You were given two unknown compounds and wanted to determine the main functional

Question

You were given two unknown compounds and wanted to determine the main functional group present within each compound. You already determined that Unknown A is either an aldehyde or a ketone and that Unknown B is either an aldehyde or ketone as well. Therefore , you performed the 2,4-DNPH and the chromic acid functional group tests. After performing the 2,4-DNPH test on both unknown compounds, a precipitate formed. Unknown compound A formed a green precipitate with the chromic acid test, while Unknown compound B didn't form a precipitate with the chromic acid test. Therefore, the functional group present within compound A is and the fuctional group present within compound B is an aldehyde, a ketone an aldehyde, an aldehyde a ketone, a ketone a ketone, an aldehyde

Explanation / Answer

Given both compounds form 2,4-DNPH derrivatives.

However, only compound A gives green precipitate when reacted with chromic acid. Aldehydes are oxidized by chromic acid, ketones are not. When an aldehyde is oxidized by orange-brown chromic acid the chromic acid is reduced to Cr+3, which is green. Consequently, chromic acid can distinguish between aldehydes and ketones.

Therefore, the functional group present in Compound A is an aldehyde and the functional group present in Compound B is a ketone.

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