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Electrolysis – Full Question & Answer Key
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1. An electrode ‘A’ is connected to the positive terminal of a battery and electrode ‘B’ to the
negative terminal.
(i) Give the names of the electrodes A & B.
(ii) Which electrode is the oxidizing electrode?
Answer:
(i) A = Anode (positive electrode), B = Cathode (negative electrode)
(ii) Anode is the oxidizing electrode.
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2. State the appropriate term used for: – A liquid or solution, which conducts electricity with
accompanying chemical change.
Answer: Electrolyte.
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3. Electrons are getting added to an element Y.
(i) Is Y getting oxidized or reduced?
(ii) What charge will Y have after the addition of electrons?
(iii) Which electrode will Y migrate to during electrolysis?
Answer:
(i) Reduced
(ii) Negative charge
(iii) Cathode
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4. Explain how electrolysis is an example of redox reaction.
Answer: In electrolysis, oxidation occurs at the anode and reduction occurs at the cathode,
both happening simultaneously, making it a redox reaction.
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5. What kind of particles will be found in a liquid compound which is a non-electrolyte?
Answer: Only molecules.
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6. Complete the sentence: Electrolysis is the passage of ……….. [electricity / electrons]
through a liquid or a solution accompanied by a ……….. [physical / chemical] change.
Answer: Electricity, Chemical.
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7. Name a liquid which is a non-electrolyte.
Answer: Kerosene (or pure water, alcohol).
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8. Name one substance which contains:
(i) ions only
(ii) molecules only
(iii) both ions and molecules
Answer:
(i) Sodium chloride solution
(ii) Carbon tetrachloride
(iii) Ammonium hydroxide solution
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9.
(i) What is meant by the term ‘electrolyte’?
(ii) What are the particles present in a compound which is non-electrolyte?
(iii) If an electrolyte is described as a ‘strong electrolyte’, what does this mean?
Answer:
(i) A compound which conducts electricity in molten/aqueous state and undergoes chemical
decomposition.
(ii) Molecules only
(iii) Completely dissociates into ions in solution and conducts electricity very well.
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10. Explain why:
(i) Solid sodium chloride does not allow electricity to pass through.
(ii) Copper, though a good conductor of electricity, is a non-electrolyte.
Answer:
(i) In solid sodium chloride, ions are fixed in a lattice and cannot move.
(ii) Copper conducts electricity by free electrons but does not undergo chemical
decomposition.
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11. Classify the substances:
Strong Electrolytes – Sodium acetate, dilute sulphuric acid, dilute hydrochloric acid,
ammonium chloride
Weak Electrolytes – Ammonium hydroxide, acetic acid
Non-electrolytes – Carbon tetrachloride
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12. Fill in the blanks:
(i) As we descend the electrochemical series containing cations, the tendency of the cations
to get ________ [oxidized / reduced] at the cathode increases.
(ii) The [higher / lower] ________ the concentration of an ion in a solution, the greater is the
probability of its being discharged at its appropriate electrode.
Answer:
(i) Reduced
(ii) Higher
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13.
(i) Name a solid which undergoes electrolysis when molten.
(ii) What should be the physical state of lead bromide if it is to conduct electricity?
(iii) What particles are present in pure lead bromide? Write the equations for the reactions.
(iv) Complete: The electrolysis of lead bromide liberates lead and bromine.
Answer:
(i) Lead bromide
(ii) Molten
(iii) Pb²⁺ and Br⁻ ions
Anode: 2Br⁻ → Br₂ + 2e⁻
Cathode: Pb²⁺ + 2e⁻ → Pb
(iv) The electrolysis of molten lead bromide liberates lead and bromine.
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14. If compound X (metal, valency 2) and Y (non-metal, valency 3) is melted and
electrolyzed, X is obtained at _______ and Y at _______.
Answer: Cathode, Anode.
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15.
(i) Write equations for reactions at cathode and anode when acidified water is electrolyzed.
(ii) Name the gas released at the cathode.
(iii) Fill in blanks: With platinum electrodes hydrogen is liberated at the _______ and oxygen
at the _______ during the electrolysis of acidified water.
(iv) When electrolysis of acidified water is carried out: [1] What is the ratio of hydrogen to
oxygen? [2] Give the equation for discharge of ions at cathode.
Answer:
(i) Cathode: 2H⁺ + 2e⁻ → H₂
Anode: 4OH⁻ → O₂ + 2H₂O + 4e⁻
(ii) Hydrogen
(iii) Cathode, Anode
(iv) [1] 2:1
[2] 2H⁺ + 2e⁻ → H₂
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16.
(i) If HX is weak acid, what particles will be in dilute solution apart from water?
(ii) Pure water consists almost entirely of molecules — will it conduct electricity?
(iii) Why is sulphuric acid added in electrolysis of water?
Answer:
(i) Mostly water molecules with few ions from the acid
(ii) Will not
(iii) Provides H⁺ and SO₄²⁻ ions, making solution conductive
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17.
(i) What is observed when copper sulphate is electrolyzed with platinum anode?
(ii) What ions must be present for electroplating?
(iii) Why is silver nitrate not used to electroplate an article with silver?
(iv) Fill blanks:
(a) Electrolyte
(b) Nickel
(c) Cathode
(d) Anode
(e) Cations
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18.
(i) From list, solution used when copper is purified – Copper sulphate
(ii) When molten, lead bromide gives lead at cathode
(b) Applications where anode diminishes – Electroplating, Purification of metals
(c)
Anode Electrolyte Cathode
Silver Potassium argentocyanide solution Spoon
Impure copperCopper sulphate solution Pure copper
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19. (Copper sulphate electrolysis with copper electrodes)
(i) Anode mass decreases
(ii) Solution colour fades when using platinum electrodes – Cu²⁺ removed, not replaced
(iii) Purification of copper – impure copper anode, pure copper cathode, copper sulphate
electrolyte, impurities form anode mud.
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20. Match:
(i) Molten ionic compound – B
(ii) Carbon tetrachloride – A
(iii) Aluminium wire – D
(iv) Solution with ions & molecules – C
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21.
(i) Cu → Cu²⁺ + 2e⁻ at anode – oxidation
(ii) Cu²⁺ + 2e⁻ → Cu at cathode – Cu²⁺ discharged first
(iii) Carbon tetrachloride is covalent, no free ions, so non-electrolyte.
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