texts: Does SiO₂ have polar covalent bonds or coordinate covalent bonds?

texts: First off, I know $\ce{SiO2}$ is a network solid. I am looking at its intramolecular forces between the $\ce{Si}$ and the $\ce{O}$ molecule. On the one hand, it seems to me that this should be a polar covalent bond, but on the other, both electrons are given to the $\ce O $ by $\ce{Si}$ which makes it coordinate covalent.


texts: Why must basis sets used in computations be non-orthogonal?

texts:
While constructing basis sets for calculations using Hartree Fock, the basis set must be non-orthogonal. And because of this, we go through many steps to put the overlap and density matrices in the 'right' basis. (See Modern Quantum Chemistry (Szabo and Ostlund) or David Sherill's notes online).

My question is: why must this basis be non-orthogonal?


texts: Competing resonance and inductive effects in a substituted benzene

texts:
A molecule of phenol is much more inclined to under go an electrophilic substitution reaction than a molecule of benzene because the $\ce{-OH}$ group is highly reaction favoring. From what I understand, this is because when the $\ce{-OH}$ group is attached, it contributes a resonance structure involving a double bond between the oxygen and the ring, which stabilizes the intermediate arenium ion.

However, from what I also understand, oxygen is also a highly electronegative atom and therefore inductively draws electron density away from the benzene ring. Despite these two competing effects (electron donating via resonance and electron withdrawing via induction), the overall effect of the $\ce{-OH}$ group is electron donating. This also applies to $\ce{-NH2}$ group.

Am I right in concluding that resonance effects are stronger than inductive effects, if not in general, then at least for electrophilic substitution of substituted aryls?


texts:
In response to this diagram (Organic Chemistry By David Klein 3rd Edition Page 364):

The textbook stated

  A comparison of the transition states for hydroboration via
  Markovnikov addition or anti-Markovnikov addition. The latter
  will be lower in energy because of decreased steric crowding.

Is it supposed to mean 'former', as the diagram obviously shows higher crowding in the latter transition state?


texts: What is the momentum of a particle described by the following equation?

texts:
$$\psi(x) = Ae^{ikx}  \ + \ Be^{-ikx}$$

The above is not an eigenfunction and to obtain its momentum my professor applied the momentum operator separately to the first and second parts. The final result was that he obtained two different values of momentum,
$$\hbar k \text{ and } -\hbar k\text{.}$$

My question: is this method correct? If yes, how to explain the separation of values?


texts: How do we know cyclopentadienylmolybdenum tricarbonyl occurs as a dimer?

texts:
Cyclopentadienylmolybdenum tricarbonyl, $\ce{MoC8H5O3}$, dimerizes to form the cyclopentadienylmolybednum tricarbonyl dimer, $\ce{(MoC8H5O3)2}$.

$\hspace{3cm}$

How was it discovered that it does this?

If you had an sample of a pure substance, but didn't know if it had dimerized or polymerized, what information would you need to find out if it had?


texts: Which of - carboxylic group or carbaldehyde group - has more negative inductive effect?

texts:
Which has more -I effect $\ce{-COOH}$ or $\ce{-CHO}$, and why?

I tried to analyze it on my own but I was confused on what to do. My teacher today taught it by shifting of electrons from $\ce{C=O}$ to the formation of a charge separated structure. Still, I was confused about it.
Mostly, I'm confused on why we are even allowed to create a charge separated structure. Even with it, it seems $\ce{-COOH}$ should have more -I effect. But I am not sure. I need help here.


texts: What are the parent compounds of the following?

texts:
I just need these two answered correctly so I have examples to work with, also if someone could label the longest continuous chain, that would be great too!

Thanks!


texts: Why is HF much more covalent than KI despite having a greater electronegativity difference?

texts:
Generally, the percent of ionic character in a two-element compound correlates quite well with the difference in the electronegativities of the two elements making up the compound, as can be seen in this graph:

(Image originally by the University of Florida, via user4076 here at ChemSE.)
Even here, though, an anomaly is visible.

HF has an electronegativity difference of 1.893 (4.193 - 2.300).
LiBr has an electronegativity difference of 1.773 (2.685 - 0.912).
KI has an electronegativity difference of 1.625 (2.359 - 0.734).
LiI has an electronegativity difference of 1.447 (2.359 - 0.912).

Based on this, HF should be mostly ionic - certainly more so than LiBr, KI, or especially LiI.  Instead, judging from the graph, HF is slightly more covalent than ionic, with ~45% ionic character, whereas LiBr is ~60% ionic, KI is ~75% ionic, and even LiI is ~52-53% ionic despite having a considerably-lower electronegativity difference than the ~45%-ionic HF.
Going along the sequence KI - LiBr - HF, the ionic character of the compound actually declines steeply as the electronegativity difference gets somewhat greater.
What is going on here?


texts: When it is said 'at constant pressure, at constant pressure ', is it about pressure & temp. of the system or surroundings?

texts:
These are the following statements:

  [...] the thermal decomposition of $1.0$ mole $\ce {CaCO3}(\text{s})$ at $1$ bar results in an increase of volume of nearly $90~\text{dm}^3$ at $800^\circ \text{C}$ on account of the carbon dioxide produced.

Is the system at $1$ bar or the surrounding exerts pressure of $1$ bar? Is $800^\circ \text{C}$ the temperature of the system or the surroundings?

  The standard state of a pure substance is the pure substance exactly at $1$ bar & at $298.15~\text K$.

I think the pressure mentioned is of surroundings but the temperature? Is it of the system or he surroundings?

  We see that at constant temperature & pressure, the change in Gibbs energy of a system is proportional to the overall change in entropy of the system plus its surroundings.

Now is the system at constant temperature & pressure or the surroundings?

Could anyone please explain me to clear this ambiguity?


texts:
Our company uses acetone and isopropanol in our manufacturing process to clean our product. Our operators get the chemicals from a large container and put it into small containers like this (http://www.soscleanroom.com/product/facilities/8-oz-esd-safe-solvent-dispenser-standard-pump/?gclid=CILep_rTzc0CFdBZhgodSWsEiA) to keep at their station.

Some times our operators say that it was more difficult to clean the product today and equate that to mean the chemicals were weaker that day.
Recently our operators stated that the chemicals seemed weak again but the next day they used the same chemicals and said they were fine now. This leads me to believe that the chemicals are fine and that there is a different problem leading to harder cleaning.

How fast does acetone or isopropanol absorb water from the air? How long will it take for the chemicals to be noticeably weaker if stored in the containers mentioned above?  Should we be dumping the chemicals everyday or would weekly dumping be fine?

The temperature and humidity is relatively constant at our factory.


texts: Why are some elements more abundant than others in the universe?

texts:
Hydrogen is the most abundant element in the universe. But what makes it so? At the time of big bang, what made certain elements more abundant than the others?

I don't find this order of abundance too predictable. What makes neon more abundant than nitrogen?


texts:
Placed in equivalent freezers, would a liter of water or a liter of lava turn from liquid to solid first? (question from a 6 year old)

Based on this page in a “Blaze” book, my six year old asked “which would win?” between water and lava. On further investigation, we refined the question to: which would turn solid first in similar conditions, a liter of room temperature water or a liter of volcanic lava?


texts: Why are Ka and Kb only used for weak acids and bases, respectively?

texts: The only answer which I found to this is that it's because strong acids and bases virtually completely dissociate, so the dissociation constants would be too large and hence aren't used. This doesn't really seem reasonable to me and I have a feeling there is another answer. Is there really another answer or is this the only answer?


texts: Explanation for solubility of group 2 halides

texts:
I understand that the solubility (in terms of moles/volume) of group 2 halides increase with increase in anion size, i.e.

$$\ce{MF2 < MCl2 < MBr2 < MI2},$$

where $\ce{M = Mg, Ca, Sr, Ba},\dots$ due to large decreases in lattice enthalpy.

But what is the explanation for the following discrepancies?

$\ce{BeF2 > MgF2 = CaF2 < SrF2 < BaF2}$
$\ce{BeCl2 < MgCl2 < CaCl2 > SrCl2 > BaCl2}$

In other words, how can I determine the solubility order of $\ce{BX2, MgX2, CaX2, SrX2, BaX2}$ (where $\ce{X = F, Cl, Br, I}$)? The given orders of solubility have been verified with data.


texts: Relation between moles, molar mass and mass

texts:
You are asked to prepare a 0.8500 M solution of aluminum nitrate. You find that you have only 50.00 g of the solid.
What is the maximum volume of solution that you can prepare?

I'm confusing my molar masses with grams. The molar mass of Aluminum nitrate $\ce{Al(NO3)3}$ is 213.0 g. If I have 50.00 g of the entire solid $\ce{Al(NO3)3}$ does that mean I have 50.00 times the amount of 213.0 g or will I end up Multiplying 50.00 g of Aluminum nitrate by 0.8500 M, then dividing that by the MM of Aluminum Nitrate. But then I don't know how to set up the rest of my dimensional analysis to reach Liters.$%edit$


texts: Anomaly in van der Waals constants of noble gases

texts:
In van der Waals equation for a real gas, the equation is

$$\left(P + a\frac{n^2}{V^2}\right)(V - nb) = nRT$$

where $P$ is the pressure of the real gas, $n$ is the number of moles of the gas, $R$ is the ideal gas constant, $T$ is the temperature, $a$ is a constant to correct for the intermolecular forces of attraction, and $b$ is a constant to correct for the size of the molecules.

It follows that gases with large intermolecular forces have large $a$ values and gases with large molecular size have large $b$ values.

Below is a table of the $a$ and $b$ values of the ideal gases:

\begin{array}{ccc}
\hline
\text{gas} & a & b \\
\hline
\ce{He} & 0.0341 & 0.0237 \\
\ce{Ne} & 0.211 & 0.0171 \\
\ce{Ar} & 1.35 & 0.0322 \\
\ce{Kr} & 2.32 & 0.0398 \\
\ce{Xe} & 4.19 & 0.0511 \\
\hline
\end{array}

Why is the $b$ value for helium larger than the $b$ value for neon even though helium's atomic radius is smaller than that of neon? Does it maybe have to do with helium's small size, and thus higher electron density surrounding the nucleus, creating more repulsions with other helium atoms?


texts: Why do atomic radii decrease across a period?

texts: It's said that atomic size/radius decreases across a period, in spite of addition of electrons. But how does this actually work?


texts: Effect of pH on positive and negative charges of a zwitterion

texts:
I read that the isoionic point is defined as the

  pH at which a zwitterion molecule has an equal number of positive and negative charges and no adherent ionic species.

I have two questions regarding this definition.

How does pH affect the number of positive and negative charges of the groups in a zwitterion?
What does "no adherent ionic species" mean?


texts: How to calculate molar mass using the ideal gas law?

texts:
It is found that 250 ml of a diatomic gas at standard temperature and pressure (STP) has a mass of 1.78 g. What is the diatomic gas?

How can this question be solved? I know that I am supposed to use the ideal gas law

$$pV = nRT,$$

but am not sure how to apply it to this question.


texts: Total oxidation of toluene free enthalpy

texts:
I have trouble finding whether this reaction is spontaneous or not :

$$\ce{C7H8 + 9O2 -> 7CO2 + 4 H2O}$$

I consider (from the CRC Handbook of Physics and Chemistry) :

And so I find :

$$\Delta_r H° = 7\cdot (-393.5)+4\cdot(-241.5) - 9\cdot0 - 1\cdot 50.5 = -3670 \;\text{kJ/mol}  $$

and

$$\Delta_rS°= 7\cdot213.8+4\cdot188.8-9\cdot205-1\cdot0= 406.8\;\text{J/mol/K}$$

So at T=298 K I have

$$\Delta_rG°=\Delta_rH° - T\Delta_rS° = -3670\cdot 10^3-298\cdot406.8= -3.8\; \text{MJ/mol}$$

This would mean the reaction is very spontaneous, but according to experimental data, it should not. (The reaction only occurs when heating and with a catalyst).

What did I get wrong ?


texts:
On an old paper, I found an interesting representation of some symmetry operations: stereographs.

Online I found a set of symmetry operations and related stereographs (see: http://newton.ex.ac.uk/research/qsystems/people/goss/symmetry/Stereographs.html), yet it's  not clear to me how the representation is related to the symmetry operations (or: how are the representations obtained?).

Some samples from the website linked above:

C4

C5h

D6

I would like to understand the geometrical (and symbolical) meaning of a stereograph, in order to relate non-mnemonically it to its symmetry operation


texts: Predict the Product(s) of a reaction of tertiary benzylic alkyl halide

texts:
I could find two products:
The first one where is $\ce{Cl}$ is replaced by $\ce{CN}$.
AND the second one where $\ce{CH3CH2O}$ replaces $\ce{Cl}$.
Did I make a mistake or miss anyone?


texts: Can the friction of air disintegrate objects if they are accelerated enough?

texts:
Can an object be thrown so fast that the individual atoms or molecules separate in air? I mean if you could accelerate an object fast enough, would it disintegrate from the friction of air?

If so, would they separate faster in denser air? I think there would be more particles the object collides with, therefore the range after which it disintegrates is much shorter.


texts: Molpro - Simple explanation of OCC, CORE, FROZEN and CLOSED orbitals

texts:
I'm beginning with quantum chemistry and I'm supposed to do some ab initio calculations with Molpro. The problem is, I don't understand the orbital specification very well.

Let's say, I have the following computation:

 {mrci;
  occ,4,2,2,0,4,2,2,0;
  core,1,0,0,0,1,0,0,0;
  wf,13,5,1;
  state,3;
  option,nstati=5;
  option,maxit=200;
  option,maxiti=200;
 }

I don't understand much the flags OCC, CORE, CLOSED and FROZEN. I've read about them in the documentation, but I have troubles understanding it. Moreover, they possess different meaning in different methods, i.e. MCSCF and MRCI.

Could you, please, explain it in a basic way and graphically, if possible? I'm not looking for the deep understanding of methods now (I'll study them later), but I need to be able to use Molpro for some simple (di/tri-atomic) systems.


texts: Ullmann's Reaction (similar to Wurtz) - aryl chloride with deactivating groups - stability of free radical

texts:
Ullmann's Reaction:

Mechanism:

Question:

My textbook says with $\ce{X} = \ce{Cl}$, the reaction gives less yield compared to using $\ce{X} = \ce{I}$ since $\ce{Cu}$ is not as reactive as $\ce{Na}$ ($\ce{C - I}$ bond is weak).

But if aryl halides with substituents such as $\ce{NO_2}$ are used, they can help in obtaining good yield.

What I observe from both the mechanisms is that adding deactivating groups in the ortho or para position relative to the halogen should actually give lesser yield since the deactivating group would cause a partial positive charge to exist on the $\alpha$-carbon hence destabilizing the free radical intermediate.

Can anyone clarify my doubt? I suspect my last argument to be wrong regarding the $\alpha$-carbon. The $\alpha$-carbon is already electron-deficient and the partial positive charge should make it worse?

Courtesy: http://www.name-reaction.com/ullmann-reaction


texts: Why do people commonly use octane as a synonym for petrol (gasoline)? Isn't petrol a mixture of hydrocarbon distillates--not a pure substance?


texts:
Alkynyl silanes can be easily hydrolyzed with TBAF like in the last step in the synthesis:

How feasible is the hydrolysis of vinyl silanes with TBAF? Does it actually happen or some other routine must be used?


texts: What are the standard math prerequisites for physical chemistry?

texts:
I'm currently a chemistry major and I know that physical chemistry requires lots of calculus.  Which mathematics courses should I take so that I am well prepared for my physical chemistry courses? Specifically, I need to take courses in thermodynamics, quantum chemistry and statistical thermodynamics and beyond, as I want to specialize in physical chemistry.

Is it true that the more mathematics courses that one takes, the easier physical chemistry becomes? I'm currently taking a multivariate calculus course now, and I wonder which is the next level of math courses I should take.

I plan to take as many mathematics courses as possible. I'm thinking of taking ordinary differential equations after i finish multivariate calculus. What additional courses beyond ordinary differential equations should I take? My school offers courses in complex analysis, real analysis, and partial differential equations. Will they be useful?


texts: Is viscosity proportional to the number of hydroxyl groups?

texts:
Is the following statement always true?

  The more $\ce{-OH}$ functional groups in the molecule, the more is its viscosity?

I think it is true, because it is known that weak intermolecular forces lead to lower viscosities and strong intermolecular forces lead to higher viscosities
and because the more $\ce{OH}$ functional groups in the molecule will give rise to a molecule having stronger molecular forces. As the case in glycerol ($\ce{C3H8O3}$) and water ($\ce{H2O}$)

Therefore the statement must be true. What do you think?


texts: When temperature is decreased, why do reactions occur at all?

texts:
I admit that my knowledge of collision theory may be lacking, but, as I understand it, when particles collide, a reaction will not occur without overcoming the activation energy.

That being said, as the temperature of the environment in which the collision takes place is decreased, I believe it is logical that the kinetic energy of these particles will also decrease. Hence, to me, it would make sense if none of these particles had the energy required to react.

So, my question is: Why do reactions still occur when the environment's temperature around a collision decreases? That is, shouldn't there be a point (such as the temperature in a freezer, perhaps?) in which the activation energy cannot be overcome at all?


texts:
I am reading Fundamental concepts of organic chemistry by Dr. Anju Srivastava (12/04/2007).

It shows that carbon-hydrogen bond in ethane is 1.1 Å long, in ethene it's 1.08 Å,  and in ethyne it's 1.06 Å. According to the book, it's clear that carbon-hydrogen bond decreases with increasing multiple bonds on the carbon atom onto which the bond is!

According to my understanding, the shorter the covalent bond, the stronger it is, and it's contrary to the fact that the hydrogen atoms in ethylene are more acidic than those of ethene and so is ethane. The more acidic the hydrogen atom, the weaker it is held in a bond.

Help please where am wrong, and also guide about the book concept.


texts: Which has stronger hydrogen bonds: water or ice?

texts:
As ice is the solid form of water and it has more hydrogen bonds than water, because it's oxygen atoms are precisely tetrahedrally positioned and each oxygen is hydrogen bonded by four neighbouring oxygen atoms.

This changes the density of ice by expanding it, but does it change the strength of hydrogen bonds of ice? Or more precisely, which one has strong hydrogen bonds, water or ice?


texts: Compounding Polyphenol Sulfonic Acid (Negatan)?

texts:
Looking for formulation of Polyphenol Sulfonic Acid (Negatan).  Any additional steps on how to make it would be helpful.
This site references it, but the ingredients shown account for roughly 45% total:
https://compoundinglab.com.au/dental-products.html
Other references:
https://pubchem.ncbi.nlm.nih.gov/compound/3080658


texts:
I would like to get some voltammetry curves with my homemade supercapacitor in order to be sure that I have only capacitive effects (capacitive current) in my cell and no redox reactions (faradic current).
One of my electrode is my carbon material and the other one is stainless metal.

I only know the 3 electrodes system, do I really need it in this case ? How should I process for my experiment ?


texts:
I have an aqueous solution of N,N-dimethylphenylalanine methyl ester hydrochloride and I need to crystallise it as a salt. I'm afraid of increasing the temperature or the concentration of acid due to the possibility of ester hydrolysis.
What crystallisation method would be the most efficient in this situation?
Any help would be greatly appreciated.


texts: Distillation: temperature not reaching azeotrope boiling point

texts: I ran a simple distillation of $\ce{HBr}$/water mixture because I wanted to purify it. Boiling point of azeotropic hydrobromic acid is approx. $\pu{124 ^\circ C}$, however my distillation ran almost all the way through at vapor temperature of $\pu{112\! -\! 113 ^\circ C}$. Atmospheric pressure is normal. It is around $\pu{8 ^\circ C}$ where I'm working though. What could be the reason the temperature never reached $\pu{124 ^\circ C}$?


texts: Why does zinc react with sodium hydroxide?

texts: If zinc is less reactive than sodium, then why does it still react with sodium hydroxide?


texts:
How do we recognize the internal plane of symmetry in meso compounds? I read online that the substituted groups attached to a stereocenter could be rotated as such, to obtain an internal plane of symmetry:

Why would rotating the bonds in a molecule not affect its optical activity?

Also, exactly how does the presence of an internal plane of symmetry render a molecule optically inactive, as seen in meso isomers?


texts:
The phenomenon of deliquescence wherein a water soluble substance absorbs water from atmosphere and dissolve in it forming a saturated solution, has thermodynamic roots. I have read the fact that the vapour pressure of the saturated solution should be lower than the the vapour pressure of water at that temperature. Why is this so?

Moreover, since deliquescence is a spontaneous process and therefore thermodynamically favourable, there must be a negative $\Delta G$ for the absorption of water vapour and conversion of solid substance into its saturated solution? How can we derive, understand or quantify various thermodynamic parameters ($\Delta G, \Delta S, \Delta H$ etc) for the process of deliquescence?
I am comfortable with basic thermodynamic manipulations, binary phase diagrams, multiphase systems and equilibria.


texts: Glassware Test Instruments CAD blocks library

texts:
I am designing a fairly simple distillation for dichloromethane.
Being an engineer I feel more comfortable working with precise dimensions of both the separate glass vessels (condensers, evaporators, flask, etc) and of the complete apparatus.

I have been looking to find a CAD library that has various glassware blocks.
This way I can visually assemble my set and be able to show a drawing to my supervisor.


texts: How to compute the number of ATP molecules that can be produced from breaking down an unsaturated free fatty acid?

texts:
From studying $\beta$-oxidation of free fatty acids, I've learned how to compute for the ATP equivalence of even-chain and odd-chain free fatty acids.

What really bothers me now is how to compute for the ATP equivalence of an unsaturated fatty acid. Since one of the major difference of the process is in unsaturated fatty acids, normal $\beta$-oxidation rounds will occur until the unsaturation is encountered. The cis-isomer will be converted to trans-isomer completely skipping the step where the fatty acyl-CoA molecule is oxidized to the trans-form with the release of FADH2.

Is the computation same and I just need to subtract a molecule of FADH2 per unsaturation (double bond)?


texts: Why do the physical properties of an egg shell change when the egg shell is exposed to vinegar for a week?

texts: When an egg is kept in vinegar for one week, its hard calcium carbonate shell changes into a soft rubbery membrane. As vinegar is weak acetic acid, how does vinegar change calcium carbonate into a soft rubbery membrane? What is the reason for this?


texts: Non-symmetric compounds with more than one Chiral Carbon

texts:
If I have a compound which has non-symmetrical ends, and it has more than one chiral carbon, with no other stereocentres.
Then can I say that all of these will be stereocentres, and so there will be 2^n isomers? Can you give an example where this is not true (if)?


texts: In C2 molecule, both bonds of the double bond are pi bonds. But isn't the rule that there should exist a sigma bond before a pi bond is formed?

texts: C2 molecules have been found in vapour state. Their double bonds are made of two pi bonds because four electrons need to be accomodated in each bond. So this is against the rule that there must be a sigma bond before a pi bond is formed in the double bond. Why the anomoly?


texts:
I am facing trouble with the following problem.

Is (R)-1,7-dioxaspiro[5.5]undecane chiral?

My idea is that the compound possess a plane of symmetry and thus should be achiral. However if we take its mirror image then the bond pointing below of the plane will become above the plane and thus it will not form a nonsuperimposable mirror image indicating that it is chiral. Certainly one of the approach is incorrect. I couldn't understand which one.


texts: Can hyperconjugation take place between lone pairs of an atom attached to an sp2 carbon?

texts: When $\ce{HBr}$ is added to 2-chloro-2-butene, the proton preferentially bonds to the $sp^2$ carbon that's not bonded to chlorine. Does this mean that hyperconjugation takes place between the lone pairs of chlorine and the positively charged $C3$? I would assume that since there is still a free rotation about the $\ce{C-Cl}$ bond and that chlorine is in a tetrahedral formation this would be the reason behind the regioselectivity.


texts: How is silica gel prepared from sand (after extracting it). How many ways can it be used? Is there a way to make it without an oven?


texts:
One of the oldest recipes to create lye is this one:

Take well burnt ashes and put them in a barrel
Fill the rest of the barrel with water
Leave the suspension for a week or two
You can now try the lye concentration with egg - if 2/3 remain above the water, the concentration is sufficient for domestic uses
Separate the lye solution from ashes by carefully draining the water. You can also use filtration.

Now I know there are traces of various metals in us, as well in flowers and trees. But how can ashes accumulate such a big amount of sodium? And how is the sodium bound into it. How does it turn into hydroxide?


texts: Difference between flame test and ability to show photoelectric effect

texts: My textbook says magnesium doesn't give flame test. But it also says that it is a good photoelectric material. Are both concepts using "visible" light to remove or excite electrons?  What is the basic difference between these two and why is magnesium showing only one of them?


texts:
I was looking for some distillation equipment on Sigma Aldrich because I wanted to perform some vacuum distillation, when I came across a vacuum-jacketed distilling column.

Now as far as I understood my high-school chemistry, I can perform vacuum distillation perfectly fine with a 'normal' column as long as there is an entry to which I can connect my vacuum source (in my case a cheap aspirator, but he it does the trick).

Before I'm buying all this pretty expensive stuff, I want to make sure that I buy the right equipment. As far as I can see it, this vacuum-jacketed distilling column has nothing to do with vacuum distillation, it is simply a vacuum jacket around a normal column. But then, where it is used for and why, or am I wrong?


texts:
I am dealing with the iodine clock reaction, which has the half-reactions:
$$\begin{alignat}{2}\ce{H2O2 (aq) + 2I- (aq) &-> I2 (s) + 2 OH- (aq)} &&\quad (\text{slow}) \\ \ce{I2  (s) + 2S2O3^2- (aq) &-> 2I- (aq) + S4O6^2- (aq)} &&\quad  (\text{fast}) \end{alignat}$$

Now, I have to find the rate law. What I did was 4 solutions – one with standard amounts, another with double the $\ce{I-}$, one with double the $\ce{H2O2}$, and one with double the $\ce{S2O3^2-}$. I recorded the amount of time for the ppt ($\ce{I2}$) to appear. Now I have to calculate the rate law.

The thing is, I am not quite sure how. Usually you take the "slow" step and set up an equation based on that, like $\text{rate}=\ce{[H2O2]$^x$ [I- ]$^y$}$. However, the reaction is not just dependent on those chemicals, it's also dependent on the $\ce{S2O3^2-}$. When it was doubled, the reaction was significantly slower (for obvious reasons).

How do I set up the rate law for this reaction? Or, if I can't, what else can I do with my data?


texts: Why does water evaporate at room temperature?

texts: When water temperature reaches $100\ ^\circ \mathrm{C}$, the molecules get so excited that the hydrogen atoms lose the bonds to the oxygen atom and therefore the water starts to become gas. I get that, but at room temperature ($23\ ^\circ \mathrm{C}$), is there no excitation in the atoms or is there?


texts: Is this product description wrong and a simple battery and not a fuel cell?

texts:
I won this "toy" at a science fair...
Now I have to make a short presentation about it in school.
On the package description they describe its energy source as "fuel cell"...
It consists out of a metal plate(magnesium), a black metal plate with a black coating and a paper-cotton-like isolator which is between those plates.
Through putting salt water on the isolator, there's a voltage difference of 1.76V between the black and the magnesium plate.
After a couple of seconds on load the voltage stays constant at 1.31V.
My theory is that it's only a simple battery, because there's no continious source of fuel which should be required for naming it fuel cell (according to wikipedia).

Is my thought right?

My idea about the black coat is, that it is a rubberd graphite or "coal" cathode, rubberd because coal or graphite would fall apart quickly. It is described as air-cathode in the package description. My idea is that the black coal or graphite coat is used to provide a larger amount of air to the reaction...

The magnesium plate gets damaged through this reaction, the black thing not.

Which material is the black coat?

and what is the full reaction?

a picture of the components


texts: Why are Dispersion Interactions Stronger in Molecules with Bigger Molecular Mass?

texts:
Usually there are two explanations:

When dipoles are induced due to movement of electrons in the molecule, they are bigger in molecules with more mass since they have/include more atoms (has sense to me)
Bigger molecules have bigger contact or "surface area"

What does "surface area" between molecules have to do with how strong dipoles are induced?


texts:
there was a reaction in my book. It is as follows:

$\ce{PbO + H2-> Pb + H2O}$

My question is Hydrogen is below lead in the reactivity series. Then how is this reaction possible?


texts: In Na extraction, is Ca2+ of CaCl2 reduced in addition to Na+ of NaCl in electrolysis

texts: In Na extraction from $\ce{NaCl}$, $\ce{CaCl2}$ is added in electrolysis to lower the melting point of the mixture to about $\pu{750 ^\circ C}$. But doesn't $\ce{Ca^2+}$ cation compete with the $\ce{Na+}$ ion to be reduced at the cathode? If so, since $\ce{Ca^2+}$ is right next to the electrochemical series, should we not have a considerable amount of $\ce{Ca}$ as impurity in the $\ce{Na}$ that we have extracted? Where do the inconsistencies lie?


texts: What is happening when KCl burns in a bunsen flame?

texts:
I did the experiment to qualitatively observe the different colours given off by different salts when placed in a flame.
But what is actually happening to the salt ?
Take $\ce {KCl}$ for example.
Does the $\ce{ KCl}$ react with $\ce {O2}$ ?
What does the reaction equation look like ?
Other salts include $\ce {LiCl}, \ce{BaCl2}$, $\ce{SrCl2}$, $\ce{CuCl2}$ and $\ce {NaCl}$.


texts:
I've been looking for extra information concerning flame atomic emission spectroscopy. I need a clear overview of which elements are detectable with this technique, but I can't find anything because flame AES seems to be quite outdated.
If there is no such overview, could there be a list of elements not detectable by flame AES, but detectable by ICP-AES? That would also work for me.


texts: What does higher electron gain enthalpy mean here?

texts:
While talking about ionic bonds my book states :

  Higher the value of electron gain enthalpy of the atom, greater the ease of formation of the anion from it, i.e., other atom should have high value of electron gain enthalpy.

Now I think it should say more negative than just higher (as negative enthalpy means release  of energy and hence more stability). So what should it be? Why the chemistry books (I have to read)  seem to always avoid the term magnitude(Is there some hidden assumption which are generally in the field of inorganic chemistry  ?


texts:
I am a mathematics and chemistry double major and I just finished my statistics requirement and a great deal of the class was spent on probability distributions (e.g. Binomial, Poisson, Geometric, Gamma, etc.) and so I was wondering since electrons have a "probability" of being in a certain location according to the Heisenberg Uncertainty Principle, what sort of probability distribution would this represent?

As in, could we treat electrons and their positions as discrete or continuous random variables? And if so, what sort of distribution could we use for an electron being in a particular cloud?


texts:
**Question: ** There are 2 flasks of equal volume, connected by a narrow tube of negligible volume, filled with nitrogen gas. When both are immersed in boiling water, the gas pressure inside the system is 0.5 atm. Calculate the pressure of the system when one of the flasks is immersed in ice water mixture, keeping the other in boiling water.

Problem: There are two ways that I am going to describe that I can think of to solve the question, but they give different answers.

Way 1: Net Temperature of the system should be 50 degree Celsius because there is no heat loss and there is symmetry. As both the flasks are identical and at 100 and 0 so it should be 50.
Calculating the answer with this assumption and the formula
P1/V1=P2/V2
The answer comes out to be about 0.432 atm

Way 2: The sum of the moles of gas in both the flasks would remain same.
And using the ideal gas equation to get n = number of moles = PV/RT
After equating the values. The pressure come out to be about 0.422 atm

I was bothered with the 0.1 change. So I took the liberty to calculate the temperature from way 2, and it came out to be about 41.82 degree Celsius.

Note : calculations were done in Kelvin itself.

So we assumed that temperature would be 50 but way 2 contradicts that. I could not find a fault in either of the ways so could not understand what temperature would it really be.

Attempt to solve: is it something about Gibbs Paradox? I was Googleing and that came, but I couldn't understand...

Please help with proper explanation on why the other way is wrong.


texts: I've been reading that a saponification reaction typically involves NaOH or KOH. I was wondering - could anything that contains an OH group cause a saponification reaction? For instance, coconut oil + ethanol? If not, why is a "strong base" needed?


texts:
This seems so simple, yet I just can't seem to manage. Apparently $\ce{S2N2}$ and $\ce{S4^2+}$ (which are isoelectronic) obey Huckel's rule (at least to some extent) and I was trying to draw the Lewis structures to show that, but I can't manage to draw them without having a diradical, which doesn't seem very likely to exist. And if there are radicals, it doesn't obey Huckel's rule anymore.

Can someone help me draw their Lewis structures that obey Huckel's rule?


texts: How does an electrolyte conduct electricity at low potential?

texts:
My understanding is that electrolytes conduct electricity by:

1) movement of ions, the negative ions migrate to the positive electrode and vice versa. This is however not enough, if these ions just remain ions, the migration and separation of charges will create a potential difference in the solution counteracting the applied potential and at that moment migration of ions will stop. This means no more current will flow.

So therefore:

2) For current to keep flowing the ions must undergo electrolysis at the electrodes to form their neutral forms. In this way their is no build-up of counterpotential, ions keep flowing and the electrons exchanged in the electrolysis can flow from one electrode to the other. (This argument is often given as the reason electrolytes are conductive when I was doing an internet search, also on this site)

Now if we have say a NaCl solution, this would mean that for electrolysis Na+ needs to be converted in to Na, and Cl- into Cl2-gas. The potential needed for the electrolysis of NaCl as calculated from my tables is more than 4V.

So does this mean that if the potential difference is less than 4 V a salt solution does not conduct electricity, ie has very low or zero conductance? If not, how exactly is the current created?

I've read that conductivity is measured in a way that electrolysis is avoided (alternating voltage, wikipedia), so I guess then only the migration of ions is accounted for, but the very definition of conductivity is the ability of a substance to conduct electricity. According to my understanding to maintain a current this requires electrolysis.


texts: Which thermodynamic ensemble does Gaussian's BOMD functionality sample?

texts:
Someone sent me a Born-Oppenheimer molecular dynamics output with the following settings line:

# b3lyp/sto-3g BOMD=(MaxPoints=35, Ntraj=1, Update=15, RTemp=298) guess=read geom=allcheck

Based on my understanding of the BOMD keyword documentation, it sounds like the temperature is only used for putting energy into the vibrational modes, which are then used to initialize the nuclear velocities. Since there is no mention of a thermostat in the output or the documentation, this implies that calculations can only be run in the NVE ensemble.

Are my assumptions correct?


texts: Is the density of a two-component mixture always between the densities of its individual components?

texts:
There exist eutectic mixtures, in which the freezing point of the mixture is below those of either component of the mixture, i.e., the freezing point of the mixture is not intermediate between that of each component, but is instead lower than both.
Can the same occur for density? Are there mixtures of substances $\ce{A}$ and $\ce{B}$ such that either $\rho_\mathrm{mix}$ is greater than both $\rho_\ce{A}$ and $\rho_\ce{B},$ or $\rho_\mathrm{mix}$ is less than than both $\rho_\ce{A}$ and $\rho_\ce{B}?$
Or is the density of a two-component mixture always bracketed by (i.e., some intermediate value between) the densities of its individual components?


texts:
I am having a problem wrapping my mind around the idea that in $230\:\mathrm{mL}$ of $0.615\:\mathrm{M}$ $\ce{KCl}$ there is $0.141\:\mathrm{mol}$ of $\ce{Cl^-}$ ions. I guess I still do not understand moles.

Is this calculation saying that there $0.141\:\mathrm{mol}$ of $\ce{K}$ and $\ce{Cl}$ in one mole of $\ce{KCl}$?

I know this may be a silly question, but I just want to make sure I am following the correct way of thinking when it comes to this concept.


texts: Calculating bond dissociation enthalpy of F-F bond

texts:
$$\ce{N2 + 3 F2 -> 2 NF3} \quad ΔH = \pu{-263 kJ mol-1}$$

  The bond dissociation enthalpies of the nitrogen triple bond and nitrogen–flourine bond are $\pu{946 kJ mol-1}$ and $\pu{272 kJ mol-1}.$
  Find the bond dissociation enthalpy of the $\ce{F-F}$ bond.

  A. $\pu{-423 kJ mol-1}$
  B. $\pu{-393 kJ mol-1}$
  C. $\pu{-141 kJ mol-1}$
  D. $\pu{+141 kJ mol-1}$
  E. $\pu{+423 kJ mol-1}$

I know that since bond dissociation enthalpy is endothermic it has to be one of the last two.

I tried substracting bond dissociation enthalpies of products from reactants and equating that to the enthalpy change but my answer is nowhere near the given ones.
Is my method wrong?


texts: Is Henry's Law sufficient for calculating CO2 solubility?

texts:
$\ce{CO2}$ reacts with water which is why it enters and exits solution slower than other gasses (if I understand correctly this is why carbonated drinks bubble gradually instead of all at once).

Henry's law is an approximation that assumes the gas solute does not react chemically with the solvent.

Is the Carbonic acid reaction significant enough that Henry's Law does not work for $\ce{CO2}$?
What about in the case of blood, where the reaction is catalyzed by the enzyme Carbonic Anhydrase?


texts:
I'm attempting to make a hard refractory cement to apply over kiln brick made of sodium silicate and Perlite. This creates a very good kiln brick, however they are susceptible to abrasion.  I've been making my own sodium silicate, and thought I might be able to make it harder with the addition of some oxides.

I added silica gel and water; then I added magnesium oxide and sodium hydroxide.   There was a extremely strong exothermic reaction.

What would this be called? I imagine it's called something like $\ce{Na2SiO4Mg}$.  Tomorrow I will try some combinations of sodium silicate with Aluminum Oxide, and magnesium oxide. What would these be called?

If you have a recipe for a hard refractory cement to protect the Perlite mix from abrasion I would appreciate the input.


texts:
Is there any particular reason why this mechanism is used in the solution manual rather than an acid-catalyzed hydration?

I was thinking of having the double bond attack a hydronium ion, which would create a carbocation. This would then create a place for water to attack. Finally, the water would be attacked by water to reform hydronium ion.

Why wouldn't this work?

Does this have anything to do with the fused ring?


texts:
I am trying to come up with a logical mechanism for the following transformation, where 2-methylenecyclobutan-1-ol is converted to cyclopentanone under acidic conditions:

What I have tried to do was contract the ring to a methylcyclopropyl carbocation as it is exceptionally stable. I also tried to expand the ring but got an unsaturated primary alcohol instead. Can somebody suggest a proper mechanism for the reaction?


texts: Is it good practise to mix double and triple zeta basis sets?

texts:
I need to compute extremely accurate single point energies using the coupled cluster method. The methods to be employed scale largely with the number of basis functions. A few basis functions may have a huge impact in the computational cost.

I planned assigning a 3ζ basis set to a central atom, and 2ζ for the surrounding atoms. I cannot compute everything at 3ζ.

Clearly, these small basis sets are intended for estimate the contribution of high excitation.

Are there any reason which prevent this mixture, or any argument supporting the usage of 2ζ for every atom?


texts: How does brewing time and brewing temperature affect the flavonoid concentration of green tea?

texts: I've searched a lot for this, but I still cannot find any good explanations for how these two factors affect flavonoid concentrations.


texts: How do phase transitions occur in the solid phase?

texts:
For example, how does graphite transform into diamond as pressure increases at a certain (adequate) temperature? I'm not sure if this is a great example to look at the bigger picture, so another example would be pure iron. At atmospheric pressure, as liquid iron cools down it solidifies to $\delta\text{-}\ce{Fe}$, with a bcc crystal structure. Further cooling down brings it to $\gamma\text{-}\ce{Fe}$, which has a fcc. Then, it keeps cooling down and it solidifies to $\alpha\text{-}\ce{Fe}$, again with a bcc structure. I don't really see how do the atoms physically rearrange to form the different crystal structures, neither do I see why would they jump back and forth between these. To add to this, I believe the difference between $\alpha$ and $\delta$ are their paramagnetic properties.

I guess the general question is, how do the atoms in the solid phase rearrange themselves by changes in pressure or temperature? (in contrast to, for example, a liquid-gas phase transition). And of course, why? What drives this change?


texts: Is it plausible to draw an enthalpy diagram for a nuclear reaction?

texts: For a project I am required to draw a enthalpy diagram for the conversion of thorium-232 to uranium-233 and I am unsure on how to proceed. I understand a certain amount of energy is lost through beta decay, but would beta decay be considered a reaction?


texts: How did early chemists measure concentrations and purity?

texts:
My chemistry teacher loves going back through the history of famous chemists. This got me wondering how these chemists would first determine the concentration of a sample before they had any other chemicals of known concentration to compare against?

What modern methods are there for determining concentrations and purity without other chemical standards to compare against?

Let me explain my question a little more clearly with an example.

If a historical scientist starts their own laboratory and wanted to do a titration, how would they start? They might produce some hydrochloric acid, or some barium sulfate, and want to confirm its concentration/purity. However, this would require they already know the concentration of something else, which they don't. So it seems a little paradoxical. How did they ever start performing analytical experiments?


texts: Reason for decreased boiling point of hexafluoroisoproponal?

texts:
Ethanol and isopropyl alcohol have boiling points 78.37 °C and 82.6 °C respectively. The increase in the boiling point is obvious due to increase in carbon chain length which resulted in increase in boiling point of isopropyl alcohol.

But recently, I come across fluorinated ethanol and isopropanol, and the trend of boiling point is the reverse. Trifluoroethanol has boiling point 78 °C whereas hexafluoroisopropanol has boiling point 58.2 °C.

what is the reason for the decrease in boiling point of hexafluoroisopropanol? Is it due to increase in the number of fluorine atom, if so then why this resulted in decrease in the boiling point?


texts: What is the correct Lewis structure of diazomethane?

texts:
I tried to google and watch YouTube videos on how to write Lewis structures properly, but I can't seem to understand how to do this correctly.

My teacher, when class was in session, gave me a set of instructions to complete Lewis structures:

Sum Valence electrons
Add electrons to outer atoms, while obeying octet or duet rule.
Then add electrons to center atom, obey octet rule, unless they're third row element or below.
Do formal charges for each atom valance charge - (unbonded electrons + 1/2(bounded electrons))
Once formal charges have been determined, minimize formal charges by using unbound electrons to make double or triple bonds
Redo formal charges to check if formal charges are as low as possible, for central atom.

So I attempted to do this for the diazomethane, but my answer (circled in green) does not match the book's answer (in red).

What did I do wrong?

After further considerations, I realized that my structures didn't obey the octet rule. So then would this revised structure be also correct?


texts: Primary kinetic isotope effect in the E1cB reaction

texts: How is the primary kinetic isotope effect (KIE) observed in the E1cB reaction when breaking of the $\ce{C}$-$\ce{H}$ bond is not the rate determining step of this reaction?


texts: When a bond is formed between an electophile and a nucleophile, they both lose energy and become more stable right?

texts: This is a section from clayden's organic chemistry textbook. I do not understand why it says energy gain and not energy loss


texts: Will an iron nail sunk in a highly concentrated salt solution rust?

texts: Assume I have a salt solution with the same concentration as the dead sea and I put a iron nail into the solution (assume it sinks). Will it rust? If yes, why? If no, why not?


texts: What is the meaning of parentheses in a condensed molecular formula?

texts: In the formula $\ce{(CH3)3-C-CH(CH3)-CH2-CH3}$, what do the parenthesized portions represent? What is the molecular structure, and how do I name the compound?


texts:
I have seen in a lot of pictures that benzyne looks like:

But aren't $\ce{C_6}$ and $\ce{C_5}$ $-$ $\ce{sp}$ hybridized?

And hence bond angle should be $180^{\circ}$ or at least near about it?

Something like :

Or,

?


texts: What is the mechanism for the creation of P(CH2OH)4+ cation?

texts:
I know that the initial reactants are phosphine and menthanal in an acid ($\ce{H+ A-}$) and that the first step in the reaction is the HOMO of phosphine (the lone pairs) and the LUMO of methanal (the π* orbital).

Then, the electrons that just moved to the oxygen atom react with $\ce{H3O+}$, so the oxygen is protonated. I'm not sure what follows, though.


texts: If one of them is an aqueous solution, in this case hydrochloric acid, why doesn't it have a different chemical formula ? How would I explain the reaction between hydrogen and chlorine without the use of water to make it acidic ?


texts: Reaction of chloroform, resorcinol and strong base

texts:
A common reaction used to identify resorcinol (benzene-1,3-diol) in the laboratory is to react it with chloroform in presence of 30% sodium hydroxide (NaOH). A red coloured solution (or precipitate) is produced. I have searched many books and websites, but none of them give any clue about the actual reaction, its products, far less the reaction mechanism.

The reaction is as follows:

$$\ce{Resorcinol + Chloroform + 30\% NaOH -> Red Colour}$$

So any ideas about what reaction is taking place?


texts: Calculating Raman Intensities from Static Raman Activities

texts:
Whenever I want to calculate a Raman spectrum, my quantum chemical programs give me Raman scattering activities. As the common Raman spectrum is dependent on the incident wavelength of the used laser this seems quite logic, because the program cannot guess which laser the experimentalists could have used.
At least in Gaussian 09, for some methods, there is the possibility to calculate the Raman scattering activities for a certain incident light frequency through cphf=rdfreq.

As far as I know, the latter would give me the dynamic Raman activities and whenever I don't enter the incident light frequency I will get static Raman activities.

To get the intensities out of the activities, I was given the following equation, which I was told only holds for the dynamic activies:
$$I_k \varpropto \frac{S_k}{\tilde{\nu}_k} \frac{\left(\tilde{\nu}_\text{in} - \tilde{\nu}_k\right)^4}{1-\exp\left(-\frac{h c \tilde{\nu}_k}{k_B T}\right)} $$

But what if the calculation method that I use is not able to produce dynamic Raman activities (i.e. because it's not implemented) and I am only able to get those static Raman activities? How do I get Raman intensities from them?


texts: Radical Chain Reaction, termination steps

texts:
In the termination step of radical chain reaction, we often neglect the recombination of hydrogen atom radicals and it will not be included in the mechanism.
Let say the reaction is between $\ce{H2}$ and $\ce{Cl2}$. I often see the recombination of chlorine radicals in the termination step but not hydrogen. Is there any specific reason for this?


texts: Is it true that according to gibbs free energy equation, insoluble salts such as AgCl don't dissolve because the process would be too endothermic? The right side of the equation, TΔS, would have to be positive because entropy increases when salts dissolve, which means that ΔH would have to be high enough to make the equation positive. Is this correct?


texts: How do I solve this problem on mass balance from blast furnace iron making?

texts:
Question

An ironmaking blast furnace produces hot metal of the composition: $\pu{93.6\%}$ $\ce{Fe},$ $\pu{2.1\%}$ $\ce{Si},$ $\pu{3.6\%}$ $\ce{C},$ $\pu{0.7\%}$ $\ce{Mn}.$ The composition of the iron ore is $\pu{78\%}$ $\ce{Fe2O3},$ $\pu{9\%}$ $\ce{SiO2},$ $\pu{5\%}$ $\ce{Al2O3},$ $\pu{1\%}$ $\ce{MnO},$ $\pu{7\%}$ moisture. Coke rate is $\pu{850 kg/thm}.$ Composition of the coke is $\pu{80\%}$ $\ce{C},$ $\pu{10\%}$ $\ce{SiO2},$ $\pu{5\%}$ $\ce{CaO}.$ Enough limestone is charged to make $\pu{45\%}$ $\ce{CaO}$ in slag and composition of limestone is $\pu{100\%}$ $\ce{CaCO3}.$
Calculate (i) Weight of ore used per tonne of hot metal production; (ii) weight of slag produced per tonne of H.M.; (iii) weight of limestone used to produce given slag composition.

Doubt
In such problems all I need to balance is iron, silica, $\ce{MnO}$ etc. However, in case of $\ce{MnO}$ the solution in my book reads $\ce{MnO}$ from ore equals $\ce{Mn}$ in hot metal plus $\ce{MnO}$ in slag.
My question is for balancing $\ce{MnO}$: why do I need to drag in $\ce{Mn}$ content? The $\ce{Mn}$ in iron ore should be equal to $\ce{Mn}$ in slag. In fact, I feel that any content apart from $\ce{MnO}$ should not be dragged into picture. The rest of the contents like alumina, iron etc. quite comply to this argument. I would require a vivid justification to this.


texts:
My text says that

  Bond energy between P-O , S-O , Cl-O follows the trend P-O < S-O < Cl-O.

But I think it should be a reverse of what's given because more the electronegativity difference more will be the bond energy and lesser the bond length
(this what I believed so far before seeing P-O , S-O , Cl-O trend)

Moreover, after searching the web for the values of the same I was unable to find for P-O , S-O , Cl-O, but I found for C-O and N-O and B.E (bond energy) for it follows C-O > N-O ( which follows my resoning)

Then why the order is different for P-O , S-O , Cl-O is it an exception or could it be explained ?


texts: Reducing temperature on dissolved Pb(NO3)2

texts:
I have pretty much zero experience in chemistry whatsoever but I wonder about how much crystal will I get from fully dissolved element when I reduce water temperature.

Variables

at $\mathrm{40^\circ C,\ 171}\pu{g}$ of $\ce{Pb(NO3)2}$ is fully dissolved in water
at $\mathrm{18^\circ C,\ }\ce{Pb(NO3)2}$ - How much is dissolved now? Everything that was not dissolved turned to crystals?

I know that it probably has something to do with this graph right here but I can't turn my mind to right direction. Can someone explain this problem and how can I find solution?


texts: Do acyl fluorides exhibit resonance donation or inductive withdrawal?

texts:
I know that in acyl chlorides, there is partial triple bond character in the $\ce{C=O}$ bond not because the chlorine is electronically donating (due to size mismatch with carbon) but because the chlorine is highly electron withdrawing and this stimulates the oxygen into partially donating one of its lone pairs to the partially positive carbon.

This is supported by IR stretch data for the $\ce{C=O}$ bond in acid chlorides; we're looking at frequencies from 1810-1775 reciprocal centimeters - somewhat higher than a vanilla $\ce{C=O}$ bond stretch frequency.

However, in acid fluorides, in which the fluorine is of comparable size to the central carbon, it seems that resonance donation is at least a possibility. However, resonance must compete with the inductive withdrawal effect. So, which one wins out in acid fluorides, and does the $\ce{C=O}$ bond exhibit more single bond character or triple bond character?

I tried looking up acid fluorides, and I can't find any mention of them. So I guess a good starting point would be: are they stable enough to even exist?


texts: reaction between Green tea and sodium bicarbonate

texts:
There is a tea in northern Pakistan called noon chai or Kashmiri chai. It is distinct between it is a pink colour.
The method involves brewing green tea leaves in cold water and adding sodium bicarbonate.

What is the chemistry here?  How does this reaction work and why does the green tea become pink when sodium bicarbonate is added?


texts:
I found a question

Which is more stable among the following?
(a) $\ce{CaCO3}$
(b) $\ce{MgCO3}$

Answer : (a)
Explanation was given as:

$\ce{Mg^2+}$ has smaller radius than $\ce{Ca^2+}$ and thus charge/radius of $\ce{Mg^2+}$ is greater , hence it is less stable.

While when reading about the coordination compound, I found the sentence

Higher the charge of central metal atom ion i.e., greater ionic potential
charge/radius then greater is the stability.

In first case higher the ratio less is the stability.
In second case higher the ratio more is the stability.
Is the difference in the answers in both cases due to a difference in the salts (i.e. simple and  complex salt) or is any one of them wrong?


texts: Dissolving Tylenol Science Experiment - why is it fastest in distilled water?

texts:
My son has a science experiment for class to dissolve Tylenol (325mg acetaminophen) in 3 different solutions (125 mL volume each):

Distilled water
Vinegar (1 part white vinegar to 4 parts water)
Salt water (1 tablespoon sea salt)

All solutions were at room temperature.  As far as I could tell, the pill had no fillers and there was no coating on them.  On the bottle, the pills are described as 325mg acetaminophen, and there is no mention of non-medical / filler ingredients.

We used pH test strips, and it seemed the vinegar solutions was a pH of about 6, the water 7 as expected, and the salt water 8 or 9. Edit: it may be the pH was 7 for the salt water, see comment below.

His hypothesis was the Vinegar solution, being acidic would dissolve the fastest.  However, the Tylenol dissolved fastest in the distilled water.  The salt water was slowest, and the vinegar solutions was second.

We also tried pure vinegar, and this dissolved even more slowly than the diluted vinegar used at first.

I should add - it didn't really dissolve in any of the solutions, the pill just came apart into small particles.  Even stirring the solutions afterwards didn't seem to dissolve completely.

I am trying to help my son to determine why distilled water broke up the pill the fastest, but I'm afraid I don't know enough to help.

Any pointers, or websites, where I can help him to research greatly appreciated.


texts: Seeking an explanation of synthetic marcasite

texts:
At least one widely available commercial product is called 'synthetic marcasite,' and perhaps two or more.  The most prominent is dark gray 'synthetic marcasite' for cheap jewelry.  Possibly different is the synthetic marcasite used in battery research as at Electrochemical Society Proceedings.

I had suppposed the latter has the chemical composition and crystal strucure of natural marcasite. But I find that people also talk about marcasite iron diselenide and ditelluride, FeSe2 and FeTe2, apparently just based on crystal structure.   Does anyone here know more about this?

The jewelry product is dark gray, and very cheap at prices like a few cents per small round stone in lots of 1,000, which you can easily find on line. So I wonder if it is actually one of the things called hematine, which are various ersatz hematites, not matching the composition of hematite but mimicking the appearance.  See for example https://en.wikipedia.org/wiki/Hematine.  Does anyone here know?


texts: Shortcut method to find atomic term symbols ignoring the spin orbit coupling

texts:
Is there any shortcut method by which we can find the atomic term symbols ignoring the spin-orbit coupling, i.e. ignoring the values of J.

For instance, when writing the d-d transitions for any complex, we write the atomic term symbols and them split them further into other states. I know the lengthy procedure to find the term symbols by considering the values of Ml, and finding the exact states including the spin-orbit coupling but is there a shortcut way by which we may find the atomic term symbols?

Like, in the above picture, how did we find the terms for d2 to be 1S, 1G, 3P, 1D, and 3F


texts: Clarification on the $\mathrm{S_N2}$ mechanism

texts:
The question is about the specifics of the $\mathrm{S_N2}$ mechanism (nucleophilic bi-molecular substitution).

(Source: Wikipedia)

As we know that in this reaction the nucelophile ($\ce{Nu-}$) approaches the molecule. The main step (According to the molecular orbital theory) of the reaction is that the the nucleophile bonds with its lone pair in the anti-bonding molecular orbital (ABMO) of the central carbon atom. As this happens the leaving group ($\ce{Lg}$) is kicked off by gradual weakening of the $\ce{C-Lg}$ bond. Now the thing that bothers me here is:

Why does carbon prefer to add electrons in its ABMO? As the $\ce{Lg}$ has to bond with the carbon atom there has to be an increase in bond order whereas, while electrons are pushed into the ABMO it clearly decreases the bond order, which directly indicates the instability of bond formation.
The main question being, what makes the reaction favourable? What is the 'driving force'? Why does it take place when there is a decrease in bond order?


texts: Why is it wrong to calculate the amount of oxygen directly from the products of a combustion reaction?

texts:
I've been stumped by a question in my textbook concerning combustion analysis.

  A $\pu{0.5438g}$ sample of a liquid consisting of only $\ce{C}$, $\ce{H}$, and $\ce{O}$ was burned in pure oxygen, and $\pu{1.039g}$ of $\ce{CO2}$ and $\ce{0.6369g}$ of $\ce{H2O}$ were obtained. What is the empirical formula of the compound?

Firstly, I calculated the amount of substance of carbon and hydrogen by dividing the masses of each product by their respective molar masses.
\begin{align}
(1.0390/44.01) = n(\ce{C}) &= 0.02360\\
2\cdot(0.6369/18.02) = n(\ce{H}) &= 0.0706\\
\end{align}

My textbook then states that I must find the sum of the masses of carbon and hydrogen, and then deduct this sum from the mass of the liquid compound to get the mass of oxygen:
\begin{align}
0.02360 \cdot 12.01 &= 0.283535\\
0.0706 \cdot 1.01 &= 0.28637\\
0.5438 - (0.283535 + 0.28637) &= m(\ce{O}) \\
m(\ce{O}) &= \pu{0.1888g}\\
\end{align}

I have no qualms with this approach, but why can't I find the amount of oxygen directly from the products?
\begin{align}
\text{I.e.}&& 2\cdot(1.0390/44.01) &= n(\ce{O}) &\text{in }\ce{CO2}\\
\text{and} && (0.6369/18.02) &= n(\ce{O}) &\text{in }\ce{H_2O}.\\
\end{align}

$$\text{Amount of oxygen in liquid compound} = n(\ce{O})\text{ in }\ce{CO2} + n(\ce{O})\text{ in }\ce{H2O}.$$

I know this doesn't work, but my question is why? It seems perfectly intuitive to me, and yet it doesn't work.


texts:
Tomorrow I have a science test, and in it there are some mixtures, and we have to identify whether they are a solution, a suspension or a colloid. Is there an easy way we can identify this WITHOUT getting the mixtures up and seeing whether they sediment or not?
Note: They are everyday mixtures, like lattes, freshly squeezed orange juice etc.


texts: What is the Si–N–C bond angle in silyl isothiocyanate?

texts:
In silyl isothiocyanate, supposedly, the value of the bond angle $x$ is $180^\circ$.

I don't know how to figure this out. There is a lone pair on nitrogen and two sigma bonds. Shouldn't it have sp2- or sp3-hybrid orbitals and thus $x$ be smaller than $180^\circ$?


texts: How do carbon content and various heat treatment cycles affect the properties of steel at the micro-level?

texts:
I watch a YouTube channel by Alec Steele where a lot of metal forging is done. From this I know that varying the carbon content in steel drastically alters the physical properties of the metal, as does different heating cycles (time for cooling and temperature of the forge). I am interested what is happening at the atomic structure during the forging process.

Here are some of my ideas on what is occurring. I think cooling time must affect the grain size of the steel microstructure. I have a vague idea that grain size affects material strength but I don't really know why. I also assume that the crystal structure varies with temperature. At a higher temperature, higher energy polymorphs are probably observed. I know adding carbon to the iron increases the strength of the material but again I don't know why. I assume there is some pi - d bonding occurring which may act akin to semiconductor doping, adding energy states for Fe electrons to populate, increasing metallic bonding?

This does not answer my question:
What chemical characteristics give types of steel their properties?
I am looking for an answer more focused on bonding and energy level population.


texts: What's the Gibbs free energy of a reaction at zero temperature and pressure?

texts:
I heard that Gibbs free energy changes with temperature and pressure as

$$ \Delta G_1 = \Delta G_0 + R T \ln Q $$

But this makes no sense when pressure is zero or temperature is zero.


texts:
So I found these reduction potentials online:

$$\begin{alignat}{2}
\ce{H2O2 + 2H+ + 2e- \;&<=> 2H2O}\qquad &&E=1.78\ \mathrm V\\
\ce{2Cl- \;&<=> Cl2 + 2e-}\qquad &&E=-1.36\ \mathrm V
\end{alignat}$$

If the net reduction potential is positive will chlorine gas be spontaneously formed when salt and hydrogen peroxide are mixed in a acidic solution?


texts: Are allotropes of sulfur two different phases?

texts: Monoclinic sulfur and rhombic sulfur are two allotropes of sulfur. In phase equilibria, part of the system that is having distinct boundary, mechanically separable and different chemical or physical properties that other part of the system is considered as a phase. Now I want to ask, do chemical properties of Allotropes differ and why so that we can consider them different phases?


texts: In zero order why we don't need the coefficient of reactant in integration of rate law?

texts:
For a reaction: $\ce{aA->product}$

The rate law is $\text{Rate}=-\dfrac{\mathrm d[A]}{a\,\mathrm dt} = k$

Where:

$k$ is the rate constant
$[\ce{A}]$ is the concentration of the reactant $\ce{A}$ in the reaction
$a$ is the stoichiometric coefficient of $\ce{A}$

If we integrate the relation, we get:

$$[\ce{A}]-[\ce{A}]_0=-akt $$

However, my instructor wrote the relation on board as below;

$$[\ce{A}]-[\ce{A}]_0=-kt$$

Why is $a$ not needed in the integrated rate law?


texts: When does phenolphthalein containing solution change colour?

texts:
We were estimating the amount of dissolved $\ce{CO2}$ in water using the American Public Health Association method. It was a Titrimetric Method using phenolphthalein indicator.

Titrant used was $\ce{NaOH}$ and analyte was sample water.

The following questions came to my mind:

Why does the phenolphthalein $\ce{[HIn]}$ solution change colour at pH 8.2-10 when addition of a little titrant $\ce{NaOH}$ could result into production of some $\ce{In−}$ ions, the ions that give the colour to the solution. Why does it show colour change in only  when there's $10^{-5.8}$ to $10^{-4}$ free $\ce{OH-}$ in the water?
Is the source of this resulting basic pH, the titrant $\ce{NaOH}$? I think so because all the $\ce{OH-}$ formed from the reaction of titrant $\ce{NaOH}$ and analyte $\ce{CO2}$ reacts with the $\ce{H+}$ ions of phenolpthalien. So its only possible that the shift from pH 7 to pH 8.2 is due to the $\ce{OH-}$.


texts: Is it possible using electrochemistry or some other method to reverse a typical single replacement reaction to go in the opposite direction.  For example, is it possible to take silver metal and copper nitrate to get copper metal and silver nitrate?  I would like to do this, because nitric acid is very expensive to ship, and I can easily buy both silver metal and copper nitrate.  I don't know how to isolate the silver the silver nitrate as it is formed because it will simply react with copper metal in a electrochemical cell.


texts:
Old samples of magnesium oxide become contaminated with magnesium carbonate. Suggest how this contamination takes place.

I don't understand what I'm meant to put for this.


texts: Preferred Lewis structure for sulphate anion and XeO4

texts:
In a section reviewing Lewis structure, the textbook Atkins' Physical Chemistry, 10th Edition, by Atkins, Paula, and Keeler, gives the following illustration of hypervalence and octet expansion:

I have two questions regarding this illustration:

With regards to the structure of the $\ce{SO4^{2-}}$ ion, notice that the lowest energy structure (1b) has the double covalent bonds placed at angles that are closer than had the double bonds been placed at opposing sides of the sulfur atom. I'm confused as to why this is supposedly the lowest energy state, since one would expect the lowest energy state to be when the two double bonds are at farthest angles from each other (which would be when they are on opposing sides of the Sulphur atom in the diagram), since this would be the case when there is the most distance between the repulsive negative charges of the electrons in the two double covalent bonds? Based on my research, it seems that what I am referring to here would resemble a linear molecular geometry (although, I am obviously not saying that the molecule would actually have a linear molecular geometry), where the we can imagine the red atom in the following image as being the sulfur atom, and the two white atoms as being the oxygen atoms that have the double covalent bond:

My next question is with regards to the $\ce{XeO4}$ molecule. It seems to me that the arrangement of all of the free electron pairs on the oxygen atoms would be in a more energetically favourable state (the molecule would be in a lower energy state) if they were farther away (at greater angles) from the double covalent bonds? It seems to me that their current arrangement would make sense in a scenario where there were an additional 2 free electrons on the oxygens, as is the case for two of the oxygen atoms of structure 1b, but since these oxygen atoms only possess 6 electrons instead of 8 (as is the case for two of the oxygen atoms of $\ce{SO4^{2-}}$), then wouldn't it be more energetically favourable to have the electron pairs at greater angles from the double covalent bonds? Based on some research, it seems that the geometry that I am referring to is a trigonal planar molecule geometry, as shown here (although, I am just referring to the Lewis structure of the molecule -- not the 3-dimensional geometry). In the following image from the same Wikipedia article, imagine the red atom as being the oxygen, and one of the white atoms as being the double covalent bond, and the other two white atoms as being the lone pairs of electrons, so that you have a $60^\circ$ angle between them:

I would greatly appreciate it if people could please take the time to clarify this.


texts: Does enthalpy of dissolution change with temperature?

texts: Dissolution can be either endothermic or exothermic. At higher temperature dissolution is much faster. However, supplying heat also leads to an increase in the internal energy of the system. Ultimately, this affects the enthalphy of product and reactant. I want to know whether an increase in temperature affects the enthalphy of dissolution?


texts: Hygroscopic behaviour of DMSO - how bad is it?

texts:
For a fluid flow experiment I am using DMSO (dimethylsulfoxide), because of its low volatility, reasonably high surface tension, low viscosity and relative safety.

In the MSDS of DMSO I find that the liquid is hygroscopic, meaning it adsorbs moisture from the surrounding environment. Unfortunately, I cannot find anywhere how much water will be absorbed (mass%) or how quickly this will happen, is it saturated in minutes, hours, days?

Therefore, my question is twofold: (i) how much water will DMSO at maximum absorb and what is the rate at which this absorption occurs? (ii) with the absorbed water, how badly do the physical properties (viscosity, surface tension, density) of the (now) mixture change?


texts:
I was asked which of the following were aromatic:

My understanding of aromatic nature is, that the molecule must be cyclic, planar, every atom in the ring must be sp2-hybridized and the molecule must have [4n+2] π electrons, where n∈N (Hückel’s rule). The molecular orbitals also have to have the correct orientation and phase for aromaticity.

A and B are aromatic since they follow conditions as above(including empty orbital of boron in conjugation.)
azulene's aromaticity is due to the “fusion” of
two aromatic ions, both with 6 π electrons, cycloheptatrienyl (tropylium) cation and cyclopentadienyl anion.

Based on the above My answer was a,b, and c .

Given answer : a,b,c,d.

I checked for d. It was aromatic as described in this link. 1. The diagram indicates only π electrons along the blue need to be considered amounting to 18 π electrons in conjugation.

My question is why only consider π electrons in blue and why not others? How do we explain the aromaticity of porphyrin?

References

https://en.wikipedia.org/wiki/Porphyrin


texts: How would you change the chirality of a compound such that (S,R) becomes (S,S)? That is how would you synthesise a compound from its diastereomer?


texts: Exceeding CPVC in exterior roof coatings

texts: We have a kynar coated metal roof that was primed with an acrylic primer and then coated with a dark blue  acrylic elastomeric paint. It was coated during spring with moderate weather. The roof surface was dry. Within a few days the coating blistered severely.  The blisters were cut out; only the coating was delaminated, the primer was well bonded. Some of the blisters held moisture, most were dry. The blisters were cut out and the roof was reprimed and recoated. The coating blistered again as it had before. It was then revealed that the dark blue coating had been blended without a tint base; the pigment was added directly to a white or gray (or a mixture thereof) paint. We suspect that the CPVC was greatly exceeded when the blue pigment was added to the white and/or gray paint, would this cause the coating to blister? What test needs to be performed to determine the PVC?


texts:
While we have done some etching of glass with hydrofluoric acid alone, to achieve a matte white finish on float glass, I am curious to know what formula and procedure is required to create a more transparent and smooth finish ?

(Lead crystal polishing is achieved after diamond grinding, dipping in a mixture of $\ce{HF}$ and $\ce{H2SO4}$, and alternating with rinsing.)

Can anyone advise on the possible advantages of mixing another acid with the $\ce{HF}$?


texts:
I'd like to accurately calibrate a digital thermometer I'm building in the range of $50^\circ$ to $120^\circ$ Celsius.

I'm aware that one can buy various chemicals that have melting points in this range, but are there any readily available household / pharmaceutical items I could use instead?

From what I have read, it looks like the two easiest candidates would be vanillin or Sodium acetate (Thanks Curt F.), but I'm not sure how one would go about creating a pure enough calibration standard at home.


texts: Why is the equilibrium constant given in litre per mole?

texts:
At $800\:\mathrm{K}$ a reaction mixture contained $0.5\:\mathrm{mol}$ of $\ce{SO2}$, $0.12\:\mathrm{mol}$ of $\ce{O2}$ and $5\:\mathrm{mol}$ of $\ce{SO3}$ at equilibrium. $K_\mathrm c$ for the equilibrium $$\ce{2SO2 + O2 -> 2SO3}$$ is $833\:\mathrm{L/mol}$. If the volume of the container is $1\:\mathrm{L}$, calculate how much $\ce{O2}$ is to be added at this equilibrium in order to get $5.2\:\mathrm{mol}$ of $\ce{SO3}$ at the same temperature.

The answer comes out to be $0.34\:\mathrm{mol}$.

I have understood the whole question and I am getting the answer. I just have a confusion why we are taking $K_\mathrm c$ as $833$ and not $1/833$ which makes it $\mathrm{mol/L}$. I think $K_\mathrm c$ should be in $\mathrm{mol/L}$.


texts: Is this an exception to the rule that strong acids/bases always replace weak acids/bases?

texts:
According to the $\mathrm{p}K_\mathrm{a}$ table: hydrochloric acid is stronger than sulphuric acid. It has a $\mathrm{p}K_\mathrm{a}$ around $-6.3$ while the $\mathrm{p}K_\mathrm{a}$ of sulfuric acid is around $-3$. The second dissociation in the case of sulfuric acid is not very extensive and doesn't contribute much to its acidity.

\begin{aligned}
\ce{H2SO4 + H2O ~&<=>~ H3O+ + HSO4^{−}&&pK_{a}~=~-3}\\
\ce{HSO4- + H2O ~&<=>~ H3O+ + SO4^{−2}&&pK_{a}~=~2}\\
\ce{HCl + H2O ~&<=>~ H3O^+ + Cl^{-}&&pK_{a}~=~$-6.3$}\\
\end{aligned}

Now $\ce{BaSO4}$ reacts with  $\ce{HCl}$ to produce very less of $\ce{BaCl2}$ because of the insolubility of $\ce{BaSO4}$.

My teacher told me that in a reaction "Strong acids or bases replace weak acids or bases". This holds good for this reaction as $\ce{HCl}$ is stronger than $\ce{H2SO4}$.

However $\ce{NaCl}$ reacts with $\ce{H2SO4}$ to produce $\ce{Na2SO4}$ and $\ce{HCl}$. In this case $\ce{H2SO4}$  replaced a stronger acid $\ce{HCl}$. How do we account for this?


texts:
Researching old (like century-old) papers it is common for chemists to describe preparations in terms of parts – e.g., "1 part water, 2 parts sulfuric acid."

Is there a reliable convention on whether this means molar parts or mass parts?  I.e., in the above example is the formula 1:2 parts by mass or by molecules?


texts:
I was asked the following question in my introductory chemistry class:

  The diameter of metal wire is often referred to by its American wire gauge number. A 16-gauge wire has a diameter of $\pu{0.05082 in}$. What length of wire, in meters, is there in a $\pu{1.00 lb}$ spool of 16-gauge copper wire? The density of copper is $\pu{8.92 g/cm^3}$.

First I converted the imperial measurements to metric. $\pu{0.05082 in} = \pu{0.12908 cm}$, $\pu{1 lb} = \pu{0.45359 kg}$, according to Google. So I can use $\pi r^2 h$ to calculate the volume (and thus, using density, calculate the mass) of one meter of wire, I figure the radius to be $\pu{0.06454 cm}$. The equation becomes $V = \pi \times (\pu{0.06454 cm})^2 \cdot \pu{100 cm}$, which equals $\pu{0.41654 cm^3}$. So that's the volume of one meter of wire.

Using the density of copper $(\pu{8.92 g/cm^3})$, I figure the mass of one meter of wire to be $\pu{3.72 g}$. If $\pu{1  lb} = \pu{453.59 g}$, then converting $\pu{3.72 g}$ to lbs gives me $\pu{3.72 g} \cdot \frac{\pu{1  lb}}{\pu{453.59 g}} = \pu{0.01 lbs}$. So assuming I did everything correct, one meter of wire is a hundredth of a pound, so in one pound of wire there is $100$ meters.


texts: What will be the coordination number in Fe(0)?

texts:
Fe(0) has its electronic configuration $\ce{3d^6 4s^2}$ in the ground state. In this case multiplicity will be either 1 or 3 during excitation. If multiplicity is 1, the vacant excited orbitals are $\ce{dsp^3}$. So, in this case it should be trigonal bipyramidal structure with the attachment of 5 ligands.

But in the case of multiplicity 3, the vacant excited orbitals will be $\ce{sp^3}$, excluding 2 singly occupied $\ce{3d}$ orbitals. If 4 ligands are there in attachment, what will be the structure -- tetrahedral or square planner?

Another additional information is also needed, is there any possibility to increase the number of ligand in this structure where multiplicity is 3? If yes, can you explain please?


texts: Balancing redox equation with oxygen on both sides?

texts:
The problem is to balance this equation in an acidic medium.

$$\ce{As2O3 (s) + NO3- (aq) -> H3AsO4 (aq) + N2O3 (aq) }$$

However, I am getting stuck balancing the oxygens after dividing them into half reactions.

How do you balance a redox reaction when oxygen is involved in both sides of the equation?


texts: Implication of negative order on kinetics

texts:
In the reaction

$$\ce{2 O3 -> 3 O2}$$

the order of reaction that I have been taught is

$$\ce{O_3 \underset{$k_{-1}$}{\overset{$k_{1}$}{<=>}} O_2 + O}$$
$$\ce{O_3 + O \overset{$k_{2}$}{->} 2O_2}$$

$$\mathrm{rate} = k_{2}[\ce{O3}][\ce{O}]$$

$$ k_{1}[\ce{O3}]= k_{-1}[\ce{O2}][\ce{O}]$$

So $$\mathrm{rate} = \frac{k_{1}k_{2}}{k_{-1}} [\ce{O3}]^2[\ce{O2}]^{-1}$$

What does this $[\ce{O2}]^{-1}$ part mean? For example, initially when there is no $\ce{O2}$, the rate should be $\infty$; how is that possible? Or is it normal and I should accept it?


texts: How does adding HCl convert AgCl into a sol?

texts:
According to the text I follow, in peptization, the ions of the added electrolyte (peptizing agent) get adsorbed by the particles of the precipitate and turn the precipitate into a sol. An example of this is, silver chloride can be converted into a sol by adding hydrochloric acid (chloride being the common ion)

What is the mechanism behind this?
And why does having a common ion matter?


texts: Why do we do electrolysis and electroplating using warm electrolyte?

texts: This is a pretty basic question, and I know it has something to do with conductivity, but I'm not quite sure how they are related.


texts: Limiting molar conductivity of multiple solutes

texts:
Suppose there is a water solution at $\pu{25 °C}$ with $\ce{Na+},$ $\ce{Mg^2+}$ cations and $\ce{Cl-},$ $\ce{HCO3-}$ anions. Concentrations $[\ce{Na+}],$ $[\ce{Mg^2+}],$ $[\ce{Cl^-}]$ and $[\ce{HCO3-}]$ are known.

I cannot understand how to apply the Kohlrausch's law of the independent migration of ions here:

$$\Lambda_\mathrm{m}^0 = \nu_+\lambda_+ + \nu_-\lambda_-$$

How this formula will transform for the solution with many kinds of ions?

Edit:

Electroneutrality condition holds, so:
$$[\ce{Na+}]+2 \cdot [\ce{Mg^2+}]=[\ce{Cl^-}]+[\ce{HCO3-}]$$
I've found the table with the limiting ionic conductivities $\lambda$ of each individual ion in water at $\pu{25 °C}$:

$\lambda_{\ce{Na+}} = \pu{50 \cdot 10^{-4} S m2 mol-1}$

$\lambda_{\ce{Mg^2+}} = \pu{106 \cdot 10^{-4} S m2 mol-1}$

$\lambda_{\ce{Cl-}} = \pu{76 \cdot 10^{-4} S m2 mol-1}$

$\lambda_{\ce{HCO3-}} = \pu{45 \cdot 10^{-4} S m2 mol-1}$

But I don't know what values for $\nu$ I should take.


texts: Why are tertiary carbocations the most reactive, if they're already stable?

texts:
This may seem silly, but doesn't it seem weird for a compound that's stable (in this context, the tertiary carbocation) to be the most reactive?

I mean, wouldn't it be the least, given that it's already stable and wouldn't want to leave that stable configuration. On the same lines, the methyl carbocation sounds like the most reactive due to its high instability, right? wouldn't it want to react in order to form a stable compound?


texts: What temperature is really required to make fused quartz?

texts: Glass transition temperature of fused quartz is 1200 °C. Does this mean it can be made by heating sand to 1200 °C, or does the melting point of $\ce{SiO2}$ has to be reached (~1700 °C) for that to happen?


texts:
Hi Chemistry enthusiasts!

I am working on my scholarship exam practice but I am considered myself as a newbie so I would like to hear your opinion :)

  From (1)-(4) below choose the metal that does not deposit silver (Ag)
  on the surface when immersed in aqueous silver nitrate. (1) Cu (2) Fe
  (3) Pt (4) Zn

The answer is Pt but I am not sure how I can solve this problem without any other given information such as electrode potential etc. Please advise.


texts: How to calculate the partial pressure of oxygen in this mixture of oxygen and argon?

texts:
A $\pu{19.3 g}$ mixture of oxygen and argon is found to occupy a volume of $\pu{16.2 L}$ when measured at $\pu{675.9 mmHg}$ and $\pu{43.4 ^\circ{}C}$. What is the partial pressure of oxygen in this mixture?

The answer is $\pu{436 mmHg}$, but I didn't manage to get to it.

I know that it is found by the formula
$$P_i=X_i\cdot P_\text{total},$$
where $P_i$ is the partial pressure and $X_i$ is the mole fraction.

$P_\text{total}$ is given to find $X_i$. I should divide the amount of $\ce{O2}$ by the total amount of substances of the mixture $n_{\ce{O2}}/n_\text{total}$.

$n_\text{total}$ is easy to find with $n=PV/RT$,
but my problem is, that I can't find the amount of substance of $\ce{O2}$. The mass in the problem is given for the mixture, so how to extract only the mass of $\ce{O2}$, or in other words, how to get the amount of substance for $\ce{O2}$?


texts: Predicting Extent of Exothermic Reactions

texts:
Sodium Acetate is widely used in hot packs due to the fact that it produces an exothermic reaction when it reacts with water.

I decided to see if other sodium salts, such as sodium bromide, sodium sulphate, etc. would produce similar exothermic reactions in hopes of finding a potential substitute for sodium acetate.

Is there a reason why some of these sodium salts would react with water to produce a larger enthalpy change than others? Is this predictable given the molecules' properties and/or geometry? Can enthalpy change at all be predicted given every property we currently know about these molecules?


texts: Is there a systematic way to determine the expected cubic structure of metals?

texts:
I've noticed that some groups of metals with similar properties tend to belong to the same cubic structure group, such as $\text{FCC, BCC, or HCP}$. What is a good explanation as to why these metals have similar cubic structures, and how can one determine a metal's expected cubic structure just from knowing its identity (if there is a way)?

For example, copper, silver, and gold all have face centered cubic structures.

This trend seems to break down at some point, I think, because $\frac{2}{3}^{rd}$ of the platinum group have $\text{FCC}$ structures and $\ce{Ru}$ and $\ce{Os}$ have simple cubic structures.


texts: When I use hot stuff like hair straightener on my hair, my hair begins to smell bad, which is very different from smell produced from burning other things. So what's the gas produced that is responsible for this smell?


texts: How to calculate the number of atoms of each element in a urea?

texts:
I have a stoichiometry question which I answered incorrectly and I am not sure where I went wrong. The question is as follows:

  Urea, $\ce{(NH2)2CO}$, is used for fertilizer and many other things. Calculate the number of $\ce{N}$, $\ce{C}$, $\ce{O}$, and $\ce{H}$ atoms in $1.68 \times 10^4~\mathrm{g}$ of urea.

First, I found the total atomic weights of each element in this compound to find the percent composition:

N: 28.02 amu
H: 4.032 amu
C: 12.01 amu
O: 16 amu
Total atomic weight of urea: 60.062

Then, I found the percent composition of urea:

N: 46.65%
H: 6.71%
C: 20.00%
O: 26.64%

Then, I converted $1.68 \times 10^4~\mathrm{g}$ into moles by dividing this amount in grams by 60.062, and found that it is approximately 279.71 moles.

After that, I took percentages of this to calculate the number of moles of each element in the sample of urea (for example, 46.65% of 279.71 to find the number of moles of nitrogen).

Finally, I multiplied each of these numbers in moles by Avogadro's number ($6.022\times10^{23}$) to obtain the number of atoms. However, when I checked my answers in my textbook, I was wrong by a significant amount.

\begin{array}{lrr}
       & \text{My answer}    & \text{Correct answer}\\\hline
\ce{N}:& 7.83 \times 10^{25} & 3.37 \times 10^{37}\\
\ce{H}:& 1.13 \times 10^{25} & 6.74 \times 10^{26}\\
\ce{C}:& 3.37 \times 10^{25} & 1.69 \times 10^{26}\\
\ce{O}:& 4.49 \times 10^{25} & 6.74 \times 10^{26}\\\hline
\end{array}

Do you know where I am going wrong?


texts: What is the purpose of the substructure section of a mol2 file?

texts:
I'm looking at the tripos mol2 format. (This is the most recent mirror of the specification document that I have found so far: http://chemyang.ccnu.edu.cn/ccb/server/AIMMS/mol2.pdf). What is the purpose of the SUBSTRUCTURE section? I notice that obabel does not include it.

It appears to specify connectivity, but that seems a duplicate of the BOND section.


texts: Why is slush hydrogen at the triple point?

texts: Slush hydrogen is a mixture of liquid and solid hydrogen at the triple point considered as a possible vehicle fuel. What is the need of having it at the triple point? Couldn't any other set of thermodynamic conditions consistent with liquid–solid equilibrium work as well?


texts: Does a benzene ring continue to oscillate at absolute zero?

texts: The carbon bonds in a benzene molecule oscillate between single and double bonds. As they do so, the distances between the carbon atoms changes (as the attached animated GIF illustrates). At absolute zero all molecular motion ceases; that is, the molecules stop bouncing into each other, but does that mean that molecules like benzene also cease their internal molecular motion?


texts:
This is but-2-yne, which is also known as crotonylene.

This is but-2-enal which is also known as crotonaldehyde.

Coming to my query, what does the word croton indicate? Does it refer to $\ce{CH3-CH=CH-R}$? Can this prefix be used anywhere or only for pre-specified compounds? If it can be used anywhere, then can but-2-en-1-ol be called as crotonalcohol or hydroxycroton?


texts: Decomposing chemical compounds - Ease of Decomposition

texts:
Someone asked me a question, that which of the following can be decomposed chemically:

Ammonia
Iron
Neon
Hydrogen
Fluorine

My Analysis:

At first attempt I answered Ammonia but changed it to 'I can't answer'. My analysis of the question is as follows

If Fluorine (the name implies fluorine gas) is decomposed, but it will require to 242kJ/mol (bond dissociation enthalpy). So, its quite difficult that we will be able to decompose it chemically.
If Hydrogen (the name implies Hydrogen gas) is decomposed, but it will require to 435.88kJ/mol (bond dissociation enthalpy). So, its even more difficult that we will be able to decompose it chemically.
If If Ammonia (the name implies Ammonia gas) is decomposed, but it will require to 389kJ/mol (bond dissociation enthalpy). So, its significantly difficult that we will be able to decompose it chemically.
Its useless to say that we will be decomposing Iron or Neon, because they are already in elemental state.

Why I tempted to answer Ammonia: I thought about Haber's Process, and remembered that the enthalpy change of the main reaction is negative (N2+3H2=NH3), about -46.1kJ/mol; this implies that the enthalpy of the just opposite reaction is positive (Enthalpy change of NH3=N2+3H2). This made me to conclude that the reaction is not feasible, thermodynamically and therefore ammonia cannot be decomposed easily. Therefore I changed my answer to 'I can't Answer'

My Question:
I asked my friend my what is the answer, he said Ammonia. I was surprised but still confused. I have written all of my thoughts above, but neither I am able to justify my answer, nor is my friend able to understand my logic. I want your discussion and a final review of the question understanding
'


texts: What are the CIP rules for cyclic substituents?

texts:
Here's what I read on Wikipedia (section "Cycles"):

  To handle a molecule containing one or more cycles, one must first expand it into a tree (called a hierarchical digraph by the authors) by traversing bonds in all possible paths starting at the stereocenter. When the traversal encounters an atom through which the current path has already passed, a ghost atom is generated in order to keep the tree finite. A single atom of the original molecule may appear in many places (some as ghosts, some not) in the tree.

I don't understand how to assign CIP priorities to cyclic systems, for example, consider this:

How do we decide the CIP priorities? What does that paragraph I found on Wikipedia really mean? Could someone please give a detailed explanation?


texts:
In another question it was noted that acetone is a useful solvent for removing pencil marks from wood surfaces.

(Source: https://woodworking.stackexchange.com/a/1870/763)

I'm used to acetone being used as a solvent for things like spray foam, nail polish, etc. but was surprised it could 'dissolve' pencil lead. I take it pencil lead is a mixture of graphite & clay substances. What enables the acetone to remove pencil marks?

Perhaps another way to think about this is, why does pencil lead adhere to surfaces like wood or paper in the first place? This is discussed in How are pencil marks "adhered" to the paper? but without mention of using solvents to remove it. How does the acetone reverse or interfere with the adhesion?


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Which of the following possesses the highest energy electron?

  $\ce{Br-}$
  $\ce{Ca^2+}$
  $\ce{Cr+}$
  $\ce{As}$

Don't bromine and arsenic have equally high energy electrons (i.e. in the $\ce{4p}$ subshell)? My book says that arsenic is the correct answer. But I don't see why $\ce{Br^{–}}$ is wrong.


texts:
Hi
my friend gave me a mysterious 10 dollars and on the back of it there's a secret code hidden but theres something weird on it covering it what i don't know how to erase it. This is the picture i feel like its thicker than an actual dollar this is all i know.
Could anyone help me solve the problem ? How and with what can i erase it?


texts: Understanding FHF- molecular orbital diagram?

texts:
I need help understanding the molecule FHF-'s molecular orbital diagram:
So I know that "ag" refers to the 2pz and 2s orbitals of fluorine atoms...but I am not sure why "ag" is labeled for the topmost orbital level? I don't really know what that is...but it's interacting with both hydrogen's 1s orbital and fluorine's 2p orbital, so does it imply that it's either antibonding or bonding orbital? And the one right below the topmost orbital--would that be the antibonding sigma 2pz orbital?

Thanks, I'd appreciate the help!


texts: Building an incomplete redox half reaction/reduction

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I can't seem to figure out this redox reaction.

$$
\ce{CH3COO- + CO2 -> CH3CH2COO-}
$$

Is the charge on the carbon in the $\ce{CO2}$ supposed to match the charge on the carbon in the $\ce{CH3COO-}$? I am supposed to build a half reaction using $\ce{H2O}$ and $\ce{H+}$ as needed, but I can't seem to figure out how many electrons are actually transferred. What are the charges on the carbon?


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How can the definition of the pH value $\mathrm{pH}=-\log\left[\ce{H+}\right]$ yield a unitless result? Since $\left[\ce{H+}\right]$ is a concentration, wouldn't it have units $\mathrm{mol/dm^3}$ and therefore following the product rule you would get: $-\log\left(x\ \mathrm{mol/dm^3}\right)=-\log\left(x\right)-\log\left(\mathrm{mol/dm^3}\right)$.

How can these units in a mathematical sense suddenly disappear?


texts: What could be a high school experiment that involves changing a condition to get the highest yield of a certain product?

texts: I am looking for ideas for a chemistry experiment and I am interested in doing one that has to do with the optimization of percentage yields. What could be a high school experiment that involves changing a certain condition to get the highest yield of a certain product?


texts: Acid catalysed dehydration of unsymmetric alcohols

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How to find the major product of acid catalysed dehydration of unsymmetric alcohols. For example, in the dehydration of butan-2-ol using conc. H2SO4, which is the major product? But-1-ene or But-2-ene?
And, in the dehydration of 1-methylcyclohexanol, the major product is 1-methylcyclohexene and not methylenecyclohexane. But how did we work it out??


texts: Why is water ignored in the ionic equilibrium of HF?

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While trying to understand the solution of a problem given in my textbook, I realized I'm having some difficulty with the solution. The problem is as follows:

  The ionization constant of $\ce{HF}$ is $3.2 \times 10^{-4}$. Calculate the degree of dissociation of $\ce{HF}$ in its $\pu{0.02 M}$ solution. Calculate the concentration of all species present $\ce{H3O+}$, $\ce{F-}$ and $\ce{HF}$ in the solution and its PF.

In the solution of this problem, the equation is given as
$$\ce{HF + H2O <=> H3O+ + F-}$$

The concentration at the time of equilibrium are given as:

\begin{align}
\ce{[HF]}   &= 0.02 - 0.02x, &
\ce{[H3O+]} &= 0.02x, &
\ce{[F- ]}  &= 0.02x
\end{align}

I have the following questions:

Why are we not adding the contribution of water to the $\ce{H3O+}$ ions?
Why are we assuming that the value $0.02x$ is dissociated from $\ce{HF}$ and not just $x$?


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The kinetic energy of an electron is $1.67 \times 10^{-17}\mathrm{J}$. Calculate the wavelength ($\lambda$) of the electron.

I know the formula $\lambda= \frac{h}{mv}$; where h is Planck's constant.

How do I find $\lambda$ without $v$ (velocity) and $m$ (mass)?


texts: Rationale behind Barton's rules for catalytic hydrogenation

texts:
Organic Chemistry by Morrison and Boyd,Seventh Edition says -

  When cyclohexanones are used as substrates, the stereoselectivity of the reduction is found to be dependent on the acidity or the basicity of the medium. The observations about this stereoselectivity are summed up in the form of a few empirical rules, called Barton's rules, which are as follows:

  (i) For unhindered cyclohexanones, in the catalytic reduction with Adam's catalyst($\ce{PtO2}$) in acidic medium, the less stable axial alcohol predominates in the product

  (ii)In a basic or a neutral medium , however, the same catalyst gives the thermodynamic product called the equatorial alcohol as the major product

  (iii) But for hindered cyclohexanones, the less stable axial alcohol is formed in all $\ce{pH}$

As far as I know, catalytic hydrogenation is a syn addition which is performed by delivering the hydrogen from the same side when the substrate is adsorbed on the surface of the catalyst. From what I know about the theory of heterogenous catalysis, it is the nature of catalyst which governs all aspects of the product formed here.So I feel that the medium's nature shouldn't have much effect here.

My question is: What is the basis/rationale for these "Barton's rules"?

The latest downvote has called my attention to this question,I guess maybe I wasn't specific enough when I had asked this question. What I wanted to know is the relation between variation of pH and the subsequent change in the stereochemistry of the product.

My ideas on the subject On giving it some more thought, I guess the acidic medium may generate a protonated ketone, which would be more electrophilic than the regular ketone. So maybe,the reaction happens quickly and therefore,the kinetically controlled product i.e. the axial alcohol is obtained. In the basic medium, the basic cleavage has to happen in a somewhat more controlled fashion on the cyclohexanone, and hence the thermodynamic product is obtained. However,this is purely my conjecture.


texts: How to determine source of air pollution

texts:
It should be determined by some metal markers (meaning originating from traffic etc.) but I cannot find any source which would describe it.
Thanks.