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JEE Advanced levelSingle correct optionDifficulty 3 of 3g2090

Piperidine and aniline have conjugate acids with pKa 11.1 and 4.6 respectively. The ratio $K_{b} (piperidine) / K_{b} (aniline)$ in water at 298 K is approximately

A $3.2 \times 1 0^{5}$
B $3.2 \times 1 0^{6}$
C $1.0 \times 1 0^{7}$
D $1.0 \times 1 0^{- 7}$

Answer: B

K_{b}

ratio

= 1 0^{p K_{b} (aniline) - p K_{b} (piperidine)}

.

p K_{b}

values: piperidine

14 - 11.1 = 2.9

, aniline

14 - 4.6 = 9.4

. Ratio

= 1 0^{9.4 - 2.9} = 1 0^{6.5} = 3.2 \times 1 0^{6}

.

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