Suggested Solutions - DONE

[Mao]

*referring to my post above*

It might just be me but the ambiguity of these acid equilibria questions is terrible...I'd be surprised if the majority of students were able to get most of the marks.

completely agree

i would not have known this if i hadn't ask coblin about this earlier this year.

[Synesthetic]

This is not in the course, but fuck, the course is over, so I'll just do it anyways:

for acid IV,

hence, when it is diluted to 0.01M, assuming the H+ from self ionisation from water is insignificant



solving this quadratic, , pH=2.64

so change in pH for IV is about 0.5, whereas it is 1.0 for I.

LOL a quadratic

Thanks a lot for that explanation; now I can see your logic...and wishing I had known of it beforehand too

Nothing prepared me for this type of question, and I do a lot of work...

I suppose 70/79 isn't a disaster, probably my worst paper of the exam period though.

[Mikey123]

I can't remember the questions. anyone got the actual paper?

[sb3700]

This is not in the course, but fuck, the course is over, so I'll just do it anyways:

for acid IV,

hence, when it is diluted to 0.01M, assuming the H+ from self ionisation from water is insignificant



solving this quadratic, , pH=2.64

so change in pH for IV is about 0.5, whereas it is 1.0 for I.

That is of course assuming that acid IV is monoprotic, which is not told either way in the question. Otherwise, denominator changes as appropriate.

[nathankb]

mao or someone else - could you upload the paper by any chance?

[Mao]

dont have scanner =S sorry

[cosmicgate]

dont have scanner =S sorry

massive ask, but maybe take photos of it???
or too much ?
u'd make thousands of people happy... literally.

[csq7]

Hey mao, for qn 2b and the 69.8 degrees, shouldnt it be to 2 sig figs, cos it said 60% of the energy.. and thats to 2 sig figs..
And, for qn 9b, i got 3.7x10^ 16.. you sure your answer is in Kj??

Thanks for the solutions

[Synesthetic]

Hey mao, for qn 2b and the 69.8 degrees, shouldnt it be to 2 sig figs, cos it said 60% of the energy.. and thats to 2 sig figs..
And, for qn 9b, i got 3.7x10^ 16.. you sure your answer is in Kj??

Thanks for the solutions

I got 3.69 x 10^19 for 9b, I initially had 10^16 then realised it wasn't the correct units;

Don't worry too much about sig. fig.'s, VCAA allows one decimal place either way (as far as I know, and I believe that's how they marked my mid-year paper too), so whether it's 2 or 3 shouldn't make a difference.

[csq7]

sweet! thanks

[nathankb]

could someone show the calculations for working out delta t on that cf question?

[csq7]

For qn 6b part 2, the one about the methanol being less that expected, I wrote that methanol evaporates.. does it evaporate even if its in solution? so is my answer valid?

[Mao]

dont have scanner =S sorry

massive ask, but maybe take photos of it???
or too much ?
u'd make thousands of people happy... literally.

my phone camera is crap

[username]

Could you have written lack of standard conditions or something really vague like that for the methanol question, 6bii?

[Synesthetic]

Could you have written lack of standard conditions or something really vague like that for the methanol question, 6bii?

Actually that's probably the safest answer...instead of what I wrote (gaseous CO2 escapes => less methanol than expected produced)