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JEE Advanced levelNumerical answerDifficulty 3 of 3ap102

A mixture of 3.76 g of phenol and 5.00 g of cyclohexanol is shaken with excess bromine water. Only the phenol reacts, giving a precipitate of 2,4,6-tribromophenol in 80 percent yield based on phenol. Use atomic masses H = 1, C = 12, O = 16, Br = 80. What is the mass of the dried precipitate in grams? Give the answer to two decimal places.

Numerical answer type, tolerance 0.05.

Answer: 10.59

Molar mass of phenol

C X_{6} H X_{5} OH = 94

, so

3.76/94 = 0.040

mol. The molar mass of

C X_{6} H X_{2} Br X_{3} OH

(2,4,6-tribromophenol) is

72 + 3 + 240 + 16 = 331

. Theoretical mass

= 0.040 \times 331 = 13.24

g, and at 80 percent yield the mass is

13.24 \times 0.80 = 10.59

g. Cyclohexanol does not react with bromine water.

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