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Give Simple Chemical Tests to Distinguish Between the Following Pairs of Compounds Propanal and Propanone - Chemistry

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Give simple chemical tests to distinguish between the following pairs of compounds

Propanal and Propanone

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Solution 1

Propanal and propanone can be distinguished by the following tests.

Tollen’s test

Propanal is an aldehyde. Thus, it reduces Tollen’s reagent. But, propanone being a ketone does not reduce Tollen’s reagent.

`CH_3CH_2CHO + 2[Ag(NH_3)_2]^+ + 3OH^(-) -> CH_3CH_2COO^(-) +  Ag darr + 4NH_3 + 2H_2O`

Propanal                              Tollen's regent              Propanoate ion              Siver mirror

Fehling’s test

Aldehydes respond to Fehling’s test, but ketones do not.

Propanal being an aldehyde reduces Fehling’s solution to a red-brown precipitate of Cu2O, but propanone being a ketone does not.

`CH_3CH_2CHO + 2Cu^(2+) + 5OH^(-) -> CH_3CH_2COO^(-) + CH_3CH_2COO^(-) + Cu_2O darr + 3H_2O`

Propanal                                                                                           Propanoate ion       Cuprous oxide(Red brown ppt)

Iodoform test:

Aldehydes and ketones having at least one methyl group linked to the carbonyl carbon atom respond to iodoform test. They are oxidized by sodium hypoiodite (NaOI) to give iodoforms. Propanone being a methyl ketone responds to this test, but propanal does not.

`CH_3COCH_3 + 3NaOI -> CH_3COONa + CHI_3 + 2NaOH`

Propanone                         Sodium aceatate          Iodoform (yellow ppt)

Solution 2

Propanal and Propanone : These two are distinguished by the iodoform test.propanal does not give iodoform test when it reacts with I2 in the presence of NaOH while propanone give iodoform test when reacts with I2 in the presence of NaOH.

 

Concept: Aldehydes and Ketones - Chemical Reactions of Aldehydes and Ketones - Oxidation
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