Zach wants to run an experiment on reaction rates. He designs an experiment testing the reaction rate changes when magnesium and hydrochloric acid react. He decides to run one trial with magnesium ribbon and 1.0 M HCl. For his second trial he rolls the magnesium ribbon into a tight coil and reacts it with 2.0 M HCl. In the third trial, Zach cuts the same amount of Magnesium into slivers and reacts them with 3.0 M HCl. What is the problem with Zach's experimental design?
Answer: In order to receive reliable results of the experiment, there must be fixed and variable parameters. In the Zach’s test there are at least two variable parameters – concentration of acid and reactant’s surface area. This will not allow determine a dependence of the reaction rate only form acid concentration. Here also the surface area of Magnesium will also influence the rate.