# Percentage Composition, Empirical Formula and Molecular Formula of Compounds

## The percentage by mass of each element present in a compound is given by percentage composition. The simplest ratio in the whole numbers of atoms of different elements present in one molecule of the compound is given by a simplest formula known as Empirical formula. With the help of empirical formula, we can calculate empirical mass of the compound. The actual number of atoms of different elements present in one molecule of the compound is denoted by the molecular formula of the compound. Molecular formula of the compound can be calculated with the help of empirical formula. The ratio between the masses of equal volumes of the gas (or vapour) and hydrogen under similar conditions of temperature and pressure is known as vapour density. A chemical equation is a balanced account of a chemical transaction. A reaction having equal number of atoms of different elements in the reactants and products is known as balanced chemical equation. In spite of having several limitations, chemical equations have various implications.

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• Q1

Percentage composition of P in Ca(H2PO4)2 is ‘A’ and percentage composition of P in Ca3(PO4)2 is ‘B’. Identify the correct relation between A and B.

Marks:1

A>B

##### Explanation:

• Q2

Vapour density of a compound X is 22. Molecular weight of compound X is

Marks:1

44

##### Explanation:

• Q3

The mass percentage of water of crystallisation in blue vitriol is

Marks:1

36%

##### Explanation:

• Q4

Empirical formula of glucose is

Marks:1

CH2O

##### Explanation:

Glucose is C6H12O6. Its empirical formula is CH2O, where n=6.

• Q5

Out of 20g Na2CO3 and 5g Na2CO3, one which has higher percentage of sodium is

Marks:1