Cambridge IGCSE Chemistry - 0620 - Core Paper 3 2015 Winter Zone 3

The structures of six gases are shown below.\n\nA: H_2C=CH_2 B: Cl_2 C: N_2 D: O_2 E: Ar F: CO_2\n\nAnswer the following questions about these gases.\nEach gas may be used once, more than once or not at all.\n\n(a) Which gas, A, B, C, D, E or F\n(i) bleaches damp litmus paper, .......................... [1]\n(ii) forms 79% of the air, .......................... [1]\n(iii) is a noble gas, .......................... [1]\n(iv) can undergo polymerisation, .......................... [1]\n(v) decolourises aqueous bromine, .......................... [1]\n(vi) is a product of respiration? .......................... [1]\n\n(b) Gas F is a compound. Define the term compound.\n..............................................................................................................................\n.............................................................................................................................. [1]\n\n(c) Give a use for gas E.\n..............................................................................................................................\n.............................................................................................................................. [1]\n\n(d) When magnesium is heated in gas C magnesium nitride, $\text{Mg}_3\text{N}_2$, is formed.\nComplete the symbol equation for this reaction.\n\_\_\_\_Mg + \_\_\_\_ \rightarrow \text{Mg}_3\text{N}_2$ [1]

Household waste can be burned to produce energy.
The table shows the energy released by different materials when the waste is burned.

[Table_1]

(a) Which material releases the most energy per kilogram when burned?
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(b) Which one of the following words best describes the energy change when a substance is burned?
Tick one box.
endothermic □
neutralisation □
exothermic □
reduction □
[1]

(c) The structure of part of a plastic is shown below.



How many different types of atom are present in this plastic?
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(d) Waste paper can be converted into an 'oil' by heating it at 350°C under pressure in the presence of a catalyst.

(i) What is the purpose of the catalyst?
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(ii) The 'oil' has the formula, $C_{22}H_{22}O_2$.
Complete the word equation for the complete combustion of this oil.

'oil' + oxygen $\rightarrow$ ......................................... + ...................... [2]

(e) Some plastics contain sulfur.
Explain why plastics containing sulfur are harmful to the environment when burned.
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(f) When organic matter decomposes, methane and carboxylic acids are formed.

(i) To which homologous series does methane belong?
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(ii) Ethanoic acid is a carboxylic acid.
State one physical property of ethanoic acid.
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(iii) Complete the formula for ethanoic acid showing all atoms and all bonds.



[1]

Hydrogen chloride can be prepared in the laboratory by heating sodium chloride with concentrated sulfuric acid using the apparatus shown below.

(a) Complete the diagram by adding the labels in the boxes. [2]
(b) The equation for the reaction is shown below.
$$2\text{NaCl} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{HCl}$$
State the name of the salt formed as a product in this reaction.
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(c) Hydrogen chloride gas dissolves in water to form hydrochloric acid.
(i) The diagram below shows the apparatus used to electrolyse concentrated hydrochloric acid.

Label the diagram to show
• the anode,
• the cathode,
• the electrolyte. [2]
(ii) Give the names of the gases collected at
X, ..........................................................................................................................
Y, .......................................................................................................................... [2]
(iii) Complete the word equation for the reaction of hydrochloric acid with calcium carbonate.
hydrochloric acid + calcium carbonate $\rightarrow$ .......................... + .......................... + ..........................
......................................................................... [3]
(d) Aqueous ammonia is added slowly to a beaker containing hydrochloric acid.
The graph below shows how the pH of the solution in the flask changes as the aqueous ammonia is added.

(i) What was the pH of the hydrochloric acid at the start of the experiment?
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(ii) Describe how the pH of the solution changes as the titration proceeds.
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Ethanol can be made by fermenting glucose.
glucose --(yeast)--> ethanol + carbon dioxide
A student investigated the fermentation of glucose at 30°C. She used the apparatus shown below.

(a) Describe how this apparatus can be used to investigate the rate of this reaction.
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[3]
(b) The graph below shows how the rate of fermentation changes with time.

(i) Describe how the rate of fermentation changes with time.
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[2]
(ii) What is the rate of reaction 40 hrs after the start of the experiment?
.......................... cm³ CO₂ per hour [1]
(iii) Suggest two ways to increase the rate of this reaction.
1 ..........................................................................................................................................................
2 ..........................................................................................................................................................
[2]
(c) If air is introduced into the fermentation mixture, some of the ethanol is converted to ethanoic acid.
Ethanoic acid has properties which are typical of most acids.
Suggest how you could distinguish between ethanoic acid and ethanol.
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[2]

(a) Mercury is a liquid at room temperature. When heated, it changes to mercury vapour.

Explain, using the kinetic particle theory, the differences in the arrangement and motion of the particles in liquid mercury and mercury vapour.
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(b) The table below compares the properties of some metals.

[Table_1]

Use the information in the table to answer the following questions.

(i) What is the state of potassium at 100°C?
Explain your answer.
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......................................................................................................................... [2]

(ii) Which two metals in the table are transition elements?
Explain your answer.
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(iii) Why is aluminium used for food containers?
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(c) Iron undergoes a form of corrosion called rusting.

(i) State the conditions needed for rusting?
.................................................. and .................................................. [2]

(ii) Explain why painting a clean iron object prevents it from rusting.
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(d) Iron reacts with hydrochloric acid. A salt with the formula $\text{FeCl}_2$ is formed as well as a gas which pops with a lighted splint.

(i) Complete the word equation for this reaction.
iron + hydrochloric acid $ ightarrow$ ......................................... + .................... [2]

(ii) Describe a test for iron(II) ions.
test ....................................................................................................................
result ................................................................................................................... [2]

(e) Stainless steel is an alloy of iron.

Give one use of stainless steel.
......................................................................................................................... [1]

(a) Name the process by which hydrocarbon fractions are separated and state the physical property which allows this process to be carried out.
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(b) Use the information in the diagram above to answer these questions.
(i) Which fraction contains hydrocarbons with the lowest relative molecular masses?
..................................................................................................................... [1]
(ii) State the name of the fraction labelled X.
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(c) In some oil refineries, naphtha is heated with steam at 800$^\circ$C. A mixture of hydrocarbons is formed. Some of these hydrocarbons are shown below.

(i) Which two of these hydrocarbons are unsaturated?
............................................. and ............................................. [1]
(ii) Compound D can be cracked to make hydrogen. Complete the symbol equation for this reaction.
$C_3H_8 \rightarrow$ ................... + .................. [2]

(d) Bitumen is a mixture of hydrocarbons. Bitumen is heated with copper(II) oxide.

(i) A pinkish-brown solid appears at the bottom of the test-tube. This solid conducts electricity. Suggest the name of this pinkish-brown solid.
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(ii) Water collects on the walls of the test-tube at W. Suggest why water collects at this point?
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(a) Chlorine is in Group VII of the Periodic Table. One isotope of a chlorine atom has a nucleon number of 35.
Describe the structure of an atom of this isotope of chlorine. In your answer refer to
• the type and number of each subatomic particle present,
• the charges on each type of subatomic particle,
• the position of each type of subatomic particle in the atom.
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(b) Chlorine reacts with sodium to form sodium chloride.
Sodium chloride contains Na⁺ ions and Cl⁻ ions.
Explain why sodium ions are positively charged and chloride ions are negatively charged.
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(c) When chlorine reacts with aqueous potassium iodide, the solution turns brown.

(i) Suggest why the solution turns brown.
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(ii) Explain why aqueous potassium chloride does not react with iodine.
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(d) The structure of a chlorofluorocarbon is shown below.

Deduce the molecular formula of this compound.
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