texts: Black Smoke Produced from Regular Lighter but Not Torch Lighter Applied to Copper

texts:
I have a piece of copper mesh from which I would like to remove all coatings/oils. The copper comes from a pot scrubber like this. In order to remove any residue, I held a standard bic lighter up to it. It gave off black smoke. I moved the lighter around the mesh, waiting for it to stop giving off any such smoke, but seemed to do so indefinitely. Even when I just held the lighter in one place, it would not stop giving off a steady stream of black smoke.

I then did the same thing with a torch lighter on a fresh piece of copper from the same source. This time it was hard to tell if there was any smoke at all-- and if there was, it stopped being produced very quickly.

With both the normal lighter and the torch lighter, the surface of the copper turned gray-black. I assume part of this is from the formation of copper oxides, but part of it may also come from the deposition of incompletely combusted carbon on the surface. In both cases I was able to restore the shiny surface by putting the mesh in $\ce{HCl}$-based toilet cleaner for a few minutes.

Why is the normal lighter producing black smoke where the torch lighter is not? What does this smoke consist of?


texts: Solving for Concentration Using pseudo-First Order Kinetics

texts:
The following graphs represent a pseudo-first order bi-molecular reversible reaction with the formula $\ce{A + B <=> C}$:

The reaction product has an extinction coefficient of $\pu{50000 M-1 cm-1}$. Solve for the concentration of $\ce{A}$.

I think you are supposed to use Beer-Lambert's equation ($A=\epsilon cl$) with the assumption that cellular path, $l=\pu{1.00cm}$, and get a value for $A$ (absorption) from the graphs to then solve for $c$. I just do not know how to get a value for absorption from the graphs. Furthermore, after getting a concentration for $\ce{C}$, I do not know where to go from there to solve for the concentration of $\ce{A}$. I think it has something to do with the equation $y=2.0172+0.498x$ (the slope is equal to $k_1$ and the y-intercept is equal to $k_{-1}$) and messing around with the rate constants to solve for $\ce{A}$.


texts: Mechanism of carboxylic acid and amide dehydration with phosphorus pentoxide

texts:
Dehydration of carboxylic acids with phosphorus pentoxide ($\ce{P2O5}$) yields acid anhydrides, and in a similar reaction, amides dehydrated with phosphorus pentoxide yield cyanides. Can an arrow pushing mechanism be given for these reactions? If there isn't a mechanism, what, at least, gives phosphorus pentoxide the ability to dehydrate carboxylic acids and amides?

Phosphorus pentoxide itself reacts with water molecules to form phosphoric acid. That enables it to remove free water molecules by a simple hydrolysis reaction, but here of course there must be some other electron movement since the water being removed is not free water.


texts: Is the middle ring of this organic compound aromatic?

texts:
Is the middle ring with 5 atoms of (4Z)-4-[(4-methoxyphenyl)methylidene]-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one aromatic?

The carbonyl group could become a negatively charged oxygen, the tertiary amine could then form a double bond with the $\ce C$ atom of the carbonyl group. The secondary amine could contribute one electron to the $\pi$-system. And the $\ce C$ atom of the ethen-group could contribute two electrons if the other $\ce C$ atom becomes positively charged, but I'm not sure if this is likely.


texts:
What is the name of this $\ce{C13H28}$ isomer:

$\hspace{5.5cm}$

I think it must be "4-ethyl-6,7-methylnonane," but I saw somewhere that its name is "6-ethyl-3,4-methylnonane". Why? The ethyl number must be smaller, isn't it? (because E is before M). Am I wrong?


texts: Why adding salt to kneading make it wetter?

texts:
Last week I tried a new recipe of pizza dough:

65mL of Water;
140g of Wheat Flour (typo 3);
7g of Yeast;
1 big spoon of Olive Oil;
25g of cooked potatoes;
1g of common salt;

I think the recipe uses cooked potatoes as direct source of strach for Yeast. I have mixed all ingredients and kneaded 20 minutes until having a homogeneous dough that is not sticky. Then I added salt (about 0.5g) to the dough and I mixed it. Then the dough became wetter and stickier, I had to add flour in order to recover from the previous state.

It was an amazing experience, because it is somehow unexpected and counter intuitive. Adding salt to preparation seems to lead to more free water in dough.

I have the feeling that water is bound into macro-structure and adding salt may release some water in exchange of ion caging.

Anyway I would like to deeper explain this phenomenon. I am looking for concrete, scientific and reliable explanation.

Update
I read comments about osmosis phenomenon but I do not think it is the good explanation, it happens but does not explain the final state. Osmotic pressure is a transient phenomenon and really need a system boundary to be defined (after all this is a Fick force applying over a surface). I agree that a gradient exists at the beginning, and when mixing but it does not explain why afterwards there is more free water in the whole system. I also agree that there are local gradient, because of macro structure (proteins, etc.) but I am not asking about the transient phenomenon, I am asking about the overall equilibrium.

I express the question in another way:
Why adding salt to a finite mass of dough (of fixed recipe) releases some water and force us to add flour to keep dough constancy as before?


texts: What do (R) and (Z) mean in chemical names?

texts:
So, I'm confused on the notation my professor uses in a certain question; could someone explain.
He says:

Draw the structure: (R)-(Z)-chloro-4,6,-dimethyl-3-octene

I get everything after '(z)'

I'm just unsure what he means by '(R)-(Z)'...

Any input is appreciated. Thanks.


texts: I have a high pressure bottle of argon gas (99.98 %) that I need to use in an experiment. The problem is that the regulator I have is a generic type that is seemingly optimized for high flow rates (welding). I need a fairly low flow rate of under 200 cm³/min. However, I do not know what kind of regulator would be suitable. Any suggestions for search description?


texts: Determine reaction order and reaction rate

texts:
In a solution of $\ce{Fe^3+}$ the concentration was measured to be:
$$\begin{array}{c|c}
t/\pu{min} & \ce{[Fe^3+]}/\pu{\mu M} \\ \hline
10\ & 238\\
20 & 227\\
40\ & 206\\
60\ & 187 \\
80\ & 169\\
100\ & 154 \\
\hline
\end{array}$$
The decrease in $\ce{Fe^3+}$ concentration is due to the hydrolysis of the ion and precipitation of hydroxide. Calculate the reaction order and reaction rate.

I am having trouble understanding how to tackle this problem. I began by find the reaction formula:
$$ \ce{Fe^{3+} + H_2O <=> Fe(OH)^{2+} + H^+} $$
So this is a second order reaction. I then did:
$$\begin{array}{c|c|c}
\text{time} & \ce{[Fe^3+]} & \text{H2O} & \ce{[Fe(OH)^2+]} & \ce{[H+]}\\ \hline
t=0 & a\ & a & - & -\\
t=t & a-x & b-x & x & x\\
t = \infty & - & b-a & a & a \\
\hline
\end{array}$$
But I am unsure if I should include water and the hydrogen ion, and also how I should continue if this is correct. Can someone please push me in the right direction here. Thank you!
EDIT
First order equation:
$$ \ln \frac{a}{a-x} = kt$$
Is a then equal to $238$ and $a-x$ is the initial value ($238$) minus the next value? e.g., $238-227 = 11$.
If I plot:
$$\begin{array}{c|c|c}
t & \ln \left (\frac{a}{a-x}\right) \\ \hline
10 & 0\\
20 & 3.07\\
40 & 2.43\\
60 & 2.53\\
80 & 2.58 \\
100 & 2.76\\
\hline
\end{array}$$
I get that the slope is $0.0168$ and that would be the rate of the reaction?


texts:
Firstly, I apologize about both the inorganic and the organic tags on this post. I couldn't get a proper tag. If anyone can suggest a better tag, please edit the post.
I'm making cooking gel using alcohol and calcium acetate.
The purpose of the calcium acetate is to make a thicker, gel like solution.
Using the calcium acetate, I get a great working solution that burns well.
However, I seem to have bought the wrong product in my last batch, and I'm sitting with a bucket of calcium phosphate.
Is there any way for me to use the calcium phosphate?


texts:
I am given a protein, BAPNA, and the initial concentration of the protein. The experiment involves reaction rates of varying protein concentrations. Each sample cuvette is inserted into a spectrometer, 100% transmittance is set, has the enzyme inserted, and then has transmittance measured every 20 s for 600 s.

I understand absorbance is given as: $A = 2 - \log (T\%)$ and that's no issue.

The problem I run into is trying to solve for the concentration or molar extinction constant. I understand that Beer-Lambert law, $A = \epsilon bc$  is used for this purpose. The only given concentration is the initial concentration. Assuming $b = 1$, we can solve for $\epsilon$ or $c$, but having 100% set in the beginning causes $A = 0$, meaning initially $\epsilon = 0$ if $c \neq 0$.

This is where my calculations run into a dead end. I'm not given $\epsilon$ or concentration at any other point, but I'm supposed to be able to calculate the final concentration and maximum reaction rate. I've only a set of transmittance numbers over time, and that initial concentration.

Is there something I am misunderstanding or not seeing?


texts: A different type of photosensitive material

texts:
I'm curious as to whether there is any small, solid or gel-like material that dissolves/liquefies/evaporates under brief exposure to bright artificial light? So, some small element or agent that would form a 'wall' between two liquids but then vaporise when exposed to light (preferably artificial)

I think I found a crystal that changed to oxygen awhile ago via google, but I cannot locate it again so any help would be well appreciated.


texts: Activation energy and degrees of freedom

texts:
According to the Arrhenius equation the rate of a reaction increases as at higher temperature a greater percentage of molecules have translational kinetic energy greater than or equal to activation energy Wikipedia.
I was recently introduced in molecular potential surfaces and I read that some reactions can proceed when excess kinetic energy is stored into vibrationals degrees of freedom than translational. But according to Wiki it seems that only translational kinetic energy matters. First, I want to understand if the factor:
$$e^{\frac{-E_a}{RT}}$$
takes into account only the percentage that have the necessary kinetic energy in translational degrees of freedom or in general the percentage with at least this energy irrespective if this energy is stored in a combination of various degrees of freedom? Also for two reactants $\ce{A}$ and $\ce{B}$ does it calculate the percentage of "pairs" $\ce{A}$, $\ce{B}$ that have this amount of energy or just the percentage of the population with at least this energy?
Secondly, if some reactions speed up depending in which type of degrees of freedom (vibrational or translational) are excited, does this mean that the Arrhenius equation even for an elementary bimolecular reaction holds only if the reactants have only translational degrees of freedom (like collision of two atoms $\ce{A}$ and $\ce{B}$ to form $\ce{A-B})?$


texts:
I had to draw the molecular shape for $\ce{NHF2}$ as a Trigonal Planar like this

But when I check to make sure it was right, I came across a source saying

  NHF2-difluoroammonia--tetrahedral, almost trigonal
  (Source 1)

After looking some more I found a source that now said it was

  Trigonal pyramidal, Bond angle of 107 degrees Bond angle of F-N-F > F-N-H
  (Source 2)

Can someone clarify which one it is so I can understand.


texts: Deciding if a molecule is polar and non-polar in cyclic carbon compounds

texts:
While discussing about dipole moment of the compounds, our chemistry teacher told that the dipole moment will be 0 for 1,4-Dichlorobenzen, and for those compounds where same atoms or group of atoms are attached in para position if the hybridization of the atom of the group which is directly attached to the carbon of the benzene ring is sp or sp2 but if it is not the case i.e if OH is attached at para positions then the dipole moment wont be 0. I want to know if there is any reason or are they just unexplained examples. Are there more such exceptions?
Please check the picture for examples.


texts: Possible Method for Testing Ammonia (and Nitrite/Nitrate) Concentration in Water

texts:
I am designing an automated system testing device for my high school's aquaponics club. We need to test for a number of ion concentrations, including ammonia and nitrite/nitrate. In my research, the few selective-ion probes that exist are quite expensive, thus I am looking for some other, more creative methods for attaining these concentrations.

The most obvious method of testing would be to use a colorimeter to assess water samples w/added indicators. However, this would be a fairly complex device to automate. I would essentially be building an autosampler, which I think would be a ton of fun, but has the disadvantage of being expensive and time-consuming (to an extent that my application writing will not allow).

My question to you, community, is if I could test concentrations of these ions through vaporizing my sample and testing vapor w/gas sensors. If I were to boil a solution containing nitrite, nitrate and ammonia, what would my products be? Could I theoretically pull this off?

Thanks!
Ethan


texts: Can an organic compound undergo ring contraction to give more stable carbocation?

texts:
Throughout my journey in organic chemistry I’ve only seen ring expansions by a compound in order to attain more stability, but yesterday I thought about the following reaction.

I feel that ring contraction resulted in a more stable carbocation.

Can someone tell whether the idea behind this reaction is correct or not?


texts: Substances that pass visible light but absorb microwaves

texts: Specifically, the substances should be water-miscible or water-soluble, but not water itself. Additionally, they should be absorptive but not opaque.


texts: Plasma cleaner Increasing pressure in vacuum

texts:
We have a plasma cleaner, in order for the plasma to be created there has to be around 200-300 mtorr.

As soon as we turn the plasma, the mtorr instantly goes up but the vacuum line is still active.

The question is: What is the plasma in the chamber doing to make the pressure increase?

If this is the wrong section of stacked exchange can someone redirect me to the right section?


texts:
I know sulfuric acid is a strong acid and acetic acid is a weak acid. However when I write them in their chemical symbol.

Sulfuric acid: $\ce{H2SO4}$

Acetic acid: $\ce{CH3COOH}$

I realise that acetic acid has 4 atoms of hydrogen whereas sulfuric acid has only 2 atoms of hydrogen. So, shouldn't acetic acid be stronger than sulfuric acid?


texts:
I'd really appreciate it if someone could explain this one, please! According to my answers sheet it is not cis nor trans. But it looks like it is cis? Why, according to my answers sheet, is this neither?

Thank you in advance!


texts: Can pressure remain constant in isothermal expansion?

texts:
An ideal gas undergoes isothermal expansion at constant pressure. During the process:

  enthalpy increases but entropy decreases.
  enthalpy remains constant but entropy increases.
  enthalpy decreases but entropy increases.
  Both enthalpy and entropy remain constant.

I applied this formula.
$\Delta H = \Delta U + p\Delta V$ (pressure is constant)
$\Delta U = 0$ (since, process is isothermal)
$\Delta V >0$ (gas is expanding)
So $\Delta H > 0$
So enthalpy must be increasing $\left(\Delta S =\frac{\Delta Q_{\text{rev}}}{T}\right)$

Since heat is supplied to expand gas $\Delta S$ must be positive. And entropy must increase. But none of the option is matching with my answer.

Also I think question is wrong since $PV= nRT$ and, at constant temperature (isothermal) and constant pressure, volume can not change.


texts:
Hückel's rule says that any planar compound with a ring of conjugated p orbitals with $4n+2$ electrons is aromatic. Here, can $n$ be any integer, or does $n$ have to be related to the number of p orbitals in the conjugated π system (as shown in the Frost circle)? For example, in benzene, there are 6 electrons in the pi system ($n=1$), which fill all 3 bonding orbitals. Thus, benzene is very stable. But say we remove 4 electrons so that there's only 2 electrons in the π system. Here, $n=0$, so is this cation considered aromatic?

On the other hand, if we add 4 electrons to benzene's π system, it has 10 electrons ($n=2$). Is this anion aromatic? It doesn't seem very stable to me, since it has now filled 2 antibonding orbitals as well.

In general, it is a requirement that the $4n+2$ p electrons exactly fill all the bonding orbitals of the pi system for the molecule to be aromatic?


texts: Electrolysis of concentrated sulphuric acid

texts:
In my textbook it is given that for electrolysis of dilute sulfuric acid  at anode following reactions can occur:

At moderate concentrations

$\ce{2H2O ->  O2 + H+ +4 e-}$

And for high concentrations

$\ce{2SO4- ->  S2O8^2- +2 e-}$

SRP value for first reaction is less than second and hence the first reaction should take place. But why does that not hold for high concentrations?


texts: Does the absolute value of enthalpy have any physical significance?

texts:
I know it is pretty hard to measure the change in volume in open systems. Accordingly, calculating the change in internal energy using the first law of thermodynamics is pretty hard also.
Is this the only reason for introducing enthalpy ($H$) as a new thermodynamic potential to make use of the constant atmospheric pressure, and to calculate the change in enthalpy ($\Delta{H}$) as it is equal to the in/out quantity of heat ($Q$) in this case?
If no, does the absolute value of enthalpy have any physical significance?


texts: Reaction between copper and silver(I) nitrate in aqueous medium

texts:
What is the reaction between $\ce{Cu}$ and $\ce{AgNO3}$ taking place in aqueous medium?

The answer given was:

  "Only" oxidation of $\ce{Cu}.$

My concern is: how is only oxidation of $\ce{Cu}$ happening, as redox will occur in pair?

So either $\ce{Ag}$ will reduce, or $\ce{NO3-}$ will. But, since $\ce{Ag}$ has higher reduction potential, it won't. What will happen?

What does $\ce{NO3-}$ reduce into, if it does at all?


texts:
I struggle to see the difference between internal energy and enthalpy, or at least the need for differentiation between the two. I understand that enthalpy, supposedly unlike internal energy, accounts for the expansion work required for the system to exist, but it seems that that would only be necessarily stated if one had failed to account for the negative contribution to work in the first place.

Could enthalpy, as $$H = U + pV$$ and thus, $$H = q + w + pV$$ not be written as equally validly as, $$H = q + w_1 + w_2$$ i.e. $$H = U \ ?$$

It would seem that this definition of enthalpy implies that internal energy accounts only for work done to the system, disregarding work done by it.


texts: Defintion of Solubility in Different cases

texts:
How do we define solubility (in moles per liter) in cases when concentration of cation is not equal to the concentration of anion?

e.g. When we put AgCN in an acidic solution (Leading to formation of HCN) or when AgCl is put in CH3COONa (Leading to precipitation of CH3COOAg)

Do we take concentration of Ag dissolved as solubility or concentration of CN or Cl as solubility?

Please answer for both cases.


texts:
While reading up on Tanabe-Sugano diagrams I noticed that many diagrams spread over the internet that all seem to come from this Wikipedia article: https://en.wikipedia.org/wiki/Tanabe–Sugano_diagram. Those graphs are all derived from this data: http://wwwchem.uwimona.edu.jm/courses/Tanabe-Sugano/TSspread.html
When I myself create the same graph from the same raw data the x-axis is not the same in regards to scale. My question is, since the creator of the Wikipedia graph left no further documentation, what step am I missing?


texts: Possible structure if a compound like AB4 is polar?

texts:
I was asked the following question in JEE Mains (2nd September, Shift 1) 2020,

If a compound AB4 is polar (having non-zero dipole moment), then it's structure could be
(A) Square planar
(B) Rectangular planar
(C) Square pyramidal
(D) Tetrahedral

My thoughts

As this compound has only 4 ligands, therefore it cannot be a square pyramidal.
It can neither be a tetrahedral nor a square planar bcoz, it would be non-polar then.

So, we are left only with "rectangular planar", which I'd never heard before. How to move on?


texts: How do you predict isomers for certain hydrocarbons?

texts:
Hexane $\ce{C6H14}$ has 5 isomers, but I'm able to draw at least 6 different structures, which initially led me to think that there were 6 isomers.

So how can I tell which structure will qualify as an isomer?

The only rule my textbook suggests is connectivity exemplified as a $\ce{CH3}$ (for example) that runs downward at the end of the straight chain, which is no different than the straight chain itself.


texts: How do you determine the amount of acrylamide in foods such as baked fries?

texts:
There are many food studies which determine the concentration of a substance in a food item.

For example, this study determines the concentration of acrylamide in solid foods like fries.

By what experimental technique is this done?


texts: Does there exist a black coloured metal?

texts: Most of the metals are just painted/coated black. Does there exist a black coloured metal, either natural or artificial, such that even when we scratch it, it will still remain black?


texts: Are there any gases more dense than liquids?

texts: Inspired by Is there any type of liquid, other than mercury, that PTFE teflon is known to "float" to the surface in?, are there gases that are more dense than liquids? (So bubbles would sink down instead of bubbling up?)


texts: Are all amino acids except glycine chiral compounds?

texts: Specifically, I was thinking of the case where the R group is a carboxylic acid functional group or an amine group. Then there would not be a chiral carbon atom. Is there a restriction on what can be an R group that I am missing?


texts: In the chapter of amines, and I see reaction occuring between amines and nitrous acid. However I am thinking why I don't see reactions of amines also react $\ce{HNO3}$ in presence of stronger acid like $\ce{H2SO4}$, that can protonate $\ce{HNO3}$, causes $\ce{H2O}$ to leave and then finally have amines to react with $\ce{NO2}$, making nitroamines?


texts: What is the safest way to hook up car battery jump cables and why?

texts:
I know that when both connecting and disconnecting battery jumper cables between two car batteries there is a prescribed safe way to do it. I can never remember the correct way because I can’t understand the reasoning behind the prescribed sequence. Is there an easy explanation / (chemical?) principle that can make this procedure (the sequence of both connecting & disconnecting the four posts) more logical and therefore easier to remember?

My confusion is that at some point you must make a connection that causes sparks (which risks battery explosion) because it completes the circuit. Completing the circuit can’t be avoided, so why does it matter which post you are connecting to when you complete the circuit?


texts: Solubility of Lead in water from leaded pipes in Roman aqueducts

texts:
Lead can undergo the following reactions when cold and hard water passes over it:
$$\ce{Pb^2+ + 2Cl- -> PbCl2}$$
$$\ce{Pb^2+ + SO4- -> PbSO4}$$

All these salts are sparingly soluble in water and have a tendency to stick to lead, rendering it passive and not allowing plumbosolvency to occur:
$$\ce{2Pb + 2H2O + O2 -> 2Pb(OH)2}$$

My question is:

How did lead dissolve in the water flowing through the aqueducts if most of it's salts are sparingly soluble?

I have considered erosion of the salt layer formed on the surface but according to Wikipedia, the aqueducts had a very gentle slope

  Vitruvius recommends a low gradient of not less than 1 in 4800 for the channel, presumably to prevent damage to the structure through erosion and water pressure. This value agrees well with the measured gradients of surviving masonry aqueducts. The gradient of the Pont du Gard is only 34 cm per km, descending only 17 m vertically in its entire length of 50 km (31 mi):

Wikipedia also has the following to say regarding lead concentration in the water:

  Where lead pipes were used, a continuous water-flow and the inevitable deposition of water-borne minerals within the pipes somewhat reduced the water's contamination by soluble lead. Nevertheless, the level of lead in this water was 100 times higher than in local spring waters.

Any insights would be much appreciated!


texts: What determines the speed of charging of a battery?

texts:
I was told on physics.stackexchange that this question belongs to Chemistry, what do you think?

Recently we have seen the surge of superfast mobile phone charging. Just an example: http://www.bbc.com/news/technology-30708945

What underlying physical principle determines the speed of charging of a battery?


texts:
I've been asked whether or not the above reaction happens - and if it does, what's the mechanism?
I'm really confused, I think it shouldn't happen; but I'd like to confirm with Chem SE, just to be sure.

If it doesn't happen, then what are the possible methods of accomplishing the conversion?


texts: Reimer–Tiemann-like reaction of catechol with diiodomethane

texts:
I have studied the Reimer–Tiemann reaction of phenol with chloroform in presence of aqueous strong alkali. It takes place with intermediate dichlorocarbene.

I have also studied the Reimer–Tiemann "carboxylation" reaction, which requires carbon tetrachloride, and proceeds with intermediate carbocation.

I am however unfamiliar with what the following question requires from me:

$$\ce{Catechol + CH2I2 + NaOH -> ?}$$

Can anyone please state the step-wise mechanisms through which this reaction occurs? Thanks!


texts: Chromic acid oxidation of aldehydes and primary alcohols

texts:
The answer has to be both A and D. Chromic acid is a strong oxidizer and will take both aldehydes and primary alcohols to carboxylic acids.

However the computer thinks otherwise. Am I just missing something really simple here?


texts: Does electrolysis of water alter the electrodes?

texts:
Today I used a 12 volt power supply to observe electrolysis of water.
I mixed table salt into the water, nothing else.
The leads coming from the power supply had clamps on their ends.
When in water bubbles started evolving on the clamps.
Does this damage the clamps in any way ?
Is there something I should put in the clamps to improve this experiment ?


texts: Is this galvanic cell representation right?

texts:
Question

13. In the galvanic cell:
$$\ce{Pt(s) | I2(g) | I-(aq) || Fe^3+(aq) | Fe^2+(aq) | Pt(s)}$$

Representation of anode is incorrect and cell will not work.
$[\ce{Fe^3+}] = [\ce{Fe^2+}] = [\ce{I-}] = \pu{1 M}$ is sufficient for $E_\mathrm{cell} = E_\mathrm{cell}^\circ.$
$\ce{I-}$ gets oxidized to $\ce{I2}$ and $\ce{Fe^3+}$ gets reduced to $\ce{Fe^2+}.$
None of these.

Given Answer

 3. $\ce{I-}$ gets oxidized to $\ce{I2}$ and $\ce{Fe^3+}$ gets reduced to $\ce{Fe^2+}.$

My Thoughts
The representation of anodic half confuses me. I am unsure whether it is right representation. According to me, it should be $\ce{I-} | \ce{I2}$ (anodic half). It seems to me that answer should be 1.


texts: Why exactly does the slowest reaction limit the instantaneous rate of a reaction even if the faster processes come after? Theoretically, if the products of the slow reaction are required for the fast reaction, the fast reaction limits the rate because even though it is fast, it will not finish in exact synchronization with the end of the slow reaction. There will be a lag between when the net reaction is done and when the slow reaction is done.


texts: Are there any examples of nuclear spin isomers having consequences for chemical reactivity?

texts:
Ortho- and parahydrogen are two forms of the $\ce{H2}$ molecule that are distinguished by their pairing or antipairing of nuclear spins, giving rise to metastable singlet (ortho-) and triplet (para-) states. This constitutes an example of nuclear spin isomerism.

Whilst the thermal properties of these two species are different, my understanding is that their chemical properties are essentially identical. Are there any examples of this kind of isomerism having nontrivial implications for chemical reactivity?


texts:
Consider the following elementary reaction mechanism where both the forward and reverse reaction mechanism are important
  $$\ce{CO + O2<->[1] CO2 + O}$$
  $$\ce{O + H2O<->[2] OH + OH}$$
  $$\ce{CO + OH<->[3] CO2 + H}$$
  $$\ce{H + O2<->[4] OH + O}$$
  How many chemical rate equations are need to determine the chemical evolution of a system defined by this mechanism? Write out the rate equation for the hydroxyl radical.

This question is from the book  Introduction to Combustion: Concepts and Applications by Stephen R. Turns.

My answer to the second part is
$$\frac{d[\ce{OH}]}{dt}=( k_{f_2}[\ce{O}][\ce{H2O}]+k_{r_3}[\ce{CO2}][\ce{H}]+ k_{f_4}[\ce{H}][\ce{O2}] ) - (k_{r_2}[\ce{OH}][\ce{OH}]+k_{f_3}[\ce{CO}][\ce{OH}] +k_{r_4}[\ce{OH}][\ce{O}])$$

Is this correct?

$k_f$ is the elementary forward rate coefficient

$k_r$ is the elementary reverse rate coefficient

[ ] refers to concentration


texts: How would one use the equation ΔG° = −nFE° to estimate the ΔG⁰f of Fe2+(aq)? Since Fe2+ appears in multiple entries in the following table, I'm not sure which value to use.


texts: should charge balance be based on activities?

texts:
We have a fluid with $\pu{0.01 M}~\ce{HCl}$ and $\pu{0.02 M}~\ce{K2HPO4}$, so if we assume activity coefficients are $1$ throughout we can find pH as $6.800012$ and confirm that at that pH there is approximately zero balance ($6.104839\!\times\!10^{-13}$) between positive and negative charges calculated as

$$\mathrm{  K^+ +H^+ – OH^- - Cl^- -}\ce{H2PO4-}\mathrm{ - 2\times} \ce{HPO4^2-} \mathrm{\ -\ 3\ \times}\ce{PO4^3-}$$

Now we can find the ionic strength and via Debye-Hückel/Davies find activity coefficients for absolute charge 1-3. This allows correction of the thermodynamic dissociation coefficients for phosphoric acid (and water dissociation) so we can correct the concentrations and find a new pH to minimize charge balance. After $4$ iterations we have pH 6.436864 at a charge balance of $1.429412\!\times\!10^{-15}$. This procedure allows reproduction of the results in a recent paper (Schell et al J Chem Eng Data 2018; 63: 2151-2161) with correlation $>0.9999$.

Now the question: these results requires the charge balance being formulated strictly in concentrations multi-plied by the relevant charges. I simply wonder why we should not for the charge balance equation multiply the found activity coefficients on the charged species so making the balance to minimize a function of $f_3\times 3\times [\ce{PO4}]$ and so forth with $f_3$ being the trivalent activity coefficient from Davies?


texts: Why are there only 7 periods in the periodic table?

texts: Is seven a hard theoretical limit (there can’t be an eighth period) or is it there just because we haven’t discovered/synthesized anything beyond that?


texts: Using UV-C (254nm) light to cleave the amino acid off of vyvanse

texts:
Vyvanse:

Desired product:

Amide bonds absorb in the region of about 190 to 240 nm, so could using UV-C light conceivably cleave the amide bond?

Also I don't think this reaction is as simple as putting vyvanase powder under a UV-C lamp because the reaction intermediates probably need to be stabilized by a proper solvent or something, correct? What would the intermediates likely be, and what solvent would likely help?

Obviously the easiest way to get the desired product is probably simple hydrolysis, as there are not really any other hydrolyzable function groups on the starting material apart from the amide C-N bond. So this is mainly a theoretical question.


texts:
Since the overlap increases with directional properties of orbital,
$$\ce{p - p > s - s > s - p}$$

However it is also observed that the bond strength of
$$\ce{H-F > H-H > F-F}$$
$$\ce{\{s - p > s - s > p - p\}}$$
Why does this happen? I've done some research and found this which says that it may depend on the p orbital's alignment with inter-nuclear axis.
The reference doesn't seem to apply here, since all the above orbitals are aligned along the inter-nuclear axis.
What am I missing here?

Bond dissociation enthalpies:
$$\begin{array}\\
\ce{H-F} &&& \pu{568 kJ/mol} \\
\ce{H-H} &&& \pu{436 kJ/mol} \\
\ce{F-F} &&& \pu{157 kJ/mol} \\
\end{array}
$$
Source


texts:
I want to do intramolecular aldol condensation of 7-oxooctanal:

I am talking about the major product. Clearly, a 6-membered ring would be a major product, but there are 2 possibilities: taking hydrogen from $\ce{C^2}$ or $\ce{C^6}$. Which one would be preferred?


texts: How to synthesize 4‐[(4,4‐dimethylpentyl)oxy]‐2,2,8,8‐tetramethylnonane starting with 4,4‐dimethylpent‐1‐ene?

texts:
<img src="https://i.stack.imgur.com/FBDDt.jpg" alt="4,4‐dimethylpent‐1‐ene to 4‐[(4,4‐dimethylpentyl)oxy]‐2,2,8,8‐
tetramethylnonane" />

My attempt:

I don’t know how to add another chain. I think I probably need to react with another A molecule, but I don’t know the mechanism. Can anyone help me with this?


texts: What is the most nucleophilic known monoanionic oxygen base? I am thinking hydroperoxide ion or perhaps an alkylperoxy anion. But perhaps there is something I am missing.


texts: Why are imines more susceptible to reduction than carbonyl compounds? Imines react with $\ce{NaCNBH3}$ while the carbonyls don't.


texts:
From my textbook, it is stated that:
e.g. If we add a basic salt $\ce{NaF}$, it will fully dissociate to give $\ce{F-}$. Then if we add $\ce{HF}$, since it is a weak acid, the high concentration of $\ce{F-}$ already present in solution shifts the equilibrium to the left, hence fewer $\ce{H+}$  forms than expected so higher $\mathrm{pH}$.
But can I explain like this: after dissociation of $\ce{NaF}$, the formed $\ce{F-}$ reacts with water to give $\ce{OH-}$ as the following equation:
$$\ce{F- + H2O <=> HF + OH-}$$. Due to the presence of $\ce{OH-}$, upon addition of $\ce{HF}$, the $\mathrm{pH}$ will be higher than expected. Are there any flaws in this explanation?


texts: Which mechanism do ethers follow when cleaved by hydrogen halides?

texts: Ethers can be cleaved under acidic conditions by treatment with hydrogen halides (HX, where X = Cl/Br/I). Some of these reactions proceed by SN1 mechanisms and some by SN2 mechanisms. How can I tell which mechanism is being followed?


texts: The solubility of different compounds relative to each other in water

texts:
Which of the following has the least solubility?

  $\ce{NH4HCO3, NaCl, NH4Cl, NaHCO3}$

The answer is given as $\ce{NaHCO3}$, but I don’t understand why.

Solubility is a chemical property referring to the ability for a given substance, the solute, to dissolve in a solvent. It is measured in terms of the maximum amount of solute dissolved in a solvent at equilibrium.

Here's what I was told:

Solubility decreases with increase in polarisibility
It increases with increase in covalent nature.
It increases with increase in hydration enthalpy and lattice enthalpy.

Which leads me to two other questions:

How do these factors really effect solubility, especially, covalent nature?
I guess polarisibility can be linked with hydration or solvolysis, so I understand it.
How can I find the order of solubility of different compounds relative to each other in water?


texts: NMR: How the relaxation times T1 and T2 depend on the correlation time / amount of molecular tumbling.

texts:
Why do nuclei that have a smaller / faster correlation time have a higher / slower T1 / T2?

From my understanding:

Fast Brownian motion creates a wide range of B.local (local magnetic field created by dipole of spin X near spin Y) fluctuation frequencies
Slow motion gives rise to fewer frequencies but more intense fluctuations
Fluctuations at the right frequency cause transitions between energy levels / relaxation / re-establishment of equilibrium
The larger a molecule the slower it tumbles (correlation time is slower)
The slower the tumbling the faster the relaxation

To me, logically, it'd make sense that if a molecule tumbles faster then the relaxation should be faster, not the other way round. Can anyone explain this?

Thanks


texts: Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics

texts:
I want to derive an expression for the internal energy of mixing, $\Delta_\mathrm{mix}U$, and entropy of mixing, $\Delta_\mathrm{mix}S$. The framework for this is the Lattice Theory of Ideal Solutions. Specifically, I am mixing $N_A$ molecules of type A with $N_B$ molecules of type B together. I am supposed to find the following two relations:

$$
\Delta_\mathrm{mix} U = 0 \\
\Delta_\mathrm{mix} S = -kM (x_A \ln x_A + x_B\ln x_B)
$$

My attempted solution

I have the canonical partition function for an ideal solution of two different components:

$$
Q = \left( q_A e^{-cw_{AA}/2kT} \right)^{N_A} \left( q_B e^{-cw_{BB}/2kT} \right)^{N_B} \frac{(M)!}{N_A!N_B!}
$$

Taking the logarithm

$$
\ln Q = N_A\ln q_A - N_A\frac{cw_{AA}}{2kT} + N_B\ln q_B - N_B\frac{cw_{BB}}{2kT} + M \ln M - N_A\ln N_A - N_B \ln N_B
$$

where $w_{xx}$ is the pairwise interaction energy, $M=N_A+N_B$ is the total number of molecules = number of lattice sites.

Further, some thermodynamical relations for this system

$$
U = kT^2\left( \frac{\partial \ln Q}{\partial T} \right)_{N,M}
$$

$$
S = \frac{U}{T} + k\ln Q
$$

The internal energy of mixing and entropy of mixing should be

$$
\Delta_\mathrm{mix}U = \Delta U_A + \Delta U_B \\
\Delta_\mathrm{mix}S = \Delta S_A + \Delta S_B
$$

Generally we have that

$$
\Delta U = U_\mathrm{final} - U_\mathrm{initial} \\
\Delta S = S_\mathrm{final} - S_\mathrm{initial}
$$

I am a bit confused about how to compare the final and initial conditions of the system. I assume that we have initially two separated and equal volumes, one containing $N_A$ of A and one containing $N_B$ of B. Then we allow flow between the two volumes. Hence, the final volume is twice the initial volume. $N_A$ and $N_B$ are constant during the mixing. So I should have something like this

$$
\Delta U_A = U_{final} - U_{initial} = kT^2\left( \frac{\partial \ln Q}{\partial T} \right)_{N_A,M} - kT^2\left( \frac{\partial \ln Q}{\partial T} \right)_{N_A,M/2}
$$

and similarly for the other component. I just replace $M$ with $M/2$ for the expression of the initial state for both components? Most of the terms will be zero when doing the derivations, and the non-zero terms will actually just cancel. This gives that $\Delta_\mathrm{mix} U = 0$, which is the expected result for an ideal solution.

Looking at $\Delta_\mathrm{mix} S$ we have

$$
\Delta_\mathrm{mix} S = \Delta S_A + \Delta S_B = [S_{f,A} - S_{i,A}] + [S_{f,B} - S_{i,B}] \\
= \left[ \left(\frac{U_{f,A}}{T} + k\ln Q_f \right)- \left( \frac{U_{i,A}}{T} + k\ln Q_i \right) \right] + \left[ \left( \frac{U_{f,B}}{T} + k\ln Q_f \right) - \left( \frac{U_{i,B}}{T} + k\ln Q_i \right) \right] \\
=\frac{1}{T} (U_{f,A} - U_{i,A} + U_{f,B} - U_{i,B}) + 2k(\ln Q_f - \ln Q_i) \\
= \frac{\Delta_\mathrm{mix}U}{T} + 2k(\ln Q_f - \ln Q_i) \\
= 2k(\ln Q_f - \ln Q_i)
$$

where I used in the last step that $\Delta_\mathrm{mix} U=0$ for an ideal solution, as explained above. However, using this last expression to calculate the entropy of mixing, I find that (most of the terms cancel directly)

$$
\Delta_\mathrm{mix}S = kM \ln (2N_A + 2N_B)
$$

which is quite different from the correct expression. Is there something wrong with my procedure? (there likely is!)

Following the commented suggestion:

$$
S = k\ln W \Rightarrow \Delta_\mathrm{mix}S = k\ln \frac{W_\mathrm{mix}}{W_AW_B} = k\ln W_\mathrm{mix} = k\ln \frac{M!}{N_A!N_B!} \\
= kM [\ln M - x_A\ln N_A - x_B \ln N_B]
$$

which is almost correct. If I could divide all logarithmic arguments by $M$, I would get the correct answer.


texts: Is reduction potential equivalent to the ease of discharge?

texts:
Loosely speaking, is the reduction potential equivalent to the ease of discharge in the context of electrolysis?

i.e. is it easier to discharge an ion with a higher reduction potential as opposed to one with a lower one?


texts: Is a polycarbonate beer mug appropriate for serving alcohol?

texts: Are polycarbonate & acrylic beer mug, whiskey glasses safe for serving alcohol? I mean does it leach or dissolve? What are the harmful effects in long run if any?


texts: Carbonic acid-hydrogencarbonate buffer system pH calculation?

texts:
I am learning about the pH of buffer solutions, and am slightly confused by my text book's calculation. For the blood's buffer system of carbonic acid and hydrogencarbonate ions as the conjugate case, the equilibrium is $$\ce{H_2CO_3 <=> H^+ + HCO_3^-}$$

The acid dissociation constant is $4.3 \times 10^{-7}~ \mathrm{mol/dm^{3}}$ and the $pH$ of healthy blood is 7.4.

So $$\ce{\frac{[H_2CO_3]}{[HCO_3^{-}]}=\frac{[H^+]}{K_{a}}}=\frac{1}{10.8}$$

I understand this calculation, however my textbook then concludes that this shows that there are about 20 times more hydrogen carbonate ions than carbonic acid. Should it not be 10 times? Why was this value doubled?


texts: Precipitation of CaCl2 and FeCl3 in Na2CO3

texts: Why does $\ce{CaCl2}$ gives precipitation of $\ce{CaCO3}$ when $\ce{Na2CO3}$ is added, but $\ce{FeCl3}$ does not give the precipitation of $\ce{Fe2(CO3)3}$ in $\ce{Na_2CO_3}$  ?


texts: Why do cotton clothes take a longer time to dry as compared to synthetic clothes?

texts: This may be in relation to the $\ce{-O-H}$ group present in cellulose, but I would like to have a more specific answer.


texts: Cahn–Ingold–Prelog Rules, cyclic structures, and breaking ties

texts:
(3S,5R)-3-ethyl-5-methylcyclohex-1-ene

Does anyone know how one reaches the conclusion that the 5C is R? I tried using the Cahn–Ingold–Prelog priority rules but kept getting confused.

From chem.libretexts.org:

  When looking for the first point of difference on similar substituent chains, one may encounter branching. If there is branching, choose the branch that is higher in priority. If the two substituents have similar branches, rank the elements within the branches until a point of difference.

From Wikipedia:

  To handle a molecule containing one or more cycles, one must first expand it into a tree (called a hierarchical digraph) by traversing bonds in all possible paths starting at the stereocenter. When the traversal encounters an atom through which the current path has already passed, a ghost atom is generated in order to keep the tree finite. A single atom of the original molecule may appear in many places (some as ghosts, some not) in the tree.


texts: Which of the following compounds do not undego electrophilic aromatic substitution?

texts:
Which of the following does not undergo electrophilic aromatic substitution?

Answer is option (D). But I am not able to understand why. All of them have lone pairs. I can notice only two differences. Functional group in Option (d) has the largest size and lowest electronegativity.

I think that may be because of a large difference in size of Selenium and Carbon, pie bond formation in between them will be a bit difficult, but that bond is not playing any role here except stabilizing the compound.

Low electronegativity seems like a good thing to me as it does not deactivates the compound.
So what am I missing here?


texts: Can the inner amine groups of Bacteriopheophorbide A become positively charged in aqueous solutions without the use of very strong acids?

texts:
In an attempt to calculate the pKa of the carboxylic acid group of Bacteriopheophorbide A (BPheo, Pubchem), I generated the structure in MarvinSketch (ChemAxon product) and I came across an interesting result. According to the software, the inner amine groups which are part of the resonance structure can become positively charged at relatively high pH. The photo below shows the calculated pKa of the groups in blue (groups of interest are highlighted in yellow). According to this software, this means that at pH 5.5 the groups will both be positively charged, whereas I was under the impression that these groups can only be altered using very strong acids such as TFA due to the aromatic ring.

Is this realistic? Or is this simply an issue with the software. I've tried looking into this myself but the literature on BPheo seems rather sparse.
Thank you in advance for your input.


texts: Feasibility of application of Boyle's law in the case of varying number of moles

texts:
While reading up on ideal gases and the Boyle's law, I encountered a question in my textbook wherein a balloon was being filled with helium (assumed to be ideal) till it was just about to burst. The pressure and volume coordinates at some intermittent time of the process, and the limiting pressure at the bursting point were provided, and the volume at that point was asked. The book solved it by applying Boyle's law at the two $\ce{P,V}$ coordinates. Also, it was given that this entire activity is being carried out at room temperature.
So, if the amount of gas in the system is constantly changing, then can we apply Boyle's law in this case? If not, then can somebody provide a solution?


texts:
In Iron man 2, the protagonist Tony Stark was anxious about his blood toxicity due to palladium core that was keeping him alive was slowly poisoning his blood. It is written here that:

  The palladium core in the arc reactor that keeps Stark alive and
  powers the armor is slowly poisoning him, and he cannot find a
  substitute.

  The palladium core

  Palladium poisoning Tony Stark

But in the wikipedia article of Palladium, it is clearly written that:

  Palladium is a metal with low toxicity. It is poorly absorbed by human
  body when digested.[...] High doses of palladium could be poisonous;
  tests on rodents suggest it may be carcinogenic, though no clear
  evidence indicates the element harms humans.

So, Palladium has no clear evidence that it is harmful to humans, why it was chosen for the film?

To quote user paracresol's question from a very, very related question:

  Is there anything realistic[...], or is it just another movie gaffe?


texts: Reverse washing soda buildup on stainless steel

texts:
In a home brewing project, I use washing soda (Na2CO3) to remove labels and glue from previously used bottles. In doing this, my flip-top bottles (which have a stainless steel flip top arm) often get unruly buildup of residual soda, which tarnishes and blemishes the steel. Is there a chemical mixture I can use to reverse this process and return the steel to a near-new appearance?

Here are a couple of photos of the bottles and buildup: the left shows a typical amount of residue; the right shows my attempt to wipe it clean with white vinegar (which partially works, but is still blemished).


texts: Relationship between Lewis Theory and Redox theory?

texts:
First of all, thank you ahead of time for taking the time to read my question and answer!

Let us take the reaction $\ce{SnI4 + I^{-} -> SnI2 + I3^{-}}$ as an example.

Here we see one obvious redox reaction, $\ce{Sn(IV)}$ gets reduced to $\ce{Sn(II)}$.
Less obviously, the iodide gets oxidized to $\ce{I(I)}$ in the triiodide anion. The other 4 iodines maintain their negative 1 oxidation state.

Is there also a lewis theory acid/base reaction here as well?
The tin acts as a lewis acid and accepts an electron from each of the two of the iodines (lewis bases)? Those iodines, now electron deficient (act as lewis acids), bond with the iodide (acting as a lewis base) to create $\ce{I3^{-}}$ product.

In this case, Tin accepts one electron from two atoms rather than a "pair of electrons" from one atom like you see in traditional examples of lewis acids.
So that would be my first question, can Tin act as a "lewis acid" even though it is accepting one electron from two different sources rather than a pair from one source? Or in other words, can the iodines be considered "lewis bases" even though they only donate one electron?

Or is the whole paragraph above a moot point because there is no acid/base reaction here because the Tin is simply regaining "ownership" of the electrons it let iodine "borrow" to create a covalent bond and thus its not actually getting any "new" electrons.

My second question is: Can we make a general statement about the relationship between lewis acids and their roles in a redox reaction? For example, can I say that ALL lewis acids are oxidants and ALL lewis bases are reductants? Or are these concepts mutually exclusive? In other words, sometimes lewis acids can act oxidants, sometimes as reductants, and sometimes as neither, like in the example below?:

$\ce{Al(III)Cl3 + Cl- -> Al(III)Cl4-}$ (no redox here)


texts: What can possibly turn litmus paper white if there is even no chlorine present?

texts:
I did a hydrocarbon test on cyclohexane with bromine solution. The mixture was put inside a dark place. To be exact, a cupboard filled with laboratory equipments. I also put a piece of wet blue litmus paper on top of the tube.
It should've stays blue because there was no reaction occured, right? But the litmus paper turned white. What can possibly cause it?


texts: Can aldol reaction occur during α-halogenation of ketone?

texts:
I know both aldol and $\alpha$-halogenation reaction well.

I know that in and aldol reaction, the carbonyl containing molecules like ketones and aldehydes attacks themselves when base like $\ce{OH-}$ attacks $\alpha$-proton.

The same thing also happens in $\alpha$-halogenation of these carbonyl containing molecules.

So my question is that in presence of halogen, before the double bond of the enol can attack halogen atom of $\ce{Br2}$, $\ce{Cl2}$, $\ce{I2}$ in $\alpha$-halogenation, can aldol reaction reaction occur by double bond of the enol attacking another carbonyl containing molecules?


texts: What factors contribute most to solubility of ionic substances in highly polar solvents, esp. ionic liquids and DES?

texts:
I am trying to determine a method to dissolve a mineral salt with a lattice energy of ≈18000 kJ/mol. I know that lattice energy is the most significant factor affecting solubility of an ionic substance in highly polar solvents, and my general understanding is that the more polar (or locally polar), the greater the ability of the solvent to dissolve materials with higher lattice energies, by contributing more hydrogen bonding and/or more efficient charge distribution.

Hence I have been testing solubility in an array of Deep Eutectic Solvents (DES) and doing research into solubility of this and similar compounds in other ionic liquids, and reached out to an expert in the field.

I have found that while these solvents are typically able to dissolve compounds with lattice energies unto around 12000 kJ/mol. in great quantity, solubility quickly drops off around 15000 kJ/mol. and the professor I contacted said that their research indicated that without other agents, this material would be insoluble in the ionic liquids they worked with because of it's high lattice energy.

My question then is what other factors would be most important in increasing the solubility of this compound in ionic liquids, anything from adding highly soluble cations, chelating agents, type of ionic liquid I might use, or any other other factors that play into solubility, and could be tuned to optimal conditions?


texts: Can we force a reversible reaction in equilibrium to achieve 100% completion?

texts:
Can we force a reversible reaction in equilibrium to become a "complete" one? If so, will the equilibrium constant change?

It's said about reversible reactions that they never go to completion & I know that's because in reversible reactions, the mixture obtained in equilibrium is more stable than the extremes (i.e. either reactant or product) But if we force the reaction to proceed in a certain direction, say in the direction of products, will it ever go to 100% completion or near 100%?

My second question is regarding the equilibrium constant. I have read about equilibrium constant that its value doesn't change if we alter the initial concentration of reactants, which I understand why, but consider this situation:
 if we force equilibrium to proceed in the direction of products by altering $p,T,V$ (only and not adding or removing any substance), the equilibrium will get disturbed and obtain a new equilibrium. Wouldn't the equilibrium constant for this new equilibrium be different from the earlier one?


texts: Does freezing tights make them more durable?

texts:
Various blog posts and articles suggest that freezing a pair of tights will make them last longer.

From a blog named Eclipsed Moon:

  Put your tights in the freezer.

  I thought that this was a silly old-wives tale, but it actually does
  work! Putting your tights in a plastic bag and storing them in the
  freezer when you aren’t using them helps keep the material firm and
  less prone to ripping.

From an article on PureWow:

  Good thing there’s a super-easy trick for extending the life of your
  tights.

  You freeze them.

  Yes, it sounds crazy, but hear us out: The next time you buy a new
  pair (and before you wear them), run them under water until they’re
  damp. Then place them in a plastic bag and freeze overnight. Take them
  out and give them a day to defrost and thaw out.

  You only need to do this once — after that, you’re good to go. The
  chilly temps firm and strengthen the individual fibers of your tights,
  making them less susceptible to runs later on.

I'm skeptical.  My questions are:

Where is the evidence?  Are there any controlled studies confirming this phenomenon?
Does the water make any difference?
Is this advice for storage, one-time treatment, or both?
If it is indeed effective as a one-time treatment, why don't they come pre-treated from the factory?
If it works, why does it work?


texts: What is the difference between polyatomic ions and compounds?

texts: I don't understand why things like hydrogen phosphate are polyatomic ions but things like potassium nitrate are compounds. Can someone explain to me what the difference is, besides that ions are charged?


texts:
An entrance JEE Main & Advanced AIEEE 2003 exam question:

Which one of the following nitrates will leave behind a metal on strong heating?
A. Copper nitrate
B. Manganese nitrate
C. Silver nitrate
D. Ferric nitrate

I looked up the answer and it was given to be silver nitrate, and I took it up as something to be remembered. However, when I checked online for the decomposition of other options such as ferric nitrate I found many research papers discussing the same which is not something one asks students who have just studied chemistry up to 12th grade.
Also, is there a way to decide which one will, because if it says strong heating, shouldn't most metals leave their salts and exist as free metals if we go on increasing temperature?


texts: Why are the sulfide ores generally converted to an oxide and then reduced?

texts:
In the elementary extraction of metals from their concentrated ores, why is the ore generally converted to an oxide, and then reduced? Why is the reduction of these metal oxides easier than the other corresponding compounds, say sulphides or carbonates.

Here are some of the elementary metals that are converted to their oxide before being reduced:

Zinc blende (sphalerite) is roasted from $\ce{ZnS}$ to $\ce{ZnO}$
Galena $\ce{(PbS)}$ is converted to $\ce{PbO}$ (Wikipedia)

Some other ores originally in their oxides remain as they were, like bauxite $\ce{(Al2O3.2H2O)}$ and hematite $\ce{(Fe2O3)}$.

An exception happens to be copper pyrite which is roasted to form copper sulphide instead of copper oxide (Wikipedia).

So, for the metals $\ce{Al, Zn, Fe}$ and $\ce{Pb}$, why is extracting the metal from the oxide favorable? And why is copper an exception?

In my book, NCERT (12) India, it is given that:

  The concentrated ore must be converted into a form which is suitable
  for reduction. Usually the sulphide ore is converted to oxide before
  reduction. Oxides are easier to reduce. Thus
  isolation of metals from concentrated ore involves two major steps viz.,
  (a) conversion to oxide, and (b) reduction of the oxide to metal.


texts: Reason for triphenyl methane being less acidic than acetylene

texts:
This question came through answering a question that talked about the acidic order of four compounds.
Upon researching the actual $\mathrm p K_\mathrm a$ values I noticed that even though there was a resonance destabilization of electrons (albeit partial) in triphenyl methane, the $\mathrm p K_\mathrm a$ values of acetylene were less than that of triphenyl methane? I was unable to find a solid reason for why this is the case.
Does anyone in the community have the reason?


texts: We all know know that Aluminium react with cupric producing Copper and Aluminium (III), but does Aluminium (III) react with Copper?


texts: Heat and water absorption by calcium chloride

texts: Can calcium chloride be effectively used as a desiccant to absorb both heat and moisture?


texts: If the longest carbon chain is symmetric numbering-wise (meaning the numbering schemes are identical both ways) and has all alkyl substituents, should one prioritize the largest alkyl group?


texts: How do I find the rate constant in this situation?

texts:
Say I have two kinds of molecules $A$ and $B$.

The molecules of type $B$ are small and bind onto molecules of type $A$.

(Any number of them may do so, but in practice this number is $\leq 8$.)

We say a molecule of type $A$ is of type $A'$ if it has at least one copy of $B$ bound to it.

More specifically, we say a molecule of type $A$ is of type $A^k$ if it has exactly $k$ copies of $B$ bound to it.

We can easily detect experimentally when a molecule is of type $A'$, but not so easily when a molecule is specifically type $A^3$, for example.

However, it was done at one point, and the researchers gave us a way (given a concentration of $A'$) to determine the individual concentrations of $A^k$'s. (Poisson distribution)

I would like to consider the dissociation reaction $$A^k \rightarrow A^{k-1} + B$$ where $k \geq 1$ and $A^0$ is considered to be $A$.

Because the molecules of $B$ are small, I can assume that the rate of this reaction is independent of $k$ and that the molecules of $B$ dissociate independently of any other molecules of $B$ attached to the same copy of $A$.

My question is: how can I find a constant $c$ so that the rate of the reaction is $r = c[A']$?


texts: How to determine the structure of organic molecules without spectroscopy

texts:
I wonder how chemists worked out the structures of organic molecules before spectroscopy (especially NMR) was invented?

Surely, we could do functional group tests, but the correct connection of atoms and function groups would be hard to tell when the number of carbon atoms get larger. E.g. How could they tell one compound was 2-hexanol rather than 3-hexanol? How could Emil Fischer and others worked out the correct structures of carbohydrates with so many chiral centers? And god forbids, how could the chemists worked out the correct structures of natural products with fused rings (eg the cholesterol family)? It's not a trivial task even with 2D NMR!


texts: Is there an intramolecular hydrogen bond in guaiacol?

texts: Is there a hydrogen bond between the $\ce{H}$ atom of $\ce{-OH}$ group and the $\ce{O}$ atom of the $\ce{-OCH3}$ group in ortho-methoxyphenol? I was told no. But I want to know why.


texts: When are the terms diphosphate and pyrophosphate used?

texts:
On the Wikipedia article about pyrophosphate, it states that:

  The group (pyrophosphate) is also called diphosphate or dipolyphosphate.

But for example, why is ADP apparently called adenosine diphosphate but not adenosine pyrophosphate? The same for geranyl pyrophosphate (GPP) instead of geranyl diphosphate?  In which context the terms diphosphate and pyrophosphate are used?


texts: Why does decreasing the distance between the electrodes in an electrolytic cell increase the rate of electroplating?

texts:
I did an experiment on the effect of the distance between the electrodes on the rate of electroplating in an electrolytic cell (copper electrodes with copper sulfate electrolyte).

As I expected, when the electrodes were closer, the current was greater and the rate of copper plating was also faster. But why does less distance increase the current? My initial thought was that less distance to travel=ions arriving at cathode quicker=greater current. That doesn't seem right though, because different ions are depositing and liberating electrons and hence not really flowing through (right?). I'm probably overthinking this, but any help is appreciated.


texts: How does steam prevent oxidation in tea leaves?

texts: I recently started branching out into different "flavors" of tea. In this endeavor I've been learning more and more about different varieties of tea and was wondering if anyone could offer an explanation as to how steam can prevent the process of oxidation in tea leaves.


texts: How does one separate ethanol from acetic acid using aqueous extraction?

texts:
Would you add in $\ce{NaOH}$, deprotonating the acid, and then wash the mixture in water, thereby removing the $\ce{Na^+}$ and $\ce{CH3O^-}$ ions in an aqueous layer? But then wouldn't the ethanol be dissolved in the water as well, as it is polar? In general, how do you separate two polar substances from each other using extraction?

If you don't use extraction, how else would you separate the two, aside from distillation?

All answers are appreciated.


texts: What exactly is a reducing equivalent and what does it do?

texts:
I've encountered this term in the context of cellular metabolism, but I can't seem to find an explanation of what a reducing equivalent is or why it is named this way. Wikipedia was not really helpful, and most other online sources seem to use the same phrasing (which I am struggling to parse).

Is a reducing equivalent something that is itself reduced, or is it something that causes reduction (thereby being itself oxidized in the process)? The Wikipedia article uses the expression "which transfer the equivalent of one electron" which has left me all the more confused.

I would be most grateful for an explanation or links to material I could read to clarify this for myself.


texts:
$3g$ of activated charcial was added to $50 ml$ of acetic acid solution ($0.06N$) and filtred after an hour and it was found to be $0.042 N$ .The amount of acetic acid adsorbed (per gram of charcoal) is

The solution for this question is exactly given as I have written below

No of equivalents before adsorption $=50\times0.06 =3$

No of equivalents after adsorption $=50 \times 0.042=2.1$

No of equivalents left $=0.9/1000 \times 60=54mg$
Acetic acid per gm $= 54mg/3=18mg$

Now I have some doubts regarding the question and it's answer

  Why is normality being decreased here?
  Why are they taking volume to be same when it generally increases when we add solutes?
  What does equivalent mean here? According to Wikipedia, it is said to be "the mass of one equivalent, that is the mass of a given substance which will 1)  combine or displace directly or indirectly with 1.008 parts by mass of hydrogen or 8 parts by mass of oxygen or 35.5 parts by mass of chlorine – these values correspond to the atomic weight divided by the usual valence; or  2) supply or react with one mole of hydrogen cations (H+) in an acid–base reaction or 3) supply or react with one mole of electrons (e−) in a redox reaction." The equivalent talked in the question doesn't meet any of this criteria so what is its role here. Can somebody please explain me this?


texts: Reconcile the Beer Lambert Law with rate of absorption

texts:
The Beer-Lambert law gives the proportion of incident light intensity that will be absorbed. Intensity isn't strictly a rate but if the light is monochromatic and the path length is constant it sort of is.
$$I=I_0\exp(-\epsilon c l)$$

But the rate of absroption of photons is given by:
$$K=B\rho$$
Where B is the Einstein coefficient and $\rho$ is the spectral energy density which is proportional to the intensity of incident radiation.

Surely the second equation should mean that the intensity decays linearly? Would the absorbed intensity double if the concentration was doubled?


texts: Are there Exchange integrals in Semiempirical methods?

texts:
One of the major features of semiempirical methods is that they significantly reduce the cost of evaluating 2-electron integrals.

In general, they follow the formula for HF, but, introduce many simplifying assumptions. In HF for same spin electrons you need to calculate both coulomb and exchange integrals.

When applying the simplification in, for instance, CNDO and INDO, that $(\mu \nu | \lambda \sigma ) = \delta_{\mu \nu} \delta_{\lambda \sigma}(\mu \mu | \lambda \lambda )$, this seems to de facto rule out calculating an exchange integral.

Is there a scenario where the exchange integral is computed in semiempirical methods (for simplicity, in the case of CNDO/INDO methods)?

Textbooks do not discuss the exchange integral when going over semiempirical, so the answer must be obvious... I just don't know if it is obvious that they cannot be performed, or if they can, and I am missing something.


texts: What anions does the loss of a proton from HOCN and HNCO produce? Are they same or different?

texts:
What anions does the loss of a proton from $\ce{HOCN}$ and $\ce{HNCO}$ produce? Are they same or different?

Once, I had asked my teacher if $\ce{HCN}$ and $\ce{ HNC }$ are different or same compunds, he said they were different and yes, they had different structures. Applying the same logic here, $\ce{OCN-}$ and $\ce{NCO-}$ are different anions because they'll have different structures.


texts: What is the balanced equation for H2O2 + KI + dish soap

texts: I am not sure how to balance $\ce{H_2O_2 + KI + dish soap}$.   Is the dish soap involved in the equation or just to show the produced gas?  Is it a double replacement or does the $\ce{KI}$ just act as a catalyst and $\ce{H_2O_2}$ is deconstructed to $\ce{2H_2O + O_2}$? It has been a while since I had chemistry.


texts:
I tried to do this using the stability of conjugate base. I can see (2) will be most stable due to resonance however my confusion lies in (1) and (3).
While in (3), the negative charge is unstable but in (1) I can't tell if it will take part in resonance because in pyridine the lone pair doesn't take part in resonance so is the same thing happening here?


texts: Reaction of 2,4-DNPH with aromatic aldehydes

texts: Does 2,4-dinitrophenylhydrazine react with aromatic aldehydes, e.g. benzaldehyde (phenylmethanal), in a condensation reaction similar to 2,4-DNPH's reaction with aldehydes and ketones ?


texts:
My question concerns how energy is used in chemical reactions. I am working with a reaction between magnesium and hydrochloric acid in a class (although this is not a homework question). What I've found is that the magnesium gives away its valence electrons to either the hydrogen or to the chloride. But in the second case, the chloride ions would first give their valence electrons to the hydrogen, and then they would accept the electrons from a magnesium atom. As I was thinking about which of the cases was more probable, I started thinking about the energy involved. For example, I would think that moving the electrons first from the chloride ions to the hydrogen, and then from the magnesium to the chloride, would use much more energy than the magnesium just giving its electrons to the hydrogen ions.

My question is, as a general rule of thumb, although I wouldn't mind a detailed answer, are reactions that, like this one (as far as I know), have multiple "ways" of reacting going to take the way that uses the minimal amount of energy?  Or are the electrons free to move to whichever atom is closest?


texts: Anhydrous calcium sulfate as a drying agent

texts:
I know that anhydrous $\ce{CaSO4}$ is used as drying agent.

I also know that anhydrous $\ce{CaSO4}$ (dead burnt plaster) is prepared by heating gypsum $\ce{CaSO4.2H2O}$ at a temperature above $\pu{393K}$, which is an irreversible process.

How does $\ce{CaSO4}$ perform the drying if it can't accept any $\ce{H2O}$ molecules? Is there some other mechanism here? Or do I have some wrong information fed in my brain?


texts:
I read a paper recently - Here. I found the concept of Electride materials very interesting and wanted to mess around with them myself. I tried to replicate the partial electron density plots shown in the paper (Bottom right of picture):

I followed their methods as exactly as I could on Ca2N (It seems to be better researched than Na2Cl as I've seen it in many other papers on the topic, but I didn't want to put their data out that's not public), but I'm not sure how they created that graph/visualization. I did a geometry opt, then SC, found the band structure which matched theirs almost exactly, then did a band-decomposed run (I tried around the fermi level they said the electron resided in, I tried individual bands, etc) and VESTA doesn't pull up anything near what they have when I graph the PARCHG's.

Is there another step to visualize it the same way they have that I am missing, or is it likely to be something else I'm doing wrong?


texts: Air recycling system(CO₂-->O₂) or (CO₂-->fuel)?

texts:
I'm not a chemist but I'm working on an eco-friendly project that is supposed to recycle $\ce{CO2}$ from the air and convert it to $\ce{O2}$ or at least a usable fuel source ,the system can use the solar system as an energy source (I know that such system isn't efficient) but for the country in which the project is applicable it would be a great economical benefit (over direct sun power).

-What is the most appropriate chemical reaction to achieve such goal ?

the reaction of course shouldn't emit toxic material(the whole purpose of the project is to benefit the environment, plus the cost of any filter or disposal mechanism isn't affordable)

is there any way to construct a circular system (Regenerative carbon dioxide removal system )
Wikipedia's article doesn't elaborate further.

Please help tag this question(this is my first time on chemistry.stachexchange)


texts: Is varnish with a flash point above 40 celsius safe in a microwave oven?

texts:
I've painted regular white mugs and want to varnish them too.
But my varnish has the following specs:

Gloss varnish based on alkyd resin.

Flash point: Above 40 degrees celsius.

Is it safe to varnish on some sections of the painting on the outside of a mug? Or will it catch fire if microwaved to boil water or something?

I have no background in chemistry... took me a while searching around before I finally decided to just ask.


texts:
I have a major confusion over the relationship between free energy change and the equilibrium constant.
I have read that $\Delta G_0= -RT\ln K$.

My first doubt is, does $\Delta G_0$ refer to free energy change ONLY at 25C?
Does $\Delta G_0$ make sense for any other temperature?

Secondly, the "T" in the equation
Does it also have to be the same temperature as the temperature for which we write $\Delta G_0$? (ie,25C)
If not so, can we write any temperature and obtain the corresponding K value?

Please explain.

If G0 can be defined for other temperatures, does that mean that S0 and H0 can also be defined for other temperatures?


texts: Effective attenuation coefficient for polychromatic light

texts:
The Beer-Lambert law gives the optical intensity of collimated light as a function of depth $z$ as:

$$I(z)=I_{0}\mathrm e^{-\gamma z},$$

where $\gamma = \alpha + \beta$ is the wavelength-dependent attenuation coefficient, with $\alpha$ and $\beta$ being the absorption and scattering coefficients respectively.

Suppose two completely different wavelengths $\lambda_1$ and $\lambda_2$ are present in the light beam. Is it possible to define the "effective attenuation coefficient" of the material $\overline{\gamma}$ for two or more wavelengths as an addition of the different attenuation coefficients?

That is,

$$\overline{\gamma}=p_{\lambda_1}\gamma_{\lambda_1}+p_{\lambda_2}\gamma_{\lambda_2},$$

where $p$ is the fraction of the beam which is of a given wavelength (indicated by the subscript). The mathematics seems to work out, but I have never seen this used in literature before. Any explanation is greatly appreciated.


texts:
As far as I know, to know whether a substance is paramagnetic or diamagnetic, we check if that particular species has got unpaired electron or not.

But my textbook lists-

Examples of Diamagnetic Materials - Copper,Lead,Sillicon,etc

Examples of Paramagnetic Materials - Aluminium,Sodium,Calcium etc

The valence shell configuration of Copper is 3d10 4s1 . So, shouldn't it be Paramagnetic?

The valence shell configuration of Calcium is 4s2 . So, shouldn't it be Diamagnetic?


texts:
In order to determine the relative contributions of resonance structures, my textbook gives the following rules (in order):

The more covalent bonds a structure has, the higher it scores.
Structures in which all of the atoms have a complete valence shell of electrons (i.e., the noble gas structure) are especially relevant and make large contributions to the hybrid.
Charge separation decreases the score.
Resonance contributors with negative charge on highly electronegative atoms score higher than ones with negative charge on less or non electronegative atoms. Conversely, resonance contributors with positive charge on highly electronegative atoms score lower than ones with positive charge on non electronegative atoms.

How to determine the relative contribution of resonance structures when different rules give contradictory outcomes?

For example, let's consider the following resonance structures:

$$\ce{\overset{+}{C}H2-\underset{1}{O}-CH3}\longleftrightarrow \ce{CH2=\underset{2}{\overset{+}{O}}-CH3}$$

The following are my conclusions with respect to the above rules:

Structure 2 scores higher than structure 1 as it has more number of covalent bonds.
Structure 2 scores higher than structure 1 as all atoms have noble gas electronic configuration. In structure 1, the leftmost carbon atom has only six valence electrons.
There is no charge separation in either of the two structures and so this rule cannot be used to determine the relative contribution.
Structure 1 scores higher than structure 2 because in the first structure a carbon atom bears a positive charge whereas in the second an oxygen atom carries a positive charge. Since oxygen is more electronegative than carbon or carbon is more electropositive than oxygen, structure 1 scores higher.

Based on conclusions 1 and 2, we could say that structure 2 contributes more. But conclusion 4 contradicts the result given by points 1 and 2. So, how could we determine the relative contributions when the outcomes of the rules contradict each other?

Are some rules (out of the given 4) superior over the other? Or do we determine the overall score by the number of votes on either sides (similar to our community's voting system based on upvotes and downvotes :) ) i.e., structure 2 scores higher since it has two votes (points 1 and 2) supporting it and 1 vote (point 4) against it? If this is the case, what if there are equal number of votes? For example what if points 1 and 2 suggest a structure A scores higher than B whereas points 3 and 4 suggest structure B scores higher than A?

Kindly do not limit your answers to the above two resonating structures. I considered it just to explain the question.

I read the question - How to determine the least stable resonance structures out of a given set? and the answers to it. In fact, that question is based on a problem from the same book I follow. But still, I don't understand how to determine the relative contributions when some rules give contradictory outcomes.

Note: I understood resonance structures are hypothetical, i.e., they don't have an existence in the real world. The molecule is best represented by the hybrid of all the structures. As commented in my previous questions on resonance, I've already read the question/answer - What is resonance, and are resonance structures real? and I feel I don't have any misconceptions on the subject.


texts: Why is solubility often listed as a chemical property? Isn't the action of dissolving just a physical change?

texts:
I am making a list of basic physical vs chemical properties.
I have been taught that when salt dissolves in water it is simply a special kind of mixture called a solution.
I have been taught that mixtures do not create a chemical change or reaction.
But I found a lot of high quality chemistry websites that list solubility as a chemical property of compounds.

Why isn't solubility a physical property if dissolving is simply forming a mixture and not causing a chemical reaction?


texts: What is the methodology to discover thousands of compounds from a complex mixture?

texts:
So this is something that has always amazed me,

  More than 1,000 chemical compounds in coffee,[1] and their molecular and physiological effects, are areas of active research in food chemistry.

https://en.wikipedia.org/wiki/List_of_coffee_chemicals

How is it possible to identify so many separate compounds from just a single matter? What methods are used?


texts: Formaldehyde has the formula $\ce{CH2O}$, and the ratio of atoms in a simple carb is $\ce{1C:2H:1O}$. This fits the formula of formaldehyde. When I researched this, I found some sources saying that formaldehyde is the simplest carb, but other sources saying it is glycolaldehyde ($\ce{C2H4O2}$). Is formaldehyde a carbohydrate?


texts: What happens when Hinsberg derivative is added to acidic solution?

texts:
The Hinsberg test of $\ce{C5H14N2}$ compound produces a solid that is insoluble in 10% aq. $\ce{NaOH}.$ This solid derivative dissolves in 10% aq. $\ce{H2SO4}.$ Which of the following would best fit these facts?

I think b or d is the answer.
The reason being it's insoluble in NaOH. That implies it should not contain 1 degree amine. Can anyone clarify any further?


texts:
In the molecule 2,3,7,8-tetrachlorodibenzo-p-dioxin, the "p" means para--because each chlorine is para to an oxygen?
In IUPAC nomenclature shouldn't "para" be replaced by a number?


texts: What is the molecular weight of bilirubin?

texts:
There is a discrepancy among different sources on the molecular weight of bilirubin, $\ce{C33H36N4O6}$:

584.673 (Fisher Scientific);
584.66 (Sigma Aldrich).

What is the correct value and why?


texts: Does removing solution affect a supersaturated solution

texts:
Given a mixture of: a saturated solution of a solute in a solvent together with excess of the solute compound as crystalline material.

If one were to change the bulk composition of the mixture by removing some of the solution could this cause dissolution or precipitation of the solid in the remaining mixture, or the concentration of the remaining solution?

Presumably one should expect some crystallisation in the portion of the solution that is removed from the mixture?


texts: Regarding allylic free radicals and anti-Markovnikov product

texts:
I was searching a question "What is the primary product when cyclohexene reacts with bromine in the presence of UV light?" and in a website they said:

  3-Bromocyclohexene will be the product because when an alkene reacts
  with $\ce{Br2}$ in presence of UV light, free radical substitution
  reaction takes place. In this case, a stable cyclohexene allylic free
  radical will form which will further react with bromine free radical
  to form 3-bromocyclohexene.

A reaction that I already studied was propene + $\ce{HBr}$ in presence of $\ce{H2O2}$
and the answer is:

The reason is that carbon radical is present on secondary carbon where the neighboring atoms can donate electron density to stabilize the radical.

But based on the first reaction I speculate that the answer should be:
because here an allylic free radical is formed.

So which is correct?


texts:
I'm trying to attach a sensor to some tubes to measure the level of liquids in them.

see here

One tube contains toluene and the other contains Recosol R55 (shellite).

I'm thinking of using a capacitance level sensor like this or this.

But I am concerned about the safety of doing this. Could the capacitance sensor ignite these liquids? is this even possible?

Obviously I need to check with the suppliers of the device. However, most of datasheets for level sensors omit this information. Perhaps they are not game enough to make any claims about their sensor in this regard.

I don't really understand capacitance and whether it can ignite flammable liquids.


texts: Is there a good sol gel method for carbon nanotube thin film deposition?

texts: I was searching for a sol gel method for deposition of carbon nanotube thin films and there aren't too many articles on that.  Does anybody know the reason?  Is it because Carbon nanotubes are difficult to disperse in many solvents or?  Does anyone know if it is possible to effectively use a sol gel method to make a CNT thin film?


texts: I recently broke a Quickfit distillation thermometer and the bulb had liquid metal in it. I assumed it's mercury and acted accordingly. However, the column looks like spirit filled (blue liquid). Has anyone seen those, and if so, do you know if the metal is indeed mercury or something else? The model is Quickfit MF 31/2 (not MF 31/2S which is the newer one). I have never seen mercury and spirit combined in other thermometers. Just curious that's all.


texts:
I had a question in my textbook to convert propane to methane. The basic idea was chlorination in presence of sunlight. However, two products are obtained in this case - namely 2-chloropropane and 1-chloropropane. So it didn't work out at all.

I came up with another idea i.e. dehydrogenation, but it has not been taught to us at all. In addition the dehydrogenation reactions I searched on google were too complex. So, I hope there's another method for this.

Can anybody help me to sort this out?


texts: Mechanism of 5‐(iodomethyl)oxolan‐2‐one synthesis from 4‐pentenoic acid and iodine in acetonitrile

texts:
There is a question in my organic chemistry textbook with an answer. What it doesn't explain (and neither does my theory textbook, I checked) is the mechanism involved in the reaction. The reaction is as follows:

Can someone help me?


texts: Animate molecular vibrations as multiple xyz coordinate files

texts:
I have a frequency calculation by Gaussian09. Now I would like to extract vibrational modes as a set of xyz coordinate files. I would like to manually recompute numerically the points along a transitional vector, since IRC calculations all fail. (I suspect it is no real saddle point, flat PES.)

Consider the formation of the Lewis-Acid-Base complex $\ce{H3N\bond{-}BF3}$ with a transition state given in $$\ce{NH3 + BF3 -> [H3N\cdots BF3]^{TS} -> H3N\bond{-}BF3}$$ where this procedure would equal a (rigid) scan of the $\ce{N\cdots B}$ bond. This would be easy to accomplish.

Things get more difficult considering the pseudo vibration of ammonia, pyramidal to planar to pyramidal. Here it is not only one variable that has to be changed. (With dummy atoms it is still manageable.)

If molecules get more complicated, the manual specification of the bond parameters is too complicated and a source of many errors.

In the days when some of the gui programs were not able to calculate the vibrations and showing them in that fashion it was common to produce a set of multiple xyz files, each of them a snapshot of the coordinates along a specified vibrational vector. (This is now done internally and you can look at fancy pictures.) One of those programs capable of doing so is XVibs. For various quantum chemistry packages they calculated the distorted geometries. Unfortunately that is now ancient. (It was possible with a Gaussian09 output.)

For Turbomole there is a tool distributed along called screwer.

Unfortunately I have no access to that program package and I also do not want to change all the computations so far done to this software.

Lordstryker already posted in the comments, that it might be done by hand with chemcraft. I tried that and it is not very satisfying. One produces too many errors.

Are there any other programs/scripts that might be able to produce these files?


texts: Can resonance take place in between biphenyls?

texts:
I thought since both phenyl rings are not coplanar, the resonance between them is not possible. But my book says the following:

  Resonance effect is partially nullified

Partially nullified means resonance is relatively weak but it's taking place


texts: Preference for tin or iron in the reduction of nitrobenzene

texts:
My NCERT book(Class 12) said the following for reduction of nitrobenzene using $\ce{Sn/HCl}$ and $\ce{Fe/HCl}$ :

Now, I have been following this mechanism for this particular reduction, and it seems to me that the metal is getting oxidized to +2 state wherever it is shown that 2 electrons are being transferred. If that is the case, then:

•Why is $\ce{Fe + HCl}$ being preferred?

•Because I looked it up on Wikipedia and it says that $\ce{SnCl2}$ also gets hydrolysed to liberate $\ce{HCl}$ as follows:
$\ce{SnCl2 (aq) + H2O (l) ⇌ Sn(OH)Cl (s) + HCl (aq)}$

Or have I interpreted the mechanism incorrectly?


texts: Equation for the equilibrium constant for the hydration of carbonyls using UV spectroscopy

texts:
I was looking through the literature when I found a paper by Greenzaid et al. [1] which states that the equilibrium constant $K_\mathrm{hyd}$ is:

$$K_\mathrm{hyd} = [\text{hydrate}]/[\text{carbonyl}] = (\varepsilon_0^\mathrm{w} - \varepsilon^\mathrm{w})/\varepsilon^\mathrm{w}, \label{eqn:1}\tag{1}$$
where $\varepsilon^\mathrm{w}$ is the molar absorption coefficient measured under conditions of hydration, and $\varepsilon_0^\mathrm{w}$  is the molar absorption coefficient of the carbonyl compound in water in the absence of hydration.

(In water solvent, $\varepsilon_0^\mathrm{w}$ usually taken as the molar extinction coefficient in cyclohexane.)
How did the researchers get to the above equation in terms of the molar absorption coefficients?
As $[\text{hydrate}]$ is equal to $[\text{carbonyl}]_0 - [\text{carbonyl}],$ the equation \eqref{eqn:1} turns to:
$$K_\mathrm{hyd} = \frac{[\text{carbonyl}]_0 - [\text{carbonyl}]}{[\text{carbonyl}]}$$
However, the Beer–Lambert law states that
$$A = c\varepsilon l,$$
where $A$ is the optical density, $c$ is the concentration, $\varepsilon$ is the extinction coefficient and $l$ is the path length.
Denoting the corresponding parameters for carbonyl without hydration as $A_0$ and $\varepsilon_0$, and the parameters for carbonyl with hydration as $A$ and $\varepsilon$, the following can be written:
$$
\begin{align}
K_\mathrm{hyd} &= \frac{[\text{carbonyl}]_0 - [\text{carbonyl}]}{[\text{carbonyl}]} \\
  &= \frac{\frac{A_0}{\varepsilon_0l} - \frac{A}{\varepsilon l}}{\frac{A}{\varepsilon l}} \\
  &= \frac{\frac{A_0}{\varepsilon_0} - \frac{A}{\varepsilon}}{\frac{A}{\varepsilon}} \\
\therefore  &= \frac{\varepsilon}{A}\left(\frac{A_0}{\varepsilon_0} - \frac{A}{\varepsilon}\right) \\
  &= \frac{\varepsilon}{A}\frac{A_0\varepsilon - A\varepsilon_0}{\varepsilon\varepsilon_0} \\
  &= \frac{A_0\varepsilon - A\varepsilon_0}{A\varepsilon_0} \\
\end{align}
$$
But we require
$$K_\mathrm{hyd} = \frac{\varepsilon_0 - \varepsilon}{\varepsilon}$$
Shouldn't this mean that $K_\mathrm{hyd}$ is actually proportional to a fraction containing the $1/\varepsilon$ values?
References

Greenzaid, P.; Rappoport, Z.; Samuel, D. Limitations of Ultra-Violet Spectroscopy for the Study of the Reversible Hydration of Carbonyl Compounds. Trans. Faraday Soc. 1967, 63 (0), 2131–2139. DOI: 10.1039/TF9676302131.


texts: Why are sulfur trioxide and nitrate not isoelectronic, even though both have the same number of outer electrons?

texts:
Though $\ce{SO3}$ has the same number of outer electrons as $\ce{NO3-}$, the two are not isoelectronic.

This statement is from JD Lee, but I could not understand why is he calling these two molecules as not isoelectronic because ultimately being isoelectronic means having the same number of electrons in outermost shell, which they clearly do! Please explain.


texts:
Battery leaks was an issue in the 80s and 90s, and since quality and innovation is constantly improving, I thought battery leak might be slowly going away. But I found that even nowadays, name brand alkaline batteries still leak after a while, even if originally concealed in a tight package of the metal shell. Is it true that the chemical in an alkaline battery inherently expands in volume over time, and make the alkaline battery leak issue unavoidable?

also why does the alkaline expand in volume over time?


texts: Are there any molecular modeling programs that can build materials made up of three or more elements into a cylindrical shape?

texts:
I would like to build a material similar to what is in the image below.

I have tried programs such as Material Studio, Quantum ATK, and VNL, but most of them can only do materials with 2 elements.


texts: Can calcium hydroxide + sulphuric acid be a way of preparing insoluble calcium sulphate?

texts:
To prepare a soluble salt, we can react an acid with an insoluble base (hydroxide or oxide).
To prepare an insoluble salt, we can use precipitation method which is by mixing two solutions of soluble compound.

However, can I prepare an insoluble salt by reacting an acid with an insoluble base (hydroxide or oxide)?

For example,
 1. Calcium hydroxide + Sulphuric acid
 2. Lead (II) hydroxide + Sulphuric acid
 3. Lead (II) hydroxide + Hydrochloric acid


texts: Is pK_{In} = pH at equivalence point still true for weak basic organic indicators?

texts:
I am reading Ostwald Theory of Titration which says that indicators are organic weak acids or bases.
To prove the relation that $\mathrm{p}K_\mathrm{In} = \mathrm{pH}$, the textbook uses the following equilibrium as an example:

$\ce{HIn(aq) <=> H^{+}(aq) + In^{-}(aq)}$

which of course produces the the required result, but a thing I noted that it was for acid type indicator, so I decided to fill in the gap and do it for base type indicator myself, but it did not proceed as imagined:

Consider a weak organic base indicator $\ce{InOH}$, for it, the equilibrium will be:

$\ce{InOH (aq) <=> In^{+} (aq) + OH^{-} (aq)}$

and it's equilibrium constant then would be:

$\displaystyle{K_\mathrm{In} = \frac{[\ce{In^+}][\ce{OH^-}]}{[\ce{InOH}]}}$

then following the reasoning as done in previous case, for a sudden color change, $[\ce{In^+}] = [\ce{InOH}]$, so that,

$\displaystyle{K_\mathrm{In} = [\ce{OH^-}]}$

so that,

$\displaystyle{\mathrm{p}K_\mathrm{In} = \mathrm{pOH}}$

which inturn implies that,

$\displaystyle{\mathrm{pH} = 14 - \mathrm{p}K_\mathrm{In}}$

which doesn't seem to match with the previous result! Am I missing something here?

Note: I doubt that the condition $[\ce{In^+}] = [\ce{InOH}]$ might be the trouble, but I think it shouldn't be as in theory, the different color arises due to the respective indicator and their respective conjugate acid or bases.


texts:
I read that (in cellular respiration) the transported electrons in NADH have a higher energy than those in FADH2.
I can't find a (simple or otherwise) explanation of what a "high-energy" electron is.
I came across a post on Reddit which asks the same question:

I am not a chemist but I am trying to understand what my biochemistry book
means by "high energy electrons" that are obtained from glycolysis and
the citric acid cycle. I am assuming that this "high energy" is not a
property of the electrons themselves, but it is not clear to me in
what way they are "high energy". Do they mean that when these
electrons are transferred to the electron carriers they are part of
molecular structures in which they sit in high energy positions?

(There were no satisfactory answers to the question).
Could anyone come up with a definition understandable by this non-chemist (i.e. me)?


texts: I want to know how the powdered formed of piezoelectric material is converted to crystal like used in quartz watches. I know that some more chemicals are mixed with the material and then it is pressed in form of tuning fork (for clocks) at particular temperature and pressure. So what are the chemicals, temperature and pressure which are used. How they are made to vibrate at that particular frequency?


texts:
Why will $\ce{Fe^3+}$ give brown ring test?

In my textbook it was given that ferric ion gives brown ring too. I am confused, if ferric ion is already present, then what will reduce nitrate ion to nitric oxide?


texts:
I am quite new to the field. So try to figure out what is meant by the equilibrium state of an electrochemical cell?

Is it, where both half cells passing the same number of electrons to either side? if yes, how do the electrons transfer during non-equilibrium state (is it like, there is a net electron transfer due to electron change from both electrodes).

Any explanation would be much appreciated.


texts: What is the degree of freedom of the calcium carbonate dissociation reaction?

texts:
Question

$\ce{CaCO3}$ dissociated in a closed system according to the reaction:
$$\ce{CaCO3(s) -> CaO(s) + CO2(g)}$$
Assuming the reaction is in thermodynamic equilibrium, what is/are the degree(s) of freedom?

Doubt
I tried applying the condensed phase rule. All that I could arrive at was
$$C - P + 1 = 3 - 2 + 1 = 2.$$
However, the answer is slightly modified in the solution. The solution reads that $$C = N - R$$
where $N = 3$ and $R = 1.$ These are the factors I do not understand. All that I ask myself is where did I go wrong? Where was the exception?Please note here N stands for the number of reactants and R for the number of reactions.


texts: Why can't Al3+ be reduced to solid, pure aluminum?

texts: There are efforts underway to develop ionic liquids for the purpose of reducing bauxite using exotic intermediates such as aluminum fluoride. However, the aqueous $\ce{Al^3+}$ ion is tantalizingly close to pure aluminum. What prevents it from being reduced?


texts: accurate measurement from inaccurate tools

texts: It is a very general question. Is there a good way to systematically increase the accuracy and precision of a measuring tool using only mathematical means?  For example, average 10 measurements can create a better one. Or using two independent tools.  I don't know if measuring theory or statistical quality control or other subject can help.


texts: Can separated and purified substances be obtained from a chromatogram?

texts:
I am studying chemistry, and I am learning about chromatography.

But I am confused about how chromatography is used to ‘separate and purify’ substances.

I have learnt about chromatography paper, which is used to check if a substance if pure or not. Spots of the substances to be tested are place on the chromatography paper, which is then dipped in solvent. If there are several components, the spot separates into several spots (1 per component) as they travel up the paper.

Is it possible for separated and purified components obtained from the separate spots on the chromatogram, as usable substances, or do chromatographs only show the purity of substances?


texts: Is there a difference in the reactions of a dilute acid and a concentrated acid?

texts: All of the exams that I've sat so far, and the homework questions I've had, always ask for the reaction between a substance and a dilute acid. Is there a difference in the reaction between a dilute acid and a concentrated acid when each is applied to a substance? If so, what is it, and how dilute is dilute?


texts: How to find the alcohol content of a probiotic liquid?

texts: Probiotics are microorganisms that are believed to provide health benefits when consumed. Water Kefir is one such probiotic drink. This has blend of bacteria, yeast (BY), sugar water and the result of action of BY on sugar water. There is alcohol. One of my problem is to find out the alcohol content in the solution. Less expensive, simpler methods/protocols are much appreciated.


texts: Can atomic number change the type of electromagnetic radiation being emitted when a electron drop from a energy level to another?

texts:
Without getting into too much/any math, I just wanna talk about intuitions if possible.

If atomic increase, the attraction increase, and consequently the potential energy increase. More energy leads to higher frequency, different radiations.

I guess the reason if this diagram is universal is that the gap between 1 and 2 is too large too that the difference in energy cannot simply be compensated by adding more protons.


texts: Why does precipitate always form so naturally?

texts:
Whether be it from a textbook or teacher, precipitation reactions always occur by rearranging the elements:

For example

But then, aren't there other factors you have to bare in mind when predicting such reactions? Like electronegativity: obviously the potassium ion is much more electronegative than Silver ion, so it wouldn't be that easy for potassium to split up with iodine.


texts: Specific examples of all-main-group complexes with significant d-orbital contribution

texts:
It is usually said that d-orbitals are not usually used in bonding, even for so-called "hypervalent" ones, in compounds that are made purely of main group compounds.

However, after reading an article (or, strictly speaking, the preview of an article) about a calcium complex explicitly involving d-orbital contribution (see Krieck, S.; Görls, H.; Yu, L.; Reiher, M.; Westerhausen, M. J. Am. Chem. Soc. 2009), I began to wonder if there could be more d-orbital all-main-group compounds or not. The molecule depicted in the aforementioned paper is unstable in air and water, but maybe the unstability (i.e. high energy of main-group d-orbitals) could be reduced.

My guess is that, one can use the anti-bonding orbitals of a sufficiently weakly aromatic ring ("weakly" aromatic, in order to have relatively high energy) as ligands and putting many electrons in the coordination center (not necessarily metallic, and it should be reasonably electronegative, such as sulfur) so that the energies of the 4s and 3d orbitals of the coordination center reasonably match the anti-bonding orbitals of the ring and the usual Aufbau principle could be applied directly (3s2, 3p6, 4s2, 4d(1~5)).

The question is, are there any explicit examples of such complexes that are stabilised by a way similar to what I mentioned above?