1.

A solution containing 0.2563g of naphthalene (molecular mass = 128) in 50g of carbon tetrachloride yields a boiling point elevation of `0.201^(@)C` while a solution of 0.6216g of an unknown solute in the same mass of the solvent gives a boiling point elevation of `0.647^(@)C`. Find the molecular mass of the unknown solute.

Answer» We know that,
`K_(b)=(DeltaT_(b)xxWxxm)/(1000xxw)`
For `C Cl_(4),K_(b)=(0.201xx50xx128)/(1000xx0.2563)=5.019`
`K_(b)` is now used in the second part of the problem
`m=(1000xxK_(b)xxw)/(DeltaT_(b)xxW)`
`=(1000xx5.019xx0.6216)/(0.647xx50)=96.44`.


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