texts: Combined Effect of Steric Inhibition of Resonance and Inductive Effect

texts: While qualitatively comparing the acidic nature of o-methyl benzoic acid and benzoic acid, we consider the steric effect due to which the $\ce{-COOH}$ group loses its planarity and the +M effect of $\ce{-CH3}$ isn't considered any longer. But still, the +I of $\ce{CH3}$ is functioning, which increases the electron density of the compound and reduces its acidity. Thus o-methyl benzoic acid should be less acidic than benzoic acid. But while confirming my results with the experimental data, I found that $\ce{pK_a}$ of o-methyl benzoic acid is 3.90 while that of benzoic acid is 4.20. How can this be explained using the basic concepts of electronic displacement effects?


texts: Which of the five main branches of chemistry has the most labwork?

texts:
Budding chemistry student here.

I am aware of the so called "five branches" of chemistry, namely organic, inorganic, bio, physical and analytical.

Which of these paths lead to work with the most lab time?

I suspect physical chemistry would be fairly academic, considering it's links to physics and maths. Which is also very appealing.


texts: How hot will a carbon electrode get in an electrolysis setup?

texts: For the electrolysis of sulfuric acid, I plan to use carbon graphite electrodes at voltages up to 6 V. I would like to know if my carbon electrodes would get considerably hot or warm (45 °C or higher).


texts: How determine the number of significant figures of a feet/inch system?

texts:
How many significant figures are there in $5~\mathrm{ft}\ 10~\mathrm{in}$.
I know that $5~\mathrm{ft}\ 10~\mathrm{in}= 5.8\bar{3}~\mathrm{ft}=70~\mathrm{in}$, so I am not sure exactly how much significant digits are in this number.


texts: Relationship Atmospheric Gases and Ocean Gases

texts:
If this question is better suited for the Earth Science StackExchange or another StackExchange please let me know.

Edit 1: Modified for clarity and brevity.

Something that's unclear to me is the exact relationship between gases within an atmosphere and the concentration of those gases within a large body of water under that atmosphere (like an ocean).

For example, the solubility of $\ce{CO2}$ at $298\ \mathrm K$ and $1\ \mathrm{bar}$ of atmospheric pressure is $\approx 1.496\ \mathrm{g/L}$ in water. My understanding is that number indicates how much $\ce{CO2}$ can be dissolved within water before the water is saturated with $\ce{CO2}$ and won't accept any more. However, this doesn't tell me what the concentration of $\ce{CO2}$ would be under given conditions, it just sets a maximum cap. For one thing it could be much less because there isn't enough $\ce{CO2}$ in the atmosphere to saturate the ocean.

(I hope I have that correct! If not please let me know where my understanding is going astray.)

Key Question: What are the calculations I need to go through to figure out the amount of gases in a body of water under an atmosphere of a given gaseous composition and pressure?

We could clarify this question through looking at an idealized situation (below). I'd like to know the steps to take to figure this out. If we need to ballpark it then that's ok, though I'd prefer to keep it as reasonably accurate as feasible.

Scenario

Assume uniform temperatures at water surface. Assume no minerals dissolved in water. Assume no gases have yet dissolved in the water from the atmosphere.

SURFACE

Total surface area: 510 million $\mathrm{km^2}$
Water surface area: 361 million $\mathrm{km^2}$
$15\ \mathrm{^\circ C}$ uniform surface temperature

ATMOSPHERE

By volume: $99.5\ \%$ nitrogen, $0.45\ \%$ carbon dioxide, $0.05\ \%$ methane
Surface pressure: $1\ \mathrm{bar}$

OCEAN

Pure water ocean (nothing yet dissolved in it)
Volume: $1.4$ billion $\mathrm{km^3}$

Q: What will be the equilibrium composition of gases in the atmosphere and in the water?

Q: How much of each gas will dissolve into the water?

… and of course how you got there.

What happens when you increase pressure and decrease temperature? How would that effect the answer?

What I really want to know is both general principles as well as establishing those principles in actual numbers. I'd also love any insight you may have on how real-world numbers are likely to differ and why.


texts:
Which of the following ions is more stable? Use resonance to explain your answer.

When we have to compare stability of resonance structures we generally check for the following features in the resonance forms (in sequence):

Neutral molecule;
More covalent bonds;
Complete octet of all the atoms;
Less separation of opposite charges;
Positive charge (if any) on more electro positive atom and negative charge (if any) on more electronegative atom.

In the above problem:

Both the molecules are charged;
Both have same nuber of covalent bonds;
Both have the octet of one carbon atom incomplete (the positively charged one);
Both have positive charges on carbon atoms.

From all of these considerations the molecules should be equally stable. But the answer given in my book is (A).
What is that I can't figure out?


texts: Can a base like OH- attack aldehyde and ketone to create hydrate instead of enol?

texts: I don't know if this question is kind of vague. But i was wondering like in the reaction of saponification of ester, where you have a base like OH- directly attacking the carbonyl carbon, can you also have a base like OH- attack the carbonyl carbon atom and then protonate the O- atom to create like a hydrate? Or does the base prefer attack hydrogen of alpha carbon of ketone and aldehyde? I am kind of confused about when a enol is create and when a hydrate is created since both of them can be formed by a base. So, hence I ask this question.


texts: When you melt an ionic compound, do you "break" its electrostatic force of attraction, or its lattice energy?

texts:
I know that the melting point and the boiling point of ionic compounds are very high. However, when I was trying to find the reason for this, I found that this is because of the high electrostatic forces of attraction.
Does this mean that when we melt an ionic compound, we break its electrostatic forces? But then that means that in the liquid state, ionic compounds have only ions? That somehow doesn't seem right to me. I tried to find out if its the lattice of the ions that we are breaking instead but found no clear answer.
So, that is my question. When melting an ionic compound, do we break its lattice or its electrostatic forces? what about boiling?
Edit: I got this from Wikipedia:

Even when the local structure and bonding of an ionic solid is disrupted sufficiently to melt it, there are still strong long-range electrostatic forces of attraction holding the liquid together and preventing ions boiling to form a gas phase.[65] This means that even room temperature ionic liquids have low vapour pressures, and require substantially higher temperatures to boil.[65] Boiling points exhibit similar trends to melting points in terms of the size of ions and strength of other interactions.[65] When vapourized, the ions are still not freed of one another. For example, in the vapour phase sodium chloride exists as diatomic "molecules".[66]

Here, the last point. "Sodium chloride, in the gas phase, exists as diatomic molecules." This means, the electrostatic forces of attraction between the ions don't break ( The ions don't get separated). Like, for NaCl, you still have "molecules" of NaCl, you don't have ions of Na$^+$ and Cl$^-$ in the gas phase.
So, in a way, the only the lattice of NaCl broke, NaCl itself ( with the electrostatic forces) didn't break.


texts: Does internal potential energy affects temperature or only kinetic energy?

texts: If I take an extreme case, where a body has only an internal potential energy with zero internal kinetic energy, does this body have a temperature? Another question related to it: if two objects A and B having different temperature: A: having only internal potential energy and B having only internal kinetic energy, can heat flow from A to B ?(temperature of A > B)


texts: Why does pH increase as a weak acid becomes more dissociated?

texts:
From Wade's Organic Chemistry [1, p. 71]:

  In most cases, the $\mathrm{p}K_\mathrm{a}$ of an acid corresponds to the $\mathrm{pH}$ where the acid is about half dissociated. At a lower (more acidic) $\mathrm{pH}$, the acid is mostly undissociated; at a higher (more basic) $\mathrm{pH}$, the acid is mostly dissociated.

I'm having a hard time intuiting this concept. Consider placing $\pu{1 mol}$ of $\ce{HF}$ in $\pu{1 L}$ of water. As the $\ce{HF}$ dissociation reaches equilibrium, I'm assuming the concentration of $\ce{H3O+}$ ions in solution increases, until the maximum concentration of $\ce{H3O+}$ ions are reached at equilibrium. If the concentration of $\ce{H3O+}$ ions in water increases as the dissociation of $\ce{HF}$ proceeds, then wouldn't the $\mathrm{pH}$ of the solution decrease (become more acidic) as the acid dissociates over time?

If any one has any thoughts on how to best interpret the quoted statement, that would be very much appreciated! Any and all new perspectives are welcomed. Thanks in advance for your generous help.

References

Wade, L. G.; Simek, J. W. Organic Chemistry, 9th ed.; Pearson: Glenview, IL, 2017. ISBN 978-0-321-97137-1.


texts: Two different electronic configurations for cerium

texts:
Depending on the textbook there are two different electronic configurations stated for cerium. On the one hand

$$[\ce{Xe}]\mathrm{4f^15d^16s^2}\quad$$

and on the other hand

$$[\ce{Xe}]\mathrm{4f^26s^2}$$

Are both configurations possible? If not, why so?


texts: Can HBr add to a non-sp2 hybridized carbon?

texts: Does this reaction make sense? Mechanistically speaking, it does not for me. Is this a special case, or just a typo in the book?


texts:
Consider some liquid in a beaker. I am measuring its temperature using a thermometer. When i put my thermometer's bulb in the liquid, the particles of the bulb gain the same kinetic energy as of the liquid particles. Now, my question is that
Do the particles of thermometer's bulb attain the same translational, rotational and vibrational energy (vibration of atoms within a particle) as of the particles of the liquid?
I have read somewhere that there is no effect of increase of rotational energy or vibration of molecules (as a whole) on temperature readings. Why so? Do the vibrations of the molecules don't change kinetic energy of the thermometer's bulb's particles?


texts: How can one synthesise a conjugated alkyne chain?

texts:
Let's take the conjugated alkyne chain (e) below, taken from Wikipedia:

How would one typically go about synthesising such a conjugated chain with a series of alkyne functions?


texts: Why do two solutes permitted to diffuse simultaneously across a semi-permeable membrane both end up at equal concentrations on both sides?

texts:
Let's say we have solute a, which is highly concentrated (let's say 99%?) on side 1 of a semipermeable membrane.

We also have solute b, which is has a much lower concentration (let's say 0.01%) on side 2 of a semipermeable membrane.

If we allow these two solutes to diffuse across a semi-permeable membrane that permits both, my reading seems to suggest that we would eventually expect 50% of solute a to occur on side 1 and 50% on side 2. We would also expect 50% of solute b to occur on side 1 and 50% on side 2.

I'm not sure that I understand this.

I completely agree that 50% of the a+b molecules will end up on side 1 and 50% of a+b will end up on side 2.

But I don't understand why different solutes travel along their own concentration gradients independent of other solutes in solution. Why would they not interact with the other solute?

Perhaps they do, and the diffusion kinetics of solute a would dictate that it reaches equilibrium much faster than solute b?

Would it be correct to predict that the larger the difference in initial global concentration, the longer the lag between when "a" reaches equilibrium vs. when "b" reaches equilibrium?


texts: What are the chemical principles behind paper/ink deterioration over time and how do I prevent them?

texts:
I have been working on a time capsule for the past few months, in which I decided to not include any electronics (ie: no USB). I am done writing the content of the capsule, but I have some concerns regarding the surface on which it'll be printed and the casing it'll be trapped in.

I know for a fact that all kinds of paper do not age well, and those that do only do so in specific conditions. An example of that would be the old report cards of my parents that have turned yellow-ish and whose paper is surprisingly light and fragile. The ink started disappearing in some areas of the report cards, and left the paper directly under it more damaged than in other, uninked, areas.

These report cards being nearly 40 years old and already slightly damaged, I am quite concerned about leaving printed paper inside a time capsule for decades (if not longer). Since it will most probaby be an encased stack of paper, I am also worried that the pages at the bottom of the stack will get damaged even faster because of the pressure.

In this case, a damaged piece of paper means either:

A) The paper has become too fragile to be held with bear hands

B) The ink has disappeared and the paper has become unreadable to human eyes

I have thought of some of the factors that I should probably account for like temperature, material of the casing, oxydation, and humidity, but besides putting the paper in a vacuum (which might not even be that good of an idea), I don't know what to do.

So, my question is: What are the chemical principles behind the deterioration over time of both ink and paper when put together, and how do I prevent/slow them over long periods of time ?

I have control over these variables:

Type of paper*
Type of ink*
The ink can either be printed using a regular/office printer or placed using writing tools
Type of paper coating*
Material of the casing*
Environment surrounding the paper: it could be a vacuumed space or any gas or liquid*
Location of the time capsule: I can place it/burry it anywhere around the world, as long as it is not unrealistically deep or in a militarized zone

*: I will accept any answers for these materials, but if cheaper alternatives do exist it's better.


texts: 2 bromo 3 methyl-butane or 3 bromo 2 methyl-butane. In general, if we have a symmetrical situation I know the functional groups should be ordered alphabetically and I also know that the smallest possible number on the functional group should be used. But what if each f-group is equidistant from the ends of the chain. Which one gets the smallest number?


texts:
I know the more general question has been asked here:

Open Database of Phase Diagrams?

And this has a link to slightly more specific question with more answers:

Phase diagram for first 10 elements

And this in turn has led me to Wolfram Alpha which has the best answer I can find so far:

http://www.wolframalpha.com/input/?i=ethanol+phase+diagram

But it's still pretty poor compared to water:

https://commons.wikimedia.org/wiki/File:Phase_diagram_of_water.svg

Are good phase diagrams really such a rare occurrence? What reference standard exists for industry?  Is there a famous book people buy that has all this data in it?


texts: Weak adhesives, has some critical chemical been banned?

texts:
I notice that in the last 10 years or so, the adhesives I encounter in everyday life have gotten noticeably weaker, is this because some critical chemical has been banned or regulated out of consumer products?

For example, the typical duct tape, packing tape, masking tape, and scotch tape that I can buy in stores now are all noticeably weaker and less adhesive than the same products 10-15 years ago. For example, duct tape used to a have thick, white adhesive that was extremely sticky, but duct tape that you would find in a hardware store now has a clear adhesive that is much less sticky.

I know that there other consumer products that have become inferior due to chemical banning; for example most plastic wrap is now made of HDPE plastic instead of the original polyvinylidene chloride, so it is greatly inferior to the original Saran wrap. Has the same thing happened to tape adhesives? If so, what is the operative chemical that has been banned?


texts: How electric field work inside a battery?

texts: Suppose Beaker A contains Zn rod submerged in zinc sulphate solution.At the electrode/electrolyte interface ,since the force felt by the solvent molecules and ions are anisotropic because of the electrode phase, the electrical neutrality breaks down on the solution side,orientation of solvent dipole take place and a net charge develops in any volume element in the solution phase near to the electrode.This creates a net electric field across the phase boundary which result in the motion of electrons on the electrode according to the field. Suppose the net charge in the solution phase is positive and induces a equal amount of negative charge on the electrode.This induction of negative charge on electrode results in some of the Zn2+ ions who have shed the electrons to leave the electrode and enter the solution resulting in a excess charge in the bulk of the solution.To maintain electrostatic condition this excess charge reside on the surface of electrolyte.The same process happens in Beaker B containing Cu and Copper sulphate solution,but the induced charge on Cu electrode is less negative compared to Zn and the excess charge residing on the electrolyte surface is also less compared to Zn.Since Zn electrode is more negative ,the direction of field lines is from Cu to Zn.On the electrolyte Since Zn electrolyte is more positive the direction of field is from Zn to Cu.Since the both field is equal and opposite they nullify each other .Thus net field is zero.If this is the case then how come electrons moves when we hook up a wire across this electrode.Can I solve this problem just by connecting a salt bridge.Or is there any flaw in the explanation


texts: How are imaginary frequencies and force constant calculated by DFT?

texts:
Computational calculations allow us to simulate the frequencies of molecules. They can even tell us if the optimized structure is a minimum, a saddle point or a maximum according to the number of imaginary frenquencies.

I was wondering how do quantum calculations could yield these frequencies. Does it have any link to the force constants of a molecule ?


texts: How can pKas differ across similar protons of the same atom?

texts: For example, citric acid has three acidic protons, all of which are carboxylic acids. Despite being part of the same functional groups, they all have very different pKas. Why (and how?) is this?


texts:
While reading about Hydrogen bonding in a book (O.P. Tandon's G.R.B. Organic Chemistry), I came across a sentence that was mentioned in a rather unstructured way relative to how comprehensive I was finding it until then.
Here is the excerpt of that.

And here I quote two of the sentences from the excerpt again which will bring me to my question.

(i) Hydrogen bond is merely an electrostatic force rather
than a chemical bond.
(v) All the three atoms in X-H- - -X lie in a straight line.

Question:
If Hydrogen bonds are electrostatic, why are they directional?

So I did some searches and found a pretty good publication by a professor of Indian Institute of Science about the exact same thing.
Here you can find a PDF of the same.
Initially I wondered why any electrostatic bond would be directional against the common understanding of Physics that I have.
Here there is a really good rationale about it.
But majority of the explanation given in it is really alien to me. Atomic basins and the computational methods are something that I've never even heard about in my senior year.

So the problem here is actually I think I don't understand the terminologies. I'm afraid my question might get closed but I really need someone to explain about it in a rather simple way. And also, could I get a suggestion about where I can read more about things like atomic basin, etc.?


texts: How to determine which reagent to use H2; lindlar catalyst vs Na;NH3(l)?

texts:
I do understand that H2; Lindlar will give a cis double bond and Na;NH3(l) will give trans double bond. However,  I am having difficulty understand how to determine which  reagent will work in this question between H2; lindlar catalyst and Na;NH3(l). The answer is given as H2;Lindlar. Second step is to add Br2 to the alkene. Then a strong base such as NaNH2 will deprotonate OH and the compound will undergo a Sn2 reaction to form the ring. The part I am having difficulty is  choosing between H2; lindlar catalyst vs Na;NH3(l).

Thanks for any help.


texts: Application of the Woodward-Hoffman rules to a [14+2] cycloaddition (follow up)

texts:
This is a follow up question to another question I made earlier.

I put some of this information into my own notes just so I can get my head around this.

So just to clarify. Does the Woodward Hoffman rule given below only apply to ground state reactions, thus the rule cannot be applied to the above reaction scheme because one of the components is in an excited state?

A ground-state pericyclic change is symmetry-allowed when the total number of (4n+2)s and (4n)a components is odd.

EDIT: (1) Correct labeling of the suprafacial components, (2) Removal of orbital phases, (3) Stereochemistry situated at the correct stereocentres.


texts: Can anybody help me with the product? Seems like Birch reduction, but Birch reduction is used for conjugated systems and alkynes.


texts: I understand that the smoke point is the temperature at which oil starts to produce smoke. But how exactly is that smoke produced? I've read that it is related to hydrolysis and oxidation, but I'd like to know a more precise link.


texts: Is it more reasonable to use stratification to separate similar compounds rather than using temperature?

texts:
In a simple reaction between butane and chlorine, it is more likely for the secondary carbons of the butane to lose a hydrogen and gain a chlorine. The carbocation is a more stable intermediate in that situation compared to a primary carbon losing the hydrogen. So if the desired synthesis is 1-chlorobutane as opposed to 2-chlorobutane then it seems reasonable that a chemist might use stratification. The reason that I believe it is less desirable to use temperature as a method of separation is because that, at least in this example, both compounds will move between the gas and liquid phase randomly providing the possibility of still having mixed samples. Is this true, and will stratification work more reliably if purification is the desired result?

Furthermore, I never really learned why mono-chlorinated products form. Will there not also be compounds that have been chlorinated twice? Or will, over time due to entropy, all compounds be mono-chlorinated assuming that the reagents are in a ratio of 1 chlorine atom per molecule of butane?


texts: Why is the pressure correction added in the Van der Waals equation?

texts:
Since real gas particles experience attraction to each other, that means the pressure must be less from what we would expect. So why do we have to add a term to correct it?
For example, in the correction for volume, we subtract a term to find the effective volume or the "real" volume. So, it follows that the "real" pressure must be less than the given one and so, should we not subtract a term?

This is mostly with regard to solving problems based on this law, where the values of pressure, volume, $a$ and $b$ are given


texts: Preparing Hypochlorous acid from salt water

texts:
I am a school student and I want help with a project
My aim:
Preparing Hypochlorous Acid (Suitable for sanitation).
I searched across the internet and found an article at https://www.hypochlorousacid.com/hocl-chemistry  in which Salt Water electrolysis was used to make HClO.
But I have two problems here:

This process entirely relies on the ion-exchange membrane.
Titanium anode and nickel cathode are used in this process.

These make the process a very costly affair.
My question :
Is there any alternative way in which I can prepare HClO? (Probably at home).
I could not find the suitable tags for this question. So if you can add suitable tags, please edit this question


texts: In crystal field theory, why do all the metal electrons enter the d orbitals and not the s orbital?

texts: Suppose we have the complex $\ce{[Fe(H2O)6]}$. Iron has 26 electrons, and its electronic configuration is therefore $[\ce{Ar}]\,\mathrm{4s^2 3d^6}$, but in crystal-field theory, we say that the $\mathrm{3d}$ orbitals have 8 electrons instead of 6. Why?


texts: Prove that a Change of Volume will not Change the Value of the Equilibrium Constant

texts:
According to my book, a decrease in volume will result in an increase in pressure for an equilibrium mixture, which will in turn cause its equilibrium to shift to the side with the least number of gas molecules, given the reaction involves gases (and according to Le Chatelier's Principle).

It also says that Volume and Pressure changes will cause the position of equilibrium to shift, but the equilibrium constant remains unchanged...

If the equilibrium constant (K) depends on the concentrations of reactants and products...

and according to the molarity formula, Volume is inversely proportional with respect to concentration...

... then why does the equilbrium constant remain unchanged?

So far I have this, but I don't know what it means...


texts: Interpretation of 4-benzoyl butyric acid H-NMR Spectrum

texts:
I am trying to undertake a first order analysis of the spectrum below:

My issue is that every signal appears to have the same coupling constant (I am aware that the value should be reported in Hz, the spectrum just has some of my rough working on it). This does not make sense to me, as I understand that would imply each hydrogen is equally coupled to each other.  I also am at a loss of what type of multiplicity the signal multiplet at 7.5ppm has.

Any help is really appreciated


texts: Running behavior of glucose, galactose and mannose in TLC

texts:
I have separated the sugars glucose, galactose and mannose by thin-layer-chromatography. My question is why these sugar have different running behaviors and a separation is possible.
Glucose have the lowest Rf-value, then galactose and mannose have the highest Rf-value in my experiments.
I thought it might be something to do with the position of the $\ce{-OH}$ groups (axial, equatorial) but I have no firm explanation at the moment.

Thanks for every explanation concerning the topic.


texts: Why would methanol and water be used for an aqueous layer in a separating funnel compared to just water?

texts: I have a protocol for separating an inorganic component from an organic mixture, which asks for the mixture to be suspended in methanol and water and then doing an extraction with hexane. I understand that this allows separation of polar components from non-polar components. I am wondering what use methanol in water has in liquid-liquid extractions compared to just using water? My only ideas are: lowering the polarity of water, increasing the density, or somehow allowing some compounds to collect at the interface.


texts:
It has been repeatedly emphasized that proton transfers "involving" three or four membered ring transition states are not favorable and should not be drawn as the primary mechanism for any reaction.

However, with regard to a recent discussion involving $\ce{H3CSH}$ it was noted that the rate of proton tunneling in the anionic form $\ce{H3CS-}$ was likely extremely high.

Carbon-Sulfur Bond Lengths; Resonance Effects (Or Lack Thereof)

So:

a) Is this a valid rule of thumb: avoid intramolecular proton transfers unless the transition state has 5 or 6 members in its ring?

b) What's more significant with regard to proton transfer - proton tunneling or physical proton transfer? Or is the answer an "it depends"?


texts: Arrange the following in increasing order of acidity: water, ammonia, ethyne and ethane

texts: I know that ethyne is more acidic than ethane because of more s character. For water and ammonia, I used the fact that oxygen is more electronegative than nitrogen and will be able to stabilize the charge better. So water will be more acidic than ammonia.Now how do I compare ammonia and ethyne?


texts: Can somebody please explain this statement (about the greenhouse effect)?

texts:
"Methane is a potent gas and over a period of 20 years has a 72 times greater effect on warming the atmosphere than carbon dioxide.
Due to my limited english, i am failing to understand how timeline has anything to do with the effect of a gas on the greenhouse effect. I think it has to do with the half life of the gas in the atmoshpere. Maybe methane is broken down more readily than CO2 and the whole thing means that if they remained in the atmosphere for the same amount of time, methane will do a greater damage. Am i right ?


texts: Nitrogen dioxide fluorescence quenching and lifetime

texts:
Nitrogen dioxide fluorescence quenching:

$$
\begin{align}
\ce{NO2 + h\nu &->[$\varphi_\mathrm{Ia}$] NO2^{\ast}}\tag{I}\\
\ce{NO2^{\ast} &->[$k_2$] NO2 + h\nu'}\tag{II}\\
\ce{NO2^{\ast} + NO2 &->[$k_3$] 2 NO2}\tag{III}\\
\ce{NO2^{\ast} + Xe &->[$k_4$] NO2 + Xe}\tag{IV}\\
\ce{NO2^{\ast} + NO2 &->[$k_5$] 2 NO + O2}\tag{V}\\
\end{align}
$$

The fluorescence lifetime of $\ce{NO2^{\ast}}$ in the presence of all the reactions, $\tau$, measured at $\pu{298 K}$ at different concentrations (molecules per litre) of the reactants:

$$
\begin{array}{crrr}
\hline
\text{Experiment} & \tau/\pu{μs} & [\ce{Xe}]/\pu{L-1} & [\ce{NO2}]/\pu{L-1}
 \\
\hline
1 & 3.38 & \pu{1.6E19} & \pu{3.2E18} \\
2 & 1.89 & \pu{1.6E19} & \pu{6.4E18} \\
3 & 3.64 & \pu{0.8E19} & \pu{3.2E18} \\
\hline
\end{array}
$$

What is the real fluorescence lifetime of $\ce{NO2^{\ast}}?$

Is this question valid? Isn't the lifetime vs the concentration of the quencher supposed to be linear?


texts: Friedel-Craft reaction with amide substituent

texts: In this question, I know that aniline will not undergo FC reaction as it forms a complex with $\ce {AlCl3}$ and precipitates out. The answer given is (c) and I agree with it. However, the benzene ring with the amide substituent in (d) will be deactivated as the amide substituent will put a positive charge into resonance. So, will it give FC reaction? Should the answer be both c and d?


texts: Can a part of a compound be a reducing agent?

texts:
I have the equation:

$$\ce{2 Cu2O + Cu2S -> 6 Cu + SO2}$$

My doubt is that since copper is reduced (it goes from $+1$ to a $0$ O.S.), then which of the two reactants is reduced? Or why would it be fine to say that only copper is reduced and not an entire reactant? Because from my experience, I've seen that an entire reactant is considered to be reduced or oxidized. So is it right to tell only a part of the compound is oxidized?


texts: How to find the second order perturbation to wave function?

texts:
Today, I'm looking for how to find the 2nd perturbation to the base in Rayleigh Schrödinger Perturbation Theory (RSPT).

SETUP

Starting from the 2nd order perturbation in Dirac's notation:

\begin{equation}
\hat{H}^0 |n^2\rangle + \hat{V}  |n^1\rangle  = E_n^0  |n^2\rangle + E_n^1 |n^1\rangle  +  E_n^2  |n^0\rangle
\end{equation}

Multiply to the left with $\langle k^0 |$

\begin{equation}
\langle k^0| \hat{H}^0 |n^2\rangle + \langle k^0| \hat{V}  |n^1\rangle  = \langle k^0|  E_n^0  |n^2\rangle + \langle k^0|  E_n^1 |n^1\rangle  + \langle k^0|  E_n^2  |n^0\rangle
\end{equation}

The hermicity of the Hamilton operator:

\begin{equation}
E_k^0 \langle k^0 |n^2\rangle + \langle k^0| \hat{V}  |n^1\rangle  = E_n^0 \langle k^0  |n^2\rangle + E_n^1 \langle k^0 |n^1\rangle  + E_n^2 \langle k^0  |n^0\rangle
\end{equation}

Cancel the third term on the right

\begin{equation}
E_k^0 \langle k^0 |n^2\rangle + \langle k^0| \hat{V}  |n^1\rangle  = E_n^0 \langle k^0  |n^2\rangle + E_n^1 \langle k^0 |n^1\rangle
\end{equation}

Gathering same inner products:

\begin{equation}
\langle k^0| \hat{V}  |n^1\rangle - E_n^1 \langle k^0 |n^1\rangle = ( E_n^0 - E_k^0  ) \langle k^0  |n^2\rangle
\end{equation}
\begin{equation}
( E_n^0 - E_k^0  ) \langle k^0  |n^2\rangle  = \langle k^0| \hat{V}  |n^1\rangle - E_n^1 \langle k^0 |n^1\rangle
\end{equation}
Replacing $| N^1 \rangle$ and $E_N^1$ with the first order perturbation to the base and to the energy:

    \begin{equation}
|n^1\rangle =\sum_{m \neq n} |m^0 \rangle \frac{\langle m^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_m^0}
\end{equation}
    \begin{equation}
E_N^{1} = \langle n^0 | \hat{V} | n^0 \rangle
\end{equation}

\begin{equation}
( E_n^0 - E_k^0  ) \langle k^0  |n^2\rangle   = \langle k^0| \hat{V}  \sum_{m \neq n} |m^0 \rangle \frac{\langle m^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_m^0}  - E_n^1 \langle k^0 \sum_{m \neq n} |m^0 \rangle \frac{\langle m^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_m^0}
\end{equation}

\begin{equation}
( E_n^0 - E_k^0  ) \langle k^0  |n^2\rangle   = \sum_{m \neq n} \frac{ \langle k^0| \hat{V} |m^0 \rangle \langle m^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_m^0}  - \langle n^0 | \hat{V} | n^0 \rangle \sum_{m \neq n}  \frac{\langle k^0 |m^0 \rangle \langle m^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_m^0}
\end{equation}

At this point, I'm not sure if the bracket algebra was done properly not even forward.

Then ... are another some algebra steps that I cannot figure out the properly path to find the respective coefficient:

$$\langle k^0 | n^2 \rangle$$

In order to replace it in:

\begin{equation}
|n^2\rangle =\sum_{k \neq n} |k^0 \rangle \frac{\langle k^0 | \hat{V} | n^0 \rangle}{E_n^0 - E_k^0 ???}
\end{equation}

QUESTION

Please, Would someone help me out to show me how to get the properly 2nd perturbation to the wave function?


texts: For thing like 8× dilution, that would be like 1 ml of a solution and then 7 ml of something like water to dilute right? Would 50 ml solution and 50 ml water be a 2× dilution? I’m a bit unsure about the terminology. If I an OD of 0.123 from a sample diluted 5×, would multiply 0.123 by 5 to get the real OD?


texts: What is the difference between a configuration state function and a Slater determinant?

texts:
I do not understand the distinction between configuration state functions and Slater determinants. Is not every Slater determinant a CSF ?

Please explain the difference and the use/need of configuration state functions.


texts: Why are tertiary carbon atoms of polymers more prone to photo-oxidation and -degradation?

texts:
In Polymer Chemistry by Seymour-Carraher:

  Saturated linear polymers such as HDPE are resistant to degradation, but slow degradation will occur in presence of $\ce{O2}$, UV, heat. Since tertiary carbon atoms are more readily attacked, PP is less resistant to degradation than HDPE.

It means a tertiary carbon atom makes polymer less resistant to photo-oxidation and photo-degradation. What makes tertiary carbon atom more likely to be attacked?


texts: Are these different neutralization pathways?

texts:
When sodium oxide is added into water, it reacts with water to form $\ce{NaOH}$.
$$\ce{Na2O(s) + H2O(l) -> 2 NaOH(aq)}$$

This means that if we were to add an acid, it would be neutralized by the sodium hydroxide.
$$\ce{Na2O(s) + H2O(l) + 2 HCl(aq) -> 2  NaCl(aq) + 2 H2O}$$

Is the following equation a totally different reaction pathway, or is it simplified from the reaction pathways above?
$$\ce{Na2O(s) + 2 HCl(aq) -> 2 NaCl(aq) + H2O(l)}$$


texts: Activated carbon filter vs. Reverse osmosis filter

texts:
I have a 5 month old baby and I'm currently using an activated carbon water filter with the city tapwater supply (I live in Mumbai, India and the water can be highly polluted sometimes with all sorts of things - bacteria and viruses, pesticides and other organic compounds, lead, mercury, arsenic, etc.).

My baby is due to start solids and water soon.  Should I install a reverse osmosis filter instead, because that supposedly eliminates all particles that are larger than a water molecule (yes, the beneficial minerals like calcium, iron, etc. would be gone but I would rather want all the harmful chemicals removed).


texts: Torquoselectivity: Disrotatory ring opening

texts:
In organic chemistry lecture we discussed the beginning of the Woodward Hoffmann Rules with a key step of the vitamin B12 synthesis.

(The initial paper from their work can be found here:
http://pubs.acs.org/doi/pdf/10.1021/ja01080a054)

Let's first see the forward reaction (the electrocyclic ring closure) as Woodward and Hoffmann found (which goes by disrotatory cyclization; 6 electrons, thermal).

I'm interested in the reverse reaction, the ring opening (6 electrons, and therefore disrotatory:

I'm thinking now about the torquoselectivity of the ring-opening  (because in an exercise we had an example with 1-Ethyl-1-ethoxy(EDG)-cyclobut-2-ene).

Is there a rule how to see why the E (E: Electron withdrawing group) is in trans position when I start with the product?

EDIT:

I'm thinking if they are some stereoelectronic effects here which explain the obtained selectivity:

See also: http://pubs.acs.org/doi/abs/10.1021/jo00244a058
(Electronic control of the stereoselectivities of electrocyclic reactions of cyclobutenes against incredible steric odds)

Well here we have a conrotatory ring-opening. I don't know if they are still valid in our 6e case for disrotatory ring-opening of the reaction from W. and H..


texts:
I have googled and found that the structure of $\ce{N4O}$ is linear with a positive and negative charge on 2 nitrogen atoms. But, the following structure seems more stable because it fulfils octet for all elements, the structure has no charge and it is resonance stabilised:

Why is this not the actual structure of $\ce{N4O}$? Are there any destabilizing effects that outweigh the stabilizing effects in this structure? The structure doesn't seem to have much angle strain. Where am I wrong?


texts: Why is there a max radius for an orbit of an electron around a nucleus?

texts:
Why is there a max radius for an orbit of an electron around a nucleus ?
I had a course in electromagnetism but I do not get this.


texts: What equipment is used for two-dimensional IR spectroscopy and how can the molecular structure of a compound be resolved?

texts:
On the Wikipedia page about two-dimensional IR spectroscopy it is said that 2D IR spectroscopy can be used to study the

  molecular dynamics with femtosecond time resolution.

According to Wikipedia it

  has for example been used successfully to study hydrogen bond forming and breaking and to determine the transition state geometry of a structural rearrangement in an iron carbonyl compound.

Now I'm curious. What equipment is necessary to perform 2D IR experiments? Does somebody have experience with 2D IR spectroscopy and could explain how the geometry of the system is inferred just from the (2D) IR spectrum.


texts: Calculate the volume of ammonium hydroxide needed to get desired pH

texts:
I have an $29\%$ aqueous solution of ammonium hydroxide. How much do I need to add to $\pu{20 ml}$ of water to get $\mathrm{pH}$ $12.8$. Ammonium hydroxide $K_\mathrm{b}$ is $1.774\cdot 10^{-5}$.

What I tried:

$$K_\mathrm{b} = \frac{[\ce{OH-}][\ce{NH4+}]}{[\ce{NH4OH}]} \approx \frac{[\ce{OH-}]^2}{[\ce{NH4OH}]}$$

Could someone explain the rational for this approximation if it is correct?

Then

$$
\begin{align}
-\log{K_\mathrm{b}} &= -2\log{[\ce{OH-}]} + \log{[\ce{NH4OH}]} \\
\mathrm{p}K_\mathrm{b} &= 2\mathrm{pOH} + \log{[\ce{NH4OH}]} \\
[\ce{NH4OH}] &= 10^{\mathrm{p}K_\mathrm{b} - 2\mathrm{pOH}} \\
&= 10^{\mathrm{p}K_\mathrm{b}-2(\mathrm{p}K_\mathrm{w}-\mathrm{pH})} \\
\mathrm{p}K_\mathrm{b} &= -\log{(1.774\cdot 10^{-5})} = 4.75 \\
\mathrm{p}K_\mathrm{w} &= 14 \\
\mathrm{pH} &= 12.8
\end{align}
$$

Plugging in:

$$[\ce{NH4OH}] = 10^{4.75-2(14-12.8)} = 223.9$$

This is much too high and does not make sense.


texts: Two different containers full up with pure water and salt water in osmosis. What happens?

texts:
I would like to understand what happens when there are two containers which are connected together and separated by only semipermeable membrane. Then in one container I fill up (all the way to the top) pure water and in the second container I put water with a lot of salt ($\ce{NaCl}$). Now In container 2 it said to be an high osmotic pressure.

Then my question is: Is the water in container 1 will drain out / will be pushed out by the osmotic pressure in container 2? (see sections a,b,c below).

■  My question popped up after reading the following things in a book called "RBS - physiology" (6t edition p. 5):

  Osmosis is the flow of water across a semipermeable membrane from a
  solution with low solute concentration to a solution with high solute
  concentration.

Example of osmosis:

  a. Solutions 1 and 2 are separated by a semipermeable membrane.
  Solution 1 contains a solute that is too large to cross the membrane.
  Solution 2 is pure water. The presence of the solute in solution 1
  produces an osmotic pressure.

  b. The osmotic pressure difference across the membrane causes water to
  flow from solution 2 (which has no solute and the lower osmotic
  pressure) to solution 1 (which has the solute and the higher osmotic
  pressure).

  c. With time, the volume of solution 1 increases and the volume of solution 2 decreases.


texts: Partial Pressure and Partial Molar Volume

texts:
When we define partial pressure and partial molar volume of a gas in a mixture, suppose $P$ is partial pressure of a gas in a mixture and $V$ is partial molar volume
then why the following equation doesn't hold
$PV=nRT$, (where $n$ is number of moles of gas) ?


texts: Calculation of concentration at equilibrium for extraction

texts:
The equation for equilibrium of solvent-solvent extraction is:
$$\ce{PhOH(toluene) <=> PhOH (aq)}$$
An aqueous solution contain $\pu{1.5 \times 10^{-2} M}$ phenol and is shaken with the same volume of toluene. Determine the equilibrium concentration of $\ce{PhOH(toluene)}$. $K_\mathrm{D} = 14$

I have done lots of similar questions and each time I think I've gotten the method of how to do these types of questions it seems like the method doesn't apply anymore. In this question, I am really confused because I initially solved it and got the right answer. But when taking a closer look, I noticed that my calculations were wrong, and did it again in the correct way (or at least what I think is the correct way), but I got the wrong answer.
My attempt at solving the problem
Given that the aqueous solution had the concentration $1.5 \times 10^{-2}$, I made the following table, where $n_a$ is what I want to calculate.
$$\begin{array}{c|c|c|}
 & \text{PhOH(toluene} & ⇌ & \text{PhOH (aq)} \\ \hline
\text{t=0} & - & &\ \pu{1.5 \times 10^{-2} M}\\ \hline
\text{n equilibrium} & n_a & &n_0-n_a \\ \hline
\text{c equilibrium} & \frac{n_a}{V} & & \frac{n_0-n_a}{V}
\end{array}$$
My question is, when writing the formula for $K_\mathrm{D}$, is the organic phase always in the numerator? and the aqueous phase in the denominator? Meaning that if my reaction is written as above, do I still have the organic phase divided by the aqueous phase or do I follow the rule of products over reactants. If I follow the rule of products over reactants, I get the correct answer, but if I take org/aq which is the formula our professor refers to, then I get the wrong answer.
Which way is the correct way to solve a problem like this? All help is truly appreciated!


texts: Converting Chlorine Dioxide to Free Residual Chlorine

texts: Our water treatment facility used Chlorine Dioxide to disinfect the produced drinking water. The analysis results indicate concentrations of 0.2 mg/l of chlorine dioxide at the source. Can we analys residual chlorine in the distribution network? We dont have water quality standards for chlorine dioxide, only residual chlorine. Can I calculate the concentration of chlorine in the water from the concentration of chlorine dioxide?


texts: What is the reasoning for higher pH values in this scene?

texts:
In this article regarding low-boiling point amine-catalyzed biodiesel transesterification reactions, it is stated that,

  "From Table 1, we can also see that, for the isomers, the
  branched amines always showed higher yields of methyl acetate
  than the normal amines. For example, the yields of methyl
  acetate for n-dipropylamine, n-butylamine, and n-propylamine
  were 25.3%, 46.1%, and 48.2%, respectively, while those for
  diisopropylamine, tert-butylamine, and isopropylamine were
  42.1%, 49.6%, and 50.7%, respectively. This was probably due
  to the high pH values of the branched amines than the normal
  amines."

Why is this the case? Why do high pH values correlate to higher yields? Does the geometry (branched or linear) of the amine play a role in this?


texts: Definition of "Diabatic" vs "Diathermic"

texts:
In Atkins' Elements of Physical Chemistry (Sixth Edition) it is written that:

  walls that permit heating as a mode of transfer of energy are called diathermic

and that the converse situation is given the label adiabatic.

Do the words adiathermic or diabatic have any meaning, and if so, how do they differ from the two above?


texts: What is the significance of effective nuclear charge of an ion

texts:
After teaching rules of Slater, our teacher gave some examples. Some of them were to calculate effective nuclear charge on an electron, but some of them involved calculating Z* of atoms and ions.

For example, he calculated screening constant of fluoride ion as follows.
The configuration is (1s 2)(2s 2 2p 6).
Screening constant for ion (not for any specific electron) = 2×0.85 (for 1s electrons) + 8×0.35 (for 2s and 2p electrons).

I asked what is the significance of this screening constant (what is fluoride ion screening? If it were to screen a 3s electron added later, the calculation will be different). The teacher could not provide any satisfactory answer.

Is there any reason for doing this calculation? This calculation actually evaluates the screening constant for an imaginary 7th 2p electron.


texts: Calculating Ka values from std. state thermodynamic data

texts:
My professor showed us a sample calculation of the Ka value for a strong acid. He used standard state thermodynamic data.

I have an issue with this:

1) Wouldn't this give us an understated Ka value?

2) Standard state conditions start with 1 molar solutions of solute. So in writing the reaction equation of an acid with water and by using that equation to find the delta G std. of reaction and then using the relationship between delta G and K to find K, wouldn't we be running into a sort of "common ion" effect issue? There's already a 1 molar concentration of hydronium ion IN solution under standard state conditions. Finding the K of an acid dissolving in water that has a pH of 0.0 doesn't give us a Ka value (or does it?)

EDIT to address Martin:

This is what he did:

$\ce{HNO_3 + H2O ->H_3O^+ +NO_3^-}$

Find ${\Delta G^o_r}$ for above reaction.

Use ${\Delta G^o_r=-RTlnK}$ to solve for K.

My question: Is this K that you find a $\ce{K_a}$ value?


texts: Why does strength of bond matter if melting only affects the the intermolecular of the molecules

texts:
So as I've been told, when a substance melts, the actual bonds of the substance aren't broken, only the IMFs (inter-molecular forces). So why is it that metal groups decrease in melting points going down when they should be increasing because more shells exist thus ions in the lattice will be larger so more IMFs therefore it takes more energy to overcome. Instead, I'm being told that since the metallic bonds get weaker due to less attraction between electron sea and the positive ion, melting point decreases.

Could someone please help me figure out what I'm missing here?


texts: How to calculate the charge distribution at the ortho/para or meta sites of a substituted benzene ring

texts:
I've modelled a few substituted benzene rings in avogadro and retrieved the partial charges of each atom; I've tried to sum the partial charges of the carbon and hydrogen atoms at the ortho/para and meta sites to see the overall partial charge at that site but results don't make sense as the para site always ends up being 0.

How can I calculate the charge at the sites?


texts: I am looking for a reusable endothermic reaction that is safe to both touch and handle, it needs to be able to be stored in a jacket and light enough to do physical activity. Any suggestions?


texts: Citric acid chelates calcium carbonate more than ethanoic acid, why does this result in a faster rate of reaction?

texts:
I performed an experiment using egg shells (calcium carbonate) to represent teeth and reacted the calcium carbonate with acids. When measuring the rate of reaction citric acid had a higher rate of reaction and from my research I saw that citric acid forms a more stable compound with calcium hence it chelates the calcium more than ethanoic acid.

In the mouth this would remove calcium ions from
$$\ce{Ca10(PO4)6(OH)2(s) + 2H+ (aq) <=> 3Ca3(PO4)2(s) + Ca^2+(aq) +2H2O(l)}$$
that equation hence the position of equilibrium shifts to the right so more tooth decay.

But with egg shells:
$$\ce{CaCO3(s) + 2H+ (aq) -> Ca^2+(aq) +CO2(g) +H2O(l)}$$

there is no equilibrium so if more calcium ions are chelated why does this increase the rate of reaction?


texts: Is it possible to have accumulation of electron density in the inter-nuclear region even if the overlap integral is zero?

texts:
Recap:
Lately, I've been studying Hückel theory where I learned about the approximation of neglecting all overlaps and making overlap matrix an identity matrix that is $S_{AB}= 0\;_; \;S_{AA}= 1$ or $S_{ij}= \delta _{ij}\;.$ He then replaced the off-diagonal Hamiltonian elements with parameter viz. $H_{AB}= \beta_{AB}\;_,$ where $\beta_{AB}$ is a negative quantity.
Question then arose if the overlap is zero as is evident from $S_{AB}$ being zero, how can there be a non-zero value of $H_{AB}$. It was known to me that $H_{AB}$ is the

contribution to the energy due to the accumulation of electron density where the two atomic orbitals overlap, including, for instance, the Coulombic attraction between the extra accumulation of electron density and both nuclei.

So, it is contradictory to simultaneously have the condition $H_{AB}\ne 0$ with $S_{AB}= 0.$
I asked this querying for the same; there I got a nice answer from Brian where he showed that even if $S_{AB}=0$; it need not be necessary to have $H_{AB}= 0$; the graphs he provided in his answer prove this otherwise a counterintuitive fact.

Present thinking & associated query:
Brian's answer confirms the fact that $S_{AB}= 0$ and $H_{AB}\ne 0$ can go with each other. But doesn't that mean there is no need to have a net overlapping of AOs between the internuclear region in order to have accumulation of electron density in the internuclear region?
For example, while using Simple Hückel Theory for ethene, Atkins put all $S= 0$ as usual per the approximation and then wrote:

[...] Finally, as explained in the derivation, he also supposed that the terms $H_{AB}$ and $H_{BA} ,$ which represent the energy of the interaction of the two nuclei with the accumulation of electron density in the internuclear region .......

Really, if he writes this after considering $S_{AB}= 0\;_,$ doesn't that mean there can be accumulation of electron in the internuclear region even if the the participating AOs are orthogonal and there is no net overlapping? He is considering the case of ethene $\pi$-network which means there is electron density that leads to $\pi$-bonding even if $S=0$.
So, is it right to conclude that there can be accumulation of electron density in the internuclear region even if there is no net overlap in the atomic orbitals?


texts: Spectral analysis of periodic table of elements in time domain

texts:
I'm trying to get the spectral analysis data of the periodic table of elements in the time domain format or find a site that has the data in the time domain format.  All the sites
I know have the data in the frequency domain which is great but I need to do my own fft analysis starting from the time domain because the frequency domain does not include the phase angle data, which I also need to use for my calculations/animations.

Does anyone know where I can get this data or can someone send me the spectral analysis data for sodium and potassium in the time domain?

Thanks


texts: Explanation of the strength of phosphorus–oxygen bond

texts:
When discussing the Wittig reaction, Clayden's Organic Chemistry (2nd ed.) cites the strength of the P=O bond formed in triphenylphosphine oxide as a driver of the reaction through enthalpy:

  The P=O bond, with its bond energy of 575 kJ mol−1, is one of the strongest double bonds in chemistry, and the Wittig reaction is irreversible and is driven forward by the formation of this P=O bond. No need here for the careful control of an equilibrium necessary when making acetals or imines.

According to this table of bond dissociation energies, the value for the P=O bond is similar to the bond energy values for bonds such as the Be–F bond (577 kJ mol−1) and the H–F bond (568.6 kJ mol−1).

However, taking into account the large differences in the p-orbital sizes of phosphorus and oxygen atoms, and the sizes of the phosphorus and oxygen atoms, I fail to understand the similarity in the strength of the P=O and other bonds listed above.

The oxygen atom is larger than the hydrogen, fluorine, while the phosphorus atom is larger than hydrogen, fluorine, and beryllium. Thus, I would imagine that the sigma orbital overlap would be weaker due to a larger distance of interaction in P=O than in the H–F and Be–F bonds.
Due to the differences in the sizes of the p-orbitals of oxygen and
phosphorus, I would naturally infer that the p-orbital interactions and, thus, the pi bond in P=O would be weak.

Are there other factors that I am failing to consider that strengthen the phosphorus–oxygen double bond?

References

Clayden, J., Greeves, N., Warren, S. Organic chemistry, 2nd ed.; Oxford University Press: New York, 2012.


texts: Heisenberg's Uncertainty Principle's inequality

texts:
In the uncertainty principle , whats the significance of the inequality sign ?
Why is it not equal to over there ?
Why do we say greater than equal to instead of just equal to ?


texts: How close are we to building an actual nanobot?

texts:
I want to know how far current nanotechnology is from creating an actual real-world nanorobot? Also, does such a thing actually exist, or is it just a nice name for an umbrella term to show off to the general public different fields of science and engineering which might not be actually linked?

P.S. I understand that the term nanorobot may be taken into consideration because it may mean different things to different people, that's why when I use it I mean something bigger than a molecule but smaller than a biological cell which could replicate and do some "stuff" like the things described in Eric Drexler's book Engines of Creation or in foresight's institute nanotechnology roadmap. I guess they will be somewhat the size of biological organelles and just like them be composed of various molecular complexes some capable of self assembly. I want to know what is the current state of research into the creation of such structures and how far are we from building them.

P. S. 2. And, please, guys can you not use only Wikipedia for your answers. I want to know what serious research is being done and where it's published in, not just a general introduction to the field. I'll be very thankful if you could provide some sound material published in peer reviewed journals or at least a list of keywords I could use for searching for articles related to the creation of real nanorobots or a list of journals where such research can be found. If you could do at least that you will have my gratitude.


texts: What is the role of sulfuric acid and mercury(II) sulfate in the oxymercuration of alkynes?

texts:
I have a homework problem where I'm given a terminal alkyne. The goal of the problem is to choose the reagent that will result in a particular ketone.

Here's a really general view of the reaction I drew out showing the reactants I chose (I don't want anyone to do my homework, just explain what's unclear to me).

$$\ce{some terminal alkyne ->[H2O][H2SO4, HgSO4] some ketone}$$

I've gone through the list of reagents given in the problem and all the others result in an aldehyde (which to me suggests anti-Markovnikov addition).

The book shows that $\ce{HgSO4}$ yields a ketone via the Markovnikov addition of water forming an enol (and undergoing tautomerization). My answer was correct, but I'm not satisfied that I really know this. The mechanism shown in the book involves only water (it doesn't show what the role of $\ce{H2SO4}$ or $\ce{HgSO4}$ is here, it only explains that it causes Markovnikov addition of water).

My only proposal is that the $\ce{HgSO4}$ adds first, in an anti-Markovnikov fashion, forcing an $\ce{H}$ from $\ce{H3O+}$ to add on the terminal carbon and thus water to add to the other side. I also am guessing that $\ce{H2SO4}$ makes the formation of $\ce{H3O+}$ more favorable.

Could someone show how this mechanism works or explain a bit about how the presence of $\ce{HgSO4}$ and $\ce{H2SO4}$ affect the reaction?


texts:
I am supposed to say what is more basic and I ran into a problem. I would like to ask if anyone has any idea what is the correct $\mathrm{p}K_\mathrm{a}\ce{H}$ value of pyrrole. I know it is easy to just google it or open a book to find the answer. I have done that, but got pretty interesting (confusing?) results:
Wikipedia: "Pyrrole is weakly basic, with a conjugate acid $\mathrm{p}K_\mathrm{a}$ of (−3.8)"
Human metabolome database (HMDB): "Pyrrole is a very weak base with a $\mathrm{p}K_\mathrm{a}\ce{H}$ of about (4)"
PubChem: "Pyrrole is a very weak base with a $\mathrm{p}K_\mathrm{a}\ce{H}$ of about (4)"
McMurry 9th edition: "pyrrole - $\mathrm{p}K_\mathrm{a}$ of ammonium ion: (0,4)"
University of Calgary: "pyrrole conjugated acid $\mathrm{p}K_\mathrm{a}$:  (-3,8)"


texts: How do salt additives and impurities affect a critical micelle concentration?

texts:
So I understand that a CMC typically decreases as more salt additives are added. What I am not clear on is how exactly.

The head groups are charged in this example (one anionic and one cationic) so I am not sure how the salts would impact this? There is a counter-ion present as well.

Thank you so much for your response, its really helpful. I'm just learning about CMC and micelle so please forgive my silly questions. When you lower a CMC, are the micelles themselves now smaller or bigger? And when the literature describes micelles as smaller, does this mean the circumference is smaller, or the number of detergent molecules is smaller.

Would the presence of salt additives and impurities be of greater concern in measuring CMC by absorbance, fluorescence or conductivity???


texts: Unexpected reaction during acid hydrolysis of cellulose

texts:
Recently I tried to hydrolyze some cellulose:

I added some acid to it ($\ce{H2SO4}$) then noticed nothing. Even after a few days there was no visible change and after doing some tests for glucose, those were negative too.

So at the end - expecting nothing would happen - I added some sodium hydroxide ($\ce{NaOH}$) to the solution to neutralize the acid and then the most unexpected thing happened, the solution began to warm up and there was an immediate color change (turning from white (from the cellulose) to yellow/brownish) I suspect that color came from the dehydration of the glucose  that was produced at that moment due to instantaneous hydrolysis of cellulose. I finally diluted the solution with more water and the reaction stopped

So somehow there was no interaction between the sulfuric acid and the cellulose, but when sodium hydroxide was added, the solution did more than just neutralize the acid!

Does anyone have any idea why this is?


texts: Would atomic oxygen and atomic hydrogen result in O2 and H2 only, or some H2O too?

texts:
Let's assume we have atomic oxygen and atomic hydrogen in a closed chamber, the temperature and pressure of which we're able to monitor (and control). Number of hydrogen atoms are twice that of oxygen.

Would this result in spontaneous formation of:

$\ce{O2}$ and $\ce{H2}$ only?
$\ce{O2}$ and $\ce{H2}$ with some $\ce{H2O}$?
and how would the process vary with temperature and pressure?
And I assume creating mostly $\ce{H2O}$ is the hardest (though I would be interested in a comment on this as well).

and how could one carry out analysis on paper to figure out what would happen? (I'm from a physics background, and my chemistry knowledge is a bit rusty. Though I do have a good background on thermodynamics, enthalpy, Helmholtz free, Gibbs free energies, etc, etc).

For the sake of brevity and focus of this question, we can ignore the question of how atomic oxygen and hydrogen came about in the first place. (This assumption is even more acceptable in the special case of carrying out molecular dynamics computer simulation, something I'm interested in, because we don't have to worry about how to form atomic $\ce O$ and $\ce H$)

edit: I guess I should clarify that I'm interested in a first principles analysis of this problem (since I'm mainly interested in MD). Also what if we had two other species of atomic gases (Ar and Ne, Ar and O, Ar and H, etc, etc). I think I'm more interested in it from a physical chemistry point of view (though without quantum mechanics if possible).


texts: Do I have to consider the molecular mass of the oxygen atom or the diatomic oxygen molecule when determining the empirical formula of an iron oxide?

texts:
In determining the empirical formula of a compound which constitutes a diatomic molecule, should we calculate the molar mass of the divalent molecule by multiplying the molar mass of the element by 2, or should we leave it as it is. Because, I happened to come across a problem, where I had to calculate the empirical formula for an oxide of iron. A similar question has been answered before, but it doesn't seem to clear my doubt - Why not to consider hydrogen and oxygen moles to determine an empirical formula. Hence, I restate it:

  If an oxide of Iron has $69.9\%$ iron and $30.1\%$ dioxygen by mass, what is the empirical formula?

Now, if I assume the mass of compound to be $100~\mathrm{g}$, then it contains $69.9~\mathrm{g}$ of iron and $30.1~\mathrm{g}$ of oxygen. If I calculate the no. of moles,

$$\text{Moles of }\ce{Fe} = \frac{\text{given  mass}}{\text{molar mass}} = 69.9/58.5 = 1.25~\mathrm{mol}$$

Moles of oxygen - this is where the problem comes. If I take molar mass of oxygen as $32~\mathrm{g}$, as in $\ce{O2}$, I get $0.94~\mathrm{mol}$. It will not make any sense, as the ratio of iron to oxygen will not be in any reasonable quantity. However, if I take the  molar mass to be $16~\mathrm{g}$, I get $1.88~\mathrm{mol}$ of oxygen, and I can divide both the numbers by $1.25$ to get the ratio as $1.88/1.25: 1.88/1.88 = 1:1.5 = 2:3$,
hence the compound will be $\ce{Fe2O3}$, which makes perfect sense. But the problem is, why should I calculate the no. of moles from the molar mass of $\ce{O}$ rather than $\ce{O2}$? After all, its is the oxygen molecule that will exist, and no the oxygen atom right?

Also, the solution is given as $\ce{Fe2O3}$, so I need to take the molar mass of oxygen to calculate the number of moles as $16~\mathrm{g}$. The question is, Why? Why not $32~\mathrm{g}$?

Does it have something to with the fact that the question states "dioxygen" rather than "oxygen"? If yes, what is the difference between dioxygen being present in $30.1\%$ or oxygen present in $30.1\%$? I am in a real mess.


texts: What are the maximum number of electrons in each shell?

texts:
In my textbook, it says that the maximum number of electrons that can fit in any given shell is given by 2n². This would mean 2 electrons could fit in the first shell, 8 could fit in the second shell, 18 in the third shell, and 32 in the fourth shell.

However, I was previously taught that the maximum number of electrons in the first orbital is 2, 8 in the second orbital, 8 in the third shell, 18 in the fourth orbital, 18 in the fifth orbital, 32 in the sixth orbital.  I am fairly sure that orbitals and shells are the same thing.

Which of these two methods is correct and should be used to find the number of electrons in an orbital?

I am in high school so please try to simplify your answer and use fairly basic terms.


texts:
Carbon electrodes are very popular, because unlike metal electrodes, carbon is quite inert during electrolysis (I'm sure that has some explanation based on electronegativity).

However they too are not eternally lasting. Especially the pencil graphite bars will slowly release black chunks into the solution.

My question is, what's happening them. The black chunks seem like carbon, so it's probably not reacting. What's damaging the structure?


texts: Name for reaction producing carbon from CO2

texts: Some years ago I heard of a reaction where hydrogen could be used to reduce $\ce{CO2}$ to carbon and water, similar to the Sabatier reaction. I believe it also used iron as a catalyst at high temperature. Can anyone remind me of the name of that reaction or correct me if I am mis-remembering the details.


texts: Why is chlorine and not fluorine labelled as the most reactive halogen for halogenation?

texts:
The reactivity of halogenation in sunlight is as follows:

$$\ce{F2}>\ce{Cl2}>\ce{Br2}>\ce{I2}$$

So why does we often label chlorine as most reactive halogen towards halogenation reaction?


texts: Ok to separate steel from aluminum with bronze? (Galvanic action)

texts:
I have an aluminum hinge that I want to use with a stainless steel hinge pin. The problem is that I cannot use the steel pin directly because there would be galvanic action between the stainless steel and aluminum which will result in corrosion. Therefore I need to put some kind of bearing liner between them. Note that the hinge will experience strong forces, so using something soft like nylon will not work.

My preference would be for a bronze bushing, but I do not know if there is galvanic action between bronze and stainless steel, or bronze and aluminum.

What material can I use? Is there a simple explanation of how I can predict whether a metallic alloy will react galvanically with a different alloy? I have Mathematica, so if there is a formula I can write in Mathematica, that would be just as good.

-------------------------------- Sacrificial Anode?

One method I have heard of to protect from galvanic corrosion is a "sacrificial anode". If I attach a bar of zinc to the back of the aluminum hinge will that somehow protect it, and allow me to use a stainless steel hinge pin?


texts: Ions not attached but included in chemical formula for tartrazine

texts:
In some diagrams for tartrazine ($\ce{C16H9N4Na3O9S2}$), I see that $\ce{SO3Na}$ is actually represented as $\ce{SO3^-}$ with a floating $\ce{Na^+}$ next to it. How does this work?

EDIT: Wait, are they just ionicly bonded together?


texts: Salting out constant in activity coefficient

texts:
Based on this Wikipedia page for activity coefficients, I know that the activity coefficient for a nonelectrolyte can be determined using a "salting-out" model with the following equation:

$$\begin{aligned}\log_{10}(\gamma_0) &= bI\\
\gamma_0 &= \text{activity coefficient}\\
b &= \text{empirical constant}\\
I &= \text{ionic strength}
\end{aligned}$$

This equation and the accompanying wiki leaves three related questions about its use:

How would I determine that empirical constant $b$?
How do I interpret the ionic strength of a nonelectrolyte solution?
What does this equation have anything to do with "salting out" - reducing the solubility of nonelectrolytes in aqueous solution by increasing the ionic strength?


texts: Semipinacol-type rearrangement leading to ring expansion

texts:
What will be the major product in the following reaction?

I tried to work out the mechanism, which starts with protonation of the alkene, and I got C to be the answer (which is the answer in the book as well). But, I've heard that three-membered rings generally don't expand due to their exceptional stability. Is this true? And between the alkene and alcohol functional groups, which is more likely to get protonated?


texts: What are the products in this SN1 reaction?

texts:
I am asked to identify the organic/inorganic products of an SN1 reaction between 3-iodopentane and ethanol. I have identified correctly that the substrate is the 3-iodopentane, the leaving group is the iodide, and that the nucleophile is the ethanol. My problem is that I do not understand what the products will be, and I am unsure why.

I decided that the products should be 3-pentanol and ethyl iodide (or iodoethane) because iodide is a good leaving group, and the oxygen takes two electrons and leaves ethane to bond with the pentane group where the iodide left off. Now it makes sense that the ethane and iodide react to create ethyl iodide.

Unfortunately, I am wrong in this case, and I just can not put my finger on why. What is the error in my thinking and what is the concept that I am missing?

I realize that my major organic product will be the ether compound which I am having trouble naming, and the other compounds are a protonated ethanol plus the iodide. The most confusing part now is the protonated ethanol and the iodide, why not just create the ethyl iodide?


texts:
Foreword:

I am developing a variable-processing program for my Computer Science research project.

One particular part of the program mimics the behavior of biological enzymes, except instead of catalyzing break downs and compositions of chemicals, its catalyzing break downs and compositions of variables (specifically arrays).

The process in question is a 2 part process:

  initiating process:

  (in terms of enzymes:) breaks down certain compounds into smaller compounds
  (in terms of program:) fragments certain variables (certain arrays) into fragments

  finalizing process:

  (in terms of enzymes:) combine the smaller compounds into larger compounds different from the originals (like mixing and matching the parts)
  (in terms of program:) combine the fragment-variables into larger variables different from the originals (like mixing and matching the parts)

The process in question all together:

  (in terms of enzymes:) breaks down certain compounds into smaller compounds,then recombines them into larger compounds that are different from the original large compounds (like mixing and matching the parts)

  (in terms of program:) fragments certain variables (certain arrays) into fragments then recombines them into larger variables that are different from the original large variables (like mixing and matching the parts)

What is the process in question called?

Afternote:

I'm looking for a name, so the word could be a new word constructed from recognizable Latin or Germanic roots, and that would be an acceptable answer.

To get full coverage of an answer, I asked this question the English Language & Usage SE site, Stackoverflow SE site, and this SE site.


texts: Why is (NH4)2[CuCl4] square planar complex but Cs2[CuCl4] is tetrahedral?

texts: Why is $\ce{(NH4)2[CuCl4]}$ square planar complex but $\ce{Cs2[CuCl4]}$ is tetrahedral even though both have same oxidation number of copper and same ligands?


texts:
I'm struggling to understand the trend of $\ce{CO}$-vibration in isoelectronic metal carbonyls.

$$
\begin{array}{lr|lr}
\hline
\text{Compound} & ν/\pu{cm-1} & \text{Compound} & ν/\pu{cm-1} \\
\hline
\ce{Ni(CO)4} & 2060 & \ce{[Mn(CO)6]+} & 2090 \\
\ce{[Co(CO)4]-} & 1890 & \ce{Cr(CO)6} & 2000 \\
\ce{[Fe(CO)4]^2-} & 1790 & \ce{[V(CO)6]-} & 1860 \\
  & & \ce{[Ti(CO)6]^2-} & 1750 \\
\hline
\end{array}
$$

Since the complexes are isoelectronic, the reason behind the trend should lie in the atomic charge $(\ce{Ni} > \ce{Co} > \ce{Fe}).$ Higher atomic charge means more attraction between metal cation and the ligand electron pair → higher electron density → more π-backbonding → weaker $\ce{C#O}$ bond → lower wavenumber.

But it is not the case here. I'm not sure why. I think it has something to do with the energy level of HOMO.


texts: How to know properties of ion Aluminum -27?

texts: How do I know the charge/properties of this Ion Aluminum -27? All the information given is that Al has an atomic number of 13. I want to know how to know that it has an electric charge of +3 from the given information.


texts: Electrochemistry - reduction potentials - an IB Chemistry Question

texts: I have re-read the Electrochemistry chapter from my textbook just now to remind my self of the exact formulae. I still don't understand how to approach this question, however - how can we work it out? I can either give you the mark scheme answers straight away and we can work backwards, or I can wait for an answer and then tell you if that is the correct solution. What ever is the norm on this forum! Thank you.


texts: Order of lewis acidity for BBr3, BCl3, BMe3, BH3, BPh3?

texts:
In case of $\ce{BCl_3}$ vs $\ce{BH3}$, which one is the controlling factor?

1) Is it p-pi p-pi interaction in $\ce{BCl_3}$ that makes it weaker than  $\ce{BH3}$?

2) Or is it the -I effect of $\ce{Cl}$ dominating over others, despite of p-pi p-pi interaction that makes it stronger than $\ce{BH3}$ as well as $\ce{BMe3}$?


texts: Calculating the solubility of cuprous iodide

texts:
I am clearly missing something obvious here. I get the $\mathrm{K_{sp}}$ from the CRC for $\ce{CuI}$ as $1.27\cdot10^{-12}$.

So, $\ce{CuI-> Cu+  +  I-}$

So the formula ought to be

$$\mathrm{K_{sp}} = \ce{[Cu+][I-]} =[s][s]= s^2$$

Doing the square root and all gives me a solubility of 2.1 mg/L. Hooray, except that everywhere I look, if the solubility is listed at all, it lists 4.2, exactly double my answer.

I have been wracking my brain on this one. It has to be a scalar but I don’t see how you would introduce it without throwing the entire calculation off by turning the square into a cube or something similar. What am I missing?

Edit: updated to reflect the full Ksp value in the CRC which I was using for my calculations (I had accidentally truncated it to 1 rather than 1.27 when posting this). I am using the online CRC from hbcponline.com, so this is current, not an old edition.


texts: How many grams of solid sodium bicarbonate will be consumed?

texts:
Excess $\ce{NaHCO3 (s)}$ is added to 510 mL of $\ce{Cu(NO3)2 (aq)}$ $\pu{0.240M}$ for the reaction
$\ce{Cu(NO3)2 (aq) + 2NaHCO3 (s) -> CuCO3 (s) + 2NaNO3 (aq) + H2O (l) + CO2 (g)}$


texts: This is a concept I have never really understood. I mean to say is how can we include such a thing in a theory? How can we use them if we know that they don't actually exist? Are they some sort of calculation tool?


texts: Distance weighted interpolation in predictor steps vs corrector steps

texts:
I got stuck while reviewing the journal article "Accurate reaction paths using a Hessian based predictor–corrector integrator".

Why is the distance weighted interpolation done in the predictor steps, instead of doing it in the correcter steps?

Source:  H. P. Hratchian and H. B. Schlegel, J. Chem. Phys. 2004, 120, 9918


texts: Is there any bad side effects for using calcium chloride to replace a running dehumidifier?

texts:
My dehumidifier costs to much to run, so I’m thinking about using calcium chloride to keep my basement dry(er) ALSO, this may keep my mouse problem to a minimum... my questions are -Will this be harmful to me breathing this when I’m in the basement?
-Will any gases be omitted to me in my main floor?
-Will this remove to much moisture that my block foundation will start to degrade?
-Are there any other side effects I’m not aware of?
The only person that goes in basement is me so I’m not concerned about anyone consuming it.


texts: Why are strong acids and bases not suitable as primary standards?

texts:
This is one of the questions with which I have puzzled over, and can arrive at no definite conclusion. Why are strong acids or bases, such as $\ce{H2SO4}$,$\ce{ HNO3}$, $\ce{HCl}$, and $\ce{NaOH}$ not suitable primary standards?

How will their higher or lower pH affect the accuracy of the results of a titration?


texts: Why does $\text{Cr}^{3+}$ not have the same electron configuration as $\text{Sc}$?

texts:
To be explicit, $\text{Cr}^{3+}$ and $\text{Sc}$ have the same number of electrons, the only difference is the nuclear charge.

This is not an isolated anomaly, it seems: the book I'm using claim that with all fourth period transition metal cations, the $4 \text{s}$ electrons are removed first. This indicates that the $4 \text{s}$ electrons are at a higher energy than $3\text{d}$.

My question: why is this the case, given that the $4\text{s}$ electrons are 'added' before the $3\text{d}$ electrons as one moves rightwards across the fourth period, indicating that they are of a  lower energy? I cannot reconcile this apparent contradiction.


texts: Can solvents like 99.9% isopropyl alcohol and/or n-hexane be "carbonated" with CO2?

texts: I'm working on a prototype for a new machine, and I'm trying to get solvents like $99.9\%$ isopropyl alcohol or n-hexane to be carbonated like a soda pop at cold temperatures. I have the machines and everything for it I just want to make sure I'm not going to explode or anything.


texts:
Okay, this will be tricky to explain. But, this is a question that i have been wondering about in quite a long time, okay lets get started, Molecules moves faster in higher temperatures and there will be more space between the molecules than in cooler temperatures, right? i wonder what is between the molecules? in pure water to an example, there should be only oxygen and hydrogen. But, what is between the H2O molecules? it got to be something, right?

I hope you guys can understand my question, my english is not the best and i am no expert in chemistry. :)


texts: Coordination Chemistry: Predict colors (simple model, old)

texts:
I remember many years ago, when I prepared for a talk on coordination chemistry I found a PDF with a theory about how to predict the colors of simple coordination compounds. I remember the name of the person, who came up with this theory was a Nordic name, like Jorgenson. It sounded pretty similar to that at least but I cannot find it.

Basically, this was a quite empirical route. The metals had different numbers for each oxidation state and the ligands as well and in the end you had to either multiply or add them together (I don't really remember) but you came up with an energy which was sometimes close to the experimental value and sometimes completely wrong.

I know this is not really a good concept to use but I am more interested in the theory itself and would like to add it to a recent summary on coordination chemistry I am writing right now. Perhaps somebody has heard of this theory before.


texts: If I drink water without sipping, is there a chance of saliva diffusing into my bottle?

texts:
I always prefer to drink water without sipping, like this:

I do this so that my saliva doesn't contaminate the water contents, which would make the water impossible to share with my friends.
But lately, I have been thinking: Can the saliva diffuse through the water stream that pours into my mouth? Saliva is mainly composed of water, some salts, and amylase. Amylase is a rather bulky protein, so I don't expect it to diffuse so quickly, but I'm a little concerned about the electrolytes. Ions like $\ce{Na+, K+, Ca^2+, Mg^2+, Cl-, HCO3-, PO4^3-}$ are quite small and might diffuse into the bottle.
I don't have access to the values of the ionic speeds, so I'd like to ask a chemist for confirmation whether these ions can diffuse into the bottle.
To make the question a bit more informative, lets assume I keep the bottle about $\pu{3cm}$ away from my mouth, so the water would be flowing at a speed of approximately $\pu{77cm s^-1}$.


texts: What is the chemistry behind smell of human perspiration(sweat)?

texts: What is the chemistry behind  the bad smell of human perspiration? also what is its composition?


texts: SCF (Roothan-Hall) Method, why Density Matrix?

texts: I've been aksing myself, when I try to variationally minimize a Hartree-Fock energy by using the Roothan equations, what I do is to set a Fock-Matrix, then transform it, then diagonalize it so I can read the energy from the diagonal elements and then I test for convergence. But why is usually the density matrix compared to the previous run and not just the sum of the diagonal elements? I know in the end they both have to be evaluated but just for testing for any changes, pretty much any parameter, which changes with the Fock-Matrix and has some relationship with the energy could be used as a criteria for convergence. Or where do I see something wrong here?


texts:
I am wondering if there are surfactants that exist in a gas state that can be used to reduce the surface tension of a liquid.

I know its a broad question, so for example, are there any gases that could reduce the surface tension of water when it is exposed to it?


texts: Where can I find the positions of the infrared band for phosphorus compounds in general? Specifically sodium hexametaphosphate

texts: Specifically I am looking for the IR of the sodium hexametaphosphate compound.


texts: What is the critical temperature for an ideal gas? It can't be found from Andrew's isotherm as it is for real gases and states critical temperature as $\frac{8a}{27 R \cdot b}$, but for ideal gases $a = b = 0$.


texts: Controversy over products of iodate and bisulfite?

texts: We know that when we are trying to recognize iodate, we use sodium bisulphite to the solution and with the help of starch paper recognize the evolved $\ce{I2}$.But when I studied the books I found actually Iodide is formed? What's the solution to this controversy?


texts: With regards to complexes, I read that thermodynamic products are favored over kinetic products, which are labile. Why wouldn't the first product formed be the most prominent?


texts: Non-chlorine bleach vs. hydrogen peroxide 3% soln from pharmacy: Disinfecting gravity water filter system

texts:
I'm seeking to disinfect a Platypus gravity water filter made with hollow fibers.  My main concern is to address any mold / mildew that may have developed inside the hollow fiber filter due to long term storage.

The manufacturer suggests

"To disinfect your Platypus filtration system, fill it with a solution of unscented household bleach and water, using a concentration of 2-5 drops per liter of water. Close and swirl for 10 seconds. Leave filled overnight.

"Filter solution through any filters and/or hoses, then rinse system (including filters and hoses) three times with hot water. Let air dry.

"Note: for an eco-friendlier option, use a chlorine-free, hydrogen peroxide-based bleach alternative.

I called the customer hotline and asked if I could just pour in hydrogren peroxide from the pharmacy, but they said I should just stick to the recommended guidelines.  The agent also reminded me that if I use chlorine bleach, it's best to use a fresh bottle.  Do you think the same is true for hydrogen peroxide bleach?

Could I dilute 2-5 drops of the pharmacy 3% hydrogen peroxide with one L of water?

I looked at the Seventh Generation non-chlorine bleach MSDS, and it lists hydrogen peroxide at 3-5% concentration:

https://www.seventhgeneration.com/sites/default/files/msds/en/sds-chlorine-free-bleach-en-20160925.pdf

Any insights would be welcome.  Thank you!


texts: Acetaldoxime Synthesis: Hydroxylamine vs Hydroxylamine HCl

texts:
Wikipedia says acetaldoxime can be prepared by reacting Acetaldehyde & Hydroxylamine in the presence of NaOH. https://en.wikipedia.org/wiki/Acetaldoxime

But the reaction shown uses Hydroxylamine Hydrochloride instead of Hydroxylamine.

Does it not matter? Do both work? Would Hydroxylamine Sulfate work as well?


texts: Why are fluoroalkyl chains hydrophobic/oleophobic?

texts:
I'm searching for an answer that explains the hydrophobicity / oleophobicity in terms of intermolecular forces, but can't really find one.

Below is an example fluoro-alkyl nano-particle, F-POSS. It has 8 ligands of a fluoroalkyl chain $\ce{(CH2)2(CF2)4CF3}$ with a silicon-oxygen cage in the center.

When grouped with other F-POSS molecules it forms a membrane with the fluoroalkyl chains:

Hydrogen Bonding - Wouldn't the hydrogen be attracted to the fluorine atoms? They're essentially electron sinks.

London Dispersal Forces - Why would other molecules not be attracted to these ligands? I was told that the ligands themselves aren't even attracted to each other.

Apologies for the lack of citation, but what's been given to me has mostly been word of mouth. Research articles I've read don't really go into the intermolecular forces.

Image source: http://pubs.acs.org/doi/abs/10.1021/la201545a?journalCode=langd5


texts:
In a previous question, I learned that we can detect lead with sodium / potassium rhodizonate, giving a nice purple color when reacting with pure (elemental?) lead.

But in the paint, lead is primarily used in the form of salts such as lead oxide, lead carbonate, lead chromate...

What if the lead in my paint is not pure, but a salt? Would sodium rhodizonate react with such salts? (I insist on sodium vs potassium, since it's cheaper to get). And if not, how can I detect these salts?


texts: Is the reaction between thiosulfate and hydronium an acid-base reaction?

texts:
Is the following reaction an acid-base reaction:

$$\ce{2 H3O+(aq) + S2O3^2-(aq) -> 3H2O(l) + SO2(g) + 1/8 S8(s)}$$

And if so, which is the acid and which is the base?


texts: Can lead-acid batteries release CO? Or can a CO sensor detect gasses other than CO?

texts:
I recently found myself troubleshooting a CO alarm on a houseboat. Inside the cabin, a Fluke CO-220 was reading 40 ppm. In the generator engine compartment, the CO level was zero (while the generator was running). We eventually found the source of the CO to be a large lead-acid "house" battery which was warm and leaking:

The OL on the display of the CO-220 indicates a value of >1000 ppm CO. I watched it count up through 600, 800, 900 before indicating OL.

Mechanics replaced the batteries, and ensured the battery box was properly sealed and vented. After this, the CO levels were at zero.

Can lead-acid batteries leak carbon monoxide?

This article discusses the chemical reactions of a lead-acid battery, and as far as I can tell there is no carbon involved whatsoever. So I believe the answer here to be "no".

Can a Fluke CO-220 detect gasses other than carbon monoxide?

The CO-220 manual says nothing about any gasses other than CO. In the specifications:

  Sensor type | Stabilized electrochemical Gas-specific (CO)

I contacted Fluke and they responded with:

  I do not know what gas batteries would put off and the CO-220 has a senor [sic] for CO only. Hope this helps.

I assume the answer here is also "no".

So then, what was going on?


texts: Why do we need incubation time during the glucose test by chronoamperometry?

texts: Also, is there any difference between with and without incubation time in the glucose test? For example, the voltage results acquired will be different?


texts: Why is the intermolecular hydrogen bond between phenol and aniline stronger than the respective hydrogen bonds?

texts:
From NCERT class 12 part 1

The way I see hydrogen bonding is that it occurs due to intermolecular charge interaction. The more electronegative nitrogen/oxygen due to the inductive effect the respective hydrogen will be more electropositive.

Since the compound cointaining the more electronegative atom (oxygen/nitrogen) has greater respective charges.Then the hydrogen bonding will be greater between the molecules of that compound i.e either the hydrogen bonding between  phenol-phenol and aniline-aniline should be greater than phenol-aniline.


texts: Difference between dissociation energy and dissociation temperature for water?

texts:
I was trying to find the temperature at which water dissociates into hydrogen and oxygen, and so I came across this Wikipedia page. It states that it takes $\pu{493.4 kJ/mol} + \pu{424.4 kJ/mol}$ to dissociate the bonds in a water molecule which gives a total of about $\pu{920 kJ/mol}$ or about $\pu{51 MJ/kg}$. So I tried to calculate the temperature that would give that huge amount of energy using the heat capacity of water vapor. I took $\pu{3.3 kJ/kgK}$ for water vapor as an average specific heat, and so by simply dividing $\pu{51 MJ}$ by $\pu{3.3 kJ}$, I ended up with about $\pu{15,000 K}$.
But on this other Wikipedia page, I found: "at $\pu{2200 ^\circ C}$ about three percent of all $\ce{H2O}$ molecules are dissociated into various combinations of hydrogen and oxygen atoms. At the very high temperature of $\pu{3000 ^\circ C}$ more than half of the water molecules are decomposed".
So now I am very confused. If $\pu{3000 ^\circ C}$ is enough to dissociate more than half of the water molecules, then it should be expected that almost all the molecules should dissociate at around $\pu{4000 ^\circ C}$ or so and not the $\pu{15,000 K}$ I calculated earlier.
So am I missing something here? Or is there an explanation to this?


texts: Total spin number 0 together with $B_2$ state - confusion

texts:
I'm trying to understand molecular symmetry and I got confused reading the Molpro documentation.

There is an example of a system with $B_2$ symmetry written like this:

$$
wf,10,3,0,
$$

which means, that the system has 10 electrons, $B_2$ symmetry and the total spin number is 0.

If I understard the total spin number well, it is 0 only when all electrons are paired in the orbitals (i.e. the system is in singlet  state).

But, on the other hand, I thought, that when the electrons are paired, then the orbital is "totally symmetric", i.e. $(\cdot)^2 = A / A_g / A_1$.

So, as far as I understand it, $B_2$ symmetry and total spin number 0 is mutually exclusive.

Is it true or do I understand it wrong? If I do, could you, please, explain my mistake and provide some simple example of the abovementioned configuration?


texts:
Will it be wrong to add reduction potentials of two intermediate reactions to get reduction potential of net reaction(just like as we do in adding enthalpies and applying Hess's law)?

What is the basic error? What should be the thinking process to avoid these kind of errors in chemistry?


texts:
Why is it that for the $\mathrm{d}$ subshell we have  $\ \ \mathrm{d}_{xy}, \ \ \mathrm{d}_{yz}, \ \ \mathrm{d}_{xz}, \ \ \mathrm{d}_{x^{2}-y^{2}},$ and $\mathrm{d}_{z^{2}}$ orbitals only?
Why aren't there $\mathrm{d}_{y^{2}-z^{2}}$ or $\mathrm{d}_{y^{2}}$ or other orbitals similar to that?
Perhaps it is because we have an empirical evidence that there are only 5 orbitals in $\mathrm{d}$-subshell, in that case, why are $\mathrm{d}_{x^{2}-y^{2}}$ and $\mathrm{d}_{z^{2}}$ orbitals named in this particular fashion only? (as the axes are arbitrary and there could have been a different choice of axes also)


texts: Difference between atomic mass, mass number, atomic weight, and relative atomic mass

texts:
I think this question is common, but i want a little help.
I'm little confused.
What I concluded.

Relative atomic mass/Atomic weight (both are exactly the same) - It is the mass of atom calculated as taking the sum of all the masses of the subatomic particles and dividing it with mass of (the same technique calculated) 1/12th of C-12 atom.

Atomic mass- It is the mass of the atom calculated as taking the mean according to their abundances in nature, of atomic weight of the different isotopes present in that sample.

Mass Number- It is the mass calculated as the sum of the nucleons , as there is only a slight difference in the mass of the proton and neutron, and the mass of electron is negligible as compared with the mass of the proton and neutron

But this is conflicting with definitions on wikipedia.
Also the relative atomic of carbon should be exactly 12, but its 12.011


texts: Deriving the equation for oxygen estimation by Winkler’s method

texts:
We were doing $\ce{O2}$ estimation by Winkler's method

The procedure and reactions involved in this experiment are:

Carefully fill a 300-mL glass stoppered bottle brim-full with sample water.
Immediately add 2mL of manganese sulfate to the collection bottle.
Add 2 mL of alkali-iodide reagent (NaOH + KI) in the same manner.
Stopper the bottle with care to be sure no air is introduced. Mix the sample by inverting several times.
Add 2 mL of concentrated sulfuric acid.Then mix well.
In a glass flask, titrate 100 mL of the sample with sodium thiosulfate to a pale straw color. Titrate by slowly dropping titrant solution from a calibrated pipette into the flask and continually stirring or swirling the sample water.
Add 2 mL of starch solution so a blue color forms.
Continue slowly titrating until the sample turns clear.

$$\begin{align}\ce{MnSO4 + 2NaOH &-> \underset{{white ppt.}}{Mn(OH)2} + Na2SO4}\\[0.6em]
%
\ce{2Mn(OH)2 + O2 &-> \underset{{orange-brown cloudy ppt.}}{2MnO(OH)2}}\\[0.6em]
%
\ce{2Na2SO4 + 2H2SO4 &-> 4 NaHSO4}\\[0.6em]
%
\ce{MnO(OH)2 + NaHSO4 + 2KI &-> \underset{{golden-brown colour}}{I2} + MnSO4 + K2SO4 \\&\quad\quad + 2Na2SO4 + 3H2O}\\[0.6em]
%
\ce{I2 + 2Na2S2O3 &-> 2NaI + Na2S4O6}\end{align}$$

And at the end of the experiment we needed to calculate the $\ce{O2}$ concentration in mg/l by the following equation:

$$c(\ce{O2})\ \mathrm{(mg/L)} = \frac{(V_1 \times N \times E \times 1000)
}{[V_4 {(V_2-V_3)/V_2}]}$$

Here,

$V_1=$ Volume of titrant $\ce{Na2S2O3}$ (ml)

$V_2=$ Total volume of water sample (ml)

$V_3=$ Volume of ($\ce{MnSO4 + KI}$ solution) added (ml)

$V_4=$ Volume of analyte taken in titration

$E=$ Equivalent weight of $\ce{O2}$

$N=$ Normality of $\ce{Na2S2O3}$ solution

So how can I derive this equation?

Reference followed: Ghosh, K. C. & Manna, B. (2005) Practical Zoology

A different book though had a different formula :

Conc. of O2 (mg/l)= 0.2 x (Volume of sample water in ml) x (Strength of $\ce{Na2S2O3}$)


texts: Titration calculations - working out cation

texts: so I was doing this question and I have some questions about what I did. Firstly am I correct to say that the concordant results = 24.1 cm^3 because there are 2 of these values. From this I then calculate that M = 32.9 however this can not be true, so what have I done wrong?


texts: Sodium Polysulfide production from NaOH and Sulfur

texts:
Does the sulfur also oxidize the $\ce{OH-}$ radicals after the $\ce{Na2S4}$ chains form? Something like this:
$$\ce{9S + 4NaOH -> 2Na2S4 + SO3 + H2O}$$


texts: Why enthalpy is defined at a constant pressure?

texts:
How absolute enthalpy and enthalpy change are defined? What is the clear difference between enthalpy and heat? Is it the constancy of pressure what makes the enthalpy a state function?

My teacher told me in very simple words that when heat goes inside a system, it is called enthalpy. Is this correct? Would constant pressure make the volume constant in a thermodynamic system?

Answers to my confusing questions would be highly appreciated.


texts: Why is the preferred IUPAC name of acetone "propan-2-one" and why not simply propanone? It doesn't make sense to specify the position of the carbonyl group as it can occupy only one position in acetone, i.e. on the 2nd carbon.


texts:
Standard electrode potential values can be used to judge the reducing ability of a metal. When I was introduced to this topic a simple picture was painted: you put a metal into a solution of its ions. An equilibrium is set up. You do so for another metal. If you now hook up the two electrodes and measure the voltage, you can tell which one is 'more negative' hence more electron donating.
I was taught like it is covered here :
  https://www.chemguide.co.uk/physical/redoxeqia/introduction.html

My question is that suppose we have two metals, A and B. A produces +1 ions. B produces +2 ions. Now even if the two have the same tendency to lose or gain electrons, the B plate would be 'more negative'( As in this plate would have more negative charge). How has the voltage helped us determine the difference in the tendencies of these two metals?


texts:
Does being able to react with hot water take more metal reactivity than being able to react with HCl? To me, it seems like a metal would need to be more reactive to be able to react with hot water since HCl is a very strong acid and so should theoretically be able to react with more metals, but I am not so sure.

Edit: Context: (Question) Al reacts with hot water (boiling pt), Mg does not react with hot water but reacts with HCl, which is more reactive? According to the reactivity trends, Mg is more reactive than Al, but according to the information given in the question, it seems logical that Al is more reactive since it reacts with hot water but Mg does not. So is Mg or Al more reactive if we were to assume that everything in the question were true?


texts:
As metal carbonates are basic would there be a reaction if a sample of, say potassium carbonate, was added to carbonic acid? If so what would be the products? A balanced equation would be useful.
Will this apply to other basic substances if they are added to an acid from which they already have an ion of?


texts:
October's synthesis golf is rather late - apologies. I've chosen a slightly different-looking target this round, with the aim of inspiring a wider variety of routes.

Muscarine is a natural product found in some mushrooms. Most notably, it is a good agonist of one class of acetylcholine receptors - these receptors are therefore called muscarinic acetylcholine receptors.

The only conditions for this round are that:

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

Otherwise, any commercially available starting material (as usual, in the Sigma–Aldrich catalogue) is fair game! There is also no restriction on the counterion.


texts: Reaction of alkyl halides with strong unhindered bases

texts:
Please look at the image on this website: http://www.physicsforums.com/showthread.php?t=765853

For (b) and (c), what the solution manual says makes no sense to me.
You're reacting a primary alkyl halide with an unhindered base $\ce{EtONa}$. They say that the only product is the alkene. Why do they not consider the $\mathrm{S_N2}$ reaction that WILL take place in larger quantity?
I'm uploading the question too on the other website