5.2 Redox

Which of the following describes oxidation ?

You can choose more than one answer

• Electrons are gained

• Electrons are lost

• Oxidation state increases

• Oxidation state decreases

What is the oxidation state of sulfur in H2SO4?

What is the oxidation state of Mn in the compound shown in the image?

• +5

• +6

• +7

• +8

Answer explanation

The total o.s. Of the ion -1.

X + 4(-2)=-1

Which substance is reduced?

Fe2O3 +3C→2Fe+3CO

• C

• Fe2O3

• Fe

• CO

Answer explanation

Loss of oxygen

Substance X turns a solution of acidified potassium manganate(VII) from purple to colourless. What must solution X contain?

• Oxidising agent

• Reducing agent

Answer explanation

Acidified Potassium manganate(VII) is an oxidising agent.

Which pair of substances act as reducing agents in the blast furnace?

You can select more than one answer

• Carbon

• Carbon monoxide

• Iron(III) oxide

• Oxygen

Answer explanation

Reducing agents are oxidases in the equation

• Fe

• Cu2+

Answer explanation

Oxidising agent gets reduced

Aqueous iron(III) chloride reacts with aqueous potassium iodide to produce a brown solution.

Aqueous iron(II) chloride reacts with acidified potassium manganate(VI) to produce a yellow / pale orange solution.

What is the role of iron(III) chloride and iron(II) chloride in these reactions?

• Iron(III) chloride is an oxidising agent

• Iron(III) chloride is a reducing agent

• Iron(II) chloride is an oxidising agent

• Iron(II) chloride is a reducing agent

Has the underlined substances reduced or oxidised?

2NH3 (g) + 3CuO (s) → 3Cu (s) + N2 (g) + 3H2O (g)

• Oxidised

• Reduced

Answer explanation

The o.s. Of nitrogen increases from -3 to 0.

Which of the following is non-redox equation?

• H2SO4 + 2KOH → K2SO4 + 2H2O

• Ag+ (aq) + Cl- (aq) → AgCl (s)

• Fe + 3Cl2 → 2FeCl3