texts: Voltage vs current density - why are both parameters important to control an electrochemical reaction?

texts:
In many electrochemistry scholarly articles/studies they talk about certain specific reactions occurring at certain voltage potentials, while in other articles they talk about current density as the determiner for which reactions happen.

Why is this? From what I know about electrical engineering you can either set the voltage, and the current will adjust accordingly, or you can set the current and the voltage will adjust to meet the current. You cannot set both of them at the same time. That would defy the laws of physics.

So what do many of these articles mean when they talk about, for instance:

  Reported reactions of this type often occur at potentials smaller than -3 V

How does this relate to the current density that is set by a power supply for instance?


texts: Why are synthetic pH indicators used over natural indicators?

texts:
Synthetic indicators seem to be exclusively used when determining the pH of a substance with an indicator (with the exception of that school experiment where you boil cabbage to demonstrate natural pH indicators) or in acid-base titrations etc. over natural indicators. Why is this the case when naturally occurring indicator can be easily prepared from accessible and sustainable methods, such as boiling cabbage?

Intuition seems to suggest that perhaps synthetic indicators are much more accurate and reliable, being specifically designed for the task, is this the case? Or are there other reasons why natural indicators are regularly used as a cost-effective, environmentally friendly and easily prepared alternative to synthetic pH indicators?

What are the advantages/disadvantages of using synthetic indicators over natural ones (or vice versa)?


texts: Reagents and intermediates for synthetic route

texts:
What are reagents 1 and 2, and what compound is A?

I was trying to solve this problem, and some ideas popped up (reductive ozonolysis, then aldol condensation and ionic addition, maybe?) but I wanted to be certain.

Thanks a lot in advance! Sorry for possible bad english.


texts:
The other day in class we were discussing the enantiomers of 1,2-dichlorocyclohexane and my teacher told us that (R,R) and (S,S) are different isomers while (R,S) and (S,R) are the same.

I understand how (R,S) and (S,R) are the same (Because they can be rotated) but I don't understand why (S,S) and (R,R) are not the same, even though they are the same if you rotate them too.


texts: Etching PCB - dealing with anhydrous ferric chloride

texts:
I'm looking into PCB etching,which requires ferric chloride (There are other etchants, but they're pretty hard to come by where I live and too expensive if I can find them).
The issue is that where I live, only anhydrous ferric chloride is sold (Which is stupid. They don't even label it properly as anhydrous - got exposed to HCl fumes for 2-3 hours, thankfully the doctor found nothing abnormal with me and I got sent off with some anti allergy meds).
I'd like to know what equipment I'll need to deal with this stuff safely. I always use nitrile gloves with these, but in particular what kind of respiratory protection will I need? I plan on just having 4 PC fans blow these fumes outside the window. If I must, I will invest in respiratory protection (It's very expensive where I live, the NIOSH approved ones at least). I'm assuming a 3M 6002 will be enough.
Please keep in mind I will be using this stuff at home. If you have any suggestions regarding alternatives, do mention them. If I can find it, I'd rather use that than this.
If this isn't the proper place to ask these questions, please direct me to a place more suitable for these questions.


texts:
I am really sorry if this is a beginner question but please still help me.
In this website, which explains balancing chemical equations mentioned the word formula unit here:

$\ce{3Ca(NO3)2}$ (just the oxygens) ---> There are 18. The 3 on the nitrate times 2 outside the parenthesis equals 6 oxygen in one formula unit. The coefficient of three times the 6 gives the final answer of 18.

My question: What does formula unit mean?


texts: Sensitivity of Carbon NMR Compared to Proton NMR

texts:
I am trying to figure out exactly how much less sensitive carbon NMR is from proton NMR. In a lecture, my professor said that carbon NMR is 1/5800th as sensitive as proton NMR for the following reasons:

Abundance of Carbon-13 is 1.1% so sensitivity is decreased by a factor of (0.011)
The precession frequency (difference in energy between the alpha and beta states) is about 1/4 of the precession frequency of a proton. Because this is equivalent to electrical output on the oscillator coil, this will be 1/4 as powerful (0.25)
The magnetogyric ratio of Carbon-13 is 1/4 that of Hydrogen-1 (0.25)
The dipole generated by Carbon-13 is 1/4 that of Hydrogen-1 (0.25)

Thus: 0.011 * 0.25 * 0.25 * .25 = 1/5800 (roughly)

My only objection is that the magnetogyric ratio is proportional to the magnetic moment and the spin number. Thus, I would not expect the 1/4 factor to be counted twice since it is assumed based on the definition of magnetogyric ratio. For this reason, I would expect the sensitivity of carbon NMR to only by 1/1600th of proton NMR.

i.e. 0.011 (abundance) * 0.25 (lower precession frequency) * 0.25 (magnetogyric ratio / dipole moment) = 1/1600

I am not sure who is right. I cannot find any sources that will detail the exact sensitivy differences between proton and carbon NMR and why it is so


texts: How are the angle bending parameters defined in the MM2 force field?

texts:
I am currently looking through the openbabel implementation of the mm2 forcefield. While I understand most of the implementation, I don't get the definition of the angle bending parameters (see https://github.com/openbabel/openbabel/blob/master/data/mm2.prm), which have the following form:

angle         1    1    1     0.450    109.470    109.510    109.500
angle         1    1    2     0.450    109.470    109.510    109.500
angle         1    1    3     0.450    107.800    109.900    110.000
angle         1    1    4     0.450    109.470    112.400    109.000
angle         1    1    5     0.360    109.390    109.410    110.000
angle         1    1    6     0.700    107.500    107.700    107.400
angle         1    1    8     0.570    109.470    108.800    109.500
angle         1    1    9     0.500    109.280    110.780    109.280
angle         1    1   11     0.650    109.500    107.500    109.500
angle         1    1   12     0.560    108.200    0.000      0.000

So they are of the form

<1.-atom-type> <2.atom-type> <3.atom-type> <force-constant> <1.angle> <2.angle> <3.angle>

However, I understand the angle bending to work like this:

There is an ideal bond angle $\theta _0$, and if the actual bond angle $\theta$ differs from $\theta _0$, this results in an increase in energy, e.g. of the form $\Delta E = (\theta _0 - \theta)^2$. Therefore, given an angle with three atom types a,b,c there should be only one angle $\theta _0^{a,b,c}$. So why are there three angles given for every combination?


texts: Why can't hot water break disulfide bonds when the energy storage in hot water exceeds the bond energy?

texts: I teach Biochemistry and know that heating water can break weak bonds like hydrogen bond or ionic interaction, but not disulfide bond (without reducing agent). The bond energy of hydrogen bond in water is about 12–30 kJ/mol, while the disulfide bond is 251 kJ/mol. I initially thought the heated water would have the energy much lower than 251 kJ/mol, but higher than 30 kJ/mol. But when I looked at the energy storage in 1 L of water at 90 degrees Celsius from here, it was calculated to 294 kJ. Now I wonder whether I can compare this energy to the bond energy. What do I miss here?


texts: Software to assist drawing of complex, three-dimensional skeletal formula from scratch or from existing crystal structure

texts:
Is there a tool that would help in creating rather intricate line drawings (not pre-rendered balls-and-sticks/wireframe/sticks/ORTEP diagrams) for a skeletal formula in 3D space?
To illustrate the question a bit further, here are two examples:

Organic molecules — An all-benzene catenane and a trefoil knot [1]:

Inorganic molecules — proton transfer in polyoxoniobate $\ce{[H_xNb10O28]^{(6-x)-}}$ [2, p. 111]:

I also saw a much larger line-art structure of an entire peptide drawn the similar way, but unfortunately I cannot find the reference at the moment.
Line-drawn structures like these are usually presented alongside with the determined crystal structures, so I naturally assume that there is a tool that would allow to convert a CIF file to an illustration like the ones shown above.
However, I wasn't able to find anything relevant by screening the IUCr software list, and this already concerns me for several years.
Do people really use molecular editors like ChemDraw for this, or there is a more optimal way?
Also, if ChemDraw is the tool for the job, are there any general recommendations as to how to efficiently draw structures like this in 3D space without loosing one's mind on estimating z-buffer for proper bonds' greyscaling/thickness/type based on the distance from the viewer as well as overlapping atoms and bonds?
I would really appreciate if someone who published similar work would share some tips regarding their workflow.
References

Segawa, Y.; Kuwayama, M.; Hijikata, Y.; Fushimi, M.; Nishihara, T.; Pirillo, J.; Shirasaki, J.; Kubota, N.; Itami, K. Topological Molecular Nanocarbons: All-Benzene Catenane and Trefoil Knot. Science 2019, 365 (6450), 272–276. DOI: 10.1126/science.aav5021.
Polyoxometalate Chemistry, 1st ed.; van Eldik, R., Cronin, L., Eds.; Advances in Inorganic Chemistry; AP, Academic Press, an imprint of Elsevier: Cambridge, MA San Diego, CA Oxford, 2017; Vol. 69.


texts:
It is well known that single atom of oxygen is not stable, and it forms $\ce{O2}$ molecule. But elements like carbon form a network of repeated bonds. As answered in another question, last atoms in such network are unstable and need to create some bonds.

Is it possible to have a (free-standing) single atom of carbon? Stable in the form of a stable powder like graphite or diamond.

If not, what is the minimum size of a carbon particle (diamond or graphite network)?

Further Clarification: I meant normal chemical stability to have a powder material at room temperature. I do not mean highly reactive carbon, quickly turning into a compound.


texts: Different formulas for copper pyrites and bauxite

texts:
In my book in the chapter on General Principles and Processes of Isolation of Elements, I found that the formula for copper pyrites was stated as $\ce{Cu2S.Fe2S3}$ at one place, $\ce{CuFeS2}$ at another place and $\ce{Cu2FeS2}$ at another place.

Are all these taken to be the formula for copper pyrites or are these printing mistakes. I have searched the internet but could not find any useful information regarding this.


texts: Finding the number of cyclic isomers algorithmically

texts:
Is there an algorithm for finding the number of cyclic isomers a given compound might have?

I've found a general algorithm for all isomers: link, but I'm not sure how to apply it for cyclic isomers only.


texts: How to calculate partition coefficients?

texts:
Below is a transcript of this doubtful question:

  A weak monobasic organic acid $\ce{HA}$ is soluble in both water
  and $\ce{CHCl3}$.  $\pu{500.0 cm3}$ of a solution of $\ce{HA}$ in $\ce{CHCl3}$, with a concentration of
  $\pu{0.057 mol dm-3}$,
  is shaken well with $\pu{500.0 cm3}$ of water and allowed
  to attain equilibrium at $\pu{27°C}$.  An aqueous layer and
  $\ce{CHCl3}$ layer then separate out; the pH of the aqueous layer is
  found to be 3.21 under these conditions.

  The dissociation constant of $\ce{HA}$ in water at $\pu{27°C}$
  is $\pu{1E-5 mol dm-3}$.

  Calculate the partition coefficient at $\pu{27°C}$
  for the partitioning of $\ce{HA}$ between water and $\ce{CHCl3}$.
  In a second experiment, a further $\pu{500.0 cm3}$ portion of the
  same $\ce{HA}$ solution in $\ce{CHCl3}$ in which the concentration
  of $\ce{HA}$ is $\pu{0.057 mol dm-3}$, is shaken well with
  $\pu{500.0 cm3}$ of a $\pu{0.027 mol dm-3}$ aqueous $\ce{NaOH}$
  solution and allowed to reach equilibrium at $\pu{27°C}$.
  Calculate the $\mathrm{pH}$ of the aqueous layer under these conditions.
  State the assumptions you make, if any, in the above calculations.

My solution for Question 1.

Since pH is given, $\ce{[H^+](aq)}$ is determined by

\begin{align}
\mathrm{pH} &=-\log[\ce{H^+~(aq)}]\\
[\ce{H^+}~(\ce{aq})] &= 10^{-3.21}\\
    &= 6.16 \cdot 10^{-4}~\mathrm{mol\,dm^{-3}}\\
\end{align}

By appropriately applying $K_\mathrm{a}$, the $[\ce{HA}~({\ce{aq}})]$ present in aqueous layer is $0.038~\mathrm{mol\,  dm^{-3}}$.
Next, $[\ce{HA}~(\ce{aq})]$ present in the organic layer can be determined by subtracting the $[\ce{HA}~({\ce{aq}})]$ present in aqueous layer
from the initial concentration of $[\ce{HA}~({\ce{aq}})]$, which results in $0.019~\mathrm{mol\,  dm^{-3}}$.
Finally, I got $K_\mathrm{D} =
   \dfrac{[\ce{HA}_\mathrm{aqueous~layer}]}{[\ce{HA}_\mathrm{organic~layer}]}
   = \dfrac{0.038~\mathrm{mol\,  dm^{-3}}}{0.019~\mathrm{mol\,  dm^{-3}}} = 2$.

I hope that this is correct, but  I am not quite sure.

My incomplete solution for Question 2.

The reaction between $\ce{HA}$ and $\ce{NaOH}$ is

$$\ce{HA}~(\ce{aq}) + \ce{NaOH}~(\ce{aq})  \longrightarrow \ce{NaA}~(\ce{aq}) + \ce{H2O}~(\ce{l})$$

The number of moles of $\ce{NaOH}$ present is $0.0135~\mathrm{mol}$.

I am confused with the concentration of $\ce{HA}$ that I needed to take for this calculation. Initially I have found the concentration of $\ce{HA}$ present in organic layer as $0.019~\mathrm{mol~dm^{-3}}$. Do I need to use that here or $0.057~\mathrm{mol~dm^{-3}}$?

What would be the assumptions that I need to assume to take out this calculation?


texts: Can carbon monoxide from a floor-heater in a poorly ventilated room eventually be ignited by the fire and explode?

texts: I have often wondered about carbon monoxide accidents caused by free-standing heaters burning in a poorly ventilated room causing fatalities. I am aware that CO is explosive between 12 and 75% volume air and wonder why it doesn't eventually ignite from the flames or glow present when the CO level reaches 12%? (This never seems to happen). Or does the decreasing oxygen content in the air due to the combustion cause the fire to die out before the critical level of 12% is reached?


texts: Why can't two Silicon tetraoxide tetrahedrons share an edge or a face?

texts: Our teacher told us about structural types of silicate minerals (neosilicate, sorosilicate, cyclosilicates ...) saying that those tetrahedrons can only share one corner (oxygen), but he didn't give us any explanation, could anyone help me with this?


texts: How much CO2 is created during water electrolysis with a graphite anode?

texts:
I'm experimenting with water electrolysis and wanted to use non-toxic materials, so I settled on pure graphite rods for both electrodes and Epsom salt (magnesium sulfate) as the electrolyte.  The system works reasonably well, but upon further reading I found that some of the $\ce {O2}$ is likely reacting with the graphite and being converted into $\ce {CO}$ and $\ce {CO2}$ at the anode.

How much $\ce {O2}$ am I probably losing to $\ce {CO}$ and $\ce {CO2}$ ?  Just a small percentage, or a majority of the potential $\ce {O2}$ production?  How can I tell?  I'm capturing the resulting mixed gas product in soap bubbles and igniting it but it seems to burn somewhat less vigorously than I was expecting, which makes me think there is rather more $\ce {H2}$ and less $\ce {O2}$ than optimal.


texts: Is alkene reaction with hydrogen to form an alkane an addition reaction?

texts:
I have seen in some textbooks that such a reaction is listed under reduction of alkenes.

I understand that the double bond is getting reduced to single bond and one hydrogen atom is added to each of the carbons.

Should I classify this reaction as an addition reaction or a reduction reaction?


texts: How to identify if a compound is organic or inorganic?

texts: What is the actual basis of distinction of organic compounds? The presence of carbon is not the only basis.


texts: The formation of ice crystals on/in frozen food that has been defrosted and then frozen again

texts:
I made a mistake. I put my ice cream in the refrigerator instead of the freezer and left it there for a night. I realized my folly the next day.
I put it in the freezer. When I took it out, I noticed it had a bunch of ice crystals inside it and on its surface. This intrigued me (not that it is a new discovery of mine or anything). I was left with the question: Are these ice crystals the product of added water, or is it just the phase change of water already present in the ice cream.
Okay, so I have to hypotheses:
Hypothesis 1
When the ice cream was defrosted, it became more liquid and as such, the bonds of the chemicals were weakened. This allowed the water that was mixed with the milk to break loose a little. When the ice cream was put back inside the freezer, it cooled down at too quick of a pace, making it so that some of the water didn't have time to fall back in line before it underwent a phase change.
Hypothesis 2
While the ice cream was hotter and more liquid, its permittivity increased. Atmospheric water, of which there is probably much of inside a refrigerator, entered the semi-melted ice cream and over-saturated it with water. When it was put back into the freezer, this over-saturation led to the crystallization of excess water.

So, which one of these hypotheses are most likely, if not surely, correct or most correct? Or is none of them correct? Or is the phenomenon caused by a combination of the two hypotheses?


texts:
The most common formula for smoke grenades and sugar rocket fuel is $60\%\ \ce{KNO3}$ (potassium nitrate) and $40\%\ \ce{C12H22O11}$ (sugar). This is a 3:2 ratio, but I've also seen 2:1 and 5:3 with similar results.

The formulas I've seen (https://www.scienceforums.net/topic/19364-kno3-and-sugar-smoke-bomb/) are: $\ce{5C12H22O11 + 48KNO3 -> 24K2CO3 + 36CO2 + 55H2O + 24N2}$ and $\ce{C12H22O11 + 24KNO3 -> 24KNO2 + 12CO2 + 11H2O}$.

Based on the first formula, using mole ratios and molar masses, it would be ideal to have $\pu{68.5 g} \;(\pu{0.2 mol})$ of sugar mixed with $\pu{194.1 g} \;(\pu{1.92 mol})$ of oxidizer. This is not even close to the advertised 3:2 ratio, being a 17:6 ratio.

Question 1: Why do you need substantially less potassium nitrate than as indicated by the chemical equation?

Now, in terms of the smoke grenade, an alternate formula I've seen used involves potassium chlorate (oxidizer) and lactose (same as sucrose). This, from what I've read, burns at a lower temperature and can produce colored smoke.

Question 2: Which one produces more smoke than the other (and why)?

Question 3: How can I modify the $\ce{KNO3}$ formula to produce more smoke. Which reactant produces the smoke? Fuel (sucrose/lactose) or oxidizer (K-nitrate/K-chlorate)? From a 60:40 ratio, should I add more sugar to make it like a 40:60 ratio, or more potassium nitrate, therefore 70:30 is better?


texts: Chlorination of Water using sodium hypochlorite

texts:
$\ce{NaClO_{(s)} + H2O <=> NaOH_{(aq)} + HClO_{(aq)}}$

This reaction is often used in swimming pools as an alternative to directly chlorinating the water.

I read that the water must be kept slightly acidic. Otherwise, $\ce{OH-}$ ions in the alkaline solution would react with the $\ce{H+}$ ions in the chloric (I) acid to form water. Consequently, $\ce{ClO-}$ ions are removed and the concentration of $\ce{H+}$ ions decreases.

So far this all seems fairly reasonable.

However, my textbook then said this:

  In alkaline solution, the equilibrium moves to the left.

This contradicts what I have read online and elsewhere. Surely if the concentration of hydrogen ions decreases, the equilibrium would shift to the right to increase the concentration of the products and thus the hydrogen ions?

Thanks in advance.


texts: Reaction of copper (II) ion reacting with sodium hydroxide

texts:
Based on an experiment, a solution that contained $\ce{Cu^2+}$ formed a precipitate with $\ce{NaOH}$. Is this how you write the equation?

$$\ce{2NaOH + Cu^{2+} -> Cu(OH)2 + 2Na+}$$

On the experiment: solution A is mixed with NaOH (solution turned white). Using a flame test solution A is color green. I figured solution A has $\ce{Cu^{2+}}$ ion.


texts:
I realized that liquids like petrol, kerosene and even perfumes are combustible when they are volatile.

Could that be the reason why water is not combustible is because it is not volatile?

Are volatile liquids all combustible?


texts:
Suppose I have a dehydration reaction of methanol to produce methoxymethane:
$$\ce{2 CH3OH(l) ->[H_2SO_4] C2H6O(g) + H2O(l)}$$
Usually, people will use sulfuric acid to dehydrate the methanol. Assuming all the methanol was reacted, how do I get rid of the water in the sulfuric acid? Will simply heating the sulfuric acid be sufficient?


texts: Why any non polar compounds dissolve in nonpolar substance like Benzene what is the reason behind it?

texts:
In case of ionic solvent the ionic solute dissolve in it because due to polar nature of water it break the bond between the ions through hydration energy and the ionic solvent dissolve in it.
So I want to ask that for what reason the non polar solute dissolve in non polar solvent ?
Means a basic framework like due to what reason it happens?
I searched on Google but I don't get slim and articles or content


texts: Why do nitrogen molecules not act as ligands in haemoglobin?

texts: Nitrogen molecules $(\ce{N2})$ have lone pairs, which, as far as I know, is the property of oxygen molecules $(\ce{O2})$ that allows them to act as ligands bonding to iron in haemoglobin in the blood. Why then is atmospheric nitrogen unable to act as a ligand and form dative bonds to iron in the blood as oxygen is able to?


texts: What is the pKa Range for weak acids and bases?

texts:
Am I correct in assuming that the following is true?

$\mathrm pK_\mathrm a < 3$ is for a strong acid
$3 < \mathrm pK_\mathrm a < 7$ is for a weak acid
$7 < \mathrm pK_\mathrm a < 11$ is for a weak base
$\mathrm pK_\mathrm a > 11$ is for a strong base


texts: Is there any scenario in which the size of a molecule increases due to an increase in temperature?

texts:
Take an ice cube for example. Heat is applied in a closed container until it is vaporized completely. Will the molecule's size be larger (on average)? Is there a substance that you know of that has odd behaviour such as changing molecular size due to temperature change? Obviously there would be more pressure in the case of $H_2O$. Have you heard of any substances that are exceptions to this rule? I would love to hear about it if you have.

If this question hasn't quite boggled your mind or you are having trouble thinking of an exception, let's say that an average diamond at about room temperature (something with entropy, ie: not a perfect lattice) and we say that this is a single macro-molecule because every carbon atom present in the diamond shares a bond with another carbon in the diamond.

Pretend we heat said diamond up a bit or let it sit for awhile. Are covalent bonds being broken and reformed as time goes on? If we heated it up enough without breaking the lattice completely, would the diamond itself, the molecule as a whole, increase in size at all? Or would the bonds just be broken more often and reformed, and the size change would be so negligible that it could hardly be considered an increase in volume?


texts:
If we look at the $\ce{ClO4-}$ anion, the chlorine atom in it is sp3 hybridised. Hence, it has a tetrahedral structure in which conjugation shouldn't be possible, but while explaining the acidic strength of $\ce{HClO4}$, I've seen many people claim that it is very acidic because the $\ce{ClO4-}$ anion is stable due to the conjugation of charge between the four oxygen atoms.

So, all of this boils down to: Is planarity really necessary for conjugation?


texts: What is the difference between activity and reactivity when discussing elements?

texts:
I screwed up on a true/false question that stated that lithium is the most active alkali metal. I answered false, because I remembered that the lower you go in this group, the more explosive the element is.

It seems, however, I was thinking of reactivity and not activity. I know about the activity series, and it's something I wouldn't like to memorize, but I would a deeper explanation on the difference between activity and reactivity. Why do we have these two terms?


texts: Is phosphorus a stereogenic centre in this phosphate ester?

texts:
My textbook says that in the above diagram that there is only 2 stereoisomers. I am guessing this is due to the stereogenic carbon atom and not due to the phosphorus atom which apparently isn't a stereoisomer.

However, it states that the above molecule has 4 stereoisomers. This must indicate that in this case the phosphorus atom, it is a stereogenic and gives rises to 2 stereoisomers.

Why is the phosphorus atom in A not a stereocenter while the phosphorus atom in B is a stereocenter?


texts: Double bond formation in alkenes during cracking

texts: In thermal or catalytic cracking, energy is used to break a long chain alkane into smaller alkanes/alkenes. Since the energy goes into breaking the bonds, how is the C=C bond in alkenes formed?


texts: Which compound releases more energy upon combustion?

texts: I know that the last two on the right are stable so they are not the answer, but can someone give me a hint on how to decide between the two on the left? what is the way of solving such question, I don't think it's only dependent on stability because there is more ring strain (two cyclobutanes) in the molecule at far left.


texts: AlCl3(aq) reaction with NaHCO₃ to form alumina Al2O3

texts:
In a demonstration, aluminum foil was add to a solution of $\ce{HCl}$ and allowed to react, the reaction was presented as
$\ce{2Al(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2(g)↑}$
After filtration, the solution appeared optically clear.
Next, baking soda, i.e. sodium carbonate $\ce{NaHCO3(s)}$, was added, and the solution then turned whitish opaque. After a while a white precipitation could be observed. In the presentation it was claimed that alumina, $\ce{Al2O3(s)}$, was precipitating out of the solution.
What reaction takes place when $\ce{NaHCO3(s)}$ is added to the solution? Is it correct to claim that $\ce{AlCl3(aq)}$ exists in the solution?


texts: Inductive vs resonance effects and the acidity of phenol

texts:
A lot of people rationalize the acidity of phenol by saying that resonance is responsible for much of phenol's acidity as opposed to aliphatic alcohols.

However, this image suggests that in fact the inductive effect is responsible for a great deal of phenol's additional acidity. As we can see in the picture immediately above, it seems that the sp$^2$ carbon neighboring to the oxygen is pulling most of the weight here; that the resonance contributors with charges on carbons are minor contributors. The additional resonance contributors for phenol seem to be doing almost nothing here.

So, who's right? Resonance>inductive effect in phenol or the other way around?

EDIT: The argument I have summarized above is presented here at this website entitled "I Judge People By Their Grammar and Knowledge of Phenol"

  While the chemistry in the paper was good, as The Chem Blog has noted,
  the authors’ lack of attention to detail was borderline disrespectful.
  I expected more from one of the most storied labs in synthetic organic
  chemistry.

  [...]

  It turns out that an inductive effect—not a resonance effect—is the
  predominant reason for the increased acidity of phenol relative to
  aliphatic alcohols.

  [...]

  For those interested, these data come from Evans’ Chem 206 lecture
  notes (Lecture 20, restricted access), where the point is hammered
  home in glorious detail. Professor Evans’ PowerPoint slides should be
  framed and displayed in the Smithsonian.

Addressing jerepierre's point

$\ce{Phenol + acetone~enolate \leftrightharpoons phenoxide + acetone ~enol}$

So, from the pKa values we know that the above equilibrium lies mostly to the right (according to jerepierre). Given this, we can conclude that the reactants are less stable in the acid-base sense than the products; acetone enolate is less stable than phenoxide.

Phenol is also less stable than acetone enol.

But I don't see how this contradict's the blog article. It does contradict ron's point about being unable to use the provided pKa values to compare the relative stabilities of the acids.


texts: Is the equilibrium constant calculation only applicable to homogeneous reactions?

texts:
In my text book, it states the general formula for the equilibrium constant is:

Then it states that "The equilibrium constant expressions described here apply to homogeneous reactions."

Does this mean that it only applies to homogeneous reactions or that it can also be applied to homogeneous reactions among other types?


texts: Why does peak decoupling occur in H-NMR spectra?

texts:
For example, when we analyze the conversion of some chemical compound, certain characteristic areas tend to decrease (ok).

However, why can a peak (i.e., one peak) generate smaller peaks (i.e., more than one peak) in this case of conversion of some chemical compound (even if the total area decreases, indicating a reaction)?


texts: What chemicals cause the smell of a septic tank?

texts: I am wondering what chemicals exactly contribute to the smell of a septic tank system. I read about $\ce{H2SO4}$, $\ce{NH3}$, but I am not sure. Is methane also a factor or is that odorless?


texts: Recoil velocity of atom when electron is excited

texts: If an electron is excited from the $n = 1$ level to the $n = 2$ level in a hydrogen atom, how can we find the recoil velocity of the atom?


texts: Why can't we choose any other antisymmetric function instead of a Slater determinant for a multi-electron system? Why do we choose our wavefunction for a multi-electron atom as a product of single-electron wavefunctions?


texts:
I ran molecular dynamics simulation with a molecule of methylcyclohexane soaked into a water box. On the other hand I ran Monte Carlo with the molecule alone (no soaking). I performed this for the equatorial and axial conformers.

The axial conformer with MD stayed axial (the methyl group). The equatorial with MD stayed equatorial. So far no visual change. Is there a way to compute the average energy in VMD for these systems (I have around 250 frames).

On the other hand, the axial conformer alone with MC was transformed into equatorial. While the equatorial stayed the same (visually speaking).

I am trying to understand what's happening here. What I read is that always the equatorial configuration is more stable as it has less steric hindrance (BTW I am computer scientist learning this), so this explains the interconversion in Monte Carlo simulation from axial to equatorial.

On the other hand, I would expect also that in MD the axial conformer turn into equatorial but it didn't, what I believe here is that the water molecules are having some "Solvation effect" on the methylcyclohexane that prevents the interconversion.

So I would like to know if my thought are good and if you could give some references to get more info about solvation effects.


texts:
I'd like to know what exactly happens when various agents are used after developing a TLC plate, during the visualization phase, of sugars with anisaldehyde for example.

I know that those compounds are used in order to make invisible stains, visible. Also, sometimes, application of heat is necessary, I reckon so as to speed the "colouring process". However, I'd like to learn what kind of reactions take place or what kind of products are there formed, since I was not able to reach a conclusion after my research.


texts: How to determine the equivalent weight of CO2

texts:
We were estimating dissolved $\ce{CO2}$ in water by American Public Health Association method. It was a titrimetric method using phenolpthalein indicator.

Titrant used was $\ce{NaOH}$ and analyte was sample water.

After the end point was reached and the volume of titrant estimated the ultimate calculation was done to find out the amount of $\ce{CO2}$ present in the sample per litre. The formula mentioned in the book was

$$\ce{CO2} \mathrm{(mg/l)} =\frac{\text{[Volume of NaOH} \times \text{Conc. of NaOH (in Normality)}\times 22 \times 1000]}{\text{Volume of sample water}}$$

$22$ here is the equivalent weight of $\ce{CO2}$. My question is how's it so?

NOTE:

Our teacher said that since 2 molecules of $\ce{NaOH}$ react with 1 molecule of $\ce{CO2}$ to form $\ce{Na2CO3}$ so $n=2$ here.

Is it right? I doubt it because I have always known $n =$ the number of $\ce{H+}$ or $\ce{OH-}$ released by an acid /base or the number of electrons released or accepted in a redox reaction.

The reaction here is
$$\ce{2NaOH + CO2 -> Na2CO3 + H2O}.$$

But as $\ce{CO2}$ is not an acid or base and even doesn't undergo redox so how do we determine its equivalent weight?

P.S. I'm a Zoology student and have learned chemistry for XII + 2 years.


texts: Will Ethanol degrade Silicone or "RTV" specifically "RTV 734", or cause it to "leach" ingredients at temperatures below 250 degrees farenheit?

texts:
Will Ethanol degrade Silicone or "RTV" specifically RTV 734, a flowable sealant produced by Dow Corning, or cause it to "leach" ingredients at temperatures below 250 degrees Fahrenheit?

Such as in the distilling process.

Thanks!


texts: Is there any reasonably inert magnetic oxide?

texts:
I spent yesterday evening looking for data on magnetic oxides. What is easily available isn't well organized, so I ask here in hope someone can remember.

I'm looking for a magnetic oxide (that is, an oxide that can be held in place by neodymium magnet in presence of liquid flow) that has magnetic properties at 350 Celsium and do not react with $\ce{H2S}+\ce{H2}+\ce{CO}$ mixture at this temperature at 50 bar. Common nonmagnetic oxides for this conditions are many $\ce{Al2O3, SiO2, TiO2,}$ to name a few. But with magnetic oxides I hit a wall.

Note: No, ferrites are not an option as they are easily reduced. Same with cobalt and nickel oxides. At first I looked at chromium and manganese componds, but compounds I checked lose magnetic ordering well below room temperature or are easily reduced.

Any suggestions?

Note: At the moment I'm researching compounds of chromium, manganese and middle rare earths, with little luck.


texts: Can iodine hydrocarbons be used as fire extinguishing agent? What are their properties?

texts:
In the German Wikipedia the following claim about fire extinguishing agents is made:

  Iodkohlenwasserstoffe haben zwar eine hervorragende Löschwirkung,
  erlangten wegen ihres exorbitant hohen Preises (in den 1950ern etwa
  Faktor 10 gegenüber Bromkohlenwasserstoffen) jedoch niemals Bedeutung.

Translated:

  Though iodine hydrocarbons have excellent fire extinguishing properties
  they never became important because of their exorbitant prices (during
  the 1950s they were approximately 10 times more expensive than bromide
  hydrocarbons).

Now I am curious because I never heard of iodine hydrocarbons. What are their properties and what advantages would they have over the traditional halogen (fluoride, chloride, bromide) components if price is irrelevant?


texts: Comparing the basicity of benzamide and acetamide

texts:
What if we were asked to compare the basicity of benzamide and acetamide?

Which one of them would be more basic? I read somewhere on the internet that benzamide must be more basic than acetamide due to cross conjugation (I am not aware of this term). Is this true? Please provide an explanation.


texts: Why does pH of a buffer solution change according to Henderson–Hasselbalch equation?

texts:
If I add a little amount of acid or base to a buffer solution, the pH of the buffer won't change. That's what the diagramatic mechanism tells us.

But according to Henderson–Hasselbalch equation, the $\mathrm{pH}$ changes!

For example, a buffer solution of $\ce{CH3COOH}$ and $\ce{CH3COONa}$:

$$\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log\left(\frac{[\ce{CH3COONa}]}{[\ce{CH3COOH}]}\right)$$

Now I add a little amount of acid $(\pu{0.01M},\;\pu{5 mL}).$ It disturbs $\ce{CH3COONa}$. Reaction:

$$\ce{CH3COONa + HCl -> CH3COOH + H2O}$$

It is noticed here that a small amount of $\ce{CH3COOH}$ is produced and a little amount of $\ce{CH3COONa}$ is spared. So simply $[\ce{CH3COOH}]$ and $[\ce{CH3COONa}]$ go high and low, respectively. As a result, the ratio between $\ce{CH3COONa}$ and $\ce{CH3COOH}$ decreases. As the $\mathrm{pH}$ depends on the ratio, the $\mathrm{pH}$ changes as well.


texts:
In a sample solution, containing $\ce{Cl-}$, while conducting the test for detection of $\ce{Cl-}$ ion first it is acidified with conc. $\ce{HNO3}$ then cooled and then $\ce{AgNO3}$ solution is added. A curdy white precipitate appears which is soluble in $\ce{NH4OH}$ but reappears on adding $\ce{HNO3}$.

My question: is the $\ce{HNO3}$ added dilute or concentrated?


texts: Could one synthesise unsubstituted "cyclohexa-1,3,5-triene"?

texts:
Is the cyclohexa-1,3,5-triene (non-aromatic benzene) possible to make or will it destabilize (or should I say stabilize?) into benzene?

Cyclohexa-1,3,5-triene is alternative name of benzene better describing its hypothetical, non-aromatic version. However they are similar and I was wondering if you made cyclohexa-1,3,5-triene would the electrons delocalise to form benzene or not?


texts: Which is the most intuitive to perform Dynamic Monte Carlo calculations?

texts: I'm trying to find a (free is possible) code to perform Dynamic Monte Carlo calculations over chemistry systems. Which one is the most intuitive one?


texts: Does quantum yield of reaction factor in number of electrons needed?

texts:
Can someone tell me if quantum yield of a reaction factors in the number of electrons needed to create the particular species? If not, is there a metric that does?

For example, I have a 4 electron reduction which means that even if I have 100% efficiency, my quantum yield is

$$\frac{\text{# molecules reduced}}{\text{# photons absorbed}} = 0.25$$

Is there a better metric I can use so that 1.0 will be 100% efficiency?


texts: Spectrophotometric determination of copper concentration

texts:
Context:
A typical lab experiment involves the addition of ammonia in excess to solutions of copper(II) to produce a complex ion whose absorbance at roughly 610 nm varies by the concentration of copper in solution.
Question:
Why is it less practical to simply test the aqueous solution of $Cu^{2+}$ rather than complexing it first with ammonia?
Thoughts:
My thoughts on this begin with the Beer-Lambert law: $$A =\epsilon lc$$
If the molar absorptivity of the ammonia complex in the visible spectrum around 600 nm is greater than that of the aqueous complex, [1] then small changes in concentration of copper can be differentiated by large changes in absorbance. This increases the sensitivity of spectrophotometric methods of determining copper(II) concentrations.
References
[1] http://chemed.chem.purdue.edu/demos/main_pages/18.8.html


texts: In a pair of diastereomers, which of the following is true?

texts:
While going through my book, I came across this question and got really confused. Here's what the problem was:

In a pair of diastereomers,

Both can be laevo-rotatory or both can be dextro-rotatory
Both can be optically inactive
One can be optically active other can be optically inactive
Presence of two chiral carbons is must in both of the isomer

As you can see, this is a multiple correct problem.

I tried going with the definition, Diastereomers are stereoisomers whose molecules are not mirror images of each other
Also, to satisfy this, I believe there should at least be two chiral carbons. So option (4) seems right. But I'm really not able to figure out the others. How can we determine this?


texts:
This question seems silly, but this just came in my mind while i was learning about hydrogen.

Means will there be any reaction when $\ce{H2O}$ will be mixed with $\ce{D2O}$?


texts: Does MgCl2 sol coagulate gold sol faster than Fe(OH)3 sol?

texts:
Here is a question from the former AIEEE 2005

The disperse phase in colloidal iron (III) hydroxide and colloidal gold is positively and negatively charged respectively. Which of the following statements is not correct?
(a) Mixing the sols has no effect
(b) Coagulation in both sols can be brought about by electrophoresis.
(c) Magnesium chloride solution coagulates the gold sol. more readily than the iron (III) hydroxide sol.
(d) Sodium sulphate solution causes coagulation in both sols.

It is a single answer correct, and it is obvious that (a) is false - hence is the answer. But the statement (c) also seems to be false (and therefore should also be an answer).
According to Hardy Schulze law,

Greater the valency of the flocculating ion, greater will be its coagulation power.

Doesn't that mean $\ce{Fe(OH)3}$ sol, having $\ce{Fe^{3+}}$ ions, will coagulate the gold sol more readily than $\ce{MgCl2}$ sol, which contains $\ce{Mg^{2+}}$ ions? Or is there any specific reason why the $\ce{MgCl2}$ sol coagulates the gold sol more readily?


texts: Can I successfully use a humidifier to distribute caffeine to wake someone up without the usual morning drowsiness?

texts:
Would I have any success putting coffee in a humidifier? Or perhaps water mixed with caffeine powder?

So I could wake up without a jolting alarm clock, feeling like I already had a cup of coffee?

I understand this will have to be a carefully controlled dose if working with caffeine powder, but is it feasible?


texts: In practice, do polar molecules actually align in an electric field?

texts:
We have all seen the following diagram (or similar) in our first chemistry class, depicting polar molecules aligned in an electric field. Is this just one of the half-truths of beginner chemistry or is this what really happens? I realize there will still be kinetic motion (spin, etc), but even statistically, is it possible for such a fluid/gas to have a net directional orientation throughout?

I have often seen the diagram depicted with water, but as the top answer on this question explains:

  "...the ions will rush to the respective electrodes and form the so-called electric double layer. Its thickness, known as Debye length, is usually quite small. As for the rest of the solution, it will be effectively shielded from the electric field."

Perhaps this would be the same issue with hydrogen fluoride?
Is it possible the Debye length would be longer for a polar covalent molecule like Acetonitrile or Chloromethane?

If there are in fact polar molecules that exhibit this field-orientated behavior on a macro scale, what would be a way that it could be demonstrated?


texts: How do the electronic properties of a catalyst affect the rate of oxidative addition?

texts:
In my project I have a coupling that was planned to be done using Pd (Suzuki or Stille possibly).

Initially, I used an aryl chloride (the SM had already the chloride so I went with it), but the oxidative addition was slow. Changing to iodide helped but still slow (can't use triflate as would be destroyed in an earlier step if carry through).

In my lectures, changing the halide is always given as a way of gaining selectivity, this is also what is taught in Clayden if you look for the information on organometallics. But a postdoc suggested changing the catalyst, as apparently changing the electronics in palladium also helps. Is this the case? Or is OA just controlled by the strength of the C–X bond?


texts: What is the specific heat and latent heat of an ethanol-water mixture?

texts:
How do I find the specific heat and latent heat of ethanol-water mixture? Let’s say the mole fraction of water is 0.3 and ethanol is 0.7.

I am working on a project and needed values for these and couldn’t find it.


texts:
Watching some movie/TV this question came to mind, purely theoretical of course, if one wanted to dissolve a human corpse, like getting rid of a body after killing someone, is it better to use an acid or a base? In the movies (as well the popular perception for some reason) they always use acid. The movie I was watching they had a bathtub full of acid in which they throw in the body. But I also remember my chem teacher telling me (a long long time ago) that if she had a choice of an acid or a base in her eye, she would take acid any day because a base will dissolve organic tissue faster. So assuming that the acid and base have the same level of strength (say a pH of 1 and 13 respectively) which is better for getting rid of a corpse?

Thanks!


texts: How to calculate the pH of a buffered solution with Henderson Hasselbalch?

texts:
Lets say you have a buffered solution containing $0.50~\mathrm{M}$ acetic acid ($K_a = 1.8 \cdot 10^{-5}$) and $0.50~\mathrm{M}$ sodium acetate, and you want to calculate the $\mathrm{p}\ce{H}$ of this solution.

This can be done in two ways: using the standard equilibrium chart (initial, change, equilibrium), or using the Henderson Hasselbalch equation.

My question is why do these two give the same result.

The Henderson Hasselbalch equation is derived starting with the equilibrium equation:

$K_a = \frac{\ce{[H+][CH3COO^{-}]}}{\ce{[CH3COOH]}}$ and then the $\ce{[H+]}$ is found, and then the $\log_{10}$ is taken. However, doesn't this assume that the system is already at equilibrium and that the concentrations of $\ce{[CH3COO^{-}]}$ and $\ce{[CH3COOH]}$ are the concentrations at equilibrium?

However, that is clearly not the case as shown by the ICE chart. However, both give the correct pH. Why is this?


texts: Understanding the pH scale for edible food!

texts:
I'm working on a website where I want to provide the pH level of plants! Although i don't even know what this is (I have zero knowledge in chemistry), I have to provide it! What I want to do is provide the pH spectrum on the website so that it would point to the correct pH level of a specific plant.
Let's use the following hypothetical examples from the database I was given:

Peas:  preferred pH : 6.0 - 7.5
Beans  preferred pH : 6.0 - 6.8

At this stage I want to point out that I'm only working with edible plants, vegetables, fruits etc.
Also here is a reference image that would be ideally used on the website:

From the image that was given above, I want to provide:
1(One pH value) : An arrow to point out the preferred pH of a plant.
2 (Range of pH values): an arc highlighting the range of the preferred pH of a plant.

Questions:

Why is there a range in the preferred pH of a plant?
Is it possible for an edible food to have a negative pH value? Answer: NOT POSSIBLE
Is a pH level let's say 20 dangerous to consume (what is the minimum and maximum values that can be safely consumed)?


texts: Why is sulfuric acid used to seal flask with highly reactive chemicals?

texts:
I the video https://youtu.be/saANxD0cqy0?t=200 (time 3:20) NileRed states that he uses sulfuric acid to seal off flask with a mixture of pottasium dichromate and table salt. He says that sulfuric acid is used to seal off flasks with highly reactive chemicals and I could not find any reasons why.

I see sulfuric acid as a very reactive chemical, that could potentionally react with substrate causing some minor problems to purity of the final product. I also wonder why he does not use any other less-reactive seal that would not react with substarte what so ever.
Thank you for your contribution


texts: Is it possible to determine the composition of a gas mixture from the effusion of a gas through a pinhole?

texts:
Typically all the problems which I've seen regarding rate of diffusion involve relating the rate of one gas to the other and from there finding either speed of effusion or diffusion or getting the formula weight. However what sort of procedure should be used when it is needed to find the composition of a mixture?

The problem is as follows:

  A certain volume of nitrogen gas $(\ce{N2})$ pass through a pinhole in $\pu{20 s}$. Find the composition of a mixture between $\ce{O2}$ and $\ce{CO2}$ if this mixture is let pass through the same slit and the measured time for this effusion is $\pu{24 s}$ and of Avogadro's conditions.

  45.5% $\ce{O2}$
  69.3% $\ce{CO2}$
  12.4% $\ce{O2}$
  69.3% $\ce{O2}$
  45.5% $\ce{CO2}$

I'm not very sure if it is possible to find what it is being asked here. It's obvious that the approach here is to use Graham's law of gas diffusion. But the problem arises on what volume should be used to establish an equation from where to find the composition of the mixture.

What I thought was:
$$\frac{v_{\ce{N2}}}{v_\text{mixture}} = \sqrt{\frac{FW_\text{mixture}}{FW_{\ce{N2}}}}$$

The thing here is that the average molecular weight can be used to find the composition of the mixture.

$$\frac{v_{\ce{N2}}}{v_\text{mixture}}=\sqrt{\frac{\chi_{\ce{O2}} \cdot FW_{\ce{O2}} + \chi_{\ce{CO2}} \cdot FW_{\ce{CO2}}}{FW_{\ce{N2}}}}$$

But the thing here is I am still stuck on where to go from here. What should be the right way to go to get the composition of the mixture. Could it be that the volume of the nitrogen is needed?. So far I'm going in circles with this. Regarding the source of this problem it doesn't indicate as far I'm aware since it is a collection of problems from different topics in gases.


texts: Attack on cyclic intermediate during NGP

texts:
I have studied that when an epoxy ring opening takes place in acidic medium, the ring opens in a way that the most stable carbocation forms. This is due to the positive charge on the oxygen, which gives partial positive character to the carbon atoms.

A very similar intermediate is formed in NGP (neighboring group participation) reactions with sulphur as the neighboring atom (source). How is the attack carried out then? Is it decided sterically as a regular SN2, or does the logic with oxygen extend to sulphur?


texts: Why is the geometry of [Ni(CN)4)]2- square planar? Why is it colorless?

texts:
Why is the geometry of $\ce{[Ni(CN)4)]^{2-}}$ square planar given that it has a coordination number of 4?  Shouldn't its geometry be tetrahedral as it would minimise the bond angle and hence repulsion?

Also, why is it colorless? I saw that it is related to how $\ce{CN^{-}}$ is a relatively strong field ligand and can cause "pairing" of the electrons which would not allow the electrons to be transferred between d-orbitals, but what does it mean by pairing?


texts: PE expression for vibrational spectra of molecules using Newton's second law

texts:
I am currently studying the textbook Infrared and Raman Spectroscopy: Principles and Spectral Interpretation, second edition, by Peter J. Larkin. Section 10. Calculating the Vibrational Spectra of Molecules, says the following:

In the case of vibrational spectroscopy, the polyatomic molecule is considered to oscillate with a small amplitude about the equilibrium position and the PE expression is expanded in a Taylor series and takes the form:
$$V = V_0 + \sum_{i = 1}^{3N} \left( \dfrac{\partial{V}}{\partial{q_i}} \right)_e d q_i + \dfrac{1}{2} \sum_{i = 1}^{3N}\sum_{j = 1}^{3N} \left( \dfrac{\partial^2{V}}{\partial{q_i}\partial{q_j}} \right)_e d q_i d q_j + \dots$$
The above expression is expressed in internal coordinates, $q_i$ and $q_j$ which are directly connected to the internal bond lengths and angles. The above expression is simplified since:

The first term $V_0 = 0$ since the vibrational energy is chosen as vibrating atoms about the equilibrium position.
At the minimum energy configuration the first derivative is zero of definition.
Since the harmonic approximation is used all terms in the Taylor expansion greater than 2 can be neglected.
This leaves only the second term in the PE expression for $V$. Using Newton's second law the above is expressed as
$$\dfrac{d^2 q_i}{d t^2} = - \left( \dfrac{\partial{V}}{\partial{q_i}} \right) = - \sum_{j = 1}^{3N} \left( \dfrac{\partial^2{V}}{\partial{q_i} \partial{q_j}} \right)_e q_j$$

Even after taking the points above into account, I don't see how we get from the first equation to the second. I'm assuming that $V$ is the potential energy (PE), right? And Newton's second law in differential equation form is $F = m \dfrac{dV}{dt}$. So how does this and points 1., 2., and 3. then lead to $$\dfrac{d^2 q_i}{d t^2} = - \left( \dfrac{\partial{V}}{\partial{q_i}} \right) = - \sum_{j = 1}^{3N} \left( \dfrac{\partial^2{V}}{\partial{q_i} \partial{q_j}} \right)_e q_j$$?
I would greatly appreciate it if people would please take the time to explain this.


texts: Removing sodium borate for the test proving thiocyanate ions

texts:
I've just learned that when carrying out the identification test for thiocyanate ions borax can induce a false positive and therefore needs to be removed. I couldn't find the answer on google so I'm asking a question here.

I would think you first carry out the test to see if borax is present; but if it is, how would you remove it?


texts: Does the term "Alkaline" necessarily indicate the presence of an actual alkali?

texts:
A month back, @CowperKettle had asked this at The Periodic Table chat room:

  Does "alkaline" imply the presence of an actual alkali?

Now I've come across the term "alkaline" on numerous occasions, and pretty much all examples that I know of (in Chemistry) actually do involve the presence of an alkali (often NaOH or KOH).

Wikipedia defines an alkali as:

  In chemistry, an alkali is a basic, ionic salt of an alkali metal or alkaline earth metal.

Further, it states:

  An alkali also can be defined as a base that dissolves in water.

Now when something is a "base", it could mean a lot of things (An Arrhenius base? A Lewis base? A Bronstedt base?), which doesn't really make the Wikipedia definition any clearer.

Take for example, this case:

  ...mucosal cells of the small intestine secrete bicarbonate ions into the intestinal lumen to render it alkaline...

I know that was from a "Biology perspective", but that raises the following questions:

1) Is there a universally accepted (I guess that would be IUPAC) definition for an alkali? (Since the Wikipedia definition seems a bit oversimplified)

2) Is it "acceptable" to refer to, say, as suspension of a (Lewis) base in water as "alkaline"? And what about that excerpt from my Bio. text book? Is that use of "alkaline" acceptable as well?


texts: Is there an isotope effect for diffusion of an ion through a crystal lattice?

texts: Consider the diffusion of natural abundance $\ce{Li^{+}}$ and $\ce{{}^{6}Li^{+}}$ through a crystalline matrix, say a spinel such as $\ce{LiMn2O4}$.  The two lithium ions will have the same ionic radius and electric charge.  They will differ only in atomic weight.  Is there any reason to believe that the lighter isotope, $\ce{{}^{6}Li^{+}}$, will diffuse through the crystal any faster than the natural abundance isotope?  When I consider the forces acting upon the ions in the crystal, I come up with coloumbic, dispersion and hard shell repulsive forces.  I cannot see how any of those would change by simply changing the mass of the ion.  Am I missing anything?


texts: Why is wavenumber used in IR spectroscopy rather than wavelength?

texts:
In IR spectroscopy, the $x$-axis is used to represent wavenumber, in $\mathrm{cm^{-1}}$. Why is wavenumber, equal to $1/\lambda$, used in place of wavelength, which is simply $\lambda$?

Sources I’ve already found explain why it was chosen rather than energy of waves, but the conversion from wavelength to wavenumber is never explained. Below are two relations from Wikipedia, which explain how it can be used in equations, but in all of these cases, $\lambda$ seems to be a choice that’s easier to work with.

What explanations are there, if anything other than “historical reasons”, for why $1/\lambda$ is favored over $\lambda$?

A spectroscopic wavenumber $\tilde\nu$ can be converted into energy per photon $E$ via Planck’s relation:

$$E = hc\tilde\nu$$

It can also be converted into wavelength of light via

$$\lambda = \frac{1}{n\tilde\nu}$$

where $n$ is the refractive index of the medium.


texts: What condenser can be used for simple distillation?

texts: I think I need some distilling (boiling) and collection flasks and a 3-way adapter with a thermometer.  I was thinking of using an open vacuum adaptor to join the lower end of the condenser to the receiving flask.  Does this sound ok?  And if so, what kind of condenser should I use?


texts:
How many p-orbitals are there in each period?a. 1b. 3c. 5d. 7e. 14

I take this to mean "how many p-orbitals are there in each period of the periodic table?" Looking at the p-block on the periodic table, it looks like there are 6 elements with p-orbitals per period. This isn't an answer, so I'm a little lost.


texts:
In my titration curve for HCl being titrated with NaOH, the initial pH-value was plotted as 2.1 according to a pH-meter. When I found the equivalence point and calculated the concentration of HCl, it was 0.075 M. I calculated how much the initial pH-value should be from that by -lg(0.075) which is around 1.12. That is way off from the original pH-value I got.
Why did this happen? Is it because the risk of me calibrating the pH-meter incorrectly? If that is the case, will the x-value of the equilibrium point also be wrong?? For the latter, I feel like the answer would be no, because what is wrong is that if the pH-meter was calibrated wrong, then all of the values would be 0.9 pH higher than what they should be, so the curve would only differ in the y-direction, but would be exactly the same in the x-direction. Is that correct?
Thanks in advance!


texts: Why might the O—H stretch in the IR of MY triphenylmethanol product be less intense than expected?

texts:
Why might the O—H stretch in the IR of MY triphenylmethanol product be less intense than expected when compared to the expected IR for triphenylmethanol?

I'm interpreting the IR I took of my product, triphenylmethanol, to the expected IR I obtained from SDBS.

My IR:

SDBS:

We performed a Grignard Reaction in lab using bromobenzene and methyl benzoate in order to synthesize triphenylmethanol.

ANY clues why my triphenylmethanol (O—H stretch) is not as intense? I really don't know.


texts:
The experiment is described in the following link: http://www.sciencekids.co.nz/experiments/invisibleink.html

I carried out a small research but I was unable to find what exactly happens. In other words which particular acids, present in lemon juice, are oxidized (e.g. citric acid, malic acid etc.)? And what causes the brownish colour?

Any kind of help would be appreciated.


texts: Where hydrogen belongs in the Periodic Table

texts: Why do some people say that hydrogen should be above lithium in the periodic table and others argue it should be above fluorine?


texts: Must a desiccant be made anhydrous before it can be used for drying?

texts:
I'm writing about the treatment of methane gas, and in one part of the process, the methane gas is dried in a tank called a scrubber. Here, a desiccant called triethylene glycol is used.
Thinking about another desiccant, magnesium sulfate heptahydrate (Epsom salt), the water must be taken away through evaporation before the salt can be used for drying. The chemical must be anhydrous, so that it'll steal away all the water from the object in need of drying.
However, is this the case with triethylene glycol? Must it be made anhydrous before it can be used for drying, or is its attraction to water molecules great enough to begin with?


texts: Spurious term in Thomas-Fermi-Hartree energy functional

texts:
I am quite a beginner in DFT and I am studying the theory behind the computational tools. I have some doubts about the Coulumb approximate functional term:
$$U[n] = \frac{1}{2} \int d^3 r \int  d^3 r^\prime \frac {n(\mathbf{r}) n(\mathbf{r}^\prime)}{|\mathbf{r} -\mathbf{r}^\prime|}$$
If I use the definition of the electronic density $$n[\mathbf(r)] = \sum_i^N \delta(\mathbf{r} -\mathbf{r}_i)$$ in the previous equation I obtain the square of the electronic charge over $\pu{0}$. In other words the energy diverges. Am I wrong?


texts: How to distinguish between benzyl chloride and chloro benzene?

texts: If I add $aq. \ce{KOH}$ to both of the compounds substitution takes place in the case of benzyl chloride and then if I oxidize with $\ce{KMnO4}$ I will get benzene carboxylic acid which will give effervescence on reaction with $\ce{NaHCO3}$. But, does $\ce{KMnO4}$ have any effect on chloro benzene?


texts: Assignment of the 13C NMR spectrum of 4'-bromoacetophenone

texts:
I was doing a 13C NMR prediction of 4'-bromoacetophenone on chemdraw but I can't figure out why positions 5 and 5' appear further downfield than positions 4 and 4'.

I know both Br and the carbonyl are deactivating groups, with Br being ortho/para directing and carbonyl is meta directing. However, the mesomeric effect of both groups should "shield" position 5 but this is not the case. I'd appreciate an explanation that'd help me understand that.


texts: What determines the density of an element?

texts:
I used to be under the (wrong) assumption that the density of an element correlates with it's atomic number $\mathrm{Z}$, I thought that since having more protons meant the atom weighed more; but of course that's wrong.

So why does make osmium $\mathrm{Os}$, with an atomic number of $\mathrm{Z}_{\mathrm{Os}}=76$ more dense than say uranium $\mathrm{U}$, with an atomic number of $\mathrm{Z}_{\mathrm{U}}=92$?


texts: I am considering attempting an experiment in which one puts two, almost severed, halves of a grape in a microwave with a glass over it. To my knowledge so far, the grape halves act as focal point for the radiation and the microwaves will burn the small part of grape skin that isn't severed, providing a spark which the microwaves will stimulate into plasma, contained by the glass jar. Three questions: is the experiment reasonably safe, am I correct in my understanding of the experiment, and what compounds will the plasma form once it cools?


texts: Why is platinum used as a catalyst in fuel cell electrodes (and elsewhere)?

texts: I have rather basic knowledge of chemistry (at the level of a first year college class). But maybe somebody can still clarify with some simple words: What makes platinum a good catalyst for the electrodes of fuel cells? And why can't other materials be used?


texts: Electronic density distribution in hydrogen bond

texts:
I'm currently studying about the atomic configuration of electrostatic interactions. Concept is there that in case of interactions like in N-H...N-H (amides), the stability depends on the position of resonating electron between H...N nuclei (THE NATURE OF THE CHEMICAL BOND. II. THE ONE-ELECTRON BOND AND THE THREE-ELECTRON BOND - Linus. Pauling).

Given that hydrogen bonds formed between N-H...N-H or N-H...O-C are partial covalent in nature so the issue of directionality comes in effect.
I'm just trying to understand, from the view-point of the electron density shared by H...N to form the bond, that how (if possible) atomic configurations/geometry affects the electron cloud distribution ?

I'm basically trying to understand the hydrogen bond forming amides (currently interested in) from the electronic density distribution's point of view; to calculate the single-point-energy using dft.

Thank you.


texts: The effect of air pressure on the melting point

texts:
What is the effect of air pressure on the melting point of a substance?
a) No effect
b) The melting point increases when the air pressure increases
c) The melting point decreases when the air pressure increases

The boiling point has inverse relation with vapor pressure of the liquid and positive relation with atmosphere (air) pressure. The melting point has positive relation with vapor pressure of the substance, but what about its relation with air pressure?


texts: Do vinyl cations adopt a classical or non-classical structure?

texts:
Whilst reading this question today, I remembered something that I had seen previously here. In the second linked question, @Martin provided a reference to suggest that vinyl cations actually adopt a non-classical structure with $\ce{sp}$ hybridization and a bridging hydrogen, as shown below:

The non-classical structure can be viewed as a protonated alkyne, in the same way that the ethyl cation, which adopts a non-classical structure, can be viewed as a protonated alkene.

What is the correct structure of a vinyl cation? Does it depend on what the substituents are? For example, in the first linked question, do the two cations (shown below) actually equilibrate to the same non-classical structure?


texts: What are the practical differences between the various DMSO oxidations (Swern, etc.)?

texts:
Recently, I was reading a paper about a total synthesis of (+)-rubriflordilactone A (the article is open access: Angew. Chem. Int. Ed. 2015, 54 (43), 12618–12621). In two different steps where an alcohol -> aldehyde oxidation was required, the authors favoured using the Parikh–Doering reaction (DMSO activated with pyridine-sulfur trioxide complex):

In practice, is there a reason why the Parikh–Doering might be favoured over the Swern (DMSO activation with oxalyl chloride), or is it simply a case of "we just got better yields with it"?

I checked in Kurti–Czako. No hints were offered, but they also did list two more Swern variants, namely Pfitzner–Moffatt (activation with a carbodiimide) and Albright–Goldman (activation with an acid anhydride). On top of that, as Jan mentioned in a comment, there is also the Corey–Kim oxidation where N-chlorosuccinimide is used to generate the chlorosulfonium salt from DMS (instead of DMSO).

In general: are there benefits or drawbacks that are specific to each variant that would influence a synthetic chemist's decision, and if so, what are they?


texts: My teacher frequently gives us questions where we have to arrange the given binary compounds on basis of their melting points or solubilities. He did give us some instructions in order to judge this order. But they don't seem to work for any questions. I asked a senior student as to how to tackle this problem, and he simply said inorganic predictions are tough to make, wo just stick to the data and make appropriate relations between the given compounds. But the problem is we don't get data in tests and have to judge the compounds solely on the basis of logic. But I have no clue as to how to figure out this logic. So is it really true that all the orders are simply unpredictable without their actual data? Is every order just not following the standard rules to figure out these orders? It would really help if someone is able to guide me how to approach such questions without knowing the related data and maybe even share some appropriate further readings. I tried looking on Wikipedia and google, but everywhere I go, they quote the experimental data. I even tried looking at some answers here on stackexchange, but the people in comments tend to confuse me even more.(some have even written the obvious answer-"stick to experimental data").


texts: Electrons are delocalized between the three centers in a  3c-2e bond. If there was a molecule with 3c-2e bond in each direction, e.g. a boron cluster, would it be aromatic?


texts: What an electrolyte "really" does in electrolysis?

texts:
I am reading about electrolysis and I have trouble to understand why an electrolyte must be added in order for electrolysis to occur. I have read this question but still can't get it. The definition of electrolyte is a substance that when dissolved produces an electrically conducting solution.
Electrolytes in electrolysis
Why we need an electrolyte in order for electrolysis to occur? In electrolysis of water the water is consumed not the electrolyte. So why we need the electrolyte? Couldn't the reaction happen without the electrolyte?
After reading the comments I have modified the question. As I said before I can't understand the purpose of the electrolyte. For example in the electrolysis of water with sulfuric acid why we add it? Water molecules are in contact with both anode and cathode. So why we need to add the electrolyte?


texts: Is there a kind of table about configurations similar to the example I gave below?

texts:
If MALDI is used as an ionization method, then TOF as an analyzer is suitable since the MALDI creates singly charged ions which have high m/z ratio and only TOF can analyze that ions, and multichannel plate should be used because the TOF is very quick and MCP's duty time is enough to capture all ions.

Is there a kind of table about configurations similar to the example I gave above? A table with reasons would be great but not certainly necessary.


texts: For example reaction of but-1-ene in the presence of $\ce{Br2}$ and light should give 1-bromobut-2-ene which is thermodynamically more stable than  3-bromobut-1-ene on the basis of number of alpha hydrogen.


texts: When can we add multiple reactions to compute yield of products in an equilibrium?

texts:
It is widely known that we can add multiple equilibrium reactions to obtain a net reaction and a corresponding equilibrium constant for the net reaction. However, I am not sure of exactly when this method can be applied. For instance consider a diiprotic acid $\ce{H_2A}$

$$\ce{H_2A <=> HA^{-} + H^{+}} $$
$$\ce{HA^{-} <=> A^{2-} + H^{+}} $$

with hypothetical first and second ionization constants $10^{-5}$ and $10^{-10}$ respectively. Note that $K_{a_1} \gg K_{a_2}$ as is the case for real acids. If we start with $0.1~\rm M $ solution of the acid then the pH is straightforward to calculate since $\ce{H^{+}}$ from the second ionization is negligible we can write

$$\frac{[\ce{H^{+}}][\ce{HA^{-}}]}{[\ce{H_2A}]} = 10^{-5}$$

Since the concentration of the terms in the numerator are equal and the concentration of the un-dissociated acid remains approx constant we get

$$[\ce{H^{+}}] = 10^{-3} ~\mathrm M$$

If instead we take the net reaction with equilibrium constant $K_{a_1}\cdot K_{a_2} = 10^{-15}$

$$\ce{H_2A <=> A^{2-} + 2H^{+}}$$

and write the equation ($x$ is amount of acid dissociated):

$$\frac{(x)(2x)^2}{0.1-x} = 10^{-15}$$

This gives

$$2x = [\ce{H^{+}}] \approx 5.8 \times 10^{-6}$$

which is quite different from the result obtained using the first method.

Note that this is just one of the many cases I have encountered in which adding equations does not work.

Why does adding the equations not work in this case? Also, in general, when is adding equations to figure out equilibrium concentrations justified?


texts: Can we make chromatography less troublesome?

texts:
Thin Layer Chromatography is a very powerful method in analytical chemistry for separating complicated chemical matrices.

As an engineer, I am interested to build device capable of automating TLC such that I can just place a droplet of my sample onto a piece of paper and let the device perform the TLC for me.

How achievable is this?


texts: Other metabolic reactions aside, what causes beta oxidation to stop?

texts:
To my understanding beta oxidation is when a fatty acid has its carbons plucked off in groups of 2 (acetyl groups) into acetly-coa which we can dump into the TCA.

At what point would this process stop ? lets say we have a short chain fatty acid like butanoate (4c) would it still transfer an acetyl group leaving an acetate molecule ?


texts: Possible Water peak in PMMA nmr spectrum

texts:
solvent: $\ce{CDCl3}$

I'm unsure as to whether the large sharp peak at ~1.5 on my NMR spectra is water, I was under the impression water gave a broad peak in proton NMR, but may be confusing it with something else.

Can anyone confirm is deny?


texts:
Would I be correct in saying that the Bohr effect is ONLY related to the concentration of [H+] in the tissues.

Obviously the concentration of carbon-dioxide can contribute to this concentration by producing protons (through carbonic anhydrase) but it isn't directly involved in the effect?


texts: Did JJ Thomson know about Eugen Goldstein’s experiment discovering canal rays?

texts: We learn that JJ Thomson discovered the electron in 1897. Several years EARLIER in 1886, Eugen Goldstein performs the same experiment but with the anode and cathode switched to produce positively charged canal rays. My question is, did JJ know about Goldstein’s experiment? I’m surmising he did not, as it wouldn’t have taken such a leap to conclude that Goldstein’s  was a positive particle as well as the negative electron JJ discovered. Does anyone know the history who can confirm this is true or prove it is false?


texts:
So I understand, electrons exist in orbitals, mainly s, p, d, f and that when they bond with one another it will form sigma and pi bonds and that whether it bonds in a certain orientation a molecular bonding orbital or an anti bonding orbital will form.

What I DON'T understand is that when an element bonds it's energy levels will ALWAYS form a series of energy levels that contain bonding and anti bonding orbitals so when they come together, the electrons are always orientated such that these orbitals will form? I also don't really understand what happens when these two atoms meet (the elements that are bonding) how are the orbitals interacting with one another? And what are the orbitals involved?

For those who would like to answer the question feel free to loosely address these questions and refer to fundamental concepts or explain bonding through orbitals briefly.


texts: Kleenex tissues are infused with long lasting scents - their scent is released when crushed. How does this work? I's like to know how to reproduce similar effect for another purpose. Who would be the person who could develop this for me? A Chemist - A Pharmacist?


texts: How much ice will reduce the chicken carcass temperature from 32 to 8 degree C

texts:
I am interested to learn through heat claculations the quantity of ice that would achieve a chicken carcass core temperature of 8 degree C.

My chilling tank has a volume of 15,000 liters of flowing water where chicken pass through at a rate of 3,000 carcass per hour having an average carcass weight of 1.4kg and deep muscle temperature of 32 degree C.The flowing water drains at a rate of 5 litres per second.

Supplementary ice added to the chilled water at 250kg per hour while 8 degree C chilled water is fed into the tank at 4800 liters per hour.

How much more ice is required per hour to reduce the core temperature of chicken to 8 degree C? Appreciate a detailed calculation.

I thank you for your time and efforts.


texts:
In most articles and texts that I've read, soaps and detergents seem to be talked about collectively. I know that they are both surfactants and that soaps are usually natural, in comparison to detergent which is artificial. However, what are the differences in terms of chemical structure and properties (between soap and detergent)?
NOTE: not the same as Is there an important difference between soap and detergent?, as I'm asking about chemical structure and properties rather than the effects in everyday life.


texts: How to determine bond length and angle in a conjugated pi-system (polymethine)?

texts:
I have a polymethine molecule with let's say 9 $\ce{C}$ atoms.

$\ce{H-CH=CH-CH=CH-CH=CH-CH=CH-CH3}$

How can I calculate the length of the whole molecule?

I need this number to compute the wavelengths the molecule will absorb (model of linear potential well).

So what are the average bond lengths and bond angles in this molecule and how are they calculated?

EDIT: Another example for polymethine (just the red part of it):


texts: Why is the water dissociation constant valid for acid/base solutions?

texts: The water dissociation constant was first defined with respect to dissociation of water into hydroxyl and hydronium ions. How then can one say that it is valid for an acidic solution, that is, even in an acidic solution the product of the concentrations of the hydronium and hydroxyl ions is $10^{-14}\ \mathrm{M}$?


texts: What is the use/function of lithium chloride as an excipient in sofradex eardrops?

texts:
Certain drugs have lithium chloride as an excipient, eg. Caprilate, NeyDop N (Revitorgan-Dilutionen N Nr 97), NeyDop N (Revitorgan-Lingual Nr 97), Nisita.

An excipient is not supposed to have a pharmacological effect, but it seems like lithium chloride is an inhibitor of various enzymes (http://www.ncbi.nlm.nih.gov/pubmed/15107743).


texts: Finding the sum of coefficients of the reaction

texts:
What is the sum of the coefficients $(a + b + c)$ in the following reaction?
$$\ce{x Zn + y HNO3} -> {a Zn(NO3)2 + b H2O + c NH4NO3}$$

Here if the equation is balanced we get 1 mol of $\ce{Zn}$ and 4 mol of $\ce{HNO3}$. As  $x + y = a + b + c$ we get sum of coefficients $a + b + c = 5$. According to me, this is the correct answer, but in the actual answer key the answer is 8.
I may be wrong, but can someone help me clarify the right answer?


texts: How to make 0.3% ammonia water from 28-30% ammonia hydroxide

texts:
Can someone tell me how to make 0.3% ammonia water from 28-30% Ammonia hydroxide?
I am trying to make a gallon or 3.78 Liters.


texts: What is the origin of the colour of azo dyes?

texts: Is it the same reason as to why transition metal complexes have colour?


texts: NMR magnetically equivalent protons for a 1,4-disubstituted benzene ring

texts:
Below I have drawn a molecule with random substituents $\ce{X}$ and $\ce{Y}$:

If the distances from $\ce{H_b}$ and $\ce{H_a}$ to $\ce{H_d}$ are considered, they are different - $\ce{H_b}$ is 5 bonds away and $\ce{H_a}$ is 3 bonds away, so $\ce{H_b}$ sees $\ce{H_d}$ differently compared to $\ce{H_c}$. The same argument can be made vice versa and also between the same pair of protons towards $\ce{H_c}$. This was what the lecturer told me regarding this compound below.

This led me to believe then that all the protons in the molecule are magnetically inequivalent and using up to $\ce{^4J}$ coupling, all protons show a doublet of doublet.

However, when I was in school, I was told that if symmetry was a property of a molecule, as above, $\ce{H_a}$ and $\ce{H_b}$ were equivalent, as are $\ce{H_c}$ and $\ce{H_d}$, and each pair of protons gives a doublet. Researching this matter on Google still held true in my undergraduate studies.

What am I getting wrong here?

I read a quote on another question highlighted here

  For two nuclei to be magnetically equivalent, they need to have equivalent coupling to all other non-chemical shift equivalent nuclei in the molecule.

So as $\ce{H_a}$ and $\ce{H_b}$ are chemically equivalent but $\ce{H_b}$ couples differently to $\ce{H_c}$ than $\ce{H_a}$ does, that therefore means that surely $\ce{H_a}$ and $\ce{H_b}$ are magnetically inequivalent?


texts: How much energy can be produced by burning sewage gas?

texts:
I am an eighth grader. I need to make a science project on the production of electricity from sewage. I know that almost sixty percent of sewage gas is Methane and most of the other constituents are combustible. I wanted to know how much energy can be produced by combustion of sewage gas and what amount of it can be converted to mechanical and thermal energy and how much of it is lost.

I was thinking of burning the gas to heat water to steam which in turn would turn the blades of a turbine, which would generate the electricity. I don't know exactly how that would work and how efficient that would be, but I am working on it.


texts: Reason for rounded fitting at the top end of Allihn Condenser

texts:
I am purchasing an essential oil distillation setup. The Allihn Condenser at the top end, and the attached glassware, are rounded. It is supposedly 24/40. I have never seen this. If one of them broke, I would have a hard time finding a replacement because of the strange shape. Thus, I am wondering if there is a good reason for the shape, or if I should ask the manufacturer to give me a normally-shaped 24/40 connection.

Thank you for sharing your thoughts, in advance.


texts: Will galvanic corrosion happen on a ring made of gold and bronze?

texts:
I have recently got a custom-made ring from a jeweler. It’s made from a byzantine-period bronze ring enveloped in a gold bangle. The bronze ring is “glued” onto the gold ring through some kind of resin, as far as he told me.
Would bimetalism with rhe corrosion of the bronze ring happen?
Thank you!


texts: Does hydrogen bonding contribute in solubility of a substance

texts:
If a compound can't hydrogen bond with itself but can hydrogen bond with the water, why does it still remain immiscible?

Take for example ethoxyethane. It can't hydrogen bond with itself but its oxygen atoms can participate in hydrogen bonding with the slightly charged H atoms of the water.

So why does ethoxyethane still remain immiscible with water?


texts: D block elements electronic configuration

texts:
We have found the electronic configuration of d block elements.As we move from left to right in the periodic table the energy of the 3d subshell is decreased and it becomes smaller than the energy of the 4s subshell.
However what makes me question it is that we have done all these experiments at room temperature.Maybe if we ultracold a d-block elements will it change somehow because there won't be any energy left for excitations of the electrons?Or have we performed the experiment in ultracold environments?


texts: Why does F replace the axial bond in PCl5?

texts:
Why does $\ce{F}$ replace an axial bond in $\ce{PCl5}$? I realize that it would be more stable there than at equatorial bond, but what is the reason of its stability? Similarly in $\ce{AB4}$ type of molecules with $\ce{sp^3d}$ hybridization (4 bond pairs and 1 lone pair) why is the geometry of the molecule that of a see-saw, where the lone pair is at equatorial position rather than at axial one?

My book states the reason to be "due to Bent's rule" but I have difficulty linking these two.
Also Bent's rule states that the hybridized orbitals of equivalent energy of central atom tend to give more %s character to the electropositive atom attached to it rather than the electronegative one. (e.g. - in $\ce{CH3F}$) Am I right? What else is more to this rule?


texts: What type of dash does one use when indicating something like F$^{-}$? I assumed it was a minus, since you indicate positive charge with a +, but there is one professor I know who insists that it should be typeset with an endash. Is there a style manual on chemical typesetting I can consult.


texts:
Disclaimer: Sorry if this is not a pure chemistry question. If it's better suited to another SE, I'm happy to have it migrated there.

I'm in the process of cleaning my father's workshop, and recently discovered an old Duracell mercury battery (picture from Wikipedia):
The battery is corroded, and I would say that the color of the corrosion is brown or dark orange.

The battery was lying in a pile of other things on a workbench. Presumably, the battery has been lying there for many years. As things have been moved around on the workbench over the years, one can expect the corrosion to have been scraped off and been mixed with sawdust, smeared on tools etc.

My concern is that I should basically treat the whole workshop as being contaminated, but still I feel it might be a bit over the top.

I would like some information on just how toxic the corrosion is, and some suggestions for what I should do. Could I swab some sample surfaces to have them tested? How expensive would this be?


texts: What happens when mixing elemental mercury with sodium hypochlorite solution

texts: Say you spilled elemental mercury from a thermometer and used household bleach on it, what would be the reaction if any?


texts: Which is a better nucleophile: hydroxide anion or amide anion?

texts:
I know that nucleophilicity order depends on what type of solvent we take, polar protic or polar aprotic and also on the basicity of nucleophile.

  In DMF, which is a better nucleophile $\ce{NH2-}$ or $\ce{OH^-?}$

Since the solvent is aprotic polar, it doesn't have any donor hydrogen to form  hydrogen bonds with nucleophile. So, the nucleophilicity should depend on which among them is more basic. Now, since $\ce{N}$ is less electronegative than $\ce{O}$, it's lone pair is more readily available than that of $\ce{OH-}$.

So, according to me, $\ce{NH2-}$ should be more nucleophilic than $\ce{OH-}$, but the answer given is the opposite, that is, $\ce{OH-}$ is more nucleophilic than $\ce{NH2-}$. How is my reasoning incorrect?

And also what are the factors we should keep in mind while deciding nucleophilicity?


texts: Comparing thermal stabilities of MgCl2 and BaCl2

texts:
I read that to compare thermal stabilities of ionic solids:

if the solid has a monoatomic anion, we compare thermal stability on the basis of lattice energy which is inversely proportional to size.

if the solid has a polyatomic anion, we compare thermal stability on the basis of ionic character which can we done using Fajans' Rule.

Could someone please confirm that these are correct?

I have a doubt because I also read from somewhere else that MgCl2 is less thermally stable than BaCl2,

which contradicts the rule as Cl- is monoatomic, Ba2+ is larger in size, so BaCl2 has lesser lattice energy so it should be less thermally stable.
So what is the correct answer?


texts: How to find the vitamin C content of orange juice?

texts:
I'm an IB chemistry SL student doing an IA on the vitamin C concentration of orange juice. We haven't learned about the titration process, so here is what I have done so far:

$\ce{5KI + KIO3 + 3H2SO4 -> 3I2 + 3K2SO4 + 3H2O}$

This is the equation for producing the iodine solution. Now using a titration process, I added the iodine solution to the orange juice. I measured the volume of Iodine solution used.

Here is the formula for the reaction between the vitamin C and the Iodine solution.

$\ce{C6H8O6 + I3- + H2O -> C6H6O6 + 3I- + 2H+}$

I'm not sure where the Triiodide comes from. Can someone explain this to me? I'm not a very good chemistry student.


texts:
What exactly is an orbital? Atomic or molecular.

Is it the function that describes the behaviour of the electron?

Is it the Schroedinger's equation solution, e.g., for Hydrogen atom?

Is it the probability of finding any electron of an atom in any specific region around the atom's nucleus?

Maybe all these describe the same thing. What is it?


texts: Why only the unstable resonating structure proceeds in the reaction?

texts:
For example, in the given image, I have starred the step where the relatively unstable resonating structure proceeds forward in the reaction.

Why?


texts: Why don't halogens form cations like H+?

texts:
The first ionization energy of hydrogen is $1312\;\mathrm{kJ\cdot mol}^{-1}$, which is larger than that of halogens such as chlorine, bromine, and iodine.

Given that observation, why don't halogens form $\ce{X+}$ ions like $\ce{H+}$?


texts: How does the molarity of a solution change on boiling off the solvent?

texts:
The dilution equation $$M_1V_2=M_2V_2$$ is an equation that can be used to calculate how adding water can impact the volume and molarity of a solution. So I was wondering if this equation would apply if you were to remove the amount of solvent through means such as boiling.

For instance, suppose I have a $\pu{100 mL}$ solution of $\ce{HCl}$ that has water as its solvent and has a molarity of $\pu{3.0 M}$. Would the molarity become $\pu{6.0 M}$ if were to boil out $\pu{50 mL}$ of water of the solvent, or would it have a different $M$ value?


texts: Two monoprotic acids vs. one diprotic acid

texts:
My intuition says that the titration curve for titrating a $1:1$ mixture of the  monoprotic acids $\ce{HA_1}$ and $\ce{HA_2}$ (having ionization constants $K_a = x$ and $K_a = y$ respectively) is identical to the titration curve obtained by titrating a diprotic acid $\ce{H2X}$, with successive ionization constants $Ka_1 = x$ and $Ka_2 = y$.

I feel that this should be correct because the "concentration" and "strength" of the acids are the same, but I am not sure how to prove if it is correct.


texts: How is plane polarized light rotated by chiral compounds?

texts:
There are plenty of questions related to this topic on this site but no proper answer.
Can anyone please explain to me how plane polarized light is rotated by chiral compounds, and why it cannot be rotated by achiral compounds?


texts: How to dissolve steel without affecting aluminium alloy

texts:
Disclaimer: I have very limited knowledge of chemistry

My problem is the following: I have motorcycle part made from some sort of Aluminium alloy - most probably 6005, 6061-T6 or 7005. And inside of this aluminium part there is steel part which is simply stuck there and it's really hard to get it out physically without damaging the aluminium part.

After a bit of googling, I've found out several ways of doing that:

By putting aluminium part with stuck steel part into water and start adding concentrated nitric acid until steel part starts to dissolve. But I've also read that dillute nitric acid (which will occur after mixing with water) will also dissolve aluminium or I'm wrong here?
By using some sort of Alum: either by using Potassium alum or Ammonium alluminium sulfate. Some guy on the forum suggested to dissolve above alum in hot tap water and then put aluminium part with steel part into resulting solution and let it stay there for a day. It should dissolve or at least damage steel part without affecting aluminium part which may ease physical removal of steel part.

Could you please advise which of above solutions is better? And in case of using alum - which of them should I buy - potassium or ammonium one?

Thanks in advance for any help!


texts: Which argon compounds exist, supported by experiment or computation?

texts:
Just as $\ce{HArF}$ was synthesized...Could something like $\ce{Li-Ar-Li}$ exist with AXE geometry $\ce{AX2E3}$? Any other argon compound proposals out there?

I also know that there are some posible excimers like $\ce{LiAr}$ and $\ce{KrF}$ (maybe $\ce{KrF2}$). Can they be considered covalent compounds, even if explained via excited dimers/excimers or the OM theory (recall the technical name for lithium-doped argon matrices in the chemical literature)?


texts: Why is a rearrangement observed for the secondary alcohol but not the primary in these examples?

texts: I am thinking that maybe only hydrogen shifts are possible and methyl shifts are not allowed in such situation? Is that the reasoning? but then again in the second example the bromide could shift to a secondary position after doing a hydrogen shift.


texts: Calculating the pH of a mixture of Na2HPO4 and Na3PO4?

texts: I know there are more questions about this on the forum, but I was just wondering: when we mix both solutions, would we have to consider the equilibria corresponding to $\mathrm{p}K_\mathrm{a2}$ and $\mathrm{p}K_\mathrm{a3}$, or just the latter?


texts: After dealing with a leak from a 73 kg compressed chlorine gas cylinder at 6 bar, there was green powder/rust/discoloration on the stainless steel tubing similar to copper chloride or copper sulphate. Any thoughts of what this might be?


texts: Proper disposal of calcium hydride/calcium hydroxide

texts:
I had probably 2-3 grams of calcium hydride leftover in a schlenk flask from predrying a distillation of benzyl chloride. For the disposal, I diluted the flask contents in about 30mL isopropanol and then, over a water bath (flask open but under heavy stream of argon), added distilled water every few minutes until well after the bubbling had stopped, which I assumed was exothermic evolution of hydrogen gas. I also thought any leftover benzyl chloride would just make trace toluene, benzyl hydroxide, and calcium chloride.

I then figured the milky-white solution was okay to pour down the sink with lots of water running and removed about half of it in this manner, although I noticed a brief but strong smell from the vapors as I did so and stopped. I checked and noticed some sites place it into a basic waste container. Was it a mistake to pour down the sink? I thought limewater would be harmless with enough water. Were there any other errors in this process? I may have to repeat this in the future with calcium hydride again or phosphorous pentoxide (seen various methods on P$_2$O$_4$, but one mentioned sink disposal as well).


texts: How does Ammonia and water mixture works in an absorption refrigeration?

texts:
As per one of the questions in this site $$\ce{NH3 + H2O -> NH4 + OH}$$

However, per another perspective in absorption refrigeration

  The mixture is placed in the same container. Then when it is heated the mixture is separated and $\ce{NH3}$ changes phase, becomes a gas which moves further to cooling, while water is trapped down in the reservoir.

Which one is correct?


texts: Excited-states properties with traditional density functional theory

texts:
Recently I was shown the book "Density Functional Theory II, Relativistic and Time Dependent Extensions" by Nalewajski in which a chapter from E. K. U. Gross et al. is printed. [1] This chapter contains an interesting statement in it's introduction:

  Excited-state properties, however, are notoriously difficult to calculate within the traditional density functional framework and time-dependent phenomena are not accessible at all.

What are those excited-state properties that are "notoriously difficult to calculate" and what makes it hard to calculate them without the TDDFT framework?

Literature:
[1] Gross, E. K. U.; Dobson, J. F.; Petersilka, M. Density Functional Theory of Time-Dependent Phenomena. In Density Functional Theory II; Nalewajski, R. F., Ed.; Topics in Current Chemistry 181; Springer Berlin Heidelberg, 1996; pp 81–172.


texts: Which is easier, the nitration of toluene or the nitration of mesitylene (1,3,5-trimethylbenzene)?

texts: Does the toluene can undergo nitration easier than mesitylene (1,3,5-trimethylbenzene), due to the high repulsion that will occur between $\ce{NO2}$ and the two adjacent methyl groups (in mesitylene nitration case)?


texts: What do s, m, w, m-w, and w-s mean in the context of infrared spectroscopy?

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I am referring to Donald Pavia's Introduction to Spectroscopy, and I found this table that tells about the intensities of the peaks of vibrations of certain bonds.

I can't understand what s, m, w, w-s, etc. are supposed to mean. My guess is that s could mean small, m could mean medium and w could mean weak. But that's crazy, since small and weak mean the same thing? So what do they mean actually?


texts: Can you extract specific compounds from infused oils?

texts:
I heard a discussion when sitting on the train this morning by a couple of cannabis folk on the way into Denver. This is in regards to coconut oil (for baking).

For example: if someone extracted THC into coconut oil, is there anyway to then separate the THC back out of the coconut oil so you end up having coconut oil in one cup, and THC in the other without affecting degradation? I'm not a smoker by any means, but I thought it was a rather interesting conversation. Feel free to be as technical as possible, as I would like to test this theory among many chemical compounds known in homeopathic medicine.


texts: What is the IUPAC preferred name of this tetracyclic natural product?

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On page 819 of Vollhardt, Organic Chemistry 7th Ed., the following "subunit of the antibacterial platensimycin" appears. I have attempted to apply von Baeyer and skeletal replacement ('a') nomenclature but am stuck deciding between numberings. Here are some vector drawings:

Is von Baeyer the preferred nomenclature for this molecule? and, if so, what is its correct numbering and preferred IUPAC name?


texts: Is there a food-safe hydrophobic liquid with a substanially higher density than water?

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Requirements

In short, I am looking for a fluid that meets these criteria:

Hydrophobic
Denser than water
Low viscosity
Food safe

Background

We are working on adding a pool and designing a backyard recreational area.  One design element that we would like to include in multiple places is waterfalls of varying sizes and styles; I love flowing water.  As an extension of that I started wondering if it would be possible to create an underwater waterfall.

Initially I was thinking this could be accomplished by creating a regular waterfall in the pool with normal water, which could then be capped with a clear glass or acrylic watertight cover.  This certainly works as an underwater waterfall, but the cover will be visible, and will likely cloud over time, not to mention the condensation issues.

So I'm wandering now if some sort of fluid exists that could actually flow underwater.  If it's dense enough it will flow down a rockface even under the water, and if hydrophobic will not mix with the surrounding water.  As it will be within a pool that humans will be in for extended periods it must be externally safe, and I'd like something food-safe as kids swallow pool water and it's possible this stuff might get kicked up.  And to add to that tall order, the wrong viscosity will ruin the visual effect.

Does such a fluid exist in a form that a normal person can purchase for a reasonable cost?  I live in the US (Pennsylvania).  Another question, Is there a readily available liquid that's more dense than water and insoluble?, seemed to be looking for something similar but the answer doesn't meet my safety requirements.


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The definition of spontaneous process states that "A spontaneous process is an irreversible process and maybe reversed by some external agency"

So, can we say that all spontaneous reactions are irreversible reactions under the absence of some external force?


texts: Expansion work by a gas when pressure is not explicitly constant?

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How is it possible to calculate the work done by a gas when pressure is not explicitly stated to be constant? The question states:

  Calculate $\Delta H$, $Q$, and $W$ when $1\ \mathrm{mol}$ of He expands from $V = 5\ \mathrm L$ at $T = 298.15\ \mathrm K$ to $V = 10\ \mathrm L$ at $T = 373.15\ K$.

I am not told that the process is isobaric, adiabatic, or even to treat He as an ideal gas (although I know it roughly approximates one).

If I treat it as an ideal gas, I can find $\Delta H$ by using the equations $$H = U + pV$$ $$p = nRT/V$$ and $$U = (3/2)RT$$ but I have no ideas about finding $Q$ or $W$ since I cannot make any other assumptions. Is there an implicit assumption I should make about He gas (or ideal gases in general) expanding, or is there simply not enough information to solve this problem?