Freezing Point Of The Solvent- Formula, Properties and Examples

The freezing point of the solvent is lowered by the addition of solutes, which is also known as freezing point depression. It is a colligative property proportional to the molality of the solute added. When the temperature of a substance is decreased, it starts freezing. The intermolecular forces increase and arrange themselves in a pattern to transform into a solid. Freezing point depression takes place when the less, non-volatile material is introduced, resulting in a temperature decline at which it starts freezing.

Table of Contents:

What is the Freezing Point of the Solvent?
Why does the Freezing Point of the Solvent Occurs?
Examples of Freezing Point
Factors Affecting the Freezing Point
Uses of Freezing Point of Depression
Practice Problems On The Freezing Point Of The Solvent

What is the Freezing Point of the Solvent?

The freezing point of the solvent refers to the particular temperature at which a substance changes from liquid to solid state. Freezing point depression can be achieved by decreasing the freezing point of the solvents by the addition of solutes to the solution.

According to Raoult’s Law, the vapour pressure of a solvent decreases by adding a solute to the solution. This is the cause of the freezing point of the solvent. The vapour pressure of a non-volatile solvent is equal to zero. Thus, the pressure of the solution is lesser than the vapour pressure of the solvent. For example, the freezing point of water is 0°C. The following formula expresses the freezing point depression of the solution:

ΔT_f = i × K_f× m

Here,

‘ΔT_f’ represents the freezing point depression
‘i’ represent Van’t Hoff factor
‘K_f’ is referred to as cryoscopic constant
‘m’ refers to the molality

Why does the Freezing Point of the Solvent Occurs?

The freezing point of the solvent occurs when a solute is added to the solution. The reasons are given below:

During the freezing point of the solvent, there is an equilibrium between the liquid and solid state of the solvent.
The vapour pressure of solid and liquid phases is equal.
Due to the addition of non-volatile solute molecules to the solution, the vapour pressure of the solution decreases more than the vapour pressure of the solvent.

Examples of Freezing Point

The seawater remains in liquid at a temperature below the freezing point of pure water. Its freezing point is below 0^oC. This is because of the salts present in the seawater.
Vodka is an example of a solution that has ethanol in water. Its freezing point is lower than water. However, the freezing point is higher than pure ethanol.
Many organisms are surviving in freezing climates due to the production of glycerol and sorbitol compounds in their body, which decreases the freezing point of their bodies.

Factors Affecting the Freezing Point

There are certain factors that affect the freezing point of the solvent, given below:

The physical and chemical changes that occur alter the freezing point of the substance.
The change in pressure of the substance also alters the freezing point of the substance.
The force of attraction between the molecules is directly proportional to the freezing point of the substance. The freezing point is low if the intermolecular forces of attraction between molecules are weak.

Uses Of Freezing Point of Depression

The freezing point depression formula is used to determine the molar mass of the solute.
It can also be used to measure the degree to which a solute dissociates in a solvent.
Sodium chloride is spread all over the road in cold areas with temperatures ranging from 0^oC to -15^oC. It helps to decrease the freezing point of water and prevent ice blocks.
In many cars and other automobile vehicles, a mixture of ethylene glycol and water is used to make radiator fluids in order to prevent the freezing of the radiator during cold seasons.

Practice Problems On The Freezing Point Of The Solvent

Q1. Which of the following is correct?

a. ΔT_f =( i×K_f) +m
b. ΔT_f = i+K_f×m
c. ΔT_f = i×K_f×m
d. ΔT_f = i×K_f+m

Ans: c. ΔT_f = i×K_f×m

Q2. Which of the following is used in the radiator fluid to prevent freezing?

a. Methane
b. Glycolic acid
c. Ethane
d. Ethylene glycol

Ans: d. Ethylene glycol

In many automobiles, ethylene glycol and water is used to make radiator fluids in order to prevent the freezing of the radiator during cold seasons.

Q4. Which of the following laws describes the freezing point depression?

a. Raoult’s Law
b. Faraday's Law
c. Newton’s Law
d. None of the above

Ans: a. Raoult’s Law

According to Raoult’s Law, the vapour pressure of a solvent decreases by adding a solute to the solution. This is the cause of the freezing point of the solvent.

Frequently Asked Questions

Q1. Is freezing an exothermic or endothermic reaction?
Answer: Freezing is an exothermic reaction similar to condensation and deposition.

Q2. What are the different phases of changes in matter?
Answer: There are six phases of changes that occur in nature. They are freezing, boiling, condensing, vaporising, sublimating, and deposition.

Q3. What is the difference between freezing and melting point?
Answer: Liquids have a certain temperature at which they turn into solid, which is known as the freezing point. Similarly, solids meltdown at certain temperatures, which is known as the melting point. There might be slight differences in the obtained quantities.