10) Electrolytic Processes
3.22 Define electrolyte - ANS-An ionic compound in a molten state or dissolved in water.
\3.23 What is electrolysis? - ANS-A process in which electrical energy, from a direct current
supply, decomposes electrolytes
\3.24 Explain the movement of ions during electrolysis - ANS-Positively charged cations
migrate to the negatively charged cathode
Negatively charged anions migrate to the positively charged anode
\3.25 Explain the products when copper chloride solution is the electrolyte - ANS-At the
cathode the hydrogen (from water) and copper ions are attracted. The copper ions are
discharged more readily than the hydrogen ions so copper is formed as a brown solid.
Remember the rule! At the cathode, the least reactive form will be discharged and produced.
Copper is less reactive than hydrogen so is discharged.
At the Anode the chloride ions and hydroxide ions (from water) are attracted. The chloride
ions are discharged more readily than the hydroxide so chloride is formed as a pale green
gas. Remember the rule! At the anode, if a halogen (group 7 so chloride or bromine etc) is
available it will be the reactant. Chloride is available so is discharged instead of the
hydroxide ions.
Overall - The copper chloride decomposes but the water stays the same (there is water
cause its a solution, so copper chloride dissolve in water.)
\3.25 Explain the products when molten lead bromide is the electrolyte - ANS-The positive
lead cations are attracted to the negative cathode, and each ion picks up 2 electrons,
enough to neutralise their charge, and forms lead metal.
Pb²⁺ + 2e⁻ --> Pb
The negative bromide anions are attracted to the positive anode, and each ion loses one
electron, enogh to neutralise their charge, and forms bromine atoms. HOWEVER bromine
exists as a diatomic molecule, so two of these atoms join together to make a bromine
molecule.
Br⁻ --> Br + e⁻
2Br --> Br₂
\3.25 Explain the products when sodium chloride solution is the electrolyte - ANS-At the
Cathode the sodium and hydrogen ions are attracted. The hydrogen ions are discharged
more readily than the sodium ions, so hydrogen gas is formed.
At the Anode the chloride and hydroxide ions are attracted. The chloride ions are discharged
more readily than the hydroxide ions, so chloride gas is formed as a pale green gas
Overall - The sodium chloride decomposes to form hydrogen and chlorine. The sodium and
hydroxide remain in the solution.
\3.25 Explain the products when sodium sulfate solution is the electrolyte - ANS-At the
Cathode the sodium and hydrogen ions are attracted. The hydrogen ions are discharged
more readily than the sodium ions, because hydrogen is less reactive than sodium. The rule
being that at the cathode the least reactive is discharged. So hydrogen gas is formed.
3.22 Define electrolyte - ANS-An ionic compound in a molten state or dissolved in water.
\3.23 What is electrolysis? - ANS-A process in which electrical energy, from a direct current
supply, decomposes electrolytes
\3.24 Explain the movement of ions during electrolysis - ANS-Positively charged cations
migrate to the negatively charged cathode
Negatively charged anions migrate to the positively charged anode
\3.25 Explain the products when copper chloride solution is the electrolyte - ANS-At the
cathode the hydrogen (from water) and copper ions are attracted. The copper ions are
discharged more readily than the hydrogen ions so copper is formed as a brown solid.
Remember the rule! At the cathode, the least reactive form will be discharged and produced.
Copper is less reactive than hydrogen so is discharged.
At the Anode the chloride ions and hydroxide ions (from water) are attracted. The chloride
ions are discharged more readily than the hydroxide so chloride is formed as a pale green
gas. Remember the rule! At the anode, if a halogen (group 7 so chloride or bromine etc) is
available it will be the reactant. Chloride is available so is discharged instead of the
hydroxide ions.
Overall - The copper chloride decomposes but the water stays the same (there is water
cause its a solution, so copper chloride dissolve in water.)
\3.25 Explain the products when molten lead bromide is the electrolyte - ANS-The positive
lead cations are attracted to the negative cathode, and each ion picks up 2 electrons,
enough to neutralise their charge, and forms lead metal.
Pb²⁺ + 2e⁻ --> Pb
The negative bromide anions are attracted to the positive anode, and each ion loses one
electron, enogh to neutralise their charge, and forms bromine atoms. HOWEVER bromine
exists as a diatomic molecule, so two of these atoms join together to make a bromine
molecule.
Br⁻ --> Br + e⁻
2Br --> Br₂
\3.25 Explain the products when sodium chloride solution is the electrolyte - ANS-At the
Cathode the sodium and hydrogen ions are attracted. The hydrogen ions are discharged
more readily than the sodium ions, so hydrogen gas is formed.
At the Anode the chloride and hydroxide ions are attracted. The chloride ions are discharged
more readily than the hydroxide ions, so chloride gas is formed as a pale green gas
Overall - The sodium chloride decomposes to form hydrogen and chlorine. The sodium and
hydroxide remain in the solution.
\3.25 Explain the products when sodium sulfate solution is the electrolyte - ANS-At the
Cathode the sodium and hydrogen ions are attracted. The hydrogen ions are discharged
more readily than the sodium ions, because hydrogen is less reactive than sodium. The rule
being that at the cathode the least reactive is discharged. So hydrogen gas is formed.
