A suitable method is distillation.

Scientific Principle: Ethanol has a lower boiling point (78.3 °C) than water (100 °C). During distillation, the mixture is heated, and the component with the lower boiling point (ethanol) vaporizes first. The vapour is then cooled and condensed back into a liquid, separating it from the water.

Procedure:

1. Set up a distillation apparatus, including a round-bottomed flask containing the ethanol-water mixture, a distillation head, a condenser, and a receiving flask.
2. Heat the mixture in the round-bottomed flask.
3. The ethanol will vaporize first, travel through the distillation head and condenser, and condense in the receiving flask.
4. The water will vaporize later and condense in the condenser.

Further Purification: The ethanol obtained from distillation may not be completely pure. A further purification step could be fractional distillation. Fractional distillation uses a fractionating column packed with glass beads or other material to improve the separation of the ethanol and water. This allows for a more efficient separation of the components based on their boiling points.

A suitable method is precipitation followed by filtration.

Procedure:

1. Add a dilute solution of sodium carbonate (Na₂CO₃) to the solution. This will react with the copper(II) ions to form a copper(II) carbonate precipitate. The balanced equation is: Cu²⁺(aq) + CO₃^2-(aq) → CuCO₃(s)
2. Allow the precipitate to settle.
3. Filter the solution to remove the solid copper(II) carbonate.
4. Dissolve the copper(II) carbonate precipitate in dilute hydrochloric acid (HCl). This will convert the copper(II) carbonate to copper(II) chloride. The balanced equation is: CuCO₃(s) + 2HCl(aq) → CuCl₂(aq) + H₂O(l) + CO₂(g)
5. Filter the solution to remove any insoluble impurities.
6. Evaporate the water to obtain solid copper(II) chloride.

Scientific Principles:

• Precipitation: The formation of an insoluble solid (the copper(II) carbonate) from the solution. The solubility product (Ksp) of copper(II) carbonate is low, so it readily precipitates.
• Filtration: Separating the solid precipitate from the liquid solution using a filter paper.
• Acid-Base Reaction: The reaction of the copper(II) carbonate with hydrochloric acid to regenerate copper(II) chloride in solution.

(a) Substance X is likely to be sodium chloride (NaCl) and substance Y is likely to be potassium nitrate (KNO₃).

Reasoning: NaCl has a well-known melting point of 801 °C and a boiling point of 1413 °C. However, the provided melting point of 88 °C and boiling point of 112 °C are significantly lower. This suggests that the substance is not pure NaCl, but rather a different compound with lower melting and boiling points. KNO₃ has a melting point of 335 °C and a boiling point of 358 °C. The provided values are closer to these values than to the melting and boiling points of NaCl. Therefore, KNO₃ is a more likely candidate for substance Y. The difference in melting and boiling points between the two substances allows for their identification.

(b) The melting point and boiling point data are useful indicators of purity.

Narrow Melting Point Range: A narrow melting point range indicates a high degree of purity. This is because impurities disrupt the crystal lattice structure, leading to a lower and broader melting point range. A pure substance will melt at a sharp, specific temperature.

Broad Melting Point Range: A broad melting point range indicates the presence of impurities. Impurities interfere with the melting process, causing the substance to melt over a range of temperatures. The wider the range, the more impurities are likely to be present. The melting point will be depressed and the range will be wider.