Edexcel AS Chemistry: 4th June 08

On the last question on 3B, I did the experiment where you heat them and measure mass change.

yay!! I wasn't the only one, that's soooo reassuring^^

Only a couple of people that I asked did that. Of the people who knew what to do most of them bubbled the gas through limewater.

Did you measure the mass change over a certain period of time, or the time it took for the mass to stop changing?

just a random question: do you think its cheating to continue writing after the invigilator has said to put ur pens down?...coz I was going to write in ethanoic solution for the potassium cynide question (unit2) but didn't coz it was the end. My mum thought I was a complete idiot for not writing it. I just want to ensure I follwed all the rules and did the paper fairly. Was what I did right or wrong?

but it was to do with thermal stability, i.e HEAT!! I continued to heat and re-weigh until there was no further change in mass then took away from initial mass of the carbonate.

LOL was gonna do HCl with limewater and calcium carbonate soln. as it was the only test I'd learnt for carbonates, but then luckily I thought it through logically

Yes it's to do with thermal stability. But heating and reweighing doesn't determine which is more stable. You need something along the lines of:
Weigh out equal number of moles of group 2 carbonates (I gave the ratio of masses). Sealed container with gas syringe. Hold container at equal heights above an equal flame to ensure same amount of heating. Stop after 2 minutes, check amount of gas evolved. Less gas = more thermally stable. I know a few people did this, and some did it by mass (Perfectly fine - lower proportion of mass at end left = less stable).

but it was to do with thermal stability, i.e HEAT!! I continued to heat and re-weigh until there was no further change in mass then took away from initial mass of the carbonate.

LOL was gonna do HCl with limewater and calcium carbonate soln. as it was the only test I'd learnt for carbonates, but then luckily I thought it through logically

Yes it's to do with thermal stability. But heating and reweighing doesn't determine which is more stable. You need something along the lines of:
Weigh out equal number of moles of group 2 carbonates (I gave the ratio of masses). Sealed container with gas syringe. Hold container at equal heights above an equal flame to ensure same amount of heating. Stop after 2 minutes, check amount of gas evolved. Less gas = more thermally stable. I know a few people did this, and some did it by mass (Perfectly fine - lower proportion of mass at end left = less stable).