Aspirin can be produced by reacting salicylic acid with ethanoic anhydride - AQA - A-Level Chemistry - Question 4 - 2020 - Paper 2

A 50 cm³ measuring cylinder should be used, as it allows for accurate volume measurement (between 10 to 100 cm³).

Concentrated phosphoric acid is corrosive and can cause skin burns or permanent eye damage.

Salicylic acid + Ethanoic anhydride → Aspirin + Acetic acid

1. Moles of salicylic acid = ( \frac{6.01 \text{ g}}{138.0 \text{ g/mol}} = 0.04355 \text{ mol} )
2. Volume of ethanoic anhydride = 10.5 cm³ = 0.0105 L. Density = 1.08 g/cm³.

Mass of ethanoic anhydride = 10.5 cm³ × 1.08 g/cm³ = 11.34 g.

3. Moles of ethanoic anhydride = ( \frac{11.34 \text{ g}}{102.0 \text{ g/mol}} = 0.1118 \text{ mol} )

4. The reaction is a 1:1 ratio, salicylic acid is the limiting reagent since 0.04355 mol < 0.1118 mol.

5. Moles of aspirin formed = 0.04355 mol (from salicylic acid).

6. Mass of aspirin produced = 0.04355 mol × 180.0 g/mol = 7.836 g.

7. For the yield, Actual yield = Theoretical yield × percent yield = 7.836 g × 0.841 = 6.60 g.

Reagent in excess: Ethanoic anhydride. Mass of aspirin: 6.60 g.

Difference 1: The melting point of crude aspirin would be lower than that of pure aspirin due to impurities present in the crude sample.

Difference 2: The melting point range of crude aspirin would be broader, reflecting the presence of various impurities compared to the sharp melting point of pure aspirin.

Precaution 1: Use a water bath instead of direct heat to avoid overheating and potential decomposition of the aspirin.

Precaution 2: Do not place the mixture on a flame; ensure the heating is gentle to prevent the risk of ignition.

The cold ethanol is added to reduce the temperature of the solution, which helps in the crystallization process of aspirin, allowing for purer product formation.

The crude aspirin would typically appear as larger, irregular crystals and may be off-white in color, while the purified aspirin would have smaller, clear, and needle-like crystals.