texts: Understanding the rate of change in titration curves

texts:
As I am looking at titration curves, a few things stand out. For now, I have a two part question:

When titrating an acid with a base, for instance, the pH rises more or less abruptly around the equivalence point. Does this have to do with the logarithmic nature of pH? In other words, is this caused by the fact that the number of particles involved in the jump from e.g. a pH of 2 to one of 3 is several orders of magnitude than the number of particles involved in the jump from 6 to 7?
When a weak acid is titrated, the rise to the equivalence point is a lot more shallow. Does this happen because of Le Chatelier's principle? That is to say, as the base is titrating the acid, some of the acid that has not dissociated will dissociate in an attempt to restore equilibrium. This should retard the titration to some degree. Is that the case?


texts: We know $\ce{H2}$ is formed with covalent bonds (just as $\ce{O2}$ is formed via covalent bonding). Hence, these molecules gain some stability. In spite of this stability, why do they react with each other to form $\ce{H2O}$ or $\ce{H2O2}$?


texts:
Estimate the $\ce{pH}$ of the solution that results when $\ce{75.0 mL}$ of $\ce{0.275 M HCl}$ is added to $\ce{50.0 mL}$ of $\ce{0.275 M Na2HPO4 (aq)}$.

My book gives the successive $\ce{Ka}$ values for phosphoric acid as: $\ce{Ka1 = 7.6*10^{-3}, Ka2 = 6.2*10^{-8}, and Ka3 = 2.1*10^{-13}}$.

I recognized that after the stoichiometric calculation, $\ce{6.875 mmol of H3PO4}$ and $\ce{6.875 mmol of H2PO4-}$ exist in the solution. I then used the Henderson-Hasselbalch equation to determine that the resulting $\ce{pH = -log(Ka1) = 2.12}$. I think ignoring the third deprotonation is justified because the successive $\ce{Ka}$ values are greater than 3 orders of magnitude from each other.

However, then answer in the textbook is $\ce{pH = 2.80}$. What am I doing incorrectly?


texts:
In the reduction of esters to alcohols, the RO group is pushed off. However, the negative charge on the O atom is destabilized by the electron donating R group. Why is the RO group able to function as a leaving group given that the resultant alkoxide is unstable?

Link to reaction mechanism.


texts:
I have built a solar panel which is used to add electrodes to $\ce{H2O}$ and $\ce{NaCl}$, evolving $\ce{H2}$ and $\ce{O2}$.

How can I safely store the hydrogen in the long-term?


texts: How can I convert cathodic energy efficiency to overall energy efficiency?

texts:
Im working on calculation which involve the energy efficiency of producing formate by CO2 electroreduction.
I wonder how to convert the reported cathodic energy efficiency (71%) of papers e.g (1) this paper or (2) this paper into an overall energy efficiency.
I want to assume that water is oxidized at an anode. If needed we can plug in an assumed efficiency for the anode reaction.
I am relatively new to electrochemistry, and trying to learn so forgive me if this is trivial, but I can barely find the term "cathodic energy efficiency" online for me to learn this.


texts: Reason for needing multiple radii for the same atom

texts: Why do we need different types of atomic radii? Why can't there be just one radii for an atom?


texts: Will heating of KClO3 be considered disproportionation?

texts:
In all examples of disproportionation I have seen, there is one particular atom whose oxidation state is both increasing and decreasing to give rise to different products

For example, on heating phosphorous acid

$$\ce{4 H3PO3 -> 3 H3PO4 + PH3}$$

the oxidation state of phosphorous changes from +3 to +5 and -3.

However, in the case of heating $\ce{KClO3}$

$$\ce{2 KClO3 -> 2 KCl + 3 O2}$$

the oxidation state of oxygen changes from -2 to 0, while that of chlorine changes from +5 to -1.
So, will such a reaction be called a disproportionation since its the same molecule giving rise to two products, or will it be simply a redox reaction?


texts: What is the molecular formula of 2-ethynyloctahydro-1H-indene?

texts: I thought the formula for this $\ce{C11H15}$, but it's not. I need assistance in finding the proper formula:


texts: What is meant by work done "expanding against atmosphere"?

texts:
In the book, Chemistry : A molecular approach, I came across this line:

Over here what does the author mean by work done by expanding against atmosphere?


texts: Why are there drastic changes sometimes in radius of isoelectronic ions?

texts: $\ce{S^{2-}}$, $\ce{Cl-}$, $\ce{K+}$, and $\ce{Ca^{2+}}$ each have the same number of electrons. Their effective ionic radii are 182, 181, 138, and 100 picometers, respectively, and the number of protons for each are 16, 17, 19, and 20. My question is, why does the effective ionic radius drastically go from 181 to 138 picometers between chlorine and potassium? Is it really necessarily because they are in different periods or is there something that I am missing here?


texts: Is it true that calcium carbonate is more soluble in NaCl than deionized water?

texts: I have two mixtures: $\ce{CaCO3}$ in NaCl and $\ce{CaCO3}$ in deionized water (DI). Is it possible to get more $\ce{Ca^2+}$ ions in NaCl solution than DI?


texts: Why does addition polymerisation of high density poly(ethene) use low temperature and pressure?

texts: Logically thinking, I thought that it would be high pressure and high temperature that would create high density poly(ethene)... However, that's not the case. Is it because of the catalyst? Why is the condition low pressure/temperature?


texts: Can't a redox reaction occur in one half cell alone without flowing through the external circuit?

texts:
Say you have two half cells. The electrolytes are connected by a salt bridge and the electrodes by a wire.

Half cell 1’s electrolyte is copper(II) nitrate and its electrode is solide copper.
Half cell 2’s electrolyte is nitric acid and its electrode is inert (graphite).

I’ve deduced that the reduction reaction will be
$$\ce{2 NO3- (aq) + 4 H+(aq) + 2e- -> N2O4(g) + 2 H2O(l)}$$

while the oxidation reaction will be
$$\ce{Cu(s)->Cu^2+(aq) + 2e-}$$

Now, the electrode (anode) of half cell 1 is supposed to release electrodes into the external circuit, which end up at the inert cathode in half cell 2. There, nitrate ions will be reduced. Then you’ve got the reordering of ions through the salt bridge etc. etc.

However, I do not understand how such a voltaic cell would be viable. There are nitrate ions already in half cell 1’s electrolyte. Why must electrons flow through the wire then? Can’t the copper electrode directly react with the nitrate ions in the solution it’s submerged in? Can’t the whole redox reaction take place in half cell 1?


texts: Simulation of a particle and chemical molecule

texts: I am currently studying the basics of simulation and want to try out some experiments. It is a known fact that gold nanoparticles can bind to chemical groups which contains thiol (R–SH group). I want to simulate the binding of a thiol group to a gold nanoparticle. How can I do this? Where do I have to start? Which software can be used for this purpose?


texts: Will mixing hydrogen and oxygen without a spark result in combustion?

texts: I plan to do the electrolysis of dilute sulphuric acid. This will produce hydrogen gas and oxygen gas at the anodes. I do not plan to collect these gases, but to simply let it form and release into the air without separating them. Would this carry any risk whatsoever, considering that an electric setup is nearby?


texts: Can a meso compund be rotated in ANY sort of way in order to show its achirality?

texts: Are there any limits to rotating a compound in order to prove that its chirality or achirality? (assuming that you're rotating about a single bond)


texts: Is the heat for constant pressure the same as for constant volume in the formation of nitric oxide?

texts:
In the reaction $\ce{N2 (g) + O2(g) -> 2NO (g)}$
my textbook[1]  says $q_v$ and $q_p$ are not the same, without any explanation.

I know that
\begin{align}
\Delta U &= q_p + w\\
\Delta U &= q_p - P\Delta V\\
\Delta U &= q_p - Δn_\mathrm{gases}RT
\end{align}

I also know that
$$\Delta U = q_v.$$

because under constant volume, work done ($-P\Delta V$) is zero, since there's no change in volume.

In the reaction mentioned,
$$n_\mathrm{gases} = 0,$$
so shouldn't
$$\Delta U = q_p$$
and therefore
$$q_p = q_v?$$

Here's a picture of question 143 in Chapter 7 of [1]. The answers say a) and d) are false:

Ralph H. Petrucci, F. Geoffrey Herring, Jeffry D. Madura, Carey Bissonnette: General Chemistry: Principles and Modern Applications, 11th edition. Published by Pearson (February 23rd 2016)


texts:
Some reactions in my textbook specify the need for the presence of sunlight,
eg-photolytic decomposition of silver bromide and substitution reaction of methane with chlorine.

What is going on in these reactions?
is there something special in light or can these reactions take place if provided with another source of energy like heat?

Also, can thermal reactions(reactions requiring heat) be done in the presence of sunlight?


texts: How to calculate the number of atoms in a gas molecule?

texts:
$\pu{20 mL}$ of sulfur vapour at $\pu{1000 °C}$ reacts with $\pu{40 mL}$ of oxygen gas to form $\pu{40 mL}$ of sulfur dioxide gas. Determine the number of atoms in the molecule of sulfur in the vapour state at this temperature.

My working out is as follows:

$$\ce{\underset{\pu{20 mL}}{S(g)} + \underset{\pu{40 mL}}{O2(g)} -> \underset{\pu{40 mL}}{SO2(g)}}$$

I then used the formula $n = m/M$ to find the amount of substance.

$$n = m/M = 20/32.07 = x$$

Then, to find the number of atoms, I used the formula $n = N/N_\mathrm{A}$.

$$N = nN_\mathrm{A} = x\cdot\pu{6.022e23} = \pu{3.80e23}~\text{(atoms)}$$

However, I am uncertain as to whether this is correct as I did not utilize any of the gas laws. For this question, which of the gas laws should I have used?

Any answers would be appreciated.


texts: What is the product of reaction between 2‐cyclobutyl‐2‐isopropyl‐1,3‐dioxane and hydrogen with Raney nickel?

texts:
I have 2‐cyclobutyl‐2‐isopropyl‐1,3‐dioxane (alcohol protection) and I have to react it with $\ce{H2}$ and Raney nickel, but I don't know what the product would be.

I have seen a similar reaction that uses sulfur atoms instead of the oxygens and at the end the entire protection is removed and leaves two $\ce{H}$ atoms in the end. I tried doing that, but my professor told me that I got it wrong. I'm thinking that there wouldn't be a reaction.


texts:
I have studied thermodynamics, in which the infamous Gibbs equation came.

$$ \mathrm{d}G = \mathrm{d}H - T\,\mathrm{d}S $$

Then my book said the criteria of spontaneity based on gibbs energy is at constant pressure and temperature.

Since $T\,\mathrm{d}S = q = \mathrm{d}H$ (since at constant pressure $\mathrm{d}H = q$), shouldn't $\mathrm{d}G$ all always be equal to $0$?


texts: How to calculate amount of nonanoic acid needed to prepare sodium nonanoate salt

texts:
I have this procedure for making sodium heptanoate, but I need to adapt it to make sodium nonanoate.

The protocol is as following:

Dissolve $\ce{NaOH}$ in pure ethanol
After all $\ce{NaOH}$ has dissolved, add acid
Precipitates will form, dry the mixture in the oven
Dilute the salt to a working solution

Here is the chemical equation I wrote: (please correct me if I am wrong)

for sodium heptanoate preparation:
$$\ce{NaOH + C2H5OH -> C2H5ONa + H2O}$$

$$\ce{C7H14O2 + C2H5ONa -> C7H13NaO2 + C2H5OH}$$

for sodium nonanoate preparation:
$$\ce{NaOH + C2H5OH -> C2H5ONa + H2O}$$

$$\ce{C9H18O2 + C2H5ONa -> C9H17NaO2 + C2H5OH}$$

Question:

How can I calculate the amount (in ml) of nonanoic acid I need to get 1L of solution?
Does the amount of $\ce{NaOH}$ dissolved in absolute ethanol matter? Because I have found related protocol using 40 g $\ce{NaOH}$ and some using 60 g $\ce{NaOH}$

Please help me to understand step by step, since I am not a chemistry student. I am a biology student and I need to prepare the salt for my experiments.

I have included the picture of the protocol for your reference. *I know the answer is 180ml for heptanoic acid preparation, but how do I get to the answer? I need to know the calculation steps, so I can calculate the ml of nonanoic acid I need to make sodium nonanoate.


texts:
From wikipedia thermodynamic activity is given as
$$ a = \exp(\frac{\mu - \mu_{0}} {RT})$$
which becomes,
$$ RT\ln(a) = \mu - \mu_{0}\tag{1}$$
And i have to do a calculation where activity is given as
$$ RT\ln(a)  = G_{M} + (1-c) \frac{\partial{G_{M}}}{\partial{c}} \tag{2}$$
where
$$G_{M} = RT[c\ln(c) + (1-c)\ln(1-c) + c\ln(1-\beta) - \ln(1-\beta c)] + \frac{\omega c(1-c)} {1-\beta c}$$
$\omega$ is the exchange energy
$\beta$ is the related to the volume ratio of mixing of two liquids.
c is the concentration of liquid A and (1-c) is the concentration of liquid B
$\mu$ is the chemical potential and
$\mu_{0}$ is the standard chemical potential
How do I get from eqn($1$) to eqn($2$)?


texts:
I tried solving the following question but am not sure I did so correctly and simply wished to verify it here.

In 50.3 gr of a compound whose formula is $Na_2X_4O_7$ (where X is an unknown atom) are 1.75 moles of oxygen atoms.

a) What is the number of Na atoms in the sample?

I figured the number of moles would simply be 1.75*2/7=0.5, hence number of atoms would be $0.5*N_A$.

b) What is the molar mass of X?

I figured that since there are 1.75 moles of oxygen at 16 gr/mole and 0.5 moles of Na at approx. 23 gr/mole, the MW of oxygen and Na together would be 1.75*16+0.5*23=39.5 gr, hence the MW of X would be: (50.3-39.5)/4=2.7 gr/mole.

I am now told that when the compound comes in contact with 500ml of hot water (in excess), the following reaction takes place:

$Na_2X_4O_{7(s)}+H_2O ->XH_{3(g)}+Na^+_{(aq)}+OH^-_{(aq)}+O_{2(g)}$

Moreover, in a certain process 0.84 moles of $XH_{3(g)}$ were formed.

1) How many grams of gaseous oxygen were formed in the process?

I first balanced the reaction thus:

$Na_2X_4O_{7(s)}+7H_2O ->4XH_{3(g)}+2Na^+_{(aq)}+2OH^-_{(aq)}+6O_{2(g)}$

I figured that if 0.84 moles of $XH_3$ were formed then 0.84*1.5 would be the number of oxygen moles formed, weighing 20.16 gr.

2) How many grams of $Na_2X_4O_{7(s)}$ reacted in the process?

I figured that 0.84/4 moles of $Na_2X_4O_{7(s)}$ must have reacted in the process, weighing (0.21/3.25) * 50.3=3.25 gr.

3) What are the volumes of the oxygen and the $XH_{3(g)}$ formed in the process at room conditions?

I figured $V_{O_2}=n_{O_2}*0.082*298$ and $V_{XH_3}=n_{XH_3}*0.082*298$, where $n_{O_2}=1.26 moles$ and $n_{XH_3}=0.84 moles$

4) What is the concentration of $OH^-$ ions in the solution obtained (500ml)?

I figured the answer would simply be 0.42/0.5=0.84M, as 0.42 moles of $OH^-$ were formed.

I'd appreciate any comments on my attempt above.


texts:
Is $\ce{NH_3}$ an acid or a base? N has a higher electro-negativity (3.04) than hydrogen (2.20), therefore nitrogen attracts the bond's electrons easily. The reaction should produce $\ce{H^+}$ because the electrons of hydrogen are attracted by nitrogen.

According to my Chemistry book, my assumption seems to be wrong because $\ce{NH_3}$ is considered a base. Why am I wrong?


texts:
Apparently the entropy change of a system can be found by

$dS=\frac{\delta q_{rev}}{T}$

I am slightly confused about this because I have seen this being used when the temperature of the system and the surroundings are not the same. However for the heat exchange to be reversible between the system and surroundings, need not the temperature of the system and surroundings be the same?

I have a feeling this might have to do with reversibility with respect to the system and the surroundings. I do not know about this and had not heard of it before I read it in a response to this post:

"So if the actual process is irreversible, the irreversibility (entropy generation) is all considered to take place in the system, rather than in the surroundings (in the case of an ideal infinite reservoir)"

Could someone please elaborate on this?


texts: Where can I find example MS, IR, NMR spectra for teaching molecular spectroscopy?

texts:
I am teaching a course on analytical chemistry, and I would like to give my students MS, IR and NMR spectra to practice with.

It would be ideal if they could analyze spectra in a more "realistic" way than looking at photocopies of spectra from SDBS. Ideally we'd get some newish (not 30 years old) spectra in an interface where students could, for instance, integrate NMR peaks and zoom into multiplets, automatically get a list of wavenumbers in IR spectra, maybe even deconvolute mass spectra.

I talked to MestReNova, but we can't afford it.

BioRad's SpectraBase might be the best resource I found so far, but it's not as interactive as I'd like it to be.

There is a nice collection at UCLA specifically for teaching but it's 20 years old, mostly static, and pixelated.

I'd appreciate any pointers to suitable collections of molecular spectra, or to free (or cheap) software for spectral analysis.


texts: Precipitating silver(I) salts from the solution of barium(II) cyanate and iodide

texts:
Consider a $\pu{10.0 mL}$ solution containing $\pu{1.0e-10 M}$ each of $\ce{Ba(CN)2}$ and $\ce{BaI2}$. If $\pu{3.5e-9 mol}$ of $\ce{AgNO3(s)}$ is added to this solution, will any precipitate(s) form? If yes, what compound(s) will precipitate?
$K_\mathrm{sp}(\ce{AgCN}) = \pu{6.0e-17}$; $K_\mathrm{sp}(\ce{AgI}) = \pu{8.5e-17}$.

The answer was only $\ce{AgCN}$ will precipitate, but I don't understand why $\ce{AgI}$ wouldn't precipitate as well since there is more than enough excess $\ce{AgNO3}$ available to precipitate with both $\ce{I-}$ and $\ce{CN-}$?


texts: "Tie-breaker" rules for IUPAC nomenclature of organic compounds

texts:
I have three questions:

To find the parent chain of a saturated hydrocarbon, we have to find the longest chain and then if we have a choice, we choose the one with the more substituents. But what if we still had a choice? What would we do next?
Similarly, for numbering the chain, the last step is to number the chain such that the substituent which comes alphabetically first gets the lower number. But what if we again had a choice? I'm not sure here, but I think we can't possibly have another choice. Can anyone confirm this?
If an alkyl substituent is attached to the parent chain by a double or triple bond, how would we name it?

Examples: Here are some examples which demonstrate the above 'tie-breakers'.

For question 1:

The (green + blue) and (green + magenta) chains are the longest and both have two substituents.

The (green + blue) and (green + yellow) chains contain the maximum double bonds and are also the longest. They both have one substituent.

For question 2: As I said, I'm not sure if there can possibly be a 'tie-breaker' here.

For question 3:

The longest chain is the green one. I'm not sure how to name the substituent attached by the double bond.


texts:
Coming straight off of some electron configuration worksheets, our teacher started to teach us how to read photoelectron spectroscopy (PES) graphs and I'm having a bit of trouble with the two.
During the previous lecture on electron configuration, we were told that electrons occupied the most stable energy level available. That came in this order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, etc.

But then, during the photoelectron spectroscopy lecture, we were told that the 3d electrons have higher ionization energy than the 4s electrons and, in fact, that this pattern continues, just counting up the orbitals: 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, 4d, 4f, etc.

Why do electrons fill orbitals in the former pattern, but leave orbitals in the latter pattern?
Why would the 4s orbital fill before the 3d if it is less tightly held by the nucleus, and thus less stable?
I assume I have been taught some simplified versions and my teacher has my interests at heart, but I'm a bit confused.


texts: Intermediates in aqueous bromination of phenol

texts:
A question in my book asks:
In the reaction:

The intermediate(s) is/are?
The correct answers are given as

However, as per my knowledge, compound (b) does not appear in the reaction mechanism. Is this an error in the book or do I know the wrong mechanism?
Correct mechanism according to me:


texts: Compressibility Factor and Generalized Compressibility Chart

texts:
From my understanding, the compressibility factor is defined by
$$Z=\frac{pv}{RT}=\frac{p\bar{v}}{\bar{R}T}$$
It can also be defined by the ratio of the real molar volume of a gas to the ideal molar volume of a gas at the same temperature and pressure. Essentially it corrects for the deviation of a real gas from an ideal gas.
On a generalized compressibility chart, the compressibility $Z$ is plotted as a function $f=f(p_R,T_R)$ of the reduced pressure and temperature. I don't understand why exactly; it would be nice if someone could explain that a little more.
Another thing I'm confused about is the psuedoreduced specific volume, given by
$$v'_{R}=\frac{\bar{v}}{\bar{R}T_c/p_c}$$
Why don't we use the reduced specific volume as opposed to the psuedoreduced specific volume?
In my thermodynamics class, I was presented with the following question:
Determine the temperature, in °C, of air at 30 bar and a specific volume of 0.013 $m^3/kg$. Use compressibility chart.
I was confused about how to figure out this problem since I can't find the reduced temperature without the actual temperature of the air.


texts: Calculating Gas Pressure with Water Vapour

texts:
$\pu{4.0 L}$ of oxygen was collected by the displacement of water at $\pu{105.0 kPa}$ pressure and $\pu{30 ^\circ C}$. If the vapour pressure of water at $\pu{30 ^\circ C}$ is $\pu{4.2 kPa}$, calculate the pressure due to oxygen alone.

In answering this question, is it correct to just take $\pu{4.2 kPa}$ from $\pu{105.0 kPa}$? I feel as though I must be missing something, considering this was given to us under the title "Challenging questions on gases", but I can't see what other calculations would need to be done.


texts: Choosing a vacuum pump for fractional distillation

texts:
I have a fractional distillation setup. I would like to purify a small  mixture ($\pu{\approx 100-150 mL}$) of high boiling point compounds (between $200$ and $\pu{300^\circ C}$). The one that interests me has a b.p. of $80\rm~^\circ C$ at $\pu{13 mmHg}$. I don't know what this mixture is composed of.

Now the tricky part and the one that give me the most headaches is the vacuum pump. I need one that has enough vacuum power to be able to distill at $\pu{13 mmHg}$ and one that is not expensive too.

I also need a system to be able to monitor and control the vacuum pressure too, so the vacuum pressure remains constant.

I figured that a diaphragm pump is not suitable since the ones that have that kind of vacuum power are way more expensive than rotatory vane pumps. Can anyone help?


texts: Determine oxidation in organic chemistry through oxidation numbers?

texts:
I want to determine the carbons that are oxidatized in an organic reaction.

Is it an acceptable way to first figure out the oxidation number of every carbon in reactants and products and then compare the oxidation numbers (for example: $\ce{+I -> +II} =$ Oxidation; electron loss)?* Or is my attempt to work with oxidation numbers false (for example: an aldehyde and keton are on one oxidation level, but their carbon has different oxidation numbers?). Maybe I should go over the oxidation levels of functional groups given in many textbooks as tabulars (but my structures aren't that easy and have not the most common functional groups)?

*I have read in many posts here, that this is a legitimate way — but there is "my problem" with the keton and the aldehyd, as mentioned above.


texts:
I am undertaking a physics experiment and have come up with a chemistry problem. Could paint perhaps become a lubricant under mild temperature. (It would take a while to explain my experiment, but an object sliding down a ramp is increasing velocity with increasing mass, this should not happen if if coefficient of friction stays constant). I am wondering if anyone has information about paints lubrication vs temperature, or anything similar. The coefficient of friction is the same before and after the experiment, so I am wondering if paint changes its coefficient of friction or lubrication when temperature increases.

I'm sorry if this questions doesn't make sense, if anyone can point me towards anything paint and friction related, thankyou.


texts: How much potassium permanganate is needed to completely oxidize ferrous oxalate?

texts:
Amount of substance of $\ce{MnO4-}$ required to oxidize one mole of ferrous oxalate completely in acid medium will be:
(a) 7.5 moles
(b) 0.2 moles
(c) 0.6 moles
(d) 0.4 moles

In acidic medium, 1 mole of $\ce{MnO_4^-}$ accepts 5 moles of electrons. Oxalate is dibasic so will give 2 moles of electrons when oxidized to $\ce{CO2}$.
$\ce{Fe^2+ -> Fe^3+ + e-} $ so total 3 moles of electrons.
$\text{Amount of substance of } \ce{MnO_4^-}=\frac{3}{5}=0.6$
However, the given answer is 0.4 moles indicating that only oxalate is considered to be oxidized.

Does  $\ce{Fe^{2+} -> Fe^{3+} + e^-} $  actually occur in this reaction?
What would be the net reaction when $\ce{KMnO_4}$ is used(not just the ions)?


texts: Explain the nomenclature of 7-amino-4-methylcoumarin

texts:
Can someone explain the nomenclature of 7-amino-4-methylcoumarin, pictured below (from the Sigma-Aldrich website)?

The alpha-carbons of the methyl- and amino-groups here are separated by a minimum of three C's, whereas the numbers 4 and 7 are separated by two digits. What am I missing?


texts:
While going through my AP chem prep book again, I came across questions asking about the color of certain aqueous solutions. For example:

Which of the following substances will produce a colorless aqueous solution?
A) $\ce{Zn2(NO3)2}$
B) $\ce{Cu(SO4)}$
C) $\ce{K2Cr2O7}$
D) $\ce{Co(NO3)2}$

I know that zinc compounds are generally colorless, so I picked that (and it was correct), but I have no idea how to predict the colors of the rest of the compounds.
So, to answer this question (and questions similar to this), would I need to use pure memorization of the common elements that produce color?
If so, where can I find information about these compounds and the color they produce?


texts: Would decomposing an object into molecules be an environmental problem?

texts:
In a thought experiment, a friend proposed to me a machine capable of decomposing any object (e.g., a brick) into its molecules. I'm not a chemist or physicist, but my initial reaction was that this was certainly an environmental issue if used in a larger scale.

Is that right? Or is a molecule so basic that there would be no health concern from such a (theoretical) decomposition.

EDIT @Aesin:
My thinking was:

objects can't disappear; the brick will be breathed in, get into
water etc.
if we start decomposing more advanced objects, we
get all kinds of harmful elements in the air (mercury etc.)
possible radiation from decomposition

As for the purpose: Let's assume it would be used for general waste destruction. Let's assume energy is not a concern (thanks for mentioning it!)


texts: Molecular chirality and optical rotation

texts:
Why does having molecular chirality result in optical rotation? The dissymetry or chirality of molecules translates to the rotation of plane polarized light, the magnitude and direction depending on the concentration and the nature of the substance. But why does molecular chirality cause the rotation of plane polarized light.
If this rotation is due to the assymetry around the bond, the different molecules are oriented in all possible directions(randomly) and hence the light will fall on them in all different orientations, and should ultimately be undeflected since for every orientation of the molecule, we can reverse the orientation such that the light appears to be falling on the molecule from a direction other than the one for our original molecule.
Moreover, why does inverting the configuration invariably reverses the direction of rotation of light?


texts: Measuring the effect of increasing salinty on the concentration of Dissolved oxygen

texts:
I want to investigate the effect of increasing salinity on the concentration of dissolved oxygen, in a water sample being distilled water.
Would that work?

My concern is, that since its not a true fresh water sample, I am worried that changing the salinity of distilled water, to create different saline solutions, would impact the oxygen content significantly?

I want to model the direct relationship, so I can apply it to a real life example. For instance the effect of road salting on oxygen concentration in fresh water habitats.


texts: In rovibrational spectra, when exactly is the Q branch forbidden?

texts:
I'm aware that the Q branch ($\Delta j = 0$) is usually not observed in rotational-vibrational spectra of diatomic molecules in the gas state, however, I've heard different things about when exactly this transition is forbidden.

I've sometimes been told that the transition is not allowed in general, for any diatomic molecule, but I've sometimes heard that this is only true if the electronic state has a $\Lambda \neq0$, so which is the correct selection rule here?

I'd love to have this clarified for me. If it is possible I would also like to know when is a Q branch observed in vibronic spectra of heteronuclear and homonuclear diatomics.


texts: Rates of solvolysis of p-dimethylamino benzyl halides

texts:
What will be the order of $\mathrm{S_N1}$ solvolysis rates for these?

I'm confused between the second and third options. $\ce{I-}$ is a better leaving group than $\ce{Br-}$, but the carbocation formed in 2 is more stable than 3. So how are we supposed to decide between them?


texts: Why does the distance between molecules increase when the temperature is raised?

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I have learnt that when we heat ice-like substances it changes to water and when I asked my teacher she said  that the distance between molecules increases.

When I thought about it a bit more a question arose: Why does the distance between the molecule increase as we raise the temperature?


texts:
Is it possible to spread a chemical or the danger of a chemical if the chemical has dried up on a piece of paper? For example if in a lab I have gotten a certain chemical on my lab paper but the chemical has dried up does that lab paper now pose a threat to my health and the health of others? Also if after touching the lab paper I touch my jacket and then after touching my jacket I eat something later on would I be in danger?

The chemical I am referring to is copper sulfate.

I have not experienced any irritation or burns (maybe some weird stomach or digestive problems).

Thank you


texts: Simplest way to convert glucose into water and carbon dioxide other than burning?

texts:
What is the simplest pathway from glucose to $\ce{H2O}$ and $\ce{CO2}$, such that

all reactions happen in aqueous solution with pH between 5 and 8,
temperature is in range between 0 and 35 °C,
no (expensive) enzymes are required,
the reaction is completed in around 6 hours, and
no toxic or harmful intermediates are formed and no toxic or harmful catalysts are used?

I realize that one possible answer to this would be, in biochemistry,

glycolysis → pyruvate decarboxylation → citric acid cycle → oxidative phosphorylation;

this is a fairly complex reaction cascade, however. Is there a way chemistry could simplify this in comparable (more or less physiological) conditions?

Aside from a possible (retro-)synthetic approach, there might be a catalytic option. I've found a publication by Degering and Upson* that describes iron pyrophosphate as a catalyst, but the reaction times are far higher (around 3 weeks), the temperature is relatively high and the reaction appears to be relatively messy in terms of products.

* Edward F. Degering and Fred W. Upson, J. Biol. Chem. 1931, 94, 423-431. DOI: n/a; URL: http://www.jbc.org/content/94/2/423.short (pdf) (no https available)


texts:
We know that half-filled and fully filled orbitals are highly stable. In ground state $\ce{Cr}$ has a $\ce{3d^5\! 4s^1}$ configuration. Therefore, the elctronic configuration of $\ce{Cr+}$ should have $\ce{3d^5\! 4s^0}$ state. The half-filled $\ce{3d}$ orbital should make the ion stable.

However, we don't see many $\ce{Cr(I)}$ compounds. There are one or two rare examples, but other than them, most compounds of $\ce{Cr}$ are $\ce{Cr(II)}$, $\ce{Cr(III)}$ and so on. Why does this happen? Why $\ce{Cr+}$ is unstable?

[If you find a reference, add it to your answer. As I am a student, it will help me immensely. But if you don't have a reference, don't hesitate to post an answer. Getting an answer is the priority.]


texts: What is this "bulbous"/"blood sugar" test tube used for?

texts:
I was at an antique and bric-a-brac store, and I found several pieces of glassware. They were pretty cheap, so I purchased some of the more interesting ones. Among them were a few somewhat strange "bulbous test tubes". I purchased 2 of them, and on sale for $2.50 each.(the blue line means half off).

Here they are:

After looking up "kimax 47121" I found an amazon listing for some, labeled as a "blood sugar tube". I could not find anything else besides this. Are they particularly useful, for anything besides stuff relating blood sugar? How are they used? Can I heat them without fear of it breaking? Would they be worth trying to sell if I cannot use them?

Answers to any of these questions would be great.


texts: Oxidation - Reduction Ionic Half Reaction

texts:
Trying to figure out how to balance the following molecular equation:

$$\ce{KMnO4 + Na2C2O4 + H2SO4 -> MnSO4 + CO2 + Na2SO4 + H2O}$$

I have compiled all of their oxidation states

$$\ce{KMnO4 + Na2C2O4 + H2SO4 -> MnSO4 + CO2 + Na2SO4 + H2O}$$

$$\ce{(+1)(+7)(-2 * 4) (+1 * 2)(+3 * 2)(-2 * 4) -> (+2)(-6)(-2 * 4) + (+4)(-2 * 2) + (+1 * 2)(+6)(-2 * 4) + (+1 * 2)(-2)}$$

Now I know that theoretically Mn changes from +7 to +2, so it gains 5 electrons. I also know Carbon in this situation goes from a state of +3 to +4, so it loses one electron.

However, after this I am drawing blanks on how to setup my ionic half reactions with these polyatomic ions, and I am suspicious that I may have set this up incorrectly. Any help at all would be appreciated, I can not find much to explain this type of equation with this particular molecular formula.

The idea of Redox reactions make sense when talking about individual atoms or more clearly depicted changes, but I am having trouble figuring out what is even changing into what in this example.


texts:
Let's say we have standard chemical reaction given by
$$A-B + C \leftrightharpoons [A\cdot\cdot B\cdot\cdot C]^{\dagger} \rightarrow A +B-C$$
I want to estimate the pre-exponential factor of this reaction using Transition State Theory.
From Fundamentals of Chemical Reaction Engineering by Davis and Davis, I see that
$$\text{rate} = \nu _i C_{\dagger} = \nu _i \mathcal{K} C_{AB} C_{C}$$
Where $\mathcal{K} = C_{\dagger}/(C_{AB}C_C)$, and $C_i$ is the concentration of species $i$.
Then we redefine $\mathcal{K}$ as
$$\mathcal{K}_C = \frac{C_{\dagger}}{C_{AB}C_C} = \frac{Q'_{\dagger}}{Q'_{AB}Q'_C}$$ where $Q'_i$ is the partition function per unit volume.
We redefine energies to lowest ground state, so
$$\text{rate} = \nu _i C_{\dagger} = \nu _i \mathcal{K}e^{-E/k_BT}$$
We know that $Q = Q_tQ_rQ_{\nu}Q_{el}$, where $t$ is for translational, $r$ is for rotational, $\nu$ is for vibrational, $el$ is for electronic partition function.
We also know that $Q'_{t} = \frac{(2\pi mk_B T)^{3/2}}{h^3}, Q_{el} \approx 1$.
Everything good so far.
My question lies with the rotational and vibrational partition function.
$$Q_r = \frac{8\pi}{h^2 \sigma} (2\pi k_B T)^{3/2} (I_1I_2...)$$ where $\sigma$ is the rotational symmetry number. My question is, what is the rotational symmetry number? How do I find it? How do I find moment of inertia for molecules? More importantly, does a single atom like $C$ even have a rotational partition function?  How do I calculate $Q_{v}$ for $A-B$? and $C$? The formula says
$$Q_v = \prod_{s=1}^n (1-e^{-hv/k_BT})^{-1}$$
The end result says
$$r = \frac{k_B T}{h} \cdot \frac{Q'_{\dagger}}{Q'_{A}Q'_{B}} e^{-E/k_BT}C_{AB}C_C$$
The final question would be, how do I simply something like this? With the $\frac{k_B T}{h}$, what exactly got simplified?
Edit: I figured out I can get moments of inertia from Calculated moments of inertia for molecules are listed in the NIST Computational Chemistry Comparison and Benchmark Database: http://cccbdb.nist.gov/).


texts: Rate of Reaction for Elementary Reactions

texts: The rate law for an elementary step of a reaction of the form $2A \Rightarrow$ Products is given by $rate=k[A]^2$, while in the form $A \Rightarrow$ products is given by $k=[A]$. Is there some sort of intuition as to why the the reaction with $2A$ is quadratic, instead of double the one with $A$? Essentially, why is the equation $k[A]^2$ instead of $2k[A]$?


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Our topic was about ketones and aldehydes (carbonyl group) including hemiketals and hemiacetals and he asked us to do a homework. I cannot find an answer to this one.Please explain me the reaction and the product formed.

PS: The figure at bottom is my best effort to do this question.


texts: Difference between Phase, heterogenous and state of matter and solution

texts:
My question has already  been answered in parts at Difference between state  of matter and phase
But for deep and real understanding I have to ask for the difference between phase and a heterogenous mixture :
Say we have a bowl made of glass. The bowl is filled with a few different solid rocks on the ground, water in the middle and some oil on top.
I try to analyse this situation for understanding:

There is a phase of oil on the top
There is a phase of water in the middle
There is a phase of rocks on the ground
Since the rocks on the ground are not equally the same they are a bunch of single phases that do not mix up to each other
The rocks on the ground are also a heterogenous mixture
The air above the water is a phase of gas
The glass is a solid phase of silicon

Is that correct?


texts:
There are a few things about VSCF that I don't understand:

Which coordinates do you work in? If you work in normal mode coordinates, how do you evaluate the effect of the average of one normal mode on another one, with a different normal mode coordinate? Why can't you just work in Cartesian coordinates?
Unlike the electronic SCF, the total number of vibrational quanta is not fixed for a particular molecule. How do you select which modes to include in your 'mean field'? Do you assume that all vibrational modes have only one quanta of energy in them?
At the end of VSCF, how easily could you go from the resulting set of vibrational modes described in terms of atomic movement to a vibrational wavefunction? E.g. a one that one could you to directly evaluate a Franck-Condon integral $\langle\psi^{\text{vib}}_0|\psi^{\text{vib}}_1\rangle$?

I feel like I have a lot of misunderstanding here, so I'd be grateful if you could bear with me and give as much detail as possible.


texts: Why is Oxygen compulsory for free radical reactions?

texts: Why is presence of oxygen compulsory for free radical mechanism? Can it take place in presence of any other element?


texts:
What is the criteria in selecting which of the available groups adjacent to a carbocation is the most favourable to be shifted?

I have two compounds: (I'm unable to post the structures, so I have to write it here)

1) A methyl and an ethyl available for shift to a carbocation

2) A nitrobenzyl and anisole as the substituents for aryl shift.

Our teacher said that in 1)Ethyl shifts on the grounds of stability of the resultant carbocation and

In 2) anisole shifts because it has "more electron donating tendency than nitrobenzene"

The two answers seem contradictory to me. Is it correct?


texts: Difference between positional isomerism and metamerism (organic chemistry)

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I don't want the definition of positional isomerism and metamerism but want what differentiates the two types of isomerism.

I know metamers have different alkyl groups on either side of it, but doesn't that just mean the position of the functional is changing? Hence shouldn't it be a positional isomer.


texts: How can i detect Formalin in food easily

texts: I am trying to detect formalin in different types of food. Formalin $(\ce{CH2(OH)2})$is an aqueous solution of formaldehyde, which is $\ce{CH2O}$ or $\ce{H2CO}$. I used many chemicals to do this, but every time I fail. Please help me to do this. I got some results in my test by using NFPA 704 and ChEMBL, but that is not enough to save all. I would like to make a simple and easy food formalin detector that can save all the people. Please help me or give me some direction.


texts: When we blow on/stir a hot drink, why aren't we making it hotter?

texts:
This may have already been a question on Chemistry StackExchange (in which case I will delete it if someone points me to the question), but I was wondering why providing even more kinetic energy into the system (stirring a cup of hot coffee) why are we expecting the coffee to become cooler?

If I understand correctly, heat is caused by molecules in a system moving rapidly and "rubbing each other" -- creating heat. So the more movement --> the more heat.
Doesn't this not make sense with the idea of stirring a cup of hot coffee?

Edit#1

Excuse me for the title and the body implying different things, I took blowing on a hot drink and stirring it as the same thing -- stimulating movement in the drink.


texts: What's the difference between radial probability and probability density?

texts: I understand that radial probability is the probability of finding an electron at some distance from nucleus in a shell. But what does that exactly mean? What does it tell us about the atom and electrons?


texts: Selective reduction of nitro group to amine, in benzene ring containing nitrile?

texts:
I would like to know if there is a possible route of synthesis that may reduce the shown compound A to the following product B.

I would normally reduce a nitro to an amine using $\ce{Pd/C}$ and $\ce{H2}$, but since the nitrile is sensitive to this method, I need an alternative.

Thanks, in advance.


texts: Effect of pKa value of acid component in Mitsunobu Reaction?

texts:
Mitsunobu Reaction is used to established C-S, C-C, C-N, C-O bond formation by condensation of acid component (Nuclephile) with primary and secondary alcohol in the presence of triphenyl phosphine (Ph3P) and diisopropyl azadicarboxylate (DIAD).

Literature suggest that Mitsunobu reaction is only possible if The nucleophile (or pronucleophile) is normally a relatively acidic compound containing an O-H,
S-H, or an N-H group with pKa<15, preferably below 11.

My question is that, why Mitsunobu reaction can't occur with acidic compound having Pka value more than 15 (pKa>15)?


texts: What causes electrons to move from zinc to copper?

texts:
Here is something that no video in youtube about electrochemistry can explain me about galvanic cells.

Suppose we have $\ce{Zn}$ metal immerse in $\ce{Zn^{2+}}$ in one side,  then $\ce{Cu}$ metal immerse in $\ce{Cu^{2+}}$ in the other side. Then, if we link the $\ce{Zn}$ metal to $\ce{Cu}$ metal with some conductor wire, electrons will flow from the $\ce{Zn}$ metal to the copper wire, but this will stop quickly without a salt bridge.

My question is why do the electrons move from $\ce{Zn}$ metal through the wire to the $\ce{Cu}$ metal in the first place? What causes that?


texts: Could thin layer chromatography separate enantiomers?

texts:
My textbook states the thin layer chromatography could separate enantiomers only if both/or the mobile and solid phases are chiral?

Why so?


texts: Basic Understanding of Relative Atomic Mass

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I’m currently trying to learn some chemistry and have run into some trouble understanding some of the basics. The confusion stems from a passage in my textbook, so I will list the brief passage and then ask my question.

  In addition to predicting molecular formulas, Avogadro’s hypothesis gives correct results for the relative atomic masses of the elements. Analysis by chemists during the 18th century had revealed that 1g of hydrogen combines fully with 8g of oxygen to make 9g of water. If Dalton’s formula for water, HO, were correct, then an atom of oxygen would have to weigh eight times as much as an atom of hydrogen; that is, Dalton’s assumption requires the relative atomic mass of oxygen to be 8 on a scale where the relative atomic mass of hydrogen is set at 1.

So far so good, I believe that oxygen has a relative mass of 8 because there are 8g of oxygen in the original reaction and likewise with the 1g of hydrogen, but this next part is where it starts to get confusing.

  From Avogadro’s hypothesis, however, each water molecule contains twice as many atoms of hydrogen as oxygen, so to achieve the experimental mass relationship, each oxygen atom must have twice as large a relative atomic mass. This gives a relative atomic mass of 16 for oxygen, a result consistent with modern measurements.

Alright, so basically what I’m confused about is how they arrived at a relative atomic mass of 16 given that there is 8g of oxygen and 1g of H in the original experiment. What exactly are they observing in order to establish the relative atomic mass of oxygen as 16. Any help understanding this and relative mass in general would be greatly appreciated.


texts: How can the compound 1,2-cyclopentanediol have 3 stereoisomers? Isn't the configuration of the OH groups fixed in a ring?


texts: Why is Cl2-P-O-Cl an unfavourable structure for POCl3?

texts:
Why is the structure $\ce{(Cl)2P - O - Cl}$ unfavourable compared to the two structures in the picture?
The latter in the picture and the one I stated both have zero formal charge, so I don't really see why the structure I made isn't favourable.


texts: What does 'organic/non-organic molecule' means exactly?

texts:
I am new to the organic chemistry world.
I was delving for the exact answer to my question, and I've found some results:

In wikipedia (french), is was mentioned that an organic molecule contains Hydrogen, so that $\ce{CO2}$ is a non-organic molecule, but wait, what about $\ce{H2O}$? It's almost said a non-organic molecule and it does contain Hydrogen.
And on other websites, I've read that an organic molecule is supposed to have 'Carbon' in its components, else, it will be called 'a non-organic molecule', the result that is an obvious contradictory to the first one.

What I've deducted from all my results is, that the organic molecule must contain Hydrogen or Carbon, and I'm not pretty sure of my deduction.


texts: The $\pi$-orbitals of benzene are well known and given in any standard undergraduate textbook. When considering anisole, phenol, etc, a lone pair in a p orbital of the O can delocalise into the $\pi$-system of the aromatic ring. How would this affect the $\pi$-orbitals of the cyclic system? Is it possible to account for the effect of this delocalisation by starting with the benzene $\pi$-orbitals and then interact those with the p-orbital, or does the change in point group disallow this - surely if we used this method, we would mix each benzene MO in turn with the p-orbital to yield 12 MOs, which is clearly not the case?


texts: I bought a new refrigerator that makes ice cubes. The instructions said to discard the first 3 full bins of ice in order to ensure the new water line is flushed clean. I dumped the full bins in my stainless steel sink each time. After the ice melted each time a chalky residue was left in the sink. I emptied a couple of extra full bins and still was left with the chalky residue. I cleaned the sink after each dumping to be certain there wasn't any left over residue from the previous dump. What is the chalky substance? Is it something to be concerned about or not?


texts: Why do electron donating groups decrease the acidity of aromatic carboxylic acids?

texts:
If we look at the resonance structures of benzoate anion, we would see that some amount of positive charge is present on the ring and this charge can get delocalised on the ring, like this:

Now, if we had an electron donating group (EDG) at the para position, then the EDG should stabilize the ring because it can donate pi electrons to the empty p orbital of carbocation (look at third resonance structure) and form a double bond, thus resulting in more resonance and more resonance implies more stability and this should imply that EDG increases acidity as conjugate base is getting more stabilized.

But, it is a well established fact that EDG decrease the acidity of the molecule (benzoic acid). For example: $\mathrm{p}K_\mathrm{a}$ (para methoxy benzoic acid) > $\mathrm{p}K_\mathrm{a}$ (benzoic acid)

Why am I facing such a contradiction?


texts:
I am in need of small amount of pure methane for laboratory purpose.

I have hydrogen generator in the lab.

Is there a possibility of generating methane from hydrogen ?

May be make hydrogen flow over heated graphite ? ( I am newbie and just trying to get the idea...)

Any help in this direction is helpful. thanks.


texts: Why does temperature affect cell potential?

texts:
The Nernst equation describes the relationship between cell potential and temperature. But why does temperature affect cell potential?

My understanding is that the collision model of kinetics is not relevant to electrochemical cells, plus an increase in temperature decreases cell potential.
So why does the potential change?


texts: Why is benzoic acid well soluble in benzene (and other unpolar solvents, see e.g. wikipedia). What causes the hydrogen bonds in the solid to break? Something (i.e. polar and ionic substances) is soluble in water because of the hydration enthalpy with water, but i can see no similar cause for a solubility in benzene!


texts: Solvent effects on acidity of ethanoic acid

texts:
Is ethanoic acid most acidic in DMSO, water or methanol?

I suspect that the conjugate base would be most stabilized by a polar protic solvent (meaning it's weakest in DMSO), however, water and methanol are both protic and polar. Which causes ethanoic acid to be most acidic lowest $\mathrm{p}K_\mathrm{a}$? This was asked in an exam question where the following $\mathrm{p}K_\mathrm{a}$ values were meant to be assigned to the acid in each of the solvents: $9.5$, $12.6$, $4.8$.


texts:
When I walk on the beach, there appears to be an upper layer of the sand that is 'crusty'.

This appears to be the opposite of what you see in sand in a dessert setting, where the individual particles are not bound together, and blow to form 'dunes'.

I'm trying to figure out what causes the sand to bind together like this.

To me the crystalline properties of salt could cause this. (Ie the way that salt binds together to form crystals could cause this salt-binding that leads to 'crustiness'.

My question is: Does the salt in the ocean act as a binding agent on sand?


texts: Does molten Aluminum Hydroxide break up to aluminum, water, and oxygen by electrolysis? It's easy to write the equation $$\ce{4Al(OH)3 -> 4Al + 6H2O + O2}$$ but is this actually possible?


texts: Stability order of octahydrobiphenylenes

texts:
I am facing trouble in the following question

  What is the stability order of the following compounds?

In my view cis is less stable than trans. So if prior groups are on the same side of the double bond then it must have less stability. Also conjugated double bond in short non aromatic cyclic system is highly unstable. So 1,2,3,4,5,6,7,8-octahydrobiphenylene (X) should be the least stable. However I could not guess the correct order.


texts: Cyanidine is not polar due to its make-up of only hydrogen atoms and carbon atoms, correct? But "like dissolve like", which means it would HAVE to be polar, or no? Is it then soluble solely because of its OH-groups being able to create hydrogen bonds with the water molecules, thereby making it miscible?


texts: Can there exist any element which has an 8th principle shell?

texts: I am a high school student . While studying the atomic structure a question raised in my mind. We know that an atom can have the highest limit of 7 bohr energy shells or principle energy shells ; K,L,M,N,O,P,Q respectively. My question is, can there exist any element that consists more than 7 energy shells having more electrons? Or , can there exist any element that has an 8th energy shell of R shell?


texts: Doubts on IUPAC name 1,1'-methylenebis(4-isocyanatobenzene)

texts:
Wikipedia states  IUPAC name of the above compound as 1,1'-methylenebis(4-isocyanatobenzene) .

I have a confusion. Shouldn't isocyanate group be given preference over the methylene group? I assume the name as 4,4'-methylenebis(1-isocyanatobenzene) .

Similar is the case with DDT.  Wikipedia states its IUPAC  name as 1,1'-(2,2,2-Trichloroethane-1,1-diyl)bis(4-chlorobenzene) .

Why is the numbering of carbon with three chlorine atoms done $1$ ? Moreover,  can it be  $1,1'$ in the first place in place of $4,4'$ ? I guess the $\text{diyl}$ term indicates that it is connected to two different carbons(of benzene)  .

To sum up,  I want to know which chain should I select as parent chain and why .


texts: Calculating mass and volume of two different substances required for one solution

texts:
I want to produce a solution, which contains $0.02~\mathrm{mol~L}^{-1}~\mathrm{Cu}^{2+}$ and $~0.2~\mathrm{mol~L}^{-1}~\mathrm{NH}_3$. The following substances are given:

copper(II) sulfate pentahydrate
$100~\mathrm{mL~H}_2\mathrm{O}$
diluted ammonia solution with a concentration of $2~\mathrm{mol~L}^{-1}$.

I need to determine the required volume ($V$) of $\mathrm{NH}_3$ and the mass ($m$) of $\mathrm{CuSO}_4\cdot 5\mathrm{H}_2\mathrm{O}$.

I have no idea how to calculate $m$. However, to calculate $V$, I solved the following system of equations:

$\dfrac{2~\mathrm{mol}}{\mathrm{L}} = \dfrac{n}{V}$

$\dfrac{0.2~\mathrm{mol}}{\mathrm{L}} = \dfrac{n}{V+0.1~\mathrm{L}}$

Therefore, $V = 0.01111~\mathrm{L}$. Is this correct?

Is $m=555~\mathrm{mg}$ correct?


texts:
Is there a way to prove that $\frac{1}{2} mv^2 $$= \frac{3}{2}RT$
The first one is kinetic energy and the second is the average kinetic energy.
Can this be proved by component of velocity.


texts: Why do many organic halogen compounds smell or taste sweet?

texts: Is it just coincidence that many organic halogen compounds (especially chlorinated ones) tend to either taste or smell sweet? Examples include dichloromethane, vinyl chloride, chloroform, and sucralose. This chart also shows that many low-carbon haloalkanes have a sweet smell. If this isn't coincidence, what is the biochemical basis for this phenomenon?


texts: How are pi-orbitals delocalized in a porphyrin chain?

texts:
According to this paper, the orbitals appear delocalized mostly from left to right, and only along 1-2 units of the chain.

Is that really the case? If so,

Why is the delocalization only along 1-2 units of the chain and not throughout the chain?
Why is there no delocalization in the up-down direction?


texts:
In a textbook1, I found the following clear definition of hydrogen bonds:

  The strongest secondary bonding type, the hydrogen bond, is a special case of polar molecule bonding. It occurs between molecules in which hydrogen is covalently bonded to fluorine (as in $\ce{HF}$), oxygen (as in $\ce{H_2O}$), and nitrogen (as in $\ce{NH_3}$). For each $\ce{H-F}$, $\ce{H-O}$, or $\ce{H-N}$ bond, the single hydrogen electron is shared with the other atom. Thus, the hydrogen end of the bond is essentially a positively charged bare proton that is unscreened by any electrons.

This is not an "etc." definition. It is made clear that we only call it a hydrogen bond when we have either of the three bonds: $\ce{H-F}$, $\ce{H-O}$ or $\ce{H-N}$.

My question is why this definition excludes compounds such as $\ce{HCl}$? $\ce{HCl}$ and $\ce{HF}$ are very similar with one covalent bond that pulls the hydrogen electron towards their "shared" region, exposing the hydrogen atom as a positive end of this permanent dipole. Both can create secondary dipole bonds to adjacent molecules of the same type.

Why is $\ce{HF}$ called a hydrogen bond while $\ce{HCl}$ is not?

1 Materials Science and Engineering by W. D. Callister & D. G. Rethwisch, Wiley, 8th edition


texts: What were some major breakthroughs in chemistry in 2016?

texts:
What breakthroughs have been made in the different fields of chemistry in the past 366 days? This might help me and others know advances made in different field.

I know this question is too broad, but however there are many  interesting advances in all sorts of branches that have been made this year, which I might have missed.

Inspired by "What were some major mathematical breakthroughs in 2016?", on Mathematics Stack Exchange


texts: Need a pair of compounds that is similar in formula but different in structure

texts:
I would like to explain chemical formulas is not representable in terms of the molecular structure of the compound.

Any good suggestions of examples?


texts: Lithium batteries a reality - why not sodium, pottasium batteries?

texts:
Lithium batteries seem to be mainstream now, offering high energy density, high output current capability.

Stepping down the periodic table there are alkali metals with greater electronegativity than Lithium: sodium and potassium, etc.

So why not sodium and potassium batteries. Can't these offer higher energy density, higher current output? Is the reactivity just so great that the chemistry can't be engineered to provide a practical battery? Or are the safety issues just too great?


texts: Should the relatively low solubility of a base be considered in the calculation of the pH?

texts:
Hydrochloric acid, $V=75.0~\mathrm{mL}$, $c=0.250~\mathrm{M}$, is added to $225.0~\mathrm{mL}$ of $0.0550~\mathrm{M}$ $\ce{Ba(OH)2}$ solution. What is the concentration of the excess $\ce{H+}$ or $\ce{OH-}$ ions left in this solution? (source)

I know the balanced equation but when considering $\ce{Ba(OH)2}$ is 'marginally soluble' which
I guess could be considered insoluble, $\ce{OH-}$ wouldn't really be in the result solution.
Am I right or at where am I wrong? thanks for reading


texts: Does solid aluminum oxide conduct oxide ions at high temperatures?

texts: Can alumina behave as a solid electrolyte for oxygen ions? Could a cell be constructed with an oxygen cathode and a molten aluminum anode producing more alumina? Would the resulting alumina deposit on the electrolyte? Would it be crystalline?


texts:
I am performing a lab experiment in which I am extracting crude caffeine from different samples of tea. I have read a couple of similar experiments in which methylene chloride has been used to extract caffeine, owing to its volatile nature and caffeine's affinity to methylene chloride. I know chloroform can be used as a substitute for methylene chloride. I was wondering if carbon disulphide can used as a substitute in the experiment.
Thank you very much!


texts: How do chemical reactions taking place in an alkaline battery produce electrons?

texts:
I'd like to understand the chemical reaction in a typical alkaline battery a little better and how that produces a flow of electrons.  I read wiki, how stuff works, and some more advanced articles.  They all seemed to either stop short of explaining the nitty gritty details, or went straight to chemical formulas.

I understand that a chemical reaction occurs between the cathode and the anode and that the electrolyte helps make that happen.  I don't really understand the flow of electrons though, and how the anode/cathode are consumed.  I read a bit about ions but not sure I grasped how that was moving electrons about.

Also, does this reaction start right away or only after a circuit is completed and electrons can flow?  Or has the reaction already started, and there is an excess of electrons on one plate that only start flowing after the circuit is completed?

What forces the potential to stop at 1.5V?


texts: Preparation of acetate buffer from sodium acetate and hydrochloric acid

texts:
A $\pu{1.0 L}$ buffer solution of $\mathrm{pH}~4.43$ is made up of $\pu{0.30 M}$ sodium ethanoate and $\pu{0.20 M}$ $\ce{HCl}$ solutions. Calculate the volume of sodium ethanoate and $\pu{0.20 M}$ $\ce{HCl}$ solutions used to prepare this buffer solution.

The answer given for volume of $\ce{HCl}$ is $\pu{750 mL}$ and for the volume of volume $\ce{CH3COONa}$ is $\pu{250 mL}.$

My approach is to assume $\ce{HCl}$ as the limiting reactant and use ICE table to determine the equilibrium concentration of the ethanoic acid and sodium ethanoate at the end of the reaction. Then I use the Henderson–Hasselbalch equation.

The answer I got was $\pu{500 mL}$ for both the conjugate base and weak acid. Is the answer wrong?


texts: Is the haloform reaction possible with fluorine and pseudohalogens also?

texts:
The haloform reaction is:
$$\ce{RCOCH3 +3X2 +4OH^- -> RCOO^- +CHX3 + 3X- + 3H2O}$$
where, $\ce{X}$ is $\ce{Cl}$, $\ce{Br}$, or $\ce{I}$. However, I was wondering if this reaction works with fluorine and pseudohalogens? For instance would the following reactions occur?
$$\ce{RCOCH3 +3N2O4 +4OH^- -> RCOO^- +CH(NO2)3 + 3NO2- + 3H2O}$$
$$\ce{RCOCH3 +3(CN)2 +4OH^- -> RCOO^- +CH(CN)3 + 3CN- + 3H2O}$$


texts: Do enzymes that digest D-glucose react with L-glucose?

texts:
D-glucose most common in nature and L-glucose is synthesized in the lab.
I know that humans can't use L-glucose in their aerobic pathways because it doesn't match the active site of the enzyme ...but I'd like to confirm and understand:

Why can't our cells use L-glucose?


texts: How to calculate the pH of an acetic acid/ calcium acetate buffer?

texts:
Problem:

  A buffer was made by mixing $\pu{500 mL}$ of $\pu{1 M}$ acetic acid and $\pu{500 mL}$ of $\pu{0.5 M}$ calcium acetate.

  What are the resulting concentrations of acetic acid (henceforth called $\ce{AcH}$), $\ce{Ca^2+}$ and acetate (henceforth called $\ce{Ac-}$, and what is the resulting $\mathrm{pH}$? $K_\mathrm{a}$(acetic acid) = $1.75\times10^{-5}.$

My attempted solution:

This problem gives me two equilibrium reactions to take into account.

\begin{align}
\ce{AcH + H2O &<=> Ac- + H3O+}\tag{1}\\
\ce{Ac- + H2O &<=> AcH + OH- }\tag{2}\\
\end{align}

In (2), I assume that calcium acetate completely dissociates in water. I also assume that the concentration of $\ce{OH- }$ from the auto ionization of water is negligible.

First I calculate the concentrations of $\ce{AcH}$, $\ce{Ac- }$ and $\ce{H3O+}$ in (1), ignoring what I assume to be minuscule amounts of $\ce{H+}$ from the auto ionization of water. To do this, I use the equation for the acid dissociation constant:

$$K_\mathrm{a}=\frac{[\ce{Ac- }][\ce{H3O+}]}{[\ce{AcH}]}\tag{3}$$

Initial values for $\ce{AcH}$, $\ce{Ac- }$ and $\ce{H3O+}$ are set to 1, 0 and 0 M, respectively. Equilibrium concentrations will then be $1-x$, $x$ and $x$ M.

Plugging this into (3), I get $x = 4.17\times10^{-3}.$

I have now found (or can at least easily calculate) the concentrations of the compounds in (1) at equilibrium.

On to (2), I know that $K_\mathrm{a}K_\mathrm{b}=K_\mathrm{w}$, and I have the values for $K_\mathrm{a}$ and $K_\mathrm{w}$, which gives me the value $5.71\times10^{-10}$ for $K_\mathrm{b}.$

Initial concentrations in (2) for $\ce{Ac- }$, $\ce{AcH}$ and $\ce{OH- }$ are 1 (because 0.5 moles of calcium acetate gives $2\times0.5=1$ moles of acetate), 0 and 0 M, respectively. Equilibrium concentrations will then be $1-x$, $x$ and $x$. Plugging this into (3) (though using the equation for the base dissociation constant instead), I get $x = 2.39\times10^{-5}.$

I have now found all the values I need to calculate the final concentrations and pH when adding the two solutions to each other, and up till this point I am fairly sure that all my calculations are correct.

Questions:

How do I write the chemical equation for the mixing of the two solutions? I tried the following; $\ce{AcH + Ac- <=> Ac- + AcH},$ but this doesn’t seem to help at all.
From my younger days, I seem to remember a much simpler and quicker method of doing these calculations than what I've shown here; does such a method exist? Please note that if it does exist I’d like to learn about it, but I would also like answers based on the method I've used.
Let’s say you mix one weak acid with one weak base, and they aren't conjugate pairs. How would the method differ from the one in this problem? I am specifically wondering about whether both the dissociation constants must be provided to be able to solve, and also how to write the chemical equation, but other observations are more than welcome as well.


texts: If the electron of a hydrogen atom transitions from energy level n=5 to n=3, which level corresponds to n1 and which level corresponds to n2

texts: which level corresponds to n1 and which level corresponds to n2 in the Rydberg equation?


texts: How exactly is activation energy defined?

texts:
In a common interpretation of the Arrhenius rate equation

$$k = A\exp\left(-\frac{E_\mathrm a}{RT}\right),$$

the activation energy $E_\mathrm a$ is understood to represent the difference in the energy of the reactants and the minimum energy required to form the activated complex or the transition state, as shown in the following diagram

But this must be wrong! As $E_\mathrm a$ is the minimum energy itself which the molecules must possess to reach the activated complex. That is, it is not the difference but the minimum energy level itself. This is the only way in which it will remain constant i.e. independent of temperature (otherwise with increase in $T$, $E_\mathrm a$ will go down) and can be used in the Arrhenius Equation where the exponential term denotes the fraction of molecules having energy higher than or equal to $E_\mathrm a$ according to Maxwell-Boltzmann distribution. Sometimes, threshold energy ($E_\mathrm t$) is defined as the minimum energy required for reaction to proceed and $E_\mathrm a = E_\mathrm t-\mathrm{KE_{average}}$. If this definition is true, then threshold energy and not activation energy should be in the Arrhenius equation. I therefore need to clarify the actual definition of activation energy $E_\mathrm a$.


texts: How to deal with non-symmorphic space groups for orbital/vibrational analysis?

texts:
I am learning about how to apply group theory analysis of MO diagrams and vibrational in the solid state context (not isolated molecules).

I think the strategy for calculating representations and getting the the orbitals/vibrations with distinct symmetry is quite clear for normal point groups. Essentially you forget about the solid state part of the problem for the most part and just look at the unit cell as a large "molecule".

To incorporate crystal momentum, the unit cell becomes large enough to contain one wavelength of the corresponding wave. This is more complicated, but it seems like you just do a symmetry analysis of a larger unit cell with (typically) lower symmetry.

Now I am trying to understand how this process extends to nonsymmorphic space groups (not point groups). Here I have trouble finding character tables online, and the screw axes/glide symmetries throw off my intuition.

So my question is: how do we apply group theory for bonding and vibrations in the context of nonsymmorphic space groups? I guess it should be the exact same as usual, but it just doesn't seem intuitive how bonding should care about screw axes or glide symmetries that connect far away atoms.


texts:
I want to know how to compare the strength or stability of ionic compounds.
Example : $\ce{Mg(HCO3)2}$ and $\ce{NaHCO3}$

I know that polarity and polarizability affect the ionic and covalent nature.


texts: How do I correctly typeset metastable radionuclide symbols?

texts:
Does anyone know if there is an officially sanctioned way to typeset symbols like technetium-99m (99Tcm or 99mTc)? I have seen both, although in more recent publications, I think, the latter predominates.

For my part, it looks somewhat wrong to place the symbol for metastable in the position you'd normally expect the charge. How would you write the ion, 99Tcm+? That looks quite clumsy.

So does anyone know if there's some IUPAC (or similarly authoritative) guidance on this?


texts: Most effective means of removing coffee stains from carpet

texts:
I have several old coffee stains on a carpet. Googling "coffee stain removal" reveals a variety of suggested cleaning substances-- vinegar, baking soda, laundry detergent, etc. I have used all of these on stains in the past to varying success, but always have a hard time totally eliminating the stain. Typically the instructions suggest iterative applications of the substance, and I usually end up with a huge pile of wet, wadded-up paper towels, each tinged slightly brown from the tiny amount of coffee absorbed.

What is the most effective way to remove old coffee stains from carpet using common household chemicals? Chemically, why is this the most effective means?


texts: Finkelstein reaction of vicinal dihalides

texts:
I recently came across the following in my OChem class:
Ethylene dichloride on reaction with  NaI in acetone reacts via E2 mechanism to give ethene.
I have three questions:

Since it is an E2 mechanism, a strong base should be present, but the iodide ion is a weak conjugate base of its corresponding acid. So why is the mechanism E2?

Bases are thought to be as proton acceptors. According to the above reaction, however it seems that the iodide ion attacks the chlorine on one of the carbons. Why is that so?

Chloride ion is less stable than iodide anion as more charge dispersion takes place in the latter. Then why is the chlorine a leaving group here, i.e. why does the reaction even occur?

I have just started OChem, so please correct me if my question has mistakes.


texts:
We talk about divers using Scuba tanks that contain a only a small concentration of oxygen diluted in a mixture of other gasses such as nitrogen or helium.

From what I've read, this is because breathing pure oxygen, or a concentration that exceeds the normal partial-pressure of oxygen at sea level, when diving can cause major health problems.

Oxygen Toxicity is a phrase that keeps getting repeated, though I've found sparse few details surrounding what it actually is/means.

I ask therefore: How does oxygen become toxic to humans when breathed-in at high concentrations or underwater or wherever — on a chemical/biolgical level — and also why this is the case?

Because really, isn't good-old $\ce{O2}$ meant to be the gas that keeps us alive?


texts:
Which substance is best suited as a pH indicator for titration of $\pu{15 mL}$ of $\pu{0.1 M}$ ascorbic acid $(K_\mathrm{a} = \pu{7.9E-5})$ with $\pu{1.0 M}$ sodium hydroxide solution?
Using the image below to find the best suited substance.

My progress:
$$\mathrm{p}K_\mathrm{a} = -\log (\pu{7.9E-5}) = 4.102,$$
then
$$\mathrm{pH} = 4.102 + \log\frac{\pu{0.1 M}}{\pu{1.0 M}} = 3.102$$
I am quite sure this is wrong, but don't know what I should do.


texts: Why are some weak acid equilibrium approximations invalid in very dilute solutions?

texts:
Using two approximations for the dissociation of a weak acid, we can write
$$K_\mathrm{a}= \frac{[\ce{H+(aq)}]^2}{[\ce{HA(aq)}]}$$
One of these two approximations we use is that the concentration of the acid HA has not changed upon dissociation, because the dissociation of a weak acid is so small compared to the starting concentration of the acid that is negligible.
However, I was taught that this approximation is invalid when the acid is stronger, but also when the solution is very dilute.
I don't understand why this approximation wouldn't work if the solution is very dilute. I have some ideas though:

The acid concentration decreases significantly when dissolved in a lot of water, so maybe the H+ would become significant then?

Maybe the H+ from water's dissociation affect the equilibrium of the weak acid's dissociation so that the dissociation becomes significant?

Are any of these right? Could someone explain why this approximation is invalid for very dilute solutions?


texts: Napthalene - Friedel Crafts Alkylation and Acylation

texts:
Where does Friedel Crafts Alkylation and Acylation occur in Napthalene? Are the reactions kinetic-thermodynamic controlled?

Here's something I came across -

While alkylation occurs at alpha position, acylation occurs at beta position. Why is it so? Are the other possible minor products also formed? Does kinetic-thermodynamic control operate here?

Although I'm worried about Friedel Crafts Alkylation and Acylation reactions at the moment, my question isn't specific to them. In general, given an electrophile for EAS with Napthalene, how do we decide which product is major? (The one formed by attack at alpha, or beta position?)

References would be of great help too.


texts:
IF an electron is excited, what can it do? Dissipate the energy to the object, emit another photon?

IF a photon hits an object and NO electron is excited, what happened there?

What are the possible causes of electron excitation?


texts: How is the chirality of sidechains written in the IUPAC name?

texts: I circled what I believe to be the chiral centers and I added the locants for the longest carbon chain. One of the chiral centers is in a side chain, so that carbon doesn't have a locant. How should its absolute configuration be included into the IUPAC name?


texts: How do you calculate the equilibrium constant with the absorbance of a substance and the absorbance constant?

texts:
When given the equation: $$\ce{Fe^3+_{(aq)} + SCN^-_{(aq)} <=> FeSCN^2+_{(aq)}}$$

How do you calculate the equilibrium constant when given the slope of the absorbance vs concentration graph ($\pu{4317 M-1}$) and the absorbance of $\ce{FeSCN^{2+}}$ (0.276)

The following information is also given: $2.000\ \mathrm{mL}$ of a $0.00200\  \mathrm{M}$ solution of $\mathrm{KSCN}$ with $5.00\ \mathrm{mL}$ of $0.00200\ \mathrm{M}$ solution of $\ce{Fe(NO3)3}$ and $3.00\ \mathrm{mL}$ of water is combined.

So from this, I assumed that the concentrations of $\ce{SCN-}$ and $\ce{Fe^{3+}}$ are both $0.002\ \mathrm{M}$.

I found the concentration of $\ce{FeSCN^2+_{(aq)}}$ to be $\pu{6.39e-5 M}$ using this equation:

$$\mathrm{Absorbance} = \mathrm{slope}\cdot \mathrm{conc.}$$

$$\mathrm{conc.} = \frac{\mathrm{Absorbance}}{\mathrm{slope}}$$

$$\mathrm{conc.} = \frac{0.276}{\pu{4317 M-1}}$$

$$\mathrm{conc.} = \pu{6.39e-5 M}$$

Using this value, I used the equation for the K constant of an equilibrium:

$$\mathrm{K} = \frac{[\ce{FeSCN^2+}]}{[\ce{Fe^3+}][\ce{SCN^-}]}$$

$$\mathrm{K} = \frac{\pu{6.39e-5}}{0.002^2}$$

$$\mathrm{K} = 15.975$$

This did not turn out to be the correct answer, but I'm not sure why. I suspect the concentrations for the two reactions are not correct since the volumes are also given.


texts:
According to this article called
The Fireplace Delusion
a wood-fire will create benzene. This surprised me and I can't find an article online that explains the chemical reaction behind that.


texts: Why doesn't rubidium react with nitrogen gas?

texts: I ran across a problem in which I was asked to predict the result of a reaction between $\ce{Rb}$ and $\ce{N2}$. I was frustrated until I found a note in my textbook which stated that out of all the alkali metals, only $\ce{Li}$ reacts with $\ce{N2}$. I am curious to know the reason for this.


texts: Which element has a greater second electron affinity, sulfur or oxygen?

texts: I found a question asking the above which states that sulfur has a lesser second electron affinity than oxygen. But since the inter-electronic repulsion in sulfur is lesser, shouldn't it be willing to take up another electron more easily than an oxygen ion with a -1 charge?


texts:
In VBT, one can understand the example of hydrogen like this - Two hydrogen atoms come closer to each other, and their orbitals overlap, stabilize, and ultimately result in a bond. This is not too difficult to understand, and can easily be visualized and seen in an intuitive manner.

MOT however, is different. Instead of the two orbitals overlapping each other to stabilize the molecule, they both mix together to form a bonding and anti bonding orbitals. Alright, the electrons from both the Hydrogen atoms go into the lowest energy orbital, which is the bonding orbital.

My main doubt however, comes from the electrons of both atoms being SHARED in a covalent bond. When two orbitals overlap in the same phase, they add up to each other (BMO). And when they overlap in opposite phase, they cancel each other (AMBO). So, two hydrogen atoms overlap in the same phase, and they make a bond and so stabilize each other and form a bonding molecular orbital. Wouldn't this mean that both the electrons are shared between the two atoms and hence both their orbitals are filled? Is this a false understanding of how bonds are formed?

Does this have to do with the mathematical equations themselves? They're as of now, too advanced for my course.


texts:
I've found good explanation what the PBE functional is. However, sometimes I see PBEPBE and I cannot find any good information about what this means and how it's different from PBE.

The Gaussian manual explains PBE and also provides the reference but at other points they talk about PBEPBE without any reference.

Can someone explain the difference? Does the second PBE just describe some kind of modification?


texts: What solvents can get rid of oil stains?

texts:
What kind of solvent would you use to remove an oil based stain?

I need help for a chemistry lab report and I tried to look it up but nothing seems to be helping me


texts:
There's a certain solubility rule stating all carbonates, phosphates and hydroxides are insoluble unless mixed with hydroxides or alkali metals.

Why is this? What makes the alkali metals so special?


texts: What are the best chemical liquids to clean metallic surfaces?

texts:
I'm just a simple man curious about things. I've no big understanding of chemistry. I had this question today in mind. What chemicals could I use to achieve the cleanest metallic surface?

For example, I could first start by using isopropyl alcohol to remove all dirt and oils. But there are other liquids such as acetone and acids.

If you were a chemist, how would you clean a metallic surface?


texts: How to properly model a mechanochemical reaction of barium titanate and copper(II) complexes?

texts:
I would like to understand, in terms of chemical kinetics, how I could equate the reaction rate between $\ce{BaTiO3}$ and copper(II) complexes under ultrasound effect.

Examples in literature would be great!


texts: What is advantage of creating elements that disappear in a flash?

texts:
More than dozen of heavy elements of periodic table do not occur naturally but are prepared artificially at nuclear reactors.. These elements are said to disappear in a flash..

So, why invest lot of money for the discovery of such elements? What are the advantages of such elements which disappear in a flash?


texts: I understand that the definition of a heterogeneous mixture is a mixture in which 2 or more phases are present, i.e. you can see the mixture is not uniform. I know a homogeneous mixture is a mixture in which only one visible phase is present, but why are suspensions and colloids considered heterogeneous, for you only see one phase as the definition states? I also know that homogeneous mixtures are usually referred to as solutions, but if only solutions are homogeneous then why do we define homogeneous as anything with 1 phase; isn't this misleading? Is there a more accurate definition of a homogeneous and heterogeneous mixtures?


texts: How to identify multiple molecules in a single xyz file?

texts:
I wonder if there exists a tool/script/algorithm to identify multiple molecules and/or atoms in a single XYZ or gaussian log file.
As an example, imagine one does a single point calculation for the ethanol-$\ce{Cl2}$ system, where the two molecules are placed next to each other at some distance. If one wants to detect all participating entities (be it molecules or atoms) what would be the best approach?
Could we use "standard" bond lengths between atoms and atoms allowed max number of bonds to do that? I suspect the problem is much more complicated than that.


texts: At which temperature does a concentrated aqueous solution of sodium chloride begin to boil?

texts: We know, solutes dissolved in water increases the boiling point of water. This question is an MCQ. The options are 96,99,100,104 degree Celsius. The correct answer is 96. Why? If the boiling point INCREASES after adding salt then why not 104?


texts: What is the reason that ice melts with increasing pressure at constant temperature (revelation)?

texts:
I've seen many explanations regarding this topic where they explain it in the sense of the anomalous expansion of water, but I actually want an answer where I can understand the different forces at play in the molecular level.
I've seen a paper where it is said that when the pressure is applied the h-bonds contract thus making them stronger but this also makes the covalent bond weaker which results in higher probability of the hydrogen to get separated from one of the two oxygen atoms which in turn decreases the energy required to break the bonds therefore lowering the melting point of ice.
Is this explanation correct?


texts:
What is the structure of SO2? I have seen two different ways the Lewis Structure is written:

The formal charges of the SO2 with the single bond and a double bond is larger than the SO2 with two double bonds. So I would assume that the one with two double bonds is the correct structure. But chemistry books I have looked at (Zumdahl Edition 5 and 7) says that it is the opposite.

Which is the correct Lewis Structure?


texts: What is the mechanism of monofunctional glycosylase catalysis?

texts:
I am learning about base excision repair mechanisms. I understand the main idea how glycosylases are working, but I am trying to understand this in much more detail. I found a paper where they have written:

  Monofunctional glycosylases catalyze the single-step displacement of damaged base via attack of an activated water molecule on c1' of the substrate

I am not sure what an "activated water molecule" is, how, for example, an aspartate residue is making a water molecule 'activated', and how this "activated water molecule" is removing the damaged base (hydrolysis N-glycosyl bond).

Source:
J Christopher Fromme, Anirban Banerjee, Gregory L Verdine: DNA glycosylase recognition and catalysis.


texts: How do I calculate the humidity inside sealed containers containing mixing salts?

texts:
At $\pu{25 ^\circ C}$:

saturated Magnesium chloride $\ce{MgCl2}$ keeps humidity 33% inside sealed containers.
saturated Sodium chloride $\ce{NaCl}$ keeps humidity 75% inside sealed containers.

I want to keep humidity at 60%. Which ratio should I mix this two chemicals?
How we can calculate humidity for mixing salts? Is there a formula or table list for this?
At $\pu{25 ^\circ C}$ temperature, $\ce{NaCl}$ sets 75% humidity and $\ce{KCl}$ sets 85% humidity. NaCl mixed 1:1 with $\ce{KCl}$ will give an RH% around 70–71 between $20$ and $\pu{30 ^\circ C}$.
What is the formula to calculate 70% with using 75% and 85%?


texts: What happens with ammonia ions in tap water after they are separated from chlorine?

texts: Tap water is increasingly treated with chloramine which is composition of chlorine and ammonia. Chlorine can be removed by catalytic activated carbon and ammonia ions are then left. What happens with them in the water? Do they bind with something or are they left in ionic form? How quickly they evaporate at room temperature?


texts: Can buffers regulate the pH, or do they just smooth out pH bumps?

texts: Hydrogen carbonate can react with hydrogen ions to create carbonic acid which degrades into water and carbon dioxide that can be exhaled or excreted otherwise. That lowers the pH, yes. However, in order to create new hydrogen carbonate ions, the reverse pathway takes place, and pH is raised. So, this will help smooth out the bumps in the pH, but can it somehow regulate it long-term?


texts: Why a TS must have only one negative frequency

texts:
The vibrational frequencies are related to second derivatives; a minimum will have only positive frequencies while transition state should have one negative frequency. The vibrational analysis must be performed at the the optimized geometry.

  Reproduced from ucsb.com

When finding a minimum (local or global), the vibrational frequencies should all be positive. This makes sense (at least looking at it simplistically) as if we travel in any direction we're always going up (else we're not in a minimum).

When looking for a transition state, the common goal is to end up with one (and exactly one) negative frequency, with all others being positive. This makes less sense to me, as, from a transition state there are (in 2D space) two possible ways to go the wrong way (down in energy) - clearly one is more favourable as it leads to a lower energy intermediate/product, but none the less, the other pathway exists.

Is my analysis too basic (i.e. thinking about a reaction profile curve is too simplistic), or is this okay but i'm missing some fundamental transition state theory?


texts: Can dust or fingerprints interfere in ultra-violet spectroscopy

texts:
My question pertains generally to any form of spectroscopy, but I'll focus on UV spectroscopy. I am trying to get information on carrying out spectroscopy, but most of it is theoretical. Wikipedia is completely useless. Textbooks generally go into more detail about the underlying sub atomic processes being carried out. However, they do not provide too much details about how spectroscopy works in practice. So my question is this

Will something like a fingerprint, or a speck of dust, or a label on the beaker (not even sure what material the beaker would be made of), or even air for that matter interfere with the absorption spectrum?


texts: Figuring out formula of a hydrocarbon from amount of products obtained and reactants used

texts:
One mole of a hydrocarbon is combusted. The products obtained are cooled down to STP and occupy a volume of $89.6\ \mathrm l$. Oxygen required for combustion was $145.6\ \mathrm l$ at STP. Find the molecular formula of the hydrocarbon.

Let the hydrocarbon be $\ce{C}_x\ce{H}_y$. The combustion reaction can be written as:
$$
\ce{C_xH_y + O2 -> H2O + CO2}
$$
Keep in mind that this is not yet balanced.
We can now find out the amount of reactants and products. Since one mole of any gas occupies $22.4\ \mathrm l$ of space at STP, we can say that we have:
$$
\frac{89.6\ \mathrm l}{22.4\ \mathrm l/\mathrm{mol}} = 4\ \mathrm{mol}
$$
of products. As for the oxygen reacted:
$$
\frac{145.6\ \mathrm l}{22.4\ \mathrm l/\mathrm{mol}} = 6.5\ \mathrm{mol}
$$.
We can now deduce that the hydrocarbon will react with $13\ce{O}_2$. Therefore, the equation becomes.
$$
\ce{C_xH_y + 13O2 -> H2O + CO2}
$$
But, There are $x$ $\ce{C}$s one the left hand side so the right hand side also has $x$ $\ce{C}$s:
$$
\ce{C_xH_y + 13O2 -> H2O + xCO2}
$$
There are $y$ $\ce{H}$'s on the left hand side. Same for the right hand-side:
$$
\ce{C_xH_y + 13O2 -> y/2H2O + xCO2}
$$
Since the amount of $\ce{O}$ has to balance as well, we have $26$ oxygens on the LHS and therefore $26$ on the RHS. Which means:
$$
26 = \frac{y}{2} + 2x \implies \frac{y}{2} = 26 - 2x
$$
We have already figured out that $4\:\mathrm{mol}$ of products are obtained. i.e.:
$$
4 = \frac{y}{2} + x = 26 - 2x + x = 26 - x \implies x = 26 - 4 = 22
$$
But this would mean that $y$ is negative. Where did I go wrong?


texts:
I am perplexed by information on the internet about the sugar raffinose.

The melting point of raffinose is 244.4°F
The boiling point of raffinose is 1,623°F

I can't find the temperature at which it will break apart into it's constituent sugars.

The boiling point seems too high to me tbh, because it should be on fire at that point.

Is it that raffinose decomposes at it's meting point?


texts: Is there such a thing as a Boron-Carbon-Lithium alloy?

texts: I am trying to create an alloy with heat resistance for a project. Is there such a thing as a boron-lithium-carbon alloy, and are there any benefits to it?


texts: How do we know if this following molecule is a superimposable mirror image or non-superimposable mirror image ? [See Image attached]

texts: How do we know if this following molecule is Super Imposable mirror image or Non Super Imposable mirror image ? [See Image attached]


texts: Products of the reaction between ethoxyethene and HI

texts:
Problem

The products formed in the reaction
$$\ce{CH2=CHOCH2CH3 + HI ->}$$
are
(a) $\ce{CH2=CHI}$ and $\ce{CH3CH2I}$
(b) $\ce{CH2=CHI}$ and $\ce{CH3CH2OH}$
(c) $\ce{CH3CHO}$ and $\ce{CH3CH2I}$
(d) $\ce{CH3CH(I)OCH2CH3}$

Answer

 (c) $\ce{CH3CHO}$ and $\ce{CH3CH2I}$

Question
Does ether cleavage occur or electrophilic addition of $\ce{HI}$ to the double bond take place or both? I'm equally inclined towards both (c) and (d).


texts:
"The vapour pressure of water at 80° C is 355 torr. A 100 mL vessel contained water-saturated oxygen at 80° C, the total gas pressure being 760 torr. The contents of the vessel were pumped into a 50 mL vessel at the same temperature. What were the partial pressures of oxygen and of water vapour, what was the total pressure in the final equilibrated state? Neglect the volume of any water which might condense."

This question is given in my module and the solution given to the same is quite vague. Could somebody please explain it to me? Thank you very much. What I could particularly not understand is how the water vapour's pressure in the 50 mL vessel remains unchanged.


texts: Can endergonic reactions be driven by heat?

texts:
I am having trouble conceptualizing endergonic reactions and their difference from endothermic reactions. An endergonic reaction is one that has a positive Gibbs free energy change, such that energy is taken in for the reaction to take place; in biological systems the very exergonic breakdown of ATP is a major source. The expression for Gibbs free energy (for a reaction at constant temperature and pressure) is given by:
$$\Delta G = \Delta H - T\Delta S$$
It is known to me that some endothermic reactions can in fact be exergonic (at certain temperature thresholds) as the entropic increase will be able to counteract the enthalpy change. However, if the reaction is endothermic and associated with a decrease in entropy, the reaction is endergonic at all temperatures. I have a hard time understanding this; isn't heat energy a source of energy as well? If we raise the temperature high enough, surely there would be enough energy to drive the reaction. Intuitively, I imagine that heat energy can't flow into the system due to a thermodynamic law, but I can't seem to figure it out. Does it have to do with entropy or anything related to transfer of heat?


texts: When a molecule of water ($\ce{H2O}$) and a molecule of hydrochloric acid ($\ce{HCl}$) react together, would they become a molecule made of molecules? What's the name for such thing? How would it be represented - just as $\ce{H2OHCl}$?


texts:
This is also one of the questions from practice papers for the JEE , asks for 2 step reaction for epoxidation of ketene

For product A , π complex is generated on c-c bond since carbon labelled 1 is electron deficient(inductive effect of sp carbon C2 and oxygen)

Is it possible to produce an epoxide from 2-bromoacetyl bromide using methyl magnesium bromide


texts: carbon electrodes have potential difference even with no electrical input?

texts:
What is happening in this photo? I set up a simple electrolytic cell today of copper (II) sulfate solution with carbon electrodes. It was connected to a powerpack (set at ~8.0V), and a variable resistor with the resistance cranked up to its maximum as in the image below. You can also see the ammeter and the voltmeter in the photo.

When the powerpack was switched off, the current fell immediately to zero, as expected, but the voltmeter still read a non-zero number (initially 0.80V, then later seemed to decrease to 0.18 V). I turned the electrodes upside-down so that the clean ends were in solution (rather than the end covered in copper), but reading still read the same. Removed the electrodes to a beaker of water (but not deionised water), and it still read 0.18V or close to.

Tried the exact same thing with pure copper electrodes, but it read 0.00V immediately upon turning off the power supply.

Tried completely taking the leads out of the power supply (which was off anyway), and the carbon rods still read a non-zero value even with the circuit obviously incomplete.

What's happening here? Copper electrodes did not show the same effect. Is there something about carbon electrodes in particular that can make them act as a capacitor? The current stayed at 0.00A the whole time. This effect was NOT seen when the electrodes were lifted out of the solution/water.

Edit, to respond to the answer below:

This would be the most interesting answer.
I did consider initially this, so first I tried up-ending the
electrodes so the clean ends were in solution, but the reading
remained the same. Second, it showed no such behaviour with the pure
copper electrodes.
I think it's unlikely to be a case of the voltmeter left floating.
Surely if that had been it, regardless of which electrodes (copper or
carbon) were used, random static charges would've been present? Plus,
the phenomenon was reproduced when I swapped out different electrodes
and then swapped back in the funny-acting ones, so the behaviour
wasn't exactly random.

However, I did forget to mention, that I also tested this with a
second clean set of carbon electrodes and got 0.00V! Support for 2nd
explanation (but if so, how does that work exactly?). I still would've
liked it to have been the 1st explanation.

I also note that I left the apparatus overnight, and by next morning
the reading was 0.02V. I've unfortunately have had to clear the
materials away now, but if I get a moment I may try replicating the
result.


texts:
I read that the electrolytic refining of Silver is done using dilute silver nitrate as an electrolyte and a small percentage of free $\ce{HNO3}$. The following reactions are possible at the anode:

$$\ce{Ag ->Ag+ + e-}$$
$$\ce{ OH- -> 1/4O2 + 1/2H2O + e-}$$

But the second reaction has $E^\circ = \pu{+0.4V}$ while the first reaction has
$E^\circ = \pu{+0.8V}$. So why does $\ce{Ag}$ of the anode get oxidised? Is it because of a low concentration of $\ce{OH-}$ ions due to poor dissociation? Or is there another reason?


texts: Equivalents Triethylamine in Swern-oxidation

texts:
Hey folks,

so I've been wondering why the use of 5 equivalents of Et3N in this case of a Swern-oxidation is necessary. I have done this reaction succesfully quite a few times now, but all the literature uses 5 equivalents as well. I am fully aware of the mechanism (shown below). I can explain one eq. for the HCl that emerges in step one:
And in the second step we need the base to form the sulfurylide:

but this should not be a equilibrium as the Ylide has no net charge and in my opinion is more stable.
If it were to just enhance the reactivity a bit, I'd think that 2 more eq. (so 3 eq. in total) are sufficient.

I hope you can help me with this.


texts: Is combustion considered a redox reaction?

texts: When carbon combusts with oxygen, is this considered a redox reaction since the oxygen atoms gain electrons and the carbon atoms lose them?


texts: In the MO diagram of $\ce{N2^2-}$, does s-p mixing happen to a significant degree to change the ordering of orbitals - $\pi_\mathrm{2p}$ orbital below $\sigma_\mathrm{2p}$? As it is isoelectronic with oxygen, I think that the s-p mixing shouldn't change the ordering.


texts: According to the Cahn-Ingold-Prelog system assign a priority to each of the following groups. (Highest priority is 1)

texts:
1-CH(CH3)CH2F
2-CHCl2
3-CH2Br
4-C(CH3)3

this is the order i did using the system but i am having a hard time understanding it and was wondering if anyone could tell me if my answer is correct, and if it is not, explain to me please


texts:
So I was wondering if pre-heating coal will improve the efficiency of a steam boiler.
I did find that intake air pre-heater and water pre-heater do increase efficiency, but I could not find anything related to pre-heating coal.

If we were to take the hot exhaust, make a hot iron platform and keep the coal on top of it, it would heat it and maybe reduce the moisture content also?!

Chemistry troll idea or actually feasible?

Note: it is a traditional hand fired boiler

EDIT:

Coal type: Lignite

Application: Industrial/Factory


texts: Using Maxwell Relations or any other mathematical or thermodynamic relations, prove that (∂Cp/∂P)=−T(∂^2V/∂T^2)

texts:
Prove that:
 $$\left(\frac{\partial Cp}{\partial P}\right)_T = -T \left(\frac{\partial^2 V}{\partial T^2}\right)_P$$

Since $Cp = (\frac{\partial H}{\partial T})_P$

$$\left(\frac{\partial Cp}{\partial P}\right)_T = \frac{\partial}{\partial P} \left(\left(\frac{\partial H}{\partial T}\right)_P\right)_T$$

Using the chain rule:

$$\frac{\partial}{\partial P} \left(\left(\frac{\partial H}{\partial T}\right)_P\right)_T = \frac{\partial}{\partial P} \left(\left(\frac{\partial H}{\partial S}\right)_P\left(\frac{\partial S}{\partial T} \right)_P\right)_T$$

From:

$dH = TdS + VdP$

$(\frac{\partial H}{\partial S})_P = T$

$$\frac{\partial}{\partial P} \left(\left(\frac{\partial H}{\partial S}\right)_P\left(\frac{\partial S}{\partial T} \right)_P\right)_T = \frac{\partial}{\partial P} \left(T\left(\frac{\partial S}{\partial T} \right)_P\right)_T$$

Expanding the derivative:

$$\frac{\partial}{\partial P} \left(T\left(\frac{\partial S}{\partial T} \right)_P\right)_T = \left(\frac{\partial T}{\partial P}\right)_S \left(\frac{\partial S}{\partial T} \right)_P + T\frac{\partial}{\partial T}\left(\left(\frac{\partial S}{\partial P}\right)_T\right)_P$$

By the cyclic rule and subsequently Maxwell Relations:

$$-\left(\frac{\partial S}{\partial P}\right)_T = \left(\frac{\partial T}{\partial P}\right)_S \left(\frac{\partial S}{\partial T} \right)_P = \left(\frac{\partial V}{\partial T}\right)_P$$

Substituting these in, I get an extra term:

$$\left(\frac{\partial V}{\partial T}\right)_P-T \left(\frac{\partial^2 V}{\partial T^2}\right)_P$$

Above was my first approach to the question. Why do I get an additional term in this version of the proof?

I was able to later prove it by finding $\frac{\partial H}{\partial P} = T\frac{\partial S}{\partial P} + V$ and solving using similar steps to get the correct answer.