You find a rock that weighs 5.4 g and that has some zinc in it. You react the zinc in the rock according to the balanced reaction below. Assuming that hydrochloric acid is in excess, you collect 6.57 g of zinc (II) chloride. What percent zinc was the original rock?
Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)'