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JEE Main levelNumerical answerDifficulty 2 of 3hc122

80 g of commercial calcium carbide containing 20 percent (by mass) inert impurities is hydrolysed to ethyne with 85 percent yield. The ethyne is then passed through a red hot iron tube, where it trimerises to benzene with 60 percent yield. Calculate the mass of benzene obtained, in grams, to two decimal places. (Atomic masses: H 1, C 12, Ca 40.)

Numerical answer type, answer in g, tolerance 0.02.

Answer: 13.26 g

Pure

CaC X_{2}

= 80 x 0.80 = 64 g = 1.00 mol (M = 64).

CaC X_{2} + 2 H X_{2} O C X_{2} H X_{2} + Ca (OH) X_{2}

gives 1.00 x 0.85 = 0.85 mol ethyne.

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

gives 0.85/3 x 0.60 = 0.17 mol benzene. Mass = 0.17 x 78 = 13.26 g.

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