Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2022 Summer Zone 1

A list of substances is shown.

aluminium oxide carbon dioxide chlorine diamond ethanol 
glucose iron(III) oxide limestone nitrogen oxygen

Answer the questions using the list of substances.
Each substance may be used once, more than once or not at all.
State which of the substances:

(a) is a reactant in photosynthesis
................................................................................................. [1]

(b) is the main constituent of bauxite
................................................................................................. [1]

(c) are two products of fermentation
......................................................... and ......................................................... [2]

(d) is used as a fuel
................................................................................................. [1]

(e) is a gas used to convert iron into steel
................................................................................................. [1]

(f) is a greenhouse gas
................................................................................................. [1]

(g) is a gas that is approximately 78% of clean, dry air
................................................................................................. [1]

(h) is a form of carbon.
................................................................................................. [1]

(a) Atoms are made of protons, neutrons and electrons. Atoms of the same element are known as isotopes.
(i) Complete the table.

[Table_1]

particle | relative charge | relative mass
electron | $\frac{1}{1840}$
neutron |
proton | +1

[2]

(ii) $^{24}_{12}Mg$ and $^{25}_{12}Mg$ are isotopes of magnesium.
Complete the table to show the numbers of electrons, neutrons and protons in these isotopes of magnesium.

[Table_2]

isotope | number of electrons | number of neutrons | number of protons
$^{24}_{12}Mg$ |
$^{25}_{12}Mg$ |

[2]

(iii) Explain why magnesium ions have a charge of 2+.
.................................................................................................................................
.................................................................................................................................

[1]

(b) $Mg^{2+}$ ions have the electronic structure 2,8.
Give the formula of the following particles which have the same electronic structure as $Mg^{2+}$ ions.

• a cation (positive ion)
.................................................................................................................................

• an anion (negative ion)
.................................................................................................................................

• an atom
.................................................................................................................................

[3]

This question is about sodium and compounds of sodium.
(a) (i) Describe the bonding in a metallic element such as sodium. You may include a diagram as part of your answer.
.....................................................................................................................................................................
.....................................................................................................................................................................
............................................................................................................................................................... [3]
(ii) Describe how solid sodium conducts electricity.
..................................................................................................................................................................... [1]
(b) Some properties of sodium chloride are shown:
• melting point of 801°C
• non-conductor of electricity when solid
• conductor of electricity when molten
• soluble in water.
(i) Name the type of bonding in sodium chloride.
..................................................................................................................................................................... [1]
(ii) Explain why sodium chloride conducts electricity when molten.
..................................................................................................................................................................... [1]

(c) A student determines the concentration of a solution of dilute sulfuric acid, $H_2SO_4$, by titration with aqueous sodium hydroxide, $NaOH$.
step 1 25.0 $cm^3$ of 0.200 mol/dm³ $NaOH$ is transferred into a conical flask.
step 2 Three drops of methyl orange indicator are added to the conical flask.
step 3 A burette is filled with $H_2SO_4$.
step 4 The acid in the burette is added to the conical flask until the indicator changes colour. The volume of acid is recorded. This process is known as titration.
step 5 The titration is repeated several times until a suitable number of results is obtained.
(i) Name the piece of apparatus used to measure exactly 25.0 $cm^3$ of 0.200 mol/dm³ $NaOH$ in step 1.
..................................................................................................................................................................... [1]
(ii) State the colour change of the methyl orange indicator in step 4.
from .................................................... to .................................................... [1]
(iii) State how the student decides that a suitable number of results have been obtained.
.....................................................................................................................................................................
..................................................................................................................................................................... [1]
(iv) 20.0 $cm^3$ of $H_2SO_4$ reacts with 25.0 $cm^3$ of 0.200 mol/dm³ $NaOH$.
The equation for the reaction is shown.
$$H_2SO_4 + 2NaOH \to Na_2SO_4 + 2H_2O$$
Calculate the concentration of $H_2SO_4$ using the following steps.
• Calculate the number of moles in 25.0 $cm^3$ of 0.200 mol/dm³ $NaOH$.
.................................................... mol
• Determine the number of moles of $H_2SO_4$ that react with the $NaOH$.
.................................................... mol
• Calculate the concentration of $H_2SO_4$.
.................................................... mol/dm³ [3]

This question is about compounds of sulfur.

(a) Sulfuric acid, $H_2SO_4$, is manufactured using the Contact process. This manufacture involves four stages.

stage 1 Molten sulfur burns in air to produce sulfur dioxide.
stage 2 Sulfur dioxide reacts with oxygen to form sulfur trioxide.
stage 3 Sulfur trioxide combines with concentrated sulfuric acid to form oleum, $H_2S_2O_7$.
stage 4 Oleum reacts to form concentrated sulfuric acid.

(i) Write a chemical equation for the reaction occurring in stage 1.
............................................................................................................................. [1]

(ii) State the essential conditions that are necessary for stage 2. Write an equation for the chemical reaction that occurs.
.............................................................................................................................
.............................................................................................................................
.............................................................................................................................
............................................................................................................................. [4]

(iii) Write a chemical equation for the reaction occurring in stage 3.
............................................................................................................................. [1]

(iv) Name the substance that reacts with oleum in stage 4.
............................................................................................................................. [1]

(b) Hydrogen sulfide has the formula $H_2S$.

(i) Complete the dot-and-cross diagram to show the electron arrangement in a molecule of hydrogen sulfide. Show outer shell electrons only.



[2]

(ii) Balance the chemical equation for the reaction of hydrogen sulfide with sulfur dioxide shown.
.....$H_2S$ + $SO_2$ $\rightarrow$ .....S + .....$H_2O$ [1]

Ethanol is manufactured by the reaction of methanol with carbon monoxide.
An equilibrium mixture is produced.
$$\text{CH}_3\text{OH}(g) + \text{CO}(g) \rightleftharpoons \text{CH}_3\text{COOH}(g)$$
(a) State two characteristics of an equilibrium.
1 .................................................................................................................................
2 .................................................................................................................................

(b) The purpose of the industrial process is to produce a high yield of ethanoic acid at a high rate of reaction.
The manufacture is carried out at a temperature of 300°C.
The forward reaction is exothermic.
Use this information to state why the manufacture is not carried out at temperatures:
• below 300°C
.................................................................................................................................
• above 300°C.
.................................................................................................................................

(c) Complete the table using only the words increases, decreases or no change.

This question is about zinc and its compounds.

(a) Zinc is extracted from its ore which is mainly zinc sulfide, ZnS.
The steps for this extraction are shown.

step 1 Zinc sulfide is converted into zinc oxide.
step 2 The zinc oxide is then reduced to zinc in a furnace. The zinc formed becomes a gas.
step 3 The zinc gas is cooled to form molten zinc.

(i) Name the ore of zinc, which is mainly zinc sulfide. [1]
...............................................................................................................................

(ii) Describe how zinc sulfide is converted into zinc oxide in step 1. [1]
...............................................................................................................................

(iii) Name the reducing agent used in step 2. [1]
...............................................................................................................................

(iv) Explain why the zinc forms a gas in step 2 inside the furnace. [1]
...............................................................................................................................

(v) State the name of the physical change occurring when zinc gas is converted into molten zinc. [1]
...............................................................................................................................

(b) Zinc sulfate crystals, $ZnSO_4 \cdot 7H_2O$, are hydrated.

Zinc sulfate crystals are made by reacting zinc carbonate with dilute sulfuric acid.
The equation for the overall process is shown.

$ZnCO_3 + H_2SO_4 + 6H_2O \rightarrow ZnSO_4 \cdot 7H_2O + CO_2$

step 1 Large pieces of solid zinc carbonate are added to dilute sulfuric acid until the zinc carbonate is in excess. This forms aqueous zinc sulfate.
step 2 The excess zinc carbonate is separated from the aqueous zinc sulfate.
step 3 The aqueous zinc sulfate is heated until a saturated solution is formed.
step 4 The saturated solution is allowed to cool and crystallise.
step 5 The crystals are removed and dried.

(i) In step 1, zinc carbonate is in excess when no more zinc carbonate dissolves.
State one other observation that indicates the zinc carbonate is in excess in step 1. [1]
...............................................................................................................................

(ii) Name a different substance, other than zinc carbonate, that can be added to dilute sulfuric acid to produce aqueous zinc sulfate in step 1. [1]
...............................................................................................................................

(iii) Step 1 is repeated using powdered zinc carbonate instead of large pieces. All other conditions are kept the same.
The rate of reaction increases.
Give a reason why the rate of reaction increases. Explain your answer in terms of particles. [2]
...............................................................................................................................

(iv) Suggest what is observed when the solution is saturated in step 3. [1]
...............................................................................................................................

(v) The formula of zinc sulfate crystals is $ZnSO_4 \cdot 7H_2O$.
Give the formula of the solid formed if the crystals are heated to dryness in step 3. [1]
...............................................................................................................................

The Periodic Table can be used to classify elements.
(a) Group I elements react with cold water to form alkaline solutions.
(i) Place the Group I elements caesium, lithium, potassium, rubidium and sodium in their order of reactivity with water.
Put the most reactive element first.
most reactive __________________________________ least reactive
[1]
(ii) Name the alkaline solution formed when caesium reacts with cold water.
..............................................................................................................................
[1]
(b) Group I elements have lower melting points than transition elements.
Describe one other difference in the physical properties of Group I elements and transition elements.
..............................................................................................................................
[1]
(c) Group VII elements are known as the halogens.
Astatine is below iodine in Group VII.
Predict the physical state of astatine at room temperature and pressure.
..............................................................................................................................
[1]
(d) Some Group VII elements react with aqueous solutions containing halide ions.
When aqueous chlorine is added to aqueous potassium bromide a reaction occurs.
The ionic half-equations for the reaction are shown.
$Cl_2(aq) + 2e^- \rightarrow 2Cl^-(aq)$
$2Br^-(aq) \rightarrow Br_2(aq) + 2e^-$
(i) Describe the colour change of the solution.
original colour of potassium bromide solution .......................................................
final colour of reaction mixture ..........................................................
[2]
(ii) Identify the species that is oxidised.
Explain your decision.
species oxidised .................................................................
explanation ................................................................
[2]
(e) Bromine monochloride, $BrCl$, is made by the reaction between bromine and chlorine. The chemical equation is shown.
$Br_2(g) + Cl_2(g) \rightarrow 2BrCl(g)$
$$\begin{array}{|c|c|}\hline \text{bond} & \text{bond energy in kJ/mol} \\ \hline Br-Br & 190 \\ \hline Cl-Cl & 242 \\ \hline Br-Cl & 218 \\ \hline \end{array}$$
Calculate the overall energy change for the reaction using bond energies.
Use the following steps.
Calculate the total amount of energy required to break the bonds in 1 mole of $Br_2(g)$ and 1 mole of $Cl_2(g)$.
$............................$ kJ
Calculate the total amount of energy released when the bonds in 2 moles of $BrCl(g)$ are formed.
$............................$ kJ
Calculate the overall energy change for the reaction.
$............................$ kJ/mol [3]