Question

If you know the formula of a substance, how can you determine its molar mass? Note: Chemists often use the term weight for mass.

Answer 1

molar mass of substance = Sum of atomic masses of all the elements in the substance

Ex:

1) CaSO4 = Ca + S + 4O

Molar mass of CaSO4 = atomic mass of Ca + atomic mass of S + 4 x atomic mass of O

                                 = 40 + 32 + (4 x 16)

                                 = 136 g/mol

2)

H3PO4 = 3H + P + 4 O

Molar mass of H3PO4 = 3 x atomic mass of H + atomic mass of P + 4 x atomic mass of O

                                 = (3 x 1) + 31 + (4 x 16)

                                 = 98 g/mol