IB Chemistry Practice Test 6

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 present in 0.250 mol of CO2?

(A) 3.01 × 10^22
(B) 6.02 × 10^22
(C) 1.20 × 10^23
(D) 1.51 × 10^23
Show Answer

Correct: (D)

Number = 0.250 × 6.02 × 10^23 = 1.51 × 10^23 molecules.

Q2What is the percentage by mass of nitrogen in NH4NO3? Molar mass of NH4NO3 = 80.05 g mol^-1.

(A) 17.5%
(B) 28.0%
(C) 35.0%
(D) 70.0%
Show Answer

Correct: (C)

Mass of N in one mole = 2 × 14.01 = 28.02 g. Percentage = (28.02 / 80.05) × 100 = 35.0%.

Q3Which electron configuration represents an atom in an excited state?

(A) 1s^2 2s^2 2p^6
(B) 1s^2 2s^2 2p^5 3s^1
(C) 1s^2 2s^2 2p^4
(D) 1s^2 2s^1
Show Answer

Correct: (B)

The atom has 10 electrons, but one has been promoted from 2p to 3s instead of the 2p sub-shell being filled first.

Q4Which element has the largest atomic radius?

(A) Na
(B) Mg
(C) Al
(D) Si
Show Answer

Correct: (A)

These elements are in Period 3. Radius decreases across the period, and Na is furthest left.

Q5What is the pressure of 2.00 mol of an ideal gas at 300 K in a volume of 0.0250 m^3? R = 8.31 J K^-1 mol^-1.

(A) 99.7 kPa
(B) 150 kPa
(C) 249 kPa
(D) 199 kPa
Show Answer

Correct: (D)

P = nRT/V = (2.00 × 8.31 × 300) / 0.0250 = 1.99 × 10^5 Pa = 199 kPa.

Q6How many moles of solute are in 500 cm^3 of 0.200 mol dm^-3 solution?

(A) 0.0400 mol
(B) 0.400 mol
(C) 0.100 mol
(D) 1.00 mol
Show Answer

Correct: (C)

Amount = 0.500 dm^3 × 0.200 mol dm^-3 = 0.100 mol.

Q7A compound has empirical formula CH2O and molar mass 60.06 g mol^-1. What is its molecular formula?

(A) CH2O
(B) C2H4O2
(C) C2H2O2
(D) C3H6O3
Show Answer

Correct: (B)

The empirical formula mass is 30.03. 60.06 / 30.03 = 2, so the molecular formula is twice CH2O.

Q8How many moles are present in 88.0 g of CO2? Molar mass of CO2 = 44.0 g mol^-1.

(A) 2.00 mol
(B) 0.500 mol
(C) 1.00 mol
(D) 4.00 mol
Show Answer

Correct: (A)

Amount = 88.0 / 44.0 = 2.00 mol.

Q9At constant temperature and pressure, the molar mass of a gas is doubled. What happens to its density?

(A) It halves
(B) It remains the same
(C) It increases by a factor of four
(D) It doubles
Show Answer

Correct: (D)

At fixed T and P, equal volumes contain equal amounts of gas, so density is proportional to molar mass.

Q10A 20.0 cm^3 sample of HCl is exactly neutralized by 25.0 cm^3 of 0.100 mol dm^-3 NaOH. What is the concentration of the HCl?

(A) 0.0800 mol dm^-3
(B) 0.100 mol dm^-3
(C) 0.125 mol dm^-3
(D) 0.250 mol dm^-3
Show Answer

Correct: (C)

Moles NaOH = 0.0250 × 0.100 = 0.00250 mol = moles HCl. Concentration = 0.00250 / 0.0200 = 0.125 mol dm^-3.

🔗 Structure 2: Models of Bonding & Structure

Q11Why do ionic compounds have high melting points?

(A) Their molecules are held together by weak forces
(B) Strong electrostatic attractions throughout the lattice require much energy to break
(C) Their ions move freely in the solid state
(D) They contain delocalized electrons
Show Answer

Correct: (B)

A large amount of energy is needed to disrupt the three-dimensional ionic lattice.

Q12What is the molecular geometry of XeF4?

(A) Square planar
(B) Tetrahedral
(C) Seesaw
(D) Trigonal bipyramidal
Show Answer

Correct: (A)

XeF4 has four bonding pairs and two lone pairs in opposite positions, giving a square planar molecular geometry.

Q13Which carbon-carbon bond is strongest?

(A) C-C
(B) C=C
(C) C-C in a long chain only
(D) C≡C
Show Answer

Correct: (D)

Bond strength increases with bond order, so a triple bond is stronger than a double or single bond.

Q14What is the dominant intermolecular force between CH4 molecules?

(A) Hydrogen bonding
(B) Ionic bonding
(C) London dispersion forces
(D) Permanent dipole-dipole forces
Show Answer

Correct: (C)

CH4 is nonpolar, so temporary induced dipoles produce London dispersion forces.

Q15In a Lewis structure of CO2, how many lone pairs are on each oxygen atom?

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

Correct: (B)

Each oxygen has one double bond and two lone pairs, giving it an octet.

Q16Which description best represents metallic bonding?

(A) A lattice of positive ions surrounded by delocalized electrons
(B) Shared pairs of electrons between two atoms
(C) Transfer of electrons to form fixed ion pairs
(D) Hydrogen atoms attracted to lone pairs
Show Answer

Correct: (A)

Metallic bonding is the attraction between metal cations and a sea of delocalized electrons.

Q17Which element forms a giant covalent lattice in which each atom is tetrahedrally bonded to four others, analogous to diamond?

(A) Sulfur
(B) Phosphorus
(C) Chlorine
(D) Silicon
Show Answer

Correct: (D)

Silicon has a diamond-like giant covalent structure with tetrahedral bonding.

Q18Which bond has the greatest polarity?

(A) H-H
(B) H-Cl
(C) H-F
(D) H-C
Show Answer

Correct: (C)

Fluorine has the greatest electronegativity, so the H-F bond has the largest electronegativity difference and is most polar.

Q19Which statement describes the C=C bond in ethene?

(A) It consists of two pi bonds
(B) It consists of one sigma bond and one pi bond
(C) It consists of two sigma bonds
(D) It is weaker than a C-C single bond
Show Answer

Correct: (B)

A double bond contains one sigma component and one pi component.

Q20Which molecule is linear in the gas phase?

(A) BeCl2
(B) H2O
(C) NH3
(D) CH4
Show Answer

Correct: (A)

Gaseous BeCl2 has two bonding domains and no lone pairs on Be, so it is linear.

📊 Structure 3: Classification of Matter

Q21Which trend occurs across a period from left to right?

(A) Metallic character increases
(B) Atomic radius increases
(C) Electronegativity generally increases
(D) First ionization energy always decreases
Show Answer

Correct: (C)

Increasing nuclear charge generally attracts bonding electrons more strongly across a period, increasing electronegativity.

Q22Why are many transition-metal compounds coloured?

(A) Their ions have completely empty outer shells in all cases
(B) They contain only ionic bonds
(C) They have no d electrons
(D) Their partially filled d sub-shell allows d-electron transitions that absorb visible light
Show Answer

Correct: (D)

Visible light can promote electrons between d orbitals of different energies, and the remaining light is coloured.

Q23To which class of organic compounds does propanone, CH3COCH3, belong?

(A) Ketone
(B) Aldehyde
(C) Ester
(D) Carboxylic acid
Show Answer

Correct: (A)

Propanone has a carbonyl group bonded to two carbon atoms, which is a ketone.

Q24What is the general formula of an acyclic alkane?

(A) CnH2n
(B) CnH2n+2
(C) CnH2n-2
(D) CnHn
Show Answer

Correct: (B)

Acyclic alkanes follow CnH2n+2.

Q25Which compound is a primary amine?

(A) CH3NHCH3
(B) CH3CH2NH2
(C) N(CH3)3
(D) CH3CONH2
Show Answer

Correct: (B)

In CH3CH2NH2, nitrogen is bonded to one carbon group and two hydrogen atoms.

Q26How many structural isomers have the formula C4H10?

(A) 2
(B) 3
(C) 4
(D) 5
Show Answer

Correct: (A)

C4H10 has two structures: butane and 2-methylpropane.

Q27What happens to the reactivity of the halogens down Group 17?

(A) It increases steadily
(B) It remains exactly constant
(C) Their electronegativity increases
(D) It decreases
Show Answer

Correct: (D)

Down the group, atoms gain an electron less readily because the outer shell is farther from the nucleus and more shielded.

Q28Which oxide is basic?

(A) SiO2
(B) P4O10
(C) MgO
(D) SO3
Show Answer

Correct: (C)

MgO is a metal oxide and reacts with acids as a base.




🔥 Reactivity 1: What Drives Chemical Reactions

Q29Which apparatus is most suitable for measuring the enthalpy of combustion of a liquid fuel accurately?

(A) Bomb calorimeter
(B) Open test tube
(C) Measuring cylinder
(D) Pipette
Show Answer

Correct: (A)

A bomb calorimeter burns the fuel in oxygen under controlled conditions and minimizes heat-loss errors compared with simple apparatus.

Q30A reaction heats 50.0 g of water by 6.00°C. How much heat is transferred to the water? Specific heat capacity of water = 4.18 J g^-1 °C^-1.

(A) 0.125 kJ
(B) 12.5 kJ
(C) 125 kJ
(D) 1.25 kJ
Show Answer

Correct: (D)

q = 50.0 × 4.18 × 6.00 = 1254 J = 1.25 kJ.

Q31Given ΔHc(C) = -394 kJ mol^-1, ΔHc(H2) = -286 kJ mol^-1 and ΔHc(CH4) = -890 kJ mol^-1, what is ΔHf(CH4)?

(A) +76 kJ mol^-1
(B) -181 kJ mol^-1
(C) -76 kJ mol^-1
(D) -966 kJ mol^-1
Show Answer

Correct: (C)

Formation from C + 2H2 has ΔH = (-394) + 2(-286) – (-890) = -76 kJ mol^-1 by a Hess cycle.

Q32Using bond enthalpies N≡N = 941, H-H = 436 and N-H = 391 kJ mol^-1, what is ΔH for N2 + 3H2 → 2NH3?

(A) +97 kJ mol^-1
(B) -97 kJ mol^-1
(C) -194 kJ mol^-1
(D) -45 kJ mol^-1
Show Answer

Correct: (B)

Bonds broken = 941 + 3(436) = 2249. Bonds formed = 6(391) = 2346. ΔH = 2249 – 2346 = -97 kJ mol^-1.

Q33Under specified conditions, a process is thermodynamically spontaneous when what condition is met?

(A) ΔG < 0
(B) ΔG > 0
(C) ΔH must be negative
(D) ΔS must be positive
Show Answer

Correct: (A)

A negative Gibbs energy change indicates a thermodynamically spontaneous process under the stated conditions.

Q34What is the sign of ΔS for 2H2(g) + O2(g) → 2H2O(g)?

(A) Positive because liquid water is not formed
(B) Zero because atoms are conserved
(C) Impossible to predict for any reaction
(D) Negative because 3 mol of gas form 2 mol of gas
Show Answer

Correct: (D)

The number of gas molecules decreases, reducing disorder and giving a negative entropy change.

Q35For an endothermic reaction, which statement is correct?

(A) The reactants have higher enthalpy than the products
(B) ΔH is negative
(C) The products have higher enthalpy than the reactants
(D) Heat is released to the surroundings
Show Answer

Correct: (C)

Endothermic reactions absorb heat, so product enthalpy is greater and ΔH is positive.

Q36Why are calculations using average bond enthalpies only approximate?

(A) Bond enthalpies are measured only at absolute zero
(B) The energy of a given bond varies with its molecular environment
(C) Bonds do not break during reactions
(D) Average bond enthalpies apply only to ionic compounds
Show Answer

Correct: (B)

Tabulated values are averages, while the actual strength of a bond depends on the atoms and groups around it.

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

Q37What are the units of k for a first-order reaction?

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

Correct: (B)

For first-order kinetics, rate / concentration has units of s^-1.

Q38In a reaction, doubling [A] doubles the rate and doubling [B] has no effect. What is the rate law?

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

Correct: (A)

The reaction is first order in A and zero order in B, so [B] does not appear in the rate law.

Q39When the temperature of a reacting gas mixture increases, what happens to the fraction of molecules with energy at least equal to the activation energy?

(A) It decreases
(B) It becomes zero
(C) It remains unchanged
(D) It increases
Show Answer

Correct: (D)

The Maxwell-Boltzmann distribution shifts to higher energies, so a greater fraction can overcome the activation-energy barrier.

Q40What is the principal reason that raising temperature greatly increases reaction rate?

(A) It changes all reactions into first-order reactions
(B) It increases the value of the equilibrium constant for every reaction
(C) A much larger fraction of collisions have energy at least equal to the activation energy
(D) It lowers the concentration of all reactants
Show Answer

Correct: (C)

Higher temperature increases collision frequency, but the much greater fraction of sufficiently energetic collisions is the principal effect.

Q41What are the units of k for a second-order reaction with rate in mol dm^-3 s^-1 and concentration in mol dm^-3?

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

Correct: (A)

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

Q42What is Kc for CaCO3(s) ⇌ CaO(s) + CO2(g)?

(A) Kc = [CaO][CO2] / [CaCO3]
(B) Kc = [CO2]
(C) Kc = 1 / [CO2]
(D) Kc = [CaCO3] / [CaO]
Show Answer

Correct: (B)

Pure solids are omitted from the equilibrium expression, leaving Kc = [CO2].

Q43An inert gas is added to an equilibrium mixture at constant volume. What happens to the equilibrium position?

(A) It always shifts toward products
(B) It always shifts toward reactants
(C) It does not shift because reactant and product partial pressures are unchanged
(D) It shifts toward the side with more gas molecules
Show Answer

Correct: (C)

At constant volume, adding an inert gas does not change the partial pressures of reacting gases, so Q remains equal to K.

Q44For an exothermic equilibrium, what happens to K when temperature increases?

(A) K increases
(B) K remains constant
(C) K first increases then becomes zero
(D) K decreases
Show Answer

Correct: (D)

Heating favours the endothermic reverse reaction for an exothermic equilibrium, reducing the equilibrium constant.

Q45For A ⇌ 2B, the initial concentration of A is 1.00 mol dm^-3 and B is zero. At equilibrium, [A] = 0.800 mol dm^-3 and [B] = 0.400 mol dm^-3. What is Kc?

(A) 0.500
(B) 0.160
(C) 0.200
(D) 2.00
Show Answer

Correct: (C)

Kc = [B]^2 / [A] = (0.400)^2 / 0.800 = 0.200.

Q46Which statement about an equilibrium system is correct?

(A) Reactant and product concentrations must be equal
(B) Both reactions stop once equilibrium is reached
(C) The equilibrium constant changes when a catalyst is added
(D) Macroscopic properties remain constant while both reactions continue
Show Answer

Correct: (D)

Dynamic equilibrium has constant macroscopic properties because forward and reverse rates are equal, not because reactions stop.

Q47What is the effect of continuously removing a product from an equilibrium mixture?

(A) Equilibrium shifts toward the products
(B) Equilibrium shifts toward the reactants
(C) The equilibrium constant decreases
(D) Both reaction rates become zero
Show Answer

Correct: (A)

Removing product makes Q < K, so the forward reaction predominates to replace some of the product.

Q48How is the initial rate of a reaction obtained from a concentration-time graph?

(A) By taking the final concentration divided by total time
(B) By finding the slope of the tangent at time zero
(C) By reading the concentration at the end of reaction
(D) By multiplying all concentrations by time
Show Answer

Correct: (B)

Rate at a given time is the gradient of the concentration-time curve; the initial rate uses the tangent at t = 0.

⚖ Reactivity 3: Mechanisms of Chemical Change

Q49What is the pH of 0.100 mol dm^-3 NH3? Kb(NH3) = 1.8 × 10^-5.

(A) 2.87
(B) 8.72
(C) 11.13
(D) 12.87
Show Answer

Correct: (C)

[OH^-] = sqrt(Kb × 0.100) = 1.34 × 10^-3. pOH = 2.87, so pH = 14.00 – 2.87 = 11.13.

Q50What is the conjugate acid of NH3?

(A) NH2^-
(B) NH4^+
(C) H3O^+
(D) OH^-
Show Answer

Correct: (B)

Adding H^+ to NH3 gives NH4^+.

Q51At the equivalence point of a titration between a weak base and a strong acid, the solution is best described as what?

(A) Acidic
(B) Neutral in all cases
(C) Strongly alkaline
(D) A buffer with equal moles of acid and base remaining
Show Answer

Correct: (A)

The conjugate acid of the weak base is present and hydrolyses to produce H^+, so the pH is below 7.

Q52In Cl2 + 2Br^- → 2Cl^- + Br2, which species is oxidized?

(A) Cl2
(B) Cl^-
(C) Br2
(D) Br^-
Show Answer

Correct: (D)

Br^- changes from oxidation number -1 to 0 in Br2, so it loses an electron and is oxidized.

Q53In a galvanic cell, where does oxidation occur?

(A) At the cathode, which is positive
(B) At the cathode, which is negative
(C) At both electrodes equally
(D) At the anode
Show Answer

Correct: (D)

Oxidation always occurs at the anode. In a galvanic cell, the anode is the negative electrode.

Q54How much charge is transferred by 0.500 mol of electrons? F = 96500 C mol^-1.

(A) 193000 C
(B) 96500 C
(C) 48250 C
(D) 24125 C
Show Answer

Correct: (C)

Q = nF = 0.500 × 96500 = 48250 C.

Q55Why can a buffer resist changes in pH when a small amount of acid or base is added?

(A) It contains only a strong acid
(B) It contains a weak acid and its conjugate base that react with added base or acid
(C) It has no ions
(D) It prevents all neutralization reactions
Show Answer

Correct: (B)

The conjugate base neutralizes added H^+, while the weak acid neutralizes added OH^-, limiting pH change.

Q56Which definition describes an electrophile?

(A) An electron-pair acceptor
(B) An electron-pair donor
(C) A species with an unpaired electron only
(D) A species that is always positively charged and never reacts at a pi bond
Show Answer

Correct: (A)

Electrophiles accept a pair of electrons when forming a new covalent bond.

Q57What type of reaction is CH4 + Cl2 in ultraviolet light?

(A) Free-radical substitution
(B) Electrophilic addition
(C) Nucleophilic substitution
(D) Acid-base neutralization
Show Answer

Correct: (A)

Ultraviolet light produces chlorine radicals, which substitute hydrogen atoms in methane.

Q58Ethanoic acid reacts with ethanol in an esterification reaction. Besides the ester, what product forms?

(A) Hydrogen
(B) Carbon dioxide
(C) Oxygen
(D) Water
Show Answer

Correct: (D)

Esterification is a condensation reaction between a carboxylic acid and an alcohol, producing an ester and water.

Q59What is the pOH of 0.00100 mol dm^-3 NaOH?

(A) 11.00
(B) 1.00
(C) 3.00
(D) 10.00
Show Answer

Correct: (C)

NaOH is a strong base, so [OH^-] = 1.00 × 10^-3 and pOH = 3.00.

Q60Conversion of ethene to ethane by reaction with H2 is classified as what type of process?

(A) Oxidation because hydrogen is removed
(B) Reduction because hydrogen is added
(C) Elimination because a double bond remains
(D) Substitution because no atoms are added
Show Answer

Correct: (B)

Addition of hydrogen to an organic compound is hydrogenation and is classified as reduction in this context.