Free IB Chemistry Practice Exam (SL/HL) with Answers

This free IB Chemistry practice exam follows the 2023 syllabus: Structure 1 to 3 (particles and moles, bonding, periodicity) and Reactivity 1 to 3 (energetics and Gibbs energy, rate and equilibrium, acids, redox and cells). Fifteen Paper 1A-style multiple-choice questions are followed by two Paper 2-style structured questions: the combustion of ethanol by three routes, and a weak-acid titration that runs into Le Châtelier and redox. It targets the usual mark losses: mixing kJ and J in Gibbs energy, forgetting to square in K, limiting reactants and oxidation states.

1. Question 11 mark · Stoichiometry
   A compound contains 52.2% carbon, 13.0% hydrogen and 34.8% oxygen by mass. Using relative atomic masses C = 12.0, H = 1.0 and O = 16.0, what is its empirical formula?
   • A.
     $\mathrm{CH_3O}$
   • B.
     $\mathrm{C_2H_6O}$
   • C.
     $\mathrm{C_2H_4O}$
   • D.
     $\mathrm{C_3H_8O}$
2. Question 21 mark · Stoichiometry
   Calcium carbonate decomposes on heating: $\mathrm{CaCO_3(s) \rightarrow CaO(s) + CO_2(g)}$. What volume of carbon dioxide, measured at STP (273 K and 100 kPa, molar volume $22.7\ \text{dm}^3\,\text{mol}^{-1}$), is produced when 10.0 g of calcium carbonate ($M = 100.1\ \text{g mol}^{-1}$) decomposes completely?
   • A.
     $1.14\ \text{dm}^3$
   • B.
     $2.27\ \text{dm}^3$
   • C.
     $4.54\ \text{dm}^3$
   • D.
     $22.7\ \text{dm}^3$
3. Question 31 mark · Stoichiometry
   Aluminium reacts with chlorine according to $\mathrm{2Al + 3Cl_2 \rightarrow 2AlCl_3}$. 0.40 mol of aluminium is mixed with 0.45 mol of chlorine. What is the maximum amount of aluminium chloride that can form?
   • A.
     0.30 mol
   • B.
     0.40 mol
   • C.
     0.45 mol
   • D.
     0.60 mol
4. Question 41 mark · Atomic structure
   Iron is element 26. What is the electron configuration of the $\mathrm{Fe^{3+}}$ ion?
   • A.
     $[\mathrm{Ar}]\,3d^5$
   • B.
     $[\mathrm{Ar}]\,3d^3\,4s^2$
   • C.
     $[\mathrm{Ar}]\,3d^6\,4s^2$
   • D.
     $[\mathrm{Ar}]\,3d^4\,4s^1$
5. Question 51 mark · Bonding & structure
   Which pair of species both have a bent (V-shaped) molecular geometry?
   • A.
     \mathrm{CO_2}$ and $\mathrm{SO_2}

     LaTeX syntax issue: KaTeX parse error: Can't use function '$' in math mode at position 14: \mathrm{CO_2}$̲ and $\mathrm{S…
   • B.
     \mathrm{H_2O}$ and $\mathrm{NO_2^-}

     LaTeX syntax issue: KaTeX parse error: Can't use function '$' in math mode at position 14: \mathrm{H_2O}$̲ and $\mathrm{N…
   • C.
     \mathrm{BeCl_2}$ and $\mathrm{H_2S}

     LaTeX syntax issue: KaTeX parse error: Can't use function '$' in math mode at position 16: \mathrm{BeCl_2}$̲ and $\mathrm{H…
   • D.
     \mathrm{HCN}$ and $\mathrm{OF_2}

     LaTeX syntax issue: KaTeX parse error: Can't use function '$' in math mode at position 13: \mathrm{HCN}$̲ and $\mathrm{O…
6. Question 61 mark · Bonding & structure
   Which compound has the highest boiling point?
   • A.
     $\mathrm{CH_3CH_2CH_3}$ (propane)
   • B.
     $\mathrm{CH_3OCH_3}$ (methoxymethane)
   • C.
     $\mathrm{CH_3CH_2OH}$ (ethanol)
   • D.
     $\mathrm{CH_3CHO}$ (ethanal)
7. Question 71 mark · Periodicity
   The ions $\mathrm{O^{2-}}$, $\mathrm{F^-}$, $\mathrm{Na^+}$ and $\mathrm{Mg^{2+}}$ all have the electron configuration $1s^2\,2s^2\,2p^6$. Which ion has the largest radius?
   • A.
     $\mathrm{O^{2-}}$
   • B.
     $\mathrm{F^-}$
   • C.
     $\mathrm{Na^+}$
   • D.
     $\mathrm{Mg^{2+}}$
8. Question 81 mark · Organic chemistry
   What is the IUPAC name of the compound $\mathrm{CH_3CH(CH_3)CH_2CHO}$?
   • A.
     2-methylbutanal
   • B.
     3-methylbutanal
   • C.
     2-methylbutan-1-ol
   • D.
     3-methylbutan-2-one
9. Question 91 mark · Energetics
   0.46 g of ethanol ($M = 46\ \text{g mol}^{-1}$) is burned completely and the energy released heats 50.0 g of water by 10.0 K. The specific heat capacity of water is $4.18\ \text{J g}^{-1}\,\text{K}^{-1}$. Assuming no energy losses, what value does this experiment give for the enthalpy of combustion of ethanol?
   • A.
     $-2.09\ \text{kJ mol}^{-1}$
   • B.
     $-20.9\ \text{kJ mol}^{-1}$
   • C.
     $-209\ \text{kJ mol}^{-1}$
   • D.
     $+209\ \text{kJ mol}^{-1}$
10. Question 101 mark · Energetics
    A reaction has $\Delta H = +50\ \text{kJ mol}^{-1}$ and $\Delta S = +100\ \text{J K}^{-1}\,\text{mol}^{-1}$, both independent of temperature. Under which conditions is the reaction spontaneous?
    • A.
      At all temperatures
    • B.
      Only at temperatures below 500 K
    • C.
      Only at temperatures above 500 K
    • D.
      At no temperature
11. Question 111 mark · Kinetics
    Which change alters the shape of the Maxwell–Boltzmann distribution of molecular energies in a gaseous reaction mixture?
    • A.
      Increasing the concentration of a reactant
    • B.
      Adding a catalyst
    • C.
      Increasing the temperature
    • D.
      Increasing the surface area of a solid reactant
12. Question 121 mark · Equilibrium
    At a certain temperature the equilibrium concentrations in the system $\mathrm{H_2(g) + I_2(g) \rightleftharpoons 2HI(g)}$ are $[\mathrm{H_2}] = 0.20$, $[\mathrm{I_2}] = 0.20$ and $[\mathrm{HI}] = 1.6$, all in $\text{mol dm}^{-3}$. What is the value of the equilibrium constant $K$?
    • A.
      0.016
    • B.
      8.0
    • C.
      40
    • D.
      64
13. Question 131 mark · Acids & bases
    What is the pH of a $0.050\ \text{mol dm}^{-3}$ solution of sulfuric acid, assuming it is completely dissociated into $\mathrm{H^+}$ and $\mathrm{SO_4^{2-}}$ ions?
    • A.
      0.70
    • B.
      1.0
    • C.
      1.3
    • D.
      2.0
14. Question 141 mark · Redox & electrochemistry
    Which change represents an oxidation?
    • A.
      $\mathrm{MnO_4^- \rightarrow Mn^{2+}}$
    • B.
      $\mathrm{Cr_2O_7^{2-} \rightarrow Cr^{3+}}$
    • C.
      $\mathrm{SO_2 \rightarrow SO_4^{2-}}$
    • D.
      $\mathrm{NO_3^- \rightarrow NO_2}$
15. Question 151 mark · Redox & electrochemistry
    A voltaic cell is made from a zinc electrode in zinc sulfate solution and a copper electrode in copper(II) sulfate solution, connected by a salt bridge. Zinc is the more reactive metal. Which statement is correct?
    • A.
      The zinc electrode is the cathode and is the site of reduction
    • B.
      Electrons flow from the zinc electrode to the copper electrode through the external circuit
    • C.
      $\mathrm{Cu^{2+}}$ ions are oxidised at the copper electrode
    • D.
      Positive ions from the salt bridge move into the zinc half-cell
16. Question 1610 marks · Energetics
    Ethanol, $\mathrm{C_2H_5OH}$, is used as a fuel. Standard enthalpies of formation, in $\text{kJ mol}^{-1}$: $\mathrm{C_2H_5OH(l)}$ $-278$; $\mathrm{CO_2(g)}$ $-394$; $\mathrm{H_2O(l)}$ $-286$. Average bond enthalpies, in $\text{kJ mol}^{-1}$: C–H 414; C–C 346; C–O 358; O–H 463; O=O 498; C=O (in $\mathrm{CO_2}$) 804.
    (a)

    Write the equation, including state symbols, for the complete combustion of ethanol.

    [1]
    (b)

    Calculate the standard enthalpy of combustion of ethanol using the enthalpies of formation.

    [2]
    (c)

    Calculate the enthalpy of combustion of ethanol using the average bond enthalpies.

    [3]
    (d)

    Suggest why the values obtained in (b) and (c) differ.

    [1]
    (e)

    Predict, giving a reason, the sign of the entropy change $\Delta S$ for the reaction in (a).

    [1]
    (f)

    The standard entropy change for the reaction is $-139\ \text{J K}^{-1}\,\text{mol}^{-1}$. Using your answer to (b), calculate $\Delta G$ at 298 K and deduce whether the reaction is spontaneous.

    [2]
17. Question 1710 marks · Acids & bases
    Ethanoic acid, $\mathrm{CH_3COOH}$, is a weak acid. A student titrates $25.0\ \text{cm}^3$ of $0.100\ \text{mol dm}^{-3}$ ethanoic acid with $0.0500\ \text{mol dm}^{-3}$ sodium hydroxide solution. In a separate experiment, magnesium ribbon is added to a sample of the acid.
    (a)

    Write an equation for the dissociation of ethanoic acid in water and identify one conjugate acid–base pair.

    [2]
    (b)

    Distinguish between a strong acid and a weak acid, and state how the pH of $0.100\ \text{mol dm}^{-3}$ ethanoic acid compares with that of $0.100\ \text{mol dm}^{-3}$ hydrochloric acid.

    [2]
    (c)

    Calculate the volume of sodium hydroxide solution needed to reach the equivalence point of the titration.

    [2]
    (d)

    Sodium ethanoate is dissolved in a solution of ethanoic acid. Predict, using Le Châtelier's principle, the effect on the pH of the solution.

    [2]
    (e)

    Magnesium reacts with the acid: $\mathrm{Mg + 2CH_3COOH \rightarrow (CH_3COO)_2Mg + H_2}$. Deduce the changes in oxidation state that occur and identify the oxidising agent.

    [2]

Finished? Get the answer key with worked solutions