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Practical chemistry for exams›CP 16 - The preparation of aspirin

CP 16 - The preparation of aspirin

An overview of CP 16 - The preparation of aspirin

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In Edexcel Core Practical 16: The preparation of aspirin, aspirin (acetylsalicylic acid) is produced by reacting salicylic acid with acetic anhydride in the presence of sulfuric acid as a catalyst.

The reaction produces aspirin and acetic acid as a waste product, after synthesising the aspirin, purification steps and testing of purity are completed.

In Edexcel core practical 16: Synthesise aspirin from 2-hydroxybenzoic acid, there are several important safety requirements to be aware of (beyond normal lab practice such as wearing goggles).

Wear a lab coat.
Perform the experiment in a well-ventilated room.
Wear heat-protective gloves when handling hot equipment.
Ethanoic anhydride and concentrated sulfuric acid are corrosive.
2-hydroxybenzoic acid is harmful.

The image depicts a step-by-step experimental method titled 'EDEXCEL CORE PRACTICAL 16' for synthesizing aspirin.

Step 1: Weigh 2.0 g of 2-hydroxybenzoic acid and place it in a pear-shaped flask. The accompanying image shows a digital scale displaying '2.0 g'.

Step 2: Add 5.0 cm³ of ethanoic anhydride and five drops of concentrated sulfuric acid to the flask. Attach a condenser to the flask. The image shows a pear-shaped flask with a dropper adding liquid.

Step 3: In the fume cupboard, heat the water bath using a Bunsen burner until all the solid dissolves. Continue heating for a further 10 minutes. An illustration shows a setup with a water bath, anti-bumping granules, a reaction mixture, condenser, and labels 'Water In' and 'Water Out'.

Step 4: Remove the flask from the water bath and add 10 cm³ of crushed ice with some distilled water. The image shows a flask with ice cubes and water.

Step 5: Filter the crude aspirin using a Büchner funnel and suction filtration. Wash the crystals with iced water. The diagram shows a Büchner funnel and flask labeled 'To water pump'.

Step 6: Recrystallise by dissolving the crude product in ethanol:water (1:3 mixture). Filter and dry the purified aspirin. The image shows a filtration setup with a water pump.

Step 7: Measure the mass of the pure, dry crystals. The digital scale displays '0.0 g'.

Step 8: Determine the melting point using melting temperature apparatus to assess purity. The apparatus is labeled 'Melting Point Apparatus' with a temperature dial.

Wearing the appropriate personal protective equipment is essential to avoid direct contact with harmful chemicals and to ensure safety throughout the experiment.

A simple illustration of a pair of goggles and gloves.

Do

Wear goggles and gloves when handling any chemicals, particularly concentrated acids, ammonia, and metal salts, as they can be corrosive or irritating to the skin and eyes.

A person wearing no goggles or gloves whilst handling chemicals.

Don't

Skip protective equipment just because ‘it’s only a few drops’.

It is crucial to use clean and dry glassware when performing analytical tests.

Five test tubes arranged in a row, with varying heights and shapes.

Do

Ensure all glassware is clean and dry before use to avoid contamination and ensure accurate results.

A test tube with a white body and brownish stains or markings on its surface.

Don't

Reuse glassware that has not been properly cleaned and dried, as this could lead to inaccurate readings or unintended chemical reactions.

Take care when filtering the aspirin product under reduced pressure.

A diagram illustrating a Bucher funnel setup. The image includes a Bucher funnel at the top, with filter paper inside it. Below, a flask is connected to a water pump, and a drop of liquid is shown falling from the funnel into the flask.

Do

Filter the aspirin gently under reduced pressure to collect the solid efficiently. Dampening the filter paper and starting the suction before adding the reaction mixture creates a good seal.

A diagram illustrating a Bucher funnel setup, with labeled components including a Bucher funnel, filter paper, and a water pump connected to a flask.

Don't

Apply excessive force during filtration – this could cause the filter paper to tear and the solid to be sucked through to the collection vessel.

Calculate the relative molecular masses of 2-hydroxybenzoic acid and aspirin.

Calculate the moles of 2-hydroxybenzoic acid then calculate the moles of aspirin. The stoichiometric ratio is 1:1.

Theoretical mass can be calculated using:

Calculate the % yield by using your mass obtained as the actual yield into the equation: