IB Chemistry Practice Test 14
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 electron configuration of Mg^2+?
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Correct: (B)
Mg (Z = 12) loses its two 3s electrons, leaving 1s^2 2s^2 2p^6, the neon configuration.
Q2How many neutrons are there in an atom of ^37Cl?
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Correct: (C)
Neutrons = mass number – atomic number = 37 – 17 = 20.
Q3What is the amount, in mol, of oxygen atoms in 0.50 mol of CO2?
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Correct: (D)
Each CO2 molecule has two oxygen atoms: 0.50 × 2 = 1.00 mol of O atoms.
Q4What is the volume of 1.0 mol of an ideal gas at STP (273 K and 100 kPa)? (R = 8.31 J K^-1 mol^-1)
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Correct: (A)
V = nRT/P = (1.0 × 8.31 × 273) / 100,000 = 0.0227 m^3 = 22.7 dm^3.
Q5What is the percentage by mass of oxygen in H2O? (Ar: H = 1.0, O = 16.0)
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Correct: (B)
Mr(H2O) = 18.0; %O = 16.0 / 18.0 × 100 = 88.9%.
Q60.250 mol of a solute is dissolved in water to make 500 cm^3 of solution. What is the concentration?
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Correct: (D)
c = n/V = 0.250 / 0.500 = 0.500 mol dm^-3.
Q7How many molecules are there in 2.00 mol of NH3? (Avogadro constant = 6.02 × 10^23 mol^-1)
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Correct: (A)
N = 2.00 × 6.02 × 10^23 = 1.20 × 10^24 molecules.
Q8A gas is held in a sealed rigid container. What happens to its pressure when the temperature is doubled from 300 K to 600 K?
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Correct: (C)
At constant volume P is proportional to T, so doubling T doubles the pressure.
Q9The photoelectron spectrum of an element shows peaks corresponding to 2, 2, 6 and 2 electrons in successive subshells. The element is
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Correct: (D)
Total electrons = 2 + 2 + 6 + 2 = 12, which is magnesium.
Q10A compound is analysed and found to contain 0.30 mol C, 0.60 mol H and 0.30 mol O. What is its empirical formula?
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Correct: (B)
Dividing by 0.30 gives the ratio C:H:O = 1:2:1, so the empirical formula is CH2O.
🔗 Structure 2: Models of Bonding & Structure
Q11Which statement best describes ionic bonding?
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Correct: (A)
Ionic bonding involves electron transfer from a metal to a non-metal and attraction between the resulting ions.
Q12What is the molecular geometry of BF3?
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Correct: (D)
Boron has three bonding pairs and no lone pair, giving a trigonal planar shape.
Q13Which C-C bond is the strongest and shortest?
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Correct: (C)
Bond strength increases and bond length decreases with bond order, so the triple bond is strongest and shortest.
Q14What is the main type of intermolecular force between methane molecules?
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Correct: (B)
Methane is non-polar, so only London dispersion forces act between its molecules.
Q15Why do metals conduct electricity in the solid state?
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Correct: (A)
The delocalised electrons in the metallic lattice carry charge through the solid.
Q16How many lone pairs are there on the nitrogen atom in NH3?
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Correct: (C)
Nitrogen forms three bonds and has one remaining lone pair.
Q17Which statement about diamond is correct?
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Correct: (D)
Every carbon in diamond is bonded to four others in a rigid network, making it extremely hard.
Q18What is the H-O-H bond angle in H2O?
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Correct: (B)
The two lone pairs on oxygen compress the bond angle to 104.5°.
Q19Which molecule is linear?
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Correct: (C)
Carbon dioxide has two electron domains around carbon with no lone pairs, so it is linear.
Q20Which compound contains both ionic and covalent bonds?
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Correct: (A)
NH4Cl has ionic bonding between NH4^+ and Cl^- and covalent bonds within the NH4^+ ion.
📊 Structure 3: Classification of Matter
Q21Which element is in group 17 of the periodic table?
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Correct: (D)
Chlorine is a halogen in group 17.
Q22Why does atomic radius decrease across period 3 from Na to Cl?
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Correct: (B)
Increasing nuclear charge pulls the same outer shell closer to the nucleus.
Q23The colours of transition metal complexes are mainly due to
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Correct: (A)
Ligands split the d orbitals, and d-d transitions absorb visible light, producing colour.
Q24What is the functional group in propanone, CH3COCH3?
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Correct: (C)
Propanone has a C=O group between two carbon atoms, which is a ketone.
Q25What is the general formula of the alkanes?
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Correct: (D)
Saturated acyclic alkanes follow the general formula CnH2n+2.
Q26What is the name of CH3CH=CHCH3?
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Correct: (B)
The double bond starts at carbon 2 of a four-carbon chain, giving but-2-ene.
Q27What is the oxidation state of sulfur in SO4^2-?
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Correct: (A)
x + 4(-2) = -2, so x = +6.
Q28Which metal is the most reactive?
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Correct: (C)
Potassium is highest in the reactivity series of these metals.
🔥 Reactivity 1: What Drives Chemical Reactions
Q29What quantity of heat is released when 50.0 g of water cools by 4.00°C? (Specific heat capacity of water = 4.18 J g^-1 °C^-1)
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Correct: (C)
q = mcΔT = 50.0 × 4.18 × 4.00 = 836 J = 0.836 kJ.
Q30Using standard enthalpies of formation (CH4 = -75, CO2 = -394, H2O(l) = -286 kJ mol^-1), what is ΔH for CH4(g) + 2 O2(g) → CO2(g) + 2 H2O(l)?
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Correct: (A)
ΔH = [-394 + 2(-286)] – [-75] = -966 + 75 = -891 kJ mol^-1.
Q31Using bond enthalpies (N≡N = 945, H-H = 435, N-H = 390 kJ mol^-1), what is ΔH for N2(g) + 3 H2(g) → 2 NH3(g)?
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Correct: (D)
Broken: 945 + 3(435) = 2250; formed: 6(390) = 2340. ΔH = 2250 – 2340 = -90 kJ mol^-1.
Q32An energy profile shows reactants at 20 kJ mol^-1, a transition state at 70 kJ mol^-1 and products at 10 kJ mol^-1. What is the activation energy of the forward reaction?
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Correct: (B)
Ea = 70 – 20 = 50 kJ mol^-1.
Q33What does the standard enthalpy change of combustion describe?
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Correct: (C)
It is the enthalpy change when one mole of a substance burns completely in oxygen under standard conditions.
Q34Which reaction is accompanied by a decrease in the entropy of the system?
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Correct: (A)
Four moles of gas form two moles of gas, so disorder decreases.
Q35A reaction has ΔH > 0 and ΔS > 0. When is it spontaneous?
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Correct: (D)
ΔG = ΔH – TΔS becomes negative only when T is large enough for TΔS to exceed ΔH.
Q36The enthalpy of vaporisation of water is 44.0 kJ mol^-1. How much energy is needed to vaporise 0.250 mol of water at its boiling point?
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Correct: (B)
q = 0.250 × 44.0 = 11.0 kJ.
⏱ Reactivity 2: How Much, How Fast & How Far
Q37For the reaction 2 NO(g) + O2(g) → 2 NO2(g), doubling [NO] quadruples the rate and doubling [O2] has no effect. What is the rate law?
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Correct: (B)
The reaction is second order in NO and zero order in O2.
Q38What is the effect of a catalyst on a Maxwell-Boltzmann distribution?
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Correct: (D)
The distribution itself is unchanged; the lower Ea threshold means more molecules exceed it.
Q39What fraction of a reactant remains after two half-lives of a first-order reaction?
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Correct: (A)
After one half-life 1/2 remains; after two half-lives (1/2)^2 = 1/4 remains.
Q40What is the equilibrium constant expression for CO(g) + 2 H2(g) ⇌ CH3OH(g)?
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Correct: (C)
Product concentration divided by reactant concentrations raised to their coefficients.
Q41For the equilibrium CH4(g) + H2O(g) ⇌ CO(g) + 3 H2(g), what happens when more CH4 is added at constant temperature?
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Correct: (A)
The system counteracts the change by consuming the added CH4, forming more products.
Q42For which reaction are Kp and Kc equal?
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Correct: (C)
Kp = Kc(RT)^Δn and Δn = 0 for this reaction, so Kp = Kc.
Q43The equilibrium N2O4(g) ⇌ 2 NO2(g) is endothermic in the forward direction. What happens to Kc when the temperature is increased?
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Correct: (B)
Heating favours the endothermic direction, so more NO2 forms and Kc increases.
Q44What is the effect of the common ion on the solubility of a sparingly soluble salt such as AgCl in a solution of NaCl?
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Correct: (D)
The added Cl^- shifts the dissolution equilibrium towards solid AgCl, lowering its solubility.
Q45Why does raising the temperature increase the rate of a reaction?
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Correct: (C)
More collisions occur and, most importantly, a larger fraction of them are energetic enough to react.
Q46A plot of ln[A] against time for a reaction is a straight line. What is the order of the reaction with respect to A?
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Correct: (A)
A linear ln[A] versus time plot is the integrated rate law behaviour of a first-order reaction.
Q47What are the units of the rate constant for a second-order reaction?
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Correct: (D)
For rate = k[A]^2, k = rate/[A]^2, giving dm^3 mol^-1 s^-1.
Q48Which statement about a system at dynamic equilibrium is correct?
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Correct: (B)
At equilibrium the forward and reverse reactions continue at equal rates, so concentrations stay constant.
⚖ Reactivity 3: Mechanisms of Chemical Change
Q49What is the pH of a 0.0010 mol dm^-3 solution of NaOH?
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Correct: (D)
[OH^-] = 0.0010, so pOH = 3.00 and pH = 14.00 – 3.00 = 11.00.
Q50What is the conjugate acid of NH3?
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Correct: (A)
Adding one H^+ to NH3 gives NH4^+, its conjugate acid.
Q51A buffer is made from a weak acid (pKa = 4.75) with [base]/[acid] = 10. What is the pH of the buffer?
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Correct: (B)
pH = pKa + log(10) = 4.75 + 1.00 = 5.75.
Q52In MnO4^-(aq) being converted to Mn^2+(aq) in acidic solution, the manganese undergoes
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Correct: (C)
The oxidation state of Mn falls from +7 to +2, which is a gain of electrons, i.e. reduction.
Q53Which statement about a galvanic (voltaic) cell is correct?
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Correct: (D)
Oxidation always takes place at the anode; in a galvanic cell electrons flow from anode to cathode.
Q54What is formed at the cathode during the electrolysis of aqueous copper(II) sulfate with inert electrodes?
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Correct: (A)
Cu^2+ is preferentially reduced at the cathode, depositing copper metal.
Q55Four weak acids have Ka values: W = 1.0 × 10^-5, X = 1.0 × 10^-3, Y = 1.0 × 10^-7, Z = 1.0 × 10^-9 mol dm^-3. Which is the strongest acid?
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Correct: (B)
The largest Ka value, 1.0 × 10^-3 for X, indicates the greatest dissociation and the strongest acid.
Q56Methane reacts with chlorine in ultraviolet light to form chloromethane. What type of reaction is this?
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Correct: (C)
A hydrogen atom is replaced by a chlorine atom in a (free-radical) substitution reaction.
Q57What is an electrophile?
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Correct: (A)
Electrophiles are electron-pair acceptors, attracted to regions of high electron density.
Q58What happens when a small amount of strong acid is added to a buffer containing ethanoic acid and sodium ethanoate?
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Correct: (D)
The conjugate base (ethanoate) removes the added H^+, forming ethanoic acid and limiting the pH change.
Q59What is the product when propan-1-ol is oxidised with acidified potassium dichromate(VI) under reflux?
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Correct: (B)
A primary alcohol is oxidised fully to the carboxylic acid, propanoic acid.
Q60For a tertiary halogenoalkane reacting with aqueous hydroxide, the rate depends only on the concentration of the halogenoalkane. This is consistent with
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Correct: (C)
In SN1 the rate-determining step involves only the halogenoalkane, so rate = k[halogenoalkane].
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