texts:
I'm planning an instructional demonstration of smelting. It seems you may be able to take rust (hematite, $\mathrm{Fe_2O_3}$) and carbon (perhaps from charcoal briquettes), place this in a crucible of ample size, light the carbon on fire, and the formed iron may melt and accumulate on the bottom of the crucible.

Yes, iron burns, everyone knows you can light steel wool.  I'm hoping that the interface above the iron will become encrusted with enough slag and ash that there won't be much of the formed iron burning, and what's specific about steel wool versus trying to light a spoon on fire is that the steel wool has a very high surface-to-mass ratio, enabling it to be heated well as well as provide ample mass transfer area.

What are the problems with this demonstration, and what kinds of solutions exist for this?  For example, I foresee that I need to use lots of extra carbon to make sure that any iron formed doesn't reoxidize.


texts:
How to get or understand a sample in chemistry without knowing its chemical name or compound or formula? I was thinking about whether there is a way to understand what the chemical compound sample that one might have. He/She doesn't know what its formula or its chemical properties or anything .He/She just got that one and was thinking what was that chemical and was interested to know about its structure. Would it be possible?
I am totally new at Stack Exchange so I doesn't know is this the proper way to ask.
And I am 15 year old so I doesn't know if these are taken in my upcoming classes but when I googled it or searched in many websites,I was not able find answers,So I am asking here.I have seen that we can guess the compound using many experiments but so also if the compound has been not found yet in human history would we be able to understand it?
Edit: This question had been closed stating it need to be more focused. I just wanted to clarify that what I wanted to know was whether there is a specific procedure to identify the chemical structure of the compound from just a sample alone.


texts: Is Polyethylene Glycol always derived from Ethylene Glycol? If not, how does it differ?

texts:
I have heard Polyethylene Glycol is derived from Ethylene Glycol, so was doing some research to see how they differ and found this.
Now this states that:

Polyethylene glycol is produced from the reaction between ethylene oxide and water, ethylene glycol or ethylene glycol oligomers.

As I understand it ethylene glycol is made from ethylene oxide and thus I assume that means PEG can be derived from either, is that what the above statement is saying? Though I'm not sure how ethylene glycol oligomers come into play here.
What I'm trying to work out, is there any difference in the PEG depending on what it is derived from or does it come out exactly the same?
If so, what is the purpose of deriving it from one or the other? Different uses? Safety elements? Human consumption?
I have also read that the molecular weight in turn determines the characteristics of each type or category of PEG.
With that in mind and the difference in what PEG is derived from, does the PEG differ at all depending on what it is used in? (Food, Medicine, Cosmetics, Vaccines etc)


texts: If caffeine is an alkaloid, why is coffee acidic?

texts:
I have just put together on my mind these two facts: caffeine is an alkaloid and brewed coffee is slightly acidic (pH = 5).

My Biology teacher and my Chemistry teacher could not elaborate satisfying answers, but my Physics teacher said it could be because of substances to the industrial coffee powder (hillbillies in Brazil, for instance, do not display gastritis attained from too much coffee).


texts:
Why is the reaction between hydroxide and water reversible, when the reaction between oxygen ions and water is not? And is there a reason why the products of reaction 2) are written separately, instead of "2OH"?

1) $\ce{OH- + H2O <=> H2O + OH-}$

2) $\ce{O^{2-} + H2O -> OH- + OH-}$


texts: I know that $\ce{NO2}$ has 3 effective pairs,  so it is likely to have trigonal planar structure. In trigonal planar structure we usually see three atoms bonded to central atom at 120°. But in $\ce{NO2-}$, I observe that though it has three effective pairs,  but still, it is not having the desired structure,  with only 2 O atoms bonded to N atom. Can anyone explain the situation?


texts: Are glucose and galactose cis-trans isomers of each other?

texts:
Glucose and galactose are diastereomers of each other. However, is it correct to say that they are cis-trans isomers of each other? Does it make a difference with regard to terminology if glucose and galactose are in cyclic form i.e. are glucopyranose and galactopyranose cis-trans-isomers of each other? And is it correct to say that glucopyranose has $2^5-1=31$ cis-trans isomers?

I would also appreciate some references to verify the correct use of terminology in this situation.

NOTE: I have edited this question to clarify that I'm interested in the cyclic form as well.


texts: Fenton's reagent application to leachate

texts: What is the experimental procedure for applying fenton's reagent to leachate? What doses of hydrogen peroxide and ferrous sulphate required? How much contact time needs to be provided?


texts: Why do different gases have the same molar volume?

texts:
Molar volume:

  The molar volume, symbol $V_\mathrm m$ is the volume occupied by one mole of a substance (chemical element or chemical compound) at a given temperature and pressure.

At S.T.P conditions the molar volume of any ideal gas is $\pu{22.711 dm^3}$. My question is: how can two gases with giant difference in molecular size (say $\ce{He}$ and $\ce{Fe}$) have the same volume, considering that the size difference between them is huge, shouldn't the volume they occupy also be different?

Thanks to @MaxW for pointing out a fault.


texts: How is bonding in the trihydrogen cation and triatomic hydrogen possible?

texts:
According to wikipedia $\ce{H^+3}$ and $\ce{H3}$ are possible and have been synthesized. It says that $\ce{H^+3}$ is stable too. Can anyone please tell me how is the bonding possible?

Hydrogen has a valency of 1 but it still bonds like Ozone. How is this possible?

Links:

$\ce{H^+3}$ - Trihydrogen Cation
$\ce{H3}$ - Triatomic Hydrogen


texts: Does increasing electronegativity imply more covalent character?

texts: If there is a larger electronegativity difference between two atoms, shouldn't the compound be more ionic? In an explanation of the diagonal relationship, it states that "on moving across the period, the elements become progressively more covalent" yet their electronegativity increases. What is even meant by an element being covalent? I thought only compounds/molecules could be covalent.


texts:
I was reading about purification of organic compounds and I came across this.
I quote below, a line from the excerpt that caused my confusion.

The organic solvent is later removed by distillation or by evaporation to get back the compound.

My question:
Why can't we just seperate the organic compound from the water by distillation/evaporation directly?

My approach:
The aim of the procedure is to - seperate out from water, the required organic compound that is presented to us in an aqueous solution form.
If the organic compound has relatively higher boiling point, use evaporation.
If the organic compound has relatively lower boiling point, use distillation.
If more than two compounds are to be recovered, use fractional distillation.

I felt like it was 'unnecessary' to mix it with an organic solvent and then proceed with evaporation/distillation of the new organic solution without water content. We could just proceed with evaporation/distillation of the aqueous solution directly and recover the organic compound - I've stated how in the 'My approach' section.

Self-evaluation:

I might not be aware of the various reasons because of my lack of knowledge and hence consider it unnecessary.
Distillation might cause reactions/decomposition because it is being heated in an aqueous medium while it might not react in an inert organic solvent.


texts: Is didehydrobenzene valid IUPAC nomenclature?

texts:
I don't know if this compound exists in real life or not. If it did, what would be the correct IUPAC nomenclature for it? According to me, it could be:

1,2-didehydrobenzene
cyclohexa-1,3-dien-5-yne


texts: How fast does MgSO4 absorb water from the air?

texts:
I had to do a lab to figure out the water of hydration of magnesium sulfate. However, after the heatings, I had a loss 0.45 g of water resulting in 0.63 g of anhydrous magnesium sulfate. This gives 0.02497 mol of water and 0.005237 mol of anhydrous magnesium sulfate. Thus, this would imply that 0.02497/0.005237 = 4.77 = 5 is the water of hydration.

However, my chemistry teacher specifically said that the actual number for the MgSO4 he gave us was 7. I couldn't figure out exactly where I went wrong, but my only guess would be that the wait of 5 minutes for cooling the substance down. Some research shows that MgSO4 is a great drying agent, and the humidity during the time I carried out the experiment was 75% humidity.

Doing the calculations, during the five minutes of cooling, it must have absorbed 0.01169 moles of water in order for 7 to drop to 4.77. Is this plausible given 75% humidity? I don't know anything about Chemical kinetics yet.

Edit: Here are the procedures.
1. Measure the mass of the empty crucible with the lid.

Add some amount of the (powdered) hydrated salt in the crucible, and measure it's total mass with the lid.
Heat the crucible for 20 minutes over a bunsen burner, with lid slightly open.
Wait for 5 minutes, and then measure the amount of mass after heating.

The relevant data is given above.


texts: Why does DMSO help facilitate halohydrin reactions?

texts:
It would make sense, due to bond energy, that water molecules would have a hard time competing with $\ce{Br}$ in a bromonium ion intermediate.

However, I was reading that by doing the reaction in DMSO, it encourages the protonation of the water molecules. How? What is the rational behind this?


texts: How to identify the repeating unit in a polymer?

texts:
Polyvinyl acetate, PVA, is a useful adhesive for gluing together articles made from wood, paper or cardboard. The monomer of PVA is ethenyl ethanoate.
   PVA is formed from B by the process of addition polymerisation.
  Draw a section of the PVA molecule containing at least 2 monomer molecules and identify clearly the repeating unit.
  (Source: University of Cambridge international Examinations, General Certificate of Education Advanced Level, Chemistry, Paper 4 Structured Questions, May/June 2011, Q4)

Shouldn't the $\ce{C=C}$ double bond break and each of the carbon atoms involved in the double bond are attached to $\ce{CH3OCO}$. so the repeating unit is $\ce{CH3OCO}$.


texts: Will squeezing lemon juice on top of foods with ferrocyanide additive release hydrogen cyanide gas?

texts:
For example, will squeezing lemon juice on top of table salt with sodium ferrocyanide ($\ce{Na4[Fe(CN)6]}$) additive (E 535) release hydrogen cyanide gas?

Examples of ferrocyanide additives:

sodium ferrocyanide (E 535)
potassium ferrocyanide (E 536)
calcium ferrocyanide (E 538)


texts: Is the conjugate base of every polyprotic acid amphoteric?

texts:
Since all compounds with an accessable free lone pair can act as a Brønsted-Lowry base, I was wondering if there was any specific example of a substance that when it loses a proton, it cannot accept a proton but can donate another proton.

Please note that I am not considering something like sulfuric acid which is a strong diprotic acid, as $\ce{HSO^{-}_{4}}$ still accepts a proton even if its to a limited extent.


texts: Long-term storage of Ascorbic Acid mixed with Sodium Bicarbonate

texts:
Every day I mix two parts of ascorbic acid powder with 1 part of sodium bicarbonate powder and place the resulting powder into an airtight container. I have noticed that if the resulting powder is mixed with water within 30-60 minutes, it fizzles indicating the release of carbon dioxide as a byproduct of the acid-base reaction. However, if I leave it untouched (within a dry and airtight container) for 6 to 8 hours, it hardens. If I crush it (so it turns into powder again) and mix it with water, it no longer fizzles.

My questions are:

Why does it harden and no longer fizzles if mixed with water after a few hours? Does the acid-base reaction take place even without adding any liquids to the mixed powder?
Most importantly, does the reaction that causes the hardening and absence of fizzling cause any kind of degradation (e.g., oxidation) to the ascorbic acid? In other words, can I mix ascorbic acid with sodium bicarbonate (both in powder form), store the resulting powder in an airtight container and consume over a few months? Would that diminish the efficacy of the Vitamin C in any way?

Thank you in advance.

Update:

I have bought sodium bicarbonate from a different manufacturer and now after mixing it with ascorbic acid, nothing happens until water is added. It can sit for 24+ hours, without hardening and it will still fizz when mixed with water. I suspect the sodium bicarbonate from the previous manufacturer was slightly moist  and this one is completely dry.


texts:
We were letting our kids play with sparklers on New Year's Eve, and my friend's son asked his Dad:

  What would happen if we threw the sparkler into the water? Would it keep burning under water.

My friend pondered that for a moment - and said it depended if the reaction was based on magnesium or not.

My question is: Are children's sparklers based on a magnesium reaction?


texts: Total Chloride Vs Organic/Inorganic Chloride

texts: I am currently running a project to detect chloride level in crude palm oil. On most lab service websites, some offer total chloride detection and others offer organic chloride detection. What are the differences between total chloride and organic chloride?


texts: Does a polyethene shrinking signify negative or positive entropy?

texts:
When I think of something shrinking, I would intuitively think it decreases in entropy as there is less movement. E.g. if a gas was to reduce in volume, there would be less movement of the particles and hence less entropy.

How about for as solid?

I have read if polyethene shrinks, it INCREASES in entropy.

Why is this the case?


texts:
I know that Aluminium Oxide is an amphoteric substance meaning that it reacts with both acids and bases. I recently learned that Aluminium has very good corrosion resistance due to the "Aluminium spontaneously forms a thin but effective oxide layer that prevents further oxidation."

However, in the test for Nitrate Ions, an Aluminium foil is added into the solution, the Nitrate Ion is reduced by the Aluminium, but this Aluminium foil surely has Aluminium Oxide which should prevent the reaction from happening, but it happens anyway. How can this phenomenon be explained?

Source: http://www.aluminiumdesign.net/design-support/aluminium-corrosion-resistance/


texts: What would be the enthalpy change for a isothermal expansion?

texts:
I was doing a question on thermodynamics and came across this one stating

During isothermal expansion of gas of an ideal gas :
a) Internal energy decreases
b) Enthalpy increases
c) Enthalpy reduces to zero
d) Enthalpy remains unchanged

I cannot agree to any of these as $\Delta H = \Delta U + W$, $\Delta U = 0$ as $\Delta T = 0$ but $W \neq 0$ so $\Delta H = W$ which is $\neq 0$ and as $W \lt 0$ the enthalpy should decrease but how much how do I know and to add to the confusion the answer given is enthalpy remains unchanged in the light of the equation $\Delta H = \Delta U +\Delta n_\mathrm gRT$ and $\Delta U$ and $\Delta n = 0$  so $\Delta H = 0$ is it right.


texts: Regarding the probability density of finding an electron in between a bond

texts:
I'd found the image attached on a website explaining the molecular orbital theory.

My question is, shouldn't the graph have a maximum at the middle of the two hydrogen atoms? since my intuition tells me that the electrons have a great chance of being in the middle rather than anywhere else. hmm, this train of thought has led me to another question, what exactly does this graph even represent? I mean, which electrons probababilty does it even show? or does it show us the probability of finding any electron participating in the constructive bonding.
another question that I have is this, if say, we were to excite one of the electrons into the higher antibonding orbital, what would exactly happen to this orbital, the shape I mean, would it simply cease to exist? since we're literally making the bond cease to exist (bond order=0) or would it assume the shape of this?

I still haven't completely grasped the true nature of such orbitals, I think it's evident from all these questions.


texts: Strong Base and weak acid reaction problem

texts: I got the above problem correct by setting up the net ionic equation and finding the limiting reactant. I found that there were 0.01076 moles of NaOH left, and then calculated it's molarity which led to the PH. I'm confused by when you have a strong base and weak acid, when calculating the pH when all of the acid is used up, why can you disregard the acid's conjugate base in the calculation of the pH. Doesn't the reaction still create a certain amount of the acids conjugate base?


texts:
I have read the test for chloride ions (chromyl chloride test). The reaction is:
$$\ce{K2Cr2O7 + 4NaCl + 6H2SO4 -> 2CrO2Cl2 + 2KHSO4 + 4NaHSO4 +3H2O}$$
My doubt here is if chlorine gas is evolved in a side reaction. Is it evolved in detectable amount? The side reaction is:
$$\ce{6Cl- + (Cr2O7)^{2-} + 14 H+  → 3Cl2 + 2Cr^{3+} + 7H2O}$$
Can someone please confirm this?


texts: Why don't all electrodes produce the same results in the electrolysis of potassium iodide?

texts:
While in lab, I accidentally used two paper clips while trying to electrolyze potassium iodide and all I saw was was phenolphthalein turning pink at the cathode and no brown at the anode.

I asked my instructor to allow me to repeat the experiment with pencil lead, which produced brown and pink, aluminum foil, which only produced pink, silicon which produced brown and pink, and copper, which produced brown and pink.

Then I used one paperclip at the cathode and a piece of pencil lead at the anode and I found that the anode turned pink and the cathode turned brown. Then I flipped the pencil lead and paper clip (anode to cathode and vice versa), and only the cathode (pencil lead) turned pink and there was no brown at the anode (paper clip).

My original hypothesis was that the increased resistance in the silicon and graphite lowered the current since the battery provided a constant $\pu{9V}$, but being able to get brown and pink with copper invalidated that hypothesis.
This has been bugging me all day, and my instructor says she does not know why this is happening.


texts:
Why does rate of evaporation of solution decreases on adding a non volatile component?

Also what happens if we add a volatile solute?


texts: rate of combustion of alcohols and hydrocarbons in relation to the number of carbons in the chain

texts:
I understand that the heat released when burning alcohols is greater as long as the number of carbons in the alcohol chain is increased (i.e the enthalpy of butanol is greater than propanol > ethanol> methanol).
my question is about the rate of combustion. which of those alcohols will burn faster? is there any relation between the rate of combustion and the number of carbons in straight alcohols (or straight chain hydrocarbons)?
I know that the evaporation rate is inversely proportional to the number of carbons in the chain, is there a different relationship regarding the rate of combustion?
this is actually my question, but i would like to share what brought me to ask this. we have made an experiment with a bomb calorimter to determine the enthalpy of combustion of the first 4 alcohols. i have made 4 plots of the temperature v.s. the time and calculated the temperature change and ultimatelty the enthalpy. yet it seems from the shape of the graph's that the increase in temperature is steeper for the long chain alcohols. i'm not sure if it's just my imagination or that there is really a significant relation here. is that actually indicating that as the number of carbons is increased- the rate of combustion is faster?


texts: How hydrate isomerism results difference in colours?

texts:
The standard example is $\ce{CrCl3.6H2O}$, which can have three distinctly different
crystalline compounds now known as

$\ce{[Cr(H2O)6]Cl3}$ (violet),

$\ce{[CrCl(H2O)5]Cl .H2O}$
(blue-green), and

$\ce{[CrCl2(H2O)4]Cl.2H2O}$ (dark green).

How does this difference of ligands in octahedral system affect the colour of compound? I think it may be due to the change of splitting energy but if that so then how does it actually work?


texts: Why is this organic compound trans, and not cis?

texts:
I'm reading a high school chemistry course online, and I'm now reading about geometric isomers.

They provide this example:

And in terms of naming it, they say this:

  Begin by identifying the parent chain - it is the continuous chain that contains the carbon-carbon double bond. The two groups that belong to the parent chain are on opposite sides.

Then supply this illustration:

And with that explains that it's trans-3-ethyl-3-hexene for that reason. I don't quite get their explanation though, becuase to me it seems like this could also be cis.

Why can't it be this one:

As far as I understand, that's also a valid way of expanding it, because it has the same amount of carbons in the chain and the numbers are still as low as they get. The only difference is that this one would be cis-3-ethyl-3-hexene instead of trans-3-ethyl-3-hexene.

So, why exactly is it that only one of them is right?


texts:
I was looking into how the solubility of amides compares to other compounds e.g. acids and amines, and came across these two statements on the wikipedia page for amides:
https://en.wikipedia.org/wiki/Amide#Hydrogen_bonding_and_solubility
"The presence of a C=O dipole and, to a lesser extent a N–C dipole, allows amides to act as H-bond acceptors. In primary and secondary amides, the presence of N–H dipoles allows amides to function as H-bond donors as well."
"Typically amides are less soluble than comparable amines and carboxylic acids since these compounds can both donate and accept hydrogen bonds."
I understand that amides can act as both H bond donors and acceptors, so I'm wondering how the second statement can make sense?
Additionally, would it be correct to say amides have greater solubility in water since they can form more H bonds in total compared to amines and acids?


texts: Why is there a factor of half in the definition of bond order?

texts:
I was recently taught about molecular orbital theory and bond order:

$$\text{Bond order} = \frac{\text{Number of bonding electrons} - \text{Number of antibonding electrons}}{2}$$

I was wondering, what is the purpose of dividing by 2?


texts:
I'm watching MIT chemistry by Donald Sadoway. In one of his lectures devoted to solutions and phase separation, he performs experiments with absinthe.
First he mixes absinthe with 5 $\times$ water which turns into milky louche.

Then he adds some cognac and the mixture becomes transparent again. I don't grasp his explanation of this.

Here is a timestamped link to the video.
I'll also briefly summarize his argument below:

  ... and why did he add cognac? ... it's cause if you have a fat phase here and you've got an aqueous phase here and if you add alcohol, you got

  $(fat)\:\textrm{CH}_3 \textrm{CH}_2 \textrm{COOH} \: \dot{}\dot{}\:\textrm{OH}_2$

  ... this can bond to the water by hydrogen bond and this aliphatic tail can stab the fat and bring them into solution. This is why you have these recipes...

What does "stabbing the fat" mean?

Does it mean that the ethanol somehow makes the surface between fat and water disintegrate thus turning the mixture into a single phase solution?
Or maybe ethanol + water + fat somehow  combine to form a single molecule so that, again, there is a single phase solution now?


texts: In an exam, we were given the following graph and asked to explain why the slope of the change in r vs. Z changes dramatically at a point along the curve. I understand that the d block causes the change in slope for all of the series, but why is the slope from $\ce{He}$ to $\ce{Ne}$ less than that from $\ce{Ne}$ to $\ce{Ar}$? Why is this trend not present for any of the other series? I initially thought that this might have to do with the introduction of the p-block, but that would not explain the absence of the trend for the other series.


texts: Relative atmospheric lifetimes of carbon monoxide and methane

texts:
In atmospheric chemistry, the lifetime of most substances is dictated by their reactions with the hydroxyl ($\ce{OH}$) radical. The rates of these reactions are listed by NIST as about $\mathrm{1.5e^{-13} cm^{3}\  mol^{-1}\ s^{1}}$ for carbon monoxide ($\ce{CO}$) and $\mathrm{6.7e^{-15}\ cm^{3}\ mole^{-1}\ s^{1}}$ for methane ($\ce{CH4}$). With atmospheric $\ce{OH}$ concentrations of about $\mathrm{1.2e^6\ mole\ cm^{-3}}$, this leads to an atmospheric lifetime of about 2 months for $\ce{CO}$ and 4 years for $\ce{CH4}$. This is indeed what's observed, so the relative reaction rates are definitely experimentally true.

My question is: what's the theoretical explanation for the $\ce{CO}$ reaction being faster? I would expect the $\ce{C-O}$ triple bond to be much more stable than any $\ce{C-H}$ bond. In atmospheric chemistry texts I've seen, the reaction goes like

$$\ce{CO + OH -> CO2 + H*}$$
$$\ce{H* + O2 -> HO2}$$

I've also come across notes from a pure chemistry class that mentions a different reaction with an intermediate:

$$\ce{CO + OH -> OCOH*}$$
$$\ce{OCOH* + O2 -> CO2 + HO2}$$

I can't get my head around how the intermediate would/should increase the reaction rate, though, or how something like electronic configuration could lead to $\ce{CO}$ being more susceptible to $\ce{OH}$ than $\ce{CH4}$.


texts: Orbital size of Carbon and Oxygen in Methanal

texts:
I was given an introductory question into Carbonyl chemistry today and I wanted to ask a question about Methanal.

The following picture was shown below of Methanal:

and I noted that the orbital sizes differed for both Carbon and Oxygen in the top and bottom diagrams. I thought one of these diagrams must be wrong.

I then knew that as Oxygen has more protons than Carbon, then its atomic radius is smaller, meaning the orbital size must be smaller too, so I thought that the bottom diagram represented the size of the p orbitals better both for anti bonding and bonding.

Is the diagram for $\pi$ bonding drawn correctly in terms of orbital size?


texts: When I asked my teacher whether a nitrogen bonded to 3 unique groups counted as a chiral center, they said that it did not because nitrogen undergoes rapid inversion at room temperature. What causes this? And what other atoms are capable of doing this?


texts: What are the correct equilibrium arrows?

texts:
I was recently subject to some atrocious teaching. One of the gems that found me was the equilibrium arrow usage. I am accustomed to write $\ce{<=>}$. Yet, the entire class had to use ⇆ throughout the semester. Teacher's argument was that each harpoon from $\ce{<=>}$ has a meaning already, the movement of a single electron in a mechanism.

I concur, but I can't think of an situation in which the meaning of a harpoon is unclear because of the context. This is unlike Y being the symbol for both EDTA and yttrium, allowing $\ce{[YY]^{-1}}$ to have a meaning.

I tried to find the correct character, but not even the IUPAC Gold Book (1) (2) has a clear stance on it.


texts: Why can Neutral Red (indicator) not test values below its pKa?

texts:
It is the only indicator I have found that does not test below its pka, and can't think of any reason for this.

Neutral Red has a pKa value of 6.8.
(
Reference 1,
Reference 2
),
but looking at its pH testing range, it only shows from pH 6.8-8.0 (Reference 3)

What would be the reason for this?

Thank you


texts: What is the chemical structure of the cocoate ion vs. the olivate ion?

texts:
I am wondering how the cocoate ion (in natural soaps, in the form of sodium or potassium cocoate and from the saponification of coconut oil) differs structurally from the olivate ion (from the saponification of olive oil)?

My family is attempting to implement the methods in solveeczema.org and believe that our children have detergent-reactive eczema and our baby is most sensitive.  In moving away from detergents and to natural soaps, we have started using soaps that result from the saponification of vegetable oils - mostly coconut oil, palm kernel oil, and olive oil.  We discovered that our other child (a toddler) seems to react to these soaps in a similar way that he would react to a cleaner containing much stronger/harsher surfactants (such as sodium lauryl sulfate).

Our toddler seems to get bad eczema flares using soaps that contain cocoate, but he has no reaction to soaps that contain 100% olivate.  I have no idea why this would be, since I would assume that both cocoate and olivate have the R-COO- structure.  Is cocoate much more hydrophilic than olivate?  Is the functional group different?  Is the cocoate ion a longer molecule that looks much more like a harsh detergent than a salt resulting from saponification of olive oil or tallow?

Please note that this question is related to two questions already asked:

1)  Is soap the natural form of Sodium Lauryl Sulfate?

2)  https://parenting.stackexchange.com/questions/5047/how-to-test-whether-my-toddler-is-allergic-to-detergent/5049#comment7644_5049


texts: What is the major product on chlorination of 2-methylbutane?

texts: I came across a question asking for the major product on chlorination of 2-methylbutane. The answer in the back of the book says it will be 2-chloro-3-methylbutane. However, I thought the major product would be 2-chloro-2-methylbutane. The later is formed through a tertiary free radical with eight hyper-conjugative structures, whereas the former forms through a secondary free radical with only four hyper-conjugative structures. How is this possible?


texts: Acid-base titration: Calculate pKa with only three values given

texts:
There's an unkown acid, diluted with an unknown amount of water and titrated with $\ce{NaOH}$.

  After adding $\pu{10.00 mL}$ $\ce{NaOH}$, a $\mathrm{pH}$ value of $4.65$ is measured.
  After adding another $\pu{12.22 mL}$ ($\pu{22.22 mL}$ $\ce{NaOH}$ in total), the equivalence point is reached.

  Calculate the $\mathrm{p}K_\mathrm{a}$ of the acid!

I'm currently facing this uncommon task regarding acid-base titration. There's quite few information in this text, only three values are given:

\begin{align}
V_1(\ce{NaOH}) &= \pu{10.00 mL}: &\quad &\mathrm{pH = 4.65} \\
V_2(\ce{NaOH}) &= \pu{22.22 mL}: &\quad &\text{equivalence point reached}
\end{align}

What I've got so far:

Before adding any $\ce{NaOH}$, the reaction should look like this:

$$\ce{HA + H2O <=> A- + H3O+}$$

I expect the neutralisation reaction to be:

$$\ce{A- + H3O+ + Na+ + OH- <=> NaA + 2 H2O}$$

In general $n = c V$. At the equivalence point $n(\ce{NaOH}) = n(\ce{HA})$, so:

$$C(\ce{NaOH}) \cdot V_2(\ce{NaOH}) = n(\ce{HA})$$

$$C(\ce{NaOH}) = \frac{n(\ce{HA})}{\pu{22.22 mL}}$$

Henderson-Hasselbalch:

\begin{align}
\mathrm{pH} &= \mathrm{p}K_\mathrm{a} + \log{\frac{C(\ce{A-})}{C(\ce{HA})}} \\
\mathrm{p}K_\mathrm{a} &= \mathrm{pH} - \log{\frac{C(\ce{A-})}{C(\ce{HA})}} \\
\mathrm{p}K_\mathrm{a} &= 4.65 - \log{\frac{C(\ce{A-})}{C(\ce{HA})}}
\end{align}

I'm unsure how to express this equation as a function of $V_1(\ce{NaOH})$. I may be on the wrong track as well. Any help is appreciated!


texts: Is there an authoritative list of chemical reactions/transformations?

texts: Is there somewhere where I can find an authoritative list of chemical reactions, energy requirements, known catalysts, etc.? If not, how do you know if and how to transform substance A to substance B? What references do you use?


texts: How is this Steampunk patina being applied?

texts:
Can anyone explain what is being deposited in this video @ 11:40?

It's Steampunk patina technique to make things look old and decrepit.

  "The mixture consists of: 50 g of 30% vinegar, 20 g of salt and 50 g of water. I used a 5 volt and 2 amp power supply. Connect the positive terminal to the part, and the negative terminal is lowered into the water.  Time of blackening of the metal somewhere in 10 minutes"

And the cathode is stainless steel. It wipes off with a scourer. So specifically,

What is being deposited?
Is the deposit related directly to the cathode material?
What happens if I change the cathode to say normal steel /copper wire?

I'm not a chemist, so I won't understand anything clever or those molecular spider diagrams...


texts: I wanted figure out what the identity of this scrap metal was. It seems to be some sheet metal but Wikipedia says sheet metal can be made of a variety of metals. My dad said it might be tin so I thought I'd try and see if it would melt easily since tin melts at a very low temperature. I heated it with a propylene torch but I could only get it red hot. I did notice that it turned yellow when heated and smelled a bit rotten. Any ideas to what this could be?


texts: Trying to understand the contradiction in the data of Proust/Dalton/Berzelius vs Gay-Lussac

texts:
I am trying to understand some of the historical context behind the discovery of atoms (pre-Avogadro).  In particular, I am getting stuck in reading the following documents:

http://physics.unl.edu/~klee/phys261/readings/class09.pdf
http://physics.unl.edu/~klee/phys261/readings/class11.pdf

My understanding is that "atoms" (as they understood them at the time) were discovered to react in whole-number ratios by Proust/Dalton/Berzelius (who measured by mass) and by Gay-Lussac (who measured by volume).  While this was highly suggestive of some sort of "atom" concept, there was a discrepancy between the two sets of measurements.  But I'm having trouble following the specific discrepancy pointed out by the above PDFs.

The first PDF gives the following mass data:

                         Mass of Nitrogen    Mass of Oxygen
Nitrous Oxide (N₂O)             100 g             58 g
Nitric Oxide (NO)               100 g            127 g
Nitrogen Dioxide (NO₂)          100 g            239 g

The text doesn't explicitly mention how this data was interpreted by Proust/Dalton/Berzelius.  Looking at the data, I don't see that much can really be said:

? N + 1 O = ? Nitrous Oxide (N₂O)
? N + 2 O = ? Nitric Oxide (NO)
? N + 4 O = ? Nitrogen Dioxide (NO₂)

The question marks are there since they didn't know what was "in" 100 g of nitrogen, which would mean that they didn't really know what was in the product, either, right?

So that's my first question:  Am I correct in thinking that the above is about as far as Proust/Dalton/Berzelius could go with that data?  Or were they pretty sure they knew how to fill in the question marks?

Now, continuing on to the second PDF, when Gay-Lussac measured by volume, he had:

                        Volume Nitrogen  Volume Oxygen  Volume Product
Nitrous Oxide (N₂O)             100           49.5             100
Nitric Oxide (NO)               100          108.9             200
Nitrogen Dioxide (NO₂)          100          204.7             200

Now, the document goes on to say that the above data might suggest the following formulas:

2 N + 1 O = Nitrous Oxide (N₂O)
1 N + 1 O = Nitric Oxide (NO)
1 N + 2 O = Nitrogen Dioxide (NO₂)

The text then says that the equation for nitrous oxide represents a contradiction.

But I don't see how that contradiction follows from the data.  As the text suggests, if we say that a volume of "50" represents one "atom" (so that volume of "100" nitrogen represents two atoms), wouldn't we say:

2 N + 1 O = 2 Nitrous Oxide (N₂O)
2 N + 2 O = 4 Nitric Oxide (NO)
2 N + 4 O = 4 Nitrogen Dioxide (NO₂)

Wouldn't that mean really it's the other two equations that don't make sense based on the number of atoms not working out?  I feel like I'm missing a basic idea in the text.

(FYI, I am not in school and so I'm not a student, nor is this homework.)


texts: Making elemental sulfur from pyrite FeS2

texts: Has anyone done this or know of a good experiment that would allow someone to make elemental sulfur from $\ce{FeS2}$ (iron pyrite)?


texts: In chemistry one can recognize that the four states of matter are solid, liquid, gas and plasma. The first is rigid, and has a definite shape and volume. The second doesn't have a shape, and assumes the shape of its container, but it has a fixed volume. The third doesn't have either a shape or a fixed volume and assumes the volume and shape of its container. What about the fourth one (plasma)?


texts: Is it true that organic chemistry as an independent research field is no longer developing?

texts:
One of my professors told me that organic chemistry has become a tool for biological research, rather than an active research field of its own.

Is this assertion valid? Does it describe correctly the general attitude towards organic chemistry in research institutions today?


texts: Benefits of a Buchner funnel w/ a fritted disc instead of Quantitative Filter Paper Circles

texts:
I was wondering if someone could enlighten me on some example us cases where one would be better of using a Buchner funnel with a fritted disc (example), as opposed to a Buchner "style" filter (example) that requires a filter paper (example).

A few times in the past when I was looking to filter a specific substance and asked about fritted discs, most of the replies were "don't use a fritted disc, just use a funnel with the filter papers instead," and this got me wondering when using a fritted disc would be preferable over a filter paper. Originally, in my chemistry naivety, I mentioned that I may end placing a filter paper inside a Buchner funnel with a fritted disc, to "get the best of both worlds" I suppose, but this idea was shot down pretty quickly.

Heres the pros/cons list for both filter types that I have thus far, hoping some can add to it:

Buchner "style" filter with filter papers

Pros

The filter papers are cheaper
Changing the filter paper pore sizes are much easier, as it's just a matter of getting the filter papers with the desired pore size
One can easily cut the filter papers to the proper diameter if needed

Cons

??

Buchner filters with fritted discs

Pros

Filters are reusable if cleaned properly
???

Cons

Fritted discs are much more expensive than filter papers
Fritted discs don't seem to have specific pore sizes
Fritted discs seem like they can be a pain to clean properly

Thanks in advance for any input!


texts: Aldehydes and ketones have electrophilic centres at their carbonyl C, since the carbonyl O polarises the bond and attracts electron density towards itself on account of its high electronegativity. But despite this electron density, the oxygen atom hardly ever acts as a nucleophilic centre. If at all, it is the alpha C, which in enols and enolates acts as a nucleophile. I only know of the Wittig reaction in which the O also reacts with the reagent (the P atom in this case). Is there any reason for the low reactivity of the oxygen? It is joined to C with a pi bond, which in any case is easy to break on attack by a reagent.


texts: What physical properties are manifested when an electron leaves Na and moves to Cl to form an ionic bond?

texts:
When an ionic bond is formed between Na and Cl, the lone electron in Sodium's outer shell leaves, and completes Chlorines outer shell.

Are there any physical characteristics that I can use as an observer to see this movement?

When the reaction begins (as seen in this video https://www.youtube.com/watch?v=oZdQJi-UwYs) a lot of light and heat is created. Is this the electron moving from one atom to the other? If not, what is causing it?

Secondary to this. Why does the reaction need help (by either adding water in the video above, or pre-heating the Sodium before dropping it in the Chlorine gas) before it gets started?


texts: Is Effective Nuclear Charge the same as Core Electrons?

texts:
I'm wondering, what is the difference between the two?

Using the equation for Eff: $\ce{Zeff = Z - S}$

Z being the number of protons in the nucleus and S being inner-shell electrons.

For example:

When calculating Lithium, I first do the electron configuration,

$\ce{1s^2}{2s^1}$

The valence electron configuration is then 1, from looking in the periodic table - it is in the first column. Then to find the core electron configuration, I subtract the valence electron number, 1, from the number of total electrons, 3. I then wind up with 2 as my core electron configuration. Am I just doing the same equation twice if I were to calculate Zeff?

$\ce{Zeff = 3 - 2 = 1}$

They're the same thing, are they not?


texts: Why do aqueous solutions of sodium chloride and silver nitrate swap ions?

texts:
So, we know that:
$$ \ce{NaCl(aq) + AgNO3(aq) -> NaNO3(aq) + AgCl(s)}$$
(In other words, the ions swap and a precipitate forms).
However, both of those compounds seem pretty stable, since $\ce{Ag}$ and $\ce{Na}$ cations both have a 1+ charge, and $\ce{Cl}$ and $\ce{NO3}$ both have a 1- charge. Since they are stable, I would assume no reaction would take place since both ions are happy with the ions they are currently bonded to (sodium and silver, respectively).
However, $\ce{Na}$ is higher on the activity series than $\ce{Ag}$, and we know that these aqueous solutions actually contain dissociated ions, so I assume this has something to do with the double-replacement. But why is this? Why does this reaction take place, even though the original compounds appear stable at first glance?
Edit
I read this question, and it says

Le Châtelier's principle only states that a system previously at equilibrium will want to stay at equilibrium - that is, if we perturb it, it will try to go back to equilibrium.

The above compounds of sodium chloride and silver nitrate appear to be at an initial equilibrium, do they not?
Edit 2
The question isn't why silver chloride is a solid, but rather, why does this reaction take place if the initial two compounds are stable to begin with?


texts: Why do the induction effects of fluorobenzene decrease electrophilic addition reactivity, conjugation effects increase selectivity?

texts: Fluorobenzene shows signs of both the electron withdrawing and electron donating groups on benzene. Electrophilic substitution to the ring is less reactive because the fluorine is very electronegative and withdraws electron density, but it can also form a weak conjugated system, which is especially pronounced at the ortho and para positions. Why is the modification of the sigma system (induction) related to reactivity, but modification of the pi system (conjugation) affects reactivity? What prevents it from being the other way around, where fluorobenzene is more reactive than benzene, but is not ortho-para directing? What difference in reactivity vs. selectivity makes this difference?


texts: How to get the enthalpy of a reaction from the enthalpy of formations with Hess' law?

texts:
Let's consider a generic reaction:
$$\sum_{i=0}^{i=I}n_{i}A_{i} \rightarrow \sum_{j=0}^{j=J}m_{j}B_{j} $$
where $n$ and $m$ are the
stoichiometric coefficients, while $A$ and $B$ are reagents and products. In order to compute the enthalpy of this reaction we use the enthalpy of formation of each product and each reagent. We know that for the reagents:
$$\sum_{s=0}^{s=S}w_{s}^{i}C_{s}^{i} \rightarrow A_{i} \qquad \Delta H^{A_i}_{f} $$
By multiplying for $n_{i}$:
$$n_{i} \sum_{s=0}^{s=S}w_{s}^{i}C_{s}^{i} \rightarrow n_{i} A_{i} \qquad \Delta H^{A_i}_{f}n_{i} $$
Summing over $i$ you get:
$$\sum_{i=0}^{i=I}n_{i} \sum_{s=0}^{s=S}w_{s}^{i}C_{s}^{i} \rightarrow \sum_{i=0}^{i=I}n_{i} A_{i} \qquad \sum_{i=0}^{i=I}\Delta H^{A_i}_{f}n_{i} $$
Note that all these passages are guaranteed by Hess law.
Let's pose for simplicity:
$$\sum_{i=0}^{i=I}n_{i} \sum_{s=0}^{s=S}w_{s}^{i}C_{s}^{i}=K_{1}$$
We can do exactly the same process for products obtaining:
$$\sum_{j=0}^{j=J}m_{i} \sum_{g=0}^{g=G}z_{g}^{j}D_{g}^{j} \rightarrow \sum_{j=0}^{j=J}m_{j} B_{j} \qquad \sum_{j=0}^{j=J}\Delta H^{B_J}_{f}m_{j} $$
Let's pose for simplicity:
$$\sum_{j=0}^{j=J}m_{i} \sum_{g=0}^{g=G}z_{g}^{j}D_{g}^{j}=K_{2}$$
With an easy passage we finally get:
$$\sum_{i=0}^{i=I}n_{i}A_{i}+K_{2} \rightarrow \sum_{j=0}^{j=J}m_{j}B_{j} +K_{1}
 \qquad \Delta H=\sum_{j=0}^{j=J}\Delta H^{B_J}_{f}m_{j}- \sum_{i=0}^{i=I}\Delta H^{A_i}_{f}n_{i}$$
Now, in my book it is written that the last enthalpy we got, is the reaction enthalpy of my initial reaction, but how you can see, it is the reaction enthalpy of the last equation, that it is not the same (there are $K_{1}$ and $K_2$ which do not cancel each other). Someone could explain this?


texts:
I came across a question asking which of the following conversion/reductions can be accomplished using ammoniated electrons.

$\ce{O2}$ to $\ce{O2^{2-}}$
$\ce{K2[Ni(CN)4]}$ to $\ce{K4[Ni(CN)4]}$
Aromatic ring
Non-terminal alkyne

I have been able to find on Wikipedia that $\ce{O2}$ is reduced to $\ce{O^{2-}}$. So I believe 1 should be incorrect. I am unsure of 2 and could not find any literature regarding the same. About 3, I know about Birch Reduction. About 4 I don't know.

The answer is 1, 2, 3, 4.


texts: Why does having identical groups on either side of the pi bond lead to no geometrical isomerism?

texts:
As far as I was taught, cis and trans isomers were categorised under stereoisomers and sub category of geometric isomers.  Qualifying properties like, rigid and restricted double bond rotation (due to pi bond electron cloud), no terminal alkenes (those with double bond at the end of carbon chain).
But, here was a quote from a LibreTexts article:

If one carbon of the double bond has two identical groups such as 2 H's or 2 Cl's or 2 CH3 etc. there cannot be any geometric isomers.

What is the basis of above claim? Why cis and trans with identical groups can't be qualified as a geometric isomer? If not what is this? Am I missing something here?


texts:
A student is provided with 500 mL of 600 ppm solutions of fructose.  What volume of this solution in millilitres contains 0.15 fructose?

Does this mean that I just have to use 600 ppm as the concentration and the 0.15 as the weight? Like this:

\begin{align*}
{600 \space ppm}
&=\frac {0.15 g}{x}\cdot 10^{6} \\
x&=\frac {0.15 }{600}\cdot 10^{6}  \\
x&=250 \space mL\\
&
\end{align*}

And when can 500 mL be used?


texts:
How does one determine the formula for two non metal elements?

Such as Nitrogen and Oxygen.

I look at the charges with Nitrogen having -3 and Oxygen having -2. How would I get to zero?

How do you build a formula based on those two elements.

Why does it equal $\ce{N2O5}$         ?


texts: For a given element do heavier isotopes form stronger bonds than lighter isotopes?

texts: I know that $\ce{C-D}$ and $\ce{C-T}$ bonds are stronger than $\ce{C-H}$ bonds, but is this generally true for isotopes of all elements? (By isotopes I mean stable ones with large half lives.)


texts: High voltage AC water electrolysis not working

texts:
I was trying to use a $500~\mathrm V$ AC power supply to split water, but nothing happened. I  tested everything with a $9~\mathrm V$ battery, and it all worked fine.

Why did it not work with the high voltage? (Do not worry, I was taking the proper precautions, such as insulation and three pairs of gloves, and I did not touch any live wires.)


texts:
Okay, so I was fiddling about in the chemistry lab, and I added:
Sodium Nitroprusside (soln) $\ce{Na_2[Fe(CN)_5NO]}$ with Potassium Ferrocyanide (soln) $\ce{K_4[Fe(CN)_6]}$.

$\ce{Na_2[Fe(CN)_5NO]}$ was a yellowish-reddish colour - actually don't remember the exact colour, while $\ce{K_4[Fe(CN)_6]}$ was pale yellow.

Nothing really happened to the mixture - except the colours mixed giving a weird yellow colour. I assume the only thing that happened was a double decomposition reaction:

$\ce{K_4[Fe(CN)_6] + Na_2[Fe(CN)_5NO] \rightarrow K_2[Fe(CN)_5NO] + Na_4[Fe(CN)_6]}$
or something like that.

Next I added a bit of dil Hydrochloric Acid. I expected nothing to happen - nothing ever happens with the chemicals they keep in labs. :P However, the colour of the mixture turned a beautiful Emerald Green!

Now I've been trying to figure out what exactly occured to produce the green colour, but I don't know. Could anyone help me?

$P.S.$ My friend's gonna send me a picture of the green we took. I'll edit it to the question when I recieve it, maybe it will help?


texts: What is the difference between concentration and effective concentration?

texts: What exactly is effective concentration in simple terms? From what I can understand it is the 'real' concentration taking part in the reaction instead of the concentration of the solute. Also, if I am right, should the effective concentration always be less than the concentration?


texts:
According to this article, the city of Los Angeles (in the USA) is facing a problem where bromate, a suspected carcinogen, has been forming in their open water supplies.  They believe that the formation of bromate has to do with exposure to sunlight, and are now distributing millions of "shade balls" into water supplies in order to block the sunlight.

Given that an overwhelming majority of water on this planet is exposed to sunlight, why are there not high levels of bromate present in all water, especially shallow bodies of water where the surface area is maximized?  Or is it?


texts: Formation of 3-chloromethylbenzene VS 3-chloromethylbenzene VS 4-chloromethylbenzene

texts:
For methylbenzene (with the methyl group at position 1), is it easier for chlorine to substitute the hydrogen at position 2, 3 or 4?

I was thinking somewhere along the lines of different charge densities around the benzene ring, and that the charge density closest to the already existing methyl group has been diminished due to the methyl group itself. However, I am unable to explain it properly enough.


texts:
If I'm trying to use the Arrhenius equation in this form:

$$\ln\left(\frac{k_2}{k_1}\right) = -\frac{E_\mathrm a}R\cdot\left(\frac1{T_2}-\frac1{T_1}\right)$$

And I am given the activation energy ($E_\mathrm a$) in kJ, do I need to convert it into J before I plug in my other givens?


texts:
I am trying to understand how to account for pH-temperature relations during industrial pH measurements.
Do I have it right?:

The impact temperature has on the pKa of strong acids are in practical terms non existent as the equilibrium at any temperature lays very far to the right.

The impact of temperature on pKa are more significant for weaker acids.

The impact of temperature on pKw is only significant around the point of neutrality. At lower pH's the few hydronium ions produced by H2O + H2O are so few that it bares no meaning on the logarithmic pH scale. In other words, the pH-temperature relationship is important when dealing with neutralization processes, but not so much when having pH setpoints set to anything in the milder acidic region and below.

Compensating for the pH-temperature relationship caused by the temperature dependent pKa is only important when doing measurements on processes where the temperature of the process differs from the temperature of the final product and where the targeted pH level during process control has to match the targeted pH level of the end product (at another temperature). For example: say I want to produce an end  product with a pH at 5 at temperature X. In order to make this product the temperature of my fabrication process has to be something other than temperature X. In this case, temperature compensation to account for changes is pKa becomes important - otherwise the end product won't have the desired pH.

in a different scenario the pH setpoint of a process becomes a means to an end. It's the pH of the process that determines the chemical reactions that takes place in that particular process (perhaps the hydronium ions merely acts as catalysts). In this case, temperature compensation in no way should be applied. This because the pH changes casued by changes in pkA are real and if the process demands say pH 3 for an optimal chemical reaction then it doesn't matter what the pH would have been at another temperature. The important thing is what the temperature is in the process right here, right now.

while pH changes that comes from changes to pKa actually do mean that a solution becomes more or less acidic, changes to pKw doesn't result in a solution becoming more or less acidic even though pH changes. This is because an equal amount of hydroxide ions a produced. So only the point of neutrality is changed.

Do I understand things correctly so far?
If so, then my question now is: What happens when we move into the alkaline region? I mean, pKb is, according to Le Châteliers principle, temperature-dependent as well, right? When looking at this graph https://ibb.co/LRs7G5y (algorithm based on NEN6411 (now
DS/EN ISO 10523:2012)) it seems as if alkaline solutions ALSO becomes more acidic with increases in temperature. Why is this? Does it mean that the equilibrium constant pKb runs in reverse of pKa when temperature increases (less OH-)? Or does it mean that pKw plays are much larger importance once we wander into the alkaline region? I don't, however, see how pKw play any importance on the temperature-pH relationship of alkaline solutions. I mean, if we have an alkaline solution of say pH 12, then any extra/or less hydronium ions produced by changes in pKw would be dwarfed by the proportional much larger amount of hydroxide ions.
Or do I get this wrong?
Last question: Why does the graph https://ibb.co/LRs7G5y indicates that no significant pH-temperature relationship exists below pH 6? Is it because the acid gets so strong at this point that the changes to pKa becomes miniscule relatively speaking?
Help would be much appreciated.
/Lars


texts: Raoult's law: is the molar fraction the molar fraction in the entire system?

texts:
I have two physical chemistry textbooks, one by Atkins and one by Levine, which seem to differ in their notation used when describing Raoult's law.

Atkins talks about the molar fraction term in Raoult's law as if it were of the entire system.

Levine says that Raoult's law has the form $P_i = x^l_i P_i^\circ$, which seems to imply that $x^l_i$ is the molar fraction in the liquid.

So what is it really? And why would Levine use that notation?

Levine also uses this notation for Henry's law.

Thanks.


texts: Why does fluorine act as a leaving group in organophosphates?

texts:
C-F bond is the strongest single bond in organic chemistry with a bond energy of  $\ce{453 kJ\,mol^{-1}}$. And it is very difficult to break this bond and F does not act as a leaving group.

However, in organophosphates, F acts as a leaving group. For example, take an organophospate such as sarin(below). When this binds with acetylcholinesterase (enzyme), F is leaving as a fluoride ion. How can this be explained w.r.t. the P-F bond energy of $\ce{490 kJ\,mol^{-1}}$, which is even higher than that of C-F. Is this possible because of the catalytic activity of the enzyme?

According to David O'Hagana, Chem. Soc. Rev. 2008, *37 , 308-319, C-F bond is very strong due to the difference of electronegativities of C(2.55) and F(4.0), and the resultant ionic character of the bond. However, the electronegativity of P is 2.19 and according to this, P-F bond must be much difficult to be broken. But, this is not the reality. Sarin can be hydrolyzed (Andrew F.   Kingery  and  Herbert E.   Allen, Toxicological \& Environmental Chemistry 1995, 47, 155-184.) at pH 6 ($\ce{25\,^{\circ}C}$) with a half life of 312 hours in aqueous solution.


texts: Model of London forces and Hydrogen Bonding; the question is carried on forward, partially, as a personal question, from another question

texts:
Does Model of London forces and Hydrogen Bonding are themselves complicated and require multiple sub-models and assisted theories to explain its correctness.

I asked this question in the form (ironically) of a question, but I came up a new doubt later on. Just read below:

["
Lighthart says, "The actual magnitude is somewhat difficult to measure (and frequently dynamically changing due to molecular motion), but their existence is used to describe non-covalent bonding interactions between molecules such as London forces and Hydrogen Bonding." So, does it implies that the Model of London forces and Hydrogen Bonding are themselves complicated and require multiple sub-models and assisted theories to explain its correctness.
Can the statement "Now with partial charges the water molecule can have a dipole moment. ... So the gist is that ionic bonds and covalent bonds are labels that we put on molecules to predict behavior. Such models are useful in limited circumstances. But if we try to overextend the model it leads to wrongful conclusions." (quoted from text written as answer by MaxW.) can be used to strengthen my question's argument."]

The link to the site is: Partial charges in a covalent bond


texts: What should be included in the equilibrium constant expression?

texts:
Some writes that pure solids and pure liquids and also solvent should not appear in the Kc, yet a book writes that an carbonyl compound, insoluble in the water, the Kc for this reaction finally includes the water as the density of water is not a constant according to the notes.

Can anyone explain to me about this and what should be included into the Kc expression? And are there any special case for me to memorise in the exam?


texts: So normality is 'equivalents' over liters solution right? I'm having a hard time understanding exactly what an equivalent is. At first from one thing I read i thought it was just the H released from acids in the reactions but then something else started talking about ti with compounds without H, and in double/single displacement reactions. From part of what I read it sounds like a single would have 1 eq and 2 for double, but what found to read was pretty brief so I'm not fully sure. Can someone please explain these a bit better?


texts: How do we know the natural abundance of isotopes on Earth?

texts:
Without knowing the Average Atomic Mass or the percent abundance, how do we know that Protium is the most prevalent hydrogen isotope? What methods did scientists use to come to this conclusion? How did they reach such a conclusion?
I'm still starting out in learning chemistry and I felt like I hit a boulder. I know the formulas and how to get the natural abundance, but I haven't heard a concrete explanation of the concept. I know that it's impossible to survey all the hydrogen elements on Earth to see which isotope is abundant, so what method did scientists use?


texts:
I went through the problems on the pictures:

The answer of the problem 119 is $\mathrm{S_N1'}$, and that of 120 is $\mathrm{S_N2'}$. I actually can't figure out what $\mathrm{S_N1'}$ ($\mathrm{S_N1}$ prime) and $\mathrm{S_N2'}$ ($\mathrm{S_N2}$ prime) are.

Also, how does the answer change by changing the nucleophile?


texts: Why oxidation number of oxygen in OF2(oxygen difluoride) is +2?

texts:
I mean oxygen is electronegative element it should have negative oxidation number
Also how it is able to make bond with fluorine which itself is electronegative?
 Why the oxidation number of oxygen is +2.?


texts: Why is electron gain generally exothermic?

texts:
I understand that we need to supply energy to counter the nuclear attraction when we remove electrons, and that is the reason why ionization energy is endothermic. However, why does an atom release energy when we add an electron to it?
With respect to ionization energy, why is energy required to remove electrons of elements like $\ce{Be}$, $\ce{Li}$ that naturally want to lose their electrons?
My teacher told me that elements with fully filled and half filled highest occupied orbitals have positive electron affinity (endothermic). Why is this true?


texts: Are there softeners in synthetic materials?

texts: Are there softeners used in polyester or polypropylene to make these materials more flexible? Or is this not needed for this kind of synthesis?


texts:
I generally work on fluid flow, so some basic concepts in chemistry are new to me.
 Work I'm doing requires use of molecular dynamics (MD) to do classical potential simulations of water–NaCl systems but this question is about water models more than simulation and software details.

The simulations require definition of a "water model."  There's apparently one already implemented in an example/tutorial I'm using (below).  I want to compare the results of simulations based on different water models.  My problem is that I'm having a lot of trouble understanding how to change my water model (which I think is SPC/E) because I don't really understand what it is.

I have found tables that provide parameters for different water models, like this table at Wikipedia:
https://en.wikipedia.org/wiki/Water_model

However, when I look at my software, I can't relate what I'm seeing to the table.
 I can't find an example of where someone has taken information from this sort of table and explained how to implement it in a simulation.  So my first request is, please point me to anything out there!  Here's the part of my software that I think defines my water model:

&FORCEFIELD
  &BEND
    ATOMS H O H
    K 0.
    THETA0 1.8
  &END BEND
  &BEND
    ATOMS O H H
    K 0.
    THETA0 1.8
  &END BEND
  &BOND
    ATOMS O H
    K 0.
    R0 1.8
  &END BOND
  &BOND
    ATOMS H H
    K 0.
    R0 1.8
  &END BOND
  &CHARGE
    ATOM O
    CHARGE -0.8476
  &END CHARGE
  &CHARGE
    ATOM H
    CHARGE 0.4238
  &END CHARGE
  &NONBONDED
    &LENNARD-JONES
      ATOMS O O
      EPSILON 78.198 ! this is K, = 0.155 kcal/mol = 0.650 kJ/mol
      SIGMA 3.166
      RCUT 11.4
    &END LENNARD-JONES
  &LENNARD-JONES
      ATOMS O H
      EPSILON 0.0
      SIGMA 3.6705
      RCUT 11.4
    &END LENNARD-JONES
    &LENNARD-JONES
      ATOMS H H
      EPSILON 0.0
      SIGMA 3.30523
      RCUT 11.4
    &END LENNARD-JONES
  &END NONBONDED
&END FORCEFIELD

I can generally see that everything up to &NONBONDED relates to water somehow because it's about charge, H, and O (I have no idea what "K" is).  But what about the "LENNARD-JONES" stuff?  I know in general what a Lennard Jones model is, but cannot see how that would be related to water models.  If it is, how? Thank you for any advice on how to understand this.


texts: How many alternative chemical ways to transport oxygen in living creatures are known?

texts:
Mammals and many other groups of animals usually transport oxygen using haemoglobin and other complex proteins, the core of which is based on an iron coordinated to a porphyrin. There are plenty of subtle differences in the protein structures but are there any notable alternatives to that central iron-porphyrin structure?
Obviously there are other chemicals that can do a similar job. Polyfluorinated hydrocarbons were once considered as a viable emergency alternative to donor-blood as they are very good at transporting oxygen. But those are not something that living creatures are likely to develop.
So the question is are there either possible or known alternative chemistries for transporting oxygen in living creatures?


texts: Thermodynamics: Relation between different types of energy: My Analogy

texts:
I have always been confused between the different kind of energies in thermodynamics so today I thought of finally getting it right. Here's my analogy(which is wrong and I need help in improving it, please read it once):

Let us suppose we take a gas at temperature $T_1<T_{room}$ in a beaker fitted with a piston and conducting walls.

Its present energy can be represented by the following diagram:

When the temperature increases both the pressure volume energy and internal enrgy increase by fixed amounts, independent of path(being state variables), according to the equation $\Delta(PV)=nR\Delta T$ and $\Delta U=3/2\ nR \Delta T$

As enthalpy is the sum of both these energies, even it is a state variable, and its change is independent of the path followed.

Now event though $\Delta (PV)$ is a state function and there is a fixed change in its value, there are 2 ways of changing (increasing in this case) it. One by increasing volume and the other by increasing pressure.
The problem is that in the process of increasing pressure-volume energy by increasing volume, the system has to do some work, which means it has to throw out some energy. But we can't let that happen. So we need to provide the system with some extra energy that it can throw out to do work. We haven't increased the energy of the system by doing that as it has come back to the surroundings in the form of work.
There is this fundamental change in energy of the system that is absorbed by the system from the surroundings and there is this extra energy $P\Delta V$ that is also absorbed but then thrown out in the form of work. The total energy absorbed is termed as heat $q$ and the energy thrown out is called work $(-w)$. They depend on the path as it depends on the way we increase the $PV$ energy.

Problem:
The biggest problem with this analogy is it cannot explain $\Delta U=q+w$. According to my analogy $\Delta U+\Delta (PV)=q+w$. This means pressure-volume energy is a part of internal energy and not something different. But then what would be the significance of enthalpy $H=U+PV$?
Moreover I don't know where to put:
1. gibbs free energy as I don't have an intuitive understanding of it, I only know the mathematical formula and the definition: maximum useful work that the system can do and
2. energy lost due to entropy ($T\Delta S$).

It would be great if someone could help me improve my understanding of thermodynamics as I am tired of getting confused each time I open this chapter. An approach coinciding with this one (something like a venn diagram) would be appreciated but anything is welcome. Please help, I really need it!


texts:
When water boils into water vapor, its temperature (average kinetic energy) does not change because the inputed energy is used to break its bonds. But how does that work?

Also, in a liquid, aren’t intermolecular bonds broken and reformed constantly anyway? Why does a phase change require a time interval for breaking bonds?


texts: Number of stereoisomers of trisubstituted cyclopentane

texts:
When 4-methylcyclopent-1-ene reacts with bromine, then 1,2-dibromo-4-methylcyclopentane forms. And I am stuck on determining the amount of stereoisomers that can form as a result.

1,2-dibromo-4-methylcyclopentane has two chiral carbon atoms, those of bromine. And an internal mirror plane, we should have 3 optical isomers.

But I am confused upon drawing the following:

1 and 4 appear to be the same, 2 and 3 appear to be the same.

5 and 7 appear to be the same, 6 and 8 appear to be the same.

This gives me 4 isomers. So I draw them different again:

The puckered structure leaves me doubting myself: while I think that the internal mirror plane causes there to be only 2 different cis structures instead of 4 (or instead of 1 if it had been 1,2-dibromo-4,4-dimethylcyclopentane), I am not sure if the trans structures are actually the same.


texts: Is oxalic acid dihydrate considered a primary acid standard in analytical chemistry?

texts:
Using oxalic acid dihydrate as a primary standard just seems really odd to me. I'd expect a primary standard to be oven dried. It just seems weird that a hydrate would be used.

Granted, I saw numerous references to using oxalic acid dihydrate on the web to standardize $\ce{NaOH}$. I assume that for high school and freshman labs that it is "good enough." Using student grade burettes and open air pan balances would greatly limit the possible precision.

Also I'd guess that "good enough purity" oxalic acid dihydrate can be purchased much more cheaply than potassium hydrogen phthalate (KHP), which would be my choice.

The analytical method as I remember from nearly 50 years ago...

Prepare a concentrated stock solution (4 molar?) of $\ce{NaOH}$ using distilled water. That went in a jug with a spout just above the bottom. It was capped with a dedicator tube filled with $\ce{NaOH}$ to absorb $\ce{CO2}$ from the atmosphere. It sat for a couple of days to allow sodium carbonate to settle out. ($\ce{NaOH}$ will have some carbonate.)

Dried KHP in an oven at $\pu{120 ^{\circ}C}$ for four hours and then put that in a desiccator to cool.

Boiled distilled water to remove dissolved $\ce{CO2}$ and stoppered that to cool.

Using the cooled boiled distilled water made an approximately $\pu{0.1 M}$ solution of $\ce{NaOH}$ by diluting the concentrated stock solution.

Using an analytical balance, weigh out 3 samples of KHP to nearest $\pu{0.0001 g}$ into flasks and carefully dissolved the KHP in the cooled boiled distilled water with swirling to minimize introducing bubbles into the solution.

Then using $\ce{NaOH}$ as the titrant, phenolphthalein was used as the indicator. Again careful to swirl solution, not shake, to prevent bubbles.

Using class 1 50-mL burette which was marked to $\pu{0.1 mL}$s but read to $\pu{0.01 mL}$.


texts: Which is the correct mechanism for the ozonolysis of an alkyne?

texts:
According to Organic Chemistry by Jonathan Clayden, Nick Greeves and Stuart Warren (2nd edition), the mechanism for alkene ozonolysis is given as

In Advanced Organic  Chemistry, Part B: Reactions and Synthesis, Francis A. Carey and Richard J. Sundberg (5th edition), the ozonolysis of alkene is given as:

But mechanism of ozonolysis of alkynes is not given.

What is the correct mechanism of the ozonolysis of alkynes?


texts: Carbon can be turned to diamond artificially, but while watching a video I learned that a diamond can be made from the ashes of a man, how is this possible?


texts: What is the transparent film that covers water-soluble dishwasher tablets?

texts:
These dishwasher tablets (Finish Powerball Shine) seem to be covered in plastic!

But that can't possibly be true since there's no unwrapping, and they're completely soluble in water.

What is the film made of?


texts: Why do NMR spectrums have the higher chem shift values closer to x-axis?

texts:
Im not understanding what the intuition is behind why the graph is represented so that the higher chem shift value is closer to x-axis (shouldnt it be the other way around?)

I understand that downfield = deshielded and will have higher ppm value which is closer to x-axis, but i dont understand why this is reversed to how an x/y graph is usually represented.? Thanks for any help


texts: It is well known that H2O spontaneously autoionizes to H+ and OH- when it is in liquid phase. I was wondering whether it does the same in gas phase, either to the same extent as in liquid phase or at all.


texts: dying fire-resistant material -- do I need acid dye?

texts:
I need to dye or just whiten/brighten dark clothing material. It's made mostly of Nomex (fire-resistant material) and the rest is cotton. Does anyone know how to do it?
I've read on the Internet that I need an acid dye but I can't get my hands on it anywhere. Do you know how to safely make it (I don't have any special equipment) or where I can get it.
I need this for my art project and would be grateful for any help.


texts: Help determining normalisation constant in SALC of methane

texts:
We have been told that a symmetry adapted combination of four hydrogen orbitals is used to create localised hydrogen orbitals for methane. These orthonormal combinations are denoted ψa1, ψt’2, ψt’’2 and ψt’’’2.
It then asks to calculate the normalisation constant for the localised orbital Ψ = ψa1 – ψt’2 – ψt’’2 – ψt’’’2.
What I have done is reduce the symmetry representation of the 4 H s orbitals to Γ = A1 + T2. From here I have drawn an MO diagram and shown that there is overlap between the C 2s orbital and the A1 combination of H s orbitals, and also overlap between the C 2p orbitals and T2 combination of H s orbitals. So I am assuming that the combinations denoted above are these respective molecular orbitals. Therefore, the orbital for which I am asked to determine the normalisation constant is just the A1 MO subtracting the 3 T2 MOs.
From here I am stuck as to how to normalise this wavefunction. I know that N = 1/sqrt(Σci^2) but I cannot determine what the ci coefficients are?
Surely they aren't just the coefficients of ψa1, ψt’2, ψt’’2 and ψt’’’2? Which would give N = 1/2 - seems far too straightforward.
I know that for Ψ to be normalised we require the integral of its square to be equal to 1 which requires each of the components' square integrals be equal to 1/4. This would suggest the normalisation constant is sqrt(1/4) = 1/2?


texts: Obtaining number of functional groups in a compound from SMILES, SDF or MOL2 format

texts: I'm looking for a tool that can give how many methyl groups, hydroxyl groups etc are in a compound's structure presented as SMILES, SDF or MOL2 format.


texts: pH and solute solubility in waste mixed water

texts:
I was reading a module on waste management. There were two interesting points.

High pH results in higher solubility of $\ce{CN-}$. I understand that for HCN:
$$\ce{HCN ->H+ + CN-}$$

Higher pH means that equilibrium will be shifted rightwards and concentration of $\ce{CN-}$ will increase.
But will cyanide salts like KCN, NaCN have the same high solubility at higher pH? If so, how?
Low pH results in greater solubility of toxic gases. How?


texts: Why the formation of PH4+ is difficult compared to NH4+?

texts:
My textbook asks this as an objective question.
What I had in mind was that the lone pair on phosporous was more distributed as compared to nitrogen(since nitrogen is more electronegative and smaller in size ) and hence the statement. But the option given in the textbook says the answer is lone pair of phosphorous resides in almost pure s orbital.
How do you know if the lone pair is placed in pure s orbital or pure p orbital


texts: What determines the elastic limit of a substance?

texts:
from what I know, the elastic limit of a substance is the maximum amount of stress/force/pressure (a bit of confusion on my behalf here) a substance can withstand and still return to its original shape afterwards. my question is what factor(s) determine this limit?

also, I have noticed that some plastics go opaque when under stress and have found the reason for this effect in  this question however, what I do not understand is why some plastics and other synthetic materials do this before the elastic limit (and turn clear upon shrinking) and others do this after the elastic limit of the substance (and the effect is permanent). why can this process of turning opaque be reversed in materials that turn opaque before the elastic limit of the substance.


texts: Why is fluorine a gas, but lithium isn't?

texts: $\ce{F2}$ is a gas, but pure lithium is a solid metal. Why is this? Lithium is much lighter, just 3 protons and 3.9 neutrons (average). Fluorine is much heaver, 9 protons and 10 neutrons.


texts:
Question

  Rank the following radicals in order of decreasing stability

Aromaticity makes a cyclic compund more stable. Here, 1 and 3 are aromatic since they follow Huckels rule(Or am I wrong here?). So, I thought maybe 3 is most stable followed by 1, then followed by 2 and 4(I dont know which is more stable out of 2 and 4). But, that's not the case. 3 is most stable, but the next stable one is 2 and not 1. I don't get how.


texts: Is E1cB possible in the reaction of cyclopentadiene with acetone in presence of ethanolate?

texts:
When cyclopentadiene 1 and acetone 2 are reacted with sodium ethoxide in ethanol, what product is obtained? I was told that the correct product 3 is formed by nucleophilic addition of cyclopentadienyl anion to the carbonyl group.

However, when I thought about it more, I wondered why an E1cB reaction to form the dimethyl fulvene 4 isn't possible in this case. I believe it should be possible because the aromaticity of the cyclopentadienyl carbanion allows the rate-determining deprotonation of 3 to proceed under strongly basic conditions.

On the other hand, there would be more ring strain in the more unsaturated compound 4.

How do I decide if E1cB is possible or not here?


texts: What kind of energies are present in an electron?

texts: I learnt that an electron loses energy as it goes closer to the nucleus and gains energy as it goes further from it. But what type of energy is involved in this process? If it's kinetic energy, then the electron must also lose its speed, but does this happen? In addition, how do I calculate the energy gained or lost due to the electron's movement?


texts: Other than CO2 release, what are the disadvantages of precipitating metal carbonates using NaHCO3 instead of Na2CO3?

texts:
Be, Mg, Ba, Zn, Ni, Ca, Cu, Fe, Mn, Cd, Pb, Hg, Al carbonate salts are all insoluble.

I (perhaps naïvely) believe that I could precipitate carbonates from those mixing a soluble salts of these (e.g. CaCl2) with Na2CO3.

I (perhaps naïvely) believe that it would also work using NaHCO3, yielding CO2 and H2O as additional byproduct(s).

So I'm wondering, what are the advantages of using Na2CO3 over NaHCO3 for the purposes of precipitating carbonate salts of these metals? or, conversely, what are the disadvantages of precipitating metal carbonates using NaHCO3 instead of Na2CO3?


texts: Formal charges can mislead when writing arrow-pushing mechanisms

texts:
We know opposing charges attract and like charges repel. By this logic then, in the two examples on the left, the curved arrows would be show the formation of an oxygen-oxygen bond. However, these mechanisms are incorrect, and instead the mechanisms on the right take place.

Can anyone explain this with some more examples?


texts: Formation of 2,4-Dichlorophenol by free chlorine mediated oxidation of Triclosan

texts:
I cannot find much guidance in the literature. This is the reaction between free chlorine in water and triclosan.
I understand ether cleavage and electrophilic aromatic substitution (maybe) involved. Any ideas as to what the mechanism of this reaction might be?


texts: Why [MnCl6]^2- has got 4 unpaired electrons instead of 3?

texts: In $\ce{[MnCl_6]}^{2-}$, $\ce{Mn}$ has +4 oxidation state which gives it a $\ce{3d^3}$  $\ce{4s^0}$ configuration. But how is it having 4 unpaired electrons?


texts: Intramolecular lactonisation in an unsaturated carboxylic acid

texts:
I am having some trouble figuring out how this reaction proceeds:

Attempt 1: The most obvious thing to do is deprotonate the acid group. I tried using the carboxylate group to attack the alkene, leaving the molecule negatively charged and not really knowing what to do next! If this happened, water would certainly protonate it and then it wouldn't be unsaturated, so it can't be that simple.

Attempt 2: Using the alkene to deprotonate the acid, there will be a positive charge at (one of) the alkene carbons. Then I tried using hydroxide to add in an alcohol group but to no avail.

Is there something special going on because of the cyclic structure?


texts:
I'm trying to read this chemical formula but I'm a bit confused. I'm hoping that someone could help break this down for me to explain what the various parts mean. Someone purchased epigallocatechin in a purchase request and I found that it's synonymous with the following.

(−)-cis-2-(3,4,5-Trihydroxyphenyl)-3,4-dihydro-1(2H)-benzopyran-3,5,7-triol

I believe that the minus up front refers to the way that the polarity changes as light passes through the molecule. What does the 3,4,5 refer to and the 2?


texts:
I am fairly new to NMR and require assistance to analyze and interpret the NMR I have provided (sorry for it being vertical). This is an unknown compound that I have derived during one of my lab classes and it would help me a lot to know and understand what compound this is.

This is what I have interpreted so far:

The compound should have between 12 - 13 hydrogens, probably 13 if there is an alcohol involved and no saturated bonding.

the multiple peaks at slightly below 4 ppm can be a ring but also can be a $\ce{CH2}$ near an oxygen and also bonded to a $\ce{CH3}$ group.

The multiple peaks at around 1.5 ppm are also $\ce{CH2}$ group bonded to another $\ce{CH2}$ group and further away from any oxygen

The triplet at slightly below 1 ppm is a $\ce{CH3}$ group attached to a $\ce{CH2}$ group

However, my interpretations don't seem to add up and I am still figuring out the double peak.


texts: Stabilizing donor-acceptor interaction between orthogonal orbitals in the SN2 transition state?

texts:
For the $\mathrm{S_N2}$ reaction between chloroacetone and iodide, my professor has drawn a donor-acceptor interaction between the iodine lone pair attacking the Cl-substituted carbon and the π antibonding $\ce{C-O}$ orbital of the molecule.

If $\mathrm{S_N2}$ requires overlap between the σ* $\ce{C-Cl}$ orbital and the nucleophilic lone pair of I with σ symmetry, how can that lone pair participate in a donor-acceptor interaction with orbitals of π symmetry? I believed these orbitals did not interact as they are orthogonal to one another and thus experience no overlap.

Could it be that the lone pairs my professor is referring to are the other lone pairs on iodine in p orbitals that extend through the appropriate symmetry planes?


texts: How should I go about picking a functional for DFT calculations?

texts: I've been looking to use time-dependent density functional theory, but reading the literature I keep getting overwhelmed by how many different functionals there are.  How should I go about selecting which functional to use?


texts:
What is a process for the extraction of urea from urine? These are the steps I have come up with:

Add 2-propanol to get rid of any bacteria present. (The 2-propanol likely contained some sodium chloride.)
Precipitate out the proteins and neutralize any acids present using sodium carbonate. (At least, that is what appears to happen upon addition.)
Crystallize out the sodium and potassium chlorides, as urea is much more soluble than those salts.

At the second step, three layers formed: a top clear yellow layer (which I assume was 2-propanol), a middle very cloudy yellow layer (which quickly disappeared into the bottom layer) and a bottom slightly cloudy yellow layer (which I assume was water). The bottom two layers contained particles floating around.

Then, I assume that the water layer remaining contains mostly urea. However, how do I get rid of everything else (urobilin, etc.)?

The end goal is to generate ammonia from the urea by adding some calcium hydroxide. However, it would also be nice to get rid of other impurities which do not impede this reaction.


texts:
My book says

  Because it (the sigma bond) lies along the line joining the two carbon atoms, the sigma bond can rotate about this axis.

But that doesn't make sense to me. So what if the sigma bond lies along the bond axis? How does that matter?


texts: Link between centrosymmetry, dipole moment and chirality

texts:
What is the relationship between the three concepts in the title?

I know all centrosymmetric molecules are achiral, but not all achiral molecules are centrosymmetric. Thus, there are no molecules that are centrosymmetric and chiral, but all other combinations exist.

What about having a dipole moment vs. centrosymmetry? And what about having a dipole moment vs. chirality? Is there a relationship between them, i.e. are some combinations possible and others not?

And if there is a link between these concepts, what is the proof? For example, for a centrosymmetric molecule, I could apply the inversion operation (which does not change the molecule as it has centrosymmetry) and then rotate it by 180$^\circ$, showing that there is a mirror symmetry. Thus, the molecule is achiral.


texts: Can two solids form in a double displacement reaction?

texts:
I am trying to react silver flouride with magnesium chloride. I know it is a double displacement reaction but so far the equation I have gotten is:

$$\ce{2AgF (aq) + MgCl2 (aq) -> MgF2 (s) + 2AgCl (s)}$$

Is this possible or am I doing something wrong? If my equation is correct would this mean that there is no reaction? I'm supposed to find the complete ionic equation and the net ionic equation but I'm not getting either with the above balanced equation. Can someone please tell me what I'm doing wrong?


texts:
I know a lot of chemists like to quote $\mathrm{p}K_\mathrm{a}$ values and subtract them to reinforce some notion about some acid-base reaction being highly favorable or highly unfavorable or whatnot.

For example, the $\mathrm{p}K_\mathrm{a}$ of acetic acid is about 5 and the $\mathrm{p}K_\mathrm{a}$ of LDA's conjugate acid is about 36. 36 minus 5 gives us 31 "zeros" of favorability.

However, $\mathrm{p}K_\mathrm{a}$ values themselves don't tell you what solvent you are using … can using this method blindly lead to problems when working across solvents? And as far as I know, a lot of $\mathrm{p}K_\mathrm{a}$ values are measured in water … but in organic chemistry we don't just use water as a solvent. So does this method even have general validity?


texts:
While looking for data about ring strain in cycloalkanes, I came across two types of data:

Ring strain per methylene group (let's denote this quantity by X): The difference between heat of combustion of the cycloalkane per methylene group and the reference value of $\pu{658.6 kJ/mol}$.
Total ring strain (let's denote this quantity by Y): The difference between molar heat of combustion of the cycloalkane and the reference value of $\pu{658.6 kJ/mol}$ multiplied by number of carbon atoms in the cycloalkane.

From what I have read till now, it appears that the first quantity is the better representation of ring strain. (I say this on the basis that Y has the same value for cyclopentane as well as cycloheptane but still cycloheptane is considered to be less strained as it has lower value of X).

I want to know why X is a better measure for ring strain than Y. When we talk about a ring, we consider it as a whole; then why do we calculate ring strain per methylene group?


texts: The question might seem kind of trivial, although it is even harder than I've thought. How can we synthesise branched alkanes from linear one? For example, I want to obtain 3,4,7,8-tetramethyldecane from n-decane. I've already found Stille coupling, but I guess I'm searching for easier method. I'm just a high school student, studying chemistry by myself as well.


texts: Is the reaction of hydronium and thisulfate an acid-base reaction?


texts: Why do we use the external pressure to calculate the work done by gas

texts:
I read in a textbook that in the case when we have a gas in a cylinder fitted with a massless frictionless piston being held with an external pressure $p_1$, and when the pressure is reduced to become the value $p_2$, the gas pushes up against the piston and then the work done by the gas for a small change in volume is calculated by:

$$\mathrm dW=p_2\,\mathrm dV$$

Here, is what I don't conceptually understand. If the gas's molecules was under some pressure $p_1$ which is equal to the external pressure in the static state then after the external pressure became lower than the internal pressure, shouldn't the work done by the gas be the difference between the two pressures?


texts: What is the reaction between oxalic acid and potassium permanganate?

texts:
I've already searched online some information about this equation, but everywhere I read, there's also sulfuric acid, which we did not use in the laboratory. We only used potassium permanganate and oxalic acid and water, there was no sulfuric acid. The purpose of the laboratory was to calculate experimentally the rate of the reaction at different concentrations, but in order to do so, I need the balanced equation. Can anyone help me out?

By the way, the oxalic acid was dihydrate.

If anyone is wondering, one of the experiments was as follows:

First we took $1.5~\pu{mL}$ of $\ce{H2C2O4}$ and added $1.5~\pu{mL}$ of $\ce{H2O}$, and finally, we added $1~\pu{mL}$ of $\ce{KMnO4}$ and then we shook the test tube until the colour changed from purple to ochre. Because from what I read, they said the $\ce{H2SO4}$ was necessary so the reaction takes place, but in the experiment, the reaction did occur and we didn't use it.


texts: Why the backbone of polylactic acid's repeating unit contains only one oxygen?

texts:
The monomer unit of polylactic acid is $\ce{CH_3-CH(OH)-CO_2H}$:

So why the backbone of the repeating unit is $\ce{-C-C-O -}$:

and not $\ce{-O-C-C-O -}$?


texts: How will the transference number of H+ ion in a dilute solution vary as temperature increases?

texts: I know that transference number depends on Ionic mobility, which depends on temperature. But is there any equation which describes the relation of Transference number and temperature, any ions like H+.


texts:
The correct answer is E

But I do not understand why?
Shouldn't (v) have the lowest $\mathrm{p}K_\mathrm{a}$ since it does not have a carboxyl group making it a strong acid? How do we determine the strength of acids?


texts:
When we have two test tubes and we add:

In the first test tube: hexane, aqueous solution of $\ce{NaCl}$ and aqueous solution of $\ce{I2}$
In the second test tube: hexane, aqueous solution of $\ce{NaI}$ and aqueous solution of $\ce{Cl2}$

We are asked to write the reactions that take place in these experiments. Do we write only this:

$$\ce{NaCl + I2 → no reaction}$$

$$\ce{2NaI + Cl2 → 2NaCl + I2 (displacement)}$$

Or should hexane appear in the reactions too?


texts: Which of the following compound will undergo rearangement?

texts:
Question

Attempt
I believe the answer should be B,C and D. In C and D the oxyge(or Nitrogen in D) can rearange by donating lone pair to carbocation.

But the books answer says B. Where am I wrong. Please help.


texts: Why is decomposition of ammonia gas on quartz a 1st order reaction?

texts:
In general, decomposition of a gas (like ammonia) on a metal surface (like platinum) is a zero order reaction.
This is because the gas is adsorbed on the metal surface due to pressure and the initial concentration is immaterial.
But, why and HOW does it behave differently with quartz?


texts:
I know this question has been asked many times but I need to confirm this doubt which has been pestering me for the past few days.

Suppose in an $\mathrm{S_N2}$ reaction (in polar aprotic solvent) we have two nucleophiles:

ethoxide $(\ce{EtO-})$ ion;
ethyl thiolate $(\ce{EtS-})$ ion.

Now, since we know fluoride $(\ce{F-})$ is stronger nucleophile than iodide $(\ce{I-})$ in polar aprotic solvent, i.e. nucleophilicity parallels basicity.
We should expect the alkoxide ion to be more nucleophilic than thiolate since alcohols are weaker acids than thiols.

But my book says the opposite. Is this a exceptional case? If so, could it be predicted in advance that thiolates are better than alkoxide even though fluoride is stronger than iodide?

Any help would be much appreciated.


texts: What does 'forces' mean in the output of Gaussian calculations?

texts:
In the output of a Gaussian calculation of frequencies, I can see a table listing all the 'forces' of all the atoms. It looks like this:

Center Number       Atomic Number       Forces (Hartrees/Bohr) X Y Z

  1        6          -0.001094502   -0.000768130   -0.006919164
  2        6           0.000528733   -0.000637636    0.005949765
  3        6           0.000424174   -0.000366750   -0.002904382
  4        6          -0.002619381   -0.000001885    0.005496979

...

What are these 'forces'? Are they related to those vibrations? But during vibrations, the force on each atom by other atoms is always changing, so why is only one constant 'force' value assigned to each atom?


texts: Why is there a subtractive volume correction in the van der Waals' equation for real gases?

texts: Why there is a subtractive volume correction in van der Waals' equation for real gases, both real and ideal gases occupy volume of container in which they are kept, so there shouldn't be any correction?


texts: Determining structure from C-NMR spectrum, is my answer correct?

texts:
Determine the structure of the compound whose spectral data is given below and explain your reasoning (5 marks for structure, 15 marks for reasoning). The peak at 7.27 ppm does not belong to the compound. What is the source of this peak?
  (2.5 marks) Looking at the full spectrum you will see small peaks at about 4.2 and 3.7 ppm. What is the origin of these peaks? (2.5 marks)

  Formula: $\ce{C9H10O3}$

  IR: small peaks observed between 3010 and 2853. The largest peak is at 1693. All peaks are in $\pu{cm-1}.$

  $\ce{^{13}C}$ NMR (DEPT-135 result in brackets): δ 190 (+), 153 (no peak), 149 (no peak), 131 (no peak), 127 (+), 111 (+), 109 (+), 58 (+), 57 (+) ppm.

  $\ce{^1H}$ NMR (300 MHz. See expansions on next page):

I mainly looked at the $\ce{^{13}C}$-$\mathrm{NMR}$ aspect of this question. Given that there is a peak at $\pu{190ppm}$, it is probably an aldehyde with a $\ce{CH}$ (which explains the +DEPT sign). The molecular formula also showed a degree of unsaturation of 5, which could be explained by a benzene ring and a double bond (which links up nicely with the carbonyl group). But in order to come up with no peaks in an aromatic ring I added some methyl groups. I eventually came up with the structure 2,3-dimethylbenzaldehyde. The +signs indicated $\ce{CH}$ or $\ce{CH3}$, the 5 $\ce{CH3/CH}$ groups could be explained by the methyl groups and the rest of the carbons in the benzene ring. Do you think this structure is correct?


texts: I need a free software to perform a conformational search on molecules with 10 to 16 rotational bonds. What software would you recommend me? Where can I download it? Where can I find a manual of this software?


texts: Does copper react with HCl when current is present?

texts: Copper does not react with hydrochloric acid, according to many sources.  However, I found an experiment posted in a video, which I will try to repeat, that shows a copper pipe dissolving into HCl and plating a nail when the copper pipe and the nail are connected to a 12-volt battery, becoming electrodes.  No other chemicals, according to the video, are present.  How does the electrical current cause the copper to react with the HCl when otherwise it would not?


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Get a metal like sodium and then you burn it to make sodium oxide because burning something is adding oxygen. Then you add the sodium oxide to an acid like hydrochloric acid. That should make a salt (sodium chloride) and water. Evaporate or filter the water away and you are just left with the salt itself.

Is this possible to do or am I just completely wrong?


texts: Can I use lye as a cooking leavener instead of baking soda?

texts:
I asked this question on the cooking site, but got unsatisfactory answers: https://cooking.stackexchange.com/questions/65520/can-i-use-lye-as-a-leavener-instead-of-baking-soda

I'm interested to try to make waffles using a concentrated food-grade lye water mixture instead of baking soda as a leavening agent. I have three questions related to this subject:

Would this potentially make my waffles fluffier (due to increased CO2 producing reactions or otherwise)?
Would it impact the flavor of the waffles?
Is it safe to ingest waffles that have had a lye water reaction occur in them? (Obviously I should let the lye reaction complete before ingesting).

How long should I let a lye reaction occur before cooking?

Notably, I often use sourdough starter in my waffles, which has an acid component - I've noticed that I get a strong reaction from the baking soda as a result, and it got me thinking that I would get an even stronger result from lye, but I'm worried about taste and ingestion safety.


texts: What is the product of following iodoform reaction?

texts:
Question

Attempt
I think the product A would be as I have attempted below, but I am getting the answer as A but book says D.

Where am I wrong? Please help.


texts: Why should 2,6-Dimethyl-4-nitrophenol be more acidic than 3,5-Dimethyl-4-nitrophenol

texts:
I was trying to compare acidity of some organic compounds but can't understand some:

Why should 2,6-dimethyl-4-nitrophenol be more acidic than 3,5-dimethyl-4-nitrophenol?

I have been trying to figure it out using various factors like hyperconjugation and induction effect of Me group but its not working. Suppose i take H.C effect 2,6-dimethyl-4-nitrophenol be "less" acidic than 3,5-dimethyl-4-nitrophenol since it destabilizes the negative charge on conjugate base. But this logic is not working.


texts: How to calculate the frequency of cyclohexane conformational interconversion?

texts:
My book mentioned that the energy barrier for cyclohexane to reach the half-chair conformation is $50.6\ \mathrm{kJ\ mol^{-1}}$. It says that from this value, it was calculated that cyclohexane undergoes $10^5$ flips per second.

How did they calculate this? We can assume that all the conformational states possible will be of the same energy as the chair conformation (so they all encounter the same energy barrier).

I'm more interested in the principles behind the calculation – why the equation works – than just seeing the calculation done.


texts: What is the best way to introduce OH group into aromatics directly?

texts:
I will try reactions to hydroxylate a haloaryl compound containing fluorines and a NH group.
I consulted databases but could not find ways where yields are good.
If there are people good ways  to introduce a OH group into the compound directly, please tell me.


texts: Is it safe to combine sodium hypochlorite (bleach) sodium triphosphate (TSP) for cleaning?

texts:
I've heard this combination can be particularly effective at cleaning biofilms, perhaps because the TSP is a surfacant, allowing bleach to "attack" more layers of the biofilm.
However, I'm also aware one should be cautious when mixing anything other than water with bleach, as there are a wide variety of reactions that can occur. But I've seen nothing about bleach and TSP. Should it be safe?


texts: Are bisulfates and bicarbonates soluble in water?

texts:
Generally, are bisulfates and bicarbonates soluble in water?
Specifically, are calcium hydrogen carbonate and magnesium hydrogen carbonate soluble in water?