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JEE MainChemistryHydrocarbons

Upon complete combustion of 1 mole of an unknown hydrocarbon, the mass ratio of carbon dioxide to water produced is 44:9 . If 2.5 moles of oxygen are consumed per mole of the hydrocarbon, what is its molecular formula?

Options

  1. AC ₂ H ₂
  2. BC ₂ H ₄
  3. CC ₆ H ₆
  4. DCH ₄

Correct answer

A. C ₂ H ₂

Step-by-step solution

Let the molecular formula of the hydrocarbon be C _x H _y . The general combustion equation is: C _x H _y + (x + y 4 ) O ₂ x CO ₂ + y 2 H ₂ O The mass of CO ₂ produced is 44x and the mass of H ₂ O produced is 18 y 2 = 9y . Given the mass ratio of CO ₂ to H ₂ O is 44:9 , we have: 44x 9y = 44 9 This simplifies to x y = 1 , which means x = y . The empirical formula is CH . We are also given that 2.5 moles of O ₂ are consumed per mole of the hydrocarbon: x + y 4 = 2.5 Since x = y , substitute y with x : x + x 4 = 2.5 1

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