texts: How to relate the conductance of an aqueous electrolyte to its conductivity

texts:
In this answer on Physics Stack Exchange, the author states that conductance $G$ is related to conductivity $\sigma$ by $$G = \sigma\frac{A}{l}$$
where $A$ is the cross-sectional area perpendicular to the direction of electric current and $l$ is the length of the conductor.
How does this relate to the conductivity of solutions such as aqueous electrolytes?
Papers in the literature often give the conductivity of aqueous electrolytes in units of $\pu{S/m}$ or $\pu{mS/cm}$.  Here is an example from Wu et al., J. Electrochem. Soc., 2015 where the authors plot conductivity in $\pu{mS/cm}$ versus molar concentration in $\pu{M}$:

But, in looking for conductivity values for sulfuric acid as a function of molar concentration, I found this report.  It states the conductance, rather than conductivity, of aqueous electrolytes (Or so it seems).
On page 7 of that pdf, for example, the authors provide a plot of $\pu{micromhos}$ versus percentage by weight:

I think that $\pu{1 micromho} = \pu{1 S}$.  What information would I need to determine the conductivity (in units of, for example, $\pu{S/m}$ or $\pu{S/cm}$) of an aqueous solution of sulfuric acid from the above plot?


texts: Why does half-reaction with largest positive potential will run as written while other is reversed?

texts: While balancing the half redox reaction, the textbook indicated that the flip of equation is dependent on the size potential. But I do not understand the reason why it is like that. Please explain for me.


texts: Multiplication of the reaction and Equilibrium constant

texts:
$$\begin{align}\ce{2A + 2B &-> 2C }\\ \ce{A + B &-> C}\end{align}$$

Why does the equilibrium constant change?

And why the rate of the first reaction square the rate of the second? I understand it mathematically, but logically and scientifically I can't understand it at all.


texts: Does Cl- Have more -I effect or +M effect ( Resonance effect)?

texts: In this question my answer was (A) because i though $\ce{NH2}$ group would give more electrons than $\ce{Cl-}$ . But the correct answer is (D) and my teacher's reason is that chlorine has more negative Inductive effect than positive Resonance effect. Is that true?


texts: We observe that nitrate ion has a trigonal planar geometry according to its lewis structure and the VSEPR theory. Its resonance hybrid consists of three contributing structure -three probable double bond organisations. According to my knowledge, we would expect that pi bond to be distributed equally over the molecule and thus, the dipole moments would cancel each other out. My question is, why such an ion would dissolve in water even though it is  non-polar?


texts: Why dont we use potassium hypochlorite for bleach

texts: I have been reading wikipedia and according to the article on potassium hypochlorite it can be used as a disinfectant. But it is not listed anywhere in the bleach article. I know we typically use sodium or calcium hypochlorite and some others but is there a specific reason we dont use potassium?


texts: Which is the major product formed on nitration of benzyl methyl ether?

texts:
Which is the major and minor product formed from the reaction of benzyl methyl ether with dinitrogen pentoxide?

I know that $\ce{NO2+}$ is behaving as an electrophile here and attacking the aromatic ring. Furthermore, the substituent directs electrophilic substitution to the ortho- and para-positions. I thought that since the ortho position is more sterically hindered, the para product should be the major product and the ortho  product minor.

However, the answer I was given says the opposite, i.e. that the  ortho product is major and the para product is minor. Where am I going wrong?


texts: In order to solve for this equation for heat capacity, do I need to treat it as a system of equations?

texts:
For a lab, we took the temperature of 15ml of tap water, $q_{cool}$, then added 20ml of tap water warmed to 80 degrees Celsius, $q_{warm}$.

We recorded a baseline temperature of 24.8, a temperature of 56 after adding the water, and a temperature of 42.9 100 seconds later.

I have the following equations:

$q=m × 4.184 J/(g*C) × ΔT$
$q_{warm} + q_{cool} + q_{calorimeter} = 0$
$q_{calorimeter} = - (q_{warm} + q_{cool} ) = C_{calorimeter} × ΔT$.

In the first formula $ 4.184 J/(g*C)$ is the specific heat of water.

To the best of my knowledge, specific heat is usually expressed in grams-Kelvin; however, the TA may have provided the info in grams-Celsius (their units are equal, so I presume they're the same thing). However, she also uses $C$ to designate heat capacity as she does in the third equation.

If, in the first equation, $C$ designates heat capacity, then I have three equations, and three unknowns: $q_{calorimeter}, q_{warm}$, and $q_{cool}$, and I'd treat it as a system of three equations and solve for them.

However, if, in the first equation, $C$ designates 'Celsius' then I could just plug in the values for $q_{warm}$ and $q_{cool}$ and solve for $q_{calorimeter}$.

Two related questions:

In the first equation, what does $C$ designate.
If it designates the heat capacity of the system, do I solve for $q$ by solving a system of equations?


texts: Froth floatation process - why CuSO4 is activating floating character of ZnS?

texts:
I read the following :

  "In a mixture of $\ce{PbS}$, $\ce{ZnS}$ and $\ce{FeS2}$, each component is separated from each other in froth floatation process by using the reagents potassium ethyl xanthate, $\ce{KCN}$, $\ce{NaOH}$, copper sulphate and acid. Here potassium ethyl xanthate acts as a collector. $\ce{KCN}$ and $\ce{NaOH}$ depress the floatation property of $\ce{ZnS}$ and $\ce{FeS2}$ particles. Thus, only $\ce{PbS}$ particles go into the froth. Now copper sulphate is added to the mixture which activates floating character of $\ce{ZnS}$ and this time only $\ce{ZnS}$ comes along with froth. The remaining slurry is acidified and $\ce{FeS2}$ floats along with froth."

Can someone help me in exactly understanding the role of copper sulphate clearly along with its specific property associated?


texts:
Why does the order of adsorption of hydrated alkali metals on an ion exchange resin decrease down the group?

I recently did a question on this topic and they say adsorption order is $$\ce{ Li+ > Na+ > K+ > Rb+}$$

I answered it the other way around.  The reason that made me choose my answer was that  $\ce{Li+}$  has a small atomic radius and hence it should have high hydration enthalpy. It should be forming $\ce{[Li(H2O)6]}$ complex which is large enough to show low adsorptivity.

So same trend should be followed as we go down the group. But, it is not the correct answer. So, please point out my mistake.


texts:
Which one of the following cyanide complexes would exhibit the lowest value of paramagnetic behaviour?

$\ce{[Cr(CN)6]^{3-}}$
$\ce{[Mn(CN)6]^{3-}}$
$\ce{[Fe(CN)6]^{3-}}$
$\ce{[Co(CN)6]^{3-}}$

Here I determined central atom configuration and it is $\mathrm{3d^3}, \mathrm{3d^4}, \mathrm{3d^5}, \mathrm{3d^6}$ for each option in order. $\ce{CN-}$ is a strong-field ligand so electron will get paired hence option 2 and 4 will have least magnetic behaviour

But only option 4 is correct. Why?


texts: why is there a net current at halfwave potential?

texts: Im wondering why there is a current measured at a halfwave potential? According to my understanding at the halfwave potential of a diffusion controlled reduction or oxiation at an electrode, there is half of the current due to anodic and the other half of the current due to cathodic current. I assume that therefore the net current is zero, since the same amount of electrons/charge leaves and enters the electrode...


texts: Why the ionization energy of Au is more than that of Cu?

texts:
As we go down the group from 3d to 5

d, size increases.

Vanderwaal radius of Cu and Au is 140pm and 166pm respectively. Since Cu is smaller in size, ionization energy of Cu must be greater.

Then why is the ionization energy of Au greater than that of copper?


texts: Does air dissolve in the R-113 (i.e. Freon 113)?

texts:
Can anyone tell me whether or not air or N$_2$ dissolves easily in the R-113 (liquid solvent) under the saturation pressure of R-113? If yes, what is the solubility roughly? From this link one can only find its solubility in water.
It will be better if you could provide a link. Thank you in advance!

PS: In Table V of this data provided by @Jon Custer, I found no solubility data for air (or N_$2$) dissolved in R-113.


texts: Trigonal bipyramidal arrangement with 2 lone pairs

texts:
So basically according to university textbooks, it is said that the second lone pair in a trigonal bypyramidal arrangement would also reside on the trigonal plane, causing the two lone pairs to be beside each other and compressing the other 3 bonded pairs (resulting in T-shape).

However, my question is: Why doesn't the two lone pairs move to the two axial groups so that the the three bonded pairs reside on the trigonal plane? Surely this would result in the less repulsion within the arrangement? Wouldn't the repulsion between a lone pair and 3 bonded pairs at 90 degrees be less than the repulsion between a lone pair and another lone pair & 3 bonded pairs?


texts: How the electronic configuration of Hydrogen can explain the strength of the Hydrogen bonding?

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So, i understand that, in this case, the partial positive charge its on the Hydrogen. And that his electronic configuration is H = 1s^1
How this fact will explain the strength of the Hydrogen bonding?
Is it because we are talking about an 1s orbital, that is much smaller, and closer to the nucleus? Or is it because the 1s orbital is electron-defficient, and, the fact that the hydrogen has a partial positive charge means that he is even more defficient on electrons. Consequently, he will "hold" this bond in a stronger way(I had a hard time on making a conclusion here).
Help on this...


texts: Irreversible chemical reaction in a battery

texts:
"In reversible reactions, as the reactants react with other reactants to form products, the products are reacting with other products to form reactants."
http://chemwiki.ucdavis.edu/Physical_Chemistry/Equilibria/Chemical_Equilibria/Reversible_vs._Irreversible_Reactions

Inside an ideal battery, the chemical reaction is reversible (at equilibrium), thus the oxydation-reduction reaction Zn + Cu2+ = Zn2+ + Cu is happening in both direction at the same rate right?

Now, for a real battery, there's resistivity inside it due to many factors, thus the chemical reaction is irreversible. My question is, during the irreversible reaction, is the reaction happening in both directions but at different rate due to resistivity inside the battery or it is just like the combustion reaction happening in one direction?


texts:
How many ligands does Fe has in heme ?
I am not sure how many are in heme and how many in cytochrome C.
Its about iron complexes.


texts: Why does increasing temperature for an endothermic reaction always increase equilibrium constant?

texts:
According to Le Chatelier's Principle, increasing temperature for an endothermic reaction shifts the reaction towards the products.

However, unless there are things that I am missing, I believe there are three ways to imagine this phenomenon, albeit they all arise from the same equation/concept.

Classic $\Delta G = \Delta H - T \Delta S$
$\Delta S_{\text{sys}} + \Delta S_{\text{sur}} = \Delta S_{tot\text{}}$
Van't Hoff Isochore: $\ln\left(\frac{K_2}{K_1}\right) = \frac{-\Delta H}{R}\left(\frac{1}{T_2} - \frac{1}{T_1}\right)$

In the second case, it makes sense that an endothermic reaction would favor an increase in temperature because $\Delta S_{\text{sur}} = \frac{-\Delta H_{\text{sys}}}{T}$ assuming constant pressure. Thus an increase in temperature would mean an increase in total entropy change, indicating a more favorable change.

Van't Hoff's isochore also predicts that an increase in temperature favors the forward reaction of an endothermic reaction as well if you do out the math.

However, in the first case of the classic equation, the equation suggests that there is actually an entropy dependence rather than an enthalpy dependence of the gibbs free energy, which is related to the equilibrium constant by $-RT \ln(K) = \Delta G$.

It further confused me when considering that case 1 derives from case 2, and case 3 derives from case 1. I need help identifying my mistake or rectifying the confusion on why equilibrium is not entropy dependent.


texts:
Oxygenated water has become popular for a variety of uses recently - for health purposes internally as well as enhanced wound healing.

Anyhow, my dad asked me recently if I knew how it is that oxygenated water does not become hydrogen peroxide. I don't know the answer to it; but it got me thinking... How does this work? Does the oxygen not bond to the water molecule? If so, how does the bottle of water not just out gas when ever it is opened until the amount of oxygen contained in the bottle is equal to that of the room air.


texts: A question about geometry of benzenetetrol

texts:
In the 3d conformation of 1,2,4,5 - benzenetetrol, how could i determine the direction to which hydrogen atoms of hydroxyl groups would point? and if there were tertiary butyl groups in positions 3 & 6 would it be more stable for hydrogen atoms to point in the direction away from t-butyl groups as a matter of steric hindrance ?

!

Source


texts: What happens when solution containing two or more cations are electrolysed at an excess potential?

texts:
$\pu{250 mL}$ of a waste solution obtained from the workshop of a goldsmith contains $\pu{0.1 M}$ $\ce{AgNO3}$ and $\pu{0.1 M}$ $\ce{AuCl}$. The solution was electrolyzed at $\pu{2 V}$ by passing a current of $\pu{1 A}$ for 15 minutes. The metal/metals electrodeposited will be:
(1) only silver
(2) only gold
(3) silver and gold in equal mass proportion
(4) silver and gold in proportion to their atomic weights

I came across this question whose answer was given as (4). But I doubt the answer. I think that the molar ratio should depend on the ionic mobilities of the cations and shouldn't equal 1.
Am I thinking right? A qualitative answer explaining this would be appreciated.


texts: How to formally calculate the surface density of layered materials such as graphene?

texts:
Typically density is defined in units of mass per volume. In the case of graphene it is mass per area, i.e. surface density. What would be the correct way to calculate the surface density (mass per unit area) of graphene, for example?

Would it be correct to multiply the density of graphite by the van der Waals gap of graphite?


texts: Rotovapping Aqueous Solutions - Need a cold trap?

texts: I am working on a large scale natural product Rotovapping project. There are two botanical extracts to evolve, combined in processing. The solvents are 50% EtOH and 50% glycerin. There is a large volume of material to dry that will require several weeks of run time. I am using a diaphragm pump that has specs for chemical resistance; I am not too concerned for any issue with EtOH. My concern is that the efficiency of the pump may be impacted by water vapors if I push the parameters to expedite the process. I know that cold traps are encouraged for high volatiles...but would it be helpful to add one to condense any water vapor also, for a run this large? The pump does not have any trap system in place currently. Not sure if it is worth the trouble to create an inline trap as or if it will enhance the speed.


texts:
In the following the reaction ,

According to me the product should be compound  (A) due to substitution reaction.

But the product formed is the compound (B) , what could be the mechanism for the reaction for that product.


texts: Value of mixing ratio and rate constant in Chapman mechanisn

texts:
In the Chapman mechanism (which tells about the activities of ozone in the stratosphere), there is a equation for the lifetime ($\tau_{\ce{O}}$) of an oxygen atom, $\ce{O}$ against conversion to ozone, $\ce{O3}$, through a certain reaction is given as
$$\tau_{\ce{O}} = \frac{1}{k_2 C_{\ce{O_2}}n_a^2},$$
where $k_2$ is the rate constant of a reaction involving consumption of $\ce{O2}$ to form $\ce{O3}$,
$$\ce{O + O2 + M -> O3 + M},$$
 $\ce{M}$ is a third body present during the reaction. $C_{\ce{O2}}$ is the mixing ratio of $\ce{O2}$ (which is given as $0.21~\mathrm{mol/mol}$), $n_a$ is the air number density.
Source: Daniel J. Jacob: Introduction to atmospheric Chemistry. 1999, To be published. Chapter 10.

I am confused regarding this mixing ratio of $\ce{O2}$. Shouldn't be this value in the stratosphere different from that in troposphere?

Also, regarding $k_2$, nothing is mentioned about how and where this was measured. I mean if the value of $k_2$ is derived through laboratory experiments, then how reliable is this value for the reactions happening in the stratosphere?


texts:
In the last step in Victor Mayer test for 2° alcohol, why do we need to add an alkali like NaOH? Isn't pseudo nitrolic acid that is formed already blue in colour?

What would be the reaction of alkali with pseudo nitrolic acid?

I thought that no reaction would occur as pseudo nitrolic acid has no acidic hydrogen, but almost all sources say that it reacts with alkali giving blue colouratiom, without specifying the product formed.


texts:
Compare the melting points of:

  1) $\ce{BeSO_4}$

  2) $\ce{CaCO_3}$

  3) $\ce{BaCO_3}$

  4) $\ce{SrCO_3}$

Okay, so there are a few statements given by my teacher:

1) Thermal stability of ionic compounds is proportional to the counterbalance effect of electropositive field of cations(magnitude of +ve charge) and electronegative field of an anion (mag. of -ve charge). (I interpret this as the lesser the difference between the magnitude of charge, the more thermally stable the compound.)

2) The real magnitude of charge is directly proportional to the number of electrons lost(basically the number we write next to an element, like $\ce{Ca^{2+}}$, right?) and inversely proportional to the size of the ion.

3) Except the second group elements and halides, all anions can be considered as "large anions" and hence their effective magnitude of charge will be same (roughly).

So since all of them are "large anions", we have to compare the magnitude of charge on the cations. Now, being large, their charge is small. So for least difference, we want the cation with the smallest charge. This means the largest size, which simply means $\ce{Ba}$. So the answer should be 3. To confirm this, I Googled the melting points of these substances.

1) $\pu{110^oC}$
2) $\pu{811^oC}$
3) $\pu{825^oC}$
4) $\pu{1494^oC}$

So according to me, the melting points in decreasing order should be:

3 > 4 > 2 > 1

When it turns out to be:-

4 > 3 > 2 > 1

Where did I go wrong?

I personally think:

1) Since the charge on anions is only roughly same, I think that when we consider the difference between the charges, that would be messed up and so we would end up with wrong answers(possibly).

2) That since this question is supposed to be for high school students, we make a lot of assumptions, which obviously don't hold true in the real world, and hence the answer is wrong? That being said,is my answer correct keeping these assumptions in mind?

3) Since chemistry has a lot of exceptionss , is this another one of those? Am I going to have to memorize this too?


texts: Why does coke foam up when I add it to (cold) black coffee (no sugar, no milk)?

texts:
Album of the different gifs detailing this situation: Album of coke-coffee related gifs
I thought that the answer would be similar to the ice-cream float situation, but I don't see what in the coffee would cause the soda to float.
Could it be some reaction with the coffee oils and the coke?

Above is a shot of my materials:

Can of Coke Zero (ingredients: Carbonated water, caramel color,
phosphoric acid, aspartame, potassium benzoate, natural flavors,
potassium citrate, acesulfame potatssium, caffeine)
Nespresso coffee    (ingredients: Roast and ground coffee, hot water)

Above is after the coffee cooled.
Experiments:
Here is a link to a gif of me pouring the coffee:
Gif of me pouring coke into the coffee
To address one of the comments, here is a gif of me pouring coke into an empty bottle: Gif of me pouring coke into an empty bottle, comparison
To address another comment, link to me pouring coke into a mug of tea (instead of coffee): Gif of me pouring coke into a mug of tea


texts: How to calculate molecular emission spectra?

texts:
Is there free software that can calculate the fluorescence emission spectra of organic molecules?
Let's say, for example, rubrene

There is a bunch of quantum free quantum chemistry software:
https://en.wikipedia.org/wiki/List_of_quantum_chemistry_and_solid-state_physics_software
However, which one would be the most suitable for this purpose? Could this be done on a reasonable up-to-date laptop? Of course, computing times will depend on the number of atoms in the molecule and the desired precision. What would be approximate calculation times? In the order of hours, days or weeks?
I can imagine that this is most probably not a simple "draw molecule and push calculate-button"-task, but any hints where to further dig into are appreciated.

Addition after the question was put on hold:
This question certainly can fill a semester of a lecture on quantum or computational chemistry. In that sense, yes, it is broad.

However, instead of detailed instructions or input scripts, I was hoping for some rough guidance about the essential steps and the available software which can be recommended for that purpose (and equally important: which software can be excluded or cannot be recommended to avoid investing a lot of time and find out later that there are much better options). And of course, whether you need a super-computer or whether you can do it on a laptop within a reasonable amount of time.


texts: Paper Towel Soaked with Isopropanol/Water Mixture Burns without Damaging the Paper. Why?

texts:
Video: https://www.youtube.com/watch?v=_qFN1hDZwp8

If you choose not to view the video, in the first demonstration a paper towel is soaked in isopropanol. As expected, the paper towel burns. However, in the second demonstration the paper towel is soaked in isopropanol and water. Surprisingly, the towel burns without being damaged.

My chemistry professor tells me that it has something to do with the energy cost of a phase change $\left[\ce{H2O}\ (l) \longrightarrow \ce{H2O}\ (g)\right]$; however, I am still very confused.

Could someone please elaborate? Thank you.


texts: It's been a while since I've studied chemistry. Now, I am reading the documentation of RDKit. At a certain point, the term "kekulization" is mentioned. What is kekulization (in RDKit, if this is not a standard chemical term)?


texts:
I have seen this phrase several times across DFT textbooks. However, I am not sure if it still holds. Was there a change or a theorem that proved it otherwise? Several programs display wavefunctions for DFT calculations. For example, Quantum Espresso has the option to collect wave functions. Some of the people that I have to talked to mention the Kohn Sham orbitals as if they were a real physical thing. Shouldn't it not be possible to obtain the wavefunction for a certain state? For example, I thought it was not possible to tell that a Kohn Sham orbital belongs to a wavefunction near the surface of a material.

I know that the Kohn Sham orbitals lack a physical meaning. They are simply wavefunctions that are used to obtain the correct density. They do not have an analogue of Koopmans' Theorem. In addition, "the exact wave function of the target system is not available in density functional theory" (Koch, 2001).

So why do people need/use wavefunctions (after all most DFT programs can group such wavefunctions)? I thought that they were Kohn Sham orbitals. Therefore, there should be seldom any use for them.


texts: Do electronic balance weighings still need to be corrected for buoyancy error?

texts:
Buoyancy error is a weighing error due to the difference in the buoyant force exerted by a medium (commonly air) on the object and on the standard masses. The difference in buoyant force occurs when the object and the standard masses have standard masses (Skoog et al., 2014).

Knowing this, I am confused as to whether electronic macroanalytical balances need to be corrected for buoyancy error because of the following factors:

Electronic macroanalytical balances still get calibrated by weighing standard masses.
Closing the doors of the balance does not make the system inside of it evacuated. It still has air which can exert buoyant force on the object and on the standard masses.

Given the factors I mentioned, do electronic balance weighings stil need to be corrected for buoyancy error?

References:

Fundamentals of Analytical Chemistry, Skoog, et al., 9e


texts: When an enzyme is diluted with water, what is slowing down the rate of reaction?

texts: I'm specifically talking about the decomposition of hydrogen peroxide by bovine catalase. The number of catalase molecule obviously doesn't change, so there's the same number of catalase molecule within an undiluted and a diluted solution. Also, seeing as water is not an enzyme inhibitor, and doesn't change the pH or temperature, then shouldn't the rate of reaction remain the same regardless of concentration, since every environmental conditions & the number of catalase molecule in the solution before dilution is the same after it is diluted?


texts: How to make a CP2K input file with Avogadro?

texts:
I am trying to learn to work with CP2K and now need to make its input file. CP2K has kind of adaptor for Avogadro2 but not Avogadro ( I don't know what is the relation between them !).  I also tried that adaptor plugin with Avogadro2 but it does not work for me ( tried on Mac OS X Yosemite and Windows 7).

I searched a lot but seems there is no way to make CP2K inputs with Avogadro . Is there any ?


texts: Testing for the presence of Hexamethylenetetramine / Formaldehyde

texts:
I read in Russian popular articles that it is allowed to preserve herring/fish with Hexamethylenetetramine in Europe. Since Soviet times, I like to buy salty herring and marinade it with Vinegar. The food-safety article says that Hexamethylenetetramine + Vinegar = Formaldehyde, which is a serious poison.

  How can I easily test presence of Hexamethylenetetramine or Formaldehyde in food?

The salty herring that I buy is sold loosely, without packaging, so that I cannot simply read the ingredients.


texts: Question regarding the mechanism of oxymercuration-demercuration of alkenes

texts:
Organic Chemistry by David R. Klein

The text in between says that the more substituted carbon bears a partial positive charge. Why not the other one? I am asking this considering inductive effect, although I am myself not too convinced by my inductive effect explanation.


texts:
Which is higher in energy? Cyclohexanone enol or cyclohex-2-en-1-ol?

Okay from what I understand a higher pi HOMO is synonymous with more nucleophilic. So I would expect cyclohex-2-en-1-ol to have the higher pi HOMO because in the case of cyclohexanol enol there would be inductive withdrawal by the oxygen connected to one of the sp2 carbons involved in the pi bond.

Or would it be the other way around? Resonance donation by oxygen into the pi bond of the enol makes it more nucleophilic? How can we tell how the HOMO/LUMO energies split?


texts: Initial rate of reaction from the graph?

texts:
I tried finding the slope between two points but I keep getting wrong values, how does one find the initial rate by using such graphs?

So I started by trying to find a slope of two points, $(0,0.4)$ and $(10,0.2)$ after calculations I got  $-0.02$, which is the opposite of the right answer in sign. I tried to check myself by trying to find the slope for other points like: $(10,0.2)$ and $(20,0.1)$ which gives me $-0.01$, I'm confused as whether my initial idea is right or not.


texts:
The electronic configuration of nickel is

Ni: [Ar] $3d^84s^2$

Here, while writing the configuration, we fill the 3d after 4s.Hence the 28th electron enters the d orbital.

But

$\ce{Ni+}$: [Ar] $3d^84s^1$

Here we take out the last electron (28th) from 4s.
Are there any rules or conventions regarding this or am I conceptually misguided.


texts:
So I was curious regarding a simple chemical equation :

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

You add heat to the system (i.e fire) and you get water vapor.

I'm curious of understanding the mechanism, which I'm sure at this point has been well studied.

Suppose I keep track of the location of each one of these atoms, and the energy nearby - my anticipation is that the reaction occurs when the atoms get close enough and there is sufficient energy present to conduct the reaction. Is there any way to summarize this critical point of water creation mathematically in this framework (i.e the combination of atoms being close enough and sufficient energy will make this reaction take place) - or is there a superior way?

Does anyone have any insight/publications that can help me understand the steps of water synthesis via reaction mechanism?


texts: What would happen if someone consumed a Silica Gel Packet?

texts:
Most packaged goods have the tiny Silica Gel Packets packed along with a clear warning on every single packet.

My question is:
What hazards of desiccant silica gel are they concerned about that it is necessary to post the warning "THROW AWAY DO NOT EAT" on the packaging?


texts: Hybridisation of similar energy orbitals

texts: Hybridisation is the mixing of orbitals of similar energies, so when we perform hybridisation, why don't we prefer $4\mathrm s$ in place of the $3\mathrm d$ orbital for hybridisation, even though $4\mathrm s$ has less and more comparable energy to $3\mathrm p$ and $3\mathrm s$? Why can't we make an outer orbital complex like $\mathrm{sp^3s}$ instead of $\mathrm{sp^3d}$?


texts:
According to this paper on dehydration by $\ce{Al2O3}$,

  Dehydroxylation causes a surface defects as Lewis acidic centers (unsaturated $\ce{Al^3+}$ ions) and basic Lewis centers ($\ce{O^2-}$ ions) creation. Water molecules deactivate Lewis centers and create strongly acidic Brönsted’s centers. Alcohols dehydration reaction performs on Brönsted’s active centers where hydroxyl groups disconnect proton from alcohol molecule. During reaction alcohol molecule adsorbed on aluminium oxide surface reacts with proton.

But I am not able to understand what they are trying to convey here.


texts: Why can you sanitize paper money notes with a Clothes Iron?

texts:
I have some Canadian and British bank notes. The first issue is that I don't know if they're paper or plastic.
Second, I don't understand this answer. Why's it safe  to iron paper bills? Won't the heat or pressure ruin the paper bill?

You can iron paper bills, like the American ones, on rather high heat. Just the same iron you use for your clothing, at the hottest setting, but no steam. It will kill all viruses.
Plastic bills can be hand washed, with the same soap you would use on your hand, you can dry them the same way you dry your hands, with a clean cloth or even the hot air dryer you use for your hands. Or you can let them air dry.
These bills can withstand some heat but I have heard not enough to iron them clean.


texts: White snow-like powder below sodium hydroxide solution

texts:
I have created sodium hydroxide solution with half cell brine electrolysis but, finally I got white snow-like insoluble powder sank below sodium hydroxide.
What should I do keep or remove it?


texts: Why is the dipole moment of acetone higher than ethanol?

texts:
It is true that acetone is less polar than ethanol.
I thought the dipole moment is proportional to polarity, and if so, the dipole moment of acetone should be lower than ethanol.
But the dipole moment of acetone is higher than ethanol.
Why is it higher?


texts:
What is the product when naphthalene is oxidized by alkaline (or acidic) solutions of $\ce{KMnO4}$?

Some possible reactions show up in a google search, but they have no references:

Naphthalene to phthalic acid by alkaline $\ce{KMnO4}$:

Another product on oxidation of napthalene by alkaline $\ce{KMnO4}$:

If possible, please include the reaction mechanisms in the answer as well.


texts: Chemical equilibrium of inorganic complexes

texts:
After mixing Cobalt(II) Chloride hexahydrate with ammonium chloride a violet complex forms, what would be the complex formed?
It was the precursor for producing hexamine cobalt chloride so I didn't characterize it.
I expect many compounds like hexaqua cobalt chloride and pentamine aqua cobalt chlride or amine chloro coblat complex?


texts: How does sulfur has atomicity 8, when its valence electrons are 6 like oxygen- ie even 2 sulfur atoms can share a pair of electrons and achieve the octet rule, why should it involve 8 atoms?


texts: Confusing definition of mol when considering second order rate equations

texts:
I am confused by "$\text{mol}$".
I denote the unit of a physical quantity with square brackets (e.g. $[V]=l$), and the value of a physical quantitiy using curly brackets (e.g. $\left\{ V\right\}$ = 0.01).
A simple second order rate equation for number concentrations $n=N/V$ is given by,
$$\dot{n} = k^*_{on}n^2,\;\;[1]$$
where the $[k^*_{on}]=l/s$.
The same second order rate equation but for molar concentration $c=\frac{N}{N_AV}$, is given by
$$\dot{c} = k_{on}c^2,\;\;[2]$$
where $[k_{on}]=\frac{l}{\text{mol}~s}$.
When transforming equation $[1]$ into equation $[2]$, we get the relation
$$k_{on} = \left\{k_{on}\right\}\frac{l}{\text{mol}~s} = k^*_{on}N_A = \left\{k^*_{on}\right\}\left\{N_A\right\}\frac{l}{\frac{1}{\left[N_A\right]}s}$$
Hence $\frac{1}{\left[N_A\right]} = \text{mol}$?
But this would be in contraction to the definition I find on wikipedia where it is written that:

In short, for particles 1 mol = $6.02214076×10^{23}$.

Hence, $1~\text{mol} = \left\{N_A\right\}$.


texts: Why H2O is a liquid (water) and H2S is a gas?

texts:
I always think about this question.
Is it due to attraction or repulsion or is there something else that makes one of them a gas and the other a liquid (water)?


texts: How photoluminescence (PL) spectroscopy works

texts:
Photoluminescence (PL) spectroscopy is used to find the energy levels in a compound but how does PL spectroscopy works? After exciting a material  with a particular wavelength whether PL machine looks for photons emitted with in a range of wavelenght?

The below image was taken from here.

To get this spectra the $\ce{CeO2}$ was excited at 345 nm and got peaks at 490 and 520 nm(approx) ie 2.53 and 2.38 eV respectively and its band gap is 3 eV. Whats happening here?


texts: Is enthalpy of a reaction meaningful at variable pressure?

texts: Why should the enthalpy of a reaction be defined at constant pressure. Why can't it be defined at variable pressure?


texts: Why isn't the base reformed in base-catalyzed hydrolysis of esters?

texts: In acid-catalyzed hydrolysis, the hydronium ion is clearly reformed; however, in the base-catalyzed hydrolysis, an alcohol is formed as a by-product, but the strong base isn't reformed. Is it a misnomer to call it base "catalyzed"?


texts: Why is the formation of double helix between non complementary sequences disfavoured?

texts:
The textbooks starts with the phenomena that double helix is an expression of the rules of chemistry.

  Hydrogen bonds are important in determining the formation of specific
   base pairs in the double helix. However in single staranded DNA, the hydrogen bond donors and acceptors are exposed to solution and can form hydrogen bonds with water molecules.
  When two single strands come together, these hydrogen bonds with water are broken and new hydrogen bonds between the bases are formed. Because the number of hydrogen bonds broken is the same as the number formed, these hydrogen bonds do not contribute substantially to driving the overall process of double helix-formation. However, they contribute greately to the specificity of binding.

I see the point that some neucleotides which form stable links are the complimentary bases (purine and pyramidine). Some bases do not form stable links. I did search my question online, I am not able to get near anything that's directly related or comprehensible at my level. So following is what I do not understand.

  Suppose two bases that cannot form Watson-Crick base pairs are brought together. Hydrogen bonds with water must be broken as the bases come into contact. Because the bases are not complementary in structure, not all of these bonds can be simultaneously replaced by hydrogen bonds between the bases. Thus, the formation of a double helix between noncomplementary sequences is disfavoured.

What's the specificity mentioned here? What does it mean by non complementary in structure? An example is appreciated.


texts: How to determine the vapor pressure of a glycerine and propylene glycol mixture?

texts:
I am looking to calculate the minimum heat needed to create vapor from a specific mixture. I have a mixture of 60 % $\ce{C3H8O3}$ (glycerine) and 40 % $\ce{C3H8O2} $ (propylene glycol, propane-1,2-diol). Total volume of the mixture is 3 ml. Here are some facts that I know

 C3H8O2
 Density = 1.04 g/cm³
 Boiling point = 370.8 °F (188.2 °C)
 Molar mass = 76.09 g/mol
 Specific Heat = 2.5 kJ/(kg·K) or 0.60 Btu/(lb·°F)

 C3H8O3
 Density = 1.26 g/cm³
 Boiling point = 554 °F (290 °C)
 Molar mass = 92.09382 g/mol
 Viscosity = 1.412 Pa·s
 Specific Heat = 2.43 kJ/(kg·K) or 0.576 Btu/(lb·°F)

At what heat will the mixture begin to create vapor? I am looking for an answer, although I am not looking for someone to come in and just leave an answer. I would rather understand how you came about the answer, i.e. equations, additional info, so that I can adjust the percentages and volume on my own. The percentages of the mixture will vary. The volume of the mixture will vary depending on the amount of heat needed to create vapor, i.e. decrease volume if not enough heat is present.


texts:
The IUPAC definition of an intensive variable is:

  Physical quantity whose magnitude is independent of the extent of the system.

Why is it defined for "a system", and not for a homogenous system, as for a heterogenous system the quantity (e.g. density, temperature) might be different for the different extents/parts of the system?


texts: Does the chemical in an alkaline battery make battery leaks unavoidable?

texts: Battery leaks was an issue in the 80s and 90s, and since quality and innovation is constantly improving, I thought battery leak might be slowly going away.  But I found that even nowadays, name brand alkaline batteries still leak after a while, even if originally concealed in a tight package of the metal shell.  Is it true that the chemical in an alkaline battery inherently expands in volume over time, and make the alkaline battery leak issue unavoidable?


texts: How to calculate the heat of dissolution from a calorimeter experiment?

texts:
A $\pu{1.50 g}$ sample of $\ce{KCl}$ is added to $\pu{35.0 g}$ $\ce{H2O}$ in a styrofoam cup and stirred until dissolved. The temperature of the solution drops from $24.8$ to $\pu{22.4 ^\circ C}$. Assume that the specific heat and density of the resulting solution are equal to those of water, $\pu{4.18 J g-1 ^\circ C-1}$ and $\pu{1.00 g mL-1}$, respectively, and assume that no heat is lost to the calorimeter itself, nor to the surroundings.
$$\ce{KCl (s) + H2O (l) -> KCl (aq)} \qquad \Delta H = ?$$
a) (2 points) Is the reaction endothermic or exothermic (circle the correct answer)?

Endothermic

b) (4 points) What is the heat of solution of $\ce{KCl}$ expressed in kilojoules per mole of $\ce{KCl}$?

$$q_\mathrm{rxn} = -q_\mathrm{cal}$$
I multiplied the sample $\pu{1.50 g}$ by $\pu{4.18 J} \cdot (-2.4) = \pu{-15.048 J}$
Divided that by $1000 = -0.015048$; thus, $0.015048$
However, my answer seems to be wrong. I know that reaction is endothermic since the temp drops, but I am wondering which values I should be using to correctly determine the "Heat of Solution".


texts: Can glucose and insulin exist in the same container without reacting?

texts:
Someone asked if glucose and insulin could be mixed in the same container and used as an injection to provide a quick energy boost. I'm not interested about the medical part of this question, but just if glucose and insulin (which is a protein) could exist in the same container without reacting with each other without forming some sort of glycoprotein. Is it possible to make a reasonable prediction what would/not happen in the mixed glucose/insulin solution in the container?

I know that insulin and glucose do not react with in the body, I want to know if in aqueous solution they would react.


texts: What does "off-hue" constitute in the context of analyzing a sample using the Pt-Co color scale?

texts: ASTM D1209, the method describing how to perform the Pt-Co color scale test for a sample, recommends reporting material that can't be matched to a particular standard as "off-hue". For color based analyses, how is "hue" measured/quantified and what is the distinction to "color"?


texts:
Why is linalyl acetate nonpolar?

From the structure of the molecule I would have assumed that it was polar since it has a $\ce{C=O}$ bond and is asymmetric. What is it that makes it nonpolar?


texts: What is the role of the Magnesium Ion in Chlorophyll

texts: Chlorophyll as the main photoreceptor molecule in photosynthesis seems to have three unique features 1) a lot of conjugated double bonds, 2) a ring like structure and 3) a central metal ion (Mg).  The conjugated double bonds make sense, as this creates delocalized electrons, resulting in excitation energies in the optical spectrum, which allows the molecule to absorb light.  The ring-like structure seems to be designed to chelate the central Mg ion, but what is the role of the Mg ion? Does it add electrons to the delocalized molecular orbital.  Its interesting that pheophytin, the next step in the redox chain,  seems to be identical to chlorophyll except it doesn't have the Mg ion.  Is this something like electron doping in a semiconductor PN junction biasing the flow of electrons towards the pheophytin?


texts: Possbile to test percent of Ethyl Alcohol in hand sanitizer?

texts: The percent of Ethyl Alcohol in hand sanitizers slowly drops over time. And manufacturers put an expiration date on the bottles. But I'd to test the percent of Ethyl Alcohol for myself for a new bottle and to see how much over time is lost as it gets close to the expiration data and beyond. Is this possible for a chemistry n00b?


texts: Gaussview GMMX grid seach: job completed before going through all the structures

texts:
I am recently using the GMMX add-on in gaussview to conduct conformer search. I was using the grid search method and the progrom suggested the number of structures is 729 (See picture below). I submitted the job and it completed normally. However when I checked the log file, the "Nmin" is 496 (See picture below). I think "Nmin" should indicate the number of times of minimizations. So what I am confused about is why it is not 729?

If it's some built-in algorithms to skipping some structures, I got even smaller Nmin when I was using smaller bond resolution.

Thanks!


texts: How are lowercase m and uppercase M used in general chemistry courses?

texts: Where do lowercase m and uppercase M make appearances in general chemistry, and what do they signify?


texts: Why is oxygen more stable than oxygen dication?

texts:
According to molecular orbital theory (MOT), $\ce{O2^2+}$ has a greater bond order than $\ce{O2}$ and two less antibonding electrons. So why is molecular oxygen $\ce{O2}$ more stable than the molecular ion $\ce{O2^2+}?$
One possible reason that comes to mind is that the antibonding (AB) orbitals, although higher in energy than the constituent atomic orbitals, are still negative in energy, so adding electrons to AB orbitals still lowers the energy. But then, by that same argument, $\ce{O2-}$ would increase stability further, which it doesn't. Am I overlooking anything?
Note: I know that from an electrostatics point of view, $\ce{O2}$ is obviously more stable as bring two negative electrons close to positive $\ce{O2^2+}$ decreases the electric potential energy of the system. I am interested in how MOT explains relative stability (or if it actually even does).


texts: Color changes of a solution of acetone and sodium hydroxide

texts:
I have put acetone and sodium hydroxide solution (approximately $\pu{1M}~ \ce{NaOH}$) in a beaker and didn't see any colour change for a day (actually, it was transparent, no colour).

After almost 2 days, I saw a dark brown colour (no precipitate, just diffused colour). Now (after 25 days) its colour seems black, but when I take a small amount and dilute it with water, it is brown. What chemical compound has formed that has this colour? What reaction has taken place? (I doubt it is an aldol condensation)


texts: What is the oxidation state of Boron in Ammonia Borane?

texts:
So I was searching about the difference between redox reactions and Lewis Acid-Base reactions and came across classical example of latter,

$$\ce{NH3 + BH3  \rightarrow NH3BH3}$$
Now in this example what is the oxidation state of borane? Is it $+4$, if yes then can this example be considered a type of redox reaction also, since boron went from $+3$ oxidation state in the products to $+4$ oxidation state?


texts: What exactly makes a carbon atom "α" in a protein residue?

texts:
I'm a computer scientist and have no biochemical background, but was working on a project recently that had me going through a lot of protein residues for one reason or other. Feel free to correct me from here on, but my understanding is that proteins, also called "peptides" also "subchains" when a part of a larger macromolecule are made of amino-acids(central dogma) which are also frequently referred to as "residues".

Upon closer (programmatic) inspection, each residue (amino-acid) turns out to be a bunch of atoms like so:

I was wondering what is the significance of that CA there in each of the residues, and whether i identified it correctly as "alpha-carbon". Protein Data Bank docs refer frequently to a residue's alpha-carbon. If it is indeed the alpha-carbon, i have two questions which are probably dead-simple to anyone with biochem background:

Why is that one(in space) considered alpha and not the carbon atom next to it?
Is it a given that each residue out there has only one alpha-carbon? Seems pretty obvious, but please.

Thanks a ton!


texts:
An Organic Chemistry Book that has only exercises? Better with solutions so to see if the answer is correct. Even more better if there is a PDF version.

The exercises I am looking for are exercises about Hydrocarbons and their reactions, Isomerism exercises, haloalkanes and their reactions, alcohol, eters and thiols, ammines, Fisher's projections and the absolute configuration, sugars, lipids, and proteins.

Thanks a lot!


texts: How does the dx2-y2 orbital bond with four ligands in square planar metal-metal complexes

texts:
I understand that the complex [Re2Cl8]2-  has a bond order of 4 between the ruthenium ions. The bond comprises of sigma interactions between
Dz2 orbitals, two sets of pi interactions between dxz and d yz, and  delta interactions  between the dxy orbitals of the two ruthenium ions. My textbook says that the dx2-y2 orbitals remain for the metal ligand bonding.
How do you fit 16 electrons from 8 ligands into two orbitals,
I thought you could only fit two electrons in an orbital.
Are the dx2-y2 orbitals forming hybrid orbitals with the empty 4s orbitals ?


texts:
I am a chemistry super noob and I was watching a MIT video where the professor states that:

"Certain molecules become charged when they come in contact with water in the natural state"

Can someone give me an example of one or more such molecules ?


texts: Calculating bond energy given the enthalpy value of burning reaction

texts:
The burning enthalpy (exothermic) of $\ce{NO +O2 ->NO2}$ is $\pu{57 kJ mol^-1}$ and $\ce{O=O}$ bond energy is $\ce{494 kJ mol^{-1}}$, then what is the bond energy of $\ce{N-O}$ ?

So I balanced the equation

$$\ce{2NO + O2 ->2NO2}$$

wrote down Lewis structures and got

$$(2\Delta H(\ce{N=O}) + \Delta H(\ce{O=O}) - 2(\Delta H(\ce{N-O}) + \Delta H(\ce{N=O})) =  \pu{-57 kJ mol^-1}$$

($\pu{-57 kJ mol^-1}$ since it is an exothermic reaction), so we are left only with

$$\Delta H(\ce{O=O}) - 2\Delta H(\ce{N-O}) = \pu{-57 kJ mol^-1}$$

thus

$$\Delta H(\ce{N-O}) = \frac{494+57}{2}\pu{kJ mol^-1} = \pu{275.5 kJ mol^-1}$$

However the right answer is

$$\frac{494-2\cdot 57}{2} \pu{kJ mol^-1}= \pu{190 kJ mol^-1}$$

and I really don't get what am I doing wrong?


texts: How to determine the phases in a complex phase diagram?

texts:
In my school notes, we have the following phase diagram that shows an example of how complex things can get when we have intermediate phases. I tried filling in phases, but I have no idea how to check if I am doing a good job or not. What is the mechanism to determine the phases starting with a diagram like this?
This is a question I have made for myself, NOT homework.


texts: Risks of using organic mercury compounds in analytical chemistry

texts:
I'm interested in speciation analysis. Hearing of fatal accidents with organic mercury compounds made me wonder about the risks for the analytical chemist trying to determine Hg species in foodstuff. Probably the most prominent accident is the death of Karen Wetterhahn who used dimethylmercury for NMR experiments. A few drops proved fatal. I'm assuming it was pure dimethylmercury she was using? Or is it usually diluted?

The concentration range in LC-ICP-MS analysis for quantificaton of MeHg in foodstuff ranges up to about 10 ppb from what I have seen so far. I'd expect stock solutions for preparing the calibration wouldn't exceed 1 g/L. So the consequences of spilling some drops of a stock solution are likely less severe in this case. Especially taking into account that today people are aware of how fast dimethylmercury diffuses through the usual gloves. Which is something I believe Wetterhahn wasn't aware of. Diluted or not, the handling still requires laminated gloves (silver shield), right?

I don't intend to work with MeHg, but I know someone who might in the context of analyzing foodstuff. It would be a comfort to know that the phrase "one drop can kill" applies to the handling of the pure chemical I guess.


texts: Which of these would most likely be a strong electrolyte?

texts:
An ionic compound
A covalent compound
A polar compound
A nonpolar compound

Previously, I have been taught that polar compounds can be either strong or weak electrolytes. I also learned that ionic compounds are generally strong. Therefore, my guess would be a, an ionic compound. However, I am not entirely sure of my answers. Could you please explain to me how I could confirm and get the right answer? Thank you!


texts: Safety concerns for radical halogenations of methane in sunlight?

texts: I wanted to know about the substitution reaction of alkanes particularly interested in the reaction of methane with fluorine and chlorine.


texts: coffee concentrate and water separated after 2 hours. How/why?

texts:
I'm asking because this makes no sense to me and making sure I'm not stupid.

I brewed 10 gallons of cold brew concentrate(TDS 12.2) and mixed it with 10 gallons of water.

I moved 10 gallons of the mixture into kegs and they ended up at TDS 6.4. Two hours later I filled the rest of the kegs. One keg was at TDS 4.8 while the rest were at TDS 0.4.

Will coffee and water separate? I've never seen this happen before and previous kegs have never tasted differently until just now.


texts: Why does iron(III) form the trithiocyanate complex instead of the triisothiocyanate one?

texts: As far as I know, $\ce{Fe^{3+}}$ is a hard acid, and thus shouldn't it favor complexation with the nitrogen's lone pair rather than the softer S?


texts:
Suppose I did this reaction by dipping a $\ce{Zn}$ rod in $\ce{CuSO_4}$ solution.

$\ce {CuSO4 + Zn -> ZnSO4 + Cu}$

Is there a way to reverse this reaction to

$\ce{Cu + ZnSO4 -> Zn + CuSO_4}$?

If so, how?


texts: standard reference for thermodynamic properties?

texts:
I'm a non-chemist attempting to put together a chemistry paper. Up to now I've got my thermodynamic data from various random pdf files found on the web, together with Wikipedia. Now that the paper is nearly finished I need to replace these with values from a single, respectable source. But I've realised I don't know how to find such a source. I have a few chemistry textbooks on my desk, which tend to have tables in the back, but they're not terribly comprehensive and none of them have all the data I need.

So is there a standard resource for thermodynamic tables? I particularly need the Gibbs energy and enthalpies of formation for gases found in the atmosphere, such as $\ce{O2}$, $\ce{CO2}$, $\ce{CH4}$ and $\ce{H2O(vapour)}$?  In an ideal world this would either be something I can access online or a book that's likely to be found in my institute's rather small library.


texts: What is the difference between enthalpy (H) and heat (q)?

texts:
It seems that in some cases it's the same (that is, $\Delta Q_p=\Delta H$)  yet in others they differ.
For example,
\begin{align}
\ce{2H2(g) + O2(g) &->2H2O(l)} & \Delta H &= -572~\mathrm{kJ}
\end{align}

The answer for one mole of $\ce{H2O}$ produced is $\mathrm{-572\times 0.5~kJ}$.
Is this under the assumption of constant pressure? Therefore it's $\Delta Q_p=\Delta H$?


texts: What is the meaning of the phase state label (cr,l) appearing in ATcT thermochemical data tables?

texts: I was examining data associated with this post on the heat of solution of ammonium nitrate when I came upon the NIST ATcT data page which lists the heat of formation of $\ce{(NH4)NO3(cr,l)}$. In this formula, what states does "(cr,l)" refer to?


texts: What solvents can solve aromatic urethane resins?

texts:
Do you have any information about chemical resistance of hexa-functional aromatic urethane acrylate?

I want to know what solvents can solve aromatic urethane resins.


texts: Why are 5-ringed saturated chelates more stable than unsaturated ones while 6-ringed unsaturated chelates are more stable than saturated ones?

texts: 5-ringed saturated chelates seem to be more stable than unsaturated ones. On the other hand, 6-ringed unsaturated chelates are more stable than saturated ones. Why do these hold true?


texts: Is a hydrogen molecule smaller than hydrogen atom?

texts:
Recently I came across a textbook of physical chemistry which stated the following:

  In the formation of a stable hydrogen molecule, two hydrogen atoms share a pair of electrons between them and two $s$-orbitals overlap along the same axis resulting in the formation of sigma $(\sigma)$ bond. As the shared electrons are attracted by both the nuclei, the size of hydrogen molecule is smaller than that of hydrogen atom.

However, the actual radius of hydrogen molecule is $120~\text{pm}$ which is greater than that of hydrogen atom i.e. $53~\text{pm}$. So, what does the author actually mean when he says that the size of hydrogen molecule is smaller than that of hydrogen atom? Moreover, does it imply that the electron density is maximum at the COM of the hydrogen molecule? Any help would be appreciated.


texts: How to calculate the electromotive force of a silver chloride/ silver bromide cell?

texts:
For the galvanic cell: $\ce{Ag|AgCl(s)|KCl(0.2M)||KBr(0.001M)|AgBr(s)|Ag}$, calculate the electromotive force (EMF) generated.
  $K_\mathrm{sp}(\ce{AgCl}) = 2.8\times10^{-10}$;
  $K_\mathrm{sp}(\ce{AgBr}) = 3.3\times10^{-13}$

I have tried this forming the cell reaction which is coming out to be
$$\ce{AgCl + Br- <=> AgBr + Cl-}$$
then using the $K_\mathrm{sp}$ of both salts I found the equilibrium constant which should be
$$K_\mathrm{eq} = \sqrt{\frac{K_\mathrm{sp}(\ce{AgCl})}{K_\mathrm{sp}(\ce{AgBr})}}$$
then I put it in the formula
$$E_\mathrm{cell} = -0.059 \log(K_\mathrm{eq})$$ but my answer is coming wrong.


texts: Why alkanes containing even number of carbons can be packed more efficiently than alkanes with odd number of carbon atoms?

texts:
Variation of boiling and melting points of alkanes with increase in the number of carbons

  The odd-numbered alkanes have a lower trend in melting points than
  even numbered alkanes. This is because even numbered alkanes pack well
  in the solid phase, forming a well-organized structure, which requires
  more energy to break apart. The odd-numbered alkanes pack less well
  and so the "looser" organized solid packing structure requires less
  energy to break apart.

  Source: https://en.wikipedia.org/wiki/Alkane#Melting_points

Why is that the alkanes containing an even number of carbons can be packed more easily compared to the alkanes containing an odd number of carbons?

Both types of alkanes can be laid next to each other; hence, why should the number of carbons even matter?

I started drawing and noticed something.

The diagram makes it pretty obvious that the alkanes with odd numbers cannot be packed efficiently.

I am not sure if this is the correct answer.


texts: How fast does atmospheric carbon dioxide dissolve into strongly basic solution?

texts:
I'm conducting some pH measurements with solutions containing NaOH and I'm a bit concerned that carbon dioxide will dissolve and affect my measurements by lowering the pH according to the reaction:
$$\ce{2 OH- + H2CO3 -> 2 H2O + CO3^2-}$$
This would consume my $\ce{OH-}$ ions; I obviously don't want that kind of interference.

Are the kinetics such that I should cover my setup, or can I ignore it's effect on a, say ~1 h timescale? Or ~24 h?

Some additional information, after request:
I don't have many cations that would form insoluble compounds with carbonate
I work at room temperature
The setup is a beaker (diameter 10cm-ish) with approximately 200ml volume
The reaction is supposed to be between sand and NaOH (tiny particles are not inert)


texts: Is the term "carboreduction" interchangeable with "carbothermic reduction"?

texts:
I am currently studying reactions involving the reduction of metal oxides by carbon at high temperature to produce refractory carbides (such as $\ce{ZrC}$) following equations such as:

$$
\ce{ZrO2 + 3C -> ZrC + 2CO (g)}
$$

I have come across both the following terms for this type of a reaction carbothermic reduction and carboreduction; they appear to be used completely interchangeably. I would like to make sure (as I have not yet found a source to say otherwise) that this is the case in chemistry terminology and not that one may be applied to an equation as above and the other to a similar reaction where the product is actually the pure reduced metal, such as that for iron ore smelting:

$$
\ce{2Fe2O3 + 3C -> 4Fe + 3CO2}
$$


texts: Are there any substances that react very slowly with water to create heat?

texts:
I know there are things like the alkali metals that react very violently with water. I was wondering if there is anything that produces a slower more controlled reaction?

Also, is there anything that reacts with water to form heat that is safe for humans to touch?

I'm trying to think of ways to melt snow besides salt.


texts: Can the Bohr atomic model be applied to sodium and other single valence electron species?

texts:
Is $\ce{Na}$ a single electron species and can I apply Bohr's Model on it?
Please explain why not as it also contains one electron in its outermost shell.


texts: ammonia, methylammonia, dimethylammonia, trimethylammonia reactions

texts: Perhaps a "basic" question (pun intended), but I have a few questions about the reactivity of ammonia and its methylated cousins.  I come from an engineering background, essentially I use a process in which thermally cracked ammonia releases its nitrogen atom to a surface under temperature.  I suppose in principle any of the other 3 molecules, with 1,2 or 3 methyl groups could do the same.  However, could I definitely determine whether they would do so at higher or lower temperature?  Essentially, is it as simple as comparing the the C-N bond vs N-H bond energy, or more involved? Would steric factors of the N ability to "see" the surface be involved? Finally, would attempting to do this in solution versus in gas state change anything significantly?  Thanks for any pointers and/or literature refs!


texts: Why are intensive properties not additive?

texts: The extensive properties are additive. An intensive property is a ratio of two extensive properties.  So I think we can add intensive properties.


texts: Baking soda & magnesium chloride reactions

texts:
Woke to this interesting reaction.
Would love any explanation of this occurrence. If it is perfectly common then I apologize for my ignorance. The mag was trace in the clear glass suspended over the white glass jar that had a strong mixture of baking soda and water. They are not touching and are as I found them. Look carefully and you can see the "gel puddle" that formed on my dish drainer. There are slight bubbles in the gel.
Or is it ectoplasm from the ghost?  (Lol)


texts: Why Use Lewis Structures to Determine Radicals

texts:
As far as I know, Lewis Structures are convenient for representing molecules, but give no insight on the actual electron orbitals.

For example: The Lewis Structure of $\ce{O_2}$ does not reflect paramagnetism. Therefore, we use MO theory to explain it.

Then, why are Lewis Structures used to show if a molecule is a radical?

For example: hydroxyl is drawn as $\ce{.OH}$ to reflect the unpaired electron. That is a Lewis Structure.

Why do Lewis Structures work in this case?


texts: Symantics of parts per (million, billion, etc)

texts:
I have always thought that parts per million meant that in a solution of one million particles, one of those particles is the particle that you are looking for its concentration in ppm. However looking at the formula ppm=(mass solute/mass solution)* 1 million, it seems like it may be meaning one part of mass per mass of solution?
Doing a example calculation for one atom of mercury in 999,999 molecules of water, I get about 11 parts per million and not the 1 ppm. It seems like the ppX changes with molar mass of the X. Am I missing some key concept here or do I have the right idea. Thanks

(1 atom Hg)(mol Hg/Avogardros#)(20.59g/mol Hg)= 3.3309E-22g Hg = variable A

(999,999 molecules H2O)(mole H2O/ Avogardros#)(18.015g/mol H2O)= 2.9915E-17g H2O=variable B

ppm=(moles solute/moles solution)*10^6
ppm=A/(A+B) *10^6 = 11.13ppm


texts: Are all protein tetramers considered to be "dimers of dimers"?

texts: Is every tetramer thought to be a dimer of dimers? Because even if every subunit is unique in structure, it could be a heterodimer of heterodimers? Or is the term "dimer of dimers" reserved for something more specific like symmetric tetramers?


texts:
here is the data booklet we must refer too:

Here is the exam paper solution:

I dont understand how they conclude this.

Peak areas and the chemical shifts seem to be different for me. For example there is a peak area of 2 for the chemical shift (ppm) of 2.0. How can this be when the group is CH3-COOR... isn't the peak area 3 if there are 3 hydrogens? Can someone please help me clarify reading this table, and deducing structures. How do link the R groups and when they bold H, does that mean the H can be any number?


texts: How to separate two liquids with both having the same properties?

texts: I was curious if it was possible to separate such liquids e.g. two vegetable oils that happened to have different ingredients, so it is a different liquid, but the same density etc.


texts:
Suppose I have $\ce{Be^3+}$. What would be its 4th ionization energy?

By trying to solve the issue I saw that its a "hydrogen-like" atom – means that beryllium left with only $1$ electron in his valance shell. Hence, I can use the Bohr atom model to solve the problem.

Is my guess right? If so, what values I need to plug in the equation and why so?


texts: Is there a direct relationship between the adsorption energy and the catalytic activty

texts:
I have seen in several papers, where people correlate adsorption energy with the catalytic activity; the greater the adsorption energy, the greater would be the catalytic activity.

I understand that in order for a catalytic reaction to take place, the adsorbates should get adsorbed on the surface of the catalyst. But what if the adsorbates are too strongly adsorbed on the catalyst. This is unfavorable for the reaction. Isn't it?

Therefore, I don't understand how one can correlate higher adsorption energies with greater catalytic activity.


texts:
I cannot for the life of me find this style of clamp holder with beaker base:

I can find beaker bases on sites like Fisher Scientific/etc., and flimsy alligator clamp soldering stands on Mouser/etc., but not this specific alligator (or other wire holding) clamp with sliding connector, on solid rod, attached to a beaker base.

Does anyone know what those sliding clamp holders are called, or where I can get this as a kit? I use this for e-chem and love it but need more.

Edit, 15-Jan This is an older version of my actual setup, which I would typically have on top of a magnetic stirring plate:

I would then be taking 2 of the 3 probes and passing them through a number of other poured solutions. My current clamping setup is great because I can simply release the counter electrode and just move my working and reference to different baths; really, I just need more of what I already have. As these experiments are limited in scope and do not require it, I do not make provisions for salt bridges, nitrogen purging, hydrogen gas aeration, etc.


texts: Why do we need three equations to find the pH of NaCN, given Ka(HCN)?

texts:
To find the pH of a 1.0 M solution of $\ce{NaCN}$, given
$\ce{Ka(HCN) =4.9E(-10)}$

The solution (refer end of question) uses three equations:

Equation 1 : $\ce{HCN + H2O <-> CN- + H+}$

Equation 2: $\ce{NaCN <-> CN- + Na+}$

Equation 3: $\ce{CN- + H2O <-> HCN + OH-}$

I am confused as to:

1) the logic behind why we need these three equations (up to this point in the course, all the similar questions have been of the form e.g. find pH of NH3 given Kb(NH3), and so we only used the NH3 acid base reaction equation.

I assume equation 1 is necessary because the Ka is given for HCN and Equation 2 is necessary because we are asked to find the pH of NaCN.  Where does Equation 3 come from? We did talk about spectator ions in class so does it have something to do with Na being a spectator ion?

2) why the ICE (intial, change, at equillibrium) table to find x is written in terms of Equation 3 and not, for example, Equation 2.

The solution from the textbook is given below:

Thank you.


texts: Why do glow-in-the-dark substances dim gradually?

texts:
Related: How do things glow in the dark?

Growing up, I had glow-in-the-dark stars on my ceiling and after being "charged" by having my lights on, they would phosphoresce for quite some time.

However, throughout the night, a star would gradually dim. I imagine that the cause of the stars becoming dimmer is that some electrons are relaxing down before others.

I thought the thickness of the star could be part of this as the more inner parts likely receive less light, so perhaps this bit would completely dim out before the surface of the star. However, my thought is that the star should either be completely "charged" or cast no light at all, like a switch.

The dimming effect is gradual. Why?


texts:
I am modelling a methanation process in MATLAB, where I have a rate equation for methanation
$$\ce{CO2 + 4 H2 → CH4 + 2 H2O}$$
in which I need partial pressure of $\ce{CO2},$ $\ce{H2},$ $\ce{CH4},$ $\ce{H2O}.$
I am struggling to understand the link between the mass flow rate of $\ce{H2}$, $\ce{CO2}$ and partial pressure of all other species. The required amount of catalyst and the volume for the fixed bed reactors in accordance with the chosen stimulation parameters.
If suppose my operational pressure is $\pu{7 atm}$, $\pu{16 mol s^-1}$ of $\ce{H2},$ $\pu{4 mol s^-1}$ of $\ce{CO2},$ what will be the partial pressures of all those species and required amount of catalyst and reactor volume.
The paper in which I referred for rate reaction is this.


texts: Adding alkyl group to benzene with a deactivating group

texts:
question:
The question is asking whether we can simply do Friedel-Crafts alkylation to a benzene bonded to a deactivating group (i.e. sulfonic acid group in this problem).
(No answers to this problem)
attempt:
I am thinking this reaction cannot work. This is because:
$\ce{R-SO3H}$ strongly deactivates the benzene, making the $\ce{C=C}$ bond less nucleophilic. Therefore, it does not have enough 'power' to attack the carbocation complex ($\ce{CH3CH2-FeBr3}$), which is a limitation in Friedel-Crafts reactions.
Therefore, my attempt is:

de-sulfonation: dil. $\ce{H2SO4}$ + $\ce{H2O}$, make it to benzene
Friedel-Crafts acylation: $\ce{CH3COCl}$ + $\ce{AlCl3}$ (catalyst), make it to acetophenone
sulfonation: conc. $\ce{H2SO4}$, make it to 3-Acetylbenzenesulfonic acid
Clemmensen reaction: make it to product

question 1:
Are there any quicker ways to perform this synthesis? I am thinking is there any way to make the group less deactivating, hence allow the alkylation to happen, but no idea how.
question 2:
Although Clemmensen reaction is a good and common choice, it uses highly-toxic mercury. However, for Wolff–Kishner reduction, I am worrying that high temperature will decompose the product, plus the base will neutralize the product acid. Overall, which reaction is better for this particular reduction step?


texts: If x and y are 2 extensive properties of a system then is x/y always intensive?

texts:
I have a case to contradict my own question but in few books, it is given that x/y is always intensive. So
I got confused. My case is as follows :
Let a wire be our system whose resistance is R,
area of cross section is A,
length is L
and constant of resistance be ρ.
V,R are extensive
V(volume) = AL
R  = ρ(L/A)
So R/V = [ρ(L/A)]/AL = ρ/A^2
ρ is a constant but, A depends on the shape and size of system. So ρ/A^2 depends on shape and size of system. So it is an extensive property.
Therefore x/y can be extensive as well.
But in the below picture which is of G.R.B Op Tandon physical chemistry, it is given x/y is always intensive. Where did I make a mistake ?
Please note that I did not understand this is related more to physics or chemistry, so I asked it here as
chemistry is where I have first come across this problem. If I should ask this in the physics website, please tell me and I will do so.


texts: Can acetone be used as a GC–MS solvent for a sample containing ammonia?

texts: Сan acetone be used as a GC–MS solvent/diluent for a sample containing ammonia? Will there be a reaction between these two species?


texts:
I understand that imines can be hydrolyzed in acidic medium. But what about in basic medium? Can imines still be hydrolyzed?

I have a plausible mechanism ... nitrogen's withdrawal of electron density makes the alpha proton relatively acidic; base abstracts the proton in an E2 reaction; nitrogen then takes back a proton to regenerate the base catalyst.

Is this correct? Does this actually happen?


texts: Formation of MnO2 vs [Mn(H2O)6]4+ in aqueous solution

texts: I am looking for reasons why $\ce{Mn(IV)}$ wouldn't be stable as a hydrate. I know that from standard reduction potentials it exists as a ppt of $\ce{MnO2}$, but what is stopping it from being a hydrated $\mathrm{4+}$ aqueous cation? Is it that the water ligands would be too polarised and therefore $\ce{H+}$ dissociation would occur very easily? Are there other factors that make it a solid rather than a solvated ion, like lattice enthalpy etc.?


texts: Photochemical reduction of benzophenone: why inverted flask?

texts:
I've come across an interesting protocol for photochemical reduction of benzophenone to benzhydrol (diphenyl methanol) with sodium alcoholate in alcohol, the 2nd protocol in https://prepchem.com/synthesis-of-diphenylmethanol/. The reaction proceeds via ketyl radical initially to benzopinacol, which is immediately cleaved by a catalytic amount of sodium alcoholate to the benzhydrol and benzophenone. The latter repeats the reaction until it's used up. The alcohol acts as a reducing agent and solvent.
I'm particularly interested in the following part:

the flask is filled to the neck with more of isopropyl alcohol ... The flask is tightly stoppered and inverted upside down in a beaker.

I want to know why is the flask inverted?
My best guess is to avoid exposure to air, since that would interfere with the reduction. But then why isn't it enough to just stopper the full flask?
Might this have more to do with the quality of exposure to the light source (neck and stopper producing a shadow in the upright position)?
Also, is there some official term for this inverted flask technique?

Notes (extra info for the interested):

The ketyl radical (which is actually a radical anion) is brightly colored, which provides a convenient way to monitor the reaction. Upon exposure to air, the color disappears, presumably because the radical anion gets oxidized back to the ketone.
Any strong enough base should work for cleavage of the pinacol. In a related synthesis where benzopinacol is the desired product, a small amount of acid is added, because the glass itself is alkaline enough to cleave the product. The sodium alcoholate is convenient in that it's the conjugate base of the alcohol. It's formed by reaction of the alcohol with sodium metal.
Cleavage of the pinacol proceeds by deprotonation to the pinacolate anion. This rearranges to the ketone and alkoxide, which protonates to the alcohol, regenerating the base.


texts: In this time of COVID-19 our establishment is being told by government sources to spray down surfaces with a 9:1 water bleach solution, and then told to throw it out within 24 hours. What makes it less effective when we have over the counter products with bleach in them that obviously sit on the shelves for months and years?


texts:
I'd like to know if there is any solvent that dissolves Norland Optical Adhesive 65 (and Rhodamine 6G), but does not dissolve PMMA that is used in e-beam lithography.

I've tried acetone, methanol, chloroform, n-hexane and toluene; none worked.


texts: Can a zeroth order reaction be reversible?

texts:
After recently studying about chemical equilibrium, I was convinced that the forward and backward reaction rates meet each other at equilibrium.

However thinking about zeroth order reaction annoyed me a little, as I could not figure out how the rates would become equal, if at all, in cases where the rate remains static throughout. Here's what I guessed:

The backward reaction of a zeroth order reaction must not be a zeroth order reaction in itself, so that it may reach the reaction rate equivalence point at equilibrium.But then this generalization is difficult to digest (for me).

or

A zeroth order reaction can not attain equilibrium (highly unlikely).


texts: Do high-energy chemical bonds indicate strong chemical bonds?

texts:
In my head it seems reasonable that a high-energy bond would indicate that the bond is strong, however a question got me thinking.
Take for example lead azide, a very explosive compound that is often used as a detonator or fuse. It has a decent amount of energy stored in its bonds while being very sensitive to heat, friction, shock, etc.
This indicates to me that the lead azide has a low activation energy and therefore weak bonds, yet still plenty of energy available to be released.


texts: Does anyone know the particle size of carbamate and protonated MEA?

texts: Does anyone know the particle size of carbamate and protonated MEA ?  that's the product when CO2 is absorbed into monoethanolamine (MEA)


texts: Should bromine water be called a solution?

texts:
Bromine water is a reagent which is used to test for unsaturation in organic compound. It is $2.8~\%$ bromine in water. In many places, it is refer to as bromine solution.

But it is observed that adding bromine to water gives hypobromous acid ($\ce{HOBr}$) and hydrobromic acid ($\ce{HBr}$) via a disproportionation reaction.

$$\ce{Br2 + H2O <=>> HOBr + HBr}$$

So, if bromine reacts with water to form a mixture of acids, how can it be called a solution? Components of solution do not react with each other.


texts:
I have been trying to solve this NMR question for about four hours and I feel like I'm always really close but never manage to find the perfect combination.

Anyway here's the info in the question

Formula is $\ce{C11H14O2}$

1.triplet at 2.4 ppm (2H)

2.singlet at 3.3 ppm (3H)

3.triplet at 3.5 ppm (2H)

4.doublet at 7.4 ppm (2H)

5.doublet at 7.5 ppm (2H)

6.singlet at 2.0 ppm integrates for 3H

I have tried a number of structures and the one I feel i got very close to was this one, each number on the side corresponds to the signal that I think it is. The X is just the area where I know i am missing a bond, I just don't know how to seal it up.

Edit: After the advice given by you all, I came up with this structure which seems to be pretty sound


texts: Boiling point elevation for a mixture of ethanol and water

texts:
Properties such as boiling point, freezing point and vapour pressure
of a pure solvent change when solute molecules are added to get
homogeneous solution. These are called colligative properties.
Applications of colligative properties are very useful in day-today
life. One of its examples is the use of ethylene glycol and water
mixture as anti-freezing liquid in the radiator of automobiles. A
solution M is prepared by mixing ethanol and water. The mole fraction
of ethanol in the mixture is 0.1.
Given:
Boiling point elevation constant of water =0.52 K kg/mol Boiling point
elevation constant of ethanol = 1.2 k kg/mol
Boiling point of water =373 K
Boiling point of ethanol =351.5 K
The boiling point of this solution is?

Now,
I am aware that for a solution of a non-volatile solute in a solvent
The elevation in boiling point is given as
$\Delta\mathrm{T}=im\mathrm{K}_{b}.$
In this case,which is the solute and which the solvent?
The material that I am studying from considers ethanol to be the solute and water,the solvent.And thus,calculates the elevation in boiling point of water.
Therefore,the new boiling point is higher than that of pure water
My problem with this is,since the boiling point of a mixture of ethanol and water,for all compositions,lies between that of water(maximum) and ethanol(minimum), how can a mixture of water and ethanol of 0.1 molarity (by ethanol) have a higher boiling point than that of water?


texts: Is Gibbs Free Energy of formation equal to Gibbs Free Energy of transition state?

texts:
Is activation energy equivalent to Gibbs Free Energy of transition state as related by Eyring equation?
$$E_a=\Delta ^\ddagger G \, \, ?$$

Is Gibbs Free Energy of transition state defined by the Gibbs Free Energy of formation?
$$\Delta ^\ddagger G :=\Delta _\mathrm{f} G \, \, ?$$
If not, which are the conditions for which such an approximation (second equation) would apply?


texts: How to draw glucose using a Fischer projection?

texts: I asked how to draw glucose as a Fischer projection from its given chair conformation but all I got was an unsatisfactory ad hoc explanation involving rotation of my neck muscles to somehow see where the hydroxyl groups were. How does one actually draw a Fischer projection of a sugar molecule from its chair conformation?


texts: Why does magnesium deposit during electrolysis of a molten mixture of MgI2 and AlBr3?

texts:
During the electrolysis of mixed salts, I read, and was taught, that the cation with a higher ionization energy would deposit at the cathode. I was also told that you cannot use the standard electrode potential to determine which cation would be reduced.

Is this ionization energy referring to the first ionization energy? If it is, why doesn't the second and third ionization energy factor into this problem seeing that magnesium would have a 2+ charge and aluminum would have a 3+ charge?


texts:
I am trying to determine if the following two grades of ethanol are equivalent:

Ethanol absolute, 99.8% Normapur AR (Analytical Reagent)
Ethanol alcohol, pure ACS reagent, ≥99.5%

Information on the technical specifications of these grades would also be helpful for comparison.


texts:
Can anybody please help me find a way to separate caffeine from coffee that uses a solvent other than DCM, ethyl acetate, or diethyl ether?

This an experiment for science class, but I don't have access to any of the above-mentioned solvents.

Can you suggest any alternatives that are easily obtainable?


texts: How to tell 'orthokinetic' apart from 'perikinetic' based on their prefixes?

texts:
During a test in colloid and surface chemistry, students were asked to distinguish between two terms: orthokinetic and perikinetic coagulation.

  The rate of aggregation is in general determined by the frequency of
  collisions and the probability of cohesion during collision.

  If the collisions are caused by Brownian motion, the process is called perikinetic aggregation;
  [If the collisions are caused] by hydrodynamic motions (e.g. convection or sedimentation), one may speak of orthokinetic aggregation.

  from  Everett, D. H. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry'. Pure and Applied Chemistry, 2009, 31 (4), 577–638, p 610. doi: 10.1351/pac197231040577

Perhaps unsurprisigly, I got the terms mixed up, and used definitions the wrong way round. The problem was that nothing too obvious popped out when considering the prefixes and the respective processes.

Question: To which meaning or association are the prefixes peri- and ortho- referring? The definitions are mostly clear. It is just that I would rather avoid memorisation, and would prefer to be able to always recall which is which based on the prefixes alone.

This means other meanings and etymology of peri- and ortho- are welcome, but will be considered off-topic on their own, unless a clear connection to the definitions of orthokinetic and perikinetic is provided. A short answer with an authoritative reference is very acceptable.


texts: Are all corrosives either acids or bases?

texts:
Are all corrosives either acid or a base? From what I could remember from school, strong acids and bases can be corrosive, but can substances be corrosive from reasons other than that? I tried my best to check for the answer with my limited knowledge.

If it is not just acids and bases what is it then, how can we categorize them, if possible in simple terms?


texts: Why are high pressures used in cracking of long-chain hydrocarbons?

texts:
If we have a long-chain hydrocarbon, such as decane, and we split it through thermal cracking (say in an industrial plant), we use high temperatures, and high pressures. Cracking produces smaller molecules - alkanes, and alkenes. It might look like this:

$$\ce{CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3}$$

Which is cracked into products like this:

$$\ce{CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3-> 2CH2=CH2 + C3H6 + C8H18}$$

Why do we use high pressure in this case? Le Chatelier's principle states that the equilibrium will shift to resist the change — in this case it would move the position of equilibrium to the left, not the right. In cracking we want maximum amount of products (ie. the right) — therefore surely a low pressure would shift the equilibrium that way.

The reaction is not dependent on molecules colliding — merely enough thermal energy has to be provided to enough molecules to cause them to split — homolytic fission — and become free radicals which react to form smaller molecules. Therefore a pressure requirement to increase the collisions doesn't seem necessary.

Why then do we use high pressure when cracking hydrocarbons?


texts: How could one calculate the Fermi level of a copper-nickel alloy? They are both structurally face-centered cubic, however how would this structure affect the Fermi level of the individual atom or the entirety of the material?


texts: What is the formula for finding the average atomic mass of an element based on the abundance of its isotopes?

texts:
In my class my teacher showed us how to find the average atomic mass of an element with a method, but he didn't really state a formula one could use. I came  up with a formula of my own, and from what I observed it works:
$$
\frac{i_1x + i_2y}{100} = A,
$$
where $A$ is the atomic mass,
$i_1$ is the first isotope's atomic weight,
$i_2$ is the second isotope's atomic weight,
$x$ and $y$ are the percentages of the isotopes, respectively,
and they add up to 100, i.e. $x+y = 100$.

Therefore: $$
\frac{i_1x + i_2(100-x)}{100} = A
$$

I'm just wondering, is there an official formula, or is this method it?


texts: How would one express pemoline in terms of phenethylamine?

texts:
Pemoline is a psychostimulant that is no longer used in most countries. Similarly to the psychostimulants amfetamine and methylphenidate I can clearly see a phenethylamine backbone to this compound. I know it is also an oxazoline, but I am writing an article on my Wiki about substituted phenethylamines and their pharmacologic and structural properties so I would like to know what its chemical name would be in terms of its phenethylamine backbone. If you want an example of what I mean, see the current revision of my Wiki article on said drug [1] and look at the chemical names I have written. For example for methylphenidate the chemical name is N,α-butyl-β-methoxycarbonylphenethylamine.

My chemistry knowledge is only first-year university chemistry level, hence why I need your help as I don't know all the adjective forms of functional groups.

Below is the 2D structure of pemoline if you would like it in order to deduce its name in terms of phenethylamine.


texts: How to change color of water based on its acidity?

texts:
I recently saw a video on YouTube in which water, when mixed with a solution (I believe iodine was involved,) changed color based on its acidity. I am attempting to replicate this experiment, but cannot concoct the solution. Any help would be much appreciated.

EDIT:
To clarify, if I had water with a ph of 10 it would turn red, but if the water had a ph of 4 it would turn green.

EDIT 2:
I found the video in question
http://youtu.be/_yi83kOB8ug


texts: Activators for non-sulphide compounds in froth floatation

texts:
I was recently studying about Metallurgy.

Concise Inorganic Chemistry by J. D. Lee claims the process of froth floatation can also be applied to non-sulfide ores such as Malachite ($\ce{CuCO3.Cu(OH)2}$) and Anglesite ($\ce{PbSO4}$) by using $\ce{Na2S}$ as an activator.

The coatings formed are $\ce{CuS}$ and $\ce{PbS}$ respectively. However, in a previous example, they used $\ce{CuSO4}$ as the activator over a $\ce{ZnS}$ surface and a coating of $\ce{CuS}$ was formed.

Therefore, going by the same co-relation in the case of Malachite and Anglesite, shouldn't the coating be a sodium compound instead?


texts: Why does the dissolution of calcium hydroxide have a negative entropy?

texts: We had an experiment on the dissolution of calcium hydroxide and we obtained the experimental entropy value $\pu{-203 J mol^-1 K^-1}$ with a percent error of $26.7\%.$ Doesn't dissolving a solid in a solvent increase entropy?


texts: Are all organic molecules with odd-numbered electron count radicals?

texts:
This question was triggered by another question on this site, about molecules with a total number of 13 electrons.

I couldn't think of any (except the boring answer of $\ce{Al}$), and the answers to the question are all about radicals, instead of 'normal' molecules. So that got me thinking: are all organic molecules with an odd total electron count radicals or radical ions? If so, is there any fundamental reason for this?


texts: Internal pressure, but from other variables

texts:
The internal pressure is derived by differentiating internal energy with respect to the natural variable in one term while holding the unnatural variable in the other term constant.
$$\mathrm dE = T\,\mathrm dS - P\,\mathrm dV \tag{1}$$
becomes
$$\left(\frac{\partial E}{\partial V}\right)_T = T\left(\frac{\partial S}{\partial V}\right)_T - P\tag{2}$$
Then, using the relevant Maxwell relation, it becomes
$$\left(\frac{\partial E}{\partial V}\right)_T = T\left(\frac{\partial P}{\partial T}\right)_V - P = \pi_T \tag{3}$$
This procedure is easily modified. For instance,
$$\left(\frac{\partial E}{\partial S}\right)_P = T - P\left(\frac{\partial V}{\partial S}\right)_P \tag{4}$$
Again using a Maxwell relation,
$$\left(\frac{\partial E}{\partial S}\right)_P = T + P\left(\frac{\partial T}{\partial P}\right)_S \tag{5}$$
This procedure can be cycled through the various variables in $H,$ $A,$ and $G$ to produce another six expressions (excluding the ones possible with the mole-chemical potential pair).
Do these expressions also have names like internal pressure? If so, what are they?


texts: Carbonation of Grignard reagent with a carbonyl group present in it

texts:
Here's the question in my book (see picture)

Option A is a standard reaction which gives a carboxylic acid.

Option B is definitely wrong because an acid base reaction will take place and CH4 will be formed after the first step. CO2 will not react with the methane gas.

So without knowing about option C, I can safely tick option A. But what happens in option C?
Here's the solution provided in the book.

Why cannot a carbonyl group and Grignard reagent be present in same substance? Also, what will be the reaction?


texts: Why is atmospheric composition compared by volume?

texts: The composition of the Earth's atmosphere by its constituent gases (nitrogen, oxygen, argon...), is often given by percent volume. (See this Wikipedia page, for example). Why are these compositions given by volume? I understand that a volume composition shows the mole fractions, which is the real point of interest. Volume compositions compare the volume taken up by different amounts of gases under the same hypothetical pressure and temperature. However, in any "container," each gas occupies the same volume as another; what differs is the partial pressure of each gas. Thus, why not base compositions off of partial pressures? It is physically correct to say that oxygen accounts for 21% of the pressure of the atmosphere, rather than saying that oxygen accounts for 21% of the volume of the atmosphere (which is thankfully not true). I understand that comparing pressure under equal volume and comparing volume and equal pressure both show the same thing, but why not use pressure if it is more physically correct?


texts: Naming rules and acidity of Cl2CHCH2COOH

texts:
How do we name $\ce{Cl2CHCH2COOH}$ ?

Is seeing branched chain our number 1 priority so we name it

1,1-dichloro-3-propanoic acid?

also

Which is more acidic $\ce{Cl2CHCOOH}$ or $\ce{Cl2CHCH2COOH}$ ?
I feel it should be the first one as there is more −I effect but not sure.


texts: Dissolving hydrated vs non-hydrated salts

texts: in chemical catalogs, salts are often sold in hydrated and non-hydrated versions.  Like sodium sulfate anhydrous and sodium sulfate decahydrate.  I tried dissolving the anhydrous and it didn't dissolve very easily, instead it clumped.  I'm wondering if I would have had easier dissolving with the hydrated form, but I don't have it to check.  Is it often the case that easier dissolving occurs with the hydrated salts with water complexed to the ion?


texts:
I'd like to ask how researchers measure/calculate the energy density for chemical fuels? Do they just measure the enthalpy change of combustion (△H combustion) in a calorimeter and then divide it by unit mass/volume? The wikipedia page seems to suggest this way, but I haven't found explicit research sources.
Also, one related question is that how people measure the energy density for energetic materials (eg. TNT, NG)? I guess the reaction here will be a decomposition reaction rather than a combustion, and it might be hard to measure in a calorimeter.
Let me know how you think! Related journal articles and papers will be especially appreciated. Thanks!


texts: How are atoms encapsulated in buckminsterfullerene molecules?

texts:
According to nature.com, buckminsterfullerene molecules (bucky balls) can be formed by vaporizing graphite by saturating it with laser irradiation.

I haven't entirely understood why the carbon forms into a regular truncated icosahedron, but my real question is, how do scientists go about doping these "bucky balls" with molecules or atoms?


texts:
Will 2-methylbutanal undergo aldol condensation?

We are taught that it will not because the +I effect makes the carbanion unstable, but if we make an enolate ion, isn't it resonance stabilized by the C=O group?


texts: Is it possible to calculate atomic radius with electron configuration?

texts: I need to know whether is it possible to calculate the atomic radius according to the number of electrons and electron configuration. Or is there any way to calculate the atomic radius using common characteristics which an atom has?


texts: Does sodium borohydride reduce C=N group?

texts:
Q.15 the major product of the following reaction is:

I have read that $\ce{NaBH4}$ reduces only aldehyde, ketone and acid chlorides. In some cases it may reduce double bonds conjugated with carbonyl groups. So shouldn't the answer here be option 1?


texts: How to optimize graphene geometry with Gaussian?

texts: I am new to Gaussian and I want to optimize graphene using DFT. After the the geometry optimization it has been severely changed, and some bonds were set as double and triple. Why am I unable to get the structural values similar to the input structure?


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Every covalent bond has some ionic character and every ionic bond some covalent character. I can understand why a completely ionic bond is an ideal situation. But completely covalent bonds can exist(?).

Take the case of $\ce{H_2}$ or any other diatomic molecule between identical atoms. How can these have any ionic character?


texts: Phase Diagram-Fe-C, and TTT: Hardness Scale

texts:
So far I know that the Hardess scale of these materials is this:

Martensite> Bainite> Perlite > Cementite> Ferrite

Where is Austenite along this scale? I know that Cementite is harder than Austenite.


texts: What happens to energy changes in non-reversible processes?

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Take internal energy for example:
$$dU\leq TdS-PdV$$
Firstly, I would like to make clear that the following question/argument relies on the following statement being correct: the left hand side of the above equation represents the change in internal energy of the system and the right hand side represents the work done on the system by the surroundings. Please clarify if that is correct.

The two equations, above, are in fact inequalities where it only becomes an equality when the system is at equilibrium (when changes are reversible). However, when  the system is not in equilibrium the inequality implies that the work done on the system by the surroundings is greater than the internal energy gained by the system; how can this be? Where does the energy difference between the energy put in and the energy gained by the system go?

Secondly, at a constant $S$ and $V$, spontaneous changes occur only when $dU \leq 0$. What's going on here? Is it as simple as: the system must lose internal energy in a spontaneous change or does it mean that work must be done on/by the system in a different way (eg. electrical work)?


texts: How do you work out whether reduction would occur based on reduction potentials

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I'm having a bit of trouble with standard reduction potentials. Specifically, when you're given a table of half reactions and reduction potentials...is the potential of the reverse reaction (the oxidation potential) just the negative of the reduction potential? So, say you were given the two reactions :

$\ce{Cl2 + 2e- -> 2Cl- }$   $     E = 1.36$V

$\ce{F2 + 2e- -> 2F-  } $   $  E = 2.87$V

and the question asked whether F- would reduce Cl2 to Cl-, so

$\ce{2 F- +  Cl2 -> 2Cl- + F2 }$

...how would you work this out?


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$\binom{16}{8}$O (n,$\alpha$)$\binom{13}{6}$C  and $\binom{9}{4}$Be ($\alpha$,n)$\binom{12}{6}$C

I had initially thought the products & reactants may be O-16 $\to$ C-13 + He-2 + p$^+$ from alpha decay, but I'm leaning towards this form O-16 + C-13 $\to$ ... now. Any help clarifying & determining products would be much appreciated.


texts:
What is the boiling point of vodka?

I have found the boiling point of ethanol, ~173 (degrees) F.

However, I am unable to find the boiling point of vodka. I found some information on it, but I do not trust the source.


texts: What's the difference between free energy and potential energy?

texts: I found different answers for this question. Was wondering to find a way to explain it to my students how to illustrate the two concepts in practical terms.


texts:
I've encountered in chemistry quite a lot of reducing agents. However one question strikes me quite often and  any research done on the same hasn't been fruitful. This is in context to organic chemistry. Now for example, in reductive ozonolysis, we often use ozone in combination with zinc and water. Zinc's presence ensures reductive results and not oxidative ones. Now, some sources(not books) which I have seen, say that some sulphur compounds would do the same like $\ce{Me2S}$. Also, in case of 1,3- dinitrobenzene,  $\ce{Sn + HCl}$ converts both the $\ce{-NO2}$ groups to $\ce{-NH2}$ groups. Now if we use $\ce{NH4HS}$ or some other nitrogen and sulphur containing ammonia like compounds, we get reduction again, but only for one group out of the two. So my question is, how do we :

Decide that there is going to be reduction
Know the extent of reduction (partial/full)

Can some insight into the inorganic properties of the elements provide an answer like d-orbital availability, lone pair, electronegativity, size/charge ratio? I've tried reasoning but haven't gotten anywhere. Or is it that memorization of the reagents is the only way to know it's function.
Note: This question is only in context to some less commonly used reagents, so as to recognize it's function if we ever see one in problems present in question books.


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Can someone please explain what photodissociation is and if it is more efficient than electrolysis while splitting water into its components?

Thanks in advance.