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JEE Advanced levelOne or more correct optionsDifficulty 3 of 3g2039

Use pKa values: phenol 10.0, phthalimide 8.3, ethanol 15.9, nitromethane 10.2. Which of these are more than 99% ionised in an aqueous solution buffered at pH 13.0?

Aphenol
Bphthalimide
Cethanol
Dnitromethane

Answer: A, B, D

Fraction ionised

= 1/ (1 + 1 0^{p K_{a} - pH})

. Phenol:

1/ (1 + 1 0^{- 3.0}) = 0.9990

. Phthalimide:

1/ (1 + 1 0^{- 4.7}) = 0.99998

. Nitromethane:

1/ (1 + 1 0^{- 2.8}) = 0.9984

. Ethanol:

1/ (1 + 1 0^{2.9}) = 0.0013

. So only ethanol is not ionised.

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