Electrolytic Processes (Edexcel GCSE Chemistry)

An electrolysis experiment is carried out on different solutions, J, K and L.

Electricity is passed through each solution as shown in Figure 3.

Figure 3

Any products formed at the electrodes are identified. The results are given in Figure 4.

Figure 4

i) State an improvement that can be made to the circuit to show that a current is flowing during the electrolysis.

(1)

Some of these solutions are electrolytes.

ii) State what is meant by the term electrolyte.

(2)

iii) Which of J, K and L are electrolytes?

(1)

Copper sulfate solution was electrolysed for five minutes using copper electrodes.

Figure 5 shows the mass of the anode and of the cathode before electrolysis and after electrolysis.

Figure 5

Calculate the mass of copper deposited.

mass of copper deposited = ............................................................... g

Identify the products formed at the anode and cathode when molten potassium iodide is electrolysed.

Anode ................................... Cathode ................................

In a different electrolysis, molten sodium fluoride is decomposed.

2NaF → 2Na + F₂

(relative atomic masses: F = 19, Na = 23)
(relative formula mass NaF = 42)

Calculate the maximum mass of sodium that could be formed from 168g of sodium fluoride.

Molten zinc bromide is electrolysed. 

The products of this electrolysis are 

During the the electrolysis of copper sulfate solution, copper ions move to the negative electrode.

What is the reason for this?

Higher Only

When copper(II) sulfate undergoes electrolysis, it produces oxygen gas at the positive electrode.

The unbalanced half equation below represents the reaction that occurs at the positive electrode.

Which numbers will correctly balance the half equation?

___ OH^-    →    O₂   +   ___ H₂O  +  ___ e^-

Electrolysis can be used to separate molten lead bromide. 

Which statement is true for what happens at the negative electrode?

Water, acidified with sulfuric acid, is decomposed by electrolysis.

The water is decomposed to produce hydrogen and oxygen.

i) A sample of hydrogen is mixed with air and ignited.

 State what would happen.

(1)

 ii) Throughout the experiment the volume of hydrogen and the volume of oxygen are measured at two-minute intervals. 

 The results are shown in Figure 9.

Figure 9

Describe, using the data in Figure 9, what the results show about the volumes of hydrogen and oxygen produced in this experiment.

(2)

Molten lead bromide is electrolysed.

The products of this electrolysis are

Calcium nitrate and calcium carbonate are both ionic compounds.

Calcium nitrate mixed with water behaves as an electrolyte.

Calcium carbonate mixed with water does not behave as an electrolyte.

Explain, in terms of solubility and movement of ions, this difference in behaviour. 

Impure copper can be purified using electrolysis.

  In this electrolysis

• the anode is made of impure copper

• the cathode is made from pure copper

• the electrolyte is copper sulfate solution.

The apparatus at the start of the experiment is shown in Figure 10. 

Figure 10

During the electrolysis three observations are made:

• the sizes of both the anode and the cathode change

• a solid appears directly beneath the anode

• the colour of the copper sulfate solution does not change. 

Explain all three observations. 

Higher Only

When molten zinc chloride is electrolysed, zinc ions, Zn²⁺, form zinc atoms.

Write the half equation for this reaction.

Sodium chloride solution can undergo electrolysis. 

What product will be formed at the negative electrode?

A student was investigating the electrolysis of zinc chloride. 

What is the correct reason for electrolysis not working? 

Figure 11 shows the apparatus that can be used to electrolyse sodium sulfate solution using inert electrodes.

Figure 11

Hydrogen is produced at the negative electrode during electrolysis.

i) Describe the test to show the gas is hydrogen. (2)

ii) What is the name of gas X that forms at the positive electrode?

(1)

iii) State what is meant by the term electrolysis.

(2)

The sodium sulfate solution was made by dissolving 28.4 g of sodium sulfate in water to make 250 cm³ of solution.

Calculate the concentration of this solution in g dm^-3. Give your answer to three significant figures.

concentration = ...................................... g dm^-3

The ions present in sodium sulfate are    

sodium Na⁺    

sulfate SO₄^2-

Write the formula of sodium sulfate using this information.

i) In Figure 11, the gases given off at the electrodes are collected in test-tubes.

However, the actual volume of gases cannot be measured using these test-tubes.

Suggest what apparatus could be used in place of the test-tubes in Figure 11 to measure the volume of gases given off.

(1)

ii) State what could be added into the circuit to show a current is flowing during electrolysis.

(1)

The electrolysis of copper sulfate solution using copper electrodes can be used to purify copper. 

The following equipment was set up: 

What changes in mass would you expect to see for each electrode? 

Aqueous copper(II) sulfate solution can be electrolysed using carbon electrodes. 

Which statement is true about the reaction?

This question is about electrolysis.

A sample of molten potassium bromide is electrolysed.

What are the two products formed?

Zinc chloride and zinc carbonate contain ions.

Zinc chloride mixed with water can be electrolysed.

Zinc carbonate mixed with water cannot be electrolysed.

Explain this difference.

In the electrolysis of sodium chloride solution, bubbles of a colourless gas form at the cathode.

This gas, when mixed with air, burns with a squeaky pop.

i) Identify this gas.

(1)

ii) Explain how this gas is formed at the cathode.

(2)

A solution of copper sulfate in a beaker is electrolysed using copper electrodes.

i) Draw a labelled diagram to show how this experiment would be set up.

The beaker has been drawn for you.

(2)

ii) During the electrolysis, the anode gets smaller, the cathode gets larger and the solution remains the same shade of blue.

Give the reason for each of these observations.

(3)

the anode gets smaller ......................................................................................................................................

the cathode gets larger ......................................................................................................................................

the solution remains the same shade of blue ...............................................................................................

Electrodes are placed in three different solutions, J, K and L.

A 6V direct current source is connected to the electrodes.

Any products formed at the electrodes are identified.

The results are given in Figure 12.

Figure 12

Explain which solutions are electrolytes.

Which material is most suitable to make the electrodes for the electrolysis of a dilute acid?

When a solution of sodium sulfate, Na₂SO₄, is electrolysed, the products formed at the electrodes are hydrogen and oxygen.

Explain the formation of the products at the electrodes.

Higher Only

Copper is purified by the electrolysis of copper sulfate solution using an impure copper anode and a pure copper cathode.

Write the half-equation for the formation of a copper atom from a copper ion.

Molten zinc chloride is an electrolyte.

i) Which row shows the products formed at the anode and at the cathode when molten zinc chloride is electrolysed? 

ii) Which of the following is the reason why molten zinc chloride is an electrolyte?

(1) 

Copper sulfate solution was electrolysed using copper electrodes.

i) Draw a labelled diagram to show the apparatus that is used to carry out this electrolysis in the laboratory.

(2)

ii) Before the electrolysis, the masses of the electrodes were determined. After the electrolysis, the electrodes were washed and dried and their masses re-determined.

Figure 6 shows these masses and the resulting changes in masses of the electrodes.

Figure 6

Explain these results.

(4)

Higher Only

When sodium sulfate solution is electrolysed, using inert electrodes, hydrogen is formed at the cathode.

Write the half equation for the formation of hydrogen gas, H₂, from hydrogen ions, H⁺.

Copper(II) chloride and lead chloride are both ionic compounds.

i) Explain why adding water to copper chloride will form an electrolyte.

[2]

ii) State why adding water to lead chloride will not form an electrolyte.

[1]

Describe what you would have to do to lead chloride so it acts as an electrolyte.

Give a reason for your answer.

Higher Only

Copper(II) chloride solution is electrolysed.

Write the half equation for the reaction that happens at the anode.

Higher Only

Explain why reduction happens at the cathode.

Use the movement of electrons in your answer.

Sodium chloride solution is electrolysed. Hydrogen is formed at the cathode.

Describe the test you would use to prove that a gas is hydrogen.

Explain how hydrogen is formed at the cathode.

Universal indicator is added to the sodium chloride solution at the start. Predict what colour the electrolyte will be at the end of the electrolysis reaction.

Give a reason for your answer.

State the products formed when molten sodium chloride is electrolysed.

Figure 1 shows the apparatus used to metal plate an iron spoon. The spoon is covered with a thin layer of silver.

Figure 1

Suggest a suitable solid compound that can be dissolved to make the electrolyte.

Higher Only

Write the half equation to show what happens at the silver rod.

Explain why the spoon needs to be connected to the negative side of the power supply.

Suggest one way to increase the rate of electroplating.