ->[\ce{KCN(aq)}][\text{heat}] CH3-CH2-C#N}$
  $\ce{CH3-CH2-C#N ->[\ce{KOH(aq)}][\text{heat under reflux}] CH3-CH2-COOH + NH3\uparrow}$

I have some questions about my proposed pathway:

Is it viable at all?
If so, what might be the disadvantages compared to other carbon-carbon bond-forming reactions such as the Grignard reaction?
If it is viable, what is the estimated yield?
If it is viable, how can I improve the yield? Can I use silver ions to increase the yield of the first step?
If it is viable, how might I isolate the product?
If it is not viable, can I fix it? If so, how?


texts: I put some papers into a biscuit tin and put it over fire and baked it. Then I made a small hole at the top and saw yellowish smoke coming out. Any idea what the smoke could be?


texts:
$$\ce{IO3-(aq) + 5I-(aq) + 6H+(aq) -> 3I2(aq) + 3H2O(l)}$$
Why does the reaction between iodide and iodate ions have to occur in an acidic medium ($\ce{H+}$) to form the iodine? what do the $\ce{H+}$ ions react with?


texts: Stabillity of ethyl, iso propyl and vinyl free radicals

texts:
Well this might seem like a dumb question but I was just wondering if any other factor would apply here as well?

By simply looking at the number of hyperconjugative structures, I could easily tell that the isopropyl would be the most stable followed by ethyl and the vinyl radical at the last.
But for the vinyl, I didn't find applying hyperconjugation satisfactory.
Would we apply some other concept while comparing the vinyl radical with the other two?


texts: Why can't ligands with "locked structures" undergo chelation?

texts:
The following quote is from the book Concise Inorganic Chemistry by J.D. Lee (Adapted by Sudarsan Guha), from the chapter "Coordination Compounds", page 177:

  ...it must be noted that $\ce{NH2NH2}$ and $\ce{N(CH2CH2)3N}$ cannot act as chelating ligands due to the formation of a three membered ring and locked structure respectively.

But, as per the accepted answer to the question Are all complexes with a polydentate ligand examples of chelation?, when a ligand forms more than two bonds to the central atom, the result is a chelated complex. This is also inline with the IUPAC Gold Book's definition of Chelation:

  The formation or presence of bonds (or other attractive interactions) between two or more separate binding sites within the same ligand and a single central atom.

As per my understanding, it doesn't seem to exclude any ligands as mentioned in my textbook.

I can understand that since $\ce{NH2NH2}$ forms a three membered ring, there would be ring strain in the structure and hence the process of chelation is not energetically feasible compared to four membered (or higher) rings. I think this would be the same for all such ligands with donors adjacent to each other, as I have not encountered any such species so far.

However, I'm unable to understand why $\ce{N(CH2CH2)3N}$ (1,4-Diazabicyclo[2.2.2]octane) cannot undergo chelation.

From its molecular structure, I can imagine that the three ethylene groups act as springs to accommodate any ring strain while bonding with the central atom and so there must be no hinderance to undergo chelation. The following molecular structure is what I think might be if $\ce{N(CH2CH2)3N}$ undergoes chelation with cobalt:

I felt given the size of the cage it would be difficult to fit the metal atom inside it and hence thought that it might be off-centred as shown in the image above.

So, it would be helpful if you could clarify whether my reasoning for the inability of $\ce{NH2NH2}$ to chelate is correct or not and why is it not possible for $\ce{N(CH2CH2)3N}$ to undergo chelation? Further, it would be helpful is you could tell why is there a contradiction between the book's statement and IUPAC definition? Is the statement from the book incorrect (because IUPAC can't be incorrect)?


texts: What is wrong with my enthalpy calculations?

texts:
I need to calculate the enthalpy of combustion for butane using bond formation energies. Thus I first balance the equation:

$$\ce{C4H10 + 6.5 O2 -> 4 CO2 + 5 H2O}$$

Then, I calculate the total bond energy difference:

$$-3 \cdot 346.0 - 10 \cdot 414.2 - 6.5 \cdot 479.9 + 4 \cdot 2 \cdot 803.3 + 5 \cdot 2 \cdot 464.4 = 2771.05~[\pu{kJ mol-1}]$$

This is different than the correct value of $\pu{2877.5 kJ mol-1}$. Why?


texts: Little to no reaction in my hot process soap

texts:
I tried to make hot process soap and it was a failure. I carefully weighed the ingredients, but when I added the KOH to the melted oil, nothing happened. When I watch videos on hot process soap making, the oil turns cloudy immediately when the alkali is added. In my case there was no color change and the oil remained clear.

I heated the mixture for over 2 hours at around 180F and got very little reaction. There was some slight coagulation of small white beads on the surface of the oil, but that was it. In videos it shows the oil turning into a mashed potato consistency in as little as 20 minutes. That did not happen in my case at all.

It was though my alkali component was grossly deficient. However, I followed the measures carefully. The formula I used was coconut oil, 5.6 ounces, palm oil 8 ounces, moringa oil 2.4 ounces, water 6.08 ounces, KOH 3.49 ounces. The KOH was in flake form. The package reads caustic potash, 93% purity, KOH.

Could the 93% purity have been the problem?

Another issue is possible water absorption by the KOH. I put some of it in the microwave and it quickly formed quite a puddle, which I mistakenly thought was molten KOH, but it must have been water on second thought, so it is possible the KOH had a high water content.


texts: Why is aluminum oxide resistant to corrosion?

texts: It is common knowledge that aluminum is relatively resistant to corrosion due to its tough oxide layer. The ultrathin (1 nm even) layer is impervious to water and oxygen. What I can't figure out is, why? What makes $\ce{Al2O3}$ so strong compared to $\ce{Na2O}$ or $\ce{MgO}$? My theory is that the aluminum oxide molecules are tightly bound together due to the high charge density of aluminum ions, and this forms a physical barrier where water and oxygen molecules can't come through. This will explain why this only applies to aluminum, as its small size and 3+ charge should make its charge density amongst the highest known. I can't find anything corroborating this claim, though.


texts: Why is the Maxwell–Boltzmann formula inapplicable at low temperatures?

texts:
This Wikipedia article states that at sufficiently low temperatures (or high pressure), quantum effects lead to a breakdown of Maxwell–Boltzmann statistics.

I know that the spacing of energy levels becomes larger at low temperatures, but doesn't the derivation of the MB distribution, as shown in the article, already consider energy levels to be discrete?
Furthermore, it also takes the degeneracy of energy levels into account.

So why and what other quantum effects are there at low temperatures that still violate the formula?


texts: How can I compute the temperature change from the de-excitation of excited particle species?

texts:
The motivation for the question in the title is that I have some formula given,

$$\Delta T=\frac{3410\ \gamma_{O_2}}{2.5+\gamma_{O_2}},$$

where $\gamma_{O_2}$ is the molar fraction of oxygen in a binary micture and the ratio of oxygen and rate gas heat capacities are supposed to be 7.5, if that helps. And there is another one with a factor $\frac{1-\eta}{\eta}$ multiplied, where $\eta$ is a singlet delta oxigen efficiency.

Where does this formula come from?


texts: Why can't we use fusion to make ourselves rich?

texts: As we know on fusing two hydrogen atoms we can convert it to helium and by breaking them we get two $\ce{H}$ atoms. So why can't we convert mercury to gold by removing 1 proton per atom?


texts: Won't the net effect of a catalyst be zero if it creates a new path with lower activation energy?

texts:
A catalyst will provide a new path with a lower activation energy (Figure 1). Won't this mean the forward and backward reactions will both speed up (as they both have a lower activation energy path to take)?

So then what is the point of using a catalyst? Or alternatively, how does the catalyst provide a net benefit for the forward reaction if both the forward and backward reaction are sped up?

I am assuming it might have something to do with the reactants having a higher energy than the products, but I can't think up a proper formal reason that a catalyst has a net benefit for the forward reaction.

Figure 1 (source: Chemguide.co.uk)


texts: What helps a sliced fruit or vegetables oxidize slower?

texts:
What helps a sliced fruit or vegetables oxidize slower ?

A need of chemical compound to use for the slowing of oxidation... we have tried using a lemon juice it actually helped by 15 mins. However it change the quality of the vegetable after being dip for 10 mins and (the problem is how do we slow down the oxidation for 10 days without changing the quality of the fruit) since lemon juice changes the quality of its compound (2-3 days rather).


texts: How to remove the foggy discoloration in polycarbonate tubes caused by acetone?

texts: Unknowing that the tubes used in the centrifuge are made of polycarbonate, I cleaned them with acetone. Following, a white smoky discolouration appeared and the tubes turned opaque. Is there any way to remove this?


texts:
I bought some scrap indium online, and I melted it down into an ingot on my kitchen stove, but my losses were very high as molten indium has a surprising ability to stick to things.

I have a lot of indium stuck to a stainless steel pot, and, unfortunately, I dropped a glass dish that had indium in it into the steel pot and it broke. So now I have broken glass that is covered in indium, and it really likes to stick to glass as well.

Is there a good way to recover the indium? Perhaps increase its surface tension so that it beads up and coalesces? I've seen something similar with sodium metal in hot oil; adding a few drops of isopropanol makes it coalesce. Is there a similar method for indium?

Also, is there a good material to cast indium in? I see that teflon melts at a higher temperature than indium, so maybe a teflon coated muffin tray? Any thoughts on that? Recommendations?


texts: How can we accurately carbon-date samples from La Brea?

texts:
TL;DR - given a sample of bone which has been encased in asphalt for tens of thousands of years and has become saturated with the asphalt, how can you get an accurate age for the specimen through carbon dating?

This past weekend I took my kids to the Page Museum at the La Brea Tar Pits in Los Angeles. While there we saw an astonishing number of fossilized Pleistocene animals. The interesting thing is that all of these fossils have a lovely (to my eyes, at least) brown color which is staining from the asphalt in which these bones have lain for thousands of years.

While there, we saw a presentation which explained that the asphalt seeps into the porous bones and it was explained that we know how old the specimens are through carbon dating. Which got me thinking - if the specimens are all highly contaminated with asphalt, how can they know that the sample they're testing contains carbon from the bone and not from the asphalt (which is presumably much older than the bone)? I did try asking one of the docents, but they're really not equipped to handle such a technical question.


texts: Why is dU an exact differential and dq an inexact differential?

texts: dU, dG, dH etc are all exact differentials and the variables themselves are known as state functions because they only depend on the state of the system. However, dq and dw for example, are inexact differentials. My questions is, what does this actually mean? I've been told that exact differentials are not dependent on the path (what does 'path' mean?) but inexact differentials are. I have been told this is related to line integrals but I am not sure how. Also is this relevant?


texts: What is the electrode potential at the equivalence point if concentrations of titrant and titrand are going to be zero?

texts:
Let's assume that the titrand is $\ce{Fe^2+}$ and the titrant is $\ce{Cr2O7^2-}$. Then

$$E = E^\circ_\ce{Fe^{2+}/Fe^{3+}} - \frac{RT}{nF}\ln\frac{\ce{[Fe^{2+}]}}{\ce{[Fe^{3+}]}}$$

$$E = E^\circ_\ce{Cr^{6+}/Cr^{3+}} - \frac{RT}{nF}\ln\frac{\ce{[Cr^{3+}]}}{\ce{[Cr^{6+}]}}$$

Adding both the above equations, we get

$$2E = E^\circ_\ce{Fe^{2+}/Fe^{3+}} + E^\circ_\ce{Cr^6+/Cr^3+} - \frac{RT}{nF}ln\frac{\ce{[Fe^{2+}][Cr^{3+}]}}{\ce{[Fe^{3+}][Cr^{6+}]}}$$

Since $\ce{[Fe^2+]=[Cr^6+]}$ and $\ce{[Fe^3+]=[Cr^3+]}$

They would all be getting cancelled, ending in

$$E = \frac{E^\circ_\ce{Fe^{2+}/Fe^{3+}} + E^\circ_\ce{Cr^{6+}/Cr^{3+}}}{2}$$

But, at equivalence point, the titrant ions would have entirely reduced and the titrand ions would have entirely oxidised, leaving

$$\ce{[Fe^{2+}]=[Cr^{6+}]}=0$$

And as we know, in mathematics, $\frac00$ is infinite or not defined.
So, how do can we actually mathematically derive the electrode potential at the equivalence point?


texts: Why is hexacyanoferrate(II) colored and at the same time diamagnetic?

texts:
I am wondering why $\ce{[Fe(CN)6]^4-}$ is colored and at the same time diamagnetic. For a transition metal to be diamagnetic all the electrons should be paired up in the d orbitals and at the same time a transition metal is colored because certain wavelength of a white light is absorbed during the electron movement to a higher energy d orbital.
With regard to this, I see a paradox. Since $\ce{[Fe(CN)6]^4-}$ is colored, it means that electron movement happened. If there has been an electron movement, not all the electrons of $\ce{[Fe(CN)6]^4-}$ are paired up
However, why is $\ce{[Fe(CN)6]^4-}$ still considered diamagnetic?


texts: Symmetry Adapted molecular orbitals of Formaldehyde

texts:
I am currently trying to find the Symmetry Adapted linear Combinations (SALCs) of Formaldehyde $\ce{H2C=O}$, and use the  1s orbitals on the hydrogen atoms, and 2s, 2px, 2py and 2pz orbitals on the carbon and oxygen atoms to construct molecular orbitals. However I am finding some issues.

I understand how to work out the SALCs of the hydrogen S orbitals, which is $A_1 = H_{1s} + H_{2s}$ and $B_1 = H_{1s} - H_{2s}$. However, I don't understand how figure out the SALCs of the orbitals belonging to oxygen and carbon.
I can only guess the combinations by drawing them, and not through calculation, like I can with the hydrogen S orbitals as these can interchange. This isn't the case with the oxygen and carbon orbitals.

Is there a way of finding this through calculation? Or do I just draw out all the possible combinations?


texts: Electrolysis of Anhydrous Sodium Hypochlorite

texts:
Considering liquid anhydrous sodium hypochlorite:

$$\ce{NaClO (l)}$$

Assuming the ions are free, What would be produced if this were electrolysed?

As I've found lots of information for it's hydrated pair (a.k.a. bleach). And while I know the half equation for sodium:

$$\ce{Na+  + e- -> Na}$$

I cannot find any half equation for the hypochlorite ion: $\ce{ClO-}$, apart from in acid, or even what would be the product (maybe $\ce{Cl2O}$ or $\ce{Cl2O2}$?)


texts: Why is this chair conformation the most stable and which leaving group is best?

texts: I'm confused about how this chair conformation was constructed and why that particular Cl leaves. Why is one of the Cl's drawn axial while the others are drawn equatorial (it seems like the others could have been drawn axial as well)? And, to reiterate, why is it that Cl that's favored to leave over the other two?


texts: Does the temperature of liquid ammonia stored at high pressure, room temperature suddenly drop to −33.35 °C when poured into a bowl?

texts:
Boiling point of ammonia is $-33.35\ \mathrm{^{\circ}C}$ and its critical temperature $132.4\ \mathrm{^{\circ}C}$ is well above the room temperature. So we can liquify the ammonia gas by compressing it into a bottle, and store it at room temperature for ever.
(Even though the bottle is kept at room temperature, the ammonia will stay in liquid state due to high pressure. )

Hope I'm correct with the above thinking. Next, I open the bottle and pour some liquid ammonia into a bowl. Since this bowl is at 1 atm, I expect something to happen. Does the temperature suddenly drop to $-33.35\ \mathrm{^{\circ}C}$? If so, why?

I'm trying to relate this to adiabatic expansion of gas – the gas does work on the surrounding as it expands and loses its kinetic energy.
But here ammonia is in liquid state as its temperature drops to $-33.35\ \mathrm{^{\circ}C}$. I don't see any work getting done by the ammonia, so I don't see how the temperature drops. I feel I'm missing some important concept.


texts: Feasibility of using Magnesium, Beryllium, Lithium as light sources?

texts:
First off, I'm asking this for worldbuilding purposes, so don't worry, nobody will get hurt ;)

Magnesium, Beryllium and Lithium burn relatively bright. If they are somehow thinned out in some other powder so they burn weaker and last longer, would it not be possible to make torches or lamps out of them?


texts: Does the laser side of laser fluorescence spectroscopy have to be so complicated?

texts: I understand the working principle behind zapping some gas and looking at spectral emissions, and I can see why photodetection is so difficult. But I thought that pointing a laser into a vacuum chamber would be the easy part. So I ask: what the heck is all this equipment that the laser has to go through before it even gets to the sample?


texts:
Are there any fuel-air bombs / thermobaric weapons that utilise ammonium nitrate as a fuel?

I know that BLU-82 is often mistakenly referred to as fuel-air bomb, so I became curious as to whether or not there were any actual fuel-air bombs that used ammonium nitrate.


texts: Why doesn't octahedral d8 system exhibit Jahn-Teller effect?

texts:
Chemistry LibreTexts stated clearly that (under the section 'Large $\Delta$' and 'Small $\Delta$') octahedral d$^8$ system does not exhibit Jahn-Teller distortions. But then it stated also:

...Some common examples (that exhibit distortions) include Cr$^{3+}$, Co$^{3+}$, and Ni$^{2+}$

Isn't Ni$^{2+}$ d$^8$(Group 10, +2, so 10 - 2 = 8) and should not exhibit distortions?

I believe this question is asking the similar thing. But then when the energy level diagrams drawn out as shown below, I saw that even for d$^8$, if singlet favoured over triplet, the distortion does lower the energy (and so should happen).

So what is wrong with the two arguments above?


texts:
I believe that electrolysis of salt water creates lye ($\ce{NaOH}$ - sodium hydroxide). In salt water, there's $\ce{Na+}$, $\ce{Cl-}$, $\ce{H+}$ and $\ce{OH-}$ as of ionts.

So at cathode, you get $\ce{Na2}$ and that should react with water into $\ce{NaOH}$.

I want to test, if this is true - how do I do it with household items? The solution didn't react with aluminium.


texts: Modification to improve antibacterial activity

texts:
I have difficulties with part b).

For C, it's clear to make a bulky dimethoxybenzene group in order to block the C=O group from reacting with b-lactamase.

However, in A, how does the structure of sulfonamide affect the bacterial activity in general?
Is there an alternative for C as well?


texts: Why do halogen substituents make molecules more lipophilic?

texts:
According to my medicinal chemistry text book, halogens increase a drug’s lipophilicty. This makes no sense to me for two reasons:

Halogens are all quite electronegative and they will form a $\ce{C-X}$ bond with a large dipole moment. Large dipole moments are associated with increased polarity.
As opposed to a methyl group, halogens are capable of donating their lone pair electrons to participate in hydrogen bonding. We see this when looking at water solubility of methyl-halogen compounds:

$$\begin{array}{cc}\hline
\text{Compound} & \text{Solubility} / (\mathrm{g \ L^{-1}})\\ \hline
\ce{CH4} & 0.055\\
\ce{CH3CH3} & 0.0568\\
\ce{CH3F} & 2.295\\
\ce{CH3Cl} & 5.325\\
\ce{CH3Br} & 15.22\\
\ce{CH3I} & 14\\ \hline \end{array}$$


texts:
This source lists polypropylene as suitable for use with NaOH.

However, this paper seems to demonstrate that NaOH slowly degrades polypropylene (even at fairly moderate temperatures).

Does anyone know more about this? Would anyone know for instance what it could degrade into (potential for trace contamination of the NaOH solution)?

There is a small possibility that some of that information is described in the body of the paper, but  unfortunately I only have access to the abstract.


texts: Why are branched isomers less polarisable?

texts:
This fact was given as an explanation as to why branched isomers of a compound have lower boiling points.

How are branched isomers less polarisable and how does this relate to London dispersion forces?


texts: React these iron oxide, ammonium nitrate, and sucrose

texts:
Two questions: what reaction forms between ammonium nitrate, black iron oxide, and sucrose; and a story related question.

So here's the whole story:

So I was playing around a few months ago and stumbled upon a mixture that generated something similar to Black Snakes (firework).
I recently decided to demo this mixture to someone, but I could not find my notes about the experiment, so I decided to try to replicate the mixture from what I remembered.

I am certain that the mixture contained ammonium nitrate, black iron oxide, and some sort of fuel (probably sucrose, impure in the form of powdered sugar).
Combining these three ingredients (one part by volume, whatever particle sizes I have), and igniting with a lighter, the mixture does form black snaking ash, and turns red and crumbles as it cools.

Q1: So, what kind of reaction has taken place between the black iron oxide, ammonium nitrate, and sucrose?

If I leave out any one of the ingredients, the ash snake does not form, so all three compounds are definitely involved. If we leave out either the ammonium nitrate or sucrose, little happens with the application of heat.

Here's a picture after the fact.

I haven't had a very good batch since I lost my notes, so maybe I am missing an ingredient, or maybe I just haven't got the right ratios.
Q2: Any Suggestions?^

Edit:
I have been having more success with this mixture (by volume):
1 part ammonium nitrate
1 part potassium nitrate
2 parts black iron oxide
2 parts sucrose

Mix contents and melt over medium indirect heat (skillet is fine); once it is all melted, immediately remove from heat and form into pellet as it cools. The mixture will reduce in volume by several times.
I suggest doing this in small batches since it can self ignite if you are not careful, or do not heat it at the right rate.

If the ammonium nitrate is omitted or substituted by potassium nitrate, the ash does not expand or cohere. So the ammonium nitrate is doing something more than just providing oxygen here.
The reduction of iron oxide seems to make the ash less monolithic, and moderate reductions in iron oxide forms snakes that fall apart quickly during production.


texts:
In ionic crystals there are mainly 3 types of structures: Face-centered cubic and octahedral interstices; face-centered cubic with tetrahedral interstices; and body-centered cubic.

My question is how can I know the edge of the unit cell of this crystals for calculating the theoretical density of a crystal?


texts: Atoms are stable so how can they pull electrons i.e how do they have any electron affinity at all?


texts: Why can potassium hydroxide not be used to remove atmospheric carbon dioxide?

texts: As we know that $\ce{KOH}$ absorbs $\ce{CO2}$, then why can't it be used to remove the excessive $\ce{CO_2}$ present in the atmosphere?


texts: What is the proof of complete ionic dissociation in water?

texts:
Is there any way to prove that ionic compounds, for instance $\ce{NaCl}$, completely dissociate into singular $\ce{Na+}$ and $\ce{Cl-}$ ions within water by hard experimental evidence?

Besides adhering to the perfect solvation model in theory, I am interested in definitive proof of monoatomic solvation in practice.

How do we know that the ionic crystal lattice isn't only partially dissolved? When the superficial reaction between water and the ionic compound takes place, could it stop at say 10-100 atom microcluster lattices ($\ce{Na/Cl/Na/Cl}$ etc), giving the appearance by standard means that it is completely dissolved?

I am only interested in experimental means of verification, not concepts taken from books.


texts:
For molecular orbital theory:
How do you determine how many electrons occupy the anti bonding orbitals?
Also, why does hydrogen gas have no anti bonding orbitals- if each atom's electrons form a molecular orbital, then their energy is reduced so where does the extra energy go ?


texts:
I read that if, after a tempering from T>723°C to T*=[250°C,550°C], I do an isothermal transformation of an eutectoid steel, I'll get bainitic microstructure.

Does this microstructure exist only if temperature remains at T=T* also after microstructure was formed?

In other words, if I do a cooling until room temperature (after bainite was formed), will it exist at this temperature?

Thank you very much.


texts: Why is a solution of PCl3 more acidic than MgCl2?

texts: Why is a solution of $\ce{PCl3}$ more acidic than $\ce{MgCl2}$? I thought that both $\ce{MgCl2}$ and $\ce{PCl3}$ would react with water to form $\ce{HCl}$ so both solutions should have a very low pH. But does $\ce{MgCl2}$ actually form $\ce{HCl}$ in water or it simply dissolves and forms $\ce{[Mg(H2O)6]^2+}$, but if it only forms this, how is it slightly acidic?


texts: Does salt hydrolysis takes place in buffer solution?

texts: I am a bit confused whether hydrolysis of salt takes place in buffer solutions because the books which I read doesnt consider them.But I think since weak base or weak acid salt is present hydrolysis should take place.


texts: Identifying the C3, C4, S4, and S6 symmetry operations in the Oh point group

texts:
The Oh character table has ten symmetry classes. I am trying to identify them, but my stumbling block is in identifying the order of each class.

I will use this diagram as a reference, from Sydney Kettle's Symmetry and Structure: Readable Group Theory for Chemists pg 191 (Wiley, 3rd edition).

The classes (with their respective orders) for the Oh table are:

$$\begin{array}{cccccccccc}E & 8C_3 & 6C'_2 & 6C_4 & 3C_2 & i & 6S_4 & 8S_6 & 3\sigma_\mathrm{h} & 6\sigma_\mathrm{d}\end{array}$$

$E$ and $i$ are obvious.
$6C'_2$ and $3C_2$ are shown in the diagram.
$8C_3$ is shown in the diagram above; however, it only displays 4 axes. The character table indicates there are 8 equivalent rotations for this symmetry operation. Where do the other 4 axes for the $C_3$ class come from?
$6C_4$ is the same issue. It's only shown as 3 axes. Where are the other 3 $C_4$ axes from?

The improper rotations are given in another diagram, this time on page 194 from the same book.

The mirror and dihedral planes, $\sigma_\mathrm{h}$ and $\sigma_\mathrm{d}$, are both shown to match the order in the character table.
Similar to above for $C_3$ and $C_4$, the $S_4$ and $S_6$ rotations are only half the order supplied in the character table.

In summary, from 10 total classes in the octahedral table, I can identify all the corresponding axes/planes for 6 of those 10 classes. For the remaining 4 classes, $C_3$, $C_4$, $S_4$, and $S_6$, I can only identify half the axes. At first I thought the character table was counting both positive and negative rotations, but then the order for the $C'_2$ and $C_2$ rotations should be doubled if that were the case ($12C'_2$ and $6C_2$).

Can anyone please advise on exactly what the $C_3$, $C_4$, $S_4$, and $S_6$ operations correspond to in an octahedral complex?


texts: Why does the acid in hops make beer taste bitter?

texts:
For years, I've learned that acids taste sour and bases taste bitter.  Recently, I've read in "The Beer Bible" and various beer sites that the hops in beer, which are acidic, cause beer to have a bitter taste.

So my question is, is it true that the acid in hops make beer bitter?  And if true, does this mean that (Arrhenius) acids aren't necessarily sour tasting, but sometimes bitter?

Alternatively, is there some kind of chemical reaction between hops and beer that make beer more basic, hence the bitter taste?


texts: Restarting a Gaussian partially constrained relaxed surface scan using GICs

texts:
I am Using Gaussian 16 rev D.01, and I want to perform relaxed surface scans where I vary a bond distance. At the same time I constrain seven atom coordinates during the entire optimization (this is an enzyme active site cluster model).

Setting up the initial input is not difficult. However, as most Gaussian users would know, the optimization is likely to fail at some point due to the "Curvilinear step not converged" error. That means restarting the optimization.

The question then becomes how to properly restart the relaxed surface scan automatically from the last point in the scan while at the same time not losing my constraints. The Gaussian manual says that

geom=(CheckPoint, NewDefinition)

should not be used, and that instead

geom=(CheckPoint, GIC)

should be used.

My attempted input looks like this

%chk=mycheckpointfile.chk
# P opt=(tight)
# pbepbe/def2svp
# scf=(MaxCycle=1000)
# int=UltraFine
# EmpiricalDispersion=GD3
# geom=(CheckPoint, GIC)
# NoSymm

Relaxed surface scan searching for transition state

-1 1

Atom 30 Frozen
Atom 21 Frozen
Atom 1 Frozen
Atom 19 Frozen
Atom 56 Frozen
Atom 39 Frozen
Atom 55 Frozen
rSC(NSteps=15, StepSize=0.05) = Bond(15,59)

but this resulted in loss of my constraints. Should I add "AddGIC" as well? What is the easiest way to restart such an optimization?

Also, if this is easier with the old "ModRedundant" keyword then such an answer is also appreciated.


texts: Software for viewing a structure and altering bond angles

texts:
Does anyone know of any good software that would allow me to view the structure of a compound while also allowing me to change the bond angles in the structure (and give me numeric values for those angles)?

I'm looking for something freely available, but that's not a major requirement. Thank you so much!


texts: Why does a reaction stop when turning into a solid?

texts:
I recently was looking at a question about the volume of carbon dioxide produced when reacting calcium carbonate with dilute sulfuric acid versus using nitric acid. In the answer it says that calcium sulfate is produced, which is a solid, which stops the reaction, but I don't get why. Calcium nitrate produces an aqueous solution which causes the reaction to carry on reacting.
The reaction equations are:
$$\ce{CaCO3(s) + H2SO4(aq) -> CaSO4(s) + H2O(l) + CO2(g)}$$
$$\ce{CaCO3(s) + 2HNO3(aq) -> Ca(NO3)2(aq) + H2O(l) + CO2(g)}$$


texts:
I read this in an old chemistry book. It says:

  When selenium is dropped into melted phosphorus, it dissolves rapidly, and the compound sinks through the liquid phosphorus in red streaks.

My question is whether the phosphorus is red or white?


texts:
What does oxidizing strength mean?

Does it mean the strength of a oxidation agent that is needed to oxidize the reduction agent, or does it just mean the tendency of a substance to lose electrons (oxidate)?


texts:
Hi chemistry enthusiasts!
I am working on my scholarship exam practice. I believe this exam assumes high school + first year university knowledge although the standard may be varied across the world. And I'm not quite sure what I did wrong. Could you please have a look?

  There is an aqueous solution containing Cu2+ and Pb2+ ions. The most
  suitable reagent to precipitate one of the two ions from the solution
  is (1) nitric acid (2) sodium carbonate (3) sulfuric acid (4) hydrogen
  sulfide

I picked answer (4) hydrogen sulfide because I think that it will react with copper (II) ions and will precipitate out. However, the correct answer is (3) sulfuric acid. How is this answer correct and what did I do wrong for hydrogen sulfide. Your advice will be much appreciated!


texts: How does one solve the following differential equation (mass balance equation)

texts:
How does one solve the following differential equation? This is a reduced mass balance equation for a cylinder containing a gas mixture of two gases (here represented by the numbers 1 and 2)):

$$\frac{p_1C_{V_1}^*}{RT_1}\frac{\mathrm dT_1}{\mathrm dt}+\frac{p_2C_{V_2}^*}{RT_2}\frac{\mathrm dT_2}{\mathrm dt}=\frac{\mathrm d}{\mathrm dt}\left(\frac{p_1}{T_1}\right)T_1+\frac{\mathrm d}{\mathrm dt}\left(\frac{p_2}{T_2}\right)T_2$$

For one gas it's easy:

$$\frac{pC_V^*}{RT}\frac{\mathrm dT}{\mathrm dt}=\frac{\mathrm d}{\mathrm dt}\left(\frac pT\right)T$$

$$\frac{C_V^*}{RT}\frac{\mathrm dT}{\mathrm dt}=\frac{\mathrm d}{\mathrm dt}\left(\frac pT\right)\frac Tp$$

$$\frac{C_V^*}{R}\frac{\mathrm d\ln(T)}{\mathrm dt}=\frac{\mathrm d}{\mathrm dt}\left(\ln\left(\frac pT\right)\right)$$

After integrating between the initial and final phase, we get:

$$\left(\frac{T_\text{final}}{T_\text{initial}}\right)^{\frac{C_V^*}R}=\left(\frac{p_\text{final}}{p_\text{initial}}\right)\left(\frac{T_\text{initial}}{T_\text{final}}\right)$$