HKDSE Chemistry Paper 1 Section A (MCQ) Practice Paper | 36 questions, 36 marks, 60 minutes

2026-10-30

HKDSE Chemistry Paper 1

HKDSE Chemistry Paper 1 MCQ practice: 36 questions, 36 marks on Microscopic World, acids/bases, redox and organic chemistry, with answers and explanations. Paper 1 is 50% of the subject; this paper practises Section A only.

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Paper details　Level: S6 (HKDSE) | Subject: Chemistry | Time: 60 minutes | Marks: 36 | Questions: 36

Part A: Microscopic World I (atomic structure, Periodic Table, bonding)

Choose the best answer. Each question carries 1 mark.

#	Question	Answer and marking notes
1	Atom X has 17 protons, 18 neutrons and 18 electrons. The ion symbol of X is: A. X⁻ (mass number 35) B. X⁺ (mass number 35) C. X⁻ (mass number 18) D. neutral X (mass number 17)	A — One more electron than proton → 1− charge; mass number = 17 + 18 = 35.
2	Magnesium has three isotopes: ²⁴Mg 79%%, ²⁵Mg 10%%, ²⁶Mg 11%%. Its relative atomic mass is: A. 24.00 B. 24.32 C. 24.50 D. 25.00	B — 24×0.79 + 25×0.10 + 26×0.11 = 24.32.
3	A chlorine atom has the electronic configuration 2, 8, 7. Its position in the Periodic Table is: A. Period 2, Group VII B. Period 3, Group VII C. Period 3, Group II D. Period 7, Group III	B — Three shells → Period 3; seven outer electrons → Group VII.
4	Which pair of substances has the same type of bonding? A. NaCl and CO₂ B. H₂O and CH₄ C. Na and Cl₂ D. MgO and HCl	B — H₂O and CH₄ are both simple covalent molecules; NaCl and MgO are ionic, Na is metallic.
5	Water is polar but methane is not, mainly because: A. water molecules contain hydrogen bonds B. water is asymmetric so the bond dipoles do not cancel C. water molecules are smaller than methane D. oxygen is less electronegative than carbon	B — Polar O—H bonds in a bent molecule give a net dipole; tetrahedral CH₄ cancels out.
6	Solid sodium chloride does not conduct, but the molten salt does, because: A. free electrons are produced on melting B. ions become free to move on melting C. molecules break into atoms on melting D. electrons are shared in the solid	B — Ionic solids conduct by ions: on melting the ions leave the lattice and move.
7	Graphite conducts electricity because: A. each carbon atom has 4 free electrons B. there are delocalised electrons between the layers C. graphite is an ionic compound D. the carbon atoms in graphite carry charge	B — Each carbon uses three electrons for bonding; the fourth is delocalised between layers.
8	Diamond is extremely hard because: A. it is a giant covalent structure B. it is an ionic crystal C. there are strong van der Waals forces between layers D. it contains metallic bonds	A — Each carbon is covalently bonded to four others in a three-dimensional network.
9	From sodium to chlorine across a period, the atomic radius: A. increases B. decreases C. stays the same D. first rises then falls	B — Nuclear charge rises while the shell number stays the same, so the radius decreases.
10	The vigour of the reaction of Group I metals with water: A. decreases down the group B. increases down the group C. does not change D. only potassium reacts	B — From lithium to caesium the outer electron is lost more easily, so the reaction is more vigorous.
11	The relative molecular mass of H₂SO₄ is (H=1.0, S=32.1, O=16.0): A. 49.0 B. 98 C. 80.0 D. 112.0	B — 2×1.0 + 32.1 + 4×16.0 = 98.
12	How many moles of CO₂ are there in 22 g of carbon dioxide? (C=12, O=16) A. 0.25 mol B. 0.50 mol C. 1.0 mol D. 2.0 mol	B — Molar mass 44 g/mol; 22 ÷ 44 = 0.50 mol.

Part B: Acids and bases, redox and chemical energy

Choose the best answer. Each question carries 1 mark.

#	Question	Answer and marking notes
13	The pH of 0.010 mol dm⁻³ hydrochloric acid is: A. 1.0 B. 2.0 C. 12.0 D. 13.0	B — [H⁺] = 0.010 mol dm⁻³, pH = 2.0.
14	What volume of 0.20 mol dm⁻³ HCl exactly neutralises 25.0 cm³ of 0.10 mol dm⁻³ NaOH? A. 6.25 cm³ B. 12.5 cm³ C. 25.0 cm³ D. 50.0 cm³	B — Moles NaOH = 25.0 × 0.10 = 2.50 mmol (1:1); volume = 2.50 ÷ 0.20 = 12.5 cm³.
15	50.0 cm³ of 0.40 mol dm⁻³ NaCl solution is diluted to 250 cm³. The new concentration is: A. 0.040 mol dm⁻³ B. 0.080 mol dm⁻³ C. 0.20 mol dm⁻³ D. 0.40 mol dm⁻³	B — Moles unchanged: 50.0 × 0.40 ÷ 250 = 0.080 mol dm⁻³.
16	The gas from sodium carbonate and dilute hydrochloric acid is passed into limewater. It will: A. turn blue B. turn milky (calcium carbonate precipitate) C. turn yellow D. not change	B — CO₂ is released; CO₂ + Ca(OH)₂ → CaCO₃ (white precipitate) + H₂O.
17	The oxidation number of manganese in KMnO₄ is: A. +4 B. +6 C. +7 D. +2	C — K is +1 and each O is −2: +1 + x + 4(−2) = 0, so x = +7.
18	A current of 0.50 A passes through copper(II) sulphate solution for 1800 s. Mass of copper at the cathode? (Cu=63.5, 1 F=96500 C) A. 0.148 g B. 0.296 g C. 0.592 g D. 1.18 g	B — Q = 0.50 × 1800 = 900 C; n(e⁻) = 900 ÷ 96500 = 0.0093 mol; Cu = 0.0093 ÷ 2 × 63.5 = 0.296 g.
19	0.050 mol of H⁺ is completely neutralised by OH⁻. If the enthalpy of neutralisation is −57 kJ mol⁻¹, the energy released is: A. 0.285 kJ B. 2.85 kJ C. 57 kJ D. 114 kJ	B — Energy = 0.050 × 57 = 2.85 kJ.
20	The enthalpy of combustion of methane is −890 kJ mol⁻¹. Burning 0.25 mol completely releases: A. 111.3 kJ B. 222.5 kJ C. 890 kJ D. 3560 kJ	B — 0.25 × 890 = 222.5 kJ.
21	The effect of a catalyst on a reaction is to: A. raise the energy of the products B. lower the activation energy without changing ΔH C. increase ΔH of the reaction D. increase the number of moles of reactants	B — A catalyst provides a route of lower activation energy; ΔH depends only on the initial and final states.
22	A rise in temperature increases the rate of reaction mainly because: A. molecules become smaller B. a larger fraction of molecules has energy ≥ the activation energy C. the activation energy falls D. the concentration of reactants increases	B — Higher temperature raises the mean kinetic energy, so many more collisions exceed the activation energy.
23	N₂(g) + 3H₂(g) ⇌ 2NH₃(g). When the pressure is increased, the equilibrium: A. shifts right (more NH₃ formed) B. shifts left C. does not shift D. shifts right then left	A — Four moles of gas on the left versus two on the right; higher pressure favours the side with fewer moles.
24	In a redox reaction, an oxidising agent: A. loses electrons and is itself oxidised B. gains electrons and is itself reduced C. donates protons D. acts as a catalyst	B — An oxidising agent oxidises the other species and is itself reduced by gaining electrons.

Part C: Organic chemistry, industrial chemistry and analysis

Choose the best answer. Each question carries 1 mark.

#	Question	Answer and marking notes
25	The general formula of alkanes is: A. CnH2n B. CnH2n+2 C. CnH2n−2 D. CnHn	B — Alkanes are saturated hydrocarbons with only single bonds: CnH2n+2.
26	Ethene is bubbled into bromine in tetrachloromethane. The solution: A. gives a white precipitate B. decolourises because of an addition reaction C. gives off hydrogen D. does not change	B — The C=C bond adds Br₂ to give 1,2-dibromoethane, so the orange colour disappears.
27	When a primary alcohol such as ethanol is oxidised, the products are formed in the order: A. ketone, then alkane B. aldehyde, then carboxylic acid C. ester, then ether D. alkane, then alkene	B — Primary alcohol → aldehyde → carboxylic acid (ethanol → ethanal → ethanoic acid).
28	A carboxylic acid and an alcohol heated with concentrated sulphuric acid give: A. an ester and water B. an aldehyde and water C. an acid anhydride D. a polymer	A — Esterification: RCOOH + R′OH ⇌ RCOOR′ + H₂O.
29	The difference between polyethene and nylon is that: A. both are addition polymerisations B. polyethene is addition (no small molecule lost) while nylon is condensation C. both are condensation polymerisations D. polyethene is a condensation polymerisation	B — Ethene units join by opening the C=C; nylon forms from a diamine and a diacid with loss of water.
30	A compound contains C 40.0%%, H 6.7%% and O 53.3%%. Its empirical formula is: A. CHO B. CH₂O C. C₂H₄O D. C₃H₆O₃	B — Mole ratio 40.0/12 : 6.7/1.008 : 53.3/16 ≈ 1.00 : 2.00 : 1.00 → 1:2:1, i.e. CH₂O.
31	At room temperature and pressure, how many moles are there in 4.8 dm³ of gas? (molar volume 24 dm³ mol⁻¹) A. 0.10 mol B. 0.20 mol C. 0.24 mol D. 2.0 mol	B — 4.8 ÷ 24 = 0.2 mol.
32	The theoretical yield of a reaction is 8.0 g but only 6.4 g is obtained. The percentage yield is: A. 64% B. 80% C. 125% D. 20%	B — 6.4 ÷ 8.0 × 100% = 80%.
33	CaCO₃ → CaO + CO₂. Taking CaO as the desired product, the atom economy is about (CaCO₃=100, CaO=56): A. 44% B. 56% C. 100% D. 28%	B — 56 ÷ 100 × 100% = 56%.
34	Fractional distillation is most suitable for separating: A. miscible liquids with different boiling points B. immiscible liquids C. a solid from a gas D. isotopes	A — Repeated vaporisation and condensation separates miscible liquids by boiling point.
35	An unknown solution gives a white precipitate with silver nitrate solution. It contains: A. Cl⁻ B. SO₄²⁻ C. Na⁺ D. NH₄⁺	A — Ag⁺ + Cl⁻ → AgCl, a white precipitate soluble in aqueous ammonia.
36	Which of the following best follows the principles of green chemistry? A. raising atom economy and reducing waste B. using more solvent C. heating as strongly as possible D. using disposable apparatus	A — Green chemistry centres on atom economy, less waste and lower energy use.

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