Pupil sheet · Redox

Redox — final check

Name ______________________ Date ____________

Work alone, with the lesson closed. Answer every question; there are no hints.

1. name / identify / explain

Tungsten for lamp filaments is made by heating its oxide in hydrogen: WO₃ + 3H₂ → W + 3H₂O. (a) Name WO₃, using a Roman numeral. (b) Which substance is reduced? Give a reason. (c) Explain why this is a redox reaction.

(a) Name of WO₃

(b) Substance reduced, and why

2. identify

For each reaction, is the substance named oxidised, reduced, or neither?

Write the number of the matching option.

neither
oxidised
reduced

1. Calcium, in 2Ca + O₂ → 2CaO: ______
2. Silver oxide, in Ag₂O + H₂ → 2Ag + H₂O: ______
3. Calcium chloride, in CaCl₂ + Na₂CO₃ → CaCO₃ + 2NaCl: ______
4. Copper(I) oxide, in Cu₂O + C → 2Cu + CO: ______

3. deduce / state / identify / explain

Supplement. Aluminium foil is put into colourless lead(II) nitrate solution, and grey lead forms on the foil: 2Al + 3Pb²⁺ → 2Al³⁺ + 3Pb. (a) Give the oxidation numbers of aluminium and of lead on each side. (b) How many electrons does each aluminium atom lose, and how many does each lead(II) ion gain? (c) Identify the oxidising agent and the reducing agent. (d) Explain why the nitrate ions do not appear in the equation.

(a) Oxidation numbers

(b) Electrons lost and gained

(d) Why no nitrate ions

4. identify

Supplement. Which reaction is NOT a redox reaction?

Circle one answer.

4Na + O₂ → 2Na₂O
CuCO₃ → CuO + CO₂
2Mg + CO₂ → 2MgO + C
2SO₂ + O₂ → 2SO₃

5. name / describe / deduce / identify

Supplement. Household bleach contains ClO⁻ ions. A few drops of bleach turn aqueous potassium iodide brown, and the chlorine in the ClO⁻ ions ends up as chloride ions, Cl⁻. (a) Name the brown substance. (b) Describe what happens to the iodide ions, in terms of electrons and of oxidation number. (c) Deduce the oxidation number of chlorine in ClO⁻, and give its change. (d) Identify the oxidising agent.

(a) The brown substance

(b) The iodide ions

(d) Oxidising agent

6. identify

Supplement. Tin(II) chloride solution, SnCl₂, turns acidified potassium manganate(VII) from purple to colourless. The tin ends up as Sn⁴⁺ ions. Which row is correct?

Row	Oxidation number of tin	Manganese is	Tin(II) chloride is
A	+4 → +2	reduced	an oxidising agent
B	+2 → +4	reduced	an oxidising agent
C	+2 → +4	oxidised	a reducing agent
D	+2 → +4	reduced	a reducing agent

Circle one answer.