PERCENTAGE COMPOSITION OF COMPOUNDS:

Law of Definite Proportions:  Compounds are consistent chemical combinations of atoms that can be expressed as:

(i)  Ratio of masses

(ii) Ratio of atoms

(iii) Ratio of moles of atoms

(iv) Percent composition

ILLUSTRATIVE EXAMPLE (1): Calculate the percent Nitrogen in Dinitrogen (N₂O) Monoxide?

SOLUTION:

ILLUSTRATIVE EXAMPLE (2): What is the % composition of each element in (Mg(OH)₂) magnesium hydroxide?

SOLUTION:

ILLUSTRATIVE EXAMPLE (3): Haemoglobin contains 0.33% of Iron by weight. The molecular weight of it is approx. 67200. The numbers of iron atoms (Atomic wt of Fe=56 u) present in one molecule of Haemoglobin are?

SOLUTION:

ILLUSTRATIVE EXAMPLE (4): The hydrated salt, Na₂SO4.nH₂O undergoes 55.9% loss in weight on heating and becomes anhydrous. The value of n will be?

SOLUTION:

ILLUSTRATIVE EXAMPLE (5): Air contain 20 % O₂ by volume. How many cm³ of air will be required for oxidation of 100 cm³(ml) of acetylene?

SOLUTION:

Since air contain 20 % oxygen by volume then amount of air required to react with 100cc/ml of C₂H₂

Try yourself:

Exercise (4): Two oxides of metal contain 72.4 and 70 of metal respectively if formula of 2nd oxide is M₂O₃ find that of the first.

Ans Key : M₃O_{4
Determination of Empirical and Molecular Formula:}