texts:
"Which oxidizing agent is more powerful" seems to depend on what is getting oxidized.

Consider for example oxygen vs chlorine. It is my understanding that chlorine is the more powerful agent for oxidizing sodium metal. The enthalpy of formation of sodium chloride is almost twice as negative as the oxide on a per-sodium atom basis (about -400 vs -200 kJ/mol Na).
However, if we are oxidizing hydrogen the picture reverses. Assuming everything stays in the gas phase and below about 600C at atmospheric pressure (see here) the equilibrium favors H2O rather than HCl.

It seems that when we are talking about dilute aqueous solutions we can define oxidant power based on standard electrode potentials, but when we generalize this concept (even if we standardize temperature and concentrations/partial pressures) there is no "right" answer unless we define a standard set of reducing agents to compare to. Is this correct?


texts:
I have a question about interpreting .SKF files, I am using these parameters to model defective graphene,

when I use parameter set given by dftbBaby/C-C (I think this is from Hotbit)
or the parameter set given by the following paper:

Porezag, D., Frauenheim, T., Köhler, T., Seifert, G., & Kaschner, R. (1995). Construction of tight-binding-like potentials on the basis of density-functional theory: Application to carbon. Physical Review B, 51(19), 12947.

(both of which give approximately $H_{pp\pi} ~ -3 eV$ at ~1.4 Angstrom) then after performing slater-koster transformations and embedding the H0 and S values into the secular equation, I get the correct band structure.

however, for other parameterizations, for example say dftb/mio, the value I get for $H_{pp\pi}$ from interpolation of hopping integrals is much smaller ~ 2eV and gives wrong band structure:

here for sure it is me who is doing sth wrong because using the same parameter set DFTB+ gives the correct band structure,

I am not sure whether I am not interpreting the SKF files properly (in a naive attempt the band structure can be corrected by increasing the value of r0 given in the SKF file which is equal to shifting the curves downwards) or is there any other step I need to perform before embedding the H and S values into the secular equation ?

Thank you for your help


texts:
In reduction of carbonyls (aldehyde and ketones) to alcohols using NaBH4/Methanol, alkoxides are formed with the Boron which usually gets protonated on addition of water/acid.

My question is what is the function of methanol in this reaction as methanol reacts with NaBH4 to form sodiumtetramethoxyborate and hydrogen gas.

Some sources say methanol protonates the alkoxide ion and after doing series of reduction experiments I find that the alkoxide formed only gets protonated to an alcohol on addition of water.

So what does methanol do in this reaction/what is the effect of methanol?


texts: Gallium - Practical use to remove aluminium

texts:
Would gallium pass through aluminium into steel?

The situation is two joined pieces of metal.

Gallium could be applied to the aluminium to degrade it, for mechanical removal, but would it pass through to attack the steel beneath or remain within the aluminium?


texts: Effects of a non-inert electrode in a half cell reaction involving hydrogen gas as the electrolyte ion

texts:
If there was a galvanic cell that had a copper cathode electrode and with a sulfuric acid electrolyte, will the copper ions be reduced and react with the electrolyte or will the H+ ions be reduced?

Normally, with a gaseous electrolyte, an inert anode material is used. I was just curious as to what happens when copper is used as supposed to an inert electrode.


texts: How to derive van 't Hoff equation for Henry's law constant?

texts:
While studying about Henry's law, I encountered this equation:
$$\frac{\mathrm d\ln H}{\mathrm d(1/T)}= \frac{-\Delta_\text{sol}H }{R},$$
where $\displaystyle\mathrm d(1/T) = -\frac{\mathrm dT}{T^2}$ and the $\displaystyle\frac{\Delta H}{RT^2}$ reminds me of some kind of $\Delta G$ equation.
I didn't know how to derive it, so I searched about it and got nothing. I tried to substitute $H$ (Henry's law constant) by $\gamma\cdot f_i$ where $\gamma$ is the activity coefficient at infinite dilution and $f_i$ is the fugacity of pure species.
But still I have no idea what to do to obtain the formula that I'm familiar with, so I welcome any idea about how to derive or how to reverse engineer the formula.


texts:
Does the water molecules in coordinated water (where water acts as ligand) form hydrogen bonding with other complex molecules? Will the water molecules inside the complex form intramolecular hydrogen bonds?
Consider the examples coordinated water and hydrogen bonded water molecules like $\ce{[Cr(H2O)6]^3+}$ and $\ce{CuSO4.5H2O}$.


texts: Mechanistic Explanation of Circular Dichroism

texts:
I'm wondering if someone can give me a physically motivated reason for why chiral molecules interact with left and right circularly polarized light (LCP) (RCP) differently. Particularly, a quantum mechanical view of what's happening here.

I understand why it is that a molecule has to be chiral in order for it to manifest circular dichroism (my use of terminology may not be perfect here so I apologize). That is, both the electric and magnetic dipole operators must be non-zero and there's an argument here on the basis of point groups.

Nothing about that, however, is particularly illuminating when it comes to understanding why I should expect a molecule to interact differently with LCP and RCP light.

I don't know what else I can even say. A good answer would address the different behavior of both the light and the molecule in these different situations, as I imagine that's a necessary piece to the puzzle.

Also, if one has some references (a review or textbook chapter etc.) that would be appreciated.


texts:
Which one has higher priority according to Cahn–Ingold–Prelog rules?
(1) $\ce{-CH2OH}$ and $\ce{-CH=CH2}$
(2) $\ce{-CH2OH}$ and $\ce{-C(CH3)3}$

The answer says $\ce{-CH=CH2}$ has higher priority, but I don't understand why.
Shouldn't the first one have higher priority since oxygen has a greater atomic number than carbon?
Same for the second question as well.


texts:
If I connect a zinc half cell (Left hand side) and a copper half cell (right hand side), I get an E cell value of 1.1V taken from the voltmeter. If I replace the voltmeter with a light bulb, I will get light and heat energy of the bulb.

I learned that the above set up is equivalent to adding Zinc to copper sulphate solution. However, in this case, there is no wire for the electron to flow...

MY QUESTION:

1.Then, where does the energy go when I add Zinc to copper sulphate solution (that in the first scenario I converted to electrical energy)? Is it released as heat?

2.As the electrons flow from the Zinc half cell to the copper half cell through the light bulb, will the voltage between the electrodes decrease as the charges on the electrodes are supposed to decrease. Then what would the formula for total energy released be?

Please correct me if any of my concepts are wrong. Thanks in advance.


texts: What is the point of using molality when we have molarity?

texts: Molality and molarity are both concentration terms. Given molarity's popularity molality seems rather antiquated.  Why is molality still discused in modern chemistry classes?


texts:
Is it necessary to consider common ion effect when suppose a strong acid like HCl is added to water?

For example in this question: 10 mL of $10^{-6 } \ce{mol/L \ HCl}$ solution is mixed with 90 mL of $\ce{H2O}$. pH will change approximately?
Normally by using $SV=constant$ I get pH will change by 1 unit (without taking common ion effect).

How will common ion effect affect the answer? Help.


texts: Explanation of calculating equilibrium constant

texts:
Hydrogen iodide is a colourless gas that will decompose into colourless hydrogen gas and purple iodine gas according to the following endothermic reaction.

  $$\ce{2 HI (g) <=> H2 (g) + I2 (g)}$$

  A $\pu{1.0 L}$ glass container was filled with $\pu{0.60 mol}$ of hydrogen iodide gas. When equilibrium was established, there were $\pu{0.25 mol}$ of iodine gas present in the container. Calculate the equilibrium constant for this reaction.
  $$
\begin{array}{|c|c|c|c|}\hline
&\ce{HI}&\ce{H2}&\ce{I2}\\\hline
\text{Initial}&0.60&0&0\\\hline
\text{Used/made}&0.50&0.25&0.25\\\hline
\text{Equilibrium}&0.10&0.25&0.25\\\hline
\end{array}
$$
  $$K=\frac{[\ce{H2}][\ce{I2}]}{[\ce{HI}]^2}=\frac{0.25\times0.25}{0.10^2}=6.25$$

This is what I understand:

Product always goes on the top, reactant on bottom
Balancing coefficients eg $\ce{2HI}$ become powers $\ce{-> HI^2}$
Initially, 0.6 moles of hydrogen iodide gas was placed, then at equilibrium 0.25 moles of iodine gas.
If there was 0.25 moles of iodine gas, there has to be 0.25 moles of hydrogen gas aswell thus the top part of the fraction becomes $0.25 \times 0.25$
I have no idea where the 0.1 moles come from …

I don't want to 'understand' these as much as I just want to be able to do them.


texts: Why do lithium and sodium corrode so easily?

texts: I want to know what is the phenomenon and explanation behind this corrosion. What is the reaction?


texts: What can one learn from a plot of calculated molecular orbitals?

texts:
What can one learn from the plots of the various iso-probability surfaces/orbitals of a given molecule/system? Can any predictions be made about bonding or kinetics by looking at these plots? Can an absorption spectrum be extracted from it? etc.

(I am aware this is a broad question, and a quick bullet list would suffice)

For example:

  Energy diagram of the molecular orbitals explored for the D6h
  structure (left) and the D3h distorted geometry (right) (source)


texts: Does the number of H+ ions in solution go up on dilution of a weak acid?

texts:
In my textbook, a footnote says:

  In case of weak acids, on dilution the total number of $\ce{H^{+}}$ ions in solution increases because dissociation of the weak acid increases

This didn't make sense to me however. Consider the general dissociation reaction of a weak acid:

$$\ce{HA (aq)  + H_2O \rightleftharpoons H_3O^{+} (aq) + A^{-}(aq)}$$

Now, the Chatelier's principle tells us that if we add more reactants ($\ce{H_2O}$), the reaction will proceed more to the right, and so the dissociation of the acid will increase, but the part about the total number of $\ce{H^{+}}$ ions in water being higher was still unclear to me.

Delving into the math a bit, we can see that

$$K_a = \frac{[\ce{H_3O^{+}}][\ce{A^{-}}]}{[\ce{HA}]}$$

Since the concentrations of the two products are equal,

$$[\ce{H_3O^{+}}] = \sqrt{[\ce{HA}]\cdot K_a}$$

Now, let us assume that we have a $1 \ M$ solution of the acid in question dissolved in 1 litre of water, plugging this into the equation, we have a $\sqrt{K_a}$ molar solution of $H^{+}$ ions. Since only 1 litre of solvent is there, we have $\sqrt{K_a}$ moles of ions.

Now, say we dump 1 litre of water into this solution. The concentration of our acid will be halved. Plugging this into the equation, we get the concentration of $\ce{H_3O^{+}}$ ions as approx. $0.7 \sqrt{K_a} \ M$. We have two litres of solvent, so we have $1.4 \sqrt{K_a}$ moles of ions, which is considerably higher. So, the numbers all work out, but what's the intuition behind it?


texts: Why does the beryllium 2+ ion have a larger radius than a helium atom?

texts: $\ce{Be^2+}$ has an ionic radius of $\pu{45 pm}$, while $\ce{He}$ has a radius of only $\pu{31 pm}$. If they are isoelectronic (they both have two elections in the $\mathrm{1p}$ orbital), and $\ce{Be}$ has more protons to attract them, why doesn't $\ce{Be^2+}$ have a smaller radius?


texts: Will monosodium dihydrogen phosphate react as base or acid in water?

texts:
Will $\ce{NaH2PO4}$ react as as an acid or a base if you make it react with water?

I got stuck here. I can figure out the reaction:

$$\ce{NaH2PO4 + H2O -> Na^+ + H2PO4^- + H2O}$$

But when I look $\ce{H2PO4^{-}}$ up, it says that it can both be an acid and a base.
Any ideas?


texts: Why doesn't the vapor pressure of water depend on the humidity?

texts:
Correct me if I'm wrong, I'd like to think of vapor pressure of water as the number of water molecules escaping from the water surface per unit area. Greater the leaving number, greater the vapor pressure. If this is right, can I conclude that the rate of evaporation is directly proportional to the vapor pressure?

My textbook says that the vapor pressure of water depends only on the temperature of the water. It doesn't depend on external pressure or humidity. But we know that the rate of evaporation decreases with increase in humidity.(Wet clothes dry faster in less humid air.) Doesn't this imply a decrease in vapor pressure with increase in humidity?


texts: Disposing of hazardous waste indicated by numbers on chemicals

texts:
I'm doing a book for the African market and the syllabus asks for discussions on proper disposal of chemicals and waste products, particularly in the classroom setting

The authors said something along the lines of:

  Chemicals numbered 1 to 4 can be rinsed down the drain with water. Chemicals labeled 5 to 8 must be disposed of with the help of an Environmental Agent or official.

What are the numbers they mention? Is there some numerical system (similar to scheduling on prescription meds) which guides us on how to dispose of certain chemicals?


texts:
I'm trying to understand why in an acidic environment, rust increases. The explanations I have seen so far basically have the following,

  "In acidic environments the cathode for the rusting of iron changes to
  $O_{2(g)}+4H^+ _{(aq)} + 4e^- \rightarrow 2H_2 O_{(l)}$. The anode
  reaction remains $Fe_{(s)} \rightarrow Fe^{2+} + 2e^-$. The  cell
  value increases as the cathodic process is lower in the
  electrochemical series, producing a more effective electrochemical
  cell, accelerating corrosion rate."

Though I don't understand why in acidic environments the cathode reaction changes? These are some of the explanations I've read

In normal oxygenated conditions hydronium ions increase the electrode potential of the reduction of oxygen making it a better oxidant.
In acidic environments the reduction of oxygen proceeds more rapidly. (This doesn't seem to really explain it)

Question
Why in acidic environments does the cathode reaction for the rusting of iron change?


texts: Fragmentation of phenyl radical cations in mass spectrometry

texts: What are the main fragmentation pathways and products of a phenyl radical cation in mass spectrometry ? I notice sometimes that there's a m/z = 51 peak after the m/z = 77 for phenyl radical cation; I assume due to loss of acetylene.


texts:
Has anyone seen a comparative list of typical run times of the techniques used in analytical chemistry? I am making a list of rough timescales of analytical techniques (for a slide). Assume that the sample preparation is aleady done.

For example:
Volumetric titration may take up to 10 minutes

Gravimetry can take several hours to a day

NMR- several minutes

Electron spin resonance ?

X-ray photoelectron spectroscopy: survey spectrum for surface analysis?

Auger electron spectroscopy for surface analysis

X-ray crystallography

Inductively coupled plasma: approximately a minute to read one sample

FTIR- minutes

Raman spectroscopy- typically a minute

HPLC- seconds to hours

GC/ Supercritical Fluid Chromatography/ Capillary electrophoresis
 - seconds to hours

Mass spec - less than a minute

Ion mobility spectrometry- milliseconds


texts: How does H's ionization energy relate to its transition energy (Bohr's Model)?

texts:
I am currently reviewing some material about orbital energy levels. In my review book there is a short snipet that reads:

  The IE of $\ce{H}$ from its ground state ($n=1$) is $1312\ \mathrm{kJ/mol}$. Because of the squaring of the principle energy level, the ionization of an $\ce{e-}$ in $\ce{H}$ from the $n=2$ level is $1/4$ of that value ($328\ \mathrm{kJ/mol}$). The transition energy from the $n=1$ level to $n=2$ level is the difference between the two values, $984\ \mathrm{kJ/mol}$.

I am confused about how exactly an atom's ionization energy relate to its transition energy. If IE is the energy required to pluck off the first e- from an atom and TE is the energy required to change between different orbitals, does this mean that an atom with greater IE will need to absorb a greater amount of energy to jump orbitals?

Lastly, is there a equation that directly ties in both ionization energy with transition energy?


texts: Is there an actual specific heat for aluminum in its gaseous state?

texts: I've scourged the internet and I can't seem to find it anywhere although I've found the specific heat values for aluminum in both solid and liquid states. I'm trying to construct a heating curve and I need the specific heat capacity of aluminum in its gaseous state in order to calculate the amount of energy that would be necessary to bring aluminum from its liquid state to a gaseous state.


texts:
If detergents were acidic rather than basic, can we still achieve a clean surface? What would be more effective? Strong acid or a weak acid?
How would the result of cleaning be different if an acid of pH 4, for example, is used?
Is it possible to achieve the same result with an acid and a base, or even if they are both present in a detergent?


texts: Is there a simple way to get the circular dichroism of a molecule from its structure?

texts: Are there any heuristics to get the relative absorbtion of left and right circularly polarized light by a molecule from its molecular structure? Is it even possible to predict which polarization is selectively absorbed?


texts:
Today I came across a "thought experiment" regarding $\mathrm{pH}$ of a diluted acid solution. This idea looks somewhat logical but obviously contradicts the reality. Can you show me where is the error?

Let's suppose we have $\pu{100 g}$ of concentrated 95% (mass) sulfuric acid. That means we have a mixture of $\pu{95 g}$ of H2SO4 and $\pu{5 g}$ of $\ce{H2O}.$ Let's calculate the amount of both compounds.

$$n = \frac{m}{M}$$

$$n(\ce{H2SO4}) = \frac{\pu{95 g}}{\pu{98.08 g mol-1}} = \pu{0.9686 mol}$$

$$n(\ce{H2O}) = \frac{\pu{5 g}}{\pu{18.02 g mol-1}} = \pu{0.2778 mol}$$

Since the amount of the solvent molecules is much much lower than the amount of the $\ce{H2SO4}$ molecules, it is not possible for the acid to be completely dissolved, which leads to the relatively small amount of $\ce{H3O+}$ cations, and $\mathrm{pH}$ of the solution is relatively high $(\mathrm{pH} = -\log [\ce{H3O+}]).$

$$\ce{H2SO4 + H2O -> HSO4^- +  H3O+}$$

If we increase the amount of the $\ce{H2O}$ molecules (dilute solution), more $\ce{H3O+}$ cations can be formed, and the $\mathrm{pH}$ will decrease.

Conclusion: dilution of acid-water solutions decreases $\mathrm{pH}.$

In reality it is completely opposite. So what is the catch?


texts: Synthesis of 2-Phenyl-2-Butanol from Grignard Reagent

texts:
The question is this:

2-Phenyl-2-Butanol can be synthesized by three different combinations of a grignard reagent and a ketone. Show each combination.

I can only think of one.

Butanone with Br-Mg-Ph

I can't think of anything else.

I'm not too sure if this will work:

phenylbutanone withe Br-Mg-Me

now i'm stuck. i can't think of the last one.


texts: The stability of the cupric and cuprous ions

texts: My teacher told me that $\ce{Cu^2+}$ is more stable than  $\ce{Cu+}$ in solution, but why? I think $\ce{Cu+}$ is $\ce{[Ar] 3d^10 }$ ,$\ce{Cu^2+}$ is $\ce{[Ar] 3d^9}$, why is $\ce{Cu^2+}$ more stable then?


texts: How can I safely store highly outgassing self-pressurizing chemicals?

texts:
I have a standard copper etching solution of 1 part $\pu{10M}$ $\ce{HCL}$ and 2 parts 3% $\ce{H2O2}$ (as described in numerous places online).

I previously had this stored in a tightly-sealed glass bottle, as described in the instructions I followed and general acid storage instructions.

However, my solution seems to be outgassing hydrogen or chlorine gas quite significantly, and when I opened the sealed container a few days later it violently liberated much of its contents into my face. (I was wearing a partial face shield and immediately went under the shower, so no ill effects were observed).

I know that for some chemicals that self-pressurize, such as cryogenic nitrogen, the storage method is essentially constant venting - is that what I'll have to resort to?


texts:
Based on some data here, I am getting the heat of dilution of 100% $\ce{H2O2}$ as approx. 1100 cal/mole.

That's about 4.6 kJ/mol if I did my math right.

Is this a correct value? Seems too low to me.

e.g. For the corresponding heat of dilution for $\ce{HCl}$ I get 74.8 kJ/mol from Wikipedia.


texts: Interpreting a thermodynamics equation using a picture

texts:
Given
$$ \frac{\partial \Gamma}{\partial p}\Bigg|_{t} =\frac{\partial \Gamma}{\partial p}\Bigg|_{v}+\frac{\partial v}{\partial p}\Bigg|_{t}\frac{\partial \Gamma}{\partial v}\Bigg|_{p} \tag{1}$$
where
\begin{gather}
\Gamma(p,v) = vp^{2}\tag{2a}\\
pv=t\tag{2b}
\end{gather}
I'm trying to interpret $(1)$ using words or preferably a picture.
Note for notations: $p$ is pressure; $v$ is volume; and $t$ is temperature.
$(2 \text{b})$ is equivalent to the ideal gas law but with temperature in units of energy. I suspect the picture we're looking after is something along the sides of a $pv$ diagram involving an isotherm. Since $t$ is held constant in this setting, my conclusion is that $(1)$ represents the isothermal compression of an ideal gas, but frankly this conclusion is shaky and I'm not sure of my interpretation.


texts: Compound formed from concentrated sulfuric acid and sulfur

texts:
In the reaction below, I know what A and B are, but I'm not sure what compound C is.

All I know about it is the following:

Deep yellow solid
Dication contains only sulfur
Raman and infra-red spectra of the dication show no common features

I think that the dication might be $\ce{[S4]^{2+}}$ since I think that this would be square planar and therefore have $D_{\mathrm{4h}}$ symmetry, which has no irreps that are both Raman and IR active, but I don't know what the anion would be.

The other likely options for the sulfur dication would be $\ce{[S8]^{2+}}$ or $\ce{[S19]^{2+}}$ but I think the fact that it's yellow would make it $\ce{[S4]^{2+}}$.


texts: What has stronger antioxidant potential: BHT or BHA?

texts:
Butyl Hydroxy Toluene (BHT) has two tert-butyl groups that can stabilize a free radical. Butyl Hydroxy Anisol (BHA) doesn't, though it has the 4-substituted methoxy group (I'm not sure what that does).

What is the stronger antioxidant?


texts: Salt solubility and solvent dissociation

texts:
A textbook, describing a qualitative test for the $\ce{Al^3+}$ cation in which you use $\ce{NH4Cl}$ and $\ce{NH4OH}$ to precipitate $\ce{Al(OH)3}$, mentioned that the solubility of this precipitate decreases in the presence of the ammonium salt.
I sort of reasoned it out to the common-ion effect decreasing the $\ce{OH-}$ concentration before I wondered why that would have an effect at all. As far as I know, the solubility of a salt only varies with the solvent used, the pressure, and the temperature (and of course, on the common-ion effect if it's present).
I made up an explanation, that a more dissociated solvent wouldn't have to physically contort to solvate the salt ions; that when the bonds are broken, the ions of the solvent can more freely arrange themselves in optimal positions to stabilize the salt constituents.
Is that line of reasoning correct? If not, how can the relation between solvent dissociation and salt solubility be rationalized?


texts:
"Atomic volume decreases along a period, reaches a minimum at the middle, and then increases for the rest of the period"

Why does the atomic volume, along a period, initially decrease, reach a minimum and then increase?
The atomic radius decreases along a period, so I would have thought that the atomic volume would also decrease along a period.


texts: Why did HF disolve this lightbulb at the surface rather than more submerged points?

texts:
I watched this video where a lightbulb is suspended in a solution of HF.  The result is that the HF dissolves the glass, but it seems like the part of glass on the surface reacted faster than fully submerged parts.  Here is an image of the lightbulb after the experiment:

The glass breaks at approximately the 2:50 mark, and it looks like at that point the bottom portion was cut from a clean line.  Perhaps the larger portion dissolved afterwards or was damaged during cleanup, I'm not sure.

Is there a reason why the glass closer to the surface would react faster than more submerged parts?  Why would the very tip not dissolve first?

My best guess is that the specific line happened to be the thinnest glass.  I find it unlikely that the specific line is the thinnest part.  Wouldn't it be much more likely for there to be random holes in the submerged portion from the thinnest part of the glass?


texts: Is it possible to curve fit GC, Mass-spectrometry and NMR peaks?

texts: I am trying to measure the amount of compounds by the peak area and I want to increase accuracy to 0.1% by curve fitting. Can I do it and what functions should I use?


texts: I have just been pondering upon the question above. I have found this example and I am sure they are enantiomers, but do they also count as geometrical isomers?


texts: Structural representation of substituted benzene

texts:
Recently, I was watching a video about separating o-chlorotoluene and p-chlorotoluene from its solution. Following was a reaction demonstrated in the video:

I was curious about the structure of chlorotoluene. In this, the chlorine substituent was directly inserted into the benzene ring rather that attached to carbon atom. What does the bonding signifies? Is this structural representation correct? Does IUPAC recommend it? I couldn't find such type of image on internet not in any literature and thus I am skeptical about this representation.


texts:
I was wondering something, if I have the same molar fraction for two different substances for a vapor on top of a solution, will this mean that the pressure of each individual substance will be the same ? Since they have the same quantity of molecules ?

This question has a link with Raoult's law : $p_{solvent}=x_{solvent}p^*_{solvent}$, where $p_{solvent}$ is the partial pressure above the solvent, $x_{solvent}$ is the mole fraction of solvent in the mixture, and $p^*_{solvent}$ is the vapor pressure of pure solvent.


texts: Phenol or ethanol as a nucleophile for ether formation?

texts:
If we react phenol with $\ce{C2H5I}$ in $\ce{C2H5O- Na+}$ (excess), $\ce{C2H5OH}$ (anhydrous) solutions .

In this reaction why is diethyl ether not formed and the actual product is phenyl ethyl ether?


texts: What is the typical range for the molar absorptivity of paint?

texts:
For example, $\ce{TiO2}$ is used a lot as pigments in paint, what is the range of molar absorptivity for that? Would I be able to determine this from this graph:

Ideally I could estimate a range for acrylic paints. I really just need a range, and it only needs to be as accurate as a few orders of magnitude.


texts:
I have to name the above compound. I am getting 5-bromo-2-chloro-7-fluorobicyclo[2.2.2]octane.
But my teacher is telling me that the answer should be 2-bromo-5-chloro-8-fluorobicyclo[2.2.2]octane.
His reasoning is that the bromo substituent should get a lower number as it comes first in alphabetical order. Which is correct?


texts: Why do atoms bond? Why are unfilled valence shells energetically unstable?

texts: I teach school Physics. And am trying to get a reasonable explanation of the root cause of the energetic instability of unfilled outermost electron shells that leads to atoms bonding. For most of what I teach, I am able to tie things back to the four fundamental interactions/forces. But unfilled valence/outer shells being the reason why atoms bond beats me.  I get Pauli exclusion. I think I get Schrodinger's equation. Yet, to me these don't provide a fundamental explanation of why a shell 'filled' by bonding is more energetically favorable than neutral atom with an unfilled outermost shell. Do I just accept this as fundamental property of our universe?


texts: The unit of energy, 1 dm³ atm, is equal to how many calories?

texts:
I surfed through the internet and visited a number of chemistry websites but only in vain. I couldn't find an answer.
Please help! Your quick response will be appreciated.


texts: What is the partial molar volume of epsomite (magnesium sulfate heptahydrate)?

texts:
I am trying to calculate the expected volume of an aqueous solution of epsomite and NaCl (308 deg K but willing to go with 298 K as close enough, and 1 atmosphere pressure).  I realize the two may interact, but as a first approximation I'm looking for the partial molar volumes of both. I found NaCl's in a paper (Archer (1992) J Phys Chem Ref Data 21(4): 793-829), but I can't find the values for epsomite.

I have a known quantity of salts and am trying to figure out how much solution I'll end up with after adding enough water to get a particular overall specific gravity. For the curious, I've got 600 pounds of epsomite, 50 pounds of NaCl, and I'm shooting for a specific gravity of 1.25.  Knowing the amount of water to add is straightforward and, unfortunately, not sufficient for this particular situation. I really need to calculate the total final volume after the salts have dissolved.

Thank you.


texts: What is the chemical formula for the synthesis of Hydroxyapatite (Ca10(PO4)6(OH)2)?

texts:
This might be a basic question but I am a little confused.
I have some lecture notes that says calcium phosphate ($\ce{Ca3(PO4)2}$) reacts with calcium hydroxide ($\ce{Ca(OH)2}$) to form Hydroxyapatite ($\ce{Ca10(PO4)6(OH)2}$).
So, the chemical formula (even when unbalanced) should be:
$$\ce{Ca3(PO4)2 + Ca(OH)2 -> Ca10(PO4)6(OH)2}$$
I can't figure out why $\ce{Ca10(PO4)6(OH)2}$ is the product of $\ce{Ca3(PO4)2}$ and $\ce{Ca(OH)2}$ and I am having trouble balancing it (see below). On Sigma Aldrich's website, it says the linear Formula for hydroxyapatite is $\ce{3Ca3(PO4)2·Ca(OH)2}$. I copied and pasted this directly. I assume the dot between the calcium phosphate and calcium hydroxide means 'plus'.
On the Sigma Aldrich's website, the calcium phosphate is written/balanced as $\ce{3Ca3(PO4)2}$, whereas the lecture notes I have are just $\ce{Ca3(PO4)2}$. Even with the three in front as the coefficient, I get $\ce{9Ca + Ca -> Ca10}$, $\ce{(PO4)2}$ and $\ce{(OH)2}$ which is $\ce{Ca10(PO4)2(OH)2}$, instead of $\ce{Ca10(PO4)6(OH)2}$. If I use the formula in my lecture notes, I get $\ce{Ca3(PO4)2 + Ca(OH)2 -> Ca4(PO4)2(OH)2}$, which is even more off.
Should it be $\ce{3(Ca3(PO4)2)}$ instead of $\ce{3Ca3(PO4)2}$ so the coefficient 3 can be applied to the subscript 2 on the $\ce{PO4}$ to give $\ce{(PO4)6}$?
What am I missing?


texts:
I have read that $\ce{NH3}$ acts as an SFL with a $\ce{M^3+}$ metal ion and acts as a WFL with a $\ce{M^2+}$ metal ion. It also states that when $\ce{NH3}$ forms a complex with the $\ce{M^2+}$ ion, its stability constant is $10^{11}$. When $\ce{H2O}$ forms a complex with the $\ce{M^2+}$ ion, its stability constant is $10^{15}$, though in the spectrochemical series, ammonia is far ahead of water (Source-Triump chemistry ,target publications).
So, if that is true then $\ce{[Ni(H2O)6]^2+}$ should be more stable than $\ce{[Ni(NH3)6]^2+}$ as $\ce{Ni}$ is in +2 oxidation state.
The crux of the question is that we must arrange the complexes in correct order for the absorption wavelength in the visible region (PYQ- AIIMS 2005) the options are  $\ce{[Ni(NO2)6]^2+}$ < $\ce{[Ni(NH3)6]^2+}$ < $\ce{[Ni(H2O)6]^2+}$ and    $\ce{[Ni(NO2)6]^2+}$ < $\ce{[Ni(H2O)6]^2+}$ <  $\ce{[Ni(NH3)6]^2+}$ .
I used $E=hc/\lambda$. So, E is inversely proportion to wavelength. Therefore the ideal answer should be $\ce{[Ni(NO2)6]^2+}$ < $\ce{[Ni(H2O)6]^2+}$ <  $\ce{[Ni(NH3)6]^2+}$ . As $\ce{[Ni(H2O)6]^2+}$ has a better stability constant, more energy is required to break it. Hence a shorter wavelength than $\ce{[Ni(NH3)6]^2+}$ , whose stability constant is less. This less energy is required, hence a longer wavelength. But the correct answer is $\ce{[Ni(NO2)6]^2+}$ < $\ce{[Ni(NH3)6]^2+}$ < $\ce{[Ni(H2O)6]^2+}$ according to the AIIMS . Please explain.


texts: What is the difference in dehydration of cis- and trans-1,2-cyclohexanedicarboxylic acid in anhydride formation?

texts:
Is there some required stereochemistry for anhydride formation? Do both of them form the same product, or does one not even undergo dehydration?

I looked up cyclohexane-1,2-dicarboxylic anhydride's structure and found two images:

Does that mean both of them are formed?


texts: hydrodynamic thickness of polymer vs. concentration of electrolyte?

texts:
I've measured the hydrodynamic thickness of a NaPSS layer on polystyrene latex and plotted it against the concentration of the supporting electrolyte, NaCl.
My graph shows a general decrease in thickness with some fluctuations at earlier concentrations. I thought that thickness would increase with concentration due to more charge screening. Can anyone help explain these results?


texts: Why don't covalent compounds dissociate in water?

texts: I understand that ionic compounds dissociate when dissolved in water. Why don't covalent compounds do the same?


texts: Does any known substance ignite on cooling?

texts:
As the title says, I'm interested in knowing if there is any substance — or combination of substances — that ignites (or even increases its chance of spontaneous ignition) when cooled.

I've never heard of such a thing, nor can I find it in Atkins' Physical Chemistry, but I might easily have overlooked it, since I don't know what to call it. Googling gives me information on substances that lower the freezing point or ignition point of explosives/fuels.

It seems that this should obviously be forbidden on thermodynamic grounds, but I can't quite rule out a phase change allowing such behaviour, for instance.


texts: Synthesis Golf VIII: 4,6-Diacetylhygrophorone A12

texts:
As usual we are a bit late on this, but here is this month's molecule:

which is known as (4R,5S,6R)-4,6-diacetylhygrophorone A12, and is an antifungal natural product isolated from mushrooms of the genus Hygrophorus.
As far as I know this compound has not yet been synthesised in the lab, but has been isolated and its relative configuration assigned by NMR measurements in anisotropic media.[1]
The criteria are the same as for the last challenge I posted:

the synthesis must be enantioselective;[2] and
no more than one chiral centre may be purchased in the form of a building block. (Chiral catalysts, ligands, auxiliaries, etc. do not fall under this rule.)

Otherwise, any commercially available starting material (as usual, in the Sigma–Aldrich catalogue) is fair game.

(1) Schmidts, V.; Fredersdorf, M.; Lübken, T.; Porzel, A.; Arnold, N.; Wessjohann, L.; Thiele, C. M. RDC-Based Determination of the Relative Configuration of the Fungicidal Cyclopentenone 4,6-Diacetylhygrophorone A12. J. Nat. Prod. 2013, 76 (5), 839–844. DOI: 10.1021/np300728b.
(2) The absolute stereochemistry was not assigned in ref 1, so you may synthesise either enantiomer. Obviously, though, that doesn't make a difference to the design of the synthetic route, so I have arbitrarily decided to display this enantiomer (following ref 1).


texts: What happens when a super-critical fluid is compressed?

texts:
Suppose that I have some substance with a critical temperature of 20°C. That means above that temperature, the substance exists neither as a gas nor a liquid, but instead as a super-critical fluid. Does it mean that no matter how high a pressure I apply on the fluid, it is not going to turn into a liquid above 20°C? Why is that so?

A substance is a liquid if the particles are close enough to interact, i.e. the space between particles is similar across different liquids. It seems that if we increase the pressure (i.e. decrease the available volume), particles should get close enough to interact.

I know that the higher the temperature of a gas, the higher the speed of the particles. How does this affect the phase transition?

What is the role of intermolecular forces? They are part of the explanation why at lower temperatures, gases condense into liquids.  It seems that we are ignoring them in the case of super-critical fluids. Are we now saying I just need to apply pressure to decrease the distance between particles? If it weren't for intermolecular forces, I would have to apply much higher pressure to turn a gas into a liquid (at temperatures below the critical temperature).

So what happens when a super-critical fluid is compressed, and how is the interplay of particle speed, intermolecular forces and distance of particles different below and above the critical temperature?


texts: Which singlet dihalocarbene has the strongest carbon-halogen bond?

texts:
There are three singlet carbenes - difluorocarbene, dichlorocarbene and dibromocarbene. Which has the strongest carbon halogen bond?

Obviously backbonding is a point to be considered, as carbene is an electron deficient species. As fluorine is the most easiest to overlap with, the $\ce{C-F}$ bond will be strongest.

But I am not able to get that whether it is possible for the singlet carbene to overlap or share electron density with empty d-orbitals on chlorine and bromine atoms?

And which is more probable, backbonding from halogens to carbene empty orbital, or the other way round (from carbene filled orbital to vacant d-orbitals)?


texts: Calculate the cathode electrode potential in this redox reaction

texts:
In this problem I'm asked to calculate the electrode potential of the magnesium electrode ($E_{Mg^{2+}/Mg}$) given the red-ox reaction:$$\text{Mg(s)}+2\text{Ag}^+(10^{-2}\text{M})\leftrightarrow 2\text{Ag(s)}+\text{Mg}^{2+}(10^{-2}\text{M})$$

The information I'm given is:

Temperature equal to $278\,K$ (the standard).
The molar concentration of the $\text{Mg}^{2+}$ ions is of $0.01\,\text{M}$.
The standard reduction potential of the $Mg$ electrode is: $E^{º}_{Mg^{2+}/Mg}=-2.34\,V$.

I know I have to use the Nernst Equation, but my solution and the book's answer are very different.

My solution:

$$E_{Mg^{2+}/Mg}=E^{º}_{Mg^{2+}/Mg}-\dfrac{0.059}{n}\,\color{#ff3300}{\mathbf{\log\frac{\left[\text{Mg}^{2+}\right]}{1}}}=\ldots=\boxed{-2.28\,V}$$

My book's solution:
$$E_{Mg^{2+}/Mg}=E^{º}_{Mg^{2+}/Mg}-\dfrac{0.059}{n}\,\color{#00ff00}{\mathbf{\log\frac{1}{\left[\text{Mg}^{2+}\right]}}}=\ldots=\boxed{-2.40\,V}$$

($n=2$ because 2 moles of electrons where exchanged per 1 mole of reaction)

I've colored the part where I go wrong (basically the logarithm). I don't know exactly why the book put the concentration in the denominator, since $\text{Mg}^{2+}$ is a product (not a reactant), therefore following what I studied, its concentration should be in the numerator.

Any help? Sorry for asking such an elementary question, but I'm still learning the basic stuff in Chemistry!

Note
I attach an image of the solution provided by the book


texts: Iron (II, III) oxide and concentrated nitric acid

texts:
According to the Russian Wikipedia, the reaction goes as follows:

$$\ce{Fe3O4 + 10HNO3 -> 3Fe(NO3)3 + NO2 + 5H2O}$$

Since $\ce{Fe3O4}$ is often written out as $\ce{Fe2O3*FeO}$, why don't we have instead

$$\ce{Fe3O4 + 8HNO3 -> Fe(NO3)2 + 2Fe(NO3)3 + 4H2O}$$

Why does the reaction evolve gaseous nitrogen dioxide?


texts:
Why, when chemical equilibrium is defined as when two opposing reactions are equal in rate, can the products or reactants be favoured?

I understand that temperature can cause either the forward or reverse reaction to be favoured. But then doesn't that mean that the rate of which the reactants or products are being formed differ from each other? So, what does it mean when they define equilibrium as I have said above.

Please keep answers simple and clear.


texts: Oxidation of certain acids by potassium permanganate

texts:
Why does potassium permanganate oxidize formic acid and oxalic acid, but has no reaction with benzoic acid and acetic acid?

The reactions were heated in a water bath (~70-80 °C). Oxalic acid had turned colorless:

$$\ce{C2H2O4 + KMnO4 + 6 H+ -> CO2 + H2O + Mn^2+ + KOH}$$

The same reaction could be said for formic, but with the formation of a brownish precipitate:

$$\ce{HCOOH + KMnO4 + 6 H+ -> CO2 + H2O + MnO2 + KOH}$$

For both the benzoic and acetic acid, they remained purple. I do not know whether the structure could be the reason for not reacting at that certain temperature, or something. Could it be possible that the temperature alone is responsible for not allowing the redox reaction to occur for both acetic acid and benzoic acid?

I looked around online and read that alkanes and aromatic compounds don't react with $\ce{KMnO4}$ from one source (Experiment 5 – Reactions of Hydrocarbons, laney.edu). I was not aware of the fact that potassium permanganate could oxidize anything under certain conditions, thank you for that fact.


texts: Changing the CO2 concentration (adding or subtracting) inside a sealed vessel?

texts:
I am looking for a method of modifying the CO2 concentration inside a sealed container that is both precise and repeatable (C02 needs adjustment every time the container is sealed, also need to be able to make additional adjustments to counteract potential slow leaks.

Is there a way I could do this electrically? Voltage across a sample of some precursor? Coating a heating wire with something that could be gradually burnt off? I read an online article from 2016 about a type of battery that actually removed CO2 from the atmosphere and used it to generate a current (and in the process reduced the concentration) - could not tell from the article if all the parts of the battery were solid - if it were then perhaps a scaled down cell?

Very much appreciate any suggestions so I have some options.


texts: Is the Aufbau principle violated in the diagram (b)?

texts:
In which of the following diagrams is the Aufbau principle violated?

Ignoring the Hund principle, the Aufbau principle states that electrons have to first fill the lowest energy levels. Now the energy level of the s-orbital has to be the lowest, and only in the option (b) the s-orbital is not filled fully. So the answer is (b).
Is my reasoning correct?


texts: What is the fundamental difference between temperature and energy?

texts: We know that temperature is proportional to the average kinetic energy of a system. We also know that temperature is not the same as energy because the temperature is intensive while the temperature is extensive. This lead me to think that temperature was some sort of energy density, like how density represents the "average" mass over a volume. However, we cannot express Kelvin in terms of Joules. So if temperature is not just an intensive version of energy, what is it really? How can we link entropy's connotations with disorder with the units J/K?


texts: Mechanism of decomposition of alkali metal halides in flames

texts:
A student recently asked an interesting question What happens when KCl is introduced in the Bunsen flame?. This apparently simply question led me to an interesting debate. We all know that emission of characteristic colors of alkali metal salts especially the halides and carbonates in ordinary Bunsen flames comes from the atomic emission not their oxy compounds (like the alkaline earth salts) or their ions.
The point of debate is point number 3:

KCl solution has to atomize and become KCl (solid).
We would get KCl in gas phase from the heat of the flame.
How does KCl (gas) convert to K atoms in a flame? What is the path? Note Thermal decomposition of salts without a flame is another story. Please do not mix, decomposition in a flame versus isolated vapor phase studies of salts.

Flame chemistry is quite complex and my understanding is that flames are electrically conducting from a very small amount of free electrons and ions. Certainly, we are not talking about cool flames like candles. Flame conductivity is a well known phenomenon and it is utilized in gas chromatography's "flame ionization detector" as well.
Herein, I am talking about spectroscopic flames used in atomic emission spectroscopy.  It is known for more than 100 years that when we introduce alkali metal salts into the Bunsen flames, the conductivity of flame increases as a function of salt concentration. For alkali halides, it is a square root function of concentration. This clearly shows that there are free ions and electrons in a flame in which alkali metal salts are introduced. The amount must be really small but significant enough to alter flame properties Electrical properties of flames.
There must be certainly thermal decomposition but it is not a complete story at all. The key question is the path of KCl(s) to K atoms!
(a) KCl goes to potassium ions in the flame, by thermal decomposition, and it becomes neutral potassium atom in flame after gaining an electron (from flame components)?
(b) KCl is thermally decomposed directly to potassium atoms and there are no intermediate potassium ions?


texts:
I would like to ask which group do actinide and lanthanide belong?
I had a question in my assingment that which group has most number of elements?
if they belong to 3rd group then the 3rd group should be the answer.
Am I wrong or Right? Please Help Me.


texts:
Amylase is an enzyme that breaks down starch in the form of amylopectin and amylose. Both amylose and amylopectin are formed by alpha glucose joined together by (1-4) and (1-6) glycosidic bonds. Glycogen is no exception, just that it has more branching.

However, why is it that a Google search shows that it is hydrolyzed by glycogen phosphorylase rather than amylase? Also, how can amylase digest both (1,6) and (1,4) glycosidic bonds?


texts: How to derive if the reaction is endothermic or exothermic based on rate constants at different temperatures?

texts:
Listed in the table are forward and reverse rate constants for the reaction $$\ce{2NO (g)  <=> N_2 (g) + O_2 (g)}$$
  \begin{array}{ccc}
\text{Temperature}/\pu{K} & k_f/\pu{M^-1s^-1} & k_r /\pu{M^-1s^-1} \\\hline
1400 & 0.29 & 1.1\times10^{-6}\\
1500 & 1.3  & 1.4\times10^{-5}\\
\end{array}
  Is the reaction endothermic or exothermic?

In my book the solution is given as

  $k_r$ increase more than $k_f$, this means that $E_a$ (reverse) is greater than $E_a$ (forward). The reaction is exothermic when $E_a$ (reverse) > $E_a$ (forward).

I can not understand what they mean by the given answer.
Can anybody explain it in more detail?


texts: Why are amidines so much more basic than amides?

texts: Both delocalize the added proton. Is it because the bond lengths in amidines are the same, or perhaps because oxygen is more electronegative than nitrogen and thus is more reluctant at keeping the proton? But how can that explane the huge difference in basicity between amidines and amides (resp $12$/$13$ versus $-1$/$0$ of $\mathrm{p}K_\mathrm{aH}$)?


texts: Mass number, (relative) atomic mass, average mass

texts:
What is the difference between mass number, atomic mass and average atomic mass?
I know the mass number is the amount of protons + the amount of neutrons. The average mass is the weighed average of the isotopes that occur in nature. But then what is the (relative) atomic mass?


texts:
Question

  Find y in this question :

The $\ce{ -CH2-Cl}$ below according to me will not take part the reaction (or please correct me) thus my answer is y=2 but actually it's y=3


texts: Why does ester hydrolysis occur in basic medium

texts:
Ester hydrolysis occurs in basic medium and this is the medium which is usually preferred for the same. But I am facing a very fundamental doubt and not able to understand the reason.
Ester Hydrolysis goes like this:

$\ce{RCOOR' + OH- <=> RCOOH + OR'-}$

Now according to me $\ce{OR'-}$ should be a better base because of +I inductive effect of alkyl group. If it is a better base then why does it not attack the acid back again !? In short, why does the equilibrium not reverse ?


texts: IUPAC numbering of carbon atoms in a chain

texts:
A chemistry handout for nomenclature of org. compounds I've been reading states a particular rule for every functional group viz.

If there is a choice in numbering not previously covered, the parent chain is numbered to give the substituents the lowest number at the first point of difference.

Can anyone explain what it means?


texts:
What is palindromic DNA and why isn't every complementary strand palindromic?

I know AGCT is palindromic, but what is an example of a strand that isn't?


texts: Does the hydrogen taken in an E1 reaction have to be antiperiplanar?

texts:
I'm wondering if the hydrogen stolen during an $E_1$ reaction has to be antiperiplanar/anticoplanar like the hydrogen in an $E_2$ reaction.

Intuitively I'd say no, because the carbocation is flat so there's less steric hindrance than an E2 reaction, but I want to check.

As an example, we could use 3-methyl-2-bromobutane. Once that carbocation forms and shifts, does it matter which hydrogen is stolen?


texts:
I'm learning about SN2-reactions, and my text book gives the following examples of these reactions:

  $$\ce{HO^- +CH_3Br -> CH_3OH + Br^-}\tag{1}$$
  $$\ce{I^- +CH_3Br -> CH_3I + Br^-}\tag{2}$$

Later I learned that $\ce{OH^-}$ is a worse leaving group than $\ce{Br^-}$, and that $\ce{I^-}$ is better than $\ce{Br^-}$. I can understand the reaction (1) is favored, since the leaving group gets worse (and therefore $\ce{CH_3OH}$ is more stable than $\ce{CH_3Br}$), but I cannot understand the reaction (2). Wouldn't the reverse reaction of (2) be favored instead? Or is (2) in fact an equilibrium?

I'm confused because $\ce{Br^-}$ seems like a better nucleophile than $\ce{I^-}$, which would favor the reverse reaction of (2)?


texts: Will supercritical nitrogen stay supercritical if we raise temperature and pressure high above critical values?

texts: Nitrogen's critical temperature is -146.96 °C and critical pressure 33.96 bar. If we maintain nitrogen at 220 bar and 400 °C, what will be the state of $\ce{N2}$? Will it be still supercritical? I know that phase diagram says after critical temperature and pressure we have a supercritical phase, but with enough p and T, more exotic states of matter occur.


texts: I am still a first year student; I was asked in the exam to identify the meso comound out of some choices. The answer key said that the compound below is meso. But I see no plane of symmetry here. Am I wrong or the question? I hope someone clarifies please. Sorry if the question was super silly.


texts:
I'm having difficulties understanding this problem.

We have in the problem that $K_\mathrm a$ for $\ce{HCN} = 6.2\cdot10^{-10}$ and $K_\mathrm b$ for $\ce{NH3} = 1.8\cdot10^{-5}$.

Write chemical equations to represent the dissociation of $\ce{NH4CN}$ in water, and the acid-base equilibrium equation.
Will the salt react as an acid or a base?

I know this is part of the solution:

$$\ce{NH4+ + H2O <=> NH3 + H3O+}$$
$$\ce{CN- + H2O <=> HCN + OH-}$$

I understand Le Chatelier's principle and I know that the reaction will shift to the side of less energy.


texts: How to predict the decomposition products of for example barium carbonate?

texts:
I am a high school student studying basic chemistry and I am confused about the process of writing decomposition reactions.

The question I have encountered asks me to decompose $\ce{BaCO3}$.

Online, I have found that this decomposes to $\ce{BaO + CO2}$.

My question is, essentially, is there a method to determine which elements go where. I'm having trouble finding answers.


texts: Moist Chlorine & Hydrogen Psychrometric or Mollier Chart

texts:
In our electrolysis of brine, $\ce{Cl2}$ and $\ce{H2}$ are produced as gaseous products along with aqueous $\ce{NaOH}$. In this scenario I require what amount of maximum moisture can $\ce{Cl2}$ and $\ce{H2}$ hold up at specific temperature & pressure (precisely 85 celsius & 1.2bar absolute). Two coolers (shell/tube exchanger with chilled water on shell side) are planned to dehumidify these two gases.

I have searched hard but without proper psychrometric data am unable to even estimate preliminary values. Link to data or other alternatives are highly welcome.

regards,


texts: Why dishwashers are corrosive to aluminum?

texts:
When I put aluminium parts into my dishwasher, they get tainted and they are sometime covered with white dots similar to salt.

I don't think it is aluminium oxide.

What are the chemical reactions that have an effect on aluminium but not other metals?


texts: I have a sheet of thin unperforated teflon that I need to perforate by tomorrow for a lab I work in. None of my coworkers know how to perforate the sheet. Does anyone know how I can do this using basic tools from my house?


texts: how a galvanic cell works with a different metal cation in electrolyte than used in electrode

texts:
A traditional galvanic uses zinc as the anode electrode submerged in a zinc sulfate electrolyte, and copper as the cathode electrode submerged in a a copper sulfate electrolyte. I wanted to know what happens if the electrolyte metal cation was not zinc or copper: What if the anode electrolyte was Potassium sulfate and the cathode electrolyte was sodium sulfate, will the cell still operate?

Should't zinc still be oxidized to zinc ion? In the cathode half cell, would the sodium ions be reduced to sodium metal, or would copper electrode interfere in some way?


texts: What's the difference between Zinc Ascorbate and Zinc Gluconate?

texts:
I've been looking at a dental product for pets, called MAXI/GUARD Oral Cleansing Gel and it states it uses zinc ascorbate/taurine, however in the ingredients I found elsewhere it instead lists zinc gluconate.

Active Ingredient(s): Deionized water, zinc gluconate, ascorbic acid (vitamin C), methylcellulose, taurine, methylparaben, propylparaben, F.D.&C. blue no. 1. May also contain zinc sulfate.

What is the difference between the two and any idea why they are listed as such?


texts: Mechanism of preparation of methylene blue

texts:
Methylene blue is prepared by reacting p-amino N,N dimethylaniline with strong acidic solution of $\ce{Na2S}$ and later adding aqueous $\ce{FeCl3}$. In this reaction does the mechanism begin with the addition of proton on amino which then undergoes substitution with another of the substituted aniline molecule?
Also how does sulfur attach to the ring?


texts: Explaning Cis & trans isomers through VSEPR

texts:
Total rewrite as was a panic-stricken 2am question.

Unfortunately I wrote on an application that VSEPR theory is a reason of Cis-Trans isomerism (specifically in fatty acids however I doubt that would make any difference). Although in my head it seemed to work at the time, I appreciated about a week after that I was actually thinking of the wrong type of thing.

My question is,

  How can VSEPR and/or the electron configurations in an unsaturated fatty acid explain how cis and trans isomerism arises?

As far as I'm aware, the Pi bond prevents (resists?) rotation around the C=C link, but I feel as if I'm missing something.

Also,

  Does the geometry caused by the repulsion of H's and alkyl electrons on either side of the C=C bond affect the isomers differently depending on whether or not they are Cis or Trans?

One of the below posters also highlighted a good question, does anybody have any insight on this?:
"I think the main question is whether there's a preference for cis or trans isomers in a fatty acid based on steric/VSEPR considerations"
(Thank you for your response)

Thanks for your help

Bonus related question:

  Is there any preference for a specific stereoisomer in the dehydrogenation of a fatty acid's alkyl chain? If so, what are they and why?


texts: How do I calculate the pressure of a known liquid in a sealed container heated above boiling point?

texts:
If I have water in a sealed container heated to say 150 degrees, how do I determine the amount of pressure being generated in the container? What about for other liquids? I have searched extensively and cannot figure this out.

I was looking for a formula of sorts, but for example reasons let's say a 5000 ml container with 4500 ml of water in it, with the rest of the space air, heated to 150 degrees Celsius.


texts: Why do middle school and high school chemistry classes teach students that electrons are little balls?

texts:
When I was in high school, I took two chemistry courses. The first was very elementary and didn't attempt to move beyond the picture of electrons, protons, and neutrons as little balls essentially. But in the second course I took (AP Chem), already confusion existed about waves vs particles and what exactly we mean by matter. And, in retrospect, I think jumping from thinking about localized particles  to waves is hard because it turns out neither description is complete enough.

I recently started studying quantum field theory and I feel like quantum fields are a lot more intuitive than delving into the whole wave-particle duality hubbub. The idea that particles are excitations of a field seems far more natural because one can envision waves and particles as excitations. Anthony Zee's book Quantum Field Theory in a Nutshell draws an analogy between quantum fields and mattresses. But the point is that I definitely think young people can imagine fields as easily as little balls. Yet there's a huge difference in how easily these initial intuitions allow you to navigate the physical sciences.
For instance, the idea of quantum fields would naturally lead students to wonder about how classical fields work.  Furthermore, for some particles, we can't define a wave function (eg photons). This becomes confusing because the wave function, at least to me, seem like the "thing" that told me how the states of a piece of elementary matter is evolving. But how can something evolve if it has no wave function?

I don't mean we have to throw out the idea of particles as little balls. The beauty of fields is that you can keep that description as a particular type of excitation. So it would complement all the tools and tricks chemists want young students to learn (eg Lewis dot structures) but give them a much clearer picture about the nature or what a particle is and ultimately I think provide a better backdrop for eventually delving deeper into the deeper questions about how quantum mechanics works exactly. This would probably help because, when they get to college, they wouldn't have to switch from an already engrained mindset. The one they would have would be more or less correct.

Maybe I am ignorant and missing something, but to me, although a bit bold, it might make more sense to introduce quantum fields earlier.


texts:
Can all lattices be described as one of the fourteen Bravais lattices?
Is the hexagonal close packed structure also one of the fourteen Bravais lattices?


texts: Why does nitration of aromatic amines give meta directed nitro compounds?

texts:
Amines are activating groups and donate electrons to the resonance structure using the lone pair of electrons on Nitrogen.
But when aromatic amines are nitrated, for example when benzyl amine is nitrated, it gives a meta nitro benzyl amine.
Given the activating nature of amine groups, shouldn't the compound be an ortho-para directing variant?
I tried figuring it out. One explanation I've come up with is that when it's nitrated, the proton from the nitrous acid forms a coordinate covalent bond with the amine group closing the lone pair electron to the bond. As a result it becomes an $\ce{NH3+}$ group. That would mean that it has a deactivating effect or electron withdrawing effect. That's why the incoming nitro groups are attached to the meta positions. But then why doesn't the same happen for nitration of hydroxide groups, for instance phenol?


texts: Can I synthesize an Amide simply by heating an amine and a carboxylic acid (with a vacuum pump)?

texts:
I am interested in creating an amide of stearic acid. I thought that simply mixing both of them in some solvent, heating the solution, and using a vacuum pump to distill the liberated water (to drive the reaction forward) would be enough.
But a bit of research showed that this synthesis is normally done with acyl chlorides derivatives or methyl ester derivatives or other more elaborate methods.
Without access to those tools, is it still possible for me to produce a good yield of amide, using only a fatty acid, a primary or secondary amine, a solvent, and heating & vacuum?
(Secondary optional question: If I use ethanolamine, what will be formed preferentially, the amino-ester or the hydroxy-amide?)


texts: Is it possible to calculate a maximum pressure attainable with a soda vinegar reaction?

texts:
Given Le Chatelier's principle, there must be a peak pressure of $\ce{CO2}$, at which, under room temperature, the reaction of soda with vinegar would stop?
$$\ce{Na2CO3 + 2 CH3COOH -> CO2 + 2 CH3COONa + H2O}$$
Is my reasoning correct and if so what formula to use to calculate it?


texts: Evaporation velocity of ethanol: adding ethanol vapour to a gas mixture

texts:
I need to add a known amount of ethanol vapour to a gas mixture (He/Ar). To do that I let the mixture bubble in liquid ethanol kept at a known temperature (14 C).

The system is made of a large steel cylinder (d=20 cm; l=138cm) lying in horizontal position and half filled with liquid ethanol. the gas is bubbled trough the liquid on one side of the cylinder and extracted on the other side.

The gas-flow trough the system is usually pretty low (~100ml/min) but I would like to increase it to ~10l/min and I need to know if this leaves enough time for the ethanol vapour to approach its equilibrium vapour pressure.


texts: Both fatty acid and polyethylene are made (mostly) of carbons with hydrogens with a very similar configuration, yet, their properties are very different. What am I missing?


texts: Why is double bond stronger than single bond?

texts: If a pi-bond is weak due to its sideways overlapping, then how can we say that breaking a double bond is a bit difficult? Is it because of the slight increase in energy as compared to a single bond to break it?


texts: How does nitrogen bond with itself to form N2 if it has no affinity for electrons? If a nitrogen atom can't pull on the electrons of another nitrogen atom how can N2 have covalent bonds.


texts:
Why does oxalic acid have exactly two water molecules of crystallization?  In other words, in the formula $\ce{C2H2O4\cdot2H2O}$, why is the number before the $\ce{H2O}$ exactly $2$?

I tried to see this from the structure of oxalic acid. Also, I tried to invoke hydrogen bonds. However, I don't see the reason why there are two water molecules of crystallization from this.

Also, with how many precision is it two?


texts: Fluorine is more reactive than Chlorine. But does it mean that Fluorine can cause more damage to living tissues? If so, why wasn't Fluorine used in WW1 instead of Chlorine?


texts: Why should a complexometric titration be kept neutral?

texts:
In my next lab, I'll be doing a complexometric titration of a copper solution with EDTA and a murexide indicator. The lab guide advises to keep the pH level nearly neutral by adding a diluted $\ce{NH3}$ solution. Why is that necessary?

I understand that during the formation of the copper complex $\ce{[Cu(EDTA)]^{2-}}$, the solution becomes more acidic. Do we need to add the basic solution in order to make sure the murexide does not change color due to the decreasing pH level? Or is it simply so that we can revert the color change (of the formation of the copper complex) and continue the titration until the equivalence point is reached (and all copper ions are in complex form)?


texts:
Can someone help with with setting up a calculation to run the new composite scheme PBEh-3c in Gaussian?
The code has been implemented in Turbomole and ORCA and it's pretty easy to run it there. Unfortunately I need to run a supramolecular stack in Gaussian because it's what we have in the cluster.
Thanks


texts: Does one atom of an element show the properties of a bulk of that element?

texts: For example, does one atom of gold have a golden color?


texts: Separation of Al-Si alloys without electrolysis

texts: Can pure (or roughly pure) $\ce{Al}$ be somehow thermally, chemically, or physically separated from the $\ce{Si}$ contained in an $\ce{Al-Si}$ alloy? How? Approximately what purity of Aluminum can be achieved in this way?


texts: How to identify the parent chain if two chains have the same number of skeletal atoms and the same number of double bonds?

texts: Please could you tell me the rule to name the given hydrocarbon ... I am just confused in which chain should I take as the parent chain . The chain from A to C or from C to B. There is no rule about it anywhere on the net or in my books .


texts:
Why is the compound 3,4-dihydroxy-3-cyclobutene-1,2-dione more acidic than acetic acid?

I don't get how its resonance stabilization is far greater than that of acetic acid despite the fact that the conjugate base has high angular strain. How is it more stable than acetate ion? In the consideration of acidity, why is only the resonance dispersion of charge taken into account and not the angular strain?

For stability comparisons of the anions so formed I am stuck at the resonance structure too:

Finally, I want to know whether it would be more acidic that formic acid?


texts: Why have citric acid only a denticity of 3 and tartaric acid of only 2?

texts:
Why can't the hydroxyl-groups in citric acid (denticity 3)

or in tartaric acid (denticity 2)

contribute to the denticity, as there are doing it in aminoethylethanolamine (denticity 3)

Why do the hydroxyl-groups can't contribute in the first two compounds?


texts: Which tautomer of hexane-2,4-dione is more stable?

texts:
Which tautomer will be more stable?

Both 1 and 2 show intramolecular hydrogen bonding and form 6 membered cyclic ring, thus increasing the stability.

I think I need to compare the effect of the two alkyl groups ,ie, methyl and ethyl  but how?


texts: Use the given information to write the formula of this compound

texts:
the question says :

Two elements, A and B, combine to form two binary compounds. In the first
compound, 3.5 g of A combines with 8.00 g of B. In the second compound,
5.0 g of A combines with 17.1 g of B. If the formula of the first compound is
AB2, then the formula of the second compound would be ?

I can't even make the first step :(


texts:
$$\ce{CF_3I + NaOH(aq) -> Major Product}$$

The Major product, according to me, should be ditrifluoromethyl ether $\ce{CF3-O-CF3}$. The hydrogen on the $\ce{-OH}$ group is quite acidic and hence reacts with $\ce{CF3I}$ to give a stable compound according to the following reaction mechanism:

However, the textbook gives the following reaction mechanism and claims that the product is trifluoromethane $\ce{CHF_3}$

Which one of these is correct?


texts: Reduction and Oxidation - Alternate definitions

texts:
Why is reduction defined as the gain of hydrogen?

Is it because hydrogen has a very low electronegativity and easily donates its electrons to other elements?

From what I understand reduction is formally defined as a decrease in oxidation state; oxidation state assignment involves supposing that all bonding is ionic and that electrons are therefore parceled to the most electronegative atom in a bond. And if something gains H - an atom of exceedingly low EN - then that element is reduced because that element will likely be more EN than H and therefore "take" the hydrogen atom's electron.


texts:
I have recently come across a statement which states:

  The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its three-dimensional aromaticity. [1]

My understanding of aromatic nature is, that the molecule must be cyclic and planar, every atom in the ring must be $\ce{sp^2}$-hybridized and the molecule must have [4n+2] $\pi$ electrons, where $n\in\mathbb{N}$ (Hückel’s rule). The molecular orbitals also have to have the correct orientation and phase for aromaticity (2).

In my understanding 1,3-dehydro-5,7-adamantanediyl dication does not follow these rules for Y-aromaticity (3).

So my question is: What is three-dimensional aromaticity and how does it stabilise the 1,3-dehydro-5,7-adamantanediyl dication?

References

Firme, C. L.; Antunes, O. A. C.; Esteves, P. M. Electronic nature of the aromatic adamantanediyl ions and its analogues. J. Braz. Chem. Soc. 2008, 19 (1), 140–149. DOI: 10.1590/S0103-50532008000100020.
LibreTexts
What is Y-aromaticity? Is the trinitromethanide anion aromatic?


texts: Experiment to demonstrate Dalton's Law of Multiple Proportions

texts:
Is there an experiment that I can do in the lab with middle or high school students to demonstrate Dalton's Law of Multiple proportions ?
For example, the reaction of $\ce{C}$ and $\ce{O2}$ to give $\ce{CO}$ and $\ce{CO2}$.
Is there an experiment where I can demonstrate that $\ce{CO}$ and $\ce{CO2}$ have these proportions ?


texts: Will this beta-branched secondary alkyl halide undergo SN1 or SN2?

texts:
What is the correct mechanism here? Would SN1 occur here? I chose SN2 because we have a secondary alkyl halide with a weak base $\ce{CN-}$.

However, the solution says SN1 is major. Can you explain why?

My friend got full credit for this:


texts: Synthesis of a bicyclo[2.2.2]octane from benzoic acid

texts:
I think that it is a Diels Alder reaction, but I don't recognize the start materials!
First I make the tertiary alcohol from carboxylic acid with organo-lithium reagent; after I try to make a Diels Alder reaction, but I don't find the right conjugated diene and dienophile.


texts:
I saw in my textbook (NCERT class 11 part2 chemistry) that oxidation is defined as

  gain of oxygen or more electronegative element by a substance.

After it was redefined and said as

  oxidation is loss of electron(s) by any species.

Again it is being redefined and stated as

  oxidation process is visualised as a decrease in electron density.

I can't understand why they are changing the definitions again and again. I mean what things they are taking into consideration, each time they define the term


texts: Regioselectivity of an amination reaction of 2,6-dichloro-3-nitropyridine

texts:
In the formation of ethyl 4-(6-chloro-3-nitropyridin-2-yl)piperazine-1-carboxylate G, why is the substitution favoured at the 2-position? I would have said that the 6-position substitution is preferred as:

In pyridines, nucleophilic substitution occurs at the 2/6th or 4th position, and as chlorine is an effective leaving group compared to hydride this rules out position 4, leaving 2 and 6 as the most feasible...
The electron withdrawing nature of the nitro group on the ring would favour nucleophilic substitution at the positions ortho or para to itself.
The chlorine at the 2 -position is ortho, and the chlorine at the 6-position is para so both are feasible...
If I didn't know what the product was, I would have said that position 6 is therefore the site of substitution as the amine reagent is quite bulky and the 6-position is less sterically hindered due to the absence of an adjacent nitro group

However, this evidently isn't the case! I found another similar reaction where the same thing occurs:

Is it something to do with the nitrogen in the pyridine ring hindering the electron density transfer to and from the para nitro group? I'm really stuck!


texts: Help with missing output from cubegen utility after density calculation in Gaussian16

texts:
I am busy trying to do density calculations in Gaussian16 as I need the .cube output for input to the PIXEL software. But my Gaussian output seems to be missing an entire chunk of data and I don't know why.

The output is supposed to look like:

However, my output is missing the entire chunk of electron density data, formatted as 6E13.5 (the block of floating point values indicating electron density at each point in the block).

My input in the route section is

#MP2/6-31G** guess=core NoSymm Pop=MK Density=MP2

And I use the following to generate the .cube file

Formchk NAME.chk NAME.fchk

Cubegen 0 NAME.fchk NAME.cube 0 h

Am I missing a keyword/command to include the electron density data?


texts: Can pheophytin be converted back to chlorophyll?

texts: Some fossil leaves are "greenish" when first exposed but rapidly darken to an "olive brown" color when they come into contact with air. If the fossil leaf contains pheophytin, can the addition of magnesium ions to an extract of the fossil change the pheophytin back to chlorophyll?


texts: Chugaev and Selenoxide Elimination giving different products

texts:
In class we are going over intramolecular elimination. In this question I will provide two similar reactants that provide a different mixture of products.

The chugaev elimination gives a 50/50 mixture of methylcyclohexene isomers while selenoxide elimination yields only one major product, but I do not understand why this is happening.

From what I can see, there is only one syn B-hydrogen available in both reactions. My professor went on to explain the significance of comparing the two reactions, saying that selenoxide elimination does not use heat while chugaev elimination does, causing a ring flip in one but not the other, which is understandable to me.


texts: Low-volatile liquids that 'ball-up' on siliconoxide or perfluoroalkanes

texts:
This is a very simple and short question. I am looking for liquids that are low/non-volatile at 20$^\circ$C (at least substantially less volatile than water) which have a high contact angle with glass and oxidized silicon (in air) or with a coating of perfluoroalkanes (specifically Perfluorodecyltrichlorosilane).

The requirement on the contact angle is say $\theta>70^\circ$, i.e. the liquid should 'ball-up' a bit. The reason I am asking is that I cannot seem to find any (common) liquids that have both the low-volatility and the high contact angle $\theta$. Does anyone know some examples? Or, if no such thing exists, can someone explain what the fundamental reason is that these liquids don't exist?


texts:
The reaction of tert-butyl bromide with azide ion in aqueous solution is proposed to proceed by the following mechanism:
  $$
\begin{align}
\ce{(CH3)3CBr(aq) &<=>[k$_1$][$k_{-1}$] (CH3)3C+(aq) + Br–(aq)}\\
\ce{(CH3)3C+(aq) + N3–(aq) &->[$k_2$] (CH3)3CN3(aq)}
\end{align}
$$
  $k_i$ is the rate constant.

  Assuming that $\ce{(CH3)3C+(aq)}$ achieves a steady-state concentration, but making no further assumptions about the relative magnitudes of the three rate constants, what is the rate law for this reaction?

The answer is

$$\mathrm{Rate} = \frac{k_1k_2[\ce{(CH3)3CBr}][\ce{N3–}]}{k_{–1}[\ce{Br–}] + k_2[\ce{N3–}]}$$

But how would I obtain that answer using multistep reaction mechanisms and not differential equations?


texts: Are there alternative ways to find n or number of e- in problems like the one pictured?

texts:
I need help understanding how we are to come up with 12 e- because according to the directions, we are supposed to focus on any element, but it doesn't tell us what to look for. I see how carbon has a -2 value in the reactants side and a +4 on the products side. the difference is 6 e- and we are suppose to multiply that by the number of carbons.

But is there another way to calcualte to find 12 e- ?

Couldn't we add the charges from the reactants and products after multiplying them respectively with the subscripts? For instance: -2 X 2 = -4 or 4 e- and +4 X 2 = 8 or 8 e- and so 4 e- + 8 e- = 12 e- ?

Isn't this a valid substitute than the explanation below? Because the directions below ask us to look for the difference in any of the elements. But this doesn't explain how to calulcate for hydrogen. But in the explanation I prepared above does, doesn't it?

But then again, this doesn't explain how we can calculate for oxygen, which has a 0 charge in it's own gas phase and a -2 in water and -2 in carbon dioxide.

So what would be another way to calculate for -12 e- ?


texts: For the elements such as rhenium, osmium, iridium how probable is for electrons in the inner 4f orbitals to gain energy and take part in a molecular orbital (such as an $f^2 d^2 s p^3$ hybrid orbital) when these elements are in their 6,7,8,9 oxidation state?


texts: Can I predict the preferred resonance structure of carbon monoxide from its molecular orbital scheme?

texts:
Because of the  8-valence electron rule I assume in CO the left resonance structure to be favored .

$$\ce{:\!\overset{\ominus}{C}#\overset{\oplus}{O}\!: ~<->~ :\!C=O\!:: ~<->~:\!\overset{\oplus}{C}-\overset{\ominus}{O}\!:::}$$

(from What is the Lewis Structure for CO?)

The molecular orbital scheme of CO looks like this:

Because the HOMO of CO is closer to the atomic orbital of O I think that the HOMO of CO is mainly localized on the oxygen atom, whereas the LUMO of CO is mainly localized on the carbon atom. Therefore I would have expected that the coefficient of the HOMO is higher on the O than on the C atom and therefore the top right resonance structure with the negative charge on the oxygen to be favored. However, in reality the top left resonance structure is favored. What is my error?

From another post, calculations have shown that the coefficient is higher on the carbon atom (How can the dipole moment of carbon monoxide be rationalised by molecular orbital theory?)
I guess my mistakes comes from the assumption that I say "HOMO closer to the AO of oxygen" means higher coefficient on oxygen. Is this assumption wrong and if yes why?


texts: How to calculate the mass of an element in a sample of a compound?

texts:
What calculations are needed to express the grams of an element from a compound dissolved in aqueous solution? For example, I have a $0.5\,\mathrm{M}$ glucose aqueous solution and I want to know how many grams of $\ce{O}$ are in there.

I have tried to calculate in this way:

Molecular weight of glucose = $180.159 \mathrm{\frac{g}{mol}}$
Atomic weight $\ce{C} = 72$; $\ce{H} = 12.09$; $\ce{O} = 96$;
I am considering $0.5\,\mathrm{M}$, so in $1\,\mathrm{L}$ I have $90.08\,\mathrm{g}$ of glucose
At this point I divide the molecular weight of glucose by the atomic weight of oxygen $\frac{90.08}{96}$, but I don't think it is correct.


texts: When the ClO2 chlorite ion loses an electron, what are the resulting products?

texts: What does ClO2 become when the chlorite ion loses and electron? (The Lewis Structure shows that Cl02 is a molecule)


texts: How can a sample that is in two different states be at a uniform temperature?

texts:
In my chemistry course, the professor has discussed how a sample that contains both solid and liquid water would be at 0 degrees Celsius no matter what the proportion of solid to liquid water is. I find this concept to be confusing, because wouldn't the areas of the sample that had already changed from solid to liquid begin increasing in temperature even while the other parts of the sample continue to be in the process of fusion?

The other part of this idea that confuses me is that if the sample was at a uniform temperature, then why do bodies of water (ex. lakes that freeze in the wintertime) continue to have different temperatures of water within them?


texts: What is the name for the equation ΔG = ΔG° + RT ln Q?

texts:
As the title states, what is the name of the equation

$$\Delta G=\Delta G^{\circ}+RT \ln Q$$

My textbook does not explicitly state the name and I could not find anything on google.


texts: How to rationalize the colour change of the thermochromic bis(diethyl-ammonium) tetrachloridocuprate(II) complex

texts:
The colour of the compound changes from deep green/green-blue to yellow upon raising the temperature. I'm trying to rationalise this by using the d-orbital splitting, but I've got myself in a logic bind.

At low temperatures, CuCl42- is square planar or distorted square planar.
At high temperatures, CuCl42- is tetrahedral.
Δt is ~0.44 Δo, but Δsp is ~1.4Δo, therefore Δt < Δsp.
This therefore implies that at low temperatures (square planar geometry), the photon absorbed to give a colour is of higher energy, and so lower wavelength.
Green corresponds to an absorption of 650 nm (in the red), whereas yellow corresponds to an absorption of 450 nm (violet absorption).

Therefore, the colours contradict my predictions. What is the cause of this?


texts: Why is sodium bisulfite needed in syn-dihydroxylation?

texts:
On the reaction of syn-dihydroxylation with stoichiometric quantities of OsO4 (not a catalytic amount) the second step is $\ce{NaHSO3/H2O}$ or $\ce{Na2SO3/H2O}$.

According to my understanding, $\ce{H2O}$ is the only thing needed to hydrolyze the cyclic osmate ester resulting from the first step of adding $\ce{OsO4}$.

So, what is the use of $\ce{NaHSO3}$ or $\ce{Na2SO3}$ here?


texts: To which block of the periodic table does helium belong?

texts:
According to quite a few books I have read, helium belongs to the p-block with reasoning along the lines of "it's an inert gas, so let's clump it together with other noble gases which are in the p-block."

However, on Wikipedia, helium is classified as an s-block element which, to me, makes sense because the last (or so-called "differentiating") electron that is added to helium will occupy an s sub-shell.

But my teachers are adamant that helium is a p-block element, and the fact that our textbook covers helium under the chapter "The p-block Elements" just gives them more reinforcement of that idea.

So: is helium an s- or a p-block element? Could someone provide concrete reasons for and against the block selection?


texts: Black Sludge Appearing When Making Iron Oxide Through Electrolysis

texts:
I am trying to make iron-oxide through electroylsis to make thermite. I'm using nails for the iron on the positive electrode in salt water. While there definitely is a good amount of rust collecting, especially at the surface, after dissolve multiple nails, there are also these black sludge-like solids forming:

I can pick them out of the solution if i'm careful, but they are very brittle
and break up and dissolve almost immediately if I  use too much force. Additionally, if I stir the up or shake the container, more of this stuff comes up from the bottom, most of it dissolved in a black-green watery, solution and you can't even see the rust anymore. If you give it time to settle, though you can see the rust again.

My question is what is this stuff, and will it make the rust impure? Do I need to get rid of it to make the thermite? Will boiling the solution to get rid of the water like I had planned be enough?

Thanks in advance.


texts:
I'm having a little trouble with definitions.

Here's a copy and paste from my hwk:

...K°P, and K°c have no units...Please enter the KP in 1/bar in  3 significant figures...

So these values even have different units, it's not a typo or anything.

Given: aA+bB $=>$ cC+dD

Is $$K°P=\frac {[C]^c[D]^d}{[A]^a[B]^b}$$
or is
$$KP=\frac {[C]^c[D]^d}{[A]^a[B]^b}$$

the question stated that K°P had no units, and the equation could be unitless if a+b=c+d, but that may not always be the case.

Can somebody tell me which "KP" matches the definition, and also provide, or link the formula for the other "KP"?

Sorry for asking such a trivial question but I'm having alot of trouble finding these definitions.

Thanks all.


texts: How are pure substances (elements, compounds, etc) produced?

texts: How are large quantities of the substances we use in the lab generally produced? (As in the process from getting the stuff out of the ground to use in the lab) How 'pure' are they? Also: is it possible to create relatively pure substances with household goods?


texts: Identifying a chloride of the unknown element from the masses of chlorine and compound as well as vapor density

texts:
1 g of a chloride of an element contains 0.835 g of chlorine. If vapour density of the chloride is 85, find weight of the element and its valency.

I tried to solve it but couldn't get to the answer then I saw its solution and I also could not understand what they want to explain. Can anyone please help me out.
By the way, it's not my homework.


texts:
Can I make N,N-dimethylaniline from aniline just by reacting it with $\ce{CH3X}$ ?

According to me, the lone pair of nitrogen in aniline is not nucleophilic enough (since it is in conjugation with the whole benzene ring) to be able to displace the $\ce{-X}$ group.


texts: Why is only mole fraction used in Henry's law and not some other measure of concentration?

texts:
Why is some other quantity like molality or molarity used?
I understand why mass percentage cannot be used as it is difficult to measure mass of gas...
Now is mole fraction used because solubility is directly proportional to the pressure and moles are directly proportional to the pressure?
Also, how do they measure the number of moles of a gas?


texts: Why do the Metal Ions in an Electrochemical Cell Not Pass Through a Salt Bridge?

texts:
I understand that the purpose of a salt bridge is to maintain the neutrality of the solutions in an electrochemical cell, but why do the ions    being oxidized and reduced not pass through the salt bridge.

For example, in this electrochemical cell, why do the silver ions not pass through the salt bridge and become reduced in the copper sulfate solution. Wouldn't this cause less resistance in the circuit, or does the salt bridge prevent the metal ions from passing through?


texts: Does energy come from fuel or oxygen? (surprise?)

texts:
Question: Is it oxygen or fuel that releases energy during burning?

The answer from this article:

Why Combustions Are Always Exothermic, Yielding About 418 kJ per Mole of O2 (Journal of Chemical Education, 2015)

  Our analysis provides simple answers to two related, important
  questions: “What makes fire hot?” and “How much heat is produced?” in
  the combustion of a certain fuel. One can now explain that the
  double bond in O2 is unusually weak, and therefore the formation of
  the stronger bonds in CO2 and H2O results in the release of heat or
  an increase in thermal motion.

  Generally, our analysis indicates that it is not the organic fuel
  but rather O2 that is “energy-rich”.

It is usually said that fuel contains energy and that oxygen only enables the release of energy in the sense like enzymes enable reactions. Does anyone want to comment this? Because, from this article it seems that it is just the opposite: fuel enables the release of energy from oxygen.

(This question was initially nutrition-related: Does energy come from nutrients or oxygen?)


texts: Routes of formation of esters with highest yield

texts:
Esters can be formed in two ways according to the syllabus I'm following:

(1) Mixing an alcohol with a carboxylic acid in the presence of sulfuric acid; and

(2) Mixing an alcohol with an acid chloride.

My question is:

Which method produces the highest yield of esters?

I think method (2) does because the $\ce{Cl-}$ will attach with the $\ce{-OH}$ in alcohol. However, I'm not exactly sure of the reason. Can someone explain it clearly with full details please?


texts:
It is well known (the simplest textbook example) that a diamond has a well-defined arrangement of sp3 carbon atoms, as each atom is connected to four others in a tetrahedral structure.

But what about the last carbon atoms at the edge? For each of these, three bonds are missing; it has a single bond with one carbon atom inside the structure. What is the hybrid and atomic (electron) structure of the carbon atoms at the edge?

I would appreciate some references explaining this in detail (books or research articles).


texts: SMILES vs. Graph representation in deep learning

texts:
I have been reading papers on machine learning and deep learning methods for learning molecular space and generating molecules. These methods use different representations of the molecules. The most popular ones in the field include SMILES and graphs [e.g. this and this]. I have seen a shift of interest from SMILES representations to Graph molecular representations in the past couple years. I was wondering what are possible benefits of graph representations over SMILES?

I can think of two reasons:

The uniqueness issue with SMILES: Two SMILE strings might correspond to the same molecule.
SMILES are abstract representations while graphs are more natural representations (although, I can't really see this. I mean, I see what it
means, but doesn't SMILES also contain the same information?)

EDIT:

some paragraph that I found online and I need interpretation for:

it is focused on molecules whose bonds fit the 2-electron valence
model
it handles a limited array of stereochemistry types
there is no standard for handling aromaticity
there is no standard way to generate a canonical representation.

are any of these corrected in graphs? From what I know:

For 2: In graphs, it takes more than just defining atoms and bonds to account for stereochemistry. For example, I should also define chirality for each node.

For 3: While in some graph representations, aromatic bonds have their specific type, I found it better to explicitly use the order of the bonds.

For 1 and 4 I don't know if graphs are any better.


texts:
In my experimental work, I'm following an article. It said that:

  A 30 nm ZnO seed layer was deposited on the glass substrates by RF sputtering of a ZnO target at room temperature.

But I haven't any tools for "RF sputtering". Is there any replacement for this technique?


texts: What is the procedure of designing a salt bridge for a galvanic cell?

texts:
I'm doing an experiment where I'm measuring the effect of changing the $\ce{Cu^{2+}}$ ion concentration on the voltage in a copper-zinc galvanic cell.

I'll be doing at least five trials for each of the five concentrations I'm testing for (from $0.2-1.0\:\mathrm{M}$), so in total that is 25 trials. However, do I need a new piece of filter paper as a salt bridge for each trial, or can I reuse the same piece of filter paper and dip it in a $\ce{KCl}$ solution each time? Do I really need to make 25 separate pieces of filter paper?


texts: How to create a buffer using CH3COOH and CH3COONa that has a pH of exactly 3.75?

texts:
I need to create a buffer using $\ce{CH3COOH}$ and $\ce{CH3COONa}$ that has a pH of exactly $3.75$.
A $\pu{50 mL}$ sample of your buffered solution will have to be able to withstand the addition of $\pu{25.0 mL}$ of $\pu{0.100 M}$ $\ce{NaOH}$ solution.
The buffered solution will break after the addition of no more than $\pu{35.0 mL}$ of the $\pu{0.10 M}$ $\ce{NaOH}$.

Here is what I have so far:
$$\mathrm{pH}= 3.75 \implies [\ce{H+}] = \pu{10^{-3.75} M} = \pu{1.78 \times 10^-4 M}$$
\begin{align}
\ce{NaCH3COO &-> Na+ + CH3COO-}  &&\text{(common ion effect)}\\
\ce{CH3COOH &<=> H+ + CH3COO-}
\end{align}
\begin{align}
K_\mathrm{a} &=\frac{[\ce{H+}][\ce{CH3COO-}]} {[\ce{CH3COOH}]}\\
1.8\times{10^{-5}} &=\frac{(1.78\times{10^{-4}})[\ce{CH3COO-}]} { [\ce{CH3COOH}]}\\
\frac{[\ce{CH3COO-}]}{[\ce{CH3COOH}]} &=\frac{(1.8\times{10^{-5}})}{(1.78\times{10^{-4}})}\\
\frac{[\ce{CH3COO-}]}{[\ce{CH3COOH}]} &= 0.1011 : 1~\text{(ratio)}
\end{align}
I found the ratio of $[\ce{NaCH3COO-}]$ to $[\ce{CH3COOH}]$, but I don't know what to do from here.
EDIT: "Break": The point where there's no acid left and the solution stops acting as a buffer. "Withstand": meaning that there can be a $\mathrm{pH}$ change of at most $1.0$. Thanks, guys!


texts: Deviation in compressibility factor in different gases

texts: Why does the compressibility factor of gases like Carbon Dioxide and Nitrogen first decrease then increase with increase in pressure , but for Hydrogen and Helium it only increases with the increase in pressure ?


texts: The dissociation of hydrogen on UO2 and PuO2 surfaces: Homolytic or heterolytic?

texts:
I have seen that $\ce{H2}$ can dissociate on a metal-oxide surface by two methods:

Heterolytically, forming a proton-$\ce{O}$ bond ($\ce{OH}$ group) and a hydride-metal bond ($\ce{M-H}$) on a metal-oxide surface.
Homolytically, where two $\ce{OH}$ groups are formed (adsorbed protons) and the two electrons of the $\ce{H2}$ molecule are transferred to low-lying $\mathrm{d}$ or $\mathrm{f}$ states of the cations. This leads to a change in oxidation state and a reduction of the oxide.

However, the reasons for the different behaviours are not obvious to me. Assuming two comparative MO compounds have the same crystal symmetry, how does the electronic structure of the metal impact which process dominates?

EDIT:

I am particularly interested in the example given by: Differences in the Existence States of Hydrogen in $\ce{UO2}$ and $\ce{PuO2}$ from DFT + U Calculations

Here, the preferential formation of a hydride ion $\ce{[(UO_{2})_{n}]^{+}H^{-}}$ or hydroxide ion $\ce{[Pu_{n}O_{2n-1}]^{+}[OH]^{-}}$ has been shown. The authors give the following explanation:

  The differences in the existence states of atomic hydrogen in the two dioxides are proposed to be dependent on the nature of $\mathrm{5f}$ electrons of uranium and plutonium; that is, uranium $\mathrm{5f}$ electrons are more delocalized and more favorable to participate in chemical bonding than plutonium $\mathrm{5f}$ electrons.

Why should the higher degree of electron itinerary (which enables electrons to more easily form chemical bonds) favour hydride formation?

This seems to conflict with: Interaction of hydrogen with actinide
dioxide (111) surfaces.

In this paper and others, $\ce{PuO2}$ has the more reactive surface. Here, the formation of a hydroxide is more favourable on $\ce{PuO2}$, and less favourable on $\ce{UO2}$. Therefore, I am confused as to how this availability of electrons changes.


texts:
In attempting to make magnetized neodymium (NdFeB) powder, I grinded neodymium magnets into a powderusing a belt sander. However, I found that the magnetic properties of the neodymium had decreased substantially. It would appear that any attempt to grind the magnets into a powder using this method seems to cause the diminishing magnetic field observed https://en.wikipedia.org/wiki/Neodymium_magnet .

Is it possible for neodymium (NdFeB) powder to be as magnetic as a solid neodymium (NdFeB) magnet?


texts: Find the partial pressure in a container

texts:
I have an air mass which consists of 78.1% $\ce{N_2}$, 20.9% $\ce{O_2}$, 0.964% $\ce{Ar}$, and 0.0378% $\ce{CO_2}$ in a container which volume $\mathrm{V=40~L}$ at a temperature $\mathrm {T = 298.15~K}$.

The total pressure is $\mathrm{p_{total} = 1.5~atm}$.

Now I am removing all the $\ce{O_2}$ in the container. What will the partial pressure of $\ce{N_2}$ be?

I know the formula $\mathrm{pV = nRT}$.

Before I remove all the $\ce{O_2}$ I can calculate the amount of substance $$\mathrm{{n_{total} = \frac{pV}{RT} = \frac{1.5 \cdot 40}{0.082 \cdot 298.15}~mol = 2.45~mol}}$$.

The molar mass of $\ce{N_2}$ and $\ce{O_2}$ is $\ce{M(N_2)} = \mathrm{28~g\ mol^{-1}}$ and $\ce{M(O_2)} = \mathrm{32~g\ mol^{-1}}$.

If I remove all the $O_2$ the new mass/volume percentage of $\ce{N_2}$ will be

$$\mathrm{m_\%(N_2) = \frac{78.1}{78.1+0.964+0.0378} = 98.7 \%}$$.
So I thought I could find the amount of substance of $\ce{N_2}$  by saying
$$\ce{n(N_2)} = \mathrm{\frac{98.7~g}{28~g/mol} = 3.525~mol}$$ but this will exceed the total amount of substance before I removed $\ce{O_2}$ so this makes no sense.

When I have found the amount of substance of $\ce{N_2}$ I think I can just replace $\ce{n}$ in $\mathrm{p = \frac{nRT}{V}}$ and get the partial pressure of $\ce{N_2}$.

Maybe I have the right percentage of $\ce{N_2}$ but I am calculating the amount of substance wrong when it's a gas? Could the correct answer be $\mathrm{98.7 \% \cdot n_{total} = 2.422~mol}$ and then inserting this in $\mathrm{p = \frac{nRT}{V}}$ which gives me around $\ce{p(N_2)} = \mathrm{1.5~atm}$?


texts: How to evacuate a glass vessel containing powders?

texts:
I would like to evacuate a vessel (a glass round-bottomed flask) and which contains a few grams of platinum. However, I am worried about the platinum powder being sucked up by the vacuum.

A few people told me that this is possible if I take some care, but I am still not convinced. I use a turbo pump in combination with a diaphragm pump for the rough vacuum. So in the end a very expensive vacuum cleaner! I know that the powder will destroy the turbo pump if the powder is sucked in. Do any of you have some experience with powders in vacuum?


texts: I'm a very beginner in chemistry. The book I'm studying says that an ion is an atom, or a collection of atoms, that has an electric charge, then it writes about the difference between molecules and ions. What I'm wondering is, if I consider a unit of, say, sodium chloride (by unit I mean one atom of sodium plus one atom of chlorine), should I say "a molecule of s. chloride" or "an ion of s. chloride"?


texts: Open resource for spectroscopic raw data

texts:
Is anyone aware of reliable resources (ideally public) which allow the user to download the raw spectroscopic data such as infrared spectrum of small organic molecules, or rotational spectrum of HCl/DCl mixtures or NMR spectra of molecules? I was looking at the NIST database but apparently there is no option for downloading the spectrum as an Excel, csv or txt file. Thanks.

NIST Spectral Database


texts: Most activated position for Electrophilic addition in substituted biphenyls

texts:
I know the first structure will go fastest electrophilic addition due to +mesomeric effect but I was wondering what would be the product(major) if a electrophile attacks

Will the electrophile attack both ring or the ring near to $\ce{OH}$ group? Also the negative charge due to resonance will resonate on both the rings then how will I decide which ring to attack to give me major product?

According to me, the ortho positions of the ring near the $\ce{OH}$ group will have a negative charge - as well as the para position - but the para position is hindered. So, the electrophile will attack the ortho positions.

If this the correct explanation of the question, then I have one more question as well, that: when negative charge delocalises to the para position, it can delocalise to the other ring as well. Then, the electrophile could attack in the second ring also, where the negative charge would be generated by resonance. So, will the electrophile attack-the first ring or the second ring?


texts: Why doesn't Grignard reagent attack alkyl halides

texts:
When we add magnesium to
 alkyl halide, Grignard reagent is formed. $$\ce{R-X + Mg -> RMgX } $$ It is highly nucleophilic in nature.  Now at this time the electrophilic alkyl halide is also present in the solution why doesn't grignard reagent simply attack the alkyl halide again ?? $$\ce{ RMgX + R-X  -> R-R + MgX2}$$ Why doesn't this reaction take place ??