Recrystallization of benzoic Acid
Abstract
The primary purpose of this experiment is the benzoic acid recovery from a compound which is of impure organic state. This technique design helps in the organic compound’s purification Benzoic. This process involves using a hot solvent to dissolve a crystalline material which upon cooling of the solvent turns to solid. Benzoic Acid was recrystallized with a 105% recovery using 95% water as the solvent. The Acid is recovered using a solvent such as water. The recovered product was a flaky white shiny, crystalline solid (MP 100 and 12C respectively) after recrystallization.
Introduction
when synthesis of compounds occurs in the laboratory, they are separated from impure compounds through recrystallization. Recrystallization is a process where purification of substances is done when substances form solids at room temperature, leaving the impurities as a liquid. Temperature is a critical factor in this process whereby many procedures rely on solubility observation of a compound as the temperature increases. Recrystallization process depends on critical conditions such as choice of solvent. Given at low temperatures a suitable solvent must not dissolve the solid during recrystallization. Pure homogeneous compounds consist of the same molecules and have similar structures. These compounds are not be purified due to possible amounts of contaminants. The process of recrystallization is used to purify a solid and remove the impurities. Recrystallization heats or cools a solvent then filters the impurities. Any impurity present in a solid sample will remain in the aqueous solution, and only pure solute will be on the filtered paper.
Results
Experiment 1 – Recrystallization of Benzoic Acid
Crystal shapes and sizes= small and circular
amount of benzoic Acid weighed =98g
benzoic acid colour = white
Mass of boat and benzoic = 1.665g
Mass of empty boat = 0.657g
Weight of boat + benzoic + filter paper =1.836g
Mass of recovered benzoic Acid = 1.029g
Percent recovered = (1.029 ÷0.98)100= 105%
Observed melting point =100oC
Known melting point =122 oC
Experiment 2 – Recrystallization of an Impure Sample of Naphthalene
Amount of naphthalene weighed= 1.00g
Naphthalene color= pink
Crystals shape and sizes=bigger crystals, different shapes
Solvent used =methanol
Amount collected= 0.75g
Percentage of recovered=75.9%
Melting point observed= 79 oC
Known melting point = 78 oC
0.14 + 0.664 =0.824g
1.583 – 0.824g =0.759g (amount collected)
Percentage collected
(0.759 ÷1.000)100 =75.9%
Discussion and Conclusion
Recrystallization method was used in this experiment due to its simplicity in the purification of the solid compound. The percentage recovered for naphthalene and benzoic Acid being high was an indication that the initial sample in our procedure had a low concentration of impurities. From the 1.00g grams of each compound used it is clear that during recovery fewer grams were obtained compared to the mass at the start of the experiment, naphthalene with 75.9% recovery and benzene with 105% recovery.
From the benzoic acid procedure, it’s clear that the solvent used in recrystallization was not the best due to the unrealistic percentage recovery of 105%. These are proven by the low boiling point recorded from the recovered compound, which is less than the expected value. For naphthalene, the recrystallization process was carried as expected. It was clear that a pure compound was obtained from the procedure which is indicated by the boiling point of the recovered compound with a melting point of 79oC compared to the melting point of the known compound.
In this experiment, a technique was used that can be used frequently in such recrystallization experiments. Purification by recrystallization; This technique allows for the purification of crude material. The small loss in yield is made up of the high gain in purity. The purity of the material obtained can be correlated to the sharpness and veracity of the melting point data, and this was observed.
Post Lab questions
- This will not have any effect on the expected results because phenacetin is more soluble in hot water than in the cold water. Acetanilide, on the contrary, crystallizes better in cold water, therefore creating a distinct crystallization point.
- Volume of water
5g-= 100ml
10g = ?
(10×100) ÷ (5) = 200ml
- Benzoic Acid crystallized
0.680 – 0.729 = 0.651g
- Salicylic acid crystals formed.
6.67 = 10ml
0.22 = ?
(0.22 × 10) ÷ (6.67) = 0.330g
Salicylic Acid will not crystallize out because, at 20°C, it is expected that all benzoic Acid will have crystallized out, leaving it in solution.
- Benzoic Acid recovered
0.651 = 75.9 %
? = 100%
(100 × 0.651) ÷ (75.9) = 0.860g
- . In the hot filtration step, material crystallized in filter paper. In the second filtration step, the material was lost on filter paper. Material did not completely crystallize from solution. With the melting point being in a specific range, it is concluded that benzoic Acid is a pure substance after recrystallization was done.