texts: How do you find the enthalpy of solution of a hydrated salt?

texts:
I am doing an experiment in school where I try to find how heating time affects the enthalpy of solution of a salt in water. I take a hydrated salt ($\ce{Na_2CO_3 \cdot 10H_2O }$), heat it for a certain amount of time (say 2 minutes) and then measure the enthalpy of solution of the salt.
Lets say after 2 minutes the fully hydrated salt turns partially hydrated (say $\ce{Na_2CO_3 \cdot 10H_{2}O ->  Na_2CO_3 \cdot 8H_2O})$. I know that for the solution enthalpy of solution of an anhydrous salt, I can find it out by adding the lattice enthalpy of the salt and the hydration enthalpy. But for hydrated and partially hydrated salts (such as  $\ce{Na_2CO_3 \cdot 8H_2O}$) how do you find the enthalpy of solution in water?


texts: Calculate the standard oxidation potential from given potentials

texts:
The standard electrode potentials for the following redox couples are given as: >$E_0(\ce{Fe^{2+}/Fe}) = x~\mathrm{V}$ and $ E_0(\ce{Fe^{3+}/Fe^{2+}}) = y~\mathrm{V}$
  What will be potential $E_0(\ce{Fe^{3+}/Fe})$ (in $\mathrm{V}$)?

My approach: $\ce{Fe^{3+} + e- + Fe^{2+} + 2e- -> Fe^{2+} + Fe}$

So $E_0(\ce{Fe^{3+}/Fe})=(x+y)~\mathrm{V}$


texts: The physical intuition behind some simplifications in electrochemistry

texts:
Find the standard reduction potential of
$$\ce{AgIO3(s) + e- <=>  Ag(s) + IO3-}.$$
$K_\mathrm{sp} = \pu{3.1E-8},$ and the standard reduction potential of $\ce{Ag +e- <=> Ag(s)}$ is $E = \pu{0.799 V}.$

So, $E^\circ$ will be standard reduction potential and $E$ will be the nonstandard.
$$
\begin{align}
E(\ce{AgIO3/Ag}) &= E^\circ(\ce{AgIO3/Ag}) - 0.0257\ln\frac{1}{[\ce{Ag}]}\\
  &= E^\circ(\ce{AgIO3/Ag}) - 0.0257\ln\frac{[\ce{IO3}]}{\pu{3.1E-8}}
\end{align}
$$
$$\pu{0.799 V} = E^\circ(\ce{AgIO3/Ag}) - 0.0257\ln\frac{1}{\pu{3.1E-8}}$$
Now, my concern is that I understand the math and like most of the principles behind all this, but how come when we set $[\ce{IO3}] = 1,$ we can also say $E (\ce{AgIO3/Ag})$ is equal to $E(\ce{Ag})?$
tl;dr: how come setting the concentration of the anion to $\pu{1 M}$ allows us to assume that variable change for the electrode?


texts: Extended Hückel method: what are the atomic orbital energies usually used?

texts: I was checking out an extended Hückel (non-iterative) code, and realised that for s-block elements it would be impossible to simply use atomic ionisation energies as an approximation to the orbital potential energies (due to the p orbitals being empty). In this case, what values are used?


texts:
I have to name the following organic cpd according to IUPAC.
My attempt:
I am unable to select a parent carbon chain as there are 2 carbon chains possible and I don’t know how do we proceed in such a type of compound.
According to the key the answer should be 3,3’ -[oxy bis(ethyleneoxy)]dipropanoic acid
Now, this seems certainly wrong to me as there is no double bond in the carbon chain so ‘ene’ must not be there, or am I missing out on something.
PubChem gives the name of the cpd as 3,3'-((Oxybis(ethane-2,1-diyl))bis(oxy))dipropanoic acid
I would be glad if somebody could explain the reason behind this nomenclature.
Thank You!


texts: Finding sulfate contamination in crystallized silver nitrate

texts:
What is the best way to check for a small amount of sulfate contamination (if any) in silver nitrate? Usually, I would use dilute barium chloride to precipitate out the resulting insoluble white barium sulfate in an unknown aqueous solution that contained sulfates. I tried this and got a white precipitate, but now I believe the precipitate I'm getting is insoluble silver chloride.

Is there a better/different method to check for sulfates in silver nitrate? I was researching for a better solvent to use, but haven't been able to find any conclusive answers so far.


texts: What is the molecular structure of the fragment ion m/z 161 of rosmarinic acid?

texts: Attached is an ESI-MS/MS spectrum of product ion scan of rosmarinic acid (m/z 359.10) (source). I'm trying to figure out the structure of the fragment m/z 161. It's not clear to me what the structure should be. Does a triple bond form perhaps?


texts: Pros and cons of Cartesian vs. Z-matrix representations of molecules?

texts:
Over the course of my studies, I have switched largely from using Z-matrix representations of molecular geometries in calculations to Cartesian representations.

The software that I use now makes it easy to add the sorts of constraints/restraints/transits that I would have previously used Z-matrices for, and I know that Z-matrix geometries can be problematic in large molecules* where minute changes in a bond angle or dihedral (due, for instance, to rounding errors/low-quality gradients) can result in large movements in peripheral atoms.

What pros or cons exist for either geometry definition that I don't know about? What circumstances recommend one representation over another?

*Or small molecules with silly Z-matrices.


texts: What Affects Tm and Tr In Chromatography?

texts:
In chromatography, a mobile phase with analytes is passed over a stationary phase. A given analyte has different solubility in the two phases and consequently spends different periods of time in them. A particular molecule while in the stationary phase remains immobile, is swept along when present in the mobile phase.
$T_m$, the time spent in the mobile phase, is the same for all analytes. The reason (I'm not so sure) must be since all analytes travel the same distance finally, with the same speed as the mobile phase, so take the same time in so doing. But since some of these spend longer times in the stationary phase than others, the total time to reach the end, that is, $T_m + T_r$ is different ($T_r$ is the time spent in the stationary phase).

But I have a bit of a trouble understanding the rate aspect of the process, and what exactly determines the $T_r$ and $T_m$ - are they the average times spent by an arbitrary molecule in the two phases? If so, are their values dependent on the rate of the process, or the solubilities?


texts: Finding half-life of a nuclide based on gas release

texts:
Full Question: The hydride of an unstable nuclide of a Group IIA metal, $\ce{MH2 (s)}$, decays by alpha emission. A $\pu{0.025 mol}$ sample of the hydride is placed in an evacuated $\pu{2.0 L}$ container at $\pu{298 K}$. After 82 minutes, the pressure in the container is $\pu{0.55 atm}$. Find the half-life of the nuclide.
Here's what I have so far:

Find nuclear equation MH2(s) ---> He(g) + Noble gas + H2 (g) (not sure if this is right)

Find total moles of gas in container at 80 mins
$$n = \frac{PV}{RT} = \frac{(\pu{0.55 atm})(\pu{2 L})}{(\pu{0.0821 L atm mol-1 K-1})(\pu{298 K})} = \pu{0.045 mol}$$

Use integrated first rate law to calculate k and half-life.
Use $\ln N_t = -kt + \ln N_i$, where $N_i$ is the initial amount of moles of $\ce{MH2}$ ($\pu{0.025 mol}$) and $N_t$ is the moles of hydride remaining after 80 minutes.

Then find half life using k.
$$t_{1/2} = \ln 2 / k$$

Here's what I'm having trouble on: How to find $N_t$, i.e. the moles of metal hydride remaining. This part has been stumping me for quite some time, so help is appreciated! Thank you!


texts: Valence Bond theory, VSEPR theory and predicting the shapes of the molecules

texts:
I read about the above mentioned theories then used them to predict the molecular geometry. However, I found that the shape/geometry of a molecule obtained from both the theories was same. For example, water has bent/angular shape according to VSEPR theory as well as Valence Bond Theory. So I wonder if there's any difference between the two theories in predicting molecular geometry.

Do these two theories ever yield different results?


texts:
Why R32 Space Group is so named? I mean, if R stands for Rhombohedral and 3 for Threefold Axis, what 2 stands for?

I don't see any Twofold Axis in the cell:

http://img.chem.ucl.ac.uk/sgp/large/155az1.htm

EDIT:

What does it means 1/2, 2/3 and 1/6 on the arrows?

R32 have two cells.

This one: http://img.chem.ucl.ac.uk/sgp/large/155bz1.htm

And this other: http://img.chem.ucl.ac.uk/sgp/large/155az1.htm

Are they equivalent?

EDIT:

I have traced some lines to mark the screw-axes and the twofold-axis, but i can't see any point that follow the simmetry operator and the element of simmetry. Maybe i don't understand how it works.

Which is the height of the green line? And, which are the points of the screw-axis of the yellow line?


texts: Boiling point of ethanamide vs propanamide

texts:
I just have a question regarding the boiling points of some primary amides. Ethanamide has a boiling point of 222 °C, while propanamide has a lower boiling point of 213 °C. Both amides are capable of hydrogen bonding, however, I would have expected propanamide (the molecule with more electrons) to have a higher boiling due to stronger dispersion forces. The same applies to butanamide which has a boiling point of 216 °C.

Is there anyway to rationalise why propanamide and butanamide have a lower boiling point than ethanamide or why the carbon chain length doesn't seem to affect the boiling point of amides?


texts: Can a food dehydrator be used as an alternative to a scientific drying oven?

texts:
I have some everyday drying needs, like drying dessicants such as calcium chloride and silica gel.

Can I use a food dehydrator for this task as an alternative to a scientific drying oven? There is a 10x cost differential in the price.


texts: Why ionic radii of Cu2+ is less than Zn2+?

texts:
Fully filled orbital has more effective nuclear charge than incompletely filled orbital. So atomic or ionic radii of elements or ions having fully filled orbitals should be less than that of elements having  incompletely filled orbitals (e.g. $\ce{F}$ and $\ce{Ne}$).

Now $\ce{Cu^2+}$ has a $\ce{d^9}$ configuration and $\ce{Zn^2+}$ has  a $\ce{d^10}$ configuration. So, $\ce{Zn^2+}$ has full filled d orbital and is thus stable. According to my assumption above, $\ce{Zn^2+}$ should have less ionic radii than $\ce{Cu^2+}$. But it is found that $\ce{Zn^2+}$ has more ionic radii than $\ce{Cu^2+}$.

Ionic radii of $\ce{Cu^2+}$ is $\ce{73}$ pm and that of $\ce{Zn^2+}$  is $\ce{74}$ pm. Why is this so?

(source)


texts: Why does my absorbance change over time?

texts:
I have a solution of black phosphorus quantum dots suspended in water that I prepared by sonicating black phosphorus powder in n-methyl-2-pyrrolidone and centrifuging to isolate the quantum dots. Repeat measurements of the absorbance of this solution over a period of days resulted in a decrease in the absorbance; I know this to be due to the instability of the black phosphorus when exposed to water, air, and light.

However, I also have a solution prepared in the same way using graphene nanoplatelets instead of black phosphorus. Testing the graphene solution over a period of days resulted in an increase in absorbance. Why might the absorbance be increasing in the case of the graphene in water?


texts: What does it mean to define entropy as a measure of a systems internal energy per unit temperature which is unavailable to do work?

texts: Entropy was defined in one of my findings as "the measure of the internal energy of a system per unit temperature which is unavailable to do work". Can someone help me understand this definition better cause I have always defined entropy as the degree of disorder in a system.


texts: [BMIM]PF6, or 1-butyl-3-methylimidazolium hexafluorophosphate, is commonly used as an ionic liquid. As has been shown by the accepted answer to this question, sodium chloride that has been made to boil actually exists either as a monomer (Molecule of NaCl), or a dimer, rather than ions, in the gas phase. What happens to 1-butyl-3-methylimidazolium hexafluorophosphate, or any other ionic liquid, that has been boiled? Would it, like NaCl, also exist as a monomer? What would happen to an ionic liquid that has been placed into a vacuum chamber from which air had been removed?


texts: What non-toxic non-water substances have a freezing point very close to water's?

texts:
I was linked to a Kickstarter for a cooling ball to be placed in drinks which claims with constant marketing hyperbole how much it relies on "Phase Change" ! which is a neat concept and seems not unreasonable, but in thinking about it I'm failing to imagine (as I'm no chemist, and of ill education) what refrigerant could be inside that meets the named requirements of non-toxic food safe, as well as passing from solid to liquid (or liquid to gas) such that a typical freezer would freeze it (−2 °C to −5 °C typically?), and it would liquefy around a temperature you'd want to keep your drink (say 1–3 °C).

Obviously water meets these requirements, however due to the expansion pressures water commits I have a very hard time imagining a small stainless steel ball containing that expansion through many freeze-thaw cycles without causing eventual deformities which would be continually weakened.

So the question is in the title, and to note the container is a sealed solid stainless steel ball of unknown thickness 2" in diameter.

Let me know if this question is off-topic, more than anything I'm just curious so I realize sometimes questions not based on a problem are poor fits for SE.

Do note: I am not interested in actually trying to do something with this, it is simply a curiosity, so don't be concerned if the things that come to mind aren't FDA tested, I'll settle for answers that simply show there are such things that are likely non-toxic regardless of thorough safety testing. Also the phase change from liquid to gas is a possible one too if you know of any safe chemicals here that wouldn't cause uncontrollable internal pressure and would have that phase change at the temperature range specified.

Just trying to come up with an idea for a compound that could meet their marketing hyperbole and finding I come up short.


texts: How can the stereochemistry of the product of an E1cb reaction be determined?

texts:
Say if this is your reagent.

I guess similarly to how you'd determine the stereochemistry of the product of an E1?


texts: Is there any rule that says that oxygen should have at least one free pair of electrons in Lewis dot structure?

texts: For example, Ozone has a double and single bond with at least one free pair of electrons in each oxygen atom. My doubt is whether ozone can have a triple bond and single bond with one oxygen atom without a free pair of electrons.


texts:
Working in a building that uses propylene glycol (PG) as antifreeze in a hydroponic heating system.  With complaints of chemical odors in offices, I conducted air sampling for glycols, aldehydes, and PAHs.  No airborne glycol or PAHs were detected, but low levels of aldehydes; acetone, acetaldehyde, butyraldehyde and formaldehyde are present building wide.  Not a chemist, so question is, if there is a leak in a closed hydroponic heating system, does the PG oxidize to aldehydes when it encounters occupied air?

A thick bioslime was present on the interior surface of the mechanical room glycol tank.  I was told that when glycol is exposed to air, it generates nutrients for microbes.  The bioslime analyzed as Yeast, and some PG is generated by Yeast and carbohydrates - all news to me.


texts: Why is E2 reactivity rate of 1-iodo-1-methylcyclohexane faster than (1R,2S)-1-iodo-2-methylcyclohexane even though the transition state is same?

texts: Why is E2 reactivity rate of the second compound said to be faster than the first compound even though the transition state is same? My teacher said that in E2 more hindrance implies faster reaction. In the first compound H atom is more hindered due to methyl group. Even then why is the reactivity of the second compound in presence of a strong base, said to be faster?


texts: How to chose wavelength in spectrophotometry? How to use Beer-Lambert Law?

texts:
How is the wavelength chosen to measure the concentration of an ion determined? and What does the wavelength correspond to in an atom/ion?

When light is shined on a solution what happens to the ions in solution? Include how and why light is absorbed or emitted from a substance.

Would a high or low concentration absorb more light?

How does the beer-lambert law relate to concentration and information from the spectrophotometer?


texts:
I know it expands when hot and grows compact when cool (that's about all I know), but I suppose many other substances do, too.

Also, and excuses for my ignorance, what the term used to describe the function of mercury in a thermometer? I mean, would you call it an "indicator" (insofar as it indicates the temperature), or is there some technical term?

Thanks!


texts:
For mhchem, I need to decide on a typographical representation of orbitals.

Wikipedia tells me, there are atomic orbitals with letters s, p, d, f and g. In a later table, there is even h.
Then, there are molecular orbitals with greek letters.
Orbital hybridisation uses the letters s, p and sp, sp², sp³.

The IUPAC green book
on (printed) page 32 uses upright characters for 1s, 2s, 2p etc.
However, in the footnotes on page 19, ‘orbitals r and s’ are in italic. (r? Wikipedia did not tell me about this.)

That is the only occurrence in an IUPAC document I could find via search. Are there more?

There are other occurences in the Blue Book in italic, but they are stereodescriptors. (1s,3s)-cyclobutane-1,3-diol.

A quick search at Google Books revealed the convention of italic font for orbitals,
e.g. Organic Chemistry, 2008
or Essentials of Organic Chemistry, 2006,
or Orbital Interactions in Chemistry, 2013,
all published by Wiley.

However, there are also
Molecular Orbitals and Organic Chemical Reactions, 2011
and
Discovering Chemistry With Natural Bond Orbitals, 2012
by the same publisher that use an upright font.

Anyhow, I need to decide for one way or the other. Is there any IUPAC document, I could base my decision on? One, that defines the meaning of the letters and not just uses them.

Second question: I need to distinuish orbitals form other notations. Are my following assumptions correct to reliably detect orbital notations?

Orbitals are always written as number + lower-case letter
Letters can be s, p, d, f, g, h.
There is no element entity in chemical notations with these (lower-case) letters. But there is p for proton.
The letters for abbreviations for organic structure fragments such as ‘c’, ‘m’, ‘p’, ‘r’, ‘s’, and ‘t’ overlap, but they are never written with a number in front of them.

Disclaimer:
I am not a chemist and am not familiar with the meaning of all of this.
I am interested in the typography, though.


texts:
I have a lighter at home which everytime I use it, generates little spikes (see picture below) which eventually disappear.
The Spikes are not an effect generated by the camera. I can confirm that since I made the picture.
Essentially this means the flame does not have a nice uniform flame shape, but is interrupted by the spikes.

Does someone know where this is comming from?

EDIT:
@JamesGaidis suggested to try holding the lighter sideways. It can be observed that the spot of the spike has roughly the same position when holding it sideways (left picture)

A different lighter with the same effect, but with the additional feature of beeing able to reduce the gas flow shows, that the spike is independent of the quantity of the gas (right picture).
The height of the spike (distance from the tip of the flame to the tip of the spike) is always the same, thus independent from the quantity of the gas. (In other words: the height from hole that emits the gas to the top the spike is only dependent on the size of the flame)

James did also suggest to light the lighter from an external source, and in this case, no spikes show up.
This implies that its not the gas alone generating this effect, but has rather something to do with the stone.

I don't really know if this is has to do with chemistry at all, or if it has more to do with physics. If thats the case, feel free to redirect me towards the correct SE site.


texts: Intramolecular Cannizzaro reaction product

texts:
I came across the following question :

My reasoning was as follows :

It can't be option (c) because there is no chance of losing a carbon during Cannizzaro's reaction
It can't be option (b) because basically option (c) gives (b) finally
It can't be option (a) or option (d) because we can't have all carb acid groups or all alcohol groups. we need a combination of both.

So, are the options wrong?


texts: Stability of MnO4- in basic vs acidic conditions

texts: Why is $\ce{MnO4-}$ more stable in basic than acidic conditions? I know that electrode potential values suggest this, but what is the underlying chemical explanation for the phenomenon?


texts: I made a solution of copper acetate using 5% Acetic acid 3%hydrogen peroxide and copper wire and copper pipe and it had produced a blue solution of copper acetate. I left it over night to continue reacting, but when I came back In the morning the solution turned clear. I didn’t do any Stoichiometry so I don’t know if they’re was a excess of H2O2 or a excess of acetic acid. I’m wondering if you know what happened


texts: Ionization enthalpies of Transition elements

texts:
“There is generally expected increasing trend in the values as the effective nuclear charge increases. However the value[First ionisation enthalpy] of Cr is lower because of the absence of regarding any change in d configuration and the value of Zn higher because it represents an ionisation from 4s level”

For, Cr it is 653 kJ/mol and for Zn it is 906 kJ/mol

It seems that the statement regarding Zn undoes what is pointed out by the statement regarding Cr, as for Zn it changes from 4s2 3d10 to 4s1 3d10 and for transition from Cr to Cr +1 the electronic configuration changes from 4s1 3d5 to 3d5, clearly both have change in their 4s configuration and not in 3d configuration.

My first question is what does this mean?
Problem in understanding this is that the book has not mentioned anything about filled 4s2 configuration of Zn, it seems that it is supposed to be understood from the statement alone.

Even after ignoring that, if I think in terms of effective nuclear charge, which is higher for Zn and as a result higher energy required for ionisation of electron from 4s2, but the problem in that that it does not seem to be the explanation of that because of that However , which seems to point to some exception.

I have checked other questions on this site regarding the irregular trend of ionisation enthalpy for transition element but they don’t seem to me to address this.


texts:
I had a question regarding the solubility of amines and amides.
I was looking into the solubility of butanamide and n-Butylamine, and it turns out that whilst butylamine is miscible in water, the solubility for butanamide is 163g/L
This would imply that amines have a greater solubility than amides. My understanding is that
the carbonyl group would add two lone pairs, which act as hydrogen bond acceptors and thus should mean amides are more soluble. (more hydrogen bonds)
It'd be much appreciate if someone could point me in the right direction or let me know how my reasoning is flawed.
(I have viewed this link but the answer given isn't too helpful: Solubility of Amides)
Thanks in advance!
Sources for Solubility Values
https://en.wikipedia.org/wiki/N-Butylamine
https://chem.libretexts.org/Under_Construction/Walker/Chemicals/Substance%3AB/Butanamide


texts: Is there a difference between negative/positive controls and control/experimental groups?

texts:
First of all, just so I can fully understand, what is the correct definition of a control regarding science experiments?

Is there a difference between the definitions of a control/experiment group and negative/positive controls?

I know that the control group is the group that will not be tested on while the experimental group is the group that will be experimented on, but that seems very similar to negative and positive control.

Is it true that negative controls are the controls in the control group while positive controls are the controls in the experiment group?


texts: By this, I mean if I buy compressed dry air from somebody like British Oxygen how much variation in composition might I expect between batches? For example, is Argon evenly distributed globally, by height, by geography etc? Is $\ce{CO2}$ removed? Are contaminants filtered out eg $\ce{NOx}$?


texts: Why are Born-Haber enthalpy calculations inaccurate for transition metal compounds?

texts:
A senior high/secondary school level exam question is about discrepancies between calculated and empirical enthalpies of formation. It asks why a discrepancy “usually” exists for d-block compounds such as copper (II) chloride.

For something like AgCl or AlCl3 the answer is covalent character. But that’s not true for CuCl2, is it?


texts: Is the order of orientation of electron box diagrams meaningful or arbitrary?

texts:
Here is my interpretation when asked to:

  By drawing arrows in the appropriate boxes, complete the outer electron structures for Cu and Cu2+

I had no problem in drawing out the electron structure, but am a little confused by the orientation of my arrows.  I understand that each normal box has to have arrows in opposing directions to represent the opposite spins on the electrons, but the mark scheme defines which way round they want them to go:

Source: OCR GCE Chemistry B F334 June 2011 Markscheme pg. 11

Ordinarily I would have said that whether you go up or down first (or even consistently) is irrelevant and arbitrary, but the comment in the guidance

  ALLOW single arrow in either direction

suggests to me that with the paired arrows, the order of directions matter.

Is there any chemical reason for putting the downwards spin arrow first?  I would happily accept by convention as a reason but I just want to be sure that I'm not missing anything chemically relevant.


texts:
Is the half-full rule and full rule followed in the 6th and 7th periods? (Note: Half-full rules is Hund's rule)

Example: What is the correct electron configuration?
$$\ce{W = [Xe] 6s^2 4f^{14} 5d^4}$$ doesn't use half full rule, or
$$\ce{W = [Xe] 6s^1 4f^{14} 5d^5}$$ uses half full rule.


texts: When will organometallics act as base or nucleophile?

texts:
I would like to ask if the hydrogen next to carbonyl group is acidic,and organometallics are strong base, when will it act as a base and extracts the acidic proton and when will it attack the carbonyl carbon?

Also I would also like to ask, for bases when will it attack the acidic proton to form a enolate and when will it attack the carbonyl carbon directly to form an hemiacetal/hemiketals?


texts: By how many pKa units will the pKa value of a ketone be minimized by addition of a Lewis acid

texts:
I want to enolize a ketone, for instance acetone with a $\mathrm{p}K_\mathrm{a}$ value of about 20 (in $\ce{H2O}$).

I'd like to know if there exists a rule of thumb to predict how the $\mathrm{p}K_\mathrm{a}$ of the ketone will decrease if we add one of the following Lewis acids:

a) $\ce{(c-Hex)2BCl}$ (chlorine anion can be eliminated)

b) $\ce{Bu2BOTf}$ (triflate anion is a good leaving group)

c) $\ce{NaI}$ (sodium is bigger than lithium, and I expect the bond to oxygen is less strong meaning the decrease of the $\mathrm{p}K_\mathrm{a}$ will be less than in d))

d) $\ce{LiI}$ (iodine is bigger than lithium, therefore good hard-soft-mismatch; and oxygen is hard as well)

e) $\ce{HCl}$ (As @SYK suggested in his answer of my recent question
[1], the proton is the strongest Lewis acid as possible and will lower the $\mathrm{p}K_\mathrm{a}$ as much as possible, that even a very weak base, may be of $\mathrm{p}K_\mathrm{a}~9$ as $\ce{NH4Cl}$ will (or won't it?) form the cis-enolate)

I'm especially interested in the lowering values for a), b) and c). My questions:

Is my qualitative lowering of $\mathrm{p}K_\mathrm{a}$ values a < b < c < d < e correct?
Do you have somes guesses for decreasing values for a, b and c ?


texts:
This is my homework question I tried it hard the question is as follow:

I attempted it as follow:

According to my understanding as acid base reaction are fastest the carbanion will gain a $\ce{H+}$. From the water formed and will the product as I made, but the answer is completely different:

Please guide me where I am wrong.


texts: Equilibrium expression for dissolution of carbon dioxide

texts:
I was asked to give the equilibrium expression for:

$$\ce{CO2(aq) + H2O(l) <=> H2CO3(aq)}$$

As water is a liquid and a solvent here, it shouldn't be included in the expression, hence I wrote:

$$K_c = \frac{[\ce{H2CO3}]}{[\ce{CO2}]}$$

However, the answer of the question included water in the denominator.

What is the correct answer in this situation?


texts:
I cannot understand that

  in an irreversible adiabatic isobaric process the enthalpy change is $ \Delta H <0$.

Could anyone please help me how to prove it.
Any help is appreciated.


texts: What is the entropy of mixing of two ideal gases starting out with different pressures?

texts:
The entropy of mixing of ideal gas is given by this equation:

$\Delta S_{mix} =  -nR(x_1\ln x_1 + x_2\ln x_2)$

Does this equation works only when the initial conditions of both compartments are at the same pressure?
If ideal gas 1 at initial conditions $n_1,P_1,V_1,T$ and ideal gas 2 at $n_2,P_2,V_2,T$ are mixed, which equation should I use to obtain $\Delta S_{mix}$ given that $P_1 ≠P_2$? Assume $V_1 + V_2 = V_{tot}$, and $T_1 = T_2 = T$.


texts: Will sodium sulfite effect the oxidization of toluene to benzoic acid with potassium permanganate?

texts:
I am trying to oxidize toluene to a mixed salt $\ce{K/Na}$ benzoate/ benzoic acid using the potassium permanganate method, but I am using OTC sourced $\ce{KMnO4}$ which has a significant amount of sodium sulfite contamination.

Will that hinder the reaction?  And is there a practical method for filtering said contaminants?


texts: Can hydrocarbon help to split molecular hydrogen into atoms?

texts:
I am a physicist and have the following chemistry problem.
When a sample is exposed to H2 (molecular hydrogen), a tiny amount of atomic hydrogen or, maybe, protons is generated. Extremely small amount but exceeding the thermally generated amount by many orders of magnitude. The origin can be traced to the ever existing surface contamination by hydrocarbons and water (monolayer). They somehow help to generate protons/atomic hydrogen on the surface.
Any tips?
Thanks,
Hengan

PS It can be H+ from adsorbed water, too, but why molecular hydrogen is then needed?

Sample: Graphite in a hydrogen atmosphere at room temperature. The graphite has probably some remnants of PMMA from processing plus it was exposed long enough to ambient atmosphere and, hence, adsorbed water and other ambient polymers (standard contamination layer of nanometer thickness).


texts: How appropriate/adaptable is HPLC for in situ sample analysis on Titan?

texts: I have a limited background in chemistry (nothing beyond general Chem 2), so I am asking for help with a group project. We have two chemists on our team, but communication is limited at the time and I am trying to answer some specific questions for myself so that we can move forward. We're designing a probe to study the chemical composition of Titan's lakes and sediment deposits in the lake beds, among other functions. We would like to adapt HPLC for the project using UV-Vis spectroscopy as the detection method. However, from what I understand, a UV-Vis spectrophotometer must be calibrated using all known solutes, which we can't know in this situation. I read that when the detector is showing a peak, some of what is passing through the detector can be diverted to a mass spectrometer and the fragmentation pattern can be used to identify unknown compounds, which is what we would like to do. However, I'm not sure how this would work or whether it would be wise given the constraints of our project. Our motivation for adopting HPLC is that we can keep all substances in their original phase for analysis. But if I'm not mistaken, mass spectrometry will require vaporization. My question then is, is there a way to use HPLC to identify unknown compounds suspended in the lake without disturbing the state of the sample? Any advice would be appreciated.


texts: Is peroxoborate and perborate the same thing?

texts:
Recently I came across the following question:-

  Preparation of Sodium Peroxoborate- Equations

The term peroxoborate came from the fact that it has the peroxo bond $\ce{-O-O}-$. So, it should be strictly called peroxoborate. But some books says  peroxoborate while other books say perborate. Is it true?

I googled sodium perborate.  Wikipedia recognizes the compound as sodium perborate. Then, I googled sodium peroxoborate, the following message appear:-

So, is peroxoborate and perborate the same thing? If so, why some book says  peroxoborate while othe books perborate? It should be strictly called peroxoborate since it contains the peroxo bond $\ce{-O-O}-$.

Update

This is what written in Weller, M.; Overton, T.; Rourke, J.; Armstrong, F. Inorganic Chemistry, 6th ed:-

  Sodium perborate is used as a bleach  in laundry powder, automatic dishwasher powders, and whitening toothpastes. Although the formula is given as $\ce{NaBO3.H2O}$ or $\ce{NaBO3.4H2O}$, the compound contains th peroxide anion, $\ce{O2^{2-}}$ and is more accurately given by $\ce{Na2[B2(O2)2(OH)4].6H2O}$.

But this is what written in Lee, J.D. Inorganic chemistry

  $$\ce{2NaBO2 + 2H2O2 + 6H2O -> Na2[B2(O2)2(OH)4].6H2O }$$
  Sodium peroxoborate is used as a brightener in washing powder. It is compatible with enzymes which are added to some biological powders.

So, what is the correct name:- sodium perborate or sodium peroxoborate?


texts: What are the g-block's predicted properties?

texts:
I have been researching for a Physics/Chemistry exam and thought; what will the future periods in the periodic table (periods 8 and above) would entail? Each block contains its own properties that allow for accurate predictions of elements in these blocks. Each block has very unique properties and benefits society in major ways. The g-block is the theoretical block thought to exist in period-8 though no elements have been produced in this period for any sustained time. My question is:

What are the predicted properties of the G-block if any?  Who and what methods have they been predicted by?

I'd also like to know if there are any ways of "stabilizing" these elements so that they take more time to decay.


texts: How do you find the heat capacity ratio of combustion products?

texts: For example, if gaseous oxygen $(O_2)$ and paraffin wax $(C_{32}H_{66})$ were to stoichiometrically combust at STP, how would one go about finding the heat capacity ratio ($\gamma={c_p \over c_v}$) of the resulting mixture of gases? I'm guessing that it involves finding the adiabatic flame temperature? (but idk how lol)


texts: Would it be possible to create a (non-toxic) alcoholic drink that, when zapped with laser, changes color?

texts:
Would it be possible to create a (non-toxic) alcoholic drink that, when zapped with a 0.5mW laser pointer, changes color?

This would be mainly for the visual effects (bartender show) so it should not require aiming the laser at the drink for more than a few seconds. The reason for choosing a 0.5mW laser is to minimize the need for eye protection.

It would not matter what color laser is used, but would this be possible?

If it is possible, what kind of chemical(s) would be needed in the drink?


texts: How do I identify how many reactions are occurring when precipitating a mixture?

texts:
An example of a question is:

  After dissolving $x$ grams of a mixture of $\ce{Na2SO4}$ and $\ce{NaCl}$ in water, you add an excess of $\ce{BaCl2}$ solution. You filter off the precipitate which forms, dry it, and find that it weighs $y$ grams. What is the percent by mass of $\ce{Na2SO4}$ in the original mixture?"

If I am correct, the reaction for this would be:
$$\ce{BaCl2 + Na2SO4 + NaCl -> BaSO4 + 3NaCl}$$

However, there are some questions which are of the same format but have two separate reactions:

  A $x$ gram mixture of $\ce{CaCl2}$ and $\ce{RbCl}$ is dissolved in water. Addition of $\ce{AgNO3}$ causes the chloride ion to precipitate as $\ce{AgCl}$. The mass of $\ce{AgCl}$ collected is $y$. What is the percent by mass of $\ce{RbCl}$ in the original mixture?

For this one, would the reaction be two equations?

\begin{align}
\ce{CaCl2 + AgNO3 &-> Ca(NO3)2 + 2AgCl}\\
\ce{RbCl + AgNO3 &-> RbNO3 + AgCl}
\end{align}

I know how to do these types of questions past the point of deciding whether or not there are two equations. I just don't understand why I couldn't write that last one as a single equation, in the same way as I did the first example. Could anybody help me? Thanks in advance.


texts: Mechanism of formation of 2-naphthol red dye (aka Sudan 1)

texts:
As you can see in the image diazonium can attack at 2 different positions to form different products then why only the first product is correct?
As there are two ortho positions available why does it attack only one?

I tried to draw the intermediates see if they are useful and correct

is it because there are 7 intermediates in the first case?
or steric factors play some role here?


texts: Exceptions to the Nitrogen Rule in mass spectrometry

texts:
The Nitrogen Rule in mass spectrometry states that (organic) molecules containing no or an even number of nitrogen atoms will have even masses, and molecules containing an odd number of nitrogen atoms will have odd masses.

Examples (all monoisotopic masses):
No nitrogen, even mass:
H2, 2 Da
HBr, 80 Da
C2H6, 30 Da
One nitrogen, odd mass:
NH3, 17 Da
C5H5N, 79 Da
 etc.

Often there is a little disclaimer saying that the nitrogen rule is only valid for molecules that do not contain "exotic atoms." What are some examples for molecules do not follow the nitrogen rule?


texts: Air contains 20 % O2 by volume. How many cm³ of air will be required for oxidation of 100 cm³ of acetylene?

texts:
Air contains 20 % $\ce{O2}$ by volume. How many cm³ of air will be required
for oxidation of 100 cm³ of acetylene?
(a) 1064 cm³
(b) 212.8 cm³
(c) 500 cm³
(d) 1250 cm³

Answer: (d)
My solution:
Equation: $\ce{2C2H2  +5O2 -> 4CO2 +2H2O}$
From stoichiometric calculations:

2 moles of $\ce{C2H2}$ will react with 5 moles of oxygen
1 $\ce{C2H5} \rightarrow $ 5/2 moles of $\ce{O2}$
$\pu{22.4L}$ $\ce{C2H2} \rightarrow 5/2\times \pu{22.4L}$ of $\ce{O2}$
1 volume of air $\rightarrow$ 0.2 (20/100) volume of oxygen

Now the only thing I don’t know is how to convert the volume into liters so that I can find the correct answer.


texts: Only valence shell electrons participate in bonding then how is Cr in H2CrO4 forming 6 covalent bonds although it has only 1 valence electron?

texts:
The structure of $\ce{H2CrO4}$ is as follows:

Shell configuration of chromium is 2,8,13,1 i.e. it has only 1 valence electron and only valence electron participate in bonding but Chromium in the above structure is forming 6 covalent bonds i.e. it is sharing 6 electrons. How's that possible ? How can it share 6 electrons when it only has 1 valence electron.

The same is the case for $\ce{Mn}$ in $\ce{H2MnO4}$ where it has only 2 valence electrons but is forming 6 covalent bonds and for $\ce{Mo}$ in $\ce{H2MoO4}$ where it has only 1 valence electron but forming 6 covalent bonds.


texts: Molecular Orbitals of Hydrogen Fluoride (HF)

texts:
This source states that the three s-orbitals of hydrogen and fluorine interact to form three new molecular orbitals, while other sources say that the 2s orbital is non-bonding.

Which one is more correct? Also, if they indeed form three new molecular orbitals, how do they look like?


texts: How many electric vehicles can our current supply of lithium power?

texts:
This Reddit comment contends

There was 870 tons of lithium mined in 2019 in the US. That enough for under 20,000 cars, assuming you're using ~50 kg per car. So that would be 40,000 in 2023, assuming all of it is used in cars. In reality only a fraction is; most is used in consumer electronics etc.

The global car production is about 100,000,000 per year, meaning you'd need like 5,000,000 tons of lithium just for cars. Current WORLD production is 77,000 tons, although there's a large reserve.

Proliferation of electric cars is, as far as I can see, completely dependent on a large step forward in battery tech.

What exactly does there's a large reserve entail? How much Li does the "large reserve" contain?

Are these calculations correct?


texts: Why does HCl both precipitate and dissolve Silver?

texts: Adding $\ce{HCl}$ to silver nitrate solution causes silver chloride to precipitate. Adding more $\ce{HCl}$ causes the silver to re-dissolve. What is happening to the silver chloride when it re-dissolves?


texts: On the addition of HCl to a conjugated diene

texts: Is this allylic chloride formed by an ionic or radical mechanism? Is it the more stable isomer?


texts: Is the Haber Process here proceeding at positive Gibbs free energy change?

texts:
$\ce{3H2 + N2 -> 2NH3}$ is the forward reaction used in the Haber process, the industrial production of ammonia. After studying Gibbs energy and how it is just another way of saying that the 2nd law of thermodynamics is obeyed if $\Delta G < 0$, I decided to apply it to some common reactions that I know, just to confirm that my understanding of the topic is correct.

When applying it to the Haber process forward reaction, I worked out change in entropy to be $\pu{-199
J K^{-1} mol^{-1}}$. The enthalpy change for the forward reaction is exothermic and has a value of $\pu{-92 kJ mol^{-1}}$. Looking up common reaction conditions for the Haber process, I found that a compromise temperature of $\pu{650K}$ is used.

Applying this to the Gibbs energy equation $-92 - 650(-199/1000)$, I calculated a positive change in Gibbs energy for the reaction of which had a value of $\pu{37.35 kJ mol^{-1}}$.

As a result of this, I am now quite confused as to how the forward reaction can be allowed to proceed by the 2nd law of thermodynamics at a temperature of $\pu{650K}$, and I was wondering where my understanding of the Gibbs energy and thermodynamics falls short. I need help to explain the pitfalls in my calculations, understanding or even whether there is another factor that I am not considering.


texts: Are precipitations exothermic and/or endothermic?

texts: Should be an easy one. I'm fumbling a concept. I've read precipitations are exothermic. Is this accurate? Why would there be no endothermic precipitation reactions?


texts:
I have bought a set of polypropylene (PP) test tubes that I wish to paint with acrylic to achieve the same effect as the following image:

Can anyone recommend a process I can apply to the test tubes (in a home setting) or type of paint (acrylic not necessary) that will bind and last and allow me to achieve a similar effect as is pictured above. My main worry is that it may bind but a year or two later will begin to flake off.

Any primer must be completely transparent.

Apologies if this is not the typical question asked here I initially posted this in arts and crafts but then realised this is less about art than it is to do with the properties of polypropylene and someone here is likely to have a greater expertise in that area.

EDIT: As far as I am aware the reason acrylics don't bond well to PP is due to the low surface energy (LSE) of PP. I have found some products that purport to raise the surface energy of PP to be used with adhesives but before I go ahead and purchase them I would love for someone with more knowledge to confirm that this is likely to work. For example:

Techsil® Clear Cyanoacrylate Primer 77 or LOCTITE® 770™


texts: When is a dipole-dipole interaction strongest?

texts: Are there any conditions that'll improve the interaction? Just like, I assume, hydrogen bonds are strongest when the difference in electronegativity is biggest.


texts: How to use zinc sulfide to produce hydrogen (via photolysis)

texts: According to wikipedia, zinc sulfide added to water and then brought into the presence of (sun?) light will split the water into hydrogen and oxygen. Is this practical (for demonstration purposes) and are any other materials/apparatus needed? I cannot seem to find much useful information which answers this question elsewhere.


texts: What does "atoms make no compromises" mean?

texts:
I was watching The Ring of Truth - 5 Atoms and in the last part of the movie (the link starts at this part), Dr. Morrison said

  "When it comes to energy, atoms make no compromises. It is all or nothing for them." - Dr. Philip Morrison (MIT)

What does this quote mean? Why can't atoms make compromises in Energy? When he says it is all or nothing for them, does that just mean that atoms can only absorb certain energy levels?

Please help me as I'm a very confused Chemistry student who is even more confused after watching a video my teacher told me would help me understand atoms better.


texts: How did Joseph Priestly discover carbon monoxide?

texts:
In my readings about the history of chemistry, I've come across the story of the incredible chemist and scientist Joseph Priestly. My question is just about one of his discoveries - the discovery of carbon monoxide.
Several places make mention of Priestly's discovery of carbon monoxide. However the best I can find is some vague language, like

There Priestley continued his research, isolating carbon monoxide
(which he called "heavy inflammable air") and founding the Unitarian
Church in the United States.

... but without a shred of detail!
I am wondering, can anyone provide some insight as to how Priestly went about doing this?
Where can I find some literature about his experiments and thought process?


texts:
Concerning alcohol dehydration, I get that it's E1 in secondary and tertiary alcohols, that it's E2 in primary alcohols, and also why E1 reaction is easier for tertiary alcohols as compared to secondary ones.
Why is the ease of dehydration for primary alcohols less than both of these? It would have been obvious it was reacting through E1, but it's doing E2, which is favourable for primary alcohols.
Why then, is it harder to dehydrate primary alcohols than either of the other two?


texts: Writing a system of differential equations with the given arbitrary reactions

texts:
We have the following elementary reactions:
\begin{align}
&\overset{k_1}{\longrightarrow}A\overset{k_2}{\longrightarrow}{B+C}\\
&C \overset{k_4}{\longrightarrow} 2D \overset{k_5}{\longrightarrow}{C}\\
&B \overset{k_3}{\longrightarrow}\\
&D \overset{k_6}{\longrightarrow}
\end{align}
Let $\alpha(t), \beta(t), \gamma(t), \delta(t)$ denote the concentrations of $A, B, C, D$, respectively.
\begin{align}
\frac{\mathrm d}{\mathrm dt}\alpha(t) &= k_1 - k_2\alpha(t)\\[3pt]
\frac{\mathrm d}{\mathrm dt}\beta(t) &= k_2\alpha(t) - k_3\beta(t)\\[3pt]
\frac{\mathrm d}{\mathrm dt}\bigl(2\delta(t)\bigr) = 2\frac{\mathrm d}{\mathrm dt}\delta(t) &= k_4\gamma(t)-k_6\delta(t)^2 \quad \text{or} \quad \frac{\mathrm d}{\mathrm dt}\delta(t) = \frac{k_4}{2}\gamma(t) - \frac{k_6}{2}\delta(t)^2\\[3pt]
\frac{\mathrm d}{\mathrm dt}\gamma(t) &= k_5\delta(t)^2 - k_4\gamma(t) + k_2\alpha(t)\\
\end{align}
Is my systems of equations correct?


texts: Determining relative changes in a generic reaction

texts:
I'm an electrical engineer by trade and I am trying to solve a problem I found in some old course notes.

Given is a reversible, homogeneous reaction:

$\ce{ A + 2B <=> C + 3D }$

A  solution of 0.2 moles of A and a solution of 0.3 moles B are added together. The solution is lengthened until 1.0 liters. At equilibrium, 0.05 moles of C is formed. The question is to determine the equilibrium concentration of D.

How should the 'relative changes' look like? I think it's:

$-x$ for A
$-2x$ for B
$+x$ for C
$+3x$ for D


texts: Does the priority go for the longer substituent, the closer one, or one which contains a pi-bond in naming Alkenes and Alkynes?

texts:
According to the new IUPAC nomenclature, the longest chain is given the priority over that which contains the most number of double bonds.

In naming this alkene:

From which end would we start numbering? Because of what substituent?


texts: Pt[BrCl(PR₃)₂] cis, trans isomer nmr - Which is cis and which is trans?

texts:
the question is,
The two square planar isomers of $\ce{Pt[BrCl(PR_{3})2]}$ have a different $\ce{^{31}P}$-nmr spectra. One shows single group of lines, the other shows two distinct resonances, each one being similar to the single resonance region of the first one. Which isomer is cis and which is trans?
Thanks.


texts: Any suggestions for a highly exothermic reaction in liquid phase but the reactants and products must be pH neutral?

texts: Need a heat producing reaction for my lab experiment.


texts: How exactly does a battery work (specifically Pb/H2SO4/H2SO4/PbO2 lead acid battery)?

texts:
Specifically talking about the lead-acid battery, I understand (or think I understand) this much:
The anode, in the presence of the electrolyte, $\ce{H2SO4}$ will be oxidised:
$$\ce{Pb (s) + SO4^2- (aq) -> PbSO4 (s) + 2e-}$$

At the same time at the $\ce{PbO2}$ electrode, two electrons from the $\ce{PbO2}$ solid are lost to the electrolyte:
$$\ce{PbO2 (s) + 2e- + 4H+ (aq) + SO4^2-(aq) -> PbSO4 (s) + 2H2O}$$

This all occurs without a solid conductive path (say a wire) between the anode and cathode, the cathode will build a positive charge while the anode builds a negative charge and ions will diffuse appropriately during this process.

When a wire is connected between the anode and cathode, electrons that have built up on the surface of the $\ce{Pb}$ will migrate to the $\ce{PbO2}$ which is of lower potential and if a load is placed along the way work can be done.
So batteries will discharge by themselves without even contributing to any work? Is this not true for all batteries?

The part that confuses me is that most people say that batteries store chemical energy.

I understand that the redox reactions release energy which can be used as electrical energy but if batteries discharge without contributing to any meaningful work then why are they still considered to be storing energy? Aren't they converting chemical energy to heat continually unless they are put to use?


texts: Why does nitration of N,N-dimethylaniline occur at the meta position?

texts: The nitration of N,N-dimethylaniline with $\ce{H2SO4}$ and $\ce{HNO3}$ gives mainly the meta product, even though $\ce{-NMe2}$ is an ortho,para-directing group. Why is this so?


texts: What is the meaning of electrode potential?

texts:
When we say that the electrode potential for $\ce{Co}^2$$^+$/$\ce{Co}$ is -0.28 V and $\ce{Cu}^2$$^+$/$\ce{Cu}$ +0.337 V, what is the physical meaning?

Can you conceptually explain when two electrons react with $\ce{Cu}^2$ or $\ce{Co}^2$to form the metal, what happens and what is the source of these different potentials?


texts: Can luciferin + ATP → luciferyl adenylate + PPi be reversed?

texts:
Reading about the light emitting reaction of luciferin + ATP, catalysed by luciferase I am confused about the following.

On this webpage the partial formula is written as:

luciferin + ATP → luciferyl adenylate + PPi

which seems to me like a one way reaction.

But on searching on Google "luciferase ATP equilibrium" I found websites like this one and this one which seem to indicate that the reaction is reversible, as there is an equilibrium.

Is it possible for this reaction to take place in reverse? And what about the link on books.google.nl showing a reversible reaction with light involved? What about that?

Thank you for clarifying.

EDIT 2014-02-25:
This article: "Kinetics of inhibition of firefly luciferase by dehydroluciferyl-coenzyme A, dehydroluciferin and L-luciferin" by Luis Pinto da Silva etc (Link) shows the following reactions:

Where Luc is firefly luciferase, LH2 is luciferin, L-CoA is dehydroluciferyl-coenzyme A, L is dehydroluciferin, ATP is Adenosine triphosphate, AMP is  adenosine-5`-monophosphate, PPi is inorganic pyrophosphate, O2 is oxygen, CO2 is carbondioxide.

Looking at the last equation, it seems it is possible to form ATP as a product, as it is on the right side of the arrow. Remarkable, I would say. still I do not see any luciferin (LH2) on the right side of any equation, so the answer to question of this topic remains no thus far.


texts: Significance of shapes of Conical flask and Kjeldahl flask

texts: What is the practical significance of the shapes of conical flask and Kjeldahl flask?


texts:
I was asked to find the hypothetical $\Delta H$ and $\Delta S$ of the decomposition of sodium carbonate and then asked to explain why it doesn't decompose.

I calculated the enthalpy and entropy change and from that I calculated the Gibbs free energy change. I was hoping to get a positive answer, but actually I got a negative answer, indicating that the process is actually spontaneous.

So is the reason that sodium carbonate doesn't decompose due to its kinetic properties, i.e. the reaction is too slow?


texts:
Workfunction is the minimum energy required to remove an electron from the surface of the material. If the striking photons does not have the required energy then it won't be able to eject the electron even though many photons can be striking the surface i.e. many low energy photons cannot be combined to get the required energy. In contrast to this many particles can combine to break a bond. Silicon for example has bond energy of 1.1eV, with an average energy of 0.026eV 42 (1.1/0.062) particles would be required to break the bond and set the electron free. Why is it that a similar thing not happen with photons?. If many photons strike the the surface than all their energy should add up and remove the electron

EDIT
I am watching lectures on Youtube on Chemistry and Semiconductor devices. In this lecture at 4:45 the instructor talks about workfunction. And in this lecture at 42:00 the instructor talks about the number of particles required to break a bond


texts: Opposite effects of Le Chatelier's Principle

texts:
How does Le Chatelier's Principle deal with a change in reaction conditions which can simultaneously effect the equilibrium in opposite ways.
For example, here's the equation for the conversion of $\ce{N2}$ and $\ce{H2}$ into $\ce{NH3}$. It's an exothermic reaction, so I've added heat as a product on the right side.

$$\ce{N2(g) + 3H2(g) <=> 2NH3(g) +\text{heat}}$$

If I increase the temperature (add heat) that would tend to push the reaction to the left because the reaction to the right is an exothermic reaction. But if I add heat (and the volume remains constant), then I'm also increasing the pressure, which should tend to push the reaction to the right, towards fewer moles of gaseous products.
Is there a simple explanation for how Le Chatelier's Principle works in such a situation?


texts: Mechanics behind auto-ignition temperature

texts:
I have some questions about the auto-ignition temperature for fuels. Per ASTM E659:

  AIT (auto-ignition temperature) is the lowest temperature at which the substance will produce hot-flame ignition in air at atmospheric pressure without the aid of an external energy source such as spark or flame. It is the lowest temperature to which a combustible mixture must be raised so that the rate of heat evolved by the exothermic oxidation reaction will overbalance the rate at which heat is lost to the surroundings and cause ignition.

The last sentence seems to say that AIT is the temperature where enough of the particles are above the activation energy such that enough heat released goes to perpetuate the remaining fuel to combust (cause ignition). Is this correct?
Per ASTM E659, ignition is subjectively defined as the appearance of a flame with a sharp rise in temperature. Why it necessary that we observe the appearance of a flame (in other words, can we have combustion without an observed flame)?
Is there an assumption of thermal equilibrium between fuel and oxidizer when defining AIT? The testing method above says air at predetermined temperature will be used, but I'm not sure how they plan to control air temperature when heating begins.


texts: Why is the cathode of a lithium-ion battery metallic, which is the opposite of most other batteries?

texts:
In most types of batteries, primary and secondary, the metallic electrode is the anode, and a non-metal acts as cathode.  Or a pure metal is the anode, and the cathode is a metal oxide.

Why is the opposite true in a lithium-ion battery?


texts: Why can't Carbon Dioxide be liquid at 1 atm?

texts:
Wikipedia says that Carbon Dioxide cannot be liquid under atmospheric pressure.

I thought the phase of an element was related to both pressure and temperature.

If that is so, then should you not be able to set the temperature conditions such that you could have a cup of liquid Carbon Dioxide?


texts: Thermodynamics of photochemical reactions

texts:
Suppose I have a photochemical reaction in gas phase, such as
$$
\ce{CO2 + {$h\nu$} -> CO + O}.
$$
I would like to work through the thermodynamics of such a reaction and understand the meaning of every term.

For a non-photochemical reaction, such as $\ce{CO + O -> CO2}$, I have a good understanding of how the change in Gibbs energy breaks down into enthalpy, internal entropy and a log-concentration term corresponding to the entropy of mixing. If I ignore the photon in the first reaction above, I can regard it as simply the reverse of this reaction, which due to its photochemical driving force is able to reduce the Gibbs energy by the same amount, $\Delta G$. All of this is unproblematic.

However, $h\nu$ itself is an energy change, which I can calculate, assuming I know the frequency $\nu$ of the absorbed light. I would like to know how to think about the thermodynamics of the whole system, including the coupling of the chemistry to the radiation field. In particular, my questions are:

How does the energy $h\nu$ relate to the other terms with energy units, such as $\Delta H$ and $\Delta G^0$?
I know that while a single photon has no internal entropy, a beam of light of a particular frequency can be thought of as having a temperature and an entropy. How should I think about the role of radiation entropy in the thermodynamics of photochemistry, and in particular, how can I do second-law calculations for photochemical reactions?


texts: Substitution of a cyclic diether by a halogen

texts: I’m in an organic synthesis class and I have to draw a mechanism for the reaction in the picture. At first I thought it was just forming a free radical but I haven’t been able to find any way to do that without UV light, which isn’t shown anywhere in the given reaction. How do I go about solving this?


texts: Why is boiling point of Ammonia greater than Arsine?

texts:
I have previously read that the boiling point of Stibane(SbH3) is greater than Ammonia(NH3) as ammonia is gas at room temperature and no hydrogen bonding exists in the gaseous form of NH3.
Hence, as SbH3 is greater in size, has greater molecular weight; its boiling pint is higher than NH3.
why does Stibane have a higher boiling point than Ammonia
In the case, of AsH3, even this molecule is gas at room temperature and its boiling point should be greater than NH3, but this is not the case and NH3 has a higher boiling point than AsH3.
I want to know what is the reason behind this trend. (NH3 having a higher boiling point than AsH3)


texts: Pyridinium chlorochromate (PCC) in $\ce{CH2Cl2}$ can be used to oxidise primary alcohols only to aldehydes. I can't however, find any reference of it oxidising methanol (which is strictly speaking not a primary alcohol). My question is, does PCC oxidise methanol to formaldehyde and if not, what can I use to achieve this reaction?


texts: What are some factors that influence the voltage of voltaic/galvanic cells and why?

texts:
Question: (2014 USNCO local exam Q#41):

  What types of changes would increase the voltage of a voltaic cell.

I have learned a bit about voltaic cells, but I haven't been able to find information about this anywhere.

What I know about voltaic cells is that to calculate voltage, you would need to know the standard reduction potential for the half reaction. Then, by adding the E(reduction) and E(oxidation) together, you would get the E(cell). The only way I can think of to change the voltage is by changing the reaction itself, or to change the standard conditions (temperature?). Electrons also flow from anode to cathode, so if more electrons are flowing across does that mean there's a greater voltage? I need help figuring this out.


texts: Composition difference between #2 and #2D fuel oil

texts:
I have read that #2 and #2D fuel oil are essentially the same, but the #2D might have less sulfur. I have read others that say that #2 has a higher cloud point, so if that is true, then there are some differences.

I tried burning #2D in my furnace and it generated a noticeable oil fume in the house compared to #2 which generates no fumes. Why would #2D be generating oily fumes if it is cleaner?


texts: Flammable lighter than air gases (safeish)

texts:
I'm an artist currently using propane and butane in my show where I put the gas into a soap bubble and light it to produce a nice flame.

But I'd like to start working with a lighter than air flammable gas, that's relatively easy to get hold of, and as safe as it possibly can be.

The propane/butane I use comes in small canisters and the biggest risk, as I see it, is forgetting to close the tap.

Any ideas?


texts: Impact of Pressure on equilibrium of Tin allotropes

texts:
The pressure at the bottom of the Mariana Trench in the Pacific Ocean is $1090$ bar. What temperature will the two allotropes of tin be at equilibrium? Assume that the molar volume, energy, and entropy change does not vary with temperature.
Relevant data: Density of white tin: $7.287$ g/mL; Density of grey tin: $5.766$ g/mL
At $1$ bar: The enthalpy change from white tin to grey tin is $-2.016$ kJ/mol and the entropy change is $-7.04$ J/mol K.

My attempt: Since the two species are in equilibrium, I thought first to use the Clausius Clapeyron equation. Assuming that the molar volume is independent with temperature, I calculated the molar volume change to be $4.26\cdot 10^{-6} \frac{\pu{m^3}}{\pu{mol}}$ from white tin to grey tin. Now, I substituted these values into the equation to find that $$\frac{dP}{dT}=\frac{\Delta S}{T\Delta V} =-\frac{1.6\cdot 10^7}{T}$$
upon integration, I find that $$P-P^\circ = 1.6\cdot 10^7 \ln(\frac {T^\circ}{T}).$$
Substituting the temperature of equilibrium at one bar from the data given I find that the temperature is $286.4 \pu{ K},$ thus $T^\circ = 286.4\pu{K}$ and $P^\circ = 10^5\pu{Pa}.$ Thus at $P = 1090\cdot 10^5\pu{Pa},$ $T = 0.317\pu{K}.$ However, the temperature given in the answer is much higher ($220.35$ K).  The given answer was derived from a completely different method not involving the Clausius Clapeyron equation.
Hence I have the following question:
Question: Why is it not valid to use the Clausius Clapeyron equation in this scenario? (Or did I make a mistake in my derivation that caused my values to be off?)


texts: Activation energy of chlorine trifluoride and hydrazine

texts:
Chlorine trifluoride was once tested in a rocket engine as an oxidizer for hydrazine. I am looking to simulate in software a rocket engine using this propellent combination. Activation energy is one of the inputs to the simulation software.

What is the activation energy of a chlorine trifluoride and hydrazine reaction?

$\ce{3 N2H4 + 4 ClF3 -> 3 N2 + 12 HF + 2Cl2}$

Is there a online chemistry source or book which might contain this value? If it has not been measured is there a way to calculate this value based on the properties of the chemicals involved? How to get the value is less important than a number I can enter into a text file.

Searching for papers on the subject mostly results in unrelated chemistry homework examples. The closest thing thing I found to an answer was looking up chemicals in the National Institute of Standards and Technology (NIST) Chemical Reactions Database. The database includes data for hydrazine reactions and chlorine trifluoride reactions separately, but not with each other.

$\ce{ClF3 -> *F + ClF2}$ reaction has $E_a = 118 \frac{kJ}{mol}$. Is it reasonable to assume this might be the first step if it is a radical reaction?


texts: What are some problems that arise from using LCAO (Linear Combination of Atomic Orbitals)?


texts: While reading my book everywhere I found that 99.9% pure metal is obtained. Is it possible by any process that we get 100% pure metal on industrial level?


texts: Why is cyclooctatetraene non planar but the cyclooctatetraenide anion planar?

texts:
I was reading some organometallics and I came upon the preparation of uranocene, $\ce{U(C8H8)2}$. It has two cyclooctatetraenide anions, $\ce{C8H8^2-}$, as ligands, with a uranium atom between them.

It was mentioned that the neutral cyclooctatetraene molecule $\ce{C8H8}$ is non aromatic and has a tub-shaped conformation, but the dianion $\ce{C8H8^2-}$ is planar but aromatic. Why is this so? Can fulfilling Hückel's rule force a cyclic molecule to become planar?


texts: Confusion about the charge of electrons while orbiting through bohr's energy shells

texts:
I came across the following part in my text book. Bohr's atomic theory explained the stability of an atom by the idea of energy shells. He said that while orbiting the nucleus through a particular orbit or energy shell the energy of electrons neither increases nor decreases. The electron does not carry energies while orbiting. The shells are charged and the energy of electrons orbiting through the shell equals to the energy of the shell and as the shells are stable therefore the energy of electrons are also stable . Now, the energy increases from shell to shell like(K,L,M,N,O,P,Q)[ascending order]. So,the energy of an electron in K shell should be less than that of an electron in Q shell. But we know that the energy of an electron is constant and is equal to (4.8*10^-10) esu. Then how can this is possible that an electron with a certain energy does not carry any energy while orbiting and it gains the same energy of its orbit while orbiting?
Note that there may be some mistakes in my informations as there may be many false informations printed in my book but still I am curious about the question. Thank you!


texts:
Here's a challenge problem I created! None of my students could get it; can you?

$25$ grams of table salt (NaCl) is dissolved in $150$ grams of water. The temperature of the solution is raised to its boiling point until sodium chloride begins to precipitate.

How much water has boiled off when precipitation begins? Also, what would be the temperature of the boiling solution when precipitation begins?


texts: Can absolute enthalpy values be used to determine reaction enthalpy?

texts:
Our teacher added this question to an exam, and there was a huge disagreement with my classmates and teacher about the correct answer. One side favoured answer 2, the other side favoured answer 4 being the false statement.

I personally selected answer 4, as it did contradict with the other 3: option 1 has $\Delta H < 0$, option 2 has $\Delta H = H_\mathrm{f} -H_\mathrm{i} = \pu{-500kJ}$ and option 3 has $\Delta H = \pu{-500 kJ}$,  so option  4 contradicts the above. However I would like to hear your thoughts.

  Which of the following options that refer to the enthalpy of a specific chemical reaction is not correct?

  $H_\mathrm{i} > H_\mathrm{f}$
  The enthalpy of the system has altered from the initial value of $\pu{1600 kJ}$ ($H_\mathrm{i}$) to the final value of $\pu{1100 kJ}$ ($H_\mathrm{f}$)
  $\Delta H = \pu{-500 kJ}$
  $\Delta H = \pu{500 kJ}$


texts: Does 12 amu really equal the mass of one carbon-12 atom?

texts:
As I was studying chemistry, I encountered atomic mass units (amu) and based on some calculations, I realized that some numbers don't work out.

Apparently, 12 amu is the mass of a single carbon-12 atom. However, the mass of the atom is (mainly) composed of six protons and six neutrons. Since both protons and neutrons weigh a tad more than 1 amu, how is this possible?

Furthermore, if it were true, that would convey that 1 amu is more than $1.661 \times 10^{-24}$ grams. It doesn't work out even without considering electrons. Did we get the numbers wrong, or the mass of an atom of C-12 more than 12 amu?


texts: Overlap between computer science and chemistry?

texts:
This isn't particularly a question about chemistry itself, but more-so the prospect of chemistry.

What kind of opportunities arise when you overlap chemistry and computer science? I'm a computer science major, but prior to going to university I had (and still have) a deep passion for chemistry. My highest marks were always in chemistry, but I decided to go down the compsci route because likewise it is a passion of mine. An opportunity has presented itself to double major in compsci and chemistry and I'm curious to know whether it's worth it.

My knowledge of chemistry is fairly barebones (a limitation of highschool education), but as I said, it was my strongest subject and for some reason it just clicks with me. I'd often spent sleepless nights perusing chemistry textbooks and online periodicals because it fascinates me to no end.

I'm not looking for greater job prospects (I already work in both compsci as a programmer and chemistry in an electronic cigarette company), I'm more-so looking for a more fulfilling pursuit of knowledge. While irrelevant, my university recently opened a new building dedicated primarily to chemistry, so facilities are recent and faculty is adept and education is modern. I'd very much like to take advantage of the opportunity, but I'm just unsure if a university-level chemistry program will scratch that itch for me.


texts: Why are so many different organophosphates able to deactivate acetylcholinesterase?

texts:
From sarin to tricresyl phosphate, there are organophosphates that are able to deactivate acetylcholinesterase.

What's so special about the simple organophosphate group that makes them able to do it?


texts: How does a hydrophobic environment help in bond formation?

texts:
The glucose-induced structural changes are significant in two respects. First, the environment around the glucose becomes more nonpolar, which favors reaction between the hydrophilic hydroxyl group of glucose and the terminal phosphoryl group of ATP.

I am unable to understand the chemistry behind this. How is a hydrophobic environment helping bond formation between two polar molecules?

Source: Biochemistry 8th edition by Jeremy M. Berg John L. Tymoczko Gregory J. Gatto, Jr. Lubert Stryer


texts: Differences between alkyl halides and alkyl tosylates

texts: What are the functional differences between alkyl halides alkyl tosylates? Both halides and tosylates are good leaving groups, yes. But is there chemistry that one will do and the other won't? Etc.? I'm not worried about their relative leaving group abilities. My prof treats the two as equivalent but I can't help but wonder if this is an oversimplification. Wikipedia doesn't point out any differences. The only difference I can think of is that an alkyl tosylate is an ester ... and this opens up the world of ester chemistry - i.e. hydrolysis with hot concentrated acid. Where as I can't see alkyl halides reacting in hot concentrated acid.


texts:
I was asked the following question in a myPAT take-home test,

  Find the maximum number of tripeptides can be synthesized by using three different amino acids.

Let those amino-acids (Z) be A, B, C.

So, taking three Z's at a time, we've only one set, ZZZ. So, total 3 tripeptides.

Next, we can take two same and one distinct (eg. AAZ),

For AAZ type, we've four sets, AAB, ABA, AAC, ACA. So, total 12 tripeptides.

Finally, take 3 distinct Z, for that we get total of 6 (i.e., 3!) tripeptides.

I am unsure if I've done it in a valid way, as answer given is 18. Where am I wrong?


texts: Loading nickel metal hydride battery for the first time

texts:
I just bought a new hair clipper and I was about to start shaving my head when I noticed that it was almost at 0%. It has a nickel metal hydride battery.
The manual says I have to load it for 24h hours before using it the first time or whenever it has been unused for a long time.

I started calculating. 24 hours are 1440 minutes. Dividing it by 100 makes it 14.4 minutes to gain 1%. To gain 20% it'll take 288 minutes (more than 4 hours).

Well I started to load it like an hour ago and it has almost 40% so far. That's not 4 hours. So it'll be at 100% in a few hours. I think in the evening it's done.

But the manual emphasized that it should be 24 hours ! So I wondered why do they want me to load it that long even when the percent-bar shows me it's fully loaded and ready to use? I also looked up some reviews where the customers wrote that the battery's lifetime is very short.

Would it cause a shorter battery-lifetime if I use it for like 10 up to 20 minutes in the evening (in about 6 hours)? Or more in general, is there something about the intrinsic chemistry of the battery which requires (in the most cases) so long before we use it the first time? Is that even necessary?


texts: What can we learn from the energies of molecular orbitals?

texts:
Molecular orbital theory is successful in calculating the structure of molecules (minimizing the total energy with respect to atomic positions). The solutions of an MO calculation are useful in deriving molecular properties such as dipole moment or vibration frequencies. These do not rely on energies of electrons in distinct orbitals, i.e. even though the theory is based on combining atomic orbitals to molecular orbitals, the somewhat arbitrary separation into orbitals is not used in these calculations.

On the other hand, many conceptual explanations of chemical properties and reactivity are based on orbital energies, such as HOMO-LUMO considerations, rationalization of electronic spectra, nucleophilicity etc. This answer suggests that the orbital energies of occupied orbitals are somewhat arbitrary and those of empty orbitals are almost meaningless. In the answer to a different question, there is a claim that you can apply orbital energies in just one way, and there is no guarantee how good the answer will be:

  Basically the only interesting quantity that you can get from an orbital energy is the first ionization energy based on Koopmans' theorem, which also is just approximately true.

So, what can you do with the orbital energies (either the numeric values or perhaps the ranking by energy)?


texts: How to calculate the rate of reaction of Sodium and Chlorine

texts:
$$\ce{2Na(s) + Cl2(g)   ->    2NaCl(s)}$$
How exactly do you calculate the reaction rate of the following equation?

Since reaction rate is usually calculated in moles per $\rm dm^3$ per second (M/s) and the reactants here are solid. I want to have a equation of $$R = K \times\ce{[Na]}^x\ce{[Cl]}^y$$


texts:
Can we use acid chloride in place of alkyl chloride in Gabriel Phthalamide Reaction?

Maybe it can be used as process to synthesize amides.


texts: Why does chewing gum get hardened after drinking water? This is a basic question, but please don't say temperature change, because I've tried that, and it never gets back to same elasticity. There must be some other chemistry at work. Even with lukewarm water or room temperature water it gets substantially harder.


texts: Why is the nomenclature glucose 6-phosphate, not 6-phosphateglucose?

texts: What exact nomenclature rule define the naming of glucose 6-phosphate?


texts: Describe the formation of the [PbCl4]2- complex ion

texts:
The $\ce{[PbCl4]^{2-}}$ complex ion is formed when $\ce{PbCl2}$ is exposed to excess $Cl^-$ ions in solution as explained here and here through the following reversible reaction:
$$\ce{PbCl2(s) + 2Cl^-(aq) <=> [PbCl4]^{2-}(aq)}$$
What I wish to understand is the mechanism behind this reaction. I managed to find the mechanism to a similar complex ion formation of $\ce{[CuCl4]^{2-}}$. It is explained here that $\ce{[CuCl4]^{2-}}$ is formed by the hybridisation of the $Cu^{2+}$ 4s and 4p orbitals:
$$sp^3:\boxed{\uparrow \ }\boxed{\uparrow \ }\boxed{\uparrow \ }\boxed{\uparrow \ }$$
Would the $\ce{[PbCl4]^{2-}}$ complex ion be obtained in a similar way by $Pb^{2+}$ forming the following hypridisation orbitals?
$$sp^3:\boxed{\uparrow \downarrow }\boxed{\uparrow \downarrow }\boxed{\uparrow \ }\boxed{\uparrow \ }$$
or no need for the above hybridisation since the 6s orbital was already filled and there is space in the empty 6p orbital so the configuration for the complex ion would be as follows?
$$6p:\boxed{\uparrow \downarrow}\boxed{\uparrow \ }\boxed{\uparrow \ }$$


texts: HCH bond angle in cyclopropane and cyclobutane

texts: I understand why the $\ce{CCC}$ bond angles in cyclobutane and cyclopropane are less than ideal $109.5^\circ$ due to the geometric restrictions they encounter in a cyclic structure. However, it is not clear to me how the $\ce{HCH}$ angles (which turn out to be greater than ideal) are affected by this constraint.


texts: Problems regarding Kc,Kp and rate of reaction

texts:
In our chemistry textbook, the equilibrium constant $K_c$ is derived this way:

$$\ce{aA + bB <=> cC + dD}$$

in this reaction, rate of forward reaction is $k_\mathrm f= k_1[A]^a[B]^b$

rate of backward reaction is $k_\mathrm b = k_2[C]^c[D]^d$

in equilibrium, equalizing the two rates we get
$$ K_c = \frac{k_1}{k_2}=\frac{[A]^a[B]^b}{[C]^c[D]^d}$$

Now, there is a problem... we know the $K_c$ depends on how we equalize the reaction... like we can write
$$\ce{H2 + 0.5O2 -> H2O}$$ or
$$\ce{2H2 + O2 -> 2H2O}$$, etc ways. But how the rate of reaction depends on the concentration? to what power?


texts: Increasing the length of a copper wire via electrolysis

texts:
I'm currently experimenting with copper coating using electrolysis. I'm using copper wire from my home, like the one you use for grounding. I want to electrolysis with longer copper wire (say 5 times the height of the container) to find out if the process will be shortened. My question here is about how I should arrange the wires in the container and if one arrangement has different effect than the other.

Here is what I have in mind:

all horizontal wires connecting to one vertical wire(this will be 5 separate pieces same length connected to the vertical wire)
bent like snake up and down (in one piece)

Do you think these two arrangements would work the same or differently?


texts:
I've gotten really into this subject lately from people who make their own cleaning agents and I was surprised how simplistic (although time consuming) everything was.

I am interested in making slaked lime. I've been putting wood ashes in my garden bed lately and it's been doing wonders but if I had a steady supply of home made lime that would do wonders.

I cook a lot on the weekends and I usually have a lot of bones left over. Some are cooked and some are uncooked. Could I use any to make quicklime with? I was trying to figure out a way to soften bones without leeching the calcium from them. I know I could use something more practical like egg shells but I have an abundance of bones lol

Thank you for any and all help.


texts: Why is the calomel electrode widely preferred despite its toxicity?

texts:
The following pagargraph is from the Wikipedia page of calomel:

  Mercurous chloride is employed extensively in electrochemistry, taking
  advantage of the ease of its oxidation and reduction reactions. [...] Over the past 50 years, it has been superseded by the
  silver/silver chloride (Ag/AgCl) electrode. Although the mercury
  electrodes have been widely abandoned due to the dangerous nature of
  mercury, many chemists believe they are still more accurate and are
  not dangerous as long as they are handled properly.

Yes, the calomel electrode is a breakthrough in electrochemical industry due to its ease of its oxidation and reduction reactions. But, the nature of mercury is such that every chemist fears it. There has been cases of mercury poisoning and deaths related to it. Despite its toxicity, electrochemist prefer the SCE
over the silver/silver cloride electrode. Why?

Due to its toxicity, the SCE has almost been replaced by the silver/silver chloride electrode. But still, the SCE is used as a reference electrode. Why? Why is the silver/silver chloride electrode not as good as the SCE?

Also, what are the safety measures/protocols undertaken by electrochemists while performing experiments using the calomel electrode?


texts: Why is p-methoxyphenol less acidic than phenol?

texts:
They have slightly different $\mathrm{p}K_\mathrm{a}$ values of 9.9 (phenol) vs 10.2 (p-methoxyphenol).
They both have the same number of resonance structures too.

My guess is that the resonance structure for p-methoxyphenol with the lone pair on the para carbon contributes less to the stabilisation of the negative charge since it's in an electron rich area (near the lone pairs of the methoxy group oxygen).

Is this a valid explanation? If not, what is the true reason?


texts: The instability of hydrated carbon dioxide or "carbonic acid"

texts:
Why is hydrated carbon dioxide - the predominant form of acid that one gets upon dissolution of carbon dioxide in solution - so unstable?

Is the below rationale valid?

Carbon in carbon dioxide has two (empty? no, but still vulnerable to attack) p-orbitals and bears a strong partial positive charge.
Oxygen's lone pair can attack an empty p-orbital and form a formal charge-separated complex with the carbon dioxide.
This is "hydrated" carbon dioxide or "carbonic acid." This form is extremely unstable and subject to disproportionation due to an unfavorable charge and the unfavorable nature of charge separation itself. The change in entropy also favors the products of disproportionation.
However, there exists a pathway to stability - that is - protonation of the oxygen with the negative formal charge by the oxygen bearing the positive formal charge.
This, however, is akin to a forbidden fruit; the ephemeral three-membered ring that would have to be formed exhibits "ring strain" (if you object to this term, can you please elaborate on your objection), and as a result, disproportionation is overwhelmingly favored, especially from an entropic standpoint (reconstitution of carbon dioxide gas is highly entropically favorable).


texts: How many gauche butane interactions are present in cis-1,2-dimethylcyclohexane?

texts:
We were asked to find out the number of Gauche-Butane interactions for this compound:

I proceeded by drawing the Newman Projection for this chair conformation as follows and marked the Gauche-Butane interactions (as shown by red curves):

They told me that I was almost correct and asked me to try once again but I can't find out where I probably went wrong.
Can someone guide me out in this regard?


texts: Why will a strong acid neutralize as much base as a weak acid?

texts: This is a simple concept that I can't seem to understand. Why will a strong acid neutralize as much base as a weak acid, if the acids are of the same volume and concentration? A strong acid will dissociate more in solution and thus have a greater number of $\ce{H^+}$ ions, as far as my understanding goes. The opposite if true for the weak base. So wouldn't the strong acid neutralize more base than the weak acid, because it has more $\ce{H^+}$ ions to neutralize the $\ce{OH^-}$ ions of the base with?


texts: Carboxylic acid bond lengths in 3-carboxycyclobutane-1-carboxylate

texts:
Select correct order of bond length of the above bond P, Q, R & S:
(A) P > R > S > Q
(B) Q > R = S > P
(C) S > Q > R > P
(D) None of these

I think the answer should be (D) because in this molecule, both carboxylic acid groups are equally acidic and the $\ce{H+}$ may migrate from one acid moiety to the other. This would be somewhat similar to the idea of resonance, although it isn't actually the same idea.
However, the given answer is (B) which we will get if this structure remains static. Because of the proton transfer, I don't think this can happen. Am I right or not?
Moreover, if we were to use some spectroscopic method to study the molecule, would we get an image in which the molecule has four equivalent bond lengths (due to proton transfer), or not?


texts:
I recently encountered two old publications on action of nitrogen iodide on various compounds (Ref.1 and Ref.2). Between them, Ref.1 described the idoform formation by methyl ketones upon treatment of the conditions:

  Ketones containing a methyl group react very readily with nitrogen iodide, iodoform, ammonia, an acid, and an amide being produced. In these reactions the methyl group appears first to be completely substituted by iodine, a tri-iodomethyl ketone being formed, which in presence of the ammonia simultaneously set free is hydrolysed to iodoform and an acid, a similar reaction between the substituted ketone and ammonia leading to the formation of iodoform and an amide.

The reactions were suggested as follows:
\begin{align}
\ce{RCOCH3 + NH3.NI3 &-> RCOCI3 + 2NH3}\\
\ce{RCOCI3 + H2O &-> RCO2H + CHI3}\\
\ce{RCOCI3 + NH3 &-> RCONH2 + CHI3}
\end{align}

This formation of idoform is understandable. Yet, Ref.2 claimed that the authors have obtained idoform from diethylketone (3-pentanone):

  Like the other ketones, diethylketone when treated with nitrogen iodide, yields the iodoketones, having very irritable odor. On effecting the interaction in a dilute solution, iodoform is formed in good quantity. It has been observed that as we rise higher and higher in the homologous series of the ketones, the tendency of the formation of iodoform gradually diminishes and the yields also gradually become less.

The reported method the authors had been used: $\pu{2 mL }$ of diethylketone are taken in a beaker and diluted with $\pu{150 mL }$ of weak ammonia. The mixture is warmed on the water bath, and to it, iodide solution is added when at first nitrogen iodide is precipitated, which is immediately taken up. The addition of iodine has to be continued, and finally a copious yellow crystalline precipitate deposits. This is iodoform. On recrystallization from alcohol, this has been obtained quite pure, melting at $\pu{119 ^{\circ}C}$. The yield amounts to $\pu{0.8 g }$.

I’m very curious about their claim and like to hear from your theory of mechanism.

Cited References:

F. D. Chattaway, R. R. Baxter, “CCX.—The Action of Nitrogen Iodide on Methyl Ketones,” J. Chem. Soc., Trans. 1913, 103, 1986–1988 (DOI: 10.1039/CT9130301986).
R.L. Datta, N. Prosad, “Halogenation. XVI. Iodination by Means of Nitrogen Iodide or by Means of Iodine in the Presence of Ammonia,” J. Am. Chem. Soc. 1917, 39(3), 441–456 (DOI: 10.1021/ja02248a013).


texts: How do transmembrane protein alpha helixes bind to the membrane?

texts:
I would post this in biology but as the question is biochemical in nature I decided this would be a more appropriate platform.

What I'm asking is how exactly does a transmembrane protein bind to the cell membrane? I realize that the transmembrane alpha helix is about 20 amino acids long with mostly hydrophobic amino acids as the inside of the membrane is hydrophobic.

What I don't realize is how exactly this alpha helix binds to the membrane and sticks to it? I've tried searching on the subject but I can't seem to find the answer. I found out that the alpha helix satisfies the hydrogen bonds internally leaving no polar R groups for the membrane as most groups are hydrophobic, but that only explains how it doesn't bind to the membrane.


texts: Isolating calcium acetate from water with electrolysis

texts:
That's a long page, so you can optionally jump to the "Thunderstorm it" part, but a bit of context is always neat :)

Context

Say I'm cooking an egg in vinegar. The egg shell is made of calcium carbonate:

$$\ce{CaCO3 + CH3COOH -> H2O + CO2 + Ca(CH3COO)2}$$

After eating the egg, is left in the cookware: a bit of calcium acetate, lots of water, acetic acid and other unidentified stuff.

It'd be neat to isolate that calcium acetate, as it could be of use sometime. I've seen that we can grow cool looking crystals out of it, maybe I could try that! Anyway chemistry is cool, so let's do it :)

But there will also be loads of water (egg cooking). I could store it all, but that wouldn't be very practical...

Getting rid of the water

I see three ways to get rid of that water.

Boil until water evaporates

Energy-hungry process. I'm a kind of environmental-crazy dude, so that's not an option.

Filtering

While boring, that could be an efficient option, if at all possible. It seems calcium acetate is soluble in water. Is there a way to filter it out without expensive equipment, or even at all?

Electrolysis

Energy-hungry as well, but I have a spare solar panel that produces 6 or 12V and anything between 0 and 4W, so that energy comes for free (albeit quite slowly in Belgium).

Thunderstorm it!

No matter how feasible are the other options, I'm here to experiment, so I'd love to do some electrolysis :) I got time anyway!

Constraints

I have very little knowledge of chemistry (but eager to learn!), and no equipment at all, except for household items. Also, this experiment would take place in living space (probably in my room), so it should be safe to do (e.g. do not produce chlorine gas or other nasty products). And if it's not smelly, it's even better :)

How I would do it

I'll need:

container: a drinking glass should suffice
anode
cathode
some electrolyte in the water
electricity: the solar panel will provide what's needed
time: we all have a pool of that in our life

I still need the anode, cathode and electrolyte. And also, I'd love to understand the process that takes place.

In my younger age, I used copper wire as both anode and cathode, table salt as electrolyte, and it would produce tiny bubbles on one end of the wire, and go green on the other end (do I remember properly?).

In this experiment though, the context is a little different:

I need to "dissolve" a lot of water, so just a copper wire won't be enough
It seems that using NaCl as electrolyte produces chlorine gas instead of oxygen, that's pretty bad

Choosing the electrolyte

Since I cooked the egg in vinegar, I'll probably have some acetic acid left in the water. Would that be a good enough electrolyte? Alternatively, I have baking soda readily available, but that would produce other salts when reacting with the remaining acetic acid...

Choosing the anode and cathode

I'm lost here. First and foremost, I remember my copper wire going green when doing electrolysis. Does that mean I'll "consume" my anode/cathode while doing the electrolysis? That sounds pretty expensive. Also, I'll have to separate calcium acetate from copper oxyde afterwards...

Questions

is the above reflection correct at all?
what's the best choice for electrolyte and anode/cathode materials
what's the exact reaction taking place?
any other way to isolate that calcium acetate?


texts: Measuring Testosterone Levels Using ELISA

texts:
I am new to this topic so please be patient. I am looking to understand ELISA better and how one may attempt to not only detect but measure the total calculated level present in a sample.

I would like to know the process and the materials required to conduct such a test, I know I need a well plate which I have but I'm unsure of the different chemicals required and in which order.

A part I am also very curious about which ties into my background is the sensor(s) used. From my understanding, a laser is commonly used a 450 nm that is shined through the sample that has reacted with colour and measures the absorbance of photons - the intensity of the colour is associated with the desired target that's present in which we're trying to quantify or measure; my question here is the laser shining on ever single individual well to get the mean?

Additionally, I am curious how the calibration sample is obtained and how it's stored for example what signature does 500 ng/ml of testosterone have that can be used as a reference point and where are these obtained.

Again please bear in mind im new to this subject and want to learn more. If you can explain this in simple terms initially and build onto the technicalities that would be great, thanks.


texts: Osmium tetroxide and meta-chloroperoxybenzoic acid

texts:
Can these be used to induce acetal ring closures? For example, when dealing with a molecule that has both a C=O functional group and an alkene as part of its structure and there is the possibility of creating a 5 or 6 membered ring through intramolecular -OH attack on the C=O ... can we just use the $\ce{OsO4}$ to create the diol and expect it to provide us sufficient acidity to catalyze ring closure?

Same question goes for meta-chloroperoxybenzoic acid.


texts:
I’m trying to make a 10 ppb Lead Nitrate solution as part of a concentration calibration step for a Beer Lambert’s Law experiment. I plan on performing a dilution in three steps. The calculations have been evaluated using:

$c_{1}v_{1}=c_{2}v_{2}$

Step 1: Creating a 1000 ppm (=1000 mg/L) stock solution (let’s call it A) by dissolving 1 gram (1000 mg) of Lead Nitrate in 1 L of distilled water [creating 1L of stock solution A]

Step 2: Creating an even more dilute  stock solution B of concentration 1 ppm (=1 mg/L = 1000 ppb) by diluting 1 mL of stock solution A with 1999 mL of distilled water. [creating 2L of stock solution B]

Step 3: Creating the desired solution C of concentration 10 ppb by diluting 0.25 mL of stock solution B with 24.75 mL of distilled water. [creating 25 mL of desired solution C)

Does this seem like an adequate method to obtain the desired solution? Should I add 1% v/v of Nitric Acid between every dilution step as a stabilizer to keep the lead ions in solution for as long as possible?

I only plan on using these solutions for about 10 days, so I’m not too concerned about the longevity of the solutions.


texts: Calculation of molarity using dilution equation

texts:
Using the formula $C_1V_1 = C_2V_2$ I am supposed to calculate the molarity of dilutions.

The original solution is $\pu{0.100 M}$ at $\pu{10 mL}$. I diluted it by mixing a $\pu{7.50 mL}$ stock solution with $\pu{2.50 mL}$ water, and made another one by mixing a $\pu{5 mL}$ stock solution with $\pu{5 mL}$ water.

Intuitively, I should get a higher molarity for my first dilution since it is higher in concentration, but when I calculate using
$$0.1(10)=C_2(7.5)$$
for the first dilution and
$$0.1(10)=C_2(5)$$
for the second, the second dilution's molarity is higher than the first. I know I am doing something wrong but I just can't figure out what.


texts: Hydrogen molecule potential energy graph

texts:
In the above graph, I was confused at the point where the internuclear distance increases and potential energy become zero. Though internuclear distance is very small and potential energy has increased to zero.

Another question that though the internuclear distance at a particular point is constant yet potential energy keeps on increasing.

I think the point where potential energy become zero we can say that attractive forces between electron and nucleus of bonding hydrogen atoms just equals the repulsive force between bonding hydrogen electrons. It's just what I am assuming not sure either its true or not.


texts: Is there a catalyst that will reduce an alcohol to an alkane?

texts:
There are many reduction methods of going from an alcohol to an alkane: http://www.transtutors.com/chemistry-homework-help/hydrocarbons/reduction-of-alcohols.aspx

And there are catalytic methods of adding hydrogen  gas to aldehydes and keystones to convert them into alcohols: http://jmcct.com/products-services/product_p404.html

However, I have not found a catalytic method of converting an alcohol into an alkane using a catalyst and possibly hydrogen. The fewer non-catalytic entities the better.


texts: Directing effects of substituent groups on aromatics

texts:
Normally, directing effects of substituent groups on aromatics are explained by drawing resonance structures of the Kekule representation of the compound. My question is that since the Kekule representation is in fact incorrect but rather there is equal electron density in all parts of the pi cloud in benzene, I am not completely satisfied with the explanation which relies on the fact that the bonds are localised.

Is there any other way to explain directing effects of substituents on benzene and other aromatic systems?

Obviously stuff like NMR analysis of phenol proves that the curly arrow predictions of the Kekule structure are true (ortho and para hydrogens have a shift of 6.7 and 6.8 ppm respectively - more shielded than normal benzene hydrogen of 7.2ppm so higher electron density in ortho and para carbons). But that could just be due to chance that the prediction is right. Also how do the curly arrows show that the ortho carbon is very slightly higher in electron density than para?