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Mole calculation

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1. can anyone help me with q2? I got 32.5% to 3sf but I think the answer is wrong:65%. Cheers
2. What is the correct answer?
3. (Original post by coconut64)
can anyone help me with q2? I got 32.5% to 3sf but I think the answer is wrong:65%. Cheers
You shouldn't really work backwards from an answer, but if you think about it, you are only out by half so have you forgotten to double something up somewhere?

The method you used to get there would be helpful so people can try to help you spot your mistake. Please post your method if you can, a picture will be fine if you cba typing it.
4. (Original post by L33t)
You shouldn't really work backwards from an answer, but if you think about it, you are only out by half so have you forgotten to double something up somewhere?

The method you used to get there would be helpful so people can try to help you spot your mistake. Please post your method if you can, a picture will be fine if you cba typing it.
I didn't work it out from the answer. Since the mole ratio is 1:2 . thx
5. (Original post by aldsgsuif)
6. (Original post by coconut64)
I didn't work it out from the answer. Since the mole ratio is 1:2 .thx
The equation isn't balanced properly, take another look and redo your steps.

It is a 1:1 ratio when balanced properly so you'l end up with x2 answer eventually which gives 65%

7. (Original post by L33t)
The equation isn't balanced properly, take another look and redo your steps.

It is a 1:1 ration when balanced properly so you'l end up with x2 answer eventually which gives 65%

Thanks, that's actually a mistake in the question itself; I simply copied it down. If there isn't a 2 in front of HCl, the mole ratio is just 1:1 then I would have got it right. That's a misleading question though.
8. (Original post by coconut64)
Thanks, that's actually a mistake in the question itself; I simply copied it down. If there isn't a 2 in front of HCl, the mole ratio is just 1:1 then I would have got it right. That's a misleading question though.
You're welcome!

My chemistry teacher used to put in equations that weren't balanced all the time to try and trip us up which was horrible, but we learned the hard way to be extra thorough (which is crucial at AS and A2). Always double check the stoichiometry before embarking on a calculation even in exams.

It's impressive chemical knowledge that went into your answer anyway! You'd definitely get error carried forward in a case like this so don't worry too much. Plus you're right they probably wouldn't be this mean in an exam, but you never know.
9. (Original post by L33t)
You're welcome!

My chemistry teacher used to put in equations that weren't balanced all the time to try and trip us up which was horrible, but we learned the hard way to be extra thorough (which is crucial at AS and A2). Always double check the stoichiometry before embarking on a calculation even in exams.

It's impressive chemical knowledge that went into your answer anyway! You'd definitely get error carried forward in a case like this so don't worry too much. Plus you're right they probably wouldn't be this mean in an exam, but you never know.
Unfortunately due to the new spec reform, these kind of questions are just going to be a piece of cake. You are right, they are just some exercise practice. Thanks for your time to help out, appreciate it.

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