1. Chemical Reactions & Mass D. Crowley, 2007

2. Chemical Reactions & Mass To understand that mass is conserved during a reaction

3. Mass Have a look at the following reaction magnesium + copper sulphate  magnesium sulphate + copper The reactants have been weighed (on the left) - can you predict the final mass of the products (on the right)? The mass of the products is the same as that of the reactants, so our mass should be 48g + 5.3g = 53.3g

4. Mass Have a look at the following reaction hydrochloric acid + magnesium  magnesium chloride + hydrogen This time the mass was actually less than expected - can you suggest why? Can you work out how much hydrogen was produced? One product was hydrogen gas - this was not collected, so the total mass was lower than expected. 45.5g + 5.3g = 50.8g But we made 49.5g, meaning 1.8g of hydrogen gas was made (50.8 - 49.5)

5. Constant Total Mass In all chemical reactions, the mass of the reactants is the same as the mass of the products No atoms are gained or lost - they are just rearranged in different ways mass reactants  mass products 100g of reactants  100g of products copper + oxygen  copper oxidecarbon + oxygen  carbon dioxide

6. Experiment Your task, working in groups, is to carry out the experiments to identify what happens to the mass of chemicals in a reaction It is vital you measure the mass of the chemicals before and after the experiment Each group has five tasks, so as a group you must follow the procedure accurately, for all the different stages Apparatus for your experiment is at your station (although it is mixed around), so read what you need to do, and remember, record your results! Good luck!

7. Reactions Station 1 copper sulphate + sodium hydroxide  copper hydroxide + sodium sulphate CuSO 4 + 2NaOH  Cu(OH) 2 + 2NaSO 4 Station 2 hydrochloric acid + sodium hydroxide  sodium chloride + water HCl + NaOH  NaCl + H 2 O Station 3 copper sulphate + iron  iron sulphate + copper CuSO 4 + Fe  FeSO 4 + Cu