Elevation of boiling point

The elevation of the boiling point means that the solvent’s boiling point increases upon the addition of a solute. The resulting solution has a higher boiling point when a non-volatile solute is added to a solvent compared to that of the pure solvent. For example,  The boiling point of sodium chloride solution and water is higher than that of pure water.

The elevation of boiling point is a colligative property of matter which means that it depends on the solvent-to-solvent ratio but not on the nature of the solute. This means that the rise of a solution’s boiling point is dependent on the amount of solution applied to it. The higher the solute concentration in the solution, the more the elevation of the boiling point.

Boiling Point Elevation

The vapour pressure of a solvent can fall when a solution is put in application. This happens because of the solute displacement of the solvent molecules. BY this means we can understand that some of the solvent molecules on the liquid’s surface are displaced by the solvent; twin electrolytic and non-electrolytic solutions will occur at once. The low number of solvent molecules on the surface means that less can change into vapour state, thus the vapour pressure is reduced. A higher temperature is needed for the vapour pressure to be as same as the ambient pressure, and a higher boiling point is observed.

 At a pressure of 1atmospheric pressure of mercury at sea level, pure water boils at 100 ∘C

. In water, a 10-molal solution of sucrose boils at around 105 ∘C.

Why Does Boiling Point Elevation Occur?

The temperature at which its vapour pressure is the same as the pressure of its surrounding atmosphere is called the boiling point of a liquid. Non-volatile liquids do not evaporate very fast and have very low vapour pressures. The vapour pressure of the resulting solution is lower than that of the pure solvent when a non-volatile solute is put into application of the solvent.

Therefore, the solution must be subjected to a large amount of heat for it to boil. The boiling point elevation is this increase in the solution’s boiling point. A rise in the concentration of the added solution is followed by a further fall in the solution’s vapour pressure and a further rise in the solution’s boiling point.

The liquid’s boiling point is dependent on the pressure of its surroundings (which is why water boils at temperatures which is lower than 100 ∘C at high altitudes, where the surrounding pressure is comparatively low).

Boiling Point Elevation Formula

The boiling point of a non-volatile solute containing solution is represented as follows:

Boiling point of solution =elevation of the boiling point + pure solvent boiling point 

The boiling point elevation is directly proportional to the solute concentration in the solution. The following equation can be used as to represent the same.

ΔTb = i*Kb*m

Where,

• It is the Van’t Hoff factor.
• Kb is the ebullioscopic constant.
• m is often known as the molality of the solute.

When the solute concentration is very high, this formula becomes less accurate. Also, this formula does not hold true for volatile solvents.

In terms of ∘C∘C

/Molal, or ∘C∘C. kg.mol-1, the ebullioscopic constant (Kb) is also expressed. 

With the help of the boiling point elevation formula, the molar mass of the solute and the degree of dissociation of the solute can be measured.

The Relationship Between Vapour Pressure and Boiling Point Elevation 

According to vapour pressure, boiling point elevation can be clarified. Vapour pressure is pressure exerted at a given temperature by a vapour in thermodynamic equilibrium with its condensed phases. It is simply a measure of the ability of the solvent molecules, in common man’s words, to escape by entering the gas phase. When the vapour pressure is equal to the air pressure, a liquid starts boiling.

Boiling Point – The boiling point of a liquid in its purest form. The liquid will start boiling when the vapour pressure of the liquid is the same as the ambient pressure.

Conclusion

We can conclude that in dilute ideal solutions, the extent of boiling-point elevation is directly proportional to the molal concentration (amount of substance per mass) of the solution according to the equation: ΔTb = Kb · b.

In General the boiling point is a point or temperature at which liquid starts boiling, and the vapour pressure is equal to the given external pressure.

The temperature at which the vapour pressure of an object equal to the external pressure rises when another compound is added.