IB Chemistry Practice Test 3

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 ground-state electron configuration of an Fe^2+ ion?

(A) [Ar] 4s^2 3d^4
(B) [Ar] 4s^1 3d^5
(C) [Ar] 3d^6
(D) [Ar] 4s^2 3d^6
Show Answer

Correct: (C)

Iron is [Ar] 4s^2 3d^6. The two 4s electrons are removed first when Fe^2+ forms, leaving [Ar] 3d^6.

Q2What is the mass of 0.250 mol of calcium carbonate, CaCO3? The molar mass of CaCO3 is 100.09 g mol^-1.

(A) 12.5 g
(B) 25.0 g
(C) 50.0 g
(D) 100 g
Show Answer

Correct: (B)

Mass = 0.250 mol × 100.09 g mol^-1 = 25.0 g.

Q3What volume is occupied by 0.500 mol of an ideal gas at 300 K and a pressure of 100 kPa?

(A) 3.12 dm^3
(B) 6.24 dm^3
(C) 24.9 dm^3
(D) 12.5 dm^3
Show Answer

Correct: (D)

V = nRT / p = (0.500 × 8.31 × 300) / 100 = 12.5 dm^3 when R is used in kPa dm^3 units.

Q4A student dissolves 5.85 g of NaCl in water and makes the solution up to 500 cm^3. What is the concentration of the solution? The molar mass of NaCl is 58.5 g mol^-1.

(A) 0.200 mol dm^-3
(B) 0.100 mol dm^-3
(C) 0.400 mol dm^-3
(D) 0.0500 mol dm^-3
Show Answer

Correct: (A)

Amount of NaCl = 5.85 / 58.5 = 0.100 mol. Concentration = 0.100 / 0.500 = 0.200 mol dm^-3.

Q5A sample of chlorine consists of 75% ^35Cl and 25% ^37Cl. What is its relative atomic mass?

(A) 35.0
(B) 36.0
(C) 35.5
(D) 36.5
Show Answer

Correct: (C)

Average mass = (0.75 × 35) + (0.25 × 37) = 35.5.

Q6A compound contains 40.0% calcium, 12.0% carbon and 48.0% oxygen by mass. What is its empirical formula?

(A) CaO
(B) CaCO3
(C) CaC2O4
(D) Ca(HCO3)2
Show Answer

Correct: (B)

Mole ratio = Ca: 40.0 / 40 = 1, C: 12.0 / 12 = 1, O: 48.0 / 16 = 3, giving CaCO3.

Q7How many molecules are present in 0.500 mol of carbon dioxide?

(A) 6.02 × 10^22
(B) 1.20 × 10^23
(C) 6.02 × 10^23
(D) 3.01 × 10^23
Show Answer

Correct: (D)

Number of molecules = 0.500 × 6.02 × 10^23 = 3.01 × 10^23.

Q8Hydrogen and oxygen react according to the equation 2H2(g) + O2(g) → 2H2O(l). When 3.00 mol of H2 is mixed with 1.00 mol of O2, what is the maximum amount of water that can form?

(A) 2.00 mol
(B) 3.00 mol
(C) 1.00 mol
(D) 4.00 mol
Show Answer

Correct: (A)

The 1.00 mol of O2 requires 2.00 mol of H2 and forms 2.00 mol of H2O. Oxygen is the limiting reactant.

Q9The theoretical yield of a product is 20.0 g and the actual yield is 16.0 g. What is the percentage yield?

(A) 20.0%
(B) 64.0%
(C) 80.0%
(D) 125%
Show Answer

Correct: (C)

Percentage yield = (16.0 / 20.0) × 100 = 80.0%.

Q10Which electron arrangement represents an excited state of a magnesium atom?

(A) 2, 8, 2
(B) 2, 7, 3
(C) 2, 8, 1
(D) 2, 8, 3
Show Answer

Correct: (B)

A magnesium atom has 12 electrons. The arrangement 2, 7, 3 has 12 electrons, but one electron has been promoted from the second to the third energy level.

🔗 Structure 2: Models of Bonding & Structure

Q11What is the molecular geometry of ammonia, NH3?

(A) Tetrahedral
(B) Trigonal planar
(C) Bent
(D) Trigonal pyramidal
Show Answer

Correct: (D)

Nitrogen has three bonding pairs and one lone pair. The lone pair makes the molecular geometry trigonal pyramidal.

Q12Which compound has the greatest lattice enthalpy magnitude?

(A) MgO
(B) NaCl
(C) KCl
(D) NaF
Show Answer

Correct: (A)

MgO contains Mg^2+ and O^2- ions. The high charges and small ionic sizes produce the strongest electrostatic attractions.

Q13In the best Lewis structure of CO2, how many lone pairs are on each oxygen atom?

(A) 0
(B) 1
(C) 2
(D) 3
Show Answer

Correct: (C)

Each oxygen forms a double bond to carbon and has two non-bonding pairs of electrons.

Q14Which substance has the highest boiling point?

(A) CH4
(B) CH3CH2OH
(C) CH3OCH3
(D) CH3CH3
Show Answer

Correct: (B)

Ethanol molecules form hydrogen bonds with one another. These are stronger than the intermolecular forces in the other substances listed.

Q15What is the F-B-F bond angle in BF3?

(A) 120°
(B) 109.5°
(C) 107°
(D) 180°
Show Answer

Correct: (A)

BF3 has three bonding pairs and no lone pair on boron, giving trigonal planar geometry and bond angles of 120°.

Q16What is the hybridization of the carbon atom in methane, CH4?

(A) sp
(B) sp^2
(C) sp^3d
(D) sp^3
Show Answer

Correct: (D)

Carbon has four electron domains in methane, corresponding to sp^3 hybridization.

Q17In diamond, each carbon atom is covalently bonded to how many other carbon atoms?

(A) 2
(B) 3
(C) 4
(D) 6
Show Answer

Correct: (C)

Diamond has a giant covalent structure in which each carbon atom forms four single covalent bonds.

Q18Under which condition does an ionic compound conduct electricity?

(A) As a solid crystal
(B) When molten
(C) It never conducts electricity
(D) Only as a gas
Show Answer

Correct: (B)

In the molten state the ions are mobile and can move to the electrodes. In the solid state they are held in fixed positions.

Q19Which molecule has a permanent dipole moment?

(A) CHCl3
(B) CCl4
(C) CO2
(D) BF3
Show Answer

Correct: (A)

CHCl3 is not symmetrical because carbon is bonded to both hydrogen and chlorine atoms, so its bond dipoles do not cancel.

Q20Why can metals be hammered into sheets without breaking?

(A) Their covalent bonds are directional
(B) Their ions are held by hydrogen bonds
(C) Their atoms form discrete molecules
(D) Layers of positive ions can slide while the delocalized electrons maintain the bonding
Show Answer

Correct: (D)

Metallic bonding is non-directional. Layers of cations can move while remaining attracted to the mobile electron sea.

📊 Structure 3: Classification of Matter

Q21Across a period, the first ionization energy generally increases mainly because

(A) the number of electron shells increases
(B) the atomic radius increases
(C) the nuclear charge increases while shielding stays similar
(D) the atoms become more metallic
Show Answer

Correct: (C)

Across a period, protons are added but electrons enter the same main energy level, so the outer electrons are attracted more strongly.

Q22Which is a characteristic property of many transition metals?

(A) They form colourless compounds only
(B) They show variable oxidation states
(C) They have completely filled d subshells in all compounds
(D) They are poor electrical conductors
Show Answer

Correct: (B)

Transition metals commonly form ions and compounds in several different oxidation states.

Q23Consecutive members of the same homologous series differ by which group?

(A) CH3
(B) CH
(C) CH4
(D) CH2
Show Answer

Correct: (D)

Each successive member of a homologous series has one additional CH2 unit.

Q24Which functional group is present in ethanoic acid?

(A) -COOH
(B) -OH only
(C) -CHO
(D) -COO-
Show Answer

Correct: (A)

Ethanoic acid is a carboxylic acid and contains the carboxyl group, -COOH.

Q25The ions Mg^2+, Na+, F- and O^2- are isoelectronic. Which ion has the largest radius?

(A) Mg^2+
(B) Na+
(C) O^2-
(D) F-
Show Answer

Correct: (C)

All four ions have 10 electrons. O^2- has the fewest protons, so its electron cloud is attracted least strongly and is largest.

Q26Why does reactivity decrease down Group 17?

(A) The atoms lose electrons more easily
(B) The outer electron is farther from the nucleus and is shielded more
(C) The number of protons decreases
(D) The atoms have fewer electron shells
Show Answer

Correct: (B)

A halogen atom gains an electron when it reacts. Down the group, the incoming electron is farther from the nucleus and experiences more shielding.

Q27To which homologous series does CH3CH2OH belong?

(A) Alkanes
(B) Aldehydes
(C) Esters
(D) Alcohols
Show Answer

Correct: (D)

The -OH functional group attached to a carbon chain identifies the compound as an alcohol.

Q28The colour of many transition metal complexes is mainly due to

(A) d-d electron transitions
(B) emission from the nucleus
(C) breaking of ionic bonds
(D) movement of electrons between ligands only
Show Answer

Correct: (A)

Ligands split the d orbitals into groups of different energy. Visible light can promote electrons between these groups.




🔥 Reactivity 1: What Drives Chemical Reactions

Q29How much heat is absorbed by 100 g of water when its temperature rises by 5.00°C? The specific heat capacity of water is 4.18 J g^-1 °C^-1.

(A) 209 J
(B) 418 J
(C) 2090 J
(D) 4180 J
Show Answer

Correct: (C)

q = mcΔT = 100 × 4.18 × 5.00 = 2090 J.

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)?

(A) -676.5 kJ mol^-1
(B) -110.5 kJ mol^-1
(C) +110.5 kJ mol^-1
(D) -221.0 kJ mol^-1
Show Answer

Correct: (B)

Subtract the second equation from the first: -393.5 – (-283.0) = -110.5 kJ mol^-1.

Q31Using average bond enthalpies H-H = 436 kJ mol^-1, Cl-Cl = 242 kJ mol^-1 and H-Cl = 431 kJ mol^-1, what is the estimated ΔH for H2(g) + Cl2(g) → 2HCl(g)?

(A) +184 kJ mol^-1
(B) -92 kJ mol^-1
(C) -429 kJ mol^-1
(D) -184 kJ mol^-1
Show Answer

Correct: (D)

Bonds broken = 436 + 242 = 678 kJ. Bonds formed = 2 × 431 = 862 kJ. ΔH = 678 – 862 = -184 kJ mol^-1.

Q32Which statement describes an exothermic reaction?

(A) ΔH is negative and heat is released to the surroundings
(B) ΔH is positive and heat is absorbed from the surroundings
(C) The products always have weaker bonds than the reactants
(D) The temperature of the surroundings decreases
Show Answer

Correct: (A)

In an exothermic reaction, energy is transferred to the surroundings, so ΔH is negative.

Q33Which process increases the entropy of the system?

(A) H2O(l) → H2O(s)
(B) A gas is compressed at constant temperature
(C) NH4NO3(s) → NH4+(aq) + NO3-(aq)
(D) CO2(g) → CO2(s)
Show Answer

Correct: (C)

Dissolving produces mobile aqueous ions from an ordered solid, increasing the dispersal of matter and energy.

Q34A reaction has ΔH = -80 kJ mol^-1 and ΔS = -100 J K^-1 mol^-1. What is ΔG at 298 K?

(A) -109.8 kJ mol^-1
(B) -50.2 kJ mol^-1
(C) +19.8 kJ mol^-1
(D) -80.0 kJ mol^-1
Show Answer

Correct: (B)

ΔG = ΔH – TΔS = -80 – 298 × (-0.100) = -80 + 29.8 = -50.2 kJ mol^-1.

Q35The standard enthalpy change of formation of a compound is the enthalpy change when

(A) one mole of the compound burns completely in oxygen
(B) one mole of a substance reacts with water
(C) one mole of a compound breaks into atoms
(D) one mole of the compound forms from its elements in their standard states
Show Answer

Correct: (D)

Enthalpy of formation refers to forming one mole of a compound from its elements under standard conditions.

Q36A 25.0 g metal sample absorbs 650 J and its temperature rises by 26.0°C. What is its specific heat capacity?

(A) 1.00 J g^-1 °C^-1
(B) 0.500 J g^-1 °C^-1
(C) 2.00 J g^-1 °C^-1
(D) 0.0400 J g^-1 °C^-1
Show Answer

Correct: (A)

c = q / (mΔT) = 650 / (25.0 × 26.0) = 1.00 J g^-1 °C^-1.

⏱ Reactivity 2: How Much, How Fast & How Far

Q37A reaction A + B → products gives these results: experiment 1, [A] = 0.100, [B] = 0.100, rate = 0.0020; experiment 2, [A] = 0.200, [B] = 0.100, rate = 0.0080; experiment 3, [A] = 0.100, [B] = 0.200, rate = 0.0020. What is the rate law?

(A) rate = k[A][B]
(B) rate = k[A][B]^2
(C) rate = k[A]^2
(D) rate = k[B]^2
Show Answer

Correct: (C)

Doubling [A] quadruples the rate, so the reaction is second order in A. Doubling [B] has no effect, so it is zero order in B.

Q38Which is true for the half-life of a first-order reaction?

(A) It doubles when the initial concentration doubles
(B) It is independent of the initial concentration
(C) It decreases as the reaction proceeds
(D) It has units of concentration
Show Answer

Correct: (B)

For first-order kinetics, t1/2 = ln 2 / k, so it depends only on the rate constant.

Q39When the temperature of a gas is increased, what happens to its Maxwell-Boltzmann distribution?

(A) The peak moves to lower energy and becomes taller
(B) The total area under the curve increases
(C) The peak moves to lower energy and the area stays the same
(D) The peak moves to higher energy, becomes lower and broader, and the total area stays the same
Show Answer

Correct: (D)

The number of molecules is unchanged, so the area is constant. More molecules have higher energies, producing a lower and broader peak shifted to the right.

Q40A catalyst increases the rate of a reversible reaction by

(A) increasing the rate of the forward reaction and the rate of the reverse reaction
(B) increasing only the rate of the forward reaction
(C) shifting the equilibrium toward the products
(D) increasing the yield at equilibrium
Show Answer

Correct: (A)

A catalyst provides a lower-energy pathway for both directions and does not change the equilibrium position.

Q41What is the equilibrium constant expression for N2(g) + 3H2(g) ⇌ 2NH3(g)?

(A) Kc = [NH3] / ([N2][H2])
(B) Kc = ([N2][H2]^3) / [NH3]^2
(C) Kc = [NH3]^2 / ([N2][H2]^3)
(D) Kc = [NH3]^2 / ([N2] + 3[H2])
Show Answer

Correct: (C)

Product concentrations are divided by reactant concentrations, with each concentration raised to its stoichiometric coefficient.

Q42The reaction N2(g) + 3H2(g) ⇌ 2NH3(g) has ΔH = -92 kJ mol^-1. What happens when the temperature is increased at constant pressure?

(A) The equilibrium shifts toward NH3 and Kc increases
(B) The equilibrium shifts toward N2 and H2
(C) The equilibrium position does not change
(D) Kc stays the same but the rate decreases
Show Answer

Correct: (B)

The forward reaction is exothermic. Increasing the temperature favours the endothermic reverse reaction.

Q43At equilibrium for H2(g) + I2(g) ⇌ 2HI(g), [H2] = 0.100 mol dm^-3, [I2] = 0.100 mol dm^-3 and [HI] = 0.800 mol dm^-3. What is Kc?

(A) 8.00
(B) 16.0
(C) 32.0
(D) 64.0
Show Answer

Correct: (D)

Kc = (0.800)^2 / (0.100 × 0.100) = 0.640 / 0.0100 = 64.0.

Q44For which condition are Kp and Kc equal?

(A) The change in the amount of gas in the reaction is zero
(B) The reaction is exothermic
(C) A catalyst is present
(D) The total pressure is 100 kPa
Show Answer

Correct: (A)

Kp = Kc(RT)^Δn. When Δn for gases is zero, the factor is 1 and Kp = Kc.

Q45What are the units of the rate constant for a reaction that is second order overall?

(A) s^-1
(B) mol dm^-3 s^-1
(C) dm^3 mol^-1 s^-1
(D) dm^6 mol^-2 s^-1
Show Answer

Correct: (C)

For rate = k[A]^2, k = rate / [A]^2, giving dm^3 mol^-1 s^-1.

Q46Increasing the concentration of a reacting solution usually increases the rate because

(A) the activation energy decreases
(B) collisions between particles occur more frequently
(C) all particles move more slowly
(D) the reaction becomes more exothermic
Show Answer

Correct: (B)

A higher concentration means more particles in a given volume and a greater collision frequency.

Q47At a particular point in a reversible reaction, Q = 12 and Kc = 3.0. In which direction does the net reaction proceed?

(A) It is at equilibrium
(B) Toward the products
(C) Neither forward nor reverse reaction occurs
(D) Toward the reactants
Show Answer

Correct: (D)

Q is greater than Kc, so there is too much product relative to equilibrium and the net reaction proceeds toward the reactants.

Q48N2O4(g) ⇌ 2NO2(g). The initial concentration of N2O4 is 1.00 mol dm^-3 and its equilibrium concentration is 0.800 mol dm^-3. What is the equilibrium concentration of NO2?

(A) 0.400 mol dm^-3
(B) 0.200 mol dm^-3
(C) 0.800 mol dm^-3
(D) 1.60 mol dm^-3
Show Answer

Correct: (A)

The concentration of N2O4 decreases by 0.200 mol dm^-3. Twice this amount of NO2 forms, so [NO2] = 0.400 mol dm^-3.

⚖ Reactivity 3: Mechanisms of Chemical Change

Q49What is the pH of 0.0100 mol dm^-3 hydrochloric acid?

(A) 1.00
(B) 12.0
(C) 2.00
(D) 0.0100
Show Answer

Correct: (C)

Hydrochloric acid is a strong acid, so [H+] = 0.0100 and pH = -log(0.0100) = 2.00.

Q50What is the pH of 0.100 mol dm^-3 ethanoic acid, for which Ka = 1.8 × 10^-5 mol dm^-3?

(A) 1.00
(B) 2.87
(C) 4.74
(D) 5.74
Show Answer

Correct: (B)

[H+] is approximately sqrt(Ka × 0.100) = 1.34 × 10^-3 mol dm^-3, so pH = 2.87.

Q51A buffer contains equal concentrations of a weak acid and its conjugate base. The pKa of the acid is 4.74. What is the pH of the buffer?

(A) 3.74
(B) 5.74
(C) 7.00
(D) 4.74
Show Answer

Correct: (D)

pH = pKa + log([base] / [acid]). Equal concentrations make the logarithm zero, so pH = pKa = 4.74.

Q52What is the conjugate base of HCO3-?

(A) CO3^2-
(B) H2CO3
(C) H3O+
(D) OH-
Show Answer

Correct: (A)

Removing one H+ from HCO3- forms CO3^2-.

Q53In the reaction Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s), which species is the reducing agent?

(A) Cu^2+
(B) Cu
(C) Zn
(D) Zn^2+
Show Answer

Correct: (C)

Zinc is oxidized from oxidation state 0 to +2. The species that is oxidized is the reducing agent.

Q54Given E values Zn^2+/Zn = -0.76 V and Cu^2+/Cu = +0.34 V, what is the standard cell potential for Zn(s) + Cu^2+(aq) → Zn^2+(aq) + Cu(s)?

(A) +0.42 V
(B) +1.10 V
(C) -1.10 V
(D) +2.20 V
Show Answer

Correct: (B)

Ecell = E(reduction at cathode) – E(reduction at anode) = 0.34 – (-0.76) = +1.10 V.

Q55A charge of 9650 C is passed through aqueous silver nitrate. How much silver is deposited at the cathode? Ag = 107.87 g mol^-1 and the Faraday constant is 96 500 C mol^-1.

(A) 1.08 g
(B) 5.39 g
(C) 21.6 g
(D) 10.8 g
Show Answer

Correct: (D)

Amount of electrons = 9650 / 96500 = 0.100 mol. Ag+ + e- → Ag, so 0.100 mol of Ag forms: 0.100 × 107.87 = 10.8 g.

Q56Which halogenoalkane reacts fastest by an SN1 mechanism?

(A) A tertiary halogenoalkane
(B) A secondary halogenoalkane
(C) A primary halogenoalkane
(D) Fluoromethane
Show Answer

Correct: (A)

SN1 reactions form a carbocation intermediate. A tertiary carbocation is the most stable of these choices.

Q57In organic chemistry, an electrophile is a species that

(A) donates a pair of electrons
(B) accepts one unpaired electron only
(C) accepts a pair of electrons
(D) always carries a full positive charge
Show Answer

Correct: (C)

An electrophile is an electron-pair acceptor and is attracted to regions of high electron density.

Q58Which statement best describes a strong acid in aqueous solution?

(A) It has a high concentration
(B) It ionizes almost completely
(C) It always has a pH below 1
(D) It reacts slowly with metals
Show Answer

Correct: (B)

Acid strength describes the extent of ionization, not the concentration of the solution.

Q59A small amount of hydrochloric acid is added to a buffer containing HA and A-. What mainly happens?

(A) The H+ reacts with HA to form more A-
(B) The pH falls to below 1
(C) The H+ remains completely free in solution
(D) The H+ reacts with A- to form HA
Show Answer

Correct: (D)

The conjugate base A- removes most of the added H+ by forming the weak acid HA, limiting the pH change.

Q60In a working voltaic cell, oxidation occurs at the

(A) anode
(B) cathode
(C) salt bridge
(D) external wire
Show Answer

Correct: (A)

Oxidation is loss of electrons and always occurs at the anode. In a voltaic cell, the anode is the negative electrode.