Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2017 Winter Zone 3

Substances can be classified as elements, compounds or mixtures.
State whether each of the following is an element, a compound or a mixture.
(a) brass .................................................................................. [1]
(b) gold .................................................................................. [1]
(c) butane .................................................................................. [1]
(d) air .................................................................................. [1]

(a) (i) Define the term \textit{molecule}.
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(ii) Define the term \textit{element}.
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(b) The table shows the composition of four atoms or ions, A, B, C and D.
[Table_1]
| number of protons | number of neutrons | number of electrons |
|------------------|------------------|-------------------|
| A | 10 | 10 | 10 |
| B | 10 | 12 | 10 |
| C | 12 | 10 | 10 |
| D | 13 | 14 | 10 |

(i) What is the atomic number of A?
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(ii) What is the nucleon number of B?
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(iii) Which of A, B, C and D are isotopes of each other?
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(iv) Which of A, B, C and D are atoms?
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(v) Which of A, B, C and D are positive ions?
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(c) Complete the table.
[Table_2]
| | number of protons | number of electrons |
|-|------------------|-------------------|
| Na | | |
| $S^{2-}$ | | |
| $Cl_2$ | | | [3]

Iron is extracted from its ore using coke in a blast furnace.


(a) Name the ore of iron which is mainly iron(III) oxide.
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(b) Describe the reactions occurring in the blast furnace.
In your answer, include
• two reasons for using coke in the blast furnace,
• a chemical equation for the reduction of iron(III) oxide,
• an explanation for using limestone in the blast furnace.
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(c) (i) Describe the bonding in iron. Include a diagram in your answer.
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(ii) Use your diagram in (c)(i) to explain why iron is malleable.
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(iii) Iron containing a small amount of carbon is known as steel.
Explain why steel is less malleable than iron.
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(d) (i) When iron is added to dilute sulfuric acid, an aqueous solution of iron(II) sulfate is formed as one of the products.
Write a chemical equation for the reaction.
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(ii) When iron(III) oxide is added to dilute sulfuric acid, an aqueous solution of iron(III) sulfate is formed as one of the products.
Write a chemical equation for the reaction.
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(e) Aqueous sodium hydroxide, aqueous potassium iodide and aqueous acidified potassium manganate(VII) are added to aqueous solutions of iron(II) sulfate and iron(III) sulfate.
• Iron(II) ions, $\text{Fe}^{2+}$, are reducing agents in aqueous solution.
• Iron(III) ions, $\text{Fe}^{3+}$, are oxidising agents in aqueous solution.
Complete the table.
[Table_1]

Hydrogen and oxygen react together in a hydrogen fuel cell. A hydrogen fuel cell is shown in the diagram.

(a) Name the process by which oxygen is obtained from air.
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(b) (i) In a hydrogen fuel cell, the hydrogen molecules are converted into hydrogen ions, $H^+$, according to the ionic half-equation shown.
$$H_2 \to 2H^+ + 2e^-$$
What type of reaction does this ionic half-equation represent?
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(ii) What type of substance reacts by donating hydrogen ions, $H^+$?
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(c) Write a chemical equation for the overall reaction that occurs in a hydrogen fuel cell.
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(d) Hydrogen fuel cells are being developed as alternatives to petrol engines in cars.
(i) Give one advantage of hydrogen fuel cells compared to petrol engines.
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(ii) Give one disadvantage of hydrogen fuel cells compared to petrol engines.
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(e) Some fuel cells use ethanol, $C_2H_5OH$, instead of hydrogen. Carbon dioxide and water are products of the reaction in an ethanol fuel cell.
(i) Write a chemical equation for the overall reaction occurring in an ethanol fuel cell.
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(ii) State an environmental problem caused by the release of carbon dioxide into the atmosphere.
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(iii) Name the process by which ethanol can be manufactured from a renewable resource.
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(f) Name the process occurring when electrical energy is used to break down an ionic compound.
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(a) (i) Name the products formed when sodium nitrate is heated.
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(ii) When copper(II) nitrate, Cu(NO_3)_2, undergoes thermal decomposition, three products are formed. One of the products is nitrogen dioxide, NO_2.
Write a chemical equation for the thermal decomposition of copper(II) nitrate.
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(b) The chemical equation shows the equilibrium between dinitrogen tetroxide (N_2O_4, a colourless gas) and nitrogen dioxide (NO_2, a brown gas).
N_2O_4(g) \rightleftharpoons 2NO_2(g)
colourless brown
A mixture of dinitrogen tetroxide and nitrogen dioxide is allowed to reach equilibrium in a closed gas syringe.
(i) In chemistry, what is meant by the term equilibrium?
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(ii) If the equilibrium mixture is heated at constant pressure, a darker brown colour is seen inside the gas syringe.
What does this information indicate about the decomposition of dinitrogen tetroxide? Explain your answer in terms of the position of the equilibrium.
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(iii) Suggest what you would see if the pressure on the equilibrium mixture were increased at constant temperature. Explain your answer in terms of the position of the equilibrium.
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(a) Alkanes and alkenes are two homologous series of hydrocarbons.
(i) What is meant by the term hydrocarbon? ................................................................................................................... [1]
(ii) What is the general formula of the homologous series of
alkanes, ...................................................................................................................
alkenes? ................................................................................................................... [2]
(iii) Other than having a general formula, state two characteristics of a homologous series.
1 ...................................................................................................................
2 ................................................................................................................... [2]
(iv) The structure of an alkene molecule with the molecular formula $C_4H_8$ is shown.

Draw the structure of a different alkene molecule with the molecular formula $C_4H_8$. Show all of the atoms and all of the bonds. [1]
(v) What term describes molecules with the same molecular formula but different structural formulae? ................................................................................................................... [1]

(b) $25 \text{ cm}^3$ of a gaseous hydrocarbon, $C_xH_y$, were burnt in $150 \text{ cm}^3$ of oxygen. This was an excess of oxygen.
After cooling, the volume of the gases remaining was $100 \text{ cm}^3$. This consisted of $75 \text{ cm}^3$ of carbon dioxide and $25 \text{ cm}^3$ of unreacted oxygen. The water that was produced in the reaction was liquid.
All volumes were measured at the same temperature and pressure.
(i) What is meant by an excess of oxygen? ................................................................................................................... [1]
(ii) What was the volume of oxygen that reacted with the hydrocarbon? .................................. cm^3 [1]
(iii) Complete the table to show the smallest whole number ratio of volumes.
[Table_1]
(iv) Use your answer to (b)(iii) to balance the chemical equation. Deduce the formula of the hydrocarbon.
$C_xH_y(g) + .......O_2(g) \rightarrow .......CO_2(g) + .......H_2O(l)$
formula of the hydrocarbon = .................................. [2]

(a) Carbon and silicon are elements in Group IV of the Periodic Table. Carbon dioxide from the air moves into green plants and is converted into carbohydrates.
(i) Name the process by which carbon dioxide molecules move through the air into green plants.
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(ii) Explain why silicon(IV) oxide cannot move through the air in the same way that carbon dioxide can.
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(iii) Name the process by which carbon dioxide is converted into glucose, $C_6H_{12}O_6$, in green plants. Give two conditions required for this process to occur. Write a chemical equation for the reaction which occurs.
name of process ......................................................................................................................................
condition 1 .............................................................................................................................................
condition 2 .............................................................................................................................................
chemical equation .................................................................................................................................. [5]


(b) Starch is a natural polymer made from glucose.
(i) What type of polymerisation occurs when glucose is converted into starch?
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(ii) What type of reaction occurs when starch is converted into glucose?
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(iii) Starch can be represented as shown.

Complete the diagram below to represent the structure of the glucose monomer.

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