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Question
Calculate the volume of dry air at STP that occupies 28 cm3 at 14°C and 750 mmHg pressure when saturated with water vapour. The vapour pressure of water at 14°C is 12 mmHg.
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Solution
Pressure due to dry air,
P = 750 - 12 = 738 mm
V = 28 cm3
T = 14°C = 14 + 273 = 287 K
P1 = 760 mmHg
V1= ?
T1 = 0°C = 273 K
Using gas equation,
`("P" "V")/"T" = ("P"_1 "V"_1)/"T"_1`
`(738xx28)/287 = (760xx"V"_1)/273`
`"V"_1 = 25.9 "cm"^3`
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