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What amount of hydrogen will be required for complete hydrogenation of one mole of pent-3-yne?

Chemistry
WAEC 1996

What amount of hydrogen will be required for complete hydrogenation of one mole of pent-3-yne?

  • A. 1 mole
  • B. 2 moles
  • C. 3 moles
  • D. 5 moles
  • E. 6 moles
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Correct Answer: Option B
Explanation

During complete hydrogenation, the unsaturated alkyne is converted into a fully saturated alkane (pentane). This process requires breaking both \(\pi \) bonds and adding hydrogen atoms across them. Each mole of pi bonds reacts with exactly one mole of diatomic hydrogen gas (H\(_2\)).

A carbon-carbon triple bond consists of one strong sigma bond and two weaker pi bonds.

  The general chemical equation for this addition reaction is:
      The general chemical equation for this addition reaction is:
   CH\(_3\)CH\(_2\)C≡CCH\(_3\)  + 3H\(_2\) → CH\(_3\)CH\(_2\)CH\(_2\)CH\(_2\)CH\(_3\)

Exactly 2 moles of hydrogen gas are required for the complete hydrogenation of one mole of pent-3-yne to form pentane. 


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