At what relative humidity will Na₂HPO₄·7H₂O(s) deliquescent when exposed to the air at 27°C? — Chemical Equilibrium Chemistry Question

💡 Solution & Explanation

Deliquescence occurs when the atmospheric partial pressure of water exceeds the equilibrium vapour pressure of the saturated solution or hydrate. For Na₂HPO₄·7H₂O, P_H₂O = 3 × 10⁻³ atm. Relative humidity = (3 × 10⁻³ / 0.04) × 100 = 7.5%. It will deliquesce if the relative humidity is above 7.5%. Therefore, correct answer is C.