Chemistry Practice Exam 1 Discussion

[stonecold]

o0o0o how do you mean?

I was struggling big time with AAS/UV-Vis problems, but I think I've finally got my head around it.

The only thing I'm worried about is if they ask us to describe fractional distillation.  What would you say...

-Mixture of compounds are placed in the fractioning column, and heated.
-Lower boiling point compounds vaporise at the top of the column, and condense, whilst higher boiling point compounds will remain towards the bottom of the column.
-Once the boiling point for a particular compound is reached at the top of the column, the fraction is removed.
-The temperature at the top of the column constantly increases, with fractions removed at their respective boiling points, until all the compounds within the column have been separated, from lowest b.p. (lowest molar mass, as there are less dispersion forces) to highest b.p. (highest molar mass, as there are the most dispersion forces)

Is that okay, have I missed anything?

A question on how a sample of DNA would be prepared for analysis would be nice.

[kyzoo]

Like working out amounts or masses or volumes or concentrations, drawing structural/semistructural formulas, naming compounds, working out stuff from spectrums, multiple-choice, anything that doesn't involve explanation lol.

[stonecold]

^ yeah, like what don't you like explaining haha!  probably should have made it clearer.

[kyzoo]

I don't mind it =/ It's just the easiest place to lose marks in my opinion.

[Greggler]

yeah explaining concepts just reminds me of biol last year where you had to prepare certain responses for certain questions lol haha and had to make sure you mentioned certain things.

but thankfully there isnt really much like that in chem.
Only theory in aos1 is pretty much errors in techniques, and how the varying spectroscopy/chromatography work qualitatively and quantitatively.

aos2 you get a bit more about properties of hydrocarbons, reaction pathways, enzymes, distillation, macromolecules and the sort.

thats all i can think of at the moment; but apart  from this its all your theory and calculations based around stoich

[stonecold]

Anyone done NEAP 2009?

I just did it, thought it was pretty intense, and took me the full time to do it.  Not as bad as the 2010 one though.

Question 1 short answer part a had me all wtf until I finally got it in like the final 3 minutes haha...

[Blakhitman]

Did it in class today...wasn't too bad, lol the first one I couldn't do at all, then last few minutes used some logic jotted some shit down and got Se2+...and it was right lol. Didn't even use ratios...can't even remember how I did it lol

[stonecold]

Ratios.  That was all it was haha.

The mol of Se was half of the mol Cr.
So I did this little equation thing:

2Cr²⁺ + Se⁴⁺ ---> 2Cr³⁺ + Se^x

x has to equal +2 for the charges to balance...

[Blakhitman]

lol I was 100% positive I needed to calculate the ratios...I just didn't see how that would help ><. but now I know lol, that's pretty smart on your part .

I think I lost about 8 marks on that exam...I'm planning on venturing into Lisachem 09 now...lol wish me luck, and pray I make it out alive...

[Martoman]

Ratios.  That was all it was haha.

The mol of Se was half of the mol Cr.
So I did this little equation thing:

2Cr²⁺ + Se⁴⁺ ---> 2Cr³⁺ + Se^x

x has to equal +2 for the charges to balance...

Yeah my reasoning was similar, although I had the oxidation equation which told me that 1 electron was given away, but given the ratio meant 2 were, and if 2 were given away, 2 must be mopped up by the janitor (ie the Se4+). When this happened, then Se2+ is created. So +2.

Anyone done NEAP 2009?

I just did it, thought it was pretty intense, and took me the full time to do it.  Not as bad as the 2010 one though.

Question 1 short answer part a had me all wtf until I finally got it in like the final 3 minutes haha...

Not so much as intense, but fair. The questions were quite out there. Just needed to think a bit. I actually find this paper much better than 2010, in terms of representativeness.

[stonecold]

Maybe it's because I'm sick, but papers have been taking me a little longer in the past couple of days, so I'm probably finding them harder than I should.  This has been my best paper so far all year though.  I was actually quite stoked when I was marking it haha...

[Blakhitman]

Lisachem wasn't hard O.o.

[Martoman]

I've heard lisachem 2010 was pissweak, but 09 was fairly good with some ridiculous questions on there.

[Blakhitman]

I just did 09, wasn't that difficult.

[stonecold]

No papers are really that difficult.  They all test the same shit.  Just worded a thousand different ways...