Question

The boiling point of water at `750mm Hg` is `99.63^(@)C`. How muCHM sucrose is to be added to `500 g` of water suCHM that it boils at `100^(@)C`.

Answer 1

Correct Answer - `1108.2g`
`T_(b)(H_(2)O` at `750mm ` of pressure `=99.63^(@)C`,
`T_(b)(` solution `)=100^(@)C`
`DeltaT_(b)=100-96.63^(@)=3.37^(@)`
`(` Note the difference in Kelvin and degree centrigrade is same `)`
`W_(1)=500g,Mw_(1)(H_(2)O)=18gmol^(-1)`
`Mw_(2)(`Sucrose`)=342 g mol^(-1), W_(2)=?`
Applying the formula,
`DeltaT_(b)=K_(b)xxm=K_(b)xx(W_(2)xx1000)/(Mw_(2)xxW_(1))(K_(b)=0.52K kgmol^(-1))`
`3.37k=0.52xx(W_(2)xx1000)/(342xx500)`
`:. W_(2)=(3.37Kxx342g mol^(-1)xx500g)/(0.52K kg mol^(-1)xx1000)`
`=1108.2g`