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Practice paper written from an analysis of every
O-Level Science (Chemistry) paper, 2010–2025
Paper 3 Chemistry
FORECAST PAPER · PAPER 3.7
For practice before the 2026 examination
1 hour 15 minutes
Candidates answer on the Question Paper.
No Additional Materials are required.
Write your name, centre number and index number in the boxes above.
You may use an HB pencil for any diagrams, graphs or rough working.
Write in dark blue or black pen.
Do not use staples, paper clips, glue or correction fluid.
The use of an approved scientific calculator is expected, where appropriate.
You may lose marks if you do not show your working or if you do not use appropriate units.
Section A
Answer all questions.
Write your answers in the spaces provided on the question paper.
Section B
Answer one question.
Write your answers in the spaces provided on the question paper.
A copy of the Data Sheet is printed on page 15.
A copy of the Periodic Table is printed on page 16.
The number of marks is given in brackets [ ] at the end of each question or part question.
The total mark for this paper is 65.
Pure water can be obtained from seawater by distillation. Fig. 1.1 shows part of the apparatus.
Complete Fig. 1.1 by drawing a condenser in the dashed box.
Label the point where cold water enters the condenser and the point where it leaves.
State the temperature shown on the thermometer while pure water is distilling over.
Chlorine is added to swimming pool water to kill bacteria. Fig. 2.1 shows incomplete electron shell diagrams of a chlorine atom and of a chloride ion. Each nucleus is labelled with its charge. Each electron is shown as a cross.
Complete the diagram of the chlorine atom in Fig. 2.1 by drawing the electrons in the outer shell.
Complete the diagram of the chloride ion in Fig. 2.1 by drawing the electrons in the outer shell and writing the charge of the ion.
Calcium chloride is also added to pool water, to keep the amount of calcium high enough.
Fig. 2.2 shows electron shell diagrams of four particles, A, B, C and D. The number in each nucleus is its charge.
Identify the particle that is a calcium ion, Ca2+. Use the Periodic Table to help you.
Chlorine has two isotopes, 3517Cl and 3717Cl.
State the number of neutrons in an atom of each isotope.
Three substances are used in the care of a swimming pool: calcium chloride, which keeps the calcium level of the water high enough; chlorine, which kills bacteria; and stainless steel, which is used for the valves of the pool pump.
Complete Table 3.1 by putting a tick (✓) in each box that applies.
A row may have more than one tick.
| statement | calcium chloride | chlorine | stainless steel |
|---|---|---|---|
| It conducts electricity when solid. | |||
| It conducts electricity when molten. | |||
| It is made of simple molecules. |
Explain why calcium chloride conducts electricity when molten but not when solid.
Stainless steel is a metal. State two general physical properties of metals.
The pH of swimming pool water is tested with Universal Indicator. Fig. 4.1 shows the pH scale and the colours of Universal Indicator. Parts of Fig. 4.1 have been left blank.
Complete Fig. 4.1.
Write acidic, neutral or alkaline in each of the three boxes above the scale and write the colour of Universal Indicator at pH 7 in the box below the scale.
A sample of pool water turns Universal Indicator yellow.
Use Fig. 4.1 to suggest the pH of the sample.
The pool owner adds sodium carbonate solution, which is alkaline, to the water. The pH rises.
Describe what happens to the concentration of hydrogen ions in the water.
Pure water is neutral.
State what is meant by a neutral solution in terms of the ions present.
Sodium carbonate powder is added to swimming pool water that is too acidic, to raise its pH.
A student reacts 2.65 g of sodium carbonate powder with excess dilute hydrochloric acid in Fig. 5.1, at 20 °C and again at 40 °C. All other conditions are the same. Table 5.1 shows how the mass of the flask and its contents falls.
| time / s | 0 | 30 | 60 | 90 | 120 | 150 |
|---|---|---|---|---|---|---|
| total mass lost at 20 °C / g | 0.00 | 0.33 | 0.55 | 0.71 | 0.82 | 0.90 |
| total mass lost at 40 °C / g | 0.00 | 0.60 | 0.90 | 1.02 | 1.08 | 1.10 |
The student adds the powder, fits the plug, then starts the stopwatch, so some carbon dioxide escapes before timing starts.
Suggest one improvement to the way the powder is added.
Use Table 5.1 to calculate the average rate of reaction at 40 °C over the first 60 s.
Give the unit of your answer.
Explain why the rate of reaction is higher at 40 °C than at 20 °C.
Use ideas about particles in your answer.
The reaction between sodium carbonate and the acid is exothermic.
State what is meant by the term exothermic.
A desalination plant that supplies water to a swimming pool complex uses a diesel generator. Burning diesel releases pollutants into the air. Table 6.1 shows information about three of them.
| pollutant | formula | source | harmful effect |
|---|---|---|---|
| carbon monoxide | CO | it is toxic: it reduces the amount of oxygen the blood can carry | |
| sulfur dioxide | SO2 | burning fossil fuels that contain sulfur | |
| NO2 | nitrogen and oxygen from the air react at the high temperature inside the engine | it causes breathing difficulties |
Complete Table 6.1.
The generator could be run on bioethanol, a biofuel made by fermenting sugar from sugar cane. Sugar cane takes in carbon dioxide from the air as it grows.
Name the process by which it does this.
Bioethanol releases carbon dioxide when it burns.
Explain why using bioethanol adds very little carbon dioxide to the air overall.
Four dilute solutions, W, X, Y and Z, are made from swimming pool chemicals. Each contains one compound. W is blue; X, Y and Z are colourless. Y is a solution of a sodium compound. The letters are not the chemical symbols. Table 7.1 shows the results of some tests.
| test | W | X | Y | Z |
|---|---|---|---|---|
| add aqueous sodium hydroxide dropwise, then in excess | light blue precipitate, insoluble in excess | white precipitate, insoluble in excess | no change | white precipitate, soluble in excess |
| add aqueous ammonia dropwise, then in excess | light blue precipitate, soluble in excess to give a dark blue solution | no precipitate | no change | white precipitate, insoluble in excess |
| add dilute nitric acid; test any gas formed with limewater | no change | no change | effervescence; limewater turns milky | no change |
| add dilute nitric acid, then aqueous barium nitrate | white precipitate | no precipitate | no precipitate | white precipitate |
| add dilute nitric acid, then aqueous silver nitrate | no precipitate | white precipitate | no precipitate | no precipitate |
Use Table 7.1 to complete Table 7.2 and identify the ions in W, X, Y and Z. You may give the name or the formula of each ion.
| solution | cation present | anion present |
|---|---|---|
| W | ||
| X | ||
| Y | – (not required) | |
| Z |
Write a balanced chemical equation, including state symbols, for any one of the reactions in Table 7.1 that forms a precipitate or a gas.
Hard water contains calcium hydrogencarbonate, Ca(HCO3)2. When hard water is boiled in a pool heater, it forms a hard scale of calcium carbonate.
A technician boils 50.0 cm3 of a sample of hard water until the calcium hydrogencarbonate has all reacted. The carbon dioxide is collected in a gas syringe. Table 8.1 shows the readings.
| time / s | 0 | 60 | 120 | 180 | 240 | 300 | 360 |
|---|---|---|---|---|---|---|---|
| volume of carbon dioxide / cm3 | 0 | 20 | 33 | 42 | 47 | 48 | 48 |
State what is meant by the term relative molecular mass, Mr.
Use Table 8.1 to calculate the amount, in moles, of carbon dioxide formed.
One mole of any gas at room temperature and pressure has a volume of 24 dm3.
Use your answer to (b) and the equation to deduce the amount, in moles, of Ca(HCO3)2 in the 50.0 cm3 sample.
Calculate the concentration of calcium hydrogencarbonate in the sample, in mol / dm3.
Calculate the relative formula mass, Mr, of calcium hydrogencarbonate, Ca(HCO3)2.
Calculate the concentration of calcium hydrogencarbonate in the sample, in g / dm3.
Four students make statements about hydrocarbons and about the plastic used for the caps of water bottles. Table 9.1 shows the statements.
Decide whether each statement in Table 9.1 is correct or incorrect.
Put a tick (✓) in one box in each row.
| statement | correct | incorrect |
|---|---|---|
| 1 Ethene is a saturated hydrocarbon because it has two hydrogen atoms on each carbon atom. | ||
| 2 Ethane and propane are in the same homologous series because they have the same general formula, CnH2n+2. | ||
| 3 Poly(ethene) is made when ethene molecules join together. The polymer still contains C=C double bonds. | ||
| 4 Ethanol, C2H5OH, is a hydrocarbon because it burns to form carbon dioxide and water. |
Write a correct statement to replace each statement that you ticked as incorrect.
Complete Table 9.2.
| homologous series | general formula | name of example | molecular formula of example |
|---|---|---|---|
| alkanes | ethane | C2H6 | |
| alkenes | CnH2n | C3H6 | |
| alcohols | CnH2n+1OH | methanol |
Chlorine is added to the water in swimming pools to kill bacteria. Chlorine is in Group 17 of the Periodic Table.
Fig. 10.1 shows the melting points and boiling points of four elements in Group 17, plotted against the period of each element. The boiling point of iodine has not been plotted. The dashed line shows the temperature of the water in a swimming pool, 28 °C.
Use Fig. 10.1 to deduce the physical state of chlorine, bromine and iodine at the temperature of the pool water.
The boiling point of iodine is 185 °C. Plot this boiling point on Fig. 10.1 with a cross (×). Draw a straight line from the boiling point of bromine to your cross.
Astatine, At, is the element below iodine in Group 17. Use the pattern in Fig. 10.1 to predict the boiling point of astatine.
Aqueous calcium bromide is colourless. Chlorine gas is bubbled into aqueous calcium bromide. State what you would observe.
Astatine, At, is below iodine in Group 17.
Name the most reactive element in Fig. 10.1.
State the number of electrons in the outer shell of an atom of astatine.
Hydrogen fluoride, HF, is a covalent compound formed when hydrogen reacts with fluorine. Draw a 'dot-and-cross' diagram to show the bonding in a molecule of hydrogen fluoride. Show only the outer shell electrons.
Chlorine water is added to colourless aqueous potassium iodide. The solution turns brown. State what this shows about chlorine.
Lead, zinc and calcium can be obtained from their oxides. A technician heats the oxide of each metal with carbon to find out whether the metal can be obtained.
Fig. 11.1 shows the apparatus, which is incomplete. The delivery tube has not been drawn. Table 11.1 shows the results for the three oxides.
| oxide | mass of oxide / g | mass of carbon / g | observations |
|---|---|---|---|
| lead(II) oxide | 2.0 | 0.5 | silvery beads of metal form after gentle heating; a gas is given off quickly |
| zinc oxide | 2.0 | 0.5 | grey metal forms only after very strong heating; a gas is given off slowly |
| calcium oxide | 2.0 | 1.0 | no change; no gas is given off |
Write the name of the contents of the hard-glass tube in box A and the name of the liquid in box B on Fig. 11.1. Lead(II) oxide is being tested.
Complete Fig. 11.1 by drawing the delivery tube so that the gas from the hard-glass tube bubbles through the limewater.
The comparison of the three oxides is not a fair test. Use Table 11.1 to identify the mistake.
Identify the oxide in Table 11.1 that is not reduced by carbon. Explain why.
Carbon dioxide is formed when lead(II) oxide is heated with carbon.
State what you would observe in the limewater when lead(II) oxide is heated with carbon.
Iron is more reactive than lead but less reactive than zinc. Iron(III) oxide is also reduced by carbon. Choose from the list the oxide that needs the strongest heating to be reduced by carbon.
Hydrogen sulfide, H2S, is a gas with the smell of rotten eggs. It is a covalent compound. Draw a 'dot-and-cross' diagram to show the bonding in a molecule of hydrogen sulfide. Show only the outer shell electrons.
The equation for the reaction between lead(II) oxide and carbon is shown.
| aluminium hydroxide | white |
| calcium hydroxide | white |
| copper(II) hydroxide | light blue |
| iron(II) hydroxide | green |
| iron(III) hydroxide | red-brown |
| zinc hydroxide | white |
Group | |||||||||||||||||
1 | 2 |
| 13 | 14 | 15 | 16 | 17 | 18 | |||||||||
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| 1 H hydrogen 1 |
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| 2 He helium 4 | ||
3 Li lithium 7 | 4 Be beryllium 9 |
| proton (atomic) number atomic symbol name relative atomic mass |
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| 5 B boron 11 | 6 C carbon 12 | 7 N nitrogen 14 | 8 O oxygen 16 | 9 F fluorine 19 | 10 Ne neon 20 | ||
11 Na sodium 23 | 12 Mg magnesium 24 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 Al aluminium 27 | 14 Si silicon 28 | 15 P phosphorus 31 | 16 S sulfur 32 | 17 Cl chlorine 35.5 | 18 Ar argon 40 |
19 K potassium 39 | 20 Ca calcium 40 | 21 Sc scandium 45 | 22 Ti titanium 48 | 23 V vanadium 51 | 24 Cr chromium 52 | 25 Mn manganese 55 | 26 Fe iron 56 | 27 Co cobalt 59 | 28 Ni nickel 59 | 29 Cu copper 64 | 30 Zn zinc 65 | 31 Ga gallium 70 | 32 Ge germanium 73 | 33 As arsenic 75 | 34 Se selenium 79 | 35 Br bromine 80 | 36 Kr krypton 84 |
37 Rb rubidium 85 | 38 Sr strontium 88 | 39 Y yttrium 89 | 40 Zr zirconium 91 | 41 Nb niobium 93 | 42 Mo molybdenum 96 | 43 Tc technetium – | 44 Ru ruthenium 101 | 45 Rh rhodium 103 | 46 Pd palladium 106 | 47 Ag silver 108 | 48 Cd cadmium 112 | 49 In indium 115 | 50 Sn tin 119 | 51 Sb antimony 122 | 52 Te tellurium 128 | 53 I iodine 127 | 54 Xe xenon 131 |
55 Cs caesium 133 | 56 Ba barium 137 | 57–71 lanthanoids
| 72 Hf hafnium 178 | 73 Ta tantalum 181 | 74 W tungsten 184 | 75 Re rhenium 186 | 76 Os osmium 190 | 77 Ir iridium 192 | 78 Pt platinum 195 | 79 Au gold 197 | 80 Hg mercury 201 | 81 Tl thallium 204 | 82 Pb lead 207 | 83 Bi bismuth 209 | 84 Po polonium – | 85 At astatine – | 86 Rn radon – |
87 Fr francium – | 88 Ra radium – | 89–103 actinoids
| 104 Rf rutherfordium – | 105 Db dubnium – | 106 Sg seaborgium – | 107 Bh bohrium – | 108 Hs hassium – | 109 Mt meitnerium – | 110 Ds darmstadtium – | 111 Rg roentgenium – | 112 Cn copernicium – | 113 Nh nihonium – | 114 Fl flerovium – | 115 Mc moscovium – | 116 Lv livermorium – | 117 Ts tennessine – | 118 Og oganesson – |
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lanthanoids | 57 La lanthanum 139 | 58 Ce cerium 140 | 59 Pr praseodymium 141 | 60 Nd neodymium 144 | 61 Pm promethium – | 62 Sm samarium 150 | 63 Eu europium 152 | 64 Gd gadolinium 157 | 65 Tb terbium 159 | 66 Dy dysprosium 163 | 67 Ho holmium 165 | 68 Er erbium 167 | 69 Tm thulium 169 | 70 Yb ytterbium 173 | 71 Lu lutetium 175 |
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actinoids | 89 Ac actinium – | 90 Th thorium 232 | 91 Pa protactinium 231 | 92 U uranium 238 | 93 Np neptunium – | 94 Pu plutonium – | 95 Am americium – | 96 Cm curium – | 97 Bk berkelium – | 98 Cf californium – | 99 Es einsteinium – | 100 Fm fermium – | 101 Md mendelevium – | 102 No nobelium – | 103 Lr lawrencium – |
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The volume of one mole of any gas is 24 dm3 at room temperature and pressure (r.t.p.).
The Avogadro constant, L = 6.02 × 1023 mol-1