The document provides information on calculating relative atomic masses (Mr) and mass of products in chemical reactions. It gives the formulas to calculate Mr of compounds by adding the atomic masses of elements. It also provides methods to calculate percentage composition and mass of products using the ratio of Mr of products to reactants. Examples are given to calculate mass of MgO from Mg, H2 from H2O, CaO from Ca, and Al from Al2O3.

1. C5 GCSE Revision Reacting Masses 09/05/11

2. Atomic mass 09/05/11 He 2 4 SYMBOL PROTON NUMBER = number of protons (obviously) RELATIVE ATOMIC MASS, A r (“Mass number”) = number of protons + number of neutrons

4. More examples 09/05/11 CaCO 3 40 + 12 + 3x16 100 HNO 3 1 + 14 + 3x16 2MgO 2 x (24 + 16) 80 3H 2 O 3 x ((2x1) + 16) 4NH 3 2KMnO 4 3C 2 H 5 OH 4Ca(OH) 2

8. Another method 09/05/11 Try using this equation: Mass of product IN GRAMMES 6g 4 36 So mass of product = (4/36) x 6g = 0.66g of hydrogen Mass of product IN GRAMMES Mass of reactant IN GRAMMES M r of product M r of reactant Q. When water is electrolysed it breaks down into hydrogen and oxygen: 2H 2 O 2H 2 + O 2 What mass of hydrogen is produced by the electrolysis of 6g of water?