Preparation of Benzoic acid from Benzamide

Benzamide is hydrolyzed to sodium benzoate by boiling with a sodium hydroxide solution. Sodium benzoate on acidification gives benzoic acid.
C6H5CONH2 + NaOH → C6H5COONa + HCl → C6H5COOH + NaCl
To prepare benzoic acid start with 3 grams of benzamide and mix it with 2 grams of sodium hydroxide dissolved in about 18 mL of water in a round bottom flask.. The flask is fitted with a Liebig’s condenser. The flask is heated on a wire gauze and the contents gently refluxed for about 50 minutes. Ammonia is evolved and the sodium salt of benzoic acid is formed in the solution. The flask is then cooled and the contents acidified with concentrated hydrochloric acid after transferring to a beaker. The precipitated benzoic acid is filtered using a Buschner funnel and the yield noted. About 1 gram can be recrystallized from hot water and the melting point can be determined to confirm the prepared compound.

Redox Titration

Potassium permanganate is a secondary standard and to standardize it, you can use ferrous ammonium sulfate ir Mohrs salt. Prepare a 0.1M Fe2+ solution pipette 10 ml into an erlenmeyer flask add 10 ML of 1M sulfuric acid and titration it against KMnO4 solution approximate concentration should be 0.02M. The end point is the Color change from clear to pale pink.

Titration Video


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Testing Rapid Quiz

1. What is the oxidation number of Mn in MnO4-