Post by: Mao on August 10, 2010, 11:31:43 pm
Note, mathematics recommended. Also, you will need to research these topics to find/work out the answer. Most of these should only require google, some light reading, very basic principles, and a fair bit of maths. Main things you'll need are literary references of Ka [or pKa], and some wikipedia pages for explanations of formulas.
Equilibrium
- Investigate the relationship between rate of reaction, and thus show how the expression for the equilibrium constant K can be derived from the rate of reaction. [wiki rate equation]
-- Follow on from that, using the Arrhenius equation, show the dependence of K on temperature, and thus verify how K changes with temperature and delta H.
- Prove Le Chatelier's principle, particularly the subsequent shift will only partially offset the initial change.
- Derive an expression for solving the pH of a weak acid without making the main assumption [HX]_equilibrium = [HX]_i
http://vcenotes.com/forum/index.php/topic,28290.msg291268.html#msg291268
http://vcenotes.com/forum/index.php/topic,28290.msg291979.html#msg291979
- How is pH affected when two weak acids of different strengths are mixed?
- Derive an expression for solving the pH of a weak diprotic acid, and a weak triprotic acid. Thus rank these polyprotic acids in order of their strength: sulfuric, phosphoric, carbonic
- Using a weak acid and its conjugate salt, derive an expression that gives the mole fractions of these two compounds to create a buffer of a specific pH
- Investigate the isoelectric point of amino acids, what do they mean? Try to derive an expression for the isoelectric point of simple amino acids. Try to derive an expression for the pH of an amino acid dissolved in water (start with simple amino acids).
This is all I can think of at this moment, maybe I'll add stuff in the future. GOOD LUCK. Winner(s) may or may not get a prize of arbitrary value. I also may or may not post solutions in the future. That is all.
Post by: happyhappyland on August 11, 2010, 08:51:01 pm
HX -> X- + H+
[X-][H+]/[HX]-[H+]
:S?
Post by: appianway on August 11, 2010, 08:59:09 pm
Post by: qshyrn on August 11, 2010, 09:02:47 pm
Post by: Russ on August 13, 2010, 04:30:03 pm
- Investigate the isoelectric point of amino acids, what do they mean? Try to derive an expression for the isoelectric point of simple amino acids. Try to derive an expression for the pH of an amino acid dissolved in water (start with simple amino acids).
Love this one lol.
Post by: Studyinghard on August 13, 2010, 07:01:49 pm
Post by: Mao on August 13, 2010, 08:16:23 pm
- Derive an expression for solving the pH of a weak acid without making the main assumption [HX]_equilibrium = [HX]_i
HX -> X- + H+
[X-][H+]/[HX]-[H+]
:S?
So far so good, but how do you keep going to solve for pH?
Post by: pooshwaltzer on August 13, 2010, 08:40:36 pm
- Derive an expression for solving the pH of a weak acid without making the main assumption [HX]_equilibrium = [HX]_i
HX -> X- + H+
[X-][H+]/[HX]-[H+]
:S?
So far so good, but how do you keep going to solve for pH?
Logging helps
Post by: fady_22 on August 14, 2010, 09:50:00 am
By changing the expression into a quadratic, and solving using the quadratic formula.
Post by: Mao on August 14, 2010, 11:23:19 am
I can't be bothered typing out the whole working, but, from there:
By changing the expression into a quadratic, and solving using the quadratic formula.
Very good. Just a small thing that it should be Ka instead of K.
Post by: fady_22 on August 14, 2010, 12:09:05 pm
I can't be bothered typing out the whole working, but, from there:
By changing the expression into a quadratic, and solving using the quadratic formula.
Very good. Just a small thing that it should be Ka instead of K.
I know, but I'm so bad at Latex, and so I couldn't be bothered typing that out. :)
Post by: DuBistKomisch on August 16, 2010, 11:05:45 pm
- Using a weak acid and its conjugate salt, derive an expression that gives the mole fractions of these two compounds to create a buffer of a specific pH
Assuming a buffer represented by HA + H2O <-> A- + H3O+.
We know that K_a = [A-][H3O+]/[HA] and that [H3O+] = 10^(-pH).
Therefore the ratio [A-]/[HA] = K_a/10^(-pH) = K_a*10^pH.
I'm not sure how to interpret "mole fractions", but I guess if you want to express n(HA) and n(A-) as percentages of n(HA) + n(A-), then say the total is x, so [HA] + [A-] = x => [A-] = x - [HA], so:
(x-[HA])/[HA] = K_a*10^pH
x-[HA] = [HA]*K_a*10^pH
x = [HA](K_a*10^pH+1)
[HA] = x/(K_a*10^pH+1) --- notice how the denominator is always greater than 1, so [HA] < x and [HA] / x < 1 :D
Then %HA = [HA] / total = (x/(K_a*10^pH+1))/x = 1/(K_a*10^pH+1)
And %A- is simply 100% minus that.
[HA] <=> n(HA) and [A-] <=> n(A-) and such are always interchangeable because the volume is constant and n and c are proportional.
Post by: charmanderp on November 21, 2012, 11:46:13 pm
Post by: nisha on November 21, 2012, 11:58:34 pm
Post by: charmanderp on November 22, 2012, 12:02:47 am
Post by: nisha on November 22, 2012, 12:04:38 am
I might borrow someone's though. I'm about to die of boredom. I never even thought that was possible.
Post by: charmanderp on November 22, 2012, 12:07:45 am
I think this makes us the epitome of nerds. Starting uni work before even finding out if we have the results necessary to apply to uni, let alone be accepted.
Post by: pi on November 22, 2012, 12:12:42 am
(http://cdn.memegenerator.net/instances/400x/30570600.jpg)
Post by: nisha on November 22, 2012, 12:13:13 am
Lol, dude. You will get into uni. Genius.
I think we've gone somewhat off-topic..
Post by: charmanderp on November 22, 2012, 12:17:54 am
You're a pretty smart cookie yourself :P Yes yes I agree, we MIGHT have derailed this thread somewhat. And I almost said epiphany instead of epitome in my last post which means I should probably go to sleep.
We'll start the chemistry challenge tomorrow. Boo yah!
Post by: Mao on November 22, 2012, 02:20:01 am
Post by: thushan on November 22, 2012, 02:31:06 am
Actually Mao - YOU should try the Russian IChO 2007 I think it was.
Post by: Mao on November 22, 2012, 11:59:41 am
Want a challenge? Do a Russian IChO.
Actually Mao - YOU should try the Russian IChO 2007 I think it was.
link me?
Post by: paulsterio on November 22, 2012, 12:36:38 pm
Want a challenge? Do a Russian IChO.
Actually Mao - YOU should try the Russian IChO 2007 I think it was.
Is it in Russian?
Post by: thushan on November 22, 2012, 01:17:06 pm
Want a challenge? Do a Russian IChO.
Actually Mao - YOU should try the Russian IChO 2007 I think it was.
http://www.icho39.chem.msu.ru/downloads/endTheoretical_task_complete.pdf
link me?
Post by: Mao on November 22, 2012, 04:43:05 pm
Want a challenge? Do a Russian IChO.
Actually Mao - YOU should try the Russian IChO 2007 I think it was.
http://www.icho39.chem.msu.ru/downloads/endTheoretical_task_complete.pdf
link me?
Procrastination mode ON.
EDIT:
Problem 1: I do not know of a quantum system that perfectly oscillates as the given wavefunction suggests. I haven't done much quantum modelling myself, but I don't think it makes sense that the dynamics of this proton tunnelling effect is so well defined. As far as I'm concerned, it is still governed by the Boltzmann distribution, the sinusoidal variation simply doesn't make sense to me.
Problem 2:
Lost interest at problem 4+. This is the kind of maths an experimentalist would encounter when trying to interpret a physical measurement. There also seems to be a particular fascination with rate equations, but my qualm with that is why should I try to deal with rate equations when I can throw it into Mathematica, and instead spend my time on problems that cannot be solved by a computer? :P
Problem 1 was the most fun.
Post by: thushan on November 22, 2012, 04:55:54 pm
BAWS.