Chemistry Practice Exam 1 Discussion

[stonecold]

Tbh azn_dj, I think because they are symmetrical, the interferences cancel each other out, hence there are no peak splits...

[Blakhitman]

Question 11. there are two H environments, both the environments are adjacent to O so two singlets.

[stonecold]

excuse my ignorance, but how do you pick molecules in this program?

[azn_dj]

err..... I have no idea tbh.....
I just went through them until I found ethandiol
lol.

[Mao]

O shields the H in OH from splitting. This is because it has a high electron density, and nuclear charge of H in OH cannot penetrate this electron density, thus it does not resonate with other nearby H environments.

Also, it is not true that splitting only occurs with other nucleus 3 bonds away. There are J4 splitting in substituted arenes, and J2 splitting in phosphorus-substituted hydrocarbons and metallic complexes. None of these should mean anything to you right now, but the point is don't make up rules and reasons just because, there are lots of physical principles behind chemistry. [e.g. the n+1 rule is based on combinatorics (specifically pascal's triangle) in probability, multiplicity often simplifies to n+1 because difference in splitting frequency is tiny, and more often than not addition of ordinates give almost the exact same curve as n+1 would predict]

[Martoman]

O shields the H in OH from splitting. This is because it has a high electron density, and nuclear charge of H in OH cannot penetrate this electron density, thus it does not resonate with other nearby H environments.

Also, it is not true that splitting only occurs with other nucleus 3 bonds away. There are J4 splitting in substituted arenes, and J2 splitting in phosphorus-substituted hydrocarbons and metallic complexes. None of these should mean anything to you right now, but the point is don't make up rules and reasons just because, there are lots of physical principles behind chemistry. [e.g. the n+1 rule is based on combinatorics (specifically pascal's triangle) in probability, multiplicity often simplifies to n+1 because difference in splitting frequency is tiny, and more often than not addition of ordinates give almost the exact same curve as n+1 would predict]

Oh that is as romantic as a valentines day card Mao!
Marry me! That was beautiful! :smitten:

[Mao]

* Mao raises eyebrow

[Martoman]

hahaaha your just awesome.... just my wonky way of saying it.

[azn_dj]

Also, it is not true that splitting only occurs with other nucleus 3 bonds away.

I meant with a Carbon. This was what TSFX said.
So..... blame TSFX, maybe?

[stonecold]

anyone done the 2008 sample paper?

how did you find it.  i thought it was probably too easy, and too short.

stupid mistakes always kill me though!

[Greggler]

Only VCAA ive done is 2009. Which i actually found alright. Maybe its because i already knew it was going to be long before i did it but i still did it to time and managed to get 88% which i was happy with. Only one that stumped me was the stoich one with the polyunsaturated hydrocarbon :S

[Blakhitman]

I reckon the 2008 VCAA one was pretty easy too...planning on doing the 09 paper today...

[stonecold]

That's a good score.  I got 83% on that...the stupid AAS question destroyed me at the end.  I found the polyunsaturated hydrocarbon question okay, accept that I bloody divided when I was supposed to multiply.

It was so stupid, I did it at like 10:30pm on a Sunday.  Really should save those good papers for when I am more alert...

[Greggler]

yeah lol. i did a physics exam last night at like 10pm and marked it this morning. made the worst mistakes, like typing things in the calculator wrong haha.

Yeah the last aas question was pretty difficult. I actually had the answer right for the mass of whatever then when i was going back over it i changed it by multiplying by 10 instead of 4 ><. 

[stonecold]

I reckon the 2008 VCAA one was pretty easy too...planning on doing the 09 paper today...

Are you talking about the sample or the actual exam?