2.26 g of impure ammonium chloride were boiled with 100 mL of NaOH solution till no more ammonia was given off. The excess of NaOH solution left over required 30 mL `2N H_(2)SO_(4)` for neutralisation. Calculate the percentage purity of the salt.
(H=1, N=14, O=16, Na=23, S=32, Cl=35.5)