1.

What concentration of nitrogen should be present in a glass of water at room frmperatrure ? Assume a temperature of `25^(@)C`, a total pressure ofone atmosphere and molefraction of nitrogen in air as 0.78 `(K_(H)"for ni trogen"=8.42x10^(-7)M/mm Hg)`.

Answer» Acoording to available information.
`p_(N_2)=x_(N_2)"is air"xx P_("total")=0.78xx760 mm Hg=592.8 mm Hg,`
`K_(H)=8.42xx10^(-7)M//mm Hg`
Mole fraction of `N_(2)(x_(N_(2)))=K_(H)xxP_(N_2))`
`=(8.42xx10^(-7)M/mm Hg)xx(592.8mmHg)`
`=4991.376xx10^(-7)M=4.99xx10^(-4)M=4.99xx10^(-4) `
`x_(N_2)=n_(N_2)/(n_(N_2)+n_(H_(2)O))=n_(N_2)/n_(H_(2)O)or n_(H_2)=x_(N_2)xxn_(H_(2)O)`
`(n_(N_2) "has been neglected in this expression since the gas isvery little soluble in water")`
`n_(N_2)=(4.99xx10^(-4))xx(1000g//18 g mol^(-1))`
` =4.99xx10^(-4)xx55.55 `mol
`=0.0277 mol=2.77xx10^(-4)` mol


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