Question

Explain the following terms (a) Mole fraction (b) Molarity (c) Molality

Answer 1

Mole fraction:

It is the ratio of number of moles of a particular component of a solution to the total number of moles of the solution.
If a substance ‘A’ dissolves in substance ‘B’ and their number of moles are n_A and n_B , repsectively, then the mole fraction of A and B are given as :

\(Mole \ fraction \ of \ A=\frac{ No.\ of \ moles\ of\ A}{ No.\ of\ moles\ of\ solution}\)

⇒\(n_A\over n_A+n_ B\)

\( Mole \ fraction \ of \ B = \frac{Number \ of \ moles \ of\ B}{ Number\ of\ moles\ of\ solution}\)

⇒\(n_B\over n_A+n_ B\) 

Molarity:

Molarity is defined as the number of moles of the solute present in 1 litre of the solution. It is the most widely used unit and is denoted by M. Molarity is expressed as follows:

\( Molarity \ (M) =\frac{ Number\ of\ moles\ of\ solute}{ Volume \ of\ solution\ in \ litres}\) 

Molality:

Molality the number of moles of solute present in 1 kg of solvent. It is denoted by m. Molality is expressed as follows:

\( Molality \ (m) = \frac{Number\ of\ moles\ of\ solute }{Mass \ of \ solvent \ in \ kilograms}\)