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JEE Advanced 2020 · Paper 2, Chemistry question 16

Consider the reaction sequence from P to Q shown below. The overall yield of the major product Q from P is 75%. What is the amount in grams of Q obtained from 9.3 mL of P? (Use density of P = 1.00 g mL⁻¹; Molar mass of C = 12.0, H = 1.0, O = 16.0 and N = 14.0 g mol⁻¹)

P (aniline) is treated with (i) NaNO₂ + HCl at 0-5 °C, (ii) 2-naphthol + NaOH, (iii) CH₃CO₂H/H₂O to give Q.
Answer and worked solution

Official answer: 18.6

The reaction. Aniline is diazotised to benzenediazonium chloride, which couples with alkaline 2-naphthol to give the orange azo dye Q, 1-phenylazo-2-naphthol, CX16HX12NX2O\ce{C16H12N2O}.

Amounts.

  • P: 9.3 mL×1.00 g mL−1=9.39.3\text{ mL}\times1.00\text{ g mL}^{-1}=9.3 g of aniline (M=93M=93), which is 0.100 mol.
  • Q: M=16(12)+12(1)+2(14)+16=248 g mol−1M=16(12)+12(1)+2(14)+16=248\ \mathrm{g\,mol^{-1}}.

Mass.
0.75×0.100×248=18.6 g.0.75\times0.100\times248=18.6\text{ g}.
Answer: 18.60

Topics:Diazonium saltsStoichiometry
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