texts: Is pH in a charged hydrogel and its supernatant solution constant?

texts:
Let us assume we deal with ideal systems without interactions.

The gel phase and the supernatant solution phase are in thermodynamic equilibrium. The supernatant solution shall consist of different ion species $i$.
The gel is in free swelling equilibrium and the total chemical potential of each ion species $i$ is constant throughout the supernatant phase and the gel phase:

$\mu_i^\mathrm{gel}=\mu_i^\mathrm{supernatant}$.
Since the total chemical potential is constant we can just write $\mu_i$ and forget about the phase in which it was determined.

Under the assumption that gel phase is always electroneutral we obtain a Donnanpartitioning of ions:
$c_i^\mathrm{gel} \neq c_i^\mathrm{supernatant}$
compare: https://en.wikipedia.org/wiki/Gibbs%E2%80%93Donnan_effect

The difference in concentration between the two phases is allowed (at same total chemical potential) because the total chemical potential not only has the ideal part but also an electric potential part (needed due to the electroneutrality constraint):

$\mu_i=\mu_i^0+kT\ln(c_i/c_0) +z_i e_0 \Psi$.
Same total chemical potential at different ion concentration therefore gives rise to the Donnan potential (https://en.wikipedia.org/wiki/Donnan_potential):

$\mu_i^\mathrm{gel}=\mu_i^{supernatant} \Leftrightarrow \Psi^\mathrm{gel}-\Psi^\mathrm{supernatant}=\frac{kT\ln(c_i^\mathrm{supernatant}/c_i^\mathrm{gel})}{z_i e_0}$

Now the question is: Is pH constant (case 1) or is it different (case 2) in the gel phase and the supernatant solution phase.

If pH is defined based on the total chemical potential, then it is constant (because chemical potential is constant) and we have the same pH in the gel and in the supernatant phase:
$pH=-\log_{10}(a_H)=-\log_{10}(\exp(\frac{\mu_H-\mu^0}{kT}))$
If we define pH based on the concentrations, then the pH is different in the gel and in the supernatant phase:

$pH^\mathrm{gel}=-\log_{10}(c_H^\mathrm{gel}/c_0) \neq pH^\mathrm{supernatant} =-\log_{10}(c_H^\mathrm{supernatant}/c_0)$

($c_0$ is the standard concentration, i.e. 1mol/l)

What is correct? What would we measure when measuring the pH in the gel? Would we measure the same pH as in the supernatant phase (i.e. the first case is correct) or would we measure a pH different from the supernatant phase (i.e. the second case is correct?)

You can view the problem also from a different perspective:
pH is defined by IUPAC (https://goldbook.iupac.org/terms/view/P04524) $pH=−\log_{10}[a_H]$, where $a_H$ is the relative activity https://goldbook.iupac.org/terms/view/A00115): $a_H=\exp(\mu_H-\mu_H^0)$

The question is do I need to use

the total chemical potential in this definition of the activity or
this definition of activity which you also find in literature (e.g. in this article "THE DONNAN EQUILIBRIUM" by Stell and Joslin, https://www.ncbi.nlm.nih.gov/pubmed/19431690):

$\mu_H=\mu_H^0+kT\ln(a_H)+z_H e_0 \Psi \Leftrightarrow a_H=\exp(\mu_H-\mu_H^0-z_H e_0\Psi)$ ?

In case 1) pH would be equal across both phases, in case 2) pH in both phases would be different: we could write $pH^\mathrm{gel}-pH^\mathrm{supernatant}=-\log_{10}(\exp(\mu_H^\mathrm{gel}-\mu_H^\mathrm{supernatant}-z_H e_0 (\Psi^\mathrm{gel}-\Psi^\mathrm{supernatant}))
=-\log_{10}(\exp(-z_H e_0 (\Psi^\mathrm{gel}-\Psi^\mathrm{supernatant}))$


texts: Derive expression for average heat flux in heat exchanger

texts:
The single-tube heat exchanger is used to increase the temperature of fluid
  I from $T_{b1}$ to $T_{b2}$. The heating oil (fluid II) used
  for this task enters at temperature $T_{02}$ and leaves at
  temperature $T_{01}$.

  a) Give the expression that describes the average heat flux from fluid II to fluid I.

I don't really know how to derive the average heat flux but the equation I immedietly think of using is:
$$q = U(T_{b1} - T_{b2})$$

Still I am not sure how I should calculate the overall heat transfer coefficient and also I recall being told that when dealing with heat exchangers you should use the logarithmic temperature difference. So the expression should be:

$$q = UΔT_{\ln}$$

where the logarithmic temperature difference is

$$ΔT_{\ln} = \frac{(T_{01} - T_{b1}) - (T_{02} -T_{b2})}{\ln\frac{T_{01} -T_{b1}}{T_{02} - T_{b2}}}$$

And an attempted solution for the overall heat transfer coefficient is:

$$U = h_1 + \frac{k}{R_0\ln(R_a/R_0)} + \frac{h_2R_a}{R_0}$$

but I feel like this isn't correct since it is used when calculating the heat transfer in a heat exchanger and not the heat flux. Is it correct or is the heat flux for a heat exchanger calculated in a different way?

All help is greatly appreciated!


texts:
Why isn't the silicon analogue of benzene flat? As far as I understand, silicon and carbon make similar structures and it doesn't make sense that its benzene analogue should be substantially different.

Quoted from the article:

  Chemists in the UK have constructed a structural analogue of benzene made from silicon atoms. The molecule is not flat like benzene, but it reveals a new type of aromatic stabilisation.

This 'new' type of aromatic stabilisation is said to occur only around the seat of the chair structure.

I am thinking that silicon's bonds are too weak to be kept in a double bond, and therefore it doesn't have enough energy to change the shape of the bonding and is thus quite unstable.


texts: Cis and Trans Isomerism given three different groups around the reference plane

texts:
In the following problem I am meant to deduce the molecules that are cis-trans isomers of each other.
This question does not make much sense in my head because I thought that cis/trans isomerism was only applied to configurational isomers if there were only two types of groups bonded to the carbon atoms in the carbon-carbon double bond i.e. the reference plane. Such that, if there are more than two groups bonded to the carbons in the reference plane then E/Z isomerism should be used. However, then I thought that cis/trans isomerism is a subcategory of E/Z isomerism and therefore I tried to work out the solution using the E/Z method of finding configurational isomers by finding the relative priorities based on the atomic numbers for the atoms attached to the carbon atoms on each side. Using this method I discovered, that the solution could only be 'A. X and Z' since X seems to be an 'E' isomer since its high and low priority groups are across from eachother and Z seems to be a 'Z' isomer since its high and low priority groups are on the same side.

Am I on the right track?


texts: How does addition of impurities in a solid decrease the melting point?

texts:
In my textbook, it is written:
The addition of impurities in a solid decreases the melting point of the solid.

How does it do so? Why can't it increase the melting point?


texts: Liquid that looks like smoke when bottled?

texts:
I am making a gift that will consist of a liquid in a sealed bottle. I want the liquid to have a magical appearance. Something like the appearance of smoke - varying opacity from almost clear to almost opaque but never completely mixing.
I am looking for a liquid or combination of liquids with the following properties:

Looks like smoke
Will not become homogeneously opaque over a relatively long period of time (months)
Non-toxic and non-reactive in a household setting (in case it is spilled accidentally)
Relatively
easily found / made assuming access to decently stocked pharmacies,
grocery and hardware stores
Can be coloured would be a bonus


texts:
This is isotherm of a real gas is represented as shown in diagram at three temperature . In my book it is written that in ACIH gas liquid transition will involve only one phase throughout .

But I could not understand how this can be possible as at A it would be gas while at H it would be liquid .


texts: Soil-solution cations in competition for exchange sites

texts:
How could one determine the likelihood of one cation displacing another on a negatively charged exchange site of a clay particle?

For example, in a soil solution containing equal parts (by number of atoms) $\ce{Ca^2+}$, $\ce{Mg^2+}$, $\ce{K+}$, $\ce{Na+}$, $\ce{Al^3+}$, which cations will find the most exchange sites and which will ultimately be washed deeper into the soil? (Assuming there are not enough sites for all of them.)

Could two $\ce{Na+}$ cations displace an adsorbed $\ce{Ca^2+}$ cation simply because they "bump" into it? Or is there some mechanism where cations are dislodged? Is it easier for two $\ce{Na+}$ to replace $\ce{Ca^2+}$ or for $\ce{Ca^2+}$ to replace two $\ce{Na+}$?


texts: Why would electrode reaction in galvanic cell stop when there's no neutrality in each cell?

texts: I know that the salt bridge produces ions to balance out the positive and negative ions in each solution, but why won't it work without a salt bride? Would it even work at the start since there's few electrons gained and lost and few ions produced?


texts: Is RDP (redispersible polymer powder) and PVA (polyvinyl acetate) same?

texts:
I am a freshman in chemistry and looking for additives to the alpha Gypsum plaster to make its surface hardness stone-like and gain it more flowability when pouring, my composition for making the product is below so far:
dehydrated Gypsum + 1 percent potassium sulfate. Now I realized that PVA(polyvinyl acetate) can add more surface hardness to the Gypsum but don't know that it could make Gypsum more flowable.
can anyone help with any additives to make the alpha Gypsum more flowable and harder?
Is it true that RDP and PVA are the same?


texts: How is sulfuric acid with a concentration of 12 M also 72% w/w?

texts:
According to LabChem, $12~\mathrm{M}$ of $\ce{H2SO4}$ is $72~\mathrm{w/w\%}$.

When I try to convert $12~\mathrm{M}$ of $\ce{H2SO4}$ to $\mathrm{w/w\%}$ I get $117\%$ which is obviously wrong.

$$\begin{multline}
12~\mathrm{M}\cdot\left(\frac{1~\mathrm{L}}{1000~\mathrm{ml}}\right)
\left(1~\mathrm{\frac{ml}{g}}\ \ce{H2O}\right)
\left(98.09~\mathrm{\frac{g}{mol}}\ \ce{H2SO4}\right)\\
= \frac{1177~\mathrm{g}}{1000~\mathrm{g}} = 1.177=1.177\cdot100\%=117.7\%
\end{multline}$$

I must be doing something wrong. How do you convert it correctly?


texts: Can Substances on Titan be Reacted at a Thermodynamic Gain?

texts:
Titan, a moon of Saturn, has readily available water ice ($\ce{H2O}$) and methane ($\ce{CH4}$) on its surface, at a frigid $\pu{93.7 K}$.

It would be significant if these (or possibly, other available hydrocarbons) could be reacted in a self-sustaining way, releasing usable energy.  I presume the best way of doing this would be to react by the simple following two step process:

Split water into hydrogen and oxygen:
$$\ce{2 H2O → 4 H2 + O2}$$
Burn oxygen and methane:
$$\ce{CH4 + 2 O2 → CO2 + 2 H2O}$$

Keeping in mind the starting temperature, does this sequence of reactions operate at a net energy release (that is, is it theoretically possible to use this reaction to power itself, with energy leftover)?  If not, could other hydrocarbons* found on Titan fit the bill?

*Methane, ethane, propane, and benzene exist. Others may as well.


texts: Recently I have started looking for two reactions that would speed each other up. That means that the products of the first reaction accelerate the second one, and in turn, the products formed in the second reaction accelerate the first one. Do you know any examples of such reactions?


texts: Increased vibration causes the atoms in an object to spread out farther away. Thus, with added heat, and object goes form a solid to a liquid to a gas (and then to plasma, with enough heat). Why is it then, that when a heat something like cake batter, it solidifies?


texts: Bond order for carbonate ion for resonance

texts:
I saw in a textbook that for carbonate ion, there are 3 resonance forms and the bond order is 1 and 1/3. So in general, how should we calculate the bond order for resonance structures?

Is there any definite way to do this?


texts: Order of Bonding in Nonaqeuous Hydrated Salts

texts:
In the chemical formula of a hydrated salt, such as $\ce{CuSO_4.5H_2O}$, is it implied from the format of the name that the the Copper (II) ion is ionically bonded to the sulfate, with water molecules surrounding both, or that the Copper (II) ion forms a coordination complex with 6 water molecules and the complex ion bonds with the sulfate ion?

I think that in the case of copper (II) sulfate, there indeed is a complex ion formed, otherwise, how could there be the blue color? I thought that the convention for this kind of nomenclature was to use the dot for the first case, and then use $\ce{[Cu(H_2O)_5]SO_4}$ when there is a complex ion involved. Thus, isn't the better name for Copper (II) sulfate, $\ce{[Cu(H_2O)_5]SO_4}$?

*Update: It seems from the comments that in this case, Copper (II) sulfate is better described by the second naming type. Are there any transition metal salts that fit the first description: where it is a normal ionic bond except with water surrounding the cation and anion?


texts: Why there is a need of independent definitions for both mass and mole?

texts:
Considering that the two quantities are linked by reality, how can be both imposed by independent definitions?
I am aware that the change taking place next May does not effect common weighing in chemistry and engineering, but still the new definition of mole (an exact number of entities, to be called Avogadro number as well) does confuse me, conceptually.
Direct counting is not a practical way of sampling, so already I do not see the good of defining mole as a fixed number of entities (of course I have thought in this way already, but I am not a definition :).
How can I now weigh a mole of substance, in principle? It seems that without a history-of-science background, armed by the mass definition and mole definition, I cannot weigh in moles despite of having both very well defined.
Before, the "only" knowledge required was a table of atomic masses, and one could have done that even ignoring the value in grams for 1 amu, if not interested in spelling out the value of Avogadro number itself. I think is what happened before mass spectroscopy sort of techniques revealed the absolute mass of particles and atoms.
To date, the Mole is conceptually and mathematically linked to a mass measurement, ie. the amu and its multiples. With the new definition the two things are distincts, as 12 g of 12 Carbon is not a Mole anymore.
Please clarify without listing the non-operational pros of the new definitions, as the fact that the latter stresses the difference between matter as mass and matter as substance even more than before, to mention one that, as a chemist,  I like much.
The abstract of this paper by B. P. Leonard,Metrologia 2010, 47 (3), L5–L8 expresses my concerns in a more elegant way: Metrologia 2010, 47 (3), L5–L8

The fundamental concept of the mole requires the number of entities comprising one mole, i.e. Avogadro's number, to be exactly equal to the gram-to-dalton mass ratio. If this compatibility condition is to be satisfied, the mole, the kilogram and the dalton cannot all be defined independently. This note concerns recent Metrologia publications that do, however, propose independent definitions of all three quantities: the mole by fixing the value of Avogadro's number and the kilogram by fixing the value of the Planck constant, while retaining the current carbon-12-based dalton. Adoption of these incompatible definitions would likely cause serious widespread confusion and might even result in a split in scholarly and technical communication between the quantum
physics and chemistry communities. Other entirely compatible alternatives are possible: either retaining the current (inexact) carbon-12-based mole and dalton with an independently redefined kilogram or redefining the mole by fixing the value of Avogadro's number, with a compatible dalton that is exact in terms of the redefined kilogram.


texts: Finding pH using the -log, why does my calculation differ from the book's answer?

texts:
An aqueous solution containing 0.0020 mol/L barium hydroxide, what is the pH? I do the following: 14-(-log(0.0020))=11.3pH. The answer is 11.6.

2.0*10^-3 mol/L sodium hydroxide solution, what is the pH? I do the following:
14-(-log(0.002))=11.3pH. The answer is 9.3

When I solve for pH of solutions with acidic solutes, I get the accurate answer, such as in the question: 2.0*10^3 mol/L nitric acid solution, where I do:
-log(0.002)=2.7pH, which matches the answer, 2.7.

My question is, why am I getting the discrepancy between the calculated and the given answer when calculating pH for solutions with base solute? Or am I not doing anything wrong?


texts: Does RMS velocity depend on number of gas molecules in a gas sample?

texts: The expression of RMS velocity clearly has square root of number of gas molecules in the denominator and square root of squares of velocities of the gas molecules in the numerator. Then why RMS velocity does not depend on number of gas molecules? By looking at the expression, it seems as if it does depend on number of gas molecules.


texts: Why does H+ attack alkene first in this reaction?

texts:
The reaction is:

Why is the double bond attacked here even though it is in conjugation with the lone pairs of O thereby making it harder to extract. Also,don't the 2 lone pairs on OH have more electron density than the pi bond?


texts: Electroplating a spoon (electrolytic cell) using a electrochemical voltaic cell

texts:
I drew a rough picture of the two cells, and marked each position with a distinct letter:

The whole reason I am asking this question is that I am bit confused and unsure about some of the chemistry and physics concepts. It will be extremely helpful if you guys can tell me if what I did is correct and why.

What I think is correct: to make this whole thing work.

Connect alligator clip x to position A, right on the zinc anode not the wire.

And connect clip y to B, on the copper cathode plate.

From what I read, the electron is forced from Ag plate, anode, through the wire (with two alligator clips on each end), then reduces $Ag_{+}$ ions to $Ag$ metal on the spoon cathode. But from the picture, it looks more like all the electrons came from the zinc anode of the voltaic cell and all the electrons from the $Ag$ anode of the electrolytic cell go to $Cu$ cathode of the voltaic cell.

Some physics aspect of this: if x clip was to be connected to position C and y clip to position D, is it true that there will be no potential difference?(unless the wire itself has a high resistance)


texts:
I just started reading about the technique of chromatography and learning how important it is.

Now I'm trying to focus on whether is possible to use this technique in the geological fields (fossils and dating for example.)

I'm just brainstorming so any thoughts will help here.


texts: In the mechanism of Cannizzaro reaction why does the hydride migrate rather than the benzene ring?

texts:
The hydride ion is not very stable. On the contrary a negative charge on a $\ce{sp^2}$ on the benzene ring would be much more stable. So why doesn't the benzene ring migrate instead of the hydride, as the benzene ring with a negative charge would be a better leaving group (as we know that less basic groups are better leaving groups)?

I've seen some examples where the benzene ring does migrate instead of the hydride for example when two nitro groups are attached at ortho positions. But I think the benzene migration should always happen instead of the hydride migration for reasons which I stated above.

P.S: Someone suggested me that the "real" mechanism is the transition mechanism. But even that does not explain why the transition state involving o-dinitro benzene would be more stable than the one involving $\ce{H}$ but the one involving just a benzene would be less stable than $\ce{H}$. How do we logically explain the discrepancy?


texts: why lithium is less reactive than sodium?

texts: Lithium lies above sodium in a group and is also smaller in size. According to periodic trend reactivity decreases from left to right in period and down the group.


texts: Does NaOH have a higher OH- concentration than NH3?

texts:
In my book it's a multiple choice question with only one correct answer.

There are two solutions of $\ce{NaOH}$ and $\ce{NH_3}$ that have similar concentrations and volumes.

These two are among the options:

$\ce{NaOH}$ has a higher $\ce{pH}$ than $\ce{NH_3}$
$\ce{NaOH}$ has a higher $\ce{OH^-}$ concentration than $\ce{NH_3}$

Wouldn't these both be correct?


texts: If I wash chloroform (stabilized with amylene) with sulphuric acid in a separating funnel, where will the chloroform be found (top or bottom)? I think the chloroform will be at the bottom, because it is heavier than sulphuric acid.


texts: Reaction between copper (II)chloride and aluminium foil

texts: When I reacted copper chloride and aluminum foil instead of getting the brown color I got green color. Can anyone share their procedure where the experiment actually succeeded?


texts: Ambiguity in definition of primary valency in Werner's theory

texts:
In Concise Inorganic Chemistry (5th Edition) on page 196 , the primary valency of $\ce{[Co(NH3)5Cl]Cl2}$ is given to be 2.

In other textbooks and in the question here, we get the idea that:

The primary valency of a compound is equal to its oxidation state.

In 'Inorganic Chemistry(4th Edition)' by Catherine E. Housecroft and Alan G. Sharpe':

Werner referred to the oxidation state of the metal ion as its ‘primary valence’ and to what we now call the coordination number  as  its  ‘secondary  valence’.

This further suggests that that they are in fact exactly identical and just a matter of how they are referred to.
The oxidation state of cobalt in $\ce{[Co(NH3)5Cl]Cl2}$ is +3 and hence would suggest a primary valency of 3.
What is the correct primary valency of the compound? I am aware that these concepts are not in modern use yet it would be useful to know how Werner originally put forward this idea.


texts: Problems with precipitation of transition metal solution

texts:
I am trying to make a solution of "trace elements"--primarily transition metals-- for use in biological media; bacteria require elements like Cobalt, Molybdenum, iron, etc. in trace amounts. I am not a chemist, but my understanding is that these elements tend to form hydroxides in physiological pH ranges (slightly above 7). Therefore the authors of the protocol I am using employ EDTA as a complexing agent in 1:1 stoichiometric proportion with the metals in solution. The problem is that EDTA solubility (and complexing capability) and transition metal stability occur at opposite sides of the pH scale, and finding a balance to make both types of reagents happy is apparently really tricky; I've tried this 4 different times with no success. I am able to get all materials into solution, but any disturbance of my flask, (e.g. further stirring or shaking) inevitably causes precipitation.

Here is my recipe and protocol. I'll describe my observations after that. My question is:

  Any thought what the precipitate is? How can I avoid it?

I have scant chemistry experience, so any insight you can provide would be useful.

Recipe

190 mM $\ce{EDTA}$ $\ce{Na4.2H2O}$ (equimolar to subsequent di- and trivalent cations)
29 mM $\ce{FeCl3.6H2O}$
80 mM $\ce{CaCO3}$
6 mM $\ce{MnCl2.4H2O}$
0.5 mM $\ce{CuSO4.5H2O}$
0.5 mM $\ce{CoCl2.6H2O}$
5 mM $\ce{ZnO}$
2 mM $\ce{H3BO3}$
66 mM $\ce{MgCl2.6H2O}$
5 mM $\ce{NaMoO4.2H2O}$

Protocol (making 1 L)

Dissolve EDTA in $\ce{750 mL}$ of water. Bring pH down to about 5.8 with $\ce{HCl}$.
Add $\ce{FeCl3}$ and watch pH; don't let it drop below 4.8.
Add $\ce{CaCO3}$. Allow to dissolve (i.e. $\ce{CO2}$ to evaporate) by maintaining pH at 4.8 with $\ce{HCl}$ and occasionally shaking vigorously (not sure why the recipe doesn't just call for something more soluble like $\ce{CaCl2}$.)
Add remaining elements in order given in the recipe, watching the pH. It should drop to about 4.2 without any addition of acid or base.
At this point solution appears clear. Bring volume up to $\ce{1L}$.
Autoclave solution (heat under pressure at $123^{\circ}\ce{C}$ for 15 minutes) ---this is required for biological sterilization, and seems to improve solubility for a time.

Observations

Solution remains transparent throughout preparation, stirring constantly throughout at room temperature. Color is orangish-green, due to iron and copper. Once all ingredients have been added, additional stirring before autoclaving leads to gradual (over 15 minutes) accumulation of a white powdery precipitate. I thought this was EDTA coming out, so I added $\ce{NaOH}$, but this only caused the iron to precipitate, forming a brown precipitate. Letting the solution sit also seems to lead to white precipitation, although less rapidly. When I autoclaved the solution, it remained transparent (color had turned to deep rust-orange) even after sitting overnight, but as soon as I disturbed it by transferring from an Ehrlenmeyer flask to a glass bottle it precipitated again. The pH of the precipitated solution seems stable at 4.2, what it was after all ingredients had been added. I have also tried this preparation adding EDTA after the boric acid and keeping pH below 6 with $\ce{HCl}$, but this caused even more rapid precipitation. I have also tried EDTA (fully protonated) after the boric acid and adding NaOH to deprotonate, but the results were even worse.


texts: Opening a shaken up bottle quickly = no fizz?

texts:
I recently watched this video:
https://www.youtube.com/watch?v=Lqk3lGic3D0

Summary: Opening up a shaken bottle of Carbonated drink extremely quickly results in almost zero bubbles forming in the drink and then the soda is 'flat'

How exactly does this work? The extremely fast sudden opening seems to causes the CO2 to react differently than normally expected?

Thanks.


texts: Why can't the reaction of grignard reagent with carboxylic acid give a ketone?

texts:
I understand that a Grignard reagent can act both as a base and a nucleophile.
It acts as a base in the presence of a proton source (eg: alcohols, amine, water, etc). But when reacting with a ketone or an aldehyde, it acts as a nucleophile and uses a specific reaction mechanism. Why isn't that same reaction mechanism not viable for reaction with carboxylic acid?

Why is this reaction mechanism wrong? Is the formation of a diol not possible due to repulsions or is there some other reason?


texts: Why do we consider all gasses to be in one phase?

texts: Why do we take the phase of all gases 1. If all gases exist in 1 phase then why do we say that some gases are heavier than air, some are light also we collects some gases in lab by air displacement method. Is this all possible if gases are completely miscible.


texts: How to prepare elemental gallium from a mixture of gallium and aluminum nitrate?

texts: How would one go about preparing and purifying elemental gallium from a mixture of aluminum(III) nitrate and gallium(III) nitrate?


texts: Hydrogen venting: Why no flame arrestors?

texts:
I was reading the guidelines for safe venting of Hydrogen. One item says "no flame arrestors".

Just wondering the scientific reason why flame arrestors may be frowned upon when for venting of most other flammable vapors / gases flame arrestors seem standard.

https://www.eiga.eu/publications/eiga-documents/doc-21117-hydrogen-vent-systems-for-customer-applications/


texts: Does dissolving a solute lowers the activation energy of a reaction of that solute?

texts: I'm formulating a reason why the use of solvents in some reactants are preferred rather then mixing just the pure components together. My gut feeling tells me that it lowers the activation energy of the reaction but, I can't find explicite answers to confirm my guess. Can someone help me with this :)?


texts: What is the pH and pKa relationship of LaCl3 in water and its precipitant La(OH)3?

texts:
In light of this question and its answers, I hope to get some insights into the $\mathrm{pH}$ of $\ce{LaCl3}$ in water and its $\mathrm{pH}$ relationship to $\ce{La(OH)3}$ precipitant's $\mathrm{p}K_\mathrm{a}$?

What can be done in order to prevent $\ce{LaCl3}$ from forming $\ce{La(OH)3}$ and maintaining the $\mathrm{pH}$ $\pu{24^\circ C} - \pu{25^\circ C}$?

When creating salt solutions of $\ce{AlCl3}$, $\ce{LaCl3}$ and $\ce{FeCl3}$; $\ce{AlCl3}$ seem to have a pretty low $\mathrm{pH}$ in water while $\ce{LaCl3}$ rapidly precipitate into $\ce{La(OH)3}$. With the rapid formation of $\ce{La(OH)3}$, $\ce{LaCl3}$ seems to show extremely low solubility in water.

Does $\ce{LaCl3}$ also acts as a Lewis acid?


texts: Calculating temperature of partial condenser, flash calculations

texts:
The iterative method I have learned to make flash calculations for a binary system where I know the inlet feed (F [mol/s]), total composition of the two components ($z_1$ and $z_2$), the amount of the mixture which is evaporated (q) and the total pressure (P [mmHg]) is as follows:

We seek T, $x_i$ (composition of liquid) and $y_i$ (composition of gas). We know F, $z_i$, q, P.
Guess T
Calculate $P_1°$ and $P_2°$. In our course we are using Antoine's equation to do this. Antoine's equation can be written in many ways but lets for simplicity stick with this version. That is:
$$P_i°(T)=10^{A_i-\frac{B_i}{C_i+T}}$$
where T is in °C and P in mmHg. $A_i,B_i,C_i$ are the Antoine constants and they are known.
Calculate $x_i$ and $y_i$. For simplicity we say that $\gamma_i=1$. This gives us that:
$$x_i=\frac{Fz_i}{V\frac{P_i°(T)}{P}+L}$$
and
$$y_i=\frac{P_i°(T)x_i}{P}$$
where V is the gas outlet stream ($V=q\cdot F$) and L is the liquid outlet stream ($L=(1-q)\cdot F$).
If $\sum x_i=1$ $\underline{and}$ $\sum y_i=1$ you have found the correct T, $x_i$ and $y_i$. Else go back to 2.

So my question is. Do we really need to calculate $\underline{both}$ $y_i$ and $x_i$? If I find the temperature which satisfies $\sum x_i=1$ doesn't that guarantee that also $\sum y_i=1$? I plotted this and played around with different values for the Antoine constants and values for F, q and P. Here is a link to my plot: https://www.desmos.com/calculator/m37slkdebb. For all of my cases it was true that if for a temperature T $\sum x_i=1$ then also $\sum y_i=1$ for that same temperature T. I asked my professor about this and he insisted that I would have as a requirement to stop my iteration when $\sum x_i=1$ $\underline{and}$ $\sum y_i=1$.
Am I correct that $\sum x_i=1$ guarantees $\sum y_i=1$?
Are there cases I have missed where you can have several temperatures where $\sum x_i=1$ but only one of these temperaturs satisfies both $\sum x_i=1$ and $\sum y_i=1$?
What happens when $\gamma_i\neq1$, is this simplification too much? If i use another model for $P_i°$ what will happen then?


texts: How are the van der waal constants 'a' and 'b' related to molecular size?

texts: 'a' represents the measure of attractive forces between the gas molecules so how is it related to the molecular size? if a1> a2 then what does it tell us about the molecular sizes of 1 and 2?


texts: I really can't understand why is the mole a unit of measurement and not just a constant. I mean, we use units to express things that we can measure but that are not countable, that are continuous - and not discrete. However, the number of atoms (or whatever) of something is clearly countable, discrete. It is also a huge number, which would request for a constant, a number to multiply to: Avogadro's constant is that number, like mega or kilo in SI for other units. We could still write 14 mole, where mole is the Avogadro constant (exactly the way it is), but every book I read so far states that the mole is a unit of measurement, official in the S.I., and so does Wikipedia. It just makes no sense to me that it is considered that way, but there is obviously a reason why... What is it?


texts: I was practising some problems on hydride shift and got stuck in this particular question. I wanted to know if hydride shift would take place in this particular case and which carbon would get the positive charge. Will a hydrogen from left or right carbon would shift??


texts: Bridging Hydride Covalent Model Electron Count - Hartwig

texts:
How can a bridging hydride be considered a 3 electron donor in the covalent model for electron counting?
On page 3 of John Hartwig's "Organotransition metal chemistry" textbook [1], he lists the number of donated electrons for common ligands according to the two standard models of electron counting in organometallic chemistry:
The ionic model: ligands are characterized according to their formal charges after cleaving the M-L bond under the assumption that both electrons reside on the ligand.
The covalent model: all ligands are treated as neutral, and the number of electrons they donate (1 $\ce{e^-}$ "X-ligands", 2 $\ce{e^-}$ "L-ligands", 3 $\ce{e^-}$ "LX-ligands" and so on) are determined by distributing the electrons from the M-L bond such that you generate a neutral ligand (he phrases this as a neutral organic group).
In Table 1.1 [1, pp. 3–4] a bridging hydride is listed as donating 4 electrons in the ionic model (in which it would be described as an "anionic, 4-e ligand"), and 3 in the covalent model.

The latter makes no sense to me. When the bonds connecting the bridging hydride are severed, the only way to produce a neutral ligand would be to generate atomic hydrogen, meaning 3 electrons from the M-H-M system would remain with the metals. How then, do we arrive at the hydride donating 3 electrons in this scheme? Is this a typo? Or is it written to somehow indicate that the 3 "donated" electrons are actually from the metals? Or the H-M composite ligand which we can view as then binding to the third metal?
Reference

Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to Catalysis; University Science Books: Sausalito, California, 2010. ISBN 978-1-891389-53-5


texts: Could the inks used in Wonder Bread container have caused lead poisoning?

texts: Decades ago I recall reading that the colorful wrapper of Wonder Bread was misprinted inside out and therefore the printed logo rubbed off on the bread itself, bread was used and kids ended up with lead poisoning. I do remember reading this but can find no further information. Is this story plausible? If so, would not some lead exposure have happened even with correctly printed packaging since it would have been touched by those taking the bread from the packaging.


texts: What is the cause for thermodynamic reversible and irreversible process?

texts:
My book defines

  Thermodynamic irreversible process is defined as the process in which the changes take place rapidly, instead of occurring in successive stages with infinitesimal changes in quantities so that the system does not get a chance to attain equilibrium and there is an appreciable difference between the driving and the opposing force.

I have some problems in understanding it.

Which equilibrium are they speaking of?
Why does rapidity of the change cannot help it to attain equilibrium (how does an infinitesimal change in a reversible process help it to reach equilibrium)?
What does they want to mean by driving and opposing force?


texts: What happens to concrete if you add lye to the mix?

texts: What happens if you’re mixing concrete and you add some lye to it? Does it make it weaker, stronger or does nothing at all? I’m guessing concrete is basic so adding lye to it might expedite the reaction, causing it harden faster?  Alternatively, it may react to with the water and starve the mixture?


texts: Give reason how can i made diamond a conductor by doping  charcoal and graphite which are allotrope of Carbon act as conductor. Whereas diamond which has a different crystal structure act as an insulator


texts: How to plate zinc evenly on a threaded bar

texts:
I need to set a number of threaded bars into cement, to hold a new gatepost. When I cut the bar into shorter pieces, the metal near the cut became red hot, presumably hot enough to evaporate some or all of the zinc with which the entire rod was plated.

Now I want to plate zinc back onto the ends, and have had mixed success so far. I dissolved some zinc oxide with hydrochloric acid and hooked it up to a little PV panel I have, and after a while it seems there is a light-coloured deposit on the cathode. The pencil-lead (6B) anode is no longer as smooth as it first was, but it doesn't seem to be losing (much) of its bulk. I assume it to be zinc, because... well what else can it be? It plated thick enough that I had to (ab)use a nut to re-cut the thread, leaving a light-coloured shiny surface that gives me more confidence that it is, in fact, zinc.

Problem: the edges of the threads seem to be taking more zinc than the valleys. In some cases the thread's valley doesn't show any evidence of plating. The fractal-like deposit on the edges is quite pretty actually, pity I can't take a (good) closeup photo.

Is there anything I can do (perhaps using some other common(ish) kitchen chemicals?) that will result in a more uniform layer of zinc? Is it worth trying lower / higher current or pulsed current? Am I overthinking things - is it even necessary for the whole stud to have a layer of zinc?


texts: What is the formula for migration rate of DNA in agarose gel electrophoresis?

texts:
Let's consider a typical agarose gel electrophoresis experiment. An appropriate quantity (not so much that it is overloaded, but not so little that it cannot be visualized) of linear DNA pieces with identical sequence and chemical structure is loaded onto the gel, and constant voltage is applied for a given time. I suspect that there is a function:

$x = f(V, t, l, c, k)$

Where the variables are:

$x$, cm, distance from well
$V$, Volt, potential difference across the gel
$t$, minutes, time over which the voltage is applied
$l$, bp, length of DNA fragments
$c$, gr/100 ml, density of the gel given in grams of agarose per 100 ml of buffer
$k$, a constant which is empirically determined for a given running buffer and gel tank

Basically, I want a formula into which I can plug in the size of my DNA and a few other parameters, and figure out how long I have to run it to get decent separation (the output variable is x because I intend to plot $x$ over $t$ for a given planned electrophoresis).

Is such a formula possible? What is it?

I have previously worked with gel documentation software which fits linear, polynomial and exponential functions to the DNA (I couldn't figure out exactly what kind of fitting the software was doing). However, after training a best-fit model on my ladder (with ~12 bands) and applying it to my samples of known size, I found all of these fits to be very inaccurate (5-10% error). Therefore, I suspect the equation governing the migration rate of DNA is in fact not a simple exponential function (as is often taught in college) but more complicated. Unfortunately, I lack the background in physical chemistry to derive the equation myself.

If you have a good argument for why the relation should be a simple exponent, eg. $x = e ^ {\alpha \cdot l}$, that is also an acceptable answer.


texts: Do the αβ and βα states of homonuclear AX system have same energy?

texts:
I was studying nuclear Overhauser effect and came across this diagram$^1$:

This diagram shows the energy levels of four possible nuclear spin states of homonuclear AX system. The white/grey boxes refer to population deficit/excess, respectively, w.r.t the population at each of the two states at the centre (α$_\mathrm{A}$β$_\mathrm{X}$, β$_\mathrm{A}$α$_\mathrm{X}$ ). This is the population distribution at thermal equilibrium.

It is stated clearly in the text that α$_\mathrm{A}$β$_\mathrm{X}$ and
β$_\mathrm{A}$α$_\mathrm{X}$  have same energy, for homonuclear AX
system.
My question is, how can the α$_\mathrm{A}$β$_\mathrm{X}$ and
β$_\mathrm{A}$α$_\mathrm{X}$ have same energy?

The energy of each state is described by:
$$E(m_A, m_X) = -hv_Am_A -hv_Xm_X + hJm_Am_X $$
For the two states, third term at RHS are common, but the Larmor frequencies of A and X are not the same despite being homonuclear (already called 'AX', chemical shift very different, Larmor frequency also differ), so the states should have different energy. Did I understand something wrong?

Peter Atkins, Julio de Paula, James Keeler. Physical Chemistry (11th Edition). OUP. 2018. Page 516.

Or, 8th Edition: page 542; 9th Edition: Page 548


texts: Difference between Reaction Rate and Rate Law?

texts:
Lets say you have the reaction

$$\ce{$a$A + $b$B -> $c$C + $d$D}$$

The rate of the reaction is given by the change in initial concentration over the change in time.

$$-\frac{\Delta \left[\ce A \right]}{a\Delta t} = -\frac{\Delta \left[\ce B \right]}{b\Delta t} = \frac{\Delta \left[ \ce C \right]}{c\Delta t} = \frac{\Delta \left[\ce D \right]}{d\Delta t}$$

However, there is also the rate expression, which is of the form

$$\text{reaction rate} = k \left[\ce  A \right]^{m}\left[\ce  B \right]^{n}$$

What is the difference between these two, and what purpose does each one serve?

Further, what does the $k$ represent?


texts: How to calculate pH of the Na2CO3 solution given ambiguous Ka values

texts:
This is the exact question I faced on an exam:

Calculate the $\mathrm{pH}$ of $\pu{0.05 M}~\ce{Na2CO3}. \\(\ce{H2CO3}: K_\mathrm{a_1}= 4\times 10^{-7},~ K_\mathrm{a_2}= 4.7\times 10^{-11})$

Solution
$$\ce{Na2CO3 ->2Na+ + CO3^2-}$$
I suppose nothing that can contribute to the $\mathrm{pH}$ of a solution happens to $\ce{Na+}$ ions and we proceed with $\ce{CO3^2-}$ which has a concentration of $\pu{0.05M}$
$$\ce{CO3^2- + H2O <=> HCO3- + OH-}$$
To calculate $\mathrm{pH}$, I need to first figure out concentration of $\ce{OH-}$ ions, and to do so I have to know $K_\mathrm{b}$ dissociation constant for $\ce{CO3^2-}$
On equilibrium concentration of species are as follows: $$[\ce{CO3^2-}] = \pu{0.05 M}-x,[\ce{HCO3-}] = [\ce{OH-}] = x$$
So, we have:
$$\dfrac{x^2}{0.05-x}=K_\mathrm b$$
All I need to know is $K_\mathrm{b}$ value for $\ce{CO3^2-}$ ion. I tried to derive $K_\mathrm{b}$ from $K_\mathrm{a}$ values using $K_\mathrm{a} \times K_\mathrm{b} = 1\times 10^{-14}$ but apparently obtained the incorrect answer. What method should I use to do it the right way?


texts: Difference between titanium and titanium dioxide electrode

texts:
I need an inert anode to perform some electrolysis.  I've tried graphite, which works to some extent, however I want to upgrade to titanium, which is pretty reasonably priced, and will perform better than the graphite.

My question is whether there is a difference between "Titanium oxide electrodes" and plain titanium.  Does a titanium dioxide electrode need to be specially treated to give it more inert characteristics, or does the oxide layer form naturally on the titanium?

I ask because I have seen this type of electrode classified as a Mixed Metal Oxide (MMO) electrode, but I have also seen some say that titanium is inert on its own.  I would like to now whether plain titanium is a viable electrode so I don't end up buying some that ends up corroding quickly during electrolysis!!

Any information in this subject would be greatly appreciated.

Thanks in advance!!


texts: I have 100 mg of a proteinase K lyophilized powder and I need to make it to a working concentration of 25 mg/mL

texts:
So I know that I need to add $4~\mathrm{mL}$ of solution to this powder, which will give me a concentration of the enzyme at $25\ \mathrm{mg/mL}$. What I do not understand is how to decide how much of each of these "ingredients" (below) to add. I have $\ce{TrisHCl}$ and $\ce{CaCl2}$ in granular form ($M = 157\ \mathrm{g/mol}$ and $111\ \mathrm{g/mol}$, respectively) and 100 % glycerol solution. Will I have to make a large batch of Tris and $\ce{CaCl2}$ just so I can actually weigh out the needed amount?

The specifications for the working solution are:

$10\ \mathrm{mM}\ \ce{Tris}$
$1\ \mathrm{mM}\ \ce{CaCl2}$
30 % glycerol
Final $\mathrm{pH} \approx 8$ (use $\ce{HCl}$ if necessary)
MilliQ $\ce{H2O}$ to volume


texts:
This is the reaction that I'm interested in. I reckon this is what occurs:

But how does the reaction proceed from there, there is a lone pair on the oxygen in right side of my picture, but how do you get rid of the CH3 group on that oxygen?

Although I do see a problem here that the structure of my final product was due to my aforementioned reaction scheme would still have RO-(PMS)-OR, where R is methyl group, instead of RO-(PMS)-R. I don't know what to do...


texts: What should be the reaction between lead oxide and dilute sulfuric acid?

texts:
I know for a fact that dilute $\ce{H2SO4}$ is a non-oxidizing acid which makes it a reducing agent. I also know for a fact that $\ce{PbO2}$ is a strong oxidizing agent. So, I thought Redox reaction should have occurred between them, but my teacher says that no reaction occurs between the said reactants because $\ce{PbO2}$ does not react with low concentration of acid. If it were so, why does $\ce{PbO2}$ react with dilute $\ce{HCl}$. Since, both dilute $\ce{HCl}$ and dilute H2SO4 are reducing acids of low concentrations, both should be eligible for the Redox reaction.

I have tried this on the internet but all I get are reaction balancing links .JD Lee's Concise Inorganic Chemistry has nothing about this also.


texts: Could you estimate the rate of reaction from the chemical structure of the reactants? If so, how?

texts: Say you have two compounds with their own unique chemical structures and you know the environment (e.g. temperature, pressure, presence of enzymes) could you then, using this information, approximate the rate of reaction? And if so, how would you? Please provide a mathematical answer, not just use some software.


texts: How to calculate the concentration of the elements after dissolution of iron(III) chloride?

texts:
I was presented with the following problem:

  In the laboratory you dissolve $\pu{24.7 g}$ of iron(III) chloride in a volumetric flask in water to a total volume of $\pu{375 ml}$.

  What is the molarity of the solution?
  What is the concentration of iron(III) cation in M?
  And what is the concentration of chloride anion in M?

I know how to do the first part of the problem, the answer is $\pu{0.406 M}\ \ce{FeCl3}$. But when I go to balance the equation, the computer system tells me the equation is wrong.

My equation:
$$
2\ce{FeCl3 -> 2 Fe + 3Cl2}
$$

The computer system:

$$
\ce{FeCl3 -> Fe^3+ + 3Cl-}
$$

I don't understand the computer systems' answer. Simply because when by itself, chlorine is a diatomic molecule therefore, should be $\ce{Cl2}$ not just $\ce{Cl}$. Am I wrong to think this? Am I correct or the computer system? If the computer system is correct, why?


texts: Can all water soluble ionic compounds conduct electricity?

texts:
I'm taking a first year university chemistry course, and I am reading a lot of contradicting things. Some people say that ionic compounds that are soluble in water are always electrically conductive, others say that it maybe conductive.  Which one is it?

I have this problem to think about:

  Suppose that an unknown chemical compound exhibits the following properties:

  it is crystalline but shows no electric conductivity in the solid state
  it melts at $\mathrm{300^\circ C}$ and decomposes at $\mathrm{400^\circ C}$
  the compound is soluble in water, the solution shows no electrical conductivity.

  What kind of chemical bond would you expect in the
  given compound? Try to describe this type of bond in detail.

Everything screams "ionic" (high melting point, solid at room temperature, crystalline structure, non-conducting in solid form) besides the fact that it doesn't conduct in water.


texts: Where can I find a downloadable spreadsheet of element properties?

texts: Sorry for the FAQ, but I really don't know where to find a full spreadsheet for element properties. I mean a table that has one row for each element, and the columns are its properties, such as name, atomic number, density, melting point, etc. I know that there are many sites or references for that, but I need it in tabular format, because I want to analyze data, make charts, etc.


texts: How do you experimentally calculate the ionization constant of the carbonate ion?

texts:
Given sodium hydrogen carbonate, $\ce{NaHCO3}$, as well as hydrochloric acid, $\ce{HCl}$, how would you experimentally determine the ionization constant for the carbonate ion, $\ce{HCO3-}$? By experimentally, I mean by actually doing the reaction and measuring the pH and such, and ignoring the already known theoretical values.

Here's what I've got so far.

The sodium hydrogen carbonate dissociates in water.
$$\ce{NaHCO3->Na+_{(aq)} + HCO3-_{(aq)}}$$

Then, titrate the ion with the hydrochloric acid, a strong acid.
$$\ce{HCO3-_{(aq)} + HCl_{(aq)} <=> H2O_{(l)} + H2CO3_{(aq)} + Cl-_{(aq)}}$$

It's at this point that I would measure the $\mathrm{pH}$ and determine the necessary concentrations, and then plug it into the formula

$$K_\mathrm{b} = \frac{\ce{[H2CO3]}}{\ce{[HCO3-][HCl]}}$$

But I'm wondering if I need to go further with the $\ce{H2CO3}$ since it would hydrolize in water:
$$\ce{H2CO3_{(aq)} + H2O_{(l)} <=> H3O+_{(aq)} + HCO3-_{(aq)}}$$


texts: How to determine the empirical formula for an unknown iron oxide?

texts:
I have to determine the empirical formula of an oxide of iron which has $69.9\%$ iron and $30.1\%$ dioxygen by mass in it.

I have started as follows:

For our convenience we take $\pu{100 g}$ of that iron oxide:
We have $\pu{69.9 g}$ of iron in it and $\pu{30.1 g}$ dioxygen in it.
We convert into amount of substance of each element:

$\text{amount of substance of iron} = 69.9/55.8 = 1.25$
$\text{amount of substance of dioxygen} = 30.1/32 = 0.94$

Is my method and calculations right?


texts:
When I was doing my Bachelor thesis I worked a lot in Niobium ampoules as we were doing solid state experiments at high temperatures with a lot of fluoride. As this attacks glass we chose Niobium instead and it seems to be quite unreactive even at those high temperatures (working in a helium atmosphere to prevent oxidation).

So when I was finished with my work I descided to try some Niobium salts only to discover that there is no real aqueous chemistry of Niobium, Tantalum and a few other elements in the PSE. They don't form any Nb(III)-ions in solution besides complex-anions for example and certainly no real hexaqua-complex. Vandium above however and also Dubnium below (at lower pH values) show a lot of aqueous chemistry and also quite often pure aqua-complexes.

This surprised me a bit first as nearly all reactions involving Nb, Ta and a few others (I think W, too) usually end with the Oxide (pentoxide) which is super stable. So I though a bit about that and came up with another example. Not only does this resemble the chemistry of Polyvanadates like the reddish decavanadates and all the stuff that forms if you acidify ammonium metavanadate but also the reactions of silicic acid which, as you try to protonate silicates often form polysilicates and SiO2.

Then I remembered the deep red colores of polychromates. If you acidify potassium chromate with HCl which is 70% water you will get the dichromate solution which is orange if you use nitric acid which has 30% of water you will get the trichromates, tetrachromates and higher, red polychromates. And if you use conc. sulfuric acid you will recieve the trioxide. I assumed for a long time that it was a simple dehydration where a H2O will be taken from a H2CrO4 to form CrO3 but then I looked at the structure of CrO3 only to discover that it is a long chain of joined tetrahedra so a high polychromate.

If you look at the structure of Niobium(V)oxide it's pretty much the same only with octahedra. So I imagine a "niobate" as it can be dissolved in basic environments will do the same elimination of water to form long chains or networks which are then called oxides. And in this case those niobates and tantalates are so basic that anything pH 8 (or whatever that point is) is considered a strong acid for it (much into comparison of chromate for example) and this is why a pH7 aqueous chemistry of Niobium or Tantalum can't work.

If this was the case I am not sure why it's exactly in the middle with those few elements. I imagine if a metal is quite electronegative and has a short bond towards the oxygen it will pull the oxygen so close that the positive charge and the hydrogen influence each other (much like with the chemistry of Beryllium) and it will be easer to deprotonate it. So in my case the lower electronegativity of the Nb and Ta in comparison to the V(III) should increase the electron density on the oxygen more making it more basic.
And if I compare the electronegativities those elements are some of the least electronegative ones (there isn't much Sc chemistry known and I think Ti, Zr and Hf don't have that much aqueous chemistry either).

But is there another maybe better explanation to why only those few elements show pretty much now real aqueous chemistry at all ?


texts: Must a good leaving group be a weak base, or a weak nucleophile?

texts: In LG Wade's textbook, he has written that a good leaving group must be a weak base. Since substitution reactions (not too sure about elimination reactions) tend to be kinetically controlled, i.e irreversible, why has the concept of a weak base (which is defined for thermodynamically controlled reactions) been used here? Why does the leaving group have to be a weak base rather than a weak nucleophile?


texts: Why Benzene is a good solvent even while it is not polar

texts:
Consider for a moment, ether, THF, benzene and hexane.

Why is the solubility of many organics in these solvents in the following order

THF > ether / benzene > hexane

What makes benzene a good solvent for many solutes when compared with hexane even while both solvents lack a permanent dipole moment.


texts: How dependent is the molal depression constant on the nature of solute?

texts:
I've been reading about the molal depression constant (freezing point depression constant) for binary solutions in class.

I encountered a problem (see below) in which the constant $K_f$ was to be evaluated first for a sucrose-water solution ($\Delta T$ and concentration of the solution was given).

Then this value of $K_f$ was used to determine the depression $\Delta T$ of the freezing point of a glucose-water solution when given it's concentration.

This is the problem:

  A $5\%$ solution (by mass) of cane sugar in water has freezing point of $271.00\  K$. Calculate the freezing point of a $5\%$ glucose water if freezing point of pure water is $273.15\ K$.

My confusion: Is $K_f$ solute dependent? If no, then why not?

I have this confusion because I'm used to solving problems in which if the solute is changed, then most of the constants related to various properties of the solution also changes.


texts: How do we know if a compound can be oxidized?

texts:
I'm studying organic chemistry, and I have to identify compounds that can be oxidized in some exercises I am doing.

For instance, an $\ce{R-CHO}$ can be oxidized further, but an $\ce{R_{3}-COH}$ cannot, and presently I can tell this only if I remember it by heart.

How do I know if a compound can be oxidized? Is there an algorithm/method to follow?


texts: What could cause one brand of carbonated water to be superiorly carbonated compared to another?

texts:
I buy a lot of carbonated water, its pretty much all I drink. There is something I've noticed that just made me curious though.

The usual brand I buy is the cheapest one available, 14 cents per 1,5l. This one almost always tries to give me a surprise shower when I open it, no matter how still I keep it prior to opening. The bubbles are large and plentiful at first but it goes flat pretty quickly, usually within the day but thats fine since I'll drink it in a day anyways.

The other brand I buy when the first one isn't available, its the second cheapest one and is 35 cents per 1.5l. Opens up pretty calmly, the bubbles are much smaller but lots of them around. The interesting bit is that it doesn't go flat nearly as quickly and I can expect some carbonation to be left even a few days later. Another point to make is that the second one behaves much more like various other brands.

The question is, what could cause such difference in the bubbling behavior?

The bottles are the same kind of clear plastic, the ingredients aren't listed which should mean that its just water + $\ce{CO2}$. Over here, if they put any other chemical in it, they are required to name it on the bottle, many water bottles have chlorine in them for example.

Could it be the carbonation process? Or the natural water composition? Maybe the transportation or storage?


texts: Understanding group theory easily and quickly

texts: Please can you explain me the group theory especially the reducible and irreducible representation and class and subclass and how to tell they are in the same group or not. I know it is a tedious task but help will be very much appreciated.


texts: Interpreting notation format 1.64E-02 from particulate emission data

texts:
I'm doing a research project for school on air pollution and part of it is studying pollution caused by aviation and I have found a table of data for the emission indices of various pollutants but I'm not 100% certain, if I'm correctly reading the numbers.

The unit is $\mathrm{g\, kg^{-1}~of~fuel}$ and the numbers are like 1.64E-02 or 2.25E+00. I'm interpreting it as E being for Exa, so in short scale 1.64E would be 1.64 quintillion and that it means 1.64 quintillion particles per g per kg of fuel. Is that the correct meaning? I have no idea what the second bit of the numbers means so please could you explain for me?


texts:
Are there any advantages/disadvantages of using toluenesulfonate instead of methylsulfonate as a leaving group in E2 and SN2 reactions? I know they are both excellent leaving groups but how do they compare to each other? Is there a green chemistry aspect to it?

Thank you!


texts: Reaction of Cu in hydrochloric acid bath with exposure to air over several months?

texts:
I assume that copper will be slowly oxidized by oxygen, dissolved in water, forming copper(I) oxide (as stated here):
$$\ce{4 \overset{\pm0}{Cu} + O2 -> 2 \overset{+I}{Cu}_2O}$$

Reaction rate might be affected by the hydrochloric acid (cf. here)

And some of the copper could actually be converted to $\ce{CuCl2}$ (cf. here):
$$\ce{2HCl (aq) + \overset{\pm0}{Cu}(s) -> \overset{+II}{Cu}Cl2(aq) + H2(g)}$$

But what will happen to $\ce{Cu2O}$?

Will it degrade to $\ce{CuO}$, which then forms $\ce{CuCl2}$? That would mean that one should find higher concentrations of $\ce{CuCl2}$ in the solution, as time goes on.
Will it not react any further but instead get solved in the hydrochloric acid solution, because it is soluable in acids?
Or will something else happen?

Note: The concentration of hydrochloric acid solution is around 10 %.

Related Questions:
Copper Doesn't React with Hydrochloric acid
Copper and hydrochloric acid


texts: Why do polysaccharides consisting of alpha-glucose have helical structures?

texts:
Why do the polysaccharides consisting of alpha-glucose such as starch and glycogen have helical structure, while the one such as cellulose consisting of beta glucose don't display such structures?
The textbook said that is because of the angle of 1-4 linkage, but what kind of angle is it that makes helical structure?


texts: Why doesn't water evaporate in a balloon filled with water?

texts:
I know for sure that if you fill a balloon with water (without leaving any air inside) and you start heating it, the balloon won't expand until the temperature reaches 100 °C.
I think it is because while the temperature is below 100 °C, the vapor pressure of the liquid is <760 mmHg so any expansion of the balloon is prevented by the atmospheric pressure.
However, let's suppose to put some water in a water bottle and close it. Initially, there was no water vapor in the bottle, there was only air. But, after a certain amount of time, water will evaporate until the pressure of the water inside the bottle reaches the vapor pressure of the water at that given temperature.
So, my question is: why can water evaporate if there is some air over it but it cannot without air, although in both cases it has to overcome the atmospheric pressure? What is the difference between a closed container with no air inside (only liquid) and a closed-one with some air inside?


texts: What is this red substance that has accumulated at the bottom of a plastic bottle full of petrol (see picture)?

texts:
About two weeks ago I put some ordinary unleaded petrol into a plastic water bottle, as a temporary measure (long story, don't ask!). It has now formed a reddish liquid at the bottom of the bottle.

The bottle was emptied prior to adding the petrol, but probably still contained a small amount of water when the fuel was poured in. The bottle was stored in ordinary room temperature.

I presume that the fuel has corroded/reacted with the plastic and left this substance, but I have looked to Stack Exchange in the hope of a more scientific answer...

So, what is the red substance and cause of it?

Please note that the brownish 'slug-shape' is merely an artifact of the light refraction...


texts: Why do weak acids like ethanol not act as a strong base in water?

texts:
In water, ethanol has a $\mathrm{p}K_\mathrm{a} = 15.9$ which means that its $\mathrm{p}K_\mathrm{b}$ is $-1.9$. Which implies that all weak acids in water are in fact strong bases. But this is not true, weak acids in fact do act like weak acids. That would mean that this equation isn't true always.

$$14 = \mathrm{p}K_\mathrm{a} + \mathrm{p}K_\mathrm{b}$$

Considering this is just the ionic product of water it should be valid always?


texts: Avoiding chemical reactions with carbonated alcoholic drinks

texts:
I'm making a cooling beverage dispenser for carbonated drinks. The keg remains room temperature and the beverage rises through a pipe that's coiled up inside a cooling unit filled with water or alcohol.
My first choice would be copper tubing because of its conductive properties, but I remember reading somewhere that it could lead to some kind of chemical reaction that would be poisonous? As I usually prefer not to kill my guests, and avoid it whenever possible, I'd like to find a good alternative that's able to cool the liquid as quickly as possible. I don't actually know what they were referring to or whether or not they were even right, I'd like some input on the uses of copper or aluminium for the piping or whether I should go with stainless steel.
I'd also like to use this for carbonated water, which might be very carbonized and I want to be able to sanitize the system by running a sanitizer like Star San through it.
Suggestions? Thanks!


texts: Finding out pKa of acid from molar conductivity

texts:
I'm reading about the electrical properties of solution where there is a problem like that:

  The molar conductivity of $0.0250\ \mathrm M$ $\ce{HCOOH(aq)}$ is $4.61\ \mathrm{mS\ m^2\ mol^{-1}}$. Determine the $\mathrm pK_\mathrm a=-\log K_\mathrm a$ of the acid. (limiting ionic conductivity of $\ce{H+}=34.96\ \mathrm{mS\ m^2\ mol^{-1}}$ and limiting ionic conductivity of $\ce{OH-}=19.91\ \mathrm{mS\ m^2\ mol^{-1}}$)

I have to solve the problem using the equation below:

$$\frac1{\Lambda_\mathrm m}=\frac1{\Lambda_\mathrm m^0}+\frac{\Lambda_\mathrm mc}{K_\mathrm a\left(\Lambda_\mathrm m^0\right)^2}$$

Here which limiting ionic conductivity should I use to solve the problem?  $\ce{H+}$ or $\ce{OH-}$?


texts: Deodorizing using baking powder instead of baking soda

texts:
I am an engineer and I understand the difference between baking power and baking soda as baking powder is baking soda (alkali) with tartaric acid (acidic) and an inert starch (why? Is this a catalyst in the presence of humidity and temperature).

So why use baking soda to deodorize a carpet and not baking powder? Is it because baking powder has both an acid and base and thus one would neutralize the other and would render the baking powder useless for adsorbing smells?

My carpet would be at a temperature of about $25~\mathrm{^\circ C}$. I am guessing this temperature and a relative humidity of $50{-}60~\%$  will not catalyze a violent reaction with either baking powder or baking soda?

Any input from chemists would be useful!
I don't want to use either on my synthetic carpet in my rented house to experiment before I get enough input from people with know-how!


texts: Would an amalgam filling under or next to a gold crown cause any electrochemical reaction?

texts: Would a mercury amalgam filling deteriorate faster if it was in contact with a gold crown?


texts: How are samples prepared for analysis with ICP-OES? Can it analyse gases?

texts:
In ICP-OES (Wikipedia page), you introduce a sample into a very hot plasma and then run a spectral analysis on the resulting light emissions. Liquid samples are sprayed into the flame. From the Wikipedia article:

  A peristaltic pump delivers an aqueous or organic sample into an analytical nebulizer where it is changed into mist and introduced directly inside the plasma flame.

From that I can imagine that you would probably dissolve solid samples (the technique is widely used in metallurgy and mineralogy) in something suitable to obtain a liquid sample. If that's correct, I'm wondering how the feeding apparatus is constructed to withstand possibly aggresive solvents, like nitric acid or aqua regia. The injection tube is apparently made from fused silica, I guess that's a probable material for the feed as well.

And how about gases? Are they analysed with ICP-OES as well? Are they simply pumped into the injection tube? For example, can we just introduce a stream of air into the plasma and get the emission spectrum for 78% nitrogen, 21% oxygen (I guess the argon will be hidden because the plasma gas is argon)? I guess since every sample will be beyond vaporized anyway by the intense heat, it can't make much difference, but are gas samples too "thin", i. e. do they contain too little atoms per volume for useful analysis?


texts: Reaction of hypohalous acids with alkenes

texts:
I have read that hypohalous acids react with alkene to give halohydrin. For example the below reaction of hypochlorous acid with 2-methyl-2-butene which I found in Wikipedia.

Now my question is: Since hypochlorous acid is an acid it should give $\ce{H+}$ and $\ce{OCl-}$ ions which it does according to Wikipedia (although it is a weak acid), so shouldn't it add as $\ce{H+}$ and $\ce{OCl-}$ like other hydrogen halides add to alkene? Why would it add as $\ce{HO-}$ and $\ce{Cl+}$?


texts: How does the position of hydroxyl group in a nucleotide monomer affect the dehydration synthesis of nucleotides?

texts:
In dehydration synthesis of nucleotides, the hydrogen atom from the 3' carbon on the deoxyribose sugar of one nucleotide reacts with the hydroxyl group on the phosphate group of another nucleotide to form water. As the water molecule forms, a new covalent bond comes into existence between the two nucleotides.
Hydroxyl group can be in different positions within the phosphate group, for example:

I'm wondering if different positions of the hydroxyl group have an impact on the dehydration synthesis between nucleotide monomers. For example, when the hydroxyl group is at the bottom, will the dehydration synthesis occur at all? Also, when the hydroxyl group is on the left, does the spatial structure of the sugar-phosphate backbone have a spatial shape different from when the OH group is on the top?


texts: Why are the ozonides of heavier elements more stable?

texts: The ozonides of $\ce{Cs}$, $\ce{Rb}$, $\ce{K}$ are well known and relatively stable, but there is little mention of the ozonides of $\ce{Na}$, $\ce{Li}$. Why is this?


texts: Does aminosugars give positive response in alkaloid tests?

texts: Does aminosugars give positive response to test for alkaloids such as tests with Dragendorff's reagent, mayer's reagent, Hager's reagent, Wagner's reagent etc?


texts:
What is the general methodology to identify Lewis acids and bases in an acid base reaction? Do we need to draw structures to identify which species is the electron donor and which one the acceptor, or is there any other way of doing this?

If you consider $\ce{HClO_4}$, oxygen $\ce{O}$ has lone pair(s), so there is a confusion whether it can donate the pair to other species or not. So in that case, although it is an acid, one may say it is a base. Similarly, in $\ce{H2S}$, sulfur $\ce{S}$ has got lone pairs and I am confused whether it will act as base or acid.


texts: How to derive the electron density of Hooke's atom?

texts:
Hooke's atom has the following wave function:

$$\Psi( \boldsymbol{r_1}, \boldsymbol{r_2}) \propto \left( 1 + \frac{|\boldsymbol{r_1} - \boldsymbol{r_2}|}{2} \right) \exp\left(-\frac{(r_1^2+r_2^2)}{4}\right).$$

Question: How to calculate electronic density $\rho (\boldsymbol{r_1})$ using this wave function?

The answer, which should contain Error function, is on Wikipedia but not method.

I tried $\rho (\boldsymbol{r_1}) = \int |\Psi (( \boldsymbol{r_1}, \boldsymbol{r_2}))|^2 d\boldsymbol{r_2}$ but got wrong answer. In spherical coordinates:

$\rho (\boldsymbol{r_1}) = \int |\Psi (( \boldsymbol{r_1}, \boldsymbol{r_2}))|^2 d\boldsymbol{r_2} = \int_0^{2 \pi} \int_0^{\pi}  \int_0^{\infty} |\Psi (( \boldsymbol{r_1}, \boldsymbol{r_2}))|^2 r_2^2 d{r_2} \sin(\theta_2) d\theta_2 d\phi_2$

$\rho (\boldsymbol{r_1}) \propto \int_0^{2 \pi} \int_0^{\pi}  \int_0^{\infty} \left( 1 + \tfrac{1}{2} \sqrt{r_1^2 + r_2^2 -2 \boldsymbol{r_1} \cdot \boldsymbol{r_2} } \right)^2 \exp\left(-\frac{(r_1^2+r_2^2)}{2}\right) r_2^2 d{r_2} \sin(\theta_2) d\theta_2 d\phi_2$

where $\boldsymbol{r_1} \cdot \boldsymbol{r_2} = r_1 r_2 \left[ \sin(\theta_1) \sin(\theta_2) \cos(\phi_1) \cos(\phi_2) + \sin(\theta_1) \sin(\theta_2) \sin(\phi_1) \sin(\phi_2) + \cos(\theta_1) \cos(\theta_2)  \right]$

Aso according to the article linked on wikipedia answer should contain Error function. However Mathematica does not yield this result upon carrying out above integral. Where is my mistake?

(Note: crosspost from physics.se).


texts: Interaction between energy and entropy in highly elastic polymers?

texts:
Consider the interaction of energy and entropy in the highly elastic materials of an ideal polymeric network.

Now Gibb's free energy cannot be used directly $\Delta H = \Delta G + T \Delta S$ where $\Delta S$ and $\Delta H=U+pV$ for the internal energy $U$ such that

$S(R) = -k_{B} \frac{ 3R^{2} }{ 2N l^{2} } + const$
$U_{eff}(R) = k_{B} T \frac{ 3R^{2} }{ 2 N l^{2} } + const $

of which I am unsure.

I think the Gibbs free energy may have some nonlinear behaviour with the material such as some correlations between different terms and more passive energy terms due to elesticity -- this may be described by things such as fugacity.

How can you describe the interaction of energy and entropy in highly elastic polymers?


texts: Nature of bond in oxyacids of phosphorus

texts:
What is the nature of the bonds between P and O in oxoacids of phosphorous?

Is it a double bond or coordinate bond?

Wikipedia says that it is "double bond" but many times I encountered "coordinate bond".


texts: Why is 1-ethylidene-4-methylcyclohexane chiral?

texts: As far as I can tell, there doesn't seem to be a chiral carbon in this compound. C-4 of the cyclohexane ring has two groups with exactly the same connectivity, and the exocyclic double bond can't give rise to optical isomerism. What am I missing?


texts: Difference between Sildenafil and Sildenafil citrate

texts: The data I found seems to show no difference between Sildenafil and Sildenafil citrate. But if they are the same things, why Pfizer use Sildenafil citrate instead of Sildenafil as their product Viagra?


texts: food chemistry maltodextrin vs organic maltodextrin

texts: what is the difference between 'normal' food additive maltodextrin and "organic maltodextrin"? Is it only the primary source (i.e.: corn, wheat etc) that is organic or is it a different process to create maltodextrin? And is maltodextrin the same as food additive 1405?


texts: NMR: Magnetic and chemical equivalence in benzene

texts:
According to my textbook, all the protons in $\ce{^{12}C_6{}^{1}H_6}$ are magnetically equivalent, but those in $\ce{^{13}C_6{}^{1}H_6}$ are not.

I understand that for two nuclei to be magnetically equivalent, they need to have equivalent coupling to all other nuclei in the molecule. I do not understand this with respect to benzene as I expect Hc to couple differently to Ha than Hb to Ha and thus for them to be magnetically inequivalent irrespective of the isotope.


texts: Why are non-polar hydrogens neglected in computational protein-drug binding studies?

texts:
Why are (non-polar) hydrogen atoms generally neglected in a protein-ligand (or drug) binding energy calculation? They do have charge and mass. Doesn't that affect the free energy calculation?

The relevant equations are given here:
$$ \Delta G_\text{bind} = -RT\ln K_\text{d} $$
$$ K_\text{d} = \mathrm{\frac{[Receptor][Acceptor]}{[Complex]}} $$
$$ \Delta G_\text{bind} = \Delta G_\text{desolvation} + \Delta G_\text{motion} + \Delta G_\text{configuration} + \Delta G_\text{interaction} $$

A system where this is the case would be the following, note that only the polar hydrogen atoms are explicitly represented.


texts: In antacids like Eno that fizz up when mixed in water, why is the citric acid important?

texts:
I know that you can get rid of the acidity if you just take some baking soda added in water. I learned that these antacids that fizz up also have some citric acid and they react when added in water and produce $\ce{CO2}$ along with some other compound.
I like to know the use of citric acid in an antacid. Is it just for the feel of the fizz that subliminally reminds us of fixing the acidity in stomach?


texts: Precipitation occurred when adding vanilla extract to oak extract. What caused this?

texts:
Sorry if this is a very obscure question, but I don't know where to ask it.

120ml of oak extract, made by soaking oak chips in ethanol, was added to a flask. At this point, the solution was very dark with zero precipitate. 13ml of vanilla extract, consisting of ethanol, water, vanilla, and corn sugar were added to the solution. This extract was also free of precipitate before being added. Immediately upon adding the vanilla extract, a large amount of precipitate fell out the solution. Can someone please explain what happened, and what fell out of solution?


texts: Does rate of Evaporation change with surface area?

texts:
Two vessels of the same volume, in the
same location and open to the atmosphere. One is of a small diameter, the
other is of a larger diameter.
 The question is will the vessel with the
larger surface area evaporate the liquid
faster than the smaller one?
If not! I need answer to other question ,if i am not wrong.
Why does vapour pressure decreases with decrease in surface area?


texts: How can I have a concerted addition of bromines?

texts:
I know how to add Bromines in the antiperiplanar position, but I have no idea how to get concerted addition:

Perhaps I am not seeing something obvious, but I would greatly appreciate any hint.


texts: Why does roasting requires lower temperature than melting point

texts: Why do processes like roasting and calcination require a temperature lower than the melting point? Since intermolecular forces are lower in a liquid won't it be easier to oxidise (roasting) / decompose (calcination) in this state than in a solid?


texts: Mixing solvents and other compounds - safety issues

texts:
I would like to know if it is safe to mix organic solvents together or organic solvents with some compounds listed below.

In a mixture with random ratios (greater than zero - all chemicals present) we have:

Ethanol
Methyl ethyl ketone (as denaturant for ethanol)
Bitrex (aka Denatonium - as denaturant for ethanol)
Isopropanol
n-butanol (as denaturant for isopropanol)
n-propanol (as denaturant for isopropanol)
Ethyl acetate
Acetic acid (in case that ethyl acetate hydrolyzes)
Water (from ethanol and isopropanol)
Acetone
Methanol
Naphtha (Hydrogenated)

In general, we have alcohols, ketones, denatonium, ester, organic acid, water, and a liquid hydrocarbon mixture (Naphtha).Ratios can be taken as equal for all chemicals except those used for denaturation.(I think ratios for denaturants  wouldn't matter in case they would react.)

Could some of these chemicals react together and produce any unstable or hazardous compound?

What conditions should be avoided? (Light,heat,etc.)

Any reaction (slow) that could happen with atmospheric oxygen? (opening and closing a bottle containing all these chemicals)

I don't know too much about organic chemistry, just asking to be sure this is safe.I want to test something that possibly involves mixing all the above chemicals and I don't know if they could probably react together.

Note: Question unrelated to waste disposal. I'm experimenting with a DIY electronics cleaner.


texts:
I am told that the sulfur trioxide molecule exhibits charge separation because of poor p-orbital overlap. Sulfur's 3p orbitals are much bigger than oxygen's 3p orbitals, and thus the $\ce{S=O}$ bond is best described as $\ce{S+ - O-}$.

So is the author's argument suggesting that sulfur trioxide is unhybridized, and that it uses pure s orbitals to form sigma bonds and pure p orbitals to form pi bonds? Because that's the only way I can see sulfur as having three empty p orbitals to utilize. If we were to assign hybridization through counting the number of sigma pairs of electrons (3) we would arrive at sp2 hybridization, and there aren't enough p-orbitals to go around.

Also while we're on this topic, Wikipedia says that sulfur trioxide is best represented as having one $\ce{S=O}$ bond and two $\ce{S+ - O-}$ bonds. Now, does bond length differ between an  $\ce{S+ - O-}$ and an  $\ce{S=O}$ bond? Wikipedia suggests not, as only one bond length is given. If bond length is equivalent between the two, why?


texts: What is the mechanism of the reaction of ethyl prop-2-ynoate to ethyl (2Z)-2,3-dibromoprop-2-enoate?

texts:
It's really weird for the product is 99％ Z-comformation?
Please tell me why?
This reaction can be found in scifinder.


texts: Is it feasible to calculate the rate law of the oxidation of ethanol using colorimetry?

texts: My IB Chemistry class needs to have our Internal Assessment ideas finalized by next week, and I'm torn between a few experiments. I'm considering performing an oxidation of ethanol and potentially using colorimetry to measure the rate of the reaction (I believe using sodium dichromate as the oxidizing agent will create a color change, but I'm not sure if it is measurable enough to calculate kinetics). I'm also considering comparing the rate of the reaction dependent on temperatures, but am unsure about how that would work (potentially with a water bath?). I've also watched some oxidation of ethanol videos (because it's an AS Chemistry practical), but am unsure of how to move forward with it. Please just tell me if it's a feasible experiment or not, I'm quite literally just asking as to make a decision about what to do for this project.


texts: We have been asked to conduct an analytic project for chemistry. It is important that the project conducted hold social implications and the conclusion achieved help inform people better. Several ideas have come to my mind for such projects, such as determining amount of phosphoric acid in cold drinks, acetic acid in fruits such as guava, amount of insecticides/pesticides in vegetables/fruits in the market. However, I am still yet to find an idea which is striking. I would like to do something unique. Any suggestions?


texts: Reaction mechanism for reduction of nitrobenzene to aniline in catalytic and acidic media

texts:
Can anyone explain the reaction mechanism of the two reactions given below?

They are the conversion of nitrobenzene to aniline in catalytic ($\ce{H2/Pd}$ in ethanol) and acidic ($\ce{Sn/HCl}$ or $\ce{Fe/HCl}$) mediums respectively.

$$\ce{Ar-NO2 ->[\ce{H2/Pd}][\ce{EtOH}] Ar-NH2}$$

$$\ce{Ar-NO2 ->[\ce{Sn + HCl} \text{ or } \ce{Fe + HCl}] Ar-NH2}$$


texts: Mathematical definition of a symmetry operator

texts:
I had a hard time understanding what it means to apply a symmetry operator to a function, so I wondered if there is a formal way to define this? As far as I understand, applying a symmetry operation to a function means the following:
$$ \hat Rf(x) = f(\hat Rx) $$
The result has then to be the same function with a coefficient in front of it. Otherwise it would not be symmetric in regard to the symmetry operator $\hat{R}$.
Is this correct and can it be shown that this is how to apply symmetry operators to functions ?


texts:
I was doing histological slide preparation with rat's liver. There as a part of the microtechnique the fixed tissue had to be dehydrated using alcohol in the order 30%, 50%, 70%, 90% and 100% for 20-30 min each.
This had to be done to get rid of the water (possibly extracellular) before it was embedded in paraffin for microtomy because paraffin is immiscible with water.

My question is how does the alcohol extract water out of the tissue?


texts:
I've read in a book that the main factor for determining SN2 reaction rate is steric hindrance. The lesser it is, the faster the reaction.

So consider this question:

  $\ce{KI}$ in acetone undergoes SN2 reaction with each of $\ce{P,Q,R}$ and $\ce{S}$. The rates of reaction vary as:

I do not understand how $\ce{S}$ is the fastest. In my opinion it should be the slowest as it is very sterically hindered. What is going on here?

Source: Joint Entrance Exam (JEE) 2013 India


texts: Band MO of Sodium Filling of electrons confusion

texts:
I wanted to ask a question about metallic bond - band electron theory.

Consider the diagram of Sodium below:

Circled are orbitals both containing $2$ electrons each which combine using LCAO to give a set of bonding and antibonding electrons.

However, the $4$ electrons involved in this bonding  appear to only give $3$ electrons in the bonding and antibonding MO's produced.

This confuses me. Surely using $4$ electrons, I expect all $4$ of these electrons to also be present in the rectangle drawn.

Why are there only 3 electrons shown? Is one electron being used for the next addition of AOs?

Any answers would be greatful!


texts: Why is the melting point of KBr higher than that of CsCl?

texts: I thought that when compounds have similar forces and charges, the one with the higher molecular weight has the higher melting point. If that is true, then why is the melting point of $\ce{KBr}$ higher than that of $\ce{CsCl}$?


texts:
Drinking water (e.g. from your home's tap) is spiked with chlorine, for an amount of just some ppm.
Purpose of this operation is to kill bacteria, for our health.

  Background: chlorine in water is potentially dangerous for plants, or better, their soil.

A common solution to get rid of chlorine in tap water is leave it in an open pot all-night-long. In this way chlorine evaporates.

Now, in my mind, chlorine in dissolved in water as chloride ion ($\ce{Cl-}$). Just like salt in water.
And just salt in water, if you leave a pot of that mix in a room, after some time water evaporates completely and salt remains on the bottom of the pot.

Question is, how can chlorine evaporate from water?


texts: Le Chatelier's Principle: Temperature dependence of endothermic and exothermic reactions (chemical equilbrium)

texts:
What effect does temperature have on endothermic and exothermic reversible reactions? Please also explain the reason why it responds like this.
And what do people mean when they say something like "increasing pressure or volume shifts the reaction to left/right"? What do people mean by "left/right reaction shift"?


texts:
I am currently reading Atkins and Friedman's "Molecular Quantum Mechanics" (4th ed), looking at the Rayleigh-Ritz variation method. Starting from the Schrödinger equation $\hat{H}\psi = E \psi$, we get the "Rayleigh ratio"

$$
E = \frac{\int \psi^*\hat{H}\psi d\tau}{\int \psi^*\psi d\tau}
$$

Setting a trial function to be the following linear combination (assuming real coefficients)

$$
\psi_{trial} = \sum_i c_i\psi_i
$$

we find that

$$
E = \frac{\sum_{i,j} c_ic_j H_{ij}}{\sum_{i,j} c_ic_j S_{ij}}
$$

where $H_{ij} = \int \psi_{trial}^*\hat{H}\psi_{trial}d\tau$ and $S_{ij} = \int \psi_{trial}^*\psi_{trial}d\tau$.

Now the goal is to minimize the expression for $E$. We should therefore "differentiate with respect to each coefficient in turn and set $\partial E / \partial c_k = 0$ in each case". Using the quotient rule, I get the following

$$
\frac{\partial E}{\partial c_k} = \frac{ \sum_{i,j} c_ic_jS_{ij} \cdot \frac{\partial}{\partial c_k} \left( \sum_{i,j}c_ic_jH_{ij} \right)  }{\left( \sum_{i,j}c_ic_jS_{ij} \right)^2} - \frac{   \sum_{i,j} c_ic_jH_{ij} \cdot \frac{\partial}{\partial c_k} \left( \sum_{i,j}c_ic_jS_{ij} \right)   }{\left( \sum_{i,j}c_ic_jS_{ij} \right)^2} = 0
$$

However, I am not sure how to simplify this to obtain the correct expression, which is

$$
\frac{\partial E}{\partial c_k}_{Correct} = \frac{\sum_j c_j (H_{kj} - ES_{kj})}{\sum_{i,j} c_ic_jS_{ij}} + \frac{\sum_i c_i (H_{ik} - ES_{ik})}{\sum_{i,j} c_ic_jS_{ij}} = 0
$$

Clearly I can cancel a factor in the first term of my expression, but I don't know how to handle the derivatives with respect to $c_k$.


texts: Which chemical properties make a substance explosive?

texts: I know that some chemical substances are used as explosives. Amongst the most famous nitroglycerin in dynamite and cyclonite in C-4. Which chemical properties (I suspect that physical properties have less of an effect) make a substance a good explosive? If we know, for example, the formula and its geometry, is it easy to predict how explosive it can be?


texts:
My wife prepares lunch for me every morning. After eating it on my desk, I typically wash the lunchbox and utensils in the company's kitchen.
I have noticed that it is very difficult to remove the oiliness from the plastic containers (think Tupperware, but also harder plastics that look like polycarbonate): I need to rub the detergent-soaked sponge extensively and rinse with very hot water, several times. This does not happen with glasses, porcelain dishes or metal utensils like forks.

In other words, all the plastic containers I have come in contact with seem to be quite lipophilic.

Is this because edible oils and plastic are chemically "similar" (i.e., both contain long-ish chains of hydrocarbons), or is there another reason that I am missing?


texts: Asymmetry in trigonal bipyramidal geometry

texts:
I teach an MCAT course in chemistry. I like to explain VSEPR by saying.. first, imagine arranging electron pairs around the central atom so they are maximally distant from each other, and uniformly arranged. If there are two pairs, they'll just be across from each other. Three? You get a triangle, and so on.

This rhetorical device fails with five pairs. Five is strange because the electron pairs are most definitely not equidistant from each other, with the equatorial pairs being 120 degrees from each other, but 90 degrees from the axial electron pairs.

My question: is this a simplifying geometry for high school / college classes, and the geometry is actually more equally arranged in 3D space among the pairs? Alternatively, if 'trigonal bipyramidal' is actually the geometry, why? What induces the asymmetry? And does that imply that molecules with the same formula and connectivity, but with an atom equatorially versus axially located correspond to distinct stereoisomers?


texts:
I read calcium carbonate is the main component of seashells and other animals' shells (such as snails), and also limestone. How can I prepare pure $\ce{CaCO_3}$?

Could someone describe the process and the chemical equations involved? I saw this video and apparently that's one way. Are there others? For example, is there a way to obtain calcium carbonate from bones?

Please do tell me about the risks, but don't worry about my safety, since this is not going to be done in real life, but in a Minecraft mod instead. It is important to know the risks though, because I would like to make those risks part of the game, to make very clear for my players that, if its risky, the same stuff that happens to Steve/Alex will happen to them. (I intend to make it realistic gruesome, meaning I won't exagerate a bit, but either will I minimize the risks because it's "just a game". I'm 14, so I know better, but I know Minecraft is played for kids as young as 7, so I really don't wan't little toddlers thinking Chemistry is all fun and games).


texts: How to convert Excel comments to ChemDraw .cdx?

texts:
Not sure whether this might be a Superuser or StackOverflow question... but I hope some Chemist can help me with this.
I have an Excel table with cells which contain comments "by Cambridge Soft". I assume that these comments somehow contain the ChemDraw data of the structure. It seems to be ASCII-characters only.

How can I get these comments into a .cdx file?
I tried to save these comments as a text file, renamed it to test.cdx and tried to open it with ChemDraw... no success. I don't have ChemOffice available, which possibly might handle this.
So far, I haven't found any useful information about this on the web. The CambridgeSoft pages are not very informative.
Since these are quite a few structures I don't want to do this manually, but in an automated process. Python would be available. Any hints or ideas?


texts: Is there a way to determine if a compound is oxygen or water sensitive?

texts:
The synthesis of $\ce{CoH[P(OPh)3]4}$ requires the use of an inert atmosphere e.g. nitrogen as the compound is air-sensitive. Is there any way to tell whether it is the oxygen or water vapour in the air specifically? I thought it might be water sensitive seeing as metal hydrides are basic and may therefore react in an acid-base reaction:

$$\ce{CoH[P(OPh)3]4 + H2O ⟶ Co[OH][P(OPh)3]4 + H2}$$

Is rationalisation correct/is there more to it than this?


texts:
We know that anything that separates the system with the surroundings is called a boundary.
It is said that a boundary can be either conducting or non-conducting, rigid or nonrigid, and real or imaginary.

What is meant by "imaginary boundary"?


texts: How to calculate atomic number of an atom when wavelength is known?

texts:
In the emission spectrum of an atom, an emission line in UV region is observed for a transition from third orbit to first orbit with the wavelength of 64.1 Angstrom. What will be the atomic number of the atom?

I tried using the formula to calculate change in energy
$$\Delta E = R_h \left(\frac{1}{n_i}+\frac{1}{n_f}\right)$$
where $\Delta E$ is change in energy, $R_h$ is the Rydberg Constant $\left(2.18 \cdot 10^{-18}\right)$, $n_i$ is the initial orbit (i.e 3rd orbit) and $n_f$ is the final orbit (i.e 1st orbit).

On finding the value of this I equated it with another formula:
$$E = -\frac{R_h Z^2}{n^2}$$
where $E$ is the energy, $R_h$ is the same as above, $Z$ is the atomic number and $n$ is the orbit.

I used this formula to find out the energy at 3rd orbit and then 1st orbit and took $Z^2$ common. Then I subtracted both the obtained values but failed to find out the value of $Z$ ...


texts: What is the benefit of using Am-241 in smoke detectors even though it is a radioactive element?

texts:
I see the labels denoting Am-241 in my smoke detectors. I am having a hard time understand why Am-241 is used in smoke detectors even though it is a radioactive element. It seems to me like a lot of trouble to use a radioisotope in consumer products and notably extra effort given that Am-241 is a synthetic isotope. Why would Am-241 be used in the manufacture of smoke detectors?

The only mitigating factor I can see is that it has a relatively long half life.


texts: Why exactly is a fluoride anion a stronger base than iodine anion?

texts:
First off, I've learnt that stronger acids produce weaker conjugate bases (through Brønsted–Lowry acid–base theory).

Then I looked at the $\mathrm{p}K_\mathrm{a}$ values of $\ce{HF}$, $\ce{HCl}$, $\ce{HBr}$, and $\ce{HI}$ and came to the conclusion that $\ce{HI}$ is the strongest among them and that explains why $\ce{I^-}$ is the weaker base.

So far so good.

But then I remembered that $\ce{F^-}$ is in fact the strongest oxdizing agent out there.
So shouldn't that mean that $\ce{F^-}$ ion is more stable than $\ce{I^-}$? And hence does not give away its electrons easily and therefore is a weaker base?

Where am I going wrong here?

I have a little bit of gut feeling that this is because of the large size of iodide ion which can hold the negative charge better than the tiny fluoride ion. But I have found nothing to back this up.


texts: How do we know that hydrogen gas consists of two hydrogen atoms?

texts: Of course I know that both 1s orbitals will combine and that the electrons will occupy the bonding MO and that the two atoms will reach a lower energy state – but how do we really know that is the case?


texts:
Propose a titration protocol for a hydrochloric acid solution of approximate concentration 0.1M using the solutions and materials available.
Solutions:
-$V_0$ = 20mL of hydrochloric acid solution of unknown concentration.
-Solution of $\ce{KIO3}$ at $C_1$=0.1 mol/L
-solution of $\ce{KI}$ at $C_1$=0.1 mol/L
-$\ce{Na2S2O3^2-}$ solution at $C_2$ = 0.01 mol/L
-concentrated sulphuric acid
Equipment: - common glassware
-no pH meter, conductivity meter or colour indicators
Data :
-Experiment 1: a solution of $\ce{I2}$ to which a few drops of soda are added becomes colourless
-Experiment 2: a solution of iodate and iodide ions to which a few drops of sulphuric acid are added becomes brownish-orange.
-Standard redox potential = E°($\ce{S4O6^{2-}}$/$\ce{S2O3^{2-}}$)=0.08V
-E-pH diagram of iodine plotted for the species: $\ce{I2}$, $\ce{IO3^-}$, $\ce{I^-}$

My ideas: Add excess $\ce{I^-}$ and excess $\ce{IO3^-}$ to the hydrochloric acid soluton. We then have $5\ce{I^- }+ \ce{IO3^-} + \ce{6H^+} = 3\ce{I2}+ 3\ce{H2O}$. The constant for this reaction can be calculated by retrieving the associated thermodynamic constants from the diagram. The $\ce{I2}$ formed is then titrated with $\ce{S2O3^{2-}}$. The $\ce{H^+}$ concentration in the initial state can be deduced from this. However, I think that this method is not good because the first reaction is largely total and the colorimetric titration is not precise enough to determine the correct values.
Is there another method that is simpler or more accurate?


texts: Mechanism for oxidative cleavage of tertiary alcohols by NaOCl

texts:
I came across this today

  An ester $\ce{C4H8O2}$ on reaction with $\ce{CH3MgCl} $ and hydrolysis gives an alcohol. The alcohol on reaction with $\ce{NaOCl}$ and $\ce{H3O+}$ gives acetic acid. Identify the structure of the ester.

But what I'm facing a problem with is the role of $\ce{NaOCl}$. My teacher said it can cleave and oxidize a tertiary alcohol, say tert-butyl alcohol, to acetic acid.

But I couldn't understand the mechanism. Any help will be appreciated.


texts: Why is methamphetamine less polar then amphetamine?

texts:
The question is as stated in the title. Is there a general way to determine relative polarity of organic compounds?
This question is for use in the context of the manner in which polarity of the components of the mobile phase in high-performance liquid chromatography determine the polarity of the stationary phase.


texts:
It is commonly known how to plate glass with silver using silver nitrate, ammonia and glucose.

With about the same effort, is there a way to plate glass with copper?


texts: What makes Citrate or Citric Acid an acid?

texts:
As far as I know, an acid is something that gives off a proton or hydrogen ion $H^{+}$.

But when I look at Citric Acid,

There are three $COO^{-}$, which I think is a carboxyl group, that lacks $H^{+}$.

They seem to rather demand a hydrogen ion from its environment than donate one, which make it basic and not acidic. But the name is still citrate or citric acid. Can someone explain?


texts: Conventional unit cell for a hexagonal crystal system

texts:
The figure shows a unit cell of a hexagonal crystal system. Drawn in bold, is the unit cell. The lightly shaded one is a unit cell as well and has a six fold symmetry along an axis, hence is more symmetrical than the one in bold.
Why then do texts define the unit cell of a hexagonal system by the one drawn in bold? For example this this


texts: Is this answer wrong? I feel like there should be a hydrogen instead of a carbon where I indicated in red. Thank you.


texts: What is the mechanism of chlorosulfonation of benzene?

texts:
The above reaction looks very similar to a conventional sulfonation reaction but if the reaction pathway is analogous to sulfonation I do not see how the $\ce{SO_2Cl^+}$ would form. Surely $\ce{Cl^-}$ would leave rather than $\ce{H_2O}$ in the formation of the electrophile? Please help me find a mechanism.

Also, I would like to approach questions, such as this one, like I would a puzzle rather than calling upon my memory. Is there a series of steps that I should follow? (i.e: 1. Identify electro/nucleophile, 2. Identify acidic protons ...).


texts: Are there chiral compounds that don't rotate plane-polarized light?

texts: I know that meso compounds have chiral centers but don't rotate plane-polarized light, and I know that there can be non-traditionally chiral compounds (e.g. ones with large substituents that prohibit much rotation around single bonds) that can still rotate light, but I haven't been able to find any molecules that are chiral but don't rotate plane-polarized light (or rotate it impossibly little). I'm imagining something like an enantiomeric pair connected by one single bond with a slight modification to one that makes it have similar optical activity but not actually be identical (so the final molecule is indeed chiral), but I don't know exactly how to make it work.


texts: Relative rate of hydrolysis of the carbon chlorine bond in thioethers and ethers

texts:
I am solving problems based on rates of hydrolysis of compounds but I don't have a general approach to such questions.

Which of the following compounds undergoes hydrolysis faster than the second under comparable conditions? It may be acid catalysed or base catalysed hydrolysis but the conditions must remain the same for each pair.

In my view since oxygen is more electronegative than sulfur, hence hydrolysis should be easier for second. But I am not sure about it.
 see part 2 here
see part 3 here