IGCSE Chemistry 0620/32 October/November 2025 Past Paper with Answers

Question 1

Which element exists as graphite, a soft form of the element that is used as a solid lubricant? Give its symbol.

1. C, carbon, whose graphite form is a lubricant
2. Cl, chlorine, a reactive non-metal gas
3. Ca, calcium, a reactive Group II metal
4. Ne, neon, an unreactive noble gas

Question 2

Every dilute acid in water contains the same positively charged ion. Which element forms this ion? Give its symbol.

1. H, because all dilute acids contain hydrogen ions, $\text{H}^+$
2. O, because all dilute acids contain oxide ions
3. Cl, because all dilute acids contain chloride ions
4. Na, because all dilute acids contain sodium ions

Question 3

One unreactive metal in the Periodic Table does not react with steam. Which metal is this? Give its symbol.

1. Ag, silver, which is unreactive and does not react with steam
2. K, potassium, which reacts violently with water
3. Ca, calcium, which reacts with water and steam
4. Na, sodium, which reacts vigorously with water

Question 4 · Answer A

Step 1: Period 3 elements are in the third row of the Periodic Table. Step 2: Chlorine is in Period 3 and Group VII, so it gains one electron to form a 1- ion. Step 3: Sodium forms a 1+ ion, oxygen is in Period 2, and calcium forms a 2+ ion, so the element is chlorine, Cl.

Question 5 · Answer A

Step 1: In a neutral atom the number of electrons equals the proton number, so there are 36 electrons. Step 2: The number of neutrons = nucleon number - proton number = 84 - 36 = 48. Step 3: So one atom has 36 electrons and 48 neutrons.

Question 6 · Answer A

Step 1: Cooling a gas makes its particles move more slowly and take up less space, so the volume decreases. Step 2: Increasing the pressure squeezes the gas into a smaller space, so the volume also decreases. Step 3: So both decreasing the temperature and increasing the pressure cause the volume to decrease.

Question 7 · Answer A

Step 1: In a liquid the particles are still close together, usually touching, but they are not in a fixed pattern. Step 2: The particles have enough energy to slide over each other and move around in random directions. Step 3: So in liquid krypton the particles are close together and slide over each other.

Question 8 · Answer A

Step 1: All six ions listed are negative ions, so compare their masses in the same 500 cm³ sample. Step 2: Nitrate has the largest mass at 8.5 mg. Step 3: Hydrogencarbonate (6.0 mg), chloride (4.2 mg) and iodide (0.4 mg) are all smaller, so the negative ion with the highest concentration is nitrate.

Question 9 · Answer A

Step 1: The ammonium ion is formed from one nitrogen and four hydrogen atoms and carries a single positive charge. Step 2: Its formula is therefore $\text{NH}_4^+$. Step 3: $\text{NH}_3$ is ammonia (a molecule), and $\text{NO}_3^-$ is the nitrate ion, so the ammonium ion is $\text{NH}_4^+$.

Question 10 · Answer A

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

Question 11 · Answer A

Step 1: The mass of ions is proportional to the volume of water. Step 2: Mass in 200 cm³ = 6.0 × (200 ÷ 500) = 6.0 × 0.40. Step 3: This gives 2.4 mg of hydrogencarbonate ions in 200 cm³.

Question 12 · Answer A

Step 1: Water for practical chemistry must be pure, with dissolved substances removed. Step 2: Distillation boils the water and condenses the pure water vapour, leaving dissolved substances behind. Step 3: Chlorination only kills microbes, filtration only removes insoluble solids and crystallisation makes solid crystals, so the process is distillation.

Question 13 · Answer A

Step 1: Carbon (often as activated charcoal) absorbs dissolved substances that cause unpleasant tastes and smells. Step 2: Passing water through carbon therefore removes bad tastes and odours. Step 3: Killing microbes is done by chlorination and removing large solids is done by filtration, so carbon is used to remove tastes and odours.

Question 14 · Answer A

Step 1: Untreated water can contain harmful microbes such as bacteria. Step 2: Chlorine kills these microbes, making the water safe to drink. Step 3: Removing tastes is done by carbon and removing solids is done by filtration, so chlorination is used to kill microbes.

Question 15 · Answer A

Step 1: Separating coloured substances by letting a solvent carry them up a piece of paper is paper chromatography. Step 2: The substances travel different distances, so they separate into spots. Step 3: Filtration, crystallisation and distillation do not separate dissolved colours up paper, so the method is paper chromatography.

Question 16 · Answer A

Step 1: As the solvent soaks up the paper it reaches a highest level before the paper is removed. Step 2: This highest level reached by the solvent is called the solvent front. Step 3: The base line is where the mixture was placed, and the spots and the solvent surface in the beaker are different, so the solvent front is the highest level reached by the solvent.

Question 17 · Answer A

Step 1: The molecular formula shows the number of each type of atom in one molecule. Step 2: Compound A has 10 carbon, 18 hydrogen and 1 oxygen atom. Step 3: Writing these counts gives $\text{C}_{10}\text{H}_{18}\text{O}$.

Question 18 · Answer A

Step 1: Aqueous bromine is decolourised by a carbon-carbon double bond, which is the feature of an unsaturated molecule. Step 2: Bromine adds across the C=C double bond, so the orange colour disappears. Step 3: Single C-H and C-C bonds and the oxygen atom do not decolourise bromine, so the responsible part is the C=C double bond.

Question 19 · Answer A

Step 1: Multiply each atom count by its relative atomic mass: carbon 10 × 12 = 120, hydrogen 16 × 1 = 16, oxygen 2 × 16 = 32. Step 2: Add the totals: 120 + 16 + 32 = 168. Step 3: So the relative molecular mass of $\text{C}_{10}\text{H}_{16}\text{O}_2$ is 168.

Question 20 · Answer A

Step 1: Fossil fuels are formed from the remains of living things over millions of years. Step 2: Coal (and natural gas) are fossil fuels, like petroleum. Step 3: Hydrogen and ethanol are not fossil fuels and uranium is a nuclear fuel, so coal is the other fossil fuel.

Question 21 · Answer A

Step 1: Fractions collected lower in the column contain larger molecules with longer carbon chains. Step 2: Lubricating oil is collected near the bottom, so it has the longest chains. Step 3: Gasoline, naphtha and kerosene are collected higher up and have shorter chains, so the longest chains are in lubricating oil.

Question 22 · Answer A

Step 1: Volatility describes how easily a substance evaporates; small molecules with low boiling points are the most volatile. Step 2: Gasoline is collected near the top of the column and has the smallest molecules, so it is the most volatile. Step 3: Lubricating oil, fuel oil and diesel oil have larger molecules and lower volatility, so the most volatile fraction is gasoline.

Question 23 · Answer A

Step 1: Fuel oil is a heavy fraction burned to provide heat. Step 2: It is used in home heating systems and to fuel large furnaces and ships. Step 3: Gasoline fuels cars, naphtha is a chemical feedstock and lubricating oil is used for lubrication, so the home-heating fraction is fuel oil.

Question 24 · Answer A

Step 1: Unsaturated hydrocarbons are alkenes, which contain a carbon-carbon double bond and whose names end in -ene. Step 2: Nonene ends in -ene, so it is the alkene and is unsaturated. Step 3: Undecane, dodecane and tridecane all end in -ane and are saturated alkanes, so the unsaturated hydrocarbon is nonene.

Question 25 · Answer A

Step 1: Alkenes are unsaturated and have names ending in -ene and the general formula $\text{C}_n\text{H}_{2n}$. Step 2: Nonene ends in -ene and fits $\text{C}_n\text{H}_{2n}$, so it is an alkene and unsaturated. Step 3: Ending in -ane or having the largest molecules or highest boiling point does not show unsaturation, so the reason is the -ene name and the $\text{C}_n\text{H}_{2n}$ formula.

Question 26 · Answer A

Step 1: Complete combustion of a hydrocarbon in excess oxygen produces carbon dioxide and water. Step 2: The other product, besides carbon dioxide, is therefore water. Step 3: Carbon monoxide and carbon (soot) are products of incomplete combustion, and hydrogen is not a combustion product, so the answer is water.

Question 27 · Answer A

Step 1: Carbon dioxide is a greenhouse gas that traps heat in the atmosphere. Step 2: Increasing its amount increases global warming, which leads to climate change. Step 3: Acid rain is caused mainly by sulfur dioxide, ozone damage is caused by other gases and blood poisoning is caused by carbon monoxide, so the effect of carbon dioxide is increased global warming.

Question 28 · Answer A

Step 1: Ethanol has two carbon atoms and one -OH (hydroxyl) group. Step 2: The displayed formula shows a CH3 group bonded to a CH2 group, and the CH2 group bonded to an O-H group, with every bond drawn as a line. Step 3: A single carbon, a C=C double bond with two OH groups, or no oxygen are all wrong, so the correct structure is CH3-CH2-O-H with all bonds shown.

Question 29 · Answer A

Step 1: Ethanol is made by the catalytic addition of steam to ethene (hydration). Step 2: The conditions used are a temperature of about 300 °C and a pressure of about 60 atm, with a catalyst. Step 3: Oxygen or hydrogen are wrong reactants and the swapped values are wrong conditions, so the answer is steam at 300 °C and 60 atm.

Question 30 · Answer A

Step 1: The group number of a main-group element equals the number of electrons in its outer shell. Step 2: Nitrogen has 5 outer electrons (configuration 2,5), so it is in Group V. Step 3: The number of shells gives the period, and proton or neutron counts do not set the group, so the reason is 5 outer electrons.

Question 31 · Answer A

Step 1: A substance is liquid between its melting point and its boiling point. Step 2: At 650 °C, tellurium is above its melting point (450 °C) but below its boiling point (988 °C). Step 3: So at 650 °C tellurium is a liquid.

Question 32 · Answer A

Step 1: Going down Group VII the halogens get darker and change state. Step 2: Bromine is a red-brown liquid at room temperature and pressure. Step 3: Chlorine is a green gas and iodine is a grey-black solid, so bromine is a red-brown liquid.

Question 33 · Answer A

Step 1: Sodium is a reactive Group I metal and is less dense than water, so it floats and moves on the surface. Step 2: The reaction gives off hydrogen gas, so it fizzes, and the heat released melts the sodium into a ball. Step 3: Sinking with no reaction, turning blue with a brown solid, or no change are all wrong, so the correct observations are floating/moving, fizzing and melting into a ball.

Question 34 · Answer A

Step 1: A reactive metal reacting with water forms a metal hydroxide and hydrogen gas. Step 2: Sodium therefore forms sodium hydroxide and hydrogen. Step 3: Sodium oxide, chloride and carbonate are not formed in this reaction, so the missing product is sodium hydroxide.

Question 35 · Answer A

Step 1: A carbonate reacting with an acid forms a salt, carbon dioxide and water. Step 2: To make sodium sulfate the acid must be sulfuric acid, $\text{H}_2\text{SO}_4$, and the other product is water, $\text{H}_2\text{O}$. Step 3: Hydrochloric acid would not give sulfate, and hydrogen or sulfur dioxide are not products, so the gaps are $\text{H}_2\text{SO}_4$ and $\text{H}_2\text{O}$.

Question 36 · Answer A

Step 1: Thymolphthalein is colourless in neutral and acidic solution. Step 2: Sodium hydroxide dissolves to form an alkali, which turns thymolphthalein blue. Step 3: So the colour change is from colourless to blue.

Question 37 · Answer A

Step 1: A base is a substance that neutralises an acid. Step 2: An alkali is simply a base that is soluble in water. Step 3: An acid, a salt and an indicator are different things, so an alkali is a soluble base.

Question 38 · Answer A

Step 1: Sodium (2,8,1) loses its single outer electron to form $\text{Na}^+$ with configuration 2,8 and a 1+ charge. Step 2: Fluorine (2,7) gains that electron to form $\text{F}^-$ with configuration 2,8 and a 1- charge. Step 3: Both ions end up with the configuration 2,8, the sodium ion 1+ and the fluoride ion 1-.

Question 39 · Answer A

Step 1: Aluminium is found mainly as aluminium oxide in an ore. Step 2: This main ore of aluminium is called bauxite. Step 3: Haematite is an iron ore, limestone is calcium carbonate and cryolite is added to lower the melting point, so the main ore is bauxite.

Question 40 · Answer A

Step 1: Carbon can only remove (reduce) a metal from its ore if the metal is less reactive than carbon. Step 2: Aluminium is above carbon in the reactivity series, so it is more reactive than carbon and carbon cannot reduce it. Step 3: This is why aluminium must be extracted by electrolysis, so the reason is that aluminium is more reactive than carbon.

Question 41 · Answer A

Step 1: Reduction is the loss of oxygen. Step 2: In the equation, $\text{Fe}_2\text{O}_3$ becomes Fe, so the iron(III) oxide has lost its oxygen. Step 3: Because it has lost oxygen, the iron(III) oxide has been reduced.

Question 42 · Answer A

Step 1: An alloy is made by mixing a metal with other elements. Step 2: So an alloy is a mixture of a metal with one or more other elements. Step 3: A pure metal, a metal oxide compound and a dissolved non-metal are not alloys, so an alloy is a mixture of a metal with other elements.

Question 43 · Answer A

Step 1: Rusting is the corrosion of iron in the presence of two substances from the air and surroundings. Step 2: Iron rusts only when both water and oxygen are present. Step 3: Carbon dioxide, nitrogen and hydrogen are not both required, so the two substances are water and oxygen.

Question 44 · Answer A

Step 1: Rust is the product of iron corroding in water and oxygen. Step 2: Its chemical name is hydrated iron(III) oxide. Step 3: Iron(II) chloride, iron(II) sulfate and other compounds are not rust, so the chemical name is hydrated iron(III) oxide.

Question 45 · Answer A

Step 1: The more reactive a metal, the faster the bubbles and the greater the temperature rise with acid. Step 2: Nb shows no reaction (least reactive), Fe reacts very slowly, Mn reacts quickly and Sr reacts most vigorously (most reactive). Step 3: So from least to most reactive the order is Nb, Fe, Mn, Sr.

Question 46 · Answer A

Step 1: A metal reacting with an acid produces a salt and hydrogen gas. Step 2: Strontium with hydrochloric acid gives the salt strontium chloride and hydrogen gas. Step 3: Oxide and water, hydroxide and oxygen, or chlorine are wrong products, so the products are strontium chloride and hydrogen.

Question 47 · Answer A

Step 1: Passing electricity through a molten ionic compound to break it down is called electrolysis. Step 2: The molten magnesium chloride is decomposed into magnesium and chlorine. Step 3: Electroplating coats an object, neutralisation is an acid-base reaction and distillation separates liquids, so the process is electrolysis.

Question 48 · Answer A

Step 1: The electrolyte is the molten or dissolved ionic compound that conducts electricity and is broken down. Step 2: Here that is the molten magnesium chloride. Step 3: The platinum rods are the electrodes, the power supply provides the current and the crucible is the container, so the electrolyte is the molten magnesium chloride.

Question 49 · Answer A

Step 1: At the anode (positive electrode), negative ions are discharged. Step 2: In molten magnesium chloride the negative ions are chloride ions, which form chlorine gas at the anode. Step 3: Magnesium forms at the cathode, and hydrogen and oxygen are not present, so the anode product is chlorine.

Question 50 · Answer A

Step 1: An electrode must carry the current and not take part in the reaction. Step 2: Platinum conducts electricity and is inert (unreactive), so it carries the current without reacting. Step 3: Dissolving, conducting poorly or reacting with the products would make it unsuitable, so the property is that platinum conducts electricity and is inert.

Question 51 · Answer A

Step 1: Electrodes need a material that conducts electricity. Step 2: Carbon, in the form of graphite, is a non-metal that conducts electricity, so it is used as electrodes. Step 3: Sulfur, phosphorus and iodine do not conduct electricity, so the non-metal used is carbon (graphite).

Question 52 · Answer A

Step 1: A chemical change makes new substances, while a physical change does not. Step 2: Electrolysis breaks magnesium chloride into the new substances magnesium and chlorine. Step 3: Because new substances are made, this is a chemical change.

Question 53 · Answer A

Step 1: Aqueous means dissolved in water, so aqueous $\text{MgCl}_2$ is dissolved in water. Step 2: Anhydrous means containing no water, so it is the solid with no water; hydrated means chemically combined with water, so it is the solid that contains water of crystallisation. Step 3: Only the first set matches all three correctly.

Question 54 · Answer A

Step 1: When the reaction is complete, no more gas is made and the total volume stays constant (the curve becomes horizontal). Step 2: Reading the height of the flat (plateau) part of the curve gives the final total volume. Step 3: The curve levels off at 132.5 cm³, so that is the total volume of $\text{H}_2\text{S}$ produced.

Question 55 · Answer A

Step 1: Increasing the concentration of the acid means there are more acid particles in the same volume. Step 2: More frequent collisions make the reaction faster, so it finishes in less time. Step 3: So the time taken for the reaction to finish decreases.

Question 56 · Answer A

Step 1: The acid is in excess, so the amount of sodium sulfide controls how much $\text{H}_2\text{S}$ can be made. Step 2: Changing the concentration of the excess acid changes the rate but not the total amount of product. Step 3: So the total volume of $\text{H}_2\text{S}$ produced does not change.

Question 57 · Answer A

Step 1: If the products are at a lower energy level than the reactants, energy is released to the surroundings. Step 2: A reaction that releases energy is exothermic. Step 3: Because the products are below the reactants in energy, the reaction is exothermic.