# Calculating the number of moles

• June 7th 2011, 11:23 PM
igcsestudent
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 :-)
• June 7th 2011, 11:38 PM
i cannot see any attached file, can you attach them?
• June 7th 2011, 11:44 PM
igcsestudent
ohh, how can I forget that? stupid me!
• June 8th 2011, 12:10 AM
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
• June 8th 2011, 01:14 AM
igcsestudent
thank you very much, I got it now...