A solution is a homogeneous mixture of two or more substances.

The substance with largest amount is called solvent and other substances with lesser amounts are called solute.

Binary solution : A solution having only two components is called a binary solution.

Types of binary solutions : On the basis of the states of solvent, there are three types of solutions as follows:

1. Solid solutions : A solution in which the solvent is a solid is called a solid solution.

2. Liquid solutions : A solution in which the solvent is a liquid is called a liquid solution.

3. Gaseous solutions : A solution in which the solvent is a gas is called a gaseous solution.

Concentration : The amount of solute present in a solution is called the concentration of the solution.

◆ Methods of expressing concentration :

1. Strength : The amount of the solute in grams present in one litre of a solution is called strength.

i.e. Strength = Mass of solute / Volume of solution(in L)

2. Mass Percent : The mass percent of the solute is expressed as follows :

Mass % = Mass of solute×100 / Mass of the solution

3. Volume Percent : The volume percent of a solution is defined as follows:

Volume % = Volume of the solute × 100/ Volume of the solution

4. Mole Fraction : If a binary solution has two components A and B having nA and nB moles then their mole fraction is denoted by xA & xB respectively where

xA = nA/(nA + nB) &  xB = nB/(nA + nB)

Key Point : xA + xB = 1

5. Molality : The molality of a solution is defined as the moles of solute per kilogram of solvent i. e.

Molality = Moles of solute / Mass of solvent(In Kg)

Key Point : Molality is denoted by ‘m’.

6. Molarity : The molarity of a solution is defined as the number of moles per litre of the solution i. e.

Molarity = Moles of the solute /Volume of the solution(In Litre)

Key Point : I. Molarity is denoted by ‘M’.

II. If the molarity of a solution changes from M1 to M2 and it’s volume changes from V1 to V2 then M1V1 = M2V2

III. Molality doesn’t change with change in temperature because it depends upon mass whereas molarity is affected by temperature because of its dependence on volume.

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