Class 10 Electrolysis Mock Test (ICSE)

Topics in Electrolysis

• Electrolytes and non-electrolytes
• Electrolysis of molten lead bromide
• Electrolysis of acidified water and copper sulphate
• Electroplating and electrorefining
• Selective discharge of ions

Electrolysis practice questions with answers

1. Q1Multiple choice·1 mark
   In the process of electroplating an article with silver, the electrolyte commonly used is:

   1. (a)Nickel sulphate solution
   2. (b)Sodium argento-cyanide solution
   3. (c)Acidified copper sulphate solution
   4. (d)Silver nitrate solution
   Show answer and step marks

   1. Correct option: (b) Sodium argento-cyanide solution+1

   Answer: (b)
2. Q2Multiple choice·1 mark
   According to the preferential discharge of ions, if an aqueous solution containing $Cu^{2+}$, $Na^+$, $SO_4^{2-}$, and $OH^-$ ions is electrolysed, the ion discharged at the cathode is:

   1. (a)Hydroxyl ion ($OH^-$)
   2. (b)Copper ion ($Cu^{2+}$)
   3. (c)Sodium ion ($Na^+$)
   4. (d)Sulphate ion ($SO_4^{2-}$)
   Show answer and step marks

   1. Correct option: (b) Copper ion ($Cu^{2+}$)+1

   Answer: (b)
3. Q3Multiple choice·1 mark
   During the electrolysis of acidified water using platinum electrodes, the gas liberated at the anode is:

   1. (a)Oxygen
   2. (b)Sulphur dioxide
   3. (c)Water vapour
   4. (d)Hydrogen
   Show answer and step marks

   1. Correct option: (a) Oxygen+1

   Answer: (a)
4. Q4Multiple choice·1 mark
   Solid lead bromide does not conduct electricity, whereas molten lead bromide is an electrolyte because:

   1. (a)Ions are free to move in the solid state but fixed in the molten state
   2. (b)Electrostatic forces keep ions rigidly held in the crystal lattice in the solid state, whereas they are free to move in the molten state
   3. (c)Lead bromide exists as covalent molecules in the solid state and ionic molecules in the liquid state
   4. (d)Free electrons are available in molten lead bromide to carry the electric current
   Show answer and step marks

   1. Correct option: (b) Electrostatic forces keep ions rigidly held in the crystal lattice in the solid state, whereas they are free to move in the molten state+1

   Answer: (b)
5. Q5Short answer·2 marks
   State two differences between an electrolyte and a non-electrolyte with respect to their electrical conductivity in the molten/aqueous state and the nature of particles present.
   Show answer and step marks

   1. Electrical conductivity: electrolytes conduct electricity in the molten or aqueous state, whereas non-electrolytes do not conduct in these states.+1
   2. Nature of particles: electrolytes contain free mobile ions in these states, whereas non-electrolytes contain only molecules and no free ions.+1

   Answer: Conductivity: electrolytes conduct when molten or in aqueous solution, non-electrolytes do not. Particles: electrolytes have free mobile ions, non-electrolytes only molecules.
6. Q6Long answer·4 marks
   During the laboratory demonstration of the electrolysis of molten lead bromide: (a) State the material of the electrodes used and give a reason why they are preferred over active metal electrodes. (b) Write the balanced ionic equation for the reaction occurring at the anode. (c) State the specific observations made at the cathode and the anode respectively during the process.
   Show answer and step marks

   1. (a) Material: Graphite (or carbon).+0.5
   2. (a) Reason: graphite is inert, so it is not attacked by the hot, corrosive bromine vapours, whereas active metal electrodes would react with bromine.+0.5
   3. (b) Anode equation: $2Br^- - 2e^- \rightarrow Br_2$ (or $2Br^- \rightarrow Br_2 + 2e^-$)+1
   4. (c) Observation at cathode: A silvery-grey deposit of lead metal is formed.+1
   5. (c) Observation at anode: Reddish-brown vapours of bromine gas are evolved.+1

   Answer: (a) Graphite (carbon), because it is inert and not attacked by bromine vapours. (b) $2Br^- - 2e^- \rightarrow Br_2$. (c) Cathode: silvery-grey lead is deposited; anode: reddish-brown bromine vapours are evolved.

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