1.

0.5 molal aqueous solution of a weak acid (HX) is 20% ionised. If K_(f) of water is 1.86 K kg "mol"^(-1) , the lowering in freezing point of the solution is :

Answer»

0.56 K
1.12 K
`-0.56` K
`-1.12` K

Solution :`{:(,"HX",hArr,H^(+),+,X^(-)),("Initial moles",1,,0,,0):}`
If `ALPHA` is the DEGREE of DISSOCIATION, then moles after dissociation.
`{:(1-alpha,,,alpha,,alpha):}`
TOTAL moles after dissociation `=1-alpha+alpha+alpha=1+alpha`
`i=(1+alpha)/(1)=(1+0.2)/(1)=1.20`
`DeltaT_(f)=iK_(f)`
`=1.20xx1.86xx0.5=1.12K`


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