CBSE Class 12 Chemistry Notes: Solutions – Basics

Solution is a homogeneous mixture of two or more chemically non reacting substances whose composition can be varied within certain limits. A solution is regarded as a simple phase having more than one component.

A solution which contains only two components is called a binary solution. The component which is present in smaller amount is called the solute and the other present in larger amount is called the solvent.

The following table shows the list of solutions and their examples:

Solutions of Solids in Liquids:

• Saturated solution is a solution which remains in contact with excess of solute.
• The amount of solute dissolved per 100 g of solvent in a saturated solution at a specific temperature represents the solubility of the solute.
• For exothermic substances such as KOH, CaO, Ca(OH)₂,M₂CO₃, M₂SO₄ etc., solubility is inversely proportional to temperature. (M = Alkali metals)
• For endothermic substances such as NaCl, KNO3, NaNO2, glucose etc., solubility is directly proportional to temperature.

Solubility of Gases:

• Solubility of gases is mostly expressed in terms of absorption coefficient, that is, the volume of the gas (at NTP), dissolved by unit volume of solvent, at 1 atm pressure and a specific temperature.
• The solubility of a gas in a liquid depends upon:

1. Temperature Solubility is inversely proportion al to temperature as dissolution of a gas is exothermic in most cases.
2. Nature of gas Gases having a higher value of Vander Waals force of attraction, that is, gases that are more easily liquefied are more soluble. For example, SO2 and CO2 are more soluble in water than O2, N2 and H2.
3. Nature of solvent Gases which can ionize in aqueous solution are more soluble in water as compared to the other solvents.
4. Pressure of the gas (Henry’s law) According to this law, “At constant temperature, the solubility of a gas in a given volume of liquid is directly proportional to the pressure of the gas over the liquid.”

Henry’s law is obeyed only when

1. Pressure is not too high.
2. Temperature is not too low.
3. Gas does not dissociate.
4. Gas is not highly soluble in the solvent.
5. Gas does not chemically react with the solvent.

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