RP10 - Preparation of an organic solid and liquid

An overview of RP10 - Preparation of an organic solid and liquid

5 min

Concentrated sulfuric acid: Handle with care to avoid skin or eye contact. Gloves must be worn when handling.
Hot water baths: Take care when handling hot beakers or flasks.
Ethanol and glacial ethanoic acid: Both are flammable; handle in a fume cupboard and ensure there are no naked flames when handling.
Separating funnel: When using the separating funnel, vent the system regularly to avoid pressure buildup.

Experimental method for AQA Required Practical 10 – Preparation of an organic solid and liquid

Part 1 Preparation of aspirin

EXPERIMENTAL METHOD AQA REQUIRED PRACTICAL 10 - PART 1. 1. Weigh approximately 6.00 g of salicylic acid and record the mass. Transfer to a conical flask. Use an analytical balance to measure the exact mass of salicylic acid and note this down. 2. Using a 10 cm³ measuring cylinder, add 10 cm³ of thionic anhydride to the flask and swirl. Read the volume in the measuring cylinder at eye level to avoid parallax error. 3. Add 5 drops of concentrated sulfuric acid catalyst and swirl for thorough mixing. Ensure only 5 drops are added to avoid excess acid which may lead to unwanted side reactions. 4. Heat the conical flask in a 400 cm³ beaker of hot water at approximately 50 °C for 20 minutes. Ensure the temperature does not exceed 65 °C. Use a thermometer to monitor the temperature and avoid overheating. 5. After heating, cool the flask, pour in 75 cm³ of distilled water, and stir. A white precipitate of solid aspirin will form. 6. Filter the crude aspirin under reduced pressure using a Buchner funnel fitted with filter paper. Ensure the filter paper is secured with vacuum before adding the reaction mixture to prevent loss of product during the filtration process. 7. Measure 15 cm³ of ethanol into a boiling tube. Add the crude aspirin, collect and stir until fully dissolved. Ensure all aspirin dissolves in the ethanol for a complete purification process. 8. Pour the ethanol solution into 40 cm³ of water in a conical flask. If no crystals form, scratch the flask or use an ice bath to induce crystallisation. 9. Filter the purified aspirin under reduced pressure and dry it on filter paper. Ensure the product is properly dried to remove residual solvent. Record the mass obtained.

Experimental method for AQA Required Practical 10 – Preparation of an organic solid and liquid

Part 2 Preparation of ethyl ethanoate

EXPERIMENTAL METHOD AQA REQUIRED PRACTICAL 10 - PART 2. 1. Add 10 cm³ of ethanol, 12 cm³ of glacial ethanoic acid, and 15 drops of concentrated sulfuric acid catalyst to a 50 cm³ pear-shaped flask with anti-bumping granules. Read the volume in the measuring cylinder at eye level to avoid parallax error. 2. Heat the mixture under reflux for 15 minutes using a water bath and ensure the water temperature does not exceed 78 °C. Maintain the temperature at 78 °C for efficient esterification. 3. Transfer the reaction mixture to a separating funnel. Shake gently by inversion. Open the valve periodically upon shaking to reduce build up of pressure. 4. Open the stopcock and drain off the lower aqueous layer into a waste beaker. Ensure only the waste aqueous layer is removed and the ethyl acetate layer remains in the funnel. 5. Transfer the remaining ethyl ethanoate into a dry boiling tube containing about 1 g of drying agent, anhydrous sodium sulfate. Agitate the tube so that any water is absorbed by the sodium sulfate. 6. Transfer the ethyl ethanoate to a pear-shaped flask and set up for distillation. Collect the distillate in a clean, dry, pre-weighed flask. Ensure the ethyl ethanoate distills at its boiling point (77-78 °C). 7. Record the mass of the purified ethyl ethanoate. Subtract the weight of the flask to obtain mass of product.

Temperature control in the preparation of aspirin is essential.

A laboratory setup featuring a beaker filled with blue liquid, a thermometer inserted into the beaker, and a Bunsen burner underneath the beaker, all resting on a wire mesh support.

Monitor the temperature carefully, using a water bath and ensuring it does not exceed 65 °C to avoid decomposing

A laboratory setup showing a conical flask containing blue liquid, placed on a wire mesh over a Bunsen burner. The burner is lit, producing a flame underneath the flask, and there are red wavy lines indicating heat.

Don't

Allow the temperature to rise above 65 °C – overheating may degrade the aspirin product.

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.

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.

When purifying ethyl ethanoate, a suitable drying agent should be used.

A laboratory flask with a narrow neck and a wide base, containing a blue liquid at the bottom.

Use anhydrous sodium sulfate to remove any water from the ethyl ethanoate before distillation.

A laboratory flask with a narrow neck and a wide base, containing a blue liquid.

Don't

Allow any water to remain in the ethyl ethanoate – this can interfere with the purity of the final product and therefore lead to inaccurate yield calculations.

Atom economy measures the efficiency of a chemical reaction in terms of how well atoms are utilized to form the desired product. For aspirin preparation, calculate the atom economy using the molecular formulas of reactants and products.

Compare this method with the alternative method using ethanoyl chloride, which has a higher atom economy but is less favored in industry due to safety concerns (e.g. more reactive and toxic by-products).

Compare the melting point of your sample of aspirin to the known value for pure aspirin,, using melting point apparatus.

A lower, broader melting point may indicate impurities in your sample.

An illustration showing a thermometer bulb, a magnifying lens, and a melting point tube and sample, with labels indicating each component.

Calculate the theoretical yield of ethyl ethanoate from the reaction between ethanol and glacial ethanoic acid.

Identify the limiting reagent:

The stoichiometric ratio is 1:1, therefore the limiting reagent is the reagent with the highest number of moles from the reactants, which is ethanoic acid.

There is also a 1:1 mole ratio of ethanoic acid to ethyl ethanoate.

After obtaining the mass of the distilled ethyl ethanoate, calculate the percentage yield:

Potential reasons for yield loss include:

Loss of product during filtration or purification
Incomplete reaction or side reactions.

Impurities remaining in the crude product affect the final mass. This is the only explanation for yields over 100%.

The purity of the ethyl ethanoate can be assessed by measuring the boiling point during distillation. Pure ethyl ethanoate has a boiling point of approximately . Any deviation from this value may suggest the presence of impurities, such as unreacted starting materials.

RP10 - Preparation of an organic solid and liquid

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Experimental aim

Safety

Method

Practical pitfalls

Analysis and evaluation