Question

a chemical compound containing 31.1% of Fe 53.3%of O and 15.6%of N is prepared by dissolving iron in cold dilute nitric acid. the molecular mass of the compound is 180g/mol. then its molecular formula is meritnation

Answer 1

First find the empirical formula

Element	%	At mass	%/ at mass	Simple ratio	Whole no ratio
Fe	31.1	56	56/31.1 = 1.8001	1.8001/1.1143 = 1.615	2
O	53.3	16	53.3 / 16 = 3.3313	3.3313/1.1143 = 2.99	3
N	15.6	14	15.6 / 14 = 1.1143	1.1143/1.1143 = 1	1

Thus the empirical formula of the compound = Fe₂O₃N
Mass of the compound = Empirical formula mass = 2 x 56 + 3 x 16 + 1 x 14 = 174
Molecular formula = Empirical formula x n
n= Molecular mass / Empirical formula mass = 180 / 174 = 1
Molecular formula = Empirical formula x n = ​Fe₂O₃N x 1 = Fe₂O₃N