texts: Is it correct to look at plane of symmetry in substituted cyclohexane for determining a meso compound?

texts:
I read this question and it's answer by @orthocresol. Now, he has written that the compound in question is meso not because there is a plane of symmetry but because of the rapid flipping of the cyclohexane ring, which makes sense to me. In reality the ring is not planar which seems to be in 2D. But, if we don't consider that ring is 3D and that it actually isn't planar, and we assume that it is planar, answer still comes out to be same, that is, for an actual meso compound, we are able to find a plane of symmetry in the 2D drawing and for a non meso compound, there is no plane of symmetry in the 2D drawing.

So, my question is why from that view also answer still comes out to be same? Is it a coincidence?
In this question, @Chakravarthy Kalyan writes "stereochemical analyses such as the preceding one can be done with drawings using planar rings", but with no explanation why. If we consider the compound 1-(chloromethyl)-3,5-dimethylcyclohexane, this is a meso compound with no plane of symmetry in the 2D drawing. So isn't it a counter example to his claim? If that is true, then why at all  people use the method of plane of symmetry for determining meso compounds in cyclic rings?


texts: Order of reaction for hydrogen ions being ignored

texts:
I have been reading through a case study about calculating the order of reaction for the following reaction:

$$\ce{H2O2 + 3 I- + 2 H+ -> I3- + 2 H2O}$$

The paper uses an iodine clock reaction with vitamin C to calculate its order of reactions, experimentally. However, when writing out the rate law, the author writes it as such:

$$\mathrm{rate} = k[\ce{H2O2}]^x[\ce{I-}]^y$$

How come it is not written as follows:

$$\mathrm{rate} = k[\ce{H2O2}]^x[\ce{I-}]^y[\ce{H+}]^z\;?$$

For what reason is the order of reaction of hydrogen omitted? My thinking was that it has an order of reaction of $z = 0$ and therefore it does not affect the rate at all. However, I was unable to find a source to verify this.


texts: Affordable, non-contaminating flexible tubing for common acids

texts:
Which tubing material is affordable, flexible, widely available, and suited for transporting very pure acids ("puriss." products) in their most concentrated form without contaminating them?
PTFE seems compatible with most if not all of them, but I don't think it's very flexible, and I'm not sure whether PTFE hoses would be affordable (nor where I could buy some).


texts:
Imagine I was your little brother, how would you explain an orbital to him? (assuming he knows what atoms electrons and neutrons are, and the rest of the basics till that point.)

I have been reading up on this and can't make heads out tails of it.
As a side how do the different energy levels relate to them.

I hope I'm clear, I'm doing my best. I read several books but can't get a clear bearing on this.


texts: Why does solubility of Carbonate salts of Alkali metals in water increase down the group?

texts:
Carbonate salts have a very large anion so hydration energy should dominate over lattice energy. Since hydration energy is inversely proportional to radius of ion, I would expect Lithium to release the largest hydration energy and thus be the most soluble. But my textbook (Concise Inorganic Chemistry by JD LEE) says that the "Solubility of carbonates and fluorides of Alkali metals increase rapidly on descending the group. The reason for this is that their Lattice energies change more than the hydration energies on descending the group." However, it provides no
further explanation as to why that is true. Could someone please explain this better?


texts: How do I find the empirical formula for cobalt oxalate hydrate with mass of oxalate and oxide produced?

texts:
I have the formula $\ce{Co(C2O4)*H2O}$ in a reaction that forms cobalt oxide $\ce{Co3O4}$
My data here says that my oxalate hydrate weighed $\pu{0.3283 g}$ and my product oxide weighed $\pu{0.1158 g}$ which I have calculated as:
$$0.1158 \times \frac{\pu{176.79 g}\, \mathrm{(cobalt\,oxalate)}} {\pu{240.79 g}\, \mathrm{(cobalt\,oxide)}} =\pu{0.08502 g\,\mathrm{(cobalt)}}$$
Then $\pu{0.3283 g (reactant)} − \pu{0.1158 g (product)}$ gives me $\pu{0.2125 g}$ water removed divided by $\pu{18.016 g/mol}$ to get $\pu{0.01179 mol}$ $\ce{H2O}$ in the sample.
How do I use this data to determine the empirical formula? I am not sure how to determine the molar ratios from this point.


texts: IR spectra and melting point range comparison

texts:
I did a Diels-Alder experiment in lab, and the desired product was 9,10-dihydroanthracene-9,10-α,β-succinic anhydride. According to my IR spectra, I believe I isolated the product. However, my observed melting point range is 269-272°C, while the literature melting point is 262-264°C.

How significant is my melting point discrepancy?
And am I overlooking peaks in my IR that would be indicative of an impurity in my sample?


texts: Which preposition to use for the reducing agent?

texts:
Which expression is correct when we use the prepositions with or by for indicating that the reduction is carried out using $\ce{NaBH4}$ as a reductor:

  It is reduced to sodium phenylselenolate with $\ce{NaBH4}$ in alkaline ethanol.

or:

  It is reduced to sodium phenylselenolate by $\ce{NaBH4}$ in alkaline ethanol.


texts: What would the name and formula be for Mo+O+Se?

texts: I do cross-stitch and want to spell the word "moose" (for a project focusing on the animal) with squares from the periodic table and present a compound formula and name that encapsulates all three elements, Mo+O+Se, in that order. I'm not looking for strictly realistic chemistry, just a formula and a name that would work IF the compound had actually existed. The number of atoms of each element is up to you. Can you help me with a formula and a name for Molybdenum + Oxygen + Selenium?


texts:
The two assumptions are that the gases are points of mass that move, they have no volume and that there is no interaction between other molecules.

But even the points of mass can collide with each other so wouldn't that be considered interaction between molecules?


texts: What is the carbon dioxide content of a soda can or bottle?

texts: I sort of know how carbonated beverages are carbonated: a lot of $\ce{CO2}$ gets pushed into the liquid, and the container is sealed. There are at least two things I don't know. First, how much carbon dioxide is actually dissolved in the liquid? Second, what is the resulitng partial pressure of $\ce{CO2}$ in the headspace and the total pressure in the headspace? I'm interested in cans, plastic bottles, and glass bottles. I know from experience that there is some variation among manufacturers even for the same beverage, so I will be happy with general numbers or a good estimate.


texts: 2-bromobutane absolute configuration from structural formula to 3D

texts:
For the 2-bromobutane drawn below, given the 3d image I can tell it is R configuration

Annotated from source:

However, given the structural formula I can't figure out how to get this 3d shape correctly.

Structural formula:

When I try to visualise it I get two possibilities:

My sticking point is: when moving the H (the lowest priority group here) to the back, which way (to the left or right) does the CH3 go? Depending on which I draw the answer changes.


texts:
I'm looking at a textbook question (Engel & Reid, Thermodynamics, Statistical Thermodynamics & Kinetics, 4 ed, Q3.1) which states the following:

  The heat capacity $C_{\mathrm m,p}$ is less than $C_{\mathrm m,V}$ for $\ce{H2O(l)}$ near $\pu{4 °C}$. Explain this result.

Their answer is that water contracts as you heat it in this regime, thus (at constant $p$) the surroundings are doing work on the system, hence $C_{\mathrm m,p}\lt C_{\mathrm m,V}$.

But the textbook also contains the following equation (which is correct, and whose only restrictions are that the system is of fixed phase and composition, and $\text{đ}w = –pdV$, i.e., pV-work only):

$C_{\mathrm m,p}-C_{\mathrm m,V} = T V_\mathrm m \beta^2/\kappa$

where $\beta$ is the isobaric thermal expansivity, and $\kappa$ is the isothermal compressibility.

Based on this, for a substance of fixed phase and composition, $C_{\mathrm m,p} \ge C_{\mathrm m,V}$, always, because, while $\beta$ can be $\le0$* (water near $\pu{4 °C}$ being a notable example), $\beta^2$, as well as $T, V_\mathrm m$ and  $\kappa$, are always positive. [*Edited from  $\lt 0$ to $\le 0$ based on Night Writer's answer.]

So is the statement in the textbook's question just a flat-out mistake, or am I missing something here?

It appears their error is in assuming the difference between Cp and Cv is due to pV expansion alone, when in fact there are two terms:

$$C_p - C_V = p \left(\partial V\over\partial T\right)_p+ \left(\partial U\over\partial V\right)_T \left(\partial V\over\partial T\right)_p,$$

where the first term on the RHS is the PV work per unit change in T, while the second term is the change in internal energy with respect to volume (which results from changing the intermolecular distance between interacting particles) times the rate at which the volume changes with temperature.

It would be nice to have direct reference-quality experimental values for $C_{\mathrm m,p}$ and $C_{\mathrm m,V}$ for $\ce{H2O(l)}$ near $\pu{4 °C}$, but I've not been able to locate them, nor do I expect to: because of the difficulty of accurately measuring $C_{\mathrm m,V}$ for a liquid, measurements are typically made at constant pressure, giving $C_{\mathrm m,p}$, and then $C_{\mathrm m,V}$ is calculated using the above equation.


texts: What's the Acid Ionization Constant of the Hydrogen Proton?

texts:
What is the $\ce{K_{a}}$ value for $\ce{H^+}$. I understand that the hydrogen proton doesn't stick around in solution by itself for very long. Nonetheless, does it have a  $\ce{K_{a}}$ value? Can it have a  $\ce{K_{a}}$? I think it can have one but quantifying it might be hard. Its  $\ce{K_{a}}$ value I think would correspond to this reaction:

$\ce{H^+ + H_2O ->H_3^+O}$

However this doesn't look like a conventional acid/base reaction; we don't have the conjugate base of $\ce{H^+}$ here, unless the definition of a conjugate base isn't what I think it is (acid missing one proton).

So my questions are:

1) Does the above mentioned $\ce{K_{a}}$ value exist.

2) Is my definition of a conjugate base too narrow?


texts: Relation between Gibbs energy and net reaction rate

texts:
I have come across some papers in biochemistry that seem to claim that a reaction can be "near equilibrium" even though the flux through the reaction (net reaction rate) is large. For example, this paper measures absolute metabolite concentrations in E.Coli cells grown on two carbon sources, performs some thermodynamic calculations, and concludes that "lower glycolysis is near equilibrium on both carbon sources, with $\Delta G$ approximately 0". Yet this pathway carries net flux in these conditions according to the authors, and usually glycolytic flux is rather large.

How can this be? In my understanding, the net rate of a reaction depends on the Gibbs energy $\Delta G$ so that, near equilibrium where $\Delta G \approx 0$, there is no net flux through the reaction. And I think this dependence should be smooth, so that $\Delta G$ must be large when the net rate is large?

The authors suggest that reaction rate depends steeply on $\Delta G$, so that "Small changes in $Q$ are accordingly adequate to tip the thermodynamically favored flux direction." (From the supplementary it looks like the reaction quotient $Q$ varies between 0.5 and 6.) I have also encountered this idea in works on thermodynamic flux analysis, where only the sign of $\Delta G$ is considered important, its magnitude $|\Delta G|$ is ignored. But if this is true, the reaction direction seems unpredictable and the system should be difficult to control?

Is this all just a question of what "small" or "large" $\Delta G$ means? Can the dependence on $\Delta G$ be sharp, so that the sign of $\Delta G$ acts like a "switch"? Can a reaction really be considered "near equilibrium" if the net reaction rate is large?


texts: What catalysts can be used to decompose nitrous oxide?

texts:
Constraints:

I'm going to need to use a lot of this stuff in various locations, so I'd prefer it not be expensive (leaving out things like platinum, palladium, and rhodium.)

While I don't believe I can get a "room-temperature" catalyst (I'm always willing to be proven wrong!) I need this to begin the decomposition reaction at as low a temperature as possible.  This will allow electric heating to get it up to heat as rapidly as possible, using as little valuable battery or fuel cell power (I haven't decided yet) as possible.

The catalyst will be mounted near (not in!) a rocket engine combustion chamber, with a flame temperature of 3,553 K.

This will be used to decompose $\ce{N2O}$ as follows:
$$\ce{2N2O -> 2N2 + O2 + heat}$$
This will (re)light LOX/LCH4 engines in-flight.  I'm thinking about a second of $\ce{N2O}$ decomposition should touch off LOX/LCH4 nicely, then cut the $\ce{N2O}$.  Landing engines will need to be lit mid-flight for a safe touchdown, and it may be necessary to relight the lifting engines for some reason, which means I'd need to have this catalyst in at least 12 locations.
8 in landing engines and  4 either in lifting engines or 1in aerospike with redundant ignition.  I'm not married to the aerospike idea yet, I'm still trying to figure out how to Regeneratively cool the center truncated spike while allowing for a "base bleed" to minimize the effects of the low pressure recirculation area at the flat end of the spike.
If I can't crack that, it will be back to four bell-nozzle lifting engines. So, minimum twelve catalyst beds per instance.


texts: What is the maximum thickness of electroplating that can be acheived?

texts: I was just wondering if you are electroplating a suitable object what is the maximum thickness that can be achieved? Is there a limit?


texts: Alcohol Nonmeclature - Organic Chemistry

texts:
I'm new to organic chemistry and having some trouble naming alcohols. I came across this molecule, I believe it's name is 3-ethyl 2-pentanol, but my online checker system is saying that I am wrong. Am I wrong, or is the online checker looking for 3-ethyl pentan-2-ol?

Thanks for your help!


texts: Are tetra- and pentanitrotoluene better explosives than TNT?

texts:
When reading about TNT (trinitrotoluene), I noticed that the aromatic ring has still 2 carbon atoms left for two more possible nitro groups ($\ce{−NO2}$), which would get you tetra- or pentanitrotoluene.

The amount of available oxygen in TNT is not enough for a complete oxidation to water and carbon dioxide, this is obvious when looking at a possible reaction:
$$\ce{2 C7H5N3O6 -> 3 N2 + \mathbf{5\,H_2} + 12 CO + \textbf{2 C}}$$
Thus tetra- and pentanitrotoluene should be better explosives than TNT, because they both provide more oxygen than TNT. Why they were never popular? Are they harder to fabricate than TNT, can you nitrify them from TNT? Are they maybe unstable?


texts: Why did the salt on the skin of my turkey react with the aluminum foil it was touching?

texts: I sprinkled salt on my turkey skin and left it to dry out over night. It was covered with aluminum foil. The next morning the aluminum foil had holes ‘burnt’ in it and the turkey skin turned silver at the spots where the salt crystals had touched the aluminum foil. Was my turkey poisoned with aluminum at this point? I did not eat it to find out.


texts: For synthesis of sodium methoxide, can we use sodium hydroxide in methanol and slow evaporation after dissolving sodium hydroxide?


texts: Deriving the entropy of mixing of a non-ideal solution

texts:
In the earlier posted question named Derive expression for internal energy of mixing and entropy of mixing using statistical thermodynamics the entropy of mixing was found by assuming an ideal solution. The user Porphyrin mentioned that in case the molecules in the solution do interact with each other, the free energy would have an additional term (n1+n2)x1x2w, with

  w≈(2E12−E11−E22) and E12E12 is the interaction energy between molecules of type 11 and 22 when they are adjacent and similarly for
  E11E11 and E22E22 all of which are negative. From a consideration of
  the energies involved ww is expected to be positive.

My question is: how do we go about finding an answer for the entropy of mixing when we do not assume that the solution is ideal?


texts: Seeking safe, water-soluble chemicals for an IR spectroscopy experiment

texts:
I am working with a custom-built device which is intended to perform some mid-infrared chemical measurements.  It consists of four thermopile sensors with optical windows.  In front of each window is a band-pass filter.  Each filter admits a distinct range of wavelengths.  We performed an initial experiment which suggests that the manufacturer may have installed the filters in the wrong positions.  I am trying to design a more definitive follow-up experiment.  I can't tell the filters apart by looking at them.
These kinds of sensors are typically used in the automobile industry to characterize engine exhaust gases.  We happen to be measuring aqueous solutions instead, so I am trying to identify useful reference solutions we can prepare.  Ideally, the solutions would absorb well at one of the three wavelengths, and transmit well at the other two.  I don't care whether the reagents are organic or inorganic.  Safe, water soluble, inexpensive, and already present in my lab are all desirable qualities though.
The center wavelengths of the three optical filters are 6.7 μm, 8.3 μm, and 9.6 μm.  In wavenumbers, these are around 1490, 1200, and 1040 cm⁻¹.  The bandpass range on each of the filters is about 0.2 μm wide.  I also have a fourth, broad-band filter which I will identify by process of elimination.
Using my limited knowledge of IR fingerprints and the NIST Webbook database of infrared spectra, I have identified two candidate compounds.  Glycine absorbs preferentially in the 6.7 μm band, and trimethyl phosphate absorbs preferentially in the 9.6 μm band.
I still need a good candidate compound for the middle band: 8.3 μm / 1200 cm⁻¹.  The best I have found so far is n-decanoic acid, but it's not really that selective in absorbing at 8.3 μm.  It also isn't particularly water-soluble.
I would greatly appreciate it if anyone has any suggestions.  Thanks!


texts: How can I choose the correct mechanism for nucleophilic substitution of aryl halides?

texts:
I was reading about nucleophilic substitutions of aryl halides, and there are three different mechanisms discussed, namely the SN1, SNAr (addition-elimination), and benzyne (elimination-addition) mechanisms.

However, I am confused as to how to identify which mechanism is operative. How can I tell this from the reaction conditions and reagents?


texts: What happens when you try to dissolve ʟ-glutamine in hot water (above 80 °C)? Does the heat destroy the ʟ-glutamine?


texts: What does the neutralisation of acids and bases mean?

texts:
From what I found in textbooks and google is that neutralisation is when acids and bases react to produce salt and water. Most examples I have learnt do so, however a reaction like:

$$\ce{NH3 + HCl -> NH4Cl }$$

It does not produce water.

So is neutralisation defined as only when salt and water produce a neutral salt and water or is it just produce any salt and water. And if it is any then how can does the example above work?


texts: What are the products of the reaction of NH4Br (aq) + Hg2(NO3)2 (aq)?

texts:
Predict the products of the following reaction based upon solubility rules. (Separate substances in a list with a comma. Include states-of-matter under the given conditions in your answer). The reaction is:

$$\ce{NH4Br (aq) + Hg2(NO3)2 (aq) -> ?}$$

I can not figure out what the products of this reaction are. I would think $\ce{NH4(NO3)(aq)}$, $\ce{Hg2Br2(aq)}$, but this is not correct.


texts: Can we use silver nitrate to distinguish between chloride and carbonate salts?

texts:
Initially, we are given a solution containing two salts, they can be either carbonate or chloride salts (we do not know their composition initially).
Generally, $\ce{AgNO3}$ is used as a confirmatory test of $\ce{Cl-}$ (a white precipitate is obtained on adding silver nitrate to solution containing the chloride salt). Therefore, can we use this method to directly identify chloride in the solution or do we need to remove the possible carbonate ions to confirm the presence of chloride before performing the test as mentioned above?
$$\ce{NaCl + AgNO3 -> NaNO3 + \underset{white}{AgCl} \downarrow}$$
$$\ce{Na2CO3 + 2AgNO3 -> 2NaNO3 + \underset{brownish white}{Ag2CO3} \downarrow}$$
(A similar question may arise in the identification of bromide and iodide ions but I have ignored it for now as they are rarely asked in exams. Still I would appreciate it if someone could give an answer for this as well.)
The question has been asked mainly because silver nitrate test is generally taught to be performed without mentioning above precautions and it is also a very famous confirmative test. So answer is expected more (not only) from a laboratory technician than theorist.


texts: I have a Thermo Nanodrop 1000 spectrometer that I have reason to believe is out of calibration. After consulting the manual, it appears as though there is a way to check the calibration of the spectrometer using a premade CF-1 calibration solution. This solution itself appears to be aqueous potassium dichromate, but I cannot find the concentration and exact specifications of the solution online. I was curious if anyone has attempted to make the calibrant from reagent they had in lab, and if so, what exactly does one use to make the solution?


texts: Error in formula for the solution to a chemical problem

texts:
The problem in my textbook goes like this:

  Burning $0.68\ \mathrm{g}$ of an unknown substance, we obtained $1.28\ \mathrm{g}$ of sulfur oxide (IV) and $0.36\ \mathrm{g}$ of water. Find the chemical formula of the burned substance, providing that it was a complete combustion.

It's quite easy to see that $0.2\ \mathrm{mol}$ of both $\ce{SO2}$ and $\ce{H2O}$ have been produced, there are $0.04\ \mathrm{mol}$ of hydrogen in the water and $0.02\ \mathrm{mol}$ of sulfur in the oxide. Calculating the masses and summing them up, we get $0.68\ \mathrm{g}$, meaning the original substance contained only sulfur and hydrogen, and it's $\ce{H2S}$.

However, the solution volume offers this equation as part of the solution process:

$$\ce{S_{$x$}H_{$y$}O_{$z$} + \frac{x + y}{4} O2 -> $x$ SO2 + \frac{$y$}{$z$} H2O}$$

The volume is full of typos (apparently a plus sign missing here), but still there must be some explanation for the coefficients which I don't get. Why do the coefficients for $\ce{O2}$ and $\ce{H2O}$ equal $(x+y)/4$ and $y/z$? If there's zero oxygen in the first term, won't we get division by zero?

How do we come up with coefficients of this sort? Maybe these particular coefficients are erroneous? (the solutions volume is quite low in quality)


texts:
Predict the most preferable structure of $\ce{NCS-}.$
$$\Large\underset{(\textbf{1})}{\ce{(:\!\!\overset{\huge.\!\!.}{N}=C=\overset{\huge.\!\!.}{\underset{\huge.\!\!.}{S}})-}}\qquad\underset{(\textbf{2})}{\ce{(\overset{\huge.\!\!.}{\underset{\huge.\!\!.}{C}}=S=\overset{\huge.\!\!.}{\underset{\huge.\!\!.}{N}})-}}$$

My Attempt
A chart for the formal charges:
$$
\begin{array}{l|rr}
\hline
\text{Atom} & (\textbf{1}) & (\textbf{2})\\
\hline
\ce{N} & -1 & -1 \\
\ce{C} & 0 & -2 \\
\ce{S} & 0 & +2 \\
\hline
\end{array}
$$
As a conclusion, in structure 2 the formal charges on $\ce{C}$ and $\ce{S}$ (i.g. bond becomes polar because of $+2$ and $-2$) make it weaker, whereas in structure 1 there are less charge separations. So, (2) must be more a accurate structure.
But according to my book, structure 2 is more stable. Why? Please explain. Is there any other approach to this question?
Edit

I got this statement in favor of structure #2 "is more stable because each atom has non-zero formal charge in the lowest energy state". But i can't understand this statement. Can anyone explain me?"


texts: How do I select a sub-freezing temperature for my experiment that will allow the formation of frost, but not supercooled liquid water (rime)

texts:
I once conducted a set of experiments in which I had to form ice by direct vapor deposition (not condensation of liquid water followed by freezing, aka riming) onto a Peltier-cooled glass-coated copper rod.

The experiments were conducted outside at night within a small wind tunnel, with ambient air temperatures ranging from -2 oC to -25 oC and the glass substrate was cooled from 1 oC to 10 oC below the ambient air temperature.  Occasionally supercooled water droplets would condense, followed by freezing (forming rime ice) rather than direct deposition of ice crystals from the vapor phase.  These events would ruin my time-consuming experiments.

The only relevant parameter under my control was the temperature of the glass-coated copper rod.  The only relevant parameters I could measure during the experiment were the air temperature and humidity. I also introduced trace-levels (single to hundreds of ppb) of several C1 to C4 alcohols in order to later measure their incorporation into ice during ice deposition from the vapor phase.  However, the low levels of these compounds did not affect whether riming or direct vapor-ice deposition would occur, as based on a series of 'blank' experiments without the trace gases.

If I were having trouble with liquid water condensation, in what way would I want to alter the glass substrate temperature so that only the direct deposition of solid ice could occur?


texts: What is an example of chemical reaction that can be assisted by both an inorganic catalyst and an enzyme?

texts:
I have been researching chemical reactions of inorganic catalysts and enzymes and cannot find a chemical process where an inorganic compound can be replaced by an enzyme (or vice versa) and have the same products. I have looked at article after article with no luck.
What is an example of chemical reaction that involves an enzyme that can be replaced by an inorganic catalyst?


texts: What is the order of the catalytic decomposition of hydrogen peroxide?

texts: I recently did an experiment to determine the activation energy of the decomposition of hydrogen peroxide using iron (III) chloride as a catalyst. I repeated this experiment at different temperatures. I know how to figure out the rate constant and the rate law, but I am not sure if this is a second-order reaction. Is there any way I can figure out the order of this reaction? (because that would impact the units of the rate constant, k, and the rate law)


texts:
I found a synthesis of diclofenac, and the last step with the addition of hydrazine and $\ce{KOH}$ seems interesting.

However, I couldn't find the mechanism behind this reaction, therefore I proposed one forming $\ce{N2}$.

Could you help me find the right mechanism regarding this type of reaction or correct mine?


texts: Based on their respective number of degrees of freedom, what's the most efficient fuel; hydrogen or gasoline?

texts:
The reaction of octane's combustion is:

$$\ce{2 C8H18 + 25 O2 -> 18 H2O + 16 CO2}$$

I am asked for computing the number of degrees of freedom of the octane given that its specific heat is $\pu{256 JK^{-1}mol^{-1}}$.

Then I have to compare the number of degrees of freedom obtained for octane with those for $\ce{H2}$. Based on this I have to argue what's the most efficient fuel.

What I've done

I assumed octane stores thermal energy only in quadratic degrees of freedom and these do not depend on $T$. Using the equipartition theorem one gets:

$$C_V = \frac{\partial U}{\partial T} = \frac{Nfk_\mathrm B}{2} = \frac{nfR}{2} $$

Where: $k_\mathrm B = \pu{1.381 \times 10^{-23}JK^{-1}}$ and $R = \pu{8.315 JK^{-1}mol^{-1}}$

Then for octane:

$$C_V = fR $$

$$f = 31$$

Aren't these too many degrees of freedom?

For $\ce{H2}$ there are $3$ translational + $2$ rotational degrees of freedom; $f = 5$

What about efficiency?

I have worked with Otto's engine model (real heat engines; internal combustion):

$$\eta = 1 - \left(\frac{V_2}{V_1} \right)^{\gamma -1}$$

Usually the compression ratio is of the order:

$$\frac{V_1}{V_2} = 8$$

Where $\gamma$ is the adiabatic exponent:

$$\gamma = \frac{f + 2}{f}$$

Thus, the efficiency of a gasoline engine:

$$\eta = 0.12$$

While the efficiency of an hydrogen engine:

$$\eta = 0.56$$

My point is that the efficiency I get for gasoline is not what I expected (at least $0.20$). So I must be missing something on calculating the degrees of freedom for octane.

Thus hydrogen is a more efficient fuel.


texts:
I am an industrial electrician apprentice who needs to learn more about pH-measurements and how the temperature effects the measurement itself (I am in charge of all the pH measurements on the powerplant I work at and I have no one to ask about this stuff as no one knows a thing about pH measurements).
So far I have learned how the temperature affects the electrochemical and physical properties of the combination electrode and how this can easily by adjusted for by incorporating an automatic temperature compensation that keeps the NERNST equation updated in real time.
So far so good.
I have, however, also read about the auto-ionisation of water and the constant pKw and how a change in temperature affects the span of the pH scale: With a change in temperature comes a change in hydronium content due to a shift in equilibrium as predicted by Le Chatelier's Principle. However, with a change in hydronium content comes an equal change in hydroxide content and so a change in this constant DOES NOT change the acidity of a solution. In other words, this particular constant decides the SPAN of the pH scale and because of this also the point of neutrality (7 at 25 degree celcius in pure water and less at higher temperatures).
And then there is the so called pKa that says something about the strength of an acid via the acids point of equilibrium in water. This dissociation constant is also temperature dependent although it is my understanding that this constant have nothing to do with the location of the neutrality point. It's simply a constant that changes with temperature and so the solution (unlike with pKw) DOES become more/less acidic as the temperature changes.
Is this correct?
If so, could you please give me an answer to the following questions I have?

Why does a solution become less temperature dependent the more acidic it is? Basic solutions are extremely temperature sensitive, neutral solution still significant sensitive, but highly acidic solutions don't seem give a damn about temperature. Why is that?

It is my understanding that pKw is only important in pure water and highly diluted solutions. But what am I to make about this? If I have a tank of an acidic solution (say pH 1) and the temperature is 50 degrees celcius, does this mean that the point of neutrality hasn't shifted as much away from pH 7 as it would had done in  pure water? Or is it because there is simply so much hydronium present that the pKa constant takes up proportionally more importance than pKw and so the autoionisation becomes a non issue to consider in every practical sense?

Thanks in advance for any help you may provide me with


texts: Rules to follow while writing a chemical formula for polyatomic ions

texts:
In Science, textbook for class IX, chapter $3$ [1,p.38], it states:

The rules that you have to follow while writing a chemical formula are as follows:

in compounds formed with polyatomic ions, the number of ions present in the compound is indicated by enclosing the formula of ion in a bracket and writing the number of ions outside the bracket. For example, $\ce{Mg(OH)2}$. [...]

Now my book further states that hydroxide ($\ce{OH–}$) and nitrate ($\ce{NO3-}$) are polyatomic ions. And then it says:

Formula of sodium nitrate:  $\ce{NaNO3}$

But the formula of calcium hydroxide:  $\ce{Ca(OH)2}$
My question is that even though both nitrate and hydroxide are polyatomic, why are we using ( ) in notation for latter in their symbolic representations?


texts: What is the order of stability of the cyclobutyl and cyclopropyl carbocations?

texts:
I know  about the exceptional stability of Cyclopropylmethyl carbocation.

In some books it is given that cyclopropyl and cyclobutyl carbocations are highly unstable due to their high strain.
That is true and quite acceptable, but just like cyclopropylmethyl carbocation they can also have resonance structures
and the cyclobutyl carbocation can rearrange itself to the cyclopropylmethyl carbocation by ring contraction.
My question is, what will the stability order between the
cyclopropyl, cyclobutyl, cyclopentyl carbocations?

Also if anyone please can help me to understand why resonance structures in cyclopropyl carbocation will not be possible?


texts: What MnO2 and graphite do I need for making a dry cell battery?

texts:
I'm playing around with making my own dry-cell battery and I want to make sure I understand the pieces before diving into it.

My plan is to make it like a layer cake: zinc sheet, paste of electrolyte, layer of $\ce{MnO2}$ powder, graphite sheet, and a metal sheet with a wire connected to it.

What I'd like to understand better is:

Could I replace the zinc sheet with Zn powder? (Also this is interesting, but I don't understand what's meant by a Zn sponge, is it Zn powder with $\ce{Ca(OH)2}$?)
How pure/fine does the $\ce{MnO2}$ powder need to be? Potters used $\ce{MnO2}$ to color clay, is this the same stuff as what's in batteries?  I tried emailing a few places but they didn't know the chemical properties and I'm not confident enough to go for it without double checking first :/
Could I use carbon filters or even crushed charcoal or does the electrode need to be a solid sheet of graphite?  I think carbon filters and graphite sheets have the same chemical properties, but I'm not sure.


texts: How come diluting a cell decreases the voltage?

texts: I just want to know why, if we dilute a cell with water, it decreases the voltage. Assume it is a galvanic cell.


texts: How to explain the structure of HNO3 with a Molecular Orbital diagram?

texts:
Take an example, $\ce{HNO3}$

  The total valence of $\ce{HNO3}$ must be 24. By using formula $\pi =6\mathrm{n}+2-\mathrm{V}$ where $\pi$ is number of $\pi$ electrons, $\mathrm{n}$ is number of atoms excluding all hydrogen atom, and $\mathrm{V}$ is total valence, the $\pi$ is $2$. It means that there would be one double bond in the structure of $\ce{HNO3}$ and the remaining bonds other than $\pi$ bond are $\sigma$ bond.

I understand the double bond has 1 $\pi$ electron and 1 $\sigma$ electron. It means 10 electrons are used for the bonds and 14 electrons are remaining.

I know it would be impossible to violate octet rule because the calculation of $\pi$ already stated.

I have trouble how to spread the 7 lone pairs. Why does the $\ce{O}$ in the single bond $\ce{N-O}$ have 3 lone pairs, while the $\ce{O}$ in the double bond has 2 lone pairs? I don't expect the answer like "Just spread the lone pairs to somewhere".
I'm worried about the odd number of unshared electrons.

I know the $-$ means rich of electron and $+$ means lack of electron. To check the formal charge in each atom is easy, but how to calculate the formal charge, if I don't know where to put the $-$ and $+$.

I think this question is not a duplicate of The Lewis structure of HNO3. I already saw that question , but I'd like to ask here again, because I need the answer for my misunderstanding, even though the answer would be general structure of $\ce{HNO3}$.

To be precise, I just don't know where I need to put unshared electrons. It's like I'm missing the bridge. I know resonance, as arrow-pushing, and mechanisms are required in organic chemistry.


texts: Is it possible to make broad spectrum light absorbing paint?

texts: Is there such a paint / pigment that absorbs most wavelengths of light (beyond the visible light range) that can be used for solar heat generating applications?  If not, would it be possible to make it?  Ideally, this paint would absorb light from the sun in an efficient manner and become heated quickly by solar light.  It should probably at least absorb infrared, and any other wavelengths of light that produce significant heat when absorbed.  This should be far more effective than normal black paint as black paint only "for sure" absorbs light in the visible spectrum, and this desired paint would absorb other types of light from the sun.


texts: Writing Ksp when the ions are on the left of the equilibrium equation?

texts:
For the equation:
$\ce{Ca^{2+} {(aq)} + ^-OOC-COO- {(aq)} <=> Ca(OOC-COO) {(s)}}$
My book gives $K_{sp} = \pu{3.0e-9 M} = [\ce{Ca^{2+}}] \times [\ce{^-OOC-COO-}]$.
However, as per Chem.Libretexts, for any  $K_c$, the right hand side substances go in the numerator and the left hand side substances go in the denominator.

"It is really important to write down the equilibrium reaction whenever you talk about an equilibrium constant. That is the only way that you can be sure that you have got the expression the right way up - with the right-hand substances on the top and the left-hand ones at the bottom."

So for $K_{sp}$, why is it not the same?
I guess intuitively for a $K_{sp}$ I would probably put the $K_{sp}$ = product of the ions. But is there any other exceptions to when the above rule from Chem.Libretexts is not followed (in regards to K values)?


texts: What are these fluffy white crystals growing out of my floor tiles?

texts:
Does anyone know what these white crystals are?

As you an see they are growing out of some floor tiling in my house. They have been appearing for some years now out of the floor, which is cleaned fairly regularly (at least, I assume so, since my cleaner does it!). They may appear more frequently when the weather is humid.

For scale, the tile is 20cm each side. The crystals form light fluffy heaps, rather like snow and would be a few millimeters in height.

My guess is that they could be common salt, or possibly something connected with the bleach or cleaning products used on the floor. The latter case prevents me from trying the taste test to prove the former.


texts: Color Visible in Large Quantities of Ethanol

texts: I am currently writing a sci-fi novel and have come upon a rather ponderous question that I have thus been incapable of discerning an answer for. If a planet were to have oceans composed not of water, but rather of ethanol or a similar alcohol, what would they look like from space, assuming an atmosphere similar to earth's? What I've found thus far implies that ethanol and other pure alcohols are simply clear, however, in small quantities (such as in a glass), water also has an apparently clear color. Knowing that water, in larger quantities, absorbs red, yellow, and green light more readily than blue, making it appear blue, I was assuming that other liquids might perform similarly, making large quantities of them a far different color than in isolated quantities.


texts: Why don't these Entropy equations contradict each other?

texts:
My textbook says that $\delta S_{rev}= \frac{q_{rev}}{T}$. It also says that $\delta S_{surr}= \frac{-q_{rev}}{T}$. Logically, this should mean that the change in entropy in both the surroundings and the system are equal in magnitude but opposite in sign.

This is NOT true, though, as it would go against the Third Law of Thermodynamics. Also, my book proves the Law by comparing the equation for $\delta S_{surr}$ to the Entropy of the system found when subtracting the products' entropies from the reactants'.

Where am I going wrong? Why can't we compare the two $\delta S$ equations and disprove the Third Law?

Note: The first equation is $q_{rev}$ due to something to do with a reversible, isothermal reaction that I don't really understand, which might be the source of my confusion...


texts:
I was given the following reaction to prove a mechanism for:

and I managed to prove the first step with ease.

The second step, forming the "base-catalysed aldol" is the part that's rather confusing me.

Consider the mechanism of a base-catalysed aldol reaction below.

For this reaction to take place, I need a second carbonyl molecule, but the $\ce{CO2Me}$ on the right hand side ring appears untouched, and likewise so does the carbonyl group on the left hand side too.

I tried the reaction a second way (giving the mechanism below) but am unsure if this is correct.
Is this the correct mechanism?


texts: Determining whether something is an acid, base, or amphoteric

texts:
I have to find whether these compounds are acids, bases, or amphoteric: $\ce{CO3^{-2}}$, $\ce{HPO4^{2-}}$, $\ce{H3O^{+}}$ and $\ce{NH4^{+}}$.

I know the first can obviously act as a base, but others can gain or lose $\ce{H^{+}}$, so I think they are amphoteric. However, according to my book, I'm wrong. Can you help me clear my doubt? Thank you very much!


texts: Is strontium more metallic than sodium? If yes then why?

texts:
I got an MCQ in my examination, "Which one of the following is more metallic?" and the options were Sr, Na, Be or Aluminium. I know that sodium is more metallic than Be or Al but my mind stuck on strontium.

-Strontium is the member of the fifth period and has greater number of shielding electrons than sodium (due to greater number of shells). This suggests that strontium should be more likeable to lose electrons.

-But sodium has half filled valence "s" orbital while strontium has fully filled "s" orbital. This suggests that sodium is more likeable to lose its only valence electron.

-I've also looked for their first ionization energy values and they are almost comparable. 495.8 for Na and 549.5 for Sr. Why the I.E of sodium is a little bit less? (And should it be more metallic due to this?)

I've looked everywhere else on the internet but haven't found the answer. My question is, which of them is more metallic and why.
And also are there any members of group IIA that are more metallic than any of the elements of group IA.


texts: Autodock Vina flexible metals and water molecules

texts:
I have some problems with water and metals in binding site when using Autodock Vina.

Is it possible to make these flexible? They unfortunately remain where they are what leads to wrong interactions.

My other idea would be to delete it before docking, reinsert them and minimize everything.

Does anyone have a solution for metalloenzymes? (e.g. PDB:3NJY)


texts: Why does ozone have a dipole moment different than 0

texts:
First of all, I know that the reason for this is the bent structure of the molecule.
However, we were taught in my class that the dipole moment of a molecule is equal to the vector sum of the dipole moment of each bond in the molecule.
But ozone only has bonds between two oxygens, so why is the dipole moment of each bond not equal to zero?


texts: Explanation of terminology in equation used for energy calculation using Hartree–Fock method

texts:
I found in the literature that the energy of the Hartree–Fock method is given by the following equation:
$$E_\mathrm{HF} = \int (\Psi^* \hat{H}\Psi)\,\mathrm d\tau$$
The term $\Psi$ is the wave function, but what would the term $\Psi^*$ be?
Does anyone have a simple of explanation of what this may be?


texts: What is the physical explanation driving current flow in a concentration cell?

texts:
In a galvanic cell, current is driven because the species at the cathode is reduced by grabbing some electrons from the cathode. The cathode now lacks electrons so it pulls them from the anode. Now the anode needs electrons, so it pulls them from the species that will be oxidized in the other half cell. So, now we have a current!
Now here is a concentration cell:

As you can see. the anode and cathode are made of the same metal. Only the concentrations of the solutions are different. Using my logic from above, since the metals are the same, they should be pulling on the electrons with equal magnitude. So how come current still flows? In other words, why are the nickel ions at the cathode more "hungry" for electrons than the nickel ions at the anode?
My attempt: It has to do with the rates of the metal dissolving. If I were to cut the wire connecting the two half-cells, I would notice that the beaker with the lower concentration solution would be increasing in concentration (from solvating the metal) faster than the beaker with the higher concentration. This is because the lower concentration one is "further" from the solubility equilibrium.
When I connect them back together the metal at the anode dissolves faster, thus demanding electron recompense from the cathode metal.
Attempt 2: The solution with higher Ni ion concentration has overall more ions dissolved in it. Maybe all these ions create an electric field greater than the one on the other side, thus prompting electron movement.
Attempt 3: It has to do with kinetics. Lets assume that everytime a nickel cation collides with an electrode, it steals some electrons. The half-cell with the higher concentration will have a higher amount of collisions per second. Thus, more electrons are being "consumed" at the cathode than anode per second, creating a charge differential, which in turn generates a current.


texts: Any false chemical element in history of chemistry?

texts: Was there any false chemical element introduced in history of chemistry? I mean a substance that after a while proved that it was not an element.


texts: Is it possible to "dope" glass to change it's refractive index?

texts: For many purposes, like in the making of achromatic lens combinations, we need transparent media of different refractive indices. Let's assume I want a transparent medium of refractive index of 1.4, how would I go about getting such a material? Can I "dope" it by dissolve some impurities into molten glass mixture and then solidify it later? How would I choose my impurity to add? How do I calculate how much to add?


texts: How do you determine if a compound can go through addition polymerisation

texts: For a polymer to form from a monomer, the monomer requires open bonds to attach itself to another monomer. Logically for me, it requires a double bond so I would go for answer C. But can the benzene ring actually open up to undergo an addition polymerisation?


texts: Why isn't protium nucleus considered most stable nucleus?

texts:
My chemistry teacher told me that $\ce{^{56}Fe}$ is the most stable nucleus because of the highest binding energy per nucleon.
But if we consider a protium nucleus, it has only 1 proton so there is no chance of separation.
so why isn't protium considered the most stable nucleus?


texts: Change in standard Gibbs energy is always zero?

texts:
So I have this statement from our professor :

  We have $\Delta G^\circ = -RT\ln K$ and under standard conditions the activities of all substances in the reaction is $1$ ($a=1$), therefore $\Delta G^\circ > 0$.

I dont understand it.If every $a=1$, then $K = 1$ (as the division of activities) and thus $\ln K =0$ which would make $\Delta G^\circ = 0$ as well instead of $>0$,right?


texts:
$\ce{NaOH}$ solution can react with $\ce{CO2}$ to form sodium carbonate.
Is there any other reason why $\ce{NaOH}$ solutions for accurate titrations cannot be stored for long (or the titre has to be updated every time). Wouldn't filling the vessel with argon fix the problem.


texts: Will the carboxylate groups of the citrate anion undergo hydrogen bonding?

texts:
The citrate anion of trisodium citrate has three carboxylate groups. I am concerned with whether or not there will be hydrogen bonding in water, with hydroxyl groups of other ions or alcohols.

It has been suggested to me that the negative carboxylate oxygens won't hydrogen bond, due to resonance delocalisation of the charge. If it mattered whether or not the oxygen was partially charged, I would hypothesize that the oxygen is charged, because carbon has a lower electronegativity.
The oxygen should have two lone pairs, yet it has either been implied that they are not there, or for some reason that they will not interact in hydrogen bonding.

My question is: will the citrate anion hydrogen bond with other molecules or polymers with hydroxyl groups, in aqueous solution?

It has been made aware to me that there is an article that has done research to show that carboxylates are strong hydrogen bond acceptors in anhydrous solvents.


texts: Are there safe inks that allow one to eat a fish after painting it?

texts:
Just came across a specific type of art called Gyotaku where specific types of ink are used to paint over one side of a fish and then a paper (rice paper, shoji paper, ...) is placed on top in order to retrieve the fish impression. After the impression, the ink is removed with water.
As catching the fish just to print doesn't seem worthy, I am wondering if there there safe types of ink that let's one eat the fish afterwards? Will washing it fully remove the ink?
Is it safe to eat the fish if one uses acrylic paints?
What kind of inks should one avoid?

Edit
Here's a video of an artist painting a oni, washing the ink out and then eating it. It is not clear if the ink is absorbed by the fish before he eats it or not. He states that he uses water-based acrylic and that it is water soluble and washable.


texts: What is the purpose of the Carothers equation?

texts: I don't really understand the equation. I feel like it is simply demonstrating the kind of exponentiality characteristic for the step polymerization reactions, but it cannot be useful for actual calculations. I mean - according to the equation a system which has executed, let's say, a polymerization reaction with 99% conversion will have an average degree of polymerization of 100 even if the system has fewer than 100 monomers. Am I missing something?


texts: Oxymercuration demercuration, PCC, NaCN/HCl reaction

texts: In this reaction of the alkene, the correct answer is below but I don't understand why it goes to that. This is my thought process - reagents 1 and 2 do oxymercuration demercuration and makes a secondary alcohol, then reagent 3 turns the alcohol into a ketone, and finally reagent 4 and 5 performs nucleophilic addition and turns the alcohol into a tetrahedral with CN attached (my steps I drew below). What am I doing wrong here? Thanks


texts: Can i make a gel/liquid/any kind of solution which supports combustion but at the same time protect the surface from getting burnt? I wanted to light a log on fire using some kind of fuel which allows the gel/liquid/solution/fuel to burn but protect the actual log from undergoing charring


texts: Can the effect of resonance on acidity be generalised?

texts:
A basic trend for acid: if the conjugate base is more stable, then the acid has a lower $\ce{pKa}$. Therefore, it would quite intuitive to think that resonance in the conjugate base will make the acid more acidic.

e.g. Cyclohexanol  $\mathrm p K_\mathrm a$  -16 ; phenol  $\mathrm p K_\mathrm a$ -10

But, there are exceptions. For $\ce{H3PO4, H3PO3, H2PO2}$ the effect is reversed. There is a more spacious resonance in $\ce{H3PO4}$ than in $\ce{H3PO3}$. But, still $\mathrm p K_\mathrm a$ of the former acid is greater than the latter.

Edit: Mithoron commented that my claim about P acids isn't true. Though I don't what claim he is referring, I think even his linked question supports my claim of the order of $\mathrm p K_\mathrm a$ as $\ce{H3PO4>H3PO3>H3PO2}$

So, my question is : can the effect of resonance on acidity be generalised?


texts:
I was reading a paper and found this elemental XPS analysis of an unmodified microscope glass slide surface.

C (1s): 17.7%

Si (2p): 28.47%

O (1s): 53.83%

It seems strange for a piece of normal glass to have almost 20% of Carbon, since most of it is silicon dioxide and other metal oxides in smaller amounts.
I am not used to XPS analysis so there might be something I am overlooking (maybe adsorbed CO2 on the surface ?), can someone tell me if this is a normal result for an XPS analysis of glass, and if it is, where does the carbon come from?


texts: Why is it that benzene diazonium salts don't give the Lassaigne's test for nitrogen. After all they've got both carbon and nitrogen.


texts:
Consider the following reaction : $\ce{H2 + Cl2 -> 2HCl}$

A) If you have 15.00 liters of hydrogen reacting with 10.00 liters of chlorine at STP, how many liters of HCl would you produce?

B) What would be the limiting reagent?

C) How many moles of excess reagent would remain?

Please explain.

Molarity = moles/Liters
to check for $\ce{H2}$: M = 2/15.00 = .13334
to check for $\ce{Cl2}$: M = (35.45 x 2)/10.00 = 7.09

But I do not think that is correct. can somebody show me the correct way to do it.


texts: Are there any descent symmetry tables for character tables of linear structures?

texts:
I know about tables containing information about descending in symmetry, i.e. from larger point  groups to their sub-groups.

We can see such tables in this answer, or in this PDF.

My question is - does any similar table exist even for $C_{\infty v}$ and $D_{\infty h}$ point groups?


texts: Calculating the molar mass of a solute from freezing point

texts:
A $\pu{4.305 g}$ sample of a nonelectrolyte is dissolved in $\pu{105 g}$ of water. The solution freezes at $\pu{-1.23^\circ C}$. Calculate the molar mass of the solute. $k_f$ for water is $\pu{1.86 C/m}$.

My steps:

$$1.23 = 1.86 \times \frac{x}{1.05},$$

where $x = y / 4.305$.

$$0.66 = \frac{x}{1.05}$$
$$x = 0.69$$
$$0.69 = y / 4.305$$
$$y = \pu{2.989 g}$$

But I know this is not correct.


texts: How can change in Enthalpy for a reaction be written like this?

texts:
If a gas expands in a container with constant external pressure then:
$W=-P_{ext}\Delta V$
Instead of $P_{ext}$ if we use $P_{int}$ then we will not get the same value because  $P_{int}$ is constantly decreasing from a certain value until equilibrium is attained, while the change in volume remains the same.
This is the reason why we use $P_{ext}$ here:
$\Delta H= \Delta U +P_{ext} \Delta V$
But then, $\Delta H$ for a reaction is:
$\Delta H= \Delta U +\Delta n_{g}RT$ ($n_{g}$ is for change in number of gaseous moles as the solids and liquids are ignored)
where $PV=nRT$ is used. However, the $P$ in the ideal gas equation is $P_{int}$.
So my question is how can $P_{int}$ be substituted in the place of $P_{ext}$ if the values of work done change when we do so?


texts: Is it valid to use Gibbs Free Energy for gases?

texts:
This has confused me for a long time now. Why do we compute Gibbs free energy when we figure out the spontaneity of a reaction involving gases? In my mind, I envision a reaction involving gases to be always in a closed container, which would clearly change the pressure of the gas, but it seems to be that constant pressure is a requirement for using Gibbs free energy.

Now if it is that we are supposed to assume that the reaction involving gases does not occur in a closed container, why do we use molar concentration of gases when computing equilibrium constants? In this situation, it seems to be that volume of gases will change.

I'm suspecting that most of my confusion is on what constant pressure actually means in a reaction, so as a third question, what does constant pressure mean when we are referring to a reaction?


texts: How stable are surfaces functionalized with APTES?

texts:
I'm wondering specifically about magnetite micro particles functionalized/silanated with (3-aminopropyl)triethoxysaline (APTES), though I assume the stability would be the same for most surfaces.
By stability, I mean can the APTES "fall off" the surface over time or in extreme conditions (pH, temperature, pressure, etc.)?


texts: SN2 reactions and inversion of configuration in compounds with more than one chiral centre

texts: Suppose I have a compound with 2 chiral centres which are at (S,S). Now, suppose I have an iodine atom attached to the back carbon, and I wish to carry out an $\mathrm{S_N2}$ type substitution in a non-polar solvent. Obviously, the iodine atom would get replaced by the nucleophile, and there should be an inversion of configuration. But is this inversion only for the back carbon or the compound as a whole? Should the product have a configuration (R,S) or (R,R)? Someone please explain this to me briefly.


texts: I have read that before the preparation of ferric hydroxide sol, the beaker must be cleaned by the steaming out process, while it is not necessary for starch sol. Why is that?


texts: Chemical theory, formula(s) that predict final *volume* of a solution?

texts:
I asked this question a couple years back regarding the volume of a mixture being less than the volume of the original solute and solvent, but this question asks if there is theory and/or formulation that can predict what the final volume would be. And based on the answers from the last question I suspect there may be more than one answer depending on the nature of constituents (ionic vs molecular solution, etc.)

Furthermore in the case of ionic salts is there a theory/formulation that predict which saturated salt solution (e.g. a chloride, acetate, bromide, etc.) would result in the most efficient packing between water molecules (at the ame temperature).

Does such theory, formulation exist?


texts: Is Nitroglycerine a Nitro Compound or an Ester?

texts:
I looked up nitroglycerine in a science dictionary (Oxford Dictionary of Science, 2003), and it explicitly mentions that nitroglycerine is an ester and not a nitro compound.

However my teacher told us in class, that nitroglycerine is a nitro compound (She didn't say it wasn't an ester though …).

The definition for a nitro compound (courtesy Wikipedia) is:

  Nitro compounds are organic compounds that contain one or more nitro functional groups ($\ce{−NO2}$).

Assuming that definition is correct, as well and looking at the structure of nitroglycerine, it appears (to me) that nitroglycerine is both an ester and a nitro compound.

So who's right here?


texts: Mixing of molecular orbitals in polyatomic molecules

texts:
I am trying to solve the following Hamiltonian,$$H=-\frac{1}{2}\nabla^{2}-\sum_{i=1}^{10}\frac{1}{|\vec{r}-\vec{R_{i}}|}$$ Here $Z=1$ . To get all ther molecular orbitals of this system. I took the following linear combination to construct the hamiltonian matrix,$$\psi(\vec{r})=\sum_{i=1}^{10}c_{i}1s(\vec{r}-\vec{R_{i}})+\sum_{i=1}^{10}a_{i}2p_{x}(\vec{r}-\vec{R_{i}})+\sum_{i=1}^{10}b_{i}2p_{y}(\vec{r}-\vec{R_{i}})+\sum_{i=1}^{10}g_{i}2p_{z}(\vec{r}-\vec{R_{i}})$$

I took this wave functions and solved for $E$ using the following equation. Usually in polyatomic molecules, one would look for symmetry to construct various molecular atomic orbitals. However, here there is no symmetry. How do I get the molecular orbitals? What combination should I have taken to solve this problem. Please suggest some references where I can read the theory of molecular orbitals for polyatomic molecules with no symmetry


texts: Abiogenesis: Formation of Lipids from Montmorillonite

texts:
I have been really interested in scientific hypotheses regarding abiogenesis, particularly the lipid-world hypothesis. However, I could not find information on the chemical pathway that leads to the synthesis of amphiphilic molecules such as fatty-acids. All I've been able to find is that it involves the mineral montmorillonite which allows the step-wise formation of fatty acids using carbon monoxide (CO) and hydrogen (H). However, I want to know the exact chemical process. Thanks! Here's a link to a video explaining Abiogenesis.  Note: I simplified the Montmorillonite structure and only included the parts that were involved (mainly the very negative oxygen atoms)

My hypothesis is the following: If alkanes were present in the earth's oceans, polymerization of fatty acids could have occurred via chain radical addition. However I'm not sure where the initial radical would come from on the montmorillonite clay particle. Just an idea.


texts: How can Hydrogen NMR be used to distinguish between these two isomers?

texts:
I am having trouble explaining how and why the spectra of these two compounds would differ:

I am sure it has something to do with how the protons will couple. In the first isomer (left), the protons are anti-periplanar whereas in the second (right), I think they are staggered? So the first may be able to couple stronger than the second?


texts: How to know about radical character of a diradical molecule?

texts:
I understand that the radical character is quantified by the occupation number of the lowest unoccupied natural orbital obtained from UHF calculations or from CASSCF calculations.
My issue is that I already have an organic diradical whose ground state is high-spin state. In this case how can I quantify the radical character ?
Is there a way to know about the mixing percentage from higher spin states which in turn could give us information about the radical character of the molecule ?


texts: How do I neutralize 1.2 % muriatic acid (134.4 liters) residue with 99 % caustic soda flakes?

texts:
I cleaned my commercial water purification system with muriatic acid but I overdid it. Now there is excess muriatic acid residue. I used 6 liters of  29 % muriatic acid and further reduced with 33.6 gallons (134.4 liters) water as solvent at 1.2 % concentration of muriatic  hcl.I believe the mole for the solution is 3.29 moles, is that right?

I have  99 % caustic soda flakes that I can use to neutralize muriatic acid residue. How do I go about it? How do I mix caustic soda at the right amount to neutralize the muriatic acid residue?

I'm not a chemist or a student so  I would really, really appreciate your help guys. I'm on the verge of losing my small business if I don't fix this.


texts: Will room-temperature water in a sealed flask evaporate?

texts: Some liquid water is present inside a sealed flask at room temperature. Is water evaporating, and is the system at equilibrium? First of all, can water evaporate in a sealed flask at room temperature? If so, is the reaction happening a reversible reaction? Any help would be appreciated. Thanks.


texts: Can the "rate coefficient" of a chemical reaction really be called a "rate constant"?

texts:
Can the rate coefficient of a reaction ever be referred to as a constant? To my limited knowledge, it cannot, because it is dependent on factors such as temperature (I'm getting that info from the Arrhenius Equation).

I'm looking for clarification here.


texts:
I have about 2g of 99.5% Potassium.

I want to get rid of it, right now it's in a glass jar sealed.

What is the proper protocol? I was going to combust it in water and wash it down the drain but the by-product potassium hydroxide is caustic and hazardous so I don't think that's best.

Could I just throw it away and it goes to a garbage facility where the vial probably breaks and it reacts with rain water and the potassium hydroxide is so small and buried that it never really has an impact?


texts: Volume expansion from phosphate buffer solution

texts:
I want to mix a phosphate buffer at $\mathrm{pH\ 7.2}$ at $20~\mathrm{^\circ C}$. I do this by dissolving $0.0036\ \mathrm{mol}$ of sodium dihydrogen phosphate monohydrate ($\ce{NaH2PO4*H2O}$) and $0.0063\ \mathrm{mol}$ of di-sodium hydrogen phosphate dihydrate ($\ce{Na2HPO4*2H2O}$) in water per liter of buffer. I add $0.15~\mathrm{M}\ \ce{NaCl}$. How much water do I add if I want $1~\mathrm{L}$ of buffer? Do I just use $1~\mathrm{L}$ of water — will the salts not expand the volume? Is it insignificant and at what point do I need take into account the volume expansion of the solution?

Notes:

  $$M(\ce{NaH2PO4 . H2O}) = 137.99~\mathrm{g/mol} \Longrightarrow 137.99~\mathrm{g/mol} \times 0.0036~\mathrm{mol} = 0.496764~\mathrm{g}$$

  $$M(\ce{Na2HPO4 . 2 H2O}) = 177.99~\mathrm{g/mol} \Longrightarrow 177.99~\mathrm{g/mol} \times 0.0063~\mathrm{mol} = 1.121337~\mathrm{g}$$

  $$M(\ce{NaCl}) = 58.44\ \mathrm{g/mol} \Longrightarrow 58.44\ \mathrm{g/mol} \times 0.15~\mathrm{mol/L} = 8.766~\mathrm{g/L}$$


texts:
I did a google and chemistry.exchange search and found several technical definitions of the exchange correlation hole.

The questions that I want to proposes are:

What the exchange-correlation hole means in common words?
How do you explain it to a non-literate person?


texts: Why beta C w.r.t. the carbonyl group has the highest coefficient in the LUMO of acrolein?

texts:
I want to know the way, how to know which atom has greatest coefficient in a particular MO level in π-MO of a π conjugated system. I faced this problem when I was going through weak nucleophile attack in the beta C of Acrolein as they say that weak nucleophiles attack the beta carbon of acrolein because it has highest coefficient in the LUMO. But I wanna know how beta Carbon has highest coefficient in the LUMO of acrolein?
Is there any method by comparing the electronegativities of the atoms? I know the process to decide this in case of normal MO but I can not get it in π-Mo of π conjugated system.


texts: Oxidation to allylic alcohols without stoichiometric metal reagents

texts:
Common methods of oxidation of alkenes to allylic alcohols in one step usually use stoichiometric metal oxidants, e.g., sodium dichromate.
Without using this type of reagent, are the other methods typically peroxide forming,  requiring further chemistry to adjust to the allylic alcohol, e.g., allylic hydroperoxides or t-butyl peroxides, or are there more "direct" methods?


texts: Relation between thermodynamic reversible process and reversible reaction

texts: I know it seems to be a weird question. But for long I have been thinking whether there is any relation between thermodynamic reversible process and reversible reaction. Do they have any connection and if so how?


texts: How many covalent bonds are there in carbon suboxide?

texts:
Calculate the number of covalent bonds in $\ce{C3O2}$.

Structure:

I am confused. I can count covalent bonds as 8 by counting single-single bonds, but also I can say that there are 4 "double covalent bonds". Which is correct?


texts: Why is N2 enthalpy zero, entropy 191.5, yet G is listed as zero and not [-T*0.1915]?

texts:
In standard tables, $\ce{N2}$ at STP has an enthalpy formation ($\Delta H_\mathrm f$) listed as $0\ \mathrm{kJ/mol}$, entropy ($S$) as $0.1915\ \mathrm{kJ/K}$, and free energy of formation ($\Delta G_\mathrm f$) as $0\ \mathrm{kJ/mol}$.

If we use the std eq.: $\Delta G = \Delta H-T\cdot\Delta S$, I don't get zero with those numbers, obviously. (assuming STP and all that) But, $\Delta G$ is zero for nitrogen?

My initial thought is that $0.1915\ \mathrm{kJ/K}$ is not $\Delta S$ as required by the equation, but just $S$, so I need to figure out $\Delta S$ for $\ce{N2}$ and use that instead. Okay, that would make sense, but it doesn't follow for this example, which I see everywhere:

$$\ce{N2 + 3H2 -> 2NH3}$$

$\Delta H$ is calculated for the reaction using the appropriate $\Delta H_\mathrm f$

$\Delta S$ is calculated using the appropriate $S$ values (So $0.1915\ \mathrm{kJ/K}$ for $\ce{N2}$, not $0$)

Then they use these reaction $H$ and $S$ to get $\Delta G$

However, if I just use the $\Delta G$ values found in databases like the CRC Handbook (so $0$ for $\ce{N2}$), I don't get the same answer using $\Delta G_\mathrm r=\Delta G_\text{products}-\Delta G_\text{reactants}$

This is driving me nuts, I know I must be missing something simple here.


texts:
Is this the right chemical formula of the $\ce{Rb[Pt(NH3)Br2Cl]}$ complex: rubidium amminedibromidochloridoplatinate(II)?

And is it correct that it has geometric isomerism, being square planar with a cis- and trans-isomers, leaving the rubidium out?


texts: Considering the d-d transition how, does tetracyanidonickelate(II) ion exist as a colored complex?

texts:
As I refer on google, the resources indicated that,

  the d block elements which have unpaired electrons as in their ions, when they are making complexes with ligands, they can absorb different frequencies in the spectrum due to degenerated d-d orbital transition.

But I am confused in understanding how there is a colour for $\ce{[Ni(CN)4]^2-}$ complex.

My question is: In the $\ce{Ni (II)}$ ion there are two unpaired electrons in the d orbitals. But while they are hybridizing there aren't any unpaired electrons, all are paired. In the solution state, the nickel ions do not exist as $\ce{Ni^2+}$ ions, but rather as $\ce{[Ni(CN)4]^2-}$ ions. But $\ce{[Ni(CN)4]^2-}$ has no unpaired electron. So it is unable to absorb energy from the spectrum and transit between d orbitals. (My logic is that there are no more spot in d orbitals to transit between after the complex occur)

But as the image below this complex is yellow in colour.

I can't find the mistake in my logic. I referred to many resources but I wasn't able to find any satisfactory answer.


texts: Stereoselectivity of Roush crotylboration

texts:
One can use a tartrate derived boronate to enact enantioselective crotyl transfer. Eg in scheme below:

I do not understand how the stereoselectivity arises. We have a chiral boronate, true, and we have facial selectivity on addition to boron centre. But I don't understand why one face is selected over the other - With one ester group on the ring, I could see that would sterically block one face of the boron centre, but with 2 ester groups it seems that each side of the boron is equally blocked.


texts: Acid chlorides and reduction by hydrogenation

texts:
An acid chloride being reduced through catalytic hydrogenation is an "unobserved" event in the context of our class, according to my professor. Nonetheless, we are expected to predict that the hydrogenation occurs because acid chlorides are very reactive in general.

Now, this sounds like a case of the right answer with the wrong reason.

Yes, acid chlorides are reactive. We've covered their hydrolysis with water. We've covered their role in Friedel-Crafts acylation. We realize that the $\ce{C-Cl}$ bond in an acid chloride is very weak and that the carbonyl carbon is highly electrophilic. This gives rise to most of the reaction pathways with acid chlorides.

But what does catalytic hydrogenation have to do with the electrophilicity of the carbonyl carbon in an acid chloride? Nothing, in my mind. Hydrogen gas and platinum metal simply work here because the $\ce{C=O}$ part of the acid chloride is flat. I don't think it has anything to do with how reactive the acid chloride is. Right? Hell, even plain jane alkenes can be hydrogenated and they aren't exactly reactive.


texts: Why doesn't this structure represent a substituted pentane?

texts:
In the following ASCI structure (single bond under "$\ce{CH}$" containing $\ce{CH2,CH2, CH3}$)

$$
\begin{align*}
\ce{CH3-CH2-CH2-&CH-CH3}\\
&|\\
\ce{&CH2-CH2-CH3}
\end{align*}
$$

The correct way to name it is "4-methlyheptane".

But when I do it the way I have been taught I get the following "4-propylpentane".
Here are my systematic steps:

Firstly, I count the longest carbon chain. In this case its 5 carbons together so suffix -pentane. Then I look to see if there are any branched chains and number it from left to right. In this case the branched chain is on number 4. The branched chain contains $\ce{CH2-CH2-CH3}$, resp. $\ce{C3H7}$, aka propyl.

Ergo, 4-propylpentane, however, the correct answer as mentioned above is 4-methylheptane.

How is it 'heptane' ? The longest chain has FIVE carbons. I got the '4-' part correct, but how is $\ce{CH2-CH2-CH3}$ Methyl? Is this a mistake in my book?


texts: How to distinguish open-pored polymer foam and foam with closed pores?

texts:
I was looking at two foam materials, where I had expected one to have closed pores.

Unfourtunately, the microscope was showing the upper layer of cut cells the same in both cases with no indication of differences in lower levels of the material.

By now, I suspect both are open-pored;

Is the difference clearly defined?

If a block of soft material can sustand high pressure based on inner air pressure in cells, the cells are clearly closed.
If a visual inspection shows mostly incomplete cells, such that parts of cells behind them are visible, it's clearly open pored.
what about holding gas only at low outer forces?
Which is similar to the common kitchen sponge, keeping fluid with low pressure, releasing it at high pressure. But here, I expect the pores to be open, and capularry forces to get the water inside.

So, I'd like to know how to tell them appart based on actual mechanical features, and to understand the difference in case they are not trivial.


texts:
I notice that saliva seems to clean well, much better than plain water. For example, tar spots on the car can be difficult to get off. I typically use really powerful solvents to get them off, like 95% acetone and things like that. Yet, saliva works too.

Why is this?


texts:
(b) Nitration: Direct nitration of aniline yields tarry oxidation products in addition to the nitro derivatives. Moreover, in the strongly acidic medium, aniline is protonated to form the anilinium ion which is meta directing. That is why besides the ortho and para derivatives, significant amount of meta derivative is also formed.

Why there is more para-substituted nitroaniline formed than ortho-substituted one even though it can form hydrogen bonding?


texts: Why does increasing the temperature for a reaction at equillibrium cause the reaction to shift to the endorthermic side?

texts: Increasing the temperature would also increase the rate of the exothermic reaction, however what drives the molecules present in the system to choose the endorthermic pathway?


texts: Phosphorus does not form pπ-pπ bonds but how could it form dπ-pπ bonds?

texts:
My textbook says phosphorus cannot form pπ-pπ bonds because their atomic orbitals are so large and diffuse that they cannot have effective overlapping.

My doubt is then how does phosphorus form dπ-pπ bonds? I mean dπ-pπ bond is supposed to be more ineffective overlapping. If pπ-pπ cannot happen then how does dπ-pπ happen?


texts: How does optimizing the molecular orbital coefficients in CASSCF improve its multi-reference capabilties?

texts:
The complete active space self-consistent field (CASSCF) method is a special kind of multi-configurational SCF procedure, attempting to combine Hartree-Fock (HF) and configuration interaction (CI). In HF, the molecular orbital (MO) expansion coefficients are varied during the procedure, but the wave function contains just one Slater determinant. In CI, the multielectron determinant expansion coeffcients are varied, but the MO's used to build the excited Slater determinants are taken from HF, and are not varied during the energy-minimization.
During CASSCF, on the other hand, all MO expansion coefficients are optimized during the energy-minimization procedure, in addition to the multielectron expansion coefficients.

CI is able to recover the dynamical correlation of the system (configuration with large weight, many configurations with small weight), whereas (properly selected) CASSCF recovers the static correlation of the system (a few configurations with about the same weight, many configurations with small weight). By having a wave function that have some configurations with about the same weight, means that the wave function has some multi-reference character. I think that it is the MO optimization that leads to this multi-reference capabilities of CASSCF, but I'm not sure I understand why.

If can be shown mathematically, instead of just by concepts, that would be great.


texts: How to measure purity of nitrogen gas in a "homemade" way?

texts: Is there any indicator or a way of measuring purity of nitrogen? The lab-way of doing things is out of my reach and I was thinking about a DIY way. I want to decrease oxidising atmosphere in a container by introducing $\ce{N2}$ but I am not sure about the purity of it.


texts: How to turn acetaldehyde into acetic acid using one of the five chemicals on the list?

texts:
From the Russian State Chemistry Test:

It's easy to see $X$ is $\ce{H2O}$: water turns acetylene into acetaldehyde.

But what can turn acetaldehyde into acetic acid?

I checked: $\ce{NaOH}$ would turn it into sodium acetate, $\ce{CuO}$ would not react (you'd need $\ce{Cu(OH)2}$), ethanol would turn it into either an acetal or hemiacetal.

Would acetaldehyde react with formic acid to produce acetic acid? I tried to google for it, and found no mention.

Would water in the presence of a heat source somehow react with acetaldehyde? I googled and discovered that it might form hydrates, not acetic acid.

So I'm at a loss. If you consider the question too easy, you could give just a hint.


texts: How to calculate the i-value of known NaCl solution, if it is isotonic with known solution of glucose?

texts:
How do I calculate the value of $i$ for 1.17% solution of $\ce{NaCl}$, if it is isotonic with 7.2% solution of glucose?

I actually do not know where to start in this question.
is it possible to calculate the value of $i$ of $\ce{NaCl}$? is value of $i$ of glucose 1? I tried putting the osmotic pressures equal but the value of $i$ remains a suspense.


texts: Why does a mixture of siloxene and cerium(IV) sulfate luminesce?

texts:
I performed an experiment where siloxene and cerium(IV) sulphate were mixed together: when I did so  the mixture produced an orange-yellow glow. Why does it glow? What is it about the two chemicals in particular that makes this happen?

Method for synthesising siloxene:

Carefully measure out 50 cm3 of concentrated hydrochloric acid into a 100 cm3 measuring cylinder. Put the acid in a 1 dm3 beaker containing a magnetic stirrer bar and place the beaker on a heater/magnetic stirrer.
Switch on the stirrer and slowly add 5 g of calcium silicide, one spatula measure at a time, to the stirred acid. Continue stirring the mixture until the reaction subsides.
Measure out a further 25 cm3 of concentrated hydrochloric acid and carefully add this to the stirred mixture. Now turn the heater on and heat the mixture to boiling. Boil the mixture for five minutes. After boiling, slowly add 150 cm3 of distilled water then boil again for approximately five minutes.
Switch off the heater and leave the mixture stirring while it cools.
Set up a Buchner funnel and flask in a fume cupboard.
Carefully pour the yellow siloxene that you have made onto a filter paper in a Buchner funnel (try to leave the unreacted grey/black solid calcium silicide in the beaker). Now wash your sample of siloxene – first with 10 cm3 of ethanol and then with 10 cm3 of ethoxyethane. Drawing air through the sample will help to dry the yellow, solid siloxene.

Method for producing the glow:

Place 0.8 g of siloxene and 75 cm3 of 1M sulfuric acid in a 250 cm3 conical flask. In a second 250 cm3 conical flask, dissolve the 0.5 g of cerium(IV) sulphate in 75 cm3 of 1M sulphuric acid. Label and stopper both flasks.
Go into a dark room. Turn out the light, add the cerium(IV) sulphate to the siloxene and swirl the mixture. You should see a fairly bright orange-yellow glow.


texts: What can be used to thionate a monosubstituted urea?

texts: I'm looking to make a thiourea from a monosubstituted urea. I haven't found any references that use Lawesson's Reagent, which I have been using for the thionation of di and trisubstituted ureas. Is there something that would prevent Lawesson's Reagent from working on a monosubstituted urea?


texts: What is the proper use of the term "pi-donor ligand"?

texts:
Robert Crabtree's The Organometallic Chemistry of the Transition Metals (7e) describes a pi-donor ligand as being a pi-donor "as a result of the lone pairs that are left after one lone pair has formed the M-L sigma bond". This, of course, makes sense, and the author goes on to explain that this pi-donation is a destabilizing effect.
Later in the chapter, he goes on to call ethylene a pi-donor because it forms the primary M-L pi-bond via the donation of pi-electrons. Of course, I understand that both types of ligands described are technically donating pi-electrons, but I find it very confusing that the term pi-donor is used to describe two entierly different ligand effects -- one that is not the primary bond and destabilizes the M-L bonding interaction and one that is the actually M-L bonding interaction.
My question is wheather or not there are better terms for differentiating the primary bonding and the secondary interactions. For example, I find it confusing to call ethylene a "pi-donor and pi-acceptor ligand" since forms its primary bond through pi-donation and back bonds via pi-acceptance.


texts: Why is incubation in dark place necessary?

texts: While estimating the  total protein through Lowry method one needs to incubate the test tubes in dark once after adding alkaline solution and once after Folin-ciocalteu solution. My teacher said it is necessary for proper colour development. But I am curious to know what is the chemistry behind it?


texts: Can we compare the vapour pressure of solutions whose concentrations and temperature is known?

texts:
If we have some solutions, in which we know the temperature and concentration of the solute particles, can we compare their vapour pressures?

Original question:

Which solution has the highest vapour pressure among the following?
a) $0.02 ~\pu M ~\ce{NaCl}$ at $50^{\circ}$C b) $0.03 ~\pu{M}$ sucrose at $15^{\circ}$C  c) $0.005 ~\pu{M} ~\ce{CaCl_2}$ at $50^{\circ}$C d)$0.005~ \pu{M} ~ \ce{CaCl_2}$ at $25^{\circ}$C

I answered this question by noting that at higher temperature and lower concentration, vapour pressure of solution should be the highest because more temperature implies more kinetic energy which means more volatility and low concentration means that the solute is less solvated so it forms less bonds with the solvent and therefore has more vapour pressure, so answer is c). Is this reasoning correct?
Now I think that these options were set so that it becomes easy to compare.
But what if I had options like $0.02 ~\pu M ~\ce{NaCl}$ at $50^{\circ}$C ,$0.03 ~\pu M~ \ce{NaCl}$ at $60^{\circ}$C,  $0.005 ~\pu M
~\ce{CaCl_2}$ at $20^{\circ}$ C, how shall we compare their vapour pressures without doing experiments?
Now, if there existed a relation between vapour pressure and concentratin or temperature, it would become easier.
For example, relation between vapour pressure and temperature can be given by Antoine equation, but I want something that also incorporates the concentration in the equation also, so that by plugging in the values, it is easy to compare.
I am also not sure, whether van't hoff factor will have a role in it or not.


texts: Why are esters meta directors? Can't the carbonyl donate electrons into the ring?

texts:
I'm having trouble understanding why an ester is a meta directing/deactivating group.

I'm not talking about an ester with its oxygen bound to the ring, like an acylated phenol. I mean the R group is bound to the ring and the alkoxy group is bound only to the carbonyl carbon.

It seems to me like the pi electrons in the carbonyl pi bond could be pushed down and delocalized into the ring. Why is this not possible?


texts: How can a detergent "designed for sensitive skin" warrant the "corrosive" hazard symbol?

texts:
The dish-washing detergent, which you can find an image of here, has the following hazard symbol on its back:

On the back, it additionally says that if it comes in contact with the skin, you should immediately wash with lots of water, however the detergent also says "specifically developed for sensitive skin" on the front.
How can these two statements make any sense together? Are the chemical regulations that it has to follow just too on-the-safe-side, or what is going on? If I google up its safety data sheet in my local language, it contains the following phrasing:

When handling chemical products, chemical resistant, impervious gloves complying with an approved standard should be used at all times if a risk assessment indicates the need for. (translated from Danish)

It also contains:

Personal protective equipment for the body should be selected on the basis of the task to be performed and the risks involved and should be approved by a specialist before handling this product. (translated from Danish)

So my question is, why does a product like dish-washing detergent that is developed for sensitive skin need these kinds of warnings?
Edit: Image of the back can be found here.


texts: Is constant pressure heat capacity = entropy during adiabatic reversible expansion of perfect gas?

texts:
For any process, ∆G = ∆H - ∆(TS).

Apply this on reversible adiabatic expansion of perfect gas, since the entropy of system does not change during this process, S is constant so

∆G = ∆H - S∆T

The process is reversible, so

∆G = 0

and hence

∆H = S∆T

For perfect gas, assume heat capacity independent of temperature,

∆H = Cp∆T

and so

Cp∆T = S∆T.

∆T is not zero during adiabatic reversible expansion- temperature drops. So divide both sides by ∆T gives

Cp = S

Is this legit? If not where is my mistake? I have a hunch that I did something terribly stupid. The final result seems to be so counter-intuitive because

The Cp and S are constant throughout the process, so at the end of the process the two will still be the same. By measuring Cp, even though your system is not doing adiabatic reversible expansion, you will get S. So we are able to measure S?


texts:
Question
  How do I found out how much $\ce{AgNO3}$ can be dissolved in 1 liter of solvent without precipitation of $\ce{AgCl}$.
  Solvent has $$M_{\ce{\,Cl-}} = 0.1\,{\rm M}\\M_{\ce{\,NH3}} = {\rm 1.00\,M}$$
  Other given values are $$K_{\text{sp}_{\Large\ce{AgCl(s)}}} = 1.8\times 10^{-10}\\K_{\mathrm{f}_{\Large\ce{[Ag(NH3)2]+}}} = 1.6 \times 10^7$$
  Answer: $4.4\rm\,g$

My effort:
 Firstly I tried to find out $\ce{[Ag]}$ in saturated solution from eq.

$$K_{sp_{\Large\ce{AgCl}}} = \ce{[Ag][Cl]} 1.8 \times 10^{-10} = [\ce{Ag}] \times 0.1{\rm\,M}\times [\ce{Ag}] = 1.8 \times 10 -9$$

Then I placed that value in formation eq.

$$K_f = \frac{\ce{[Ag(NH3)2]+}}{\ce{[Ag] * [NH3]^2}}$$

$$1.6 \times 10^7 = \frac{x}{(1.8\times10^{-9} \times 1.0{\rm\,M}-2)}$$

$$x = 0.0288\,\rm M$$

and tried to find out $\ce{AgNO3}$ mass by using that by

$$m~\ce{AgNO3} = 0.0288\rm\,M \times 1.0 {\rm\,dm^3} \times 169.9 \frac{g}{mol} = 4.89\,\rm g$$

That value doesn't seem to be the answer. What did I do wrong?


texts: I have acquired the crushed magnet out of a motor I was given. If I'm correct that the magnet is $\ce{NdFeB}$ magnet, how could I separate out all the metals into a pure or oxide form? And for hard drive magnets, is there any way to remove the $\ce{Ni}$ coating without having to get nitric acid?  I don't have any proper chemistry equipment at all.


texts: How can molecular mass be calculated from vapour density?

texts:
An organic compound contains 71.7% carbon, 6.7% hydrogen, 10.4% nitrogen and 11.8% oxygen by mass. Given that its vapour density is 67.5, determine its empirical formula and molecular formula.

From the mass percentages, I have found out that the empirical formula is $\ce{C8H9NO}$. However, to find the molecular formula we usually require the molecular mass.

What does "vapour density" mean, and how can I use it to calculate the molecular mass of the compound?


texts: Why do elements in columns 6 and 11 assume 'abnormal' electron configurations?

texts:
When I look around for why copper and chromium only have one electron in their outermost s orbital and 5/10 in their outermost d orbital, I'm bombarded with the fact that they are more stable with a half or completely filled d orbital, so the final electron enters that orbital instead of the 'usual' s orbital.

What I'm really looking for is why the d orbital is more stable this way. I assume it has to do with distributing the negative charge of the electrons as evenly as possible around the nucleus since each orbital of the d subshell is in a slightly different location, leading to a more positive charge in the last empty or half-filled d orbital. Putting the final electron in the s orbital would create a more negative charge around the atom as a whole, but still leave that positive spot empty.

Why does this not happen with the other columns as well? Does this extra stability work with all half or completely filled orbitals, except columns 6 and 11 are the only cases where the difference is strong enough to 'pull' an electron from the s orbital? It seems like fluorine would have a tendency to do do this as well, so I suppose the positive gap left in the unfilled p orbital isn't strong enough to remove an electron from the lower 2s orbital.


texts: Protoporphirinogen IX formation in Heme synthesis

texts:
This picture shows one of the step of heme synthesis. In this step, two propanoate groups of Coproporhyrinogen III are decarboxylated to from protoporphyrinogen IX. The enzyme used is oxidase. Oxidase enzymes catalyze the removal of hydrogen in the presence of oxygen to from water or hydrogen peroxide.

So, will a water molecule form in this step. 2H+ will come from the two carboxylic groups and oxygen will combine with it to form water. Will water molecule form in this way?


texts: Electron configurations for d-block and p-block

texts:
Question 1: Why is it that when you get to the transition metals (or the d-block), the energy of the $\ce{3d}$ orbitals becomes slightly less than that of $\ce{4s}$, making $\ce{4s}$ have the electrons with the most energy?

Also, is it correct to write electron configurations for transition metals with the $\ce{4s}$ orbital being the outermost one? For example like this $\ce{Sc = 1s^2 2s^2 2p^6 3s^2 3p^6 3d^1 4s^2}$ instead of this $\ce{Sc = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^1}$

Question 2: If my first thought is true, then do you write electron configurations for the p-block just like the d-block, with the $\ce{4s}$ orbital being the outermost one? Or do you follow the regular pattern of letting the $\ce{3d}$ block comes after the $\ce{4d}$ block?

For example, would it be like this $\ce{Ga = 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^10 4p^1}$ or would it be like this $\ce{Ga = 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^1}$

According to google, if you search up "scandium electron configuration" it would say my first one). If you search up "gallium electron configuration", you would see my second one)


texts:
In class we had been taught that Rutherford's model was unsuccessful because it failed to show that the orbits are stable because the electrons would lose energy because of electromagnetic radiation.

Bohr had suggested that electrons would move in orbits having well defined energy levels, but my question is that what would prevent these electrons from emitting radiation and collapsing into the nucleus.


texts: How do delocalized π electrons satisfactorily fill π orbitals?

texts:
The above example is benzene.

Only six electrons contribute to the 6 π  bonds and pπ  orbitals. Normally, an orbital requires two electrons to satisfactorily "fill" it. I don't understand how this rule is not abided yet bezene is still considered a stable molecule.

Am I to understand that a single electron can be shared by 6 orbitals simultaneously? Do all 6 π orbitals completely spread out amongst each other to each this?


texts: Why would a polar protic solvent favor the addition of HBr to an alkene?

texts:
I understand that a polar solvent will help dissociate the $\ce{HBr}$ into ions.
But why a protic solvent?
Why would we want a solvent that would encage the $\ce{Br}$ and $\ce{H}$ ions?
Why is the aprotic solvent not favored? My textbook does not discuss this and I searched online, with no result.


texts: How can we determine how many delocalised electrons every atom of gold contributes to the 'sea of delocalised electrons'? More generally, how can we determine the number of electrons any metal contributes? Must we have thermodynamic data to determine this?


texts: Transition metals have a half filled s band in their metallic states

texts: I was reading this "Chemical bonding at surfaces and interfaces" book. Here in page 69, they argued that interactions of transition metals to s band of adsorbate would be same because transition metals have half filled s band at their metallic state. My confusion is in electronic arrangement of transition metals I am seeing $s^2$ except for atoms having $d^5$ or $d^{10}$. Even $d^{10}$ is actually d block metals not transition metals. What could be the possible explanation of this line?


texts: Is there a substance I can use to coat a projectile to eliminate friction heat?

texts:
Let's say that I was going to shoot a can of beer into space from one of those "vacuum cannons." I would expect that the friction with the air around the projectile would cause the whole thing to just melt and burn (explode).

Is there such a substance that, if used to coat the projectile of my contraption, would eliminate the heat problem by basically "consuming the heat in a reaction" on the way out of the atmosphere?


texts: Is it possible to measure pH without physically coming into contact with a solution?

texts:
I've been researching ocean acidification, and the way that ocean pH is typically measured is by using sensors placed throughout all of the oceans. This is costly and time-consuming, and being able to measure ocean pH from space would be much more efficient as a global map could be created in a relatively short time and updated regularly.

However, when I researched pH measurement techniques, they all involve an instrument physically touching a solution, which would obviously not be possible from space. Ocean pH maps that have been created using satellite data measure pH indirectly by measuring ocean salinity, temperature, and other conditions, and they point out areas where it is "likely" that pH levels are low enough to harm ocean life. Is is possible to directly measure pH from a large distance? Would it be necessary to do so, that is to say, is measuring ocean pH levels indirectly accurate enough for environmental monitoring?


texts: Is there a general term for a vertex in a skeletal formula?

texts: When a carbon atom is single bonded to a residue, it is referred to simply as "methyl." When it is single bonded to two attachments, it is methanediyl, or methylene bridge. When it is single bonded to one atom and double bonded to another, it is called methine. Is there a generic term for the class of single-carbon-atom groups of the form  $\ce{CH$_n$}$, or to an unmarked vertex in a skeletal formula with sufficiently many hydrogen atoms to satisfy valence?


texts: Variations in protonation in reaction mechanisms

texts:
English and German Wikipedia give slightly different mechanisms on Fischer indole synthesis. The thing bugging me is the protonation of N and the source of the proton.

Look at the intermediates 8 (Ger) and 5 (Eng). In the German Wikipedia imines are not protonated, in the English they are. Or look at intermediates 10/11 (Ger) and 7 (Eng) - protonation occurs but on different N-atoms of the aminoacetal. Ammonia won't leave the molecule unless it is previously protonated, but how important is protonation in other steps? Aren't those molecules in an equilibrium with all their protonation variations anyway?
And so does the reaction mechanism even specify the source of the proton? Do specific steps take a proton from the molecule, whereas other steps take it from the surroundings? I always thought the molecule simply grabs the most available proton (the closest and "loosest" one).

German Wikipedia:

English Wikipedia:


texts: Nomenclature of an alkyne with bromo and hydroxy substituents

texts:
Is the IUPAC name of above compound 7,7-dibromo oct-5-yn-4-ol or 2,2 dibromo oct-3-yn-5-ol ?
I understand that the former name is given keeping in mind -OH as the functional group but by giving the latter name we will have the least sum of locants (ie, following lowest sum rule) .
When should the lowest sum rule be dropped ?
Thank You in advance.


texts: How does the Wurtz reaction produce alkynes?

texts: Wikipedia mentions that alkynes can be produced from geminal dihalides through the Wurtz reaction. However, I am unsure of the reaction mechanism for this reaction. I have not been able to find any sources which show the mechanism for this reaction. Does anyone have any idea how the reaction is likely to occur?


texts: Naming of bicyclo[2.2.1]hept-5-ene-1,4,5,6-tetramethyl-3-bromo-2-ethyl carboxylate

texts:
I've synthesized a molecule (depicted above) using a Diels-Alder reaction, and I can't find it in any database (I used scifinder for my search), so I need advice about the name.

The name I came up with, based on similar structures is bicyclo[2.2.1]hept-5-ene-1,4,5,6-tetramethyl-3-bromo-2-ethyl carboxylate. Is that correct?


texts: How do I calculate the cell voltage using the following half-reactions and solubility products?

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The concentrations of $\ce{NaCl}$ and $\ce{KI}$ are at $\pu{0.120 M}$ and $\pu{0.090 M}$, respectively, in the following electrochemical cell:

$$\ce{Cu_{(s)}|CuI_{(s)}|I^{–}_{(aq)}||Cl^{–}_{(aq)}| AgCl_{(s)}|Ag_{(s)}}$$

How do I calculate the cell voltage using the following half-reactions:

\begin{align}
\ce{Cu+ + e- &<=> Cu(s) & E^\circ &= \pu{0.518 V}} \\
\ce{Ag+ + e- &<=> Ag(s) & E^\circ &= \pu{0.7993 V}}
\end{align}

The solubility products $(K_{sp})$ for $\ce{AgCl}$ and $\ce{CuI}$ are $\pu{1.8e–10}$ and $\pu{1.0e-12}$, respectively.


texts:
I have been reading a book titled "High Voltage Engineering". It seems to me that in this book it is considered that in a gas when they collide an electron with a molecule, the molecule is stationary and the electron is not. This is because the $v_\text{molecule} \ll v_\text{electron}$.

What do you think about this?


texts: Difference between sodium ion and a transition metal ion dissolving in water?

texts:
In class, I learned that when $\ce{NaCl}$ is dissolved in water, the partially negative oxygen part of the water molecules surround the $\ce{Na+}$ ion and energy is given off (hydration enthalpy)

Likewise, when a transition metal ion like $\ce{Fe^2+}$ is dissolved in water, water molecules surround the ion. However, in this case, we say that a complex ion is formed.

Can someone please tell if there is really a difference in the two cases and if yes, could someone specify them.


texts:
I’ve found 4H‐1,4‐oxazocine in my chemistry book and I’m perplex as it states as aromatic:

I can count 6 electrons on p orbitals which could satisfy Hückel’s $n = 1,$ but the oxygen is sp3-hybridized. Even if we’d consider one lone pair as one sp2-bonding, the second lone pair would add 2 electrons to the p system, counting a total of 8 electrons, which doesn’t satisfy Hückel’s rule.