Question

A chemist finds that when platinum is added to a reaction, the reaction speeds up. He thinks the platinum may be acting as a catalyst. What measurement should the chemist make to determine whether it is a catalyst?

Answer 1

Measure the change in volume of the solution.

Answer 2

He should measure the speed of the reaction without platinum and with platinum and compare the difference (with a known quantity of platinum) and if the speed is indeed faster and there is no  other factor involved, then that should verify it.