3.2.7 The extraction of metals Principles of metal extraction

314 minutes 308 marks

Page 1 of 31

Q1.

(a)

(i) Write an equation for the reaction which is mainly responsible for the high temperature in the Blast Furnace. .............................................................................................................

(ii)

Write an equation for a reaction in which iron is formed from its oxide in the Blast Furnace. .............................................................................................................

(iii)

Iron from the Blast Furnace can contain sulphur. Write an equation to show how this impurity is removed. .............................................................................................................

(iv)

Iron from the Blast Furnace contains carbon. State how most of this carbon is removed. Give one reason why this removal is necessary. Removal of carbon............................................................................... ............................................................................................................. Reason................................................................................................. ............................................................................................................. (6)

(b)

(i)

State why carbon cannot be used to reduce titanium(IV) oxide directly to titanium. .............................................................................................................

(ii)

Carbon is used in one of the steps in the batch process for titanium extraction. Write an equation for the reaction which occurs in this step and state a condition under which this reaction is carried out. Equation .............................................................................................. Condition ............................................................................................. (4)

(c)

Aluminium is not usually extracted by heating aluminium oxide with carbon, but carbon does have a use in the extraction of aluminium from aluminium oxide. State how carbon is used during the extraction process and write a half-equation showing how aluminium is produced. Use of carbon .............................................................................................. Half-equation................................................................................................ (2)

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(d)

State three factors which determine the choice of reduction method used for the extraction of metals from their ores. Factor 1 ....................................................................................................... Factor 2 ....................................................................................................... Factor 3 ....................................................................................................... (3) (Total 15 marks)

Q2.

(a) In a blast furnace, iron can be extracted from an oxide ore which also contains silicon dioxide as an impurity. Identify the additional raw materials needed in the extraction process, state why they are needed and write equations for the reactions occurring. (10)

(b)

Iron produced in a blast furnace is impure. The iron contains carbon, sulphur and phosphorus. State how each of these impurities is removed. Explain why sulphur is removed before carbon and phosphorus. (6)

(c)

Although there are large reserves of iron and aluminium ores in the world, both metals are recycled. (i)

State one social benefit of recycling iron and state why it is particularly easy to separate iron from other scrap metal.

(ii)

Give one main reason why it is much cheaper to recycle aluminium than it is to extract the metal from its ore. Give one major factor in the cost of recycling aluminium cans. (4) (Total 20 marks)

Q3.

In this question, credit will be given for appropriate equations. (a)

Describe the process by which titanium metal is extracted from titanium(IV) oxide. Explain why this extraction process causes titanium to be an expensive metal. (11)

(b)

Explain how the impurity silicon(IV) oxide is removed during the extraction of iron in the Blast Furnace. Discuss the chemical reactions by which impurities are removed from iron in the basic oxygen converter. (13)

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(c)

Describe how scrap iron is recycled. Discuss the social and environmental benefits of this recycling. (6) (Total 30 marks)

Q4.

(a) Iron is extracted in a Blast Furnace by a continuous reduction process. Identify two reducing agents present in the Blast Furnace. In each case, write an equation to show how the reducing agent reacts in the formation of iron. Reducing agent 1 ......................................................................................... Equation ....................................................................................................... Reducing agent 2 ......................................................................................... Equation ....................................................................................................... (4)

(b)

Titanium is extracted from TiO2 using two separate batch processes. For each of these processes, write an equation for the reaction occurring. Equation 1 ................................................................................................... Equation 2 .................................................................................................... (4)

(c)

Suggest in general terms how metals can be extracted from sulphide ores. Explain how pollution problems can arise from such extractions. Extraction ..................................................................................................... ...................................................................................................................... ...................................................................................................................... Pollution problems ........................................................................................ ...................................................................................................................... ...................................................................................................................... (4) (Total 12 marks)

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Q5.

Metal reactivity and required purity are important considerations when choosing the method of extracting a metal. Each of the following is a reduction process used in the industrial extraction of one or more metals from its ore. Method 1 Method 2 Method 3

high temperature reaction between an oxide and carbon electrolysis of a molten compound displacement from a compound using a more reactive metal

(i)

For each method of extraction, identify one metal which is extracted using this process and write an equation for the reaction in which the metal is formed.

(ii)

Give two reasons why Method 3 is a very expensive extraction process.

(iii)

When beryllium oxide is heated with carbon to a very high temperature, beryllium carbide, Be2C, is formed. This carbide reacts with water to form beryllium hydroxide and methane. Write an equation for the reaction of beryllium carbide with water. (Total 10 marks)

Q6.

(a) Explain, with the aid of equations, how the silicon-containing impurity in iron ore is removed in the Blast Furnace. Identify the major impurity in the molten iron from the Blast Furnace and explain with the aid of an equation how this element is removed from iron on an industrial scale. (8)

(b)

Describe how aluminium is manufactured from purified bauxite. Illustrate your answer by writing equations. State the major economic benefit arising from the recycling of aluminium. What is the major problem associated with this recycling process? (7) (Total 15 marks)

Q7.

(a) When iron(III) oxide is reduced in the Blast Furnace, both carbon and carbon monoxide act as reducing agents. (i)

Write an equation to illustrate how carbon monoxide is formed in the Blast Furnace. .............................................................................................................

(ii)

Write an equation to illustrate how carbon monoxide reduces iron(III) oxide. .............................................................................................................

(iii)

Suggest in terms of collisions why, in the Blast Furnace, carbon monoxide reacts more rapidly with iron(III) oxide than does carbon. ............................................................................................................. ............................................................................................................. (4)

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(b)

State why carbon is not used to reduce the oxide of titanium to the metal. ...................................................................................................................... (1)

(c)

(i)

Name the converter that is used to remove impurities from the iron obtained from a Blast Furnace. .............................................................................................................

(ii)

Write an equation to illustrate how the sulphur impurity is removed from the iron. .............................................................................................................

(iii)

State how the phosphorus impurity is removed from iron in this converter. ............................................................................................................. .............................................................................................................

(iv)

Explain two major benefits of using some scrap iron in this converter. Benefit 1 ............................................................…...........................… ............................................................................................................. Benefit 2 ....................................................…...................................... ............................................................................................................. (7)

(d)

Give two reasons why titanium is a more expensive metal than iron. Reason 1 ...................................................................................................... Reason 2 ...................................................................................................... (2) (Total 14 marks)

Q8.

Reducing agents are used in the extraction of metals. (a)

In terms of electrons, state the function of a reducing agent. ...................................................................................................................... (1)

(b)

Identify a reducing agent used in the extraction of iron. Write an equation for the redox reaction in which iron is formed from iron(III) oxide using this reducing agent. Reducing agent............................................................................................. Equation ....................................................................................................... (2)

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(c)

Identify a reducing agent used to obtain titanium metal from titanium(IV) chloride. In addition to a high temperature, state a condition that is used for this reaction and explain why this condition is necessary. Reducing agent ........................................................................................... Condition ..................................................................................................... Explanation .................................................................................................. ...................................................................................................................... (3)

(d)

(i)

State two essential conditions used for the electrolytic extraction of aluminium from aluminium oxide. Condition 1 .......................................................................................... Condition 2 .......................................................................................... .............................................................................................................

(ii)

Write an equation to illustrate how aluminium is formed from aluminium ions in this process. ............................................................................................................. (3) (Total 9 marks)

Q9.

In this question, where appropriate, illustrate your answer with equations. (a)

Explain how iron is produced in the Blast Furnace from an iron ore that does not contain sulphur impurities. In your answer, state the source of the energy for this process and mention any environmental problems that may arise from the operation of the Blast Furnace. Explain why limestone is added to the Blast Furnace. (10)

(b)

Phosphorus is a significant impurity in iron from the Blast Furnace. Explain how this impurity is removed in the steel-making process. (5) (Total 15 marks)

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Q10.

Iron is extracted from iron(III) oxide in a continuous process, whereas titanium is extracted from titanium(IV) oxide in a batch process. (a)

Suggest why a high-temperature batch process is less energy-efficient than a hightemperature continuous process. ...................................................................................................................... ...................................................................................................................... (2)

(b)

Write an overall equation for the reduction of iron(III) oxide in the Blast Furnace. ...................................................................................................................... (2)

(c)

Write two equations to show how titanium is extracted from titanium(IV) oxide in a twostage process. Equation for stage 1 .................................................................................... Equation for stage 2..................................................................................... (4)

(d)

Give the major reason, other than its production in a batch process, why titanium is a more expensive metal than aluminium. ...................................................................................................................... ...................................................................................................................... (1)

(e)

Give the major reason why aluminium is more expensive to extract than iron. ...................................................................................................................... ...................................................................................................................... (1) (Total 10 marks)

Q11.

Metals can be extracted from their ores by reduction. This question refers to the metals copper, iron and titanium. (a)

A common ore of copper is malachite which contains copper carbonate (CuCO3). Copper was first extracted about 3000 BC in Anatolia (now Turkey) by smelting copper ore in ‘Fire Pits’. The ore was smelted with charcoal to produce impure copper. (i)

Write an equation for the smelting of malachite with charcoal to produce copper and carbon dioxide. .............................................................................................................

(ii)

State the chemical acting as the reducing agent in the smelting process. ............................................................................................................. (2)

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(b)

A common ore of iron is haematite which contains iron(III) oxide. Iron was not extracted from this ore until about 1500 BC. (i)

Suggest why it took another 1500 years before iron was extracted from its ore. .............................................................................................................

(ii)

Name a gaseous reducing agent which can reduce iron(III) oxide to iron. Write an equation for the reaction. ............................................................................................................. (2)

(c)

Titanium metal has only been extracted from its ore rutile (TiO2) in the last 50 years. It is a very expensive two–stage process. Give an equation for each stage of the process. Stage 1 ........................................................................................................ Stage 2 ........................................................................................................ (4)

(d)

Suggest how metals can be extracted from their sulfide ores. Explain how pollution problems can arise from such extractions. Extraction ..................................................................................................... ...................................................................................................................... ...................................................................................................................... Pollution problems ....................................................................................... ...................................................................................................................... ...................................................................................................................... (4) (Total 12 marks)

Q12.

This question is about the extraction of metals. (a)

Coke is mainly carbon and is a raw material used in the extraction of iron from iron(III) oxide. (i)

Write an equation for the formation of carbon monoxide from carbon. ............................................................................................................. (1)

(ii)

Write an equation for the reduction of iron(III) oxide to iron by carbon monoxide. ............................................................................................................. (1)

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(iii)

The Earth’s resources of iron(III) oxide are very large and commercial ores have a high iron content. Give one economic and one environmental reason for recycling scrap iron and steel. Economic reason ................................................................................ ............................................................................................................. Environmental reason ......................................................................... ............................................................................................................. (2)

(b)

Pure titanium is extracted by the reduction of titanium(IV) chloride, but not by the direct reduction of titanium(IV) oxide using carbon. (i)

Write an equation for the conversion of titanium(IV) oxide into titanium(IV) chloride. ............................................................................................................. (2)

(ii)

Write an equation for the extraction of titanium from titanium(IV) chloride. ............................................................................................................. (2)

(iii)

State why titanium is not extracted directly from titanium(IV) oxide using carbon. ............................................................................................................. (1)

(c)

Aluminium is extracted by the electrolysis of a molten mixture containing aluminium oxide. (i)

State why the electrolysis needs to be of a molten mixture. ............................................................................................................. (1)

(ii)

Write an equation for the reaction of oxide ions at the positive electrode during the electrolysis. ............................................................................................................. (1)

(iii)

State why the positive electrodes need frequent replacement. ............................................................................................................. (1)

(iv)

Give the major reason why it is less expensive to recycle aluminium than to extract it from aluminium oxide by electrolysis. ............................................................................................................. (1) (Total 13 marks)

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Q13.

Barium can be extracted from barium oxide (BaO) in a process using aluminium. A mixture of powdered barium oxide and powdered aluminium is heated strongly. The equation for this extraction process is shown below. 3BaO(s) + 2Al(s) → 3Ba(s) + Al2O3(s) Some standard enthalpies of formation are given in the table below.

(a)

(i)

Substance

BaO(s)

Al2O3(s)

∆H fο / kJ mol–1

–558

–1669

State what is meant by the term standard enthalpy of formation. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (3)

(ii)

State why the standard enthalpy of formation of barium and that of aluminium are both zero. ............................................................................................................. (1)

(iii)

Use the data to calculate the standard enthalpy change for the reaction shown by the equation above. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (3)

(b)

(i)

Suggest the major reason why this method of extracting barium is expensive. ............................................................................................................. (1)

(ii)

Using barium oxide and aluminium powders increases the surface area of the reactants. Suggest one reason why this increases the rate of reaction. ............................................................................................................. (1)

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(c)

(i)

Write an equation for the reaction of barium with water. ............................................................................................................. (1)

(ii)

A solution containing barium ions can be used to test for the presence of sulfate ions in an aqueous solution of sodium sulfate. Write the simplest ionic equation for the reaction which occurs and state what is observed. Simplest ionic equation ............................................................................................................. Observation ......................................................................................... (2)

(iii)

State how barium sulfate can be used in medicine. Explain why this use is possible, given that solutions containing barium ions are poisonous. Use ..................................................................................................... Explanation ......................................................................................... ............................................................................................................. (2) (Total 14 marks)

Q14.

Copper is extracted from the ore chalcopyrite (CuFeS2) in a three-stage process. (a)

In the first stage of this extraction, the chalcopyrite is heated with silicon dioxide and oxygen. (i)

Balance the following equation for this first stage in which copper(I) sulfide is formed. .......CuFeS2 + .......SiO2 + .......O2 → Cu2S + .......FeSiO3 + .......SO2 (1)

(ii)

Give one environmental reason why the SO2 gas formed in this reaction is not allowed to escape into the atmosphere. ............................................................................................................. ............................................................................................................. (1)

(iii)

State one use for the sulfur dioxide formed in this reaction. ............................................................................................................. ............................................................................................................. (1)

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(b)

In the second stage of this extraction, the copper(I) sulfide is converted into copper(II) oxide. This occurs by roasting the sulfide with oxygen at high temperature. Write an equation for this reaction.

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

(c)

In the third stage of this extraction, copper(II) oxide is reduced to copper by its reaction with carbon. Write an equation for this reaction.

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

(d)

Scrap iron can be used to extract copper from dilute aqueous solutions containing copper (II) ions. (i)

Explain why this is a low-cost method of extracting copper. ............................................................................................................. ............................................................................................................. (1)

(ii)

Write the simplest ionic equation for the reaction of iron with copper(II) ions in aqueous solution.

............................................................................................................. (1) (Total 7 marks)

Q15.

Hydrogen gas is used in the chemical industry. (a)

Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3). (i)

State the role of the hydrogen in this reaction. ............................................................................................................. (1)

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(ii)

Write an equation for this reaction.

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

(iii)

State one risk of using hydrogen gas in metal extractions. ............................................................................................................. ............................................................................................................. (1)

(b)

Hydrogen is used to convert oleic acid into stearic acid as shown by the following equation.

+ H2 oleic acid

(i)

CH3(CH2)16COOH stearic acid

Use your knowledge of the chemistry of alkenes to deduce the type of reaction that has occurred in this conversion. ............................................................................................................. (1)

(ii)

State the type of stereoisomerism shown by oleic acid. ............................................................................................................. (1)

(c)

Hydrogen reacts with nitrogen in the Haber Process. The equation for the equilibrium that is established is shown below. N2(g) + 3H2(g) (i)

2NH3(g)

State Le Chatelier’s principle. ............................................................................................................. ............................................................................................................. (1)

(ii)

Use Le Chatelier’s principle to explain why an increase in the total pressure of this equilibrium results in an increase in the equilibrium yield of ammonia. ............................................................................................................. ............................................................................................................. ............................................................................................................. ............................................................................................................. (2)

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(d)

Hydrogen reacts with oxygen in an exothermic reaction as shown by the following equation. H2(g) +

O2(g) → H2O(g)

∆H = –242 kJ mol–1

Use the information in the equation and the data in the following table to calculate a value for the bond enthalpy of the H–H bond.

Mean bond enthalpy / kJ mol–1

O–H

O=O

+ 463

+ 496

...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (3) (Total 11 marks)

Q16.

The method of extraction of zinc has changed as different ores containing the element have been discovered and as technology has improved. Extraction process 1 In the earliest process, calamine (impure zinc carbonate) was heated with charcoal in earthenware pots. This two-stage process gave a low yield of zinc. ZnCO3(s) → ZnO(s) + CO2(g) ZnO(s) + C(s) → Zn(s)   + CO(g) Extraction process 2 Deposits of calamine were being used up and a new two-stage process was developed using zinc sulfide ores. All of the waste gases from this process were released into the atmosphere. 2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) ZnO(s) +  C(s) → 

Zn(s) + CO(g)

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Extraction process 3 The modern process uses the electrolysis of aqueous solutions of very pure zinc sulfate. The first step in this process is the same as the first step in Extraction process 2. The second step uses sulfuric acid made from the SO2 collected in the first step. The third step involves the electrolysis of zinc sulfate solution to form pure zinc. 2ZnS(s) +

3O2(g) → 2ZnO(s) 

+ 2SO2(g)

ZnO(s) + H2SO4(aq) →  ZnSO4(aq) + H2O(l) ZnSO4(aq) (a)

Zn(s)

In the first stage of Extraction process 1 the following equilibrium is established when zinc carbonate is heated in a closed container. ZnCO3(s)

ZnO(s) + CO2(g)

Use Le Chatelier’s principle to suggest and explain the effect on the yield of zinc oxide of allowing the carbon dioxide to escape from the container. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (3)

(b)

State and explain one environmental reason why Extraction process 3 is an improvement over Extraction process 2. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (3)

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(c)

Give one reason why Extraction process 3 is an expensive method of making zinc but one which is justified in terms of the product formed. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (2)

(d)

Deduce the half-equation for the formation of zinc from zinc ions during the electrolysis of zinc sulfate solution and identify the electrode at which this reaction occurs. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (2)

(e)

Identify one reaction from the three extraction processes that is not a redox reaction and state the type of reaction that it is. In terms of redox, state what happens to the carbon in Extraction process 2. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (3)

(f)

Zinc and magnesium both react with steam in a similar way. Write an equation for the reaction of zinc with steam and name the products of this reaction. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (2) (Total 15 marks)

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Q17.

Sea water contains large amounts of dissolved magnesium compounds. Approximately 1 kg of magnesium can be extracted from 1000 dm3 of sea water. (a)

The first step in the extraction process is to react the magnesium ions in sea water with hydroxide ions to produce a precipitate of magnesium hydroxide. Write the simplest ionic equation for this reaction. ...................................................................................................................... (1)

(b)

The second step in the extraction process is to react magnesium hydroxide with hydrochloric acid to give magnesium chloride. Write an equation for this reaction. ...................................................................................................................... (1)

(c)

In the final step, molten magnesium chloride is electrolysed to form magnesium and chlorine. This is similar to the method used to extract aluminium. Deduce an equation for the reaction that occurs at the negative electrode in the electrolysis of magnesium chloride. ...................................................................................................................... (1)

(d)

Magnesium is used in the extraction of titanium. (i)

Write an equation for the conversion of titanium(IV) oxide into titanium(IV) chloride. ............................................................................................................. (2)

(ii)

Write an equation for the extraction of titanium from titanium(IV) chloride using magnesium. ............................................................................................................. (1)

(iii)

State the role of magnesium in this extraction. ............................................................................................................. (1)

(e)

Use your knowledge of the reactions of Group 2 metals with water to explain why water should not be used to put out a fire in which magnesium metal is burning. ...................................................................................................................... ...................................................................................................................... ...................................................................................................................... (2) (Total 9 marks)

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Q18.

(a)

Pure manganese is extracted from the ore pyrolusite (MnO2) by reduction using

carbon monoxide. Write an equation for the reduction of MnO2 to manganese using carbon monoxide. ...................................................................................................................... (1)

(b)

Impure manganese is extracted by reduction of Mn3O4 using powdered aluminium according to the following equation. 3Mn3O4 + 8Al

9Mn + 4Al2O3

Deduce the redox half-equation for aluminium in this extraction process. ...................................................................................................................... (1)

(c)

Copper can be extracted by the high-temperature carbon reduction of copper(II) oxide. Write an equation for this reaction. ...................................................................................................................... (1)

(d)

Scrap iron is used in a low-cost process to extract copper from aqueous solutions containing copper(II) ions. (i)

Give one reason, other than the cost of scrap iron, why this method is low-cost. ............................................................................................................. ............................................................................................................. (1)

(ii)

Write the simplest ionic equation for the reaction of iron with copper(II) ions in aqueous solution. ............................................................................................................. (1) (Total 5 marks)

Q19.

Metals are usually extracted from oxides. Some of these oxides occur naturally. Other oxides are made by roasting sulfide ores in air, producing sulfur dioxide as a by-product. For the extraction of some metals, the oxide needs to be converted into a chloride. (a)

The ore molybdenite contains molybdenum disulfide (MoS2). The first stage in the extraction of molybdenum is to roast the ore in air to form molybdenum oxide (MoO3) and sulfur dioxide. (i)

Write an equation for the first stage in this extraction. ............................................................................................................. (1)

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(ii)

The release of sulfur dioxide into the atmosphere causes environmental problems and wastes a valuable resource. Identify one environmental problem and identify one use for the sulfur dioxide. Environmental problem ....................................................................... ............................................................................................................. ............................................................................................................. Use for sulfur dioxide .......................................................................... ............................................................................................................. ............................................................................................................. (2)

(iii)

Pure molybdenum is formed in the second stage by the reduction of MoO3 using hydrogen. Write an equation for this reaction. ............................................................................................................. (1)

(iv)

State one risk in using hydrogen gas in metal extractions. ............................................................................................................. ............................................................................................................. (1)

(b)

Calcium is an expensive metal. It is extracted by the electrolysis of molten calcium chloride. (i)

State why calcium chloride must be molten for electrolysis to occur. ............................................................................................................. ............................................................................................................. (1)

(ii)

Write an equation for the reaction that takes place at the negative electrode during this electrolysis. ............................................................................................................. (1)

(iii)

Identify the major cost in this extraction of calcium. ............................................................................................................. ............................................................................................................. (1) (Total 8 marks)

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Q20.

This question is about the extraction of titanium from titanium(IV) oxide by a two-stage process. The first stage in the process produces titanium(IV) chloride. In the second stage, titanium(IV) chloride is converted into titanium. The enthalpy change for the second stage can be determined using Hess’s Law. (a)

Give one reason why titanium is not extracted directly from titanium(IV) oxide using carbon. ..................................................................................................................... ..................................................................................................................... (1)

(b)

Give the meaning of the term enthalpy change. ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... (1)

(c)

State Hess’s Law. ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... (1)

(d)

Define the term standard enthalpy of formation. ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... ..................................................................................................................... (3)

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(e)

The following standard enthalpy of formation data refer to the second stage in the extraction of titanium.

ΔHfο/ kJ mol–1

(i)

TiCl4(g)

Na(I)

NaCl(s)

Ti(s)

–720

+3

–411

0

State why the value for the standard enthalpy of formation of Na(I) is not zero. ............................................................................................................. ............................................................................................................. (1)

(ii)

Use data from the table to calculate a value for the standard enthalpy change of the following reaction. TiCl4(g) + 4Na(I)

4NaCl(s) + Ti(s)

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

(iii)

State the role of sodium in this reaction. ............................................................................................................. (1) (Total 11 marks)

Q21.

(a) (i)

Iron is extracted from iron(III) oxide using carbon at a high temperature. State the type of reaction that iron(III) oxide undergoes in this extraction. ............................................................................................................... (1)

(ii)

Write a half-equation for the reaction of the iron(III) ions in this extraction.

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

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(b)

At a high temperature, carbon undergoes combustion when it reacts with oxygen. (i)

Suggest why it is not possible to measure the enthalpy change directly for the following combustion reaction. C(s,graphite)

+

O2(g)

CO(g)

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

(ii)

State Hess’s Law. ............................................................................................................... ............................................................................................................... ............................................................................................................... (1)

(iii)

State the meaning of the term standard enthalpy of combustion. ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... ............................................................................................................... (Extra space) ........................................................................................ ............................................................................................................... (3)

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(c)

Use the standard enthalpies of formation in the table below and the equation to calculate a value for the standard enthalpy change for the extraction of iron using carbon monoxide.

∆Hfϴ/ kJ mol–1

Fe2O3(s)

+

Fe2O3(s)

CO(g)

Fe(l)

CO2(g)

– 822

– 111

+14

– 394

3CO(g)

2Fe(I)

+

3CO2(g)

........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (Extra space) ................................................................................................. ........................................................................................................................ (3)

(d)

(i)

Write an equation for the reaction that represents the standard enthalpy of formation of carbon dioxide.

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

(ii)

State why the value quoted in part (c) for the standard enthalpy of formation of CO2(g) is the same as the value for the standard enthalpy of combustion of carbon. ............................................................................................................... ............................................................................................................... (1) (Total 12 marks)

Q22.

The silicon chip industry requires the production of pure silicon. Silicon is extracted from its ore, silicon dioxide (SiO2), by a process similar to that used in the extraction of titanium. (a)

(i)

Write an equation for the formation of SiCl4 from SiO2 using chlorine and carbon.

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

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(ii)

Suggest how the liquid SiCl4 is purified. ............................................................................................................... ............................................................................................................... (1)

(b)

The final stage in the extraction of silicon involves the use of hydrogen gas to convert the SiCl4 into silicon and hydrogen chloride. (i)

Write an equation for this reaction.

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

(ii)

State the role of hydrogen in this reaction. ............................................................................................................... (1)

(iii)

Give one risk associated with the use of hydrogen gas. ............................................................................................................... (1)

(c)

The magnesium used to make magnesium ferrosilicon alloys is extracted from magnesium oxide using silicon. Write an equation for this reaction to produce magnesium and silicon dioxide.

........................................................................................................................ (1) (Total 6 marks)

Q23.

Metals can be extracted by different methods. (a)

Give one reason why titanium cannot be extracted directly from titanium(IV) oxide using carbon. ........................................................................................................................ ........................................................................................................................ (1)

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(b)

Titanium steel is an alloy of titanium and iron. Titanium steel is extracted from the mineral ilmenite (FeTiO3) in a two-stage process. Purified FeTiO3 is first converted into a mixture of two metal chlorides. These two metal chlorides are then reduced simultaneously using sodium. (i)

Write an equation for the reaction of FeTiO3 with chlorine and carbon to produce iron (III) chloride (FeCl3), titanium(IV) chloride and carbon monoxide.

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

(ii)

Write an equation for the simultaneous reduction of the mixture of iron(III) chloride and titanium(IV) chloride to iron and titanium using sodium.

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

(c)

Scrap iron is used to extract copper from dilute aqueous solutions containing copper(II) ions. Explain, in terms of redox, what happens to the copper(II) ions in this extractio. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (2)

(d)

Aluminium is an expensive metal because it is extracted from molten aluminium oxide using electrolysis. Write the half-equation for the reaction that occurs at the positive electrode during this extraction.

........................................................................................................................ (1) (Total 6 marks)

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Q24.

This question is about the extraction of metals. (a)

Manganese can be extracted from Mn2O3 by reduction with carbon monoxide at high temperature. (i)

Use the standard enthalpy of formation data from the table and the equation for the extraction of manganese to calculate a value for the standard enthalpy change of this extraction.

ΔHfϴ/ kJ mol−1

Mn2O3(s)

CO(g)

Mn(s)

CO2(g)

−971

−111

0

−394

Mn2O3(s) + 3CO(g)

2Mn(s) + 3CO2(g)

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

(ii)

State why the value for the standard enthalpy of formation of Mn(s) is zero. ............................................................................................................... (1)

(b)

Titanium is extracted in industry from titanium(IV) oxide in a two-stage process. (i)

Write an equation for the first stage of this extraction in which titanium(IV) oxide is converted into titanium(IV) chloride. ............................................................................................................... (2)

(ii)

Write an equation for the second stage of this extraction in which titanium(IV) chloride is converted into titanium. ............................................................................................................... (2)

(c)

Chromium is extracted in industry from chromite (FeCr2O4). (i)

In the first stage of this extraction, the FeCr2O4 is converted into Na2CrO4 Balance the equation for this reaction. .........FeCr2O4 + .........Na2CO 3 + .........O 2

.........Na2CrO4 + 2Fe2O 3 + 8CO2 (1)

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(ii)

In the final stage, chromium is extracted from Cr2O3 by reduction with aluminium. Write an equation for this reaction. ............................................................................................................... (1) (Total 10 marks)

Q25.

Group 2 metals and their compounds are used commercially in a variety of processes. (a)

Strontium is extracted from strontium oxide (SrO) by heating a mixture of powdered strontium oxide and powdered aluminium. Consider these standard enthalpies of formation.

ΔHfϴ / kJ mol−1 3SrO(s) + 2Al(s)

SrO(s)

Al2O3(s)

– 590

– 1669 3Sr(s) + Al2O3(s)

Use these data and the equation to calculate the standard enthalpy change for this extraction of strontium. The use of powdered strontium oxide and powdered aluminium increases the surface area of the reactants. Suggest one reason why this increases the reaction rate. Suggest one major reason why this method of extracting strontium is expensive. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (5)

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(b)

Explain why calcium has a higher melting point than strontium. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (2)

(c)

Magnesium is used in fireworks. It reacts rapidly with oxygen, burning with a bright white light. Magnesium reacts slowly with cold water. Write an equation for the reaction of magnesium with oxygen. Write an equation for the reaction of magnesium with cold water. Give a medical use for the magnesium compound formed in the reaction of magnesium with cold water. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ (3) (Total 10 marks)

Q26.

The price of copper is increasing as supplies of high-grade ores start to run out. The mineral covellite (CuS), found in low-grade ores, is a possible future source of copper. (a)

When copper is extracted from covellite, a reaction occurs between copper(II) sulfide and nitric acid to form a dilute solution of copper(II) sulfate. (i)

Balance the equation for this reaction.

3CuS(s) +

.......HNO3(aq)

........CuSO4(aq) +

.......NO(g) + ...H2O(I) (1)

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(ii)

Give the oxidation state of nitrogen in each of the following. HNO3.............................................. NO ................................................. (2)

(iii)

Deduce the redox half-equation for the reduction of the nitrate ion in acidified solution to form nitrogen monoxide and water. ............................................................................................................... (1)

(iv)

Deduce the redox half-equation for the oxidation of the sulfide ion in aqueous solution to form the sulfate ion and H+(aq) ions. ............................................................................................................... (1)

(b)

Use your knowledge of metal reactivity to state and explain a low-cost method for the extraction of copper from a dilute aqueous solution of copper(II) sulfate. Write the simplest ionic equation for the reaction that occurs during this extraction process. ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ ........................................................................................................................ Simplest ionic equation ........................................................................................................................ (4) (Total 9 marks)

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