1.

(a) A solution containing `0.5g` of naphithalene in `50g C Cl_(4)` yield a boiling point elevation of `0.4K`, while a solution of `0.6g` of an unknown solute in the same mass of the solvent gives a boiling point elevation of `0.65K`. Find the molar mass of the unknown solute. (b) The boiling point of a solution of `0.1g` of a substance in `16g` of ether was found to be `0.100^(@)C` higher that of pure ether. What is the molecular mass of the substance. `K_(b)` (ether) `=2.16K kg "mol"^(-1)`

Answer» Correct Answer - (a) `M=94.52,` (b) `m=135`
(a) Let the molar mass of the unknown solute is `m`
Now, for nephthalene solution
`DeltaT_(b)=K_(b)="molality"`
`0.4=K_(b)xx(0.5//128)/(50//1000)` .... (i)
for unknown solution
`0.65=K_(b)xx(0.6//m(50//1000)` ....(ii)
Dividing eq. (i) by (ii), we get
(b) `DeltaT_(b)=K_(b)` molality
`0.100=2.16xx(0.1//m)/(1000)`


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