Question

A gas decolorizes alkaline KMnO4 solution but does not give precipitate with AgNO4 is

Answer 1

Alkanes are saturated hydrocarbons. It means that every carbon is bonded to as many hydrogen atoms as possible. They participate in very few reactions. One of them being free-radical reactions.Alkenes, on the other hand, are more reactive than alkanes. Alkenes are unsaturated hydrocarbons. When alkenes react with alkaline KMnO4, the alkenes are oxidized to alcohols. One hydroxyl group attaches to each carbon on either side of the carbon-carbon double bond. KMnO4 is first reduced to MnO4(2-), a dark green solution and then it's further reduced to MnO2, a dark brown precipitate.This same reaction happens with acidic KMnO4 as well. But KMnO4 gets reduced all the way down to Mn2+ ions.

Answer 2

Hey dear,

● Answer -
Ethylene (CH2=CH2) decolorizes alk.KMnO4 soln but dont give ppt with alc.AgNO3.

● Explanation -
Alkenes on reaction with alk.KMnO4 gives dihydroxylated alkenes.
R-CH=CH2 + 2OH- --> R-CH(OH)-CH2-OH

For example, ethylene reacts with alk.KMnO4 gives ethan-1,2-diol.
CH2=CH2 + 2OH- --> HO-CH2-CH2-OH

Alkenes don't react with alc.AgNO3, hence no change is observed when ethylene is treated with AgNO3.

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