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2 molal solution of a weak acid HA has a...

2 molal solution of a weak acid HA has a freezing point of `3.885^@C`. The degree of dissociation of this acid is _______ `xx10^(-3)` .(Round off to the Nearest Integer).
[Given : Molal depressing constant of water =1.85 K kg `mol^(-1)` Freezing point of pure water =`0^@C` ]

Text Solution

Verified by Experts

The correct Answer is:
50
`HAhArrH^(+)+A^(-)`
`1-alpha,alpha,alpha`
( `alpha` - degree of dissociation)
Van.t Hoff factor (i) `=1+ alpha`
Assuming given freezing point is `- 3.885^@C`
`DeltaT_f = ik_f .m `
`implies 3.885 = (1+alpha)xx1.85xx2 `
`implies (1+alpha)=1.05`
`alpha = 0.05 `
`=50 xx10^(-3)`
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