Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2020 Winter Zone 1

(a) This question is about elements.

aluminium
carbon
iron
hydrogen
oxygen
silicon
sodium
sulfur

Answer the following questions about these elements.
Each element may be used once, more than once or not at all.

(i) Name the element that can be used as a fuel.
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(ii) Name the element that forms an oxide with a similar structure to diamond.
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(iii) Name the element that forms an amphoteric oxide.
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(iv) Name the element that has oxidation states of +2 and +3.
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(v) Name the element extracted from bauxite.
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(vi) Name the element that has atoms with the electronic structure 2,6.
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(b) Iron rusts when it is in contact with oxygen and water.

(i) Explain how sacrificial protection prevents rusting.
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(ii) State one other method of rust prevention.
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Zinc is extracted from an ore containing zinc sulfide.

(a) State the name of this zinc ore.
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(b) This ore is converted to zinc oxide, ZnO.
Zinc oxide is then reacted with carbon.

(i) Write a chemical equation for the reaction of zinc oxide with carbon.
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(ii) State what type of chemical change happens to the zinc in zinc oxide in this reaction.
Explain your answer.
chemical change ........................................................................................................
explanation ................................................................................................................

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(iii) Explain why aluminium is \textbf{not} extracted from aluminium oxide by heating with carbon.
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(iv) Suggest an alternative method for the extraction of zinc from zinc oxide.
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(c) Brass is an alloy of zinc.
Explain, in terms of particles, why brass is harder than pure zinc.
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(a) Aqueous ammonium sulfate, $(\text{NH}_4)_2\text{SO}_4$, is warmed with aqueous sodium hydroxide. The pungent-smelling gas ammonia, $\text{NH}_3$, is produced. Balance the equation for this reaction. $$(\text{NH}_4)_2\text{SO}_4 + \ldots \text{NaOH} \rightarrow \ldots \text{NH}_3 + \ldots\text{H}_2\text{O} + \text{Na}_2\text{SO}_4$$ [1]
(b) A 2.8 g sample of impure ammonium sulfate is found to contain 0.7 g of impurities. Calculate the percentage of ammonium sulfate in this sample.
percentage of ammonium sulfate = ......................... % [1]
(c) Describe a test for ammonia gas.
test ..........................................................................................................................
result ....................................................................................................................... [2]

(d) Ammonia gas is prepared at the front of a laboratory. The pungent smell of ammonia spreads throughout the laboratory slowly.
(i) Name the process that occurs when ammonia gas spreads throughout the laboratory. ..................................................................................................................... [1]
(ii) Explain, using ideas about particles, why ammonia gas spreads throughout the laboratory. ........................................................................................................................................... ........................................................................................................................................... ....................................................................................................................................... [2]
(iii) Explain why carbon dioxide gas, $\text{CO}_2$, will spread throughout the laboratory at a slower rate than ammonia gas, $\text{NH}_3$. ..................................................................................................................... [1]

(e) Ammonia is produced in the Haber process. The equation for the reaction is shown. $$\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightarrow 2\text{NH}_3(\text{g})$$
(i) In the Haber process, a temperature of 450 $^\circ$C and a pressure of 200 atmospheres are used in the presence of finely-divided iron. A larger equilibrium yield of ammonia would be produced if a lower temperature and a higher pressure are used. Explain why a lower temperature and a higher pressure are not used.
lower temperature ............................................................................................... ...........................................................................................................................................
higher pressure ................................................................................................. ........................................................................................................................................... [2]
(ii) State the role of iron in the Haber process. ..................................................................................................................... [1]

(f) Ammonia is a weak base.
(i) Explain the meaning of the term base. ........................................................................................................................................... ....................................................................................................................................... [1]
(ii) Suggest the pH of aqueous ammonia. ..................................................................................................................... [1]

(a) State the percentage of clean dry air which is oxygen. Give your answer to the nearest whole number.
................................. % [1]

(b) Oxygen and nitrogen are useful gases that can be obtained from air.
(i) Name the process used to separate oxygen and nitrogen from liquid air.
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(ii) State the property of oxygen and nitrogen that allows these gases to be separated using this process.
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(c) Carbon dioxide, $\text{CO}_2$, is a covalent molecule.
Complete the diagram to show the electron arrangement in one molecule of $\text{CO}_2$.
Show only the outer electrons.
[2]

(d) The graph shows the concentration of carbon dioxide in the atmosphere over a 60-year period, measured in parts per million (ppm).

The data shown in the graph is of global concern.
Explain why.
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(e) Name the process in the carbon cycle by which plants remove carbon dioxide from the atmosphere.
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(a) Dilute sulfuric acid is electrolysed using the apparatus shown in the diagram.

(i) State what is meant by the term electrolysis.
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(ii) Explain why inert electrodes are used.
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(iii) Name the products formed at each electrode.
negative electrode ..........................................................................................................
positive electrode ........................................................................................................... [2]
(iv) Write an ionic half-equation for the reaction at the negative electrode. [2]

(b) Sulfuric acid is manufactured using the Contact process. This manufacture involves four stages.
(i) Stage 1 involves the combustion of sulfur to form sulfur dioxide.
Write the chemical equation for stage 1.
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(ii) The equation for stage 2 is shown.
$2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$
The reaction can reach equilibrium.
Explain what is meant by the term equilibrium.
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(iii) The energy level diagram for the forward reaction in stage 2 is shown.

Explain what the diagram shows about the energy changes in the forward reaction.
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(c) In stage 3 sulfur trioxide, $SO_3$, is converted to oleum, $H_2S_2O_7$.
In stage 4 oleum reacts to form sulfuric acid, $H_2SO_4$.
State what oleum reacts with in stage 4.
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(d) A sample of sulfuric acid, $H_2SO_4$, has a concentration of $0.75 \text{ mol/dm}^3$.
Calculate the concentration of sulfuric acid in $\text{g/dm}^3$.
............................................................ $\text{g/dm}^3$ [2]

(a) Ethane, propane and butane are members of the same homologous series.
(i) Name this homologous series.
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(ii) State two ways members of the same homologous series are similar.
1 ..............................................................................................................
2 .............................................................................................................. [2]

(b) One mole of ethane, $C_2H_6$, contains $6.02 \times 10^{23}$ molecules.
Calculate how many molecules are in 15g of ethane.
number of ethane molecules = ................................. [1]

(c) Propane reacts with chlorine.
(i) Write the formula of the product which does not contain carbon.
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(ii) Draw the structure of an organic product formed. Show all of the atoms and all of the bonds.
[1]
(iii) State the name of this type of reaction.
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(d) (i) Aqueous bromine was added to a sample of ethene.
Give the colour change seen.
from .................................................... to .................................................. [2]
(ii) Explain, in terms of bonding, why there is no colour change when aqueous bromine is added to ethane.
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(e) There are two structural isomers with the formula $C_4H_{10}$.
(i) Draw the structures of both of these isomers, showing all of the atoms and all of the bonds.
[2]
(ii) Butane is formed when longer chain hydrocarbons are cracked.
Complete the chemical equation to show the other product when butane is formed by cracking.
$C_6H_{14} \rightarrow C_4H_{10} +$ ............................... [1]

(f) A compound contains 85.7% carbon and 14.3% hydrogen by mass.
(i) Calculate the empirical formula of this compound.
Show your working.
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(ii) The molecular mass of the compound is 112.
Calculate the molecular formula of this compound.
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(a) Ethanol can be manufactured by two different methods.

Method 1: fermentation of a sugar, $C_6H_{12}O_6$

$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$

Method 2: reaction of ethene with steam

$C_2H_4 + H_2O \rightarrow C_2H_5OH$

(i) Give one advantage of using fermentation compared with Method 2.
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(ii) Give one disadvantage of using fermentation compared with Method 2.
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(b) Ethanol reacts with acidified potassium manganate(VII) to form water and a product that turns litmus red.

(i) State the name of the product that turns the litmus red.
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(ii) State the type of reaction that ethanol undergoes when it reacts with acidified potassium manganate(VII).
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(c) Ethanol reacts with methanoic acid to form an ester.

(i) Name the ester formed in this reaction.
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(ii) Draw the structure of the ester formed. Show all of the atoms and all of the bonds.
[1]

(d) The table shows the melting points of ethanol and sodium chloride.

[Table_1]

The difference in melting points is due to differences in attractive forces between particles in these substances.

Name the type of attractive force in each substance, which is responsible for the difference in melting points.

ethanol ..............................................................................................................................

sodium chloride ...................................................................................................................... [2]