(a) What is meant by: (i) Colligative properties (ii)Molality of a solution
(b) What concentration of nitrogen should be present in a glass of water at room temperature? Assume a temperature of `25^(@)C`, a total pressure of `1` atmosphere and mole fraction of nitrogen in air of `0.678`. [`K_(H)` for nitrogen `=8.42xx10^(-7) M//mm Hg`]

Explanation

(a) (i) Colligative properties : The properties of solution which depend upon the number of solute particles and not upon the nature of the solute particles are known as colligative properties. There are four colligative properties
(i) Relative lowering of vapour pressure
(ii) Elevation of Boiling point
(iii) Depression of Freezing point
(iv) Osmotic pressure.
(b) Given `P_(N_(2))=1`atm.
Applying Henry 's law
`P_(N_(2))= K_(H).X_(N_(2))`
`X_(N_(2))=(P_(N_(2)))/(K_(H))=(1)/(8.42xx10^(-7))`
Since , `X_(N_(2))=(n(N_(2)))/(n(N_(2))+n(H_(2)O))~~(n(N_(2)))/(n(H_(2)O))`
`n(N_(2))=X_(N_(2)).n(H_(2)O)` " " `[:'n(H_(2O))=(1000)/(18)=55.5 "moles"]`
`=(1)/(8.42xx10^(-7))xx55.5`
`=6.59xx10^(7)` moles.
Hence concentration of nitrogen in water `=6.59xx10^(7)"mol"L^(-1)`.