2014 Chemistry Exam Solutions

[RKTR]

Isn't 8bii 1300ppm?
For the question of Br and Q , is it ok if my equations do not have H in them?

[thushan]

@apreslapulie - Caught me napping there. Nah, there are electrons. I fixed it.

@Chalkhous - Nah, you should get 2H2O -> 2H2 + O2. And whoops, 7biii - you're right, you should write both lysine and aspartic acid.

@Edward Elric - I don't know :/ I wouldn't since they only showed oxidation half equation. Redox is short for reduction-oxidation, meaning both reduction and oxidation have to occur.

[thushan]

Isn't 8bii 1300ppm?
For the question of Br and Q , is it ok if my equations do not have H in them?

RKTR - I might have made a mistake, how did you get 1300 ppm? :/

As for not having the H, not sure. Question said Br2 converted to HBr. But not having the H+ is acceptable with me, but not sure abt VCAA.

[RKTR]

RKTR - I might have made a mistake, how did you get 1300 ppm? :/

As for not having the H, not sure. Question said Br2 converted to HBr. But not having the H+ is acceptable with me, but not sure abt VCAA.

0.130g / 100mL =1300mg/ L =1300ppm

[thushan]

Ah - it asked for the concentration of the SO2 in the apricot sample, which is 0.130 g in 50.00 g of apricot.

[acinod]

0.130g / 100mL =1300mg/ L =1300ppm

Yeah I did that at first too, then realised that's the concentration in the water.

[S61778]

0.130g / 100mL =1300mg/ L =1300ppm

I got 2.6 x 10^4 ppm

I did 0.130g in 5g
Therfore, 0.026g in 1g
Then, 0.026 x 10^6 ppm = 2.6 x 10^4

Is this right?

[RKTR]

Ah - it asked for the concentration of the SO2 in the apricot sample, which is 0.130 g in 50.00 g of apricot.

Ohno T.T

[patel.aayush]

I think you are correct in that we can extrapolate down: http://en.wikipedia.org/wiki/Standard_addition

So 16 is B (for now I guess)

I also put C because my tutor also kept telling me never go outside the max and min of standard solutions. the question does state 'most' so if u look at it is there a region that is even more accurate than 1-4?
^thats pretty much my thinking process when i did the q

[thushan]

I got 2.6 x 10^4 ppm

I did 0.130g in 5g
Therfore, 0.026g in 1g
Then, 0.026 x 10^6 ppm = 2.6 x 10^4

Is this right?

Working is fine, but it's 50 g of apricot, not 5g :/

[S61778]

Ah - it asked for the concentration of the SO2 in the apricot sample, which is 0.130 g in 50.00 g of apricot.

Used 5g instead of 50g 

[S61778]

Working is fine, but it's 50 g of apricot, not 5g :/

Just realised :/

[thushan]

I just had a look at MCQ 16, my opinion:

I'm going with C for the following reason:
- you can extrapolate down, yes, but it wont be as accurate (not 100%, maybe 99%) as between 1-4 ppm; you cannot be fully certain of its accuracy
- in 2011 VCAA there was a similar question and the position was that you can't extrapolate "beyond the range of the graph" (i.e between the points)

[DSubShell]

I just had a look at MCQ 16, my opinion:

I'm going with C for the following reason:
- you can extrapolate down, yes, but it wont be as accurate (not 100%, maybe 99%) as between 1-4 ppm; you cannot be fully certain of its accuracy
- in 2011 VCAA there was a similar question and the position was that you can't extrapolate "beyond the range of the graph" (i.e between the points)

I feel like people are also getting a bit confused, because most of the time there is a "blank" or standard of 0 concentration put in. Thus, you can interpolate between 0 and 1. However, they only put 1-4 this time. idk

[Chalkhous]

wouldnt 10a. not have the OH bit in there and just be Zn(s)->Zn2+(s)+2e-, since if it had the OH- bit in there, what would the reduction equation be? Since there is no other products apart from Zn(OH)2 what would the O2 and H2O become?