65g of nitric acid are produced in a reaction. 2.5g of platinum are added to the reaction vessel at the start of the reaction to act as a catalyst. How much platinum will there be left in the vessel at the end of the reaction?

2.5 g of platinum

Explanation:

Recall that a catalyst is a specie added to a reaction system to increase the rate of reaction. A catalyst does not participate in the chemical reaction hence it remains unchanged at the end of the chemical reaction. A catalyst merely provides an alternative reaction pathway by lowering the activation energy of the reaction system. Hence a catalysed reaction usually proceeds faster with less energy requirement than the uncatalysed reaction.

Since the catalyst does not participate in the reactions and remains unchanged at the end of the reaction, the mass of platinum will remain the same (2.5g). The mass can only change if a specie participates in the chemical reaction. Hence the answer.