Electrolysis of Solutions and Getting Reactive Metals Out of Ores · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Solutions, ores and who wins

Science · Matter & Materials · ages 15-16
Name ______________________   Date ____________

  1. Concentrated brine is electrolysed using inert electrodes. What forms at the anode?

    • Chlorine
    • Oxygen
    • Hydrogen

  2. Sodium chloride solution is electrolysed using inert electrodes. What forms at the cathode?

    • Sodium metal
    • Chlorine gas
    • Hydrogen gas

  3. In the usual industrial methods, iron is extracted from its oxide by carbon-based reduction, while aluminium is extracted by electrolysis.

    Circle one:   True   False

  4. Why is aluminium oxide dissolved in molten cryolite during aluminium extraction?

    • It turns oxide into aluminium without any electricity.
    • It keeps the mixture molten at a lower temperature.
    • It prevents all electrode reactions during extraction.

  5. Copper sulfate solution is electrolysed using inert electrodes. Why does copper form at the cathode instead of hydrogen?

    • Sulfate ions prevent hydrogen from reaching the cathode.
    • Copper is above hydrogen in the reactivity series.
    • Copper is below hydrogen in the reactivity series.

  6. Why does recycling aluminium use far less energy than extracting new aluminium from ore?

    • It reuses the metal without extracting it from ore.
    • It removes the need to collect or sort used aluminium.
    • It turns aluminium oxide into metal at room temperature.

  7. Aluminium is more reactive than hydrogen. An aqueous aluminium salt is electrolysed using inert electrodes. Under the rules taught here, why is aluminium not deposited at the cathode?

    • Aluminium forms only at the positive electrode.
    • The aluminium ions are too large to reach the cathode.
    • Hydrogen forms from water instead of aluminium.

  8. Sodium sulfate solution is electrolysed using inert electrodes. What forms at the anode?

    • Sulfur from sulfate
    • Oxygen from water
    • Chlorine from chloride
LightMySky · lightmysky.comW1-mt_l-t_JxRR7f-s1

Answer key

For grown-ups. Fold this page away before handing over the rest.

Solutions, ores and who wins W1-mt_l-t_JxRR7f-s1

  1. Chlorine · Brine is sodium chloride solution. Concentrated chloride ions are oxidised at the inert anode to form chlorine.
  2. Hydrogen gas · Sodium is more reactive than hydrogen. Water is reduced to produce hydrogen rather than sodium metal.
  3. True · Iron is below carbon in reactivity, while aluminium is above it. Their usual industrial extraction methods reflect this difference.
  4. It keeps the mixture molten at a lower temperature. · The mixture stays liquid below the melting point of pure aluminium oxide. This reduces the energy needed to maintain the molten electrolyte.
  5. Copper is below hydrogen in the reactivity series. · Copper is less reactive than hydrogen. Copper ions gain electrons at the cathode and form copper metal.
  6. It reuses the metal without extracting it from ore. · Recycling still needs collection, sorting, cleaning and melting, but avoids producing new aluminium from ore by electrolysis.
  7. Hydrogen forms from water instead of aluminium. · For a metal more reactive than hydrogen, the taught aqueous cathode rule predicts hydrogen instead of the metal. Industrial aluminium extraction uses a molten electrolyte.
  8. Oxygen from water · With an inert anode, this sulfate solution gives oxygen from water. It contains no chloride ions to produce chlorine.
Worksheet · LightMySky