Question:

What is the freezing point of a solution containing 8.1 g HBr in 100 g water, assuming that the acid to be 90% ionized? $(K_f (H_2O) = 1.86 \,K \,kg\, mol^{-1})$

Updated On: Jun 23, 2023
  • $0.85^{\circ}C$
  • $-3.8^{\circ}C$
  • $-0^{\circ}C$
  • $-3.5^{\circ}C$
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The Correct Option is D

Solution and Explanation

Consider the dissociation of 1 mol HBr. The degree of dissociation is 90%, i.e., $\alpha = 0.90$ $\begin{matrix}&HBr_{\left(aq\right)}&\to&H^{+}\left(aq\right)&+&Br^{-}\left(aq\right)\\ Initial\, conc.&1\, mol&&0&&0\\ Final \, conc.&1 - 0.90 = 0.10\, mol&&0.90\, mol&&0.90\, mol\end{matrix}$ $\therefore\quad$ Total number of particles $= 0.10 + 0.90 + 0.90$ $= 1.90\, mol$ van?? Hoff factor $\left(i\right) = \frac{1.90}{1.00} = 1.90$ $\Delta T_{f} = iK_{f} \frac{W_{B}}{M_{B}\cdot W_{A}} = \frac{1.90 ? 1.86 \,K\,kg\,mol^{-1} ? 8.1 \,g}{81 \,g \,mol^{-1} \times 100 \times10^{-3} \,kg}$ $= 3.5 \,K = 3.5^{\circ}C$ F.P. of solution = F.P. of solvent - depression in F.P. $= 0^{\circ}C - 3.5^{\circ}C = -3.5^{\circ}C$
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Concepts Used:

Solutions

A solution is a homogeneous mixture of two or more components in which the particle size is smaller than 1 nm.

For example, salt and sugar is a good illustration of a solution. A solution can be categorized into several components.

Types of Solutions:

The solutions can be classified into three types:

  • Solid Solutions - In these solutions, the solvent is in a Solid-state.
  • Liquid Solutions- In these solutions, the solvent is in a Liquid state.
  • Gaseous Solutions - In these solutions, the solvent is in a Gaseous state.

On the basis of the amount of solute dissolved in a solvent, solutions are divided into the following types:

  1. Unsaturated Solution- A solution in which more solute can be dissolved without raising the temperature of the solution is known as an unsaturated solution.
  2. Saturated Solution- A solution in which no solute can be dissolved after reaching a certain amount of temperature is known as an unsaturated saturated solution.
  3. Supersaturated Solution- A solution that contains more solute than the maximum amount at a certain temperature is known as a supersaturated solution.