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# Calculate the molecular masses of H$$_2$$ , O$$_2$$ , Cl$$_2$$, CO$$_2$$, CH$$_4$$, C$$_2$$H$$_6$$, C$$_2$$H$$_4$$, NH$$_3$$, CH$$_3$$OH.

We know that molecular mass of a substance is the sum of the atomic masses of all the atoms in the molecule of the substance.

The molecular mass of H$$_2$$  = atomic mass of H + atomic mass of H = 2 × atoms atomic mass of H = 2 × 1 = 2u

The molecular mass of O$$_2$$  = 2 × atoms atomic mass of O = 2 × 16 = 32u

The molecular mass of Cl$$_2$$  = 2 × atoms atomic mass of Cl = 2 × 35.5 = 71u

The molecular mass of CO$$_2$$   = atomic mass of C + 2 × atomic mass of O = 12 + ( 2 × 16) = 44u

The molecular mass of CH$$_4$$  = atomic mass of C + 4 × atomic mass of H = 12 + ( 4 × 1) = 16u

The molecular mass of C$$_2$$H$$_6$$  = 2 × atomic mass of C + 6 × atomic mass of H = (2 × 12) + (6 × 1) = 24 + 6 = 30u

The molecular mass of C$$_2$$H$$_4$$  = 2 × atomic mass of C + 4 × atomic mass of H = (2 × 12) + (4 × 1) = 24 + 4 = 28u

The molecular mass of NH$$_3$$  = atomic mass of N + 3 × atomic mass of H = 14 + (3 × 1) = 17u

The molecular mass of CH$$_3$$OH   = atomic mass of C + 3 × atomic mass of H + atomic mass of O + atomic mass of H = 12 + (3 × 1) + 16 + 1 = 12 + 3 + 17 = 32u