Redox

What is the oxidation of sulfur in Na₂SO₃?

• 0

• +2

• +4

• -4

Which reaction is an example of a redox reaction?

• 2SO₂ + O₂ → 2SO₃

• Ag⁺ + Cl^- → AgCl

• CuO + H₂SO₄ → CuSO₄ +H₂O

• H⁺ + OH^- → H₂O

Which of the following is involved in reduction?

• loss of oxygen

• loss of hydrogen

• loss of electrons

• increase in oxidation state

In which of the following changes is the first substance reduced?

• KCl into KClO₃

• Br₂O into Br₂

• HCl into Cl₂

• Na₂SO₃ into Na₂SO₄

A reducing agent ______________________.

• decreases in oxidation state

• is reduced at the end of a reaction

• gains oxygen

• accepts electrons

Which compound, in aqueous solution, when added to aqueous iron(II) sulfate, takes part in a redox reaction?

• acidified potassium manganate(VII)

• ammonia

• copper(II) nitrate

• sodium hydroxide

Substance X changes aqueous potassium iodide from colourless to brown and changes aqueous potassium manganate(VII) from purple to colourless. Which statement correctly describes X?

• It is an oxidising agent only.

• It is a reducing agent only.

• It is an oxidising agent and a reducing agent.

• It is neither an oxidising agent nor a reducing agent.

A drop of solution S turns acidified potassium dichromate(VI) to green chromium(III) ion.

What does solution S behave as?

• an acid

• an oxidising agent

• a reducing agent

• neither oxidising nor reducing agent

Ozone gas is a colourless and a powerful oxidising agent. What colour change would you expect to see when ozone is bubbled through aqueous potassium iodide?

• colourless to brown

• brown to colourless

• purple to brown

• purple to colourless

State the oxidation state of Cr in CrO₄^-.

(a)