Fig. 1 is a lattice model used by an engineer selecting a material for a reusable heat pack. The model represents calcium chloride, which dissolves in water...
Question 1 Report
Fig. 1 is a lattice model used by an engineer selecting a material for a reusable heat pack. The model represents calcium chloride, which dissolves in water and releases energy. Calcium ions and chloride ions are held together by strong attractions. The engineer compares it with paraffin wax, a molecular substance, before deciding which material can be stored safely as a solid.
(a) Name the type of structure represented in Fig. 1. [1]
(b) Use the charges in Fig. 1 to complete the formula: CaCl__. [1]
(c) Describe the force holding calcium ions and chloride ions together. [2]
(d) Explain why calcium chloride has a higher melting point than paraffin wax. [2]
Answer Details
(a) The model is a giant ionic lattice, also called an ionic lattice. [1 mark]
(b) The formula is \(\mathrm{CaCl_2}\), so the missing number is \(2\). [1 mark]
(c) Calcium and chloride ions are held together by strong electrostatic attraction between oppositely charged ions. [2 marks]
(d) Calcium chloride has strong ionic attractions throughout its lattice. Paraffin wax is molecular and has weaker forces between its molecules, so less energy is needed to melt it. [2 marks]
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