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Question
Pressure exerted by saturated water vapour is called aqueous tension. What correction term will you apply to the total pressure to obtain pressure of dry gas?
Solution
Whenever a gas is collected over water, it is moist and saturated with water vapour which exerts their own pressure. The pressure due to water vapour is called aqueous tension. Thus, the total pressure of the gas \[\ce{P_{(moist gas)}}\] is
\[\ce{P_{moist gas} = P_{drygas}}\]
Thus P drygas is given as
\[\ce{P_{drygas} = P_{moist gas}}\] – aqueous tension. Hence, the correction term applied to the total pressure of the gas in order to obtain pressure of dry gas is \[\ce{P_{moist gas}}\] – aqueous tension.
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