Copper sulphate reacts with sodium hydroxide to form a blue precipitate of copper hydroxide and sodium
sulphate. In an experiment, 15.95 g of copper sulphate reacted with 8.0 g of sodium hydroxide to form
9.75 g of copper hydroxide and 14.2 g of sodium sulphate. Which law of chemical combination is illustrated by this data ? Give reason for your choice.
Solution
Chemical reaction:
CuSO4 + NaOH → Cu(OH)2 + NaSO4
15.94g 8.0g 9.75g 14.2g
Total mass of reactants = Total mass of products
23.95g 23.95 g
The above reaction and data illustrate the law of conservation of mass which was proposed by Antoine Lavoisier.
The law states that the mass of elements remains constant over time i.e. mass can neither be created nor destroyed. In the above reaction, the mass of reactants (23.95 g) is exactly equal to the mass of their product (23.95 g). There is no change in the mass of the product after the reaction.
