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HA(aq) ⇌ H⁺(aq) + A⁻(aq) The freezing point depression of a 0.1 m aqueous solution of a monobasic weak acid HA is 0.20°C. The dissociation constant for the acid is 1.8 × 10⁻⁵. Given: Kf(H₂O) = 1.8 K kg mol⁻¹, molality = molarity

1. 1.1 × 10⁻²
2. 1.38 × 10⁻³
3. 1.90 × 10⁻³
4. 1.89 × 10⁻¹

Correct answer: 1.38 × 10⁻³

Solution

The correct option is right because the freezing point depression is directly related to the molality of the ions produced by the dissociation of the weak acid. By applying the formula for freezing point depression and considering the dissociation constant, the calculated concentration of ions aligns with the given data, leading to the conclusion that 1.38 × 10⁻³ is the accurate value.

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