A mixture of nitrogen and water vapours is admitted to a flask which contains a solid drying agent immediately after admission, the pressure of the flask is 760 mm. After some hours the pressure reached a steady value of 745 mm. (a) Calculate the composition, in mol and percent of original mixture. (b) If the experiment is done at $20^0 C$ and the drying agent increases in weight by 0.15 g. What is the volume of the flask? (the volume occupied by the drying agent may be ignored)?

The drying agent absorbs the water vapour, so the pressure drop from 760 mm to 745 mm gives the initial partial pressure of water vapour as 15 mm Hg. Using the ideal gas law, PV = nRT, the volume is calculated as (15/760) atm multiplied by 0.0821 and 293 K, divided by the 0.00833 moles of water absorbed (0.15 g / 18 g/mol). This calculation results in a flask volume of 10.2 L.

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