To find the moles of calcium, we need to use the information given in the problem as well as the molar mass of CaCO3. The molar mass is found from the sum of the atomic masses found on the periodic table for each of the elements in the compound.
For CaCO3, the molar mass is 100.1 g/mol. The first step is to find the moles of CaCO3, then we can find the moles of Ca. To find the moles of CaCO3, we need to convert 500 mg to g by dividing by 1000 to get 0.500 g CaCO3.
Now, we can convert 0.500 g to moles by dividing by 100.1 g/mol to get 0.00500 moles of CaCO3. Now, we can look at the subscripts in the molecular formula to see that for every one mole of CaCO3, we get 1 mole of Ca. So the number of moles of CaCO3 (0.00500 moles) equals the number of moles of Ca so it will also be 0.00500 moles.