HOW TO DIFFERENTIATE AND TEST OF ALCOHOL AND KETONE

AS I THINK KETONE GIVE NO COLOUR ON FEHLING SOLUTION . DOES THIS OCCUR WITH ALCOHAL . IF OCCUR WE CANNOT FIND OUT TEST OF ALCOHAL AND KETONE

To differentiate between alcohols and ketones, we can use various chemical tests, including the Fehling's test. You are correct that ketones generally do not react with Fehling's solution, which is a key point in distinguishing them from certain types of alcohols. Let's break this down step by step to clarify how these tests work and what results you can expect.

Understanding Fehling's Test

Fehling's solution is a mixture of two solutions: Fehling's A (copper(II) sulfate) and Fehling's B (alkaline tartrate). This test is primarily used to identify reducing sugars and aldehydes, as they can reduce the copper(II) ions to copper(I) oxide, resulting in a characteristic red precipitate.

Reactivity of Alcohols and Ketones

• Aldehydes: These compounds will react with Fehling's solution, producing a red precipitate.
• Ketones: Most ketones do not react with Fehling's solution, so you will not see any color change.
• Alcohols: Primary and secondary alcohols can sometimes give a positive result under certain conditions, particularly if they can be oxidized to aldehydes or ketones.

Testing for Alcohols and Ketones

To differentiate between alcohols and ketones, you can use several other tests in addition to Fehling's solution:

1. Oxidation Tests

Alcohols can be oxidized to aldehydes or ketones, while ketones are generally resistant to oxidation. You can use:

• Chromic Acid Test: This test can differentiate between primary and secondary alcohols (which will oxidize) and ketones (which will not). A color change from orange to green indicates the presence of an alcohol.

2. Iodoform Test

This test is specific for methyl ketones and some secondary alcohols. If you add iodine and sodium hydroxide to a sample and a yellow precipitate forms, it indicates the presence of a methyl ketone or a secondary alcohol that can be oxidized to a methyl ketone.

3. 2,4-Dinitrophenylhydrazine (DNPH) Test

Both aldehydes and ketones will react with DNPH to form yellow or orange precipitates, known as hydrazones. This test is useful for identifying carbonyl compounds but does not differentiate between aldehydes and ketones.

Summary of Key Points

In summary, while Fehling's test is effective for identifying aldehydes, it does not provide a clear distinction between alcohols and ketones since ketones do not react. To differentiate between these two classes of compounds, consider using oxidation tests, the iodoform test, or the DNPH test. Each method provides unique insights into the chemical nature of the substances you are testing.

By employing these various tests, you can effectively distinguish between alcohols and ketones, even in cases where one test alone might not provide conclusive results.