Chemistry Examination Discussion

[Stick]

Just wait, for the percentage purity of copper I think I get 87%
I thought we were meant to subtract the final amount of impure copper by the initial? How is that wrong? :|

As did I. :|

[thushan]

It's because some of the lost mass isn't copper - it's more reactive elements like Zn that would have dissolved in the H2SO4

[simba]

It's because some of the lost mass isn't copper - it's more reactive elements like Zn that would have dissolved in the H2SO4

Ah damn. I just assumed they fell to the bottom and became part of the mud or whatever the textbook sais

Oh wait, that ^ makes like no sense, just ignore it haha!

[random_person]

The time taken to electroplate - will i get marked down by writing 12.1 days instead of 12?

[thushan]

Ah damn. I just assumed they fell to the bottom and became part of the mud or whatever the textbook sais

Yeah, the mud is composed of metals less reactive than copper.

The time taken to electroplate - will i get marked down by writing 12.1 days instead of 12?

Nup, I wrote 12.1 days in my solutions

[Dismounted]

What were the masses for Section B Q2 which are cut off on the PDF?

Just doing up my own set of solutions.

[DefyingGravity]

Nup, I wrote 12.1 days in my solutions

Shouldn't it be to 2 significant figures? Because the question uses 24A, which you then use in the formula...?

[andyse7en17]

I don't think they'll be that picky T_T I wrote 12.1 as well...

[presto]

Shouldn't it be to 2 significant figures? Because the question uses 24A, which you then use in the formula...?

Also, the calculations were done in time units of seconds right? So that'd be to 2 sig figs in seconds. And since conversion to second-->day is something concrete, without experimental values or anything, I think 12.1 days would be justified.
Although, if I remember correctly, I think I gave my final answer as 12 days not 12.1 days...

[thushan]

Shouldn't it be to 2 significant figures? Because the question uses 24A, which you then use in the formula...?

Good point. It should be 12 days. LOL my brain isn't working properly, just had my last exam today.

[simba]

Good point. It should be 12 days. LOL my brain isn't working properly, just had my last exam today.

WOO PARTY!

I thinkish I got about 110-117/120 which is probably the bast I've done in any chemistry exam (normally I average 80-90%)

[joey7]

In question 9, where you had to use the proton NMR, the infra red and the mass spec., did your analysis have to be able to pinpoint ethyl ethanoate as the molecule or could you say parent peak shows molecular mass of 88 consistent with ethyl ethanoate and so on?

[joey7]

thats fine. no single piece of evidence could have isolated the molecule as ethyl ethanoate besides, if you looked at the explanation given for the 13C NMR spectrum and moulded your answers to look like that, you couldnt have gone wrong!

I hope so!
 are you sure though? it did say to identify, and in the worked solutions the three observations combined could pinpoint the molecule

[beastly101]

Worst case for me is 109/120! still think I can scrape an A+?

[charmanderp]

Worst case for me is 109/120! still think I can scrape an A+?

Definitely possible! That'd be a bit over 90% I think, and I think the A+ cutoff will be a bit less than that, despite what others are saying.