Consider the above reaction. The percentage yield of amide product is __________. (Round off to the Nearest Integer).
(Given : Atomic mass : C : 12.0 u, H : 1.0 u, N : 14.0 u, O : 16.0 u, Cl : 35.5 u)

Solution

Chemistry ma’am · 3 steps

Find the limiting reagent in moles first; the theoretical yield comes only from that one.

1. The reaction. Benzoyl chloride acylates diphenylamine: C₆H₅COCl + (C₆H₅)₂NH → C₆H₅CON(C₆H₅)₂ + HCl. One mole of each reactant gives one mole of amide.

   Compound	Molar mass	Mass taken	Moles
   Benzoyl chloride, C₇H₅ClO	140.5 g mol⁻¹	0.140 g	9.96 × 10⁻⁴, limiting
   Diphenylamine, C₁₂H₁₁N	169 g mol⁻¹	0.388 g	2.30 × 10⁻³, in excess
   Amide, C₁₉H₁₅NO	273 g mol⁻¹	0.210 g obtained	product

2. Theoretical yield. Benzoyl chloride runs out first, so at most 9.96 × 10⁻⁴ mol of amide can form. That is 0.140/140.5 × 273 = 0.272 g.

   % yield = 0.210/0.272 × 100 = 77.2

3. So. The percentage yield of the amide is about 77.2%, which rounds to 77.

The common slip: 34. Basing the theoretical yield on diphenylamine gives 0.627 g and a yield of 34, but diphenylamine is in excess, so it cannot set the maximum.

The idea to keep. Percentage yield is actual mass over the mass the limiting reagent could give. Always compare reactants in moles, never in grams.

Answer from the NTA final answer key. Solution by PrepWiser.