texts: Mathematical explanation behind dq = TdS

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Can somebody mathematically prove why $$\mathrm dq = T\,\mathrm dS$$ for a reversible process?

I realize I am supposed to provide some research but I can't find anything. The best I got is $\mathrm dE = T\,\mathrm dS$ which is basically $\mathrm dG = \mathrm dH - T\,\mathrm dS$ and it seems to be a circular argument (since for derivation of $G$ most proofs use the equation $\mathrm dq=T\,\mathrm dS$).


texts: Effect of +M and +R effect in basicity of 4-methoxy aniline

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We know that methoxy group exerts a +M effect, as a result of which basicity should increase even after resonance as +M effect is considered to be stronger than resonance effect.
So by this reason 4-methoxy aniline must be more  basic than cyclohexane amine, but this is not true.
I am not able to understand what factor should make cyclohexane amine more basic than 4-methoxy aniline.


texts: How to use this salt analysis chart to determine the cations present in a given solution?

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With the only possibilities being $\ce{Ba^2+, Ca^2+, Cu^2+, Fe^2+, Fe^3+, Pb^2+}$, what cations are present in a solution which:
a) Forms a white precipitate with sulfate and with fluoride, no precipitate with chloride, and a blue precipitate with hydroxide which dissolves in ammonia solution

I have the answer with me, but I am not too sure how to use the above chart for determining cations in a solution, to answer the question. I can sort of make it out, but I am not completely sure.


texts: Why are there two contradicting formulas for Enthalpy (Delta H):

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1) Delta H = Bonds broken - Bonds Formed

2) Delta H = $H_{products} - H_{reactants}$

In the first formula, bonds break in the reactants and form in the products, so its basically saying "bonds energy of reactants" minus the"bond energy of products", which is the complete opposite of what the second formula gives. How so? And when you know to use each formula?


texts: Tin in silver nitrate, any soln color change?

texts: I have lab question in which a $\ce{AgNO3}$ solution with a tin strip placed in it is mentioned. This isn't a reaction we actually did in the lab, but due to a color change in the solution of one we did do, I was wondering if there would be any for this reaction. Googling I found that the $\ce{AgNO3}$ solution is initially colorless, but that's all I could find. So would there be for this one, or would the solution remain colorless?


texts: Polluting agents generated by road traffic in a city

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I want to measure the air quality according to road traffic in a city.
What are the polluting agents (generated by fuel combustion) strictly related and generated by road vehicles that is worth measuring?

Among $\ce{CO}$, $\ce{CO2}$, $\ce{NO_$x$}$, PM2.5, PM10, $\ce{NH3}$, $\ce{O3}$, $\ce{SO2}$ which are the most significative? Should I add or remove any agent?


texts: Why do electronegative atoms depress coupling constants?

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Related to this previous question about detection of small couplings between protons.

In a recent conversation with our labs NMR technician, it was stated that coupling constants decrease in the presence of electronegative atoms:

  ...and you have a lot of electronegative atoms around, so thats going to make those coupling constants drop off significantly...

  Source: 'Personal communications', aka the labs NMR-tech

Thinking about it, this is something I've always known but possibly never thought about to any great deal, despite the fact it shows up in even the most basic organic chemistry textbooks:

  ...electronegative atoms, which decrease 2J and 3J couplings between protons

  Source: Organic Chemistry, Clayden & Warren

Digging a little deeper, this idea comes up a lot in NMR textbooks too, and a few trends are discussed, for instance in Günther's NMR spectroscopy:

  For substituted ethanes the relation between the change of electronegativity, caused by the replacement of a hydrogen atom with a group X, and the coupling constant is given by:

  3J = 9.41 – 0.80 (EX – EH).

  Source: NMR spectroscopy, Günther

What I can't find, in any great detail, is why the coupling constant depends on electronegativity the way it does.

From what I've read, it has something to do with the polarisability of the bond, but again, its maybe not completely intuitive how this effects coupling between two protons separated by 2/3 bonds.


texts: Direction of mass transfer in two film theory

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In an extraction process compound A is transferred from one solvent to another solvent. The two solvent may be, for example, water and dichloromethane. These two solvents are immiscible and when mixing them together, one of the solvents, say solvent 1, forms droplets that are dispersed in solvent 2, as depicted [...].

Fig. 4 shows the concentration profile across the interface between the two solvents. For this concentration profile, answer the following questions:
(a) In which direction is the mass transfer, from solvent 1 to solvent 2 or vice versa? Motivate your answer by a short explanation (2 pt).

How can you tell which direction the mass transfer will go?
I would assume that because solvent 1 forms droplets in solvent 2, then solvent 1 should be the organic phase. Would the mass transfer be from solvent 2 to solvent 1? Because the aqueous phase would contain compound A.
Edit
Just to see if I have understood it correctly, if I am given the concentration profile below. Then mass transfer would occur from the aqueous phase to the organic phase because the aqueous phase has a higher concentration.


texts: Does 30% hydrogen peroxide eat away at platinum?

texts: if I soaked a platinum dish with 30% hydrogen peroxide, will it eventually eat away at it?


texts: Is it possible to measure the entropy of a chemical reaction through calorimetry?

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My broad question is how do you measure entropy change? I was doing a bit of digging into how thermodynamic tables are developed at I got this from NIST. Basically it seems like you need to indirectly determine the entropy of a substance from other experimental parameters. What NIST says is

You use heat capacities and phase transition enthalpies to do a ground up calculation
Statistical mechanics methods once you have a partition function
Measure temperature dependence of equilibrium constants from van't hoft plot
Calculate it from previously determined enthalpies and free energies.

The thing that's bothering me is that all of these measurements depend on other experimental parameters and it just seems to be a raw calculation of entropy after determining these other quantities.
My primary question then is it possible to do a calorimetry experiment to calculate $\Delta S_{reaction}$? After all, how did people measure entropy experimentally in the olden days before we had copious information on heat capacities?
I tried to think about this for a constant pressure apparatus. A reaction happens and I have a thermometer to measure $\Delta T$. I can correlate this to $\Delta H$ using the heat capacity of the calorimeter. If I have a resistive circuit running through the calorimeter, I can supply heat externally to lower $\Delta T$ so now I can say that $\Delta H$ occurred at the same initial and final temperatures
However, this only tells me about the $\Delta S_{surroundings} = -\frac{\Delta H}{T}$. How do I calculate the change in the reaction system? I tried to imagine the reversible path but if I start and end at the same point, then isn't $\Delta S_{system} = 0$? Where is the flaw in my reasoning or is it just something we cannot end up measuring?


texts: Dealing with different units (psi) in ideal gas equation

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My assignment is as follows:

A sample of air is trapped in a container at $\pu{16.2 psi}$. If the initial temperature is increased from $\pu{10 ^\circ C}$ to $\pu{32 ^\circ C}$, what is the final pressure?

I am really confused as to what $\pu{psi}$ is and how am I supposed to convert it to figure out the final pressure.


texts: When I place a chunk of 99,99% pure sodium metal in a beaker of (100% chemically pure) acetone, the sodium metal starts reacting and dissolving into the acetone and it forms a yellow/brown liquid. When the acetone evaporates it leaves a dark-brown goo that is like a gel. And it smells like tar or something similar. What is this substance?


texts: I'm in the second year of my biochem major, taking organic chemistry, and I feel like I've learned a lot about acids. The most popularly recognizable property of acids is their corrosive power. There are pop-culture depictions of acids everywhere, and all they seem to do is corrode stuff. Yet, with all I've learned about them, it's never been explained to me why they have this property, or how and when it works.


texts: Why does Sodium Hydrogen Sulfate (Sodium Bisulfate) produce moisture?

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In my chemistry lab, I have a vial of Sodium Hydrogen Sulfate (Sodium Bisulfate). I've noticed that when I take a spoonful using a spatula, the spatula gets covered in many tiny droplets, and the lid of the vial always has a layer of tiny droplets on the inside.

Does the Sodium Hydrogen Sulfate (Sodium Bisulfate) react in any way to produce this moisture? Is this to do with the salt being hydrous or anhydrous?


texts: How often is the IUPAC Goldbook Updated?

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I was wondering how often does the IUPAC update its Gold Book, ie, IUPAC Compendium of Chemical Terminology - the Gold Book.

It poped in my mind when I saw this question about jellium aromaticity, that the term should be there. However, it was not. Whereas, the term has been used several times in the linked references (1 2), which I like to consider credible.

So, I was wondering how up-to-date the book is and how much can one rely on it for latest information.

PS While I understand that this question is primarily and heavily opinion based, I think it is equally relevant to all of us as we delve further in the chemical world.


texts: How do organic chemistry mechanisms become accepted?

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Now I have been learning chemistry for five years. I remember when I started organic chemistry, it was fun to draw arrows between molecules to show, as if in a mathematical demonstration, how the reactions occurred. In every lesson I had, teachers explained to us how a specific reaction (for example the Shapiro reaction) occurs step by step, explaining the chemistry of each group in each intermediate as if things were obvious (you know how teachers are).

But I've been wondering for some weeks now how does a mechanism come to be considered as accepted or still discussed?

If they use some, what kind of spectrometry techniques are used to measure the amount of each intermediate? If not how do they proceed? Do they use computational chemistry? Because for example for a reaction such like a $\mathrm{S_N2}$ it doesn't look too tricky to find how it works, whereas for Fries rearrangement (I don't know if the mechanism is considered as accepted or not) it seems to be more tricky.

(Ref.)

So can you explain the methods (at least the most used) to confirm a mechanism? I am aware that "confirm" does not mean that we are 100% sure, but rather that it is simply the best we have found so far.


texts: Explain why can't zinc be plated out from a Zn(II) solution using standard reduction potentials

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I am currently learning about electrochemistry using Zumdahl's Chemistry [1, pp. 709–710]. One of the critical thinking questions is

Why can $\ce{Zn}$ not be plated out from an aqueous solution of $\ce{Zn^2+}$ using the choices in Table 18.1?

I feel like it would be plated out when with a half-reaction with a lower potential such as
$$\ce{Al^3+ + 3e- -> Al}$$
Combined,
$$\ce{3 Zn^2+(aq) + 2 Al(s) -> 3 Zn(s) + 2 Al^3+(aq)}$$
Also, looking at the reactivity series, it seems that there are plenty of options that should be able to plate out zinc. It would great if someone could explain to me what's wrong with my thinking.
References

Zumdahl, S. S.; Zumdahl, S. A.; DeCoste, D. J. Chemistry, 10th ed.; Cengage: Boston, MA, 2017. ISBN 978-1-305-95740-4.


texts: NaHCO3 required to raise pH of weak HCl solution from 3.5 to 7.2 (doubting my calculations)

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I'm a dentist, working on a medical device that will make shots at the dentist office hurt a lot less. The device mixes a drug (2% Lidocaine) that has been acidified with $\ce{HCl}$ to pH 3.5 for storage, with $\ce{NaHCO3}$ to bring it to physiological pH (about 7.2) just prior to injection.

The current method is by manually mixing an 8.4% $\ce{NaHCO3}$ solution with the drug in a 1:9 ratio V/V. In medicine, an 8.4% solution typically means 84mg of drug / ml of solution. So, the current protocol of mixing 100 ml of bicarb solution with 900 ml of drug solution, means the doctors are delivering 8400mg of $\ce{NaHCO3}$ /L , which is a LOT more than the 27mg that my current calculations (please see below, and please let me know if I'm off on the wrong track) say they need to do the job. You can see why I was (and am) skeptical of my calculations.

Assuming the calculations below are correct, then the next problem is:

If I want to deliver the $\ce{NaHCO3}$ in the form of a fluid (whether a solution, slurry, or any other way to make it flow), what is the best way to do that, and how much $\ce{NaHCO3}$ can I fit into a vessel with volume of 35 cubic millimeters (pretty small, and all the room I have available in my device)? In other words, what is the maximum concentration of $\ce{NaHCO3}$ that will stay in solution at a standard temperature and pressure with no head space in the vessel? Or, can I make a slurry that will hold an even higher concentration that remains fluid, and what would that concentration be? I only need to fit 27mg/L x 2ml = 0.054mg of $\ce{NaHCO3}$ into the space, and it would be a lot easier to manufacture if it were a liquid rather than a powder.

Also, I'm in need of some physical testing of the device to confirm that mixing has properly occurred at the tip of the needle when the prototype is built in a few weeks. There is some thought that we could use excess $\ce{NaHCO3}$ in a chamber, and have bypass mixing occur as the drug passes through the chamber and into the needle, instead of trying to get the whole volume (2ml) mixed prior to moving any drug out of the needle. If there is someone on here that might be interested in performing those validation experiments to help pass FDA gates, then please let me know how to find you. Thanks, Scott

The chemical reaction: $\ce{HCl + NaHCO3 → NaCl (aq) + CO2(g) + H2O(l)}$

The initial hydrogen ion concentration is: (pH = 3.5) [H+]i = 10-3.5 = $\pu{3.16228 x 10^-4 M}$

The required final hydrogen ion concentration is: (pH = 7.2) [H+]f = 10-7.2 = $\pu{6.309573 x 10^-8 M}$

moles $\ce{H+}$ reacted = moles of $\ce{HCl}$ reacted = $(\pu{3.16228 x 10^−4} − \pu{6.309573 x 10^−8}) = \pu{3.1616467 x 10^−4 mol}~\ce{HCl}$

moles of $\ce{NaHCO3}$ required = moles $\ce{HCl}$ reacted = $\pu{3.1616467 x 10^−4 moles}$

mass of $\ce{NaHCO3}$ required = $\pu{3.1616467 x 10^−4 moles}~\ce{NaHCO3} \times \pu{84g}~\ce{NaHCO3} / \pu{1 mole}~\ce{NaHCO3} = \pu{0.027 grams￼}$


texts: Understanding how electrons are counted for lone pairs vs. bonds especially when understanding resonance?

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This is taken from the book Organic Chemistry as a Second Language from page 35.
In the following image:

It is seen that when the electrons from the double bond are pushed into the lone pair electrons, we get 2 electrons as a lone pair.  And when a lone pair electrons are pushed to from a double bond we remove 2 electrons from the oxygen.
The part that confuses me is how the electrons are being counted (especially for octet rule). Let's take the example of oxygen that starts out double bonded (the molecule left of the double headed arrows) and then the double bond electrons get pushed into a lone pair (Oxygen on the right of the double headed arrow with a formal charge of 1).  If I count the first oxygen (double bonded oxygen to the left of the double headed arrow), I get 6 electrons where the double bond counts as 1 electron for each bond, now if I go to the right of the arrow I see that same oxygen I count 7 electrons.  How can a lone pair which is made up of 2 electrons result as being counted as 1 electron when it becomes part of a bond or vice versa?


texts: What's the purpose of an ice bath when preparing a nitration mix from KNO3?

texts: Most preparations for nitrocellulose from $\ce{(KNO3 + H2SO4)}$ mixture require the use of an ice bath during the process of dissolving $\ce{KNO3}$ into $\ce{H2SO4}$. Last time I did this I omitted this step and the nitrocellulose turned out to be of very low quality, but there's a number of other possible causes I can think of. Therefore, for the sake of troubleshooting I have this question: What is the purpose of an ice bath during this step? Is it to just limit the fuming, or does omitting it lead to decomposition of $\ce{HNO3}$ significant enough to impact the yield? I did not see any brown $\ce{NO2}$ fumes coming out, just the typical white mist of acid.


texts:
Question 1:

A compound A reacts according to the following hypothetical equation and has a molecular weight of 48.36 g/mol.

3 A (s) +B (aq) ––> 2 C (aq) ∆H° = ?

A sample of A, weighing 0.152 g reacts in a flask containing 250.00 g of water and the water temperature increases from 24.85 °C to a temperature of 26.26 °C. Calculate ∆H° for the reaction as written in the equation.

Answer: -1408 kJ

Question 2:

For which of the following reactions is ∆H° = ∆H°f, the heat of formation?

i. C (s) + 2 F2(g) ––> CF4 (g) ∆H° = – 221.0 kJ
ii. H(g) + Br (g) ––> HBr (g) ∆H° = –366.2 kJ
iii. 2 C(s) + H2(g) + 3 Cl2(g) ––> 2 CHCl3 (g) ∆H° = –268.2

Answer: i only

Also, could someone explain exactly what delta H means in terms of Thermochemistry. I would like to have a better understanding of it.

Thank you very much!  :)

For the first question I attempted to use the q=m x s x (delta) T for the water and I attempted to use stochiometry for substance A but I always receive the wrong answer. Could someone help me on where to start with these types of problems?

Water calculation:

(250) x (4.184) x (26.26-24.85)

= 1474.86 kJ


texts: Is there a reusable and safe exothermic reaction

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I am looking for an alternative to the sodium acetate reaction used in e.g. heat packs. I need something similiar but that generates more heat, so that I could for instance warm 200ml of water to a temperature of 37 °C.
So is their any safe and reusable reaction as used in heat packs but that generates more heat?
NOTE: I am a beginner when it comes to chemistry.


texts: Calculating the equilibrium constants for parallel reactions

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So, I am attempting to calculate the equilibrium constant for two separate reactions.
$$\ce{A + B<=>C + D}$$
$$\ce{A + B <=> C + E}$$
I have figured out the final pressures at equilibrium for $\ce{A}$, $\ce{B}$, $\ce{C}$, $\ce{D}$, and $\ce{E}$.
I was wondering if the equilibrium constant is calculated as normal using just the final pressures and molar ratios in the equations, or if the final pressures have to be adjusted somehow to compensate for the fact that the second reaction is also consuming the same products and producing one of the same reactants.


texts: Conversion of oxalic acid to malonic acid

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The reagents I have used here are $\ce{LiAlH_4}$ which reduces the carboxylic groups into alcohol.Used $\ce{HIO_4}$ which breaks up the molecule into methanal. Then  I applied Grignard reagent which consisted ethyl for the alkyl part.Then I tried to oxide the terminal carbon into $\ce{COOH}$  but could not find a suitable reagent.

What is a better approach and a method to solve this question.


texts: Lowering the melting point of water with salt

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I was trying to calculate amount of salt needed to lower the melting point of water by 5 °C. According to my solutions, I need to make sure $$n\mu(\ce{H2O(s)}) =n\mu(\ce{H2O(l)})+ RT\log(x)$$where $ x=\frac{n}{n+2m}$

I, however, thought that I need to make sure that

$$n\mu(\ce{H2O(s)})+m\mu(\ce{NaCl(s)}) =n\mu(\ce{H2O(l)})+m\mu(\ce{NaCl(aq)})$$

After all, the solid ice still has a certain contribution. And I would have assumed that water can be seen as the solved according to the first convention? So why don't we need to consider the solid ice, and what is wrong with my way of thinking?


texts: Measure low DOM absorbance values in a microplate reader. Is there a suitable deep well microplate with flat bottoms available?

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I would like to use a microplate reader to measure the absorbance of dissolved organic matter (DOM), but the measured values are close to the lower detection limit. To overcome this, I thought of deep well plates as the pathlength is longer then. Nevertheless, I have not found any deep well plates with flat bottoms, which might be best for absorbance measurements. I want to avoid measuring in a photometer with 5 cm pathlength because the available amount of sample is limited and the microplate would need much less.

Does anybody have experience with similar problems?

Can anyone suggest a suitable microplate?

What is your opinion on the influence of the material?


texts: Converting Lactic Acid to Potassium Lactate

texts: I am looking to try an experiment incorporating potassium lactate into soap making. This seems to be new territory for soap makers in that sodium lactate is usually used. I found a bottle of "Lactic Acid 88%" at a beer making supplier and already have 90% potassium hydroxide but do not know how much of one is needed to neutralize the other. Can anyone point me to the right tables or resources to do the calculations?


texts:
In an exercise, I have derived that

$$\mathrm dS_\mathrm{m} = \frac{3R}{2T}\mathrm dT + \frac{R}{V}\mathrm dV$$

using the 1st and 2nd law of thermodynamics (1 mol ideal gas).

Now, I want to write $\mathrm dS$ as a function of $T$ and $P$ instead of $T$ and $V$. How can I do that?

I have tried to do this:

$$\frac{R}{V} = \frac{P}{T}$$

and

$$\mathrm dV = \frac{\mathrm dV}{\mathrm dP}\mathrm dP = -\frac{RT}{P^2}\mathrm dP$$

This gives me

$$\frac{R}{V}\mathrm dV = -\frac{R}{P}\mathrm dP,$$

which is wrong according to my T.A.

How can I write $\mathrm dS$ as a function of $T$ and $P$?


texts: Could I get a hint on the structure of this molecule based on HNMR spectra?

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Chemical formula is $\ce{C7H6O3}$. The IR spectrum has a peak at $\pu{3238 cm-1}$, which I believe could be due to an alcohol, phenol, or carboxylic acid. There's an additional peak at  $\pu{3015 cm-1}$, which I believe is due to either an alkene or aromatic group. The presence of aromatic and phenol peaks makes me think there's a phenol group in this compound.

What I'm stuck on are the four protons in the 7-8 ppm range. Especially the one split into a quartet. If I'm right about the IR, I just can't think of a way to get one proton with three neighbors to split with in a phenol.


texts: How to determine if a compound is likely to become a solid at room temperature?

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Reasoning: My guess would have to be that it has to do with the strength of the intermolecular forces between each molecule. For example, molecular compounds that have a very low molar mass like $\ce{CO}$ and $\ce{CH4}$. Both of theses molecules have a very small molar mass, a very low London dispersion force, and thus a very low boiling point. This in turns makes it easier to break the bonds that hold each individual atom and more than likely cause them to turn into a gas in normal conditions.

Then when you look at ionic compounds like $\ce{MgCl2}$ and $\ce{NaCl}$, it is more likely for these compounds to become solid because of the strong intermolecular force that they have (ionic bonds).

Is my reasoning correct and is there something else that I should consider?


texts: Does it make a difference in energy if a reaction is done in many steps or in one step?

texts: I am particularly interested in knowing about glucose breakdown. If we artificially burn glucose, will the energy released be the same if it is broken down in steps(like in a living cell)?


texts: Detecting trash (plastic) burning smoke with sensors

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I’m not a chemist, but a software engineer. I’m trying to build a device that could detect if someone is burning trash (mostly plastics and similar materials) vs wood or diesel. At my disposal I have the following sensors: https://www.mysensors.org/build/gas

What sensor or combination of them would be most reliable to detect smoke resulting from burning illegal waste?


texts: Lithography: Is isopropanol a developer and/or a stopper?

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In the ebeam lithography with PMMA resists isopropanol is often used in a mixture 3:1 (IPA:MIBK) as a developer solution. To my knowledge the developing process is usually stopped by putting the sample in distilled water and drying it with a nitrogen airgun. But I also see collegeaus who use the 3:1 mixture for developing and then "stop" the development in pure IPA. I actually think they develop further, as I know some people also use pure IPA instead of 3:1 mixture for developing.

What am I missing, I know there many different recipes in lithography, but this IPA thing doesn't make sense to me, using IPA as a stopper means to me the developing process is strengthened further and the resist isotropically resolved, which you normally want to avoid with kind of written sharp edged rectangular structures written by ebeam


texts: Fireplace window: Can one influence how fast soot is building up?

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I'm sorry for such a stupid question, but after googling for half an hour I know two things

There are at least a zillion pages, blog-posts and articles about how to keep your fireplace window clean or how to clean it.
There is not a single page which explains what I'm looking for and which doesn't make claims without supporting them with scientific facts.

Therefore, here the short form of my question: Assuming I have a fireplace with a window, which looks like this after a while:

Further assume I'm able to keep all other factors constant (like type of wood, temperature of the fire etc.), is there something I can apply/do to the cleaned window to prevent the building of soot for a longer time?

The reason I'm asking is this article I stumbled over, which claims that normal corn-starch can be used to fill the pores of the glass. This left me with more questions

does each glass (especially my one) have pores with a size that starch particles can fit in? I read somewhere that starch has a diameter between 2-170 µm depending on the type.
I'm making a fire where I burn wood! Why wouldn't the starch simply burn and create itself the soot?
As we know for a while now making a surface really smooth doesn't mean it keeps clean. With a size of 10-20 µm of the lotus papillae, it seems to fall in the same range as starch.

And for the diligent, here two more sub-questions:

How does soot building work? I mean, why does the soot stick so hard at the window? After all it's just little particles flowing around and landing on the window. (I know it's called burning in, but how does the heat work on a already burned particle?)
Is there some connection to the pores (if any) in the glass in this process?

Update
After using my fireplace one winter, I'd like to make recommendation based on my experience so far. Important is that I can easily remove the window from my fireplace for cleaning. In case the window is fixed, cleaning might become a bit messy. Let me bring it down to 3 tips:

My current method is to use a cleaner for ceramic glass cooktops. This works like a charm. In case someone wants to know the specific product: it's a cleaning stone for class ceramic which is probably only available in Germany but I guess something similar can be found all around the world. This thing comes with a sponge and you just have to rub the wet sponge a few times over the cleaner to apply some. Cleaning the window with this is done in less than a minute, even if there is a lot of soot.

If you don't want to invest any money, the most simple and very effective cleaning method is to use the ash itself to scrub the window. Simply take water and a newspaper, if possible make the window itself wet or better rinse it with water. Take a sheet of newspaper, make it wet and apply ash directly from the fireplace itself. It's really surprising how easily the soot can be scrubbed away with this method.

Last tip: Heat! As already said in the accepted answer, soot is basically the deposition of incomplete combustion products from a flame. There is no doubt and I have tested this very often: a dirty window can partially be cleaned by make a hot fire with very dry wood and a lot of air. Therefore, try to fill your fire-room with the maximum possible amount of wood, open all air-valves and let it burn for a while.


texts:
As I know, uranium and iron simply aren't mixable, which means there are no U-Fe alloys. The Google says, uranium is insoluble in molten iron.

But, if something is "insoluble", it actually means only that there is a very low maximal concentration.

What if we want to mix only 1ppm of U in molten Fe? What if 0.01 ppm? What is the maximal concentration?


texts: Why is this scintillator component turning into a milky-white emulsion?

texts:
I am a chemistry and physics double major doing some chemistry work in a nuclear physics lab. My mentor is a physicist, so his area of expertise is occasionally mismatched with what I need for my chemistry end of the project.

The scintillator fluid we use is commercially made, so I don't know all of the specific components, just that it is primarily diisopropylnapthalene (DIPN). I was trying to replace a LiCl emulsion (a standard scintillator cocktail component) with a lithium carboxylate.

I have tried dissolving my lithium salts into the scintillator, both the standard commercially-made one and a custom one that's the same composition but without the surfactants. Using only fractional molar concentrations (as low as 0.1-0.2 M) it turns milky. LiCl emulsions in our lab were stable between 1M to 10M, at least.

I know that water contamination can cause a milky emulsion to appear in oils. I think I used a strong enough desiccant to remove all the water, and I couldn't find -OH groups in IR spectra of my samples.

Could this be the O- parts of the carboxylates getting emulsified? Or something else? Why would my lithium carboxylates be milky but a LiCl emulsion not milky?

Any ideas would be great. I'm trying to understand the interactions going on here so I can either revise my methodology or choose new molecules to try. Thank you!

Edit: Given my UV-Vis data, the transmission was worse without the surfactants, which I think is because the surfactants made my carboxylates dissolve more easily. But I'm not sure if that has anything to do with the milky appearance.


texts: The differences between integrals evaluations of contracted an uncontracted basis functions

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I wanna to evaluate molecular integrals (overlap, kinetic and etc) using Gaussian basis functions. To do so, there are two approaches: contracted and uncontracted basis functions in which the former means the primitive Gaussian functions ($G_1$ and $G_2$) are summed to form contracted ones and finally by summing the contracted functions  ($\phi_1$ and $\phi_2$) using appropriate coefficients, the final molecular orbital is formed, for two contracted basis functions and three primitives we have:

$$
\psi=c_1\phi_1+c_2\phi_2
$$
$$
\phi_1=d_{11}G_{11}+d_{12}G_{12}+d_{13}G_{13}
$$
$$
\phi_2=d_{21}G_{21}+d_{22}G_{22}+d_{23}G_{23}
$$
$$
G_{11}=e^{-\alpha_{11}r^2}
$$
where the exponents are given as a 2x3 matrix (generally exponents matrix in contraction basis functions approach is a [number of electrons]x[number of primitive Gaussians] matrix and for uncontracted functions approache is a [number of electrons]x[number of basis functions] matrix).
In this way the final overlap matrix for example is

$$
\begin{bmatrix}
c_1c_1\phi_1\phi_1 && c_1c_2\phi_1\phi_2\\
c_2c_1\phi_2\phi_1 && c_2c_2\phi_2\phi_2\\
\end{bmatrix}
$$

For simulating total wave function using two uncontracted basis functions, we have

$$
\psi=c_1\phi_1+c_2\phi_2
$$
where it's not necessary to use any summation to obtain $\phi_1$ and $\phi_2$, instead we can construct them directly by knowing Gaussian exponents:

$$
\phi_1=e^{-\alpha_{11}r^2}
$$

Again the overlap matrix has a form like above matrix.

Are the mentioned explanations true? How should we apply these differences in a Mathematica code?


texts:
I want to create a small wind tunnel for testing of aerodynamics for Radio controlled units (Cars, planes and helicopters).

In real wind-tunnels water mists are used but water isn't a good thing for the electronics.

I have considered the following:

Smoke bombs, but the smoke develops too fast.
Burning stuff like laves or coal, but it creates odor, and i don't want my RC stuff to smell.
Incense, same as above.

My chemistry level is a College equivalent degree of chemistry that has been unused for 15 years.

And the materials to make this should be somewhat harmless, and legally available.

Any suggestions on how to do this would be highly appreciated.


texts: Detection of NaF levels in aqueous solution also containing NaCl

texts:
Is it possible to determine the concentration of sodium fluoride, more specifically fluoride ions, in a solution that also contains sodium chloride?
I have looked into using an ion-specific electrode, but this seems very expensive.


texts: What is heterogeneous catalysis in gas phase?

texts:
Give examples of heterogeneous catalysis (i) in gas phase and (ii) in liquid phase.

Now, I came to know that heterogeneous catalysis involves different phases between the catalyst used and the reactants. That way, either the catalyst can be in solid phase where the reactants can be in gas/liquid phase. But in the above question, what does "in gas phase" mean? Is it about the gas phase of the catalyst or the gas phase of the reactants?

Also, it would be of great help if you could provide me with examples of the above question.


texts: Why is the alpha particle called a particle when it is made of four particles?

texts:
We know the alpha particle is the nucleus of helium. It contains four subatomic particles - two protons and two neutrons. The protons and neutrons are further made of particles called up and down quarks. So why call an alpha particle a particle. And similarly, why do we say electrons, protons, neutrons etc. are particles, even though, they are made of particles?

I can understand the case of electrons, protons, and neutrons as when they were discovered and named, quarks were not discovered. But the helium nucleus is a different case.

I reckon talking about an English word's meaning changes in the frame of reference. We do not call a quark an object, although, an object could be any real or virtual thing. So in chemistry, I don't think calling an alpha particle a particle is a good practice. I do understand there are dust particles and all but we mention them only while talking about the macroscopic world. Not so in the case of chemistry. I hope you get my point.


texts:
I tried to make Rochelle's salt. It didn't work!

7 oz cream of tartar
1 cup distilled water
heat to 180 F and keep there
add 1/2 tsp sodium carbonate at a time until there is no fizzing
filter and let cool

The solution ended with a strong yellow/brown tint. It took at least an hour of adding sodium carbonate. While cooling it rapidly formed a crystallized honey look and that was it. I reheated and added more distilled water to lighten it up a bit thinking it needed to evaporate slower. This time when it cooled nothing happened.

The sodium carbonate was 100%, and the cream of tartar was McCormick. It's possible that came with some impurities hence the brown/yellow grossness.

Is there as way to save this batch? Should I just try again? Is there a better recipe?

My first instinct is that it didn't work because you don't science with Imperial units.


texts: Explaining a biochemical reaction (protein labelling, e.g. with fluorescent probes)

texts:
I am an immunology master student without prior knowledge of biochemistry.
Could someone explain to me the following 6 reactions?
What I want to understand is why exactly the reactions happen at this site ( in terms of donor/acceptor ).  What is the donor, what is the acceptor?


texts: Change in water vapor with change in pressure and volume

texts:
Given a closed (air tight) container (Volume $V_0$) held at the room temperature ($T_0$) and pressure ($P_0$). The container contains 100% saturated water vapor with no air (at $T_0$ and $P_0$).
Now assuming the container is compressible (say a balloon whose volume can be changed by applying uniform external force/pressure how does the water vapor inside the container change when we apply external pressure on its surface ($P_1$) and its volume changes ($V_1$).
Assuming the Ideal Gas Law I assume none of the water vapor would condensate with any such change in external pressure and volume or i am missing something?
Edit 1: the container contains no air and no liquid water either. Just water vapor at 100% saturation (whatever its value is at initial room temperature and pressure i.e. $T_0$ and $P_0$).


texts: What stops intermediates of alcohol hydration and dehydration reacting in the same way?

texts:
I am aware they both occur under different conditions and that water attaches in a secondary position in elimination but primary position in hydration.

(Stage 2)

(Stage 3)

But both appear to be the same intermediate, why exactly do different reactions follow this stage?


texts: Intermolecular forces in secondary amines compared to primary amines

texts:
Secondary amines form hydrogen bonds, but having nitrogen in the middle of the chain rather than at the end makes the permanent dipole on the molecule slightly less. The lower boiling point is due to the lower dipole-dipole attractions in the dimethylamine compared with ethylamine.

Could someone please tell me why nitrogen, being in the middle of the molecule (as in secondary amines) causes the permanent dipole to be slightly less.


texts: Methods used to compare two spectra in order to determine the effects of irradiation of sample

texts:
I would like to compare two absorption spectra (or interferograms) and conclude whether between these two there are statistically significant differences at particular wavelength intervals. At the moment, I have data of two experiments that look like this:
    # A tibble: 6 x 5
      t     x1     y1     x2     y2
  <dbl>  <dbl>  <dbl>  <dbl>  <dbl>
1 3999. 0.0124 0.0132 0.0122 0.0113
2 3998. 0.0125 0.0130 0.0122 0.0116
3 3997. 0.0122 0.0131 0.0122 0.0113
4 3996. 0.0121 0.0136 0.0122 0.0114
5 3995. 0.0124 0.0139 0.0122 0.0122
6 3994. 0.0125 0.0141 0.0122 0.0129

The first column represents the wavenumber, the x columns represent the absorbance of sample and the y columns represent the absorbance of irradiated sample (before and after).
I was wondering whether I could compare these data (x and y) as time series and if so, what could be the method to quantify the differences, if any, between the samples before and after irradiation. Maybe it's already been done and there is somewhere some information as to how to compare the spectra if the wavenumber is interpreted as time ($x$ axis).
I did the t-test in R and in both experiments the null hypothesis could not be rejected, although for the second experiment (x2, y2) the $p$ value was much lower than for the first. If I average the x and y, and then plot both data, I see that there are visible differences at certain wavelength intervals. But how can I check for sure the differences between spectrums?
Here is a project with similar experiments by Zezell et al. [1]. For statistical analysis they use ANOVA and Tukey's test, but how do I do it for the vectored data?
Reference

Zezell, D. M.; Benetti, C.; Veloso, M. N.; Castro, P. A. A.; Ana, P. A. FTIR Spectroscopy Revealing the Effects of Laser and Ionizing Radiation on Biological Hard Tissues. J. Braz. Chem. Soc 2015. DOI: 10.5935/0103-5053.20150246.


texts: Why are the two CH2 groups in allene perpendicular to each other?

texts: Allene, $\ce{H2C=C=CH2}$, has two $\ce{=CH2}$ groups perpendicular to each other. This is the same as hydrogen peroxide's $\ce{H}$ atoms. Is there any reason why they adopt the perpendicular arrangement, when the VSEPR model allows both the perpendicular and planar arrangements for the groups on the ends? I don't think it's a steric effect, because the hydrogen atoms/methylene groups are facing opposite directions and far apart.


texts: Calculating volume of a vessel using idea gas law

texts:
To an evacuated vessel with movable piston under external pressure of $\pu{1 atm},$ $\ce{0.1 mol}$ of $\ce{He}$ and $\pu{1 mol}$ of unknown compound (vapour pressure $\pu{0.68 atm}$ at $\pu{273 K})$ are introduced. Considering ideal gas behavior, calculate the total volume of 2 gases at $\pu{273 K}.$

Why can't I add the amounts of substance for helium and the unknown compound and directly use $PV=nRT?$ Why is the vapour pressure given?


texts: Expectation value of an observable in quantum system

texts:
In quantum systems, sometimes if the wave function is not an eigen value of an operator then it is expanded in terms of bases states, then we apply the operator over the bases states and we get different eigen values for an observable with different probabilities corresponding to the projection coefficients of the bases states.

  In a book, I read that after making a measurement we get an observation, and the probabilities of other observations shrink down to zero. The observation remains the same for howsoever times we make it after the measurement. Like if a coin is tossed, if we get head after first measurement it remains head, even if we make any number of observations.
  My question is that what is the need of expectation value of an observable (given by formula as summation of the product of probability associated with an observable and the eigen value of observable) as after measurement we get only one eigen value of the observable with 100% certainty. I think knowing only the possible values of the observable is sufficient. What is the significance of expectation value and then does the formula for expectation value given in books is for before the measurement?


texts: Why should I not use different battery types together?

texts:
Everyone knows about this but I'm curious about why one should never mix batteries of different types. By type I mean the same shape of the cell like AAA but with different chemical reactions and voltages inside.

Would it just mess up the voltage and the instrument that is operated with the battery? Or would it lead to unexpected reactions in the battery itself that could lead to leakage/explosion or other catastrophies?


texts:
The definition of dead time ($t_\mathrm m$) is mentioned as the time taken for elution of an unretained species. It is also mentioned that the retention time ($t_\mathrm r$) is sum of the time analyte spends in mobile ($t_\mathrm m$) and stationary phases ($t_\mathrm s$). But how can time spent by analyte in mobile phase be equal to the time required for an unretained species to pass through (dead time, $t_\mathrm m$)?

Both seems independent of each other. An analyte's time in the different phases is dependent on its affinity while the unretained species takes the same amount of time no matter what.

Please explain how they are same.


texts: Commonly, the empirical formula $\ce{N2O}$ refers to the molecule with structure $\ce{N\bond{~--}N\bond{~-}O}$.  Is the isomer $\ce{N-O-N}$ known to exist? I'm guessing it is significantly less stable than the NNO isomer, but that doesn't mean it's completely unknown.


texts: Liquid crystal structure: Equivalent effect of alkoxy group?

texts:
Consider a structure like this,

R - Cy - Cy - Ph - OR'

where Cy represents a cyclohexane ring, Ph is a phenyl ring, and R, OR' is alkyl group and oxygen bonded to different alkyl group.

If 2 linearly bonded fluorines on top of the phenyl ring are moved to either cyclohexane ring, do you get the same effect?
What "effect" means I'm not sure, but this is related to liquid crystals having  $\Delta\varepsilon=\varepsilon_{\parallel}-\varepsilon_{\perp}<0$.

My initial guess is that because cyclohexane rings have $\sigma\rightarrow\sigma^*$ transitions, resulting in lower birefringence $\Delta n=n_e-n_0$, the effect is the not the same. I'm also assuming the dipole will be different? This is an organic chemistry question but sort of physics related so i wasn't sure where to put this question.


texts:
What is the working principle that allows zeolites to be catalysts in hydrocracking?
Is it only their acidic ability to hold hydrogen and release to crack the oil?


texts:
I'm trying to find a program/algorithm/API that can find the equivalent atoms in a molecule when given a molecule (knowing the complete geometry with x, y and z coordinates, and bonds between the atoms). Equivalent in the sense that they show up as one peak in the NMR spectrum.

Example: I supply ethanol and the program needs to return that the three H's on one C are equivalent and that the two H's on the other C are also equivalent. So that my program knows that it should only have 3 (sets of) peaks in my NMR spectrum and not 6.


texts: What is the official file extension for SMILES and SMARTS files

texts: I want to know what is the officially used file extension for files containing SMILES and SMARTS strings. Somewhere I see .SMI/.SMA and somewhere its the full .SMILES/.SMARTS.


texts:
For an ideal gas, how can someone obtain this:

$$ \bar{V}dP = RdT- P \bar{dV}$$

from which it can de deducted, that for a constant temperature

$$ \frac{dP}{\bar{dV}} = -RT $$


texts: When we talk about the substance $\ce{H2O}$ with a molar mass of $\pu{18.0 g/mol}$, what hydrogen and oxygen isotopes are present in the $\ce{H2O}$ molecules? In other words, what isotopes do the symbols represent?


texts:
I took the $\mathrm{^{1}H}$-NMR (CDCl3 solvent) of my product, 2,2-dimethoxy acetic acid. Below is what I see:

  $\delta \: \pu{4.862 ppm}$ (1H), $\delta \: \pu{3.521 ppm}$ (6.78H), $\delta \: \pu{2.271 ppm}$ (5.39H)

Peaks at $\delta \: \pu{4.862 ppm}$ and $\delta \: \pu{3.521 ppm}$ indicate my product I believe, but I cannot rationalise a peak at $\delta \: \pu{2.271 ppm}$.

I did dry my organic phase over $\ce{Na2SO4}$ so this cannot be water. I have never really seen a broad singlet in 2-3 ppm region. Does anyone have any idea what this would be? Would appreciate any thoughts&ideas.


texts: Identify the type of structural isomerism

texts:
Question:

My Approach:

Since both the compounds have the same principal functional group, they can't be functional isomers. Obviously they are different compounds. Now options A and C are ruled out. Further the substituent ketone in first compound and aldehyde in the second compound have the same locant, so the given compounds cannot be positional isomers. So the compounds must be Chain Isomers. Further, we can just say, as there is difference in the chain length, the compounds are chain isomers. But the answer is incorrect.

The solution in my book, for this problem states, since compounds have different functional groups ketone in first compound and aldehyde in the second compound, they are functional isomers.

Now, I am totally confused. Please explain how to attend this question. Is the solution incorrect?


texts: Why can the anion NO3- behave as a L-type ligand while BF3 can not?

texts: The fluorine has a lone pair, and the oxygen has a lone pair. Both are donate-able, so they should both act as ligands. I know fluorine is more electronegative, but oxygen is quite electronegative itself, so the reason must lie somewhere else.


texts:
Can you reflux without any problems/dangers with a tilted condenser (e.g. because you don't have enough space in your fumehood)? I would say there isn't a problem, because both the surface area of the refluxed liquid and the length of the condenser (and thus the length of the trajectory of the water flowing through the condenser) remain unchanged. Is this thought correct?

This is my current setup

Also you should use countercurrent exchange right?


texts:
Sulfur is a diamagnetic element, meaning that it has no unpaired electrons. But its electronic configuration for valence shell is just like oxygen because they are in the same group i.e ns2, np4.

My question is that why is sulfur diamagnetic? If there are 4 electrons in p-orbital of its valence shell then shouldn't it have 2 unpaired electrons?


texts: In nuclear chemistry, how does a neutron split to form a proton and an electron?

texts:
I'm studying radioisotopes at the moment and balancing nuclear reactions isn't making sense in that more matter is coming out of the equation in negative β⁻ decay equations:

$$\ce{_6^{14}C -> _7^{14}N + e- + \bar{\nu_e}}$$

Notice how the original element has decayed into a new element with an unchanged mass number but an atomic number that has increased by one.

In positive β⁺ decay equations, it makes sense:

$$\ce{_{12}^{23}Mg -> _{11}^{23}Na + e+ + \nu_e}$$

How can you create something with the same mass but with another proton?


texts:
Why does blood take on such a colour after a couple of hours?

Is this the iron in my blood being oxidised to iron (III) oxide or is this something else?

I have checked this article, and no I do not find a definite answer to my question. I want to learn about the chemistry behind this change in colour of blood from bright red to brown. thanks


texts: How is it possible that meta xylene exists?

texts:
Methyl group is ortho para directing so it should direct the
 second methyl group to ortho or para position giving rise to ortho or para xylene but how can meta xylene be formed?


texts: You are running an ICP-MS (Inductively coupled plasma mass spectrometry), with bracketing standards of 10 ppm(mg/L) K+ and 100 ppm K+ and sample of 500 ppm, prepared 5 mL diluted to 100 mL. Shouldn’t you adjust your upper limit bracketing standard, instead of just diluting your sample? Your original sample concentration of K+ (500 ppm) should not change adjusted for the dilution factor. What am I not understanding mathematically?


texts: Attack of HClO4 to dipropylcycloprop-2-en-1-one

texts:
What are the products when $\ce{HClO4}$ attacks this compound?

I expect $\ce{HClO4}$ to protonate the ketone, forming an (aromatic?) carbocation. I don't know where to go from here.
Answer suggests formation of butanoic acid and production of $\ce{CO2}$. Unsure what really happens here. All hints appreciated.

This question appeared in the JEE 1997.


texts:
I understand that you can react enantiomers with a chiral molecule to resolve the enantiomers of interest into diastereomers.

However I do not understand how exactly the added chiral molecule can make the enantiomers of interest into diastereomers.

Can someone please explain the process/mechanism ?

For example: here is a picture from my textbook.

How are those two salts Diastereomers, even though they are mirror images of each other.


texts: How much does oxygen enrichment improve some combustion engines?

texts:
This question is about how much the combustion efficiency increases with oxygen enrichment in modern combustion engine designs. A desirable way to answer is to give the fuel efficiency dependency on oxygen percentage of air volume intake.
Some clues can maybe be had from

Engineering Science and Technology,
Volume 19, Issue 1, March 2016, Pages 438-443
Effects of oxygen enriched combustion on pollution and performance characteristics of a diesel engine  P.Baskar, A.Senthilkumar

and

THE EFFECT OF OXYGEN-ENRICHED AIR ON THE PERFORMANCE AND
EXHAUST EMISSIONS OF INTERNAL COMBUSTION ENGINES
,VARADARAJA SETTY, B.E.
MASTER THESIS
IN
MECHANICAL ENGINEERING
, Texas Tech University

Reports like the following are less interesting, since spark timing is the regulating mechanism with increased oxygen levels. Spark timing techniques are considered outmoded.

J.X. Zhou, B. Moreau, Christine Mounaïm-Rousselle, Fabrice Foucher. Combustion, Performance
and Emission Analysis of an Oxygen-Controlling Downsized SI Engine. Oil & Gas Science and
Technology - Revue d’IFP Energies nouvelles, Institut Français du Pétrole, 2016, 71 (4), pp.49.
ff10.2516/ogst/2015035ff. ffhal-01597165f


texts:
I was testing an organic dye for nitrogen today in lab.

First I added powdered ferrous  sulfate (.2 g) and the mixture gave prussian blue precipitate. Then I boiled and cooled it. When I acidified the mixture using diluted sulfuric acid, the mixture cleared and only a few small blue crystals remained, when there should've been a bluish-green precipitate, ensuring the presence of nitrogen(organic dyes should contain nitrogen).

Where did it go wrong?


texts:
In which of the following processes is energy transferred into the substance by work ($w > 0$)?

  a) Expansion of a gas against the surroundings
  b) Expansion of a gas into a vacuum
  c) Vaporization of one mole of water at 50˚C in an open container
  d) Melting of 100 g of ice on a laboratory benchtop
  e) Combustion of methane in a constant volume container.

The correct answer is given as (d), but I needed to find a physicist to explain it to me.  This problem can being thought of entirely in terms of thermodynamic work.

So, we know that
$$w = P \Delta V.$$

From this, we see that no work is done in (b) and (e).  Also, since the gas expanded against its surroundings, it did work on its surroundings, which isn't what the question asked, thus (a) is not the correct answer.

Now, although (c) appears to be a heat transfer, and it is, there is a little more going on.  The heat that was given to the water is converted into work as the water vaporizes, this causes a volume expansion (the gas rising).  Intuitively, one can think of the surroundings as a tube with a movable piston.  When vaporizing, the water vapor will push against the piston, increasing the pressure and thus the piston will move, causing the water to do work.

The last choice is (d), the correct answer, but there is also an intuitive way to think about this.  As the ice is heated, it melts (this process is also, as we correctly deduced, a heat transfer), however, this heat also causes the surrounding atmosphere to do work on the ice.

Again, think of a tube with a movable piston with a cube of ice that is slowly melting in the presence of normal air.  As the ice melts, the volume will decrease, and thus the nitrogen and oxygen molecules in the air have more space to move about, decreasing the pressure, which causes the piston to move down, thus doing work upon the ice.

Hopefully this makes sense to everyone who has been either watching or contributing to this discussion.

Unfortunately, I don't know what the authors of this question had in mind. This came up as I was working through an old Chemistry GRE exam. It wouldn't have occurred to me to consider this problem through mechanical work. As a side note, only 18% of the people who answered this question got it right, which essentially means that people just guessed the answer.


texts: Change in inductive effect of a susbstituent when -R group replaces -H atom

texts:
There are several examples where the negative inductive effect of a substituent gets increased when a hydrogen atom on that substituent is replaced by an alkyl group.

Some particular examples:

$$\ce{-NR3+} > \ce{-NH3+} \qquad \ce{-OR} > \ce{-OH}$$

I don't understand why it should be that way, as an alkyl group shows more positive inductive effect than a hydrogen atom which should, in turn, reduce the negative inductive effect of the substituent.

The answer here gives the reason that a carbon atom is more electronegative than a hydrogen atom and hence it should increase the −I effect (the answer also talks about bond length but I think it's irrelevant to mention that). But wouldn't the inductive effect shown by the whole group be a better parameter than the electronegativity of its primary atom to judge its electron withdrawing/donating ability?

Then there are also examples where replacing hydrogen atom by an alkyl group reduces the negative inductive effect of the substituent, as with $\ce{-CHO}$ and $\ce{-CRO}$ groups. I would usually explain it using the +I effects of $\ce{-R}$ and $\ce{-H}$ groups, but since that logic doesn't hold for the previous case, there should be some other reason for it.

So my question is: How does replacing an H atom in a substituent by an alkyl group affect the inductive effect of the substituent?

P.S. There is a related question, but it is too specific and does not have an answer to my question.


texts: Should chemistry students worry about quarks and such?

texts: Even chemistry textbooks less than five years old start by describing atomic structure based only on protons, neutrons and electrons. Is an understanding of chemistry fundamentals likely to become out of date when the textbooks start to include quarks, leptons and the dozens of other sub-atomic particles?


texts:
Liebig's blue devil or the "barking dog" reaction is the gas phase oxidation of carbon disulfide with either nitrous oxide or nitric oxide.

What are the gas phase reaction steps in this reaction, I would like to know the nature of the reactive species and the mechanism of the reaction steps. If you can give me literature references to support your answer it would be much better.barking dog reaction


texts: Why does potassium dichromate always reacts in an acidic medium?

texts: On the other hand, potassium manganate reacts in both acidic and alkaline media.


texts: Creating Boric Acid from Borax and Hydrochloric Acid

texts:
I'm working on an experiment in school and I need to create 200 mL of 2 mol/L boric acid. According to a formula I found on wikipedia, boric acid can be created with a reaction with hydrochloric acid.

  $$\ce{Na2B4O7·10H2O + 2 HCl -> 4 H3BO3 + 2 NaCl + 5 H2O}$$

So to calculate the amount of moles of boric acid needed, I multiplied the volume with the concentration to get 0.4 mol. After using the molar ratios in the equation, the molar mass of borax decahydrate and the concentration of HCl, I calculated that I would need 38.14 g of borax and 33.56 mL of 5.96 mol/L HCl in order for a complete reaction.

After mixing these together, I ended up with about 40 mL of a really thick solution, which is not the intended 200 mL. What did I do wrong and how do I actually create boric acid of this volume and concentration? Am I missing steps in between?


texts: How does the "methylamine test for sugars" work exactly?

texts:
There is a test that enables distinction of sugars between mono- and oligosachharides.
It consists letting methylamine react with an aqueous solution of the sugar under alkalic conditions and elevated (~70°) temperature.
Monosachharides always produce a yellow color; reducing oligosaccharides a red one and nonreducing sugars no coloration.

I wondered how this reaction works and of what "kind"/structure the resulting dyes might be.


texts: What would be the product of following elimination reaction?

texts:
Question

Doubt

The answer is given B. But why cant it be C after all formation of cyclopropane would increase angle strain?


texts: Reason for no change in electrode potential in reference electrodes

texts:
Reference electrodes such as the saturated calomel electrode and silver chloride electrode have a constant potential because the $\ce{Cl-}$ concentration (or, to be more precise, the activity) is constant.
The semi-reaction for those electrodes are:
$$\ce{Hg2Cl2 + 2e- <=> 2Hg + 2Cl-}$$
$$\ce{AgCl + e- <=> Ag + Cl-}$$
Now, since chloride ions are produced (or consumed, when the electrode is an anode) from the half-reactions, how is it possible that their concentration remains constant?
Is the quantity of chloride produced or consumed is negligible compared to that coming from the $\ce{KCl}$ dissociation?


texts: What is the result of the combustion of the mixture?

texts:
I prepared a little experiment about solid rocket propulsion. I have used water ($H_{2}O$), potassium nitrate ($KNO_{3}$) and saccharose ($C_{12}H_{22}O_{11}$).

I made the mixture in a pan by cooking it. I put 100ml of water into the pan. Then I added 50g of potassium nitrate and 100g of saccharose at the same time when the water boiled up. I started to mix it using a spoon and it took like 35-40 minutes to water evoporation. After the cooking there is only a mixture of dough consistency solid left. It had a light-yellow colour.

When the mixture got cold I wanted to test it. I took a little piece of it and then start the fire, it burned like firewoek.

I wonder the equation of the mixture after it mixed. I mean,

$$KNO_{3}(s) + C_{12}H_{22}O_{11}(s) + H_{2}O(l) \rightarrow \dots \text{(Result 1)(s)}$$

And the after burn result of the combustion.

$$\text{(Result 1)(s)} + heat \rightarrow \dots \text{(Result 2)}$$

I hope I gave you enough informations about the mixture and combustion.


texts: Is there anything in the literature that supports revolutionary claims for this "new" sulfuric-acid battery?

texts:
I've got the following from a supposed new energy-storage technologist. It's supposed to be a fancy new cheap, high-powered, highly scalable battery. I want to know if this is known chemistry, and if there's anything genuinely revolutionary about it:

  "Basic materials in MEG's E-SOURCE™ power cells are lead metal, absorptive glass mat paper, and sulfuric acid solution. Materials unique to the MEG advanced power cell are S2 glass fiber yarn; sodium sulfate; Teflon emulsion, glass-filled polypropylene; bituminous, petroleum-based wax; and metal-free nano-oxides. "

The lead is apparently in the form of lead oxide.

The claim is that this is a radical new cheap energy-storage system - but someone makes that claim for yet another technology every week or two. Is there anything in the recent literature that would give credibility to this one?


texts: How can I check if this mystery compound is strontium bromide?

texts:
Trying to identify a mystery compound, here are some of my notes, I'm trying to get a second opinion on what it might be!
Observations
Appears as a white powder, some chunks are formed, sticking to side of tube slightly
Solubility
3 drops of distilled water, all of substance dissolved
Flame Test
Red Flame
Sodium Hydroxide Test
A white ppt was formed when mystery liquid was combined with sodium hydroxide
Concentrated sulfuric acid test
A yellow colored gas formed when 4 drops of sulfuric acid were added with substance in test tube
My thoughts based on these results narrow the cation down to lithium and strontium. After performing a precipitate test again with my two knowns (lithium, strontium)strontium was the only one to form a ppt. So I'm almost 100% sure that my cation is strontium.
I have the anion narrowed down to bromide, nitrate, and nitrite. It has to be one of those three! I'm leaning towards bromide as the anion, just interested on what you guys think from my notes.
Here are the options again, with my choice in bold:
Cation

Lithium
Strontium

Anion

Bromide ?
Nitrate
Nitrite
Iodine

To summarize:
I have a book with 16 possible cations, and 11 possible anions. Based on my results and the information given in the book, I've narrowed it down to 2 cations, lithium, and strontium, and 3 possibly 4 anions. I'm almost certain the cation is strontium, based on the fact that it formed the same white ppt. that the mystery substance did when mixed with sodium hydroxide. Lithium did not. As for the anion, I'm not sure, I'm leaning towards bromide, but was looking for a second opinion. I've been doing some research on how bromide reacts with sulfuric acid, and the results online have been almost identical to what happened with the unknown substance, however in my option book it says bromide and nitrate have very similar reactions.
If you have any more thoughts on how I could identify to anion, please let me know!


texts:
If 4-hydroxy-3-methoxybenzaldehyde undergoes Clemmensen reduction, will the hydroxyl group (OH) be converted to a chloro group (Cl)?

I know that it happens in cyclohexanes, and I am not sure if this is true for aromatic compounds as well.


texts: Why do Group 10 transition metals (and Cu) lose an S electron to fill the D shell?

texts: I don't understand why it varies between Group 10 metals (as with Palladium, Platinum and Darmstadtium) and Copper (Group 11). If each of Palladium, Platinum and Darmstadtium entirely filled the 3d/4d/5d shells then it would make more conceptual sense, but both Platinum and Darmstadtium still have +1/2 spin in the final 4d/5d shell.


texts: Why is the carbon atom omitted from the molecular formula?

texts:
In my chemistry textbook, the following reaction was given:

I have two questions related to the marked in orange boxes/parts of the image:

Why is the molecule symbolized by $\ce{(CH3)3Cl}$ instead of $\ce{(CH3)3CCl}$ or $\ce{C(CH3)3Cl}$? Why is the carbon atom omitted?
Why is the "inversion" molecule with a $\ce{CH2}$ instead of a $\ce{CH3}$ attached to it?

I would greatly appreciate an answer. This is high-school chemistry that I have just learned and I am a bit confused.

Thanks :)


texts: Why are diagonal arrows disallowed in Jablonski diagrams?

texts: My professor mentioned in one of our lectures that diagonal arrows in a Jablonski diagram are disallowed. As far as I know, horizontal arrows signify conservation of energy, while vertical arrows signify conservation of momentum. Is this true/connected to the issue?


texts: Calculate thr unit cell length of perovskite

texts:
In a ideal unit cell of perovskite $\ce{KMnF3}$ (closed packed with purely ionic bondings),  calculate the unit cell length:

radius:  $\ce{K}=1.7~$  $\ce{F}=1.2~$   $\ce{Mn}=0.8$

The structure

Green $\ce{K}$, red $\ce{F}$, blue $\ce{Mn}$. (ignore the sizes in the picture)

Am I going right by using the $\ce{F-K-F}$ diagonal length to calculate the cell length  using pytagroas, as the Mn diameter is to small and therefore the $\ce{Mn-F-Mn}$ will have some spacing on it and are not fully adjacent.

I would get unit cell length =4.101.   can somebody confirm this?

Just a bit confused as I have the radius of $\ce{Mn}$ but don't use it for calculation

Many Thanks


texts: Electrolysis of dilute and concentrated sodium chloride and the Nernst equation

texts:
Interested to know if there is a critical concentration at which $\ce{Cl-}$ will oxidise over $\ce{H2O}$ and if this can be determined using the Nernst equation.

That is, obviously if $[\ce{Cl-}]>3.0\ \mathrm{mol/l}$ then it will oxidise, but if $[\ce{Cl-}]<1.0\ \mathrm{mol/l}$ it will not, since

$$\begin{alignat}{2}
\ce{2H2O(l) \;&<=> 4H+(aq) + O2(g) +4e-}\quad&&E^\circ=-1.23\ \mathrm V\\[6pt]
\ce{2Cl- (aq) \;&<=> Cl2(g) + 2e-}\quad&&E^\circ=-1.36\ \mathrm V
\end{alignat}$$

However, in attempting to use the Nernst equation to determine the exact concentration at which $\ce{Cl-}$ will oxidise over $\ce{H2O}$, I get an obviously incorrect number,

$$\begin{align}
1.23\ \mathrm V&=E^\circ-\frac{2.569\times10^{-2}\ \mathrm V}{2}\ln\left( {\frac{\left[\ce{Cl- (aq)}\right]^2}{\left[\ce{Cl2(g)}\right]}}\right)\\
\frac{0.13\times2}{2.569\times10^{-2}}&=\ln\left[\ce{Cl- (aq)}\right]^2\\
\ln\left[\ce{Cl- (aq)}\right]&=\frac{0.13}{2.569\times10^{-2}}\\
\left[\ce{Cl- (aq)}\right]&=\mathrm e^\frac{0.13}{2.569\times10^{-2}}\\
&=157.643\gg3
\end{align}$$

In this above relationship, I have set the $E$ value to that of $\ce{H2O}$'s reduction potential to determine the concentration of chlorine ions required to get the same voltage. But obviously my number is too large!


texts: Fate of compounds after radioactive decay

texts: Let us say there is a $\ce{CO2}$ molecule containing $\ce{^{14}C}$ isotope. $\ce{^{14}C}$ undergoes decay to form $\ce{^{14}N}$. What happens to the molecule?Does it form $\ce{NO2}$? How are the electrons and bonds rearranged?


texts: What is the difference between Alkanes and Polymers?

texts:
As far as I understand, Polymers are long molecules made of smaller monomers which are Alkenes. But polymers don't have double bonds, so they are saturated. What is the difference between Alkanes and Polymers structures.

The first one is an Alkane, but if the chain was much longer, it would be structurally the same as the Polymer (Second image).


texts: How do electrolytes allow electrolysis to occur?

texts:
From what I know, when two electrodes are places in a electrolyte (say $\ce{H2SO4}$, which decomposes into $\ce{H}^{+}$ and $\ce{SO4}^{2-}$ in aqueous solution), the negative ion is attracted to the positive electrode and is oxidized while the cation is attracted to the negative electrode and is reduced.

This transfer of electrons from the negative electrode to the cation and from the anion to the positive electrode "completes" the circuit and electricity is conducted through the wire.

What I don't understand is how the electrolyte allows for the electrolysis of water, since the electrons are used in the redox reaction of the ions in the electrolyte in which water isn't even involved.


texts: Calculating the biological standard potential

texts:
I have an electrochemical cell with following overall reaction:
$$\ce{5 Sn^4+ + 2 Mn^2+ + 8 H2O <=> 5 Sn^2+ + 2 MnO4- + 16 H+}$$

I have defined the half reactions as:

$$
\begin{align}
\ce{Sn^2+ &-> Sn^4+ + 2 e-} \\
\ce{MnO4- + 8 H+ + 5 e- & -> Mn^2+ + 4 H2O}
\end{align}
$$

I have trouble calculating the biological standard electrochemical potential. This is what I've tried:

The standard potential can be found from tables:

$$E^\circ = \pu{1.51 V} - \pu{0.15 V} = \pu{1.36 V}$$

Then I use Nernst equation in which all species except $\ce{H+}$ are in their standard states, so their activities are all equal to $1:$

$$
\begin{align}
E &= E^\circ - \frac{RT}{vF}\ln(10)\cdot \mathrm{pH} \\
  &= \pu{1.36 V} - \frac{\pu{8.314 J mol-1 K-1} × \pu{298.15 K}}{10 × \pu{96485 C mol-1}}\ln(10) × 7 \\
  &= \pu{1.31 V},
\end{align}
$$

which is wrong. Is there something wrong with the calculations or the understanding?


texts: Determination of carbon content of steel by liquid chemistry

texts:
It seems like the typical laboratory methods for determining the carbon content of steel are to cuppellate it in a stream of oxygen and then measure the volume of the evolved $\ce{CO}$ and $\ce{CO2}$, which involves many high-temperature complexities.

Why can't the carbon content of steel be measured by dissolving it in acid and reacting out the carbon at low temperature?


texts:
Why does acetone evaporate faster than ethanol yet still has a higher surface tension?

I would expect it to have a lower surface tension... I got the data from surface-tension.de.


texts: Question about reactions that are always spontaneous and non spontaneous

texts:
I wanted to ask for examples of spontaneous chemical reactions meaning that their enthalpy would be negative (exothermic) and their variation of entropy would increase, therefore the Gibbs energy would be also negative and the reactions would be spontaneous at all temperatures (?).

I was thinking about the boiling of water as the reaction feels hot and the entropy change is positive as it goes from liquid to gas (entropy increases) but then I thought that to do that, we need an external energy and so the reaction would be non-spontaneous?

Another one could be dropping mentos into a carbonated drink. I can be sure that the reaction doesn't requiere an external force to happen BUT the reaction itself doesn't feel hot (I think I saw it once when they did it in primary school but I'm assuming it isn't releasing any heat?)

I know that when enthalpy is negative and entropy is negative, it would only be spontaneous if the temperature was low enough.

For the non spontaneous reactions, I can't really think about one that has positive enthalpy and negative entropy. I CAN think of a reaction that needs a push to "occur" like taking off a stain of a shirt or even a reaction of decomposition of water into h2 and o2.

I think I'm getting something wrong.


texts:
What would be the dissociation of Hydrosulfuric acid in the presence of water?

I was thinking that Hydrosulfuric acid or $\ce{H2S}_{(aq)}$ would form $\ce{2 H+}$ and Sulfur ions.

With this logic, I keep getting the wrong answer :(

The right answer of this question is it would not dissociate at all.

Shall appreciate some help on explaining this. Thanks!


texts: What is "dot" sign in •NO? I know that it is radical nitric oxide, but I don't know if it is necessary to put the "dot". Is there any difference between •NO and NO?


texts:
Polymorphism is defined as the ability of a solid material to exist in more than one form or crystal structure, whereas allotropy is defined as the property of some chemical elements to exist in two or more different forms, in the same physical state, known as allotropes of these elements. (From wikipedia).

In the case of crystal solids, it seems clear that allotropy is a particular case of polymorphism... but this is always true? That is, both terms, polymorphism and allotropy refer always to crystal structures? Polymorphism definition mentions "crystal structures" but "crystal" does not appears in the definition of allotropy...

Thanks in advance.

UPDATE
Thank you for your answer Then, in some cases allotropy is more general than polymorphism. For instance, dioxygen and ozone are allotropes but not polymorphisms. But... my question arises from my TRUE/FALSE set of questions which I have to answer, and one of them is:

  In a non-crystal material the concept of allotropy or polymorphism does not exist.

What would you answer to that? My conclusion is that the question is not clear... For polymorphism is true whereas for allotropy it is not.


texts: Removing chloride ions from humic acid purification

texts: I used HF and HCl in humic acid purification, and now I need to remove the Cl ions from solution. What should I do to remove the Cl ions? Do I just wash it with distilled water, or is there another procedure for this?


texts: What does bond polarity have to do with acid strength?

texts: Why does increasing bond polarity affect acid strength? For instance, why is $\ce{HF}$ a stronger acid than $\ce{CH4}$?


texts:
I have a square piece of metal from a processor heat sink that looks a lot like copper. I'm trying to find the alloy composition but I'm not sure how.

I happen to have both a digital caliper and a milligram-precision scale. The piece has a rectangular shape so volume wasn't hard to find. The volume is 5.378 cm³ and the mass is 52.395 g, that gives a density of 9,27 g/cm³. The density of copper is 8.96, nickel is 8.91, zinc is 7.14, lead is 11.34.

If I use this formula (which may be wrong):

$$p = a \cdot p_a + b \cdot p_b$$

$a$ being the volume fraction and $p$ the density. The density is higher than that of copper, this means there has to be a metal with a density higher than copper in the alloy, maybe lead? Using the formula I get 87 % copper and 13 % lead by mass, looks a bit too much.

Is this a good way to find the alloy or an alloy doesn't have a density or volume proportional to that of its components?


texts: Parameters by which to distinguish SN1 from E1

texts:
I am new to organic chemistry and am struggling with the following very basic question:

Given is the following reaction:

$$\ce{(CH3)3CCl + NH3(aq) →}$$

I am supposed to analyse the end-product (the temperature is not given). However, how do I determine whether this is $\mathrm{S_N1}$ or $\mathrm{E1}?$ I understand $\ce{NH3}$ is a weak nucleophile and that the carbon atom is tertiary, which together eliminate $\mathrm{S_N2}$ and $\mathrm{E2},$ but I was not given any other parameters with which to carry out the evaluation.

Obviously, the end-product will depend on whether the reaction is $\mathrm{S_N1}$ or $\mathrm{E1},$ so how do I establish which one of the two it will be?


texts: Order of second iozination energies of lithium,berillium,neon,carbon and boron?

texts:
The correct arrange of them is like this:

Be < B < Li ... But why?

Li will have the greatest IE2 (second ionization energy) because that will involve removing a core electron, but what I am confused about is about Be and B.

I think Be will have greater IE2 than B, because B has 2 electrons in the same orbital, so the repulsive force between them will make it easier to remove one of them, but in Be there is only one electron in the orbital and there is no repulsive force in the same orbital, therefore
$$\ce{ B < Be}$$

What do you think?


texts: Can a brine water electrolysis be looped?

texts: Electrolysis of brine yields hydrogen and chlorine gases and aqueous $\ce{NaOH}$. So is it possible to combine the gases to form $\ce{HCl}$ gas, and mix it back with the aqueous $\ce{NaOH}$, so it returns to brine water?


texts: IUPAC salt definition makes bases be classified as salts?

texts:
The IUPAC salt definition is: "A chemical compound consisting of an assembly of cations and anions" (Compendium of Chemical Terminology Gold Book, Version 2.2.3, 2014)
So it means that a base like NaOH, that's also an ionic crystal, is a salt? I'm quite certain it's not but it seems the definition says so.
Then, a if a base is not a salt, what would be a better definition for salt?


texts:
I am doing a homework where I am supposed to calculate estimate od distance between two ions in cytoplasm. I have only been given the concentration of an ion. Any help how I should start looking this problem?

Only solution I have been able to create is the one where you force some number out from consentration by using ion radius and assume them all to have same distance. However, this feels too, I dunno, mechanical way to solve this problem.


texts:
It was given in my text book that reducing character of group 15 hydrides increases down the group. I am a bit confused about this. For $\ce{NH3}$ this is fine as I assume that:

$$\ce{NH3 -> N + H^+ + 3e^-}$$

My doubt arises in the higher elements of the group. In $\ce{SbH3}$, $\ce{H}$ is present as $\ce{H^{-}}$ and $\ce{Sb}$ as $\ce{Sb^3+}$. So would $\ce{Sb^3+}$ be oxidised to $\ce{Sb^5+}$ or would $\ce{H^{-}}$ be oxidised to $\ce{H2}$?  I know that for $\ce{Sb}$, $\ce{Sb^3+}$ is more stable than $\ce{Sb^5+}$ . So would  $\ce{H^{-}}$ be oxidised to $\ce{H2}$ ?

Also electronegativity of $\ce{As}$ and $\ce{H}$ is given tobe equal in my textbook. So what would be oxidation product of $\ce{AsH3}$ ?

For $\ce{BiH3}$ it seems like:

$$\ce{Bi^3+ -> Bi^5+ + 2e^-}$$

is more feasible as $\ce{Bi^5+}$ is more stable. Can someone please tell me the oxidation products of group 15 hydrides? Also can someone tell $\ce{E°_(H^{-}/H2)}$ value as I couldn't find it on net?


texts: How to calculate electric force on valence electron?

texts:
In order to understand the periodic trends more fully, I wanted to calculate the net force exerted on the electron (with the highest principal quantum number and azimuthal quantum number) of an atom.
I decided to use the following procedure:

First, I found the effective nuclear charge of the electron in a table from Wikipedia.
Then, I found the calculated atomic radius of the respective atom (which tells me the distance from the nucleus to the electron) using another table from Wikipedia:
Lastly, I converted these units into Coulombs/meters and then used Coulomb's law and the charge of an electron to calculate the electric force.

This is the graph that resulted from these calculations.

For example, for lithium:

2s electron - effective nuclear charge: $\pu{1.279 e} \implies \pu{2.05e-19 C}$
atomic radius: $\pu{167 pm} = \pu{1.67e-10 m}$
Coulomb's law: $\displaystyle \frac{kq_1q_2}{r^2} = \frac{(\pu{8.99e9})(\pu{2.05e-19})(\pu{-1.602e-19})}{(\pu{1.67e-10})^2}$
Magnitude of force: $\pu{-1.06e-8 N} \implies \pu{1.06e-8 N}$

Is this a proper way to calculate the electric force exerted on the electron I specified?
If so, how does this graph relate with other atomic trends, like ionization energy and electronegativity?


texts: How to calculate the solubility of CaF2 at different temperatures?

texts:
At $\pu{25^\circ C}$ I used the free energy table for $G$ for the reaction and got $K_\mathrm{sp}= 10^{-9.02}$.

I now need to find out what the solubility is at $10$, $20$ and $\pu{30^\circ C}$. Could you also show what equation you used and how to work out the solubility by one of these other temperatures?


texts: I want to do some experiments on enantiomers. As it involves some calculations of potential energy surfaces, I would like to do this experiment on a simple enantiomer (For example $\ce{CHBrClF}$). But this is in liquid form I think. I need an enantiomer sample in the powder form. Can anyone suggest a simple sample? Either one I can buy or can easily make in a chemical lab with the help of a chemist.


texts:
For a product to be called "vinegar", it must contain at least $5.0$% acetic acid by mass. A 10.0 g sample of a "raspberry vinegar" is titrated with $0.125 \mathrm{M}$ barium hydroxide and required $37.50 \mathrm{mL}$ for complete neutralization. Can the product be called "vinegar"?

My professor said that the product is vinegar, but I did not understand how he solved it. Could you please tell me what to do? What formulas should I use to solve this kind of problem?


texts: kinetic reaction rate greater than extent of reaction for equilibrium

texts:
I'm comparing a model with chemistry at equilibrium versus a kinetic one.
I take a network of two reactions: methane steam reforming (MSR) and water gas shift (WGS) at 700°C.

I calculated extent of reaction of both reaction, with the equilibrium hypothesis, solving a system of two non-linear equation containing the two $ K _{eq} (T) =f(\lambda_{MSR}, \lambda_{WGS}) $ equations, which give me these results:

$\lambda_{MSR} =  1.4167e-4 [mol/s]$
  $\lambda_{WGS} = -6.6788e-5 [mol/s]$

Then I calculate rates of reaction with an homogeneous and stoichiometric coefficient expression, with Temperature dependence constant (Arrhenius) taken here, I get:

$r _{MSR} = 20.9761e-4 [mol/s/m^3]$
  $r _{WGS} =        0.0 [mol/s/m^3]$ (I have no reactants nor products...)

Now to compare them I have to multiply $r$ for reactor's volume.

Here start my doubt:
taking for sake of simplicity $1[m^3]$ reactor, I get

  $r_{MSR}>\lambda_{MSR}$

this what does it mean?
does it have a physical meaning?
what is the meaning of a so large reactor?

My thoughts, my idea, is that equilibrium shows the maximum rate of reaction so kinetic should, or better must, respect it giving me a lower value of reaction rate; but, as you can easily see in my above example, this statement (that I have never read somewhere in any chemistry book, so I can take it as truth) can be superimposed, forced. How do you explain it?


texts: Why does the conductivity of a conductivity probe decease if you shake the solution in which it is kept?

texts:
Figure showing $3M$ solution $\ce{NaOH}$ conductivity while shaking (The circled area is the time of shaking and drop)

When I took the reading again, without shaking, I got the following graph:


texts: Why does the position of equilibrium depend only on the relative Gibbs energies of the products and the reactants?

texts:
The position of equilibrium, I read, is dependent only on the relative Gibbs energies of the products and the reactants. Why is this so? Surely one must take into account the entropy of mixing of the products and the reactants, which wouldn't be dependent on the Gibbs energies, to work out the lowest point (energy wise) and find the position of equilibrium. Why, therefore, is the position of equilibrium between products and reactants only dependent on the relative gibbs energies of the products and reactants.
Thanks!


texts:
I have heard so many times that aluminium pots should not use for cook sour(acid) foods But I like to know the chemical  reason why it is not suitable for cooking sour(acid) foods? Also I want to know,

*Do the aluminium foils not suitable only for cooking sour foods, does  it not suitable for package sour(acid) foods such as lemon juice?


texts: How much CO2 can I fit in a 0.5 L plastic bottle?

texts:
Let's say I have a 50 lb CO2 tank which can probably contain about 1000 L of the gas at 122 atm. Suppose I want to use the tank to fill a 0.5 L plastic bottle which only has air in it.

We know that gases always assume the shape and volume of their container. If that is true then that would mean that I can transfer the whole 1000 L of CO2 into the plastic bottle.
What happens in reality is that the pressure in the 0.5 L would have to rise to about 244 thousand atm, so how do I know how much CO2 to put into that 0.5 L bottle before it would presumably explode?


texts: According to the rules of writing ionic equation, only compounds in aqueous state can be split or dissociated into their ions, whereas elements or compounds in solid, liquid or gas state remain as they are. But what about molten sodium chloride which is NaCl(l) in liquid state, isn't it dissociated into ions when melted? So can we split it into its respective ions when writing ionic equations?


texts: How much energy is converted in light when you burn a candle?

texts: When a candle burns the reaction is C25H52 + 38 O2 → 25 CO2 + 26 H2O. So it seems equal at both sides. But isn't there any light and heat (low elektromagnetic waves) produced. So how many Joule is produced of light of each candle molecule?


texts: Methods to extract sucrose from tea after it's been stirred in?

texts:
Sugar is often labelled  "white poison" now-a-days and a lot of negative health consequences happen due to increased sugar consumption.

Keeping this in mind, if I were handed a cup of tea (with sugar already stirred in), what methods/processes can I employ to separate/remove the sugar from it?


texts: Alphabetical priority of the isopropyl group

texts:
This passage is contradictory. I've boxed the section that confused me.

Why would the book tell me to alphabetize substituents, only to clearly ignore its own rule about alphabetizing substituents?

Seems to me that "isopropyl" should come before "methyl," as the letter "i" is most definitely before the letter "m" in the alphabet. And the book makes no mention about ignoring the "iso-" prefix.

So:

1) Should methyl come before isopropyl?

2) If so, why?


texts: Should one pronounce “periodic” the same in “periodic acid” and “periodic table”?

texts:
In “periodic table”, the adjective is related to the noun period, and comes from Ancient Greek περίοδος through French périodique. In “periodic acid”, it is formed from the prefix per- and iodic (like peroxide and permanganate).

Wiktionary lists their respective UK pronunciations of as /pɪə(ɹ).iˈɒdɪk/ and /ˌpɜːraɪˈɒdɪk/, markedly different: pɪə (as in piece) vs. pɜː (as in perfume); then i (as in it) vs. aɪ (as in eye).

However, is that distinction really made in practice? Would a native US/UK/Aussie speaker make the difference when talking in the lab?


texts:
Why is the basicity of hypoboric acid $\ce{H4B2O4}$? Is it $2$ even though it has $4$ hydroxyl groups?

My teacher told us that the basicity of this acid is $2$ but I am not remembering the exact reason for it.


texts: Why is the entropy of container A the greatest?

texts:
Question

  9.35 Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The containers
  all start at $T_\mathrm{i}$ and the temperature is increased to $T_\mathrm{f}.$ Rank the containers in order of increasing change in entropy. Explain
  your reasoning.

Answer

   B < C < A

My Approach

I thought that you were supposed to assume that container C had the most number of atoms and therefore a greater entropy automatically.


texts:
I want to calculate the Gibbs free energy for an ideal monoatomic gas, i.e. $$U=\frac32nRT.$$
Free energy is defined as $G(T,p)=H-TS$ and using the definition of enthalpy $$G(T,p)=U+pV-TS=U+nRT-TS.$$

To calculate the entropy I use the total differential of entropy given by
$$\mathrm{d}S=\left(\frac{\partial S}{\partial T}\right)_p \mathrm{d}T
  +\left(\frac{\partial S}{\partial p}\right)_T \mathrm{d}p.$$

Using the Maxwell relation
$$\left(\frac{\partial S}{\partial p}\right)_T =
-\left(\frac{\partial V}{\partial T}\right)_p,$$
and for an ideal gas with $V=\frac{nRT}{p}$ we hence get
$$\left(\frac{\partial S}{\partial p}\right)_T=-\frac{nR}{p}.$$
Further
$$\left(\frac{\partial S}{\partial T}\right)_p =
\frac{c_p}{T}=\frac{\frac52nR}{T},$$
 so all in all
$$\mathrm{d}S=\frac{\frac52nR}{T}\mathrm{d}T-\frac{nR}{p}\mathrm{d}p.$$

How do I calculate $S$ from here, because integrating would leave me with $\Delta S$ which I cannot use?

The point of reference should be standard conditions ($1~\mathrm{atm}$, $1~\mathrm{mol}$, $298~\mathrm{K}$, ...)


texts:
As the wikipedia article for the exchange interaction so aptly notes, exchange "has no classical analogue."

How wonderful.

Exchange shows up essentially while enforcing the condition that two electrons should not be distinguishable.

That makes sense as a condition to enforce, but I don't understand how this should influence the energetics of the system.

For instance, when two neon atoms interact, there is a very small amount of energy contribution which is attributed to exchange. I understand that exchange is not a force because there is no force carrier, but there is indeed an interaction taking place which affects the energy of the system. What then am I meant to believe is going on? Am I supposed to believe that two electrons spontaneously switch places so as to maintain their indistinguishability? This seems ridiculous. Especially because such a process ought to happen over a finite period of time and thus be observable, but this doesn't seem to be the case (at least as far as I've heard).

What is exchange then? I understand this may not even be an answerable question beyond the fact that it is an effect which drops out of the math and simply is.

Hopefully someone has some interesting insight for me here.

Also, I have seen this question which I believe is referencing the same effect because exchange is known to play a role in ferromagnetism, but nothing ever really caught hold there probably because the question referenced a specific application and so was very difficult to answer well.


texts: Where do the electrons come from to make the carbon stable during bombardment of alpha particles on beryllium

texts:
When beryllium is bombarded with alpha particles, where do the electrons come from to make the carbon stable?

Source: https://en.wikipedia.org/wiki/Triple-alpha_process


texts: How to synthesize cyclopentane from cyclohexane?

texts:
Does this route work to synthesize cyclopentane from cyclohexane?

Free-radical halogenation.
Elimination with strong base to form cyclohexene.
Ozonolysis to make di-aldehyde.
Oxidation to make di-carboxylic acid.
Esterification with ethanol, acid, and heat.
Alpha-proton elimination with ethoxide ion.
Intramolecular attack of other carbonyl carbon; loss of ethoxide leaving group.
Acid, high heat, water to return to carboxylic acid. Expulsion of ethanol.
Heat for decarboxylication. Loss of carbon dioxide.
Not illustrated: removal of carbonyl using Wolff-Kishner and Clemmensen.

I think a few modifications I could make are:

Formation of methyl ester using diazomethane. This would not involve heat and acid. But it would involve something that is potentially explosive.
Alternately, make an acid chloride and then go down to the ester if I wanted to avoid the heat involved with Fischer esterification.


texts: how to determine the volatility of an organic compound using the physical properties of organic molecules

texts:
How do you tell if a compound has a high volatility?

Also can the boiling point of a compound be taken into consideration when determining if a compound has a high volatility?


texts: Physical implications of the simple harmonic oscillator quantum mechanical solutions

texts:
Take a look at the wavefunctions for the different energy levels of a simple harmonic oscillator (a crude approximation for a diatomic).

The wavefunctions seem to make sense: they tend to zero as x tends to plus or minus infinity so it is normalisable. The number of nodes increases by one with increasing energy levels etc.

However, when you take a look at $|\psi(x)|^2$ which represents the probability density of the particle to be found at that point in space (or the diatomic to be in that particular state/bond length) I struggle to see how a node can exist. This is because a diatomic will stretch and contract through the full range of extension/contraction - the quantum representation does not seem to conflict this in the sense that there is a non zero probability when the potential is equal to the total energy. However, to reach this state from, for example, $x=0$ in the $n=2$ energy level it must pass through a node. What does this mean? surely a bond can't cease to exist as it stretches from equilibrium to some extended or contracted state? What's really going on here?


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Can anyone suggest a protocol for preparing 1 Litre ammoniacal solution (pH 7.8, NH4-N, 3000 mg/L) from NH4Cl and NaOH?
I have worked out that I need 10.7g NH4CL and 0.45 g NaOH -is this correct? I am assuming that 1st step is to prepare 0.45 g NaoH in 0.5 L distilled water and then to that add 10.7 g NH4CL solution in 0.5 L of  distilled water.Total volume is 1 L?
Or are there better methods?


texts: Structure diagrams indicate plausible structures?

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Structure diagrams have a hexagonal, "chicken wire" shape, which leads to more elegant representations of some molecules than others.

For example, the following diagram must deviate from the usual convention such as the horizontal connection above the nitrogen.

The following hydrocarbon would have the same problem.

  H H
  | |
H-C-C-H
  | |
H-C-C-H
  | |
  H H

Does this indicate anything about these molecules, for example they are rare or unstable, or is it just a weakness of this type of diagram?


texts: What happens chemically to 5'-radiolabeled aqueous thyroxine (thyroid prohormone) when its I-131 undergoes beta+gamma decay?

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Related to this question about $\ce{^{14}C}$ beta decay in $\ce{CO2}$, what happens when the $\ce{^{131}I}$ in radiolabeled thyroxine (thyroid prohormone, or "T$_4$") undergoes beta-plus-gamma decay to form $\ce{^{131}Xe}$?

In order to narrow the scope of the question to something tractable, assume that despite its low aqueous solubility the thyroxine is in dilute solution in deionized water, and that it bears a single $\ce{^{131}I}$ at the $5'$ position (click image to enlarge):

As well, as noted above, assume that the $\ce{^{131}I}$ undergoes its most common mechanism of tandem electron & gamma decay:

$$
\ce{^{131}_{53}I -> ^{131}_{54}Xe + \beta^-~+ \gamma}
$$

I assume the resulting chemical species remaining will start out as a (very transient) xenon-bearing cation:

What happens next?


texts: Do there exist aromatic compounds similar to azulene?

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So for this question I'm considering a chemical to be "similar to azulene" if it obeys the following conditions:

It is aromatic and obeys Hückel's rule,
It is a fused bicyclic compound,
One component ring is aromatic as an anion,
The other ring is aromatic as a cation,
It is not azulene, and
It has been synthesised before and the synthesis has been confirmed.

For instance, I believe bicyclo[3.1.0]hexa-1,3,5-triene should follow all of the previous conditions except possibly the last (but I don't know that it hasn't). Do any chemicals obey all of these conditions?


texts: When is the Assumption that Enthalpy is Constant over Temperature Change Invalid?

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In a question, I was asked to integrate the Gibbs-Helmholtz equation to derive some formula. Then the next question asked:

  Identify one assumption that you have made in deriving the above equation and identify one
  scenario where it is a very bad assumption, and explain why the assumption fails

Now the assumption that was made was the $\Delta H_{\mathrm{fus}}$ is constant over the change in temperature. However, could someone please explain when and why this assumption fails.

Thanks.


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I have a few questions about this two relations:
We know that:
$K_p$ = $e^{\frac{-\Delta G^0}{RT}}$ $(1)$
and
$K_c = K_p (RT)^{\Delta n}$ $(2)$
Ok now I'm solving this problem about solubility:

The solubility product $K_s$ of $Ni(OH)_2$ is $6.0\times10^{-16}$ at $T=25ºC$
Calculate $\Delta G^0$ of this reaction at $25ºC$

I checked my teacher's resolution and he is using $(1)$ to directly calculate $\Delta G^0$? But is that correct since $K_s$ is equivalent to $K_c$ and not $K_p$?
But I also thought about converting $K_s$ to $K_p$ using $(2)$ but does that make sense since we are not dealing with gases?
Can someone please clarify me what's the best process to follow here?
Thanks!


texts: Is glycerol/glycerin soluble in ethanol?

texts: As titled, I wish to know if glycerol/glycerin is soluble in ethanol (not soluble, slightly soluble, very soluble)


texts: Free radical substitution - bromination of ethane

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I am new to this service so please overlook any mistakes.

My question is with regards to free radical substitution. I understand the three step process of the bromination of ethane and what would occur if chlorine was in excess.

I do not however understand what would happen if ethane was in excess. What would occur and what would be the major product produced?


texts: Hybridization theory (orbitals used in different hybridizations)

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Why is $d_{x²-y²}$ orbital used in $sp^3d$ (square pyramidal geometry) while $d_{z^2}$ orbital in $sp^3d$ (trigonal bipyramidal geometry)?
I came across this information while reading J.D.Lee Concise inorganic chemistry.


texts: Why are some addition reactions syn and some anti?

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Is it experimentally observed or do we know proper reasons for why some addition reactions are syn and some anti?

Like for halogenation to a double bond, I believe that the ring formed will cause hindrance and so only anti can be formed.
But for hydrohalogenation, either can happen. Is this because there is no hindrance in any case?

Similarly for hydrogenation, it is always syn? Why is that? What is the mechanism behind hydrogenation?