IB Chemistry Practice Test 13
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
Q1How many electrons are there in a ^23Na^+ ion?
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Correct: (A)
Sodium has 11 electrons as an atom; forming Na^+ removes one, leaving 10.
Q2A sample of chlorine contains 75% ^35Cl and 25% ^37Cl. What is the relative atomic mass of chlorine in the sample?
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Correct: (B)
(0.75 × 35) + (0.25 × 37) = 26.25 + 9.25 = 35.5.
Q3What is the ground-state electron configuration of Fe^3+?
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Correct: (C)
Iron is [Ar] 4s^2 3d^6; the 4s electrons are removed first, then one 3d electron, giving [Ar] 3d^5.
Q4A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula?
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Correct: (D)
Moles: C = 40.0/12.0 = 3.33, H = 6.7/1.0 = 6.7, O = 53.3/16.0 = 3.33. Ratio 1:2:1 gives CH2O.
Q5What is the amount, in mol, of 8.8 g of CO2? (Mr CO2 = 44.0)
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Correct: (A)
n = m/Mr = 8.8 / 44.0 = 0.200 mol.
Q6What pressure is exerted by 0.50 mol of an ideal gas in a 10.0 dm^3 container at 300 K? (R = 8.31 J K^-1 mol^-1)
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Correct: (B)
P = nRT/V = (0.50 × 8.31 × 300) / 0.0100 m^3 = 124,650 Pa ≈ 125 kPa.
Q7A 25.0 cm^3 sample of 2.00 mol dm^-3 solution is diluted to a total volume of 250.0 cm^3. What is the new concentration?
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Correct: (C)
c2 = c1V1/V2 = (2.00 × 25.0) / 250.0 = 0.20 mol dm^-3.
Q8How many water molecules are there in 0.250 mol of H2O? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct: (D)
N = 0.250 × 6.02 × 10^23 = 1.51 × 10^23 molecules.
Q9An element has two isotopes, ^79X (51% abundance) and ^81X (49% abundance). Its relative atomic mass is closest to
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Correct: (B)
(0.51 × 79) + (0.49 × 81) = 40.3 + 39.7 = 80.0.
Q10The first four ionisation energies of an element are 578, 1817, 2745 and 11,578 kJ mol^-1. To which group does the element belong?
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Correct: (A)
The large jump after the third ionisation energy shows three valence electrons, so the element is in group 13.
🔗 Structure 2: Models of Bonding & Structure
Q11What is the molecular geometry of NH3?
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Correct: (C)
Nitrogen has three bonding pairs and one lone pair, giving a trigonal pyramidal shape.
Q12What is the H-C-H bond angle in CH4?
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Correct: (D)
Four bonding pairs arrange tetrahedrally, giving bond angles of 109.5°.
Q13Which compound has the greatest lattice energy?
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Correct: (A)
Lattice energy increases with ion charge and decreases with ion size; MgO has 2+/2- charges and a small cation.
Q14Which molecule contains polar bonds but is non-polar overall?
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Correct: (B)
The C-Cl bond dipoles in tetrahedral CCl4 cancel by symmetry, so the molecule is non-polar.
Q15What is the strongest type of intermolecular force between ethanol molecules?
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Correct: (D)
The O-H group in ethanol allows hydrogen bonding between molecules.
Q16How many valence electrons are there in a CO2 molecule?
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Correct: (C)
Carbon contributes 4 and each oxygen contributes 6: 4 + 6 + 6 = 16.
Q17Which allotrope of carbon conducts electricity?
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Correct: (A)
Graphite has delocalised electrons within its layers, allowing electrical conduction.
Q18What is the hybridisation of each carbon atom in ethene, C2H4?
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Correct: (B)
Each carbon has three electron domains in a trigonal planar arrangement, corresponding to sp^2 hybridisation.
Q19How many pi bonds are there in an ethyne molecule, C2H2?
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Correct: (C)
The C≡C triple bond consists of one sigma bond and two pi bonds.
Q20Which statement about ionic compounds is correct?
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Correct: (D)
Strong ionic attractions require much energy to break, and the ions are mobile only when molten or aqueous.
📊 Structure 3: Classification of Matter
Q21Which element has the largest atomic radius in period 3?
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Correct: (B)
Atomic radius decreases across a period as nuclear charge increases; sodium, on the left, is largest.
Q22Which element has the highest first ionisation energy?
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Correct: (A)
Mg = 738, Na = 496, K = 419 and Ca = 590 kJ mol^-1; magnesium has the highest value.
Q23Which property is NOT characteristic of transition metals?
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Correct: (D)
Transition metal ions are often coloured because of their partially filled d subshells.
Q24What is the functional group in ethanoic acid?
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Correct: (C)
Ethanoic acid contains the -COOH carboxyl group.
Q25What is the general formula of the alkenes?
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Correct: (B)
Alkenes have one C=C double bond, giving the general formula CnH2n.
Q26Which compound is an isomer of butane, C4H10?
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Correct: (A)
2-methylpropane also has the formula C4H10 but a different structure, so it is an isomer of butane.
Q27What is the oxidation state of chromium in K2Cr2O7?
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Correct: (D)
2(+1) + 2x + 7(-2) = 0, so 2x = +12 and x = +6.
Q28Which element is the most electronegative?
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Correct: (C)
Fluorine, at the top right of the periodic table, is the most electronegative element.
🔥 Reactivity 1: What Drives Chemical Reactions
Q29What quantity of heat is absorbed when 100 g of water is heated by 5.0°C? (Specific heat capacity of water = 4.18 J g^-1 °C^-1)
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Correct: (D)
q = mcΔT = 100 × 4.18 × 5.0 = 2090 J = 2.09 kJ.
Q30Given: C(s) + O2(g) → CO2(g), ΔH = -393.5 kJ mol^-1, and CO(g) + 1/2 O2(g) → CO2(g), ΔH = -283.0 kJ mol^-1. What is ΔH for C(s) + 1/2 O2(g) → CO(g)?
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Correct: (C)
By Hess's law: -393.5 – (-283.0) = -110.5 kJ mol^-1.
Q31Using bond enthalpies (H-H = 436, Cl-Cl = 242, H-Cl = 431 kJ mol^-1), what is ΔH for H2(g) + Cl2(g) → 2 HCl(g)?
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Correct: (B)
Bonds broken: 436 + 242 = 678; bonds formed: 2 × 431 = 862. ΔH = 678 – 862 = -184 kJ mol^-1.
Q32Which process is endothermic?
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Correct: (A)
Melting requires energy to be absorbed from the surroundings to break forces between water molecules.
Q33Which equation correctly represents the standard enthalpy change of formation of water?
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Correct: (D)
Enthalpy of formation is for one mole of a compound formed from its elements in their standard states.
Q34Which process is accompanied by an increase in the entropy of the system?
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Correct: (C)
Dissolving a solid produces mobile, dispersed aqueous ions, increasing disorder.
Q35A reaction has ΔH = -100 kJ mol^-1 and ΔS = -200 J K^-1 mol^-1. What is ΔG at 298 K?
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Correct: (B)
ΔG = ΔH – TΔS = -100 – (298 × -0.200) = -100 + 59.6 = -40.4 kJ mol^-1.
Q36The enthalpy of combustion of methane is -890 kJ mol^-1. How much heat is released when 0.50 mol of methane burns completely?
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Correct: (A)
0.50 mol × 890 kJ mol^-1 = 445 kJ released.
⏱ Reactivity 2: How Much, How Fast & How Far
Q37Experiments show that doubling [A] doubles the rate of a reaction, while doubling [B] has no effect on the rate. What is the rate law?
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Correct: (A)
The reaction is first order in A and zero order in B, so rate = k[A].
Q38What are the units of the rate constant for a first-order reaction?
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Correct: (D)
For rate = k[A], k = rate/[A], giving units of s^-1.
Q39A first-order reaction has k = 0.0693 min^-1. What is its half-life?
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Correct: (B)
t1/2 = ln 2 / k = 0.693 / 0.0693 = 10.0 min.
Q40On a Maxwell-Boltzmann distribution curve, what happens to the curve when the temperature is increased?
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Correct: (C)
At higher temperature the distribution spreads out: a lower, broader peak shifted to higher energies.
Q41How does a catalyst increase the rate of a reaction?
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Correct: (C)
A catalyst works by offering a different mechanism with a lower activation energy barrier.
Q42What is the equilibrium constant expression for N2(g) + 3 H2(g) ⇌ 2 NH3(g)?
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Correct: (B)
Products are raised to their stoichiometric coefficients and divided by the reactants raised to theirs.
Q43The reaction 2 SO2(g) + O2(g) ⇌ 2 SO3(g) is exothermic and involves fewer gas moles on the product side. Which change increases the equilibrium yield of SO3?
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Correct: (D)
Increasing the pressure shifts the equilibrium towards the side with fewer gas molecules, the products.
Q44For H2(g) + I2(g) ⇌ 2 HI(g), the equilibrium concentrations are [H2] = 0.10, [I2] = 0.10 and [HI] = 0.80 mol dm^-3. What is the value of Kc?
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Correct: (A)
Kc = [HI]^2 / ([H2][I2]) = (0.80)^2 / (0.10 × 0.10) = 0.64 / 0.010 = 64.
Q45At a certain point in a reversible reaction, Q = 1.0 and Kc = 10. In which direction does the net reaction proceed?
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Correct: (B)
Since Q < Kc, the mixture must form more products until Q = Kc.
Q46On an energy profile diagram, the activation energy of the forward reaction is the difference in energy between
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Correct: (C)
Activation energy is the energy barrier from the reactants up to the transition state.
Q47A reaction is zero order with respect to reactant X. What happens to the rate when [X] is doubled?
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Correct: (D)
For a zero-order dependence, rate does not depend on the concentration of X.
Q48What is the effect of adding an inert gas at constant volume to the equilibrium N2O4(g) ⇌ 2 NO2(g)?
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Correct: (A)
At constant volume the concentrations and partial pressures of the reacting gases are unchanged.
⚖ Reactivity 3: Mechanisms of Chemical Change
Q49What is the pH of a 0.010 mol dm^-3 solution of HCl?
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Correct: (B)
HCl is a strong acid, so [H^+] = 0.010 mol dm^-3 and pH = -log(0.010) = 2.00.
Q50What is the conjugate base of HCO3^-?
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Correct: (C)
Removing one H^+ from HCO3^- gives CO3^2-, its conjugate base.
Q51A buffer contains equal concentrations of ethanoic acid (pKa = 4.75) and sodium ethanoate. What is the pH of the buffer?
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Correct: (A)
pH = pKa + log([base]/[acid]) = 4.75 + log(1) = 4.75.
Q52A strong acid is titrated with a weak base. Which statement about the equivalence point is correct?
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Correct: (D)
The conjugate acid in the salt hydrolyses, producing an acidic solution at the equivalence point.
Q53In the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s), which species is the oxidising agent?
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Correct: (D)
Cu^2+ gains electrons (it is reduced), so it causes oxidation and is the oxidising agent.
Q54Given E°(Zn^2+/Zn) = -0.76 V and E°(Cu^2+/Cu) = +0.34 V, what is E°cell for Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s)?
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Correct: (A)
E°cell = E°(cathode) – E°(anode) = +0.34 – (-0.76) = +1.10 V.
Q55What is produced at the cathode during the electrolysis of molten lead(II) bromide, PbBr2?
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Correct: (C)
Pb^2+ ions are reduced at the negative cathode to form lead metal.
Q56According to the Brønsted-Lowry theory, an acid is
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Correct: (B)
A Brønsted-Lowry acid donates a proton (H^+).
Q57What is the pH of a 0.10 mol dm^-3 solution of ethanoic acid? (Ka = 1.8 × 10^-5 mol dm^-3)
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Correct: (A)
[H^+] = sqrt(Ka × c) = sqrt(1.8 × 10^-5 × 0.10) = 1.34 × 10^-3, so pH = 2.87.
Q58What happens when a small amount of strong base is added to an ethanoic acid / ethanoate buffer?
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Correct: (D)
The weak acid component of the buffer removes the added hydroxide ions, keeping the pH nearly constant.
Q59Ethene reacts with bromine to form dibromoethane. What type of reaction is this?
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Correct: (C)
The Br2 adds across the C=C double bond, so it is an addition reaction.
Q60In the reaction of a halogenoalkane with aqueous hydroxide ions, the hydroxide ion behaves as
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Correct: (B)
OH^- donates a lone pair to the carbon bonded to the halogen in a nucleophilic substitution.
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