Solutions A (iodate) and B (bisulfite) are mixed at room temperature in differing concentrations, producing a blue-black starch/iodine complex after a length of time that depends on the concentrations ...

When carrying out the experiment, care has to be taken that other variables that affect the rate of reaction, such as concentration of reactants, are kept constant. These are control variables.

The speed of a chemical reaction is affected by temperature, concentration, particle size and the presence of a catalyst. It can be calculated by measuring changes in reactants/products.