Extraction of metals

Question 1

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

Answer 1

Calcium has a higher melting point than strontium, because1.Correct reference to size of cations/proximity of electrons(For Ca) delocalised electrons closer to cations / positive ions / atoms / nucleusOR cations / positive ions / atoms are smallerOR cation / positive ion / atom or it has fewer (electron) shells / levels2. Relative strength of metallic bonding (Ca) has stronger attraction between the cations / positive ions / atoms / nucleus and the delocalised electronsORstronger metallic bonding

Question 2

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.

Answer 2

2Mg + O2 ——>2MgOM2 Mg + 2H2O Mg(OH)2 + H2Magnesium hydroxide is used as an antacid / relieve indigestion (heartburn) / neutralise (stomach) acidity / laxative

Question 3

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

Answer 3

Because it is an element / elemental

Question 4

Titanium is extracted in industry from titanium(IV) oxide in a two-stage process.Write an equation for the first stage of this extraction in which titanium(IV) oxide is converted into titanium(IV) chloride.

Answer 4

TiO2 + 2Cl2 + 2C ———>TiCl4 + 2CO

Question 5

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

Answer 5

TiCl4 + 4Na ————->Ti + 4NaCl

Question 6

Chromium is extracted in industry from chromite (FeCr2O4).In the first stage of this extraction, the FeCr2O4 is converted into Na2CrO4 Balance the equation for this reaction……….. FeCr2O4 + ………. Na2CO3 + ………. O2 ———> ………. Na2CrO4 + 2Fe2O3 + 8CO2

Answer 6

4FeCr2O4 + 8Na2CO3 + 7O2 ———->8Na2CrO4 + 2Fe2O3 + 8CO2

Question 7

In the final stage, chromium is extracted from Cr2O3 by reduction with aluminium. Write an equation for this reaction.

Answer 7

Cr2O3 + 2Al ——–>Al2O3 + 2Cr

Question 8

Metals can be extracted by different methods.Give one reason why titanium cannot be extracted directly from titanium(IV) oxide using carbon.

Answer 8

Ti is not producedORTiC / carbide is produced OR titanium reacts with carbonORProduct is brittleORProduct is a poor engineering material

Question 9

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

Answer 9

FeTiO3 + 31⁄2Cl2 + 3C ——>FeCl3 + TiCl4 + 3CO

Question 10

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

Answer 10

FeCl3 +TiCl4 +7Na —————>7NaCl+Fe+Ti

Question 11

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 extraction.

Answer 11

The Cu2+ / copper(II) ions / they have gained (two) electronsOR Cu2+ + 2e– ——>CuOR oxidation state / number decreases (or specified from 2to 0)ANDThe Cu2+ / copper(II) ions / they have been reduced

Question 12

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.

Answer 12

2O2– ————>O2 + 4e–

Question 13

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.

Answer 13

reduction

Question 14

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

Answer 14

Fe3+ + 3e– ————-> Fe

Question 15

At a high temperature, carbon undergoes combustion when it reacts with oxygen. Suggest why it is not possible to measure the enthalpy change directly for the followingcombustion reaction.C(s,graphite) + 1/2 O2(g) —–> CO(g)

Answer 15

CO is not the only product OR(Some) complete combustion (also)occurs ORCO2 is (also) formedFurther oxidation occurs

Question 16

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

Answer 16

One from 1  Ti is not produced TiC / carbide is produced (NOT TITANIUM CARBONATE) OR titanium reacts with carbon Product is brittle Product is a poor engineering material

Question 17

Give the meaning of the term enthalpy change.

Answer 17

Heat (energy) change at constant pressure

Question 18

Define the term standard enthalpy of formation.

Answer 18

The enthalpy change / heat change at constant pressure when 1 mol of a compound / substance / product is formed from its (constituent ) elementswith all reactants and products / all substances in standardstates i.e. 100 kPa / 1 bar and any specified T (usually 298 K)

Question 19

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.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.Write an equation for the first stage in this extraction.

Answer 19

2MoS2 + 7O2———->2MoO3 + 4SO2

Question 20

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.

Answer 20

Acid rain (NOT GREENHOUSE GASES)SO2 could be used to make H2SO4 / sulfuric acidORTo make CaSO4 or plaster of Paris / plaster board

Question 21

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

Answer 21

MoO3 + 3H2 ————–>Mo + 3H2O

Question 22

State one risk in using hydrogen gas in metal extractions.

Answer 22

Explosive or easily ignited

Question 23

Calcium is an expensive metal. It is extracted by the electrolysis of molten calcium chloride.State why calcium chloride must be molten for electrolysis to occur.

Answer 23

To allow ions to move (when molten) ORIons cannot move in the solid

Question 24

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

Answer 24

Ca2+ + 2e- ———–>Ca

Question 25

Identify the major cost in this extraction of calcium.

Answer 25

electricity

Question 26

Titanium and aluminium are both extracted from their oxides. Both extraction processes require high temperatures.5 (a) Outline the essential features of the extraction process used to obtain titanium from titanium(IV) oxide. Illustrate your answer with equations.Give three reasons why the manufacture of pure titanium is expensive(7)

Answer 26

React with carbon/coke and chlorineTiO2 +2C+2Cl2—–> TiCl4 +2COReact with Na (or Mg); TiCl4 + 4Na ——>Ti + 4NaClNa / sodium neededCl2 / chlorine neededArgon needed/ TiCl4 hydrolysedEnergy needed to give the high temp Batch process

Question 27

here has been a great deal of research into finding cheaper methods of extracting pure titanium but so far none has been commercially successful.Give a reason why a cheaper method, using direct reduction of titanium(IV) oxide by carbon, has been unsuccessful.State one property of titanium which makes it more useful than aluminium

Answer 27

TiC /carbide forms Stronger/ higher melting point ./more resistant to corrosion

Question 28

In the presence of cryolite, aluminium is extracted from its oxide by electrolysis. State the essential condition for this electrolysis and write half-equations for the reactions occurring at the electrodes. Give the main reason why this process is expensive

Answer 28

MoltenAl3+ + 3e- —–>Al2O2− —–>O2 +4e- A lot of electricity needed

Question 29

Give two reasons why recycling aluminium is environmentally beneficial.

Answer 29

Less CO2 / greenhouse gas given off; No unsightly landfills;Conserves earth resources;Less mining;Avoids fluoride pollution

Question 30

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.

Answer 30

MnO2 + 2CO  ——> Mn + 2CO2

Question 31

Impure manganese is extracted by reduction of Mn3O4 using powdered aluminium according to the following equation.3Mn3O4 + 8Al → 9Mn + 4Al2O3Deduce the redox half-equation for aluminium in this extraction process

Answer 31

Al  ——> Al3+ + 3e―

Question 32

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

Answer 32

2CuO + C  ——->2Cu +CO2 ORCuO + C  ———>Cu + CO

Question 33

Scrap iron is used in a low-cost process to extract copper from aqueous solutions containing copper(II) ions.Give 3 reasons, other than the cost of scrap iron, why this method is low-cost.

Answer 33

Low(er) energy requirementLow(er) temperatureCopper is obtained from low grade ore

Question 34

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

Answer 34

Fe + Cu2+  ———>Fe2+ + Cu

Question 35

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

Answer 35

Mg2+ + 2OH– ——-> Mg(OH)2

Question 36

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.

Answer 36

Mg(OH)2 + 2HCl  ———> MgCl2 + 2H2O

Question 37

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.

Answer 37

Mg2+ +2e– ——–> Mg

Question 38

Magnesium is used in the extraction of titanium.Write an equation for the conversion of titanium(IV) oxide into titanium(IV) chloride.

Answer 38

TiO2 + 2Cl2 + 2C  ——–> TiCl4 + 2COorTiO2 + 2Cl2 + C  ———> TiCl4 + CO2

Question 39

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

Answer 39

TiCl4 + 2Mg ———>  Ti + 2MgCl2

Question 40

State the role of magnesium in this extraction.

Answer 40

Reducing agent OR reduces TiCl4 ORElectron donor

Question 41

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

Answer 41

Hydrogen / H2 producedcausing an risk of explosion

Question 42

In the first stage of zinc extraction process 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

Answer 42

The yield of zinc oxide increases / greaterthe removal of the carbon dioxide results in the equilibrium either shifting / moving / goes to the right(By Le Chatelier’s principle) the reaction/equilibrium will respond so asto replace the CO2 / lost product

Question 43

Hydrogen gas is used in the chemical industry. Tungsten is extracted by passing hydrogen over heated tungsten oxide (WO3). State the role of the hydrogen in this reaction.Write an equation for this reaction.

Answer 43

Reducing agent 1ORReduce(s) (WO3 / tungsten oxide)ORelectron donorORto remove oxygen (from WO3 / tungsten oxide or to form water)WO3 +3H2 ——-> W+3H2O

Question 44

State one risk of using hydrogen gas in metal extractions.

Answer 44

H2 is• explosive• flammable or inflammable• easily ignited