texts: How to sloppy freeze a dihedral angle within a range in a Gaussian modredundant optimization?

texts:
I would like to perform an optimization in Gaussian 09 of my molecule with two dihedral angles being frozen. I would like that the values of these dihedral angles are not fixed, but can relax within a range of ±5°. In Gaussian 03 it seems to be possible using Opt=ModRedundant keyword and the following syntax:

[Type] N1 [N2 [N3 [N4]]] [[+=]value] [A | F] [[min] max]]

I have tried using the same syntax in Gaussian 09, but it doesn't work. Is it possible to perform such calculation in Gaussian 09 or 16 without using the scan approach?

The calculation fails with the following error:

The following ModRedundant input section has been read:
Invalid extra data found.


texts: Can the prefixes like iso,neo be used in the IUPAC nomenclature of organic compounds and can all the common names of aromatic compounds be used in their IUPAC name?


texts: Writing the chemical equation given molarity

texts:
If I am given the molarity of two substances and I know how they react, how can I write the balanced chemical reaction? i.e. experimentally I found:

$\pu{1.0 M}$ $\ce{NH_3(aq)}$ mixed with $\pu{0.1 M}$ $\ce{BaCl_2(aq)}$  yielded no precipitate when $\pu{1ml}$ of each were mixed together. My unbalanced chemical equation so far looks like:

$$\ce{N^{-3}H3+(aq) + (1/10)Ba^{+2}Cl2-(aq) -> N^{-3}Ba^{+2} + Cl^{-2}H+}$$

My logic being: since the solutions are administered in equal volumes, their molarity determines the molar coefficients. Right off the bat I can tell that $\ce{NH}$ is not soluble, but the other compound I think is, which would contradict my observations. Either way, I am incredibly lost.


texts: Crystal field splitting pattern with strong field and weak field ligands

texts: What will be crystal field splitting pattern for octahedral complexes if some of the ligands are strong and some are weak field ligands?


texts: Converting Disolved Oxygen from micromole/L to millimole/kg

texts:
I have dissolved oxygen data that is in units of µmol/liter.

I need to convert it to mmol/kilogram.

I have been told by someone who knows more about chemistry than I do (but only a little bit more) that I need to know the mass of my sample as well (which I don't know).

So only knowing my original DO data (in µmol/L) and the density of SW (assume 1.027 g/cm³), how does one convert the data to mmol/kg?


texts: Equilibrium constant Kp for vaporization of water?

texts: For the reaction H2O(l) -->H2O(g) it is given that Kp = p(H₂O(g))/p° where p° is the atmospheric pressure. Why is it not just equal to p(H₂O(g))?


texts: What is the minimum number of given sets of information required to complete an ICE chart for an equilibrium reaction?

texts:
I'm considering creating a program that automatically completes an ICE chart/table when the minimum given information is provided. The reason I'm posting my question here is because I need to know the possible cases of minimum information required before I can even start the program.
I know you can complete the table if you're given these following sets of information:

K and initial concentrations
K and final concentrations
K and initial concentrations of reactants and final concentrations of products

I also believe there are a ton more, but I'm not sure how to complete the list.


texts: Determining solubility of silver sulfate in its saturated solution

texts:
Question:

  Calculate the molar sulfate concentration in a solution that is $0.200$ M in $\ce{Ag+}$ and saturated with $\ce{Ag2SO4}$.

My attempt:

Looking through old notes and googling lead me to this webpage. Example #2 looked similar to my problem, and my notes from general chemistry involved something called an ICE table to deal with stoichiometry and concentrations of ions. This is what I did:

Write the dissociation equation  $\ce{Ag2SO4 + <=> 2Ag+ + SO4^2-}$
Write the solubility constant formula $$K_\mathrm{sp} = \frac{\text{products}}{\text{reactants}}$$

I was given the value of $K_\mathrm{sp}$ as $1.6 \times 10^{-5}$ and I assume these values are listed in an appendix in my text or online.

Also $\ce{Ag2SO4}$ is supposed to be a solid, I think? Because the question states the solution is "saturated" with $\ce{Ag2SO4}$ and does "saturation" not imply that the $\ce{Ag2SO4}$ is going in and out of solution as a solid and as an ion? And therefore since it is a solid we do not consider it for the equation (not sure why, but this is similar to what I have in my notes)?

$$1.6 \times 10^{-5} = \text{products}$$

$$1.6 \times 10^{-5} = \ce{[Ag+]^2 * [SO4^2- ]}$$

Here is an image if that is acceptable of the ICE table I used (note: $\text{I+C=E}$).

$$\begin{array}{|c|c|c|}\hline
&\ce{Ag+}&\ce{SO4^2-}\\\hline
\text{I}&\pu{0.200M}&x\\\hline
\text{C}&\frac x2&0\\\hline
\text{E}&\pu{0.200M}+\frac x2&x\\\hline
\end{array}$$

Now I substitute the values I obtained for concentrations from the ICE table into my formula:

$$1.6 \times 10^{-5} = [0.200~\text{M} + \frac{1}{2}x]^2 \times [x]$$

Now since $K_\mathrm{sp}$ is less than $1 \times 10^{-5}$ we can ignore the $\frac{1}{2}x$? I guess because it is very small and therefore negligible?

$$1.6 \times 10^{-5} = [0.200~\text{M}]^2 \times [x]$$

$$ \frac{1.6 \times 10^{-5}}{[0.200~\text{M}]^2}  = x = 0.0004$$

$$ x = 4.0 \times 10^{-4}~\text{M}$$

Therefore the concentration of $\ce{SO4^2-}$ is $ 4.0 \times 10^{-4}~\text{M}$?


texts: Can the oxidation of hydrogen peroxide be reversed?

texts:
Hydrogen peroxide is said to be unstable, for it undergoes auto-oxidation on standing/heating:

$$\ce{2H_2O_2 -> 2H_2O + O_2}$$

where $\Delta S=\pu{70.5 J {mol}^{-1}K^{-1}}$ and $\Delta H^{\Theta} = \pu{-98.2 kJ {mol}^{-1}}$.

I speculate if the decomposition can be reversed in some way under suitable conditions, particularly at infinite pressure and near absolute zero temperature. At once this seems to be a problem of entropy reversal. But I seek a more rigorous treatment of the problem with the help of quantum theory. Consider the molecular wavefunctions $\Psi_{1A}$ , $\Psi_{1B}$ of water (2 molecules) and
$\Psi_2$ of dioxygen respectively. By studying the interaction potentials of these three wavefunctions as a function of different thermodynamic coordinates, it can be possible to find the desired suitable conditions.

However, the problem begins here – this is not a case of just two molecules where we have a number of methods of analysing the system, I am talking about three molecules, so the calculation is not simple. Moreover, I doubt if I need to study the wavefunction of hydrogen peroxide too in some respect. Overall, I am lacking some theoretical and computational knowledge. Any help is greatly appreciated.


texts: Significance of this unusual matrix element

texts:
Recently, I was solving some questions on Rigid Rotor. I found this question very amusing.

Evaluate the integral

i) <$Y_{l,m+2}$ | $L_{x}^{2}$ | $Y_{l,m}$ >

I evaluated it, found that the value is

$$\hbar^2/4 \sqrt{[(l(l+1)-(m)(m+1)][(l(l+1)-(m+2)(m+1)]}$$

But I didn't get the point of evaluating it. Is there any application of such kind of integrals?
Is there any physical significance of it?
I know similar kind of integral are evaluated in case of transition dipole integral  where we take two different wave function.
What is actual significance of such operations ?


texts: Place cooling bath apparatus in freezer to speed up the process?

texts:
As part of an at-home lab, my chemistry class is creating cooling baths to measure the freezing point of different solutions. We have to determine the molar mass of the solutes in these solutions by observing the freezing point. The cooling bath is constructed from ice and salt inside a 500 mL beaker, into which are placed test tubes of solutions (one at a time). A thermometer sticking out of the test tube hypothetically measures the freezing point. The problem is that the ice bath is taking hours to freeze the solution.
To speed up this process, can I just stick the whole apparatus in the freezer and check it every 10 minutes or so to see the temperature at which the solutions freeze?
Will the freezing point of salt water and calcium chloride water (the solutions in question) be radically different if frozen in an ice bath vs. frozen inside a kitchen freezer?


texts:
Changes in which factors affect both the rate and the rate
  constant of a first order reaction?

  I. temperature

  II. concentration

  (A) I only (B) II only
  (C) Both I and II (D) Neither I nor II

I would think that the answer would be (C), both temperature and concentration.

Concentration would obviously affect it (from the rate expression), and the temperature would also affect it because the Arrhenius equation for the rate constant is $$
k = A e^{-E_a/(R T)}
$$

and thus temperature would have an influence on the rate constant, and since the rate constant is part of the rate equation, it would also affect the rate of the reaction itself.

However, the given answer is

  A

I don't understand why this is.


texts: Is the attached compound a chiral or achiral overall? My lecturer said that this is an achiral compound because it has a superposable mirror image but I don't get that. So I tried to figure out the configuration of both stereogenic centers because what I understood is when you have an even number of chiral centers and if they have opposite configuration, say (R,S) or (S,R), they will cancel out each other so that specific rotation is zero and two chiral centers are overall achiral, which gives you a meso compound.


texts:
I recently came across this reaction in my undergraduate labs. The experiment is taken from this article: J. Chem. Educ., 2008, 85, 413.

The condensation of 2-methoxynaphthalene with cinnamoyl chloride leads to the formation of 9-hydroxyphenalenone:

I think it's fairly clear that the first step is a Friedel-Crafts acylation. Subsequently to form the new C-C bond, there must be a Michael addition of some sort; however this would imply that the phenyl group leaves as "$\ce{Ph-}$". There are two things I'm not very sure about:

How does the phenyl group even leave?
How does the oxygen get demethylated? I am guessing that the mechanism should be similar to that with $\ce{BBr3}$, i.e. coordination of oxygen to the Lewis acid followed by nucleophilic attack of $\ce{Cl-}$ on the methyl carbon. Would that be right?

I looked up the original synthesis, which was reported quite a long time ago, in J. Org. Chem., 1941, 6, 558. The authors write that the reaction proceeds via the intermediacy of this compound:

which suggests that the initial nucleophile in the Michael addition is not the aromatic ring but rather the -OMe (or -OH) group. Unfortunately, that just makes things more confusing.


texts: Work done by system of ideal gas in isobaric expansion

texts:
Consider a system of ideal gas in a container with piston and  the isobaric expansion of gas takes place.
As the process is isobaric, so initially the pressure of gas is equal to atmospheric pressure as the piston remains in equilibrium over the container. Then, first we increase the temperature and as a result pressure of gas increases and the piston rises till the pressure reduces to atmospheric pressure. So at initial and final state pressure of gas is constant thus the process is isobaric.
So, work done by gas should be
$dW=F_{applied\;by\;gas}(x).dx$
$dW=P_{applied\;by\;gas}(x)Adx$
$s.t.\;P_{applied\;by\;gas}(x_{initial\;state})=P_{applied\;by\;gas}(x_{final\;state})=P_{atm}$
So, total work done, $W=\int_{x_{initial}}^{x_{final}}P(x)Adx$
So, we should know pressure as a function of $x$ to calculate the work done by gas.
My question is that in books, they directly use the argument that work done by gas is dependent on $P_{external}$ and as it is constant, they give the expression of work as $dW=-P_{external}Adx$.
I don't understand how they do that and use external pressure in the expression of work done.
I think we should take into account pressure of gas as a function of $x$ to find the work done by gas.
Please help me in clarifying the doubt.


texts:
There seems to be an endless debate about using vinegar as rinse aid in dishwashers, which is explicitly allowed in some models (such as Miele, see p. 25) but usually not mentioned in user's manual. The main contra argument is that acetic acid is somehow destroying the rubber seals, leading to malfunction. On the other hand, common commercial rinse aids also contain various acids (e.g. see here, 5.7% glycolic acid). Also, I haven't heard about rubber being sensitive to acids, at least to weak ones.

Is there a specific property of acetic acid I'm not aware of that makes it aggressive to rubber?

PS. I have asked a related question here.


texts: Toxicity of Mercury (II) Iodide and dicopper (I) tetraiodomercurate (II)

texts:
This is a continuation from my previous post.
Could you please give me some info on the toxicity of compounds $\ce{HgI2}$ and $\ce{Cu2[HgI4]}$? I found on sigmaaldrich.com that these are very dangerous but could not find any information on the dosages for skin contact and swallowing.


texts:
In writing net ionic equations involving strong acids, one needs to know how strong acids dissociate. For example, the dissociation of $\ce{H2SO4}$:

\begin{align}\ce{
H2SO4 &-> 2H+ + SO4^{2-}\\
H_SO4 &-> H+ + HSO4^{-}\\
}\end{align}

The reason I ask is because apparently the molecular equation

$$\ce{H2SO4 + 2KOH -> 2H2O + K2SO4}$$

has the net-ionic form $$\ce{H+ + OH- -> H2O}$$

It would be helpful if you could describe in general how I should write the dissociation of the strong acids in the net ionic equation.


texts: How does the composition of ice differ from that of water in a partly frozen solution?

texts:
Take any solution, then start freezing it at sufficiently low temperature. Soon a small amount of ice forms. I'd like to know how the composition of dissolved salts and gases in the bit of ice differs from that in the water that's still liquid.

Assume that the solution is far from saturation and whatever other extreme conditions there can be. I don't have any particular solution in mind - it's the general principles that I'm interested in.


texts:
The answer given is an epoxide.

But is an epoxide stable at room temperature?
And also epoxides tend to open in presence of water. Even if methyl alcohol is treated as a solvent, then too methyl alcohol is more acidic than water. Then if in water we expect the alpha-bromide alcohol, then why not in methyl alcohol?


texts: compression set of tin catalyzed silicone better than platinum?

texts:
Platinum silicone is more dimensionaly stable, it shrinks less when it cures.

However, i just need silicone which has good compression set (small change by compression), and perhaps, once they are cured, platinum and tin catalyzed silicone become the same material - silicone elastomer. Perhaps that tin silicone, having shrunk, is more resistant to compression set?

Does tin silicone have better compression set? Are the highest quality o rings made from tin silicone?


texts: Spontaneity of an exothermic reaction when temperature is decreased

texts:
How is the spontaneity of an exothermic reaction changed when temperature is decreased?
Assuming the entropy is negative.

Using Gibbs free energy equation, $\Delta G=\Delta H-T\Delta S$, $\Delta G$ should become less negative as temperature is decreased meaning the reaction is less spontaneous. However, using Le Chatelier's principle, as temperature decreases the reaction should shift towards the right towards the products, becoming more spontaneous.

What's wrong here?


texts: Can a half-reaction be oxidation if it has the higher reduction potential?

texts:
I am working on a problem that provides these two half-reactions:

$$
\begin{align}
\ce{Fe^3+ (aq) + e- &-> Fe^2+ (aq)} &\quad E^\circ_\mathrm{red} &= \pu{+0.77 V}\\
\ce{S2O6^2- (aq) + 4H^+ + 2e- &-> 2H2SO3 (aq)} &\quad E^\circ_\mathrm{red} &= \pu{+0.60 V}
\end{align}
$$

What is confusing me is the way the question is worded:

  Write the balanced chemical equation for the oxidation of $\ce{Fe^2+ (aq)}$ by $\ce{S2O6^2- (aq)}$.

Isn't this backwards though? Because the $\ce{Fe}$ half reaction has the higher reduction potential, shouldn't it be reduced while the $\ce{S2O6^2- (aq)}$ half reaction reverses to become oxidation?


texts: Metal catalysts used in C-H bond functionalisation

texts:
Why are the late transition metals used for C-H bond activation/functionalisation? What atomic properties of the late TM make them attractive for coordinating C-H sigma bonds?
Thanks.


texts: Solvent for copper(I) iodide, copper(I) thiocyanate, silver iodide for HTM deposition; safety for methylammonium lead iodide

texts:
I'm a student working in a high school laboratory that is looking to pursue research into perovskite cells for next year, but I have some solubility and safety questions.

What would be a good solvent (please be specific) of copper(I) iodide?, copper(I) thiocyanate?  Silver iodide?

I want to deposit these materials out of solution onto the substrate.  Christians et al. in 2014 deposited copper(I) iodide from a 1:39 chlorobenzene/di-n-propyl sulfide solution, but my mentors have rejected chlorobenzene as a substance with high environmental toxicity and difficult disposal procedures.

Ideally, the solvent for any of the three compounds would dissolve the compound well, and then evaporate off with heating, while having no to low toxicity.

Additionally, I have received approval for purchasing methylammonium iodide and lead(II) iodide which I will dissolve in gamma-butyrolactone in 1:1 molar.  There are no safety sheets for the product, methylammonium lead iodide, so my mentors wanted me to see if there were any harmful properties that would come about from making this compound, ie: is there anything more dangerous or something more to watch for from methylammonium lead iodide than methylammonium iodide or lead(II) iodide?

Article: An Inorganic Hole Conductor for Organo-Lead Halide Perovskite Solar Cells. Improved Hole Conductivity with Copper Iodide


texts: Crystallographic terminology associated with the honeycomb structure

texts:
I'm trying to quickly learn basic crystallographic principles in 2D under pressure (it's me whose under pressure, not the lattice) so I'm checking many sources to find those that "speak to me" the best (including this excellent answer). Many sources (books, papers, researcher's websites) cite the "honeycomb lattice" as an example of a lattice which is non-Bravais in order to reinforce their explanation of what a Bravais lattice is.

some online examples where honeycomb is a "lattice" but not Bravais: slide 3 and here and slide 7
some online examples where the "lattice" designator is avoided: here and slide 20
ambiguous or noncommittal as to being a "lattice" slide 6

Briefly (I don't have the various texts with me right now to transcribe the paragraphs) it seems to me that a 2D Bravais lattice any set of points $m \vec a + n \vec b$ for all integers $m, n$.

The vertices of a honeycomb don't satisfy this because if you try to use that expression, 1/3 of the points are missing. If you want to use a Bravais lattice, you have to define a unit cell with two "atoms" in it.

Question: Can the vertices of a honeycomb or "honeycomb lattice" really be called a proper lattice (but just not a Bravais lattice), or should we really call it either a net† or a regular complex apeirogons or something else, but not refer to it as a lattice?

From http://www-personal.umich.edu/~sunkai/teaching/Winter_2018/01302018.pdf (click for full size)

†The Five nets

From Elizabeth A. Wood's classic Vocabulary of Surface Crystallography Journal of Applied Physics 35, 1306 (1964); https://doi.org/10.1063/1.1713610

  In triperiodic structures the equivalent points form
  a three-dimensional lattice in which the space units are
  unit cells. In diperiodic structures the equivalent points
  form a two-dimensional net in which the area units are
  unit meshes. The fourteen Bravais space lattices are
  replaced, in the diperiodic case, by five nets, described
  in Table I and diagrammed in Fig. 2.


texts:
I'm specifically talking about having a hydroxy- group on the ferrocene ring.

Is it simply impossible because the ring is anionic?
I haven't seen any hydroxyferrocene molecules available online. (unless they are a methanol group)


texts: Reactions which confirms the presence of cyclic structure of glucose

texts:
Are there any reactions that can be explained only on the basis of the cyclic structure of glucose rather than the open chain thus confirming its presence in the solution? Like a reaction that can only be given by hemiacetals thus confirming its presence and hence confirming the existence of the cyclic structure.

Any help would be appreciated.


texts:
This is from Laitinen and Harris, "Chemical Analysis, An Advanced Text & Reference" which describes a simple acid-base equilibrium. They derive a relation in the end directly. I haven't seen this expression in many books which teach solution equilibria. The authors cite an article from the Journal of Chemical Education for the expressions (4 & 5). I didn't find article very useful. How should we derive the equations 4 and 5 in a better way than the author's explanation in italics?

The authors start from very simple equations:

  $\ce{HA + H2O <=> H3O^+ + A-}\tag{1}$

  Conventionally,

  $\ce{HA <=> H+ + A^-}\tag{2}$

  and the ionization of water,
  $\ce{H2O <=> H+ + OH-}\tag{3}$

  If $C_{HA}$ and $C_{A^-}$ are the analytical concentrations of $\ce{HA}$ and $\ce{A^-}$, and if $\ce{[HA]}$ and $\ce{[A^-]}$ are the equilibrium concentrations, the relations...

  $\ce{[HA]} = C_{HA} - \ce{([H^+] - [OH^-])}\tag{4}$

  $\ce{[A^-]} = C_{A^-} + \ce{([H^+] - [OH^-])}\tag{5}$

The authors explain ...

"result because the analytical concentration of HA is diminished by the amount of hydrogen ion produced in Reaction (2), which in turn is the total hydrogen ion concentration minus the hydroxyl ion concentration."


texts: The oxidation of aldehydes and alpha-diketones with peroxy compounds

texts:
Recently, I have been reading up on the Baeyer-Villiger (BV) oxidation. The oxidation is most commonly discussed for ketones. However, the oxidation also works for aldehydes and $\alpha$-diketones (Rojas, 2015).

The above image is Scheme 2.2 from Rojas (2015).

I have mainly two queries:

Does the oxidation of aldehydes to carboxylic acids by peroxy compounds, such as peracids, proceed via a BV oxidation where the hydride is the migrating group? This would be seemingly different from the oxidation mechanism for the oxidation by $\ce {MnO4^-}$ or $\ce {CrO3}$ where the aldehyde is oxidised when it is in the gem-diol form.
Why does the oxidation of $\alpha$-diketones yield the corresponding anhydride and not an $\alpha$-ketoester? This is extremely puzzling because the acyl group is terribly bad at stabilising any partial positive charges on the acyl carbon. How is it possible that such a BV oxidation can occur?

Reference

Rojas, C. M. (2015). Molecular Rearrangements in Organic Synthesis (1st ed.). Hoboken, New Jersey: John Wiley & Sons, Inc.


texts: Why is the Standard Entropy of a Proton Zero?

texts: It was my assumption that the standard entropy was the absolute entropy of a substance at standard state; however, my textbook states various standard entropies ranging from $-144.77\ \mathrm{J/(mol\ K)}$ for $\ce{Al^3+}$ to $0\ \mathrm{J/(mol\ K)}$ for $\ce{H+}$ to $213\ \mathrm{J/(mol\ K)}$ for $\ce{CO2}$. It is clear that these values are not absolute entropies, as the only substance that can have an absolute entropy of $0$ is a perfect crystal at $0\ \mathrm K$ according to the third law of thermodynamics. Why are standard entropies notated like this instead of just stating their absolute form? My assumption is that this is just a way to make calculations involving entropy easier, since they merely involve changes in standard entropies; however, why is the standard entropy still notated $S^\circ$ and not instead $\Delta S^\circ$ (since it is not absolute)?


texts: What is the name of the "primary" carbon in a benzene derivative?

texts: If we have a benzene with a single substituent, such as chlorobenzene, what do we call the carbon atom to which the group is attached? I'm familiar with the ortho- meta- para- nomenclature, but the last one escapes me.


texts: Can someone help me understand the motivation behind and visualize the dihedral potential and the Urey-Bradley potential?

texts:
I am studying statistical mechanics and force-fields, and I see a lot of this formula being thrown around with no explanation:
$$U_{\mathrm{dihedral}} = \begin{cases}
       k(1+\cos (n\psi + \phi)),&  n>0 \\
      k(\psi - \phi)^2, & n=0 \\
   \end{cases} $$
The only explanation I read is: this is a 4-body torsion angle (known as the dihedral angle) potential, which embodies the potential due to the angular spring between the planes formed by the first 3 atoms, and the other 3 atoms. $\psi$ is the angle between the planes, and $\phi$ is the phase shift angle, while $k$ is a multiplicative constant.
Could anyone please provide a visualization for this? and why should there be a $\cos$ term in the potential? Why is there an $n$ in the mix? Looks an awful lot like an eigenvalue of sorts.
Same applies for the Urey-Bradley potential. But I want to understand why such a potential was introduced in the first place. The 3-body potential described angular vibrational motion:
$$U_{UB} = k(\theta - \theta_0)^2 + k_{ub}(r_{ik} - r_{ub})^2$$
where $\theta$ is the angle between $r_{ij}$ and $r_{jk}$, and the second term is for the covalent spring bond between atoms $i$ and $k$. I don't understand - if these atoms are not bonded, why cook up a new bond?


texts: Why is ΔE described as Q-W and Q+W in different contexts?

texts: Depending on the textbooks looked at, the energy change is described as either Q+W or the signage is changed to Q-W. Which is correct? Is it solely context dependent? Could anyone explain the background?


texts: Why don't minerals evaporate from seawater along with the water?

texts: When water evaporates from the ocean, of course the minerals such as salt remain in the ocean-- that's why seawater is so saline. However, I'm very puzzled: why don't minerals evaporate along with the water? Could you give me a somewhat simple answer for this? (I never studied chemistry, so I really have no clues as to the possible answer.)


texts: Major product of the reaction of m-hydroxyphenol in boiling aq NaHCO3

texts:
The reaction: (a) m-hydroxyphenol + aq. $\ce{NaHCO3}$/boil; (b) workup with $\ce{H3O+/H2O}$

I know that $\ce{CO2}$ will be formed by boiling aq. $\ce{NaHCO3}$, and so the reaction will be like Kolbe-Schmitt type, i.e. $\ce{COOH}$ group will be attached on the benzene ring.

But I have a doubt that where will the addition of $\ce{COOH}$ group take place,

  (1) ortho-position w.r.t. both hydroxy groups
  $$\text{or}$$

  (2) ortho-position w.r.t. one hydroxy group and para-position w.r.t. the other group.

So, Which will be the major product and why?


texts: Open Source tools to draw a set of 2d molecular graphs from sdf file

texts: I have a sdf file for around 50 small-molecules for which I am doing structure-activity study. I would like to draw 2d graphs of all the molecules such that the image would fit into a single journal page. For example, in this paper, page number 3, they have listed 2d molecular structure. I have attached the image file from the same paper. I have software tools like MarvinSketch which give me 2d or 3d graph for a given sdf file. But I want the integrated image like shown below suitable for publication.


texts: What makes the enthalpy of hydration of calcium chloride dihydrate unique?

texts:
I have recently done an experiment in an attempt to find the relationship between the water ratio in a hydrate and the enthalpy of hydration, and my results showed a correlation, but an anomaly for calcium chloride. My results were:
Sodium carbonate monohydrate: 10.03 kJ
Calcium chloride dihydrate: -19.51 kJ
Sodium acetate trihydrate: 28.98 kJ
Sodium thiosulfate pentahydrate: 47.37 kJ
Sodium sulfate decahydrate: 66.32 kJ

I have tried researching about what makes calcium chloride dihydrate unique, but I can't seem to find anything. And this is not a random error, as each of these salt compounds had 3 trials each, with consistent results.


texts: Crystmet or alternative metals/alloys/intermetallics powder diffraction database

texts:
Does anyone know what happened to Crystmet, the metals structure database? The website seems to have disappeared.
Is there any way to access the database or is there a recommended powder diffraction database for metals/alloys/intermetallics that goes beyond PDF or ICDD? I would like to have access to CIF files for relatively uncommon non-stoichiometric intermetallics.


texts:
What can I predict about the $\ce{^{31}P}$ spectra of $\ce{TiP2O7}$?
To get the required information about the crystal structure of the compound

Here is a screenshot from the ICSD website:

Since there is only one oxidation state (+5) for $\ce{P}$, there will be only one peak. And from the Wyckoff symbol, 4c, the intensity of the signal is 4, i.e. 4 $\ce{P}$ atoms in the unit cell.
I can't go any further to complete the task and extract all the relevant information. I'm using SIMPSON software to simulate the spectra. Can somebody walk me step by step through this?


texts: Show the mechanism of the Pinacol-Pinacolone Rearrangement reaction

texts:
In the reactant, due to $\ce{H+}$ ion, a positive charge will be created by removing water in place of the rightmost $-\ce{OH}$.
But then how will it give such a product. I cant see any way to make the cyclic pentane first.
There would be a Pinacol-Pinacolone Rearrangement but how ?


texts: Oxidation number of hydrogen in compounds

texts: In a given compound that contains three elements (e.g. a metal, a non-metal, and hydrogen), how can it be determined whether hydrogen is connected to the metal or the non-metal so that its oxidation number can be assigned accordingly?


texts: Does almond extract made from bitter almonds contain any cyanide?

texts:
NOTE: This question is not seeking medical advice. I am just trying to understand the chemistry behind why bitter almonds are poisonous but bitter almond extract (presumably) isn't.

A friend made pancakes and decided to add flavor by adding almond extract, the ingredients of which were "water, organic alcohol, glycerin, natural bitter almond oil". She added about a teaspoon.

Later she was feeling very nauseated and had a stomach ache. After a couple hours, the nausea went away followed by the stomach ache. Other people in the house ate the same pancakes and she was the only one who got sick. (And there similarly wasn't evidence that it could be food poisoning from the night before since she ate the same as others.)

(She does have an allergy to sunflower seeds and certain nuts, but she has no problem eating regular sweet almonds.)

I read that eating a small number (like 10) of bitter almonds can be fatal because of the cyanide. Does almond extract made from bitter almonds contain any cyanide, and could this be related to her getting sick? I tried to Google it and found lots of info about bitter almonds being dangerous, but nothing that mentioned problems eating a lot of almond extract.


texts: Quantum mechanical (or QFT) description of mesomeric effect

texts:
This is rather a question about finding the right literature, since the answer would probably exceed a typical forum post.

In organic reactions, mesomeric and inductive effects are of tremendous importance for the prediction of reactivity. I can work with Lewis structures and electronegativity, but I still wonder if there are more accurate descriptions arguing in terms of symmetries of the potential that is generated by the nuclei; how it allows for different coexisting standing waves; and that also consider 3D geometry dependences of the inductive effect.

Most texts argue in terms of atomic orbitals that are somehow bent and combined and hybridized, but electrons don't have a memory so they don't mourn after the times when they belonged to single atoms. Is there any readable description that looks at the whole molecule from the start, possibly written by physicists? Or is this just a thing for computers?

I searched the local university library and google scholar, to no avail. I have Clayden and Anslyn/Dougherty, but those don't really answer this question.


texts: Units of the rate constant for reactions whose order is greater than 1

texts:
In many textbooks, it is written that:

  The value of rate constant depends on the nature of the reactants, temperature and catalyst. It is independent of the concentration of the reactants.

However, the unit of the rate constant is

$$\left(\frac{\mathrm{mol}}{\mathrm{l}}\right)^{1-n} \mathrm{s}^{-1}$$

where $n$ is the order of reaction.

Therefore, except for first order reactions, the unit of the rate constant will have a concentration term $\displaystyle\frac{\textrm{mol}}{\textrm{l}}$ for all other reactions. Does this contradict the statement given in books?


texts: Is there a phase diagram available for hydrogen fluoride?

texts:
Has a phase diagram for hydrogen fluoride been published in an article on the internet or in a book ?

Or is there a table for HF for different pressures up to 100 atm. and temperatures up to 500$⁰$ C ?

Or, even better, is there a calculator for HF, like this one for steam ?


texts: The electron configuration and electron density distribution in singlet oxygen

texts:
The molecular orbital schemes for singlet ($\mathrm{^1\Delta_g}$) and triplet oxygen ($\mathrm{^3\Sigma_g^-}$) are typically given as shown in the image below.

Figure 1: Molecular orbital schemes of two types of singlet oxygen and triplet oxygen with the highest energy electrons highlighted in red.

It is pretty clear that the dioxygen molecule, if just observing the position of the nuclei, must be $D_\mathrm{\infty h}$ symmetric. This implies that both $\unicode{x3c0}^*$ bonds are symmetry equivalent. Therefore, it seems logical that in the $\mathrm{^3\Sigma_g^-}$ triplet state the two orthogonal $\unicode{x3c0}^*$ bonds are each populated by a single electron, leading to an overall rotation-symmetric linear molecule.

In the $\mathrm{^1\Delta_g}$ singlet state, this degeneracy seems to be destroyed, just by looking at the MO scheme. We now seem to have one populated $\unicode{x3c0}^*$ orbital and one unpopulated one, going by my understanding of this scheme.

What does this imply for the electron density distribution of $\mathrm{^1\Delta_g}$ singlet oxygen? Is it valid to assume that two (arbitrary) opposite sides have a higher electron density than the two other orthogonal sides? How can this be interpreted?


texts: Will a Galileo's Thermometer containing liquid paraffin explode in my car if the temperature is above 35 degrees Celsius?

texts: I'm driving from Sydney to Melbourne (approximately 12 hours trip) and I'm wondering if it's safe to have this Galileo's Thermometer in my car during the trip if it's going to be a scorcher of a day. It could easily reach 35 degrees Celsius or over during the trip. I'm a little worried that it might explode. Any help much appreciated!


texts:
I had about 5 ug DNA suspended in water, which I dried thoroughly in a vacufuge.

I obtained a whitish crystal (very similar to table salt, although the structure seems uneven and it's hard to tell) at the bottom of my wells, apparently of about 30 ul volume (I am not counting the dead space in between bits of crystals).

Is this crystal DNA? Or is it some sort of salt that was bound to the DNA? It was my understanding that DNA is very hard to precipitate without using ethanol (I didn't) but it seems I precipitated something anyway.

The DNA came from a prep (a Qiagen kit), so it's highly pure - the A260-A280 ratio is about 1.8.


texts: What makes oceanic desalination so expensive?

texts: What specifically makes oceanic desalination so expensive?


texts: We use ordinary spirit to polish wood, and it contains ethanol. What makes ethanol a good polishing agent for wood? What effect does it causes on wood so that it shines?


texts:
Is a pH value outside 0 - 14 possible?
I asked my teacher who said: yes, it is, but very difficult to achieve.

Then on the internet, I found multiple answers, one saying it is but because of a fault in the pH glass meter we can't be sure, the other said that it is not possible because of the intrinsic value of water to ionize.
As you can see, I'm getting mixed answers from different sources and I'm really confused now. Could somebody here give a concise answer whether or not it is possible? A deep argument will be valuable.


texts: Calculating amount of alkali additions to get desired pH in (hard) cider

texts:
This is linked to my question over on the HomeBrew SE site: https://homebrew.stackexchange.com/questions/18837/reduce-acidity-of-hard-cider

I haven't done chemistry since I was 17/18 but I remember doing molar calculations and so on, and the principle of OH ions binding with H ions to reduce acidity. I would prefer a more scientific method than trial and error.

Given an initial pH, desired pH and volume of liquid, how can I calculate the mass of a given salt to add... and is it as simple as that or are there more 'parameters' needed to generate some equations?

The salts I am likely to consider using are:

sodium bicarbonate (sodium hydrogen carbonate?)
magnesium carbonate
calcium carbonate
potassium carbonate

Is it as simple as working out how many moles of OH each of these contains per gram, and plugging that into a pH equation?


texts:
How I could find the bulk Debye–Waller factor for tetragonal rutile type $\ce{SnO2}$ at room temperature?
I have been doing some online digging with no luck. If anyone has a reference I could use that would be awesome.


texts: Validation of _atom_site_frac_*: Range outside of [0,1)?


texts: Propose the mechanism of a hypothetical reaction

texts:
I was given a hypothetical reaction $\ce{A + 2B + 4C -> 2D + E}$ for which I have to propose the possible mechanism with a requirement, that the third step is rate determining.

From the other given inputs I determined that the rate law for this reaction will be $\ce{B + 2C}$.

I came up with a number of "possible" reaction steps, all of which seem to me equally unrealistic. Examples:

A +  B -> X
C +  X -> Y
B + 2C -> 2D + Z
C +  Z +  Y -> E

This does not make sense to me as $\ce{C}$ reacts with $\ce{X}$, $\ce{B}$ and with the product of its reaction with $\ce{B}$.

A +  B -> X
C +  X -> 2D + Y
B + 2C -> Z
C +  Z +  Y -> E

Same problem here, $\ce{C}$ reacts with just about everything.

A +  B -> 2D + X
C +  X -> Y
B + 2C -> Z
C +  Z +  Y -> E

Needless to say I am skipping the variation where the last step uses 3 reactants and produces 2 products, as it's obviously introduces another multi-step reaction:

A +  B -> X
C +  X -> Y
B + 2C -> Z
C +  Z +  Y -> 2D + E

Of course there can be 4 variants of each of the above approaches, achieved by simply combining the variables in a different order.

The above considerations do not seem to be bothering the author of the course. For the hypothetical reaction $\ce{2A + 3B + 5C -> 2D}$ they consider the following the correct answer:

2A + B -> W
2C + W -> D + X
B + 2C -> Y
C +  X -> Z
B +  Y + Z -> D

Here $\ce{C}$ reacts with $\ce{B}$ and the product of its own reaction with $\ce{W}$. I do not understand how it is possible to come up with a "realistic" mechanism of a reaction where the specific substances are unknown.

I tries google and found a number of videos explaining reaction mechanisms on the example of $\ce{NO2 + CO -> NO + CO2}$. In those videos they propose a mechanism, where $\ce{NO2}$ reacts with itself to form $\ce{NO}$ and $\ce{NO3}$. (Are they kidding? If this was possible, production of nitric acid would be a joke.) If I was to follow this approach, there could be a number of variations of the mechanism above where each of the reactants and intermediate products reacted with itself. I estimate that would introduce several hundreds of variants.

How is an average grade 12 student expected to solve this task?


texts: Hybridisation of terminal nitrogen in diazomethane

texts:
I have a few questions about the terminal nitrogen (highlighted in red) in diazomethane, $\ce{CH2N2}$.

Is that nitrogen $\mathrm{sp}$ or $\mathrm{sp^2}$ hybridised?
What type of orbitals do the lone pairs on that nitrogen reside in?
Does the negative charge on nitrogen undergo resonance?


texts: What's the pH of vinegar containg 5% acetic acid?

texts:
Vinegar generally contains 5% acetic acid. We would expect the pH of vinegar to be approximately:
  a. 0
  b. 3
  c. 7
  d. 9
  e. 12

I don't have the key for this question, so I just want to make sure that I got it right and what I got doesn't seem to be one of the answer choices.

My answer was 1.3, so I rounded it to 1 and there wasn't an answer choice. Here is what I did:

$$\log(.05/1) = -1.3010$$

How else would you do it because you were already given the final concentration from the original concentration?

Am I missing something here?

Edit: The professor said to use this formula for calculating it:

$$K_\mathrm{a} = \frac{(.05x)^2}{x}$$

and got 3, which made no sense, any way this is possible?


texts: How to extract limonene from the orange peels?

texts:
What is a reasonable procedure to extract the orange essential oil from the rinds?  I thought this would be a common experiment.
Here's what Wikipedia had to say, they  identify the essential oil as mostly D-limonene (it's an isomer):

Orange oil is an essential oil produced by cells within the rind of an orange fruit (Citrus sinensis fruit). In contrast to most essential oils, it is extracted as a by-product of orange juice production by centrifugation, producing a cold-pressed oil. It is composed of mostly (greater than 90%) d-limonene, and is often used in place of pure d-limonene. D-limonene can be extracted from the oil by distillation.

A centrifuge seems to be more involved than I'd like, since these are just household objects.  I considered for example boiling the water with orange rinds in it (as would be the recipe) except maybe something evaporates into the air.  Should I consider using a different solvent? Wikihow suggested I use vodka or olive oil. There's also a video on YouTube for extracting lemon oil.  It doesn't look so elementary.


texts: Do molecules with polar bond, but with no dipole moment experiences a greater effect from the london dispersion forces?

texts: Do molecules that have polar bonds and a structure that makes the polarity of those bonds cancel each other out, experience a greater effect from the London dispersion force, than molecules with a similar size, bond length, shape, and mass, but with non-polar bonds?


texts: Are certain substances in furniture truly toxic?

texts: I'm looking to purchase a sofa, but have been bombarded with all kinds of internet info about the toxicity of certain materials used to make sofas.  For example, polyurathane foam is labeled as toxic--is this true?  Is something like a blend of cotton/polyester and polyurethane toxic?


texts: Nitrogen oxides produced in diazotization

texts:
My A level exam board describes an experiment to produce methyl 2-hydroxybenzoate (methyl anthranilate) from methyl 2-aminobenzoate (methyl salicylate).

I did the experiment as described (including keeping the temperature below 5 degrees), but when I added the sodium nitrite solution, a significant amount of brown gas was produced, which I identified as nitrogen dioxide. My teacher said this shouldn't happen, and wasn't sure why it was happening. What is wrong with the plan?

Edit: I think too much sodium nitrite is used; calculation suggests about 3g of it should be added, so I think a decimal point is missing. Am I right in thinking this?

Here is the plan:

  Requirements:
  2-aminomethylbenzoate 5 cm3 (6.5 g),
  concentrated sulfuric acid 5.6 cm3 (10 g),
  sodium nitrate(III) solution 60 g in 100 cm3 water,
  urea (solid).
  Measure out 45 cm3 of distilled water into a 250 cm3 conical flask. Slowly and carefully add 5.6 cm3 (10 g) of concentrated sulfuric acid to the water. Add to this warm solution 5 cm3 (6.5 g) of 2aminomethylbenzoate. (You may have to warm this first as its melting point is 24 ºC). Place the flask in an ice bath and add about 45 g of ice to the solution in the flask. Slowly add 20 cm3 of sodium nitrate(III) solution to the flask making sure that the temperature does not rise above 10 ºC. Now warm the solution slowly to 25 ºC and hold at this temperature for 5 minutes. Add about 4 g of solid urea to remove the excess sodium nitrate(III). Warm the solution to 80 ºC and then boil it for no more than 5 minutes. Pour the mixture into a 250 cm3 beaker that contains about 50 g of ice cubes. Separate the oily lower layer and dry using anhydrous sodium sulfate. Re-distill the oil. The boiling point of pure 2-hydroxymethylbenzoate is 223 ºC. Think about how you can check the identity of your product.


texts:
How concentrated can an acid be without it being supersaturated? Is there a certain limit to how concentrated an acid or base can be?

When I mean concentration, I mean molarity; so how concentrated can an acid or base be?

NOTE: Can be a strong or weak acid/base. Because we are just looking for the amount of solvent needed to dissolve to start the dissociation process.

EDIT: No autoprotolysis please. Acids that need a solvent to dissociate.


texts: Why does chromium metal not react with a solution of Mg^2+ even though their standard cell potentials produce a net positive voltages?

texts:
Write net equations for the spontaneous redox reactions that occur during the following or NONE if there is no extensive reaction. Use the lowest possible coefficients. Include states-of-matter under the given conditions in your answer.

My effort:
Chromium metal is added to a solution of $\ce{Mg^2+}$
\begin{align}
\ce{2Cr^3+ (aq) + 6e- &-> 2Cr(s)}\\
\ce{3Mg(s) &-> 3Mg^2+ (aq) + 6e-}
\end{align}
The net equation is
$$\ce{2Cr^3+ (aq) + 3Mg(s) -> 2Cr(s) + 3Mg^2+ (aq)}$$
Standard reduction potential of $\ce{Cr}$ is $\pu{-0.74 V}$ and the standard reduction potential of $\ce{Mg}$ is $\pu{-2.36 V}$.
$\ce{Cr}$ reaction is cathode reaction and therefore it is $\ce{Cr^3+}$ getting reduced, $\ce{Mg}$ is anode reaction and therefore it is
$$\ce{Mg(s) -> Mg^2+ (aq) + 2e^-}.$$
$$E^\circ_\mathrm{cell} = \pu{-0.74 V} - (\pu{-2.36 V}) = \pu{1.62 V}$$
Yet apparently my homework here says that that is wrong.  Does anyone see anything wrong with how I am going about this problem?


texts: How does voltage and resistance affect an electrolysis?

texts:
At school we've learned about calculating the voltage needed to perform an electrolysis. The current is how many electrons pass per time. The formula is given $$I = \frac UR$$

This means that given an electrolysis with $U=\pu{4.0 V}$ we get $$I = \frac{\pu{4.0 V}}{R}$$

If I am correct, what would decide how fast the electrolysis will go, is the resistance. Is the resistance fixed, or can I do anything to lower it? How would increasing the voltage affect the electrolysis? Would it just make it go faster (because $I$ is increased)?


texts: The reaction rate when the rate-determining step has a back reaction

texts:
For some reason, I am reviewing general chemistry and I find that the elementary reaction for the rate-determining step (RDS) is assumed to be irreversible, that is, single arrow, in all questions that I see.

For example, think a reaction consisting of two elementary reactions:

$$\ce{A + B <=>[k_1][k_1^\prime] C} \tag{fast, reversible}$$

$$\ce{C ->[k_2] D} \tag{slow}$$

Then the overall reaction is $\ce{A + B -> D}$, and the rate is then

$$\text{rate} = k_{2}[\mathrm{C}].$$

Now, I'm curious about the rate when the equation becomes like

$$
\ce{A + B <=>[k_{1}][k_{1}^\prime] C \:(\mathrm{fast, reversible)} \\
C \color{red}{<=>[k_{2}][k_{2}^\prime]} D\:(\mathrm{slow)} }
$$

In this case, I think the rate expression should be changed.
From the overall chemical equation ($\ce{A + B -> D}$), the rate itself is defined as
$$
\mathrm{rate} = \frac{\mathrm{d}[\mathrm{D}]}{\mathrm{d}t},
$$
and checking the reactions related to $[\mathrm{D}]$ in the RDS,
$$
\frac{\mathrm{d}[\mathrm{D}]}{\mathrm{d}t} = k_{2}[\mathrm{C}] - k_{2}'[\mathrm{D}].
$$
Thus, the rate is
$$
\mathrm{rate} = k_{2}[\mathrm{C}] - k_{2}'[\mathrm{D}].
$$

Though, I'm not sure if the reasoning is right. Is it correct?


texts: Liquid that does not spoil for a mineral aquarium

texts:
I want to create a decoration - a mason jar "aquarium". I want to take a large mason jar, put some nice mineral specimens in it, fill the jar with liquid and seal it with lid.

I believe I can't use pure water because there is a chance that it will go bad after some time.

So I want to know if there is some liquid that is not too aggressive (in terms of mineral decay) or dangerous that has indefinite shelf life. I want it to last for years.

I know that vodka basically never goes bad, but it's pretty expensive and the alcohol would probably be too harsh for the minerals in the jar.

Additional information: I am considering water with salt.


texts: How can I remove the bitartrate anion from an organic bitartrate salt?

texts:
I have a compound, dimethylaminoethanol (DMAE) bitartrate, which I originally purchased as a supplement and possible smart drug. I bought an absurd amount of it. It didn’t do anything for me as a supplement. I understand that DMAE, not the bitartrate salt, is commonly used in cosmetics, & I’d like to play with it for that purposes, maybe mixing it with glycerin, etc. Is there a simple way to strip off the bitartrate anion and have it precipitate or sublimate or something, leaving the DMAE behind? Or otherwise separating the DMAE out from the salt?

I have a strong preference for any other reactants and reaction products being non-toxic


texts:
I'm trying to solve a simple problem which is driving me crazy. It says:

  Estimate the pH of a solution that contains 1 gram of $\ce{H_2SO_4}$ dissolved in 1 liter of water.

When I solve the problem, I dissociate the $\ce{H_2SO_4}$ like this: $$\ce{H2SO4 + H2O <=> H3O+ + HSO4-}$$

And I get a pH of around 1.99

However, following my book's solution, the dissociation occurs as follows: $$\ce{H2SO4 <=> 2H+ + {SO4}^2-}$$
And they say the pH is around 1.69

Now, my question is: why is my dissociation equation wrong?


texts: Could compressed refrigerant be stored feasibly in residential setting?

texts:
In Vapor-compression refrigeration, a refrigerant is compressed releasing heat (typically outside a building) and then decompressed in another location, absorbing heat.

A residential air conditioner works on this principle with a compressor outside the home and a blower over the decompression coils to circulate cold air.

Would it be feasible to compress ahead of cooling demand, storing the compressed refrigerant in a high pressure container for use at a later time of the day, thus shifting the power consumption to times of the day where there is less electrical demand?

By feasibility, I'm thinking of questions like:

How much storage volume would one need for a typical household usage over an afternoon of running air conditioning given a container type that would be available cheaply, ex: propane canisters?
What would be the sources of efficiency loss added by something like this?
etc.


texts: Calculating Final Temperature and Volume of Adiabatic Expansion

texts:
A $\mathrm{5.00\ L}$ sample of $\ce{CO2}$ at $800 \ \mathrm{kPa}$ underwent a one-step (irreversible) adiabatic expansion against a constant external pressure of $100\ \mathrm{kPa}$. The initial temperature of the gas was $300\ \mathrm{K}$.

  An alternative path between the initial and final states consists of a reversible isothermal expansion from $5.00\ \mathrm{L}$ to the final volume $V$, followed by (reversible) constant volume cooling to the final temperature $T$.

  a) Give equations (in terms of $V$ and $T$, the final volume and temperature of the gas) for $\Delta U$, $Q$ and $W$
  for all three processes.

  b) Briefly state why $\Delta U$ is the same for both paths.

  c) Hence or otherwise calculate the final volume and temperature of the gas.

My Attempt

Part A

I can do this part. I am pretty sure I got the correct answers except for $\Delta U$ for the cooling process. Could you please check if my answers are correct.

Adiabatic expansion: $\Delta U = 33.33(T-300)$, $Q = 0$ and $W = 33.33(T-300)$

Isothermal expansion: $\Delta U = 0$, $Q = 4000\ \ln\frac{V}{5}$ and $W = -4000\ \ln\frac{V}{5}$

Cooling: $\Delta U = 33.33(T-300)$, $Q = 33.33(T-300)$ and $W = 0$

Part B

That is just because internal energy is a state function, independent of the path taken.

Part C

What confuses me here is the word 'hence', which implies that I need to use the fact that internal energy are equal for the two process. However I have no idea how to use this to find the final temperature and volume. I suspect that I might gotten the expression for $\Delta U$ wrong for the cooling process.


texts:
The given reaction is $$\ce{NH4NO2 \rightarrow N2  +  2H2O}$$

The way I did it was
$$\ce{NH4+ \rightarrow \frac{1}{2} N2 + 4H+ + 3e-}$$
and
$$\ce{NO2- +3e- +4H+ \rightarrow \frac{1}{2} N2 + 2H2O}$$
Therefore n factor is 3

But the book I am referring to says 6. Can someone please help?


texts:
I've been using aluminium foil and table salt to clean my silverware for a long time without actually concerning myself with the chemistry behind it. A couple of days ago i started digging into the chemistry and found this page on wikipedia

Reactivity series

and when I looked closer i saw that both silver and tin where less reactive than aluminium. Does that mean that I can safely use the same technique with my tinware as with my silverware?


texts: How is electron-impact mass spectrometry data formally reported?

texts:
NMR data has the following format when reported in a paper:

How would I go about reporting my EIMS data formally? I tried looking for documents online but couldn't find anything.


texts: Do some particles get ionised to 2+ or higher in a mass spectrometer or do they only get ionised to 1+?

texts:
In a mass spectrometer the sample is vapourised, then ionised, then accelerated.
My textbook says that the high energy electrons from the electron gun knock electrons off the sample molecules and hence ionise the particles by 1+.
But do some particles get 2 or more electrons knocked out or is it always just one ?
I suppose once it has been ionised by 1+ it gets accelerated through the tube so it won't hang around for long but I would think that there is still a small window of time for further ionisations.


texts: How to draw wedged double bond in ChemDraw?

texts: How can I draw a wedged double bond in ChemDraw? When I try to draw BINAP, making the wedged double bond seems impossible. It is however possible to draw a bold double bond.


texts: Why are the absorption and emission spectra mirror images of each other?

texts:
In one of my chemistry courses we learned that the absorption and emission spectra are mirror images of each other, but I can't rationalize why.

I know that the electronic transitions in emission spectra is not very different from that of absorption spectra, however the spectra is shifted slightly to the right due to the presence of non-radiative decays releasing some of the energy absorbed. I can see how similar energy transitions can account for a similar shape, but why is it a mirror image in most cases?


texts: How to calculate the amount of substances product produces from the masses and amounts of starting materials?

texts:
Calculate the amount of carbon dioxide formed when we burn 1 mole of carbon in the presence of 16 g of dioxygen.
  $$\ce{C + O2 -> CO2}$$

1 mole of carbon means 12 g. Therefore amount of carbon dioxide is 12 + 16 = 28. Am I correct?


texts: Why are yields of some chemical reactions so dependent on the stoichiometry of the reagents?

texts:
Back in chemistry class in high school I was working with a partner doing a chemical reaction. We measured the amounts of reagents well, but not perfect, and our yield suffered greatly. On the other hand my friend and his partner came up with quite a high yield. He told me it was because they measured each amount of reagent exactly.

So I wonder... Why are these reactions so dependent on perfect measuring of reagents? Why can't you just use more than enough of one reagent to completely react with the other and remove the excess reagent?

Also does this apply to all chemical reactions, or just a select few?


texts:
An electrical heater is placed between two layers of insulation. The three layers (the heater and the two layers of insulation) have the same thickness. The figure below shows different temperature profiles at steady-state. The air temperature at the front- and backside of the heater is $\ce{T_{front}}$ resp. $\ce{T_{rear}}$. Heat transfer in the air film adjacent to the heater is negligible.

  a) Which profile corresponds to that of a turned on heater?

  b) Which profile corresponds to that of a turned off heater?

  c) Which profile is impossible?

  d) Which of the three layers has the lowest thermal conductivity? Which layer has the highest?

I have no answer for a) or b).

c) My reasoning is that since a heater is a conductor, the k-value needs to be high, resulting in a fairly straight line in the temp. profile. Hence, (C) is impossible. Is this correct thinking?

However, I don't know what it means when a temperature profile has that kind of curvature for one of the layers, such as in (A) and (B), so if someone could please explain that, I would appreciate it.

d) Based on the fact that low k-values give a steeper line, I would say that layer 3 has the lowest thermal conductivity. And because the heater is a conductor it should have the highest thermal conductivity.

Also, how can you tell if the heater is turned on or off from looking at different temperature profiles? I am having a very difficult time understanding this and would appreciate if someone could make this a bit clearer.

I apologize if these types of questions are considered off-topic, but I really want to know how to determine these things and we have not been provided with any  answers nor explanations.


texts: How to transfer precise volumes of viscous substances from a container to a beaker?

texts:
Pipetting doesn't work with viscous materials because the suction/pressure is not strong enough and because relatively high volumes of the liquid remain at the external walls of the pipette tip when withdrawing from the liquid.

So how can I transfer precise volumes (hundreds of microliters +/- 10%) of viscous substances?


texts: What does the question mean by how many electron pairs are in 2p orbitals? How does one tell? Given that both the oxygen and the nitrogen are $\ce{sp^2}$ hybridized, wouldn't there be two 2p orbitals?


texts: Mechanism for the addition of hydrogen iodide to 3,3‐dimethylbut‐1‐yne

texts:
The following reaction mechanism was given as a solution to a solved problem in my textbook1 for the addition of hydrogen iodide to 3,3‐dimethylbut‐1‐yne:

It can be seen that that 2,2-diiodo-3,3-dimethylbutane (a geminal dihalide) is the product according to this mechanism. I arrived at a different product 2,3-diiodo-2,3-dimethylbutane (a vicinal dihalide) by using the following mechanism:

The difference is due to the methanide shift I did on the second step, converting 3,3-dimethylbut-1-en-2-ylium cation to 2,3‐dimethylbut‐3‐en‐2‐ylium cation. I consider this to be a reasonable carbocation rearrangement because after the methanide shift, the 2,3‐dimethylbut‐3‐en‐2‐ylium cation is tertiary as well as in conjugation with the double bond. Moreover, the initial carbocation has a positive charge on a more electronegative $\mathrm{sp^2}$ hybridized carbon atom. Due to this, I believe, the methanide shift produces a more stable carbocation. But, why did the author proceed without making this rearrangement?
When I discussed this in chat, there was a consensus that the product of this reaction must be a geminal dihalide as obtained by the author. The only way, I could think of, by which I can obtain the geminal dihalide even after the rearrangement discussed earlier is to do another rearrangement during the addition of second molar equivalent of hydrogen iodide as given below:

The problem with this mechanism is the carbon bearing the postitive charge after the methanide shift also has an iodine atom attached to it. Earlier, I learnt that chlorine atom is the only halogen for which the positive mesomeric effect is stronger than the negative inductive effect thereby stabilizing the positive charge. But here, due to the presence of iodine, I think the carbocation is not stable after rearrangement.
Even after neglecting this fact, there seems to be a major difference betweeen the author's mechanism and the modified mechanism, which I've emphasized using a carbon-12 labelled reactant as given below:

It can be seen that even though we obtain geminal dihalides through either of the mechanism, the products formed aren't exactly the same. One has the iodine attoms attached to the normal carbon whereas in the other they are attached to the carbon-12 atom.
In short, what happens when hydrogen iodide is added to 3,3‐dimethylbut‐1‐yne?
Reference

Solomons, et al. Organic Chemistry for JEE (Main & Advanced). Edited by MS Chouhan, Third Edition; Wiley India Private Limited. ISBN 978-81-265-6065-3


texts:
I'm writing a novel set 28 years in the future in which the protagonist attempts to manipulate a communications satellite by directing a swarm of nanorobots (or possibly micro-robots, depending on plausibility).

An initial wave of nanorobots is tasked with creating a path, such as a tunnel, through the satellite's casing so that a second wave can enter.

Inspired by real-life nanotechnology that delivers chemotherapy drugs only to leukemia cells, I thought to have each nanorobot carry a tiny amount of super acid, each depositing its payload onto the same spot of the metallic hull of the satellite. My thinking is that the vacuum of space would carry off the product of metal + acid, leaving fresh metal for the next microrobot to attack.

Is it plausible to erode a narrow path through metal in this manner? What acids would be well-suited to the task? How would I go about calculating the order-of-magnitude number of nano-robots needed to complete a path through a given thickness of (let's say) aluminum?


texts:
What is the purpose of calculating an average oxidation state for a certain element in a compound?

  Hence the “average oxidation state” of carbon in acetic acid is 0.

And

  the oxidation state value for carbon atoms in acetic acid is, however, computed as zero. This latter value represents an average of the values for the two carbon atoms derived by the rigorous assignment rules.

What does this tell me? Why not just stick with individual oxidation states? Is there something the overall oxidation state is supposed to tell me about acetic acid?

The only reason I can think of is that perhaps this average oxidation state of 0 for the carbon atoms tells me that acetic acid has some ionic character. Hence the oxidation state of 0 for carbon (as opposed to +4 for carbon in its elemental form).


texts: Will molecules containing heavy isotopes tend to rise up in a liquid?

texts:
When you have a bag of chips or nuts or something else with big and small pieces and you shake it, the bigger pieces will rise up and the smaller pieces will rise down. This is known as the brazil nut effect.

I'm curious, does something similar happen with molecules in a liquid? For example: say you have a glass filled with water. Is the concentration of $\ce{HDO}$ and $\ce{D2O}$ larger at the top in comparison to the bottom?


texts: Why doesn't the bromide anion attack during electrophilic addition of bromine in methanol solvent?

texts:
It is known that addition of bromine (in methanol) to ethene will yield 1-bromo-2-methoxyethane. The reaction proceeds with the formation of a bromonium intermediate in the first step. In the second step, methanol attacks either carbon through the lone pair on its oxygen atom. In the last step, the $\ce{CH3OH+}$ loses a proton, which combines with the bromide anion obtained in the first step, to release $\ce{HBr}$ as a by-product.

My question: Why doesn't the $\ce{Br-}$ (obtained in the first step) attack as a nucleophile in the second step?

We know that nucleophilicity is directly proportional to the atom's charge and size. Bromide anion has a unit negative charge as opposed to the neutral oxygen atom in methanol. Bromide anion is also much larger in size. Both these factors favor bromide anion being a much better nucleophile than the neutral oxygen atom in methanol. Yet, the latter only attacks in the second step. Why?


texts:
The figure is a portion of the titanium copper phase diagram for which only single-phase regions are labeled. Specify all temperature composition points at which eutectics, eutectoids, peritectics and congruent phase transformations occur.

I think i've found the eutectic and congruent point. (aprox 960 and 980 celsius) but how do I find the eutectoid and peritectic point?

Sorry for blurry image!


texts: Friedel Crafts Acylation: Reaction of acyl halide with catalyst

texts:
To form an electrophile for this reaction to occur, the acyl halide interacts with the catalyst. However, on reviewing the conditions for the reaction, I have encountered that the 2 equivalence of the acyl halide is required.

In the case of the acyl chloride, there are 2 ways the acyl chloride can react with the catalyst.

(Sorry for the sloppy diagram)

In the case of the first reaction, Cl is good leaving group, but what is the reasoning of the second reaction to occur?


texts: When is Raoult's Law valid for solid-liquid solution?

texts:
Raoult's Law for solid-liquid solution is stated as such in my books that it is applicable for all non-volatile solutes.
However different solutes must have different attractive or repulsive forces and in such a case, all of them will probably hamper vaporisation in different ways.
Then how come can we simply define the law as:
$$P_\text{vapour}=P_\text{vapour}^0\chi_\text{solvent}$$
where
$$\chi_\text{solute}+\chi_\text{solvent}=1$$
Here the equations do not provide any information about the solute.

Is the law valid for only a class of solutes?


texts: Why is Frost's Circle an extension of Huckel's 4n+2 rule? What physics leads to the emergent property that the circle can predict relative MOs?

texts: The Frost Circle is a useful mnemonic to determine the relative energies for the molecular orbitals of an aromatic ring. One vertex of the polygon of the cycle is drawn pointing downwards and the entire polygon is inscribed in a circle. At this point, the location of each vertex corresponds to the MO relative energies. What is the physical explanation as to why a Frost Circle can accurately be used to predict the relative energies of molecular orbitals in aromatic compounds? What quantum mechanical phenomena lead to this emergent property? I'm looking for a connection between an equation and the circle I suppose.


texts: Converting Chlorine Dioxide concentration to Chlorine

texts:
Looking for a little guidance. I have been given some water quality data as part of a project. Specifically I'm interested in the concentration of Chlorine in river water. The analysis results indicate concentrations of  0.6 mg/l of chlorine dioxide but not chlorine. However, there are no water quality standards for chlorine dioxide, only chlorine. Can I calculate the concentration of chlorine in the water from the concentration of chlorine dioxide?

Thanks


texts:
I've searched on net which provides a lost of hard bases and soft bases . Is there a logical way to compare the relative softness of bases
I have  a list of bases

$CH_3NC$ and $ CH_3CN$

$F^-$ and $H^- $

$Br^-$ and $Cl^-$

$HS^-$$HO^-$

I know that soft bases have higher polarizability than hard bases based on this I've compared 2.,3.,4., but what factor helps differentiating 1


texts:
Is there a SMARTS pattern for cis (and trans) amide bonds?

This seems to be the SMARTS for any amide:

[NX3][CX3](=[OX1])[#6]

But I am not sure whether or not the SMARTS format has cis/trans definitions for “single” bonds such as amides.


texts: In a crucible, we added copper carbonate and the total weight of both is 37.04g. After, we heated the crucible with the copper carbonate. It was easy to judge when the reaction had taken place as the colour of the substance had changed from the light green of copper carbonate to the black of copper oxide.After we observed this, we weighed the copper oxide and we notified the result which was 36.42g. We should have heated and weighed the crucible again, but we weren't able because it was broken(due to temperature change). But theoretically, which would be approximately the value of the second weighing?I'm curious because after searching on the Internet, I have seen both increase and reduction of the remaining mass.


texts:
Sorry for what is likely a naive question. I haven't worked with chemicals at all and have only had some brief lab safety instruction.

I need to create a mixture of chloroform and methanol 2:1 for a lipid extraction from bone.

I have read the safety data sheets for both chemicals but can't find any other information about how to safely create this mixture other than doing it in a fume hood. I need about 200 ml total.

If anyone has any information or can direct me to where to look that would be MUCH appreciated.

Thank you!!!


texts: How to come up with overall equation of a galvanic cell

texts:
How are overall equations of the galvanic cell written? In a zinc-copper cell, the overall equation is

$$ \ce{Cu^2+(aq) + Zn(s) -> Zn^2+(aq) + Cu(s)} $$

So in order to come up with this equation, do you take the net ionic equation that occurs when $ \ce{Zn} $ is placed into $ \ce{CuSO4} $ solution (the electrolyte for copper half cell)? In other words, do you calculate the overall equation of the galvanic cell by coming up with the net ionic equation of the single displacement reaction that occurs between the anode electrode and the cathode electrolyte?

In this example, it would be

$$ \ce{Zn(s) + Cu^2+(aq) + SO_4^2- (aq) -> Zn^2+(aq) + Cu(s) + SO4^2- (aq)} $$

where $ \ce{Zn(s)} $ would be the anode electrode and $ \ce{CuSO_4} $ would be the cathode electrolyte.

And the $ \ce{SO_4^{2-}} $ will cancel out since it is a spectator ion to give the overall equation of the galvanic cell.

Am I doing this right?


texts: Why is the boiling point of ethyl fluoride lower than that of hydrogen fluoride?

texts:
The book, Solomons' Organic Chemistry (for JEE Mains and Advance), contains the following question:

  Hydrogen fluoride has a dipole moment of $\pu{1.82 D}$; its boiling point is $\pu{19.34 ^{\circ} C}$. Ethyl fluoride ($\ce{CH3CH2F}$) has an almost identical dipole moment and has a larger molecular weight, yet its boiling point is $\pu{-37.7 ^{\circ} C}$. Explain.

Now while explaining the (very)  concept of boiling point and why it differs for different substances the book considers:

Dipole-dipole forces
London dispersion forces
Molecular weight

But when I tried to explain the phenomenon stated in the question, I found it hard to explain the lower melting point. Following is my approach on the explanation:

Since both have the same (similar) dipoles therefore there would be very negligible difference in their boiling points.
London dispersion forces increase in magnitude as the surface area of the molecule increases. So contrary to what was said $\ce{CH3CH2F}$ should have stronger dispersion force interaction (due to larger surface area)  and hence higher boiling point as compared to $\ce{HF}$ (given other properties were same).
Given that $\ce{CH3CH2F}$ has higher mass than $\ce{HF}$, therefore it should lead to higher boiling point (as is stated in the question itself).

Now it can be clearly seen that the above stated arguments are against the phenomenon, so I believe that I am missing something in my explanation.

So

What is (if any) wrong/missing in my explanation?
Why is the boiling point of $\ce{CH3CH2F}$ lower than that of $\ce{HF}$?


texts: Is there an algorithm that takes atom coordinates and produces VSEPR geometries?

texts:
That is, you would give the coordinates of an atom, the coordinates of four (for example) other atoms, and it would return "tetrahedral" or "square planar" or whatever.

I'm currently writing a function that does just that, but (1) I feel like I'm making a lot of arbitrary decisions in the angle tolerance cutoffs I am using, and (2) I'm not sure it's very efficient the way I am doing it.

I have searched but haven't found a prior implementation of this - is there one?


texts: How is the alpha carbon defined in alkyl halides?

texts: The α carbon refers to the first carbon that attaches to a functional group. According to this information, the alpha carbon in 2-bromobutane should have been the carbon next to the one with bromine. But in my book it says that the alpha carbon in that compound is the one with bromine atom. How is this possible?


texts:
I use Gaussian 09 and Turbomole to do a same calculation (B3-LYP/6-311G) for a same molecule. But the results are not same, Turbomole shows SCF total energy = -772.16125945927, while Gaussian shows SCF Done E(UB3LYP) =  -772.402241773, no UHF energy shows. I use UB3-LYP in Gaussian, while in Turbomole cannot specify that.
I use TmoleX to create the input file for Turbomole. It does not have UB3LYP or RB3LYP in the method part, I can only select DFT > B3LYP as my method. In previous part for molecular attributes, I can select multiplicity: UHF, then generate MOs.
The input file of Gaussian is very simple: UB3LYP/6-311g followed by cartesian coordinates of the molecule.

The energy is not the same in both of these cases. What causes the different results?


texts:
I am studying for the International Chemistry Olympiad and some of questions involve synthesis of complicated organic compounds and i have no idea how to do them.

The setting of the questions is usually like this: they give you a rough idea of the end product however some of the groups are replaced with R. They replace all the other intermediates with A, B, C ... They also give the reactants and catalysts for each step.

Most of the time the catalysts are lewis acids. I wondering if you were able to provide mechanisms and general resulting reactions of these catalyses so i could predict what the product will be.

Also, is $\ce{NaBH4}$ a lewis acid?


texts: I conducted some experiment and I want to know the resulting redish black thing

texts:
I placed two electrodes in a jar
and poured the sparking water with lemon flavor.
After about 5 hours, the water turned to blue and
the negative probe had the redish black thing.
I'd like to know what it is. Please, reply for me.

Materials : 9V battery, battery holder&wire, jar, copper wire and trevi (sparkling
water)

Connecting battery

After about 5 hours

Result : redish and black thing.


texts: lindane extraction from aqueous solution using hexane

texts: I am studying the degradation of lindane using iron nanoparticles. I have prepared lindane solution with an acetone and water mixture (1:9 v/v). I tried to extract lindane after reaction with nanoparticles using hexane as a solvent. a viscous third layer has formed between the two layers. I have no idea why this happened. Can anyone please explain why this has happened?


texts:
How can one determine (at home) if the product shown below is Potassium Alum? I held a piece of it in a gas flame (assuming that the flame would become violet if potassium were present), but there was no change in the color of the flame. [Got product for use as astringent and antiseptic after-shave -- and people say (do not know why) that for such use, it has to be potassium-(not something else)-alum.]

Update: As mentioned in the comments to the chosen answer (by @James Gaidis), the product is ammonia alum. Just to be double sure, I repeated the tests with McCormick's Alum powder whose ingredient is potassium alum. (1) The picture of the flame test is below.

(2) With the McCormick Alum, the test involving sodium bicarbonate resulted in sound and definitely no ammonia gas.  (3) The solution of Fatkari had a salty taste that became sour in a second or so; the K-alum was tasteless and became sour in a second or so.


texts: Overpotential for photocatalytic water-splitting with TiO2

texts:
What is the meaning of overpotential in the context of photocatalytic water-splitting? That is light drives charge separation inside TiO2 and the generated electrons and holes react with water to produce hydrogen and oxygen.

I have seen many papers talk about the high overpotential associated with the oxygen evolution half of the reaction. I understand overpotentials as the potential you apply to (an electrochemical) cell in order to drive the reaction without energy barriers. However, in a photocatalytic system, there are no bias voltages. So, what is the physical significance of overpotential here?

Thanks!


texts: Help solve this specific linear schrodinger equation, please

texts:
$$\left[-\frac{1}{2}\nabla^2 - \frac{2}{r} + C\right]\phi(r) = E\phi(r)$$

where $C$ is a known function. I am just looking for some help on the strategy to solve explicitly  for $\phi(r)$. One thing I am having trouble understanding is how we can solve this equation without expressing $\phi(r)$ in terms of $E$, but it seems like it is done all the time:
http://chemwiki.ucdavis.edu/Physical_Chemistry/Quantum_Mechanics/05.5%3A_Particle_in_Boxes/Particle_in_a_1-dimensional_box

Thanks!


texts:
What are the rules for choosing main branch?
Wikipedia states:

Identification of the parent hydrocarbon chain. This chain must obey the following rules, in order of precedence:

It should have the maximum number of substituents of the suffix functional group. By suffix, it is meant that the parent functional group should have a suffix, unlike halogen substituents. If more than one functional group is present, the one with highest precedence should be used.
It should have the maximum number of multiple bonds
It should have the maximum number of single bonds.
It should have the maximum length.

I don't understand how 3 and 4 differ. Which single bonds are we counting? Only carbon-carbon single bonds in the main chain, right?
Also, I heard there is a rule that says if you've two equal length chains, then choose the more substituted one. Why is it not given here?
And now now imagine you've two choices for a chain, like this:

The chemdoodle program gives the name as 2-(1-Hydroxybutyl)-3-methylhexanoic acid .
I simply do not understand why the methyl substituted chain is chosen instead of hydroxy substituted one and how that fits with IUPAC rules given in Wikipedia.


texts: What legal guidelines exist for completeness of a Materials Safety Data Sheet?

texts:
I know that the answer to this question will vary by country, but some aspects must be similar amongst those countries that have authorities overseeing chemical and industrial hygiene. The Wikipedia article on the topic is not so good. My understanding for the US is that a MSDS must be correct and complete to the best knowledge of the preparer of the sheet.

My question is thus:

  Is there are legal requirement to the correctness and completeness (to the best of the preparer's knowledge) for a MSDS? If not, then why bother with MSDS at all?

This question was inspired by the commercial for this product from 3M. You can view the commercial by clicking on the videos link at the bottom of the site. Never mind how much nonsense their claim of "botanically pure ingredients" is, I was intrigued by the MSDS link at the top of the page. I wanted to know what the "botanically pure" substances were.

There are two versions of this product, with different scents. The MSDS for each is linked: Breeze and Lemongrass. Section 2: Ingredients lists the same four items for both products:

Water 65-80%
Cloth 20-30%
Sodium lauryl sulfate <3% (surfactant, not a naturally occurring substance)
Thyme Oil <0.1% (antibacterial, at least thymol is, and botanical in origin, but certainly not a pure substance)

No odorant is listed in the ingredients, but Section 3 clearly indicated they have different smells. 3M knows what odorant was added, and if legal requirements exist for completeness, then 3M is earning a finger-shaking and a slap on the wrist. So, again,

  Is there are legal requirement to the correctness and completeness (to the best of the preparer's knowledge) for a MSDS? If not, then why bother with MSDS at all?


texts: Does electron shielding increase or stay constant moving LEFT to RIGHT across a period?

texts:
Does electron shielding increase or stay constant moving left to right across a period?
I have read about both, and I just want to know which one is right.

I believe that electron shielding remains constant because when you move across a period, you are essentially adding more valence electrons, not shielding electrons, in your valence shell.    Therefore, your
valence-electron-count increases from left to right in a period, but your shielding-electron-count stays the same.

So the overall shielding remains constant, just the amount of valence electrons increases

However, my explanation has a flaw:
It does not support the reason why an atom's radius increases when it becomes an anion.

When an atom becomes an anion, it adds more valence electrons to its outermost shell. Now this is controversial to what I said previously, because a gain in valence electrons, but not shielding electrons, wouldn't increase the electron shielding of the atom. So the atomic radius wouldn't increase either!

The only way for an atom's radius to increase when it becomes an anion is if the electrons that are added to the valence shell have some sort of effect on the shielding, right?

This supports the first thought in my question that if we move left to right across a period, shielding increases.

But the idea that electron shielding increases as we move left to right has a flaw as well:
It is controversial to another periodic trend: ionization energy

If electron shielding did increase across a period from left to right, then this would mean that ionization energy is lower as we move from left to right, which is not true.

The only way for ionization energy to increase across a period is if the  only the number of protons and valence electrons have effect on the amount of energy required, not the shielding electrons. So the shielding-effect must stay the same all throughout a period.

This goes with the what I had initially said about electron-shielding remaining constant.

So now we have a flaw for each possible answer to my question!
Please correct me if I am wrong in any of my context.


texts:
In an electrolysis situation I have identified a slight brightness change on a copper electrode.
What might have happened?
I'm dealing with different experiments and this reaction occurs in some of them.
In this experiment I am doing an electrolysis using a water solution with $\ce{NaCl}$, a Lechanché and two copper bars. The brightness change happens on the anode.
I also get bubbles and a color change in the solution of the cathode, I'm guessing it is due to the reduction of water.


texts: Why is the 8-electron rule more important than the 2- or 18-electron rule

texts: Why is the fulfilled electronic configuration of only $p$ orbital  is stable. I mean why $II-B $ group with fulfilled $d$ orbital,$II-A$ group with fulfilled $s$ orbital...are not stable. Why makes $p$ orbital so special?


texts: What is the purpose of froth in washing clothes?

texts: I stay at a rented place and there is no washing machine. I, now, wash clothes in a bucket. When I add detergent, sometimes there is froth, sometimes there is not. I wonder if this had any impact on the washing process. Though I am aware of micelles and all that, but I wonder if froth formation is nearly redundant.


texts: Why does the solubility of Group II hydroxides increase and the solubility of sulphates decrease down the group?

texts:
I know that, solubility of alkaline earth metal hydroxides increases down the group and solubility of alkaline earth metal sulfates decreases down the group.

I wish to understand the reason for these trends.


texts: How to carry out basis set fitting and extrapolation

texts:
I am playing around with basis set extrapolations, and i would like to perform some simple tests by doing some parameter fitting and checking the errors.
The functional form of the fitted curve is this
$$
E(X) = E_\infty + Ae^{-\alpha X}
$$
where $X$ is the cardinal number of the basis set used, and $E$ is the energy. This function makes sense because the rate of decay empirically fits the convergence (of correlation concistent basis sets) and the exponential term vanishes as $x\rightarrow\infty$.
We want to use energies from two low-cardinal numbers, and extrapolate to the $E_\infty$ as given by the function and the fitted parameters.
Assume that for the cardinal numbers $X$ and $Y$ we have the corresponding energies $E_X$ and $E_Y$. We then have the relationship
$$
E_X = E_\infty + Ae^{-\alpha X} \\
E_Y = E_\infty + Ae^{-\alpha Y}
$$
By using that $A = \frac{E_X - E_\infty}{e^{-\alpha X}}$, we can solve for $E_\infty$ to obtain
$$
E_\infty = \frac{E_Ye^{-\alpha X} - E_Xe^{-\alpha Y}}{e^{-\alpha X} - e^{-\alpha Y}}
$$
and solve for $A$ to obtain
$$
A = \frac{E_Y - E_X}{e^{-\alpha Y} - e^{-\alpha X}}
$$
From what I can see, if all I want is to obtain the extrapolated energy, then I do not need take $A$ into any consideration. I just need the cardinal numbers, the energies, and $\alpha$. In Python syntax this would be something like this
def extrapolate(X, Y, E_X, E_Y, alpha):
    gamma = np.exp(-alpha*X)
    omega = np.exp(-alpha*Y)
    return (E_Y * gamma - E_X * omega) / (gamma - omega)

Is the above approach the normal one for curve fitting and extrapolation?
In some tests I find that the extrapolated energy is virtually identical to the energy with the highest cardinal number used in the extrapolation. So either there is no benefit of my extrapolation, or I am doing something wrong.
(Note that I am not using Gaussian basis sets, but a MultiWavelet basis, and that the cardinal numbers are not really cardinal numbers, but a defined precision relative to the CBS. Still the approach should be the same regardless - even if the function I use for the fitting perhaps not is the perfect choice.)


texts:
I'm not a chemist.

I understand that phosphorus comes in multiple forms, one of which is white, volatile, and highly toxic.  I know that phosphors come in multiple chemical forms, two of which are zinc sulfide and strontium aluminate for glow-in-the-dark products like light sticks, etc, many of which kids use.

In doing some research for a magazine article I'm writing, I read a sentence that said "Chemists have been able to mimic phosphors …" and the word "mimic" leaves me wondering if this was done because original phosphors were (and still can be) from phosphorus?


texts: How to measure the amount of lactose in milk/dairy using high school lab equipment?

texts:
I am currently a high school student doing their Biology IB IA. For those who don't know, an IA is, in simple terms, an experiment that you design and execute yourself. My topic is "The effect of temperature on lactase activity in milk".

However, to determine the effectiveness of lactase, I need a reliable method to measure how much lactose will remain in a sample of milk (or some other dairy product if milk doesn't work). So far, what I've seen online calls for some highly advanced equipment that a high school lab does not exist. I am open to all methods (titration, measuring mass, chemical reactions, etc).

What can I do to measure this?


texts: What is the difference between molarity and concentration?

texts: I learned these two words in school but still I don't understand what the difference is between them. From my understanding, molarity and concentration means the number of moles in a certain solution. So, what is the difference between the two?


texts: calculate cell potential for the voltaic cell where its involving the two cobalt species with Copper

texts:
Calculate the cell potential for the voltaic cell that results when the following two half-cells are connected at $\pu{25 ^\circ C}$:
(1) A platinum electrode inserted into a solution of $\pu{0.10 M}$ $\ce{Co^3+}$ and $\pu{0.0010 M}$ $\ce{Co^2+}$
(2) A copper electrode inserted into a solution of $\pu{0.010 M}$ $\ce{Cu^2+}$ ions

Answer. $\pu{1.66 V}$

how it's calculated?
I know how to calculate the second cell half but what about the first half?
Edit 1
will I need more than this equation?
Cathode
$\ce{{Co^{3+}} + e− ⇌ {Co^{2+}}  ->   1.92V}$
Edit 2 from Nicolas Answer
$\ce{E=E^0 -0.059*log \frac{[Co^{2 +}]}{[Co^{3 +}]}}$
$\ce{E=1.92 -0.059*log \frac{0.001}{0.1}}$
$\ce{E=2.038}$
Now how to use the Nernst equation again, which concentration I will use for Co?

I Thought I will use it for the cell, not just half cell which requires two concentrations

Edit 3
Applying Nernst to the second half
anode:
$\ce{Cu^{2 +}(aq) + 2e- → Cu(s) ->  +0.34}$
$\ce{E=E^0 - \frac{0.059}{2}*log \frac{1}{[Cu^{2 +}]}}$
$\ce{E=0.34 -\frac{0.059}{2}*log \frac{1}{0.01}}$
$\ce{E=0.281}$
E cell = E cathode - E anode = 2.038 - 0.281 = 1.757
The answer is 1.66 did I make everything right and That's a book's mistake?
Edit 4
trying to solve it in one step
Cathode
$\ce{{2Co^{3+}} + 2e− ⇌ {2Co^{2+}}  ->  1.92V}$
Anode :
$\ce{Cu ⇌  Cu^{2 +} + 2e- ->    0.34V}$
Cell:
$\ce{{2Co^{3+}} + Cu ⇌  Cu^{2 +} + {2Co^{2+}} ->    1.58V}$
$\ce{E=E^0 - \frac{0.059}{2}*log \frac{[Co^{2 +}]^2[Cu^{2 +}]}{[Co^{3 +}]^2}}$
$\ce{E=1.58 -\frac{0.059}{2}*log \frac{0.001^2 * 0.01}{0.1^2}}$
E = 1.76
So I think it's a book's mistake written 1.66 instead of 1.76


texts: Why is including phase info in chemical reactions important?

texts: I would like to ask why do we have to include the phase change in a chemical reaction e.g from  solid to aqueous or liquid. Why is it important actually?


texts: Find the stoichiometric coefficient of a reactant given Kp, Kc, and the stoichiometric coefficient of the product

texts:
Have an hypothetical equilibrium reaction:

  $$\ce{2 A (s) + x B (g) <=> 3 C (g)}$$

  With the constants

  \begin{align}
K_\mathrm{p} &= 0.0105 \\
K_\mathrm{c} &= 0.45
\end{align}

  both at $\pu{250 ^\circ C}$. What is the value of $x$?

Since $\ce{A}$ is solid, I guess we can ignore it, right?

$$\ce{x B(g) <=> 3 C (g)}$$

Using $K_\mathrm{c}$:

$$0.0105 = \frac{\left[\ce{C}\right]^3}{\left[\ce{B}\right]^x}$$

Then

$$\left[\ce{B}\right]^x = \frac{\left[\ce{C}\right]^3}{0.0105}$$

But to solve this, I need the concentration of $\ce{C}$. How can I find it out?


texts: Why does calculating formal charges help us draw correct Lewis structures?

texts:
Reading about how to draw Lewis structures, all I know is that formal charge is the charge assigned to an atom in a molecule assuming that electrons are shared equally, regardless of differing electronegativity between atoms. It is just a concept used to arrive at the correct Lewis structure and does not represent actual charges on atoms. But what I don't understand is, why does using this concept lead us to the correct structure?

For example, right now I am looking at the example of the sulfate ion. I get to this point before formal charges need to be calculated:

All the atoms have an octet around them (though I'm aware sulfur can have more than eight electrons around it), but it is not the correct structure. Why does considering the formal charge give the right structure, if as stated above it doesn't reflect any actual charges? It also says on Wikipedia "Formal charge is a test to determine the efficiency of electron distribution of a molecule. This is significant when drawing structures.", but I am not sure what it means by this.


texts: Find the number of copper spheres in a box

texts:
A box contains a mixture of small copper spheres and small lead spheres. The total volume of both metals is measured by the displacement of water to be $\pu{420 cm^3}$ and the total mass is $\pu{5.4 kg}$. What percentage of the spheres are copper?

I can't get the right answer. I did this:

Given:

$m_{\text{total}} = 5.4\;\mathrm{kg} =5400\;\mathrm{g}$

$V=420\;\mathrm{cm^3}$

$\rho_{\ce{Cu}} = 8.96\;\mathrm{g} ~\mathrm{cm^-3}$

$V\times{\mathrm{\rho_{\ce{Cu}}}} = 3763.2\;\mathrm{g}$

$\frac{m_{\ce{Cu}}}{m_{\text{total}}}=69.9\%$

Can someone tell me how to approach this problem?


texts: Charge, Size, and Movement in Aqeuous Ions as Electrolytes

texts: Would a pair of aqueous $+2$ and $-2$ ions necessarily conduct electricity better than the same concentration of $+1$ and $-1$ ions? Furthermore, would more massive ions not conduct as well as less massive ions because they cannot travel as rapidly? It seems to me that ions move in the liquid to conduct electricity, because solid ionic crystals do not conduct electricity. If they move, then size and charge should both be factors affecting electrolyte strength. However, if ions are moving, why don't they ever achieve the most stable position and stop moving?


texts: Why does electronegativity create a stronger acid, but so does greater electron distribution?

texts:
I just learned that:

Acids get stronger with:

Increasing electronegativity of atom bonded to $\ce{H}$.
Size of atom bearing negative charge.
Hybridization of negative charge (more s character, $\ce{e-}$ closer to nucleus, more acidic).
Resonance stabilization (like size, greater distribution of electrons).

So basically, the  more concentrated the negative charge (think $\ce{F-}$, $-1$ and very small), the tighter it's going to "hold on" to the proton. With resonance and large negative groups, the charge is less concentrated, so it's not going to "hold on" to the proton as well.

However, electronegativity is the tendency for an atom to "hog" electrons. Therefore, the more electronegative, the more electrons there are in a similarly sized space.

More concentrated electrons = more stable base = weaker acid.

But electronegativity = more concentrated electrons (even though size trumps it).
And electronegativity = stronger acid.

Feel free to edit if you see what I'm trying to say but can say it better!


texts: What is the criterion for filling up of electrons in molecular orbitals of increasing energy in simple diatomic species?

texts:
So far I have found different ways in different books.
For e.g.
One says

  "In MO electronic configuration of diatomic species up to 14 electrons, $\sigma2p_z$ orbital (considering $z$ as the internuclear axis) is greater in energy than $\pi2p_y$ and $\pi2p_x$ orbitals. For species with more than 14 electrons, $\sigma2p_z$ orbital is lower in energy than $\pi2p_y$ and $\pi2p_x$ orbitals."

Whereas the other book used 16 as the no. of electrons instead of 14. This leads to different ways of filling electrons in molecules with 15 electrons such as $O_2^{+}, NO$ etc. I want to know which one is correct.


texts: How can we recreate old pharaos' perfumes?

texts:
There is ongoing research where efforts were launched to find out the original constituents of a perfume for the female pharaoh Hatshepsut:

(Source)

In a perfume flask that was found in her tomb, there are apparently some remnants of the (assumed once-liquid) perfume that she used to wear. The perfume flask was sealed, so there was probably a very low amount of gas exchange taking place during the millennia that the flask took to wait for being discovered with its treasure.

However, there should still be a lot of reactions that can happen in this timescale, and since most of the reactions that just happen by themselves tend to lower energies, at some point different organic molecules would lead to the same product (e.g. acetic acid, or similar).

It seems to me, that then the only reasonable approach is to make a list of possible constituents and then start to play with the amounts thereof and model the decay reaction pathways. Then you could check if your theory predicts the experimental results.

Is this really how you find out what an ancient perfume was made of?

References:
Here, this, this one and that (talking about Tutankhamun, but the same principles would apply).


texts: What specific toxins are formed during deep frying? And how (chemically) do they attack the body cells?

texts:
From what I understand, deep frying causes the oxidation of lipids into advanced lipid oxidation products. When these are consumed and metabolized by the body, they release ROS or free radicals which damage DNA and other cellular components, paving the way for age related decline, chronic inflammation and terminal illnesses such as cancer, Alzheimer's etc.
What are the names of some of these carcinogens from frying?
Here's an arbitrary example: Lets say we had some chicken fingers and french fries. What specific carcinogens are formed when the chicken and potato are kept in hot oil for a long period of time?
And what are the biochemical mechanisms by which they harm the body?


texts: Doubts about IUPAC nomenclature of 4-ethyl-1-fluoro-2-nitrobenzene

texts:
Why is 4-ethyl-1-fluoro-2-nitrobenzene (structure is in the attached picture) called so ?

Shouldn't it be called as 1-ethyl-4-fluoro-3-nitrobenzene since the precedence of ethyl is greater than halogens?


texts: Why does the pH of a weak acid not increase by 1 when diluted by a factor of 10?

texts: Strong acid pH increases by one unit when diluted by a factor of 10, but why do weak acids not?


texts: Does Temperature Affect Rate of Reaction of Electrolytic Cell

texts: I completed an electrolysis experiment. I used copper electrodes and a copper sulphate solution, and my independant variable was the temperature of the electrolyte. I was just wondering if increasing the temperature has a positive correlation?


texts: Is it correct to say H2SO4 behaves like an acid in this reaction?

texts:
I came across this equation :
$$\ce{ZnCO3 + H2SO4 → ZnSO4 + CO2 + H2O}$$
I wanted to know if $\ce{H2SO4}$ behaves like an acid in this reaction?

How do we generally determine if a compound acts as an acid?


texts: Why does soda explode if artificial sweetener or other powders are added?

texts: I opened a can of soda and spilled some generic artificial sweetener into the soda and it exploded. Why did this happen? I am not talking about mentos, I mean artificial sweeteners like Splenda.