Experiment 40

Objective: To identify the presence of a carboxylic acid group.

Introduction:

Carboxylic acids are organic acids with the general formula R-COOH. In aqueous solutions, they donate a proton (H⁺), leaving behind the carboxylate ion (R-COO⁻)                 The presence of a carboxylic group can be confirmed by its reaction with sodium bicarbonate (NaHCO₃), producing carbon dioxide (CO₂) gas, which is seen as bubbles.

Reaction:

 R-COOH + NaHCO3 → R-COONa + H2O + CO2 (Bubbles)↑

Materials:

Chemicals:

Organic acid sample (e.g., acetic acid)Sodium bicarbonate (NaHCO₃)Calcium hydroxide [Ca(OH)₂] solution

Apparatus:

Test tubesSpirit lampTest tube holder

Procedure:

1.    Take 10 mL of the carboxylic acid sample in a test tube.

2.    Add 2 grams of sodium bicarbonate (NaHCO₃) to the test tube containing the acid.

3.    Heat the mixture gently using a spirit lamp.

4.    Observe the reaction, specifically the release of gas bubbles.

Observation:

Gas bubbles are released during the reaction. When the gas is passed through a calcium hydroxide solution [Ca(OH)₂], insoluble calcium carbonate (CaCO₃) forms, confirming the presence of CO₂.

Questions:                                                  

1.    What is the general structure of carboxylic acids?

2.    How can you confirm the presence of a carboxylic acid in this experiment?

3.    Why is sodium bicarbonate (NaHCO₃) used in the carboxyl group test?