A gas occupies 100 mL when collected over water at 15°C and 750 mm pressure. It occupies 92 mL in dry state at N.T.P. Find the vapour pressure of water (aqueous tension) at 15°C

Given conditions                     At N.T.P P1=750mm−pmm              P2=760mmV1=100mL                             V2=92mLT1=15+273=288K              T2=273K  P1V1T1=P2V2T2;(750-p)mm×100ml288K=760mm×92mL273K (750×100×273)−(100×273p)=760×92×28820475000−27300p=20136960;27300p=338040∴  p=33804027300=12.38mm