REACTIONS IN SOLUTION
Molarity
 Molarity (M) is defined as number of moles of solute dissolved in one litre (or one cubic decimetre) of solutio
 where W_{B} is the mass of solute and M_{B} is the molar mass of the solute.
 For dilution; where M_{1} is initial molarity, V_{1} is initial volume, M_{2} is final molarity and M_{2} is final volume.
 M_{1}V_{1} = M_{2}V_{2}
 are called molar, decamolar, decimolar, pentimolar, semimolar and centimolar solution respectively.
Molality
 Molality (m) is defined as the number of moles of the solute per kilogram (kg) of the solvent and is expressed as:
 Molality (m) = (Given mass / molecular mass) * ( 1/mass of solvent in Kg )
 Its SI unit is moles / Kg
 It is represented as m or molal solution.
Difference between Molarity and Molality
Molarity 
Molality 
The molarity of a given solution is defined as the total number of moles of solute per litre of solution. 
Molality is defined as the total moles of a solute contained in a kilogram of a solvent. 
Mathematical expression is M = number of moles of the solute / Volume of solution given in terms of litres. 
The mathematical expression m = Number of moles of solute / Mass of solvent in Kg

Depends on the volume of the whole solution. 
Depends on the mass of the solvent. 
Unit sign expressed as (M). 
Unit sign expressed as ( ). 
Molarity has a unit of moles/litre. 
Molality has a unit of moles / kg 
Vapour density
 Vapor density is the ratio of the mass of a volume of a gas, to the mass of an equal volume of hydrogen, measured under the same conditions of temperature and pressure.
 It is a unitless quantity.
Relation between Vapour density and Molecular weight
 Molecular weight = 2 X Vapour density
Normality
 Normality (N) It is defined as the number of gequivalents of solute per litre of solution or as the number of mgequivalents of a substance per millilitre of solution.
 If specific gravity is known, normality is calculated as