Calculate the number of water molecules: a) 0.2 b) 2.0 c) 5.0 moles.

According to Avogadro’s law, one mole of any substance contains 6 x 10 to the 23 power of molecules. In order to find out how many molecules are contained in a certain amount of a given substance, you need to multiply Avogadro’s number by the number of moles:
1) 0.2 mol of water contains 0.2 x 6 = 1.2 x 10 to the 23rd degree of molecules;
2) 2.0 mol of water contains 2 x 6 = 12 x 10 to the 23rd degree of molecules;
3) 5.0 mol of water contains 5 x 6 = 30 x 10 to the 23rd degree of molecules.