1.

The vapour pressure of water at 20^(@)C is 17.54 mm. When 20 g of a non-ionic substance is dissolved in 100g of water, the vapour pressure is lowered by 0.30 mm . What is the molecular weight of the substances

Answer»

`210.2`
`206.88`
`215.2`
`200.8`

SOLUTION :`(P_(o)-P_(s))/(P_(s))=(w)/(m)xx(M)/(W)`
`P_(o)=17.54 MM`
`P_(s)=17.24 mm`
M = 18
W = 100
w = 20
m = ?
`(17.54-17.24)/(17.24)=(20)/(m)xx(18)/(100)`
`(30)/(17.24)=(360)/(100M)`
`m=(360xx17.24)/(100xx30)rArr206.88`


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