An ether solution contains benzoic acid (pK_a 4.20), 4-nitrophenol (7.15), 4-methylphenol (10.2) and toluene. It is extracted successively with aqueous NaHCO3 (pK_a of H2CO3 6.4), aqueous Na2CO3 (pK_a of HCO3- 10.3) and aqueous NaOH. Taking log K geq 2 as essentially complete, the Na2CO3 extract (second step) contains mainly

JEE Advanced levelSingle correct optionDifficulty 3 of 3g2162

An ether solution contains benzoic acid ( $p K_{a}$ 4.20), 4-nitrophenol (7.15), 4-methylphenol (10.2) and toluene. It is extracted successively with aqueous $NaHCO X_{3}$ ( $p K_{a}$ of $H X_{2} CO X_{3}$ 6.4), aqueous $Na X_{2} CO X_{3}$ ( $p K_{a}$ of $HCO X_{3} X^{-}$ 10.3) and aqueous $NaOH$ . Taking $lo g K \geq 2$ as essentially complete, the $Na X_{2} CO X_{3}$ extract (second step) contains mainly

Step 1:

NaHCO X_{3}

removes benzoic acid (

6.4 - 4.20 = 2.2

) but not 4-nitrophenol (

6.4 - 7.15 = - 0.75

). Step 2: carbonate with 4-nitrophenol has

lo g K = 10.3 - 7.15 = 3.15

(complete), but with 4-methylphenol only

10.3 - 10.2 = 0.1

. So 4-nitrophenol is extracted in the second step; 4-methylphenol goes only with

NaOH