Topic 5 - Transition Metals/alloys, Dynamic Equilibria, Quantitative Analysis & Chemical/fuel Cells

Question 1

Many metals corrode.
An experiment is carried out to see if magnesium ribbon wrapped around a piece of iron rod has an effect on the rate at which the iron rod rusts. Method:
• an iron rod, with magnesium ribbon wrapped around it, is placed in boiling tube A
• 10 cm3 water from a measuring cylinder is poured into this boiling tube
• an identical rod but with no magnesium ribbon wrapped around it is placed in a 2nd
boiling tube - B
• 10 cm3 water from a measuring cylinder is poured into this boiling tube.
Both boiling tubes are left for a few days.
Explain why iron rod rather than stainless steel rod is used in this experiment. (2)

State why it is not necessary to use a pipette to measure out 10 cm3 water. (1)

Answer 1

Stainless steel is resistant to corrosion/rusting/corrosion rate is lower (1)
Neither rod would rust/react in a few days (1)

Measuring cylinder is accurate enough/accuracy of pipette is not needed (1)

Question 2

• an iron rod, with magnesium ribbon wrapped around it, is placed in a boiling tube
labelled A
• 10 cm3 water from a measuring cylinder is poured into this boiling tube
• an identical rod but with no magnesium ribbon wrapped around it is placed in a second
boiling tube labelled B
• 10 cm3 water from a measuring cylinder is poured into this boiling tube.
After a few days the two boiling tubes were examined.
Explain the results of this experiment. (2)
Boiling tube A = appearance of iron rod hasn’t changed, magnesium has started to disappear
Boiling tube B = a small amount of brown deposit has formed around the rod

Answer 2

A has corroded/rusting has taken place in B (1)
Because magnesium is more reactive than iron (1)

Question 3

Painting iron objects prevents corrosion.
Explain why painting iron objects prevents corrosion. (2)

Answer 3

The paint acts as a protective barrier (1)
Excludes air/water/oxygen (1)

Question 4

Corrosion of iron objects can be prevented by painting them or by electroplating them.
State one other way of preventing the corrosion of iron objects. (1)

Answer 4

Sacrificial protection

Question 5

Copper is a transition metal.
Magnesium reacts with copper sulfate solution to form copper and a solution of magnesium
sulfate.
Magnesium sulfate solution is colourless.
Describe two changes you would see during this reaction. (2)

Answer 5

Colour/blue fades/colourless solution forms (1)
Red-brown solid forms (1)
Magnesium disappears (1)

Question 6

Pure metals are often converted into more useful alloys.
E.g., aluminium is converted into an alloy used in aircraft, iron is converted into an alloy used in cutlery and gold alloys are used in jewellery.
These processes of alloying change the structures of the metals.
Explain how alloying changes these pure metals to make the alloys more suitable for the given uses. (6)

Aluminium- 2.7g/cm^3 easy to bend, weak
Iron- 7.75g/cm^3 easy to bend, weak
Gold- 19.3g/cm^3 easy to bend, weak

Answer 6

• an alloy is a mixture of metals
• because larger/different sized atoms introduced in alloying,
• stop layers moving easily over one another
• therefore individual alloy is stronger/harder
• an aluminium alloy is magnalium
• pure aluminium is not suitable for making aircraft as it bends too easily / too weak
• aluminium alloy stronger
• magnesium atoms lighter than aluminium atoms,
• therefore alloy still low density / lower density than aluminum alone
• an iron alloy is stainless steel
• pure iron is not suitable for cutlery as it bends too easily / too weak
• iron corrodes,
• corrosion would contaminate food
• stainless steel does riot corrode
• gold alloy harder
• therefore more hard wearing
• gold alloys less likely to change shape when worn
• alloying can change the colour of the gold

Question 7

Pure metals can be made more useful by converting them into alloys or by electroplating them.
Explain what alloying and electroplating are and how they can make metals more useful. (6)

Answer 7

• in an alloy another metal is added / a mixture of metals
• in a pure metal, all atoms are of the same size • layers of atoms can slide over one another easily
• so a pure metal is malleable / soft
• alloys are stronger
• because atoms of different sizes
• disrupt layers of atoms in the alloy
• layers cannot slide
• alloys can be used e.g. in metal beams / airplanes parts / bridges
• because the alloy is stronger than the pure metal
• electroplating means that a (corrosion resistant) metal {coating / layer} is added on top of the (pure) metal / alloy • (more reactive) metals can corrode when exposed to air and water • (corrosion resistant) metal coating does not react with oxygen in air • therefore pure metal object does not corrode • object remains shiny • object looks more attractive • base metal is often cheaper e.g. copper plated with gold in jewellery • therefore object may be cheaper • electroplating involves creating a circuit • object to be plated is made the cathode • plating metal is the anode • electrolyte made from plating metal salt solution

Question 8

Alloys of gold are often used to make jewellery.
The purity of gold is measured in carats.
Different alloys of gold have different carats.
18 carat gold. 75% gold, 15% silver, 10% copper
24 carat gold. 100% gold, 0% silver and copper
Explain why 18 carat gold is stronger than 24 carat gold. (2)

Answer 8

18 carat gold contains atoms of different sizes (1)
Prevents layers from sliding over one another (1)

Question 9

Aluminium alloys are used instead of pure aluminium in aircraft manufacture.
Explain, in terms of the arrangement of metal particles, why aluminium alloys are stronger
than pure aluminium. (3)

Answer 9

In pure aluminium, all of the atoms are the same size, whereas in aluminium alloys, the atoms are all different sizes (1)
In aluminium, layers of atoms easily slide over each other (1)
In alloy, layers cannot easily slide over each other (1)

Question 10

Explain why covering iron tools with a thin layer of grease prevents rusting. (2)

Answer 10

Air/oxygen excluded (1)
Water excluded (1)
Air/oxygen/water need for corrosion (1)

Question 11

Sacrificial protection is another way of preventing rusting.
An example of sacrificial protection is when lumps of zinc are connected to the iron-containing structure of an oil rig.
Explain how the zinc protects the iron from rusting. (2)

Answer 11

Zinc is more reactive than iron (1)
So reacts instead (1)

Question 12

Alloys are mixtures of two or more metals.
Magnalium is an alloy of magnesium and aluminium. It is often used for aircraft parts.
Aluminium-2.7g/cm^3 low strength high resistance to corrosion
Magnalium- 2g/cm^3 high strength very high resistance to corrosion
Explain, using the information, why magnalium, rather than pure aluminium, is used for aircraft parts. (3)

Answer 12

Magnalium has a lower density than aluminium (1)
Magnalium is stronger than aluminium (1)
Magnalium has a higher resistance to corrosion than aluminium (1)

Question 13

Iron rusts when it is left in certain conditions.
The apparatus used to investigate the rusting of some iron nails:
A- test tube with air + water
B- test tube with air + drying agent
C- test tube with oil + boiled water
Explain why the iron nail in tube A would rust but the iron nails in tubes B and C would
not rust. (3)

Answer 13

Both water and oxygen is needed for rusting (1)
Tube a has both water and oxygen present (1)
Tube b has no water present (1)
Tube c has only water present (1)

Question 14

Magnesium is more reactive than iron.
An iron nail is wrapped with a strip of magnesium around it, placed in some water.
The tube was left for a few days.
State what would happen to this iron nail. (1)

Answer 14

No rusting/doesn’t corrode

Question 15

When iron rusts, a brown solid forms on the surface of the iron.
What happens to the iron as the rust forms?
(1)
A the iron is hydrated
B the iron is neutralised
C the iron is oxidised
D the iron is reduced

Answer 15

the iron is oxidised

Question 16

An iron bucket is coated in zinc.
Over many years of use, the iron bucket has been scratched and left outside in the rain.
Although some of the zinc coating has been removed to expose iron, the iron bucket has not rusted.
Explain why the iron has not rusted. (2)

Answer 16

Iron hasn’t rusted because zinc is more reactive than iron (1)
So zinc corrodes instead of iron (1)

Question 17

Alloy steels are made when iron is alloyed with other transition metals such as cobalt and
chromium.
Iron fences can be galvanised by coating them with a layer of zinc. When the layer of zinc is
scratched exposing the iron to the weather, the iron does not rust.
Explain why the exposed iron does not rust. (2)

Answer 17

Zinc corrodes in preference to iron/zinc reacts with air and water instead (1)
Zinc is more reactive than iron/is a sacrificial (1)

Question 18

Alloys are mixtures of 2 or more metals.
Brass is an alloy of copper.
Brass pins are used in an electric plug.
Brass is harder than copper.
Give a reason why using a harder substance for the pins is an advantage. (1)

Answer 18

Pins do not bend

Question 19

Give 2 advantages for electroplating some metal objects (2)

Answer 19

Improve appearance (1)
Help prevent corrosion (1)

Question 20

Give one reason why metals are electroplated. (1)

Answer 20

Improve appearance/more corrosion resistant

Question 21

The rate of rusting can be increased by using sea water.
Describe a simple experiment to compare how much an iron nail rusts in sea water when
compared to water. (3)

Answer 21

Clean iron nails (1)
Place nails into separate test tubes of water and seawater (1)
Leave test tubes for a period of time (1)
Observe the test tubes and record any changes to compare appearance/mass

Question 22

Alloys are mixtures of two or more metals.
Alloy steels are formed when other metals are mixed with iron.
Cutlery is made of stainless steel.
Give two reasons why cutlery is made of stainless steel rather than iron. (2)

Answer 22

Stainless steel doesn’t rust/cortode (1)
Stainless steel is tronger (1)

Question 23

Metal objects can be electroplated with gold.
Give two reasons why metal objects are electroplated with gold. (2)

Answer 23

Improve the appearance (1)
Increase resistance to corrosion (1)

Question 24

The pure metals aluminium, copper and gold and the alloys brass and magnalium are used
to make many useful articles.
The way in which these metals and alloys are used is related to their properties, such as their density, electrical conductivity, resistance to corrosion and strength.
State some uses of aluminium, copper, gold, brass and magnalium and explain how each use is related to their properties. (6)

Answer 24

• suitable use of aluminium eg cooking foil
• related property - malleable, low toxicity, low reactivity
• suitable use of copper eg water pipes
• related property - low reactivity
• suitable use of gold eg electronic contacts
• related property - does not corrode, good electrical conductor
• suitable use of brass eg pins for electric plugs • related property - strong and hard wearing
• suitable use of magnalium eg aircraft parts
• related property - low density

Question 25

Gold alloys can be used to repair teeth. One reason that gold alloys are used is that they can be hammered into shape. Give one other reason why gold alloys are used to repair teeth. (1)

Answer 25

Doesn’t corrode/insoluble/inert

Question 26

In a hydrogen-oxygen fuel cell, hydrogen and oxygen react at the electrodes. Some metal objects are electroplated. State two reasons for electroplating a metal object. (2)

Answer 26

Improves the appearance/shiny (1) Improves resistance to corrosion (1) Can make an object look more expensive than it actually is (1)

Question 27

Transition metals have many uses. Most iron produced is converted into alloys of iron. State why alloys have more uses than pure metals. (1)

Answer 27

Alloys are stronger/more corrosion resistant

Question 28

Platinum acts as a catalyst. State, in terms of its position in the periodic table, why you would expect platinum to act as a catalyst. (1)

Answer 28

Platinum is a transition element

Question 29

Many metals corrode. Hydrazine, N2H4, reacts with oxygen. N2H4 + O2 → N2 + 2H2O A metal in water corrodes faster than an identical piece of metal in the same volume of water containing dissolved hydrazine. Use the information to explain how hydrazine slows corrosion. (2)

Answer 29

Oxygen is removed by the hydrazine (1) Oxygen is needed for rusting/corrosion (2)

Question 30

Alloy steels are made when iron is alloyed with other transition metals such as cobalt and chromium. Explain how lubricating a bicycle chain with oil prevents corrosion of the steel chain. (2)

Question 31

State the meanings of the terms actual yield and theoretical yield. (2)

Answer 31

Actual yield - Mass of product formed in reaction (1) Theoretical yield - calculated mass of products formed using the balanced equation/calculated mass of products if all reactants used to form products only with no losses (1)

Question 32

State two reasons why the actual yield of a reaction is usually less than the theoretical yield. (2)

Answer 32

Some reactants remained un reacted (1) Side reactions may occur (1) Some product is lost during the reaction (1)

Question 33

The concentration of dilute sulfuric acid can be determined by titration with sodium hydroxide solution of known concentration. - 25.00 cm3 of dilute sulfuric acid was measured out using a pipette and transferred to a conical flask. - A few drops of methyl orange indicator were added to the acid in the conical flask. Sodium hydroxide solution was added to the acid from a burette until the indicator changed colour. - The titration was repeated until 2 concordant results were obtained. - The accurate result was the average of the two concordant results. Further detail can be added to this method to ensure that anyone following the method will obtain an accurate result. Explain 2 details that could be added to this practical method to ensure an accurate result is obtained. (4)

Answer 33

read bottom of the meniscus on the burette/pipette scale / read burette/pipette at eye-level (1) to obtain accurate volume of sodium hydroxide solution / sulfuric acid added (1) add alkali 1 drop at a time near end point (1) to identify exactly when colour change of indicator takes place (1) use a white tile (1) to make it easier to see exactly when colour change of indicator takes place (1) make sure no air bubbles in burette or pipette when measuring volumes (1) so exact volumes are recorded (1) continually swirl flask (1) to ensure complete mixing of acid with alkali (1) wash inside of conical flask with a little deionised/distilled water (1) to wash reactants into reaction mixture (1) wash burette / pipette with appropriate solution before titration (1) to ensure burette / pipette is riot contaminated (1)

Question 34

A titration is to be carried out to find the concentration of a solution of sodium hydroxide. The sodium hydroxide solution is titrated with dilute sulfuric acid. The available apparatus includes a burette, a pipette, a funnel, a conical flask & an indicator. State 1 safety precaution that must be taken when using sodium hydroxide solution and dilute sulfuric acid. (1)

Answer 34

Wear gloves to prevent contact with skin/safety (1) Spectacles to prevent contact with eyes (1)

Question 35

Write the balanced equation for the reaction of dilute sulfuric acid, H2SO4, with sodium hydroxide. (2)

Answer 35

2NaOH + H2SO4 → Na2SO4 + 2H2O

Question 36

The method used to make the lead sulfate is: • pour 100 cm3 lead nitrate solution into a beaker • add drops of sodium sulfate solution until a precipitate is seen • allow the precipitate to settle to the bottom of the beaker • pour off the liquid • use a spatula to transfer the solid lead sulfate onto a filter paper. Explain two ways of improving this experiment in order to increase the amount and quality of lead sulfate that could be obtained from 100 cm3 of lead nitrate solution. (4)

Answer 36

Add excess sodium sulfate solution rather than a few drops (1) so more reaction occurs to form more lead sulfate (1) Filter the reaction mixture rather than pour off the liquid (1) so none of the lead sulfate is lost in separation (1) Wash the lead sulfate (1) so the impurities are removed (1) Place the lead sulfate in an oven/warm place (1) so the lead sulfate is dry (1)

Question 37

The mass of solid left in the crucible is less than the theoretical mass of calcium oxide that should be obtained. A possible reason for this is that (1) A some solid was lost from the crucible B the solid remaining absorbed some water from the air C some carbon dioxide remained in the crucible D the decomposition was incomplete

Answer 37

some solid was lost from the crucible

Question 38

A student wanted to find the volume of dilute hydrochloric acid that would react with 25.0 cm3 of lithium hydroxide solution. They used some equipment to carry out a rough titration and then a further 2 accurate titrations. Describe how the rough titration should be carried out once the dilute hydrochloric acid, lithium hydroxide solution and indicator are placed in the burette and conical flask. (4)

Answer 38

Read the initial volume of the burette (1) Open the tap/add acid to alkali (1) Swirl the mixture (1) Until endpoint/indicator changes colour (1) Close the tap, then read the final volume of acid in burette (1)

Question 39

Describe the experimental procedure to carry out a titration to find the exact volume of sulfuric acid needed to neutralise 25.0 cm3 of sodium hydroxide solution and obtain pure, dry crystals of sodium sulfate. (6)

Question 40

The volume of dilute sulfuric acid required to neutralise 25.0 cm3 of ammonia solution can be found by titration. In the titration, a few drops of methyl orange indicator were added to the ammonia solution in a conical flask before adding the dilute sulfuric acid. The titration was repeated to obtain a mean volume of dilute sulfuric acid required to neutralise the 25.0 cm3 of ammonia solution. The volumes of the 2 solutions were measured accurately. Explain 2 other practical steps that should be used in the titration to ensure that an accurate titre volume is obtained. (4)

Answer 40

use of white tile (1) easier to see precisely when indicator changes colour (1) near to end point add acid slowly/in small quantities each time (1) easier to stop excess acid being added (when indicator changes colour) (1) swirl flask when adding acid (1) ensures complete mixing of both reactants (1) touch tip of burette on inside wall of flask and/or rinse walls of flask (1) ensures all acid takes part in reaction (1) rinse burette with acid/pipette with ammonia/flask with water beforehand (1) no impurities to affect result (1) remove funnel from burette (1) to stop any extra drop of acid falling into burette (1)

Question 41

Methane reacts with steam to form hydrogen and carbon dioxide. The reaction takes place in 2 stages. Stage 1: CH4(g) ↔️ 3H2(g) + CO(g) Stage 2: CO(g) + H2O(g) ↔️ H2(g) + CO2(g) Stage 1 takes in heat energy, it is endothermic. Explain the effect of increasing the temperature on the yield of the products of stage 1.

Answer 41

Shift equilibrium to the right/forward direction (1) Increase yield of product (1)

Question 42

Potassium hydroxide reacts with hydrochloric acid to form potassium chloride and water. potassium hydroxide + hydrochloric acid → potassium chloride + water A student carried out a titration to find the exact volume of dilute hydrochloric acid that reacted with 25.0 cm3 of potassium hydroxide solution. There were 5 steps in the titration. The steps shown are not in the correct order. step J - pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution step K - fill a burette with the dilute hydrochloric acid and record the initial reading from the burette step L - use a measuring cylinder to obtain 25 cm3 of potassium hydroxide solution step M - take a final reading from the burette & calculate the volume of the dilute hydrochloric acid reacted step N - run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour. A student was then asked to produce a pure sample of solid potassium chloride. After finding the volume of acid reacted in step M, the student added this volume of acid to a fresh 25.0 cm3 sample of the potassium hydroxide solution. This mixture was then evaporated. Explain why this new mixture was evaporated rather than the original mixture from the titration, to produce a pure sample of solid potassium chloride. (2)

Answer 42

Solution from titration contains an indicator (1) Indicator would contaminate salt (1)

Question 43

There were 5 steps in the titration. The steps shown are not in the correct order. step J - pour the potassium hydroxide solution into a conical flask and add a few drops of indicator to this solution step K - fill a burette with the dilute hydrochloric acid and record the initial reading from the burette step L - use a measuring cylinder to obtain 25 cm3 of potassium hydroxide solution step M - take a final reading from the burette & calculate the volume of the dilute hydrochloric acid reacted step N - run the dilute hydrochloric acid from the burette into the conical flask until the indicator changes colour. Write the steps in the correct order (1)

Answer 43

K L J N M

Question 44

A titration of sodium hydroxide solution with hydrochloric acid can be carried out as follows: 1 - a pipette is used to measure 25.00 cm3 of sodium hydroxide solution into a conical flask 2 - a few drops of indicator are added to the sodium hydroxide solution 3 - the burette is filled with hydrochloric acid 4 - the hydrochloric acid is added to the sodium hydroxide solution until the indicator changes colour. Describe how the pipette should be used to measure exactly 25.00 cm3 of sodium hydroxide solution into the conical flask. (2)

Answer 44

Use a pipette filter (1) Wash pipette with sodium hydroxide solution (1) Draw the liquid up so the bottom of the meniscus touches the line (1)

Question 45

The burette is first washed with water. It is then rinsed with some of the acid before it is filled with the acid to begin the titration. Explain why the burette is rinsed with the acid. (2)

Answer 45

To remove water from the burette (1) Because this would dilute the original acid (1) This will give an inaccurate result (1)

Question 46

The industrial production of sulfuric acid involves several steps. One of these steps is the reaction of sulfur dioxide, SO2, with oxygen to form sulfur trioxide, SO3. What volume of sulfur trioxide, in dm3, is produced by the complete reaction of 750 dm3 of sulfur dioxide? (all volumes of gases are measured under the same conditions of temperature and pressure) (1) A 375.5 B 750 C 1125.5 D 1500

Answer 46

750

Question 47

The volume of dilute sulfuric acid required to neutralise 25.0 cm3 of ammonia solution can be found by titration. In the titration, a few drops of methyl orange indicator were added to the ammonia solution in a conical flask before adding the dilute sulfuric acid. When the ammonia solution was neutralised by the dilute sulfuric acid, a solution of ammonium sulfate was formed. Complete the balanced equation for the reaction between ammonia solution and sulfuric acid. (2) ............ NH3 + H2SO4 → .................

Answer 47

2NH3 + H2SO4 → (NH4)2SO2

Question 48

Ammonia solution and dilute sulfuric acid are used to prepare pure, dry ammonium sulfate crystals. In an experiment a titration is carried out to determine the volumes of ammonia solution and dilute sulfuric acid that react together. Then an ammonium sulfate solution is prepared from which the pure, dry crystals are obtained. Describe in detail, using suitable apparatus, how this experiment should be carried out. (6)

Answer 48

• pipette to measure out the ammonia solution (25 cm3) • into a suitable container, e.g. conical flask • add few drops of methyl orange indicator • put flask on a white tile • fill burette with sulfuric acid solution • read level of liquid in burette • add acid from the burette • swirl flask gently / mix • add drop-wise near end-point • until {indicator just changes colour} • read level on burette • repeat experiment until concordant results • mix the same volumes of sulfuric acid and ammonia solution (determined from the titration experiment) • but leaving out the indicator/methyl orange • pour solution into an evaporating dish • heat the solution to point of crystallisation • leave to cool • filter off crystals • leave to dry

Question 49

Ammonium sulfate and ammonium nitrate are used as fertilisers as they both contain nitrogen, which will increase the yield of crops. Suggest one other reason for using solid ammonium sulfate and solid ammonium nitrate as nitrogenous fertilisers. (1)

Answer 49

Both are soluble/dissolve in water (1)

Question 50

Ammonium nitrate can be made by the reaction of ammonia with nitric acid. Write the balanced equation for this reaction. (2)

Answer 50

NH3 + HNO3 → NH4NO3

Question 51

Describe one similarity and one difference between the industrial production of ammonium sulfate and the laboratory preparation of ammonium sulfate. (2)

Answer 51

Both use sulfuric acid (1) Both are examples of neutralisation (1) Industrial process is on a much larger scale than the laboratory process (1) The industrial process involves much more stages than the laboratory process (1) Ammonia is a gas in the industrial process but a solution in the laboratory process (1) Laboratory preparation uses titration and crystallisation (1)

Question 52

When hydrogen is removed from an alkane, an alkene is formed. This is an example of a dehydrogenation reaction. Under certain conditions the dehydrogenation of propane forms propene and a dynamic equilibrium is reached. State what is meant by dynamic in this context. (1)

Answer 52

Both forward and backwards reactions take place at the same time (1)

Question 53

C3H8(g) ↔️ C3H6(g) + H2(g) The forward reaction takes in heat energy and is endothermic. A manufacturer produces large quantities of propene using this equilibrium reaction. Suggest, with explanations, suitable conditions that the manufacturer could use to maximise the yield and rate of production of propene from propane. (6)

Answer 53

- use of suitable catalyst (any suitable metal eg Pt) - helps increase rate of forward reaction and - helps increase rate of back reaction - so increases rate of attainment of equilibrium - but has no effect on equilibrium yield - increase temperature would increase rate of reaction - shifts equilibrium to right hand side - so increases equilibrium yield - so use a high temperature (range 200-600 °C - anything would be reasonable) - use of very high temperatures increases energy use - so makes product more expensive - as fewer molecules on left hand side than right - so use low pressures - moves equilibrium to right hand side - so increases equilibrium yield - high pressure increases rate but decreases yield OR low pressure increases yield but decreases rate - pressure used is a compromise between rate and yield

Question 54

The reaction between nitrogen and hydrogen is exothermic. If nitrogen and hydrogen were reacted at 150 atm pressure and 300 °C, without a catalyst, some ammonia would be formed. In the Haber process a pressure of 150 atm and a temperature of 450 °C are used, in the presence of an iron catalyst. Explain why the conditions used in the Haber process are better than the first set of conditions for the manufacture of ammonia. (6)

Answer 54

The effect of the temperature rise on the rate of attainment of equilibrium and on the equilibrium yield are considered by: • higher temperature reaches equilibrium faster because molecules move faster • therefore there are more frequent collisions because molecules have more energy • therefore more collisions have required energy but yield will be lower • because higher temperature favours endothermic reaction and so equilibrium shifts to left hand side • which is decomposition of ammonia / ammonia reforms elements • catalyst causes reaction to reach equilibrium faster / catalyst increases rates (of both forward and back reactions) • lowers the activation energy (of both forward and back reactions) but does not affect yield • equilibrium position not affected.

Question 55

In industry, ammonia is manufactured by reacting nitrogen with hydrogen. Write the word equation for this reaction, including the correct symbol to show that the reaction is reversible. (3)

Answer 55

Nitrogen + hydrogen ↔️ ammonia

Question 56

Explain the importance of fertilisers in farming (2)

Answer 56

Crops require fertilisers to grow (1) Fertilisers contain N, P and K compounds (1) Promote plant growth (1) Increased yield (1)

Question 57

Fertilisers contain compounds that promote plant growth. State the name of an element in these compounds that promotes plant growth. (1)

Question 58

Potassium nitrate is present in some fertilisers. Potassium nitrate is formed by the reaction of potassium hydroxide solution with nitric acid. Complete the balanced equation for this reaction. (2) KOH + HNO3 → ................ + ....................

Answer 58

KOH + HNO3 → KNO3 + H2O

Question 59

Fertilisers are sometimes added to soil. State why fertilisers are added to soil. (1)

Answer 59

To make plants grow faster/bigger/more

Question 60

Hydrogen and oxygen are reactants in some fuel cells. Which word equation shows the overall reaction that occurs in these fuel cells? (1) A hydrogen + oxygen → hydroxide B hydrogen + oxygen → sulfuric acid C hydrogen + oxygen → water D hydrogen + oxygen → hydrochloric acid

Answer 60

hydrogen + oxygen → water

Question 61

Complete the half-equation for the reaction taking place at one of the electrodes in a hydrogen-oxygen fuel cell. (2) O2 + .............. H+ + .............. → ............ H2O

Answer 61

O2 + 4H+ + 4e- → 2H2O

Question 62

Chemical cells produce a voltage. A chemical cell can be made by placing the metals copper and zinc in a beaker of sodium chloride solution. Describe what will happen to the brightness of the light bulb over a long period of time. (2)

Answer 62

Starts bright (1) Becomes dimmer (1) Goes out (1)

Question 63

A torch contains a chemical cell. The torch is turned on and then left on for many hours. Describe what you would see happen when the torch is turned on and then left for many hours. (2)

Answer 63

Bright light at start (1) Fades/gets dimmer (1) Then goes out (1)

Question 64

Hydrogen-oxygen fuel cells can be used to provide electrical energy in a spacecraft. The reaction that takes place in the fuel cell is hydrogen + oxygen → water Evaluate the advantages and disadvantages of providing electrical energy in a spacecraft using hydrogen-oxygen fuel cells rather than chemical cells. (6)

Answer 64

advantages: • once set up, fuel cells require no maintenance • chemical cells will need to be replaced / chemical cells have a limited lifetime • fuel cells operate as long as reactants are supplied • voltage drops in chemical cells as reactants are used up • once used chemical cells cannot be used again or need re-charging • used chemical cells take up valuable space on spacecraft • new chemical cells need to be transported to spacecraft • used chemical cells need to be transported back to earth • water produced in the fuel cell is the only product • water can be used on the spacecraft as drinking water disadvantages: • hydrogen and oxygen must be supplied • gas tanks need to transported by spacecraft • storage of hydrogen is difficult because it is a gas • hydrogen is flammable • fuel cells are expensive to manufacture conclusion: • either cell can be chosen as the preferable one but suitable reasons must be given

Question 65

The voltage of a cell is 1.5 V. Give a reason why this voltage of the cell decreases when the cell is left connected in a circuit. (1)

Answer 65

Reactants are being used up

Question 66

Hydrogen-oxygen fuel cells, rather than chemical cells, can be used to power some vehicles. Give one advantage of using a hydrogen-oxygen fuel cell, rather than using a chemical cell, to power a vehicle. (1)

Answer 66

Voltage is constant (1) Chemical cells contain harmful/toxic substances (1)

Question 67

Hydrogen can be used in a hydrogen-oxygen fuel cell. Give the name of the product formed in this fuel cell. (1)

Answer 67

Water

Question 68

In a hydrogen-oxygen fuel cell, hydrogen and oxygen react at the electrodes. The overall reaction occurring in this fuel cell is a reaction of hydrogen with oxygen. Write the balanced equation for this reaction. (2)

Answer 68

2H2 + O2 → 2H2O

Question 69

Explain what is meant by a dynamic equilibrium. (2)

Answer 69

Forward and backwards reactions take place at the same time/rate of forward and backward reaction is the same (1) No overall Chang in the amount of substance/no observable change (1)

Question 70

In industry, the reaction between nitrogen and hydrogen is affected by the conditions used. The pressure used is 250 atmospheres. Explain how the use of a higher pressure would affect the equilibrium yield of ammonia. (2)

Answer 70

Higher pressure favours forward reaction/equilibrium shifts to the right (1) Because decrease in the number of molecules (1) Yield increases (1)

Question 71

The reaction between nitrogen and hydrogen to form ammonia is exothermic. The temperature used is 450°C. Explain how the use of a lower temperature would affect the equilibrium yield of ammonia. (2)

Answer 71

Lower temperature favours forward reaction/equilibrium shifts to the right (1) Because forward reaction is exothermic (1) Yield increases (1)

Question 72

The reaction between nitrogen and hydrogen to form ammonia is exothermic. The temperature used is 450°C. Even at 450°C, the reaction is very slow. State what is used in industry to overcome this problem. (1)

Answer 72

Catalyst

Question 73

What is the source of the hydrogen used in the Haber process? (1) A air B reaction of zinc with dilute sulfuric acid C electrolysis of water D natural gas

Answer 73

Natural gas

Question 74

When nitrogen reacts with hydrogen, the amount of ammonia gradually increases until it becomes constant. N2(g) + 3H2(g) 2NH3(g) Explain why the amount of ammonia remains constant. (2)

Answer 74

Forward and backwards reactions takes place/dynamic (1) At the same time/equilibrium (1)

Question 75

The minimum volumes of nitrogen and hydrogen that must react completely to form 5000 dm3 of ammonia are calculated. These volumes are mixed and left, under appropriate conditions, until the reaction reaches equilibrium. Explain which gas or gases will be present when equilibrium is reached. (2)

Answer 75

All 3 gases present/nitrogen, hydrogen and ammonia (1) Ammonia decomposes/turns back to reactants (1)

Question 76

The Haber process is carried out under a pressure of about 200 atm. Explain the effect on the equilibrium yield of ammonia, if the process is carried out at a pressure higher than 200 atm. (2)

Answer 76

Higher yield (1) Because fewer gas molecules/moles on RHS/equilibrium shifts to the RHS (1)

Question 77

Explain the effect on the rate of attainment of equilibrium, if the process is carried out at a pressure higher than 200 atm. (3)

Answer 77

Rate increased/time to reach equilibrium reduced (1) Because gas molecules closer/more concentrated (1) So increased collision rate/more frequent collisions (1)

Question 78

The concentration of a solution of an alkali can be determined by titration with an acid. 25.0 cm3 portions of the solution of the alkali are transferred into a conical flask and titrated with the acid solution, using a suitable indicator. Describe how you would measure out and transfer 25.0 cm3 of the solution of the alkali. (2)

Answer 78

Pipette (1) Draw liquid up to line/use pipette filler/rinse first/read at eye level (1)

Question 79

Some salts dissolved in water cause the water to be hard. When mixed with a small volume of soap solution, hard water does not form a lather. You are provided with 3 unlabelled samples of water. - one is soft water - one is permanent hard water - one is temporary hard water You are provided with soap solution and the usual laboratory apparatus. Describe tests that you should carry out on each sample to identify the type of water in each sample. (6)

Answer 79

soft: • add soap (solution) • shake/ mix • lather (immediately) • no scum/ no precipitate permanent hard: • add soap (solution) • shake • no lather / less than with soft water • scum/ precipitate • boiled sample • same results / boiling does not change • becomes soft after ion exchange but not after boiling temporary hard: • add soap (solution) • shake • no lather / less than with soft water • scum/ precipitate • boiled sample • after boiling precipitate / (lime)scale formed • lather (immediately)

Question 80

Suggest why universal indicator must not be used in titration experiments. (1)

Answer 80

No sharp/clear/distinct change in colour (1) Gradual colour change (1) There are too many different colours (1)

Question 81

Sodium chloride solution can be made from dilute hydrochloric acid and sodium hydroxide solution. Describe a titration experiment to find the exact volume of hydrochloric acid needed to neutralise 25.0 cm3 of sodium hydroxide solution and how you would use this result to obtain pure, dry crystals of sodium chloride. (6)

Answer 81

titration experiment: • rinse pipette with alkali and burette with acid • measure alkali using a pipette • into suitable container e.g. flask/beaker • add a few drops of indicator / suitable named indicator (eg methyl orange/phenolphthalein) • flask on a white tile • fill burette with acid • read level/volume (of acid) in burette • add acid from burette to the flask slowly / swirl the flask • until {indicator just changes colour/correct colour change for named indicator (eg methyl orange yellow to peach/orange, phenolphthalein pink to colourless)/solution is neutral} • read level/volume (of acid) in burette • repeat experiment • until concordant results salt preparation: • mix the same volume of alkali with the volume of acid determined from the first experiment but do not add indicator (or add (activated) charcoal to remove indicator, then filter) • pour solution into an evaporating basin • {heat solution/leave the water to evaporate} until pure salt crystals are left

Question 82

During a titration, the indicator used changed colour at the end point. Which of the following shows an indicator with the colour change that would be seen in this titration? (1) A phenolphthalein colourless in alkali, pink at end point B phenolphthalein pink in alkali, yellow at end point C methyl orange red in alkali, yellow at end point D methyl orange yellow in alkali, orange at end point

Answer 82

methyl orange yellow in alkali, orange at end point

Question 83

Transition metals and group 1 metals have many properties in common because they are all metals. However some properties of transition metals are different from properties of group 1 metals. Which is a property of transition metals but not of group 1 metals? (1) A good conductor of electricity B high melting point C malleable D shiny when cut or polished

Answer 83

high melting point

Question 84

Which option correctly shows two metals that are in group 1 and 2 metals that are transition metals? (1) group 1 transition metals A lithium and zinc (group 1) calcium copper (transition metals) B potassium and caesium (group 1) copper and iron (transition metals) C sodium and potassium (group 1) copper and magnesium (transition metals) D sodium and magnesium (group 1) manganese and nickel (transition metals)

Answer 84

potassium and caesium (group 1) copper and iron (transition metals)

Question 85

Describe the structure of metals in terms of the particles present in their structures. (2)

Answer 85

Regular arrangement of +ve ions/cations (1) Surrounded by delocalised electrons (1)

Question 86

Explain how metals conduct electricity. (2)

Answer 86

Electrons (1) Move/flow (1)

Question 87

Describe what you would see when a small piece of sodium is added to water. (2)

Answer 87

Floats (1) Moves around (1) Effervescence/fizzing/bubbles (1) Melts/changes to ball shape (1) Becomes smaller/disappears (1)

Question 88

Write the balanced equation for the reaction of sodium with water to form sodium hydroxide and hydrogen. (3)

Answer 88

2Na + 2H2O → 2NaOH + H2

Question 89

Gold is used to make some jewellery. Explain why gold is used to make jewellery. (2)

Answer 89

Doesn’t corrode/tarnish (1) Unreactive (1) Shiny (1) Malleable (1) Expensive/maintains its value (1)

Question 90

Gold can be alloyed with other metals to produce alloys that have a higher strength than pure gold. Explain why gold alloys are stronger than gold. (3)

Answer 90

Gold atoms all the same size (1) Layers easily slide over each other (1) In alloys metal atoms are different sizes (1) Distrusts structure of gold atoms (1) Prevents layers of atoms from sliding (1)

Question 91

Iron and aluminium occur in the Earth’s crust as their oxides. Different methods are used to extract iron and aluminium from their oxides. Explain, in terms of the position of the metal in the reactivity series and the cost of the extraction processes, why iron and aluminium are extracted by different methods. (6)

Answer 91

reactivity series: • aluminium more reactive than iron/aluminium higher than iron in reactivity series • aluminium forms stronger bonds with oxygen than iron does • aluminium oxide more stable (to decomposition) than iron oxide • aluminium more reactive than carbon/aluminium higher than carbon in reactivity series cost: • electrolysis/electricity (more) expensive (than heating with carbon) • heating with carbon is (relatively) cheap method Iron: • carbon more reactive than iron/iron less reactive than carbon • iron oxide reduced • by heating with carbon • no need to use (expensive) electrolysis Aluminium: • aluminium oxide difficult to reduce • aluminium oxide cannot be reduced by (heating with) carbon • (cheaper) reduction with carbon does not work • need more powerful method of reduction • therefore must use electrolysis

Question 92

Describe how iron is extracted from its ore (2)

Answer 92

Hear (1) With carbon (1)

Question 93

Copper oxide reacts with hydrogen to form copper and water. The equation for the reaction is CuO + H2 → Cu + H2O Explain how this reaction involves both oxidation and reduction. (3)

Answer 93

Reduction is the loss of oxygen (1) Copper (oxide) loses oxygen (1) Hence copper oxide is reduced (1) OR Oxidation is the gain of oxygen (1) Hydrogen gains oxygen (1) Hence hydrogen is oxidised (1)

Question 94

Some modern spectacle frames are made of shape memory alloys. Explain why shape memory alloys are better than other alloys for making spectacle frames. (2)

Answer 94

When bent/deformed (1) Shape memory alloys return to their original shape (1) OR Shape memory alloys return to their original shape (1) But other alloys stay deformed (1)

Question 95

1 cent coin is made of steel, coated with copper. Suggest why the 1 cent coin is coated with copper. (1)

Answer 95

Steel corrodes/rusts (1) Prevents corrosion/rust (1) Copper doesn’t rust (1) Copper oxidises slower (1) Kills bacteria (1)

Question 96

The 1 euro coin has a silver-coloured centre and a gold-coloured rim. Compare the compositions of the two parts of the coin to suggest which metal causes the alloy to become gold-coloured. (1)

Answer 96

In pure metal, layers slide over each other easily (1) 2nd metal, particles are larger (1) Disrupt structure (1) Prevents layers from slipping (1)