Write the balanced equations for the preparation of the following salts in the laboratory:
(a) A soluble sulphate by the action of an acid on an insoluble base,
(b) An insoluble salt by the action of an acid on another salt,
(c) An insoluble base by the action of a solube base on a soluble salt,
(d) A soluble sulphate by the action of an acid on a metal.
