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The electrolysis of sodium chloride solution produces useful substances.

(a) (i) Choose a word from the box to complete the sentence.

covalent ionic non-metallic

Electrolysis takes place when electricity passes through ..................................

compounds when they are molten or in solution.(1)

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(ii) Choose a word from the box to complete the sentence.

alkenes elements salts

During electrolysis the compound is broken down to form...............................(1)

(b) The table of ions on the Data Sheet may help you to answer this question.

The diagram shows an apparatus used for the electrolysis of sodium chloride solution.

Reproduced with the permission of Nelson Thornes Ltd from PATRICK FULLICK et al,

ISBN 0-7487-9644- 4. First published in 2006

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Identify the products A, B and C on the diagram using substances from the box.

chlorine gas hydrogen gas oxygen gas

sodium hydroxide solution sodium metal

(i) A is ....................................................................................................................(1)

(ii) B is ....................................................................................................................(1)

(iii) C is ....................................................................................................................(1)

(Total 5 marks)

The electrolysis of sodium chloride solution is an industrial process.

(a) Why do chloride ions move to the positive electrode?

........................................................................................................................(1)

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(b) Sodium chloride solution contains two types of positive ions, sodium ions (Na+) andhydrogen ions (H+).

Tick ( ) the reason why hydrogen is produced at the negative electrode and not sodium.

Reason Tick ( )

Hydrogen is a gas.

Hydrogen is less reactive than sodium.

Hydrogen is a non-metal.

Hydrogen ions travel faster than sodium ions.

(1)

(c) Solution X is alkaline.

Which ion makes solution X alkaline?

........................................................................................................................(1)

(d) Electrolysis of sodium chloride solution produces hydrogen and chlorine.The hydrogen and chlorine can be used to make hydrogen chloride.

(i) The diagrams show how the outer electrons are arranged in atoms of hydrogen andchlorine.

Complete the diagram to show how the electrons are arranged in a molecule ofhydrogen chloride (HCl).

(1)

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(ii) Name the type of bond between the hydrogen and the chlorine atoms in a moleculeof hydrogen chloride.

................................................................................(1)

(iii) Some hydrogen chloride was bubbled into water. This made a solution with a pH of 1.

Which ion gave the solution a pH of 1?

................................................................................(1)

(Total 6 marks)

The table below shows information about three metals.

Metal Mainly found as% of metal inEarth’s crust

Relative cost of1 kg

Aluminium Aluminium oxide, Al2O3 8.2 4.2

Gold Gold 0.0000001 30000

Iron Iron(III) oxide, Fe2O3 4.1 1

(a) Suggest why gold is a very expensive metal.

........................................................................................................................

........................................................................................................................(1)

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Iron is extracted from iron oxide by reduction with carbon.

Aluminium cannot be extracted by reduction with carbon.

(b) (i) What is the name of the process used to extract aluminium from aluminium oxide?

...............................................................................................................(1)

(ii) Why is it more expensive to extract aluminium than iron?

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...............................................................................................................(1)

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(c) Complete and balance the symbol equation for the reaction to produce iron from iron(III)oxide.

.................... + .................... → .................... + .......... CO2

(2)(Total 5 marks)

This question is about potassium.

(a) Humphrey Davy was a professor of chemistry.

In 1807 Davy did an electrolysis experiment to produce potassium.

(i) Davy first tried to electrolyse a solid potassium salt to produce potassium.

Explain why this electrolysis did not work.

...............................................................................................................

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...............................................................................................................

...............................................................................................................(2)

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(ii) Humphrey Davy was the first person to produce potassium.

Humphrey Davy’s experiment to produce this new element was quickly accepted byother scientists.

Suggest why.

...............................................................................................................

...............................................................................................................(1)

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(b) A student dissolved some potassium chloride in water. The student tried to electrolyse thepotassium chloride solution to produce potassium.

The apparatus the student used is shown in the diagram.

The student expected to see potassium metal at the negative electrode, but instead sawbubbles of a gas.

• Name the gas produced at the negative electrode.

• Explain why this gas was produced at the negative electrode and why potassium wasnot produced.

The reactivity series of metals on the Chemistry Data Sheet may help you to answer thisquestion.

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........................................................................................................................(3)

(c) The student tried to electrolyse molten potassium chloride to produce potassium.

(i) Potassium metal was produced at the negative electrode.

Describe how potassium atoms are formed from potassium ions.

...............................................................................................................

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...............................................................................................................(2)

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(ii) Complete and balance the equation for the reaction at the positive electrode.

...........Cl− Cl2 + ...................(1)

(iii) Complete the diagram to show the electronic structure of a chloride ion (Cl−).

(1)

(Total 10 marks)

The electrolysis of sodium chloride solution is an industrial process.

The diagram shows the apparatus used in a school experiment.

(a) One of the products of the electrolysis of sodium chloride solution is hydrogen.

(i) Why do hydrogen ions move to the negative electrode?

...............................................................................................................

...............................................................................................................(1)

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(ii) How does a hydrogen ion change into a hydrogen atom?

...............................................................................................................

...............................................................................................................(1)

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(b) Hydrogen is used to make ammonia (NH3).

Complete the diagram to show the bonding in ammonia.

Use dots (●) and crosses (x) to show electrons.

Show only outer shell electrons.

(2)

(c) The table shows the ions in sodium chloride solution.

Positive ions Negative ions

hydrogen chloride

sodium hydroxide

In industry, some of the waste from the electrolysis of sodium chloride solution is alkalineand has to be neutralised.

(i) Which ion makes the waste alkaline?

...............................................................................................................(1)

(ii) This waste must be neutralised.

Write the ionic equation for the neutralisation reaction.

...............................................................................................................(1)

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(d) In this question you will be assessed on using good English, organising information clearlyand using specialist terms where appropriate.

The electrolysis of sodium chloride solution also produces chlorine and sodium hydroxide.

In industry, the electrolysis of sodium chloride solution can be done in several types ofelectrolysis cell.

Some information about two different types of electrolysis cell is given below.

Mercury cell Membrane cell

Cost of construction Expensive Relatively cheap

Additional substances used

Mercury, which is recycled.Mercury is toxic so anytraces of mercury must beremoved from the waste

Membrane, which is madeof a polymer. Themembrane must bereplaced every 3 years.

Amount of electricity usedfor each tonne of chlorineproduced in kWh

3400 2950

Quality of chlorine produced PureNeeds to be liquefied anddistilled to make it pure.

Quality of sodium hydroxidesolution produced

50% concentration. Steam isused to concentrate thesodium hydroxide solutionproduced.

30% concentration. Steamis used to concentrate thesodium hydroxide solutionproduced.

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Use the information and your knowledge and understanding to compare the environmentaland economic advantages and disadvantages of these two types of electrolysis cell.

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........................................................................................................................(6)

(Total 12 marks)

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The diagrams represent the electronic structure of a magnesium atom and a chlorine atom.

Magnesium reacts with chlorine to make the ionic compound called magnesium chloride. Thiscontains magnesium ions, Mg2+, and chloride ions, Cl-

(a) (i) Which structure, A, B or C, represents a magnesium ion?

The magnesium ion is Structure

(1)

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(ii) Which structure, D, E or F, represents a chloride ion?

The chloride ion is Structure

(1)

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(b) Magnesium metal can be extracted from sea water.Sea water contains magnesium chloride, MgCl2

(i) Calcium hydroxide, Ca(OH)2, is added to the sea water.Magnesium hydroxide, Mg(OH)2, is produced as a solid.

This is the equation for the reaction:

MgCl2(aq) + Ca(OH)2(aq) → Mg(OH)2(s) + CaCl2(aq)

Draw a ring around the correct answer to complete each sentence.

soluble

Magnesium hydroxide forms as a solid because it is insoluble in water.

dissolved

precipitation.

This type of reaction is called neutralisation.

thermal decomposition.

(2)

(ii) How is the solid magnesium hydroxide separated from the solution?

...............................................................................................................(1)

(iii) An acid is then added to the solid magnesium hydroxide to make magnesiumchloride.

Draw a ring around the name of this acid.

nitric acid hydrochloric acid sulfuric acid

(1)

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(c) Electrolysis is used to extract magnesium metal from magnesium chloride.

(i) What must be done to solid magnesium chloride to allow it to conduct electricity?

...............................................................................................................(1)

(ii) Why do the magnesium ions move to the negative electrode?

...............................................................................................................

...............................................................................................................(1)

(iii) Name the product formed at the positive electrode.

...............................................................................................................(1)

(Total 9 marks)

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This question is about the electrolysis of two compounds.

Figure 1 shows the electrolysis of molten lead bromide.

Figure 1

(a) The electrolyte contains lead ions (Pb2+) and bromide ions (Br–).

Complete the sentences.

Use words from the box.

atoms bromide bromine ions

lead molecules oxygen

At the positive electrode the gas produced is.................................................

At the negative electrode lead .......................................................................

gain electrons and ..................................... .(3)

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(b) A student measured the volumes of each gas produced during the electrolysis of water.

The table below shows the student’s results.

Time in minutes

Volume of gas produced in cm3

Hydrogen Oxygen

0 0 0

2 11.2 5.4

4 20.1 11.4

6 32.5 17.6

8 40.0 23.7

10 60.9 30.0

The student plotted a graph of the results for oxygen. Figure 2 shows the graph.

The student did not put a scale on the y axis.

On the graph in Figure 2:

• complete the scale for the y axis

• plot the results for hydrogen

• include a line of best fit.

Figure 2

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(3)

(c) Use the graph to calculate the mean volume of oxygen produced per second.

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Mean volume of oxygen produced = ................... cm3 / s(3)

(Total 9 marks)

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Some students investigated reactions to produce magnesium.

(a) The students used electrolysis to produce magnesium from magnesium chloride, as shownin the figure below.

(i) Magnesium chloride contains magnesium ions and chloride ions.

Why does solid magnesium chloride not conduct electricity?

...............................................................................................................

...............................................................................................................(1)

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(ii) One of the products of the electrolysis of molten magnesium chloride is magnesium.

Name the other product.

...............................................................................................................(1)

(iii) Why do magnesium ions (Mg2+) move to the negative electrode?

...............................................................................................................

...............................................................................................................(1)

(iv) At the negative electrode, the magnesium ions (Mg2+) gain electrons to becomemagnesium atoms.

How many electrons does each magnesium ion gain?

........................................(1)

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(b) The students did the experiment four times and weighed the magnesium produced.

The table below shows their results.

ExperimentMass of magnesiumproduced in grams

1 1.13

2 0.63

3 1.11

4 1.09

(i) There is an anomalous result.

Suggest one possible reason for the anomalous result.

...............................................................................................................

...............................................................................................................(1)

(ii) Calculate the mean mass of magnesium produced, taking account of the anomalousresult.

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Mean mass = ........................................ g(2)

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(c) The formula of magnesium chloride is MgCl2

The relative formula mass of magnesium chloride is 95.

The relative atomic mass of magnesium is 24.

(i) Use the equation to calculate the percentage mass of magnesium in magnesiumchloride.

Percentage mass of magnesium = × 100%

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Percentage mass of magnesium in magnesium chloride = ................... %(2)

(ii) Draw a ring around the relative mass of chlorine in MgCl2

71 95 119

(1)

(d) Magnesium is also produced from the reaction of magnesium oxide with silicon.

(i) The equation for the reaction is:

2 MgO(s) + Si(s) SiO2(s) + 2 Mg(s)

What is the meaning of this symbol ?

Draw a ring around the correct answer.

neutralisation reaction precipitation reaction reversible reaction

(1)

(ii) The forward reaction is endothermic.

Draw a ring around the correct answer to complete the sentence.

In an endothermic reaction the temperature of the surroundings

decreases.

increases.

stays the same.

(1)(Total 12 marks)

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The figure below shows an apparatus to produce elements from a solution of an ionic compound.

(a) What is the name of the process in the figure?

Tick one box.

Combustion

Crystallisation

Distillation

Electrolysis

(1)

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(b) The table below shows the products formed from three experiments using differentcompounds and the apparatus shown in the figure above.

Compound State Product atcathode

Product at anode

Copper chloride Molten Copper Chlorine

Copper chloride Aqueous solution Copper Chlorine

Potassiumbromide

Molten Potassium Bromine

Use the table above to name the products formed at each electrode if using an aqueoussolution of potassium bromide.

At cathode .............................................. At anode .......................................

........................................................................................................................(2)

(c) Explain why copper is formed at the cathode during the electrolysis of its salts.

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(Total 5 marks)

Copper can be produced from copper(II) sulfate solution by two different methods.

Method 1 – Electrolysis

(a) To produce copper by electrolysis a student has inert electrodes, a d.c. power supply, aswitch and electrical wires for the external circuit.

Draw and label the apparatus set up to produce copper from copper(II) sulfate solution byelectrolysis.

(2)

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(b) Suggest why the colour of the copper(II) sulfate solution fades during the electrolysis.

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(c) Explain how copper is produced from copper(II) sulfate solution by electrolysis.

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Method 2 – Displacement

(d) The chemical equation for the displacement of copper using iron is:

CuSO4 + Fe Cu + FeSO4

Calculate the minimum mass of iron needed to displace all of the copper from 50 cm3 ofcopper(II) sulfate solution.

The concentration of the copper(II) sulfate solution is 80 g CuSO4 per dm3.

Relative atomic masses (Ar): O = 16; S = 32; Fe = 56; Cu = 63.5

Give your answer to 2 significant figures.

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Mass of iron = ................................... g(4)

(Total 13 marks)

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the electrolysis of sodium chloride solution produces ... · €€€€€€€€€ the...

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