All Questions
45,379
questions
42
votes
3
answers
16k
views
Why do impurities lower the melting point of an isolated substance?
It is known that impurities in a desired isolated product lower the melting point of the mixture, even if the impurities' melting point is much higher than the desired product. Why is that so?
- 1,742
15
votes
2
answers
515
views
Can recent developments improve the total synthesis of B-12?
The total synthesis of vitamin B-12 by Robert Burns Woodward and Albert Eschenmoser, is over 30 years old. At its time, it was considered a landmark in the field.
With current developments (e.g. ...
- 271
18
votes
2
answers
4k
views
Color of chromate and permanganate
I've heard quite a few times that the chromate and permanganate have a $d^3s$ configuration. Also, their colors arise due to a rapid switching of electrons between the oxygen and metal atoms.
I don't ...
- 15.2k
15
votes
1
answer
8k
views
What is the mechanism of APTES mono-layer formation on glass substrates?
The reagent APTES is a fairly common "ink" for microcontact printing, a technique that forms covalent bonds between the silanols found on the surface of the glass and the silane in the the APTES. It's ...
- 203
21
votes
1
answer
578
views
Precedence of 1,2 carbocation rearrangement
How can one choose which group has more shifting tendency in 1,2 carbocation rearrangement? The obvious order is via the stability of the carbocation of the group. But, phenylic groups have high ...
- 15.2k
26
votes
4
answers
3k
views
What software can calculate aqueous solution equilibria?
What software is available out there to calculate the equilibrium in a set of reactions in aqueous solution? In particular, I'm interested in software general enough to simulate things like titration ...
- 23.8k
30
votes
3
answers
11k
views
Is activated carbon classified as organic or inorganic?
Organic compounds are typically defined as “molecules containing carbon”. Wikipedia states that there for some historical (read: non-logical) reasons,
a few types of carbon-containing compounds ...
- 23.8k
18
votes
1
answer
1k
views
Stability of organophosphorous vs organophosphates?
In environmental chemistry, most of the organophosphorous compounds we worry about are actually organophosphate compounds.
Is there something about the $\ce{C-P}$ bond that makes it less stable (and ...
- 1,050
24
votes
3
answers
736
views
What is the origin of the bactericidal properties of silver in water?
I often hear that water gets purified by being in a silver vessel, which sounds plausible because of bactericidal feature of silver. What doesn't sound plausible, though, is the way it's explained: ...
- 667
26
votes
1
answer
8k
views
Are there any general rules for choosing solvents for recrystallization?
Re-crystallization is a nice way of purifying a product, but choosing a suitable solvent, if you can't rely on the literature, seems like a lot of trial-and-error.
Are there any general rules on ...
- 6,133
48
votes
2
answers
17k
views
Why does nitration of N,N-dimethylaniline occur at the meta position?
The nitration of N,N-dimethylaniline with $\ce{H2SO4}$ and $\ce{HNO3}$ gives mainly the meta product, even though $\ce{-NMe2}$ is an ortho,para-directing group. Why is this so?
- 2,322
39
votes
4
answers
30k
views
Gibbs free energy-minimum or zero?
A reaction proceeds towards the direction of lesser Gibbs free energy (at constant $T$ (temperature) and $P$ (pressure)). So, we could say that Gibbs free energy at equilibrium is minimum.
On the ...
- 15.2k
24
votes
4
answers
5k
views
How does NaCl maintain its crystalline structure?
My understanding is that $\mathrm{NaCl}$ is an ionic compound, in which $\mathrm{Cl}$ becomes (effectively) $\mathrm{Cl^-}$ and $\mathrm{Na}$ becomes $\mathrm{Na^+}$. So I understand why I would get a ...
- 563
37
votes
3
answers
47k
views
Why do atoms generally become smaller as one moves left to right across a period?
It seems to me that the addition of electrons and protons as you move across a period would cause an atom to become larger. However, I'm told it gets smaller. Why is this?
- 827
23
votes
2
answers
12k
views
Side reactions of N-hydroxysuccinimide esters with nucleophiles
N-Hydroxysuccinimide (NHS) chemistry is commonly used in chemical biology to react with primary amines like lysine and the N-terminus of proteins. I was curious how labile NHS esters are to other ...
- 2,400