Experiment 158

Objective

To systematically identify the unknown organic sample, hypothesized as Acetamide, through elementary analysis, melting point determination, and functional group tests.

Introduction

Sample Characteristics

●      Color: Colorless

●      Physical State: Needle-shaped crystals

●      Odor: Odorless

●      Melting Point: 82°C

This organic compound can be identified by performing elementary analysis and functional group tests, followed by comparison to known melting point data and chemical behavior to confirm its structure.

Solubility Tests

Materials

Chemicals

●      Sample (suspected Acetamide)

●      Distilled water

●      5% HCl, 5% NaOH, 5% NaHCO₃

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

●      10% Sodium nitrite (NaNO₂) solution

●      20% NaOH, 2% Bromine solution

Apparatus

●      Test tubes, test tube holders

●      Bunsen burner, thermometer

●      500 ml flask, pipette

●      Mortar, pestle, fusion tube, test tube stand

Reagents Preparation:

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

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

●      Take HNO₃ and AgNO₃ in separate beakers.

●      Prepare 20% NaOH solution.

Procedure

1. Elementary Analysis

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

●       Nitrogen Test: Add 1 ml of ferrous sulfate to 1-2 ml of stock solution and boil. After cooling, add a few drops of H₂SO₄. A Prussian blue color confirms nitrogen presence.

●       Halogen Test: Acidify 1 ml of stock solution with nitric acid, boil for 6-7 minutes, then cool and add silver nitrate. Absence of white, pale yellow, or yellow precipitates indicates no halogens (chlorine, bromine, iodine).

●       Sulfur Test: Acidify 1 ml of stock solution with dilute acetic acid, then add lead acetate. No black precipitate indicates sulfur is absent.

2. Functional Group Tests

●       Unsaturation Test: Dissolve 0.2 g of sample in 2 ml CCl₄, add 2% bromine solution dropwise. No color change suggests unsaturation is absent.

●       Primary Amine (-NH₂) Test: Dissolve sample in dilute HCl, add 10% NaNO₂, and transfer drops to a test tube with alkaline α-naphthol. Absence of orange-red precipitation indicates -NH₂ is absent.

●       Secondary Amine (-NH-) Test: No reaction observed upon adding excess NaNO₂ solution, confirming -NH- is absent.

●       Tertiary Amine (=N-) Test: Dissolve sample in dilute HCl, add NaNO₂, and heat with NaOH. Absence of green crystals confirms =N- is absent.

●       Substituted Amide (-NHCOR) Test: Boil the sample with 20% HCl, cool, and add to α-naphthol. Orange-red precipitation indicates -NHCOR is present.

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

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

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

●       Phenol (Ar-OH) Test: Dissolve sample in rectified spirit, add FeCl₃. Absence of color change suggests -OH is absent.

●       Aromatic Hydrocarbon Test: Dissolve sample in alcohol, add picric acid solution. Absence of orange-red crystals suggests aromatic hydrocarbon is absent.

Observations

The functional groups identified are nitrogen (N) and -NHCOR. The melting point of 82°C and chemical properties confirm the sample as Acetamide.

Questions

1.    What is Acetamide?

2.    What is an amide?

3.    How is an amide group identified?

4.    How is an amide formed?