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Reply 780
Original post by badatgow
i'm not sure if it's correct but: Since we know the colour is "titanium yellow", and we know that the colour we see is the colour reflected i put a curve with maximum at the middle (yellow) going down to 0 at the red and blue ends.


me tooooooo :biggrin:
Original post by badatgow
i'm not sure if it's correct but: Since we know the colour is "titanium yellow", and we know that the colour we see is the colour reflected i put a curve with maximum at the middle (yellow) going down to 0 at the red and blue ends.

I did that too!
Reply 782
I found the paper overall pretty tough, but i'm confident i've done pretty well because I managed to finish quite fast and had plenty of time (like 40 mins) thankfully to check over everything a couple of times. While I was checking the paper I felt a lot better about my chances, because in hindsight most of the questions were relatively straightforwards. While doing the questions for the first time I felt like I was struggling a lot, but that's probably due to seeing unusual thinks like isoprenes etc.

The interesting question IMO was the one about the calcium carbonate shells. My reasoning was that, increasing acidity increases [H+], so second equation equilibrium concentration shifts to the right. This increases concentration of [HCO3-]. I figured this would increase the concentration of [CO3 2-] in the first equation, so equilibrium would shift to the left to oppose the change. As a result, calcium carbonate concentration would increase and the shell thickness would increase. However, writing that down made me feel like a mug the entire time because i'm pretty sure if you pour acid on calcium carbonate it would just dissolve...but I couldn't see the chemistry to disagree with me. Oh well, only 2 marks if i'm wrong anyways.
Original post by badatgow
The answer was like 180g. The solution is as follows:

Moles of thiosulfate = concentration of thiosulfate x volume of thiosulfate
Moles of I2 UNREACTED = moles of thiosulfate / 2

Moles of I2 REACTED = total moles of I2 (given) - Moles of I2 Unreacted

Moles of I2 reacted x Mr of I2 = Mass of I2 Reacted with 0.2g.
Mass of I2 Reacted calculated above is for 0.2g, hence

Iodine Number = Mass of I2 Reacted x 500.

WHERE DID THEY GIVE US THE TOTAL NUMBER OF MOLES :O :O coz I went and had to calculate it manually, undead up getting it wrong.. but my method was the same arghhhhhh DPMO :angry: :angry: :angry:
Reply 784
Original post by ActaNonVerba
WHERE DID THEY GIVE US THE TOTAL NUMBER OF MOLES :O :O


In the second line of the question I believe.
Anyone got a copy of the paper?

I'll even attempt the unofficial mark scheme if someone gets me it...
Original post by badatgow
In the second line of the question I believe.

I thought that was just the concentration, and had to manipulate it to work out moles.. but we weren't given a volume to calculate it? or was it literally the number of moles -_-
Reply 787
Hi everyone, I hope it all went as good as it could have done for all of you.
Since I am the creator of this thread I will create a poll to see what the grade boundaries will be. Judging by your comments it seems like an average one. Should I add a numerical poll asking what the number for an A should be, or a qualitative poll? Asking how and or how good it went?
Reply 788
can anyone remember what the 'suggest the equation' question was? and what they put? there might have been two actually...
For the MMR of the compound did everyone go for the peak furthest to the right???
Original post by badatgow
I found the paper overall pretty tough, but i'm confident i've done pretty well because I managed to finish quite fast and had plenty of time (like 40 mins) thankfully to check over everything a couple of times. While I was checking the paper I felt a lot better about my chances, because in hindsight most of the questions were relatively straightforwards. While doing the questions for the first time I felt like I was struggling a lot, but that's probably due to seeing unusual thinks like isoprenes etc.

The interesting question IMO was the one about the calcium carbonate shells. My reasoning was that, increasing acidity increases [H+], so second equation equilibrium concentration shifts to the right. This increases concentration of [HCO3-]. I figured this would increase the concentration of [CO3 2-] in the first equation, so equilibrium would shift to the left to oppose the change. As a result, calcium carbonate concentration would increase and the shell thickness would increase. However, writing that down made me feel like a mug the entire time because i'm pretty sure if you pour acid on calcium carbonate it would just dissolve...but I couldn't see the chemistry to disagree with me. Oh well, only 2 marks if i'm wrong anyways.

I totally agree! Why is that we are wrong if we did work backwards on that seashell Q?
Reply 791
Original post by ActaNonVerba
I thought that was just the concentration, and had to manipulate it to work out moles.. but we weren't given a volume to calculate it? or was it literally the number of moles -_-


nope it was just number of moles added (an excess). Some of it was unused (obviously) so here is the titration to calculate how much was unused.
How many marks was the mass spectrum part worth?
Reply 793
Original post by stealth_writer
How many marks was the mass spectrum part worth?


About five maybe.
Original post by DoeADeer
Oh nooo, I multiplied it by 2 I think :frown:(((

Posted from TSR Mobile


i agree
Original post by david2457
About five maybe.


What did you get as the Mr of the compound?
Reply 796
Original post by stealth_writer
What did you get as the Mr of the compound?


32, and the compound I got it as CH3OH
The buffer pH question that involved the proportion of acid and salt changing was as follows:

You were told enough alkali was added to react with half the acid in the previous part of the question (when salt/acid = 1/1). Therefore you essentially now have 1.5 parts salt and 0.5 parts acid, which simplifies down (1.5/0.5) to 3. Therefore to find pH you simply divided the Ka by three and found the -log.
Original post by david2457
32, and the compound I got it as CH3OH


Which was the peak furthest to the right??

Correct.?
How many marks was the CH3OH part worth?
(edited 10 years ago)
Reply 799
Original post by stealth_writer
Which was the peak furthest to the right??

Correct.?


Yes