Determine the purity of the recrystallized benzoic acid by determining its melting point and comparing this melting point to the value reported in literature.

Purification of an organic solid by recrystallization

Objective: To purify a sample of benzoic acid contaminated with sand by recrystallization from water

Crystalline state of matter is a highly organized state of matter. To form crystals, the molecules of the substance must arrange themselves in an orderly manner. Any impurity present in the sample of the substance will prevent the orderly organization of molecules of the substance. Thus, a sample obtained in a crystalline form is likely to be a pure substance. A sample of an impure solid substance can be purified by recrystallization.

Recrystallization Method:

Identify the impurity in the sample and the approximate degree of contamination

Identify a solvent suitable for purifying the impure sample of benzoic acid by crystallization. [An ideal solvent for recrystallization for a substance is a solvent that will (1) partially dissolve the substance at room temperature, and (2) completely dissolve the substance while hot . In addition, the hot solution of the substance in the solvent, when cooled will allow the substance to form crystalline solid.]
Separate the impurity by mixing the impure sample with minimum amount of the hot solvent and filtering off the insoluble impurity by gravity filtration.

Allow the filtrate to cool slowly to room temperature or below, for the pure substance to crystallize.

Isolate the recrystallized benzoic acid by vacuum filtration, dry the residue and determine the amount of sample recovered. Calculate the % recovery of benzoic acid

Determine the purity of the recrystallized benzoic acid by determining its melting point and comparing this melting point to the value reported in literature.