Chapter 1 Practice Paper: Oxidation and Reduction — question paper

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1. 1

   Which change is reduction?

   1. Airon losing electrons to form Fe²⁺
   2. Bchlorine changing from 0 to −1
   3. Csulfur rising from −2 to 0
   4. Dcarbon burning to carbon dioxide
   ( )
2. 2

   In the reaction 2H₂S + SO₂ → 3S + 2H₂O, sulfur dioxide is

   1. Athe reducing agent, because sulfur in it rises from +4 to 0
   2. Bthe oxidising agent, because sulfur in it falls from +4 to 0
   3. Cthe reducing agent, because sulfur in it falls from +4 to 0
   4. Dunchanged, acting as the solvent
   ( )
3. 3

   Aqueous sodium sulfate is mixed with aqueous barium nitrate. Why is this NOT a redox reaction?

   1. Abecause the product is insoluble
   2. Bbecause the reaction happens too quickly
   3. Cbecause barium is too reactive
   4. Dbecause no element changes its oxidation state
   ( )
4. 4

   Which observation shows that chlorine water has acted as an oxidising agent on a metal above hydrogen in the reactivity series?

   1. Athe pale green colour deepens
   2. Bthe solution turns universal indicator purple
   3. Cwhite fumes are given off
   4. Dthe chlorine colour fades while the metal dissolves away to form its ions
   ( )
5. 5

   Rust prevention by attaching magnesium blocks to an iron structure works because magnesium

   1. Acoats the iron with an unreactive layer
   2. Babsorbs all the water before iron can react
   3. Cis oxidised preferentially, keeping the iron from losing electrons
   4. Dreacts with rust to reform iron
   ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Include state symbols where the question asks, and balance every equation.

1. 1

   Hydrogen gas is passed over heated copper(II) oxide: CuO + H₂ → Cu + H₂O.

   1. (a)

      State which substance is oxidised and which is reduced, in terms of oxygen transfer.

      [2]
   2. (b)

      Name the oxidising agent and the reducing agent.

      [2]
   3. (c)

      State one safety precaution when heating hydrogen in air, with a reason.

      [2]
2. 2

   Chlorine gas is bubbled into aqueous potassium bromide until the solution turns orange-brown.

   1. (a)

      Write the ionic equation, with state symbols, for the reaction.

      [2]
   2. (b)

      Write the half-equation for the change to bromide ions.

      [1]
   3. (c)

      Identify the oxidising agent and state the oxidation-state change it undergoes.

      [2]
3. 3

   Determine the oxidation state of the named element in each species.

   1. (a)

      Nitrogen in the nitrate ion, NO₃⁻.

      [1]
   2. (b)

      Sulfur in sulfuric acid, H₂SO₄.

      [1]
   3. (c)

      Carbon in the carbonate ion, CO₃²⁻.

      [1]
   4. (d)

      Oxygen in hydrogen peroxide, H₂O₂.

      [1]
4. 4

   An underground steel pipeline is protected by connecting it to buried magnesium blocks. A separate steel fence post is protected only by paint.

   1. (a)

      Explain, using half-equations, why the magnesium protects the pipeline even in damp soil.

      [3]
   2. (b)

      The fence paint is scratched to bare metal. Predict and explain what happens next.

      [2]