Description: Separation using a suitable solvent, also known as dissolution, involves dissolving a solid substance in a solvent to separate it from impurities. The desired substance is then recovered from the solution by evaporation of the solvent.

Explanation: The success of this method relies on the principle that different substances have different solubilities in different solvents. A suitable solvent is one that:

• Dissolves the desired substance readily.
• Does not dissolve the impurities.
• Is easily removed (e.g., by evaporation).
• Is non-toxic and inexpensive.

Factors to consider when choosing a solvent: The polarity of the solvent is crucial. "Like dissolves like" – polar solvents dissolve polar substances, and non-polar solvents dissolve non-polar substances. The boiling point of the solvent is also important for ease of removal.

Advantages: Relatively simple and inexpensive. Can be used to separate a large amount of material.

Disadvantages: May not be effective if impurities have similar solubilities to the desired substance. Can lead to loss of product if the solvent is volatile. Requires careful selection of a suitable solvent.

(a) The unknown solid is likely to be sugar (C₁₂H₂₂O₁₁).

Explanation: The melting point range of 105-110 °C is closest to the melting point of sugar (186 °C) listed in the table. While the melting point of sugar is significantly lower than the melting points of NaCl, KNO₃, and Cu, the provided range is the closest match. It's important to note that melting point ranges are often given to account for experimental error and gradual melting.

(b) A melting point range is reported rather than a single melting point temperature because:

• Impurities: Impurities disrupt the crystal lattice structure of a solid. This means that impurities cause the solid to melt over a range of temperatures, rather than melting at a single, sharp temperature.
• Experimental Error: It is difficult to determine the exact moment when a solid starts to melt and the exact moment when it is completely melted. A range reflects the spread of temperatures observed during the melting process, accounting for potential experimental error.
• Gradual Melting: When a solid is heated, it doesn't always melt instantaneously. The temperature gradually increases as the solid transitions to a liquid. The melting point range reflects this gradual transition.

Therefore, reporting a range provides a more accurate assessment of the purity of the substance.

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.