texts:
According to JD Lee's Concise Inorganic Chemistry:

  The double bond $\ce{P=O}$ in $\ce{P4O10}$ contains p(π)–d(π) backbonding, where a full p-orbital on oxygen overlaps with an empty d-orbital on $\ce{P}$.

The four oxygens around each $\ce{P}$ form a tetrahedral shape. Then one lone pair from  $\ce{P}$ in it's $\mathrm{sp^3}$ orbital will donate to an empty p-orbital on $\ce{O}$ (created by pairing of electrons in it's remaining two p-orbitals), only then can the "doubly-bonded" oxygen attain it's octet. There is no "single electron from each" bond here. Is my understanding correct?

In earlier similar questions (Hybridisation of POCl3) and (Bonding in the phosphate ion) the d-orbital theory has been said to be disproven, but then how do you explain the different bond lengths in the double (1.43 Å) and single (1.65 Å) $\ce{P-O}$ bonds?


texts:
Water is pooling in my garden next to my neighbour's fence. He has been harassing us in multiple ways for 8 years.

It is the only place on my property where this is happening. It has never happened like this before until last year.

Last year, in the driest summer we have had in years, we saw my neighbour had a hose up to the fence which he kept on which flooded our garden. This year we can see water trickling down from his garden, but due to rain cannot be absolutely sure as we cannot see the hose. The water turns on and off, but not relating to any rain. All winter with multiple weather conditions there was no pooling. It only happens during the summer when we try and use our garden.

This water pools a few inches deep, so it is easy to take a sample.

Is there any home way of testing this water to see if it is tap water or rain water? This test has to be something that can be purchased in the UK.

If not, is there any cheap way of getting someone else to test it?

His house is a good distance from the trickling area, so it is unlikely to be a leak in his garden as there will be no piping there.


texts: Why is molar extinction coefficient for dithiocyanatobis(triphenylphosphine)nickel(II) so high?

texts:
I recently looked at a data set where $\ce{[Ni(SCN)2(PPh3)2]}$ had 0 unpaired electrons (from magnetic moment calculation) which indicated to me that it was square planar. I wondered how it could have a high molar extinction coefficient of $\pu{3210 L mol-1 cm-1}.$
I have been trying to research into it and have heard of charge transfer complexes. I really want to understand what is going on here.


texts: Naming of elements 113, 115, 117, and 118

texts: Does anyone know of a blog, website, news server, or listserv to which one may subscribe to be notified when these elements get their official names?


texts: Can a precipitate dissolve upon addition of a diluted acid?

texts:
Is it true that precipitates dissolve upon addition of diluted acids?
If a precipitates is dissolve , does it disappear from solution , or  any thing else  happened out there?

I  am just curious about this. Because I have heard that precipitates can be dissolved if you  add a diluted acid. But why it would happen? And is it valid for any diluted or strong acid ?.Do all the precipitates dissolve upon addition of any acid ?.I would like to know more about this.


texts: Why is high molar molar mass a requirement of good primary standards for volumetric analysis?

texts:
I have been taught that using primary standards with a relatively high molar mass will reduce the error between the equivalence point and the end point during titration. However, I am unsure as to why this is the case.

It would be great if someone could point out to me what the purpose of using primary standards with a high molecular mass is.


texts: As I understand it, acids are substances which have a high concentration of H+ ion which makes acid an acid. When interacting with our skin, acid can damage it. How does this concentration of protons cause damage to skin?


texts: Do catalysts undergo physical changes during a reaction?

texts: I know that catalysts don't undergo chemical changes during a reaction, but do they undergo physical changes? If they do, are there any examples?


texts:
I was attempting to synthesize hydrochloric acid and it seems to have formed another form of chlorinated acid. The smell is more of chlorine and is extremely powerful. I got some on my jeans and it bleached them white but caused me no burn. In fact as an acid it seems pretty weak by comparison to the smell which is overpowering and appears to be extremely toxic. The reaction was performed in a membrane separated electrolytic cell with $\ce{NaCl}$ as the electrolyte, $\ce{PbO2}$ anode, $\ce{Cu}$ cathode, $\pu{19.5 V}$.

I'm pretty sure it's not hydrochloric acid, I've worked with $\ce{HCl}$ a lot and I'm sure thats not $\ce{HCl + H2O}$, so what kind of acid did I form?

Is it just chlorine and water. If it is just $\ce{Cl}$ shouldn't it react with water to form a compound?

MODERATOR : I do not see how a chemical synthesis question is off topic. However, I rarely receive accurate answers to my questions, do feel free to delete this question and all of my previous questions and even my profile for that matter as I find this entire network rater useless. I get much better assistance from other venues.
I do thank anyone who has provided any assistance in the past, it's appreciated.
Back to meandering around the internet for answers.
Good Bye!

Above is what I distilled from the product.


texts: Why is mercury's surface tension so high, when its viscosity is low?

texts:
At a basic level, both surface tension and viscosity are the result of forces between particles. Usually we'd talk about intermolecular forces, because liquids are usually molecules, but obviously that doesn't work for mercury, which isn't made of molecules at all. Stronger forces between particles give higher surface tension, and usually also higher viscosity. So water's fairly high surface tension is usually credited to hydrogen bonding, and mercury's exceptionally high surface tension is put down to metallic bonding; while the increasing viscosity of aliphatic hydrocarbons with more carbons is said to be due to increasing London dispersion forces.

It's easy to see that the two are poorly correlated, though. Ethanol has almost identical surface tension to acetone, for example, but it's more than three times as viscous. Most strikingly, mercury has really extraordinarily high surface tension, but is no more viscous than cold water.

Is it completely wrong to expect at least some kind of loose correlation between surface tension and viscosity? Is viscosity just a far more complex phenomenon, a proper explanation of which lies way beyond the hand-wavy school science that chemistry teachers use to give a vague idea about things like trends in the alkanes? Would it be better to emphasise entanglement of long molecules when trying to explain the viscosity of longer alkanes, rather than just stronger forces?

Is mercury's low viscosity mainly down to its small particle size, or is there much more to it than that?


texts: Why diethyl ether does not absorb in UV region?

texts:
Explain why diethyl ether does not have a UV spectrum, even though  it has lone-pair electrons.

Can we say that π* molecular orbital does not exist because there are no π-bonded electrons in diethyl ether?


texts:
An amine can react with an acid just like any other base to form a salt:

$$\ce{RNH2 + HCl-> RNH3+ Cl-}$$

According to my textbook (unreliable), amines also react with bases just like any other acid:

$$\ce{RNH2 + NaOH -> RNH- Na+}$$

Do amines (if not all amines, at least the ones substituted with a strong withdrawing group) react with bases as shown in the above reaction?

In  other words: Are amines amphoteric?


texts:
I'm a little confused about the interpretation of the 1s orbital diagram.
I know that the outer boundary is where the wave function of the 1s orbital has a constant value, which means means there's a constant probability of finding an electron on that outer boundary.

The reason I'm confused is because, isn't there an infinite number of distances from the nucleus where there's a constant probability of finding an electron around a cross-sectional slice of the sphere?

What I mean is, if we choose r, meaning distance from the nucleus as 50 pm, you could draw a circle representing that boundary as r = 50pm. You could do the same with an infinite amount of distances from the nucleus and have the same result.

Basically I'm confused as to how/why the boundary is chosen -- does the probability density need to go beneath a certain value for the boundary to be defined? Or is it arbitrary? If r < infinity, there's a finite probability of finding an electron at that distance. So doesn't this mean that the boundary is pretty meaningless?

Graphically what i mean is:

Why not:

?

Your help is greatly appreciated :D


texts: What products did this aldol condensation create?

texts:
I followed a procedure in my organic chemistry lab, but I don't understand what product the procedure created. Can someone tell me what chemicals reacts with which to create the product?

First $\ce{NaOH}$, water, and ethanol were mixed together and cooled. Then acetone was added, followed by benzaldehyde (the reaction mixture then turned yellow/orange). The reaction was stirred for a while. The product was washed with water and ethanol before being recrystallized from ethyl acetate. After crystal formation the product was reduced then cooled.

If I understand correctly the acetone and benzaldehyde reacted together and the ethyl acetate was only used as a solvent?


texts: If the half-life of an isotope exceeds the age of the Universe, then how is it measured?

texts: According to this Wikipedia article, the half-life of Bismuth-209 is 19 billion billion years, which exceeds the age of the Universe by factor on the order of a billion. How is the half-life of an element measured and experimentally verified if the half-life exceeds the age of the Universe?


texts: Why does a certain number of moles of gas occupy a set volume?

texts:
In class, I was taught that 1 mole of an ideal gas occupies a set volume eg 22.4 L at STP. Why does the gas only occupy a certain volume and not just keep expanding forever, having limitless volume?

Ideal gases neglect inter-molecular forces so shouldn't they just keep expanding?


texts: Getting structural formula of complex molecules?

texts:
How is it possible to precisely map huge molecules? Somehow, scientists easily know the structure of a compound of any complexity.

What techniques are used to know the sturcture of molecules like this one, or complex proteins that can be constructed of thousands of atoms, like the ones used in intracellular processes? It is so common to see them drawn as structural formulaes or pictured in a video, with a fine per-atom precision... but how?

UPDATE

This update addresses the comments about the question being too broad.

Firstly, I want to say that for me this question is rather exact - here and there, in lots of places over the internet, I see structural formulas and 3D models of countless chemical compouds that claim to bear a 100%-precise depiction of the actual molecule structure (I have linked an example). And I am interested in how all this data is gathered and why is it 100%-correct? I am so used to the pictures of all these complex compounds that I take them for granted. But recently I became to wonder, how do we even get these, how this knowledge is received?

Secondly, although there's certainly a difference between a structural formula and a dynamic 3D model like in this video, it is not so important in this question. The fact that we can precisely depict any compound or molecule is not even in question, it looks like that there's no problem in doing so for any chemical.

The very exact question is: what is(are) the method(s) of getting such precise formulas and pictures for objects (molecules) that are not even visible to the naked eye or microscope?

Of course, there can be differences in how the mapping is done for different molecules, or some data, like the 3D model can be complemented by some computation conducted with help of a computer, but all in all, what is the basis of our confidence of being able to exactly know a structure of any molecule?

Though, especially, after reading the comments, I think that a proper answer could be too large and include historical data..


texts: Which will be the most acidic hydrogen in the following organic compounds?

texts:
Which will be the most acidic hydrogen in both cases? Please explain.

According to me, in the first compound 2 should be most acidic as in both 1 and 2, resonance occurs but 2’s carbon is closer to the oxygen, which can stabilize the negative charge on carbon.

In the second compound, 1 should be the most acidic as there is $+I$ at 2 by carbon 3, which destabilizes the negative charge on it after removing hydrogen from carbon 2.

Am I correct?


texts:
A previous question (April 2017) asked about black $\ce{NiO}$ did not supply any answer. Sadly, such a referral only deters colleagues from commenting on the current question.

There is a great deal of literature on cation defects in non-stoichiometric nickel (II) oxide. There is much on charge-transfer in defective crystal structures. But, I can't find any attempt to marry the two together - which may explain how the deep colour (black) is observed.
Of course, it may simply be that I have not  discovered it yet. I did find a question on how/why copper (II) oxide is black. This one has semiconductor properties; so, $\ce{CuO}$ and non-stoichiometric $\ce{NiO}$ may be black for similar reasons?
Can anyone comment?


texts: Platinum engagement ring as oxidation catalyst

texts:
I know platinum is used in the catalytic converter to oxidize pollutants.

For a pollutant ($\ce{N_xO}$, $\ce{CO}$, etc., your choice), I'd like to get an order-of-magnitude rate of catalysis, assuming partial pressures found in a major city (NYC?)
At room temperature (or body temperature)
Let's assume the ring has 1 $\mathrm{cm^{2}}$  of surface area (I'm not rich, I assume  1 $\mathrm{cm^{2}}$ is reasonable)

Obviously using bulk platinum metal is an cost-ineffective method of catalysis, so it doesn't seem to be well studied. I know reaction is more efficient at high temperature, and while my girlfriend may figuratively be from Venus, I'd like to know the catalysis near STP. And perhaps a support is needed to prevent catalyst poisoning.


texts: Are risks (hexavalent chromium) during Chrome plating temporary, or remain with the product?

texts:
Since some chrome plating production processes generate hexavalent_chromium compounds, which are reportedly highly toxic/carcinogenic, I wonder:

Do the hexavalent chromium substances only occur (temporarily) during the production process (i.e. the chrome plating) or will they remain with the product?

My naïve impression has been that after the chrome plating process is over, the product will have an additionally a more or less thick layer of native Cr. Is this correct?

Should I expect impurities or residuals of toxic forms (e.g. hexvalent chromium) to be with the chrome plated this is possible do primitive test exist to detect product?

If it is possible that the chrome plated object could have
worrisome concentrations/amounts of Cr(IV), is there a primitive test to detect this?

Update
Some internet resources, such as tests/detection procedures for Cr(IV) described here, mention

  The screening method can be used to determine chromium(VI) in
  passivation layers on metal pieces.

Also test kits for Cr(IV) sold online mention in their description to be

  test[s] to detect leachable Cr (VI) ions on virtually any solid surface.

both giving reason to thing that the Cr (VI) might remain in worrisome amounts after the chrome plating. True.

update 2

one of the answers mentioned that "chrome plating", being understood as a general term, does not necessarily imply which material is being plated. If permissible I would like to add that I am most interested in those risks of the base material being copper.

update3

The most upvoted answer has stated little risk if chrome plating procedure is carried out well.

As new information the CHROME PLATINGANDCHROMIC ACID ANODIZING SURVEY strongly suggests that the term chrome plating, can be divided regarding the categories a) Tank process (Hard plating; decorative; chromic acid anodizing) and b) *Tank constituent(s) (Hexavalent chrome; trivalent chrome).

This information to raises the aspect, if the outer passivated layer should be expected to have only Cr(III), irrespective of the used tank constituents.


texts: Calculating the value of equilibrium constant in terms of pressure

texts:
A mixture of $\pu{1 g}$ of $\ce{H2(g)}$ and $\pu{1.06 g}$ $\ce{H2S(g)}$ in a $\pu{0.5 L}$ flask come to equilibrium at $\pu{1670 K}.$ At equilibrium, there are $\pu{8E-6 mol}$ of $\ce{S2(g)}$ present. Determine $K_p.$

I set up an ICE table:
$$
\begin{array}{ccc}
\ce{& &2 H2 &+ &S2 &<=> &2 H2S} \\
\text{Initial} & &\pu{1 M} && 0 && \pu{0.062 M} \\
\text{Change} & &2x && x && 2x \\
\text{Equilibrium / Final} & &?  && \pu{1.6E-5 M} && ?
\end{array}
$$
From the $\ce{S2}$ column we see that $x = \pu{1.6E-5 M}$, so I calculated the equilibrium constant as follows:
$$K_p = \frac{(0.062 + 2\times\pu{1.6E-5})^2}{(\pu{1.6E-5})(1-2\times\pu{1.6E-5})^2} = 240$$
What is wrong with my solution?


texts: Can not find structural formula with compounds' IUPAC name

texts:
I currently need to read a paper. In that paper the following compound was mentioned:

1,2-benzo-6-(N-ethyl-N-isobutylamino)fluoran

I tried to find the corresponding structural formula using the OPSIN parser at: http://opsin.ch.cam.ac.uk/
but I got the error message:

  1,2-benzo-6-(N-ethyl-N-isobutylamino)fluoran was uninterpretable due to the following section of the name: 1,2-benz

I also tried just googleing the compounds name but the only thing I found where patents which weren't very useful.

I hope somebody can help me find the structural formula.


texts:
In the p sub shell there are 3 orbitals,
m=-1, m=0, m=1
which are listed by axis x,y, and z.
Some show as -1=x,0=y,1=z
Another shows -1=x,0=z,1=y
Some pictures and text also show the filling order as ‘xyz’ and others state that the z axis is filled first m=0 and then the x axis as m=-1 making the filling order z,x,y

What is the correct filling order?
If I know this then I can figure out the d and f sub shells.
d~m=-2,-1,0,1,2
F-m=-3,-2,-1,0,1,2,3
Thanks, HJS


texts: Exothermic reactions at high temperature and the chemical equilibrium

texts: Why are many exothermic reactions, like Haber process, conducted at high temperature, thus  their unfavourable equilibrium position?


texts: How many electrons does boron have on average in B2H6?

texts: The boron interaction with hydrogen gives it one electron I suppose, but then the octet is not complete. So how many electrons does the boron atom have exactly and why?


texts: Diels Alder reaction with maleic anhydride. Reactivity of different dienes

texts:
I don't understand question 6, although I took notes and the professor mentioned an explanation in class.

Can someone please help using easier terms?


texts:
I want to simulate Raman spectra of benzene in Gaussian 09.

Calculated spectra for a single ring Benzene ($\ce{C6H6}$) in Gaussian differs about $\pu{40 cm^{-1}}$ for each peak, compared with experimental Raman's databases.

How can I solve this problem?
Gaussian file created with GaussView6:
MP2 config

DFT config:

Parameters: (for optimization)


texts:
I was taught that the following reaction happens:

It is called the "ipso-substitution". My professor had told me that it occurs in the case of $\ce{-SO3H}$ and $\ce{-COOH}$. But he had ended the topic there. My textbook doesn't detail any more either.

My searches landed me up at the fact that ipso-substitution is also employed in the preparation of picric acid from nitrobenzene. But I couldn't find answers all my other questions, which are:

Does the ipso-substitution occur only for these two groups, or are there more? I guess there is a "threshold" value for some parameter, above (or below) which ipso substitution cannot occur, but I am unable to come up with what that parameter is. I guess it's the high stability of the leaving group $\ce{SO3-}$, but I am not sure.
Is ipso-substitution affected by the choice of the electrophile and the solvent? What if, instead of bromine water, I chose bromine in acetic acid? Or something even simpler as $\ce{FeCl3/Cl2}$. Would ipso substitution occur then?
I know that no organic reaction produces 100% of only one compound, as its other isomers are always also formed. Ipso substitution should be no exception. But how do we decide whether the ipso product is a major product or a minor product? I know how to decide major/minor products between ortho/meta/para substitution (electron density/steric hindrance/H-bonding), but I haven't been taught any logic to decide the same for ipso substitution.


texts: Reaction an ROH-resonance-stabilized Group with Hydroxide/Acid-Base Reactions

texts:
The book says there is no reaction.

However, I do not understand why.

The ROH group is resonance-stabilized with the benzene-like group. Its conjugate base is stable. There is an inductive effect of the cloud of electrons that make the oxygen more electronegative. However, resonance effects are always more important than inductive effects.

So, why is there no reaction?


texts: In which cases does the 3d subshell take precedence over the 4s subshell?

texts:
I've learnt in Chemistry that for example in Chromium, the 4s subshell only has one electron in favor of making the 3d subshell half-full. Also, for Copper the same happens.

What other circumstances does this happen under? Do ions obey the same pattern, e.g. Mn+?


texts: Is preference given to long alkyl group or branched cycloalkane?

texts: Could you tell me whether it will be 1-(1-ethylcyclopropyl)hexane or 1-ethyl-2-hexylcyclopropane ? I don't know the rule or the preference order.


texts: How was water formed if oxygen and hydrogen exist as molecules?

texts:
I have learnt that both hydrogen and oxygen  exist as molecules. If so how was $\ce {H2O}$ formed?

In water there is two hydrogen molecule and one oxygen atoms but how is this possible? Oxygen only exists as a molecule in our earth then how does the molecule oxygen react with molecule hydrogen to form water.

Moreover, if water is formed by combining of hydrogen and oxygen molecules, then the chemical formula of water should be $\ce{H2O2}$, shouldn't it?


texts: Are there any (liquid) chemicals that experience rapid, extensive, and controllable volume changes in reaction to heat?

texts: The larger purpose of this question is the engineering of liquid filled sacs that change their volume according to heat. They'd need to have diverse ranges of volume, at least a factor of ten (a 10 ml to 100ml transition).


texts: Amending soil pH to change the color of hydrangea flowers

texts: I would like to ensure that my hydrangeas are blue. I am told that adding ammonium sulfate or aluminium sulfate will cause the soil to be more acidic. I am also told that adding elemental sulfur will help. Will adding magnesium sulfate to the soil help?


texts:
I am looking for something rather odd and specific.

I need a chemical resin that is liquid up to 250 deg. F,  Is a thermoset (it cures at temperatures above 250 F), and is biocompatible in that if the resin is consumed or enters the blood stream it is not toxic to humans in quantities up to 2 cm^3.  If anyone has insight it would be extremely helpful!


texts: What functional group is this in this specific molecule?

texts: I know without the nitrogen this molecule would probably be considered a crown ether. What exactly would the nitrogen/oxygen functional groups be named as in this molecule shown below? Any help would be greatly appreciated.


texts: Why wouldn't solvents be interchanged in isotonic solutions?

texts:
While studying osmosis, my book remarks that

Two solutions having same osmotic pressure at a given temperature are called isotonic solutions. When such solutions are separated by semipermeable membrane no osmosis occurs between them. For example, the osmotic pressure associated with the fluid inside the blood cell is equivalent to that of 0.9% (mass/volume) sodium chloride solution, called normal saline solution and it is safe to inject intravenously.
On the other hand, if we place the cells in a solution containing more
than 0.9% (mass/volume) sodium chloride, water will flow out of the
cells and they would shrink. Such a solution is called hypertonic. If
the salt concentration is less than 0.9% (mass/volume), the solution
is said to be hypotonic. In this case, water will flow into the cells
if placed in this solution and they would swell.

But why would the osmosis simply stop? If I'm understanding osmosis correctly, then it is simply due to the fact that there is an SPM separating the two solutions, and hence the solvent (Or rather, the one with the size smaller than what the SPM allows, although I doubt it'd make a very big difference for a dilute solution) flows from the lower to higher concentration and eventually, equilibrium is attained.
In this case, even if you do inject somebody with a saline solution with $0.9%$ mass/volume sodium chloride solution, the SPM of the blood cell should still trade the solvent from the injection with the material inside (Since equilibrium does not translate to no flow, as confirmed by experiments with heavy and light hydrogen in the formation of NH3) it and the blood cell should still swell up. Obviously, that doesn't happen, though, or else I would have quite a different memory of getting a shot! Where did I go wrong in my reasoning?
Note: In the above, I'm assuming that the fluid inside the blood cells is something other than water. Please correct me if I'm wrong.
Edit: I realized the error. It says in the above paragraph itself that the fluid is water.


texts: Decades ago my job was to find the silicon content in cast iron gravimetrically. The first step was dissolving the sample in hot Nitric acid. Did this turn all of the constituents in the sample, except the silicon, into water soluble salts? Was the silicon then bound as silicon dioxide?


texts: How do partially protonated sulfate ligands affect a metal's charge?

texts: I'm currently reviewing the Periana-Catalytica system and I have a question about one of the intermediates, namely $\ce{[(bpym)Pt(OSO3H)2]^+}$, which is found in the following tutorial review. How do the $\ce{OSO3H}$ ligands affect the oxidation state of the metal? If I count each of these ligands as a monoanionic ligand, and also factor in the positive charge of the complex, wouldn't the oxidation state of the metal be +3? This seems a bit strange to me, seeing as Pt typically has oxidation states of +2 or +4, but never +3.


texts: Is there a way to make a liquid cold by a chemical reaction?

texts:
I'm looking for a way to combine two substances in a chemical reaction that uses a lot of energy, therefore absorbing heat, to make a substance cold.

I'm thinking about a two-chamber thermos that in the middle chamber is, for example, juice and in the outside chamber will be placed the other substances. When these substances react, is it possible that they absorb heat, making the juice colder?


texts:
A small amount of natural carbon is $\ce{^{14}C}$.  This is radioactive and decays to $\ce{^{14}N}$.  This is exploited in radiocarbon dating.

This $\ce{^{14}C}$ is taken up by living organisms.  I know that natural biochemical processes can be sensitive to isotopes but I expect that the $\ce{^{14}C}$ can occur in any context where $\ce{^{12}C}$ could occur.  (Please correct me if I am wrong here.)

So, $\ce{^{14}C}$ might occur as part of the backbone of a fatty acid:

$$. . . \ce{-CH2-{^{14}C}H2-CH2 -} . . .$$

When the $\ce{^{14}C}$ decays, this will become:

$$. . . \ce{-CH2-NH-CH2 -} . . .$$

(I assume one of the hydrogens would be lost.)

Are any of these unusual compounds stable or do they promptly react in some way?

Are they studied?

Do they have any interesting properties?


texts: Separation of argon in Dewar's charcoal method

texts:
I was studying about the Dewar's charcoal method. It says in the book Modern Inorganic Chemistry by R. D. Madan on p. 1291 that at $\pu{-100 ^\circ C}$ Ar, Xe and Kr is adsorbed by the charcoal.

Then, if the charcoal is further cooled to $\pu{-180 ^\circ C}$, then Ar (boiling point $\pu{-186 ^\circ C}$) gets liquefied  and thus separated.

Xe (boiling point $\pu{-107 ^\circ C}$) and Kr (boiling point $\pu{-152 ^\circ C}$) should also be liquefied and separated. So why do they remain adsorbed?


texts: Why are 2 ways to calculate the energy of the ground state?

texts:
Setup

I found in Szabo, Quantum chemistry page 88, these two ways to calculate the energy of the ground state:

$$E_0= \sum_a^N \langle a|h|a\rangle + \frac{1}{2} \sum_a^N \sum_b^N \langle ab||ab\rangle $$

and

$$E_0= \sum_a^N \langle a|h|a\rangle + \sum_a^N \sum_{b>a}^N \langle ab||ab\rangle $$

Question

Why?


texts: Would dissolving a salt and letting it sit for 48 hours have an effect on the solution?

texts:
If one were to dissolve magnesium citrate (about $100~\mathrm{mg}$) in water (about $70~\mathrm{ml}$) and let the solution sit for 48 hours, would the solution be exactly the same as one dissolved and consumed right away?

How does one explain the difference in taste from a 48-hour solution and a 5-minute solution?


texts: Identifying if reaction is reduction or oxidation. Is there an error in this question?

texts:
I am looking at this reaction:

I am trying to determine if it is reduction or oxidation.

In the initial molecule I calculate the overall oxidation numbers as:

ox(Cl)*6 + ox(H)*6 + ox(C)*6 = 0
-6 + 6 +ox(c)*6 = 0
hence, ox(c) = 0

In the subsequent molecule, I calculated the oxidation numbers as:

ox(Cl)*4 + ox(H)*6 + ox(C)*6 = 0
-4 + 6 +ox(c)*6 = 0
hence, ox(c) = 6/2 = 1/3

However, my textbook says the oxidation number of ALL carbon in the second molecule is 2. I am very confused by this, since if all the carbons have an oxidation number of 2 then the molecule would be charged overall? Then I am unsure if my oxidation numbers can be fractional. Is my textbook wrong, and I wrong or are we both wrong?

Overall, what I am really trying to get at is if the molecule is being oxidized or reduced, and how many electrons are being transferred. Is there a better way of doing this?

Thank you kindly


texts: Which conformations of 2,3-dimethylbutane are more stable?

texts:
I am not sure what the proper arrangement of these conformations are from least to most stable. I got the wrong answer, but my thinking was this:
 First, I thought that because 2 and 4 are in eclipsed conformations they are least stable.  From there I thought that 4 was less stable than 2 because of the steric interactions of the methyl groups.  Then of the two staggered conformations 1 and 3, it appears to me that 1 has more steric interaction of the methyl groups than 3.  So my ordering from least to most stable was 4,2,1,3.  Is there an error in my line of reasoning?


texts: How can one determine if all reagents will react in the reaction?

texts:
Is it correct that all the reagents above the arrow will participate to form an intermediate product, to which the reagents below the arrow are then added, and they react to form the final product?
Thank you in advance.


texts: Is the kinetic gas equation valid for non-cubical containers?

texts:
I have seen the derivation of the following equation for a cubical container with $N$ molecules.

$$PV = \frac 13 mNu^2 $$

How is this equation valid even for spherical container or any other non cubical shaped container?

(I prefer rigorous equation-based proof but I'm okay even with analytical proof )


texts:
I was wondering if there is an original scientific publication showing why $C_1V_1 = C_2V_2$ works.
Or perhaps, who described/used it first?


texts:
I need an adhesive that can bind to ABS plastic but is highly resistant to ethanol, isopropanol, and water. It's for use in an environment where it will spend a significant amount of time soaking in >95% alcohols, with agitation.
Temperature and pressure requirements aren't a big deal, this is for use at near room temperature and pressure. Strength requirements aren't anything crazy either, it just needs to survive light vibrations and light fluid flow. UV exposure is also a non-issue. However, I do need the adhesive to be watertight (where "water" = the solvents too).
My default is a cyanoacrylate-based adhesive but according to an incidental note on this page (emphasis mine):

The bottom line is cyanoacrylates have poor resistance to polar solvents and better resistance to non-polar solvents.

So it seems like CA glues are out. What classes of adhesives could I use here? My gut says maybe a silicone-based adhesive, although I don't like working with those when possible (messy cleanup). Or maybe some type of epoxy adhesive?


texts:
Since oxygen is more electronegative than chlorine, if I introduce $\ce{O2}$ gas to $\ce{AlCl3}$ and apply some heat, will the chlorine be replaced by oxygen, resulting in $\ce{Al2O3}$ or $\ce{Al(ClO2)3}$, then evolving the remaining $\ce{Cl2}$ into the air? I suspect not, but why?

Is there a standard way of converting $\ce{AlCl3}$ to $\ce{Al2O3}$?


texts: How do I convert benzoic acid to m-nitrobenzyl alcohol using 2 steps?

texts:
The question asks to carry out the following conversion in not more than 2 steps:

Benzoic acid to m-nitrobenzyl alcohol

I first used nitration (conc. $\ce{HNO3}$ /conc.$\ce{H2SO4}$) and then I'm got stuck, as reducing the $\ce{-COOH}$ group would also reduce $\ce{-NO2}$ group (using $\ce{LiAlH4}$).

I tried to reduce $\ce{-COOH}$ group using $\ce{LiAlH4}$ to $\ce{-CH2OH}$ and then proceed to nitration but got confused whether $\ce{-CH2OH}$ is o/p or m-directing. I think it should be o/p directing.


texts: Wouldn't CO2 be IR inactive because of its non-polar bonds?


texts: Why glucose and other similar carbohydrates are oxidised fully by HIO4?

texts:
$\ce{HIO4_{(aq)}}$ requires the vicinal diols to have syn configuration, as it forms a cyclic periodate ester.

But glucose does not have syn configuration at C3, and if you consider cyclic forms of glucose it shouldn't oxidise fully at all because alternate hydroxy groups with anti configuration will be unreactive. But it still gets oxidised by $\ce{HIO4}$ to give 5 molecules of methanoic acid, $\ce{HCOOH}$, and one molecule of formaldehyde, $\ce{HCHO}$.


texts:
I am working through some MIT lecture notes trying to understand adiabatic flame temperature. There is a section in these notes where $K_p$ is calculated for the following reaction at $\pu{1600K}$.
$$\ce{CO + \frac{1}{2}O_2 \rightleftharpoons CO_2}$$
The notes find $K_p$ by using the following values:
@$\pu{1600K}$:
$$\log K_p (\ce{CO}) = 8.234$$
$$\log K_p (\ce{O2}) = 0$$
$$\log K_p (\ce{CO2}) = 12.940$$
$$\log K_p (\text{RXN}) = 12.940-0-8.234=4.706 \implies K_p \approx 5 \times10^4$$
What is the significance of these $\log K_p$ values? I'm confused because I thought that $K_p$ was a value pertaining to a reaction as a whole, not specific reactants. Also, where can I find these values online? My notes pointed me towards https://webbook.nist.gov/chemistry/, but I am having difficulty finding these $\log K_p$ values in that database. I would appreciate any guidance/intuition you may be able to provide!


texts: Using Wilkinson's Catalyst to reduce esters?

texts:
I was solving some questions on alcohols when I came upon a question in which it was asked that whether esters can be reduced  using hydrogen in the prescence of wilkinson's catalyst.

Now I know that this reaction can take place using hydrogen in the prescence of nickel or platinum to give two alcohols.So is the same true for using wilkinson's catalyst also?

And if it cannot be so then on which functional groups can this be used on?

Also what would happen differently if wilkinson's catalyst is used?


texts: Reaction of styrene oxide with hydrogen iodide

texts:
The question is to find the product of the reaction of Styrene Oxide with Hydrogen Iodide.
According to me, this should be the mechanism-

As the benzylic carbocation will be more stable, therefore the product made from A should be major and the other one should be minor. But, in my book the answer to this question is the opposite of mine. Where did I go wrong?


texts: Are solvent effects the reason for the methoxide ion to be a stronger nucleophile than the thiomethoxide ion?

texts:
Between $\ce{CH3O-}$ and $\ce{NC-}$, $\ce{NC-}$ is a better nucleophile than $\ce{CH3O-}$ in a polar protic solvent, while $\ce{CH3O-}$ is a better one in a polar aprotic solvent, because in a polar aprotic solvent $\ce{CH3O-}$ is free to move and $\ce{O-}$ has more electron density.
Does the same reason apply for $\ce{CH3O-}$ and $\ce{CH3S-}$, is $\ce{CH3O-}$ a stronger nucleophile than the latter one in polar aprotic solvent?


texts: Shouldn't the 5-membered ring expand to a six membered one in this nucleophilic addition reaction?

texts:
I am dealing with a problem involving addition of $\ce{HCl}$ to a ring:

According to what I think, the ring should expand to a six-membered following carbocation formation at the tertiary site, as a 6-membered ring will involve less strain than the current 5-membered one.
However, the correct product is:

Which is what would form if the expansion is not favored.
My guess is that the rearrangement is less likely to occur due to a tertiary carbocation, and that the rearranged product will then form in a minor concentration.


texts: Water solubility comparison of stereoisomers of bicyclo [4.4.0] decane-3,4-diol

texts: I think, (I) must be more soluble in water. It is due to trans configuration and thus, forming more effectively inter-molecular hydrogen bonds with water molecules.


texts: What is the term used as correction for attractive forces in the Van der Waals Equation?

texts:
I have seen a question in my textbook which is little bit confusing,

The term that corrects for attractive forces present in real gas in van der Waal equation is
(i) ${nb}$
(ii) $\frac{an^2}{V^2}$
(iii) $\frac{-an^2}{V^2}$
(iv) ${-nb}$

Since the question is about term  "forces" I do not see any of the four options dimensionally correct as (i)&(iv) are related to volume and (ii)&(iii) are related to pressure.
But in my textbook answer the correct answer given is (ii) so how is it dimensionally correct?


texts: Why in -COOH group the C atom pulls electron cloud from the OH group O where as the double bonded O pulls the electron cloud towards itself?

texts: Should both the oxygen pull the cloud as O is more electronegative than C . I think that as the cloud density decreases near carbon therefore it pulls . A proper explanation please .


texts: Difference between 'Preferred IUPAC Name' and 'Systematic IUPAC Name'

texts:
When looking at different chemicals, I come across the 'preferred IUPAC name' and the 'systematic IUPAC name'. I've noticed that when I name chemicals, I name them by their 'systematic IUPAC name', as I've been taught to name them using this system.

When is the 'preferred IUPAC name' used? I sometimes come across it when looking at aldehydes, ketones and carboxylic acids. However, the fact that it's 'preferred' makes me wonder whether chemists use this method more often than the other system.


texts:
I am reading a paper where they develop the phosphate spots on a paper chromatogram using what they call " Acid-molybdate spray of Hanes & Isherwood  (1949)".

Any idea what this reagent is?

I tried looking up the original reference but unfortunately I cannot fine a full text version. http://www.ncbi.nlm.nih.gov/pubmed/15398090?dopt=Abstract&holding=npg

Sigma has "Ammonium molybdate tetrahydrate" reagent available which is described as a component of the "Hanes and Isherwood reagent " but not sure what else is supposed to go in there.

http://www.sigmaaldrich.com/catalog/product/fluka/09880?lang=en&region=IN

Any ideas?


texts: Can I use my extech pH 60 meter to measure soil pH if so how?

texts:
Can I use my extech pH60 meter to measure soil pH if so how?
I included a link to the meter.

Extech pH 60


texts: Is it incorrect to use Fisher Projections for carbons that don't have stereocenters?

texts:
For example:

Is a cross specifically used for stereocenter representation?


texts: Why are d-orbitals required/used for hypervalent molecules (where the central atom has expanded its octet)

texts: Period 2 elements like carbon, oxygen and nitrogen cannot expand their octet because they cannot make use of d orbitals in that energy level (they don't exist). However, period 3 elements like sulfur and chlorine can because they can utilize the d orbitals with the same principal quantum number. However, the the 4s orbitals are lower in energy than the 3d orbitals (from the order of filling of electrons) so why can't they be used/ why aren't they? Moreover, why can't period 2 elements use the 3s orbital?


texts: Why is pressure negative in force and work

texts:
The equation to measure work is $$w=F\cdot D$$

However, the equation for force is  $$F=(-P \cdot A)$$

Plugging this into the work equation we have:

$$w=-P\cdot A\cdot D$$

My question is, why is pressure negative in force?


texts: What are the molecular orbitals shaped like in diberyllium (mono)cation?

texts:
I think one way of describing the result is that the bond in $\ce{Be^+_2}$? cation is a resonance hybrid of two possible pi bonds. Each pi bond has a bond order of 1 so the resonance hybrid structure has two partial pi bonds. But then can it further be in a resonance hybrid of different rotations and so be an even cylinder?

I guess if you wanted to be silly you could say that that the electron configuration for each beryllium ion is like:

$$ \underset{2s}{[\uparrow \downarrow]} \underset{(2p)^2}{[\uparrow \vert \;]} \underset{2p}{[\;]} $$


texts:
Is there anyone who can give me a convincing argument about the ketone, or the carbonyl oxygen in the ketone being nucleophile or not? . I really don't know what to write anymore. Everyone says something different. My instructor said that the Ketone oxygen can be protonated, thus reacting as a nucleophile. Others says that  Protonating the ketone in fact makes it more electrophilic.

Here is the molecule I'm working with (attached) and I have to mention all the nucleophilic sites - I've done that. This is the only one that really is confusing me. Hoping for some clarification.

http://imgur.com/a/20NAw


texts: Is there a simpler way to detect alcohol in a blood sample using IR spectroscopy?

texts:
I have seen all sorts of ways to detect alcohol using NIRS (Near InfraRed Spectrscopy) or FTIR, but they are all quite complicated in that they are using and analyzing a very wide spectrum. In addition, it is not clear as to the environment of where the alcohol is measured in. Some presentations are talking about measuring the OH-stretch of the RO-H in the region of 3200-3650 cm^-1.

Some related, but not very helpful questions are:

O-H infrared band dependence of alcohol concentration in water
These there is this book section which mentions various problems of published spectrum.

Is there a cheaper and more simple way to do this detection, using off-the-shelf components, like IR lasers or diodes?

I suppose "cheaper" would mean to use just one or very few frequencies, so that one doesn't have to analyze an entire spectrum.
What are these frequencies and how are they determined?

UPDATE:

Apparently the Blood Alcohol Concentration (BAC) is measured differently in different parts of the world. Just for reference:

0.1 g alcohol in 100 mL blood equals:

0.1% (U.S., Canada, Australia)
100 mg% (UK)
1 ‰ = 1 permille grams alcohol per 1 liter blood  (EU)
22 mmol/L (in hospitals) millimols alcohol per liter blood.


texts:
An unknown compound was found to react with sodium hydride with the evolution of hydrogen. The compound could not be acetylated under the normal conditions for acetylation. The compound resisted oxidation under mild conditions, and under vigorous conditions yielded only products of molecular weight much smaller than the unknown. On the basis of these facts the compound is:

  a primary alcohol
  an aldehyde
  a secondary alcohol
  a tertiary alcohol
  a secondary amine

The correct answer is (4).

From the first statement, it is clear that this compound must be an alcohol (since alcohols react with sodium hydride and produce hydrogen gas in this reaction).  I could guess that the answer was a tertiary alcohol as secondary and primary alcohols would easily oxidize, but I'm not sure what the products of the oxidized tertiary alcohol would be?

Also, why wouldn't a tertiary alcohol undergo acetylation?  I don't see any reason why it shouldn't?


texts: Electrolysis of brine with filter paper bridge

texts: What would be the problem with connecting the two dishes up with a piece of metal wire?


texts:
Nafion membrane is used as a proton exchange membrane (PEM) in fuel cells due to its selectively high permeability to hydronium ions $(\ce{H3O+})$ and water.
A permeability study was done on small organic polar molecules like 1-propanol and d1-propanol and dimethyl methylphosphonate [1] showing that those small organic polar molecules can pass through the membrane, however, I can't find anything about bigger molecules like the examples below.

Questions

Is Nafion permeable to polar organic molecules with bigger dimensions than typical solvents?
Is Nafion permeable to non-polar organic molecules?

References

Rivin, D.; Meermeier, G.; Schneider, N. S.; Vishnyakov, A.; Neimark, A. V. Simultaneous Transport of Water and Organic Molecules through Polyelectrolyte Membranes. J. Phys. Chem. B 2004, 108 (26), 8900–8909. DOI: 10.1021/jp037448h.


texts: Oxidation of Aromatic Methyl to Aldehyde by CAN

texts:
I read in my text that Ceric Ammonium Nitrate is used for oxidation of primary alcohols. But the surprising part was that, according to the book, it could oxidise aromatic methyl group to a -CHO group.
Is this actually true?


texts:
I just came across a table with interesting hybridisation schemes I have never seen before. The table is shown below. I was wondering if anyone could give me some examples of atoms in particular molecules which possess one of those weird hybridisation schemes (e.g. spd, p2d2 etc.).

 Image taken from: Shriver, D.; Weller, M.; Overton, T; Rourke, J.; Armstrong, F. Inorganic Chemistry; WH Freeman: New York, 2014


texts: E, Z designation - what to do when substituents are identical on one side of the double bond?

texts: Here, A has a greater atomic number than B, which has a greater atomic number than C. To assign E,Z designations you would divide the double bond into left and right portions and assign priorities. On the right side, A > C. However, on the left side, B = B. A (first priority on right side) is simultaneously on the same side and on opposite sides to B (first priority on left side). How would you class this compound then?


texts: What is difference between intramolecular redox and disproportionation redox

texts: I can not understand difference between the intramolecular redox reaction and the Disproportionation redox reaction. Both involve the same molecule as substrate, but what is difference?


texts: How do you identify reducing / non-reducing sugar by looking at structure?

texts:
Identifying reducing / non-reducing sugar been confusing me for a while now , I know that reducing sugar contain aldehyde or ketone group . It's easy to identify them in monosaccharides but this becomes confusing in case of disaccharides!

I fail to see carbonyl group here, How can I identify reducing / non-reducing sugar by looking at structure in picture? can anyone help me out?


texts: Misleading features of Lewis Dot Representation

texts:
Today I had an embarrassing experience when I sat to help my nephew learn Lewis' Dot Representation and realized that I actually don't get it at all. I have a physics background and always thought that the Lewis Structure in chemistry mimics the physical picture, but soon realized that it doesn't.

First of all, the "sockets" where the dots go on Lewis Diagrams do not correspond to actual physical orbitals. They are neither 4-fold symmetric, nor are equivalent (s-orbitals are spherically symmetric, p-orbitals are lobed, etc), so I couldn't give any explanation to my nephew what their physical interpretation is.

Also, I noticed that the rule for filling these "sockets" do not follow the Aufbau rule. For example, in the ground state of carbon, Nature first fills the $\ce{2s}$-orbital and just after that inserts an electron in two of the $\ce{2p}$-orbitals. In contrast, the rules of Lewis' Dot Representation say that C should have a single dot in each of its 4 "sockets", and just after they get exhausted, one starts pairing them. (I wonder how this principle explains compounds like methylene, in which carbon has its $\ce{2s}$-shell pair present... but anyway.)

All of this prompted me to ask, what is the story behind Lewis' Dot Structure and what goals Gilbert Lewis pursued when he introduced it? I guess if I learn this, I'll be able to explain its misleading features and not get embarrassed in front of a 14-year-old.


texts: Limiting the minimum percentage of oxygen in atmosphere maintained by an oxygen absorber / scavenger?

texts:
I'm aware that oxygen in the atmosphere of a sealed package can be readily removed by using oxygen absorber/scavenger such as granulated iron and sodium chloride but my understanding is that these bring the O2 content all the way down from 21% only limited by the permeability of the packaging to oxygen and the ratio of scavenger to package volume to something approaching 0%.

My question is if there is a way to formulate an oxygen scavenger that would be limited by some other processes to higher floor of say 5% to 10%... Without having to measure and calculate appropriate ratio of scavenger to package on a per use basis ?


texts:
I thought that I already know how the Electrophilic Aromatic Substitution (EArs) for Aromatic rings work but then this reaction was shown to me and I was really sure that my professors didn't bothered teaching or even mentioning to us this reaction:

In my defense, at my University, our Org Chem professors always use benzene or benzene derivative rings for demonstration of EArS so I never knew how an acylation of a five-membered aromatic ring works.

Can someone please explain to me how this reaction works?


texts:
In an article I recently submitted, a reviewer asked that I provide a concentration in μg/kg instead of ppb (parts per billion), and mentions that the later is not correct. I am not a chemist, and I thought that 1 μg/kg = 1 ppb.

Is 1 ppb equal to 1 μg/kg ? What is a reason to consider ppb as incorrect ?


texts: Reasons for existence of eutectic point for alloy systems

texts: Why does a eutectic point exist for a system of alloy ? Why is it that there is such a definite ratio of composition at which this occurs ?


texts:
If $\ce{1.84\times10^{-4}}$ moles of element A was completely reacted with element B to create $\ce{1.231\times 10^19}$ molecules of $\ce{(A3B2)_x}$ a hypothetical compound, what is the value of x?

I tried this:

$\pu{1 mol} = 6.02 \times 10^{23} ~\pu{molecules}$

$y~\pu{mol} = 1.231 \times 10^{19} ~\pu{molecules}$

$y = \pu{2.0449 \times 10^-5 mol}$

$\ce{(A_3B_2)_x} : 1.84\times10^{-4}+ {2\over 3}(1.84\times10^{-4})=3.067\times10^{-4}$

So it produces $3.067\times10^{-4}$ mol of the compound

and, $3.067 \times 10^{-4}~\pu{mol} \div 2.0449 \times 10^{-5}~\pu{mol} = 15$

And since 1 compound has 5 atoms, $15 \div 5 =3$

Therefore, $x$ is 3

I am not sure if I did this question correctly. Even if I did, is there a more efficient and organized way of solving this problem?


texts: mechanism of mechanically triggered explosion

texts:
There are several well known explosives which can be mechanically triggered. I am curious about the mechanism of such a reaction, though.

I guess one can give an easy answer when the explosive is sensitive to everything, flames and mechanical activation, too. What puzzles me is that several of these compounds, e.g. nitroglycerin or ammonium-nitrate much more difficult to trigger by simple flame. How mechanical activation is different?


texts:
I am asked to draw the most stable chair conformation of compound 1.

After doing so I am a little uncertain which of the conformations is the most stable. The most stable conformation is the one where the most bulky group is positioned equatorial. However, do I prioritize Cl over the methyl- and isopropyl-group or are the two groups more prioritized due to them being bonded to Hydrogens which take up more space than a Cl-atom. From what I have read, I would say that the chair conformation on the top is the most stable, prioritizing the methyl- and isopropyl-group. Is that correct?


texts: How to calculate and denote small uncertainties?

texts:
I am writing a report and I'm stuck on determining how to write the uncertainty.

I have this:

$$1.0 \times \left( 0.1000 \pm 0.0005 \right).$$

If I multiply the values, I need to keep two significant figures, but then my uncertainty would be beyond the correct amount of decimal points. What would I do in this case?


texts: How do I call the functional group of this alkane?

texts: Given the following chain of carbon atoms (imagine they are all saturated with the correct number of hydrogen atoms), how do I call it? 4-(dimethyl-ethyl)-octane? I'm having trouble naming the short carbon chain extending from the 4th carbon atom of the octane. Can you help me out please?


texts: What lubricant can be used for mechanical parts in a system containing diethyl ether?

texts:
I make a thermal actuator that works with the expansion of diethyl ether at its boiling point of around 34 °C. For sealing and lubrication of the polypropylene piston and barrel, I need a lubricant that is immiscible with diethyl ether and does not react with it.

I found that diethyl ether is slightly soluble in water, and that it dissolves oils. I suppose this means that many of the everyday oil- and water-based lubricants are not fit for this application (as diethyl ether will dissolve in the lubricant)?

Any other suggestions for a lubricant that can be used here?


texts: What is the purpose of subtracting the blank when constructing an analytical calibration curve?

texts:
When building a calibration curve for quantification of some analyte using any spectroscopic technique, what is the purpose of subtracting the intensity of the blank from the intensity of each point of the curve?
I can build two calibration curves using the same measurements, one plotting the total intensity recorded at each point (F) and the other plotting the total intensity recorded minus the intensity when the concentration of the analyte is zero (F-F0), both against analyte concentration.
When making a linear regression for each curve, the slope will be the same and the difference between the intercepts will be the intensity of the blank (F0). If I try to quantify an analyte in a given sample with a different matrix than the one used in the standard (different solvent, for instance) maybe the "blank of the sample" so to speak would be different than the blank of the standards (F0). In that case, the result would be equally wrong, using either of the curves, because I would either be comparing the response of the sample-F0 to analytic curve based on F-F0 or the total response of the sample to analytic curve based on F.
It would make sense to me if I could, when analyzing an unknown sample, measure an exact blank of the sample, and use this measurement to compare with the analytical curve built using F-F0. Then I would be comparing two intensities associated only with the analyte, but that is't possible.
Am I missing something? Does subtracting the blank helps in any way when the objective is to quantify the analyte in samples?
I've checked two different undergraduate level analytical chemistry books and found no answer. They just say it is done this way.


texts:
I'd like to programm a toy chemical reaction program. Rough simplifications that deviate from industry and academia are totally acceptable. Not very educationaly accurate, but fun.

Are there methods to calculate rate of reaction for dozens and hundreds of reactants in a closed system?
Or I can blatantly use original r = k(T)[A][B] for every pair of reactants while selectively ignoring presence of other molecules?

Or should I use something else to evaluate what will happen with hundred of reactants after two seconds?

Sample gas composition below:


texts: nucleophilic aromatic substitution reaction

texts: I am in a project in organic synthesis writing about nucleophilic aromatic substitustion reactions. I cant´t figure out why the nucleophile (benzylmethylamine) attacks the chloro-binded carbon when bromide is a better leaving groupe? (See picture)


texts: I am studying fragmentation patterns in mass spectrometry and I am confused about why alpha cleavage occurs. Why does the carbon-carbon bond adjacent to a functional group break instead of the bond between the alpha carbon and the fucntionalized moiety?


texts:
I need to calculate the angles between CCC, CCH, HCH in the following molecules:

ethene ($\ce{H2CCH2}$),
propa-1,2-diene ($\ce{H2CCCH2}$), and
buta-1,2,3-triene ($\ce{H2CCCCH2}$).

If I'm not mistaken, the Lewis structures of all of these molecules have the carbons in the middle, connected by double bonds to each other, and the hydrogen atoms connected to the carbons in the edge. For example:

H           H
 \         /
  C = C = C
 /         \
H           H

The carbons at the edge are $\mathrm{sp^2}$ and the middle carbon is always $\mathrm{sp}$ .

This means that the angle CCC is always 180°. But how can I determine the angles CCH, HCH?

In addition, how can I determine if the hydrogen atoms in the three molecules lie on the same plane?


texts: "Proof" that the chemical potential is less than zero for irreversible material changes

texts:
From Levine's Physical Chemistry 6th edition:

In a closed system, $\mathrm dG = -S\,\mathrm dT + V\,\mathrm dP$ not only applies to constant composition but also reversible changes in composition (page 116).
For an irreversible process: $\mathrm dG = -S\,\mathrm dT + V\,\mathrm dP + \mu\,\mathrm dN \lt -S\,\mathrm dT + V\,\mathrm dP$, thus $\mu\,\mathrm dN \lt 0$ (page 130).

For 1), why do we even bother with the chemical potential for closed systems if we can just find a reversible path in which 1) applies?

For 2), I thought that although $\mathrm dG = -S\,\mathrm dT + V\,\mathrm dP + \mu\,\mathrm dN$ can apply to irreversible processes, you had to calculate a reversible path. If so, that would mean that the $-S\,\mathrm dT$ on the left was calculated for a reversible path and the $-S\,\mathrm dT$ on the right was calculated for an irreversible path and they wouldn't cancel.


texts: Why does an anion not only bind to a single cation?

texts:
When $\ce{Na}$ binds with $\ce{Cl}$ to form $\ce{NaCl}$, why does the Na bind with multiple $\ce{Cl}$'s and not only one? A Na-ion is positively charged due to donating an electron and a $\ce{Cl^-}$ion is negatively charged due to accepting an electron. That's why they bind. But salts form a grid where each Na-ion binds with 6 $\ce{Cl^-}$ions and vice versa.

Shouldn't be the Na-ion already be "used" after binding with a $\ce{Cl^-}$ion? Or does it stay charged and attracts all ions that are negatively charged?

I hope someone can help me to understand.


texts: Rust removal with phosphoric acid created more rust

texts:
I wanted to remove the rust on numerous steel parts with phosphoric acid. After removing all the grease in trichloroethylene, I put my parts into a 50 % solution of phosphoric acid ad 40 °C for 5 minutes.

When all the rust was removed, I rinsed the parts with clean water to remove all the acid. At that time, I decided to not neutralize the solution in $\ce{NaOH}$.

In about 5 minutes all the cleaned parts exposed to air rusted. The parts into the water became greenish (I guess it is $\ce{FePO4}$ residue).

I would like to understand why I get this ultra fast oxidation and how I can prevent it to occur.


texts: It is observed that actinides do not exhibit +2 oxidation state, contrary to that of some of the lanthanide elements. Why?


texts:
Let's assume a mixture which can be heated without decomposing. This site explains that while pure substances have a sharply defined melting point and boiling point, mixtures tend to have a melting range. But what about the boiling point of mixtures? Is it always a point, always a range, or sometimes a point and something a range? If it is "sometimes", is one of the cases the rule and the other the exception, or are both pretty common?

To keep the question simple, we can stay with atmospheric pressure.


texts: Question related to Hydration of Alkynes

texts: There will be Markovnikov addition of water and hence —OH will be added to the carbon with triple bond having less number of hydrogen and —H will be added to the one having more number of hydrogen. Then the adduct will tautomerise to form the product corresponding to option A but the answer given is option B. Where am I going wrong?


texts: Relationship between Gibbs free energy, enthalpy, entropy and rate of reactions

texts:
I'm having a little trouble constructing the bigger picture of chemical reactions.

From the collision theory we know that molecules react if: 1) they collide 2) they collide bearing a sufficient amount of energy to surmount the activation energy and collide at a specific geometric orientation.

From the relationship between Gibbs free energy, enthalpy, entropy and temperature we know: $\Delta G = \Delta H - T\,\Delta S$,
and that a reaction is only thermodynamically favored when $\Delta G < 0$. And even when $\Delta G < 0$ the reaction may still not occur at a measurable rate because it has too high an activation energy.

From the Arrhenius equation we know: $k = A ~\mathrm e^{-E_\mathrm a / (RT)}$

Linking all these together:
1. Reactions only occur when particles can collide with each other.
2. Colliding particles will only react if they bear sufficient energy (can be increased through temperature and/or adding other external energy sources) and have correct orientation (chances can't be increased?).
3. Only particles in thermodynamically favored reactions have enough energy to overcome $E_\mathrm a$ and so will spontaneously occur without external energy applied. But they may occur extremely slowly if they have a very high $E_\mathrm a$ (according to the Arrhenius equation).

Is this reasoning correct?


texts: In halogenation of ethene using bromine for example, why does the lone pair of bromine attack the C atom?

texts:
In the presence of the electron rich (pi bond) of ethene, the bromine molecule becomes a temporary induced dipole, one end being electron deficient and acting as the electrophile. (The pi bond in) ethene attacks the electrophile.

At the same time, one of the lone pair of electrons in bromine attacks one of the C atom. Why does this happen?

Normally, I'm familiar with the same process, but with the carbocation being formed without the lone pair of electrons of bromine attacking the other C atom:

Does this have something to do with resonance as shown by the diagram below?


texts: Dissociation of zinc anode during electrolysis

texts:
Example electrolysis setting:
Cathode: copper
Anode: zinc
Electrolyte: dilute aqueous sodium chloride [$\ce{NaCl(aq)}$]

During electrolysis, zinc is more reactive than copper, hence electron flows from zinc anode to copper electrode.

At the zinc anode:
$\ce{Zn(s)->Zn^2+ (aq) + 2e-}$
Q: What is this process known as?
("Dissociation" is usually applied for salts that dissolve to form mobile ions, and "discharge" is usually used for ions in the electrolyte itself that gain/lose electrons. Hence, what would a proper term be?)

When the zinc anode "dissociates" in the  electrolyte, $\ce{Zn^2+}$ ions are formed.
Q: Do the $\ce{Zn^2+}$ ions remain "isolated"?
(Because $\ce{H+}$ions are selectively discharged at the copper cathode, this leaves the $\ce{Zn^2+}$ions  $\ce{Na^+}$ions are bonded to  $\ce{Cl-}$ions, so does the  $\ce{Zn^2+}$ions form just move into the electrolyte just like that, with an unstable electronic configuration?)


texts: Why water can't mix with oil or cooking oil?

texts: Why water can't mix with oil or cooking oil (both saturated and unsaturated)?


texts: You spend a lot of time in chemistry talking about molecular amd ionic compounds, but I'm interested in what you can do with metals only. What is the difference between the properties (physical & chemical) of pure metals and those of alloys? Is it possible to predict the properties of alloys before making them? Can you make alloys with mercury?


texts:
Question: Given that $\ce{Zn, Hg}$ are in the same group, how to explain that $\ce{Hg(CH3)}$ is stable but $\ce{Zn(CH3)}$ is unstable and $\ce{Hg(CH3)Cl}$ is stable? $\ce{Hg(CH3)}$ seems to have an unpaired electron and hence is unstable.

Background and Thoughts
Some similarities of zinc and mercury: All of $\ce{M(CH3)Cl, M(CH3)2}$ and $\ce{MCl2}$ are stable, where $\ce{M=Hg, Zn}$.
For the causes of the differences of the stabilities of $\ce{M(CH3)}$, I can only think of the following reasons:
1. Mercury ion is soft and zinc ion is not very soft. $\ce{CH3}$ is very soft. According to the HSAB theory, methyl mercury is stabler than the other one. I'm not very sure of whether HSAB theory can be applied here.
2. Zinc is reactive while mercury is stable.
3. Perhaps it is related to $d-\sigma$ conjugation?

For why both $\ce {Hg(CH3)}$ and $\ce{Hg(CH3)+}$ are stable, I think maybe the reason is strongly related to the fact that $\ce{Hg-C}$ bond is covalent.


texts: Relating properties and structures of polymers

texts:
Why would it be more favorable for a polymer designer to design copolymers with irregular chain structures, rather than design homopolymers?

Hint: Discuss intermolecular bonds

I understand that copolymerization allows for greater variation in polymers and there properties, but am unsure how exactly to relate this to intermolecular forces. Would it also depend on the intended use of the polymer?


texts: Replacing Salt Bridge with Platinum Sheet

texts:
What would happen, if in a galvanic cell, the salt bridge is replaced by an inert platinum sheet?

Would charges accumulate on the sheet? Would the cell still work, and produce less emf than earlier, or stop working at all?

P.S.
I know why a salt bridge is necessary for the functioning of a galvanic cell - my question is rather specific to what would happen if I were to use a platinum sheet instead, and why we can't use it.
(Hence, not a duplicate.)


texts: Explanation for increasing wave number trends for hydrocarbons

texts:
At my university, we had an organic chemistry exam question that stated,"The trend in the values of the ir absorbtions for the c-h bonds of methane ($\ce{CH4}$: $2995\,\mathrm{cm}^{-1}$), (ethylene: $3080\,\mathrm{cm}^{-1}$), and (acetylene: $3305\,\mathrm{cm}^{-1}$) can be explained by...

The answer was " by the increasing bond strength of the carbon-carbon single, double, and triple bonds. I thought the correct answer was  "increasing s character of the carbon atoms". Could I get an explanation as to why the first response is valid?

Thanks!


texts: How can we tell if an ion is amphiprotic

texts:
If I had the following ions:
$$\ce{HCO3^-}$$
$$\ce{H2PO4^-}$$
$$\ce{CH3COO^-}$$

Which ones would be amphiprotic?

Looking at my $ K_A$ chart, it looks like each ion is formed by the disassociation of weak acids, so It looks like all of them are amphiprotic because they could all technically act as a bronstead-lowry base.

The answer is the first two ions, but why?

Thanks for answering :)


texts: What's an appropriate ligand for Pd-Ag redox?

texts:
I want to reduce palladium with silver (in cellulose): $\ce{Pd^{2+} + 2Ag->2Ag+ +Pd}$. What is a good ligand and spectator ion for both metals? (The pH is not critical.) Ones I have considered:

$\ce{[Pd(H2O)4](NO3)2}$: Unstable; hydrolyzes to insoluble hydroxides over time, except in strong acid, where the nitrate will oxidize the silver.
$\ce{[PdCl4]^{2-}}$: Will precipitate $\ce{AgCl}$.
$\ce{[Pd(NH3)4]^{2+}}$: $\ce{[Ag(NH3)2]}$ can precipitate explosive $\ce{Ag3N}$.
$\ce{[Pd(en)2}]^{2+}$, other common organic ligands: These are all seem to be very poisonous.
Glycine-$\ce{(NO3)-}$: Maybe. I can't find any stability constant data.
$\ce{(NH4)5[Pd(S2O3)4]}$: Definitely stable with silver, although I can't find a stability constant for palladium. EDIT: "This complex is not thermodynamically stable, and S-bridged oligomers are ultimately formed" according to [1], although maybe it could be stabilized somehow.
$\ce{(NH4)+}$-$\ce{(SCN)-}$?

Are there any reasonable candidates that I haven't thought of? Any sources for stability constants, especially for thiosulfate?

[1] Thiosulfate Complexing of Platinum Group Elements.
Elizabeth Y. Anthony, Peter A. Williams. https://pubs.acs.org/doi/abs/10.1021/bk-1994-0550.ch033


texts: Comparing basic strength of acetamidine and 2-imidazoline

texts:
My approach:

Conjugate acids of both molecules have the same number of stable resonance structures. So no conclusion from here.
Conjugate acid of 2-imidazoline will have negative inductive on the lone pair donating nitrogen by the other nitrogen atom. Since this effect is absent in acetamidine, acetamidine should be a stronger base.

Is the above approach right? Can ring strain affect the basic strength of 2-imidazoline in any way? Should I consider any other factor too to make the right comparison of the basic strength of the above two molecules?

Related Questions:

Comparing basicity of imidazole and 2-imidazoline

How to predict the basicity of organic amines?


texts: What is the most likely reaction between minocycline and tramadol in physiological conditions?

texts:
Minocyline (left) and Tramadol (right) are two commonly prescribed medications containing typical organic functional groups.

What would an expert chemist surmise as the first or most-likely reaction involving these drugs in the human body, if any? For example, in the stomach, in a highly acidic environment?

I realize the chemistry here is obviously complex, so an answer excluding biological components is fine. e.g. what would these compounds do in a solution of $\ce{HCl}$ alone?

I'm not an organic chemist, but my guess is that $\ce{HCl}$ can protonate an amine to encourage some kind of reaction.

In any case, some research has shown that the drugs may have a synergistic effect for pain relief: https://www.ncbi.nlm.nih.gov/pubmed/22964800.


texts:
It is given in my book that the structure in figure-1 is the unit cell of hcp structure.
So why then is the structure in figure-2 not the unit cell as we can repeat the structure in figure-2 to get the original hcp structure?
Also the structure in figure-1 is not a Bravais lattice so how then can it be called a unit cell?


texts: Which one really determines how people feel. Heat or temperature?

texts: We use water to cool down some machines because water has high heat capacity, which means it takes more energy to increase 1 degree. Heat transfer occurs only when temperature is different. We cool down the machine because we don't want it to be too hot, but what does the hot mean? The temp or the heat? When we touch water and another liquid at the same temperature but contain different heat. We feel the heat or the temp?


texts:
I have stumbled upon these instructions on how to create $\ce{ZnO}$ nanoparticles.
I am interested in making a DIY ink, for use with a parallel metal plate pen and a piezo-actuated microdrop nozzle.
My question is:
What is a reasonable way of controlling the viscosity of such an ink? Is it possible to replace the water with a mixture of water and isopropanol, for example?


texts: Net ionic equation with only aqueous ions

texts:
When you turn a balanced equation into a net ionic equation, you ignore all the ions that are spectator ions (aqueous on one side as well as the other). You only write the solid and the aqueous ions that form that solid.

So, what happens when you try to write a net ionic equation if ALL the ions are aqueous? Would you write down every ion in the reactants/products, or write nothing?


texts: Error with explaination of shape of weak acid strong base titration?

texts:
I have read the other posts on the same question posted on chemistry exchange such as this one: Shape of Weak-Strong Acid-Base Titration

and here : What does the small, steep curve at the very beginning of a weak acid strong base titration curve come from?

However, I don't see why their explanation is valid. They typically explain the little dip at the start and the following plateau as a result of creating a buffer solution. When a strong base is added to a weak acid, as more $\ce{OH-}$ is added this will react with the acid molecules in solutions and form more of the conjugate base, forming a buffer solution which I do agree with.

$$\ce{CH3COOH + H2O <=> H3O+ + CH3COO-}$$

However, I do not see this is useful. Isn't having the conjugate base only useful if you want to add in more $\ce{H3O+}$ but we are not! As we only add in $\ce{OH-}$ how is having buffer capacity of $\ce{CH3COO-}$ in the other direction useful (as $\ce{CH3COO-}$ and $\ce{OH}$ don't react)? I agree this is a buffer, but how does the reverse reaction help at all? This buffer doesn't seem like it would help to reduce pH changes


texts: Why does crystalline solids have well defined 3d geometry

texts:
Crystalline solids have well defined geometry because the intermolecular forces are uniform throughout the solid unlike amorphous solid where it varies from place to place.

But still the question hold why does some solids have this property like why $\ce{NaCl}$ forms a crystalline solid but not glass or something else.

I thought it is because crystalline solids are ionic but diamond is an counterexample among many.

Question :

Why does some solids have crystalline structure while others don't ?


texts: How much more salt can I dissolve in hot water compared to cold water?

texts:
Hot water increases not only the speed of solubility but also the amount.

I don't know whether this is for all materials in water, apart from salt.

But, if this is the case, what causes hot water to dissolve more salt (or other solutes)?


texts: Question about the role of d-orbitals in polarisation

texts:
I know that, although many elementary books say that d-orbitals are involved in the bonding of hypervalent main group compounds period 3 or higher such as the sulfate ion but in reality they are only barely, if at all, involved in bonding.

The question is- is it true that "the d-orbitals are not directly involved in bonding but rather in polarisation" and what does that exactly mean? I saw that statement on the comment sections of a post of mine but don't know the proof.


texts: Stable physiological buffer to make NAD+ solution

texts:
I was wondering what would be the most stable physiological buffer for nicotinamide adenine dinucleotide (NAD+), for potential storage as frozen aliquots - 6 months stability or around there would be ideal. A buffer that is physiologically compatible is essential (e.g. suitable for in vivo use).

I would also be interested in potential solubility limits. I've seen reports of people achieving up to 200 mg/mL solutions, but others stating that they made 50 mg/mL.

I have read from Sigma that

  NAD is soluble in water at 50 mg/mL, and that an aqueous solution may be made by adjusting the pH using NaOH or a sodium bicarbonate buffer.

Does this not imply that a carbonate buffer would be usable? They then also state that

  As per external source information β-NAD is soluble in PBS pH 7.2 at 10mg/ml.

This to me implies that a phosphate buffer would be suitable. However, they finally said the following:

  Aqueous solutions between pH 2 - 6, stored as single-use aliquots at -70 °C, are stable for at least 6 months. Neutral or slightly acidic solutions are stable at 0 °C for at least 2 weeks. Solutions are rapidly degraded upon heating and are very labile in alkaline solutions, especially in the presence of phosphate, maleate, or carbonate.

The last part of this sentence makes me think that phosphate or bicarbonate buffers would thus be inappropriate. I'm not sure why they say conflicting things, and they were not able to provide me with any further information.

They do confirm that neutral or slightly acidic pH should be fine for long-term storage.


texts:
I have an exercise and I have to find the formula of those ions:

Arsenate ion
Perbromate ion
Selenite ion
Hydrogen Tellurate ion

The solution tells: $\ce{BrO4-,\space SeO3^{2-}, AsO4^{3-}, HTeO4^{-}}$.

My question is, how do I get to those results and how do I know their charge to be 1-, 2-, 3-, and 1-?


texts: Distillation of diethyl ether and tetrahydrofuran

texts:
In the lab, I'm working in over summer, there is a set of solvent stills.

Most of them use $\ce{CaH2}$ as a drying agent, however ether and THF use Na and K respectively in the presence of benzophenone.

What I don't understand is why the ether still uses Na, whilst the THF uses K. Equally, I'm not sure what the purpose of the benzophenone is — it makes the stills blue, but none of the other solvents (DCM, toluene, triethylamine) have this property.


texts: Do metals react with ammonia gas (not liquid phase)?

texts:
In my chemistry notes I have two chemical equations as follows:

$$
\begin{align}
\ce{2 NH3(g) + 6 Li(s) &-> 2 Li3N(s) + 3 H2(g)}\tag{R1} \\
\ce{2 NH3(g) + 2 Na(s) &-> 2 NaNH2 + H2(g)}\tag{R2}
\end{align}
$$

Before digging into the reasons for different products in two equations, when I searched in the internet to find the clear picture of what are the metals (like alkali metals, alkaline earth metals, transition metals) that can react with ammonia in gaseous form, I could only find metals dissolving in liquid ammonia.

I would be grateful if someone could tell that metals don't react with gaseous ammonia, or, if it reacts, what are the metals those react with gaseous ammonia? And are there any conditions needed for the reaction (like heat)?


texts: How to estimate the equilibrium constant of the reaction between NaF and HCl

texts:
Since $\ce{HCl}$ is more acidic than $\ce{HF}$, the left hand side of a reaction has a stronger acid than the right hand side.

Since $\ce{NaF}$ is more basic than $\ce{NaCl}$, the left hand side has a stronger base relative to the right hand side.

$$\begin{align}\text{Stronger Acid/Base} & \ce{->} \text{Weaker Acid/Base}\\ \text{(Less Stable)} & \ce{->} \text{(More Stable)}\end{align}$$

So shouldn't the equilibrium constant be larger than $1$?

My textbook says the equilibrium constant is less than $1$.


texts: What are the Waves Modeling when Referring to the Atomic Orbitals

texts:
It is taught that the orbital shapes derive from wave functions with different numbers of nodes. For example, the "s" orbital comes from a wave that has one node. But what are the waves modeling? A light wave for example is showing a relationship between an electric field and magnetic field. What relationship does an atomic orbital wave show? In other words, if you were to label the axes, what would the labels be?

Thanks!


texts: Can vapour pressure be used to 'generate' work for free?

texts:
Given a bottle of water, a closed system, some of the water molecules in the liquid phase will have enough energy to escape that phase, forming water vapour, contributing to vapour pressure.
Now consider the simple setup below:

Water is used as an example, does not have to be water. The work for pumping water is converted to gravitational potential energy of water. But the system seems to be capable of doing extra work on the mass while retaining that gravitational potential energy gained. Where does this capability come from? Doesn't the existence of this capability already violate First Law?
P/S: I know the pressure increment due to formation of vapour will be small, but just because it is small and so negligible does not mean that the 'minor violation' of First Law can be overlooked, so I believe something must have been wrong with the argument above.


texts: Does sodium ethoxide (sodium ethanolate) have a boiling point, or does it decompose?

texts: According to Wikipedia, $\ce{C2H5ONa}$ melts at 260°C, but no boiling point is given. What will happen if $\ce{C2H5ONa}$ is heated further?


texts: What does the process of prilling something like, say, calcium nitrate, involve? Do you need other chemicals to prill the substance?


texts: (Effective) number of molecules interacting with light to produce optical activity

texts:
The question is: How can I get a sensible and concrete (not relative) value for the number of molecules light has interacted with to cause an optical activity phenomenon?

Specifically, my issue in answering the question is that although initially I thought of calculating the number of molecules contained in the volume that the light is occupying, this does not seem correct to me. The reason is that the optical activity is independent of the volume, it only depends on the path length but not the transverse area. So it seems to come down to some kind of "effective" number of interactions, which is invariant to the transverse spread of the light.

Thanks for any help you can give me!


texts: why disproportionation of free radicals does not happen in kolbe's electrolysis if we use secondary or tertiary carboxylic salt as substrate?

texts:
In notes given by chemistry teacher, for secondary carboxylic salts the final products are alkane and ester.

but i guess, as the reaction intermediates involve secondary/tertiary free radicals, some radicals should also go under disproportionation reaction and produce alkene.

why this doesn't happen?


texts: Aluminium isopropoxide electronic structure

texts:
From Wikipedia:

A tetrameric structure of the crystalline material was verified by NMR spectroscopy and X-ray crystallography. The species is described by the formula $\ce{Al[(μ-O-i-Pr)2Al(O-i-Pr)2]3}$. The unique central $\ce{Al}$ is octahedral, and three other $\ce{Al}$ centers adopt tetrahedral geometry. The idealised point group symmetry is $D_3$.

I can understand that the 3 external $\ce{Al}$ atoms can be (inaccurately?) described as assuming an ${sp^3}$ hybridization. With 4 bonds per $\ce{Al}$ atom, the valence shell is complete, following the octet rule. This too may deserve some additional attention, since $\ce{Al}$ formally has only 3 electrons available for bonding, yet here it forms 4 bonds. At least one of these is dative, I assume?
I'm less clear on the central $\ce{Al}$ atom. My initial instinct was to invoke the ${sp^3d^2}$ hybridization. But this answer re $\ce{SF6}$ suggests that may not be the case. There are clearly similarities to the $\ce{SF6}$ case, but surely, also some differences? After all, $\ce{Al}$ is not $\ce{S}$.
In short, what is the electronic structure of the four $\ce{Al}$ centers?


texts:
What is the correct way of writing the mechanism for substitution at the sulfur atom of thionyl chloride:

Should one write the cleavage of the $\ce{S-O}$ π bond? The argument for the first option is that $\ce{S}$ is already tetrahedral and direct displacement could occur. The argument for the second option is that the π bond will be cleaved first as it is the weakest. Another possibility would be the formation of a tetravalent sulfur species (like the $\mathrm{S_N2}$ substitution at silicon). Is there any experimental or computational evidence regarding the matter?


texts:
The specific gravity of a $50\%$ aqueous solution $\ce{NaOH}$ is $\pu{1.5298 g cm-3}.$
To my understanding, the $50\%$ means $50$ mass fraction $w,$ i.e. $\pu{500 g}$ $\ce{NaOH}$ in $\pu{500 g}$ $\ce{H2O}:$
$$w(\ce{NaOH}) = \frac{m(\ce{NaOH})}{m(\ce{NaOH}) + m(\ce{H2O})} = \frac{\pu{500 g}}{\pu{500 g} + \pu{500 g}} = 0.5.\tag{1}$$
However, when I try to calculate the density of that solution I end up with
$$
\begin{align}
\rho(\ce{NaOH}) &= \pu{2.13 g cm-3}; \\
\rho(\ce{H2O}) &= \pu{1.00 g cm-3}.
\end{align}
$$
$$V = \frac{m(\ce{NaOH})}{\rho(\ce{NaOH})} + \frac{m(\ce{H2O})}{\rho(\ce{H2O})} = \pu{234.74 cm^3} + \pu{500 cm^3} = \pu{734.74 cm^3},\tag{2}$$
$$\rho_\text{sln} = \frac{\pu{1000 g}}{\pu{734.74 cm^3}} = \pu{1.361 g cm-3}.\tag{3}$$
What am I missing here?


texts: Twisting stereoisomers with rings to determine R/S

texts: I know that if the smallest atomic number group is not in the back, we can twist the molecule so that it is in the back and then determine if it is R/S (Left image). But if the chiral center is attached to a ring, can we still simply twist the molecule (right image)? If so, how? Or is there another way to make the smallest atomic number group go to the back for molecules with rings?


texts: Why is an alkoxide released instead of hydroxide in the attack of trialkyloxyborane by hydroxide?

texts:
In the mechanism of a hydroboration-oxidation, the oxidation part includes a nucleophilic attack of a hydroxide on a trialkyloxyborane ( $\ce{B(OR)_3}$ where $\ce{R}$ is an alkyl group).

It creates a tetrahedral intermediate consisting of a negative center of boron with four groups attached to it (the hydroxide nucleophile and the three alkoxides). This step is followed by the loss of an alkoxide as the leaving group. However, to my understanding, the alkoxide is a stronger base than the hydroxide. Thus, why doesn't the nucleophilic attack fail?

Edit: Is it because of steric comparisons between the size of the alkoxide versus the hydroxide (since boron is a relatively small atom)?


texts:
Starting with benzene, describe the synthesis of 2-phenylethan-1-amine providing all the reagents and conditions.

I am not really great at organic chemistry and my knowledge is pretty limited.

I am currently thinking of forming toluene by Grignard reagent and then reacting with $\ce{Cl2}$ to form benzyl chloride. Then react with sodium cyanide to form benzyl cyanide and then react it with $\ce{HCl}$ and $\ce{H2O}$ to form an amide. Then reduce it with $\ce{LiAlH4}$ to form the compound.

I am not sure if that is correct as it seems a bit complicated for the synthesis of a seemingly simple compound. Also I am not sure on the exact conditions for the chlorination step.

I was also thinking of acylation with ehtanoyl chloride followed by Wolff-Kishner reduction to form ethyl benzene. However I am not sure on how to from the $\ce{NH2}$ group.


texts: Calculate concentration gradients in FPLC

texts:
Our FPLC works with two solutions:

A: 20 mM Tris.HCl, 0.2 M NaCl, pH 7.8
B: 20 mM Tris.HCl, 1.6 M NaCl, pH 7.8

I'm interested in sample volume from 102 mL to 117 mL. The FPLC will have a linear concentration gradient: At 24 mL it will be 75% A and at 144 mL it will be 5% A (the rest is filled up with B).
For visualization, I made a graph (y = -7/1200*x + 0.89):

Now, I have a sample with the whole output between the two indicated points (102 mL and 117 mL, so I have 15 mL in my tube) and would like to calculate the NaCl concentration.


texts: Besides alpha, beta, and gamma, are there any other types of radioactive decay? If so, what are they? Is there any type of radioactive decay that is more powerful than gamma?


texts: Reaction intermediates of MnO2 catalyzed H2O2 decomposition reaction

texts:
Manganese dioxide catalyzes the decomposition of hydrogen peroxide to water and oxygen gas.

But what are the intermediates in this catalyzed reaction?


texts: Why doesn't the acetic anhydride moeity react with the nucleophilic carbonyl oxygen of salicylic acid?

texts:
I know that salicylic acid with acetic anhydride under acidic conditions gives acetylsalicylic acid (aspirin). But my question is, why is it that post the protonation of carbonyl oxygen of acetic anhydride as mentioned here, the nucleophilic carbonyl oxygen of the the $\ce{-COOH}$ group doesn't attack the delta postive charge on the carbonyl carbon of the protonated carbonyl group?
What makes the phenolic oxygen more nucleophilic than the carbonyl oxygen?


texts:
Why do we get isoproyl benzene on treating benzene with 1-chloropropane instead of n-propyl benzene?

Is it because of Markovnikov's rule?


texts: What is the region of this wavelength (462 nm)?

texts: My lecturer said 462 nm is infrared region. I think the wavelength is visible light. Which region is the correct one? I need confirmation about this one.


texts: What is the chemical composition of the human body?

texts: What is the average percent composition of each element in the average human body?


texts: Difference between internal energy of combustion and enthalpy of combustion?

texts:
I am having real trouble understanding the first law of thermodynamics and I think the question, below, highlights most of my issues:

1) (a) A bomb calorimeter was calibrated by igniting a $0.825\ \mathrm{g}$ sample of benzoic acid in the presence of excess oxygen. The heat given out made the temperature of the calorimeter rise by $1.940\ \mathrm{K}$ from $298\ \mathrm{K}$. The internal energy of combustion of benzoic acid is $-3251\ \mathrm{kJ\ mol}^{-1}$. Calculate the heat capacity of the calorimeter.

(b) In two separate experiments in the same apparatus, $0.498\ \mathrm{g}$ of fumaric and $0.509\ \mathrm{g}$ of maleic acid (both of RMM 116) were ignited and gave temperature rises of $0.507\ \mathrm{K}$ and $0.528\ \mathrm{K}$ respectively. Use the heat capacity of the calorimeter, calculated in (a), to calculate (i) the molar internal energy of combustion, (ii) the molar enthalpy of combustion, and (iii) the molar enthalpy of formation of fumaric and maleic acids. Comment on the difference. The standard enthalpy of formation of water is $285.8\ \mathrm{kJ\ mol}^{-1}$ and of $\ce{CO2}$: $-393.5\ \mathrm{kJ\ mol}^{-1}$.

Part (a) was fine - the heat capacity at a constant pressure = change in internal energy/temperature change. Then divide by number of moles.

Part (b) is where I struggle conceptually. I got the answer correct but only by following lecture notes. Sticking with just fumaric acid because there's no point talking about both. It's easy to find the molar change in internal energy using the constant volume heat capacity ($-1338\ \mathrm{kJ\ mol}^{-1}$).

However, to find the molar enthalpy change, the change in $H = U + pV$. but since $\ce{pV=nRT; H=U+nRT}$ where n depends on the change in the number of gaseous moles from products to reactants - in this case +1. So $H = U + RT$ giving $-1336\ \mathrm{kJ\ mol}^{-1}$ (less exothermic).

Firstly: Why are the values negative. If the system is the fumaric acid/products of reaction then surely there is an increase in internal energy because the particles will be moving faster after the bonds have broken. (Am I right in thinking that the system is the chemical)?

Secondly: Why is the enthalpy value less exothermic? (I have a very poor grasp for what enthalpy is especially in a situation like this).

Any help with answering my questions or helping me with this concept would be greatly appreciated. Also, do you know any good books/videos I could watch to help me undertand?


texts: Are matrices a good way to do stoichiometry?

texts:
I was never taught in school to use matrices to balance my equation in stoichiometry. But I recently started to review my chemistry and, as I have taken linear algebra, I was suddenly struck by the idea this would be a really efficient way to balance equations. It might save me from making a lot of errors.

Are matrices a common tool for chemists when balancing equations? Does anyone have a good reference for learning about this?


texts:
I am minimizing energy of butane on the CHARMM Force Field and I am confused on how to go about getting a uniform unit for each different PE  as in the potential energy for bond, angle, torsion, VDW, ES of butane. For instance if you compute the angle PE you will be using angles vs bond length PE which will be in Ångstrom. I am confused on how to set everything within the same units or parameter.

Also I am programming this in python using numerical methods and will not be using a simulator.


texts:
For some DFT calculations I performed with localized (Gaussian) basis sets, I wonder how the basis sets I used are properly named. The names I could gather are:

H, C and O: 6-311G(d,p)
Al: 8-511G*
Ga: 86-4111d41G

(They all come from this website.)

However, I am not sure that the above names are consistent. Specifically:

Shouldn't I write 6-311G** instead of 6-311G(d,p), for consistency with 8-511G*?
86-4111d41G looks weird to me, but I don't know how it could otherwise be named. My knowledge of basis sets naming conventions didn't really cover anything beyond the third period of the periodic table!


texts: Why isn't the ion-product constant the sum of the molar concentrations of H+ and OH-?

texts:
The Chemistry texts I have present the ion-product constant as:

$$K_\mathrm w= 1.0 \times 10^{-14} = [\ce{H+}][\ce{OH-}]$$

Additionally I'm told that this constant at (25 °C) is an equilibrium. As one concentration rises, the other declines.

It seems easy to imagine a constant as a sum which the $[\ce{H+}]$ and the $[\ce{OH-}]$ concentrations add up to in a mixture but it's very difficult for me to grasp the idea that they are a product of multiplication.

What am I missing here?


texts: Ka relating to Dissociation of Weak acid and Water

texts:
I am studying $K_a$ currently and there is a passage in the book that doesn't appear to make sense.

It states that from the equation

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

that $$K_a = \frac{[H^+][A^-]}{[HA]}$$

The following passage says When dealing with weak acids, you can assume that dissociation of the acid is much greater than the dissociation of water.

It continues to say that you can assume all the H+ ions come from the acid.

hence $$K_a = \frac{[H^+]^2}{[HA]}$$

What I don't understand is the dissociation of water.

The book gives the equation of dissociation of water as the following -

$$\ce{H_2O(l) + H_2O(l) <=> H3O+ + OH-}$$

but where does the H+ come from from this dissociation - it's made a Hydroxonium ion?

Is it because the $H_3O^+$ can act as the conjugate acid and release the proton?

Please help!


texts: How is the change in Gibb's free energy a condition for spontaneity for reactions not happening under constant pressure conditions?

texts:
According to what I have studied, the change in Gibb's free energy is only a condition for spontaneity for processes happening at constant pressure and temperature conditions.

Consider a reversible reaction happening in a closed vessel at a constant temperature.
We check the feasibility of the reaction at any instant using the following equation:

$\Delta G = \Delta G^{.} + RT\ln(Q)  $

As the reaction happens, the partial pressures of each gaseous component will keep on changing as well as the total pressure. Then how can we use Gibb's free energy for checking spontaneity?


texts: Why does the definition of ionisation energy only include gaseous atoms?

texts:
I know that in physics there is thermionic emission and the photoelectric effect. These are both method of removing electrons. I think these affects are only for metals due to their de-localized electrons.

So why do they say that you can remove the valence electron of a gaseous atom? Can you not do this with atoms in their solid or liquid state, and does being a metal, non metal or metalloid affect this?


texts: Which silver halide is the most soluble?

texts: Halides are group 7 elements. They generally have a low melting and boiling point. They are highly reactive. Silver chloride and silver bromide are not soluble in water. So they will be precipitates. However, I do know that they have varying solubilities. So, they will form different amounts of precipitates. I want to know why they have different solubilities and which is the most soluble halide.


texts: When are all cannabinoids infused into grape seed oil using non-decarboxylated, dried plant matter?

texts:
I am unsure which is the correct terminology, infusion or extraction? For all practical purposes I will continue using infusion here. (What is the difference between the two?)

When making the infusion1 I'm using a ratio of 2 oz of dried, but not decarboxylated plant matter to 1 quart of grape seed oil. Any brand will work. The plant matter mainly consists of the buds and colas. These have gone through the curing phase already and are dry.

I put the plant material in the oil inside of a small 1.5 qt crockpot. The last time I did this, I let the crockpot sit on high for 8 hours before switching to low for 3 days (72 hours).
A lot of tutorials and online videos will say leave it sit for 4, 8, 24, or all the way up to 72 hours and more.
How long will it actually take until most cannabinoids are infused into the oil, without infusing other, unwanted compounds like chlorophyll?

I'm assuming that there is a breaking point where the plant matter is done decarboxylating, and the oil has extracted all of the cannabinoids.

I've done this kind infusion using coconut oil and I didn't get the same potency as when I did the infusion with grape seed oil. What is the reason on a molecular level that allows grape seed oil to infuse cannabinoids more easily?

1 Legality is not an issue since I live in a state where I am allowed to grow up to 6 plants of varying maturity and also produce my own grape seed oil infusions.


texts: What is the relationship between the molecular weight of a polymer and that of polystyrene?

texts:
So, I read in a similar chemistry thread that you can get Mn and Mw of the polymer of the interest by comparing the result of the sample obtained from GPC/SEC with the standard known molecule weight polymer like polystyrene.
I don't understand how this works. You compare what of the polymer with what of the polystyrene to determine the molecular weight?? There has to be a constant factor when determining relative values between two things, and what is it in the case of polystyrene and the polymer of the interest?
What do you mean by polystyrene equivalent value? What is the point of determining the relative molecular weight of a polymer based on the polystyrene equivalent value??

Thank you!