texts: Nomenclature of aldehydes with double bonds and stereoisomerism

texts:
I'm struggling to name this compound shown below:

I'll post my chain of thought here so it can be corrected!

longest chain is marked as below:

this is because the functional group with the highest priority is the aldehyde (HCO) functional group, so the chain should contain this functional group
the chain continues down to to bottom-right to obtain the maximum length with the greatest number of substituents (although actually looking at it now, could the carbon chain go left and skip the double bond?)
there's a butyl side chain on carbon 3
there's a double bond at carbon 3
there's an ethyl side chain on carbon 4
there are two methyl groups on carbon 5
following CIP rules, the groups with highest priority are arranged opposite each other, so the molecule is E

Therefore, would the molecule be (E)-3-butyl-4-ethyl-5,5-dimethylhex-3-enal?
Or have I got myself completely mixed up...
Thanks for any help!


texts: Two 2" solid steel bearings for stress relief hand-rolling. Safe? What's that smell? How to thoroughly clean?

texts:
I bought these two 2" solid steel ball bearings for the purpose of rolling them in my hands. Just for something to do while sitting at my computer, without those silly bells inside. (They're still a bit noisy, but it sounds much cooler than bells.)

Aside from being moderately scary (I cracked my ceramic sink while cleaning them, when I dropped one about six inches. Some shards exploded off of the underside...don't tell my wife, luckily it's not leaking), I'm wondering if there's anything I need to worry about health-wise.

I've read that they might have nasty lubricants on them, and that rubbing alcohol should clean it. I soaked them in alcohol for the night, then rubbed them down with an alcohol soaked washcloth, and then cleaned them with soap and water.

But they still smell, and it makes my hand smell as well. Not that strong, but significant and yucky, and I'm wondering if it's something to be concerned about, or if that's just the nature of steel.

How can I thoroughly clean them? Is the smell something to be concerned about, or should I just wash my hands when I'm done and forget about it? Is there a safe way to coat/paint them, without causing further health issues? Anything else I should know?

Thank you.


texts: Electrolysis of sodium chloride solution

texts: I am trying to understand electrolysis. My question  is: when electrolysis is done with a NaCl solution I have learnt that sodium metal is not formed. Why is this?


texts: Is ammonium ion a positive ligand? If yes, please explain how does it coordinate with metal

texts:
In some books the examples for positive ligands are given as: $\ce{NO+}$, $\ce{NO2+}$, $\ce{NH2-NH3+}$, $\ce{NH4+}$, $\ce{H3O+}$, $\ce{PH4+}$. I can understand about the first three examples, but wondering about the last three examples.

It would be great if someone can explain if the latter three are positive ligands and if yes, please explain how it coordinates with metals.


texts: Does it make sense to have a control group for a school chemistry experiment?

texts:
I'm wondering if it makes sense to have a control group for the following experiment:

measure the speed of gas produced  when hydrochloric acid and calcium carbonate react, as a function of surface area of the calcium carbonate.
independent variable: coarseness of calcium carbonate ($\ce{CaCO3}$) as a way to control the surface area of the $\ce{CaCO3}$ from large chips down to powder.
dependent variable: speed of glass production measured using water displacement in a calibrated volume.

Usually I think of a control group as being used to control uncontrollable variations in the experiment, especially in biology or psychology experiments. But in this case, assuming that the volumes of $\ce{HCl}$ and $\ce{CaCO3}$ are measured carefully, and the gas is accurately measured, are there other variables that a control group would assist with?

We know that there will be an effect of mixing $\ce{HCl}$ and $\ce{CaCO3}$. We can hypothesize that increased surface area will speed the reaction. But does it make any sense to have a control where we mix $\ce{CaCO3}$ and water? Or $\ce{HCl}$ and pieces of unreactive glass?


texts: Selecting a good test solution for Cyclic Voltammetry

texts:
So I have a textbook headed my way for this but need to get a head start.

I have a 3-electrode voltammetry setup but I want to test it for some standard values (for educational purposes) before I start working on my actual project. For now, I'd like to use the equipment I have to run Cyclic Voltammetry tests at a basic, neutral, and acidic pH to verify that it's reading correctly and that I know how to read it.

Problem is, I've been out of Chem for a while. So asking about choosing test chemicals is sort of a multi-pronged question.

Given some chemical, say Potassium Ferrocyanide in a water and KCl solution, how do I calculate the pH? I've seen the equations concerning hydron concentrations, but I'm not too sure how to calculate hydron concentrations (had a little difficulty finding info).
Will performing this calculation tell me anything about the reversibility of the redox reaction, or is that something that it typically found empirically?
Is there anything else I need to be aware of in doing this calculation?

Sorry for the spread question, but I'm just getting started with all of this.

Oh, as a note, I have Pt and AgCl for my electrodes (AgCl wire and I should be getting an AgCl electrode soon).

Thanks!


texts: Is it absolutely necessary to use centrifuge to separate ethylene glycol from precipitate?

texts:
I've been trying to synthesize intermetallics of $\ce{XY}$ type using transition metal salts and main group element salts. For my system, EG, DEG, and TEG are good solvents. However, because of them being highly viscous, I've experienced normal drying doesn't do the trick and that the precipitate remains puffy even after drying (which shouldn't be the case) before sintering but by using centrifugation, I've been successful at removing the puffy texture of the precipitate.

Recently, I came upon this paper where they haven't used centrifugation for the main sample. Could anyone please explain how does this work?


texts: Addition of oxygen molecule to given aromatic compound

texts: I did figure out that the hydrogen atom is reactive as it has three electron donating groups attached to it, I know it reacts. But the answer given is that 6 different compounds can be formed (minor and major; including stereoisomers). But I need some help figuring them out.


texts:
In the chloride process (the process used to create titanium oxide from titanium ore), how is TiO2 collected? What prevents the TiO2 from building up on the walls of the reactor chamber?

It's my assumption that the solid titania produced in a TiCl4+O2 reaction (assuming that the TiCl4 and O2 are all gases at 200 C) would plate out on the walls of the reactor chamber (since it is the one solid in the reaction). When manufacturing titania, how do manufacturers prevent the titania from plating out on the walls? Also, how would they collect it?


texts:
TLDR: Does urine make concrete hygroscopic enough to absorb moisture from the air so much that a spot of humidity is visible? Are uric acid crystals moisture-absorbent? (Urea apparently is according to Wikipedia)
Here is the story:
In my parents' house, there is a mystery that we were unable to solve.
During the renovation, certain spots on the cement floor appeared wet (used to be covered by glued carpet). Even worse, some spots appeared to evolve and sometimes grow.
We assumed the worst. Since this was the ground floor (there is no basement) we thought groundwater might be infiltrating the house. One particularly intriguing spot was near the hinge side of an interior door. The door is in a wall of cored brick next to an interior concrete pillar. The spot on the floor was next to this pillar.
Several investigations have been made:

A dig outside the house to check the depth at which water could be found. It was deep enough.
Checking if there is hydro-isolation on the foundation. There was.
Checking on the outside of the base of the house for humidity. It was dry.
Checking the heating pipes buried in the floor. They were nowhere near and eventually the in-floor pipes were abandoned.

All of the people who investigated (engineers, constructors) were mystified as the spot kept evolving even though we properly ventilated the area for a significant time.
Even more puzzling, the concrete pillar was dry.
Eventually, believing there might be a spring under the house (and that the pillar was ok due to the hydro-isolation on the foundation) we broke the first layers of the cement floor.
Underneath the first layer, there was a layer of extruded polystyrene thermal insulation. Underneath that, a hydro-isolation layer. And underneath that the concrete slab of the floor. All were dry.
At this point, all other people just gave up and some even suggested we call an exorcist.
However, this meant a return to one of the first theories about these spots.
In the house used to live several cats and unfortunately, there have been plenty of times when some of them peed on the carpet floor. The spot near the pillar was one of the preferred places. This was one of the reasons for completely removing the glued carpet. This theory was initially rejected because the house was ventilated for more than 2 months with the carpet removed and the cats long gone. During this time and more the spots evolved and grew. We believed that since the spot grew noticeably (we traced the edge) and since it didn't smell it could not be because of the cats and it had to be from below (of above, but the roof and the ceiling were ok so we eliminated that possibility).
Now with layers below also dry, the only possible source of humidity left was the air.
So, does (cat) urine make concrete hygroscopic enough to produce a visible wet spot?
I have searched Google and Wikipedia about the moisture absorbant properties of uric acid but I have not found anything relevant. According to Wikipedia, urea is hygroscopic and highly soluble in water. I decided to ask this here since it is about the physical properties of a chemical compound.
The closest I have found is this:
https://pubs.acs.org/doi/10.1021/ja00836a027
What makes these particles hygroscopic?
Salt + Sodium Bicarbonate releasing water in carpet


texts: Why does benzaldehyde not respond to Fehling's test?

texts:
All aldehydes are supposed to respond to Fehling's test. So why doesn't benzaldehyde respond to it?

Does it have something to do with the fact that benzaldehyde is an aromatic compound? If so, then how?


texts:
This excellent answer explains at length what's happening in this fascinating video entitled Liquid Electrons - Periodic Table of Videos. In the screenshot below, the metallic-looking solvated electron layer (middle) has a bronze color.

I am trying to understand what "solvated electron" even means. Is the way that these electrons move around in solution more like a solvated ion, or proton in an acidic aqueous solution, or more like the conduction electrons in a typical liquid metal we might see in a laboratory, such as mercury or gallium? Or are both of those completely inadequate analogies?

I chose proton as the lightest thing I could think of that could be roughly thought of as a "bare charge". It is, of course, the opposite sign, so maybe a lithium ion?


texts: Why do buffers need to be composed of equal amounts of the acid and salt?

texts:
Say you have $\ce{NaOH}$ and $\ce{CH3COOH}$ and want to make a buffer.
Theory teaches 6 mols of $\ce{CH3COOH}$ and half, 3 mols, of $\ce{NaOH}$ would be needed.
Then you'd be left with 3 mols of $\ce{H2O}$, 3 mols of $\ce{NaCH3COO}$ and 3 mols of $\ce{CH3COOH}$.

However, what if you mixed 3 mols of $\ce{NaOH}$ with 12 mols of $\ce{CH3COOH}$? According to my calculations, you'd be left with 3 mols of $\ce{H2O}$, 3 mols of $\ce{NaCH3COO}$, and 9 mols of $\ce{CH3COOH}$.

In the latter example there is a clear imbalance in the salt:acid ratio. However, won't this still act as a buffer, while not as strong as an equally concentrated 1:1 buffer? So it will work, it's just not ideal?


texts:
The periodic table has 7 periods and they have 2,8,8,18,18... elements respectively from 1 to 7. But from what I understand, the periods each state the number of electron shells that the elements in that period has. So if that is the case, shouldn't period 3 have more elements, since it can hold up to 18 electrons, and therefore it can have up to 18 more protons from the largest atomic number element in period 2? (Since period 3 has a M electron shell, it can also have a p orbital, and in total therefore can have 18 elements.)

The same could be said for elements in group 4, group 5, group 6 and so on since they can have f,g, and h orbitals as well. Am I missing something here?


texts: Is it possible to synthesize permanganate electrochemically?

texts:
I have been researching the production of peroxy acids and other strong oxidizers. I was wondering if it's possible to produce permanganic acid if I were to cast an anode containing Manganese Dioxide from a battery?

Update

I was able to produce what I would believe to be the permanganate anion based on the color of the solution and the composition of one of the electrodes.


texts: Need a malleable solid which dissolves in HCl, acetone, or water

texts:
I need to temporarily plug the end of a 3 mm ID copper tube with some sort of malleable solid solute that I can dissolve at later point by flushing with a solvent/acid via syringe. I need to keep the area at around room temperature, so I cannot use dry ice or excessive heat.  I'm using it to prevent liquid silicone from seeping up the end of a tiny copper tube while I seal the tube, so it needs to be relatively inert to the copper tube and the silicone.

I've tried using Styrofoam and acetone (which is almost ideal), but this leaves behind a residue of slimy gunk that is difficult to remove, and I need the tube to be clear of foreign residues.  Low melting point solid materials may be possible to use, but they can't leave behind any residue for my purposes.  I can obtain any special chemicals through my university.


texts: tolerable error, CASSCF simulation of UV/Vis spectrum

texts: Please forgive my ignorance of experimental spectroscopy. I am a computational chemist, not an experimental one. My question is: what would be considered a tolerable or reasonable difference between an experimental lambda max from that taken from a CASSCF simulation? I am currently trying to design my active space, etc. My target is 4.56 eV but I can only get as close as 5.26 eV (+0.7 eV error) so far. Is it bad or should I proceed to my next step?


texts: What kind of materials are plastic syringes made from?

texts:
I'm trying to figure out what kind of materials my disposable plastic syringe is made from. I have a Medefil MIS-1130 syringe and when I visited the company website I couldn't find any information on what the disposable syringes were made from (although they did tell me a lot on what's NOT in them).

I'm trying to find a regulation or something that could help me identify what kind of plastic and rubber are used to make the shill, plunger and seal that make up the disposable syringe. Can anyone on here please give me some guidance?


texts:
Majority of texts (at high school level) say that when $\ce{SO2}$ is dissolved in water sulphurous acid $\ce{H2SO3}$ is formed. However my text book states that it forms clathrate $\ce{SO2.6H2O}$ when dissolved in water, and can significantly exist as $\ce{H+ + HSO3-}$.
I found similar finding on Wikipedia:

Sulfur dioxide is fairly soluble in water, and by both IR and Raman spectroscopy; the hypothetical sulfurous acid, $\ce{H2SO3}$, is not present to any extent. However, such solutions do show spectra of the hydrogen sulfite ion, $\ce{HSO3−}$, by reaction with water, and it is in fact the actual reducing agent present:
$$\ce{SO2 + H2O ⇌ HSO3− + H+}$$

However there's no mention of clathrate on the whole page. Do what's the actual product on dissolution of $\ce{SO2}$ in water?


texts: What is the empirical formula of Haemoglobin?

texts:
Everywhere I look on the internet tells me a different formula. Are there genuinely different formulas for Haemoglobin, or are some of my internet sources incorrect?
(I know there are different formulas for oxyhaemoglobin, deoxyhaemoglobin, carboxyhaemoglobin, etc but the formulas I am seeing are very varied and do not account for this... I don't think)


texts: Overlapping oxygens in crystal structure -- what's going on?

texts:
This is a screenshot of  a portion of a metal organic framework (MOF).  These are two oxygens of two NMP solvent molecules.  What I am wondering is why they are so close and overlapping like this.  I checked the CIF file, and occupancy for all atoms in this structure is 1, so it doesn't seem to be the case that there is only one NMP molecule in two equally likely positions.

Could someone explain this?  Thanks


texts: Why does the value of Δo increase with increased charge on the metal?

texts: A greater positive charge means the ligand is strongly attracted and pulled closer, and thus it creates a stronger crystal field. The potential energy value of the barycentre should thus be higher, since repulsion experienced by the d electrons is stronger. Why is though the value of the Δo increased - the potential energy difference between the various differently oriented d orbitals? Each orbital experiences stronger repulsion if charge on metal ion increases and the ligand is pulled closer, but how can anything be said of the energy difference Δo? Both t2g and eg are at a higher level, that's all.


texts: How can I synthesize 2‐amino‐3‐(chlorosulfonyl)benzoic acid from toluene or benzene?

texts:
I am trying to design a proper synthesis route for 2‐amino‐3‐(chlorosulfonyl)benzoic acid, though methyl 2‐amino‐3‐(chlorosulfonyl)benzoate—using an ester group in lieu of a carboxylic acid—would also be acceptable.

I am thinking a good starting material would be toluene or benzene. Here is my proposed route.

I determined the ortho-para ratio for toluene nitration from p. 816 of "Organic Chemistry, 6e" by Loudon & Parise.

Typically, para substitution predominates over ortho substitution, but not always. For example, nitration of toluene gives twice as much o-nitrotoluene as p-nitrotoluene. This result occurs because the nitration of toluene at either the ortho or para position is so fast that it occurs on every encounter of the reagents; that is, the energy barrier for the reaction is insignificant. Hence, the product distribution corresponds simply to the relative probability of the reactions. Because the ratio of ortho and para positions is 2 : 1, the product distribution is 2 : 1.

Also, according to the same page,

The boiling points of o- and p-nitrotoluene, 220 °C and 238 °C, respectively, are sufficiently different that these isomers can be separated by careful fractional distillation.

Is there a better method? Please identify any mistakes I may have made in my synthesis and suggest improvements. Note that I install t-butyl as a blocking group in order to direct the sulfonyl chloride group ortho to the amino group.


texts: How long does it take Freon refrigerant to disappear from a room after an accidental major leakage?

texts:
I would like to know please how long does it take Freon refrigerant to completely disappear from a room after an accidental major leakage?  Does it stick to surfaces , clothes or walls? Does natural ventilation get rid of it? Does it disappear 100%?

Thank you very much in advance.


texts: How can I find the smaller symmetric structure from big crystal unit cell?

texts:
I have Pyrope (Mg3Al2(SiO4)3) crystal structure, downloaded from materialsproject:
https://materialsproject.org/materials/mp-6073/#

It appeared as triclinic cell, but if you download CIF file and open it from softwares like Avogadro or VESTA, it appeared as a orthogonal simple cubic (a=b=c, alpha = beta = gamma = 90 degree). I also checked that this geometry is the same with what I downloaded from American Mineralogy Material Database.

Now, I wish to run DFT or quantum calculations for them. So, I excluded atoms in periodic boundary, unit cell contains total 160 atoms. I'm afraid this might be too big, might takes too long time to calculate via DFT or any other quantum simulations. All I need to do is just geometry optimizations, but still, 160 atoms seems too big.

Using VESTA or Avogadro or any other software, is this possible to find the symmetric structure inside this or other "big" unit cell, and make a smaller / simpler version of unit cell for faster calculation?

Or, can I manually cut this unit cell in 1/4 size, 40 atom system with 1/2 size for x, y, and z direction, and run the minimization? It seems that the Pyrope unit cell have some sort of repeating structure inside the big unit cell. But I'm not sure if it is "safe" to find symmetry and divide the unit cell manually.

Thank you


texts:
Can someone please explain to me what is the differences between $\ce{Si(OH)4}$, $\ce{H4SiO4}$, and $\ce{SiO2.2H2O}$? I am currently studying sandstone acidizing geochemical models and this question came to me. It seems that $\ce{SiO2.2H2O}$ and $\ce{Si(OH)4}$ are basically the same thing and are considered minerals that may precipitate during the process, but $\ce{H4SiO4}$ is the aqueous form.
References

Quinn, M. A., Lake, L. W., & Schechter, R. S. (2000, February 1). Designing Effective Sandstone Acidizing Treatments Through Geochemical Modeling. Society of Petroleum Engineers. doi:10.2118/60846-PA
Walsh, M. P., Lake, L. W., & Schechter, R. S. (1982, September 1). A Description of Chemical Precipitation Mechanisms and Their Role in Formation Damage During Stimulation by Hydrofluoric Acid. Society of Petroleum Engineers. doi:10.2118/10625-PA
Sevougian, S. D., Lake, L. W., & Schechter, R. S. (1995, February 1). A New Geochemical Simulator To Design More Effective Sandstone Acidizing Treatments. Society of Petroleum Engineers. doi:10.2118/24780-PA


texts:
In the slides i'm studying (about the production of PZT), is given the following formula for lead zirconate titanate :
$$\ce{PbZr(Ti)O_3}$$
with the explanation:

It is a solid solution of two oxides: lead zirconate $\ce{PbZrO_3}$, and lead titanate $\ce{PbTiO_3}$

Later on, it's used an other formula (acceptor doping: $\ce{K^{1+}}$ replacing $\ce{Pb^{2+}}$ site)
$$\ce{(Pb_{1-x}K_x)(Ti,Zr)(O_{3-x/2}V_{O\,x/2})}$$
where $\ce{V_O}$ indicates oxigen vacancies
even later (acceptor doping: $\ce{Fe^{3+}}$ replacing $\ce{Ti^{4+}}$/$\ce{Zr^{4+}}$ site)
$$\ce{Pb\{(Ti,Zr)_{1-y}Fe_y\}(O_{3-3y/2}V_{O\,3y/2})}$$

Now, what's the meaning of parenthesis in this context?

Is this the standard notation to indicate solutions? In this case, which is the general rule? Because it seems that quite multiple ways were used here..


texts: Could you form quartz crystals by melting and cooling sand very slowly?

texts:
Since glass is amorphous quartz and when you slow the cooling of something enough it will crystallize, couldn’t you melt $\ce{SiO2}$ (sand) and then very slowly cool it to cause spontaneous nucleation and form quartz crystals?

If so, then why hasn’t it been used before? It would seem to be a better method than flux because in flux you need many chemicals and a dissolving chemical or mix and it is a complicated and very long process to grow very small crystals throughout the whole mix. If you simply cooled a molten mixture slowly enough to cause complete crystallization, then the entire mix of molten crystal would need to form crystal because it all is cooling down.


texts: How do I find out what benzene containing compound this is with IR and NMR?

texts:
I have the following IR and NMR of an unknown substance. Can someone tell me what is a possible structure of the compound or point me in the correct direction. So far I am thinking of a benzene ring based compound with an OH group. Something like 2-phenylethanol but not sure.

Some properties:

melting point: $\pu{116 ^\circ C}$.
Composition: white powdery solid.
Soluble in $\ce{NaOH}$ and $\ce{NaHCO3}$.

Based on the IR, the broad peak at $\pu{3424 cm-1}$ represents an alcohol while the 4 humps in the region $\pu{2100-2600 cm-1}$ is indicative of an aromatic ring (most likely a benzene ring). The medium peak around $\pu{1660 cm-1}$ is most likely a carbon-carbon double bond. NMR is where I get stuck; I know there should be 6 distinct types of protons and since most of the peaks are around $\pu{7-8 ppm}$, it is most likely the benzene ring protons, but I am not sure how to calculate J values and splitting as it was done in


texts: Why does chlorine trifluoride ignites concrete and sand?

texts: Concrete and sand are highly unreactive to most of the chemical attacks. But chlorine triflouride is so dangerous that it will ignite concrete, sand and other fire retarding substances. Which property does ClF3 possess to cause this ignition and why?


texts:
Some of my friends are in Flint and I'm horrified by their situation. I would like to learn how to test for lead independently.

After all if you can't trust the state sending them water to test is not sufficient. The testing procedures I have read about give too many type II errors. A procedure with a bias toward type I errors would be better since then I could pay a professional lab to see if it was real.

For tests that only detect high levels of lead, could they be made more sensitive by evaporating the water then testing a larger sample?


texts: If you add sodium salt to carbonated water (sparkling mineral water), could you produce sodium bicarbonate?

texts:
I know that $\ce{CO2}$ can dissociate into bicarbonate ions within $\ce{H2O}$. If Na is added, then sodium bicarbonate is produced.

Could you then create sodium bicarbonate using carbonated mineral water and sodium in the form of table salt or does that have too many minerals aside from $\ce{H2O}$ in it?


texts: Does PEO particle size decrease when dissolved in water?

texts:
I am looking to make metallic ink for inkjet printing and using PEO 1 wt%  (MW ~600,000) as a binder. The print head I am hoping to use has a nozzle diameter of 80 microns. The metal powder dispersed in the ink is ~100nm. If I dissolve the PEO into deionized water, will the PEO particles be too big to pass through the nozzle?  The PEO purchased is from sigma aldrich (https://www.sigmaaldrich.com/catalog/product/aldrich/182028?lang=en&region=IE)

(Physicist asking a chemistry question!)

Thanks :)


texts:
Generally, anti-conformations are more stable. But in the case of 2-fluoroethanol, the gauche confirmation is more stable.

It's given in March's advanced organic chemistry book that intramolecular hydrogen bonding is not the correct reason for the stability. Wikipedia explains it using hyperconjugation, but I am not able to understand it. What is the actual reason for the gauche effect?


texts: How do I find a concentration from a sample tested on a spectrophotometer?

texts:
I have an assignment to calculate the concentration from a sample. The assignment is:

You have 100 µL of RNA. You take 10 µL from the sample and put it in 990 µL of water in the cuvette. The OD is 0.05. Calculate the concentration of RNA in the sample. Calculate how many µL you have to take to make a solution of 100 ng.

Thus far I have succeeded to calculate the concentration from the OD. It is 2 µg/µL. I used the formula that I found on the internet :
$$OD\times \text{Standard coeff.}(\pu{40 µg/ml})\times \text{Sample dilution}$$
but I cannot figure out how from that I can calculate the solution with 100 ng, because there is not mentioned the final volume for 100 ng, or how to calculate how much I have to take µL from the cuvette. I do not understand where to begin from.
I tried with the formula $C_1V_1=C_2V_2$, but I could not figure that out.


texts: Why does formic acid give positive Fehling's test?

texts:
$$\ce{HCOOH ->[\text{Fehling's solution}] CO2 + H2O}$$

The points discussed in a previous question do not account for the fact that formic acid also gives positive Fehling's test since it is not enolisable. Then what is the reason/mechanism for the reaction?


texts: Selective sorption of toxins by polymethylsiloxane polyhydrate

texts:
Polymethylsiloxane polyhydrate (PMSPH) is used as enterosorbent for a couple of decades (nowadays under the trademark "Enterosgel"), intended for binding in the gastrointestinal tract and excretion of toxic substances of various nature, agents that can cause diseases and metabolites. Approximate matrix composition (2D) per micell looks like this:

Pharmacodynamics shows that PMSPH effectively bounds endogenous and exogenous toxic substances of various nature, including bacteria and bacterial toxins, antigens, food allergens, drugs and poisons, heavy metal salts, alcohol, metabolic products of the body (bilirubin, urea, cholesterol and lipid complexes).

What makes this gel so selective towards the adsorption of toxins only? Why nutrients (carbohydrates, fats, amino acids, vitamins) are mostly preserved and can be assimilated by the human body regardless?

I suspect it might have something to do with the pore size and geometry, involving a docking-alike behavior, but I don't have a solid enough background in biochemistry to prove it right or wrong. Manufacturer puts a warning "Protect from freezing!", so it might also have to do with the precisely controlled pore size (which is imminently changed after solidification of trapped water).


texts: Bending of water and methanol towards a charged objects

texts:
I just had a question about why does water, methanol or any other polar substances tend to bend towards the charged object.

I think it is because of a slight dipole dipole movement between the charged object and the polar substance, but not sure if that's the reason.


texts: How does UV affect skin colors in dark-skinned people?

texts:
Skin color is one of the things one would rather not ask anything about! Only in humans, it can vary from very dark brown to pale pink. In darker-skinned people, the color is mainly due to melanin, which is produced by melanocytes.
There are three types of melanin: eumelanin, pheomelanin, and neuromelanin. Eumelanin is the most common; so it must be the reason of the dark skin of the dark-skinned. And that's true, since the two major groups of eumelanin are black and brown species.
The first ray produced by sun that comes to mind when you think about affecting the attributes of skin is UVA, since it penetrates most into the skin (Even though its energy is lesser than UVB). So, when I attach these two together I reach the fact that if UV rays do not cause free radicals they will eventually change the skin's color. (This is what is mostly believed and its effect on natural selection is impossible to hide)
Now, I give up. How does UV do to the skin that makes it darker? This must be very easy, huh? What am I missing?


texts:
The osmotic pressure of an aqueous solution at $25$ Celsius is $92.0$ $kPa$. Calculate the boiling point
of the solution. (Assume that the density of the solution is $1.0$ $g/mL$, ignore the mass of the
solute)
Using the formula $\pi = cRT = \rho g h$, we can find the concentration value and height; however, how one should proceed to evaluate the boiling point using the ebullioscopic constant and morality of the solution? Are there any suggested ideas for solving it, considering all the givens are outlined in the statement?


texts: Which transparent plastic to use for electrolysis of dilute sulphuric acid

texts: I plan to do an experiment which involves the electrolysis of dilute sulfuric acid (1 M or 1 mol/L). I would like to carry it out in a long transparent plastic container (easier to handle and clean). What would be the suitable plastic for this?


texts: How to separate copper(II) chloride from 4-iodophthalic anhydride?

texts:
I am planning a reaction in which I iodate phthalic anhydride. My reaction is I2, phthalic anhydride, and copper(II) chloride as a catalyst. The solvent is 99.9% isopropanol. How do I separate the product (4-Iodophthalic anhydride) from the copper(II) chloride and remaining iodine?
Edit: I planned to boil away the solvent, and sublimate away the iodine from the remaining solid. How do I separate my product from the resulting mix? At the moment, I only have isopropanol.


texts:
I'm probably doing overkill trying to learn a bit of everything, but here's my story. I have a B.S. in Math with a minor in Microbiology, and I'm currently taking Computer Science courses online to meet the pre-requisites for a Master's in CS where I'll focus on machine learning. I want my thesis to be on the Molecular Modeling of a cellular process.

After receiving my Master's, because I want more research experience (and it will count as job experience for indistry), I want to work as a paid research assistant to a laboratory where I help code machine learning algorithms to aid biological modeling.

Let's say I do this for 3-4 years and I have permission to take up to three courses each fall/spring as a non-degree seeking student (realistic?). Would taking courses such as:

Physics: Modern Physics, Stachistical Mechanics, Thermodynamics, Quantum Mechanics, Computational Physics, Biophysics.

And

Chemistry: Physical Chemistry, Analytic Chemistry, Intermediate/advanced Organic Chemistry, Reaction Kinetics, Intro to drug discovery.

Be beneficial to me?

Sorry if this is too opinion based or off topic. However, what will probably benefit me the most when I get to a research assistantship, is that I'll speak to faculty and they'll  direct me on what courses to take. I'd still like your input though before the post is removed.


texts: Why do fluoride ions "win" over thiocyanate ions in a solution with iron ions?

texts:
When you mix aqueous iron(III) nitrate and potassium thiocyanate together you get a red solution. Then if you add sodium fluoride, the red colour disappears.

This is basically because the $\ce{Fe(SCN)^2+}$ ions are red, but $\ce{FeF^2+}$ ions are colourless.

I get Le Chatelier's principle in that, the more iron ions that are stolen by the fluoride, the less $\ce{Fe(SCN)^2+}$ ions there will be because they keep dissociating etc.

The thing I wonder about is why the fluoride atoms get all the iron. I can think of a couple of potential reasons for this, but I don't know which, if any of them, are true, even after googling a fair bit.

Could it be the case that iron is a lot more attracted to fluoride than thiocyanate? Or that the fluoride reaction isn't reversible? And if either of those is true, can this experiment be seen as evidence for that?


texts: Why are solid phase organics often conjugated to HCl?

texts: Many uncharged organic compounds are sold in solid phase with HCl conjugate - e.g. the antihistamine diphenhydramine.HCl or the derivitizing agent pentafluorobenzyl hydroxylamine.HCl, among many others. Assuming the compound will be dissolved at relatively low concentrations in a buffered medium (for instance when a drug enters the bloodstream) the HCl shouldn't have much chemical effect. Why is it there - does it aid crystallization, or perhaps it's leftover from synthesis and is difficult to separate?


texts: What is the rate-determining step in free radical halogenation?

texts:
Recently, we were learning about free radical halogenation in school. A set of notes given to us wrote that the rate-determining step is the propagation step. This seems to go against my understanding of the chemistry of this reaction. The step that likely has the highest activation energy should be the initiation step as it is the only step that involves bond-breaking solely. I have looked up various sources and they also seem to suggest that the rate-determining step ought to be the first step.

Advanced Organic Chemistry (5th ed.) by Carey and Sundberg states that:

  Free radicals are usually highly reactive and the individual steps in a chain reaction typically have high absolute rate constants. However, the concentrations of the intermediates are low. The overall rates of reaction depend on the balance between the initiation and termination phases of the reaction, which start and end the chain sequence.


texts:
If we take a look at the electromagnetic specter, microwave wavelength is higher than infrared, which means its energy is very small. To break  chemical bonds, the energy required is 100-1000 kJ/mol, and this kind of energy can be afforded only by UV and VIS. Due to this, we can conclude that microwave radiation has only a vibrational effect on molecules of food and does not break any bonds ( the food remains the same ).

Considering those facts, why is the microwave avoided in concern for health?


texts: Difference between spin-orbit coupling and the Russell-Saunders Effect?

texts:
The Russell-Saunders effect is the same thing as 'spin-orbit interaction, correct?
The reason I am asking is because I was reviewing the Wikipedia page on 'spin-orbit interaction' and it does not mention Russell-Saunders at all...


texts: Why does Sulfur dioxide incompletely freeze when entrained in a helium stream inside tubing dipped in liquid nitrogen?

texts:
Background - In a laboratory setting, I use typical elemental analysis (EA) to generate about 50 µg of sulfur in the form of sulfur dioxide (SO2). The EA uses a helium carrier. As an example, a sample of silver sulfide wrapped in tin falls into the reactor set to 1000 °C at the same time as an oxygen pulse, hopefully leading to flash combustion and creation of SO2. The SO2 is carried through a desiccant (Magnesium perchlorate) followed by a quartz chip reactor set to 800 °C, and a GC column to separate out impurities by polarity. The helium flow rate through the EA is typically 80 mL / min. The pressure of helium at the top of the EA is set to approximately 135 kPa. The end detector is a stable isotope ratio mass spectrometer where we measure mass / charge (m/z) 64 and 66 (the hot quartz chip reactor exchanges oxygen atoms so as to force all SO2 to have the same oxygen isotope composition so that our only variability is from sulfur isotopes 34 and 32. The above scenario is routine and can be found in Fry B, Silva SR, Kendall C, Anderson RK. (2002) Oxygen isotope corrections for online δ34S analysis. Rapid Communications in Mass Spectrometry 16, 854-858. doi: 10.1002/rcm.651.
Observation - We were experimenting with analyzing smaller quantities of sulfur by tightening up the SO2 peak using a stainless steal loop dipped in liquid nitrogen for a standard amount of time followed by warming it to room temperature. The tubing is 1/16” OD and allowed to completely cool to liquid nitrogen temperatures before the sample is dropped into the reactor. I observed SO2 at the detector downstream of the loop still residing in liquid nitrogen at helium carrier flow rates above 30 mL / min. I had to reduce the flow rate to about 10 mL / min to completely trap all SO2 in the liquid nitrogen immersed tubing. Based on the phase diagram of SO2, even at this higher helium pressure, it seems like I am still well within the solid phase space.
Question - Are these observations expected and if so please help me understand why?
UPDATE - To add information that addresses the existing answers and comments, I have indeed tried larger diameter tubing, longer tubing, and tubing that loops into the liquid nitrogen back out and back in again which should handle the snow flake example. Also, this approach of freezing out of a helium stream works perfectly at high flow rates with N2O and CO2. My question to this Chemistry Stack then, is what about SO2 prevents easy freezing as I can accomplish with CO2 or N2O?


texts: From my lab book it says it is black? I don't understand how we know the color of it is black. Can anyone explain?


texts: How to make a buffered 10% formalin solution

texts:
How can you prepare a solution of 50 mL buffered 10% formalin using the following reagents?

100% formalin (100 mL)
Phosphate buffer (100 mL)

I know I can mix 5 mL of formalin and 45 mL of distilled water together to make 50 mL of 10% formalin, but if I add phosphate buffer later the volume of formalin would exceed 50 mL.

Can I mix like 1 mL of formalin and 9 mL of distilled water together and then make up the remaining volume with 40 mL of phosphate buffer? Is the concentration of formalin remaining the same as long as the proportion of distilled water to formalin kept constant no matter how much phosphate solution I add?


texts: Viscosity of liquid interrupts accuracy of micropipette?

texts:
Does viscosity of liquid interrupt accuracy of micropipette?

I would like to dilute 85% $\ce{H3PO4}$ acid to $\pu{1.194 mol/dm3}$ so I had to pipette 366 microliter into 4.634 mL of water. Then, I adjusted the pH to 11 by dropping 25% $\ce{NH3}$ solution. I did 4 times but final volume was not equal (about 50, 50,100, 200 mL). I think the problem is viscosity of liquid when I pipetted concentration acid.


texts: Is having a lone pair sufficient and necessary for a Lewis base? What about empty orbitals and Lewis acids?

texts: Is any molecule with a lone pair and/or a pi bond considered a Lewis base? Also, is any molecule with an incomplete octet a Lewis acid?


texts: Electronic strucure of cyclopropene radical cation

texts:
Suppose I have a cyclopropene molecule with a + charge on the singly bonded carbon.I think the singly bonded carbon is $\mathrm{sp^2}$ hybridised, isn't it? To obtain this species from cyclopropene, one can consider removing two hydrogen atoms, one homolytically (the one bonded to pure p orbital of carbon) and the other heterolytically (the one bonded with $\mathrm{sp^2}$ orbital of carbon).

So, finally, there is one electron in the pure p orbital and one unit positive charge on one $\mathrm{sp^2}$ hybridised orbital, shouldn't the electron in the pure p shift to the $\mathrm{sp^2}$ orbital as $\mathrm{sp^2}$ has more s character (so it is near the nucleus), does this shift happens?

I am unclear about this scenario, can someone please explain where the electron and the positive charge reside in the C atom.


texts:
Lately I have been seeing quite a few videos on YouTube about molten salt, specifically table salt (NaCl). One of the things that interests me about it is that regardless of what melting technique or type of crucible, the salt always ends up black afterwards.

Is the issue that the salt is highly reactive and is pulling chemicals out of the crucible regardless of what the crucible is made of? Wouldn't that mean that different crucibles would impart different colorations on the end result? That is the speculation I've seen on the comments of many videos (for example), but nothing definitive.

Or is it perhaps an optical change due to the change of the crystal structure? Or maybe something in the salt itself oxidizing or reacting with something in the air?


texts:
I know that to find the composition in a two phase region of a binary diagram we have to draw the isotherm and to look at the intersection with phase boundaries.

But why? Is there a demonstration?


texts: Fick’s first law of diffusion can be used when $\mathrm{d}C/\mathrm{d}t=0$. If the concentration gradient is time-variant, then we must use Fick’s second law. However, when is diffusion steady-state and when is it nonsteady-state? How do I know when the concentration gradient will change with time and when it won’t?


texts: Compute minimum energy paths from arbitrary positions on the potential energy surface

texts:
The minimum energy path is a useful concept in understanding chemical reaction paths. As I understand it, such MEP's are most often computed to verify that a transition state structure connects two minima of interest. Several algorithms exist for computing MEP's, but I suppose all have in common that they are able to follow the gradient.

I am in a situation where I think it would be useful to follow the gradient, but not from a TS structure. Can this be done? I think the IRC functionality of software expects to follow the gradient in two directions, and demand the reaction vector.

Is there a simple and common way of computing MEP's from arbitrary positions on the PES? (I will use Molcas). What would happen if I just do a geometry optimization from the arbitrary position? It is my understanding that geometry optimization algorithms displace the atoms in the direction of the force, and in that way a lower energy is guaranteed for each successive step. But will this actually follow the gradient?


texts: Is ingesting water during swimming harmful?

texts:
Sometimes I feel the water in the pool is heavily chlorinated. However it is impossible for me to swim without ingesting some water. I am only a learner but even advanced swimmers do concede that they do ingest some water at times.

Could this be potentially harmful depending on the chemical content in the pool? Are there studies which advise on the extent of permissible chemicals that can be added to a pool?


texts: Why are signals of carbon and hydrogen atoms (in NMR spectra) split by coupling to 19F?

texts:
Why signals of carbon and hydrogen atoms (in NMR spectra) are split by coupling to $\ce{^{19}F}$? Some spectra books only states that

  $\ce{^{19}F}$ (natural abundance 100%) has a spin quantum number I of ½. The signals of carbon and H atoms up to a distance of about four bonds are split by coupling to $\ce{^{19}F}$.

but there is no explanation. Could someone please explain why $\ce{^{19}F}$ can couple with H or C and split their signals.


texts:
The heats of combustion of $\ce{C_xH_y}$, $\ce{C}$, and $\ce{H2}$ are $a, b,\text{and } c$ cal respectively. The heat of formation of $\ce{C_xH_y}$ will be:
The answer is
$-\left(x b+\frac{y c}{2}-a\right)$ cal
But I am getting negative of it by adding equations:
$$\ce{C_xH_y} + (x+\frac{y}{4})\ce{O2->}x\ce{CO2}+\frac{y}{2}\ce{H2O} \text{ , }\Delta H=a \tag{1}\label{1}$$
$$\ce{C} + \ce{O2->}\ce{CO2}\text{ , }\Delta H=b \tag{2}\label{2}$$
$$\ce{H_2} + \frac{1}{2}\ce{O2->}\ce{H2O} \text{ , }\Delta H=c \tag{3}\label{3}$$
$\Delta H_f=-1\times\eqref{1}+x\times\eqref{2}+\frac{y}{2}\times\eqref{3}=-a+bx+\frac{cy}{2}$


texts: Why is sodium cyanide an inorganic compound?

texts:
I have been told that sodium cyanide is an inorganic compound during a lab experiment but I don't know the reason for this.

Shouldn't sodium cyanide be an organic compound because it has a carbon atom bonded to nitrogen?

The Wikipedia article  on cyanide also says that it is an inorganic compound but I fail to find why it is so.

How do we differentiate between an organic compound and an inorganic compound?


texts: About purifying ethanol - What type of ethanol?

texts:
I'm reading this book, trying to learn some basics of chemistry. One of the experiments is about purifying ethanol.

Now, I have some difficulties in deciding what kind of ethanol solution I should try to purify. The drugstores appear to typically sell denatured ethanol (so it could contain e.g. methanol?) or solutions with ethanol and isopropyl alcohol.

Could potable alcohol be used? I think there's glucose in those.

PS. Doing this in my country is legal. It seems that is not the case in all parts of the world (or has not been).


texts:
My approach was that when the carbon attached was a secondary one, it would have a greater inductive effect compared to the primary one.

Why is the answer 3? Is it due to steric reasons or am I missing some other factor?


texts:
I was told there is a proton leak during ATP production. When going through the mechanisms we went over in class, I was unable to find when this occurs.

During what part of ATP production is there a proton leak and what are the ramifications of this?


texts: Is it possible to obtain n-butane by treating halopropane grignard reagent with methanol?

texts:
The answer is a,b.

My mechanism however doesn't give n-butane when R is propyl. Is this a case of textbook errata?

Himanshu Pandey, Advanced Problems In Organic Chemistry, 9th edition 2017


texts: Interpreting a Formula Tattoo (Bipolar?)

texts: Found This Online. Something to do with bipolar disorder?


texts: How to calculate mass of calcium fluoride that will dissolve in sodium fluoride solution?

texts:
The solubility product of calcium fluoride, $\ce{CaF2},$ is $\pu{1.46E-10 mol^3 dm^{-9}.}$
What mass of calcium fluoride will dissolve in $\pu{500 cm^3}$ of $\pu{0.10 mol dm^{-3}}$ sodium fluoride solution? (Molar mass of $\ce{CaF2}$ is $\pu{78.1 g mol^{-1}}.)$

I tried using the following method:
$$
\begin{align}
[\ce{Ca^{2+}}][\ce{F^-}]^2 &= K_\mathrm{sp}(\ce{CaF2})\\
x(2x)^2 &= \pu{1.46E-10 mol^3 dm^{-9}} \\
x &= \pu{3.3E-4 mol dm^{-3}}
\end{align}
$$
Solubility $s$ of $\ce{CaF2}$ can be found as such:
$$s(\ce{CaF2}) = xM(\ce{CaF2}) =  \pu{3.3E-4 mol dm^{-3}}\times\pu{78.1 g mol-1} = \pu{2.6E-2 g dm^{-3}}.$$
Finally, the mass of $\ce{CaF2}$ dissolved in $\pu{500 cm^3}$ would be
$$m (\ce{CaF2}) = s(\ce{CaF2})\times V = \pu{2.6E-2 g dm^{-3}}\times\pu{500 cm^3} =\pu{1.3E-2 g}.$$
However, my answer differs from the given answer, that is $\pu{5.7E-7 g}.$
How should I approach this question instead?


texts: Why do impurities lower the melting point of an isolated substance?

texts: It is known that impurities in a desired isolated product lower the melting point of the mixture, even if the impurities' melting point is much higher than the desired product. Why is that so?


texts: Entropy as an intrinsic property of matter

texts:
I would like to ask how we can see entropy as an intrinsic property of molecules, namely as something depending also on their geometry (and not only as gross disorder). Is this what is called the "shape entropy" or there's no relation between the two concepts? Which are the parameters that determine this "geometric" or conformational entropy?

EDIT:
The answer written by Buck Thorn provides an interesting mathematical insight of entropy considering the conformations or "geometries" available to molecules in thermal equilibrium.

Is there also a qualitative analysis of this phenomenon (in terms of the possible conformations playing a role in entropy - the parameters I was referring to in the question)?


texts: Flame color vs electrical discharge color

texts:
I don't know the right terms to frame the question but here it goes:

Neon and argon give their characteristic colors when a current is passed through them at low pressure.  Balmer series etc, I understand what's going on there.

Other compounds like boron will give a nice green in a flame test.  Boron in alcohol for example.  But in an electrical discharge, nothing happens.
I'm not understanding where the difference is in the manner of exciting the boron atoms.

How can I find a compound that will give a strong green color with an electrical discharge, at low pressure (1 torr)?


texts: Why does a potential on the reference electrode create an offset on the measure electrode of a pH probe?

texts:
I am making an analog front end for a pH probe and i encountered a design where creating an offset on the reference electrode, creates an offset on the measure electrode.
How does that work ? Does the charge go through water ?
Experience based on TI application notes : https://www.ti.com/lit/an/snoa529a/snoa529a.pdf?ts=1619613280868&ref_url=https%253A%252F%252Fwww.qwant.com%252F
(I don't want to details electronics design because it's not the point)
So here is a pH probe and my mesurement setup:
The voltmeter measure the potential described by the nernst equation.
What happens when I shift the polarity of the reference should be like that:

Now the voltmeter measure U= Nernst eq + 300 mV
But how having this polarised metal rod in the solution change the measure of the pH electrode ?
My understanding is that the charge on the electrode mooves to the water and to the other electrode ?
But the glass membrane should only let hydrons go through so it "should" be isolated from other change of ions. But it maybe let the current flow from the reference electrode to the measure electrode ?


texts: Homemade preservative for natural aloe-vera gel?

texts:
I suppose this question can be extrapolated to food in general, but it is the case that I would like to know if there are any methods that would help me to keep the aloe gel fresh, i.e. avoiding it to rot.

I mostly squeeze the gel and pour it into a small jar. So far I have tried the following methods, being some of them obvious, but would appreciate corroboration anyway:

Sterilize the container and the tools, e.g. boiling or steaming.
Keep it in the fridge.
Stir with C and E vitamin powder to avoid oxidation.

I know little about chemistry, but have heard about pasteurization and some other methods that I couldn't afford at home so, even if you mention those, I will be mainly interested in homemade methods.

PS: I am forced to choose the tags for the post but I am not sure if they are the ones that best suit the question. Please, let me know if I should change them.


texts:
[![enter image description here][1]][1]
Question is in the image 'match' each option having multiple answers. I have invested a considerable time over this but couldn't solve it. Anyone explaining how to see the solubility in those cases will be appreciated. I am having confusion. Or you can give a hint to each given in column 2 or you can also suggest some specific reading.
 I tried this through reaction like agbr+h2o --->agoh+hbr now how do I know its solubility is greater or smaller than expectations!? Similar problems I am facing with other options. [1]: https://i.stack.imgur.com/0Yaot.jpg


texts: Obtaining chemical graph complexity index from SMILES or InChl

texts: I wonder if anyone knows a readily available way to obtain some chemical graph complexity index (like the J index) from the SMILES or InChl representations?I'm looking for some existing implementation, e.g. in R, or OpenBabel, prior to trying to define mine if no one else exist... Thanks!


texts: Will oxidation/reduction of copper still occur in an electrochemical cell if it is not in an aqueous environment?

texts:
Notation of the reduction and oxidation of copper typically includes the aqueous state. Illustrated below:
$$\ce{Cu(s) -> Cu^2+(aq) + 2e-}$$
This event usually occurs at 0.34 V. What if the copper was in an organic environment instead? I ask because I am doing cyclic voltammetry of a capacitor with copper as the current collector and need to measure the non-faradaic capacitance. Our current setup is using $\ce{KOH}$ as the electrolyte and we are basically just seeing a non-reversible/quasi-reversible CV like below:


texts: How can I understand the Lewis acid-base interaction of iron(III) and water?

texts:
The interaction between $\ce{H+}$ and $\ce{NH3}$ as respectively a Lewis acid and a Lewis base is clear for me. $\ce{NH3}$ has a lone electron pair and $\ce{H+}$ has no electrons, or, saying politely, an incomplete duet, and can use nitrogen's lone pair to complete its duet, and a dative (coordinate) bond is formed in the process.

However when I think about $\ce{[Fe(H2O)6]^3+}$, I don't see where these six lone pairs of electrons (which are coming from water molecules) can go in the iron ion. The electron configuration of $\ce{Fe^3+}$ is: $\mathrm{1s^2\ 2s^2\ 2p^6\ 3s^2\ 3p^6\ 3d^5}$. It has five 3d electrons, and all (namely, 2) of its 4s electrons are gone. All five 3d electrons have the same spin, and they occupy five d orbitals. OK, I do remember that 3d orbitals are funny and in the transition metals 3d orbitals get divided into low and high energy level 3d orbitals (hence the color of transitional metal solutions).

But even with this, how do six water molecules position their lone pairs there? We have space for one pair of electrons (where 4s electron left) and then space for 5 more electrons, so in total, for 7 electrons. 6 molecules of water would give us at least six pairs of electrons, i.e. 12 electrons. So we are 5 places short to place all these electrons.

So the question is: how are they placed?


texts: What is the most acidic proton of 2-methylcyclopent-2-en-1-one?

texts:
In an acid-base reaction of $\ce{HO-}$ with 2-methylcyclopent-2-en-1-one, which is the most acidic proton?

I had assumed it was one of them coming off C-5 according to IUPAC numbering (the sp3 carbon α to the carbonyl group). However, the answer book claims it to be C-4 (γ when going in the direction of the double bond).
I assumed C-5, since it seemed it would distribute the charge due to resonance more with the $\ce{O}$ atom. What am I doing wrong?


texts: What is the magnitude of the current in an electrolyte?

texts:
if a battery is connected to an electrolytic cell, what is the magnitude of the current in the electrolyte compared to the the magnitude of the current in the wire? This doesn't make sense to me because there are cations flowing in one direction and anions flowing in the other in electrolytes, so is the current twice the magnitude of the current in the wire? does ohm's law still hold? Is current not uniform in the circuit? I hope somebody can help. Thanks!

Edit: Sorry for asking an off-topic question. Thank you so much for the answers and comments!


texts: Why are anti aromatic compounds unstable?

texts:
Just like aromatic compounds, anti aromatic compounds have several resonance structures and some of them are also conjugated ( 1,3-cyclobutene).

Why is it that just having 4n electrons makes them unstable?


texts: What is the importance of iron in complexes and in the process of electron transport?

texts: What is the importance of the iron in complexes and in electron transport? This question is related to synthesis of ATP. I have read about iron-sulfur proteins, but I don't understand how this works.


texts: How to determine interaction of photon with a hydrocarbon Bixin

texts:
Bixin is an apocarotenoid found in annatto with 25 carbons with  carboxylic acids at each end of the chain. It is an insoluble orange red pigment.

I am interested to study photon interaction with this molecule. Please, give me some head start on what to read. It is a red pigment, therefore it absorbs photons below 670 nm or so. How can I determine if this molecule allows luminescence in any degree? Electronic transitions?  or just any refraction or scattering.


texts:
After reading various answers here on StackExchange (like Why is the methyl group electron-donating via the inductive effect? and Strongest negative inductive effect group between trimethylammonium, ammonium and dimethylsulfonium groups), I am repeatedly seeing that -CH3 is electron donating through hyperconjugation. Otherwise is is electron withdrawing. So when comparing the acidic nature of the above two compounds, should we use electron withdrawing or electron donating nature of the methyl group?

Also will there be a difference if there is a normal cyclohexane instead of the conjugated benzene.


texts: What does "percentage by mass" mean in the context of a compound dissolved in a solution?

texts:
Copper can be recovered from low-grade ores by 'leaching' the ore with dilute $\ce{H2SO4}$, which converts the copper compounds in the ore into $\ce{CuSO4(aq)}$. In a $\pu{50 cm^3}$ leach solution, the concentration of copper ions is $\pu{7.8 x 10^-3 mol/dm^3}$. Find the percentage by mass of copper in the leach solution.

Isn't it impossible to find the percentage by mass in this case? We don't know the total mass of the leach solution, and it could be anything. Is the question wrong, or is the definition of percentage by mass different than what I'm using?

Also, how does $\ce{H2SO4}$ react with copper compounds to form $\ce{CuSO4}$? I thought copper couldn't reduce hydrogen ions.


texts: Best way to dissolve and consume cysteine HCl monohydrate powder

texts:
Does cysteine break down in filtered water?  Should this made more acidic?

If I mix cysteine powder in juice (something acidic maybe), does it remain at cysteine?  It seems that it can oxidize into cystine and lose some of its qualities.


texts: What is the number of lone pairs of central atom when it has an odd number of electrons?

texts:
What does it mean in asking the number of lone pairs of central atom when it has an odd number of electrons?
As lone pairs means the no. of non bonding pairs of electrons does it exclude the one odd electron if present in the central atom?


texts: Can carboxylic acids like act as nucleophiles in substitution reactions?

texts:
Can carboxylic acids like formic acid act as nucleophile in $\mathrm{S_N2}$ or $\mathrm{S_N1}$ reactions?
For example can formic acid react with an alkyl/aryl halide like benzyl bromide?

I'm asking because I found a very similar question while going through some old organic chemistry test papers. However none of the book's I have read says that carboxylic acids can act as nucleophile in such cases.


texts: Can a first degree carbocation form if a methyl shift is possible?

texts:
I was going through a reference book when I stumbled upon this question

Is that even possible?


texts: Is there an abundance threshold of a 'synthetic' element for it to be considered natural?

texts:
I always (possible naively) thought that elements are either natural or synthetic, either one or the other.  But, according to the Wikipedia page about Synthetic Elements, it states that:

  All elements with atomic numbers 1 through 98 are naturally occurring at least in trace quantities, but the following elements are usually produced through synthesis. Except for Francium, they were all discovered through synthesis before being found in nature.

These are shown in pink in the image below:

Image attribution: "Periodic table, good SVG" by Incnis Mrsi - Own work. Licensed under CC BY-SA 3.0 via Wikimedia Commons.

I understand that the amounts of these elements exist naturally in trace quantities, not necessarily on Earth, for example, according to the Jefferson Lab page about promethium:

  Promethium does not occur naturally on earth, although it has been detected in the spectrum of a star in the constellation Andromeda.

This leads me to my question:

Is there a natural abundance threshold of a 'synthetic' element for it to be considered natural?


texts: find the pH where is maximum the concentration of a amphiprotic substance

texts:
Considering a general amphiprotic substance NaHA. I know that the maximum concentration of the specie $HA^-$ is found at $pH = \dfrac{pKa1+pKa2}{2}$. Why? How i can confirm this statment?

The equations are:

$$ \ce{HA^- + H_2O <=> A^{2-} + H_3O^{+}} \quad Ka2$$
and
$$ \ce{HA^- + H_2O <=> H_2A + OH^{-}} \quad Kb=\dfrac{Kw}{Ka1}$$


texts:
Reactions for the lead acid battery are:

$$
\begin{array}{}
\text{Oxidation}&\ce {Pb(s) + HSO4^-(l) &-> PbSO4(s) + H+(l) + 2e-}\\
\text{Reduction}&\ce{PbO2 + HSO4^-(l) + 3H+(l) + 2e- &-> PbSO4(s) + 2H2O}\\
\text{Total reaction}&\ce{Pb(s) + PbO2(s) +2HSO4^- +2H+ &-> PbSO4 + 2H2O}\\
\end{array}
$$

What will be the cell notation for this battery? My attempt:$$\ce{Pb(s), Pb^2+(s)| HSO4^-(l)| PbO2(s), Pb^2+(s),Pb(s)}$$

The things that I have in mind,

In both sides the electrode material is $\ce{Pb(s)}$
Separate every element that is in the same phase with a comma
Separate every element with different phases with a single bar
Separate the two half reactions with a single bar (as I find no salt bridge here)

I am having a tough time learning cell notation. Anyways this was a challenging one for me and I tried my best shot. I am really not sure whether everything is right or not. So please identify my mistakes and show me the right way to do it.


texts:
I need 500 ml of 0.2 mol/L  H2SO4 for a tutration lab. What volume in mL  of the 18 mol/L stock solution should you use?

I think this is a dilution question asking me to use C1V1=C2V2. I am confused because it sounds like s dilution question, but its asking for volume so i could possibly be using the (v/v) formula. If someone could help me out that would be greatly apprecaiated, trying to study for a test.


texts: How to distinguish between a coordinate bond and a covalent bond?

texts: I’m confused as I am unable to find a completely trusted way of finding coordinately bonded compounds from a bunch of other compounds.


texts:
In a lot of (mainly older) papers discussing organic synthesis,  Δ is used to describe alkenes. As far as I know, this is no longer (if ever) IUPAC recommended nomenclature, so I haven't been able to find any reference to its intended use.

The main area I'd seen it used was in steroid synthesis, where I assumed it had some specific use relating to that class of natural product (i.e. related to the biosynthesis etc.). However it does appear in other places, such as in the synthesis of Rifamycin:

 Scheme from Nicolau Rapamycin synthesis. Taken from Classics in Total Synthesis I

"… the Δ35,36 double bond …" is used in the text to describe the alkene that gets reduced. Given that this could easily be referred to as the (E)-alkene or even just 206, I suspect that there is a special reason why Nicolau chose Δ35,36 however that reason isn't apparent to me.


texts: What does it mean for chemical reaction network to be in equilibrium?

texts:
What does being in "equilibrium" mean for a set of chemical reactions? If we have some number $n$ of $\ce{A}$ molecules and $m$ of $\ce{B},$ and the following reaction where $\ce{A}$ and $\ce{B}$ can reversibly bind:

$$
\begin{align}
\ce{A + B &->[$k_\mathrm{f}$] AB} \\
\ce{AB &->[$k_\mathrm{r}$] A + B}
\end{align}
$$

Suppose $k_\mathrm{f} = 2,$ $k_\mathrm{r} = 1.$ Can this system be "in equilibrium" and what would it mean? Does it mean all reactions have to be reversible and that as $t \to \infty$ go on at the same rate? In that case it seems that this system cannot be in equilibrium, since $k_\mathrm{f} \neq k_\mathrm{r}.$


texts: How to lose as little heat as possible to the surroundings from an endothermic reaction?

texts:
For an experiment, I'm adding several substances (as powders) to hydrogen chloride, and measuring the temperature changes to calculate enthalpy. What is a container I could perform it in (other than a styrofoam cup) that would minimise the heat lost to the surroundings?

I looked up using a vacuum flask of some sort, but would that be appropriate for this sort of reaction? The temperature is being measured via a temperature probe.


texts: I need to electroplate selenium onto a conductive metal (for an experiment). The end goal is a thin film of pure, elemental selenium. Unfortunately I can't find anything on the internet: Ideally, I'd like a simple, inexpensive, and easy to make and/or find solution. Does anyone have any suggestions. (Also tips on suitable anodes would be helpful too!)


texts: Number of enolizable hydrogens in 2-methylcyclohex-2-en-1-one

texts: The number of enolizable hydrogen atoms according to me is four, but the answer given for the question says it has seven enolizable hydrogens. Where are the rest of them?


texts: What are these crystals on my champagne cork?

texts:
I opened up a bottle of champagne that was left in a wine cooler for approx. 8 years. To my astonishment there were small crystals at the underside of the cork.

The crystals are colorless, odorless and have no specific taste at all. What is going on here?

Image:

Close up:


texts: What is the senior parent chain in the following compound?

texts: Will the IUPAC name be (2-hydroxymethyl) but-3-ynoic acid (or) 2-ethynyl-3-hydroxy propanoic acid?


texts: could potassium cyanide be turned into potassium nitrate in a single pot reaction?

texts: Is there a way one could turn potassium cyanide into potassium nitrate (actually oxidize the cyanide anion)? It's fairly easy to convert it to ammonia by hydrolysis, but the conversion of ammonia to nitrate is difficult (bionitrification is out of question). Would peroxide be able to attack it?


texts: Evaporating water from a combination of dietary minerals: will it work safely or react?

texts:
I've combined multiple elements dissolved in water into a preferred ratio, but would like to evaporate some of the water to increase the concentration (let's say at 200 $^{\circ}\mathrm{C}$ in the oven). The elements in question and the amounts are: 2 mg chromium, 5 mg lithium, 2 mg vanadium, 140 mg iron, and 50 mg boron. The volume of water is about 60 ml.

I would like to know if I can safely do this procedure without a) causing a reaction; and b) evaporating any of the elements.


texts:
I have denatured ethyl alcohol which was obtained this formula;

In 100 L ethyl alcohol there is 0.8 gr denatonium benzoate and 78 gr tert-Butyl alcohol.

Is there any way to obtain absolute ethyl alcohol from that mixture.


texts: Algebra of conserved quantities for chemical reactions

texts:
So there is the standard formation enthalpy $\Delta H^0_f$ and there is also formation entropy.

Are there more (independent) quantities? What about the heat capacity? Is there a general theoretical structure where one can show one got all the conserved quantities associated with a chemical reaction? It seems to me that one could this on a quite rigid structure and invesigate the properties of chemical processes from that point of view.

And to what extend are the procedures like using Hess's law just rules of thumb or what are some insights about he deeper structure where they come from.


texts:
I'm aware of the fact that active mass is defined as the molarity of a substance, but my textbook states that

  "Active masses are dimensionless quantities but for our purposes we generally take them with dimensions of molarity, partial pressures etc."

What point is my textbook trying to get across to me? Why do active masses have no dimensions? Why have we defined this quantity in the first place, if we use it interchangeably with the term "molarity"?

Edit: Please keep in mind that I have only just graduated high school and would be very grateful if you could explain this concept to me in simple terms.


texts: How do you name an alkene using IUPAC rules if the longest carbon chain in this alkene does not include the double bond?

texts:
For example, which is the right way to name this compound:

Is it 2-bromo-4-methylenehexane or 4-bromo-2-ethylpent-1-ene?

Does the larger number of carbon in a chain take priority, as in the former, or does the carbon-carbon double bond take priority, as in the latter?


texts: Will OTs ever act as a nucleophile and substitute with an alcohol?

texts: If you reacted TsOH with a secondary or tertiary alcohol, will you ever see a racemic mixture of OTs substituted products after the water group leaves? Is OTs just too weak of a nucleophile to ever substitute?


texts: How to predict one equilibrium constant given two others?

texts:
$$\begin{alignat}{2}
\ce {CO2 (g) + 3H2 (g) \;& <=> CH3OH (g) + H2O (g)}\qquad&&{k_1=\;?} \\
\ce {CO (g) + H2O (g) \;& <=> CO2(g) + H2(g)}\qquad&&{k_2= 1.0\times10^5} \\
\ce {CO (g) + 2H2 (g) \;& <=> CH3OH(g)}\qquad&&{k_3= 1.4\times10^7}
\end{alignat}$$

What is the value of $k_1$? I have tried reversing equation two and then multiplying $k_2$ and $k_3$ together, but I am not sure how to work this problem out.


texts: What organizational methods pre-date the Periodic Table?

texts:
Dmitri Mendeleev noticed patterns in elements which allowed him to design the periodic table which ultimately led to the modern periodic table.

How were elements organized before this? Was there any method that served as a crude standard?


texts: Why does 1 cubic meter = 1000000 cubic centimeters?

texts: I have the SI chart in front of me. It states that a centi is 10^-2 and since they are already designated cubic meters why does 1 cubic meter equal 1000000 cubic centimeters?


texts:
I have been struggling with geometry optimization of a prostaglandin molecule (20 carbon atoms). I finally got the optimization, all right. Then I did the Frequency job on the optimized structure (I opened the Optimization job .LOG file scrolled up to the last geometry (highest number) and launched the Frequency job from there). Below is my route line from the .gjf file:

# freq=noraman cphf=noread b3lyp/6-31g(d) geom=connectivity

The Frequency job terminated normally and that's what I got in the Frequency job .LOG file:

          Item               Value     Threshold  Converged?
 Maximum Force            0.000005     0.000450     YES
 RMS     Force            0.000001     0.000300     YES
 Maximum Displacement     0.013516     0.001800     NO
 RMS     Displacement     0.003867     0.001200     NO
 Predicted change in Energy=-2.250043D-08

Unfortunately, there is no statement: "Stationary point found", however according to Gaussian manual: "A stationary point is found when the Maximum Force and RMS Force are two orders of magnitude smaller than the thresholds shown, regardless of the values of the displacements."

Is not it just the case? If so, why wouldn't Gaussian kindly state that the stationary point was found?


texts: Best reagents state for air free chemistry. Choosing halide for grignard synthesis

texts: I am planning to synthesize a grignard and I have a choice between the iodo or chloro aryl halide. The iodo is a solid and the chloro is borderline. For my previous reaction I melted the chloro and then tranfered it using a flushed sringe. As an alternative I could just weigh out the iodo and then pull vacuum on it a few times before running my reaction. Is there a better option between the two or they are just the same?


texts: Why does phosphoric acid mask the colour of iron(III) complex in water?

texts:
In the redox titration of iron(III) with permanganate or dichromate, we use phosphoric(V) acid to "mask" the color of iron(III) because it interferes with the end point color change.

What's the chemistry behind this?


texts: Scratching the inside of a flask to crystallize aspirin - what is it called and has it been scaled up?

texts:
I've just watched the Periodic Table of Videos on Aspirin and saw some "tricks" used to induce crystallization after the synthesis. Rapid heating with a heat gun followed by rapid cooling in ice was not sufficient, but scratching the bottom of the flask with a stirrer seems to have triggered rapid crystallization.

Warning: For those who are sensitive to the sound of chalk or fingernails on blackboards, better lower the volume during the actual scratching starting after 07:10, it's quite loud!

There is a little bit of an explanation for how the scratching helps:

  When you scratch it you are actually forming a nice surface for the crystals to aggregate on.

but I am not sure I really understand what is really happening.

Question: Is the scratching just glass-on-glass? Is this crystallization happening on the (probably) invisibly small scratches only, or does it happen throughout the solution? Is there an "official" name for this technique? Has it ever been scaled up in some way?

For example, this answer says that the scratching produces a rough surface on the bottom of the glass for nucleation, but this answer says it is shards of glass in solution that are providing the nucleation sites. I'm trying to understand what is actually happening when chemists rub stirrers on the inside of flasks to induce crystallization, and once that's understood, to find out if the phenomenon is scaled up in manufacturing situations.

below: "Before" and "after" screenshots showing the clear liquid becomes thick with crystals after scratching the glass.


texts: How does Resonance stabilize a molecule?

texts: How does resonance lower the potential energy of the molecule? Take $\ce{O3}$ as an example.


texts: Why are solids and liquids not included in the equilibrium constant? What about in a reaction rate calculation?

texts:
Take for instance the reaction

$$\ce{H2(g) + I2(s) <=> 2HI(g)}$$

The equilibrium constant would not include the solid $\ce{I2}$, but why is this? I have read that its concentration is a constant, but what does that mean? If you increase the amount of $\ce{I2}$ the reaction should shift towards the right so logically it does appear to play a part in the equilibrium.

For liquids, I can understand why you don't include it when you have something like water which (usually) does not play a part in the reaction, but why do you still not include when the liquid takes part in the reaction?

Also, do you include solids/liquids for reaction rates? Increasing the amount of a solid should increase the surface area and thus make for a faster reaction, so it seems like you should, but I am not too sure.


texts: Electrolysis with baking soda solution, a penny as the cathode and graphite for the anode

texts:
I set up an electrolysis experiment to show my kids and wanted to explain to them what is happening.
My setup has a penny as the anode and graphite for the cathode. The solution is water with baking soda mixed in.
I see bubbles at each of the electrodes which I assume are hydrogen and oxygen bubbling out. I also see some cloudy substance coming off the penny, which I assume is some sort of copper compound, but I'm not sure.
Can someone help me figure out what's going on in the setup at the two electrodes?
Edit : corrected the electrode descriptions. I earlier stated penny as the cathode and graphite as the anode.


texts: What would you suggest me to use for oxidation of vitamin C to dehydroascorbic acid instead of bromine water?


texts: Why Inductive effect operates only through single bonds?

texts: I am not able to find any examples of the inductive effect operating through multiple bonds. Why can't electron displacement take place in multiple bonds?


texts:
I have read that no work is done during free expansion and temperature of an ideal gas undergoing free expansion doesn't change.

Let us assume an ideal system of piston and gas which has vacuum around it. The gas will expand but we say there is no work done by the gas. Why so ? Gas applies a pressure(& hence a force) on the piston and the piston gets displaced. So acc to F.s = work , there is work done by the gas !


texts:
Trends for electron affinity going across the group increases negatively.
Does this mean Noble gases' electron negativity is more negative than halogens?
I'm confuse here.
Noble gases should have a positive electron affinity as adding an electron would make it unstable and thus, will not form.
But for halogens, their attraction for that 1 electron to fill up the $\mathrm{p}$ subshell is very strong.
But according to the theory that electron affinity increase negatively across the period, does this theory has an exception of noble gases?
Next, what about $\ce{Be}$ and $\ce{Mg}$? Their electron affinities are not negative.


texts: Why is the electron-nucleus attraction modelled with only electrostatic interactions?

texts:
While reading about the structure of an atom, I've encountered (even in some renowned books) the statement that electrons and nuclei are attracted due to electrostatic, or Coulombic, attractions.

However, since the charged particles (electrons and nuclei) are moving, how can the Coulombic force be sufficient to describe their interactions? Surely electrostatics cannot be used in this context. Is it merely an approximation?


texts: Reduction of butadiene with Na/NH3 - stereoselectivity

texts: Why is the major product of the reduction of butadiene with sodium in liquid ammonia cis-2-butene (60:40) when it is thermodynamically less stable than trans-2-butene?


texts: Why do we excite electrons before hybridisation?

texts: In case of hybridisation like $\mathrm{sp^3}$ hybridisation of carbon or nitrogen why do we excite electrons before hybridisation? Why couldn't we just mix orbitals without exciting electrons?


texts:
What mass of chromium is in $\pu{100 mL}$ of $\pu{0.0400 mol/L}$ $\ce{(NH4)2Cr2O7}$?

The specific concept is how to find the mass of a certain ion/element in a substance, given the concentration. I am at a total loss to this.

At first I tried to find the molar mass of the chromium itself, which resulted in roughly $\pu{104 g/mol}$. I then tried to find the amount of moles in the concentration, which is

$$\pu{0.1 L} \cdot \pu{0.04 mol/L} = \pu{0.004 mol}$$

Then I multiplied the molar mass of chromium from the amount of moles in the concentration, and I got $\pu{0.208 g}$.

This is not the answer. The answer was $\pu{0.800 g}$

I then tried a different approach. I tried to find the molar mass of my original substance, then divided the molar mass of chromium from the molar mass of ammonium chromate, which will give me the amount of chromium per ammonium chromate. Then I thought all I needed to do was to multiply it by the concentration. This just messed up everything and I was back to square one.

How do I approach this problem?


texts: How are bond lengths measured experimentally?

texts:
How is the bond length between any two atoms in a compound measured?

For example, in the case of graphite, the bond between its two layers is 340 pm. This number must have been measured, so what are experiments that can give lengths with that precision?


texts: Why is more of a catalyst added, when it is not consumed?

texts:
… catalysis, the acceleration of chemical reactions by substances not consumed in the reactions themselves—substances known as catalysts.

(Source)

Now as I’ve understood, to keep a reaction going, you must keep the solution heated and sometimes add more of the catalyst. Why then, is the definition that the catalyst is not consumed? Something of the catalyst must surely be consumed.


texts: Equilibrium constant for a solid-solid equilibrium

texts:
Suppose there are two equations:

$$
\begin{align}
\ce{A(s) &<=> B(g) + C(s)} &\quad &K_1 \tag{R1}\\
\ce{B(g) &<=> D(s) + E(s)} &\quad &K_2 \tag{R2}
\end{align}$$

These reactions have equilibrium constants $K_1$ and $K_2$, respectively. Both of these reactions are occurring simultaneously inside a container.

When I add these equations, I get

$$\ce{A(s) <=> C(s) + D(s) + E(s)} \tag{R3}$$

Since I added the reactions, I must multiply the equilibrium constants to get the equilibrium constant for above reaction which essentially is the net of the two reactions.

I have two questions:

How do I even write equilibrium constant for solid solid equilibrium?
Since $\ce{B}$ doesn't appear in equilibrium constant, is it safe to say that the concentration of $\ce{B}$ doesn't affect the equilibrium concentrations of any other species?


texts: Why are gas laws only applicable to gases?

texts: Why are the gas laws (such as Boyle's Law, Charles's Law, and Avogadro's Law) only applicable to gas and not liquids or solids?


texts:
Calculate the pH in a buffer prepared from $\pu{50 mL, 0.30 M}$ formic acid ($\ce{HCOOH}$) and $\pu{30 mL, 0.40 M}$ sodium formate ($\ce{HCOONa}$).

My way of solving:

$n_{\ce{HCOOH}} = 0.05 \times 0.3 = \pu{0.015 mol}$

$n_{\ce{HCOONa}} = 0.03 \times 0.4 = \pu{0.012 mol}$ (which means $\ce{NaOH} = \pu{0.012mol}$)

$\ce{HCOOH + NaOH <=> HCOONa + H2O}$

After doing a BCA-table, I got that the remaining moles of HCOOH = $\pu{0.003 mol}$

and HCOONa = $\pu{0.012 mol}$

Calculating the new concentration:

[HCOOH] = $\ce{0.003 / 0.08 = 0.0375M}$

[HCOONa] = $\ce{0.012 / 0.08 = 0.15M}$

Using the Henderson–Hasselbalch equation:

pH = pKa + log [HCOONa]/[HCOOH] = $\ce{3.75 + 0.60 = 4.35}$

So my answer is that the pH of the buffer is $\ce{4.35}$

Answer key

However, in our answer key, they found the new concentration of HCOOH and HCOONa by simply taking:

[HCOOH] = $\ce{(0.05 *0.3)/0.08 = 0.1875M}$

[HCOONa] = $\ce{(0.03 *0.4)/0.08 = 0.15M}$

and when using those concentrations in the Henderson–Hasselbalch equation they get the answer pH = $\ce{3.65}$

Question

Is the answer key correct? If we are adding a base, then the pH should increase to become more basic, not decrease as in the answer key. If the answer key is correct, why does the pH decrease?


texts: Why does the reduction of a Weinreb amide give an aldehyde instead of an amine?

texts: The reduction of a regular amide with $\ce{LiAlH4}$ yields an amine. However, with a Weinreb amide, the product is an aldehyde. How can this be justified? I can't find the mechanism for the Weinreb amide reduction - is it known?


texts: Buffers calculating amounts of acid & base

texts:
Quick run down, I was given pH of buffer 4.5 and then pKa of acid 4.79
I then had to work out volume of acid and volume of base using $\text{pH=pKa}+\log_{10}{\left(\dfrac{[\ce{A-}]}{[\ce{HA}]}\right)}$. Using that I calculated the volumes of acid and base required to make 15 ml of the buffer $\ce{CH3COOH,CH3COONa}$:

$V_{\ce{HA}}=9.7\ \text{ml}$ and $V_{\ce{A-}}=5.3\ \text{ml}$ (both acid and base used to make buffer are of 0.1 M conc, probably come in handy later).

Then I am now asked to calculate the amounts of acid and base in 15ml of my buffer
they give me
Acid: $n_{\ce{HA}} = [\ce{HA}]\cdot V_{\ce{HA}}=0.1\cdot V_{\ce{HA}}$

Base: $n_{\ce{A-}} = [\ce{HA}]\cdot V_{\ce{A-}}=0.1\cdot V_{\ce{A-}}$

Which I don't really get?
I then have to find out the amount of acid was added, some context is that this is n experiment I conducted using a pH probe I added three drops and recorded the pH for a total of 60 drops the final pH reading is 3.52 of an initial reading of 4.38, would I use the simple $\text{pH} = -\log_10[\ce{H+}]$?
They have given me $[\ce{H^+}]\cdot V=0.1\text{ M}\cdot\dfrac{1\text{ ml}}{1000\text{ L}}=...\text{mol}$ which I also don't really know what to do with it.
After that I calculate the new concentrations of acid and conjugate base after all added H+ reacts
initial and final.
you don't have to use my example just explain EVERY SINGLE STEP and guide me through the process :) much appreciated!  I know I am asking a lot in one go but this all correlates with one another, if anyone can help thanks a lot!


texts: Is enthalpy of combustion the 'heat released' or 'enthalpy change'?

texts:
In a constant volume calorimeter, $\pu{3.5 g}$ of a gas with molar weight $\pu{28 g}$ was burnt in excess $\ce{O2}$ at $\pu{298 K}.$ Temperature of calorimeter increased from $298$ to $\pu{298.45 K}$ due to combustion. If heat capacity of calorimeter is $\pu{2.5 J/K},$ then magnitude enthalpy of combustion of gas in $\pu{kJ/mol}$ is?

In this question, according to me $ΔU = 2.5 × 0.45 = 1.125,$ i.e. $1.125/(3.5/28) = \pu{9 kJ/mol}$, and $ΔH = ΔU + nRΔT = 1.59.$

But according to my teacher, we have to find the heat evolved (which in isobaric process equals ΔU). So answer is $9$.

This is a question from IIT-JEE so I think there is no error in question or answer.

Isn't enthalpy of combustion the change in enthalpy?


texts: Diffusion equation I can't seem to find anywhere

texts:
So I was looking through some old lecture notes from a few years back when I stumbled upon a useful and simple equation that should, according to my former professor describe the diffusion in solid state compounds quite easily. As I forgot however what the single variables mean I tried to find the equation anywhere. I can only find Fick's laws and differential equations with their solution but I haven't found this equation yet.

$$D=\frac{f⋅σ⋅k⋅T}{n⋅(z⋅e)^2}$$

I remember that we used to describe a lot of things with the help of that equation like how diffusion is slower when higher charged ions are used or that warmer temperatures have to be used for reactions. Or how you can use fluxes to lower the concentration and therefore increase the mobility.

Does anyone either know what the other variables describe or can anyone tell me where to find this equation?

I could only guess here, k and T come from Boltzman's part, n should be something related to the number of ions, z and e have the charges and  f  is probably some specific diffusion constant. So σ may, for example, be something like the specific surface (hence describing why you have to grind your reactants to a fine powder) but I just don't know.


texts: Hydrogen fuel cell - why do the H+ ions move through the electrolyte

texts:
Consider the following hydrogen fuel cell

http://butane.chem.uiuc.edu/pshapley/Enlist/Labs/FuelCellLab/FuelCell.html

At the anode, hydrogen is oxidised (losing electrons). My first question is this: why is the anode negative if it is attracting electrons?

My second question refers to the fact that once the hydrogen atoms are iodised, the H+ ions move through the electrolyte towards the oxygen ions at the cathode, reacting to form water.
If the anode is negative, why would positive H+ ions move away from it?


texts: How to choose a UV lamp for photoisomerization of 4,4'-azobenzene dicarboxylic acid?

texts:
I have prepared a thin film containing 4,4'-azobenzene dicarboxylic acid and I want to study the photoresponsive behaviour of them. For the trans-cis isomeration , I used a 365 nm UV LED with irradiation intensity varied in the range of 5-50 mW/cm². Not seeing any isomeration I have the doubt if I am using the right lamp.  Articles which have prepared thin films containing 4,4'-azobenzene dicarboxylic acid have used other types of lamps such as 200 W Xenon-doped mercury lamp(using a 355 nm cut off filter), 500 W high pressure mercury lamp or 400 W high pressure mercury lamp. I also took the UV-Visible spectroscopy of my films and noticed that the absorption of trans azobenzene-4,4'-dicarboxylic acid is centered at 330 nm.

Am I using the right lamp?


texts:
Ester is quite a random nomenclature for a compound derived from a parent acid and parent alcohol.
Is there any reasoning behind using the word 'ester' to name such compound (for memorising purpose)?
One explanation for such nomenclature I found is quoted below from this website

The word "ester" was coined in 1848 by German chemist Leopold Gmelin,
probably as a contraction of the German Essigäther, meaning acetic
ether.

But even then, how does 'acetic ether' has to do with anything about ester being a nomenclature for a compound derived from a parent acid and parent alcohol?


texts: Why is twice as much hydrogen produced than chlorine in the electrolysis of brine?

texts:
I have seen a great many number of diagrams which show the electrolysis of brine in a diaphragm cell, but show twice the volume of hydrogen produced. For example:

On the other hand, other diagrams show that the same volume of hydrogen and chlorine is produced. For example:

So who's right and why?


texts: I saw a meme that was joking around about Lithium and Argon bonding (see pic below). It got me wondering: Can Lithium and Argon bond in any circumstance?


texts:
Hygroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment.

Why are some compounds hygroscopic and others are not? What is it about their structures that allows them to hold water? Is it due to the atoms being arranged in a certain structure due to bonding?

How can you tell if a compound is more hygroscopic than another?


texts: Applying Avagadro's law: the relationship between moles and volume of a gas

texts:
If $\pu{2.4 mol}$ of gas fill a volume of $\pu{175 mL}$, what volume, in mL, will $5.4$ additional moles of gas fill?

This was a quiz question which I got wrong the first attempt, and I think I got it right this time however I would like some confirmation that it is/is not. The unnamed gas is assumed to be ideal.
$$\frac{\pu{2.4 mol}}{\pu{175 mL}} = \frac{\pu{7.8 mol}}{X}, \quad \text{or} \quad X = \frac{\pu{7.8 mol} \times \pu{175 mL}}{\pu{2.4 mol}} = \pu{568.75 mL}$$
Is this accurate?


texts: Establish the formula of an oxide of chromium

texts:
An oxide of chromium used in chrome plating has a formula mass of
  100.0 u and contains four atoms per formula unit. Establish the formula of this compound, with a minimum of calculation.

  Express your answer as a chemical formula.

So the question tells me that the mass of the Chromium Oxide is 100.0 amu and has 4 atoms for very unit. Thus, the question wants to know a formula that has 4 atoms? Right?

Hence, if $\ce{Cr}$'s (Chromium) molecular mass is 51.9961 and since the question is stating that we are dealing with an oxide, which would mean that it is a ionic compound (Chromium gives two electrons to Oxygen [15.999 amu]), wouldn't the answer be $\ce{Cr2O2}$; but that would equal 135.9902 grams.

On the other hand, if I am supposed to view a formula unit as an empirical formula, wouldn't that require me to write the simplest formula for a compound?

Yet, $\ce{CrO}$ would give me (51.9961 + 15.999) 67.9951 g/mol and that is not correct, or is it?


texts: What is the best material for my particles?

texts:
I'm investigating collision of a particle and a water droplet ($v_\mathrm{drop}=1~\mathrm{m/s}$, $v_\mathrm{particle} \approx 8\ \mathrm{m/s}$, $D_\mathrm{d}=2.8\ \mathrm{mm}$, $D_\mathrm{p}=2.0\ \mathrm{mm}$). Due to a head-on collision, particle penetrates into droplet and changes the droplet shape (collision outcome). I need to see that what effect particle wettability has on collision outcome. So, all other particle parameters, like density, should remain constant. I can use particles made from any material as long as I can create different contact angles on particle surface. Do you think which particles are the best for this purpose?

P.S: Currently, I've purchased glass particles and I'm trying to create different contact angles through silanization. But, any other suggestion is appreciated.


texts: Significant figures when standard deviation is 0

texts:
For analytical chem lab, our group did a titration in which we got the same exact value every single time. As a result, our standard deviation was 0 and our instructor says to report answer using real rule of sig figs (our last significant figure should be the first digit in the uncertainty measurement) I am not sure what to do as my STDev doesn't have any significant digits?

edit: Molarity is the measurement in question!


texts: What is the function of ZnCl2 in lucas test?

texts:
One mechanism I found on the internet (even on chemistry stackexchange) for the lucas test is:

Here I don't see ZnCl2 participating in any of the steps. So what does it actually do? Another mechanism that I found on internet and in the book of David klein is Zncl2 forms a complex compound by forming a bond with oxygen. Then oxygen has a formal positive charge and the leaving group turns into a good one than before. The next steps are simple SN1 reaction. If this is the right one then why H+ ion from HCl doesn't do the job that ZnCl2 is doing like the previous reaction?


texts: Proving a thermodynamic relation between $(\partial H/\partial T)_p$ and $(\partial U/\partial T)_V$

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(This question is taken from Problem 1.1(b) of the book Chemical Thermodynamics: Principles and Applications.)$\require{begingroup} \begingroup \newcommand{\pd}[3]{\left(\frac{\partial #1}{\partial #2}\right)_{\!#3}}$

  Prove $$\pd HTp = \pd UTV + \left[ V - \pd HpT \right] \pd pTV. \tag{1}$$

First, I expressed $H$ as  $U + PV$, and took the partial derivative against $T$, keeping pressure constant:

$$\pd HTp = \pd UTp + p\pd VTp \tag{2}$$

Expressing $U$ as a function of $(T, V)$:

$$\pd UTp = \pd UTV + \pd UVT \pd VTp \tag{3}$$

Using the well-known identity that $$\pd pVT \pd TpV \pd VTp = -1, \tag{4}$$

$$\pd UVT \pd VTp = -\pd UpT \pd pTV = \left[ V - \pd UpT - V\pd ppT \right]\pd pTV \tag{5}$$

This, of course, means that

$$\pd HTp = \pd UTV + \left[ V - \pd HpT \right]\pd pTV + p\pd VTp \tag{6}$$

Based on my working, there is an additional $$p\pd VTp$$ term. Is my working incorrect? I can’t find my mistake.$\endgroup$


texts: Degree of dissociation of strong electrolytes in concentrated solutions of ionic substances

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Why is the dissociation of strong electrolytes complete in very dilute solutions of ionic substances but less likely to be so in more concentrated solutions?

Before seeing this, I thought a strong acid will always dissociate no matter the situation.


texts: Determining which compound is more 'ionic'

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I was going through my chemistry textbook (IB Pearson), and it explicitly stated that the higher the absolute difference between the electronegativity of elements in a binary compound, the more 'ionic' that compound is, which does make intuitive sense given that a higher electronegativity difference leads to the compound being more 'polar.'

However, the book came up with the following example:

  Which of the following pairs will form the most ionic compound?

  1) Be and F (the electronegativity difference is $|4-1.6| = 2.4)$
  2) Si and O (the electronegativity difference is $|3.4-1.9| = 1.5)$
  3) N and Cl (the electronegativity difference is $|3.2-3| = 0.2)$
  4) K and S (the electronegativity difference is $|2.6-0.8| = 1.8)$

  $\ce{K2S}$ will be the most ionic compound as the difference in electronegativity is the greatest.

I don't get how this works, the difference in electronegativity between beryllium and fluorine is visible greater, so why does the book say that the binary compound formed by K and S is more ionic?


texts: I would like to find a solution that can kill roof algae, fungus, mold, mildew effectively without using environmentally unfriendly products but don't know enough about chemistry to make a solution myself.


texts: Bond Type of Lead: Metallic or Network Covalent?

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I know that lead is classified as a metal, from its appearance, nonexistent band gap, and its position on the periodic table... etc. However, all of the elements above it (carbon, silicon, germanium, and tin) usually form covalent network bonding with four surrounding atoms. Why is lead suddenly different, engaging in delocalized metallic bonding when it has enough electrons?
Or is it different? Lead has a low melting point for a metal (600 K), and a lower melting point than, say, copper.


texts: I'm having difficulty deciphering this 13C and 1H-NMR spectra. I've tried figuring it out, and have gotten close and am pretty sure it contains a methoxy group attached to a benzyl group, but hit a rut in regard to the other structure. Any help would be super appreciated!