texts: What is the relationship between the constant of equilibrium (Kc) and the position of equilibrium?

texts:
I understand that the constant of equilibrium is a ratio of the concentration of the products to the reactants and that this value allows one to estimate whether the position of equilibrium lies to the right (in which there will be more product at equilibrium) or lies to the left (where there will be more reactant at equilibrium). I'm also aware that Kc is affected only by a change in temperature and not a change in concentration, pressure etc.

I know the position of equilibrium is affected by changes in concentration, pressure and temperature (unlike Kc which is only affected by change in temperature). I understand Le Chatelier's Principle and how the position of equilibrium shifts in order to minimise the change, and that this maintains the equilibrium constant.

My problem arises when trying to relate the two. The position of equilibrium shifts so that the equilibrium constant will be maintained however I don't understand how this works or why!
When we say that the position of equilibriums shifts (to the right for example), what does this actually mean? I know that the amount of product will increase but what is actually happening. Is the rate of the forwards reaction increasing? In other words, what actually is the position of equilibrium? If Kc is the ratio of product concentration to reactant concentration then what actually is the position of equilibrium?

Thank you in advance!


texts:
Τhe electrons in the antibonding MO are the unpaired electrons of the molecule? E.g. $\ce{O2}$, by writing down the diagram for the MO we notice that there are only 2 electrons in the top antibonding orbitals thus 2 unpaired electrons, yet by writing down the Lewis structure, the molecule turns out to have 0 unpaired electrons..
So, what do the electrons in the anti bonding orbitals do if they don't represent the unpaired electrons of the molecule?


texts:
I am new to chemistry (I have only done a GCSE in it) so forgive me if I am missing something obvious. But I am trying to very roughly simulate some chemical reactions. My background is in Artificial Life and Adaptive Systems rather than computational chemistry or chemistry in general. My stumbling block is that I am unsure exactly why bonds break and when they break.

Here are the things I am confused about:

Is the breaking of bonds by using energy a prerequisite for new bonds to be made with the involved atoms? If so, is this because the more energy there is, the more the atoms will move/vibrate, eventually pulling the bond apart? Otherwise, can bonds be broken by a new bond sort of pulling it apart in some way?

Is the strength/length of the bond what determines the amount of energy needed to break it? I'm also unsure of what the strength or length of a bond is based on. Am I correct in thinking that bond order is about the number of shared electrons in a covalent bond? But what about ionic bonds? Is it the amount of electrons "taken" by the more electronegative atom?

I know that there are multiple questions here. But they all answer the bigger question. Why and when do bonds break exactly? I have had a hard time trying to figure this out by searching on the internet alone. Often I just get pages explaining the energy requirements of a reaction. Thanks in advance, any help would be appreciated.


texts: Why is dp/dv zero for a real gas in critical conditions?

texts: I have read this fact in various websites but cannot understand the reason. What is an intuitive explanation of this?


texts: Does liquid ammonia react with hydrogen gas?

texts:
This may seem like a basic question to educated chemists, but I failed to get this answer on Internet searches.  I keep getting more complicated stuff like the Haber process which is not relevant.

At this website it describes how the absorption cooling process works in a propane powered refrigerator.  The system uses ammonia, water, and hydrogen in closed loop system.  In the evaporator section, it says liquid ammonia reacts with hydrogen gas thus vaporizing it and this process of ammonia boiling in hydrogen absorbs heat from the fridge box. It doesn't mention what the end products of the ammonia and hydrogen reaction are.

Is there a chemical reaction between hydrogen and ammonia here?  Or is there no actual chemical reaction, just partial pressure vaporization of ammonia liquid in hydrogen gas?


texts: What happens if at equilibrium pressure is increased by decreasing the volume?

texts:
I think, according to Le Châtelier's principle both the conditions i.e. increasing the pressure and decreasing the volume must shift reaction towards the side on which there are less amounts of gaseous molecules. And if there are the same stoichiometric coefficients for the gaseous substances (i.e. $∆n_g = 0$) then it must not have any effect on the reaction.
But increasing the pressure and decreasing the volume increases the number of collisions between the molecules of reacting substances and hence the concentration of products must increase.

Both these thoughts confuse me.

Questions I encountered:
$$ \ce{H2O(g) + CO(g) <=> H2(g) + CO2(g) + Heat }$$
In this question $∆n_g = 0$ so there must be no effect of increasing pressure and decreasing the volume. But the answer mentions that the concentration of both $\ce{CO}$ and $\ce{CO2}$ will increase.

There was also another question of same type:
$$ \ce{SO2Cl2(g) <=> SO2(g) + Cl2(g) }$$
Here the reaction must shift backward as pressure is increased and volume is decreased.
But again the answer mentions that concentration of all the gasses increases.


texts: Final pressure of an ideal gas mixture, when two separate gases are put into one vessel

texts:
At constant of 200 cm³ of $\ce{N2}$ at 720 mmHg and 400 cm³ of $\ce{O2}$ at 750 mmHg are put together into one litre flask. The final pressure of the mixture is:

My question is how to use ideal gas law for mixture of two gases. For one gas, it is easy but for two it becomes difficult for me. I am assuming that these gases won't react or else it would have been given in the question. Can somebody tell me how to apply ideal gas law for two gases and what happens when they are kept together?


texts: Coloration of substances because of F-Centers

texts:
In case of metal deficient defects in the crystal lattice of a metal, the positive voids are filled by electrons.

How does this result in the coloration of a substance?
Does this condition arise only in the case of metals?


texts: Identifying T1 and T2 in the Claperyon equation

texts:
Is there a way to identify T1 and T2 in the two point form of the claperyon equation?

I suspect that the greater temperature is T1 and the smaller temperature is T2.


texts: How will water move across a membrane that is permeable to only one solute?

texts: If there are two solutions separated by a membrane, which is permeable only to one solute and the solvent, will there be any net movement? Let's assume the two solutes are glucose and sodium ions, with the same molarity, and only the glucose and water can pass through the membrane.


texts: Differentiating random and ordered sequential mechanisms in enzyme kinetics

texts: Can random and ordered sequential mechanisms be descern by Lineweaver-Burk plot? Why or why not? Because for orederd sequential mechanism I got different LB plot depending on which substrate is held constant (when A, which binds first to the enzyme, is held constant lines for different concentrations of A in Lineweaver-Burk plot have same intercept 1/Vmax). And how are they differed based on product inhibition studies?


texts: Are there any tests which distinguish between triglycerides and polar lipids/impurities that can be conducted in a high school setting?

texts:
I am currently writing a research essay about using a mixed polar (methanol) and non-polar (heptane) solvent system to extract oil from mango seed kernels. One of the difficulties of using polar solvents is the fact that it also extracts polar lipids which can't undergo the transesterification process to produce biodiesel.
I need to find a method which can distinguish between non-polar lipids and polar lipid/impurities in the extracted substance. I've had a look online and read about the Sudan III test, but I'm not clear on whether it works only on non-polar lipids or just all fats in general.


texts: Butane blowtorch condensing liquid on heating surface

texts:
I have a small Butane blowtorch, and use it to heat an Aluminium plate. The plate is thick so takes 20 seconds or so to really start heating up.

As soon as I apply the heat, droplets of some liquid start "condensing" on the surface of the metal around the general area of the flame.

The liquid is colorless and odorless and is at room temperature, note this happens when the metal is still at room temperature as it hasn't heated up much yet.

What is this liquid exactly and why/how does it form? I suspect it could be a $C_{4}H_{10} + O_{2}$ reactant but not sure.  Thanks!


texts: What is the inter-particle bonding in elemental mercury?

texts: In most pure metals, there is metallic bonding where there exist positive monoatomic ions and a sea of electrons. Is this the same with mercury? If not, then in elemental (liquid) mercury, what kind of ions are present (polyatomic?)? Thanks.


texts: NMR spectrum of plasma treated glucopyranoside

texts:
This is a 1H NMR spectrum of plasma treated methyl alpha D-glucopyranoside.

Now I'm having problems trying to read the spectra and interpreting if there are any changes to it. What I suspected would happen during plasma treatment is that the methoxy group would break off, leaving it or replacing it with any other possible ROS or RNS. I don't know how to identify the methoxy groups present or to read those peaks to see if there are other possible structural changes.


texts: Greek letters in front of inorganic/mineral formulas

texts: What do Greek letters in front of the formulas for minerals/inorganic compounds mean, such as $\gamma\textit{-}\ce{Al2O3}$ or $\alpha\textit{-}\ce{Fe2O3}$?


texts: What is the difference between cyanato, cyanido and cyano? When should i use which?

texts: I understand that cyanido is the newly adopted naming in place of cyano but what is cyanato? Can anyone please give examples to illustrate the difference?


texts:
According to the first step,nbs performs allylic bromination,replacing one H from -Ch3 group. Now,as iodine is strongly bonded to the ring due to resonance,CH3SNa replaces Br and forms NaBr as an additional product
My final answer comes out to be A,but the given answer is None of the above. What will then be the final product?


texts: Why are ionic compounds bad conductors of electricity in solid state?

texts: I understand the fact that ionic compounds are good conductors of electricity in molten state. But why aren't they good conductors in solid state. Cannot ions vibrate about their mean position and transfer electricity in the same way as they transfer heat?


texts: Why some cloths become rough after drying?

texts: I line dry my cloths and every now, they become rough after drying. This mostly happens with socks. They are regular cotton socks and once I start to wear them they become soft again. Any idea why this is happening?


texts: Run a command at every step of a relaxed scan

texts: In Gaussian, I'm trying to do a relaxed scan and for each step obtain the volume. However, when I use the volume keyword, it seems to only output the volume for the initial and final steps. Is there a way to ensure a keyword runs for every step of a scan? A similar question (How to obtain the Raman spectrum along every coordinate of a scan in Gaussian?) was asked earlier this year, but I want to confirm whether Gaussian doesn't allow any other keywords to run during a scan.


texts: I want a certain Ion in my solution. How do I choose which chemical to buy?

texts: thanks for taking the time. I am physicist doing experiments in which I need certain Ions (at the moment, Ru(II)) in solution. I have no chemical training excepting what I'm learning right now. What I need is a research strategy on how to find which salts or compounds containing Ru(II) will dissolve in water in such a way, that the Ru ions are available to the biological system that I'm studying. Do you have any resources that you could point my way or any good starting points? Thank you again


texts: Equivalent points for 3 fold and 6 fold symmetry

texts: In a crystal Lattice how to find the equivalent points for 3 fold and 6 fold symmetry?


texts: Determining the amount of water to create a given pressure in a sealed container

texts:
I have a sealed container with a volume of 1 liter. I want to go from an initial pressure of $P_{1}=1\ \mathrm{atm}$ and an initial temperature of $T_{1}=298\ \mathrm{K}$ to a final pressure of $P_{2}=9.95\ \mathrm{atm}$ and a final temperature of $T_{2}=453\ \mathrm{K}$..

I want to use water to create the pressure. But I do not know how to determine the amount of water. How would I do that?


texts: Is there a gauche interaction between C-3 and C-6 in cyclohexane?

texts: To my understanding, a gauche interaction occurs between two R groups when staggered by 60 degrees in a Newman Projection. When looking down the C-1 to C-2 bond of a cyclohexane, the Newman Projection shows that C-3 and C-6 are staggered by 60 degrees. Would this still be a gauche interaction, and if so, why does it not result in an energy increase in the chair conformation? I was told this is because cyclohexane in the chair conformation acts as a long chain carbon, but I did not understand how that results in no energy increase.


texts:
Sharp air cleaners has a technology called PlasmaCluster. They say that it produces negative ions $\ce{O-}$ and positive ions $\ce{H+}$ (the difference with classical ionization is that ionization produces only $\ce{O-}$, PlasmaCluster also produces $\ce{H+}$)

The air contains oxygen molecules so oxygen can be ionized. But the question is how H+ is created ? I know that the air is $5.5 \times 10 ^{-5}\%$ Hydrogen gas. Is this small quantity of hydrogen in the air ionized, or is water in the air is split via electrolysis, creating the $\ce{H+}$ ions?


texts: Rates of hydrolysis in bicyclic and monocyclic compounds

texts:
Which of the following compounds, 1-bromo-1-methylcyclohexane 1 or 1-bromobicyclo[2.2.2]octane 2, hydrolyzes faster (under comparable conditions)? It may be acid catalyzed or base catalyzed hydrolysis, but the conditions must remain the same for each pair.

In my view because of the steric hindrance in first compound, hydrolysis should be easier for second, but I am not sure about it.
See part one of my question here.


texts: Why other benzene derivatives do not undergo nitrosation

texts:
Solomon and Fryhle $11 th$ ed :

Most other benzene derivatives except phenols and tertiary aromatic amines do not undergo C- nitrosation reaction.

I agree that if there is a primary or secondary aromatic amine, the reaction will follow other routes but in case of other activating substituents EAS is the only route left for the electrophile $\ce{-^+N=O}$ for example with anisole.

Also it seems to contradict  ron's answer

So which one is correct?


texts: Why might the ratio between two Q-band peaks in ZnTPP decrease with increasing temperature?

texts:
In ZnTPP (Zinc tetraphenylporphyrin), there are two Q-band emission peaks. When I run steady state emission measurements at different temperatures, the ratio of their respective peak intensities decreases with increasing temperature. This seems to me like an unusual behaviour compared to many other porphyrins, where the ratio remains constant.

Why is this?

The molecule has been around for a while so I would expect to find the answer in the literature, I am currently searching it and might post the answer if I find it before someone else answers.


texts:
I have the following question:

  A $100\ \mathrm{ml}$ sealed flask with $60\ \mathrm{ml}$ acetonitrile is heated to $140\ \mathrm{^\circ C}$. The boiling point of acetonitrile is $82\ \mathrm{^\circ C}$. What will be the pressure in the flask?

1) I understand I can use the Antoine equation, $\log{p} = A-B/(C+T)$, to calculate the vapor pressure of acetonitrile, but that equation only applies if there is some liquid acetonitrile left in the flask. How do I know if this is the case, or instead all acetonitrile has boiled and is in the vapor phase?

2) The total pressure is the sum of the partial pressures of acetonitrile and air. I can calculate the air pressure inside the flask with the ideal gas law, PV=nRT. However, I'm not sure what is the volume? Is it the total volume minus the acetonitrile volume ($100\ \mathrm{ml}-60\ \mathrm{ml}=40\ \mathrm{ml}$), or is it $40\ \mathrm{ml}+x$, where $x$ is the additional volume due to the conversion of liquid acetonitrile into vapor?

Any ideas are welcome.


texts: Producing ketones from secondary alcohols using hydrogen peroxide

texts:
Usually, to produce ketones from secondary alcohols (e.g. propanone from 2-propanol), people use a solution of potassium or sodium dichromate with a small amount of sulfuric acid. Can other oxidizers like hydrogen peroxide be used, and will the use of hydrogen peroxide produce organic peroxides?

$$\ce{C3H8O + H2O2 -> C3H6O + 2 H2O}$$

This is not for any particular purpose.


texts: Does the property of additivity for the amounts of different substances hold up for ideal gas law?

texts:
A mixture contains $\pu{8.00 g}$ each of $\ce{O2},$ $\ce{CO2},$ and $\ce{SO2}$ at STP.  Calculate the volume of this mixture.  Which of the gases would exert the greatest pressure and why?

Here is my work:

$$
\begin{align}
n(\ce{O2}) &= \frac{\pu{8.00 g}}{\pu{32.00 g mol-1}} = \pu{0.250 mol}\\
n(\ce{CO2}) &= \frac{\pu{8.00 g}}{\pu{44.01 g mol-1}} = \pu{0.182 mol}\\
n(\ce{SO2}) &= \frac{\pu{8.00 g}}{\pu{64.07 g mol-1}} = \pu{0.125 mol}
\end{align}
$$

$$n_\mathrm{tot} = \pu{0.250 mol} + \pu{0.182 mol} + \pu{0.125 mol} = \pu{0.557 mol}$$

$$pV = nRT \quad\implies\quad V = \frac{nRT}{p}$$

$$V = \frac{\pu{0.557 mol}\times\pu{0.0821 atm L mol^-1 K^-1}\times\pu{273 K}}{\pu{1.00 atm}} = \pu{12.5 L}$$

Considering $p = nRT/V,$ the gas that takes up the least amount of volume with the greatest amount of particles will exert the greatest pressure. This will be $\ce{O2}$ because it has the lowest molar mass/volume.

Is this how handling the amounts of substance work (can different substances be added like this)?


texts: Hyperconjugation - concept clarification

texts:
As I currently understand it, Hyperconjugation occurs in carbocations and alkenes via the interaction of the electrons in the MO of a C-H bond at an adjacent carbon to bring stability to the system.The interaction requires for in phase overlap and occurs when the C-H bond is in the same plane as the vacant p orbital. (or the pi bond in case of alkenes) It is thus not seen if the beta hydrogens are in the plane perpendicular to them.

If this is true, then how does hyperconjugation work, if at all in cyclic systems where free bond rotation is impossible and thus the orbitals will never align perfectly? What conceptual bridge am i missing here?


texts:
The solutions manual said that enamine B with its roughly sp2 methyl group can force the nitrogen out of the plane and this messes around with the conjugation.

How about the fact there is a significant degree of resonance donation by the nitrogen, which places a significant partial negative charge on carbon. In enamine A, this carbon is secondary. In enamine B, this carbon is tertiary. Extra inductive donation from the methyl group destabilizes the product.


texts: How to derive the Gibbs-Helmholtz equation?

texts: Can someone please explain to me how to derive the Gibbs-Helmholtz relationship from $G = H - TS$?


texts: If ions are floating around in a solution, how do we know they combine to form a compound in a solution?

texts:
I apologize if my question sounds confusing I am not sure how to properly convey it here's an example:

For the reaction between lead nitrate and ammonium phosphate you get the reaction:

$$\ce{3Pb(NO3)2 (aq) + 2(NH4)3PO4(aq) -> Pb3(PO4)2(s) + 6NH4NO3(aq)}$$

but the ionic equation is
$$\ce{3Pb2+(aq) + 6NO3-(aq) +6NH4+(aq) + 2PO4^3-(aq) -> Pb3(PO3)2(s) + 6NH4+(aq) + 6NO3-(aq)}$$

so how do we know the compound $\ce{6NH4NO3}$ is formed if its just $\ce{6NH4+}$ and $\ce{6NO3-}$? Do the ions combine and then immidiately disassociate again? I'm very highly confused I would appreciate an explanation, and i apologize if this makes no sense.


texts: SCF procedure performed for some quantum-chemical methods, but not others. Why?

texts:
The SCF procedure is used to find solutions to the Schrödinger equation, and obtain energy of the molecular system. It uses a "guess-and-check" approach, where an initial guess is needed to solve the equation, giving the charge density, which can be used again and again until the results become self-consistent.

So, why don't some quantum-chemical methods perform SCF, while others like HF do?


texts: How to calculate dew point of air-water system

texts:
I want to calculate the maximum water holding capacity of air at a given temperature (as in $\frac{max\ mass\  of\   water}{mass\  of\  dry\  air} $ vs temperature)
I looked up online and there are various models to do such calculations. However for most of them the temperature range is not more than 100 C. Are there any relations which cover a higher temperature range, upto 300-400 C?
If not, is not possible to determine saturation point above the boiling point of water?

Edit: I am considering a constant atmospheric pressure. Thus, I want to check variation only with temperature.


texts: What are appropriate techniques to ensure homogeneous solidification of an agar-based aqueous solution?

texts:
I am making a T1 weighted phantom for an MRI project. I'm trying to see if I can calculate how much a persons head heats up during an MRI scan. It consists of distilled boiling water, $\pu{7 g/L}$ agar, $\pu{10 g/L}$ $\ce{NaCl}$ and $\pu{1 g/L}$ $\ce{CuSO4}$. As the phantom cools it will get a jelly like texture. What I would like is for the phantom to be as homogeneous as reasonably possible when it solidifies. What do you think is the best way to do so?

I was thinking of having the mixture on a vibrating plate, or maybe a centrifuge or even just inverting the mixture at regular intervals. Any ideas would be greatly appreciated.


texts: Detail from Integral Evaluation in Szabo (Appendix)

texts:
This is a step from Appendix A in Szabo and Ostlund's Quantum Chemistry. In short, the question is how to get from \ref{A.20} to \ref{A.21}. We can factor out some constants $K$ in the expressions to get:

\begin{align}
  (A| -Z_C/r_{1C} |B)
  &=
    K \left(\frac{1}{2\pi^2}\right)
    \int \mathrm{d}\mathbf{k} \; e^{-k^2/4p} k^{-2}
    \exp\big(-i\,\mathbf{k}\cdot(\mathbf{R}_P - \mathbf{R}_C)\big)
    \tag{A.20}\label{A.20}\\
  &=
    K \left(\frac{2}{\pi|\mathbf{R}_P-\mathbf{R}_C|}\right)
    \int\limits_0^\infty \mathrm{d}k \; e^{-k^2/4p} k^{-1}
    \sin(k|\mathbf{R}_P-\mathbf{R}_C|)
    \tag{A.21}\label{A.21}
\end{align}

Part of the note between these steps is that (paraphrasing) we can let $\mathbf{R}_P-\mathbf{R}_C$ lie on the $z$-axis and use that $k\cdot (\mathbf{R}_P-\mathbf{R}_C)= k|\mathbf{R}_P-\mathbf{R}_C|\cos\theta$, "then we can easily perform the angular part of the integration over $\boldsymbol{k}$ to obtain [\ref{A.21}]."

What I have done: It seems that Euler's formula must be applied to the second exponent in \ref{A.20} but using the hint we'd have something like $$\cos(k|\mathbf{R}_P-\mathbf{R}_C|\cos\theta) + i\sin \dots \text{etc}. \tag{???}$$
 I guess that the sine in \ref{A.21} follows integration of the (real) cosine in Euler's expansion. In line with this, \ref{A.21} is multiplied by a factor of $2\pi$.

I will keep at this but I think if it puzzles me, then others may have stumbled over it so I am posting.
Hopefully removal of the common factors ($K$) makes this easier to read but the problem is on pages 413-414 of Szabo and Ostlunds book.


texts: Changing solubility of metal complex by adding ethanol

texts:
After creating a solution of copper(II)-sulfate-pentahydrate, water and concentrated ammonia, the newly formed complex (tetraamminecopper(II)-sulfate-monohydrate) is completely dissolved in water. By adding ethanol, one is able to decrease the solubility of that complex in water and have crystals percipitates out of solution.

Since the complex is not soluble in ethanol, I am having trouble understanding why adding ethanol changes anything about the solubility of the complex. Would adding some organic phase like petrol ether or a non-soluble solid such as ceramic pellets do the same?


texts: Are all PP(Polypropylene), i.e. resin code 5 plastics, safe for microwave and steaming?

texts: If a plastic is marked PP as in Polypropylene (i.e. resin code 5), is it automatically safe for steaming and microwaving, such that it wouldn't leach chemicals into the food(besides not melting)?


texts: Does mercury fulminate really look like crystal methamphetamine?

texts:
In the AMC series Breaking Bad , Walter (aka Heisenberg) smuggles in a bag of mercury fulminate under the guise of crystal methamphetamine and threatens to blow the room up if he doesn't get his money.

Does fulminated mercury really have the translucent white/blue crystal appearance as was shown in this scene?

Is the compound that sensitive that throwing it against the wall would cause detonation?


texts:
Considering the example where $0.3212\ \mathrm g$ of glucose (molar mass = 180) being burnt in bomb calorimeter of heat capacity $641\ \mathrm{J\ K^{-1}}$: the temperature rises by $7.793\ \mathrm K$. Is the heat (say '$E$') obtained taking $E=641 \times 7.793 \times 180/0.3212$ the internal energy or heat of combustion? Why? Answer explained in detail will be highly appreciated!

What is the fundamental difference when we completely burn fumaric acid in a bomb calorimeter? Why do we take the heat released as the internal energy? IS it because volume is constant?

Reference: Elements of Physical Chemistry (Paula, Atkins) Q.no:3.21 and 3.22


texts:
I want to formulate the condensation reaction mechanism for the formation of siloxane links.

I don't see how to express it as an addition-elimination reaction, because even though the silicone atom is positively polarized, it cannot form a fifth bond that would result from a nucleophilic attack by the other silanol. Is it a concerted reaction?

Any input is helpful, so no limit on conditions.

Any key publications?


texts:
I need a little help with one of the problems below. Any help on the problem below will be appreciated. I don't want to sound like an idiot, I will also provide my work.

  Solid $\ce{NaHCO3}$ decomposes to form water vapor, carbon dioxide and sodium carbonate.
  $$\ce{NaHCO3 -> H2O + CO2 + Na2CO3}$$
  If $2.00\ \mathrm g$ of $\ce{NaHCO3}$ decompose at $500\ \mathrm{^\circ C}$ and $700\ \mathrm{mmHg}$, how many liters of $\ce{CO2}$ should be produced?

$$\mathrm{\frac{750\ \mathrm{Torr}}{760\ \mathrm{Torr}}=0.99\ \mathrm{atm}}$$
$$pV=nRT$$

$$2.00\ \mathrm g\ \ce{NaHCO3} \cdot \frac{1\ \mathrm{mol}\ \ce{NaHCO3}}{84.02\ \mathrm g} \cdot \frac{1\ \mathrm{mol}\ \ce{CO2}}{2\ \mathrm{mol}\ \ce{NaHCO3}} \cdot \frac{22.4\ \mathrm L \ce{CO2}}{1\ \mathrm{mol}\ \ce{CO2}} = 0.287\ \mathrm L\ \ce{CO2}$$

$$0.99\ \mathrm{atm}\cdot0.287\ \mathrm L=n\cdot773\ \mathrm K\cdot0.0821\ \mathrm{L\ atm\ K^{-1}\ mol^{-1}}$$
$$n = 0.004159\ \mathrm{mol}\ \ce{CO2}$$

$$0.004159\ \mathrm{mol}\ \ce{CO2} \cdot\frac{22.4\ \mathrm L}{1\ \mathrm{mol}\ \ce{CO2}} = 0.09317\ \mathrm{L}\ \ce{CO2}$$


texts:
The basic strength is determined by the ability of an ion or molecule to accept a proton. How do I know whether RSH is more stable than ROH?
(R is an alkyl group)


texts: Why does the earth have more radon in some locations?

texts:
I am not a chemist so I'm not going to give specific amounts of radon; different countries use different units. My question: why do some areas have more radon? For instance, Australia has a spreadsheet of all locations and their radon levels. I've looked it up and where I used to live, nearby, has half the listed Radon levels of where I live now. Wikipedia was a bit general to me for American examples:

  Iowa has the highest average radon concentrations in the United States due to significant glaciation that ground the granitic rocks from the Canadian Shield and deposited it as soils making up the rich Iowa farmland.

So it is rock or soil types or weather or something else that causes the different amounts?


texts:
How do I calculate principal quantum numbers of the Lyman series?

I've been given that the lowest line is 121.6nm and the 5th line is 93.8nm

The formula of the wavenumber is   v=-R(1/n2^2 - 1/n1^2)

My taught was that as the wavenumber is known (1/wavelength) I could create an equation

v/-R = 1/(x+4)^2 - 1/x^2   and solve for x to get the principal quantum numbers

However this equation seems to be too hard to solve and I guess there is a different way to solve this.

Many thanks in advance


texts: Educational practice problems/systems/reactions in computational chemistry

texts:
I am not sure if this question is suitable for Chemistry SE, but I think fairly objective answers can be given, and not just I will benefit from them

I have almost completed the first year of a MSc program in theoretical (and computational) chemistry, and have gone from knowing absolutely nothing about computational chemistry, to having heard of some of the stuff I need to master. I just took the step of installing GAMESS on my personal computer, and I intend to start doing test calculations on my own.

While courses provide theoretical foundations, my experiences are that actual computations are quite limited. I took the initiative to engage in a student research project which started February this year, and during this time I have gained a lot of practical experience with calculations (exploring the PES, finding and optimizing transition state structures, calculating MEP's, looking at molecular orbitals). And to me this kind of experience is extremely valuable.

So I would like to practice with well-studied systems/reactions/whatever. In short, I want a diverse set of systems, some of which may require "manual labour" (e.g. CASSCF). With well-known systems I can find experimental and theoretical values to compare with, and likely also discussions about how certain methods perform for each system. These systems should be small enough so that they can be comfortably run on a Macbook Pro (2,9 GHz Intel Core i7, 8GB RAM, SSD) without taking too long.

So question basically is this: What is a good set of educational systems/reactions, suitable for an interested student in computational chemistry?


texts: Sound or light reversible super glue possible?

texts:
Sorry if this is a stupid question and help me to improve it.

Super glue is meant to be quick and mostly universal but we can stick to ceramics and/ or wood.

Imagine you put parts with the glue together.

Then later on a specific light or sound frequency would weaken the glue bonds.

Total nonsense, reality or research topic?


texts:
Why do molecular orbitals in solids merge to bands?

For example: In silicon every atom is sp3 hybridised, but when I merge two of these orbitals then it yields a bonding and an antibonding MO. When a third atom binds to one of the $\ce{Si}$ atoms in this configuration, then again we should get two MOs, separated by the same energy. This way we we don't get so called bands. How do the bands form?

I have tried wikipedia and other sites but they answer in brief.


texts: I just went though a reaction wherein hydrogen gas is liberated and hence restricts the product formed to ferrous and not ferric salt. I just want to know how H2 gas gets its reducing property? It has a moderate bond strength also if I am not wrong.


texts: Stability of carbocation on doubly bonded carbon

texts:
What can be said about the stability of the following carbocation?

I think that it would have something to do with hybridisation as, clearly one carbon is sp hybridised and the other is sp2.

Can anyone confirm this or elaborate on this?

Also what would happen if the Hydrogens are all replaced by a carbon chain?
And what if there's positive charge on both the given carbons?


texts: Typesetting oxidation state and charge simultaneously

texts:
I'm currently trying to typeset the ion $\ce{Cr2O7^{2-}}$ with oxidation numbers on. My first thought was to put the oxidation state above the atom, but according to IUPAC, the oxidation state should be in the right superscript. Combined with charge, it looks ugly and wrong:

My current ways of doing this are below

The oxidation number in right superscript. Looks weird with both numbers so close.
The oxidation number above. Looks better, but is against IUPAC.

My question therefore is: Which is the preffered way to typeset this?

Also, I would like to excuse beforehand if this should rather be in tex.stackexchange.


texts: Will bonding molecular orbital be formed?

texts:
Which of the following statements is not correct regarding bonding molecular orbitals?
  A Bonding molecular orbitals possess low energy than the atomic orbitals from which they are formed;
  B Bonding molecular orbitals have low electron density between the two nuclei;
  C Every electron in bonding molecular orbitals contributes to the attraction between the atoms;
  D They are formed when the lobes of the combining atomic orbitals have the same sign.

I am confused about option D, I think this should be right as same sign means lobes are in the same phase, so they should form BMO. But the answer key states that the statement is incorrect.

Can anybody please explain me this and is my reasoning correct?


texts: Why does a molecular sieve work for gas separation?

texts:
I was looking at membrane separation of air to nitrogen / oxygen and saw some details on the molecular sieve which on Wikipedia states you can get much higher purity from an adsorber / sieve, but when I look at these images, it doesn't make any sense.

Molecular Sieve material / Zeolite seems to be supplied in granules that are fairly large, why doesn't the compressed gas just go around all the material instead of going through it?

Without melting it / packing it into a solid column, it doesn't seem like it would be much more efficient than just glass beads since there are so many ways to get around each piece. Are you really supposed to just dump it in and have it work?

http://www.instructables.com/id/Nitrogen-gas-generator/


texts: Why is HCl not considered to have hydrogen bonding?

texts:
A molecule that has hydrogen bonding usually follows these two premises.

1.) There is a hydrogen atom involved
2.) Hydrogen must be bonded to a highly electronegative element which are nitrogen ($\ce{N}$), fluorine ($\ce{F}$) and oxygen ($\ce{O}$).

Seeing that both oxygen and chlorine have a small difference in their electronegativity (oxygen being roughly 3.5 and chlorine being roughly 3.0), why does chlorine in a hydrogen chloride molecule ($\ce{HCl}$) have a dipole-dipole interaction, while the oxygen in a water molecule ($\ce{H2O}$) causes the water molecule to have a stronger form of dipole-dipole interaction called hydrogen bonding? I do not understand this since chlorine is just as electronegative as oxygen and nitrogen?
Edit: I should also added that nitrogen and chlorine have the same EN value (3.0)


texts: Which has higher priority between unsaturated ring and unsaturated chain in the nomenclature of organic compounds?

texts:
According to the IUPAC rules of nomenclature, alkenes have higher priority over rings but what if the ring also contains a double or a triple bond?
For eg:

Is this compound going to be named as 1-(2-chlorocycloprop-2-enoxy)propene or 1-chloro-3-propenoxycyclopropene?


texts: Photoelectrochemical (PEC) water splitting

texts: I'm starting to prepare for my research project on photoelectrochemical (PEC) splitting of water into H and O using (F doped) titanium dioxide as the photoanode. I've been unsuccessfully searching in the literature for any particular reason(s) which could make PEC better than other methods of photocatalytic water splitting. What is, if anything, special about PEC water splitting compared to other approaches?


texts: Equilibrium Constants for Diatomic Gases at High Temperatures

texts:
I'm new here and I haven't taken chemistry beyond high school, so please forgive the ignorance. I am reading a book about hypersonic aerodynamics, and I am trying to connect some chemistry knowledge into my reading. I have four reactions listed in my book:

$$
\begin{align}
\ce{O2 &-> 2 O} &\quad (\pu{2000K} < T < \pu{4000K})\\
\ce{N2 &-> 2 N} &\quad (\pu{4000K} < T < \pu{9000K})\\
\ce{N &-> N+ + e-} &\quad (T > \pu{9000K})\\
\ce{O &-> O+ + e-} &\quad (T > \pu{9000K})
\end{align}
$$

Now, the book doesn't go into the chemistry here really at all. I know that some minor dissociation happens at cooler temperatures, and there will still be some diatomic oxygen/nitrogen at higher temperatures too. But I'm trying to answer for myself just how much is around at those temperatures, and how much they change in the ranges that they list. Assuming I remember correctly, I need the dissociation constants for this. However, I'm having trouble finding them.
NIST chemical reaction searching tool doesn't seem to have the information I'm looking for, and Wolfram|Alpha (which generally helps) is not understanding what I'm trying to tell it… so I'm at a loss. My chemical engineer family member mentioned I could find it in the CRC Handbook of Chemistry and Physics, but unfortunately we can't seem to find our copy. My chemistry-major friend in college knew that it was possible to get the numbers, but he couldn't quite remember where I should start.
Either way, I'm looking for the equilibrium coefficients of:
$$
\begin{array}{clr}
\hline
\# &\text{Reaction} & T/\pu{K} \\
\hline
1 & \ce{O2 -> 2O} & 2000 \\
2 & \ce{O2 -> 2O} & 4000 \\
3 & \ce{N2 -> 2N} & 4000 \\
4 & \ce{N2 -> 2N} & 9000 \\
5 & \ce{N -> N+ + e-} & 9000 \\
6 & \ce{N -> N+ + e-} & 11000 \\
7 & \ce{O -> O+ + e-} & 9000 \\
8 & \ce{O -> O+ + e-} & 11000 \\
\hline
\end{array}
$$
Can anyone either provide those values or help me find them somewhere? Even the reaction equilibrium constants that I can find are only listed at a single temperature (and never this high, because these temperatures are… uncommon).


texts: How fast a surface oxide layer is formed on bulk chromium?

texts:
If a chromium piece is cut in half, how long would it take for an oxide layer to form on the new surface (room temperature)? i.e. is it a matter of seconds/minutes/hours/days/weeks?

The closest study I found is by G. Thurner and P.H. Holloway (1992), but I can't really tell from their results what would happen at ambient conditions:

(I found several publications about high temperature oxidation, but none for surface oxidation at ambient conditions)


texts: Why does the hydrogen atom in HCl (when dissociated in water) bond to the oxygen rather than staying with the chlorine atom?

texts:
Why does the hydrogen atom in $\ce{HCl}$ (when dissociated in water) bond to the oxygen rather than staying with the chlorine atom. They ($\ce{Cl}$ and $\ce{O}$) have roughly the same electronegativity (3.5).

I saw this question:
Dissociation of HCl in aqueous solution
but it doesn't answer what I'm asking.


texts: With knowledge of ring strain, placing a double bond within a cyclopropane ring would increase the "angle strain" from $109.5 ^\circ$ to $120 ^\circ$ so are cyclopropenes stable? So far, I have only come across the famous aromatic cyclopropene cation but yet to see a neutral cyclopropene ring containing molecule. However, cyclopropanes are quite stable and sometimes occur in nature, so are cyclopropenes well known too?


texts: What is the simplest formula for the mineral beryl which contains 5.03% Be, 10.4% Al, 35.5% Si and 53.58% O?

texts:
Beryl is a mineral which contains 5.03% $\ce{Be}$, 10.4% $\ce{Al}$, 35.5% $\ce{Si}$ and 53.58% $\ce{O}$. What is the simplest formula for beryl?

So I tried to follow a 3 step rule to solving this equation:

Divide each % by it's own atomic mass
Divide each of those by whichever is smallest
Find the lowest whole #

Amount of $\ce{Be}$ = 5.03% / 9 = .558 moles
Amount of $\ce{Al}$ = 10.04 / 26.98 = .372 moles (smallest number)
Amount of $\ce{Si}$ = 31.35% / 32 = .979 moles
Amount of $\ce{O}$ = 54.58% / 16 = 3.3 moles
Proportionate amount of $\ce{Be}$ = .558 / .372 = 1.5
Proportionate amount of $\ce{Al}$ = .372 / .372 = 1
Proportionate amount of $\ce{Si}$ = .979 / .372 = 2.63
Proportionate amount of $\ce{O}$ = 53.58 / 16 = 3.3
From here I don't know what I have done wrong, but these numbers are all whack silly and I can't see to get a number that leads me to the answer.
The correct answer is $\ce{Be4Al(SiO3)8}$


texts:
In this question I am not able to decide by what process this reaction is happening.
I first thought that one of the $\ce{H}$ from $\ce{CH3}$ will depart $\ce{Br}$ from $\ce{CBrCl3}$ but I am wrong. Would someone tell me what is the right process for this reaction?


texts: Visual explanation between Molecule vs Compound vs Element vs Atom vs Substance?

texts:
Im a visual learner and am trying to find a visual explanation between the meaning of those words.

Is this Venn diagram accurate?

Can you draw a better Venn diagram, perhaps one that would also include other words like homogeneous, heterogeneous, and mixture?

Even if you draw it in Paint, I can re-do it and see if you like it.

Or is this one better?


texts: Can I safely use a separatory funnel to extract the precipitate from a solution?

texts:
Can a separatory funnel be used to collect a precipitate, or would that risk clogging the stopcock on it?

I'd like to recoup the precipitate for filtering without passing the entire solution through a filter (to avoid contaminating it, and also for convenience / saving time).


texts: Feasibility of using ionic liquid fuels in an MHD type reactor

texts:
First off I would like to say that my knowledge on chemistry, even general chemistry, is basic if not poor.

That said, I have some intuituions on this matter. I haven´t found any paper regarding this kind of system, and that is pretty much a killer for me.
Even with that I´d still like to ask the question.

Ionic liquids, liquid salts, are regarded as having some conductive capacities, being low to moderate conductors due to their ionic nature.
I know that salts have been used in MHD (magnetohydrodynamic) systems due to their high melting points -the ionic bond being particularly strong- and their conductive potential.

I have an specific fuel reaction in mind, An hydrazinium based propellant + LOX (liquid oxygen) as oxidizer,

[HO-C2H4-N2H4]+[NO3]- + 2.25 O2 = 2 CO2 + 1.5 N2 + 4.5 H2O

for example.
I read that ionic liquid salts do not need to be dissolved for the anion and the cation to conduct electricity (https://www.researchgate.net/post/How_is_the_electrical_conductivity_of_ionic_liquids_in_comparison_with_metals)
Outside of that I´d like to know if hydrainium based reactions do have some electric potential, or if by any reason wich I did not manage to grasp, it is simply out of the question to use them in such machines.

I would be very pleased to know if something is just worng or has been misunderstood.

Source for the reaction: http://cdn.intechweb.org/pdfs/20222.pdf, page 9 (455 in the original text).

Overal description of how a MHD machine works: https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator

*Edit:
The majority of the volume is occupied by the reaction products. Using just conventional fuels like liquid hydrogen is just more practical.

Still, we could use a thermal/catalytical decomposition reaction, like 6 NH3OHNO3(aq) = 2 N2(g) + 2 NH4NO3(s or l) + 6 H2O(g) + 4 HNO3(g), where both a salt and water are produced.


texts: Which is the major product of bromination of 3-(dimethylamino)benzamide, ortho or para?

texts: I know that A will most probably not happen because of high steric hindrance. However between B and C, will B become the major product? Because $\ce{-N(CH3)2}$ is less bulky compared to $\ce{C=O-NH2}$, so there will be less steric hindrance.


texts: Basis sets - negative contraction coefficients?

texts:
I was looking through Basis Set Exchange when I noticed quite a few basis sets (STO-3G to STO-6G, for example) have negative contraction coefficients for some primitive Gaussians. As (based on what I know) the overlap between two STO-nG basis functions is equal to the sum of the overlap integrals between the pGTOs used to approximate the STO, this means that the diagonalised overlap matrix may have some negative elements.

If this happens, what would the program do?


texts: Reaction of furan with chloroform in base

texts:
This reaction looks like the Riemer-Tiemann reaction. The only difference is the reactant. First step is the formation of carbene. Second step involves the attack of π-electrons of furan on the vacant orbital of carbene which results in two possible type of products:

The answer given is of type (B) (That is, dichlorocarbene is attached like product B). But both results in the same position of carbocations. Aren't both products produced in equal quantity?

Also, in the case of pyrrole, the opposite happens. That is, the major products are:


texts: Chirality in coordination octahedral compounds

texts:
Isn't this molecule achiral? I mean if I flip the mirror image on right by 180 degrees(like we do to determine chirality in tetrahedral carbons) it would be superimposeable? But apparently it is chiral. How am I flipping wrong?

EDIT
I finally got the hang of it (I think). Are the images below correct?


texts: How does existence of alpha and beta form of glucose prove that it exists as a cyclic structure

texts:
My book says that

  Glucose is found to exist in two different crystalline forms which are
  named as $\alpha$ and $\beta$.

Next it says that

  This behaviour could not be explained by the open chain structure for
  glucose.

I am not able figure out how does existence of two crystalline forms prove that glucose exists as a cyclic structure? Are there no noncyclic compounds which exist in more than once crystalline forms?

And why can't it be explained by the open chain structure?

I think I am missing something, but what?

Thanks!

Edit:

If we take the example of glycine, it exists in two different crystalline forms, but doesn't have a cyclic structure like that of glucose. So why does existence of two crystalline forms for glucose seen as a supporting evidence of its ring form?


texts:
How can we find the bond angle between 3 atoms in a compound?
Please specify an equation which can be used for all compounds.


texts: The use of silyl enol ethers over aza-enolates

texts:
I do not quite understand how alkylations using tertiary halides would work better with silyl enol ethers, compared with using the aza-enolate nucleophile. The following was mentioned in Clayden, Greeves & Warren (2012) on p. 594:

  Aza-enolates are the best general solution for alkylating aldehydes with most electrophiles. With very $\ce {S_N2}$-reactive alkylating agents, enamines can be used, and with very $\ce {S_N1}$-reactive alkylating agents, silyl enol ethers must be used.

I would think that it does not matter what nucleophile is used when alkylating with tertiary halides since $\ce {S_N1}$ processes do not depend on the nucleophilicity of the nucleophile. Thus, whether the nucleophile is very strong and basic, in the case of an aza-enolate, or relatively weaker, in the case of a silyl enol ether, the alkylation would still proceed at around the same pace.

Reference

Clayden, J., Greeves, N., & Warren, S. (2012). Organic Chemistry (2nd ed.). New York : Oxford University Press Inc.


texts: How is spiro[4.4]nonatetraene antiaromatic? I know that spiro compounds exhibit homoaromaticity, but how do they exhibit antiaromaticity?


texts: What equipment to use to make liquid oxygen?

texts:
I'd like to do some experiments with liquid oxygen but as a first step I'll have to make some. Unfortunately I don't have any experience designing cryogenic experiments. I'm thinking I'll cool gaseous oxygen using liquid nitrogen as the coolant and then I want to collect the liquid oxygen condensate in a small dewar of some kind.

It needs to be high purity so I'll be using 99.9% purity "scientific grade" oxygen from a cylinder.

Does it make sense to use conventional condenser glassware like a dimroth condenser for instance? Alternatively what's the best equipment to use and what's the best way to rig a cryogenic setup like this?

Also what safety precautions should I take?


texts: Ionic liquids and deep eutectic solvent cation vs anion shape

texts:
If we consider an ionic liquid of a deep eutectic such as the choline chloride type DESs, why are ionic liquids (and deep eutectics) with not very symmetric cations and very symmetric anions more common than ionic liquids which are the other way around.

Consider for example Choline chloride (plus ethylene glycol) and butyl-methylimidazonium hexafluorophosphate


texts: Equilibrium constant in terms of mole fractions

texts:
$$\ce{CO + H2O <=> CO2 + H2}$$
  A stoichiometric mixture of $\ce{CO(g)}$ and $\ce{H2O(g)}$ is allowed to reach equilibrium. $x$ is the mole fraction of $\ce{H2(g)}$ present.

I am meant to find the result that $$K_p=\frac{4x^2}{(1-2x)^2}$$

However, I only get: $K_p=\frac{x^2}{(1-x)^2}$

Here's what I am thinking:

$$K_p=\frac{x_{\ce{CO_2}}x_{\ce{H_2O}}}{x_{\ce{CO}}x_{\ce{H_2}}}$$

But: $x(\ce{CO})=1-\alpha=x(\ce{H_2O})$ and $x(\ce{CO_2})=\alpha=x(\ce{H_2})$.

Then substituting this in gives me my result. What am I doing wrong?


texts:
The following equilibrium occurs:

$$\ce{2 NOCl(g) <=> 2 NO(g) + Cl2(g)}$$

A gaseous mixture of $\ce{NOCl}$, $\ce{NO}$ and $\ce{Cl2}$ is put in a container. After a few minutes it is found that two moles of $\ce{NOCl}$ react for every three moles of products which react. Is the mixture at equilibrium? Why? In other words, how does the mole ratio relate to whether or not the reaction is at equilibrium? Thanks.


texts: I am looking for a software (can be freeware or purchased) to look up water and steam thermodynamic properties (e.g. density, enthalpy, entropy) preferably a macro in excel. What do you use for this application?


texts: Accurate method to calculate the pH of a salt from a weak acid and weak base

texts:
Can someone help me with this?

The problem is as follows:

  Find the $\mathrm{pH}$ of $\pu{1M}$ solution of $\ce{NH4CN}$. Their respective
  hydrolysis constants are:

  $K_h = 5.6\times 10^{-10}$

  $K_h = 2.5 \times 10^{-5}$

The alternatives given are as follows:

$\begin{array}{ll}
1.&2.8\\
2.&3.5\\
3.&6.4\\
4.&11.7\\
5.&12.2\\
\end{array}$

What I've attempted to do was to establish the following reactions:

$\begin{array}{lllll}
\ce{NH4+ + H2O <=> NH3 + H3O+} &k_{h}=\frac{K_\mathrm{w}}{K_\mathrm{b}}\\
\ce{CN- + H2O <=> HCN + OH-} &k_{h}=\frac{K_\mathrm{w}}{K_\mathrm{a}}\\
\ce{H3O+ + OH- <=> 2H2O}&k_{h}=\frac{1}{K_\mathrm{w}}\\
\end{array}$

This meant that:

$K=\frac{K_\mathrm{w}}{K_\mathrm{a}\times K_\mathrm{b}}$

For the given information it can be calculated:

$K=\frac{10^{-14}}{\frac{10^{-14}}{5.6\times 10^{-10}}\times\frac{10^{-14}}{2.5 \times 10^{-5}}}=1.4$

All of this is translated into:

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

From this equation it can be established the equilibrium equation:

$K=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$

Returning to the previous equation I'm getting:

$\begin{array}{cccccc}
&\ce{NH4+ + CN-  & <=> &  NH3 + HCN }\\
i&1&1 & & &\\
c&-x&-x &  &+x &+x\\ \hline
e&(1-x)&(1-x) &  &x &x\\
\end{array}$

Using this relation with what was established earlier it becomes into:

$K=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$

$1.4=\frac{\ce{[NH3][HCN]}}{\ce{[NH4+][CN-]}}$

$1.4=\frac{x^2}{(1-x)^{2}}$

Solving this for $x$ results into:

$x=0.54196$

and

$x=6.45804$

The thing here comes on which to choose for the concentration. I decided that the first seems more logical as it will not produce negative concentration in the denominator.

Therefore the concentration for $x=0.54196$

This means:

$\ce{[NH3]=[HCN]}=0.54196$

$\ce{[CN-]=[NH4+]}=1-0.54196= 0.45804$

Then to get the $\mathrm{pH}$ can be established from the hydrolyzation of $\ce{HCN}$:

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

Then:

$K=\frac{10^{-14}}{2.5\times 10^{-5}}$

$K=\frac{\ce{[CN-][H3O+]}}{\ce{[HCN]}}$

$4.0\times 10^{-10}=\frac{\ce{[H3O+]}(0.45804)}{(0.54196)}$

$[\ce{H3O+}]=4.73286\times 10^{-10}$

$\mathrm{pH}=-\log(4.73286\times 10^{-10})=9.3248$

Which seems kind of logical that the $\mathrm{pH}$ is within the range of an alkaline solution as $K_\mathrm{b}>K_\mathrm{a}$.

But since this option does not appear within the alternatives. I'm not convinced whether my solution is right or not.

I've found this equation which relates the $\mathrm{pH}$ with the $\mathrm{p}K_\mathrm{w}$ and $\mathrm{p}K_\mathrm{a}$ and $\mathrm{p}K_\mathrm{b}$ and the concentration:

It states:

$\mathrm{pH}=\frac{1}{2}[\mathrm{p}K_\mathrm{w} - \mathrm{p}K_\mathrm{b} + \mathrm{p}K_\mathrm{a} + \log c]$

where $c = \text{concentration}$ of the salt.

Inserting the given values in the above equation yields:

$\mathrm{pH}=(0.5)\left[-\log(10^{-14})+\log\left(\frac{10^{-14}}{5.6\times 10^{-10}}\right)-\log\left(\frac{10^{-14}}{2.5\times 10^{-5}}\right)+\log(1)\right]$

$\mathrm{pH}=9.3248$

which also checks with what was obtained previously.

But again none of these seem to check with any of the alternatives given. Could it be that my procedure was wrong?

The thing which it bothers me here is if this could be accepted as a general procedure to calculate the $\mathrm{pH}$ of a salt which has a weak acid and weak base ions. Can somebody help me here? And more importantly, how to prove that equation for $\mathrm{pH}$? I'm not sure if the hydrolyzation constants given in the problem are right or accurate. Does somebody has access to cross reference and check if those values are correct?

Can somebody help me with that part too?


texts: Can vinyl alcohol react as a dienophile in Diels-Alder reactions?

texts:
For my organic chemistry exam I needed to synthesize cylcohexanone and in one of the steps a Diels-Alder reaction was required. I chose to use vinyl alcohol followed by an elimination reaction to get the desired product.

My professor said that this could not work because a dienophile needs to be electron deficient and that vinyl alcohol is electron rich. Is there any argument I can make as to why the reaction would actually work? It was a reaction of diene + vinyl alcohol to yield cyclohexanol.

The actual answer he said was to use two dienes, one as the diene and the other as the dienophile followed by a few subsequent reactions ending with ozonolysis to get cyclohexanone.


texts: Why does the Hydrogen proton "prefer" to join the $\ce{H2O}$ molecule instead of remaining bonded to the chlorine atom?


texts:
The previous question contained too much unnecessary information and was edited.

I am wondering about the "hierarchy" of wavefunctions. If one can combine atomic orbitals (AO) into molecular orbitals (MO) through the LCAO method, could one combine MOs to form a supra wavefunction, or an LCMO?

I've done some research and found a paper on an approach to finding the MO of molecules by effectively taking a LCMO of smaller molecules or constituents. While interesting, this is not what I'm referring to as a "supra" wavefunction, if there's such a thing.


texts: Relation between electron gain enthalpy and electron affinity

texts:
The correct relation between electron gain enthalpy $(Δ_\mathrm{eg}H)$ and electron affinity $A_\mathrm{e}$ at any temperature '$T$' is
A) $Δ_\mathrm{eg}H = -A_\mathrm{e} - \frac{5}{2}RT$
B) $Δ_\mathrm{eg}H = \frac{A_\mathrm{e}}{RT}$
C) $Δ_\mathrm{eg}H = \frac{-A_\mathrm{e}}{RT}$
D) $Δ_\mathrm{eg}H = \frac{-A_\mathrm{e}}{RT} + \frac{1}{A_\mathrm{e}^2}$

I have read that electron affinity could be taken as electron gain enthalpy at absolute zero, i.e. 0 K. So, maybe we could use Kirchoff's law for temperature $T$, but why is $C_p$ taken and not $C_v$ or something else, is it from the definition?


texts: Is there a way to extract caffeine from coffee completely?


texts:
I am trying to find out about methylated spirts/denatured alcohol. As far as I can fine, methylated spirits is roughly 95% ethanol. Will it conduct electricity?

I have done some research, but I have not found much of anything. This reference discusses ethanol's pKa value (15.9, no source for value). I am aware that the reason why pure water conducts is because it dissociates into ions. Additionally, acid dissociation is written about on Wikipedia, but it always involves two reagents (something and water) - except for water self-ionization.

Water self-ionization is caused because of autoprotolysis. This led me to research autoprotolysis constants. Some specific research was conducted in this area by Faraji, Farajtabar and Gharib (Determination of Water-Ethanol Mixtures Autoprotolysis Constants and Solvent Effect). This roughly concurs with the pKa of 15.9 (Faraji et al. found a pKa of 16.62 with 90% ethanol and 10% water).

According to Wikipedia, the higher the acid dissociation constant the lower the chance that it will dissociate at any given pH. Since the pKa of pure ethanol would be higher, would it dissociate (I am unaware of what threshold is required). Even though I read the article, I was unsure about the autoprotolysis constant that it claimed to be investigating. It seems to me that the constant is just a pKa value, not anything more.

So, is it possible to determine whether high concentrations of ethanol conducts electricity or not? Will methylated spirits conduct electricity? In my research, I was not able to find anything like a conductivity or resistivity constant. Are these available for ethanol? What are they?


texts: Reaction of Iron with Concentrated and dilute hydrochloric acid

texts:
Does Iron react differently with dilute and concentrated hydrochloric acid?
A. I know that with dilute hydrochloric acid Iron (II) chloride is formed.
B. I read on the internet that with concentrated hydrochloric acid Iron reacts to form Iron (III) Chloride.
Could someone tell me:
1. Is FeCl3 formed as a product of reaction between HCl (conc.) and iron?
2. If yes, then what is the complete chemical reaction?

Thank you.


texts: In a battery what would happen if you had a perfectly uniform and pure cathode?

texts: I have been watching some videos on how batteries work and they seem to talk about the cathode being the most important. I also watched another video a long time ago and while my memory is blurred it talked about impurities in the cathode being the only reason the electrical charge doesn't flow constantly. While I found this weird I also wonder how generates seem to get this unlimited supply of electrons also so it's only fair for me to assume that the battery can also.


texts:
Can a liquid which is saturated with a single solute, dissolve a different solute, or is saturation a universal thing? I ask because I’ve seen that different solutes have different points (amounts) at which they become saturated in water, for example, which caused me to think that maybe each solution was perhaps independent, even though that would produce some interesting extreme implications. Something like, take a water & sucrose mix that is saturated; can this mixture then dissolve salt?

The specific implication I am asking about is this: If I dissolve xylitol (a sugar alcohol) in water until it is saturated (200 g xylitol to 100 g water at 25 °C / 77 °F) can I then dissolve erythritol (a different sugar alcohol) into the solution?

Obviously, we could heat the liquid and enter super-saturation, but that’s not what I’m asking. I’m asking if this can be done without super-saturating (i.e. risking precipitation/crystallization) once cooled.


texts: Why might my limelight experiment have failed and how can I improve it?

texts:
I was teaching the lime cycle to some children yesterday. I had a limestone chip (about 10g) held at the tip of a blue Bunsen flame for several minutes. It decomposed and disintegrated but only glowed very slightly, and was mostly orange with a bit of white at the tip.

It certainly gave off white light, but nowhere near the quantities required to light a theatre stage, which is what this stuff is famous for, not by a few orders of magnitude.

I tried sitting it on gauze and bringing in a second Bunsen flame from the side, but this did not improve the effect. I recall seeing quite a bright light when this was shown to me as a child.

Any theories on what went wrong? Any gotchas for doing this kind of experiment?


texts: Converting 1,4-benzenedimethanol to benzene and methanol?

texts:
I have the molecule 1,4-benzenedimethanol:

How could I produce two methanol molecules and one benzene molecule? (Is there a catalytic reaction method available for this?)
I'm guessing that hydrogen ions could be used to split off the methanol molecules on both sides?


texts: How do the pressure acting on the reactants and the initial temperature of the reactants affect the enthalpy of reaction?

texts:
In an exothermic reaction that occurs under constant pressure, does the pressure acting on the reactants affect the enthalpy of reaction? Does the initial temperature of the reactants affect the enthalpy of reaction? If so, how and why?

The idea of "standard enthalpy of reaction" seems to imply that the pressure acting on the reactants and the initial temperature of the reactants do affect the enthalpy of reaction.

According to Wikipedia,

  The standard enthalpy of reaction (denoted $\Delta H_r^{⊖}$) is the enthalpy change that occurs in a system when matter is transformed by a given chemical reaction, when all reactants and products are in their standard states.

"Standard states" means that the reactants are at $\pu{10^5 Pa}$ and $\pu{298.15 K}$, implying that if the reactants are not at their standard states, the enthalpy of reaction will be different.

However, I don't understand why the enthalpy of reaction would change. After all, if the same number of moles of reactants form/break bonds in the same way, shouldn't the heat released be the same, regardless of the pressure and the initial temperature?

EDIT: I recently learned about Le Chatelier's principle, which describes how changes in concentration, temperature, volume, and pressure affect a system in dynamic equilibrium. Is this principle related to my original question? Or am I heading in the wrong direction?


texts:
Rearranging the Eyring equation leads to the following:

$$\Delta^\ddagger S^\circ = R \ln{\frac{k \times h}{{k_\text{B}}{T}}}+\frac{\Delta^\ddagger H^\circ}{T}$$

where $k$ is the rate constant, $h$ is the Planck constant, $R$ is the universal gas constant, $k_\text{B}$ is the Boltzmann constant, $T$ is temperature, $H$ is enthalpy, and $S$ is entropy. The entropy term should ultimately be in units of $\mathrm{\frac{J}{mol\ K}}$. The right term of the equation will clearly yield the correct units. For the left term, the universal gas constant can be expressed in $\mathrm{\frac{J}{mol\ K}}$, which means that the log term should be dimensionless. For the bottom part of the fraction, the units evaluate to $\mathrm{J}$. For the top part, the Planck constant has units of $\mathrm{J\cdot s}$. To get the top part of the fraction to evaluate to $\mathrm{J}$, the rate constant would have to be in units of $\mathrm{s^{-1}}$. For first order reactions, this is indeed the case. For reactions of higher order, this will never work out to the correct units.

This makes me think that the Eyring equation is simply using the unitless values of these variables. This still leads to some ambiguity about which value of the rate constant to use. Take for instance a second-order reaction in which the rate constant is in units of $\mathrm{M^{-1}\ s^{-1}}$. If we rearrange the units to SI units ($\mathrm{m^3\ mol^{-1}\ s^{-1}}$), the value of the rate constant changes. So is the rate constant $k$ in the Eyring equation simply the value of the rate constant when that rate constant is expressed in certain units? And if so, are the concentration units always expressed in molarity? I kept missing a homework problem because I was converting $k$ from molarity to SI units, which makes me believe this is indeed the case.


texts: What reaction is used for calculating pH of the solution obtained after ethanol oxidation with potassium permanganate?

texts:
If $\pu{30.0 ml}$ of $\pu{0.20 M}$ ethanol solution reacts with $\pu{1.80 g}$ potassium permanganate, what will be the final $\mathrm{pH}$ of the solution? Assume a complete reaction and that only the products of the reaction contribute to the final $\mathrm{pH}.$

I am not sure what is the correct reaction, so I cannot solve for $\mathrm{pH}.$
Is it
$$\ce{2 KMnO4 + 3 C2H5OH -> 2 MnO2 + 3 CH3CHO + 2KOH + 2H2O}?\tag{R1}$$
But $\ce{KMnO4}$ can also oxidize $\ce{EtOH}$ to a carboxylic acid:
$$\ce{CH3CH2OH + KMnO4 -> CH3COOH + H2O}.\tag{R2}$$
Should I compute $\mathrm{pH}$ based on the $\ce{CH3COOH}?$
$$\ce{CH3COOH(aq) -> CH3COO- + H+}?\tag{R3}$$


texts: Nowadays, a lot of frying pans are made with a non-stick coating. That's usually teflon, or chemically speaking polytetrafluorethylene - $\ce{(C2F4)}_n$. Can you be poisoned if some of that teflon gets in your meal by scraping the pan or in any other way? And if so, what happens (chemically speaking) in your body after ingestion?


texts: Why Birch reduction of alkyne is E-selective?

texts:
From Organic Chemistry(Clayden, Greeves and Warren, 2nd edition), pp. 682:

  The sodium donates an electron to the LUMO of the triple bond (one of the two orthogonal $\pi^\ast$ orbitals). The resulting radical anion can pick up a proton from the ammonia solution to give a vinyl radical. A second electron, supplied again by the sodium, gives an anion that can adopt the more stable trans geometry. A final proton quench by a second molecule of ammonia or by an added proton source (t-butanol is often used, as in the Birch reduction) forms the E alkene.

I have some questions on this reaction:

(1) Double bond on the vinyl anion blocks rotation, but how can anion adopts trans geometry between cis and trans without rotation?

(2) Why anion with trans geometry is more stable? If it is because of steric repulsion between $R^1$ and $R^2$, why electronic repulsion between lone pair and $R^1$ can be ignored?


texts:
I've studied Transition State Theory since I asked this a while ago, but so far I have not been able to find a detailed explanation of how tunneling corrections are implemented into reaction rates computations.

I am thinking specifically in reactions involving proton transfer along a hydrogen bond. Electrons don't pose any trouble, because they are treated quantically. But for protons, which are usually beheld as classical particles, semiclassical corrections accounting for tunneling must be made, since a full quantum treatment of protons seems undoable.

First idea: If one performs a molecular dynamics simulation, one could at each step think of the proton "just for a moment" as a quantum particle, find an approximated wavefunction thanks to the WKB method and perform a Monte Carlo simulation to decide "where" will we find the proton at the next step. This seems doable, but it's not what is done, as far as I know (sometimes performing molecular dynamics simulations is not possible, or not useful).

Second idea/ problem: Imagine we have a Free Energy surface (I am concerned with two-dimensional problems, where there are two relevant reaction coordinates to be tracked), which informs us about the precise changes in free energy along infinitely many reaction pathways. For each of those, a classical reaction rate can be computed by means of Eyring equation and then we could take averages over some sets of paths via path integrals or something like that. Even better, one can employ Variational Transition State Theory to derive estimations for the reaction rate, once the Free Energy surface is known. I expect this will not be hard. But I don't have a clue as to how to make the tunneling corrections for the reaction rate in this scenario, although I suspect is in this setting where most tunneling corrections are made.

I've certainly found a lot of bibliography dealing with Quantum Transition State Theory and Tunneling Corrections, but absolutely nowhere do they explain with all the mathematical and physical details the concrete formulas they are employing. Instead, they write a lot (without much equations), give you other references, where you can find still some more references -and so on.

So, in brief, my question is: could anyone provide me with a reference containing a thorough, complete and detailed explanation, not lacking the mathematical details, of how does one compute the tunneling corrections for reaction rate constants?


texts: A galvanic cell with a salt bridge for demonstration purposes (high school)

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I want to design a meaningful galvanic cell experiment for my high school science class. I am tempted to do an experiment without a salt bridge. Why? Because the most common batteries (i.e. lead batteries) only use one electrolyte ($\ce{H2SO4}$) and no salt bridge.

I am not aware of technology or processes that would justify the salt bridge. Anyone who can enlighten me? If so -- very grateful :)


texts: Working with typical glass: What temperatures would I be dealing with?

texts:
I want to be able to melt down typical glass (the kind you usually find at home) and mold it into other shapes. What temperatures would achieve this?

For comparison; if I were to take some sand and convert it to glass (as we know it), what temperatures would I have to generate?

Furthermore, would "heat-treating" glass in some way make it tougher? I mean "Tougher" along the lines of "bullet-proof".


texts: The third shell must contain at least 18 electrons. But in iron there are 14 electrons in third and 2 electrons in 4th. Why are there 14 electrons in the third shell of iron atom?


texts: Can anyone help me with this question on vibrational modes of free base porphyrin (C20H14N4)?

texts:
4 a. The structure of free-base porphyrin $(\ce{H2P}$, chemical formula: $\ce{C20H14N4})$ is shown below. Given that this molecule belongs to the $D_\mathrm{2h}$ point group (character table given above) identify the symmetries (irreps) for all the vibrational modes of this planar polyatomic molecule;

(i) Identify the number of vibrational modes in $\ce{H2P}$. [3 marks]
(ii) Work out the reducible representation for the vibrational modes. [6 marks]
(iii) Use the reduction formula to identify the (irreps) for all the vibrational modes. [6 marks]
(iv) Identify which of the vibrational modes are Raman-active and which are IR-active. [4 marks]

In particular I'm getting stuck with figuring out the unmoved atoms when applying symmetry operations. I know i need to calculate gamma vib in order to use the reduction formula but I cannot picture how to apply the symmetry operations to calculate unmoved atoms for each symmetry class (aside from E) because it is a more complicated structure than I'm used to dealing with (h20, benzene etc)


texts: Why doesn't the boiling point of an aqueous solution depend on intermolecular attraction?

texts:
I understand that boiling point is a colligative property for aqueous solutions, and that it empirically depends on the mole fraction of the solute, rather than the identity of the solute. I understand the van't Hoff factor / ionic strength and why it matters. I also get that an increase in entropy is the primary driving force for boiling point elevation.

My question is, why does the influence of intermolecular attraction go out the window for solutions, as opposed to pure substances? Shouldn't the identity of the specific dissolved species - that is, their charge and their size, affect the intermolecular attractions in the solution? Shouldn't greater intermolecular attraction increase the boiling point by reducing vapor pressure, just as it does for pure substances? For example, neutral molecular solutes as opposed to strong electrolytes, or large ions like iodide vs smaller ones like fluoride.

Is the effect simply too small to matter compared to the entropy factor, or am I missing something theoretically?


texts: Why the atomic (metallic) radius of gallium is less than that of aluminium?

texts:
It is a well known fact that on moving down the group of p-block elements, the atomic radius is expected to increase. However, gallium is an exception. The atomic radius i.e., the metallic radius of gallium ($135~\mathrm{pm}$) is less than that of aluminium ($143~\mathrm{pm}$).

My book provides the following reason:

  It is due to the presence of additional 10 d-electrons in gallium which offer poor screening effect for the outer electrons from the increased nuclear charge.

But if that is the case, why the effect is not that same in case of the heavier members?

Moreover, there must be something else which governs this exceptional property of gallium. Maybe the structure, but I am not sure. Can someone elaborate?


texts: What is the rule for the punctuation marks for a bicyclo compound?

texts: What is the rule for the punctuation marks within the bracketed figures for a bicyclo compound? Is it a 'dot' or 'comma'? In some books there are commas whereas dots in some others.


texts: How to choose the correct volumes when preparing a dilution series?

texts:
Original Question

A solution of dye, Amido Black 10B dye ($10~\mathrm{mM}$, $6.165~\mathrm{g\over L}$), as-provided absorbs light much too strongly for measurement of an absorbance value. It is therefore necessary to dilute it before proceeding with an experiment to construct a standard curve of absorbance vs. concentration or amount of dye. The stock $10~\mathrm{mM}$ Amido Black solution needs to be diluted $200\times$ using purified (RO) water. To achieve the dilution, it is recommended that serial dilutions be used.
How would you dilute the Amido Black 10B $200\times$ to a total volume of $3~\mathrm{mL}$? Assume you only have pipettes that cannot dispense less than $20~\mu\mathrm L$.

Comments
We've already been through this question together in class but despite asking a lot of questions I still didn't understand what my tutor was trying to explain. I already have the answers, but I want to know how to figure it out for myself. My tutor's way was this:

Adding $50~\mu\mathrm L$ of dye into $50~\mu\mathrm L~\ce{H2O}$ gives a $1$ in $2$ dilution.
Take $30~\mu\mathrm L$ of the new solution and add $2970~\mu\mathrm L~\ce{H2O}$, giving a further $1$ in $100$ dilution.

I do not understand where she got $50~\mu\mathrm L$ of dye and $50~\mu\mathrm L$ of $\ce{H2O}$ if it's $1\!:\!2$. I know she split $1\!:\!200$ into $1\!:\!2$ first because the pipettes can't dispense less than $20~\mu\mathrm L$.  I also don't understand where she got the $30~\mu\mathrm L$ from in the second step.


texts:
Are there any solids with hydronium ion in its crystal structure?

If so, what are they?

If not, why not? I understand there are hydroxide-containing solids and gels such as aluminium hydroxide but why not hydronium ions? Does this have to do with the positive charge of hydronium ion? I could see the positive charge of hydronium ion excluding the possibility of forming any salts/solids with the group 1 and 2 metals.


texts: Why I get acidic solution at brine anode?

texts: I have decomposed $\ce{NaCl}$ solution (brine) with electrolysis and yield $\ce{NaOH}$ at cathode, at anode I got acidic while expected was $\ce{NaClO}$ (alkaline) if it is $\ce{HOCl + HCl}$. Where does sodium ion goes, and if it doesn't, then why?


texts: Schrödinger's equation and spin quantum number

texts:
As spin quantum number cannot be derived from Schrödinger's  equation, it cannot predict opposite electron spin.
I mean to ask that how do we obtain the information conveyed by the spin quantum number when we don't speak of it in this theory.


texts: Can I deduct heteronuclear van der waals parameters from homonuclear parameters in a forcefield?

texts: I got a forcefield (OPLS-AA in this case) that lists lennard-jones parameters for all homonuclear van der waals interactions. Is there a way to deduct the heteronuclear vdw-interaction parameters from those?


texts:
Could combining amphetamine and a (possibly selective) MAOI (MonoAmine Oxidase Inhibitor) increase the amphetamines potency without serious toxic side effects? If so by what factor, and would this be profitable for clandestine amphetamine producers to lower production costs?

I guess this is most at home at the Chemistry Stackexchange. I'm looking into this matter from a medicinal chemist point of view.


texts: Why is CuSO4 used as electrolyte while purifying copper?

texts:
During the electrolytic purification of copper, the electrolyte is taken as copper(II) sulphate ($\ce{CuSO_4}$). Is there any particular reason for this? Could another salt of copper, say $\ce{CuCl_2}$ work?

I mean, I don't see any reason why it shouldn't. The only difference will be, that at the anode chlorine instead of oxygen will be evolved, which doesn't seem to be such a big thing.

Why, then, is $\ce{CuSO_4}$ preferred?


texts: Derivation of the van der Waals equation

texts:
I’m trying to rationalize the van der Waals equation for a non-ideal gas. I understand it conceptually, but I cannot finish the algebra:

Begin with the ideal gas law: P V = n R T

This is really: P(ideal) V(ideal) = n R T       (1)

Now consider the particle-particle interactions. This has the effect of decreasing the pressure, relative to the ideal condition. It also decreases the real, or effective volume occupied by the gas.

Express this as: P(real, or observed) = P(ideal) – P(due to particle-particle interactions)

Rearranging: P(ideal) = P(real) + P(interactions)        (2)

We also have: V(real) = V(ideal, or measured) - V(due to particle-particle interactions)

Rearrange this to: V(ideal) = V(real) + V(interactions)   (3)

Now consider again the volume occupied by the gas, and start with the understanding that the expression “volume of gas” is not literally correct. The “P”, “n”, and “T” are intrinsic properties of the gas particles, but “V” refers to the volume that the gas occupies, not the sum of the volume of the individual gas particles.

In the ideal condition, the measured volume of the container is equal to the volume occupied by the gas. Given that a real gas has finite volume, the volume available for the gas particles to occupy decreases by the volume of the gas particles themselves.

Express this as: V(occupied by the real gas) = V(total, of the container) – V(of the gas particles)

I consider that the measured volume of the container is the theoretical maximum volume that the gas particles may occupy (maybe here is where I’m going off the rails, but what is the correct argument?)

Rearrange this to: V(ideal) = V(occupied by the real gas) + V(of the gas particles)         (4)

Substitute equation (2) into equation (1): [P(real) + P(interactions)] V(ideal) = n R T     (5)

But now, substitute equations (3) and (4) (they express the same concept; V(real) < V(ideal)) into (5), and I get:

[P(real) + P(interactions)] [V(occupied by the real gas) + V(of the gas particles)] = n R T        (6)

The volume expression is incorrect.

I’m thinking that the logic error is somehow related to the fact that “volume” is the volume occupied by the gas, and not an intensive property of the gas particles themselves, but I can’t find how that translates to an error in my argument above.

So, let’s cheat. Logically, at any rate. Let’s assume the van der Waals equation, and see if I can go backwards, without logical error:

The volume term in the van der Waals equation is: (V – nb)

Since it arises by substitution into the ideal gas law, it follows that: V(ideal) = V – nb.

This makes the “V” on the right a real volume. If it was ideal, then either “n” is zero (no gas), or “b” is zero (no volume), or both. Logically impossible.

It must be that: V(ideal) = V(real) – nb

This implies that the volume that may be occupied by a real gas is always greater than the volume that may be occupied by an ideal gas. But the volume occupied by an ideal gas is equal to the volume of the container. Therefore, the volume of a real gas is greater than the volume of the container it occupies. This cannot be.

Where am I going wrong?

I appear to be left with the notion that deriving the van der Waals equation by substitution into the ideal gas law is not correct, but why?

And if it is correct, is there a rationale for the volume expression like that for the pressure expression? In other words, what is the logical argument, that makes sense when implemented algebraically?


texts: Why titrating strong base with weak acid doesn't end at pH 7?

texts:
If I understand this titration correctly, if we titrated 50mL 1.00M acetic acid with 1.00M NaOH, the equivalence point would happen at a pH greater than 7, and less than 50mL of NaOH would need to be used.

What I'm curious about is why the titration does not take 50mL of both and why it does not end at pH of 7.  I can accept the numbers above, but I would like to know why.

The reason I struggle with this is because since the sodium hydroxide is a strong base and will ionize almost entirely, its hydroxide ions will react with whatever hydrogen ions have been ionized from the acetic acid.  This neutralization will force more acetic acid to be ionized, and the process will repeat.  Then, the same volume and molarity of each will be used, and the titration will end with complete neutralization at pH 7.  Why is this not the case?  Can weak acids and bases not be forced to ionize in such a way?  Is there some point at which a weak base or acid will not ionize any more, no matter what?


texts:
Task: Explain the reaction mechanism of 1,4-Dioxane in terms of how you get peroxides. Start here with the autoxidation with one radical X.

My explanation:

in the first step 1,4 Dioxan reacts with Dioxygen, so one gets an initiatorradical and and HOO* (* symbolises here a free electron, a radical). In the second step the initiatorradical reacts with oxygen and one receives a peroxyradical. In the end the peroxyradical reacts with an hydrogen atom and one comes to hydroperoxide. Is that right?


texts: Do extreme homeopathic dilutions still retain quantities of the starting materials?

texts:
This Indian Institute of Technology Bombay  press release quotes some research papers which claims to prove that homeopathic remedies do retain original substances even when diluted.

  The paper reports the fascinating observation that certain high potency (highly diluted)
  homeopathic remedies made from metals still contain measurable amounts of the starting
  material, even at extreme dilutions of 1 part in 10 raised to 400 parts (200C).  It is well known that a series of 1:99 dilutions done sequentially will produce a significant dilution of the starting material in very short order. Specifically, if the starting material is at one molar concentration (6.023x10e23 molecules per liter), then at about the 12th dilution (12C) there should be no or very nearly no molecules left of the starting material. At 200th dilution (200C) the likelihood of there being even one atom of the starting material approaches zero. However, dilution does not work so simply, according to this paper. Using electron microscopy (TEM), electron
  diffraction, and atomic spectroscopy, Chikramane et al. found that, contrary to the arithmetic, there are nanogram quantities of the starting material still present in these ‘high potency’ remedies in the form of nanoparticles.

This was published in a homeopathy journal and not a chemical engineering journal, although the department was chemical engineering.

A later paper, Why Extreme Dilutions Reach Non-zero Asymptotes: A Nanoparticulate Hypothesis Based on Froth Flotation suggests that nano-particles are distributed unevenly, floating to the top of the container, which may interfere with dilution predictions,  public in a journal from the American Chemical Society.

  However, physicochemical studies of these solutions have unequivocally established the presence of the starting raw materials in nanoparticulate form even in these extreme (super-Avogadro, >1023) dilutions. In this article, we propose and validate a hypothesis to explain how nanoparticles are retained even at such enormous dilution levels.

Another researcher in a Letter to the Editor that the original element was found may be be because those original elements were stuck to the inner walls of lab glass:

  Further-more, soluble compounds can be captured by nanosized structure, often nanobubbles, lining the boron-silicate glasses with which dilutions, subjected to mechanical stresses, are made. Therefore, an imprecise fraction of compound may be dispersed into the solvent from the glass wall whenever a mechanical stress is applied to the dilution, possibly giving gelsemine concentration far from the theoretical evaluation into pure water.

(The "mechanical stress" presumably refers to the succussion during homeopathic preparation.)

In practice, are some of the original materials still found in 200C dilutions?


texts: Mechanism for reaction between aluminium and iodine

texts:
What should be a suitable mechanism for the reaction between aluminium and iodine, catalysed by water?

In my initial approaches, I had first thought of repeated attacks of the lone pairs of oxygen in water on aluminium, then formation of $\ce{Al(OH)3}$ by losing $\ce{H+}$, then $\ce{H+}$ attacking $\ce{I2}$, and formation of $\ce{HI}$, and finally formation of $\ce{AlI3}$.

But actually $\ce{Al2I6}$ is formed, so how can I accommodate its formation in that?

Is anything wrong in the above suggested mechanism? If the actual mechanism is something else, please write it in your answer.

A Lewis dot structure of the mechanism would be appreciated.


texts:
Schrodinger's equation has been successfully solved in one-electronic systems, such as the ionic molecular hydrogen $\ce{H2+}$.

What is the exact reason that this equation can not be applied for multielectron atoms?


texts: How to find trace methanol content in fermented fruit/distillate?

texts: Suppose we have some fermented (optionally also distilled) fruit/fruit juice. The sample therefore contains water, sugars, ethanol etc. Which analysis method is the simplest to find out whether the toxic methanol is also present?


texts: Does the addition of acid change alkalinity?

texts: I'm attempting to speed up the dissolution of calcium carbonate by the addition of hydrochloric acid. However, I'm using the calcium carbonate as a source of carbonate for a water sample. But would the addition of acid counteractively lower the alkalinity in the process, therefore lowering the carbonate concentration?


texts: Help with absolute configuration of a substituted cyclohexane?

texts:
How is the absolute configuration decided when it is a cyclohexane and several stereocenters? Up to now we have only worked with simple molecules which are only 1. I believe the stereocenters here are the 2nd, 4th and 5th carbon but what are their configurations?

Thanks!


texts:
How do semi-permiable membranes handle salts that can separate into an acid and a base based on the "rules" of the membrane?

For example, say I have a nanofiltration membrane that rejects multivalent ions (eg $SO_4^{-2}$) but passes monovalent ones (eg $Na^+$) (common in nanofiltration membranes). If I supply a pressurized feed of an aqueous mixed-valency salt solution, say $Na_2SO_4$, what happens?

I can't find any literature that describes what happens in a simple case like this without other ions around. I can imagine two options are most likely:

The salt gets rejected. This is implied by lots of literature, but I can't find it explicitly stated.
The monovalent ion passes, in the above example creating $NaOH$ solution permeate and $H_2SO_4$ solution retentate. Evaluating the osmotic pressure in this case would be very odd as I guess you would have to include the disassociation energy of water.

What happens in this type of situation?


texts: How long can solid DPPH powder last for in terms of shelf-life before its free-radical status is quenched by the atmosphere?

texts:
I am writing in my research on the free-radical scavenging activity of various flavylium compounds. I may need to have DPPH shipped as a result of a lack of supply; I am just wondering what sort of precautions I might have to take and how viable it is to do so.

I understand that DPPH solutions need to be stored very well, but I'm assuming DPPH is most likely shipped in its powder form. What I'm wondering is what its stability as a whole is in solid form. Should it be constantly kept in darkness so as to prevent photooxidation and kept in a cold place, i.e. a freezer?

Even so, how long would its shelf life be by then, and how long would it be without taking precautions and leaving it at room temperature and normal lighting?

I'm asking so as to prevent or minimise the loss of its free-radical status.


texts: In a substance do atoms actually touch each other?


texts: Comparing the stabilities of allylic, benzylic, and tertiary radicals

texts:
Which is the most stable free radical among the given species?
  (1) $\ce{CH2=CH-CH2^.}$ (allyl radical)
  (2) $\ce{C6H5-CH2^.}$ (benzyl radical)
  (3) $\ce{(H3C)3C^.}$ (t-butyl radical)
  (4) $\ce{C2H5^.}$ (ethyl radical)

The book claims the answer to be the allyl radical, option 1. But how can we definitely say that the allylic free radical is more stable, compared to the benzyl radical (option 2) which is also resonance-stabilised, or the tertiary radical (option 3) which has more hyperconjugative donation from α-hydrogen atoms?


texts: Why was atomic mass scale changed from Oxygen - 16 to Carbon - 12?

texts: Why was unified atomic mass scale introduced and why was Oxygen - 16 replaced by carbon - 12 for standardizing atomic scale?


texts: Which dihydroindenyl cation is the most stabilised?

texts:
I am facing difficulty in the following problem.

The carbocation which is most stabilised among the following is …

In my view c) should be most stabilised because even if one hydrogen is abstracted it will help in restoring the aromatic character. However my book gives the answer as a).


texts: How does the Wave-Mechanical model reconcile with the particle definition of an electron?

texts:
While just starting chemistry, I have a little pit of particle physics knowledge. I was introduced with the wave-mechanical model of an atom and was slightly confused, because from particle physics, I know an electron is a fundamental particle.

How does this reconcile with the idea of electrons as "standing waves"? Or is the standing wave idea something that explains how electrons never really have a definite location? I have had zero years of calculus so please keep calculus equations and jargon to a minimum.


texts: How does entanglement explain myoglobin's preference for O₂?

texts:
I was reading this article (full PDF here) about the myoglobin's unusual preference for O2  than CO, in which it was written:

  It turns out that some electrons in the myoglobin involved in binding CO and O2  exhibit a strong ‘entanglement’ effect, which means that their motion cannot be described independently. The all-important strength of this effect is primarily controlled by a property of quantum mechanics (Hund’s exchange) that has been traditionally neglected in such simulations; the team now believe that classical electric repulsion effects are far less important in determining which of CO and O2  is more energetically favourable for binding.

But I cannot understand how entanglement explains this phenomenon. Has it been concluded from this (quantum mechanical) perspective? If yes, can anyone explain how?


texts: is bleach residue (after evaporation) safe?

texts:
I have been preparing bleach disinfectant lately in a spray bottle and has been spraying on my couch, door mat, door knots, etc...
I don't rinse it... So I assume there is bleach residue left after evaporation?
Is it safe to leave the residue?

I felt some very mild burn like feeling on my arms when putting my arms on my couch lately; I don't know if this is some kind of placebo effect or if it is real.


texts: Determine reaction rate from reaction time?

texts:
These are the results of my experiment (solution A and B were reacted and the reaction time was measured).

Data Table Edit:

How would I determine the rate of reaction (so I can find the rate law) from the reaction time?

Solution A: $\pu{4.3 g}$ of potassium iodate per $\pu{1 L}$ of water

Solution B: $\pu{2 g}$ of sodium bisulphite, $\rm5~mL~1.0~M~\ce{H2SO4}$, 4 g soluble starch per $\pu{1 L}$ of water

I found the concentrations of $\ce{[KIO3]}$ by dividing mass of $\ce{KIO3}$ by molar mass of $\ce{KIO3} (\rm214.001\frac{~g}{mol})$ and then dividing that by volume of solution A. I also divided the mass of $\ce{NaHSO3}$ by molar mass of $\ce{NaHSO3} (\rm104.061\frac{g}{mol}$) and then dividing that by volume of solution B to find the concentrations of $\ce{[NaHSO3]}$.

I then tried to find the reaction rate by $$\frac{1}{3}\times\frac{\ce{[NaHSO3]}}{t}$$ and $$\frac{\ce{[KIO3]}}{t}$$ as the reaction is $$\ce{IO3- + 3 HSO3- -> I- + 3 HSO4-}$$

Not sure if I'm on the right track or not.

Source:

Reaction Rate was found by $[\ce{NaHSO3}]$/Reaction Time and $[\ce{KIO3}]$/Reaction Time.

Rate order was found by log(Reaction Rate)/log([$\ce{NaHSO3}$]) and log(Reaction Rate)/log([$\ce{KIO3}$]).

Would appreciate it if anyone could tell me if I did this correctly.


texts: change in state (sublimation and deposition)

texts:
I am slightly confused as to how I should think of changes in state (especially sublimation and deposition). Should I think of sublimation and deposition as skipping the liquid phase (fig 1) or should I think of it as a circular pattern (fig 2).

fig 1

fig 2

Why during sublimation and deposition is the liquid phase skipped and how is it skipped, would not all matter have to be a liquid in between solid and gas?

Is it due to the fact that some substances are unable to be liquids? if so what prevents it from being a liquid?


texts:
It states mathematically $ p=Kx $ where $x$ is mole fraction of dissolved gas and $p$ is partial pressure of the gas.
Dissolution of gases is exothermic, so with increase in temperature, solubility $x$ decreases.
But increase in temperature also means an increase in partial pressure $p$ which in turn means an increase in solubility $x$. Where am I going wrong?


texts: What is the enol form of 4-methylcyclohex-2-en-1-one?

texts:
What is the enol form of this compound?

I have made an attempt, but it doesn't look quite right.

Which hydrogen should be taken off (left or right hand side of the carbonyl)? And I don't think the ring is aromatic so I don't know how it is stabilized.


texts: How does one find the ground-state term symbol for a configuration that is exactly half-filled?

texts:
For instance, the ground-state configuration of N atom is a $p^3$ configuration of all parallel spins and one electron in each $2p$ orbital, which has:

Total spin angular momentum, $S = 3 * \frac{1}{2} = \frac{3}{2}$
Spin multiplicity, $2S + 1 = 2(\frac{3}{2}) + 1 = 4$
Total orbital angular momentum, $L = (-1) + (0) + (1) = 0$

and so, $J = {|L - S|, |L - S + 1|, . . . , |L + S - 1|, |L + S|} = {\frac{1}{2}, \frac{3}{2}}$. Thus, I've found that the two candidates are ${}^{4} S_{1/2}$ and ${}^{4} S_{3/2}$.

But my textbook (Pilar, from the '60s!) says that the ground state is ${}^{4} S_{3/2}$. How could I figure something like this out?

Hund's Rules from my text (as far as I can tell---this text is hard for me to read) don't specify how we treat exactly half-filled subshells, only less-than-half-filled, or more-than-half-filled, assuming equal $L_{max}$ and $S_{max}$ already.

(As a side note, my usual McQuarrie textbook is not with me this week, so I cannot simply refer to McQuarrie.)


texts: What is the meaning of the J value in term symbols

texts:
I understand how to work out the J values of term symbols.

e.g. a d1 configuration gives J values of 5/2 and 3/2. resulting in 2D 3/2

However I dont understand the meaning of it, and why it arises.


texts: Benzylic Oxidation of Cyclic Molecules Using KMnO₄

texts:
What is the product of the permanganate oxidation of 1-methylindane (1-methyl-2,3-dihydro-1H-indene)?

There are two choices of benzylic protons (one proton on the carbon with the methyl group at the top of the cyclopentane, and two protons on the carbon in the cyclopentane at the bottom of the molecule).

I figure that the ketone is added to the carbon that has two benzylic protons, and that the other carbon with a benzylic proton is untouched. Am I correct?


texts: Why is formic acid more acidic than benzoic acid?

texts:
Why is formic acid(pKa=3.751)  more acidic than benzoic acid(pKa=4.204)?

Here's what I understand:

1) Phenyl ring is electron withdrawing therefore it should decrease electron density on oxygen thus stabilizing the anion obtained after deprotonation. Considering this argument, benzoic acid should be more acidic than formic acid.

2)

It looks like resonance of phenyl ring with carboxylate should destabilize the anion and therefore, formic acid should be a better acid. But the "aromatic ring is so thermodynamically stable that the phenyl ring donating electrons to the carboxylate is not a major resonance structure".

Considering the two above factors, benzoic acid should be stronger than formic acid. Then why it's not?


texts:
H-O-H (water), H-O-O-H (hydrogen peroxide), H-O-O-O-H, H-O-O-O-O-H, etc.

This is analogous to hydrocarbon chains, methane, ethane, propane, butane, etc.

Note the Hydroxygen Chains satisfy 2 covalent bonds for every oxygen atom, just as every Hydrocarbon Chain satisfies 4 covalent bonds for every carbon atom. Yet the oxygen chains seem unstable. Why?

I can't imagine it has anything to do with shells deeper than p. And carbon and oxygen are very close together on the same row, so it would appear the valence shells are the same and thus governed by the same laws.

I'm also aware of those weird exceptions, Ozone and Red Oxygen. Maybe that has something to do with it, but I don't know how those bonds work either.

I also saw this related question. It just asks if they're possible. I didn't see any explanation about why they're unstable.