Question

If asked to separate an equal mixture of benzoic acid [pKa ? 4.2] and 2-naphthol [pKa ? 9.5] using a liquid–liquid extraction technique, explain why an aqueous solution of NaHCO3[pKa ? 6.4] would be far more effective than the stronger aqueous solution of NaOH[pKa ? 15.7].

Answer 1

If we use sodium hydroxide as the extracting solution both the compounds 2-naphthol and  benzoic acid will become the salt and get extracted [NaOH being the very strong base it will also abstract hydrogen from binapthol(less acidic compare to benzoic acid) which is not possible if we will use NaHCO₃ ] whereas if we use NaHC0₃ then only benzoic acid would be converted to its salt while 2-naphthol would stay as such. Therefore, to separate the mixture we use sodium bicarbonate ..