Ideal solution

Introduction

Solutions were formed when different types of compounds are mixed. Mainly by the dissolution of solute on a solvent. There are two types of solutions; they are homogeneous and heterogeneous solutions. The solutions that possess uniformity in their properties are homogeneous.

While the one which doesn't have any uniformity in their properties are heterogeneous solutions. There are many laws associated with solutions. Raoult's law is one such law. The French chemist François-Marie Raoult discovered Raoult's law in the year 1880 for explaining the ideal solution. This law mainly focuses on the properties of ideal solutions. But it also works in some solutions that are very dilute.

What is an Ideal Solution?

The mixture of substances is a solution. Ideal solutions are a homogeneous mixture of Ideal solutions of Raoult's law for a broad extent of concentrations. The physical properties of ideal solutions are linearly related to the properties of pure substances such as solute and solvent. The interaction of the different molecules of different components is the same as the interaction between molecules of the same component itself. This means that there is no particular reaction or interaction between molecules of solute and solvent. This is similar to ideal gas molecules which is why it is named the ideal solution. But unlike the ideal gas molecules, the molecules present in ideal solutions exert some force on each other. When these forces become equal the solution is said to be ideal.

The solution is formed by the mixing of substances that have almost similar molecular mass and the same intermolecular forces. And every molecule is easily distinguishable even though it has formed a solution. For such solutions, the value of enthalpy of solution is zero. That is $\mathrm{\Delta\:H_{solution}\:=\:0}$. Ideal solutions can be prepared by dissolving two substances that have almost similar molecular mass. For example, the mixture of toluene and benzene will make an ideal solution and is because of its similarity with molecular mass.

Characteristics of an Ideal Solution

The characteristics of the ideal solution are very unique. And is the reason why an ideal solution is very important. Some of the characteristic behaviours of ideal solutions are pointed out below.

• For a solution to form there must be two different compounds such as X and Y. The dissolution of these two compounds will result in some sort of intermolecular forces. And they are $\mathrm{X\:-\:X\:,\:Y\:-\:Y,\:and\:X\:-\:Y}$ interactions. For an ideal solution, all the interaction between two compounds is the same.

• The thermodynamic quantities of ideal solution such as $\mathrm{\Delta\:_{mix}H\:=\:0\:and\:\Delta\:_{min}V\:=\:0}$.

• The compound used for making an ideal solution must have a similar molecular mass and structure.

• The separation of respective components present in the ideal solution does not need any complex process, simple fractional distillation can be used for the separation.

• For an entire range of concentrations, the ideal solution obeys Raoult's law.

What is Raoult's Law and Derive it?

Raoult's law deals with the partial vapour pressure of solvents. According to Raoult's law, the partial vapour pressure of a solution is identical to the product of vapour pressure of true solvent and mole fraction of the corresponding solution formed. Mathematically it can be conveyed as,

$$\mathrm{P_{solution}\:=\:X_{solvent}\:P_{solvent}^{0}}$$

Where,

$\mathrm{X_{solvent}\:=\:solvents\:mole\:fraction}$

$\mathrm{P_{solution}\:=\:solutions\:vapour\:pressure}$

$$\mathrm{P_{solvents}^{0}\:=\:pure\:solvents\:vapour\:pressure}$$

For a mixture obtained by the dissolution of A and B, the equation for Raoult's law becomes,

$$\mathrm{P_{A}\:=\:X_{A}\:P_{A}^{0}}$$

$$\mathrm{P_{B}\:=\:X_{B}\:P_{B}^{0}}$$

The total vapour pressure associated with the solution can be calculated as,

$$\mathrm{P_{r}\:=\:X_{A}\:P_{A}^{0}\:+\:X_{B}\:P_{B}^{0}}$$

In this way, total vapour pressure can be calculated using Raoult's law.

AngelVelOre, Presion de vapor disoluciones reales, CC BY-SA 4.0

What is the Importance of Raoult’s Law?

There are many important aspects to this law. Some of the importance of Raoult's law is explained below

• Raoult's law explained the ideal solution.

• Raoult's law also explains that the vapour pressure of the mixture is always less than the vapour pressure of the true solvent.

• The vapour pressure associated with a non-volatile solute is also explained with the help of Raoult law.

• Raoult's law explained that all solids and liquids compounds have a vapour pressure.

• Raoult's law explained the dynamic equilibrium between liquid and vapour particles.

Properties of an Ideal Solution

Some of the properties of ideal solutions are explained in the below points.

• There will not be any change in enthalpy upon mixing components that will form an ideal solution.

• The interactions present between molecules present in the ideal solution is the same as that of individual molecules interaction. This means that the solute-solute and solute-solvent interactions are the same.

• The activities of components present in an ideal solution are equal to the mole fraction.

• The properties of solvent rely only on the concentration of solute particles.

• The intermolecular forces are not zero in the case of ideal solutions but are the same for all types of interactions.

Conclusion

Ideal solutions are a type of solution that is different from normal solutions. They show ideality in some behaviour because of the presence of components that have an almost similar structure and molecular masses. The characteristic properties shown by the ideal solution are different. The interaction present between components of ideal solutions is the same.

For an ideal solutionB, there will not be any change in the enthalpy of a solution upon dissolving two different components. The volume change is zero after dissolving two components for forming an ideal solution. Ideal solutions of Raoult's law deal with a vapour pressure of a mixture. The mixture of toluene and benzene is an example of an ideal solution that follows all the criteria of the ideal solution.

FAQs

1. Give some examples of ideal solutions?

Some examples are N-heptane and n-hexane, Chlorobenzene and bromobenzene, Ethyl bromide and ethyl iodide, etc

2. What is a non-ideal solution?

A solution that doesn't obey any of the criteria of an ideal solution is a non-ideal solution. The intermolecular forces between components present in non-ideal solutions are not the same. And also, non-ideal solutions will not follow Raoult's law.

3. Given an example of a non-ideal solution?

There are many examples of non-ideal solutions, and it is not a complex process to produce non-ideal solutions compared to ideal solutions. One such example of a non- ideal solution is the mixture of acetone and chloroform.

4. What are ideal gases?

It is a hypothetical concept in which gas molecules of the ideal type do not have any interactions and are only involved in an elastic collision. They show different properties compared to real gases.

5. What is Henry's law?

The law focuses on the dissolution of the gas in liquids. The gas dissolved in a liquid has a weight similar to the pressure of the gas on the liquid. This law only explains the dilute solutions and also gases with low pressure. So, the solubility of a particular gas is linearly associated with its pressure.