texts: What is role of palladium in hydrogenation reactions?

texts: Why is palladium used in hydrogenation reactions? Is there any theory about the role of palladium and other catalysts in those reactions?


texts: Why is an electropositive metal like Zinc capable of plating out?

texts:
I know that electronegative metals like copper or silver can electroplate out of an aqueous solution in electrolysis. However, I've also noticed $\ce{ZnSO4_(aq)}$ can electroplate out when electrolyzed, yet Zinc is more electropositive than hydrogen. This doesn't happen with other electropositive ionic solutions like $\ce{Al(C2H3O2)3_(aq)}$.

Why does this happen, and why is it limited only to Zinc?


texts: CH4 + O2 => CO2 + 2H2, what's wrong with it?

texts:
It says in my textbook that:

$$\ce{CH4 + 2 O2 -> CO2 + 2 H2O}$$

which seems like a displacement reaction to me. Shouldn't the reaction be:

$$\ce{CH4 + O2 -> CO2 + 2 H2}$$

since $\ce{4H}$ are displaced by $\ce{O2}$ (becoming $\ce{2 H2}$), which makes the reaction balanced?

Why is the reaction $\ce{CH4 + O2 -> CO2 + H2O}$, which is further balanced as my textbook says?


texts: House-hold chemistry experiments for a high-school student

texts:
I want to experiment the things which we learn in chemistry as a twelfth grader.I want to do them at my home but I'm not supplied with enough reactants.What can I do by using such reactants.

I tried to carry out paper chromatography at home and that was the separation of a mixture of inks. I didn't have  filter paper so I used a tracing paper.
My solvent was a common organic solvent. But to my dismay,solvent front didn't rise so high. So my experiment didn't succeeded but I'm hopeful I can do other things too which'd be successful.
It was first experiment

Can someone recommend a few projects/experiments (or sources that do the same) for a school student who's looking to improve her understanding of basic chemistry?


texts: How much CO2 is produced in burning of a candle?

texts:
I've been reading this book, page 149. In chapter 15 the following experiment is suggested,

  Fix a candle in a container. Fill the container with water. Light the candle and then cover it with an inverted glass.

It is said that the oxygen in the space of inverted glass will be used up and to fill the space that was previously occupied with oxygen the water level will rise.

My question is, when the wax burns since $\ce{CO2}$ is emitted, won't this $\ce{CO2}$ fill up the space of used up $\ce{O2}$? What amount of $\ce{O2}$ is used up and what amount of $\ce{CO2}$ is released in the burning of wax of candle?


texts: Are any bonds broken when NO2 becomes N2O4?

texts:
This reversible reaction occurs in room condition:

$$\ce{2NO2 <=> N2O4}\quad(\Delta H=-57.23\mbox{ kJ/mol)}$$

This is the Lewis structure of $\ce{NO2}$ (courtesy Ben Mills via Wikipedia):

This is the Lewis structure of $\ce{N2O4}$ (courtesy ChemSpider):

To me, it seems that no bonds need to be broken for the forward reaction ($\ce{2NO2 -> N2O4}$) to occur, which is strange indeed.


texts: Beryllium carbonate is reported to be unstable under normal conditions and should only be kept in a atmosphere of $\ce{CO2}$. Why and how this stability is maintained? Why does this compound decompose when kept in an atmosphere of oxygen?


texts:
Are there any other colligative properties other than lowering of vapor pressure, osmotic pressure, boiling point elevation, and freezing point depression? I was wondering whether surface tension of an aqueous solution is colligative or not, but I mostly think it should be. Can anyone help?

Edit: I am pretty aware of what a colligative property is. It's a property's of the solution that doesn't depend on the nature of solute, rather only concentration of the solute, and the nature of solvent.


texts: What is the 3D shape of an ethane molecule?

texts:
I am currently teaching a course on groups, and want to give my students "real life" examples of symmetry groups to think about. The ethane molecule would be one such.  But, the on-line sources don't all agree on the exact shape. I'm fairly sure ethane looks like either this

or this.

I oriented the molecules in such a way that the carbon atoms are on top of each other. The difference between the two choices is how the groups of three hydrogen atoms relate to each other. In the latter alternative the molecule is its own mirror image with respect to the plane bisecting the line segment joining the carbon atoms. Meaning that the hydrogen atoms also pair up in a way that they are on top of each other. However, in the former version this is not the case, and you would need to rotate one triple of hydrogen atoms by 60 degrees to move them on top of each other.
To turn this into a homework problem I would like to know which is correct?
Wikipedia suggests that the one on the top is correct. However, the picture below also appears in some places. Like here.
My theory: Whatever little I know about physics/chemistry suggests to me that the top one is more likely. The reason being that the similarly charged hydrogen atoms repel each other (possibly this is only a dipole or a higher order effect?). Therefore it stands to reason that one triple of hydrogen atoms is aligned in a way that they use the "in-between" angles.
Nitpick: The "correct" answer probably is that neither of these two images is quite right. You see, I generated them using the tetrahedron (=methane) angle of 109.5 degrees everywhere (simpler for me to do it that way). But Wikipedia says that the angle between the carbon-carbon bond and a carbon-hydrogen bond is slightly larger, 111.17 degrees. So the hydrogen atoms at the top should be pushed a teensy bit further up and similarly the ones at the bottom a little further down. A bigger similar effect is that in the actual molecule the distance between the carbon atoms is larger than the carbon-hydrogen distance. Neither of these has an effect on the collection of symmetries the molecule has, but the answer to my main question does have an impact. That's why I am asking.
If somebody is inclined to elaborate on the reason(s) why we don't have that methane angle everywhere, I will be educated further :-)


texts: Effect of Steric Environment on Selectivity of Protection by Sisyl Chlorides

texts:
(sorry about the poor diagram. I don't know how to add in the arrows and stuff)

  Draw the product when the following compound is reacted with sisyl chloride in the presense of DMF catalyst at $\pu{-10^\circ C}$?

My Attempt

I know that sisyl methyl is a silicon protecting group that readily forms $\ce{Si-O}$ bonds. However I am not entirely sure how the different steric environments will effect which oxygen is protected.

I am guessing that the primary alcohol group will get protected since it is a primary alcohol, hence there will be less steric hindrance for the bulky sisyl chloride molecule to attack the primary alcohol group compared to the secondary alcohol group.

I am not sure if there are other factors that effect which oxygen will get protected. For example, I am not sure the effect of the double bond on the secondary alcohol (I don't think that there is an effect since it is too far away).


texts: Are the coefficients and exponents of contracted gaussian same for cartesian and pure form?

texts:
The cartesian form of contracted gaussian is something like
$$\phi^{CGF}=\sum_{n} s_nx^iy^jz^k \exp(-\alpha_nr^2)$$
and these is also a pure or spherical harmonic version (which I don't know the details about).
Are the coefficients and exponents same between the two, different for $\ge d$ orbitals, or different for all orbitals.


texts: Find the major product when Benzoquinone reacts with HBr

texts:
What is the major product when Benzoquinone reacts with $\ce{HBr}$ ?

My effort: I thought it would be an $\text{SN}_{1}$ mechanism, but the carbocation at either double bond wouldn't be stable.


texts: why is tertiary carbocation more stable than primary allylic carbocation?

texts:
According to general organic chemistry the order of stability is as follows:

aromaticity > resonance > hyperconjugation > inductive effect

Since primary allylic carbocation shows resonance as well as hyperconjugation, moreover resonance is greater than any other effect then why is primary allylic carbocation less stable than tertiary carbocation.


texts: Is there any sort of correlation between melting point and the degrees of freedom for the molecules of a substance?

texts: Suppose I had a solid whose molecules did not have rotational freedom. But if I were able to make it so that the molecules had rotational freedom ceteris paribus, is there a way to tell how the melting point would change compared to the original solid. Here I assume that the molecules have rotational freedom in the liquid phase always.


texts: My son put Lysol in the oven, how do I make it safe again? I really don't want to blow up my house over a chicken pot pie. I have new recipe that I really want to try out and it does not include bleach, or Lysol.


texts: Nomenclature in case when same fucnctional group is present more than once

texts:
here since Only CN group is present, it is the major functional group. In this molec. we cannot have a chain which has carbons of all CN group. hence in such compounds we do not take any carbon of cn in the parent chain.so answer should be 3.
but few books and many reference texts are showing
name as option d.


texts:
I'm studying about formulation of Born-Oppenheimer approximation from Atkins, Molecular quantum mechanics, 5th edition. In chapter 8.1 I found the following:

I keep wondering where did this W come from in equation 8.4.? It says later in text that it is responsible for non-adiabatic effects, but I don't see how it just appeared here. If someone is willing to explain, I'd be greatful.

Also, if anyone has tips on where to find more nice and clean text about more general formulation of Born-Oppenheimer approximation, since this one is confined to particular system.

Thanks!


texts: The partition coefficient for a chemical species across a membrane

texts:
What factors influence the partition factors across a membrane for a chemical species? Wikipedia defines the partition coefficient as:

  In the physical sciences, a partition-coefficient (P) or distribution-coefficient (D) is the ratio of concentrations of a compound in a mixture of two immiscible phases at equilibrium.

If we let these "two immiscible phases" be either side of the membrane, In this situation the equilibrium concentrations would be determined by the solution either side of the membrane? If there is water either side of the membrane would they have a P of 1?

I'm not a chemist (or biologist for that matter) so apologies for any misuse of terminology or ambiguity.


texts: What route to take in converting ethanol to crotonic acid?

texts:
The question asks to write the theoretical transformation steps to convert ethanol to crotonic acid in considerable yield. One constraint is that you cannot use any external organic compounds but inorganic catalysts and reagents are allowed and aldol condensation is prohibited. I do not know the answer, but I came up with the following steps:-

Treatment with $\ce{HBr}$ to form $\ce{CH3CH2Br}$ via $S_N2$.
Treatment with $\ce{Mg}$ in ether, to form corresponding Grignard reagent.
Oxidation of ethanol by Pyridinium chlorochromate to ethanal, and then treating it with the formed Grignard reaction to form $\ce{CH3CHOHCH2CH3}$.
Acid catalysed dehydration to form $\ce{CH3CH=CHCH3}$.
Using NBS (N-Bromo Succinimide) as an allylic halogenating agent, followed by treatment with aq. $\ce{KOH}$ to give $\ce{CH3CH=CHCH2OH}$.
Oxidising this with PCC followed by Tollen's reagent to selectively oxidise alcohol to acid, to finally yield crotonic acid.

I am unsure if any of these steps are incorrect, i.e if any of these steps will not give appropriate yields of the desired product owing to side reactions. Another problem is that this transformation is too long. Is there any shorter way to carry out this conversion in proper yields?


texts:
When we write for an equilibrium that $$\Delta G^\circ = -RT \ln(K)$$  Which type of  $K$ , ie is it $K_\text{concentration}, K_\text{pressure}$ or $K_{\chi}$ because all these have different numeric values which will give different values of $\Delta G^\circ$ which is obviously not possible.

Edit: In the question marked as being duplicate of, they still don't tell which $K$ it is. Even if we divide by the appropriate standard value, and make it unitless, $G$ will still give different values based on $K_\text{concentration}$, $K_\text{pressure}$ or $K_{\chi}$.
Also can $K_{\chi}$ also be used as it is dimensionless less too?


texts: Why is Polonium the only metal to crystallize forming Simple Cubic Cell?

texts: I have read that Polonium is the only metal that crystallizes forming SCC. I searched for a concrete explanation but all they were saying is the stability of Polonium at STP. I can't really comprehend their explanation.


texts: Cheap silocone casting resin (1 or 2 component resin)?

texts:
I searched in many places and on Youtube and I found ways
to make silicon mold putty from cheap silicone using ordinary
household stuff and kitchen stuff.

But nowhere is a recipe on making silicon casting resin out of the cheapest everyday silicone.

Clearly, casting resin has a much better usage spectrum than molding putty and it is the way molds should be created. Ethylene-Acetate dissolves silicone and results in very long
hardening times (weeks or months) and I suspect that it also
could make the molds shrink a lot while hardening. Any ideas?

I am not dependent on kitchen materials and I can buy some
chemicals like Ethylene-Acetate in the local painter's store.


texts: Is there an adhesive with an on-and-off switch?

texts: Is there a strong adhesive (can carry about 2 kg in the air) that can be switched on or off, for example with electricity or changing the acidity of the surrounding medium, though I prefer electricity if possible. I have found a few articles on the internet but can't verify them. This is one of them.


texts: What is the evolutionary reason for the existence of rings in molecules?

texts:
Just to give you a bit of context, I don't have any background in Chemistry. I'm actually a Computer Scientist adventuring myself in the world of Chemoinformatics (more specifically, we're developing algorithms to improve drug discovery).

I noticed that many molecules (or at least drug-like molecules) have rings, but I was wondering: from an evolutionary perspective, what does it mean? Why did molecules evolve to have this "feature", do molecules with rings have better properties then similar ones without rings?


texts: We determined the hydrogen wavefunctions exactly, and the orbital approximation says that we approximate the orbitals of multi-electron atoms with hydrogen wavefunctions. How do we know that this is an okay approximation to make? How much error is there in assuming this?


texts: IUPAC Naming of CH3C(p-ClC6H4)2CH(Br)CH3

texts:
According to the locant rule, the numbering should be done from left end, as from left end locant positions are 2,2,3 and from right it is 2,3,3.

So, the IUPAC name should be 3-bromo-2,2-bis(4-chlorophenyl)butane. But according to most textbooks, its name is 2-bromo-3,3-bis(4-chlorophenyl)butane. Is alphabetical prefrence given to bromine, and if so, why?


texts: Other liquids for collecting gas by displacement method for SO2

texts:
I am looking for a low cost method of quantifying gases evolved from a reaction. The gas mixture is expected to have $\ce{H2}$, $\ce{SO2}$ and $\ce{CO2}$ but likely others too. I am considering using a syringe but am somewhat apprehensive about syringe friction and back pressure distorting volume. Commonly used water displacement method obviously would not work due to soluble and reactive gases in the mix. Is there an inert replacement for water for this method to work with $\ce{SO2}$?

I thought about allowing the $\ce{SO2}$ to react in the water and then calculating the amount through pH change. However, $\ce{CO2}$ is also soluble (and others too perhaps)

Without access to chromatographic or other elemental analysis equipment, is there a primitive way of just measuring the volume of this gas mixture?


texts: E / Z Isomers GC peaks for identification; Would GC-MS help?

texts:
Does a GC analysis typically seperate E / Z isomers? I'm reading a paper that confirms that the product it synthesized was indeed the (E,E) isomer by coinjecting a standard sample on the GC.

My question is, had they actually made an (Z,Z) or (E,Z) or (Z,E) would a typical GC show two different peaks?

In other words, for isomer verification of this nature is a GC co-injection a sufficient control? Or would it be more prudent to co-inject standard samples of the other samples too in other runs to demonstrate that those indeed elute differently?

The paper also claims they have verified the compound as a (E,E) by a GC-MS analysis but would (E,E) (E,Z) etc. show different patterns on a GC-MS?


texts: How to know which way to calculate an extraction

texts:
I have been solving a number of extraction problems and thought I had figured out how to solve each problem depending on if I started in an aqueous solution or in an organic solution. However, I just tried to solve a problem which I believe goes against what I thought to be correct. Hopefully someone here can tell me if I have gone mad or if I am right and the answer key is wrong.
For an extraction going from aq to org
I have used the following formula to determine the fraction left in the aqueous phase:
$$ p = \frac {1}{1+ (K_D * V_b/V_a)}$$
For an extraction going from org to aq
I have used the following formula to determine the fraction left in the organic phase:
$$ p = \frac {1}{1+ ( V_b/(K_D*V_a))}$$
So in the following problem I have

$$PhOH (toluene)  ⇌ PhOH (aq) $$
$200$ml of aqueous solution which contains $1 *10^{-3}$M PhOH is shaken seven times with $25$ml toluene. How great is the fraction of phenol extracted from the aqueous solution to toluene?

From what I stated above I should use the first equation (aq to org), which gives me:
$$ p = (\frac {1}{1+ (K_D * V_b/V_a)})^7 = (\frac {1}{1+ (14 * 25/200)})^7 = 8.41*10^{-4} $$
Amount extracted to the org phase: $1-8.41*10^{-4} = 0.999 = 99.9$%
This is not the correct answer, but if I use the second equation (org to aq) I get the answer which is correct:
$$ p = (\frac {1}{1+ ( V_b/(K_D*V_a))})^7 = (\frac {1}{1+ (25/(14*200))})^7 = 0.939 $$
Amount extracted from aq phase: $1-0.939 = 0.06 = 6$%
Have I misunderstood how these equations work? Or why is it that I should solve the problem as if I am starting in the organic phase? All help is appreciated!


texts:
What chemical can be used to absorb $\ce{O2}$ from the air at normal temperature and pressure, then release the $\ce{O2}$ at normal pressure and elevated temperature, below $\pu{900 ^\circ C}$ ($\pu{1650 ^\circ F}$), that can be cycled many times?
Closest solutions I've found are silver, but its quite expensive, and absorbs oxygen slowly at normal temperature. And possibly phosphorous, but it is toxic and needs a solution.
Same question about $\ce{N2}$. I'm interested in separating $\ce{N2}$ and $\ce{O2}$ without the use of single-use chemicals or pressure pumps. Using cycled heat as a source to drive the reaction.
I expect there is some oxide that can switch oxidation levels back and forth with temperature, like hematite and magnetite.
Idea solution will be something like $\ce{CaCO3}$ is for $\ce{CO2}$. A cheap material, that quickly reacts with $\ce{CO2}$ at normal pressure and temperature. Quickly releases the $\ce{CO2}$ at elevated temperature and normal pressure.
I did check the search, it seems people usually offer to use electrolysis for this task. But water is way too costly to electrolyze in terms of power. Is there something that can be electrolyzed with $10$ times less energy, to get oxygen, that can be safely oxidized again later? Hydrogen is rather dangerous too.


texts:
How do we define an equivalent when we are not talking about any particular reaction? Like, we say that equivalent volume of Oxygen is 5.6L, so we have taken the n-factor to be 4, and in CO2 we take n-factor = 2.
What is the defining factor for an equivalent here?


texts: Deviation of Ytterbium from general trend

texts: What is the reason for deviation of ytterbium from the general trend of lanthanides in terms of hardness, melting point, density etc.?


texts: Column Dispersive Mass Balance analytical / numerical solution

texts:
Is there any analytical solution for the most common expression of column mass balance:
$\dfrac{\partial C}{\partial t} + \left(\dfrac{1+\varepsilon}{\varepsilon}\right)\dfrac{\partial q} {\partial t} + u \dfrac{\partial C}{\partial t} \:\:=\:\: D_{\mathrm{axial}}\:\dfrac{\partial^2 C}{\partial t^2} $
This is the most common isothermal form for just one gaseous solution (two expressions for concentration change between the phases, convective flow and flow dispersion). If you consider adsorption from the "side" of adsorbent (solid phase), the density of fixed bed $\rho_{{\mathrm{bed}}}$ should be considered. $\partial q\big/\partial t$ is expressed by LDF (linear driving force) model which simplifies PDE to ODE.
What I would like to know:

I know that these equation can be always solved numerically, but is
it possible to solve this balance analytically for certain boudary /
initial conditions? If so, how would you express $\partial
   C\big/\partial t$ ? (I cannot find a direct question anywhere, some suggest it may be solved analytically with certain simplifications without giving any details)
There are several mathematical models for numerical solution. Which one would be suitable for adsorption? Unfortunately, literatures I found does not go into details.


texts: How to recreate bioluminescence in fireflies in a lab?

texts:
I have several mg/mL of D-luciferin, luciferase (firefly), ATP solution (25 mmol) and MgSO4 (for the mg2+ ions). The experiment has to be done in cuvettes of 2,5 mL (if I get any results, it will be measured with a spectrophotometer).

I was wondering if you can give me an idea/tips/advice how I can recreate bioluminescence with those chemicals.

I am struggling with the ratio's of the chemicals, pH and whether I should dilute the solution or not.

I don't know how I should mix the ratio's of D-luciferin, luciferase, ATP solution etc.
Next thing is pH, I dont know what the optimal pH will be of this mixture and how I can change the pH accurately. These two points go with dilution as well, because I want to use water as a solvent and for dilution, but I dont know if it is needed or not.

(Also, if you know how the other chemicals might impact the energy that will be absorbed in the mixture and how it will be released when you know that the emission wavelength of D-luciferin is around 530 nm in water, please share you knowledge if you want)

I would greatly appreciate it if someone can give me advice or lead me to the right direction on the problems that I am facing with this bioluminescence experiment. I have tried asking this to other people, but no one was willing to help me, please.


texts:
I feel that there are very few textbooks that treat the chemical potential of mixtures in an understandable clear way, which is why I wanted to ask here about certain things. Although I do not have a single question, but 5 of them, I think that it is merely impossible to separate them thematically, which is why I hope to meet an expert here.

If we have an ideal gas then if we know the chemical potential for a particular $(p,T)$ we have:

$$\mu(p_2,T) \approx \mu(p_1,T) + \left(\frac{\partial \mu}{\partial p} \right)_T(p_1,T) (p_2-p_1) = \mu(p_1,T) + \frac{V}{N}(p_2-p_1).$$

Similarly for changes with respect to temperature we have
$$\mu(p,T_2) \approx \mu(p,T_1) + \left(\frac{\partial \mu}{\partial T} \right)_p(p,T_1) (T_2-T_1) = \mu(p,T_1) - \frac{S}{N}(T_2-T_1).$$

Now, if we have either a gas or a liquid (Question 1: is this true, does this law hold for both fluids?) $\ce{A}$ and put another material $\ce{B}$ into it, then we have by Raoult's law:

$$\mu_{\mathrm{A,~with~mixed~B}}(p,T) = \mu_A(p,T) + RT\ln\left( \frac{N_A}{N_A + N_B} \right)$$

Question 2: Now, is the chemical potential of the total fluid given by $A$ and $B$ then the sum $\mu_{\mathrm{A+B}} = \mu_{\mathrm{A,~with~mixed~B}}(p,T) + \mu_{\mathrm{B,~with~mixed~A}}(p,T)$?

Let's imagine that $A$ and $B$ would be gases, would this mean that

Question 3 : $$\mu_{\mathrm{A,~with~mixed~B}}(p,T) = \mu_\mathrm{A}(p,T) + RT\ln\left( \frac{p_\mathrm{A}}{p_\mathrm{A} + p_\mathrm{B}} \right) ?$$

Question 4 : And what if $\ce{A}$ and $\ce{B}$ would be two two miscible liquids? could we still use the vapour pressures to calculate the chemical potential of the liquids mixture?

$$\mu_{\mathrm{A,~with~mixed~B}}(p,T) = \mu_A(p,T) + RT\ln\left( \frac{p_\mathrm{A}}{p_\mathrm{A} + p_\mathrm{B}} \right) ?$$

Now, imagine that I have a liquid $\ce{A}$ and salt $\ce{B}$ in it. Also, I have a gas layer $\ce{C}$ of $\ce{A}$ above the liquid. What exactly is now in equilibrium: $\mu_{\mathrm{A+B}} = \mu_\mathrm{C}$, or $\mu_{\mathrm{A,~with~mixed~B}} = \mu_\mathrm{C}$?

Question 5: My last question would be: Imagine that you have a liquid (let's say water) and some gaseous water phase above (according to the vapour pressure). Now, you add oxygen to this. What would this mean for the chemical potentials of the liquid/gas water?


texts: Meaning of mass concentration "units" % m/v

texts:
In a saline solution that is 5.750% (m/v) potassium iodide $(\ce{KI}),$ there are:
a) 5.750 mL $\ce{KI}$ per 100.0 mL $\ce{H2O}$
b) 575.0 mg $\ce{KI}$ per 10.00 mL of $\ce{KI}$ solution
c) 5.750 g $\ce{KI}$ per 100.0 g $\ce{H2O}$
d) 5.750 g $\ce{KI}$ per 100.0 g of $\ce{KI}$ solution
e) 5.750 g $\ce{KI}$ per 100.0 mL of $\ce{H2O}$

I figured it should be e because for the equation of $(\text{m/v})\%$ is
$$(\text{m/v})\% = \frac{\text{mass solute (g)}}{\text{volume solution (ml)}}$$
and it's $\pu{g/100 mL},$ but it's not the correct answer.


texts: Confusion in naming a carboxylic acid with a cyclohexyl group

texts:
For the below compound  .

According to me the answer should be 1-carboxymethylcyclohexane.
But the answer given as 2-cyclohexylethan-1-oic acid
Why the name given by me is wrong .
Whereas the name given to

Is cyclohexane-1-carboxylic acid
Why it is not 1-cyclohexylmethan-1-oic acid


texts: Molecular Orbital Hybridization vs Delocalization for positive charge stabilization

texts:
While studying Molecular Orbital Theory, I ran into a comparison of basicity between pyridine and piperidine. The latter was concluded to be more basic because of the sp3 hybridization of the positively charged nitrogen opposed to the sp2 hybridization of the pyridine nitrogen. The p orbitals are higher in energy, hence, the higher the p influence on the final hybrid orbital the bigger it will be in energy. Higher energy orbitals result in higher stability for positive charges.

On another moment, when reading about carbocation stability, it was stated that tertiary carbocations are more stable due to the delocalization of the positive charge.

Both statements regarding the positive charge stabilization makes sense, but here's where I started getting confused:

If positive charge delocalization plays a big role on carbocation stability, wouldn't the π-system of the pyridine help delocalize the positive charge through resonance? Wouldn't that compensate the effect of the orbitals lower energy (due to higher s orbital character)?
Considering the answer to the above question was that the orbital hybridization actually plays a bigger factor in positive charge stabilization than delocalization, then why alkynes like methylacetylene are attacked in the secondary carbon (which are sp hybridized in the carbocation form?) and not in the sp3 hybridized carbon? (Consider R = CH3 in the image below)

Could someone give me a light on those matters? I assume I might be making a confusion regarding the carbocation hybridization of methylacetylene, would the secondary carbon have a sp geometry when it's positively charged?


texts: Determining the amount of chlorine in a swimming pool

texts:
I need to determine the amount of chlorine in a swimming pool. How do I get started? What kind of experiment would I need to carry out?
What equipment would I need for this experiment?


texts: High pressure modification to the van der Waals equation

texts:
I get that a gas behaves non-ideally under high pressure and low temperature conditions. At high pressures, the density of a gas increases and attraction forces operate among molecules due to short intermolecular distance. This allows us to somehow modify the ideal gas equation. If a molecule is approaching the wall of container in order to collide, the neighbouring gas molecules soften their impact.

$$p_\text{ideal}=p_\text{real}+\frac{an^2}{V^2}$$

How was the term $\frac{an^2}{V^2}$ derived?
My thoughts about that term, $\frac{n^2}{V^2}$ may be the extra pressure thats why the $V$ lies on the numerator (inverse relationship)


texts: My lecturer said that in a $\ce{C-S}$ bond, sulfur is slightly $\delta^{-}$ and the carbon slightly $\delta^{+}$, although they have (almost) the same electronegativity. What is the cause of this phenomena if it is not electronegativity?


texts: Why is a ketone not capable of hydrogen bonding among themselves?

texts:
The ketone has one oxygen atom in it and there are two lone pairs hanging out, both of which make it seemingly capable of hydrogen bonding. But in reality it is not.

Did some research and found this on chemguide:

  In methoxymethane, the lone pairs on the oxygen are still there, but the hydrogens aren't sufficiently δ+ for hydrogen bonds to form. Except in some rather unusual cases, the hydrogen atom has to be attached directly to the very electronegative element for hydrogen bonding to occur.

Based on the info, I am assuming that the carbon atom in carbonyl group is not electronegative enough to give a partial charge large enough for hydrogen bonding to the hydrogen atoms, say in pentanone.


texts: Is there a way to control the shape of metal? Suppose I have a fast melting metal, is there a way to make it take a specific shape? Of course I don't mean to like put it in a template to take the shape of a template, but rather to control the shape using a computer or something. Is something like this possible or done? If not possible, then why?


texts:
I'm trying to understand how carbons are numbered in organic molecules (i.e. as in the following image).

(source: Principles of Biochemistry by Nelson and Cox, p. 532)

I've read and heard different methods, among which:

the end of the carbon chain with the highest oxidation state is assigned the lowest number.
the end of the carbon chain with the highest total mass is assigned the lowest number. the number of bonds is used as a kind of multiplier (i.e. O=C-OH corresponds to a total mass of O*2+C+O+H). (source: What is the convention of numbering carbon atoms in organic molecules?)
the end of the carbon chain with the substituent of the highest atomic number is assigned the lowest number (source: Principles of Biochemistry by Nelson and Cox, p. 73).
the carbonyl, acetal or hemiacetal carbon is given the lowest possible number (source: Carbon numbering in carbohydrates)

These methods could come to contradictory conclusions, though. One example I could think of:

Phosphorous would be the highest atomic number constituent, while the remaining rules (carbonyl carbon, total mass and oxidation state) would assign the carbonyl carbon the lowest number.

I assume some are just simplifications. What is the correct method, or is there no single general one?


texts: Something I don't understand about batteries

texts:
someone explained how a zinc copper battery works but there's already something I don't understand in the beginning.

Here is the reaction this person said happens in the battery

$$\ce{Zn + Cu^2+ -> Zn^2+ + Cu}$$

I understand how $\ce{Zn}$ transforms in $\ce{Zn^2+}$ (because it gives electrons to the wire, the $\ce{Zn^2+}$ then goes in the electrolyte) But I don't understand where the $\ce{Cu^2+}$ comes from. I understand that the $\ce{Cu^2+}$ gets electrons from the wire and turns into $Cu$ but the copper electrode that is in the battery is made out of $\ce{Cu}$ not $\ce{Cu^2+}$ so where does it come from?

It comes from the first answer here: https://physics.stackexchange.com/questions/247725/why-electrons-flow-through-a-wire-connected-to-a-battery


texts: New technology that has replaced the old radioisotope

texts:
What technology has the radioisotope Cobalt 60 replaced in medicine?

E.g.,PET preferred over CT scans


texts: What system of nomenclature can I use to indicate the positions of specific kinds of atoms of a surface reconstruction?

texts:
I was reading a journal based on SiC reconstructions, and they seem to mention that every dangling bond in the $(1\times 1)$ unreconstructed Si face or the $(0001)$ direction bonds up with a Si adatom placed in the corresponding $T_4$ position and hence leads to a $(\sqrt{3}\times \sqrt{3})R30^o$ reconsruction.

Now, I do realize what is happening extremely clearly, but I want to know which nomenclature they use to name the position of the Si adatom on the C atoms (dark red dots) as the $T_4$ position. I would be really grateful for the help, any books or article citations in that direction would also help. I absolutely do not know whether it is a symmetry group or something else.


texts:
What is the major product of the following reaction:

I think methanol will be formed. Although formaldehyde is more reactive to nucleophilic addition, the rate determining step of the Cannizzaro reaction is the hydride transfer. So instead of a nucleophilic attack of $\ce{OH-}$ on formaldehyde, nucleophilic attack takes place on the aromatic aldehyde.
Is that correct?


texts: Do "random" "2D" polymers constrained to a box actually form "space filling" curves?

texts:
Background: The self avoiding walk model is (allegedly) a reasonable model for polymers, at least with respect to certain "universal" (i.e. lattice independent) constants -- see section 1.1. in this survey.

Consider an $n \times n$ square grid, with lower left corner marked $a$, and upper right corner marked $b$. Let $S_n$ denote the set of self avoiding walks in the grid from $a$ to $b$.

There is a family of probability distributions on $S_n$, parametrized by a single number called the "fugacity." (Allgedely, a measurement of pressure.) In particular, for $ x > 0$, define $\nu_x$ as the probability distribution on $S_n$ that awards a walk $\omega \in S_n$ mass proportional to $x^{|\omega|}$, where $|\omega|$ is the length of the walk.

This family of probability distributions is known to have a phase transition around certain values of $x$. In particular, for $x > 1 / \mu$, where $\mu$ is the connective constant of the square lattice, a walk is "space filling" with high probability. (My usage of space filling here is heuristic, it is made precise in the linked article.)

Mathematically, this is all very interesting. I'm wondering if there is empirical evidence that complements these results. This leads to my imprecise question, but first some caveats.

Caveat one: These results I mentioned concern $2D$ self avoiding walks. The closest analogue in our 3D world is presumably polymer systems under tight constraints, such as in this. I'll call these 2D-ish in the question.

Caveat two: I ask this question as a mathematician extremely ignorant of chemistry. Please take that into account in your answers, if possible.

Question: Is there a physical process that produces a "random" (that is, $\nu_x$ distributed) polymer chain in a 2D-ish medium or 3D medium, and if so, is it "space filling" for sufficiently high pressure / fugacity $x$?

Totally naive thoughts:

I debated whether to include these -- I decided to err on the side of sounding ignorant but at least communicating a better picture of what I'm curious about, and where the boundaries of my knowledge are.

As far as making the process, what if just chucked some monomers in a solvent along with a polymer strand and waited for it to grow by random rerouting attachments? Is there any incentive for a long polymer path to replace one of the monomers in our starting strand? I guess one hard part is insuring that you get one chain, and not one chain and many polymer loops. Maybe there are physical reasons why the loops would like to merge into the chain, at least under high pressure? Or maybe it's not a problem that there are extra polymer loops, as long as we can somehow point to our favorite polymer chain.
Taking inspiration from the algorithm in that last link, one process I can imagine is sticking a long polymer into solvent in a 3D container, shaking it up (very gently), and then squeezing down one of the sides of the container. It seems hard to ensure that this can be squeezed thinly enough to make criss-crossing of the polymer impossible. Maybe instead of physically squeezing the polymer to one side, we can squeeze it using some other force (magnets???) ? Or maybe criss-crossing is inevitable if you try to do something like this?


texts: Producing carbon nanotubes from graphite

texts: I am searching for the carbon nanotubes for very low cost. I have one idea, which is to use graphite (such as that found in pencils.) Can it be converted to carbon nanotubes? If so, what would be the procedure for this?


texts: How to write correct NMR integrals in a formula?

texts:
for my masterthesis I want to include the Equation how I calculate my conversion in a polymer reaction.
It is pretty easy, but I still want to write it down.
Basicly the equation is: (Integral A usally 4-5 and Integral B always 1 beacuse its one Proton, Integral B and C are equal)
$$ Conv=\frac{Integral_A-Integral_C}{Integral_A+Integral_B}=\frac{Integral_A-1}{Integral_A+1}
$$
But the formular with "Integral" in it looks not very nice while I thin the $\int{}{}$ sign seems to be a bit over the top.

If someone wants to know how I end up with the equation, here is the explanation:

It comes from the point, that my Monomer has 2 protons on each side of the double bond. When the polymer is formed they shift forming one broad signal. In the polymersolution I can identify one proton of the monomer which gets the Integral 1 while the other big peak contains the polymer as well as one proton from the monomer. Because both monomer protons have the same integral, both get a 1. My "clean" polymersignal is therefore the broad Integral -1. This has to be devided by the overall Integral which is the broad signal (which already includes one monomer proton)+ the other proton.


texts: How is chemical and dynamic equilibrium related?

texts:
I have been told that dynamic equilibrium is attained when the reactants and products of a system has achieved the same concentration or when their rates of formation are the same. And I also know that even though nothing seems to go on in a dynamic equilibrium there's still so much activity.
Now assuming I've got that right. I want to know how is chemical equilibrium any different from what I mentioned abt dynamic equilibrium.
Also can chemical and dynamic equilibrium coexist??


texts: Why is ΔH (enthalpy)=Σreactants-Σproducts and not Σproducts-Σreactants?

texts:
I was told that ΔH=Σreactants-Σproducts in regards to finding the enthalpy, given average bond enthalpies.

Why is the case? It seems counterintuitive, because of the delta, which would imply ΔH=Σproducts-Σreactants.

Is this the case, because of the fact that for breaking the bonds in the products energy is required, while for forming the bonds in the products, releases energy and that enthalpy is equal to the heat released?


texts: Dehydrobromination of 3-bromo-3-cyclopentylhexane and number of possible alkene products

texts:
I faced a question like this:

  The total number of alkene products possible from the dehydrobromination of 3-bromo-3-cyclopentylhexane is:

The answer is given 5. But I only found 3.

3-cyclopentylhex-2-ene
3-cyclopentylhex-3-ene
(hexan-3-ylidene)cyclopentane

I can't find the other 2. Any hint?


texts: How can a catalyst not be included in a rate equation if, by definition, it speeds up a chemical reaction?

texts: I thought that anything not in a rate equation was automatically zeroth order and therefore did not affect the reaction. However, I have heard that catalysts can be involved in a reaction while not being in a rate equation. How can this be possible?


texts: Why does copper gain electrons in redox reactions, when it instead has a tendency to lose them?

texts: Cu has tendency to lose electrons. But in some redox reactions, it gains 2 electrons and become neutral. Why is it so? How can it gain them?


texts:
I couldn't find the derivation of Arrhenius equation. So, How can we derive the Arrhenius equation:
$k = A \mathrm e^{-E_\mathrm a/(R T)}$?


texts: How to move forward in balancing this equation?

texts:
I want to get the molecular formula for this reaction:

$$\ce{{$trans$-stilbene} + {$m$-chloroperoxybenzoic acid} -> {$trans$-1,2-diphenyloxirane}}$$

and if you do you get this:

$$\ce{C14H12 + C7H5ClO3 -> C14H12O}$$

but what do I do about the chlorine not being present in the products, is it released as $\ce{Cl2}$?


texts:
Endohedral fullerene is the name given to a brand new chemical species with the following attributes:

  A metal, usually a transition metal, is "trapped" inside the fullerene, like $\ce{C60}$ and $\ce{C82}$. These transition metals are often La, Sc, Ce, Y, or, Ba and Sr etc.

Without any "binding" forces, the atom couldn't be possibly trapped inside the fullerene.

Here it's been discussed that the bonding is the type of "donor-acceptor". Later within, it was explained that

  Though there isn't empirical proof, It's believed for these species to have metallic structure.

I have two questions:

Is there another simpler name for this "donor-acceptor" bonding? My thoughts lead to wierd names!
How "close" is this type of bonding to metallic bonding?

Edit: Citation: The second article:

Publisher: [AIP]; German journal of chemical physics. Volume 115, number 15, page 7215. (15 Oct 2001) (Juelich GMBH or something; Couldn't figure the name out, maybe German fellows would help.)

DOI: 10.1063/1.1406500

Authors: R. Klingeler, G. Kann, I. Wirth, S. Eisebitt, P. S. Bechthold, M. Neeb, and W. Eberhardt (Dr. Rudiger Klingeler is the main author)

Title: $\ce{La$@$C60}$: A metallic endohedral fullerene.

Unfortunately the other mirror links are behind paywalls. (But this article is available in Researchgate, in case you've got institutions to be able to create an account)

$%edit$


texts: Assumption behind Gibbs energy and maximum work

texts:
I'm somewhat confused by this derivation (in Schroeder's Book of Thermal Physics) of the fact that in a closed system, the change in the Gibbs Energy is always less than the Non-Expansion work done on the system.

If we take the change in the entropy of the universe (system + ideal surroundings maintained at constant temperature and pressure also assuming that reactions are taking place in system only i.e. the composition of various species present in surroundings remain constant), then it turns out (in this derivation) that it equals to negative of change in Gibbs Energy divided by Temp of system (which is same as that of surroundings).

Now since entropy of Universe always increases it turns out that Gibbs Energy of system will always decrease. But this is only true in absence of Non-Expansion work.

However during this derivation nowhere it's mentioned that 'no non expansion work assumed' yet the result only holds true in absence of non expansion work.

I think that maybe it was assumed somewhere and I'm not able to spot where. Please help me to clear my doubt.


texts: Why does the Electron Affinity of Selenium is more than that of Oxygen?

texts: I got that the electron affinity of oxygen is due to its smaller size which leads to more repulsive effect relative to that of lower groups. But, I am bit confused in why the order $\ce{S > $\bf{Se}$ > O}$ in terms of electron affinity.


texts:
I'm just a curious high school student. Sorry if this sounds dumb.
How exactly did the concept of atomic subshells and orbitals come about? And why exactly are there n-1 subshells and 2l+1 orbitals?
Based on what I've heard, these things were a step forward after the Sommerfeld atomic model. But orbitals???
Again, sorry if this sounds dumb.
I just want to know how these things came about.


texts:
This question left me wondering what other very light (condensed) fluids could exist, at any environmental condition.
Obvious candidates for the list are (at their Bp./1 bar)

LH2 (0.07 g/ml)
LHe (0.18)
LNe (nope, 1.21)
methane (0.42)
ethane (0.54)
propane (0.58)

plus those mentioned in the other question

$\ce{4NH3 \cdot Li}$ (0.48)
isopentane (lightest "normal" liquid at 25°C, 0.62 g/ml)

To give a definit boundary on possible answers, let´s say the density must be below that of isopentane.
The question is, is there anything else? Perhaps at very high temperatures?
(The term "fluids" of course also includes gases and supercritical fluids, those are obviously out. You can always reduce the pressure, and thereby density, on those, until you either have a liquid, or you hit the bottom line of your phase diagram at $p=0$. That makes no sense, so I want actual condensed matter.)


texts:
I'm trying to search for substructures with RDKit.

I would like to search for structure 1 as substructure in other structures. I don't understand why it doesn't find this structure in structures 3 and 5. I assume this is not a bug in RDKit, but more the result of my limited chemistry understanding. Something with aromaticity? Something wrong with the structures?
Can someone explain to me why it doesn't find structure 1 in structures 3 and 5?
How should the search structure look like that I will find all structures 2-5?

from rdkit import Chem

smiles_list = ['C12=CC=CC=C1C3=CC=CC4=C3C2=CC=C4', 'C12=CC=CC=C1C3=CC=C4C5=C(C=CC2=C35)C6=C4C=CC=C6', 'C12=CC=CC=C1C3=CC=C4C5=C(C=CC2=C35)C=C4', 'C12=CC=CC=C1C3=CC=C4C5=C(C=CC2=C35)C6=C4C=C7CCCCC7=C6', 'C12=CC=CC=C1C3=CC=C4C5=C(C=CC2=C35)C6=C4C=C7CC8=CC=CC=C8CC7=C6']

pattern = Chem.MolFromSmiles(smiles_list[0])
for idx,smiles in enumerate(smiles_list):
    m = Chem.MolFromSmiles(smiles)
    print("Structure {}: pattern found {}".format(idx+1,m.HasSubstructMatch(pattern)))

# Result:
# Structure 1: pattern found True
# Structure 2: pattern found True
# Structure 3: pattern found False
# Structure 4: pattern found True
# Structure 5: pattern found False


texts:
Salicylic acid is a relatively polar compound hence I thought that normal phase would be preferred as the stationary phase of normal phase is polar. However, it is said that reverse phase would be the preferred option instead.

Can somebody explain to me why reverse phase HPLC is preferred for salicylic acid? And would reverse phase produce better graphs/results than normal phase?


texts: What is the difference between protein domains, motifs, and supersecondary structures?

texts: I was just wondering if there is any difference between supersecondary structure and motifs. As well, is a protein domain an independently folded region of a protein that has a particular function associated with it - that may or may not contain one or multiple motifs.


texts: Why aren't the copper(II) ions in CuSO4 precipitated by hydroxide ions from water?

texts:
From my own experience and literature, I know that $\ce{CuSO4}$ is well soluble in water and dissociates into $\ce{Cu^2+}$ and $\ce{SO4^2-}$. $\ce{Cu(OH)2}$, however, is not: $K_\mathrm{sp} = 2 \cdot 10^{-19}$.

Therefore, in pure water which has a pH of $7$, $c(\ce{OH-}) = 10^{-7}$. This means that a concentration of $2 \cdot 10^{-19} / (10^{-7})^2 = 2 \cdot 10^{-5}$ of $\ce{Cu^2+}$ would be enough to cause precipitation. How come, when dissolving $\ce{CuSO4}$, the $\ce{Cu^2+}$ stays in solution, and doesn't precipitate with the $\ce{OH-}$ ions of water to form $\ce{Cu(OH)2}$?


texts: Derivation of Henderson–Hasselbalch equation

texts:
While deriving the Henderson–Hasselbalch equation why don't we consider the hydrolysis reaction?
For example if we consider an acidic buffer of acetic acid and sodium acetate, why do we not consider the hydrolysis of the acetate ion furnished by sodium acetate?


texts: How many litres of water will be sufficient to generate 1600 psi when heated?

texts:
Here's my setup. I have a pressure vessel with x liters of water. I'll be heating the water at 320 C. I want to achieve at least 1600 psi of force inside the pressure vessel.

So how do I calculate the minimum amount of water required to achieve that pressure?


texts: Why is white phosphorus soluble in $\ce{CS2}$ but red phosphorus not? Is it something in relation with the structures of both? Please explain.


texts: Briggs-Rauscher Reaction Temperature vs Oscillation Period

texts:
I am investigating the effect of temperature on oscillation period in the Briggs-Rauscher Reaction. By period I mean the average of the time the reaction to take one cycle (orange --> blue).

I have attempted to make a connection to the Arrhenius Equation with my data. However, I have no information about the rate constant and I am curious about how my period data connects to the rate constant.

Below is the graph I produced after assuming that the rate constant is linearly related to the period. Any insight on this problem would be very appreciated.


texts: Why do certain compounds dissolve in oil? Why do some types of compounds dissolve in oil, yet not water?

texts:
Sorry if this is an obvious answer. I tried rewording this question every way I could, but search engines came up with nothing- they all skirted around this exact question.
Why do certain compounds, such as fatty acid or Vitamin A, dissolve in oil?
Polar substances can dissolve in water because water molecules are polar and literally pick apart the [polar] molecules in the solute by attracting to them. However, oil is nonpolar and has no such ability.
How, then, does it make certain compounds dissolve? Is there some other bond it can form with certain compounds?
On a second question, I read something about London dispersion and Van der Waals forces being the main force of attraction between oil solvents and solutes that can dissolve in oil. If this is the case, that means the electrons in orbit around the solute's molecules shift around and form temporary dipoles with each other.
But what makes it so that some solutes can only dissolve in oil-- and not water [molecules], which are polar, and could also interact with these temporary dipoles?
edit: A comment said that this not energetically preferable. So I think the second question can be considered answered.
Thanks!


texts: Among Benzyl carbocation (Ph-CH2+) and Methyl methoxy carbocation (CH3-O-CH2+), why is the latter more stable?

texts: Benzyl Carbocation could form multiple conjugation, then why isn't that stabler? In Methyl methoxy carbocation, Oxygen donates the lone pairs but so does the double bond in the benzyl Carbocation.


texts: Rusting of an Iron nail at oil water boundary surface

texts:
Recently at school, I did some experiments on corrosion. Everything mostly went as expected, but the result in one of the test was quite baffling.

This test had an iron nail in water with some of the nail protruding the surface. The tip of the nail was then covered by oil so that it was completely submerged. It was left as is for 4 weeks. At the end of this time, there was a bit of rusting (as I had expected), but most of it was right at the surface of the water, right where it and the oil meet. Is there any reason why this would be?

Edit
I had a beaker with the nail in it, leaning upright against the wall of the beaker. I put about 200 ml of water in, then about 50–100 ml of oil. The water didn't completely cover it, but the oil did. After 4 weeks, there was rust, mostly situated around (but below) the oil/water border. As for why it was done, I don't know. My lab partner decided to test this. I think it was kind of testing how much it would rust when starved of oxygen.


texts: Fertiliser analysis - Why doesn't it show ureic nitrogen when it does have urea?

texts:
I have had two types of urea fertiliser analysed, the results are as follows:

$\mathrm{46\%N}$ (46% nitrogen) - which is sold as a urea fertiliser, tests at 46.1% ureic nitrogen.

$\mathrm{38\%N~ 19\%S}$ (38% nitrogen, 19% sulphur) - which I understand to contain ammonium sulphate and urea, tests at 33% nitric nitrogen and 7.4% ammoniacal nitrogen

My question is-  why does the $\mathrm{38\%N~ 19\%S}$ show no ureic nitrogen when it is supposed to contain urea - the same as the $\mathrm{46\%N}$?

edit - the analysis company has admitted a mistake- the test  result should have read 33% ureic nitrogen and not 33% nitric nitrogen.


texts:
My book states that:

  When isopropyl magnesium bromide is added to diisopropyl ketone, the expected tertiary alcohol is not obtained; instead the secondary alcohol; diisopropyl carbinol is obtained resulting from reduction".

I know this has happened due to steric crowding but can anyone tell the mechanism for this?


texts: How can you qualitatively tell when the hydrolysis of aspirin is over?

texts:
I'm doing an experiment on the effect of temperature on the time taken to produce acetic acid and salicylic acid. Are there any qualitative observations I can make about when the reaction has finished?
I am using a 0.01 M aspirin in pure water.


texts: Looking for a chemical to calibrate a temperature sensor

texts:
The best method for calibration would be a bath filled with a chemical at its melting point with a solid/liquid composition.
The constraints being that it must be hydrophobic and relatively non-corrosive and non-toxic with a melting point between (say) 20 °C and 60 °C. Needless to say, but I’ll say it anyway, the chemical must have a very precise melting point. Any ideas?


texts: Can we fill potato chips bags with a gas other than nitrogen?

texts:
I understand that we fill potato chips bag with nitrogen to prevent oxidation. But why do we use nitrogen, instead of neon or hydrogen or something else?
My first guess is that nitrogen is lighter than neon/argon but what about hydrogen or helium?


texts: Which of the following are true based on this comparison?

texts:
In the following chart, the horizontal line is time and vertical line is temperature. $K$ and $L$ are solid matters that are placed in two identical pots within the same room and are being heated up with identical heaters.

(Translation: Sıcaklık = temperature, Zaman = time, dak (dakika) = minute, maddesi = substance)

Which ones of the following are true?

A-) If $K$ and $L$ are different matters, they have the same mass.

B-) If masses of $K$ and $L$ are different, they can be the same matter.

C-) If masses of $K$ and $L$ are equal, they are different matters.

I chose "only $B$" which turned out to be wrong while the correct answer is "$B$ and $C$" and in the explanation it said "You picked the wrong answer because you think different matters can't have the same boiling/melting point." which is true because they can't, right?


texts: Does organic chemistry somehow defy the periodic table?

texts:
My physics lecturer was introducing the idea of what a Theory of Everything was, and said something like this:

  Other sciences have their own theories of everything too, fundamental axioms from which everything else can be derived from. In mathematics, we have ZFC, and well, the entire framework of abstract mathematics and axiomatic systems. Even in Chemistry, all of modern chemistry can be derived from the periodic table and the laws of atomic structure. Well ... except for two words: Organic Chem.

Is this true? Can organic chemistry somehow not be derived within the framework of the periodic table?


texts: Which base is stronger? Ammonia of phosphite?

texts:
$\ce{NH4+}$: $K_\mathrm{a} = 5.6 \times 10^{-10}$;
$\ce{HPO3^2-}$: $K_\mathrm{a} = 4.5 \times 10^{-13}$

My understanding is that $K_\mathrm{b}(\ce{A-}) = K_\mathrm{w} / K_\mathrm{a}(\ce{HA})$. Thus:

$\ce{NH3}$: $K_\mathrm{b} = 1.8 \times 10^{-5}$; $\ce{PO3^2-}$: $K_\mathrm{b} = 2.2 \times 10^{-2}$

Since the $K_\mathrm{b}$ for phosphate is greater than the $K_\mathrm{b}$ for ammonia, phosphite is a stronger base. However, my professor's solution lists ammonia as the stronger base. Is his solution incorrect?


texts: Do alkali metals react with ammonia to form hydrogen gas?

texts:
I was recently studying about s-block alkali metals and I found the following reaction:
$$\ce{\underset{alkali\\ metal}{M\phantom{_y}} + \underset{solution}{$(x +y)$ NH3} -> \underset{ammoniated\\ metal cation}{[M(NH3)_x]+} + \underset{ammoniated\\ electron (blue)}{[e(NH3)_y]-}}.$$
It is also known that nitrogen has electronegativity of 3.0 on Pauling's scale. So, the hydrogen attached to it is an active hydrogen. Also, it shows H-bonding, so the hydrogen is an active-H.
Alkali metals react with active-H compounds to release hydrogen gas. But the reaction that takes place here is in contradiction to the aforementioned fact.
Do we have an explanation for this? Or is it a  mistake on my part?


texts: What is this device? (Constant level device?)

texts:
Found this in my lab on a random shelf (water quality lab). It is old enough that nobody knows where it came from. I think it's a constant level device. It has in- and out-flow connections, as well as electrical plugs for some kind of monitoring equipment. The only writing is on the glass, which says "FSTREEM [ASTREEM?] MADE IN ENGLAND". The inside float looks like it is meant to float up and down, while the thin metal wire keeps track of its level via a small electric recorder. What is this thing called, and where can I find more info?

Thanks!


texts: Reaction of unsaturated lactone and alcohol

texts:
Image source
I found this equation to turn this compound into an ketoester but I am unsure of the reaction mechanism.
I postulate that the alcohol attacks the carboxyl carbon, the O becomes formally negative. It reforms the double bond and the leaving is the O in the ring which takes the electrons in the bond.
Here my thought differs from the image (gotten from one of the United States Patent Office Patents). I thought the end product would be an ester OHCCCCOOR. Alcohol then alkene and at the end an ester but the picture shows a ketone and no alcohol.


texts: Relationship between auto-ignition temperature with pressure and fuel

texts:
Experimentally it appears that increase in pressure, fuel concentration, and chain length causes AIT to decrease until a minimum where even further increase in these parameters increases the AIT. Additionally, it seems that AIT is lowered by increasing the vessel volume.

From the last page of this paper:

  Semenoff's equation seems to indicate that it is possible to lower the AIT to arbitrarily low values by increasing the pressure. But the higher the total pressure of the fuel/air mixture, the higher is also the partial pressure of the fuel required to reach the most critical fuel concentration. At some temperature, the required partial pressure will become equal to the fuel vapor pressure. At even higher pressures and lower temperatures, it is impossible to reach the critical fuel concentration, and the depression of the AIT is expected to stop. A similar mechanism has been employed to explain the reincrease of the standard AIT with chain length for very long chain molecules /5/.

Edit: Article title is Autoignition Temperature for Mixtures of Flammable Liquids at Elevated Pressures by Brandes, Hirsh, and Stolz

1) From this, it seems that pressure and fuel concentration effects are related. Is the critical fuel concentration related to the equivalence ratio and the ability to reach this equivalence ratio based on the saturation pressure of the fuel?

2) I do not get the relation between the above explanation and the last sentence regarding re-increase of AIT for longer chain molecules?

3) I'm not sure why larger volumes leads to lower AIT as stated in ASTM E659 Appendix X2.


texts: Fraction of concentration of benzene in air water

texts:
We have a 120 ml water sample with an unknown concentration of benzene. If the bottle size is 160 ml (with 40 ml of air) and benzene has reached equilibrium, what fraction of benzene is left in the water?

We are only given Hcc (Henry constant - Cair/Cwater) 0.225 and Log Kow (to which I believe is needed for a later question) 2.53.

I'm not sure where to start. We do not know mole fraction so we cannot find partial pressure using Henry's law. Also this rules out Raoult's Law.

Also we can't use the Ideal gas law since we do not have a lot of the variables. I'm stumped. But we can make assumptions such as T for example.

Any suggestions?


texts:
So I have an unsaturated air parcel in the atmosphere that ascends adiabatically from the $1000\:\mathrm{mbar}$ level to the $700\:\mathrm{mbar}$ level with its initial temperature being $10\:°\mathrm{C}$.

I have to find the initial specific volume in $\mathrm{m^3}\:\mathrm{kg^{-1}}$.

I know that the specific volume formula is $v=1/\rho$ and that the equation of the state of an ideal gas can be written as $p=\rho RT$ where $R$ is $8.3143\:\mathrm{J\:mol^{-1}\:kg^{-1}}$

So I have $1000\:\mathrm{mbar}=\rho(8.3143\:\mathrm{J\:mol^{-1}\:kg^{-1}})(283.15\:\mathrm{K})$ and solve then for $\rho$ and then get $0.42477$ and plug that for $v=1/0.42477$ and get $2.354\:\mathrm{m^3}\:\mathrm{kg^{-1}}$ as the initial specific volume. Am I doing this right?


texts: What are the prerequisites in hydrogen bonding?

texts: I know when a hydrogen bond is, but - can hydrogen bonds only occur between two molecules containing hydrogen? Or, only one of the molecules should contain hydrogen and the other one may not contain hydrogen, but should have a large electronegative difference between two of its sides?


texts: A way to calculate orbital energy of an electron

texts:
Maybe this is just not included in my course, but I still wonder how to calculate the binding energy of an electron .at a certain electron orbital.

Intuitively,The ionization energy of an element should vary depending on which orbital the valence electron is in.

PS: I only know how to calculate ionization energy using principle level.


texts: Why does the SnAr reaction proceed by the Meisenheimer complex?

texts: I am studying SNAr mechanism from this webpage. I am confused as to why this convoluted mechanism occurs. It seems as though we simply create an anion when the hydroxide attacks in order to quench it directly after by pushing out the chloride. Why does the hydroxide not push out the chloride in a typical substitution reaction? Also, what evidence do we have for the Meisenheimer complex actually forming?


texts:
Bulk gold has a very characteristic warm yellow shine to it, whereas almost all other metals have a grey or silvery color. Where does this come from?
I have heard that this property arises from relativistic effects, and I assume that it has to do with some distinct electronic transition energies in the gold atoms. But what changes with the "introduction" of relativistic effects, that then changes the energy of the frontier orbitals in such a drastic manner?


texts:
I was under the assumption that corrosion (rust specifically) required water + oxygen to occur. But the word equation below states that only oxygen is necessary. I know this is true but I do not know the explanation behind it. Could someone help me understand? Apparently water magically appears from somewhere.

A middle to high school level of explanation would be ideal, not too advanced.

metal + oxygen ->  metal oxide

metal + oxygen + water -> metal oxide


texts: Why is free radical chlorination exothermic whereas bromination is endothermic?

texts:
In the energy profile diagrams below, it can be clearly seen that the free radical chlorination of an alkane

$$\ce{RH + Cl2 -> RCl + HCl}$$

is exothermic. However, the corresponding bromination

$$\ce{RH + Br2 -> RBr + HBr}$$

is endothermic. Why is there a difference?


texts: Which of the these SN1 solvolysis of two alkenyl bromides reactions is faster?

texts:
The SN1 solvolysis of one of the following alkenyl bromides is in MeOH approximately 100000 times faster than the other one. Which is the more reactive one? Draw the mechanism including the transition state, determine the rate determining step and draw the reaction product of each compound.

Now what is apparently important here is the rotation of the substituent in each relative to the aromatic ring. In the second compound (with two methyl groups), the rotational profile shows destabilized molecule except when 90 degrees. That means the rotation in the second molecule helps with the leaving of Br and this (rate determining) step is much faster than when there are no methyl groups (first compound).
Is that a complete explanation or I am missing something important? Also is there anything special about the mechanism of the two reactions and the products in each case?


texts: What is the typical resistance of a piece of 1 cm^2 of carbon paper?

texts:
I have been using carbon paper (Carbon sheet 99.8% from STERM CHEMICALS) to load catalysts for fuel cell study. Just now, I realized that for a 1 cm^2 piece the resistance is about 3 ohms!
Is that a typical value? I can't find any info on Google or the seller's webpage.
Thanks!


texts: Thermochemistry: forms of energy & pressure

texts:
I've been in a few classes now that teach about energy, and I feel they're always so bad. There is always such a rush to start using equations to get problems solved, and I often feel I don't have an intuitive grasp on energy at all. I guess this question is also about pressure.

Questions:

Does pressure decrease with time? If pressure is caused by the force of gas molecules hitting the inside surface of a container, don't they transfer energy and eventually slow down enough to totally reduce pressure?
Along the same lines, energy can be released or absorbed by a reaction as work or heat. If the only change that happens is through work (in something that is totally insulated - where gas is formed and pressure is created), after the pressure is created, doesn't it require continuous energy to maintain pressure against a constant force of 1 atm (or whatever it is)? Heat dissipates to all things, and that makes sense as everything gets colder in time. The same does not seem true for pressure.

Thanks in advance.

Noobsauce


texts: Mass Spectroscopy peak assignments in but-3-en-1-ol

texts:
i have the mass spectrum for the molecule but-3-en-1-ol. The Mr of this is 72

There are four peaks that are labelled which I have to name the species responsible for forming that peak.

The peaks are:
m/z = 66
m/z = 67
m/z = 71
m/z = 73 - this peak is labelled as (M + H)^+

My answer so far...
The peak at m/z=73 is the but-3-en-1-ol with one added hydrogen, somewhere to the double bond?
For the other peaks am I just removing hydrogens as the mass only decreases by 8 in total so i couldn't remove a carbon or the oxygen.

Does this mean that the peaks are:
m/z=71 is the removal of 1H
m/z=67 is the removal of another 4H (5H in total)
m/z=66 is the removal of another 1H (6H in total)

is this is correct? Which hydrogens are removed first and what does each species look like for each peak, and are there any charges on the species produced. Also is there a special name for this sort of fragmentation, e.g alpha cleavage?


texts: Diastereoisomer of quinic acid and its proton NMR?

texts:
Question:

  Quinic acid, A, has the gross structure shown below:

  (i) Draw all the possible diastereoisomers of A and indicate which are chiral.
  (ii) Quinic acid is optically active and the marked hydroxyl groups are cis to one another; which of your structures is consistent with this data?

  Using the $\ce{^{1}H}$-NMR data below, draw a likely conformation for quinic acid, making sure that you fully assign all these data.

  $\ce{^{1}H}$-NMR for quinic acid in $\ce{D2O}$: δ 4.09 (1H, q, 3 Hz), 3.99 (1H, ddd, 11 Hz, 9 Hz, 5 Hz), 3.39 (1H, dd, 3 Hz, 9 Hz), 2.12 (1H, dd, 13 Hz, 5 Hz), 2.05 (2H, d, 3 Hz), 1.86 (1H, dd, 13 Hz, 11 Hz).

My working so far:
$\hspace{29ex}$

Firstly, have I missed any diastereoisomers? And what does it mean by 'conformation' of quinic acid? Does it mean a chair conformer?

But I'm not sure about the shift at 4.09 ppm since I made the assumption that the quartet is actually a doublet of doublets. Also surely $\ce{H_{f}}$ would vicinal couple with $\ce{OH}$ on the same carbon?


texts: Whats the driving force behind simple diffusion? Is it just the count of molecules?

texts:
If I were to have two separate containers with solutions of different concentrations with a small opening, most of the molecules would flow down the concentration gradient. Does this occur just because more molecules can pass through the opening or is there a force pushing them out?
My second question is if the molecules could pass through the opening under normal conditions even against the gradient?


texts: Why does shower gel / shampoo foam a lot more on hairy than non-hairy body parts?

texts:
We usually use shower gel by rubbing it on our palms and then applying it to each body part in turn in order to clean oily substances that clung to it since our last shower. This procedure does not cause the gel to foam (if it is applied to a completely hairless place, such as a clean-shaven head or back, it will produce some small amount of foam (also depending on how much you rub it); if it is applied to a place with relatively small clusters of hairs, such as arms or legs, it might foam up a bit more, and so on).

However, when applying shower gel or shampoo to a hairy place, such as the head, the groin, etc. it usually foams up significantly and rather quickly. A clear shower gel or shampoo will become a white foam in a short time.

Why is that? Is it the air trapped among the hairs?

(Please do not confuse this question with this one, they are different enough).


texts: Determine bond length via rotational spectroscopy

texts:
Estimate the bond length of 12C16O (pure rotational spectrum) given J''=3 (15.356 cm-1) and J'=9 (38.356)

I understand that the first step is the calculate the rotational constant. So to do this I assume I would use one frequency value and one J value? And the equation to use would be

$$\nu = BJ(J+1)$$

If I do this with the numbers for $J=3$, then I get $1.28$ for $B$, which is apparently incorrect. I have seen someone else's attempt and they use

$$12B = (38.356 - 15.365)=1.916$$

And solved for B this way and they get the correct answer. Why is the way I thought not correct? Why is the second way correct and where did B come from?


texts: Active methylene group nucleophilic substitution

texts:
The first product formed after reaction with $\ce{^-CH(COOEt)2}$ followed by hydrolysis is [2-(naphthalen-1-yl)ethyl]propanedioic acid:

But is the reaction $\mathrm{S_N1}$ or $\mathrm{S_N2}$?

On heating, decarboxylation takes place because of an $\alpha$-carboxylic acid group.

Then $\ce{SOCl2}$ followed by $\ce{AlCl3}$ is Friedel–Crafts acylation because using $\ce{SOCl2}$ gives an acid chloride. After that, an intramolecular electrophilic substitution takes place.

But where will the electrophilic attack take place?


texts: how to measure the efficiency of carbon filter [or of activated carbon/charcoal]?

texts:
Fake HEPA filters are easy to spot using DIY PM sensor and DIY Air Purifier (we just need to turn the fan ON, place the sensor's tube in front of it, and read the data).

But what about carbon filters?

I bought a filter like this to clean the air, but I wonder if it really works (there are many fakes out there).

I'm looking for some tricks to know if it works, and (much better) to evaluate its efficiency (using Arduino sensors or any basic ways).


texts: What is the oxidation state of copper in Gilman's Reagent?

texts: What is the oxidation state of copper in Gilman's reagent? In $\ce{R-Cu}$ bond the oxidation state is +1. Thus in $\ce{R-Cu-R}$ bond the oxidation state has to be +2. But if that so why positive $\ce{Li}$ act as counter ion in Gilman's reagent? And why is it named as dialkyl cuprate (-ate for anionic complexes)?


texts:
One child has claimed to have find a solution to all physical problems. On asking for details, he said that all periodic elements has common components, i.e. electrons, protons, neutrons.
The child has suggested a solution: convert atom to another by adding electron. This way one can get substance like $\ce{H2O, Au, He}$ in abundance.
How can it be done?


texts: Why do electrodes need to share an electrolyte in a lemon battery?

texts:
From what I understand of a lemon battery, there are two electrodes one zinc, and one copper. The electrodes are then both placed separated in the same electrolyte, in this case a lemon. The Zinc dissolves into the electrolyte oxidizes and loses 2 electrons. Those 2 electrons stay on the zinc electrode. On the copper electrode 2 h+ combine with 2 electrons from the copper and then form h2. the h2 bubbles up and leaves the electrolyte. The extra electrons from the zinc then move to the copper when there is a connection between the anode and cathode. This reaction continues until the zinc is too dissolved or if there is not enough h+ in the electrolyte to take electrons from the copper.

If my understanding is correct (please correct me if I'm wrong), then why can't each electrode have is own electrolyte, completely separated. For example the anode in half a lemon and the cathode in the other half. Both half's separated by air.


texts:
I always receive two type of explanation for the decreasement of atomic size for elements across the period.

Explanation according to proton number

This explanation is from my teacher.

The proton number of elements increases across the period.
The force of attraction between the proton in the nucleus and the electrons is stronger across the period as the proton will pull the electrons towards the nucleus.
So, the atomic size of the elements will decrease across the period

Explanation according to number of valance electron

This explanation is from my friends

The valance electron of elements increases across the period.
The force of attraction between the valance electrons and the proton in the nucleus is stronger across the period between the valance electrons is pulled towards to the nucleus
So, the atomic size of the elements will decrease across the period.

My question is which explanation is more suitable for the statement

  the atomic size of the elements decrease across the period.


texts: If I buy a loaf of freshly-made bread and leave it out at room temperature for a day or two, when I reach into the bag the air inside is much warmer than the rest of the room. Why?


texts: Both $\ce{H2}$ or $\ce{O2}$ are stable molecules. However when given energy they heat up and form $\ce{H2O}$. My teacher explained that the increased energy breaks the bonds, allowing new ones to form. However, why don't the old forms reform instead? Why are new bonds created?


texts: What chemical compounds were used in CRT phosphors?

texts:
In the old days computer monitors and televisions were built from cathode ray tubes (CRTs) where the image was generated by an electron beam hitting phosphors which emitted light approximating the three primary colours.

What were the phosphors made from and what were the key reasons why the particular substances were chosen?


texts: Do halogens bond more commonly with each other or themselves?

texts:
To me it seems like diatomic elements like $\ce{F2}$, $\ce{Cl2}$, etc. occur more prevalently than diatomic molecules with both, like $\ce{ClF}$.

Is this the case, and if so, what causes diatomic elements to be favored?


texts: Terminology for describing nuclei participating in metallic bonds

texts:
I've read many times that in metals (for example sodium metal), what constitutes the crystal lattice is an arrange of atoms, since no electron is given or lost, they are just shared between all the atoms within the structure.

In other texts though, it is written that metallic bonding is comprised of cations "surrounded" by free electrons since electrons are not held to the nucleus as in a single metal atom in the gas phase. From a formal point of view, which of the two statements is correct? Does it make a difference to consider cations or atoms when describing metallic bonding?

Which is the more appropriate terminology?


texts: Does 95.8% silver tarnish as fast 92.5% silver?

texts:
I've been trying to find out whether 95.8% (Britannia silver) would tarnish as fast as 92.5% (Sterling silver)? I haven't been able to find much on tarnish for Britannia silver.

Given that both silvers are kept in the exact same environment, would the Britannia silver tarnish at the same rate as Sterling silver? If not which of the two tarnishes quicker?


texts: Pair of analogous periods on the periodic table

texts: On the periodic table, period 2 and 3, 4 and 5, 6 and 7 and so on have similar blocks, identical length and groups. What are such pairs of analogous periods called?


texts: How to determine whether a given compound is paramagnetic or diamagnetic?

texts:
Well i am very confused whether we can determine the magnetic property of compounds..

If it us asked for elements we can say by looking at electronic configuration...

For ex-
how is N2O diamagnetic?
How is NO paramagnetic?
How is NO2 paramagnetic?
What about N2O5


texts: I noticed Heinz Ketchup has a salt substitute version that uses potassium chloride instead of the usual salt. If this is safe and tastes like salt could it be a better additive than sodium chloride? Since it has potassium wouldn't this be a benefit for Heart health or against stroke if not used too much?


texts: Is a heating block necessary for heating small chemistry samples? I figure it helps a ton (not to mention it stabilizes too) in getting heat to the reaction but is there anything else it does?


texts: How to convert cell diagram to a chemical equation?

texts:
How would one convert on the right side of the cell diagram:
$$\ce{Zn(s) | Zn^2+(aq) || MnO4-(aq), Mn^2+(aq), H+(aq) | Pt(s)}$$
$$
\begin{align}
\ce{Zn(s) &-> Zn^2+(aq)} \tag{ox}\\
\ce{MnO4-(aq) &-> Mn^2+(aq)}\tag{red}
\end{align}
$$
Obviously, one would then balance and combine the half-equations. I just need to know if the unbalanced half-equations are correct.


texts: What are polydisulfide polymers? How are these polymers applicable in energy sectors such as rechargeable batteries?


texts: Concept of heat of reaction in a isolated system

texts:
One description of the concept is that heat of reaction (exothermic) is the quantity of heat that would given off to the surrounding by the product of a reaction if we allow the product to cool down.

If this description is valid for all exothermic reaction in a isolated system, would it also be valid for all endothermic reactions??


texts:
When I underwent plateletpheresis, something that the staff called "citrate" was added to my blood as an anticoagulant. Everything I can find about this product online refers to it as just "citrate". But from what little I know about chemical names, citrate is an ion, normally found not by itself but rather as magnesium citrate, potassium citrate, calcium citrate, vel sim.

What's the other half of this anticoagulant: which citrate is it?


texts: How are the electrons of benzene actually configurated?

texts:
I found this diagram:

According to it, it is not true that the six electrons of carbons in the pi-orbitals above the ring are all identical.

But, how can it be the case, seeing that this molecule should have an order-6 rotational symmetry?


texts: Do I need a license or certificate to practice chemistry or what are the advantages if did have one?

texts:
What can I do as a non-professional chemist that is legal?

If a license is not required, then what are the advantages to having one, such as ordering compounds, getting a job, etc.?


texts: I’ve recently been experimenting blanketing coffee with argon and nitrogen. I’m finding that argon has a more positive result. I can’t find any data or information that would confirm this other then taste! Can anyone help me to determine why argon is better to use with roasted coffee? I know argon is less reactive to other things then nitrogen. But is that anything backed up with data including some that is relatable to coffee?


texts: If i keep adding sulfuric acid into water, will it keep dissolving forever?


texts: Difference between Ziegler–Natta method and Phillips method

texts:
I have to compare the similarities and differences between the Zieglerr–Natta method and Phillips method of producing polyethylene. However, the only difference I can find is the difference in catalyst used.

Any help with this is greatly appreciated!


texts: Why can't all electrophiles act as Lewis acids?

texts: We know that all Lewis acids are electrophiles but I have a confusion whether the reverse is also true. Electrophiles are molecules that are in search of electrons while Lewis acids are short of electrons. So can't all electrophiles act as Lewis acids?


texts: What is the reason for the blue color of an ammoniated electron?

texts:
I am quoting a line from a book regarding reactivity of alkali metals with liquid ammonia.

The blue colour of the solution is due to the ammoniated electron which absorbs energy in the visible region of light and thus imparts blue colour to the solution

Now my question is:

How does the independent electron get excited (without transitional levels)?

Why do salts of particular alkaline metal always have a fixed flame color if transitions of electrons can be from any energy level.
(I am asking this question based on my knowledge of school where we only studied transitions among hydrogen like species)


texts: Does a calibration curve of absorbance vs concentration need to pass exactly through the origin?

texts: If you are making a calibration curve for $\ce{CuSO4}$ where you plot absorbance against concentration and the curve deviates slightly from the origin, does it make the calibration curve useless?


texts: Are homemade batteries a practical alternative during a blackout?

texts:
If your home lost power without warning; are homemade batteries (such as the lemon/potato variety described in this question Are homemade batteries economically practical?) a practical alternative for powering your appliances while you wait for the electrician or what have you?

Are there other, better, non-produce-dependent methods for producing use-able electricity from household materials and minimal expertise?


texts:
What's the difference between bisulfate and "something" hydrogen sulfate?

Has there historically been a preference for one over the other?


texts:
Apologies in advance as I am not a science person by any definition. By most, I'm probably not a person but we'll let that be.

I am studying the notion of "change" in things and focusing on chemical change. Could someone please let me know if:

the change in the color of a photogray (photosensitive, photochromic) lens is a "chemical" change?
the change in a baby's diaper when it gets wet is a chemical change (and if it is similar in any nature to the change in #1) and if that is the same as the change in a pregnancy test or a urinalysis stick
if the change in a thermochromic/temperature sensitive item (a beer can that changes color in the cold, a color changing thermometer or spoon or mood ring ) is the same type of chemical change

Sorry if this is too much for one question, or if it can't be explained to a lay person, but I appreciate any responses. I'm too newbie on this board to post all the links as links so the questioned items are connectable through the list of urls.

TIA.

Lenses

Diapers

Pregnancy test

Blood detection

Coors Light Cold-Activated Bottles

Color changing thermometer

Frozensolutions

Mood ring -wiki

-----edit---------------
The question of "chemical" change would be, in my mind different from "physical" but I don't know if that distinction comes into play here, or is an issue when the change is permanent or temporary.


texts: How will the X ray diffraction pattern change if the crystal changes its lattice structure

texts:
(I asked this question on another community without getting much help there,I hence post it here as it may be more of a chemistry question. I apologize if my question has an obvious answer, I'm only a beginner)
A text says:
An X - ray diffraction experiment is carried out on a crystalline solid having  FCC structure at room temperature. The solid undergoes a phase transformation on  cooling and shows orthorhombic structure with small decrease in its unit cell  lengths as compared to the FCC unit cell lengths. As a result the 311 line of the XRD pattern corresponding to the FCC system will split into a triplet
Now this is what i could think about it:
We know that the interplanar distance for an orthorhombic lattice is given as $$
d=\frac{1}{\sqrt{\frac{h^{2}}{a^{2}}+\frac{k^{2}}{b^{2}}+\frac{l^{2}}{c^{2}}}}
$$ and using Bragg's law we can find the angle at which constructive interference occurs as $$
\sin \theta=\frac{\lambda}{2 d}=\frac{\lambda}{2} \sqrt{\frac{k^{2}}{a^{2}}+\frac{k^{2}}{b^{2}}+\frac{l^{2}}{c^{2}}}$$
using the values of$${h k l}$$$$={3 1 1}$$ we obtain the diffraction angle which is unique as given by the above equation. Beyond this I cannot understand what to do,how does any splitting occur, what am I missing.


texts: Order of acidity in aromatic molecules with various functional groups

texts:
What factors need to be considered in order to rank the acidity of aromatic molecules with various substituents?

Given benzene with 1 $\ce{OH}$ group. How does adding the following functional groups affect acidity, and what are the rules to determine this?

an additional $\ce{OH}$ group
$\ce{Cl}$
$\ce{NO2}$
$\ce{NO2 + Cl}$
$2\times\ce{NO2}$ groups
$3\times\ce{NO2}$ groups

Based on what I know about acids, the following increase acidity:

charge - the less electrons, the more acidic (more able to grab hydrogen)
electronegativy increases.
compounds with more resonance (more double and triple bonds) - more stability.
more electron withdrawing groups.
lower orbitals - the more s character (less p,d,f), the closer the electrons are to the nucleus, and the lower the energy, which means more stability.

The following decreases acidity

steric hindrance - where 3D structure of a molecule make solvent less accessible, and thus more weakly stabilised. (The difference may be small)
larger molecules tend to require a larger number of solvent molecules to solvate them.


texts: What is the differences between partial pressure and vapour pressure?

texts:
Was looking at Henry's law and Raoult's law
constants and there seemto be lots of
equations involved.
Henry's law involves partial pressure and the latter involves the vapor pressure.
Wondering what the difference is?


texts: Why do C-F bond has less dipole moment than C-Cl bond?

texts:
Larger the difference in electronegativities of bonded atoms, the larger the dipole moment.

(this statement has been extracted from chemwiki-dipole moment)
The electronegativity difference between carbon and fluorine is about $1.43$ (Pauling scale), $1.649$ (Allen scale). The electronegativity difference between carbon and chlorine is about $0.61$ (Pauling scale), $0.325$ (Allen scale). Although, the electronegativity difference of $\ce{C-F}$ bond is greater than electronegativity difference of $\ce{C-Cl}$ bond, dipole moment of $\ce{C-Cl}$ bond ($\pu{1.860 Debye}$) in $\ce{CH_3-Cl}$ is greater than dipole moment of $\ce{C-F}$ bond ($\pu{1.847 Debye}$) in $\ce{CH3-F}$, why?


texts: I am currently writing a paper for my Advanced Analytical Chemistry course, and the topic I am writing on is the analysis of Arsenic in drinking water. The EPA's literature describes how to perform this method but does not describe how many samples should be taken or when and where blanks should be used. The three blanks required for analysis are the rinse blank, calibration blank, and the laboratory reagent blank. My question is, if we assume we are analyzing twenty water samples using ICP-MS, when should each type of blank be run?


texts: How does a halogen react in an electrophilic substitution reaction

texts: From what I understand, electrophiles are electron deficient and therefore would be attracted to the electron-rich benzene ring. So would the correct answer be A?


texts: How can there be concentration and pressure terms simultaneously in the Nernst equation?

texts: In the Nernst equation we are taught that the reaction quotient can have pressure terms and concentration terms simultaneously. According to my knowledge this does not happen anywhere else, so why can it happen here?


texts: How to calculate the volume of a sodium hydroxide solution necessary to add to water, to raise the pH to a certain value?


texts: Solvents adequate for dissolving overheated polyethylene terephthalate glycol-modified (PETG) residue?

texts:
I work in 3D printing. One of the materials we use is polyethylene terephthalate glycol-modified, or PETG. It is a pretty good material, both in strength and appearance. It is melted and pushed through a "hot end" nozzle, typically either brass or hardened steel, at about 230 degrees C.

Unfortunately, it is rather sticky, and tends to accumulate on the hot metal surfaces, where it slowly degrades due to the heat. The resulting residue is black, and somewhat hard to remove. I have tried blowtorching it, which works with polylactic acid (PLA), but that just results in the same black substance.

I have seen recommendations to use either acetone, dichloromethane, or phenol. Other substances like toluene are recommended - some say they work, some say they don't. However, all of these seem to be recommended for dissolving/welding the plastic in its original form. There doesn't seem to be any advice for dissolving the residue after it has degraded from heat, at which point its chemical composition has changed.

From my research, the residue may be composed primarily of acetaldehyde. I was not able to find information (that I can understand as a lay person) about how to dissolve that.

So far, I've tried putting a brass nozzle caked with PETG residue into a 50C acetone bath for an hour. A little of it came off, but not much. The ideal solvent would attack the residue so completely that it would come off without too much force. The inside bore of the nozzles (the melt zone) is typically on the order of 1-2 millimeters, so the best option is to use an abrasive cleaning filament. Something tougher, like a wire brush, is not possible in that confined space, as far as I know.

If anyone has a good answer, I'll spread it around the 3D printing community, so you won't just be helping me. Thanks in advance!


texts: Electrophilic Aromatic Substitution of phenols

texts:
What happens if 2,4,6-tribromophenol is forced to undergo further bromination?

In phenol, the benzene ring is activated towards electrophilic substitution. Therefore, phenol on bromination gives 2,4,6-tribromophenol. If now, 2, 4, 6-tribromophenol is forced to undergo bromination, the group attached to the benzene nucleus makes phenol not suitable to undergo Friedel–Crafts reaction due to adduct formation with Lewis acid.


texts: Normal Phase TLC using ethyl acetate as eluent

texts:
Compounds 1-3 were analyzed by normal phase TLC (shown) using ethyl acetate as the eluent. Assign spots on the TLC plate to compounds 1-3.
  1: 2-acetoxybenzoic acid 2: 2-hydroxybenzoic acid 3: benzoic acid

I asked a question about TLC and I received some mixed answers, so I'd like to see if my understanding of TLC is fine.

We're using normal phase TLC so lower Rf compounds will be more polar. $0.47$ is the most polar compound, $0.70$ is the least polar compound.

Ethyl acetate is polar. Does the eluent polarity just determine where the compounds will run on the TLC?


texts: In making cast iron from pig iron - the cruder form of iron - coke and limestone are added to pig iron and scrap iron in a furnace. Cast iron is   more refined form of iron and has lesser carbon content as well. What exactly occurs in this process of making cast iron - what reactions happen in the furnace? Why is coke added as well, when the purpose is to decrease the carbon content?


texts: pH of liquid hydrogen chloride vs hydrochloric acid

texts:
Is hydrogen chloride in liquid state acidic like hydrochloric acid?
I know that hydrochloric acid is hydrogen chloride dissolved in water but I was wondering if liquid hydrogen chloride was also an acidic substance.
Is this the same for other acids?


texts: Calculating the concentration of acetic acid in vinegar from pH

texts:
DavePhD was kindly helping me with this problem but the site indicated the discussion had gone on too long. Calculating vinegar strength I don't have enough units to start a chat so I am starting a new thread.

The formula above is for determining the concentration or percentage of acetic acid in a vinegar sample when the ph is known. The farmer will get the ph with a ph meter, do the math and calculate the percentage acidity of her vinegar. The Ka, according to the formula DavePhD gave, is .000174 because the pKa for vinegar is 4.76. The molar mass is 60.05196 g/mol. So assuming the ph is 3, could someone write out the "long math" for this? I need someone to walk me through this, step by step to solve for c.

The last time I took algebra was about 50 years ago so, while I remember some things, it is probably better to assume I don't know much :-). Let me know if you need other numbers. Dave says the "M" is just a place holder


texts:
I am collecting a database of perovskite materials and could not decide if $\ce{LiNbO3}$ is categorized as perovskite or not. $\ce{LiNbO3}$ has been identified as a perovskite [1] as well as non-perovskite [2 , appendix] in literature. Which is correct? Usually the structure type of some compounds are written as ($\ce{LiNbO3}$-type or LN-type), are these perovskites or not?
Relevant publications are also appreciated.
EDIT:
Goldschmidt tolerance factor of $\ce{LiNbO3}$: 0.748 (should appr. be between 0.8 and 1.1 to be perovskite)
Tau factor of $\ce{LiNbO3}$(as proposed here): 8.678 (should be less than 4.18 to be perovskite. Tau factor is proven to be more accurate than tolerance factor)
These tolerance factors indicate $\ce{LiNbO3}$ should be non-perovskite, however, I found some other materials such as $\ce{BiSrCr2O6}$ that pass tolerance factor tests but still form LN-type structure. This is where the confusion comes :(


texts: Do SN2 reactions always invert absolute configuration?

texts: I know that an $\mathrm{S_N2}$ reaction proceeds through complete inversion of configuration, but is it necessary that the absolute configuration (R/S) of the chiral centre change after an $\mathrm{S_N2}$ attack ?


texts: How to determine the stereochemistry after elimination of anti-1-bromo-2-methylcyclohexane?

texts:
The question is asking for the product and the answer is C.
My expected answer was E. Here's how I tried to solve it:
Since Br (the leaving group) is at the equatorial position, the structure would 'ring flip'.

Since $\ce{CH3}$ is pointing downwards, I assumed it would have methyl group point outwards (dashed), however, the correct answer is a wedge.

After elimination, how would we know whether the substituent would be pointing inwards, outwards, or even right on the plane? (no wedge or dash)


texts: I don't understand why arsenic is toxic and why it does damage to humans. Could it be that it is so similar to phosphorous? If so, would that make antimony toxic as well?


texts:
We say that hybrid structure is real. It has distinct properties as compared to its Resonating Structure. Is it because that all the experiments we carry out are on a sample, lots of molecules are present. Are they hybrid or are they lots of Resonating Structures in an equilibrium state that they collectively show properties of the hybrid. Also, some structures are said to contribute more to a hybrid structure. What does that mean?

Also, in charged molecules like carbonate ion, the charge is fractional. Won't that mean that electrons get "divided"? I know that partial charges can arise in covalent bonds due to a difference in electronegativity, but this seems different from that.


texts:
I'm hoping that this isn't too obvious of a question (it's been awhile since I've taken chemistry), but I was looking at the solubility table on Wikipedia, which gives the solubility as grams per 100 mL. My understanding is that 100 mL of water weighs 100 grams.

So here's what I was having trouble wrapping my head around: it lists the solubility as 108 (at least at 20 °C). If I understand that right, that would mean that I can absorb 108 grams of urea in 108 grams of urea in only 100 grams of water, right? Can someone explain why it's possible to have more urea than water in this case?


texts:
I was reading Peter Atkins' Elements of Physical Chemistry where I came across this line:

  Bonds do not form because electrons tend to pair; bonds are allowed to form by the electrons pairing their spins.

What does this line mean? What does Atkins want to say through this line & why did he italize the words I bolded above?


texts: Does ultrasonic bath cleaning damage laboratory volumetric glassware calibration?

texts: As an analytical chemist, I'm always ensuring my glassware is thoroughly clean before I start an analysis. However, my supervisor always states that using ultrasonic bath to clean volumetric glassware damages its calibration, rendering it imprecise for analytical usage. Does that hold true, or is it okay to use an ultrasonic cleaner?


texts: Why do triple bonds have a low NMR value?

texts: Double bonds has a positive shift compared to single bonds. It seems like that there would be a trend but then the triple bond negatively shifts, despite having great electron density similar to the double bond. Any insight.


texts: What is the role of hydrochloric acid in a copper electroplating bath?

texts:
Considering water as a given, the third most important ingredient in a copper electroplating solution, as a short survey of related recipe webpages will show you, is hydrochloric acid (HCl). Here's a sample link: http://www.thinktink.com/faqs/cupltfaq/cupltf01.htm

I can guess that the role of sulfuric acid (the second most important ingredient; the first being copper sulfate) is to provide you with sufficient anions to allow copper cations to easily enter the solution at the anode. But in almost all recipes that I have seen, a small amount of hydrochloric acid is added. I wanted to know how useful it is and what is the opportunity cost associated with it.