Question

38.00 mL of moist nitrogen gas were collected at `27^(@)C` and 746.5 mm pressure. Calculate the volume of the gas at `0^(@)C` and 760 mm pressure, (Aq. Tension at `27^(@)C` is 26.5 mm).

Answer 1

`{:("Given Conditions","Final Conditions"),(V_(1)=38.0 mL,V_(2)=?mL),(P_(1)=746.5-26.5=720 mm,P_(2)=760 mm " "("Pressure of dry gas")),(T_(1)=27+273=300K,T_(2)=0+273=273 K):}`
Applying the general gas equation :
`(P_(2)V_(2))/(T_(2))=(P_(1)V_(1))/(T_(1)), i.e.," "(760xxV_(2))/(273)=(720xx38)/(300) :. V_(2)=(760xx38)/(300)xx(273)/(760)=32.76 mL`
Volume of nitrogen at `0^(@)C` and 760 mm pressure =32.76 mL.
Note carefully that in applying gas equation, pressure of dry gas is taken and not that of the moist gas.

Comments

Why have you taken the volume of nitrogen as 38ml when water vapour also accounts for some amount of the volume

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The effect of moisture on volume is less as compared to the pressure.