texts: What is the Criteria for a Compound Being Non-aromatic vs. Anti-aromatic?

texts: Anti-aromatic compounds are formed with a cyclic system of planar, overlapping p orbitals containing a non-Huckel number of electrons (i.e. not 4n+2 electrons -n being a natural number-). Non-aromatic compounds do not contain a continuously overlapping cyclic system of p orbitals. If a compound is antiaromatic, it is generally possible for the molecule to adopt a different conformation in order to disrupt the continual overlap of p orbitals. For example, 1,3,5,7-cyclooctatetraene, which would otherwise be antiaromatic, will adopt boat conformation to alleviate ring strain and antiaromaticity.  Some molecules containing a lone pair or empty p-orbital can hybridize in order to eliminate anti aromaticity. What I don't understand is when a molecule will hybridize its lone pair or adopt a different conformation to become non-aromatic. Are non-aromatic compounds more stable than antiaromatic compounds all of the time? Will a molecule that is capable of bending or hybridizing it orbitals in order to avoid anti-aromaticity always do so, or are there special circumstances? Also, can an empty p orbital sp3 hybridize to render a compound non-aromatic?


texts:
The following question has troubled me for a while.

For gases that are slightly soluble in water, there is a proportional relationship between the partial
pressure, $P$, and the mole fraction, $x$, of the gas molecules dissolved in water (Henry's law):
$\ce{P = k_H*x}$
A container ($V$ = $570$ $mL$) is filled with water ($V_l$ = $500$ $mL$) and pressurized with $CO_2$ gas ($P_0$ = $50$ $atm$), before it is allowed to stand at $10^\circ$C until the vapor–liquid equilibrium is established.
Calculate the pressure of $CO_2$ $[atm]$ in the container and the amount of $CO_2$ $[mol]$ dissolved in the water. The Henry coefficient of $CO_2$ for water at $10^\circ$C is $k_H$ = $0.104 × 10^4$ $atm$, and we will consider that the reaction of $CO_2$ in water can be ignored.

I did the following calculations but I am unsure with the outcome.
$\ce{n_{total}\approx n(H_2O) = \frac{\rho V}{M(H_2O)} = 27.753 mol}$
$\ce{x = \frac{P_0}{k_H} = 0.048077}$
$\ce{n(CO_2)_{dissolved} = x*n_{total} \approx 1.3343 mol}$
$\ce{P_1 = \frac{nRT}{V} = \frac {1.3343*0.0831451*1.01325*283}{0.570} = 55.8 atm}$
Shouldn't the final pressure be smaller than the initial pressure ($50$ $atm$)?


texts: What aspects of a molecule's chemical makeup determine which portions of it will react?

texts:
Is there a specific way to know how two or more arbitrary molecules will react?

An example that prompted this question: $\ce{(HOC6H4)2CMe2 + 2 NaOH → (NaOC6H4)2CMe2 + 2 H2O}$ (from here). How can you know how those molecules will react? Is it just a bunch of substitutions, with certain atoms in the reacting molecules reacting better than others? What factors would determine which atom in the molecule would react with the other molecule?


texts: Can we break the covalent bonds of water molecules using resonance frequencies?

texts: Can we break the covalent bonds of water molecules $\ce{H2O}$ using resonance frequencies? What is the wavelegth of the water's molecule? Can we create a vibration like this and use it to separate hydrogen from oxygen?


texts:
Just had a conceptual question from radial wave functions.

I wanted to know if probability density AT the nucleus is maximum, or zero.

From the attached images, it is clear that the function is at zero for p and d orbitals, but TENDS to infinity as approaching r = 0 for the s-orbitals. Is the value of the function 0 at r = 0?

Intutively, as the distance from the nucleus is the least, there should be maximum probability density.

Additionally, can there be some other interpretation for the phrase "at the nucleus"? It is quite confusing.

Thanks a lot.

EDIT: Apologies, don't know what was going through my head while posting - I initially posted something about PROBABILITY of finding an electron at the nucleus (I know the answer to that, oops).

I have changed it to what I meant to ask.


texts: What is a molecule’s smallest set of smallest rings?

texts: It is been a while since I've studied chemistry. Now, I am reading the documentation of RDKit, where they mention the expression "smallest set of smallest rings" (SSSRs). I understand that a ring is a cycle in a molecule. I also understand that the SSSRs is, as the name suggest, the smallest set of smallest rings, but how do you determine what the smallest sets and rings are?  What is a molecule's smallest set of smallest rings? What is a SSSRs used for?


texts: Purity of precipitate in selective precipitation

texts:
An aqueous effluent contains $12\ \mathrm{mol\ l^{-1}}$ $\ce{Cd^2+}$ and $10\ \mathrm{mol\ l^{-1}}$ $\ce{Mg^2+}$ as solution of nitrates. Current practice is use $\ce{NaOH}$ to selectively precipitate the metals.
(a) Is it feasible to get 0 $\ce{Cd}$ impurities in $\ce{Mg}$ precipitate by using $\ce{NaF}$ instead of $\ce{NaOH}$ (back up your answer with adequate calculations)
(b) What trade-off with respect to yield and purity do you have to accept if you use $\ce{NaF}$ instead of $\ce{NaOH}$?
(c) If consider switching the precipitating agent during the process which sequence should be used

Attempt at answer:
Part (a)
Using $\ce{NaF}$:

$K_\mathrm{sp}(\ce{MgF2}) = 3.7\times10^{-8}$
$K_\mathrm{sp}(\ce{CdF2}) = 6.44\times10^{-3}$
$K_\mathrm{sp}(\ce{MgF2}) = [\ce{Mg^2+}][\ce{F-}]^2$
$K_\mathrm{sp}(\ce{CdF2}) = [\ce{Cd^2+}][\ce{F-}]^2$

As the $K_\mathrm{sp}$ of $\ce{MgF2}$ is smaller it is less soluble and will precipitate first. You need to add $\ce{F-}$ to the point where $\ce{CdF2}$ will just not start precipitating. The limiting concentration is when the ion product = $K_\mathrm{sp}$.
Limiting concentration for $\ce{MgF2}$:
$[\ce{F-}]=\sqrt\frac{K_\mathrm{sp}(\ce{MgF2})}{[\ce{Mg^2+}]} = \sqrt\frac{3.7\times10^{-8}}{10} = 6.08\times10^{-5}\ \mathrm{mol\ l^{-1}}$
Limiting concentration for $\ce{CdF2}$:
$[\ce{F-}]=\sqrt\frac{K_\mathrm{sp}(\ce{CdF2})}{[\ce{Cd^2+}]} = \sqrt\frac{6.44\times10^{-3}}{12} = 0.023\ \mathrm{mol\ l^{-1}}$
The limiting concentration of $\ce{Mg^2+}$ is lower so this will precipitate first. By adding $\ce{F-}$ up to the limiting concentration of $\ce{Cd^2+}$ no $\ce{Cd}$ will precipitate so $\ce{MgF2}$ precipitate will be pure.
Part (b)
I assume you need to find the yield and purity for both methods (using $\ce{NaF}$ or $\ce{NaOH}$).
To find the purity of $\ce{CdF2}$ need to know how much $\ce{Mg^2+}$ is left in solution at the point when $\ce{CdF2}$ starts precipitating.
$[\ce{Mg^2+}]_\text{sol} = \frac{K_\mathrm{sp}(\ce{MgF2})}{[\ce{F-}]^2} = \frac{3.7\times10^{-8}}{0.023^2} = 6.99\times10^{-8}$
Purity of $\ce{CdF2}$: $\frac{[\ce{Cd}]}{[\ce{Cd}]+[\ce{Mg2+}]_\text{sol}} \times 100\ \% = 99.99\ \%$
I assume the yield of $\ce{CdF2}$ would be $100$ as you can keep adding $\ce{F-}$ until it’s all precipitated out.
I’m not sure if to calculate the yield of magnesium I need to do the original concentration − impurities in $\ce{CdF2}$/original concentration. If I did this then:
$\frac{10-6.99\times10^{-8}}{10} \times 100\ \% = 99.99\ \%$
To compare with using $\ce{NaOH}$ as the precipitating agent:

$K_\mathrm{sp}(\ce{Mg(OH)2}) = 1.8\times10^{-11}$
$K_\mathrm{sp}(\ce{Cd(OH)2}) = 2.5\times10^{-14}$
$K_\mathrm{sp}(\ce{Mg(OH)2}) = [\ce{Mg^2+}][\ce{OH-}]^2$
$K_\mathrm{sp}(\ce{Cd(OH)2}) = [\ce{Cd^2+}][\ce{OH-}]^2$

As the $K_\mathrm{sp}$ of $\ce{Cd(OH)2}$ is smaller it is less soluble and will precipitate first.
Limiting concentration for $\ce{Mg(OH)2}$:
$[\ce{F-}]=\sqrt\frac{K_\mathrm{sp}(\ce{Mg(OH)2})}{[\ce{Mg^2+}]} = \sqrt\frac{1.8\times10^{-11}}{10} = 1.43\times10^{-6}\ \mathrm{mol\ l^{-1}}$
To find the purity of $\ce{Mg(OH)2}$ need to know how much $\ce{Cd^2+}$ is left in solution at the point when $\ce{Mg(OH)2}$ starts precipitating.
$[\ce{Cd^2+}]_\text{sol} = \sqrt\frac{K_\mathrm{sp}(\ce{Cd(OH)2})}{[\ce{F-}]^2} = \frac{2.5\times10^{-14}}{(1.43\times10^{-6})^2} = 0.0138\ \mathrm{mol\ l^{-1}}$
Purity of $\ce{Mg}$: $\frac{10}{10+0.0138}\times100\ \% = 99.86\ \%$
Yield of $\ce{Cd}$: $\frac{12-0.0138}{12}\times100\ \% = 99.86\ \%$
For part B the way the question is phrased I assume the purity or yield using $\ce{NaF}$ shouldn’t be as great as using $\ce{NaOH}$ but I don’t know if I have done my calculations right as from my results it would seem they’re both accurate methods.


texts: Are PCC and Collin's reagent completely identical in their oxidizing action? Is there any advantage (or disadvantages) over the other?


texts: What is the most accepted mechanism for the reaction of ketones with m-dinitrobenzene?

texts:
This is a commonly used confirmatory technique in organic functional group analysis. The test is performed by addition of meta dinitrobenzene to the given organic sample followed by addition of a base such as  sodium hydroxide. The indication is given by a violet colouration.

Is the probable mechanism based on carbanion formation? Also it would be helpful if exceptions to this reaction and other variants in colour produced by different ketones. My main requirement is to know why aldehydes do not respond to this test.


texts: I know Huckel's rule states that an aromatic species must have $4n+2$ π-electrons. Is the last molecule also aromatic?


texts:
I have seen two electron configurations for $\ce{_{28}Ni}$ in my chemistry textbook:
$$[\ce{Ar}]~3d^8~4s^2$$
$$[\ce{Ar}]~3d^9~4s^1$$
Which of those is ACTUALLY the correct one (in real life, reality)? Why exactly?


texts: Why is the fluorescence spectrum of pyrene time-dependent?

texts:
I've got a solution of pyrene and I excite it with a laser. If I measure the emission spectrum 1 ns after absorption, a well‐structured emission with a small Stoke’s shift is observed.
However, if the emission is measured with a delay of 100 ns, a broad, featureless spectrum with a much larger Stoke’s shift is obtained.

Is this purely because pyrene has had some time to undergo solvent reorganization and thus the individual excited pyrene molecules have larger differences or is there something else at play?


texts: Comparison of evaporation rate of liquids

texts:
Evaporation: Evaporation
is a type of vaporization that occurs on the surface of a liquid as it
changes into the gas phase. When a molecule near the surface absorbs
enough energy to overcome the vapour pressure, it will escape and
enter the surrounding air as a gas.
Boiling point: The
boiling point of a substance is the temperature at which the vapour
pressure of a liquid equals the pressure surrounding the liquid and
the liquid changes into a vapour.
Volatility:
Volatility is a material quality which describes how readily a
substance vapourizes.
Flash Point: The flash
point of a volatile material is the lowest temperature at which its
vapours ignite if given an ignition source.
Autoignition
temperature:
The autoignition temperature or kindling point of a substance is the
lowest temperature in which it spontaneously ignites in a normal
atmosphere without an external source of ignition, such as a flame or
spark.
Fire point: The fire point
of a fuel is the lowest temperature at which the vapour of that fuel
will continue to burn for at least five seconds after ignition by an
open flame of standard dimension.
Smoke point: The smoke
point, also referred to as the burning point, is the temperature at
which an oil or fat begins to produce a continuous bluish smoke that
becomes clearly visible, dependent upon specific and defined
conditions.

How can we compare the evaporation rate for water, alcohol, petrol and kerosene oil?
If we consider intermolecular forces as the criterion, then the order of evaporation would be:
water < alcohol < kerosene oil < petrol
But part of intermolecular forces still act in vapour phase...
What should be the criteria to compare evaporation rate of liquids at a given temperature?


texts: How to know the formula of different compounds?

texts: For example, if I didn't know the compound tin chloride, and I was asked to write out its formula, how would I know how to? Because it seems unreasonable to know the formula of every compound in existence. Many thanks for the help!


texts: Why is radium oxide yet to be isolated when a wide range of other radium (II) compounds are known ?


texts: Why is the base-centered orthorhombic crystal lattice a unique crystal system?

texts:
I'm having difficulty understanding why the base-centered orthorhombic crystal system is a unique crystal system. When I draw two base-centered orthorhombic unit cells next to each other there appears to be a primitive crystal that is contained within the union of the two lattices as shown in the image below.

This primitive crystal system appears to be monoclinic--though I wouldn't be surprised if I'm wrong on that front--if you take δ to be the typical β angle of a monoclinic crystal system (I've set δ ≠ 120° to avoid the rhombohedral scenario). Why does this not make the base-centered orthorhombic lattice redundant? Am I misguided in trying to understand these crystal systems in terms of their lattice points and unit cell lengths instead of their symmetry?


texts: Number of geometrical isomers when a cyclic ring is involved along with axis of symmetry

texts:
This is an question from my Chemistry study material and it asks to find the number of Geometrical Isomers of the following compound in the picture.

  Basically the method/formula given in my book to find number of Geometrical
  Isomers of a compound is:

Using this formula I put $n=3$.Morever since both ends are same I get $p=(3+1)/2=2$.So final answer according to me is $2^{3-1}+2^{2-1}=4+2=6$.

But the answer given is $2^3=8$.

Where did I go wrong?

Related: How to derive these general formulae for number of stereoisomers of a compound with a possible plane of symmetry?


texts: Cahn–Ingold–Prelog priority of CN vs CH2NH2

texts: Why does $\ce{CH2NH2}$ have lower priority than $\ce{CN}$? The carbon on the first molecule is bonded to (N,H,H) while the carbon on the second molecule is just bonded to (N). I can't seem to find this scenario anywhere online.


texts: I want to produce alginate nanoparticles from NaAlg. I choosed nebulizing NaAlg solution into $\ce{CaCl2}$ solution but 2% (m/v) NaAlg solution is quite viscous. What should I do to make it inviscid?


texts:
Reading Wikipedia on "Beta Decay" they list the equation of Carbon-14 decaying into N-14.
see equation https://en.wikipedia.org/wiki/Beta_decay

I presume the 14 refers to total protons and neutrons.  The 6 in C, I believe means six protons.  In N, I believe the 7 refers to protons. Where did the seventh proton come from the decay of  C-14 into N-14?  I understand neutrons can decay into protons, but the math doesn't work for me.


texts: Does it exist a transgression to Hund's rule of maximum multiplicity principle in this given electron box notation?

texts:
The following question arises from a set of statements from which I'm asked to state whether they are true or false.

This is as follows:

  Indicate which of the following statements are true or false

On $\underset{np}{\underline{\uparrow}\,\underline{\uparrow}\,\underline{\downarrow}}$ there is a transgression to Hund's rule of maximum multiplicity
The given box notation $\underset{np}{\underline{\uparrow\,\uparrow}}$ is a transgression to Pauli's exclusion principle.
The following configuration $1s^22s^22p^13s^1$ is a transgression to Pauli's exclusion principle.
The electron configuration of Silver $(Z=47)$ is $[Kr]5s^{1}4d^{10}$.
Two chemical species with the same number of electrons not necessarily have the same configuration.

Given these statements I found it difficult to make a proper interpretation of what was intended with the fifth and the first option.

The second option is true. As two electrons occupying the same orbital cannot have the same quantum numbers.

The third option is not true due that's not a transgression to Pauli's exclussion principle. But rather to Aufbau's build up principle. Because it states that the electrons will occupy the orbital with the lowest energy possible.

The fourth option is correct, that's the electron configuration of Silver.

But the problem arises from the first option as I don't know if it does make a transgression to Hund's principle of maximum multiplicity?. As I understand there isn't any reason to justify that the electron will always have to be filled with a $m_s=-\frac{1}{2}$. It only states that the most stable configuration will be the one where electrons fill the most orbitals as possible.

Then the fifth option is a bit hard to understand, as I don't get very clear what's the meaning of chemical species. I'm assuming since this question is related with atomic structure chapter, it is referring to atoms. In the given context ions more specifically, and understood in such way it does say that two isoelectronic atoms will not have the same configuration. But is that possible?. How can it be justified?.


texts: Hydrolysis of Sucrose over Sn1Ac or Sn2Ac

texts:
In "March's Advanced Organic Chemistry" I have read about the general mechanism of the acetal hydrolysis. It names the acid-catalyzed SN1 or SN2 as a possible mechanism for a Acetal-hydrolysis.

Now I am interested to know if SN1 or SN2 is mainly going on at the Hydrolysis of Sucrose to Glucose and Fructose. So I compared the different parameters which influence SN1/SN2.

Polarity of the solvent: Water -> really polar -> SN1 preferred.
Stabilization of a possible Carbokation-Intermediat: Primary (Anomeric C!), so not really stabilized by Hyperconjunction -> SN2 preferred. (Is there Hyperconjunction also in the ether-O?)
Mesomeric stabilization There is also a mesomeric stabilization between the resulting carbocation and a Oxonium-Ion in the SN1-Mechanism.
Steric Hindrance: In my opinion, through the planar region around the anomeric C (planar ether), there is no steric hindrance -> SN2 possible.
Temperature: high temperature -> SN1 preferred.

So to conclude: Many different aspects. Because of the main points "steric hindrance" and the destabilized primary carbocation intermediate I would conclude that the hydrolysis of Sucrose goes mainly (maybe a little bit over SN1) over SN2.

Have I forgotten something important? Are my assumptions "No steric hindrance" and primary carbocation-intermediate correct?

I have attached my possible SN1-mechanism.


texts: I want to electrolyze water to get oxygen and hydrogen. I want to mix them in a regular balloon and ignite it. How much hydrogen would you need in a 2:1 ratio with air for it to be dangerous? Is this generally a safe experiment?


texts: Despite being less reactive,alkanes are highly flammable

texts:
I read in my book that alkanes are saturated compunds and the valencies of carbon are satisfied by single bonds. I knew that propane and butane are highly flammable and could cause explosion.
My question
If alkanes are less reactive then why they are highly flammable and could cause unfortunate explosion?


texts:
Is a racemic mixture always an equi-molar solution of two enantiomers, both in the same state? Is it necessary for both isomers to be in the liquid state for racemisation to occur, or does racemisation also occur in the gaseous and solid states?
Thirdly,can the two enantiomers still form a racemic mixture if they are initially at different temperatures?


texts: How do the two half cells of Daniel cell know when they are connected?

texts:
I'm currently studying electrochemistry in school, and there is something I don't can't quite understand about Daniel cell.

When you put $\ce{Zn}$ solid into $\ce{ZnSO4}$ solution, does the electrode become negatively charged even before connecting it with the $\ce{Cu}$ half cell?

I searched but I wasn't able to form a clear understanding, I read that the answer to the previous question is no, the the two cells need to be connected for the redox reaction to happen.
If that was the case, how do the half cells communicate, how do they know when they are connected even when there is distance between them?

If the electrodes were charged before connecting them that would make perfect sense for me, the electrons repel each other and when connecting the two half cells with a wire, the electrons move because of the negatively charged electrode, but from what I've read that is not the case?

I'm really sorry if that is a stupid question but I really can't find an answer.


texts: IUPAC Recommendations for Concentration Units (ppb, ppm)

texts:
In a recent interesting post, (Is 1 ppb equal to 1 μg/kg?)
it was pointed out that IUPAC advises to abandon parts per million, parts per billion quantities and instead it suggests to employ micromole/ mole for ppm and nanomole/mole for ppb. An example is given on page 98 of the Green Book
"The volume fraction of helium is 20 ppm".

May be I am missing a point or I see a problem here with the moles in the denominator of these suggested replacement definitions.

a) If we analyze Zr in a rock and find 5 mg Zr in a 20 gram rock, how would one apply the mole definition because one cannot define the moles of a rock. We have to stick to the classical definition:

ppm =10^6 * (mass of analyte / mass of sample).

b) How can one express ppm of Ar in air, and how should we define the moles of air? If we wish to generalize this case, what if our solvent system consists of several components.

The ambiguity I feel in micromole/mole definition is the mole in the denominator. Are we referring to the moles of the solvent or  moles of solvent plus solute.

If this replacement is analogous to molal concentration, where the denominator is clearly definied to be kg of solvent not the kg of solvent plus kg of solute, then IUPAC should clearly define it.


texts: Comparison of COSY and TOCSY for detection of small couplings between protons

texts:
I routinely run COSY spectra to help with assignment of my proton NMR.

The experiment is fast to run and generally useful, however some of the intermediates I've recently been making have had sufficiently small coupling constants that the COSY hasn't been terribly useful in certain regions(a 'standard' COSY isn't giving the resolution needed).

Typically, I get around this by running a set of HMBC and edited-HSQC, which allows me to trace the protons along the molecule, in a similar way as I'd be able to do with the COSY. The issue with this is that with the quantity of material I have, the HMBC takes significant amounts of time to run, making this method unhelpful for day-to-day work.

A colleague suggested using 2D-TOCSY to see which protons are in the same spin systems (not the same information as in the COSY, but would give me what I need).

Looking through the ever useful Claridge, it seems that the mixing pulse from the COSY gets replaced with a 'spin lock' sequence. What is less clear to me from this though, is whether TOCSY is also dependant on the magnitude of the coupling (i.e. if the J values are minimal, will the TOCSY suffer from the same issues as the COSY), or whether the spin systems are detected indirectly/through some other property.

Standard 2D COSY spectrum

Standard 2D TOCSY spectrum


texts: Here, when they write $v/(\mathrm{mol\ s^{-1}\ (kg\ \text{protein})^{-1}})$ is $0.30$ for the first row first column, do they mean that the value is $0.30\ \mathrm{mol\ s^{-1}\ (kg\ \text{protein})^{-1}}$ or $0.30/(\mathrm{mol\ s^{-1}\ (kg\ \text{protein})^{-1}})$?


texts: Inter electronic repulsion in s and d orbitals

texts:
This was written in a lecture slide:

  Two electrons present in the same d-orbital repel each other more strongly than do two electrons in the same s-orbital.

Why is there a difference in the amount of inter electronic repulsion in each orbital? Does it have to do with the shape of the orbital?


texts: Thermal reduction of other metal oxides beside Fe2O3

texts:
In the firing of ceramic glazes you can make an effect called oil spot.
This is done by making two layers of glaze. A bottom layer rich in iron oxide (+15%) and a top white layer that's fairly permeable. Once your reach 1225° C, the iron loses it's bond with the oxygen and goes into reduction, despite being in an oxygen rich electric kiln. So the oxygen bubbles up to the surface, taking along a bit of the iron. It then turns into FeO, and it also has something to do with magnetite which I don't understand.

Anyway, the result is that you get a white glaze with dark spots surrounded with grey/green parts, or some yellow.This effect is very nice but it only works with iron oxide as far as I know.

So my question is: are there other oxides that can have the same thermal reduction effect, and if so at what temperature. I know somebody found a way to make it in blue (it took him 4 years) so maybe he used cobalt oxide, though that looks to me to be to obvious to take 4 years. Anyway, he's not a chemist, he's a potter.

For a potter this is hard to find out but maybe for a chemist this is not that difficult to resolve, so I thought why not go to the people who know this stuff much better than us potters.


texts:
Does aromaticity depend on temperature?  I recently read about a compound (tropone) which changes its aromatic nature with temperature. Is it plausible? If yes then why
does it happen?


texts: The chemical formula of urea is $\ce{CO(NH2)2}$ or is sometimes written as $\ce{CH4N2O}$. How would I decompose or precipitate the $\ce{CO}$ from urea to get ammonia? I know that in the olden days people used to make gunpowder (potassium nitrate) and ammonium nitrate from human urine, which was made by reacting ammonia and nitric acid, so it should be possible. (Just as a side note: this is for a high school chemistry project, I am not attempting to make explosives out of this).


texts: Is it possible to produce sodium bicarbonate from potassium bicarbonate?

texts:
I balanced the chemical reaction which is as follows:

NaCl + KHCO3 = NaHCO3 + KCl

I've also gathered solubility values which are the following:

KHCO3
22.4 g/100 mL (20 °C)
NaCl
35,9 g/100 mL (20°)
KCl
34.2 g/100ml (20°C)
NaHCO3
9.6 g/100ml (20 °C)

Since NaHCO3 is less soluble than the other compounds, I could separate it by boiling off some of the water up to a certain point, but I'm not sure how to predict which way the reaction will be going and if it will proceed completely.

How do I find out which way the reaction will proceed, and to which extent it will be complete?

I'd be glad for any help.


texts: Why do the units of rate constants change, and what does that physically mean?

texts:
Just to be clear, I do understand that the units of the rate constant k is selected to make the equation dimensionally consistent. That is not what I am asking.
It should be the case that k 'means' something physically, which is implied by its dimensions/units. And I would also assume that what k 'means' should not be dependent on the order of the reaction, since I cannot see any obvious reason why it should. But we know that the overall order of a reaction changes the units of the rate constant, so I must be wrong.
My question is as stated: Why do the dimensions of the rate constant change depending on different reaction orders, and what does that physically mean?
As an extension to this, I would also like to understand how the same thing works for the equilibrium constant, where the stoichiometric coefficients of the species or the number of products/reactants change the units of the constant. Again, I cannot see the reason why these would change what the constant means dimensionally.
Sorry if this an obvious question. I am not a chemist.
Edit:
I wanted to clear up a few things.
First of all, as I understand I was expecting there to be a deeper meaning to the dimensions of the rate constant even though there isn't always an obvious one, since it is an empirical equation which merely simplifies a process rather than describing the fundamental workings of it. But I still want to understand intuitively (if there is indeed an intuitive reason) why the units are different for each overall order. As in the examples Maurice gives in his answer, a reaction of order zero produces dimensions of amount per time whereas a first order reaction produces [ratio] per time and so on for other real number orders. It just seemed strange to me that a constant in the equation, which seems to be doing the same job regardless of order, express something in completely different dimensions depending on order.
After reading your answers, this is what I thought: In a zeroth order reaction where the rate is constant, amount per time seems to be the only reasonable way to describe the rate since ratio per time inevitably produces a curve. Similarly for a first order reaction, amount per time wouldn't work because this value changes constantly. So, the constant is expressed in terms of the units which can describe the reaction given its nature. This was stated/suggested in some replies but thinking of it over an example is what cleared it up (if it is correct) and thank you for your responses. Perhaps this was obvious but a constant with varying units was not something I was familiar with.


texts: How were the first molecular formulas determined?

texts: How were molecular formulas determined before spectroscopy and spectronomy? I know that John Dalton thought that the formula of water was "HO" but we now know it to be "H2O." How did Dalton even know that water had hydrogen and oxygen in the first place?


texts: What element or compound could be used to make the ocean more basic?

texts: The ocean is becoming acidic. This is not a natural evolutionary change but happens through human negative effect on the environment. What element or compound could be used to create a more base ocean? How much of it would be needed? How could it be distributed?


texts: HSO4- ion equilibrium, which side more acidic

texts: I did an experiment in involving the reaction $\ce{HSO4- + H2O -> H3O+ + SO4^{2-}}$. An acid/base indicator was added to the solution. When more   $\ce{SO4^{2-}}$ was added to the solution, it turned pinkish red indicating that the acidity has increased, pH lowered. more $\ce{SO4^{2-}}$ should mean a shift to the left, producing more $\ce{HSO4-}$ and $\ce{H2O}$. Based on Ka values, I thought the right side of the equation should be the one to show more acidity and lower pH, but this doesn't seem to be the case. Can someone explain this?


texts: What is the oxidation state of sulphur in sulphur dioxide?

texts:
So for $\ce{SO2}$, here's the solution when finding for the oxidation number of sulfur.

$$x + 2(-2) = 0 \\
x - 4 = 0 \\
x = +4$$

$x$ here would be the oxidation number of sulfur, so the compound would now be
$\overset{+4}{\ce S} \overset{-2}{\ce{O2}}$.

Now if I tried using oxygen as the $x$ it would become:
$$1(-2) + 2x = 0 \\
-2 + 2x = 0 \\
2x = 2 \\
\frac{2x}{2} = \frac 22 \\
x=1$$

So, in this case the compound would actually be $\overset{-2}{\ce S} \overset{+1}{\ce{O2}}$.

I'm pretty confused about this since we just got into this today and haven't checked many examples. There is probably something I'm missing in the solution or a rule. Can someone explain to me the correct one? And also can't sulfur's and oxygen's oxidation number both be -2 as they're in group VI(A)?


texts: Adiabatic compressibility factor of ethyl alcohol

texts: I am looking for a source where I can find the adiabatic compressibility factor of ethyl alcohol at approximately 15 degrees Celsius. I have found the compressibility factor at 20 degrees. Is there maybe a way to convert this to the desirable temperature?


texts: Reason for the differences in third ionisation energy between elements (magnesium and fluorine)

texts:
The question is "Why is the third ionisation energy of magnesium higher than that of fluorine?"

Although I understand that differences in ionisation energy have several factors governing it, e.g. the shielding effect, distance from the nucleus, whether the electron is in its own orbital or paired with another electron etc.

The answer to this question is that "Even though the valence electrons of both elements are removed from the same shell, Mg has greater nuclear charge."

I am confused what the answer means about nuclear charge. Doesn't the third ionisation energy of Mg and F have the same nuclear charge as they are both 3+?


texts: Photochemistry and steady state approximation

texts:
I am unsure whether to ask this in physics or chemistry as there is overlap but I am taking this in a chemistry module.

System A undergoes photophysical pathways:
$$\ce{A + hv -> A\mathrm{*}}$$
$$\ce{A\mathrm{*} -> A + hv   \tag{k1}}$$
$$\ce{A\mathrm{*} + B -> A + B\mathrm{*} \tag{k2}}$$
$$\ce{B\mathrm{*} -> B + hv      \tag{k3}}$$
$$\ce{B\mathrm{*} -> C           \tag{k4}}$$

It wants me to show that the quantum yield of energy transfer is equal to the quantum yield of fluorescene B and the quantum yield of photochemical conversion from B to C.

I am quite stuck on this problem. I assume the steady state approximation needs to be employed in order to determine quantum yields for the processes asked for.
I am wondering what the general strategy would be to answer this question?


texts:
Since ionic solids are not molecular, can a single sodium chloride unit exist and if so, what is such a unit called? I am aware of the concept of "formula units", but as far as I can tell, this is a notional term and does not describe any physical structure. Is "unit cell" the correct term and can a single unit cell exist?
Just to be sure people understand the question: I am talking about solid sodium chloride and not an aqueous solution of it.


texts: How does molecular structure affect physical properties?

texts:
The question sounds vague and non-specific because my background in chemistry is limited to undergrad college courses.  However, I am interested in learning the correlations between the atom-by-atom structure of molecules (simple, complex...) and the resultant physical properties thereof.

So far, it seems most the material online directly referencing the phrases "molecular structure" and "physical properties" is in the form of highly specialized research publications.  Surely, there is a Basics to the Relationships between Molecular Structure and Physical Properties 101 out there, somewhere.

Ultimately, my questions sum up to the following:

Where may I go to learn these things?
What material may I read?
Who might I ask?
Where do I begin?

Thank you very much.


texts:
I am very new to this site and this is my first ever question. I want to know what is this black material in this sensor film kit. I am creating a weight sensor by using this very sensor kit. Now I am short of this black film. I want to purchase it now locally but do not know the composition of this material.
This material behaves as a resistance between two aluminium foil, just to inform.
If any one can help me in this.


texts: what is the basic factor which determines the order of ionization energies of K,Li,Ca,S?

texts:
There was a question which was asking about the order of ionization energies of
K,Li,Ca,S.
The electronic configuration of all the elements were as follows

Li:${1s^2 2s^1}$
K :${1s^2 2s^2 2p^6 3s^2 3p^6 4s^1}$
Ca :${1s^2 2s^2 2p^6 3s^2 3p^6 4s^2}$
S :${1s^2 2s^2 2p^6 3s^2 3p^4}$

From the electronic configurations:

Potassium should have lowest ionization energy as it is very easy to remove electron from 4th shell.
Then it should be followed by Calcium as its nuclear charge increases from going across the period
Then it should be followed by sulphur as it is more easier to remove the electron from 3rd shell than from 2nd shell.
Then it should be followed by Lithium as it has lowest principle quantum number(n) so it is more difficult to remove an electron from 2nd shell than from 3rd and 4th shell.

So according to my calculation the order should be  K < Ca < S < Li.
But the correct answer in my textbook is K < Li < Ca < S. If I am wrong anywhere then what factor would help in determining the Ionization energies of the following elements, and what would be the exact order of I.E for these elements.


texts: Can Diels-Alder reaction occur using reagents of Robinson annulation?

texts:
Robinson annulation seemed somewhat like the Diels-Alder reaction to me, if all ketonic groups were to be represented as enol then cyclohexanone would be like diene and the Michael acceptor as a dienophile.

On trying out this thought, I got pyran derivatives. The doubt is attached as the following image.

"Heathcock, C. H., Ellis, J. E., McMurry, J. E., & Coppolino, A. (1971). Acid-catalyzed Robinson Annelations. Tetrahedron Letters, 12(52), 4995–4996. doi:10.1016/s0040-4039(01)97609-9 " report that Robinson annulation can be achieved using sulphuric acid instead of a base. Though no mechanism is reported in it, I think enol is formed as an intermediate.

I request you to clear this doubt of mine whether if there is any slightest possibility in Robinson annulation that basic/acidic medium would enolize the ketone then undergo diels-alder reaction on providing heat.
Also, if it does then would it follow Woodward-Hoffmann rules as Robinson annulation looked like a thermally allowed cycloaddition reaction

The following paper reports such possible diels-Alder reaction with enols though not directly for reagents of Robinson annulation: "Akbulut, N., Hartsough, D., Kim, J. I., & Schuster, G. B. (1989). The triplex Diels-Alder reaction of 1,3-dienes with enol, alkene, and acetylenic dienophiles: scope and utility. The Journal of Organic Chemistry, 54(11), 2549–2556. doi:10.1021/jo00272a017 "

.

( Reference: https://en.wikipedia.org/wiki/Oxo-Diels–Alder_reaction and https://en.wikipedia.org/wiki/Inverse_electron-demand_Diels–Alder_reaction )


texts: Our teacher told us that $\ce{OCH3}$ is a less bulky group when compared to other bulky groups like $\ce{CH3}$, $\ce{NO2}$ etc. Is this true? If yes, why?


texts: Why does sodium chloride not conduct as much as aluminum chloride in water?

texts:
I understand how $\ce{NaCl}$ and $\ce{AlCl3}$ dissolves in water but I'm wondering why one is more conductive than the other. Is it their extra ions to conduct the electricity?

I know that in $\ce{NaCl}$ the water molecules 'steals' the Sodium or the Chloride depending on which end becomes closest to the material due to the Dipole-Dipole attraction. However, this reaction alone cannot break down the ionic lattice alone so there is a separate endothermic reaction. But I still can't understand the science behind why one conducts more than the other.


texts:
I have three histidine residues that are next to each other in a protein. When I compute the fraction of unprotonated states for each individual histidine as a function of $\mathrm{pH}$ my titration curve has a non-Henderson–Hasselbalch (HH) shape. Hence I can't fit it using the HH equation for 1 site:

$$\frac{1}{1 + 10^{n(\mathrm{p}K_\mathrm{a} - \mathrm{pH})}}$$

in order to solve for the Hill coefficient $n$ and $\mathrm{p}K_\mathrm{a}.$

Obviously the three histidine $\mathrm{p}K_\mathrm{a}$'s are dependent on each other since they are very close to one another and are probably sharing the proton. So how do I go about fitting the curves? Should I sum the total unprotonated states in all three histidines and fit the curve with the three site equation

$$\frac{1}{1 + 10^{n_1(\mathrm{p}K_\mathrm{a1} - \mathrm{pH})}} + \frac{1}{1 + 10^{n_2(\mathrm{p}K_\mathrm{a2} - \mathrm{pH})}} + \frac{1}{1 + 10^{n_3(\mathrm{p}K_\mathrm{a3} - \mathrm{pH})}}?$$

When I use this equation I still don't get a good fit and I get unreasonable $\mathrm{p}K_\mathrm{a}$'s $(-1.4, 7.7, -1.3).$ Any suggestions?

As requested below, the matlab code I used for the fit is the following:

ft=fittype('(1/(1+10.^(a1*(p1-x))))+(1/(1+10.^(a2*(p2-x))))+(1/(1+10.^(a3*(p3-x))))', 'independent','x','dependent','y');
opts = fitoptions('Method','NonlinearLeastSquares');
[fitresult, gof] = fit( xData, yData, ft, opts );
h = plot(fitresult,xData,yData)

I posted values for p1, p2, p3 which should report $\mathrm{p}K_\mathrm{a1},$ $\mathrm{p}K_\mathrm{a2}$ and $\mathrm{p}K_\mathrm{a3}.$


texts:
Let's assume a setup with a static linear molecule with three identical atoms connected by bonds and a single atom, identical to the other three, being shot at the molecule. Let's also assume that everything happens in 1D and can therefore be illustrated by this simple scheme:

(projectile) A ->    A-A-A (molecule)

Where the direction of the arrow is the direction of motion of the projectile and the dash signs in the molecule are the bonds between atoms.

[EDIT - must change next paragraph as the description does not fit what would happen: stand-by, no time to do it right now!]

Assuming a low-energy, non-relativistic, perfectly elastic collision, the projectile will stop dead in its track while the molecule will be set in motion at 1/3rd of the projectile's speed, as it has 3 times the projectile's mass (conservation of Momentum). Balancing also the equations for the Kinetic Energy easily reveals that 2/3rds of projectile's kinetic energy must have been locked away in internal vibrations of the molecule.

Now, it's easy for us to calculate these numbers by considering the projectile and the molecule as just two separate systems and conveniently attaching a total mass to each. But in reality the universe doesn't group atoms into molecules, does it? Each bond in the setup doesn't "know" about the existence of the other bond and each atom could be said to be unaware of all but the atoms bonded or colliding with it.

In this context, not "knowing" total masses, how does the universe "calculates" that in this case the molecule must store 2/3rds of the projectile kinetic energy into internal vibrations, no more, no less?


texts: What is the Structural Activity Relationship of Cocaine?

texts: Cocaine, also known as coke is a widely known drug for both recreational and pharmacological use. What is exactly the relationship of it's structure to it's drug activity?


texts:
I want to conduct in-situ XRD of a cathode in my battery using this coin cell with a kapton viewing window. I assume this cell configuration is the best I can find for my purpose, and that I can't easily make a better cell. However, the viewing window isn't super helpful if I still need to use a stainless steel current collector, as I have previously.

Thus it seems I have two options:

Make a donut-shaped anode and separator, and XRD through the hole in the donut to hit the cathode. However, I worry that the cathode may not fully lithiate in the center, because it is not as close to in contact with my anode.
Find a current collector which is transparent to XRD. Does anyone have a suggestion for such a current collector?


texts: Is there a hypervalent molecule which has no contribution of d-orbitals at all?

texts:
I thought that d-orbitals were used to "extend the octet rule" in these molecules until I looked it up on Google and saw that they actually contributed only a little to the molecule. A little, but not zero.

Is there a hypervalent period-3-element molecule that has mathematically been proved not to involve d-orbitals at all?
Do they have a role, any role, in the chemical properties of the final molecules?


texts:
The Medium.com article Mars Phoenix Lander, 10 Years Later shows several remarkable images and discoveries on Mars by the Mars Phoenix Lander circa 2008.
One image (shown below) shows what looks like droplets of liquid water, condensed on the surface of one of the lander's legs.
The article says (emphasis mine):

Shortly after landing, the camera on Phoenix’s robotic arm captured views of blobs of material on one of the landing struts. Over time, these blobs moved, darkened, and coalesced, behaving like droplets of liquid water. The hypothesis here was that these blobs “splashed up” on the struts when the descent thrusters melted the ice exposed upon landing mentioned above.
But if liquid water isn’t stable on the martian surface, how did Phoenix observe liquid water on Mars? The key here lies in salt. If you live anywhere that gets snow, you’re probably familiar with salt as a de-icer for roads, sidewalks, etc. Salt lowers the freezing point of water, allowing it to remain liquid at temperatures lower than that of non-salty water. For example, pure water freezes at 0 °C/32 °F, but ocean saltwater freezes around −2 °C/28.4 °F. While the de-icing salts you get at the hardware store lower the freezing point by a few degrees, more exotic salts can lower the freezing point as much as −70 °C/−89 °F! Phoenix discovered some of these exotic salts in the soil around the lander—in particular, magnesium perchlorate. (note, minor editorial changes have been made)

Question: Which "exotic salt" can lower water's freezing point by 70 °C?
Is it in fact magnesium perchlorate (which was found on Mars) or is it a different salt?

Blobs of possible brine (really salty water) imaged on one of Phoenix’s landing struts shortly after arriving on Mars. Credit: NASA/JPL-Caltech/University of Arizona/Max Planck Institute


texts: Why is the Debye Hückel Limiting Law called the "limiting law"?

texts:
I could not find any source which explains this point well.

I looked up Atkin's physical chemistry and Castellan's physical chemistry book but could not quite understand the logic bhind it being called the limiting law.


texts: How do nucleophiles change Sn1 energy profiles?

texts:
Suppose two different nucleophiles react with a single substrate via SN1. Would the energy of activation for the second transition state (nucleophile reacts with carbocation) be less for the better nucleophile? Would the products be of equal energy and produce a 1:1 mixture for both nucleophiles?

I know SN1 is unimolecular so changing the nucleophile would not change the reaction rate. Additionally, since the activation energy for the rate determing step was already surpassed, I believe the products will form in 1:1 mixture where both nucleophiles react equally and both products are of equal energy.


texts: Relation of pressure and temperature for an ideal gas at constant volume

texts:
I have a tank of ideal gas with volume $3.1\ \mathrm L$; I have $R = 8.314$, and 11 moles. The tank is filled at $23\ \mathrm{^\circ C}$ (not sure why that's relevant) and the tank will rupture at $P = 100\ \mathrm{atm} = 1.013\cdot 10^7\ \mathrm{Pa}$. At what temperature does the tank rupture?

I divided $PV$ by $nR$. However, plugging those numbers in gives

$$\frac{3.1 \times 1.013\times 10^7}{8.314\times 11} = 342374$$
in kelvin. However, my book gives $70.2\ \mathrm{^\circ C}$ as the correct answer. I assume my units are somehow profoundly messed up. Or maybe that mysterious 23 has something to do with it? What am I doing wrong?


texts: In my chemistry lab, we are testing the amphoteric properties of this metal. I understand zink can react with an acid or a base to form different compounds in solution based on pH. In one part of the experiment we are testing when ammonia in added gradually to $\ce{Zn(OH)2(s)}$ if it redissolves as $\ce{Zn(OH4)^2-}$ or if it redissolves as $\ce{Zn(NH3)4^2+}$. We are also testing the solution with indicators. So I’m assuming we are using the indicators to determine if there is a pH change because if there wasn’t, the complex ion $\ce{Zn(NH3)4^2+}$ would be using up all the weak base for this formation and none of it (or very little of it) would be able to act in solution and deprotonate water and generate $\ce{OH-}$?


texts: How to solvethis problem related to redox titration?

texts:
A $1.0\ \mathrm{g}$ sample containing $\ce{BaCl2*2H2O}$ was dissolved and an excess of $\ce{K2CrO4}$ solution added. After a suitable period, the $\ce{BaCrO4}$ was filtered, washed and redissolved in $\ce{HCl}$ to convert $\ce{CrO4^2-}$ to $\ce{Cr2O7^2-}$. An excess of $\ce{KI}$ was added, and the liberated iodine was titrated with $84.7\ \mathrm{mL}$ of $0.137\ \mathrm{M}$ sodium thiosulphate. Calculate the percent purity of $\ce{BaCl2*2H2O}$.

I first found the number of mili-equivalents of sodium thiosulphate  and equated that to the number of moles of pure $\ce{BaCl2*2H2O}$ times the n-factor i.e. $2$.

From this equation I get the number of moles of pure $\ce{BaCl2*2H2O}$ and then multiply this by its molecular mass to get the mass of pure $\ce{BaCl2*2H2O}$. But it comes greater than $1\ \mathrm{g}$. How to solve this?


texts: How do I determine molality from mole fraction without knowing how much of the solution I have?

texts:
What is the value of $x$ if $x$ molal solution of a compound in benzene has a mole fraction of solute equal to 0.2?

I tried calculating the moles of $x$ through the value given but there are two variables, i.e mole of $x$ and mole of benzene so I am stuck.


texts:
On rainy days there is a strong urin smell on trains in Tokyo.
I suspect this smell comes from ammonia.
On Wikipedia I read:

  Ammonia and ammonium salts are also found in small quantities in rainwater […] Ammonium salts are found distributed through fertile soil and in seawater.

Both is valid for Tokyo. In rainy season especially there is a lot of rain. And Tokyo is located at the sea.

Air conditioners work by drying the air.
Tokyo trains make extensive use of air conditioning.
Could this process intensify or make the ammonia to fall out and thus create the strong urine smell?
What other possibility is there for the strong smell?


texts:
Ammonia has a heat of formation of $-46 \:\mathrm{kJ/mol}$ (which means that it's formation from the elements releases heat). When mixed with iodine at room temperature, it makes nitrogen triodide (heat of formation +146 complexed with ammonia, +287 pure). With the slightest touch it decomposes explosively back into nitrogen and iodine. Thus the net reaction for both steps seems to be ammonia decomposing into its elements.

Iodine seems to be catalyzing its decomposition. However, such a highly endothermic reaction seems unlikely (evaporating water is only $40.65 \:\mathrm{kJ/mol}$). Also, ammonia's formation is spontaneous ($-26 \:\mathrm{kJ/mol}$) despite the entropy cost with $1 \:\mathrm{atm}$ reactants. This shouldn't go backwards.

So where do we get the energy to make this unstable compound? Iodine is a weak halogen, it barely reacts with hydrogen. Could oxygen drag this reaction forward by stealing hydrogen from ammonia?


texts: Positive electrode of an electrochemical cell?

texts:
I had the following problem:

Relevant information from Data Book:

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

  $E^0 = +0.80$

  and

  $\ce{Fe^3+ + e^- <=> Fe^2+}$

  $E^0 = +0.77$

This means $E_\mathrm{cell}$ is +0.03. (right)

And (I thought) that the left ($\ce{Fe}$) half cell has the positive electrode/anode as the ions lose electrons to the anode. I thought that the half equation with the more positive $E^0$ value went forwards.

However this is wrong. Where did I go wrong in my reasoning?


texts: Is white phosphorus really a cool burning fuel?

texts:
About 11 months ago, I posted a question on this SE site on cool flames.

One of the answers mentioned white phosphorus. However, a few weeks earlier, I played a game called Spec Ops: The Lines, in which the protagonist uses white phosphorus laden mortar munition, horribly burning dozens of soldiers and civilians. I was confused that the answer mentioned WP because of that moment from the game, and further googled it to find that WP munitions are actually heavily regulated, and using them against civilians is considered a warcrime. To me, that doesn't really seem compatible with "cool burning" at a temperature you can hold your hand in.

It's not my intent to cause this answer to be downvoted, but I'm confused whether the answer is factually accurate. According to Google, it burns at 5,000 degrees Fahrenheit, but that's the munitions.


texts: UV-Visible Spectroscopy in the analysis of sodium chloride in potato chips

texts:
Here is the question and answer out of an exam paper:

Firstly, I thought UV-Visible can also use radiation in the visible spectrum. Also when analyzing sodium chloride (a molecule), then UV-Visible would be more appropriate than AAS, because AAS would be used for just Na (Sodium). Would I be wrong to have said UV-Visible?


texts: What can be a metal cleanser for aluminum?

texts: I want to remove corrosion products in aluminum, but I don't have supply of nitric acid, as suggested by an ASTM method. Which can be a good substitute?


texts: Why does the cathode in an OLED require a low work function and the anode require a high work function?

texts:
I am currently doing some research on organic light emitting diodes and am just trying to get my head around some of the terminology and concepts because I am more from the organic chemistry side don't have a strong material sciences/physics background.
My reading indicates that the work function is the amount of energy required to extract an electron from a material. Electrons are injected via the cathode and electrons are extracted from the anode (i.e hole injection)
I keep reading that for OLEDs, the cathode should have a low work function to match the energy of the LUMO of the electroluminescent layer, and the anode should have a high work function to match the HOMO. I've read this in many journals and review papers but none of them explain why.
Any help would be appreciated.


texts:
I'm currently extracting some platinum from an electrode. One part seems stuck in some way (possibly welded) to a piece of steel. I'm guessing it's steel because it's magnetic. I did a heat test on the piece. Results:

Left side is platinum, right side suspected steel, and the platinum is not oxidized, as expected. What would be the best/easiest way to

determine if this is actually steel/iron;
dissolve or otherwise separate it?

My resources are limited, I've got a propane torch and household items, and can of course order chemicals if needed, but no acetylene torch or anything.


texts: I want to reduce vanadyl to vanadium (III), can somebody please suggest some appropriate methods for it? I am trying to make a redox flow battery for a project but I have only vanadyl sulfate.


texts: Supercooling, freezing point depression, and finding the right freezing point

texts: Pure liquid can be supercooled below its freezing point. Conversely, impurities in the liquid will cause a freezing point depression. How then is the freezing point accurate?


texts: Coffee and tap water reaction - results in gray tint

texts:
I use filtered water to make my coffee.

If I mix a few drops of said coffee with our tap water, it turns a grayish color; it's much darker than the coffee would turn the water by itself (I compared by doing a side by side comparison and adding an equal amount of coffee to filtered water, resulting in a much lighter brown (not gray) color that is closer to what I'd expect from coffee). It's a very pronounced effect (i.e. easily visible when you rinse out a coffee mug that has just a few drops of coffee at the bottom). Because of the distinct color change and the fact that it's significantly darker than it should be from simple mixing, it's obviously a chemical reaction.

What common tap water contaminants would react with coffee in this manner? Iron perhaps?


texts: Why are unpaired electrons especially reactive? Does pairing electrons decrease the reactivity of the electrons? But then doesn't forcing two electrons into the same orbital cost energy?


texts: Why can't a nucleophile attack the intermediate of an electrophilic aromatic substitution?

texts:
During an electrophilic aromatic substitution, the aromatic pi cloud interacts with an electrophile to form an arenium ion (AKA sigma-complex). The following image (from my organic chemistry class) suggests that aromaticity is always restored and that a nucleophile can't interact with the resonanced carbocation of the arenium ion.

If I were to replace the base in the above image with a nucleophile that is an extremely poor base (such as iodine), could the nonaromatic cyclodiene be formed?
Or would the reaction just halt instead?

Follow up question: If electrophilic aromatic subsitution doesn't work, how would one go about making the cyclodiene (with Nu and E substituents) from an arene? Is it possible?


texts: Is there any molecule visualizing software for Python?

texts:
I am looking for a free and open-source software written or wrapped for Python that would simply allow me to generate bunch of figures (in eps, jpg, or pdf format) from a set of xyz files, e.g. water clusters of different sizes.

I am aware of PyMol, but it seems a bit complicated to use (it has its own script language) for such a simple task and I guess it does not recognize xyz files, so I'd first need to convert to pdb format, etc.


texts:
As far I know fluorine is the most electronegative element in the periodic table and caesium is the most electropositve element. I had a conception that the reaction between the both would be the most violent as they have extreme opposite natures and perhaps they would do it faster than other elements.

But recently, I came across a book where I read that the electron gain enthalpy of chlorine is a bit higher than fluorine. This means when a reaction would occur with chlorine it would liberate more energy than that of the reaction with fluorine and therefore more violent. But, chlorine is less electronegative than fluorine.

So which reaction would be more sudden or fast and will liberate huge amounts of energy?


texts: If I add cooked grape juice to vinegar, does the juice undergo fermentation and also change to vinegar? Are there other conditions like exposure to air? How long would such a process roughly take?


texts: Is the triplet state of the cyclopentadienyl cation really aromatic?

texts:
While checking the ASAP articles of the Journal of the American Chemical Society I came across a very interesting contribution by Costa et al. who synthesised a $\ce{BF3}$ stabilised cyclopentadienyl cation 1 and confirmed that its singlet state was indeed antiaromatic as predicted by various definitions.[1] The authors, however, also included the following sentence:

  According to Baird’s rule, “the lowest triplet state for $4n$ rings is aromatic since the bonding energy is significantly greater than for the diradical reference structure”.[1]

This statement confuses me. In my introductory organic chemistry classes, I was taught the $4n+2$ rule along with simplified Hückel analyses to predict the relative energy levels. It was always pointed out that $4n$ (if planar and a single π system) represents an unstable, antiaromatic state which the system will avoid by distortion. This was explained by the triplet, biradicallic structure of the $4n$ systems. Yet here by Costa et al. I read that $4n$ triplets are actually aromatic.

How can I reconcile this new information with what I was taught previously? Reading the article and the references has not been able to help me.

Reference:

[1]: Costa, P.; Trosien, I.; Mieres-Perez, J.; Sander, W. Isolation of an antiaromatic singlet cyclopentadienyl zwitterion. J. Am. Chem. Soc. 2017, 139 (37), 13024–13030. DOI: 10.1021/jacs.7b05807.


texts: Forming ester from amide using protonated alcohol as catalyst

texts:
In my level of understanding, if I want to make an amide from an ester, I should add:

$\ce{H3O+}$ for hydrolysis to make carboxylic acid
$\ce{SOCl2}$ to form acid chloride
$\ce{ROH}$, pyridine to form the ester as product

I think this is a good way since it is difficult to form a more reactive product compared to the reactant, but in one of the question, I really want to try to make the 3-step process 1-step:

My attempt is to use a protonated $\ce{ROH}$ as acid-catalst, this time, to form a methyl ester. I used methanol, and somehow I can get to the end.
[for the 4th intermediate, I searched online and found that $\mathrm{p}K_\mathrm{a}$ of $\ce{(CH3)2NH = 10.73}$, $\mathrm{p}K_\mathrm{a}$ of $\ce{CH3OH = 15.56}$, this means that $\ce{(CH3)2NH+}$ is a better leaving group (lower $\mathrm{p}K_\mathrm{a}$ --> lower basicity --> more stable in the reaction mixture)]
Can someone please kindly tell me what is wrong with my mechanism? I know it should be wrong, since the 3-step process is the most suitable way and yield the most.


texts: Is it possible to design molecules of desired qualities?

texts: I was thinking if it would be possible to take into account every property of every atom known to man so that they can compute any type of compound they want. Is it possible to accomplish something like that with the present computation technologies or are the variables that are accounted in making of any kind of molecule and determining its properties too high?


texts: Why don't all atoms stick together due to dispersion forces if these forces are ubiquitous?

texts: If dispersion forces are always there wherever there are electrons, why don't two pieces of copper for instance meld together when put next to each other? Or why don't other substances stick to each other? For instance, I saw on a video that geckos have "sticky feet" due to dispersion forces.


texts: Can a benzyl ether be removed in the presence of an ester?

texts:
I'd like to deprotect a benzyl group for a Fráter–Seebach alkylation. Would it be possible to do this with a Birch reduction using Li/NH3 (or Na/NH3), without also reducing the ester carbonyl group?

If not, hydrogenation over Pd/C seems to be a plausible alternative. How else can I remove the benzyl group on oxygen?


texts:
I have found recommendations for making a soldering flux using boric acid mixed in with ethyl alcohol in 50/50 ration or 60/40 depending on the consistency desired.

Some have recommended that methyl alcohol is better to use as more of the boric acid can be dissolved in it? Is this correct?

If so, how do I calculate how much boric acid I can dissolve in isopropyl alcohol? What would be the best solvent to create a paste of boric acid to use as a soldering flux?


texts:
Basalt melting point: wet vs dry

I had a student ask me this in class the other day; I thought about it, but I still can't work it out.

Many mineral and rock hydrates (take basalt, for instance) have much lower melting points than their anhydrous counterparts.  I could not craft a plausible explanation for this.

I realize that hydrates have different crystal structures due to the presence of water, but I am unsure how this will affect the melting points.  If anything, the possibility of hydrogen bonding would make the melting point higher, no?


texts: What is causing a blue colour when sodium bicarbonate, vinegar and aluminium are reacted together?

texts:
My 10 year old has been experimenting in my kitchen!
The other day he wanted to know why when he reacted bicarb soda and boiling vinegar in a container with some aluminium foil, the solution turned blue.
I have no idea!
Your help is much appreciated.


texts: In the formula $\ce{[nBu4N]2[(UO2)2(\mu-\eta^2:\eta^2-O2)(NO3)2(\mu-Au(CN)2)2]}$, what does the colon stand for? Is this an official notation?


texts: Why is the vanadium(3+) ion paramagnetic?

texts:
I know that the electron configuration of vanadium is $[\ce{Ar}]\mathrm{4s^2 3d^3}$.

None of the electrons in the 3d subshell are paired. Once it loses these three electrons, shouldn't the remainder of the electrons be paired? How can $\ce{V^{3+}}$ be paramagnetic if it loses all its unpaired electrons?


texts: Pure Hydrogen and Dry Hydrogen Difference

texts: Do pure and dry hydrogen are the same? What does dry hydrogen actually means. And what does pure hydrogen means.


texts: Preparation of p-chlorobenzoic acid from p-chloronitrobenzene

texts:
I was reading my book where I spotted the preparation of p-chlorobenzoic acid from p-chloronitrobenzene.

The preparation method there was given as such:

$\ce{Sn/HCl}$
$\ce{NaNO2 + HCl}$ ($\pu{0-5 ^\circ C}$)
$\ce{CuCN}$
$\ce{H2O/H+}$

Now, the thing is that, I recall the first two steps from the process of forming diazonium salts but I have never seen the last two steps give the $\ce{-COOH}$ group.

Also I recall that $\ce{CuCN}$ gives us the nucleophile $\ce{CN-}$ where the negative charge is on the nitrogen atom and also that $\ce{H2O/H+}$ is used for hydration but I don't see how these two could help us form p-chloronitrobenzene from Benzenediazonium chloride.


texts:
Is it possible to incorrectly predict that two bond angles are different from van der Waals repulsions alone?

I'm thinking that because bond lengths differ when different atoms are involved that we could, at least theoretically, have two identical bond angles involving different molecules.

For example, say we are considering the bond angles of molecule $\ce{AXY}$ and $\ce{BZA}$.

X and Y are highly electron dense and also big. The first suggests a big bond angle; the second suggests a long bond length, which in turn suggests the possibility of a smaller bond angle.

Now consider $\ce{BZA}$. Z and A are not electron dense but also large. The first suggests a small bond angle. The second suggests a long bond length and thus a smaller bond angle.

Is it still possible for the two to have identical bond angles?


texts: C=O bond length comparison among cyclohex‐2‐en‐1‐one and cyclohex‐3‐en‐1‐one

texts:
I can see that in the first case a resonance would occur, and in the second case, there would be no resonance effect. I have read the fact that resonance reduces bond length due to partial double bond character.

According to that, shouldn't the $\ce{C=O}$ bond length in 1 be lesser than that in 2? The answer in my book is that the $\ce{C=O}$ bond in 1 is longer (reason is simply given as: "Resonance"). Could someone help me understand what's going on here?


texts: Reaction of aluminium trichloride with water

texts:
Since $\ce{Al^3+}$ is an acidic cation, shouldn't it react with water like this?
\begin{align}
  \ce{AlCl3 + 6H2O &<=> [Al(H2O)6]^3+ + 3Cl^-} \tag1\\
  \ce{[Al(H2O)6]^3+ +H2O &<=> [Al(H2O)5(OH)]^2+ + H3O^+} \tag2\\
  \ce{[Al(H2O)5(OH)]^2+ + H2O &<=> [Al(H2O)4(OH)2]^+ + H3O^+} \tag3\\
  \ce{[Al(H2O)4(OH)2]^+ +H2O &<=> [Al(H2O)3(OH)3](s) + H3O^+} \tag4\\
\end{align}

The 3rd step of the equilibrium rarely happens in water. But if we add a base, strong or not ($\ce{NaOH}$, or $\ce{Na2S}$) the equilibrium weighs to the right and $\ce{Al(OH)3}$ is formed.

But I've seen people write it as this.
$$ \ce{AlCl3 + 3H2O -> Al(OH)3 + 3HCl}$$
Is this correct? I need a certain answer.


texts:
https://youtu.be/ANlXQdpv6cc?t=1006
In this lecture, I am learning on the reaction of alcohol to alkyl halide using SOCl2 and pyridine. However, there are 2 different approaches on the first step.

The 1-step initial step, which is printed on many reference books.

The 2-step 'inital step' (forming the same intermediate), which the lecturer says is correct. This is because during a SN2, the sulfur (atom bonded to the leaving group - Cl) must be sp3 hybridized, otherwise, SN2 cannot happen (so figure 1 is wrong).
I have no idea why figure 1 is wrong though. Sulfur in SOCl2 is sp3 hybridized. (1 lone pair, '3' bonds), while the lecturer says the sulfur is actually dsp3 hybridized, not sp3. So my questions are:

is sulfur dsp3 or sp3 hybridized?
Why can't SN2 reaction happen if it is not sp3 hybridized?

(3.) Which step above is the most plausible?


texts: Is it possible to convert a combustion reaction directly into an electrochemical one?

texts:
I'm fairly inexperienced in chemistry so forgive me if this question is silly but, why is it not possible to convert a combustion reaction to an electrochemical one directly and harvest the electrical energy instead of the thermal energy? For example in my chemistry textbook it says:

$$\ce{CH4(g) + 2 O2(g) -> CO2(g) + 2 H2O(g) + energy}$$

The book then says: "Even though none of the reactants or products in this reaction is ionic, the reaction is still assumed to involve a transfer of electrons from carbon to oxygen"

my question is, why is it necessary for us to burn fuel in say combustion engines if technically electrons are being transferred, is it possible to create a new engine that will take say one of the hydrocarbons found in gasoline plus oxygen and instead somehow turn the generated energy to the electrical form directly without burning it? Perhaps some complicated engine that uses a cycle similar to the ATP cycle


texts: What are the major factors that influence LogP

texts: The partition coefficient is a very useful metric in characterizing compounds particularly drugs. What chemical properties influence that partitioning? Are chemical moieties additive in their LogP? What if the compound has both hydrophobic and hydrophilic ends?


texts: How difficult is it to synthesize Novichok agents?

texts: In the light of the current UK-Russia events, how difficult is to synthesize Novichok agents (with known structures)? Is it something that can be made at any well-equipped university and/or chemical factory, or does it involve some very specialized or possibly secret knowledge?


texts: Statistical model of ligand substitution

texts:
Recently, I was told that in case of a particular step of a generic ligand substitution reaction:

$$\ce{M(OH2)_{$N - n$}L_{n} + L <=> M(OH2)_{$N - n - 1$}L_{$n + 1$} + H2O}$$

The probability of the forward reaction and by extension, the equilibrium constant of this step, $K_n$ would be proportional to

$$\frac{N - n}{n + 1}$$

by a purely statistical analysis. Now I have thought about this for quite a bit, but I can't understand the mathematical reasoning behind arriving at this expression. I suspect it has something to do with the numbers of the ligand being replaced and the ligand which is replacing the other one. Can anyone explain the process of arriving at this expression using simple (if possible) reasoning?


texts: Why does Co(I) have a 3d8 configuration?

texts:
Why is the electron configuration of $\ce{Co^+}$ $[\ce{Ar}](\mathrm{3d})^8$?
Since neutral $\ce{Co}$ itself has a $[\ce{Ar}](\mathrm{4s})^2(\mathrm{3d})^7$ configuration, wouldn't the ionised electron be lost from the $\mathrm{4s}$ orbital, leading to an electron configuration of $[\ce{Ar}](\mathrm{4s})^1(\mathrm{3d})^7$?


texts: What do ε₀ and V mean in a Pourbaix diagram?

texts:
From Wikipedia:

What does this graph mean?
What is $\varepsilon$?  It looks like $\varepsilon_0$, like the vacuum permittivity, but what does this have to do with the polymorph and/or isomers of ferrite or hematite?
And what is the V or 'five' in square brackets after the $\varepsilon_0$?


texts: What kind of stereoisomerism do cisplatin and transplatin exhibit?

texts: Cisplatin and transplatin are obviously isomers, more precisely stereoisomers. Now, they aren't chiral, so they cannot be enantiomers. They cannot be diastereomers either since they don't have two stereocenters. They don't belong to cis/trans stereomers either since they are a subgroup of diastereomers and again require two stereocenters. So - what the heck?


texts:
Hydrocarbons have some of the highest energy densities and specific energies of any chemical fuel.  Unfortunately, our primary use of them is in thermal engines, whose efficiency is limited by Carnot's Theorem.  Batteries, on the other hand, do not have this limitation and can be engineered to arbitrary efficiency.
Sony has designed a biobattery which runs on glucose.  While this is an impressive achievement, liquid propane and butane have a much higher specific energy (> 3x) than glucose, as well as a higher energy density (not surprising, since glucose contains oxygen atoms which are basically dead weight for a battery).
Is there any reason that the enzyme catalyst approach could not be applied to simple short-chain hydrocarbons like propane through octane?  I assume that the battery's performance (current discharge) is proportional to the amount of enzyme present, and thus, the weight overhead for the battery depends on the amount of desired current.  Are the enzymes expected to be a significant fraction of the mass/volume of the battery?
It seems that an electric airliner running on Jet-A fed to bio-batteries could theoretically have more than twice the range of best current turbofans.  Is this an unreasonable conclusion?


texts: Predicting order of nucleophilic substitution reactivity

texts:
What order of reactivity do you predict will be observed when each alkyl halide is mixed with sodium iodide in acetone?

  1-Chlorobutane
  1-Bromobutane
  2-Chloro-2-methylpropane
  Bromobenzene
  2-Chlorobutane
  1-Chloro-2-butene

I know that $\ce{I-}$ is the best leaving group, followed by $\ce{Br-}$ and $\ce{Cl-}$.
For the $\ce{NaI}$ reaction, tertiary halides should react fastest and primary halides should react slowest.

  What order of reactivity do you predict will b observed when each alkyl halide is mixed with silver nitrate in ethanol?

  1-Chlorobutane
  1-Bromobutane
  2-Chloro-2-methylpropane
  Bromobenzene
  2-Chlorobutane
  1-Chloro-2-butene

For the $\ce{AgNO3}$ reaction, primary halides should react fastest and tertiary halides should react slowest.

Which takes preference, leaving group or rank? Also, how do I rank 1-chlorobutane vs. 1-chloro-2-butene? They are both primary and the halide is $\ce{Cl-}$ for both.


texts: Scan type of DFT calculations adding Freq=Raman keyword

texts:
I´m doing a scan calculation by adding Freq=Raman keyword. My objective is to obtain the Raman spectrum of each conformation in my compound. However, when i write the Freq=Raman Keyword, only the Raman spectrum of the last conformation in the scan is calculated . How can i solve this problem?
Thanks!


texts: Why is this molecule considered a cis isomer of 2-bromobut-2-ene?

texts: I know that we have two CH3 groups on one side and restricted rotation around the double bond but aren't we supposed to have two similar groups on the other side as well ? Does this mean that we only need one side of the molecule to have identical groups/atoms in order to call it a cis isomer ?


texts: What makes a species "fluorescence quencher"?

texts: I just came across an article where they said that sodium fluoride is not quencher (in the context of fluorescence). Why is NaF not a quencher but NaBr is one?


texts: Is it always the case that when a reaction's products are higher in energy than its reactant, then the reaction is not favored?

texts: If this is the case, can you give a brief explanation why is this always the case?


texts: Why there is hydrogen bonding involved in salt bridge formation between glutamic acid and lysine?

texts:
I saw this figure on Wikipedia:

After seeing this image I got really confused about the difference between these two, or maybe the similarities. Of course, I understand that a hydrogen bond can be seen as +/- interaction (because of the dipole). However, I don't understand why this Lys + Glu interaction would also make a hydrogen bond. If it would, I would expect the hydrogen bond between the double bounded oxygen and the $\ce{N}$ atom from the $\ce{NH3+}.$
I hope someone can explain me what this figure means in respect to both of the interactions shown.


texts: How does Carbon Dioxide have a degree of freedom of 6?

texts: Carbon Dioxide has a degree of freedom of 6, yet from what I understand, it is a linear molecular shape. Therefore, the number of axis of linear movement is 3 (x,y,z) but there are only two axis of rotational movement since the center of mass essentially does not rotate on one of the axis due to its linear shape. Yet I'm pretty sure my textbook is saying that carbon dioxide has a degree of freedom of 6 when that should be wrong. Can someone explain?


texts: How to prevent losing solvent into the vacuum pump in rotovap solvent collection?

texts:
This is a practical question about the use of rotary evaporators ("rotovap"). So I'm asking for answers from people who actually use the things.

A rotovap typically uses a cold condenser to condense the solvent into a collection flask. But the distillation is typically done under weak vacuum as well. So the solvent sitting in the collection flask seem susceptible to re-vaporizing and getting sucked into the vacuum pump. Now I have a cold trap in front of my pump that should be cold enough (-50C) to trap most solvents under weak vacuum.

I think the answer is that if the vacuum is weak enough to vaporize the solvent under the hot water bath, but not under the cooler ambient air temperature, then the loss to the pump should be minimal. Indeed, this is what the instructions for the rotovap suggest.

  Question: In practice, what are the risks to losing solvent into the pump?


texts: Why is logP quite a bit lower in cyclohexane than in hexane?

texts:
http://www.rsc.org/suppdata/nj/b3/b303016d/b303016d.pdf

If anyone doesn't know the definition, logP is the the log of the ratio of a molecule in dioxane to water. So a high logP would mean the molecule is mostly in the organic dioxane layer rather than water. E.g a molecule with a logP of 2 would prefer the organic layer 100 times more than water, and would be considered hydrophobic/lipophilic.

Hexane logP=4.15, very hydrophobic and almost all of it will stay in the organic layer.

Cyclohexane logP=3.66, still very hydrophobic, but hexane is almost 4 times more hydrophobic than cyclohexane. Can anyone please try to explain why the cyclic molecule appears to like water slightly more than its straight chain counterpart?


texts:
Am giving presentation over Coenzyme Q10 Wednesday for my final project, but we haven't studied any biochem this year.  So questions have arisen.

CoQ10 has a Quinone head, an isoprenyl tail, and these additional oxygens on the left and three methyl groups not a part of the Quinone head or tail.

Is there a name for these two oxygens and three methyl groups?  Or a category?  Like the benzene ring and two oxygens is the Quinone head, what are the additional oxygens and methyl groups called, if anything?

CoQ10 diagram: http://www.mysupplementstore.com/media/wysiwyg/structure-of-CoQ10.jpg


texts: Do ligands with a positive charge exist?

texts:
Are there positively charged ligands which can bind to a central metal atom to form coordination compounds?

My thoughts:

I know that ligands are Lewis bases which donate a pair of electrons, and the central metal atom is usually a Lewis acid.

However, a positive charge on a species usually means it is electron-deficient. In that case, there would be no suitable electrons for it to bond to the central metal atom. So, even if positively charged ligands do exist, I think there would be very few. In such cases, it might bond with central atom which is electron rich forming the coordinate bond in the opposite way. Is that possible?


texts: How to predict which type of optical isomerism

texts: When I learnt about optical activity in school, my teacher told me that there is no way to theoritically predict whether a compound is dextrorotatory or leuvorotatory. How is that possible?


texts: Carcinogenicity of polynuclear hydrocarbons and benzene rings

texts:
(1933) established that polynuclear aromatic hydrocarbons (PAHs) were
carcinogenic components of pitch. ... Although less is known about
their health effects than about those of PAHs, it is clear that some
nitro-PAHs are potent mutagens and carcinogens.(1)
Benzene and polynuclear hydrocarbons containing more than two benzene
rings fused together are toxic and said to possess cancer producing
(carcinogenic) property. Such polynuclear hydrocarbons are formed on
incomplete combustion of organic materials like tobacco, coal and
petroleum.(2)

From the two sources cited above, I keep seeing that polybenzenoid compounds like 1,2-benzanthracene, 3-methylcholanthrene and 1,2- benzpyrene are mentioned to be carcinogens.

In general, why are polynuclear compounds carcinogenic? I google searched on this topic and all I could find is their effects and concentrations in various substances.
My questions are:

Why are they carcinogenic

Is there a reason for a given organic compound to be carcinogenic?

References

Potential Carcinogenic Effects of Polynuclear Aromatic Hydrocarbons and Nitroaromatics in Mobile Source Emissions, STEPHEN S.HECHT(link)
pg403, NCERT Class XI part 2(pdf link)


texts: How can I model cellular membranes in terms of topology?

texts:
I'm reading from Principles of Physical Biochemistry by Kensal E van Holde (1998-01-06) in order to review some biochemistry and work my way toward a more mathematical approach to understanding chemistry.

On page 18, chapter 1 (Biological Macromolecules), I read

  "The structure of an integral membrane protein can be thought of as being inverted relative to the structure of a water soluble-protein, with the hydrophobic groups now exposed to the solvent, while the hydrophilic atoms form the core. An example of this inverted topology is an ionic channel (Figure 1.12). The polar groups that line the internal surface of the channel mimic the polar water solvent, thus alloweding charged ions to pass readily through an otherwise impenetrable bilayer."

I don't have a picture handy to show you Figure 1.12, but essentially it is a channel protein.

What's interesting to me about this passage is their use of the word topology. It reminded me of algrabraic topology's notion of a topology on a set, but I can't seem to state this membrane chemistry in terms of the mathematical formalism.

In algebraic topology, a topology $\tau$ on a set $X$ is a subset of the powerset $\mathcal{P}(X)$ where the elements of $\tau$ are open, meaning they satisfy

Containing the original set and the empty set:$$X \in \tau, \emptyset \in \tau$$
Unions of sets in the topology are closed. $$\{ U_i \}_{i \in I} \subseteq \tau \implies \bigcup_{i \in I} U_i \in \tau$$
Closure under finite union. $$\{ U_i \}_{i=1}^n \subseteq \tau \implies \bigcap_{i=1}^n U_i \in \tau$$

My initial thinking on this is that the membrane could be one set, the extracellular matrix a second set, and the intracellular matrix as a third set. Each of these sets might be thought of as their own topologies, and that their mutual intersections should be empty so long as you cleanly partition the spaces. But then again, membranes have a lot of intermolecular spaces within them; seems structurally complicated.

While knowingly extrapolating beyond the original intended meaning of the authors, how can I model  cellular membranes in terms of topology?


texts:
I have encountered this equation:
$$\ce{SO4^2- -> S2O8^2-}$$
In this reaction 2 of the oxygen ions change from $-2$ to $-1$ so they are getting oxidized.

It is because two oxygen ions are connected together.

A question rises: why can't we oxidize oxygen ions in $\ce{NO3-}$ or any other?


texts: The Heisenberg uncertainty principle implies that it is not possible to calculate the position and velocity of a body at the same time accurately. Electrons follow this principle since their orbitals are just probabilities where they may occur. But in the case of protons, we are kind of certain about their position in the atom. So shouldn't they have a very, very, very high velocity to balance the certainty in position?


texts: Why does the CO2 gas quantity in Sodastream cartridges differ in different nations?

texts:
Just was looking at the $\ce{CO2}$ cartridge for the Sodastream soda / seltzer maker I was planning on buying and this bit of info caught my eye:
Any idea why they may want to pack $\pu{25 g}$ less $\ce{CO2}$ for South Africa? Is it some regulatory issue? Marketing gimmick?
Or more interestingly, some technical factor?


texts:
Elementary reactions of decomposition of ozone with chlorine are as follows (substance with $^*$ is reaction intermediate):
  \begin{align}
\ce{Cl2 + O3 &-> ClO^* + ClO2^*}\tag{1}\\
\ce{ClO2^* + O3 &-> ClO3^* + O2}\tag{2}\\
\ce{ClO3^* + O3 &-> ClO2^* + 2O2}\tag{3}\\
\ce{2ClO3^* &-> Cl2 + 3O2}\tag{4}\\
\ce{2ClO^* &-> Cl2 + O2}\tag{5}
\end{align}
  Calculate decomposition rate of ozone using steady-state approximation.

I have this physical chemistry homework, and tried to solve, but it was too complicated for me to do. Could anyone help me?

(I'm sorry, but I'm not good at English, so maybe my sentences are strange.)


texts: How to trace an energy versus time diagram?

texts:
I'm looking for data to create a simple graph of an exothermic or endothermic reaction but can't find any.
Could someone help me with some enough data to create a simple graph displaying energy as function of time.


texts: What will be the reaction between tin (II) chloride and copper (II) chloride?

texts:
I just tried conducting an experiment during lunch today. Now, I calculated this reaction 4 days ago dealing with electrochemistry,

$$\ce{SnCl2 + CuCl2 -> Cu(s) + SnCl4}$$

Theoretically, I got these 1/2 cell reactions from a couple different sources (one of which are posted below):

$$\ce{Sn^2+ -> Sn^4+ + 2e-} \quad E° = -0.15~\mathrm{V}$$

$$\ce{Cu_{(s)} -> Cu^2+ + 2e-} \quad E° = -0.34~\mathrm{V}$$

Using basic electrochemistry, we know that Copper prefers to be copper metal. Due to its overbearing power over the tin(II) ion, the copper(II) ion forces the tin(II) ion to become tin(IV).

I did not check the reduction or oxidation potential of the chloride ion (since the chloride ion is the most stable form of chlorine due to its (relative to the other compounds in this experiment) high ionization potential. I concluded that chloride would be a spectator ion.) Finally resulting in this net ionic reaction.

$$\ce{Sn^2+ + Cu^2+ -> Cu_{(s)} + Sn^4+} \quad E^\circ_{\rm cell} = 0.19~\mathrm{V}$$

I mixed the compounds in $150~\mathrm{ml}$ of deionised water. Later combining them only to end up with a milky-green colored solution. I saw some brown-red precipitate at the bottom of the beaker. however, only a small amount of what I think is copper precipitated. Tomorrow I will place the beaker with the solution onto a hot plate in hopes of speeding up the reaction.

I was wondering if a smaller difference in electrical potential between the two half cells results in a slower reaction. The other thing I was wondering concerns any other ideas or misconceptions I may have faced while conducting this experiment.


texts: Is there a (carbon) heterocyclic compounds named from number three to infinity?

texts: For example, oxepane is a 7-atom ring. Can there be 8-atom ring or 9-atom ring … or million-atom ring to infinity?


texts: Do we get high on "methampetamine" naturally?

texts:
First off, I'm new here and I cant tell if this is a chemistry or a biology question. It's both and if I ask on biology forums, they say to ask on chemistry forums and vice versa. So sorry if this question is more geared towards biology.

I am really amazed that our brain produces Phenethylamine any time we do something rewarding. I need to confirm this, because if this is true, I'm high right now... (wait so meth isn't bad?)

Phenethylamine gets biosynthesized in our brain to get converted into dopamine (and also L-DOPA). But the funny thing is that the molecular formula of Phenethylamine is exactly the same as methamphetamine just without the two methyl groups.

From my understanding, if you consume methamphetamine the liver metabolizes methyl groups into hydroxyl preventing it from metabolizing Phenethylamine instantly and making the hydroxyl group a free radical, so the hydroxal group is separated once it reaches the brain, therfore consuming methamphetamine would be 10x more potent then if you consume Phenethylamine. The same way the high from Dextroamphetamine (the chemical used in Adderall which is the same as methamphetamine, just with one methyl group instead of two, making it not as potent) is 5x weaker then methamphetamine.

Consuming pure Phenethylamine would make the liver metabolize 90% of it making the brain receive only around 10% of it. Phenethylamine is naturally occurring and is sold on Amazon as pure powder.

So my question: is Phenethylamine the same as meth, just with 1/10th of a high, considering that is what methamphetamine gets metabolized into?

I didn't mean get high on methamphetamine in the title, but the end product of methamphetamine (apples and oranges)

And does that mean that meth isn't that bad as the media claims it is (besides hepatoxicity)?


texts: Why in thermodynamics, some reactions are taken at constant temperature and pressure? What is its significance?

texts: To be more specific while deriving relation between cell emf and free energy, constant temperature and pressure  assumptions were taken. Why?


texts:
Are there any examples of Schottky defect in ${\ce{AB_2}} $ type crystals.
Does Schottky defect require that the cation and anion be of equal size?
According to me it is not necessary that the two ions are of equal size as even ${\ce{NaCl}} $ shows Schottky defect but ${\ce{Na+}} $ has radius is 95 pm and ${\ce{Cl-}}$ has radius of 181 pm which is a bit less than double of that of ${\ce{Na+}} $


texts:
This makes little sense to me, with a lot of contradictory statements I have learnt.
For example:
$$\ce{N2 + 3H2. <--> 2NH3}$$

($\mathrm{\Delta h = -46.2~kJ~mol^{-1}}$)

I have been told a higher kc = large amount of product being formed in the equilibrium.
So therefore why if I increase the pressure why don't I get a increase in kc as the forward reaction is favoured creating more product?

After asking around I have come to the conclusion that a reaction has many kc values depending on temperature , but then I don't see how the kc equation can work as you can get different concentrations of A B C and have constant temperature by increasing pressure.
And also the statement of higher kc = more product is also wrong.

Obviously I'm wrong but I'm just explaining where my confusion lies in my logic.
Where have I gone wrong? Or is there an explanation that will clear things up?


texts: Is it correct to say that 'x' litres of a gas were produced in a reaction, calculating x using the ideal gas equation, since the volume occupied by a gas is taken to be the volume of the container it is in?


texts: Which of the following represents the steps needed to produce crystals from a solution?

texts:
From a solution of zinc sulfate, we have excess zinc in a solution and need to form pure crystals.

Possible methods:
A- Filter, concentrate the solution, evaporate to crystallization point.
B- Filter, evaporate to crystallization point, distill.

My thoughts:
In choice A, how can we concentrate the solution (without heating it) if there already is some excess zinc? And in choice B, the last step (distillation), do they mean that we will heat the mixture of crystals and un-crystallized solution so the solution will evaporate and we will be left with the crystals? Wouldn't that remove some of the water of crystallization of the crystals too?


texts: Nitration of pyrrole with sulfuric and nitric acids

texts:
Would 2,5-dinitropyrrole be a product of nitration of pyrrole with $\ce{H2SO4/HNO3}$? It seems that 2,5-dinitropyrrole is not formed when using $\ce{Ac2O/HNO3}$ (ref 1). Is this just because of the mild conditions used, or does this reflect the pyrrole ring being more deactivated by the first nitration than a benzene ring would be?

1 Cooksey, A. R.; Morgan, K. J.; Morrey, D. P. Nitropyrroles—II : The nitration of pyrrole. Tetrahedron 1970, 26 (21), 5101–5111. DOI:10.1016/S0040-4020(01)93163-1


texts: Are LiBr and LiCl ionic or covalent? Are they soluble in water? Some texts say they are partially soluble in water and in organic solvents also. Or can it be believed that they have more of a covalent character than ionic character ?


texts: Choosing Stationary Phase Column Chromatography

texts: When using column chromatography to purify an amine, alumina is the best choice of stationary phase (rather than silica gel.) Could this be due to alumina being slightly basic and thus the impurities are retained in the column longer?


texts: Does any element have nutritional (caloric) value?

texts:
Is there any single element (e.g. possibly carbon) that can be eaten, which has a nutritional value such that it provides calories?

I found on Wikipedia (dietary element) that there are certain elements that our bodies require.  I suppose oxygen could count as such a nutritional element, although we breathe it instead of eat it.


texts: What is the largest non-polymeric heterostructured molecule possible?

texts:
I must admit I'm not a chemist but a biologist, so please forgive me if I'm getting some of my terminology wrong. I want to ask a question about the biggest possible complex molecule that can exist in Nature.

I know that certain crystals like quartz and gems like ruby and diamond can grow very large and they could be called molecules. Also, polymers can grow very long with a complex 3D structure.

However my question is about a chemical compound which isn't a polymer but has a complex non-repetitive 3D structure of many covalently bound atoms. If we rely only on synthesis and try to construct the biggest molecule possible how big can we get?

Does the answer vary if we are talking about molecular size, molecular mass, number of atoms, 3D structure (I imagine there can be some very big molecules containing cavities which are lighter and have fewer atoms than other who have more atoms and are heavier but are dense) and so on ?

Or is there a single class or maybe even a single molecular species which combines all these characteristics and can produce the largest molecules no matter what characteristic we use to measure this quantity?

If there is such a class of compounds what it is and how do we synthesize it?


texts: What are aryl chlorides currently used for?

texts:
In a recent paper by Gustafson et al. (DOI: 10.1021/acs.orglett.6b02650) the authors open with the argument that

  aryl chlorides are both versatile synthetic handles and common functionalities in drug discovery.

However, they fail to give examples of current use in industry and pharmaceutical research.

I know of only one reaction that aryl chlorides are used for, and that would be the Ullmann biaryl (ether) coupling. Are there any other ones for which aryl chlorides are a good starting material?
And then, about the second part of the sentence: Why are aryl chlorides a common functionality in drug discovery? Is it simply that compounds are chlorinated and then compared to their unchlorinated analogues?

All in all, please provide examples for the quoted statement above.


texts: Solubility and heat release of ytterbium (III) sulfate in water

texts:
Question:

  The plot of solubility of some salts against temperature is given on the right. A salt like $\ce{NaCl}$ can be recovered fully, when dissolved in a solvent and the solvent is removed by evaporation. Choose the correct statement(s):

  No heat is absorbed or released when $\ce{NaCl}$ is dissolved in water.
  More heat is released when the ions of $\ce{Yb2(SO4)3}$ are solvated than that absorbed when the ions are separated.
  The heat of solution is negative for $\ce{H3BO3}$.
  When $\ce{AlCl3}$ is dissolved in water and the water is evaporated, solid $\ce{AlCl3}$ is recovered.

My approach: (1) is clearly correct. (3) and (4) are clearly wrong. My confusion lies with (2).


texts: Reaction of magnesium with the surrounding air

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In my lecture notes for inorganic chemistry, it is stated that magnesium has high affinity for oxygen but is rather stable at room temperature in air.

Can anyone explain why this is the case?


texts: What does the "h" "k" and "(5.2.2.02,6)" mean in Dibenzo(h,k)-4-oxatricyclo(5.2.2.02,6)undec-8,10- diene-3, 5-dione

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I am preparing to do an experiment that involves synthesizing Dibenzo(h,k)-4-oxatricyclo(5.2.2.02,6)undec-8,10- diene-3, 5-dione via a Diels-Alder reaction.

Could someone please explain the nomenclature for this molecule? Specifically, what the "h", "k" and (5.2.2.02,6) mean?

Below is the reaction:


texts: Why aren't the R-side-chains of acidic and basic amino acids the site of polypeptide synthesis?

texts:
If polypeptides are synthesized by acid-base reactions between the carboxyl group of one amino acid and the amine group of another amino acid, what stops the formation of a peptide bond between the alpha amine group of one amino acid and the carboxyl group (that's in the side chain) of another amino acid?

For example, why doesn't the side chain of glutamic acid bond to the alpha amine of another amino acid (essentially creating a new branch at which polypeptide synthesis can occur)?


texts: Are there notable organic compunds which look very similar but have very different properties?

texts:
I've seen people arguing for some questionable "miracle cure-all" alternative medicines not scientifically, but by their own logic. A common claim is, that if a compound looks very similar to an important compound found in our body, it must be very beneficial. By looks very similar I mean the drawings of their structures look similar, as in, similar as images.

I found this reasoning alone to be unscientific. (correct me if I'm wrong). I would like to explain it to people, but it's hard to do if they lack even basic understandings in chemistry, and have claims like "I think it might happen to be like this, so it's a proof that it's like this".

So, I'm looking for a counter-example. Are there famous and well-known (organic) compounds which look similar on a structure drawing, but have vastly different properties, for example one is either beneficial or a necessary component of our body, and the other is highly toxic?

I'm sorry for the possible unclear terminology, English is not my first language and I didn't find any better term to say "structure drawing" for something like this


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So a teacher at school told me that strong acids do not create an equilibrium in general, while weak acids do (thats the difference, strong acids namely ionize completely). However, I lately stumbled upon a passage reporting that when experimenting with extreme pH, so extreme concentrations of acids, strange things start to occur and strong acids are not able to ionize completely, resulting in an equilibrium. I would explain this by the extreme concentration -> less water molecules in the vicinity of acid to react -> less chance to ionize.
But then I thought, are strong acids in fact not also creating an equilibrium, but because they react so strongly, they immediately release their proton. The conjugate bases are extremely weak, but they should be able to pick up a proton right? They simply become and acid, and release it immediately again. Please clarify this entire situation for me, thanks already.


texts: Calculating the x, y and z distances between two molecules - AMBER (Molecular Dynamics)

texts:
I am interested in calculating the x,y and z distance between two molecules over a given simulation time. I know how to calculate the total (r) distance between them, but I want the distance between them along all three dimensions.

For the total distance, cpptraj can be used as:

parm prmtop-file
trajin netcdf-file
distance DIST :1-4@heavy-atoms-from-molecule-1 :5-8@heavy-atoms-from-molecule-2 out dist.out
run
quit

But like I said before, I do not want the r-distance. Is there anyway to calculate the x,y and z-distances in cpptraj? If not, what other alternatives do I have?