Moderate

How many moles of H2 are added up when benzene is heated with hydrogen in the presence of platinum ?

Correct answer: B. Three

  • A. Two
  • B. Three
  • C. Four
  • D. Six

Explanation

Complete catalytic hydrogenation converts benzene, C6H6, into cyclohexane, C6H12: C6H6 + 3H2 -> C6H12. Therefore, 3 moles of H2 are added per mole of benzene. Students may choose 6 moles by counting the six carbon atoms instead of balancing the change in hydrogen atoms.

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About Benzene and Aromatic Compounds

Benzene has a planar ring of delocalised π electrons, giving aromatic stability and equal carbon-carbon bond lengths. The topic covers resonance, electrophilic substitution reactions such as nitration, halogenation, sulphonation and Friedel-Crafts reactions, along with substituent effects and the distinction between substitution in benzene and addition in ordinary alkenes.

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