Cambridge IGCSE Chemistry - 0620 - Supplement Paper 4 2024 Winter Zone 3

1. A list of substances is shown: bauxite, carbon dioxide, cryolite, ethane, ethanol, ethene, graphite, helium, hematite, hydrogen, silicon(IV) oxide, sodium chloride. Answer the following questions using only the substances from the list. Each substance may be used once, more than once, or not at all.
(a) State which substance is manufactured by fermentation. [1]
(b) State which substance is monatomic. [1]
(c) State which substance is a reactant in photosynthesis. [1]
(d) State which substance is a solvent in the extraction of aluminium. [1]
(e) State which substance is an ore of iron. [1]
(f) State which substance is manufactured from methane. [1]
(g) State which substance is a compound with a giant covalent structure. [1]
(h) State which substance is used as a lubricant. [1]
(i) State which substance is tested for with limewater. [1]

2. This question is about electrolysis.
(a) State the meaning of the term electrolysis. [2]
(b) Table 2.1 gives some information about the electrolysis of two electrolytes using graphite electrodes.
[Table_1: Table 2.1 with Anode, Cathode, Electrolyte, Observation, Name of Product]
(i) Complete Table 2.1. [4]
(ii) Oxygen is produced at the anode by the electrolysis of aqueous copper(II) sulfate. Write the ionic half-equation for this reaction. [2]
(c) Aqueous copper(II) sulfate is electrolysed using copper electrodes instead of graphite electrodes.
(i) Explain why the mass of the anode decreases during this electrolysis. [1]
(ii) Name the product formed at the cathode. [1]
(iii) State what change, if any, is observed in the appearance of the aqueous copper(II) sulfate. [1]

3. This question is about compounds of tin.
(a) Tin(IV) oxide has the formula $\text{SnO}_2$. The relative formula mass, $M_r$, of $\text{SnO}_2$ is 151. Calculate the percentage by mass of tin in $\text{SnO}_2$. [1]
(b) $\text{SnO}_2$ is an amphoteric oxide. $\text{SnO}_2$ reacts with aqueous sodium hydroxide, NaOH, to form a sodium salt and water only. The sodium salt contains a negative ion with the formula $\text{SnO}_3^{2-}$.
(i) State the meaning of the term amphoteric. [1]
(ii) Write the symbol equation for the reaction between $\text{SnO}_2$ and NaOH. [2]
(c) Tin is a metal that forms both covalent and ionic compounds. Suggest why this is unusual for a metal. [1]
(d) (i) Tin(IV) chloride, $\text{SnCl}_4$, is covalently bonded. A tin atom has four electrons in its outer shell. Complete the dot-and-cross diagram for a molecule of $\text{SnCl}_4$. Show the outer shell electrons only. [2]
(ii) Tin(II) oxide, SnO, is ionically bonded. The melting points of SnCl 4 and SnO are shown in Table 3.1.
[Table_2: Table 3.1 with Melting points of SnCl4 and SnO]
Explain, in terms of structure and bonding, why SnCl 4 has a much lower melting point than SnO. [3]
(e) Part of the reactivity series is shown: magnesium most reactive, tin, aluminium, copper least reactive.
(i) When aluminium foil is added to aqueous tin(II) sulfate, a reaction does not occur even though aluminium is above tin in the reactivity series. Explain why a reaction does not occur. [1]
(ii) An aqueous solution of tin(II) sulfate contains $\text{Sn}^{2+}$ ions. Two experiments are carried out. Experiment 1: Copper is added to aqueous tin(II) sulfate. Experiment 2: Magnesium is added to aqueous tin(II) sulfate. Write an ionic equation for any reaction that occurs in each experiment. If no reaction occurs, write 'no reaction'. [2]
(f) Hydrated tin(II) nitrate, $\text{Sn(NO}_3$ ) $\text{2} \cdot 20\text{H}_2\text{O}$, decomposes when it is heated.
(i) State what is meant by the term hydrated. [1]
(ii) Complete the equation for the decomposition of $\text{Sn(NO}_3$ ) $\text{2} \cdot 20\text{H}_2\text{O}$. $2\text{Sn(NO}_3$ ) $\text{2} \cdot 20\text{H}_2\text{O} \rightarrow \ldots\text{SnO} + \ldots\text{NO}_2 + \text{O}_2 + \ldots\text{H}_2\text{O}$ [2]

4. This question is about sulfuric acid, $\text{H}_2\text{SO}_4$.
(a) Dilute sulfuric acid and aqueous sodium hydroxide can be used to prepare sodium sulfate crystals using a method that involves titration. The apparatus for titration is shown in Figure 4.1.
[Image_1: Diagram of titration setup]
Thymolphthalein is used as an indicator for this titration.
(i) State the colour change of thymolphthalein at the end-point of this titration. [2]
(ii) Suggest why universal indicator is not used for this titration. [1]
(b) 25.0 cm$^3$ of aqueous sodium hydroxide, NaOH, of concentration 0.100 mol/dm$^3$ is neutralized by 20.0 cm$^3$ of dilute sulfuric acid, $\text{H}_2\text{SO}_4$. The equation for the reaction is shown: $2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O}$. Calculate the concentration of $\text{H}_2\text{SO}_4$:
1. Calculate the number of moles of NaOH used. [1]
2. Determine the number of moles of $\text{H}_2\text{SO}_4$ that react with the NaOH. [1]
3. Calculate the concentration of $\text{H}_2\text{SO}_4$. [1]
(c) A student is provided with an aqueous solution of sodium sulfate. Describe how to prepare a pure sample of sodium sulfate crystals from this solution. [3]
(d) Potassium hydrogen sulfate, $\text{KHSO}_4$, can be prepared by a reaction between aqueous potassium hydroxide and dilute sulfuric acid. Water is the only other product. Write a symbol equation for this reaction. [1]
(e) Potassium hydrogen sulfate, $\text{KHSO}_4$, dissolves in water to form solution X. Solution X contains $\text{K}^+$, $\text{H}^+$ and $\text{SO}_4^{2-}$ ions.
(i) Name the type of solution that contains $\text{H}^+$ ions. [1]
(ii) State the observations when the following tests are done: [5]
1. A flame test is carried out on X.
2. Solid copper(II) carbonate is added to X.
3. Aqueous barium nitrate acidified with dilute nitric acid is added to X.
(f) 0.325 g of Zn is added to dilute sulfuric acid which contains 0.0100 moles of $\text{H}_2\text{SO}_4$. The equation for this reaction is shown: $\text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2$.
(i) Determine whether Zn or $\text{H}_2\text{SO}_4$ is the limiting reactant. Explain your answer. [2]
(ii) In another experiment, 48.0 cm$^3$ of hydrogen gas, $\text{H}_2$, is produced. The experiment is carried out at room temperature and pressure, r.t.p. Calculate the number of molecules in 48.0 cm$^3$ of $\text{H}_2$ gas measured at r.t.p. The value of the Avogadro constant is $6.02 \times 10^{23}$. [2]

5. This question is about the rate of reaction and equilibrium. A student investigates the rate of decomposition of aqueous hydrogen peroxide, $\text{H}_2\text{O}_2$, using manganese(IV) oxide as a catalyst. The equation for the reaction is shown:
$2\text{H}_2\text{O}_2 (aq) \rightarrow 2\text{H}_2\text{O} (l) + \text{O}_2 (g)$.
The student uses the apparatus shown in Figure 5.1.
[Image_2: Diagram of the apparatus setup with cotton wool, balance, and catalyst]
The student: adds the catalyst to the aqueous hydrogen peroxide, replaces the container on the balance, starts a stop-watch, records the mass at regular time intervals.
(a) Table 5.1 shows the mass recorded at regular time intervals.
[Table_3: Table 5.1 with time/s and mass/g]
(i) Suggest why the mass decreases as time increases. [1]
(ii) After a certain time, the reaction stops. Explain why the reaction stops. [1]
(iii) Suggest why it is not possible to use the results in Table 5.1 to determine the exact time when the reaction stops. [1]
(b) Figure 5.2 shows a graph of the mass against time.
[Graph_1: Graph of mass vs. time]
The experiment is repeated at a higher temperature. All other conditions remain the same.
(i) Explain, in terms of collision theory, why the rate of reaction is higher at a higher temperature. [3]
(ii) On Figure 5.2, sketch the line expected when the experiment is repeated at a higher temperature. [2]
(c) Manganese(IV) oxide is the catalyst in this reaction.
(i) Explain the meaning of (IV) in manganese(IV) oxide. [2]
(ii) State how the mass of the catalyst has changed, if at all, at the end of the experiment. [1]
(d) Nitrogen monoxide gas, NO, and oxygen gas, $\text{O}_2$, react to produce nitrogen dioxide gas, $\text{NO}_2$, at room temperature. The reaction can reach equilibrium. The equation is shown: $2\text{NO} (g) + \text{O}_2 (g) \rightleftharpoons 2\text{NO}_2 (g)$, $\Delta H = -113 \text{kJ/mol}$. NO(g) and $\text{O}_2$(g) are passed into a beaker as shown in Figure 5.3.
[Image_3: Diagram of the beaker setup with NO and $\text{O}_2$ gases]
(i) Explain why the method shown in Figure 5.3 will not allow the reaction to reach equilibrium. [1]
(ii) The apparatus is changed and equilibrium is reached. The temperature of the equilibrium system is then increased, and the position of equilibrium shifts to the left. Explain why the position of equilibrium shifts to the left. [1]
(iii) The pressure of the equilibrium system is then increased. State the direction, if any, in which the position of equilibrium shifts. Explain your answer. [2]

6. This question is about hydrocarbons.
(a) State the meaning of the term hydrocarbon. [1]
(b) Propene, $\text{C}_3\text{H}_6$, can be made from long-chain alkanes such as dodecane. Dodecane contains 12 carbon atoms.
(i) Deduce the molecular formula of dodecane. [1]
(ii) Name the type of reaction that occurs when long-chain alkanes are converted into shorter chain alkenes. [1]
(c) Propene is an unsaturated hydrocarbon. Propene reacts with bromine.
(i) State the meaning of the term unsaturated. [1]
(ii) Write the molecular formula of the product formed when propene reacts with bromine. [1]
(d) A styrene molecule is represented as shown in Figure 6.1.
[Image_4: Diagram of the styrene molecule]
(i) The molecular formula of styrene is $\text{C}_8\text{H}_8$. Determine the empirical formula of styrene. [1]
(ii) Styrene can be polymerised into poly(styrene). State the type of polymerisation that occurs when styrene is converted into poly(styrene). [1]
(iii) Draw the structure of one repeat unit of poly(styrene). Include all of the atoms and all of the bonds. The $\text{C}_6\text{H}_5$ group should be represented as $\text{C}_6\text{H}_5$. [2]