Synoptic Exam Questions (AQA AS Chemistry): Exam Questions

A student prepares the ester propyl ethanoate by reacting ethanoic acid with propan-1-ol, using concentrated sulfuric acid as a catalyst. The mixture is heated under reflux.

CH₃COOH + CH₃CH₂CH₂OH ⇌ CH₃COOCH₂CH₂CH₃ + H₂O

The student starts with 5.75 g of propan-1-ol and an excess of ethanoic acid. After purification by distillation and separation, the student obtains 6.55 g of propyl ethanoate.

State the role of the concentrated sulfuric acid in this reaction.

The reaction is reversible. Suggest a reason why the apparatus is set up for distillation after the initial reflux period to separate the ester from the reaction mixture.

Calculate the percentage yield of propyl ethanoate.
(M_r of propan-1-ol = 60.0; M_r of propyl ethanoate = 102.0)

The student uses infrared spectroscopy to check the purity of the final product.

State one key absorption that would be present in the spectrum of the starting material, propan-1-ol, but absent from the spectrum of the pure product, propyl ethanoate.

You should describe the bond responsible and its approximate wavenumber.

Ethanol can be produced industrially by two main methods: the fermentation of glucose and the direct hydration of ethene.

The hydration of ethene uses a catalyst of solid silicon dioxide coated in phosphoric(V) acid.

State the conditions of temperature and pressure used in this process.

The fermentation of glucose (C₆H₁₂O₆) produces ethanol and carbon dioxide.

Write a balanced equation for this reaction.

 A student carries out the fermentation of 15.0 g of glucose. After purification, 6.25 g of ethanol is collected.

Calculate the percentage yield of ethanol.

Explain why the first ionisation energy of calcium is greater than that of strontium.

Draw a 'dot-and-cross' diagram to show the bonding in calcium iodide.
Show outer shell electrons only.

Solid calcium iodide is reacted with concentrated sulfuric acid. This is a redox reaction where the iodide ion acts as a reducing agent.

8I⁻ (s) + H₂SO₄ (l) + 8H⁺ (aq) → 4I₂ (s) + H₂S (g) + 4H₂O (l)

Explain why the iodide ion is a more powerful reducing agent than the chloride ion.

State the element that is oxidised in the reaction shown in part (c) and the change in its oxidation state.

Identify the element that is oxidised in the reaction shown in part (c) and state the change in its oxidation state.

CaCO₃ (s) + 2HI (aq) → CaI₂ (aq) + H₂O (l) + CO₂ (g)

The resulting solution is transferred to a 250.0 cm³ volumetric flask and made up to the mark with deionised water.

Calculate the concentration, in mol dm^-3, of iodide ions (I^-) in the final solution.

(M_r of CaCO₃ = 100.1)

A student is given a sample of an unknown straight-chain carboxylic acid, X.

The student dissolves 1.85 g of X in deionised water and makes the solution up to 250.0 cm³ in a volumetric flask. A 25.0 cm³ sample of this solution is titrated with 0.100 mol dm^-3 sodium hydroxide solution. The mean titre required for neutralisation is 25.0 cm³.

State the colour change that would be observed at the end-point if the student used phenolphthalein.

Assuming X is a monoprotic acid, use the titration data to calculate the relative molecular mass (M_r) of X.

The empirical formula of X is C₃H₆O₂.

Use your answer from part (b) to determine the molecular formula of X.

Draw the displayed formula of X and state its systematic name.

Name the primary alcohol that can be oxidised under reflux to form X.

Identify two key absorptions that would be expected in the infrared spectrum of X.

For each, state the bond responsible and the approximate wavenumber.

Cyclohexene can be prepared in the laboratory by the acid-catalysed dehydration of cyclohexanol. The reaction is reversible.

Draw the mechanism for the acid-catalysed dehydration of cyclohexanol to form cyclohexene.

In an experiment, 0.200 mol of cyclohexanol was heated with an acid catalyst in a sealed container of volume 1.50 dm³. At equilibrium, 0.160 mol of cyclohexene had been formed.

Calculate the value of the equilibrium constant, K_c, for this reaction.

Cyclohexene can undergo addition polymerisation.

Draw the repeating unit of poly(cyclohexene).

Explain why poly(cyclohexene) is a solid at room temperature, whereas the monomer, cyclohexene, is a liquid.