texts: Rust forming and being washed off by water

texts:
I have noticed that, when exposed to water for a few days, the steel in my wagon turns into rust. After several more weeks, the rust that formed is dissolved in the water, and once I pour the water out there isn't any rust where there previously was rust.

This is unusual because iron oxides and iron hydroxides (the components of rust) don't normally dissolve in water, and so the water just keeps being reduced and the iron keeps being oxidized.

How can it apparently happen such that steel turns to rust, then back to steel with no rust, in the presence of water if rust does not normally dissolve in water?

This happens in a cycle like this:

steel + water = rust -> rust + water = steel + rusty water


texts: not understanding buffering region vs equivalence point

texts:
"During the titration of a weak polyprotic acid with a strong base, the first stoichiometric equivalence point occurs when the moles of added base are equal to the moles of the initial acid species.  Prior to the equivalence point, a buffering region forms in which both the weak acid and its conjugate base are present and the pH is determined by the pKa and the ratio of the acid and base species concentrations.  When the concentrations of the acid and base species are equal, pH = pKa."

The bolded statements seem like they're saying the same thing. What is the difference between the buffering region and the equivalence point?

Isn't the buffering region when [HA] = [A-], so that in the HH equation, pH = pka? The first bolded statement makes it sound like the first equivalence point is also when [HA] = [A-].


texts: How many non-cyclic isomers exist for C4H7Br?

texts: The compound Q has the formula $\ce{C4H7Br}$ and contains a double bond. How many non-cyclic isomers exist for Q? Should include cis-trans and any other form of isomers as well.


texts: E/Z stereoisomers : assigning priorities with a cycloalkane group

texts:
For the following compound

Right hand side of double bond:
$\ce{CO2CH3}$  is highest priority due to the extra carbon (as we work along both chains)

But for the left hand side oft he double bond I am stuck.

I thought maybe we take the blue path, and as there is 3 carbons as opposed to 2 on the orange path, the blue path is the highest priority :

But my book gives the opposite answer :

There is a similar question here How to assign E/Z configuration according to the Cahn-Ingold-Prelog rules when subsituents differ only by stereochemistry   but in the case of my question the carbons on the cyclo which are directly after the double bond do not have groups attached.


texts: Does resonance overrule hyper conjugation in terms of stability in alkenes?

texts:
Which of the following is more stable ?

  $\ce{CH2=C(CH3)-CH=CH2}$
  $\ce{CH3-CH=CH-CH3}$

I was going for answer 2 because it has 6 hyper conjugative effects. I found the answer given to be 1, which has 3 hyper conjugations but more resonance structures. Will the R-effect meet the deficit of 3 hyper conjugations and make 1 more stable than 2?


texts: How do I decide the parent chain of an organic compound that has a ring as well as a side chain while naming the compound?

texts: I think that this is decided by the number of carbon atoms. The part which has greater the number of carbon atoms, is considered the parent chain. But this fact is not leading to the correct result always. Are there some rules that govern this fact besides the number of carbon atoms.


texts: Which is most likely the acidic proton in ascorbyl palmitate?

texts: The structure of ascrobyl palmitate contains a vinyl group, so I assume the red proton would be:


texts: Nitration of Naphthalene Having Electron Withdrawing Group

texts:
In the following nitration which one out of 50 and 51 will be the major product.

In my book it is said that (51) will be major.But in this video it is said that (50) will be major.I'm confused.

Oh yes I saw this answer too Nitration in anthracene and naphthalene but did'nt help in my case.


texts: Finding molecules that you randomly create using a modeling kit

texts: I recently bought https://snatoms.com/ (which is just a real-life modeling kit for atoms/molecules) and was just keen on learning about chemistry in general. I often randomly join atoms to make up some molecule. Was wondering if there is an easy way to find the molecule i created?


texts:
As we all know, if we put $\ce{H^+}$ ions in water then water reacts with them and produces $\ce{H_3O^+}$:

$$\ce{H_2O + H^+ <=> H_3O^+}$$

My question is, why does water react with $\ce{H^+}$ in the first place? It doesn't have an electron, then how can the reaction occur?

And again, it's already stable and adding one more $\ce{H^+}$ will, in my understanding, destabilize it as it will have one more proton in the molecule.


texts: Solubility of carbon dioxide in 1M sodium hydroxide solution?

texts:
I know that carbon dioxide is soluble and forms carbonic acid, but exactly how is solubility measured?

How soluble is carbon dioxide in a 1M solution of sodium hydroxide?


texts: Why is calcium stearate (soap scum) insoluble in water while potassium/sodium stearate are soluble in water?

texts:
So, potassium and sodium containing soaps work because they have a polar end and a non-polar structure for the rest of the molecule - they can thus be dissolved in polar and non-polar solvents. This is why they're used for cleaning, as they can basically clean off anything non-polar like oil while still lathering/rinsing off with water.

Now, my question is, what changes when 'hard soap' is formed? Here, when the stearate ion of soap is released in hard water, an ion of magnesium/calcium bonds with it forming 'hard soap'. The thing I don't get is why it is now insoluble in water. What's changed?

Based on electronegativity values, there's very little difference between atoms of potassium, sodium and calcium/magnesium, not enough to change the polarity. The ion from the hard water bonds with an oxygen atom, and the electronegativity difference between an atom of calcium/magnesium and an atom of oxygen is still large enough for it to be polar at the same end as it was with sodium/potassium.

What's going on?


texts: Why is the boiling point of polonium less than that of tellurium?

texts:
My textbook states that polonium has a lower boiling point than tellurium because it has weaker intermolecular forces of attractions (van der Waals forces).

Why are van der Waals forces of attraction less in polonium as compared to tellurium?

Polonium's atomic size is greater than tellurium, and I believe van der Waals forces are directly proportional to the surface area. Is this the reason?


texts: Mirror reaction - avoiding silver nitride

texts: I am interested in experimenting with depositing silver on glass (mirror). I've read several papers and watched youtube videos but wish to be better informed about the risk of explosion. The mixture is silver nitrate solution, sodium hydroxide solution, ammonium hydroxide and dextrose solution. Is there a combination, or concentration of any of these that forms silver nitride in less than 3 hours? One video suggested heating the mixture to enhance the deposition onto microscope slides, but neglected to mention a temperature, or whether it hastens the formation of the explosive silver nitride. Any comments on whether $\mathrm{50^oC}$ for 1 hour would have ample margin of safety? Thanks!


texts: adiabatic expansion vs Joule-Thomson Effect

texts:
Source: The1stLawofThermodynamicsLesson4

I am looking for difference between adiabatic expansion and Joule-Thomson effect. Looking at the setup demonstrating Joule-Thomson effect, I find no essential difference between the set-up for the two.

What is the feature of the setup for Joule-Thomson effect that makes the process isenthalpic, as oppose to adiabatic expansion? (I am not looking for proof initial H= final H)

What is the use of the throttle/ porous plug? If it is the throttle that makes the process isenthalpic, what is the physical reason behind it?

From another source,

  The gas is first compressed isothermally, then expanded isothermally
  (may be at different temperature as initial temperature)

I am not sure what it means. Does it mean that its temperature jumps abruptly from initial temperature to final temperature? It has only two temperature throughout the process? How is this possible? I expect the temperature to change continuously, because the volume of the gas changes throughout the process.


texts: Definitive Guide To Removing Stains From Baby Clothes

texts:
I'd like someone to explain, scientifically, what makes some baby clothes' stains so hard to remove, and what the right way to treat the stains is, chemistry-wise. A lot of internet sites have solutions (pardon the pun) that are 'my experience' and anecdotal, which is better than nothing, but not always transferable (and sometimes may damage clothes).

So yeah... how do you get out the hard to remove orange stains (e.g. from iron, or carrot/sweet potato soup)? How about other things? Why? I'd love someone to make this the definitive guide to removing stains from baby clothes, if you can :D. (Feel free to expand beyond my stated question above so there's just a one-stop reference question here.)


texts: Why is the iron inter-system crossing non-negligible at high temperatures?

texts:
Inter-system crossing (ISC) is a radiationless process involving forbidden transitions between singlet and triplet state. These are more common with heavy atom molecules, so I understand that ISC is dependent on the atomic number.

How does the temperature influence the ISC? Is this related to activation energy? Is the ISC rate coefficient temperature-dependent?


texts: Will a Lewis acid catalyze the reaction of HBr with primary alcohols?

texts:
It is well-established that a Lewis acid catalyst (popularly $\ce{ZnCl2})$ is necessary to form an alkyl chloride when reacting $\ce{HCl}$ with a primary alcohol. This actually changes the mechanism: the Lewis acid complexes with the alcohol and the resulting leaving group is $\ce{[Zn(OH)Cl2]-}$ instead of water. For $\ce{HBr}$ and $\ce{HI}$ this is technically not necessary.

However, practically speaking $\ce{HBr}$ alone is also insufficient as its azeotrope is insufficiently concentrated. Generally one adds conc. sulfuric acid to increase the acidity.

I am curious as to whether the addition of a Lewis acid could be used instead. Bromide is a stronger nucleophile (in protic solvents) than chloride, so I expect that it would. Has anyone ever tried this?


texts: Reaction mechanism of 2-amino-4,6-dimethylpyrimidine as a nucleophile

texts: My understanding tells me that 2-amino-4,6-dimethylpyrimidine can be deprotonated quite easily because the conjugated base is stabilized be resonance and act as nucleophile attacking aldehyde carbon. But I found no resource in literature about this reaction:


texts:
I had read some where that in glasses the surface tension is high, but in a lota the surface tension is low.

My question how much time does the surface tension take to change? I mean that there was water in a glass but I put it into a lota in how much time will the surface tension of water change? Immediately?
This is a lota:


texts: What is the product formed after nitrosation of ketones (HNO2 + ketone)?

texts: On C-nitrosation of ketones we get oximes. After this, the oxime formed is hydrolyzed ($\ce{H3O+}$ is added). What will be formed in the end? Does it follow Beckmann rearrangement or what?


texts:
The double bond at position '4' appears to be showing a 'E' geometry because the priority 1's are on opposite sides of the double bond ie top-left of bond4 is '1' (because Oxygen > Carbon)); bottom-left of bond4 is '2'; top-right of bond4 is '2' and bottom-right of bond4 is '1'(because it has more carbons than the other side).
I am unable to see why 'Z' is the correct geometry.
Appreciate any suggestions.
Thank you


texts: Molar conductivity in compounds showing coordination isomerism

texts:
Question

Which of the following complex has lowest molar conductivity?

$\ce{[Co(NH3)6][Cr(NO2)6]}$
$\ce{[Cr(NH3)5(NO2)][Co(NH3)(NO2)5]}$
$\ce{[Cr(NH3)4(NO2)2][Co(NH3)2(NO2)4]}$
$\ce{[Co(NH3)5(NO2)][Cr(NH3)(NO2)5]}$

Answer

 3. $\ce{[Cr(NH3)4(NO2)2][Co(NH3)2(NO2)4]}$

My approach
My textbook only has examples of single centered complex ions, unlike what seems to be coordination isomers in the question. Normally, I see stuff with hydrates and ammine ligands which we predict by the number of active anions in the primary valency. But I have no clue on how to proceed with this question and the website does not provide any solution/ reference.


texts: Balancing the reaction of potassium permanganate and sulfuric acid with hydrogen peroxide

texts:
A problem on redox reactions invites the reader to balance the actual reaction from which the redox simplification arose. After some hunting I found the balanced equation and attempted to re-derive the coefficients using:

$$\ce{a H_2SO_4 + b KMnO_4 + cH_2O_2 -> dK_2SO_4 + eMnSO_4 + fH_2O + gO}$$

We can quickly derive some valid relations by looking at each element:

$$
\begin{array}{cll}\\
\ce{H}&\quad a+c &=& f\\
\ce{O}&\quad 4a+4b+2c&=& 4d+4e+f+g\\
\ce{S}&\quad a&=& d+e\\
\ce{K}&\quad b&=& 2d\\
\ce{Mn}&\quad b&=& e
\end{array}
$$

This can be massaged a little but because there are 5 equations and 7 unknowns it seems that the system is underdetermined.

If we let $a=3,~b=2,~c=5,~d=1,~e=2,~f=8,~g=10$ the equations all work.

My question is:

  Could we arrive at these values without guessing or actually doing an experiment to measure (say) the oxygen evolved?

FWIW, I notice an old paper - J. Am. Chem. Soc. 1889, 11 (6), 94-98 - of which I can only see the first page seems to take a similar approach and gets two possible equations, maybe for the reason above.


texts: Oxidation reaction of dimethylselenide / Selenourea with hydrogen peroxide

texts:
For my paper,  I need to find the reaction between $\ce{(CH3)2Se2}$ and $\ce{H2O2}$ and between $\ce{SeC(NH2)2}$ and $\ce{H2O2}$. The mechanism below shows how I think it goes. The reaction should give an anion, an inorganic form of the selenide or selenourea but I'm unsure when the forms become anionic.

And

$$\ce{\overset{+IV}{Se}O3^2- + H2O2 -> \overset{+VI}{Se}O4^2- + H2O}$$

If anyone could give me a push in the right direction or can confirm if the reactions in the picture are correct, I'd appreciate it very much.
Thanks in advance!


texts: What is the difference between ignition temperature and flash point?

texts: I am trying to clarify this for Class 8 Science. Their textbook says "It is the lowest temperature at which a substance catches fire". However, it does not clarify whether it is on its own or due to an external source. I read through various websites and there are both kinds of definitions put up! Some also mentioned a flash point. So wanted to know what the proper definition of ignition temperature is and how it differs from flash point. Thanks!


texts: Statistical methods used for testing the homogeneity of the sample

texts: So, if I have multiple FTIR spectra each taken on different location of the sample and averaged from ~20 spectra, how can I check if the sample is homogeneous, i.e., if there are statistically significant differences between the spectra based on location? For visuals, I tried to compute at each wavenumber confidence upper and lower limits, but I am not sure if this method is valid even for visualisation and it does not give anything exact or quantitative.


texts: Curly arrow mechanism for reaction between sodium borohydride and water?

texts:
I was asked to compare the reaction between sodium hydride and water and sodium borohydride and water. I know that the former acts more violently than the latter, but apparently, I must use a curly arrow mechanism to show this.

I think that the HOMO for the latter reaction is the oxygen lone pairs, and the LUMO is the B-H bond, but I'm having difficulty moving on from there.

What attacks what first?


texts:
What happens to the intramolecular bonds when a network covalent substance is melted? I understand that in covalent molecular substances, the intermolecular bonds weaken between the molecules once molten. My confusion is with what happens to the bonds between network covalent substances when melted.

Do the intramolecular bonds break, leaving only the individual atoms (carbon for example in graphite or diamond).
Do the intramolecular bonds weaken
The basis for this query is when I was asked to predict the electrical conductivity of graphite and silicon dioxide in molten states (Graphite sublimates, but under pressure is liquid). I started by researching the atomic and bonding structure of the elements when they are melted but could find very little information.

TLDR: What happens to covalent network bonds when they melt

Thankyou


texts: How to calculate the parts-per-million concentration from a percent concentration?

texts:
I am asked to find the concentration of magnesium ions in ppm for a $0.025\ \%$ solution of $\ce{MgCl2}$. I can use this formula:
$$\text{concentration in ppm} = \frac{\text{mass solute}_\mathrm{(g)}}{\text{mass solution}_\mathrm{(g)}}\times10^6$$

Assuming $100\ \mathrm g$ of solution, $2.5 \mathrm g$ solute/$\ce{MgCl2}$, and $97.5\ \mathrm g$ solvent, I get $\pu{95.205u}$ for $\ce{MgCl2}$, and then $0.026259\ \mathrm{mol}$ of $\ce{MgCl2}$, and thus $0.026259\ \mathrm{mol}$ of $\ce{Mg}$. That times $24.305\ \mathrm{g\ mol}^{-1}$ for $ \ce{Mg}$ gives me $0.63823\ \mathrm g$ of $\ce{Mg}$. $\frac{0.63823\ \mathrm g}{100\ \mathrm g}$ solution gives me $0.00638$, so that multiplied by $10^6$ would be $6382.28$. But the only options for the questions don't go over $500$. Like $64\ \mathrm{ppm}$ or $500\ \mathrm{ppm}$. Nothing even close to as high as I'm getting.


texts: In making gummies with pectin, the pH is very important and needs to be at or below 3.4.  USP indicates dissolving it in a 10% solution to test the pH, while some use a 50% solution.  I'm told the resulting pH is the same, but my rudimentary understanding of pH is that pH is the hydrogen ion concentration in solution.  Why would the pH be the same if the concentration of gummy to water is different?


texts: Reason for sodium chloride to show colour in flame test

texts:
My textbook states the following:

The alkali metals and their salts impart
characteristic colour to an oxidizing flame. This
is because the heat from the flame excites the
outermost orbital electron to a higher energy
level. When the excited electron comes back to
the ground state, there is emission of radiation
in the visible region as given below

I understand the reason for $\ce{Na}$ to impart flame colour since its $e^-$ gets excited. But what is the reason that $\ce{NaCl}$ ($\ce{Na^+}$) exhibits flame colour, since $\ce{Na^+}$ doesn't have any electron in its outer orbital ?


texts: Change in Gibbs free energy of vaporization reaction

texts:
In my chemistry book, I see the equation

$$\Delta G_{rxn} = \Delta G_{rxn}^0 + RT \ln(Q)$$

where $\Delta G_{rxn}^0$ is the change in Gibbs free energy under standard conditions (1 atm pressure in this case), R is the gas constant, T is the absolute temperature, and Q is the reaction quotient. Consider the reaction

$$\ce{H2O (l) -> H2O (g)}$$

Clearly in this example, $Q = P_{\ce{H_2 O}}$, the pressure of water vapor.

Here is my confusion. The earlier expression for $\Delta G_{rxn}$ implies that anytime $P_{\ce{H_2 O}} = 1\ \mathrm{atm}$, we have $\Delta G_{rxn} = \Delta G_{rxn}^0$, which is $8.59 \mathrm{kJ/mol}$ for this reaction. We should see this regardless of temperature, according to this expression.

However, when $T = 100\ \mathrm{^\circ C}$, liquid water and water vapor are in equilibrium at $P_{\ce{H_2 O}} = 1\ \mathrm{atm}$! And if they are in equilibrium, it stands to reason that we should see $\Delta G_{rxn}=0$, which clearly we do not.

Could anyone help me understand this apparent contradiction? My only guess at the moment is that it arises because $\Delta G_{rxn}^0$ is not temperature-independent and at the higher temperatures, perhaps the value of $8.59\ \mathrm{kJ/mol}$ becomes inapplicable. If anyone could explain this to me I would be very grateful!


texts: Regioselectivity of the Beckmann rearrangement

texts: It seems to be that the Beckmann rearrangement is a nice way to prepare secondary amines. This can be achieved by removal of oxygen via the use of $\ce{HI}$/$\ce{P}$. However, if ketones are used, which side gets the $\ce{NH2}$ group?


texts: Is there a way to experimentally measure entropy?

texts: I've been doing thermodynamic chemistry, and recently focusing on Gibbs Free Energy. Whilst doing calculations using, $$\Delta G = \Delta H - T \Delta S$$ I have been given a table of values for $\Delta H$ and $\Delta S$, and a temperature to work with. I was wondering , as the unit for entropy is $\mathrm{J/K}$ or $\mathrm{J\ K^{-1}}$ how exactly one would experimentally measure entropy/change in entropy, or can you?


texts: Why does temperature affect the dissolved oxygen concentration?

texts: I know that an increase in temperature decreases the solubility of oxygen in water, but I don't know why. Could anybody explain?


texts: How are partial molar Gibbs excess functions correctly defined?

texts:
I think I've found a mistake in my thermodynamics textbook, Chemical Thermodynamics for Process Simulation, but as thermodynamics is hard and I'm a relative novice, I wanted to check here.

The textbook, in talking about partial molar Gibbs excess functions of species in solutions, writes that we can express the partial molar Gibbs free energy of a species $\bar{g_i}$ in solution, as the sum of the partial molar Gibbs free energy in an ideal solution, $\bar{g_i}^\mathrm{id}$, and an excess function, $\bar{g_{i}}^\mathrm{ex}$:

$$\bar{g}_i = \bar{g}_i^\mathrm{id}+\bar{g}_i^\mathrm{ex}.$$

It doesn't specify whether we are thinking of evaluating $\bar{g}_i^\mathrm{id}$ at the system pressure or at a reference pressure, but immediately after it 'expands' the above expression into the form:

$$\bar{g}_i(T,P) = \Big(\bar{g}_i^\mathrm{pure}(T,P_0) + \mathcal{R}T\ln x_i\Big) + \left(\mathcal{R}T\ln \frac{f_i}{x_if_i^0}\right)$$

Clearly we're comparing $\bar{g}_i$ to the ideal value, $\bar{g}_i^\mathrm{id}$, at standard pressure $P_0$. However, they then go on to define the activity $a_i=f_i/f_i^0$ and the activity coefficient $\gamma_i = a_i/x_i$ and substitute these in to get

$$\bar{g}_i(T,P) = \bar{g}_i^\mathrm{pure}(T,P_0) + \mathcal{R}T\ln x_i  +  \mathcal{R}T\ln \gamma_i.$$

Now, I'm all fine up to here. The first part, $\bar{g}_i^\mathrm{pure}(T,P_0) + \mathcal{R}T\ln x_i $, is the ideal solution Gibbs free energy at standard pressure, and the final term, $\mathcal{R}T\ln \gamma_i,$ is a correction in two ways: It corrects for the non-ideality of the solution, and it corrects for the fact that we may be at a different pressure $P$.

But the book then says:

  For an ideal mixture the excess part is equal to zero, since the activity coefficient is $\gamma_i=1$.

I think this is ridiculous: we can only make this conclusion if we have an ideal solution at $P=P_0$.

Is this an error in the textbook? Also, I can see two possible routes to an error: Either $\bar{g}_i^\mathrm{id}$ is actually to be evaluated at system pressure, in which case their last statement is correct but the formula they give is wrong, or else their definition of excess functions is the standard one (actual value minus ideal value at ref. pressure) but they made a mistake in concluding $\gamma_i=1$ for all ideal solutions, independent of the pressure.


texts:
If I test a pure solution of an acid chloride with a pH-meter, will I get a reading of pH 7?

When I add water to it, I know $\ce{HCl}$ gas will form, but this gas will dissolve in water to give an acidic solution.

My main confusion is that we call ethanoyl chloride an "acid" chloride, but is its pure solution acidic?


texts: When NaI is in acetone and we have R-X, then I replaces X by Finklestein mechanism (Sn2 => Inversion). But when we have acetone and water, why do we get a racemic mixture?


texts: Can I expect 18O-hydroxide when adding slight amount of NaOH-16O to 18O-water?

texts:
In adding $\ce{^{16}O}$-sodium hydroxide to $\ce{^{18}O}$-water to get a $0.25\pu M$ solution, is the hydroxide in form of $\ce{^{16}O}$-hydroxide or $\ce{^{18}O}$-hydroxide?

is there an oxygen exchange between  $\ce{^{16}O}$-hydroxide and  $\ce{^{18}O}$-water?


texts: In what ways (other than color) does black Aluminum Oxide differ from white?

texts:
I work in a (physics) lab in which an aluminum oxide coating is applied to the inner surface of a plasma confinement vessel (made of Cu) to provide an electrically insulating layer that can withstand high temperature environments. The product we use comes in a medium that allows it to be brushed or sprayed onto the metal surface (something like: http://www.zypcoatings.com/aluminum-oxide-coatings/  -- see the data sheets).

I'm wondering if a similar product might exist for black aluminum oxide. I've seen that black aluminum oxide powder exists, but cannot find information on a coating product that is black.

I'd like to understand what the difference is between the two: Does black aluminum oxide have the same physical properties as the white variant? Is it reasonable to expect that a similar suspension or solution of black aluminum oxide in water or a different solvent could be made? What makes one black and the other white? Any information on their differences would be helpful.

Thanks!


texts: Why are alkyl halides used as solvents for relatively non polar compounds and not polar compounds?

texts:
It is written in my textbook that :

  Alkyl halides are used as solvents for relatively non polar compounds.

Alkyl halides are themselves polar with carbon having delta positive charge and halide having delta negative charge. If polar compounds are dissolved in them, then there will be more interactions between the compound and alkyl halide. The polar compound should dissolve in it.

What do they mean "relatively non polar compounds are soluble in alkyl halides" ? How will non polar compounds become soluble and why the textbook does not mention solubility of polar compounds?


texts: can an alloy be used to make another alloy?

texts:
The answer is likely very obvious but I know pretty much nothing about this so:

Can I make an alloy, using an alloy? That is, could I make an alloy of steel (in itself an alloy of iron and carbon) and silver?


texts:
For (a) (iii), how do you get the second product listed in the answers manual? I just can't visualize it.

What about (c) (i), why are there three resonance structures? If a hydrogen is taken away from a specific carbon of the initial molecule to have a radical, there is no way you can have three resonance structures.


texts: During rearrangement of carbocation, we have three choices: methyl shift, hydride shift and phenyl shift. If we have a situation where all the three are possible, then what will be the preference order?


texts: Interchange of axial and equatorial groups in Me2NPF4

texts:
The $\ce{^{31}P}$ NMR spectrum of $\ce{Me2NPF4}$ when recorded at room temperature consists of a quintet with intensities $1:4:6:4:1$. However, at $-100~\mathrm{^\circ C}$, the spectrum is as shown below:

Propose a structure for $\ce{Me2NPF4}$ that is consistent with these observations.

The phosphorus has five groups surrounding it so it must have some sort of five-coordinate geometry. The low temperature spectrum shows a triplet of triplets with similar coupling constants, which is what you would expect from a trigonal bipyramidal structure with two axial and two equatorial fluorines. On this basis I assigned the structure as below:

However, I don't understand why all four fluorines are equivalent at higher temperatures. Does this mean that they are constantly interchanging and if so, what is the mechanism for this?


texts: Ethyl alcohols use on polycarbonate and acrylics

texts:
I have an interesting question about the use of ethyl alcohol on polycarbonate windshields.  I have had friends asking me about the use of Pledge Multi-Surface cleaner on their windshields. Some insist it will degrade, yellow, or even crack and soften their windshields. Others have been using it for years with no apparent effect.

Pledge does have a small amount of ethyl alcohol, but does it have enough to degrade and ruin motorcycle windshields or does ethanol do any damage anyway?

Pledges' MSDS states ethyl alcohol weight at 0.01-1.00  (http://www.scjohnson.ca/pdfViewer.aspx?pkMSDSId=367&language=en).

So what are the effects, if any, on using this cleaner on polycarbonate windshields?

Thanks


texts: Names of the f suborbitals. (Reference Request)

texts:
Today, I have been browsing the internet to know the names of the "f" orbitals. But I have varying answers on the web. Different sources seem to be stating different names. Like here,

and here

Besides the first 2 pictures, this question on Quora also gives different names.
By names, I mean names of suborbitals like $d_{xy}$, $d_{z^2}$ etc.
Right now, I am really confused. An answer with a solid reference would definitely make my day.


texts: Is there any empirical upper limit for order of reaction?

texts:
I learned from one of my teachers that empirically reaction with order greater that 3 are never found. But, I am suspicious of the truth value of his claim.

To add to my suspicion there is this paper from 1932 referring to a fourth-order reaction

It seems to me theoretically there should be no upper limit for a  reaction as it is possible for 4,5,6... chemical species to come together with the right activation energy in the right direction.

However, empirically making 4 or 5 chemical species to form a transition species is very hard. So, there should be a empirical limit to order of reaction in the light of chemistry we know today.

What is this limit?


texts: Primitive Technology - Extract Silica and Sulfur from ash

texts:
Given some plant ash containing silica and sulfur, we need to find a way to extract the silica and sulfur using only resources available to a primitive person stuck on an island, with access to a forest, lake, and coal vein. (This is part 2 of my Primitive Technology series. Part 1)

I've imagined a way to extract the silica, but I am not sure if it would work. Can I get this reaction confirmed possible?

$$
\begin{align}
\ce{SiO2(ash) + NaOH &->[Heat] Na2SiO3 + H2O}\tag{1}\\
\ce{Na2SiO3 + 2 HCl &->[Heat] 2 NaCl + SiO2 + H2O}\tag{2}
\end{align}
$$

I am unsure whether the sulfur content could be feasibly extracted in this scenario.

Notes

Some plant parts, such as rice husk, have high silica content (over 90%).
Coal and sea water typically have substantial sulfur content. Sulfur is a by-product of coke production.


texts: Examples of electronically conductive foods?

texts:
There are many foodstuffs that are ionically conductive (for example, anything moist and salty). What about foods that have a high electronic conductivity?

The only thing I can think of would be something which has been charred – presumably the char, being mostly carbon, would have a fairly high conductivity.


texts: A question about rotational symmetry of organic molecules and in particular, the cyclic Isomers of C3H4X2

texts:
I was thinking about an organic chemistry problem a few days ago but reached a dead end. There were 2 parts to this question.
The first was thinking about the isomers of 'C3H4X2' [where X could be anything like a halogen or a deuterium etc].
I came up with the following 7 isomers:

(I've really tried to make it as clear as possible! Hopefully it has worked!)
...but a website I found stated that there were only 4:
A -
B -
C -
D -
;with their 'D' representing a deuterium.
So this is the first aspect of my quandary - what am I doing wrong when I draw these isomers!
The second aspect to this question was about considering the symmetry of these organic molecules. In particular, considering firstly 'plane symmetry' [which I understand] and 'rotational symmetry' [which I thought I understand but clearly I don't!]
The same website says that molecule A (from above) plane symmetry and rotational symmetry, which is fine.
But it also says that molecule C has plane symmetry but not rotational. Why is this? Surely if I rotate this molecule 60 degrees I get the same shape?
And then finally, they say that molecules B and D have rotational symmetry but not plane symmetry which I think I understand but would appreciate any further comments if anyone had them.
Ultimately, I would be very grateful if someone could point me towards something which could help me understand rotational symmetry in organic molecules and in particular why these examples given above have their particular symmetries! Thank you very much, everyone!
Best wishes,


texts: Variation in atomic sizes in the transition elements

texts: From left to right across a period, effective nuclear charge increases in the transition series, just like in the p block, and so atomic size decreases. Here the electrons are being added to the d orbital, where shielding is relatively poor compared to the p orbital. It should follow that the increase in the effective nuclear charge is more significant for the transition elements than the p block in a given period, leading to greater size variation among successive members - but the size variation is smaller in the transition elements instead. In fact atomic size increases from Ni to Zn. Is there any logical explanation for the fact?


texts: Building an average model from MD snapshots

texts:
I am performing a molecular dynamics simulation, and I am taking "snapshots" of the system at regular intervals.

The aim is that of finding the preferred geometry of a molecule in solution.

Are you aware of any software capable of automating to some extent the superposition of different geometries, and maybe of building an "average" structure?


texts: Calculating current for electrolysis process

texts:
Is there a way to calculate the current during electrolysis of a dilute NaCl solution.

I need to oxidise the chloride ions to create hypochlorite ($\ce{OCl-}$), so I was thinking of using 2 inert electrodes (Graphite) with an applied voltage slightly greater than 2.19 V.

I want to calculate the current because I want to see how long I will have to run the electrolysis for to produce 0.5mg/L of ($\ce{OCl-}$), and how long the batteries will last. I was thinking of estimating the resistivity of the liquid but I'm not sure.


texts:
Ethanoic acid dissociates according to the following equation:
$$\ce{CH3COOH + H2 O -> CH3COO- + H3O+}$$
I want to know if it is a redox reaction or not. In the ethanoic acid I obtained that the oxidation number of carbon in it is 0 by calculation, but it is (-2). What is the error in my answer?


texts: How do I obtain Chrysoidine from Benzene?

texts: So, basically I can convert Benzene to Phenol using Dow's synthesis process and then use $\ce{NH3}$, $\ce{ZnCl2}$, $\ce{HNO2}$, $\ce{NaNO2}$ under 0-5 °C controlled temperature and convert the phenol to Diazonium Chloride Salt. Then with Coupling Reaction, I can convert the Diazonium Chloride to Aniline Yellow. But, Chrysoidine has another $\ce{-NH2}$ group attached to the Ortho position. So, an explanation would be greatly appreciated as to how to obtain Chrysoidine from there on.


texts: What gives milk its characteristic white color?

texts:
The other day, my kid brother asked me this:

  What pigment gives milk a white color?

Now, I found that particular question quite interesting since, as a student of Biology, I already had a rough idea as to what constitutes (cow's) milk: Water, sugars, fats, and a whole bunch of vitamins and minerals. Yet as far as I know, none of them play a "pigment"-like role anywhere else in nature... which has left me deeply perplexed.

So what pigment is responsible for milk's characteristic white color?


texts: Electrochemical cell polarity and electrodes

texts:
In an electrochemical cell, the anode undergoes oxidation and the cathode undergoes reduction. This means that the anode loses electrons while the cathode gains electrons.

However, the anode is negatively-charged while the cathode is positively-charged. Why is this so?


texts:
What is the point group of of cis- and trans-decalin?

I watched a video saying that it is $C_\mathrm{2h}$ for cis-isomer, but my friend says it is $D_\mathrm{2h}.$ I'm so confused.


texts:
Under the Wikipedia entry for Metaldehyde is listed a Melting Point of $\pu{246^\circ C}$ and a Boiling point of $\pu{110^\circ C}$ (actually, it says it sublimes).

How can a Boiling point be lower than the Melting Point? Even if $\pu{110^\circ C}$ is actually a sublimation temperature how can it then subsequently melt at a higher temperature of $\pu{246^\circ C}$?


texts: How can we say whether or not an organic compound is soluble?

texts:
In the exam recently conducted by my school, they asked whether 2-hydroxyacetophenone is water soluble or not.

I thought that since there is intramolecular H-bonding in this compund, it won't be soluble. But my teacher marked it wrong. Also, when I checked it on internet, I saw in some websites it was mentioned to be water-soluble. My question is how can we say whether or not an organic compound is soluble?


texts: Confused on the peak intensities in this mass spectrometry problem

texts:
A problem from Introduction to Spectroscopy by Pavia et al. [1, p. 137]:

*4. An unknown hydrocarbon has a molecular ion peak at $m/z = 84,$ with a relative intensity of $31.3.$ The $\ce{M + 1}$ peak has a relative intensity of $2.06,$ and the $\ce{M + 2}$ peak has a relative intensity of $0.08.$ What is the molecular formula for this substance?

I normalized $31.3$ to $100\%,$ so the relative intensity $I$ was calculated as follows:
$$
\begin{array}{lr}
\hline
\text{Peak} & I/\% \\
\hline
\ce{M^+} & 100.00 \\
\ce{(M + 1)+} & 6.58 \\
\ce{(M + 2)+} & 0.25 \\
\hline
\end{array}
$$
The textbook is saying the molecular formula is $\ce{C6H12}.$ To me the answer doesn't make sense because if I calculate the $\ce{(M + 1)+}$ intensity using this formula from my textbook given for $\ce{C_xH_y}$:
$$[\ce{M + 1}] = 1.1x + 0.015y$$
Thus for $\ce{C6H12}$:
$$[\ce{M + 1}] = 1.1 × 6 + 0.015 × 12 = 6.78\%$$
However, $6.78\%$ is off from $6.58\%$ by about $0.2\%$. Am I missing something or is there some sort of acceptable tolerance for peak intensity differences?
Reference

Pavia, D. L.; Lampman, G. M.; Kriz, G. S.; Vyvyan, J. R. Introduction to Spectroscopy, 5th ed.; Cengage Learning: Stamford, CT, 2015. ISBN 978-1-285-46012-3.


texts: Using quantiative analysis to find empirical and molecular formula

texts:
A compound of Ca, C, N and S was subjected to quantitative analysis and formula mass determination, and the following data were recorded.
A $\pu{0.250 g}$ sample was mixed with $\ce{Na2CO3}$ to convert all of the Ca to $\pu{0.160 g}$ of $\ce{CaCO3}$.
A $\pu{0.115 g}$ of the compound was carried through a series of reactions until all of its S was changed to $\pu{0.344 g}$ of $\ce{BaSO4}$.
A $\pu{0.712 g}$ sample was processed to liberate all of its N as $\ce{NH3}$ and $\pu{0.155 g}$ of $\ce{NH3}$ was obtained.
The formula mass was found to be $\pu{156 g mol-1}$. Determine the empirical formula of this compound.

My issue here is that we don't really know what the starting compound is and particularly how much of each Ca, C, N, and S is there. Without knowing that, how can you balance your reaction equation and find the number of moles needed to get the empirical formula?


texts: I have 1 litre of water at 45 °C. How long would it take to evaporate when ambient temperature is 25 °C?

texts:
As a fun experiment, I'm trying to evaporate water in my kitchen. I've heated the mixture to 45 °C, and I'm wondering how long it might take to completely evaporate.
Assume that the water is 2 cm deep in a flat pan (if that is relevant).


texts: Storage issues with o-phthaldialdehyde (OPA) reagent used to derivatize amino acids

texts: I have made up an o-phthaldialdehyde (OPA) reagent according to Handbook of HPLC page 715 that will be used to derivatize amino acids before an HPLC run. There is no information given on reagent storage, but the OPA crystals themselves must be stored in the fridge. However, storing this reagent in the fridge causes clear crystals to form that cannot be redissolved into solution. Has anyone had similar issues? Is it possible to store this reagent at room temperature without having the reagent lose strength?


texts: SERS Gold nanoparticles performing poorly in organic solvents?

texts:
We have been working with some organic solvents lately and noticed a sharp decrease in surface-enhanced Raman spectroscopy (SERS) performance from our gold nanoparticles deposited in an organic solvent such as methanol.

With reference to the graph attached: the top line is 5 ppm Malachite Green Oxalate dissolved in water, the bottom line is 5 ppm Malachite Green Oxalate dissolved in 50/50 water/methanol

As you can see, the SERS performance of the gold nanoparticles decrease significantly when methanol is added.

We consulted our vendor and this is the explanation given: "Since the nanoparticles are stabilized in an aqueous solutions, the addition of methanol will destabilize it. I think in this case there is too much methanol, so the nanoparticles are over-aggregating, hence the decrease in SERS performance."

I have the following questions:

Why will the nanoparticles over aggregate in organic solvents? Is this specific to my vendor's nanoparticles?
Why would that even matter? How does over aggregation lead to poor SERS performance?
Since methanol is immiscible in water, shouldn't the analyte molecules (Malachite Green) on average have the same average distance to the SERS gold nanoparticles?


texts: Which salt will best be able to buffer the addition of HCl?

texts:
From these three salts, which will be best able to buffer the addition of $\ce{HCl}$?

ammonium chloride

sodium carbonate

ammonium acetate.

I think sodium carbonate is the right choice because when it dissociates in water forms a basic solution, so when $\ce{HCl}$ mixes with sodium carbonate it will be the best buffer, but it's a weak base so I'm confused. So can someone explain which is best?


texts:
Please help explain what is happening to this nail. It has been in this wall filler for a good few months.

The substance being excreted was rising up forming these stalagmites, with a liquid forming on them.

Removing the nail, there were also excretions at the part that was sunken.


texts: Why reverse reaction is not possible in the case of dissociation of strong electrolytes and thus non existence of ionic equilibrium?

texts:
In chemistry textbooks there is generally written that ionic equilibrium can’t be achieved in the case of strong electrolytes (because their degree of dissociation is almost equal to 1) but it can be achieved in the case of weak electrolytes(because their degree of dissociation is much much less than 1) Now my question is that what does degree of dissociation has to do with whether the reverse reaction is possible or not. Suppose we have a strong electrolyte which almost dissociates completely now why don’t the reaction occurs in the backward direction(please don’t say that it is so because the dissociation is almost 100%. If so then what, it doesn’t mean that reaction can’t occur in the backward reaction there is possibility that the almost 100% dissociated ions may again recombine to make the reaction go backwards and reach a state where the rate of the forward equals the rate of backward). But this doesn’t happen(acc. To textbooks) why?

According to me(my understanding of Arrhenius’ theory of electrolytic dissociation) the electrolytes dissociate in water to furnish ions and these ions are continuously recombining to form the electrolyte molecules and thus are in equilibrium and therefore the strong electrolytes must also follow the same principle but we can say that in this case particularly the equilibrium is very highly established towards the product side(but it will be still said to be equilibrium however product sided it may be)

One more fact in favour of my argument i.e. the values of equilibrium constants are present on the web for  strong acids so if the equilibrium never exists in the case of strong electrolytes then how come we are able to calculate these constants?

NOTE- I’m a high school student.


texts: Cobalt Chloride in various solvent/water mixtures - tested

texts:
In a recent post the solvatochromic behaviour of cobalt chloride in acetone was discussed. There were some ideas how the acetone might influence the ratio between the blue $\ce{[CoCl4]^2-}$ and the pink $\ce{[Co(H2O)6]^2+}$.

An interesting thought was the change in the dielectricity constant, which would influence the dissociation of $\ce{CoCl2}$ and therefore, if lowered, cause the $\ce{Co^2+}$ and $\ce{Cl^-}$ ions to form the blue $\ce{[CoCl4]^2-}$ complex again. Atleast this is how I understood the explanation.

Using this idea any solvent, that is miscible with water and does not form a differently colored complex with $\ce{CoCl2}$ should have a similar effect if the dielectricity constant is close or lower than the one for acetone.
So I gave it a test and used the first solvents I could find in our lab, dmf, acetone, isopropanol and thf (in descending order of permittivity).
The solutions were prepared by dissolving a spatula of $\ce{CoCl2 * 6 H2O}$ in a few ml of solvent so it was fully saturated. The liquid layer was transfered to a test tube and diluted with water until the color had changed to pink.
Solvent was then added until a blue hue was visible again. To limit the amount of solvent used it was not added until a strong blue color appeared.

For the acetone you can see the best effect. It quickly turned blue again and upon adding more acetone even became quite intense.
Dmf had a much lighter solution to begin with, the blue complex was formed quite quickly but it was not as intense as for acetone.
Isopropanol gave only a poor result. A few drops of water were enough to completely discolor the solution (still more drops were added to have about equal volumes in all tubes). Even after adding a large amount of isopropanol no intense blue color showed.
THF gave good results when the layers were not allowed to mix but once the solution was stirred it quickly discolored again.

As you can see all solvents gave quite intense blue colors with the pure $\ce{CoCl2}$ but even though THF has a much lower dielectricity constant it only gave poor results. I don't really know if this can be explained by the given theory but perhaps someone can find some clues through this experiment.


texts: Determine the ΔH for the reaction in kJ/mol of ethanol?

texts:
A $1.000~\mathrm{g}$ sample of ethanol, $\ce{C2H5OH}$, was burned in a bomb calorimeter whose heat capacity had been determined to be $2.71~\mathrm{kJ/^\circ C}$. The temperature of $3.000~\mathrm{kg}$ of water rose from $24.284~^\circ\mathrm{C}$ to $26.225~^\circ\mathrm{C}$. Determine the $\Delta H$ for the reaction in $\mathrm{kJ/mol}$ of
  ethanol?

I said :

\begin{aligned}
q_\mathrm{cal} &= C_\mathrm{cal}\cdot T\\
        &= (2.71\ \mathrm{kJ/^\circ C})(1.94\ \mathrm{^\circ C})\\
        &= 5.26~\mathrm{kJ}\\
\end{aligned}

Then the $q_\mathrm{r}=-5.26\ \mathrm{kJ}$

Then calculated the number of mol by dividing the mass g over molar mass and I got $0.02171~\mathrm{mol}$.

Finally I divided $-5.26\ \mathrm{kJ}$ by $0.02171\ \mathrm{mol}$ and I got $= -242.3~\mathrm{kJ/mol}$.

But the correct value is $-1365~\mathrm{kJ/mol}$. What's wrong?


texts: What does "n" stand for in n-akyldiols, n-alkanes, n-dicholoroalkanes?

texts:
I have read two conflicting answers upon a google search:

  " 'n' in this context stands for normal or the latin equivalent. That is why, like other Latin and Greek abbreviations, it is in italics. It refers to straight chain alkanes. If we weren't dealing with n-alkanes we would have branched chain isomers to consider and potentially very different answers. It is old nomenclature from the days when adjacent carbons in a molecule were designated alpha,beta,gamma, etc and when acidity was given in 'N' units of normality."

and

  " 'n' in science is like "x". It is just a reminder that a number needs to be there. You need to know that numbers can be replaced by x, x/y, n, or any variable and that groups can be replaced by their generic names."


texts: Is contribution to pH by an acid or base always greater than salt hydrolysis?

texts:
I was solving a titration question and the reaction I came to was this:

$$
\begin{array}{lcccc}
 \ce{&BOH(aq) &+ &HCl(aq) -> &BC(aq)  &+ &H2O(l) }\\
\text{Initial} & x & & & 0 & & 0 \\
\text{Final} & x/4 & & & 3x/4 & & 3x/4
\end{array}
$$

Titration was done with $\ce{HCl}$ and $\ce{BOH}$ is a weak base. I got the answer treating this as a buffer but then I thought why would the salt formed i.e. $\ce{BCl}$ not get hydrolyzed and have an impact on the $\mathrm{pH}.$ Tried thinking about it and could only come to the conclusion that that $\ce{HA}$ being acid would have major contribution to the $\mathrm{pH}$ though I am not satisfied.


texts: Will alcohol or soap damage plastic or rubber?

texts:
I have read conflicting advice on various sites about the appropriate methods for cleaning plastic and rubber items and would like to ask people who actually know what's going on what they would recommend.

I realize some of my assumptions may be false:

I am (perhaps wrongly) assuming that most plastics would have similar properties as it relates to cleaning with alcohol or soaps/detergents and that you don't need me to give you the actual chemical structure of a specific polymer.
I am (perhaps wrongly) assuming that most soaps and detergents would act similarly on either a plastic or a rubber item.  If this is false please give your understanding of what an "average" soap or detergent would do.

I am not assuming that plastics and rubber will respond the same to either alcohol or soaps and detergents.  If they are different, please note which will have what effect.
I am not assuming that synthetic and real rubber will act the same.  If they are different and you know the answer for both, please mention the difference.

I am hoping that it's okay to ask "applied" questions here.  This seems like the best of all stackexchange.com sites, not just because none of the less theoretical sites are deal with this sort of question, but also because it really boils down to a matter of chemical reactions.

Update: by "alcohol" I mean rubbing alcohol, or isopropanol.


texts: Finding molarity of hyposulfite solution used in titration

texts:
$\pu{0.1 g}$ of $\ce{KIO3}$ is treated with excess $\ce{KI}$ solution. The liberated iodine required $\pu{44 ml}$ of $x$ molar hypo solution. Calculate the value of $x$.

I have used the equivalent concept and got the answer as $\pu{0.026 M}$.
But the correct answer to this question is $\pu{0.063 M}$.
Can you tell me where I have gone wrong in my solution?

$$
\begin{array}{cc}
\ce{&KIO3 &+ KI -> &I2}\\
&\frac{0.5}{214}~\mathrm{meq} & &\frac{0.5}{214}~\mathrm{meq}
\end{array}
$$

$$
\begin{array}{cc}
\ce{&I2 &+ &2 Na2S2O3 &-> 2 NaI + Na2S4O6}\\
&\frac{0.5}{214}~\mathrm{meq} & &\frac{0.5}{214}~\mathrm{meq}
\end{array}
$$

$$∴\frac{0.5}{214} = 44\times10^{-3}\times x\times 2 \to n\text{-factor of hypo}$$

$$∴x = \pu{0.026 M}$$


texts:
So I find this everywhere:
"Mixtures showing large deviations from Rault's law form azetropic mixtures at specific compositions"
My questions are:
(a)Why is it so?Why deviation from Raoult's law is needed at all.
Wikipedia simply skips over the answer stating its a mathematical consequence.
(Quoting wikipedia:
When the deviation is great enough to cause a maximum or minimum in the vapor pressure versus composition function, it is a mathematical consequence that at that point, the vapor will have the same composition as the liquid, resulting in an azeotrope.)
(b) why can't ideal mixtures form azeotropes?
P.S: (a)A more intuitive answer would be appreciated although maths may be included if necessary.
(b)I did my research but nowhere the reason was to be found. It's presented as a very obvious consequence everywhere.


texts: Heating of Enamel coated cooking utensils and health hazards

texts:
I've tried to research about the issue of health concerns about enamel coating of cooking utensils (i.e. dutch ovens) and failed. I should prepare a small report about the health concerns if they exist.

Could you please help to answer that question? Any reliable sources would be greatly appreciated, especially scientific articles.

Thanks.


texts:
What is the salt formation for iron(III) sulfate?

Wikipedia tells me that the production of iron(III) sulfate is:

$$\ce{2 FeSO4 + H2SO4 + H2O2 → Fe2(SO4)3 + 2 H2O}$$

I was wondering if there was a difference between salt formation equation and production, because I thought it would've went something more like:

$$\ce{2 Fe(OH)3 + 3 H2SO4 → Fe2(SO4)3 + 6 H2O}$$


texts:
I want to know the difference b/w phosphonic acid and phosphorous acid.

The formula for both is H3PO3.

Websites give me conflicting answers.
Which one of them is dibasic and which one is tribasic?


texts: Is the effective nuclear charge only defined for valence electrons?

texts: I've just been taught about the effective nuclear charge and screening effect in school. I'd like to ask and confirm if the effective nuclear charge is only defined for valence electrons. If not then why don't we consider the repulsion from the electrons further away from the nucleus than the test electron, which by common sense should add to the attractive force by nucleus?


texts: Does potassium nitrate solution degrade?

texts:
I have created a solution of $\ce{KNO3}$ and table sugar in order to create fuse from hemp rope. I wet the rope in the solution and let it dry - I repeat this process several times.

It works and produces very slowly burning rope which is easy to set off. The problem is that after 24 hours, my solution started to stink. Something between garlic, onion and vinegar. I have a bad feeling about that.

Does my solution degrade, or is this stink caused by some impurities (the solution isn't very pure)?


texts: Does a molecule need to be placed symmetrically in the unit cell?

texts:
I was watching an OCW by MIT (3.091X) on solid state. My previous notion of lattice point and unit cell got shattered after this example.
Where are the unit cell and lattice points in this picture?

Unit Cell is the smallest group of atoms which has the overall symmetry of a crystal, and from which the entire lattice can be built up by repetition in three dimensions.
Lattice is the arrangement of points in space such that any point us identical to any other.

So using these definitions, the answer is

Green is the unit cell, and red ones are the lattice points.
Previously I used to think that a molecule should be symmetrically placed in a unit cell such that its center of mass lies on the lattice point. But in this example, the center of mass (shown by the yellow-green circle) is way off the lattice point.
My question is, Are there any other similar examples where the center of mass of molecule doesn't coincide with the lattice point or at least doesn't placed symmetrically in a unit cell (like on the face center, body center)?


texts: Ionisation of a gas - from gas to plasma

texts:
Is it possible to ionise a gas such as Carbon Dioxide? If you continue to heat up a gas eventually the electrons from the gaseous atoms are stripped away and those e- gain energy (endothermic reaction) to become a plasma. A plasma is a sea of gaesous cations and electrons that are not too far apart from each other (unlike a gas).

Having done some research, it is certainly possible:

http://www.dynamicscience.com.au/tester/solutions1/chemistry/isotopes/isotopes4.htm

https://link.aps.org/doi/10.1103/PhysRev.36.472

How do I represent this change from gas to plasma using an equation?

CO2 (g) -> X+ (g) + Xe-

Ionisation of Carbon and Oxide ion:

C (s) -> C+ (g) + e-

O2^2- (g) -> O2- (g) + e-

Related key terms: ionisation, recombination


texts: Why is change in volume of the solution zero in case of an ideal solution?

texts: In my textbook it is written that $ΔV_{mix} = 0$ for ideal solutions i.e. $V_{solution} = V_{A} + V_{B}$. But why is this true? There is literally no explanation in my textbook as to why this is true. I am so confused. Please can someone explain it rigorously. Please help.


texts: The molarity of pure water is 55.5 M at which temprature is obtained this value? Further, you will come across that 1000 mL = 1000 g (for water only, but at which temprature?)


texts: How is the unit of measure "equivalent" abbreviated?

texts: I usually use "eq" but I have been told to use "equiv." in order to avoid confusion with "equation". Is there a reference I can check?


texts: Why sodium is the worst reducing agent in group 1?

texts:
Analysing the oxidation enthalpies for $\ce{Li}$, $\ce{Na}$ and $\ce{K}$, we have their respective values:

$\ce{Li} = \pu{162 kJ/mol}$
$\ce{Na} = \pu{202 kJ/mol}$
$\ce{K} = \pu{188kJ/mol}$

Sodium has the largest positive oxidation enthalpy, which means that its oxidation will be less likely to happen according to its Gibbs free energy. But, why does this happens to sodium?


texts: How is the reaction rate constant affected by concentration?

texts:
Consider the concentration-time dependence graph for two first-order reactions.

  Which reaction has a larger rate constant?

  Unable to determine
  The reaction represented by the upper curve
  The reaction represented by the lower curve correct

The above question is confusing me.
It gives two concentrations vs. time curves, and asks which reaction has the larger rate constant. The answer is (3) the reaction represented by the lower curve.

I know that the reaction is first-order, hence
$$\mathrm{rate} = k[A].$$
Thus, algebra reveals that
$$[A] = \frac{\mathrm{rate}}{k}.$$
Thus, it makes sense that increasing the value of $k$ means dividing rate by a larger number, yielding a smaller concentration at any given time. This makes sense why the lower curve is the correct answer.

However, I also understand that the value of $k$, the rate constant, does not depend/is not correlated with the concentration of the reactant(s). Thus, is my logic not applicable? How else can you reason your way to the correct answer?


texts: Relation of temperature and intensive property

texts:
I came across a question that inquired about whether there exists any intensive property of a system, that is independent of temperature and then seeks proof for the presence/absence of such properties, from a quasi-theoretical standpoint. The question mentions that the system shall be assumed to be non-ideal (ideal gas laws don't hold true et al).

How to proceed, for the latter? Does there exist any such property, in the first place?


texts:
It is written here that chelation increases overall entropy?

I thought it should decrease entropy because the ligands are now bonded to the central metal atom forming a ring like structure. According to me entropy must decrease because the ligands can no longer move around so there is a decrease in randomness. Why this logic is not correct?


texts: What is the function of toluene in this reaction?

texts:
I'm trying to find the mechanism for this reaction:

My (tentative) thought for a possible mechanism is:

EDIT: New thought for mechanism:

But this leaves some loose ends that I haven't been able to figure out. How does the H on OH get removed? (Does it get removed at all?) Most importantly, what is the function of the toluene in this reaction? Why is there a time and temperature given? Any help is greatly appreciated.


texts: Reaction of Benzene with 2-methylpropene?

texts: I'm studying organic chemistry at the moment and it's really confusing. What could ever happen between benzene and an alkene? and why is $\ce{H2SO4}$ there?


texts:
Is it necessary to include the "1" in the name to indicate that the OH group is at the 1st carbon? Isn't it kind of assumed?

Is it necessary to name a compound "2-(3-methylbutyl)-1-cyclopentanol"?

Or is "2-(3-methylbutyl)cyclopentanol" sufficient?

Thanks!


texts: How do biochemists seperate nucleotides from DNA to add to the PCR

texts:
How do chemists separate single nucleotides from DNA strands?  How do they add those nucleotides to e.g. a PCR reaction in order to replicate DNA?

I ask this because in my microbiology class, my teacher didn't know the exact answer.

Do you cleave off nucleotides by hydrolysis?  Do you somehow build nucleotides?


texts: The Compressibility of a substance, dependent on

texts:
My Chemistry book states that (talking about compressibility equation):

  "A sample with Volume V is subjected to a pressure increase, delta P,
  and the resulting change in volume, change in V, is measured.  The
  ratio is divided by V; thus, the tabulated value depends only on the
  substance being measured and not on the geometry of the sample."

I'm not sure exactly how they are drawing this conclusion.  How does dividing by (-) volume cause the compressibility factor to not be dependent on the "geometry" of the sample?

Thanks.


texts:
In the chapter on Biomolecules in my book, the following points are given regarding carbohydrates.

Numbering the C-chain with consecutive rank
The C-atom present in the aldehyde group of aldoses and the terminal C-atom nearest to the keto-group of the ketoses are numbered as the first carbon or C1.
D- and L- Configuration
i) The D- and L- symbols refer to the configuration of monosaccharides. These do not indicate the dextrorotatory or laevorotatory specific rotations.
ii) In case of a monosaccharide, if the asymmetric C-atom of the highest rank is similar to the asymmetric carbon of D-glyceraldehyde (H-atom on the right,-OH group on the left) then the monosaccharide is of D-configuration. If the H-atom is on the left and -OH group is on the right, then the monosaccharide is of L-configuration.
iii) As per convention, if in a monosaccharide unit (expressed by Fischer projection formula), the -OH group falls on the right of the highest ranked asymmetric carbon, then the monosaccharide has D-configuration and if the hydroxyl group falls on the left, it has L-configuration.
Use of + and - sign
D- and L- symbols are followed by '+' and '-' in brackets. These repesent the dextro- and laevo- specific rotation. There is no relation between optical activity and nature of rotation. Example: Both glucose and fructose have D-configuration, but their optical activities are positive (dextrorotatory) and negative (laevorotatory) respectively.

Points ii and iii seem to be contradictory to me. Can someone please shed some light on this. I noticed that point iii is talking about Fischer projection. May be point ii is talking about some about mode of representation. Can someone please explain the paragraph under Use of + and - sign


texts: Carcinogenicity of home coated cast iron pans

texts:
Cast iron pans are a traditional cooking utensil and are becoming more and more popular in recent  years.
I myself switched from Teflon/ PFC pans to cast iron pans.
To use the pan they are normally coated with oil, which is baked in. For this mostly line seed oil is used, as it polymerizes well.
The normal procedure is explained in this video
Now my question is how likely is it that this process produces carcinogenic substances like PAH (Polycyclic Aromatic Hydrocarbons) which are often associated with heating oil.
EDIT:
As matt_black pointed out, I am interested of the amount of these substances. And if food that is cooked in a freshly coated pan contains significant more, than a pan with other coatings. The next question would be of course if so, how long this increase can be detected after multiple uses.


texts: Explain the enolisation process of 5,8-dihydroxynaphthalene-1,4-dione

texts:
I have no idea really how to get started...

Where does the hydrogen for the first deprotonation come from?

My working thus far:


texts: What is the Difference Between the Conjugate Effect and the Inductive Effect?

texts: As the title suggests, what is the difference between the conjugate and the inductive effect in organic chemistry.


texts: When is a molecule with fluorine considered more acidic than one with chlorine?

texts:
I am learning about acids and bases.  Here is the problem I am stuck on:

According to organic chemistry as a second language the molecule to the right with fluorine is more acidic than the molecule with chlorine.  I would think that since chlorine is bigger it is more stable resulting in a more stable conjugate base?


texts:
Lithiated dithianes have a few uses in organic synthesis (albeit fairly niche ones) such as the Corey-Seebach alkylation / Corey-Seebach reaction, which uses dithianes as masked acyl anions (d1 synthons) as shown below.

Searching through the 2013 IUPAC recommendations for organic nomenclature for dithian, dithiane didn't come up with any useful results, and the usual technique of looking for the corresponding oxygen analogue seems redundant in this case as the corresponding molecule with oxygen is impossible!

In most papers, the authors avoid explicitally naming the lithiated intermediate (certainly one way to get around the issue):

  Lithiation of dithiane X with t-BuLi followed by alkylation with epoxide Y resulted in Z upon quenching.

In others, a derivative name is used based on the 1,3-dithiane itself:

  2-lithio-1,3-dithiane derivatives are usually prepared by deprotonation with n-BuLi in THF at low temperatures2 and the anionic species obtained are able to react with many types of electrophiles.

  Taken from Tetrahedron 2003, 59, 6147

ChemDraw outputs something more in-keeping with other nomenclature:


texts: Is glass amorphous solid or supercooled liquid?

texts: I've read that glass is a supercooled liquid. But lately I've came to know in a science info post that glass is amorphous solid. How? Please someone explain me.


texts: Does a neutral dimercury molecule exist?

texts:
Is a neutral $\ce{Hg2}$ molecule possible, as a gas under extremely low (partial) pressures? What is the enthalpy of formation or similar?

It is my impression that usual mercury vapors are monatomic? I think it is well-known that a dimer ion $\ce{Hg2^{2+}}$ exists under some conditions.

Somewhat related threads: Is it possible to have a diatomic molecule of sodium in gaseous state? and Which elements can be diatomic?


texts: How polarization effects from cations affect H-bond strength

texts:
The average hydrogen-bond strength in pure water is higher than the average H-bond strength between the first and second hydration shells around a $\ce{Al^3+}$ ion (or any cation, for that matter). This leads to a shift in the OH stretch toward the lower frequencies.

This has something to do with the induced polarization resulting from the positive charge, no doubt, but I fail get why the H-bond becomes weaker. The H-bond would get stronger if the electron density around the H-atom participating in the H-bond gets smaller (larger coulombic attraction between H and O). When $\ce{Al^3+}$ approaches the O-atom of a water molecule, electron density will be forced toward the positive charge, ultimately affecting the H-bonded H-atom, which would give stronger H-bond, at least in my head.

So what's wrong with this picture?


texts: Does storing apples alongside potatoes keep potatoes from sprouting?

texts:
I am looking for a chemical explanation which I wasn't able to find.

I have read in several sources such as this one that, in order to prevent potatoes from sprouting, it is sufficient to store a few apples alongside them. This is due to the fact that the apples produce ethylene.

But this is a bit odd, since the ethylene is typically a ripening agent. This reddit thread also discusses the same doubt, but doesn't dive much into the details. There is also this article and this Quora answer, none of which give a specific chemical reason about why and how this works.

Chemically speaking, do we actually know the exact reason and the necessary conditions to make this work?


texts: Determining enthalpy of neutralization and heat capacity of calorimeter by overlying with straight lines or "eye-o-metric method"

texts:
Below is a model example of how to interpret gathered data. Temperature on y-axis, time on x-axis.
We are supposed to read  (temperature change by neutralization) and  (temperature change by resistive heating - to determine heat capacity of calorimeter) by overlaying the selected area with straight lines.

What I don't get is the way the straight lines are put the way they are. Maybe the bottom one: we expect the temperature drop caused by heating the calorimeter will continue by this straight fashion so we must take it into account in subsequent temp change reading.

But what about the upper line? Why read the upper value above the graph and not on its local maximum?


texts: How much worse is methane than CO2 as greenhouse gas?

texts:
I can't find a coherent answer to this question. The numbers are all over the place.

25 times greater
84 times more potent

The reason I'm looking is because I can't find a reason in physics why this would be so*:

  There is nothing “special” about methane that makes it much powerful than $\ce{CO2}$ (link to source)

What makes $\ce{CH4}$ absorb more infra-red than $\ce{CO2}$? What experiments have shown this?

Methane absorbs infra-red at different bandwidths than $\ce{CO2}$ (see here). Does the earth radiate more heat in those bandwidths?


texts:
I was making a solution of spermidine, and noticed that Sigma Aldrich warns that spermidine solutions deaminate over time. I tried to think of how that would happen, and made a diagram:

Assuming some of the spermidine has the secondary amine in an uncharged state, the lone pair electrons can attack either charged terminal amine group. I don't know which is more likely, I have drawn the 4 membered ring, but the other amine would make a 5 membered ring, which would probably be more stable. Either way, this would kick off an ammonia, which would be stable enough in water. Then a water molecule would attack a carbon on the ring and open it, making an OH2+ charged group, which would give up a proton. Of course the protons would be balanced because the ammonia would pick up a proton.

Does this make sense? It reminds me of nitrogen mustard chemistry, but must not be as reactive because spermidine is used to condense DNA, and nitrogen mustards are used to damage DNA.

Additionally, spermidine seems hard to work with. I tried to make 10mL of a 10mM solution, and calculated what volume to use to get the right mass, because spermidine melts at 20-25C. However, when I used that volume, I had about 2.5 times as much mass as I wanted. I assume this is because the spermidine was not totally thawed out, and the density was higher than I assumed (925mg/mL at 25C). Has anyone worked with this compound and has suggestions for how to handle it better?


texts: Functional difference of Benedict's solution and Fehling's solution

texts:
Chemically, Benedict's solution and Fehling's solution are very similar, with copper sulfate as a source of copper (II) ions, sodium carbonate, and sodium hydroxide respectively as alkalis, and sodium citrate and sodium potassium tartarate respectively as chelators. They are also both used to test aldehyde groups which can reduce the copper (II) ions into copper (I) ions, giving a precipitate of $\ce{Cu2O}$. Hence, they are often used in testing for the presence of aldehydes, and by extension, reducing sugars.

Are there any differences in function between the two reagents, perhaps in sensitivity, types of compounds that test positive, etc?


texts: Determining the torsion energy profile of butadiene by molecular dynamics

texts:
Disclaimer: this question is related to my previous question, although it is much more detailed

Consider the following rotation of butadiene:

I want to determine the relative energy of each dihedral angle by molecular dynamics (MD).

My initial idea was to simulate butadiene in the NVT ensemble and use the relative frequencies of each dihedral angle to determine the relative energy. In the NVT ensemble, the probability of each microstate $P_i$ is:

$$P_i = \frac{\mathrm e^{-E/RT}}{Z}$$

Thus, I performed MD simulations in the NVT ensemble and recorded the dihedral angle periodically. With $N$ total dihedral angles, I made a histogram of the dihedral angles (e.g. a bin every 5 degrees). If we define the number of angles contained in a given bin as $n_i$, I am using the following equation:

$$n_i = \frac{\mathrm e^{-E/RT}}{N}$$

This equation can be rearranged to isolate the approximate energy associated with that dihedral angle:

$$-RT \ln(n_i N)= E$$

However, the curve obtained does not match the distribution I obtained by a simple relaxed scan of the dihedral:

Where is the problem in my method?


texts:
What is the relation between the inductive effect on bond length and strength.

how would one rank the bond strength of

$\ce{CH3-H}$, $\ce{CH3CH2-H}$, and $\ce{(CH3)2CH-H}$

I know that alkyl groups donate electron density by induction, but how does electron density in a bond affect its length or strength?


texts: What is the standard potential of carbon?

texts:
What's the value of standard potential of carbon?

The hydrogen and Carbon are in the electrochemical series despite being non metals hydrogen has zero potential difference what about carbon?


texts: Suppose we have a T-S diagram of some vapor thermodynamic cycle , say the rankine cycle , and we are interested for example in the composition of the liquid and the vapor in the middle of the condensation process ;  knowing only the entropy of both the liquid and vapor at that point (or the enthalpy) , how exactly do we get the composition at that point ?


texts:
Which of the following is the more stable carbocation?

I thought the 1st carbocation would be the more stable one as the pi-electron density of phenyl group can overlap with the vacant orbital on the sp-hybrid carbocation (1st one). But my tutor pointed out that the vacant orbital on carbon can never be parallel to the p-orbitals of the phenyl group carbons and overlap cannot occur. So only negative inductive effect of phenyl group has to be considered, and so the 2nd one will be more stable.

Please explain. Please also mention about some sources where I can read about these type of carbocations.


texts: How to remove dichlorometane from water?

texts:
I will have water that have been through dichloromethane. Doing so, the dichlorometane (solubility $2~\%$) will contaminate my water by forming an azeotrop which will have a $38~\mathrm{^\circ C}$ boiling point. Would putting that mixture to $40~\mathrm{^\circ C}$ will make that azeotrop leave? Leaving me dichloromethane free water?

If not I could I extract it?


texts: Using Ethylene Glycol as anti-freeze in a biodigester gas storage system

texts:
I am busy building a bio-digester to produce biogas for cooking/water heating in a cold climate.

I am using the 3 IBC tank solution.
Tank 1 is the digester itself.
Tank 2 is the gas storage unit.
Tank 3 is the pressure for the gas outlet.

Tanks 2 & 3 will be linked. As tank 2 fills with gas, water overflows into a container with sump pump and is then pumped up to tank 3. When cooking, etc, the return valve is opened, allowing water pressure from tank 3 to push the gas in tank 2 towards the house.

I will be keeping tank 1 warm via a combination of insulation and surrounding the tank with decomposing matter from tree cutting & autumn leaves. I will also be running a hot water line through it from a compost heater.

Tanks 2 & 3 pose a bigger logistical challenge.

I brew beer for a living and use ethylene glycol to keep our fermentors & chillers from freezing over. I was wondering if it could also be used in this sort of set up. Aside from the gas outlet from tank 2 to the house, it is a closed system as far as the water is concerned.

However, I am unsure of how the ethylene glycol would react with the biogas. Is it safe?

The biogas will be produced from a mixture of food waste, cooked malts, and animal manure. It will be run through a water filter to prevent blowback (between the house and tank 2) and a steel wool filter (to remove hydrogen sulfates).

Other than pollution issues, should I be aware of anything else? I am worried about the glycol evaporating into the biogas causing an explosion.


texts: In my text book it states that a phosphate group is considered to be $\ce{-OPO3^{2-}}$. However, online it states that phosphate is $\ce{PO4^{3-}}$. Why do these contradict? Am i confusing phosphate the chemical with the phosphate group? Please see image for reference.


texts: Shouldn't the Hofmann product be preferred in this elimination?

texts:
Shouldn't the exocyclic alkene (Hofmann) be the major product? The base is $\ce{t-BuO-}$ (tertiary butoxide ion), which is pretty bulky. I think the Saytzeff product should be the minor product.

Also, the solution says "E2, some E1". It's a 3° alkyl halide (more sterically hindered than 1° and 2°), so shouldn't it undergo E1 elimination?


texts:
What is the correct product of the Diels-Alder reaction between 2-ethoxybuta-1,3-diene and (Z)-acrylaldehyde-3-d?

It keeps mentioning that my regio-selectivity is incorrect. And that I should consider the charge distributions of the diene and dienophile to figure it out correctly, but I honestly have no idea.


texts:
Alkali metals (Li, Na, K, Rb, Cs) and the alkaline earth metals (Ca, Sr, Ba - sometimes Mg is included also) form hydroxides that are well-known to be soluble or at least slightly soluble and create strongly basic solutions. Apparently these solutions of hydroxides are also known as alkali.

Since the more well-known d metals (Cr, Fe, Mn, Cu, Zn, Ni, Co, Ti etc.) forms no soluble hydroxide, I used to assume that apart from the 9 metals stated at the top, there is no more metals that corresponds to soluble hydroxides.

However, while searching my (non-English) version of Constants of Inorganic Substances: A Handbook by Lidin, Andreyeva and Molochko, I discovered that Europium (II) hydroxide was written as if it is soluble in a chemical equation in the Europium section. Later, I did search for information on the compound with the keywords ""Europium II hydroxide" soluble" , and I found some results:

  europium (II) sulfate is scarcely soluble in water, while europium (II) hydroxide dissolves readily and gives an alkaline reaction

(Concise Encyclopedia Chemistry, page 392)

Is there any other research on the compound Europium (II) hydroxide? Is it really soluble?

Which metal hydroxides, apart from those of those group 1 and 2 metals, are soluble? Is there any specific reason why europium (II) is such an anomaly? If there are other such cations, is there a specific reason for that particular cation to form such a soluble hydroxide?


texts: Inter-classification of organic chemistry functional groups (carboxyl vs alcohol & ether vs ester)

texts:
I have a few questions about whether organic functional groups can be classified as another.

First, can carboxylic acids be also be considered alcohols (they have $\ce{-OH}$)? If not, can they at least behave like alcohols?

Similarly, can esters ($\ce{RCOO-R'}$) be considered ethers because the $\ce{R'}$ group is linked to the other half of the ester via an $\ce{-O -}$ linkage? In whichever case, what are some chemical characteristics that distinguish ethers and esters?


texts: Is that correct to say that osmosis happens with water only?

texts:
Is that correct to say that osmosis happens with water only (based on the definition below) or it can happen with other liquids as well?

I've read the following definition in a book called "BRS - physiology" (6th edition, p.5):

  "Osmosis is the flow of water across a semipermeable membrane from a
  solution with low solute concentration to a solution with high solute
  concentration."


texts: Why is bipolar resonating structure less stable than monopolar structure?

texts:
In my book, it is written:

  Resonance energy of a system involving monopolar resonance structures is greater than that involving bipolar resonance structures.

The book cites example:

  Carboxylate ion which contains negative monopolar charge is in fact more stable than the corresponding carboxylic acid which contains both negative and positive charge.

But what's the reason?? What is going on?? Please help me with a math-free explanation.


texts: Minimizing Gibbs free energy with Helmholtz free energy expressions

texts:
If I have an expression for the Helmholtz free energy (from statistical associating fluid theory for a polymer system), can I still find the Gibbs free energy minimum under constant $T,P$ conditions?

Seems that since

$\mu_i = \left(\frac{\partial A}{\partial n_i}\right)_{T,V,n_j} = \left(\frac{\partial G}{\partial n_i}\right)_{T,P,n_j}$

where $A$ is the Helmholtz free energy and $G$ is the Gibbs free energy and $\mu_i$ is the chemical potential of component $i$.

If I can just find the expressions for $\mu_i=\left(\frac{\partial A}{\partial n_i}\right)_{T,V,n_j}$ I should be able to use this in the expression for $G = \sum_i \mu_i n_i$ and find its minimum, without having to worry about an equation of state to relate change in volume ($dV$) with respect to constant pressure ($P$)?

Edit I should clarify that I wonder about the Gibbs free energy because I'm interested in the constant $T,P$ (isothermal, isobaric case), and in the case especially for liquids. If you needed to introduce an equation of state to parameterize the change in V as a function of $T,P$ this would not be too difficult for an ideal gas, but for liquids it would be a challenge. So in this case, I wonder how to handle the $PV$ term (for constant $P$) in the Helmholtz free energy which does not appear in the Gibbs.


texts:
Which of the following is the product of the series of reactions shown above?

The correct answer is (C).

So the first step of the first reaction meant to create an enolate (deprotonating the hydrogen sandwiched between the two carbonyls), which upon addition of the substrate, forms:

.

I think the second step, potassium hydroxide is meant to hydrolyze the ester to a carboxylic acid.

Finally, the third step is meant to decarboxylate the acid by emitting $\ce{CO2}$.

However, I'm unsure as to what role the acid plays in the last step.  The only thing I could think of is that the acid helps the enol (the actual product from decarboxylation) tautomerize, but I don't think acid needs to be present for tautomerization.


texts: Origin of diastereoselectivity in Simmons–Smith cyclopropanation of allylic alcohol

texts:
In Organic Chemistry by Clayden et al., the following reaction is shown:

The cyclopropane ring is formed on the same side as the alcohol group. Is this because of the interaction between Zn and the OH group, which directs the reagent to approach from the same side as the OH group?


texts:
I am having some problems reading character table. I will describe what I understand and thought to be right.
Consider the $\pi$ MOs formed from overlap of p-orbitals in benzene.
These two degenerate $\pi$ MOs below have $E_{1g}$ symmetry:

I don't understand why that is the case. Based on what I have read, if a symmetry operation $g$ maps an orbital to itself, e.g.

then $\chi'(g) = 1$.
Elif $g$ maps the orbital to negative itself (invert the sign of orbital),

then $\chi'(g) = -1$.
Else, $\chi'(g) = 0$.
For two degenerate orbitals as above, final $\chi(g)$ is the sum of $\chi'(g)$ for two orbitals, where $\chi(g)$ is character of a symmetry operation $g$, that is recorded in the character table.

Applying this, consider the $C_6$ of benzene,

Not mapped to $\pm$ itself, so $\chi'(g) = 0$.

Also not mapped to $\pm$ itself, so $\chi'(g) = 0$.
So $\chi(g) = 0 + 0 = 0$.
But if we look at the character table for $D_{6h}$, for the symmetry species $E_{1g}$, $\chi(C_6) = 1 \neq 0$.
Enlighten me, please, I must have understood something terribly wrong.


texts: Why do atoms on the periodic table have the number of valence electrons that they do?

texts:
I'm studying year 11 and am learning about valence electrons and how these electrons drive intermolecular bonds.
What I have not been able to find an explanation to is why all the elements on the periodic table have the number of valence electrons that they do.
To me, it seems intuitive that if the halides are so eager to gain an electron, why would their natural state not be to have the 8th electron in their shell?


texts: Automated chemistry test machines? What is currently done, and what is research leaning towards?

texts:
There are small and large chips and machines to effect admixtures,blends, fusions of different chemicals into a variety of test samples, and there are machines to measure many vials of all kinds of biological and synthetic compounds.

The challenge is that there are so many ways to synthesize materials, using pressure, condensation, temperature, phase change onto centrifugal plate, and 100ds of other synthesis methods, lasers, using for example 40 interesting materials, there are too many possibilities for an unlimited number of machines for synthesis, the topic is unfathomable from the very start.

If we take 40 chemicals, we have billions of possible experiments to do with them, it makes the concept of fast robotic chemistry labs suitable for the synthesis and measurement of many exotic materials, and it's a very confusing topic.

What work has been done with automated chemistry synthesis and testing machines, and what will they be able to do in the next 10 or 20 years?

Are any automated test machines used to test the result of an automated compound creation machine?

Are there presently automated R&D labs that mass produce random combinations of materials in the constant search for new useful discoveries, can you shine some light on some research in the subject?


texts: I am currently learning about transition metal complexes, however I keep seeing complexes like $\ce{[Al(H2O)6}]^{3+}$ but aluminium isn't a transition metal. Is this a case that any metal can form a metal complex or is it just transition metals and a few others, if so which ones and why?


texts: Why is the magnesium(II) ion preferred over other ions in chlorophyll?

texts: Chlorophyll has a $\ce{Mg^2+}$ ion. Why is it preferred over other ions? For example, what happens if there is $\ce{Zn^2+}$ or $\ce{Ca^2+}$ or any other (divalent) cation instead of $\ce{Mg^2+}$?


texts:
I'd imagine the answer to the question posed in the title is no - bond angles are not constant. Covalent bonds are not infinitely rigid; hence IR as a spectroscopic technique.

If so, how can we accurately determine bond angles? What margin of error might we expect from an experimentally measured bond angle?


texts: Steric factor is greater than one will the collision frequency determined by the arrhenius equation be greater or less than the experimental value?

texts:
In a bimolecular reaction the steric factor p was experimentally determined to be 4.5 Experimentally determined value of frequency factor is higher than that predicted by Arrhenius equation

According to arrhenius theory $$k=Ae^{-E_A/RT}$$
According to collision theory

$$k=pZ_{AB}e^{-E_{A}/{RT}}$$

In the arrhenius equation the frequency factor is $A$ and in the Trautz-Lewis theory it is $Z_{AB}$ . Now $p=4.5$ and since on comparing both the equations we get $$A=pZ_{AB}$$ This means the experimental value, of collision frequency $Z_{AB}$ is in fact lower than $A$ $\left(Z_{AB}=\frac p {4.5}\right)$.

This contradicts the above statement?


texts: Why do cyclic ethers have higher boiling points than their acyclic isomers?

texts:
TL;DR version is the question title. Some context and data follow.

I was creating an assignment for my organic chemistry students in which they would need to draw as many isomers as they could from a simple formula, for example $\ce{C3H6O}$ (which fits 7 structures - 9 if you count minor enol tautomers and 11 if your count stereo). In this set (ignoring stereo and enols) there are:

  Two alcohols

Cyclopropanol - boiling point $=101-102\ ^\circ\text{C}$
Allyl alcohol - boiling point $=97\ ^\circ\text{C}$

  Two carbonyl compounds

Propanal - boiling point $=46\ ^\circ\text{C}$
Acetone - boiling point $=56\ ^\circ\text{C}$

  Three ethers

Propylene oxide - boiling point $=34\ ^\circ\text{C}$
Oxetane - boiling point
$=49-50\ ^\circ\text{C}$
Methyl vinyl ether - boiling point $=6\ ^\circ\text{C}$

The boiling point of methyl vinyl ether immediately stood out as anomalous. The fully saturated ethyl methyl ether has a boiling point of $7.4\ ^\circ\text{C}$.

Here are some more data comparing cyclic ethers to their acyclic isomers (and some analogs). The gap appears to be closing as the number of carbons increases.

  Four carbons

Tetrahydrofuran - boiling point $=66\ ^\circ\text{C}$
1-Butene oxide - boiling point $=61-65\ ^\circ\text{C}$
Ethyl vinyl ether - boiling point $=33\ ^\circ\text{C}$
Allyl methyl ether - boiling point $=42-43\ ^\circ\text{C}$
Diethyl ether - boiling point $=34.6\ ^\circ\text{C}$
Methyl propyl ether - boiling point $=38.8\ ^\circ\text{C}$

  Five carbons

Tetrahydropyran - boiling point $=88\ ^\circ\text{C}$
2-Methyltetrahydrofuran - boiling point $=80.3\ ^\circ\text{C}$
Allyl ethyl ether - boiling point $=65-66\ ^\circ\text{C}$
Butyl methyl ether - boiling point $=70-71\ ^\circ\text{C}$


texts:
Why is the boiling point of a solution higher than that of a pure solvent?
I think when a non-volatile solid solute is added to a solvent, some of the liquid solvent molecules are replaced by solute molecules at the surface. The lesser the number of solvent molecules at the surface that fewer molecules evaporate, and thus the vapor pressure of the solution will be lower than the pure solvent.

Is this correct?


texts: Looking for a common solid which is very soluble in water, insoluble in a volatile solvent, and doesn't corrode ferrous metals

texts:
I'm looking for a way to make a shiny object 'matte', but temporarily. I'd like to be able to spray on a coating which is a uniform colour and wash it off easily, even from small 'nooks and crannies' in the surface.

I've looked into chalk paint ( https://www.montana-cans.com/en/spray-cans/spray-paint/chalk-400ml/montana-chalk-400ml ) but these use suspensions of eg. Carbon black or Titanium Dioxide, which are insoluble in water and difficult to wash off.

I'm wondering if there is a readily available compound which forms a suspension in a volatile solvent (for when it's sprayed on), which is soluble in water (so it's easy to wash off) and doesn't corrode ferrous metals (because the object I'm trying to coat is made from chrome steel with small rust pits already).

Any ideas?


texts: How to perform a total synthesis on paper ? (Think before to make it in lab)

texts:
I studied organics chemistry during five years. All those years I just made reactions to made them, the only moments where I had to perform a synthesis on paper was during exams or exercises but all steps were given. So, even if, it was very interesting, there were no really fun to apply all this knowledge to think about the synthesis of a molecule. Obviouly with all these lessons I'm not that bad and I'm able to do a little bit of retrosynthesis.

However I know that total synthesis of natural origin molecules is perform a lot for some decades, we can find a lot of examples here, and sometimes it looks pretty weird to think that human people were able to think on how to make a synthesis in more than twenty steps.

For example, the weirdest synthesis I found, is the synthsis of Azadirachtin "only" perform in $79$ steps. That is abosolutely insane.

My question:

  I'm wondering, for every molecules in general, how do chemist do to
  think about the retrosynthesis of such big molecules which contain in
  general a lot of stereocenters which then add more difficulties?
  I mean without to use a computer, is there some rules, such like theorems in mathematics, to think in the best possible way? Because with a bit of luck for $79$ steps at $90$% yield it makes a final yield of $0.024$%...


texts:
I am school student. In my school text book there is a fact about diamond. That is

  Each carbon atom is covalently bonded to four other carbon atoms. A lot of energy is needed to separate the atoms in diamond. This is because covalent bonds are strong, and diamond contains many covalent bonds. This makes diamond's melting point and boiling point very high.

If a diamond is a single molecule, how does a single molecule melt? Is that fact correct? Please tell me the answer!


texts: Smelly matters in urine - do they have lower or higher boiling point than water?

texts: I don't know what exactly are the compounds that causes urine to be smelly, but does it (or do they) have higher or lower boiling points than water? If I have both liquid and exposed them to open air, will the water dry up first or will the smell disappear first?


texts:
I have come to an example which suggests that +M effect of -OH is better than =O . How is that possible?
Here is the picture with their Hydride affinities (in Kcal/mol)

I think -OH should have stronger +M , as it's lone pair's hybridization is sp2 which will be closer in energy of sp2 orbital of carbon  centre as compare to sp hybridization of =O .

Source: www.cpp.edu/~psbeauchamp/pdf/315_SN_E_answers.pdf

Problem no. 21 , page no. 10 .


texts: Why equivalents of reactants and products come out to be equal in a reaction? I am seeking logic behind the law of chemical equivalence and i have just asked it for clarifying the concept.


texts: What databases or repositories are there that have generalized SMILES for functional groups?

texts:
Does a resource exist that has the SMILES formula of the generalized pattern that represents the group?

For instance: I have the aldehydes group, which has the pattern: -CHO.  Is there a resource that lists each functional group with the generic pattern that defines the group and its SMILES representation?

I'm hoping for, at the very least, getting the SMILES formula for the functional groups represented in this pdf: EPA Chemical Compatibility Chart

Follow up question: Is SMILES still relevant or are there better ways to represent chemicals?


texts: How can I estimate reaction rates in water with computational chemistry?

texts:
I want to estimate rates of substitution reaction of esters with nucleophiles in water.
How can I estimate them with a computational chemistry software (preferably GAMESS(US))?
Or is it practically impossible?
I know that this is possible in gas phase, but I don't know how to do it in solution.


texts: Which functional group is more polar in a drug: primary amide or a carboxylic acid?

texts: There is a lot of speculation as to which functional group is more polar, I've read a lot around this on the web and I can't decide which one is actually more polar? Can someone help because I need to know how to identify the most polar groups in drugs to create some drug monographs.


texts: IUPAC Nomenclature for cyclic compounds without principal functional group

texts: I am struggling naming cyclic compounds with multiple substituents and no principle functional group . If anyone can please elaborate the rules, it would be appreciated.


texts: Show proposed mechanism is consistent with the experimental rate law

texts:
The mechanism for the reaction:
\begin{align}
\ce{NO_{(g)} + O_{2(g)}  &<=>[k_{-1}][k_{1}] NO_{3(g)}} &\text{(fast)}\\
\ce{NO_{3(g)} + NO_{(g)} &<=>[K_{2}] 2\,NO_{2(g)}}      &\text{(slow)}\\
\end{align}

The experimental rate law:
$$Rate=-\dfrac{\Delta\ce{[NO]}}{\Delta t}=k\ce{[NO]}^2\ce{[O_{2}]}$$

At equilibrium, the forward and reverse rates are equal to each other. We then have
$$k_{1}\ce{[NO]}\ce{[O_{2}]}=k_{-1}\ce{[NO_{3}]}$$

This can be re-arranged to
$$\ce{[NO_{3}]}=\dfrac{K_{1}}{K_{-1}}\ce{[NO]}\ce{[O_{2}]}$$

Since $2\,\ce{NO}$ disappear in the overall reaction for every NO that reacts in the second step, we multiply the overall reaction rate by two and thus have:

$$2k_{2}\ce{[NO_{3}]}\ce{[NO]}$$

I understand everything up to this point. What I do not understand is how we get to this equation from the previous one.

$$Rate=2k_{2}\dfrac{k_{1}}{k_{-1}}\ce{[NO]}^2\ce{[O_{2}]}$$


texts: Extraction of calcium carbonate from liquid

texts:
I'm using calcium carbonate ($\ce{CaCO3}$) in apple juice to reduce the acidity of the juice.  Once the $\ce{CaCO3}$ reacts with the apple juice and raises the pH, the juice is left cloudy in color BUT has the desired pH of 3.4.  I need a way to extract (separate) the $\ce{CaCO3}$ precipitate from the apple juice which leaves the resulting liquid (apple juice) drinkable still...

The pure juice has an initial pH of 2.9. I want to reduce the acidity and be left with pH of say 3.4. Perhaps by blending with another drink?  I did a test using the pH meter, I started with water (pH 6.0) and slowly added apple juice, and the pH drops to 2.9 adding 1 part juice to say 10 parts of water.  So blending another higher pH drink (tea/water/etc) would totally dilute the apple juice before the pH would reach 3.4. How can I raise the pH and still keep the apple juice pure or close to pure?

Apple juice out of the carton tests at 2.9 pH with digital pH meter.
My tap water tests at 6.0 pH.
Calcium carbonate - pill form from health food store (oyster shell derivative)


texts: Does nitrogen inversion affect the basicity of amines?

texts:
If I were to compare the basic strength of 1-azabicyclo[2.2.1]heptane and triethylamine:

Can I say that 1-azabicyclo[2.2.1]heptane is more basic than triethylamine because the lone pair of electrons is less available in the latter due to rapid nitrogen inversion? Nitrogen inversion is not possible in the bicyclic amine.

There is not much difference in the inductive effect. In both cases, the nitrogen atoms are $\mathrm{sp^3}$ hybridized.


texts: Why does a glass tube show white bands after being heated with a torch?

texts:
When I use a torch to split a glass tube, there's always a hazy white band which appears. Does anyone know what the cause of this is?

It was a hydrogen-oxygen torch. The glass is fused quartz glass, which should be pure silica.