Electrolysis
AQA GCSE Chemistry revision on Electrolysis. Aligned to the AQA GCSE Chemistry 8462 specification. This bank has 8 practice questions on this topic.
Sample questions (3 of 8)
-
Question 1
In electrolysis, positive ions (cations) move to which electrode?
- A) Anode (+)
- B) Cathode (-)
- C) Both equally
- D) Neither
Show answer
Answer: Cathode (-)
Cathode (-) attracts cations (+ ions: metals, H+). Anode (+) attracts anions (- ions: non-metals, OH-). At the cathode, positive ions GAIN electrons (reduction). At the anode, negative ions LOSE electrons (oxidation). The substance broken down by electricity = ELECTROLYTE; the products separate. Used to extract very reactive metals (Al, Na) + to electroplate.
-
Question 2
During electrolysis of molten lead bromide, the product at the cathode is...
- A) Bromine gas
- B) Lead metal
- C) Hydrogen gas
- D) Oxygen gas
Show answer
Answer: Lead metal
PbBr2 melted -> Pb2+ and Br- ions free to move. At cathode (-): Pb2+ + 2e- -> Pb (lead pools at the bottom). At anode (+): 2Br- -> Br2 + 2e- (brown bromine gas given off). Demonstrates that ionic compounds can conduct when molten because the ions are free to move. (Solid ionic compounds don't conduct - ions locked in lattice.)
-
Question 3
To extract aluminium, the aluminium oxide is dissolved in cryolite mainly to...
- A) Increase the price
- B) Lower the melting point
- C) Add fluorine to the product
- D) Make it smell better
Show answer
Answer: Lower the melting point
Pure aluminium oxide melts at 2050C - electrolysing at this temperature would be ridiculously energy-intensive. Cryolite (Na3AlF6) dissolves Al2O3 forming a conducting mixture that melts at ~950C. Saves ~half the energy. The aluminium ions in this molten mixture are still free to migrate + be reduced at the cathode. Carbon anodes get burnt away (need replacing) because oxygen at the anode reacts with carbon -> CO2.
Want to test yourself on the remaining cards for this topic?
5 more questions on Electrolysis — plus mistakes tracking and spaced repetition across the whole Chemistry spec.