What are the Solutions?

Solutions can be considered as homogeneous mixtures which contain two or more than two chemical substances. The chemical substance which is the greater part is defined as solvent. And the chemical substance that is dissolved in a solvent is referred to as solute. Solution chemistry plays an important role in chemistry since it supports many commercial applications of solutions.

Solute and Solvent

In order to understand solutions and their compositions, one must know what are solvents and solutes in detail. Solutions can be considered as a system of solvents and solutes.

Definition of Solvents

A solvent is a chemical substance that can dissolve solid, liquid, or gaseous substances.

Water is referred to as a universal solvent since it can dissolve almost all chemical substances with some exceptions.

Definition of Solutes

The solute is a chemical substance that gets dissolved in a solvent.

For instance, when table salt (NaCI) is dissolved in water, water is the solvent, and table salt is the solute

Solubility

The solute is the component that dissolves in the solvent. The maximum amount of solute which can be dissolved in a solvent at a given temperature is referred to as solubility. Here the temperature is the important factor that alters the dissolving capacity of a solute in a solvent.

Solute + Solvent = Solution

When a solute is added to a solvent, it is not necessary to dissolve in the solvent. Some solutes will dissolve in a particular solvent while they may not be soluble in another one. For example, sugar and salt (sodium chloride) will easily dissolve in water. on the other hand, naphthalene or anthracene will not get soluble in water. however, they are easily soluble in benzene. Thus, all solutes are not soluble in all solvents.

'Like Dissolves Like'

There is a common principle regarding solubility which is ‘like dissolves like'. This can be explained as polar solutes will tend to dissolve in polar solvents and non-polar solvents will tend to dissolve in non-polar solvents. Since water is a polar solvent it will dissolve polar solutes like sodium chloride, potassium chloride, etc. While non-polar solvents like benzene will have the ability to dissolve non-polar solutes (most common organic compounds)

Crystallization

Crystallization is the process in which a solute leaves the solution as solid crystals. This happens when a solution is saturated (dissolved the maximum amount of solute insolvent). When the amount of solute balances the amount of solute crystalizing, the condition is called dynamic equilibrium.

Effect of Temperature and Pressure

Generally, the solubility of a solute in a solvent will be the same under a given temperature and pressure. When the temperature and pressure change the rate of solubility can also change. The increase in temperature will increase the kinetic energy of the molecules which will help in breaking the solute molecules more easily and rapidly.

The impact of temperature may vary depending upon the nature of the solutions. If the dissolution of solute into the solvent is an exothermic process (∆sol H < 0) the solubility will decrease with increase in temperature. While, if the dissolution of solute into the solvent is an endothermic process (∆H_sol> 0)the solubility will increase with the increase in temperature.

In the case of a solution formed by solid solute and liquid solvent, the pressure does not have any important role. This is because of the incompressible nature of solids and liquids.

Solubility of Solid in Liquid

When the solute added to the solvent is in solid-state, it becomes a solution of solid in a liquid. the process by which a solid solute dissolves in a liquid solution is referred to as dissolution.

Take the example of sugar crystals dissolved in water, here the sugar crystals are solute which is in solid-state. Water is the solvent and it is in a liquid state. Thus, this is solid in a liquid solution.

Solubility of Gas in Liquid

Gases are found to be soluble in solvents like water. For example, the dissolved oxygen in water is the basis of all maritime life. Hydrochloric acid, ammonia and carbon dioxide are also found to be soluble in water. the solubility of gases in a liquid solvent greatly depends on the temperature and pressure. When the pressure is increased, the solubility is also found to increase.

For gas to get soluble in a solvent, the solvent must provide enough space for the gas by moving its molecules apart. The first law regarding the solubility and pressure of the gas was proposed by Henry which is known as Henry’s law. According to Henry’s law solubility of a gas is directly proportional to the partial pressure of the gas. The proportionality constant is referred to as Henry’s constant

Ions in Solutions

All soluble ionic mixtures are strong electrolytes. They direct very well since they give an ample stock of ions in solutions. An electrolyte solution conducts electricity as a result of the development of ions in solutions. The larger the concentration of ions, the better the solutions conduct.

Colligative Properties

The properties of arrangements that rely upon the number of solute particles and are autonomous of their compound personality are called colligative properties. Colligative properties have been utilized to decide the molar mass of solutes. Solutes which separate in arrangement display molar mass lower than the genuine molar mass and those which partners show higher molar mass than their real qualities.

The properties which are colligative is given below,

• Vapor pressure lowering
• Boiling point elevation
• Freezing point depression
• Osmotic pressure

Practice Problem

Clarify what changes and what remains similar when 1.00L of an answer of NaCl is weakened to 1.80L.

(a) The number of moles consistently remains distinctive in a weakening. The focus and volume don’t change in a weakening.

(b) The quantity of moles consistently remains the equivalent in a dilution. The fixation and the volumes change in a weakening.

(c) The particle in the arrangement changes by the focus and the volume in a weakening

Solution: (b)

a. The quantity of moles consistently remains the equivalent in a weakening.

b. The fixation and the volumes change in a weakening.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses, especially for,

B.Sc. Chemistry

M.Sc. Chemistry