texts: Why is introductory chemistry so non-rigorous?

texts:
In introductory chemistry books, courses, ...

Many "definitions" contain words like: typically, most, often, likely, generally.

I read since questions on this site mentioning different definitions of same concept in different books.

I just read about a concept where the explanation contained smth like "some other chemists believe it should be the other way".

Why are there many non-rigorous definitions in introductory chemistry?


texts: How to ionize a liquid and apply a force using electrohydrodynamics

texts:
I would like to create a contactless force on the surface of a liquid by ionizing it and placing the container between a cathode and anode, however I'm not sure how I would go about actually ionizing it.

The liquid is a photopolymer resin, although the specifics of it can be tailored to whatever we need so it makes the question rather broad. So I'm wondering if someone could give me some advice on how to create a surface force on a liquid using electricity.


texts:
For these two metals, the standard reduction potentials are:
$$
\ce{2e-} + \ce{Cd^{2+}} \rightarrow \ce{Cd}:\mbox{ } E^0 = -0.403 V\\
\ce{2e-} + \ce{Ni^{2+}} \rightarrow \ce{Ni}:\mbox{ } E^0 = -0.25 V
$$

But the simple ionization energies are:

$$ \ce{Ni} \rightarrow  \ce{Ni^{2+}} \mbox{   } \Delta H=\Delta H_{i_{1}} + \Delta H_{i_{2}} = 2490 \ce{kJ. mol^{-1}}$$ $$ \ce{Cd} \rightarrow  \ce{Cd^{2+}} \mbox{   } \Delta H=\Delta H_{i_{1}} + \Delta H_{i_{2}} = 2500\ce{kJ. mol^{-1}}$$
The difference in $E^\theta$ is greater than the difference in ionization energy of both elements.
How can this be explained?


texts: Can a solid material exist, such that it shatters if you hit it lightly (with a solid object) but it deforms and doesn't shatter if you hit it hard (say with a hammer)?


texts: Regarding reversible phase transition of a real gas

texts:
According to change in entropy for a reversible phase transition, say from liquid to gas at constant pressure $p$ and temperature $T$
: $\Delta S =\frac{\int dq_p}{T} $  which comes out to be $\Delta S =\frac{\Delta H_{vap}}{T_b}$. This means that this process is spontaneous since Entropy change is positive. But the Gibb's Energy change for this process is $0$. Why is that?
Change in entropy for this process suggests that this is a spontaneous process but Gibb's Energy change suggests it is not. Why does irregularity occur?


texts: can magnesium chloride and iodine react together?

texts: If everything is in a mixture of alcohol and water, would it be possible for magnesium chloride and iodine to react and produce something?


texts: Which species dissociate completely in ionic equations?

texts:
I am tasked with writing a molecular equation, an overall ionic equation, and a net ionic equation for the reaction between an aqueous solution of phosphoric acid, $\ce{H3PO4{(aq)}}$ and an aqueous solution of sodium hydroxide. The products are sodium phosphate and water.

I have already figured out the balanced molecular equation of the following:

$$\ce{H3PO4 {(aq)} + 3 NaOH {(aq)} -> Na3PO4 {(aq)} + 3 H2O {(l)}}$$

However, I am uncertain how to write the proper ionic equations. I know that the ions are separated, but how do you format this properly when writing with multiple molecules. If this is based on the disassociation of the chemicals, how do you determine which ions disassociate?

I have arrived at:

$$\ce{3H+ {(aq)} + PO4^3- {(aq)} + 3 Na+ {(aq)} + 3 OH- -> 3 Na+ {(aq)} + 3 H2O
{(l)} + PO4^3- {(aq)}}$$

However, I still do not know why this is the best answer. Why does the $\ce{NaOH}$ show separated in the equation while the $\ce{PO4}$ does not? How would you know which ones separate by simply looking at the problem?


texts: What is degree of dissociation for polyprotic acids?

texts:
My textbook says that degree of dissociation= [HA]dissociated/[HA]initial * 100%.
However, it also says that citric acid has a greater degree of dissociation than acetic acid because citric is triprotic whereas acetic is monoprotic.

This reasoning doesn't fit with the top definition because, more protons donated doesn't necessarily mean more acid molecules dissociated (triprotic acid vs monoprotic acid for example; for every acid molecule dissociated, triprotic acid donates more protons).

So my question is, how does one define degree of dissociation for polyprotic acids?


texts: Figuring out the theoretical mass of reactants

texts:
I'm working on my chemistry lab report. The initial instructions were to test the hypothesis that the mass of products of a reaction will equal the mass of the reactants.
Basically we where given a equation, our job was to balance and figure out the theoretical mass of reactants, and the theoretical mass of products.
There we're a total of three questions. In the first one I got the following differential values, 0.2 and 0.1. This seemed to be the most logical for me since I knew the law of conservation of mass implied that mass cannot be created nor destroyed but could be transformed. I attributed this small differential value to this transformation theory.
However, the next two questions I attempted still gave a very large differential value (40-120), which rejects my initial hypothesis.
I believe I may have missed something in the second and third question, below are my attempted solutions.
Question 1:
Initial Equation: $\ce{CH4 + O2 -> CO2 + H2O}$
Balanced Equation: $\ce{CH4 + 2O2 -> CO2 + 2H2O}$
$$
\begin{array}{ccccccc}
\ce{CH4} & + & \ce{2O2} & \ce{->} & \ce{CO2} & + & \ce{2H2O}\\
1(12+4) & + & 2(32) & \ce{->} & 1(12+32) & + & 2(2+16)\\
1(16) & + & 2(32) & \ce{->} & 1(44) & + & 2(18)\\
16 & + & 64 & \ce{->} & 44 & + & 36\\
\end{array}
$$
Theoretical Calculation:
$$
\begin{array}{ccc}
\ce{CH4}=\pu{16g} & & \ce{H2O}=\pu{36g}\\
+ & \ce{->} & +\\
\ce{O2}=\pu{32g} & & \ce{CO2}=\pu{44g}\\
\end{array}
$$
Actual Calculation:
$
\ce{CO2}=\pu{43.8g}\\
\ce{H2O}=\pu{35.9g}\\
$
Differential Value(Theoretical Calculation - Actual Calculation):
$
\ce{CO2}=\pu{0.2g}\\
\ce{H2O}=\pu{0.1g}\\
$
Question 2:
Initial Equation: $\ce{C2H6 + O2 -> CO2 + H2O}$
Balanced Equation: $\ce{2C2H6 + 7O2 -> 4CO2 + 6H2O}$
$$
\begin{array}{ccccccc}
\ce{2C2H6} & + & \ce{7O2} & \ce{->} & \ce{4CO2} & + & \ce{6H2O}\\
2(24+6) & + & 7(32) & \ce{->} & 4(12+32) & + & 6(2+16)\\
2(30) & + & 7(32) & \ce{->} & 4(44) & + & 6(18)\\
60 & + & 224 & \ce{->} & 176 & + & 108\\
\end{array}
$$
Theoretical Calculation:
$$
\begin{array}{ccc}
\ce{C2H6}=\pu{60g} & & \ce{H2O}=\pu{108g}\\
+ & \ce{->} & +\\
\ce{O2}=\pu{224g} & & \ce{CO2}=\pu{176g}\\
\end{array}
$$
Actual Calculation:
$
\ce{CO2}=\pu{78.59g}\\
\ce{H2O}=\pu{48.2g}\\
$
Differential Value(Theoretical Calculation - Actual Calculation):
$
\ce{CO2}=\pu{97.41g}\\
\ce{H2O}=\pu{48.2g}\\
$
Question 3:
Initial Equation: $\ce{C3H8 + O2 -> CO2 + H2O}$
Balanced Equation: $\ce{C3H8 + 5O2 -> 3CO2 + 4H2O}$
$$
\begin{array}{ccccccc}
\ce{C3H8} & + & \ce{5O2} & \ce{->} & \ce{3CO2} & + & \ce{4H2O}\\
1(36+8) & + & 5(32) & \ce{->} & 3(12+32) & + & 4(2+16)\\
1(44) & + & 5(32) & \ce{->} & 3(44) & + & 4(18)\\
44 & + & 160 & \ce{->} & 132 & + & 72\\
\end{array}
$$
Theoretical Calculation:
$$
\begin{array}{ccc}
\ce{C3H8}=\pu{44g} & & \ce{H2O}=\pu{72g}\\
+ & \ce{->} & +\\
\ce{O2}=\pu{160g} & & \ce{CO2}=\pu{132g}\\
\end{array}
$$
Actual Calculation:
$
\ce{CO2}=\pu{82.5g}\\
\ce{H2O}=\pu{45.0g}\\
$
Differential Value(Theoretical Calculation - Actual Calculation):
$
\ce{CO2}=\pu{49.5g}\\
\ce{H2O}=\pu{27.0g}\\
$
Not sure if it matters, but we where given this program to enter our calculations to simulate the reactions.


texts: Action of H2S and OH- on an alkyl halide?

texts:
What would be the action of $\ce{OH-}$ and $\ce{H2S}$ on 2,6 dichloroheptane? I came across this question in my organic chemistry workbook but I have simply never seen a question of this type before. I think a cyclic compound may be formed, but I am not sure which.

I thought really hard with help from the comments under my question, I came up with this solution.  However in my book it says that there should be only one sulphur atom in the cyclic compound. How does this make sense as there are two halogens in the original haloalkane? Is my mechanism incorrect?


texts: Are chlorinated solvents generally avoided in reducing reactions?

texts:
Are chlorinated solvents incompatible with reducing reagents? Is reductive dechlorination the reason?

There also seems to be exemptions, in J. Org. Chem. 1996, 61, 3849-3862, 1,2-dichloroethane was used as a solvent for a reductive amination reaction. NaBH(OAc)3 was used as the reducing agent in this paper.


texts:
How can I calculate overlap integral (J) between fluorescence and UV-Vis spectra in FRET mechanism?
I want to use this formula: J=(∫ϵ(⋋) F_D (⋋)  ⋋^4  d⋋)/(∫F_D (⋋)d⋋)
How can I find  ϵ(⋋) for every lambda in suitable range, I only have fluorescence spectrum of donor and uv-vis spectrum of acceptor. How can I calculate this integral.


texts: Why is BCl3 a monomer whereas AlCl3 exists as a dimer?

texts: What makes dimerization possible in $\ce{AlCl3}$? Are there 3c-2e bonds in $\ce{Al2Cl6}$ as there are in $\ce{B2H6}$?


texts: Are there compounds that melt under their own weight?

texts:
Is there a compound that can melt under its own weight? That is, a block of such material remains solid when put horizontally but starts to melt when put vertically or remains solid in microgravity, but melts in normal gravity?

The question is motivated by a documentary which I saw on TV some years ago where they claimed that a metal block (indium or its alloy) melts under its own weight. It is suspicious though because it was quite a crank documentary which featured alleged "red mercury" for instance.


texts: Is there dye that attaches only to human DNA?

texts: I am looking for simple way to tell if blood stain is from human blood or some other animals. I know there are fluorescent DNA dyes, but is there dye that only attaches to human DNA?


texts: API formulations - are excipients required

texts:
I have the following API's
Itraconazole, Ivermectin, Fenofibrate, Pyrvinium Pamoate,  Sulfasalazine, Artesunate,  All-Trans Retinoic Acid, Doxycycline,  Atovaquone,  Extremestane, Syrosingopine and Mebendazole
Why is it that API's require excipients?
Are they necessary for the active pharmaceutical ingredients bioavailability?
Or are the excipients used more as stabilises, preservatives, flavourings, binders and fillers so that as a finished pharmaceutical drug, it can hold its integrity/ shelf-life / taste etc.?


texts: Mechanism for hydrolysis of enol ether to aldehyde

texts:
I'm fairly confident in my answers for steps 1-3, but I am not certain how to have the methyl group bonded that is bonded to the alkene carbon leave in step 5 without forming methanol.

Here is what I have worked out so far.


texts: How can elements have the same number of electrons, but different electron configurations?

texts:
$\ce{Ti}$ and $\ce{Cr^2+}$ are isoelectronic, yet their electron configurations are different, with the former's being $\ce{[Ar] 4s^2 3d^2}$ and the latter's being $\ce{[Ar] 3d^4}$.
How can that be explained?


texts: It is known that dessicant agents such as magnesium sulfate can be used in order to trap water. But I was not able to find what quantity has to be added ideally compared to the amount of water that would be trapped. I know you can put it in excess but it could be a waste sometimes.


texts: Are all lone pairs considered as π-electrons?

texts:
According to me, in methylenepyran 8 π-electrons are present as there are 3 double bonds. Therefore, 2 × 3 = 6 π-electrons and 2 π-electrons as one of the two lone pairs of oxygen will participate in resonance.

But the correct answer is 10 π-electrons. How? Are both lone pairs of oxygen are being considered? If yes, then why?


texts:
The question in my class notes read as:

  Calculate the p-value for each ion in a solution that is $2.00 \times 10^{-7}\ \mathrm{M}$ in $\ce{NaCl}$ and $5.4 \times 10^{-4}\ \mathrm{M}$ in $\ce{HCl}$.

I was confused how to approach it, but my teacher did the solution on the board with the work done out and obtained the values of $\mathrm p\ce{H}$, $\mathrm p\ce{Na}$ and then used the totals of those values to get the concentration of [$\ce{Cl-}$]. From that, she then took the negative log of the concentration of [$\ce{Cl-}$].

For reference, she obtained the following values:
 $$\begin{align}
\mathrm p\ce{H} &= 3.27, \\
 \mathrm p\ce{Na} &= 2.699, \\
 [\ce{Cl-}] &= 2.54 \times 10^{-3}, \\
 \mathrm p\ce{Cl} &= 2.595
\end{align}$$

I understand how one has to take the negative log of a given concentration to obtain the p-value of it in a "rote" type of sense.

But what I misunderstood was the log rules and the calculation of the first $\mathrm p\ce{H}$ value.

Her work for the calculation of $\mathrm p\ce{H}$ was as followed:

(1st step)

$\mathrm p\ce{H} = -\log[\ce{H3O+}] = -\log[5.4 \times 10^{-4}]$

(use the log rule, $\log(a \cdot b) = \log(a) + \log(b)$)

(2nd step)

$\mathrm p\ce{H} = -\log 5.4 - \log 10^{4}$

(3rd step)

$\mathrm p\ce{H} = 3.27$

But why in the 2nd step above is the $\log 10^{4}$ not have a negative value, such as $\log 10^{-4}$?

In her solution of p$\ce{Na}$ it was the case that the second additive had a  negative exponent, which can be seen below in the second step.

(1st step)

$\mathrm p\ce{Na} = -\log[2.00 \times 10^{-3}]$

(2nd step)

$\mathrm p\ce{Na} = -\log2.00 + \log10^{-3}$

(3rd step)

p$\ce{Na}$ $= -0.301 -(-3.00) = 2.699$

Also if anyone could explain to be why we sum the values of $\mathrm p\ce{H}$ and $\mathrm p\ce{Na}$ to obtain $[\ce{Cl-}]$? Does this have to do with the "stoichiometry" of something? My chemistry is not great, nor is my math. Thank you.


texts: Does water really 'go bad' after a couple of days?

texts:
Among my friends it is a sort of 'common wisdom' that you should throw away water after a couple of days if it was taken from the tap and stored in a bottle outside the fridge, because it has 'gone bad'.
First of all, the couple of days is not very well defined, which already makes me a bit suspicious. Second, I cannot think of anything in tap water that would make the water undrinkable after a couple of days already.

Can someone clarify this issue for me? Does tap water really 'go bad' after a couple of days outside the fridge? Why?


texts: Solubility of Iodine in Some Organic Solvents

texts:
The solubilities of iodine in $\ce{CCl4,n-Hex,Et2O,PhCH3}$ were given respectively as 19 g/kg, 13 g/kg, 337 g/kg, and 182 g/kg. These results puzzle me for the following reasons:

1) Iodine, being a non-polar substance, should dissolve the most in nonpolar solvents. Yet diethyl ether the best solvent for iodine.

2) Toluene and n-Hexane, both being hydrocarbons, should have similar solubilities of iodine. Yet the solubility of Iodine in Toluene almost 20 times that of n-Hexane.

How do we qualitatively predict these results?

Note: This question's source is from HBCSE INCHO 2012, a chemistry test for high school students, without fancy tools such as the Abrahams' equation.


texts: I know that fire in a few words is the exothermic reaction of a fuel with an oxidizing agent, but I can't fully understand what exactly happens to piece of wood when it is ignited. How do molecules start producing a flame? In other words, what is the chemistry behind the production of flame?


texts: How does complex ion differ from ligand complex?

texts: As I understand, in terms of "colouring", ligand complex cause a transition metal cation centre's d-shell to split, allowing the electrons in that region to absorb specific frequencies of light, and thus resulting in colouring, does the same apply for complex ions such as chromate? Does the oxygen atoms/ions around chromate cause d-shell splitting and thus "colouring" effect?


texts: What is the function of tosylchloride in the synthesis of an ether?

texts:
Considering the following reaction:

Today my teacher explained this reaction as follows:
The electron pair of $\ce{OH}$ (in the first compound) will "attack" the $\ce{S}$, making the $\ce{Cl}$ "jump out". This is something I didn't understand clearly:
Why does the electron pair attack the $\ce{S}$ and not one of the oxygens, or even the ethanol? Is there any particular reason?

I'm not a chemical engineering student (I study engineering physics) so I don't have a great background in organic chemistry.


texts: Narrow range of pH for the formation of polyoxometalate clusters

texts: The molybdate ion in aqueous solutions, speciates as clusters known as polyoxometalates (POMs) when it is acidified, but these clusters only aggregate in a very narrow pH range "polymeric range" in the diagram. What causes this pH dependence of cluster formation?


texts: Equations for internal energy and their relevance to the derivation of the equation for entropy for perfect gases

texts:
My lecture handout proves derives an expression for entropy thus:

  For a perfect gas $U=U(T)$ (i.e. is not dependent on volume; only temperature). Therefore, $(\frac{\partial U}{\partial V})_T=0$

  Therefore:

  Equation 1) $$dU=(\frac{\partial U}{\partial V})_TdV+(\frac{\partial U}{\partial T})_VdT=C_VdT$$ Since $(\frac{\partial U}{\partial T})_V=C_V$

  Now, for a reversible change:

  Equation 2) $$dU=dq_{rev}+dw_{rev}=dq_{rev}-PdV$$

  Equation 3) $$dq_{rev}=PdV+dU=\frac{nRT}VdV+C_VdT$$
  Then divide by $T$ to make the equation equal to entropy rather than heat:

  $$dS=\frac{nR}{V}dV+C_VdT$$

I have a couple of issues with this. Mainly stemming from the fact that $U=U(T)$ and therefore that $(\frac{\partial U}{\partial V})_T=0$. I understand it on a physical level why this is the case (no intermolecular forces). I am not asking for a proof of this; I just have an issue with the implications of this. Let me explain:

An equation for dU is:

$$dU=TdS-PdV$$

This is understandable. $TdS$ accounts for heat transfer in/out of a system and $PdV$ accounts for work done by/on the system. However, surely this equation implies that $U=U(S,T)$ since both $dS$ and $dT$ appear in the expression.

The crux of it is: how can $dU=C_VdT$ and $dU=TdS-PdV$. Please help me understand what's going on here.


texts: Calculate the concentration in milimoles per litre (mM) of a solution that is 20% H2SO4 by mass and that has a density of 1.198 g/L

texts:
Calculate the concentration in milimoles per litre ($\pu{mM}$) of a solution that is $\pu{20\%} \ce{H2SO4}$ by mass and that has a density of $\pu{1.198 g/L}$.

For the answer, please provide two decimal places.

I calculated an answer but I'm just checking to see if I am correct...

I got $\pu{61.7 mM}$

First, I calculated the molar mass of $\ce{H2SO4}$ which is $\pu{98.086g/mol}$ and then I multiplied it by $\pu{20\%}$ which then got me $\pu{19.6172g/mol}$.

Second, I divided density by mass to cancel out the grams to get $\pu{mol/L}$ which then came out to $\pu{0.06106M}$ and then I divided it by $1000$ to get $\pu{mM} = \pu{61.07mM}$

If someone could check if this is correct that would be great, thanks!


texts: How to calculate the heat capacity of a calorimeter based on a neutralisation reaction?

texts:
I've looked at the other similarly worded questions but I can't seem to make heads or tails out of them.

So here's my case. I need to find the heat capacity of the calorimeter (in Joule/degree Celsius), and I've been provided with the following information:

$$\ce{NaOH (aq) + HCl (aq) -> NaCl (aq) + H2O}$$

$\Delta T = 11.5\ ^\circ \ \text{C}$
$\Delta_r H = -58.3 \text{ kJ/mol}$
$s_{p,\ce{NaCl}} = 3.91 \text{ J/(g}\cdot \ ^\circ \text{C)}$
$d_{1\ \text{M NaCl}}=1.0037\text{ g/mL}$
$V= 100 \text{ mL}$

So far I've calculated the mass of $\ce{NaCl}$:

$$m = d\cdot V = (1.037 \text{ g/mL})(100 \text{ mL}) = 103.7 \text{ g}$$

Then I calculated the heat capacity of $\ce{NaCl}$...at least I think that's what I did. I'm not even sure if I was supposed to do this:

$q = m\cdot s_{p,\ce{NaCl}}\cdot \Delta T$
$q = (103.7 \text{ g})(3.91 \text{J/(g} \cdot\  ^\circ \text{C}))(11.5 \ ^\circ \text{ C})$
$q = 4662.8 \text{ J}$

Now I'm confused as to the next step, and I don't know how to use $\Delta_r H$ in this problem.

Any help would be immensely appreciated.

Edit: Below I've added more things I've tried in my attempt to find the answer.

I saw this equation in a textbook so I gave it a shot:

$q = - \Delta H\cdot n_{\text{limiting reactant}}$
$q = (- 58,300 \text{ J/mol})(1.62 \text{ mol HCl})$
$q = 94,446 \text{ J}$

But I don't know how/if this fits anywhere in the problem.

Another equation I tried:

$q = C_P\Delta T$
$-58,300 \text{ J}= C (11.5 \ ^\circ \text{C})$
$C = 58,300 \text{ J} / 11.5 \ ^\circ \text{C}= 5069.5 \text{ J/}\ ^\circ \text{C}$

Which is at least the correct unit of the heat capacity I'm supposed to find.

Finally, I tried subtracting the heat capacity I found for $\ce{NaCl} \ (4662.8 \text{ J})$ from the supposed heat capacity of the system $(5069.5 \text{ J})$, I get $406.76 \text{ J}$

I'm kind of at a loss...


texts: What is the best way to convert SMILES strings to file names?

texts:
I would like to convert SMILES strings into file names. There are many characters to avoid in file names, i.e. \/:*?"<>| or maybe even []()^ #%&!@:+={}'~ (see discussion) for convenience.
I would like to escape such characters that appear in SMILES. However, I could not see a list of allowed characters for SMILES to decide on how to escape them. There might be also some existing convention to do this for databases, so I am all ears for any help.

An alternative is using InChIkeys but since they are not human readable, I want to avoid that option.

Edit: I am mainly interested in small organic molecules with less than 20 atoms.


texts: Why does changing the salt of the salt bridge effect the voltage produced in a galvanic cell?

texts:
My experiments results showed that the voltage decreases down $\pu{Group 1}$: $\ce{Cl-}$ salts in the salt bridge. All other variables were kept constant. $\ce{Zn}$ and $\ce{Cu}$ rods were used. Concentrations of the salt in the salt bridge were $\pu{1M}$.

I dont understand this result. What could the reason be behind this?


texts: Will a strained three membered ring open up when exposed to heat or acids/base?

texts:
I was wondering if a three membered ring or a three membered epoxide would ever open up spontaneously when exposed to heat, or acids/bases?

I would think at some point, but will it routinely happen to a three membered epoxide?


texts: Why do power requirement figures for water electrolysis on the web seem to be wrong?

texts:
I need to calculate the power needed to electrolyse 1 mole of water for a project.
We will either use Polymer Electrolyte Membrane Electrolysis or Alkaline Water Electrolysis, they operate on 1.75V-2.20V and 1.8V-2.4V respectively. And each has a maximum efficiency of about 69%. So, I have done further calculations assuming that the potential difference between the electrodes is 1.8V and the efficiency is 70%. As per my requirements, I have also considered that I have 8 minutes for conducting electrolysis.

Here are the calculations :

The reaction : 2H2O 2H2 + O2
Half Reactions:
Reduction at cathode: 2 H+(aq) + 2e−  H2(g)
Oxidation at anode: 2 H2O(l)  O2(g) + 4 H+(aq) + 4e−

1 mole of hydrogen gas will be produced from 1 mole of water ie 18 g of water or 18 cc of water.
Time available for electrolysis = 8 minutes ie 480 seconds
Number of moles of electrons = 2
Charge = 2 x 96,485 C/F = 192,970 C
Current = Charge / Time = 192,970 / 480 = 400 Amperes (approx.)

Considering 70% efficiency, Current required = 570 Amperes
Potential Difference = 1.8V (common to both PEM electrolysis and Alkaline water electrolysis)

So, Power Required = 1026 Watts ≈ 1 kW (for 8 minutes per mole)

I took reference of this webpage to learn how to calculate it.

However, then I came across this figure on the internet -
per mole water splitting requires at least 241.8 kJ of energy
Source: The first answer to this question.

So I am a little confused. I guess, this 241KJ energy figure came out because the person might be considering 1.23V potential difference (which is considered ideal), and 100% efficiency. I can't say anything because he has stated, that the values of enthalpy of formation (which he has used) are experimental, but hasn't provided the voltage and neither other conditions for the reaction.  He has just used the values of enthalpy of formation and not considered the efficiency of the method in use, in fact, that figure seems to be so general for all methods. As, PEM Electrolysis and Alkaline Water Electrolysis are the most efficient methods and both don't operate on that "ideal" 1.23V potential difference. Also, I think my reasoning is correct because if I redo the calculations considering 1.23V and 100% efficiency, the answer comes out to be the same as his.

Is my reasoning correct? and if not what is the reason for having different answers.


texts: Why is the ratio between Silicon and Oxygen 1:3 in single chain silicates?

texts: I thought that the ratio of silicon to oxygen in a silica tetrahedron was 1:4, so if a single chain is just many of these linked together, why does the ratio become 1:3?


texts: How to determine the empirical formula for terephthalic acid from its combustion products?

texts:
Terephthalic acid is an important chemical used in the manufacture of polyesters and plasticisers. It contains only $\ce{C}$, $\ce{H}$, and $\ce{O}$. In one experiment, $0.4953~\mathrm{g}$ of the acid was burnt in excess oxygen. The gases produced were passed through $\ce{CaCl2}$ and $\ce{NaOH}$. It was found that the mass of the $\ce{CaCl2}$ increased by $0.1613~\mathrm{g}$ and the mass of the $\ce{NaOH}$ increased by $1.0495~\mathrm{g}$. What is the empirical formula of terephthalic acid?

We have:
$$\ce{C_{$x$}H_{$y$}O_{$z$} + O2 -> CO2 + H2O ->[\ce{CaCl2 + NaOH}] CaCl2 + NaOH}$$

The anhydrous $\ce{CaCl2}$ absorbs the $\ce{H2O}$ produced, and the $\ce{CO2}$ is absorbed from $\ce{NaOH}$? So the products are $\ce{CaCl2. 2H2O}$ and $\ce{Na2CO3}$

I may have just figured the empirical formula out, and was wondering what the final answer is so I can compare and see where I went right/wrong. I realised that instead of $\ce{Na2CO3}$, $\ce{NaHCO3}$ would be produced.

Working out:
Via conservation of mass, the $\ce{CO2}$ and $\ce{H2O}$ must also be $0.4953~\mathrm{g}$.

Therefore: conservation of mass (mass of $\ce{CO2 + H2O}$) - increase in mass of $\ce{CaCl2 + NaOH}$

$0.4953 - (0.1613 + 1.0495) = 0.7155~\mathrm{g}$ <--- mass of $\ce{CaCl2}$ and $\ce{NaOH}$

Mass of $\ce{CaCl2.2H2O} = 0.7155 + 0.1613 = 0.8768~\mathrm{g}$

Mass of $\ce{NaHCO3} = 0.7155 + 1.0495 = 1.765~\mathrm{g}$

     C:               H:              O
 1.765x(12/84):     0.8768x(4/147.1):

 (m) 0.252142857:     0.023842284:   0.4953-(0.252142857+0.023842284)= 0.219314859

 (n) m/12       :     m/1         :    m/16

 0.021011905 : 0.023842284     :  0.013707179

       (Divide by lowest value)

( 1.53      :     1.74        :    1 ) x4

  6         :       7         : 4

Therefore $\ce{C6H7O4}$


texts:
In an exam paper it says that the lattice energy of NaCl is more exothermic than MgCl as the Na+ cation has a smaller ionic radius than Mg+.
Here are the resources given:

What is the reasoning for for Na+ having a smaller ionic radius even though Mg+ has a higher proton number?

Thanks.


texts: Why is brine solution more effective than granular salt in melting ice on a surface?

texts: Why is a brine solution consisting of a small fraction of salt in water, more effective in melting ice on a surface, than just pure salt?


texts: What is meant when people say a molecule has high multi-reference character?

texts:
I have read some other posts explaining what multi-reference and multi-configuration are with regards to the wave-function (such as What exactly is meant by 'multi-configurational' and 'multireference'?).

However, what does it mean for a molecule specifically to exhibit high multi-reference character? Does it just mean the results from calculations will be strongly dependent on if the level of theory incorporates multi-reference?


texts: Tip of my tongue: what is the name of this process?

texts: I remember back in Chemistry class, we did this thing where we would drop some liquid into a solvent. The moment it touched the solvent, it would turn into a gel sphere with the solvent inside it, and you could take these little spheres out and they'd essentially be capsules of solvent. What is the name of this process? The closest thing it reminds me of is Prince Rupert's Drop.


texts:
I notice that most optical calcite for sale seems to be from natural (mined) sources.

Also, I know in World War 2, mining optical calcite was a strategic objective.

Is there some reason why high-grade optical calcite cannot be lab grown?


texts: Energy of mercury(II) oxide decomposition

texts:
Study check 9.11 from [1, p. 298]:

  Mercury(II) oxide decomposes to mercury and oxygen.

  $$\ce{2 HgO -> 2Hg + O2}\quad ΔH = \pu{+182 kJ}$$

  […]

  b. How many kilojoules are needed when $\pu{25.0 g}$ of mercury(II) oxide reacts?

Correct answer is $\pu{20.5 kJ}.$ I get $\pu{10.5 kJ}.$ Here's how I did it:

Grams to moles: $200.59 + 16 = \pu{216.59 g}$ (using molar masses)

$$\pu{25 g} × \frac{\pu{1 mol}}{\pu{216.59 g}} = \pu{0.12 mol}$$
Moles to kJ:

$$\pu{0.12 mol} × \frac{\pu{182 kJ}}{\pu{2 mol}} = \pu{10.5 kJ}$$

What did I do wrong?

References

Timberlake, K. C. Basic Chemistry, 5th ed.; Pearson: Boston, 2016. ISBN 978-0-13-413804-6.


texts: ZnO spontaneous combustion during transport

texts:
I found your contact information researching $\ce{ZnO}$ reactions. I was hoping you could please help me or orient me in the right direction to find an answer to my problem.

The company I work for produces brass alloys in a furnace and one of our byproducts is zinc oxide dust. We sell this zinc oxide to other manufacturers. The last shipment we sent on a truck combusted, it burned out of the plastic bag, burned the wooden pallet it was on and it burned a hole in the wooden bed on the truck.

This has only happened twice in the 30 year span of the company. We keep our zinc oxide for two weeks before we sell it, to make sure it has cooled down, we also use two plastic bags, closed off with tape to avoid contact with moisture.

Based on a past profile done on our material, some of the other elements found in our zinc oxide dust are: $\ce{H2O}$ 1.92%, $\ce{Cd}$ 0.13%, $\ce{Cu}$ 0.66%, $\ce{Fe}$ 0.17%, $\ce{Pb}$ 7.43%, $\ce{Mn}$ 0.01%, $\ce{K}$ 0.36%, $\ce{Na}$ 1.18%, $\ce{Ca}$ 0.06%, $\ce{Mg}$ 0.01%, $\ce{Al}$ 0.02%

Do you have any idea what could have caused this reaction? Can you please suggest a source I can look into for more information and answers? We don’t want to risk shipping this substance if there is a chance it will combust and put people in danger.


texts: How to perform oxidation of keto group in presence of hydroxyl group?

texts: How to perform oxidation of keto group in presence of hydroxyl group. I fear there may be halogenation at $\ce{OH}$ group. Is there a way to protect the $\ce{OH}$ group ?


texts: Why a higher s character increases a carbon atom's electronegativity?

texts:
To make us understand certain phenomenon like the higher acidity of alkynes than alkanes and alkenes, our teacher told us to learn this as a general rule:

  Higher s character leads to a more electronegative carbon atom.

Note: By s character I mean the percentage of s in the hybridisation of the carbon atom(eg $25\%$ s character in $\ce{sp^3}$ hybrid carbon)

Though this well explains the above mentioned phenomenon (and certain others like the decreased $\ce{C-Cl}$ bond length in chlorobenzene), but I was unable to figure out  why this thing(increased electronegativity) happens after all.

This did not provide me a satisfactory answer. Electronegativity is after all the ability of an atom to attract the shared pair of electrons towards itself. So, how would one explain this using the concept of orbitals or molecular orbital theory?

I would also like to know if the same argument is valid for other p-block elements?


texts: Must compounds formed between solids be a solid as well?

texts:
My teacher gave us a long list of compounds and asked whether they are solid, liquid, or gas at room temperature and normal atmospheric pressure. I only know the more common compounds (eg. carbon dioxide, ammonia) and elements but not the rest.

Can I assume that a compound is solid because its constituent elements are solids at normal temperatures and pressures as well? If so, does the same goes with liquids and gases? If so, what if its constituting elements are not of the same physical state?

If not, then how can I determine the answer? Or must I memorize the physical state of the compounds in order to answer the questions?


texts: How do I solve such questions on paramagnetism and ferromagnetism?

texts:
Match the type of magnetism given in Group I with the material given in Group II:

  $$
\begin{array}{ll|ll}
\hline
 & \textbf{Group I} & & \textbf{Group II} \\
\hline
\text{P} & \text{Ferromagnetic} & 1 & \text{Nickel oxide} \\
\text{Q} & \text{Ferrimagnetic} & 2 & \text{Sodium} \\
\text{R} & \text{Antiferromagnetic} & 3 & \text{Magnetite} \\
\text{S} & \text{Paramagnetic} & 4 & \text{Cobalt} \\
\hline
\end{array}
$$

  A) P-4, Q-3, R-1, S-2
  B) P-4, Q-1, R-3, S-2
  C) P-1, Q-2, R-4, S-3
  D) P-3, Q-2, R-1, S-4

It was taken from a mock test sheet for GATE in India.
With regard to whether a material is ferromagnetic or paramagnetic etc. All that I know is to check the magnetic domains and decide. However, with regard to such compounds I have been facing extreme difficulties. Is this something that is totally experimental and that I need to know by information? Or is there a certain intrinsic property of the elements which can help me to decide? If yes, please explain how to solve such questions.


texts: Mechanism involved in bromine water test

texts:
$$\ce{CH3CH=CH2 ->[Br2] CH3-CHBr-CH2Br}$$

In the reaction mechanism, why does the nucleophile attack at the 2nd carbon atom? Shouldn't it attack at the 1st one, so that in the transition state, the carbanion is relatively more stable?


texts: Thermal stability of interhalogen compounds

texts:
I am striving over the question that what would be the stability order of the following interhalogen compounds : $\ce{ClF3, BrF3}$ and $\ce{IF3}$.

One probable answer I got is that stability of interhalogen compounds decreases as the size of central atom decreases due to electronegativity difference. Hence, the stability order should be $\ce{IF3} > \ce{BrF3} > \ce{ClF3}$.

Is the above mentioned logic correct? Can someone please elaborate?


texts: What is happening to my chlorine dioxide when I add too much bleach or citric acid?

texts:
I have some sodium chlorite and Chinese mystery powder which are meant to be mixed with water, then mixed together to form chlorine dioxide. I wanted to try a more food safe (and less mysterious) route for making small amounts of chlorine dioxide, so I diluted the sodium chlorite, then mixed in some bleach and a tiny bit of citric acid. I don't have a firm understanding of the reactions, but know $\ce{Cl2}$ and hypochlorous acid will react with sodium chlorite, but plain bleach may not, so the acid is to acidify the bleach and shift its equilibrium away from being hypochlorite. It worked, as evidenced by a pale yellow color. (It was very dilute, which is not a bad thing, for this chemical).
What I don't understand is that when I add more citric acid or more bleach, the color turns clear again. Either the chlorine dioxide is reacting or coming out of solution. What are the reactions with excess citric acid or bleach that might eliminate $\ce{ClO2}$?


texts:
When learning about amino acids, the primary things that were pointed out were that they had an amino group and a carboxyl group, and side chain that varies from one to the other.

The amino group of one can attach to the carboxyl group of another, making a peptide bond and water.

Both groups are clearly important, but what is it about the amino group that that's what goes in the name "amino acid"? Is the amino group in some way more important? Is it just something about the way/order in which they were discovered/identified that the name just came about?

Why amino acid? Not carboxyl acid, or some mix of the two, or something else?


texts: How was the composition of DNA studied before the knowledge of its structure?

texts:
In a large polymer molecule (such as a DNA chain) which is made from multiple component monomers containing many atoms, how was it determined that the chain was made up from the four groups of specific combinations of monomers of elements (in this case, adenine, thymine, guanine and cytosine)?
In other words how were they able to determine that the DNA contained the four specific bases before they knew the structure of the DNA molecule?
In general, doesn't breaking up a large molecule into its constituent atoms also break up the monomers?


texts:
I have long known that mixing bleach and peroxide produces oxygen gas:

$$\ce{NaOCl + H2O2 -> O2 + H2O + NaCl}$$

However I only recently learned that the specific form of oxygen produced by the reaction is singlet oxygen:

$$\ce{NaOCl + H2O2 -> O2(a^1\Delta_{g}) + H2O + NaCl}$$

Is there a simple chemical demonstration that can show the difference between singlet oxygen and triplet (ground state) oxygen?  Will singlet $\ce{O2}$ relight a splint "faster", or decolorize a dye faster when bubbled through solution, or otherwise be distinguishable from triplet oxygen in a home lab?


texts:
The question reads:

For the part were they ask about the total gas pressure, would it be correct to say that the total gas pressure doesn't change? Instead of $0.8$ $atm$ of $N_2O$, it is now $0.8$ $atm$ of various partial pressures of $N_2O$, $N_2$ and $O_2$?


texts:
What is the general name for acids that can only lose one hydrogen ion? (i.e. $\ce{HCl}$)
What is the general name for acids that can lose $n$ hydrogen ions? (i.e. $\ce{H_3PO_4}$, which can lose 3)

The answers to these questions are probably mentioned a million times on the internet, but I could not find them.


texts: Competition between aromatic sulphonation and nitration

texts:
Say you take a substituted benzene* and react it with oleum and nitric acid. Would it result in a nitrated ring, a sulphonated ring, or some sort of a combination?
Thinking about it in terms of the first step, the stronger base of $\ce{SO3}$ and $\ce{HNO3}$ seems likelier to get protonated first, making the preferred protonated electrophile (say it's A) less reactive than the other possible intermediate (say that one's B). But then the next step, the r.d.s, requires a pretty strong, reactive electrophile to attack the ring, which would make B the probable winner.
How do I decide between these factors, if such a general assumption can be made?

*I assumed a substituent wouldn't make a difference in this comparison. The answer, if so, would be more widely applicable than if the question were just about benzene. If there are differences, a note on them would be appreciated.


texts: Why do we need acid when making acetone peroxide?

texts:
Acetone peroxide is a very dangerous explosive, easily detonated by mild heating, friction or shock. It appears in the form of small white crystals.

This compound forms from the mixture of hydrogen peroxide, acetone and hydrochloric or sulphuric (and maybe any other) acid. The acid, however, is only a catalyst in the reaction.

I'm curious why the acid is required for the reaction to happen. Is it actually necessary? Does the acid change during the reaction?


texts: Can density functional approximations including dispersion correction perform worse than without it?

texts:
I am trying correlate some experimental properties of a molecule to its calculated equilibrium geometry. To do so, I calculated the geometry and energy of some conformers.
Now, I obtain mixed results when performing the same energetic calculation with dispersion-corrected (D3) and not corrected functional (B3LYP): when no correction is applied, a conformer has lower energy, while with D3 correction another conformer has lower energy.
The idea of using D3 looked reasonable, as the molecule has two aromatic and two aliphatic wings, which from the D3-uncorrected geometry seemed to promote to some degree an aliphatic-aromatic stacking interaction.

The point is: my intuition drove me to the use of the dispersion correction, and indeed the D3-corrected result would agree wonderfully with spectroscopic results. But is there a case in which a D3-uncorrected result would be more accurate than the corrected one? Or, alternatively, is there a way to understand quantitatively if the uncorrected model does not describe correctly the system?

I saw a lot of reviews talking about the "benefits" of DFT-D3, but could it do worse than DFT alone?

Edit, to answer Marvin's questions:
Yes, the molecule is organic. It all started with a "routine calculation set-up": b3lyp/6-31g*, but it later became evident that more refinement was required, so the current level might be seen as an expansion of the original calculation. Beyond the 6-31+g** level, I don't stress on Pople's basis anymore, and if more refinements will be required, Alrichs basis sets will be employed. Yes, I omitted it, but B-J damping was employed. At the moment I have optimized one structure with D3(BJ), the other one is being optimized. Of both the geometries optimized with B3LYP, the D3BJ-energy was calculated, together with the uncorrected one.
The two molecules arise indeed from a semiempirical conformational search, followed by a fast and inaccurate hf/3-21g* optimization on 100 geometries. A dozen of low energy conformers was optimized with hf/6-31g*, and the two outliers/low lying conformers were subject to further study with the methods discussed. The molecule contains 90 atoms, and the calculated energy difference is less than 0.5 kcal/mol, but as NMR experiments show a net predominance of one geometry, it's likely that the low energy difference is coupled with an high isomerization barrier, which I still haven't calculated: at the moment I am focusing on the equilibrium geometry.
As soon as the "new" geometry calculations will complete, I will probably do more calculations with a functional better suited for dispersion corrections, thank you very much!

Note: an NMR calculation is planned, but as good results require time and a strong basis set, it will probably be the last thing I will do, starting with better geometries.


texts: Molecular dynamics (Mac OSX user): what software can I use to plot RDFs for NPT simulations? VMD only works for NVT (constant volume)

texts:
I would be very grateful if someone could recommend a way to plot RDFs for NPT ensemble molecular dynamics simulation results.

I use CP2K to run NVT simulations and usually use VMD to process results, but I don't see a way in VMD to deal with NPT results, where the volume is different at each time step.  I'm hoping that someone can recommend a piece of software that can deal with my CP2K output (i.e., a position file in terms of atomic xyz coordinates and a file that contains volume output) on a Mac or Linux system.

I have spent several hours online looking for a solution, but haven't even come across discussions of this problem.  This seems odd so maybe I'm using the wrong search terms.  If anyone can point me to online discussions of this issue, that would be great.

I'm also not having much luck tagging this question!  If anyone knows of any molecular dynamics-related tags I could use to reach people or perhaps of a more appropriate StackExchange site, I would welcome any suggestions.  Thank you.


texts: Is hydrazine a better nucleophile than ammonia?

texts:
Which is a better nucleophile, $\ce{NH3}$ or $\ce{NH2NH2}$? For the sake of limiting scope, I want an answer for behavior in a protic solvent though non-protic solvent answers are welcomed.

My logic is that since $\ce{NH2NH2}$  has 2 lone pairs it will be a better nucleophile. I would like to know if this conclusion and reasoning is correct, or if I'm correct for the wrong reason why, or if I'm wrong, why is ammonia a better nucleophile?


texts: Formulation of a suspension of Magnesium Hydroxide

texts:
For a school project of mine, I have to formulate a suspension of Magnesium Hydroxide which contains at least 50% of solid matter.

This suspension is prepared from Magnesium Oxide 98% with a granulometry of around 75 micrometers. Unfortunately, I don't have a way to crush it more than it is until it is the ultimate solution.

The hydratation process will be made prior to the addition of additives to maintain the whole thing in suspension.

As my particles are relatively large and heavy, I know I have to fight against gravity. For that, I need additives that have dispersive properties and allow the mix to have a decent viscosity while avoiding sedimentation.

But, as I'm more specialized in enviromental chemistry, I'm not very good at proposing which surfactant/dispersant would be the most suitable for this project even after in-depth studies of papers talking about this.

From what I know, I think a polymer could seal the deal ? Maybe Sodium Polyacrylate as I saw it works fine with Calcium. Some Polyelectrolyte ? Or even multiple additives ? And in what quantities ?

I don't even know if the project is viable without crushing the particles of MgO so if you have any idea, I thank you in advance for your answer.

S.Berthels


texts: Why is $\ce{[HIn] = [In-]}$ at equivalence point of a titration? I know that at equivalence point moles of known solution is equal to the moles of unknown solution, but I'm not able to relate that fact with the above conclusion. Perhaps I'm don't know something.


texts: Relative stabilities of tropylium and cyclopropenyl carbocations

texts:
How can the stabilities of the tropylium and cyclopropenyl carbocations be compared?

Both are aromatic according to Hückel's rule. I think that to compare the stabilities, we must either count the number of resonance structures, or perhaps we could say that cyclopropenyl is less stable due to angle strain. Am I on the right track?


texts: which oxygen atom make intramolecular hydrogen bond in salicyclic acid?

texts:
When I googled about intramolecular hydrogen bonding in Salicylic acid, I found that there are two type of hydrogen bonding. Which one is more appropriate?

And another question, if there ARE two types of hydrogen bonding, why doesn't the 15.2 ppm peak of NMR specturm doesn't split in two? It seems that the two form of hydrogen bonding has diffrent energy level.


texts: Do SN1 reactions have dependency on the nucleophile?

texts:
'The rate of the reaction of tertiary butyl bromide with the hydroxy ion is dependent on the concentration of the tertiary butyl bromide, but is independent of the hydroxy ion.'

This means that the rate of SN1 is independent from the nucleophile. Why does that happen?


texts: What is it meant by two different groups in stereoisomerism?

texts:
I understand there are some properties in an organic compound that allow stereoisomerism.

double bond can't rotate
two double bonded carbon atoms each have two different atoms or groups attached

I'm unsure by the meaning of two different atoms/groups around on each side of the double bond.

With respect to but-2-ene. From my understanding, both sides of the carbon atom have $\ce{-CH3}$ on either side of the double bond so how does this comply with the rule that "Two different atoms or groups attached around each carbon of the double bond"


texts: How to find the oxidation numbers of individual ions of a transition metal with an average fractional oxidation state

texts:
In the classical example compound of $\ce{Fe3O4}$, we know that $\frac 23$ of Fe ions display +3 oxidation state and $\frac 13$ of Fe ions display +2 oxidation state fulfilling charge neutrality condition. However, this is the only solution considering the most common oxidation states of Fe are +2 and +3.

Now, consider the compound $\ce{La(Ni_{0.1}Mn_{0.9})O3} \rightarrow \ce{La10NiMn9O30}$,

Assume, the oxidation numbers of La, Ni and O are +3, +2 and -2. Therefore, under charge neutrality condition, the charges of 9 Mn ions should add up to 28. Knowing that the most common oxidation states of Mn are +2, +4, +7, we will have two solutions where charges add up to 28.

4 Mn ions showing oxidation number of +2 and 5 Mn ions showing oxidation number of +4
7 Mn ions showing oxidation number of +2 and 2 Mn ions showing oxidation number of +7

How could I decide what is actually happening?

If it helps, I need to know this to calculate the average ionic radius of a B-site cation of a perovskite structure.

EDIT

Edited the typo by changing ox. state of La to +3.

Furthermore, I am looking for an answer that makes sense theoretically (real world formation may be different). It would be great if somebody could guide me for a relevant publication, if there is any.


texts: Can a used-up buffer solution be used again in the other direction?

texts:
Suppose a strong base is added into an acidic buffer (such as acetic acid buffer) up to the endpoint. This means that the acetic acid molecules neutralize the hydroxide ions to the point that the solution contains mostly acetate ions (with their counter ions, of course), a negligible amount of acetic acid molecules due to Le Chatelier's principle and water.

My question is: can this resulting solution be immediately used as a basic buffer, since it contains a base with its conjugate acid?

Can the same buffer solution be used back and forth in the lab?


texts: What is the exact meaning of ionic and covalent character?

texts:
In my textbook, it is written that 'Even in case of covalent bond between two Hydrogen atoms there is some ionic character.'
Didn't get that.


texts: What does boiling point of a metal depend on, specifically manganese?

texts:
Boiling point, as I understand, generally depends on molar mass and the intermolecular interactions in the liquid phase.

What are the other influencing factors?
What intermolecular forces are present in liquid metals?
Why does the boiling point of manganese deviate?


texts: Suppose that a raidoactive brick of an unknown element with a half-life of one year (dangerous stuff!) is left on a regular desk for a day. After the day has passed, the brick is removed. Does the desk now exhibit any radioactivity even when artificialy induced radioactivity is considered?(Assume that the brick exhibits alpha, beta, and gamma decay products and ignore the dimensions of the brick and the realism of placing a radioactive brick on a random desk.)


texts:
I was reading about gold number and a book defined gold number as following:

  It is the minimum mass in milligrams of a stabilizing agent which is added to the 10 mL of red gold sol to protect it against coagulation caused by 1 mL of 10% (by mass) NaCl.

Is this the definition? Because I am not able to understand above definition.
Is NaCl used as the standard?


texts: Reduction of copper oxide by hydrogen in the lab

texts: Why does the hydrogen which is passing continuously through the tube have to be burnt when it is passing out from the tube? Why can it not be allowed to just escape simply?


texts:
I was given two equations as part of a problem into Copper Wiring production for planes:

$$\ce{4CuFeS2 + 9 1/2 O2 + 4SiO2 \rightarrow Cu2S + Cu2O + 2SO2 + 4FeSiO3}$$
$$\ce{Cu2S + 2Cu2O \rightarrow 6Cu + SO2}$$

This question later became the source of a Chemistry exam question for the English IB equivalent.

I was given the following information.

  The previous equations are part of the manufacture of copper for wiring in planes.
  A passenger jet contains $4050\ \pu{ kg}$ of copper wiring.
  A rock sample contains $1.25$% $\ce{CuFeS2}$ by mass.
  Calculate the mass, in tonnes, of rock needed to produce enough copper wire for a passenger jet. ($\pu{1~tonne} = \pu{1000~kg}$)

Now, I tried to solve it as follows:

Adding both equations gave:

$$\ce{4CuFeS2 + 9 1/2 O2 + 4SiO2 + Cu2O \rightarrow 2SO2 + 4FeSiO3 + 6Cu + SO2}$$

Now, I can see that $4$ moles of $\ce{CuFeS2}$ from the ore would give us the required $\ce{6Cu}$ for the production.

However, the solution states that Cu and $\ce{CuFeS2}$ are in a $1:1$ ratio, which I couldn't explain why.

Using the equation I formed above, this idea didn't make sense.
Why is the ratio of Cu to $\ce{4CuFeS2}$ $1:1$?


texts: Justifying the tremendous −I effect of trimethylammonium group by molecular orbital theory

texts:
The $\ce{-[NMe3]+}$ group is ranked almost at the first position in the −I effect series, which is often given at the very beginning of the teaching of general organic chemistry.

I know this can be justified by hyperconjugation, but I am interested in a rigorous justification by molecular orbital theory.


texts: How does mass affect bond stretching in UV spectroscopy?

texts:
If, for example, you have a bond on the form:

H - X, where H is hydrogen and X is some other element.

How does the mass of X affect the stretching of the bond during UV spectroscopy? Why do heavier atoms require a less 'energetic' wave to cause them to stretch?


texts: How does a catalyst affect the rate equation?

texts: If I determine the order of the reactants in a reaction without using a catalyst, and then use a catalyst, will the order of the reactants then be different?


texts: Is there a way to quantify the 'surface area' or simply the shape of organic compounds?

texts: I wish to write an investigation into the effects of the shape of organic compounds and the location of the functional groups on the enthalpy of combustion of the organic compounds. Thus, I wonder if there is a way of quantifying these variables, as databases I have looked at do not provide much of an answer.


texts: Total number of stereoisomers of 2,3,5,6-tetrachlorooctane

texts:
Total number of stereoisomers for:

I tried the following combinations:
RRRR, SSSS, RRRS, SSSR, RRSS, RSRS, SRRS, RSSR, RSRR, SRSS, RRSR, SSRS, SSRR, SRSR.
So, total number of stereoisomers I got is 12, but my teacher says it's 16. I don't know how to figure out what other four isomers are.


texts: I have an aqueous solution of either $\ce{MgCl2}$ or $\ce{CaCl2}$ in solution with $\ce{K2SO4}$. There is a white precipitate that forms on the bottom that does not dissolve when $\ce{HCl}$ is added (maybe it needs to be in excess?). Is there any way to find out if it's $\ce{Mg^2+}$ or $\ce{Ca^2+}$? I have already tried adding $\ce{NaOH}$, and the result was a not very cloudy, white precipitate, which is not really jelly like, but when compared to stock samples of $\ce{MgCl2}$ and $\ce{CaCl2}$ with $\ce{NaOH}$, they don't match. I tried a flame test but only could see the $\ce{K+}$ (violet flame).


texts: How do I get a value of the Gibbs energy of formation at 0 K and 0 bar?

texts:
The standard Gibbs free energy of formation for copper(II) oxide, $\ce{CuO}$, is $\Delta_\mathrm fG (\pu{298.15 K},\pu{1 bar}) = \pu{-129.7 kJ mol-1}$.

How can I get $\Delta_\mathrm fG (\pu{0 K},\pu{0 bar})$, the limiting value of this?

I want to compare it with the approximate value obtained by density functional theory calculations:

$$\Delta_\mathrm fG (\pu{0 K},\pu{0 bar}) \approx E^\text{Total}_\ce{CuO} - E^\text{Total}_\ce{Cu} - \frac{1}{2}E^\text{Total}_\ce{O2}$$


texts:
I was working on my homework which was to write a description of what would occur if zinc and sulfur reacted and what steps would a scientist have to make in order to make them react. When I researched I bit, I saw that it would be a exothermic reaction, and I wanted to show this by using enthalpy. I haven't been taught this however, and as a result, I'm confused. I know that enthalpy equals the heat transfer and there is some sort relationship with bond energy, but I don't know how to apply this to the reaction.

Zinc Powder + Sulfur Powder = Zinc Sulfide + Energy

$\ce{Zn_{(s)} + S_{(s)} -> ZnS_{(s)}}$ + $205.98 \text{ kJ}$

Because $205>0$ this is an exothermic reaction. But where did this $205.98\text{ kJ}$ come from?


texts: How to determine if a compound is a strong, weak, or non-electrolyte?

texts:
I'm stuck on questions asking whether a given chemical formula is a strong or weak electrolyte in an aqueous solution. I did some research online, but could not get a specific solution that I could readily comprehend.

My conception right now is that ionic compounds are strong electrolytes? But I have no idea when it comes to organic compounds or covalent bonds.

Can somebody explain?


texts: Mono chloro substituted products of naphthalene

texts:
My chemistry teacher today told that only two mono chloro substituted products are possible for naphthalene. He explained this by saying since the naphthalene molecule is symmetrical  about the axis passing through the C-C bond where the benzene rings are fused, the corresponding positions should be identical & hence only two such products are possible. I personally don't find this convincing & hope to look for a genuine answer. I will be extremely thankful to anyone who helps.

If someone is unable to understand my teacher's explanation, just ignore it. I myself wasn't able to understand it properly so could have mistaken it for something else.


texts: Identification of zinc/aluminium/magnesium with copper sulphate solution

texts: We are doing an experiment and would like to be able to identify zinc/aluminium/ magnesium . Would a copper sulphate solution work ? I hear that it turns black on contact with zinc, stays clear on contact with aluminium and fizzes on contact with magnesium.


texts: Why can the standard enthalpy of formation be calculated for different states of matter when the temperature should be constant?

texts:
If the standard enthalpy of formation needs to be determined at $25ºC$ and 1 atm of pressure then why is it possible for the enthalpy of formation to be calculated for the liquid, solid, and/or gas states for the same substance?
For instance (at $25ºC$):
$$H_2O(l): -285.8$$
$$H_2O(g): -241.818$$


texts: Naming a molecule with both alcohol and aldehyde functional groups

texts:
How would you name this molecule as it has an alcohol and aldehyde group. The aldehyde surely has the higher priority but if I start numbering there, I'm not sure how to write alcohol.

Best try I have is 3-methylpent-2-ene-1-hydroxy-2-al.


texts: ADP + P has one oxygen and two hydrogen more atoms than ATP. Are these atoms released as water in the reaction ADP + P => ATP? To balance the equation, would ADP + P => ATP + H2O be more correct?


texts: How can we say that Helium (He) is liquid at "absolute zero"?

texts: According to Wikipedia, Helium can never be solidified at $\pu{1 atm}$ ($\pu{101325 Pa}$) pressure, not even at absolute zero. A minimum of $\pu{25 atm}$ pressure is required to make Helium solid. But absolute zero ($\pu{0 K}$) is not attainable, how can we say that Helium is liquid at absolute zero with $\pu{1 atm}$ pressure? It can never be proved. Is it a theory?


texts: Which is the parent chain in Neopentyl chloride? and why?

texts:
Which is the parent chain in this structure?
and since all have 3 carbons so should any of them be the parent chain, if not ..
then which should be and why? is it a rule in IUPAC naming?

(source: chemspider.com)


texts: Effect of adding pure solid/liquid in heterogenous equilibrium

texts:
QUESTION

Consider the following reaction as an example:
$$\ce{NaNO3(s) <=> NaNO2(s) + 1/2O2(g)}$$
Once this reaction has achieved equilibrium and then if we added pure $\ce{NaNO3}$ to this system, then is it correct to say that it will favour forward reaction?

My Thoughts
I have gone through a lot of questions related to this topic in Chemistry Stack Exchange and all of them have explained in detail that why it will not affect the value of equilibrium constant (as their "concentration" would not change and I fully agree with that), but no one answers the core question.
That if we add or remove a pure solid/liquid then why wouldn't "moles" of other compounds in the reaction change which are included in equilibrium expression?


texts: Why are the electronegativities of elements in the middle of the transition groups quite high compared to surrounding elements?

texts: Is it something to do with the d orbital being used, and if so, what effect does this have and why does it make the electronegativity higher?


texts: Removing aluminum oxide from impure silica

texts:
We have an assay for a mine. Our goal is to have only silica. Is there a cost effective way to extract the contaminants? The product is a fine powder called diatomaceous earth, or fossil shell flour. Our goal is to use the product to help poor pacific islanders increase their silica uptake and assist in heavy metal detox. Many members of the pacific island nations suffer from heavy metal poisoning. The composition of the powder is:

> 84.7% $\ce{SiO2}$
< 4% $\ce{Al2O3}$
< 2% $\ce{Fe2O3}$
< 0.33% $\ce{CaO}$
< 0.36% $\ce{MgO}$
< 0.5% "other"

We aren't concerned with the calcium, iron or magnesium oxides, just the aluminum oxide.

Is there a simple process to reduce the aluminum oxide levels?
Also, what is the easiest process to convert the silica to orthosilicic acid for increased bio-availability?


texts: Is there a consensus on whether amber can seal in air bubbles for millions of years?

texts:
I read about deriving the oxygen content in the atmosphere in the Cretaceous by analyzing the air trapped in bubbles in amber from that period, but I have also found papers disputing the study's methods and showing that air isn't actually trapped in the bubbles because it's capable of diffusing through the amber (the amber isn't a perfect sealant), and thus the air found in that amber isn't necessarily as ancient as the amber itself.

My problem is is that almost all the relevant papers are from the late 80's; all those I've found are pro- or con-, I don't have the background to tell who is right, I haven't found a source that describes an actual consensus the field would have come to since then, and I see the claim about the original study showing what oxygen levels were in the Cretaceous cited in various places, but I find it hard to tell if it's because the objections were dismissed or if it's because it's a zombie claim.

Some sources:

What seems like the first paper to make the claim:
Gas bubbles in fossil amber as possible indicators of the major gas composition of ancient air
This source seems to be more recent and find the same conclusions but it's hard to tell (looks like at least one person is the same as the 1988 source):
Air Bubbles, Amber, and Dinosaurs - USGS
The main disagreement:
Is the air in amber ancient?
Some back-and-forth:

Google Scholar: "is the air in amber ancient"
The relative contribution of adsorption to the overall sorption and transport of small molecules in amber

An unrelated recent paper that comes to a different conclusion on Cretaceous air content (based on amber as well but carbon isotope analysis thereof):
Stable carbon isotopes of C3 plant resins and ambers record changes in atmospheric oxygen since the Triassic

Does anyone know if a consensus was arrived at on this question, and/or if one side is clearly more right than the other?


texts: Electrical conductivity and the limits of Kohlrausch's law

texts:
I am currently writing a lab report on electrical conductance and I realized that my partner prepared $\pu{0.1 M}$ solution instead of $\pu{0.01 M}$. Now, I am supposed to find the molar conductivity of the solution at infinite dilution. Although the data gathered fits beautifully in the regression, the value found for $\Lambda_0 $ is wrong. What is the best way to explain that? By saying that at such concentrations, the effects $\sqrt{c}$ become negligible and are and not having enough steps in the data between a concentration in solution of $\pu{0-0.01 M}$ induces a big error on our value ?
Or is there something else/better to do ?


texts: How to get meniscus down to the calibration mark with a volumetric pipette

texts:
I am having trouble taking aliquots using the 10 ml volumetric pipette.

After rinsing, I draw the solution up past the calibration mark and stopper the pipette with my index finger. Then I slowly rotate the pipette and try to let a tiny bit of air inside to get the meniscus down to the calibration mark. But every time, the solution just shoots down, or goes just below the calibration mark.

How can I improve my technique?


texts: Can we find 100% probability region in an orbital if the position of an electron is limited by speed of light?

texts:
The square of the wavefunction gives probability density of finding an electron somewhere in the orbital.

The text I'm referring to says that the value of probability density is always higher than zero at any finite distance from the nucleus.

My question is, provided that we knew position of an electron at a give time, could we now draw a boundary surface diagram that encloses a region in which probability of finding the electron is 100% for some point in time in future?

This would be possible because the electron cannot travel faster than the speed of light, so we could draw a sphere of radius $3*10^8$ meters centered at the current known position and say that probability of finding the electron after one second will not be beyond the region enclosed by the sphere.

Or is this question invalid because we can't know the position of an electron ever, not even within a finite uncertainty that would allow us to draw such a sphere?


texts: I need Iron powder. What's the best way to produce it?

texts:
I have Ferric Chloride and Aluminum...

I also have steel filings from grinding steel objects, though some Iron Oxide have be separated (I do have Oxalic Acid and Citric Acid). Though that would give me steel powder, not iron.

Which is the most economical and would yield purest samples?


texts: Why is the Suzuki coupling done under inert atmosphere?

texts: There are plenty of sources saying that the Suzuki coupling is air-sensitive (even though there are some versions that require oxygen). However I'd like to know why a typical Suzuki coupling is air-sensitive. I cannot find what the oxygen actually does.  Pd(0) doesn't seem like it would get oxidised in air that easily, does it?


texts: In a redox reaction, why does more than one oxidation state of an element form?

texts:
Consider the reaction 100ml 10M $\ce{NaOH_{(aq)}} +$ 100ml 10M $\ce{NaHSO3_{(aq)} +}$ 100mL 0.01M $\ce{KMnO4_{(aq)}}$

In the picture posted here, the left columns give information on the Molarity of species present before 100mL 0.01 M $\ce{KMnO4}$ is added. The right column is after $\ce{KMnO4}$ is added.

In the resulting solution, $\ce{Mn}$ is oxidized to various states: $\ce{Mn^2+ Mn^4+ Mn^6+ Mn^7+}$ (where $\ce{Mn^7+}$ is the original form).

I would like to know, why do different oxidation states of $\ce{Mn}$ appear? How can we predict the concentration of oxidation states?


texts:
I am new to the concept of neutralization.
My teacher told me that acids do not react with neutral salts.
I want to know why not.

If both are dissolved in water and both completely dissociate, why can't the ions of acid and salt exchange and perform a double displacement reaction.

Moreover I have seen the following reaction in a book: $$\ce{2 NaCl + H2SO4 -> 2 HCl + Na2SO4}$$


texts: What is the chemistry behind this "petrol from air" technology?

texts:
A recent news report in the UK claimed a breakthrough in making a petrol equivalent from carbon dioxide and water:

  A small British company has produced the first "petrol from air" using a revolutionary technology that promises to solve the energy crisis as well as helping to curb global warming by removing carbon dioxide from the atmosphere.

It sounds like the news reports are over-hyping it a little (and I'm not sure it is that new), so what is the real chemistry behind it? What are the key reactions and how much input energy is required?


texts: The Evans auxiliary: rotational freedom of the benzyl group - stereoselectivity still guaranteed?

texts:
I created the L-Phenylalanine based Evans auxiliary bearing a benzyl group with help of a molecular model set and got into some questions. The structural formula will do:

As I suppose a low rotational barrier, the phenyl group can be aligned off (a) and towards (b) the alpha position of the N-propionyl group. I suppose maximum sterical repulsion for attacking electrophiles for (b).

The phenylalanine and valine based auxiliaries (Bn or i-Pr) are the most commonly involved types of Evans auxiliaries. But why do I get good stereoselectivities for this Bn auxiliary? There are no corresponding carbon-carbon rotational freedoms in the valine species.


texts:
I've steam distilled a couple of different powdered seeds/herbs to obtain the essential oils from them.

Somehow some of the extracts won't separate and stay in an emulsion.

I've seen that some fixed oils that where extracted too are separating in cool conditions, but I can't see any essential oil layer forming. Even when letting the extract (emulsion) sit for 2 weeks.

Can anyone explain why this is happening (or not) and how I could break the emulsion? Acidifying or salting it out?

Since if I would try to boil the water of off the emulsion, its vapors would carry the oils with it, so is there any way to evaporate the water but leaving the oils?

I live in a country where it's hard to obtain some chemicals, so are there any easily obtainable chemicals/solvents to use for further or better processing?
I have access to $95~\%$ bio ethanol, $95~\%$ acetone, sodium hydroxide, sodium chloride and I've managed to get some naphtha.

So my possibilities are limited as you can imagine …

I've thought about using a Soxhlet extraction with ethanol or acetone where I could simply distill the extracted and concentrated solution to recover the solvent and be left with the extract (essential oil, fixed oil, etc.).

What can I then do to separate the fixed oils from the essential oils that I want?


texts:
How can I remove labels from jars?

Sometimes I like to recycle jars for my own use, but normally I want to remove the label first. I find this extremely difficult to do. With ordinary stickers, like the stickers found as price tags on books, acetone works very reliably.

However, the labels on food jars are stuck on with a much more tenacious glue that does not respond to vegetable oil, acetone, methyl ethyl ketone, hot vinegar or ethanol. What is this stuff and how can I dissolve it?

Right now the only way I have found is to laboriously scrape them off with razor blades, but it is extremely time consuming to do this.

(Note that the tough labels I suspect are "hot melt" adhesives used to affix polypropylene labels. For example, traditional hot melt compositions are ethylene/vinyl acetate copolymer and ethylene/(meth)acrylate copolymers, but obviously there are others. I am hoping somebody with expertise can identify the range of typical compositions and corresponding solvents.)


texts: Barron states that 4.18×10⁸ joules equal 1 kcal, is this correct?

texts:
Here is a paragraph in Barron's SAT chemistry prep book:

  Work itself is measured in Joules, and so is energy. In some problems, however, energy may be expressed in kilocalories. The relationship between these two units is that $4.18\times10^8$ Joules equals 1 kilocalorie (kcal).

Is this correct? Isn't 1 kilocalorie 4180 Joules?


texts: How to find the balanced reaction equation for the decomposition of potassium dichromate in non aqueous conditions?

texts:
I can't find a method to balance a reaction: the heating of potassium dichromate, which forms potassium dichromate (III), dichromate oxide (III) and oxygen.
I can't add water products as $\ce{H+}$, $\ce{{}^{-}OH}$ because we are not in solution.
So, how can I balance it?

Who oxidises in this redox? The oxygen inside the salt? The oxygen of $\ce{H2O}$ which is in the air?


texts:
I am not a Chemist, but I took enough undergraduate Chemistry classes to understand the basic properties of s, p and d orbitals and how the behaviour of electrons contributes to different kinds of chemical bonds and elemental/molecular properties.

I stopped before we got to actual quantum mechanics - my maths wouldn't have been good enough to stand it. It still isn't.

However, I was always fascinated as to why none of the lecturers would ever tell us about f-orbitals. When asked, they muttered dark hints that they were significantly different from lower electron shells, and that explaining why was not only a waste of time but might spoil our existing understanding.

I left university 20 years ago, but I was suddenly blindsided by remembering this question out of nowhere. And now I want to know the answer. Google searches reveal a lot of maths that I can't follow. So can someone explain:

What are some of the basic properties of elements with electrons in f-orbitals, and how do they differ from lower orbital positions?
I assume this is related to the fact that most (all?) elements with f-orbitals manifest as metals, so how and why? And why do some elements without f-orbitals display metallic properties?
Why were my tutors so unwilling to try and explain this to non-Chemists who were supposed to stop at their appreciation of lower orbitals and basic covalent bonds?


texts: H2Te dipole and electronegativities of H and Te (high school level chemistry)

texts:
I saw somewhere that $\ce{H2Te}$ is a polar molecule, but as far as I know the only time dipole-dipole forces arise (giving molecules the possibility of becoming polar) are when there is a difference in electronegativity. I know $\ce{H2Te}$ is not a linear molecule but if there is almost no (less than 0.4) difference in electronegativity values the shape shouldn't matter as electrons wont be more drawn to either atom (or 'side' of the molecule). In other words, it seems to me the intermolecular forces should be induced-dipole induced-dipole (making the molecule non-polar), not dipole dipole.

I should clarify, I first saw this statement in the answers to a high school chemistry exam. I then googled it, and got the same answer (i.e that the molecule is polar).


texts: How to decide between different possible substitution/elimination mechanisms under given conditions?

texts:
I'm trying to figure out the major product. At the moment I'm leaning towards an $\mathrm{S_N2}$ reaction, because there's a polar aprotic solvent, and sort of unhindered electrophile. However to me it could just as easily be an $\mathrm{S_N1}$ reaction (electrophile does have some hinderence and there's a weak nucleophile and weak base). $\mathrm{S_N1}$ would attack the tertiary carbocation and $\mathrm{S_N2}$ would go for the primary.

So how do I know if it's $\mathrm{S_N1}$, $\mathrm{S_N2}$, or even $\mathrm{E1}$/$\mathrm{E2}$?

I guess the main question is I don't know if the electrophile is hindered "enough" so we can say that an sn2 reaction is definitely not happening.


texts: Why does sp2 hybridization result in a greater chemical shift in carbon NMR?

texts: Carbon NMR has a very wide chemical shift range. This is attributed to the relative proximity of electron-withdrawing groups (1-2 bonds separation) compared to proton NMR (2-3 bonds separation) along with the hybridization state of the carbon atom (plus other factors such as diamagnetic anisotropy). The reason for the chemical shift difference between proton and carbon NMR due to electron-withdrawing groups is conceptually easy; however, I am having a difficult time understanding why sp2 hybridization results in a greater chemical shift. Hybridization results in smaller, more compact orbitals  (closer to the carbon atom). This is what throws me off. I would expect greater electron density near the carbon atom due to sp2 hybridization to result in a shift upfield (not downfield). Is there any simple explanation for this?


texts: What would a (gas) chromatogram look like if two compounds have the same retention times?

texts:
In gas chromatography, the number of peaks represents the number of compounds in an unknown sample, as retention times for each component differ.
But what would happen if two components have the same exact retention time? Would you see two separate peaks or one?


texts: Equivalent hydrogens in 2,3-dimethylbutane

texts: So while calculating for the relative yield of monochlorination for 2,3-dimethylbutane, I was counting the primary hydrogens, I counted 6, but in fact it was 12. Why is it 12? How do you find equivalent hydrogens? Since the compound is symmetrical doesn't the hydrogens on both sides be equivalent to each other?


texts: The role of halogens in electrophilic aromatic substitution

texts:
I'm trying to understand what halogens do in electrophilic aromatic substitution. Consider the following.

Bromobenzene is introduced to a carbocation. Bromobenzene will likely react, but at a slower rate than unsubstituted benzene, because the bromine is inductively withdrawing. The bromine is also not resonance donating/activating, but can stabilize the intermediate product through resonance donation.

The bromine is an ortho/para director, but not because it donates electron density to these positions. Rather, when bromobenzene attacks a carbocation, the meta positions are formally positive, and through resonance donation, bromine can complete an octet in one of the resonance depictions.

Is this an accurate depiction of what a halogen does to benzene?


texts:
Why is sand that insoluble?

Sand is a polar molecule but does not dissolve in water.
Is it because of the big structure that sand makes?


texts: Allred-Rochow vs Pauling Electronegativity scale

texts:
While observing the trends in electronegativity of the elements, I found a discrepancy between Allred-Rochow and Pauling scales. In Pauling's scale, chlorine is the third most electronegative element ($\ce{F > O > Cl > N}$). In Allred-Rochow's, it is the fourth ($\ce{F > O > N > Cl}$).

While of course the numeric values of the two scales are different, I thought that the rank of the elements would be the same, being electronegativity related to the properties of the atoms (for instance, the partial charge of molecules such as nitrogen trichloride relies on the electronegativity).

So, I was wondering: which scale is more accurate? And, if one is wrong, why are both scales still in use?


texts: Are all concerted electrophilic addition reactions of alkenes syn?

texts:
The Organic Chemistry book I am using (8th edition Carey, et al.) doesn't say it straight out, but I am wondering if it's a universal rule that all concerted electrophilic additions of alkenes are syn.

In every concerted example I have seen so far in the textbook, the bonds that are being made wind up on the same side, but I don't know if it's a rule. For example: epoxidation, transition metal catalyzed hydrogenation, and hydroboration are all concerted and all syn.


texts: Why are NMR typically taken for a power of 2 scans?

texts: Why do we typically take $n^2$ scans, even in the basic NMR experiment? I've heard various explanations, including that it helps the fast Fourier transform, and would like to know the real reason.


texts: Why is the name 'propylene oxide' preferred for epoxypropane?

texts:
This is the molecule I know as epoxypropane:

In my neck of the woods (example), this molecule is used as one of the standard examples of small chiral molecules. The name 'epoxypropane' makes a heck of a lot of sense to me $-$ an epoxy bridge  spanning a single bond of what would otherwise be propane.

It seems, however, that most everyone thinks that a better name for this is propylene oxide, from Wikipedia upwards. Now, I'm an atomic physicist, so bear with me:

I can see how the name 'propylene oxide' fits that structure. You've taken propylene and you've oxidized it.
However, I cannot see why the name 'propylene oxide' doesn't also apply to other ways to oxidize propylene, say, sticking that oxygen over at one end or in the middle,

i.e. what Wikipedia calls propionaldehyde (also propanal) and acetone, or making that bridge over the (1,3) combination in what Wikipedia calls oxetane,

none of which is chiral.

Now, I imagine that IUPAC has all sorts of rules to suss these things out, so:

why is 'propylene oxide' the preferred name for epoxypropane? and
why is epoxypropane the only isomer encompassed by the designation 'propylene oxide'?


texts: I saw somewhere (can't recall where) that KF is the most ionic compound.  I expected CsF.  Does the greater polarizability of Cs allow it to more easily form covalent bonds compared to K?  Does this overcome the fact that K being in n = 4 should bond better with F in n = 2?


texts: Finding the concentration of ferrous thiocyanate in calibration solutions

texts:
Concentration of $\ce{Fe(SCN)^{2+}}$ in calibration solutions

Recall that the concentration of $\ce{Fe(SCN)^{2+}}$ in the calibration solutions is essentially the concentration of the $\ce{SCN-}$ initially in the solution. So, determine the concentration of $\ce{SCN-}$ initially in each of the $\pu{10.0 mL}$ calibration solutions. This is a simple dilution!

The lab checker is saying that this is wrong. Am I even going about doing this problem correctly?


texts: Can x = 1 for a compound of the form x-methyl-3-hexene?

texts:
I came across a question in a textbook Chemistry Live by Declan Kennedy:

Draw the structural formula for the compound 1,3,5-trimethylhex-3-ene.

My issue is with the 1-methyl part. Isn't this compound just the same as 2,4-dimethylhept-3-ene?
I don't think it is a typo as it appears again in an updated version of the same book.


texts: What is the nomenclature of this alkane?

texts:
In this alkane, the blue line is parent chain. It is 12 carbon based.
I wonder why red line cannot be parent chain. It does not compete with blue line about the position of substitution.

And also, i understand 5-isopropyl part but i cannot understand octan-4-yl part. As i learned, when we take substituent part of already substituted part, we take carbon number one on the branch point. So i think this molecule has nomenclature about 6-(1-propylpentyl) but it is wrong. Is there any nomenclature rule that i have missed?


texts:
I'm currently studying some organic chemistry at highschool level. I understand that when naming an organic compound, the names for substituents should be done in alphabetical order. For instance 3-bromo-3,4-dimethylhexane (B in bromo before M in methyl), or 3-chloro-3-ethyl-4-methylhexane (C in chloro before E in ethyl before M in methyl).

However, it doesn't seem to be the same for functional group suffixes. For instance, for one compound I wrote but-1-amin-3-ene, while the correct answer was apparently but-3-en-1-amine. What's more, these are referred to as suffixes, while what I thought was prop-3-amin-1-ol was in fact 3-aminopropan-1-ol.

So is there some kind of pattern or rule as to the order of writing functional group "suffixes" in organic compounds? At first I thought perhaps it follows the priority the groups have over each other in numbering the parent chain carbons (i.e. alcohol > amine > alkene, etc), but this doesn't seem to be it either. It's possible that it'll be explained further on in the course, but I want to make sure I haven't missed anything.


texts:
Are the following structures aromatic?

I have not seen this type of question anywhere so I do not know the answer.
This is just a problem that has been roaming around in my head that I may have seen somewhere.
My approach: since aromaticity leads to stability the carbon-carbon bond in both structure should be polar leading to aromaticity like this:

But this is just a thought and I do not know if it is right.
Is any of the two structures aromatic?


texts: Confusion in solubility expressions in Henry's Law

texts:
While reading about Henry's law and solubility I frequently come across two relations:

$C = k_{h}P$ (c = concentration of a dissolved gas)
$P = k_{h}x$ (x = solubility/mole_fraction)

What is the difference in these two expressions, do they seem to contradict each other? I am not able to decide whether a gas with higher $k_{h}$ would be more soluble or less soluble.
Please help me out with the same I am new to this topic


texts:
Normally, we think of combustion as occurring only in the gas phase. I think I understand the main reason for this - in the gas phase it's very hard for a bimolecular reaction to produce a single product, which makes it more likely for radical chain reactions to propagate rather than being terminated - but I'm curious about whether it's possible for combustion to occur in the liquid state at all.

For example: suppose I mixed liquid $\ce{CH4}$ with liquid $\ce{O2}$ under high pressure and reasonably low temperature. Would they react immediately? If not, could I 'ignite' the mixture in the same way as I could in the gas phase? (Note that the combustion of $\ce{CH4}$ into $\ce{H2O}$ and $\ce{CO2}$ doesn't change the mole number, so the volume change should be relatively small.) Would the reactions that occur be similar to the reactions that occur during combustion of $\ce{CH4}$ in the gas phase, or would they be completely different?

If this reaction wouldn't resemble combustion, is there some other example of a self-propagating oxidation reaction in liquid or aqueous phase with similar properties to combustion?


texts: Question on organic chemistry where we are required to find enol content

texts:
Which of the following compounds is expected to  have maximum enol content in ethanol?
(A) $\ce{CH3COCH2CO2CH3}$
(B) $\ce{CH3COCH2CO2C2H5}$ ✔(I think this is the correct answer)
(C) $\ce{CH3COCH2COCH3}$
(D) $\ce{CH3COCH(CH3)COCH3}$

I think the ketoesters will have greater enol content than the diketones because they have stronger $-I$ effect resulting in greater positive charge on the hydrogen atoms of the $\ce{CH2}$ group in between the ester and ketone group. This leads me to believe the hydrogen will be lost easily. Now between option one and two I think option (A) makes no sense because it will be converted to option (B) via trans esterification, so I have marked option (B). Please let me know where I am going wrong and the correct concept involved if what I think is not right.


texts: What determines the consistency of hydrogen foam when reacting aluminium with sodium hydroxide solution?

texts:
I was using $\ce{NaOH}$ solution to remove hardened grease from my stove burners, and it began to generate a lot of bubbles, some of which merged into a big bubble and erupted into the surface, but most formed a very thick foam.
I left it reacting for a few minutes and it started making way too much foam, about 3 liters of it.
And then I remembered that the burners were cast aluminum, and this should be $\ce{H2}$ foam.
I took a mere spoonful and set it on fire (far from the main pot where I left it) and it produced a very loud and instantaneous bang with a fast flash instead of a slow and fiery deflagration.
This is worrying, that meant the whole foam had a very good hydrogen and air mix, if the whole thing were to explode it would cause at least a hell of a mess and would scare all my neighbors.
I guess not much $\ce{H2}$ escaped into the room, but I thoroughly ventilated the ceiling to remove any accumulated $\ce{H2}$ just in case (after dissolving all the foam in water).
Then I thought to myself, "Why didn't anyone warn me about this explosive foam? Using $\ce{NaOH}$ solution to dissolve grease is so common here".
But I couldn't find any videos on YouTube where $\ce{NaOH + Al}$ resulted in such an explosive and thick foam as mine.
Instead it just bubbles out of the solution, and setting it on fire never resulted in such a crisp bang.
And when people intentionally made foam, they didn't make it like that, instead they bubbled pure $\ce{H2}$ through a soap solution.
But my solution had no soap. Just $\ce{NaOH}$ and the aluminum pieces.
Am I missing something here?
Did the little soap produced by the reaction with the grease made all of that?


texts: Acidity order of xenon fluorides,oxides and oxofluorides

texts:
The acidity order of xenon oxides,fluorides and oxofluorides is:
  $\ce{XeF6 > XeO2F4 > XeO3F2 > XeO4 > XeOF4 > XeF4 > XeO2F2 > XeF3 > XeO3}$.

How to justify this order?

My thoughts were that the acidity order of xenon fluorides, oxides and oxofluorides is based on its tendency to accept an oxide(as these are the most common reactions). As fluorine is more Electronegative than oxygen, we can safely say that $\ce{XeF6}$ would be the most(As $\ce{Xe}$ would be most electron deficient and  can accept an oxide easily). $\ce{XeO2F4}$ would be the second most and the last would be $\ce{XeO3}$, based on number Fluorine+Oxygen atoms, with priority to fluorine. However evidently, "the more number of fluorine atoms" logic doesn't apply to all of them. Looking at the structure of each molecule I'm unable to deduce any logical explanation for the above mentioned order.

Also, I know for a fact that $\ce{XeF6}$ corrodes glass and $\ce{XeF4}$ doesn't. Upto which xenon compound would corrode with glass?


texts: Understanding secular equation derivation

texts:
In many basic derivations of the secular equations for the energy of two molecular orbitals from a linear combination of atomic orbitals, we see the following reasoning which I find confusing.

We have a trial wavefunction $\phi = c_a\psi_a + c_b\psi_b$

The energy of the trial wavefunction is

$$\begin{align} \langle E\rangle &= \frac{\langle \phi | H | \phi \rangle}{\langle \phi | \phi \rangle}\\
&= \frac{c_a^2H_{aa}+2c_a c_b H_{ab} + c_b^2 H_{bb}}{c_a^2 S_{aa} + 2c_a c_b S_{ab} + c_b^2 S_{bb}} \end{align}$$

Where $S_{aa}$ and $S_{bb}$ equal 1. Now per the variational principle, we take the partial derivatives with respect to the coefficients $c_a$ and $c_b$ and set them equal to zero to find the optimal coefficients to minimize $\langle E \rangle$.

But instead, things follow a different route. We take the equation and move the denominator over:

$$
\langle E \rangle (c_a^2 + 2c_a c_b S_{ab} + c_b^2) = {c_a^2H_{aa}+2c_a c_b H_{ab} + c_b^2 H_{bb}}
$$

And then it's stated that this equation is differentiated with respect to $c_a$ and $c_b$ such that

$$
\langle E \rangle(2c_a + 2c_b S_{ab}) + \frac{\partial\langle E\rangle}{\partial c_a} (c_a^2 + 2c_a c_b S_{ab} + c_b^2) = 2c_a H_{aa} + 2c_b H_{ab}
$$

with a similar expression for differentiation wrt $c_b$.

Now the partial derivatives are set to 0, such that you end up with

$$
c_a(H_{aa}-E) + c_b(H_{ab} - ES_{ab}) = 0 \\
c_a(H_{ab}-ES_{ab}) + c_b(H_{bb} - E) = 0
$$

which then you can solve for E.

Is my understanding correct that we've obtained the minimum energies in a single step by first rearranging the equations and then differentiating? Of course we do not obtain values for the coefficients. How is the approach valid?

THe final equations are called the secular equations, which for linear systems isa way of finding the eigenvalues of the system by $A - \lambda I = 0$. But here we have off-diagonal terms $-ES_{ab}$, so I do not see the connection to linear algebra here.


texts: Why Benzene Cannot be chlorinated using HOCl?

texts: Why HOCl doesnt do the job please , can anyone show me the mechanism ?


texts: Oxidation states of Cu in YBa2Cu3O6 based on crystal structure

texts:
How does on go about this? I understand There is a +5 charge distributed on 3 copper ions. So either we have 2+, 2+ and 1+ or 3+, 1+, and 1+. Judging from the structure there are to unequivalent types of Cu ions. But how does one determine which is which and if the formal charges are +2 and +1 or +3 and +1 respectively

Any help is appreciated


texts: How can I update a map/mesh and coordinates in a PyMol session file?

texts:
I have a PyMol session file I was using to create my figures.  It contains a protein and ligand broken into several groups of atoms with a fair bit of overlap.  There are also a few meshes built from a density map for a few figures.

Unfortunately, I wasn't quite done with refinement, and now Refmac has given me shiny new PDB and MTZ files with subtly different coordinates and terms.  Is there a way to "update" my coordinates (despite the myriad groups, all the atoms still have the same name) with the new PDB?  With all the groups I made that are shown/hidden/colored differently for several scenes to produce all the figures, I'd rather not recreate it all manually.

I'm more pessimistic about the map/mesh, but I created them via a script so I can repeat that.  Should I also script the coordinate to figure stuff in the future if it's not finalized?


texts:
I'm currently building a small chemistry lab and I'm wondering about which type of floor would be the best to use. Currently I'm mainly doing electrochemistry experiments with lithium and other metals. Although my interests might change in the future.

I was thinking about ceramic tiles. Since it's not flameable and unreactive. Are there better types of floor for my application ?


texts: Is ground-state structure of a molecule entirely determined by the positions of the nuclei?

texts:
I'm a computer science with only a weak undergraduate chemistry background, but have recently become interested in simulation methods for computational chemistry. Many simulation methods, such as DFT, make the Born-Oppenheimer approximation (nuceli are static) and solve for some properties of the electrons (in the case of DFT, the density). In fact, when using Gaussian-16, I only need to specify the locations of the nuclei in space.

What then, is the role of actual bonds? Are bonds, bond order, etc. just a convenient abstraction for what the electrons are doing? If I tell you the location of some nuclei in 3D, can you then (theoretically) uniquely determine the bond structure?


texts: Why does the reaction between potassium permanganate and oxalic acid result in a yellow/brown solution?

texts:
The reaction between potassium permanganate and oxalic acid is a redox reaction and produces $\ce{Mn^2+}$ ions, the final solution however goes yellow/brown.
If $\ce{Mn^2+}$ ions are colourless, and its complex ions are pink, where does the yellow/brown colour come from?


texts:
What is the rate expression for decomposition of $\ce{H2O2}$ in the presence of a catalyst?

As far as I know for catalase, it is like this: $$\ce{Rate = k[H2O2][Catalase]}$$

I don't know what it is for the catalysts $\ce{MnO2}$ and $\ce{Fe2O3}$. Another question in my mind is that even if it's similar to that of catalase, since these are powdered and so do not have a concentration, how can I express it?

It is kind of emergency so any help would be greatly appreciated.

$$\ce{2H2O2 + Catalyst ->2H2O + O2}$$

I found on web that both reactions are probably (still not sure even though I saw it) first order reactions.

Edit: Is it possible that there shouldn't be anything to be added and it will only affect the $\mathrm{k}$?


texts: How to calculate bicarbonate and carbonate from total alkalinity

texts:
It's been a long time since I did my chemistry classes and I'm currently trying to analyze groundwater samples for hydrogeology purposes. I would like to evaluate carbonate and bicarbonate concentration from groundwater samples, but I only have values of total alkalinity as $\ce{CaCO3}$, $\mathrm{pH}$, and temperature. Is it possible? Some of the $\mathrm{pH}$ values are above 8.3.

I know that:

If $\mathrm{pH}$ is above 8.3: $[\mathrm{alk}_{tot}]=[\ce{HCO3-}]+2[\ce{CO3^2-}]+[\ce{OH-}]-[\ce{H+}]$
If $\mathrm{pH}$ is under 8.3: $[\mathrm{alk}_{tot}]=[\ce{HCO3-}]+[\ce{OH-}]-[\ce{H+}]$

With the $\mathrm{pH}$, I can find calculate $[\ce{OH-}]$ and $[\ce{H+}]$. But how can I calculate $[\ce{HCO3-}]$ and $[\ce{CO3^2-}]$?

Thank you!


texts: What buffering chemical/supplement will reduce lactic acid for runners but not generate $\ce{CO2}$?  Sodium bicarbonate does so but causes gastric upset.


texts: Assigning locants in halo alkanes/alkenes

texts:
In the first example, if you add up the number of carbon which has a substituent, you will get 2+4+4 = 10. However, if you start from left to right, then you'd get 2+2+4=8. Why don't we follow the latter one when it gives us a lower number? (Lowest set of locant rule.)

The same applies for the second problem: we could've gotten 2+3+4, but we chose 2+4+5, why so?


texts: HOBt and DCC in the synthesis of peptides

texts: DCC is a well known reagent used for the synthesis of peptides, aiding the formation of the amide bond by forming an intermediate with the carboxylic acid that contains a leaving group. During my research on the reagent HOBt, or hydroxybenzotriazole, I came across a scheme which showed DCC and HOBt being used in conjunction as a method for peptide synthesis (picture shown below). What is the point of the HOBt being used here? Doesn't the intermediate formed by the DCC molecule already contain a sufficient leaving group?


texts: What is the balanced equation of BH3/THF with an amide to form an amine?

texts: I am doing a green chemistry project as an undergraduate and need the balanced equation to complete the calculations. I cannot find the right information online so any help would be greatly appreciated.


texts:
I'm trying to apply IUPAC rules to name the compound below.

TLDR: Why is this 3-ethyl-2,3,4-trimethylpentane and not 2,3-dimethyl-3-(1-methylethyl)-pentane?

Is this the correct source to use?
According to above, p. 60:

  P-15.1.7.1.4
  The longest chain is numbered from one end to the other by arabic numbers, the direction being chosen so as to give the lower locants to the substituent groups (side chains) [see P-14.4(f)]. The lower set of locants is defined as the set that, when compared term by term with other locant sets cited in order of increasing magnitude, has the lower term at the first point of difference (see P-14.3.5).

The longest chain possible here is a pentane chain, and ChemSketch says that this is 3-ethyl-2,3,4-trimethylpentane.

However, if I want to select the lowest set of locants, wouldn't 2,3-dimethyl-3-(1-methylethyl)-pentane be preferred, as its ordered set (2,3,3) is lower than (2,3,3,4)?
Also, is 1-methylethyl preferable to prop-2-yl?

That doesn't affect 3., as it would be 2,3-dimethyl-3-(prop-2-yl)-pentane.

Am I correct in assuming that prop-2-yl is preferable to isopropyl?

Otherwise, that would make it 2,3-dimethyl-3-isopropylpentane.


texts: Why can't sodium borohydride reduce carboxylic acid and ester groups?

texts:
Sodium borohydride ($\ce{NaBH_4}$) is a reducing agent used in various organic reaction to reduce aldehydes, ketones and acyl chlorides.
Why can't sodium borohydride reduce carboxylic acid groups and esters? Why can it reduce acyl chlorides but not esters, both which are derivatives of the carboxylic acid group?
I read somewhere that it had to do with the oxidizing property of sodium borohydride, but I'm not sure if it is correct or how it explains the same.