Answers section
Questions 2.3(b)
What mass of magnesium sulphate (MgSO4) has the same number of moles as 1.06 g of anhydrous sodium carbonate (Na2CO3)? (C = 12; O = 16; Mg = 24; Na = 23; S = 32.)
Answers to Questions 2.3(b) 
Mass of one mole (molar mass) of Na2CO3 is (23 x 2) + 12 + (12 x3) = 106 g So 1.06 g is 1.06/106 = 0.01 moles. This is the same number of moles of MgSO4. But 1 mole of MgSO4 weighs 24 + 32 + (16 x 4) = 120 g. Therefore 0.01 moles of MgSO4 weigh (0.01/1) x 120 = 1.2 g.