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

If

∆ T_{b}

, is the elevation of boiling point and

m

is the molality of solution, show that

∆ T_{b} = K_{b} m

.

Accepted Answer

If boiling point of solution is $T_{b}$ and the boiling point of solvent is ${T_{b}}^{0}$ then,

Elevation in boiling point ${ΔT}_{b } = T_{b } - {T_{b}}^{0}$

Elevation in boiling point is directly proportional to lowering in osmotic pressure.

${ΔT}_{b} \propto ΔP$

According to Raoult's law, lowering in vapour pressure is directly proportional to mole fraction of solute, hence, ${ΔP}_{a} \propto x_{B} (x_{B} =$ mole fraction of solute)

Hence,

${ΔT}_{b} \propto x_{B} $ or

${ΔT}_{b} = {kx}_{B} = k \frac{n_{B}}{n_{A } + n_{B }} = k \frac{W_{B} / M_{B}}{W_{A} / M_{A} + W_{B} / M_{B} } $

For dilute solution $\frac{W_{B}}{M_{B}} < < \frac{W_{A}}{M_{A}}$ and hence $\frac{W_{B}}{M_{B}}$ may be neglected in denominator as compared to $W_{A} / M_{A}$

∴ ${ΔT}_{b} = k \frac{W_{B} / M_{B}}{W_{A} / M_{A}} = k \frac{n_{B}}{W_{A}} M_{A} [∴ \frac{W_{B}}{M_{B}} = n_{B} ] $

If $W_{A }$ is the mass of solvent in kg, then $\frac{n_{B}}{W_{A}} $ is equal to molality (m) of the solution.

Here $k$ and $M_{A}$ are constants and hence their product i.e., ${kM}_{A}$ is replaced by another constant $k_{b}$ .

${ΔT}_{b} = K_{b} m$

Where $K_{b}$ is called boiling point-elevation constanr or molal elevation constant or molal ebullioscopic constant.

If $∆ T_{b}$ , is the elevation of boiling point and $m$ is the molality of solution, show that $∆ T_{b} = K_{b} m$ .

Important Questions on Solutions

Learn and Prepare for any exam you want !

If ∆Tb, is the elevation of boiling point and m is the molality of solution, show that ∆Tb=Kbm.

Important Questions on Solutions

Learn and Prepare for any exam you want !

If $∆ T_{b}$ , is the elevation of boiling point and $m$ is the molality of solution, show that $∆ T_{b} = K_{b} m$ .