IB Chemistry Practice Test 16
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 molecules are there in 22.0 g of carbon dioxide? (Mr CO2 = 44.01; Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct: (C)
n = 22.0 / 44.01 = 0.500 mol. Molecules = 0.500 × 6.02 × 10^23 = 3.01 × 10^23.
Q2What is the ground-state electron configuration of a chromium atom, Cr?
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Correct: (A)
Chromium is an exception to the normal filling order: a half-filled 4s and half-filled 3d set of subshells, [Ar] 4s^1 3d^5, is especially stable.
Q3A sample of 1.00 mol of gas occupies 24.0 dm^3 at a certain temperature. The pressure is doubled at constant temperature. What is the new volume, in dm^3?
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Correct: (D)
At constant temperature pV is constant (Boyle's law), so doubling the pressure halves the volume: 24.0 / 2 = 12.0 dm^3.
Q4What is the percentage by mass of oxygen in calcium carbonate, CaCO3? (Mr CaCO3 = 100.09; Ar O = 16.00)
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Correct: (B)
Mass of O per formula unit = 3 × 16.00 = 48.00. Percentage = (48.00 / 100.09) × 100 = 48.0%.
Q525.0 cm^3 of a 2.00 mol dm^-3 solution is diluted with water to a total volume of 250 cm^3. What is the concentration of the diluted solution, in mol dm^-3?
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Correct: (A)
Amount of solute = 2.00 × 0.0250 = 0.0500 mol. c = 0.0500 / 0.250 = 0.200 mol dm^-3.
Q6The successive ionization energies of an element show a very large increase between the second and third values. To which group of the periodic table does the element belong?
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Correct: (D)
The large jump after the second electron shows that the first two electrons are valence (outer-shell) electrons and the third is a core electron, so the element has 2 valence electrons and is in group 2.
Q7A compound is found to contain 2.40 g of carbon, 0.400 g of hydrogen and 3.20 g of oxygen. What is its empirical formula? (Ar: C = 12.01, H = 1.01, O = 16.00)
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Correct: (C)
Amounts: C = 2.40/12.01 = 0.200 mol, H = 0.400/1.01 = 0.400 mol, O = 3.20/16.00 = 0.200 mol. Ratio 1 : 2 : 1. The empirical formula is the simplest ratio, CH2O (C2H4O2 is a multiple of it, not the empirical formula).
Q8What is the mass, in g, of 0.250 mol of calcium hydroxide, Ca(OH)2? (Mr Ca(OH)2 = 74.09)
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Correct: (B)
m = n × Mr = 0.250 × 74.09 = 18.5 g.
Q9Which sample has the greatest mass? (Molar gas volume at STP = 22.7 dm^3 mol^-1)
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Correct: (D)
Masses: He = 4.0 g; O2 = 16.0 g; CO2 = (11.2/22.7) × 44.01 = 21.7 g; H2O = 2.0 × 18.02 = 36.0 g, which is the greatest.
Q10How many neutrons are there in an atom of chlorine-35, ^35Cl? (Atomic number of Cl = 17)
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Correct: (A)
Neutrons = mass number – atomic number = 35 – 17 = 18.
🔗 Structure 2: Models of Bonding & Structure
Q11Which substance has a giant covalent (network) structure?
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Correct: (B)
In SiO2 every silicon atom is covalently bonded to four oxygen atoms in a continuous three-dimensional network. I2, S8 and ice are molecular solids.
Q12What is the H-C-H bond angle in methane, CH4?
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Correct: (C)
Four bonding pairs arrange themselves tetrahedrally around carbon, giving bond angles of 109.5°.
Q13Which molecule has a lone pair on the central atom and a trigonal pyramidal shape?
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Correct: (A)
Nitrogen in NH3 has 3 bonding pairs and 1 lone pair, so the shape (based on atoms only) is trigonal pyramidal.
Q14Which compound has the highest melting point?
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Correct: (D)
MgO has a giant ionic lattice with 2+ and 2- ions attracting very strongly, giving a much higher melting point than NaCl; water and CO2 are molecular.
Q15What is the hybridization of the carbon atoms in ethyne, C2H2?
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Correct: (C)
Each carbon in ethyne has two electron domains (one C-H bond and one C-C triple bond region), giving linear geometry and sp hybridization.
Q16Which bond is the most polar?
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Correct: (B)
Fluorine is the most electronegative element, so the H-F bond has the largest difference in electronegativity and is the most polar.
Q17Why does graphene conduct electricity?
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Correct: (D)
Each carbon in graphene is bonded to three others, leaving one electron per atom in a delocalized pi system that can carry charge across the sheet.
Q18Which statement about solid sodium chloride is correct?
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Correct: (A)
In the solid the ions are in fixed positions and cannot move. In solution (or when molten) the ions are mobile and can carry charge. NaCl has a high melting point, a giant lattice and is brittle.
Q19A triple bond consists of
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Correct: (B)
The first bond formed between two atoms is a sigma bond; the second and third components of a multiple bond are pi bonds.
Q20Which type of intermolecular force acts between molecules of iodine, I2, in solid iodine?
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Correct: (C)
I2 is a nonpolar molecule, so only temporary-dipole (London dispersion) forces act between its molecules.
📊 Structure 3: Classification of Matter
Q21Which element in period 3 has the largest atomic radius?
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Correct: (D)
Atomic radius decreases across a period as the nuclear charge increases. Sodium, the first element of period 3, has the largest radius.
Q22Which element is classified as a transition element because it forms at least one stable ion with an incompletely filled d subshell?
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Correct: (B)
Fe^2+ has the configuration [Ar] 3d^6, an incompletely filled d subshell. Zn^2+ is 3d^10 (full), and Ca and Al are not d-block elements.
Q23The first ionization energy of aluminium is lower than that of magnesium, even though aluminium has a greater nuclear charge. This is mainly because
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Correct: (A)
In Al the outer electron is in the 3p subshell, which is higher in energy and more shielded than the 3s subshell of Mg, so it is removed more easily despite the extra proton.
Q24Successive members of a homologous series differ by which group?
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Correct: (C)
Members of a homologous series have the same functional group and general formula, and each successive member differs by a CH2 unit.
Q25What is the functional group in propanal, CH3CH2CHO?
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Correct: (A)
The -CHO group at the end of the chain is the aldehyde functional group.
Q26Which oxide reacts with water to give an acidic solution?
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Correct: (D)
SO2 is a non-metal oxide and dissolves in water to form an acidic solution (sulfurous acid). Na2O and MgO are basic oxides; Al2O3 is amphoteric and insoluble.
Q27The blue colour of an aqueous solution of Cu^2+ ions is caused by
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Correct: (B)
Ligands split the d orbitals into two energy levels; visible light promotes electrons between them, and the complementary colour is seen.
Q28But-1-ene, CH3CH2CH=CH2, belongs to which homologous series?
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Correct: (C)
The molecule contains a C=C double bond and fits the alkene general formula CnH2n, so it is an alkene.
🔥 Reactivity 1: What Drives Chemical Reactions
Q290.100 mol of a fuel is burned in a calorimeter and heats 200 g of water by 30.0°C. What is the enthalpy change of combustion of the fuel, in kJ mol^-1? (Specific heat capacity of water = 4.18 J g^-1 K^-1)
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Correct: (A)
q = mcΔT = 200 × 4.18 × 30.0 = 25 080 J = 25.1 kJ. ΔHc = -25.1 / 0.100 = -251 kJ mol^-1.
Q30Using standard enthalpies of formation (CH4(g) = -75, CO2(g) = -394, H2O(l) = -286 kJ mol^-1), what is the enthalpy change for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (C)
ΔH = sum of ΔHf(products) – sum of ΔHf(reactants) = [-394 + 2(-286)] – [-75 + 0] = -966 + 75 = -891 kJ mol^-1.
Q31Using average bond enthalpies (N#N triple bond = 945, H-H = 436, N-H = 391 kJ mol^-1), what is the estimated enthalpy change for N2(g) + 3 H2(g) → 2 NH3(g)?
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Correct: (B)
Bonds broken: 945 + 3(436) = 2253 kJ. Bonds formed: 6 N-H bonds = 6 × 391 = 2346 kJ. ΔH = 2253 – 2346 = -93 kJ mol^-1.
Q32A reaction has ΔH = +50 kJ mol^-1 and ΔS = +0.200 kJ K^-1 mol^-1. What is ΔG, in kJ mol^-1, at 300 K?
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Correct: (D)
ΔG = ΔH – TΔS = 50 – (300 × 0.200) = 50 – 60 = -10 kJ mol^-1, so the reaction is spontaneous at 300 K.
Q33For the reaction 2 NH3(g) → N2(g) + 3 H2(g), the entropy change of the system is
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Correct: (C)
The number of moles of gas increases from 2 to 4, so the system becomes more disordered and ΔS is positive.
Q3450.0 cm^3 of 1.00 mol dm^-3 HCl is mixed with 50.0 cm^3 of 1.00 mol dm^-3 NaOH in a calorimeter. The temperature rises by 6.50°C. What is the enthalpy change of neutralization, in kJ mol^-1? (Total mass of solution = 100 g; specific heat capacity = 4.18 J g^-1 K^-1)
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Correct: (A)
q = 100 × 4.18 × 6.50 = 2717 J. Amount of water formed = 1.00 × 0.0500 = 0.0500 mol. ΔH = -2717 / 0.0500 = -54.3 kJ mol^-1.
Q35Why do enthalpy changes calculated from average bond enthalpies usually differ from experimentally measured values?
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Correct: (D)
A given bond (e.g. C-H) has slightly different strengths in different molecules, so tabulated values are averages and the calculated ΔH is only an estimate.
Q36The lattice enthalpy of an ionic compound is the enthalpy change when one mole of the solid is formed from
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Correct: (B)
Lattice enthalpy is defined for the process MX(s) formation from separate gaseous ions: M^+(g) + X^-(g) → MX(s).
⏱ Reactivity 2: How Much, How Fast & How Far
Q37What are the units of the rate constant k for a zero-order reaction?
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Correct: (C)
For a zero-order reaction, rate = k, so k has the same units as rate: mol dm^-3 s^-1.
Q38A reaction is first order with respect to A and zero order with respect to B. What is the rate law?
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Correct: (A)
Zero order in B means [B] does not appear in the rate law, so rate = k[A]^1 = k[A].
Q39The equilibrium constant for a reaction at a given temperature is Kc = 1.0 × 10^-10. Which statement is correct?
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Correct: (D)
A very small K means the equilibrium mixture contains mainly reactants; the forward reaction is far from complete.
Q40For the equilibrium 2 SO2(g) + O2(g) ⇌ 2 SO3(g), ΔH = -197 kJ mol^-1. Which change will increase the equilibrium yield of SO3?
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Correct: (B)
The forward reaction is exothermic, so lowering the temperature shifts the equilibrium towards the products. (A catalyst speeds up both reactions equally and does not change the yield.)
Q41For the equilibrium CO(g) + H2O(g) ⇌ CO2(g) + H2(g), the equilibrium concentrations are [CO] = [H2O] = 0.20 mol dm^-3 and [CO2] = [H2] = 0.40 mol dm^-3. What is the value of Kc?
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Correct: (A)
Kc = ([CO2][H2]) / ([CO][H2O]) = (0.40 × 0.40) / (0.20 × 0.20) = 0.16 / 0.040 = 4.0.
Q42How does adding a catalyst increase the rate of a reaction, in terms of the Maxwell-Boltzmann distribution?
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Correct: (C)
The distribution of molecular energies is unchanged, but the activation energy is lower, so a greater proportion of molecules have energy equal to or greater than Ea.
Q43For a second-order reaction, the half-life
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Correct: (D)
For second order, t1/2 = 1 / (k[A]0), so a higher initial concentration gives a shorter half-life. (Constant half-life and ln 2 / k apply to first-order reactions.)
Q44In an initial-rates experiment, the concentration of one reactant is doubled while others are kept constant, and the rate increases by a factor of four. The order with respect to that reactant is
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Correct: (B)
Rate multiplied by 4 = 2^2 when concentration is multiplied by 2, so the reaction is second order in that reactant.
Q45Which statement about a system in dynamic equilibrium is correct?
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Correct: (B)
In dynamic equilibrium both reactions continue at equal rates, so the macroscopic concentrations stay constant (though they are not necessarily equal).
Q46For the equilibrium N2(g) + 3 H2(g) ⇌ 2 NH3(g), how are Kp and Kc related? (Δn = change in moles of gas = -2)
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Correct: (D)
Kp = Kc(RT)^Δn, and Δn = 2 – 4 = -2, so Kp = Kc(RT)^-2.
Q47For a reaction mixture, the reaction quotient Q is less than the equilibrium constant K. The net reaction will proceed
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Correct: (A)
If Q < K there are too few products relative to equilibrium, so the net reaction moves forwards, towards the products, until Q = K.
Q48Why does raising the temperature increase the rate of a reaction, according to collision theory?
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Correct: (C)
Temperature does not change Ea or ΔH. The main effect is that many more molecules have kinetic energy at or above the activation energy, so far more collisions are successful.
⚖ Reactivity 3: Mechanisms of Chemical Change
Q49What is the pH of a 0.00100 mol dm^-3 solution of hydrochloric acid?
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Correct: (D)
HCl is a strong acid and dissociates completely, so [H^+] = 1.00 × 10^-3 mol dm^-3 and pH = -log(1.00 × 10^-3) = 3.00.
Q50Ammonia is a weak base with Kb = 1.8 × 10^-5. What is the Ka of its conjugate acid, NH4^+? (Kw = 1.0 × 10^-14)
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Correct: (B)
Ka × Kb = Kw, so Ka = Kw / Kb = (1.0 × 10^-14) / (1.8 × 10^-5) = 5.6 × 10^-10.
Q51A buffer solution contains 0.200 mol dm^-3 ethanoic acid and 0.100 mol dm^-3 sodium ethanoate. The pKa of ethanoic acid is 4.74. What is the pH of the buffer?
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Correct: (A)
pH = pKa + log([salt]/[acid]) = 4.74 + log(0.100/0.200) = 4.74 + log(0.5) = 4.74 – 0.30 = 4.44.
Q52What is the oxidation number of chromium in the dichromate ion, Cr2O7^2-?
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Correct: (C)
Let the oxidation number of Cr be x. 2x + 7(-2) = -2, so 2x = +12 and x = +6.
Q53Standard electrode potentials: E°(Zn^2+/Zn) = -0.76 V, E°(Fe^2+/Fe) = -0.44 V, E°(Cu^2+/Cu) = +0.34 V, E°(Ag^+/Ag) = +0.80 V. Which metal is the strongest reducing agent?
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Correct: (B)
The metal with the most negative E° is oxidized most easily, so zinc is the strongest reducing agent.
Q54A current of 2.00 A is passed through silver nitrate solution for 30.0 minutes during electrolysis (cathode reaction: Ag^+ + e^- → Ag). What mass of silver is deposited? (Faraday constant = 96 500 C mol^-1; Ar Ag = 107.87)
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Correct: (D)
Q = It = 2.00 × (30.0 × 60) = 3600 C. Moles of electrons = 3600 / 96 500 = 0.0373 mol, so 0.0373 mol of Ag forms. Mass = 0.0373 × 107.87 = 4.02 g.
Q55Methane reacts with chlorine in ultraviolet light by free-radical substitution. The initiation step involves
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Correct: (A)
UV light provides energy for homolytic fission: Cl2 → 2 Cl•, producing the free radicals that start the chain reaction.
Q56What is the major product of the reaction between propene and hydrogen bromide?
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Correct: (C)
By Markovnikov's rule for electrophilic addition to an unsymmetrical alkene, the hydrogen adds to the carbon that already has more hydrogen atoms, so the bromine ends up on the middle carbon, giving 2-bromopropane.
Q57Three weak acids have the following Ka values: HX = 3.5 × 10^-4, HY = 1.8 × 10^-5, HZ = 7.0 × 10^-3. Which is the strongest acid?
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Correct: (A)
The larger the Ka value, the greater the extent of dissociation and the stronger the acid. HZ has the largest Ka.
Q58What is the pH of a 0.0100 mol dm^-3 solution of potassium hydroxide, a strong base?
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Correct: (D)
KOH dissociates completely, so [OH^-] = 0.0100 mol dm^-3. pOH = -log(0.0100) = 2.00, so pH = 14.00 – 2.00 = 12.00.
Q59A weak acid is titrated with a strong base. The pH at the equivalence point is
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Correct: (C)
At the equivalence point the solution contains the conjugate base of the weak acid, which hydrolyses to produce OH^- ions, so the pH is greater than 7.
Q60In the reaction CuO(s) + H2(g) → Cu(s) + H2O(l), which species is reduced?
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Correct: (B)
The oxidation number of copper falls from +2 in CuO to 0 in Cu, so copper(II) oxide is reduced. (H2 is oxidized.)
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