texts:
Im writing up a lab report at the minute and part of it concerns ions in solution and how they affect conductivity. I've been doing lots of reading and I think ive got the grasp of most of it, but its left me with a few questions.

  Symbols used:

  Resistance ($R$), Resistivity  ($\rho$), Conductance ($G$), Conductivity ($\kappa$), Area of cross-section of the electrode ($A$), distance between the electrodes ($L$), Molar conductivity ($\mathrm{Λ_{m}}$)\, The molar conductivity of the electrolyte at infinite dilution ($\mathrm{Λ_{M}}^0$), The molar conductivities of the component ions at infinite dilution
  ($\lambda{_{M+}}^0+\lambda{_{A+}}^0$)\, Concentration (c)

$$\;
[1]\;\; R = \rho \frac{L}{A}\\$$
$$[2]\;\;R = \frac1G\\
$$

$$\;[3]\;G = \frac{{\kappa}A}{L}$$

$$[4]\;\;\kappa = \frac{GL}{A} = G\kappa_{cell}$$

$$[5]\;\;\kappa_{cell} = \frac{L}{A}$$

$$[6]\;\;\mathrm{Λ_{m}} = \frac{k}{concentration}$$

$$[7]\;\;\mathrm{Λ_{m}} = \mathrm{Λ_{M}}^0 - k\sqrt{c}$$

$$[8]\;\;\mathrm{Λ_{M}}^0 = \lambda{_{M+}}^0+\lambda{_{A+}}^0$$

So as I understand it,

Conductance is the ability of a component to conduct electric current.

Conductivity is the ability of a material to conduct electric current, regardless of its dimensions.

Molar Conductivity is the conductivity of an electrolyte solution divided by the molar concentration of the electrolyte, and so measures the efficiency with which a given electrolyte conducts electricity in solution.

Conductivity is related to the amount of ions in solution, the more ions, the higher the conductivity.

Molar conductivity varies with concentration, perhaps counter intuitively, as concentration increases the molar conductivity decreases. The molar conductivity also varies depending on the amount of dissociation (strong electrolyte/weak electrolyte).

The relationship between molar conductivity and concentration is caused by the asymmetric/relaxation effect and the electrophoretic effect.

Here are my questions:

1) For what condition do the equations [6] and [7] apply? I think that [7] is for strong electrolytes at low concentration though im not sure. So what about at high concentrations of strong electrolytes? What about weak electrolytes?

2) When would you use equation [6], when would you use equation [7]? Are they equivalent?

3) In what situation should you use equation [8]?

4) One of my questions is to calculate the concentration of impurities in tap water, using the conductivity measurement. How can I do that when I have more than one unknown in the equation?

Ive not been given a lecture on this topic so im struggling a bit here. Any help is greatly appreciated


texts: Is the equilibrium constant in the expression based on pressure or concentration?

texts:
$$\Delta G^\circ=-RT\ln K$$

I have always assumed it to be $K_p$ because $\Delta G^\circ$ represents standard free energy change and the standard state for a gas is 1 bar. So I thought we must express the activities of gases as ratios of partial pressures to $\pu{1 bar}$. But while solving sums, I found my answer to match only if I consider $K$ as $K_c$. Where am I wrong? Or am I missing something trivial?


texts: What is the difference between phase of matter and state of matter?

texts: I am still confused on the differences between the phase of matter and state of matter


texts: How to determine the calorimeter constant from its heat capacity

texts:
A bomb calorimeter contains $600\;\mathrm{mL}$ of water. The calorimeter is
   calibrated electrically. The heat capacity of the calorimeter is
   $785\;\mathrm{J\,K^{-1}}$. The calorimeter constant would be closest to:

  A. $3.29\;\mathrm{kJ\,ºC^{-1}}$

  B. $4.18\;\mathrm{kJ\,ºC^{-1}}$

  C. $4.97\;\mathrm{kJ\,ºC^{-1}}$

  D. $789\;\mathrm{kJ\,ºC^{-1}}$

My (rather mindless) attempt is as follows:
$$
E=mC_PT\to E/T=mC_P\to C_{\mathrm{cal}}=mC_P=(600)(8.314)(10^{-3})=4.9884\;\mathrm{kJ\,ºC^{-1}}
$$
The closest answer to my result seems to be C ($4.97\;\mathrm{kJ\,ºC^{-1}}$), however I know I'm wrong.


texts: What are the key chemical characteristics that determine the octane rating of fuel?

texts:
The octane rating of petrol (gasoline) is a measure of the how much compression a fuel air mixture can have before detonating (which in petrol engines is a bad thing as you want the mix to combust only when the spark plug arcs).

What are the key chemical characteristics that determine this rating? What is the molecular-level explanation? And how do the various non-hydrocarbon additives work to modify the result?


texts:
What is the mechanism for dehydration of aldoximes by acetic anhydride?

My attempt:
I doubt if it's correct.


texts: Long-term durability of linen vs polyamide vs polyester?

texts:
What is the comparative long-term durability of linen vs polyamide vs polyester when exposed to oxygen, but not sunlight?

I assume that linen, polyamides (Nylon) and polyesters will all oxidize and become brittle over long periods of time (decades). What is the comparative longevity of the three materials in this regard?


texts: Will UVC light/ozone affects color on fabrics?

texts:
I'm planning to put a low power UVC light bulb into my wardrobe to kill bacteria and prevent bad smell on clothes but I'm wondering will it affect color on the clothes? I've done some research but haven't got into a conclusion if UVC light will affect color faster than sunlight or not (because there's no UVC light reaches the earth surface).

I have 2 light bulbs, 1 able to produce ozone and the other doesn't, ozone can help reaching the dead spots which UV rays can't reach but I've read that ozone will cause cracking on some plastic do fabrics also get affected by that?


texts: Effect of sodium hydroxide solution on copper plate

texts:
I have a copper etching plate that has over 100 years of dried ink in the lines of the plate. Someone suggested flake sodium hydroxide as a possible solvent for the ink. My concern is preventing damage to the copper itself.

Suggestions? For example, what should the concentration of the solution (in water) be?


texts: Where does the energy required for excitation of electrons in hybridization come from?

texts:
We're commonly taught that when atoms want to hybridize in for instance methane, an electron is excited from $2s$ to $2p$ to allow for four unpaired electrons, which is necessary for bonding.

Where does the energy for this excitation come from?


texts:
Recently, I started reading about the cleavage reactions done by $\ce{HIO4}$.I came across a statement which read

$\ce{HIO4}$ can't cleave acetals but it can cleave hemiacetals.

But when I tried to reason out, I thought acetals should have more tendency to get cleaved in acidic medium, because the reverse reaction of acetal formation will have more favourable entropy change than reverse reaction of hemiacetal formation.But this doesn't explain the above statement.
Which part in my reasoning is wrong?


texts: Two liquids that react to produce a gas less dense than air at room temperature

texts:
Does anybody know two liquids (or a solid and a liquid) that can react to produce a gas less dense than air (or similar) at room temperature?

This question is intended to make a chemical induced reaction when a lever is pulled to produce gas and decrease an object's mass.


texts: Particle suspension and re-suspension of nano-particles

texts: I am doing a senior project that synthesizes PbS quantum dots and our particles keep crashing out of solution. I was wondering if anyone can give me some advice or information on stabilizing the colloidal solution. The solvent is DI water. I am interested in the chemistry behind stabilization. like what needs to be added to lower the surface energies of particles? why it is added? and how it stabilizes the colloids?


texts: Is it possible to have only liquid in a closed container?

texts:
I recently read an answer by Aman Rusia for this question: Is a liquid in a container always in equilibrium with its vapour?

In it, they say that

  You can't have a container filled with only liquid. Think about that
  for a moment. Similarly you can't have a container filled with only
  ice. Some water, or water vapour, or even combination of the two will
  appear alongside.

However, my textbook says that

  Imagine that you have a sample of water in a cylinder fitted with a piston at low pressure. Suppose that the temperature is held constant at 50 °C, and that weights are placed on a piston to exert a pressure of 1.0 atm. Only liquid water is present. The piston presses on the surface of the liquid. Now gradually reduce the pressure by removing some of the weights. At first, nothing seems to happen. The high pressure is keeping all the water molecules in the liquid state, and the volume of a liquid changes very little with pressure. However, when so many weights have been removed that the pressure has fallen to 0.12 atm (the vapor pressure of water at 50 °C), vapor begins to appear. The sample is now at the vapor-liquid boundary on the phase diagram. The pressure remains constant so long as the liquid and vapor phases are both present at equilibrium and the temperature remains constant. You are free to pull up the piston by an arbitrary extent, but enough water will evaporate to maintain the pressure at 0.12 atm. When you pull the piston out far enough, the liquid phase disappears; you are now free to modify the pressure of the vapor at will.

Atkins, Jones, and Laverman, Chemical Principles

So, is it true that you can have a container filled with only liquid?


texts: Why does Cobalt have different coordination numbers in its complexes with water and thiocyanate?

texts:
I'd like to know why does cobalt(II),  $\ce{Co^2+}$, form $\ce{[Co(H2O)6]^2+}$ complex with water while  it forms $\ce{[Co(SCN)4]^2-}$ with the thiocyanate? Why is there $\ce{6H2O}$ but only $\ce{4 SCN-}$? And is the cobalt's  coordination number 6 in these cases?
Thanks.


texts:
What is the reason behind the fact that methane on controlled oxidation gives methanol in presence of Cu catalysts whereas formaldehyde is obtained if we use molybdenum oxide ($\ce{Mo2O3}$)?

IUPAC says:

  The term selectivity (S) is used to describe the relative rates of two or more competing reactions on a catalyst.

What is the reason behind favouring one products?

Would I be correct that in controlled oxidation of methane in presence of Cu catalyst, we get both methanol and formaldehyde?

Should I need to memorise what catalyst yield what products? Or there is any other way?


texts: How to quantify the amount of paracetamol present

texts:
What is the most accurate way of determining the number of moles of paracetamol from a solution, mixed with acid or base?
I do not have access to more advanced laboratory methods like liquid chromatography, but can use methods such as titration and spectrophotometry.


texts:
As I am learning about the valence bond theory, the model of hydrogen that Heitler and London created, seems to make sense. But, the theoretical and the experimental results are not the same.

Experimental results:

For the molecule to form, the distance between atoms should be $r=74.1~\mathrm{pm}$

and the energy on the other hand $E= -4.474~\mathrm{eV}$.

The theoretical results are this way:

$r= -\frac{1}{4}~\mathrm{pm}$ and $E= 89.9~\mathrm{eV}$

My question is, is it known why these deviations occurred?

Or is this considered as a correct calculation with approximation?


texts:
I have an element collection and noticed that the lanthanide (rare earth) element samples seem to be reacting with the mineral oil I've used to help prevent oxidation.

When I originally placed the samples I researched the lanthanides and found that the lower atomic numbers indeed tend to oxidize in air. Even though I've stored them in jars, I also filled the jars with mineral oil, similar to how I've stored the alkali metals. And at least for the alkali metals, the mineral oil has served as a good barrier to keep out oxygen.

So why would the lanthanides, which are a lot less reactive to oxidation, corrode so quickly? Is there another, perhaps organic reaction going on, between the lanthanides and the mineral oil?


texts: Molecular diffusivity of a three-component mixture

texts:
I usually used a following expression by Fuller & Schettler & Giddings to predict molecular diffusivities of binary mixtures:
\begin{equation}
D_i = \dfrac{1\cdot 10^{-4}\left(0.00143\cdot T^{1.75}\right)}{\left(P\cdot {M_{ib}^{1/2}}\cdot \left(\left(\sum \nu_i\right)^{1/3} + \left(\sum \nu_b\right)^{1/3}\right) \right)^2}
\end{equation}
(where $P$ is a pressure, $T ...$ temperature, $\nu ...$ molecular constant, $M ...$ molecular weight) as it gives a decent accuracy for most of the binary mixtures.
There are other formulas to predict a diffusivity, but to my knowledge, all them are for a binary mixtures.
What would you recommend for a molecular diffusivity prediction of a three component mixture of $\ce{N2}$, $\ce{CO2}$ and $\ce{O2}$?


texts: Is (S)-3-hydroxypalmitoyl-CoA a hydroxy fatty acyl-CoA?

texts:
Is there anything special about (S)-3-hydroxypalmitoyl-CoA comparing to those with different number of carbons, e.g. (S)-3-hydroxyoctanoyl-CoA, (S)-3-hydroxydecanoyl-CoA, (S)-3-hydroxylauroyl-CoA?

I am not a chemist at all; I am looking at the ChEBI ontology and wondering why (S)-3-hydroxyoctanoyl-CoA, (S)-3-hydroxydecanoyl-CoA, (S)-3-hydroxylauroyl-CoA are descendants of hydroxy fatty acyl-CoA, while (S)-3-hydroxypalmitoyl-CoA is not (it is only a descendant of long-chain fatty acyl-CoA).


texts: Chemical to remove nail polish but retain ink

texts: I have a 1954 team signed New York Yankees baseball with 5 Hall of Famers on it. When I was little and showed it to my friends, the signatures started to smudge a little so my Mother put clear nail polish on it to protect it. Is there a chemical I can use to eliminate the polish without hurting the signatures?


texts: What effect on boiling and melting points does intramolecular hydrogen bonding have?

texts:
I know that intermolecular forces increase the boiling and melting point of a compound, but what is the effect of intramolecular forces on boiling and melting points?

I found contradicting answers while searching on the web.


texts: What is the numbering of substituted benzene derivatives according to IUPAC nomenclature?

texts:
According to the lowest locant rule shouldn't the numbering of the compound 1 start from the carbon at the 4th position, thus giving the IUPAC name as 1,2-dimethyl-4-hydroxybenzene?

For compound 2 they could have prioritized the functional group, but they have prioritized the lowest locant rule instead.


texts: Method and Tips for Inorganic Qualitative Analysis

texts:
In a few weeks time, I will be doing an inorganic qualitative analysis test which is very pressed for time (a majority of people don't finish). The form of the test is most likely going to be that there will be around 9 unknown solutions (each contains 1 cation and 1 anion) which I have to identify. I will be given a list of all the possible cations and anions (there will be around 20 cations and  20 anions) and also we will have pH paper and a heat gun.

I wondering if anyone could suggest any tips on how to go about determining the composition of each unknown solution.

Currently, my method is to do it systematically by making a table and reacting all the solutions together. However, this can very time-consuming and probably not the most efficient way to identify the solutions.

Also, is there any distinctive reactions or properties that we will help me identify certain ions. For example, antimony and sulfide will give a unique peachy pink precipitate, or adding water to bismuth may cause a precipitate (as acid is usually required to make bismuth go into solution so by adding water, the acid is diluted and the bismuth precipitates out.)


texts:
We've been asked to draw the mechanism for the following pericyclic reaction:

I know that the tin tetrachloride will act as a Lewis acid and activate the one of the carbonyl groups of the ethyl glyoxylate (I'm not sure which one). I've been trying to see where the cyclic transition state could come from but when I've been drawing the curly arrows I can't seem to get a cyclic transition state (which is required for a pericyclic reaction).

If someone could show me the initial steps of the mechanism then I would be very grateful.

We don't need to consider the stereochemistry for this reaction.


texts: Why is $\ce{H-OH}$ more acidic than $\ce{CH3CH2-OH}$? A common answer to this question is because of the $+I$-effect of $\ce{CH3}$ the negative charge at $\ce{O}$ increases making it less acidic. But if we compare electronegativity difference, the difference between $\ce{O}$ and $\ce{H}$ is more than that between $\ce{O}$ and $\ce{C}$ so there should be even more negative charge at $\ce{O}$ in case of $\ce{H2O}$. In this way $\ce{H2O}$ should be less acidic than $\ce{CH3CH2-OH}$. This is also the reason that $+M$ (electron donating ability) of $\ce{-OH}$ (which is having more negative charge at $\ce{O}$) is greater than the $+M$ of $\ce{-OR}$.


texts: What exchange timescales are needed to cause decoupling in NMR?

texts:
I'll try to explain the source of my confusion as clear as possible:

(*) The methyl protons in toluene are decoupled because the C-C bond between the methyl group and benzene allows very fast rotation. Hence, on average, these protons will see the same environment.

It is said that the time scale for the rotation must be faster than the time scale of the instrument. For a 250 MHz apparatus this would be (1/250MHz)=4 nanoseconds.

(*) In impure solvent the methylene protons of ethanol don't couple to -OH,  since fast exchange of the OH protons results in decoupling and the protons will see an average environment.

Here it is said that this occurs if the timescale of exchange must be faster than the coupling constant J for the coupling. This is typically around 5-10 Hz. So in this case, if the exchange is in the 100 millisecond timescale decoupling already occurs.

This utterly confuses me, in the first case averaging requires nanosecond timescales (related to the frequency of the instrument) and in the second case almost second timescales (related to the small difference in frequency between coupled peaks)? Why?

ALSO and maybe related to this, why do we see in the spectrum of ethanol peak broadening for the OH proton, but not for the methylene group?


texts: Relation between activation energy and rate constant

texts:
Consider two types of reaction. One has more activation than other. If we increasing temperature by same amount in both, rate constant of which reaction will increase more?

My attempt: as we know that $k = A\mathrm e^{(-E/(RT))},$ if temperature is same in both, then the one having more activation energy will have lesser rate constant. Am I correct?


texts:
The temperature of 1 mole of a liquid is raised by heating it with 750 joules of energy. It expands and does 200 joules of work, calculate the change in internal energy of the liquid.

I want to use the expression:
$$\Delta U = \Delta Q + \Delta W$$
so that:
$$\Delta U = 750\,\mathrm J- 200\,\mathrm J = 550\,\mathrm J$$

but it strikes me that it can't be that simple (first year college exam paper). Also, of what significance is the '1 mole' of liquid?


texts: Can wedge and dash bonds on 1, 2 position of cyclohexane ring be used to signify trans orientation of the substituents?

texts:
I've to make the structural isomers for cyclohexane. On position 1, there's a methane group with wedge bond and on position 2, a methane with dash bond. So I'll have to make the trans isomers only as they are not in the same plane or should I make the cis isomers too?

Or, can wedge and dash bonds on 1, 2 position of cyclohexane ring be used to signify trans orientation of the substituents? Is it actually trans or is it there just to show that the molecules lie in different planes or something?

For reference: as it is the 1,2 position, cis will be axial on 1. equatorial on 2. Trans will be axial on both 1 and 2.


texts: Deriving rate law from a reaction mechanism for a chain reaction using steady-state approximation

texts:
I am trying to derive the overall rate equation for the photocatalysed halogenation (chlorination) of an alkane that proceed via this 4 step chain reaction:

$\ce{Cl2->2Cl^. \quad(1) initiation}$
$\ce{Cl^. +RH->R^. + HCl \quad(2) propagation}$
$\ce{R^. + Cl2-> RCl + Cl^. \quad(3) propagation}$
$\ce{R^. + Cl^. ->RCl \quad(4) termination}$

I have calculated the differential rate equations for $\ce{R^.}$ and $\ce{Cl^.}$ and set them to zero at steady state.
[The free radical dot symbols are omitted from this point onward for brevity]
This gives me $$\ce{For Cl ,2k1[Cl2]-k2[Cl][RH] +k3[R][Cl2] -k4[R][Cl]=0 \quad(5)}$$
$$\ce{For R, k2[Cl][RH] -k3[R][Cl2] -k4[R][Cl]=0 \quad(6)}$$
Adding these two equations,
$$\ce{[Cl]=\frac{k1}{k4}\frac{[Cl2]}{[R]}}$$
Then I tried substituting this into equation (6), which gives me a quadratic equation. The solution of the quadratic equation is of the form $$\ce{[R]=constant +\sqrt{\mathrm{constant [RH]}}}$$
The overall rate law from this expression is a very complicated equation.
This looks wrong because the rate law for radical halogenation is usually of the form $\ce{k[RH]\sqrt{\mathrm{[Cl_2]}}}$ (Wikipedia)
Where am I going wrong?


texts: Prediction/computation of mass spectral ionisation intensity

texts:
There are quite a few approaches (ranging from empirical additive rules based on presence of functional groups to full blown in silico QM calculations) to predicting molecular properties such as UVmax absorption or IR vibrational frequencies. While not perfect, they give a general ballpark range of what to look for.
I’ve recently been doing some quantitative MS work which has involved a lot of dilutions and calibrations.
It got me curious  if there are approaches to predict peak intensity as it’s not really something I’ve ever read about (or even included in software similar to basic IR/NMR prediction). It obviously wouldn’t be useful for quantification, but could give a vague sense of how strongly something will be observed (if at all).
To give an example, imagine mixing 1 mmol of paracetamol and 1 mmol of aspirin in DMSO and recording an LCMS of this—although you have the same amount of both the intensity in the MS TIC will vary significantly.
It seems to me that the parameters are quite well controlled (voltage, temperature, $\mathrm{p}K_\mathrm{a}$ etc.)—is it possible?


texts: When Compounds are Considered Compounds and Their Types

texts:
I'm a bit new in chemistry, so I need help with a couple of things. Although I don't mind complicated answers, please try to keep it around high school level, and not rocket science. Thanks!

Can someone describe exactly what makes a compound a compound? Is it just the simple definition of "multiple elements combined" or can someone get a more specific?
Sodium chloride is an ionic compound, but it's not made out of "molecules". So does that mean Sodium Chloride isn't an actual molecule (like $Na^+$ and $Cl^-$ are combined as separate ions but they can't be combined in a 1 to 1 fashion)
Can someone explain to me exactly what the law of gaseous reaction is, (it doesn't show up on internet specifically, but it's a law by Gay-Lussac).

Thank you in advance!


texts:
Is it possible for minerals in drinking water to solidify when high temperatures are applied? The minerals in mind are: iron, copper, aluminum, magnesium.

Background: I have small, brittle, darkish flakes appearing in my hot water system. The manufacturer of my tankless hot water heater said it's possible for these elements to solidify in this manner over time.

Looking at their website, I found this brief explanation:
http://support.noritz.com/article/faq-what-is-water-hardness-46.html

  "Water hardness is the measure of dissolved calcium, magnesium, and other minerals in your drinking water. It is typically measured in grains of hardness which equates to 17.1 mg/L of dissolved calcium carbonate. If not treated hard water can cause mineral build-up in your heater. Mineral build-up reduces flow and produces flakes at your fixtures."

We got out water hardness measured, and it came back as 68 mg/L.

The temperature of the water heater is set to 130F. I believe that the heater has a higher internal temperature.

I'm not sure why they are dark/black in color, all the pictures I'm seeing for calcium carbonate are white.

Thank you


texts:
In which of the following chemical compounds are the building blocks molecules?
(A) $\ce{AgNO3}$
(B) $\ce{HNO3}$
(C) $\ce{KNO3}$
(D) $\ce{NaNO3}$

(B) is the correct answer, but I have no idea why. Could you briefly explain why this is the correct answer?


texts: How can we find the eV value of molecular orbital diagrams for a given atom?

texts: It seems like sometimes the electron volt value of the molecular orbital is given but most of the time it just shows relative values of s p d orbitals. Is there some lookup table for such values?


texts: Why does Avogadro's Law hold true for ideal gases?

texts: Avogadro's Law states that the volumes of ideal gases are proportional to the number of molecules that are present in the gas (or the number of moles in the gas). I've been trying to find out more about it, but I can't seem to find out why this holds true, at least for ideal gases.


texts:
Various ethers are used for hydroxyl protection. My question is about their removal. I know that there are various methods but I want to specify on the use of acids.

Certain groups are removed easily like Trityl, by using aqueous acetic acid. If I'm not mistaken, the mechanism is Sn1, as the trityl carbocation is stabilised through delocalisation on the phenyl groups.

However, other similar groups like benzene or PMB are not removed that easily. Can't they follow the same logic, as the postive charge could again be delocalised in the aromatic ring? Is it because the delocalisation is not good enough, as in the case of trityl?

Also, I've noticed that in order to remove smaller groups like methyl, haloacids are mainly used. Why can't a more weak acid do the job?


texts: How to convert Gaussian input file .gjf to SMILES?


texts:
Citric acid has both alcohol and carboxylic acid groups, so could it "esterify" with the other citric acid molecules in solution?

I notice that it is a tertiary alcohol. I don't suppose that would significantly hinder esterification, would it? Then again, it's not as if citric acid simply polymerizes with other citric acid  molecules in solution anyway.


texts: Why does everything go in the direction of positive entropy change?

texts:
I read about entropy from different sources. Still don’t get why (universal) entropy change has to be greater than zero for irreversible process, i.e. $\mathrm{d}S_\mathrm{Univ}>0$. Is it a result of pure observation or is there any theoretical background of this phenomena?

Unfortunately the linked question "Does adsorption violate thermodynamics?" does not answer this, as it only shows that overall entropy change is greater than zero. But doesn’t provide a reason where it comes from.

I am looking for a simple explanation in classical thermodynamics.


texts: Can a organic compounds such as hydrocarbons contain an ionic bond?

texts: Can organic compounds like hydrocarbons have types of bonds other than covalent bonds? Can they also possess ionic bonds?


texts: On the oxyacids of +III pnictogens and +IV chalcogens

texts:
Phosphorus in its $\mathrm{+III}$ oxidation state is known to exist as the phosphonic acid tautomer rather than phosphorous acid one. All salts isolated containing $\ce{H2PO3-}$ are (to the best of my knowledge) hydrogen phosphonates rather than dihydrogen phosphites. Similarly, all $\ce{HPO3^2-}$ salts should be phophonates rather than hydrogen phosphate. Only as organic esters (which cannot tautomerise easily as carbocations are less stable) are both forms observed: trimethyl phosphite and dimethyl methylphosphonate both exist.

A similar picture is true for sulfur in the $\mathrm{+IV}$ state. Sulfurous acid and sulphonic acid are both known as far as I know, and both structures have been isolated in salts. Similarly, methyl methylsulfonate and dimethyl sulfite are both known to the best of my knowledge.

The corresponding elements of the second period do not show this tautomerism. For oxygen, this is due to its high negativity preventing the formation of ‘oxyacids’ altogether. For nitrogen, this is because an $\ce{N=O}$ double bond is more stable than two $\ce{N-O}$ single bonds so that nitrite ($\ce{NO2-}$) is already devoid of protons and cannot tautomerise. However, remnants of this behaviour still exists in organic compounds where both the nitro group $\ce{-NO2}$ and organic nitrites $\ce{-ONO}$ are known.

What is the case for the heavier homologues of both phosphorus and sulfur? Do the elements arsenic/antimony/bismuth and selenium/tellurium/polonium exhibit both an -onic acid and an -ous acid or is one form preferred over the other? Is there a general trend going down the groups or are secondary effects (e.g. lanthanide contraction) more important?

Answers backed with references to crystal structures of anions (or the free acids) and/or corresponding quantum-mechanical calculations (both in references or self-performed) are preferred.

Note that the fully oxidised pnictogen(V) or chalcogen(VI) compounds are not part of this question,


texts: Is there a means to measure pH without indicators?

texts:
I have created a solution that should contain hydroxide ions. Therefore, the pH > 7, but is there any way to roughly estimate the pH in absence of any indicator? Maybe using current, or checking whether it dissolves certain chemicals?

Please mind that I am limited in equipment and so complex science is not feasible for me.


texts: Why is Kevlar stronger than nylon? They both contain Hydrogen bonding and should have equal strength but this is not the case instead Kevlar is fire resistant. What makes it stronger. Greater hydrogen bonds?!


texts: Why is M1*V1 = M2*V2 only used for diluting solutions?

texts: Why is $M_1V_1 = M_2V_2$ only used for diluting solutions? Why can it not be used to figure out how many moles to add to make a solution more dilute?


texts: Molecular mechanics force fields for metals?

texts:
I know of several general molecular mechanics methods suitable for metals, including Dreiding and UFF.

I know it's difficult to get many things right for such classical treatment of inorganic / organometallic molecules, because oxidation state, spin state and other factors can greatly influence geometries and energetics.

But I'm surprised that so few attempts have been made to improve on these methods. Are there no other methods published since 1992? I'm looking for force fields that cover a substantial part of the periodic table (or at least most metal-ligand interactions) and are completely published - proprietary methods don't count.


texts: Will freezing water still expand width-wise in a pipe (possibly breaking it) if it's free to expand lengthwise?


texts: Does the level of water go down when you add salt to it?

texts:
My textbook states: Did you know that if you pour a handful of salt into a glass of water the water level will actually go down rather than overflowing the glass?
I tried this experiment and the glass overflowed.
I did a bit of research online and I think what the writer was referring to is that the volume of the salt solution is less than the volume of the sum of the water initially and the salt initially, not that the volume of the salt and water is less than the volume of the water alone.
Is my understanding correct here?
I'm looking for a yes/no answer if possible.


texts:
I know the general Lewis dot structure of carbon dioxide is the one where there are two double bonds connecting oxygens to carbon.

However the question is, does $\ce{CO2}$ have resonance structures?

We could have moved one of the bonds (pi bond in this case) to the other $\ce{O-C}$ bond, leaving us with a single bond and a triple bond forming $\ce{CO2}$.


texts: Can somebody explain as concrete as possible, how the change of temperature and the change of pH  leads to deviations of this law?


texts: Applying Raoult's Law in volatile solids–liquid solutions

texts:
My textbook explains applying Raoult's Law for the two cases:

liquid–liquid solutions, in which the vapour pressure of the solution is due to both the components
non-volatile solids–liquid solutions, in which the vapour pressure of the solution is only due to the liquid component of the solution

I am curious as to what will happen (how things change for the application of Raoult's Law) if the solution consisted of some volatile solid like camphor, in some liquid (possibly some liquid hydrocarbon).

Certainly, the solid now also contribute to the total vapour pressure of the solution, but does it still block the escaping of the solvent molecules into vapour phase as much as the non-volatile solid blocks the liquid solvent molecules?

If yes, then how can I apply Raoult's Law for the case to find the total pressure of the solution?


texts:
I am using 3% hydrogen peroxide for a series of operations, and the common practice is to prepare it on-site from 30% hydrogen peroxide and saline. This is time consuming and somewhat more prone to error than preparing a 3% stock. I was told this is not done because 3% hydrogen peroxide has a short shelf-life (~a week).

Is this true?
If so, why?
Would the shelf-life be extended if the solution were prepared with phosphate-buffered saline or just with deionized water (instead of saline)?


texts: Dielectric polarization: how to identify what part of the total polarization (dipolar+electronic+ionic) I need (conceptual question, I use DFPT, VASP)

texts:
I am doing polarization calculations to get data for use in other calculations.  To start with, I want to calculate the static dielectric constant. However, I'm a newbie to polarization and it is a struggle to relate my calculation output to the static dielectric constant. If someone could point me in the right direction, I would be grateful.  I'm using VASP software for the first time.
The total polarization is mainly the sum of dipolar, ionic, and electronic terms.  VASP implements a method (DFPT; density functional perturbation theory) for polarization calculations that seems to calculate only the ionic and electronic terms.  This is a concern because my fluid may have a significant dipolar component.  If anyone thinks I'm wrong on this, a heads-up would be great.
The reason I mentioned that DFPT may only calculate the ionic and electronic contributions to total polarization is that I have managed to get VASP output for the electronic term.  In the output file (.xml, for any VASP aficionados), it is in the form of a dielectric function that has six elements.  Three of the elements belong to a "real" part and three belong to an "electronic" part of the dielectric function. From my reading, it looks like the "real" part should somehow correspond to the static dielectric constant. My question is, which part of the total polarization is this likely to represent?
In other words, does each of the three terms in the total polarization contribute to the static dielectric constant, where this one is likely to be the electronic contribution?  Or is the output I have likely to be the total (dipolar too) static dielectric constant?  I ask because I read that only the dipolar and ionic terms contribute significantly to the static dielectric constant.


texts:
What is meant by the lowest photometric error?
why it is important to work in the $0.2\ \mathrm{to}\ 0.7$ absorbance range for a single beam instrument?
Why $0.4\ \mathrm{to}\  1.4$ for double-beam instrument?


texts: Why is H2Te the strongest acid among the following?

texts:
Among H2S, H2Se, H2Te the strongest acid is H2Te. The reason being that the bond strength in it the weakest so it dissociates easily.

But my question is that why does it looses H+ in first place because in order to loose H+ the hydrogen must be appreciably partial positive and for the hydrogen to be partial positive the difference of electro negativity between the two atoms must be appreciable but hydrogen and tellurium are having same electronegativity and therefore no partial positive hydrogen and thus it should not dissociate.

So what’s going on why is it dissociating even then ?


texts: If metals want to "lose" electrons, then why will copper ions take electrons from a zinc electrode?

texts: According to my book, metals want to "lose" electrons to achieve noble gas configuration. But at the same time, copper ions in a galvanic element are going to gain electrons from a zinc electrode. Why is it so? Is it because one of them HAS to gain/lose electrons, and zinc wins out in terms of achieving noble gas configuration?


texts:
Disclaimer: I am not a chemist, but I figured this may be the place to ask.

So, recently, there has been a lot of news going around about the homemade slime burning a child's hands and I got curious as to whether the ingredients were harmful and if the parents just didn't know any better:

Borax (Sodium Borate)
Elmer's Glue-All
Warm Water

And realized that none of these are really harmful to handle on your own.

Would mixing these create a harmful compound?

Here's one of the news articles, they're mostly all about the same incident: 11-year-old girl's hands covered in third-degree burns after making "slime"


texts: Calculating acid dissociation constant for polyprotic acids

texts:
I'm confused with $K_{a1}$ and $K_{a2}$ for a polyprotic acid and how they are found, consider the following:

A solution of $1 M$ of $\ce{H2SO4}$ would yield $1 M$ of $\ce{H3O+}$ and $\ce{HSO4-}$ since $K_{a1}$ is very large.

In the case of the second ionization, $\ce{HSO4-}$ would give $1+x$  M of $\ce{H3O+}$ and $x$ M of $\ce{SO4^2-}$ , if $x$ is known how do we calculate K$_{a2}$

Do we use first concentration + second concentration as following

•   $K_{a2} = (x+1)(x)/(1-x)$

Or only second concentrations

•  $K_{a2} = (x)(x)/(1-x)$

Which one is correct and why?


texts: Why different Asbestos types are hydrophobic and hydrophilic

texts:
I was doing research into the structure of asbestos to see that white asbestos chrysotile is hydrophilic where as both brown and blue asbestos is hydrophobic.

Could you please explain why this is?


texts: Why does gas not liquify at a temperature above the critical temperature no matter how much pressure is applied on it? Why?

texts: My textbook says that critical temperature is the temperature above which a gas cannot be liquified no matter how much pressure we apply on it. But why? What is so special about this 'critical temperature'? I mean, if we apply a ridiculous amount of pressure, the gas molecules have to come closer to one another and they have to liquefy. What exactly happens to the gas molecules at critical temperature? Do they become immovable and have infinite inertia or what?


texts: Are there any (simple) molecules with very different absorption and emission dipole directions?

texts:
When a single molecule absorbs or emits light, it does so perpendicular to the direction of the respective transition dipole. In principle, the directions of the dipoles for absorption and emission can be different, due to different electronic configurations of the ground and excited states of the molecule, but in practice the difference is very small. Photons are thus preferentially reemitted into the same plane in which absorption took place.

A large angle between these two dipoles would probably require a significant change in the molecular structure when the molecule is excited. I have heard of some fluorescent proteins which exhibit large angles between absorption and emission directions, but I do not know any details. (Edit: I found this interesting paper, which reports negative fluorescence anisotropy in YFP and a large angle between the absorption and emission dipoles.)

I would be interested in specific compounds which have a large angle between the two transition dipoles. Particularly, are there any simple compounds (less than ~100 atoms) that show such a behavior?

I have read about twisted intra-molecular charge transfer (TICT), in which a segment of the molecule rotates by ~90 degrees upon excitation. I could imagine that in such a case the emission might take place in a plane perpendicular to the original plane of absorption, but I haven't found any confirmation of this either.

Update: to illustrate, I have created a small sketch that outlines what I have in mind. The molecule I drew is just for illustration and does not necessarily show that behavior; I also don't know how exactly such a restructuring process actually takes place (the one I drew would correspond to a rotation of the rings on the right around the single bond). I further assumed that the dipole directions coincide roughly with the positions of the two rings, which might not actually be the case.

That said, the process I have in mind looks as follows:

A photon with a polarization vector parallel to the dipole direction arrives (its direction of propagation is necessarily perpendicular to the dipole direction)
The photon is absorbed and the molecule is left in an excited state
In the excited state some internal rearrangement of the molecular structure takes place, such that the dipole direction changes
A fluorescence photon is reemitted perpendicular to the new dipole axis. The photon has been effectively "redirected" (and shifted to higher wavelengths)


texts: If we have a buffer solution as follows where HA is a weak acid and $\ce{A-}$ is its conjugate base, $\ce{HA + H2O<=>H3O+ + A-}$, do we ever consider $\ce{A- + H2O<=>HA + OH-}$? This is because in all of the buffer system problems I've done we only use the first reaction to find pH and other values but, we never consider the reaction of the conjugate base with water to form hydroxide ions which should increase the pH. Why is this so?


texts: d-Menthol vs dl-menthol: Does an enantiomer and its racemic mixture have different melting points?

texts:
I am checking out Wikipedia and it shows a different melting point (m.p.) for l-menthol $(\pu{42 ^\circ C}$ to $\pu{45 ^\circ C})$ vs dl-menthol $(\pu{36 ^\circ C}$ to $\pu{38 ^\circ C}).$

How is this possible? d-menthol and l-menthol being enantiomers, shouldn't they have identical physical properties including the m.p.?

  The two enantiomers of a molecule possess the same physical properties (e.g., melting point, boiling point, polarity etc.) and so behave identically to each other.

If so, why would the racemic mixture have any different m.p.? I.e. you can't just physically  mix two pure materials with the same m.p. and end up with a material with a different m.p., right?

I checked out Common Fragrance and Flavor Materials by Surburg and Panten [1, p. 55] just to be sure and the data agrees. The m.p. of the d-menthol and dl-menthol again seem to be different:

  Other physical constants of commercially available levorotatory and racemic
  menthols are: (−)-menthol [2216-51-5], mp $\pu{43 °C},$ $n_\mathrm{D}^{20}~1.4600,$ $[α]_\mathrm{D}^{20}~–50^\circ;$ (±)-
  menthol [15356-70-4], mp $\pu{38 °C},$ $n_\mathrm{D}^{20}~1.4615.$

References

Surburg, H.; Panten, J. Common Fragrance and Flavor Materials: Preparation, Properties and Uses, 5th, Completely Revised and Enlarged edition; Wiley-VCH: Weinheim, 2006. ISBN 978-3-527-31315-0.


texts: What can be used as substitute to dichloromethane for breaking optical cement bonds?

texts: An optics supply company recommends using a dichloromethane solution to break bonds between optical elements joined with its UV-cured optical cement.1 The page mentions that dichloromethane-based paint strippers also work. Use of dichloromethane in paint strippers has been phased out in the USA  as of last year. Is there an obvious chemical property that dichloromethane possesses which causes it to break UV cement bonds and if so are there any more readily available hardware store chemicals which could be used as substitute?


texts: Why don't calcium chloride and sodium nitrate react?

texts:
$$\ce{CaCl2 + 2NaNO3 -> 2NaCl + Ca(NO3)2}$$

Why doesn't the above reaction occur? Does it have to do with the metal activity series or solubility rules?


texts: How large is the energy difference between keto- and enol-form of guanine and uracil?

texts:
The nucleobases in DNA and RNA are generally present in the keto-form, and not in the enol-form. As an interesting historical note, James Watson and Francis Crick did initially believe them to adopt the enol-form, which isn't compatible with the correct model of the DNA they later proposed.

But there are some reports indicating that in certain RNA structures guanosine and uridine form essentially a Watson-Crick basepair where one of the two bases is present in the enol-form, instead of the usual G-U wobble base pair.

Is there anything known on how large the energy difference between the keto- and the enol-form of those bases actually is?


texts: How do I comment on the Gibbs energy values standard and reaction in different situations?

texts:
I have the following graphs:

Taking into account the following graphs, how do I comment on the Gibbs energy values
standard and Gibbs energy of reaction in different situations (a, b and c), and how do I relate the values of the latter to the spontaneity of the reaction? I'm really lost here.


texts:
I am wondering about chemical reactions when the reactants are in a plasma state.  Consider hydrogen and oxygen.  Heated, these would react to form water.

If hydrogen and oxygen plasma were combined, would the separation of electrons from nuclei prevent normal chemical reactions?  Or would the reaction take place in the plasma state?


texts: What is the reason for including excited states in the wave function in post-Hartree Fock methods?

texts:
I'm new to computational chemistry, so perhaps this question has an obvious answer. I'm wondering what the intuitive reason for constructing Slater determinants that involve excited states is, when one tries to describe correlations, starting from the Hartree-Fock picture. I understand that the single determinant in the Hartree-Fock model only describes exchange (antisymmetry of fermionic wave functions).
I am trying to understand the logic behind why constructing Slater determinants involving excited states can give us a picture of correlation. I guess I don't understand the relation between excited states and correlations (especially thinking about it from the point of view of DFT, which is interested only in the ground state, but correlations are still important).


texts:
I was wanting to know using a butane extraction method for hemp flower (cannabis sativa) would also extract the microbial DNA present on the flower as well as deriving the cannabis oil (oleoresin)? This extraction process is used to obtain oleoresin(hash) from flower and I want to know if microbial DNA (or living microbes) can also be extracted? The goal of the extraction is to obviously have no microbes present in the end (this is for human consumption). If someone could explain the chemistry as to why it does or doesn't work I would appreciate it.

Thanks,

Kelsey


texts: How do I arrive at the α-trimethylsilyloxy ketone from an unmodified ketone using TMSCl, triethylamine and mCPBA?

texts: I'm confused about what is going on here. I gather that step 1 is typically supposed to protect an OH group, but there isn't any in the starting material.


texts: Condensation reaction between catechol and acetone

texts:
I was thinking of ways to synthesize 2,2-bis(dihydroxyphenyl) propane and I thought it could be made by a condensation reaction between dihydroxybenzene (catechol) and acetone in strongly acidic conditions.

At first, the catechol would probably form the acetal (even though the former compound could also take part in the reaction). This would then react with acetone, form a cation and this would react with another molecule of the catechol. At last, the diacetal would be hydrolyzed to make the desired compound.

My question is, whether this makes sense. I am especially worried about self-condensation of acetone, which might ruin the reaction.


texts:
The article by Hu et al. [1] mentions a compound "dithreitol" in the Saliva Proteome Analysis section (emphasis mine):

  For the "shotgun" approach, saliva samples (1 mL) were pre-fractionated with the use of Millipore ultracentrifuge filters (Millipore Corp., Billerica, MA, USA).
  Individual fractions were treated with 10 mM dithreitol for 30 min and then 50 mM iodoacetamide for 30 min.

PubChem doesn't reveal any details as to what this compound exactly is and suggests alternative spelling, e.g. D-threitol.

Google Books search results in several mentions of this compound in the literature, but I didn't find any further details except that it's probably a sulfhydryl reagent.
This makes me think that "dithreitol" could be another name for dithiothreitol, but I didn't manage to find any solid references to support this proposition.

To sum it up: what is dithreitol, exactly, and what chemical and structural formulas does it posses?

References

Hu, S.; Li, Y.; Wang, J.; Xie, Y.; Tjon, K.; Wolinsky, L.; Loo, R. R. O.; Loo, J. A.; Wong, D. T. Human Saliva Proteome and Transcriptome. J Dent Res 2006, 85 (12), 1129–1133. DOI: 10.1177/154405910608501212.


texts: Will CO2 bubbles ever fully dissolve in water?

texts:
Background:
Many aquarists keeping freshwater planted tanks add $\ce{CO2}$ from a pressurized canister to their aquaria to promote plant growth. Injection is at a slow rate to get dissolved $\ce{CO2}$ in the neighborhood of 30 ppm. Methods vary, but a ceramic discs to release a very fine mist of bubbles are popular, as are $\ce{CO2}$ reactors which trap the bubbles in a bell or canister and stir them around with a water pump.
In any case, within the hobby there is an odd fixation on getting the gas bubbles to dissolve completely, I suppose on the reasoning that a bubble that pops at the surface is $\ce{CO2}$ that escaped to air rather than being dissolved in the water.
I'm skeptical of this logic -- I'd think while the bubble is dissolving, water vapor and whatever other dissolved gasses will be diffusing into the bubble. At some point the bubble becomes just humid air in equilibrium with the surrounding water, and no amount of stirring will get more $\ce{CO2}$ out of it. This is just my guess, based on casual observations where the bubbles will diminish to less than 10% of their initial volume within 30 seconds, and thereafter they don't seem to get any smaller.
Questions:
Is that correct, and does it mean the aquarist's quest for a "100% efficient" $\ce{CO2}$ bubbler that never lets bubbles pop at the surface is doomed to eventual failure?
And if so, what are the basic principles that describe this equilibrium and how can we figure how much $\ce{CO2}$ can be extracted from a bubble, and how big the bubble will be after it's become just humid air?
If not, why does it seem the bubbles will rapidly dissolve in the water at first, but never fully dissolve even though the solution is far from saturated?


texts: Ozone resonance structure: differing opinions

texts:
I've always thought that the two-form resonance structure of ozone was the scientific concensus (from Wikipedia]:

Then today I found two other opinions. A three-form structure:

And a four-form structure:

Is there a consenus? Are the two and three-form representations just simplifications of the four-form structure? Please include references.
EDIT: The second resonance structure on the four-form image above is drawn incorrectly, as pointed out by @ron. The upper oxygen atom should have a lone pair and a positive charge, just like the second structure of the two-form.


texts: Why does the sodium become transparent after burning?

texts:
I know that if we throw a piece of sodium into water then it will melt first then it will explode.

But under different conditions, the above situation will not happen. If we keep a piece of sodium on a wet cloth then it will not explode. Rather, it will burn and turn into a transparent small ball and then the ball will bust. (Video of example.)

What is the reason behind such situation? What reaction actually occurs when the sodium is kept on wet cloth?


texts: What chemicals have been named after Star Wars characters?

texts:
The molecule below is whimsically named Yoda1 because it "uses the force" to open channels in a class of animal proteins known as piezo ion channels (which appear to be part of their pressure sensing nervous systems). See this Nat. Commun. 2018, 9 (1) for a description and other links.

This raised the question for me of how many and what other interesting chemicals have been named after Star Wars characters?


texts: Finding molar mass of uranium fluoride using Graham’s law of diffusion

texts:
Problem

A sample of uranium fluoride is found to effuses at the rate of $\pu{17.7 mg/h}.$ Under comparable conditions, gaseous iodine effuses at the rate of $\pu{15.0 mg/h}.$ What is the molar mass of the uranium fluoride?

Answer

 $\pu{354 g mol^-1}$

My approach
Perhaps I’m still having issues with significant figures, but I am getting the wrong answer. I know to use Graham’s law of diffusion, which leaves me with:
$$\frac{\pu{17.7 mg h^-1}}{\pu{15.0 mg h^-1}} = \sqrt\frac{\pu{253.8 g mol^-1}}{x}$$
I get $x = \pu{181.70 g mol^-1}.$ I know that the molecular mass of uranium fluoride should be less than iodine, so the answer makes no sense to me.
What am I doing wrong?


texts: Attack of 3-methylbutan-1-ol on benzene in acidic medium

texts:
That's how I proceeded with the question. However the answer is tert-butylbenzene. I can't figure out why do I have an extra carbon atom.

SOURCE
- JEE Advanced 1994


texts: What is the IUPAC systematic name for methane?

texts:
The 1993 IUPAC Blue Book claims that "methane" is a semisystematic name:

  Semisystematic names also exist, such as "methane", "propanol", and "benzoic acid", which are so familiar that few chemists realize that they are not fully systematic. They are retained, and indeed, in some cases there are no better systematic alternatives.

Propan-1-ol and phenylmethanoic acid are obvious systematic versions of propanol and benzoic acid. (Though I disagree that they are "better".)

What is the "fully systematic" name for methane—or is this a case where there is no "better systematic alternative"?


texts:
If we are creating a precipitate of (say) Barium Sulfate from a solution of Barium Chloride mixed with Sodium Sulfate, what determines the particle size?
I assume one of the factors will be concentration of reactants in the solutions, but what else?


texts: Why does Coca-Cola Zero Sugar Contain Sodium Despite no Sodium Ingredients?

texts:
According to the Coca-Cola website and every label I read, Coca-Cola Zero Sugar is a mixture of organic compounds:

  CARBONATED WATER (OC(OH)₂), CARAMEL COLOR (Various sugars), PHOSPHORIC ACID (H₃PO₄) , ASPARTAME (C₁₄H₁₈N₂O₅), POTASSIUM BENZOATE (C₇H₅KO₂), NATURAL FLAVORS, POTASSIUM CITRATE (C₆H₅K₃O₇), ACESULFAME POTASSIUM (C₄H₄KNO₄S), CAFFEINE (C₈H₁₀N₄O₂).

The label also says 40 mg sodium. There's a perceptible salty taste in the beverage, which suggests to me that something activates the taste receptors for saltiness, but a potassium cation can do that just fine.

There is no sodium in any of those molecules. That means "Natural Flavors" must contain the sodium... but in what form? The essential oils in things like OpenCola seem to all be hydrocarbons without sodium. And if it's plain old NaCl table salt, why wouldn't they just list it as "salt"?

Where's the sodium in Coke coming from?

EDIT: The discussion has centered around the sodium content of "still" drinking water; what about the process of carbonating the water? Some processes add a sodium carbonate to the solution; could that be the source, contained in the ingredients list as "carbonated water"?


texts: Is diffuse reflectance measurement superior to transmittance for determining band gap energy?

texts:
Some papers report band gap estimation using Diffuse Reflectance Measurement (e.g. here).

Why would the results of diffuse reflectance be superior to regular transmittance measurement? And why diffuse reflection and not specular reflection?

(source)


texts: Why does acid hydrolysis of glucose-1,6-bisphosphate produce glucose-6-phosphate and not glucose-1-phosphate?

texts: A paper I found details treating glucose-1,6-bisphosphate with 6M HCl to produce glucose-6-phosphate. I'm curious why glucose-1-phosphate (and then even plain glucose) isn't formed instead?


texts: How to report result to the nearest 0.01 mg/L?

texts:
what is meant by reporting result to the nearest 0.01 mg/L?
The test result in certificate show 7 mg/L showing no decimal point.


texts: Are the tars in cannabis considerably more dangerous than those in tobacco?

texts:
The claim that "the tars in cannabis are considerably more dangerous than those in tobacco" is made in Patricks An Introduction to Medicinal Chemistry (4th edition, p. 169). It's just a simple one line statement and not much attention is given to it, but from what I already knew this is to say the least a very controversial statement (see for example the independent website about drugs Erowid) and I expect better for a frequently used University level book.

The question is to what degree (from a chemical point of view) there is truth (or falsehood) to this statement given current more or less objective (not like the Heath monkey studies) knowledge? Is the author in his right to boldly state this?


texts: When are pure liquids included in the equilibrium constant?

texts:
For an esterification reaction of pure liquids only, the equilibrium constant will take into account all species, however for an aqueous based esterification reaction, water is not included in the constant

Why are pure liquids used in the first reaction and pure liquids not used in the second reaction, don't pure liquids have an activity of one hence can't we just assume that the equilibrium constant for the first reaction is one, or do we only exclude pure liquids when they act as a solute or they are present in a heterogeneous equilibrium?

Also note that I have a very vague knowledge of thermodynamics.


texts: activating and deactivating groups and directing effect

texts:
In electrophilic aromatic substitution:
I have just learnt a 'rule' about benzene with more than 1 substituents attached (excluding the effect on steric hindrance):

if a strong activating group (EDG) and a strong deactivating group (EWG) are attached, activating group wins hence the electrophile adds on ortho & para position relative to the activating group.

if a weak activating group (EDG) and a strong deactivating group (EWG) are attached, deactivating group wins hence the electrophile adds on meta position relative to the deactivating group.

I understand rule 2 (strong must dominate the weak), but I do not understand what is the principle behind rule 1:

e.g. methoxide group wins over nitro group, although they are both strong EDG & EWG. I understand if the methoxide group is replaced by a methyl group, nitro group wins as $\ce{R-CH3}$ only has a much weaker inductive effect (compared to strong resonance effect). However, both methoxide and nitro groups use resonance to exert their respective directing effect, why activating groups always win?


texts: Is sodium acetate strong or a weak electrolyte?

texts: Since it is formed of a strong base and a weak acid it should be a strong electrolyte but a chemistry teacher said that it is a weak electrolyte.....


texts:
The $\ce{CN}$ molecule has been observed spectroscopically in comets where pressure has been estimated to be as low as $10^{-10}\ \mathrm{mmHg}$. Draw a Lewis structure for $\ce{CN}$. Suggest an explanation as to why this species can persist in a comet but is unstable under normal terrestrial conditions?

Having drawn the Lewis structure, the molecule is a free radical, hence it is very unstable. Would the species be unstable under terrestrial conditions due to a higher temperature (hence pressure) there? Or more specifically, how does a change in pressure effect a free radical molecule?


texts:
I've got 2 problems with reaction:

1) Does the nitrogen or the carboxyl group react with the methanal?
   Do I have to use a protecting group?

2) Is there a chance it reacts similar to a marquis reaction?


texts: What is the structure of powdered sulfur?

texts:
Quoting this paper:

  A variety of allotropic states of elementary sulfur have been identified.
  Solid crystalline sulfur exists either as rings of 6-12 sulfur atoms (cyclohexasulfur, $\ce{S6}$, cyclooctasulfur $\ce{S8}$, etc. or as chains of sulfur atoms (catenasulfur $\ce{S_{\infty}}$).

As said on the same paper, Alpha-sulfur (orthorombic - $\ce{S_{\alpha}}$) is the thermodynamically stable form under ordinary conditions.

What happens with powdered sulfur (also called "dusting sulfur", normally used as fungicide)? Are sulfur atoms still organized in rings or chains?

Can we associate a precise crystalline phase to powdered sulfur?


texts:
Calculate the ppm of $\ce{Fe^2+(aq)}$ if $\pu{0.0055 g}$ of $\ce{Fe(NO3)2}$ is dissolved in $\pu{2.0 kg}$ of water.

I have tried converting g of iron nitrate into moles, using mole ratio between iron nitrate and iron(II) ions and then converting to grams of iron(II) ions. I then took these grams and divided by grams of solution ($0.0005 + 20000$).


texts: Pure substances have only one kind of atom

texts:
I read in a book recently that no substance is ever totally pure, even if we take great care to separate it from other substances.
And also that pure substances contain only one kind of matter.
But I actually have some doubts related to both of the notes.
I would rather number...

Pure substances contain only one kind of matter? True for elements but what about compounds? Are compounds not pure substances? They are homogenous at composition, right?
No substance is totally pure? Reactive elements are found in combined state, but what about less reactive or maybe radioactive?
As well, can't we obtain any substance with 100% purity?

I did surf the questions but did not get any reasonable explanation. Also, please do correct me where I am wrong.


texts: Predicting products of chemical equations?

texts: Consider the equation $\ce{2 NaOH (aq) +Cl2 (g) —> NaOCl (aq) + NaCl (aq) + H2O (l)}$. How would one know the products of this reaction? Is there a general way of doing this? I would have no earthly knowledge of predicting this. Is it that we would look at each molecule and decide which goes with which on the basis of octet? Also, why does it just so happen that 2 moles of $\ce{NaOH}$ react with 1 mole of chlorine? What would happen if it was a 1:1 ratio?


texts: Why doesn't core charge increase down a group?

texts: Atomic radius increases down a group because the electrons feel a lesser attraction to the positive nucleus (due to shielding from inner shells). Why then, doesn't core charge decrease seeing as core charge is just the attraction felt by the valence electrons towards the nucleus (and that attraction is said to decrease down a group as per the reasoning for the increase in atomic radius)?


texts: Rate of cathodic reaction vs Tafel slope

texts:
One of my reference engineering books says that for the cathodic protection process (in seawater):

Al $\rightarrow$ Al$^{3+}$ + $3e^-$ (anode, setting the protection potential at about -900 mV SCE)

2H$_2$O + 2$e^- \ \rightarrow$ H$_2$ + 2OH$^-$

Book says that the rate of hydrogen evolution grows roughly one order of magnitude every -120mV of over-polarization (more negative potential).
I found online that the Tafel slope for the hydrogen evolution process is roughly $\beta$=200 mV/dec in seawater (should be $\beta$=120mV for uni-molecular mechanisms).
Following this reasoning, I get (using the Tafel equation):

ln$\frac{i*}{i}$=ln10=-$\frac{1}{\beta} \left ( \eta^*-\eta \right )$

therefore the rate should rise one order of magnitude every $\Delta\eta$=460 mV ($\beta=200mV$, and $\Delta\eta$=276 mV if $\beta=120 mV$).
Does anybody see any mistake in my reasoning? If this is correct either my Tafel constant is off (should be about 55 mV) or the book has a typo...

Thanks in advance.


texts: Can cycloaddition reactions be antarafacial?

texts:
Cycloaddition reactions of the form [4+2] and [2+2] are always suprafacial, as the geometry is too constrained to allow for antarafacial interaction between the FMO's. However, for cycloaddition of longer chains, say [6+6] cycloaddition, can the cycloaddition be antarafacial?
Here's a small scheme I came up with for antarafacial cycloadditions, and the resulting product:

Is this reaction possible? I haven't been able to encounter any literature online for reactions of this type, which is why I'm doubtful. I just took [6+6] as an example, but if there are references of other conjugated systems undergoing antarafacial cycloaddition, they would be helpful.


texts: Optimum pH range for formation of Schiff bases

texts:
What is the optimum range of pH for the formation of Schiff Bases by the addition of hydroxylamine to an aldehyde or a ketone?

According to Peter Sykes' A Guidebook to Mechanisms in Organic Chemistry,

"The initial addition step or the dehydration step can be made rate limiting at will, depending on the pH of the solution. At neutral and alkaline pHs it is generally dehydration, that is the slow and rate limiting step while at acidic pHs it is the initial addition which is slow and rate limiting. This clearly has significance in preparatory terms, and formation of such derivatives of carbonyl compounds tends to exhibit pH optima."

My doubts are :

How does the pH change the rate limiting step? That is, why is dehydration the rate limiting step at neutral and alkaline pHs and why is addition the rate limiting step at acidic pHs?
What is the significance in preparative terms that Sykes is taking about?
How will this significance determine the pH and what is that pH (or the range of pHs)?


texts: Why do seemingly reliable sources give NFPA 704 Health ratings ranging from 1-4 for elemental mercury?

texts:
Recently a user posted the question Do Mercury have a NFPA 704 classification?.

Why the present question is not a duplicate:
Although there is no accepted answer to the above question, I think it's a fairly obvious "yes", and that my question rather is regarding how there could be such a diversity of classifications arising from this single, widely used standard.

Background:
According to the US National Fire Protection Association (NFPA), NFPA 704: Standard System for the Identification of the Hazards of Materials for Emergency Response:

  This standard shall address the health, flammability, instability, and related hazards that are presented by short-term, acute exposure to a material under conditions of fire, spill, or similar emergencies.

These are typically displayed in the widely recognizable "fire diamond" (generic image from Wikipedia, not for mercury):

Here, blue indicates health hazard, red indicates flammability, and yellow indicates chemical reactivity.

Data:
The following are some values given from different sources for the "health" rating (scale of 0-4, where 0 is the most benign and 4 the most hazardous) for elemental mercury:

The National Institute for Occupational Safety and Health (NIOSH): Health = 1
MSDS from NIST: Health = 2
MSDS from Fischer Scientific: Health = 3
MSDS from Sigma-Aldrich: Health = 4 (link from comment on first link above by MaxW)
SDS from Sigma-Aldrich: Health =2

Question:
My question is simply: why is there such disparity in the NFPA health ratings given for elemental mercury?


texts: Effect of evaporation on the concentration of a saturated solution

texts:
When evaporating a saturated solution, does the concentration remain the same?

My thinking is that because the solution is saturated, and the volume is decreased, the excess solute would precipitate out of the solution. Therefore maintaining the original concentration.

On the other hand, would the precipitate be included when measuring the concentration? And therefore evaporation of a saturated solution would lead to an increase in concentration?

For example: if you have a 100mL of 2.5M saturated NaCl solution and evaporate it until the volume is 50mL, what would the final concentration be?


texts: Predicting the products of a redox reaction

texts: How can you predict how a given reactant will be reduced/oxidized? How can you predict how a given reactant will be reduced/oxidized? I would like to be able to do this without being given an electrochemical series chart. How can I then complete the half reaction?


texts:
A chemist mixes 16.3 mL of 1.23 M sodium nitrate with 6.28 mL 0.823 M solution of calcium nitrate. What is the final molar concentration (molarity) of the nitrate ions in the resulting solution?

What I know: I know I can add the volumes to use it to find the final molarity. After I multiply both volume and molarity and get amount of substance, I multiply by the ratio to get the amount of product and use those amounts to calculate molarity. But I don't know how to isolate the amounts of nitrate from the overall amount of product. Can someone explain how I do that?


texts: Combining enthalpies of formation and combustion in the context of Hess's law

texts:
I know that you can use enthalpy of combustion to work out formation, and Formation to work out enthalpy change. But can you use enthalpy of formation and combustion data is the same Hess's cycle to work out enthalpy change?

For example, we are trying to work out the enthalpy change for the reaction

$$\ce{A -> B}.$$

The alternative route is

$$\ce{A -> X -> B}.$$

We have been given combustion enthalpy data for $\ce{A -> X}$ and formation enthalpy data for $\ce{X -> B}.$

Could you work this out? Or does it always have to be the same type of enthalpy data in the alternative route?


texts: Why is a spin change favourable in intersystem crossing?

texts:
All phosphorescent molecules go through the following transitions:
 $$\text{excited singlet state}$$
$$\Bigg\downarrow$$
$$\text{[intersystem crossing]}$$
$$\Bigg\downarrow$$
$$\text{ excited triplet state}$$
Why does that spin change always occur, given it’s a “forbidden” transition and, thus, unfavourable and much less likely to take place?


texts: Can 1 mole of H2 react partially with one mole of O2?

texts:
I am currently studying stoichiometry (high school level) and we came across the following equation in school:

$\ce{2H2 + 1O2 -> 2H2O}$

which is clear to me. We learned in school that reactions in chemistry only happen if there are enough atoms/molecules to react (so every molecule/atom can react), therefore the following reaction won't do anything:

$\ce{1H2 + 1O2 -> nothing happens}$

So now my first question: Why does the following not happen:

$\ce{1H2 + 1O2 -> 1H2O + 1O}$

And, as a follow up question, why does the following not work?

$\ce{H2 + O2 -> H2O + 1/2O2 (Left) }$

What do I do wrong? (maybe I simply misunderstood our teacher)

Are there any explanations for this? I'm especially interested in the answer of my example with $1$ mole of $\ce{H2}$ and $1$ mole of $\ce{O2}$. According to our teacher nothing will happen at all. I would assume that at least all $\ce{H2}$ molecules react with half of the oxygen molecules to $\ce{H2O}$ - leaving half a mole of $\ce{O2}$ left over.
(otherwise this would mean that all molecules "know" each other so they are "aware" that not all molecules/atoms can react)

Can somebody help me? Or point out what I am doing wrong?


texts: C-N bond lengths in 2-bromo-1,3,5-trinitrobenzene

texts:
Are all the $\ce{C-N}$ single bonds in 2-bromo-1,3,5-trinitrobenzene the same or different? I am of the view that the $\ce{C_1-N}$ and $\ce{C_3-N}$ bonds are of the same length and they are longer than the $\ce{C_5-N}$ bond, due to steric hindrance. Am I right or am I missing out something?

(source: nist.gov)


texts: In which beta-elimination reaction do the structures of the carbocations formed influence the reactivity?

texts:
I believe there is a mistake. If we go back to the mechanisms, E2 does not go through a carbocation. So, there should not be any impact.

E1 does however. So, E1 should be circled. Is there a missing point or argument in my logic.


texts: Partial pressure of gases in a container with a piston

texts:
I've been having problems with the following problem.

Figure 1.

A container with a piston like that shown in Figure 1 is filled with $0.10$ $mol$ of Ar and $1.00$ $mol$ of water (liquid and vapor). The temperature of the entire container is $87 °C$ and the total pressure is $1$ $bar$. It is assumed that the volume of the liquid or cup is negligible with respect to that of the gas, and that the temperature of water and Ar is always maintained at $87 °C$. In this initial situation, the partial pressure of Ar is $A$ $bar$, the partial pressure of water vapor is $B$ $bar$, the volume of the gas is $C$, and the number of moles of liquid water is $D$ $mol$.

The piston is then pulled back quickly to fix the gas volume to $15.8$ $L$. At the moment when the piston
is pulled, the partial pressure of Ar decreases to $E$ $bar$ and the partial pressure of water vapor
decreases to $F$ $bar$. In this situation, the water will boil, because the total pressure of the gas is
lower than the saturated vapor pressure of water at $87 °C$, which is $0.6226$ $bar$. The partial pressure of water vapor increases
due to the boiling until the boiling eventually stops. When the boiling stops, the number of moles of
liquid water is $G$ $mol$. After that, evaporation proceeds until equilibrium is reached. At
equilibrium, the number of moles of liquid water is $H$ $mol$.

Calculate the appropriate numerical values for blanks $A$ - $H$.

The reason I am having trouble solving the problem is the fact that there seems to be too many unknown variables: the initial volume of the container $(V_0)$, the partial pressures of Ar $(p_{Ar,1})$ and water $(p_w)$ and the number of moles of liquid water $(n_{w,l})$. I've come up with the following formulas but I am unable to get any further.
$\ce{p_{total}=p_{Ar,1} + p_{water}=1 bar}$
$\ce{n_{total}=n_{Ar,1} + n_{water,g}=0.10 mol + (1 mol-n_{water,l})}$
$\ce{p_{Ar,1}=\frac{n_{Ar}*R*T}{V_0}}$
$\ce{p_{w,1}=\frac{n_{water}*R*T}{V_0}}$
$\ce{V_0=\frac{n_{total}*R*T}{p_{total}}}$


texts: Is there a compound or element with properties similar to H2O?

texts:
Is there an existing compound or element with properties similar to H2O?
( Liquid, non toxic, stable, and with a clear / blue coloration )  I would expect that any such element or compound would not exist in a stable form, however, I curious to see whether something similar may exist.

I need this for a fictional piece I am working on as a substance from an alien planet.


texts: Chemical compatibility of polycarbonate and carbonate esters

texts:
I am designing a battery box to house lithium ion batteries in an electric vehicle. These batteries use an electrolyte which probably contains carbonate esters (eg. ethylene carbonate, dimethyl carbonate, diethyl carbonate).

If I use polycarbonate as the battery box material, should I be worried about an interaction with the electrolyte in the event of a battery leak?


texts: Changes in UV-Vis spectra in host-guest complexes

texts:
I'm doing some background reading before conducting an experiment, but am getting a little confused.  What serves as evidence for the formation of a host-guest complex when conducting analysis through UV-visible absorption?

From the sources that I have read and have personally observed in the lab, formation of host-guest complexes can push equilibrium to favour a specific species, like an acidic form or a basic form of the guest molecule due to stabilizing interactions within the host (think cyclodextrins + phenolphthalein).  This is reflected in absorption spectra as an increase/decrease in absorbance of the peaks to reflect the increasing/decreasing proportion of acidic/basic species of the guest molecule.

Another way of telling if the host-guest complex is formed is if the there is an increase in the molar absorption coefficient or a shift in the absorption peaks of the guest molecule.  Another conflicting source tells me that when a guest molecule is complexed, absorption of the guest molecule should decrease.  Can anybody clarify which of these changes serves as evidence for formation of a host-guest complex?


texts: What are the different types of catalysts used in catalytic hydrogenation of alkynes?

texts:
This is a question from Org. Chem. by Solomons, Fryhle & Snyder, adapted for JEE by M.S. Chouhan :

In the first step, I expected that the reaction would stop at alkene formation via syn addition of $\ce{H_2}$ since Lindlar catalyst is poisobed and heterogeneous. What are some other other poisoned catalysts that stop at alkene?
In the second step, I expected syn addition of $\ce{D_2}$ since $\ce{Pd-C}$ is a heterogeneous catalyst, forming product (a). But the answer given is (c) — does this mean that some heterogeneous catalyts can give anti addition, or is it just an error on the adapting author's part?


texts:
why cookware does not melt down
On stove supllied with butane gas which has a flame temperature of 1970°C?

http://www.engineeringtoolbox.com/flame-temperatures-gases-d_422.html


texts:
I'm searching for an audio file of the ringing of a ringing gel - does anyone know a source?
(I already searched on different video- and sound-platforms and looked up in the literature)


texts:
What is a common cause of peak tailing?
a. The distribution constant decreases as analyte concentration increases.
b. The distribution constant increases as analyte concentration increases.
c. The plate height increases as analyte concentration increases.
d. The plate height decreases as analyte concentration increases.


texts: When SiO2 changes state, what forces/bonds are being overcome/broken?

texts: When silicon dioxide changes state, are the covalent bonds being broken (ie. the intramolecular forces) or is it the intermolecular forces?


texts: Determining the reduction potential of a half cell reaction at a given pH

texts:
$E^\circ_\ce{Cu^2+|Cu} = \pu{0.34 V}$.
  What will be reduction potential at $\mathrm{pH} = 14$ for the same couple?
  Given that $K_\mathrm{sp}$ of $\ce{Cu(OH)2}$ is $10^{-19}$.

My Attempt

I think that this problem might be solved by using the Nernst equation

$$E = E^\circ - \frac{0.0591}{n}\log_{10} K,$$

but I don't know how do I apply that.
We have the $E^\circ$ and the number of electrons participating (which is equal to 2), but I don't know how do I determine the equilibrium constant.

Any help or hint would be appreciated.


texts: What is Molar Conductivity of an electrolytic solution

texts:
Please explain the physical meaning it carries ? And how is it that it can increase with dilution ?

And why is it called Molar ?

And what is equivalent conductivity ?


texts: What kind of algorithm does computational software use to process molecular symmetry?

texts:
Background
I'm forced into using GAMESS-UK for an older software package. Using a cs-symmetry molecule, I've noticed that GAMESS will reorient the molecule before running a standard SCF calculation. This is related to the algorithm the software uses to process the symmetry of the molecule. For instance, If I were to input my molecule as having C1 symmetry, no reorientation would occur; the scf calculation would run using the exact same coordinates from the input file.
For some molecules, I've noticed a rotation for the reorientation as large as about 45°. For other molecules, it might only rotate 5° from my input coordinates. This for the same system of molecules—all cs symmetry, same functional groups, only the alkyl backbone has a variable number of carbons. As a result of this, my molecular axis is being defined differently across my various output integral files. It'd be more convenient for me if that were possible to avoid.
I'd like to better understand what conditions determine the reorientation of the molecule. I realize Gamess-UK is old, so any kind of symmetry algorithm from other computational software would also be useful to know about. Maybe I can see if it's similar to the one I'm encountering.
Question
Does anyone know how computational software determines the reorientation of input coordinates prior to a calculation?


texts: What kind of water would Oxygen-15 and tritium create?

texts:
I've recently become interested in chemistry, and have some questions about water.

I've heard of semi-heavy, heavy, tritiated, and oxygen-heavy water. However, what about various combinations of isotopes? Let's say: Oxygen 15 + Tritium? How about Oxygen 18 + Deuterium?

Would these all have distinct properties from one another? Have all the stable combinations been extensively studied and lab tested?


texts:
I am learning adding alkyl groups to benzene using Fridel-Crafts alkylation:

I know that it is very common to use $\ce{AlCl3/AlBr3}$ as Lewis acid catalyst in this reaction. But I am just wondering whether I can use a Bronsted acid, e.g., $\ce{H2SO4}$, as the catalyst or not. For example, in a $\mathrm{E1}$ or hydration reaction, $\ce{H2SO4}$ is added to alkene or alcohol, respectively, forming a carbocation, which is the same ultimate result when $\ce{AlCl3}$ is used (make the alkyl group more electrophilic).
I am thinking $\ce{AlCl3}$ is the only way if I am adding primary alkyl halide since in  $\mathrm{E1}$/hydration reactions, an actual primary carbocation is impossible to be formed (too unstable), while it exists in a complex with $\ce{AlCl3}$ (not entirely a carbocation, so can be formed).
SO, what is the problem with secondary/tertiary alcohols if I use the Bronstad acid? If there is a problem, way? Both Lewis and Bronsted acid ways will lead to carbocation rearrangements (I have not learnt the acylation).


texts: What is the reaction mechanism of a selective catalytic reaction with urea?

texts:
What is the reaction mechanism of the following reaction:

$$\ce{4NO + 2(NH2)2CO + O2 -> 4N2 + 4H2O + 2CO2}$$

I expect that the catalyst is vanadium oxide and titanium oxide.
Where can I find a detailed description of the reaction mechanism?


texts: Can 1 gram hyaluronic acid really hold 6L of water?

texts:
According to this study (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3970829/), they make an (uncited) claim about hyaluronic acid: "One of its most important properties is that it can attach and hold large amounts of moisture; approximately 6L of water in just lg ."

Now, the MW of HA is $776.651$ g/mol, so there are about $\pu{0.00128865979}$ moles of HA in a gram. And about $\pu{7.757732e20}$ molecules.

Using google, 6L of water has $\pu{2.007e26}$ molecules.

So this is essentially telling me that roughly 1 million water molecules are able to hydrogen bond with 1 molecule of HA...

Firstly, is this fact true? And if so, how is this possible??


texts: Will fluoride evaporate from tap water at the same rate as chlorine

texts: Chlorine evaporation is an overnight process from standing tap water in a gallon pan. Does fluoride evaporate in the same way/rate?


texts: Why is Fluoride anion less stable than iodide anion?

texts:
Down the halogen group , electropositive character increases , then why is it that Fluoride ion is the least stable ?
The counter arguement is that fluoride ion has four lone pairs and a small size which makes it least stable.Down the group , since atomic size increases the extra electron is stabilized.
In all such stability trends there are multiple counteracting factors , how to decide which one to give more weightage ?


texts: Calculating the concentration of product in a solution based on the peak area of HPLC

texts:
Please help me resolving the following:

A sample solution, $\pu{0.24mg/mL}$ Compound A, is exposed to heat to form Compound B. From HPLC data report I have peak area for Compound A and Compound B.  The  STD  concentration is 0.3 Compound A. The concentration of Compound A in sample solution is $\pu{0.20mg/mL}$ Compound A calculated using STD Compound A information. Which is the correct way to calculate concentration of Compound B?

My advisor in the project I'm participating insist I must calculate the concentration of Compound B since is a degradation of Compound A  in term of the amount lost of Compound A is the amount gained by Compound B (she call it a indirect method for calculating the concentration). I'm at lost! Originally I performed the calculation using a STD Compound A at the LOQ level of the impurity:
$$\text{[Compound B]} = \frac{\text{Area Compound B} \times \text{[STD Compound A]}}{\text{Area STD Compound A}}$$
The new approach is calculate the [compound A] using a STD at the level of the sample and then indirectly calculate the [Compound B].


texts: Is it possible to unambiguously identify a substance with a rapid test?

texts:
I've seen a documentary about the narcotics control at the Jorge Chávez International Airport in Peru. The officers used a rapid test to identify cocaine. They put a cotton swab into the substance. The test was positive if it turned turquoise.

How does the test work? Is it really possible to unambiguously identify a substance by the color change? How can any known or even yet unknown substance be ruled out to react in the same way?


texts: Can dimethylmercury originate from cleaning up a broken thermometer with disposable wet wipes?

texts:
I broke a CFL in my home (so elemental mercury is present in a small amount) and wiped up some of the mess with a clorox wipe.
The wipe in question contains dimethyl benzyl ammonium chloride and dimethyl ethylbenzyl ammonium chloride.

I'm not chemical-phobic, but can someone please tell me, I didn't accidentally expose myself to dimethylmercury? I realize that it is something you don't find outside of very specific lab environments.

Edit: Thanks everyone for the quick responses. It's been a long time since I took a chem class! Can you help me to better understand why this will not methylate the mercury?

For example, I had been cleaning my carpet at the same time with resolve (water, hydrogen peroxide, sodium lauryl sulfate, probably other ingredients too) and threw out paper towels soaked with it to clean the rug into the same bag as the CFL. Am I correct to assume that despite the methyl group on the SDS, it is also stable like the BZK and thus unlikely to methylate the mercury?


texts: Failed synthesis of aspirin due to excess sulfuric acid

texts:
Last week, I tried synthesizing acetylsalicylic acid - the reaction is shown below - using $\ce{H2SO4}$ as a catalyst. However, as the title suggests the synthesis failed as I used too much $\ce{H2SO4}$ - approximately four times more than the prescribed volume. Needless to say, I had to redo the synthesis.

But now I try to understand why the synthesis failed - I know that catalysts are used in small amounts, but I thought that much of it would only lead to equilibrium state being reached faster.

I think that maybe the acidity of the reaction environment could've somehow explained why the synthesis didn't take place. But I don't understand why - shouldn't more protons in the environment lead to faster protonation of the carbonyl oxygen of acetic anhydride? Could you please explain it to me?


texts: How exactly does the electrolysis of water work?

texts:
When we pass electricity through water it breaks into hydrogen and oxygen gas.

$$\ce{2H2O -> 2H2 + O2}$$

What I couldn't understand is how the electrical energy is converted to breaking the bonds of water molecule. I've searched a lot but couldn't find any satisfactory answers on how the energy conversion happens.

Few thoughts :

The fast moving electrons from the battery hit the water molecules breaking them into hydrogen and oxygen ions.
I think above idea is incorrect as pure water is an insulator and blocks passage of electrons. Then it might have to do with the electric field that exists through out the water between the anode and cathode. Does this electric field somehow transfer energy to the water molecules and split them ?
Above idea makes sense to me as we can think of each $\ce{H2O}$ molecule as a dipole $\ce{2H+-O^2-}$, so it can interact with electric field.
I feel all above ideas are silly and there is some sophisticated way to reason this which I don't know yet.


texts: Does benzene have isomers and resonance structures?

texts:
Does benzene have both isomers and resonance structures?

I know that it has resonance structures because you can manipulate the position of the double bonds but what about isomers?


texts: How are the Van der Waals constants a and b related to each other?

texts: I know that the constant $a$ represents the attractive forces between the molecules while the constant $b$ represents the size/repulsion between them. Does that mean that $a$ and $b$ are "inversely proportional" or are they independent of each other? If we have two gases and we can compare their sizes and attractive natures, can we compare $a$ and $b$ for the two gases? If $a$ is greater for gas 1 will $b$ always be lesser for gas 1 as compared to gas 2?


texts: Does the change in Gibbs free energy depend on initial and final concentrations?

texts: Suppose there is a decomposition reaction, and by varying different factors, the equilibrium can be disturbed to alter the final concentration of compounds. So, does the value of ∆G here depend upon the initial and final concentration? The basic rule of ∆G = G(products) - G(reactants) seems unsatisfactory, because, it seems pretty absurd to me, that the value of ∆G is the same when 0.01% of a gas decomposes, and when 85% of it decomposes.


texts:
What process happens between an enol and a ketone, so that the ketone will enolate and become acidic?

Please, explain what happens with them in this process?


texts: What is the difference between volatility and evaporation?

texts:
I've been trying to find the difference between volatility and evaporation and I can see almost everywhere that the volatility is the tendency of a substance to vaporize. So Q1: what makes the volatility special? I understand that the fuels are generally volatile, and I understand that they vaporize faster than water, for example. But Q2: is this the only difference?

I was thinking that volatility also makes the vapor have a different chemical composition, or did I get it wrong?

For instance, the water (a non-volatile liquid) vapor is still $\ce{H2O}$, right? Q3: Will the vapor of benzene $\ce{C6H6}$ still be $\ce{C6H6}$ or it brakes into other compounds?


texts: Why are only sigma bonds used in determining the geometry and bond angle in VSEPR theory? Why aren't pi bonds used?

texts: I have read that in VSEPR theory, multiple bonds are considered or treated as single bonds when predicting the geometry of a molecule? I've read in Yahoo! Answers that it is because only sigma bonds are used in determining their shape. What's the reasoning behind this?


texts: Which has the higher chemical shift E/Z alkene?

texts:
If you have a simple alkene for example 1-methyl-But-2-ene

then you will have two methyl groups on one side of the double bond, which one of these will have the highest. Will the one on the same side as the rest of the chain of butene have the higher ppm or will it be the one in trans with the butene.

By the way, on my spectra, these two methyl groups are not equivalent. I need to know if the E or Z will have a higher chemical shift and why, thanks.


texts: Electron flow: How does osmium tetroxide react with alkenes?

texts: This is a question that has bothered me for some time. I have always thought that the part of one molecule will only attack part of another molecule if it has a higher positive charge. So with this in mind, why does the alkene double bond attack the $\ce{O}$ atom of $\ce{OsO4}$. Isn’t the $\ce{O}$ atom negatively charged?


texts: We study enantiomers in detail. But what makes them more important to study than, say, diastereomers? What I'm trying to ask is, enantiomers are simply a type of stereoisomers that can rotate plane polarized light in opposite directions by the same amount. What makes them more important than other stereoisomers?


texts: Interpretting relative probabilities based on Boltzmann's probability distribution?

texts:
I understand that Boltzmann's probability distribution gives the relative probability of one microscopic state in comparison to the other (P1/P2) but I don't know how exactly to understand this.

For example when looking at Hydrogen's ground state and Hydrogen's first excited state at some temperature T, let's say that P1/P2 is 0.3 what does this mean in words? Does this mean that at whatever temperature T, P1 happesn 30% of the time? Or am I interpreting this incorrectly?


texts: Does hydrogen bonding strength correspond to Brønsted basicity in a given medium?

texts:
It does seem that there is a correlation. Both are measures of proton affinity. Heck, isn't hydrogen bonding present in the transition states of most acid base reactions (excluding those involving proton tunneling?) Also, it seems that hydrogen bonding would be subject to the same limitations as Brønsted basicity; i.e. it seems that steric hindrance in some molecule would inhibit both proton transfer and limit hydrogen bonding capability. At least it seems that way to me prima facie.

Also why do we depict acid base reactions as concerted? Is it because the time scale is extremely small for proton transfer reactions, so who cares if it's actually stepwise or concerted?


texts: metals that have a low number of occupied shells such as lithium and potassium should have a stronger electrostatic attraction to their nuclei, so what causes them to always lose their electrons during ionic bonding with a non metal?


texts: pH effect in the hydrophobic interactions between two polypeptide chains

texts:
The rise in pH can change the protein conformation by changing the ionic interactions and hydrogen bonds between two polypeptide chains. This is a fact that I understand very well because the change in amino-acid ionization with pH. I would like to know if by changing the pH value the hydrophobic interactions between two chains can also be changed. If yes, what is the mechanism?
Article: a pH Induced increase in hydrophobicity...


texts:
In class we performed an experiment which I am unable to understand the results for
Why does the the amount of soot produced vary? What is the amount of soot  produced  dependent on?

Experiment:

  We had to have four test tubes upside down in a beaker of water. The test tubes were filled with water in them as well. We had to insert pieces of calcium carbide under the test tubes and have them as follows: one full of acetylene, one 3/4 full, one 1/2 full, one 1/10 full. Then remove the rubber stopper and bring a burning splint to the mouth of the test tube to ignite the acetylene gas.

Results:

The full one: burned slow and produced a little bit of soot
3/4: burned fast and lots of soot
1/2: burned fast and lots of soot
1/10: burned fast and no soot


texts: Charge of polyatomic ions doesn't equal the charge of ions it consists of?

texts: I'm taking entry level collage chem. class, and we got to this topic that I don't really understand. I think I understood what an ion is (a atom whose amount of electrons is not equal to amount of protons, so it has positive or negative charge). But then polyatomic ions... Lets say peroxide; consists of two Oxygens, whose ions have charge of -2. Consequently, two of these anions are suppose to have charge of -4, but peroxide has charge of -2. How does this work? If polyatomic ions don't just sum the charge of ions they consist of, how else can I predict and understand their charge?


texts: Why are sulphide salts of p and d block coloured?

texts:
I have studied that sulphide salts of s block are colourless while p and d block salts are coloured.

But colour intensity of a salt is directly proportional to polarisation in salt.

And s block cations being smaller offer more polarisation. According to this logic, s block salts should be coloured.

Is my knowledge incomplete? Or am I using wrong logic?


texts:
One of my colleagues is working on a homogeneous catalyst ($\ce{X}$) for proton reduction. The simplified proposed mechanism for it is the following.

$$\ce{X + 2 e^- ->[$k_1$] X^{2-}}    \tag{1}$$

$$\ce{X^{2-} + H+ <=>[$k_2$,\,slow][$k_{-2}$] XH-}    \tag{2}$$

$$\ce{XH- + H+ <=>[$k_3$][$k_{-3}$] X + H2}   \tag{3}$$

However, this is not a true catalyst and it degrades over time:

$$\ce{X ->[$k_\text{inact}$] X_\text{inact}}$$

We monitor $\ce{H2}$ at different time intervals and we plot the turnover number (TON), defined as the total number of moles of $\ce{H2}$ produced per mole of initial catalyst (so if we produce 20 mmol of $\ce{H2}$ in an experiment where we started with 2 mmol of catalyst, the TON at that time is 10).

Is there a way to derive an equation for the TON vs time plot that only depends on total $\ce{H2}$ and time? (We get something that looks hyperbolic, like Michaelis Menten plots, but we don't know if it's hyperbolic, exponential, or something else).

My attempt:

Assuming steady-state of the intermediate, $\ce{XH-}$ (and I'm not sure we should!):

$k_2[\ce{X^{2-}}][\ce{H+}] + k_{-3}[\ce{X}][\ce{H2}]= k_{-2}[\ce{XH-}][\ce{H+}] + k_{3}[\ce{XH-}][\ce{H+}] $

$\displaystyle [\ce{XH-}] = \frac{k_2[\ce{X^{2-}}][\ce{H+}] + k_{-3}[\ce{X}][\ce{H2}]}{(k_{-2}+k_3)[\ce{H+}]}$

The rate law is given by:

$\displaystyle \frac{d[\ce{H2}]}{dt} = k_3[\ce{XH-}][\ce{H+}] - k_{-3}[\ce{X}][\ce{H2}]$

So:

$\displaystyle \frac{d[\ce{H2}]}{dt} = k_3\left(\frac{k_2[\ce{X^{2-}}][\ce{H+}] + k_{-3}[\ce{X}][\ce{H2}]}{(k_{-2}+k_3)}\right) - k_{-3}[\ce{X}][\ce{H2}]$

From here I am not sure how to proceed. I think it is safe to assume that $[\ce{X}]$ is constant in the catalytic cycle so we can say that $[\ce{X}] = [\ce{X}]_0 e^{-k_\text{inact}t}$. However, I'm not sure how to treat $[\ce{X^{2-}}]$, and I'm not exactly sure how to solve the integral for $[\ce{H2}]$ from there. Any suggestions are appreciated.


texts: Target temperature for infused cooking oil

texts:
A little context: I make craft chili oils for friends and family. I use a two-step infusion process. First, I infuse the oil for flavor by simmering spices in the oil held around 250 degrees Fahrenheit. Second, I add dried chili flakes into the flavored oil around 250 degrees Fahrenheit. I have used canola and grapeseed oil.

Questions: -Is there an ideal temperature to best extract flavors/fragrances from spices (for ex, from cumin seeds or star anise) into the oil?

-Do the flavor compounds deteriorate with prolonged cook times even if oil temp is kept below smoke point? For example, how does the oil change when kept at 250 degrees Fahrenheit for 1 hour vs 2 hours?