Question

To 500 `cm^(3)` of water, `3.0xx10^(-3)` kg of acetic acid is added. If 23% of acetic acid is dissociated what will be depression in freezing point ? `K_(f)` for water is 1.86 K kg `mol^(-1)` and density of water is 0.997 g `cm^(-3)`.
A. `0.186 K`
B. `0.228 K`
C. `0.372 K`
D. `0.556 K`

Answer 1

Correct Answer - b
`CH_(3)COOH` dissociates in water as :
`CH_(3)COOHhArrCH_(3)COO^(-)+H^(+)`
`alpha=(i-1)/(n-1)or 0.23=(i-1)/(2-1)`
`i=1+0.23=1.23`
`"Molality (m)"=W_(B)/M_(B)xx(1000)/W_(A)`
`=((3g))/((60g))xx1000/((500xx0.997))`
`=((3g)xx1000)/((60g)xx(498.5g))=0.1`
`DeltaT_(f)=ixxK_(f)xxm`
`=1.23xx1.86xx0.1=0.228 K`.