john taylor 22nd june 48 marks:...

GCSE Chemistry

Revision questions from past GCSE papers Answer the questions then use the markscheme to correct your answers

Name:

Class:

Author: John Taylor

Date: 22nd June

Time: 48

Marks: 48

Comments:

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Q1. This question is about copper.

(a) Copper can be extracted by smelting copper-rich ores in a furnace.

The equation for one of the reactions in the smelting process is:

Cu2S(s) + O2(g) 2 Cu(s) + SO2(g)

Explain why there would be an environmental problem if sulfur dioxide gas escaped into the atmosphere.

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(b) The impure copper produced by smelting is purified by electrolysis, as shown below.

Copper atoms are oxidised at the positive electrode to Cu2+ ions, as shown in the half equation.

Cu(s) Cu2+(aq) + 2e−

(i) How does the half equation show that copper atoms are oxidised?

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(ii) The Cu2+ ions are attracted to the negative electrode, where they are reduced to produce copper atoms.

Write a balanced half equation for the reaction at the negative electrode.

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(iii) Suggest a suitable electrolyte for the electrolysis.

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(c) Copper metal is used in electrical appliances.

Describe the bonding in a metal, and explain why metals conduct electricity.

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(d) Soil near copper mines is often contaminated with low percentages of copper compounds.

Phytomining is a new way to extract copper compounds from soil.

Describe how copper compounds are extracted by phytomining.

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(e) A compound in a copper ore has the following percentage composition by mass:

55.6% copper, 16.4% iron, 28.0% sulfur.

Calculate the empirical formula of the compound.

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

You must show all of your working.

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Empirical formula = ............................................................ (4)

(Total 16 marks)

Q2. This question is about iron and aluminium.

(a) Iron is extracted in a blast furnace. Figure 1 is a diagram of a blast furnace.

(i) Calcium carbonate decomposes at high temperatures.

Complete the word equation for the decomposition of calcium carbonate.

calcium carbonate ................................. + ................................ (2)

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(ii) Carbon burns to produce carbon dioxide.

The carbon dioxide produced reacts with more carbon to produce carbon monoxide.

Balance the equation.

C(s) + CO2(g) .......... CO(g)

(1)

(iii) Carbon monoxide reduces iron(III) oxide:

Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g)

Calculate the maximum mass of iron that can be produced from 300 tonnes of iron(III) oxide.

Relative atomic masses (Ar): O = 16; Fe = 56

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Maximum mass = .............................. tonnes (3)

(b) Aluminium is extracted by electrolysis, as shown in Figure 2.

Figure 2

(i) Why can aluminium not be extracted by heating aluminium oxide with carbon?

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(ii) Explain why aluminium forms at the negative electrode during electrolysis.

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(iii) Explain how carbon dioxide forms at the positive electrodes during electrolysis.

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(Total 13 marks)

Q3. Use the periodic table and the information in the table below to help you to answer the questions.

The table shows part of an early version of the periodic table.

(a) Hydrogen was placed at the top of Group 1 in the early version of the periodic table.

The modern periodic table does not show hydrogen in Group 1.

(i) State one similarity between hydrogen and the elements in Group 1.

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Group 1 Group 2 Group 3 Group 4 Group 5 Group 6 Group 7

H

Li Be B C N O F

Na Mg Al Si P S Cl

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(ii) State one difference between hydrogen and the elements in Group 1.

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(b) Fluorine, chlorine, bromine and iodine are in Group 7, the halogens.

The reactivity of the halogens decreases down the group.

Bromine reacts with a solution of potassium iodide to produce iodine.

Br2 + 2KI 2KBr + I2

(i) In the reaction between bromine and potassium iodide, there is a reduction of bromine to bromide ions.

In terms of electrons, what is meant by reduction?

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(ii) Complete the half equation for the oxidation of iodide ions to iodine molecules.

2I−

(2)

(iii) Explain, in terms of electronic structure, why fluorine is the most reactive element in Group 7.

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(Total 8 marks)

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Q4. A student was trying to produce hydrogen gas.

Figure 1 shows the apparatus she used.

Figure 1

(a) No gas was produced.

The student’s teacher said that this was because the substances in the flask did not react.

(i) Suggest why the substances in the flask did not react.

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(ii) Which two substances could the student have put in the flask to produce hydrogen safely?

Tick (✓) one box.

(1)

Gold and dilute hydrochloric acid

Potassium and dilute hydrochloric acid

Zinc and dilute hydrochloric acid

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(b) Another student did produce hydrogen from two substances.

Figure 2 shows the apparatus the student used to collect and measure the volume of the hydrogen gas.

Figure 2

Give the name of the apparatus labelled X.

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(c) The student did the experiment four times. Her results are shown in the table below.

(i) One of the results is anomalous.

Which result is anomalous? Write your answer in the box.

Give a reason for your choice.

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Experiment Volume of hydrogen collected in

one minute in cm3

1 49

2 50

3 35

4 48

(ii) Calculate the mean volume of hydrogen collected in one minute.

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Mean volume = ........................................ cm3

(2)

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(iii) Give a reason why the experiment should be repeated several times.

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(d) A teacher collected two tubes full of hydrogen gas, as shown in Figure 3.

Figure 3

She tested tube A with a lighted splint as soon as she took the bung out.

She tested tube B with a lighted splint a few seconds after taking the bung out.

(i) Suggest why tube B gave a much louder pop than tube A.

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(ii) Complete and balance the chemical equation for the reaction that takes place when the hydrogen reacts in this test.

H2 + O2

(2) (Total 11 marks)

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M1. (a) because sulfur dioxide causes acid rain 1

which kills fish / aquatic life or dissolves / damages statues / stonework or kills / stunts growth of trees

if no other mark awarded then award 1 mark for sulfur dioxide is toxic or causes breathing difficulties.

1

(b) (i) electrons are lost 1

(ii) Cu2+ + 2e−→ Cu

allow Cu2+→ Cu − 2e−

ignore state symbols 1

(iii) copper sulfate allow any ionic copper compound

1

(c) (lattice of) positive ions 1

delocalised electrons accept sea of electrons

1

(electrostatic) attraction between the positive ions and the electrons 1

electrons can move through the metal / structure or can flow

allow electrons can carry charge through the metal / structure if wrong bonding named or described or attraction between oppositely charged ions then do not award M1 or M3 − MAX 2

1

(d) (copper compounds are absorbed / taken up by) plants allow crops

1

which are burned 1

the ash contains the copper compounds do not award M3 if the ash contains copper (metal)

1

(e) / Ar

55.6 / 63.5 16.4 / 56 28.0 / 32

moles 0.876 0.293 0.875

ratio 3 1 3

formula Cu3FeS

3

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award 4 marks for Cu3FeS3 with some correct working

award 3 marks for Cu3FeS3 with no working

if the answer is not Cu3FeS3 award up to 3 marks for correct steps

from the table apply ecf if the student has inverted the fractions award 3 marks for an answer of CuFe3S

4 [16]

M2. (a) (i) calcium oxide

in either order 1

carbon dioxide accept correct formulae

1

(ii) C(s) + CO2(g) → 2CO(g)

allow multiples 1

(iii) 210 (tonnes) award 3 marks for the correct answer with or without working allow ecf for arithmetical errors if answer incorrect allow up to 2 marks for any of the steps below: 160 → 112 300 → 112 / 160 × 300 or moles Fe2O3 = 1.875 (× 106) or 300 / 160

moles of Fe = 3.75 (× 106) or 2 × moles Fe2O3

mass Fe = moles Fe × 56 105 (tonnes) scores 2 (missing 1:2 ratio) 420 (tonnes) scores 2 − taken M

r of iron as 112

3

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(b) (i) aluminium is more reactive than carbon or carbon is less reactive than aluminium

must have a comparison of reactivity of carbon and aluminium accept comparison of position in reactivity series.

1

(ii) (because) aluminium ions are positive ignore aluminium is positive

1

and are attracted / move / go to the negative electrode / cathode 1

where they gain electrons / are reduced / Al3+ + 3e− → Al

accept equation or statements involving the wrong number of electrons.

1

(iii) (because) the anodes or (positive) electrodes are made of carbon / graphite 1

oxygen is produced (at anode) 1

which reacts with the electrodes / anodes do not accept any reference to the anodes reacting with oxygen from the air

equation C + O2 CO2 gains 1 mark (M3)

1 [13]

M3. (a) (i) any one from:

• one electron in the outer shell / energy level • form ions with a 1+ charge

1

(ii) any one from:

• hydrogen is a non-metal • (at RTP) hydrogen is a gas • hydrogen does not react with water • hydrogen has only one electron shell / energy level • hydrogen can gain an electron or hydrogen can form a negative /

hydride / H–ion

• hydrogen forms covalent bonds or shares electrons

accept answers in terms of the Group 1 elements 1

(b) (i) (bromine) gains electrons it = bromine do not accept bromide ion gains electrons ignore loss of oxygen

1

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(ii) I2

must both be on the right hand side of the equation 1

+ 2e–

2I– – 2e– ➔ I2 for 2 marks

1

(iii) fluorine is the smallest atom in Group 7 or has the fewest energy levels in Group 7 or has the smallest distance between outer shell and nucleus

the outer shell must be mentioned to score 3 marks 1

fluorine has the least shielding or the greatest attraction between the nucleus and the outer shell

1

therefore fluorine can gain an electron (into the outer shell) more easily 1

[8]

M4. (a) (i) copper is less reactive than hydrogen or copper is unreactive 1

(ii) Zinc and dilute hydrochloric acid 1

(b) (gas) syringe 1

(c) (i) 35 allow 3

1

because not close to others accept it is much lower than the others ignore references to trends or patterns dependent on the first mark

1

(ii) (49 + 50 + 48) / 3

= 49 correct answer with or without working gains 2 marks

1

allow ecf from anomaly identified in (i) for 2 marks: • Exp 1 anomalous gives 43.3 • Exp. 2 anomalous gives 44 • Exp. 4 anomalous gives 44.7 answer of 45.5 or 46 (anomaly not excluded) gains 1 mark correct working excluding anomaly but with wrong answer gains 1 mark

1

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(iii) so that a mean can be calculated accept improves accuracy of the mean or so anomalies can be identified / discarded or to reduce effect of random errors ignore makes it a fair test ignore reliability, validity, repeatability, reproducibility

1

(d) (i) idea of mixing with oxygen / air, letting air / oxygen in accept converse

1

(ii) H2O

do not accept incorrect additional products 1

balancing 2 … (1) … 2 allow fractions or multiples dependent on first mark

1 [11]

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john taylor 22nd june 48 marks:...

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