IB Chemistry Practice Test 1
60 original IB Paper 1-style multiple-choice questions with answers & explanations — covering all six themes of the IB Chemistry syllabus (SL & HL).
Note: These are original practice questions written in the IB Paper 1 style — not reproduced IB exam questions. Use them to test your readiness for the real IB Chemistry exam.
📱 How to use: Try each question first, then click “Show Answer” to check. Covers all 6 IB themes: Structure 1 (particulate matter), Structure 2 (bonding & structure), Structure 3 (classification), Reactivity 1 (drivers of reactions), Reactivity 2 (amount, rate & equilibrium), and Reactivity 3 (mechanisms).
⚛ Structure 1: Models of the Particulate Nature of Matter
Q1What is the number of protons, neutrons and electrons in the ion ^31P^3-?
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Correct: (A)
Phosphorus has atomic number 15, so neutrons = 31 – 15 = 16; the 3- charge means 3 extra electrons, giving 15 + 3 = 18 electrons.
Q2What is the ground-state electron configuration of an Fe^2+ ion?
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Correct: (B)
Fe is [Ar] 4s^2 3d^6; on ionisation the 4s electrons are removed first, leaving [Ar] 3d^6.
Q3How many molecules are present in 8.8 g of carbon dioxide, CO2? (Mr of CO2 = 44)
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Correct: (C)
Amount of CO2 = 8.8 / 44 = 0.20 mol; number of molecules = 0.20 × 6.02 × 10^23 = 1.2 × 10^23.
Q4A gas occupies 0.50 dm^3 at 27°C and a pressure of 200 kPa. How many moles of gas are present? (R = 8.31 J K^-1 mol^-1)
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Correct: (D)
n = PV / RT = (2.00 × 10^5 × 5.0 × 10^-4) / (8.31 × 300) = 100 / 2493 ≈ 0.040 mol.
Q5How many moles of sodium hydroxide are present in 25.0 cm^3 of 0.200 mol dm^-3 NaOH(aq)?
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Correct: (A)
n = c × V = 0.200 × (25.0 / 1000) = 0.00500 mol.
Q6A 0.60 g sample of an organic compound contains 0.24 g of carbon, 0.04 g of hydrogen and 0.32 g of oxygen. What is its empirical formula?
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Correct: (B)
Moles C : H : O = (0.24/12) : (0.04/1) : (0.32/16) = 0.020 : 0.040 : 0.020 = 1 : 2 : 1, so the empirical formula is CH2O.
Q7An element X has two isotopes, ^63X (69.0% abundance) and ^65X (31.0% abundance). What is the relative atomic mass of X?
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Correct: (C)
Ar = (63 × 0.690) + (65 × 0.310) = 43.47 + 20.15 = 63.6.
Q8What is the frequency of electromagnetic radiation of wavelength 600 nm? (c = 3.00 × 10^8 m s^-1)
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Correct: (D)
f = c / λ = (3.00 × 10^8) / (6.00 × 10^-7) = 5.00 × 10^14 Hz.
Q9Which sample contains the greatest number of atoms?
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Correct: (C)
Amounts of atoms: H2 gives 1.0 mol of molecules × 2 = 2.0 mol of atoms; O2 gives 0.50 × 2 = 1.0 mol; NH3 gives 1.0 × 4 = 4.0 mol; H2O gives 1.0 × 3 = 3.0 mol. NH3 contains the most atoms.
Q10The theoretical yield of a reaction is 12.0 g and the actual yield obtained is 9.6 g. What is the percentage yield?
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Correct: (B)
Percentage yield = (9.6 / 12.0) × 100 = 80%.
🔗 Structure 2: Models of Bonding & Structure
Q11Which compound contains both ionic and covalent bonds?
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Correct: (C)
K^+ and NO3^- ions are held together ionically, while the N-O bonds within the nitrate ion are covalent.
Q12How many lone pairs of electrons are there on the central atom of a water molecule?
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Correct: (D)
Oxygen has 6 valence electrons; two are used in the two O-H bonds, leaving four electrons as two lone pairs.
Q13What is the molecular geometry of PCl3?
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Correct: (A)
Phosphorus has three bonding pairs and one lone pair, giving a trigonal pyramidal molecular geometry.
Q14Which molecule has the smallest bond angle?
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Correct: (B)
Bond angles are BF3 120°, CH4 109.5°, NH3 107° and H2O 104.5°; the two lone pairs in water compress the angle the most.
Q15Which molecule has a permanent dipole moment?
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Correct: (D)
NH3 is trigonal pyramidal and unsymmetrical, so its bond dipoles do not cancel; CO2, BF3 and CCl4 are symmetrical and nonpolar overall.
Q16Which substance has the highest boiling point?
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Correct: (B)
Water forms an extensive hydrogen-bonded network between its molecules, giving it an anomalously high boiling point for its molar mass.
Q17In diamond, each carbon atom is covalently bonded to how many other carbon atoms?
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Correct: (C)
Each carbon atom is sp^3 hybridised and tetrahedrally bonded to four neighbouring carbons in a giant covalent lattice.
Q18Why does graphite conduct electricity?
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Correct: (B)
The fourth valence electron of each carbon is delocalised within the layer and can carry charge.
Q19What is the hybridisation of the carbon atom in carbon dioxide, CO2?
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Correct: (A)
Carbon has two electron domains (two double bonds) in a linear arrangement, corresponding to sp hybridisation.
Q20How many sigma (σ) and pi (π) bonds are there in one molecule of ethene, C2H4?
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Correct: (B)
Four C-H sigma bonds plus one C-C sigma bond make 5 sigma bonds; the C=C double bond contributes one pi bond.
📊 Structure 3: Classification of Matter
Q21Which element has the largest atomic radius?
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Correct: (D)
All four are in Period 3, and atomic radius decreases across a period as nuclear charge increases, so Na is the largest.
Q22Which element has the highest first ionisation energy?
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Correct: (C)
Ionisation energy generally increases across Period 2, and nitrogen's half-filled 2p subshell gives it a higher value (1402 kJ mol^-1) than oxygen (1314 kJ mol^-1).
Q23Which is a property of transition metals?
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Correct: (D)
Partially filled d orbitals allow d-d transitions that absorb visible light, so transition metal compounds are typically coloured; they also show variable oxidation states.
Q24What is the functional group present in propanoic acid, CH3CH2COOH?
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Correct: (C)
The -COOH group is the carboxyl functional group, characteristic of carboxylic acids.
Q25Which statement about a homologous series is correct?
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Correct: (A)
Members of a homologous series share the same functional group and general formula, and successive members differ by CH2.
Q26The compound CH3CH2CH(OH)CH3 is best described as:
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Correct: (B)
The -OH group is attached to a carbon bonded to two other carbon atoms, so it is a secondary alcohol (butan-2-ol).
Q27Which compound is a structural isomer of butane, C4H10?
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Correct: (B)
2-methylpropane has the same molecular formula, C4H10, but a different carbon skeleton.
Q28An element has the electron configuration 1s^2 2s^2 2p^6 3s^2 3p^4. To which group of the periodic table does it belong?
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Correct: (C)
The element (sulfur) has six valence electrons, placing it in Group 16.
🔥 Reactivity 1: What Drives Chemical Reactions
Q29Which process is exothermic?
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Correct: (C)
Acid-base neutralisation releases heat (ΔH ≈ -57 kJ mol^-1); sublimation, melting and vaporisation all require an input of heat.
Q30In a calorimetry experiment, 100 g of water in a calorimeter increases in temperature by 10.0°C. How much heat is absorbed by the water? (Specific heat capacity of water = 4.18 J g^-1 °C^-1)
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Correct: (A)
q = mcΔT = 100 × 4.18 × 10.0 = 4180 J = 4.18 kJ.
Q31Given: C(s) + O2(g) → CO2(g), ΔH = -394 kJ mol^-1; H2(g) + 1/2 O2(g) → H2O(l), ΔH = -286 kJ mol^-1; CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l), ΔH = -891 kJ mol^-1. What is the enthalpy of formation of methane?
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Correct: (D)
By Hess's law, ΔHf(CH4) = -394 + 2(-286) – (-891) = -394 – 572 + 891 = -75 kJ mol^-1.
Q32Using bond enthalpies (H-H = 436, Cl-Cl = 242 and H-Cl = 431 kJ mol^-1), what is ΔH for the reaction H2(g) + Cl2(g) → 2 HCl(g)?
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Correct: (A)
Bonds broken = 436 + 242 = 678 kJ; bonds formed = 2 × 431 = 862 kJ; ΔH = 678 – 862 = -184 kJ mol^-1.
Q33For which reaction is the entropy change of the system positive?
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Correct: (C)
A gas is produced from a solid, so the disorder of the system increases and ΔS is positive.
Q34A reaction has ΔH = -100 kJ mol^-1 and ΔS = -200 J K^-1 mol^-1. What is the value of ΔG at 300 K?
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Correct: (B)
ΔG = ΔH – TΔS = -100 – 300 × (-0.200) = -100 + 60 = -40 kJ mol^-1.
Q35A reaction takes place in 200 g of water in a calorimeter and the temperature rises by 5.0°C. The reaction uses 0.10 mol of the limiting reactant. What is the enthalpy change of the reaction? (c = 4.18 J g^-1 °C^-1)
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Correct: (D)
q = 200 × 4.18 × 5.0 = 4180 J = 4.18 kJ released; ΔH = -4.18 / 0.10 = -41.8 ≈ -42 kJ mol^-1 (negative because the temperature rose).
Q36The standard enthalpy change of formation of a compound is the enthalpy change when:
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Correct: (A)
This is the definition of the standard enthalpy change of formation, ΔHf°.
⏱ Reactivity 2: How Much, How Fast & How Far
Q37A reaction was studied experimentally. Doubling [A] doubled the rate, and doubling [B] quadrupled the rate. What is the rate law for the reaction?
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Correct: (B)
The reaction is first order in A (rate × 2 when [A] doubles) and second order in B (rate × 4 = 2^2 when [B] doubles).
Q38On a Maxwell-Boltzmann distribution curve, what happens when the temperature of a reacting mixture is increased?
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Correct: (C)
The curve flattens and shifts to the right; the total area stays constant, but more particles have E ≥ Ea, so the rate increases.
Q39A first-order reaction starts with a reactant concentration of 0.80 mol dm^-3. What is the concentration after exactly two half-lives?
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Correct: (D)
The concentration halves each half-life: 0.80 → 0.40 → 0.20 mol dm^-3.
Q40Which statement about a catalyst is correct?
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Correct: (B)
A catalyst provides a different mechanism with a lower activation energy and is regenerated by the end of the reaction.
Q41What is the equilibrium constant expression, Kc, for the reaction N2O4(g) ⇌ 2 NO2(g)?
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Correct: (A)
Kc is the product concentrations raised to their stoichiometric coefficients divided by the reactant concentrations raised to theirs.
Q42Ammonia is manufactured by the reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g), ΔH = -92 kJ mol^-1. Which change will increase the equilibrium yield of ammonia?
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Correct: (D)
The forward reaction is exothermic, so lowering the temperature shifts the equilibrium towards the products; a catalyst affects only the rate, not the yield.
Q43For the equilibrium A(aq) ⇌ B(aq), the initial concentration of A is 0.50 mol dm^-3. At equilibrium, [A] = 0.10 mol dm^-3. What is the value of Kc?
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Correct: (B)
[B] at equilibrium = 0.50 – 0.10 = 0.40 mol dm^-3, so Kc = 0.40 / 0.10 = 4.0.
Q44What are the units of the rate constant, k, for a second-order reaction?
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Correct: (C)
From k = rate / [A]^2 = (mol dm^-3 s^-1) / (mol dm^-3)^2 = mol^-1 dm^3 s^-1.
Q45The half-life of a reaction is found to be the same whatever the initial concentration of the reactant. The reaction must be:
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Correct: (D)
A constant half-life that is independent of concentration is the defining feature of first-order kinetics.
Q46Increasing the concentration of a reactant in solution increases the rate of reaction because:
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Correct: (A)
More particles per unit volume means a greater collision frequency, so more successful collisions occur per unit time.
Q47For a given equilibrium reaction, the value of Kc changes only when:
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Correct: (D)
Kc depends only on temperature; changing concentration, pressure or adding a catalyst changes the position of equilibrium but not Kc.
Q48Carbon monoxide and water react according to the equation CO(g) + H2O(g) ⇌ CO2(g) + H2(g). Initially, [CO] = 1.0 mol dm^-3 and [H2O] = 1.0 mol dm^-3. At equilibrium, [CO2] = 0.60 mol dm^-3. What is the value of Kc?
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Correct: (C)
At equilibrium [CO2] = [H2] = 0.60 and [CO] = [H2O] = 1.0 – 0.60 = 0.40, so Kc = (0.60 × 0.60) / (0.40 × 0.40) = 0.36 / 0.16 = 2.25.
⚖ Reactivity 3: Mechanisms of Chemical Change
Q49What is the pH of 0.010 mol dm^-3 hydrochloric acid?
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Correct: (A)
HCl is a strong acid and fully dissociates, so [H^+] = 0.010 mol dm^-3 and pH = -log(0.010) = 2.00.
Q50What is the pH of 0.100 mol dm^-3 ethanoic acid? (Ka = 1.8 × 10^-5 mol dm^-3)
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Correct: (B)
[H^+] = sqrt(Ka × c) = sqrt(1.8 × 10^-5 × 0.100) = sqrt(1.8 × 10^-6) = 1.34 × 10^-3 mol dm^-3, so pH = 2.87.
Q51A buffer solution contains equal concentrations of ethanoic acid (pKa = 4.76) and sodium ethanoate. What is the pH of the buffer?
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Correct: (D)
pH = pKa + log([salt] / [acid]) = 4.76 + log(1) = 4.76.
Q52What is the conjugate base of HCO3^-?
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Correct: (B)
A conjugate base is formed by removing one H^+; removing H^+ from HCO3^- gives CO3^2-.
Q53What is the oxidation number of sulfur in the sulfate ion, SO4^2-?
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Correct: (C)
Let the oxidation number of S be x: x + 4(-2) = -2, so x = +6.
Q54Lead is obtained by the electrolysis of molten lead(II) bromide. What is formed at the negative electrode (cathode)?
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Correct: (C)
Pb^2+ ions are attracted to the cathode and gain electrons: Pb^2+ + 2e^- → Pb. Bromine forms at the anode.
Q55Ethanoic acid is titrated with sodium hydroxide solution. At the equivalence point, the pH of the solution is:
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Correct: (A)
The ethanoate ions formed hydrolyse in water (CH3COO^- + H2O ⇌ CH3COOH + OH^-), making the solution alkaline at the equivalence point.
Q56In the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s), the oxidising agent is:
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Correct: (D)
Cu^2+ gains electrons and is reduced, so it is the species that oxidises the zinc; Zn is the reducing agent.
Q57Given the standard electrode potentials Zn^2+/Zn = -0.76 V and Cu^2+/Cu = +0.34 V, what is the standard cell potential for the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s)?
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Correct: (A)
E°cell = E°(reduction) – E°(oxidation couple) = 0.34 – (-0.76) = +1.10 V.
Q58Ethene reacts with hydrogen bromide to form:
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Correct: (A)
HBr adds across the C=C double bond by electrophilic addition, giving bromoethane.
Q59Methane reacts with chlorine in ultraviolet light by free-radical substitution. Which step is the initiation step?
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Correct: (D)
Ultraviolet light provides the energy for homolytic fission of the Cl-Cl bond, producing the first chlorine radicals; the other steps are propagation (A, B) and termination (C).
Q60Which halogenoalkane reacts fastest by an SN1 mechanism?
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Correct: (A)
SN1 rate depends on the stability of the carbocation intermediate; 2-bromo-2-methylpropane forms a stable tertiary carbocation.
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