Name: Solid Solutions
Uploaded: 2019-07-19
Duration: 2 min 56 s
Description: Solutions can be categorized as solid, liquid, and gaseous based on the physical states of solvents and solutes. In this video, let's learn about solid solutions.

Question

A solution of urea in water has a boiling point of

100.18 ° C

. Calculate the freezing point of the solution. (K_f for water is

1.86 K \cdot Kg \cdot {mol}^{- 1}

and K_b for water is

0.512 K \cdot Kg \cdot {mol}^{- 1}

).

Accepted Answer

Boiling point of the given solution ( $T$ ) $=$ $100.18 ° C$

We know that the boiling point of the solvent, pure water ( $T_{b}$ ) = $100 ° C$

Elevation in boiling point ( $∆ T_{b}$ ) is:

$T - T_{b} = 100.18 - 100 = 0.18 ° C$

Depression in freezing point ( $∆ T_{f}$ ) : ?

[Note: The value of $∆ T_{b}$ and $∆ T_{f}$ is the same on both Celsius and Kelvin scale.]

Elevation of boiling point is given by:

$∆ T_{b} = K_{b} \cdot m$

and, depression in freezing point is given by:

$∆ T_{f} = K_{f} \cdot m$

Molal elevation constant or ebullioscopic constant ( $K_{b}$ ) (given) $=$ $0.512 K \cdot Kg \cdot {mol}^{- 1}$

Molal depression constant or cryoscopic constant ( $K_{f}$ ) (given) $=$ $1.86 K \cdot Kg \cdot {mol}^{- 1}$

Therefore, for the solution of same molality (m) we have,

$\frac{∆ T_{f}}{K_{f}} = \frac{∆ T_{b}}{K_{b}} \Rightarrow ∆ T_{f} = \frac{∆ T_{b}}{K_{b}} \times K_{f} = \frac{0.18}{0.512} \times 1.86 = 0.65390625 \approx 0 . 654^{°} C$

Freezing point of the given solution ( $T_{0}$ ) $=$ ?

We know that the freezing point of the solvent, pure water ( $T_{f}$ ) = $0 ° C$

We know that,

$∆ T_{f} = T_{f} - T_{0} \Rightarrow 0.654 = 0 - T_{0} \Rightarrow T_{0} = - 0.654 ° C$

Answer: The freezing point of the given solution is $- 0 . 654^{°} C$ .

A solution of urea in water has a boiling point of $100.18 ° C$ . Calculate the freezing point of the solution. (K_f for water is $1.86 K \cdot Kg \cdot {mol}^{- 1}$ and K_b for water is $0.512 K \cdot Kg \cdot {mol}^{- 1}$ ).

Important Questions on Solutions

Learn and Prepare for any exam you want !

A solution of urea in water has a boiling point of 100.18°C. Calculate the freezing point of the solution. (Kf for water is 1.86 K·Kg·mol-1 and Kb for water is 0.512 K·Kg·mol-1).

Important Questions on Solutions

Learn and Prepare for any exam you want !

A solution of urea in water has a boiling point of $100.18 ° C$ . Calculate the freezing point of the solution. (K_f for water is $1.86 K \cdot Kg \cdot {mol}^{- 1}$ and K_b for water is $0.512 K \cdot Kg \cdot {mol}^{- 1}$ ).