texts: Hydrogen disulfide heterogenous equilibrium

texts:
Hydrogen sulfide can be removed from natural gas by the reaction
$$\ce{2 H2S(g) + SO2(g) -> 3 S(s) + 2 H2O(g)}$$
a) Calculate $ΔG^\circ$ and $K$ for this reaction at $\pu{298 K}.$
b) What is the mass of sulfur at the equilibrium (at $\pu{298 K})$ when $\pu{1.00 mol}$ sulfur dioxide are sealed in a vacuumed 1 liter vessel?
$$
\begin{array}{lrrr}
\hline
  & Δ_\mathrm fH^\circ/\pu{kJ mol-1} & Δ_\mathrm fG^\circ/\pu{kJ mol-1} & S^\circ/\pu{J mol-1 K-1} \\
\hline
\ce{H2S(g)} & -20.6 & -33.4 & 205.8 \\
\ce{SO2(g)} & -296.8 & -300.1 & 248.2 \\
\ce{S(s)} & 0 & 0 & 32.1 \\
\ce{H2O(g)} & -241.8 & -228.6 & 188.8 \\
\hline
\end{array}
$$

I was able to calculate the Gibbs free energy and the equilibrium constant, using the formula
$$ΔG = -RT\ln K$$
and got the following answers, though I am not sure whether they are correct:
$$
\begin{align}
ΔG &≈ \pu{-90.2 kJ mol-1} \\
K &≈ \pu{6.28E15}
\end{align}
$$
Next, I tried to solve for the mass of sulfur but was unable to do so. I tried to solve it in the following way, which led to no solutions:
$$\begin{array} {c c c c c c c}
\ce{&2 H2S(g) &+ &SO2(g) &-> &3 S(s) &+ &2 H2O(g)} \\
c_\mathrm{alku}/\pu{mol dm-3}&1.00 && 1.00 && 0 && 0 \\
c_\mathrm{loppu}/\pu{mol dm-3}&1.00 - 2x && 1.00 - x && 3x && 2x
\end{array}$$
$$\pu{6.28E15} = \frac{(2x)^2}{(1.00 - 2x)^2(1.00 - x)}$$
I would like to know whether my answers for step a are incorrect and how I should approach step b.


texts: Why is the molar entropy of hexane lower than that of butane?

texts:
Entropy is dependent on the complexity of the molecule.
Due to this, I expected entropy to increase as the complexity of the molecule increased.
According to p 918 of Atkins' Physical Chemistry (9th ed.), I noticed that the standard molar entropy of n-hexane at is $\pu{204.3 J mol-1 K-1}$, whereas that for n-butane is $\pu{310.23 J mol-1 K-1}$.
How can butane have a higher standard molar entropy, even though it is a smaller molecule?


texts: Activated carbon + zeolite: Does relative humidity affect retention of VOCs?

texts:
I have a very common air purifier: HEPA filter with a heavy duty helping of activated carbon and zeolite.  My particular filter is designed for 5 years of operation under typical home conditions.  In reality, I expect a few years, if not 5. I found this to be the case in the past.
I put an air purifier in the bedroom, which I keep colder than the rest of the apartment unit.  After using a new filter for about 6 months, I noticed a sign that the filter was done: A sour smell.  Very odd, since another purifier was working in the living room and kitchen for 1.5 years with no such sign.
Strange also that the smell was greater when the thermostat was turned down for the night.  I would have expected higher temperature equals more energetic gases, and lesser binding with the filter material.  That points to less effective filtration with higher temperature, which was the opposite of what I observed.
The only other explanation I could fathom was relative humidity (RH).  Colder air has less vapour capacity, so RH goes up for the same amount of water in the air.  Maybe that was the cause (somehow).  I got some evidence that this was the case.  When I moved the dehumidifier into the bedroom, I could hardly notice the smell from the air purifier anymore.
The dehumidifier was dialed to 35%, but I actually had to make it operate continuously (unregulated) in order for it to run.  Without continuous operation, it would only regulate to down to 35% RH (plus/minus 3%).  With continuous operation, the readout showed 30%.  For all I know, this could be the lower limit of the sensor, but it does show that the RH is lower than under regulated operation.
I know that reliable RH measuring is tough, so I view the dehumidifier readout as a rough indicator only.  But it does seem to show that higher RH yields smellier filter output, possibly indicating that captured VOCs are being released.
I'm not a chemist, but was wondering whether those with expertise in the field can comment on whether retention of trapped VOCs actually lessens with higher RH?  Or perhaps there is a 3rd causal factor, leading to correlatino of RH with less filter retention?  Or maybe it's not even that -- maybe the colder temperature or higher RH simply makes one's sense of smell more sensitive.


texts:
Why do we mix water with different temperatures to calculated the heat capacity of the calorimeter?
Why can't we calculate it directly using just warm water?
Asked differently, would the following be wrong? (With $T_E$ the equilibrium temperature and $T_C$ and $T_W$ the initial temperatures of the caloriemeter and water)
$$
c_{C}=\frac{\Delta Q}{m_{C} \Delta T}=\frac{c_{W} m_{W}\left(T_{E}-T_{W}\right)}{m_{C}\left(T_{C}-T_{E}\right)}
$$


texts: Comparison between hot conc. KMnO4 and cold KMnO4

texts:
Recently while solving carbonyl compounds I came across this. What all can cold KMnO4 do?
Can it oxidize aldehydes too, along with oxidizing alkene to vicinal diols?
(I need a thorough comparison in hot conc. and cold`s properties.)

(hot conc KMnO4)looks a bit like oxidative ozonolysis

I found all these but I cant seem to find specific conditions for oxidation of aldehydes.


texts: Could metal hydride storage tanks for hydrogen store helium as well, given their repective atomic radii?

texts: With atomic radii very similar, could helium dissolve into metallic foam about as well as hydrogen, thus making metal hydrite hydrogen tanks suitable for helium as well?


texts: Why do we use LiCl as a source of chloride ions as nucleophile but not other alkali metal chlorides?

texts:
$\ce{LiCl}$ has higher covalent character than other alkali-metal chlorides, so in polar solutions like ethanol, its ioniztion will be less, and so less chloride ions will be available for participating in substitution reaction.

So why don't we use sodium chloride or other alkali metal halides which are more ionic?


texts: What is the expected product in the reaction of hydrogen chloride with allylbenzene?

texts: Shouldn't it be 4th option since since the carbon attached to the ring is secondary as well as resonance stabilized?


texts: How do I model non-covalent interactions in Gaussian?

texts:
I'm doing some research about the dyes found in photography, and found Organic Chemistry of Photography
by Shinsaku Fujita, which shows the dyes used. I'm looking at doing an excited states and UV-VIS calculation, of course optimized before with a geometry optimization, with some of the dyes presented in the book. Right now, I'm trying to build number one in the image below, but have come upon a bit of a stumbling block.

The problem is the $\ce{(CH2)3SO2O-}$ and $\ce{(C2H5)3NH+}$ part on the rightmost nitrogen, as I'm not sure how to model the interaction between $\ce{(CH2)3SO2O-}$ and  $\ce{(C2H5)3NH+}$ (triethylamine), as both have no more covalent bonds available.

To visualize the problem, I built out two molecules (everything but triethylamine as one, then triethylamine below). As you can see, both are connected with as many covalent bonds as possible.

How can I model the interaction between the two molecules (pictured above) in Gaussian, for UV/Vis calculations?


texts: What is Redox reaction? Is it really possible?

texts: I was a reading a book that a senior gave me, it said that redox is a type of reaction in which both reduction and oxidation take place. I know about oxidation but not reduction. After googling reduction reaction I found it's simply just the opposite. But then how can a reduction and oxidation take place together? It would be better if you put forth some examples.


texts: How much should I scan an aromatic dihedral?

texts:
Suppose I have a napthalene-like molecule (attached), and I would like to scan (relaxed) its aromatic dihedral (highlighted atoms). I used CGENFF to obtain its dihedral parameters as follows,
HGA4 CG2DC2 CG311 CG331 0.2000 3 0.00
As shown, the dihedral force constant is 0.2, periodicity is 3, and angle is 0.
However, the penalty factor is high >50. Hence, in order to obtain new parameters and following the typical charmm protocol using MP2/6-31G*, should I perform a full scan +/- 180 degrees? +/- 180 seems unphysical (as compared to a rotatable bond) for a dihedral that belongs to a ring. If so, how much should I lower this value to?


texts: Why baking soda neutralize the flavor of coconut oil?

texts:
I discovered recently that adding baking soda to a recipe can neutralize the strong flavours of the coconut oil. Does anyone know how it is working and what is, in a simple way, the chemical reaction for this?
Thank you very much.


texts: What is the term for a collection of chiral molecules of unequal amounts of left- and right-handed enantiomers?

texts:
This is what I found on wiki:

In chemistry, a racemic mixture, is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.

Homochirality can also refer to enantiopure substances in which all the constituents are the same enantiomer ...

But what is the term for a collection of chiral molecules of not exactly the equal amounts of left- and right-handed enantiomers?


texts: How to explain the different regioselectivity of ketones/imines reacting with LDA?

texts:
When 1 equivalent of LDA is reacted with, for example, 2-pentanone, you get the thermodynamic (more substituted) product. But when you react butan-2-imine with 1.0 LDA, you receive the kinetic (less substituted) product. Why?

I found out that the 2-pentanone reaction conditions included a temperature of around 0 degrees celsius, explaining the thermo product. The reaction conditions needed for the kinetic product would need a temperature of about -78 degrees celsius with more than 1.0 equivalent of LDA base. The reaction condition for the butan-2-imine included a temperature of -78 degrees celsius.


texts: Cyclopentanone is treated with piperidine

texts:
cyclopentanone is treated with piperidine in acid catalyzed conditions to form the organic product (A). (A) on reaction with benzyl bromide followed by hydrolysis gives another organic product (B) containing aromatic ring. If the sum of degrees of unsaturation of (A) and (B) is x and the difference of the number of carbon atoms in (A) and (B) is y, then find the value of x/y.

According to me compound (A) is an enamine, but I'm not sure about (B)!

So according to this, my answer is x/y = 10/7
But the actual answer is x/y = 4.5

I don't know where am I going wrong!


texts: Does the potential energy increase when temperature is raised?

texts:
The potential energy of a material is its ability to do work. So I would suspect the potential energy to increase during phase changes that increase entropy (solid $\rightarrow$ liquid and liquid $\rightarrow$ gas), and decrease in the opposite direction.

However, what about when the temperature is raised for a solid, up until the melting point - will the potential energy increase? The heat from a 1500 K gold plate could do work on liquid water (evaporate) to a higher extent than a plate at 300 K, so I guess the potential energy has increased. So would the potential energy as a function of temperature, of an arbitrary material, look something like this ($K$ should be $T$)?


texts: Equilibrium constant in terms of partial pressures

texts:
$K_p$ is defined as $\Pi_j(\frac{P_j}{P^{\Theta}})^{\nu j}$ where $P_j$ is the partial pressure of component j and $\nu$ is the stoichiometric coefficient. I have a couple of questions already. Firstly, $K_p$ is meant to be dimensionless so therefore, $\frac{P_j}{P^{\Theta}}$ must be dimensionless. However, surely $P_j$ alone is dimensionless as it's a partial pressure defined by dividing a pressure by a pressure - leaving no units. How does that work? Or am I wrong by assuming that a partial pressure has no units?

Given that, suppose I want to write the expression for $K_p$ in terms of partial pressures for the following reaction:

$$\ce{\frac12 O2_{(g)} + C_{(s)} <=>CO_{(g)}}$$

Do I assume that $\frac{P_{c}}{P^\Theta}=1$ leaving me with:

$$K_p=\frac{P_{\ce{CO}}}{(P_{\ce{O_2}})^{\frac12}}\frac{1}{P^\theta}$$


texts:
When acetylcholinesterase that has been inhibited by an organophosphorus compound is reactivated by an oxime, a phosphoryl-oxime is formed, which is then somehow hydrolyzed in the blood.
One study suggested that enzymes of the paraoxonase family are responsible [1], while another suggested that this may not be so [2].
What is/are the pathway(s) by which phosphoryl oximes are hydrolyzed?
References:
[1] Luo, C., Saxena, A., Smith, M., Garcia, G., Radić, Z., Taylor, P., & Doctor, B. P. (1999). Phosphoryl Oxime Inhibition of Acetylcholinesterase during Oxime Reactivation Is Prevented by Edrophonium. Biochemistry, 38(31), 9937–9947. doi:10.1021/bi9905720
[2] Kiderlen, D., Worek, F., Klimmek, R., & Eyer, P. (2000). The phosphoryl oxime-destroying activity of human plasma. Archives of Toxicology, 74(1), 27–32. doi:10.1007/s002040050648


texts: How do Lewis acids interact with 1,4-diketones and amines to form an alkaloid?

texts:
The following double cyclization was used to generate the ring system of the lycoanitine alkaloids in 2005. Demonstrate your understanding of this C−C bond-forming process by providing a mechanistic rationale (using arrows that represent
  electron movement) for the boxed reaction.

From what I know in my current synthetic organic chemistry class, this question appears to me like a Paal–Knorr reaction, but the product isn't a pyrrole. I don't even know where to start, and I'm not entirely certain how and where the Lewis acid interacts.

Ignore the boxed part, that's for me to do; I'm just curious to know how the carbons attached to the methoxy group on the tertiary amine are able to bond with the C2 carbons on the 1,4-diketone.


texts: Can the oxygen in an ester participate in resonance donation? I think so, although the donation is slight. The hybridization is correct. However, resonance withdrawal by the ring via the oxygen doesn't seem possible as my picture depicts. Therefore, because of resonance donation from the oxygen in the conjugate base of the ester, would that make benzoic acid the stronger acid? It seems that the resonance donation would destabilize the conjugate base of the ester.


texts: CuAAC "Click" reaction giving inconsistent results

texts:
I apologize in advance for the large amount of text and thank all those who take the time to read it.

The "Click" reaction after Fokin and Sharpless is known to achieve high yields without long reaction times or harsh reaction conditions. The reaction is used mainly because of its high selectivity. Many publications prove that the reaction is not significantly disturbed by other molecules and does not place any special demands on the choice of solvent. In the search for a suitable reaction to derivatize a molecule, which is shown in scheme 1, I remembered the CuAAC reaction, which was presented in a lecture.  So I ordered copper acetate and sodium ascorbate as well as 3-azidopropylamine and started with the reaction.

Scheme 1: Reaction of the alkyne with 3-azidopropylamine to the "click" product.

I did a first test with 100 ng of the alkyne. To this, 40 eq of azide as well as 40 eq of $\ce{Cu(OAc)2}$ and 80 eq of $\ce{NaAsc}$ were added. The alkyne was present as dry matter, the azide was dissolved in $\ce{MeCN}$, the copper acetate and the sodium ascorbate were present as aqueous solutions. The total volume of 20 µL was filled with a $1:1\,\ce{H2O}:\ce{THF}$ mixture. Incubation was performed at room temperature at a rotating wheel with a reaction time of one hour. The reaction mixture was then quenched with 80 µL of 0.2% formic acid and injected into an LC-MS/MS. A signal could be assigned to the calculated mass of the derivative, which confirms that the reaction was successful.

Since 100 ng is way too much for my purposes (I would have to be in the range of about 1-10 pg) the reaction was carried out with a dilution series (1 pg, 10 pg, 100 pg, 1 ng, 10 ng, 100 ng). Here it turned out that a usable signal can only be found with 100 ng.

In order to optimize the reaction, it was investigated whether $1:1\,\ce{H2O}:\ce{THF}$ is the correct solvent or whether $1:1\,\ce{H2O}:\ce{MeCN}$ does not work better. This could be refuted very well. The signals are significantly better in a $1:1\,\ce{H2O}:\ce{THF}$ mixture (Figure 1). The reaction was then stopped and analyzed after different reaction times. Here it was shown that the turnover is lower with increasing reaction time (Figure 1).

Figure 1: (a) Peak intensities for the "click" product using 10 ng, 50 ng and 100 ng of alkyne in a $1:1\,\ce{H2O}:\ce{MeCN}$ and a $1:1\,\ce{H2O}:\ce{THF}$ mixture. (b) Average peak intensities for the "click" product from three samples. In each sample 50 ng of alkyne were used. The reaction was stopped after 1, 2, 3, 4, 5 and 6 hours.

Now to my questions:

Do you have any idea what else I could try to do to get the reaction working in the quantity range I need?

Why is the turnover lower with increasing reaction time? Even if a longer reaction time does not bring any profit, I would not have expected a reduction of the intensity. As far as I am aware, 1,2,3-triazoles are pretty stable, even under harsh conditions. My starting molecule is also quite stable and should not decompose in the short time and under the mild reaction conditions.


texts: What happens electrochemically when bird droppings corrode cars?

texts:
I think the metal of the car first goes through an acid corrosion, followed by an electrochemical corrosion. First, the uric acid in bird poop corrodes with iron: 2Fe+C5H4N4O3 -> C5N4O3Fe2+2H2. Then, after the acid is used up, the moisture in the poop participates in an electrochemical corrosion(?). Can someone explain what exactly happens electrochemically?

And please correct me if any of my conclusions were wrong, as I mainly used my own limited knowledge and guessed. I am confident that there is some electrochemistry involved though.


texts: How does one tell if a specific molecule is acidic or basic?

texts:
Let's take the $\ce{KOH}$ molecule into account. I know it is a base from literature, but how would one go about determining if a molecule is acidic or basic simply based on the structure of the molecule? How about amphoteric?

Also, I understand that there are two complementary systems - Lewis and Brønsted-Lowry theories. How do they work and how do they fit together?


texts: In a two electrode system, is the applied current density referring to just the working electrode or to the auxiliary electrode as well?

texts: I'm doing an experiment electrosynthesizing a polymer using a two electrode cell and it says to do it under 0.5 mA/cm^2. However, I am unsure if that means 0.5 mA per square centimeter of surface area on the working electrode or for both electrodes. If anyone could clarify this for me, it would be most appreciated.


texts:
I'm reorganizing my garage (I do metalworking and some machining), and now I have an empty white cabinet that I'd like to dedicate to chemical stuff. I'm not a chemist, and I don't have the typical assortment of chemicals that a chem lab would have; the stuff I'm referring to is typical stuff you'd find in a garage: adhesives, lubricants, solvents, paint, etc. (household cleaners are stored elsewhere).

I'd like to organize things by functional groups (like those listed above). Is there a convention/standard for organizing shop chemicals?


texts: Help with molecular dynamics and computational modelling to check validity of hypothesis regarding SN2 reaction mechanisms

texts:
Polar aprotic solvents have a less hindered electronegative atom pointing out, namely oxygen, fluorine, and nitrogen, all of which have lone pairs besides having a partial negative charge. Now, all the molecules inside a reaction mixture are moving at great speeds. Not all nucleophiles will attack the carbon at 180° to the leaving group since this provides the best overlap between the nucleophile's lone pair and the C–X σ* antibonding orbital. Other nucleophiles running in random directions can maybe bounce off the solvent molecules’ oxygens’ exposed lone pair right into the antibonding orbital, thereby increasing the number of molecules that successfully overlap in some unit time. The nucleophiles are also negatively charged which increases the repulsion while 'bouncing off'. This is illustrated in the picture attached. I am aware of the present explanation which suggests that oxygen or fluorine can solvate the corresponding cations of the nucleophile and it makes sense. This is just another reason that I had thought of(there can be more than one favorable reasons for phenomena?). The number of solvent molecules will obviously outnumber the substrate and nucleophiles, the ones which are roaming around idly can maybe aid this acceleration ( vis-a-vis the repulsion hypothesis) and increase the rate doubly (not doubly but slightly more than the previously anticipated increased rate).

There is a paper that I am currently working on regarding this. I have been made to realize that I'm going to need a molecular dynamics software to check if this phenomenon is statistically more or less likely. However, I'm currently in high school, hence I do not know anything about the same. Can someone please recommend a software and guide me through the basics? Is this something that I can independently work out, or will I need some assistance from a university( or professors)? How much time and work will it take to simulate?


texts: Regioselectivity in the formation of an imidazo[1,2-a]pyrimidine

texts:
In the heterocycle synthesis below (taken from Org. Process Res. Dev. 2006, 10 (3), 398–402), a 5,6-fused heterocycle (an imidazo[1,2-a]pyrimidine) is formed by treating 2-amino-4-(trifluoromethyl)pyrimidine with the diethyl acetal of bromoacetaldehyde, with the cited paper claiming to get a 25:1 selectivity for 5 (minimal amounts of 5a also produced were able to be easily removed).

  Ref: Org. Process Res. Dev. 2006, 10 (3), 398–402.

There are (as ever with heterocycle syntheses) a few different mechanisms one could draw, however, no matter which way round one draws the mechanism, the major product is always the one that arises from what appears to be the less favoured intermediates.

By less favoured intermediates, what I mean to say is that to arrive at the major product, necessarily a cation ends up closer to the electron withdrawing trifluoromethyl group than it would do if the minor product was formed.

Given that all the steps are essentially reversible, is the product distribution arising from a purely ground state thermodynamic preference for 5 over 5a, or is there a mechanism that I'm completely neglecting (sorry for the lack of pictures, I'm not able to ChemDraw right now).


texts:
How to prove that chloroform is more acidic than fluoroform?

Using the concept that the inductive effect is dominant over the resonance (mesomeric effect) in the case of halide substituents: $\require{mediawiki-texvc}$

Since both have single hydrogen, let's compare stability of carbanions $\ce{CF3-}$ and $\ce{CCl3-}$.
Since fluorine shows more negative inductive effect than chlorine, $\ce{CF3-}$ should have been more stable than $\ce{CCl3-}$, so some greater cause must be acting here.
In $\ce{CCl3-}$ carbon has non bonded electrons in 2p orbital and chlorine has an empty 3d orbital, but since the energy difference is very high, $\ce{p\pi-d\pi}$ backbonding is barely possible. Worst case scenario, even if it's possible, then giving preference to backbonding will violate our initial rule (that inductive > mesomeric).
Bond lengths, $\ce{C-Cl}=1.75\AA, \ce{C-F}=1.35\AA$, but since chlorine is bigger than fluorine, they both will have approximately same electronic $\ce{p-\pi}$ repulsion (of lone pair of halogen and at anionic centre).

Which of my reasoning are wrong? How do I prove the fact that chloroform is more acidic than fluoroform?

Data: $\mathrm pK_\mathrm a (\ce{CHBr3})=13.7$ and $\mathrm pK_\mathrm a (\ce{CHCl3})=15.5$ and $\mathrm pK_\mathrm a (\ce{CHF3})=28$ (source - page 2)


texts: Difference between shells, subshells and orbitals

texts: What are the definitions of these three things and how are they related? I've tried looking online but there is no concrete answer online for this question.


texts: Finding reaction rate constant for second order equation in Wolfram Mathematica

texts:
I’m working in Mathematica for my master’s project and I can’t work out how to find $k$ in the second order rate equations where I have a concentration vs time graph for $\ce{AHA}:$
$$\mathrm{rate} = k[\ce{AHA}][\ce{H}].$$
I have the starting concentrations for $\ce{AHA}$ and $\ce{H}.$


texts: How to calculate the mass of iron with a temperature of 325 °C needed to melt ice and raise the temperature of water from 0 to 22 °C?

texts:
A large well-insulated container holds a mixture of $75\ \mathrm g$ of ice and $100\ \mathrm g$ of water at $0\ \mathrm{^\circ C}$. Using the data given below, calculate the mass in grams of solid iron, $\ce{Fe}$, at $325\ \mathrm{^\circ C}$ that you would have to add to this mixture in order to melt all of the ice and raise the temperature of the resulting $175\ \mathrm g$ of water to $22\ \mathrm{^\circ C}$.
Specific heat capacity of water is $c_p(\ce{H2O})=4.184\ \mathrm{J\ g^{-1}\ ^\circ C^{-1}}$
Specific heat capacity of iron, $\ce{Fe}$, is $c_p(\ce{Fe})=0.45\ \mathrm{J\ g^{-1}\ ^\circ C^{-1}}$
Molar enthalpy of fusion (melting) of water is $\Delta_\text{fus}H_\mathrm m(\ce{H2O})=6.01\ \mathrm{kJ\ mol^{-1}}$
$M(\ce{H2O})=18\ \mathrm{g\ mol^{-1}}$

My answer was that you needed $25041.67\ \mathrm J$ to melt the ice and $16108.4\ \mathrm J$ to raise the temperature to 22 degrees Celsius.
Therefore $mc \Delta T(\ce{Fe}) = -(25041.67\ \mathrm J + 16108.4\ \mathrm J)$ and dividing this by the mass of iron and the change in temperature results in a mass of $301.8\ \mathrm g$.
Is this correct?


texts:
A $\pu{1.1g}$ sample of an oil was treated with Wij’s solution and excess potassium iodide solution. The liberated iodine reacted with $\pu{7.3 cm3}$ of $\pu{0.1 mol/dm3}$ sodium thiosulfate solution. The blank titration required $\pu{43.5cm3}$ of sodium thiosulfate. What is the iodine value?

I've been asked this question but there are no examples of calculating iodine value in my textbook. I'm aware that the iodine value is the mass of iodine to react with $\pu{100g}$ fat/oil and the question gives a $\pu{1.1g}$ sample of an oil. Does this mean $1.1$ should be divided by $\pu{100g}$? I'm just a bit confused how to even start this question.


texts: Are there any major exceptions when comparing electron affinity?

texts:
I was tasked with figuring out whether carbon or nitrogen has a more negative electron affinity value. I initially picked nitrogen, just because nitrogen has a higher $Z_\mathrm{eff}$, creating a larger attraction between electrons and protons, decreasing the radius, causing a higher ionization energy, and therefore decreasing the electron affinity value, but I was actually wrong, and the solutions manual explains it as this:

  "As you go from C to N across the Periodic Table you would normally expect N to have the more negative electron affinity. However, N has a half-filled p subshell, which lends it extra stability; therefore, it is harder to add an electron."

Are there any major exceptions to the rules when comparing electron affinity? I'm hesitant to use nitrogen as an exception, because I don't know how far it extends. If nitrogen has a more positive EA than carbon, does that also extend to boron, aluminium, or phosphorus?

I later found that this also applies when comparing silicon and phosphorus. The explanation given was the same.

What exceptions should be noted when comparing electron affinities? Are there any at all? And how far does the exception with atoms with half-filled p subshells extend?


texts: Is there a database on chemical reactions, similar to NIST, but far more complete?

texts:
The only thing I'm interested in is to be able to search all reactions involving that compound in the database. Equilibrium constant, reaction rate and energy of activation would all be very welcome, but in case these data are absent it's no big deal.

Doesn't need to be an online database either, I can download a software if it contains such data.


texts: Chemical Equilibrium - finding equilibrium constant given degree of dissociation

texts:
$\ce{N2O4}$ is dissociated $20\ \%$ at 27 degrees Celsius and 1 bar. Find the equilibrium constant of that reaction. What percentage of $\ce{N2O4}$ dissociates at $13.15\ \mathrm{kPa}$?

An explanation of the solution is below, but there are two things I do not understand.

  Why do we have $1 + \alpha$ in the denominator in equations ${\text(6)}$–${\text(9)}$?

  How do we get the fraction $\dfrac{(2\alpha)^2}{1-\alpha}$ in equation $\text{(11)}$?

If the degree of dissociation is $\alpha$, then the amounts of substances present $n_0$ dissociated is $n_0 \alpha$, and the remaining amount of undissociated substance $n_0 (1-\alpha)$. Since each molecule $\ce{AB}$ dissociates into molecules of $\ce{A}$ and $\ce{B}$, the amounts of each substance is
$$\begin{align}
n_{\ce{A}} &= n_{\ce{B}} = n_0 \cdot \alpha \tag{1}\\
n_{\ce{AB}} &= n_0 \cdot (1-\alpha) \tag{2}
\end{align}$$
In the case of the dissociation of dinitrogen tetroxide, $\ce{N2O4}$, it will be
$$\begin{align}
n_{\ce{A}} &= 2n_0 \alpha \tag{3}\\
n_{\ce{AB}} &= n_0 \cdot (1-\alpha) \tag{4}\\
\sum{n} &=n_0 (1+\alpha) \tag{5}\\
x_{\ce{A}} &= \dfrac{2\alpha}{(1+\alpha)} \tag{6}\\
x_{\ce{AB}} &= \dfrac{1-\alpha}{1+\alpha} \tag{7}\\
x_{\ce{NO2}} &= \dfrac{2\alpha}{(1+\alpha)} =\dfrac{0.40}{1.20}=0.3333 \tag{8}\\
x_{\ce{N2O4}} &= \dfrac{1-\alpha}{1+\alpha}=\frac{0.80}{1.20}=0.6666 \tag{9}\\
K_p &= \dfrac{(P_{\ce{NO2}})^2}{P_{\ce{N2O4}}}=P\cdot \dfrac{( x_{\ce{NO2}})^2}{ x_{\ce{N2O4}}} = \mathrm{ 1\ bar \cdot \dfrac{(0.3333)^2}{0.6666} = 0.1667\ bar} \tag{10}
\end{align}$$
We obtain the degree of dissociation of $\ce{NO2}$ at a pressure of $13.15\ \mathrm{kPa}$:
$$\dfrac{K_p}{P} = \dfrac{(2\alpha)^2}{(1-\alpha)}=\mathrm{\dfrac{0.1667\ bar}{0.1315\ bar}=1.268} \tag{11}$$
From here, we get:
$$
4\alpha^2 = 1.268 (1-\alpha) = 1.268 -1.268\alpha  \tag{12}$$
Which becomes
$$
4\alpha^2 =1.268\alpha – 1.268 = 0  \tag{13}$$
For the degree of dissociation, we get:
$$\alpha =\dfrac{-b + \sqrt{b^2} -4ac}{2a} = \dfrac{-1.268 +\sqrt{1.268^2}+20.288}{8} \\= \dfrac{-1.268 +4679}{8} = 0.426  \tag{14}$$
Check your results:
$$K_p = \dfrac{(P_{\ce{NO2}})^2}{P_{\ce{N2O4}}}=P\cdot \dfrac{( x_{\ce{NO2}})^2}{ x_{\ce{N2O4}}} = \mathrm{0.1315 \cdot \dfrac{(2\alpha)^2}{1-\alpha} =0.1315 \cdot \dfrac{0.852^2}{0.574}= 0.1663\ bar}  \tag{15}$$


texts: How do I find the final temperature of a calorimeter using specific heat capacities?

texts:
What is the final temperature of water and iron if a $\pu{30 g}$ piece of iron at $\pu{144 °C}$ was dropped into a calorimeter with $\pu{40 g}$ of water at $\pu{20 °C}$?
Specific heat of water is $\pu{4.184 J g-1 ^\circ C-1}$, and of iron is $\pu{0.449 J g-1 ^\circ C-1}$

Here is my work:
\begin{align}
Q &= mc\,\Delta T\\
Q_1 &= (\pu{30 g})(\pu{0.449 J g-1 ^\circ C-1})(x - \pu{144 ^\circ C}) \tag{Iron}\\
Q_2 &= (\pu{40 g})(\pu{4.184 J g-1 ^\circ C-1})(x - \pu{20 ^\circ C}) \tag{Water}\\
\text{Since,} \quad Q_1 &= -Q_2\\
13.47 (x-144) &= - (167.36)(x-20)\ \pu{J}\\
13.47x - 1939.68 &= -167.36x + 3347.20\\
180.83x &= \pu{5286.88 ^\circ C} \\
x &=  \pu{0.03420 ^\circ C}
\end{align}

This is giving me an answer that isn't correct according to my book. What did I do wrong, and how can I fix it?


texts:
Whenever we add $\ce{H+}$/ Ethanol to glucose in its hemiacetal form, why doesn't pinacone/pinacolone rearrangement take place in place of nucleophillic substitution. The product would lead to formation of a carbonyl bond and so, should be the favoured product.

The actual pathway is:

But, why can't the reaction occur like this with ethanol as a polar solvent?:


texts: How are chemistry and materials science related?

texts:
I'm currently a chemistry major and now I am considering doing a minor in materials science.

Before making a decision, I would like to know how the two disciplines are related and what are their differences such as techniques, approaches, emphasis, etc.

How will my knowledge in chemistry be useful in my understanding of materials science, and how useful is a knowledge of materials science to a chemist?


texts: How does chloroform degrade nitrile gloves?

texts:
Many of us have experienced the failure of nitrile gloves when exposed to chloroform. What's going on at a mechanistic level when this occurs?

I would guess that the chloroform dissolves some of the polymer into its constituent monomers, but I've never heard anything more definite than that. Is it a similar mechanism to what happens when chloroform is left too long in a plastic bottle?


texts: Precipitation of citric acid by CaCl2 and Ca(OH)2?

texts:
I need to precipitate citric acid from an aqueous solution in the form of calcium citrate. There are, to my knowledge, two different methods of doing this:

using $\ce{CaCl2}$ and which will react in an unknown way
using $\ce{Ca(OH)2}$ which will react as such:

$$\ce{2C6H8O7(aq) + 3Ca(OH)2(s) <-->Ca3(C6H5O7)2 . 4H2O(s) + 2H2O}$$

Does anyone know the pros and cons of each method and how the reactions occur with the first method?


texts: Why is anhydrous copper(II) sulfate white while the pentahydrate is blue, even though both have one unpaired electron?

texts:
We all know that $\ce{CuSO4.5H2O}$ is blue and it turns to $\ce{CuSO4}$ on heating which is white. I also learnt about coordination complexes and d–d transitions and how transition metal compounds are colored. Recently I came to know that $\ce{CuSO4.5H2O}$ is also a coordination compound and in its structure four water molecules are coordinated with $\ce{Cu^2+}$ and one is hydrogen-bonded to $\ce{SO4^2-}.$ So, I thought lets try to apply the theory here and see what causes the blue color of copper sulfate.

$\ce{CuSO4}$ has $\ce{Cu^2+}$ ions and I wrote down the electronic configuration as $\mathrm{(3d)^9(4s)^0}.$ Since no d–d transition is possible, it should be white.

$\ce{CuSO4.5H2O}$ is actually $\ce{[Cu(H2O)4]SO4.H2O}$ and the complex ion is $\ce{[Cu(H2O)4]^2+}$. $\ce{H2O}$ is a weak field ligand, therefore the electronic configuration is $\mathrm{(3d)^9(4s)^2(4p)^6}.$ But still no d–d transition is possible, so it should also be white!? What went wrong in my estimation?


texts: Stubborn CuAAC reaction as derivatization for ESI-MS

texts:
Problem description
I have a substance that is extremely non-polar and therefore does not ionize in the ESI source, which makes it impossible to quantify small amounts. The substance contains only two functional groups, which are a point of attack for possible derivatization. One is an alkyne, and the other is a hydroxyl group. Both groups are attached to the same carbon. Since the substance is to be detected from blood plasma, I decided against derivatization at the hydroxyl group, since numerous side reactions with proteins, which also carry a lot of hydroxyl groups, are to be expected. The alkyne, however, is a good point of attack and is suitable for bioorthogonal reactions. A professor once said about the copper(I) catalyzed alkyne-azide cycloaddition (CuAAC) that this is a reaction that "any fool could manage". I have been trying to get the reaction going for a few days now, but so far, I have not been able to detect any product in LC-MS... Decide for yourself what this says about me as a chemist.
Since I have followed several approaches from papers, I slowly ask myself if my substance is not suitable for a CuAAC. Since the research project and the substance are new and unpublished, I cannot provide a complete structural formula here. But this much can be revealed: It is essentially a steroid, which carries a hydroxy group and an alkyne on carbon C17.

What was done
I performed the reaction with the pure substance (i.e. without blood plasma) according to Presolski et al., but I did not use THPTA nor aminoguanidine. All concentrations were used as described in the paper and the reaction was performed at 40°C according to the suggestion under "Troubleshooting". The azide was dissolved in DMF. Thus, there were 10 µL DMF (5%) in the buffer solution.
I also performed the reaction with the pure substance according to Hong et al.. Again, the proposed concentrations were used but neither THPA nor aminoguanidine were used.
I also tested different variations of those protocols with much longer reaction times (8 to 24 hours), more or less temperature, with and without pH 7 buffer.
As far as I know, the 4-substituted 1,2,3-triazoles formed by CuAAC should be extremely stable, even to metabolic degradation (Agalave et al.), so I do not believe that they decomposed so quickly that they were all destroyed by the measurement. To avoid ion suppression, I purified the reaction after the one-hour reaction time by RP-SPE, using the SigmaAldrich/Merck protocol.
Questions

Does anyone have experience with CuAAC reactions that do not want to run?
Which parameters should I at best adjust to make the reaction successful?
Is it possible that a hydroxide in alpha-position disturbs the reaction? I haven't found anything on this yet.
What advice is there to make the reaction successful even at very low (< 10 pg/mL) substance concentrations?

Update as of 24/07/2020
The reaction was, in fact, successful when applying the already cited protocol by Presolski et al. and using a DMF-water-ratio of 3:1 and incubating at 60 °C for 2 h. Unfortunately, though, the intensities are pretty weak which means that the reaction turnover is not great. The peak of my original substance is at 9.6 × 107 (50 µM concentration) and the intensity of the derivatized product, which should be way better ionized, is 4.2 × 107.
New question

How to get a better turnover while maintaining a reasonably short reaction time?


texts: Possible E2 products of S-2-bromo-2-methyl-1-phenylbutane

texts:
I have been asked to predict wether the following reaction will proceed by elimination or substitution.

$\hspace{2.4cm}$

I believe that the reaction would proceed by the $\mathrm{E2}$ mechanism. I am confused, however, as to what products what would be formed from this reaction. Currently I believe that there would be a total of five products: 2 sets of E/Z isomers, and a product with a double bond with no carbon substituents on one end (i.e along the dashed bond). Is this the case?


texts:
As we all know $\ce{H2O}$ is bent ($C_\mathrm{2v}$) in its ground state equilibrium structure, rather than linear ($D_\mathrm{\infty h}$), which can be readily understood e.g. from the MO diagram of bent versus linear case:

The question, that puzzles me here, is if that apparent case of "symmetry breaking" can be described by a Jahn-Teller or Renner-Teller effect? Jahn-Teller seemingly is ruled out since the "high symmetric" from is linear, which is excluded from the Jahn-Teller theorem while the Renner-Teller effect is apparently a subtle ro-vibronic effect.

Since the water ground state is a closed shell singlet (even in the linear case), my take on it would be, that it must be a second-order JT-effect of coupling between ground and excited states by virtue of the bending distortion. But I am not sure since I never heard or read about water as a second-order JT-example.

Can anyone comment on that?


texts: Brown ring from the anion detection of NO3-

texts:
Today in our practicals I observed that when I did the wet test for nitrate (Making a 1 ml solution of salt solution+$\ce{FeSO4}$ solution+hot concentrated $\ce{H2SO4}$);
The brown ring appeared for a very short time and then disappeared.

But later on I came to know that it was nitrate only. What may be the possible reason for this temporary appearance of a tinge of a brown colour and then its sudden disappearance?


texts: Let's say I have a trigonal prism in my crystal structure and this is further capped by two ions it's called a bicapped trigonal prism. If I have three ions it's called a tricapped trigonal prism. But what about four? I cannot find anything like quadcapped, fourcapped, fourfold capped trigonal prism. How would you name that?


texts:
I'm using Gamry Potentiometer for taking CV measurements for finding the appropriate voltage values for oxidation/reduction peaks and Echem Analyst for analyzing. CV measurements has performed on liquid electrolyte in order to find if working electrode accept Li ions. My question is about interpreting the results.

How can I interpret if potential difference equal or below 1V has no oxidation or reduction peak (or has only one of them) while potential sweep between -2V to 2V bring good results but if I change it to 1 to -3 no reduction peak again. Moreover, going to negative values has a bad consequences such broke the working electrode. What does it mean going to negative values?

That was my first question, my second question is: Is it possible perform Chronoamperometry measurements (in other word, simulate) by using existing CV measurements via Echem analyst script editor?


texts: Determining equilibrium concentrations from initial conditions and equilibrium constant

texts:
The equilibrium constant for the following reaction at $\pu{600^{\circ}C}$ is 4.0.  Initially, two moles of $\ce{CO}$ and one mole of $\ce{H2O}$ were mixed in a $\pu{1.0 L}$ container.  Determine the concentration of all species at equilibrium.

Attempt #1:

$$\ce{CO (g) + H2O (g) -> CO2 (g) + H2 (g)}$$

\begin{array}{|r|c|c|c|}
\hline
\text{Initial}~(M)     & 2.0      & 1.0     & 0  & 0 \\ \hline
\text{Change}~(M)      &  -x      & -x      & +x & +x \\ \hline
\text{Equilibrium}~(M) & 2.0 – x  & 1.0 - x \\ \hline
\end{array}

  Plug $x$ into the equilibrium expression and solve for $x$. $4.0  = 2[x]$, so $x = 0.85 [1.0 – x][2.0 – x]$.

  Determine concentrations: the equilibrium values become 2.0 – 0.85, 1.0 - 0.85, 0.85, and 0.85, giving 1.2, 0.1, 0.85, and 0.85.

Where does the 0.85 come from? Could it be cross multiplied some way or is there another way this is done?

Furthermore, I want to make sure that I've done the 3.00 correctly for $\ce{Fe(SCN)2+}$.

  Consider the reaction represented by the equation: $$\ce{Fe^3+ (aq) + SCN- (aq) -> Fe(SCN)2+ (aq)}$$

Attempt #2:

\begin{array}{ccc}
\text{Initial}     & \pu{6.00 M}\ \ce{Fe^{3+} (aq)} & \pu{6.00 M}\ \ce{SCN^{−} (aq)} \\
\text{Equilibrium} & \pu{? M}\ \ce{FeSCN2^+ (aq)}, \ K = 0.33
\end{array}

\begin{align}
\frac{1}{3}x^2 - \frac{124}{25}x + \frac{297}{25} &= 0 &
 x_{(1;2)} &= \frac{\color{red}{\pmb{-}}(-\frac{124}{25})\pm\sqrt{\left(\frac{124}{25}\right)^2 - 4\cdot\frac13\frac{297}{25}}}{\frac{2}{3}} \\
&& x_{(1;2)} &= \frac{124/25\pm\sqrt{\frac{15376}{(625)}-\frac{15601}{1000}}}{\frac{2}{3}} \\
&&           &= \left(124/25\pm{3}\right)\cdot\frac{3}{2} \\
&& x_{(1;2)} &= 12;3
\end{align}


texts:
Does $\ce{Ni((en)2(Cl)2)}$ show cis-trans form ?

And if No

Why not ?


texts: How can I isolate glycolic acid from sugarcane juice?

texts:
This beginning of a bachelor thesis uses ethylene glycol as a catalyst in the isolation of glycolic acid. I can't find the rest of the article (it ends in the middle of the description) to find out how they did it.
I'm wondering if someone could please help me I want to learn how to do this as an amateur dermatologist. Currently studying pre-med, small knowledge of chemistry.


texts:
Is there a database or a website with a list of oil : water partition coefficients of substances ?

I actually want the oil:water partition coefficients of :

cholesterol, starch , methyl citrate , citric acid , iso- citrate , methyl urea , carotene


texts: How to quantify amount of pigments in plant leaves?

texts:
Using thin-layer chromatography, it is possible to see what pigments plant leaves contain. For example, I can test whether there are chlorophyll a or b, carotenoids, or anthocyanins.

What kind of technique I would need to quantify the amount of these pigments in the leaves?


texts: What is the difference between dynamical and non-dynamical correlation and which one is accounted for in Hartree-Fock theory?

texts:
It is my understanding that dynamical is related to the movement of individual electrons. I don't fully understand what this means though.

Non-dynamical correlation is still very unclear from my notes and how it relates to HF theory is very confusing. Any clarification would be appreciated.


texts: Why is the rate of reaction of polar EAS favored by inductive effects and the rate of less polar EAS reactions through hyperconjugation?

texts:
1. Reactions involving strong electrophiles (nitration) are
       said to be governed
       by
       Inductive effects thus the order of nitration is
                                       D>C>B>A
  2.Chlorination is a less polar reaction thus chlorination said the be governed by hyper conjugation.
                                        A>B>C>D

My question is,  why?

The factors controlling EAS in both the cases will be  the same for both the substitutes.
Hyperconjugation and inductive effects will both operate without distinction in both the cases.

So why is it that
The rate of reaction of polar EAS favored by inductive effects and the rate of less polar EAS reactions through hyperconjugation.

SOURCE   A guidebook to mechanism Peter Sykes

EDIT
I have been asking around for an answer to this question.

No one has been able to answer it conclusively , the primary school of thought   is that

  In Highly polar reactions , inductive effects dominate as more electron density is available , hyperconjugation on the other hand is just redistribution of electrons.

First of all is this correct ?   Even if it's correct but how does it explain the opposing rate orders for nitration and bromination?


texts: Are labile tetrahedral [Mabcd] complexes optically active?

texts:
In the above mentioned complex, there is a chiral centre at the metal, and hence it seems the compound must be optically active.

But my course notes say that the ligands keep on changing their their positions at a very fast rate and as a result such complexes get converted into their mirror images and are hence optically inactive.

I am unable to reconcile my understanding of the stereochemistry with this statement in the notes. How can such complexes be optically inactive?


texts: Lagrange Multipliers for the derivation of Maxwell-Boltzmann distribution

texts:
When deriving the MB-Distribution while taking the number of quantum states $g_j$ into account, the final equation I'd have to solve would be:
$$\ln(g_j)-\ln(n_j)+\alpha+\beta\cdot E_j=0$$
Where $n_j$ is the number of particles at energy level $E_j$. The $\alpha$ and $\beta$ are the applied Lagrange Multipliers restrictions.
I have understood that adding or subtracting the Lagrangian Multipliers should not matter for the end result.
Now, when I continue with this equation, I'd eventually get:
$$n_j=e^\alpha\cdot e^{\beta\cdot E_j} \cdot g_j$$
When I want to derive the probability distribution formula of Maxwell-Boltzmann, I'd have to consider energy to be continuous. Substituting $g_j$ with the energy density formula times $\mathrm dE$, the total number of particles $N$ would then be:
$$\int_0^\infty\frac{V\cdot 2^{2.5}\pi\cdot m^{1.5}}{h^3}\cdot \sqrt E\cdot e^{\alpha}\cdot e^{\beta\cdot E}\cdot \mathrm dE=N$$
However, the result of this integration up to infinity would simply give the outcome $0$. But when you subtract the Lagrange Multipliers in the initial equation, the constants would have negative signs and the integration would give the correct formula for $N$.

But this means that it does matter whether you add or subtract the Lagrange Constants. What am I doing wrong here?


texts: Electrophilic substitution of benzene with conc. HNO₃ and HNO₂

texts:
The following question was given in my FIITJEE study material:

  $$\ce{Benzene + \text{conc.} HNO_3 + HNO_2 ->}$$ Final product of the reaction is:

,
,
,

I started with the solution by deciding the Lewis acid out of $\ce{HNO_3}$ and $\ce{HNO_2}$. I guess $\ce{HNO_3}$ should be Lewis acid as O.S. of N is higher in it. Hence, I wrote the reaction to generate electrophile:

$$\ce{HNO_3 + HNO_2 -> NO_3^- + H_2O + NO^+}$$

Now, it is a bit clear who's the electrophile. Hence, I thought that first option would be the final product. But, according to the answer key it was wrong.

What I am doing wrong?

The correct answer was:

   Second one (nitrobenzene)


texts: Are all deliquescent salts highly soluble?

texts: $\ce{Na2CO3}$ is deliquescent in nature, and $\ce{NaHCO3}$ is not, for example, so $\ce{Na2CO3}$ should have been more soluble than $\ce{NaHCO3}$ in water ($\ce{NaHCO3}$ I always thought was less soluble since it precipitated easily in the Solvay process). But my book says $\ce{Na2CO3}$ is less soluble than $\ce{NaHCO3}$ in water. Isn't deliquescence though an indicator of high solubility in water?


texts: Why oxidation potential of an electrode equals negative reduction potential of the same electrode?

texts:
My textbook states that:

  $E^\circ_\mathrm{ox} = -E^\circ_\mathrm{red}$ (of same electrode)

I know that electrons flow from anode half cell (oxidation) to cathode half cell (reduction).

But if $E^\circ_\mathrm{ox} = -E^\circ_\mathrm{red}$ in each electrode, then potential in each electrode of the galvanic cell should be 0 volts (oxidation cancels reduction).

Hence potential difference in the whole circuit is 0 volts (no electricity is generated).

Do not get me wrong, I am just a high school student and I know my question might sound trivial, I am new to electrochemistry.


texts: Mechanism for synthesis of 4-nitrophenylhydrazine from the diazonium salt of 4-nitroaniline

texts:
I am trying to figure out the mechanism to create 4-nitrophenylhydrazine from the diazonium salt of 4-nitroaniline. I've found a couple of explanations for what reactants are used, but I don't understand the mechanism behind them.
The mechanisms overall seem to suggest that $\ce{HCl}$ is used, and the $\ce{Cl-}$ bonds to the $\ce{N2+}$. That makes sense, but then it is suggested that $\ce{Na2SO3}$ and $\ce{SnCl2}$ are used to somehow change this into 4-nitrophenylhydrazine. If anyone could explain how this works, I would be very grateful!

Here is the article showing which reactants are used.


texts: Can metal matrix composites be alloyed after their creation?

texts:
I've done a little research on metal matrix composites (MMCs), purely for fun and out of interest. Different types of metal powders are combined with reinforcement materials, to produce a reinforced metal.
As the structure of the reinforcing material is an important factor, would the resulting composite then be able to be alloyed with other metals? If I made a magnesium-carbon fiber composite, could I then melt it and combine it with, let's say copper? Or would the process destroy the structure of the carbon fibers, weakening the material?
Also, what would happen, assuming alloying works, if I combined two MMCs with different reinforcements, let's say, for example, one is an aluminum-glass fiber composite, and the other is a titanium-ceramic particle composite? Could they combine?


texts: Is electrochemically activated water a real technology?

texts: In essence what I'm asking is if the applications of Electrochemically activated water (ECA water) as a bactericidal-disinfectant is real and profitable (especially this last part). The principle at first seems very dull just take salt water through an electrolysis process and you get anolytes and catholytes, with disinfectant proprieties. Why is that only now is it viable?


texts: Can we produce tritium from helium 3? If yes how?

texts: I want to know the best and economic way of the manufacture of tritium from helium-3


texts: How to find the concentration of barium ions in a mixture of barium sulfate and barium thiosulfate?

texts:
I have a hard time with selective precipitation problem.

  A mixture of $\ce{BaSO4}$ and $\ce{BaS2O3}$ is shaken with pure water until a saturated solution is formed. Both solids remain in excess. What is $[\ce{Ba^{2+}}]$ in the saturated solution? $K_\mathrm{sp}(\ce{BaSO4}) = 9 \times 10^{-11}$ and $K_\mathrm{sp}(\ce{BaS2O3}) = 4 \times 10^{-10}$.

My solution:

Because $K_\mathrm{sp}$ of $\ce{BaSO4} < \ce{BaS2O3}$, $\ce{BaS2O3}$ will dissolved first. When $\ce{BaS_2O_3}$ dissolved, the concentration of $[\ce{Ba^{2+}}] = [\ce{S2O3^2-}] = \sqrt{K_\mathrm{sp}(\ce{BaS2O3})} = 2 \times 10^{-5}$.

That means, in the solution, there are:

\begin{align}
[\ce{Ba^2+}] &= 2 \times 10^{-5}\\
[\ce{S2O3^2-}] &= 2 \times 10^{-5}\\
[\ce{SO4^2-}] &= \frac{K_\mathrm{sp}(\ce{BaSO4})}{[\ce{Ba^2+}]} = \frac{9 \times 10^{-11}}{2 \times 10^{-5}} = 4.5 \times 10^{-6}
\end{align}

But the solution is $\ce{[Ba^2+]} = \sqrt{4.9 \times 10^{-10}}$.

What have I missed?

EDIT 1 :
\begin{align}
\ce{BaSO4 &<=> Ba^2+ + SO4^2- }\\
\ce{BaS2O3 &<=> Ba^2+ + S2O3^2- }
\end{align}

The Solubility Product Equation :

\begin{align}
K_\mathrm{sp}(\ce{BaSO4}) &= [\ce{Ba^2+}] \times [\ce{SO4^2-}] \\
K_\mathrm{sp}(\ce{BaS2O3}) &= [\ce{Ba^2+}] \times [\ce{S2O3^2-}]
\end{align}

When the solids dissolves, it will produce $\ce{Ba^2+}$ ion, $\ce{SO4^2-}$ ion and $\ce{S2O3^2-}$ ion.

$\ce{BaSO4}$ will stop dissolving when $\ce{Ba^2+}$ ion concentration in solution when multiply with $\ce{SO4^2-}$ ion concentration is equal to solubility product of $\ce{BaSO4}$, which is $K_\mathrm{sp}(\ce{BaSO4}) = 9 \times 10^{-11}$

And at the same time,

$\ce{BaS2O3}$ will stop dissolving when $\ce{Ba^2+}$ ion concentration in solution when multiply with $\ce{S2O3^2-}$ ion concentration is equal to solubility product of $\ce{BaS2O3}$, which is $K_\mathrm{sp}(\ce{BaS2O3}) = 4 \times 10^{-10}$

Solubility of $\ce{BaSO4}$ in water is
\begin{align}
 s &= \sqrt{K_\mathrm{sp}(\ce{BaSO4})}\\
 s &= \sqrt{9 \times 10^{-11}} \\
 s &= 3 \times 10^{-5.5}
\end{align}

Solubility of $\ce{BaS2O3}$ in water is
\begin{align}
 s &= \sqrt{K_\mathrm{sp}(\ce{BaS2O3})}\\
 s &= \sqrt{4 \times 10^{-10}}\\
 s &= 2 \times 10^{-5}
\end{align}

Now, when the solids is mixed in water, There should be $[\ce{SO4^2-}] =3 \times 10^{-5.5} $ and $[\ce{S2O3^2-}] =2 \times 10^{-5} $.

Now I confuse what ion concentration should I use to determine $[\ce{Ba^2+}]$

EDIT 2:

\begin{align}
K_\mathrm{sp}(\ce{BaSO4}) &= [\ce{Ba^2+}] \times [\ce{SO4^2-}] \\
\frac{K_\mathrm{sp}(\ce{BaSO4})}{[\ce{Ba^2+}]} &= [\ce{SO4^2-}] \\
\end{align}
and
\begin{align}
K_\mathrm{sp}(\ce{BaS2O3}) &= [\ce{Ba^2+}] \times [\ce{S2O3^2-}] \\
\frac{K_\mathrm{sp}(\ce{BaS2O3})}{[\ce{Ba^2+}]} &= [\ce{S2O3^2-}] \\
\end{align}

From @santimirandarp answer, I got that :

\begin{align}
[\ce{Ba^2+}] &= [\ce{S2O3^2-}] + [\ce{SO4^2-}]\\
[\ce{Ba^2+}] &= \frac{K_\mathrm{sp}(\ce{BaS2O3})}{[\ce{Ba^2+}]} + \frac{K_\mathrm{sp}(\ce{BaSO4})}{[\ce{Ba^2+}]}\\
[\ce{Ba^2+}] &= \frac{4 \times 10^{-10}}{[\ce{Ba^2+}]} + \frac{9 \times 10^{-11}}{[\ce{Ba^2+}]}\\
[\ce{Ba^2+}] &= \frac{4.9 \times 10^{-10}}{[\ce{Ba^2+}]} \\
[\ce{Ba^2+}]^2 &= 4.9 \times 10^{-10} \\
[\ce{Ba^2+}] &= \sqrt{4.9 \times 10^{-10}} \\
\end{align}

My problem solved. Thank You


texts: Identifying an extra NMR peak in silyl protection reaction

texts: I protected a phenol with the TIPSCl/triethylamine procedure. The product was isolated by column (hexanes/EtOAc) and shows an extra singlet at 1.05 ppm in $\ce{CDCl3}$, integrating to ~10 H. Whatever this is I cannot find in under UV or various TLC stains ($\ce{KMnO4}$, vanilin, PMA). The integration of the peak goes smaller after one more column. Any suggestions? Thanks!


texts: Has IUPAC been inaccurate in their 1994 definition of kinetic stationary state?

texts:
Summary of IUPAC definition
$\def\d{\mathrm{d}}$In IUPAC recommendations from 1994[1, 1166–1167], the authors discuss the process
$$\ce{A <-->[$k_1$][$k_{-1}$] X\\ X + C ->[$k_2$] D}$$
A kinetic stationary state or steady state is defined very reasonably:
$$\frac{\d\ce{[X]}}{\d t}=0.\tag2$$
They go on to emphasise that condition $(2)$ is not equivalent to $\ce{[X]}$ being constant, 'not even approximately'; simply that the change in $\ce{[X]}$ is small compared to changes in concentrations of $\ce{[A]}$ and $\ce{[D]}$ because $\ce{[X]}$ itself is small. If $\ce{[X]}$ were constant in a stationary state, they claim it would lead to the following contradiction.

Say reactant $\ce{C}$ is in excess. Assume that $\ce{[X]}$ is constant. Then the law of mass action $v = k_2\ce{[X][C]}$ would reduce to some $v = k'\ce{[C]} \overset{\mathrm{excess}}{\approx} k\in\Bbb{R}$. In other words, production of $\ce{D}$ could continue at a constant rate even after $\ce{A}$
has run out.

The document concludes that $\ce{[X]}$ cannot possibly be constant in steady-state conditions.
How I would resolve the apparent contradiction
I do not see a way around $\ce{[X]}$ being constant. Indeed, for any reasonable function[a] $\ce{[X]}:t'\to \Bbb{R^{0+}}$ equation $(2)$ implies
$$\int_0^t \frac{\d\ce{[X]}(t')}{\d (t')}\d(t')= \ce{[X]}(t) = r \in \Bbb{R^{0+}}\tag3$$
where $t'$ was simply a dummy variable.

Resolution to contradiction: If $\ce{C}$ is in a large excess, $\ce{[X]}$ is small, and $\ce{A}$ has run out, it is simply not possible for steady-state conditions to hold. In other words, it is our stationary state approximation $(2)$ which fails to hold for $\ce{X}$. So we can easily keep condition (3) for a steady state.
More accurately, if $\ce{A}$ has run out, the only possible stationary state would have been $\ce{[X]} = 0$. This is because, at a stationary state,
$$\ce{[X]} = \frac{k_1\ce{[A]}}{k_{-1} + k_2\ce{[C]}} \overset{\ce{[A]} = 0}{=} 0.$$
If $\ce{[X]} = 0$, it is unfeasible for the reaction to continue at non-zero constant velocity since $v = k'\ce{[C]} = 0$ (where $k' = k_2\ce{[X]}$).

Question

Is / is not the concentration of $\ce{X}$ constant, approximately or otherwise, in a kinetic stationary state (steady state)?

IUPAC states $\ce{[X](steady\ state)}$ is not even approximately constant because it would lead to contradictions.
I claim that $\ce{[X](steady\ state)}$ is constant, and contradictions surface when a steady state itself is impossible given certain constraints (or the constraints themselves are contradictory).

[a] Among other things that it is diffentiable everywhere in its domain (i.e., reaction rate is defined for every time $t'$).
[1] Muller, P. Glossary of Terms Used in Physical Organic Chemistry (IUPAC Recommendations 1994). Pure and Applied Chemistry 2009, 66 (5), 1077–1184. DOI: 10.1351/pac199466051077. pages 1166–1167


texts: Why doesn't D block contraction affect the other P block groups 14 15 16 etc

texts:
Usually we come across anomalies in the trends of periodic properties for example the size [Atomic radius value from Raymond Chang Chemistry 9th Edition] of Gallium (135 pm) is smaller than Aluminium (143 pm) as opposed to the basic trend that atomic size increases down the group. This is usually attributed to the fact that the poor shielding of nuclear charge by intervening D orbitals leads to a greater $Z_\mathrm{eff}$ hence the radius is less as opposed to the trend.

If that's the reason why don't we observe similar effects for other groups like group 15 having Phosphorus (110 pm) and Arsenic (120 pm) [Here the size doesn't increase much but is still significant as compared to changes taking place in group 13] , where the size actually increases even when there are D orbitals to intervene. Or in short why are the effects so profound for group 13 and not the other members?

There's another example of In (166 pm) and Tl (171 pm). Both belong to group 13. As compared to other groups these two members have the lowest increase in atomic radius.


texts: How can should one separate and purify benzophenone from salicylic acid?

texts:
I am working with two solids and I know that they are  benzophenone (s)(ketone) and salicylic acid (s) (carboxylic acid). I am curious to know what is/are the best method of extraction and purification?

In other words, would extraction be the only method that these two can be separated because one is neutral and the other is an acid?

Also, what kind of qualitative test/s can you use for salicylic acid? I mean I understand that the acid/base test is most commonly used but can you use it again to test for -COOH functional group?

Apologizes for the questions but not being able to physically see this makes this 10X hard basing this off of hypotheticals.


texts: What is the @ symbol used for in material science?

texts:
I came across the phrase "Silicone Rubber/Paraffin@Silicon Dioxide" also written as $\ce{SR/pa@SiO2}$, utilising the @ symbol.

How can I understand what this means?


texts: Yeast Fermentation with YPD + Apple Juice

texts:
I am working on a project for my General Chemistry class.

I am trying to compare the EtOH production (and the rate of EtOH production) between seven types of yeast strains by fermenting the YPD media, apple juice, or both, if necessary. I can describe the difference between the yeast strains if asked, but I don't think it is necessary right now.

Right now, I have only tested plain YPD media, which is 1% yeast extract, 2% peptone and 2% d-glucose mixture. All strains yield around 8-9 mg/mL of EtOH, and the fermentation stops after ~24 hours. My next step is to test YPD + apple juice media (because the project asks for "fun" element), and I was wondering if I should use the same method for analyzing this YPD + apple juice fermentation.

The method I used for YPD media is:

Grow each strain (total of 7 strains) in ~5 mL YPD media at 30 degrees shaker ~250 rpm overnight.
Subculture each strain into new fresh YPD media so that the new media is 50 mL and has 0.5 OD at 600 nm. Use the "special" flask designed for anaerobic growth. This flask is a 250 mL flask with a special cap. The cap is plastic at the outer radius and rubber at the inside. This allows me to grow yeast anaerobically and poke a needled syringe and retrieve small amount of sample without letting the air in.
Flush all flasks with nitrogen gas for four minutes.
After 6 hour, 12 hour, and 24 hour growths, use syringe to retrieve ~1.5 mL of sample.
Measure OD600 of each sample. (This is used to get the number of yeast cells in the media)
Centrifuge samples for 8 minutes in 14,000 rpm.
Pipette 1 mL of the supernatant into a GC vial.
Use HPLC to obtain concentration of ethanol. I am using refractive index detector, ion exclusion column(?) (I forgot the type of column used at this moment), and sulfuric acid as mobile phase.

For YPD + apple juice fermentation, I was thinking of doing the same procedure with 50 mL YPD + 50 mL apple juice in each "special flask". Will this work? Will this be good for the same HPLC setting?


texts: Symmetry and NMR linewidths of quadrupolar nuclei

texts:
The linewidth of peaks when taking NMR spectra of quadrupolar nuclei (11B or 14N for example) is often very broad, making their interpretation challenging.

Recently, when acquiring 11B-NMR spectra of some boronic esters I'd made, the NMR technician pointed out that the linewidth is much improved in highly symmetrical environments (which my boronic esters were not) – she proved this by running a sample of $\ce{LiBH4}$, but couldn't really offer an explanation of why this was the case, other than to point out that its a relaxation effect.

Claridge[1] confirms this point about symmetry:

  14N linewidth of $\ce{N(Me)4+}$ is less than 1 Hz whereas that for $\ce{NMe3}$ is nearer to 80 Hz.

Arguably, both $\ce{N(Me)4+}$ and $\ce{NMe3}$ are fairly symmetrical, being Td and pseudo-C3v respectively, which leads me to think that what the molecule needs is some kind of spherical symmetry, which only Td (and Oh, arguably less useful in synthetic organic chemistry) can provide.

Some further reading through Claridge[1] reveals that this is something known as quadrupolar relaxation, with Reich[2] confirming, though not really expanding beyond an equation describing the relaxation process and a comment that there is "friction" between the nucleus and the surrounding electron.

All of the explanations I've found have focused a lot on explaining this mathematically (Levitt describes it quite nicely, but slightly beyond my understanding). Is there an intuitive explanation for the relaxation taking place in quadrupolar nuclei, and why high symmetry environments lead to narrow peak shape?

[1]: Claridge, T. D. W. High Resolution NMR Techniques In Organic Chemistry; Elsevier:Amsterdam, 2016

[2]: https://www.chem.wisc.edu/areas/reich/nmr/08-tech-01-relax.htm, accessed 20/08/2017.


texts: Bolt head corrosion in soup. Toxic? Zinc? Cadmium?

texts:
This may not be quite the right forum for this question, but please help me if you can.

I recently repaired the lid of my grandma's crockpot using a bolt I found in a miscellaneous fastener box in the garage. I've been using the crockpot quite a lot since then, and I just noticed that the bolt head is corroding with white gunk. I also noticed a white film floating on the middle of the soup I left cooking all night, obviously from some of the corrosion dripping onto the soup. My grandma and I had both tasted the soup before I noticed the corrosion and film. I've been doing a little research to try and identify the bolt's coating by its appearance, and I am concerned that it might be zinc or cadmium, which are apparently highly toxic. [EDIT: apparently zinc is not highly toxic, so I guess my main concern is: is this cadmium? Also, the bolt may well be over 50 years old, as it's from my grandparents' garage]

I'm hoping someone here who's more familiar with these materials can tell me:

What metal this corrosion looks like
Whether I should be concerned about toxicity considering the quantities present

I'm including a picture of another bolt that matches the one in question, with yellow zinc plated wood screws and some U.S. currency for visual reference.

I will of course be replacing the bolt with something explicitly food-safe, but having already consumed some of the soup, I want to know if we should be high-tailing it to the emergency room, or if in fact it's safe to finish the soup (it's good soup!).


texts:
We know that stability of higher oxidation state (+3) decreases and stability of lower oxidation state (+1) increases, so thallium is most stable in its +1 oxidation state due to the inert pair effect and paired s electrons.

In the compound $\ce{TlI3}$, since $\ce{I3}$ exists as a linear molecule $\ce{I3-}$  so the oxidation number of $\ce{Tl}$ is +1 which is stable and the compound should exist but I have read in many of the books that it does not exists. Why is it so?


texts: Making metal powders using electrolysis - chosing the right electrolyte

texts:
Really fine metal powders are good for two things: making paints and pyrotechnics. For this purposes, I can see people usually use thing called ball mill.

It's basically a barell stuffed with heavy balls and the thing to be powdered. You leave it for a while, rotating all the time, and the balls slowly crush your substance into smaller and smaller pieces.
There are many disadvantages to this:

I'd need to construct it
It would be running and making loud mess all the time
soft metals, like aluminium and copper don't even crush into pieces

So I have figured out a different way. More chemical one I'd say. I can dissolve metals in acid by forming salts out of them and then electrolyse those salts. Not so long ago, I complained that instead of copper plating I got copper powder. That's just what I want now. I'm really sorry that powder I created the other day is already flushed down the drain. It could make beautiful green flames.

Now while the general idea is easy, I'm not so sure about choosing the right electrolytes. My theoretical knowledge of electro-chemistry unfortunately sucks. And I'm afraid that every metal will need different electrolyte.

For example I think using any acid for Aluminium could cause something nasty since it reacts with them little bit too quickly. For Iron, I tried hydrochloric acid and then I found out thet $\ce{HCl}$ dissolves iron to form iron chloride.

Are there general rules to figure this out? If not, what sould I consider to find electrolyte individually for these metals:

Aluminium
Iron
Copper
Magnesium

Powdered metals can be bought of course, but I don't want to waste good money for something, that can be easily made from trash (old nails, aluminium foils from chocolate...).


texts: Frequency region and "uncoupled oscillators" in vibrational spectroscopy

texts:
I am currently studying the textbook Infrared and Raman Spectroscopy by Larkin. In the first chapter of the textbook, the author presents the following table and accompanying explanation:

The vibrational spectrum may be divided into typical regions shown in Fig. 1.1. These regions can be roughly divided as follows:

$\ce{X-H}$ stretch (str) highest frequencies (3700-2500 cm$^{-1}$)
$\ce{X#Y}$ stretch and cumulated double bonds $\ce{X=Y=Z}$ asymmetric stretch (2500-2000cm$^{-1}$)
$\ce{X=Y}$ stretch (2000-1500cm$^{-1}$)
$\ce{X-H}$ deformation (def) (1500-1000cm$^{-1}$)
$\ce{X-Y}$ stretch (1300-600 cm$^{-1}$)

The above represents vibrations as simple, uncoupled oscillators (with the exception of the cumulated double bonds). The actual vibrations of molecules are often complex and as we will see later, typically involved coupled vibrations.

I have two questions:

What do the $\ce{X}$, $\ce{Y}$, and $\ce{H}$ values mean in the above explanation?
Can someone please elaborate, with some detail (including mathematics), on this concept of "uncoupled oscillators", and its relevance in the above context? To be specific: What specifically is an "uncoupled oscillator", how is it described mathematically, and what is its relevance in the above context?

I appreciate it if someone would please take the time to clarify these points. Thank you.


texts: Database with organic reaction mechanisms (curly arrows)

texts: Is there any database or book that has an index of organic reactions where the mechanisms are written out, complete with curly arrows? It would really help if I could look up a reaction and see a proposed mechanism with curly arrows.


texts: Calculating the pH of buffer solution made of two salts of a polyprotic acid

texts:
When we are making a buffer solution by solutions of a weak acid and its salt like $\ce{CH3COOH}$ and $\ce{CH3COONa}$, or by a weak base and its salt like $\ce{NH3}$ and $\ce{NH4Cl}$, we can use the Henderson equation to determine its $\mathrm{pH}$. But, when we are making a buffer solution by two salts of a polyprotic acid like $\ce{Na2HPO4}$ and $\ce{NaH2PO4}$, how can we calculate the resulting $\mathrm{pH}$? Can Henderson's equation still be used? Or, is there any other formula?

For example, the pH of a solution of $\ce{NaHCO3}$ is given by the formula $\frac{1}{2}(\mathrm{p}K_\mathrm{a1} + \mathrm{p}K_\mathrm{a2})$. But what would be the formula if the salt is from a triprotic acid? Again, what will be the formula if the solution is a mixture of salts?

I need a theoretical calculation of the $\mathrm{pH}$, and this is not for any laboratory type experiment.


texts:
I am not a Chemist or did not learn chemistry as a student. I have faced this phenomena from a natural visualization. So this question.

Experiment: What will be happen if we add a solution of ammonia and water over bad quality iron? When it shall be dried I shall pour again. Several day It shall be done regularly in open nature. Some reaction will take place. Rust will be created on iron.

Here is the main question:

Common people will not see anything significant except rust. But As a chemist how do you understand after three to four days after completion of the experiment that I pour ammonia solution on it? Assume that this three or four days it was in open nature. Something will be produced after reaction except rust. How much of them is water soluble?


texts: Is there any replacement for ethyl mercaptan in LPG?

texts:
Ethanethiol, commonly known as ethyl mercaptan, is a colorless gas added to LPG in order to detect its leakage.

Apart from ethyl mercaptan, is there any gas or liquid that may be used as a replacement to this?


texts: Does all processes that consume energy from outside result in negative entropy change?

texts: In any spontaneous process entropy increases.In biological systems disordered elements are converted into highly ordered tissues etc(-ve entropy change) which make up living organisms. But, it requires energy from the sun(ultimately). So,does that mean all processes that consume energy from outside result in negative entropy change? Endothermic reactions consume energy in the form of heat from outside so, is all endothermic reactions causing the entropy to decrease?


texts: Why are higher acids solid while lower acids are liquid?

texts:
I was just going through acids on Wikipedia in my free time, and noticed this neat trend:

Formic acid, Ethanoic acid, uptil Nonanoic acid, are all liquids. The first few are colourless, while the latter are yellowish and also "oily" (more viscous).
Decanoic acid and all its elder brothers are white crystals (or "powders")
Aromatic acids like benzoic acid or picric acid are solids.

I am unsure if there could be a reasonable logic for the colours. But, I am sure there could be a good logic for the physical state of these acids at room temperature.

To me, all these acids have hydrogen bonding common, so we can rule out that factor. Apparently, the physical state seems to be related to the "size" of the acid. The heavier acids  are solids, while the lower ones are liquid. My question is: why is it so?

PS: List of all acids at one place is at the bottom of this Wikipedia page.


texts: Cyclobutadiene - Jahn–Teller effect or not?

texts:
In transition metal chemistry the Jahn–Teller effect arises when the configuration of the metal ion and d orbital splitting set up a doubly degenerate state, which is less stable than a state without the degeneracy but with lower symmetry.

In Ian Fleming's Molecular Orbitals it is stated that cyclobutadiene would be a diradical considering Huckel theory:

but it isn't because of Jahn–Teller distortion (it is actually rectangular and ESR shows no spin).

There isn't a doubly degenerate state in this case, yet Jahn–Teller distortion happens according to Fleming. How is this so?

(In the singlet state it would be doubly degenerate, but how to know it a priori?)


texts: How to Locate the Excited State Dipole Moment in Turbomole Output (TD-DFT)

texts:
I want to calculate the dipole moment for the first excited state with a Q.C. program (TURBOMOLE: TD-DFT). The calculation lists the following output:

ground state total dipole moment:

-1.129096
-2.295685
 0.000000

I think that's $\langle\Psi_0|\vec{\mu}|\Psi_0\rangle$ with $\Psi_0$ the wavefunction for the ground state.

1st excited state electric transition dipole moment (length representation):

-2.413321
 0.367463
 0.000000

Should be $\langle\Psi_1|\vec{\mu}|\Psi_0\rangle$ with $\Psi_1$ the wavefunction for the 1st excited state.

2nd excited state electric transition dipole moment (length representation):

 0.841417
-0.329533
 0.000000

Should be  $\langle\Psi_2|\vec{\mu}|\Psi_0\rangle$.

And a summary:

             nuc           gs,e       ->  gs,tot          excit     ->  total
 ------------------------------------------------------------------------------
   x     -29.158609      28.029513      -1.129096       1.370060       0.240963
   y      48.811850     -51.107535      -2.295685       0.086529      -2.209156
   z       0.000000       0.000000       0.000000       0.000000       0.000000

I don't know how to get the values denoted by excit in the summary and they are not present anywhere else in the output. There's also no hint which excited state they apply to, so how do you calculate the total dipole moment for the 1st excited state e.g.?


texts: Adsorption of Cu2+ using banana peels for pH 2,2.5,3,3.5,4

texts:
so basically I did my experiment which is the title. This is my procedure and results:

Make 0.05M CuSO4
pipette 50ml CuSO4
change to respective pH values using HCl
Add 2g of oven-dried banana peels
wait for half an hour
Filter the solution into 100ml volumetric flask
add 5ml of 2M HCl to change all replicates to approx. pH 1
top up to 100ml mark using deionized water
mix well
put solutions into cuvettes and place the into the UV-vis spectrometer to measure absorbance
compare it with the calibration curve to determine concentration

my 入max was 811.
For those wondering why I made all the replicate the same pH after filtration, it was so that the pH at the end would not affect the absorption value, because I found out that pH changes the colour of the solution.
results:

edit: so the first reading is a blank, the 2nd reading is the absorbance of the pH 2 solution after it has been made to pH 1, the 3rd reading is the absorbance of the pH 2.5 solution after it has been made to pH 1, the other readings are for pH 3,3.5 and 4 (in order). The K*abs value doesn't matter.

calibration curve:

Does this look right? Cus I can't find any research papers that do this. The ones that I found do pH 2,3,4,5,6 and use extremely small concentrations of CuSO4, something like 0.0002M. Even if u assume the trend will be the same, my results don't follow the same trend, which is that the concentration of CuSO4 left in the solution after the experiment decreases as pH increases. Basically it means that at a higher pH, the banana peels can adsorb more Cu2+ ions.


texts: NaOH being added to Formic Acid (Please catch my error!)

texts:
I am adding 0.55 mL of 0.1M NaOH to 10 mL of 0.5M Formic Acid.

Here are the values I calculated to use.

Moles H+ : 0.5 * (10mL / 1000) = 0.005 mol

Moles OH- : 0.1 * (.55mL / 1000) = 0.000055 mol

volume : (10mL / 1000) + (0.55mL / 1000) = 0.01055 L

Moles Total : moles H - moles OH = 0.005 - 0.000055 = 0.004945 mol

M Total : moles Total / volume = 0.004945 mol / 0.01055 L = .46872 M

Moles Salt : 0.000055 mol

M Salt : moles salt / volume = 0.000055 mol / 0.01055 L = 0.00521 M

Calculations to find the pH

pH = -log(1.80E-4) = 3.745

3.745 - ( -log(M Salt / M Total) ) = 3.745 - 1.95407 = 1.791

However, this value is too low as the lowest pH of 0.5M Formic Acid is ~2.03.

If the volume of NaOH were to say, 0.5 mL, then the M Salt / M Total value would be less than 1/90, and the pH could then be found by

-log( sqrt( 1.80E-4 * M Total ) ) = 2.036

...which makes more sense, but doesn't apply to the initial problem.

Any idea of where I'm going wrong?


texts: What is the white substance left behind after boiling down water

texts: I was boiling down water in a stainless steel pot as an experiment the other day. When the water was completely vaporised, a white substance was left behind on the bottom of the pot. I tried rubbing it off the bottom, but it would not come off. I'm unsure what this substance is. What is this substance?


texts: Any method for testing Nitrate and Nitrite in biological fluids like aqueous humour?

texts: If anyone knows the methods of detection of nitrate and nitrite in biological fluids such as aqueous humor, saliva of animals, please let me know. Any relevant literature for the same is available, kindly share.


texts: Quantitative elemental analysis in mixtures with internal standard normalization

texts:
I am trying to make a quantitative model for Laser Induced Breakdown Spectroscopy (LIBS) analyzing metal alloy samples. I am using an internal standard normalization (so far it produced the best repeatability results) and would like to some how to keep using it in the quantitative model. My issue is that if the base element of an alloy is Fe and I am trying to measure %w of Ni and Cr, then the ratio of Ni/Fe is not only affected by the %w Ni, but also by the %w of Cr as well, since more Cr means less Fe and a different Ni/Fe value for the same %w Ni.

I have standards with different and more-or-less known amount of Ni and Cr.
If there a standard way to handle this type of problems?

It seems like something people have run into many times and there should be cookie-cutter solutions, but I have a lot of difficulty to find one. So far the only discussed models I've seen is a change in %w of one element, while others are locked constant.
A textbook or a journal paper discussing the solution would do just fine.

Thanks in advance!


texts:
I am a microbiologist forming a growth media which has glyphosate in it. Unfortunately, I am having troubles dissolving it in water. At a .2M solution in 200ml of water, it is not completely dissolving. Does anyone know why this is chemically happening? Even upon adjusting pH and raising temperatures, I am unable to dissolve it.
https://pubchem.ncbi.nlm.nih.gov/compound/glyphosate
If you have any ideas please let me know.


texts: Effect of adding an acid or base to water with respect to concentration of ions

texts:
So I know that there's auto-ionization of water according to:
$$\ce{2H2O <=> H3O+ +OH-} \tag{1}$$
If I have pure water where the concentrations of both $\ce{H3O+}$ and $\ce{OH-}$  is $10^{-7}$
Say I add $\pu{10^{-5} M}$ $\ce{HCl}$, I'd have [$\ce{H3O+}$] = $ 10^{-5} + 10^{-7}$ (approx $10^{-5}$) and the [$\ce{OH-}$] = $10^{-7}$ (still)
but since these are in equilibrium, according to reaction ($1$), the reaction will shift to the left so this would consume $\ce{H3O+}$ and $\ce{OH-}$ until their concentrations product is $10^{-14}$, how will this happen?
Will the $\ce{OH-}$ decrease much more less than what the $\ce{H3O+}$ will decrease, in a way that what the $\ce{H3O+}$ loses is negligible compared to what $\ce{OH-}$ lost? in a way that would keep [$\ce{H3O+}$] = $10^{-5}$ and [$\ce{OH-}$] = $10^{-9}$?
In brief, how is equilibrium brought back to the concentration of ions are concerned?


texts: Ammonia decomposition on platinum surface

texts:
I was given a problem I have to solve, unfortunately I cant wrap my head about it. I've searched the page for answers but they doesnt seem to fulfill my needs, so i'm asking for little guidance.

The problem:

  When the decomposition of ammonia is carried out on platinum surface at 1000°C the
  hydrogen binds strongly on the surface. Prove the that the rate is
  equal to $\frac{dp(NH_3)}{dt}=-k\frac{p(NH_3)}{p(H_2)}$.

I dont understand why we have to divide with the partial pressure of hydrogen. In my understanding the rate is $\frac{dp(NH_3)}{dt}=-kp(NH_3)$. I know I have to use the fact that hydrogen binds strongly at the surface, but I'm lost. Can you please explain to me how should I derive this, or just hint me to the right direction.

I lack of good understanding on this topic, so sorry for this novice question.

What I've searched:

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

What is the molecularity of the RDS of a zero order complex reaction?

Thank you for your time.


texts:
The fluorescence excitation spectra show the change in fluorescence intensity as a function of the wavelength of the excitation light.
I'm interested in the certain physical implications of the above.
Does that mean, that at the wavelength of excitation maximum the most of the molecules get excited? Or do they just emit more photons per molecule per unit time?
Additionally, if the former is correct, is there any relationship between the percentage of excited molecules and the excitation spectra?


texts: What explains the trend of ionization potential in coinage metals?

texts:
The expected pattern for ionization potential is
$$\ce{Cu} > \ce{Ag} > \ce{Au},$$
but the observed patter or experimental value is
$$\ce{Au} > \ce{Cu} > \ce{Ag}.$$
What could be a justification for this?
The simple way to look upon is a general increase in size which fails here. So, I suspect introduction of f-orbital in gold has to do something with it which is absent in copper and silver.


texts: Gas chromatography/mass spectrometry: Can I use peak ratios and molecular mass to derive quantity?

texts:
Can derive the quantity of a substance from a GC/MS report if I know:

the ratio to another substance in the data,
the quantity of that second substance, and
the molecular mass of both substances.

The site was very dense and vague regarding how GC/MS test work, but fairly upfront regarding how they derive their ratios.

Here are the numbers (slightly tweaked, but more or less in proportion):

Substance A:

Quantity: $300 \:\pu{mg}$ (Know already, not part of GC/MS report)
Mol. Mass: $500 \:\pu{g/mol}$ (found in external source)
Peak Proportion: 3

Substance X:

Quantity: Unknown
Mol. Mass: $425 \:\pu{g/mol}$ (again, external source)
Peak Proportion: 1

To be clear, the ratio of 1:3 means that substance X has a horizontal peak $\frac13$ of substance A.  I'm not clear on what the x-axis is actually a measurement of, which is part of why I'm at a loss. The site does make it very explicit that the ratios are not directly proportional  to mass ratio (so if it found a ratio of 3:1 of glucose to arsenic, this doesn't mean the substance is 75% glucose and 25% arsenic, only that the glucose "peaks" 3 times higher, which I've taken to mean "3 times the oomph", but that may be incorrect, as well).

So, if I know that the molecular mass($\rm M$) of substance X is 0.85 of substance Y, can I derive the actual mass of substance X using the formula:

\begin{equation}\mathrm{qty}_X=\frac{\mathrm{qty}_A\times(M_X/M_A)}{\mathrm{peak}_A/\mathrm{peak}_X}\end{equation}

with data being:

\begin{equation}\rm qty_X=\frac{300\:\pu{mg}\times(425/500)}{3/1}\end{equation}

Which simplifies to:

\begin{equation}\rm qty_X=(300\:\pu{mg}\times 0.85)/3\end{equation}

and finally the result of $85 \:\mathrm{mg}$.

So I guess in the end there are 3 questions:

Is this even how GC/MS results work?
If so, is my assumption to derive the mystery quantity using the molecular mass correct?
Is the math itself in order? (I'm specifically worried that I should invert either the mass ratio or the peak ratio or both).

Of course, if the answer to the first questions is no, then my true question is: can I derive the quantity of substance X with the given data, and if so, what would be the right approach?

If anyone is curious for some context, I need to know the actual quantity of substance X as I know that, by mass, it has a threshold between harmless and toxic, so just knowing substance X is $\frac13$ "peak" of substance A doesn't let me know if I should let my dog/child/self ingest it.


texts: Conditions for free radical bromination using NBS and peroxides?

texts:
In the free radical bromination of 1-methylcyclohexene using NBS and peroxides a very important consideration to get the appropriate product is:

A. The wavelength of light used for initiation
B. The polarity of the solvent
C. Temperature
D. None of the above

You would need a high enough temperature / low enough wavelength to form the radicals but he said nothing about polarity of the solvent, and there can only be one answer.


texts: How to compare electrical conductivity of ionic liquids and aqueous electrolytes

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I am trying to compare the electrical conductivity of selected ionic liquids (ILs) and aqueous electrolytes.
By ionic liquid (IL), I mean a pure IL -- no water. Electrical conductivity of ILs is measured in units of Siemens per length. For example, the following table from Leys et al., J. Chem. Phys., 2008 gives the electrical conductivity of selected ILs in units of S/m:

On the other hand, aqueous electrolytes are obviously salts in water. I think, then, electrical conductivity of aqueous electrolytes are concentration-dependent. The following table in the CRC Handbook gives the electrical conductivity of selected aqueous electrolytes in units of S cm^2 / mol:

How can I compare the electrical conductivities of ionic liquids and aqueous electrolytes?
In other words, is there a way to relate ionic ($\sigma$ in S/m) and molar ($\Lambda$ in S cm^2 / mol) conductivities?


texts: I have seen $\ce{CuCl}$ and $\ce{Cu2Cl2}$ used interchangeably; they seem to be equivalent. If that is the case, then why does the latter have the '$2$' subscripts?


texts:
In what way can hybridization or molecular orbital theory be used to explain paramagnetism?

For instance, when something is hybridized to make enough bonding electrons, do all the electrons end up paired? Or are some left unpaired, explaining paramagnetism?


texts: In case of checking for the optical activity of cyclohexane or its derivative why we check for POS and COS in its cyclic 6 membered planar eclipsed state but not by its real conformation it forms chair, boat,twist boat etc)  .


texts: Negative Ohm reading from a Electrochemical reaction?

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The purpose of my experiment is to determine which salt is the best electrolyte. The setup is a tarnished spoon (Ag2S) is placed on top of thin plastic pieces that separate it from a container coated with aluminum foil. A solution of 1.0 M Salt and .2 M baking soda is heated and then poured into the container.  The following electrochemical takes place 3 Ag2S(s) + 2 Al(s) → 6 Ag(s) + Al2S3(s), the redox reaction being  Al + 3 Ag+ → Al3+ + 3 Ag. A multi-meter set to 200 ohms is attached, the positive end to the foil, and the negative end to the spoon. The picture included is my set up.

My logic was I could take the resistance measurement, take its reciprocal, and then find the conductance. I thought whichever salt would give me the best conductance would be the best electrolyte. However, I've only gotten readings of Negative ohms. My readings have been -190 ohms and then it steadily increased. The problem there can't be a negative conductance. From research I've found this, "conductivity is negative, it means that the resistance is negative, right ? This may occur if you have created a generator in your experiment, for example through a non-desired oxydoreduction phenomenon between two metals. If a current is produced in your experiment due to such reaction between 2 metals of different oxidation potentials, and if you material acts as en electrolyte, your apparatus may interpret it as a negative resistance."

How could I use the negative Ohms reading? Should I be collecting data in a different way? Help!


texts: How do you explain very high vanadyl phosphate NMR chemical shifts?

texts: Generally, phosphates have chemical shifts in the range -20 to 10 ppm. For vanadyl phosphates containing $\ce{V^{4+}}$, the isotropic chemical shift is about 1500 ppm. Why?


texts: Are Alloy Compositions Given in Weight Percent or Atom Percent

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Often times I see alloys described like this,

Lockalloy is an alloy that consists of 62% beryllium and 38% aluminum

Are the precentages mentioned here in weight percent or atom percent?  Is there a standard somewhere that governs this notation?  I don't see this mentioned anywhere in the literature, how does everyone know when people are talking about weight or atom percentages?


texts: Enthalpy of formation and reaction equations

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I'm disagreeing with my chemistry teacher over this enthalpy of formation problem, so can someone tell me if I am right or why I am wrong?

  The enthalpy of formation of gaseous sulfur trioxide is $-396~\mathrm{kJ/mol}$. What is the enthalpy of the reaction represented by the following balanced equation?

  $$\ce {2 SO_3 (g) -> 2 S (s) + 3 O2 (g) }$$

  (A) $-396~\mathrm{kJ}$   (B) $396~\mathrm{kJ}$   (C) $792~\mathrm{kJ}$   (D) $-792~\mathrm{kJ}$   (E) $198~\mathrm{kJ}$

I got (C) by flipping the sign of the enthalpy of formation given (because the equation given proceeds in the opposite direction from the formation of sulfur trioxide) and multiplying it by two (because there are 2 moles of sulfur trioxide).
My teacher and most of my other classmates said that it was (B) instead. They said that I shouldn't multiply by 2 because the equation given is at it's lowest realistic coefficient values.
I don't understand this for a few reasons:

the enthalpy of formation is defined as the enthalpy change per mole of substance
in previous problems, we would change the chemical equation to make the product only have one mole

For example, here's one problem:

  For which of the following reactions is the heat of reaction equal to the heat of formation of the product?
  \begin{align}
\text{(A)} &&\ce{N_2 (g) + 3 H_2 (g) &-> 2 NH_3 (g)}\\
\text{(B)} &&\ce{1/2 N_2 (g) + O_2 (g) &-> NO_2 (g) }\\
\end{align}

We narrowed it already down to (A) and (B).

My teacher said the answer was (B), because while both equations had the elements in their elemental form, the first reaction produces 2 moles of product while the second produces 1 mole of product. Thus the fraction coefficients were necessary.


texts: Why is the specific heat of ethanol not representing experiments

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I am in my last year of high school completing an assignment hot and cold packs, and particular the enthalpy behind them.

My major lack of understanding is why my calculations are working for heat of water but not for heat of ethanol.

In the past week, I have tested $0.1$–$0.4~\mathrm{M}$ of calcium chloride, magnesium sulphate and potassium chloride and ammonium chloride, in $100~\mathrm{ml}$ of distilled water.

Before doing these experiments I did some basic calculations Using  $\Delta H= mc\Delta T$
for each solute and its respective concentration, I assumed water temperature to be $25~\mathrm{^\circ C}$ to just get a rough understanding of the temperature I could expect and got some calculation which looked like this:

I got the heat of solution from a PDF I found.

I then did the experiments and got results which were very close to what these calculations showed.

However, this week I decided to test another solvent, ethanol. I found its specific heat to be $2.44\ \mathrm{J/g}$ and did the calculations again. I saw that almost all the estimated temperature increased/decreased drastically depending on if it was an exothermic reaction or endothermic reaction. However, after doing this experiment the results I got was very different. I decided to just test $0.2~\mathrm{M}$ of each solution and my calculations estimated these temperatures

But my calcium chloride temperature ended up only reaching $42\ \mathrm{ \circ C}$ whilst the potassium chloride and ammonium chloride barely changed at all, if anything they went up by $0.1~\mathrm{^\circ C}$.

So where is the problem with my thinking of what I have done incorrectly. I'm guessing ethanol can't be modelled the same as water but I cant find any research supporting that.


texts: Which is more basic, hydrazine or ammonia?

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Which of the following will be more basic, hydrazine $\ce{H2N-NH2}$ or ammonia $\ce{NH3}$?

My chemistry teacher said that $\ce{NH3}$ is more basic since after giving $\ce{H+}$ to hydrazine results in $\ce{H3N+-NH2}$, and accommodation of the lone pair of $\ce{-NH2}$ is not possible by $\ce{-N+H3}$, since it doesn't have the space. So instead, $\ce{-NH2}$ will pull electrons from it making it unstable. Ammonia has no such problem so it must be more basic.

I am not so pleased with this argument. In $\ce{H3N+-NH2}$, although the lone pair cannot be accommodated, but the positive charge present on its sides , to an extent, should neutralize the intensity of the lone pair, making it somewhat stable. And also, not to forget, hydrazine has two spots where we can get the electrons, therefore, its ambident nature should also support it's basicity.

I need a bit of clarity on this.


texts: There have been some claims saying that drinking reboiled water is dangerous because it produces arsenic, nitrates, etc. Is this true?


texts: Why aren't chaperones considered catalysts?

texts:
I'm reading about protein folding on Wikipedia and I stumbled on a bit about a class of proteins called chaperones that aid in the folding of proteins by:

  ...reducing possible unwanted aggregations of the polypeptide chain that might otherwise slow down the search for the proper intermediate...

However, they aren't considered to be catalysts because they do not actually speed up the folding process. My thought is that without these chaperones, the polypeptides chain would go through a long process of finding a proper intermediate and therefore should be considered catalysts.

Where am I going wrong in my thinking?


texts: Why are the plastic balls used to reduce evaporation in this reservoir black instead of white?

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Plastic balls have been added to a reservoir in drought stricken California in order to reduce evaporation.  (Link to news story here.)

Why are the balls colored black instead of white?  I would think that white would decrease heating and therefore evaporation.

Edit:  Apparently the balls are there to block sunlight from converting bromide to carcinogenic bromate.

Youtube video explaining the purpose of the balls


texts: Significance of Law of reciprocal proportions

texts:
The laws of conservation of mass, definite proportions multiple proportions makes sense and were definitely useful for chemists in the early days of modern chemistry.
The law of reciprocal proportions states that

If element A combines with element B and also with C, then, if B and C combine together, the proportion by weight in which they do so will be simply related to the weights of B and C which separately combine with a constant weight of A.

I don't understand how the law of reciprocal proportions is useful. It seems too unnecessarily complex for someone to intuitively come up with.
Is there any intuition/specific reason that Jeremias Richter came up with it?


texts: What is the product when ferric chloride reacts with propan-1-ol?

texts: I tried to dissolve ferric chloride in propan-1-ol and I saw ferric chloride partially dissolve in it, but I couldn't identify which reaction had occurred. If any one knows about this, please give me your suggestions.


texts: Search for the last step of an altered Raschig process reaction mechanism

texts:
The Raschig process (according to the german wikipedia) is divided in the following steps:

$\ce{2NaOH + Cl2 -> NaOCl + NaCl + H2O}$
$\ce{NaOCl + H2O -> HOCl + NaOH}$
$\ce{HClO + NH3 -> NH2Cl + H2O}$
$\ce{NH2Cl + NH3 -> N2H4 + HCl}$
$\ce{N2H4 + 2NH2Cl -> N2 + 2NH4Cl}$

But what happens now if one changes $\ce{NH3}$ into $\ce{R-NH2}$, with $\ce{R}=$?

Starting from step 3 of the Raschig process I came up to the reaction of the produced hydrazine derivate to give an azo compound.

$\ce{HClO + R-NH2 -> R-NHCl + H2O}$
$\ce{R-NHCl + R-NH2 -> R-NH-NH-R + HCl}$
$\ce{R-NH-NH-R + x~R-NHCl -> R-N=N-R~+~?}$

The last reaction step bothers me a little ... is it simply
$$\ce{R-NH-NH-R + 2R-NHCl -> R-N=N-R + 2R-NH2Cl}$$
but without the cleavage?