Ionic bondingIB MYP Sciences: Subtopic test

1. 1
   Salt is harvested from shallow seawater pans in Sri Lanka. The salt is sodium chloride, an ionic compound formed when sodium reacts with chlorine. A sodium atom has the electron arrangement 2,8,1 and a chlorine atom has the electron arrangement 2,8,7.

   (a)

   What happens to a sodium atom when it forms a sodium ion, Na⁺?

   [1 mark]

   • AIt gains one electron
   • BIt loses one electron
   • CIt shares one electron with chlorine
   • DIt gains one proton

   (b)

   What is the electron arrangement of a chloride ion, Cl⁻?

   [1 mark]

   • A2,8,7
   • B2,8
   • C2,8,8
   • D2,8,8,1

   (c)

   Describe, in terms of electrons, how sodium atoms and chlorine atoms form the ions in sodium chloride.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A steelworks in Brazil lines its furnaces with magnesium oxide bricks, because magnesium oxide, MgO, can withstand very high temperatures. Magnesium oxide is an ionic compound formed from magnesium, in Group 2, and oxygen, in Group 6.

   (a)

   Which row shows the ions in magnesium oxide?

   [1 mark]

   • AMg⁺ and O⁻
   • BMg²⁻ and O²⁺
   • CMg²⁺ and O⁶⁻
   • DMg²⁺ and O²⁻

   (b)

   Why does magnesium oxide have a very high melting point?

   [1 mark]

   • AA lot of energy is needed to overcome the strong electrostatic attraction between the oppositely charged ions in the lattice
   • BWeak forces between separate MgO molecules are hard to break
   • CIt contains strong covalent bonds inside each MgO molecule
   • DDelocalised electrons hold the structure together

   (c)

   Describe what a dot-and-cross diagram of magnesium oxide shows about the electrons.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Dubai is given two white solids, X and Y. One is an ionic compound and the other is a simple molecular substance. Solid X only melts at a very high temperature in a hot flame. It does not conduct electricity as a solid but it does conduct when dissolved in water. Solid Y melts below 100 °C in a warm water bath, does not dissolve in water and does not conduct electricity in any state.

   (a)

   Explain which solid is the ionic compound.

   [3 marks]

   (b)

   Outline how the student could test whether solid X conducts electricity when dissolved in water. Name the independent variable, the dependent variable, one control variable and one safety precaution.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Cities in cold countries, such as Toronto, spread calcium chloride on icy roads in winter to melt the ice. Calcium is in Group 2 and forms Ca²⁺ ions. Chlorine is in Group 7 and forms Cl⁻ ions. When the ice melts, the salt solution runs into drains, soil and rivers.

   (a)

   Explain, using electron transfer, why the formula of calcium chloride is CaCl₂, and why it conducts electricity when molten or dissolved but not when solid.

   [6 marks]

   (b)

   Discuss and evaluate the use of calcium chloride to melt ice on roads.

   [6 marks]

   Total for question 4: 12 marks

End of questions