Experiement 148

Objective

To identify the unknown organic sample, suspected to be m-dihydroxybenzene (resorcinol), through systematic analysis including melting point determination and functional group tests.

Introduction

Sample Characteristics

●      Color: White

●      Physical State: Needle-like crystals

●      Odor: Odorless

●      Melting Point: 110°C

This compound can be identified through elementary analysis, solubility tests, and functional group characterization, compared against standard data to confirm its structure.

Solubility Tests

Materials

Chemicals

●      Sample (suspected Resorcinol)

●      Distilled water, 5% HCl, 5% NaOH, 5% NaHCO₃

●      Ferrous sulfate, Nitric acid, Silver nitrate, Ferric chloride

●      10% Sodium nitrite (NaNO₂), 2% Bromine solution, 20% NaOH

●      Test tubes, test tube holder, Bunsen burner, thermometer

●      500 ml flask, test tube stand, pipette, fusion tube, mortar, pestle

Apparatus:

Reagents Preparation:

●      Prepare 5% solutions of HCl, NaOH, and NaHCO₃ in 500 ml flasks.

●      Prepare 5% Ferrous sulfate and 10% NaNO₂ solutions.

●      Take HNO₃ and AgNO₃ in beakers.

●      Prepare 20% NaOH solution.

Procedure

1.    Elementary Analysis

●      Preparation of Stock Solution: Place a piece of clean, dry sodium in a fusion tube, heat until it melts, add a small amount of sample, and heat until dull-red. Drop the fusion tube into a mortar with 3-5 ml distilled water, break the tube, and filter for use as the stock solution.

●      Nitrogen Test: Add 1 ml of freshly prepared ferrous sulfate to 1-2 ml of stock solution, boil, cool, then add H₂SO₄. Absence of Prussian blue confirms nitrogen is absent.

●      Halogen Test: Acidify 1 ml of stock solution with nitric acid, boil for 6-7 minutes, cool, then add silver nitrate. No precipitate confirms halogens (chlorine, bromine, iodine) are absent.

●      Sulfur Test: Acidify 1 ml of stock solution with dilute acetic acid, then add lead acetate. Absence of black precipitate indicates sulfur is absent.

2.    Functional Group Tests

●      Unsaturation Test:

o   Dissolve 0.2 g of sample in CCl₄, add 2% bromine in CCl₄ dropwise. Bromine color discharge indicates unsaturation.

o   Dissolve 0.2 g of sample in acetone or water, add 2% KMnO₄. KMnO₄ color discharge confirms unsaturation.

●      Nitro (-NO₃) Group Test: Boil sample with tin and HCl, cool, dilute, add NaNO₂, and test with alkaline α-naphthol. Absence of color confirms -NO₃ is absent.

●      Carbonyl (=C=O) Group Test: Dissolve sample in rectified spirit, add 2,4-DNPH, and observe. No orange-red precipitate confirms =C=O is absent.

●      Carboxylic Acid (-COOH) Test: Add sample to NaHCO₃ solution. Absence of reaction confirms -COOH is absent.

●      Phenol (Ar-OH) Test: Dissolve sample in rectified spirit, add 5% FeCl₃. Intense coloration (purple, blue, red, violet, green) confirms the presence of an -OH group.

●      Aromatic Hydrocarbon Test: Dissolve sample in alcohol, add picric acid solution. Formation of orange-red needle-shaped crystals confirms aromatic hydrocarbon.

Observations

The sample does not contain N, X, or S, but has an -OH functional group. The melting point of 110°C and chemical properties confirm the sample as m-dihydroxybenzene (Resorcinol).

Questions

1.    What is Resorcinol?

2.    How is Resorcinol identified?

3.    How is the phenol group identified?

4.    What reagent is used in the phenol group test?