Question:
$75.2\, g$ of phenol is dissolved in a solvent of $K_f = 14$. If the depression in freezing point is $7 \,K$ then find the $\cdot %$ of phenol that dimerises.
$75.2\, g$ of phenol is dissolved in a solvent of $K_f = 14$. If the depression in freezing point is $7 \,K$ then find the $\cdot %$ of phenol that dimerises.
Updated On: Jun 23, 2023
- $75\%$
- $80\%$
- $70\%$
- $100\%$
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The Correct Option is A
Solution and Explanation
$\begin{matrix}&2C_{6}H_{5}OH&\rightleftharpoons&\left(C_{6}H_{5}OH\right)_{2}\\ \text{initially}&C&&0\\ \text{at equil}&C\left(1-\alpha\right)&&C\alpha /2\end{matrix}$
Total number of moles $= C - C\alpha + \left(C\alpha /2\right)$
$=C - \frac{C\alpha}{2} = \frac{2C-C\alpha}{2}$
$= \frac{C\left(2-\alpha\right)}{2}$
$C = \frac{\text{Weight}}{\text{Molecular weight}}$
$= \frac{75.2}{94} = 0.8$
$\Delta T_{f} = K_{f} \times m$
$\Rightarrow 7 = 14 \times 0.8\left(\frac{2-\alpha}{2}\right)$ or,
$1= 0.8\left(2-\alpha\right)$
$\alpha = 0.75 = 75\%$
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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:
- Unsaturated Solution- A solution in which more solute can be dissolved without raising the temperature of the solution is known as an unsaturated solution.
- 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.
- Supersaturated Solution- A solution that contains more solute than the maximum amount at a certain temperature is known as a supersaturated solution.