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EXAM QUESTIONS AQA TRILOGY

CHEMICAL CHANGES

Q1-6 FOUNDATON

Q3-9 HIGHER

MARK SCHEME AT THE END OF ALL THE QUESTIONS

Q1.

This question is about making copper salts.

The figure below shows the apparatus given to a student.

[pic] 

Outline a safe plan the student could use to make pure, dry, crystals of the soluble salt copper sulfate from the insoluble metal oxide and dilute acid.

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(Total 6 marks)

Q2.

This question is about the reactions of acids.

(a)     When dilute hydrochloric acid is reacted with sodium hydroxide solution there is a temperature change.

Explain how the temperature changes.

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(2)

(b)     Acids produce hydrogen ions in aqueous solutions.

What is the ionic equation for neutralisation reactions?

Tick one box.

 

|H+ (aq)   +   H2O(l)     [pic]      H3O+(aq) |[pic] |

|H+ (aq)   +   OH–(aq)     [pic]      H2O(l) |[pic] |

|2 H2O(l)      [pic]      H3O+(aq)   +   OH–(aq) |[pic] |

|H2O(l)      [pic]      2 H+(aq)   +   O2–(aq) |[pic] |

(1)

(c)     Sulfuric acid reacts with copper carbonate to produce a salt, water and carbon dioxide.

H2SO4   +   CuCO3      [pic]       CuSO4   +   H2O   +   CO2

What is the name of the salt produced?

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(1)

(d)     A student reacted four metals with water and with a dilute acid to work out the order of reactivity of the metals.

The table below shows some of the observations.

 

|Metal |Reaction with water |Reaction with dilute acid |

|Calcium |Bubbles of gas |X |

|Copper |Y |No bubbles of gas |

|Magnesium |Few bubbles of gas |Bubbles of gas |

|Zinc |No bubbles of gas |Bubbles of gas |

Write the observations for X and Y.

Observation at X   ____________________________________________________

Observation at Y   ____________________________________________________

(2)

(e)     Write the four metals, calcium, copper, magnesium and zinc, in order of reactivity.

Start with the most reactive metal.

_____________     _____________     _____________     ______________

(2)

(f)     Some gases given off in reactions can be identified by chemical tests.

Draw one line from each chemical test to the name of the gas.

Chemical test                                                            Gas

[pic] 

(3)

(g)     Acids react with bases to produce salts and water (H2O).

The electronic structure of a hydrogen atom is 2,1

The electronic structure of an oxygen atom is 2,6

Draw a diagram to show the arrangement of the outer shell electrons in a molecule of water.

(2)

(Total 13 marks)

Q3.

This question is about the electrolysis of two compounds.

Figure 1 shows the electrolysis of molten lead bromide.

Figure 1

[pic] 

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

Complete the sentences.

Use words from the box.

 

|atoms           bromide           bromine           ions |

|lead                  molecules              oxygen |

At the positive electrode the gas produced is_________________________

At the negative electrode lead ____________________________________

gain electrons and ___________________ .

(3)

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

The table below shows the student’s results.

 

|Time in minutes |Volume of gas produced in cm3 |

| |Hydrogen |Oxygen |

|0 |0 |0 |

|2 |11.2 |5.4 |

|4 |20.1 |11.4 |

|6 |32.5 |17.6 |

|8 |40.0 |23.7 |

|10 |60.9 |30.0 |

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

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

On the graph in Figure 2:

•        complete the scale for the y axis

•        plot the results for hydrogen

•        include a line of best fit.

Figure 2

[pic] 

(3)

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

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Mean volume of oxygen produced = __________ cm3 / s

(3)

(Total 9 marks)

Q4.

This question is about metals and metal compounds.

(a)     Copper oxide reacts with hydrochloric acid to produce copper chloride and water.

Copper oxide is insoluble in water.

Copper oxide is gradually added to hydrochloric acid until in excess.

Sketch a graph on Figure 1 to show how the pH of the hydrochloric acid would change.

Figure 1

[pic]

(3)

(b)     Magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen.

Plan an investigation to find the accurate volume of hydrogen produced from magnesium.

You do not need to write about safety precautions.

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(6)

A student reacts different masses of copper oxide with excess zinc to produce copper.

Figure 2 shows the student’s results.

Figure 2

[pic]

(c)     Calculate the gradient (slope) of the line on Figure 2.

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Gradient = ____________________ g of copper per g of copper oxide

(2)

(d)     Determine the mass of copper that can be produced from 75 g of copper oxide.

Use Figure 2

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Mass = ____________________ g

(3)

(Total 14 marks)

Q5.

Lead nitrate solution reacts with potassium iodide solution.

The reaction produces a solid.

Figure 1 shows the reaction occurring.

Figure 1

[pic] 

Lead Iodide By Der Kreole (own work) (CC-BY-3.0) via Wikimedia Commons

(a)     (i)      Give the name of this type of reaction.

Tick (✓) one box.

|Combustion |[pic] |

|Neutralisation |[pic] |

|Precipitation |[pic] |

(1)

(ii)     Write the missing state symbols in the chemical equation.

Pb(NO3)2(aq)    +    2KI(___)    [pic]    PbI2(___)    +    2KNO3(aq)

(2)

(iii)    Complete the word equation for the reaction.

lead nitrate + _________ [pic] lead iodide + _________

(2)

(iv)    How is solid lead iodide separated from the solution?

Draw a ring around the correct answer.

Distillation                Electrolysis                Filtration

(1)

(b)     A group of students investigated the movement of particles.

The students filled a container with water.

The students added a crystal of lead nitrate at position X and a crystal of potassium iodide at position Y, as shown in Figure 2.

Figure 2 – view from above

[pic] 

After 3 minutes solid lead iodide started to form at the position shown in Figure 3.

Figure 3 – view from above

[pic] 

(i)      Tick (✓) the correct box to complete the sentence.

Lead ions and iodide ions move through the water by

|diffusion. |[pic] |

|evaporation. |[pic] |

|neutralisation. |[pic] |

(1)

(ii)     What conclusion can you make about the speed of movement of lead ions compared with iodide ions?

Give a reason for your answer.

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(2)

(iii)    The students repeated the experiment at a higher temperature.

The solid lead iodide formed after a shorter period of time.

Explain why, in terms of particles.

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(2)

(Total 11 marks)

Q6.

A student investigated displacement reactions of metals.

The student added different metals to copper sulfate solution and measured the temperature change.

The more reactive the metal is compared with copper, the bigger the temperature change.

The apparatus the student used is shown in Figure 1.

Figure 1

[pic] 

(a)     State three variables that the student must control to make his investigation a fair test.

1. _________________________________________________________________

2. _________________________________________________________________

3. _________________________________________________________________

(3)

(b)     Figure 2 shows the thermometer in one experiment before and after the student added a metal to the copper sulfate solution.

Figure 2

 

|Before adding metal |After adding metal |

[pic] 

Use Figure 2 to complete Table 1.

Table 1

 

|Temperature before adding metal in °C |________ |

|Temperature after adding metal in °C |________ |

|Change in temperature in °C |________ |

(3)

(c)     The student repeated the experiment three times with each metal.

Table 2 shows the mean temperature change for each metal.

Table 2

 

|Metal |Mean temperature change|

| |in °C |

|Cobalt |4.5 |

|Gold |0.0 |

|Magnesium |10.0 |

|Nickel |3.0 |

|Silver |0.0 |

|Tin |1.5 |

(i)      On Figure 3, draw a bar chart to show the results.

Figure 3

[pic] 

(3)

(ii)     Why is a line graph not a suitable way of showing the results?

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(1)

(iii)    Use the results to work out which metal is the most reactive.

Give a reason for your answer.

Most reactive metal _________________________

Reason _______________________________________________________

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(2)

(iv)    Explain why there was no temperature change when silver metal was added to the copper sulfate solution.

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(2)

(v)     It is not possible to put all six metals in order of reactivity using these results.

Suggest how you could change the experiment to be able to put all six metals into order of reactivity.

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(2)

(Total 16 marks)

Q7.

Acids and bases are commonly found around the home.

(a)     Baking powder contains sodium hydrogencarbonate mixed with an acid.

(i)      When water is added, the baking powder releases carbon dioxide. How could you test the gas to show that it is carbon dioxide?

Test _________________________________________________________

Result of test __________________________________________________

(2)

(ii)     Complete and balance the chemical equation for the reaction of sodium hydrogencarbonate with sulphuric acid.

NaHCO3  +  H2SO4  →  ____________  +  ____________  +  _________

(2)

(b)     Indigestion tablets contain bases which cure indigestion by neutralising excess stomach acid.

[pic] 

(i)      One type of indigestion tablet contains magnesium hydroxide. This base neutralises stomach acid as shown by the balanced chemical equation.

Mg(OH)2  +  2HCl  →  MgCl2  +  2H2O

         Write a balanced ionic equation for the neutralisation reaction.

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(2)

(ii)     How does the pH in the stomach change after taking the tablets?

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(1)

(c)     Ammonium sulphate is used as a lawn fertiliser.

[pic] 

          Using ammonia solution, describe how you would make the fertiliser ammonium sulphate.

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(3)

(Total 10 marks)

Q8.

This question is about copper.

(a)     Most of the copper extracted is used in electric circuits.

The figure below shows how impurities change the electrical conductivity of copper.

[pic]

                Percentage of impurities in copper

Copper extracted by smelting is about 99% pure.

The 99% pure copper produced by smelting is purified to 99.9999% pure copper by electrolysis.

Use values from the graph to explain why copper is purified to 99.9999%.

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(2)

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

Read the information in the box.

 

|Copper extraction |

|World demand for copper for the year 2011 was about 20 million tonnes. |

| |

|World reserves of copper are estimated to be 700 million tonnes. |

| |

|Most of the copper used is obtained from copper ores, which are mined. |

| |

|The copper ore chalcopyrite is heated in a furnace to produce copper sulfide, CuS |

| |

|The furnace is heated by burning fossil fuels. |

| |

|Air is then blown through the hot copper sulfide, to produce copper and sulfur dioxide. |

|CuS + O2 → Cu + SO2 |

A scientist made the statement: ‘Copper should be recycled’.

Use the information in the box and your own knowledge and understanding to justify the scientist’s statement.

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Extra space _________________________________________________________

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(6)

(c)     Phytomining is used to obtain copper from land that contains very low percentages of copper compounds.

Describe how copper compounds are obtained by phytomining.

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(3)

(Total 11 marks)

Q9.

Two students investigated the electrolysis of copper sulfate solution.

When copper sulfate solution is electrolysed, copper is produced at the negative electrode.

(a)  What substance is produced at the positive electrode when copper sulfate solution is electrolysed?

Tick one box.

 

|Hydrogen |[pic] |

|Oxygen |[pic] |

|Sulfur |[pic] |

|Sulfur dioxide |[pic] |

(1)

(b)  The students varied and measured the current in the circuit.

Complete the diagram below to show a circuit that could be used.

[pic] 

(3)

The students made the following hypothesis:

‘The mass of copper deposited on the negative electrode will be directly proportional to the current.’

The table below shows the students’ results.

 

|Current in amps |Mass of copper deposited on the|

| |negative electrode in grams |

|0.12 |0.024 |

|0.24 |0.047 |

|0.36 |0.057 |

|0.48 |0.095 |

|0.60 |0.118 |

|0.72 |0.142 |

(c)  Student A said that the results did support the hypothesis.

Student B said that the results did not support the hypothesis.

Explain the extent to which the data in the table above supports the students’ hypothesis.

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(4)

(d)  Calculate the number of moles of copper deposited on the negative electrode when the current is 0.72 A

Give your answer in standard form.

Use the table above.

Relative atomic mass (Ar) of copper = 63.5

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Number of moles = ______________

(2)

(e)  What change to the investigation would increase the mass of copper deposited on the negative electrode?

Tick one box.

 

|Decrease the concentration of copper sulfate solution |[pic] |

|Decrease the volume of copper sulfate solution |[pic] |

|Increase the distance between the electrodes |[pic] |

|Increase the time the circuit is switched on for |[pic] |

(1)

(Total 11 marks)

Mark schemes

Q1.

Level 3 (5–6 marks):

A coherent method is described with relevant detail, which demonstrates a broad

understanding of the relevant scientific techniques, procedures and safety precautions. The

steps in the method are logically ordered with the dependent and control variables correctly identified. The method would lead to the production of valid results.

Level 2 (3–4 marks):

The bulk of a method is described with mostly relevant detail, which demonstrates a

reasonable understanding of the relevant scientific techniques, procedures and safety precautions. The method may not be in a completely logical sequence and may be missing

some detail.

Level 1 (1–2 marks):

Simple statements are made which demonstrate some understanding of some of the relevant scientific techniques, procedures and safety precautions. The response may lack a logical structure and would not lead to the production of valid results.

0 marks:

No relevant content

Indicative content

Named chemicals

•        copper oxide

•        sulfuric acid

•        copper sulfate

Correct use of apparatus

•        stirring rod

•        spatula

•        beaker

•        filter funnel and filter paper

•        evaporating basin

•        Bunsen burner

•        tripod and gauze

•        bench mat

•        conical flask

Method

•        add (excess) copper oxide to sulfuric acid

•        heat the mixture

•        filter the mixture

•        method to evaporate some of the water from the filtrate eg using a water bath or evaporating to half volume

•        leave solution (to cool and) to form crystals

•        remove and dry crystals

Safety

•        wearing of safety glasses / goggles

•        care with use of sulfuric acid as corrosive

•        warming not boiling mixture of copper oxide and sulfuric acid

•        hold beaker containing warm mixture with tongs whilst filtering

[6]

Q2.

(a)     it goes up / increases

1

because the reaction is exothermic or transfers energy to the surroundings

allow gives out thermal / heat energy

1

(b)     H+ (aq)   +   OH−(aq)   [pic]    H2O(l)

1

(c)     copper sulfate

1

(d)     X bubbles of gas

1

Y no bubbles of gas

1

(e)     calcium>magnesium>zinc>copper

if not all correct allow 1 mark for at least two metals in the correct position

2

(f)       Chemical test                                     Gas

[pic] 

extra lines from a test negate the mark

3

(g)     

[pic] 

two pairs of shared electrons

1

oxygen has four other electrons not bonded

1

[13]

Q3.

(a)     bromine

1

ions

1

atoms

1

(b)     correct scale on y axis

1

points correctly plotted using the scale

± ½ small square

1

best-fit line drawn

1

(c)     value for oxygen divided by corresponding time

1

× 60

1

= 0.05 (cm3 / s)

allow 0.05 with no working shown for 3 marks

1

[9]

Q4.

(a)

[pic] 

initial pH of hydrochloric acid is 0–3

1

pH increases as CuO is added

1

horizontal from pH = 7 (from any mass of copper oxide)

1

(b)    

|Level 2: The plan would lead to the production of a valid outcome. All key steps are |4-6 |

|identified and logically sequenced. | |

|Level 1: The plan would not lead to a valid outcome. Some relevant steps are identified, but |1-3 |

|links are not made clear. | |

|No relevant content |0 |

|Indicative content |  |

|[pic] | |

|an ideal plan would be: | |

|•   use a rule to measure the length / use a balance to find the mass of the piece of | |

|magnesium | |

|•   put magnesium into conical flask | |

|•   use measuring cylinder for dilute hydrochloric acid | |

|•   add dilute hydrochloric acid to conical flask | |

|•   connect bung (& delivery tube) into conical flask | |

|•   measuring cylinder is filled with water and inverted / upside down in bowl of water OR | |

|uses a gas syringe | |

|•   hydrogen flows through a delivery / rubber tube into measuring cylinder | |

|•   wait until all magnesium reacts / use excess dilute hydrochloric acid | |

|•   record volume when bubbles stop | |

|other things they could mention: | |

|•   use accurate / 2 dp balance | |

|•   to collect gas use measuring cylinder / gas syringe with best resolution | |

|•   add bung quickly to ensure no gas escapes | |

|•   gas is collected in graduated apparatus (not test tube) | |

|•   repeat experiment (with same length / mass of magnesium) | |

|•   repeat at same temperature since volume of gas will be different | |

6

(c)     (working)

[pic] 

data from candidate’s graph

1

(answer)

0.8 (g of Cu per g of CuO)

1

(d)     (working on graph)

extension of straight line and finding y value when x = 7.5

1

factor of ×10

1

(answer) 60 (g)

or

(using gradient)

y = 0.8 x

accept ecf from question part (c)

0.8 × 75

accept part (c) × 75

60

or

(stoichiometric method)

[pic] 

[pic] 

= 59.9 (g)

1

[14]

Q5.

(a)     (i)      precipitation

1

(ii)     (aq) on left hand side

1

(s) on right hand side

1

(iii)    potassium iodide

1

potassium nitrate

1

(iv)    filtration

1

(b)     (i)      diffusion

1

(ii)     iodide ions move / diffuse faster than lead ions or travel further in the same time

Must be a comparison

Accept converse

1

because the lead iodide forms much closer to the lead nitrate (or X) than the potassium iodide (or Y).

allow because iodide ions are smaller than lead ions

allow references to potassium iodide and lead nitrate

1

(iii)    the particles / ions move / diffuse faster

ignore which particles / ions the student refers to

1

because they have more energy or will collide / meet sooner

ignore reference to frequency of collisions

1

[11]

Q6.

(a)     any three from:

•        concentration of (salt) solution

•        volume of (salt) solution

ignore amount of solution

•        initial temperature (of the solution)

ignore room temperature

•        surface area / form of metal

•        moles of metal

allow mass / amount

ignore time

ignore size of tube

3

(b)     20

1

32

1

12

allow ecf

1

(c)     (i)      four bars of correct height

tolerance is + / - half square

3 correct for 1 mark

2

bars labelled

1

(ii)     one variable is non-continuous / categoric

accept qualitative or discrete

accept no values between the metals

1

(iii)    magnesium

1

because biggest temperature change

accept gives out most energy

ignore rate of reaction

dependent on first mark

1

(iv)    does not react / silver cannot displace copper

1

because silver not more reactive (than copper) or silver below copper in reactivity series

do not accept silver is less reactive than copper sulfate

1

(v)     replace the copper sulfate

could be implied

1

with any compound of a named metal less reactive than copper

allow students to score even if use an insoluble salt

1

[16]

Q7.

(a)     (i)      test: limewater

accept calcium hydroxide solution

1

result: ‘goes’ cloudy

accept white or milky

do not accept misty or chalky test must be correct before result mark can be considered

1

(ii)     2 NaHCO3 + H2SO4 →

Na2SO4 + (2) H2O + (2) CO2

1

correctly balanced

1

(b)     (i)      H+ + OH–

1

→ H2O

         deduct one mark if incorrectly balanced

accept H3O+ instead of H+ then 2H2O needed for balance

1

(ii)     pH increases

accept numerical indication

1

(c)     addition of sulphuric acid

1

correct use of an indicator

accept idea of forming a neutral solution

1

crystallisation (of neutral solution)

accept description using evaporation

1

[10]

Q8.

(a)     pure copper is twice as good a conductor as 99% pure copper

accept reverse argument

accept answers quoting 2 correct values from the graph scores 2

qualitative answer (e.g. pure copper is a better conductor than impure copper) scores 1

or

answers quoting a conductivity value from the graph scores 1

2

(b)     Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response.

0 marks

No relevant content

Level 1 (1–2 marks)

Simple list of a limited number of points given, with no linking between ideas

Level 2 (3–4 marks)

A broader set of points made. There will probably not be links between ideas

Level 3 (5–6 marks)

Answer includes linking between ideas, showing the consequence of either not recycling or the advantage of recycling. Answers such as less fossil fuel needed so less carbon dioxide produced or less carbon dioxide produced so less global warming

examples of the points made in the response

resources

(recycling) conserves supplies of ores

copper available for longer

as (at present rate of use) copper ores will run out in about 35 years

(recycling) conserves supplies of fossil fuels or energy

less fuel used at a lower cost

land pollution

mining scars landscape or produces noise pollution

mining destroys wildlife habitats

(recycling) less need to mine ores / fossil fuels

so less habitat destroyed or less scarring of landscape

(recycling) less need to use landfill for waste

atmospheric pollution

burning fossil fuels produces carbon dioxide / greenhouse gas

which (may) cause global warming or climate change

extraction produces sulfur dioxide

which causes acid rain

which can kill trees / fish

6

(c)     grow plants

accept plants absorb copper (through roots)

1

then plants are burned

1

ash (from burning) contains copper compounds

1

[11]

Q9.

(a)  oxygen

1

(b)  correct symbol for cell / battery with positive terminal connected to anode

ignore + and − symbols on cell / battery

do not accept voltmeter if connected in series

1

correct symbol for ammeter connected in series

1

correct symbol for variable resistor connected in series

allow variable power supply in place of variable resistor

1

ignore additional components that would not affect the circuit working

any order of components

(c)  calculation / statement including data to show effect of doubling current on mass of copper deposited

allow 1 mark for recognising that comparing doubling of one quantity to doubling of another is needed

or

allow 1 mark for recognising that a scaling factor needs to be applied

or

calculation of two quotients, e.g.

[pic] 

could be opposite way round (giving around 0.2)

[pic] 

2

(therefore) results support student A

or

results show direct proportionality

this mark must be supported by relevant calculations / statements

1

(however) there is an anomalous result at 0.36 A, 0.057 g

allow in terms of quotient (6.32 instead of ~5 or 0.16 instead of ~0.2)

1

(d)  [pic]

allow an answer that rounds to 0.00224

1

= 2.24 × 10−3

allow an answer that rounds to 2.2 × 10−3

1

an answer of 2.24 × 10−3 scores 2 marks

an answer of 0.00224 scores 1 mark

(e)  increase the time the circuit is switched on for

1

[11]

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