The boiling point of a liquid is the temperature at which the vapour pressure of the liquid is equal to the atmospheric pressure above the liquid.Liquids boil at temperatures higher than their normal boiling points when external pressures are greater than 760 torr. When external pressures are less than 760 torr, liquids boil at temperatures below their normal boiling points. Thus, the boiling point of water fluctuates with changes in atmospheric pressure. The formula for boiling point is given by,

Where $\Delta T$ is the boiling point elevation, $k_{b}$ is the boiling point elevation constant and m is the molal concentration.

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Let us discuss the problems related to boiling point.

### Solved Examples

**Question 1: **Calculate the boiling point of the given solution whose m = 0.0285m and $k_{b}$ = 0.512°C/m? Here the solvent is water.

** Solution: **

Given parameters are,

m = 0.0285m, $k_{b}$ = 0.512°C/m

Since the solvent is water $T_{solvent}$ = 100°C

The formula for boiling point is,

$T_{solution}$ = $T_{solvent}$+$\Delta T$

$\Delta T$ = $k_{b}$m

$\Delta T$ = 0.512$\times$0.0285 = 0.0145°C

So, $T_{solution}$ = 100+0.0145 = 100.0145°C

**Question 2: **Boiling point of a solvent is given as 70°C, the value for k_{b} and m are 0.3°C/m and 0.015m respectively. Calculate the boiling point of the given solution?

** Solution: **

Given parameters are,

m = 0.015m, $k_{b}$ = 0.3°C/m

Since the solvent is water $T_{solvent}$ = 70°C

The formula for boiling point is,

$T_{solution}$ = $T_{solvent}$+$\Delta T$

$\Delta T$ = $k_{b}$m

$\Delta T$ = 0.3$\times$0.015 = 0.0045°C

So, $T_{solution}$ = 70+0.0045 = 70.0045°C

Given parameters are,

m = 0.0285m, $k_{b}$ = 0.512°C/m

Since the solvent is water $T_{solvent}$ = 100°C

The formula for boiling point is,

$T_{solution}$ = $T_{solvent}$+$\Delta T$

$\Delta T$ = $k_{b}$m

$\Delta T$ = 0.512$\times$0.0285 = 0.0145°C

So, $T_{solution}$ = 100+0.0145 = 100.0145°C

Given parameters are,

m = 0.015m, $k_{b}$ = 0.3°C/m

Since the solvent is water $T_{solvent}$ = 70°C

The formula for boiling point is,

$T_{solution}$ = $T_{solvent}$+$\Delta T$

$\Delta T$ = $k_{b}$m

$\Delta T$ = 0.3$\times$0.015 = 0.0045°C

So, $T_{solution}$ = 70+0.0045 = 70.0045°C