texts:
I have been preparing lessons for some of my students about preparing acidic and basic solutions, and I keep finding pre-made labs in which the students "standardize a basic solution" by titrating it with an acid of "known" concentration.

The problem is that the students create a solution of NaOH by measuring a certain mass and adding it to a volumetric flask, filling with water to the desired volume.  But the students will do the same thing with an acid (potassium hydrogen pthalate, for example).  They will measure out a specific mass, do the calculations to determine the molarity of the KHP solution, and then do the titration to determine the molarity of the NaOH solution.  But if the students took the mass of the NaOH in the beginning, can they not just use that information to determine the approximate molarity of the solution?

As the title says, why bother to standardize?  If our NaOH solution had some room for error in measurement and calculation, surely titrating against another solution of "known" concentration would only introduce more error, no?


texts:
Instead of using oxalyl chloride and DMF then $\ce{AlCl3}$, could $\ce{SOCl2}$ followed by $\ce{AlCl3}$ been used to achieve the same result? If yes, is one pathway preferred over the other and why?

This reaction comes from Simmons, E. M.; Sarpong, R. Ga(III)-Catalyzed Cycloisomerization Strategy for the Synthesis of Icetexane Diterpenoids:  Total Synthesis of (±)-Salviasperanol. Org. Lett. 2006, 8 (13), 2883–2886.


texts: Neutralising sulfuric acid but not boric acid

texts:
I have another question here which refers to me asking how to separate boric acid from other compounds, and this is partially a follow-up.

Suppose I was to go down the route of making boric acid by the reaction of:
$$\ce{Na2B4O7·10H2O + H2SO4 → Na2SO4 + 4 H3BO3 + 5 H2O}$$

Which in actual fact, I just did 10 minutes ago and failed miserably.
The issue I'm having is that no matter what happens in a home-experiment, you're going to have contaminants, and in this case, they are the sodium sulfate and left-over sulfuric acid.

I added sodium bicarbonate in to remove the sulfuric acid which was stupid because I required so much but then realised that it will also neutralise the boric acid. So next I am going to attempt to neutralise the acid with sodium hydroxide.

But sodium hydroxide will also target the boric acid and just change it back into borax. Is there a way I can neutralise the sulfuric acid without touching the boric acid?


texts: Which formula is correct for calculating the heat of dissolution?

texts:
I want to calculate the energy change when a solute is dissolved in water. I know that I can achieve this by using the equation $q=mc \Delta T$. My question is does the mass ($m$) change with the amount of solute added to the solvent?

For example, if I had 25g of water ($c=4.18$) as my solvent and 5g of sodium chloride as my solute. Would the energy change equal:

$$q=25 \cdot 4.18 \cdot \Delta T$$
or
$$q=(25+5) \cdot 4.18 \cdot \Delta T$$


texts: How does ice formation glue things together?

texts:
Today, I took two crumpets out of the freezer, which had become stuck to each other where moisture between them had frozen. They were two separate crumpets, the top one stuck fast to the bottom one, so they didn't go into the freezer attached to each other in any way.

And it made me wonder, what causes the crumpets to become stuck? Why don't you just have a crumpet, a thin sheet of ice, and then the other crumpet? What's going on at the chemical level that explains why these two crumpets became stuck to one another?


texts: Hopefully this is not TMI. I mistakenly used some expired Anusol recently, and noticed that the product is 12 years expired. One of the listed ingredients is Zinc Oxide, which is also used in sunscreen. This led me to ask myself "why do consumer drug products expire?", which led to the question, "How does Zinc Oxide, one of the active ingredients of sunscreen and Anusol, degrade over time?"


texts: How would I find an apporpriate dopant element for a lattice

texts:
I am trying to figure how would I go about finding a dopant element that would fit in a copper lattice? I already have the data for the atomic dimensions and structure (available below), however how would I find a dopant element that would make it a P-Type material? (Relatively new to chemistry, so bear with me if I ask a stupid question)

Atomic dimensions and structure
Atomic Radius 145 pm
Covalent Radius 138 pm
Van der Waals Radius 140 pm
Crystal Structure Face Centered Cubic
Lattice Angles
π/2, π/2, π/2

Lattice Constants
361.49, 361.49, 361.49 pm

Space Group Name Fm_ 3m
Space Group Number 225


texts: How to synthesise N,N,3‐trimethylbutanamide from 1‐chloro‐2‐methylpropane?

texts:
Suggest a synthetic route to amide C from the alkyl chloride B (reaction mechanisms are not required). Standard reagents and solvents may also be used.

In this question immediate reaction is to make a grignard reagent with B by reacting it with magnesium and have it attack $\ce{COX(N(Me)2)}$ to form C.
I'm not sure how it would be possible to make $\ce{COX(N(Me)2)}$ from standard reagents.
Are there any obvious synthesis ideas I'm missing in making $\ce{COX(N(Me)2)}$ as surely if I started from $\ce{COXY}$ where $\ce{X}$ and $\ce{Y}$ are Leaving groups, I would end up with $\ce{CO(N(Me)2)2}$ on reaction with $\ce{NH(Me)2}$ which would give an alcohol as the end product, as the amine isn't a good leaving group?
Also would $\ce{COXY}$ i.e. $\ce{COCl2}$ even count as a standard reagent? I have no idea what that really entails.


texts: What changes are expected in chemical reaction when deuterium(D) is attached in place of hydrogen(H)

texts: Our teachers told that deuterium (D) in place of H in organic reaction only matters when the C-H is broken in a reaction . But does it really matter only then ? Will it affect the stability of the compound so formed ?


texts: How can you perform an acid-base titration with antacids if substances, like aluminium hydroxide, are insoluble?

texts: I am trying to perform an experiment in order to determine the efficiency of different antacids. An online search later shows that you add an HCl solution in a solution created with a base/antacid. However, the substances do not dissolve in water and hence precipitate in the bottom. Is there a step I am missing?


texts:
Does the magnetisation process affects the reactivity of a magnetic material?
Does the electronegativity change if a metal is magnetised?


texts: Which group will migrate in this BVG oxidation?

texts: I know that H has a higher migratory aptitude order than phenyl. But, in this case, the phenyl ring has electron donating groups attached to it which enhances its migratory aptitude. So, which group is more likely to migrate, H or phenyl?


texts:
Remember asking my chemistry teacher this question in 1979/80: in the reduction of 1,3-dinitrobenzene with hydrogen sulphide/ aqueous ammonia, why is only one nitro group reduced?. He said that the reaction must be driven by the electon-depleted ring (two nitro groups); as one nitro-group becomes an amino, electron density in the ring increases, by definition; therefore, the reaction stops.

This is almost certainly true; but, is there a more fulsome explanation? Attempts to find the mechanism, on the net, have established that it has not yet been elucidated.

Any thoughts; theories; ideas; or, is this a worthy Ph.D. project for an ambitious young student?


texts: Anti Markovnikov Product with Oxymercuration - Demercuration

texts:
Consider the Oxymercuration - Demercuration of the following compound with $\ce{Hg(OAc)2}$ followed by treatment with $\ce{NaBH4}$ in basic medium:

Here, if we go according to Markovnikov addition of water to the double bond, the $\ce{OH}$ group should get attached the carbon having the 2 methyl groups

But if go by the mechanism, we find that a more stable intermediate is formed when the partial positive charge lies on the carbon having the phenyl group as a benzyl carbocation is considered to be more stable than a secondary carbocation and thus we could very well expect an $\ce{OH}$ group on the carbon having the phenyl group.

So which one would be the major product in this case - The Markovnikov or Anti-Markovnikov product?


texts:
Given this concentration profile, I am to (1) determine at which side substance A will diffuse out of the membrane and (2) chose one of the following profiles below which represents the concentration of a substance A at steady-state.

(1) Diffusion occurs from an area of high concentration to an area of low concentration. Therefore, substance A would diffuse from the left to the right. However, in the question when they ask "at which side will the substance diffuse out of the membrane", should I answer at the right side or that the substance stays within the membrane?

(2) I know that the concentration profile at steady-state should be linear, however I'm wondering what the difference between (A) and (B) is. I assume that (A) is the correct answer to this question since substance A has a higher concentration than the concentrations at the membrane wall and hence the slope should start a little above the concentration at the wall. Is this correct or does steady-state affect the concentration profile of the substance?


texts: Why can't this be another structural isomer of ethanol?

texts: Are the two structures depicting the same molecule? Why? Why not?


texts:
I'd like to produce a synthetic version of foot odor for joke purposes. My company sells novelties.  What could I use to create something virtually identical? Would simply mixing the correct proportions of 3-Methylbutanoic acid, Propionic acid, Butyric acid & Methanethiol do it?  Would I need Ammonia?  (I found this.)

I probably don't need all the other fatty acids.  Since Methanethiol is a gas, how would I integrate that?


texts:
I've come across the term base-pair stacking (with reference to B-DNA) in my school text book, and I had posted a question in that regard on Bio.SE.

I've also seen a similar (albeit brief) version of my question on Chem.SE.

I looked up the term online, and after checking out a couple of links, I'm led to believe that this term stacking refers to the forces of attraction between aromatic rings on account of the de-localized pi-electron clouds on either side of their (the aromatic rings) planes.

Now I'm not sure if I skimmed over some important details when I read up on 'stacking', but I'm unable to find a simple and solid explanation as to how these interactions are brought about.

If 'stacking' is the interaction between pi-electron clouds, then shouldn't these interactions be repulsive (on account of 'like-charges repel')? But I'm told they're attractive interactions.

I thought about it for a bit, and I realized that if you consider the fact the the pi-electrons, despite being de-localized all over the plane of the aromatic ring, can only be found at one particular location at any given instant of time, resulting in a 'partial' negative charge being formed there. The other regions of the electron cloud probably acquire a 'partial' positive charge on account of the fact that the electron is not present there at that instant. It's these opposite, partial charges formed that results in the attraction. (Essentially the same idea that governs London Dispersion Forces)

But the thing thing is I'm not sure if my 'hypothesis' is correct in the present case. If this isn't what happens then I've no idea what makes 'stacking' attractive interactions.

So my question stands: How exactly does stacking give rise to attractive interactions between aromatic ring? Why don't they result in repulsive interactions?


texts: Does the natural atomic orbital analysis result in natural electron configurations of molecules?

texts:
In my understanding, the natural atomic orbital (NAO) analysis is a method of calculation to get occupancy of electrons in center of each atoms. In other words, the result of NAO-occupancy indicates the electron configuration about a non-bonded molecule. More specifically, electrons are rearranged in each atom according to the surroundings of such atoms within a molecular configuration.

In this way of understanding, is it correct to say the data in table is result of the NAO analysis?

And, have I no misconception about NAO method?


texts: Does the reaction between phosphorus and chlorine produce phosphorus trichloride or phosphorus pentachloride

texts:
Phosphorus has two covalent compounds it can form with chlorine, where it is a single, central atom bonded to chlorine, which are phosphorus trichloride and phosphorus pentachloride.  Because of this, I am not sure as to whether phosphorus will react with chlorine to form the trichloride and the pentachloride.

I am thinking that it would probably be more likely for it to form the trichloride, since it is more favorable for phosphorus to not have an expanded octet, but does the amount of chlorine gas in relation to the phosphorus (excess or not) play a role in what compound will be formed?


texts: What happens if a buffer is made up with only half as much NaH2PO4 compared to Na2HPO4?

texts:
A solution of $\ce{NaH2PO4}$ and $\ce{Na2HPO4}$, when provided in equal amounts at the same concentration, form an excellent buffer. What happens is that the two sodium-phosphate compounds each dissociate independently:
\begin{align}
\ce{Na2HPO4 &<=> HPO4^2- + 2Na+}\tag1\\
\ce{NaH2PO4 &<=> H2PO4^- + Na+}\tag2
\end{align}

What would happen if you made up a solution that had only half of the reactant in (1)?

Am I right in saying that Le Chatelier's principle is not involved, and that shifts in equilibrium don't occur?

Will the solution just have a lower buffering capacity for bases relative to acids?


texts: Can water be produced by mixing hydrogen gas and oxygen?

texts: Could there be some kind of process, a kind of "retrograde electrolysis" where hydrogen gas (or in some other form) and oxygen gas (or in some there form) are mixed with required energy to combine to form water as a byproduct?


texts: How does the position of an electron donating group affect acidity in benzoic acid?

texts: I  know that the closer the electron withdrawing group to the $\ce{-COOH}$, the stronger is the acid. I am interested as to how this relationship works out in the case of an electron donating group.


texts:
Entropy of indistinguishable particles $S$ is

$$S = k\ln W,$$

but in some places notation is different:

$$S = k\ln Q + \frac{U}{T}$$

Can you explain, please?


texts: Problem digesting sample for Ti analysis using ICP-OES

texts: I'm having trouble digesting a paper sample for $\ce{Ti}$ analysis using our ICP-OES. I've been digesting my ash samples with 50% $\ce{H2SO4}$, but I'm still getting lower $\ce{TiO2}$ results than the target. What is the best way to digest paper sample with $\ce{TiO2}$?


texts:
I think I numbered it the correct way but I do not know which is the correct way to name it. Also please give the correct reason.

My answer was:

cyclohexane 1-carboxylic acid 2-oxo 4-carbaldehyde

OR

4-carbaldehyde 2-oxocyclohexane - carboxylic acid


texts: Enthalpy of Formation problems using Hess's Law

texts:
How do I solve problems where I'm asked for $\Delta H^\circ_f$ and given $\Delta H^\circ_f$ values for equations with the involved elements? For example:

  Find the $\Delta H^\circ_f$ of the following reaction:
  $\ce{C + O2 -> CO2}$, given:

  $\ce{SrO + CO2 -> SrCO3}$ ; $\Delta H^\circ_f = \pu{-234 kJ}$

  $\ce{2SrO -> 2Sr + O2}$ ; $\Delta H^\circ_f =  \pu{1184 kJ}$

  $\ce{2SrCO3 -> 2Sr + 2C + 3O2}$ ; $\Delta H^\circ_f = \pu{2440 kJ}$

I know that I'm somehow supposed to manipulate the equations to make them "add up" (adding straight down) to the target equation, but I'm not sure how, exactly, to achieve this.

Also, is there a different and/or better method for doing these?

I've made some progress on my own, using this About.com page. What I'm wondering now, is if elements are locked into compounds, can I split them up, as long as I keep them on the same side? In the example above, I've manipulated it to where I have $\ce{2CO2 + O2 -> 2C + 3O2}$; am I allowed to split the $\ce{2CO2}$ into $\ce{2C + 2O2}$?

I've made it as far as getting to $\ce{2C + 2O2 -> 2CO2}$. If you take these as molar ratios, it's the same as $\ce{C + O2 -> CO2}$, which is the target equation. What do I have to do to the enthalpies to go from the first to the second?


texts: Temperature and pressure for three phase equilibrium of aqueous sodium chloride solutions

texts:
I am currently investigating the effect of adding Salt(NaCl) to water on its triple point. Let us assume the mass ratio of water to NaCl is $1:1$. I asked a similar question previously. But, I still haven't been able to find the temperature(s) of the triple point(s).

I understand that according to the Gibbs equation $f = C-P+2$ Therefore, in my case of Salt water, $f = 1$. Thus we have a range of temperatures/presures where the triple point exists.

But how can we find this range of temperature or pressures? IS there an experimental methods?


texts:
I am learning molecular orbital in general chemistry. I have come across this question that asks me to show that the Lewis structure of $\ce{O2}$ is actually an excited state when viewed in terms of the molecular orbital energy.(Zumdahl 9th edition, chapter 9, Excercise number 50) The solution book tells me that the Lewis structure of $\ce{O2}$ is an excited state because the two electrons in the $\pi ^*2p$ does not follow Hund's rule(the two electrons there exist in the same $\pi ^*2p$ orbital while leaving the other $\pi ^*2p$ orbital empty.) And it further states that the reason why the two electrons in $\ce{O2}$ Lewis structure are paired is because the Lewis structure of $\ce{O2}$ shows every electron to be paired. But my question here is, why does being paired in the Lewis structure equate to being paired in MO? I mean, when MO is formed, aren't all orbitals reconfigured, and therefore all electrons are also reconfigured?

While I was thinking about this, another question popped out of my mind. Why are the name of MOs like $\sigma$ and $\pi$? Doesn't $\sigma$ and $\pi$ get used when talking about $\sigma$ and $\pi$ bonds? Are $\sigma$ orbitals and $\sigma$ bonds correlated in anyway?


texts: Are we using an assumption in calculating the ratio of first state excited to unexcited chemical species using the Boltmann distribution?

texts: In calculating the ratio of first state excited to unexcited chemical species using the Boltzmann distribution, are we assuming that we only have species in the unexcited and first state excited states? It seems to me that this must be the case, because there's no part of the equation that accounts for the population of e.g. the second excited state.


texts:
When HBr reacts with ethene it proceeds by the attack of proton on Ethene to give Ethyl carbocation and then attack of nucleophilic bromide ion to give Bromoethane.

My question is why does the proton react with Ethene earlier than the bromide ion? Is a proton more reactive than bromide ion or is there some other reason?


texts: If the pH is zero, what would be the normality of a sulphuric acid solution?

texts:
If pH of the solution is zero, what would be the normality of $250 \, \mathrm{ml}$ $\ce{H2SO4}$ solution?

My work:
$\mathrm{pH} = 0$, hence the concentration of $\ce{H+}$ ions is $\pu{1 mol L^-1}$, which implies that the molarity of the solution is $\pu{1M}$ hence the normality of the solution must be $2~\mathrm{N}$.  Is this correct?


texts: Sulfuric acid from elemental sulfur and hydrogen peroxide

texts:
Will this reaction proceed under standard conditions? I don't really care if it is quite slow, as long as it takes less than a month to finish:

$$\ce{S8(s) + 24 H2O2(aq) -> 8 H2SO4(aq) + 16 H2O(l)}$$

My rationale for this happening is that the elemental sulfur can be oxidized by hydrogen peroxide to form sulfur dioxide, which is further oxidized by hydrogen peroxide to form sulfur trioxide. This then reacts with water to form sulfuric acid.


texts: Does the addition of chlorine to carbon-carbon double bonds proceed through a halonium ion?

texts:
I need some serious help with the mechanism of ionic addition, both my textbook and my teacher are at odds with internet videos (khan academy) which both seem to be at odds with quote, "recent evidence" on the topic.

I don't need to know much of this for my exam, but basically I want to understand it properly because I hate the idea that my foundation is built up badly from the start.

Here's the deal:

During the ionic addition of say, Bromine-Bromine to ethene, my textbook says that 'recent evidence shows' that there is a 'bridged structure' formed when the diatomic bromine breaks up and attacks the double bond.

I get this, the bromine becomes polarised when approaching the ethene at a right angle, leading to one bromine atom losing an electron to the other, more negative bromine.

This positively charged bromine which is two electrons short of a full shell now needs two bonds, right? So it attacks the ethene double bond, forming the 'bridged structure' my book mentions by bonding with each Carbon on the ethene molecule. Fine. Cool. Then eventually the other negatively charged bromine atom can form a bond on the opposite side of the molecule from the first bromine, leading to a lovely looking (1,2)-dibromoethane:

Except now, my book goes on to completely ignore what it just did during the exact same process with Chlorine gas, which makes no sense. No bridged structure, the pictures even say that the Chlorines end up on the same side of the molecule as seen on wikipedia and on any quick google image search of 'addition reaction':

I've seen this in different places on the web too... Bromine somehow undergoes a different ionic addition than Chlorine which makes no sense, it basically bonds to one carbon even though it needs two (like the bromine did), so no bridged structure.

I don't get it folks. Bromine and Chlorine have the same valency, and they're more electronegative than Carbon or Hydrogen. Why are these two processes different, and why do they end up with significantly different products?


texts: Different elution profiles of carvacrol and thymol

texts:
I have identified carvacrol and thymol via thin-layer-chromatography and via gas chromatography
On a normal silica plate the thymol has a higher Rf-value then carvacrol. The explanation for this would be the position of the hydroxyl-group and the difference size of the nearby methyl or isopropyl group. I think thymol should be more hydrophobic then carvacrol, explaining the less interaction with the silica gel resulting in a higher Rf-value.

The problem is, that the analysis by gas chromatography with a non-polar column shows a different elution profile. I would expect that thymol, according to the higher hydrophobicity, should have a higher retention time then carvacrol. This isn't the case. Carvacrol (27.08 min) elutes after thymol (26.51 min).
Is there any explanation I'am not aware or is my thinking simple wrong?


texts: Why chlorine acts as a strong field ligand in tetrachloridoplatinate(II)?

texts:
In most of the cases I have learnted, halogens act as a weak field ligand. However, I recently learned somewhere on the web that the strength of a ligand also depends upon the size of the atom. A classic example is tetrachloridoplatinate(II): $\ce{[Pt(Cl)4]^2-}$.

Why is it so, and how can I predict the hybridization correctly in such exceptions, if I come across them for the first time?


texts: Why radioactive elements emit alpha beta and gamma rays

texts: I am confused about this that why radioactive elements emits alpha beta and gamma rays WHILE other elements can't do so.


texts: Sorry for the irrelevant tag because I was unable to find An appropriate one .Suppose there is a vaccum chamber and i filled completely with O2 without any traces of any other gases . Can a normal person breathe in it comfortably. I suspect it as pure O2 may act as oxidiser but since we need it for breathing . Can our organs manage that.


texts: Why coefficient doesn't change amount of substance

texts:
$\ce{3Mg + 2As -> Mg3As2}$ ($10\ \mathrm g$ of $\ce{Mg}$ and $10\ \mathrm g$ of $\ce{As}$)

I don't understand why coefficient doesn't change the amount of substance, here's what I did:

$n_{\ce{Mg}}=3\cdot\frac{10\ \mathrm g}{24.31\ \mathrm{g/mol}}=1.233\ \mathrm{mol}$ of $\ce{Mg}$

But the correct solution is:

$n_{\ce{Mg}}=\frac{10\ \mathrm g}{24.31\ \mathrm{g/mol}}=0.411\ \mathrm{mol}$ of $\ce{Mg}$


texts: Titration of sodium carbonate and nitric acid

texts:
I am trying to find the pH of the following problem (Answer key is $\mathrm{pH}=10.77$)

  Calculate the $\mathrm{pH}$ of a $\pu{100 mL}$ solution containing $\pu{40.0 g}$ of $\ce{Na2CO3}$ after   $\pu{400 mL}$ of $\pu{1.00 M}$ $\ce{HNO3}$ has been added. Ignore  the volume  of water    produced    by  the reaction

My approach:
$$\ce{Na_2CO_3~(aq)~+~2HNO_3~(aq)\rightarrow CO_2~(g)~+~H_2O~+~2NaNO_3~(aq)}$$

I start with $\pu{0.377 mol}$ $\ce{Na2CO3}$ and $\pu{0.4 mol}$ $\ce{HNO3}$.  Because of the 2:1 ratio, I use up all of the $\ce{HNO3}$, and create $\pu{0.4 mol}$ $\ce{NaNO3}$ and have $\pu{0.177 mol}$ of $\ce{Na2CO3}$ left over.

I am unsure how to go about setting up the ice table.  Should I use that
$$\ce{NaNO3 + H2O -> HNO3 + Na+ + OH-}$$
where I have the initial amount of $\ce{NaNO3}$?


texts:
I was watching Periodic Video's chlorine video, which discusses chlorine's ferocity in stripping electrons whenever possible, and the professors mentioned its consequent use in WWI as a chemical agent. This got me thinking, if I were in that situation (say Syria if they decided to go old-school or a chemical leak), what could I do to protect myself against gaseous chlorine using the chemistry of everyday materials around me?

I imagine a wet towel won't help much to prevent the chlorine from getting in my lungs. Are there any easily obtainable substances I could safely breath through that would neutralize the chlorine? Or are there any (realistic) MacGyver solutions to quickly building a semi-functional gas mask? Just kinda curious what could be done.


texts:
I need to have the highest concentration of (bi)carbonate ions in a water solution.

Thus far, my only idea was to use Potassium Bicarbonate (safe and cheap) as it has the highest solubility but it is yet not enough.

I was thinking whether adding both Sodium AND Potassium Bicarbonate, to saturation, would increase the total amount of dissolved Carbonates.
Another solution, which might be more promising is using a complementary salt to make use of the 'Different ion effect' and increase the solubility.

Would any of these options be useful for my purpose? Thanks alot for the help.


texts: Why is there visible liquid (possibly water) on matches when they're burning?

texts: I was just burning a normal standard match and I observed visible liquid running down the wooden shaft as the fire burns and consumes it, what could explain such phenomenon ? could it be that the wood "sweats" when it's burning ?


texts: Why is lutetium part of the lanthanide series?

texts:
I’ve been looking at the periodic table and began to wonder - why is lutetium part of the lanthanide series? Or, for that matter, why is lawrencium part of the actinide series?

This isn’t readily apparent when looking at the traditional periodic table because the lanthanides and actinides are separate and below the main table. However, on the extended table, the two elements don’t appear that they should be in the groups that they are in: lutetium contains the $5d$ electron shell whereas the lanthanides do not, and lawrencium contains the $6d$ electron shell whereas the actinides do not.


texts: How can the 18 electron rule be used to explain that Fe(η5-C5H5)2 doesn't react with hydrogen but Ni(η5-C5H5)2 does?

texts:
Fe(η5-C5H5)2 does not react with hydrogen, but its nickel analogue, Ni(η5-C5H5)2 is readily hydrogenated to give Ni(η5-C5H5)(η3-C5H7). Use the 18 electron rule to explain this behaviour.

My answer so far...

Fe(η5-C5H5)2 18 electron rule = valence electrons from Fe is 8, electrons from C5H5 is 5 therefore 8 + 5 + 5 = 18 so it is stable.

Ni(η5-C5H5)2 18 electron rule = valence electrons from Ni is 10, electrons from C5H5 is 5 therefore 10 + 5 + 5 = 20 so Ni is not in most stable form

Ni(η5-C5H5)(η3-C5H7) 18 electron rule = valence electrons from  Ni is 10, electrons from C5H5 is 5.....

how many electrons from (η3-C5H7) and how does this all explain why the iron complex doesn't react with hydrogen but the nickel one does? It is to do with the fact it has two too many electrons (20e) so it bonds with two protons from hydrogen? Also what does this symbol η mean?


texts: Chemically Speaking, What's Bad About Inhaling Plastics?

texts: I hear about things like dioxin, but I really don't see what's dangerous about plastics-shouldn't you be ble to just breathe it out, or pass it out of your system? How would it cause cancer?


texts: How do significant figures work on this computation?

texts:
This isn't a homework question although it may seem like one. We've never really discussed significant figures and it was just introduced to us when we were learning how to solve word problems regarding gas laws.

  Find $V_2$ when $V_1=\pu{400 mL}$ and $T_1=\pu{32^\circ C}$ and $T_2=\pu{-12^\circ C}$.

My computation goes like this:

$$V_2=\frac{T_2V_1}{T_1}=\frac{(\pu{261 K})(\pu{400 mL})}{\pu{305 K}}=\pu{342.295082 mL}$$

As per the given, the least number of significant figures is one (from $\pu{400 mL}$). How do I approximate $\pu{342.295082 mL}$ to one significant figure?

I didn't know how to create a search query about this so I went here. Thanks.


texts: Extrapolating from a calorimetry lab to find a new delta T with different volumes and grams of substance

texts:
So, we just finished an AP chem lab where the question was basically:

Given the results of the lab were that $\pu{5 grams}$ of $\ce{CaCl2}$ and $\pu{45ml}$ of water produced a $\pu{13.33 ^\circ C}$ change, find the new temperature change of $\pu{10 grams}$ of $\ce{CaCl2}$ in $\pu{40ml}$ of water.

Our teacher used a ratio strategy where basically $$\frac{\pu{5 grams}}{\pu{10 grams}}=\frac{\pu{13.33 ^\circ C}}{x}$$
Then, since x turns out to be $\pu{26.66 ^\circ C}$;
$$\frac{\pu{26.66 ^\circ C}}{45ml}=\frac{x}{50ml}$$
solving for $x$, the final temperature change is $\pu{29.6 ^\circ C}$.
My question is basically whether this is true, because I find the denominator in the first fraction of the second ratio sketchy - its saying $\pu{10 grams}$ for 35 ml of water, but, the $\pu{26.66 ^\circ C}$ is derived from finding $\pu{10 grams}$ with same amount of water. Thus, shouldn't it be 50, since in the first ratio we only changed amount of grams of solution, so water is still 40 ml, and now $\ce{CaCl2}$ is  $\pu{10 grams}$. $\pu{40ml + 10 grams = 50 grams}$.  Thus, shouldn't the first fraction be $$\frac{\pu{26.66 ^\circ C}}{50ml}$$
The final answer happens to be $\pu{26.66 ^\circ C}$ (which is pretty and convenient), but  I think that's just because we chose 5 grams to 10 grams which is a nice number to double and the volume decreases by 5, so everything cancels out nicely.
Kinda of a big segue and separate question but related:
What's wrong with the following logic to solve the problem?
$$\pu{50 g}\times \pu{4.184 J g-1 ^\circ C-1} \times \pu{13.33 ^\circ C}=\pu{2789 J}$$
Basically, using q=mcat (m is mass of water, 45, plus mass of solution, 5) to find q of 5 grams $\ce{CaCl2}$ and 45 ml water, and then, assuming if we double the mass we double the q, work backwards? (If my logic is wrong, I think it occurs in this assumption)
thus, since we need 10 grams and 40 ml in the end, the mass is still 50 grams, but the 2789 is multiplied by 2 (since mass is doubled) and 13.33C becomes an X.
$$\pu{50 g} \times \pu{4.184 J g-1 C-1} \times x = \pu{5578 J}\\
x = \pu{26.66 ^\circ C}$$
Basically, I think the answer is $\pu{26.66 ^\circ C}$ and my teacher thinks it's $\pu{29.66 ^\circ C}$.
I'm honestly very confused about q... Google does not seem to help answer this question, if amount of water in a solution/reaction (ie water and $\ce{CaCl2}$) changes, but mass of reactant stays the same, does q change?


texts:
In my book is given the mechanism of $\ce{HBr}$ forming and I understand every step of it. We did the calculations of the rate of each reaction, which is easy depending on the sign (-,+) of compounds formed or spent, and knowing those rates we were finally able to find the rate of $\ce{HBr}$ which is well defined by the empirical equation of Bodenstein and Lind. If you know all those reactions, its not hard to find the equations you need, but my questions are :

Is there any way we can know which exactly are those reactions (mechanism)  for other examples?

How would we know if any reaction is a branched one ?


texts:
The evaporation rate of water (kg/s) is given by:
$$g = \frac{P}{P_o} AΘ$$
Where $P$ is given in Pascals and $A$ is the surface area (in $m^2$) and $Θ$ is the empirical evaporation coefficient:
$$Θ = 12v + 16$$
where $v$ the wind speed (perpendicular to the water's surface).
a) Calculate the evaporated mass of water in one hour when $v = 0$.
b) Calculate the enthalpy and entropy difference within $1$ hour when $v = 0$.

What I have tried:
a) I understand $P$ to be the partial pressure of water vapor in moist air and $P_o$ to be the atmospheric pressure of moist air.
I am not given neither the values for these pressures nor the surface area... How am I supposed to calculate the evaporated mass without such data? (It's stated that all the necessary information is provided)
b)
$$\Delta H = \Delta U + P\Delta V$$
Holding fixed the number of molecules:
$$dH = TdS+ VdP$$
But again I don't have enough information...
Are there flaws in this exercise or am I missing something?


texts: What is a probable mechanism for acid catalysed decarboxylation of alpha-hydroxy acid?

texts:
The following question was on one of the tests we had recently

Now i worked out the intermediates and the product as follows:

The first step is an intramolecular Cannizzaro reaction in which the aldehyde is oxidised to acid and the ketone reduced to base

In the next step decarboxylation takes place and we are left with benzyl alcohol (B)

Oxidation of (B) using Pot. Permanganate gives benzoic acid and decarboxylation of benzoic acid using soda lime gives us benzene as the final product which is the correct answer to the question.

Now i am quite satisfied with the validity of all the other steps excluding the acidic decarboxylation of the alpha-hydroxy acid

Can someone explain to me the probable mechanism for that reaction?

Or correct any other mistake i may have made in any of the other steps/conversions


texts: How to connect structures in Avogadro at certain angles?

texts:
I am working with this carbon nano-structure in Avogadro and the junction between my two nano-structures I try to join never seems to be aligned well. It always seems to be off kilter, which is most likely due to how I move the junction into position (manually dragging).

I posted a picture of my issue above. Where the two white arrows are is what is bothering me. I would like those to be as vertical as possible but I do not know of ways to do this aside from manually adjusting the atoms/bonds, which I assume would not get them to align exactly.

UPDATE:

As per khaverim's advice, I followed his first instructions, using MMFF94 instead of UFF (forgot to change it and my structure is large so it takes a while to optmize, will try with UFF later), and got the following structure:

I am pretty sure they are all equal angled, at least they look to be so, so thanks.


texts: Salt is very commonly added to ice even at room temperature to prevent it from melting. Can anyone explain how does it really work?


texts: Finding root-mean-square speed of neon using kinetic energy

texts:
Find the root-mean-square speed of $\ce{Ne}$ atoms at the temperature at which their kinetic energy is $\pu{6.24 kJ mol-1}.$

I tried using the kinetic energy formula
$$\mathrm{KE} = \frac{mv^2}{2},$$
but I don't really understand how to achieve the necessary values.
I tried to do it by converting mass of one atom to mass of a mole since the given energy is per mole, but I'm still not getting the answer. I understand that I need to do $\displaystyle\sqrt{\frac{3RT}{M}},$ where $R= \pu{8.3145 J mol^-1 K^-1}$ and $M = 20,$ but how would I get the temperature?


texts: How do cells unite to form a solid structure. For example a plant body is made up of a number of cells. The cells are not solid structures. Their consistency is in between solid and plasma. So how come they form solids. In solids i know that the constituent particles which may be ions or atoms or molecules are present very close to each other forming an amorphous or crystalline solid structure. But in plant body there are cells. So how are the cells are arranged to form a solid structure a solid body. why not a liquid or a gaseous. I have looked up in various sources but i have not found any mention of this topic. I am reallt desperate to know more on this. So any help will be appreciated. This is not a homework question and if anybody requires me to edit the question then please say so. Thanks


texts: How to write the redox reaction of chlorate to chlorine and oxygen using half rections?

texts:
I know how to solve redox reactions, but this one is really confusing me since I can't really write half reactions for it.

$$\ce{ClO3- -> Cl2 + O2}$$

The answer is apparently:

$$\ce{2H+ + 2ClO3- -> 5/2 O2 + Cl2 + H2O}$$

This makes sense. I understand that 12 electrons would be lost from oxygen if it all went to $\ce{O2}$ but only 10 electrons are gained by the two chlorine(V)'s so you have to use a water to make the charge balance work out. I just don't see how you'd come to this conclusion on your own.


texts: Calculating the effects in a fractionating column

texts: Consider a fractionating column used to separate a mixture of acetone (A) and toluene (B) with a liquid molar composition of acetone called x. The feed is F, the distillate is D, the waste is W and the molar vaporation enthalpy is λ. How can one get an approximate difference between the effects in the boilar and condenser using only the given values for F, λ, x(F), x(D) and x(W)


texts: Are there scales that record weight continuously?

texts:
I would like to monitor the weight of something continuously (e.g. once a minute) and access the data easily via a phone app.  Is there something like that?
There are numerous options for similar devices if you want to measure ambient temperature and humidity (e.g. https://www.amazon.com/SensorPush-Wireless-Thermometer-Hygrometer-Android/dp/B01AEQ9X9I).
But all my searching for scales with similar functionality have failed.  I've found many lab scales and kitchen scales, and body weight scales.  Only the body weight scales interact with apps on your phone, but they do not record continuously.
If you know of one, or just have better google-fu than me and can suggest a more precise search term, any pointers would be appreciated.
[ In case you are curious about the application (which is not chemistry), I want to measure water transpiration and evaporation in a bonsai tree, and measuring the weight of the tree in its pot is my proxy for water usage.  This has worked well with manual measurements, but I want to go to the next level. ]


texts: Why does menthol (e.g. peppermint) feel cool to the tongue?

texts: Especially when drinking water after the fact, mint can give a sharp cold sensation inside one's mouth.  What process causes the sensation to occur?


texts: Why is my sodium acetate not resulting in any crystals?

texts:
My son received a chemistry set for Christmas and we've been working through the experiments over the last few weeks.

One of them involves boiling white vinegar and adding baking soda to produce sodium acetate. After boiling this down it is supposed to result in some crystals forming on the pan. However, after trying it a couple times we haven't been successful in producing any crystals. What are we doing wrong?

Our process is:

Add 4 cups of distilled vinegar to a pan. Boil it on the stove.
Stir in 4 tablespoons of baking soda. Do this 1 tablespoon at a time, stirring gently to dissolve each spoonful before adding more.
Keep at a high boil until it is no longer fizzing.
Reduce to a medium heat and boil until only 1 cup remains. This usually takes about an hour.

At this point our booklet says that crystals should be forming around the outside of the pan. However, both times we have no crystals - only a liquid that looks like weak tea.


texts: Why is the less substituted alkene favoured in Hofmann elimination?

texts: In the reaction, $\ce{OH-}$ group attacks a hydrogen ion in an E2 reaction, forming a transition state in which simultaneously $\ce{NCH3}$ is removed. In this reaction, the $\ce{OH-}$ should attack, like in other case of E2 so as to form the Zaitsev product, but due to "steric hindrance" the less substituted alkene is formed. But surely the $\ce{OH-}$'s attack is not affected by $\ce{CH3}$ groups? It can be affected by the $\ce{NCH3}$ group - but whichever way it attacks, it's going at the beta carbon - so is at the same distance from that group in all cases. How can steric hindrance affect its attack? Why is the Hofmann product (less substituted product) favoured?


texts: What will be the colour of HCl with methyl orange?

texts:
I am new in chemistry and this question can be silly, but I am troubled with this question.

According to the pH range of methyl orange, if I add methyl orange into water, it gives a yellow color (pH 7). Then, if I add some HCl drops (a very little amount) into the water, what will be the color?

Usually, the colour of HCl is red with methyl orange (because of acid), but when HCl is added to water, will it be a colour within yellow and red, or pure red in colour?


texts: What is the product of reaction between 3,3-dimethyl butanal and SeO2 followed by conc. OH- ions?

texts: So basically first step will be replacement of $\ce{-CH2 -}$ by a ($\ce{=O}$ bond) making a aldehyde and ketone side by side. Now what should I do after this? I tried attacking the aldehyde first as it is more electrophilic. I think both carbonyl groups will be attacked because of high concentration of hydroxyl ($\ce{OH-}$) ions. I even tried dehydration of  the formed product after attacking with $\ce{OH-}$ ions but I always end up with a ketone and a carboxylic acid by its side  after this.


texts: Temperature Dependent Specific Heat of Nitrogen

texts:
Calculate the change in enthalpy as 1kg of nitrogen is heated from 1000K to 1500K, assuming the nitrogen is an ideal gas at a constant pressure. The tempreature dependent specific heat of nitrogen is Cp = 39.06 - 512.79T^1.5 + 1072.7T^2 - 820.4T^3 where Cp is in kJ/kg-mol and T is in K

Answer is 697.27 kJ

This is the first time i've ever encountered something like "Temperature Dependent Specific Heat"

So I know

H = m*C_p*(T2-T1);
Cp = 39.06 - 512.79T^1.5 + 1072.7T^2 - 820.4T^3

So I try to make something like C_p1:

C_p1 = 39.06 - 512.79T^1.5 + 1072.7T^2 - 820.4T^3; where T = 1000
C_p1 = -8.1934*10^11

C_p2 = 39.06 - 512.79T^1.5 + 1072.7T^2 - 820.4T^3; where T = 1500
C_p2 = -2.766466215*10^12

Cp2 - Cp1 = -3.8585 * 10^12

So yeah... Its not looking too good. Am i missing a formula?

The function looks like its easy to differentiate or integrate. Should I be doing something involving calculus?


texts: Is the scientific explanation behind Smartkleen legit?

texts:
I'm trying to have a conversation/debate about the SmartKleen laundry detergent alternative, but lack the knowledge to understand if their explanation is science or pseudoscience.

Far Infrared emission at cold water temp, smaller water molecule clusters, magnets that increase levels of dissolved oxygen, etc., can someone offer a solid critique?


texts: Why does cobalt have a higher atomic mass than nickel?

texts:
I understand that this deviation from the general trend of increasing atomic number and atomic mass is because cobalt's isotopes tend to have more neutrons than nickel's. Why is that the case? How would one go about predicting similar cases like this?

I've read a bit about the shell model. I understand that 28 is a "magic number" of nucleons, i.e. a filled shell. In that case, wouldn't it be the most stable for both atoms to mainly be found with 28 neutrons; and so, cobalt-55 and nickel-56 would be the most stable isotopes of each element. Why is that not the case? Am I missing or misunderstanding something?


texts: What is the justification for using the Marcus rate equation to model charge transport in organic semiconductors?

texts: I am trying to understand the history of how Marcus theory moved from describing electron exchange reactions in aqueous ionic solutions to also being applied to describe transport in organic semiconductors. As in who and when was the connection made and justified?


texts: Is the cyclic hexenone drawn correctly in this depiction?

texts:
I'm learning organic chemistry from Clayden's book (2e). I've noticed they draw the cyclic hexenone below like this:

However, since the carbon on the carbonyl group is sp2 hybridized I am wondering if this is correct. Shouldn't this just be planar and look like this:

Ie, more of an envelope conformation? Or am I not grasping something correctly, like is it maybe not convenient to draw it like an envelope? The below structure was made in ChemSketch and using the 3D optimization function.


texts: Molecular orbital diagram for carbene-metal and carbodiphosphorane-metal interaction

texts:
I am interested in understanding how carbenes and carbodiphosphoranes interact differently with a transition metals. I would like to use qualitative molecular orbital theory arguments (with an emphasis on qualitative) in order to highlight key differences.
A carbene is a di-valent carbon, with a long pair (in some structures it may be a diradical). It is a very strong $\sigma$-donor, in addition to being a $\pi$-acceptor: It can form a nice bond with an empty $d_{z^2}$ orbital from a metal, and it can accept two pi electrons into its empty p orbital ($p_x$ or $p_y$ depending on our coordinate system).
The geometry of the carbene, including the lone pair, is trigonal planar.

A carbodiphosphorane, on the other hand, is zero-valent, and has two lone pairs. These may be used in various different bonding schemes (see for example introduction of this paper).
The geometry here, including the lone pairs, is tetrahedral.

Assuming it binds to a metal in the following manner:

then I expect that the $d_{z^2}$ orbial is not involved in the bonding, but rather that for example $d_{xz}$ and $d_yz$ interact with the two lone pairs from the carbon.
But I find it difficult to summarize the bonding for a carbene and carbodiphosphorane into (over)simplistic MO diagrams.


texts: Molecular orbital theory & predicting the stability of a molecule?

texts:
A question in my general chemistry textbook gives me a list of formulas for molecules and ions. It then asks me to determine, using molecular orbital theory, whether or not each would exist in a relatively stable form.

How can I tell this? The chapter covers molecular shapes, valence bond theory, and molecular orbital theory which all builds on what was taught in the previous chapter (mainly on Lewis structures.) I can't tell what concepts to use in telling what will be stable and what won't.


texts: Photodissociated iodine laser and population inversion

texts:
Iodine molecules ($\ce{I2}$) can absorb in the visible region and dissociate into $\ce{2 I^.}$ radicals. One of the I atoms is in ground electronic state $\mathrm{^2P_{3/2}}$ and the other I atom is in the excited $\mathrm{^2P_{1/2}}$. So, photodissociation of $\ce{I2}$ produces 50% of the species in the excited state and 50% in ground state.
The $\mathrm{^2P_{1/2}\rightarrow^2P_{3/2}}$ of iodine has been extensively used in laser production, in chemical iodine laser or methyl iodide photodissociation laser for example. But in those cases, most of the $\ce{I}$ atoms are produced in the excited state. The criteria for laser production is population inversion, where >50% of the species are in the excited state.
Here I am not sure if the photodissociation of iodine molecule satisfies the criteria of population inversion, as exactly 50% of the species is in excited state. So my question is—can we consider 50% excited species as population inversion and if so can photodissociated $\ce{I_2}$ generate laser?


texts: Does >2e contribution of an atomic orbital (AO) to a hybrid AO of a molecule violate Pauli exclusion?

texts:
This question is inspired by On the Role of d Orbital Hybridization in the Chemistry Curriculum J. Chem. Educ., 2007, 84 (5), p 783.

The article calculates 6 bonding sulfur atomic orbitals in SF6 as each having a 0.768s term (s meaning 3s). This implies $6\times0.768^2 = 3.5$ of the 6 valence electrons corresponding to 3s character.

Is it valid to say there is that much 3s character?


texts: Why is phosphorous acid diprotic and not triprotic?

texts: In H3PO3 only only 2 hydroxide groups exist, instead of 3. If there is 3 hydroxide group, the phosphorous will have 1 lone pair electrons, which will still satisfy the valence electron of Phosphorous.


texts: I’d like to make a rather large scale camera obscura and use the light reflected inside of it to recreate the first process for a permanent image so I need a sheet metal as well as a chemical (the recommended is bitumen of judea), to expose the sheet metal to create a heliograph image, it is then said that Niepsce used oil of lavender to wipe off unexposed bitumen(I’m assuming it’s a solvent so I’d also need one to pair with whatever chemical you’d recommend for exposing). The end result is going to be rather large scale so I’d like to use a lens that won’t let in as much light as a glass lens because I believe that this will cause the image to be overexposed I was curious as to what chemical I should use to apply to the metal sheet, and what type of metal to use to get the best result that will be the most light sensitive and result in a clear final product. If this doesn’t make sense I apologize and I’d be glad to try and make as much sense of it as possible, any help is good help thank you!


texts: Does boron form compounds without covalent bonds?

texts:
I have read that boron, due to the very high sum of its first three ionization energies, it is not able to form its +3 ions, and thus it generally forms only covalent compounds. But in a popular Indian engineering entrance exam: JEE MAINS-2014 19th April paper, this question was asked:

Which of these statements is not true ?

In aqueous solution, the $\ce{Tl+}$ ion is much more stable than Tl (III)

$\ce{LiAlH4}$ is a versatile reducing agent in organic synthesis.

$\ce{NO+}$ is not isoelectronic with $\ce{O2}$

$\ce{B}$ is always covalent in its compounds.

The answer given was 4.
I get that there might be an exception but I'm not able to find it anywhere. If there exists an ionic compound of boron, could someone please mention that to me?


texts: What is has a higher priority in naming organic compounds, alkyl groups or halides?

texts:
2-Chloro-3,3-dimethylbutane or 3-Chloro-2,2-dimethylbutane?

According to these sources, both are correct:

NIST/TRC Web Thermo Tables (WTT)
ChemSpider


texts: Would adding water to a fish tank with sand lower the level of sand?

texts:
Let's say I have a typical 10 gallon tank with dimensions 10" x 20" x 12", and it's filled halfway (5" in height) with dry sand for hermit crabs.

If I fill the tank up with water, will the level of sand decrease?

I'm thinking that it doesn't because of this answer -- sand is insoluble.  So the water would just fill the gaps of air first.  If that's not the case though, what are some things to take in to consideration?

Not quite sure where this question belongs, so if it's in the wrong place, let me know -- or mods, feel free to move it.  Thanks!


texts: Iron-II to iron-III change in complex formation

texts:
We have an iron dust sample, which is treated with hydrogen chloride in aqueous solution. The solution enters in a reaction with a sodium hydroxide powder, from which we obtain a precipitate. Could we solubilize the precipitate with excess of ammonia? Note that, at the end of the reaction, qualitative chemical analysis identified the ion $\ce{Fe^{3+}}$, but not $\ce{Fe^{2+}}$.

First reaction is, obviously:
$$\ce{Fe + 2HCl -> FeCl2 + H2 ^}$$
Then, we have:
$$\ce{FeCl2 + 2NaOH -> 2NaCl + Fe(OH)2}$$
We observe that we have, now, only $\ce{Fe^{2+}}$ in the aqueous solution, not $\ce{Fe^{3+}}$. Precipitate solubilization means coordinative compounds formation. If for iron we have a similar reaction to the one with copper ion:
$$\ce{Cu(OH)2 + 4NH3 -> [Cu(NH3)](OH)2}$$
We would have only $\ce{Fe^{2+}}$. So, is there any redox process happening in background? Or a physical process (non-chemical)?


texts:
I was quite puzzled by the answer for this question in my Carboxylic Acids and Derivatives tutorial question set. It is question 6 (a), on the synthesis of malic acid, as shown in the image below.

The idea for the synthesis is to convert the $\ce {Br}$ to $\ce {CN}$ and the carbonyl group to a cyanohydrin, then convert the $\ce {CN}$ to $\ce {COOH}$. I have no disputes about the last step, which is to heat with aqueous hydrochloric acid, or some other mineral acid. However, what I proposed was to perform the two initial conversions in one step, which is to heat the compound with $\ce {KCN (aq)}$ and ethanol. Would that not allow for both the nucleophilic addition, as well as the substitution, to take place, all in one step?

The proposed answer for steps 1 and 2 was to first heat with reflux, with ethanolic $\ce {KCN}$, then react with $\ce {HCN (aq)}$, with trace $\ce {KCN}$, or $\ce {NaOH}$ as catalyst, under temperature of 10-20 degrees C. Is it really necessary to perform the initial two conversions in two separate steps?


texts: Finding the enthalpy of formation of magnesium oxide using Hess' Law

texts:
I have the following reactions:

$$\begin{align}
\ce{Mg(s) + 2HCl(aq) &-> MgCl2(aq) + H2(g)}\\
\ce{MgO(s) + 2HCl(aq) &-> MgCl2(aq) + H2O(aq)}\\
\ce{H2(g) + 1/2O2(g) &-> H2O(l)}\\
\ce{Mg(s) + 1/2O2(g) &-> MgO(s)}
\end{align}$$

I also have $\Delta H$ in $\mathrm{kJ/mol}$ for the first three reactions.

Out of this information, I need to find $\Delta H^\circ_\mathrm{f}{\left(\ce{MgO(s)}\right)}$.

I’m pretty sure I have to use Hess’ law but I don’t know how to apply it here. I’ve tried using the second reaction as my “main” reaction and then I can use the third and fourth reaction as formation reactions for two of the compounds of the main reaction but after that I’m not sure how to proceed.


texts: Is the proper formula for phosphorus oxide(V) P4O10 or P2O5?

texts: I would like to ask about formula of phosphorus oxide(V). Should it be $\ce{P4O10}$ or $\ce{P2O5}$? Which is right when I have to write the molecular formula?


texts: Does the Location of Line-Dash-Wedge Notations Matter?

texts:
In Line-Dash-Wedge notation, when illustrating that an atom or bond is directed towards or away from the viewer (solid triangle for coming forward, dotted lines for going back), does the location of these lines matter when doing illustrations?

For example, a THC molecule.

The two hydrogen atoms there. Could they be placed inside the carbon rings instead of appearing outside, like below?

I understand that there's a whole host of issues with that otherwise, but just asking about the triangle and dashes in particular.


texts: Software for predicting chemical reactions

texts:
I wondered if it was possible to predict the product(s) of a reaction (or even the equilibrium) based on the reactants and the temperature/pressure.

I found an answer to a similar question here:

  No, there is no such thing as chemical reaction are not that easily
  predictable. You can get result right in some cases, but it is
  impossible to count all factors.

What (significant) factors also influence a reaction? Is it the arrangement or state of the chemicals? Is it too related to other physical properties to ignore them?

Please name the most important ones.


texts: Is it reasonable to use natural orbitals of an unrestricted HF calculation as a basis to start a CASSCF calculation for a radical

texts:
Let's say we want to run a CASSCF calculation of a radical, for example the cation of a neutral closed-shell molecule (therefore, we calculate an open-shell radical cation). MOLCAS, as well as probably every other program package out there, needs starting orbitals when performing a CASSCF calculation. For a neutral species, these are normally assumed to be the regular old Hartree-Fock orbitals. Usually, when dealing with a cation, it seems that the Hartree-Fock-SCF calculation is performed for the neutral species or the di-cationic species to yield the necessary HF starting-orbitals. They are in these cases the result of closed-shell calculations. MOLCAS also permits the use of a UHF calculation as the basis for a subsequent CASSCF calculation. Then, the natural orbitals of the unrestricted calculation are used.

Is the usage of the natural orbitals of an unrestricted HF calculation reasonable as a basis for a subsequent CASSCF calculation? If not, why? When is it a good idea / when is it a bad idea? What are the differences in using natural UHF orbitals in contrast to the SCF orbitals of the neutral or di-cationic species? What are the pitfalls?

Edit: I am aware (or at least it is my understanding) that conceptually it is no problem to perform the CASSCF using the natural UHF orbitals, as it could for example also be performed using only the alpha orbitals of the UHF calculation. My question is therefore aimed at finding out in which cases it is generally a good or bad idea to use the natural UHF orbitals.


texts: I have absorption curves for three species that are nominally the same concentration that I need in order to calculate spectral overlap. Part of that process is dividing the curve through by the concentration as a normalization process. The curves of two species are a factor of 10 lower than the other (not necessarily a problem), but that is true even out away from where the peaks from these species are. All curves were taken on the same spectrometer. It seems to me like maybe someone changed out the blank solvent in-between data taking (a possibility in a shared lab). Is there a way to normalize this prior to calculating spectral overlap?


texts: Chemistry write-ups in LaTex - is it worth drawing figures in LaTex?

texts:
Being an undergraduate chemistry student I have to write a significant amount of hand-ins e.g. lab reports. Up until now I've been using LaTex with mhchem for equations and siunitx for numbers/units, but I've not invested the time and effort in learning other, more complicated chemistry related packages. This means, that I usually draw mechanisms with ChemDraw and other figures with image editors.

So my question is: which packages is it worth spending the time on learning (and using)?

E.g. chemfig for complicated reaction schemes, modiagram for molecular orbital diagrams, bpchem for IUPAC names and common idioms, etc.


texts: Relative magnitudes of 2- and 3-bond coupling constants

texts: Why is geminal coupling weaker than 3-bond coupling in complex coupling? It would make more sense that atoms that are closer to each other influence each other more. Take methyl acrylate for example. The $\mathrm{H_a}$ is causing the bigger split, and the $\mathrm{H_b}$ the smaller ones. Why?


texts: Why does acetone have a greater dipole moment than dimethyl ether?

texts:
Below are the lewis structures for dimethyl ether and acetone. My chemistry textbook indicates that acetone has a larger dipole moment than dimethyl ether. I am familiar with dipole moments and the fact they are created by an unequal sharing of electron density. However I do not understand why acetone is more polar than dimethyl ether. My best guess is that having an extra carbon provides more electrons which allows the molecule to establish a larger difference in electron density between the oxygen and the rest of the molecule. I am unsure if this is correct and would greatly appreciate a more in depth explanation.

Dimethyl ether


texts: In some books it is written that +M  (mesomeric effect)  effect of OH is less than that of OR . The reason they give is inductive effect of R (group) which sounds senseful . But at some places it is written +M of OR is less (which is correct). But I am not able to understand the reason which they give.


texts: trialkyl phosphine ligands in aqueous micellar Suzuki-Miyaura coupling

texts: I have seen $\ce{P(tBu)3HBF4}$ salt used as a precursor to the phosphine ligands for aqueous Pd-catalyzed micellar Suzuki-Miyaura coupling, but why does it work - after $\ce{Et3N}$ has liberated the tributyl phosphine ligand why does it not deactivate in the presence of water?


texts: Is there any difference between table salt and common salt?

texts: Iv'e been reading about $\ce{NaCl}$ and this doubt crossed my mind. Are they anything other than just household terms?


texts: I recently learned that you can clean up latex paint wash-up water by flocculating it: adding aluminum sulfate and hydrated lime. I vaguely remember how flocculation works in clay slurries (change in pH changes the electrostatic charge on kaolin plates, causing them to attract and then precipitate). Does flocculation in paint work the same way? (Is it exactly the same? Is there kaolin in paint?) What exactly is happening when you add aluminum sulfate and hydrated lime to the paint?


texts: Methane seems to dissolve more readily in cold water. Why?

texts:
When you are diluting air in the system and/or properly evacuating it, you must consider water temperature. Methane is completely dissolved in water at 42 degrees Fahrenheit (5.5 C) but can be completely released (as a gas) at 58 degrees F (14.5 C). (source)

This would seem to imply that the enthalpy of solution for methane in water is negative (i.e. the process is exothermic). But, intuitively, it seems that you would have to input energy to force non-polar and polar to mingle.

Can anyone explain why this might be the case?


texts: In the Favorskii rearrangement, why doesn't the base grab the alpha hydrogen of the carbon bearing the halogen?

texts: In the Favorskii rearrangement, the base (like hydroxide) always abstracts the alpha hydrogen of the carbon not bearing the halogen. But to me the hydrogens on the carbon directly connected to the halogen should be more acidic due to the electron pulling inductive effect of the halogen (which indeed does happen in the haloform reaction). This should result in an aldol condensation type reaction. Why is this not so?


texts:
How do we detect equivalence point from a titration of an acid with a basic titrant from thу titration curve ($\mathrm{pH}$ vs. Volume of titrant added)?

Can we predict an equivalence point just by seeing the shape?
Some people say that

  when $$\frac{\mathrm{d(pH)}}{\mathrm{d}V} = 0,$$ equivalence point has been reached.

Is it correct? I doubt if it is correct. It is also written that there is a distinct "break" in the curve at equivalence point. What is this break?


texts:
How to convert ethanol to 1,1-dichloroethane?

My approach: Convert ethanol to ethene followed by $\ce{HCl}$ addition. But that's no use. Well if it is possible to create gem-diol from here, then maybe it can be done. But not getting a suitable reaction. Can't seem to figure out anything. Please help!


texts:
I am a high school student and my professor mentioned that the Gibbs free energy is the maximum amount of work (or useful work) that a system can do, whereas entropy is a measure of the non-available enthalpy.

I am not able to understand this and it would be helpful if you could explain this or link to some resources that could explain this at a high school level (I know some multivariable calculus, but not that comfortable with it) as I have difficulty finding them.

Also, we used the fact that Gibbs free energy is the maximum amount of work to derive the equation $∆G = -nFE$ and then proceeded to derive the Nernst equation.


texts:
What is the structure of pyrophosphorous acid?

I asked this question here because the answer which I found on web and other resources are inconsistent which each other.
For example, following data is given regarding the structure of pyrophosphorus acid in my textbook, which is not consistent with the number of oxygen atoms.

On checking here,and here there are no double bonds of phosphorus with oxygen, however here there are. And here both the structures are given on the same website.


texts: How to measure/know the moles of carbon dioxide (as dry ice) when in KOH solution

texts:
I am doing an experiment where I am dropping dry ice in a $\ce{KOH}$ solution. I want to know how I can figure out how many moles of $\ce{CO2}$ reacted with the $\ce{KOH}$. I am pouring $25 \,\mathrm{g}$ of $\ce{KOH}$ in $100 \,\mathrm{mL}$ of water and I am using $50 \,\mathrm{g}$ of dry ice. The experiment is conducted at room temperature.

I know one way to do this is by isolating the product of $\ce{K2CO3}$ but because $\ce{K2CO3}$ is soluble, it is going to be very hard to isolate this product and weight it and use simple stoichiometry to figure out the moles of $\ce{CO2}$ reacted.

I was thinking maybe the pH meter will help but again, I do not know how to use the pH to calculate how many moles of carbon dioxide reacted.

Observations

During experimentation, I saw the pH decreased when I added the $\ce{CO2}$.Will this fact be useful to calculate moles of $\ce{K2CO3}$ formed? The pH decreased from 13 to 10.

Can someone please help?


texts: How can we separate a mixture of two sulphide ores using froth floatation method?

texts:
As we know froth floatation method makes use of the wetting properties of mineral particles.

  Mineral particles (sulphide) become wet with oils, while gangue particles get wet by water

According to my textbook (NCERT Class 12), we can use the froth-flotation method to separate a mixture of sulphide ores also using depressants.

How do these depressants actually work in this process?


texts: How do lone electrons impact the charge of an ion?

texts:
This is a quite elementary question, but I still can't wrap my head around it.

I know how to calculate the formal charges of an ion or a molecule, but I don't understand what happens when oxygen (when sharing a single covalent bond with sulfur in a sulfate ion) has a lone electron that doesn't bond nor pair. I don't understand why this puts a -1 charge on the atom. What happens?

I've attached an image which explains what I'm trying to figure out:

See those two red dots? What do they mean? I understand that they symbolize the lack of a single electron needed to complete an octet. But why does it give the atom a negative charge?


texts: Why does the trimethylammonium cation have a larger -I effect than the ammonium cation?

texts:
Why does $\ce{N(CH_3)_3^+}$ have a larger $-I$ effect than $\ce{NH_3^+}$?

Since the methyl group is good at donating electrons it would stabilize the charge on nitrogen atom, decreasing its potential to withdraw electrons hence its $-I$ effect.

I can't figure out why its the other way around. Can someone help me understand this?


texts: Is ethylene diamine tetra acetate a misnomer?

texts:
Since there is no double bond, I thought EDTA should be ethane... instead. Am I missing something?
I understand this is not the complete IUPAC name, but why name it wrong on purpose?


texts: What is the mathematical basis behind the Jahn-Teller effect?

texts:
Both first-order and second-order Jahn-Teller distortions play a very important role in chemistry.

It is often said that the Jahn-Teller effect is based on symmetry arguments, and hence nothing can be said about the extent or the exact form of the distortion.

What are these "symmetry arguments", and how can they be derived?


texts:
I'm reading McQuarrie's Physical chemistry textbook [1]. On p. 281, the author explains:

If we use a more flexible trial function of the form in which $\psi(\mathbf{r_1},\mathbf{r_2})$ is a product of one-electron functions, or orbitals,
$$\psi(\mathbf{r_1},\mathbf{r_2})= \phi(\mathbf{r_1})\phi(\mathbf{r_2})\tag{8.15}$$
and allow $\phi(r)$ to be completely general, then we reach a limit that is both practical and theoretical. […]
This limiting value is the best value of the energy that can be obtained using trial function of the form of a product of one-electron wave equations (Equation 8.15). This limit is called the Hartree-Fock limit.

But why does Hartree–Fock limit exist? If we increase the number of parameters of the trial function we use, we may expect better calculation results. Nevertheless, why is the wave function multiplied by the two trial functions limited to the accuracy that can be achieved?
My guess is that the functional form does not properly consider the interelectronic correction term by treating the two trial functions independently. But can't this difference be overcome by using more parameters? I wonder if I can theoretically explain the existence of the Hartree–Fock limit.
In addition, if this limit exists, the function will have to be altered to produce better calculation results. I wonder what theory computational chemistry has developed about this.
Reference
McQuarrie, D. A.; Simon, J. D. Physical Chemistry: A Molecular Approach; University Science Books: Sausalito, California, 1997. ISBN 978-0-935702-99-6.


texts: What do the dots mean in HN.CO.CH3 connected to the second carbon of N- Acetylglucosamine? And what do the N and acetyl indicate?


texts: What is the necessity of re-hybridisation of carbon in the transition state of SN2 reaction?

texts:
In March's Advanced Organic Chemistry (The SN2 Mecahnism, page 374), it's stated:

  When the transition state is reached the central carbon atom has gone from its initial sp3 hybridisation to essentially sp2 with an approximately perpendicular p orbital.

I would like to know why and how this happens. Is there an underlying mechanism? How is this rehybridisation feasible?

What makes it difficult to understand is that SN2 reactions are concerted because bond formation and breaking occur simultaneously.


texts: How to recrystallize boric acid into flakes?

texts: I am putting 100 g of boric acid, 400 g of water and trying to crystallize at low temperature and letting cool slowly, however it recrystallizes as needle like texture. I need soft large crystals like mica. Can someone help out?


texts: Do formic acid and phosphorus pentoxide react at room temperature?

texts:
If I add phosphorus pentoxide to formic acid at atmospheric pressure and 20°C will they react? At what rate will CO be produced?
I have not been able to find a reference discussing this.


texts:
I understood Le Chatelier's principle perfectly but my question is: Why should a  system try to reverse any change that has been done to it?

I understand equilibrium constant, mole concept and partial pressures but I do not understand quantum mechanics yet. If you use any other technical terms in your answer, please also explain them. Answers with intuitive examples will be highly appreciated.


texts: Can buffer solutions be used to control the pH of ethanol?

texts: For my experiment, I want to investigate the effect of differing pH on the solubilities of a sparingly soluble drug. However, the solubility is too low for me to conduct a reliable study on the solubility (0.003 mg/ml in water). In ethanol, the solubility increases to 10 mg/ml. Can I simply add buffer solutions and acids into ethanol to change its pH as I would do with water? Are there alternatives to adjusting the pH of ethanol?


texts:
From Work-Energy Theorem we have,

Work = Change in kinetic energy
         = Final K.E - Initial K.E

This shows that work only depends on the final and initial value of K.E independent of the path.

I'm lost. Can someone clear this up for me?


texts: Mechanism of alkaline hydrolysis of cyclic amide

texts:
In this mechanism, I got a pretty different mechanism from the solution. From the model answer, there is an intramolecular proton transfer just before the formation of the carboxylate ion. However, in the second intermediate, I think the electrostatic repulsion between nitrogen and oxygen is large, increase separation between nitrogen and hydrogen, hence reducing chance of intramolecular transfer.
My purposed mechanism rely on the H2O given in reaction mixture to undergo proton transfer, forming OH- (matching basic condition) and then pull the proton from R-COOH to form the carboxylate salt (product).
Is my mechanism plausible? What mistakes I have made if the model answer is the only correct mechanism?
Also, please suggest ways that I can improve this type of questions, thank you very much.


texts: Identifying organic compounds in Infrared spectrum

texts: What further information would allow you to make a positive identification of an organic compound from an infrared spectrum?


texts: Why calcium chloride is used to melt ice over sodium chloride

texts:
I'm not quite sure I understand this. My question is:

  Calcium chloride is a salt used widely to melt ice on sidewalks and roads.  Explain why one mole of $\ce{CaCl2}$ would be more effective than one mole of $\ce{NaCl}$.

So from everything I've learned, $\ce{NaCl}$ would be more effective for the melting, because calcium chloride dissociates into three ions and sodium chloride dissociates into two, so that would make the boiling point of water with calcium chloride higher.  Therefore, it shouldn't be used to melt ice over sodium chloride, as it would make the water have a higher boiling point so wouldn't melt it as well!


texts: A IChO-2014 problem involving reaction mechanism

texts:
This is a problem of IChO-2014(&solution).But I am having trouble working out reaction mechanism of the second reaction or even how the product B formed. This reaction is somewhat new to me. And googling didn't help much.

Just need a little hint on this regard.


texts:
(S)-1-bromo-1-fluoroethane reacts with sodium methoxide to give pure (S)-1-fluoro-1-methoxyethane.

This is an SN2 reaction so inversion should take place , hence the product should be R but it is not so . Why?


texts: Is there a terminology contradiction about whether the conjugate of a strong acid is a "weak base"?

texts:
(Please note, I am not simply asking, "Is the conjugate of a strong acid a weak base?"  I'm asking about the contradictory ways those terms seem to be used.)

I was revisiting strong/weak acids/bases to help some high school chemistry students and found a lot of apparent contradictions in the way that sources use the terms.  One is whether the conjugate acid of a strong base is considered a "weak acid".

I understand that the strongER the base, the weakER the conjugate acid, and all sources use the relative terms consistently.  The contradiction is in the use of the absolute terms "strong" and "weak".

There seem to be two conflicting conventions in use.  In Convention I, the conjugate of a strong base is indeed called a weak acid (whereas weak bases and weak acids can also be conjugates), so you have these conjugate pairings:

\begin{array}{cc}
\hline
\text{acid} & \text{base} \\
\hline
\text{strong} & \text{weak} \\
\text{weak} & \text{weak} \\
\text{weak} & \text{strong} \\
\hline
\end{array}

In Convention II, the conjugate of a weak acid is a weak base, and vice versa; the conjugate of a strong base is too weak to be considered an acid, and the conjugate of a strong acid is too weak to be considered a base:

\begin{array}{cc}
\hline
\text{acid} & \text{base} \\
\hline
\text{strong} & \text{not a base} \\
\text{weak} & \text{weak} \\
\text{not an acid} & \text{strong} \\
\hline
\end{array}

You can find examples of both just by googling "conjugate of a strong acid", "conjugate of a weak base", etc.  Many sources complete the sentence "conjugate of a strong acid [or base]" with "is a weak base [or acid]" (Convention I).  On the other hand many sources complete "conjugate of a weak acid [or base]" with "is a weak base [or acid]" (Convention II).

I just want confirmation different sources really are using these terms in ways that contradict each other, so I can pass that on to my students and move on.

So, which of the following is true?

There is no contradiction; I'm reading it wrong.  (This seems unlikely since you can literally google "conjugate of a weak acid" and get what seem to be multiple contradictory answers.)
One usage of these terms is correct, and the sources that say otherwise are using the terms incorrectly.  (In particular, the more reliable sources seem to skew towards saying that the conjugate of a weak acid is a weak base, i.e. Convention II.  Maybe the sources that say "the conjugate of a strong base is a weak acid" are wrong, and they're just garbling the (correct) statement that the strongER the base, the weakER the conjugate acid.)
There is no agreed-upon definition of "weak acid" and different sources use it in contradictory ways, but real chemists don't care because they just use Ka values.

To avoid horrible confusion, please be clear in your answer if you're voting for #1, #2, or #3, or something else not listed here.


texts: Why does the concentration of the acid equals that of the base at the mid-point of titration?

texts:
Consider this graph of the titration of a weak acid and a strong base:

The buffering region is strongest at the midpoint of titration because there is equal concentrations of acetic acid and its conjugate base.

  My question is why at the midpoint of titration does the concentration of the acid equal the concentration of its conjugate base? Also, why does the $\mathrm{p}K_{a}$ of the acid = the $\mathrm{pH}$ at this point?


texts: Factors dominating forces between acetone and chloroform

texts:
What type of interaction is present between acetone and chloroform?
According to me, acetone has weak hydrogen-bonds with chloroform, the hydrogen on an electronegative atom has electron density that is getting pulled on by an electronegative atom nearby.
While there is weak hydrogen bonding present, are dipole interactions not more prevalent?


texts: Pulling Calcium Phosphate from Animal Bones

texts: I am looking to pull Calcium Phosphate out of animal bones (chicken, fish, etc) without destroying the collagen. If I soak animal bones in brown rice vinegar will the vinegar pull out Calcium Phosphate leaving behind the collagen 'bendy bone'? Or is it just pulling out Calcium?


texts: What are the order of the reaction under the following conditions?

texts:
The experimental rate of a reaction
$$\ce{A + 2B -> C + D}$$
$$\frac{\mathrm dx}{\mathrm dt} = K[\ce{A}][\ce{B}]^2$$
Calculate the order of the reaction when (i) $[\ce{A}]\gg[\ce{B}]$  (ii) $[\ce{B}]\gg[\ce{A}]$

My efforts :
Should we ignore the concentration of the reactant that is present negligibly? And thus the orders will be:
(i) Order = 1
(ii) Order =2
Please guide.


texts: When is the n+l rule followed when working with energy of different orbitals?

texts:
While going through my book, I came across a problem which gave some options about the order of energy of 3s, 3p and 3d orbitals of hydrogen atom. The correct answer was given as:

3s, 3p and 3d orbitals all have the same energy

I also read somewhere that the order of energy of different orbitals increases as the value of $n+l$ increases where $n$ is the principal quantum number and $l$ is the azimuthal quantum number. So my guess was $3s<3p<3d$ .
What is the reason for this?


texts: Carbon dioxide sequestration in Limestone

texts:
The chemical reaction where dissolved carbon dioxide forms carbonic acid and then reacts with various calcium containing minerals to form calcium carbonate and bicarbonate is rather slow. I know that several years ago there was research into possible ways to speed up the reaction, possibly as a candidate for a truly long term way to scrub $\mathrm{CO}_2$ from the atmosphere. The inspiration for this idea is to speed up the part of the geologic carbon cycle that regulates atmospheric $\mathrm{CO}_2$ concentration.

Does anyone know how the research into catalysts or processes to speed this up are going?


texts: Why does a chemical have more than one oxidation number?

texts:
Like for group I metals, it is understood that all the elements in the group would have an oxidation number of +1.

As far as I know, oxidation number is how much electron the element loses/gains.

Hence my question is, why does an element like Iron, Manganese or even oxygen have more than one oxidation state unlike elements like Magnesium or Potassium.

Edit: If I have stated any terms incorrectly, please let me know because I'd want to know where I went wrong.


texts: Regioselectivity of deprotonation of 1,4-dicarbonyl

texts:
In the intramolecular aldol condensation of hexane-2,4-dione (above), why does the base abstract one of the $\ce{-CH3}$ protons instead of one of the $\ce{-CH2}$ protons? Both sets of protons are α to a carbonyl group and should therefore be acidic.

I'm confused because I've seen similar reactions where the proton is taken from the $\ce{-CH2}$ group.


texts: How to obtain the distance of maximum probability of finding an electron on x axis

texts:
I have the radial component of the wavefunction
$R_{nl}(r)=r^2e^{-2r/3a_{0}}$ so to obtain the maximum distance on x axis I do not know if I have to compute the second derivative of $R_{nl}^2(r)$ or $R_{nl}$ or of the radial distribution function ($r^2R_{nl}^2(r)$).

Thanks in advance.


texts: Theoretically, Which d orbital participates in sp3d and sp3d2?

texts:
This question is regarding the old way (inaccurate) $\ce{PCl5}$ and $\ce{SF6}$ are taught in elementary chemistry.

In the crystal field splitting diagram for triagonal bypyramidal geometry, $\mathrm{d}_{z^2}$ has the highest energy. Now, since $\mathrm{s}$, $\mathrm{p}$, $\mathrm{d}$ of same shell hybridise, then the $\mathrm{d}$ orbital closest in energy to $\mathrm{s}$ and $\mathrm{p}$ should take part, which should be $\mathrm{d}_{xz}$ or $\mathrm{d}_{yz}$. Instead, the hybridisation is said to be $\mathrm{sp^3d}_{z^2}$.

A similar problem arises for molecules with an octahedral shape. It has $\mathrm{d}_{x^2-y^2}$ and $\mathrm{d}_{z^2}$ which are higher in energy than the rest and have higher energy difference with $\mathrm{s}$ and $\mathrm{p}$ orbitals of the same shell. There is no such problem for $\mathrm{d^2sp^3}$, $\mathrm{d^3s}$, $\mathrm{dsp^2}$.

EDIT: Let me change the question to ask the same thing. In outer shell octahedral complexes ($\mathrm{s,p,d}$ of same principal quantum numbers take part) why are the $\mathrm{e_g}$ orbitals taking part in sigma bond formation when they are furthest away from $n\mathrm{s}$ and $n\mathrm{p}$ orbitals?

There is no such problem for inner shell complexes.


texts: Titration of alpha-amino acid with strong base

texts:
Question:

$\mathrm{50~ml}$ of the conjugate acid $\ce{H3N+CH(R)COOH}$ of an $\alpha$-amino acid required $\mathrm{30~ml}$ of $\mathrm{0.1~M}~\ce{NaOH}$ to completely convert into the dipolar ion $\ce{H3N+CH(R)COO-}$. The pH of the solution was 6.4 during the titration with $\mathrm{15~ml}$ of $\mathrm{0.1~M}~\ce{NaOH}$ and 7.8 at the isoelectric point. Calculate the dissociation constants for the amino acid.

Attempt:

Reactions involved:

$$\ce{H3N+CH(R)COOH <=> H3N+CH(R)COO- + H+}$$

$$\ce{H3N+CH(R)COOH + OH- -> H3N+CH(R)COO- + H2O}$$

At the isoelectric point, $\mathrm{pH}=\frac{\mathrm pK_{\mathrm a1}+\mathrm pK_{\mathrm a2}}{2}$.
Initially, number of milli moles of conjugate acid = number of milli moles of NaOH = $\mathrm{30\times 0.1=3~mmol}$ of salt during titration (neglecting the amount produced by acid) = 1.5

A buffer forms during titration. My doubts is, does the concentration of acid which was present initially, change while adding NaOH? Using Henderson equation will give pH of Buffer.
I know the concentration of salt and pH. But I am stuck with the concentration of acid. 1.5 milli moles of acid will react to form salt. If I use 1.5,I get wrong answer. If I use 3, I get right answer.


texts: XRF is "non-destructive," but what actually happens to the sample?

texts:
Editing for clarity and more details.

My colleague has been using XRF to quantitatively analyze 47-mm diameter Teflon membrane filters for metals, minerals, and rare earths. Much of their analysis has been focused on quantifying metals like iron, steel, and copper. It seems they are looking into replacing their large floor-standing WD-XRF with a benchtop ED-XRF or another floor-standing WD-XRF.

They are also planning to attempt quantification of trace metals that others report to be in the ppt range, so they are considering adding an ICP-MS downstream of the XRF. However, ICP-MS is completely destructive (the membrane filters go through solvent extraction).

My colleague and I discussed that if they were going to put an ICP-MS downstream anyway for trace metals analysis, perhaps it would be better to budget for a benchtop ED-XRF upstream and a more expensive ICP-MS downstream, so that the XRF acts more as a selection mechanism for which filters should be extracted for ICP-MS.

One important question we have is on our assumption that XRF is "non-destructive" to the sample. The membrane filter will certainly be intact after XRF, but will there be some amount of loss of particulate matter that will be significant for trace metals being analyzed in the ICP-MS step of this hypothetical measurement setup?

Thanks for your time and help.


texts:
There are two points of view for the answer of this question:

The biological view, the only one that I faced during my research, states that since it can trigger perilous conditions like metabolic acidosis, cause a neurologic sequelae, etc. methanol is toxic.
The chemical point of view in an answer, which is the one I seek, is the reactions that occur in the body with methanol as a reactant.

Why should it be a reaction? Because I assume something will be toxic for humans when it reacts and disables some of their bodies' vital compounds; e.g.: Hydrogen cyanide reacts with enzymes, renders their active sites useless, and finally causes heavy reduction in bio-chemical reactions that results in quick death.

So, the question is: What reactions use methanol in the body that makes it toxic for us?


texts: Biologically inert water mixture (or other fluid) for heat-exchange purposes

texts:
I have a steel chamber submerged in a 14 deg water bath to keep it at constant temperature. The setup needs to operate without intervention for a very long time (weeks or months).

The bath is exposed to open air in the lab and we have been having issues with mold development in the bath despite adding bleach to the water.

Can you suggest a different additive (or a different liquid altogether) to use to make sure the bath stays reasonably sterile?


texts: Chemical reasons for choosing Salt Water or Chlorinated pool?

texts:
I am currently researching as too which is better for maintaining the chemical balance in a swimming pool. I have obviously tried the standard Google search for Salt Water or Chlorinated Pools and have come up with lots of results. The only problem, is that most of these results are based more around peoples opinions or psuedo-scientific observations. So, to the question:

What chemical reasons are there for choosing a salt water pool over a chlorinated pool?

Note: Salt water meaning the chlorine is generated and chlorinated meaning that you add the tablets/pucks etc.


texts: Compatibility of Grignard reagents with aromatic nitro groups

texts:
Is it possible to form a Grignard reagent from 1-chloro-3-nitrobenzene, as shown below?

Specifically, will the nitro group react with the Grignard reagent formed?


texts: Why is AlCl₃ is known as aluminium chloride while PCl₃ is known as phosphorus trichloride?

texts:
Why is $\ce{AlCl3}$ is known as aluminium chloride while $\ce{PCl3}$ is known as phosphorus trichloride?

I think it is due to variable valency if phosphorus. Is it true?


texts: In silanization, how to clean kerosene from glass surface completely?

texts:
I'm doing some silanization experiments using kerosene to dilute the silan solution. For instance I use a mixture of 10% silan in kerosene. However, after several tests I realized that I cannot completely clean the surface from the remaining kerosene after silanization, and in fact the contact angle that I read is more related to kerosene rather than silan. After silanization, I wash the glass surface with a stream of water and then put the surface in a bottle of acetone and then shake the bottle for 20 sec to clean the kerosene, but apparently it is not enough.
What is the most effective way to get rid of the remaining kerosene on the glass surface?


texts: Elimination of tertiary alkyl halide with lithium aluminium hydride to give alkenes

texts: I'm confused about the mechanism and thus cannot decide which alkene would be the product. Reaction with primary and secondary alkyl halides gives alkanes. What about this case?


texts: How do we measure the energies of molecular orbitals?

texts:
This question came on my mind after a sentence of a teacher who said during a lesson:

  If you imagine hydrofluoric acid, to make the MO's diagram because the
  energy gap between the $\text{2s}$ of fluorine and the $\text{1s}$ of
  hydrogen is quite important you can make the hypothesis at first there
  is no interaction between both. But experiments show that the bonding
  MO's of $\ce{HF}$ has an energy a bit different than the energy of the
  $\text{2s}$ of fluorine.

At first it not supprised me that much, I knew it. But know there is one question.

Question's':

How is that possible to measure the energy of a specific MO? Is that also possible if there is no electron in the MO or if it is an anti-bonding MO?


texts: Which material to use for athletic accessories?

texts:
I'm looking for some guidance in selecting the right material for dance shoes heels and women's self-defense accessories.

I'm looking for a material that 1) has a superb strength-to-weight ratio, can withstand punishing and frequent impact, and very light (like plastic).

The part for the shoe will be very, very slender (stiletto heel), but will have to be able to endure hours of jumping, sliding, stomping, spinning, and skidding dancers… is compression strength the right term?

2) The material must also be safe to use as jewelry, so nothing toxic. Also, I am looking for something that tends to snap, rather than shatter, when it fails under pressure.

3) Lastly, it would be great if this material can be 3D printed, although that is not a must.

An inexpensive material would be ideal, of course, but I am open to learning about a fuller range of materials, including the more expensive ones. I am willing to consider a higher priced material if it will offer substantial value to the accessories in terms of strength, quality, and safety.


texts: Why isn't HCl called hydrogen monochloride?

texts: Since HCl is a covalent compound, then it would be expected to be called hydrogen ***mono***chloride following the rules for naming. Instead it is named as if it were an ionic compound, without any prefixes. Why?


texts: Do both iodine and potassium iodide turn dark in the presence of starch?

texts:
I will do a titration to standardise a solution of sodium thiosulfate with potassium permanganate solution and potassium iodide solution.
My book says that when the potassium permanganate solution begins to lighten, add a few drops of starch indicator and titrate until the solution turns clear.
This seems to suggest to me that starch turns $\ce{I_2}$ dark but not $\ce{KI}$ as some of the $\ce{KI}$ solution would be still in the flask. Is this the case?


texts: Electric Attraction Vs Resonance Energy in Electrophilic Aromatic Substitution Reaction

texts:
Image Credits: MHHE

In the electrophilic aromatic substitution attack of Benzene by the nucleophile, as shown in the figure, nucleophile attacks hydrogen of the intermediate, instead of attacking the positive charge distributed ring; leading to substitution reaction.

Bezene's closed shell of six pi electrons is said to give it an extra stability (resonance energy)$_1$, but it is not clear and precise in the explanation of how the electric attraction is overcome by this another tendency which is described. So, the question is, how is this electrostatic attraction towards positive ring overcome by other tendency of stability?

$_1$ Organic Chemistry 11e by Solomons, Fryhle, Snyder, pg.671.


texts: Exceptional electromagnetic properties of lanthanide series elements

texts:
Why do so many lanthanide series elements have exceptional electromagnetic properties? They can form strong magnets and are also used in superconducting applications. The number of elements in the lanthanide series displaying these properties is far higher than other blocks in the periodic table

One thought is that these properties arise as a result of the magnetic moment of the atoms themselves: filling up the f-orbital contributes to both angular orbital momentum as well as spin orbital momentum. Is this speculation correct?

References:

  Another important use of neodymium is as a component in the alloys used to make high-strength neodymium magnets—powerful permanent magnets.

Neodymium - Wikipedia, the Free Encyclopedia

  Europium becomes a superconductor when it is cooled below 1.8 K and compressed to above 80 GPa. This occurs because europium is divalent in the metallic state,[8] and is converted into the trivalent state by the applied pressure.

Europium - Wikipedia, the Free Encyclopedia

  Samarium doping of iron-based superconductors – the most recent class of high-temperature superconductors – allows enhancing their transition temperature to 56 K, which is the highest value achieved so far in this series.

Samarium - Wikipedia, the Free Encyclopedia


texts: Can nuclear fission or fusion occur together with bond formation in a reaction?

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Is it possible for a nuclear reaction to occur simultaneously with a chemical reaction involving bond formation?

Can anyone suggest an example of this, please?


texts: What happens to the oxygen when carbohydrates turn into hydrocarbons?

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According to the biogenic theory of hydrocarbon formation, hydrocarbons come from pressurized carbohydrates.

I am looking for an explanation of what happens to the oxygen in the process. How could the oxygen break away from the hydroxyl groups of molecules like glucose to form hydrocarbons?


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Is there any such thing as a twist chair conformation?

Also, the boat and the chair conformations are achiral, while the twist boat conformation of cyclohexane is chiral and dissymetric.
What about the half chair conformation? Am I right in thinking that it is achiral because it has a plane of symmetry?


texts: Why are NaCl and NaBr not soluble, whereas NaI is soluble in acetone (in the Finkelstein reaction)?

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My book states that:

  Finkelstein reaction is particularly useful for preparing iodoalkanes. The iodoalkanes are obtained by heating chloro or bromoalkanes with a concentrated solution of sodium iodide in dry acetone.
  $$\ce{R-X~+~NaI->[\ce{acetone,~reflux}]R-I~+NaX}$$
  $(\ce{X=Cl,~Br;~R=alkyl ~group})$
    Sodium chloride and sodium bromide being less soluble in acetone get precipitated from the solution and can be removed by filtration. This also prevents the backward reaction to occur according to Le Chatelier's principle. The reaction gives the best results with primary halides.

My question:

Why are $\ce{NaCl}$ and $\ce{NaBr}$ not soluble, whereas $\ce{NaI}$ is soluble in acetone?
All we can observe is that, sodium iodide has greater molecular weight than sodium chloride or sodium bromide. But, how do this account for solubility of sodium iodide?


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I've read this site for a long time but I had never asked a question, so this is my first time :).

So, i'm currently working on a computational chemistry project on radical cyclization reactions and I'm having trouble trying to understand the reactivity of the radical. Here I show one of the reactions i'm studying:

As you can see, the radical is centered on a carbon atom which is bonded to two chlorine atoms and also to an amide group. As far as I know, chlorine atoms attached to a carbon-centered radical stabilize it due to inductive effect. Also, chlorine atoms can be considered EWG due to their electronegativity. This alone would lower the energy of SOMO orbital, wouldn't it?

In addition to that, amide groups are also EWG, which again would lower the energy of SOMO orbital. So my questions are:

1) Am I correct to say that the more stable a radical is, the less reactive it is?

2) Am I ignoring some other effects which can affect reactivity?

P.S. Below I show the optimized structures of the reactant and transition state calculated at the B3LYP/6-31++G(d,p) level of theory.

Thanks for your attention.

EDIT: Well, I think I wasn't very clear about what's bothering me. I have the energies of the reactant, ts and product and they are ok, nothing wrong. It had just came to my mind that the radical is very stabilized in the reactant and I just wanted to know if my reasoning was correct. Also, in that same reasoning, could it be that a carbon-centered radical with no chlorines be more reactive? Again, this is a curiosity that came to my mind and I'm want to be sure I'm thinking it in the correct way.


texts: How do we define "volume" of the gas undergoing free expansion in vacuum?

texts: Usually volume occupied by the gas is defined as the the volume of the container, but as it expands freely (Joule's free expansion), we can't say anything about volume in a concrete sense as we don't have a rigid container. How do we think about this in a more concrete way?


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We can predict whether a reaction can occur spontaneously by calculating the change in Gibbs' free energy.

I was just wondering whether there is any general measure of the thermodynamic stability of any substance?

Can I look at a random substance and using a table of thermodynamic values predict whether this substance is stable or not within a range of given conditions (pressure, temperature, etc.).


texts: How to calculate the final concentration of calcium ions from known starting masses of carbonate and calcium ions?

texts: If $\pu{50.0 mg}$ of $\ce{CO3^2-}$ and $\pu{50.0 mg}$ of $\ce{Ca^2+}$ are present  in one liter of water, what will be the final (equilibrium) concentration of $\ce{Ca^2+}$ expressed in moles per liter?