Sec 4 Chemistry Electrolysis topical questions

Define the terms electrolyte, cathode and anode.

Predict the product at each electrode when molten potassium bromide is electrolysed using carbon electrodes.

1. (a)Product at the cathode[1]
2. (b)Product at the anode[1]

State why a sugar solution does not conduct electricity but aqueous sodium chloride does.

Name the gas released at each electrode during the electrolysis of dilute sulfuric acid with platinum electrodes, and state the volume ratio.

1. (a)Gas at the cathode[1]
2. (b)Gas at the anode[1]
3. (c)Volume ratio (cathode : anode)[1]

Molten lithium chloride is electrolysed using carbon electrodes (Li = a very reactive metal).

1. (a)Write the half-equation at the cathode and name the product.[2]
2. (b)Write the half-equation at the anode.[1]

Complete the comparison of electrolysis of sodium chloride molten against its aqueous solution (inert electrodes).

1. (a)Give the two missing products for the molten salt.[2]
2. (b)Name the substance left in solution after the aqueous run and explain where it comes from.[2]

Concentrated aqueous sodium chloride (brine) is electrolysed using inert electrodes. State the product at each electrode and the substance left in solution, writing a half-equation for each electrode.

Explain why electrolysis of concentrated sodium chloride gives chlorine at the anode, while dilute sodium chloride gives oxygen. State the half-equation for the oxygen-forming reaction.

A steel bracelet is to be electroplated with nickel.

1. (a)State the electrode the bracelet should be and the electrode the nickel bar should be.[2]
2. (b)Name a suitable electrolyte.[1]
3. (c)Write the half-equations at both electrodes.[2]

Copper(II) sulfate solution is electrolysed with carbon electrodes until the blue colour disappears.

1. (a)Write the half-equation at the cathode and identify the product.[2]
2. (b)Write the half-equation at the anode and name the gas.[2]
3. (c)Explain the change in pH of the solution.[1]

A student electrolyses molten sodium iodide using carbon electrodes and records the observations.

1. (a)State what forms at each electrode.[2]
2. (b)Write both half-equations.[2]
3. (c)State one safety precaution for the anode product.[1]

Concentrated aqueous copper(II) chloride is electrolysed with inert (carbon) electrodes.

1. (a)State the observation at each electrode.[2]
2. (b)Write the half-equation at each electrode.[2]
3. (c)Explain why chlorine forms at the anode rather than oxygen.[1]

Copper(II) sulfate solution is electrolysed using TWO COPPER electrodes (not inert ones).

1. (a)State and explain what happens at the anode.[2]
2. (b)State what forms at the cathode.[1]
3. (c)Explain why the blue colour of the solution stays constant.[2]

Three simple cells are made in dilute sulfuric acid, each pairing a metal strip with copper: cell P (magnesium/copper), cell Q (zinc/copper) and cell R (iron/copper).

1. (a)Arrange the cells in order of expected voltage, largest first, with a reason.[2]
2. (b)For cell Q, write the half-equation at the zinc and state what happens at the copper.[2]
3. (c)State the direction of electron flow in the external circuit of cell Q.[1]

Impure copper is refined electrolytically using copper(II) sulfate solution.

1. (a)State the role of the impure copper and of the pure copper sheet.[2]
2. (b)Write the half-equations at both electrodes.[2]
3. (c)Explain what happens to (i) gold impurities and (ii) zinc impurities.[2]

Two simple cells are set up in dilute sulfuric acid: cell P with magnesium and copper strips, cell Q with iron and copper strips. Both are connected in turn to the same voltmeter.

1. (a)State which metal is the negative terminal in each cell.[2]
2. (b)Write the half-equation occurring at the negative terminal in cell P.[1]
3. (c)State and explain which cell gives the larger voltage.[2]
4. (d)State what would happen with two copper strips.[1]

A colourless solution X is electrolysed with inert electrodes. Colourless gas bubbles form at BOTH electrodes; the cathode gas pops with a lighted splint, the anode gas relights a glowing splint; the solution turns alkaline around the cathode.

1. (a)Identify both gases and write the cathode half-equation.[3]
2. (b)Suggest the identity of solution X, explaining the alkaline cathode region.[2]
3. (c)State the expected volume ratio and explain why it differs from 1 : 1.[1]

In industry, brine electrolysis is run in a cell that keeps the anode and cathode compartments separated by a membrane.

1. (a)State the product at each electrode and the substance remaining in solution.[3]
2. (b)Explain why the compartments must be separated, naming the reaction that would otherwise occur.[3]