Ionic bondingIB MYP Chemistry: Subtopic test

1. 1
   A teacher in Nairobi burns a strip of magnesium ribbon in air. It burns with a dazzling white flame and leaves a white powder of magnesium oxide, an ionic compound. Magnesium atoms have two electrons in their outer shell and oxygen atoms have six.

   (a)

   Which statement describes what happens to magnesium atoms when they react with oxygen to form magnesium oxide?

   [1 mark]

   • AEach magnesium atom gains two electrons
   • BEach magnesium atom loses two electrons
   • CEach magnesium atom shares two electrons with an oxygen atom
   • DEach magnesium atom loses two protons

   (b)

   Which row gives the charges on the ions in magnesium oxide?

   [1 mark]

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

   (c)

   Describe, in terms of electrons, how magnesium oxide forms from magnesium atoms and oxygen atoms.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A geologist in Chile examines a cube-shaped crystal of rock salt, which is sodium chloride. When she taps the crystal with a hammer it splits into smaller pieces that are also cube-shaped. Sodium chloride is an ionic compound.

   (a)

   Which statement describes the arrangement of the particles in a crystal of sodium chloride?

   [1 mark]

   • AA regular repeating pattern of alternating positive and negative ions
   • BSeparate NaCl molecules, each held together by a shared pair of electrons
   • CA random arrangement of positive and negative ions
   • DA regular pattern of positive ions only, with electrons shared between them

   (b)

   What holds the ions together in a crystal of sodium chloride?

   [1 mark]

   • AShared pairs of electrons between neighbouring ions
   • BAttraction between positive ions and a sea of delocalised electrons
   • CStrong electrostatic attraction between oppositely charged ions
   • DWeak forces between separate molecules

   (c)

   Explain why the crystal splits into smaller pieces that are also cube-shaped.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student in Lisbon makes a saturated solution of sodium chloride. She pours some into a shallow dish on a warm windowsill and some into a shallow dish in a cool cupboard, then leaves the water to evaporate and compares the crystals that form. She predicts that the slower the water evaporates, the larger the crystals will be.

   (a)

   Identify the independent variable, the dependent variable and one control variable in her investigation.

   [3 marks]

   (b)

   Write a hypothesis with a scientific reason, and outline how she should collect results so that the comparison is fair.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city in northern Europe is deciding whether to spread calcium chloride, CaCl₂, on its roads in winter to stop ice forming. Calcium chloride is an ionic compound. Calcium atoms have two electrons in their outer shell and chlorine atoms have seven.

   (a)

   Describe what a dot-and-cross diagram of calcium chloride, CaCl₂, shows and explain why two chloride ions are needed for each calcium ion.

   [6 marks]

   (b)

   Discuss the social, economic and environmental implications of spreading calcium chloride on roads, and evaluate whether the city should do so.

   [6 marks]

   Total for question 4: 12 marks

End of questions