Name: Non-ideal Solutions
Uploaded: 2019-07-19
Duration: 8 min 43 s
Description: We know that an ideal solution is a theoretical concept. So, what are non-ideal solutions? Why do they show a deviation from Raoult's law? Let's explore!

Question

Show graphically how the vapour pressures of a solvent and a solution in it of non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

Accepted Answer

Elevation in boiling point with the help of vapour pressure-temperature curve of a solution.

The vapour pressure curve for solution lies below the curve for pure water. The diagram shows that $∆ T_{b}$ denotes the elevation of boiling point of a solvent in solution.

When a non-volatile solute is dissolved in a pure solvent, its vapour pressure is decreased. The difference $∆ T_{b}$ of boiling points of the solution and pure solvent is called elevation in boiling point.

It is directly proportional to the molal concentration of the solution. The amount the boiling point is elevated is determined using the equation:

$∆ T_{b} = K_{b} \times m$

The boiling point of a solvent will increase when a solute is dissolved in it. The elevation of the boiling point is directly dependent on the amount of solute present in the solution, but it is not based on the identity of the solute, so it is considered a colligative property.

Show graphically how the vapour pressures of a solvent and a solution in it of non-volatile solute change with temperature. Show on this graph the boiling points of the solvent and the solution. Which is higher and why?

Important Questions on Solutions

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