2025 Cambridge IGCSE Chemistry (0620) Practice Paper with Answers

A pure substance is cooled from a gas to a solid. At which stages does the temperature of the substance remain constant as thermal energy is released to the surroundings?

When \( 0.20\text{ mol} \) of a hydrocarbon is completely combusted in an excess of oxygen, \( 17.6\text{ g} \) of carbon dioxide and \( 10.8\text{ g} \) of water are produced.

What is the formula of the hydrocarbon?

An aqueous solution of a metal sulfate, \( \text{MSO}_4 \), is electrolysed using inert electrodes.

During the electrolysis, a pink-brown metal is deposited at the cathode, and a colourless gas which relights a glowing splint is evolved at the anode.

Which row identifies the metal \( \text{M} \) and the gas evolved?

The equations for four chemical reactions are shown. In which equation is the bold reactant acting as an oxidising agent?

Which method is most suitable for preparing a pure, dry sample of the insoluble salt lead(II) sulfate?

Purified aluminium oxide is electrolysed to extract aluminium metal.

Which statement about this industrial process is correct?

The structure of an ester is shown below.

\( \text{CH}_3\text{CH}_2\text{COOCH}_2\text{CH}_2\text{CH}_3 \)

Which row gives the correct name of the ester and the reactants used to prepare it?

Catalytic converters are fitted to car exhaust systems to reduce the emission of toxic gases into the atmosphere.

Which equation represents a reaction that occurs in a catalytic converter to convert toxic gases into non-toxic gases?

Two gas syringes are filled with equal volumes of different gases at room temperature and pressure. Syringe 1 contains carbon monoxide, CO. Syringe 2 contains sulfur dioxide, SO2. The gases are allowed to diffuse through identical small apertures. Which statement about the rate of diffusion of the two gases is correct?

The equation for the reaction between hydrogen sulfide gas and chlorine gas is shown. H2S(g) + Cl2(g) -> S(s) + 2HCl(g). Which statement correctly describes the redox process?

Iron is extracted from its ore, hematite, in a blast furnace. Calcium carbonate is added to the furnace to remove acidic impurities. Which row correctly describes the role of calcium carbonate?

Ethane reacts with chlorine in a substitution reaction. What are the correct conditions and the formula of an organic product formed in this reaction?

A concentrated aqueous solution of sodium chloride is electrolysed using inert platinum electrodes. Which row correctly identifies the products formed at each electrode?

Gaseous pollutants from car engines are passed through a catalytic converter. Which reaction takes place in the catalytic converter to remove these pollutants?

Which statement about the chemical properties of aqueous ethanoic acid is correct?

An excess of dilute hydrochloric acid is added to 4.8 g of magnesium ribbon. Mg(s) + 2HCl(aq) -> MgCl2(aq) + H2(g). What volume of hydrogen gas, measured at room temperature and pressure, is produced? (The relative atomic mass of Mg is 24. One mole of any gas occupies 24 dm3 at r.t.p.)

During a paper chromatography experiment to separate a mixture of amino acids, the solvent front travels 8.0 cm from the baseline. A spot of amino acid X travels 3.2 cm from the baseline. Why is a locating agent sprayed onto the chromatogram, and what is the Rf value of amino acid X?

The ionic equation for a redox reaction is shown: 2Fe3+(aq) + 2I-(aq) -> 2Fe2+(aq) + I2(aq). Which statement correctly describes this reaction in terms of electron transfer?

What is the maximum volume of carbon dioxide gas, measured at r.t.p., produced when 10.0 g of calcium carbonate, CaCO3, reacts completely with an excess of dilute hydrochloric acid? (Mr of CaCO3 = 100; the volume of one mole of any gas is 24 dm3 at r.t.p.)

Three metals, W, X and Y, are tested. Only W reacts with cold water. Both W and X react with dilute hydrochloric acid, but Y does not. Heating the oxide of Y with carbon produces metal Y, but heating the oxide of X with carbon does not produce metal X. What is the order of reactivity of the three metals, starting with the least reactive?

Concentrated aqueous sodium chloride is electrolysed using inert electrodes. Which row correctly identifies the products formed at each electrode and the change in pH of the remaining solution?

Methane reacts with chlorine in a substitution reaction. What is the essential condition for this reaction to occur, and what is a gaseous inorganic product of this reaction?

A student wants to prepare a pure, dry sample of the insoluble salt lead(II) sulfate, PbSO4. Which pair of aqueous solutions should the student mix together to achieve this?

Which statement about the chemical properties of ethanoic acid is correct?

What is the oxidation number of manganese in potassium manganate(VI), \( \text{K}_2\text{MnO}_4 \), and potassium manganate(VII), \( \text{KMnO}_4 \)?

Which statement about the structure and properties of silicon(IV) oxide, \( \text{SiO}_2 \), is correct?

An increase in temperature increases the rate of a chemical reaction. Which statement explains this effect?

The equation represents a reversible reaction.

\( \text{X(g)} + 2\text{Y(g)} \rightleftharpoons 2\text{Z(g)} \) (forward reaction is exothermic)

Which conditions of temperature and pressure will produce the highest yield of \( \text{Z(g)} \) at equilibrium?

Concentrated aqueous sodium chloride (brine) is electrolysed using inert electrodes. Which row correctly identifies the products formed at the electrodes and the nature of the remaining solution?

An atom of element X is represented as \( ^{37}_{17}\text{X} \). Which statement about a neutral isotope of X is correct?

An ester has the structural formula \( \text{CH}_3\text{COOCH}_2\text{CH}_2\text{CH}_3 \). What is the name of this ester and which carboxylic acid is used to prepare it?

What volume of carbon dioxide, measured at room temperature and pressure (r.t.p.), is produced when \( 10.0\text{ g} \) of calcium carbonate, \( \text{CaCO}_3 \), reacts completely with excess dilute hydrochloric acid?

[Relative formula mass: \( \text{CaCO}_3 = 100 \); the volume of one mole of gas at r.t.p. is \( 24\text{ dm}^3 \)]

A sample of pure naphthalene solid is heated steadily from \(20\ ^\circ\text{C}\) until it melts at \(80\ ^\circ\text{C}\) and eventually boils at \(218\ ^\circ\text{C}\).

Which statement describes the naphthalene at \(80\ ^\circ\text{C}\) while it is melting?

Under the same conditions of temperature and pressure, which gas diffuses the fastest?

An ion of element \(X\) contains 16 protons, 18 neutrons and 18 electrons.

What is the correct symbol for this ion?

An oxide of sulfur contains 40.0% sulfur and 60.0% oxygen by mass.

What is the empirical formula of this oxide?

[Relative atomic masses, \(A_{\text{r}}\): \(\text{S} = 32\), \(\text{O} = 16\)]

Consider the following single-displacement reaction:

\(\text{Mg(s)} + \text{Cu}^{2+}\text{(aq)} \rightarrow \text{Mg}^{2+}\text{(aq)} + \text{Cu(s)}\)

Which statement is correct?

Concentrated aqueous sodium chloride (brine) is electrolysed using inert carbon electrodes.

Which row shows the products obtained at the cathode and the anode?

Three metals, \(X\), \(Y\), and \(Z\), are reacted with aqueous solutions of their nitrates. The following observations are recorded:

- Metal \(X\) displaces metal \(Y\) from its salt solution.
- Metal \(X\) does not displace metal \(Z\) from its salt solution.

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

An ester has the structural formula shown below:

\(\text{CH}_3-\text{CO}-\text{O}-\text{CH}_2-\text{CH}_2-\text{CH}_3\)

What is the name of this ester?

A student determines the concentration of a sample of dilute sulfuric acid, \(\text{H}_2\text{SO}_4\), by titrating it with a standard solution of sodium hydroxide, \(\text{NaOH}\).

(a) State the colour change of methyl orange indicator when the end-point is reached as sodium hydroxide is added to the acid in the conical flask.
From ............................................................. to ............................................................. [2]

(b) Describe why a volumetric pipette is preferred over a measuring cylinder to measure the volume of the acid. [1]

(c) The student uses \(25.0\text{ cm}^3\) of the sulfuric acid solution. The titration requires \(18.40\text{ cm}^3\) of \(0.150\text{ mol/dm}^3\) sodium hydroxide solution for complete neutralisation.

(i) Write the balanced chemical equation for the reaction. [2]
(ii) Calculate the number of moles of \(\text{NaOH}\) used in the titration. [1]
(iii) Determine the number of moles of \(\text{H}_2\text{SO}_4\) that reacted. [1]
(iv) Calculate the concentration of the sulfuric acid in \(\text{mol/dm}^3\). [2]
(v) Calculate the concentration of the sulfuric acid in \(\text{g/dm}^3\). (Relative molecular mass, \(M_r\), of \(\text{H}_2\text{SO}_4 = 98.0\)) [2]

(d) Explain why the student must rinse the burette with the sodium hydroxide solution before filling it, rather than just with distilled water. [2]

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

(a) (i) Name the gas produced when zinc blende is heated strongly in air (roasted). [1]
(ii) Write the balanced chemical equation for this roasting reaction. [2]

(b) The zinc oxide formed is then reduced in a furnace using carbon (coke).

(i) Explain why carbon can be used to reduce zinc oxide, with reference to the reactivity series. [1]
(ii) State the two roles of carbon in this furnace. [2]
(iii) Write the balanced chemical equation for the reduction of zinc oxide by carbon monoxide. [2]

(c) Define the term redox in terms of electron transfer. [2]

(d) In the extraction furnace, zinc is produced as a gas and is then condensed.

(i) Explain why zinc is produced as a gas in a furnace operating at \(1000\text{ }^\circ\text{C}\). (Melting point of zinc is \(420\text{ }^\circ\text{C}\), boiling point is \(907\text{ }^\circ\text{C}\).) [1]
(ii) State how zinc is separated from other remaining solid materials in the furnace. [1]
(iii) Suggest why aluminum cannot be extracted from its oxide using carbon. [1]

Alkanes are a homologous series of saturated hydrocarbons.

(a) Describe two characteristics of a homologous series, other than having similar chemical properties. [2]

(b) Explain why alkanes are generally unreactive. [1]

(c) Propane, \(\text{CH}_3\text{CH}_2\text{CH}_3\), reacts with bromine in the presence of ultraviolet (UV) light.

(i) State the name of this type of organic reaction. [1]
(ii) Explain the role of ultraviolet light in this reaction. [1]
(iii) Give the structural formula and state the IUPAC name of the two different monosubstituted organic products that can form when propane reacts with bromine.

• Product 1 structural formula:
Name:
• Product 2 structural formula:
Name: [4]

(d) Define the term structural isomers. [2]

(e) Write the molecular formula of an alkane containing 8 carbon atoms, and state its physical state at room temperature and pressure. [2]

A student prepares a pure, dry sample of the insoluble salt lead(II) sulfate, \(\text{PbSO}_4\), using aqueous lead(II) nitrate, \(\text{Pb(NO}_3)_2\), and aqueous sodium sulfate, \(\text{Na}_2\text{SO}_4\).

(a) (i) Write the ionic equation, including state symbols, for this precipitation reaction. [2]
(ii) Describe the experimental steps the student should take to obtain a pure, dry sample of lead(II) sulfate once the precipitate has formed in the mixture. [3]

(b) The student is provided with an unknown solid, salt W. The student carries out two tests on W and records the observations in the table below.

• Test 1: Add aqueous sodium hydroxide to a solution of W and warm gently. | Observation 1: A gas is evolved which turns damp red litmus paper blue.
• Test 2: Add dilute nitric acid followed by aqueous barium nitrate to a solution of W. | Observation 2: A white precipitate forms.

(i) Identify the gas evolved in Test 1. [1]
(ii) Identify the cation present in W. [1]
(iii) Identify the anion present in W. [1]
(iv) State the chemical formula of salt W. [1]

(c) A different salt, Z, contains chloride ions.

(i) Describe a chemical test to confirm the presence of chloride ions in a solution of Z. [2]
(ii) If salt Z also gives a lilac colour in a flame test, identify salt Z. [2]

Electroplating is used to coat a steel object with a layer of nickel. The apparatus consists of an electrolysis cell with an aqueous solution of nickel(II) sulfate, \(\text{NiSO}_4\).

(a) State the name given to the positive electrode and the negative electrode. [2]

(b) To coat the steel object with nickel:
(i) State which electrode (positive or negative) the steel object must be connected to. [1]
(ii) Name the metal that should be used as the positive electrode. [1]

(c) Write the ionic half-equation for the reaction occurring at the negative electrode during this electroplating process. [2]

(d) State and explain any changes that occur to the concentration of nickel(II) ions in the electrolyte during this electroplating process. [2]

(e) The student replaces the nickel positive electrode with an inert carbon electrode.
(i) State what gas is observed bubbling at this carbon positive electrode. [1]
(ii) Write the half-equation for the reaction occurring at this carbon positive electrode. [2]
(iii) State what change, if any, will now happen to the colour of the blue nickel(II) sulfate solution as the electrolysis continues. Explain your answer. [2]

This question is about gases, their properties, and atmospheric pollutants.

(a) Two gases, methylamine (\(\text{CH}_3\text{NH}_2\), \(M_r = 31\)) and hydrogen bromide (\(\text{HBr}\), \(M_r = 81\)), are released at opposite ends of a long glass tube.

(i) Define the term diffusion. [1]
(ii) Explain, in terms of particles, why gases diffuse. [1]
(iii) State and explain at which position (closer to methylamine, in the middle, or closer to hydrogen bromide) the gases will react to form a white solid. [3]

(b) When a pure solid substance is heated, its temperature rises until it begins to melt. During melting, the temperature remains constant.

(i) Explain why the temperature remains constant during melting, even though thermal energy is still being supplied. [2]
(ii) Describe the difference in both arrangement and motion of particles between the solid state and the liquid state of this substance. [2]

(c) Carbon monoxide and oxides of nitrogen are common pollutants found in car exhaust emissions.

(i) State one adverse effect of carbon monoxide on human health. [1]
(ii) Explain how oxides of nitrogen are formed in car engines, and state one environmental problem caused by them. [3]

A student investigates the rate of reaction between magnesium ribbon and dilute sulfuric acid.

(a) Draw a labelled diagram of the apparatus used to react magnesium ribbon with dilute sulfuric acid, collect the hydrogen gas produced, and measure its volume over time. [3]

(b) State the observation, other than the cessation of bubbling, that shows the reaction is complete if the magnesium ribbon was the limiting reactant. [1]

(c) The rate of reaction decreases as the reaction progresses.
(i) Explain, in terms of collision theory, why the rate of reaction decreases. [2]
(ii) State what happens to the rate of reaction if the temperature of the acid is increased, and explain your answer in terms of particle energy. [2]

(d) The student repeats the experiment using the same mass of magnesium ribbon but cuts it into smaller pieces.
(i) State the effect of this change on the initial rate of reaction. [1]
(ii) State the effect of this change on the final volume of gas produced. [1]

A student determines the concentration of a solution of hydrochloric acid by titrating it against standard sodium hydroxide solution.

(a) The student records the burette readings for two titration experiments:
- In Experiment 1, the initial burette reading is \( 0.5\text{ cm}^3 \) and the final burette reading is \( 23.1\text{ cm}^3 \).
- In Experiment 2, the initial burette reading is \( 1.2\text{ cm}^3 \) and the final burette reading is \( 24.0\text{ cm}^3 \).

Complete the table below to record the burette readings and calculate the volume of sodium hydroxide added in each experiment. [3]

| | Experiment 1 | Experiment 2 |
|---|---|---|
| Final burette reading / \(\text{cm}^3\) | | |
| Initial burette reading / \(\text{cm}^3\) | | |
| Volume of sodium hydroxide added / \(\text{cm}^3\) | | |

(b) Calculate the average volume of sodium hydroxide added from these results. [1]

(c) The titration is performed using methyl orange indicator. State the color change of the indicator at the end-point when adding sodium hydroxide from the burette into the hydrochloric acid in the conical flask. [2]

(d) (i) State why the conical flask is placed on a white tile during the titration. [1]
(ii) State why the conical flask is swirled continuously during the addition of the sodium hydroxide. [1]

(e) The student used a measuring cylinder to measure the volume of hydrochloric acid.
(i) Name a more precise piece of apparatus to measure this volume. [1]
(ii) Explain how using this apparatus improves the accuracy of the experiment. [1]

A student carries out tests on a green hydrated solid salt, **W**.

(a) **Test 1**: A sample of solid **W** is heated in a dry test-tube.
- Observation: Condensation of a colorless liquid forms at the top of the test-tube, and the green solid turns into a black powder.
(i) Name the colorless liquid that condenses. [1]
(ii) Describe a chemical test to confirm the identity of this liquid. [2]

(b) **Test 2**: The remaining black powder from Test 1 is dissolved in dilute sulfuric acid to form a blue-green solution. This solution is divided into two portions.
(i) To the first portion, aqueous sodium hydroxide is added dropwise, then in excess.
- Observation: A green precipitate forms.
State the identity of the cation shown to be present by this test. [1]
(ii) To the second portion, aqueous ammonia is added dropwise, then in excess.
Describe the observations expected. [2]

(c) **Test 3**: A fresh sample of solid **W** is dissolved in distilled water. Dilute nitric acid is added, followed by aqueous silver nitrate.
- Observation: A cream precipitate forms.
(i) State the identity of the anion present in **W**. [1]
(ii) Deduce the chemical formula of anhydrous salt **W**. [1]

(d) Write an ionic equation, including state symbols, for the reaction occurring in Test 3. [2]

Chlorophyll is a green pigment found in plants, which is soluble in organic solvents but insoluble in water.

Design an investigation to extract the pigments from fresh grass leaves and separate them using paper chromatography to show that grass contains more than one colored pigment.

You are provided with: fresh grass leaves, sand, a mortar and pestle, propanone (a liquid organic solvent), chromatography paper, and standard laboratory apparatus.

Your plan should include:
- how to extract a concentrated solution of the pigments from the grass
- how to set up and run the chromatography experiment
- the observations that would show that grass contains more than one pigment
- two safety precautions when handling propanone. [10]