Electrolysis of molten ionic compounds

This question is about electrolysis and the extraction of metals.

Why can some molten substances be electrolysed?

Tick () one box.

Table 3 shows the products of the electrolysis of some molten compounds.

Complete Table 3.

Aluminium is extracted by electrolysing molten aluminium oxide.

Balance the equation for the reaction.

Choose numbers from the box.

Calculate the relative formula mass (M_r) of aluminium oxide (Al₂O₃).

Relative atomic masses (A_r): O = 16 Al = 27

Figure 13 shows part of the reactivity series of metals.

The non-metal carbon has been included.

Metals can be extracted from their compounds by:

electrolysis

reduction with carbon.

Electrolysis is more expensive than reduction with carbon.

Predict one metal that would be extracted by each method.

Use Figure 13.

This question is about ionic compounds and electrolysis. Sodium chloride is an ionic compound.

Figure 8 represents part of the structure of solid sodium chloride.

Complete Figure 8.

Give one reason why molten sodium chloride conducts electricity. Refer to ions in your answer.

Table 3 shows products of the electrolysis of two molten ionic compounds. Complete Table 3.

Aluminium is extracted by electrolysis. The electrolyte is a molten mixture of aluminium oxide and cryolite. Why is a mixture used instead of pure aluminium oxide as the electrolyte? Tick (✓) one box.

Electrolysis of an aqueous solution of sodium sulfate produces hydrogen and oxygen. What is the source of the hydrogen and the oxygen produced during the electrolysis of aqueous sodium sulfate solution? Tick (✓) one box.

Electrolysis of an aqueous solution of sodium sulfate produces hydrogen and oxygen.

Why is hydrogen produced instead of sodium in the electrolysis of aqueous sodium sulfate solution? Tick (✓) one box.

Figure 9 shows the relationship between the volume of hydrogen and the volume of oxygen produced during the electrolysis.

Give one conclusion that can be made about the volume of hydrogen produced compared to the volume of oxygen produced.

This question is about electrolysis.

Ionic compounds decompose when they are electrolysed.

A student electrolyses sodium sulfate solution.

Figure 13 shows the apparatus used.

Sodium sulfate solution contains:

• hydrogen ions

• hydroxide ions

• sodium ions

• sulfate ions.

Oxygen is produced at the positive electrode.

Which ions are discharged at the positive electrode to produce oxygen?

Tick (✓) one box.

Figure 14 shows one of the measuring cylinders during the electrolysis.

What is the volume of gas in the measuring cylinder?

Ionic compounds can be electrolysed when molten or dissolved in water.

Why can ionic compounds not be electrolysed when solid?

You should answer in terms of ions.

Table 7 shows the products of electrolysis of two molten compounds.

Complete Table 7.

The electrolysis of molten sodium chloride is used to extract sodium metal.

Why is sodium metal extracted by electrolysis instead of by reduction with carbon?

Tick (✓) one box.

What is the state symbol for molten sodium chloride?

Tick (✓) one box.

Titanium can be produced from titanium oxide by electrolysis.

The equation for the reaction is:

Calculate the percentage atom economy for the production of titanium from titanium oxide by electrolysis.

Use the equation:

Relative atomic mass (A_r): Ti = 48

Relative formula mass (M_r): TiO₂ = 80

This question is about electrolysis. Molten sodium chloride is electrolysed in an industrial process to produce sodium. Figure 8 shows a simplified version of the electrolysis cell used.

Which is the correct half equation for the production of sodium? Tick (✓) one box.

A mesh is used to keep the products of the electrolysis apart.

Suggest one reason why the products of the electrolysis must be kept apart.

Which type of particle passes through the mesh in the electrolysis of molten sodium chloride? Tick (✓) one box.

Aqueous sodium chloride solution is electrolysed in a different industrial process. Two gases and an alkaline solution are produced.

Which two ions are present in aqueous sodium chloride solution in addition to sodium ions and chloride ions?

Name the alkaline solution produced.

Explain how the alkaline solution is produced. You should refer to the processes at the electrodes.

This question is about electrolysis.

Some students investigated the electrolysis of silver nitrate solution.

This electrolysis produces silver at the negative electrode.

Figure 11 shows the apparatus.

This is the method used.

1. Weigh the negative electrode.

2. Set up the apparatus shown in Figure 11.

3. Switch on the power supply.

4. Switch off the power supply after five minutes.

5. Rinse the negative electrode with water and allow to dry.

6. Reweigh the negative electrode.

7. Repeat steps 1 to 6 for different times.

Some silver did not stick to the negative electrode but fell to the bottom of the beaker.

The students needed to weigh this silver.

How could the students separate the silver from the silver nitrate solution?

Tick (✓) one box.

Table 5 shows the students’ results.

Draw a graph on Figure 12.

You should:

• use a suitable scale for the x-axis

• plot the data from Table 5

• draw a line of best fit.

Determine the mass of silver that would be produced after 12 minutes.

Use Figure 12.

A student investigated the electrolysis of two aqueous salt solutions.

Hydrogen is produced at the negative electrode when the metal in the salt solution is more reactive than hydrogen.

Complete Table 6 to show what the student would observe at the negative electrode for each salt solution.

A teacher demonstrates the electrolysis of molten lead bromide.

The products at the electrodes are lead and bromine.

Why should the teacher do the demonstration in a fume cupboard?

Two other molten compounds are electrolysed.

Complete Table 7 to show the molten compounds and the products.

A student investigated the electrolysis of sodium chloride solution.

Figure 4 shows the apparatus.

The student measured the volume of gas collected in each measuring cylinder every minute for 20 minutes.

Figure 5 shows the volume of hydrogen gas collected in the measuring cylinder after 8 minutes.

What is the volume of hydrogen gas collected?

Figure 6 shows the results of the investigation.

Which of the lines on Figure 6 show that the volume of gas collected is directly proportional to the time?

Tick one box.

Which of the lines on Figure 6 show a positive correlation between the volume of gas collected and time?

Tick one box.

A teacher demonstrates the electrolysis of different substances using graphite electrodes.

Figure 7 shows the apparatus used.

Figure 7

Why can graphite conduct electricity?

Tick one box.

The teacher demonstrates the electrolysis of:

molten zinc chloride

potassium bromide solution.

Complete Table 3 to predict the products.

Choose answers from the box.