ATARNotes Official Solutions to VCAA 2012 Unit 4 Chemistry Examination

[qwerty12]

3bii) so OOCCH2CH(OH)COO2- is completely wrong, or is there a chance of the mark?

[thushan]

Personally...I'm sorry I couldn't pay that... there is an outside chance that an examiner may pay it, but I doubt it :/

[HelloBrittany]

Do you think they could possibly accept that delta H was for two moles in the experiment? And with the wet coal, how about reference to it containing water and therefore some of the energy released being used to heat this water, as well as the lower percentage of carbon?

[Suzanne]

Would measuring the time over which the CaCo3 dissolves also be correct for Q1.a? And if not would i get a conseq mark for Q1. bii? Thanks

[dfgjgddjidfg]

thushan what do you rate the difiulty of this exam compared to previous years and what do you think i could get with a high A unit3 High A or LOW A+ unit 4 and A for sacs?

[baddin]

Lol for the coal question i made up complete garbage haha. I said the dry coal is stored deeper in the earth where as wet coal is found closer to the surface, therefore the dry coal has absorbed for CO2 overtime than wet coal. One mark lol?

[thushan]

thushan what do you rate the difiulty of this exam compared to previous years and what do you think i could get with a high A unit3 High A or LOW A+ unit 4 and A for sacs?

About the same as last year I reckon. A+ cut I reckon 63/72.

And I reckon about a 35-37.

[suvyyy]

Would you get the mark for the wet brown coal question if you say that some of the energy produced through combustion would be used to vaporise the high content of water, leading to less useful energy produced?

[50inTheatreStudies]

In regards to Question 3C: I said it would decrease.

(cant remember equation) but my logic was, as K is very small there will be a lot more conjugate base of the acid (reactant) compared to the OH- ions. Even though HCl will react more readily with OH- ions the fact that there are so many conjugate bases means the more significant reaction will be with the base. Therefore the base concentration will go down, and it shifts to the left.

Can you explain why I am incorrect? cheers.

[thushan]

Would you get the mark for the wet brown coal question if you say that some of the energy produced through combustion would be used to vaporise the high content of water, leading to less useful energy produced?

I had that answer in mind actually!

Maybe. Not sure what they mean by "energy content"

[bubblefighter]

For the first question, would change in temperature be an acceptable answer?

[thushan]

In regards to Question 3C: I said it would decrease.

(cant remember equation) but my logic was, as K is very small there will be a lot more conjugate base of the acid (reactant) compared to the OH- ions. Even though HCl will react more readily with OH- ions the fact that there are so many conjugate bases means the more significant reaction will be with the base. Therefore the base concentration will go down, and it shifts to the left.

Can you explain why I am incorrect? cheers.

Because the base, when it reacts with HCl, becomes sorbic acid!

[suvyyy]

Sorry last question: for the necessity of a catalyst in the fuel cell question, can you say that the reaction has a high activation energy (as it involves a gas) and that the rate needs to be decreased using a catalyst to ensure that the cell is economical? Or would that be awarded 0? Do you have to mention temperature?

[SJC]

In regards to Q.6b,
I wrote that the data book value is only for 1 mol of methanol and the experiment uses two mol there it is double the value and also there is a discrepancy as a result of poor insulation. Would I get any marks?

[thushan]

You said poor insulation, that's fine