Chemistry 3/4 2013 Thread

[teletubbies_95]

@stick: nah , I've just been brushing up on my organic chem. so I've just been looking / reading at stuff, which I know from 3/4 biol. I don't get all the instrumental stuff at all.

Can someone give me an example of another amino acid , which isn't alpha amino acid?
Thanks.

[Aurelian]

Can someone give me an example of another amino acid , which isn't alpha amino acid?
Thanks.

An amino acid is just any organic molecule with both an amino functional group and a carboxyl functional group present. An alpha amino acid, then, is just an amino acid which has the amino group bonded to the carbon next to the carboxyl group.

Hence we can easily conceive of any hypothetical amino acid which isn't an alpha amino acid - e.g. NH2CH2CH2CH(R)CH2COOH or even simply NH2CH2CH2COOH (3-amino propanoic acid). We might not find it in nature, but it's still an amino acid (and perhaps we could synthesize it in a lab).

[thushan]

http://en.wikipedia.org/wiki/Beta-alanine

[curry_bro]

This is just a technicality, but are these two redox equations the same? is any one specific variant more accepted? would both get the same number of marks on an exam?

MnO2(s) + 2HCl(aq) + 2H+(aq) --> Mn2+(aq) + 2H2O(l) + Cl2(g)

oooooooooooorrr

MnO2(s) + 2Cl-(aq) + 4H+(aq) --> Mn2+(aq) + 2H2O(l) + Cl2(g)

the overall charge is also the same, but the orientation of atoms is a bit different

[thushan]

Both will give you full marks, and they're practically synonymous yes.

[curry_bro]

Both will give you full marks, and they're practically synonymous yes.

cool thanks. i came to the first equation in response to a particular question, but the solutions had the second equation. just wanted to make sure that i wasnt wrong i didnt think i was, but just wanted to confirm with the chem geniuses out there

[McFleurry]

Help please!

Q: calculate the concentration of a solution of sulfuric acid that has a pH of 1.2

So what I've done is calculate concentration of H+ ions: 10^-1.2=approx 0.063; then divide by two; so answer is 0.032

is this right??

thanks!

[teletubbies_95]

Thanks Aurilien and Toucan!

@ Fluer:
H2SO4
= strong diprotic acid

its diprotic , since there are two hydrogen protons present !

therefore 2x [H2S04] , instead of dividing by 2

therefore , the answer is 0.126191 ( mind my sig figs , copied it from the computer calc)

hope that helps and keep on posting !

[thushan]

Ohh....!!!

Fleur consider that a really bad question. In fact, its more complicated than that, a lot more complicated. This is because whilst H2SO4 is a strong acid, HSO4- is a weak acid. In other words, the first proton falls off easily, but the second proton is only partially removed.

[teletubbies_95]

Im confused !

[thushan]

You'll understand once you study equilibria.

Take a 0.10 M solution of H2SO4.

You are right in that the first proton falls off. Suppose only the first proton falls off, so you have a mixture of 0.1 M H+ and 0.1 M HSO4-.

Now, HSO4- is a weak acid, so it only partially ionises. It turns out that HSO4- starts to ionise until the following equation (you'll learn more about this in Unit 4) is satisfied:

[SO4 2-][H+]/[HSO4-] = 0.012 (will be given in your Data Book).

With the calculations (you won't have to do this unguided in the exam) you end up with [H+] = 0.11 M, so barely any change from when the first proton dropped off.

The only way the question would make sense is if the question stated to assume that HSO4- was a strong acid too.

[McFleurry]

Thanks toucan

[teletubbies_95]

I've been doing some stuff from Chem , that I've done in Bio last year , ie . DNA , proteins //

1. In one of the books I was reading it talked about " DNA being a large biomolecule found in chromosomes in the nucleus of every living cell" ? But isn't that untrue (with my biol knowledge) , because prokaryotes dont have membrane bound organelles?

2. When DNA is made into a polymer , why is it a condensation reaction?

3. Do we need to know transcription /translation for VCAA exams in detail?

4. Is it right , that we do not need to know about Forensic Applications of DNA this year ?

Thanks !


Oh and thanks Thush !

[thushan]

I've been doing some stuff from Chem , that I've done in Bio last year , ie . DNA , proteins //

1. In one of the books I was reading it talked about " DNA being a large biomolecule found in chromosomes in the nucleus of every living cell" ? But isn't that untrue (with my biol knowledge) , because prokaryotes dont have membrane bound organelles?

2. When DNA is made into a polymer , why is it a condensation reaction?

3. Do we need to know transcription /translation for VCAA exams in detail?

4. Is it right , that we do not need to know about Forensic Applications of DNA this year ?

Thanks !


Oh and thanks Thush !

1) You're right. The textbook is wrong on that occasion. Even red blood cells in humans don't have nuclei.
2) Because H2O is produced - the OH from the phosphate and the OH from carbon-3 in the ribose of the next sugar do their thing - like the OH in COOH and the OH in ROH (alkanols), and H2O is lost. (VERY SIMPLIFIED!)
3) No
4) You're right.

[Mr Keshy]

You can thank teletubbies for the absense of simple questions in this thread. Worked solutions are gold!!

Tank you wery much once again!