MCQ Questions

Question No. 1

Give one term for each of the following descriptions.

Answer :

a) An ionic solution that conducts electricity

b) An electrochemical cell that supports self-sustaining electrode reactions

c) An electrochemical cell in which electrical energy is converted to chemical energy

d) The process in which electrons are gained during a chemical reaction

e) The reaction type in which electrons are transferred

f) The chemical species that undergoes oxidation in a chemical reaction

g) The half-reaction that happens at the anode of an electrochemical cell

h) The U-shaped tube that connects two half-cells in a galvanic cell.

Question No. 2

Choose the correct word in column B for each statement in column A.

Answer :

a) Electrode where oxidation occurs — A. zero B. maximum C. positive D. negative E. anode F. cathode G. oxidation H. reduction I. oxidising agent J. reducing agent K. galvanic cell L. electrolytic cell

Question No. 3

Define the term electrolysis and answer the following.

Answer :

a) Define electrolysis.

b) Which electrode, Fe or C, is the anode?

c) At which electrode does reduction occur?

e) Explain why Ca metal will not form.

f) Explain why Na metal collects at the top of the cell.

g) Why is it necessary to place a screen between the electrodes?

h) If a current of 5 A flows for 2 h, what mass of sodium will form?

d) Write the half-reaction that takes place at electrode C.

Question No. 4

Hydrogen peroxide is commonly used as a bleaching agent. When manganese dioxide is added to H₂O₂, water and oxygen are formed while MnO₂ is not consumed. Use the table of standard reduction potentials to answer the questions.

Answer :

a) Give the equation for the oxidation half-reaction.

b) Give the equation for the reduction half-reaction.

c) Give the balanced equation for the net reaction.

d) What is the function of MnO₂ in this reaction?

e) What property of hydrogen peroxide is responsible for its bleaching action?

Question No. 5

A zinc bar is attached to a buried iron pipe. Use standard potentials to explain corrosion protection.

Answer :

Question No. 6

Two half-cells Pb²⁺/Pb and O₂/H₂ in acid are used to set up a cell under standard conditions.

Answer :

a) Give the standard conditions.

b) Which half-cell is the anode?

c) Write the oxidation half-reaction.

d) Write the reduction half-reaction.

e) Give the balanced net reaction.

f) Calculate the emf of the cell.

Question No. 7

The following half-reactions occur in a nickel-cadmium battery: Cd(OH)₂ + 2 e⁻ → Cd + 2 OH⁻ (E° = –0.82 V); NiO(OH) + H₂O + e⁻ → Ni(OH)₂ + OH⁻ (E° = +0.48 V).

Answer :

a) Which electrode is the anode?

b) Write the oxidation half-reaction.

c) Write the balanced cell reaction.

d) Calculate the emf.

e) In which direction do electrons flow when recharging?

Question No. 8

What current must be supplied to deposit 5.00 g of gold from AuCl₃ in 20 min?

Answer :

Question No. 9

Electrolysis is an important industrial process used to decompose compounds, extract metals from their ores and to purify metals like gold and copper. The simplified diagram below represents the Downs cell used to produce sodium metal. The cell is filled with a molten mixture of NaCl and CaCl₂. The CaCl₂ lowers the melting point of the mixture from 801 °C (for pure NaCl) to 580 °C.

Answer :

a) Define the term electrolysis.

b) Which electrode, Fe or C, will be the anode?

c) At which electrode does reduction occur?

d) Write down the half-reaction that takes place at electrode C.

e) Explain why Ca metal will not form.

f) Explain why Na metal collects at the top of the cell.

g) Why is it necessary to place a screen between the electrodes?

h) If a current of 5 A flows for 2 h, what mass of sodium will form?

Question No. 10

The chlor-alkali industry is the second largest consumer of electricity among electrolytic industries. It makes use of brine as electrolyte to produce chlorine gas, hydrogen gas and sodium hydroxide. The overall reaction can be represented by the following equation: 2 NaCl(aq) + 2 H₂O(ℓ) → 2 NaOH(aq) + Cl₂(g) + H₂(g)

Answer :

a) Define the term electrolyte.

b) Give a reason why brine conducts electricity.

c) Write down the name of the reducing agent in the above reaction; give a reason for your choice.

d) Write down a half-reaction to explain how hydroxide ions are formed.

e) At which electrode (anode or cathode) is chlorine gas formed? Give a reason.

f) Give one reason why it is not advisable to build a chlor-alkali plant close to a residential area.

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