Types of Substance (Edexcel GCSE Chemistry: Combined Science)

A student carried out the electrolysis of copper chloride solution using graphite electrodes.

Figure 1 shows the apparatus they used.

Figure 1

Explain why copper chloride solution, rather than solid copper chloride was used.

Cu²⁺ and H⁺ ions are attracted to the cathode.

State the ions attracted to the anode.

Graphite electrodes are chosen because they are inert and can conduct electricity.

Explain why it is important inert electrodes are used.

Explain, in terms of its structure, how graphite can conduct electricity

Cobalt is a transition metal.

Cobalt has the atomic number 27.
State one thing this tells you about cobalt atoms.

 Describe the structure of cobalt.

Cobalt’s melting point is 1495°C.

Explain why cobalt has a high melting point, using its structure.

Alloys can be made by mixing other metals, such as chromium, with cobalt.

Figure 1 shows the difference in structure between pure cobalt and an alloy.

Figure 1

Use Figure 1 to explain why a cobalt and chromium alloy is less malleable than pure cobalt.

This question is about three substances: calcium, calcium chloride and calcium carbonate.

Calcium chloride and calcium carbonate contain ions: Ca²⁺, Cl^- and CO₃^2-;

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At room temperature, calcium can conduct electricity but calcium chloride cannot.

Use their structure to explain why.

Explain what you could do to prove that dissolving calcium chloride in water will allow it to conduct electricity.

Calcium carbonate is insoluble in water.

Describe what you would have to do to make calcium carbonate conduct electricity.

Explain why this would work.

Figure 1 shows some different ways used to represent the structure of an ammonia molecule.

    Dot and cross diagram               ball and stick diagram               space filling diagram

Figure 1

Draw the displayed formula of ammonia.

Give one advantage of the dot and cross diagram.

Discuss the limitations of the dot and cross and space filling diagrams.

Ammonia has a low boiling point (-33°C).

Explain why, using its structure.