How do you calculate the amount of moles of a (solid) substance from its mass?

Use the equation:Moles = Mass ÷ Relative mass
For example: How many moles are there in 10g of CaCO₃ ? ( to 3 significant figures)Find the relative mass of CaCO₃ by adding up the masses of the atoms that make it up.Ca = 40C =12O = 16
1 x Ca + 1 x C + 3 x O = 40 + 12 + 3 x 16 = 100 = relative mass
Moles = Mass ÷ Relative mass = 10 ÷ 100 = 0.100 moles (3 s.f.)