GCSE Chemistry Electrolysis questions by topic

Complete the sentences about electrolysis.

1. (a)Electrolysis needs the compound to be molten or …[1]
2. (b)Positive ions move to the …, the negative electrode.[1]
3. (c)Reduction (electron …) happens at the cathode.[1]
4. (d)Name the product at the anode when molten potassium bromide is electrolysed.[1]

Copy and complete the table for electrolysis with inert electrodes.

1. (a)Complete the cathode column.[2]
2. (b)Complete the anode column.[2]

A student electrolyses molten zinc chloride.

1. (a)State the product at the cathode.[1]
2. (b)State the product at the anode.[1]
3. (c)Explain why the solid zinc chloride does not conduct before melting.[2]

In the aluminium extraction cell, alumina dissolves in molten cryolite before the current flows.

1. (a)State the product at the cathode.[1]
2. (b)State the product at the anode.[1]
3. (c)Explain why cryolite is added.[2]
4. (d)State what happens to the carbon anodes over time.[1]

Match each gas test to the gas.

1. (a)Bleaches damp litmus paper.[1]
2. (b)Gives a squeaky pop with a lighted splint.[1]
3. (c)Relights a glowing splint.[1]

Inert electrodes dip into molten calcium chloride and the current is switched on.

1. (a)Name the electrode that attracts Ca²⁺ ions and state its polarity.[1]
2. (b)Name the product formed at that electrode.[1]
3. (c)Name the product formed at the other electrode.[1]
4. (d)Explain why the ions move during electrolysis but not when the salt is solid.[1]
5. (e)Write the half equation for the change at the anode.[1]

Using the aqueous rules, complete the products table for electrolysis with inert electrodes.

1. (a)Cathode product for zinc nitrate.[1]
2. (b)Anode product for zinc nitrate.[1]
3. (c)Cathode product for silver nitrate.[1]
4. (d)Anode product for silver nitrate.[1]
5. (e)Cathode product for potassium sulfate.[1]

Predict and explain the products of electrolysis of these aqueous solutions with inert electrodes.

1. (a)Magnesium chloride solution — both electrodes.[3]
2. (b)Silver nitrate solution — both electrodes.[3]

A student electrolyses concentrated hydrochloric acid and notices a pale green gas at the anode and a colourless gas at the cathode.

1. (a)Identify both gases and the tests.[2]
2. (b)Write the half equation at the anode.[2]
3. (c)Explain why the solution’s pH rises as the electrolysis continues.[2]

Explain the differences when copper sulfate is electrolysed with (a) inert carbon electrodes and (b) copper electrodes.

1. (a)State the cathode and anode products with carbon electrodes.[2]
2. (b)State what happens with copper electrodes and why the anode dissolves.[2]
3. (c)Explain why the solution’s blue colour fades in (a) but stays constant in (b).[2]

Two inert electrodes dip into a beaker of molten potassium bromide and the current is switched on.

1. (a)State the products at each electrode.[2]
2. (b)Write the half equation at the cathode.[2]
3. (c)Write the half equation at the anode.[2]

A factory electrolyses brine, its concentrated solution of sodium chloride, using inert electrodes.

1. (a)Write the cathode half equation and explain why sodium is not the product.[3]
2. (b)Write the anode half equation.[1]
3. (c)Write the overall equation and explain why the solution left behind is alkaline.[2]

Impure copper is refined by electrolysis using copper sulfate solution, with the impure copper as one electrode and a thin pure copper sheet as the other.

1. (a)State the polarity of the impure copper electrode and write its half equation.[2]
2. (b)Write the half equation at the pure copper sheet.[1]
3. (c)Explain why the anode’s loss in mass equals the cathode’s gain in mass (ignoring impurities).[2]
4. (d)State what happens to the unreactive impurities in the anode.[1]

Explain why electrolysis of dilute sulfuric acid produces twice as much hydrogen as oxygen by volume.

1. (a)Write both half equations.[4]
2. (b)Use the half equations to explain the 2 : 1 ratio.[2]

A Key Industry Question: why is aluminium extraction so energy-intensive? Use the cell to answer.

1. (a)Explain why aluminium cannot be extracted by heating with carbon.[2]
2. (b)Write both half equations for the cell.[4]
3. (c)State two costs of the process besides electricity.[1]

A student electrolyses aqueous sodium bromide of moderate concentration with inert electrodes.

1. (a)Predict the products at each electrode with reasons.[4]
2. (b)Write both half equations.[4]

Two electrolysis cells are wired in series so the same current passes through both. Cell A contains molten sodium chloride; cell B contains molten aluminium oxide dissolved in cryolite. The current delivers 0.60 mol of electrons to each cell.

1. (a)Explain why the same current guarantees the same number of electrons is delivered to each cell.[2]
2. (b)Calculate the mass of sodium formed in cell A (Na 23).[2]
3. (c)Calculate the mass of aluminium formed in cell B, explaining the extra step (Al 27).[3]

A student writes: “Electrolysing dilute sodium chloride solution must give chlorine at the anode, because chloride ions are halide ions and halides always win at the anode.”

1. (a)Is the student’s prediction correct for dilute solution? State the actual anode product.[2]
2. (b)Explain why the concentration of the halide changes which product forms.[2]
3. (c)Write the half equation for the anode reaction in the dilute solution.[2]
4. (d)Explain why concentrated brine does give chlorine, and why the industrial cell uses concentrated solution.[2]