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Qualitative Tests for Alcohol

Updated: Mar 1


  • Qualitative tests for alcohol are analytical methods used to confirm the presence or type of alcohol in a sample.

  • They are important in fields like forensic science, the food and beverage industry, pharmaceuticals, and environmental monitoring.

  • These tests do not measure the quantity of alcohol but confirm its existence or identify its type.

1) Chromic Acid Test (Jones Test)

Reagent

  • Chromic acid (H₂CrO₄) prepared from sodium or potassium dichromate (Na₂Cr₂O₇ or K₂Cr₂O₇) and sulfuric acid (H₂SO₄).

Procedure

  • When primary or secondary alcohols are added to chromic acid, the solution turns from orange to blue-green, indicating the reduction of Cr(VI) to Cr(III).

Result

  • Positive for primary and secondary alcohols. Tertiary alcohols do not react.

2) Lucas Test

Reagent

  • A mixture of zinc chloride (ZnCl₂) and concentrated hydrochloric acid (HCl).

Procedure

  • Alcohols are added to the reagent. Tertiary alcohols react almost immediately, causing turbidity, while secondary alcohols react more slowly. Primary alcohols generally do not react.

Result

  • Turbidity indicates the presence of secondary or tertiary alcohols.

3) Ceric Nitrate Test

Reagent

  • Aqueous solution of ceric nitrate (Ce(NO₃)₄).

Procedure

  • Alcohols react with ceric nitrate, forming an alkoxide complex, which causes a color change to red or pink.

Result

  • A color change indicates the presence of an alcohol.

4) Iodoform Test

Reagent

  • Iodine (I₂) in the presence of sodium hydroxide (NaOH).

Procedure

  • Alcohols that can be oxidized to methyl ketones (e.g., ethanol, certain secondary alcohols) react to form a yellow precipitate of iodoform (CHI₃).

Result

  • A yellow precipitate indicates the presence of ethanol or methyl ketones.

5) Fehling’s Test and Benedict’s Test

Reagent

  • Complex copper(II) salt in an alkaline solution.

Procedure

  • Alcohols that can be oxidized to aldehydes and further to carboxylic acids reduce copper(II) ions to copper(I) oxide (Cu₂O), which precipitates as a red or reddish-brown solid.

Result

  • Formation of a red or reddish-brown precipitate indicates the presence of alcohols that can be oxidized under these conditions.

These tests provide different ways to identify the presence and type of alcohols in various samples.



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