1. You use an ice bath when adding nitric acid to sulfuric acid. Why?

The process of mixing nitric acid and sulfuric acid is very exothermic, and the heat given off could evaporate nitric acid which is volatile.

The use of an ice bath is to cool down the mixture, and thus to avoid the evaporation of nitric acid.

Sulfuric acid is the pure liquid, the Nitric acid is a 15M solution in water. The heat comes from protonating the excess water. (H2SO4 + H2O --> HEAT)

Large amounts of heat can be generated. It can become hot enough to break the HNO3 into water and NO2 (gas).