3.2 Electrolytic Processes

1a1 mark

Two compounds of barium are barium sulfide and barium chloride.

The hazard symbol shown in Figure 5 is on bottles containing barium metal.

Figure 5

State the meaning of this hazard symbol.

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1b1 mark

Give the names of the elements combined in barium sulfide.

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1c2 marks

Barium chloride is toxic.

Explain one safety precaution that should be taken when using barium chloride.

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1d2 marks

A beaker of barium chloride solution and a beaker of dilute sulfuric acid were placed on a balance, as shown in Figure 6.

fig-6-qdi-1cho-1f-paper-1-june-2018

Figure 6

The total mass reading on the balance was 25.7 g.

The dilute sulfuric acid was poured into the barium chloride solution and the beaker replaced on the balance, as shown in Figure 7.

figure-7

Figure 7

The mixture formed contained a white precipitate.

State the total mass reading on the balance after the reaction.

(1)

ii)

Give the name of the white precipitate formed by the reaction of barium chloride solution with dilute sulfuric acid.

(1)

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1e4 marks

Solid sodium chloride is dissolved in water.

The sodium chloride solution is electrolysed in the apparatus shown in Figure 8.

fig-8-q5e-1cho-1f-paper-1-june-2018

Figure 8

State why sodium chloride solution, rather than solid sodium chloride, must be used in this experiment.

(1)

ii)

The formulae of the ions present in the sodium chloride solution are

${Na}^{+}$ ${CI}^{-}$ $H^{+}$ ${OH}^{-}$

Circle the ions that would be attracted to the anode.

(1)

iii)

Molten lead bromide can be electrolysed to form molten lead and bromine gas.

Explain how a student could modify the apparatus shown in Figure 8 to carry out this electrolysis.

(2)

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1a2 marks

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.

solution	solution conducts electricity	product at cathode	product at anode
J	yes	copper	chlorine
K	yes	hydrogen	oxygen
L	no	none	none

Figure 12

Explain which solutions are electrolytes.

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1b1 mark

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

☐	A	zinc
☐	B	sulfur
☐	C	iron
☐	D	graphite

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1c4 marks

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.

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1d2 marks

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.

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1a4 marks

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

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

fig-3-q4-1cho-1f-specimen-2018

Figure 3

Any products formed at the electrodes are identified.

The results are given in Figure 4.

solution	solution conducts electricity	product at cathode	product at anode
J	yes	copper	chlorine
K	no	none	none
L	yes	hydrogen	chlorine

Figure 4

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)

☐	A	K only
☐	B	J and L only
☐	C	K and L only
☐	D	J, K and L

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2 marks

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.

	anode	cathode
mass of electrode before electrolysis / g	1.16	1.28
mass of electrode after electrolysis / g	0.85	1.57

Figure 5

Calculate the mass of copper deposited.

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

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1c2 marks

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

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

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2 marks

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.

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6a3 marks

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

The water is decomposed to produce hydrogen and oxygen.

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.

time in minutes	volume of hydrogen in cm³	volume of oxygen in cm³
0	0	0
2	4	2
4	8	4
6	12	6
8	16	8

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)

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6b1 mark

Molten lead bromide is electrolysed.

The products of this electrolysis are

☐	A	hydrogen and bromine
☐	B	hydrogen and oxygen
☐	C	lead and bromine
☐	D	lead and oxygen

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6c2 marks

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.

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6d6 marks

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.

fig-10-q9d-1cho-1f-paper-1-june-2019

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.

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6e2 marks

Higher Only

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

Write the half equation for this reaction.

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Positive ions move towards the negative electrode
Negative ions move towards the cathode
Negative ions remain in solution
Positive ions move towards the anode
Negative ions move towards the cathode

		H⁺ion	OH^- ion
☐	A	Hydrate	Oxide
☐	B	Hydrate	Hydroxide
☐	C	Hydrogen	Hydroxide
☐	D	Hydrogen	Oxide

	mass of electrode before electrolysis in g	mass of electrode after electrolysis in g	change in mass of electrode in g
anode	11.27	10.42	− 0.85
cathode	11.32	12.17	+ 0.85

		Anode	Cathode
☐	A	Decrease	Increase
☐	B	Increase	Decrease
☐	C	Increase	Increase
☐	D	Decrease	Decrease

Edexcel GCSE Chemistry

Topic Questions

3.2 Electrolytic Processes

Higher Only

Higher Only

Higher Only

Higher Only

☐	A	Copper atoms are attracted to the anode
☐	B	Copper ions are attracted to the anode
☐	C	Copper atoms are attracted to the cathode
☐	D	Copper ions are attracted to the cathode

☐	A	it contains molecules that can move
☐	B	it has a giant structure
☐	C	it contains delocalised electrons
☐	D	it contains ions that can move

☐	A	Zinc and oxygen
☐	B	Zinc and bromine
☐	C	Hydrogen and bromine
☐	D	Hydrogen and oxygen

☐	A	Copper is less reactive than hydrogen and consists of negatively charged ions
☐	B	Copper is more reactive than hydrogen and consists of negatively charged ions
☐	C	Copper is less reactive than hydrogen and consists of positively charged ions
☐	D	Copper is more reactive than hydrogen and consists of positively charged ions

☐	A	Lead atoms are oxidised
☐	B	Lead atoms are reduced
☐	C	Lead ions are oxidised
☐	D	Lead ions are reduced

☐	A	Solid zinc chloride has been used
☐	B	The electrodes don't conduct electricity
☐	C	The power supply is not connected properly
☐	D	The crucible is too small to allow ions to flow

☐	A	A pink coating is seen around the positive electrode
☐	B	Gases are given off at both electrodes
☐	C	The gas given off at the positive electrode can be tested with a burning splint
☐	D	The blue colour of the solution slowly fades

☐	A	hydrogen and oxygen
☐	B	hydrogen and bromine
☐	C	potassium and oxygen
☐	D	potassium and bromine

☐	A	Electric
☐	B	Electrolyte
☐	C	Electrode
☐	D	Electron