Solution and Its Types

Solution and Its Types

Solution and Its Types

Definition of Solution

• A homogeneous mixture of two or more pure non-reacting substances whose composition can be varied within certain limits is called a solution.

Binary and Ternary Solutions

• When a solution is composed of only two components, it is called a binary solution.

Example:

• Solution of NaCl in water.

• Similarly, a solution containing three components is called a ternary solution.

Example:

• A solution of NaCl and KCl in water.

Components of a Binary Solution

In a binary solution, there are two components:

1. Solute

2. Solvent

The component which is in smaller proportion or amount in solution is called solute, while the one present in excess is called solvent.

Example: In a binary solution of sugar in water, sugar acts as a solute, while water is the solvent.

Solvent and Dielectric Constant

• The better solvent is one which has a high dielectric constant.

• Water is a universal solvent because it has a high dielectric constant.

Classification of Binary Solutions Based on States of Matter

Types of Solutions Based on Solute Amount

Saturated Solution

• A solution that can not dissolve any more of the solute at a given temperature is called a saturated solution.

Unsaturated Solution

• A solution in which more of the solute can be dissolved at a given temperature is known as an unsaturated solution.

Supersaturated Solution

• A supersaturated solution at a particular temperature is one that is more concentrated (contains more solute) than its saturated solution at that temperature.

Dilute Solution

• It is the solution in which the amount of solute present is rather small compared to the mass of solvent.

Concentrated Solution

• It is the solution in which the amount of solute present is relatively large for a given mass of solvent.

Solubility

Definition

The maximum amount of solute in grams which can be dissolved in 100 g of solvent to form a saturated solution at a particular temperature is called the solubility of that solute.

Formula:

• Solubility = mass of solute in grams of solvent × 100 \text{Solubility} = \frac {\text{mass of solute in grams}} {\text{mass of solvent}} \times 100 Solubility = mass of solvent/mass of solute in grams × 100

Factors Affecting Solubility

The solubility of the substance depends upon the:

• Nature of solute and solvent

• Temperature

• Pressure

Effect of Temperature on Solubility

Endothermic Dissolution

The solubility of the substance increases continuously with an increase in temperature if the process of dissolution is endothermic.

Examples:

• The dissolution of NaNO₃, KNO₃, NaCl, and KCl in water is an endothermic process. So, their solubility increases with an increase in temperature.

Exothermic Dissolution

If the process of dissolution is exothermic in nature, the solubility of a substance decreases with an increase in temperature.

Examples:

• The solubility of cerium sulphate, lithium carbonate, sodium carbonate monohydrate (Na₂CO₃·H₂O), etc., decreases with an increase in temperature.

Transition Temperature Example

The solubility of Na₂SO₄·10H₂O first increases up to 32.4°C and then begins to decrease.

So, 32.4°C is the transition temperature.

• Above 32.4°C → Na₂SO₄

• Below 32.4°C → Na₂SO₄·10H₂O

Gaseous Solubility and Temperature

• The solubility of a gas decreases with an increase in temperature because the dissolution of a gas in a liquid is exothermic in nature.

Effect of Pressure on Solubility

• Pressure has very little effect on the solubility of a solid in a liquid because solids and liquids are highly incompressible.

• The solubility of a gas in a liquid increases with an increase in pressure.

Henry’s Law

• The effect of pressure on the solubility of a gas in liquid was studied by Henry in 1803 and is called Henry's law.

• It states that the mass of a gas dissolved in a given volume of the liquid at constant temperature is directly proportional to the pressure of the gas present in equilibrium with the liquid.

Colligative Properties

Those properties of ideal solutions which depend only on the number of particles of the solute (molecules or ions) dissolved in a definite amount of the solvent are called colligative properties.

Important Colligative Properties

The important colligative properties are:

(i) Relative lowering of vapour pressure.

(ii) Osmotic pressure.

(iii) Elevation of boiling point.

(iv) Depression in freezing point.

These properties do not depend on the nature of the solute.

Semipermeable Membranes

These are the membranes which allow only the movement of the solvent molecules through them. These may be naturally occurring, such as parchment, cellophane, or the bladder of goat or pig.

Chemically semipermeable membranes have also been prepared.

Example: When aqueous solutions of potassium ferrocyanide and copper sulphate are mixed in a porous pot, the gelatinous precipitate of copper ferrocyanide fills in the pores of the porous pot and acts as a semipermeable membrane.

Osmosis

Definition

• The spontaneous flow of the solvent molecules from the solvent to the solution or from a less concentrated solution to a more concentrated solution through a semipermeable membrane is called osmosis.

Difference Between Osmosis and Diffusion

The basic difference between osmosis and diffusion is that:

(i) In osmosis there is only flow of solvent molecules, and that too through a semipermeable membrane, but in diffusion, the solvent as well as the solute molecules move directly into each other.

(ii) Osmosis takes place from lower concentration to higher concentration, while diffusion takes place from higher concentration to lower concentration.

Types of Solutions

True Solution

• The true solution is a homogeneous solution in which size of solute particles is less than 10 m.

• In a true solution, the solute particles and solvent molecules cannot be distinguished even under a microscope.

Example:

• Sodium Chloride in water.

Suspensions

• A suspension is a heterogeneous solution in which the size of solute particles is more than 10 m.

• The particles of suspensions are visible to the naked eye or under a microscope.

Colloidal Solution

• A colloidal solution is a heterogeneous solution in which size of particles of dispersed phase lies between 10 m and 10 m.

• The colloidal particles can pass through ordinary filter paper but cannot pass through animal membrane.

• The colloidal particles cannot be seen by the naked eye, but they can be seen by ultramicroscope.

Examples: Milk, gum, blood, ink, etc.

Dispersion System

A system consisting of a substance distributed as very small particles of a solid, droplets of a liquid or tiny bubbles of a gas in a suitable medium is called a dispersion system.

The distributed substance is called the dispersed phase, whereas the medium in which it is dispersed is known as the dispersion medium.

Types of Colloidal Systems

Sols

• The colloidal systems with solid as the dispersed phase and liquid as the dispersion medium are known as sols.

• Rubber gloves are manufactured from rubber soles by the process of electroplating.

Aerosols

• The colloidal systems with solid or liquid as the dispersed phase and gas as the dispersion medium are known as aerosols.

• In smoke, the dispersed phase is solid, and the dispersion medium is gas.

• In fog, the dispersed phase is liquid, and the dispersion medium is gas.

Note:

• When the dispersion medium is water, alcohol or benzene, then it is aquasol (or hydrosol), alcosol or benzosol, respectively.

Foam

• Foam is a colloidal solution in which the dispersed phase is gas and the dispersion medium is liquid.

Properties of Colloidal Solutions

Brownian Movement

• The continuous zig-zag movement of colloidal particles in the dispersion medium in a colloidal solution is called Brownian movement.

• It is due to unequal bombardment of the moving particles of dispersion medium on colloidal particles.

Tyndall Effect

• When a beam of light is allowed to pass through a colloidal solution, the colloidal particles can be seen. This effect is called the Tyndall effect.

• The Tyndall effect arises due to scattering of light by colloidal particles present in a colloidal solution.

Purification and Separation Processes

Dialysis

• The process of separating the particles of colloids from those crystalloids by diffusion of the mixture through an animal membrane (or parchment membrane) is known as dialysis.

• It is the process of purification of colloidal solution.

Coagulation (Flocculation)

• The colloidal particles are either positively or negatively charged particles.

• When an electrolyte is added to a colloidal solution, the particles of the colloidal solution take up the oppositely charged ion of the added electrolyte and get neutralised.

• The ion responsible for the neutralisation of charge on colloidal particles is called the coagulating ion or flocculating ion, and the process is called coagulation.

Electrophoresis

• The movement of colloidal particles towards a particular electrode under the influence of an electric field is called electrophoresis.

• The positively charged colloidal particles move towards the cathode, and the negatively charged colloidal particles move towards the anode.

Final Thoughts

A solution is a homogeneous mixture of two or more non-reacting substances whose composition can vary within limits. When a solution contains two components, it is called a binary solution, and when it has three, it is a ternary solution. The smaller component is the solute, and the larger one is the solvent.

Solutions can be solid, liquid, or gaseous, depending on the states of their components. They are further classified as saturated, unsaturated, supersaturated, dilute, or concentrated based on solute amount.

The solubility of a substance depends on temperature, pressure, and the nature of solute and solvent, forming the foundation for understanding colligative properties in chemistry.