texts: How do you identify parent chain of molecule?

texts:
Imagine a molecule that has aldehyde and alkene group, then how do you choose the longest chain to name as parent chain. Does the parent chain have to include both aldehyde and alkene group even if there is a larger one just with an aldehyde group?

My TA says that you choose the parent chain that has both aldehyde and alkene chain, if possible, even if it is the shorter chain, without giving any further reasons for that. So then my question is that is it possible for parent chain to include more than 2 functional groups? Like I know the likelihood of seeing such an example may be rare, but if you have a molecule that includes a chain, among other candidates, with more than 2 functional groups, like a carboxylic acid, alkene, alcohol or aldehyde and so on all in one chain… then can you choose such a chain as a parent chain over any other chain anytime when that other chain has fewer functional groups or is even longer or shorter? If yes, then would you say that when finding the parent chain we should try to find parent chain that not only has the highest priority substituent but also the one that has most high priority substituent as possible?

Also, one more question, let's say you have a parent chain that has ketone at second carbon atom from one side of the linear chain and an alcohol group on carbon 1 when viewed from the other end? Even though ketone has higher substituent than alcohol, where would you start numbering the molecule? Would carbon with aldehyde be numbered 2 and carbon attached to alcohol 6 or 7? Or would carbon with alcohol be 1 and ketone be numbered 5 or 6?


texts: Will ferrocene undergo electrophilic aromatic substitution?

texts:
Ferrocene has two structure 1 and 2.It is bonded to an aromatic ion cyclopentadienyl anion.Aromatic species such as benzene , cyclopentadienyl anion undergo electrophilic aromtic substitutions.

Then,will Ferrocene undergo  electrophilic aromtic substitution ?

Which conformer between 1 and 2, would preferentially undergo friedel crafts acylation reaction?


texts:
I need to find the most basic site of Adenine:

The $\ce{NH2}$ group and $\ce{NH}$ cant be strong base as electrons are delocalised. This leaves us with $1,7,3$. I thought that electron density on $1,3$ nitrogens is enhanced due to $+R$ effect of $\ce{NH2}$.

But is this correct, I still cannot decide which is the strongest basic site.

To add: Both $1,3$ nitrogen have two nitrogen in neighbourhood which destablise their conjugate acids by $-I$ effect. So still I can't decide.


texts: Why does Benzoin give positive Tollen's Test?

texts:
Certain alpha hydroxy ketones which can tautomerise to form an aldehyde will give a positive Tollen's Test. I was pretty clear with this idea until I came across this question and the answer given is A,B,C. I can't figure out why Benzoin gives a positive Tollen's Test as it can't give an aldehyde by tautomerisation.

What exactly does happen to Benzoin over here and why does it give a positive test? Is my idea about tautomerisation of alpha hydroxy ketones to aldehydes wrong?


texts: I'm so much confused about what active mass actually is, my text book states that, active mass is a dimensionless quantity, but for our convenience and purposes, we take it with dimensions of molarity, partial pressure, etc. But I searched, and I got that, historically, what Guldberg and Waage stated about active mass in the law of mass action, is " Parts of body present in 1cc of the total volume " (Rough translation), now it contradicts that, it's dimensionless. On Google I found, that active mass is actually a ratio of mass which participates in reaction and total mass and it goes true with the fact written in my text book, that active mass of pure liquid and pure solids is unity. So, what is actually the definition of active mass ? What is actually about the dimensions ? And why we take active mass of pure solids and liquids as unity ?


texts:
For all the three parts, only methane has been given as the product in my textbook.

In 1) and 2), according to the mechanism I wrote, I get both ethane and methane as products. I think both these products should be formed in good yield. Then, why my products do not match?

In 3) , I got methane as the only product as given in the textbook. Can you please check the mechanism?


texts: Why does insufficient data lead to random errors?

texts: I've read up on the causes of random error and noticed insufficient data to be one of the causes of random error. However,  I'm confused as to why insufficient data could possibly lead to random errors. Could someone provide some context for why this might be?


texts: What is reactivity really, and can it be quantified?

texts:
I understand the concept of a reactive species on a sort of vague and intuitive level: a reactive species is one that has lots of reactions that it can participate in. These tend to have large kinetic constants, be thermodynamically downhill and often have products that are also reactive, leading to knock-on effects. But reactivity isn't the same as energy, and it's possible to have highly reactive species with relatively low free energies and vice versa.

I'm interested in whether there's any kind of formal theory of reactivity, and/or a quantitative definition of the concept. For example, we're often told that free radicals are reactive because they have an unpaired electron and they "want" to fill their outer shell. This makes perfect sense on an intuitive level, but I'd like to know if it can be taken further. Is there some way we can write down an equation that will tell us how reactive a species will be in a given environment, or is there some way we can measure a species' reactivity empirically and use it to make predictions?

To clarify, I'm not looking for quantum-level predictions, although I will look into the theories mentioned in Sam and Greg's answers. Rather, I'm looking for something a bit more heuristic that will help me get a handle on what reactivity really is. In particular, what does it really mean to say that one species is more or less reactive than another? Can we put a number to it and say that a species has a reactivity of 8.2 on some meaningful scale?

ron's answer is a start. It surely must be the case the reactivity relates to the energy landscape. But ron's answer deals with a one-dimensional landscape, corresponding to a single reaction. Reactivity is a concept that involves many reactions, and so a satisfying theory of reactivity would have to involve the properties of a massively multidimensional landscape. If there is anything that has been written about it from that point of view I would be very happy to read it.


texts: Does the aluminium chloride assay (Ordonez et al.2006) for total flavonoid content work on coloured extracts?

texts:
It is said that after applying aluminium chloride assay, the extracts will turn yellow due to formation of Al-Flavonoid complexes. So I was wondering if the assay still works if the extracts are already yellow.
For example, the yellow extracts are applied aluminium chloride assay and determined for total Flavonoid content using colorimetric method.
Then, would the result show the TFC (total flavonoid content in those yellow extracts?


texts: Percentage of trans-stilbene traces in cis-stilbene H NMR

texts:
This is H NMR spectrum of cis-stilbene. There are some traces of trans stilbene. I have to determine how many trans-stilbene is present, the exact percentage and I have problem with that.

I guess that it has to do with integration of peaks but I'm still not sure is trans-cis isomer ratio 1:10 or am I wrong?


texts: What is the mechanism of the reduction of organic acids with borane? Borane reductions don't work well with electron deficient carbonyl groups. Why is that so, and how isn't the carboxyl group an electron deficient group?


texts: Is peroxynitrous acid an isomer of nitric acid?

texts:
Structure of nitric acid:

Structure of peroxynitrous acid:

Nitric acid and peroxynitrous acid have the same structural formula, $\ce{HNO3}$ and in both the compounds, O.N. of nitrogen is +5. So, is peroxynitrous acid an isomer of nitric acid?

It seems that peroxynitrous acid is a very, very unstable compound and I don't think it has been synthesised in pure, stable form. This video shows the preparation of peroxynitrous acid but it readily converts into nitric acid and thus the peroxynitrous acid yield is very poor.

Keeping aside its stability and considering only their structure and structural formula, is peroxynitrous acid an isomer of nitric acid?


texts: Why is ammonia less acidic than terminal alkynes?

texts:
Here's a picture from Organic Chemistry by Solomons, Fryhle & Snyder :

Why is it that ammonia is less acidic than terminal alkynes even though water, and even alcohols, are more acidic than them?

Water and ammonia seem to be very similar to me:

Electronegativity difference of oxygen and nitrogen is only 0.4 (Pauling scale)
Both are very similar and differ by only number of hydrogen atoms.
Both are $\ce{sp^3}$ hybridized
Oxygen and nitrogen atoms have similar size

However, the difference in acidic strength is huge. If my understanding of $\mathrm{p}K_\mathrm{a}$ values is correct, water is nearly $10^{10}$ times more acidic than terminal alkynes, whereas ammonia is less acidic than terminal alkynes by a factor of $10^{13}$!

Shouldn't the list be like: water > alcohols > ammonia > terminal alkynes > terminal alkenes > alkanes or water > ammonia > alcohols > amines > terminal alkynes > terminal alkenes > alkanes ?


texts:
From Wikipedia:

  intercalation is the reversible inclusion or insertion of a molecule
  (or ion) into compounds with layered structures.

What is the "driving force" / mechanism that's responsible for intercalation? I assume it's not just diffusion.

In particular, why intercalation continues beyond the periphery? i.e. imagine the process has started and the periphery is now occupied by the intercalant: what drives subsequent intercalation to occur if all the periphery is already occupied by low energy host-guest arrangements?


texts: How many molecules does it take to have a phase?

texts:
A single molecule can't be solid, liquid or gas. It's just a molecule. A mole of something can be any of the three. So, how many molecules does it take for phases to be meaningful?

I realize that this may depend on the molecules in question. The minimum number that can form a solid might depend on the configuration that molecules adopt when solid. The smallest crystal of a lattice for example. How about a gas though? Can two molecules be called a gas if they exist under conditions where a larger quantity of the same moiety would be in a gaseous state?

In short, can a minimum number of molecules necessary to adopt a particular phase be defined?


texts: Effect of different electron withdrawing/transition state stabilising groups in nucleophillic aromatic substitution

texts:
I have been asked the following question in my problem sheet:

The only differemce between reaction A and reaction B is the electron withdrawing group that stabilises the anionic transition state changes from $CN$ in reaction A to $NO_2$ in reaction B. I can see no glaringly obvious reason why there should be a different rate. The problem is really (at least in my mind): what is the better electron withdrawing group out of $CN$ and $NO_2$. Is this a reasonable interpretation? If so, what reasoning can I bring to the answer to suggest that one is a better EWG than the other?


texts: Overall ring strain seems to be a big issue when it comes to organic chemistry. That is why cyclopentane may be in an "envelope form" or why cyclobutane may be in a kinked, kite form. Both of these example molecules are not planar. So, why is epoxide (oxacyclopropane) a stable molecule, if at all?


texts: The safest and easiest way of working with solid LDA

texts:
I have a 25-gram bottle of solid LDA (lithium diisopropylamide), factory sealed. I'm going to setup an aldol reaction with it, but I don't know how to organize work properly.
I think of quickly weighing some amount into a flask flushed with argon and flushing the bottle with argon for storage. Then I'll dissolve the LDA in the flask in THF and use this solution. The only concern is stability of the rest of LDA in bottle.
If you have some ideas how to organize it better, please share.


texts: Why is the temperature graph sigmoidal in simple distillation of components with very different bps?

texts:
I'm writing an organic chemistry lab report on distillation and I thought I understood this, but the more I look at my lab textbook, I realize I don't.  My textbook 1 explains that the temperature of a mixture will rise continuously while it boils and distills if it is composed of two components with similar boiling points, but take on a sigmoidal shape when they are

When a liquid mixture is distilled, often the temperature does not
remain constant but increases throughout the distillation. The reason
for this is that the composition of the vapor that is distilling
varies continuously during the distillation (see Figure 14.3B).

I don't understand this sentence: "The reason for this is that the composition of the vapor that is distilling varies continuously during the distillation." I understand why it is true, but not why it is an explanation for the shape of these graphs. Let's say I'm distilling volatile component B from non-volatile component A. If the boiling point of the mixture is the point at which the vapor pressure of the mixture equals the atmospheric pressure, what does the composition of the vapor have to do with anything?  The relevant pressure is the atmospheric pressure, right?  I would think that as component B is boiled off, the vapor pressure of the mixture would decrease, because the mixture has less B, by Raoult's law, Ptotal = PA + PB = PA°NA + PB°NB, and as its vapor pressure goes down, its boiling point goes up.  I don't see why this isn't happening continuously.
Is the relevant pressure not the atmospheric pressure, but some additional pressure exerted by the vapor in the flask?  (It's been a long time since I took general chemistry.)

Pavia, D. L., Lampman, G. M., Kriz, G. S., & Engell, R. G. (2011). A small-scale approach to: Organic laboratory techniques. Belmont, CA: Thomson Brooks/Cole


texts: Abnormal deviation of CO2 from ideal gas behaviour

texts: Why does carbon dioxide show larger abnormal deviation from ideal gas behaviour than other gases. Why does carbon dioxide first show negative deviation and then positive?


texts: Safe & Convenient method to hydrate CaO into Ca(OH)2?

texts:
I'd like to prepare a solution of $\ce{Ca(OH)2}$ from $\ce{CaO}$.

Ideally I guess I'd go for slowly adding the powder to a water-cooled round flask containing pure water but I have no mechanism to control the slow release of powder nor am I sure that the reaction wouldn't be fast enough to send the powder right back out of the flask.

Is the reaction slow enough for it to be safe and convenient to set pure water to slowly drip into the flask containing the powder (bathing in a large volume of water to dissipate the heat)? This would allow me to have my hands & mind free and control the flow to allow the heat to  slowly dissipate at the desired rate, if necessary I could change the water in the cooling bath once it reaches a certain temperature. This solution would appear more convenient though I have some concerns (if the reaction it too fast steam would pop $\ce{CaO}$ around in the flask, creating some airborne $\ce{CaO}$ coming out of it, I could do a closed system to work that around but if steam is produced I feel an open system would be safer). I'll wear protective equipment to set up everything, though I'd still rather not take unnecessary risks.

In the worse case I could hydrate a portion of $\ce{CaO}$ with steam in a cooled down space but that setup might be unnecessary.

Also, how can I calculate the amount of energy that will be released per quantity or weight from $\ce{CaO}$? (to know how much energy I'll need to dissipate)


texts:
I have come across use of the terms cis and trans electrodes in the context of nanopores and driving charged biomolecules through a pore using an electric field [1]:

FIG. 1. Drawing of the cis negative electrode and trans positive electrode chambers. The arrows show the direction of electric field lines. The pore diameter $d$ and length $l$ and the capture radius $r$ are also shown.

I wondered what the origin of the term is.
I know about cis and trans isomers, but I have not come across the term before in terms of electrodes. Is there a simple explanation?
I can just assume that cis/trans are just another terms for cathode and anode, but I think I am missing something. If the cis electrode is the cathode and the trans electrode is the anode, then why not just call them that? Is there any additional meaning?
Reference

Grosberg, A. Y.; Rabin, Y. DNA Capture into a Nanopore: Interplay of Diffusion and Electrohydrodynamics. The Journal of Chemical Physics 2010, 133 (16), 165102. DOI: 10.1063/1.3495481.


texts: What ion remains in the largest concentration at equilibrium: 0.1 M H₃PO₄ and 0.2 M KOH?

texts:
Mix equal volumes of $0.1~\mathrm{M}$ $\ce{H3PO4}$ and $0.2~\mathrm{M}$ $\ce{KOH}$. What ion remains in the largest concentration at equilibrium?

My approach: suppose we mix $1~\mathrm{L}$ of each solution. For $\ce{H3PO4}$, $K_{a_1}=7.5\cdot10^{-3}$ and $K_{a_2}=6.2\cdot10^{-8}$, so in terms of the dissociation of $\ce{H3PO4}$, the only ions produced in non-neglible quantities are $\ce{H^+}$ and $\ce{H2PO4-}$. Furthermore the quantities of $\ce{H^+}$ and of $\ce{H2PO4-}$ are both less than one mole, since there is less than 1 mole $\ce{H3PO4}$. We have 2 moles $\ce{OH^-}$ from the $\ce{KOH}$, but since of the $\ce{OH^-}$ neutralizes the $\ce{H^+}$, in particular less than a mole $\ce{OH^-}$ is used in this neutralization reaction. Thus at least one mole $\ce{OH^-}$ remains, at most 1 mole $\ce{H2PO4-}$ remains, and all other ions remain in negligible quantities, so the answer is $\ce{OH^-}$.

Apparently, this is wrong - the answer is $\ce{HPO4^2-}$. I don't see how this is possible because we already established that the amount of $\ce{HPO4^2-}$ formed is negligible from the $K_a$ values, and since we are adding a strong base to a weak acid we know the resulting solution will be basic, so we should expect from the beginning that $\ce{OH^-}$ appears in large concentration.

I don't understand what's wrong with my reasoning?


texts: this might be very childish question but i am comfused because they say that organic molecules are those that contain H and C if that is so how can you call carbontetrachloride organic, even it hasn't any H atoms


texts: Why is the peak-to-peak separation of cyclic voltammetry is 57 mV?

texts:
I'm studying CV, and I wonder if I can calculate the peak-to-peak separation of CV for a reversible redox system.

I found that the separation is 57 mV on my textbook, and my teacher taught me that is can be calculated theoretically using Nernst equation,
but I think it is more complicated.

Is it easy enough (for sophomore) to calculate the value?
And if it is, I want to know the way.

(Sorry for my poor English)


texts: Nucleophilic Substitution rate comparison 1-bromobutane and 2-bromo-2-methylpropane with NaOH

texts:
I want to ask a question about the hydrolysis of haloalkanes to form alcohols.

I have been presented with a flowchart diagram of possible reactions of haloalkanes below:

Now, I have been presented with the question below:

I have identified the reagent I relevant to the question as NaOH (aq)

First, I need to compare 1-bromobutane and 2-bromo-2-methylpropane.

I can see that there are 3 alkyl groups in 2-bromo-2-methylpropane and only 1 alkyl group donating electrons to the Carbon atom attached to the Bromine.

So, during the reaction, the carbocation intermediate formed by reaction of NaOH with 2-bromo-2-methylpropane will form be more stable than the carbocation intermediate formed with 1-bromopropane (application of Markownikoff's rule) as alkyl groups are electron-donating groups and the three methyl groups will stabilise the positive charge on the carbon atom to a greater extent in 2-bromo-2-methylpropane.

However, I am slightly confused.

Why does this mean that the rate of reaction with 2-bromo-2-methylpropane is faster than the reaction with 1-bromopropane?


texts: What phase of matter is salt when dissolved in water?

texts:
Being an ionic solid, salt is very susceptible to being torn apart by the polar molecules of water. Inside the water, salt exists as sodium and chlorine anions; but what state of matter is it in? My instinct tells me it is in a solid state, as salt's melting point is 800°C, but it sure doesn't really act like a solid.

EDIT: I think I ought to rephrase, I mean what state of matter are the individual sodium and chlorine ions inside the water.


texts: How one calls temporal changes of chemical content due to nuclear reactions?

texts: So, I am trying to find the term for subject question: temporal change of chemical content due to nuclear reactions. Specifically, I am interested in time evolution of the number of atoms of each isotope in, let say, spontaneous decay chain but without any interest in potential chemical compounds. I was googling for "stoichiometry dynamics" and "nuclear chemistry kinetics" but these seem to have specific meaning clearly distinct from what I had in mind.


texts: Why is carbon tetrachloride a liquid at room temperature?

texts: From what I can understand, $\ce{CCl4}$ has only London dispersion forces between its molecules. However, it is still liquid at room temperature. $\ce{CCl4}$ has just five atoms, making it a relatively small molecule, so how come its intermolecular forces are strong enough for it to be a liquid at room temperature and atmospheric pressure?


texts: Find oxidation number of a metal in a compound

texts:
Calculate the oxidation number of $\ce{Fe}$ in $\ce{Fe2O3}$.

Alright. So we have a metal and an non metal. This means that iron will lose electrons and give them to oxygen. So it will be a positive oxidation number for iron I guess.

The question is, how much? A wild guess is $2+$ because, well, each iron would is bound to two oxygens so I imagine each oxygen will take one electron each?


texts: Master equation for catalyst and substrate binding?

texts:
I recently asked this on Biology.SE, and need to start with the master equation for the reaction:
$$\ce{E + S -> ES}$$
Where $\ce{E}$ is our enzyme and $\ce{S}$ the substrate to get a probability density function for the binding time of a substrate with one specific enzyme to be:
$$f{\left(t\right)}=k\left[\ce{S}\right]\mathrm e^{-k\left[\ce{S}\right]t}$$
I have read up on master equations, but really have no idea where to start in this derivation, any help would be appreciated?


texts: Explosive reaction based on reaction rate

texts:
Question

  We have the following chemical reactions:

  $$
\begin{align}
\ce{A + B^* &-> C + D^*}\tag{1}\\
\ce{D^* &-> B^* + B^*}\tag{2}\\
\ce{B^* &-> B}\tag{3}
\end{align}
$$

  If the initial concentrations are $[\ce{A}] = \pu{100e-6 mol cm-3}$ and $[\ce{B}] = \pu{1e-6 mol cm-3}$, is the system explosive? We know that $k_1 = \pu{1e6 cm3 mol-1 s-1},$ $k_2 = \pu{50 s-1}$ and $k_3 = \pu{25 s-1}.$

My solution

So I found the rate expressions for $\ce{A}$ and $\ce{B},$ by applying steady-state approximation (SSA) on $[\ce{D^*}].$ I get the following expressions:

$$
\begin{align}
\frac{\mathrm d[\ce{A}]}{\mathrm dt} &= -k_1 \cdot [\ce{A}] \cdot [\ce{B^*}]\\
\frac{\mathrm d[\ce{B}]}{\mathrm dt} &= (k_1 \cdot [\ce{A}] - k_3) \cdot [\ce{B^*}]
\end{align}
$$

Upon entering the numbers into the above expressions, I get the following numbers:

$$
\begin{align}
\frac{\mathrm d[\ce{A}]}{\mathrm dt} &= \pu{-\frac{1}{10000} mol cm-3 s-1}\\
\frac{\mathrm d[\ce{B}]}{\mathrm dt} &= \pu{\frac{3}{40000} mol cm-3 s-1}
\end{align}
$$

My conclusion was that the system is not explosive since the rate of formation of $\ce{B}$ is quite low. Since if the rate is too low, then the reaction can not be considered explosive.

But the problem with my explanation is that I would like to have a reference number. Is there a reference such as f.e. rate higher than $10$ is considered explosive, etc? I have tried looking everywhere but could not find any 'value.' Could anyone provide some insight into this:

Are my explanation and conclusion correct?
Is there a reference value for explosive reactions?

I have an additional question. What is the connection between an explosive system and the steady-state approximation? If the system is explosive, can I still use SSA or does it become invalid?


texts:
I have a question regarding the denaturation of industrial ethanol with methanol to discourage its consumption.

The boiling point of methanol is 64.7 °C, while the boiling point of ethanol is 78.37 °C. Wouldn't it be trivial then, to separate the methanol by simply distilling industrial ethanol at 64.7 °C ?

Is there some technical reason as to why this wouldn't work? Because if it does work, then why isn't it a widespread practice among criminal elements and such.


texts: Boiling/melting points of cyclohexane and cycloheptane

texts: I’m looking at a chart in my book, and while cycloheptane has a higher boiling point than cyclohexane like I’d expect, cycloheptane has a melting point of −12 °C, while cyclohexane has a melting point of 6.6 °C. Why does it have a lower melting point only?


texts: Is a 50/50 mix of Acetone and Water inert?

texts:
We are cleaning a gel out of a fuel tank that is dissolved by Acetone.  We want to neutralize the acetone by adding water to achieve a mix of 50/50 so that (PERHAPS) the acetone will not damage rubber / plastic compounds in the fuel system.

We have an electric fuel pump we are going to use to get the acetone and water out and we need to make sure we don't damage it. THEN there are the two brand new mercruiser marine fuel pumps, fuel filter and carburetor seals we don't want to damage.   We CAN  add more water than a 50/ mix as well.

We know we can't get all the contents of the tank out and so we want to make sure any remaining acetone will not be of a concentration to ruin the fuel system components.  By the way... this is for a famous movie director Roman Coppola.


texts: Shape of the blood CO2 dissociation curve

texts: What equation determines the shape of the blood $\ce{CO2}$ dissociation curve? I know that since it factors all possible forms of $\ce{CO2}$ carriage, there are a bunch of factors (e.g. Henry's law, formation of bicarbonates and carbaminohaemoglobin, how these are affected by protonation and oxygenation of haemoglobin, etc.) but these don't really seem to explain the non-linear shape. Whereas for oxygen it's fairly straightforward (saturation can be derived using equilibrium kinetics).


texts: Why does the presence of EWG's on the aryldiazonium ring increase the yield of a Meerwein arylation?

texts:
In my textbook, Strategic Applications of Named Reactions in Organic Synthesis, the author says the following regarding properties of the Meerwein arylation:

  The general features of this reaction are: 1) the procedure is simple; no special laboratory equipment is needed;  2) the aryldiazonium halides are prepared by the diazotization of aromatic amines using sodium nitrite and aqueous hydrohalic acids and are not isolated, rather immediately reacted with the alkenes in the presence of an organic solvent (e.g., acetone, acetonitrile); 3) the presence of electron-withdrawing substituents on the aromatic ring tends to increase the yield, whereas electron-donating groups often give lower yields; 4) the alkene component usually has an electron-withdrawing substituent and mostly α,βunsaturated carbonyl compounds are used;

I don't really understand why that is. If anything, I would think that EDG's (in para position) would increase the yield because they stabilize the aryl cation that would form if the aryl diazonium decomposes and loses its diazo group as nitrogen gas (N2).

Could it be that an EDG would make the aryl diazonium compound too unstable and decompose too quickly? Allowing for side reactions to occur?


texts: How to determine and derive the protonation state of a functional group based on its pKa?

texts:
In our biochemistry class we were introduced to a rule of thumb, which goes something like this:

"If the pH of a solution is one or more units below the $\mathrm{p}K_\mathrm{a}$ of a group, then said group is protonated and if it is one or more unit above, then the group is de-protonated"

However, we weren't provided with a mathematical derivation of this fact.
I attempted one by myself using:

$$\ce{HA + H2O <=> A- + H3O+}$$
thus, $$\ce{pH} = \mathrm{p}K_\mathrm{a} + \log\frac{\ce{A-}}{\ce{HA}}$$
or, $$\ce{pH} = \mathrm{p}K_\mathrm{a} + \log\frac{1-\alpha}{\alpha}$$

and then define $\mathrm{p}K_\mathrm{a}$ as the point where ${\alpha=0.5}$ i.e proton occupancy is 50%

$$\alpha(\ce{pH}) = \frac{1}{1+\exp\left\{-\ln10(\mathrm{p}K_\mathrm{a}-\ce{pH})\right\}}$$

where $\alpha$:= degree of proton occupancy.

By looking at this function, I can sort of get that if pH goes up, $\alpha$ goes down i.e case of protonation, and if pH goes down  $\alpha$ goes up i.e case of deprotonation.

This seems a little bit "back of the envelope" to me. Is this sufficient, or am I missing something.


texts: What is the liquid used in instant shoe shiner?

texts: What is the liquid used in instant shoe shiner products? Ive tried refilling it with WD-40 but I would like to know if there are any cheap alternatives to refill it?


texts:
What does the pKb (or $K_b$) of a strong acid mean?
For instance this link reports the Kb of HI, an extremely strong acid. Are they reporting the reaction constant of the reaction:
$HI + H_2O \implies  H_2I^+  + OH^- $
Is the $K_b$ for the equation?
That reaction seems so bizarre; it seems like the products are so unstable and reactive.


texts:
I tried to extract hydrogen for my kid's birthday, by mixing caustic soda with water and aluminum foil (mixed in a glass bottle). A lot of heat and (hopefully)hydrogen was released.
However, within 2-3 hours, the balloons started losing altitude and began falling down. I supposed it was caused by losing the gas slowly.
But when I tried to burn the ballon the next day it did not create the pop sound for the hydrogen test.
Please excuse me if this is a naive question. I'm curious since this is the first time I'm dealing with hydrogen and balloons. I attempted this for almost 4-5 time. And every time the balloon stopped flying within 2-3 hours. All other balloons filled with air did not lose gas.
I want to know what happens to the gas. Does it go out? Is it some sort of diffusion?
Thanks.


texts: Are Lewis Structures the same throughout solids, liquids, and gases?

texts: For example, is the lewis structure for water constant even when it is in a solid, liquid, or gas phase?


texts: Melting point is the critical point at which a solid starts to be transformed into a liquid? Does this mean that the geometric lattice of a solid is broken?


texts: Process of transferring kinetic energy in regard to photons.

texts: Now I know that temperature is the average kinetic energy of atoms, molecules and compounds. Photons increase the kinetic energy/temperature of molecules since photons are pure energy. Hence, wouldn't the transfer of kinetic energy mean that photons need to be transferred from a higher temperature molecule to a lower temperature molecule?


texts: HOCl + ethyne reaction-hypochlorous acid with acetylene

texts:
What is the product of acetylene ($\ce{C2H2}$) and hypochlorous acid ($\ce{HOCl}$) reaction?

I gathered that $\ce{Cl}$ acts as electrophile and so $\ce{HOCH=CHCl}$ is formed. Now two things can happen: it could tautomerize to keto form since enol form is unstable, or another molecule of $\ce{HOCl}$ can add itself, if it adds again there are two ways of adding them, both chlorine atoms could end up on the same carbon or on adjacent carbons. How do we decide what will be the final product?


texts: How to speed up flash powder flaming reaction

texts:
Do you have an idea how can be flaming of flash powder (probably $\ce{KClO_4} $ (60%) + $\ce{Al}$ (40%) ) can be speeded up? Of course we consider the pure oxygen-in-air conditions. So how? With some kind of catalyst?
Thanks.


texts: Does Malaprade reaction occur in oxalic acid?

texts:
I've seen the Malaprade cleavage reaction , using the periodic acid, in vicinal diols, vicinal diketo and in vicinal keto-ol, but I was wondering if the same can be done in the case of HOOC-COOH.
Since it contains carbonyl groups on adjacent atoms, my sensibilities suggested that it might occur, but I am unable to find any references confirming the same.


texts:
I just read about the theory of auto-catalysis, and here's one thing which is sort of unclear to me:

  In this type of catalysis, one of the reaction product catalyses the reaction. For example, in the oxidation of oxalic acid by potassium permanganate, Mn(II) cation is formed which is known to accelerate the reaction. So when potassium permanganate is added to a warm solution of oxalic acid in presence of dilute sulphuric acid (acid medium catalysis), initially there is a time lag before decolourisation occurs. As more permanganate is added, the decolourisation is observed to be nearly instantaneous.

Points I didn't understand:

How does the formation of Mn(II) cation accelerate the reaction? Could someone please help me with understanding the mechanism?
What is the reason for time lag in decolourisation of the solution? Also, what exactly do they mean by decolourisation here? My guess is that it's referring to the bright purple coloured permanganate solution losing its colour after getting reduced to Mn(II) cation.
How does the time lag reduce? Are there ways to estimate or determine the same? Of course, it'd depend on the reaction kinetics; but I'm looking for a mathematical viewpoint on how the catalyst influences reaction kinetics, except for decreasing the activation energy.

Thank you.


texts: What [if anything] is special about the boiling process of purifying water (excluding temperature)?

texts:
I know that water boils at $100~^{\circ}\rm C$. I also know that the standard way to purify water is to boil it for roughly a minute. What I'm curious about is, what properties of the boiling process purify the water?

Is it purely a temperature thing? Are we saying "roughly a minute" so that the temperature actually increases beyond $100~^{\circ}\rm C$, thus reaching some actual temperature needed to kill bacterial/viral stuff? Or, does the "rolling" of the boil actually add a physical benefit to the purification process?


texts: Free Open Source Gas Chromatography Software

texts:
Collecting data is one thing, however sometimes one needs to plot or analyse data at a later date when access to the original software may no longer be feasible or possible.

Open Source software is at times a good alternative to commercial products. In this case, please list open source and/or free software for gas chromatography.
(Having said that, the databases for mass spectrometry are not open as far as I am aware, though suggestions are also welcome.)


texts: What does the salt $\ce{K3Fe(CN)6}$ change to when it is dissolved in water? I mean, I think its going to ionize, but in what way? Is there a way to know this? I tried to search the web but wasn't able to find the answer.


texts: Can molten Strontium and Barium Hydroxides be electrolysed to give the metals?

texts: Can strontium and barium hydroxides be electrolysed to give the metals? I've noticed they have relatively low melting points. What challenges would this present?


texts: I'm the youth ed manager at Denver Water in Colorado. We do a water treatment demo in the classroom, and currently we use the first part of the Winkler DO test to create floc. I'm looking for a better demo that creates white floc and doesn't turn the water brown. I've tried using alum and mixing it with alkaline iodide azide reagent. It creates wonderful, white floc. What I don't know is if it's safe in a classroom setting. Can you help?


texts: Do ions still "conduct electricity" if a physical connection made by aqueous electrolytes between the anode and the cathode is nonexistent?

texts:
I always had the misconception that when people say ions conduct electricity, what they actually mean is a connection is made between the cathode and the anode by the ions and electrons can flow from the cathode to the anode through this connection.
However, I recently learned that ions conduct electricity because chemical reactions are happening around the electrodes.
Taking the example of the electrolysis of sodium chloride water solution. At the cathode, $Na^+$ captures electron ($Na^+ + e^- \rightarrow Na$); at the anode, $Cl^-$ releases electron ($2Cl^- \rightarrow Cl_2 + 2e^-$). And this is because the battery takes electrons from the anode and feeds electrons to the cathode, and positively charged anode attracts anions and negatively charged cathode attracts cations. That is to say electrons do not flow from cathode to anode but are given to and taken from the ions.
I still feel confused after knowing this explanation because it seems to me that the anode and the cathode do not need to be connected by aqueous electrolytes to "conduct electricity". Suppose the cathode and the anode are placed into different solutions in different containers, anode still attracts anions and cathode still attracts cations. So that there should still be electricity flowing through the circuit.
Some people say that a "closed circuit" is required for ions to conduct electricity. If that is the case then what am I missing here?


texts: Why is partial pressure proportional to mole fraction in Henry's law?

texts:
According to Henry's law of partial pressure,  partial pressure of a gas above a solution is directly proportional to the mole fraction of the gas in the solution.

But my question is: If the mole fraction of a gas in solution is greater, then that should mean there are less gas molecules in the air and so the partial pressure should be less. Why is it the other way round?


texts: I need a fine aluminum powder for many reactions/experiments. Could I dissolve the metal in an acid and then drop it out of solution using a base, or vice versa? What would be the best chemicals/process to produce a high yield of aluminum powder?


texts: Difference between exothermic and exergonic

texts:
In High School I learned that an exothermic reactions releases energy, while an endothermic reaction needs energy to occur. Now I learned that there is a separate, somewhat similar classification scheme of exergonic and endergonic reactions.

What is the difference between these two classification schemes? Are exothermic reactions always exergonic, and if not, can you give me an example?


texts: Can I get some pointers on what to do in calculating the hardness of water?

texts:
Information provided: $\pu{1.64 g}$ of $\ce{Ca(NO3)2}$ and $\pu{0.94 g}$ of $\ce{MgCl2}$ are dissolved in $\pu{10 L}$ of water, calculate the hardness of water.

I have used these two equations: $m = n \cdot M$ and $c = \frac nV$.

What I have done is simply insert the molar mass of both $\ce{MgCl2}$ and $\ce{Ca(NO3)2}$ in the first equation, isolated $n$, then used that answer to isolate $c$ in the next equation. But I need to find the mass for $\ce{Ca^2+}$ and $\ce{Mg^2+}$ only, how do I do that? Have I found the concentration of the wrong things?

Please explain in simple language. Thanks!


texts: Is there any way of guessing what a compound smells like?

texts:
I am aware that we can predict the colours of compounds, on the basis of their electron transition energies, and many other physical properties (on the basis of other theories.)

Smell works in an inherently different manner, as the compound binds with smell receptors in our noses, and we smell a distinctly different smell for many compounds, quite unlike colour, or crystalline/amorphous nature, etc. It's also highly subjective, varying slightly from person to person. But, so does observed colour...

However, I don't see any way of predicting the smell of a random substance with any technique, except when we know what it is (e.g. hydrogen sulphide smells like rotten eggs, ammonia like rotten fish, benzaldehyde like almonds, etc.)

So, I guess my actual question is, is smell an actual physical property affected by the chemistry of a compound, or is it highly random? Are there any theories predicting the smell of compounds on the basis of their structures, functional groups, etc?


texts: What is the length of a unit cell of CuCl assuming that it is fcc?

texts:
The density of $\ce{CuCl}$ is given – $x\ \mathrm{g/cm^3}$
The crystal structure is assumed to be fcc.

My teacher is claiming the we can apply the formula

$$\rho=\frac{Z \cdot M}{a^3 \cdot N_\mathrm A}$$
And he took $M = 35.5\ \mathrm{g\ mol^{-1}}+63.5\ \mathrm{g\ mol^{-1}} = 99\ \mathrm{g\ mol^{-1}}$,
$Z = 4$ as it is fcc.
But my question is how can we take $M = 99\ \mathrm{g\ mol^{-1}}$? It means every particle in the fcc has mass $99\ \mathrm u$ doesn't it?


texts: Why does ring contraction take place in Wagner–Meerwein rearrangement?

texts:
An example of Wagner–Meerwein rearrangement given in my textbook is substitution by $\ce{AgNO2}$ in iodocyclohexane. One of the product, cyclopentylnitromethane is through ring contraction.

I don't understand how this took place. Can anyone explain the mechanism?


texts: Software for technical calculation of chemical reactors

texts:
I'm not a chemical engineer and don't have good background in it.
Just my father asked me to do something for him, as I'm a computer engineering graduate.

This is a software for calculation of technical parameters of reactor. I haven't seen it. I've just printed output of it. Fields are like following:

5  REM**************
10 REM***********
20 REM  Name etc.
~~~~~~~~~~~~
35 REM ********** PRODUCTIVITY********
~~~~~~~~~~~~
155 REM ***** INPUTS*******
~~~~~~~~~~~~~~~~~~~~~~~~
220 DTB
240  DTS
~~~~~~~~~~~~~~~~~~~~
555 REM *********** CALCULATIONS****************
~~~~~~~~~~~~~~~~~~~~~~~~~
~
~
~
********RESULTS*************
DTO=75
G=543.2
Q=XXXX
XXXXXX

Can anyone help me to find what is the software for calculation. I'd be very grateful if you can help.


texts: Is histidine drawn wrong in these mechanisms for chymotrypsin?

texts: While trying to understand the mechanism of chypotrypsin, I have been looking at a few mechanisms, which are found in my lecture notes, and one found in my textbook. In both cases, it looks like the histidine has the wrong connectivity with the rest of the amino acid chain. Is there a reason for this, or is it an oversight on behalf of the publishers?


texts: Why is the para carbon in Benzaldehyde NMR more deshielded than the ortho and meta carbons?

texts: Assuming this image is correct, why is the Carbon-3 more deshielded than Carbon-2 and Carbon-1? From what I understand, deshielding is the greatest when the Carbon atom is closer to electron withdrawer and it appears Carbon-3 is the farthest.


texts: Influence of pH on precipitate crystallite sizes?

texts:
It's normally assumed that a higher pH of solution would slow nucleation rates and hence lead to larger crystal formation. I've found literature that it is due to solid-liquid inter-facial tension. Which is a concept that I do not fully understand.

In my experiments, higher pH solutions led to the formation of smaller crystallites. I can't make sense of why its contradicting the literature. Here are the images from my experiments:

My samples are precipitates produced from mixing aqueous $\ce{CaCl2}$ +$\ce{MgCl2}$ and $\ce{Na2CO3}$ solutions. The elevated pH images were produced through the addition $\ce{NaOH}$ to the previously mentioned mixture.

If you have any comments or ideas, it would be greatly appreciated. I am a engineering student who is trying his hand at inorganic chemistry.

Thanks in advance.


texts:
The question is basically to figure about the steps for the following transformation.

Since ethene is a electron donating group and weakly ortho para directing so it makes electrophilic substitution difficult.hence we must add bromine water($\ce{HOBr}$) to the double bond.After this if we add $\ce{Cl2}/Fe$ we will get ortho and para positions substituted by chlorine.However I am facing difficulty changing the ortho chlorine atoms to iodine.Please suggest me a way to proceed.Thanks.


texts:
I am looking for a material with the same properties of silicone (flexible, easy to manipulate, soft, etc.) but without being a thermal isolate.

I need this material to do the junction between a temperature sensor and the human skin (this is why I need it to be soft).

So far I've used the ELASTOSIL® E43 but without good results.


texts: How to measure deuterium concentration in DDW at home when you try to DIY DDW from freezing process?

texts: I tried to automatize the Deuterium Depleted Water (DDW) receiving from the freezing process, but the result can be reached only after deuterium concentration measurement. Anybody knows how to make it easy, maybe not so accurate.


texts: What is the mechanism followed in the hydrolysis of geminal dihalides using sodium hydroxide?

texts:
When a geminal dihalide is treated by alkaline $\ce{NaOH}$ we get a geminal diol which subsequently gets dehydrated to give carbonyl compounds.
What type of mechanism is followed in this reaction?
I don't think SN1 will be favored because the carbocation is destabilized by the highly electron withdrawing halogen atom. So will it follow SN2? But in SN2 there is also a problem since there is a high steric hindrance particularly if the alpha carbon is a 2 degree carbon. So which type of mechanism is occurring here?


texts: Relation between acidity and reactivity?

texts:
Up till high school, I've been taught that reactivity and acidity of a substance in a relation that if a substance is acidic and if it's acidity is higher (comparatively to some other substance) than its reactivity will also be higher. Examples were mostly given of $\ce{HCl}$ and $\ce{H2SO4}$ stating that since $\ce{H2SO4}$ provides more hydrogen ions when ionized hence its reactivity is much higher than $\ce{HCl}$.

However today I stumbled onto a contradiction of this theory. It was stated in a website that the acidity of phenol is much greater than an average alcohol due to a greater stability of conjugate base.
Some links ahead it was also stated that the reaction of acyl chloride is less vigorous with phenol as compared to other alcohols due to reactivity of $\ce{-OH}$ group being stabilized by delocalization.

My question is, why does the theory "Acidity is proportional to reactivity" not applies for reaction of acyl chlorides with phenols and alcohols?


texts: Reactivity and selectivity in free radical halogenation of alkanes

texts:
I read about the free radical halogenation of alkanes with $\ce{X2}$ and I have the following questions:

Given that the first step is the homolytic breaking of the $\ce{X-X}$ bond, and the homolytic bond dissociation enthalpies of halogens (page 23, 31, and 34 of the PDF - I think it does not have data on $\ce{I-I}$ - but I'll use values from my textbook) are in the order $\ce{I_2 < F_2 < Br_2 < Cl_2}$, why is the order of reactivity of halogens $\ce{F_2 > Cl_2 > Br_2 > I_2}$?
My book said that bromine is very selective when reacting with alkanes - it will prefer a tertiary carbon greatly over primary or secondary ones. Chlorine is less selective and fluorine is not selective at all - it's happy to react with all types of carbons. Why is this so?

PS: I am using the textbook 'Organic Chemistry For JEE' by Solomons, Fryhle, and Snyder.


texts: Why do different impurities create different colors in diamonds?

texts: Traces of nitrogen make diamonds yellow while traces of boron make them blue.  What accounts for the differences in color for a given element?


texts:
According to this question/answer, isolated atoms are spherical – and don't have, for example, p-orbital lobes sticking out. The reason is that each complete set of p-, d- and f-orbitals taken together is spherically symmetrical – and the overall wavefunction will be a superposition of all possible states. That superposition will be spherically symmetric, so the atom will be, too. (Sorry for paraphrasing, simplifying etc!).

So my question is: apart from the orbitals involved in making e.g. sigma and pi bonds, is 'the rest' of the atom spherically symmetrical? I have done this rough picture.

You will notice that down the left, the p-orbitals are shown (even though in an isolated atom they would not exist like that – I've kept them so they can show potential 'bonding sites'). But on the right, in the 'finished' molecules, all but the orbitals involved in bonding disappear, into a spherically symmetric shape as before.

I realise there are several to many simplifications here, but this is for a general audience, and I just want to give a sense of molecular orbitals without getting anything horribly wrong. (In every artwork I find online, people only seem to focus on the orbitals involved, as if they are separate from the rest of their respective atoms.)

I'd really appreciate any help and thoughts. Thank you.


texts:
Carbohydrate like glucose undergoes periodic cleavage by $\ce{HIO4}$ and forms respective products are five moles of formic acid and one mole of formaldehyde.

Here is my question , what is mechanism and what are the products by fructose with the same? Do we have any specific rules for that?


texts: I have prepared hydrogel nanoparticles in aqueous solution. How to calculate concentration of hydrogel nanoparticles ?


texts: How to calculate the magnetic exchange coupling in a charged radical complex?

texts: I have a neutral complex with two magnetic centers. For this case it is easy to calculate the exchange coupling as the broken symmetry state is converged properly. But when I am making the complex charged, there is radical that is introduced. So now I have charged radical species and this radical is not localized on just one site but spread over a group of atoms. In this case I am not able to reach the proper broken symmetry state using Noodleman's formalism employed in ORCA. What are the possible ways to achieve the proper broken symmetry state and calculate the exchange coupling.


texts: During Fries Rearrangement, oxygen donates its lone pair to $\ce{AlCl_3}$ forming $\ce{-O^+-AlCl3}$. Since this is a strong electron withdrawing group, shouldn't the final product be meta-substituted?


texts: Help with finding intermediates in the synthesis of Ritalin

texts:
Here I have a Chemistry Olympiad question I'm doing that outlines the synthesis of Ritalin. So far I've worked out A, Anion B -, and compound C. You can see my workings, as I've attached them here too.

  Nucleophilic substitution with the nucleophile $\ce{C#N-}$ produces A:

  A proton is taken away from the $\alpha-\ce C$ to deprotonate it to form Anion B -:

  Anion $\ce{B-}$ acts as a nucleophile and substitutes $\ce{Cl}$ to produce C:

But how would I work out the structures of D, E and F?

I'm not familiar with all the mechanisms/reactions of nitriles and am unsure how to proceed.


texts: Rate of EAS in chlorobenzene and fluorobenzene

texts:
In both chlorobenzene and fluorobenzene, both the halogens show a −I effect where fluorine has more electron withdrawing effect than chlorine.

Now, if we consider the mesomeric/resonance effect, both show +M/+R effect. On comparison of resonance effect and inductive effect, resonance effect dominates over inductive effect. Then:

Why does −I effect dominates over +M/+R effect of chloro and fluoro group in the case of chlorobenzene and fluorobenzene? Give reason.

I know that the −I effect dominates over the +M/+R effect of the chlorine and fluorine substituents in case of chlorobenzene and fluorobenzene. Now, on the basis of this chlorobenzene should be more reactive for electrophilic aromatic substitution reaction than fluorobenzene (as −I effect: $\ce{-F~ >~ -Cl}$). But, it is not true though vice-versa is true.

Why is fluorobenzene more reactive for electrophilic aromatic substitution reaction than chlorobenzene? Give reason.


texts: Is this statement for the First Law of Thermodynamics correct?

texts:
My Biochemistry book states the First law of Thermodynamics like this:
"The First Law of Thermodynamics states that in a closed system, energy is conserved".
My book defines Closed System as a system which can exchange energy with its surroundings but not matter.
My doubt is how can energy be remain conserved(constant) if the system can exchange energy with its surroundings.
Please clarify.


texts:
Isn't it a misconception to assume that dipole moments are similar to vectors in their behavior? My reasons are as follows:

Let us take an example: Methane ($\ce{CH4}$)

Clearly, the hydrogen atoms pushing their electrons into the more electronegative carbon only enforce the effects of each other. But, we assume for no particular reason that dipole moments must behave like vectors. We then go on to add the vectors and finally decide that the net dipole moment is $0$. Why?


texts: Only d orbital electrons for spin only magnetic moment

texts:
During my chemistry lessons and self studies, I have come upon many instances where I observed that during calculations of spin only magnetic moment of transition elements only the d orbital electrons are to be counted.  To gain a deeper insight into these instances of "calculations", I would like to expand my question as follow around the same point (i.e. spin only magnetic moment):

Is spin only magnetic moment calculated only for ions? If not, what would be it for $\ce{Cr^0}$: I mean would the $\mathrm{4s^1}$ electron be taken into consideration? If yes, then why?
Are there some other instances apart from $\ce{Cr^0}$ which supports your views?


texts: How does one properly do this alkali melt? (Pfleger's indigo synthesis)

texts:
TL;DR: Needing advice on the best procedure (e.g., preparation of reagents, and the order of addition) for an alkali melt/fusion used in Pfleger's indigo synthesis.

I need some advice on how to carry out the alkali fusion/melt step in Pfleger's industrial synthesis of indigo. SciFinder comes up with nothing but vaguely-worded patents and two horrible documents.

I would love to find a recently-written procedure on how it is made industrially (e.g., indigo for jeans, or however it would be made when ordering it from Sigma-Aldrich), but I can't find anything like that. All original documents (e.g., Pfleger's patent) lack important details.

This scheme (#3) outlines the synthesis that is used industrially; a melt of NaOH, KOH, and NaNH2 forms indoxyl out of phenylglycine, which then spontaneously (in the presence of oxygen) oxidatively couples using a radical mechanism to form indigo. The part that I'm having trouble with is finding a good procedure on how to do the melt.

I've seen arrow-pushing mechanisms that show NaNH2 being used for either deprotonation or for imine formation (depending on the literature source), while another source says that it's merely a dehydrating agent, Le Châteliering the reaction forward.

Since I don't want to waste my NaNH2 by having it react with water, I figured that I should dehydrate my NaOH and KOH first. So far, I have ground NaOH and KOH together and brought the temperature up to about 200 °C, at which point they become a liquid. Putting this on a vacuum, I see a fair amount of water come off, and when I remove the vacuum, the mix solidifies (but is still soft, probably because I haven't removed all of the water).

I'm assuming that I would then add the sodium/potassium salt of phenylglycine, then the NaNH2. In the Nigerian papers, they simply grind 5:5:1 NaOH, KOH, and NaNH2 (seemingly in open air), then add nitrobenzene and reflux. I'm leery about grinding NaNH2 in open air (safety guidelines suggest grinding it under a hydrocarbon solvent, though perhaps I'm being overly cautious?), and I'd expect that the NaNH2 would react with the water in the NaOH and KOH.

Assuming that nobody has a good literature procedure for this, I'm hoping to get some guidance on things like preparation of reagents, and the order of addition. I'm also interested in any other advice that anyone may have.


texts: Basicities of meta-nitrophenoxide and para-nitrophenoxide

texts:
The negative oxygen is the site of protonation. Size and EN are the same for both oxygens. We are mainly looking at resonance (and possibly inductive) effects here. We want the least resonance withdrawal of electron density from the oxygen. And if possible, the least inductive withdrawal of electron density from the oxygen (although this is not a major issue; resonance trumps induction). Recall that the nitro group cannot withdraw electron density via resonance effects at the meta position. Therefore meta-nitrophenoxide should be more basic than para¬-nitrophenoxide.

Is my reasoning correct?


texts:
I am having trouble understanding why the structure

$$\ce{C(CHClMe)4}$$

has only five stereo isomers. According to my textbook, the stereo isomers correspond to the following series of absolute configurations:

(R,R,R,R)
(R,R,R,S)
(R,R,S,S)
(R,S,S,S)
(S,S,S,S)

But my question is, does not the order in which these appear change the total? Isn't (R,S,R,S) different from (R,R,S,S)?


texts: How would an increase in the concentration of a sucrose solution affect the rate of its acidic hydrolysis?

texts:
Regarding the acidic hydrolysis of sucrose

$$\ce{\underset{sucrose}{C12H22O11} + H2O + \underset{catalyst}{H+} -> \underset{glucose}{C6H12O6} + \underset{fructose}{C6H12O6} + H+},$$

I think that its mechanism can be described as a 2-step reaction consisting of a step which involves the H+, and then the step which involves the $\ce{H2O}$, and I believe the latter step to be a rate limiting step.

My question in detail is:

  Would an increase in the concentration of a sucrose solution, with a constant $\ce{H+}$ concentration, have a 1-to-1 influence on reaction rate (for example, if doubling the concentration of the sucrose solution would result in a hydrolysis reaction twice as fast), or would the addition of $\ce{H2O}$ in the second step significantly limit the change in reaction rate?


texts: Can class D fire extinguishers be used for other fire types than metal fires?

texts:
Burning metals like sodium should not be extinguished with standard fire extinguishers, but they require either sand or a special class D fire extinguisher.

Now, if there is a fire in the lab and the closest fire extinguisher is one of those class D extinguishers meant for metal fires, can those be used for other types of fires?

The main case where there might not be enough time to get specific equipment is probably when people are on fire. Can a class D extinguisher be used in this case, if it's the closest available one?


texts: Nomenclature - Common vs IUPAC Names and Alphabetical Priorities

texts:
I got a problem with this:

What if we stuck with the IUPAC name and called the isopropyl group a 1-methylethyl group? That would definitely reverse the alphabetical priorities; because the substituents here on the hydrocarbon are on equivalent positions, we must give the lower number to the substituent that comes first in the alphabet.

But that's the rub! (No isopropyl alcohol pun!)

Isopropyl - "I" comes before "M" as in methyl.

But if we name the isopropyl group systematically,

Methylethyl comes after just methyl in the alphabet.

So could the name of this also be:

2,2-dimethyl-7-(1-methylethyl)bicyclo[3.2.0]heptane?


texts: Synthesis methods of inorganic materials

texts:
On our exams we are asked to determine which synthesis method is best suited for a given compound. We have discussed direct synthesis methods such as high temp. and ampull, and indirect synthesis methods such as solvothermal, sol-gel, and ion exchange.

I thought that the direct high temperature synthesis was mostly used for compounds with three or more elements such as $\ce{BaTiO3}$. However, in our exam the compound $\ce{Fe3O4}$ is said to be synthesized by the direct high temperature method.

For example, one question states:

  Propose and motivate two methods (each) of synthesis of $\ce{NaAlSiO4}$ and $\ce{Cu(CN)(pyr)2}$

I believe one method for $\ce{NaAlSiO4}$ should be direct high temp. because that method is applicable for aluminosilicates but have no idea what the second one could be. Is there a specific way to determine the synthesis methods of different compounds just by looking at them?

All help is truly appreciated!


texts: Can 99% isopropyl alcohol be stored in a clear container?

texts:
I'm planning to get hold of some 99% isopropyl alcohol (aka rubbing alcohol) for the purpose of cleaning electronics, and am going to transfer it from the plastic bottle it comes in to a smaller, clear dropper bottle or similar. However, I vaguely remember being told that isopropyl alcohol shouldn't be stored in a clear container - possibly something to do with speedier evaporation, but I'm really not sure.

Is this true? Are there any downsides to storing 99% isopropanol in a clear container? Will storing the solution in direct sunlight change this at all?


texts: Why is arginine's positive side chain classified as basic and not acidic?

texts:
Arginine has a positive side chain.

Doesn't this mean it wants to lose a proton H+? Isn't something that wants to lose or donate a proton an acid?

Yet my book states, "arginine has a positively charged side chain, i.e it is
basic" .


texts: How to correctly define anode and cathode?

texts:
I am very much confused: in a simple voltaic cell ($\ce{Zn}$, $\ce{Cu}$ in $\ce{H2SO4}$), $\ce{Cu}$ is positively charged and is the anode, where in a Galvanic cell ($\ce{Zn}$ in $\ce{ZnSO4}$ and $\ce{Cu}$ in $\ce{CuSO4}$),
$\ce{Cu}$ is positively charged but is the cathode. How can I define it, where both are electric or voltaic cell?


texts: I noticed while looking through a couple of books (specifically, Wade, Carey, and Vollhardt/Schore) that the mechanism of concerted hydride and alkyl shifts is always shown with alcohol leaving groups.  I understand that these are difficult, equilibrium-driven processes.  But, I would assume they can happen with other leaving groups, such as a halogen, right?  Is it just the matter of fact that dehydrations are usually done at elevated temperatures while SN2 is not?  If that's all it is, though, we would expect to see rearranged primary E2 products, which Carey mentions does happen, but the other books remain silent on.


texts:
What is formed when you leave iron(II) sulfate in plain air?

Knowing that iron(II) is easily oxidised to iron(III), and assuming that the reactive component of air is oxygen, I solved it this way:

$$\ce{FeSO4 + O2 -> Fe2O3 + SO2}$$

But in my textbook it's given that iron(III) sulfate, $\ce{Fe2(SO4)3}$, is formed. Is this because $\ce{Fe2O3 + SO2}$ react to form $\ce{Fe2(SO4)3}$?


texts: Are electron shells probability distributions?

texts: I know that orbitals are probability distributions. Are electron shells probability distributions too?


texts: If 18g of ice at a temperature of -6 ℃ is placed in 250 g of water at 20 ℃, we know that there is enough energy supplied by the water to completely melt the ice and transform it into liquid. My question is: during the phase change of the ice, when the temperature of the ice has reached 0 ℃, is mass from the ice transferred to the surrounding water? In other words, is the mass of the ice changing during phase change or is it constant? By the mass of ice, I mean mass that is still solid.


texts: Relationship between Equivalence Ratio and Adiabatic Flame Temperature for Fuel Rich Combustion

texts:
I'm reading a combustion text and would like help interpreting the following passage (diagram attached). It is regarding the relationship between equivalence ratio and adiabatic flame temperature:

  For equivalence ratios between  $\phi$ = 1 and $\phi$ ($T_{max}$), the heat capacity decrease more rapidly with $\phi$ than $\Delta H$, while beyond $\phi$ ($T_{max}$), $\Delta H$ falls more rapidly than does the heat capacity. The decrease in heat capacity is dominated by the decrease in the number of product moles formed per mole of fuel burned, with the decrease in the mean specific heat being less significant.

I’m assuming that we are keeping the total mass of reactants constant (just changing the proportion between them). I get that total heat generated goes down since less fuel is reacting. But I don’t understand why heat capacity (I think this is extensive) decreases. Octane (at least at 300K
) has a higher specific heat than $\ce{CO2}$ and $\ce{H2O}$, so doesn’t having more fuel vapor increase the heat capacity?

For the last sentence, I don’t understand why a decrease in heat capacity is more significant than the decrease in mean specific heat?

The phrase “decrease in the number of product moles formed per mole of fuel burned,” does “mole of fuel burned” include fuel that technically didn’t react, since we have a fuel rich mixture?


texts: Is the Standard hydrogen electrode potential at T other than 298 K also zero?

texts:
The standard hydrogen electrode potential by conventional at 298 K is taken to be 0.00 volts.

This is what I have been taught. It talks about SHE at 298 K, so is the hydrogen electrode potential at a temperature other than 298 kelvin also defined to be zero ? If not, how do we calculate at any other temperature?


texts: How to perform Mulliken population analysis by hand with GAMESS output?

texts:
I did a simple calculation on hydrogen fluoride with GAMESS and I wanted to reproduce the Mulliken population analysis for atomic orbitals.

A molecular orbital is a linear combination of atomic orbitals and if I understand correctly the Mulliken analysis uses coefficients to calculate population (overlap or atomic).

In the molecular orbital part of my GAMESS output, if I want to calculate the population of the 1s orbital of the hydrogen, I'm summing every coefficients squared of the contribution of this AO in all the MO, but I'm not getting the right answer.

Would someone be able to clarify this?

INPUT:

 $CONTRL SCFTYP=RHF RUNTYP=OPTIMIZE COORD=CART ICHARG=0 MULT=1 $END
 $SYSTEM TIMLIM=90  MEMORY=1000000 $END
 $STATPT OPTTOL=1.0E-4  NSTEP=100 $END
 $BASIS  GBASIS=STO NGAUSS=3 $END
 $SCF DIRSCF=.TRUE. $END
 $GUESS  GUESS=HUCKEL  $END
 $DATA
 HF
C1
H     1.0     0.00000     0.00000     0.00000
F     9.0     0.00000     0.00000     1.0000
 $END

OUTPUT:

      ------------------
      MOLECULAR ORBITALS
      ------------------

                  1          2          3          4          5
              -25.9035    -1.4599    -0.5737    -0.4631    -0.4631
                 A          A          A          A          A
1  H  1  S    0.005341   0.150431  -0.533704   0.000000   0.000000
2  F  2  S   -0.994746  -0.250678  -0.078268   0.000000   0.000000
3  F  2  S   -0.022260   0.946703   0.410905   0.000000   0.000000
4  F  2  X    0.000000   0.000000   0.000000  -0.004070   0.999992
5  F  2  Y    0.000000   0.000000   0.000000  -0.999992  -0.004070
6  F  2  Z    0.002673  -0.078256   0.698060   0.000000   0.000000

                  6
                0.5898
                 A
1  H  1  S    1.054350
2  F  2  S    0.080571
3  F  2  S   -0.515861
4  F  2  X    0.000000
5  F  2  Y    0.000000
6  F  2  Z    0.816436

           ----- POPULATIONS IN EACH AO -----
                         MULLIKEN      LOWDIN
          1  H  1  S      0.80774     0.85856
          2  F  2  S      1.99913     1.99848
          3  F  2  S      1.94822     1.88452
          4  F  2  X      2.00000     2.00000
          5  F  2  Y      2.00000     2.00000
          6  F  2  Z      1.24491     1.25844


texts: preparation methods of nicotinoyl glycine

texts: How can we prepare nicotinoyl glycine  from nicotinic acid ?Is that possible by reaction between nicotinic acid and glycine?


texts:
I am having trouble wit the following question on my problem sheet:

"The reaction $\ce{Br- + ClO^- \to BrO^- + Cl^-}$ occurs with a rate constant of $\text{0.35 dm}^3 \text{mol}^{-1}
\text{s}^{-1}$

at
298 K. For the following initial conditions calculate the time taken for the Br^-
concentration to fall to half its original value:

i) $[\ce{Br-}]=[\ce{ClO-}]=0.0017$

ii) $[\ce{Br-}]=0.0017$ and $[\ce{ClO-}]=0.084$"

I am sure I could do this question if I knew the rate equation but it isn't given. From the units of the rate constant the reaction must be second order but how am I supposed to know whether it's second order with respect to one of the reactants (and thus zeroth order w.r.t the other) or first order with respect to both? Also, what's the significance of the concentrations being equal (there's another question that stresses that the concentrations of both the reactants are equal).


texts: Is water the most common multielemental compound?

texts: Water is a very common substance, not just on Earth, but also in space. Although water usually occurs in space as a solid and occasionally as a gas and relatively rarely as a liquid, the most common compound is H₂. I believe based on the abundance of elements in the universe (ignoring helium because it is a noble gas) that water is the most common multielemental (having more than one type of element in its structure) compound. Are there more common ones, or is water the most common one?


texts:
Q: A student standardizes sodium hydroxide by weighing out 1.207 grams of potassium hydrogen iodate, dissolving the compound in water and titrating to a suitable endpoint:

If the volume to reach the endpoint is 32.80 mL, what is the concentration of sodium hydroxide?

The molar mass of PHI is $389.75 \text{g/mol}$. if 1.207g is added to the titrand beaker, then there are:
$$\frac{1.207\text{g}}{389.75\text{g/mol}} = 0.0031\text{mol of KHI in the titrand beaker}$$

NaOH reacts with KHI in a 1:1 molar ratio, and 32.8mL of NaOH was added to reach the endpoint. This means that 0.0031mol of NaOH was added. So, the concentration of NaOH is:

$$\frac{0.0031\text{mol}}{0.0328\text{L}} = 0.0945\text{M}$$

This is coming up as a wrong answer in my book. Can anyone explain where I'm going wrong?


texts: What exactly is going on in this reaction: sodium bicarbonate (supersaturated aqueous), isopropyl alcohol, and acetic acid (vinegar)?

texts:
I had observed this reaction by playing around with vinegar and baking soda and do not completely understand it.

Everyone knows that baking soda and vinegar goes crazy and starts creating carbonic acid that decays into carbon dioxide forming bubbles, but I never saw anyone adding vinegar to a supersaturated solution of baking soda and water. So, I decided to try it myself.

To no surprise, the reaction goes very similarly to how it would with just solid sodium bicarbonate. However, I then decided to try and see what rubbing alcohol would do. So, I grabbed the 92% rubbing alcohol and added it to the mixture before adding the vinegar.

You could see the alcohol mix slowly with the supersaturated sodium bicarbonate solution. However, when the vinegar was added...well I do not really know.

I added the vinegar to the solution really slowly and some minor bubbling occurred on the top. However, the solution never started to boil up like it does normally. Instead, it just sort of sat there. at which point, I decided to just take it to the sink and pour it out and try some new stuff, but I accidentally gave the glass a slight bump and all of the sudden, the reaction took place and proceed very rapidly shooting the bubbles out of the volumetric glassware I was using and getting everywhere. I have done this reaction several more times and it is very repeatable, although, I do not know how the addition of alcohol makes the reaction not occur until the solution is disturbed.

Volumes used are 150mls supersaturated solution of baking soda in water, 20mls 92% isopropyl alcohol, and 40mls of vinegar.

Any help with understanding this reaction would be greatly appreciated. The only thing I have come up with so far is that the alcohol is changing the water's ability to dissolve the baking soda and that when a slight jolt is added to the system the baking soda is dislodged out of solution long enough for the vinegar to attack it, but that is just a guess.


texts: What are the effects of the repulsive forces between electron on the potential energy graph for the dihydrogen molecule?

texts: This diagram is from my textbook. It states that as long atoms get closer, the energy decreases due to the attractive forces between the electrons and the nuclei. When the nuclei get too close, the nuclei’s repulsive forces drives the energy upward. However, what of the repulsive forces between the electrons? As the atoms get closer and closer from infinity, where are the effects of the increasing repulsive forces between the electrons?


texts: Water color additive that will maintain color when water is a thin film

texts: I'm producing thin sheets of liquid (50 to 100 microns) from a nozzle and trying to photograph them.  I think it would help if I could color the water. However, typically as water becomes more of a thin film it tends to lose color.  I'm wondering if anyone has any thoughts on this.  I think white would be a particularly good color.   Food coloring containing titanium dioxide might work.  I know that just using milk will work, but it's a mess to deal with because I am dealing with sprays traveling at a minimum 5 meters per second.


texts: Electrolysis using electrodes of metals whose ions are in solution

texts:
So when we perform electrolysis of say an aqueous solution of silver nitrate with silver electrodes, silver ions having a greater reduction potential than water, accepts electrons and deposits at the cathode.At the anode however, silver just leaves the electrode and enters into its solution.
The anode must just be a metal rod whose sea of electrons is much poorer than what it must be.Why does the silver get oxidized and leaves the rod as an ion? Water could get oxidized instead and that appears to be a more logical expectation.
Secondly why does this not happen if we do the same reaction using platinum electrodes? What is preventing the metal from leaving the anode as an ion,moving to the cathode causing gradual thinning of one electrode and thickening of another?


texts: Do I understand why heat capacity is called 'heat *capacity*'?

texts:
The notion of heat capacity seemed a little odd to me. I thought that the word 'capacity' could be throwing me off. Do I understand the notion correctly?

I take the word 'capacity' to express, roughly, 'the maximum amount of something that a thing can take'. My first intuition is that the maximum temperature of a system equals whatever temperature corresponds to every molecule in that system moving at the limit of the speed of light. Accordingly, if 'heat' denotes a certain species of energy transfer, then the heat capacity (i.e. the maximum amount of energy that a system can receive) should be equal to the number calculated by, for each molecule in the system, taking the difference between the speed of light and the molecule's starting speed, summing those differences, and then dividing by the number of molecules in the system. Accordingly, if everything else is equal (i.e. pressure and volume), then the heat capacity of a system is a function of the starting temperature of the system and its volume. At first blush, that conception of heat capacity seems compatible with the equation
$C_x = \frac {Q}{\Delta T_x}$.


texts: Why is osmotic pressure the best colligative property?

texts:
The osmotic pressure method has the advantage over
  other methods as pressure measurement is around the room
  temperature and the molarity of the solution is used instead of molality.
  As compared to other colligative properties, its magnitude is large
  even for very dilute solutions. The technique of osmotic pressure for
  determination of molar mass of solutes is particularly useful for
  biomolecules as they are generally not stable at higher temperatures
  and polymers have poor solubility

This is the text from my Class 12 Chemistry Book Part 1 NCERT (India) (page 54). I didn't get why:

Molarity is used instead of molality. I think it is probably because we can measure the volumes of solutions easily using measuring cylinders, but mass of solvent in already prepared solution is difficult to measure.
It's magnitude is large even for dilute solutions. Why? I didn't get this one.


texts: Why do liquid crystal displays (LCDs) visually distort under pressure?

texts:
A venerable question, as old as LCDs themselves. I assume it has something to do with pressure-induced changes in the path length across the display, but that's just a guess. Of particular interest to me as I press my fingernail into my (TFT LCD) phone screen1 are the observations of:

A symmetrical bilobate distortion in the direction of movement of my fingernail.
Ripples of colour distortion that radiate outwards at about a centimeter per second.
A trail of slight colour distortion that with a persistence of a few seconds.

Any ideas as to the cause of this rich behaviour?

[1] Don't worry, it's a nokia n95 and as such will likely outlive the human race if not the solar system.


texts: Solve for wavelength of photon given threshold frequency

texts:
The threshold frequency of a potassium metal plate is $\pu{4.35\times10^14 Hz}$. Determine the wavelength of a photon required to reach $\pu{2.50 eV}$ of the maximum kinetic energy of an emitted electron.

Options:
A. $\ \ \ \pu{2.88\times10^2 nm}$
B. $\pu{-4.96\times10^2 nm}$
C. $\ \ \ \pu{9.50\times10^-21 nm}$
D. $\ \ \ \pu{6.69\times10^2 nm}$
E. $\ \ \ \pu{2.02\times10^15 nm}$

From what I understand, I used the equation $KE = h\nu + h\nu_0$ and replaced $\nu$ with $\frac cA$ because wavelength and frequency are inversely proportional. Then I plugged in the given components, $\nu_0$ and a fraction of $KE$ to solve; however, I don't understand how to approach this as I'm only given $2.5 \pu{eV} (4.005 \times 10^{-19} \pu J)$ of maximum $KE$, not an actual value for $KE$. The answer I'm getting is $\pu{1.14 \times 10^{-12} nm}$ if I just use $\pu{2.5 eV} = KE$ max, which isn't an answer choice, and the given answer is A. $2.88 \times 10^2 \pu{nm}$. Please help.


texts:
As a non chemist I have read in the Wikipedia article Curcumin that:

  Curcumin becomes bright red when it interacts electrostatically with
  phospholipid film.

This text appeared without source under this image in the article:
https://en.wikipedia.org/wiki/Curcumin#/media/File:Curcumin_thin_lipid_film.jpg

As an amateur of cooking Indian dishes (which often have bright red "Tandoori" color):

Is there a way to create natural Red food coloring from Turmeric in the house kitchen?

That is to ask; what edible supermarket products contain phospholipid films and how should I use at least one together with Turmeric (fresh-grinned or dry-powdery) to get a bright red solution?

Update

I should note that I didn't intend to ask this question as a "how to make Tandoori colored seasoning paste" question;

About six years ago, I was told by the owner of a large Indian restaurant in Israel, what is the secret (or at least one of the secrets) and the following seems to be that secret from what I understood then and did and replicated several times:

1) Take about 500 gram of dried Kashmiri peppers; clean them from pedicel, placenta and seeds.

2) Put the dried Kashmiri peppers in a metal pan and pour boiled water upon them.

3) Let the dried Kashmiri pepper boil and cool ("water-marinate") about 3-6 hours but don't cook them.
Mere boiling, without cooking, enhances pigmentation but doesn't destroy some pigments as in cooking.

4) Remove the water and let the peppers dry.

5) Grind the processed peppers into a paste with a bit of water and cooking oil and add a tablespoon of that paste as a basis for any Tandoori paste you are making (along with salt, lemon, garlic, ginger and possibly other spices).


texts: What is the chemistry behind why reactions of order >1 exist? And what role does the number of activated complexes formed have in determining reaction rate?


texts: Ortho-para directing and meta directing groups: Activating or deactivating the aromatic ring?

texts:
Determine the reactivity of the above compounds (activating or deactivating; ortho-para or meta directing). Explain your answers. You may use resonance structures in your explanation. Which molecule will have the highest rate of reaction?
What are the products formed when the above compounds are reacted with $\ce{Br_2}$ and $\ce{FeBr_3}$. Predict the major and minor compound, if there is any.

My answers:
For Question (1):
E is an activating group because it has a nitrogen with a lone pair. F is a deactivating group because $\ce{C=O}$ is directly attached to the benzene ring. In G, $\ce{N}$ is an activating group but $\ce{C=O}$ is deactivating, so I'm not sure if G is an activating or deactivating compound. Also, How can resonance structures help to explain the reactivity of the compound? I'm not sure how to draw the resonance structures. How do we draw resonance structures that has two substituents such as G. For F, does the lone pair on $\ce{N}$ affect the resonance?
For Question (2):
E: $\ce{Br}$ will attach at ortho and para, so it has two products.
F: $\ce{Br}$ will attach at meta with 93 % (major) and ortho 7 % (minor).
G: I think $\ce{Br}$ will attach para to $\ce{N}$ because $\ce{N}$ is a strong activating group and it will not go to between the two substituents because it is crowded, is this true?


texts:
Most of us here would know that flames can be colored by adding an appropriate salt to the 'fuel' or by simply introducing it into a flame. Boron and Barium salts give the flame a green tinge, Strontium colors it red, Sodium does gold, copper a bluish-green, etc, etc.
Now from my (not-so-in-depth) high-schooler level of understanding, the energy released by whatever is being burnt to produce the flame in the first place (as is usually the case), excites electrons in metal ions in the salt to higher energy levels. And when these electrons 'de-excite' and drop back to the original energy levels, they emit that extra energy as photons (whose frequencies are determined by the Planck equation $E = h\nu$ ) and these photons are what we perceive as the colored flame.
If I'm not mistaken the book Harry Potter and the Philosopher's stone mentions a 'black flame' of sorts, being one of the obstacles Harry has to circumvent in order to reach the Stone. (Artist's depiction)

Now, as I understand it, for something to be 'black', it must absorb all ( or at least a fairly significant amount of) visible light, encompassing a wide range of frequencies.
Going back to colored flames, I mentioned that the ions must emit light energy, not absorb it, in order to color the flame.
Armed with all this information, would anyone know if it really is possible to create 'black colored flames'? Has it ever been achieved?
[I tried thinking it out myself.....just gave me a headache]
Edit 1: And yes, I've made note of what @Mithoron mentioned, but what I mentioned was just conventional logic, it isn't universal though.
...Newtonian mechanics was 'conventional logic', but we all saw how that failed in relativistic scenarios. So I didn't want to take the risk, hence I've asked If it actually is possible...
Edit 2: Just because someone mentioned otherwise in an answer... I emphasise that by black flames I don't mean invisible flames.


texts:
In a closed system the reacting species interconvert but do not leave the system. Therefore the amounts of different species in the system would be bound by a conservation rule.

  A simple example:
  $$\ce{A -> B}$$

Here the conservation rule would be: $\ce{A + B = constant}$, which says that at any point of time during the reaction the sum of the amount of both the species would be constant.

  A more complex example
  $$\ce{2A -> B}$$

Here, the conservation rule would be: $\ce{A + 2B = constant}$.

Let's take a more complex system:

  $$\begin{align}
\ce{A &-> B} \\
\ce{2B &-> C} \\
\ce{C &-> D + E} \\
\ce{2A + C &-> F}
\end{align}$$

From empirical analysis I can deduce that the conservation rule would be: $$\ce{A + B + 2C + D + E + 4F = constant}$$

However, I am not able to deduce a mathematical equation that gives these co-efficients. I assume that the stoichiometry matrix may give a clue but I am not sure. The stoichiometry matrix for the above system is:

$$\mathbf{S}=\begin{bmatrix}
-1 & 0 & 0 & -2 \\
1 & -2 & 0 & 0 \\
0 & 1 & -1 & -1 \\
0 & 0 & 1 & 0 \\
0 & 0 & 1 & 0 \\
0 & 0 & 0 & 1
\end{bmatrix}$$

This is relatively easier to figure out empirically as there is only one starting reactant (A). For reaction systems with multiple starting reactants (as shown below), the deduction of conservation rule(s) becomes even more difficult.

$$\ce{aA + bB -> cC + dD}$$
The problem seems quite elementary but I am not able to solve it. Am I missing something obvious?


texts: Temperature dependence of emission lines from gases, for example, neon

texts:
Emission lines from Ne are frequently used as wavelength standards in spectroscopy. Reading around Wikipedia, I found about the Paschen law regarding the voltage required to start a discharge.

My question, do emission line intensities have dependence on the voltage applied and the temperature of the electrodes. Just to clarify, I am not thinking about the band positions but the relative intensities.

About voltage dependence, at present I have no idea.
About temperature : Since the electronic states are involved, and this is an electric discharge, the temperature maybe quite high so as to affect the Boltzmann population significantly.

This question is related to plasma physics, but also to electronic spectroscopy.


texts: Material properties differing between vacuum or pressure filtration

texts:
During vacuum filtration of a very fine suspension, all solids that need to be removed are, but there is minimal solids loss. If the same material is pressure filtered (1-2 bar), desired solids removal is effective but the precipitated material matrix retains more liquid and other components entrained within. The thin slurry was tested and shown not to be a colloid.
What is the rationale for the filtered solids differing behaviour?


texts: Different chemoselectivity of transition metals in catalytic hydrogenation

texts:
I am quoting my Clayden et al 2nd edition:

  Some catalysts are particularly selective towards certain classes of compound – for example, Pt, Rh and Ru will selectively hydrogenate aromatic rings in the presence of benzylic C-O bonds, while with Pd catalysts the benzylic C-O bonds are reduced faster.

My question is, why $\ce{Pt, Ru, Rh, Pd}$ all being transition metals still show different chemoselectivity in hydrogenation reactions?

1st edit: (After reading ringo's comment I think I should add something more) Well, I first thought that the number of $\ce{d}$ electrons is the cause. But, both $\ce{Pd}$ and $\ce{Pt}$ have same number of $\ce{d}$ electrons. Yet, they show different chemoselectivity. I think the difference is because $\ce{Pt}$ has an $\ce{f}$ orbital filled up.

And, I guess as $\ce{Ru, Rh, Pd}$ belong to same period, they show similar chemoselectivity.


texts: When is ammonia and water a strong ligand?

texts: While studying the spectrochemical series, my sir said that as ammonia and water lie in the center, their behaviour as a ligand is tough to judge. For example if we have CO as a ligand, we know that the electrons of the central atom tend to pair up, but he said that the same cannot be predicted for water and ammonia. Is this true, or is there some logic which will help to predict whether the electrons pair up or not. For example in [Co(NH)6]+3, the electrons pair up and the hybridization is d2sp3. But such pairing up is not seen at times in other compounds.


texts: What substance(s) will prevent superglue from hardening in its tube?

texts: Superglue often sets in the tube, so I was wondering if ethanol or even water could stop it from hardening and going to waste. Ideas, anyone?


texts: Comparison of alkali and alkaline earth melting points - MO theory

texts:
If you compare the melting points of alkali and alkaline earth metals, you see that the latter have higher melting points. However, if you look at MO theory, then alkaline earth metals should have quite a considerable proportion of the antibonding part of the bands occupied (even if there is an overlap with the p-band). So, why should the bond in alkaline earth metals be stronger?

(I realise that according to the electron sea model you just say that alkaline earth metals contribute two electrons, not just one, wich solves the problem. MO theory should also be applicable, so what am I overlooking?)


texts: Will the concentration of 3% w/v H2O2 be lowered after 3 weeks?

texts:
I have read online that $\ce{H2O2}$ decomposes if exposed to sunlight and air. If this is the case then will the concentration of 3% w/v of $\ce{H2O2}$ be lowered if it is left out in the open at around 25-degree celsius for a few hours?

Background:
The question arises from a titration experiment that I conducted where I had to verify the concentration of $\ce{H2O2}$ to be 3% w/v. But the titration found the concentration to be lower and other groups in the class found the same.


texts: I was reading a science magazine the other day when I came across an article on superatoms. I am now wondering if these structures form their 'superorbitals' in a similar way to the pi rings in benzene molecular orbitals or is something different going on?


texts: Avogadro's gas Law doesn't make sense? (it does actually)

texts:
It says equal volumes of all gasses under same conditions of temp. and pressure contains the same number of atoms/molecules.

Now suppose you have 1L of Chlorine in a box and 1L Hydrogen in another box , now the comparitively huge size of the Cl atom means less of it will fit in the box , whereas lots of hygrogen will. ( breaking the law)

But, well this should have an effect in pressure , how does all that boil down to avogadro being right ?


texts: Ethene to ethanol: electrophillic additions involving ethyl sulfates

texts:
http://www.chemguide.co.uk/mechanisms/eladd/symh2so4.html

I was reading my textbook and this website. I just cannot find the mechanism for what happens when we go from CH3CH2OSO3H to ethanol by the addition of water and heat.

I understand the electrophillic addition part.

But, what happens next? Is there some kind of Sn2 reaction to make HSO4- the leaving group? Then, why does the EtOH2+ molecule give out one of its acidic protons to HSO4- and not to H2O which is a more powerful base?

I hate when my textbook leaves out the details and I obsess on them :(


texts: How to choose which reactants to have in excess?

texts:
In a precipitation reaction, how do I know which soluble reactant I should put in excess?
E.G.
$$\ce{Na2SO4 +Pb(NO3)2 -> PbSO4 + 2NaNO3}$$
In my book, $\ce{Na2SO4}$ is added in excess, but can we add $\ce{Pb(NO3)2}$ in excess?


texts: Butler-Volmer equation with concentration dependence?

texts:
For a simple elementary reaction on electrode

\begin{equation}
O+e^-\rightleftharpoons R
\end{equation}

We can derive the Butler-Volmer equation. But it seems that the formula found on John Newman's Electrochemical System seems to be different from the one found on Allen Bard's Electrochemical Methods, both of which are considered classics. Below is my understanding, if not incorrect.

In the most general case, Newman writes

\begin{equation}
i = i_0\biggl[\exp\biggl(\frac{(1-\beta)nF}{RT}\eta_s\biggr)-\exp\biggl(-\frac{\beta nF}{RT}\eta_s\biggr) \biggr]
\end{equation}

where $\eta_s=V-U$. $U$ is the equilibrium which depends on the surface concentration, and so do $i_0$, the exchange current.

Bard, on the other hand, writes, in the most general case, the current-overpotential equation
\begin{equation}
i_n = i_0\biggl[\frac{C_O}{C_O^*}\exp\biggl(-\frac{\alpha nF}{RT}\eta_s\biggr)-\frac{C_R}{C_R^*}\exp\biggl(\frac{(1-\alpha) nF}{RT}\eta_s\biggr) \biggr]
\end{equation}
which only leads to Butler-Volmer equation if mass-transfer is not concerned. Here $\eta_s=E-E_{eq}$ (with its notation). $E_{eq}$ is the equilibrium potential established on bulk concentration, which is a constant taken to be initial condition. $i_0$ is dependent on the bulk concentration.

Aside from the anodic, cathodic sign convention different, what Bard has written explicitly depends on the surface concentration, which in a sense suggest that even if the over-potential is negative (which, in Bard's convention, leads to positive cathodic current), anodic reaction can still be established if $C_R$ is sufficiently high.

The more widely known equation (also found in Bockris's Modern Electrochemistry vol.2) is the one Newman wrote. But the equation will only lead to (in Newman's convention) positive anodic current if the over-potential $\eta_s$ is positive, even if $C_O$ dominates (which leads to cathodic current in Bard's formula).

It seems that the derivation differ on the reference potential: Newman sets equilibrium potential $U$ to be dependent on the surface concentration while Bard let it be referenced to the open-circuit potential with bulk concentration. What's right and wrong?


texts: "4K-metal chelated" A chemical term used in Sagan's Cosmos

texts:
Maybe this question doesn't belong here. It's about a hypothetical xenobiology imagined by a prominent scientist in a seminal work of popular science. So I dunno. Tell me to go away and I'll see if some other SE can help me.

I'll never forget the races Sagan made up in his book Cosmos. He gave descriptions of them in the form of excerpts from his imagined Encyclopedia Galactica, a compendium of all the races in the galaxy.

There was one term that never made sense to me: "4K-metal chelated". What does the "4K" part mean? Here is the context:

Civilization Type: 2.3 R
Society Code: 1H1, "We Who Became One".
Interstellar civilization, no planetary communities,
  utilizes 1504 supergiants, OV, BV, AV stars and
  pulsars.
Civilization Age: 6.09 * 10^15 s.
First local initiated contact: 6.09 * 10^15 s ago.
Receipt first galactic nested code: 6.09 * 10^15 s ago.
Source civilization, neutrino channel.
Local Group polylogue.
Biology: C, H, O, Be, Fe, Ge, He. 4K metal-chelated
  organic semiconductors, types various. Cryogenic
  superconducting electrovores with neutron crystal
  dense packing and modular starminers; polytaxic.

(By the way, if anyone knows what "Local Group polylogue" is supposed to mean, I care about that too.)


texts: Why Normal modes of vibration are important when compared to translational and rotation modes. And why the frequencies for rotational and translational modes are close to zero?


texts: Intermolecular forces of attraction between positional isomers of alcohols

texts:
This seemingly trivial question is as follows: Why is the boiling point of 1-butanol ($\ce {117.7 ^\circ C}$) higher than that of 2-butanol ($\ce {99 ^\circ C}$)?
The only reason I can think of is that the former molecule has a "straighter" chain than the other and a "straighter" chain has a greater surface area allowing for stronger van der Waals forces to exist between the molecules. As molecules in the liquid state do not pack themselves close to each other, ideas of "packing efficiency" would not be useful in explaining these boiling point differences. Perhaps, it is instructive for us to first observe if the trend is persistent for longer chains?
\begin{array}{|c|c|c|c|} \hline
\text {No. of C} & \text{1-alcohol} & \text{2-alcohol} & \text{3-alcohol}\\ \hline
\ce{5} &  138 & 119.3 & 116\\ \hline
\ce{6} & 157 & 140 & 135\\ \hline
\ce{7} & 175 & 159 & 156\\ \hline
\ce{8} & 195 & 178.5 & 173\\ \hline
\ce{9} & 214 & 194 & -\\ \hline
\end{array}
As can be seen from the above table, where the boiling points are all sourced from Wikipedia, with units of $\ce { _^\circ C}$, the trend is indeed persistent. The alcohol isomer with the $\ce {-OH}$ group attached to the 2-position consistently exhibits lower boiling points of around $\ce {16}$ to $\ce {20}$ $\ce {^\circ C}$. Shifting the hydroxyl group further along the chain by one more position also lowers the boiling point of the molecule but to a lesser extent.
The explanation I can come up with for this is the same as aforementioned: By placing the hydroxyl group at the end, there is the maximum surface area for interaction of the alcohol molecules with each other. Furthermore, the hydroxyl groups, being placed at the ends, would cause the least amount of disruption to the hydrophobic interactions between the alkyl chains. Does anyone have better explanations for the above trends?


texts: Paracetamol: does oxygen participate in the delocalization of p-orbitals

texts:
I'm analyzing the molecular structure of paracetamol and one of the things I have to do is to make a commentary about the delocalization of p-orbitals in this compound. Well I know that in the cyclic structure of carbons there is indeed delocalization of p-orbitals. I wonder if the oxygen that makes the double covalent bond participates in this delocalization or not... Can you help me figuring this out?

Also if only the 6 carbons have the delocalization of p-orbitals then we will have 6 molecular orbitals $\pi$ delocalized and so we will have 3 $\pi$ bonding orbitals full 3 $\pi^*$ antibonding orbitals empty, right? I saw this on a book (about other compound) and I want to know if this is related to the fact that molecular orbitals number needs to be the same as atomic orbitals number? But for example, if we had 8 $\pi$ molecular orbitals would we have 4 bonding and 4 antibonding? Does that happen?


texts: How to know the ionization power of an unknown metal? - difficult

texts:
Imagine having the 4 following beakers:

where P, Q, R and S are metallic plates. In beaker 1 and beaker 2 nothing happens. However in beaker 3 and 4 the metalic pieces become thinner.

How would you orden the ions $P^{p+}, Q^{q+}, s^{s+}, R^{r+}$ the following ions by oxidizing power?

I think it is one of the following possibilities:

$P^{p+} < Q^{q+} < s^{s+} < R^{r+}$

I think that P and Q clearly have the highest oxidizing power as in beaker 3 and 4 the metallic plates become thinner. But I have no idea whether R has a higher oxidizing power than S. Or is it the other way around?

Could someone help me and explain how I can order these ions by oxidizing power?