What is the van’t Hoff factor for Na2SO4?
The correct answer and explanation is:
Correct Answer: 3
The van’t Hoff factor (denoted as i) represents the number of particles a compound dissociates into when dissolved in a solvent, typically water. It is used primarily in colligative properties such as boiling point elevation, freezing point depression, and osmotic pressure. The more particles a substance dissociates into, the higher the van’t Hoff factor, which directly influences these properties.
Sodium sulfate (Na₂SO₄) is an ionic compound composed of two sodium ions (Na⁺) and one sulfate ion (SO₄²⁻). When Na₂SO₄ dissolves in water, it dissociates completely into its constituent ions:
Na₂SO₄ → 2 Na⁺ + SO₄²⁻
From this dissociation, it is clear that each formula unit of sodium sulfate produces three ions in solution — two sodium ions and one sulfate ion. Therefore, the van’t Hoff factor i for Na₂SO₄ is 3.
The value of i assumes complete dissociation, which typically happens in dilute aqueous solutions of strong electrolytes like Na₂SO₄. In concentrated solutions or in the presence of ion-pairing effects, the effective van’t Hoff factor might be slightly lower than the ideal value due to limited dissociation or ion interactions. However, under standard dilute conditions, the ideal value of 3 is used for most calculations involving colligative properties.
Understanding the van’t Hoff factor is important in solution chemistry because it affects how substances influence properties like vapor pressure and boiling or freezing points. A higher i means more particles are present in the solution, which results in a greater impact on these physical properties. This makes the van’t Hoff factor a key concept in thermodynamics and physical chemistry.