2025 Cambridge IGCSE Chemistry (0620) Practice Paper with Answers

A pure solid substance, Y, is heated at a constant rate until it has completely boiled. The temperature of Y is recorded at regular intervals. Which statement describes the behavior of Y during the period when it is melting?

Which row correctly identifies the number of protons, neutrons, and electrons in the phosphide ion, \(^{31}\text{P}^{3-}\)?

The formula of the nitride ion is \(\text{N}^{3-}\) and the formula of the calcium ion is \(\text{Ca}^{2+}\). What is the correct formula of calcium nitride?

An aqueous solution of concentrated copper(II) chloride is electrolysed using inert carbon electrodes. Which products are formed at each electrode?

The equation for the combustion of hydrazine is shown.
\(\text{N}_2\text{H}_4(\text{g}) + \text{O}_2(\text{g}) \rightarrow \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{g})\)
Some bond energies are given in the list:
- \(\text{N}-\text{H}\): \(391\text{ kJ/mol}\)
- \(\text{N}-\text{N}\): \(158\text{ kJ/mol}\)
- \(\text{O}=\text{O}\): \(498\text{ kJ/mol}\)
- \(\text{N}\equiv\text{N}\): \(945\text{ kJ/mol}\)
- \(\text{O}-\text{H}\): \(463\text{ kJ/mol}\)
What is the enthalpy change, \(\Delta H\), for the reaction?

The following reversible reaction reaches dynamic equilibrium in a closed container:
\(\text{PCl}_3(\text{g}) + \text{Cl}_2(\text{g}) \leftrightharpoons \text{PCl}_5(\text{g})\) \(\Delta H = -88\text{ kJ/mol}\)
Which change would increase the yield of \(\text{PCl}_5(\text{g})\) at equilibrium?

Three metals, X, Y, and Z, are tested with the following results:
- X reacts vigorously with cold water.
- Y does not react with dilute hydrochloric acid.
- Z reacts slowly with dilute hydrochloric acid but does not react with cold water.
What is the order of reactivity of the metals, from most reactive to least reactive?

Which statement about alkenes is correct?

An element, E, has two isotopes: \(^{63}\text{E}\) and \(^{65}\text{E}\).

The relative atomic mass of E is 63.6.

What is the percentage abundance of the heavier isotope, \(^{65}\text{E}\)?

Concentrated aqueous potassium bromide is electrolysed using inert electrodes.

Which row shows the products formed at each electrode and the change in pH of the electrolyte during the electrolysis?

| | Product at anode (+) | Product at cathode (-) | Change in pH of electrolyte |
|---|---|---|---|
| **A** | bromine | hydrogen | increases |
| **B** | bromine | potassium | decreases |
| **| C** | oxygen | hydrogen | no change |
| **D** | oxygen | potassium | increases |

A molecule of methanol has the formula \(\text{CH}_3\text{OH}\).

How many bonding pairs of electrons and how many non-bonding outer-shell electrons are there in one molecule of methanol?

| | Bonding pairs of electrons | Non-bonding outer-shell electrons |
|---|---|---|
| **A** | 5 | 4 |
| **B** | 5 | 8 |
| **C** | 6 | 4 |
| **D** | 6 | 8 |

An oxide of nitrogen contains 30.4% nitrogen by mass.

What is the empirical formula of this oxide?

(Relative atomic masses: \(A_r(\text{N}) = 14\), \(A_r(\text{O}) = 16\))

The reaction between hydrogen gas and chlorine gas to form hydrogen chloride gas is represented by the following chemical equation:

$$\text{H}_2\text{(g)} + \text{Cl}_2\text{(g)} \rightarrow 2\text{HCl(g)}$$

The bond energies are shown in the table.

| Bond | Bond energy / kJ/mol |
|---|---|
| \(\text{H-H}\) | 436 |
| \(\text{Cl-Cl}\) | 242 |
| \(\text{H-Cl}\) | 431 |

What is the energy change for this reaction?

Four metals, W, X, Y and Z, are added separately to aqueous solutions of their metal nitrates. The observations are recorded in the table below.

| Metal | Solution containing \(\text{W}^{2+}\) | Solution containing \(\text{X}^{2+}\) | Solution containing \(\text{Y}^{2+}\) | Solution containing \(\text{Z}^{2+}\) |
|---|---|---|---|---|
| **W** | - | no reaction | no reaction | Z metal formed |
| **X** | W metal formed | - | Y metal formed | Z metal formed |
| **Y** | W metal formed | no reaction | - | Z metal formed |
| **Z** | no reaction | no reaction | no reaction | - |

What is the order of reactivity of the metals, from most reactive to least reactive?

Ethene gas reacts with steam to produce ethanol.

Which set of conditions is required for this industrial addition reaction to take place?

An unknown salt, Y, is dissolved in distilled water. The following tests are performed:

- The addition of aqueous sodium hydroxide to the solution produces a green precipitate that is insoluble in excess.
- The addition of dilute nitric acid followed by aqueous barium nitrate to the solution produces a white precipitate.

What is the identity of salt Y?

Some bond energies are shown in the table.

| Bond | Bond energy / kJ/mol |
| :--- | :--- |
| \(\text{H}-\text{H}\) | 436 |
| \(\text{Br}-\text{Br}\) | 193 |
| \(\text{H}-\text{Br}\) | 366 |

What is the enthalpy change, \(\Delta H\), for the reaction shown below?

\[\text{H}_2\text{(g)} + \text{Br}_2\text{(g)} \rightarrow 2\text{HBr(g)}\]

Concentrated aqueous copper(II) chloride is electrolysed using platinum electrodes.

Which row correctly describes the products at the electrodes and the visual change in the electrolyte?

Ethene reacts with chlorine gas at room temperature and pressure.

What is the structural formula of the organic product formed?

What is the volume of \(0.88\text{ g}\) of carbon dioxide gas, \(\text{CO}_2\), at room temperature and pressure (r.t.p.)?

(Molar volume of a gas at r.t.p. is \(24\text{ dm}^3\); \(M_r\) of \(\text{CO}_2\) is 44)

Which statement about the giant structures of diamond, graphite, and silicon(IV) oxide is correct?

Three metals, \(W\), \(X\) and \(Y\), are tested for their reactivity.

- Metal \(W\) reacts with aqueous copper(II) sulfate, but does not react with aqueous zinc sulfate.
- Metal \(X\) reacts with aqueous zinc sulfate.
- Metal \(Y\) does not react with aqueous copper(II) sulfate.

What is the correct order of reactivity of these three metals, from most reactive to least reactive?

A student is given an unknown colourless solution.

- When dilute hydrochloric acid is added and the mixture is warmed, a gas is evolved that turns acidified aqueous potassium manganate(VII) from purple to colourless.
- When a fresh sample of the solution is acidified with dilute nitric acid and aqueous barium nitrate is added, no precipitate is formed.

Which ion is present in the solution?

Which row correctly pairs a mixture with its most suitable separation technique?

A substance Y is heated from \(-10\text{ }^\circ\text{C}\) to \(110\text{ }^\circ\text{C}\). It melts at \(-5\text{ }^\circ\text{C}\) and boils at \(85\text{ }^\circ\text{C}\). Which statement describes the arrangement and movement of the particles of Y at \(25\text{ }^\circ\text{C}\)?

An atom of element Z has 16 protons, 18 neutrons and 16 electrons. What is the nucleon number of this atom and to which group of the Periodic Table does it belong?

Which row describes the number of shared pairs of electrons and the total number of non-bonding outer shell electrons in a molecule of methanol, \(\text{CH}_3\text{OH}\)?

Molten lead(II) bromide is electrolysed using inert carbon electrodes. What is observed at each electrode?

The reaction between nitrogen and hydrogen to form ammonia is exothermic.

$$\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons 2\text{NH}_3(\text{g}) \quad \Delta H = -92\text{ kJ/mol}$$

Which statement about this reaction is correct?

Equal masses of four metals, W, X, Y and Z, are separately added to equal volumes of dilute hydrochloric acid of the same concentration. The temperature of each mixture is measured before the metal is added and after the reaction is complete. The results are shown in the table.

| Metal | Initial temperature / $^\circ\text{C}$ | Final temperature / $^\circ\text{C}$ |
| :--- | :--- | :--- |
| W | 20 | 25 |
| X | 20 | 20 |
| Y | 20 | 41 |
| Z | 20 | 32 |

What is the correct order of reactivity of these metals, from most reactive to least reactive?

An organic compound has the molecular formula \(\text{C}_5\text{H}_{10}\). Which statement about this compound is correct?

A student performs a paper chromatography experiment to identify the food dyes present in a green sweet. The chromatogram shows two spots, one blue and one yellow. The solvent front travelled \(8.0\text{ cm}\) from the baseline. The blue spot travelled \(6.0\text{ cm}\) and the yellow spot travelled \(3.2\text{ cm}\). What is the \(R_f\) value of the yellow dye?

The melting points and boiling points of four substances, A, B, C and D, are shown in the table.

$$\begin{array}{|c|c|c|} \hline \text{Substance} & \text{Melting point / } ^\circ\text{C} & \text{Boiling point / } ^\circ\text{C} \\ \hline \text{A} & -95 & 36 \\ \hline \text{B} & -115 & -85 \\ \hline \text{C} & 0 & 100 \\ \hline \text{D} & -5 & 80 \\ \hline \end{array}$$

Which substance is a liquid at \(-10\ ^\circ\text{C}\) and a gas at \(50\ ^\circ\text{C}\)?

An atom of element X contains 18 protons, 22 neutrons and 18 electrons. Which row correctly identifies the nucleon number of X, its Group in the Periodic Table, and the number of electron shells in X?

$$\begin{array}{|c|c|c|c|} \hline & \text{nucleon number} & \text{Group number} & \text{number of electron shells} \\ \hline \text{A} & 40 & \text{VIII} & 3 \\ \hline \text{B} & 40 & \text{VI} & 3 \\ \hline \text{C} & 22 & \text{VIII} & 4 \\ \hline \text{D} & 18 & \text{VIII} & 3 \\ \hline \end{array}$$

Which statement about the formation of ions in magnesium oxide is correct?

Concentrated aqueous copper(II) chloride is electrolysed using inert carbon electrodes. Which products are formed at each electrode?

The reaction of hydrogen with chlorine to form hydrogen chloride gas is exothermic.

\[H_2(g) + Cl_2(g) \rightarrow 2HCl(g)\]

The bond energies are shown in the table.

$$\begin{array}{|c|c|} \hline \text{Bond} & \text{Bond energy / kJ/mol} \\ \hline \text{H–H} & 436 \\ \hline \text{Cl–Cl} & 242 \\ \hline \text{H–Cl} & 431 \\ \hline \end{array}$$

What is the overall energy change for this reaction?

A student tests a gaseous hydrocarbon to determine whether it is an alkane or an alkene. Which test and observation would confirm that the hydrocarbon is an alkene?

A student wants to investigate the rate of reaction between calcium carbonate and dilute hydrochloric acid by measuring the volume of gas produced over time. Which set of apparatus is most suitable for this experiment?

An unknown aqueous solution X is tested.

- Addition of aqueous sodium hydroxide produces a green precipitate that is insoluble in excess.
- Addition of dilute nitric acid followed by aqueous barium nitrate produces a white precipitate.

What is the identity of X?

Hydrazine, \(N_2H_4\), is used as a rocket propellant. It reacts with oxygen, \(O_2\), to form nitrogen gas, \(N_2\), and water vapor, \(H_2O\).

(a) Draw the displayed formula of a molecule of hydrazine, \(N_2H_4\). [2]

(b) Write a balanced chemical equation for the combustion of hydrazine. [2]

(c) This reaction is exothermic. Draw an energy level diagram for this reaction, labelling the reactants, products, activation energy (\(E_a\)), and enthalpy change (\(\Delta H\)). [4]

(d) Use the following bond energies to calculate the enthalpy change (\(\Delta H\)) for the reaction in kJ/mol.
- N-H: 391 kJ/mol
- N-N: 160 kJ/mol
- O=O: 498 kJ/mol
- N\equiv N: 945 kJ/mol
- O-H: 463 kJ/mol [5]

Aqueous sodium sulfate, \(Na_2SO_4\), is electrolysed using inert platinum electrodes.

(a) Describe what is meant by the term electrolysis. [3]

(b) State the observations at both electrodes during this electrolysis.
- cathode (negative electrode) [1]
- anode (positive electrode) [1]

(c) Write the ionic half-equation for the reaction at the cathode. [2]

(d) Write the ionic half-equation for the reaction at the anode. [3]

(e) Describe how the pH of the solution changes around each electrode during electrolysis. Explain your answer.
- near the cathode [2]
- near the anode [2]

Propene, \(C_3H_6\), is an unsaturated hydrocarbon.

(a) Define the term unsaturated. [1]

(b) Describe a test to show that propene is unsaturated. Include the observations. [2]

(c) Propene can be converted into propanol by reacting with steam.
- (i) State the name of this type of reaction. [1]
- (ii) State the catalyst and conditions required for this reaction. [3]

(d) Propene undergoes addition polymerisation to form poly(propene).
- (i) Explain what is meant by addition polymerisation. [2]
- (ii) Draw the structure of a single repeat unit of poly(propene). [2]

(e) Draw the displayed formula of propene. [2]

Bromine has two naturally occurring isotopes, \(^{79}\text{Br}\) and \(^{81}\text{Br}\).

(a) State the meaning of the term isotopes. [2]

(b) Complete the table below to show the number of protons, neutrons, and electrons in a bromine-79 atom and a bromine-81 bromide ion (\(^{81}\text{Br}^-\)).

| Particle | Protons | Neutrons | Electrons |
| --- | --- | --- | --- |
| \(^{79}\text{Br}\) atom | | | |
| \(^{81}\text{Br}^-\) ion | | | | [4]

(c) The relative atomic mass of this sample of bromine is 79.90. Calculate the percentage abundance of each isotope. Show your working. [4]

(d) Bromine is a Group VII element.
- (i) State the physical state of bromine at room temperature and pressure. [1]
- (ii) Describe what is observed when aqueous bromine is added to aqueous potassium iodide. Write the ionic equation for this reaction. [3]

Zinc is extracted from its main ore, zinc blende, which contains zinc sulfide, \(ZnS\).

(a) Zinc blende is roasted in air to produce zinc oxide, \(ZnO\), and sulfur dioxide.
- (i) Write the balanced chemical equation for this reaction. [2]
- (ii) State one environmental consequence of releasing sulfur dioxide into the atmosphere. [1]

(b) Zinc oxide is then reduced in a blast furnace using carbon monoxide.
- (i) Write the chemical equation for the reduction of zinc oxide by carbon monoxide. [2]
- (ii) Explain why zinc is obtained as a vapour from the top of the blast furnace. [2]

(c) Brass is an alloy of zinc and copper.
- (i) Explain why alloys like brass are stronger than pure metals in terms of their structures. [3]
- (ii) State one use of brass. [1]

(d) Explain why zinc, rather than copper, is used for galvanising iron. [2]

An experiment is carried out to find the formula of a hydrated salt of copper, \(CuSO_4 \cdot yH_2O\).

(a) A student heats 6.24 g of hydrated copper(II) sulfate. After heating to constant mass, 3.99 g of anhydrous copper(II) sulfate, \(CuSO_4\), remains.
- (i) Calculate the mass of water of crystallisation lost. [1]
- (ii) Calculate the number of moles of anhydrous copper(II) sulfate remaining. (\(M_r\) of \(CuSO_4\) = 159.5) [2]
- (iii) Calculate the number of moles of water lost. (\(M_r\) of \(H_2O\) = 18.0) [2]
- (iv) Determine the value of \(y\) in the formula \(CuSO_4 \cdot yH_2O\). [2]

(b) In a different reaction, 50.0 cm³ of 0.200 mol/dm³ hydrochloric acid is neutralized by 25.0 cm³ of aqueous sodium hydroxide.
- (i) Write the balanced chemical equation for this reaction. [2]
- (ii) Calculate the concentration, in mol/dm³, of the sodium hydroxide solution. [2]

(c) Deduce the empirical formula of a compound containing 40.0% carbon, 6.7% hydrogen, and 53.3% oxygen by mass. [2]

A student investigates the thermal decomposition of a green copper salt, basic copper(II) carbonate, \(\text{CuCO}_3\cdot\text{Cu(OH)}_2\), to produce copper(II) oxide, carbon dioxide, and water vapor.

(a) State the name of the apparatus used to heat the solid. [1]

(b) Describe the color change of the solid in the test-tube during heating. [2]

(c) The carbon dioxide gas is bubbled into a test-tube containing limewater. State the observation in this test-tube. [1]

(d) Explain why the delivery tube must be removed from the limewater immediately when heating is stopped. [2]

(e) Suggest one safety precaution, other than wearing safety glasses, that the student should take during the heating process. Give a reason for your answer. [2]

(f) Suggest how the apparatus could be modified to collect and measure the volume of carbon dioxide gas produced. [2]

A student investigates the temperature change during the displacement reaction between zinc powder and aqueous copper(II) sulfate.

\(50.0\text{ cm}^3\) of \(0.20\text{ mol/dm}^3\) copper(II) sulfate solution is placed in a beaker. The temperature is recorded every 30 seconds. Excess zinc powder is added at 60 seconds.

The results are shown in the table.

$$\begin{array}{|c|c|}
\hline
\text{Time / s} & \text{Temperature / }^\circ\text{C} \\
\hline
0 & 20.0 \\
\hline
30 & 20.0 \\
\hline
60 & 20.0 \\
\hline
90 & 28.5 \\
\hline
120 & 33.0 \\
\hline
150 & 35.5 \\
\hline
180 & 34.5 \\
\hline
210 & 33.5 \\
\hline
240 & 32.5 \\
\hline
270 & 31.5 \\
\hline
\end{array}$$

(a) Plot the results on a grid of temperature (y-axis) against time (x-axis). [4]

(b) Draw two straight lines of best fit:
- one through the points from 0 to 60 seconds
- one through the cooling points from 150 to 270 seconds.
Extrapolate both lines to 60 seconds. [2]

(c) Use your graph to determine the maximum temperature reached at 60 seconds and calculate the maximum temperature change, \(\Delta T\). Show clearly on your graph how you obtained your answer. [2]

(d) Explain why zinc powder was used instead of zinc granules in this experiment. [1]

(e) Suggest why the experiment would be more accurate if carried out in a polystyrene cup rather than a glass beaker. [1]

A student is provided with a green crystalline solid, salt F, which contains one cation and two anions.

The student dissolves Solid F in distilled water to make Solution F, and carries out the following tests. Complete the expected observations and conclusions.

(a) To the first portion of Solution F, aqueous sodium hydroxide is added dropwise, and then in excess. [2]

(b) (i) The mixture from (a) is warmed gently in a test-tube. A pungent gas is evolved which turns damp red litmus paper blue. Identify the gas. [1]
(ii) State the conclusion that can be made about the cation present in Solid F. [1]

(c) To the second portion of Solution F, dilute nitric acid is added followed by aqueous silver nitrate. No precipitate is formed. State the conclusion about halide ions in Solid F. [1]

(d) To the third portion of Solution F, dilute hydrochloric acid is added followed by aqueous barium chloride. A white precipitate is formed. State the name of the anion identified. [1]

(e) Solid F is known to contain iron(II) ions as its other cation. Identify the three ions present in Solid F. [3]

(f) Write the chemical formula of the gas identified in (b)(i). [1]

Vinegar is a solution containing ethanoic acid, which is a weak carboxylic acid.

Plan an investigation to determine which of three commercial brands of vinegar, X, Y, and Z, is the most concentrated.

You are provided with:
- samples of vinegar brands X, Y, and Z
- aqueous sodium hydroxide of concentration \(0.10\text{ mol/dm}^3\)
- phenolphthalein indicator
- common laboratory apparatus.

Your plan should include:
- the apparatus you would use
- the step-by-step practical procedure
- the measurements you would make
- how you would use your results to determine which vinegar is the most concentrated. [10]