How do I convert mole percent to grams? Is this calculation correct? If I have 15 mol% A and 85 mol% B. Then mass of A needed= (15*Molecular weight of A in g/mole)/100 ? (x g) and mass of B needed= (85*molecular weight of B in g/mole)/100 (y g). But should I dissolve A and B in a solution of 100 ml of water?