Exam Suggested Solutions

[cooldude312]

ahhhh... damnit! I was just gonna point out there was that sixth isomer. Well thanks, that solves the problem.

[csq7]

hmm with qn 2 on the short answer shouldnt your answer be to 2 significant figures seeing that you took 35mg/L off the graph, using 2 sig figs in the qn should result in 2 sig figs in your answer.

[ed_saifa]

hmm with qn 2 on the short answer shouldnt your answer be to 2 significant figures seeing that you took 35mg/L off the graph, using 2 sig figs in the qn should result in 2 sig figs in your answer.

Ask your chem teacher. He would know

[shinny]

but reading the graph would be accurate to 3 decimal places approx. the lines were pretty big =p either way it doesnt matter, vcaa allow 1 sig fig either way so u wont lose the mark

[Mao]

hmm with qn 2 on the short answer shouldnt your answer be to 2 significant figures seeing that you took 35mg/L off the graph, using 2 sig figs in the qn should result in 2 sig figs in your answer.

but seeing as it crossed the dots exactly, i could well have assumed it was 35.0 or 35.00 if i wanted to.

i think VCAA will be trying to assess the ability to analyse "data" (as in the data they have given you), as opposed to how many sig figs you can read off a graph.

[ice_blockie]

vcaa allow 1 sig fig either way so u wont lose the mark

I remember actually reading somewhere that they weren't going to continue that policy and were now looking for exact numbers of sig figs...but i can't seem to find that info...anyone?

[nathankb]

could someone post the actual question 20 on multi-choice...if possible? i know its hard cos there was a picture...

[shinny]

vcaa allow 1 sig fig either way so u wont lose the mark

I remember actually reading somewhere that they weren't going to continue that policy and were now looking for exact numbers of sig figs...but i can't seem to find that info...anyone?

haven't heard about that, but it does make sense. i mean, one sig fig either way usually means that u'll get it no matter what even if ur not thinking about how many sig figs u should have; u'll probly by chance score the mark so i found the policy a bit...pointless. thing is, my schools chem handbook still mentions that vcaa has that policy in exam marking, but i actually havent seen that policy mentioned in any vcaa examiners reports since..2002 i think it was? or maybe they just assumed we all knew

[pfftlah]

hey does anyone know which question was the one where they looked at your significant figures? and for the question, can you be off by one figure and still get the mark?
and if i said that ethanol was a biochemical fuel because it was renewable and carbon neutral cos the carbon dioxide used during photosynthesis was released during fermentation, would they accept that answer?
thanks in advance 

[Synesthetic]

vcaa allow 1 sig fig either way so u wont lose the mark

I remember actually reading somewhere that they weren't going to continue that policy and were now looking for exact numbers of sig figs...but i can't seem to find that info...anyone?

In any case, it doesn't make sense to me that if a particular question was worth ONE mark, that you would gain NO marks if you were off by one significant figure. (This is the case for question 3 part d, where absorbance=0.96 was used while most people used three significant figures in their answers (e.g. I wrote concentration2=9.06 ug/mL).

Your presented argument might apply to stoichiometric questions worth three marks, for example. But as recent as 2005, VCAA has continued its practice of allowing one significant figure either way in their marking scheme, even for e.g. 3-mark questions. Check out the following link:

[ http://www.vcaa.vic.edu.au/vce/studies/chemistry/assessreports/2005/Chemassessrep0605.pdf ]

On page 8 of 14, part of the solution to #2)b)iii) reads as follows:

"Significant figures were checked on this question. Acceptable answers included 1.565x10^-3 and 1.6x10^-3 [where the suggested answer was 1.57x10^-3], which was CONSISTENT WITH PAST PRACTICE OF ALLOWING ONE MORE OR ONE LESS THAN THE ACTUAL NUMBER OF SIGNIFICANT FIGURES."

Anyway, I'm browsing the VCAA website for any changes they may have implemented with regards to this policy, but no luck so far.

[Synesthetic]

hey does anyone know which question was the one where they looked at your significant figures? and for the question, can you be off by one figure and still get the mark?
and if i said that ethanol was a biochemical fuel because it was renewable and carbon neutral cos the carbon dioxide used during photosynthesis was released during fermentation, would they accept that answer?
thanks in advance 

I suspect having the correct number of significant figures really only matters for the gravimetric/dilution questions - such as questions 1,2,3,8 [short-answer]. So those are the questions I think where s.f.'s matter. As I outlined above, I doubt they'd deduct marks for questions worth a single mark if the solution was off by one significant figure.

Your answer to the biofuels explanation should be accepted. I wrote that they were carbon neutral because the feedstock is primarily derived from plant materials (and hence carbon neutral due to photosynthesis) - essentially what you stated. In fact I suspect the best answers must have a reference to plant feedstock / photosynthesis process.

[Synesthetic]

could someone post the actual question 20 on multi-choice...if possible? i know its hard cos there was a picture...

Three compounds undergo fractional distillation - boiling off sequence X,Y,Z (shown in the given diagram). You had to pick the only true statement, which was A ("Y is more volatile than Z").

[pastiche]

vcaa allow 1 sig fig either way so u wont lose the mark

I remember actually reading somewhere that they weren't going to continue that policy and were now looking for exact numbers of sig figs...but i can't seem to find that info...anyone?

^ I recall having read/being told that too, & would also like to know. Thanks to the communischtchemistrystudent who posted these, I'm off to calculate my mark...

[sam2703]

hey guys first timer, want to thank mao for both physics and chem solutions, really appreciated !

i was just wondering if they'll accept KOH as the reagent, mao wrote NaOH which is definately right but is KOH acceptable aswell?

anyway once again cheers mao ur a hero

ps. this is a great site cant believe i havent heard of it before!. great forums aswell

[hoopa]

thanks for posting the answers! its been a big help!