Oxidation and reductionIB MYP Chemistry: Subtopic test

1. 1
   A student in Athens burns a strip of magnesium ribbon in air. It burns with a bright white flame and leaves a white powder of magnesium oxide, MgO, as shown by the equation 2Mg + O₂ → 2MgO. Magnesium oxide is an ionic compound made of Mg²⁺ ions and O²⁻ ions.

   (a)

   Magnesium gains oxygen when it burns. What is this process called?

   [1 mark]

   • AOxidation
   • BReduction
   • CNeutralisation
   • DDecomposition

   (b)

   Which statement describes oxidation in terms of electrons?

   [1 mark]

   • AGain of electrons
   • BLoss of electrons
   • CGain of protons
   • DLoss of neutrons

   (c)

   Write the half-equation for magnesium atoms forming Mg²⁺ ions and explain why this is oxidation.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A teacher heats black copper(II) oxide, CuO, in a stream of hydrogen gas. The black solid turns into a pink-brown solid, copper, and steam is formed: CuO + H₂ → Cu + H₂O.

   (a)

   Which substance is reduced in this reaction?

   [1 mark]

   • AHydrogen
   • BWater
   • CCopper(II) oxide
   • DCopper

   (b)

   Which substance is the reducing agent?

   [1 mark]

   • ACopper
   • BCopper(II) oxide
   • CWater
   • DHydrogen

   (c)

   Explain why this is a redox reaction, in terms of oxygen.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Students at a school in Manila investigate the conditions needed for iron to rust. They set up three test tubes, each containing a clean iron nail. Tube A has boiled water with a layer of oil on top. Tube B has dry air and a drying agent, calcium chloride. Tube C has tap water and is open to the air. They leave the tubes for one week.

   (a)

   State a hypothesis for this investigation, with a scientific reason.

   [3 marks]

   (b)

   After one week only the nail in tube C is covered in orange-brown rust. State the conclusion, explain why rusting is oxidation in terms of oxygen, write the half-equation for iron forming Fe³⁺ ions and suggest one improvement to the investigation.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A recycling company in Poland recovers copper from waste electronics. The copper is dissolved to make a blue solution of copper(II) sulfate, and scrap iron is added. The iron displaces the copper, which is collected as a solid and sold: Fe + CuSO₄ → FeSO₄ + Cu. The pale green iron(II) sulfate solution left over must be treated before it can be disposed of. The company says this is better than mining new copper ore, which needs a lot of energy and damages land.

   (a)

   Explain, in terms of electrons, why this displacement reaction is a redox reaction. Include half-equations and name the oxidising agent and the reducing agent.

   [6 marks]

   (b)

   Discuss the benefits and drawbacks of recovering copper from waste in this way rather than mining new copper ore, and evaluate whether the company's claim is justified.

   [6 marks]

   Total for question 4: 12 marks

End of questions