You are told to prepare a closed experimental environment ( a box) for student mice. The box volume will be 294 litres ( about `10 ft^(3)`) and the entire air volume will be changed every minute. The relative humidity of the air entering the box is to be controlled at 40% at `21^(@)C`. What weight of `H_(2)O` must be added to the flow of dry air per minute ? ( Equilibrium vapour pressure for `H_(2)O` at `21^(@)~= 19` torr )
( R =0.082 liter atm`mol e^(-1) deg ^(-1) `mol wt`: H_(2)O =18)`

Answer

2.2 g