Hypothesis: If the acid concentration is increased then the reaction rate will increase
She will place hydrochloric acid with different concentrations into five conical flasks. She will then add a single strip of magnesium metal to each one and measure the amount of hydrogen gas produced.
The reaction between magnesium and hydrochloric acid is exothermic, so it releases heat. This could be a problem for Gemma's investigation because temperature also affects reaction rate. The rise in temperature could therefore influence the outcome in addition to the independent variable, concentration.
Identify one way that Gemma could deal with this problem to improve the validity of her experiment.