Solutions

Solution

A homogenous mixture of 2 or more pure substances is called a solution.

Solute

The substance present in smaller quantity is called the solute.

Solvent

The substance present in larger quantity is called solvent.

Solute: Solid Solvent: Liquid

Salt in water

Benzoic acid in benzene

Sugar in water

Seawater

Solute: Solid Solvent: Solid

Metal alloys like brass and bronze

Solute: Solid Solvent: Gas

Iodine in air

Solute: Liquid Solvent: Liquid

Gasoline

Petrol

Ethanol in water

Solute: Liquid Solvent: Solid

Amalgam of mercury with metals (Zn-Hg) (Na-Hg)

Solute: Liquid Solvent: Gas

Chloroform in N2

Solute: Gas Solvent: Liquid

Carbonated water (CO2 in H2O)

Solute: Gas Solvent: Solid

H2 in palladium

H2 over nickel

Solute: Gas Solvent: Gas

Air

Solubility of a solution

Amount of solute per unit volume of saturated solution at that temperature is called solubility of a solution.

Unit of solubilty

mol/L

First factor affecting solubility of a solute in solvent

a. Polar substances dissolve in polar solvents. Here solute-solute, solute-solvent, solvent-solvent interactions are of same magnitude.

Ex- NaCl dissolves in H2O

b. Non polar substances dissolve in non polar solvents.

Ex- Cholesterol dissolves in benzene

c. Sugar dissolves in water due to formation of intermolecular hydrogen bonding between sugar and water.

Effect of temperature of solubility of solute in solvent

1. Solubilities of NaBr, NaCl and KCl increase only slightly with rise in temperature.

2. Solubilities of KNO3, NaNO3 AND KBr increase appreciably with rise in temperature.

3. Solubility of Na2SO4 decrease with rise in temperature.

4. For gas dissolved in liquid, solubility of gas decreases with increase in temperature.

Henry’s Law

Solubility of a gas in liquid is directly proportional to the pressure of the gas over the solution.

S = K*P

Define Kh

It is defined as the solubility of a gas in liquid when pressure of the gas over the solution is 1 bar.

Exceptions not following Henry’s laws

NH3 and CO2

Raoult’s Law

The partial vapor pressure of any volatile component of solution is equal to vapor pressure of pure component multiplied by its mole fraction in the solution.