Experiement 154

Objective

To systematically identify an unknown organic sample, hypothesized to be 1,2,5-trihydroxybenzene (phloroglucinol), through physical analysis, solubility testing, and functional group tests.

Introduction

Physical Properties of the Sample

●      Color: White

●      Physical State: Crystalline solid

●      Odor: Odorless

●      Melting Point: 218°C

This compound can be identified through elementary analysis and functional group tests, followed by comparing its melting point to known data.

Solubility Test

Materials

Chemicals

●      Supplied sample (phloroglucinol)

●      Distilled water

●      5% HCl, 5% NaOH, 5% NaHCO₃

●      Ferrous sulfate, nitric acid, silver nitrate

●      Ferric chloride, 10% NaNO₂, 2% bromine solution

Apparatus

●      Test tubes

●      test tube holder

●      Bunsen burner

●      thermometer

●      500 mL flask

●      test tube stand

●      pipette

●      fusion tube

●      mortar and pestle

Reagents Preparation

●      5% HCl, 5% NaOH, and 5% NaHCO₃: Prepare in 500 mL flasks.

●      5% Ferrous Sulfate: Prepare in a 250 mL flask.

●      HNO₃ and AgNO₃: Use directly from a beaker.

●      2% Bromine and 10% NaNO₂ Solution: Prepare as needed.

Procedure

1.    Elementary Analysis

●      Preparation of Stock Solution

●      Place a clean, dry piece of sodium in a fusion tube.

●      Heat until the sodium melts, then add a small amount of the sample and heat to a dull red.

●      Drop the hot tube into a mortar containing 3-5 mL of distilled water, break the tube with the pestle, and filter the solution for testing.

●      Tests

●      Nitrogen Test: Mix 1-2 mL of stock solution with 1 mL fresh FeSO₄, boil, cool, then add H₂SO₄. (Result: No Prussian blue precipitate; nitrogen absent)

●      Halogen Test: Acidify with HNO₃, boil, cool, and add AgNO₃. (Result: No white, pale yellow, or yellow precipitate; halogens absent)

●      Sulfur Test: Add lead acetate after acidifying with acetic acid. (Result: No black precipitate; sulfur absent)

2.    Functional Group Tests

●      Unsaturation Test

o   Bromine in CCl₄: Dissolve 0.2 g of sample; bromine color discharges, indicating unsaturation.

o   KMnO₄ Test: Dissolve sample in acetone/water; KMnO₄ color discharges, confirming unsaturation.

●      Nitro Group Test (-NO₃)

o   Heat with granulated tin and HCl, cool, and add 10% NaNO₂. (Result: No orange-red precipitate; nitro group absent)

●      Carbonyl Group Test (=C=O)

o   Dissolve in rectified spirit and add 2,4-DNPH solution. (Result: No orange-red precipitate; carbonyl group absent)

●      Carboxylic Acid Test (-COOH)

o   Mix sample with 5% NaHCO₃. (Result: No reaction; carboxylic acid absent)

●      Phenol Test

o   Dissolve sample in rectified spirit, add 5% FeCl₃. (Result: Intense color; phenol group (Ar-OH) present)

●      Aromatic Hydrocarbon Test

o   Dissolve in alcohol, add saturated picric acid solution. (Result: Orange-red needle crystals; aromatic hydrocarbon present)

Observation

The organic sample lacks nitrogen (N), halogens (X), and sulfur (S). It possesses an -OH group, characteristic of phloroglucinol, confirmed by a melting point of 218°C, identifying the compound as 1,2,5-trihydroxybenzene (phloroglucinol).

Questions

1.    What is phloroglucinol?

2.    How is phloroglucinol identified?

3.    How is the phenol group identified?

4.    Which reagents are used in the phenol group test?