Lab #1 (Section 102)
September 17, 2002
Recrystallization and Melting Points
Abstract:
Benzoic Acid was recrystallized with a 41% recovery using 95% ethanol and water as
the mixed-solvent. Benzoic acid was also recrystallized with a 79% recovery using water
as the solvent. The product was a white crystalline solid (MP 114-122C and 121-127C
respectively) after recrystallization. The melting points of Acetanilide, Unknown A, and
Acetanilide plus Unknown A were the following: 101-106.5 C, 100-107 C, and 100-104
C.
Introduction:
This experiment was conducted in order to explore the methods of
recrystallization and in order to determine the melting points of various solids.
Recrystallization involves dissolution of a solid in a solvent at elevated temperatures and
the reformation of the crystals as the solution cools, allowing for impurities to remain in
the solution (Gilbert and Martin 89). This technique is important to chemistry because it
is one of the most often used methods for purification of solids, allowing one to achieve
one of the highest states of purity. Once a solid has been recrystallized, it is important to
determine the purity of the recrystallized solid. An easy way to do this is by taking the
melting point of the solid.
Materials and Methods:
Recrystallization of Benzoic Acid was performed according to the method of
Gilbert and Morgan (2001, section 3.2). Instead of using water to recrystallize benzoic
acid, ethanol was used in 3.2B part 1. The solution was also decolorized twice instead of
once. Once the solution had cooled and no crystals appeared to form, 20mL of water was
