(a) PCl5:
Molecular mass of PCl5 = (1 x atomic mass of P) + (5 x atomic mass of Cl)
Atomic mass of P = 30.97 u
Atomic mass of Cl = 35.45 u
Molecular mass of PCl5 = (1 x 30.97 u) + (5 x 35.45 u) = 208.23 u
(b) C4H10:
Molecular mass of C4H10 = (4 x atomic mass of C) + (10 x atomic mass of H)
Atomic mass of C = 12.01 u
Atomic mass of H = 1.01 u
Molecular mass of C4H10 = (4 x 12.01 u) + (10 x 1.01 u) = 58.12 u
(c) NF2:
Formula mass of NF2 = (1 x atomic mass of N) + (2 x atomic mass of F)
Atomic mass of N = 14.01 u
Atomic mass of F = 18.99 u
Formula mass of NF2 = (1 x 14.01 u) + (2 x 18.99 u) = 52.99 u
(d) Al2O3:
Formula mass of Al2O3 = (2 x atomic mass of Al) + (3 x atomic mass of O)
Atomic mass of Al = 26.98 u
Atomic mass of O = 16.00 u
Formula mass of Al2O3 = (2 x 26.98 u) + (3 x 16.00 u) = 101.96 u
(e) Fe(NO3)3:
Formula mass of Fe(NO3)3 = (1 x atomic mass of Fe) + (3 x (1 x atomic mass of N + 3 x atomic mass of O))
Atomic mass of Fe = 55.85 u
Atomic mass of N = 14.01 u
Atomic mass of O = 16.00 u
Formula mass of Fe(NO3)3 = (1 x 55.85 u) + (3 x (1 x 14.01 u + 3 x 16.00 u)) = 241.99 u
(f) Mg3N2:
Formula mass of Mg3N2 = (3 x atomic mass of Mg) + (2 x atomic mass of N)
Atomic mass of Mg = 24.