Question

The correct order of boiling points of the given aqueous solutions is

• A. 1 N KNO₃>1 N NaCl>1 N CH₃COOH>1 N sucrose
• B. 1 N KNO₃ = 1 N NaCl>1 N CH₃COOH>1 N sucrose
• C. Same for all
• D. 1 N KNO₃ = 1 N NaCl = 1 N CH₃COOH>1 N sucrose

Hint:

Colligative properties depend on the number of solute particles. Strong electrolytes dissociate completely, producing more particles than weak electrolytes or non-electrolytes.

Answer 1

The Correct Option is B

The boiling point elevation is a colligative property, which depends on the number of solute particles in the solution:

• KNO₃: Strong electrolyte, dissociates into 2 ions (K⁺ and NO⁻₃).
• NaCl: Strong electrolyte, dissociates into 2 ions (Na⁺ and Cl⁻).
• CH₃COOH: Weak electrolyte, partially dissociates into CH₃COO⁻ and H⁺ ions.
• Sucrose: Non-electrolyte, does not dissociate.

23

Since strong electrolytes like KNO₃ and NaCl produce more particles in solution compared to weak electrolytes like CH₃COOH and non-electrolytes like sucrose, the order of boiling points is: 1 N KNO₃ = 1 N NaCl>1 N CH₃COOH>1 N sucrose.

Answer 2

Correct Answer:

Option 2: 1 N KNO3 = 1 N NaCl > 1 N CH3COOH > 1 N sucrose

Explanation:

Boiling point elevation is directly proportional to the number of solute particles in the solution. The van't Hoff factor (i) indicates the number of particles a solute dissociates into.

• 1 N KNO3: i = 2 (K⁺, NO3^-)
• 1 N NaCl: i = 2 (Na⁺, Cl^-)
• 1 N CH3COOH: i is slightly greater than 1 (weak acid, partial dissociation)
• 1 N sucrose: i = 1 (non-electrolyte, no dissociation)

Therefore, KNO3 and NaCl have the same, and highest, boiling point. CH3COOH has a slightly lower boiling point, and sucrose has the lowest.