Question

A 300–mL volume of hydrogen is collected over water at 22 °C under a barometric pressure of 740 mmHg. What is the volume of this hydrogen, at the same temperature and barometric pressure, when dry? (vapor pressure of water at 22 °C = 20 mmHg)

the answer is 292 mL. PLEASE EXPLAIN HOW YOU GET THIS ANSWER :(

Answer 1

Initially it is given that V₁=300 ml of hydrogen gas is collected over water under pressure of P₁=740 -20 =720mm of Hg which means that hydrogen gas is under pressure of both vapour pressure of water as well as hydrogen but we have to account for pressure of hydrogen only so we subtract the vapour pressure of water from barometric pressure.

At same tempreature and pressure when dry condition is there then in that case the pressure exerted by hydrogen gas be just abe given by P₂=740 mm of Hg which is the barometric pressure and let V be the volume of hydrogen in this condition.

Using Boyle's law at same tempreature and pressure

P₁V₁ =P₂V₂

So V =(720*300)/740=292 ml