Calculate what amount of substance is 40 g of CuSO4.

In order to calculate the amount of a substance, you should use the formula: n = m / M. Where m is the mass of a substance (under the condition of 40 grams), M is the molar mass of a substance, equal to the sum of atomic masses (atomic masses can be viewed in the periodic system of chemical elements D I. Mendeleev).
M (CuSO4) = Ar (Cu) + Ar (S) + 4Ar (O);
M (CuSO4) = 64 + 32 + 4 * 16 = 160 (g / mol).
n = 40/160 = 0.25 (mol).
Answer: the amount of CuSO4 substance is 0.25 mol.