ATARNotes Suggested Solutions for VCAA 2012 Chemistry Unit 3 Exam

[thushan]

Hi guys, for the question that asked how the sample can be tested to be pure I wrote GC but said something along the lines of:
If only one peak is present in addition to the carrier gas peak (assuming carrier gas produces a peak) then the sample is likely to be pure.

Last night I just remembered that the carrier gas is inert and won't produce a peak... So I'm wondering if I would get atleast 1 mark out of the 2 marks allocated for the question?

Defs. Your answer was fine apart from that minor slip up. 1/2

[BambooPanda]

Thanks Thushan, that puts me at ease. =)

[gablett]

for question 7 i miss calculated the mass of lead iodide, i think i might have calculated mols instead or something lol. obviously i wasn't thinking. but would i get consequential marks for the next part if i used my answer from part iii to get an answer to iv if i did everything correct in part iv?

apart from that i got everything pretty much, but i reckon i'll lose a few marks on explain question. but can't believe i made that mistake above.... do u reckon i can still get 3 marks on part a. iv of question 7 though. im really worried about this, cause im not sure about consequential marks in chem.

[thushan]

for question 7 i miss calculated the mass of lead iodide, i think i might have calculated mols instead or something lol. obviously i wasn't thinking. but would i get consequential marks for the next part if i used my answer from part iii to get an answer to iv if i did everything correct in part iv?

apart from that i got everything pretty much, but i reckon i'll lose a few marks on explain question. but can't believe i made that mistake above.... do u reckon i can still get 3 marks on part a. iv of question 7 though. im really worried about this, cause im not sure about consequential marks in chem.

i think you'd get full marks for part iv

[gablett]

for question 7 i miss calculated the mass of lead iodide, i think i might have calculated mols instead or something lol. obviously i wasn't thinking. but would i get consequential marks for the next part if i used my answer from part iii to get an answer to iv if i did everything correct in part iv?

apart from that i got everything pretty much, but i reckon i'll lose a few marks on explain question. but can't believe i made that mistake above.... do u reckon i can still get 3 marks on part a. iv of question 7 though. im really worried about this, cause im not sure about consequential marks in chem.

i think you'd get full marks for part iv

thanks thusan that makes me feel better, i was kicking myself over that mistake cause i thought i would lose 4 marks cause of it. what do u reckon a score of about 70/75 would get me study score wise, if was around the same mark next exam as well and im ranked number 2 in a very strong cohort.

[thushan]

for question 7 i miss calculated the mass of lead iodide, i think i might have calculated mols instead or something lol. obviously i wasn't thinking. but would i get consequential marks for the next part if i used my answer from part iii to get an answer to iv if i did everything correct in part iv?

apart from that i got everything pretty much, but i reckon i'll lose a few marks on explain question. but can't believe i made that mistake above.... do u reckon i can still get 3 marks on part a. iv of question 7 though. im really worried about this, cause im not sure about consequential marks in chem.

i think you'd get full marks for part iv

thanks thusan that makes me feel better, i was kicking myself over that mistake cause i thought i would lose 4 marks cause of it. what do u reckon a score of about 70/75 would get me study score wise, if was around the same mark next exam as well and im ranked number 2 in a very strong cohort.

Hard to say, I would hazard a guess at 43-46?

[mr.politiks]

Hey thush these solutions are amazing man! Thanks a heap.

[|ll|lll|]

hey thushan, not sure if this has been mentioned, but there's an error in Q4b of your short-answer. It's 1-propanol and not ethanol. don't worry, i made that mistake in my exam too, managed to change it just before time's up

[Louise clover]

i did almost everything in pencil, does that mean i am going to get penalised??

[thushan]

hey thushan, not sure if this has been mentioned, but there's an error in Q4b of your short-answer. It's 1-propanol and not ethanol. don't worry, i made that mistake in my exam too, managed to change it just before time's up

ah yes forgot to put that extra ch2.

[thushan]

i did almost everything in pencil, does that mean i am going to get penalised??

Nah. The problem with pencil is that the pencil (if written lightly) may not come out in the scanner properly.

[Louise clover]

for this equation, CH3CH2OH (l) + CH3CH2COOH (l) -> CH3CH2COOCH2CH3 (l) + H2O (l), i made the states of propanol and propanoic acid and the ester aqueous, it that wrong?

[thushan]

for this equation, CH3CH2OH (l) + CH3CH2COOH (l) -> CH3CH2COOCH2CH3 (l) + H2O (l), i made the states of propanol and propanoic acid and the ester aqueous, it that wrong?

i actually kinda made a mistake it's meant to be:

CH3CH2CH2OH (l) + CH3CH2COOH (l) -> CH3CH2COOCH2CH2CH3 (l) + H2O (l)

and yeah, they can't be aqueous, otherwise basically no ester will be produced (you'll learn the reason for this in unit 4)

[polkadot]

Thanks for the solutions I was just wondering if OH- (aq) + HCl (aq) ---> H20 (l) + Cl- (aq) would be acceptable for question 8a?
And also for question 4d would it be okay to use GC but expect two peaks with one being for the solvent and one with the same retention time as a a sample of know pure propyl propanoate?

[thushan]

Thanks for the solutions I was just wondering if OH- (aq) + HCl (aq) ---> H20 (l) + Cl- (aq) would be acceptable for question 8a?
And also for question 4d would it be okay to use GC but expect two peaks with one being for the solvent and one with the same retention time as a a sample of know pure propyl propanoate?

Hey - haha I think i wrote that "any variant can be written (for the OH- + H+ --> H2O qn) so long as you don't include random species" keeping your answer (you put it on the discussion thread) -- I think your answer is fine

As for the GC one - there is no solvent - you'd directly inject the reaction mixture!