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Sodium bicarbonate test

Sodium hydrogen carbonate, also known as sodium bicarbonate, reacts with acidic solutions to form carbon dioxide, which is released as gas from the solution, resulting in so-called brisk effervescence. Sodium hydrogen carbonate can be used to test for carboxylic acids. If effervescence occurs, then an acid group is present.

The reaction is as follows:

There are two reactions. The first is the reaction of a negatively charged bicarbonate ion with a positively charged hydrogen to form water and carbon dioxide. The second is the reaction of a carboxylic acid, R C O O H, with sodium hydrogen carbonate to form a sodium carbonate salt, R C O O N a, water, and carbon dioxide.

Phenol is a weak acid meaning it dissolves in sodium hydroxide solution but does not dissolve in sodium hydrogen carbonate solution. Stronger acids, such as carboxylic acids, dissolve in both solutions. This can be useful for separating mixtures of acids.

Materials

  • Test tubes

  • Test tube rack

  • Sodium hydrogen carbonate solution

  • Compound to be tested

Safety

Acidic solutions are corrosive. Sodium hydrogen carbonate is an irritant.

Procedure

  1. Put 2 mL of a saturated aqueous solution of sodium hydrogen carbonate in a clean test tube.

  2. Add a few drops of the liquid compound or a few crystals of the solid compound to it. Add the compound slowly so that effervescence is clearly visible.

  3. Brisk effervescence of carbon dioxide indicates the presence of a carboxylic acid group.

References:

  • NCERT Lab Manual for Functional Group tests