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Test for Phenolic group

The tests that can be used to ascertain the phenol functional group are as following:

Litmus Test

Purpose: The purpose of the litmus test is to determine the presence of a phenol functional group in a given material.

Conjecture - Litmus paper changes colour depending on whether the solution is acidic or basic in nature. Blue litmus paper changes to red in acidulous solutions. Red litmus paper changes to blue in basic solutions. Because phenols are acidic in nature, they pass the litmus test.

Materials needed: blue Litmus paper, a dropper, a test tube, and so on.
Procedure: Place 1-2 drops of the supplied solution in a test tube and place it on the blue litmus paper.

Remark: The colour of the litmus paper shifts from blue to red.

Outcome: The supplied solution may include phenol as a Outcome.

Ferric Chloride Test

Purpose: The purpose of the ferric chloride test is to determine the presence of a phenol functional group in a given material.

Conjecture - This test is based on the verity that phenols produce a colourful complex when mixed with a neutral ferric chloride solution. C6H5OH interacts with ferric ions of ferric chloride to generate a colourful complex [Fe(C6H5O)6]3- . The following is a reaction:

1

Materials needed: test tube, ferric chloride solution, dropper, and so on.

Remark – The presence of a phenol group is indicated by the colour of the solution changing to red, blue, violet, or green. The colour violet or blue is produced by ortho, meta, or para – cresol, and resorcinol. - naphthol produces a green colour while - naphthol produces a pink tint. Deep red hue is produced by acetic acid and formic acid.

Outcome: The proposed solution includes phenol as a Outcome.

Phthalein Dye Test

The majority of phenols do this test correctly and show the Outcomes precisely.
Purpose: The goal of this test is to detect the presence of a phenol functional group in a given material.

Conjecture - When phenol is heated with phthalic anhydride in the presence of conc. sulfuric acid, it condenses and produces phenolphthalein. In the presence of a little quantity of sodium hydroxide, phenolphthalein produces pink coloured compounds, however in the presence of an excess of sodium hydroxide, it produces a colourless chemical.

Materials needed include a test tube, the supplied organic chemical, phthalic anhydride, concentrated sulfuric acid, sodium hydroxide, distilled water, a burner, an oil bath, a dropper, and so on.

Procedure

  • Begin with a clean, dry test tube. In this test tube, place 100 mg of the indicated chemical substance.
  • In the same test tube, add 100 mg of phthalic anhydride.
  • In the same test tube where the sample and phthalic anhydride were obtained, add 2–3 drops of pure sulfuric acid.
  • For around 2 minutes, place the test tube in an oil bath.
  • The test tube mixture should be cooled.
  • Carefully pour the test tube liquid into the beaker, which contains 15 mL of weak sodium hydroxide solution.
  • Take note of the hue shift.

Remark - If the colour of the reaction mixture changes to pink, red, green, or blue, it indicates that the provided organic molecule has a phenol group. However, if a considerable volume of sodium hydroxide solution is added, the colour may evaporate and we will end up with a colourless molecule.

Outcome: The given organic compound has a phenol group as an outcome.

The Libermann Test

This test is performed by phenols with a free para position.
Purpose: The goal of this test is to detect the presence of a phenol functional group in a given material.

Conjecture: When phenol is dissolved in conc. Sulfuric acid and sodium nitrite are added. The sodium nitrite then interacts with concentrated sulfuric acid to produce nitrous acid and sodium sulphate in this combination. Nitrous acid now interacts with phenol to form p-nitrosophenol. This, p-nitrophenol with an excess of phenol, generates indophenol complex, which is red in colour when diluted. When the indophenol complex combines with a strong alkali (NaOH), a blue indophenol anion is formed. The reactions that are involved can be written as follows -

2NaNO3 + H2SO4 🡪 2HNO2 + Na2SO4

Sodium nitrite Sulfuric acid Nitrous acid Sodium sulfate

Materials needed include a test tube, a test tube holder, the provided organic chemical, concentrated sulfuric acid, sodium hydroxide, sodium nitrite, distilled water, and a burner.

Procedure:
1. Begin with a clean, dry test tube.
2. Fill it with a little amount of sodium nitrite crystals.
3. Now add 100 mg of the provided phenolic compound and gently heat the test tube for 30-35 seconds.
4. Set aside the test tube to cool.
5. Add 1 ml of the concentrated sulfuric acid and gently shake the test tube to combine the contents.
6. Examine the colour change and dilute the solution with water.

Remark - When we dilute the solution with water, it gets red, but when we add NaOH to it, it turns blue (deep blue).

Outcome: The presence of phenol in the provided sample is confirmed by the deep blue hue.

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