True or False: A 1.0g sample of calcium citrate, Ca3(C6H5O7)2 (molar mass 498 g/mol), contains more Ca than a 1.0g sample of calcium carbonate, CaCO3, (molar mass 100g/mol). The answer is false, but can someone explain why?

Question

True or False: A 1.0g sample of calcium citrate, Ca3(C6H5O7)2 (molar mass 498 g/mol), contains more Ca than a 1.0g  sample of calcium carbonate, CaCO3, (molar mass 100g/mol). The answer is false, but can someone explain why?

jfraser · Answer

The real difference is the molar masses of these 2 molecules. A mole (or even a single molecule) of calcium citrate weighs just about 5 times as much as a mole (or single molecule) of calcium carbonate. So on a molecule-for-molecule comparison, the calcium citrate weighs a whole lot more.

Now there are three calcium atoms per calcium citrate, so you might be tempted to think that there's 3 times the calcium mass, but they make up a much smaller percentage of the overall calcium citrate molecule, than the calcium atoms in the calcium carbonate do. If you can find the mass percent of calcium in calcium carbonate, and compare it to the mass percent of calcium in the calcium citrate, you should see why the answer is false. I can do the math for you, but you really ought to try it yourself, first.

anonymous · Answer

Thank you, I understand it now. It's about mass percentage rather than the amount of atoms.