Question

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

Answer 1

`W_(B)=(M_(B)xxDeltaT_(b)xxW_(B))/K_(b)`
Molar mass of sucrose `(C_(12)H_(22)O_(11))(M_(B))=12xx12+22xx11xx16=342"g mol"^(-1)`
mass pf water`(W_(B))=500g -0.5 kg`
Elevatio in b.p. `(DelataT_(b))=100^(@)C-99.63^(@)C=37^(@)C=0.37 K`
Molal elevation constat `(K_(b))=0.52 K kb mol^(-1))`
`W_(B)=((342g mol^(-1))xx(0.37K)xx(0.5 kg))/((0.52 K kg mol^(-1)))=121.7g`