IIT-JEE 2012 · Paper 1 · Chemistry Q31

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ChemistryMultiple correct+4Question 31 of 60

Identify the binary mixture(s) that can be separated into individual compounds, by differential extraction, as shown in the given scheme.

Scheme: a binary mixture of Compound 1 and Compound 2 is treated separately with NaOH (aq) and with NaHCO₃ (aq); in each case it separates into Compound 1 + Compound 2.

\ce{C6H5OH}

and

\ce{C6H5COOH}

\ce{C6H5COOH}

and

\ce{C6H5CH2OH}

\ce{C6H5CH2OH}

and

\ce{C6H5OH}

\ce{C6H5CH2OH}

and

\ce{C6H5CH2COOH}

Answer and worked solution

Official answer: B, D

The scheme needs a pair that separates with NaOH(aq) and with $\ce{NaHCO3}$ (aq): one component must dissolve in both bases and the other in neither.

(A) Phenol and benzoic acid both dissolve in NaOH. Fails with NaOH.
(B) Benzoic acid dissolves in both NaOH and $\ce{NaHCO3}$ ; benzyl alcohol in neither. Works.
(C) Phenol dissolves in NaOH but not in $\ce{NaHCO3}$ (it is weaker than carbonic acid), and benzyl alcohol in neither. Fails with $\ce{NaHCO3}$ .
(D) Phenylacetic acid dissolves in both bases; benzyl alcohol in neither. Works.

(B), (D)

Topics:Acidity and basicity Purification and characterisation

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IIT-JEE 2012 · Paper 1, Chemistry question 31