# Thread: Calculating the number of moles

1. ## Calculating the number of moles

Hi friends,
tomorrow I have a very important chemistry exam that would literally determine my future...
I am having some difficulties with some past papers, especially with moles....
Take the attached question for example, firstly I managed to calculate the moles of carbon dioxide correctly (0.24/24=0.01), but then, they asked for both calcium carbonate and magnesium carbonate, I got 0.01+0.01=0.02, but it should be 0.01, why, shouldn't we add them?
Also, and most inportantly, why is the answer for the number of moles of calcium carbonate 0.05!! we just calculated it and it is 0.01 moles right? this doesn't make any sense to me...

part (ii) I understand, so no need to explain that.

Thank you very very much, please reply ASAP as I have to much work and so little time :-)

2. i cannot see any attached file, can you attach them?

3. ohh, how can I forget that? stupid me!

4. no, $CO_2$ is produced by both $MgCO_3$ and $CaCO_3$ since the amount of $MgCO_3$ and $CaCO_3$ are same half of the $CO_2$ is produced by each of them. Since the ratio between $CO_2$ and $CaCO_3$ (and $MgCO_3$) is 1:1 , number of moles in $CaCO_3$ should be 0.005

5. thank you very much, I got it now...