Ar(H) = 1; Ar(C) = 12; Ar(N) = 14; Mr(HCN) = 1 + 12 + 14 = 27.
Ar(H) = 1; Ar(N) = 14; Ar(O) = 16; Mr(HNO3) = 1 + 14 + (16 × 3) = 1 + 14 + 48 = 63.
Ar(H) = 1; Ar(Cl) = 35,5; Ar(O) = 16; Mr(HClO4) = 1 + 35,5 + (16 × 4) = 1 + 35,5 + 64 = 100,5.
Ar(C) = 12; Ar(H) = 1; Ar(O) = 16; Mr(C2H5OH) = (12 × 2) + (1 × 5) + 16 + 1 = 24 + 5 + 16 + 1 = 46.
Ar(C) = 12; Ar(H) = 1; Ar(O) = 16; Mr(CH3(CH2)2COOH) = (12 × 4) + (1 × 8) + (16 × 2) = 48 + 8 + 32 = 88.