IB Chemistry Practice Test 17
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
Q1Which particles are found in the nucleus of an atom?
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Correct: (A)
The nucleus contains protons and neutrons; electrons occupy the space around the nucleus.
Q2An atom of an element has a mass number of 59 and contains 28 neutrons. What is the atomic number of the element?
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Correct: (B)
Atomic number = mass number – number of neutrons = 59 – 28 = 31.
Q3How many electrons are there in a magnesium ion, Mg^2+? (Atomic number of Mg = 12)
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Correct: (C)
A neutral Mg atom has 12 electrons; forming Mg^2+ removes 2, leaving 12 – 2 = 10 electrons.
Q4What is the electron configuration of an iron atom, Fe? (Atomic number of Fe = 26)
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Correct: (D)
Fe has 26 electrons: 18 in the argon core, then 4s fills before 3d, giving [Ar] 4s^2 3d^6.
Q5How many molecules are present in 0.50 mol of carbon dioxide? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct: (A)
Number of molecules = 0.50 × 6.02 × 10^23 = 3.01 × 10^23.
Q6A compound contains 40.0% carbon, 6.7% hydrogen and 53.3% oxygen by mass. What is its empirical formula?
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Correct: (B)
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, so the empirical formula is CH2O.
Q7What is the mass, in g, of 2.0 mol of sulfur dioxide, SO2? (Mr = 64.07)
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Correct: (C)
Mass = 2.0 × 64.07 = approximately 128 g.
Q8What volume, in dm^3, is occupied by 0.50 mol of an ideal gas at a pressure of 100 kPa and a temperature of 300 K? (R = 8.31 J K^-1 mol^-1)
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Correct: (D)
V = nRT/P = (0.50 × 8.31 × 300)/100 000 = 0.0125 m^3 = 12.5 dm^3.
Q95.85 g of sodium chloride (Mr = 58.5) is dissolved in water and made up to 500 cm^3 of solution. What is the concentration, in mol dm^-3?
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Correct: (B)
Moles of NaCl = 5.85/58.5 = 0.100 mol; concentration = 0.100/0.500 = 0.20 mol dm^-3.
Q10Hydrogen and oxygen react according to the equation 2 H2(g) + O2(g) → 2 H2O(l). What is the maximum amount, in mol, of water that can form from 0.60 mol of H2 and 0.40 mol of O2?
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Correct: (C)
0.60 mol of H2 needs only 0.30 mol of O2, so H2 is limiting and forms 0.60 mol of H2O.
🔗 Structure 2: Models of Bonding & Structure
Q11Which compound contains ionic bonding?
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Correct: (D)
MgO is formed from a metal and a non-metal with transfer of electrons from Mg to O, giving an ionic lattice.
Q12How many lone pairs of electrons are there on the nitrogen atom in ammonia, NH3?
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Correct: (A)
Nitrogen has 5 valence electrons; three are used in N-H bonds, leaving one lone pair.
Q13What is the shape of a methane molecule, CH4?
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Correct: (B)
Four bonding pairs around carbon repel equally, giving a tetrahedral shape with 109.5° angles.
Q14What is the approximate H-N-H bond angle in ammonia, NH3?
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Correct: (C)
The lone pair repels the bonding pairs more strongly, compressing the tetrahedral angle from 109.5° to about 107°.
Q15Which substance has hydrogen bonding between its molecules?
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Correct: (D)
Hydrogen bonding needs H bonded to a highly electronegative atom such as N, O or F; only NH3 qualifies here.
Q16In diamond, each carbon atom is covalently bonded to how many other carbon atoms?
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Correct: (A)
Diamond is a giant covalent structure in which each carbon forms four single bonds in a tetrahedral arrangement.
Q17Metals conduct electricity in the solid state because:
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Correct: (B)
Metallic bonding leaves outer electrons delocalised and mobile, so they can carry charge through the lattice.
Q18Which bond is the most polar?
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Correct: (C)
Fluorine is the most electronegative element, so the difference in electronegativity across the H-F bond is the largest.
Q19Which substance is a giant covalent (network) structure?
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Correct: (A)
In SiO2 the atoms are joined by covalent bonds throughout the whole structure; the others are simple molecular substances.
Q20Which substance has the lowest melting point?
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Correct: (D)
Solid CO2 is a simple molecular substance with weak London dispersion forces between molecules, so very little energy is needed to separate them.
📊 Structure 3: Classification of Matter
Q21Which property generally decreases across Period 3 from sodium to chlorine?
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Correct: (B)
Across a period the nuclear charge increases while the shielding stays similar, so the atoms become smaller; electronegativity and ionisation energy generally increase.
Q22First ionisation energies decrease down Group 1 mainly because:
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Correct: (C)
Down the group the outer electron is in a shell further from the nucleus with more inner shells shielding it, so it is removed more easily.
Q23Which is a typical property of transition elements and their compounds?
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Correct: (D)
Transition metal compounds are typically coloured, show variable oxidation states and often act as catalysts.
Q24What is the oxidation state of copper in the complex ion [Cu(NH3)4]^2+? (NH3 is a neutral ligand)
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Correct: (A)
The ligands are neutral, so the oxidation state of Cu must account for the whole 2+ charge: it is +2.
Q25Which functional group is present in propanoic acid, CH3CH2COOH?
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Correct: (B)
The -COOH group is the carboxyl group, characteristic of carboxylic acids.
Q26Which compound belongs to the same homologous series as C3H6?
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Correct: (C)
C3H6 fits the alkene general formula CnH2n; C4H8 also fits CnH2n, so both are alkenes.
Q27What is the IUPAC name of the compound (CH3)3CH?
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Correct: (D)
The longest chain has 3 carbons with a methyl group on the central carbon: 2-methylpropane.
Q28How many structural isomers are there of C4H10?
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Correct: (A)
Butane has two structural isomers: the straight chain and the branched chain (2-methylpropane).
🔥 Reactivity 1: What Drives Chemical Reactions
Q29In an exothermic reaction:
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Correct: (C)
Exothermic reactions release heat to the surroundings, so the enthalpy of the products is lower and ΔH is negative.
Q30How much energy, in kJ, is needed to raise the temperature of 50.0 g of water by 10.0°C? (Specific heat capacity of water = 4.18 J g^-1 K^-1)
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Correct: (D)
q = mcΔT = 50.0 × 4.18 × 10.0 = 2090 J = 2.09 kJ.
Q31When 0.0500 mol of a fuel is burned, it raises the temperature of 200 g of water by 12.0°C. What is the enthalpy 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)
Heat released = 200 × 4.18 × 12.0 = 10 032 J = 10.0 kJ; per mole = 10.0/0.0500 = 200 kJ, and combustion is exothermic, so ΔH = -200 kJ mol^-1.
Q32Given: C(s) + O2(g) → CO2(g), ΔH = -394 kJ mol^-1; CO(g) + 1/2 O2(g) → CO2(g), ΔH = -283 kJ mol^-1. What is ΔH, in kJ mol^-1, for C(s) + 1/2 O2(g) → CO(g)?
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Correct: (B)
By Hess's law, subtract the second equation from the first: ΔH = -394 – (-283) = -111 kJ mol^-1.
Q33Using bond enthalpies (H-H = 436, Cl-Cl = 242, H-Cl = 431 kJ mol^-1), what is ΔH, in kJ mol^-1, for H2(g) + Cl2(g) → 2 HCl(g)?
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Correct: (C)
Energy to break bonds = 436 + 242 = 678 kJ; energy released forming bonds = 2 × 431 = 862 kJ; ΔH = 678 – 862 = -184 kJ mol^-1.
Q34Using standard enthalpies of formation (CH4 = -75, CO2 = -394, H2O = -286 kJ mol^-1), what is ΔH, in kJ mol^-1, for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (D)
ΔH = [-394 + 2(-286)] – [-75] = -966 + 75 = -891 kJ mol^-1.
Q35Which process is accompanied by an increase in the entropy of the system?
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Correct: (A)
A gas has far more disorder than a liquid, so vaporisation increases entropy; the other processes all decrease disorder.
Q36A reaction has ΔH = -100 kJ mol^-1 and ΔS = -0.200 kJ K^-1 mol^-1. What is ΔG, in kJ mol^-1, at 298 K?
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Correct: (B)
ΔG = ΔH – TΔS = -100 – (298 × -0.200) = -100 + 59.6 = -40.4 kJ mol^-1.
⏱ Reactivity 2: How Much, How Fast & How Far
Q37Increasing the temperature increases the rate of a reaction mainly because:
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Correct: (A)
At higher temperature more particles have at least the activation energy, so a greater fraction of collisions are successful; the activation energy itself does not change.
Q38The reaction A + B → products was studied. Experiment 1: [A] = 0.10, [B] = 0.10, rate = 0.020. Experiment 2: [A] = 0.20, [B] = 0.10, rate = 0.040. Experiment 3: [A] = 0.10, [B] = 0.20, rate = 0.080. (Concentrations in mol dm^-3, rates in mol dm^-3 s^-1.) What is the rate law?
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Correct: (B)
Doubling [A] doubles the rate (first order in A); doubling [B] quadruples the rate (second order in B), so rate = k[A][B]^2.
Q39What are the units of the rate constant, k, for a second-order reaction?
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Correct: (C)
For rate = k[A]^2, k = rate/[A]^2 = (mol dm^-3 s^-1)/(mol dm^-3)^2 = dm^3 mol^-1 s^-1.
Q40Which statement correctly describes the effect of adding a catalyst, shown on a Maxwell-Boltzmann distribution?
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Correct: (D)
A catalyst provides an alternative pathway with a lower activation energy; the distribution of particle energies is unchanged.
Q41A first-order reaction has a half-life of 20 s. What percentage of the reactant remains after 60 s?
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Correct: (D)
60 s is three half-lives: 100% → 50% → 25% → 12.5% remaining.
Q42What is the equilibrium constant expression, Kc, for the reaction N2O4(g) ⇌ 2 NO2(g)?
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Correct: (C)
Kc is the product concentrations raised to their coefficients divided by the reactant concentrations raised to theirs: [NO2]^2/[N2O4].
Q43For the equilibrium H2(g) + I2(g) ⇌ 2 HI(g), Kc = 64. At equilibrium [H2] = 0.10 mol dm^-3 and [I2] = 0.10 mol dm^-3. What is [HI], in mol dm^-3?
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Correct: (B)
Kc = [HI]^2/([H2][I2]), so [HI] = sqrt(64 × 0.10 × 0.10) = sqrt(0.64) = 0.80 mol dm^-3.
Q44For the reaction N2(g) + 3 H2(g) ⇌ 2 NH3(g), ΔH = -92 kJ mol^-1, what happens to the yield of ammonia when the pressure is increased at constant temperature?
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Correct: (A)
The product side has fewer moles of gas (2 compared with 4), so increasing the pressure shifts the equilibrium to the right, increasing the yield; Kc is unaffected by pressure.
Q45Which statement is correct for a system at dynamic equilibrium?
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Correct: (A)
At dynamic equilibrium both reactions continue at equal rates, so the concentrations remain constant (but are not necessarily equal).
Q46A reaction is endothermic in the forward direction. What happens to the value of Kc when the temperature is increased?
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Correct: (B)
For an endothermic reaction, raising the temperature shifts the equilibrium towards the products, so Kc increases.
Q47For a reaction A → products, the half-life is found to be constant at 10 minutes, regardless of the initial concentration of A. What is the order of the reaction with respect to A?
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Correct: (C)
A half-life that is independent of the starting concentration is the characteristic behaviour of a first-order reaction.
Q48What is the equilibrium constant expression, Kc, for CaCO3(s) ⇌ CaO(s) + CO2(g)?
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Correct: (D)
Pure solids are omitted from the equilibrium expression, so Kc = [CO2].
⚖ Reactivity 3: Mechanisms of Chemical Change
Q49What is the pH of a 0.010 mol dm^-3 solution of hydrochloric acid?
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Correct: (B)
HCl is a strong acid and fully dissociates, so [H+] = 0.010 mol dm^-3 and pH = -log(1.0 × 10^-2) = 2.0.
Q50What is the conjugate base of HCO3^-?
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Correct: (A)
A conjugate base is formed by removing one H+; removing H+ from HCO3^- gives CO3^2-.
Q51Which mixture acts as a buffer solution?
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Correct: (D)
A buffer contains a weak acid together with its conjugate base (the salt), which is the ethanoic acid / sodium ethanoate mixture.
Q52What is the pH of a 0.100 mol dm^-3 solution of ethanoic acid? (Ka = 1.8 × 10^-5 mol dm^-3)
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Correct: (C)
[H+] = sqrt(Ka × c) = sqrt(1.8 × 10^-5 × 0.100) = 1.34 × 10^-3, so pH = -log(1.34 × 10^-3) = 2.87.
Q53What is the oxidation state of sulfur in the sulfate ion, SO4^2-?
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Correct: (C)
With four oxygen atoms at -2 each: x + 4(-2) = -2, so x = +6.
Q54Aqueous copper(II) sulfate is electrolysed using inert graphite electrodes. What is the product at the cathode (negative electrode)?
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Correct: (D)
Cu^2+ ions are discharged at the cathode in preference to hydrogen, depositing copper metal.
Q55Given E°(Cu^2+/Cu) = +0.34 V and E°(Zn^2+/Zn) = -0.76 V, what is the standard cell potential, in V, of a voltaic cell made from these two half-cells?
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Correct: (A)
E°cell = E°(more positive) – E°(more negative) = +0.34 – (-0.76) = +1.10 V.
Q56Bromoethane reacts with aqueous sodium hydroxide to form ethanol. In this reaction the hydroxide ion acts as:
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Correct: (B)
OH^- donates a pair of electrons to the carbon atom bonded to Br, so it acts as a nucleophile in a nucleophilic substitution.
Q57Ethene reacts with bromine to form dibromoethane. What is the type of this reaction?
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Correct: (D)
The Br2 molecule acts as an electrophile and adds across the C=C double bond: electrophilic addition.
Q58Propan-1-ol is heated under reflux with acidified potassium dichromate(VI). What is the main organic product?
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Correct: (C)
Under reflux the primary alcohol is fully oxidised to the carboxylic acid, propanoic acid; propanal forms only if it is distilled off as it forms.
Q59Which gas is produced when ethanoic acid reacts with calcium carbonate?
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Correct: (B)
Acids react with carbonates to give a salt, water and carbon dioxide.
Q60Which solution has the lowest pH?
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Correct: (A)
The strong acid is fully dissociated, giving the highest [H+] (pH 1.0); the weak acid is only partially dissociated, ammonia is alkaline and water is neutral.
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