Experiment 168

Objective

To identify the presence of salicylic acid in an unknown organic sample.

Introduction

This experiment includes an analysis of the physical properties of the unknown compound, followed by solubility testing and functional group analyses. The compound’s identity is confirmed by comparing its melting point with known values.

Physical Characteristics of Sample

·       Color: Colorless

·       State: Crystalline

·       Odor: Odorless

·       Melting Point: 159°C

Solubility Test Results

Materials

Chemicals

·       Unknown organic sample (presumed salicylic acid)

·       Distilled water

·       5% HCl, 5% NaOH, 5% NaHCO₃

·       Ferrous sulfate, Nitric acid

·       Silver nitrate, Ferric chloride

·       10% NaNO₂, 2% bromine solution

Apparatus

·       Test tubes and holder

·       Bunsen burner

·       Thermometer

·       500 mL flask, test tube stand

·       Pipette

·       Fusion tube

·       Mortar and pestle

Preparation of Reagents

·       Prepare solutions of 5% HCl, 5% NaOH, 5% NaHCO₃, and 5% ferrous sulfate in a 500 mL flask.

·       Prepare a 10% NaNO₂ solution and a 20% NaOH solution for specific tests.

Procedure

1.    Elementary Analysis (Stock Solution Preparation)

Heat a piece of sodium in a fusion tube until molten.Add a small amount of the sample, heat to a dull red, then drop the tube into a mortar with 3-5 mL of distilled water.Crush the tube, filter the solution, and use it for further testing.Test for Nitrogen: Add 1-2 mL of the stock solution to freshly prepared ferrous sulfate, boil, cool, and add a few drops of H₂SO₄.

·       Observation: No Prussian blue indicates nitrogen is absent.

Test for Halogens: Acidify 1 mL of boiling solution with nitric acid, boil, cool, and add silver nitrate.

·       Observation: No white, pale yellow, or yellow precipitate indicates no halogens (Cl, Br, I).

Test for Sulfur: Acidify 1 mL of solution with acetic acid and add lead acetate.

·       Observation: No black precipitate indicates sulfur is absent.

2.    Functional Group Tests

·        Test for Unsaturation: Dissolve 0.2 g of the sample in CCl₄, then add bromine solution.

·       Observation: No color discharge, indicating absence of unsaturation.

·        Carbonyl Group (=C=O): Dissolve in rectified spirit, add 2,4-DNPH.

·       Observation: No orange-red precipitate, indicating carbonyl group is absent.

·        Carboxylic Acid (-COOH): Add sample to NaHCO₃ solution.

·       Observation: Effervescence of CO₂, turning limewater milky, confirms -COOH.

·        Phenol Group (Ar-OH): Dissolve in rectified spirit, add 5% FeCl₃.

·       Observation: Intense coloration indicates phenol group is present.

·        Aromatic Hydrocarbon: Dissolve in absolute alcohol, add picric acid solution.

·       Observation: Orange-red needle-shaped crystals confirm aromatic hydrocarbon.

Observation

Identified Functional Groups:

·        Elements: None (N, X, S absent)

·        Functional Groups: Carboxylic acid (-COOH), Phenol (-OH)

Based on the melting point of 159°C and the presence of these functional groups, the sample is identified as salicylic acid (2-hydroxybenzoic acid).

Questions

1.    What is salicylic acid?

2.    How is the -COOH group identified?

3.    How is the -OH group identified?

4.    What is the Liebermann test?

5.    How is salicylic acid identified?