OXIDATION-REDUCTION, ELECTROCHEMICAL CELLS and ELECTROLYSIS

In which one of the following does hydrogen act as an oxidising agent?
1. C₂H₄ + H₂ => C₂H₆
2. Cl₂ + H₂ => 2HCl
3. 3 N₂ + 2 H₂ => 2 NH₃
4. 2 Na + H₂ => 2 NaH
In which one of the following does the underlined element have an oxidation state of +5?
1. CO₃^2-
2. ClO₃^-
3. MnO₄^-
4. SO₃^2-
Consider only the underlined element in each of the following compounds. Which element has the highest oxidation state?
1. KF
2. KNO₂
3. K₂MnO₄
4. K₂SO₃
Which one of the following solutions would oxidise Br^- in 1 mol L^-1 NaBr?
1. a solution containing Fe³⁺ and dilute H₂SO₄
2. a solution containing H₂O₂ and dilute H₂SO₄
3. a solution containing Sn⁴⁺ and dilute H₂SO₄
4. dilute nitric acd solution
When an electric current is passed through 1 mol L^-1 KI solution between two platinum electrodes, which one of the following half-reactions occurs at the anode?
1. 2 H₂O => O₂ + 4H⁺ + 4e^-
2. 2 I^- => I₂ + 2e^-
3. 2 H₂O + 2e^- => H₂O + 2OH^-
4. K⁺ + e^- => K
During discharge of the lead acid accumulator, a white solid builds up on the grids inside the battery. What is this substance?
1. Pb
2. PbO₂
3. Pb(OH)₂
4. PbSO₄
An electric current is passed through a solution containing:

1 mol L^-1 each of CuSO₄, NaBr and KCl using two platinum electrodes

Which one of the following species is produced at the anode?
1. Br₂(aq)
2. Cl₂(g)
3. Cu(s)
4. O₂(g)
An electric current is passed through a solution containing:

1 mol L^-1 each of CuSO₄, NaBr and KCl using two platinum electrodes

Which one of the following species is produced at the cathode?
1. Cu(s)
2. H₂(g)
3. K(s)
4. O₂(g)
Which underlined element has the highest oxidation state?
1. KMnO₄
2. Mn²⁺
3. Na₂SO₃
4. PCl₃
One solution contains AuCl₃ and a second solution contains AgNO₃. A quantity of electricity is passed through the two solutions as shown in the diagram below.

What s the ratio of the number of moles of gold deposited to the number of moles of silver deposited> {that is, n(Au): n(Ag)}.
1. 1:1
2. 1:3
3. 2:1
4. 3:1
Potassium permanganate solution is standardised using the following procedure: sulfuric acid is added to 25.00mL of a standard solution of oxalic acid (ethanedioic acid), and the mixture warmed and titrated with the potassium permanganate solution. Which one of the following will cause an error?
1. leaving the conical flask (titration vessel) wet after rinsing with distilled water
2. rinsing the burette with distilled water, then with a little of the permanganate solution, and then filling it with the permanganate solution
3. rinsing the pipette with distilled water, then using it to dispense the oxalic acid(ethanedioic acid) solution
4. washing down the sides of the conical flask with distilled water from time to time during the titration
In which one of the following compounds is the oxidation number of the sulfur higher than in any of the other compounds listed ?
1. CuSO₄
2. NaSH
3. Na₂S₂O₃
4. SO₂
An electric current is passed through a solution containing 1 mol L^-1 each of MgSO₄, KI and HCl, using two platinum electrodes.

Which one of the following species is produced at the anode?
1. Cl₂(g)
2. I₂(aq)
3. Mg(s)
4. O₂(g)
An electric current is passed through a solution containing 1 mol L^-1 each of MgSO₄, KI and HCl, using two platinum electrodes.

Which one of the following species is produced at the cathode?
1. H₂(g)
2. I₂(aq)
3. K(s)
4. Mg(s)
A quantity of electricity is passed through the two solutions as shown in the diagram below.

What is the ratio of the number of moles of copper deposited to the numbe rof moles of mercury deposited? {that is, n(Cu):n(Hg)}.
1. 1:1
2. 1:2
3. 2:1
4. 3:1
For the following equation, 2H₂O₂(l) => 2H₂O(l) + O₂(g) which one of the following statements is true?
1. Hydrogen peroxide is acting as an acid
2. Hydrogen peroxide is acting as an acid and a base
3. Hydrogen peroxide is acting as an oxidising agent only
4. Hydrogen peroxide is acting as an oxidising and reducing agent
Using the standard reduction potential tables predict which one of the following reactions will possibly occur spontaneously?
1. Zn²⁺ + Sn => Zn + Sn²⁺
2. MnO₂ + H₂O₂ + 2H⁺ => Mn²⁺ + 2H₂O + O₂
3. 2 MnO₄^- + 4H₂O + 6Br^- => 3Br₂ + 2MnO₂ + 8OH^-
4. Cr₂O₇^2- + 11H⁺ + 3Cl^- => 2Cr³⁺ + 4H₂O + 3 HClO
When doing oxidation-reduction titrations between potassium permanganate solution and oxalic acid solution, sulfuric acid is used to acidify the potassium permanganate. Hydrochloric acid is not used for this purpose. Why is this?
1. Hydrochloric acid will react with the oxalic acid
2. Sulfuric acid produces more hydrogen ions than hydrochloric acid
3. The chloride ions can be oxidised to chlorine gas by the permanganate ions
4. The sulphate ions are used to maintain the electrical neutrality of the solutions
Which one of the following is true of a standard solution?
1. It must contain a primary standard substance
2. It must contain hydrochloric acid
3. It must have an accurately known concentration
4. It must have a concentration of 0.100 mol L^-1
Using the standard reduction potential tables predict which one of the following reactions will possibly occur spontaneously.
1. 3 H₂O₂ + 2NO => 2NO₃^- + 2H₂O + 2H⁺
2. 2Fe²⁺ + O₂ + 2H⁺ => 2Fe³⁺ + H₂O₂
3. Mg²⁺ + Zn => Mg + Zn²⁺
4. Mn²⁺ + 2H₂O + Br₂ => MnO₂ + 4H⁺ + 2 Br^-
Which one of the following arranges the substances in order of strongest to weakest reducing agent?
1. Cl₂ > Al³⁺ > Na⁺
2. Cl₂ > Si > Mg
3. Mg > Al > Cl^-
4. Na⁺ > Al³⁺ > Cl^-
Which one of the following equations does not represent an oxidation-reduction reaction?
1. 2MnO₄^- + 2H₂O +3C₂O₄^2- => 2MnO₂ + 6CO₃^2- + 4H⁺
2. Cr₂O₇^2- + H₂O => 2CrO₄^2- + 2H⁺
3. 2 Br₂ + N₂H₅⁺ => N₂ + 5H⁺ + 4 Br^-
4. 6I^- + 14H⁺ + Cr₂O₇^- => 3I₂ + 7H₂O + 2Cr³⁺
In which one of the following is the oxidation number of nitrogen lower than in any of the other substances listed?
1. Cu(NO₃)₂
2. N₂
3. N₂H₄
4. NO₂
An electrochemical cell based on the following reaction has an Eo = 1.03 V

Cl₂ + 2 V³⁺ + 2H₂O => 2 VO²⁺ + 4H⁺ + 2 Cl^-

What is the standard reduction potential for the reduction of VO²⁺ to V³⁺?
1. -3.05 V
2. Zn + Ag₂O => ZnO + 2Ag
3. PbSO₄ + 2H₂O => PbO₂ + Pb + H₂SO₄
4. 2H₂ + O₂ => 2H₂O
Which one of the following equations best represents the reaction occurring in a dry cell?
1. 2 MnO₂ + 2NH₄Cl + Zn => ZnCl₂ + 2 NH₃ + H₂O + Mn₂O₃
2. Zn + Ag₂O => ZnO + 2Ag
3. PbSO₄ + 2H₂O => PbO₂ + Pb + H₂SO₄
4. 2H₂ + O₂ => 2H₂O
In the production of aluminium, alumina is electrolysed in a cryolite solution. Why is the recovery of aluminium based on electrolysis?
1. Aluminium is amphoteric, so alumina dissolves in sodium hydroxide solution
2. Aluminium is a reactive metal, so alumina is not easily reduced
3. Cryolite lowers the melting temperature of the alumina
4. Electrical power is expensive
For the reaction

3 Au ⁺(aq) => Au ³⁺ (aq) + 2 Au (s)

which one of the following statements is true?
1. Au⁺(aq) disproportionates
2. Au³⁺(aq) is a reducing agent
3. Au(s) is oxidised
4. None of (a), (b) or (c) is true.
An electrolytic cell with inert electrodes was operated in turn with each of the following electrolyte solutions.

I 1 mol L^-1 CuSO₄

II 1 mol L^-1 H₂SO₄

III 1 mol L^-1 NaOH

IV 1 mol L^-1 NaCl

For which of the solutions would hydrogen gas be produced at the cathode and oxygen gas at the anode?
1. I, II, III and IV
2. II only
3. II and III only
4. II, III and IV only
In which one of the following does manganese have an oxidation state of +6?
1. Mn₂O₃
2. MnO₂
3. MnO₄^2-
4. MnO₄^-
What is the change in the oxidation number of bromine in the following reaction?

2BrO₃^-(aq) + 10I^-(aq) +12H⁺(aq) => 5I₂(aq) + Br₂(aq) + 6H₂O(l)
1. +7 to 0
2. +7 to -1
3. +5 to 0
4. +5 to -1
In which one of the following pairs do the underlined elements have the same oxidation number?
1. Cr₂O₇^2- and CrO₄^2-
2. HF and MgH₂
3. H₂O and H₂O₂
4. NO₂ and HNO₃
Consider the elements Al, Cr, F, Fe, N and Zn.

Which one of the elements exhibit variable oxidation states in their compounds?
1. all six of the elements
2. Al, Cr, Fe and Zn
3. Al, Cr, Fe, N and Zn.
4. Cr, Fe, and N.
A mixed solution containing both 1 mol L^-1 ZnSO₄ and 1 mol L^-1 CuSO₄ was electrolysed in an electrolytic cell using inert electrodes.

Which one of the following statements is correct?
1. Copper is produced at the cathode and zinc is produced at the anode
2. Copper is produced at the cathode and oxygen gas is produced at the anode
3. Hydrogen gas is produced at the cathode and oxygen gas is produced at the anode
4. Zinc is produced at the cathode and oxygen gas is produced at the anode

OXIDATION-REDUCTION, ELECTROCHEMICAL CELLS and ELECTROLYSIS

Multiple Choice Quiz on Oxidation-Reduction, Electrochemical Cells and Electrolysis