IGCSE Chemistry 0620/32 May/June 2025 Past Paper with Answers

Question 1

A list of substances includes aluminium, bromine, magnesium, neon, oxygen and potassium. Which of these is an element that forms an ion with a 2- charge?

1. oxygen, which gains two electrons to form a 2- ion
2. bromine, which gains one electron to form a 1- ion
3. aluminium, which loses three electrons to form a 3+ ion
4. potassium, which loses one electron to form a 1+ ion

Question 2

A list of substances includes carbon dioxide, magnesium oxide, neon, oxygen and sulfur dioxide. Which of these is an ionic compound?

1. magnesium oxide, formed from a metal and a non-metal
2. carbon dioxide, formed from two non-metals
3. sulfur dioxide, formed from two non-metals
4. oxygen, which is an element rather than a compound

Question 3

A list of substances includes calcium, carbon dioxide, iron, neon and oxygen. Which of these is used as a catalyst in the manufacture of ammonia (the Haber process)?

1. iron, which catalyses the Haber process
2. neon, an unreactive noble gas
3. oxygen, a reactive gas in the air
4. carbon dioxide, a waste gas from combustion

Question 4 · Answer A

Step 1: Clean dry air is about 78% nitrogen and 21% oxygen, with small amounts of other gases. Step 2: The gas making up roughly 21% is therefore oxygen. Step 3: Carbon dioxide is about 0.04%, neon is a trace gas and sulfur dioxide is a pollutant, so the answer is oxygen.

Question 5 · Answer A

Step 1: In photosynthesis, plants take in carbon dioxide and water and use light energy to make glucose and oxygen. Step 2: The gas needed (a reactant) is carbon dioxide. Step 3: Oxygen is a product (released), neon is unreactive and sulfur dioxide is a pollutant, so the gas needed for photosynthesis is carbon dioxide.

Question 6 · Answer A

Step 1: In the reactivity series, potassium is near the top and reacts very vigorously. Step 2: Potassium reacts violently even with cold water, more vigorously than calcium, magnesium, aluminium or iron. Step 3: So the most reactive metal in the list is potassium.

Question 7 · Answer A

Step 1: Acidified aqueous potassium manganate(VII) is purple and is decolourised by a reducing gas. Step 2: Sulfur dioxide is a reducing gas, so it turns acidified potassium manganate(VII) from purple to colourless. Step 3: Carbon dioxide (limewater), oxygen (glowing splint) and neon have different or no tests, so the gas tested with potassium manganate(VII) is sulfur dioxide.

Question 8 · Answer A

Step 1: Noble gases are the unreactive elements in Group VIII (Group 0) of the Periodic Table. Step 2: Neon is in Group VIII, so neon is a noble gas. Step 3: Oxygen is a reactive Group VI element, carbon dioxide is a compound and potassium is a metal, so the noble gas is neon.

Question 9 · Answer A

Step 1: Group VII contains the halogens, such as chlorine, bromine and iodine. Step 2: Bromine is a halogen, so it is in Group VII. Step 3: Calcium is in Group II, potassium in Group I and aluminium in Group III, so the Group VII element is bromine.

Question 10 · Answer A

Step 1: The formula $\text{MgSO}_4$ contains a magnesium ion and a sulfate ion, $\text{SO}_4^{2-}$. Step 2: A compound of magnesium with the sulfate ion is named magnesium sulfate. Step 3: Magnesium sulfide would be MgS and magnesium sulfite would be $\text{MgSO}_3$, so $\text{MgSO}_4$ is magnesium sulfate.

Question 11 · Answer A

Step 1: The mass of compounds is proportional to the volume of sea water. Step 2: The mass from 750 cm³ = 12.0 × (750 ÷ 500) = 12.0 × 1.5. Step 3: This gives 18.0 g of compounds from 750 cm³.

Question 12 · Answer A

Step 1: Carbonates react with dilute acids to form a salt, water and carbon dioxide. Step 2: Calcium carbonate is a carbonate, so it reacts with acid to produce carbon dioxide. Step 3: Sodium chloride, magnesium sulfate and potassium bromide are not carbonates, so the compound that produces carbon dioxide is calcium carbonate.

Question 13 · Answer A

Step 1: Halide ions are tested by acidifying with dilute nitric acid and then adding aqueous silver nitrate. Step 2: With bromide ions a cream precipitate of silver bromide forms. Step 3: A white precipitate indicates chloride, a yellow precipitate indicates iodide and limewater tests for carbon dioxide, so the correct test gives a cream precipitate with silver nitrate.

Question 14 · Answer A

Step 1: A calcium atom has 20 electrons arranged 2,8,8,2. Step 2: Losing the two outer electrons leaves 18 electrons arranged 2,8,8. Step 3: Losing two negative electrons leaves the ion with a charge of 2+, so the ion is 2,8,8 with a 2+ charge.

Question 15 · Answer A

Step 1: In a solid the particles are packed closely in a regular arrangement (rows or a lattice). Step 2: They have only enough energy to vibrate about fixed positions, so they cannot move from place to place. Step 3: So the particles in a solid are in a regular arrangement and vibrate about fixed positions.

Question 16 · Answer A

Step 1: Nitrate ions are found in fertilisers (NPK fertilisers contain nitrogen). Step 2: When fertilisers are washed off farmland by rain, the nitrate ions are carried into rivers and the sea. Step 3: Dissolved gases and insoluble rock do not provide nitrate ions, so fertilisers are a correct source.

Question 17 · Answer A

Step 1: The group number of an element equals the number of electrons in its outer shell. Step 2: Phosphorus is in Group V, so a phosphorus atom has 5 electrons in its outer shell. Step 3: The number of shells gives the period (not the group), and neutrons or relative atomic mass do not decide the group, so the reason is that it has 5 outer electrons.

Question 18 · Answer A

Step 1: The proton number is 15, so each atom has 15 protons and (being neutral atoms) 15 electrons. Step 2: Neutrons = mass number − proton number, so phosphorus-31 has 31 − 15 = 16 neutrons and phosphorus-32 has 32 − 15 = 17 neutrons. Step 3: So phosphorus-31 is 15 protons, 16 neutrons, 15 electrons and phosphorus-32 is 15 protons, 17 neutrons, 15 electrons.

Question 19 · Answer A

Step 1: The product $\text{P}_4\text{O}_{10}$ contains 4 phosphorus atoms, so 4 P are needed on the left. Step 2: It contains 10 oxygen atoms; each $\text{O}_2$ has 2 oxygen atoms, so 10 ÷ 2 = 5 molecules of $\text{O}_2$ are needed. Step 3: So the balanced equation is $4\text{P} + 5\text{O}_2 \rightarrow \text{P}_4\text{O}_{10}$.

Question 20 · Answer A

Step 1: Non-metal oxides are generally acidic, while metal oxides are generally basic. Step 2: Phosphorus is a non-metal, so phosphorus(V) oxide is an acidic oxide. Step 3: It is therefore acidic because phosphorus is a non-metal.

Question 21 · Answer A

Step 1: NPK fertilisers contain nitrogen (N), phosphorus (P) and potassium (K). Step 2: The K in NPK stands for potassium. Step 3: Krypton, nickel and platinum are not part of NPK fertilisers, so the other element is potassium.

Question 22 · Answer A

Step 1: Crops take up nutrients such as nitrogen, phosphorus and potassium from the soil as they grow. Step 2: Fertilisers replace these elements, allowing crops to grow better and increasing the yield. Step 3: So farmers use fertilisers to increase crop growth by replacing elements removed from the soil.

Question 23 · Answer A

Step 1: Count the atoms in $\text{Ca}_3(\text{PO}_4)_2$: 3 Ca, 2 P and 8 O. Step 2: Multiply by the $A_r$ values: Ca = 3 × 40 = 120, P = 2 × 31 = 62, O = 8 × 16 = 128. Step 3: Add them: 120 + 62 + 128 = 310, so the relative formula mass is 310.

Question 24 · Answer A

Step 1: A hydrocarbon is a type of organic compound. Step 2: It contains only the two elements hydrogen and carbon. Step 3: Compounds containing oxygen as well, elements, or mixtures do not fit the definition, so a hydrocarbon is a compound of hydrogen and carbon only.

Question 25 · Answer A

Step 1: Petroleum is separated by fractional distillation, which relies on the fractions having different boiling points. Step 2: The petroleum is heated and vaporised, and the fractionating column has a temperature gradient (hot at the bottom, cooler at the top). Step 3: As the vapours rise and cool, each fraction condenses when it reaches its own boiling point, so the correct outline uses fractional distillation and different boiling points.

Question 26 · Answer A

Step 1: Kerosene is a fuel for aircraft, so it is used as jet fuel. Step 2: Bitumen is a thick, tarry fraction used for surfacing and making roads, and gasoline (petrol) is used as fuel for cars. Step 3: So the correct matching is kerosene → jet fuel, bitumen → making roads, gasoline → fuel for cars.

Question 27 · Answer A

Step 1: Ethanol is $\text{C}_2\text{H}_5\text{OH}$: a CH3 group joined to a CH2 group joined to an OH group. Step 2: Every bond is a single covalent bond drawn as a line, including the C-O bond and the O-H bond. Step 3: So the correct displayed formula shows CH3-CH2-O-H with all bonds drawn, including the O-H bond.

Question 28 · Answer A

Step 1: Ethanol is made by the catalytic addition of steam to ethene. Step 2: The conditions are a high temperature (about 300 °C), a high pressure (about 60 atm) and an acid catalyst (phosphoric acid). Step 3: So two correct conditions are a high temperature of about 300 °C and an acid catalyst.

Question 29 · Answer A

Step 1: Tetramethylsilane has one silicon atom bonded to four CH3 groups. Step 2: Four CH3 groups contain 4 carbon atoms and 4 × 3 = 12 hydrogen atoms. Step 3: Adding the one silicon atom gives the molecular formula $\text{SiC}_4\text{H}_{12}$.

Question 30 · Answer A

Step 1: Carbon and silicon are both in Group IV of the Periodic Table, each with 4 outer electrons. Step 2: Hydrogen sits separately at the top and is not in Group IV. Step 3: So the two elements in the same group are silicon and carbon.

Question 31 · Answer A

Step 1: A metal oxide (a base) reacts with an acid to form a salt and water. Step 2: Zinc oxide with sulfuric acid gives the salt zinc sulfate plus water. Step 3: Sulfuric acid gives sulfate salts (not sulfide or chloride), and a metal oxide with acid gives water (not hydrogen), so the products are zinc sulfate + water.

Question 32 · Answer A

Step 1: The excess zinc oxide is an insoluble solid in a solution. Step 2: Filtration separates an insoluble solid from a liquid: the solid stays on the filter paper as residue and the solution passes through as filtrate. Step 3: So the method used to remove the excess solid zinc oxide is filtration.

Question 33 · Answer A

Step 1: The salt solution is heated to evaporate some of the water until it reaches the point of crystallisation (a saturated solution). Step 2: It is then left to cool so that crystals form, and the crystals are filtered off. Step 3: The crystals are dried (for example between filter papers), so the correct method is evaporate to crystallisation point, then filter and dry the crystals.

Question 34 · Answer A

Step 1: The cathode is the electrode connected to the negative terminal of the power supply. Step 2: The electrolyte is the substance that conducts electricity and is broken down, which here is the molten zinc chloride. Step 3: So the cathode is the negative electrode and the electrolyte is the molten zinc chloride.

Question 35 · Answer A

Step 1: An inert electrode must conduct electricity but not react with the electrolyte or its products. Step 2: Graphite (carbon) conducts electricity and is inert, so it is a suitable electrode material (platinum is also used). Step 3: Zinc and sodium would react, and wood does not conduct, so the suitable material is graphite (carbon).

Question 36 · Answer A

Step 1: In molten zinc chloride the ions are $\text{Zn}^{2+}$ and $\text{Cl}^-$. Step 2: Positive metal ions ($\text{Zn}^{2+}$) go to the negative electrode (cathode) and form zinc; negative chloride ions go to the positive electrode (anode) and form chlorine. Step 3: So chlorine forms at the positive electrode and zinc at the negative electrode.

Question 37 · Answer A

Step 1: An ionic bond forms when a metal transfers electrons to a non-metal, making positive and negative ions. Step 2: These oppositely charged ions attract each other by a strong electrostatic force. Step 3: So an ionic bond is the strong electrostatic attraction between oppositely charged ions.

Question 38 · Answer A

Step 1: The more vigorously a metal reacts with acid (more bubbles of hydrogen), the more reactive it is. Step 2: B bubbles most (most reactive), then C, then D, and A produces no bubbles (least reactive). Step 3: So the order from most to least reactive is B, C, D, A.

Question 39 · Answer A

Step 1: A reaction slows when particles collide less often or less successfully. Step 2: Decreasing the temperature gives slower, less frequent collisions, and using larger pieces of metal reduces the surface area for collisions (lowering the concentration would also work). Step 3: So two ways to decrease the rate are lowering the temperature and using larger pieces of metal.

Question 40 · Answer A

Step 1: Flame tests give characteristic colours for different metal ions. Step 2: Potassium ions give a lilac (light purple) flame colour. Step 3: Red is lithium, yellow is sodium and blue-green is copper, so potassium gives a lilac flame.

Question 41 · Answer A

Step 1: A mixture of a metal with one or more other elements (usually metals) is called an alloy. Step 2: Brass is a mixture of two metals, so brass is an alloy. Step 3: A compound has chemically bonded elements, an element is a single substance and an isotope refers to atoms of one element, so the correct name is an alloy.

Question 42 · Answer A

Step 1: Brass is an alloy made from two metals. Step 2: Those two metals are copper and zinc. Step 3: Copper and tin make bronze, iron and carbon make steel and magnesium and aluminium make magnalium, so brass is copper and zinc.

Question 43 · Answer A

Step 1: In an alloy, atoms of different sizes disrupt the regular layers, making it harder for layers to slide. Step 2: This makes magnalium harder and stronger than pure magnesium. Step 3: So the useful property is that magnalium is harder/stronger than pure magnesium.

Question 44 · Answer A

Step 1: A chemical change forms a new substance and is usually hard to reverse. Step 2: Burning methane forms new substances (carbon dioxide and water) and rusting of iron forms a new substance (iron oxide), so both are chemical changes. Step 3: Boiling water, dissolving salt and mixing ink and water are physical changes (no new substance formed), so the two chemical changes are burning methane and rusting of iron.

Question 45 · Answer A

Step 1: A reversible reaction can go forwards and backwards. Step 2: This is shown by a double half-arrow, $\rightleftharpoons$, with one arrow pointing each way. Step 3: A single arrow shows a one-way reaction, an equals sign and a plus sign are not reaction-direction symbols, so the reversible symbol is $\rightleftharpoons$.

Question 46 · Answer A

Step 1: The temperature change is the difference between the final and initial temperatures, ignoring sign. Step 2: Experiment 1 changes by 5, experiment 2 by 2, experiment 3 by 4 and experiment 4 by 10 (29 − 19). Step 3: The largest change is 10 °C, so experiment 4 shows the greatest temperature change.

Question 47 · Answer A

Step 1: In an endothermic reaction, energy is taken in, so the temperature falls. Step 2: Experiments 2 and 3 show falls (2 and 3 fall in temperature); experiment 3 falls the most (18 → 14, a fall of 4 °C). Step 3: So the most endothermic experiment is experiment 3.

Question 48 · Answer A

Step 1: $\text{MgCl}_2$ contains 2 chlorine atoms, so 2 HCl are needed on the left to provide them. Step 2: The 2 HCl provide 2 hydrogen atoms, which form one molecule of hydrogen gas, $\text{H}_2$. Step 3: So the balanced equation is $\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2$.

Question 49 · Answer A

Step 1: A reaction pathway diagram has energy on the vertical axis and progress of reaction on the horizontal axis. Step 2: In an endothermic reaction, energy is taken in, so the products end up at a higher energy than the reactants. Step 3: So the vertical axis is labelled energy, with the reactants on the lower line and the products on the higher line.

Question 50 · Answer A

Step 1: Activated carbon adsorbs substances that cause tastes and odours, so addition of carbon removes tastes and odours. Step 2: Sedimentation lets insoluble solids settle out, removing solids, and chlorination adds chlorine to kill microbes. Step 3: So the correct matching is carbon → tastes/odours, sedimentation → solids, chlorination → microbes.

Question 51 · Answer A

Step 1: A pure substance has a sharp, fixed melting point. Step 2: Pure water melts sharply at exactly 0 °C, so if the sample melts sharply at 0 °C it is pure. Step 3: An impurity lowers the melting point and makes it melt over a range, so impure water melts below 0 °C or over a range, which is how melting point tests purity.

Question 52 · Answer A

Step 1: Sulfur dioxide dissolves in rain water to form an acid, causing acid rain. Step 2: Particulates (small solid particles) can be breathed in and cause respiratory problems (and can cause global dimming). Step 3: So sulfur dioxide causes acid rain and particulates cause respiratory problems.

Question 53 · Answer A

Step 1: Sulfur dioxide is an acidic gas. Step 2: In flue gas desulfurisation, a base such as calcium oxide (or calcium carbonate) reacts with the sulfur dioxide. Step 3: This neutralisation removes the sulfur dioxide from the flue gases, so it is reduced by neutralising the acidic gas with a base such as calcium oxide.