texts: Rationale for titant standardization in alkalinity measurements [ISO 9963-1:1994]

texts:
I work in a environmental chemistry laboratory and I will start to do some alkalinity measurements in my project. My research group is pretty big on following any and all standardization possible, which most often mean compliance according to ISO-standards.

In the ISO-document Water quality - Determination of alkalinity - Part1: Determination of total and composite alkalinity (ISO 9963-1:1994), you need to prepare your titrant, in this case $0.1 \text{M HCl}$ and a standard solution $0.025 \text{M Na}_{2}\text{CO}_{3}$. Then you need to standardize your titrant using either a potentiometric detection (titrate a dilute standard solution to pH 4.5 and note the volume used) or visual endpoint detection (titrate a dilute standard solution with bromocresol green-methyl red indicator until color change). And lastly, a blank using water as the titrand instead of the standard solution.

Using these two acid volume consumption you then recalculate your $0.1 \text{M HCl}$ to it's actual concentration. And if you keep your stock acid solution for a longer period you should perform this standardization every week. Then you can perform the actual titration and determination of the alkalinity in the sample.

My question is, why is this necessary? Why does the ISO stipulate this standardization?

I understand that if I prepare an acid it won't be super precise since there are effects that influence the preparation such as my handling, age of chemical, pipetting, graduated cylinder error intervals etc. But the same would apply to my preparation of the sodium carbonate. In principle I am shifting the error effects from the acid preparation to the sodium carbonate preparation which I am standardizing against.


texts: Is this asking for the equivalence point?

texts:
Is this question asking for the equivalence point of the titration curve?

  At what point does the concentration of acetic acid equal the concentration of the acetate ion? What is the pH of the equimolar, ideal buffer solution at this point.

At first, I thought this question was asking about the point right before the titration curve shoots up. However, I don't recall ever learning about such a point.


texts: Can single molecules of C and O2 react in isolation, and if so how will momentum be conserved?

texts:
I am trying to figure out how is it possible to reconcile the reality of exothermic reactions, which means that kinetic energy is transferred to (heats) the surrounding matter, with the principle of conservation of momentum, in particular when the product is a single molecule.
I have been exploring the question but found no sufficiently explanatory answer to the question of how the bond energy that is released may create movement (heat). The nearest to an answer that I can imagine is that the reactants enter some transitory combined state of vibration and that further contact with some other molecule results in the separation of each of them in opposite directions with equal but opposite momenta increments thus preserving the overall momentum, while at the same time reducing the vibration and stabilizing the product molecule.
If that were the correct answer (at least in some cases), I would like to know a bit more about the details of the process, which I suppose entail some description about how binding energy is transferred to that vibration.
In any case, it would be interesting to know whether is it actually possible for a single carbon atom and oxygen molecule to react (if they collide with the necessary energy) and produce carbon dioxyde or not, be it for the reason above or another one, since if they are in isolation, the transfer of vibration energy cannot be realized and thus the reaction could not be completed, and then I suppose that would eventually end with the spontaneous separation of the components.


texts: Analysis of cations using sodium thiosulphate

texts:
A question in an exam was as follows:[1]

How many of the following salts are first soluble in $\ce{Na2S2O3}$ solution, followed by the formation of a white precipitate and finally the precipitate turns black on standing
$\ce{AgNO3}$, $\ce{Pb(CH3COO)2}$, $\ce{Hg(NO3)2}$, $\ce{BiCl3}$, $\ce{CuSO4}$

The answer given is:

 $5$, which means that all of them give this test.

I understand that this is a test for cations since the reagent is sodium thiosulphate.
A pre-emptive guess on what the reactions would be that the first reaction forms the thiosulphate of the cation followed by the conversion of thiosulphates into sulphides (from the color change given).
However, I was unable to find any text referencing this test and so haven't been able to verify the actual reactions that take place.[1]
What cations does this test give a positive result for? What are the reactions that take place?

[1]: The previous version of the question asked for a test using sodium dithionite which was a typo (due to reasons provided in the answer below), confirmed after M.Farooq's suggestion to ask the professor who set the exam.


texts:
Cotton is mostly cellulose, a plant saccharide. Superglue refers to a class of cyanoacrylates. What is it about the two that causes ignition?

I'd imagine that the cellulose in cotton is in its linear form and not in its ring form since the ring-linear form interconversion only occurs in solution. Is it that the cellulose attacks the cyanoacrylate?

  The three hydroxyl groups, one primary and two secondary, in each repeating cellobiose unit of cellulose are chemically reactive

So, do the hydroxyl groups attack the carbonyl group in superglue?


texts: What is the nature of the mysterious Kw, the ionic product of water?

texts:
In pure water, [H$^+$] = 10$^{-7}$ M and [OH$^-$] = 10$^{-7}$ M. So, we conclude pH of water is 7 and so is the pOH. We define the ionic product of water as Kw = [H$^+$][OH$^-$] = 10$^{-14}$ M$^{2}$. Till this, everything is fine.

Now, without any premise, it is concluded that the product [H$^+$][OH$^-$] of all concentrations in solutions of all sorts is the same, i.e. 10$^{-14}$.

This leads to the conclusion that for all acidic, basic and neutral solutions, pH + pOH = 14.

So, why is it concluded that [H$^+$][OH$^-$] = 10$^{-14}$ M$^2$? What is the nature of Kw, the ionic product of water, that mysteriously is applicable to all solutions?


texts: How to determine age of stones (and other inorganic matter)?

texts:
I'd like to ask how can one determine /with relative precision/ the age of stones and stone monuments, like statues, columns, stone walls or stone tablets? I know that one determines the age of organic substances by radiocarbon dating, however, this method is inapplicable for rocks, so what else can we try?

Under age I mean the period since a stone was carved into a historical artifact and I'm interested in periods that are accurate up to a historic age, like Antiquity or the Renaissance - I suppose one cannot ask for more, unless there are visual marks on the artifact, which provide clues?

PS I hesitated much whether my question is Chemistry- or Physics- related and decided to post it here, since it's purely practical. If you decide otherwise, I'll move it to Physics.SE ;)


texts: What temperature does oxygen have to be at to bond with carbon monoxide?

texts: I was wondering how I would go about calculating the required temperature of oxygen to bond one oxygen particle with carbon monoxide (CO). I know that it depends on some other factors such as air pressure, but that's the extent of my knowledge. I would be really grateful if someone could explain what environment I would need to combine the two.


texts: how to find pressure of a liquid when given volume (1 and 2) and one pressure?

texts:
A 5 mL sample of an unknown liquid is placed into a 250 mL flask that has had all of the air removed.  The pressure measured in the flask is found to be 35.4kPa.  In a seperate trial the student puts 214 mL of the same liquid into the same flask at the same conditions.  What will the pressure measure (in kPa) in the second trial?

I've looked through my notes and I don't have a formula or anything in there that I can use volume with. Can someone help me start this question?


texts: Home science optical absorption test for approximate caffeine quantity in coffee?

texts:
I started with How can you measure the caffeine content of a liquid at home? in the cooking stackexchange, but the test strips were only qualitative (yes/no) and don't seem to exist anymore, and the part about rubbing dichloromethane on ones gums frightened me off.

The 2014 NY Daily News article Scientists working on at-home caffeine detection test links to Validation of Caffeine Dehydrogenase from Pseudomonas sp. Strain CBB1 as a Suitable Enzyme for a Rapid Caffeine Detection and Potential Diagnostic Test (Mohanty, S. K., Yu, C. L., Gopishetty, S. and Subramanian, M., J. Agric. Food Chem., 2014, 62 (31), pp 7939–7946) but that's not for home use. I found this nice experiment but that is still serious analytical chemistry.

However the article does mention the use of UV spectrophotometry, and that's something I could imagine playing with at home personally, using UV LEDs or other light sources, a Raspberry Pi camera or some photodiodes, a piece of diffraction grating film, basic physics, duct tape, etc. I'm OK with the optics and electronics, it's the chemistry I need the most help with.

The 1994 paper A Simple Method for Determination of Caffein Content in Tea Samples shows a correlation of caffeine assay from various types of brewed tea with absorption at 440 nm. Strong coffee would contain perhaps 5X more caffein, but being coffee, would probably be 100X or more higher in absorption in blue or UV.

This and this discuss UV absorption of caffeine in a solvent, but I am not sure if there are any solvents that I can find or use at home. Further, while I might be able to find a 275nm LED, it probably limits me to glass optics and expensive detectors, most plastics probably absorb too much there, and most silicon detectors have thin inactive layers that absorb this wavelength of UV; backside-thinned detectors are usually necessary. However, possibly the longer wavelength tail in the direction of 300nm might be useful.

My Chemistry Question: Are there any ways to separate the caffeine in coffee from the organics that make it so dark, using "household chemistry", so that I could try to check  blue or UV optical absorption?

I'm only looking for a way to tell if brewed coffee has a big or a small caffeine "kick" to it, so even something as bad as +/-20% repeatability might do in a pinch. I don't need an absolute measurement - just something that roughly tracks the caffeine content.

Possibly helpful reddit, What wavelength should I measure the absorbance of my coffee to get an idea of how strong it is?, which links to an article I can't read right now, as I am drinking coffee on the wrong side of the paywall: Measurement of caffeine in coffee beans with UV/vis spectrometer.

above: An old Certificate of Analysis from a Caffeine Standards Kit, from Agilent.

above x2: Caffeine absorbance in water, from here (top) and here (bottom).


texts: Why is BDE low in Iodine, but not behaves like Fluorine?

texts:
When halogens have a low Bond dissociation energy, BDE, their free radicals are stable.

$\ce{Cl-Cl}$ (BDE: $\pu{58 kcal/mol}$) and $\ce{F-F}$ (BDE: $\pu{38 kcal/mol}$). $\ce{Cl}$ free radical is less stable than $\ce{F}$ free radical. But why that doesn't happen with iodine ($\ce{I-I}$, BDE: $\pu{36 kcal/mol}$). Iodine free radicals are unstable.


texts: In Simonini reaction how does the $2:1$ ratio of reagents enable formation of ester as major product?

texts:
The Wikipedia article on Simonini reaction says:

  The ratio of the reagents play an
  important role in the determination of products, namely, if $1:1$
  ratio of salt and iodine is used alkyl iodide is formed. On the other
  hand, a $2:1$ ratio gives $\ce{RCOOR}$ and $3:2$ ratio gives both the
  products.

For $1:1$ ratio I understood why alkyl iodide is formed (found the mechanism here). But for $2:1$ ratio why is ester formed as major product ?


texts:
When undergoing copolymerization via free radical mechanism Buna-N forms a certain way.
Actual product and possible products

Can we predict which of the products will be formed based on the substituents?
If so, how?


texts: Why are these molecular orbitals invalid for hexatriene?

texts:
Here are the MOs (more accurately, the breakdown of the MOs) for conjugated hexatriene:

Now, when first asked to draw the MOs myself, I drew this one for $\psi_3$:

It still has two nodes, and is still symmetric. I see nothing wrong with it, except that it doesn't match the "correct" MOs.

Similarly, for $\psi^*_4$, I can draw

Now, as I understand it, MOs are formed from various combinations of atomic orbitals, subject to a few rules regarding symmetry. From what I know, the two MOs I've given above should be valid MOs for hexatriene, or at least components of an MO of hexatriene.

Why aren't these two MOs valid? Also, is there a methodical way to obtain the sequence of MOs in the general case(of a conjugated polyene)?


texts: Relationship between Gibbs free energy and potential energy (related to reaction coordinate diagrams)

texts:
For a rate law, the rate constant $k$ is given by the equation

$$\ln k = \ln A - \frac{E_\mathrm{a}}{RT}\tag{1}$$

If $k_\mathrm{fwd}$ is the forward rate constant and $k_\mathrm{rev}$ is the reverse rate constant:

$$\ln k_\mathrm{fwd} = \ln A - \frac{E_\mathrm{a,fwd}}{RT}\tag{2}$$

$$\ln k_\mathrm{rev} = \ln A - \frac{E_\mathrm{a,rev}}{RT}\tag{3}$$

Subtracting the two equations yields

$$\ln\frac{k_\mathrm{fwd}}{k_\mathrm{rev}} = \frac{E_\mathrm{a,rev}}{RT} - \frac{E_\mathrm{a,fwd}}{RT} = \frac{1}{RT} (E_\mathrm{a,rev} - E_\mathrm{a,fwd})\tag{4}$$

If $K$ is the equilibrium constant for the reaction, then $\displaystyle K = \frac{k_\mathrm{fwd}}{k_\mathrm{rev}}$:

$$-RT\ln K = \Delta E\tag{5}$$

where $\Delta E$ is the change in potential energy on a reaction diagram, such as the one shown here.

However, we know that

$$-RT\ln K = \Delta_\mathrm{r} G^\circ\tag{6}$$

Does this mean that potential energy is equal to the standard Gibbs free energy of reaction?


texts: I need to compare GaussView output files (same reaction, one HF method and the second PBEh1PBE)

texts:
I added 2 TS molecules. I need to compare them. The left picture was done via PBEh1PBE and the one on the right via HF.

Where can I find information about each level of theory that would be relevant for comparing the structure differences between the two?


texts: What is the meaning of parentheses in "NAD(P)H"?

texts:
If someone writes "NAD(P)H is oxidized by ...", does that mean they are referring to both NADH and NADPH?

If so doesn't that lead to confusion when thinking quantitatively since the reactions may proceed at different rates, NAD may be present in a different concentration than NADPH, etc?

If not, what do the parentheses around P mean?


texts: Why is the specific gravity of 0.9 % saline 1.0046?

texts:
Medical Normal Saline (0.9% Saline) contains 9 g of salt dissolved in 1000ml of water.

Hence a litre of NS should weigh 1.009 kg.

Hence its specific gravity should be 1.009, but it’s only 1.0046.
(I've measured it, and verified it on-line. It is apparently, a fact.)
I thought I understood SG, it’s a simple concept but I am missing something.

EDIT: after more reading, I learned that dissolving NaCl in water results in a reduction in the original volume. So my question now becomes:
We're dissolving NaCl in pure water at a temperature where 1.000kg mass of water has a volume of 1.000 litres. By my (erroneous) reasoning:
Say the volume decreases by 1 ml, giving a final volume of 0.999 litres.
So the density of the solution would be 1.009 kg/ 0.999 l = 1.010 kg/l
Giving an SG of 1.010 (because water has a density of 1.000 kg/l, as above) If the volume didn't change, it would be 1.009, but it increases because of the reduction in volume.
BUT: The known, published SG of 0.9% w/v NaCl solution is 1.0046.
Can anyone explain why, please? or at least, why the SG is below 1.009, when it should be greater?


texts: Absolute limits on solubility of immiscible solutes?

texts: I know that for a particular, immiscible solute, there is a limit on how much of it can be dissolved in a solvent at a given temperature. However, I was wondering if there is only so much "total solute" that a given solvent can dissolve. As a simple example, suppose you saturate water with salt, then start dissolving sugar into it. Does the fact that it is saturated with salt limit how much sugar it can dissolve? My mental image is one of each water molecule being able to suport only so many solvation structures, regardless of the chemicals participating in the structure.


texts: What is the most stable pear-shaped nucleus?

texts: I have heard on the Internet that there are at least three pear-shaped nuclei: radium-224, radon-220 (a direct product of the previous isotope), and barium-144. CERN has a webpage about this discovery https://home.cern/news/news/experiments/first-observations-short-lived-pear-shaped-atomic-nuclei and it calls them "short-lived". Their half-lives are all less than one week and I wonder if radium-224 is the most stable pear-shaped nucleus or if there are more stable ones that have that property in common.


texts: Non-wetting fluids for precise volume measurements

texts:
I need to precisely measure the internal volume of an open steel fixture.  I was planning to do this via displacement, but I'm wondering what the best fluid would be.  Ideally it should have no surface tension so that it readily penetrates every facet of the fixture.  It would also be convenient if it was non-wetting which (if I understand that term correctly) means that it would not adhere to the steel when removed.

One suggestion I heard was to use water-soluble cutting fluid.  Are there any other readily-available fluids with these characteristics, or well suited to this application?


texts: Why does only one reaction occur when so many are possible?

texts:
Why does only one reaction take place, although so many would be possible? I'm more of a physics and math guy, so simply "accepting" it without a proper explanation is kind of hard for me. For example:
$$\ce{Na2CO3 + HCl -> NaCl + H2O + CO2}.$$

Why can't $\ce{H+}$ combine with $\ce{CO3^2-}$ to form a compound?

I'm going to highschool, and I am great at physics and mathematics, and I dislike chemistry since it's mostly memorizing. Please describe it in terms I can understand. Also, this is something that I genuinely want to understand rather than memorize, it is not related to school.


texts: Why isn't standard Gibbs energy zero at equilibrium?

texts:
At equilibrium, everything that $G$ depends on is constant.
The Gibbs' free energy may have been given to you without really emphasizing that it is actually a function of temperature, pressure, and the moles of involved reactants and products:
$$G=f(T, p, n_i)$$ When we are at equilibrium, we really mean all of the following are occurring:

Thermal equilibrium
Pressure equilibrium
Dynamic equilibrium

And hence the  moles of reactants and products is steady/constant (but may react if disturbed).
But when all those things are constant, the Gibbs free energy simply isn't changing at all. If the variables on which $G$ is dependent are constant, $G$ (for a single state) is constant.

Standard Gibbs energy is basically Gibbs energy but at standard states i.e. $\pu{1 bar}$ pressure and substances at their standard states.
So this standard Gibbs energy is also a function of $T$, $p$, and $n$, which at equilibrium are constants. But still $$\Delta G^\circ=-2.303RT\log K$$ at equilibrium which clearly isn't zero.
Why isn't change in standard Gibbs free energy $\Delta G^\circ$ zero at equilibrium while $\Delta G_r$ is?


texts: What is the influence of citrate on PEG-modified polyacrylamide hydrogels?

texts:
I've been having a puzzle explaining the experimental results with the citrate anions and PEG modified polyacrylamide:
According to the experimental data there is a hydrogel swelling whenever citrate is added to a 10mM PBS solution. However, according to the Hofmeister series, citrate is a well known salting-out agent, which would absorb water, thus make the hydrogel contract. In addition that, the swelling is diminished when the concentration of salts (ionic strength) is increased in a bulk solution. Any ideas?


texts:
For enthalpy calculations why is it that in some cases the "heat of formation method" is used? I know that $ΔH_f$ represents the heat required to form the compound at standard temperature and pressure ($25^oC$, $1$ atm) but why is it used?

For example, in $Ex.1$

  NO(g, $300^oC$):  $H$ = $\int (Cp)_{NO}dT$
  where $T_1 = 25^oC$ and $T_2 = 300^oC$

The enthalpy of nitrogen monoxide is simply the integral from the initial temperature to the final temperature.

However, in $Ex.2$

  $CH_4$($150^oC$):  $H$ = ($ΔH_f)_{CH_4}$ +$\int (Cp)_{CH4}dT$
  where $T_1 = 25^oC$ and $T_2 = 150^oC$

The enthalpy of methane is the heat of formation + the sensible heat from the initial temperature to the final temperature.

What tells me when I should add the heat of formation?


texts: Maximum number of double bonds a carbon atom can make

texts:
What is the maximum number of double bonds a carbon atom can make?

Well, carbon has $4$ valence electrons so... it needs $4$ more to fulfill the octet rule right?

If a double bond yields $4$ electrons, does it mean that the carbon atom can make only one double bond?

OR does it mean it can create up to TWO double bonds (because they would yield $8$ electrons which fulfill the octet rule)?

What about Calcium? I ask because Calcium doesn't follow the Octet rule: it only wants to have 4 electrons, so...


texts: In chemistry what do they mean by disorder when in the context of entropy?

texts: Entropy is often the amount of disorder is present in a system, but when they refer it to the degree of disorder in a system what do they mean. It just seems the term is quite vague and not very descriptive. Does it refer to the number of choices a molecule possesses in interacting with other molecules in a system or does it mean something else?


texts: Does the rate of movement of ions in a salt bridge affect the total voltage produced by a Galvanic cell?

texts:
I was thinking that different salts used in a salt bridge in a voltaic cell may have different rates of flow of ions in them (perhaps ionic radius or some other property affects the rate?)
I was wondering, if some ions in the salt bridge flow through the solution more quickly, will this have any effect on the overall voltage produced by the cell?


texts:
How do people decide if a molecular orbital (MO) is bonding or antibonding? From Wikipedia article on antibonding MO:

  [...] if the antibonding interactions outnumber the bonding interactions, the molecular orbital is said to be antibonding

and vice versa.

How do we define what an "antibonding interaction" is for cyclic molecules? Does one nodal plane count as 1 or 2 antibonding interactions? For example, the π2 molecular orbital of benzene may have 1 nodal plane, but how many antibonding interactions would that MO have?

Similarly, how do we define "bonding interactions" for cyclic molecules?


texts: Will a copper anode and hydride ion cell work?

texts:
Can a galvanic cell with the overall reaction
$$\ce{Cu(s) + 2H+(aq) -> Cu^2+(aq) + H2(g)}$$ work?

$\Delta G$ of this reaction is negative (because $E^{\circ}$ of the reaction is $\mathrm{0.34~V}$ as the standard electrode potential of copper will be $\mathrm{-0.34~V}$ as it is acting as an anode). This shows the cell is spontaneous;

However, I have read that $\ce{Cu(s)}$ cannot reduce $\ce{H+}$ so I was wondering if this cell would work?


texts: What is the conversion rate in a chemical reaction?

texts:
Consider the following chemical reaction

$$\ce{X <=>[w_1][w_2] Y}$$

where $w_1$ is called the conversion rate of $X$ to molecule $Y$. What is the exact meaning of this conversion rate? Is it the same as probability?

The reference paper is:
Ref


texts: Why is a third body needed in the recombination of two hydrogen atoms?

texts:
In the article Discuss. Faraday Soc. 1962, 33, 205, the authors say that in order to form molecular
hydrogen from collision to atom we need a third body to remove the excess energy. That is we have the reaction $\ce{H + H + M -> H2 + M}$.
I suppose the reason is because if we have the excess this energy will break the bond. If it this the case why the energy can not be transferred to the electron and so would have $\ce{H + H -> H2^*}$, where $\ce{H2^*}$ denotes an excited state of $\ce{H2}$?


texts: How many liters of hydrogen gas is produced per gram of aluminium?

texts:
How many liters of $\ce{H2(g)}$ at STP is produced per gram of $\ce{Al(s)}$ consumed in the following reaction?  $$\ce{2Al(s) + 6HCl(aq) -> 2AlCl3(aq) + 3H2(g)}$$
  Express your answer to four significant figures and include the appropriate units.

My attempted solution is included below:

$$ 1.00~\mathrm{g~Al} \left( \dfrac{1~\mathrm{mol~Al}}{26.9815385} \right)
\left(\dfrac{3~\mathrm{mol~H_2}}{2~\mathrm{mol~Al}} \right)
\left( \dfrac{22.4~\mathrm{L}}{1~\mathrm{mol~H_2}}\right) = 1.245~\mathrm{L}$$

This is being marked as the wrong answer.  Where is my error?


texts: Why is it important to use a salt bridge in a voltaic cell? Can a wire be used?

texts:
I was learning about voltaic cells and came across salt bridges. If the purpose of the salt bridge is only to move electrons from an electrolyte solution to the other, then why can I not use a wire?

Also, will using $\ce{NaCl}$ instead of $\ce{KNO3}$ in making the salt bridge have any effects on voltage/current output of the cell? why?

Plus if it matters, I'm using a Zinc-Copper voltaic cell with a tissue paper soaked in $\ce{KNO3}$ as salt bridge


texts: Use of basis set in DFT (Density Functional Theory)

texts:
Basis sets are used to guess the electronic wave functions for Hartree Fock or similar methods, which are quite legitimate since these methods deal with the wave function of each and every electron.

Density functional theory, on other hand, uses the electron density at every point of space for optimization and the calculation of properties. This has led to two doubts which I want to clarify:

Is the basis set used to estimate the initial electron density of the system? If so, how the basis functions of an STO or GTF basis set change in order to exhibit the electron density? If not, what exactly is the application of basis set in DFT calculation?
In HF SCF, the coefficients of basis functions (for basis sets with GTF) along with geometry changes with change in nuclear geometry while optimising the structure. Does optimisation with DFT follow a similar procedure?

P.S.: Please do not suggest me this question, since this is not the answer I am searching for.


texts: Different statements of second law of thermodynamics

texts: This may sound trivial but I am having a hard time linking different statements of second law. What I get from second law is that heat cannot be completely converted into work and hence efficiency of heat engine is always less than one. Please explain what it has to do with entropy. Also from second law, entropy of any isolated system never decreases. How are the two statements similar? Please use simple layman terms, I am simply trying to grasp the idea.


texts: Regioselectivity in nitration of a 1,2-disubstituted aromatic compound

texts:
For 1,1,4,4-tetramethyl-1,2,3,4-tetrahydronaphthalene:

What would be the products following a standard nitration with $\ce{NO2+}$?

My reasoning is thus:

Since the substituent group is alkyl then it is ortho- or para- directing. But surely there are steric hindrance factors to be considered due to the bulk of the ring which would mean para- is favoured instead of ortho. However, when I try to draw out the structure it seems the arrows are meta- instead!


texts: Why does hydrogen fluoride have a boiling point so much lower than that of water?

texts:
$\ce{F}$ has more unshared electron pairs and is very electronegative, so $\ce{H}$ of another $\ce{HF}$ molecule can $\ce{H}$-bond with it.

$\ce{HF}$ has normal boiling point of $\pu{19.5^oC}$ while $\ce{H2O}$, as you know, has normal boiling of $\pu{100^oC}$.


texts: Determining water of crystallisation in a hydrate from the mass percentages

texts:
How would I find the amount of water in a hydrate if all I was given was the mass percentage of one element in the compound? For example, a question asks:

  $\ce{Zn(ClO3)2. $x$H2O}$ contains $21.5\%$ zinc. Find the value of $x$.

After thinking for some time I now know that I need to find the mass of $\ce{Zn(ClO3)2}$, and then find the mass and amount of water, and then divide by the amount of $\ce{Zn(ClO3)2}$. But I can't seem to find the mass of $\ce{Zn(ClO3)2}$.


texts: Why does FeCl3 react with carboxylic acid, but not with sulphonic acid in this question?

texts:
I was solving a question where I was asked to identify the reagents given in the question which could react with a compound provided.
The first compound was methanoic acid. One of the reagents given was $\ce{FeCl_3}$. According to the answer key, these 2 could react. On googling the reaction, I found that methanoic acid loses its acidic proton and is attacked by $\ce{FeCl_3}$ and the proton released then removes chlorine to form the complex. It all made sense because $\ce{CH_3COOH}$ was an acid.
But the next compound was 3-carboxy-4-nitro-benzene sulfonic acid. And I wanted to check its reactivity with $\ce{FeCl3}$. So, I felt that the compound being acidic due to the sulfonic group would work similarly as the first compound and thus react with $\ce{FeCl_3}$. However on verifying with the answer key, I found that it would not react with $\ce{FeCl_3}$. But I couldn't think of a reason why.


texts: Why is the carbon fluorine bond stronger than the carbon oxygen bond?

texts:
From this wiredchemist.com, I obtained values of the bond dissociation energies of the $\ce{C-O}$ and $\ce{C-F}$ bonds:
\begin{align}
D_0(\ce{C-F}) &=  \pu{485 KJ mol-1}\\
D_0(\ce{C-O}) &=  \pu{358 KJ mol-1}
\end{align}
I have read an explanation saying that is because of fluorine being more electronegative than oxygen, consequently the dipole moment across the bond is greater. As a result the delta negative on $\ce{F}$ and delta positive on $\ce{C}$ attracts each other more compared to the situation in $\ce{C-O}$.
There is another explanation of better overlap resulting in stronger bond. However in this case the orbital overlap seems quite similar and if not $\ce{C-O}$ has better overlap than $\ce{C-F}$, so this explanation doesn't apply.
However, if this is the case, then why in many organic reaction mechanisms, the polar bonds are more prone to break when the atom with delta positive on is attacked by a nucleophile? Would you give examples for nucleophilic addition-elimination and for nucleophilic substitution?


texts: Correct term/word for bias in calculations?

texts:
I ran an experiment recently and made several approximations in the calculations that led to the results being around 2 orders of magnitude less then the literature values.  I will be re-doing the calculations but in the meantime I need a word to describe what is wrong with this data set (ie what the effect was on the data by making the approximations).

I thought saying the approximations resulted in a "statistical bias", or "analytical bias" might be right, but this is a little different that regular bias because the data is all fine and unbiased, its the approximations/calculations that are making the final results off by ~100x literature values.

I'm not sure if this is the right place to ask this, so if you think it belongs on the statistics stackexchange, please let me know.

If you're interest (or if it matters), the approximation was to ignore epithermal neutron capture in NAA analysis.


texts: How does methyl vinyl ketone dimerise with heating?

texts: (A) to (B) is simply reduction, tosylation followed by intramolecular reaction and removal of tosylate. However, I am not able to guess how dimerization will take place, seems similar to Rauhut–Currier reaction, but can't guess. Any hint?


texts: Why is enol content higher in non-polar solvents?

texts:
Apparently, for keto-enol tautomerism, the enol content of a given carbonyl compound increases when in a non-polar solvent.

What is the reason for this?


texts: Voltage needed for electrolysis of water

texts: Reading the wiki for electrolysis it reads that a potential of 1.23V is needed to separate hydrogen from the oxygen. With that being said, how was that calculated? Does it change with the water volume and conductivity?


texts: Calcium Carbide is banned as a ripening agent in many countries because it contains traces of arsenic and phosphorus. Will it still be unsafe if pure Calcium Carbide is used?


texts: What's the difference between reactant, excess reactant and limited reactant in a balanced equation?

texts:
In some reactions, the reactant is mentioned as being "excess". For example, "phosphorus pentoxide forms in excess oxygen" or "pentahalides form with excess halogen".

But since the balanced equation shows exactly how many moles of a reactant are necessary, what is "excess" about the reactant? And how does it contrast with "limited reactant" and just "reactant"? (Ie: What's the difference in a balanced equation between oxygen, limited oxygen and excess oxygen?)

Does each balanced equation need to explicitly say somewhere that this is specifically an excess/limited reactant, or can this be inferred from the stoichiometric coefficients of the balanced equation? Do you need at least two equations side by side to see that one is excess and the other isn't?

Additionally, taking for example the following two reactions

$$\ce{P4 + 3O2 -> P4O6}\\[1em]
\ce{P4 + 5O2 -> P4O10}$$

it seems to me that mathematically on a mole basis, sure we can say that tetraphosphorus hexoxide will form with 3 moles of O2 available (per mole of P4), but tetraphosphorus decoxide needs 5 moles of O2, however, given the huge amount of actual molecules in the reaction, how do the molecules know when there's excess? I mean, why doesn't the phosphorus just form a lot of P4O10 and then just a few molecules of P4O6 with the few leftover O2 molecules, or would this be some kind of unstable situation and the phosphorus molecules are pretty considerate and don't start forming P4O10 until every P4 has at least 3 O2 attached to it?

To sum up, my questions are:

What's the difference between "reactant", "limited reactant" and "excess reactant" in a balanced equation?
Can the fact that the reactant is excess/limited be inferred from the balanced equation?
Why is it that the same reactant (such as P4) proceeds in two different ways depending on whether the second reactant is excess/limited?


texts: If a molecule contains four chlorine atoms, how many molecular ion peaks will this compound show in its mass spectrum?


texts: What is the greenish substance formed after the electrolysis of two graphite electrodes in a sodium sulphate solution?

texts:
Today at school we tried the electrolysis with two graphite electrodes in a sodium sulphate solution. We put the electrodes in two test tubes and filled them with some more sodium sulphate so that the solution could react with the electrodes and after that, we quickly turned them over and put them in a beaker filled with sodium sulphate. After that, we added some bromothymol blue in it to see where the hydrogen and oxygen would have gone. Afterwards, we turned the power on and saw that it was producing gas and everything was normal at first (1st image).

Some time after that we didn't see the volumes between the two test tubes changing so we waited some more. Later, we saw that the solution started assuming a green color and something started forming on the surface (2nd image).

It became more and more green so we decided to turn the power off. Then we noticed that on the bottom of the beaker was something yellowish and brownish (3rd image). We checked if the wires were consumed by the solution or if they had reacted with it but nothing was wrong with them. I have no idea what it is and my teacher told me and my lab group to find an explanation to that. What is the problem here?

List of the materials used:

1 beaker
2 test tubes
two electrodes connected to wires (graphite)
$\ce{Na2SO4}$ (sodium sulphate)
bromothymol blue


texts: What factors influence the resultant oxidation state of Fe in 3Ca(OH)2+2FeCL3?

texts:
$\ce{3Ca(OH)2 + 2FeCl3 -> 2Fe(OH)3 + 3CaCl2}$

What factors influence the resulting oxidation state in the iron hydroxide molecule in this reaction? Since iron's oxidation state ranges from +2 to +6, and there exists iron hydroxide (II), how do we know what the oxidation state will be in this reaction?

Would this equation yield $\ce{Fe(OH)2}$ under some conditions?

I googled and found that in order to obtain $\ce{Fe(OH)2}$ we react $\ce{FeCl2}$ and $\ce{KOH}$ with no air present:

  $\ce{FeCl2 + 2KOH -> 2KCl + Fe(OH)2}$

Would my initial equation yield $\ce{Fe(OH)2}$ in the absence of air? If yes, why?

The oxidation state of $\ce{Fe}$ before the reaction is +3.

$%edit$


texts: What explosive compound would be the most likely first explosive developed by a race?

texts:
Elaboration on title: What would most likely be the first explosive compound that some individual would create if they were just mixing together random things they had available? I'm not talking about our world history, where it was the discovery of black powder in China about 1200 years ago. I'm talking about some arbitrary race somewhere in the universe; what would most likely be the first explosive they develop, combining anything organic they could get? Would it be black powder? Nitroglycerin? Nitrocellulose?

(Keep in mind that this question is coming from someone who isn't really a chemistry nerd :p)


texts:
The order of decreasing basicity in the four halide ions is:

  $\ce{I- > Br- > Cl- > F-}$
  $\ce{Cl- > Br- > I- > F-}$
  $\ce{F- > Cl- > Br- > I-}$
  $\ce{Cl- > F- > Br- > I-}$

The answer is option 3) but i'm getting as option 1).

My reasoning is that these elements belong to the same group, and the atomic radius increases down the group. Bases are electron donors, and iodide is the largest, so it can donate electrons the easiest, hence it should be most basic. Why is this incorrect?


texts: How to clean a copper pan from black burned fat chemically?

texts:
I have several copper pans which I use daily. I don’t have the time to always clean them. Now they have a thick crust of black burned fat. When I wash it with dish soda, nothing changes. And I don’t want to use abrasive mechanics (steel sponge), because I am afraid this will scratch the copper surface.

Is there a chemical trick to dissolve the black crust? What is that black crust chemically and why is it so strong?


texts: Intuituve reason for the constant of proportionality 2/3 in pv=nRT=(2/3)U

texts:
Why is there a $\frac23$ term?

I fully understand that it makes sense for pressure to be the volume weighted average kinetic energy. And the equation above shows that this is so (for an ideal gas). I also fully understand how to prove this with momentum and force. I'm wondering is there an intuitive reason why the for one cubic meter, the the pressure should be two thirds of the total internal kinetic energy, not some other value. Or is it just because the math says so?


texts: Octahedral Crystal Field Splitting Orbital Degeneracy

texts:
How are the $\mathrm{e_g}$ orbitals degenerate with each other?

Note: This isn't a homework question. After the semester ended (I don't go to MIT), I ended up on MIT open course-ware to watch some videos about areas of chemistry I haven't covered yet or haven't covered well. I am asking the question here because I have no other avenue in which to ask questions to other people. I'm just trying to use my time during the pandemic to build my knowledge of chemistry. I don't have a lot of understanding about this, I'm just looking for some help


texts: Significance of 4π in the uncertainty principle

texts:
What is the significance of the quantity 4π in the Heisenberg uncertainty principle?
$Δp \times Δx = \frac{h}{4π}$
The focus of the question is to learn why the ratio of a circle's circumference to its diameter, universally known as $π$, is used in the denominator in the term $\frac{h}{4π}$. To put it another way, why is this geometric number relevant in Heisenberg's formula?


texts: Clarification on the Clausius inequality

texts:
In Atkins' Physical Chemistry the criteria for spontaneity using Gibbs energy was calculated using the Clausius inequality:

$$\mathrm dS ≥ \frac{\mathrm dq}{T},$$

and at constant pressure, $\mathrm dq = \mathrm dH.$ Thus, $\mathrm dH - T\,\mathrm dS$ is negative.

So, if we define a function $G = H - TS$ at constant pressure and temperature, we get

$$\mathrm dG = \mathrm dH - T\,\mathrm dS ≤ 0,$$

which we use as a criteria for spontaneity.

My issue with this argument is that it implies that the Clausius inequality is for spontaneous processes only, otherwise we would end up with $\mathrm dG ≤ 0$ for all processes.

However, the derivation of the inequality simply used the fact that

$$|\mathrm dW_\mathrm{reversible}| > |\mathrm dW_\mathrm{irreversible}|$$

when the system does work.

So, where is it implied that the derivation is for spontaneous processes only?


texts:
When does 'H' Shows +I/-I effect and why does T,D show better +I effect?

In my book Hydrogen is given in both +I & -I effect showing group ,i was curious to know under what conditions does it shows such opposite/dual effects? Also are there any other commonly encountered groups which show both +I/-I contition to condition?


texts: How do I lower the surface tension of water without using a detergent?

texts:
For many years I've used a Rainbow vacuum, which uses a reservoir of water as the filter.   While I'm quite pleased with it, I've found that when trying to vacuum cement dust or wood ash not all of the  particles are captured in the water.   I believe a remedy to this would be to lower the surface tension of the water.  Yes, I can always be sure to use hot water, but I'd like to go further.  Obviously I can't use a suds-producing detergent because the vacuum produces lots of turbulence in the reservoir.

What commonly available chemicals could I use that would give me the greatest reduction of surface tension? So far I've tried to research trisodium phosphate, sodium carbonate, and a product called Haemo-Sol which is a non-ionic surfactant... but I can't find surface tension numbers for any of these much less the concentration to use.

The manufacturer suggests adding a tablespoon of vinegar, which I think is
rather lame.

Can anyone make a good guess or point me in the right direction?


texts: In which cases do you say "oxide" when naming a molecule?

texts:
Based on the names of following molecules I got quite confused about the correct nomenclature:

$\ce{NaHCO3}$
$\ce{K2SiO3}$
$\ce{PbCrO4}$

In none of the above molecule names you ever say "oxide" although there is a oxygen atom. Why? What is the applied rule for the nomenclature? In which cases do you actually say the word "oxide" in the name of the molecule?


texts:
Why is radioactive strontium-89 is considered medically useful for bones (along with other benefits) whereas strontium-90 (also being radioactive) is harmful for human body?

How does the addition of one atomic mass has adverse effects on human body?


texts: I need to find a mechanism for the above reaction but I cannot make much progress. I do have something in mind but it doesn't seem entirely plausible: First the tert-butyl group leaves (this seems wrong but tert-butyl cation is stable and thus a reasonable leaving group maybe? Also the negatively charged ring that it would leave behind would be stabilised by the EWG Bromines). The cation is then attacked by Cl and the ring is attacked by a proton (one product formed). Then a Friedel-Craft alkylation to make the other product (hence the excess of benzene to promote only mono-substitution). I doubt that is right, purely because of the first step. Can you help?


texts: How does Brita filters out calcium from water (since active carbon only filter negative charged particule)?

texts: I read that the carbon in (Brita) filter is “activated” by adding a positive charge, which enhances the adsorption of contaminants that have a negative charge. But if the Calcium in water is positive charged (ca2+) it should pass through the activated carbon, right?


texts: Oxidation of polycyclic aromatic compounds using KMnO4

texts:
How is tetracene oxidised by $\ce{KMnO4}?$ It appears that the product is a white solid with a benzene ring inside.

What is the reaction mechanism? Is it radical based? Or does the $\ce{MnO4-}$ ion react with tetracene in a similar manner as alkenes are hydroxylated to diols?

Do I have to consider the inherent aromaticity of tetracene to deduce which "double bond" (because there's no "true" double bond) the $\ce{MnO4-}$ species reacts with?


texts: How to create a 3 M solution of ammonia from 25% ammonia

texts:
We have ammonia $25\%$. We also know $\rho_{\text{ammonia}} = \pu{0.86 \frac{g}{cm^3}}$, $\pu{25 ^\circ C}$. We want to produce $\pu{3 M}$, $\pu{0.5dm^3}$ ammonia.

This means that there are some calculations we need to do in order to produce $\pu{3 M}$, $\pu{0.5dm^3}$ ammonia.

I try to calculate the required mass by the following method: $\text{m}=\text{C}\cdot \text{V}\cdot M \cdot 0.25$. Is this method correct?


texts: Regarding the mechanism behind Marcus theory, I was wondering if reaction occurs through tunneling when it does not have sufficient activation energy? Wouldn't expecting reactions to occur this way be like expecting random combustion to happen in the arctic?


texts:
The respective speed of five molecules are 2, 1.5, 1.6, 1.6 and 1.2 km/s. The most probable speed in km/s will be?
  1. 2
  2. 1.58
  3. 1.6
  4. 1.31

I think the answer should be 1.6 km/h but the answer given in book is 1.31 km/h.
Most probable speed should be the mode of the given speeds, which is equal to 1.6 km/h. Am I correct?  If I am wrong, then what's the definition of most probable speed and how do I solve this problem?


texts:
So on the data, it said that we can reduce potassium permanganate by utilizing oxalic acid, thus producing carbon dioxide.
But can anyone propose a reaction mechanism of how the whole reaction happens, and how did oxalic acid break up into $\ce{CO2}$?
Thanks in advance!


texts: Why do chromyl bromide and chromyl iodide not exist?

texts:
It is known that chromyl chloride exists (popularly known as the product of a test for presence of chloride ion) but chromyl bromide and chromyl iodide are unknown.

Why is it so? Why don't they exist? I'd guess it has something to do with the large size of bromine and iodine compared to chlorine, but I'm not sure.

What are the possible reasons for their non existence?


texts: Cleavage of C-C bond in 1,2-diketo compounds with periodic acid

texts:
Today we learned the Malaprade reaction in class. My teacher told me that a similar reaction can take place when the substrate is a 1,2-diketo or 1-keto-2-hydroxy or even 1-hydroxy-2-amino(in presence of periodic acid):-

(A similar one with 1-hydroxy-2-amino)
I wanted to know the mechanism of this reaction. This is the closest thing I could find.


texts: Could someone advise me on sources for crystallography and surface sciences?

texts:
I'm a physicist learning crystallography and surface science on the side of my research and I came across the concepts: surface reconstruction in hexagonal materials, unit mesh of surfaces, etc.
I was given problems to solve but they are too advanced for me. These are based on the book Modern Techniques of Surface Science 3rd ed. by Dr. Woodruff.
Can someone advise me with some other sources of information to better understand Lattice Planes and Miller Indices, to the level shown in the Cambridge website.


texts: Effect of rain on water and soil samples contaminated by petroleum

texts:
I am about to perform research on the impact of petroleum fire disaster on the soil and water sources within the region of disaster, using heavy metals and total petroleum hydrocarbons as impact markers.

My supervisor suggested I collect samples during raining season and dry season and compare.

My question is, would there really be any significant difference between the  two samples in the rainy and dry season?


texts: Chemistry behind lip balm coloring based on skin pH

texts:
I stumbled across an ad for a clear, colorless lip balm that purportedly tints your lips a shade of pink determined by your skin's pH.

  This balm stain applies on clear then reacts with your skin's pH levels, uniquely creating the perfect shade of pink lips just for you.

Out of curiosity (and the fact that I'm an easy target for marketing), I read further. The product contains the following ingredients:

Hydrogenated Polyisobutene
C12-15 Alkyl Benzoate
Diisostearyl Malate
Octyldodecanol
Dibutyl Iauroylflutamide
Dibutyl Ethylhexanoyl
Thylhexanoyl Glutamide
Isononyl Isononanoate
CI 45410
Chrysanthemum (a whole flower added to the bottom of the tube, presumably just to make it look nice.)

Other than CI 45410, I can't find anything on the above list that mentions anything about color -- and there's nothing listed that I think could change color based on pH.

Note: Some of the ingredients are very hard to find data for, but most seem to be thickening agents.

Does this clear lip gloss actually have the ability to change color based on pH or does the color come from the CI 45410? If it's from the CI 45410, what causes it to go from clear to pink?


texts: What chain(s) of reactions are used to produce L-glucose? I did a search on Google scholar but to my surprise nothing came up. My guess would be that the synthesis starts from D-glucose for which there are abundant natural sources. References would of course be highly appreciated!


texts:
What is the pH of CsBr?

  3.8
  7
  9
  12

According to me,

$\ce{Cs+ + H2O <<=> CsOH + H+}$   (because $\ce{CsOH}$ is a strong base, the forward reaction should not occur, right?)

$\ce{Br- + H2O <<=> HBr + OH-}$ (because $\ce{HBr}$ is an acid, the forward reaction should also not occur, right?)

So the answer should be $\mathrm{pH} = 7$.


texts: Why group 13 elements don't show +2 as their major oxidation state?

texts:
These are the things I understand:

  1) Group-13 elements show +1 and +3 as their major oxidation
  states(OS).

  2) The general configuration of G-13 elements is $ns^2$ $np^1$.

  3) In the excited state, their electronic configuration is $ns^1$
  $np_x^1$ $np_y^1$ .

On losing two electrons from their excited state,
their configuration will become $ns^1$ $np_x^0$ $np_y^0$

I don't understand why will this configuration be unstable?


texts: Z* effective charge and Ionization Energy

texts:
I'm trying to figure out the patterns for Ionization Energies. I am familiar with the periodic trend, however things become quite different when we hit the 1st I.E. For example, Na has an I.E(1) of 495.8 kJ while its second I.E. rockets up to 4562 kJ while the atoms towards the right are much lower than this. The trend says that the I.E. increase up and right of the periodic table, which is not the case here.

My point is, in order to get a better estimate, would it be safe to say that the Zeff charge and atom size relate to the I.E?

Example: Effective Charges

Mg = 2
Al = 1
S = 4
Si = 2
Na = 1

We see that the strongest pull towards the charged center would be Al and Na in this case. However, having Al being the smaller atom would require more energy to remove the electron from its valence shell.

Now in the case of first Ionization Energy we have:

Mg = 3
Al = 2
S = 5
Si = 3
Na = 2

In this case, Na now has reduced its size due to the fact it jumped from n=3 to n=2 level and Al also reduced in size but is still a bigger atom than Na due to our trend.

My question is, is this approach fairly accurate or should I be looking somewhere else?


texts: How can three p orbitals per atom bond in tin (II) sulfide?

texts:
Tin (II) sulfide, a mainly covalent compound, bonds using its p orbitals only (the 5s orbitals are considered to be part of the core in divalent tin). Its structure is made up of Sn–S–Sn–S chains, which are further stabilized by Sn–S bonding across the chains:

How would VB or MO theory explain the fact that the tin molecule bonds three times, when only two of its p orbitals are half filled (Electron configuration: [Kr]5s24d105p2), while the third is empty? The observed bond angles of ca. 90° (96°/88°) would indeed suggest plain p orbital bonding, as suggested by this paper, but how is this possible?

And how could sulphur bond three times (Electron configuration: [Ne]3s23p4) with similar bond angles, when one p orbital is full?

The only thing that comes up to my mind is a dative covalent (co-ordinate) bond, in which sulphur provides both p electrons, thus permitting coordination. But then, the tin atoms would have a negative charge attached to them (due to having more electrons around than protons) and the sulphur atoms a positive one. Wouldn’t this be energetically unconvenient, considering that the compound has ca. 9% of ionic character, which depends on the tin ions being positive and the sulphur ions negative?

Addendum:

The dative bond assumption clashes against the bond lengths observed in tin (II) sulfide. The paper I cited above states that the Sn–S bond length on the chains are 2.68 Å long, while those between the chains are 6 pm shorter (2.62 Å). The IUPAC Gold Book says that dative bonds

  are distinguished by their significant polarity, lesser strength, and greater length

when compared to covalent bonds. This is exactly the opposite of what happens in tin (II) sulfide.


texts: Nomenclature and chemical formulae for bridged dinuclear chromium complexes

texts:
In theory, $\ce{[Cr(H2O)6]^3+}$ ions have a bluish violet colour. However, many times in the lab we end up with a dark green solution. This is due to hydrolysis, coordination with sulphate (or other) ions, and polymerisation, most often dimerisation.

Hydrolysis$$\ce{[Cr(H2O)6]^3+(aq) +H2O(l) <=> [Cr(OH)(H2O)5]^2+(aq) + H3O+(aq)}$$

Coordination and dimerisation

The degree of coordination depends on conditions, e.g., temperature. It is common to find the following equilibria.

$$\ce{2[Cr(OH)(H2O)5)]^2+(aq) + $\mathrm{SO}_4^{2-}$(aq) <=> Picture1(aq) + 4H2O(l)}$$

$\ce{Picture1}$:

$$\ce{2[Cr(OH)(H2O)5)]^2+(aq) + 3\ $\mathrm{SO}_4^{2-}$(aq) <=> Picture2(aq) + 6H2O(l)}$$

$\ce{Picture2}$:

Question

How can one write these ions in condensed structural formulae? I wish not to lose any information.
How can one unambiguously name these two ions?

I am looking for official IUPAC names and formulae using latest recommendations for complexes. For instance, $\ce{[Pt(NH3)4][Pt(Cl)4]}$ is named tetraammineplatinum(II) tetrachloroplatinate(II); $\ce{[Cr(OH)(H2O)5]^2+}$ is pentaaquahydroxochromium(III) ion.

Thank you in advance!

P.S. Pictures were drawn using the free online software eMolecules. Also, feel free to correct any formatting and/or grammar errors. As for chemistry-related mistakes, please comment rather than edit.


texts: Are there any semiempirical methods that work with heavy alkaline earth metals?

texts: I did some research. Found some semiempirical methods that work even with heavy lanthanide compounds (RM1). But could not find any references to semiempirical methods compatible with the heavier members of the alkali earth group: Sr, Ba and Ra. If there is such method, does any open source / free software implements it? I'm learning to use Gamess-US, but the only semiempirical methods implemented in this package are MNDO, AM1, PM3 and RM1 (refs file).


texts: When will acid-base reactions occur before substitution reaction

texts:
For example, given the reaction below:

The substrate is secondary, the solvent is aprotic and it is to react with a strong bulky base. From this, I assumed that the reaction would be $\ce{E2}$. However, it instead begins with an acid-base reaction where the tert-butoxide removes the proton of hydroxide and then proceeds with a $\ce{Sn1}$ reaction where the oxygen attacks the carbon of the leaving group to form an epoxide.

How can you determine if an acid-base reaction will take place before proceeding with a substitution reaction?


texts: Alkane, alkene, alkyne boiling point comparison

texts: Which of the following has higher boiling points? Alkanes, alkenes, or alkynes? And why?


texts: Hydrolysis products of chlorides of group 15

texts:
$\ce{NCl3}$ on hydrolysis produces $\ce{NH4OH}$ and $\ce{HOCl}$.

$\ce{PCl_3}$ when hydrolyzed produces $\ce{P(OH)3}$ i.e. $\ce{H3PO3}$.

$\ce{AsCl_3}$ when hydrolyzed produces $\ce{As(OH)3}$.

However when $\ce{SbCl3}$ or $\ce{BiCl3}$ are hydrolyzed they produce $\ce{SbOCl}$ and $\ce{BiOCl}$ respectively.

Why are the products so widely varying ? How can we explain the reactions theoretically ?


texts: Can a chemical reaction cause a cigarette to taste bad?

texts:
I'm currently researching an idea where I'd like to find out if there is any chemical we can put in toothpaste that would react badly with tobacco smoke?

The idea is that smokers can just brush their teeth as anyone would normally do, but when they light up a cigarette it would taste awful. So the actual question is, of all the stuff that's in tobacco, is there anything we can make react that is

safe to put in toothpaste.
reacts solely by giving a bad taste.
doesn't let that bad taste last for longer than 10 minutes.

I just want to know if this is technically possible since I don't have a background in chemistry. Thanks for your help!


texts: Why is latent heat of vaporization not exactly proportional to boiling point?

texts: Latent heat of vaporization and boiling point are both chemical properties related to the bond strength of the molecule. In general, the higher the boiling point is, the higher the heat of vaporization will be. However, there are some molecules that break this trend. For example, ammonia has a higher heat of vaporization than you’d expect based on its boiling point relative to other molecules with similar boiling points. See table here: https://en.m.wikipedia.org/wiki/Enthalpy_of_vaporization. Why does ammonia (and other substances) break this trend?


texts: What role does heat play in the combustion process.Specifically, does the amount of heat  determine whether complete or incomplete combustion occurs, and is the amount of heat impacted by the amount of oxygen


texts:
The picture above is a drug called Setraline. Suggest a likely mode of degradation of sertraline hydrochloride alone in aqueous solution, giving likely structures of the degradation products.

From my knowledge, degradation in aqueous solution can only mean hydrolysis and sertraline does not contain hydrolysable groups like amide or ester. What are the other forms of degradation besides hydrolysis? in aqueous solution.


texts: Flood Control - electrolysis - limit to rate of conversion?

texts:
Flood control - is it possible to use electrolysis to remove flood waters by converting water into oxygen and hydrogan gas?   Is there a limit to the amount of water that can be converted at a time?

I know that this is a bit crazy and I respect what you are saying, BUT I am not trying to vaporize the entire Mississippi river, only enough to keep flood waters from ebbing into a house.

Maybe a different appreach - how about freezing the water place (in blocks) and then transporting it elsewhere

if only water was compressible....


texts: Application of Markovnikov's rule with EWG's and Resonance

texts:
I want to ask a question concerning Markovnikov's rule.
Consider the following question:

We can tell that there will be two types of stabilisation upon formation of the carbocation:

Resonance via the phenyl group
sigma-hyperconjugation via the methyl group

When attempting this question, I thought the more stable carbocation would be the one where the positive charge lies to the left of the alkene double bond, and can be stabilised by the phenyl group, since resonance stabilisation is stronger than sigma hyperconjugation to yield the major isomer.
However, the answers state the opposite:

They state that the more stable carbocation is the one that can be stabilised by sigma-conjugation, yielding the alternate product, due to more carbon (groups) being attached to the carbon on the double bond. I thought it would be less stable as it is destabilised by the EWG aldehyde group and stabilised by the weaker sigma-hyperconjugation.
What is the correct interpretation of the answer?


texts: How do gelatin and aluminium sulfate strengthen paper?

texts:
When wet, the hydrogen bonds between the cellulose chains in paper are disrupted due to the formation of hydrogen bonds with water. This leads to the paper becoming extremely weak. This is the case with most paper, however, additives such as gelatin and aluminium sulfate are added to the paper to strengthen it.

I can't see how the addition of either of these strengthens the paper. I would guess that it aids the bonding between cellulose chains, perhaps by creating a 'bridge' between them, but I'm not sure if this is correct or how it would happen. Another idea is that the aluminium could form a complex ion, and then perhaps form a chelate to strengthen the paper, though I have little confidence in this.

So, how do the gelatin and aluminium strengthen the paper - particularly filter paper, which is almost pure cellulose.


texts: pH probe bulb - what is happening within the glass?

texts:
I am trying to understand how the glass bulb of a pH electrode of a pH meter works - the glass bulb itself. Not the reference electrode or the rest of the electrode (HCl, Ag/AgCl wire, etc...), the math, or the equilibrium yet. For this question just the glass bulb of the pH electrode.

Here is what I have learned so far. This is my current understanding. I'm not saying it is right - but it's where I am right now.

The thin-walled glass bulb has a conductive solution inside, and the outside should be kept in liquid at all times as well. This hydrates a thin layer of the glass on the outside and the inside. I assume these layers are manufactured differently, otherwise, the glass should be uniformly hydrated after a long enough time. It is important that the middle layer of the glass remains very low conductivity so that a potential difference can be maintained; there are likely other reasons as well.

The glass is amorphous and in this case, the exterior layers are somewhat porous, so there is a large volume of Si-O groups exposed to the solution. Protons will stick to these groups and establish a negative charge on the outside of the glass. The number is related to the pH or hydronium concentration of the solution on the outside of the electrode.

edit: I have just started to read this early discussion, where the idea that the glass itself may behave as a sort of buffer:

  Hughes (3) has pointed out that the hydrogen ion concentration in the glass phase may be held relatively constant by the buffer action of the glass which is a mixture of the salt of a weak acid $(\ce{Na2SiO3})$
   with the anhydride of that acid (excess $\ce{SiO2})$.

Note: The hydrated layer is also called a "gel layer", but it is not clear if this is formed naturally as the glass hydrates, or if there is a special gel-enabling material applied to each surface during manufacture.

Do these have to be specially prepared layers of more porous, hydratable glass on the inside and outside of the glass bulb? If so, roughly speaking how is this done? If not, what does limit the depth of the hydrated layer?
When inserted into an acid/base solution, is it just protons diffusing into the hydrated layer of the pH probe bulb by jumping between Si-O sites, or is it the hydronium ions in solution that is diffusing into the glass?
Why is it this often called an ion exchange process? (e.g. not in the Mettler link but in the other two links below, and several random textbooks pulled from a library shelf). Are there Li or Na ions in the glass that are moving? What is being "exchanged"?

below: From A Guide to pH Measurement – the Theory and Practice of pH Applications, Mettler, Toledo.

below: From Theory and Practice of pH Measurement.

below: From The Glass pH Electrode by Petr Vany´sek.


texts: How many resonance structures does the oxalate ion have?

texts:
I have drawn the Lewis structure of the oxalate ion, and I see that two oxygens are double bonded to the carbons. When finding the resonance structures, I said there are 2, but the exam solutions state 4, which was confirmed by internet images such as this:

However, I see no real difference btween structures 1 and 2, and 3 and 4. Are they considered different resonance structures?


texts: Is it possible to vacuum distill citric acid?

texts:
I'm wondering if

it is at all possible to vacuum distill citric acid without the slightest decomposition;
it is something that can easily be done in a small lab with widely available equipment.

I've looked on internet and found the following data:

~154 °C melting point (anhydrous citric acid)
~175 °C starts decomposing
~310 °C boiling point
~$10^{-8}$ mmHg vapor pressure at 25 °C


texts: Why is the only H NMR resonance of 1,4-dibromobenzene a singlet?

texts: I am working on a chemistry problem set and the answer key says all H's will show up as singlets. This does not make much sense to me as there are adjacent hydrogens to each carbon which should mean the H's show up as a doublet. What am I thinking incorrectly about this?


texts: Unitary Transformation of the HF equations

texts:
I am working on a code to preform a HF procedure and I am a bit confused about the unitary transformation of the basis. My instructions are as follows.

specify the basis and geometry (done)
Evaluate and store overlap, Kinetic energy, nuclear attraction, and electron repulsion integrals (done)
diagonalize $ \mathbf{S}$ and find $\mathbf{S}^{-1/2}$ which is the unitary transformation matrix.
Use the core hamiltonian to find the initial Fock matrix:
$$ \mathbf{S^{-1/2}}^{T} \mathbf{H}~\mathbf{S^{-1/2}}\equiv\mathbf{F}_0$$
Diagonalize the Fock matrix to find the mo coefficients:
$$\mathbf{F}_0 \mathbf{C}^{'}_0=\mathbf{C}^{'}_0\epsilon_0$$
Back transform the coefficients.
$$\mathbf{C^{'}_0}~\mathbf{S^{-1/2}}=\mathbf{C}_0$$
compute the density, use the density to evaluate new fock matrix, find new coefficients repeat until convergeance.

Now step 7 kinds glazes over a lot of the work but I understand that part, so It isn't important to the question.

I am confused by the $\mathbf{S}^{-1/2}$ matrix.  Is this literally one over the square root of each element of $\mathbf{S}$? Or is there some decomposition I should preform that I just do not understand.  I can carry out the whole procedure but without orthonormalization my results are nonsense.


texts: Best Way to Store Copper Acetate Solution?

texts:
I am preparing to copper electroplate an ABS plastic sheet in my home and wanted to know what the best container/environment would be to store the copper acetate solution.
First, I created the solution using copper metal, vinegar and hydrogen peroxide.
Can I simply store this solution in a plastic container?
Should it be closed with an air-tight lid?
Would food-grade LLDPE plastic container be acceptable?
Does the color of container matter? Is black color better than clear color as it reflects more light?
Is it OK to leave it in my home at room temperature or should it be refrigerated?
Thanks!


texts: How to calculate the concentrations of the species in the carbonate equilibrium from a titration with hydrochloric acid?

texts:
Lake water contains dissolved sodium carbonate and sodium hydrogen carbonate. The following equilibrium exists:
  \begin{align}
\ce{HCO3- &<=> H+ + CO3^{2-}}&
\frac{\ce{[CO3^{2-}]}}{\ce{[HCO3-]}}  &= 0.958
\end{align}
  When $\pu{10 cm^3}$ of lake water were titrated with  $\pu{0.2 mol/dm^3}$ $\ce{HCl}$, $\pu{22 cm^3}$ of acid were required to neutralise all the carbonate and hydrogen carbonate ions according to the following equations:
  \begin{align}
  \ce{H+ + HCO3- &-> H2O + CO2}\\
  \ce{2H+ + CO3^{2-} &-> H2O + CO2}\\
\end{align}
  Calculate the total amount of substance of acid used, and thus, by using the ratio quoted, calculate $\ce{[CO3^{2-}]}$ and $\ce{[HCO3-]}$ in the lake.

I was able to find the amount of substance of acid $\ce{HCl}$, which is $\pu{4.4E-3 mol}.$ How do I go on?


texts: Why were elements discovered "out of order" after 1950?

texts:
I'm referring to the fact that there is one element that corresponds to one proton in an atom, a second that corresponds to two protons, up to, I believe, an element with 115 protons. These elements are listed in the periodic table discovered by Mendeleev in the 19th century, or modern expansions thereof.

By "out of order," I'm referring to a situation where elements were not discovered consecutively by number of atoms, e.g. where an element with 103 protons was discovered before an element with 102 protons, and again with 109 protons before 108, according to this table. I use the qualification "after 1950", that is, the "modern era," because this would have given scientists time to sort out Mendeleev's Table after it gave us a road map to atoms. Perhaps more to the the point, the scientific process is a lot more organized than it was in Mendeleyeev's time.

What were the circumstances of these out-of-order discoveries? Isn't it exponentially harder to discover elements with 103 protons than 102 or 101, etc.? Or wouldn't scientists concentrate on creating the atom with the "next" number of protons, e.g. 116 using advanced technology nowadays? Because this is a process that is different from "randomly" coming across atoms commonly found in nature.


texts: Is it possible to crystallize a solid ingot of metal from an (acidic) aquaous solution?

texts:
To my knowledge, metalic ions only precipitate from a solution as salts & and a process that could possibly produce monocristalline metal would be very interesting indutrially - I've never heard of one, so I don't think it is possible.

But: is it not conceivable to dissolve a metal in an acid (or maybe base), and then (later) neutralize the acid, without resulting ions that form a salt with the metal?

What am I missing?

As an aside, I arrived at this question while thinking if there could be a biological, and thus wet-chemical, pathway from ores to pure metals (in metallic form). The last step in a such a process would be the precipitation/crystallization as a metal.


texts: LogP of halogen derivatives of aromatics and aliphatics explanation

texts:
Benzene logP = 2.13 (logP=log([benzene in octan-1-ol]/[benzene in water]))
Fluorobenzene logP = 2.27 (slight increase, slightly more hydrophobic)
Chlorobenzene logP = 2.84
Bromobenzene logP = 2.99

So as we go down group 7, logP or hydrophobicity increases. What can explain these trends? Furthermore on aliphatic compounds, we observe this trend which confuses matters more.

-Fluorine DECREASES logP slightly (by -0.17) on an aliphatic compound. The book doesn't give a reference as to which alpiphatic compound this is and which hydrogen is substituted, but oh well.
-Chlorine increases logP (by 0.39) on the same aliphatic compound.
-Bromine increases logP even more (by 0.60) on the same aliphatic compound.

So a few questions:
1. Why does a fluorine substitution decrease logP slightly on the aliphatic but increase slightly on the aromatic?
2. Why do chlorine and bromine substitutions increase logP in aliphatics and slightly more in aromatics.

Answers to these trends would be greatly appreciated, thanks.


texts: I have to etch a pattern on a plastic film similar to the ones used to protect phone screens. I want a very thin etch, one that is only visible on close inspection. How can I get that done?


texts:
I have been able to slightly unpack the NMR spectrum for the nicotinic acid to understand the order of signals and what ones correspond to what protons but I am having a problem with why some of the signals produced a different number of peaks I can not explain. I understand how simple and complex spin-spin splitting works to an extent when producing a number of different types of groups such as, s, d, t, m, dd, dt and many others.

The spectrum below is one for nicotinic acid, and the peaks are in order of most downfield to least, signals for H on carbons 2, 6, 4 then 5.

Looking at the environment proton two is in it has no equivalent neighboring pairs so why is it producing a doublet?

Same goes for the proton at carbon six.  Why is it producing a double of doublets when it only has one neighboring pair?

As for the signal for proton five that is simple to understand and it should produce a double of doublets because the neighboring protons are in-equivalent, but yet again this is still not the case for the splitting of the signal. The same for proton 4 which produces a double triplets.

Would some one be able to explain why this is occurring?


texts:
A full FAQ post has been written on meta.chem.SE, explaining the premise of synthesis golf and the 'rules'. Please take a look at this before answering (if you haven't already).

This fifth round of golf concerns the synthesis of (−)-α-(3,4-Dimethoxyphenethylaminomethyl)-4-hydroxybenzylalcohol (denopamine), a synthetic drug indicated for use in the treatment of angina.

The challenge is to propose a route to denopamine. You may start with anything that has less than 10 carbons, but it must be available in the Sigma-Aldrich catalogue. A method should also be included to set the oxymethine stereocentre (no buying it!).

Given the relative simplicity of the target and the need for large quantities of the drug, consideration to step count and scalability should also be taken.


texts: How is the yield of a complex organic synthesis defined?

texts:
I just watched the Periodic Table of Videos episode Deadly Strychnine that describes the history of this particularly challenging synthesis. University of Nottingham chemist Rob Stockman calls the problem "an "Everest" of synthetic chemistry."

What is the definition of yield in this case? How is it calculated? Is it as simple as mass of product divided by total mass of all reactants, or something more specific and meaningful?


texts: I am currently messing around with gallium compromising aluminum. I am using a titalium lock which is just a brand of aluminum padlock and I put a gallium-indium euctic alloy on the surface of it. It’s been around 10 minutes and on the surface of the liquid is a gold colored substance. What is this? Any idea why it’s happening??


texts: Formamide and Hoffmann Bromamide Reaction

texts:
I encountered a problem to identify the compound which does not give Hoffmann bromamide degradation reaction. One of the options was formamide, and it was given as the answer.

Why can't formamide give Hoffmann bromamide reaction? I feel that the answer is wrong (it should produce ammonia).


texts:
While studying about reversible reactions, my professor stated that the following reaction is a reversible reaction:

$$\ce{Fe + H2O <=> Fe3O4 + H2}$$

She also stated that the product $\ce{Fe3O4}$ is formed by a mixture of $\ce{FeO}$ and $\ce{Fe2O3}$. However, there was no mention of the type of reaction or the reason due to which the mixture of $\ce{FeO}$ and $\ce{Fe2O3}$ resulted in the formation of $\ce{Fe3O4}$.

So, my questions are as follows:

What type of a reaction is it? (I think it's a displacement reaction but from what I know, there are ions present in a displacement reaction).
Why have we combined $\ce{FeO}$ and $\ce{Fe2O3}$ resulting in the formation of $\ce{Fe3O4}$? (According to me, mixtures and compounds are two different things and that we can't combine them.)


texts:
I saw a different mechanism for esterification of tertiary alcohol in a book.

They say that first the $\ce{OH}$ is protonated and it leaves to form the tertiary carbocation. Then the oxygen's lone pair from the carboxylic acid attacks to form the ester.

Is this mechanism actually correct?


texts: Can any body Suggest me a set up that I can build it up to study the surface roughness of transparent polymeric fibres?

texts: I need to study the surface of nylon-6 blank fibres with a thickness of nearly 40 micrometre, I work in optics lab with many optical components such as beam splitters, lenses, mirrors ... etc, can I build a system to study the topology of this fibre?


texts: In an SN1 reaction, 1-bromohexane reacts with NaOH, but would the Na or H be the nucleophile that substitutes the Bromine?

texts: The answer says that the Bromine would be replaced with OH and NaBr would be formed, along with CH3(CH2)4CH2OH, but why? Does it have to do with stability? And if so, how does the OH replacing Br make the product more stable? Thanks.


texts: Why are the ethyl ester methylene protons not diastereotopic in ethyl (+-)-2-methylbutyrate?

texts: In the following compound, there is one chiral center and two methylene groups.  Why are the protons on the ethyl ester methylene not diastereotopic?


texts: How, chemically, would you remove protruding phenyl groups? I mean for instance in the molecule phenethylamine there's a phenyl group sticking out (or protruding) how would you go about removing this phenyl group?


texts: Why green leaf turns brown in Brine solution?

texts: I immersed a semi dry green leaf in glass of concentrated NaCl solution . I left it in mild sunlight for around 3 hours . Solution before was clear but afterwards it became reddish brown and the color of leaf turned brown. I want to know why this happened? Please help.


texts:
The kinetic theory says that temperature is the measure of the average kinetic energy. That would mean then: The temperature rises with the rise in kinetic energy. We know that when matter changes state 'latent heat' helps in 'breaking the bonds' at the transition phase and that this 'extra heat' is not noticed on a thermometer. But energy can neither be made nor destroyed. Taking that into consideration latent heat has to convert into some form of energy. Since temperature is not rising, it's not kinetic energy it's getting converted to. What energy does it get converted to?

Note: I already know why the temperature does not change.
What I want to know is what the latent heat energy gets converted to.


texts: Which coloring agents are responsible for the color in red tea and yellow tea?

texts: Have this question in a biochemistry course, can't seem to find it anywhere. Anyone happen to know an alkaloid or something else involved? Thanks a lot!


texts: Ambiguous oxidation state of phosphorus in phosphorous acid

texts:
I was doing a question in which we were required to find the oxidation state of $\ce{H3PO3}$. I knew the structure that is:

Now, phosphorus being less electronegative than oxygen gets $+2,+1,+1$ charge from respective oxygens. Now we see that in case of hydrogen, it is taught that phosphorus being more electronegative than hydrogen thus it gets $-1$ charge from it, and finally adding all the charges we get Oxidation state of Phosphorus $=+3$.
Now my doubt is that I found on the internet that hydrogen is more electronegative than phosphorus that is, electronegativity of hydrogen$=2.2$ whereas electronegativity of phosphorus$= 2.19$.
Therefore, phosphorus must get $+1$ from hydrogen thus oxidation state of phosphorus $=+5$ but I know this is wrong and the probable reason I could figure out is that hydrogen is more stable in $+1$ form. Therefore, oxidation state of phosphorus is $-1$.
Please tell me if this reason is correct or please add to it.


texts: Extraction Techniques for Organic Compounds from Aqueous Media

texts:
I am looking to attempt an extraction of an organic compound that had just been prepared using a Friedel-Crafts acylation. The compound was prepared in MDC (~20 mL in total). After the reaction, the organic compound was poured into ~20 mL of ice-cold distilled water. The protocol I am referring to states

  "The reaction mass was cooled and water was added slowly under stirring condition. Product was extracted in MDC (12 X 2) and washed with water followed by treating with saturated sodium chloride solution (20 mL) ... "

I don't want to make any inferences as to what this means since I am new to synthetic lab work, but my guess is that it means 2 portions of 12 mL of MDC were used to separate the compound from the aqueous phase. I am not sure why they follow this by washing with water unless I am interpreting what "Extracted in MDC (12 X 2)" means. Similar sections in the paper include a little more detail that confirms my original speculations regarding what is meant by (12 X 2), but it still does not make sense to me why this would be followed by washing with water and not skip immediately to washing with a saturated NaCl solution. Here is the DOI to the paper: https://doi.org/10.1016/j.bmc.2018.05.016. The section I am looking at is 2.1.4.


texts: What's the difference between perfect and ideal gas?

texts:
There are all kinds of different dinstinctions in the internet, and I'd like to see what you guys thought.

Actually, I've been asked if the heat capacity of an ideal gas es independent of temperature. I've said no, even though it's practically invariant under small ranges.

Namely the result $C_V/n = \frac{3}{2}R$ is derived from a perfect gas and not an ideal gas and is only an approximation to the latter.

Is this true?

What really is an ideal gas? What's its difference with a perfect gas? Is my answer to the question I was posed correct?

Thanks.


texts: Rate of electrophilic bromination in aromatic nucleus

texts:
In Clayden,  the increased rate of electrophillic aromatic substitution is explained  by the stabilization of the intermediate through sigma conjugation. In Solomon & Frhyle, the same is explained through inductive effects.

Both  the factors  oppose each other in the following compounds: toluene, ethylbenzene, isopropylbenzene, and t-butylbenzene, respectively.

My question:

  What should be the order of electrophillic aromatic substitution for the above molecules ?


texts: How is Cu(OH)2 a base if it can't dissolve in water?

texts:
As the title says, how is $\ce{Cu(OH)2}$ a base if it can't dissolve in water?

I mean if it can't dissolve in water then it won't produce any $\ce{OH-}$ ions.

And if it won't produce any $\ce{OH-}$ ions then how can it be called a base?

Same question for $\ce{Fe(OH)2}$ and every other base which is not an alkali.

I feel like this question is quite obvious and don't know how to describe it more. So please help.


texts: Can functional groups exist by themselves

texts: Just started to study organic compounds and I am curious about functional groups. I want to know if functional groups can exist as molecules themselves.


texts:
I stumbled upon an interesting organic chemistry problem:

Previously I thought $\ce{AlCl3}$ would only be used with benzene in acylation and alkylation, but apparently it can also be used in reactions with alkenes. Because of this, I am wondering what the product of the reaction above will be. My first thought was that there is an addition of $\ce{HCl}$ to the alkene and then the $\ce{AlCl3}$ would react in some way, though this is very likely incorrect. This left me wondering what the role of $\ce{AlCl3}$ is in this particular reaction and whether the $\ce{HCl}$ is just a catalyst.


texts:
Do dendrites effect lithium-ion polymer batteries?

I recently came across this video which shows dendrites at a microscopic level durring the charge and discharge cycles of a standard Li-Ion battery.

I have come to understand that the primary difference between Li-Ion and Li-Poly batteries is the electrolyte used between electrodes - Li-Ion using a liquid electrode, and Li-Poly using some type of polymer chain.

  Do dendrites form across the polymer the same as the do through a liquid electrolyte?


texts: Is 98%+ purity Reagent Grade Ca-EDTA powder as safe to use as USP Grade in the body?

texts: Is $98\%+$ purity reagent grade $\ce{Ca}$-EDTA powder as safe to use as USP grade in the body?  Or, does the reagent grade have unsafe impurities that USP grade would not have even though they are the same purity?


texts:
In my biochemistry laboratory class, I designed an experiment to study the effect of a His-tag on enzyme activity. First, I measured the activity of the His-tagged enzyme. Then, I cut off the His-tag (using enterokinase) and measured the activity again.
After data analysis, I was able to calculate the $K_\mathrm{M}$ values and $k_\mathrm{cat}$ values for both enzymes. How should I interpret the data? I hypothesize that the His-tag could interfere with kinetics. But, how do I use the data to show this? Should I compare $K_\mathrm{M}$ values or $k_\mathrm{cat}$ values?


texts: Order of boiling point of group 14 halides

texts:
Find out the species having lowest boiling point:
(A) $\ce{SnCl4}$
(B) $\ce{GeCl4}$
(C) $\ce{SiCl4}$
(D) $\ce{CCl4}$

I have considered the inert pair effect of $\ce{Sn}$ here which will make the compound $\ce{SnCl4}$ least stable (and perhaps the one with lowest b.p.) and hence came up with the answer being option A. But, when I checked the answer, it was option C.
Why was my assumption incorrect and what should be the way of approach here?


texts: Why is the standard enthalpy of formation of elements in their native forms zero?

texts:
Why is the standard enthalpy of formation of $\ce{O2}$ and other reference forms of elements equal to zero?

Well, from what I know, bonding releases energy.

Also, does anybody know a source for finding the reference form of an element at standard conditions?


texts: Effective nuclear charge and Ionization energy

texts:
A common reason given on why 3rd ionization energy > 2nd > 1st is because of increasing effective nuclear charge.

As per my book $Z_\mathrm{eff}$ = Atomic number $-$ Number of inner electrons.

Now let us consider a Carbon atom. C has an Electronic configuration of $\ce{[He] 2s^2 2p^2}$ or $2,4$

Right now the effective nuclear charge is $6 - 2 = 4$

Now if we remove the first electron the first ionization energy will be $=\pu{1086.45 kJ/mol}$

After doing this effective nuclear chrarge is still $6 - 2 = 4$

Now if we remove the second electron the second ionization energy will be $=\pu{2352.62 kJ/mol}$

If the effective nuclear charge in removal of 1st and 2nd electron is same then why is 2nd ionization energy > 1st.

note : these values are taken from here


texts: Calculate specific heat of a substance given other information

texts:
What is the specific heat of a $\pu{20 g}$ substance that releases $\pu{979 J}$ of heat when changing from $\pu{70 ^\circ C}$ to $\pu{20 ^\circ C}$?

I started out with the following equation: $c = \frac{Q}{m\Delta T}$ and $Q = 979\ \mathrm{J}$ and $m = 20\ \mathrm{g}$ and $\Delta T = 45\ \mathrm{^\circ C}$.

My final answer was $2202.75\ \mathrm{J}$

Did I use the right equations?


texts: Lab safety - Long vs. Short Sleeves on Lab Coats

texts:
I have three lab coats, two with long sleeves, and one with short sleeves.
I saw that the concepts about lab safety vary from country to country; in some places it looks like the short-sleeve coat aren't allowed or they tell you to avoid it.

I'm a little confused about it: When should I use long-sleeves and when should  I use the short-sleeve coat?

Are the short-sleeves really wrong in a chem lab?


texts: Chemical bonding based on hybridisation model

texts:
A snippet from a textbook:

  Therefore, the hybridization model predicts that an $\mathrm{sp}$-hybridized carbon atom is more electronegative than an $\mathrm{sp}^3$-hybridized carbon atom. Evidence for this effect is that the positive end of the dipole moment in $\ce{N#C-Cl}$ is on the $\ce{Cl}$ atom. We conclude that the carbon atom in the cyanide group is more electronegative than a chlorine atom.

The paragraph suggests that the $\ce{N#C}$ bond has a different hybrid orbital compared to the $\ce{C-Cl}$ bond, doesn't it? I am a bit confused since there is only $1~\ce{C}$ atom but somehow it has $2$ hybrid orbitals of different state (namely $\mathrm{sp}^3$ and $\mathrm{sp}^2$). Is this due to different ligands with which the central atoms connect?

And point of interest is why the conclusion isn't

  the nitrogen atom in the cyanide group is more electronegative than a chlorine atom

instead of carbon? Because I would imagine that the electron density of both $\ce{N#C}$ and $\ce{C-Cl}$ bonds would lie dominantly on $\ce{N}$ and $\ce{Cl}$, respectively. Hence, it is more reasonable to me to compare the electronegativity of $\ce{N}$ and $\ce{Cl}$ instead that of $\ce{C}$ and $\ce{Cl}$.


texts:
In lab, I gathered everything and my partner weighed everything, I didn't realize til now that there is a problem. She measured the copper and the crucible separately, she got 0.89 g for the copper and 11.63 g for the crucible. Those two numbers combined equal 12.52 g. However, when we put the copper in the crucible it weighed 12.54 g.

Which number should I use for the calculation, 12.52 g or 12.54 g?


texts:
In the van't Hoff equation, why do we say that the change in enthalpy at standard pressure is constant? My book derives the equation for a mixture of ideal gases reacting with each other. The proof itself is good, until the authors declare that the equation says that the graph of $\ln K$ with $\frac{1}{T}$, where $K$ is the equilibrium constant and $T$ is the temperature of the mixture, will be a straight line. This would only be true if the change in enthalpy is constant (since the slope of the curve is proportional to this change). But isn't the enthalpy of an ideal gas proportional to temperature? So why is the change in enthalpy constant in $T$, then?
I've attached an example of this effect, as presented by the book. See the image below.


texts:
Actually, I'd like to compute decay rate using :

$$ \Gamma = 2\pi \ | \langle ab|V|cd \rangle|^2 \delta\ (\epsilon_f-\epsilon_i) $$

where a, b, c, d are the MOs and V is coulomb interaction, and $\epsilon_f$ and $\epsilon_i$ are final and initial energy of the system.

I am interested in computing this value regarding to a special atom (for example atom A) which means MOs should be expandes in terms of basis set:

$$ \Gamma = 2\pi \ \sum_{\mu, \nu,\lambda, \sigma \ \in A  }C_{\mu,a}\ C_{\nu,b}C_{\lambda,c}C_{\sigma,d}|\langle \mu\nu|V|\lambda \sigma \rangle|^2 \delta \ (\epsilon_{\mu}-\epsilon_{\nu}-\epsilon_{\lambda}+\epsilon_{\sigma}) $$

where $\mu, \nu, \lambda, \sigma$ are states in Gaussian basis sets, and $\epsilon$ are corresponding energies.

It seems a straightforward calculation, but I am completely confused because I don't know how I can calculate the energy of basis sets! I think the energy of the basis set is not meaningful.

Somebody, suggests using a numerical atomic orbital basis set to compute this kind of decay rate. (for numerical atomic orbital, the energy of states is meaningful) but I also don't know how to compute this kind of basis set!

Is there any suggestion to resolve this problem?


texts: What are some other gases that liquify at around the same temperature as ammonia?

texts: I am looking for gases that have a liquefication that falls within or on the edges of the liquefication range of Ammonia. I am mainly looking for gases that are comprised mainly of Carbon, Nitrogen, Oxygen, Hydrogen, Chlorine and Fluorine and liquify in a similar temperature and pressure range. This is for a worldbuilding project, but since the question is real, not theoretical, chemistry, I thought it would be better to ask about it here.


texts:
$\ce{O2}$ has a double bond in its normal form. That is $\ce{O=O}$. There are no unpaired electrons in this case are there since there are 2 lone pairs on each oxygen.

However 1 resonance structure would be $\ce{O-O}$ (result of homolytic cleavage of double bond) where each $\ce{O}$ is a free radical (a negatively charged one at that). If you have this in hydrogen it is likely going to form hydrogen peroxide.

You could also have $\ce{O-O}$ where 1 is positive and the other is negative and this is also 2 free radicals.

And finally there is $\ce{O#O}$ where both oxygens are positively charged and are free radicals. Why are both positively charged? It is because 3 bonds already to oxygen means 1 lone pair and 5 electrons around oxygen is +1.

Is it because of these resonance structures giving 2 free radicals in $\ce{O2}$ that $\ce{O2}$ is considered a biradical?


texts:
Why is SO32- sp3 hybridized even though it forms a double bond with the oxygen (in resonance)?

I thought double bonds needed a p orbital so I would think it would be sp2d so it can still have an unhybridized p orbital for the double bond. Thanks!


texts: How do thiol groups act as reducing agents?

texts:
In my biochemistry practicals, we used reducing agents such as beta mercaptoethanol:

and dithiothreitol (DTT)

Both of these have S-H groups, and I am sure that these are involved in the reduction process. However I am not sure as to how. I know that when you have two S-H groups close to one another in cysteine residues in amino acids that form a disulfide bridge, which must be oxidation because I know they are reduced in the reducing environment of the cytosol (hence are not found in cytosolic proteins, in general):

The only way I can think of that S-H groups act as reducing agents is when they form disulfide bridges between them, and an electron (and H+ ion) is released. Is this what happens? If so, it would result in two molecules of the beta mercaptoethanol becoming bonded together, and with the DTT it could either form a long chain with S-H groups between molecules reacting, or it could form rings of any size in which the end S-H groups form a disulfide bridge. I think this should result in the solution becoming viscous and 'gooey' due to the long chains and larger molecules.

Is this how S-H groups can act as reducing agents?


texts:
So, obviously the ripening of bananas involves changing it’s chemical composition. For example, ripe bananas have a much higher amount of sugar.

It is also known that reaction rates are generally increased with increasing temperature, yet bananas ripen faster in a refrigerator.

Why do bananas ripen faster in the fridge, even though it’s colder? And is there any difference (except ripening time) between ripening a banana in the fridge, and having it ripen in room temperature?


texts: How does the volume of a mole of ideal gas relate to pressure and temperature?

texts:
The volume of a mole of gas is:

$\ce{22.4 l}$
directly proportional to pressure and Kelvin temperature.
directly proportional to pressure, inversely proportional to Kelvin temperature.
inversely proportional to pressure, directly proportional to Kelvin temperature.
inversely proportional to pressure and to Kelvin temperature.

I said the answer is 3 because the ideal gas law is $PV=nRT$ and "proportional to" is the same as saying which ones are on opposite sides. So $n$ and $P$ are on opposite sides and temp is on the same side as $n$.  But I'm wrong and the answer is not 3, but I don't know why.


texts: Can a Boc protecting group be removed with trifluoroacetic acid?

texts:
I am trying to cleave a tert-butyloxycarbonyl (Boc) protecting group from an aminooxy group ($\ce{-O-NH-Boc}$) with trifluoroacetic acid (TFA) in $\ce{CH2Cl2}$ but i get minimum product and too much starting material.

I need the product to be a TFA salt and not an HCl salt so I need to use TFA. Any solutions?


texts: What makes some metals melt at higher temperature?

texts:
I'm looking at the melting temperature of metallic elements, and notice that the metals with high melting temperature are all grouped in some lower-left corner of the $\mathrm{d}$-block. If I take for example the periodic table with physical state indicated at $\pu{2165 K}$:

I see that (apart from boron and carbon) the only elements still solid at that temperature form a rather well-defined block around tungsten (which melts at $\pu{3695 K}$). So what makes this group of metals melt at such high temperature?


texts: How many significant figures should I report calculating volume concentrations?

texts:
Let's say a $\pu{300mL}$ solution of $\ce{CuCl_2}$ was diluted to $\pu{900mL}$. I am then asked to calculate the concentration of the new solution. My solution to the problem is as follows:

$$\begin{align}M_1 \times V_1 &= M_2 \times V_2\\[0.5em]
\pu{300mL} \times \pu{4M} &= M_2 \times \pu{900mL}\\[0.5em]
M_2 &= \pu{1.33M}\end{align}$$

Now I'm wondering how many significant figures my final answer should have. From what I know, I have to refer to the least significant measurement, which happens to have one significant figure. Should my answer be 1 instead?


texts:
The order of bond length of $\ce{Xe-F}$ in $\ce{XeF2}$, $\ce{XeF4}$, $\ce{XeF6}$ is?

My thoughts:

As hybridization of $\ce{Xe}$ in $\ce{XeF2}$ is $\ce{sp^3d}$, $\ce{XeF4}$ is $\ce{sp^3d^2}$, $\ce{XeF6}$ is $\ce{sp^3d^3}$.

%$\ce{s}$ decreases from $\ce{XeF2}$, $\ce{XeF4}$ to $\ce{XeF6}$, so bond length should increase, but my book says the opposite, i.e. $\ce{XeF2} > \ce{XeF4} > \ce{XeF6}$.


texts:
Is chemical energy basically stored energy?

I'm not sure how to define "chemical energy" while I know many physical formulas for energy e.g. potential, movement and other.

Is chemical energy an energy that is "conserved" and if so, why is chemical energy not just potential energy?

Additional questions:

If chemical energy is an "own" form of energy, why does it not have a specific equation?
Did we have chemical energy before the big bang or when did it start?
Can you have chemical energy at or close enough to absolute zero?
How much of the total energy in the universe is chemical energy?
What's the point of many different definitions of energy?


texts: What would chemistry seniors like to hear about industrial hygiene?

texts:
I have a master degree in physical chemistry with close to 10 years experience as a chromatographer in pharma.  About two years ago I made a career change into industrial hygiene.

Right now I am prepping to give a senior seminar talk about my professional experiences as an industrial hygienist at the college where I earned my BS in chemistry.  The talk will be half lecture and half lab - I'll be bringing in some equipment to demonstrate.

What would chemistry students be particularly interested in hearing about from someone in industry?