Metallic bonding and alloysIB MYP Chemistry: Subtopic test

1. 1
   An electrician in Johannesburg chooses copper for the electrical cables in a new school building because copper conducts electricity very well. Copper is a metal.

   (a)

   Which statement describes metallic bonding?

   [1 mark]

   • ATransfer of electrons from metal atoms to non-metal atoms
   • BAttraction between positive metal ions and a sea of delocalised electrons
   • CShared pairs of electrons between pairs of atoms
   • DWeak forces between separate metal molecules

   (b)

   Why does copper conduct electricity?

   [1 mark]

   • AIts positive ions are free to move through the metal
   • BIts electrons are held in fixed shared pairs
   • CIts atoms each have a full outer shell
   • DIts delocalised electrons are free to move and carry charge

   (c)

   Describe the structure of a metal such as copper.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A craftsperson in Marrakech hammers a flat sheet of copper into a bowl. The copper changes shape without cracking or breaking.

   (a)

   What does it mean to say that copper is malleable?

   [1 mark]

   • AIt can conduct electricity
   • BIt is hard and brittle
   • CIt can be hammered or bent into shape without breaking
   • DIt dissolves in water

   (b)

   What happens to the delocalised electrons when the metal is hammered into shape?

   [1 mark]

   • AThey stay between the ions and keep them bonded together
   • BThey are lost from the metal
   • CThey become fixed to individual ions
   • DThey form covalent bonds with the ions

   (c)

   Explain why the copper changes shape without breaking.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student compares the hardness of pure copper with brass, an alloy of copper and zinc. She drops the same steel ball bearing from the same height onto a strip of each metal and measures the diameter of the dent. She does three trials on each strip. The dents in copper measured 3.5 mm, 3.4 mm and 3.3 mm. The dents in brass measured 2.2 mm, 2.0 mm and 2.1 mm.

   (a)

   Calculate the mean dent diameter for each metal and state which metal is harder, giving a reason.

   [3 marks]

   (b)

   Explain, in terms of structure, why brass is harder than copper, and evaluate how reliable her results are.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A town council plans to build a new footbridge. Pure iron is too soft for building, so the council will use steel, an alloy of iron with a small amount of carbon. The steel could be made from iron ore or from recycled scrap steel.

   (a)

   Explain, in terms of structure and bonding, why pure iron is soft but steel is harder.

   [6 marks]

   (b)

   Discuss the social, economic and environmental implications of making the steel from recycled scrap rather than from iron ore, and evaluate which the council should choose.

   [6 marks]

   Total for question 4: 12 marks

End of questions