Chapter 3, Problem 113FP

A hydrate of copper(II) sulfate, when heated, goes through the succession of changes suggested by the photograph. In this photograph. (a) is the original fully hydrated copper(II) sulfate: (b) is the product obtained by heating the original hydrate to 140 °C; (c) is the product obtained by further heating to 400 °C; and (d) is the product obtained at 1000 °C.

A 2.574 g sample of ${\text{CuSO}}_{\text{4}}{\text{×H}}_{\text{2}}\text{O}$ was heated to 140 °C, cooled, and reweighed The resulting solid was reheated to 400 °C, cooled, and reweighed. Finally, this solid was heated to 1000 °C, cooled, and reweighed for the last time.

a. Assuming that all the water of hydration is driven off at 400 °C, what is the formula of the original hydrate?
b. What is the formula of the hydrate obtained when the original hydrate is heated to only 140 °C?
c. The black residue obtained at 1000 °C is an oxide of copper. What is its percent composition and empirical formula?