(a) What is meant by : Colligative properties
(b) What concentration of nitrogen should be present in a glass of water at room themperature ? Assume a temperature of `25^(@)` C , a total pressure of 1 atmosphere and mole fraction of nitrogen in air of 0.78 `[K_(H) " for nitrogen"=8.42xx10^(-7)M//mmHg]`

Answer

(a) (i) Colligative Properties: These are properties of a solution which depend upon the number of paarticles and helpful for determination of molecular weight of solute.
(ii) Molality of a solution means of that number of solute in a given weight of solvent which is preseent in `kg`.
`m=("No. of moles of solute"xx1000)/("Wt. of solvent" Kg.)`
`(b) `T=25^(@)C+273=298K`
Total pressure `=1` atm.
`N_(2)=K_(H)xxN_(2)`
`P_(N_(2))=` Partial pressure of Nitrozen.
`K_(H)=` Henry's constant
`X_(n_(2))=` Mole fraction of `N_(2)`
`P_(N_(2))=8.42xx10^(-7)xx0.78`
`P_(N_(2))=6.56xx10^(-7)` atm.
For conc.
`PV=nRT`
`P=(n)/(V)RT ; C=(n)/(v)`
`P=CRT ; C=(6.56xx10^(-7))/(24.46)`
`C=0.268xx10^(-7) m//litre`