Benzoic Acid Essay

1. Introduction and background
The experiment that will be conducted is the preparation of benzoic acid.
Benzoic acid is a carboxylic acid and this has been established in the 16th century. The molecular structure of benzoic acid can be seen in the following figure.

Figure 1 – Molecular Structure Benzoic acid is used to prepare esters with the very high boiling points and is used as plasticisers. Plasticisers are compounds that are added to plastics to make it softer and more user friendly at low temperatures.
Some of benzoic acid esters are used as fragrance enhancers. The salts of benzoic acid serve as the preservatives. Most sodas and juices are preserved with sodium benzoate.

2. Literature study
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Only a small amount of carboxylic acid solves in water to form a weak acid solution. Benzoic acid reacts like a typical carboxylic acid which forms salts in reactions with bases . Sodium, potassium and ammonium salts of carboxylic acids are more soluble than the corresponding carboxylic acid.
A common strategy used to isolate a carboxylic acid from a solution carboxylic acid salt , is to add a strong acid to the solution. You will precipitate benzoic acid from a solution of sodium benzoate by acidizing the solution with hydrochloric acid. Acidification of the solution shifts the equilibrium to the left and precipitates the insoluble carboxylic acid.

Synthesis of benzoic acid
Benzoic acid is produced extensively and on a large scale by partial oxidation of toluene with oxygen at moderate temperature and pressure in the presence of a catalyst. Most industrial processes uses catalysis - one of the principles of green chemistry . The process uses cheap raw materials and delivers a high
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Use the 5cm3 syringes, the 1cm3 pipettes and connecting pipe to build an apparatus to measure and transfer liquids.
Measure out 1 cm3 methyl benzoate with a 1 cm3 pipette and place it in a pear flask.

Figure 4 – Different kinds of pipets

2. Add 15 cm3 of 2m sodium hydroxide and a spatula tip of boiling stones (anti-bumping granules) to the pear flask.

3. Assemble a reflux setup well. Inspect your wire gauze to make sure that it does not have holes in the fire proofing that will allow the flame to reach the pear flask. (Ask your gauze to be replaced if broken).

4. Bring the mixture in the pear flask to boil. CAUTION! The bottom of the pear flask may not touch the wire gauze – this will prevent overheating of the mixture. Reflux reaction mixture for 45 minutes. {The reflux time starts the time when the mixture in the pear flask boils. The mixture boils approximately after 5 minutes.

5. Put out the flame and allow the reaction mixture to cool for 5 minutes.

6. Decant the liquid in the pear flask into a 250 cm3 containing 25 cm3 3M hydrochloric acid . (A thick white precipitate should form.)

7. Filter the precipitates using gravity filtration. Allow the water to drain and then wash the precipitate with small volume (Approximately 2cm3) of distilled water. Allow this water to drain and repeat washing procedure

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