How do varying concentrations of lead nitrate (0 mol/dm3, 0.1 mol/dm3, 0.2 mol/dm3, 0.3 mol/dm3, 0.4 mol/dm3 and 0.5 mol/dm3) affect the rate of enzyme activity of liver catalase in the decomposition of hydrogen peroxide, by measuring the amount of oxygen produced in 2 minutes using a gas syringe?