The purpose of this experiment is to purify benzoic acid by crystallization.
1. 0.5g impure benzoic acid was placed in a 50mL Erlenmeyer flask. 15mL of water was added and the mixture was heated to a boil on a hot plate. 0.5mL of water was added to the flask, while swirling the flask. The mixture was boiled until the benzoic acid completely dissolved. The total volume of water used was recorded. The black solid that remain in the dissolved mixture was the impurity.
2. A filter was prepared by placing a fluted filter paper in a 3 inch funnel. The funnel was placed onto a 100mL beaker with 5mL of water at the bottom. The filter paper was moistened. The water was heated to preheat the filter with steam. The solution prepared in step 1 was filtered.
3. A watch glass was placed over the beaker that contained the filtrate and the filtrate was undisturbed until it had cooled to room temperature and when no more crystals had formed.
4. The beaker was placed in an ice-water bath for 10 minutes.
5. The crystals were collected by using a Hirsch funnel by vacuum filtration. The filter cake was then washed with 2 small portions of 0.5mL of cold water. The crystals were pressed dry as possible on the funnel with a spatula.
6. The melting point of recrystallized benzoic acid was determined. The weight of the recrystallized benzoic acid was determined. The percent recovery was calculated using the equation:
Recovery%= weight of pure compound recovered/weight of the original sample
The answer was then multiplied by 100.
7. The sample was submitted to the T.A in a labeled vial.
Results and Discussion:
Weight of original sample: 0.505g
Total volume of water used: 15mL
Weight of pure compound recovered: 0.262g
Melting point of recrystallized benzoic acid: 122-126 degrees Celsius
Recovery %= 0.262g/0.505g x 100= 52%
Pure benzoic acid was obtained by the process of recrystallization. 0.505g of