Colligative Properties

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.

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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.

Given:

- Depression of freezing point for PQ₂: 0.8°C

- Depression of freezing point for PQ₃: 0.625°C

- Mass of benzene = 51 g

- K_f of benzene = 5.1 K·kg/mol

We can use the formula for depression in freezing point:

Where:

is the depression in freezing point,

is the cryoscopic constant (given as 5.1 K·kg/mol),

is the mass of the solute (in g),

is the molar mass of the solute (in g/mol).

First, for PQ₂:

Solving for :

Next, for PQ₃:

Solving for :

Now, for the molar masses of the individual atoms P and Q, assume:

Solving these two equations:

1.

2.

Subtract the first from the second:

Substitute into the first equation:

Thus, the atomic masses of P and Q are 55 and 35, respectively.