The law of constant composition - 3 | Ionic and Covalent Compounds

Chapter 7 - Ionic and Covalent Compounds

Find the empirical formula of a compound which is 31.9% K, 28.9% Cl and 39.2% O.

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Solution

Empirical formula is K_XCl_YO_Z⇒ M_KxClyOz = X M_K + Y M_Cl + Z M_O = 39.1 X + 35.4 Y + 16.0 Z

%K = 39.1 X / M_KxClyOz = 0.319
%Cl = 35.4 Y / M_KxClyOz = 0.289
%O = 16.0 Z / M_KxClyOz = 0.392

If X = 1, M_KxClyOz = 122.57 g.mol^-1 and Y = 1 and Z = 3.

X, Y and Z are the smallest whole number possible, so the empirical formula of this compound is KClO₃

General Chemistry 1 - The law of constant composition - 3