Copper sulfate is made from copper oxide and sulfuric acid: CuO + H2SO4 gives CuSO4 + H2O. First measure some dilute sulfuric acid into a beaker and warm it in a water bath, a beaker of hot water. Add black copper oxide powder a little at a time, stirring, until no more dissolves and some solid is left at the bottom. The copper oxide is in excess, which makes sure all of the acid has been used up. The solution turns blue.
Filter the mixture to remove the excess copper oxide. This is filtration. The blue solution that passes through the filter paper is the filtrate and contains only copper sulfate and water. Pour it into an evaporating basin and heat it gently over the water bath until about half of the water has evaporated, then leave it to cool and crystallise slowly.
Blue crystals of hydrated copper sulfate form. Filter them off and dry them by pressing gently between pieces of filter paper. Do not heat the solution until it is completely dry, because this would drive off the water in the crystals.
