texts: How is it that I could obtain endothermic Temperature ~ Time plots for a calculated Exothermic Enthalpy of Solution?

texts:
I recently conducted a coffee-cup calorimetry experiment in which we attempted to measure if the dissolution of inorganic crystals such as LiCl, NaCl, and SrCl were endothermic or exothermic based on a change in temperature over time plot, including measure the enthapy of solutions, but I'm not sure how to do that.

Methods:
We measured 7.9204 grams of SrCl2, 4.2143 grams of LiCl, and 2.9290 grams of NaCl and decanted these into separate coffee cups filled with 50 mL of deionized of water. (These were about 1 - 2 mole/liter solutions.). A temperature probe measured the temperature change over 600 seconds, recording a measurement twice a second. I've only displayed about 140 seconds of the measurement, because the temperature was just continually oscillating 0.1 degree Celsius after that point as it reached equilibrium.

We made plots for each of the chemicals, where an increasing curve shows an exothermic reaction, and an endothermic reaction displays a decreasing curve. Over time, these solutions (Temperature ~ Time) curves should equilibriate to room temperature.

Theoretically, we predicted we could determine if the enthalpy of solution like so ...

Enthalpy of solution = Lattice Enthalpy + (Hydration Enthalpy of cation + Hydration Enthalpy of Anion),

where the Lattice Enthalpy is a measure of the stability of the compound crystal which is at least a function of the charges of the cation and anion, as well as their size, and the structure of the crystal body centered cubic vs face centered cubic, and the hydration enthalpy is the energy it takes to dissolve the gaseous ions after breaking the crystal lattice.

Schematically, the Lattice Enthalpies ( Δ H):
LiCl(s) ----> Li+ (g) + Cl- (g); ΔH = 852 kJ / mole
NaCl(s) ----> Na+ (g) + Cl- (g); Δ H = 787 kJ / mole
SrCl2(s) ---> Sr2+ (g) + 2 Cl- (g); ΔH = 2153

Source:
These Lattice Enthalpies were obtained from Table 18B.4 of my textbook:
Physical Chemistry Thermodynamics, Structure and Change, 10th Edition, VOlume 1, by Peter Atkins & Julio de Paula

Then the Enthalpies of Hydration are these:
Li^(+) (g) ---> Li^(+) (aq); ΔH = -519 kJ / mole
Cl^(-1) (g) ----> Cl^(-1) (aq) ; ΔH = -381 kJ / mole
Na^(+) (g) -------> Na^(+) (aq); ΔH = -409 kJ / mole
Sr^(2+) (g) -------> Sr^(2+) (aq); ΔH = -1443 kJ / mole

Source of Enthalpies of Hydration (Tables 1 - 2):
The Enthalpies of Hydration that I've used are experimental.

Smith, Derek W. "Ionic hydration enthalpies." Journal of Chemical Education 54.9 (1977): 540.

Therefore, the enthalpy of solution for LiCl, NaCl, SrCl2 is this:

For LiCl,

ΔHsolution, LiCl = (852 kJ / mole) + [(-519 kJ / mole) + (-381 kJ / mole)] = -48 kJ / mole < 0, so this reaction should be exothermic and it is as predicted.

For NaCl,

ΔHsolution, NaCl = (787 kJ / mole) + [(-409 kJ / mole) + (-381 kJ / mole)] = -3 kJ / mole < 0, so this reaction should be exothermic.

I've been searching the web about this reaction and most sources say it's endothermic which I my graph shows, but my calculations do not show that. What?

Doing the same kind of mathematics, the Enthalpy of solution for SrCl2 is this:

ΔHsolution, SrCl2 = [2153 + (-1443 - 2 * 381)](kJ / mole)
= -52 kJ / mole < 0, so this reaction should be significantly exothermic.

BUT MY PLOT SHOWS that It's significantly endothermic!
What's going on? Is my mathematics faulty. Am I using too concentrated solutions? Is the SrCl2 that we are using impure or not really SrCl2? I suppose that's possible, but we didn't do any validation because this lab took quite some time. How is it possible that my experiments don't match theory mostly?
Thank you for you for your help.


texts: $\ce{CuCl2}$ is green in colour while $\ce{CuCl}$ is white. What is the reason for this? Is it because the first compound exists as a complex ion and has d-d transitions?


texts: Monobromination of napthalene derivative

texts:
How does this reaction take place? Why does the bromine attach to that one particular location?

I do know that

since is $\ce{FeBr3}$ is present only 1 $\ce{Br}$ will attach
non-substituted areas of benzene will get $\ce{Br}$


texts: Would ionic conduction be halted by shielding at the electrodes?

texts:
I've done this experiment myself and seen it front of my eyes. Set up a basic circuit with a battery, an LED, and connect the circuit with a salt-water solution and copper wire. The LED lights up.
If a potential difference is applied across two ends of the wire with the battery, positive charges move towards the end with lower potential and negative charges towards the higher potential.
Why does this conduction keep continuing? Shouldn't there eventually be a pile up of Na+ and Cl- on opposite ends to cut off the circuit? This is with a typical 9V battery. Is there a teensy bit of electrolysis going on in the wire that continuously supplies electrons to the circuit?
EDIT: In doing my own reading the next day, I seem to have forgotten the very important fact that water itself is electrolyzing at the surface of the electrodes. The salt water only helps to prevent the resulting electrolysis from quickly shielding the electrodes. The reason I was confused was because I was very skeptical of NaCl being electrolyzed and turns out this is exactly not the case


texts: Calculating a theoretical degree of polymerisation of ethylene oxide

texts:
This is the problem: Researchers add 88 grams of ethylene oxide. This reacts fully to 92 grams of poly ethylene oxide. Calculate the degree of polymerisation.

I thought: molecular weight of ethylene oxide is 44 grams. So you have 2 moles in 88 grams and when this polymerizes, you'll get 2 moles of monomers and thus n=2. However, the answer states that n=9.
This is the answer included in the test:

Calculating moles ethylene oxide: 88/44, - 1 point
Concluding that 4 g H20 reacted , - 1 point
Amount of moles formed of poly ethylene oxide (= amount of moles H2O reacted) =   4g H2O / 18, - 1 point
average n = amount of moles ethylene oxide that reacted / amount of moles of poly ethylene oxide formed - 1 point
Concluding that n=9, - 1 point

Thanks alot!


texts: Uranium enrichment via effusion through a porous membrane

texts:
The following problem is from Principles of General Chemistry, Silberberg, 1st edition:

  One way to utilize naturally occurring uranium ($0.72\%$ $\ce{^235U}$ and $99.27\%$ $\ce{^238U}$) as a nuclear fuel is to enrich it (increase its $\ce{^235U}$ content) by allowing gaseous $\ce{UF6}$ to effuse through a porous membrane. From the relative rates of effusion of $\ce{^235UF6}$ and $\ce{^238UF6}$, find the number of steps needed to produce uranium that is $\ce{3.0 mol}\ \%$ $\ce{^235U}$, the enriched fuel used in many nuclear reactors.

Elsewhere in the text the following ratio is given:

  $$\frac{\text{Rate}(\ce{^235UF6})}{\text{Rate}(\ce{^238UF6})} = \sqrt\frac{M(\ce{^238UF6})}{M(\ce{^235UF6})} = 1.0043$$

I've found two different ways to solve this that give different answers.

Solution 1 based on similar problem in LibreTexts Chemistry:

$$\begin{align}
1.0043^n &= \frac{0.030}{0.0072} \\[5pt]
n &= 333
\end{align}$$

Solution 2 based on similar problem in Principles of Modern Chemistry by Oxtoby, Gillis, Butler:

$$\begin{align}
1.0043^n &= \left(\frac{3.0}{97.0}\right) \left(\frac{99.27}{0.72}\right) \\[5pt]
n &= 338
\end{align}$$

Which of these approaches is correct? 2 makes more sense to me but 1 is closer to the answer given in the book (332).


texts: Are the collisions between the real gas particles perfectly elastic?

texts: Well my question is simple, if two real gas particles are colliding (head on collision) then will the kinetic energy will be conserved i.e. will it be a perfectly elastic collisions?


texts: What is the derivation for the expression of depression in freezing point?

texts:
In my textbook, it is written that the expression for depression in freezing point is
$ΔT_{f}=K_{f}m$
But how did this expression come? There is literally no derivation given in my textbook. Can someone please rigorously prove this expression? I am so confused. Please help. (There is also a graph given in my textbook for the derivation; I am not sure if it is a triple phase diagram or not so I did not understand the derivation; Please someone explain).


texts: What are common procedures for lab absorption spectroscopy of gases?

texts:
I'm doing research for applications of absorption spectroscopy. I'm trying to find common practices such as how the gasses are mixed, measured, contained, and discarded.

The gases involved will be those commonly found in the atmosphere or the human body. Top among these will be $\ce{NO2}$, $\ce{CO2}$, and $\ce{CO}$.


texts: Why do hydroxyl ions migrate towards the anode in a Bacon Cell?

texts:
Why do hydroxyl ions in a Bacon cell migrate towards the anode? Is it because of the relative concentration of the different ions in the set-up? According to the set-up of the bacon cell, the anode is negatively charged, thus would actually repel the incoming negative hydroxyl ions, but does not seem to do so. Please let me know if any further details are required.
I read on a wikipedia link explaining cathodes that this kind of migration (i.e negative ions towards a negative electrode) is in fact typical of discharging cells, chemical energy being the driving force behind this sort of "uphill" motion. Could someone please elaborate on this?


texts: Will the motion of particles always increase with the rise of temperature?

texts:
I came across this following question while poring over my textbook.

  Predict the change in the motion of particles you would expect in the following if the temperature was increased:
  a) Solid
  b) Liquid

I think if the temperature increases, solid or even liquid particles will receive more energy and therefore their motion will speed up. I'm not sure why there are two parts for this question. Aren't they supposed to be similar?

Thank you so much for helping! Since this is my first post, please pardon me if I accidentally violate any rules of the forum.


texts: How to melt and roll silver chloride into sheets

texts:
I want to make silver chloride cathodes for a magnesium salt water battery.
Are there any tips on how to proceed?
I hope to melt the silver chloride in a covered ceramic crucible in an electric furnace, then cast a small ingot.
This ingot will be pressed and rolled into a thin sheet.
Silver chloride is nonconductive and is made conductive by superficially reducing the surface to silver by immersion in a photo-graphic developing solution.
By forming a silver outer surface that is porous, no base grid need be used with silver chloride.
Any help or direction to information is appreciated so I don't have to "reinvent the wheel".


texts: Am I using the Nernst equation correctly?

texts:
From my understanding the Nernst equation is

$$E = E^\circ - \frac{RT}{nF}\ln Q$$

Where $Q$ is the reaction quotient.

So for a Daniell cell with copper and zinc (valence of 2) shouldn't the coefficient in front of $\ln Q$ be $0.0128$ at $25\ ^\circ\mathrm{C}$? Everywhere I'm looking the coefficient seems to be $0.0295$ but I can't work out where this number comes from. Could somebody explain this please?


texts:
Does $\ce{PH3}$ exhibit $\ce{sp^3}$ hybridization?

Arguments against hybridization:

$\ce{PH3}$ is less basic than $\ce{NH3}$.
This jibes with the supposition that $\ce{PH3}$ keeps its lone pair in what is essentially an unhybridized $\ce{s}$-orbital.
$\ce{s}$-orbitals are symmetrical and therefore do not concentrate electron density anywhere.
This lack of concentrated electron density as opposed to $\ce{NH3}$ which is $\ce{sp^3}$ hybridized makes $\ce{PH3}$ a poorer base.

However, my professor writes in his book that it can be argued that $\ce{PH3}$ exhibits $\ce{sp^3}$ hybridization.

Another professor told me that the wave function "blows up" when putting an electron pair in an s-orbital. What does that mean?


texts: Is there a way to search for adducts by exact mass?

texts: We found an unknown of exact mass 217.082. Is there a tool that one can search by an exact mass get a list of possible compounds. We have considered desmethylnaproxen as a possibility, but found its mass as 217.086 for the proton adduct.


texts: Is the condenser for a Soxhlet extraction left open on top

texts: My question is about the condenser used in a Soxhlet extractions. It's unusual looking compared to the rest of condensers, used in distillation for example, I've noticed it has a thin and short tube on top and my question is, do one leave it open when performing a Soxhlet extraction or should it be stopped with a stopper or something?


texts: What decides the nature of emulsifying agents?

texts:
I read

  The emulsifying
  agent forms an interfacial film between suspended particles and the
  medium. The principal emulsifying agents for O/W emulsions are
  proteins, gums, natural and synthetic soaps, etc., and for W/O, heavy
  metal salts of fatty acids, long chain alcohols, lampblack, etc.

What specific property of each type of emulsifying agent makes it suitable for the particular application for O/W or W/O emulsion?


texts: What chemical properties of ethanol make it usable for drinks as compared to that of methanol?

texts:
Methanol ($\ce{CH3OH}$) and ethanol ($\ce{C2H5OH}$) both are the organic compounds having an alcoholic group. The alcoholic beverages (liquors and spirits) for human consumption (albeit injurious to health) contain a certain percentage of ethanol but nothing of methanol.
What chemical properties of ethanol ($\ce{C2H5OH}$) make it usable in beverages as compared to those of methanol ($\ce{CH3OH}$)?
EDIT: I am looking for a comparison of chemical properties of ethanol and methanol with respect to suitability for drinks i.e. comparison of their mechanism upon consumption.


texts: Is there a difference between a chelate ligand and a polydentate ligand?

texts: I'm confused because my lecture notes state that chelate ligands are a subset of polydentate ligands.


texts: Why do Hydrogen and Helium have molar volumes higher than an ideal gas?

texts: In my chemistry textbook, there is a table of the molar volumes for different gases. Most of them are below 22.42 l/mol, the ideal gas molar volume, but I noticed that hydrogen and helium do not. Hydrogen is 22.433 l/mol and helium is 22.434 l/mol. Why is this? What makes these particles, with mass, have higher molar volumes than the basically mass-less particles of an ideal gas? And why does the molar volume increase when going from Hydrogen to Helium?


texts: Latimer diagram for a metal in basic solution

texts:
Write the four half cell reactions from the Latimer diagram for a metal $(\ce{M})$ in basic solution.
$$\ce{\overset{+6}{M}O4^2-(aq) ->[\pu{0.25 V}] \overset{+5}{M}O4^3-(aq) ->[\pu{0.55 V}] \overset{+3}{M}O(OH)(s) ->[\pu{0.42 V}] \overset{+2}{M}(OH)2(s) ->[\pu{-0.89 V}] \overset{0}{M}(s)}$$

I can only come up with the first half reaction, which I believe is:
$$\ce{MO4^2- + e- -> MO4^3-}$$
But for the others I'm having trouble with knowing whether the $\ce{MO4^3-}$ will react with water or hydroxide ion to create, for example, $\ce{MO(OH)}?$


texts: In cold countries, it is a common phenomena to add salt to melt or clear snow. However, only specific salts are being commercially. So my question is that why only sodium chloride and $\ce{CaCl2}$ are used for addition to snow, to melt/clear it?


texts: Why does ordinary water have a triple point?

texts:
Triple points and triple lines for pure substances and mixtures

My understanding is that pure substances can have triple points.  But mixtures of substances have triple lines, i.e. there isn't a single point but a one-dimensional path in $PT$ space where three phases can coexist.

This is understanding comes from the Gibbs phase rule that $F = C - P + 2$, where $F$ is the degrees of freedom, $C$ is the number of components, and $P$ is the number of phases.  At a triple point (or triple line) $P = 3$.   For a two-component system like a mixture of ethanol and water, $C = 2$.  If we apply the equation, then we find that in this case, $F = 1$, i.e. there is one degree of freedom.  If we pick $P$ then $T$ is defined for us by the constraints of any two-component, three-phase system.  That's a "triple line".  For a one-component system, the equation says that if $C = 1$ and $P = 3$, then $F = 0$.  A triple point.  We don't get to pick either $P$ or $T$.

Water isn't exactly a pure substance

But, ordinary water is not actually a pure substance.  It is a mixture of different isotopologues, e.g. $\ce{HDO}$ and $\ce{H2^{18}O}$, etc.  It is also a mixture of para- and ortho-isomers that differ only in the relative spin states of the two $\ce{H}$ atoms, as I learned from reading this very site the other day.

Does ordinary water have a triple point?

Pure $\ce{D2O}$ has a triple point distinct from that of $\ce{H2O}$.  For example, one web site says that $\ce{H2O}$ has a triple point of 612 Pa and 0.01 °C, while $\ce{D2O}$ reportedly has a triple point of 661 Pa and 3.82 °C.  But most (all?) water samples in the world are not 100% isotopically pure.  And very little work has been done separating para- and ortho spin isomers of water.

So given that water isn't a pure substance, how does it have a well-defined triple point?  "The" triple point of water was until recently fixed by the definition of SI units, so it seems that for most practical purposes the impurities in water don't matter much.  Why not?  What is the triple point of para-$\ce{H2O}$?  Of ortho-$\ce{H2O}$?  Of para-$\ce{H2^{18}O}$?  Etc. etc. etc.  Why doesn't the phase rule apply to these species?


texts: What is the point of POAC? Why can't one just balance?

texts:
I have been studying the principle of atomic conservation, but have not understood why it even exists. For example:

  What mass of $\ce{O2}$ is produced by 1.23 g of $\ce{KClO3}$?

Couldn't this question be solved very easily by just balancing it, and the using no. of moles to find the mass of $\ce{O2}$ produced?

Am I missing something here?


texts: Finding final temperature for adiabatic expansion

texts:
An ideal gas, molar heat capacity $C_V=\frac{5}{2}R,$ is expanded adiabatically against a constant pressure of $1\ \mathrm{atm}$ until it doubles in volume. Given initial temperature of $25\ \mathrm{^\circ C}$ and initial pressure of $5\ \mathrm{atm}$, calculate final $T$ (etc.).*

The author uses the First Law to calculate $T_2$ as $274\ \mathrm K$.

My question is, why can't we use the relation $T_1V_1^{\gamma-1}=T_2V_2^{\gamma-1}$?

It appears we cannot, since $\gamma =C_p/C_V$ and so, since $V_2=2V_1$, $T_2=274\ \mathrm K$, $T_1=298\ \mathrm K$,

$$\log_2\frac{T_1}{T_2}+1 =\gamma = \frac{C_p}{5/2}\rightarrow C_p\approx 2.8, $$

so assuming $C_p - C_V = R$, giving $C_p = \frac{7}{2}R$, does not seem to work.

Can someone explain why the highlighted equation doesn't apply?

*This is adapted from an example in Castellan, Physical Chemistry.


texts:
I would like to ask about a concentration unit.
What does it exactly mean when stock concentration of something is,
for example, 5X?

Thank you in advance!


texts: Why do some dentists claim mercury "leaks out" of amalgam fillings?

texts: From a chemistry point of view, if dental amalgam is a compound of mercury and other metals, and compounds are elements which are chemically bonded, how would it be possible for mercury to "leak out" of fillings if no further chemical reaction would be taking place?


texts: Homemade spectrophotometer to exemplify Beer-Lamberts law

texts:
I have built a 12-band spectrophotometer, and i'm currently keen on proving Beer-Lamberts law through a small practical example.

The solution that I'm going to test with my spectrophotometer, is orange juice that I thin with water. I naturally know I0 and I1, I.e. the absorption, and the path length that the light has to travel. Meaning that I have 2 unknowns, respectively the concentration and the molar absorptivity.

I am aware that I can figure out the molar absorptivity by doing multiple assays at different concentrations, plot them into a coordinate system and find the slope between the coordinates, which will be equal to epsilon*pathlength.

Unfortunately, I don't know how I find the molarity concentration of the orange juice that I intend investigate. I do however have the weight and the amount. Will that be sufficient to calculate the concentration molarity?


texts: Applying the constant number of electrons in DFT density optimisation

texts:
(Previous related question: Finding mathematically the ground state density in DFT)

I am studying the density optimisation procedure (in particular for Orbital-Free DFT) this thesis.

The derivative of the energy is given as:

$$\frac{\delta E[n(r)]}{\delta n(r)} = v(r) + v_i(r) + \frac{1}{2}(3\pi^2)^{2/3}\left(n(r)\right)^{2/3},$$

where $v(r)$ is the external potential and $v_i(r)$ is the Hartree potential, or electron-electron repulsion.

The chemical potential can thus be obtained after integration:
$$\mu = \frac{1}{V} \int_{\Omega} \frac{\delta E[n(r)]}{\delta n(r)}dr.$$

What confuses me is the next equation, which allows to find the density of the next step $k+1$:
$$n(r)^{(k+1)} = n(r)^{(k)} - t\left(\frac{\delta E[n(r)]}{\delta n(r)} - \mu\right),$$
where $t$ is a step size to help convergence.

If I understand this correctly, $\mu$ is an average variation of energy. The density at a given $r$ is thus varied by the difference between the derivative at that position and the average derivative.

$v(r)$ is a constant for a given position, and $v_i(r)$ depends only on the density, just like the kinetic term above (Thomas-Fermi in this case). It thus seems like the variation of density will never quite get to zero except if the density is exactly the right value to balance the external potential. This seems simplistic and wouldn't explain orbitals beyond the $s$ orbital.

In parallel, I am implementing a simple code for the hydrogen atom, but I can't get anything to converge nor give reasonable values; I must be doing something wrong somewhere.


texts: Stability comparison of benzylic carbocation and benzene

texts:
Which is more stable - benzylic carbocation or benzene - and why?

Benzylic carbocation may have more resonance structure, but these structures are destroying its aromaticity as well. So, how do we compare its stability with benzene?


texts: How can value of acid dissociation constant is vary with concentration of acid?

texts:
First of all I have learned that $K_\mathrm{a} = \frac{[\ce{H+}] [\ce{A-}]} {[\ce{HA}]}$ . Also I have been informed that $K_\mathrm{a}$ value is independent of concentration.

So let us take an example. Suppose 1 mole of acid $\ce{HA}$ dissociates to form 0.9 moles of $\ce{H+}$ ions and 0.9 mole of $\ce{A-}$ ions and 0.1 mole of undissociated $\ce{HA}$. So, the $K_\mathrm{a}$ value will be $K_\mathrm{a} = \frac{[0.9] [0.9]} {[0.1]}=8.1$.

But if we take 2 moles of same acid then, 1.8 moles of H+ ions and 1.8 moles of A- ions will be formed leaving 0.2 moles of undissociated HA. This time $K_\mathrm{a} = \frac{[1.8] [1.8]} {[0.2]}=16.2$.

So we can see that $K_\mathrm{a}$ has increased with increase in concentration. Can you tell me where my assumption is wrong?


texts: I have $\approx\pu{2 g}$ of elemental sulfur that I need to convert to dissolved sulfate in DI water. What's the easiest lab chemistry that will get me there?


texts: Is there a definitive model of the Elements as a Periodic Tetrahedral

texts:
i.e. Is there a specific reason why these diagrams exist? Is the "neatness" of the design simply a graphical representation of the mathematical constants, or is there some underlying reason why a person would envision this?

To be clear: I am asking if there is a physical phenomenon being portrayed or is this just a mathematical trick that is pleasing to the eye?

I have seen several depictions and they vary considerably in their complexity.
Example: https://www.youtube.com/watch?v=f7o0kah6soA

Here is a site that is less of an incoherent jumble of science jargon.
(although it still says nothing about the underlying reason for applying it)
http://weise.symmetry-us.com/pythagorean-approach-in-chemistry-tetrahedron/


texts: Why does basicity of group 15 hydrides decrease down the group?

texts:
In my textbook it is written that the order of basic strength of pnictogen hydrides is

$$\ce{NH3 > PH3 > AsH3 > SbH3 > BiH3}$$

I tried but could not find any explanation as to why this happens. What is the explanation?


texts: Raoult's Law explained with thermodynamics/ free energy

texts:
I got some confusion going on with this explanation of Raoult's  Law.

This is what my book say:

  Because the ideal solution has a higher entropy than the pure solvent, the energy of a vapor increases as its molecules expand into a larger volume, that is, if they are at a lower pressure. Thus, solutes in a solution reduce the vapor pressure of the solvent.

Also, I should mention both solutions have the same $\Delta S$ based on the same $\frac{\Delta H}{T}$.

The point is I am confused about the last part of this explanation about how molecules expand. First off, this is all in a closed container, otherwise there's no vapor pressure. If so, the volume should be the same there is no larger or smaller volume.


texts: Why does boron add to the less substituted carbon in the hydroboration of an alkene?

texts:
In the hydroboration of a typical alkene, the boron fragment ends up attached to the less substituted carbon:

What are the electronic or steric factors that lead to this regioselectivity?


texts: Trial by fire: Safely heating sand without it agglomerating?

texts:
Wikipidia quotes a melting point of 1713C for sand.
I went on the beach to get some sand. I assume it's a mix of all kinds of stuff.
The finality is to prepare a big pile of clean sand to use as filtering aid above paper filter (among other uses).
I'd like to get rid of plastics & organics by heating it up.
What temperature can I bring it up to before the smallest particles start to agglomerate? What temperature would you recommend for pyrolysing as much of everything in there that is not SiO2 such that it either degrades or later more easily disssolves in water?


texts: Electron-donating trends for ligands bound to metal complexes

texts:
Imagine an inorganic complex with a bunch of terminal ligands. All else the same, would $\ce{F-}$ or $\ce{Br-}$ ligands be more electron-donating and why?

Of course, in terms of $\mathrm{p}K_{\mathrm{a}}$, $\ce{F-}$ is more basic than $\ce{Br-}$, predominantly due to the smaller size of the $\ce{F-}$ anion. I have also read in multiple places that the $\mathrm{p}K_{\mathrm{a}}$ trends can be used to describe Lewis acidity/basicity trends, although it's not immediately clear to me why this is true. If one takes the prior statement at face-value, then it appears that that $\ce{F-}$ is more Lewis basic and, by the very definition of a Lewis base, is more electron-donating than $\ce{Br-}$. However, why would $\ce{F-}$ be more electron-donating if its electronegativity is higher than $\ce{Br-}$? These two points seem paradoxical.

For full context, I am trying to understand why $\ce{F-}$ would be better at stabilizing higher oxidation states of metals in inorganic complexes than $\ce{Br-}$, which based on the literature appears to be related to the electron-donating strength of the ligands (with more electron-donating ligands increasing the stability of higher oxidation states).


texts:
This paper describes the measurement of streaming potential using a potential divider configuration. However it is unclear where the potential difference is created. From the diagram it appears that it is created across the length of the flow channel, so at one side there is a low potential and the other a high potential. However this doesn't seem to agree with the description of streaming potential. From other sources it appears that the potential difference is across the outside of the flow channel near the surfaces, to the inner middle of the flow channel (at the point furthest away from the surface). Which is correct?

EDIT: there isn't a tag for electro-chemistry, so I have just put this under battery chemistry. However this is not necessarily for a battery.


texts:
I really don't know anything about chemistry, but I was wondering about the following vague question: has any substance been created that does not contain any metallic elements, but is metallic?  In fact, the only nonelemental metals I know of are alloys, so I may as well ask whether we have ever created any metallic compounds, with or without metallic constituents (without preferred).  Both Wikipedia and the tag wiki here claim that metallic compounds do exist but don't give examples.

My vague understanding of what makes an element metallic is that it has something to do with the sharing of electron clouds between atoms, and this question is motivated by wondering whether this kind of quantum effect can be induced from nothing in an appropriately constructed molecule.


texts: Why does glass shatter when heat is applied to it?

texts: When I poured hot tea into a cup, the cup shattered after about three seconds. The cup was made of glass. It was pretty thin. How did the glass and the tea react in terms of chemicals. This is a bit odd because wasn't heat applied to sand in order to make glass, shouldn't the glass break up into the reactants that made it?


texts: Finding the kp with density, temperature, and pressure

texts:
Consider the following reaction
$$\ce{3O2(g) <=> 2O3(g)}$$
At $\pu{175°C}$ and a pressure of $\pu{128Torr}$, and equilibrium mixture of $\ce{O2}$ and $\ce{O3}$ has a density of $\pu{0.168g/L}$. Calculate $K_p$ for the above reaction at $\pu{175°C}$.

I used the ideal gas law $pV=nRT,$ $K_p=K_c(RT)^n$, and $\rho=M \times c$ but I am not certain what to do after finding the total $c$ of the reaction. I was thinking of using the ICE chart to find the concentration of reactant and products which will lead to the $K_c$ and then $K_p$ value but since I don't know the initial concentration of $\ce{O2}$ I end up with an equation with two variables.
I was thinking of using the density to find the molar mass of the reaction and then somehow the  weight of $\ce{O2}$ and $\ce{O3}$ in grams but it seems like a stretch.
$$pV=nRT$$
$$T=175\ \mathrm{^\circ C}=448\ \mathrm K$$
$$p=128\ \mathrm{Torr}=0.1684\ \mathrm{atm}$$
$$0.0821=\frac nV\times\left(0.0821\ \mathrm{\frac{atm\ l}{K\ mol}}\times448\ \mathrm K\right)$$
$$0.0821=\frac nV\times36.78\ \mathrm{\frac{atm\ l}{mol}}$$
$$\frac nV=0.00457\ \mathrm{\frac{mol}l}=c$$
$$ \begin{bmatrix}
  & \ce{3O2} & \ce{2O3} \\
  \mathrm I & y & 0 \\
  \mathrm C & -3x  & 2x \\
  \mathrm E & y-3x & 2x
 \end{bmatrix}0.00457\ \mathrm{mol/l}=(y-3x)+2x$$


texts: Is the effect of hydroperoxyl radicals significant in the oxidation of organic compounds in the Fenton reaction? Why or why not?

texts:
In the Fenton reaction, a ferrous catalyst and hydrogen peroxide are used to generate hydroxyl radicals which in turn oxidise organic compounds. The reaction is commonly seen in the treatment of wastewater and operates using the following mechanism:

  $$
\begin{align}
\ce{Fe^2+ + H2O2 &-> Fe^3+ + ^.OH + OH-}\tag{1}\\
\ce{Fe^3+ + H2O2 &-> Fe^2+ + ^.OOH + H+}\tag{2}\\
\ce{Fe^3+ + ^.OOH &-> Fe^2+ + H+ + O2}\tag{3}\\
\ce{RH + ^.OH &-> H2O + R^{.}}\quad\text{(chain propagation)}\tag{4}\\
\ce{R^. + Fe^3+ &-> R+ + Fe^2+}\tag{5}\\
\ce{R^. + H2O2 &-> ROH + ^.OH}\tag{6}
\end{align}
$$

In the reactions, hydroperoxyl radicals $(\ce{^.OOH})$ are produced as a byproduct of the reduction of the ferrous catalyst, among other reactions. However, literature regarding the impact of the hydroperoxyl radical on the oxidation of organic compounds is limited, with most papers ignoring the effect of the hydroperoxyl radical completely. So, is the effect of the hydroperoxyl radical significant in the oxidation of organic compounds? Why or why not?


texts: Reactivity towards nucleophillic addition

texts:
Phenyl ethanal or ethanal

I thought phenyl methanal is less reactive towards nucleophilic attack due to presence of bulky group. But answer in my book suggest ethanal is less reactive.

Para-methoxybenzaldehyde vs para-methylbenzaldehyde.

in this case due to the prescence of $\ce{OCH3}$ $\ce{O}$ will act as an electron withdrawing group as well as electron donating (resonace) whereas $\ce{CH3}$ group will only donate it's electron (resonance) thus para-methoxybenzaldehyde  should be more reactive. Again, the answer in my book states para-methylbenzaldehyde is more reactive.


texts: Is selenium disulfide polar or non-polar?

texts:
So I saw in some internet site that $\ce{SeS2}$ is a polar molecule. When I drew the Lewis structure of the molecule, it showed up as a linear molecule like this:
$$\ce{S=Se=S}$$
The electronegativity difference of $\ce{Se-S}$ is just $0.01$ and the linear form shows that vectors cancel each other. Yet, some websites state that this molecule is polar, when everything to me indicates is a non-polar molecule.
Are they wrong or am I missing something here?


texts: Is it possible for the remaining solute of a saturated solution to form a single even phase from top to bottom (similar to that of a colloid)?

texts: If a solute that dissolves in a liquid solvent has reached high enough levels to cause saturation within the solution, is it possible for the remaining solute particles to form an evenly distributed phase from top to bottom similar to that of a colloid (where settling would not occur or take very long to occur)? I realize behavior varies depending on the solute and solvent in question, I am just curious if this is possible. Thanks so much!


texts: Why several of isomers of octane such as 2,3-dimethylhexane and 2,4-dimethylhexane doesn't have a value for melting point from any databases?

texts: This is a very rough data (as shown below) I have collected from CRC Handbook of Chemistry and Physics 93rd edition in black and ChemSpider in blue. As you can see, I am not quite done, but I was wondering why several of the isomers of octane such as 2,3-dimethylhexane and 2,4-dimethylhexane doesn't have a value for melting point from both databases? (I have tried searching up the melting point for each on a reliable database and have come up with no value given. Wikipedia does give a melting point, but I am very cautious about using that data as it does not a source to prove it.


texts: What does the "s" mean in s-cis and s-trans conformations

texts:
I am learning about conjugated unsaturated systems, and came upon s-cis and s-trans conformations in conjugated dienes.

So what does the "s" mean in s-cis and s-trans conformations?


texts: Discussion about Warren-Cowely Parameter

texts:
The Warren-Cowely Parameter (WCP) for short range solution order is defined as:
$$\mathrm{WCP}_{ij} = 1 - \frac{Z_{ij}}{x_j \cdot Z_i}$$

where $Z_{ij}$ is the partial Coordination Number (CN) of  j atoms around i, $Z_{i}$ is the total CN around i, and $ x_{j}$ is the nominal composition of j.

Consider a two component solution of $\ce{A}$ and $\ce{B}$.  If $\mathrm{WCP}>0$, like neighbors are preferred, If $\mathrm{WCP}<0$, unlike neighbors are preferred.

If both of $\mathrm{WCP}_{AA}$ and $\mathrm{WCP}_{BB}$ are positive, which one is preferred?


texts: Why do some solvents bubble more than others when boiling?

texts:
This question about boiling milk reminded me of my everyday lab work at the rotavap: Some solvents and solutes are feared for the intense bubbling they create while the solution is boiling — be it at ambient pressure like the milk or at reduced pressure in the rotavap. For most of the infamous solvents, the bubbles will even create a somewhat stable foam (that usually ends up on the wrong side of the rotavap).

Well known in my lab are dissolved triphenylphosphane and the solvent toluene while isohexane (‘mixture of hexane isomers including methylcyclopentane’) is known to hardly ever give bubbles.

Why is this so? Why are bubbles often so much more stable even for just a solvent (toluene)?


texts: Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?

texts: My chemistry book explains that even though electrons in the $\mathrm{2p}$ orbital are closer to the nucleus on average, electrons from the $\mathrm{2s}$ orbital spend a very short time very close to the nucleus (penetration), so it has a lower energy. Why does this tiny amount of time spent close to the nucleus make such a big difference? It seems like it should be the average distance that matters, not the smallest distance achieved at any one point, in determining stability. What makes that momentary drop in energy so important that it is outweighs all the time spent farther away from the nucleus with a higher energy?


texts: Is Body Centred Cubic arrangement also a kind of packing in solids?

texts:
I am confused about the packing thing in solids . I read about Hexagonal Closed packing(HCP) and Cubic closed packing(CCP) then realised this stuff named as Body Centred Cubic(BCC) under the heading of "Arrangement in solids" . Now what is the real difference between packing and arrangement? After all they are arranged in 3d and finally form a crystal

IT would be very kind if someone can clear my doubt... :)


texts: What defines basis sets in computational chemistry?

texts:
I have a simple question about the Linear Combination of Atomic Orbitals (LCAO):

$$
\psi_{i} = \sum_{r} c_{ir} \phi_{r}
$$

where

$\{\psi\}$: Set of molecular orbitals
$\{c\}$: Set of coefficients
$\{\phi\}$: Set of atomic orbitals

When we talk about basis sets, do we mean here the coefficients or the atomic functions?


texts: The following picture is from E. V. Anslyn Physical Organic Chemistry and shows constructing of MO of methyl using QMOT. MOs $\textbf{E'}$ and $\textbf{D'}$ are formed by mixing $\textbf{D}$ and $\textbf{E}$. I can't quite imagine how the mixing goes here.


texts: Why is ΔS the same regardless of whether a process is irreversible or reversible?

texts:
Why do we take the entropy change of the system to be the same in both irreversible and reversible processes? What is the idea behind this?

It would be nice if anyone could give me an example with some data.


texts: Can energy savings be estimated from activation energy differences?

texts:
Imagine two companies X and Y. Both companies use very similar technical equipment to carry out a biotechnological process where a chemical reaction is catalyzed by an enzyme. Company X uses an enzyme with a reaction barrier of, say, 15 kcal/mol, while company Y uses a slightly different enzyme to catalyze the same reaction but this enzyme has an activation energy of only 12 kcal/mol.
The reaction energies in the two reactors are, obviously, the same since both companies do $\ce{A} \rightarrow \ce{B}$. Still, as I see it, company X has to input 3 kcal per mole of product more into activating the enzyme.

Does company Y therefore require 3 kcal less energy to produce 1 mole of product?


texts: In the molecular structure of a DNA it is seen that purines (adenine and guanine) bind with pyrimidines (cytosine, uracil and thymine) through hydrogen bonds, and this is always between a purine and a pyrimidine. Can't there ever be hydrogen bonds between 2 purines or between 2 pyrimidines?


texts:
One base is bulkier than the other, that's my observation. How does it affect the product? Could someone please give proper reasoning and the product? Thanks a lot.

P.S.
I guess both follow E2


texts: Why does cyclopropane react with bromine?

texts:
In my exam, I was asked why cyclopropane could decolourise bromine water (indicating that it reacted with the bromine).

All I could guess was that it is related to the high angle strain in cyclopropane, as the C–C–C bond angle is $60^\circ$ instead of the required $109.5^\circ$. No book I have read mentions this reaction. What is the product formed, and why does it occur?


texts: How to rationalise the difference in halogen bonding?

texts:
Can anyone explain the difference in halogen bonding to me. I understand the explanation in (c). It appears to me, that accepting that would contradict the answers to parts (a), (b), and (c).
Is the reason for part (a) because the first molecule does not have resonance and for (b) the $\ce{F3C-I}$ molecule has a larger inductive effect? If so, that would not make sense for (c) to be correct.


texts: Is volume expansion possible upon dissolution of solute?

texts:
I am aware that there is volume reduction upon dissolution of ionic solutes, due to the formation of hydrated spheres of aqueous ions where water molecules aggregate around the solute ions.

But similarly could there be a volume expansion?


texts: Stereoselectivity of ring closure in intramolecular iodolactonisation

texts:
What is the product of the reaction above?

I am mainly confused between the following two options:

How do we decide the resulting stereochemistry of the $\ce{CH_2I}$ group?
The answer given is the one in which $\ce{CH_2-I}$ is coming out of the plane, i.e. (a).


texts: Most economical method to convert potassium oxide to potassium nitride.

texts:
I have a compound potassium oxide($\ce{K2O}$) and I am trying to convert it into potassium nitride ($\ce{K3N}$).
Here are a few possible reaction methods :

Split potassium oxide into the constituent elements potassium and oxygen  (Not very good  as a lot of energy is required)
$\ce{K2O + N2 -> K3N + O2}$ (however this won't happen(?) because nitrogen has a lower electronegativity value than oxygen does)

and so on.

Does anyone know how can I convert the oxide to the nitride, releasing oxygen in the process, by not having to use a lot of energy-requiring processes?


texts:
I'm reasonably unfamiliar with chemical notation, and recently I've come across something I'm not sure how to interpret.  In this article, the authors refer to the "surface groups" denoted by $\ce{#Ti-F}$ and $\ce{#Ti-OH}$.

Similarly, this article refers to surface functional groups $\ce{#Si-O-}$ and $\ce{#Si-OH}$.

To my (limited) knowledge, "$\ce{#}$" denotes a triple bond.  If this is the case, what am I to take from this?  Are they referring to a (triple) dangling bond, or is this some notation I'm not familiar with to denote surface species?  The first page of the first article does state that "$\ce{#Ti-X}$" refers to surface species, but I'm finding it difficult to believe the notation was chosen arbitrarily.

I appreciate any explanation.  As I've said, I am a novice with chemistry and chemical notation.


texts: How does the acidity of soft drinks not affect certain drugs, such as opiates? What about drugs and stomach acid?

texts:
Here's a very random introduction. I heard the term, "dirty Sprite" (it's some rap album/slang term) on a YouTube advertisement. I Googled "dirty Sprite", and it's apparently a recreational drug: codeine syrup in Sprite lemon-lime soda. People allegedly get high off of it, meaning the opiates in codeine is metabolized properly. My question is, how does harsh acidity of the Sprite (pH of 3.4-3.8 if you trust Google) not interfere with the codeine structure and mitigate its metabolism?

Then, this turned into a meta philosophical question: how does the acidity of the stomach, which is more acidic than Sprite, not interfere with not only codeine, but other substances?


texts: Relation between the number of hybridised orbitals and the number of sigma bonds

texts:
March's Advanced Organic Chemistry (8th Ed.), has in its first chapter several tantalizing statements of the following variety;

Boron has only three valence electrons available to form bonds, hence the valence of 3. Any hybridization model must take this into account.

If ethene is examined... each carbon has three σ bonds, one to
each of the three atoms. Therefore, sp2 orbitals are used to form those three bonds.

When carbon is connected to another carbon atom by a triple bond, as in ethyne... each carbon is connected to only two other
atoms by a σ bond and hence uses sp hybridization.

The key is to understand that an atom forms two σ bonds for sp hybridization and three σ bonds for sp2 hybridization.

From reading that section, I  understood the author's technique of determining hybridisation as;

You call those bonds that form when there's maximum overlap between the bonding orbitals "sigma bonds" , and such initial bonds that form while using the author's method, are arranged so that they do so at max overlap(the atoms are arranged in space so as to have such a configuration).
You make a bond each between the central atom and the others this way, and the remaining orbitals, if any contain electrons left over, interact to form pi bonds(and they're not sigma bonds because in the simple molecules examined, these leftover electrons aren't in orbitals that overlap terribly well. So you make a name for them-pi bonds- and say they interact in the way they do).

Now, all these statements seem to border on stating that the number of sigma bonds formed and the number of hybridised orbitals are the same, and that kind of makes sense to me. By the method of determining hybridisation (detailed above as I understood it), $\pi$-bonds seem to be defined to be those that're formed from unhybridised orbitals.
But the author never makes such a statement. And it's a chemistry textbook. Cue the alarm bells in my head.
On looking it up, there isn't any statement on the internet of that sort, either, except for this Quora thread where the general consensus seems to be that yeah, pi bonds can be formed from hybridised orbitals. But I don't get how.
Is there any such rule? If not, why?


texts: how protons(H+) react with matter and cause the solution to be acid?

texts: For example if my hands were put in a HCl solution how does the protons in the solution which in high amounts will interfere/react with my hand(skin->proteins..) and cause it to burn...or how protons react with a plastic bag and cause it to melt.


texts: How does one recognized Td/Oh symmetry in molecules?

texts:
The identification of point groups of a molecule is usually done following a strict scheme, either manually or algorithmically. In all textbooks I could find, however, the first step of the scheme is actually not explicited: in this example scheme drawn from Housecroft and Sharpe,

you can see that there is a very unhelpful step “Does this molecule have $I_h$, $O_h$ or $T_d$ symmetry?”. It is implied that one would recognize e.g. an icosahedral molecular compound on sight. However, I wonder: how can one strictly identify these “special” point groups? What set of rules is to be followed (again, either manually or algorithmically)?


texts: How does turbidity affect dissolved oxygen?

texts:
I have to do a EEI for school about turbiduty of water and finding the most cost effective method for purifying a sample of water. My group was planning to do a standard test where we use materials such as filter paper, cloth, sand, gravel, etc. and run the turbid water through it. As our school has no turbidometers we wanted a way to have some quantitative data. To do this we were planning on conducting a dissolved oxygen test (wrinklers method) as we found some sources linking turbidity to oxygen levels. Would this be a valid test? Would the filtered water need to sit overnight, for example, before we tested the DO?

And help is appreciated!!!


texts:
My high-school chemistry teacher taught us the mantra "bases are slippery-soapy-slimy!"

This question and this answer in Quora say this is due to saponification - conversion of lipids from the top layer dead skin cells into a soap-like substance.

During some household cleaning I ended up with a small amount of a fairly strong solution of bleach in water between my thumb and forefinger and noticed it felt quite slippery, and it took several seconds of rubbing under water for it to stop.

In this case I would guess that saponification is not the explanation for the very slippery feeling. Is there another explanation?


texts:
I got how the real pressure would be less than ideal pressure due to net force of attraction between gas molecules acting towards the center.
But, why is the real volume greater than ideal volume? I thought the real volume would be less than ideal one since the ideal volume is the volume of container (volume of gas particles negligible) while the real volume is the available volume for gases to move excluding their individual volumes i.e. Vi = Vr + volume of gas particles


texts: What organic molecules have a relatively small work function, preferably in the visible spectrum? Polycyclic aromatic hydrocarbons are in the low UV spectrum, making it unsuitable for the photocathode requirement. A work function in the green-cyan spectrum, or anything below3 eV is the main focus. Efficiency, thermal stability, etc is not the main focus for the time being


texts: How does pH of soda drink vary with time

texts:
Basically I have done an experiment where I measure the pH of my soda drink at a specific temperature over $\pu{45 min}$. At every temperature, the $\mathrm{pH}$ of my soda drink increases, but much faster for higher temperatures.

For instance, I measured at $\pu{25 ^\circ C}$ how fast the pH increases of my soda drink over $\pu{45 min}$. Next I measured at $\pu{35 ^\circ C}$ how fast the $\mathrm{pH}$ increases of my soda drink over $\pu{45 min}$. Continued for the next 4 temperatures.

I plotted the graph of how $\mathrm{pH}$ increases with time for 6 temperatures (getting me 6 graphs), but I have difficulty finding out the relationship I have is linear or exponential. The current trend I have only seems to be linear from the $\pu{45 min}$ time period I performed my experiment for, but I was wondering, if it just looks linear because my experiment was faulty, or it is actually supposed to be linear in relationship. I basically do not know if there is a theory which states that the relationship I am looking for is or is not linear.

I will appreciate the assistance.


texts: Why Na+ ion is discharged at cathode rather than H+ ion when Mercury is used as cathode in electrolysis of aqueous NaCl solution ?


texts: Expressing solubility in binary solvents with non-additive volumes

texts:
I have experimentally obtained data that shows the molarity of a saturated solution   in mixed solvents, with different proportions of solvents.

The issue here is that the two solvents (water/ethanol) have non-additive volumes, and expressing the solubility as $\mathrm{mol}$ $\mathrm{L^{-1}}$ thus seems a bit odd, especially when comparing solubilities between different solvent ratios. Would mole fraction be a better alternative? If so, why? And is it possible to convert from the "old" amount-per-volume answer to the new, better one?

Also, I include a graphical representation of my results, with solvent composition on the x-axis and solubility on the y-axis. Would it be appropriate to use mole fraction (or whatever other unit is better suited) on both axes: the mole fraction of solvents on the x-axis and that of the solute in the mixed solvent on the y-axis?


texts: Reagent choice in the formation of Wittig reagent

texts:
During the formation of Wittig reagent, BuLi is used as it is a VERY strong base (pKa = 50). According to Wikipedia, however, sulfur ylide is 'especially conveniently' made from dimsyl anion (pKa = 35), which is a relatively weaker base although it is also used for preparation of Wittig reagent.
If there is a stronger base is allowed (BuLi), why is dimsyl anion used 'conveniently'? To prevent side reactions or just by what is available at hand?

Typically phosphorus ylids are made from PPh3. What is the purpose of having 3 phenyl groups linked to the phosphorus atom in Wittig reagent? Can't be as small as sulfonium ylide molecule? I have no idea what is the use of adding 3 bulky and sterically-hindered groups in the ylide.


texts: What is the maximum number of electrons that can be found in an atom when its last electron has the following quantum numbers?

texts:
The question is as follows:

  What is the maximum number of electrons that can be found in an atom when its last electron has the following quantum numbers: $n=4, m_{l}=+3$

Since $m_{l}=+3$ I know that $l=3$ and then I wrote them all:
$$1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2, 3d^{10}, 4p^6, 5s^2, 4d^{10}, 5p^6, 6s^2, 4f^{14}$$
which means that the maximum number of electrons is $70$, but the actual configuration in the answer was:
$$1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 4s^2, 3d^{10}, 4p^6, 5s^2, 4d^{10}, 5p^6, 6s^2, 5d^1, 4f^{14}$$
which means that the maximum number of electrons is 71. What didn't I count for?


texts: Which gas is a oxidizing agent as well as a reducing agent?

texts:
I think it's Hydrogen, because,

$\ce{PbO + H2 -> Pb + H2O}$

Here $\ce{PbO}$ is reduced to $\ce{Pb}$ and $\ce{H2}$ acts as a reducing agent.

But, in $\ce{2K + H2 -> 2KH}$, hydrogen gains a electron and undergoes reduction
Thus, $\ce{K}$ is oxidized to $\ce{KH}$ and hydrogen works as oxidizing agent.

My teacher says it's wrong but doesn't give any explanation.

Can someone explain why my reasoning is wrong.


texts: Why does bromine react with iron(II) but not iodine?

texts:
My question comes from the answer (C) to this question:

Firstly, (correct me if I'm wrong please) I thought that the answer could either be C or D since the other answers are negative ions which can't react with iodine or bromine since they (as diatomic molecules) have a full shell of outer electrons. Now, from looking at the question, I knew it had something to do with oxidation and reduction as well as displacement reactions, however, as iodine and bromine aren't on the reactivity series, we can't determine which would react with which metal. From there, I just had no more ideas. Could anyone provide me with a hint or a guide as to how to do this ?


texts: How do I control the negative temperature in an experiment?

texts:
If one were to adjust the positive temperature in an experiment, they would use a heating plate, or a stovetop.

How would one adjust negative temperatures in an experiment? (Not keeping the temperature constant, but decreasing and increasing the temperature at my will in specific amounts).

What I tried so far: "Spraying" liquid nitrogen at my work surface until it cools to the desired temperature.  It is really inaccurate though.


texts: When a candle burns, why does the top of wick glow if bottom of flame is hottest?

texts:
Totally an elementary question.

Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest.

Is the reason for this that the concentration of liquid wax is greater at the bottom, offsetting the greater temperature at the bottom?


texts:
As we all know that there are 5 tastes : sweet, sour, bitter, umami, salty.
So what chemicals are there that help form these tastes, in other words how do our tastebuds experience these tastes?

Also can there be more tastes than these basic five. I am not saying that there should be a blend of these to make a taste but rather are there any other undiscovered tastes?

Maybe we haven't tasted them yet?


texts: Which dicarboxylic acid has the most acidic hydrogen?

texts:
Which of the following acids (maleic, fumaric, succinic, or malonic) has the most acidic hydrogen?

I think that malonic acid should have the most acidic hydrogen due to the presence of an active methylene group.
The extraction of hydrogen atom from malonic acid would lead to high resonance stabilization, which is not the case in other acids.
However the answer key says that maleic acid has the most acidic hydrogen. Can someone please explain it to me why?


texts:
I do not fully understand the idea of coupling and why chemically equivalent hydrogens do not couple.

I wanted to work with the alkanes, so let's take propane first:

There would be a triplet signal due to the $\ce{CH3}$ groups in blue and green, due to the $n+1$ rule for neighbouring protons, so the neigbouring carbon for the two $\ce{CH3}$ groups would be the $\ce{CH2}$ group circle in red.

Then the $\ce{CH2}$ group in red would have a septet signal due to the two surrounding $\ce{CH3}$ groups is what I would predict.

Moving on to butane, this is where I get more confused:

For the $\ce{CH3}$ group in blue, there would be a triplet signal due to the neighbouring $\ce{CH2}$ in red, and the same can be said for the $\ce{CH3}$ in black.

Then for the $\ce{CH2}$ groups, I am not exactly sure what would happen but here is what I think:

The $\ce{CH2}$ group in red will have a quartet signal on the NMR spectrum because equivalent hydrogens do not couple and so the $\ce{CH2}$ will not couple with the green $\ce{CH2}$ group. This means that only the $\ce{CH3}$ group will couple. Using the $n+1$ rule, a quartet will be present and the same can be said for the $\ce{CH2}$ group in green. However, I think that the red $\ce{CH2}$ will have a triplet of quartets or a multiplet if that is correct, with the same being said for the green $\ce{CH2}$ group.

I would like to extend this further to pentane, which I am also confused about. Can this be clarified with the two examples above so that I can attempt to do pentane myself?


texts: Is home synthesis of cellulose acetate possible, and why?

texts:
Is it remotely possible to synthesize detectable quantities of cellulose acetate from materials available in common department stores (such as cotton balls, vinegar, and battery acid) and using tools available in a home kitchen (such as ovens, stoves, freezers, glass jars, and metal pots)?  If so, how would the reagents need to be pre-processed, and what would the procedure be?  If not, where do the insurmountable difficulties lie?

On a webpage titled "From Cotton to Cellulose Acetate" it is indicated that, in general, cellulose acetate is manufactured from specially prepared cellulose in a solution of 100% acetic acid with acetic anhydride.  That same site goes on to specifically state that immersing cotton balls in vinegar will only result in "cotton balls that smell like pickles".  Other sources add concentrated sulfuric acid into the mix.  And an answer to another question on the Chemistry SE indicates that household vinegar could possibly be concentrated up to 58% using fractional freezing in a kitchen freezer.

It's difficult to tell from the sources available whether making homemade cellulose acetate is completely impossible, somewhat inconvenient, surprisingly hazardous, or merely commercially unviable.


texts: What do you get when you melt and solidify sand?

texts: Would you get something brittle like glass or something like granite?


texts: Salt concentration and electrical permittivity of water

texts:
We know that the electric flux density $D$ can be related to electric field intensity $E$ as

$$D = \epsilon(\omega) E$$

where

$$\epsilon(\omega) = \epsilon_0 \epsilon_r(\omega)$$

and $\epsilon_0$ is the permittivity of vacuum and $\epsilon_r(\omega)$ is the relative permittivity of the material.

At the low-frequency limit, I would like to know how the value of $\epsilon_r (\omega)$ of water changes with temperature and salt ($\ce{NaCl}$) concentration. Please explain,

the rationale of the variation (from quantum mechanics or statistical mechanics etc)
observed trend holds good for any liquid or only for highly polar solvents
any references that you know of which talks in detail about these variations


texts: Fluorescent polycarbonate changing optical qualities after melting

texts:
So I'm trying to figure out how to melt fluorescent poly without it changing. What it's doing after it's melted, under UV it's fluorescing a sort of opaque white instead of it's original color. Keep in mind that normally fluorescent acrylics look almost the same under UV as they do in daylight, just a little more brilliant. However after I melt the stuff I get this opaque white crap. Could someone point me in a direction to look for answers as to what's happening, why it's happening, and how to avoid it?
Thanks a heap

About how fluorescent poly is supposed to look under UV:


texts:
In a reaction between $\ce{R-OH}$ and $\ce{Br2}$, what will the product be?
Initially I thought it would be $\ce{R-Br}$, but that doesn't seem right.

I'm oscillating between the product being either $\ce{R-OBr}$ or no reaction occurring at all. I've searched a bit on the web too, but couldn't get an answer.

What is the product?


texts:
There is a common belief that Peanut Butter can dissolve certain types of glue. I've tested it and it does on a few common stickers. A forensic science crime procedural TV show (Bones) made a statement that

  The oils in the peanut butter will break down the cohesion of the cyanoacrylates.

The most common cyanoacrylates based glue is Super Glue, which hardens quickly.

How does Peanut Butter interact chemically with the CA glue and why? Does it make a difference when the CA has hardened or not?


texts: Mechansim of reaction between 1‐bromo‐2‐fluorobenzene and furan in the presence of Li/Hg

texts:
Problem
From FITJEE AITS test series:

What is the mechanism of the following reaction?

Solution

My approach
It looks like Birch reduction with $\ce{Li}$ converting to $\ce{Li+}.$ But I can't make anything much out it.
Maybe there's a typo given in solution because $\ce{Br}$ and $\ce{F}$ should be present initially, or do they get removed by any means?


texts: How can carbon dioxide be converted into carbon and oxygen?

texts:
How can $\ce{CO2}$ be converted into carbon and oxygen?

$$\ce{CO2 -> C + O2}$$

Alternatively:

$$\ce{CO2 + ? -> C + O2}$$

I'm aware that plants are capable of transforming $\ce{CO2 + H2O}$ to glucose and oxygen via photosynthesis, but I'm interested in chemical or physical means rather than biological.


texts: Why aren't there any triangular molecules?

texts:
Look at the molecular structure of benzene:

It's a perfect hexagon. Why aren't there any molecules arranged in a triangular fashion with bonds forming the edges and the molecules the vertices? Or, for that matter, square molecules? And what about other n-gonal molecules? octagons?


texts:
$\ce{BF3}$ can react with $\ce{F-}$ to give $\ce{BF4-}$ where we have for $\ce{B}$ in this molecule the 2s orbital and the three 2p orbitals  filled totally (hybrid orbitals).

In case of $\ce{NH3}$ we have the 2s orbitals and the three 2p orbitals of $\ce{N}$ filled;

So i am asking this: can the hydride ion $\ce{H-}$ make a dative bond with the 3s orbital of $\ce{N}$ (which is vacant) to form $\ce{NH4-}$? If not, why?


texts: Where does the RT term come from in the derivation for the activation enthalpy from the Eyring equation?

texts: It is easy to show an Arrhenius-like equation from the Eyring equation, but if you do this, you get that the activation energy is about equal to the activation enthalpy. However, the real approximation is that $E_\mathrm{a} = \Delta H^\ddagger + RT$. Why is this?


texts: How are standard bond enthalpy values experimentally produced?

texts: The question's essentially it. I've always wondered about how these values are produced, since we refer to them heaps in the lab to assess our experimental results, but I don't actually know how they're produced.


texts: stone which turns to black on exposing to atmosphere?

texts: My mom is using a stone like substance as a dye for hair recommended by a herbalist. That stone becomes black when exposed to air. Do you know which compound is this?


texts: Does combustion occur more easily at higher oxygen concentrations or just higher oxygen partial pressure?

texts:
I saw a trailer for The Martian and started thinking about space flight.  I know that spacecraft and spacesuits often operate at low pressure with high oxygen content (near 100% $\ce{O2}$ at about 20 kPa), which is harmless to humans and keeps the mass of the space vehicle lower.  Humans do just fine with an oxygen partial pressure of 20-30 kPa as long as other gases present are in safe amounts.

But an issue I hadn't considered is the effect on combustion.  A lot of people mistakenly believe that the Apollo 1 fire was due to using pure oxygen in the test, but that's only part of the issue, and astronauts routinely use nearly pure oxygen at low pressure even today.

So my question is, is flammability affected by the total concentration of oxygen in the atmosphere, just its partial pressure, or some combination of the two?

As a specific example, what affect would a 30 kPa almost pure oxygen atmosphere have on flammability?


texts: When is it true that more nodes equals higher energy?

texts:
Consider all the MOs of some isolated molecule. (It could be a single
atom too; I'll use MO to refer to AOs as well.) Number them in
increasing order of the number of nodes (node = surface where the wave
function has zero density). Orbitals with the same number of nodes can
be numbered in any order. Now you have a sequence of orbitals $O_1,
O_2, ...$. Let their respective energies be $E_1, E_2, ...$.

It seems to be "common knowledge" that $E_n \le E_{n+1}$ for any such
system and any $n$. As Martin put it to me yesterday, "An orbital
with 47 nodes can never be lower in energy than one with only 46." (Follow up on Counting Nodal Planes in cyclopropane.)

For various reasons, given below, I think this cannot be true in
general, and I'd really like to know under what conditions it is
known to be true. "Known" here can mean either a rigorous statement
with a reference to a proof (a trivial example would be: It is true
for a one-electron atom; we can calculate the energies exactly) or a
precise statement with empirical justification (something like "no
counterexamples are known for class X of molecules" - again with a
reference).

Important: Please, I'm not looking for an explanation that re-states
the rule in some equivalent or even looser fashion ("more nodes means
the orbital is larger and less dense, therefore it must be higher in
energy").

Why do I think the statement can't be always true? Well, a calcium
atom has a filled 4s orbital and empty 3d orbitals. If this does not
count as a counterexample, please explain what notion of orbital
energy the statement applies to.

In general, I'm happy to believe that two MOs must satisfy the rule if
they have "comparable" sets of nodes (say, constant $n_x$ and $n_y$ in the
example I'm about to discuss), but I'd like to understand what is
meant by "comparable" in general. In a molecule with no symmetry, are
there comparable MOs at all? If so, how do we know if two given MOs
are comparable?

The case of a much simpler system, the 3D rectangular box, may
also be relevant.  The energy levels for such a box are of course
$$
\frac{\hbar^2\pi^2}{2m}\biggl(
\frac{n_x^2}{L_x^2}+
\frac{n_y^2}{L_y^2}+
\frac{n_z^2}{L_z^2}
\biggr),
$$
where $n_x$, $n_y$ and $n_z$ are one more (or one less, if you count
the walls) than the number of nodal planes in the respective
direction. If we take $L_x = L_y = 1$ and $L_z = 0.1$ (say), the
wavefunction with $n_x=5$, $n_y=1$, $n_z =1$ has energy $5^2+ 1^2 +
(1/0.1)^2 = 126$ and 4 nodes (or 10, if you count the walls), while
the wavefunction for $n_x=1$, $n_y=1$, $n_z=2$ has energy $402$ and 1
node (or 7). So clearly the rule is not true here.

Granted that molecules are not boxes, but this does show that
arguments based simply on the number of sign changes are not rigorous,
so they don't answer my question.


texts: When there's a photoelectric effect, do the electrons leave altogether or leave one by one?

texts: When a strong light, or even a laser, hits a metal surface or some molecules, and causes lots of electrons to fly away, do the electrons leave together, or do some of them leave first? If it's the latter, then do the valence electrons leave first and then inner layers? If so, how long are the intervals between their leavings?


texts: Is sublimation a property of all substances?

texts:
I wonder if sublimation can be done only on certain substances like iodine, or it can be done on all substances.

In other words, can sublimation be done, for example, on water? If it cannot, then why?


texts: Can I synthesize iron acetate like this?

texts:
The oxidation state of the iron doesn't matter too much; I am just trying to make an attractive red-brown ink. Here are some instructions I prescribed to a friend.

  Here's an approximately decent iron acetate recipe. I don't know if it'll work, though. Maybe you'll want to heat the acetic acid. The optional first step is to oxidize the iron by hydrogen peroxide or by heating in air. Pour enough heated acid to corrode the iron plenty. Wait. Filter what is now the aqueous solution of iron acetate and acetic acid through some filter paper to remove the undissolved iron. Let the (I hope so) red-brown solution dry: this is because you want to evaporate the acetic acid. When it is dry, you may dissolve what I hope to be a dark red-brown powder in as little distilled water as possible and some alcohol if you so desire. Adjust dilution to suit your hue/shading preference.

Would this synthesize iron (I or preferably II) acetate?


texts:
I'd want to implement SCF method using Modern Quantum Chemistry (Szabo). But when I want to calculate overlap matrix for H2 (STO-3G basis) my results aren't equal to true overlap matrix that there's in the book. However when I compare my results in other basis (STO-1G) I get exact overlap matrix. Below my code for calculation overlap values.

class gauss():

  def __init__(self, alpha, Ra, k = 1):

    self.alpha = alpha
    self.Ra = np.array(Ra)
    self.k = k

  def __mul__(self, other):
    'calculate integral'
    lenght = (self.Ra - other.Ra)
    scalar = np.dot(lenght, lenght)

    return np.exp(-self.alpha*other.alpha*scalar/(self.alpha + other.alpha))*np.pi/(self.alpha + other.alpha)**(3/2)

def overlap(first, second):

  s11 = 0
  for i in first:
    for j in first:

        s11 += i * j * i.k * j.k

  s12 = 0
  for i in first:
    for j in second:

        s12 += i * j * i.k * j.k

  return s11, s12

## gaussian primitives:
s1 = gauss(0.168855404, (0.0, 0.0, 0.0), 0.444634542)
s2 = gauss(0.623913730, (0.0, 0.0, 0.0), 0.535328142)
s3 = gauss(3.42525091, (0.0, 0.0, 0.0), 0.154328967)
s1b = gauss(0.168855404, (1.4, 0.0, 0.0), 0.444634542)
s2b = gauss(0.623913730, (1.4, 0.0, 0.0), 0.535328142)
s3b = gauss(3.42525091, (1.4, 0.0, 0.0), 0.154328967)

first = [s1, s2, s3]
second = [s1b, s2b, s3b]

s11, s12 = overlap(first, second)

print(s12 / s11) # print normalized s12

  0.781180936263708

but exact value from book = 0.6593 (1.4 Bohr)

and if I choose basis as:

s = gauss(0.4166127, (0.0, 0.0, 0.0))
sb = gauss(0.4166127, (1.4, 0.0, 0.0))

I get exact value:

  0.6647924143035879

from book: 0.6648


texts: What is this fluorinated organic substance?

texts: The corresponding author of the paper where this formula was published as appendix passed away. Can someone help me with identifying what is the name of this compound and why have strange zig-zag between Nitrogens


texts:
This is a very basic question and I'm surprised it only just struck me. The nature of the bond in coordination complexes is a coordinate covalent bond. Only the ligand donates electrons for bond formation between the metal and ligand.

Why is it that we never place a positive charge on the ligands? For example, in $\ce{[Pt(NH3)5Cl]Br3}$, $\ce{NH3}$ is attached to three Hydrogens and the lone pair is donated for forming the coordinate bond. So there should be a positive charge on $\ce{NH3}$, right?


texts: How do I start studying chemical nomenclature?

texts: Chemical nomenclature seems to be the way chemistry "talks", allied with the mathemathics. But where to start?... and what reasons and theories are behind? Some "names" come from latin... I know there are rules IUPAC etc, but it is so demanding and exaustive to learn all that rules at once, for organic and inorganic chemistry. Maybe there are reasons and rules that help us to name a chemical or compound... Since I am interested in metallurgy, can you give me some advice to start? To associate theory to the formula, ad strutural formula, it would be nice. The implicit "why" in everthing included is always welcome.


texts: Effect of magnetism on dissolved Na+ and Cl- ions in water

texts:
Suppose we have put some salt in water. My state of knowledge is, that a hydration envelope is formed from the oxygen side of the water molecules on the Na+-Ions and one another from the hydrogen side of the water molecules on the (Cl-)-Ions to drag these out of the crystal.
My questions now are:

When the hydration envelope is formed on the ions, does it (partially) change the charge of the ions?

(Now the main question) If I would put two magnets with opposite poles on both sides of the container, in which the salt solution is, would the ions be pulled to the side of the opposite pole, (if yes or no, then why)?

I made a little sketch an let the hydration envelope out for the sake of the little place.
And one another thing. There is no reason to downvote my question, because I am not playing around here, but the question just jumped in my head


texts: What makes certain zeolites better at ion exchange?

texts:
I would have thought that the bigger the pores in the zeolite, the more ions it can contain, and therefore the better the use of the zeolite for ion exchange.

However, zeolite A has small pores but its main use is as an ion exchanger, as opposed to many other zeolites which have larger pores but are not used as ion exchangers.

Therefore, why are some zeolites better than others at ion exchange? Or, what influences the ion exchange capabilities of zeolites beyond pore size?


texts: Isoelectric point pH, mV, for a metal oxide nanopowder

texts:
I'm trying to make a solution of $\ce{TiO2}$ that will coat stuff in as dense a monolayer as possible.  To do so, I'm using nano sized $\ce{TiO}$ particles and trying to get them to get as close to each other as possible.  From what I understand, the way to get these little guys to get close to each other is to get the solution to its isoelectric point thereby eliminating any repulsion caused by charge.

So: what pH should I set my water and $\ce{TiO2}$ powder at to attain my isoelectric point?  I ask because finding such a number has proven to be elusive.  I've found pH numbers from 3.8 to 9 to attain isolectricity for such a solution.  Does anyone have any experience with the stuff such that a true pH to attain isoelectricity revealed?

In addition, the meter to which I have access for pH also measures mV.  Is there a way to relate mV to the isoelectric point?  Is it as obvious as it seems i.e. keeping adding an acid until my little meter says that mV equals zero?  Or is there something more going on (there always is)?  Are this mV value and the isoelectric point even related?

Thanks for any help!


texts: Chair conformation. Wedged lines vs no wedged lines?

texts: As the title suggests, I have been wondering why some chair conformations utilize wedged lines for some of the bonds while others have regular thin lines for all bonds, you can take cyclohexane as an example.


texts: Why does radical chlorination and bromination of propane occur at different positions?

texts: When propane reacts with chlorine, we will mostly (theoretically) get an isomer with a chlorine on the end. ($\ce{CH_3-CH_2-CH_2Cl}$). However, when propane reacts with bromine, we will mostly get an isomer with bromine attached to the second carbon ($\ce{CH_3-CHBr-CH_3}$). Could anyone please explain why this happens?


texts: Does optical isomerism fall under the category of stereoisomerism?

texts:
I have been asked to find the total number of dichlorination products (including stereoisomers) for the following reaction:

I have figured out nine possible structures out of which two are optically active.
Should I count the additional six isomers (three for each of the optically active structures - RR, RS, SS)?
I am confused about whether to count the optical isomers or not.
Please provide clarification on this.


texts: Can hydride shift and methyl shift happen one after another in a carbocation?

texts:
Can a hydride shift be followed by a methyl shift for stabilizing a carbocation?
In case both are possible, which will occur first?


texts: Significant figure rules when plugging a value into an equation or formula

texts:
I have not been able to find an answer to what may be a silly question so I am asking it on here as a last resort.

If I am to plug in say a number like 14.0 Celsius into the formula that solves for temperature in Fahrenheit.  So I would do 9/5 times 14.0 to get 25.2.  When I then add the 25.2 to 32 does the rule for addition matter here?

Would the answer be 57.2 or 57?

Is there a general rule for when I am plugging in a measured value into a formula that is given to me?  I believe that only the measured values are significant and all numbers in the formula are exact with infinite significant digits.


texts: Minimum heating temperature for dehydration of Cobalt Chloride

texts: I've been looking on line and have found several sources that state 100°C for a rapid dehydration of cobalt chloride in its various forms. I'm wondering if that's a minimum, or would it be possible to dehydrate it at a much lower temperature, provided ambient humidity is controlled.


texts: LCAO (Linear Combination of Atomic Orbitals) and Phases

texts: So when combining atomic orbitals to form molecular orbitals, you can either add the wave functions or subtract them. But at the same time, orbitals can exist in opposite phases (say one lobe of the p orbital is '+' and the other '-'). So what happens when you subtract two 1s orbitals of opposite phase, is that the same thing as constructively interference of the wave functions?


texts:
If $125$ Calories of heat is applied to $60.0\text{g}$ piece of copper at $21.0^\circ\text{C}$, what will the final temperature be? The specific head of copper is $0.0920 \text{ cal/gC}$.

All I have to answer this question is a formula:

$SH = \text{heat/(mass}\times \Delta T)$


texts: Kinetics of air evolving from water on heating

texts:
Is there a simple relationship describing the kinetics of air evolving from water on heating?

For example, if I let water at room temperature and pressure saturate with air, it should have some concentration. Then, if I heat that water up to 90°C, the solubility of air will be much lower by Henry's law. The evolution of air is, presumably, not instantaneous. Is it fast or slow compared to a reasonable heating rate? Does it depend on just how far the system is from equilibrium or on other conditions like the amount of air-water surface boundary?


texts: Why cannot the Schrödinger equation be solved exactly for systems in which more than two particles interact?

texts:
Is it so because it is impossible to solve mathematically? If so, why? Or is it possible to solve the equation mathematically, but no physical interpretation of the solutions is possible? Or is it because of practical issues, i.e. exact solutions would require more computer power than we have available today?

Several books state that the Schrödinger equation can only be solved exactly for systems of maximum two interacting particles, but fail to explain why. For example, Andrew R. Leach mentions the impossibility, but fails to elaborate on why that is so, in his "Molecular Modelling: Principles and Applications" (2nd ed., page 34).

If the answer could be explained in terms that a new master student in theoretical chemistry would understand, that would be great!


texts: Why is carbon monoxide the product in reactions that produce high flame temperatures?

texts:
I was looking at substances that produce the highest flame temperatures upon combustion. I note that the equations for combustion are producing carbon monoxide rather than carbon dioxide.

$$\ce{(CN)2 + O2 -> 2CO + N2}$$

Why isn't carbon dioxide produced? Why doesn't the production of carbon dioxide give a hotter flame? It seems that a higher flame temperature would be generated by complete combustion. My thinking is that the heat of formation of carbon dioxide is around −400 kJ/mol while the heat of formation of carbon monoxide is around −100 kJ/mol so the additional heat released by producing carbon dioxide should account for carbon dioxide's greater heat capacity.


texts: Why are actinides not commonly included in rare earth metals?

texts:
According to the German Wikipedia, the rare earth metals include all elements of the third side group except actinium, and all lanthanides.

  Zu den Metallen der Seltenen Erden gehören die chemischen Elemente der 3. Nebengruppe des Periodensystems (mit Ausnahme des Actiniums) und die Lanthanoide – insgesamt also 17 Elemente.

https://de.wikipedia.org/wiki/Metalle_der_Seltenen_Erden

Since actinides (like lanthanides) should be part of the third side group, why aren't they considered part of the rare earth metals?


texts: I mixed L Arginine with l Citrulline in Hibiscus and green tea water which was red in color. Once the red liquid hit the mix of powdered Aminoacids the solution changed green. Can someone tell me why? Thanks so much for any info!


texts: How can isotope labelling be used to determine the mechanism of ether cleavage with hydrogen iodide?

texts:
When methyl tert-butyl ether (MTBE) is treated with one equivalent of hydrogen iodide, the ether C–O bond is cleaved.

I read that if the oxygen in MTBE is isotopically labelled, it is possible to work out the mechanism, but I am not able to understand the function of $\ce{^{18}O}$.

$$\ce{CH3-^{18}O-C(CH3)3 + HI ->[S_N1/S_N2] products}$$

How does isotopic labelling help determining the mechanism?


texts: How to make sure molded silicone rubber adheres to the ABS mold?

texts:
For one of my experiments I need to coat a 3D printed ABS part with a thin layer of silicon rubber:

Basically I want to make sure the molded silicon will adhere to one mold (the negative side in the picture above) but not the other. I'm using V-SURE SILICONE NL Standaard from VOSSCHEMIE BENELUX :

To ensure the positive side will be realised after rubberisation I use the realise agent V-SURE TRENNSPRAY 400 GR from the same company:

I was wondering if there is anything similar for adhesion. Something like a spray glue or something I can smear with a brush. Thanks for your help in advance.

P.S.

I have absolutely no idea what are the products I'm using. I just bought them in a local shop for sculpting. I tried translating the website or googling the names with no good results. It would be also a great help if you could help me know what is the official/scientific names of the mentioned products.
I'm not able to find the right tags for this post. I would appreciate if the moderators could guide me with that.
I have also posted this question on Reddit (molding, modelmakers and ResinCasting)
Maybe there are other moldable ruberry materials which have a better adherence to ABS? Any other type of flexible, wear resistance and strong rubber will do. For example I have seen lots of tinkers all over the internet using Caulk mixed with some moist absorbent powder (e.g. cornstarch) and oil, or soaked in water+soap.
Surprisingly the silicon sticks firmly to the glass beaker. I can't even remove it with a cutter!


texts: Why do DMSO and acetone have such radically different melting temperatures?

texts:
DMSO and acetone have almost identical structures, except for us replacing the carbonyl carbon with sulfur to obtain DMSO. DMSO's melting point is $19~\mathrm{^\circ C}$, whereas acetone's is $-95\ \mathrm{^\circ C}$.

Is the dominant factor DMSO's larger molecular weight? Probably not. While acetone is $58\ \mathrm{g/mol}$ vs. DMSO's $78\ \mathrm{g/mol}$, 2-pentanone is $86\ \mathrm{g/mol}$, but still has a very low melting temperature of $-77\ \mathrm{^\circ C}$.

The only protons on all of these species are aliphatic, so hydrogen bonding is probably not the dominant contributor to this effect either.

What's going on?


texts: Parietal cells in the stomach are known to expel $\ce{H+}$ ions into the gastric juice to keep the pH acidic. When $\ce{H+}$ $\ce{[H3O+]}$ can fully function as acid in the gastric juice, why do cells combine $\ce{Cl-}$ to form $\ce{HCl}$ in the stomach?


texts: Is there a better coordinate framework and symmetry operator for constructing molecular orbitals of molecules with higher-order geometry?

texts:
The following excerpt is taken from [1] (with a few rewording, emphasizes are mine).

In an attempt to construct molecular orbital (MO) of any molecule, one needs to determine the symmetries of possible symmetry-adapted linear combinations (SALCs) that are formed from pendant-atom atomic orbitals. This prequisite can be proceeded with following steps:

Use directional properties (i.e. vectors) of orbitals on the outer atoms as a basis for a representation of the SALCs in the point group of the molecule.
Generate a reducible representation for all possible SALCs by noting whether vectors are shifted or not by each class of operations of the group.
Decompose the representation into its component (irreducible representations) to determine the symmetry species of the SALCs.

So far, I have practiced of constructing MOs of several molecules having simple geometry (low-order molecules) e.g. $\ce{H2O}$, $\ce{NH3}$, and others but I am worry with higher-order molecules, particularly adamantane, $\ce{Re2Cl8}$ cluster, arachno-$\ce{B4H10}$, and others.
I want to accomplish those tasks with hands and pens. I know there are several softwares where one can draw the molecules, assign the point group, and draw the molecular orbital but here, I want to know the process behind it and I want to figure it without using any software, so I am alright if the tasks will be very exhaustive and tedious. I want to know if there exists any method to simplify the process. At there, I want to ask several questions as below.
On the first step above from the excerpt, to generate group orbitals based on the representation of basic symmetry requirements, I am getting difficult with the natural way to place several atoms on Cartesian coordinate and I am wondering if there is any applicable projection or cartography that can ease up the process of generating the coordinates because most molecules are not planar. There are some books that present $\ce{CH4}$ molecule in a cubic framework which can ease the assignment of the coordinates for the atoms but I can not find any evidence of placing those higher-order molecules on polyhedral framework (perhaps like Bravais lattices that I can define the unit cells and so on). I got several papers of how these molecules had processed on the softwares but it turned out that the molecules were having coordinates that I worry I will get sloppy when I need to symmetrize it again. Is there any literature that can deal with this problem?
For the second step from the excerpt, is there a generator or a (matrix) operator that can ease up the process? Most matrices I found are already worked in backward process, that after visual inspection of symmetry operation, then the matrices were generated, which is totally very useless to me in this case. If this exists, it would be very relieving because so far I can not find any digestable mathematical method (not visual inspection) or algorithm that can perform such symmetry operations on those higher-order molecules.
Thank you.
P.S.: If possible, please illustrate your answers like a student trying to understand and answer the problems so I can work on those molecules later. Use molecules that are not as simple as water but not fullerene (small cluster molecules that are on par with molecules that I will work on) because most papers give examples of the latter one that I feel too strenuous to draw it with hands and pens.
References

Carter, R. L. Molecular Symmetry and Group Theory (Wiley, 1998).


texts: Can someone intuitively explain the reason for the units of entropy (J/K )?

texts: If entropy is just a measure of the "randomness" or "chaos" of a system, then why does it have specific units. What is the reason behind the units of entropy being J/K?


texts:
I am familiar with the process of IR spectroscopy and the preparation of IR samples.

However, I am curious as to why you cannot use hygroscopic or protic solvents for IR spectroscopy. Is it just because it dissolves the cell (KBr/NaCl), or does it give an OH peak, or are there other reasons?

And are there any protocols that allow you to use water as a solvent for obtaining an IR spectrum?


texts: How do you find the pH of a solution with a known pKa and Molarity?


texts: How does one create a "product-favored reaction equilibrium"?

texts:
For the following reaction equilibrium, which of the following actions
  would not only temporarily increase the yield of product, but also
  result in a more product-favored reaction equilibrium overall (i.e.,
  increase the Keq)?

  $\ce{2A(s) + 3B(g) ↔ A2B3(g)}$

  ΔH = −50 kJ/mol

  (1)  compressing (decreasing the volume of) the reaction vessel and
  increasing the temperature

  Correct answer: (2)  compressing (decreasing the volume of) the
  reaction vessel and decreasing the temperature

  (3)  expanding (increasing the volume of) the reaction vessel and
  increasing the temperature

  (4)  expanding (increasing the volume of) the reaction vessel and
  decreasing the temperature

  Wrong answer I'm curious about: (5)  increasing the amount of A(s)
  and decreasing the temperature

I know that increasing the amount of A(s) will not affect the equilibrium because it is a solid and solids exist at a constant concentration in general, so we ignore them in equilibrium constants.

I think that there are actually two parts to this question:

  For the following reaction equilibrium, which of the following actions
  would not only temporarily increase the yield of product, but also
  result in a more product-favored reaction equilibrium overall (i.e.,
  increase the Keq)?

To temporarily increase the yield, we must increase the pressure/decrease the volume of the container. But to actually change the K so that it is increased, we must change the temperature. Since this reaction is exothermic, decreasing the temperature will do the trick.

Is my reasoning valid?


texts: Would ABS plastic degrade in a dishwasher?

texts:
I printed an object with a 3D printer and I used a roll of light green ABS plastic filament.

I would like to use the dishwasher to clean it. The temperature would be kept below 70°C, well below the glass transition temperature of about 110°C.

The dishwasher uses standard tabs, not one of the phosphate-free tabs.

What would be the effect of said cleaning on objects made of ABS plastic?


texts: Order of internal pressure resistance to expect from laboratory glassware?

texts:
I have a need to use more pressure differential than can be afforded by vacuum vs atmospheric pressure alone, and so I've come to consider using pressurised laboratory glassware for part of my setup.

I've made a little bit of research here on stack-exchange and on google and the general information I've gathered is that the physical shape of laboratory glassware and reaction vessel lends better to resisting external pressure (when we use them with internal vacuum), than to resisting internal pressure, though I'm left wondering what to expect to be doable in terms of pressurising glassware.

I have two pieces of glassware I'm considering using on the pressurised end of my setup: One is a 5,000mL flat bottom flask and the other is a 20,000mL flat bottom flask. Both are borosilicate glass, neither are perfect (they both have one or two tiny air bubbles in the glass at places) but both have shown very good resistance while being used with internal vacuum.

Is it realistic to expect them to be fine while adding an internal pressure up to 3 Bars? (I would put the glassware inside of a big metal cylinder for safety in case of "explosion")

What will be the best Resistance vs Glassware Shape / Glassware Volume / Temperature / etc. ?

Does anyone have any tips on the topic?


texts: How to find the temperature change of a solution?

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Right now I'm doing a calorimetry lab and for the pre-lab we have been asked to determine the temperature change (in Celsius) of ammonium chloride in water.

The question asks for the expected temperature change ($\Delta T$) of $\pu{8.5 g}$ of $\ce{NH4Cl}$ in $\pu{100 mL}$ (or $\mathrm{g}$) of water, with the molar enthalpy ($\Delta H_\mathrm{sol}$) of the solution being $\pu{0.277 kJ/g}$. The conversion of $\mathrm{kJ/g}$ is throwing me off and I cannot figure out how to solve for $\Delta T$ with the given info.

I know that there are $0.165048...$ moles of solution, which gives me everything I need to solve. We were given the equation

$$n \Delta H_\mathrm{sol} = mC \Delta T,$$

where $m$ - mass of water and $C$ - specific heat capacity of water. I am assuming it needs to be rearranged to

$$\Delta T = \frac{mC}{n\Delta H_\mathrm{sol}}$$

Any help is greatly appreciated and I can explain in further detail if necessary. Sorry for the Celsius, we apparently don't use Kelvin in our calculations.


texts: Lack of polysubstitution in Friedel–Crafts t-butylation of phenol

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According to our lab manual:

In general, Friedel–Crafts alkylation is not employed to make monoalkyl benzene derivatives because of the polysubstitution.

But our professor told us that while we are doing this experiment, polysubstitution is quite impossible.

I know the when the electrophile is bigger and amounts are exact, it is harder for polysubstitution to occur but not impossible.
So I wonder if the reason why she said that, is about chemical properties of the reagents (like being activating) or is it something about the method we use in the experiment?


texts: Writing the overall cell reaction for the Calomel electrode

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I an studying about electrochemical cells, and came across the Calomel electrode. It turns out that the half cell reactions and the overall reaction are as follows.
Anode half-cell: $\text{Hg}_{2}\text{Cl}_{2}\rightarrow \text{Hg}_{2}^{2+}+2\text{Cl}^{-}$
Cathode half-cell: $\text{Hg}_{2}^{2+}+2e^{-}\rightarrow 2\text{Hg}$
Overall cell reaction: $\text{Hg}_{2}\text{Cl}_{2}+2e^{-}\rightarrow 2\text{Hg}+2\text{Cl}^{-}$
I am not sure why while writing the overall reaction, the electron was not gotten rid of. Besides why is there no net exchange of an electron in the anode half-cell reaction. Clarification would be appreciated. Thanks.


texts: Why do Bence-Jones proteins behave differently in urine heat test?

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The preliminary test for proteinuria (proteins in urine) is precipitation/turbidity on heat due to denaturation. This turbidity should not disappear when 10% acetic acid is added - to differentiate from phosphates.
Bence-Jones proteinuria is found in multiple myeloma and they are light chains of IgG and are definitely proteins! They have this unusual behaviour, i quote,

  Bence-Jones proteins are light chains of γ-globulin. These are excreted in multiple myeloma and other parapro- teinaemias. In heat and acetic acid test performed under temperature control, these proteins are precipitated at lower temperature ($\mathrm{56\ ^\circ C}$) and disappear on further heating above $\mathrm{90\ ^\circ C}$ but reappear on cooling to lower temperature again.

How is this behaviour explained?


texts: What is the significance of an organic compound's M peak?

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Background

On the topic of identifying an organic compounds using peaks generated in Mass Spectrometry, a rule of thumb expressed in the UK educational textbook, CGP, is that that "the M peak is the one with the second highest mass/charge ratio".

Question

What is the significance of this M peak anyway?


texts: Have P-acyl phosphines ever been synthesized?

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I've done some amount of searching and can't seem to find any evidence in the literature that there exists a phosphine analogue of carboxyl amides. I'm looking for compounds of the form $ \ce{ R(C=O)PR_{2}} $; basically a moeity similar to a primary or secondy amide but with a phosphorous atom instead of a nitrogen.

I would also wonder what the proper name for these functionalities would be. Taking a shot in the dark I might guess "phosphomide", "acyl phosphine", or "acyl phosphinide".

I would like to specifically disqualify Acyl-phosphine oxides or any compounds where the acyl-connected phosphorous is also connected to an oxygen.


texts: How is antioxidant activity of carotenoids determined?

texts: I am doing some research regarding carotenoids and beta-carotene. After extracting the sample, I have not been able to find a way to measure antioxidant activity of beta-carotene. I have $\pu{0.1mM}$ of DPPH (2,2-diphenyl-1-picrylhydrazyl) solution dissolved in methanol, but I just read that you cannot use DPPH to measure beta-carotene free radical inhibition. Is this true? How should I go about doing this?


texts: I read that the chemicals potassium hydroxide and sodium hydroxide are extremely corrosive and will cause severe burns but I also see videos of people saying that if you get lye on you, then just wash it off and you’ll be fine. Is that actually ok. The fact that the stuff is sold in hardware stores makes it seem even less dangerous than the warnings make it out to be. Which is it?


texts:
So what I know is, a salt is an ionic compound between a metal and a non-metal which exchange electrons. Like in $\ce{NaCl}$, $\ce{Na}$ is the metal and $\ce{Cl}$ is the non-metal, $\ce{Cl}$ hogs up the valence electron of $\ce{Na}$ and so the atom becomes charged.

But in the salt $\ce{NH4Cl}$, neither nitrogen, hydrogen nor chlorine are metals. All of them are non-metals. How can it be a salt?


texts: organic chemistry of alkyl halides and alcohols

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What happens if a primary alcohol that also bears a halide substituent on the alcoholic carbon (the carbon to which the hydroxyl group is attached) when it is reacted with copper at 300 °C ?
   I know primary alcohols, on treatment with copper at 300 °C react to give  aldehydes.  But I am confused what happens if halides are present on the same alcoholic carbon.