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Which of the following will give a precipitate…

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CHEMISTRY

Which of the following will give a precipitate with an aqueous solution of copper (1) chloride?

  • A. But-2-ene
  • B. But-1-ene
  • C. But-2-yne
  • D. But-1-yne

QUICK ANSWER…

D

SOLUTION 

Ammoniacal copper (1) chloride can be used to distinguish between alkenes and alkynes.

While some alkynes react with it, alkenes do not.

Ammoniacal copper (1) chloride can also be used to differentiate between terminal alkynes and non-terminal alkynes.

All terminal alkynes like ethyne, prop-1-yne, but-1-yne, pent-1-yne, hex-1-yne and so on, reacts with copper (1) chloride to form a reddish-brown precipitate.

All none-terminal alkynes like but-2-yne, pent-2-yne, hex-2-yne, hex-3-yne, and so on, do not react with ammoniacal Cucl.

Now for the right answer to the above question:

  1. Option A is incorrect. alkenes do not form precipitates with copper (i) chloride.
  2. Option B is incorrect. alkenes (both terminal and non-terminal) do not form precipitates with copper (i) chloride.
  3. C is incorrect. but-2-yne does not form precipitate because it is not a terminal alkyne.
  4. D is the correct answer. only terminal alkynes form precipitate with ammoniacal copper (i) chloride.

KEY-POINTS…

You may please note these/this:

  • Only terminal alkynes respond to ammoniacal copper (i) chloride, forming a precipitate.
  • Non-terminal alkynes do not form precipitates with copper (i) chloride.

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/culled from 2019 JAMB-UTME Chemistry question 2/

1 Answers

  1. 0 Votes Thumb up 0 Votes Thumb down 0 Votes

    Pls what is the reddish brown precipitate formed

    Dglory1 - Nov 16, 2021 | Reply


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