Properties of ionic compoundsIB MYP Chemistry: Subtopic test

1. 1
   A student in Cairo heats a few crystals of sodium chloride in a crucible over a Bunsen burner. The crystals do not melt, even though the flame is very hot. A furnace is needed to melt sodium chloride, at 801 °C.

   (a)

   Which type of structure does sodium chloride have?

   [1 mark]

   • ASeparate simple molecules
   • BA giant covalent structure
   • CA giant ionic lattice
   • DA metallic lattice with delocalised electrons

   (b)

   What happens to the ions in the lattice when sodium chloride melts?

   [1 mark]

   • AThey gain enough energy to break free from their fixed positions and move around
   • BThey turn into neutral atoms
   • CThey are destroyed and new atoms are formed
   • DThey stay in fixed positions but vibrate faster

   (c)

   Explain why sodium chloride has such a high melting point.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher in Auckland gives students a white solid labelled X. They find that X does not conduct electricity when solid, melts only above 700 °C, and conducts electricity well when molten. X also dissolves in water, and the solution conducts electricity.

   (a)

   What does the evidence suggest about X?

   [1 mark]

   • AX is a metal
   • BX is a simple molecular compound
   • CX is a giant covalent compound
   • DX is an ionic compound

   (b)

   Which particles carry the charge when molten X conducts electricity?

   [1 mark]

   • ADelocalised electrons that are free to move
   • BIons that are free to move
   • CNeutral molecules
   • DProtons moving through the liquid

   (c)

   Explain why X does not conduct electricity when solid but does when molten.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Kuala Lumpur investigates how well salt solutions conduct electricity. She dissolves 0 g, 2 g, 4 g, 6 g and 8 g of sodium chloride in separate 100 cm³ portions of distilled water and measures the current in each solution, using the same circuit and electrodes every time. The ammeter readings were 0.00 A, 0.18 A, 0.35 A, 0.52 A and 0.69 A. She predicted that the more sodium chloride dissolved, the greater the current.

   (a)

   Describe the trend in her results and explain it.

   [3 marks]

   (b)

   Evaluate the investigation: state whether her prediction is supported and why, and suggest one weakness in the method with an improvement.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A company in Thailand makes sodium chloride by letting seawater flow into large shallow coastal pans, where the sun evaporates the water and leaves salt crystals. The salt is sold for food and to chemical factories that use it as a raw material.

   (a)

   Explain, in terms of structure and bonding, why sodium chloride has a high melting point, dissolves in water, and conducts electricity only when it is molten or dissolved.

   [6 marks]

   (b)

   Discuss the social, economic and environmental implications of making salt in coastal pans, and evaluate whether the company should expand.

   [6 marks]

   Total for question 4: 12 marks

End of questions