Question

Assertion :Decolourisation of $KMn{O}_4$ solution is used as a test for unsaturation. Reason: Alkenes on reaction with cold, dilute aqueous solution of potassium permanganate produce vicinal glycols.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Answer:-

The Baeyer's test or $KMn{O}_4$ test for unsaturation is for determining the presence of carbon-carbon double-bonded compounds, called alkenes or carbon-carbon triple bonded compounds, called alkynes.

$\stackrel{|}{\underset{|}{C}}=\stackrel{|}{\underset{|}{C}}+H_{2}O+O\underset{273K}{\overset{dil.KMn{O}_4}{\to }}OH-\stackrel{|}{\underset{|}{C}}-\stackrel{|}{\underset{|}{C}}-OH$

In the above reaction, colour of $KMn{O}_4$ changes to colourless which confirms the presence of unsaturation.

Treatment of alkenes with cold, dilute basic $KMn{O}_4$ leads to 1,2-diols (vicinal diols).