What is the solubility of a salt if 0.4g of it is obtained on evaporating 200$cm^{3}$ of its saturated solution to dryness?

Analyze the question: Solubility here is expressed in g/dm³, meaning the mass of solute that dissolves in 1 dm³ (1000 cm³) of saturated solution.

Concept: Solubility (g/dm³) = mass of solute (g) ÷ volume of solution (dm³)

Solution:

• Mass of salt = 0.4 g
• Volume of saturated solution = 200 cm³ = 0.2 dm³

Solubility = 0.4 ÷ 0.2 = 2.00 g/dm³

Check using proportion: 200 cm³ contains 0.4 g 1000 cm³ contains (0.4 × 1000) ÷ 200 = 2.0 g

Answer: B. 2.00 g/dm³

Tip: Always convert cm³ to dm³ by dividing by 1000 (or scale the volume up to 1000 cm³). A quick shortcut: 200 cm³ is one-fifth of 1000 cm³, so multiply the mass by 5: 0.4 × 5 = 2.0 g/dm³.