texts: Constructing two body Hamiltonian for Helium atom in hydrogen slater orbitals single particle basis

texts:
I am trying to construct a two body states to calculate the matrix elements of electronic Hamiltonian of Helium atom. $$H=-\frac{1}{2}\nabla^{2}_{1}-\frac{1}{2}\nabla^{2}_{2}-\frac{2}{\vec{r}_{1}}-\frac{2}{\vec{r}_{2}}-\frac{1}{|\vec{r}_{1}-\vec{r}_{2}|}$$

Constructed the following two body (slater determinant) states (spinless fermion so spin states are excluded), $$|\psi_{1s}\psi_{2s}\rangle, |\psi_{1s}\psi_{2p_{x}}\rangle,|\psi_{1s}\psi_{2p_{y}}\rangle,|\psi_{1s}\psi_{2p_{z}}\rangle,|\psi_{2s}\psi_{2p_{x}}\rangle,|\psi_{2s}\psi_{2p_{y}}\rangle,|\psi_{2s}\psi_{2p_{z}}\rangle,|\psi_{2p_{x}}\psi_{2p_{y}}\rangle,|\psi_{2p_{x}}\psi_{2p_{z}}\rangle,|\psi_{2p_{y}}\psi_{2p_{z}}\rangle$$

where each ket is actually slater determinant for example,$$|\psi_{1s}\psi_{2s}\rangle:=\frac{1}{\sqrt{2}}[\psi_{1s}(\vec{r}_{1})\psi_{2s}(\vec{r}_{2})-\psi_{1s}(\vec{r}_{2})\psi_{2s}(\vec{r}_{1})]$$

I am trying to construct the matrix elements for the above hamiltonian with 10 two body slater determinant states (i have used only $1s$,$2s$ and $2p$ single particle states).While constructing the matrix ($10\times10$ matrix), I have a problem in evaluating the coulomb repulsion term. $$\int\frac{1}{\sqrt{2}}[\psi_{1s}(\vec{r}_{1})\psi_{2p_{x}}(\vec{r}_{2})-\psi_{1s}(\vec{r}_{2})\psi_{2p_{x}}(\vec{r}_{1})]\frac{1}{|\vec{r}_{1}-\vec{r}_{2}|}\frac{1}{\sqrt{2}}[\psi_{1s}(\vec{r}_{1})\psi_{2p_{x}}(\vec{r}_{2})-\psi_{1s}(\vec{r}_{2})\psi_{2p_{x}}(\vec{r}_{1})]d^{3}\vec{r}_{1}d^{3}\vec{r}_{2}$$

How do I evaluate those integrals if not analytically, How do i do numerically this six dimensional integration. Can someone suggest a numerical technique to evaluate such an integral or a python code or C code ?


texts: Do acyl halides react similarly to alkyl halides with nitriles with TBAB/NaOH?

texts: I am referencing page pg. 665 in Clayden where it is shown that a nitrile can be alkylated using an alkyl halide with tetraalkylammonium chloride and NaOH. Would acyl halides behave similarly resulting in substitution at the carbon adjacent to the nitrile group?


texts:
Are there any molecules that are chiral that are also gases at room temperature?

Failing that, what chiral molecules have a high vapor pressure? Propylene oxide has a boiling point of only 34 C, so that seems like a good one. Are there others?

EDIT: I appreciate all of the great suggestions! I should have mentioned before, but I am looking for something that can be purchased in both R and S enantiomers.


texts: What is the joke that is shown in this picture?

texts:
There is supposedly a joke shown in this picture relating to periodic trends.
Does anyone know what it is? And could they also explain where the elements on the eye exam came from?


texts: Enthalpy change for exothermic and endothermic reactions

texts:
I understood the concept behind endothermic and exothermic but finding it hard to understand it numerically.Let me describe my confusion through example.

Suppose for a reaction,
reactants require energy=$\rm40~J$
which on forming product give energy=$\rm50~J$ (so yes it is exomthermic)
where change in enthaply=$\rm10~J$

But as per the equation:
"Enthalpy change=Enthalpy of products- Enthalpy of reactants."
since enthalpy at constant pressure is Total heat content.
So I should have

Change in enthalpy=[U(internal energy)-50]-[U+40]=-90J

Could You explain it where I am getting this wrong? Is my understanding of enthalpy correct?


texts:
Why is it so difficult to perform DFT calculations that consider temperature?

I have seen that time-dependent DFT is needed to model systems at high temperature.
Why is this the case? What about finite temperature functionals? Why is it also acceptable to use zero-temperature functional with TD-DFT?

I have also read that thermal fluctuations can result in the occupation of electronic states (excited states) above the ground state.

I have tried to rationalise the fact that the electron density changes with temperature as:

If the ions in the until cell move, their degree of orbital overlap and electron density will change. The degree of orbital overlap influences the band-structure, which then impacts all of the electronic and physical properties.

Is this accurate?


texts: Formula for finding how much base to add to buffer to obtain a desired pH

texts:
Given: molarity and volume of the weak acid, molarity of the strong base, desired $\ce{pH}$, $K_{a}$ of the acid. I tried coming up with a formula to solve for the amount of base to add in order to reach the $\ce{pH}$.
$$\ce{HA + OH- -> H2O + A-}$$

After addition of $\ce{OH-}$:

$n_{\ce{HA}}=M_{\ce{HA}}V_{\ce{HA}} - M_{\ce{OH-}}V_{\ce{OH-}}$

$n_{\ce{OH-}}=M_{\ce{OH-}}V_{\ce{OH-}} - M_{\ce{OH-}}V_{\ce{OH-}} = 0$ mol

$n_{\ce{A-}}=0 + M_{\ce{OH-}}V_{\ce{OH}} = M_{\ce{OH-}}V_{\ce{OH-}}$

$$\ce{HA + H2O <=> H3O+ + A-}$$
Using an ICE table, the concentrations at equilibrium become:

$[\ce{H3O+}]=10^{-\ce{pH}}$ (given the desired $\ce{pH}$)

$\ce{[HA]}=\frac{n_{\ce{HA}}}{V_{soln}}=\frac{M_{\ce{HA}}V_{\ce{HA}} - M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}}-[\ce{H3O+}]=\frac{M_{\ce{HA}}V_{\ce{HA}} - M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}}-10^{-\ce{pH}}$

$[\ce{A-}]=\frac{n_{\ce{A-}}}{V_{soln}}=\frac{M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}}+[\ce{H3O+}] = \frac{M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}} + 10^{-\ce{pH}}$

Writing a $K_{a}$ expression gives:

$$K_{a}=\frac{\ce{[H3O+][A-]}}{\ce{[HA]}}=\frac{10^{-\ce{pH}}\left(\frac{M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}} + 10^{-\ce{pH}}\right)}{\frac{M_{\ce{HA}}V_{\ce{HA}} - M_{\ce{OH-}}V_{\ce{OH-}}}{V_{\ce{HA}} + V_{\ce{OH-}}}-10^{-\ce{pH}}}$$
I tried rewriting this to solve for $V_{\ce{OH-}}$ and got:

$$V_{\ce{OH-}} = \frac{ V_{\ce{HA}}(10^{-2\ce{pH}} - K_{a}M_{\ce{HA}}) }{ -10^{-\ce{pH}}(-10^{-{\ce{pH}}}+M_{\ce{OH-}}) -K_{\mathrm{a}}M_{\ce{OH-}} }$$

Is this a valid formula? Could this be used to determine how much strong base to add to a buffer in order to reach a desired $\ce{pH}$? Is there an easier way to write this? Is it useful at all? Thanks.


texts: What are potential sources of low recovery in this acid-base extraction experiment?

texts:
I did an acid-base extraction experiment. First extracted a solid mixture containing benzoic acid, p-nitroaniline, and naphthalene into three separate solutions:

NaOH extract
HCl extract
3.organic with the neutral compound.

Then the HCl and NaOH extracts were neutralized and underwent vacuum filtration to isolate crude p-nitroaniline and crude benzoic acid, while the organic solution underwent rotary evaporation to get crude naphthalene.

Crude benzoic acid was purified by recrystallization using hot filtration, and then benzoic acid crystals were isolated by suction filtration. The melting range of the benzoic was relatively pure.

How can I improve this experiment? My recovery of benzoic acid was less than 40%

And as for sources of error, extraction processes always lose some compound during each step. What are other probable sources of error?


texts: How come the reaction with glycerol and formic acid to form glycerol formates is not as probable as with acetic acid to yield glycerol acetates

texts:
I come across various literature when searching for the esterification reaction between glycerol and acetic acid to yield three glycerol acetates as in the image below. Essentially, each OH- group of the glycerol reacts with the H+ of the acid forming an ester bond and releasing water (This happens stepwise as in below):

However, I cannot find much (4-5 papers only) literature on the reactions between glycerol and formic acid yielding the expected products (glycerol formate, glycerol diformate and glycerol triformate), I was expecting a similar reaction to pattern as with acetic acid. Is there a reason why an esterification reaction between glycerol and formic acid would not be as probable as with acetic acid?
Reaction Temperature between 70-170 C in presence of an (Brønsted–Lowry) acid catalyst.


texts: Determining the mass of a substance using calibration curve produced by HPLC

texts:
I hope everyone is doing well and safe! Yesterday, I was fortunate enough to be taught about how to read a chromatography calibration curve through this stackexchange! Special thanks to those who explained to me patiently and meticulously. Anyways, I've tried to solve some questions regarding this field but ended up no-where with this one. Could someone run me through the procedure of how to solve this question? Huge thanks in advance!!! <3 <3

Info: A $\pu{1.0mL}$ aliquot of a drink was diluted to $\pu{50.0mL}$ with deionized water. A sample of the drink was run through the HPLC to produce the calibration curve below. In this experiment, the mass of caffeine in the drink was determined by HPLC. The peak area obtained for this diluted sample was $2800$ arbitrary units.

Question: What is the mass of caffeine in grams, in a $\pu{330mL}$ can of this drink?

Answer = $\pu{825mg}$
P.S.: Could someone explain to me the significance of the peak area ($2800$ arbitrary units) that is obtained? And thank you for the constant support and help. Much love to this community!!!


texts: How does hyperconjugation affect bond lengths in alkenes?

texts:
How does the number of hyperconjugates affect the $\ce{C=C}$ bond length in the compounds propene and 3,3-dimethylbut-1-ene?

In general, is bond length directly or inversely proportional to the number of hyperconjugates?


texts: Could neutralisation of safe chemicals produce dangerous ones?

texts:
I'm basically thinking whether I could potentionally poison myself while neutralising strong acid/base by some weak base/acid when I accidentally spill it, touch it or when I'm cleaning reaction product.

Combinations of chemicals that are non-toxic in my opinion:

$\ce{HCl + NaHCO3}$
$\ce{H2SO4 + NaHCO3}$
$\ce{NaOH + CH3COOH}$

None of these are poisonous. I just thought these up, for example the first one produces table salt, $\ce{NaCl}$.

But could there be a combination of non-toxic acid and base that would produce some nasty salt when neutralised? Something worse than what I would be getting rid of?
Is there a combination where I should better just wash myself with water?


texts: How do repulsive solute interactions affect the van't Hoff factor?

texts:
Context. Consider an ideal solution, one in which the intermolecular solvent-solvent, solute-solute, and solute-solvent interactions are all equal. The presence of a solute therefore produces (solely) an increase in entropy due to the increase in configurational microstates. This increase in entropy leads to the well-known colligative properties, characterized by the van't Hoff factor, the number of effective solute particles per molecule or salt of solute.

Now consider a solution in which the solute-solute intermolecular interaction is changed by $+\epsilon$, so that solutes are more attracted to each other. This decreases the van't Hoff factor due to clumping of the solutes, which we can rationalize from two different perspectives:

probabilistic: solute particles are more likely to be found close to each other (due to the favorable attraction between them), so we effectively have less solute particles as a whole, resulting in a lower van't Hoff factor
statistical-mechanical: microstates in which solute particles are close to each other are weighted more heavily; this perturbation from the uniform distribution of microstates decreases the entropy of the system, effectively decreasing the "strength" of the colligative effect and hence resulting in a lower van't Hoff factor

Both factors agree, so that's good.

Now consider a solution in which the solute-solute intermolecular interaction is changed by $-\epsilon$, so that solutes are less attracted to each other. Consider the two perspectives again:

probabilistic: solute particles are less likely to be found close to each other (due to the unfavorable attraction between them), so we effectively have more solute particles as a whole, resulting in a higher van't Hoff factor
statistical-mechanical: microstates in which solute particles are close to each other are weighted less heavily; this perturbation from the uniform distribution of microstates decreases the entropy of the system, effectively decreasing the "strength" of the colligative effect and hence resulting in a lower van't Hoff factor

Questions.

Why don't the probabilistic and statistical-mechanical viewpoints agree in the latter case?
How can the incorrect viewpoint(s) be modified to make them correct?

I am inclined to believe the statistical-mechanical viewpoint is correct, since it's more fundamental. I'm also somewhat leery of the implication that solute particles being less likely to be close to each other leads to effectively more solute particles.

If this implication is indeed wrong, why is it wrong? How about the converse, that because solute particles are more likely to be found close to each other, we effectively have less solute particles as a whole?
If this implication is actually right, why is it right?


texts: Hazards of trivalent chromium and hexavalent chromium

texts:
I am examining a material safety data sheet that reports on trivalent and hexavalent chromium in chemical films. It covers each type where it is used in a product individually.

Is there a practical difference in safety between the two, such that they should be reported separately?


texts: Introducing n-propyl group to benzene using cyclopropane

texts:
I am studying Friedel–Crafts alkylation reactions and my textbook states the following proposition [1, p. 1090]:

Another very good means of introducing $n$-propyl group is to use cyclopropane as the alkylating agent.

I do understand the mechanism of Friedel–Crafts alkylation, but I am not able to write the mechanism for this particular reaction. Any hints are appreciated.
Reference

Shahi, R. Essential Organic Chemistry for JEE Main & Advanced; Arihant  Prakashan: New Delhi. ISBN: 978-93-13192-10-7.


texts: How to determine whether a compound is gas or liquid or solid?

texts:
My book says, methyl chloride, methyl bromide, ethyl chloride and some cholorofluromethanes are gases at room temperature, whereas higher members are liquids or solids. Why?
With this question, I got another question for which the former would be subset. How to determine whether a compound is gas or liquid or solid (assume room temperature)? Thinking about this question, I thought molecular force between the molecules is going to be the key for answer of this query door. But how to determine, whether a compound has stronger intermolecular force between the molecules or not?
We have another way to check if a compound is gas or solid or liquid, i.e. entropy (randomness), which is given by heat gained or lost divided by temperature. In general, compound which has greater randomness will be gas. We can expect most of the compounds to be gases, which have standard molar entropy greater than $200\ \mathrm{J K^{-1} mol^{-1}}$ at $298\ \mathrm{K}$.
Entropy concept brings many questions under light, for example, $\ce{H2}$ gas has standard molar entropy of $130.7\ \mathrm{JK^{-1}mol^{-1}}$, which is lesser than $\ce{Br2}$ liquid, which has standard molar entropy of $152.3\ \mathrm{JK^{-1}mol^{-1}}$. We would had expected $\ce{H2}$ gas to have greater randomness than $\ce{Br2}$ liquid, because gases should have greater randomness than liquids. Anyway it becomes difficult, to determine a compound as solid or liquid or gas using entropy.

LINKS

http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/gases1.html#roomt (This link helps to determine a compound as gas, but leads to still more questions like: Why most non metals are gases? Why all the gases are covalent bonded that contain two or more non metals? Why gases are defined to have low molecular weights, in spite of knowing that molecular interactions matter? Can’t ionic bonded compounds be gases?)
I will try to find list of solid and liquid compounds, but now I have just the above link. If any one have links related to this particular topic, they are welcome.


texts: Why is the iodide anion a good nucleophile but a poor base?

texts: The $\mathrm{pK_{aH}}$ of $\ce I^-$ is very low which indicated that it is not favourable for it to bond with a proton. However, why would it be likely to bond with any other atom (mostly carbon when considering it's nucleophilic properties).


texts:
To summarize from my textbook:

rate of evaporation:

proportional to surface area
but essentially independent from pressure (of surrounding gas)

rate of condensation

proportional to both surface area
and concentration (#molecules/volume) of (appropriate) molecules in the gas

At some concentration the rate of evaporation = rate of condensation.
The pressure corresponding to this concentration is called "vapor pressure of the crystal".

(There is some example about iodine in a sealed flask in the same chapter, but there is no explicit statement of assumptions about sealed container or not having another gas, like air "around". Textbook: College Chem by Pauling.)

My question:

For a liquid/crystal in a closed vacuumed container, this seems straightforward, since pressure would be a function of concentration (and temperature), I believe. So there is 1 pressure corresponding to the concentration (at the given temperature). But then why is it not called "vapor concentration"? Which the mentioning of its proportionality, as the only relevant one, would suggest.

The only reason for the name "vapor pressure", I can imagine, is that not only concentration matters.

For example, considering the cases where the sealed container has initially near vacuum or 1atm or 2atm of air besides the liquid/crystal. Then the pressure of the gas at equilibrium in those cases will surely be different, even if the concentration of the evaporated substance is the same.

The book does not mention "partial pressure" or "pressure contribution".

My alternative thinking is that "vapor pressure" does not describe the equilibrium state of arbitrary mixed gas of arbitrary container and initial pressure, but confusingly enough, just the property of liquid/crystal which only depends on chem composition and temperature. Which I would call "in-vacuum evaporation rate". And the reason for the naming is the special experimental scenario used to measure/define this property. Neither the total pressure of the possibly mixed surrounding gas, nor the partial pressure of any component is equivalent to it, just merely equal in certain scenarios.

Is this correct?

I am confused. Isn't the book a bit incomplete with the explanation?


texts:
The yellow color of urine is due due a compound known as urochrome, or urobilin. Why is this chemical yellow? There isn't any coordination complexes. What else could cause this color?

I have not learned organic chemistry yet so please make it simple.


texts: Calculating how many grams will I get from a reaction

texts:
Question:

  $$\ce{2NH3 + CO2 -> (NH2)2CO + H2O}$$

  If we have $637.2\ \mathrm{g}$ of $\ce{NH3}$ and $1142.0\ \mathrm{g}$ of $\ce{CO2}$ how many grams of $\ce{(NH2)2CO}$ will we get?

This is the explanation I was given:

  First, convert reactives to moles:

  $637.2\ \mathrm{g}$ of $\ce{NH3}$ are $37.5$ moles.
  $1142.0\ \mathrm{g}$ of $\ce{CO2}$ are $26$ moles.

  Second, define the stoichiometric proportion between reactives and
  products...

  From $2$ moles of $\ce{NH3}$ we get $1$ mol of $\ce{(NH2)2CO}$
  From $1$ mol of $\ce{CO2}$ we get $1$ mol of $\ce{(NH2)2CO}$

  Third, calculate the number of product moles we would get if each
  reactive was completely consumed:

  Consuming all the $\ce{NH3}$ we would get $18.75$ moles of $\ce{(NH2)2CO}$
  Consuming all the $\ce{CO2}$ we would get $26$ moles of $\ce{(NH2)2CO}$

  The limiting reagent is $\ce{NH3}$, so the most we will get of
  $\ce{(NH2)2CO}$ is $18.75$ moles. Now convert that to grams, we get
  $1125.0\ \mathrm{g}$.

Why are we ignoring the existence of $\ce{H2O}$? Does it not matter?
IF the formula is unbalanced, do I have to balance it first before making this calculation? What if I can't balance it?


texts:
I am looking for normal resolution IR-spectra of: $\ce{O2}$ and $\ce{N2}$ at high concentrations and; common minor gas in atmosphere: $\ce{H2O}$, $\ce{CO}$, and $\ce{CO2}$ at environmental concentrations. I have found some reference on internet (mostly from Green House Effect articles), but I cannot found it on a free, accurate and reliable source even on the free part of NIST databases.

Where can I find good references for such spectra?
Thank you.


texts: Atomic emission spectrum assumption n_f = 3

texts:
It's a standard question on the atomic emission spectrum.

  An atomic emission spectrum of hydrogen shows three wavelengths: 1875 nm, 1282 nm, and 1093 nm. Assign this wavelengths to transitions in the hydrogen atom.

I understand how to calculate it, but from both the answers in my book and the answer from slader.com. Both just say

  since these wavelengths are larger than those of visible light, then we assume $n_\mathrm{f} = 3.$

However, I don't understand why we could assume $n_\mathrm{f} = 3.$ Is it because we just look at Paschen series (Bohr series, $n′ = 3$) and the Paschen lines all lie in the infrared band? Could anyone explain it?


texts: Why do carbonyl compounds undergo nucleophilic and not electrophilic addition?

texts:
Why aldehydes and ketones undergo nucleophilic addition reactions and not electrophilic addition?

Alkenes show electrophilic addition because of pi bond, which is also present in aldehydes and ketones. But there is nucleophilic addition only. Why?


texts: Does the addition of water to N2H4 produce N2H4

texts:
I am currently calculating the $\ce{pH}$ of a species.

The reaction is as follows,

$$\ce{N2H4 + H2O <=> N2H_{$A$}+ + OH-}$$

However, I'm not sure what the value of $A$ will be. In my textbook it says $4$, which is stumping me as in every other example with a weak base the subscript increases.

What is the value of $A$ and why?


texts: What does the horizontal axis on cyclic voltammograms mean?

texts:
In cyclic voltammograms (like the one in the attached image) what exactly is the horizontal axis' voltage refering to? Is it the measured voltage between the reference electrode and working electrode? If so, and assuming the measurements are made with a standard voltmeter, which electrode is considered the cathode and which is considered the anode (as in, which is attached to the positive lead and which is attached to the negative lead)?
I was also wondering if these voltages would represent standard electrode potentials or would that depend on the conditions of the data collection


texts:
I have seen these small test tube looking doohickeys being supplied from many chinese suppliers, but never with any description as to what they are for. They almost invariably have the description "Automatic Filling Tube Liquid Test Tube With Spout" which didn't lead me anywhere.
With most glassware, even relatively complex pieces, I can usually discern what it is for and why it is designed in that way but this has me stumped. My best guess so far is that it is meant to collect liquid from a sealed flask where the long stem passes through a bung to the bottom of the flask and gas pressure pushes some liquid up and into the tube. So maybe it is for volumetric reagent dispensing? If you had a squeeze bulb on the bottle it would push liquid up into the tube, then suck back and reduce the level to a consistent volume, but you would have to tip the whole bottle to pour it out so idk?
If anyone is familiar with what these are for and how they are used it would be much appreciated because this has been bothering me for a while.


texts: How does increasing the ionic strength of an aqueous solution decrease the activity coefficient?

texts:
Activity is a new concept for me, and I am having a little bit of trouble understanding it.

For the equation:

$$\ce{aA + bB<=>cC + dD}$$

$$K_c= \frac{[\ce{A}]^a[\ce{B}]^b}{[\ce{C}]^c[\ce{D}]^d}$$

As I understand it, this is not the true equilibrium constant expression for the chemical equation above. My textbook calls $K_c$ in this instance the "concentration quotient." The technically correct equilibrium constant expression is:

$$K=\frac{(a_\ce{A})^a(a_\ce{B})^b}{(a_\ce{C})^c(a_\ce{D})^d}$$

Where $K$, in this equation, is the "true" equilibrium constant determined by the activity, $a$, of each species in equilibrium with each other. The activity is represented by the equation: $a_\ce{A}=\gamma_\ce{A} [\ce{A}]$, where $\gamma$ is the activity coefficient.

My textbook Quantitative Chemical Analysis (Ninth Edition, by Daniel C. Harris), states that "the equilibrium 'constant' is not really constant." And then it goes into how increasing ionic strength increases the solubility of ionic compounds in aqueous solution. It then later states "the activity coefficients must decrease with increasing ionic strength."

This would seem to contradict the idea that increasing ionic strength increases the solubility of an ionic compound, would it not? If the ionic strength increases the solubility of an ionic compound, then wouldn't that mean that the concentrations of the ions that make up that ionic compound would increase, and thus the activity coefficient, therefore, must increase to show an increase in activity, otherwise known as the "effective concentration?"

Or is the activity independent of the ionic strength such that in order to keep the activity the same under higher concentrations, the activity coefficient must be smaller? This would then bring up the question: is the equilibrium constant, $K$, (determined by the activities of the components in the equilibrium expression) constant even under different ionic strengths, while the "concentration coefficient" (determined merely by the concentrations of the components in equilibrium with one another) does vary under different ionic strengths? I'm not sure I'm getting this very well.


texts: Why does silver plating require undercoats of copper and nickel?

texts:
I came across a question that was about silver plating (of steel), but I couldn't help but wonder why the sequence was illustrated as this:

step 1 A coating of copper is applied to the object.

step 2 A coating of nickel is applied to the object.

step 3 The coating of silver is applied to the object.

Why are these initial coats of copper and nickel required, and why this seemingly random sequence (since nickel is in between but has the highest reactivity)?


texts: Why is the reverse aldol cleavage of fructose 1,6-bisphosphate highly endergonic under standard conditions?

texts:
I have another question similar to this one.  I just don't have intuition for why reactions are thermodynamically favorable or unfavorable and I'd like to build it.  This time I'd like to ask about the reverse aldol reaction $$\ce{Fructose-1,6-Bisphosphate -> Dihydroxyacetone Phosphate + Glyceraldehyde-3-Phosphate}$$
The standard free energy of this reaction is +23.8 kJ/mol.[1]
I was hoping someone could help me understand why.  The larger molecule has lower entropy and charge-charge repulsion.  Why is it so thermodynamically unfavorable for it to break apart?
[1]
Cornish-Bowden, A. Thermodynamic Aspects of Glycolysis. Biochem. Educ. 1981, 9 (4), 133–137.


texts:
I am thinking cheap material that can be used between two layers of carton that absorbs water.
I want to use air but I still think that there may be other materials available that

absorb water
can be easily removed when the outer carton layer is damaged

Possible materials

carbon (well absorbing)
air (cheap and easy)
sand (should be bad)

What is cheap material that absorbs water in packaging?


texts: Do aromatic dienes undergo the Diels-Alder reaction?

texts:
Do aromatic dienes undergo Diels-Alder reactions?

My understanding is that the $\pi$ bonds in aromatic compounds are not as localised as they are in other compounds, such as aliphatic dienes. Therefore, the dienophile shouldn't be as willing to go to these compounds. Am I correct?


texts: Comparing the emission spectrum of ethanol and mixture of alcohols

texts:
Sorry if this question has a simple answer, but I've been unable to find it elsewhere.

  Using a diffraction grating, burning ethanol (99.9%) will produce a rainbow of colours. However, when burning a mixture of alcohols (methanol 76.6%, ethanol 21.4%, propanol 0.3%) the rainbow pattern is missing. Could someone explain?

If methanol only emits a small range of wavelengths, why wouldn't there be a dimmer  ethanol rainbow?


texts: Yield of monohalogenated products of organic compounds

texts: We say that to increase the yield we must increase the concentration of hydrocarbon, so that there is a greater probablity of collisions of molecules, but isn't there an equal probality of dihalogenated products, as there are two free radicals formed during initation step? I'm not able to understand how the maximum probability of collision between hydrocarbon and the halogen will maximise the yield, please explain it.


texts:
The structure of xenon fluoride is a capped octahedron. The lone pair is stereochemically active, i.e. it will rotate about.

The dipole moments of the axial fluorides will get cancelled, and so will those of the four equatorial fluorides will also cancel each other. Thus, overall, the molecule should be nonpolar.

But what effect will the stereochemically active lone pair have on the polarity? Will the polarity keep on changing?


texts:
How is it a polyphenol if it doesn't have a hydroxyl group?

If it isn't which subclass would you put it in, and which functional groups does it contain?


texts:
What happens when these 3 chemicals are mixed in air?

Pentanone/Di-isopropyl Ketone (2,4-Dimethyl-3-Pentanone)
Iodine, reagent grade
Sodium Iodide, reagent grade.

The 3 parts make up a liquid in a tilt switch.  The tilt switch can leak giving off a very unpleasant smell.  Also corrosion can occur on the part.  What is the smell?  How dangerous is the smell?  Using a fume cupboard etc, what exactly are we emitting into the atmosphere?


texts: Why is partial pressure used as a metric for oxygen in blood?

texts:
I know haemoglobin basically acts as an oxygen buffer. But when we talk about non-bound oxygen in blood (or water), we're referring to the amount of O2 in solution (aqueous state). From a biochemistry point of view, the concentration seems like a good metric to me.

So why is it that medical papers report blood oxygenation in terms of partial pressure pO2 instead of concentration?

What does a partial pressure inside a liquid even mean? I tried interpreting the arterial pO2 value of 11% atm (i.e. about 11kPa). When using the formula P = CRT at 310K (body temp), I found an oxygen concentration of about 4.3 mM. This value is 20× higher than the maximum O2 concentration for water according to Henry's law. For those more familiar with DO values in mg/L, it would be 137.6 mg/L.

According to Henry's Law there is a limit to the amount of O2 that can dissolve into water at a given pressure and temperature. I know the lungs experience a slightly lower partial pressure than the atmosphere. So how can the oxygen concentration be so high? Does their metric include the oxygen bound by haemoglobin (which would be misleading at the least), or is my calculation off somewhere?

Or does a pO2 value correspond to the steady-state equivalent concentration at that pressure, in which case the arterial concentration in my example would be 0.14 mM (based on this table in wikipedia).

This similar question didn't answer my question:
What is the state of aggregation (gas, liquid) of oxygen in blood?


texts: Warning during geometry optimization via Gaussian

texts:
I have some recurrent problem with my DFT calculations [functional: hseh1pbe; basis:6-31+g(d,p), object: porphyrin derivative]. During the MO setting I get:

**** Warning!!: The largest alpha MO coefficient is  ***D+03

**** Warning!!: The smallest alpha delta epsilon is  ***D-01

I did some first-step research over the internet: the only considerable suggestion I found was to decrease the basis since some MOs got linear-dependent. I already decreased it from 6-311++g(d,p) so I assume that it didn't help much. Moreover, simplifying the basis set would mean increase in inaccuracy, right?

Did someone meet and solve this issue before?


texts: Does benzene vapor react with air in a closed barrel?

texts:
If we would have benzene in a closed barrel for quite a while at room temperature, some vapor would form fast due to its volatility, right? But let's say that when the barrel was closed, some air got trapped inside. So it's inside at any time. Is there any chance that the benzene would react with the components in the air at room temperature? Or would we simply have benzene vapor and air? Or would we have benzene, some products of reaction and air? I made a sketch for a better understanding of my question.

So which one is the real one? And if it is the second one, would the reaction be similar to combustion, or?Is temperature a major player in this? And if so, how strongly would it affect the reaction?


texts: How much sodium hydroxide would it take to dissolve one tonne of bauxite?

texts:
Generally speaking what proportion of NaOH would be typically required to dissolve one tonne of crushed bauxite of average purity?

Also are varying quantities required for gibbsite, böhmite and diaspore respectively and how do they differ?


texts: I am trying to look for the entropy explanation but I do not understand anything I can find. Please keep it simple but talk about it from a entropy point of view. Use water and a volatile solute as an example if you need one. I do not understand how the addition of a volatile solute to water increases the vapour pressure of the solution.


texts: Change of potential difference during electrolysis while adding salt

texts:
I was conducting a simple experiment at home on electrolysis. Obviously, when you build a circuit with a 9V battery, a lamp, and put two electrodes in water you measure a potential difference of ~9V on the two electrodes while the potential difference on the lamp is 0 (really close to 0). Then as I kept adding salt in water, I first measured that the potential difference across the lamp got higher and higher (reaching 6V), then suddenly, as I got from 40g /250ml of salt in water to 50g /250ml, the potential difference across the lamp fell to 4V.

Why is that? Maybe is it because of the ion association occurring in water as the concentration of salt gets higher?

4.5 V lamp. 8.6 e.m.f battery.


texts: Thermodynamic quantities for the freezing of water

texts:
I am trying to do the following problem:

Freezing of water at $273~\mathrm K$ and $1~\mathrm{atm}$
Which of the following is true for the above thermodynamics process?
p) $q=0$
q) $w=0$
r) $\Delta S_\mathrm{sys}<0$
s) $\Delta U=0$
t) $\Delta G=0$

My answer was r, s, and t:

Since the reaction happens at constant temperature, internal energy is constant (yes for s)
Since the reaction is open, it is isobaric in nature; and since the volume changes due to the phase change the work done is not zero (no for q)
Heat must be exchanged (first law of thermodynamics) (no for p)
Randomness decreases so $\Delta S_\mathrm{sys} < 0$ (yes for r)

But, the answer given is q, r, and t. I don't understand why q is correct but s is not.


texts: How to calculate pH of basic salt solution mixed with strong base?

texts:
Calculate $\mathrm{ pH }$ of $\pu{ 0.05 mol }$ of $\ce{Zn(CH3COO)2}$ and $\pu{ 0.025  mol }$ of $\ce{ NaOH }$ dissolved in $\pu{ 1 L }$ of distilled water?

I tried to use the systematic method by forming the following equations to extract cubic equation which can  be solved by computer :
\begin{array}{   }
[\ce{ CH3COO- }]_I &= 2\times {0.05} = \pu{ 0.1 M }\\
[\ce{Zn^{2+}}] &=\pu{ 0.05 M }\\
[\ce{Na+}] &=\pu{ 0.025 M }\\
0.1 = [\ce{CH3COO-}]_I &= [\ce{CH3COO-}]_e + [\ce{CH3COOH}]_e\\
2\ce{[Zn^{2+}] + [Na+] +[ H+]_e &= [CH3COO-]_e +[ OH-]_e} \\
K_\mathrm{a} &=\frac{ [\ce{ H+}]_e\cdot{ [\ce{CH3COO-}]_e}}{[\ce{CH3COOH}]_e}\\
[\ce{OH-}]_e &=\frac{ K_\mathrm{w}}{[\ce{H+}]_e}
\end{array}

First question: Are the equations correct?

Second question: Is there a simple approximate method to solve the above problem? How?

I appreciate any help?

$\large \text{ --------- Maxw Notes ---------}$

Editing the answers with all the markup is painfully slow, so I added different analysis in a number of different answers to this problem. No doubt that will be confusing to someone looking at this problem. So let me summarize the answers.

  Note: I am going to carry "extra" significant figures in the  calculations to gauge the mathematical exactness, but this is of course is ridiculous for the chemistry since the equilibrium constants are not known to that precision. If the true solution values are within 5% of the mathematically calculated values that's really good.

Exact Solution

Setup an ICE table and solved the nasty linear equations with Wolfram Alpha to get an "exact solution."

Iterative Solution

Setup an ICE table and then simplified the problem to create a "Simplified ICE Table". Went through some head pounding to create an iterative solution. Realized the original ICE table could be used for iterated solution so calculated that solution too.

Reducing the Problem to a Single Variable

I had tried to solve the problem first with what I am calling the Iterative Solution. I could tell all the species other than $\ce{[Na+]}$ were independently pH controlled, but I couldn't figure out how to iterate the solution. Using the charge balance finally occurred to me so I tabulated the data to show that the approach would work.

Solution with Cubic Equation

Used charge balance of solution, and one assumption to solve the simplified problem with a cubic equation with $\ce{[OH-]}$ as the variable. Solved the cubic equation with Wolfram Alpha.

Assumption:

$\ce{[CH3COO-]_{equil} \gg [OH-]_{equil}}$

Solution with Quadratic Equation

Used charge balance of solution, and two assumptions to solve the simplified problem with a quadratic equation with $\ce{[OH-]}$ as the variable. Solved the quadratic equation with Wolfram Alpha, but is reasonable to assume that solution could have been done by hand.

Assumptions:

$\ce{[CH3COO-]_{equil} \gg [OH-]_{equil}}$
$\ce{[CH3COO-]_{equil} \gg K_b }$
That the normalization tweak works. (I know that it did from the exact solution, but the calculations showed that it worked too.)


texts: Reconciling multiple inorganic properties for the purposes of learning these elements

texts:
How can I reconcile all of the chemical properties, physical properties and peculiar behaviour of metals in inorganic chemistry for the purposes of studying these systematically?

It is very hard to learn all of these for each group.


texts: Is there a very stinky chemical solution that isn't a health hazard?

texts: An effective way to disperse rioters & looters would be to send an armored vehicle in to spray them with a very stinky liquid. Is there a chemical that stinks but is not  a health risk and that breaks down after a few hours, or could be neutralized with another solution after a few hours?


texts: Cauchy-Schwarz inequality for integral derivatives

texts:
The Cauchy-Schwarz inequality for regular two electron integrals is given as:

$$\left(\left.ab\right|cd\right)\leq\sqrt{\left(\left.ab\right|ab\right)}\sqrt{\left(\left.cd\right|cd\right)}$$

Now this can be differentiated with respect to $x$:

$$\frac{\partial}{\partial x}\left(\left.ab\right|cd\right)\leq\frac{\partial}{\partial x}\sqrt{\left(\left.ab\right|ab\right)}\sqrt{\left(\left.cd\right|cd\right)}$$

By using the chainrule for $\frac{d\sqrt{f(x)}}{dx}=\frac{df(x)}{dx}\frac{1}{2\sqrt{f(x)}}$, now giving:

$$\left(\left.\frac{\partial a}{\partial x}b\right|cd\right)+\left(\left.a\frac{\partial b}{\partial x}\right|cd\right)+\left(ab\left|\frac{\partial c}{\partial x}d\right.\right)+\left(ab\left|c\frac{\partial d}{\partial x}\right.\right)\leq\frac{\sqrt{\left(\left.cd\right|cd\right)}}{2\sqrt{\left(\left.ab\right|ab\right)}}\left[\left(\left.\frac{\partial a}{\partial x}b\right|ab\right)+\left(\left.a\frac{\partial b}{\partial x}\right|ab\right)+\left(ab\left|\frac{\partial a}{\partial x}b\right.\right)+\left(ab\left|a\frac{\partial b}{\partial x}\right.\right)\right]+\frac{\sqrt{\left(\left.ab\right|ab\right)}}{2\sqrt{\left(\left.cd\right|cd\right)}}\left[\left(\left.\frac{\partial c}{\partial x}d\right|cd\right)+\left(\left.c\frac{\partial d}{\partial x}\right|cd\right)+\left(cd\left|\frac{\partial c}{\partial x}d\right.\right)+\left(cd\left|c\frac{\partial d}{\partial x}\right.\right)\right]$$

By using the symmetry of the two electron integrals $(ab|cd)=(cd|ab)$, it can simplified to:

$$\left(\left.\frac{\partial a}{\partial x}b\right|cd\right)+\left(\left.a\frac{\partial b}{\partial x}\right|cd\right)+\left(ab\left|\frac{\partial c}{\partial x}d\right.\right)+\left(ab\left|c\frac{\partial d}{\partial x}\right.\right)\leq\frac{\sqrt{\left(\left.cd\right|cd\right)}}{\sqrt{\left(\left.ab\right|ab\right)}}\left[\left(\left.\frac{\partial a}{\partial x}b\right|ab\right)+\left(\left.a\frac{\partial b}{\partial x}\right|ab\right)\right]+\frac{\sqrt{\left(\left.ab\right|ab\right)}}{\sqrt{\left(\left.cd\right|cd\right)}}\left[\left(\left.\frac{\partial c}{\partial x}d\right|cd\right)+\left(\left.c\frac{\partial d}{\partial x}\right|cd\right)\right] \tag{1}$$

Now by comparing terms it can be seen that:

$$\left(\left.\frac{\partial a}{\partial x}b\right|cd\right)\leq\frac{\sqrt{\left(\left.cd\right|cd\right)}}{\sqrt{\left(\left.ab\right|ab\right)}}\left(\left.\frac{\partial a}{\partial x}b\right|ab\right)$$

$$\left(\left.a\frac{\partial b}{\partial x}\right|cd\right)\leq\frac{\sqrt{\left(\left.cd\right|cd\right)}}{\sqrt{\left(\left.ab\right|ab\right)}}\left(\left.a\frac{\partial b}{\partial x}\right|ab\right)$$

$$\left(ab\left|\frac{\partial c}{\partial x}d\right.\right)\leq\frac{\sqrt{\left(\left.ab\right|ab\right)}}{\sqrt{\left(\left.cd\right|cd\right)}}\left(\left.\frac{\partial c}{\partial x}d\right|cd\right)$$

$$\left(ab\left|c\frac{\partial d}{\partial x}\right.\right)\leq\frac{\sqrt{\left(\left.ab\right|ab\right)}}{\sqrt{\left(\left.cd\right|cd\right)}}\left(cd\left|c\frac{\partial d}{\partial x}\right.\right)$$

For geometrical detrivatices $x$ would be a cartesian direction of a nuclie. Now my question is, for geometrical derivatives when would be the right point to use the Cauchy-Schwarz inequlity for screening the integrals?

I think I could either $(1)$ and screen the total derivative $\frac{\partial}{\partial x}(ab|cd)$, or use the last four equations and screen the four different (up to three for geometrical derivatives) contributions individually.

Also what would be a reasonable threshold for derivatives?

For regular integrals $10^{-10}$ or lower is often used.


texts: Why is CuI2 not stable in solution while other copper(II) halide salts are?

texts: Why is $\ce{CuI2}$ (copper (II) iodide) not stable in solution while other copper(II) halide salts are? And how can you tell this from the redox potentials?


texts: 2-step reaction mechanism for the decomposition of NO2Br

texts:
I need to propose a 2-step reaction mechanism for the following reaction:
$$\ce{2NO2Br -> 2NO2 +Br}$$
And prove the mechanism is consistent with: $$v=k[\ce{NO2Br}]^2$$
For the mechanism to be consistent with the rate equation, the first equation would have to be the limiting one and also be in this form:
$$\ce{2NO_2Br -> Products}$$
I've tried using:
$$\ce{2NO2Br -> N2O4 +Br2}$$
$$\ce{N2O4 -> 2NO2}$$
But  the problem with this mechanism is that $\ce{N2O4}$ is not unstable enough to be consumed immediately.
Any help with this problem?
Would also appreciate some advice on proposing reaction mechanisms. Thank you.


texts: Fourier transform for spectroscopy spectra?

texts:
I was thinking back to my chemistry major days and remembering the bunch of cool spectra we produced by various means (HNMR, IR, UV/Vis) and I remember all the cool 'self-interference' like couplets, triplets doublets, etc.

My question is basically motivated by the complexity of spectra, and the reductionist instinct to 'break it down' into simpler components. The FFT or DFT is known to separate out some periodic components of signals, as are SVD or tensor decompositions known to isolate independent components.

I am completely not an expert in any of this but I am interested to hear from any coal-face chemists if they regularly use some 'spectra decomposition' method to aid in interpretation or analysis. I remember being taught how to read various peaks in spectra and analyze them, but I can't help thinking, for some very complex molecules, surely it gets pretty hard. And what if, we don't actually know the structure beforehand?

So given that Fourier transform is used in NMR, my question is : is there ever a need to take a spectrum and do a computer analysis of it that isn't just about matching peaks to a database of known signals? What other nifty things can be done with a spectrum once it is obtained?


texts: Does acetamide respond positively to iodoform test?

texts:
This answer explains why acetic acid does not give a positive iodoform test.

Does acetamide respond positively to the test?


texts:
I'm doing a study a study on voltaic cells.
I've been working with them for a while and one of the questions that I've had is how does the salt bridge affect the cell. I mean, I know it allows ions to move and that it'a a basic component of the pill. But, does its' concentration affect the voltage of the cell itself?
Thank you.


texts:
In all the sites I have searched, shielding effect has been defined as the reduction of the nuclear attraction upon the outer electron/electrons, due to the core electrons that repulse the outer electron.

So, is the shielding effect specifically defined for outer shell electrons? Can't the shielding effect be defined for inner shell electrons?

If it can be defined, do the electrons in outer shells than that shell have any impact on the shielding effect?(They too must repulse the electron in the inner shell, possibly helping the nuclear attraction)
If not, why?

Can someone help me out? Tks


texts: What is the effect of applied magnetic field on absorption spectrum?

texts:
Upon application of a weak magnetic field, a line in the microwave absorption spectrum of rigid rotor splits into $3$ lines. The quantum number $(J)$ of the rotational energy level from which the transition originates is
(a) $0$
(b) $1$
(c) $2$
(d) $3$

Can anyone explain the answer (a) for this?
For rotational levels, each level is $(2J+1)$ fold degenerate. According to that, the answer should be (b).


texts: What is the condensation point of water?

texts:
The boiling point of water is $\pu{100^\circ C}$. However, we find that even at room temperature, water can evaporate into gas.
Therefore, water vapor can exist at temperatures of, say, $\pu{50^\circ C}$.

At what temperature, can you say for certain that all water vapor will turn into liquid?
In other words, what is the condensation point of water?


texts: Avogadro's law is V1/n1 = v2/n2 - volume and number of  moles are directly proportional. My question is - can this law apply to two different gases - for example, Hydrogen with volume v1 and number n1, and Oxygen with volume v2 and number n2 - are they proportional?


texts: Is equilibrium constant at a given temperature derived from Gibbs free energy of reaction valid for doing simple kinetic modelling?

texts:
I intend to do a kinetic study of simple alcohol catalytic dehydrogenation reactions in the gas phase. I want to start with simple power law kinetics using $K_\mathrm{eq}$ to account for the reversibility of the reactions. Would the equation below, knowing the Gibbs free energy of reaction, be valid?

$$Δ_\mathrm{r}G^\circ = -RT\ln K_\mathrm{eq}$$

I came across a paper that used this equation to calculate $K_\mathrm{eq}$ to build a kinetic model of the ethanol-to-butadiene reaction. However, other papers I read, i.e. on the methanol-to-diethyl ether reaction, have used complex equations derived from empirical observations to calculate $K_\mathrm{eq}.$ Why use one approach over the other?


texts: Should moderately soluble compounds like calcium hydroxide be denoted (aq) or (s)?

texts:
I'm learning to write balanced molecular and ionic equations. For "moderately soluble" compounds such as calcium hydroxide, how do I know whether to write the state symbol as (aq) or (s)? This is the equation I'm supposed to work with:

$$\ce{Al2(SO4)3 + 3 Ca(OH)2 -> 2 Al(OH)3 + 3 Ca(SO4)}$$


texts:
During nitration of phenol, both para- and ortho-nitrophenols will be formed.

Is there any way in which we can synthesize para-nitrophenol  only?


texts: Applicability of Enthalpy-Heat relation for a non-isobaric process

texts:
Consider a process in which state variables changes from $(p_1, V_1, T_1)$ to $(p_2, V_2, T_3)$ . I've learned that to calculate the change in enthalpy for any process, we consider a hypothetical isobaric process (Since enthalpy is a state function, it doesn't depend on the path).
Should the hypothetical process have the same initial and final state variable or just the same initial and final temperature? Because if we consider the same initial and final state variables, then we can't form a hypothetical isobaric process since the pressure changes in the actual process and the formula $\Delta H = q_p = n \cdot c_p \cdot \Delta T $ fails here.


texts: I've read that bromothymol blue can be mixed in with the electrolyte in the demonstration of electrolysis using a Hoffman apparatus. The indicator clearly shows the local differences in pH for the anode and cathode. And the blue color provides good visual contrast between the fluid and the gases that evolve. But I've found this indicator tends to break down quickly into a colorless solution while operating the apparatus, and after awhile you lose the indicating effect as well. Does anyone know of a better choice of indicator to use that will last longer?


texts: Is there a notion of generalized acidity for lithium ions?

texts:
From my understanding, the basic notions of acidity can be explained by considering a cup of pure water, and then adding a substance to it which creates either free $\ce{H+}$, or free $\ce{H3O+}$ and $\ce{H5O2+}$ etc...
And these ions are free to react and give rise to what we consider acidic behavior. The classic example is hydrogen chloride characterized with the following reaction
$$\ce{HCl +H2O = H3O+ + Cl-} $$
Whereas $\ce{H3O+}$ is our famous hydrochloric acid.
I wonder if it is possible for an analogous reaction to happen with other polar molecules. For example liquid $\ce{Li2O}$ (I believe it melts around 1438 Celsius) should be a polar liquid for the same reasons that $\ce{H2O}$ is (though maybe not as strongly polar), and therefore: $\ce{LiCl}$ should dissolve in molten $\ce{Li2O}$ to create positive charged lithium ion species such as $\ce{Li3O+}$. Which ought to function as an "acid" of sorts, in that they react with most thing which are dissolved/reacted by hydrochloric acid by acting as a positive charge donor (clearly not a proton donor since we are using lithium and not hydrogen to do the deed here)
Is my line of reasoning sound and has this been experimentally detected before?


texts:
Why do krypton and xenon have high electronegativity? Noble gases are supposed to be "happy" with the amount of electrons they have, because they have 8 valence electrons (thus, most noble gases have no electronegativity). So why do krypton and xenon have electronegativity? Why do they tend to "want" one more electron? It makes no sense... their outer shells are already full!

I'm going to do a research paper on this question, so I would really like some good resources that could help me answer this question for myself. Know any?


texts:
We dissolve $10\ \mathrm{g}$ of $\ce{CuCl2}$ in $0.1\ \mathrm{L}$ of water.
Given that:

$M(\ce{Cl})=35.5\ \mathrm{g/mol}$
$M(\ce{Cu})=63.5\ \mathrm{g/mol}$

How can one calculate the molar concentration of $\ce{Cu^2+}$ and $\ce{Cl-}$?

First of all I calculated the the quantity of matter of $\ce{CuCl2}$:

$n(\ce{CuCl2})=0.074\ \mathrm{mol}$

The the molar concentration:

$c=\frac{0.074\ \mathrm{mol}}{0.1\ \mathrm{L}}=0.74\ \mathrm{mol/L}$

Then I don’t know how can I calculate the molar concentration of $\ce{Cu^2+}$ and $\ce{Cl-}$ because I don’t know the quantity of matter of them!

But here im blocked!


texts:
I have a large CRT monitor that, by the weight of the monitor, I estimate to contain over two pounds of lead.  I want to know if the lead oxide is a mixture with the glass, or if it is chemically bonded to the glass.

I also want to know if there is any way (preferably extraction using heat) I can remove the lead in pure form or in oxide form. I know for sure you'd crush the glass.

I bring up heat extraction because chemicals are expensive, and I've heard of it being done that way on a large scale.

Edit: I'm not concerned about making a profit because I don't really have the setup to do so. I'm just curious about it because I've seen it done on an industrial scale using heat, so could it be replicated on home scale.

In what form would the lead be if you smelted it out?  Does heating lead oxide reduce it to lead again? If so, would the lead melt out and flow to the bottom?


texts: Do molecules with bridges through rings exist?

texts:
Do molecules with bridges through rings (in a manner illustrated by this) exist?

I sometimes get results like this when doing Energy Minimization on molview.org. For example:

Is this actually a thing?

EDIT: As a slightly more realistic example, consider this:


texts: Reference request on formate potash process

texts:
Wikipedia article on Potassium Formate mentions a so-called "formate potash process" for production of potassium, presumably referring to elemental metal.

Concise encyclopedia chemistry by Mary Eagleson, page 888 is a given as a reference, but I can't find a PDF, hence this request.


texts: Explaining allene IR stretching frequency

texts: So I was comparing the IR stretch frequency of ethyne, ethene and allene. Of course triple bond is stiffer than double bond so ethyne has a higher stretch frequency. The problem then is where allene sits when compared to these two. I guess it should be the lowest because I just think of the cumulated double bonds as serial spring, which should give lower spring stiffness than only one double bond in ethene. Obviously, I'm wrong... It turns out allene IR stretch frequency is in the middle of ethene and ethyne.  I wonder how might we explain that. Thanks!


texts: What types of glycosidic bonds are in oligosaccharides that occurs naturally not in the lab?

texts:
An oligosaccharide is a carbohydrate formed by two or more monosaccharides.

If both monosaccharides are pyranose types, they can bond through ($\alpha$ or $\beta$)1-4 or ($\alpha$ or $\beta$)1-6. If one monosaccharide of them is of furanose type, they can bond through ($\alpha$ or $\beta$)1-2.

Examples:

or

Is any other type of glycosidic bond type between monosaccharides in oligosaccharides that occurs naturally not in the lab?


texts: How to balance the reaction equation of potassium permanganate, calcium oxalate, and sulfuric acid step by step?

texts:
I have been desperately trying to balance the following equation, and finally (ultima ratio) used an online program to get it done (posted the same question there as well).
$$\ce{KMnO4 + CaC2O4 + H2SO4 -> MnSO4 + K2SO4 + CaSO4 + CO2 + H2O}\tag{I}$$

No worries, balancing the K, Mn, Ca, C and S - but by then the H and O got out of my control. So this is how far I got myself:
$$\begin{multline}\ce{2KMnO4 + CaC2O4 + 4H2SO4 ->\\
 2MnSO4 + K2SO4 + CaSO4 + 2CO2 + 4H2O}\tag{II}\end{multline}$$

So the only thing left to be balanced, was the O, having 28 on the reagents' side and 24 on the product side. I started off, getting up to 36:33 O (reagents:products), and I felt that I was getting nowhere.

Anyone who would guide me through the steps following the balancing until equation II above?


texts: Displacement of leaving groups in organic reactions

texts:
When I initially learned about substitution reactions, there would be times where a poor leaving group had to be changed into a better one in order to proceed with a substitution reaction. For instance, changing a poor leaving group (-OH) to a better one, such as water:

After the "good" leaving group is made, it is displaced via an SN2 reaction. The displacement of the water required a nucleophile. However, I recently came across this mechanism (dehydration):

In this case, the water leaves by itself. My question is:

If I ever come across an instance where water (a good leaving group), must leave, how should I assess whether it can leave BY ITSELF or not?


texts: Standard curve of absorption and concentration

texts: I just wanted some quick help with a lab I'm doing, based on absorption spectroscopy.  I'm given an aqueous stock solution of Yellow Dye #5 with a concentration of 54.5 micro moles. I'm asked to create a standard curve.  It gives me the diluted volume as 50 mL, and has a data table with the volume of stock solutions and absorbance values for each.  It asks me to create a standard curve (absorbance versus concentration) in excel for the Yellow Dye #5.  First off, would I just use the constant concentration of 54.5 micro moles for this standard curve graph and the absorbance values in the data table?  I'm not familiar with what a standard curve is, or if the volume of stock solution affects the concentration value in the graph. If anyone replies I'll probably comment on the right answer with a couple more, thanks for the help!  It means a lot!


texts: Deflection of Alpha Particles in Rutherford's model of atom

texts: Rutherford stated that deflection of alpha particles is due to repulsive positive charge of nucleus. Why can't alpha particles be deflected by attraction of so many electrons revolving around nucleus?


texts: Percent Dissociated from Titration Curve

texts:
Question 818 references the titration curve. Answer is A because $\ce{H+}$ conc $= 10^{-4}$. This is conc of dissociated acid. The conc of the undissociated acid is the original concentration minus this: $0.1 - 0.0001$, which is about $0.1$. So then its $\frac{0.0001}{0.1}\times 100 = 0.1\%$.

Where in the world are they getting the original concentration? how did they get $0.1$ as the concentration of undissociated acid?


texts: What is the correct order of chemical reactivity in terms of oxidising property for the following elements: F, Cl, O, and N

texts: This is a textbook question. I am confused as to which factors i should consider while sorting out these elements. If I take electron gain enthalpy, then Cl should be greater than F, but if i consider electronegativity F is greater than Cl . I'd be grateful to anyone who provides  some idea..


texts: Why do liquids and solids have constant concentrations?

texts: I don't understand why liquids and solids have constant concentrations. Can anyone explain this to be in simple terms?


texts: Does the anti-rust properties of bluing carbon steel disappear at a certain temperature?

texts:
Yesterday I blued my new carbon steel wok over a very high (200K BTU) burner which is capable of getting the wok to 1000+ degrees with ease.
I understand that bluing adds a rust-resistant layer which is triggered by a chemical reaction at around around 575 F.
In this case I decided to blue the wok all the way up to 1100-1200 F given that this will be used on a very high temperature stove, and while I won't cook at those temps, the pan itself will get that hot from time to time (through accident, burning off stuck on oil, etc).
As I was doing this it brought some questions to mind. I tried researching but I have no knowledge of chemistry so I came here instead.

Does the rust-resistant property of tempered carbon steel vanish after you leave the blue temperature zone? In this case, I got it to the "very slight red" or "slight red" zone.

Are other properties affected as well at these temperature zones, in addition to rust resistance? It seemed from Googling that hardness is likely plummeting, which I suppose isn't important for a wok. It got me to thinking what else is changing in this pan.

Thanks!
In process:

Completed:


texts: Can a reactor be operated at both reflux and above atmospheric pressure?

texts:
I'm not a chemist by trade so my experience in the lab has probably not been as in-depth as most of you. I've been tasked with investigating a proposed reaction in which an organic mixture (mostly formic acid) is to be heated at reflux for several hours.

The complication being that a pressure of approx. 4 bar is required during the reaction. How would one go about achieving this? The reflux condensors I've browsed through are all open to atmosphere on one end.

Is there some sort of pressure regulator I can attach on the output of the condensor to maintain the pressure at 4 bar?

I'm told that the reaction may produce $\ce{CO2}$ and $\ce{NH3}$ by-products which means pressure is expected to increase and fluctuate as the reaction proceeds. Ideally I'd like to occasionally vent these to drive the reaction equilibrium forward.

The formic acid is quite corrosive to anything not plastic or glass.


texts: How to store bulk gas products and reagents?

texts:
Suppose I'm doing a batch process where an intermediate (non-hazardous) reagent is a gas, and I need to produce and temporarily store something on the order of a cubic meter of it to later feed back into a reaction.  Assuming the gas can't be condensed at anywhere near STP, isn't there some sort of standard flexible lab gas storage apparatus?

I've been looking for something like a large mylar (or other relatively impermeable) bag with a tube insert I can put on a barb and valve.  Either I don't know what this would be called, or it doesn't exist and I should be using something else.

I realize I could try to pump out a large rigid container, but once we're talking about a few cubic meters, and trying to avoid contamination, that seems like a pain compared to a flexible gas bag.


texts: Treatment of 2-vinylbicyclo[2.2.2]oct-5-en-2-ol with potassium hydride

texts:
What happens when this bicyclic compound is treated with KH in THF?

Does $\ce{KH}$ simply act as a base here? $\ce{H-}$ from $\ce{KH}$ could potentially act as a nucleophile, but I don't find any electrophilic centre in the compound. What happens?


texts: What kind of structure could give you a HNMR spectrum consisting of a singlet integrating to 5 protons?

texts:
A clean spectrum was given to me with the integrations filled in. I just need to assign peaks.

I just don't see how it's possible to have a singlet integrate to 5 protons.
I've considered symmetry, but still, 2 or 3 way symmetry wouldn't give me anything.

The chemical formula is $\ce{C11H14O2}$, with 5 degrees of unsaturation.
The spectrum is as follows:

5H, singlet, 7.5 ppm
2H, singlet, 5.1 ppm
2H, triplet, 2.4 ppm
2H, quartet, (or sextet?) 1.8 ppm
3H, triplet, 1 ppm

I'm just looking for a hint on what a 5H singlet could be.


texts: Effect of temperature and Le Chatelier's principle

texts:
The question
  $$\ce{2NO(g) + H_2(g) <=> N_{2}O(g) + H_{2}O} + \pu{351kJ}$$
  If the temperature is increased in the reaction above, which of the following occurs?

  A. The concentration of $\ce{H_{2}O}$ increases
  B. The concentration of $\ce{N_{2}O}$ decreases

My teacher said the answer is B;
however, I thought that since the reverse reaction is endothermic, adding more heat would produce more $\ce{2NO}$ and $\ce{H_2}$ which will cause an increase in pressure. But in order to maintain the same pressure, the system needs to decrease the number of moles so it favors the forward reaction because there are 3 moles of the reactants and 2 moles of the products.
Did my teacher make a mistake? If he did not can you please explain why he is correct.


texts: Choosing fish-oil that won't oxidize in long travel?

texts:
Fish oil, is susposed   to suffer from rancidity(i.e. oxidation) when stored improperly , for example in hot temperature.

I'm interested in buying fish oil from abroad(usa) it will be shipped by air and won't be kept in a cold chain,i live in a mediternean nation(climate wise).

How should i choose my fish oil , such that when i recieve it ,it will be OK and not rancid ? is it even possible ?


texts:
I have a small metal, most likely silver, cross. It is an old object and has turned dark. In order to clean it, my mother told me to boil it for a few minutes in water containing sodium bicarbonate.

Could someone explain what kind of reaction(s) occur(s)?


texts: Does 1,3‐dichloroallene show geometrical isomerism?

texts: Since the attached groups are present in different planes, $\ce{ClCH=C=CHCl}$ should not show geometrical isomerism, but my book say that it does. Why?


texts:
How to calculate or determine enzymatic activity?
The only information that I have are the substrates concentrations and the absorbance.


texts:
I am trying to create a PTC ink similar to Henkel ECI8120 , I researched PTC rubber and found that it was Polydimethylsiloxane (PDMS) loaded carbon nanoparticles, I was wondering if anyone here has some input on how to go about this.

I was thinking of dispersing carbon nanoparticles into the PDMS , but how do I get this to cure/solidify ?

I want to express that I am just asking for experimentation pointers/tips and not a complete solution.


texts: I do not understand how to use the equivalents to find the millimoles of the theoretical product. This is the part that I'm struggling with the most. My TA says that after I find the millimoles using the equivalents, then I can solve for grams and the mL of water.


texts: Why are there quantised energy levels in the vibrational energy of a molecule?

texts:
Why are the energy levels for vibrational energy in a molecule discrete as opposed to continuous?
I don't understand how a vibration can't have continuous amounts of energy that depend on the frequency of any infrared photon.

Can someone combine this question onto my stack exchange account: olly_price, because I can't sign in on this computer.


texts: Determining (approximately) the amount of a strong base needed to change a buffer's pH by a certain number of units

texts:
I'm measuring buffer capacity by titrating $\ce{NaOH}$ into a buffer of $\ce {H3PO4 + NaH2PO4}$. I'm measuring buffer capacity by recording the amount of $\ce{NaOH}$ required to increase the $\mathrm{pH}$ of the buffer by 2 units, and then taking the ratio.

My problem is that I have no idea how much $\ce{NaOH}$ I'll need to change the $\mathrm{pH}$ by that much. If I've underestimated the strength of my buffer, I might have to reduce the drop in $\mathrm{pH}$ to just one unit. I need to have a rough idea so I can organize how much of each I'll need to prepare.

Basically, is there any way I can predict (roughly) how much $\ce{NaOH}$ I'll need?

Details:

$1\:\mathrm{M}$ $\ce{H_3PO_4}$ and $1\:\mathrm{M}$ $\ce{NaH_2PO_4}$
Buffer volume: $50\:\mathrm{mL}$
$1\:\mathrm{M}$ $\ce{NaOH}$


texts: Using non-food grade NaOH for pH control

texts:
I would like to use non-food grade $\ce{NaOH}$ for $\ce{pH}$ water treatment. Any problem with this mixing with water that contains iron?

The $\ce{NaOH}$ will be pumped into a well. As a $25\%$ solution. Then sent through an ozone filter and a water softener.  Eventually, it will be used for pet and human consumption.


texts: Why is allyl chloride more reactive towards substitution than alkyl chloride?

texts:
I can understand that the reactivity of alkyl halide is more than vinyl and aryl halides because the halogen atom in alkyl halide is connected to the sp3 carbon.

Whereas in vinyl or aryl the halogen atom is connected to the sp2 carbon.

But how allyl halide is more reactive than alkyl halide?


texts: Will mixing methyl 2-cyanoacrylate and cellulose make the cellulose harden quickly?

texts: The other day I was gluing together cotton fabric with methyl 2-cyanoacrylate (superglue) and the fabric started heating up and then eventually began smoking. I have been working on making a 2-part plastic-like substance for personal reasons for some time now, and I know that ionic liquids pull the individual polymer chains that make cellulose apart and that once they are separated they go into solution easily. This in mind, could I get the dissoluted cellulose and add superglue to create a cheap plastic-like material?


texts: Why is gold unreactive when only one electron is in the outer shell?

texts:
I've been trying to answer my (high school) daughter's questions about the periodic table, and the reactivity series, but we keep hitting gaps in my knowledge.

So I showed that the noble gases have a full outer shell, which is why they don't react with anything. And then over the other side of the periodic table we have potassium and sodium, which have only one electron in their outer shell, which is what makes them so reactive, and at the top of our reactivity list. (And the bigger they get, the more reactive, which is why we were not allowed to play with caesium in class...)

But then we looked up gold, which is at the bottom of the reactivity series, and found it also has only one electron in its outermost shell (2-8-18-32-18-1).

Is there an easy explanation for why gold doesn't fizz like potassium when you drop it in water?

(This question could be rephrased as "What properties of each element decide their ranking in the metal reactivity series?" if you prefer; that was the original question we were trying to answer.)


texts: How can water exist in three states in freezing point?

texts: Freezing point is temperature on which vapor pressures of solid and liquid are equal. This is definition from my book. How can water ice and vapor of those co-exist when water that is only possible in triple point? How can vapor of those even  exist when in freezing point (melting point) there is equilibrium between solid and liquid? Is it when phases co-exist there is always  equilibrium between them question is only is it placed more towards one phase or the other?


texts:
In this question, 2a1H-cyclopenta[cd]indene is said to be aromatic.
My doubt is that the central C atom (connecting the three cyclic rings) is sp³ hybridized. So I think it should be non planar thus making compound non aromatic

Can someone please explain this compound’s aromaticity?


texts:
I want to understand what are the particles of a colloid in the microscopic scale. According to Wikipedia:

A colloid is a phase separated mixture in which one substance of
microscopically dispersed insoluble or soluble particles is suspended
throughout another substance.

What I can't understand is how we can have a phase seperation when we have soluble particles? I looked for some pictures and I got more frustated. For example in the following picture Colloids:
the particles seem to be like ordinary atoms/molecules just scaled up. So how can this particles exhibit bulk properties and classified as "solid" particles? Is the picture a simplification? I mean should colloid particles be represented as clusters forming a phase (e.g. solid) that is invisible to human eye?


texts: Where does the name ‘aliphatic’ come from?

texts:
Generally, carbons and the hydrogens bonded to them are classified as one of the following:

aromatic
olefinic
aliphatic
(something for triple bonds I don’t know)

The meaning of aromatic is rather clear to anybody: They belong to aromatic systems (even though the Hückel rule has nothing to do with a certain type of smell). Olefinic is also clear enough: Olefins were originally those gases which could generate an oily substance by reaction with e.g. chlorine ($\ce{C2H4 + Cl2 -> C2Cl2H4}$; the latter being 1,2-dichloroethane); the name olefin derives from French gaz oléfiant — oil-creating gas.

But I have no clue where the adjective aliphatic or the noun aliphat derive from, which are applied to saturated carbons. What was its original meaning and why do we use it?


texts: Acetone - Can it already be anhydrous when purchased?

texts: If I have 99.9% Reagent ACS, Lab grade Acetone, is it safe to say that it's free of moisture/Anhydrous?


texts: Is there a convention as to what order to write reactants and products in a reaction?

texts:
When doing homework, it can be time-consuming to check the answers in a redox reaction due to different order of the reactants and products.

For example, while $$\ce{2MnO4- + 5Fe^2+ + 16H+ -> 2Mn^2+ + 5Fe^3+ + 8H2O}$$ and $$\ce{5Fe^2+ + 16H+ + 2MnO4- -> 5Fe^3+ + 8H2O + 2Mn^2+ }$$ are equivalent, they are not visually equivalent and to mark them as correct/incorrect takes a lot of time.

Is there a convention of what order to write these reactants/products in? If so, what is this convention?


texts: I understand that phosphate is bonded covalently, however, it is characterized as a polyatomic ion. This is making me confused on whether it's polar or non-polar.


texts: My teacher told yes that salt is paramagnetic and it is attracted by magnet slightly. But when I tried that at home it did not work.


texts: How does % purity on household products work?

texts: For example, toilet bowl cleaner is 9.5% HCl. Does this mean that for every 90.5 moles of H2O (or other stuff) there is 9.5 moles of HCl? Does it mean that for every 90.5 g of H2O there are 9.5 g of HCl?


texts: Today, I learned that  $\ce{N_3^-}$ is referred to as azide. I was wondering why $\ce{N_3^-}$ is referred to as azide. I checked Wikipedia for an answer, but I didn't find one. Does anyone know why this ion is assigned this name?


texts: Is it possible to estimate a substance's water solubility from data like the substance's partition coefficient, dissociation constants, etc.?

texts: If it is possible, how would you estimate a compound's water solubility from data like its partition coefficient, $ \log P $, its dissociation constant, $pK_a $, its molar mass, etc.?


texts: Do any pharmaceuticals increase in potency or toxicity over time?

texts:
Pursuing a question raised in these comments:

Are there any known pharmaceuticals that increase in potency or toxicity during storage, or over periods of months to years?

If not, what if we broaden the question to include any bioactive chemical?

My hypothesis is that the answer is no due to the following considerations:

If we limit the scope to pharmaceuticals we often find that the bioactive components of a chemical are specific isomers.  In that case other isomers are relatively inert.  Over time racemization can only decrease the concentration of the bioactive isomers,* so under this mechanism potency can only decrease with time.  (I can't find any examples in which non-therapeutic isomers are more toxic than the therapeutic isomers.)
The other mechanisms of chemical change that I can think of chemically affecting a bioactive substance during extended storage are heat, light, evaporation, and atmospheric oxidation and moisture.  We might rule out all of these but heat in the case of properly stored pharmaceuticals, which are formulated and/or packaged to prevent exposure to these influences.  But even if we allow for exposure to any or all of these (keeping heat within reason – say under 60°C) I can't think of any examples by which these processes increase toxicity of any chemical.

Any specific examples or general suggestions to the contrary are welcome!

* Silas W. Smith, Chiral Toxicology: It's the Same Thing…Only Different, Toxicological Sciences, Volume 110, Issue 1, July 2009, Pages 4–30, https://doi.org/10.1093/toxsci/kfp097
provides an extensive survey of this question.  I certainly could have missed something during reading, but it does state early on that in drugs offered only as enantiomers "...the other isomer has no clinical effect or adverse effects in vivo."  Some examples show that while "adverse" effects (which I'll classify under "toxicity") can be found in non-therapeutic isomers, they do not exceed the adverse effects found in the therapeutic isomer.  So in the worst case it appears that a pharmaceutical can lose potency but not toxicity over time due to racemization, but this does not constitute an increase in "toxicity."


texts: What does it mean by degree of aromaticity of a molecule?

texts: This is a fundamental question, though I didn't really get the meaning/idea what does it mean by aromaticity or degree of aromaticity. Does it mean the ability of a molecule to be aromatic?


texts: How does copper rich "weld thru" primer protect iron / steel?

texts:
In the automotive industry, to protect steel which cannot be painted (e.g. the gap or seam between two sheet panels), a product known as weld thru primer is sometimes used.
This is a coating of zinc-rich or copper-rich material which is meant to prevent rusting of the steel, especially at the weld points.
From the reactivity table below, zinc is more reactive than iron, so I can understand how this would protect the iron via sacrificial corrosion. Similar to galvanized steel.
However, copper is less reactive than steel. When salt water get's in between the sheet metal seams, would this not corrode the steel? How would applying a layer of copper to the steel protect it?


texts: What type of spectroscopy can display several vibrational energy levels around the electronic transition?

texts:
My question is illustrated as the figure. As far as I know, due to the Franck-Condon principle, the absorption spectrum is related to the ground state to the excited state with the same geometry. Here I marked as $|X \nu_0\rangle \rightarrow |A \nu_m \rangle$, where $\nu_0$ is the ground vibrational state, $\nu_m$ is the vibrational state in the first electronic excited state with the same geometry as the ground state.
The emission spectrum is related to the excited state to the ground state with the same geometry. Here it is labelled as $|A \nu_0 \rangle \rightarrow |X \nu_n \rangle$, where $\nu_n$ is the vibrational state with the ground electronic state geometry.
The difference between absorption and emission spectrum is known as Stokes shift.
My question is, is there any type of spectroscopy has the resolution for many vibrational states around the electronic states? E.g.,  $|X \nu_0\rangle \leftarrow \rightarrow |A \nu_0\rangle$ ,  $|X \nu_0\rangle \leftarrow  \rightarrow |A \nu_1\rangle$ , $|X \nu_1 \rangle \leftarrow  \rightarrow |A \nu_0\rangle$  etc. If yes, what is the name of it?


texts: Biological activity of the isotopes of the same element

texts:
I have a question regarding biological activity of different isotopes of the same elements, notably $\ce{^206Pb}$ and $\ce{^208Pb}$. Lead is known to be toxic, such that it can replace calcium from bones and iron from hemoglobin for example. Would one isotope behave differently than another in such cases?
When it comes to hydrogen/deuterium chemical activities, some difference could arise as one isotope is twice as large as another. Would this be the case for heavier elements, such as lead?


texts: Why does the rate-determining step determine the overall rate of reaction?

texts:
I can appreciate that the rate determining step affects the rate of reaction. What I take issue with however is the exact wording given in the definition of the RDS.  From here:

  The rate determining step is the slowest step of a chemical reaction that determines the speed (rate) at which the overall reaction proceeds.

The last part about the RDS determining the rate baffles me. The RDS would affect the rate by slowing down a succeeding step, but in what way does it determine it?


texts: Why is phosphorus (v) oxides molecular formula P4O10 and not P2O5

texts: I understand that the name derives from the empirical formula; however, I do not understand why it does not exist as $\ce{P2O5}$. Is there a compound that exists with this as its molecular formula?


texts: Why the colour of KMnO4 at the end point of titration may disappear after some time?

texts:
In the redox titration of $\ce{FeSO4}$ with $\ce{KMnO4}$, the colour change of the solution at the end point is colourless to light pink. Most laboratory manuals and books advice us to check whether the light pink colour stays or not for 30 seconds. If the colour stays after 30 seconds, then end point is reached. If the colour disappears before 30 seconds, then the titration is not finished, so more $\ce{KMnO4}$ should be added.

As far as I understand, at the end point, all the reducing agent is depleted. So, the colour of $\ce{KMnO4}$ stays. And, if I have interpreted my book correctly, the colour of $\ce{KMnO4}$ is to stay for more than 30 seconds so that we can say that the end point is reached.

This means, that the colour of $\ce{KMnO4}$ might disappear after 30 seconds even though the end point is reached. But why? All reducing agents are depleted. Aren't they?

Now, I have found some reactions which might possibly cause the discharge of colour after the end point:

\begin{align}
\ce{3 MnSO4 + 2 KMnO4 + 2 H2O &-> 5 MnO2 + K2SO4 + 2 H2SO4}\\
\ce{3 MnSO4 + 2 KMnO4 + 8 H2SO4 &-> 5 Mn(SO4)2 + K2SO4 + 8 H2O}\\
\ce{4 KMnO4 + 2 H2O &-> 4 MnO2 + 4 KOH + 3 O2}
\end{align}

I am not sure which of them occur in reality.
So, which of the reactions are the reasons for the 30 second rule?
And why is it 30 second anyway? Why not 40 second or 1 minute?


texts:
I am facing a ween problem. I am trying to find out, how would look like the graph for fluroscence of aesculine (intensity of fluoroscence on Y axis and pH on X axis).
I know, that increasing the pH causes a corresponding increase in the maximum fluorescence intensity from 77.74 (units) in the acidic sample to 146.13 at neutral pH and 232.69 at alkaline pH.
But, can I apply this on aesculine?


texts: Why do ions form condensation centres in isopropanol vapour?

texts: In cloud chambers the particles are detected when a particle passes through the chamber causing the vapour to condense into a "cloud". What Process causes this observed phenomenon? In other words, how exactly do the particles tracks form in a cloud chamber?


texts: For a system to undergo a spontaneous change at constant temperature and pressure the Gibbs free energy must decrease, but how?

texts:
$$\mathrm dG < V\,\mathrm dp - S\,\mathrm dT$$

For a process at constant pressure and temperature ($\mathrm dp = \mathrm dT = 0$), and in the absence of any non-pV work, $\mathrm dG < 0$. Since energy cannot be created or destroyed (and Gibbs free energy is a measure of energy) where does the energy go when this spontaneous change occurs? Likewise for internal energy: $\mathrm dU = T\,\mathrm dS - p\,\mathrm dV$?

Also, why is this even useful? I understand that it's easy to hold temperature and pressure constant in a lab but we only seem to measure enthalpy anyway using $\mathrm dH = C_p\,\mathrm dT$. If it's so easy to keep temperature and pressure constant yet so hard to keep entropy constant then why do we measure enthalpy (which decreases for a spontaneous change when entropy and pressure are held constant) rather than Gibbs free energy. I suspect I am barking up the wrong tree and I am hoping that you'll be able to put me right; the only thought that I had was that the fact that Gibbs free energy muct decrease for a spontaneous change would help to predict whether a spontaneous change would occur when done in a lab - given that $p$ and $T$ will be constant; is this right?


texts: Why do gases coexist as liquid and vapour?

texts:
I have having difficulty in understanding the liquefaction of gases.In the graph
of isotherms of $\ce{CO2}$ I cannot understand how can gas coexist as liquid and  vapour under area of $\mathrm{XCEBY}$.

I have read the following statements in my textbook:

At $\pu{21.5 ^\circ C}$, $\ce{CO2}$ remains a gas up to point $\mathrm B$. At point B a liquid of specific volume appears.In fact,the gas and liquid  $\ce{CO2}$ coexist along the horizontal line $\mathrm{BC}$. The decrease of volume represents condensation of more and more $\ce{CO2}$ gas till point $\mathrm C$ is reached.

A careful study of isotherms reveal that it is possible to change gas to liquid by following a path in which a single phase is present throughout the process.For example,move vertically from $\mathrm{A}$ to $\mathrm{F}$ by increasing the temperature of the gas.Now move from point $\mathrm{F}$ to point $\mathrm{G}$ by increasing pressure at constant temperature.Move from point $\mathrm{G}$ to point $\mathrm{H}$ by lowering the temperature.As soon as we cross point $\mathrm H$ we get a liquid.

(i)Why $\ce{CO2}$ coexist as liquid and vapour in the area of $\mathrm{XCEBY}$?(instead of converting directly into liquid by condensation of all the molecules simultaneously)
(ii)Why under some range of pressure and temperature $\ce{CO2}$ converts directly into liquid without going through the two-phase region?


texts: Can you make R-Candy without heating the propellant mix?

texts:
I'm wondering if there's any way you can make "Rocket Candy" (or R-candy) fuel without cooking it. I'm building a model rocket that I'm hoping will get about 3 km on my first build (It's not going to be super big), and I thought R-candy was a good idea. I am just getting into this stuff, but I'm doing a ton of research and trying to be safe.
In every recipe I've seen, it says that you need to "cook it" on a stove or use some other heat source. I'm wondering if you can avoid using a stove, oven, etc.
If there's no way to make R-candy without cooking it, is there some other fuel I can make from household materials?
P.S. The ammonium–aluminum fuel isn't an option for me.


texts: In the pH system of acids and bases, are there 10^-7 loose ions per liter (at pH of 7) or per mole of solvent? (Or per mole of total substance?)

texts:
Most places tell me that the number on the pH scale tells you the number of dissociated ions, in moles, per liter of substance.    But, Wikipedia's article pH says this....:

... For a commonplace example based on the facts that the masses of a mole of water, a mole of hydrogen ions, and a mole of hydroxide ions are respectively 18 g, 1 g, and 17 g, a quantity of $10^7$ moles of pure (pH 7) water, or 180 tonnes ($18\times10^7$ g), contains close to 1 g of dissociated hydrogen ions (or rather 19 g of H3O+ hydronium ions) and 17 g of hydroxide ions.

But, if there are 10^-7 moles of hydrogen cations (protons) per LITER, and one mole of protons is approximately one gram (as Wiki's example says), then there is one mole (one gram) of protons per 10^7 liters of water, right?  One gram of hydrogen cations per 10,000,000 liters?
As opposed to what Wiki says, claiming one gram of loose hydrogen ions per 180 tonnes of water?
(One liter of water weighs about one kilogram, and there are a thousand kilograms in a tonne, correct?)
EDIT: Wiki's section on pH and all the incorrect numbers have been corrected.


texts: Classifying some molecular orbitals after Hartree-Fock calculation

texts:
I have done a Hartree-Fock (HF) calculation on a dioxetane molecule with one methyl group on one of the C-atoms (Fig 1), with minimal basis (using Molcas). I want to identify the active space that will be used in later CASSCF calculations on the same molecule. The interesting molecular orbitals (MO's) for this active space are the following ones: $\sigma_{CC}$, $\sigma_{CO}$, $\sigma_{CO}^{'}$, $\sigma_{OO}$, $\sigma_{CC}^*$, $\sigma_{CO}^*$, $\sigma_{CO}^{*'}$, $\sigma_{OO}^*$, $n_{OO}$, and $n_{OO}^{'}$. So basically all the ring bonding and anti-bonding MO's, plus the two non-bonding MO's on the oxygen atoms.

The CO MO's are not localized for just one CO pair, but rather they both exist at the same time in an "out-of-phase" and "in-phase" version. These are given in Figs 2-5. The same goes for the non-bonding MO's; they both exist in an out-of-phase and in-phase version, given in Figs 6 and 7. Then there are only the CC and OO MO's left. In the same calculation for 1,2-dioxetane (zero methyl groups, only H atoms on the carbons), I find separate CC and OO MO's. However, for this one-methyl dioxetane, it looks like the CC and OO MO's are combined, giving out-of-phase and in-phase version of both the bonding and anti-bonding. My issue is that the MO's look a bit ambiguous, in that some of the lobes are not where I expected them to be. These MO's are given Figs 8-10.

For it to be a $\sigma$ orbital, the electron density should be in the bond axis between the atoms. However, in Figure 8 this is not the case. It's like the same-phase lobes attract each other and overlap instead inside the ring. Is it correct to interpret this as the CC/OO in-phase bonding MO? Figure 10 looks more like the $\sigma_{OO}^*$ than the in-phase $\sigma_{CC/OO}^*$, as the orientation of the lobes on the C atoms seem strange to me. Especially the MO in Figure 11 is not obviously classified, in my opinion. The OO contribution seems very small, and the lobe orientations on the oxygens are not what I would expect for an anti-bonding $\sigma$ orbital.

However, there are no other candidates for these MO's, so I'm left with the current classification, even if it feels a bit incorrect. Perhaps this is a common issue in analyzing molecular orbitals in computational chemistry.

P.S. I apologize for the bad figure qualities, I don't know how to visualize molden files in any other way.

Figure 1. The molecule

Figure 2. CO bonding in phase

Figure 3. CO bonding out of phase

Figure 4. CO anti-bonding in phase

Figure 5. CO anti-bonding out of phase

Figure 6. Non-bonding in phase

Figure 7. Non-bonding out of phase

Figure 8. CC/OO bonding in phase

Figure 9. CC/OO bonding out of phase

Figure 10. CC/OO anti-bonding in phase

Figure 11. CC/OO anti-bonding out of phase


texts: I am a freshman majoring in chemistry. I am aware that one of the tasks required in this field is extensive research, and I am encountering a big problem. I am lost as to how to think of a plausible paper— I am not sure how to think of proper "topics" that would suffice the requirement in this field. I am once advised to look for societal problems and how my field can potentially propose solutions to it, but as of now, I'm still blank to any topics and/or ideas. I hope any of the people here can guide me through this so that once that I'm actually assigned to write, I can think of a topic without any problems.


texts: Does the electron displacement effect act only on sigma electrons?

texts:
Our teacher told us that the inductive effect or the electron displacement effect can only affect the sigma electrons. I did not understand why this should be.
I reasoned it can not affect the pi electrons, because they are "delocalized".
Also, for measuring the displacement, the C-H bond is taken as a reference. The C-H bond does not have a pi bond, and so we can not consider pi electrons as being affected
Is it true that the inductive effect or the electron displacement effect affects only sigma electrons? Why should it be so?

I am not asking if it operates through single bonds only, as asked in this question.


texts: What is the influence of an alkyl-hydroxy group on a benzene ring?

texts:
We all know that an $\ce{NO2}$ group attached to a benzene is a deactivator, and it directs and substituents that would be adding to the meta position to the $\ce{NO2}$.  For an alkyl group attached to a benzene it is an activator, and it directs to the positions ortho/para to the alkyl group.

I haven't found any information on how a $\ce{-CH2-OH}$ group would affect the reactivity of the benzene ring shown below


texts: False positive in lucas test for primary alcohol due to formation of tertiary carbocation by rearrangement?

texts:
From Wikipedia:

The Lucas test in alcohols is a test to differentiate between primary, secondary, and tertiary alcohols. It is based on the differences in reactivity of the three classes of alcohols with hydrogen halides via an $\mathrm{S_N1}$ reaction:
$$\ce{ROH + HCl -> RCl + H2O}$$
The differing reactivity reflects the differing ease of formation of the corresponding carbocations. Tertiary carbocations are far more stable than secondary carbocations, and primary carbocations are the least stable.

So since alkyl halides are insoluble, they give a turbid solution upon formation, which easily happens for tertiary alcohols.
Consider a primary alcohol, like $\ce{(CH3)3-C-CH2OH}$, which forms a tertiary carbocation, $\ce{(CH3)2C+-CH2CH3}$ by an alkyl shift from primary carbocation during the substitution process. So will Lucas test give a false positive in this case, since a tertiary alkyl halide can be easily formed from a primary alcohol?


texts: Strong Base combined with Sp2 carbons in Nucleophilic Substitution and Beta-Elimination Reactions

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When we are given this problem, there is a certain problem. We have a strong base, but hydrogen on the carbon of the phenyl. E2 is impossible. Also, SN2 is not possible since we have a hindered base.

The only product we could get is SN1. My teacher put up the answer in handwritten black in the above picture.

However can SN1 reactions happen when there is a strong base in the solution? Would that strong base be the nucleophile or the solvent tert-butyl alcohol be the nucleophile?


texts: Removing aluminum oxide before galvanic current and potential measurements

texts: I have an aluminum sample stored about 1 month ago. I am going to couple it for galvanic current and potential measurements. I think the Al sample grew an oxide film due to exposure to air. Would the aluminum oxide film can affect the measurements? Should I remove it first? How?


texts: How can we separate carbon monoxide from wood gas?

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I am thinking about using open source wiki designs from allpowerlabs to construct a wood gas generator.  The motivation came from experiencing a 10 day power outage after super storm Sandy.  The utility company could not provide power due to damaged transformers, power lines, and other grid infrastructure.  Most of the gasoline service stations did not have backup power to run the pumps and meters and those that did had huge queues to wait through.

Meanwhile there was tons of biomass available in my 2 acre yard.  I used some of the wood in our wood stove for heating and some cooking but did not have a way of getting the energy stored in wood and other biomass to electrical energy.

The solution is a wood gas generator that converts the stored solar energy in wood to a gas that can be combusted in a hacked generator to provide electrical power.  Allpowerlabs.com has a turn key solution all ready to go but it is beyond my budget, but they offer the open source build it yourself GEK (Gasifier Electricity Kit), mentioned earlier, that I would like to build.

Instead of using the wood gas to run a hacked Briggs and Stratton  generator, I would prefer to route it to a BIY (Build It Yourself) fuel cell.  Wood gas consists of hydrogen, carbon monoxide, carbon dioxide, water vapor, and small amounts of other.  For fuel considerations hydrogen(H2) and carbon monoxide(CO) are usable.

While molten carbonate and solid oxide fuel cells can use CO, the operating temperatures are too high to be practical and we want to sequester the carbon instead of releasing to atmosphere.  I would like to separate the carbon oxides from the wood gas and use the H2 directly into a fuel cell or store it for later use.

I know that we can remove CO2 from the wood gas or exhaust with low cost or Brew it yourself sodium hydroxide (NaOH), via caustic scrubbing.

My question is: How can we cost effectively separate the CO from the wood gas?  I am not sure how NaOH reacts with hydrogen gas and CO.


texts: Why May K Expressions Be Manipulated As Such?

texts: Why is the above massaging of various K expressions valid? Something in me says "Hess's Law." But then doesn't that deal with enthalpy? What's the true reason?


texts: Why are radical intermediates are more stable on tertiary carbons?

texts: Is this because there's more electron density? More carbons around means the tertiary carbon "has more electrons around it"?


texts: Why is charcoal useful as a fuel compared to wood? Don't we lose energy by making it?

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Charcoal is produced by partially burning wood. However, as the wood is burned, some of its energy is lost. Why is it that charcoal is still preferred as a fuel instead of wood in many cases?

Doesn't charcoal contain less energy than wood? Is the main reason that wood contains a lot of water which would form unwanted vapor?


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See the following question:

I think the answer is A because of the hydrogen bond in the side group, thus the degree of secondary bonding between parallel chain segments is higher.  Is my thinking correct?


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This is rather a bunch of questions that I decided to post on Chemistry StackExchange since I thought the chemists would have the most knowledge about the chemical processes of life.

So recently I have came across stem cells and a lot of revolutionary medical products that can rebuild tissue and even organs.

And then I thought that can we use these products to transplant our organs and in a sense, rebuild our own body. I have even came across making a heart and lungs as well.

If so is there any thing that stands between having a longer life?

What else do we need to have in order to prolong and in a sense immortalize ourselves.

I know that it would be impossible to do this for everyone since our planet cannot sustain more life, but theoretically is it possible to do this?

What are you views into this?


texts: Assignment of the IR spectrum of 2,4-pentanedione (acetylacetone)

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The IR spectrum is shown here:

My assignments so far:

The 1728 and 1708 stretches correspond to $\ce{C=O}$ stretches in the keto form - the symmetric/asymmetric stretches respectively.
The 3003 stretches are typical $\ce{C-H}$ stretches.
The 1606 stretch corresponds to the $\ce{C=C}$ in the enol form. However, hidden under this peak there is also the $\ce{C=O}$ stretch in the enol form, which is lowered by conjugation to the $\ce{C=C}$ and the $\ce{O}$ of the $\ce{-OH}$ respectively.

I have two questions about the spectrum, however:

Why is there no $\ce{-OH}$ peak? Even if the enol is hydrogen bonded to itself, there should still be an $\ce{-OH}$ peak in the $\pu{3400 cm^{-1}}$ range?
Does the fact that the carbonyl peak in the enol form is hydrogen bonded change its shift? Assuming the only contribution to the lowering of the $\ce{C=O}$ stretching frequency is conjugation to the one $\ce{C=C}$ bond, this would lower the peak to ~$\pu{1655 cm^{-1}}$: Surely this would be seen as a peak in its own right? It seems to be shifted even lower to be fully hidden by the 1606 peak.


texts: I have got this IMAGE peculiar chemical reaction and  tried to find reason behind it. But I couldn't. Can you write the reason?