texts: Are monosubstituted cyclopropanes achiral or chiral?

texts: A classmate an I were discussing the chirality of this molecule which is a monosubsituted cyclopropane. I argue this is an achiral molecule because that carbon which is bonded to bromine cannot be a stereocenter. If you try to determine a point of difference between the other two "substituents," there is none. But if you draw a mirror image, it appears to be non-superimposable which is a trademark of chiral molecules. Is my reasoning on the right track, or is there something unique about the chiral or achiral nature of cyclopropanes such as these.


texts: Is it possible to express Gibbs free energy as following?

texts:
We know $$\Delta G =\Delta H -T\Delta S$$
$$\Delta S= \frac{Q_{rev}}{T} $$
Hence $$\Delta G=\Delta H-Q_{rev} $$


texts: How can I know when I have added an excess of magnesium oxide?

texts:
The following instructions were used to prepare magnesium sulfate crystals, $\ce{MgSO4 . 7H2O}$.

Measure $50~ \mathrm{cm^3}$ of dilute sulfuric acid into a beaker and warm the solution.
Using a spatula, add some magnesium oxide and stir the mixture. Continue
adding the magnesium oxide until excess is present.
Separate the excess magnesium oxide from the solution of magnesium
sulfate.
Heat the solution until crystals form. Obtain the crystals and dry them.

The question I have an issue with is this: How would you know when excess magnesium oxide is present in step 2?

The answer key says that I would know when no more solid (that is, no more magnesium oxide dissolves). However, since we are talking about dilute sulfuric acid, there should be water, and I read on the internet that $\ce{MgO}$ is soluble in water.


texts: Substitute molten salt bath with temperature range from 400–500 °C

texts: I'm looking for a suitable substitute for a $\ce{NaNO2/KNO3}$ salt bath (for quite obvious reasons due to the other applications of the latter chemical). The salt mixture needs to have around 400 to 550 °C of molten working temperature (the lower ranges are not interesting), and preferably be reasonably safe to work with (as safe as the aforementioned salt bath, so totally harmless isn't the goal). The purpose is precise annealing of brass alloys in a home shop environment (so no fume hoods and blast cabinets available).


texts: Need to normalize lattice enthalpy by no. of nearest-neighbor (NN) interactions to equate to NN interaction strength?

texts:
I've seen electrostatic interaction energy (from $E\sim \frac{q_1 q_2}{r}$) used to explain differences in lattice enthalpies between different crystalline solids.  For example, I've seen it explained that $\ce{NaF}$'s $\pu{910 kJ/mol}$ lattice enthalpy is less than $\ce{MgCl2}$'s $\pu{2326 kJ/mol}$ because of $\ce{Mg}$'s greater cationic charge (+2 vs. +1).

Question: Isn't the lattice enthalpy defined per stochiometric unit, rather than per nearest-neighbor interaction? And if so, if one is going to use electrostatic models of nearest-neighbor interaction to explain differences in lattice enthalpy, shouldn't the respective lattice enthalpies first be divided by the number of nearest-neighbor interactions per stochiometric unit?


texts:
Order for solubility of isomeric alcohols in a book was given as:

Primary alcohol >Secondary alcohol >Tertiary alcohol
After this I found a question as :

1) Which is more soluble in water?

(a) 3-ethyl-3-hexanol

(b) 2-octanol

Ans:- (a) & the reason was that (a) has more compact alkyl portion than (b). But as (a) is a tertiary alcohol while (b) is a secondary one ,so according to the given order answer should be reverse.

Also while comparing

2-methyl-2-propanol & 1-butanol

Here 1-butanol had higher solubility which matched the given order. I am not understanding what's wrong about the first case. Please explain me.


texts: Does conductivity change in a solution due to rust?

texts:
I plan on conducting an experiment in which I place an iron nail in water and analyze its rate of corrosion into rust with different concentrations of NaCl.

My original plan was to cover the water in a beaker with oil then use a dissolved oxygen probe to measure the drop in oxygen levels as the reaction went on. However, I was thinking that maybe conductivity would change as the reaction went on?

In short, in a solution containing iron, salt, oxygen, and water, will conductivity change as the iron rusts?


texts: Do chemical garden coral formations leach toxins?

texts:
Short version, I want to make a coral garden with sodium silicate and salts, and I would like to put that in my fish tank, but I'm concerned about the fish getting poisoned.

https://en.wikipedia.org/wiki/Chemical_garden
https://www.thoughtco.com/make-your-own-magic-rocks-607653

The above pages describe the chemicals needed. The articles say that once the corals have formed, they can be rinsed to remove the sodium silicate, and kept in fresh water. Most of the articles I've read say the same thing, in different ways. But none of them say whether the coral degrades, or if it is stable.

Are there experiments that I can do to test this? How can I be sure?


texts: Why is Nitrogen 15 found almost exclusively in marine environments?

texts:
Prelude

The following story was told to me earlier this summer

Every year during October, the Pacific rain creates an ideal spawning condition for the wild Pacific salmon in the coastal forests of British Columbia. Of course, when we think of salmon swimming upstream in the Pacific Northwest, some images might come to mind.

Black bears and grizzly bears carry hundreds of kilos of fish out of the water and into the forest to consume. Naturally in the areas proximal to the rivers, fish carcasses are littered throughout, with the bears having ate what they wanted, leaving behind the rest to decompose.

Scientists several years ago took to examining the nitrogen uptake and found that trees in nearby the river received a significant amount of their nutrients from the fish. Through their findings they showed a case that reverses the land to sea flow of nutrients. The study has been used to argue for the dedication of resources to rebuild and maintain wild pacific salmon runs.

Source: David Suzuki Foundation

Chemistry and the Question

The study above uses the abundance of $\ce {^{15}N}$ found naturally in the ocean, and transported via salmon, to support their findings. $\ce {^{15}N}$ has a 0.365% natural abundance, and according to the story, it is almost exclusively found in marine environments. Which leads us to my question: why? Why is this isotope largely found in the ocean and not on the land?


texts: In a hypothetical enclosed membrane only permeable to water (including hydronium), where inside the pH is lower than the outside, would water move inside?


texts: Effect of drinking on internal energy and entropy of the universe

texts:
I have just been doing some questions on thermodynamics and have come across a strange question that I can't seem to grasp.

The question asks me to estimate the change in body temperature as well as the entropy change of the universe when a man drinks a litre of 273 K cold beer in an isolated pub. I am given the mass of the man, as well as the specific heat capacity of water, and its density. I also am told to assume that the human body is mainly made up of water, and am given body temperature as 310 K.

I've been thinking that the answer must involve the fact that the pub is isolated and thus that the change in internal energy of the system is constant but I'm not quite sure how to go about it. I have also derived earlier in the question that for a system at constant volume:

$$
\begin{align}
U(T_2) &= U(T_1) + \int_{T_1}^{T_2}C_V(T)\,\mathrm dT,\tag{1}\\
S(T_2) &= S(T_1) + \int_{T_1}^{T_2}\frac{C_V(T)}{T}\,\mathrm dT.\tag{2}
\end{align}
$$

Any hints or help would be much appreciated!


texts: How to calculate the latent heat when there is a boiling temperature range?

texts:
I have a DME (dimethyl ether)- methanol - water mixture with the mol fraction composition: DME 0.4295, methanol 0.1353, water 0.4351.

This mixture has a boiling temperature range: dew point 141.6 °C and bubble point 69.95 °C, and the heat applied for the phase change (condensation) is a latent heat. How can I calculate it?

I know that for pure compounds, during the condensation process, there's no temperature change, so the latent heat is the result of:

Q = mass flow * latent enthalpy (constant value)

For a mixture that has a condensation temperature range, can I use the same equation? If this is not the case, how can I calculate the latent enthalpy for a mixture in function of the temperature?


texts: Living-cationic vs cationic polymerization

texts:
To my understanding, cationic polymerization is a type of living polymerization but my teacher's notes and Wikipedia seem to suggest they're different. I can't see the difference.

The same goes for anionic polymerization. From what I've studied so far, the difference must be subtle, if there is one.

Is there such a difference?


texts: Will charcoal briquettes (not activated) absorb water out of the air in the house in a subtropical climate?

texts: I live in Florida, an incredibly wet environment where it's very difficult to get moisture out of house without using a dehumidifier 24/7, which is too expensive.  Would charcoal briquettes be of any use?


texts: EMF measured while verification of Nernst equation keeps on increasing

texts:
I was doing this experiment to verify Nernst equation in my school's lab. I had two beakers one with $\ce{ZnSO4}$ and the other with $\ce{CuSO4}$ both having a concentration of $1~\mathrm{M}$. I had a saltbridge having $4~\%$ Agar in $1~\mathrm{M}\ \ce{KCl}$. The temperature was $21.3\ \mathrm{^\circ C}$ Now the problem was that when I connected a multimeter across the electrodes it showed an EMF of $0.8\ \mathrm{V}$ initially and it went on increasing to $1.001~\mathrm{V}$. The increase was rapid initially and became slower and slower. The EMF still kept on increasing but with a very slow pace.

By what I have studied the EMF I get initially should be the maximum one and then go on decreasing as the equilibrium is attained.

So why was the EMF in my experiment increasing? Is it because I had not used wool at the ends of the salt bridge? But the Agar was already a thick gel and was not flowing out of the U-tube.

I asked my teacher and she said that there might be some problem with the multimeter. Does any one of you know the reason for the increasing EMF?


texts: Equilibrium: Equations with complex roots

texts:
I'm studying civil engineer in my first year. We have a course called "General Chemistry". One of the chapters was about chemical balance of a reaction (called equilibrium in English, I think). We got exercises on this were we had to calculate the amount of chemicals got converted to others, using acidity constants Ka.

For example, the equations we had to solve were easy and looked like this:

$$K_a = \frac{(x)^2}{(0.1 - x)(0.2 - x)}$$

These exercises were easy. But then came the point were we combined two reactions at the same time and had to calculate the balance for both at the same time. The equations we get were:

The tutor used to make simplifications by getting rid of the "$-x$" and "$-y$" in the denominator, assuming x and y would be so small it would almost make no difference. I don't like making such simplifications: I want the correct answer. So, what I did was putting the equations in WolframAlpha and let it compute it, since I don't know how to solve such a system of equations. The result shocked me: the solutions for x and y were complex (so, with a real and imaginary part).

WolframAlpha says this:

Whereas the tutor found (due to simplification):

The tutor's solution is in the complex plane not really far away from the correct solution to the equation (WolframAlpha's solution #3).

So, my question is: How do you explain these roots are in fact complex? I don't think a complex amount of chemicals can react right?


texts: Will N,N‐diethylbenzamide show geometrical isomerism?

texts:
I know for a compound to show geometrical isomerism it should

have site of restricted rotation;
be connected to two different groups on either side of site of restricted rotation;
the distance between the groups on the either side of site of restricted rotation should be different.

I think conditions 1 and 3 hold true here. I am confused if or not 2 is true.


texts: Phenolphthalein as a indicator for the titration of benzoic acid

texts:
Question: Justify the use of phenolphthalein $(\mathrm{p}K_\ce{in}=9.4)$ as a indicator for the titration of benzoic
  acid $(K_\mathrm{a}=6.3\times 10^{-5})$ with $\ce{NaOH}$.

My attempt:

I can calculate the $K_\mathrm{b}$ of $\ce{NaOH}$ from the above data.

And I also know the formula

$$\mathrm{pH} = \mathrm{p}K_\mathrm{b} + \log \frac{\ce{In}}{\ce{HIn}}$$

I know that this is the titration of a strong base and a weak acid. So the equivalent point will be at a $\mathrm{pH}>7$ and hence phenolphthalein is a good choice.

But how can I conclude mathematically that this is a correct choice?


texts: My textbook states that members of a homologous series have the same general formula (ex. $\ce{C_{n}H_{2n}}$ for alkenes) as they only differ from one to another by additional $\ce{CH_2}$ (methylene) groups. However, alkenes can have more than 1 carbon-carbon double bond, which should alter their general formula right?


texts: Finding the concentration of each ion in saturated solution of lead(II) hydroxide

texts:
Question

If the solubility of $\ce{Pb(OH)2}$ is $\pu{0.155 g/L},$ then the concentration of each ion in a saturated solution of $\ce{Pb(OH)2}$ is
A. $[\ce{Pb^2+}] = \pu{0.155 g/L}$ and $[\ce{OH-}] = \pu{0.155 g/L}$
B. $[\ce{Pb^2+}] = \pu{0.052 g/L}$ and $[\ce{OH-}] = \pu{0.103 g/L}$
C. $[\ce{Pb^2+}] = \pu{6.43E-4 mol/L}$ and $[\ce{OH-}] = \pu{1.29E-3 mol/L}$
D. $[\ce{Pb^2+}] = \pu{6.43E-4 mol/L}$ and $[\ce{OH-}] = \pu{6.43E-4 mol/L}$

Answer

 C. $[\ce{Pb^2+}] = \pu{6.43E-4 mol/L}$ and $[\ce{OH-}] = \pu{1.29E-3 mol/L}$

My Approach
What I did is that I wrote the dissociation equation:
$$\ce{Pb(OH)2 <=> Pb^2+ + 2 OH-}$$
Then I used to mole ratio to discover that:
$$
\begin{align}
γ(\ce{Pb^2+}) &= \pu{0.155 g/L}\\
γ(\ce{OH-}) &= \pu{0.31 g/L}
\end{align}
$$
I then converted the mass concentration $γ$ into molar concentration $c$ since the $\pu{mol/L}$ is commonly used to describe solubility:
$$\pu{0.155 g/L} × \frac{\pu{1 mol}}{\pu{207.2 g}} = \pu{7.48E-4 mol/L}$$
However, that's not the answer. What did I do wrong?


texts: Which areas of chemistry require calculus?

texts:
I didn't have much chemistry in school/college, and am now building up my knowledge again. I am studying maths in parallel, building up to calculus.

I noticed that the introductory chemistry books (even at the college level) don't use any calculus. However, more advanced books do tend to use calculus.

Can anyone tell me which areas of chemistry require (or make use of) calculus?


texts:
Recently I started renovating a bicycle. The frame has been painted probably over 30 years ago, and despite holding well, big patches of rust are showing. So it's time to give the bike a new paint job. And before that, I need to sand the frame and remove the current paint.

Sadly it came to my attention that some bikes around that age have lead paint. Toxic, obviously.

I'm by no means a pro chemist. Far from that actually: if you show me a bunch of formulas, I might understand it, but I'm not skilled for manipulations neither properly equipped.

Provided that I can scratch a bit of that paint with sandpaper, what's the easiest way to test it for presence of lead? Apparently some lead test kits exist, but they're incredibly hard to find here.


texts: Conversion of 4-nitrotoluene to 2-bromobenzoic acid

texts:
In the above conversion why doesn't bromine add to methyl group? Is the first reaction following free radical or polar reaction (Friedel-Crafts). If it's following free radical mechanism then Br should add to CH3, if it's F-C substitution then why there is no catalyst when NO2 is deactivating group?

What would be the change if I first do seconds step (i.e reduction to amine) and then bromination? Would it be wrong to do bromination at last?

Is the intermediate (2-bromo-4-nitrotoluene) the only major product of first step?


texts: How does sodium bicarbonate act as a deodorizing agent?

texts:
I was reading this other question on the site: Deodorizing using baking powder instead of baking soda.

Apparently, baking soda is used quite often as a cleaning and deodorizing agent. From what I know, it's cleaning effects are because it can denature proteins and saponify oils (convert oils to soap) since it is a weak base.

But when you take a look the Wikipedia page on aroma compounds, the only compounds that could possibly be affected by a weakly basic substance are esters (which would undergo hydrolysis). Most of the compounds are polyunsaturated aldehydes, ketones and alcohols which are not affected by (weak) bases.

Note: I assume here that compounds which cause bad odors would have a similar structure to compounds that are fragrant since they both have to activate whatever receptors there are in the nose. Also I have read that usually the same compound can cause both a bad and a good smell depending on the concentration of the compound, such as indole.

So I ask: Does $\ce{NaHCO3}$ really have any deodorizing effect and if so, what is the mechanism (reactions involved) behind it. Also would it be possible to achieve the same effect with any random alkaline substance ($\ce{NaOH}$ maybe, although not very practical).


texts: Why isn't an Acid-base titration curve linear?

texts: Sorry if this is a stupid question, but why is a acid-base titration curve not linear? As you add more acid solution to a basic solution, shouldn't the pH of the basic solution slowly go up in proportion to the amount of acid added? Why is there such a sudden increase?


texts: Why is it that reactions that cause an increase of temperature are exothermic?

texts:
I've been taught that if you have two aqueous reactants that react together and produce heat it is exothermic. Shouldn't that be endothermic? Did my professor misspeak?

If it's gaining heat, that means it's pulling heat from the outside. The opposite of what happens when water freezes and releases heat (which is actually exothermic).


texts: Why is the dissociation reaction of acetic acid in water initially endothermic and then exothermic?

texts:
Why is the dissociation reaction of acetic acid in water initially endothermic as temperature is increased and then becomes exothermic as it is increased further?
My understanding from Le Chatelier's principle is that a rise in temperature "adds" heat to the system and a drop in temperature "removes" heat from the system. Correspondingly, a temperature increase would favour the endothermic (heat absorbing) direction and a temperature decrease would favour the exothermic (heat releasing) direction. Why is this contradiction? My thoughts are that maybe the autoionisation of water is endo or exo, which somehow dominates the reaction, but I don't know. Could someone please provide a possible explanation?


texts:
Why is atomic size mismatch a sign of poor bond strength? Wouldn't orbital overlap be proportional whether the two atoms are small or the two atoms are big?

For example I heard someone comment that an argument that the C-I bond is weaker than the C-F bond based on orbital overlap made no sense to them, because why would the size of the individual orbitals matter in overlap? Small atom, big atom and small atom, small atom - shouldn't their overlaps be proportional? Or something along the lines of that. I'll have to pull up the post again ...


texts: How to estimate HCN content in a volatile mixture?

texts: How can you accurately qualitatively and quantitatively determine the HCN in a volatile product from water?


texts: How would a pH curve look like for titration of diluted weak base compared to concentrated one?

texts:
Let's say I take $\pu{80 g}$ of a weak base, dilute it with  $\pu{50 ml}$ of water and titrate it with a strong acid. I get a titration curve. Now I take again $\pu{80 g}$ of the same weak base but this time I dilute it with $\pu{200 ml}$ of water and titrate it with the strong acid. What will be the new titration curve compared to the first one?

And here is what confuses me:

On one hand, the diluted base should have lower $\mathrm{pH}$. But on the other hand, at half-equivalence point, $K_\mathrm{b}=\mathrm{pOH}$, and since it's the same base, $K_\mathrm{b}$ is the same, and thus $\mathrm{pOH}$ and $\mathrm{pH}$ at half equivalence point should be the same. I am also not sure about the endpoint.


texts:
We have to compare the nucleophilicity of $\ce{OH-,NH2-,CH3CH2-}$ and $\ce{CH#C^{-}}$. I managed to find out that $\ce{CH3CH2-}>\ce{NH2-}>\ce{OH-}$ and that $\ce{CH3CH2-}>\ce{CH#C-}$. But I don't know how to compare $\ce{CH#C-}$ with either $\ce{OH-}$ or $\ce{NH2-}$.

My attempt:

I know that the acidity order of the 2nd period is $\ce{CH4}<\ce{NH3}<\ce{H2O,HF}$. Now the stronger an acid is, the weaker its conjugate base will be. Therefore, the conjugate base order will be:
$$\ce{CH3-}>\ce{NH2-}>\ce{HO-}>\ce{F-}$$

We know that nucleophilicity parallels basicity along the period, therefore the nucelophilicty order will be as the basicity order:
$$\ce{CH3-}>\ce{NH2-}>\ce{HO-}$$

Now we can compare $\ce{CH3CH2-}$ with $\ce{CH3-}$.

Since methyl is an electron donating group, it will increase the negative charge on the carbanion and therefore $\ce{CH3CH2-}$ will be more nuceleophilic than $\ce{CH3-}$.

Since $\ce{CH3-}$ is more nucleophilic than $\ce{NH2-}$ and $\ce{OH-}$. Also $\ce{CH3CH2-}$ is more nuceleophilic than $\ce{CH3-}$. As a result $\ce{CH3CH2-}$ will be more nuceleophilic than $\ce{NH2-}$ and $\ce{OH-}$ and $\ce{CH3CH2-}$.

We can also compare $\ce{CH3CH2-}$ and $\ce{CH#C-}$. Since $\ce{CH#C-}$ has sp hybridization, it will be less nuceleophilic than $\ce{CH3CH2-}$.

But how can I compare $\ce{CH#C-}$ to either $\ce{OH-}$ or $\ce{NH2-}$?


texts:
I want to use the Briggs-Rauscher experiment to demonstrate oscillating reactions, and then explain it using a numerical model.  How much is known about this reaction?  Is it possible to write down a set of differential equations for the concentrations of each chemical, and solve it to find oscillatory behaviour?

If so, what is a fairly simple but realistic set of differential equations for Briggs-Rauscher, and what are good parameters to find oscillations?

(By fairly simple I mean that it could be handled in an Excel spreadsheet or similar by talented school students.)


texts: Organic problem: acidity of benzene substituents

texts: Ortho nitro benzoic acid is more acidic than para benzoic acid since intermolecular H bonding comes into play in the latter compound. But why is that among para nitro phenol and ortho nitro phenol, para compound is more acidic than that of ortho? There is intermolecular H bonding in para nitro phenol too, right?


texts: Which of the following molecules are enantiomers?

texts: My book says that only molecule 7 is enantiomer of molecule 1. Why is this? Why can't molecule 1 and 2 be enantiomers?


texts: what's the name of this org. compound. RR'-C=NNH2

texts:
What's the name of this compound? It's a semi-product of Wolff-Kishner reduction.

The complete reaction is:


texts: Equilibrium between barium carbonate, and barium oxide and carbon dioxide

texts:
The USNCO 2017 Question 33 is as follows:

Barium carbonate, $\ce{BaCO3}$, is stable at ambient temperatures, but decomposes to barium oxide and carbon dioxide at higher temperatures.
$$\ce{BaCO3(s) <--> BaO(s) + CO2(g)}$$
At a certain temperature, this system in in equilibrium in a closed system and contains appreciable amounts of all three compound. Which changes will lead to an increase in the pressure of $\ce{CO2}$ present at equilibrium?
I. Adding more $\ce{BaCO3(s)}$
II. Increasing the volume of the container
(A) I only
(B) II only
(C) Both I and II
(D) Neither I nor II

What I understand so far:

Concentrations of reactants and products at equilibrium are affected by:

Increasing/decreasing concentrations
Change in pressure/volume
Change in temperature

Temperature remains unchanged, so that factor can be ruled out

(I) does not change concentration, as $\ce{BaCO3(s)}$ is considered to have a constant concentration, and it could be assumed that change in volume due to the addition of $\ce{BaCO3(s)}$ is negligible. Hence, (A) nor (C) are correct

(II) If $\ce{CO2}$ was in a closed system itself, increasing the volume of its container will lead to a decrease of pressure and decrease of concentration.

However, according to Le Châtelier’s Principle, the system should react by favouring the forward reaction, leading me to believe (D) is the correct answer

How do I judge whether or not the increase in volume of the container can be balanced by the increased rate of the forward reaction, such that the pressure of $\ce{CO2}$ remains unchanged at the new equilibrium?


texts:
Just to preface this, I have a very basic understanding of chemistry, so forgive me if what I'm asking is super basic.

How difficult is it to produce diatomic hydrogen? I've been doing some reading on the internet about diatomic hydrogen and a fair amount of the stuff I've come across are health articles relating to the benefits of drinking hydrogen rich water, so I assume that it's not terribly difficult to come across.


texts: In Ion Chromatography instrument, Does the specific conductivity (peak area) of an analyte depends upon background conductivity?

texts:
In Ion Chromatography instrument,
Does the specific conductivity  (peak area) of an analyte depends upon background conductivity ?

Assume Specific Conductivity (peak area) of fluoride ion is 4 unit for 1 ppm fluoride standard with background conductivity of 15 uS/cm (Carbonate/ bicarbonate eluent with suppression.

What will happen if the background conductivity increases to 30 uS/cm or 50 uS/cm.

Pl do not consider the change in retention time.

https://www.metrohm.com/easyDB/Web-61006520_std_carbonate/orig


texts: What is left over when water and sodium hypochorate decompose, i.e. household bleach?

texts:
I am having some confusion in understanding the decompostion of household bleach. One website says bleach decomposes to  salt and sodium chlorate, simple enough.
Orther wedsites say bleach decomposes to salt and nothing else. I called Clorox customer service and their vote is it converts to salt only. I have 3 votes for salt only and 2 votes for salt and sodium chlorate thus far.


texts: Why is the term not squared in the antigen-antibody interaction formula?

texts:
From Antigen-antibody interaction (Wikipedia):

We've basically multiplied two similar terms, because inverted Kd is Ka - why isn't there any square signs (power of two)?


texts: Importance of halogens and nitrogen in degree of unsaturation

texts:
Why is oxygen (or other elements) isn't present in the formulae for calculation of the value of degree of unsaturation $(\mathrm{DU})$ as it usually more common than nitrogen and halogens.
And whats so special about nitrogen and halogens to be in the formulae
$$\mathrm{DU} = C + 1 - \frac{H + X - N}{2},$$
where $C,$ $H,$ $N,$ $X$ are the numbers of carbon, hydrogen, nitrogen and halogen atoms present in the compound, respectively?


texts:
I understand the statement of 'Law of mass action', but I don't understand clearly what 'mass action' means.

I investigated it and found the following descriptions.

The law was originally suggested as a law about 'active mass'. [from Wikipedia]
The term 'active mass' is a historical term that professional chemists do not use anymore. 'Active mass' meant 'amount per unit volume'. [from Chemistry Stack Exchange #58141]

From these explanations, I understood that 'active mass' corresponds to 'concentration' in modern words, which is usually expressed in the unit 'mole per liter' today.

However, a question still remains for me. What does the term 'mass' intend to originally? I am not a native English speaker, so I cannot understand the nuance well.

The word 'mass' has some different meanings.

a physical quantity expressed by the unit kilogram,
a large amount of a substance,
a lot of people, etc.

Of all these meanings, which do native English speakers understand the word 'mass' as?

Background of this question

In Japan, 'Law of mass action' has been translated as '質量作用の法則' (shitsuryou-sayou-no-housoku). '質量' corresponds to 'mass'. Nowadays, however, this is accused as a mistranslation because the law states the nature of concentration and it does not relate to mass. On the other hand, if native English speakers also understand the word 'mass' as 'a physical quantity expressed by the unit kilogram', the translation is not a 'mistranslation' but just a historical word originally. So I would like to consult those who are familiar with both chemistry and English.


texts: Is it possible to "brute-force" material creation through algorithms?

texts:
I know its a bit of a soft question, but lately I've wondered what important properties and calculations would a program that iterates through certain types of molecules and atoms need in order to calculate their individual properties like color, conductivity, reactivity with common substances, etc..

Are there any projects out there that already target something similar to what I have in mind? I know there are a multitude of variables that will come into play, but for the most part say if you were to keep a variety of them constant.


texts: What is the priority order of the four groups?

texts: I'm trying to figure out whether this is in R/S configuration....I thought it would be R since the groups seem to be decreasing in priority in the clockwise direction (since F has the largest atomic number). However, the answers say that it is actually in the S configuration....could someone explain this to me? Have I incorrectly assigned priority?


texts: Can decarboxylation be done under carbon dioxide?

texts:
From Why is the decarboxylation of 2-hydroxybenzoic acid (and related compounds) done 'under nitrogen'? I confirmed that nitrogen is used to exclude oxygen - in order to prevent oxidation of the material.

Can $\ce{CO_2}$ be substituted for nitrogen, or will the presence of carbon dioxide slow down the decarboxylation reaction (which is causing carbon dioxide to be released)?


texts:
I came across this term while going through a research paper for the first time of organic chemistry on diastereoselectivity of tricyclo[2.1.0.02,5]pentan-3-ones. I am not familiar with the term and on doing a google search I came across papers on pi facial selectivity.
This is my first time reading a research paper which is of certainly a different standard all together, so any kind of help in letting me know about the general definition of the term and how it is related to diastereoselectivity will be very much appreciated.
Thank you very much.


texts: Why is the rate law typically written in terms of reactants whilst equilibrium constants are written in terms of products*?

texts:
That is, equilibrium constants are written in terms of products/reactants or for Ksp, in terms of products only.

Why doesn't the rate law also focus on products?

I usually see it written in terms of reactants.


texts: Suitable safe cleaning solution for aliphatic urethane

texts:
I am looking for a suitable cleaning solution for a sprayed on coating that is an acrylic aliphatic urethane. My end goal would ideally be something that can neutralize rust, whiten and brighten the surface, and also include a powerful enough solvent that can loosen stuck on dirt/soap scum but not harm the urethane.

The urethane is approximately 70% solids (don't know if that matters or not). I'm not a chemist so layman's terms would help greatly.


texts: Is Hoffman elimination anti or syn elimination?

texts:
I read an amazing PDF from nptel on elimination reactions...but I was really confused when it used used $\ce{^+NMe3}$ as a leaving group in the reaction pathway via:

$\mathrm{Ei}$ (syn-elimination)
$\mathrm{E2}$ (anti-elimination)
And also, in an illustration for $\mathrm{E1_{cb}}$.

My organic chemistry teacher also did syn-elimination but in the problem solving book and on various online sites it took the $\mathrm{E2}$ elimination pathway.


texts: How does partially thawing a frozen solution affect concentration?

texts: I have a mixture of antibiotics at a concentration of 100X and it is in the frozen state. Now some volume of the frozen mixture has been liquefied. Will the concentration of that liquefied part be 100X, or will it be less than that?


texts: Assigning R/S stereochemistry of a cyclic molecule

texts:
I've been dealing with assigning stereochemistry and I seem to be doing okay, but I've come across a molecule that I've found a little tricky to deal with.

I've identified three stereocentres, highlighted below. My first question would be to confirm that this is correct.

No. 1 is standard fare and I got that it was an R enantiomer.

But for 2 & 3, does the fact that both carbons are bonded to the oxygen have an effect on the rotation of the molecule? As in, when you go through the process of rotating the lowest priority group to the back and then tracing from first priority to third, does this affect the process? It may seem a silly question, but I don't have ball & stick models to easily visualise it so I'm struggling a bit. I treated them as normal and got that they were both R enantiomers, but I'm wondering if I've missed a trick.


texts:
I'm studying medicine, not chemistry, but I hope you can help me anyway.

I just had to solve a question where it is given that the drug Propranolol has a $\text{p}K_{\text{a}}$ of 9.5 and the un-ionized form is non-polar.

Is there any way to say if propranolol is an acid or base just from the $\text{p}K_{\text{a}}$?

Hope to hear from you, and sorry if it is a stupid question.


texts: Electrolysis not running, maybe dependant on distance of electrodes?

texts: So I created a DC power supply of 15 V (special transformator connected to the net) and I have a graphite anode and stainless steel cathode. When I put them in a beaker next to each other in water, the electrolysis takes place as I see gas bubbles. However, when i put them in another container that consists of two beakers connected with a tube to allow liquid to flow through but to separate the gases, the reaction doesn't run while it is the same setup more or less. How come? It is true that the tube connecting the beakers is relatively thin and the distance is also quite large (10 cm or sth), so does this lead to a higher required overpotential? I really don't know why it doesn't work in the larger container. Any help is appreciated!


texts:
İ heard that :
Charge of a mole of electrons/charge of single electron =avagadros constant
How is this derived ?


texts: Arrange these compounds: CO2, CH3OH, RbF, CH3Br in order of increasing boiling points

texts:
Arrange these compounds: $\ce{CO2}$, $\ce{CH3OH}$, $\ce{RbF}$, $\ce{CH3Br}$ in order of increasing boiling points.

I think I should consider the forces between them, that is:

$\ce{CO2}$: dispersion forces
$\ce{RbF}$: dispersion and  ionic forces
$\ce{CH3OH}$: Dipole-dipole interactions, Hydrogen bonding and dispersion forces
$\ce{CH3Br}$: Dipole-dipole interactions and dispersion forces

It is obvious that $\ce{CO2}$ is the smallest one and because $\ce{CH3OH}$ stronger than $\ce{CH3Br}$ it will have higher boiling point

But how to arrange the rest? Or how to compare ionic forces with Dipole?


texts:
I'm probably missing a simple component of this reaction, but for some reason I not seeing it.

These are two steps that compose a radical process of the Briggs-Rauscher reaction (that are autocatalytic):

$IO_3^- + HIO_2+H^+ \rightarrow 2IO_2 \cdot +H_2O$
$IO_2 \cdot + Mn^{2+} + H_2O \rightarrow HIO_2 + Mn(OH)^{2+}$

This process is autocatalytic in the sense that 2 $HIO_2$ is produced for each one consumed.  However, I'm just not seeing that for some reason.  Like I said, it's probably a simple thing I overlooked. So, I'm looking for an explanation for what's going on here.


texts:
Does deuterium peroxide exist? Wikipedia has no reference. Also, the sites for delivery of chemicals like "Pubchem" or "Chemspider" have no reference.

In my book, a preparation of $\ce{D2O2}$ is given,

$$\ce{K2S2O8 + 2D2O -> 2KDSO4 +D2O2}$$

If $\ce{D2O2}$ exist, what are its physical properties (structure and appearance etc.)?


texts: Does a complex that has no overall charge still have color?

texts: The iron complex $\ce{[Fe(H2O)6]^2+}$ is colored but I'm wondering, if a pair of chloride ion is inserted on its secondary valency to form [FeCl2(H2O)6], does the complex loose its color or not?


texts: Which pH indicator will give a dramatic color change with small changes in the amount of carbon dioxide dissolved in water?

texts:
I want to do a demonstration for students where they take a capped syringe and change the volume above a solution of seltzer water.  The amount of carbon dioxide dissolved will vary, hopefully changing pH enough to cause an indicator to change color, the more dramatic the color change, the better.

I have tried universal, bromcresol green, and methyl red with little success.  I can add substances to the seltzer water or change the temperature of the water.  I'd like a SAFE system I can create that will change color upon moving the plunger.


texts:
In the picture below a proportionality equation is shown:

$$\omega \propto \nu \exp\left(\frac{-\Delta G_m}{RT}\right)\propto \dots$$

While $\Delta G_m$ is the Gibbs free energy, $R$ is the gas constant, and $T$ is the temperature, what are the parameters $\omega$ and $\nu$ exactly?

You can see the context on the picture: Yttria-stabilized-zircona.


texts: Reference value for two-electron repulsion integral over GTO's

texts:
I am currently trying to implement a Full CI program from scratch. The energies I get are a bit too high, so I'm looking for the mistake.

One possibility is my implementation of the two-electron repulsion integrals,
$$\int_{-\infty}^\infty \int_{-\infty}^\infty \frac{e^{-\alpha_1 \boldsymbol{r}_1^2} e^{-\alpha_2 \boldsymbol{r}_1^2} e^{-\beta_1 \boldsymbol{r}_2^2} e^{-\beta_2 \boldsymbol{r}_2^2}} {\left| \boldsymbol{r}_1-\boldsymbol{r}_2 \right|\ } \mathrm{d}\boldsymbol{r}_1^3 \mathrm{d}\boldsymbol{r}_2^3 $$

with $\boldsymbol{r}_1=(x_1,y_1,z_1),  \boldsymbol{r}_2=(x_2,y_2,z_2).$

However, I cannot find any values I could compare my results to. I tried (numerical) integration in Maple, but that's way too slow and/or numerically unstable because of the singularity at  $\boldsymbol{r}_1=\boldsymbol{r}_2$. I tried installing the libraries libint and Libcint, and the python module pyscf, which all should be able to do this kind of computations, but I horribly fail at installing things not made for Windows (MINGW is only half working, and I don't have a proper Linux installation available right now...).

So, could someone who has such a program installed please give me a number this integral evaluates to, for whatever numbers $\alpha_1 \ldots \beta_2$ ?


texts: Gibbs energy and chemical equilibrium : false proof of spontaneous generation, but why?

texts:
Let’s assume we have a reaction medium containing only simple molecules such as $\ce{H2O}$, $\ce{CH4}$, $\ce{NH4+}$ (and maybe some more).

Now we consider the following equation ;

  $\Delta G_\mathrm r = \Delta G_\mathrm r^{\circ} + RT \ln Q_\mathrm r$

were $\Delta G_\mathrm r$ is the Gibbs energy change associated to a chemical reaction occurring in this reaction medium, $\Delta G_\mathrm r^{\circ}$ the standard Gibbs energy change of this reaction and $Q_\mathrm r$ the mass action ratio of the reaction in the reaction medium at a given time.

Let’s consider the reaction consisting of the synthesis of a very complex molecule from the simple molecules of the reaction medium (for example, a protein). Whatever the complex molecule is, it is so complex that we are sure that it is absent from the reaction medium, i.e. its concentration is exactly 0. Also, the standard Gibbs energy change of this reaction must be very high (positive), but not infinite.

If the concentration of the complex molecule starts at 0; then $Q_\mathrm r$ is 0; then $RT \ln Q_\mathrm r$ is $-\infty$ ; as $\Delta G_\mathrm r^{\circ}$ is finite, $\Delta G_\mathrm r$ is $-\infty$. So in these conditions, the synthesis of at least one copy of our very complex molecule is infinitely exergonic. This reasoning could be applied to any molecule whose concentration in the reaction medium is 0 at a given time and whose synthesis from the reaction medium is theoretically possible. In the thermodynamics courses I attended, a negative Gibbs energy change was associated with the “favourableness” of a reaction, so those reactions would be “infinitely favourable”.

Of course, this is absurd. But why?


texts: What happens when hydrogen bonds stretch?

texts:
I'm researching about the Mpemba effect and I came across an explanation saying that the effect occurs because at higher temperatures, the hydrogen bonds between the water molecules stretch and store energy and when the water starts to cool, the hydrogen bonds go back to normal and release the stored energy on top of the normal cooling process, that's why hot water freezes faster than cold water.
I'm quite new to hydrogen bonds, so I don't really understand how hydrogen bonds can store energy. I thought bonding was something like a magnet attracting something, the further you get, the weaker the attractive force becomes. Or am I understanding it wrong?
The article that I saw this in is Hot water freezes faster than cold water; physicists solve the Mpemba effect


texts: Why is the dissolution of AgCl considered endothermic?

texts:
The solubility constant of $\ce{AgCl}$ at $25\mathrm{\,^{\circ}C}$ degrees is $1.6\cdot 10^{-10}$.

At $100\mathrm{\,^{\circ}C}$, the $K_{\mathrm{sp}}$ increases to $2.15\cdot 10^{-8}$.

Why is the dissolution of $\ce{AgCl}$ at $100\mathrm{\,^{\circ}C}$ considered endothermic? I would have thought it was exothermic.


texts: Having trouble naming hydrocarbons with the IUPAC nomenclature rules

texts:
First of all, thanks a lot for taking the time. I'm homeschooling and don't currently have any proper teachers, so I thought this would be a good place to ask. Its an easy question I think, but it has me very confused.
In my chemistry book, they showed this hydrocarbon
Translated from Spanish, it would be something like 4-ethyl -1,2 dimethylcyclohexane. Now, my question is, according to the rules, when there is more than one different type of ramification, you number the carbons giving the radical with alphabetical preference the lowest value, in this case, ethyl is first in the alphabet than methyl, so shouldn't it be 1-ethyl- 3,4 dimethylcyclohexane? They would all still be between the first 4 carbons, so the rule of lowest value wouldn't really change. Unless, the di, indicating the 2 methyl radicals counts and gives it alphabetical preference, but to my understanding, those prefixes aren't considered when giving alphabetical preference. Thanks for your time and have a great day!


texts: the textbooks say that it is the amount of electrons lost or gained by an atom in a bond but in a covalent molecule the atoms never technically lose electrons ,instead share them to in such a way to complete their octet.for eg:- In OF2 molecule, it is said that the oxidation state of oxygen is +2 which implies it has lost 2 electrons. However it also must be gaining electrons from the other flourine atoms, right? please help me out with this.


texts: Why do the halides run in reverse orders in the spectrochemical series and the trans-effect series?

texts:
Spectrochemical series: $\ce{F^-}>\ce{Cl^-}>\ce{Br^-}>\ce{I^-}$

Trans-effect series: $\ce{I^-}>\ce{Br^-}>\ce{Cl^-}>\ce{F^-}$

This seems slightly odd to me because their relative ordering surely should be the same because both series depend on sigma donor ability. Does this have something to do with π donor ability?

In what order does σ donor and π donor ability go for halides in transition metal systems?


texts:
In an aqueous solution of $\ce{NaOH}$ exposed to the atmosphere one can probably expect some degree of $$\ce{NaOH(aq) + CO2(g) -> NaHCO3 (aq)}$$

But, what would happen if just a solid block of $\ce{NaOH(s)}$ was placed in some completely anhydrous environment, populated only by excess $\ce{CO2(g)}$ at STP? After all,

$$\ce{NaOH(s) + CO2(g) -> NaHCO3 (s)}$$

is technically a spontaneous process with $\Delta G^\circ = -76.91\ \mathrm{kJ/mol}$, but I can only think of three possibilities:

Nothing happens—no water (i.e., as a catalyst), no reaction!
A passivation layer of $\ce{NaHCO3(s)}$ forms on the surface, preventing the rest of the $\ce{NaOH(s)}$ inside from reacting^
No passivation layer—the $\ce{NaOH(s)}$ just keeps reacting away until it's all $\ce{NaHCO3(s)}$!


texts: Why alkyl shift happens during hydroboration oxidation?

texts:
In this oxidation step, where alkyl shift happens for 3 times to kick out the OH- to obtain the boron-ester. But why does this happen? Won't the boron atom become less stable as the empty p orbital is regenerated? Won't this cause the OH- (strong nucleophile) to attack the boron (electrophile) again?
What is the mechanism of trialkylborane oxidation with hydroperoxide? (I have read this but sorry I don't get it. before this reaction, isn't the boron atom also bonded to an oxygen atom? Why would this reaction make it more stable?)


texts:
I was doing some questions on equilbrium. I got stuck in this particular question.

Identify which of the following reactions are reversible.
$$
\begin{align}
\ce{Fe + S &-> FeS }\label{rxn:1}\tag{1}\\
\ce{NaCl + AgNO3 &-> AgCl + NaNO3}\label{rxn:2}\tag{2}\\
\ce{H2SO4 + Ba(OH)2 &-> BaSO4 + 2 H2O}\label{rxn:3}\tag{3}\\
\ce{H2 +I2 &-> 2HI }\label{rxn:4}\tag{4}\
\end{align}
$$

I know that \eqref{rxn:2} and \eqref{rxn:3} cannot be reversible because one of the products is precipitated.
I could not reach a conclusion between \eqref{rxn:1} and \eqref{rxn:4} (although I know that \eqref{rxn:4} is reversible).
Is there a way to determine without actual experiments whether a reaction is reversible or not?


texts:
I am doing my chemistry homework and I am supposed to write the products when strong acids react with water, but I am unsure of the physical state for hydronium ions. Should it be liquid (l) or aqueous (aq)?

Example:

$\ce{HI(aq) + H2O(l) -> ?}$

Should it be

$\ce{H3O+(aq) + I^{-}(aq) }$ ?

Or should it be

$\ce{H3O+(l) + I^{-}(aq) }$?


texts: Alpha-haloketone reaction with H2O in acid medium

texts:
I need help with this reaction, I know that in the first step an alpha haloketone is formed, but I can't figure out what reaction is going to happen between the alpha Haloketone and $\ce{H2O/H+}$.

I read your answers and this is some information and assumptions that I can share.
For the reaction between the alpha haloketone and the $\ce{H2O/H+}$ ,I thought that the oxygen of the carbonyl could be protonated so the $\ce{C}$ atom becomes more electrophilic, then the water (the nucleophile) could attack that C atom of the carbonyl group.

I found a paper (Erian, A. W, 2003)  where they report a general mechanism for the reaction of alpha haloketones with nucleophiles

So, considering that, I thought this might be the product of this reaction.

What do you think? I'm not really sure of the answer, but that's what I have so far.
This is the complete reference:
Erian, A. W., Sherif, S. M., Gaber, H. M. (2003), "The chemistry of α-haloketones and their utility in heterocyclic synthesis", Molecules, 8(11), 793–865. (https://doi.org/10.3390/81100793)


texts: The electrons in the 1s orbital of chlorine have a binding energy of 273 MJ/mol, but the 1s electrons in sulfur have a binding energy of 239 MJ/mol. Why is this?


texts: How is nomenclature decided in this case (formyl vs oxy)?

texts:
I was asked the IUPAC Name of the following compound in JEE Mains (2nd September, Shift 1) 2020.

There were two names occuring to me:

5-formyl-2-methyl-hex-2-enoic acid
(2,5)-dimethyl-6-oxo-hex-2-enoic acid

I finally chose (2), but the temporary answer key says (1). Can someone please tell which is the correct one and why?
Note: As I realised after receiving a comment, I've accidentally made the double bond have (E) configuration. This is an unintended error due to the website I used to construct the compound's structure. Please note that the original compound did not have any stereochemistry indicated


texts: Trend in the melting point down the group

texts:
We know that the atomic radii increases down the group. So, less energy is required to pull out the outermost electron as we go down the group, hence,  gradually melting point decreases down the group.  The topmost element has large melting point because of its small atomic radii and so more energy is required to pull out its outermost electron.

But, it is observed that the melting point slightly increases in case of the bottom-most element of group as compared to the previous element. Why?

Examples:

Group 13 - indium - $\pu{156.6^\circ C}$ but  thallium - $\pu{304^\circ  C}$
Group 14 - tin - $\pu{231.92^\circ  C}$ but lead - $\pu{327.46^\circ C}$
Group 17 - iodine - $\pu{113.5^\circ  C}$ but astatine - $\pu{302^\circ C}$


texts: How to convert the D'Arcy and Watt model from activity to concentration in mol/m^3

texts:
The D'Arcy and Watt 1970 model in "Analysis of sorption isotherms of non-homogeneous sorbents" for water adsorption is as follows:

$$W = \frac{KK'a}{1+Ka} + ca + \frac{kk'a}{1-ka},$$

where:

$W$ is weight of vapour adsorbed per $1~\pu{g}$ of substrate per $1~\pu{g}$ sorbent ($\pu{g/g}$)
$a$ is the water activity or relative humidity (no units, number between $0$ and $1$ or if relative humidity is used - is percentage)
rest are constants with no units

I want to use this model to consider water concentration in $\pu{mol m^-3}$ instead of water activity.

How do I convert this?


texts: Why don't ionic compounds show stereoisomerism?

texts: When I was reading about crystalline nature of ionic compounds, I came across the statement that ionic compound doesn't show stereoisomerism. What does that mean and can anybody explain the reason with an example?


texts: Reaction between free radicals and water

texts: Free-radical substitution does not occur in aqueous solution as free radicals react with water (from school textbook). What does the reaction between free radicals, say Br, and water produce?


texts: Will Ammonia react with Gasoline mixed with Ethanol?

texts:
Recently the South Koreans invented a car that runs on an 70% ammonia 30% gasoline fuel mix.  (link) In America we already have instituted policies that require refueling stations to mix Ethanol produced from corn stills with gasoline to extend our fuel supply.

My question is, if you added a ammonia to an ethanol/gasoline fuel mix, would it cause a reaction?  If not, would it still burn and be able to be used as fuel?


texts: Do indigo and leuco-indigo have fully conjugated pi systems?

texts:
I've just come across a figure indicating the positions of conjugated bonds in indigo and leucoindigo, and I'm quite confused about why both molecules aren't fully conjugated.

My reasoning is as follows:

Both carbons above and below the bond are sp2 hybridized and have π electrons.
The carbon to the left is sp2 hybridized and has π electrons, and the nitrogen to the right has a lone pair.
Same as 2.
Same as 1.

I also want to ask about why leuco-indigo isn't planar. According to Wikipedia:

  In indigo white, the conjugation is interrupted because the molecule is nonplanar.


texts: How is it possible to safely use carbon monoxide as a fuel?

texts:
Is there anything that will allow carbon monoxide to be used as a fuel? It is quite toxic, but has attractive properties otherwise (only produces CO2 with no water, also no smoke or soot). Aside from a permanent spark, or a pilot light, I can't see any way of doing this.

Is there some catalyst that will help the reaction? Apparently, platinum can be used as catalyst between hydrogen and air.


texts:
I know it is usually easier to go from an acyl chloride to an aldehyde,

but is there a way to synthesize acyl chlorides from an aldehyde?

Edit:

Upon some textbook reading (Wiley: Organic Chemistry 11th Ed, Solomons), I realized that aldehydes could also be oxidized to carboxylic acids with chromic acid in aqueous acetone (the Jones Oxidation) and then you could react the carboxylic acid with thionyl chloride or phosphorus trichloride to yield the acyl chloride.

Another method was to convert the aldehyde into a cyanohydrin and through hydrolysis the -CN group could be then converted into $\ce{RCOOH}$. Then react $\ce{RCOOH}$ with $\ce{SOCl2}$ to get the acyl chloride.


texts: Make very accurate solutions without weighing

texts: I am currently facing a hen-egg problem. For a LC-MS method development I need to prepare reference solutions which are used to calibrate the method. Since the method is to be used for quantification in the pg/mL range, the reference solutions should have the most accurate concentrations possible. Of course I know how to prepare exact solutions in volumetric flasks, but here substance quantities are used which can be weighed easily and also quite exactly. In my case, only a few milligrams of the substance are available to me, which is why I cannot weigh high masses. The precision balance that I have at my disposal has a lower weighing limit of 1 mg, which is about the same as the mass that I would have to weigh. However, since the lower limit is very error-prone, I do not like this method. Unfortunately, I cannot think of an alternative solution that would allow me to create an exact solution without weighing. One could of course dissolve any amount of substance in the desired solvent and then determine the concentration by LC-MS, but this is exactly where the hen-egg problem mentioned above occurs. I cannot quantify via LC-MS until I have a suitable method and an internal standard. Are there any other ideas how to get exact concentrations using small amounts of the desired substance?


texts:
Maybe someone here is familiar with supramolecules calculations using Spartan? I am new in this area and trying to figure out some things:
First - what's the best way to draw them? I tried to draw one molecule and then using copy-paste append the others but then they overlap and it takes forever to minimize their energy so they make hydrogen bonds in the places I need. Maybe there is any way to 'freeze' hydrogen bonds? Because I now where they shoud be (or at least want to calculate different structures with hb in different places of molecules). If I try to put this molecules near when sketching still when I try to minimize the energy hb forms not in the exact places I need them to be. And I need four molecules to form kinda cyclic-structure.
Thank you in advance!

hb I need between two molecules are:


texts: Are there atoms with different numbers of protons, but the same number of electrons, with different orbital occupations?

texts:
Imagine there is an electron-stripped nucleus with $Z$ protons, in high vacuum and isolated. Then you add electrons, one by one, and check which orbitals are filled. Will this depend on $Z$ at all, or does it only depend on the number of electrons that are added?

In other words, will an ion have different orbits filled than the corresponding neutral atom with the same number of electrons?

In other words: are there atoms with numbers of protons $Z_1$ and $Z_2$, both with $n\leq\operatorname{min}(Z_1, Z_2)$ electrons that have different orbital fillings?


texts: Why does the energy difference of a reversible process not equal that of an irreversible process in an adiabatic expansion?

texts: Suppose that one mole of an ideal gas at $P_1$ and $V_1$ adiabatically expands to $P_2$ and $V_2$, reversibly and irreversibly (two separate processes). Since $\Delta U$ is a state function, why is it wrong to say that $\Delta U_{rev} = \Delta U_{irrev}$? (Since in an adiabatic process, there is no heat transfer, we know that $\Delta U = w$)?


texts: In meta hydroxy benzaldehyde which position (w.r.t hydroxy group) is more prone to electrophilic attack?

texts:
In meta hydroxy benzaldehyde which position (w.r.t hydroxy group) is more prone to electrophilic attack ?

My approach:I considered hydroxy group as the stronger +M group.So my guess was para position w.r.t hydroxy group.But that's not the correct answer.

The answer is actually given as ortho w.r.t hydroxy and para w.r.t -CHO group!!


texts: What is the mechanism for the ozonolysis of a nitronate anion? What gas is produced in this reaction? Is there any chemoselectivity in the presence of a double C=C bond in the molecule?


texts: How to measure quantities at standard state when this state is a hypothetical one?

texts:
Consider the reaction

$$\ce{A(g) + H2O(l) <=> B(aq) + C(g)}$$

If all gases and solutions were ideal, the standard state would be pure water, the solute B at a concentration of 1 M, the gases A and C each at a pressure of 1 bar, and the system at a pressure of 1 bar.

For non-ideal gases and solutions, it would be the hypothetical state where all the activities are 1 (i.e. equal to the activity of an ideal gas at 1 bar, activity of a solvent with infinitely diluted solutes, and equal to the activity of a solute behaving ideally at a concentration of 1 M).

This hypothetical state can be quite different from a real state. How can the pressure be 1 bar while two gases are at a partial pressure of 1 bar each? What if the solute B is barely soluble, how do you get an activity of 1? How can you have pure water when it is acting as a solvent?

So how to you measure quantities like $\Delta_\mathrm{r} G^\circ$ when the standard state is a hypothetical one?


texts: Identify "decoupling sites" in glucose oxydase reaction

texts:
Given the following coupled reactions:
  $$\ce{glucose + O2 + H2O + glucose~oxydase -> gluconic~acid + H2O2}$$
  $$\ce{H2O2 + TMB(star) -> TMB}$$

  Identify:

  A potential reagent or product that could act as a decoupling site leading to a falsely high glucose concentration.
  A potential reagent or product that could act as a decoupling site leading to a falsely low glucose concentration.

Note: The second reaction is just hydrogen peroxide reacting with $\ce{3,3',5,5'-Tetramethylbenzidine}$, to form the more absorbent version (I can't remember if it's reduced or oxidized).

The experiment involves running the above reaction on a sample with an unknown amount of glucose, then running the sample through a spectrometer to determine the absorbance and thus the concentration of glucose.

The only thing I can think of is that if the sample warmed up too much you might lose some of the oxygen, resulting in a lower than expected glucose measurement. Though you'd have to lose enough oxygen for it to become the limiting reactant, which I don't see as being too plausible.

I can't find anything anywhere else and I'm stumped.


texts: Measured g-factor of a free-radical changing as a function of something. But I cant work out what?

texts:
I'm looking at EPR of a paramagnetic organic molecule in solution that has a very stable free-radical signature with gfactor ~2.0035. All good. Except when watching one particular experiment I saw that the g-factor was drifting [the zero-crossing was slowly moving to the right over the course of 24hrs, i.e. the g-factor was dropping]. The Vpp was not changing. I am happy to believe that the molecule was self-aggregating. I would be even happier if there was a theory that related g-factor to particle size (e.g. via tumbling rate) because then I could estimate aggregation by looking at the gfactor. And that is where I get stumped. Are there any theoretical papers that discuss rotation effects on organic free radicals?
Or maybe my EPR machine is just drifting :-(


texts: Electrophilic substitution of an indole as opposed to benzofuran and benzothiophene

texts:
Regioselectivity in electrophilic aromatic substitution of benzofuran and indole

This response as to the regioselectivity of the electrophilic aromatic substitution of indole left me with a few more questions than it did answers.

In figure 3b, does the pi bond in the bottom half of the benzene on the left get pushed to the nitrogen, allowing for stabilization across the benzene ring in addition to the resonance structures of the nitrogen cation? And if so, and this is the case of a viable nitrogen cation contributing to the stabilization of a valid resonance structure, is it true that all (or most) polycyclic compounds that undergo electrophilic substitution at a location on the nitrogen-containing ring that result in the temporary resonance structure of a nitrogen cation along with stabilization across a benzene ring will be more stable than substitution at a location that would only provide the resonance across the benzene (e.g. without the possible nitrogen cation, had electrophilic substitution occurred elsewhere)?

Furthermore, does this imply that in the electrophilic aromatic substitution pattern of benzothiophene, seeing as how sulfur is less electrophilic than both oxygen and nitrogen, that we would see a similar substitution pattern at the 3-position, as opposed to the substitution at the 2-position that we would see (And that is, to my puny little brain, comprehensible) on benzofuran?


texts: Pipetting strong acid with plastic material

texts: Can I pipette concentrated sulfuric acid using a plastic pipette tip? Will either the plastic or the acid be affected?


texts: Are there any tricks I can use to pull SO2F2 out of the air?

texts:
A massive apartment complex near where I live is being fumigated with Vikane gas (sulphuryl flouride, $\ce{SO2F2}$).  The process will take a long time (weeks) because there are a lot of buildings, and their tents appear to have rips in them, clearly visible: several neighbors have complained of symptoms of exposure to the gas, and I'm worried about it in my home.  Obviously we should try to get them to stop / etc., but that's a matter of law and politics not meant for a chemistry site.

In the meantime, what I would like to know is if there is any safe way I can use to pull the gas out of the air if it should waft its way into my home.  My understanding is that activated charcoal will not work for this molecule.  I've heard that either strong bases (usually photo-developing chemicals are mentioned) or heavy water vapor reacts with the gas; but I'm not sure what that reaction is, or if it would result in something better or worse than the gas itself.  I've tried Googling but with just a high school chemistry exposure some decades ago, I can't make much headway.  Please note that I do not have access to any chemicals or machines I can't readily buy in a nearby store.  My goal is to turn it into some liquid or solid, or bind it to such, so that I can't breath it in.


texts: Order of reaction / Rate-determining step in enzyme catalysed reactions

texts:
According to my chemistry book, there are 3 simplified steps within an enzyme catalysed reaction:

$\displaystyle\ce{S + E -> ES}$
$\displaystyle\ce{ES -> EP}$
$\displaystyle\ce{EP -> E + P}$

Where S is substrate, E is enzyme, ES is enzyme substrate complex, EP is enzyme product complex and P is product.

It is my understanding that at first, when substrate concentration is low the rate determining step is step 1, as this is the slowest step in the mechanism.

When you increase substrate concentration to a certain level, where there are no free enzymes remaining to bond with them, adding more substrate will not make the reaction faster, so the order has become 0 with respect to substrate conc.

Is the rate determining step now 2 or 3? I thought it would be 3 as that is the step that frees up more enzymes which could go on to catalyse more reactions. My book says that it is step 2, as "it depends on how fast the ES can convert into EP". But surely this step won't free up more enzymes to catalyse reaction further?

Is the book correct? Can anyone help me understand this?


texts: Why is ammonium chloride rather than an alkylammonium chloride salt the product of nucleophilic substitution of a chloroalkane by ammonia?

texts: My textbook said that when an excess of ethanolic ammonia is heated with a haloalkane ($\ce{R-X}$) one should give the products as being $\ce{R-NH2}$ and $\ce{NH4Cl}$ as opposed to $\ce{RNH3Cl}$. I understand that in reality an equilibrium will exist between the alkylammonium and ammonium cations, but I thought amines were stronger bases than ammonia, so I find it odd that I would be asked to give the ammonium salt and an amine rather than the alkylammonium salt as the major product of this reaction. Have I misunderstood something?


texts: What is a relationship between Volumetric Analysis and Titration Theory?

texts:
I believe that Volumetric Analysis and Tetration Theory are not the same subject.
But I need to know what is a main difference between those subjects and what is a main intersection?


texts: High or low spin complex of Zn2+ and Ti3+

texts:
The zinc ion in its +2 state can show no more pairing, since all the electrons are already paired - so in any complex it forms it will have the same magnetic moment as it does right now. $\ce{Ti}$ in its +3 state will show both outer and inner orbital complexes without any electrons pairing.

So while calling these complexes high spin or low spin complexes is not useful, since there is no possibility of pairing involved in either - but all the same, won't they be called high spin complexes, since no lowering of magnetic moment occurs?

My teacher said, however, that since $\ce{Zn}$ in +2 state forms only outer orbital complexes, its complexes will be called high spin - and $\ce{Ti}$ in its +2 state similarly when it forms inner orbital complexes (which it does without pairing), will be called low spin because the complex is inner orbital. But shouldn't such a complex of $\ce{Ti}$ be a high spin complex? (I'm saying this in reference to VBT).


texts: How do chemists measure purity in high purity metals and other reagents?

texts:
I have noticed that gold bars are often marked "999.9" fine:

Whenever I have metallurgical assays done, they always seem to do them with ISP or DSP or whatever, some spectrometer-based system. These systems have errors of 1% to 2%. When I complain about the high error, they say "it's good enough" and "nobody does the old fashioned stuff anymore". So, if ± 2% is the new standard for assayists, how are these banks determining that the gold is pure to a 9999 out of 10,000 standard?


texts: Suspension liquid for ferrofluid that makes it float

texts: I am currently devising a project to create a kinetic sculpture, similar to Sachiko Kodama. Does anyone know any suspension liquids that when applied, the ferrofluid floats on top?


texts: Question about relation between two time constants

texts:
I am not a chemist, but a neuroscientist, so bear with me. I have struggled with this problem for over a week now and have realized it's a chemical question. I'll try to explain it so no neuroscience background is needed.

I am trying to fit a model to experimental data. The data describes how a certain channel opens and closes in response to a change in membrane potential of the cell the channel sits in. This is captured in two datasets:

The fraction of open channels at equilibrium for different values of the membrane potential (an example of a plot of this can be found here. This fraction I call G/G$_{max}$
The time constant describing the time it takes for the fraction to come to its equilibrium. This time constant I call $\tau_{G/G_{max}}$

It is thought that for each open channel, 4 gates have to be in the 'open' state. That is, it is thought that:

G/G$_{max}$ = n$_{\infty}^4$

The gate n, too, can be described by its fraction of open-state/total.
The rates of n moving between these two states are described by $\alpha_n$ and $\beta_n$. Once there are four gates in the open-state, the channel is instantly open.
 If I try to describe this in a chemical reaction, I would guess something like:

$$\ce{C_n <=>[\alpha_n][\beta_n] O_n}$$

where $C_n$ and $O_n$ depict 'closed' and 'open' n-gates respectively. And

$$\ce{4\cdot O_n <=>[instant][instant] O_{ch} }$$,
where $O_{ch}$ describes the whole channel being open.

Now is the data I've got for G/G$_{max}$(V) and $\tau_{G/G_{max}}$ (this is the only thing the experimentalists can measure). However, to model this behavior, I need $\alpha$(V) and $\beta$(V). I already know that

$n_{\infty} = (G/G_{max})^{1/4}$

but I cannot figure out how $\tau_n$ and $\tau_{G/G_{max}}$ are related to each other. Even though the reaction 4O --> open channel is instant, the shape of approaching the equilibrium differs and thus the point that they cross 1-1/e would as well. n will reach its equilibrium with a single exponential, while G/G$_{max}$ reaches it with an exponential to the fourth power.

I think the answer should be quite simple, and should only depend on the 4'th power.

I hope my question is clear, but if there are more details that will help solve this I am more than happy to clarify certain points.

Edit: Here is a figure that shows how the 'measured' time constant and the one for the differential variable n differ. Also, it shows that there is not a linear relationship.

Just to be clear about what I did:

The differential system describing this model looks like:
G/G$_{max}$ = n$^4$
with
$\frac{dn}{dt} = \alpha_n(V)(1 - n_{\infty}(V)) - \beta(V) n_{\infty}(V)$

As one of the answers pointed out (sort of), a solution to this system with initial condition V1 is:

$n(t) = n_{\infty}(V) \cdot e^{-(\alpha_n(V) + \beta_n(V))} + n_{\infty}(V) \cdot \Big(1 - e^{-(\alpha_n(V) + \beta_n(V))}\Big)$

and thus

$G/G_{max}(t) = n(t)^4$

To find the $\tau$ of either of these traces (the time constant being the time it takes to reach $1-1/e \cdot$(final value) (see link), I plotted:

$\frac{n - min(n)}{max(n) - min(n)}$

and

$\frac{n^4 - min(n^4)}{max(n^4) - min(n^4)}$


texts: Taking Castor Oil from room temperature to 300 degrees Celsius

texts:
I am doing a project where I heat up a container (around 500ml) filed with castor oil at room temperature. I want to add a pressure/safety valve that opens up when the castor oil reaches around 300 degrees Celsius (boiling temperature). In order to get the right valve I have to know how much the pressure increases with in that process. How can I calculate this? And were can I find the required data?

Is there something else I need to consider?

Thanks,

EDIT: Like I have experienced, it seems impossible to find the required data. What if I used mineral oil instead?


texts: Draw a simplified MO diagram for the pi system of Methyl vinyl ether

texts:
My attempt at the answers:

i) 2 bond pairs and 2 lone pairs on oxygen atom therefore bond angle of slightly less than 109.5 degrees, around 104 degrees.

ii) 120 degrees bond angle therefore $\mathrm{sp^2}$ hybridization.

iii) From what I understand, the sigma-pi separation means that you can neglect interactions between the $\mathrm{p_z}$ and $\mathrm{p_x,p_y}$ orbitals?

The $\ce{CH2}$ carbon would form $\mathrm{sp^2}$ hybrid orbitals.

The $\ce{CH3}$ carbon would form $\mathrm{sp^3}$ hybrid orbitals and would then form 3 sigma bonds with the hydrogen leaving only one orbital to interact with the oxygen. I assume that the oxygen $\mathrm{s}$ orbitals do not match the energy level of the carbon and will form non-bonding orbitals. Therefore the $\ce{C-O}$ sigma bond would be $\mathrm{sp^3-p}$.

I am unsure how to use this knowledge to actually draw the MO diagram? I have tried an attempt below. I can draw MO diagrams for simple diatomic molecules. And how would the MO diagram explain the observed 120 degree bond angle?

iv) I haven't used the MO diagram to draw these resonance structures but I have come up with two based on the octet rule:


texts: I calculated internal energy at various temperatures and pressures. My results differ from someone else's. Is this OK?

texts:
I would like to make sure that my understanding of internal energy is correct.  I'm not a thermodynamicist, so apologies in advance for what is probably a basic question.
I previously calculated density for a liquid system via molecular dynamics (NPT ensemble).  I needed the results for use in fluid flow simulations.  The calculations also generated internal energy, which I have so far ignored.  However, someone has expressed interest in comparing my internal energy results with his.  He looked at the same system, but used a different calculation method.
His internal energies, E, for all temperatures and pressures are between -11000 to -12000 kJ/mol.  Mine are between -38000 and -40000 kJ/mol.
Here's my question.  Is it correct that I don't need to worry that one of us has made a mistake--that it's OK for the absolute values to differ as long as the differences are consistent?  For example, his highest-temperature, highest-pressure data point differs from his lowest-temperature, lowest-pressure data point by about the same amount as mine does.


texts: What is substance that has high melting point in its powder form?

texts:
In laminated glass bending process 2 glass sheet will be superposed in a furnance.The seperation powder will be interposed between layer for avoid 2 glass sheet being bound together.

I'm trying to find substance that can be replaced baby powder as a lubricant in the process of glass-bending. It has to be cheaper, able to be found as a powder, and it should not be a human hazard.

Recently, I found magnesium sulfate, and I believe that it could be used for my purposes. However, it is so hard to find $\ce{MgSO4}$ in a compact and powdered form.

Does anybody know of any suitable replacements for baby powder in the process of glass-bending?


texts: Which theta should be taken from x-ray diffraction pattern for calculating Scherrer's equation?

texts:
We use Scherrer's equation to calculate crystalline size of a particle:

$$d = \frac{Bλ}{β\cos{θ}}$$

But which theta should we take from the XRD pattern for this calculation?

For example, the following plot shows the diffraction pattern of nano (above) and bulk (below) silicon and it has two diffraction peaks at $2θ \approx 69^\circ$ and $2θ \approx 76^\circ$. Which theta should we take for calculating crystalline size of nano silicon and why?


texts: How is the UV-visible spectra of carbonatotetraamminecobalt(III) nitrate interpreted?

texts:
In a laboratory practice I have done a characterization of the $\ce{[Co(NH3)4CO3]NO3}$ and obtained the following spectra:

I don't know if the band between 300 nm and 400 nm can be due to the effect of the counteranion or if it is a d–d transition.


texts:
I have encountered this reaction when I am learning entropy:

I don't understand why there is an increase in entropy (said to be slightly larger than 0).
What I am thinking is:

both reactants and products are in the same states, so there isn't any change in entropy in terms of states.
both the reactant and products have the same number of moles i.e. the same number of molecules, which means in a constant volume, means the 'disorderliness is the same throughout the reaction, hence the entropy.

According to my lecturer and the internet, it is said that "Pure substances tend to have lower entropy than compounds" and "the pure substances are arranged 'tidier' than its compounds", which I don't understand why, especially the meaning of 'tidier'.
Therefore, I would like to ask what makes this reaction has an increase in entropy, and how can I determine that?
Thank you.


texts: Determine molecular weight of biomass based on ultimate analysis

texts:
The ultimate analysis (by weight percent) for beech wood is:
$$\ce{C}=49.05\,\%,\; \ce{H}=5.83\,\%,\; \ce{O}=45\,\%,\; \ce{N}=0.12\,\%$$
Using the ultimate analysis values, the molar mass of each element, and assuming 100 grams of wood (therefore C = 49.05 g, H = 5.83 g, etc.), a representative formula for the beech wood is:
$$
\ce{C} = 49.05/12.01 = 4.0841\; \ce{mol} \\
\ce{H} = 5.83/1.01 = 5.77\; \ce{mol} \\
\ce{O} = 45/16 = 2.81\; \ce{mol} \\
\ce{N} = 0.12/14.01 = 0.0086\; \ce{mol} \\
\ce{C}_{\,4.0841\,}\ce{H}_{\,5.77\,}\ce{O}_{\,2.81\,}\ce{N}_{\,0.0086\,}
$$

What is the molecular weight of the beech wood based on the representative formula?


texts: Why do we multiply two wavefunctions in valence bond theory instead of adding them?

texts: The combined wavefunction of a hydrogen molecule in valence bond theory is the product of two wavefunctions, while in molecular orbital theory it is the sum of two wavefunctions.


texts: Rietveld (FullProf) general background function

texts:
I was reading through Eric Mittemeijer's book 'Modern Diffraction Methods' when I found the following statement in the Rietveld chapter by Robert Dinnebier.

  It is common practice to use orthogonal Chebyshev polynomials of higher order
  (typically 5–10) in combination with an 1/(2θi) term to describe a steep increase in the background at low scattering angle [...]. If higher-order polynomials are used, different types of correlations can occur, which require careful checking of the correlation matrix.

When I am usually describing my background in FullProf I use the '6-Coefficients polynomial function'. But this seems to cause more problems the more parameters I refine. So I switched to the 'Chebyshev polynomial' and refinded all 24 parameters (just to make sure). This caused a large jump in the X² from about 10 to 6.5 while the background was much better described.

My question is, although it is mentioned in the book, that Chebyshev is more common and I should be careful with using higher order polynomials, is this something I can use in general for my refinements? Can I just automatically assume for most x-ray determined backgrounds that using a Chebyshev polynomial with as many parameters refined as possible will give me useful results? By useful I mean good and especially 'allowed' results. Because sometimes FullProf refines parameters into regions where they are not defined like a negative η for the Pseudo-Voigt function.


texts: Cathodic protection of tubes in Shell & Tube Heat Exchanger

texts:
Our $\ce{Cl2}$ liquifier is of the following type:

It is entirely made of mild steel (shell as well as tubes plus the connecting pipelines). At shell side there is Freon (R-12) with its refrigeration cycle (not shown here); at the tube side there is dried & compressed $\ce{Cl2}$ gas from compressor section (~2bar max). One must realise that drying of $\ce{Cl2}$ is done physically via passing it through packed glass wool columns & then washing it in $\ce{H2SO4}$ scrubbers & then again through glass wool columns...Compression is done via $\ce{H2SO4}$ liquid ring compressors.

Problem we face is excess corrosion of tubes which thus lose their thickness & may in time compromise...For instance every 2-3 weeks we open up this liquifier & wash the tubes (via high pressure demi/RO water) & we found quiet an amount of dark-green/brown sludge indicating ineffectiveness of our drying section. Lab test are yet to be done so that I can clearly say what this sludge is made of. From the WIKI what I understand the compounds of such colour can either be oxides or chlorides of Iron because sulphates of iron are yellow in colour...

In a nutshell what I can do is increase the number of drying towers or increase the number of glass wool columns, but the most active measure I am thinking of cathodic protection via impressed currents. Have any user here applied impressed currents to a S&T heat exchanger & how can it be done? I would love any literature on it.

As a side note our liquifier can be electrically isolated using gaskets & insulated teflon bolts on any flange fitting.


texts: Is Orca wrongly breaking bonds? Why can it only optimize the molecule with COPT activated?


texts:
I performed an experiment about the corrosion of iron. I used acid and base in the experiment.

I understand that the acid speeds up the corrosion of iron. But I don't understand why the base also corrodes iron. I can't find out the answer even after I've googled it.

In my experiment I mix an ulcer drug into a glass of water, then I put in an iron nail. After I let it sit for a few days, the iron nail becomes rusty. I don't know of any reaction between a base and iron that gives rust.


texts:
What are the conditions for the evaporation of water?

I know that for the boiling of water, the vapor pressure of water must equal the partial pressure of water vapor.

But what about for evaporation? Is it the same condition above in addition to the requirement that the relative humidity cannot be 100%?

Can we have boiling when the relative humidity is 100%?


texts:
The order of successive ionization enthalpies of group 15 are as follows :

$$\Delta H_1<\Delta H_2<\Delta H_3$$

But as all the fifteen group elements have a very stable electronic configuration with half filled p orbital so it would require more energy to remove an electron from an extraordinarily stable configuration so the order according to me should be $\Delta H_1>\Delta H_2>\Delta H_3$.

please guide me if I am wrong.


texts: I understand that by adding Nitrogen to my water my Lucerne plants will grow better. Firtsly, is this correct? Secondly, if so, I further understand that I must add/mix Ammonia (NH3) and nitric acid (HNO3) to form nitrogen which is added to the water, is this correct? However I understand that these two (Ammonia (NH3) and nitric acid (HNO3)) is highly corrosive, therefore would this corrode my irrigation system or damage my lucerne crops, rather than increase the growth? Help will be appreciated!


texts: Stereoisomers of metaldehyde and paraldehyde

texts:
(1) In case of paraldehyde I see 3 similar chiral carbons. So I divided it into 2 subcases
-two methyls above the plane and one below the plane
-all three above the plane
so, that makes it 2. When I looked this up on Wikipedia I found this,

can,(1) and (4) not be obtained by simply ring flipping, doesn't that make them conformers? Do I need to count them separately in my count of stereoisomers?

this according to me should have 4 stereosiomer(not including conformers) can someone confirm this answer? Are there any more im missing out?


texts: Does SiCl2 exist and its possible structure

texts:
It's known that the elements in IVA all have valence +2 and +4. I also know there exists $\ce{GeCl2}$ and $\ce{SnCl2}$. So my question is does $\ce{SiCl2}$, or even $\ce{CCl2}$ exist? If yes, what about their molecular structure?

In addition, what makes +2 valence in $\ce{Ge}, \ce{Sn}$ more stable?


texts: Water competes with any ions in solution for both oxidation and reduction. There are $1000\ \mathrm{g\ l^{-1}}/18\ \mathrm{g\ mol^{-1}}\approx55.56\ \mathrm{mol\  l^{-1}}$. That is truly huge in comparison to any amount of salt we can dissolve. Why doesn't water dominate any electrolysis reaction since even if a small percentage of the collisions of water can accomplish the reaction? The sheer number of collisions on its side will ensure it wins. Also, if hydrogen ions and hydroxide ions alone participated, a concentration of $10^{-7}$ means that it's several orders of magnitude away from the dissolved salt's ion concentration, which means that water can never dominate. Yet, we use a comparison of the thermodynamic feasibility in the form of reduction potentials to decide which competing ion gives the product. How is it that the concentration effects become comparable enough to allow this in most cases?


texts: Enthalpy of neutralisation for weak acids and weak bases at standard state

texts:
I recently read about why for weak acids and bases the enthalpy of neutralisation is less as compared to the strong ones. This was because the acids and bases being weak, they dissociate incompletely and even in this they absorb energy.

I have two questions regarding this:

At standard state, for a solute, we take the hypothetical case of unit molality behaving as one which is infinitely diluted, then shouldn’t even weak acids or bases act as strong acids/bases (because they are, at least in theory assumed to behave as if they were infinitely diluted)?
It's mentioned that during dissociation they (weak acids/bases) absorb heat. Wouldn't even strong ones absorb at least some heat to effect their dissociation.

I find the first question to be more important in terms of conceptual value.


texts:
I'm currently taking chemistry 12. On our test we were asked, when given a $0.1~\mathrm{M}$ solution of certain compounds whether the resulting solution when added to water would be acidic, basic, or neutral.

At first, I thought the solution would be neutral, because we learnt in class that alkali earth metals and chloride are spectator ions and therefore don't interact with water and pH.

However, I then realized that $\ce{Mg(OH)2}$ has low solubility in water, and I assume that adding $\ce{MgCl2}$, would dissociate and then precipitate $\ce{Mg(OH)2}$ from the solution, therefore the resulting solution would be acidic. My final answer was acidic.

The teacher marked my answer wrong, but when questioned could only say that $\ce{Mg}$ and $\ce{Cl}$ are both spectators, but was unable to give direct contradictory proof against my answer.

I looked elsewhere online and Wikipedia states that anhydrous $\ce{MgCl2}$ is a Lewis acid, despite being a weak one. But anhydrous seems to mean without water, so I currently have no idea which answer is correct.

I would like an explanation to why it is acidic or neutral and why the contradicting argument (both spectators vs low solubility of $\ce{Mg(OH)2}$ ) is invalid or flawed.


texts: Why do unsaturated hydrocarbons burn with a sooty flame while saturated hydrocarbons burn with a clear flame when burnt in the air?

texts:
Why do saturated hydrocarbons burn with a clean flame while unsaturated hydrocarbons burn with a sooty flame when burnt in air?

My chemistry book says that it happens due to the amount of carbon being more than the amount of hydrogen in unsaturated hydrocarbons. But isn't that also the case with saturated hydrocarbons?


texts:
The question: In the lab described below, why did the decolorization reaction described, which should be first order in each of the two reactants, go most slowly when the reactants were most concentrated?

As part of the introduction to our kinetics unit, I asked my students for factors that they thought would influence the amount of time it takes a reaction to occur.  Not surprisingly, they came up with a variety of things, including temperature and the concentration of reactants.  I set up a simple lab to compare temperature and concentration conditions based on the reaction of crystal violet with sodium hydroxide.  Later in the unit we will come back to the reaction and analyze its kinetics more carefully, but for the moment, I just wanted my students to do a more basic analysis.

The students did trials for 4 conditions, and each involved the same quantity of reactants: 25 ml of 0.10 mM crystal violet and 25 ml of 1.0M sodium hydroxide.  The reaction was performed by adding the crystal violet to a flask, adding water to dilute, adding the sodium hydroxide to the flask, stirring, and timing the reaction until it no longer showed visible purple.  (Yes, that's a sloppy endpoint, but it was sufficient for this activity's purposes.)

Trial 1: 25 ml crystal violet, 150 ml room temp distilled water, 25 ml sodium hydroxide (a 1:8 dilution of stock reactants)

Trial 2: 25 ml crystal violet, 150 ml hot distilled water, 25 ml sodium hydroxide

Trial 3: 25 ml crystal violet, 50 ml room temp distilled water, 25 ml sodium hydroxide (a 1:4 dilution of stock reactants)

Trial 4: 25 ml crystal violet, 0 ml distilled water, 25 ml sodium hydroxide (a 1:2 dilution of stock reactants)

The results:

The hot reaction went much faster than the cold.
The 1:4 dilution went faster than the 1:8 dilution.  (~6 minutes vs 9 minutes, respectively)
The 1:2 dilution went much, much more slowly than any other. (~16 minutes)

Result #3 is the anomaly.  It involved the most concentrated solutions and so should have been the fastest of the 3 room temperature reactions, but it was far and away the slowest.

Things I've considered:

The reaction isn't significantly endo- or exothermic, so the solution
didn't have a different temperature due to its minimal mass.  (All of
the reactions except for the one with hot water added were within a
couple of degrees of each other.)
The students didn't make a mistake in execution - this was observed by multiple groups over multiple trials.
The difference was not due to the sloppy endpoint of the reaction.  Though the reduced volume meant that a given amount of remaining crystal violet would be most purple in this trial, the difference in color was enormous and obvious.
The reverse reaction never becomes significant with such a massive excess of sodium hydroxide.
New idea: The unusual result is the only trial without distilled water - maybe the water is contaminated or something like that, but in a way that is promoting the reaction?  I was excited when I thought of this (I actually popped up out of a dead sleep with it in my head,) but it seems unlikely, I used the exact same container of water an hour earlier to make each of the stock solutions...

I've wracked my brain, but I can't figure out a reasonable explanation for what we observed.  Any suggestions would be welcome.


texts: Reaction between anisole and concentrated HI in excess

texts:
Question:

My Attempt:  In most of the ethers reaction of HI in excess yields alkane iodide products. But in case of anisole two scenarios are possible, I believe:

The HI breaks bond between methyl and oxygen leading to formation of phenol and methyliodide.
The phenol formed further reacts to form phenyliodide.

But would HI be strong enough to break partial double bond in phenol?


texts:
Recently, I carried out the synthesis of dibenzylideneacetone. I had a lot of problems with the purification process, especially the part involving recrystallisation. I was instructed to carry out the recrystallisation using an "ethanol/water" pair. That means to say, I was supposed to dissolve the crude product in ethanol until just enough dissolved, then add a small volume of water until some of the non-polar dibenzylideneacetone precipitated out of the solution and lastly, add another small volume of ethanol to re-dissolve the precipitate that had just formed. Once done, the beaker is removed from the hotplate and left to cool at room temperature. Subsequently, the crystals were washed with cold ethanol to finally obtain the final product. It is similar to what was done in this video.

During the practical I had to repeat the recrystallisation step multiple times for a variety of reasons. Firstly, there were some instances when the dibenzylideneacetone melted to form a yellow oily liquid. Secondly, there were also some instances when the crystals "crashed out" of solution upon cooling. This resulted in poor-quality crystals which clumped together. I am just wondering if anyone has any tips on how I could have improved my procedure so that I don't have to perform recrystallisation multiple times and yet still obtain poor-quality crystals.


texts: Confusion about prioritizing functional groups in case of poly functional organic compounds

texts:
According to Wikipedia,
sulfonic acid $(\ce{-SO3H})$ is comparatively stronger than carboxylic acid $(\ce{-COOH})$.

Then why is sulfonic acid lower in priority than carboxylic acid (while naming poly functional organic compounds) in this priority chart? Even my textbook prioritizes $(\ce{-COOH})$ over $(\ce{-SO3H})$.

Or is the strength not the only factor while assigning priority?

Correct me if I'm wrong or missing something. I'm currently learning about IUPAC nomenclature.


texts: Nernst equation for a fuel cell when gases are stored separately

texts:
I have run some tests with a PEM fuel cell and the voltage we have found was $1.44\ \mathrm{V}$. Given that the standard potential for a fuel cell is $1.229\ \mathrm{V}$ what is causing the difference in our measurement?

Initially we provide power to the fuel cell so it can generate oxygen and hydrogen into separate containers. These containers are submerged in water so there is water pressure keeping them contained.

All measurements were done in standard conditions, except that the pressure of each container is slightly different (hydrogen displaced twice the amount of water since there are twice the moles of atoms present).

I am not sure how to calculate this using the Nernst equation since the conditions of both the oxygen and hydrogen are slightly different (each gas is of a different concentration in its respective container since there is different water pressure and water vapour pressure present).

My equation is:

$$E_\text{cell} = 1.229\ \mathrm{V} - \frac{RT}{2F}\cdot\ln\left(\frac{[\ce{H2O}]}{[\ce{H2}][\ce{O2}]^{0.5}}\right)$$

For $[\ce{H2}]$ I am using the molar concentration of the gas in its containing cylinder (I believe this accounts for water vapour).

I also do the same thing for $[\ce{O2}]$

I'm not sure what to use for $[\ce{H2O}]$

The answer I am getting is $1.24\ \mathrm{V}$. What am I missing?


texts: What undergoes reduction in a zinc-copper voltaic cell?

texts:
In a $\pu{Zn-Cu}$ voltaic cell, the electrolyte is sodium chloride solution. The question was:

  In this cell, which of the following undergoes reduction?

My answer was copper, but why is the exact answer "a hydrogen ion"?


texts: What is the possible maximum value of the monolayer capacity? Is it possible for the monolayer capacity to exceed more than $(100)\frac{mol}{g}$ or even $(1000)\frac{mol}{g}$? Any help is highly appreciated. Thank You.


texts:
I created this equation of state as a personal undergraduate summer project (here is the link)  seven years ago:

$$\frac{PV}{nRT}-1 \propto \left(\frac{nRT}{PV}\right)^2 \left[\left(\frac{nRT}{PV}\right)^2 - 1\right]$$

I tried to show it to my professors but none of them replied to my emails. I had since forgotten about it until I recently came across it in the cloud. Here is a table comparing its theoretical predictions for the critical temperatures of various gases to the actual experimental values


texts: How to predict ease of oxidation or reduction for a given oxidising or reducing agent?

texts:
I have never understood which agent will be able to oxidize or reduce which type of reactants and yield which type of products will be formed. For example I want to know about DIBAL-H and how is it able to reduce some groups but not carboxylic acid. Here is what all I want to know:

What are the criteria for judging which agent will oxidize or reduce?
What will be the condition in which it will be able to oxidize or reduce a given molecule.
What type of products will be formed?

Note: I am in high school and thus need an explanation which I will be able to understand.


texts: What will the final product of this synthetic sequence be?

texts:
What is the major product formed in the following reaction?

NBS should do allylic bromination but where will it attack in the larger ring or smaller one ?


texts: Why is the inductive effect for a protonated amino group greater than that of a nitro group?

texts: Why does $\ce{NH3+}$ have a higher $-\ce{I}$ effect ( inductive effect) than $\ce{NO2}$ even though oxygen is more electronegative? Does it have something to do with positive charge on $\ce{N}$?


texts: How to calculate theoretical yield if there are minor products?

texts:
Calculating theoretical yield for a reaction with a single product is pretty trivial: Multiply the amount of moles of limiting reagent to the molar ratio of the limiting reagent and product to the molecular weight of the product.

However, if the reaction is also capable of producing side product, this method no longer works because some portion of that limiting reagent would be used to create the minor product. Therefore, the ONLY way to calculate theoretical yield for a reaction with multiple products would be to know the ratio between them. In other words, if the ratio of major to minor product is unknown, then it would be impossible to calculate theoretical yield for that reaction. Is this correct?

We can use an example to illustrate this. Take 1-methyl,1-bromo-cyclohexane. When mixed with a strong base, we get two E1 products, a major trisubstituted alkene and minor disubstituted alkene. In order to calculate the theoretical yield of the major product, we would have to know its molar ratio to the minor product?
If I did know the ratio, was lets say, 80 to 20. All I would have to do is multiply the mass of the limiting reagent by 0.8 because only 80% of the mass would be used to create major product?

Thanks!


texts: Enthalpy of the reaction between hydrogen and oxygen

texts:
The reaction between hydrogen and oxygen to yield water vapor has
  $\Delta H^\circ = \pu{- 484 kJ}$. How much $pV$ work is done, and what is the value of $\Delta E$ in kilojoules for the reaction of $\pu{0.50 mol}$ of $\ce{H2}$ with $\pu{0.25 mol}$ of $\ce{O2}$ at atmospheric pressure if the volume change is $-\pu{5.6L}?$

  $$\ce{2H2(g) + O2(g) -> 2H2O(g)} \qquad \Delta H^\circ = \pu{- 484 kJ}$$

I use the formula $\Delta E=\Delta H - p\Delta V$ to determine $\Delta E.$ However, when determining the enthalpy, the solutions manual does this:

  $$\Delta H = \frac{\pu{-121 kJ}}{\pu{0.50 mol}~\ce{H2}}$$

Where does the $-121$ come from? From my understanding, since there are two moles $\ce{H2}$, $\Delta H$ should be $-\pu{242 kJ}$. Or do we take into account all four hydrogen atoms? That would give us $\pu{-484 kJ}/4 = -\pu{121 kJ}.$


texts: Significant Figures in almost-scientific notation

texts: For a homework assignment on significant digits, I have to find the number of significant digits in the number $0.40 \times 10^3$. I know that in scientific notation, the number of significant digits is equal to the number of digits in the stem. However, I've also learned that for a number to be in scientific notation, it must have a stem between $1$ and $10$. What is the rule for this situation? Is the number of Significant digits $2$ or $3$?


texts:
While the Beer's law equation is $A=a \cdot b \cdot c$, according to my book, $a$ is a coefficient which is:

  a characteristic property of the analyte in a specific solvent, and its values will depend on the wavelength of absorption radiation.

This is quite unclear to me.

If we have for example  $a= 1.5$, what does that exactly tell us ? What do we know when this coefficient is given ? Or is this just a constant that helps us to solve the equation?