Chem Lab

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Experiment #4A- A Separation and purification Scheme
Amena Alkeswani, PHCC
Dhanlal Murally, PHCC
September 27, 2012

There are millions of different organic compounds. Most of them are found in mixtures and in order to achieve a pure form they need to be separated, isolated, and purified. However, there are endless numbers of possible mixtures, which make it impossible to have a pre-designed procedure for every mixture. So chemists often have to make their own procedures. The purpose of this experiment was to prepare the student to the real world by them designing their own procedure which will help them understand the techniques of separation and purification better. The goal was to extract two of the components of the mixture that consisted of 50% benzoic acid, 40% benzoin, and 10% dibromobenzene. The benzoic acid was extracted by the use of base and extraction technique. Then a crystallization was performed in order to separate benzoin by the use of hexane a solvent, leaving the dibromobenzne in the mother liquor. The percent recovery for benzoic acid was 91.8% and 80.3% for the benzoin. The MP for benzoic acid was 119-122°C (1) and 135-136°C (2)for the benzoin. The high percent recovery and closeness of measured MP to the literature value indicate that the designed procedure was successful. Results and Discussion:

The initial sample consist of:
Table 1:
Benzoic acid (50%)| Benzoin (40%)| Dibromo-benzene (10%)| (3)| (4)| (5)|

1) Dissolve 1.0 g of the mixture in methylene chloride in a centrifugal tube 2) Set up the separatory funnel.
3) In order to extract the benzoic acid add 5.0 ml of the 1 mol NaOH solution, then shake the funnel 1 time per second and open it while it is upside down to allow the pressure out. 4) Allow the solution to settle.

5) The NaOH layer will extract the benzoic acid .
6) Perform a second extraction on methylene chloride repeat the steps from 2-6. 7) Add 2...
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