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Two grams of benzoic acid (C(6)H(5)COOH)...

Two grams of benzoic acid `(C_(6)H_(5)COOH)` dissolved in `25.0 g` of benzene shows a depression in freezing point equal to `1.62 K`. Molal depression constant for benzene is `4.9 K kg^(-1)"mol^-1`. What is the percentage association of acid if it forms dimer in solution?

A

(a) `90.2%`

B

(b) `99.2%`

C

( c) `9.8%`

D

(d) `0.8%`

Text Solution

Verified by Experts

The correct Answer is:
B
`Delta T = (1000 xx K_(f) xx w)/(m xx W)`
`= (1000 xx 4.9 xx 2)/(122 xx 25) = 3.213`
`i = (Delta T_(exp.))/(Delta T_(cal.)) = 1-alpha + (alpha)/(n)`
`:. (1.62)/(3.213) = 1- alpha + (alpha)/(2)`
`:. alpha = 0.992` or `99.2%`
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