texts: Why does blood get further oxidized than Iron oxide?

texts:
Oxygenated blood is bright red and deoxygenated blood is dark red or brown.

If you take oxygenated blood and leave it in the air it will turn dark red, then brown, then finally a bluish green from exposure to atmospheric oxygen.

Why does it oxidize this far to get a copper oxide color to it after it has passed the phase where it is the same color as iron oxide? Why doesn't it stay at the iron oxide color?

This often happens during the last few days of my period that the bleeding is extremely light and the color of it when it first comes out is reddish brown (sort of like iron oxide) and after a few hours, it starts turning bluish green (sort of like copper oxide). However, this happens very slowly and after 24 hours of exposure to atmospheric oxygen still only a fraction of the blood is further oxidized. I don't take medications or drugs that have a lot of sulfur so I don't think it is from $\ce{H2S}$ or $\ce{SO4-}$ (which would give it a dark green color, not light bluish green) and I don't have excess copper in my blood either.

I think that it is Iron(II,III) oxide with the Iron(III) released and the autoionization of water (which happens in both the liquid and gas phase) forming Iron(II) Hydroxide which can be further oxidized to Iron(III) hydroxide which has that bluish green color along with a small amount of Copper oxide forming (Due to the fact that our bodies need some copper and like Iron there is always some copper in the bloodstream).


texts: Major product formed when 1,1,1-trichloropropane is treated with aqueous KOH

texts:
What are (is) the product formed when 1,1,1-trichloropropane is treated with aqueous potassium hydroxide?

I think the major product should be propionic acid, but I'm not sure.


texts: Is this relation in case of a mixture of ideal gases valid?

texts:
I came across the following relation in a book (written as a fact, with no proof), for a mixture of ideal gases both at the same pressure and temperature.  The final volume of the mixture of gases after mixing is:
$$ V_\text{mix} = \frac {M_1V_1 + M_2V_2}{M_1+M_2} $$

where $M_1$, $M_2$ are the molar masses of the individual gases and $V_1$, $V_2$ are the respective volumes.  I could not figure out its proof.  Is this relation valid at all?
Please do not confuse with a similar looking relation,with $ M $ corresponding to molarity, in case of a solution mixture.


texts: How to Separate Copper Nanowires in an Alumina Membrane

texts: So, in my Chemistry Lab we had an experiment to use Whatman alumina membranes and GaIn eutectic to create Nickel nanowires through electrodeposition. So essentially Nickel wire electrode and alumina membrane taped to the copper electrode with GaIn between the membrane and the copper to act as a conductive layer. My group wanted to push beyond just the regular protocol with the extra time we had, so we attempted to perform an identical experiment using copper instead of Nickel. So, everything worked perfectly, we currently have copper nanowires confined inside the alumina membranes and GaIn still stuck on the back of the membranes. The issue is that for Nickel we used Nitric Acid to remove GaIn and then KOH to dissolve the membrane, and we could isolate the nickel wires with magnets, but we obviously can't do so with copper wires. So as of now, we have our copper-GaIn eutectic- Alumina Membranes in solutions of 6M KOH and we do not know how to isolate the copper nanowires. We've thrown around ideas for how to resolve this but nothing certain. So any help would be greatly appreciated!


texts: Raman Spectrum of carbon chains: How to identify the vibrational modes

texts:
So I am using NWChem to calculate the raman spectra of C2H2 and C4H4. For example for the first I obtained the following frequencies:

#  freq [ 1/cm]  S [Ang**4/amu]
------------------------------------------------------------
  1   644.63        0.0087
  2   679.18        0.0076
  3   792.83        0.0001
  4  2146.53        8.0917
  5  3506.05        0.0007
  6  3645.57       37.8189

and for example, when comparing with the expected results from http://www.chem.purdue.edu/gchelp/vibs/c2h2.html , I could say that my mode number four corresponds to C-C stretching.
So now, when I perform the same calculation for C4H4, I get the following:

#  freq [ 1/cm]  S [Ang**4/amu]
------------------------------------------------------------
  1   216.77        2.3873
  2   305.29        0.7775
  3   548.05        0.8095
  4   643.94        1.7042
  5   677.47        0.5218
  6   700.29        6.8906
  7   893.88        0.1890
  8   928.98        0.5379
  9  1033.68        0.1554
  10  1134.09        1.5802
 11  1357.84       16.9774
 12  1504.93       31.2415
 13  1715.33       17.1094
 14  2269.08       38.4659
 15  3293.55       19.5975
 16  3313.05       78.1132
 17  3449.94       44.9757
 18  3578.50       24.6781

My question is this, how could I identify the vibrational mode corresponding to C-C stretching now?
And if I performed the same calculation for C6H6, how could I identify the C-C vibrational mode?
Is there a way of identifying what each mode corresponds to? not only in calculation but also in experiments?

thank you


texts:
I would like to purify my peptide having cysteine residue by using HPLC. It is known that thiol containing peptides undergo oxidation and form disulfide linkages. In order to prevent it I used proper cocktail solution during cleavage from the resin. However, I am still worried what if my peptide undergo oxidation during HPLC purification? How can I prevent it?

I searched in research gate, but I couldn't find suitable answers.


texts: How to calculate the rate constant of a zero order reaction?

texts:
The reactant concentration in a zero-order reaction was $7.00×10^{−2}~\mathrm{M}$ after $160~\mathrm{s}$ and $2.50×10^{−2}~\mathrm{M}$ after $345~\mathrm{s}$. What is the rate constant for this reaction?
  What was the initial reactant concentration for the reaction described in part one?
  The reactant concentration in a first-order reaction was $7.70×10^{−2}~\mathrm{M}$ after $50.0~\mathrm{s}$ and $1.60×10^{−3}~\mathrm{M}$ after $85.0~\mathrm{s}$. What is the rate constant for this reaction?

Background info: The integrated rate laws for zero and first order reactions may be arranged such that they resemble the equation for a straight line,
$y=mx+b$.

\begin{array}{lccc}
\text{Order}& \text{Integrated Rate Law}& \text{Graph}& \text{Slope} \\\hline
  0 &  [A]=−kt+[A]_0      & [A]\text{ vs. }t    & −k\\
  1 & \ln[A]=−kt+\ln[A]_0 & \ln[A]\text{ vs. }t & −k\\\hline
\end{array}


texts: Why do internal energy/heat and enthalphy differ? What is the physical significance of the $PV$ term for enthalphy of an ideal gas?

texts:
Let it be noted that this is not a duplicate of this downvoted-to-hell question, simply because I hope to ask it better!
I've been reading a thermo textbook and I've got a simple question.
The enthalpy of an ideal gas is $h = u + PV$. I understand that the specific internal energy, $u$, is the sum of all rotational, vibrational, translational, electronic/nuclear bonding, and lattice (ignored for ideal gasses, I presume) energies of the substance per unit mass. I further understand that $w + q =\Delta u$ for specific transferred  work and heat $w$ and $q$, implying that $\delta w + \delta q = du$ (forgive my deltas in place of a proper inexact differential symbol). Finally, I understand that since $h = u + PV$ and $PV = N\hat{R}T$, for a constant amount of ideal gas, $PV$ is solely a function of temperature. It can be demonstrated that for an ideal gas, $u$ is also a function solely of temperature, so that means $h$ is as well.
So what's the difference between $u$ and $h$? Clearly, it's that $PV$ term, but what does that physically represent? I don't grok it.
All incoming energy, whether mechanical or thermal, goes into a change of $u$--that makes sense. Add energy to a gas, it's going to vibrate/translate/rotate more & maybe change its bonding state. Say you adiabatically compress your gas. You do work on it and $u$ and $T$ rise, but $PV$ stays constant. Adiabatically unconfine the gas and the same thing occurs the other way. But $h$ still varies because $u$ does, it's not conserved over adiabatic actions.
So the "energy" of the $PV$ term represents something somehow separate to internal energy, inherent to the system, invariate to mechanical work done on it... unless that work ends up raising the temperature? What is this term physically represent? Where does it exist? Why bother with the enthalpy concept at all? I don't get it & I know I'm missing something fundamental.


texts: How to calculate ion concentrations for a precipitation from the solubility product constant?

texts:
The equilibrium constant for dissolving the insoluble substance gold (I) iodide, AuI (s), in aqueous
  solution is 1.6 × 10^-23
  at 25ºC. Write the equilibrium constant expression and calculate the concentration
  of Au + (aq) and I (aq) ions in a solution in which 0.345g of AuI(s) is in equilibrium with the aqueous ions.
  The answer is 4x10^-12.

So 1.6x10^-23=products/reactants. The products = x^2, but what does the reactant equal to? I think they got the answer by ignoring the reactants, is this possible?


texts: I know that a radial node is a value of $r$ where the probability of finding an electron is zero, and nodal planes are planes where the probability of finding an electron is zero, but I haven't been able to find a good definition of an angular node. What are they exactly?


texts: Trans junctions in fused cyclopentane rings

texts: Is it possible for the ring junction to be trans in a molecule containing 2 fused cyclopentane rings? I am aware it is not possible for fused cyclobutane rings but am not sure about the 5-membered counterpart. In case the question isn't clear, the ring junction I am referring to is the one that has stereochemistry drawn in the decalin molecules below.


texts: Does a constrained wave function method exist similar to constrained density functional theory?

texts: I am trying to find out if a constrained wave function method exists for running quantum chemistry calculations. I know that constrained DFT exists and can be used to constrain the charge density to certain parts of molecule but I was wondering if a similar method exists for Hartree Fock, if not why not? Are there limitations that prevent similar constraints from being applied to Hartree Fock?


texts: Why is monohydrogen phosphate an incorrect name?

texts:
In my Ap chem class I got this sheet with the names of a bunch of common polyatomic ions. One of them is named monohydrogen phosphate ($\ce{HPO4^2-}$). In naming, I learned not to use ‘mono-’ if it’s at the beginning of a name.

Is this simply a mistake? Or is there a reason?


texts: Hill's system alphabetizes elements symbol or name?

texts:
Take monosodium glutamate.
Its chemical formula is $$\ce{C5H8NO4Na or   C5H8NNaO4}$$
First way nitrogen, oxygen, sodium, with is in order of element's name.
Second way, N, Na, O, in order of element's symbol.
Have seen it both ways, hoping someone could clarify. Thanks.


texts: Is the activity coefficient always a constant?

texts:
The activity of a species $i$ is defined as $a_i = e^\frac{\mu_i-\mu_i^\ominus}{RT}$, with $\mu_i$ the chemical potential, and $\mu_i^\ominus$ the chemical potential under standard conditions.

Very often, for a species in a non-ideal solution, the activity is written $\gamma_i x_i$, where $x_i$ is the mole fraction and $\gamma$ is a constant known as the activity coefficient for that species. This implies that $\mu_i = \mu_i^\ominus + RT\log \gamma_i x_i$.

What I don't have a good idea of is whether the $\gamma_i x_i$ formula is exact (under some assumptions) or an approximation. Are there situations in which the activity depends on the mole fraction in some non-linear way, or upon the concentrations of other species in addition to species $i$? Is the formula $a_i = \gamma_i x_i$ an exact one under some circumstances, or are there always (in principle) nonlinear correction terms that would make it more accurate?


texts: What does CH4 form when dissolved in aqueous solution?

texts: So I understand $\ce{CH4}$ has a low solubility, but when it does dissolve, what does it form? E.g. $\ce{HCl_{(g)} + H2O -> H3O+_{(aq)} + Cl^{-}_{(aq)}}$. So what does $\ce{CH4 + H2O}$ form?


texts:
I have recently been reading about membrane potentials in the cell and how they are derived. The textbook (Guyton and Hall Textbook of Medical Physiology, 13th Ed) gave this equation:
$$EMF=\pm\frac{61}{z}\log\frac{C_i}{C_o}$$
Where $i$ refers to the interior of the cell, $o$ refers to the exterior of the cell, $z$ is the relative magnitude of the charge of the cation/anion, $EMF$ is the potential in the cell, taking the external potential as 0. Additionally, the sign is + for anions and - for cations.
I understand that this comes from the Nernst Equation:
$$E=E^o-\frac{RT}{\nu_eF}\ln Q$$
Where $\nu_e$ is the number of electrons transferred per mole of reaction.
I understand that $E^o=0$ because at equilibrium, the concentrations of ions on both sides of the membrane are equal and I also understand where the magnitude comes from: $$61=\frac{1000RT}{\log eF}$$
Where $\frac{1000}{\log e}$ is used to change the base of the logarithm and change the units to mV and T is taken to be the body temperature of 37 C, converted to Kelvins.
However, what confuzzles me is

The sign convention: Why are cations - and anions +.
How do we derive the $-\frac{RT}{\nu_eF}\ln Q$ for transfer of ions, since unlike the Nernst Equation, which is derived for electrons, ions are being transferred instead?
How do we measure the membrane potential? According to the text, they put one electrode in the extracellular fluid and pierce another electrode (a typical Ag/AgCl electrode) into the cell, in contact with the intracellular fluid, as shown below. Since there is no transfer of electrons, how does this apparatus actually work?


texts: Where does the residue accumulate in the boiling point composition curve?

texts: My teacher was teaching me the boiling point composition curve for fractional distillation and in the class notes he gave the following diagram (I have given below). It says that the residue starts accumulating at the point on the vaprous line just above the liquidus line (above $χ_{A},χ_{B}$). Note that $χ_{A},χ_{B}$ don't represent the coordinates, they represent the liquid composition of the two components $A$ and $B$. Similarly, $y_{A}, y_{B}$ represent the vapour composition of the vapour in equilibrium with the liquid with composition $χ_{A},χ_{B}$. But why does residue accumulate at that point? My teacher literally gave no explanation as to why. I am so confused. Please can someone explain. Please help.


texts: Which chemical reaction has the highest specific energy?

texts:
Which set of chemicals, reacting together, produces the highest amount of energy, per unit of mass of the substrates?

Let's limit the substrates to reasonably stable chemicals (nothing like monoatomic oxygen gas or neutronium; nitroglycerine level unstable is okay.) and reasonable set of physical conditions (not metallic hydrogen, or bose-einstein condensate, although a primary explosive to initiate the reaction, or liquid hydrogen temperatures are ok). Also - a pure  chemical reaction. No nuclear fusion or anti-matter annihilation please :)

The question is related to "Is there a maximum Isp for “exothermic chemical reaction rockets”?" - a theoretical top limit will be the kinetic energy of unit of propellant being equal to chemical energy of unit of fuel+oxidizer. Popular $O_2 + 2 H_2$ is chosen for high specific energy, abundance and not being too terrible in handling, but I know there are reactions of higher specific energy, if not too practical in rocketry.


texts: Why isn't pressure filtration popular compared to vacuum filtration?

texts:
I want to build a DIY vacuum filtration apparatus with a bike pump but it's very difficult to find one the could be easily converted into a vacuum pump. This prompted an idea to simply build a reverse version where above atmospheric pressure is forcing the liquid to flow through the filter. I notice pressure filtration is rarely mentioned in write-ups, unlike vacuum filtration. Is there a reason for this lack of popularity or a reason why such a DIY apparatus would likely not work?

Could it be that vacuum is necessary for drying the paste that forms at first because it enhances evaporation?


texts: Why V can't have the valence 7 by taking an electron from the 3p orbital and putting it into 3d?

texts: Does that happen because 3p already has a bond?


texts: Is hot air or hot water more effective at melting a frozen pipe?

texts: This question is related to specific heat, and I thought I understood it but I've managed to confuse myself. My initial reasoning was that since in both cases, the pipe is the same, the amount of energy needed to raise the temperature will depend on the specific heat only, and since air has a lower specific heat, it will be more effective. After I started thinking about it more, I thought that the specific heat of the pipe is actually what is important in determining how much energy will be needed to raise its temperature. In this case, the amount of energy needed to unfreeze the pipe should remain constant, and since the specific heat of water is higher, it is more effective at passing on higher amounts of energy than air. Are either of these reasons correct or am I really misunderstanding something? I appreciate any help or illumination you can offer! Thanks!


texts: Viewing and capturing real time values of Electronic balance measuring instrument on television set and computer monitor larger screens

texts:
https://en.wikipedia.org/wiki/Weighing_scale
Is it possible to view and capture real time values of Electronic balance measuring instrument using wired, wireless,CCTV technology on television set or computer monitor larger screens?
Scenario
Chemistry labs - Electronic balance interfaced wired/wireless with the television set or computer monitor i.e.Larger display screen display taking into account.Viewing the mass recording of a object in real time.


texts: Alkane nomenclature - choosing the parent chain - maximize or minimize substituents?

texts:
Given structure:

Here's my go at it. The longest carbon chain has 10 Carbon atoms, so the root -- decane. Next: let's take the substituent in position 3, we get 3 ethyl. And finally, we get 5-(2, 2-Dimethylbutyl). Adding them all up:

5-(2, 2-Dimethylbutyl)-3-ethyldecane.

However, the solution in my book is given as follows:

And the answer given is: 5-(2-Ethylbutyl)-3, 3-dimethyldecane

What I don't get is: Why is the main chain taken by me incorrect?


texts: How would one determine an element simply by looking at its binding energy?

texts:
I am self studying MIT OCW chemistry 5.111 2014, one of the lecture questions states the following:

  Consider a neutral atom with 8 distinct electron binding energies: −14 eV, −28 eV, −94 eV, −218 eV, −293 eV, −1730 eV, −1921 eV, and −14326 eV.
  (a) Name all of the possible ground state atoms that could have these binding energies (without looking up any values).

It seems like the values are quite arbitrary without having a reference place to begin from i.e. electron configuration, quantum numbers, period and so on.

I thought maybe to use equation

$$E_{nl} = -\frac{Z_\mathrm{eff}^2R_\ce{H}}{n^2}$$

as it has an energy parameter, but it appears I have one equation and two unknowns.

Any ideas on how to go about this?


texts:
As an organic chemist, I'm comfortable deriving the pi molecular orbitals of linearly conjugate systems to give the following result:

In a qualitative sense, these molecular orbitals are easily arrived at. For a polyene of n-atoms, the lowest energy combination will have 0 nodes (all in-phase) and the highest energy combination will have n-1 nodes (in, out, in, out...).

Is there a way of arriving at the same result using a more rigorous, formal molecular orbital approach?


texts:
I recently confronted a mission to plot a pC-pH graph('p' stands for the p-value notation, and 'C' stands for the concentration of a species), which meets the conditions below:

Plot the pC-pH graph when a monoprotic acid is added - salts and strong acids can be co-added.

Therefore, I initally assumed that the monoprotic acid to be $\ce{CH3COOH}$, strong acid to be $\ce{HNO3}$, and the salt to be $\ce{NaCl}$ in order to avoid the overlapping of the species.

But it led me to so much unknowns: so I changed the species to $\ce{CH3COOH}$, $\ce{HCl}$, $\ce{CH3COONa}$ each. However it still didn't quite work out. Is it even possible to plot this?

This is actually supposed to be an environmental engineering problem, so there might be some assumptions which won't make the circumstance way accurate but make it simpler.


texts:
Having recently begun studying Quantum and computational chemistry in depth... I am looking for a manual, text, or guide of any form that could explain the basic formulations and potential of the Functionals used in DFT.

My focus lies primarily on their physical significance, preferably derived mathematically...

Could someone kindly help me out with this...


texts: If a mixture of Mn$^{2+}$, Zn$^{2+}$, Co$^{2+}$, Ni$^{2+}$ and Al$^{3+}$ salts is dissolved in water, a white dim solution is obtained. I guess that the aluminium and zinc ions hydrolysed and the respective hydroxides are formed. Am I right, or maybe one of them won't hydrolyze so much that the solution becomes dim or maybe some other cation could have hydrolysed, too?


texts: How does increasing ionic strength affect the pH of solution?

texts: I'm having trouble interpreting the data for an experiment. With increasing ionic strength, I found lower solubility but also lower pH of the solution. What is the effect of the ionic strength on the pH? I'm looking at the solubility of boric acid and changing ionic strength by varying concentrations of NaCl solutions.


texts: Form ice from water in a non-deformable, completely sealed box

texts:
Suppose that I put some water in a non-deformable, completely sealed box, in a way that all the space is occupied by water, and reduce the temperature to transform water to ice.

Since ice takes more space than water, what would happen to the water and to the box?


texts: Hydration number: Carbonic acid in water

texts:
Carbonic acid ($\ce{H2CO3}$) is known to be soluble in water, and that this particular compound is unstable, so much so that according to the 2014 article from Berkeley Lab:
New Insights on Carbonic Acid in Water, it only exists for a fraction of a second (300 nanoseconds according the article).

Newly reported experiments and observations from the Berkeley Lab found that:

  “Our results support an average hydration number of 3.17 with the acid’s two protons each donating a strong hydrogen bond to solvating waters, the carbonyl oxygen accepting a strong hydrogen bond from solvating water, and the hydroxyl oxygen molecules accepting weak hydrogen bonds from the water”

What is not clear is how is the hydration number calculated and how does this relate to the short existence of carbonic acid in water?


texts:
In the reaction:

$$\ce{H2SO4 +CaCO3 \to CO2 + H2O + CaSO4}$$

Does altering the concentration of the sulfuric acid change the volume of the carbon dioxide produced [the volume of the sulfuric acid is constant]


texts: Strange Sticky Substance on Digital Camera

texts:
I purchased a used Canon Powershot A1100 IS camera online. When I received it in the mail it had a very strange sticky substance that looked like a thin film.

It resisted attempts at cleaning. Water, water + soap, baking soda + vinegar, baking soda only, vinegar only and rubbing alcohol all did not resolve the issue. Only vigorous scrubbing kind of helped.

In addition I could not get it off my hands at all even after about 10 hand washing attempts and soaking my hands in soap and water. After my hands dried the areas where my hands touched the camera were still sticky. The only thing that helps was after it dried rubbing my hands with a paper towel. When wet it was not sticky then when it dried it came back.

The battery terminal was completely corroded with a blue color and it seems like there was some but possibly less of the substance internally.

This is part of the battery door. It is used to complete the circuit between the two AA batteries that the camera takes.

Scraping away the blue crystal only results in more of what you can already see in the picture. Metal that looks grey in some places and brown/red in others.

The closest thing I can think of is petroleum jelly but I can't be sure that, that is it. I don't have any and don't work with it much so I can't compare what it looks like.

Based on my description do you have any possible ideas on what it is?

If you do have something that matches these symptoms would you happen to know what its toxicity is and proper cleanup procedure?

Also in general how should one handle touching something they don't have knowledge of but that could be dangerous and when hand-washing is not working/removing it.

Thank you in advance for your questions and answers.


texts: Difference between polarizability and dipole moment?

texts: In my head, any molecule that is very polarisable, has a dipole moment. Is this true? I am very confused and can't seem to find anything that helps my thought, and I can't seem to distinguish between the two without both intertwining.


texts: Example of an achiral molecule without a plane of symmetry or inversion center?

texts:
Some websites, such as this textbook, mention how generally a plane of symmetry or inversion center in a molecule is enough to consider it achiral. Nonetheless, this source clarifies

but if these symmetry elements are absent the molecule should be checked carefully for an  S$_n$  axis before it is assumed to be chiral.

Furthermore, Wikipedia notes the definition of chirality as "a molecule which has no S$_n$ axis for any value of n is a chiral molecule."
Thus, are there any molecules lacking plane of symmetry/center of inversion but that are achiral due to presence of an axis of improper rotation? Are there are also examples of vice-versa, where a molecule has a plane of symmetry/center of inversion, but lacks an axis of improper rotation and is thus chiral?
edit: This post does cover some definitions which is helpful, but the point of this question was to see an actual example.


texts: Does ICP-OES detect molecules in suspension?

texts: I'm curious whether ICP-OES has the ability to detect molecules in suspension?


texts: Why at constant pressure and temperature Gibbs energy change of a process can be negative?

texts:
$dG < 0$, for a spontaneous reaction at constant Temperature $T$ and Pressure $P$, this means that at contant $T$ and $P$, $dG$ can be negative
$dG = VdP -SdT$, this means that at constant $P$ ($dP =0$) and constant $T$ ($dT = 0$), $dG = V\cdot 0-T\cdot 0 = 0$. At constant $P$ and $T$ according to this equation $dG$ is always zero.

Statement $1$ contradicts statement $2$. Why does this happen?


texts:
The heat content of the products is more than that of the reactant in an ............. reaction.

In this question the answer given is "exothermic"; yet I thought the answer would  be endothermic as the products have more heat content and energy cannot be created nor destroyed. Therefore, from the reactants' side, more energy should have been put in for the heat content of the products to be greater.

Also mathematically endothermic make sense as: $$\Delta_\mathrm{r}H = \sum \Delta_\mathrm{f}H_\mathrm{P}-\sum \Delta_\mathrm{f}H_\mathrm{R}$$

And as: $\sum \Delta_\mathrm{f}H_\mathrm{P} \gt \sum \Delta_\mathrm{f}H_\mathrm{R}$
,$\Delta_\mathrm{r}H \gt 0$

Could someone please explain where am I wrong and why the answer is 'exothermic'?


texts:
Glowing press releases and news articles in 2015 proclaimed a new allotrope of carbon. However, even the journal article is light on chemical detail (e.g. no structural formula).

What is its bond structure?
Why is it ferromagnetic? fluorescent? harder than diamond? etc?
Or is it an erroneous result?

Update: as of late 2020, Bhaumik & Narayan have published further papers about Q-carbon, but I still have not seen any reports of replication by others.

Ref: Jagdish Narayan and Anagh Bhaumik J. Appl. Phys. 2015, 118, 215303.


texts: How come the same reaction can be balanced in two distinct ways?

texts:
I faced this reaction which can be balanced in $2$ distinct ways which are not multiples of each other.

$$\begin{align}\ce{6XeF4 + 12H2O &-> 2XeO3 + 24HF + 4Xe + 3O2}\tag{1}\\[0.4em]
\ce{4XeF4 + 8H2O &-> 2XeO3 + 16HF + 2Xe + O2}\tag{2}\end{align}$$

The first reaction is as it is given in the books and the second reaction was balanced by me.

I sense that only a mechanism can resolve this. I found a similar question on googling, but the answer is unsatisfactory. (It's Yahoo Answers. What can you expect?)

I also found two independent reactions here which on adding produce equation $(2)$. I am confused as to what exactly happens.


texts:
For hydrogen fuel cell to produce electricity, hydrogen  will need to be supplied to the anode. To split oxygen and hydrogen from water and obtain hydrogen, we need to use electrolysis. To use electrolysis, we need to use a battery.

My question is, why do we bother splitting up hydrogen and oxygen and then feed it into the fuel cell instead of just using battery to generate electricity? Or is it not practical to obtain hydrogen and oxygen from electrolysis and use it to generate electricity from fuel cell? Thank you


texts:
According to Wikipedia Etard reaction proceed via a ene reaction with chromyl chloride forming a Etard complex(Chromium complex) which is then decomposed by a [2,3] sigmatropic shift to give aldehyde.

But the reaction given in my textbook is as follows,

Mechanism of this reaction suggested by Wikipedia does not create the intermediate of this reaction given in my textbook.The Chromium complex is further hydrolysed to give benzaldehyde.

Some sources which I referred suggest that Etard reaction proceed via a radical mechanism.
https://pubs.acs.org/doi/suppl/10.1021/ic200877f/suppl_file/ic200877f_si_001.pdf

What is the correct mechanism of this reaction?Is the Chromium complex given in my textbook correct?


texts: reactions for alcohols into alkyl halides with 100% retention

texts:
I learnt that alcohols can be converted into alkyl halides in the following ways with 1/2 steps:

adding H-X (X=Cl/Br/I): primary alcohol: inversion (SN2), secondary / tertiary alcohol: racemization (forming Carbocation)

PBr3 + pyridine / SOCl2 + pyridine: primary / secondary alcohol: inversion (SN2), tertiary alcohol: no reaction as unavaliable for SN2

TsCl + pyridine: primary alcohol: inversion (SN2), secondary / tertiary alcohol: racemization (forming Carbocation, if I am correct on this mechanism)

Is there any way for me to make a 100% retention alkyl halide from any degrees of alcohol with 1/2 steps?


texts:
I was going through the properties of titanium when a certain thing caught my eye: It was the reaction of burning of titanium in nitrogen. I was astonished to read it as I knew that neither is nitrogen a supporter of combustion nor does it burn itself. But then how can titanium burn in nitrogen? Moreover it is one of the few elements to do so.

It was written that titanium burns in pure nitrogen.


texts:
In terms of nanometers, what would the size be of an individual sulfate ion in solution?

Would its size exceed 0.5 nm? Enough to displace something that is held together with a gap of 0.35 nm?


texts: Why some reaction have no transition state?

texts:
All stationary point are local minimum, if any parameters changed the energy should be increase. There is no way for a stationary point that energy go straight down to reach another.

I was told that radical reaction have no transition state, but why? What kind of reaction also do not have transition state?
Is there any way to confirm there is no transition state using quantum chemical calculation method?


texts: Hill equation with inhibition and activation

texts:
The Hill equation for an activating enzymatic interaction with cooperative multiplicity $n$ is

$$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = V_\mathrm{max}\frac{[\ce{S}]^n}{K_\ce{S} + [\ce{S}]^n}\tag{1}$$

and for an inhibitory interaction

$$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = V_\mathrm{max}\frac{K_\ce{I}}{K_\ce{I} + [\ce{I}]^m}\tag{2}$$

What would the equation be for competing activating and inhibiting compounds $\ce{S}$ and $\ce{I},$ respectively?

My sort of ansatz is that it would be of the form

$$\frac{\mathrm d[\ce{P}]}{\mathrm dt} = V_\mathrm{max} \frac{c_\ce{S}[\ce{S}]^n}{K_\ce{SI} + c_\ce{S}[\ce{S}]^n + c_\ce{I}[\ce{I}]^m}\tag{3}$$

I spent about an hour trying to derive the actual answer, but I'm no expert in physical chemistry/biochemistry and increasingly have the sense I should turn to someone who is.


texts: Variation of Boiling point with pressure from Clausius-Clapeyron equation

texts:
For a first-order phase transition such as water to steam , we write Clausius-Clapeyron equation as:
$\frac{dP}{dT}= \frac{L}{T \Delta V}$
Now  what I infer from this equation is that if the phase-transition takes place at a lower T (that is boiling point is lower) then the rate on the Left Hand Side increases which basically means that at that temperature any small change in T will cause high change in P. This inference is unsatisfactory to me and as such I want to understand what information this equation essentially gives.
More specifically, I wanted to understand a statement I had come across which said that this equation explains why boiling point of a liquid increases with increases in pressure. Although, physically I understand why this is true but how is this fact deduced from looking at the Clausius-Clapeyron equation?
I tried varying "stuff" in this equation to check whether I could get some sort of understanding but I just couldn't deduce that from this equation.


texts: How to determine number of alpha hydrogens in a cyclic compound?

texts:
How do we determine the number of alpha hydrogens in a compound? Where should we start the naming from?
For example, bicyclo[4.2.0]oct-7-ene and bicyclo[4.2.0]oct-3-ene:

Compare the stabilities of the following alkenes

In both these structures, I need to determine their stabilities based on their hyperconjugating structures. I need to determine the number of alpha hydrogens it has, to determine the number of hyperconjugating structures it makes. Where do I start?
I am aware that stability is directly proportional to the number of hyperconjugating structures. More the number of alpha hydrogens, greater is the number of hyperconjugating structures, and hence greater the stability.


texts: Endothermic reactions with significant activation energy

texts: Are there any chemical reactions where in order to induce the reaction, you have to heat up a substance but after the reactions occurs, the substance is much colder than even before you started heating it up?


texts: After adding 4 drops of fabric whitener in water, what should I add to decolorize the solution and turn it clear like water?


texts:
I have some questions about the mechanism above:

why does ethanol attack the tertiary C before O-C bond breaks?  Shouldn't the mechanism proceed via an $S_{N}1$ mechanism?
Why is ethanol, as a weak nucleophile, able to attack tertiary carbon?
In a lecture it's said that a partial tertiary carbocation is involved, but left secondary carbon is also losing its electrons to oxygen, therefore becoming a partial carbocation; and if two carbon are both partial carbocation, then the tertiary carbon would be more stable and ethanol should attack the secondary carbon.


texts: Can caustic soda (sodium hydroxide) be used to dissolve urine odour?

texts:
I have an area of artificial grass at home in the back garden and during the summer months, the area emits a smell which I can only think is from the dog's urine when he pees all year long. The smell isn't a problem in the winter or during wet days.

I read a lot of posts online about using white vinegar and baking/bicarbonate of soda

I don't have any of that at home, but I do have caustic soda from unblocking drains/pipes that I use once in a while. I wonder if caustic soda can be used in a Pump Sprayer with Water or some other cleaning agent to help break down the smell from urine?

I'm a complete noob with chemistry but I thought this is the right forum to ask the question.


texts: How does one synthesise 2-Monoglycerides from Triglycerides?

texts:
How does one synthesise 2-monoglycerides from triglycerides with additional ingredients if necessary?

My first instinct would be to add a catalyst for the reaction of $triglyceride \rightarrow 3 FA + glycerol$ (FA=fatty acid; for instance a catalyst could be sodium hydroxide) and then add additional glycerol so as to cause the reaction: $FA + glycerol \rightarrow 2$-$monoglyceride $ to occur but I just wanted to ask if this is true because to me this seems too simple to be true.


texts: Reaction kinetics, relating half life to reaction rate

texts:
How do I relate the half life to the overall rate of reaction?

I argued that from the data, doubling the partial pressure of either reactant, keeping the other constant, will half the half life.

So try t1/2 =
$\frac{\ce{[1]}}{\ce{[k][PA_0][PB_0]}}$ and since pressure of A is always greater than B, so t1/2 = $\frac{\ce{[1]}}{\ce{[k'][PB_0]}}$ ?

I then wrote:
$$\frac{-\mathrm{d}[PB]}{\mathrm{d}t} = k [P_B]^m $$, where k = k[PA]


texts: How exactly is ammonium sulfate formed in a Kjeldahl analysis?

texts:
When conducting a Kjeldahl analysis,  ammonium sulfate is formed from nitrogen which protein consist of.

How in a picture of formation of ammonium sulfate there is involved no nitrogen but only some compounds containing nitrogen.


texts:
Question

  Compare the acidity $(K_\mathrm{a1})$ of the following three acids:
  $\ce{H3PO4},$ $\ce{Ph-PO(OH)2}$ and $\ce{H3C-PO(OH)2}.$

Thoughts

These three acids are of type $\ce{R-PO3H2},$ where $\ce{R} = \ce{OH}, \ce{Ph}, \ce{CH3}.$ The ionization equations of them are

$$\ce{R-PO3H2 <=> R-P(=O)(OH)O- + H+}$$

Comparing with hydrogen, benzene ring can reduce the charge of the anion because of the delocalised $\pi$ bond. Also, methyl group is an electron donating group, which will destabilize the anion. Hence, the $\mathrm{p}K_\mathrm{a1}$ I suggest is $\ce{CH3} > \ce{OH} > \ce{Ph}.$ This answer is analogue to $\ce{R-SO3H}.$

One thing I'm not sure is that this logic does not apply to $\ce{R-CO2H}.$ Clearly, the acidity of carbonic acid is weaker than methanoate acid. I don't know which explanation should be applied in the situation of phosphorus.


texts: How do you determine the NIE equation of a buffer?

texts: For example, I have formic acid and sodium formate. How do I know the NIE(net ionic equation) equation is $\ce{HCHO_2 + H_2O <=> H_3O+ + CHO_2-}$ and not $\ce{HCHO_2 + OH- <=> H_2O + CHO_2-}$ ? If I added $\ce{HCl}$ or $\ce{NaOH}$, would that help decide which equation? Is a buffer always added to water? Why or why not?


texts:
A calibration solution contains $\pu{0.02M}$ $\ce{Cr^3+}$ and $\pu{0.02M}$ $\ce{Cu^2+}$. In order to control the solution $\mathrm{pH} = 12$, a phosphate buffer is used with the weak acid being $\ce{HPO4^2-}$ and the weak base being $\ce{PO4^3-}$. The maximum permissible change in $\mathrm{pH}$ is 0.2 units, how many moles of strong acid can be buffered per mole of weak base present?
  $\ce{H3PO4}$: $K_\mathrm{a3}$ = $4.2 \times 10^{-13}$

I have tried to formulate an equation for the reaction but I'm not sure which metal ion is/if both are taking part and therefore finding it hard to produce a $K_\mathrm{a}$ expression.


texts: Why are alkali metal compounds like sodium hydride or sodium amide strong bases but weak nucleophiles?

texts:
I understand why compounds such as $\ce{NaH}$ or $\ce{NaNH2}$ are weak nucleophiles: as they aren't very soluble in organic solvents, they react only on the clusters' surface. But why are they strong bases?

I could understand why they are in water, as they are soluble in water, but in my organic chemistry class it was said that they accelerate E2 reactions. So how can they be strong bases in organic solvents if they aren't soluble in organic solvents?


texts: Why isn't nitrous acid a product of nitrite and water?

texts:
Question
  Predict the products of the following acid-base reactions, and predict whether the equilibrium lies to the left or to the right of the equations
  $$\ce{NO2- + H2O -> ?}$$

I thought it would be $\ce{NO2- + H2O -> HNO2 + OH-}$, but my textbook says that the correct products are $\ce{HNO3}$ and $\ce{OH-}$. What am I doing wrong here? The answer that they give doesn't even seem to balance.


texts: How are subshells and shells arranged in an atom?

texts: If $\mathrm{2s}$ and $\mathrm{2p}$ are in the second energy level, and $\mathrm{3s}$, $\mathrm{3p}$, and $\mathrm{3d}$ are in the next (3rd) energy level, how are these subshells arranged in space in relation to one another? Particularly, could this be pictured as the $\mathrm{2s}$ and $\mathrm{2p}$ orbitals being relatively the same size (although different shapes) and superimposed over them being the $\mathrm{3s}$, $\mathrm{3p}$, and $\mathrm{3d}$ orbitals all of a relatively larger size than orbitals of the 2nd energy level?


texts:
In calcination why is the ore heated in the absence of air in a reverberatory furnace,
does the presence of oxygen affect any thing?


texts: How to determine which aqueous solution has the largest freezing point depression

texts:
Question

This is more of a conceptual question. Let's say that we are given different aqueous solutions and we are asked to choose the one with the highest freezing point depression, which do we choose? Is there a pattern? do we choose the one with salts inside of it?

Example question

  Which aqueous solution exhibits the largest freezing point depression?
  $$\begin{align}(\mathrm{A})&\  1.0\ \mathrm{M}\ \ce{KBr} & (\mathrm{C})&\ 0.5\ \mathrm{M}\ \ce{MgCl2} \\
(\mathrm{B})&\ 0.75\ \mathrm{M}\ \ce{C6H12O6}& (\mathrm{D}) &\ 0.25\ \mathrm{M}\ \ce{Ga2(SO4)3}\end{align}$$

now this question is a bit different because it has concentrations, so do we choose the one with the highest concentrations or the one with salts?

BTW

The answer is A)

But my hypothesis is that we only look at the ones that contains salts/ions inside of them and then the one with the highest concentration. Please let me know if this is correct or not


texts: What substance has the lowest solubility product?

texts: What substance has the lowest $K_\mathrm{sp}$ and what is its value? The lowest I could find is $2.6\cdot 10^{-124}$ for cobalt(III) sulfide $\ce{Co2S3}$.


texts:
I have read that it is possible to revive a dead Li-ion battery by putting it in the freezer for three to seven days, then letting it get back to room temperature.

Can this process work, and if so, how does it work?

Notes:

Somehow the opposite, i.e. heating (cooking) the battery, is more intuitive to me. After all, in the dead battery, there is "something stuck" (crystallized?), and heat could break that. But I don't know if it's a good idea to try that at home. ;-)
I also found that hitting a Li-ion battery, against a table, for example, has some effect. At the moment, I have a battery in an IBM ThinkPad T41 laptop that, although still working, is on it's way to death. When it runs flat and I connect the laptop to mains, then the battery is not detected properly (battery status LED continues blinking orange). So, I take it out, hit it, put it back in, and the problem is solved (LED constantly orange). Also, I have the impression that hitting gives some extra charge. It could be all just a coincidence, of course.
I am asking in part for a friend whose laptop battery has been dead, I believe, already for some weeks or months. He said that the battery is not that old, but he has let it run flat in cold weather (up in the mountains). Anyhow, whether the process works for this particular battery should not influence my decision on accepting an answer. I am primarily interested in understanding a little bit more about battery chemistry, just to broaden my general knowledge.


texts: How to calculate the amount of substance of sodium that are in 10 mL of 30% sodium chloride?

texts:
How much of sodium is there in 10 mL of 30% sodium chloride?

$30\%$ of $\ce{10 ml}$ is $\pu{3 g}$ $\ce{NaCl}$. There is $\pu{3000 mg}$ of $\ce{NaCl}$ and would that be divided by the molecular weight of $\ce{NaCl}$ or of just $\ce{Na}$?
I divided $\pu{3000 mg}$ of $\ce{NaCl}$ by $\pu{58.44 mg/mol}$ and got $\pu{51.44 mol}$ $\ce{NaCl}$.
Since there is one mole of $\ce{Na}$ for every mole of $\ce{NaCl}$ there would be $\pu{51.44 mol}$ of \ce{Na}.
My teacher divided $\pu{3000 mg}$ (he didn't express what he had $\pu{3000 mg}$ of) by $\pu{22.99 mg/mol}$ of $\ce{Na}$ to get $\pu{130.5 mol}$ of $\ce{Na}$.  I have found other similar problems on the internet and feel I am correct.  My teachers only response was to read the question.  If I am wrong please help me understand why.


texts: How can Nernst equation apply in this redox reaction?

texts:
$$\ce{CuSO4 + Zn -> ZnSO4 + Cu}$$
What is the cell potential of the voltaic cell with copper and zinc electrodes if the system is at 50 degrees and the solutions are both at 1 mol? How can it be equal to the standard potential from the nernst equation? $$E_\text{cell} = E^\circ – \frac{RT}{nF}\ln Q$$

If the solutions are at 1 mol concentrations each then $Q = 1$ and $\ln Q = 0$ resulting in $E_\text{cell} = E^\circ$.
But the above basically shows that concentration affects cell voltage but temperature doesn't have an effect on cell potential – which isn't the case. How can I calculate how different temperatures affect the cell voltage?


texts: Balancing and combining the half equations in redox

texts:
I can understand redox equations of the following form, I break these down into half equations and combine them.

$$\ce{MnO4^- + C2O4^{2-} -> Mn^{2+} + CO2}$$

Where I have issue is with the following (unbalanced) equation:

$$\ce{H2 + NO -> NH_3 + H2O}$$

I am asked to show balanced half equations and the final combined equation.

I can see the following changes in oxidation states
reduction: $$\ce{ H -> H^{1+} + e^{1-} }$$ (for both the $\ce{H}$ in water and ammonia)
oxidation: $$\ce{ N^{2+} + 5e- -> N^{3-} }$$

My issue is then with balancing these and combining them, I am not sure if the half equation involving $\ce{H}$ should have $\ce{H2O}$ as the product or the $\ce{H3}$ from $\ce{NH3}$.

How should I go about breaking this into half equations?
Is it ok for both the half-equations to have molecules of the same compound in the product?
Should I ever have water as the product when trying to show a half equation (ie $\ce{H -> H_2O}$)?


texts: Which Additives May be Present in Cellulose Filter Paper?

texts:
I'm wondering what, other than cellulose, might be contained in filter paper (the kind routinely used in Buchner filters / normal funnels).
A search here on Chemistry Stackexchange shows that at least one  additive is used to modify the visual appearance of some filter paper (for improved "whiteness" / "fluorescence").
What additives may be contained in filter paper? What are their properties (solubility and potential chemical interference)? And how could one get rid of them prior to use, without consequence on the paper's filtering properties?
When used to filter away precipitated contaminants I usually rinse my filters in hot purified water before use (more with residual acid traces in mind). How would you guys prepare them for extreme minimal contamination?


texts:
I'm now analysising the water-soluble ions in atmopsheric aerosol. With ultrasonic concussion and filtering impurity, the anion and cation from the particle sample are examined  in Ion Chromatography System(IC) separately.

We test $\ce{Cl-, SO4^2-, NO3-}$ and $\ce{Ca^2+, Mg^2+, Na+, NH4+, K+}$ as 8 major ion species to quantify the concentration level and seasonal variation in the sampling area.

But when I combine the anion and cation data together for same particle sample, the ratio of [ Total charge of anion]/[Total charge of cation] are much larger than  1.

In my opinion, the cation and anion inside particle should keep the balance of charge. The 8 ion species I choose should take up the majority of the total water-soluble ions (added with $\ce{F-}$, organic acid radical, etc).

I have also searched some paper, some results  of their ion-sample are also not keep the balance, but some observed.

Are the ratio of (+-)charges differed by sampling sites? The anion especially $\ce{SO4^2-}$ are larger comparing with the cation species. Are there any missing cation that I have not deteced?


texts: pH of a buffer made with boric acid and potassium dihydrogen borate

texts:
The Problem

  Calculate the pH of a buffer that is $\pu{0.200M}$ $\ce{H3BO3}$ and $\pu{0.122M}$ $\ce{KH2BO3}$. The $K_\mathrm{a}$ for $\ce{H3BO3}$ is $7.3\times10^{-10}$

What I Tried

For each of these methods, I used $\pu{0.200M}$ as the concentration for the acid, $\ce{H3BO3}$, and $\pu{0.122M}$ as the concentration of its conjugate base, $\ce{H2BO3-}$.

Method one – Henderson–Hasselbalch equation

$\mathrm{p}K_\mathrm{a} = -\log(K_\mathrm{a}) = 9.13668$

${\mathrm{pH} = \mathrm{p}K_\mathrm{a} + \log \left(\frac{0.122}{0.200}\right) = 9.13668 + (-0.21467) = 8.92201}$
Method two – Rice Table
$$
\begin{array}{c|lcr}
 & \text{$\ce{H3BO3}$} & \text{$\ce{H3O+}$} & \text{$\ce{H2BO3-}$} \\
\hline
\text{I} & 0.200 & 0 & 0.122 \\
\text{C} & -x & +x & +x \\
\text{E} & 0.200-x & x & 0.122+x
\end{array}
$$
use x is small approximation
$K_\mathrm{a} = \ce{\frac{[\ce{H3O}][\ce{A-}]}{[\ce{HA}]}}$
$\ce{K_\mathrm{a} = \frac{0.122x}{0.200}}$
$x = 0.200 \times \frac{K_\mathrm{a}}{0.122}$
$x = 1.19672*10^{-9}$ – This equals the number of moles $\ce{H3O+}$
$\mathrm{pH} = -\log([\ce{H3O+}]) = 8.92201$

Check $x$ is small approximation: $\frac{x}{0.122} = 9.081\times10^{-9}$ which is less than $5\ \%$, so the approximation is valid.

My question

The answer I got using both of these methods, $\mathrm{pH} = 8.92$, is not correct. The only conclusion I can come to is that I have missed some nuance of this question or I am making a careless mistake. Can somebody please tell me what I'm overlooking here?


texts: Please explain the mystery of the equilibrium constant expression for chemical reactions

texts:
Given a reversible chemical reaction, e.g.
$$\ce{CuCl4^2-(aq) <=> Cu^2+(aq) + 4Cl-(aq) + \text{heat}}$$
occurring in a medium, the equilibrium constant is defined as
$$K = \frac{[\ce{Cu^2+}][\ce{Cl-}][\ce{Cl-}][\ce{Cl-}][\ce{Cl-}]}{[\ce{CuCl4^2-}]}$$
where [X] is the molarity or molar concentration of X = amount$_X$ / volume.

Then, as you can read anywhere (e.g. google 'equilibrium constant equals 1' to see (1st hit) - 'The Equilibrium Constant, K - Chemistry LibreTexts' -

  If K is about equal to 1, the reaction will reach equilibrium as an
  intermediate mixture, meaning the amounts of products and reactants
  will be about the same.

Yet, if the 'amounts of products and reactants' are the same, that means to me the sum of the molarities of the products would equal the sum of the molarities of the reactants, but K = 1 means that the products of molarities are the same.

I can't attach any intuitive meaning to the product of the molarities.

Note:  the first answer is exactly what I needed.  This question was a pedagogical question - as noted above the first google hit gives a textbook with incorrect info on the equilibrium constant.  That had me confused.  Also, I note that my kid's 10 grade honors chemistry text defines the equilibrium constant as the ratio the product of the molarities of the products divided by the product of molarities of the reactants when the system is in equilibrium, and not as in answer 1 below as the ratio of forward and reverse reaction coefficients, and the latter is a much better definition.


texts: Will adding apple cider vinegar to freshly pressed fruit juice preserve it

texts: Would adding apple cider vinegar to freshly cold pressed fruit juice be able to preserve the fruit juice and extend its shelf life? Would the juice change into vinegar with time?


texts: How to determine the equation for the reaction of europium with sulfuric acid based on experimental measurements?

texts:
I was given a set of results by a fellow researcher where he reacted $0.608~\mathrm{g}$ of europium ($M = 152$) with an excess of $\ce{H2SO4}$ and collected $144~\mathrm{cm^3}$ of $\ce{H2}$ gas at room temperature and pressure.

I was then asked to derive the equation for the reaction using these figures.

This is what I did.

I know that $1~\mathrm{mol}$ of gas is $24000~\mathrm{cm3}$.
I found out that $144~\mathrm{cm^3}$ is equivalent to $0.006~\mathrm{mol}$ of $\ce{H2}$.

Then, I did $0.608 / 152$ to get $0.004~\mathrm{mol}$.

This meant that europium and hydrogen gas were in the ratio $2:3$.

The equation I wrote was $$\ce{2Eu + H2SO4 -> Eu2SO4 + 3H2}$$

But I am wrong and I don't know where.


texts: What is the Difference Between the "Degree of Conversion" and the "Degree of Cure" - If Any

texts:
I am currently investigating the degree of conversion / degree of cure of UV-curing acrylic adhesives using dynamic scanning calorimetry.
A thorough google (scholar) search lets me know that the term "degree of conversion" seems to used more often. I am still wondering if the term "degree of cure" is equivalent. Does anybody here happen to know if it's the same thing or if there are any differences?
Definition of the Degree of Conversion
"Degree of conversion (DC) is an important parameter in determining the final physical, mechanical and biological properties of photo-activated composite resins. The DC is determined by the proportion of the remaining concentration of the aliphatic C=C double bonds in a cured sample relative to the total number of C=C bonds in the uncured material."
Galvão et al.: Evaluation of degree of conversion and hardness of dental composites photoactivated with different light guide tips, 2013
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3571515/


texts: Why is there a sudden drop in the concentration of ammonia in this graph?

texts: So initially they are mixed with the mole ratio of $\ce{H2}$ and $\ce{N2}$ being 3:1 respectively. It seems as the reaction proceeds, both these quantities decrease and the quantity of ammonia increases until a point at which $\ce{NH3}$ stagnates. What happens at this point?


texts: Decide major product for first order elimination reaction

texts:
This is my own created question.

The favourable thing for (c) to be a major product is  conjugation of double bonds and highly acidic nature of hydrogen (resulting in elimination of hydrogen at a higher rate) adjacent to carbonyl group (credit $-$ Rover). According to information I have the above reaction is most probably reversible in nature.
(b) should be major product as per mechanism I have given. So which will be the major (or only) product. You may take high temperature conditions if temperature is required as we are doing elimination reaction.


texts: What is the reaction mechanism of a 5-endo-trig cyclization?

texts: I am trying to solve this mechanism for a disfavoured 5-endo-trig cyclisation to generate the disfavoured product (4) from starting material (1). The favoured 5-exo-trig is given by (2), which I have got a mechanism for. My efforts take me to intermediate (3) as shown below, but I'm not too sure on how to generate the desired product without reagent reduction.


texts: Where does the extra electron go in ionic compounds?

texts:
In ionic compounds, where does the extra electron go? Or, in case of a cation, from which shell does it come?

Consider, for example, $\ce{OH^{-}}$, where did this extra electron go in the electronic configuration? And, what about $\ce{OH^{+}}$? There exists no such ion. Why?


texts: Space groups: Herman-Maugin notation, diagrams and Wyckoff positions

texts:
I am currently taking an Introduction to Crystallography course. After studying and understanding the punctual symmetry groups (2mm, 4/m 2/m 2/m, 32,...), the flat groups and the diverse elements of symmetry that exist: helical axes, sliding planes, symmetry planes, among others.

I have doubts when building the diagram of a certain spatial group. For example, in an exercise, I am asked to construct the diagram of the spatial group Pmab.

Pmab implies the existence of:
 an ordinary plane of symmetry perpendicular to the crystallographic axis a,
 a sliding plane of type a perpendicular to the crystallographic axis b,
a sliding plane of type b perpendicular to the crystallographic axis c.

Also, Pmab is an abbreviated notation, because, in reality, there are also two helical binary axes parallel to the axes "a" and "b", and a binary axis parallel to the axis "c".

On the other hand, Pmab belongs to the orthorhombic (rhombic) system and derives from the point symmetry group 2/m 2/m 2/m 2/m.

This is all the information I get from the Herman-Maugin notation. If there is something wrong that I have understood, I hope you will tell me.

Once here I don't know how to start building the diagram, which would look like this:

As far as Wyckoff positions are concerned, I am often asked for them, but I am not quite sure what they are.


texts: How did Thomson calculate the momentum of electron when he didn't know the mass of electron?

texts:
This was proven in 1903 by J. J. Thomson who calculated that the momentum of the electrons hitting the paddle wheel would only be sufficient to turn the wheel one revolution per minute. source

J. J. Thomson measured the charge to mass ratio of electron in year 1897, and R. K. Millikan measured charge of electron in year nearly about 1910, i.e., Thomson knew only the charge to mass ratio of electron in 1903.
Then how did he was able to determine the momentum of electron when he didn't knew the mass of electron?


texts: In acidic solution, what does ClO₃⁻ reduce into?

texts:
In acidic solution, what does $\ce{ClO3-}$ reduce into and, most importantly, why? It's $$\ce{6e- +ClO_{3}^- +6H^+ -> Cl^- + 3 H_2O}.$$

Now, with the gift of foresight, why was the equation for its oxidation not instead $$\ce {2e^- +ClO_{3}^- +2H^+ \rightarrow Cl^- + O_2 + H_2O}?$$
Obviously it balances and charge is conserved. However, the latter equation would seem more likely: less charges have to be pulled apart (so less work has to be done to move these charges), and the bond energy of bonds in a water molecule is almost twice that in an oxygen molecule?

Where is there a flaw in my logic and does there exist a rough set of rules to determine how things will split up under oxidation or reduction?


texts: Is light a reactant in photochemical reactions?

texts:
According to IUPAC a photochemical reaction is a reaction caused by absorption of light. I still can't understand how we should consider light as a part of a reaction. Is a catalyst or a reactant?
In some reactions there is the $hν$ notation above the reaction arrow. For example we may have the following reaction:
$$\ce{A ->[$hν$] B}$$
I want to understand how light affect reactions and chemical equilibriums. I read somewhere about photoisomerization and that favors the less thermodynamic stable product and that make me think of how is it possible for the value of equilbrium constant to change (considering interoconversion as a "reaction").
Light in photoabsorption
When a molecule absorbs a photon it moves to an excited state. This process is associated with a probability factor, lets call it $P$. We can write such a transition as:
$$\ce{A + $hν$ -> A^*}$$
Suppose we have a box with molecules $\ce{A}$ that initially is a closed system. That is photons can enter the box. Now we use a laser and pump photons of specific wavelength into the box and after that we isolate the system, that is no energy can go in or out of the system. Does the above arrow $\ce{->}$ implies a reaction? I was thinking that if $P = 0.2$ then after the light enters the box we will have $[\ce{A}^*] = 0.2$ and $[\ce{A}] = 0.8,$ so the equilibrium constant will be $\displaystyle K = \frac{0.2}{0.8} = 0.25$ (I have omitted concentration units for simplicity).
But this doesn't make sense because first a new thermal equilibrium will be reached and the relative concentrations (populations) will be in accordance with Boltzmann distribution. Secondly if it is indeed a reaction then we must include light also. Also, the concentration $[\ce{A^*}]$ should depend on the incident light intensity.
So is photon absorption just a physical process and therefore the chemical equilibrium concept doesn't apply? I thought that if photoabsorption reaches an equilibrium such that:
$$\ce{A <=> A^*}$$
then for interconversion from cis to trans of a compound $\ce{A}:$
$$\ce{A_\textit{cis} <=> A_\textit{trans}}$$
by populating the excited state of the one isomer the equilibrium position should change. But still this doesn't make sense because Gibbs free energy change of the reaction take into account both ground and excited states of both products and reactants.
Light in chemical reactions
First the notation $hν$ can't be thought to be a catalyst as it doesn't make sense because isn't regenerated. For example, the chlorination of methane to yield chloromethane
$$\ce{CH4 + Cl2 ->[$hν$] CH3Cl +  HCl}$$
uses light to initiate the reaction. But it isn't regenerated in any other step so it shouldn't be a catalyst. Then how one should think about light in a chemical reaction? It is a reactant? In other words could we write the chlorination of methane in the following way?
$$\ce{CH4 + Cl2 + $hν$ -> CH3Cl +  HCl}$$
If that is the case can we find an equilibrium constant that includes the concentration of photons? Because for every reaction there must be a corresponding equilibrium constant according to thermodynamics.
I am asking the above because as I said I read about photoisomerization and I couldn't understand how is it possible to favor a thermodynamically less stable product via radiation.


texts: Why does (2z²-x²-y², x²-y²) have -1 trace in the character table of Td for C3 rotation?

texts:
I'm trying to understand the irreducible rep for $(2z^2-x^2-y^2, x^2-y^2)$ in the $T_\mathrm{d}$ point group. Specifically, for $C_3$ rotations, a trace of $-1$ is listed in the character table for this group. For any matrix, one can rotate the coordinates (basis for the matrix) - i.e. an orthogonal transformation, yielding a matrix with different entries, but the trace will remain the same. So in the case of $120^\circ$ rotations around an axis through a vertex and opposite face of the tetrahedron, one can rotate the coordinates so that the $z$-axis aligns with rotation axis making the calculation of the trace easier.

Any rotation in this basis will leave $2z^2-x^2-y^2$ unchanged, ie. a $1$ on the diagonal. However, the projection of a rotated $x^2-y^2$ back to its own basis will yield $(\cos 2\theta)(x^2-y^2)$. The trace will then be $1 + \cos 2\theta$.
Can anyone help me where I went wrong?


texts: Is most of the weight you lose actually released as carbon dioxide when you exhale?

texts:
I've heard that most of the weight you "lose" is actually carbon dioxide released when you exhale. In percent its much more than what is released in pure heat energy and feces. Does anyone have statistics on what's the split between where the energy leaves your body?

How many percentage of food weight is actually released through carbon dioxide when its burned in your body? For example when you eat a hamburger and fries, is all the carbon released later when you exhale? How much is heat energy? Provided it does not go into fat reserves.


texts: Why do cookies prevent toothpaste from foaming?

texts: If I eat cookies and subsequently brush my teeth such that there is still small amounts of cookie material stuck to my teeth, the toothpaste will not foam as well as usually, making the process less enjoyable. This effect is consistently reproducible with most (sweet) cookies but any not other foods I have tried so far. The toothpaste contains typical foaming agents, such as sodium lauryl sulfate. What could be the mechanism behind this effect?


texts: Oxidation of an aldehyde - how is this a loss of electrons?

texts:
I've been reviewing redox reactions and have been using the OIL RIG acronym to classify oxidations vs. reductions. Generally this makes sense, and many resources I've looked at repeat the "Oxidation Is Loss - Reduction Is Gain of electrons" statement.

But, I also know that aldehydes can be oxidized to carboxylic acids:
$$
\ce{RCHO -> RCO2H}
$$

The compound $\ce{RCHO}$ does not lose electrons when oxidized to $\ce{RCO2H}$ -- in fact, it gains a whole new oxygen atom. So, there appears to be a net gain of electrons here. Does OIL RIG not always hold, or am I misunderstanding something?


texts: Why are the pentahalides of group 15 elements more covalent than the trihalides?


texts: Why might PM2.5 concentration increase or stay the same when SO2 is reduced?

texts: The question is in the title. I've made some research, but in every paper I found the correlation between $\ce{SO2}$ and $\mathrm{PM_{2.5}}$ is described as positive. Thus if $\ce{SO2}$ is reduced, $\mathrm{PM_{2.5}}$ should also be reduced.


texts: What happens to the NMR of an alcohol when D2O is added?

texts:
What difference you expect in the 1H NMR spectrum of phenol in $\ce{CDCl3}$ after a drop of $\ce{D2O}$ is added to the test tube?

1) Since the $\ce{-OH}$ of the phenol is quite acidic, it undergoes rapid $\ce{H+/D+}$ exchange with the $\ce{D2O}$. My expectation is that the $\ce{-OH}$ signal from the original phenol will get reduced and broadened (maybe even disappear, but I am not sure) because it is replaced with an $\ce{-OD}$ group.

2) Aside from this, will the aromatic regions of the NMR spectrum change at all? I expect that the ortho and para $H$ can slowly turn into $D$ through EAS, but I am not sure if that is possible when only "one drop of $\ce{D2O}$ is added", especially without acid and base present.

My book does not contain an answer key, but I would like hear if my thought process is correct.


texts: Cyanide from seeds breaking down in a pond

texts:
I have a large loquat tree that overhangs a pond. The loquat seeds apparently contain cyanide of some sort, so I'm trying to find the effect the seeds have when they fall in the pond.
Over time I imagine the seeds would break down.
What happens to the cyanide? Does it escape into the air, or remain in the water?


texts: Deviation from ideal solutions - activities and concentrations

texts:
What are some examples of solutions deviating significantly from ideal behavior, and, by extension, showing pHs significantly different from those predicted by usage of concentrations instead of activity coefficients in K expressions?

I know Wikipedia lists two examples but what other examples are there? Do all dilute solutions behave ideally or mostly ideally? Or are there major exceptions in which the use of concentrations instead of activities fails?

Also, is there an easy way to incorporate activities into the calculation of pH for complex systems?


texts: GGA functionals requiring second derivatives?

texts:
In "Lecture Notes in Quantum Chemistry II" from the European Summer School in Quantum Chemistry, the authors note that when discussing the LYP functional and other GGA functionals, that

Thus one can immediately see that an evaluation of $v_{xc}$ demands an evaluation fo the second derivatives of basis functions.
(pp102).

Indeed, when (for a functional like B88) I start with the functional itself and compute the functional derivative (either by hand or with a CAS), I arrive at a (messy) expression that involves second derivatives with respect to space. However, libraries like libxc only need scalar functions of the gradient to be passed, in particular $\nabla \rho \cdot \nabla \rho$ , in order to compute $v_{xc}$. Now libxc contains the expressions for its functionals in Maple and then performs symbolic differentiation on them and then uses the maple-to-C translator; thus the actual C code in libxc is uninterpretable by a human.
Is there a known expression for $v_{xc}$ for B88 or another GGA-like functional that might give me a hint as to how to simplify the functional derivative to only depend on these parameters?


texts:
The energy level of a hydrogen atom in its ground state is $-13.6\ \mathrm{eV}$.
How is this value calculated and how can we calculate the same for different orbits?


texts: Why does the nature and oxidation state of a central metal affect field split?

texts:
I know the following factors affect the value of field splitting in a coordination compound:

No. of ligands surrounding the central atom.
Strength of the ligand (as per spectrochemical series)
Nature of the metal ion
Oxidation State/charge on central atom

I have understood why the first two are contributing factors, but the 3rd and 4th points do not ring a bell.

For the 4th point, i.e., ox. state of central atom, my guess was that if there is a lower oxidation state present, then less number of electrons will be present in the orbitals of the central atom, and hence due to lesser repulsion between ligands, value of field splitting will decrease.

Am I correct in this?

As for the 3rd point, i.e., the nature of the metal ion, I am completely at a loss. What does nature specify here, and how does it affect the value of field splitting?


texts: What is difference between density of the equilibrium and vapour density of the mixture

texts:
While solving question on calculating degree of dissociation,  I came across this question:

At 627 degrees Celsius and 1 atm $\ce{SO_3}$  is partially dissociated into $\ce{SO2}$ and $\ce{O2}$ by the reaction;
$$\ce{SO_3 <=>  SO2 + 1/2O2}$$
the density of the equilibrium mixture is 0.925 gram per liter what is the degree of dissociation?"

In  answer, they calculate the the molecular mass of mixture at equilibrium(Mmix) by using density of equilibrium which comes 63.348 and we know molecular mass of $\ce{SO3}$ is 80 , vapor density of $\ce{SO3}$ will be 80 by 2 is equal to 40 ,vapour density of mixture is equal to molecular mass of mixture by 2 is equal to 68.348 by 2 is equal to 34.174 and from here we can calculate degree of dissociation by using the formula(x=D-d/(n-1)d ) but my doubt is what is the difference between vapor density of mixture and density of the equilibrium mixture?


texts:
What are the products of the reaction between methanamine and nitrous acid?

I'm finding this particular reaction very problematic. Here's why:

My teacher tells me that methanamine, when treated with nitrous acid (created by reacting sodium nitrite and hydrochloric acid) converts to an the unstable (at room temperature) intermediate: methane diazonium chloride, which decomposes in the (aqueous) solution to yield methanol, hydrogen chloride and dinitrogen.

A friend of mine (who happens to be a fairly trustworthy senior), tells me that the actual products are methoxymethane and dinitrogen, since methanamine is an exception and doesn't give the same kind of products the other primary aliphatic amines do (he read it up a long time ago, but doesn't remember where).

In hope of clearing up this mess, I resorted to my trusty copy of Organic Chemistry (Morrison and Boyd, 7th edition), according to which, the products of a reaction between a primary aliphatic amine and nitrous acid should be: dinitrogen and a mixture of alcohols and alkenes.

It doesn't mention anything about methanamine being an exception, and "a mixture of alcohols and alkenes" is a little ambiguous. Also I didn't discard this idea because maybe - through some method I don't even know - the methyl bits from the amines might couple and somehow result in an alkene. I wouldn't know since I'm relatively new to amine + nitrous acid reactions, so I won't take the risk.

I couldn't find any trust-worthy reference on this issue for this reaction. I need help resolving this ambiguity.


texts:
I thought molecules that have a ring have an added degree of unsaturation, but this explanation has confused me:

How can something like cyclohexane which has degree of unsaturation of 1, be considered to be "saturated"? Are there different meanings of saturation?


texts: Why do some substances ionize instead of dissolving in water?

texts:
My question can also be understood as

  what make something electrolyte or nonelectrolyte?

I think this question stems mainly from my confusion with the definitions of ionizing and dissolving.

Dissolving of a ionic substance is due to ion-dipole attraction be/wn water molecules and ionic formula unit. If water molecule has enough attraction to break down the ionic compound, the the substance will dissolve.

Ionizing. Uh, all I know about it is...I don't really know. I think only ionic compound will ionize because it is composed of ions. So once it dissolves it basically ionize, right?


texts: What are the crystals that have formed around the top of a conc. nitric acid bottle?

texts: I was looking through my chemicals cupboard and found that this decades-old bottle of conc nitric acid had grown a beard. I can't think of any reaction between (presumably) $\ce{NO2}$ and any airborne substance that could produce this. Any ideas?


texts:
I'm stumped by this question:

  Why has nature evolved to put a porphyrin (i.e. chlorophyll) as the chromophore in a leaf?

I've thought that it might have something to do with how sun emits light at different wavelengths, in the green wavelength of 565 especially (as the sun emits green light), and therefore, through evolution, plants have evolved to incorporate chlorophyll as the chromophore in the leaf to absorb the wavelength of the sun?


texts: Why is the decarboxylation of 2-hydroxybenzoic acid (and related compounds) done 'under nitrogen'?

texts:
I was reading Cannabinoid Chemistry - 6.2 Extraction & pondered over the following:

  Cannabis must be dried be(fore) it is extracted, because it is not possible to remove more than 50% of the cannabinoids from fresh material. THC-Acid is difficult to extract. If you plant(sic) to convert the THCA to THC, the plant material should be thoroughly decarboxylated by heating it under nitrogen at 105℃ for 1 hour before performing a solvent extraction.

Why is decarboxylation done 'under nitrogen'?  My first guess would be that at 105℃ the plant begins to oxidize (but that is just my naive guess).

I've also sourced this graph:

Effect of heating time and temperature on the THC content of an n-hexane
marihuana extract after heating on the glass surface in an open reactor.  Journal of Chromatography 520 (1990).

Which suggests that 122℃ for 27-30 minutes will be even more effective for decarboxylation, but if the sample begins to oxidize at 105℃ it seems even more important to get the right mixture of gases around it at 122℃.


texts: How to find the lifetime of sodium atoms in the 3p using information on the spectral line width?

texts:
I am trying to find the lifetime of sodium atoms at the 3p state using the relationship between the spectral linewidth and the uncertainty principle:
$$ \Delta E \times \Delta t = h / 4\pi $$
The information I have is the full-width-half-maximum (FWHM) linewidth of the sodium atomic absorption spectrum $\lambda = \pu{9.2E-14 m}$. How would I use this equation to find the lifetime?

The atomic transition from ground 3s to excited 3p states has a wavelength $\lambda = \pu{589.0 nm}$.

I used the relationship
$$ \Delta E = \frac{h c \Delta \lambda}{\lambda^{2}} $$

Plugging in $\Delta \lambda = \pu{9.200E-14 m}$, then
$$ \Delta E = \frac{h \cdot \pu{3E8  m} \cdot \pu{9.200E-14 m}} {(\pu{589.0E-9 m})^{2}} $$

So using the uncertainty relationship, we have that
$$ \Delta t = \frac{h}{ 4 \pi \Delta E} = \frac{(\pu{589.0E-9 m})^{2}}{4 \pi (\pu{3E8 m s^-1} \cdot \pu{9.200E-14 m})} = \pu{1.000E9 s} $$

My attempt to convert the linewidth from unit of $\pu{nm}$ to $\pu{eV}$:
$$ E = \frac{hc}{\lambda} = \frac{\pu{6.626E-34 J s} \cdot \pu{3E8 ms^-1}}{\pu{9.200E-14 m}} = \pu{2.161E-12 J} = \pu{1.348E7 eV} $$


texts: Baking soda bath to deacidify newsprint?

texts:
I have some oil-pastel sketches on newsprint I would like to treat for framing (and longevity). My plan is to rinse them in a deacidifying bath, then use wheat paste to wet-mount them to heavyweight pH-neutral 100% rag paper. And finally, to frame them with UV-protective glass recommended for art.

My question is this: Is there any reason not to use baking soda for the deacidifying bath?

I have experimented with it, and it seems to work great. I used a garden-soil pH test solution before and after, and sure enough, the treated paper shows no sign of acidity. The wheat paste bond seems just as good with the treated newsprint as with the untreated newsprint. The oil pastel colors seem unaffected (not surprising, oil pastel being very water-resistant).

Is there anything about sodium bicarbonate that might, over time, cause a visible effect on the paper?


texts: Relative reactivities of alkyl halides in an E2 reaction

texts:
What is the exact order of reactivity of alkyl halides in an E2 reaction?

Organic Chemistry by Paula Yurikanis Bruice says that the order is $3^\circ>2^\circ>1^\circ$. And I think this order is correct because the transition state of the tertiary alkyl halide will be better stabilized by more hyperconjugating structures as compared to the secondary and primary halides.

But my teacher made me write that the order is $3^\circ<2^\circ<1^\circ$ and I even saw the this order in a book.

So I'm kind of confused about the correct order in E2  mechanism.
Any help will be appreciated.


texts: Redundant out of plane bends in gaussian not recognised


texts: Why does sodium hydroxide react with aluminum oxide?

texts: I have seen all the chemical formulas for the reaction between sodium hydroxide, water, and aluminium. I understand that the hydrogen gas comes from the aluminum reacting with the water and the sodium hydroxide just breaks down the aluminum oxide. But why does sodium hydroxide break it down? Also since aluminum oxide is amphoteric can you do this reaction with a strong acid instead of a strong base?


texts: I found a old bottle of methyl orange in my microscope kit, in solid form. I added water to it to form methyl orange solution. I tried putting 2 drops of methyl orange on a spot plate, then adding sodium bicarbonate. I got pink foam, which is not what i expected, as methyl orange is suppose to turn yellow on sight of a base. Does anyone know what this "methyl orange" might be instead of methyl orange? This did come from the manufacturer of the microscope kit, which has a label saying Methyl Orange, so I am confused on why it does not act as an indicator. It was originally in the kit to act as a dye for biological samples.


texts: Maximum number of atoms in the ground state

texts:
I was given the following question.

A sample contains $100$ identical and hypothetical $H$-like atoms ( $Z$ may be fractional). Out of the given atoms, some are in the ground state, while others are in a higher energy level ($n=x$). The $P.E$ of the electrons in the ground state is $-192\ \mathrm{eV}$.
The sample is subject to radiations of wavelength $155\ \mathrm{nm}$, and the electrons jump to a higher energy level ($n=x+3$). Upon back-transition, a total of $10$ different spectral lines are observed
If the final state the electrons reach after absorbing photons of $\lambda=155\ \mathrm{nm}$ is $a$ , and the maximum number of atoms which had electrons in the ground state initially is $b$, find $\frac{b}{a}$

By equating ${}^{x+3}C_2$ to $10$, I found $x$ to be $2$. Then, $a$ must be $x+3$, which is $5$.
As to finding the value of $b$, I am stuck. Can we use the fact that $\frac{|P.E|}{2} = |T.E|$? The energy associated with each photon comes out to be $8\ \mathrm{eV}$, so the total energy absorbed is $800\ \mathrm{eV}$ (Since there are $100$ atoms). Maybe we can use this?
Any help would be greatly appreciated.
Edit:- The answers given are $x+3=6$ and $96$ , so I ended up getting the first part wrong as well.


texts: Does gold always become gold chloride when dissolved with HCl and an oxidizer and can it always be precipitated with sodium metabisulfate?

texts:
I tried to extract gold from computer parts by STRIPPING the gold using $\ce{HCl}$ and $\ce{H2O2}$ by dissolving the copper & nickel underneath but i added FAR too much $\ce{H2O2}$ by a stupid mistake and I ended up dissolving the gold... I didn't know that could happen? I am correct in understanding the $\ce{HCl}$ dissolves the gold, but it needs both energy and oxygen to do so? Nitric acid (commonly added to $\ce{HCl}$ to form aqua regia which dissolves gold) is $\ce{HNO3}$ which has lots of oxygen and Hydrogen Peroxide is $\ce{H2O2}$ which has oxygen also, albeit less than Nitric Acid.....

My mixture is VERY dark red... It's fuming very lightly, and makes you choke if you get near it. It's not see-through but rather very dark and a bit murky, but could be transparent if you added 200% of water.

I am afraid to try anything because if I screw it up I will lose $200 of gold but am I correct in understanding that adding sodium metabisulfate will drop the gold? What if it is too acidic? Will I have to add Urea or Sodium Bicarbonate to neutralise the pH??? HELP!!


texts: Does possibility of Tunneling influence Ground State Energy of PIB with and without finite energy barriers?

texts:
Suppose there are two Particle in a Box models with the same initial energy and same size. Suppose model A has a finite wall or barrier in between the two infinite walls, and the system has sufficient energy for tunneling to occur.

Would the occurrence of Tunneling influence the ground state? If so, how? Which model would have a higher or lower state and why?


texts: Second order reaction half life equation?

texts:
For the reaction:
$$2A\to p$$
The rate, $v$ may be given as:
$$v=-\frac12\frac{d[A]}{dt}=k[A]^2$$
Correct?

Integrating this gives:
$$-\frac12\int_{[A]_0}^{[A]}\frac{d[A]}{[A]^2}=k\int_0^tdt$$
$$\frac1{2[A]}-\frac1{2[A]_0}=kt$$
Rearranging...
$$\frac1{[A]}=\frac1{[A]_0}+2kt$$
Now substituting $t=t_{1/2}$ and $[A]=\frac{[A]_0}2$...
$$\frac2{[A]_0}=\frac1{[A]_0}+2kt_{1/2}$$
Minus $1/[A]_0$ from each side...
$$\frac1{[A]_0}=2kt_{1/2}$$
This then gives:
$$t_{1/2}=\frac1{2k[A]_0}$$

However, I have seen in textbooks that this should be written:

$$t_{1/2}=\frac1{k[A]_0}$$

Have I gone wrong somewhere? If so where?

I need to know which equation is correct because when figuring out the rate constant, would the gradient be equal to $\frac{1}{2k}$ or $\frac{1}{k}$?


texts:
Even the simplest ingredients used in cooking, such as a banana, contain hundreds of chemical compounds. When we cook we mix several of these ingredients and apply heat, which makes a perfect environment for chemical reactions between the various compounds. Actually cooking is the art of initiating the right chemical reactions.

For a typical recipe there are billions of possible reactions between the initial compounds and there are many possible recipes with different initial compounds.

Why are none of the chemical products of this vast space lethal enough to harm a human? In other words why aren't there ingredients that must not be mixed?


texts: Is nucleus at the centre of the atom? If so why?

texts:
In postulates of Bohr's model of the atom, it is said that the nucleus is at the centre of the atom. In Rutherford’s α scattering experiment he said that out of 20,000 alpha particles only 1 particle is deviated by $180^\circ$. If the particles in the atom are moving continuously (like an electron), why is that nucleus at the centre of the atom? If that is so, then when we focus all the α particles at the nucleus (the point where an α particle got deviated by $180^\circ$) all should get deviated by $180^\circ$ right?

What I mean is that why is the nucleus at the centre of the atom?


texts: How do we calculate N factor and why is it useful in calulations?

texts:
I don't understand the concept of N factor at all. Why is it important?

I know that it is something dependent upon the oxidation number, for example N factor of Na would be 1 since it has oxidation number of +1.

For acid and bases we look at the replaceable $\ce{H+}$ or $\ce{OH-}$ present in them.

Apart from this, I didn't really understand how I can use N factor for calculation or how to find the N factor for whole chemical reactions. Please correct me where I'm wrong.


texts:
Recently in The Periodic Table, there was a short discussion regarding this structure:

At first sight, I couldn't figure out what is the structure. After a quick google search, I came to know it is trichloromethane or chloroform (chemspider).
Now, I thought of the structure of dichloromethane and found out to be:

From the structures, It is observed that these are the skeletal formula of tri- and dichloromethane and generally in these structures, the letter C is not denoted, the C-H bond in not denoted and C-Me is denoted by a dash.

Now, following these rules, I was now curious of the skeletal formula of methyl chloride. Is it just a chlorine protruding a bond??

I couldn't find out this structure on the internet and this means that this formula is not valid although, this formula follow the basic rules. Am I wrong in my argument or are the rules vague?

Further, hydrocarbons are the basic skeleton of organic compounds. To draw really complex organic compound, we first have to figure what are the hydrocarbon chains. But still, methane and ethane cannot be drawn using skeletal formula. From propane onwards, you can represent them in skeletal formula.

So, there are certain ambiguities regarding skeletal formula (some simple and basic compounds cannot be drawn) but they are widely preferred. Why is this so?

I searched hard and eventually found out the structural formula of ethane. It is a dash as expected but still, it is a dash. Who would mind that it is ethane?


texts:
According to my organic chemistry textbook, Cis-Decalin has the two rings nearly perpendicular to one another, with the middle hydrogens cis to one another. Trans-Decalin has the ring nearly flat (planar), with the middle hydrogens trans to one another.

However, typing Cis-Decalin and Trans-Decalin into ChemBioDraw (where they appear correctly in 2D form) and copying them into ChemBio3D shows the exact opposite conformations.

Is this a bug with ChemBio3D, or a mistake in the textbook?


texts: Calculating base dissociation constant given the molarity and pH

texts:
At $\pu{25°C}$, a $\pu{0.100 M}$ aqueous solution of $\ce{C_6H_5NH_2}$ has $\mathrm{pH}=8.80$. Find the $K_{\mathrm{b}}$.

I figured I would have to use an ICE table, but I am not too sure how to set it up.

I can find the equation, which is $$\ce{C6H5NH2 -> C6H5NH3^+ +OH-}$$ but I don't think it helps. I only have an elementary knowledge of acid/bases, so I am hoping for a simple answer.


texts: I've seen that it's defined as $h_0 = h + \frac{v^2}{2}$, where $h_0$ is the total enthalpy per unit mass. I can see that the $\frac{v^2}{2}$ term probably has something to do with kinetic energy, but I am still really confused. Doesn't $h$ already account for flow work? And also, how can both sides of the equation have the same units if $h_0$ is "per unit mass"?


texts:
I don't know where to begin with this question.

  A scientist discovered that the state of the unknown gas can be well described by the equation of state below:
  $$P = \frac{RT}{\overline{V}} + \left(\frac{a + bT}{\overline{V}^2}\right)$$
  Find the partial derivative $\left(\frac{\partial \overline{V}}{\partial T}\right)_P$ which is expressed in terms of $\overline{V}, R, b$, and $P$. (Hint: If $\overline{V}$ is a function of two variables $T$ and $P$ (i.e. $\bar{V} = f(T, P)$), then the total differential can be expressed as
  $$d\bar{V} = df(T, P) = \left(\frac{\partial \overline{V}}{\partial T}\right)_PdT + \left(\frac{\partial \overline{V}}{\partial P}\right)_TdP$$
  Use a particular condition to derive the expression $\left(\frac{\partial \overline{V}}{\partial T}\right)_P$ in terms of $\left(\frac{\partial \overline{V}}{\partial P}\right)_T$ and $\left(\frac{\partial P}{\partial T}\right)_{\overline{V}}$.)

This problem is related to the physical chemistry of the gas law. What is the correct approach?


texts: Seeing a case where both + and - mesomeric effect is shown

texts: I came up with that -N=O group shows both +M and -M and I understand that. In my textbook it was written that " -N=O group attached to benzene shows both + m and -m depending on the nature of other groups attached to benzene" I really couldn't get it,how are that groups how to see owe to which group N=O will show +m and by which it will show -m?


texts: On the localized screening of cerium (when compared to iron)

texts:
I was reading the paper 'A linear response approach to the calculation of the effective interaction parameters in the LDA+U method' by Cococcioni - (Paper here) .

Quoting from the first paragraph on page 9, 'The screening in metallic cerium is extremely localized..'. Even though this section deals with the calculation of the Hubbard 'U' (which might be more appropriate for a physics forum), the underlying chemistry is still intact, I understand. But I can't reconcile this from a chemistry point of view. To furnish more context, the authors compare the results of metallic cerium with metallic ion (from the previous section in the paper).

To recapitulate, the assertion here is that the screening in metallic cerium is extremely localized when compared to metallic iron. I know this is directly related to the electronic configuration, but I would be happy if someone would be able to provide an explanation for this.

PS: I added a bounty and even though it says 'answer required from reputable source', I will accept any detailed answer that solves the ambiguity, even if you don't cite or refer any sources.


texts:
I've observed several notations for the ligand in the literature in general, say, for the typical complexes like $\ce{MX_n}$ ($\ce{M}$ - metal) where ligand $\ce{X}$ is denoted as (according to my subjective frequency of occurrence):

$\ce{L}$;
$\ce{Lig}$;
$\ce{Lg}$;
$\ce{Lgnd}$.

I can imagine $\ce{Lg}$ being a poor choice as it can be easily confused with leaving group, and $\ce{Lgnd}$ which looks more like a company's NASDAQ code, but what about the first two options? And what normative document governs the proper notation anyway?

Regarding the $\mathrm{L}$ use for leucine (see comments section here and a thread on Biology.SE What is the preferred way to abbreviate amino acids?), I encountered more sources using $\mathrm{Leu}$ for that matter rather than $\mathrm{L}$. I guess 1-letter code for 20 amino acids is quite suitable and eliminates confusion between leucine ($\mathrm{L}$) and lysine ($\mathrm{K}$), but for me handling $\mathrm{Leu}$ and $\mathrm{Lys}$ is mnemonically easier.


texts: Why does mixing inks make subractive colors?

texts:
I have little knowledge of color theory and chemistery. Recently I came to know that printers use CMYK colored inks and combine them in different proportions to achieve any color on print.

Let us suppose I fill white paper fully with red sketch then white light will fall on inked surface and all colors(wavelengths) except red will be absorbed and only red will be emitted/reflected. Good. Now I overfill that paper with green sketch. Now two things can happen:

Both the inks of sketches mix but do not interact molecully. Like two chemicals A and B mixed in water and both A and B are everywhere in water but they are still distinct molecules. A's and B's molecules don't react chemically.
Both the inks of sketches mix and interact molecuelly. Like HCL and Na2SO4 are mixed in water and they react molecually to make h2SO4 and NaCl.

Now if 1 is true then on any point on paper's surface I have two types of molecules, 1. that reflect red light and 2. that reflect green light. So when white light will fall on paper then from every point two colors will be reflected, red and green. When they'll reach someone's eye then the perceived color will be red+green = yellow. So inks should make additive color.

On the other hand if 2 is true then molecules of red and green ink will react chemically to make a new kind of compound. Now it is not necessary that the new kind of compound absorbs both red and green. It could emit/reflect any random color. So the paper could be of any color depending upon the chemical formula of inks used. So in this case too inks don't make subtractive colors.

Sadly in reality inks make subtractive color and the color of paper actually is dark brownish black not bright yellow. So in reality the mixed ink absorbs almost all colors including red and green which were remaining.

So my question is why does both red and green got subtracted from the mixed ink? In general why does mixture of inks produce subtractive color rather than additive?


texts: How do I calculate the enthalpy change when a gas is being used to heat water?

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The question I'm trying to answer is:

Calculate the mass of butane gas that would be needed to heat $724\ \mathrm{cm^3}$ of water from an initial temperature of $7.44\ \mathrm{^\circ C}$ to $50.7\ \mathrm{^\circ C}$. The thermochemical equation for the combustion of butane is:
$$\ce{2C4H10(g) + 13O2 -> 8CO2(g) + 10H2O(l)}\quad\Delta H=-5748\ \mathrm{kJ/mol}$$

I know that the equation for enthalpy is
$$Q=m\times c\times\Delta T$$
and I calculated this for water:
$$Q=724\times4.18\times43.26$$
$$Q=130918.6032$$
I don't know where to go from here in order to figure out the mass of butane needed.  Please tell me if I have done something wrong or if you can help me to solve the rest of the problem.


texts: Computational determination of unique adosrption sites

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I'm not sure it's a chemistry question or physics question or math question. Since I'm active on this site, maybe someone here can point me in the right direction. I'm trying to enumerate all the possible unique adsorption site on a crystal structure. For common FCC(111) and HCP(0001) surface, we have four possible adsorption sites, namely top, bridge, fcc, and hcp. Now, what if I have a binary alloy structure like CuRe (AB/ L10) or Cu3Re (A3B/ L12) or more complex structure like perovskite or zeolites. My idea for finding adsorption site on a simple binary alloy is:

1) Identify all the top site (that's easy, as I have my geometry in fractional coordinate).
2) Find all the bridge site using the formula $\frac{x_1+x_2}{2}$ in x direction and similarly all the bridge site in y direction.
3) Then use traigle like algorithm between three top site to find three fold hollow site and so on.
4) Now calculate Coulomb matrix$^*$ for all the site within the given neighboring radius and layers. So, if I want to include two nearest neighbor and 2 layers, it will calculate Coulomb matrix for all the sites within that range. Now, sort the Coulomb matrix in descending order. If I have repeated Coulomb matrix for any two sites than they are identical sites.
From my analysis, it should be enough to find all the unique adsorption site without using complex topological formulation; however, I would rather be right than go for this simple formula. My idea about topology related mathematics is on the surface level. But I'm ready to invest time on that now.

My question is two fold:
1) Is this method good enough?
2) If not, what do I need to study to find a better method (preferably with some good reference sources)?

$^*$Coulomb matrix:
$$CM=\frac{Z_1 \times Z_2}{r_{12}}$$
Here, $Z_1=$ 1 for bridge/fcc/hcp site and molecular weight for top site. And $r_{12}$ is the distance between those two sites.


texts: How do I figure out how many hydrogens my compound actually has using a mass and NMR spectrum?

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Question 3:

It said $m/z = 122,$ and $m/z = 124$ is in a $3:1$ ratio, so I figured that meant that chlorine is present. Then I thought $m/z$ was the actual compound's molecular mass.

So I used the rule of 13, and did:

Chlorine's molar mass = 35

122 - 35 = 87

Using the rule of 13

87/13 = 6C + 9H/13

So the molecular formula is $\ce{C6H9Cl}.$ But the integral values I rounded are: 2,2,2,2 and 3 adding up to 11. Did I use the wrong mass to charge ratio? What am I missing?


texts: Find ratio of number of atoms of $A$ and $B$

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However I am thinking of this question to be damn easy but still I'll not say as I am not getting it,

  There are two radio nuclei $A$ and $B$. $A$ is $\alpha$ emitter and
  $B$ is $\beta$ emitter and their decay constant are in ratio $1:2$.
  What should be the number of atoms of $A$ and $B$ at time $t=0$, so
  that probability of getting $\alpha$ and $\beta$ particles are same at
  $t=0$.

So here how can the decay constant be dependent on number of atoms of $A$ and $B$ so that $\alpha$ and $\beta$ particle are in same ratio? I really need a right approach for this one.


texts: Can I solve the partial derivative (dG/dH)s ? Does it make sense?

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It is possible to express   ,   in terms of Cp, Cv, V, P, kt etc. ?

I know that G and H are both derived from the Legandre transformation of U, so they are the same equivalent representation of internal energy but expressed like G=G(T,P) and H=H(S,P).

So I'm wondering if this partial derivative makes sense...


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I am wondering is there any open source software that predict NMR spectra by giving the chemical shift?

Something like Spinach library http://spindynamics.org/group/?page_id=12 (Matlab is not free, so...).


texts: Mismatch of coefficients in rate law expression

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For example, for the reaction $\ce{A + 2B -> C}$, we have

$$\text{rate} = -\frac{1}{2}\frac{\mathrm d[\ce{B}]}{\mathrm dt} \quad \text{and} \quad \text{rate} = k[\ce{A}]^x[\ce{B}]^y.$$ Together, this means that

$$-\frac{1}{2}\frac{\mathrm d[\ce{B}]}{\mathrm dt} = k[\ce{A}]^x[\ce{B}]^y$$

However, in many books it is also written simply that

$$-\frac{\mathrm d[\ce{B}]}{\mathrm dt} = k[\ce{A}]^x[\ce{B}]^y.$$

Which is correct?


texts:
I am designing an industrial process which can remove oxygen from air.
This chemical should combine readily with oxygen in the presence of heat.

In particular, I am looking for a chemical with the following properties:

Combines readily with oxygen, thus removing the oxygen in air
Inexpensive
Environmentally friendly

For point #1, heating is available if it is an endothermic reaction.


texts: Why is boric acid written as B(OH)3 and not H3BO3?

texts: Why is boric acid written as $\ce{B(OH)3}$ and not just $\ce{H3BO3}$, like it should be for an acid?