Explain the complete method for determining empirical and molecular formulae with an example.

📘 Answer: Percentage Composition

Percentage composition is the percentage by mass of each element present in a compound.

It tells us how much mass of a particular element is present in 100 g of the compound.

📐 Formula

% of an element = (Mass of the element in one mole of compound ÷ Molar mass of compound) × 100

🧮 Suitable Example: H₂O

Let us calculate the percentage composition of Hydrogen and Oxygen in H₂O.

Step 1: Write the atomic masses

H = 1      O = 16

Step 2: Calculate the molar mass of H₂O

Molar Mass of H₂O
= (2 × 1) + (1 × 16)
= 2 + 16
= 18 g mol⁻¹

Step 3: Calculate percentage of Hydrogen

Mass of Hydrogen in H₂O = 2 × 1 = 2 g

% H = (2 ÷ 18) × 100

= 11.11%

Step 4: Calculate percentage of Oxygen

Mass of Oxygen in H₂O = 16 g

% O = (16 ÷ 18) × 100

= 88.89%

✅ Check:
11.11% + 88.89% = 100%

🎬 H₂O Molecular Animation

H₂O contains 2 Hydrogen atoms and 1 Oxygen atom.

H

O

H

H₂O

🔵 H = 1

🔴 O = 16

Total Mass = 1 + 1 + 16 = 18

🎯 Final Result

Hydrogen = 11.11%
Oxygen = 88.89%