Electrolysis

Sodium chloride is an ionic compound.

Sodium chloride is made from sodium ions, Na +, and chloride ions, C l –. (a)

Fig. 13.1 shows a model for the ionic lattice of sodium chloride.

Complete by writing in the missing sodium ions, Na +, and chloride ions, C l –. Fig. 13.1

Fig. 13.1

What is the formula of sodium chloride?

Sodium chloride can be split up into its elements using electrolysis.

During electrolysis, sodium chloride must be heated until it is a liquid.

The table shows the melting point and boiling point of sodium chloride.

Suggest a temperature that sodium chloride should be heated to so it is a liquid.

Fig. 13.2 shows a diagram for the electrolysis of molten sodium chloride.

Fig. 13.2

What is the name of the piece of equipment, X ?

Name the gas produced at the anode.

A student thinks that the electrodes (anode and cathode) should be inert and made from graphite.

Complete the sentences to explain why the student is correct.

Graphite is reactive / unreactive. It is an electrical conductor / electrical insulator.

Sodium chloride contains 39% sodium.

Calculate the mass of sodium that is produced from the electrolysis of 160 kg of sodium chloride.

Give your answer to 2 significant figures.

* Fig. 13.3 shows the dot and cross diagram for sodium chloride.

Fig. 13.3

Sodium atom Chlorine atom Sodium ion Chloride ion

Explain how sodium and chlorine atoms form sodium and chloride ions.

Use information:

• from Fig. 13.3

• your knowledge of chemical bonding

• ideas about the electron arrangement in the atoms and ions.

The equation for the reaction is

Complete the balanced symbol equation for the reaction by writing in the missing state

symbol for copper chloride solution.

The student thinks that the experiment shows that electrode X is the cathode.

Explain why the student is correct. Use the diagram.

Use the data in the table to show that the mass of copper produced doubles as the current doubles.

Plot a graph of the results on the grid.

Draw a line of best fit.

The student thinks that the result for the mass of copper produced at 3 A is incorrect

Explain how the student knows this result is incorrect.

Use your graph to predict the mass of copper that should have been produced at 3 A.

The diagram shows the electrolysis of molten copper chloride, CuCl₂.

Chlorine is formed at electrode X and copper is formed at electrode Y.

Which row in the table describes electrodes X and Y ?

Potassium chloride, KC l, is an ionic compound.

It is made from potassium ions, K +, and chloride ions, C l –.

Explain why potassium is found in Group 1 of the Periodic Table.

Use ideas about the arrangement of electrons in an atom of potassium.

Explain how an atom of potassium reacts with an atom of chlorine to make potassium chloride.

A student electrolyses potassium chloride.

The diagram shows the equipment they use.

Describe and explain two ways the student could change the experiment to make it work.

In the successful electrolysis of potassium chloride, potassium is made at the cathode.

Explain how potassium atoms are made from potassium ions.

Aluminium is produced from aluminium oxide by electrolysis.

The diagram shows the industrial electrolysis of aluminium oxide.

Look at the equation for the electrolysis of aluminium oxide.

Complete the balanced symbol equation for the reaction.

Molten aluminium oxide contains Al³⁺ and O²⁻ ions. (b)

Explain why the aluminium oxide must be molten during electrolysis.

Explain why aluminium is produced at the cathode.

Aluminium melts at 650 °C.

Describe two reasons why it is cheaper to recycle aluminium than to produce it from electrolysis.

Copper can be produced from a copper(II) sulfate solution by electrolysis.

A student investigates how the mass of copper produced changes with the size of the current used during the electrolysis. The student varies the current used during electrolysis and investigates the mass of copper produced at the cathode.

The diagram shows the apparatus they use.

Copper(II) sulfate solution

The student:

• Measures the mass of the dry cathode at the start of the experiment.

• Switches the power pack on for 10 minutes.

• Removes the cathode and washes it with water.

• Dries the cathode.

• Measures the mass of the cathode again.

• Calculates the mass of copper formed at the cathode.

The student repeats the experiment at different currents.

They plot a graph of their results.

The copper(II) sulfate solution contains copper ions, Cu²⁺. (a)

Write the balanced half equation for the formation of copper at the cathode.

Include state symbols in the equation.

Look at the graph.

The student decides that the result for the mass of copper formed at the cathode at 2 A is incorrect.

Give a reason for this result.

Has the student drawn the correct line of best fit?

Give a reason for your answer.

Explain how repeating the experiment could improve the accuracy of the results.

Use the graph to calculate the mass of copper produced by a current of 15 A.

Give your answer to 1 significant figure.

Explain the term electrolysis.

Electrolysis involves the reactions of cations and anions.

Describe the difference between cations and anions.

The electrolysis of molten potassium chloride makes potassium at the cathode.

Write the balanced half equation for the formation of potassium.

State and explain if this equation shows oxidation or reduction.

Name the product formed at the anode when an aqueous solution of potassium chloride, KC l (aq), is electrolysed.

Give a reason for your answer.