texts: Stability of alkenes tri>di>mono, but how to explain tetra

texts:
When we tell students about the formation of alkenes (by elimination for example), we often tell them that reactions will favour the thermodynamically favourable most substituted alkene. Zaistev's rule empirically described this:

  "The alkene formed in greatest amount is the one that corresponds to removal of the hydrogen from the β-carbon having the fewest hydrogen substituents"

The stability of the alkene with increasing substitution mono>di>tri is easily explained by hyperconjugation/qualitative MO theory (Phillip wrote a concise answer about that here). As an example to clarify, if theres a choice between eliminating to form a trisubstituted double bond over a mono substituted, the tri will predominate in most situations.

What I often struggle to explain in any detailed way is why tetra-substituted alkenes don't entirely follow the trend.  They are generally quite difficult to form (metathesis aside, but that isn't an elimination in the classical sense), and if formed, are generally quite reactive (on a similar order of magnitude to di-substituted alkenes if some studies on hydrogenation and some calculations are correct).

My general answer is 'sterics', based on the fact that 4 substituents around the same alkene is quite crowded, but I'm the first to acknowledge that this 1)doesn't really address all of the deviations from expected properties and 2)isn't really an explanation.


texts: Distinguishing stereoisomers using reagents

texts:
Given the following possible reagents:

acetone,
$\ce{MnO2}$,
ozone, or
aluminium propoxide,

which one would distinguish between the cis and trans isomers of cyclopentan-1,2-diol?


texts:
I have a large amount of copper sulfate available and I am interested in obtaining copper chloride from it. What is the easiest way to do so?

I have considered mixing an aqueous solution of copper sulfate with sodium chloride, but I think that it would be difficult to separate the resulting sodium sulfate from the copper chloride. My other idea is to first react the copper sulfate with sodium carbonate and then react the resulting copper carbonate with hydrochloric acid, which would produce copper chloride (the other products would be $\ce{CO2}$ gas and water).  I am trying to find a cost effective method for performing this reaction.


texts: In a galvanic cell,do charges accumulate on electrodes 1st (then redox occur) which produce E in the wire when we connect between electrodes?

texts: We study that when we connect a wire between the terminals of a battery ,an electric field in established between terminals  due to potential difference .Is the potential difference result of accumulated charges on terminals. In other words   when an electrode is put in the solution like Zn in ZnSO4  will Zn electrode will become -vely charged ? If not then how does electric field established into wire at exact moment when we connect wire between terminals (electrodes) which essential for electric current .


texts: Molecular orbital diagram of hydroxide ion?

texts:
I would like to understand how to create a molecular orbital diagram for the hydroxide ion from scratch. This includes understanding the shape of the molecular orbital.
Here is an attempt I have come up with:

Where the top MO is sigma* and the bottom is simply sigma.
But this makes no sense. I haven't used up all the available electrons of the oxygen atom, and the diagram seems to suggest that there is a bond order of zero between the two atoms?
However, this goes against my understanding of MOs - surely only two molecular orbitals can be formed from a p orbital and an s orbital (sigma/sigma*) and none others? I couldn't form a pi molecular orbital, for instance.
I think I've made a mistake in that I need O$^{2-}$ instead of O, but even then I don't see how that helps.
Once I can understand that, hopefully I will be able to visualise the HOMO of the OH- ion.


texts: What's the most efficient way to find crystal structures of drugs?

texts: I'd like to be able to find the crystal structures of drugs, for example at the moment I want to find the crystal structure of (R)-fluoxetine so that I can use Jmol to create an accurate 3D model of it. This is so I can then upload it to Wikimedia Commons so it may be used alongside Benjah-bmm27's structure of (S)-fluoxetine on the Wikipedia page for fluoxetine. I have tried this database [1] but when I searched for the SMILES of (R)-fluoxetine, CNCCC@HOC2=CC=C(C=C2)C(F)(F)F (from ChemSpider [2]), I obtained no search results.


texts: Are all molecular structure symmetric either in relation to a plane within itself or in relation to other molecules? Are there any completely asymmetrical structures when looking at molecular geometry? Are there any studies into the reason for symmetry?


texts:
A good balance is an important piece of equipment for chemistry. For home chemistry, the price of the balance is unfortunately limiting ..

How should one go about picking a balance (for home chemistry; general guidelines are welcome too)? Specifically, I'm thinking whether to buy a model with 0.01g precision (up to 200g), or a one with 0.001g precision (up to 20g) (the latter is a so called "diamond balance" but probably does the job). Which one would serve me better?


texts: How does Le Chatelier's principle work in a gaseous system?

texts:
My textbook said Le Chatelier's principle normally applies to gases but there is no explanation.

I did some Googling and it said if you increase the pressure, it will shift to the side with less moles of gas.

What does this really mean? Could someone clarify Le Chatelier's principle for me?


texts: Has a concept of temperature ever been defined in the context of a single atom?

texts:
I wonder if this answer to What would happen if we supercool and then superheat an atom very abruptly?  goes far enough.

I almost wrote the comment:

  I don't think we can even talk about the temperature of a single atom, at least based on its kinetic energy. Now if there were several electrons in one atom simultaneously in higher orbits at the same time, then it might be possible.

but then decided to cast this in the form of a question.

One way to think of the temperature of a group or ensemble of atoms can be the average of a particular energy. There can be more than one temperature; e.g. kinetic energy, the distribution of excited states and nuclear spins (What is the ortho/para issue with LH2 as a fuel?) If they are different we can say that they are out of equilibrium, but we can still talk about each as a different temperature in cases where coupling between different partitions is slow compared to the timescale of interest.

In a strongly interacting quantum system like an atom, there can be some processes that can excited several electrons to higher energy states at once.

Question: Has a concept of temperature ever been (usefully) defined in the context of a single atom?

This would likely be an extreme situation and may not happen in conventional reactions, maybe an intense and ultra-short laser pulse or nuclear decay or reaction, or possibly in the case of some explosive reaction.

update: comments mention a related question in Physics SE Can a single molecule have a temperature? with several answers, though they don't directly answer this question because I'm trying to find out if this "has ever been defined in the context of a single atom", and not asking if you think it should/shouldn't or can/can't be. It is possible that at some point in some, (and possibly extreme) experimental contexts this may have been workable.

The answer there that I do find most helpful is @JohnRennie's. Still though, I'm asking primarily about excitations within a single atom rather than the rotational/vibrational states of a large molecule.


texts:
I'm reading about Lysine and doing some calculations on it's charge under various $\ce{pH}$.

Depending on the source, Lysine is usually stated as a charged amino acid with a $\ce{NH3+}$ group. However the video I'm watching is calculating the charge at 5 pH and it writes Lysine out with $\ce{NH2}$ and goes on to say that because the solution is pH 5, then $\ce{NH2 -> NH3+}$ and arguments that THIS is why Lysine is charged.

Does the literature state Lysine as a charged acid, assuming it is at pH 7? Or is the video I am watching wrong and it should not gain a charge as $\ce{NH3}$ will not accept a hydrogen?

Bonus: Why are only SOME groups given a Pka value?

http://www.geneinfinity.org/images/aapks.jpg

http://www.cem.msu.edu/~cem252/sp97/ch24/ch24aa.html

How would I calculate the charge for Isoleucin for example?


texts: Why weren't the moles of oxygen calculated the same way as C?

texts:
Combustion analysis of a $\rm1.500~g$ sample of ascorbic acid yields $4.023\rm~g$ of $\ce{CO2}$ and $\rm0.96~g$ of $\ce{H2O}$. What is the empirical formula of ascorbic acid?

Actually my question is that in many solutions I saw it's solved like that:

In $\ce{CO2}$ the moles of C is calculated as $$\frac{4.023}{44.02}=0.9139\rm~mass=1.0976~g$$

and the $\ce{H2O}$ is solved with getting out the H moles with same way that C was solved and the mass is
$$\rm m~H=0.10761~g$$
 the mass of O will be $$\rm 1.500-(0.10761~g-1.0976~g)=0.29489~g~moles=0.1842$$
My question is why didnt we use the same procedure we did with H and C to compute the moles with O? Why did we make it in the last step?


texts: Can inductive effect be the sole driving force for carbocation rearrangement?

texts:
I've been taught that a carbocation mainly rearranges because of:

increasing degree (1 to 2, 1 to 3, or 2 to 3)
+M stabilization
ring expansion (in an exceptional case, ring contraction as well).

However, I've never been taught whether the following carbocation A would rearrange:

My professor would say that this carbocation would not rearrange, since at the alpha position we only have two hydrogen atoms, and either of the hydride shifts would still yield a two degree carbocation B:

However I believe that B is stabilized by the strong inductive effect of three extra methyl groups (at the alpha position) that were absent in A. I believe this is a strong enough driving force for rearrangement.

So, can we say A will rearrange into B? Is there experimental evidence to support the fact that A rearranges/does not rearrange into B? Finally, based on these, can inductive effect be the sole driving force for carbocation rearrangement?


texts:
My book states- " the one that has ...less separation of opposite charges ,...., more dispersal of charge is more stable than others"

Aren't 'less separation ' and 'more dispersal' opposite to each other?
Please explain with an example.


texts: Isocyanides undergo addition reactions, but cyanides do not. Why?

texts:
My book mentions addition reactions of isocyanides with halogens, ozone, sulphur, etc. but it doesn't mention any such reaction for cyanides. Instead, it bluntly states: "Cyanides do not undergo addition reactions". My question is: why is this so?
 I understand the structures of the ions, but am unable to relate the exact correct logic in this situation.

Here are the addition reactions of isocyanides I am talking about:

$$
\begin{align}
\ce{R-NC + O3 &->RNCO + O2}\text{(methyl isocyanate)}\\
\ce{R-NC + 2HgO &-> RNCO + Hg2O}\text{  (methyl isocyanate)}\\
\ce{R-NC + S &-> RNCS} \text{  (methyl isothiocyante)}\\
\ce{R-NC + Cl2 &-> RNC\cdot Cl2} \text{ (methyl imino carbonyl chloride)}\\
\end{align}
$$


texts:
After studying chemical bonding I am stuck at a question that is fundamental to my understanding of chemistry:

  What is it that makes 8 electrons in the valence shell stable?

I googled it and got answers like it is a "noble gas electron configuration". But that doesn't answer my question. What is so special in the configuration of noble gases that makes them so stable? How does octet give stability to an atom?


texts: For the half reaction HSO3- -> S2O6^2- why is it that 2e- are on the right hand side when balancing and not one electron?

texts:
$$\ce{HSO3- -> S2O6^2-}$$

The oxidation number of $\ce{S}$ on the left is +4 and +5 so when adding electrons to balance the oxidation number why is $\ce{2e-}$ added to the right instead of one?
Why is 2 placed in front of the $\ce{HSO3-}$?


texts: Quantum calculation of free energy change in neat conditions

texts:
I am slightly baffled by a seemingly simple situation: I want to calculate the free energy of association between a molecule $\ce{A}$ and the solvent $\ce{B}$ using quantum methods (e.g. DFT).
From what I've understood, the basic way to do this in most situation is to optimize the geometry of each compound, then perform frequency calculations to obtain free energy corrections to the SCF. Let the SCF plus the corrections for specie $\ce{X}$ be $\ce{G_X}$. This yields the free energy of each compound at 1 atm, which can be converted into the free energy at 1 M via a factor of 1.89 kcal/mol. Thus, for the complexation $\ce{A + B \rightleftharpoons AB}$, the free energy of complexation would be
\begin{align}
\Delta G_{comp}^0 &= (G_{AB}^0 + \pu{1.89 kcal/mol}) - (G_{A}^0 + \pu{1.89 kcal/mol}) - (G_{B}^0 + \pu{1.89 kcal/mol}) \\
&= G_{AB}^0 - G_{A}^0 - G_{B}^0 - \pu{1.89 kcal/mol}
\end{align}
However, in the case of association between molecule $\ce{A}$ with concentration $\ce{C_A}$ and solvent $\ce{B}$ with concentration $\ce{C_B}$, how could one obtain the free energy of complexation?
There is the equation $\Delta G = \Delta G^0 - RT \ln\left(\frac{C_{AB}}{C_A*C_B}\right)$, but the "initial" concentration of the adduct is null. There seems to be a $RT \ln(C_B)$ term floating around in the literature, but I'm not too sure where it's coming from and how to handle this situation rigorously.


texts: How are class II force field cross-terms derived?

texts:
In some class II force fields, there are cross-terms that characterize bond-bond, bond-angle interactions and others. Example of equations below:
$$\sum_{bond-bond}^{}k_{bb}(b-b_{0})(b^{'}-b^{'}_{0})$$
$$\sum_{bond-angle}^{}k_{ba}(b-b_{0})(\theta^{'}-\theta^{'}_{0})$$
My question is: how do I get the $k_{bb}$ and $k_{ba}$ values?
I thought of two possibilities:

$k_{bb}$ must be obtained by some combination rule (e.g., Lorentz-Berthelot) that involves two $k_{b}$ values (of the bonds of interest). A similar procedure could be done for $k_{ba}$.

Or $k_{bb}$ and $k_{ba}$ are adjusted as a total energy of the molecule of interest (e.g., I take the force field and adjust the "global" equation for various geometric configurations, where the energy values are obtained by quantum chemistry).

If "1." approach exists, could someone kindly provide me with an article that reports the existing combination rules for that purpose (i.e., if you face it)?


texts: What factors could lower the voltage of a galvanic cell

texts: Recently I conducted a lab in which the voltage of a galvanic cell between two metals was recorded. Both metals were placed in an solution of their own ions with nitrate and a salt bridge was made by dipping some paper in salt water. The only issue is the voltage recorded in the cell was lower than that calculated using standard reduction and oxidation potentials. Does anyone have any ideas as to why this might be? I known the metals were not super clean although I don't think that would have an affect on the voltage.


texts: Exocyclic vs. endocyclic double bonds in E1 elimination

texts:
What will be the major product of this elimination reaction?

The exocyclic product has more substituent groups on the alkene which should make it more stable but I have heard that exocyclic alkenes are less stable than their endocyclic counterparts. Why is this the case and is it a strong enough effect to outweigh the stability provided by a fourth alkyl substituent?

Additionally, what influence will kinetics have on this reaction? I think that the endocyclic product should be kinetically favoured because there is less steric hindrance for deprotonation of the intermediate cation at the ring position than at the isopropyl position.


texts: Why is the nitroso group a deactivating group for electrophilic aromatic substitution?

texts: Does the lone pair of nitrogen in nitrosobenzene take part in resonance? If not, then why? If it takes part in resonance then the hybridisation of nitrogen is sp. Can a sp hybridised atom be attached to the ring?


texts: Magnetic properties of potassium dichromate

texts:
Is $\ce{K_2Cr_2O_7}$ diamagnetic or paramagnetic?
While näive theory predicts it's diamagnetic, but we can't be sure.
I cannot find any literature on this topic.
Nor does Wiki has that information.
Even Chem spider doesn't.
I don't know about any other reliable sources.


texts: Continuous series of inorganic hydrates (from mono- to deca-)

texts:
I'm doing some research for university and it has to do with crystals. I'm currently experimenting with $\ce{CuSO4 * 5 H2O}$. I know we refer to the formula as copper sulfate pentahydrate. And also, I'm experimenting with $\ce{ZnSO4 * H2O}$ which is a monohydrate.

What chemical compound can be bought with all the 'versions' of the hydrates? I would like to purchase copper sulfate monohydrate, dihydrate, trihydrate, tetrahydrate, pentahydrate, hexahydrate, heptahydrate, octahydrate, nonahydrate, and decahydrate, but I can't find them all (only pentahydrate which I have bought).

Same with $\ce{ZnSO4}$, I have the monohydrate, but I would still like to purchase all the hydrates for my project. I'm a newbie at chemistry. Please, can anyone explain whether there a chemical compound such as the ones above, which can be bought with all the version of the hydrates?


texts: Entropy as a state function independent of the path

texts:
When entropy is a state function and the entropy change for a reversible process is

$$\mathrm dS_\mathrm{rev} = \frac{\delta Q_\mathrm{rev}}{T} = 0,$$

how can an irreversible process be calculated by the same formula? $\delta Q_\mathrm{irr}$ is not a state function, therefore $\mathrm dS_\mathrm{irr}$ cannot be a state function.

Another description I have found was that the irreversible path should be seen as divided in a infinite amount of reversible steps. But an infinite times zero is also zero.

Can you help me please?


texts: Reactivity order of DIBAL-H and diborane with esters and acids

texts:
I have been taught in class that

DIBAL-H is more reactive towards esters than carboxylic acids while opposite is true for diborane.

Also DIBAL-H mentioned is taken under low temperatures (−78 °C).
I was given no reason for the difference in preference.
Now I would suppose that ester would be slightly more nucleophilic and bulky than acids. From these conditions it is hard to conclude the above mentioned order.
According to me opposite order could be true because as DIBAL-H is bulky so it would be easier for it to approach a less bulky molecule.
Who do we rationalise the mentioned order? Besides is the difference between preference very large or is there just slight more preference for one than the other?


texts: Factors affecting Kp (pressure constant)

texts:
Initially, I found that $K_\mathrm{p}$ depends only on temperature; but later I found that it depends on pressure of $\ce{CO2}$ gas in case of $\ce{CaCO3 (s, aragonite) → CaO (s) + CO2}$.

How do we know whether it depends upon partial pressure of reactants and products or not? Or, this is a special scenario?


texts: Transition state - multidimensional surfaces

texts:
I've been reading an explanation about transition states in Smith's Organic Synthesis:

  A transition state is an energy maximum along the reaction coordinate. However, a chemical
  reaction where the reactant contains N atoms actually involves movement over an energy surface
  with 3N-6 dimensions, and a transition state is actually an energy minimum in each of the remaining
  (3N-7) dimensions. Liken a chemical reaction to a drive across a mountain range. The “goal” is to
  go from one valley to another, just as the goal of a chemical reaction is to go from one minimum
  on the energy surface (the reactants) to another minimum (the product). The road moves about a
  two-dimensional surface whereas the energy surface for a chemical reaction may involve dozens
  or even hundreds of dimensions. There is no need to climb to the top of a mountain (a maximum
  in both dimensions) to go from one valley to another. Rather, is sufficient to go through a pass
  between mountains (a maximum in one dimension but a minimum in the other). Similarly, it is
  only necessary to pass through an energy maximum in one coordinate (the reaction coordinate)
  for a chemical reaction.
  Because a transition state is an energy maximum (albeit only in one of many dimensions) it cannot
  function to “trap” a molecule, let alone collect a population of “trapped” molecules. This means
  that a transition state cannot even be observed experimentally let alone isolated or characterized.
  Quite simply, a transition state does not exist in the sense that a molecule exists.

This multidimensional explanation completely confounds me. Could someone explain this in a more understandable language? What is this surface with 3N-6 dimensions? How did the author use it to conclude that TS can't be observed experimentally?


texts: Why are there two structures of L-Glucose in the Fischer projection?

texts:
We are told that L-Glucose is an enantiomer of D-Glucose, which would mean that they are mirror images of each other. But then we're also told that the L and D forms is determined by the spacial relationship to glyceraldehyde.

Which of the structure is correct? Are they the same?


texts:
I am looking for any kind of fluid which has a freezing point below the temperature of a regular freezer  (about -20 C). My plan is to keep this liquid in my freezer for fast cooling of beverages, so the liquid needs to be harmless to drink in case some is left on the can.
Suggestions? Or maybe the liquid will cool down the beverage too fast making it impossible to get a proper even drinking temperature without freezing the beverage?


texts: What does the amount of acetic acid in vinegar depend on?

texts: I have different types of vinegar and I'm wondering what factors influence how much acetic acid is present in different vinegars (e.g wine vinegar/white vinegar/apple cider). I was thinking maybe it has something to do with different fermentation processes. Any thoughts?


texts: Thermochemistry questions regarding enthalpy

texts:
I have a few questions about heat of combustion. I have two different scenarios that I was to present:
Scenario 1: Given heat of combustion in the equation
$\ce{CH4 + 2O2 -> CO2 + H2O}$ and $\Delta H =\pu{-889kJ mol-1}$
Q1: Would $1$ mol methane produce $\pu{889 kJ}$; whereas, $1$ mol of oxygen would produce $\pu{444.5 kJ}$?
Scenario 2: Given the energy produced per mol of a molecular compound
$\ce{C2H6O + 3O2 -> 2CO2 + 3H2O}$ and $\Delta H=?$
However, we are given that the oxygen produces $\pu{400 kJ}$ of energy.
Q2: Would that mean that the $\Delta H=3 \times400=\pu{1200 kJ mol-1}$?
It would be really great if someone could explain the theories behind thermochemistry.


texts: Why does fructose reduce Tollen's reagent and Fehling's solution?

texts: Even though fructose is a ketohexose (ketone-containing hexose, a six-carbon monosaccharide), it reduces Tollen's reagent and Fehling's solution. Generally, a ketone does not reduces Tollen's reagent and Fehling's solution. So, why is this possible in the case of fructose?


texts: What does x mean in (1-x)A – xB composite materials, molar ratio, weight ratio or volume fraction?

texts:
I've been collecting data about ceramic materials and often I get to see composite materials are described as $(1-x)\ce{A} - x\ce{B}$. I am confused what this $x$ means. And I haven't seen any of the papers mention what $x$ is unless %wt is given specifically.

For an example in $(1-x)\ce{MgO} - x\ce{LiF}$ ceramic material, does $x$ mean molar ratio or weight ratio? For me it doesn't make sense to think of $x$ as a volume fraction as most of the times powders of these materials are taken for sintering.

If nothing is mentioned, is it all right to assume $x$ as the molar ratio?
Can we assume volume fraction is equal to molar ratio even in solids or liquids?


texts: When acrolein is heated with hydrazine we get dihydropyrazole. But I can't see how. First I think hydrazine should add on acrolein to form corresponding hydrazone, but what will happen next? Also is my first step correct?


texts: Preferred IUPAC name of Protoporphyrin IX

texts:
I was looking up protoporphyrin IX and was surprised to find that no two websites gave the same IUPAC name for the compound. Here are some examples:

3,3'-(7,12-Diethenyl-3,8,13,17-tetramethylporphyrin-2,18-diyl)dipropanoic acid (EPA)
3,3'-(3,7,12,17-Tetramethyl-8,13-divinyl-2,18-porphyrindiyl)dipropanoic acid
(CHEMSPIDER)
3-[18-(2-carboxyethyl)-8,13-bis(ethenyl)-3,7,12,17-tetramethyl-22,23-dihydroporphyrin-2-yl]propanoic acid (PUBCHEM)

Anyone know if an IUPAC name is agreed upon among scientists or if there is a preferred IUPAC name?


texts: Why do dihaloalkanes lose both halogen atoms during mass spectrometry?

texts:
I was looking through mass spectrums of haloalkanes and found the one for 1,2-dibromobutane confusing:

The base peak is at 55 m/z, and the only fragment I can think of with that ration will be $\ce{C4H7+}$. The two bromine atoms must be absent as the relative molecular mass of one bromine atom is 80. I can't think of how this will happen. Does the removal of one bromine atom force the other off? Does it form an alkene? It is present in all positional isomers (1,3-dibromobutane, 1,4-dibromobutane etc.) I initially thought that the lone pair of the bromine will be donated to the positively charged carbon, but if the carbon is 2 carbons away from the bromine, I can't imagine this happening.
I feel like this is somehow related to the addition of bromine to alkenes, maybe the bromonium ion is an intermediate and bromine gas is formed? The chemical formula might be that of an butene radical. But since the peak still shows in the spectrum of 1,4-dibromobutane, I don't think that is the case.
If anyone has any theories, please do share!


texts: How much oxygen is formed in this first order reaction?

texts:
We have a reaction
$$\ce{2N2O5 -> 4NO2 + O2},$$
which has a rate constant $k=6,2\cdot10^{-4}/\mathrm{min}$ at temperature $T=318.15\ \mathrm{K}$. How much oxygen is formed in litres when $1.00\ \mathrm{mol}$ of $\ce{N2O5}$ is at $318.15\ \mathrm{K}$ in $104\ \mathrm{kPa}$ pressure for $20$ hours. Correct answer: $6.67\ \mathrm{l}$

My attempt:

For gases we use partial pressures to measure rates. So using equation
$$\ln P_t=-kt+\ln P_0$$
we get $P_t=49421.76426\ \mathrm{Pa}$. This means that oxygen has a partial pressure of $P_{\ce{O2}}= \frac{104000\ \mathrm{Pa}-49421.46426\ \mathrm{Pa}}{5}=10915.64715\ \mathrm{Pa}$.

Now we say $n_{\ce{O2}}=x$ so according to the reaction $n_{\ce{N2O5}}=1-2x$. If the total volume is $V$ we can type two equations:
$$
\begin{align}
P_t&=\frac{n_{\ce{N2O5}}RT}{V}\\
P_{\ce{O2}}&=\frac{n_{\ce{O2}}RT}{V}
\end{align}
$$
Solving for $x$ and $V$ yields $x=0.153195\ \mathrm{mol}$ and $V=0.0371657\ \mathrm{m^3}$. Now calculating the volume for oxygen at $104\ \mathrm{kPa}$ gives
$$
V_{\ce{O2}}=\frac{0.153195\ \mathrm{mol}\cdot 8.3145\ \mathrm{\frac{Pa\ m^3}{K\ mol}\cdot318.15\ \mathrm{K}}}{104000\ \mathrm{Pa}}=3.900828\cdot 10^{-3}\ \mathrm{m^3}\approx3.9\ \mathrm{l}
$$
My answer is somehow incorrect but what I am doing wrong here?


texts:
I have learnt about group theory before I learnt MO theory, so I have a mathematical understanding of those orthogonality theorems and character tables.

I will use the character table of $D_{4h}$ to ask my questions:

About basis functions

In the character table, we can see that the basis functions of $A_{1u}$ are not listed. Does it mean that any function can be a basis function of the corresponding invariant subspace?

For $E_{u}$, we know that the dimension of the invariant subspace is two, then does it mean that any pair of functions listed can be regarded as a set of basis functions?
About labels of irreducible representations

I learnt that those labels for irreducible representations are called Mulliken symmetry labels. But I don't understand what are the symmetries that we check? For instance, $A_{1g}$, is that we check the symmetries of $x^2 + y^2$ or $z^2$ (which are basis functions) that we get such a label?


texts: How to calculate the number of protons in a sphere given the volume and the pH?

texts:
The spherical radius of a nano-droplet of a solution ($\mathrm{pH}$ of which is $6$) is given as $\pu{20nm}$.

I can find the molar concentration of $\ce{H+}$ and subsequently the number of $\ce{H+}$ ions, but I am getting a fractional number ($\approx 2 \times 10^{-2}$). This is obviously wrong as there should be at least $1$ proton in a compartment which has an acidic $\mathrm{pH}$. What am I doing wrong?


texts: Why is finding [H+] when given [OH-]= 3.57e-5 M wrong when I use -log[OH-]?

texts:
Question/Problem

I know that [H+][OH-]=$10^{-14}$

And the problem asks to find out the concentration of H+ when the concentration of OH- is $3.57*10^{-5}$M

By using the equation above i find that the concentration of H+ is 2.67E-10

But if I use a different method as follows:

-log[OH]=pOH so by substitution, -log[$3.57*10^{-5}$]

then that gives me 4.425.......

then i subtract 14 from that number to get 9.574......

which that is pH

then i set 9.574=-log[H+]
so then you "e" everything which the answer comes to be  6.95E-5

why is this wrong?


texts: Analysis of multiple spectra to determine an unknown structure

texts:
I've been trying to solve the structure of a molecule from a $^{13}\ce{C}$ and proton NMR as well as a MS spectrum, but I've been stumped, I've been staring at it for a while with no improvement.
I've attached the images below. From the MS, I understand the Mr of the molecule to be 122, the $^{13}\ce{C}$-NMR suggests six different environments.
The part that confuses me the most is on the NMR. There is a 3 hydrogen doublet and a 4 hydrogen singlet.  I went on to assume that the structure might be some sort of aromatic and symmetrical, and maybe 2 carbons in the same environment so that the formula might be $\ce{C7H10N2}$, this accounts for the Mr and the fact there is an exchangeable proton peak.
The spectra I've been provided are poor quality, so I can't even work out the coupling constants, or properly view the peaks.
I still can't figure out what it might be. Can you point me in the right direction please. I have a feeling I've been confusing myself over something that's simple.


texts: How many structural isomeric alkenes ($\ce{C_6H_{10}}$) can be hydrogenated to give methylcyclopentane? Would there be three? I drew out what I thought was correct but I just want to confirm that there are three.


texts: Difference between nickel catalyst and Raney nickel catalyst

texts:
Many times I have seen the catalyst as Raney nickel instead of nickel catalyst. Raney nickel catalyst is developed by Murray Raney, and I think Raney nickel catalyst and nickel catalyst are two different things, because various sources use both names.

How do they differ from each other?


texts: Correct flask for reacting and distilling on hotplate?

texts:
I'm running a distillation reaction at under 100 °C with the heat coming from a hotplate (combined with magnetic stirrer).  Is a Florence flask the correct vessel to use on the hotplate?

Given the small contact area of the flask relative to the surface area of the hotplate I'm wondering if it wouldn't be better to use a fully flat-bottomed flask on the hotplate, and if so what best practices are?  Regardless, I need to keep a stirrer running during the process.

(I intend to have a Kjeldahl bulb on top of whatever flask before feeding the condenser.)


texts: I am working with Morse interatomic potential, I searched through the Internet but I could not find any Morse parameters for Zirconium element. Is there any table, handbook or something like these which list these parameters? or Is it possible to calculate these parameters for hcp metal elements?


texts: Do lone pairs contribute towards the pi electron count of heterocycles?

texts:
I'm not able to understand how the following compounds are aromatic.

When should the lone pairs on heteroatoms be taken into consideration when counting the number of π electrons?


texts: Does anybody know where to find a database for atomic and molecular energy levels, with the corresponding energy values for each level? It would be needed just for small molecules. I tried the NIST website but it only has the ground state energies.


texts:
In a classical reaction, phenolphthalein is synthetised from phthalic anhydride and phenol with acid catalyst. When one uses substituted phenols, one obtains similar compounds (e. g. cresolphthalein, thymohlphthalein).

However, some acid-base indicators contain a sulfo- group instead of a carboxy- group of phthaleins. Does that mean that they are synthetised from phenols and the anhydride of o-sulfobenzoic acid? Phthalic anhydride is fairly cheap, but how is o-sulfobenzoic anhydride prepared?


texts: Are there any safety guidelines for mixing sulfate with chloride?

texts:
Some ceramicists decorate pottery using soluble salts (usually chlorides and sulfates e.g. copper chloride, cobalt sulfate) which are used individually or mixed to produce different colors.

I have been exploring the use of these chemicals on porcelain.  From the MSDS of each chemical I've become aware of the safety concerns and the proper precautions to take when mixing, applying, and firing them in a kiln.

But I don't know much about chemistry and do not understand the reactions when mixing these chemicals.  Are there any chemicals which should absolutely not be mixed together?  For instance, the Wikipedia article on Potassium permanganate says "Concentrated sulfuric acid reacts with $\ce{KMnO4}$ to give $\ce{Mn2O7}$, which can be explosive."  Does this mean I should not mix Potassium permanganate with a sulfate like Copper Sulfate?  In general, what happens when a sulfate is mixed with a chloride?  Are there any general safety guidelines you could offer?  Is there a fairly simple way to understand these interactions without the requirement of years of Chemistry study?

Apologies for my ignorance!

Some chemicals that ceramicists have used before:

Color

gray

copper chloride (heavy application and heavy reduction can give pinks and reds)
palladium chloride
ruthenium chloride
selenium (selenous acid, selenium toner)
silver nitrate
tellurium chloride
vanadium (vanadyl sulfate, vanadium pentoxide)

blue

cobalt chloride
molybdenum (molybdic acid)

green

ammonium chromate
nickel chloride
potassium dichromate
sodium chromate

brown

iron chloride (iron chloride emits heat when mixed with water so the water    should be added gradually in small amounts)

pink/purple/maroon

gold chloride (1-5% solution, adding either cobalt, manganese or
tellurium will give different shades)

yellow

praseodymium chloride (very pale color)

black

cobalt chloride (50% solution) and iron chloride (100% solution)
cobalt chloride (50% solution) and nickel chloride (50% solution)


texts: Does sublimation happen only on the surface or throughout the body?

texts: Like evaporation happens only on the surface of a liquid, and boiling/vapourisation takes place throughout the body, how does sublimation occur? Why?


texts: What is the pressure belonging to in Boyle's Law?

texts:
Just a hour ago, I was reading the great and highly interesting, Boyle's Law. In my textbook, there is given Boyle's Law and leaving some pages, there is stated Dalton's Law of Partial Pressure.

Boyle's Law is stated as, "As so long as the mass of the gas and temperature is constant, the product of pressure by volume of the gas remains constant."

Experiment of U-tube is well known. I am not going to copy it here but I would directly explain my problem. From U-tube experiment, I grasped that the pressure, mentioned there, is one that is applied and not of the gas. However, the difference stays vague in the law stated earlier that whether this is the pressure applied by external agency or the pressure applied by gas molecules or gas.

Later, I read there the Dalton's Law of partial pressure. There is a primary equation concerning to partial pressure of a gas viz.,

$$\frac {P_{gas}}{P_{mixture}}=\frac{m_{gas}}{M_{mixture}}$$

It is clearly mentioned there that this pressure either $P_{gas}$ or $P_{mixture}$ is the pressure applied by gas/mixture and not the pressure applied by external agency. This is even more clear from the relevant experiment.

The problems start when I begin to analyze the derivation for the equation above. Author of my textbook hasn't given any derivation for it but my teacher let us did that.

Derivation:

Consider  the mixture of gases A, B and C.

Let the number of moles of gas    $A=n_A$

Similarly, number of moles of gas $B=n_B$

And that of C is given by $n_C$

Total number of moles=$n_T=n_A+n_B+n_C$

We know that, $$P=\frac{nRT}{V}$$

Therefore pressure applied by gas A is given by, $\color{red}{P_A=\frac{n_ART}{V}}$

For gas B, $\color{red}{P_B=\frac{n_BRT}{V}}$

And for gas C, $\color{red}{P_C=\frac{n_CRT}{V}}$

For mixture of A, B and C, $\color{red}{P_T=\frac{n_TRT}{V}}$

Diving $P_A$, $P_B$ and $P_C$ individually by $P_T$ we get,

$$\frac{P_A}{P_T}=\frac{n_A}{n_T}$$

$$\frac{P_B}{P_T}=\frac{n_B}{n_T}$$

$$\frac{P_C}{P_T}=\frac{n_C}{n_T}$$

  The red marked statements are where my previous concepts were denounced. I was thinking that the derivation maybe wrong but I am not sure so I want you people to judge my concepts and my teacher as well and inform me.

Thanks.


texts: What are the key differences between Raoult’s Law and Henry’s Law

texts:
Raoult’s Law ($p_A = \chi_A \cdot p_A^\circ$) becomes a special case of Henry’s Law ($p_A = K_H^{px} \cdot \chi_A $) when $K_H^{px} = p^\circ_A$, but where do these laws differ from each other?

There’s a statement in my text book which I’m having trouble understanding.

The statement:

  As a real solution approaches the limit of infinite dilution its components behave more ideal. The solvent obeys Raoult's law whereas solute (minor component) obeys Henry's law for dilute solutions.


texts:
Geiger counters can detect radioactivity because nuclear radiation consists of particles or radiation of sufficiently high energy to eject electrons from atoms. Consequently, this type of radiation is called "ionizing radiation." What is the longest wavelength of radiation that can be detected by a Geiger counter using neon gas as the ionizing medium?

I know the ionization energy of neon is $\pu{2080 kJ/mol}$, or $\pu{3.46*10^{-18} J/atom}$ of Ne (calculated by dividing the I.E. by avogadro's number).

Since $E = \frac{hc}{\lambda}$, I can calculate $\lambda$ to be $57.3$ nm. However, the textbook's answer is $3.64$ nm. I'm not sure why.


texts: Radial Probability Distribution Curve versus ψ² versus r curve for 1s orbitals

texts:
My question is basic, but I have already referred to a couple of books.

This is an excerpt from Linus Pauling's book:

  the most probable distance of the electron from the nucleus, which is the value of $r$ at which $D(r)$ has its maximum value, is seen from Figure 21-1 to be $a=\pu{0.529 \mathring{A}}$, which is just the radius of the normal Bohr orbit for hydrogen.
  [Figure 21-1 is the Radial Probability Distribution Curve (RPDC) for the 1s orbital, see below.]

And on the next page he states that:

  The function ${\psi^2_{100}}$ has its maximum value at $r=0$, showing that the most probable position for the electron is in the immediate neighborhood of the nucleus; that is, the chance that the electron lie in a small volume element very near the nucleus is larger than the chance that it lie in a volume element of the same size at a greater distance from the nucleus.

Don't these two statements contradict each other? $\psi^2$ versus $r$ says that the probability density is highest at $r=0$. RPDC says that the probability is highest at $r=\pu{0.529 \mathring{A}}$. Why is there such a stark difference between probability density and probability? When $r$ tends to $0+$ we observe high electron probability density (wrt the $\psi^2$ curve) but minimized electron probability (wrt the RPDF curve)

I do understand, however, that Radial Probability Distribution Curve represents probability and $\psi^2$ versus $r$ represents probability density. But why is there a difference in these two?

For reference:


texts:
Well, I have seen many comical acts where people balance a spoon (or a fork) on different parts of the face like on the tip of the nose, forehead etc.
The do this by blowing moist air (see below) and immediately putting it on the face

So i wanted to know is what is the force that temporarily binds the skin to the fork. I doubt it's friction or Van Der Walls force.
Can someone please clarify this for me? Is it some sort of chemical bond?

Some addition
Also another method of doing this was to rub the concave part of the spoon on the tip of the nose. This article states how to do it properly. In the 2nd point it states

  Eventually you will feel a slight tendency for the spoon to resist on the downstroke.

What is this resisting tendency?


texts: Help understanding how "steric effects" are distinct from "electronic effects"?

texts:
@jakebeal's excellent answer to Why do animal cells “mistake” rubidium ions for potassium ions? includes the following passage:

In the case of potassium versus sodium, which are both very important in biochemistry, a recently discovered mechanism in sodium-potassium pumps uses binding properties to grab both, then atomic size (via steric hindrance) to distinguish sodium versus potassium as described nicely in the answers to this question.

Wikipedia's Steric effects says:

Steric effects are nonbonding interactions that influence the shape (conformation) and reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel.

Since "the way that opposites attract and like charges repel" sounds "electronic" to me, why does one say that "Steric effects complement electronic effects" instead of simply being electronic effects?


texts:
I'm translating a Russian text in which there is the following diagram of tryptophan degradation:

Further on in the text, hydroxytryptophan is called "the mono-oxidized form" (моноокисленная форма) and dihydroxytryptophan is called "the dioxidized form" (диокисленная форма). Is this correct and would this be understood by the readers if I translate it as-is?


texts: Which one of displayed formula below does not represent an isomer of heptane?

texts:
All of these appeared to be correct. I’ve already counted their hydrogen and carbon number. Please help!

[1]: https://i.stack.imgur.com/tnQvO.jpg


texts:
What does 5% aqueous solution of glucose mean? Note that it's just 5% and not 5%w/w. Do we assume it to be w/w?
The question is

If the osmotic pressure of 5% aqueous soultion of glucose is $\pi_1$ and that of 5% aqueous solution of urea is $\pi_2$ then:
A) $\pi_1=\pi_2$
B) $\pi_1<\pi_2$
C) $\pi_1>\pi_2$

Does 5% mean that the solutions are equi-molar/molal?


texts: Calculating Gibbs free energy for the reaction of burning methanol

texts:
Calculate $Δ_\mathrm{r}G^\circ$ for the following reaction:
$$\ce{2 CH3OH(l) + 3 O2(g) -> 2 CO2(g) + 4 H2O(l)}$$
using $Δ_\mathrm{r}H^\circ$ and $Δ_\mathrm{r}S^\circ$ at $\pu{298.13 K}$ $(\pu{25 °C}).$ The values for $Δ_\mathrm{f}H^\circ$ and $Δ_\mathrm{f}S^\circ$ can be found in Appendix G of the textbook.
Also state if this reaction is spontaneous at this temperature.

In Appendix G of the textbook (Openstax Chemistry), I found the $Δ_\mathrm{f}H^\circ$ to be $\pu{-239.2 kJ mol-1}$ and the $Δ_\mathrm{f}S^\circ$ to be $\pu{126.8 kJ mol-1}.$
The values of the Gibbs free energy of formation for both the reactants and products were also listed in the Appendix G, this is where I got them. So I plugged those values into the equation, leaving out the $\ce{O2}$ because it is just an element, and multiplied the appropriate values by the numbers in front of the compounds, and that is how I got the Gibbs free energy of the reaction:
$$
\begin{align}
Δ_\mathrm{r}G^\circ &= \sum Δ_\mathrm{f}G^\circ(\text{products}) - \sum Δ_\mathrm{f}G^\circ(\text{reactants})\\
  &= [2 × (\pu{-394.4 kJ mol-1}) + 4 × (\pu{-228.6 kJ mol-1})] - [2 × (\pu{-163.3 kJ mol-1})]\\
  &= \pu{-1379 kJ mol-1}
\end{align}
$$
However, I don't know how to get the Gibbs free energy by using the $Δ_\mathrm{f}H^\circ$ and $Δ_\mathrm{f}S^\circ,$ and I don't know if it was spontaneous or not. Can anybody point me in the right direction, please?


texts: Dipole Moment of the following organic compounds

texts:
Question: Which of the following compounds will show highest dipole moment and why?

I figured out that, (4)th compound is very symmetric - so net dipole moment on the compound must be null.

How should I go about finding the compound with the highest dipole moment? Any help or tips are welcome!

[Question borrowed from the JEE - Main]


texts: Why is ammonium a weak acid if ammonia is a weak base?

texts: $\ce{NH3}$ is a weak base so I would have expected $\ce{NH4+}$ to be a strong acid. I can't find a good explanation anywhere and am very confused. Since only a small proportion of $\ce{NH3}$ molecules turn into $\ce{NH4+}$ molecules, I would have expected a large amount of $\ce{NH4+}$ molecules to become $\ce{NH3}$ molecules.


texts: Calculating the free energy of separation in AMBER

texts:
I am currently busy with my master's research project and I'm trying to calculate the free energy of separation of two cellobiose molecules in ionic liquid, that is, calculate the free energy of separating two molecules from a distance of 35 nm to 215 nm. I have tried steered molecular dynamics with the Jarzynski relation, taking the logarithm of the radial distribution function and various umbrella sampling methods, but none of them seem to give me good FE profiles.

I think my system (1-butyl-3-methylimidaozlium acetate) just isn't going to give good FE profiles, but my supervisor is convinced that it will. I am currently trying thermodynamic cycles out so I hope that works.

So, my question is, what other methods for calculating the FE of separating the cellobiose molecules are there? And can you provide tutorials for me for those? I am aware of slow growth, ABMD, NFE, metadynamics, etc. but either these do not have any useful tutorials or don't work in the AMBER force field.

I have been struggling with this for more than two months now and my supervisor does not want me to stop my analysis. What other method can I use? Is there other computational methods available for determining the interaction between two systems?

Thank you in advance.


texts: Calculate force on atoms given the energy of configuration, trajectory of simulation and position of atoms in each frame

texts:
Background

I am using a neural network to calculate the potential energy of atoms in a configuration and then adding energy of all atoms to compare it with the true energy of the configuration(label) to update the weights.

I am doing so for 10000 configurations of 100 atoms each for liquid Argon at 100K.

Note I don't have the actual energy of each atom and only the energy of the configuration.

Problem

I need to calculate the forces on each atom to see if the sum of forces for all the atoms is zero in X,Y,Z axis. In case it is not I want to find out how off is it from zero.

How do I calculate the force on atoms using their position and potential energy for a given trajectory. I know I need to do $\frac{dE}{dr}$ but what should be my E and r. Also since I don,t a formula for E(r), what should my $dE$ and $dr$ be respectively?


texts: Is the 5d orbital involved in triiodide ion?

texts:
Is the $5\mathrm{d}$ orbital involved in the triiodide ion, $\ce{I3-}$?
There are $5$ electron pairs around the central iodine.

(Almost) all of the hypervalent compounds involve the most electronegative elements: $\ce{F}$, $\ce{O}$, $\ce{Cl}$.

Also, the bonds involving the electronegative elements are often almost ionic:

  For sulfuric acid, computational analysis (with natural bond orbitals) confirms a clear positive charge on sulfur (theoretically $+2.45$) and a low $3\mathrm{d}$ occupancy.

So, we can say that $3\mathrm{d}$ is (almost) not involved in the central sulfur atom of sulfuric acid.

Is there any experimental data to show if $5\mathrm{d}$ is involved in the triiodide ion?


texts: Acidity of naphthol vs hydroxynaphthoquinone

texts:
I have the following two compounds whose acidity I need to compare. I tried drawing out the resonating structures but I seem to not be able to draw final conclusion.

I know that the conjugate base of Q has more resonance structures, but R is still more acidic according to the book, with its resonance looking like this:

Why such resonance makes it more acidic?


texts:
Should a crude compound should be dissolved completely in cold solvent and then heated up?

I think non-polar solvents are best choice for recrystallization of polar compounds, no?

Recrystallized product is then isolated using vacuum filtration

Can scratching the inside of the flask can help initiate crystallization?


texts: Is styrofoam soluble in gasoline or paint thinner?

texts:
Why doesn't gasoline or paint thinner melt through Styrofoam when I try it yet there are videos of others melting Styrofoam in gasoline and paint thinner? Is there something I am doing wrong? This is the link to the paint thinner, I used.
http://www.kleanstrip.com/uploads/products/Paint-Thinner-gallon-metal-GKPT94002-900.jpg

For gasoline, I used gasoline from a jerrycan which was sitting for a couple of months.

Please help me out by pointing out where and how I might have made a mistake. No excessive chemistry terminologies please. I am merely a fourth grader ( guardian ) trying to work this out.

Thank you,
Guardian of fourth grader


texts: What is the mechanism for oxidation of ketones by the Popoff's rule?

texts:
Ketones are relatively much harder to oxidise, but they do undergo oxidation reactions at extreme temperatures. Our teacher also told us about Popoff's rule which states that, on oxidation of unsymmetrical ketones, the $\ce{>C=O}$ group remains with the smaller alkyl group. Could you please give me a hint as to how this happens, and the probable reaction mechanism for this?

Also, please give the complete balanced equation when butan-2-one is oxidized to a carboxylic acid.


texts: Predicting the product of bromination of acetanilide

texts:
I figured the answer would be option (B) as the group attached to the benzene ring is ortho- and  para- directing.

I thought $\ce{FeBr3}$ would be used in electrophilic aromatic substitution.

However, the model answer to the question is (D).

Is this correct? If so, what makes it possible?


texts: Is calcium hydroxide or potassium hydroxide more efficient at removing carbon dioxide?

texts: In biology, we commonly use $\ce{KOH}$ in respirometers to remove carbon dioxide. A common test in chemistry to detect the presence of carbon dioxide is to bubble it through limewater, turning it milky. This has led me to wonder which is more efficient in removing carbon dioxide—$\ce{KOH}$ or $\ce{Ca(OH)_2}$—when both solutions are sitting in the atmosphere (i.e. they’re just passively absorbing $\ce{CO_2}$ and $\ce{CO_2}$ is not bubbled through either solution). An explanation would be much appreciated.


texts: Can a lone pair be involved in cis/trans isomerism?

texts:
I was trying to find whether a molecule showed isomerism, and this is what I came up with.

I thought this was the case as I took the nitrogen to be sp2 hybridised, thus trigonal planar (with the lone pair not shown on the diagram). The molecule can't rotate about any single bonds because resonance makes the whole molecule planar. Am I right in thinking this shows cis trans isomerism? If not, what sort of isomerism might it show?


texts: Does Chemical Formula of Matter Influence on how would it be Charged?

texts:
Firstly: Suppose we rub glass ($\ce{SiO2}$) against paper (which is made from cellulose $\ce{(C6H10O5)_{$n$}}$). We receive positively charged glass and negatively charged paper. Is that because of total ionization energy of molecule stronger than glass or crystal system too?

Secondly: When we rub atoms against other atoms, do electrons accelerate each other by the same electrostatic charge and change their orbitals to higher orbits due to synchrotron radiation they emit. Or is it because of the fact that protons are more close are ionizing electrons by electrostatic attraction? Am I correct?


texts: Using the steady state approximation in the decomposition of nitramide to determine rate law

texts:
$\ce{O2NNH2 (aq) ->[\mathit{k}_1] O2NNH- (aq) + H+ (aq)}$
$\ce{O2NNH- (aq) + H+ (aq) ->[\mathit{k}_{-1}]  O2NNH2 (aq)}$
$\ce{O2NNH- (aq) ->[\mathit{k}_2] N2O(g) + OH- (aq)}$
$\ce{H+ (aq) + OH- (aq) ->[\mathit{k}_3] H2O(l)}$
We assumed the first two steps were fast and gave a rapid pre-equilibrium, while the third step that generated $\ce{N2O}$ was slow. The last step is very fast.
(i) For this question, use the steady state approximation for [$\ce{O2NNH-}$], assuming it is a reactive intermediate, to derive an expression for the rate law.

 The solution given is
 $$\frac{\mathrm d [\ce{N2O}]}{\mathrm d t} = k_\mathrm{obs}\frac{\ce{[O2NNH2]}}{\ce{[H+]}}$$

My attempt at the solution is as follows:
$$\frac{\mathrm d[\ce{N2O}]}{\mathrm dt} = k_2\ce{[O2NNH-]}$$
Using the steady state approximation,
\begin{align}
\frac{\mathrm d[\ce{O2NNH-}]}{\mathrm dt} = k_1[\ce{O2NNH2}] - &k_{-1}[\ce{O2NNH-}][\ce{H+}] - k_2[\ce{O2NNH-}] = 0 \\
\ce{[O2NNH-]} &= \frac{k_1[\ce{O2NNH2}]}{(k_{-1}\ce{[H+]} + k_2)} \\
\frac{\mathrm d[\ce{N2O}]}{\mathrm dt} &= \frac{k_2k_1[\ce{O2NNH2}]}{(k_{-1}\ce{[H+]} + k_2)}
\end{align}
I have done this so far, but this doesn’t seem right to me. I’ve been looking over at it for seemingly ages but I can’t see where I am going wrong or if I have misunderstood something about the steady state approximation. Any insight would be greatly appreciated.


texts: What explains the very high density of osmium and iridium?

texts:
Iridium with a density of $22.56$ g cm-3 & osmium with $22.59$ g cm-3. Data from their respective Wikipedia pages.

Only these two naturally occurring elements have such a high density. I wish to know why. Also If possible the factors affecting the density of any/every elemental substance.


texts: Microfiltration for saturated solutions of highly hygroscopic compounds?

texts:
Is it possible to pass saturated solutions of compounds with very high solubility through filters with small pores (e.g. passing a saturated aqueous ZnCl2 solution at 90C through a 2mcm glassfiber filter with the help of partial vacuum)?
Will it work well? Are there preferred methods for this? If not, is there any (reasonable) solution to filter out microparticles from such solutions?


texts: How can epimerization during peptide synthesis be detected? And how can we change or modify the coupling conditions to stop epimerization occurring?


texts: Supersaturated conversion of sodium acetate utilizing electricity

texts: Is it possible to use electricity to take crystallized sodium acetate back to a supersaturated solution?


texts: Why are compounds of V5+ and Cr6+ colored?

texts: As far as my knowledge goes, transition metal complex ions show a color due to a transfer of electrons between the levels of split $\mathrm d$-orbitals. In the case of $\ce{V^5+}$ and $\ce{Cr^6+}$ however, there are no electrons in the $\mathrm d$-orbitals, and the electronic configuration of both is similar to $\ce{Ar}$, yet $\ce{V^5+}$ and $\ce{Cr^6+}$ show color(yellow/brown and orange respectively).


texts: What determines "polarizability" of an element?

texts: In this question, the answer given discusses that fluorine has a good orbital overlap with hydrogen and also that fluorine is not very polarizable. However, is it always true that strong bonding is inversely related to polarizability?


texts: Control the pressure of Hydrogen in a small container without the use of a pressure regulator

texts:
I had recently asked this question, and due to the comments and general consensus of safety concerns, I decided to re-ask the question, attacking the problem from another angle.
The Problem
I need to store a relatively large amount of Hydrogen in a small (12 cc) Aluminum container at about 1000 psi. The problem is not the generation of the hydrogen, nor the transfer of the hydrogen into the container at that high pressure, but how to extract the hydrogen out of the container without using a pressure regulator.
I am afraid that the container is too small for a pressure regulator to fit in it, and the whole device has to be small on the outside, so one cannot fit it on externally...
The output pressure I desire would be about 200 psi
An Idea: (I'm an Electrical Engineer, don't laugh!)
Emulate Vapor Pressure
Gasses like CO2, Butane, and Propane have relatively low vapor pressures, allowing them to form a liquid at reasonable pressures. At about 800 psi, CO2 will form a liquid, making it so that any container holding liquid CO2 will let out CO2 at that somewhat constant 800 psi of pressure until there isn't enough CO2 to keep itself in liquid form. Hydrogen, however, will not do this because it's vapor pressure curve is far too sensitive. It would have to be cooled down to some ungodly temperature, which is not an option:

I was wondering if I could somehow emulate this behavior by possible adding something to mix with the hydrogen and change it's vapor pressure. Is this even possible?
Edit:
Flow rate doesn't directly matter, but the more flow the better.


texts: How to name alicyclic compound with hydroxymethyl substituent?

texts:
What is the IUPAC name of the given compound?

Is it cyclohexane dimethanol (or) 1,2-dihydroxymethyl cyclohexane?


texts: Can you do SERS without a Raman microscope?

texts:
Surface-enhanced Raman spectroscopy or surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces or by nanostructures such as plasmonic-magnetic silica nanotubes.
Does this require a Raman microscope? Remember you are not scanning on a large object or liquid in vials but molecules in the rough metal surfaces. If you just use a normal Raman spectrometer. Will it work on the SERS sample?


texts:
Hasok Chang, a chemist, but perhaps more a philosopher recently published the book Is Water H2O? . Chang used the question and an extensive web of arguments ultimately as a platform to support a pluralistic approach to scientific endeavor. I don't know that I buy it all, but in a latter chapter he made some statements regarding 'fundamental' components of chemical reactions, and one in particular that interested me and brings me to the point of my question.

Hydrogen gas as I understand it naturally occurs as a hydrogen molecule - two hydrogen atoms stuck together as a diatomic molecule. If ionized, the electron is stripped from the atoms and you have hydrogen ions or rather protons. But what about single hydrogen atoms? Are these non-existent or just a rare thing? Is there some way I can arrange to have a container of single hydrogen atoms and prevent their grouping into hydrogen molecules without ionizing them?

For what answers that follow - do these apply in general to the stable nature of all diatomic gases?


texts: What does it mean by " concentrations are (value) in relation to each other"?

texts:
This is not a home work help question or something like that, these days I self learn chemistry and when I was doing a model paper I came across this question. And the question itself is not difficult but I don't understand this term.

More accurately, I am not familiar with this term,

that part of the question says,

  The cation Ag+(aq) and Hg2^2+ are in an aquesous solution.Their concentrations are 0.2 moldm-3 in relation to each other. Find which cation precipitates first as its iodide when a solution of NaI is added gradually to the above solution... and there are some other sub questions,

If you can explain to me if what it means by "Their concentrations are 0.2 moldm-3 in relation to each other", I think I can do the question easily, Thank you!


texts:
I have been messing around with making Indigo dye while waiting for bacteria to grow. I have been following the Baeyer-Drewson method. Basically, you mix nitrobenzaldehyde with an acetone water mix and slowly add NaOH. The solution turns black and you get a dark sludge. I have been separating the sludge from the liquid by centrifugation. I have noticed that the supernatent has a dark reddish brown color.

I was wondering if anyone knew what the red byproduct was?
My indigo is black when dried, wikipedia shows nice bright blue chunks. What could be causing this color difference? Maybe the red byproduct?
Does indigo dissolve in anything without needing to be reduced first? I have had no luck with the organic solvents available in our lab.


texts: Electrophilic aromatic substitution reaction of dihydrofuran-2,5-dione with anisole

texts: I am having trouble understanding the reaction of anisole with dihydrofuran-2,5-dione (succinic anhydride) in presence of $\ce{AlCl3}$ and acid works or how an electrophile is formed. I feel like the product should be something like $\ce{C11H12O4}$.


texts: While treating 4-aminophenol with acetic anhydride why does the reaction stop at Paracetamol and does not undergo esterification with acetic acid?

texts:
This needs a little background so I will be showing you a question from one of my Organic Chemistry problem books:-

Now, the book shows the answer as Option (c)  which is Paracetamol.
I tried to work out the mechanism and I was pondering over the fact that the
products left in the reaction are Paracetamol and Ethanoic acid . Now Paracetamol contains an -OH(Hydroxy group) and O(Oxygen) atom can easily aquire positive charge by mesomeric stabilisation and attack Ethanoic acid to further form ester (as in Option (a)) . Can someone please help me out ?


texts: Free software for calculating the net charge of an amino acid as a function of pH?

texts: Does a free software for calculating the net charge of amino acids as a function of pH exist?


texts: Is there an easy way to test for the amount of iron (Fe) in water?

texts:
I have a rusty metal rainwater tank, and I'd like to find the amount of iron in the water. (The water I've collected is perfectly clear.)

How would chemists in the 1800's have gone about this? What chemicals/apparatus would I need to purchase?

So far, I've soaked a tissue in the water and am letting it air dry to see if any rust discoloration becomes apparent.

The following info from the WHO might be helpful:

  Iron (as Fe2+) concentrations of 40 µg/litre can be detected by taste
  in distilled water. In a mineralized spring water with a total
  dissolved solids content of 500 mg/litre, the taste threshold value
  was 0.12 mg/litre. In well-water, iron concentrations below 0.3
  mg/litre were characterized as unnoticeable, whereas levels of 0.3–3
  mg/litre were found acceptable (E. Dahi, personal communication,
  1991).

  In drinking-water supplies, iron(II) salts are unstable and are
  precipitated as insoluble iron(III) hydroxide, which settles out as a
  rust-coloured silt. Anaerobic groundwaters may contain iron(II) at
  concentrations of up to several milligrams per litre without
  discoloration or turbidity in the water when directly pumped from a
  well, although turbidity and colour may develop in piped systems at
  iron levels above 0.05–0.1 mg/litre. Staining of laundry and plumbing
  may occur at concentrations above 0.3 mg/litre (4).

  Iron also promotes undesirable bacterial growth ("iron bacteria")
  within a waterworks and distribution system, resulting in the
  deposition of a slimy coating on the piping (4).
  http://www.who.int/water_sanitation_health/dwq/chemicals/iron.pdf


texts: database for catalytic reaction mechanism

texts:
I am looking for a database containing detailed reaction mechanisms for (homogenous) catalytic reactions. Regular organic textbooks or papers generally draw some broad picture of how the mechanism may work, but generally, they skip many steps.
Is there any collection of detailed mechanisms?
I am primarily interested in catalytic reactions.
For clarification:

I am primarily looking for homogenous, metal-catalyzed, non-enzymatic reactions of small molecules.
Searching so far in places like Reaxys or SciFinder did not really result in much more than the bibliography.


texts: Why is the inductive effect of σ-electrons only along saturated carbon chains?

texts:
In my book the following is written:

  When an electron withdrawing atom such as a halogen is attached to the end of a carbon chain, the $\sigma$-electrons of the $\ce{C-X}$ bond are attached to or displaced towards the more electronegative halogen atom, as a result $\ce{X}$ acquires a small negative charge and $\ce{C_1}$ acquires a small positive charge. The small positive charge on the $\ce{C_1}$ in turn attracts the $\sigma$-electrons of the $\ce{C_1-C_2}$ bond towards it. As a result $\ce{C_2}$ acquires a small charge, of course smaller than on $\ce{C_1}$.

Then as $\ce{C_2}$ acquires a small a charge shouldn't the positive charge of $\ce{C_1}$ become less than earlier? Shouldn't it be true?

  ...This type of a displacement of $\sigma$-electrons along a saturated carbon chain whenever an electron withdrawing group is present the end of the chain is called inductive effect.

Why is there displacement of only $\sigma$-electrons not $\pi$-electrons and why does it happen along a saturated carbon chain only?


texts:
What is the most reliable way to calculate mixing enthalpy of binary solvent mixture using GROMACS?

[EDIT]

I have simulated two-component systems of water and organic solvent with GROMACS. In a research paper from my field of study, authors calculate 'enthalpy of mixing' with the software in order to compare it with experimental mixing enthalplies. Under the Experimental Section of the paper, authors show that they do this according to this term:

A comment added in the text says the following:

"The internal energy, U, of the liquid mixture was obtained directly from the potential energy (see Tables S1
and S2) during the simulation, and yi is the molar fraction of component i."

I am interested in calculating same thermodynamical properties for my systems. I am aware that I can do that with g_energy function in GROMACS, or at least some parts of it (Pressure, Volume, Potential Energy).

My question is:
Firstly, is this an appropriate way of calculating enthalpy of mixing in GROMACS via this equation?
Secondly, how can one specify with the g_energy function which of the liquid's U(or potential energy), P and V is calculated if I initiate the function with .edr files, i.e. how can I choose to calculate i'th component's properties?

Reference for the image and quote:

Aguilera-Segura, S. M.; Di Renzo, F.; Mineva, T. Structures, Intermolecular Interactions, and Chemical Hardness of Binary Water-Organic Solvents: A Molecular Dynamics Study. J. Mol. Model. 2018, 24 (10), 292. https://doi.org/10.1007/s00894-018-3817-2.


texts: Rate equation for an elementary reaction

texts:
Yesterday, I had a debate with a friend of mine over the determination of the rate of elementary reactions. He said:

  Rate equation of elementary reaction can be directly given by just raising the reactants concentration terms to the respective coefficients of the balanced chemical equation whose rate is to be determined.

and he also gave the example of this reaction

$$\ce{2NO (g) + O2 (g) -> 2NO2 (g)}$$

whose rate is

$$
\ce{[NO]^2[O2]}.
$$

Questions:

Can I write the rate equation of an elementary reaction by just simply looking at the stoichiometric coefficients in the balanced equation and raising them over the concentration of reactants?
Are there any examples of elementary reaction where the exponential powers on the concentration terms in the rate equation comes different than the stoichiometric coefficients of that reaction?


texts:
I am writing a small simulator for situations where water is the medium of all reactions.

A quick googling confirmed that there are water models available in computer readable formats. Being a beginner in molecular chemistry, I was hoping someone can direct me to already mature libraries which I can use to read water models.

Following seems to be good candidates:

http://msl-libraries.org/index.php/Main_Page
http://ball-docs.bioinf.uni-sb.de


texts: Why does adding salt to boiling water cause it to flare up suddenly?

texts: I was expecting that the water would become less "boily" since the ions in $\ce{NaCl}$ would require energy to disassociate. Instead it turned whitish and the water level suddenly rose and then subsided. I think the white color can be attributed to the fact that table salt is white but why did the water suddenly flare up ?


texts: Chemical bonding and hybridization of organic compounds

texts:
What happens to the lobe of the p-orbital during sp² hybridization?

During the formation of $\ce{C2H4}$ molecule:

We know that both the carbon atoms will have a total of 3 p-orbitals and they will be involved in hybridization.

Let us number the carbon atoms as $\ce{C}1$ and $\ce{C}2$.

Now the p-orbital of $\ce{C}1$ along $x$-axis will form a $\unicode[Times]{x3C3}$ bond with the p-orbital of $\ce{C}2$ and a $\unicode[Times]{x3C3}$ bond with the s-orbital of hydrogen.

And similarly the p-orbital of $\ce{C}2$ along x-axis will form a $\unicode[Times]{x3C3}$ bond with hydrogen.

So both the lobes of the p-orbital of $\ce{C}1$ and $\ce{C}2$ along $x$-axis are involved in sigma bond formation.

Lets say the p-orbital of $\ce{C}1$ and $\ce{C}2$ along the $y$-axis forms a $\unicode[Times]{x3C0}$ bond.

So here also both the lobes of p-orbital of $\ce{C}1$ and $\ce{C}2$ are involved in hybridization.

Let say that the p-orbital of $\ce{C}1$ which is along the $z$-axis forms a $\unicode[Times]{x3C3}$ bond with the s-orbital of hydrogen.

And similarly the p-orbital of $\ce{C}2$ along $z$-axis forms a $\unicode[Times]{x3C3}$ bond with the s-orbital of the other hydrogen.

Now my confusion is that here two p-orbitals along the $x$ and $y$-axes have four lobes and all of them are involved in bond formation.

But the p-orbital which is along $z$-axis has only one of its lobes involved in bonding. What happens to the other lobe of this p-orbital?


texts: how to add a methyl group to a straight carbon chain

texts: I mean like how can I convert ethane into propane, ethene into propene and like this further on


texts: Why can the electron gain process be endothermic or exothermic whereas the ionistation process is always endothermic?

texts:
I know that this may seem a very silly question to some of you but please help me.I am extremely confused.
PS:Sorry if you accidentally stumbled to this question.I can't find the appropriate tags


texts: Why does Pubchem show cis-1,3-cyclohexanediol with the hydroxyls in the equatorial position?

texts:
I am a beginning organic chemistry student and trying to reason about something based on information in my book, but seeing that Pubchem gives a different structure than I'd expect.

In considering a disubstituted cyclohexane with hydroxyl groups at 1 and 3, I'd think, ok, there's a competition between steric strain and hydrogen bonding.  If hydrogen bonding were the more important force, the molecule would be more stable with the hydroxyl groups in the axial position. If steric strain were more important, the molecule would be more stable with the groups in the equatorial position.

The solution manual for Klein's Organic Chemistry [1, p. 128] says in an answer to the problem 4.75 that the stabilizing effect of intramolecular hydrogen bonding between two hydroxyl groups in a gauche conformation is 20 kJ/mol:

  This calculation must be modified when we take into account the effect of two $\ce{OH}$ groups that are gauche to each other, as seen in conformers A and B.  We should expect an $\ce{OH-OH}$ gauche interaction to be less than a $\ce{Me-Me}$ gauche interaction (less than 3.8 kJ/mol), because an OH group appears to be less sterically encumbering than a methyl group (compare $\ce{CH3}$ and $\ce{OH}$ in Table 4.8). Therefore, the destabilizing effect associated with an $\ce{OH-OH}$ gauche interaction (less than 3.8 kJ/mol) should be overshadowed by the stabilizing effect that results from the hydrogen bonding interactions between the two $\ce{OH}$ groups, which is expected to be approximately 20 kJ/mol (see section 1.12). As a result, we expect extra stabilization to be associated with any conformer in which two $\ce{OH}$ groups are gauche to each other.

My book also (in the same answer) says the upper bound for the steric strain in an $\ce{OH-OH}$ gauche interaction is 3.8 kJ/mol, i.e., lower than the value for an $\ce{Me-Me}$ interaction.  It further tells us that 1,3-diaxial interactions are gauche interactions. Klein's Organic Chemistry [2, p. 166] gives in a different table the value of two $\ce{OH-H}$ 1,3-diaxial interactions in a monosubstituted cycloalkane to be 4.2 kJ/mol.

It seems to me like the OH's have steric interactions with each other (3.8 kJ/mol), and they each have an interaction with an axial H (4.2 kJ/mol for both of them).  So at 8 kJ/mol steric strain, it seems like the hydrogen bonding effect should swamp the steric effects.

But Pubchem shows the hydroxyl groups in the equatorial position.  I assume it's showing me the lowest energy conformer.  I don't understand what's wrong with my reasoning above.

References

Klein, D. R. Student Study Guide and Solutions Manual, 3e, 3rd ed.; Wiley, 2017. ISBN 978-1-119-37869-3.
Klein, D. R. Organic Chemistry, 3rd ed.; John Wiley & Sons, Inc: Hoboken, 2017. ISBN 978-1-119-31615-2.


texts:
Why does $\ce{CH2Cl2}$ have a higher dipole moment than $\ce{CHCl3}$?

My argument being that the $\ce{CCl3-}$ ion being rather stable, can generate a good amount of polarity in the bond, moreover, shouldnt the dipoles of both $\ce{Cl}$ atoms cancel out?


texts: Preference of locants in organic nomenclature

texts: Why can't we write the compound 5-ethyl-4-methyloctane as 4-ethyl-5-methyloctane?


texts: Domestic cleaning products and types of solvents

texts: I have a floor cleaner which washes and vacuums the floortiles.   The instructions advise not to use solvent cleaners with it.  My understanding is that even water is a solvent.  The manufacturers/agents will just try to sell me their product.  I want to use cheap domestic solutions (eg. Sugar Soap, Pinoclean, Bar Keepers Friend).    Can anyone advise please? At present I use just hot water, sodium bicarbonate ($\ce{NaHCO3}$) and vinegar of a small amount of washing up liquid.   Thanks.


texts: Moment of inertia for a triatomic molecule

texts: What does the moment of inertia for a molecule mean? How is it useful? Most importantly, how would I go about solving it for a triatomic molecule?


texts: Correlation between 1H and 13C shifts - coincidence or not?

texts:
A quick glance at any table of typical chemical shifts will reveal that the chemical shifts of protons $(\delta_\mathrm H)$ tend to correlate pretty well with the chemical shifts of the carbons to which they are attached $(\delta_\mathrm C)$. This correlation is frequently taught in introductory organic chemistry and the rule of thumb

$$\delta_\mathrm C \approx 20 \cdot \delta_\mathrm H,$$

although simplistic, actually holds up fairly well. To illustrate the point further, here is a diagram taken from the textbook by Silverstein et al. on organic spectroscopy:

Image taken from: Silverstein, R. M.; Webster, F. X.; Kiemle, D. J. Spectrometric Identification of Organic Compounds, 7th ed.; Wiley: Hoboken, NJ, 2005, p 207.

To the beginner such a correlation might seem intuitive. However, delving deeper into NMR theory, one learns that the $\ce{^{13}C}$ chemical shifts are generally dictated by paramagnetic shielding, while $\ce{^{1}H}$ chemical shifts are generally dictated by diamagnetic shielding and effects due to neighbouring groups. See, for example, this question:  NMR chemical shift range of different elements.

In light of this, how much should we make out of the general correlation seen? i.e., is it best understood to be a pure coincidence, or is there more to it than that?


texts: Cleaning a stubborn Electrospray residue

texts:
I have an electrospray ionization capillary tip that sprays into a chamber that contains some circuit boards. An aqueous CsI sample is apparently causing a white residue to build up on these boards after some time. I thought the residue was the salt itself, but I can't dissolve it with water. I tried methanol and that didn't work either. Does anyone know what this could be and how to clean it? I'm worried about excess build up over time.

I considered that it might be CsOH, but that should also rinse away with water because its so soluble.


texts: Measuring mole fraction in lab using Raoult's law

texts: I was reading in my textbook of chemistry on the vapour pressure in liquid compounds, and came across a doubt regarding vapour pressure. If I have two liquids, one is A and another is B, and if I know their vapour pressure in a pure state and their initial mole fraction, would their mole fractions be the same in the vapour phase (after mixing them)? If the answer is yes, how can we prove it? Secondly, if it is practically not possible what other factors should I take into account while solving their value using Raoult's law?


texts: Using an eluent of 1.00 mM NaHCO3 and 8.00 mM Na2CO3 in Milli-Q water, chromatographs were taken of the following anions: fluoride, chloride, nitrate, sulfate And phosphate. Why were the  retention times of sulfate and phosphate longer than those of chloride, nitrate, and fluoride? The retention time of phosphate is not longer than the retention time of sulfate, why? What data do I use to find pH


texts: What's the configuration of chromium(III) in aqueous medium according to crystal field theory?

texts: It has $\mathrm{3d^3}$ configuration, but how will we decide if they enter $\mathrm{t_{2g}}$ or $\mathrm{e_g}$ orbitals since we don't know which complex will form?


texts: Boiling aluminum in high-alkalinity water

texts:
This question ultimately relates to brewing beer, but more specifically to water treatment before brewing.

Though I can't get a water quality report, I suspect I have high levels of bicarbonate alkalinity in my tap water because boiling it causes a white precipitate (which I think is calcium carbonate) to form. I base this assumption on this formula, in the book Brewing:

$$\ce{Ca(HCO3)2 ->[heat] CaCO3 + CO2 + H2O}$$

I wanted to sanitize some aluminum foil so I boiled it in fresh tap water for about 15 minutes. I noticed a few things:

The precipitate formed much faster than it normally would without foil in it.
The foil began to blacken in certain parts.
I'm not positive, but the precipitate seems a bit finer in texture than it normally is.

I thought at first maybe the foil was just providing nucleation points for the carbonate to form around. But then I thought I remembered reading somewhere that aluminum competes with calcium in certain situations (I think it was regarding osteoporosis, maybe). The question I have, then, is whether or not it's feasible that aluminum could be affecting a different reaction than what I'm assuming normally occurs in this situation?


texts:
I saw an old ad for kerosene in which it was advertised at "150 degree test".

What does that mean?


texts: What is the significance of "magic numbers" of atoms in nanoparticles?

texts:
In gold nano particles, as the synthesis method improves to form smaller and smaller nanoparticles, they tend to congregate in magic numbers.

I want to know if these magic numbers occur in other metals besides gold, and whether they contribute to stability, reactivity, catalysis, increased surface area, and their lattice structure? In short, what are the main differences between magic and non-magic nanoparticles?


texts: How to rationalise that when we dilute a weak acid, the pH increases but also the dissociation increases?

texts: When water is added to a weak acid like ethanoic acid, the number of ethanoic acid molecules that dissociate increases, however, pH increases (less acidic), too. Why is this so?


texts: Easily removable material that sticks to skin

texts:
I am looking for some kind of material that can be used to easily latch something to someone's finger. This is for a first year engineering project. The idea is to use this material to latch small motors on someone's fingers in the same way that the motor in this picture is attached. The person should be able to move their fingers around without the motor falling off and the motor should be removable with a slightly strong pull. Also the material should create as small a barrier between the finger and motor as possible so that when the motor vibrates, it can easily be felt by the finger.

I'm thinking more along the lines of a sticky polymer sheet that readily sticks to the skin than some sort of adhesive or fluid glue, but I'm open to hearing all ideas.

Are there polymer materials out there (or particular functional groups) that match this description?


texts: H2O2 (Hydrogen Peroxide) catalysis in clear plastic bottle?

texts:
I am buying some 30% H2O2 which will be in probably black HDPE bottles. If I want to make some 3% - 5% solution, can I store that in clear bottles? How much faster will it catalyse versus having it in a dark bottle?

Will shelf life be significantly shorter? How much effect does sunlight (or other light) have on the H2O2 solution? Any way to measure this?

Regards,


texts: Effect on kinetic energy of a body with change in temperature

texts:
Why doesn’t the energy of a body doubles when temperature in degrees Celsius is doubled?
I know that it doubles in case of kelvin scale.


texts: Do Chemists "discover," "invent," or "create" things?

texts:
I am an ESL teacher, and am designing an activity to teach my engineering students the differences between the words "invention," "discovery," "innovation," and "creation," words that are often confusing for non-native speakers (and as I'm finding out, native speakers.)

I have looked on the internet for usage and it seems to be all over the map: Nobel either invented dynamite, created it, or discovered it, and Teflon was called a discovery.

In my view, physical laws are discovered, as are molecules, fundamental particles, and forces because they already exist naturally.  Teflon cannot be said to be discovered because it does not exist naturally; neither does DDT and thousands of other molecules and compounds.  Is there a plant that produces nitrous oxide?

Based on the usage of "creation" I feel that this word more aptly describes the "process" of chemistry.  Teflon was created, not discovered or invented.

As chemists what usage do you prefer?  Do you prefer the use of inventor, creator, or discoverer?  If there are multiple answers can you help me see why you choose that word?


texts: How to determine the solubility of a Metal Fluoride in liquid Gallium

texts:
How do I determine if a Metal Fluoride is soluble in liquid Gallium and under what conditions the Metal Fluoride will stay in solution in the liquid Gallium?

I am involved in a project that is testing approaches to using CVD to form a graphene layer on liquid Gallium. Fluorine has been used in the process to disassociate methane into carbon and hydrogen and to speed the deposition of carbon. In our project, we are using Acetelyne.

We want to try a different approach of adding a small amount of Fluorine into the liquid gallium itself. With the energies involved it should allow a small amount of F to interact with the process at the surface. I am familiar with all the other aspects but I have never dealt with trying to dope liquid gallium with Fluorine.

My thought was to add a Metal Flouride to liquid Gallium at an appropriate temp/pressure to have it dissolve in the liquid metal. The resulting liquid would be used as a base for deposition at temperatures between 200c to 700c at varying plasma energy levels.

I am considering a few options; SnF2, GaF3, and NaF

Gallium Fluoride would be the best for my application, but the other two are easier to obtain and should still work.

This is going to be < 1 milligram of Metalic Fluoride compound per gram of Gallium and never more than 10 grams of the resulting product at any time.


texts: Why is the dz2 orbital so different from the rest?

texts:
What makes dz2 orbital so special?

Although degenerate with other d orbitals,
It has no nodal planes, instead it has  2 nodal "cones".

Instead of having 4 lobes, it has 2 lobes and 1 ring.

Also, its electron density is prominently distributed in all x,y and z directions unlike others.

I know the wave function is what determines the shape, but what makes this particular orbital different?
Is there any fundamental reason?


texts: Percent composition of nitrogen in fertilizer

texts:
The question was posed as follows:

  Fertilizers supply the essential elements, nitrogen, phosphorus and potassium for plant growth. A bag of fertilizer contains 500g of ammonium sulfate, $ \small \ce{(NH4)2 SO4}$, and 500g of potassium nitrate, $\small \ce{KNO3}$. Calculate the percentage by mass of nitrogen in the bag of fertilizer.

This came in a test of mine and I got the answer wrong, now I did a redo and here's my solution:

(42 * 2)/227  * 100 = 37%

Is this answer correct?


texts: Reaction of coumarin with phenylmagnesium bromide

texts:
I came across this problem..

I thought that the Grignard reagent, PhMgBr, would cleave the lactone and then subsequently add to the ketone formed, giving an allylic tertiary alcohol after aqueous workup. Treatment with acid would then lead to intramolecular etherification, giving 2,2-diphenyl-2H-1-benzopyran:

But then our chemistry professor gave out a different mechanism for this reaction as follows.

What is the correct product?


texts:
I'm probably overthinking this but would appreciate a peer check.
Mole fraction of element $i$ in compound: $\frac{\mathcal{M}_i}{\mathcal{M}}$
I used script M so as not to confuse with molar mass (often denoted as capital M).
Atom fraction of element $i$ in compound: $\frac{N_i}{N}$
Now, if Avogadro's number is atoms/mol then isn't the mole fraction equal to the atom fraction?
$$
\frac{N_i}{N}\frac{[\text{atom}]}{[\text{atom}]} \cdot \frac{N_a}{N_a}\frac{[\text{atom}/\text{mol}]}{[\text{atom}/\text{mol}]} = \frac{\mathcal{M}_i}{\mathcal{M}} \frac{[\text{mol}]}{[\text{mol}]}\\
\frac{N_a}{N_a}=1\\
\frac{N_i}{N}=\frac{\mathcal{M}_i}{\mathcal{M}}
$$


texts: Difference between intermediates and transition states

texts:
Can someone please explain what exactly the difference between an intermediate and a transition state is?

I understand that they are formed as part of the process in converting the reactants to products in a chemical reaction. Other than that, all I know is that usually a transition state exists very briefly (if at all) whereas an intermediate can be isolated. But why?


texts: I know that if there exists a carbon atom with single bonds only (with other atoms),then it is $\mathrm{sp^3}$ hybridized. And if at least one of the bond is double bond then its $\mathrm{sp^2}$ hybridized (not talking about two double bond on same carbon atom). And if there is at least one triple bond then its $\mathrm{sp}$ hybridized. But then carbon in carbon dioxide should be $\mathrm{sp^2}$ hybridized. But if I am right our teacher told it was $\mathrm{sp}$ hybridized. How is that possible if the carbon atom bears no triple bond?


texts:
According to Henry's law

  The solubility of gas in a liquid is directly
  proportional to the partial pressure i.e S=Kp

My book says that higher the value of K at a given pressure lower is the solubility of the gas in the liquid.
I don't understand how. I know I am overseeing something really simple over here as all the books that I have and online websites seem to conclude the same from the given equation. A little help maybe. Thanks.


texts: Variation of angle in GeX2 molecules where X is an halogen

texts:
I'm wondering what is the exact reasoning to explain why in $\ce{GeX_2}$ the angle $\widehat{XGeX}$ is smaller when $\ce{X}=\ce{F}$ than when $\ce{X}=\ce{I}$.

I ask this question because I had an exams some days ago and I failed in this question and for me my reasoning is not false.

What I said is that

  From $\ce{F}$ to $\ce{I}$ the difference of
  electronegativity between the germanium and the halogen is
  decreasing. Then the electrons in the $\ce{Ge-X}$ bond are more near
  $\ce{X}$ when $\ce{X}=\ce{F}$ than when $\ce{X}=\ce{I}$. Then the two
  bonds repulse themselves more for $\ce{GeI_2}$ than for $\ce{GeF_2}$ and so the angle increase from $\ce{F}$ to
  $\ce{I}$.

Why my reasoning is absolutely false, and what could be the perfect one?


texts: Roothaan matrix equation equation orbital coefficients

texts:
To go from the Hartree_Fock

$f\psi{_i}=\epsilon\psi{_i}$

to the  Roothaan equation

$FC=SC\epsilon$.

equation we expand the orbitals as

$\psi{_i}=\sum C_{\mu i}\phi_i$

But for Helium atom we have just one orbital function so the coefficient $C_{\mu i}$ should be a vector not a matrix.
My question is  what is the interpretation of the matrix coefficient $C$ in the Roothaan equation  $FC=SC\epsilon$ for the helium atom since we've got just one spatial orbital function?


texts: How do I distinguish between internal energy and enthalpy?

texts:
I am finding it hard to distinguish between the two. Can someone explain the two terms and the difference between them?

I tried learning from Wikipedia, but it said for both the above terms that it is the total energy contained by a thermodynamic system.


texts: I was wondering whether or not the reason some noble gases, like neon, fluoresce at particular frequencies of the visible spectrum is because of a Stokes effect? I mean, do the neon dimers get stretched out dramatically at a more LUMO state, resonating with high energy electricity due to the high stability of noble gases, and then contract back to a more HOMO state, releasing red light, which has a much lower frequency? Noble gases, like neon, have a high quantum yield, correct?


texts: Heat capacity of mixtures is higher than their pure contituents?

texts:
I'm currently studying the effects of how changing mixed-refrigerant compositions effects their heat capacity. Surprisingly, my data suggests that some combinations of mixed-refrigerants have heat capacities larger than their pure constituents. This seems to violate Kopp's Law which states:

  The molecular heat capacity of a solid compound is the sum of the atomic heat capacities of the elements composing it; the elements having atomic heat capacities lower than those required by the Dulong–Petit law retain these lower values in their compounds.

The mixed refrigerant compositions include: methane, ethane, propane and nitrogen. The graph below shows average, minumum and maximum heat capacity values over the temperature range from $\pu{130 K}$ to $\pu{280 K}$ and pressure range from $\pu{1 bar}$ to $\pu{100 bar}$.

Is there another possible explanation as for why a combination of the above components would have a higher capacity than their pure constituents? I was thinking along the lines of molecular interactions and deviations from the ideal gas law.

Here is a graph of my findings:

Note: I am using a gas physical property software for these calculations.

link: https://www.dnvgl.com/services/gasvle-8331


texts: Is the XRF spectroscopy equally sensitive for every element?

texts: I am curious whether or not every element can be equally well detected by using X-Ray-fluorescence-spectroscopy. Might there be any contitions or circumstances that make it hard/impossible to detect a certain element in a probe?


texts:
Suppose you've got some reaction that has a positive $\Delta H$, and also has positive $\Delta S_\mathrm{sys}$. Due to the equation
$$\Delta S_\mathrm{tot} = \Delta S_\mathrm{sys} - \frac{\Delta H}{T}$$
a low enough temperature will cause $\Delta S_\mathrm{tot}$ to be negative. At this point the reaction won't happen anymore because second law and whatnot.

What exactly is happening at the molecular level that prevents molecules from reacting with each other? The orientation of the molecules is more or less random, and the Maxwell–Boltzmann distribution means there ought to be some particles with sufficient kinetic energy, so what's happening? If the reactants are left long enough, 2 molecules with acceptable orientations & kinetic energies should whack into each other.

A while ago I found the "micro-states per macro-state" explanation of entropy. I get that entropy isn't a property of a single particle, or even of a specific arrangement (microstate) of particles (please correct if wrong). Honestly this just makes me even more clueless as to my above question.

I hope I haven't made this too unclear.


texts: What makes Coke and other soft drinks acidic?  These drinks are carbonated, so a freshly-opened can should have a lot of dissolved carbonic acid, but the ingredients also lists phosphoric acid.  Would flat Coke be significantly less acidic than carbonated Coke?


texts:
A kid asked me this question just the other day, and I said that the positive part of $\ce{H2O}$ attracts the negative $\ce{Cl}$ ion and the negative part of the $\ce{H2O}$ attracts the positive Na ion.

Then he asked me several questions which stumped me:

Why doesn't $\ce{NaCl}$ dissolve water instead (break water into $\ce{H}$ and $\ce{O}$)?
If $\ce{H2O}$ is electrically neural, why would it attract any ions?
Why doesn't $\ce{NaCl}$  stick together, how can one know if one molecule will attract the ions hard enough that the ions breaks away?
Why is Na positive and $\ce{Cl}$ negative?

Hopefully someone can help me answer the above questions as I have not done chemistry in years!


texts: How can a Hydrogen make such a difference?

texts:
Looking at familiar bodily fluids for a learning session. At first glance they both look the same. Then I noticed the N=C in biliverdin and HN-C in bilirubin. How can a N=C (imine group) and HN-C (secondary amine) make such a difference in colour? They look like structural isomers of each other to me. Or is there any stereoisomeric differences as well to this colour functional group change?

(Jaundice is directly related to bilirubin, urine is a product of bilirubin, I reckon there must be a real good reason and help aid from the colour change representation.)

e.g.

image 1: bilirubin is a brown pigmented substance while biliverdin is green pigment

image2


texts: electrolysis in aqueous solution. Why is hydroxide discharged at the anode when no halide ions are present

texts: Why are hydroxide Ions discharged when halide ions aren’t present in aqueous solution during electrolysis


texts: How does the relative acidity of 2,3-dinitrophenol compare to that of 2,4-dinitrophenol?

texts:
I am assuming that the -I inductive effect in 2,3-dinitrophenol is stronger than in 2,4-dinitrophenol since it operates through less bonds, therefore on inductive grounds it should have a lower $\mathrm{p}K_\mathrm{a}$?

However it's unclear to me whether there are any differences in  π-resonance effects. Any help?


texts: What is the order of dipole moments for $\ce{SO3, SiO2, P2O5,}$ and $\ce{Cl2O7}$? This question is from a book and the answer given is $\ce{Cl2O7 < SO3 < P2O5 < SiO2}$. Can someone explain why? When I drew the Lewis structures and applied VSEPR theory, it seemed that all the given compounds have zero dipole moment.


texts: What is a electronic configuration of scandium ion?

texts:
The electronic configuration of Scandium is: $\ce{[Ar] 4s^2 3d^1}$

What is the electronic configuration of Scandium ion?

Also about the electronic configuration of Cobalt, which is $\ce{[Ar] 4s^2 3d^7}$. So What is the electronic configuration if Cobalt ion?

Is it $\ce{[Ar] 4s^2 3d^6}$ or $\ce{[Ar] 4s^1 3d^7}$ ? And why?

Thanks for your help.


texts: How much energy is stored when H+ is converted to H2?

texts:
I'm doing a write-up for this for my students:

Source: Amirav Research Group (Facebook)

The energy of formation of isopropyl alcohol is $-318.2~\mathrm{kJ/mol}$ (kilojoules per mole), that of acetone is $-249.4~\mathrm{kJ/mol}$, so $68.8~\mathrm{kJ/mol}$ are gained on this end.

But I'm getting confused about the hydrogen end. I'm seeing that The energy of formation of $\ce{H+}$ is $0~\mathrm{J/mol}$ (it can be treated as a free proton), and that of $\ce{H2}$ is also $0~\mathrm{J/mol}$. Of course you would say that oxygen has $0~\mathrm{J/mol}$ as well, so since  water has enthalpy of formation of $241.83~\mathrm{kJ/mol}$, I'd expect it to yield that much energy in the combustion.

But hydrogen gas has an “energy density” as a fuel of $71~\mathrm{kJ/mol}$. So the treatment that $\ce{H2}$ and $\ce{O2}$ have $0~\mathrm{J/mol}$ enthalpy of formation and water has enthalpy of formation of $242~\mathrm{kJ/mol}$ seems to not square with that. Where's the rest of the energy?

Particularly, in the diagram above you see the charge separation as the electron pair moves to the hydronium, producing hydrogen. But a charge separation (J = coulomb volt) is energy, so moving the electrons to the hydrogen has to be adding energy to them, which seems to indicate that the $\ce{H+} = 0~\mathrm{J}$ and $\ce{H2}$ also = $0~\mathrm{J}$ things is wrong. But I don't know where to go from here, does anyone feel confident helping with this?