Acidity of Alkynes

Acidity of Alkynes MDCAT MCQs with answers

7 past paper MCQs on Acidity of Alkynes, from the Chemistry of Hydrocarbons unit of MDCAT Chemistry. The year each question appeared is shown where known; tap “Show answer” for the correct option and a short solution.

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1.Which of the following compounds is more acidic? (MDCAT 2022)

  1. alkane
  2. alkene
  3. alkyne
  4. cycloalkane
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Correct answer: (c) alkyne

The $sp$ carbon of a terminal alkyne holds its electrons closest, so its hydrogen comes off most readily.

2.Which of the following reagents can be used to distinguish between 1-pentyne and 2-pentyne? (MDCAT 2023)

  1. $\mathrm{AgNO_3+NH_4OH}$
  2. dilute alkaline $\mathrm{KMnO_4}$
  3. $\mathrm{Br_2/CCl_4}$
  4. $\mathrm{K_2Cr_2O_7+H_2SO_4}$
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Correct answer: (a) $\mathrm{AgNO_3+NH_4OH}$

Only the terminal alkyne has an acidic hydrogen, so only 1-pentyne gives a silver acetylide precipitate.

3.Terminal alkynes show acidic character due to: (UHS MDCAT 2025)

  1. Terminal carbon atoms are sp hybridized.
  2. Terminal carbon atoms are sp2 hybridized.
  3. Terminal carbon atoms are sp3 hybridized.
  4. Terminal carbon atoms show hydrogen bonding.
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Correct answer: (a) Terminal carbon atoms are sp hybridized.

The sp hybridized carbon holds its electrons close, so the terminal hydrogen leaves as a proton.

4.Which among the following will react with ammonical cuprous chloride: (SZABMU MDCAT 2025)

  1. 1-butene
  2. 1-butyne
  3. 2-butene
  4. 2-butyne
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Correct answer: (b) 1-butyne

A terminal alkyne is acidic enough to give a red copper acetylide; but-2-yne has no terminal hydrogen.

5.Which of the following compound is more acidic? (UHS MDCAT 2023)

  1. Alkane
  2. Alkene
  3. Alkyne
  4. Cycloalkane
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Correct answer: (c) Alkyne

The sp carbon of a terminal alkyne holds its electrons closely, so its hydrogen leaves most readily.

6.White precipitate is formed when _ _ _ _ is passed through ammoniacal solution of silver nitrate. (PMC MDCAT 2022)

  1. Methylene
  2. Ethylene
  3. Acetylene
  4. Vinylene
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Correct answer: (c) Acetylene

A terminal alkyne is acidic enough to give a white silver acetylide.

7.What is the color of silver acetylide, AgC=CAg? (PMC Practice 2021)

  1. Red
  2. White
  3. Brown
  4. Pinkish
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Correct answer: (b) White

Silver acetylide comes down as a white precipitate.

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