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After breathing in a test tube that contains acidified K\(_2\)Cr\(_2\)O\(_7\), a man noticed a change...

Chemistry
JAMB 2025

After breathing in a test tube that contains acidified K\(_2\)Cr\(_2\)O\(_7\), a man noticed a change in the colour of the acidified K\(_2\)Cr\(_2\)O\(_7\) from orange to green. This suggests the presence of 

  • A. alkanoic acid
  • B. alkanal
  • C. alkanol
  • D. alkanone
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Correct Answer: Option C
Explanation

The test is commonly used in breathalyzers to detect alcohol consumption, where the orange-to-green change confirms the presence of alcohol. 

The colour change of acidified K\(_2\)Cr\(_2\)O\(_7\)from orange to green upon breathing into a test tube indicates the presence of an alkanol (specifically ethanol). The ethanol is oxidized to ethanal/acetic acid while the dichromate ions (Cr\(_2\)O\(_7\)\(^{2−}\)) are reduced to green chromium(III) ions (Cr\(^{3+}\)). 

There is an explanation video available below.


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Explanation Video

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