(2) for a different mass fraction of the dilute sulfuric acid and the same zinc grains reacted to produce the same volume of hydrogen, the experiment wants to explore is the mass fraction of the solute on the rate of the reaction, so fill in: to investigate the mass fraction of the solution of the reaction on the rate;
(2) to change to different mass fractions of dilute sulfuric acid and zinc grains reacted to produce the same volume of hydrogen, this experiment wants to explore is the mass fraction of the solvent rate of reaction;
(3) in the order of metal activity, zinc in front of copper, can react with copper sulfate to produce zinc sulfate and copper, so fill in: Zn + CuSO4 ═ ZnSO4 + Cu.