2010 VCAA Chemistry U4 Suggested solutions

[monicapham93]

for Q2 3ii
about the ammonia

is it wrong to say that if theres an excess there will be no change?? cause i thought it meant, what effect does it have on the relitive proportions of the product gasses in the atmosphere (according to the eqn)

Hey Monica, Chris from NYSF here. You were referring to section B - Question 3 - Part a ii right??? I put down what I thought would be produced, considering the yields would be different between the two parts. I also said that NH4OH would be produced in excess ammonia.

ooh chris, as in from camb boys???
heyyyaaa!

yeah ... im probs all wrong, i didnt really get the question so i tried to answer it the only way that made sense to me
... lucky its one mark though!

[ckg93]

For 2.5a "iii, Provide alternative reaction pathways with lowe ractivation energy"
I wrote "It lowers the activation energy required for the reaction to proceed but did not mention alternative pathway.. will i still get the mark?

By adsorbing the reactants to the surface of the catalyst, the catalyst allows a greater percentage of collisions to react. Hence the activation energy is reduced by the catalyst adsorbing the reactants to the catalyst surface. I'm not sure that you will get the mark, but be hopeful (it was a relatively tricky exam)

[Mao]

also catalyst foro sulfuric is vanadium pentoxide..

That is the same as Vanadium (V) oxide

According to the to my chem teacher, it MUST be PENToxide to get the full mark, however, the PROPER name is Di-vanadium Pentoxide.

yes, that is one of its names. I assure you that other name names (Vanadium pentoxide, vanadium (V) oxide, divanadium pentaoxide, etc) will also be accepted.

[ckg93]

Ah ok Mao.

And yeah mon, it is me. I bet you'll still beat me lol.

Also Mao, for Section B - Question 2 - Part a iv; can you also say that "The experiment would been conducted under standard conditions"? I said this because the K value for lactic acid was used, and that value in the data booklet was based on standard conditions.

[darkphoenix]

Thanks Mao!

[ckg93]

Just realised I put the wrong Enthalpy for Question 4 - Part a

Also, your equation is not balanced properly, it should be 17(oxygen gas) and also 14(Carbon Dioxide) There are 7 Carbons in benzoic acid.

[Aden]

A friend of mine is arguing that the answer to multiple choice Question 7 is either A or C, and not D.

Basically, his rationale is that if you were to make every species in each reaction 1mol in a 1L container (yes, it is impossible given the nature of the reversible reaction, but for simplicity's sake lets just go with it), then it goes like this:

Initial CF/K:
A.
B. Not applicable at all
C.
D.

The volume is halved, so the concentration of each species will double, therefore CF immediately after:
A.
B. Not applicable
C.
D.

So the percentage change in each case is:
A. 100%
B. Whatever
C. 100%
D. 75%

So... to prove him wrong... we...?

[stonecold]

A friend of mine is arguing that the answer to multiple choice Question 7 is either A or C, and not D.

Basically, his rationale is that if you were to make every species in each reaction 1mol in a 1L container (yes, it is impossible given the nature of the reversible reaction, but for simplicity's sake lets just go with it), then it goes like this:

Initial CF/K:
A.
B. Not applicable at all
C.
D.

The volume is halved, so the concentration of each species will double, therefore CF immediately after:
A.
B. Not applicable
C.
D.

So the percentage change in each case is:
A. 100%
B. Whatever
C. 100%
D. 75%

So... to prove him wrong... we...?

I stuffed this question and chose A.  But looking at it again, I can see why it is D....

[Aden]

I stuffed this question and chose A.  But looking at it again, I can see why it is D....

My friend is arguing that A or C are both correct, since they have the largest percentage change as shown by my previous post =\

[stonecold]

I stuffed this question and chose A.  But looking at it again, I can see why it is D....

My friend is arguing that A or C are both correct, since they have the largest percentage change as shown by my previous post =\

lol i dunno.  for my sake i hope he's right but i doubt it.

vcaa don't seem to reward the smart ass approach to questions...

[m@tty]

They obviously weren't looking for that approach as it yields two answers..

The was I looked at it was A-factor of 2; B-factor of 2; C-no change; D - reduce by a factor of 4. Clearly the one which has undergone the biggest 'change' is D.

[TehGullz]

Also Mao, for Section B - Question 2 - Part a iv; can you also say that "The experiment would been conducted under standard conditions"? I said this because the K value for lactic acid was used, and that value in the data booklet was based on standard conditions.

I said this too, anyone think it'd get marks?

[stonecold]

Also Mao, for Section B - Question 2 - Part a iv; can you also say that "The experiment would been conducted under standard conditions"? I said this because the K value for lactic acid was used, and that value in the data booklet was based on standard conditions.

I said this too, anyone think it'd get marks?

This will certainly get marks.  It is a valid point.

[m@tty]

Also Mao, for Section B - Question 2 - Part a iv; can you also say that "The experiment would been conducted under standard conditions"? I said this because the K value for lactic acid was used, and that value in the data booklet was based on standard conditions.

I said this too, anyone think it'd get marks?

This will certainly get marks.  It is a valid point.

Yeah that's what I said. Though I do suspect that they were looking for the answer which Mao gave. Certainly should get the marks though.

[happyhappyland]

FUELS CELLS ARE NOT F******* RECHARGABLE... YOU PUT REACTANTS IN TO KEEP IT RUNNING... YOU DONT CONVERT THE PRODUCTS BACK INTO THE REACTIONS SO ITS NOT RECHARGABLE..................... if your dad is a doctor please tell me where he works cos im not going to see him