Sec 4 Combined Science (Chemistry) Redox Reactions topical questions

Define oxidation and reduction in terms of oxygen transfer.

State what OIL RIG stands for.

In Cl₂ + 2KI → 2KCl + I₂, state which species is oxidised and which is reduced.

State the colour change seen when a reducing agent is added to acidified potassium manganate(VII) solution.

For each reaction, state whether it is redox and, if it is, name the substance oxidised: (a) 2Zn + O₂ → 2ZnO; (b) HCl + NaOH → NaCl + H₂O; (c) Mg + 2HCl → MgCl₂ + H₂.

Hydrogen gas is passed over hot copper(II) oxide: CuO + H₂ → Cu + H₂O. (a) State which substance is oxidised and which is reduced, in terms of oxygen. (b) Name the oxidising agent in this reaction and explain your choice.

Write the two half-equations for the reaction Zn + CuSO₄ → ZnSO₄ + Cu, and use them to state which reactant is the reducing agent.

A solution of a metal salt is colourless. When aqueous potassium iodide is added, the mixture turns red-brown. (a) State what species has formed to give the red-brown colour. (b) State what this result proves about the metal salt solution. (c) Name the visual confirmation that would make the result certain.

In Fe₂O₃ + 3CO → 2Fe + 3CO₂, use oxidation states to explain which element is oxidised and which is reduced.

Work out the oxidation state of: (a) sulfur in SO₃; (b) nitrogen in NO₂; (c) copper in CuO, and state how the copper's state changes when CuO is reduced to Cu.

Magnesium ribbon is placed in copper(II) sulfate solution: Mg + CuSO₄ → MgSO₄ + Cu. (a) Write the two half-equations. (b) State which reactant is oxidised and which is reduced. (c) Name the oxidising agent and the reducing agent.

Three colourless solutions X, Y and Z are known to be an oxidising agent, a reducing agent and neither. Plan tests, using aqueous potassium iodide and acidified potassium manganate(VII), that sort them, stating the positive result for each class.

Two colourless solutions, A and B, are tested. A decolourises acidified potassium manganate(VII). B turns aqueous potassium iodide red-brown, and the brown mixture gives a dark blue colour with starch. (a) State what each test proves about A and B. (b) Explain, with an ionic half-equation, what happened to the iodide ions in B's test. (c) Predict, with a reason, what B would do to acidified potassium manganate(VII).

A student heats a mixture of iron filings and sulfur, which reacts: Fe + S → FeS. (a) Explain, in terms of electrons, why this is a redox reaction. (b) State the oxidation state changes of iron and sulfur. (c) The student then adds dilute hydrochloric acid to the iron sulfide: FeS + 2HCl → FeCl₂ + H₂S. Identify the redox pair in this second reaction, or state that there is none, with a reason.

Copper(II) oxide is reduced by passing ammonia gas over it when hot: 3CuO + 2NH₃ → 3Cu + 3H₂O + N₂. (a) State which substance is oxidised and which is reduced, in terms of oxygen and in terms of oxidation states. (b) Show that the oxidation states you quote are consistent with the formulae given.

Iron is extracted from iron(III) oxide using carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂. (a) Explain why this is a redox reaction using the oxygen-transfer view. (b) Confirm with oxidation states. (c) Carbon monoxide is described as the reducing agent. State what this means about the electrons, and why the carbon monoxide must be supplied in excess.

Bromine water is added to aqueous potassium iodide: Br₂ + 2KI → 2KBr + I₂. (a) Write the two half-equations. (b) State which species is oxidised and which is reduced. (c) Name the oxidising agent. (d) State the colour change observed and explain what causes it.

Lead(II) oxide is heated with carbon monoxide: PbO + CO → Pb + CO₂. Two students make claims. Student A: "Lead(II) oxide is reduced because it loses oxygen." Student B: "Carbon monoxide is the reducing agent." Use oxidation states to evaluate both claims, and state the oxidation state changes of every element.