Chemistry questions and solutions
Browse original practice and official past-paper questions. Each question has its own link, with its source and worked solution.
364 questions · Page 2 of 16
- Q25 · 2025 QCAA · Paper 1 · 4 marksOrganic chemistryQUESTION 25 (4 marks) But-2-ene can form structural isomers and geometric isomers. a) Draw one structural isomer of but-2-ene and apply IUPAC rules to name this isomer. [2 marks] IUPAC name: b) Draw one geometric isomer of but-2-ene and apply IUPAC rules to name this isomer. [2 marks] IUPAC name: Note: If you make a mistake, cancel it by ruling a single…
- Q26 · 2025 QCAA · Paper 1 · 3 marksChemical synthesisQUESTION 26 (3 marks) One step of the contact process involves reacting sulfur dioxide (SO2) and oxygen (O2) to produce sulfur trioxide (SO3), as shown. 2SO2(g) + O2(g) 2SO3(g) The equilibrium constant (Kc) for the forward reaction is 5.6 × 104 at 350 °C and 9.2 × 101 at 800 °C. a) Determine whether the forward reaction is exothermic or endothermic. [1…
- Q27 · 2025 QCAA · Paper 1 · 4 marksRedox and electrochemistryQUESTION 27 (4 marks) Determine the product formed at the cathode and the oxidation half-equation that occurs when various NaCl electrolytes undergo electrolysis using inert electrodes. Include states of matter in your response. Electrolyte Cathode product Oxidation half-equation concentrated (25%) NaCl(aq) molten NaCl(l)
- Q28 · 2025 QCAA · Paper 1 · 8 marksAcids, bases and titrationQUESTION 28 (8 marks) A 10.0 mL volume of a weak monoprotic base (BOH) was pipetted into a volumetric flask and diluted to a final volume of 50.0 mL using distilled water. A 25.0 mL aliquot of the BOH solution was then titrated with 0.1 M hydrochloric acid (HCl). The reaction and titration curve are shown. BOH(aq) + HCl(aq) → BCl(aq) + H2O(l) 12.0 10.0 8.0…
- Q29 · 2025 QCAA · Paper 1 · 6 marksChemical synthesisQUESTION 29 (6 marks) The oxidation of meso-hydrobenzoin (C14H14O2) to produce benzaldehyde (C7H6O) was carried out via three different reaction pathways to evaluate atom economy and E-factor. Atom economy is a measure of reaction efficiency based on the percentage of the total mass of reactants successfully converted to the desired product. E-factor is a m…
- Q1 · 2025 QCAA · Paper 2 · 8 marksRedox and electrochemistryQUESTION 1 (8 marks) A galvanic cell was constructed using copper and magnesium electrodes. V Salt bridge Mg Cu 1 M Mg(NO3)2(aq) 1 M Cu(NO3)2(aq) a) Determine the half-equation occurring in the Mg | Mg(NO3)2 half-cell. [1 mark] b) Contrast the flow of electrons and the movement of anions in the cell. [2 marks] c) Describe two changes that would be observ…
- Q2 · 2025 QCAA · Paper 2 · 3 marksOrganic analysisQUESTION 2 (3 marks) An organic compound is analysed using mass spectroscopy and infrared spectroscopy. a) Describe how the mass spectrum could be used to determine if the organic compound is hexanal or hexan-2-one. [2 marks] b) Explain how the infrared spectrum could be used to determine if the organic compound is hexanal or hexanoic acid. [1 mark]
- Q3 · 2025 QCAA · Paper 2 · 5 marksAcids, bases and titrationQUESTION 3 (5 marks) Alizarin yellow R is an acid–base indicator that is yellow in its non-ionised form (HIn) and red in its conjugate base form (In−). HIn(aq) + H2O(l) H3O+(aq) + In−(aq) Yellow Red The dissociation constant (Ka) for alizarin yellow R is 7.9 × 10−12. a) Determine the pKa. [1 mark] b) Explain the…
- Q4 · 2025 QCAA · Paper 2 · 5 marksAcids, bases and titrationQUESTION 4 (5 marks) Hypochlorous acid (HOCl) is a weak acid formed by dissolving chlorine (Cl2) gas in water. Hydrochloric acid (HCl) is also formed in this process. Cl2(g) + H2O(l) → HOCl(aq) + HCl(aq) The dissociation constant (Ka) for hypochlorous acid is 2.8 × 10−8. a) Describe the dissociation of HOCl(aq) and HCl(aq) using balanced chemical equations…
- Q5 · 2025 QCAA · Paper 2 · 6 marksOrganic analysisQUESTION 5 (6 marks) A section of a protein was hydrolysed and then underwent electrophoresis in a buffer of pH 5. The amino acids present in the electrophoresis gel shown were arginine (Arg), cysteine (Cys), glutamic acid (Glu) and an unknown amino acid, X. Power supply (+) (−) P Q R X a) Determine the amino acids represented by spots P, Q and R. Explain…
- Q6 · 2025 QCAA · Paper 2 · 10 marksOrganic chemistryQUESTION 6 (10 marks) The table shows the boiling points and molar masses of several organic compounds. Compound Class Name Molar mass Boiling point (g mol−1) (°C) CH3CH2CH2CH2CH3 alkane pentane 72 −1 CHO2CH2CH3 ester 74 32 CH3CH2CH2CHO aldehyde butanal 72 49 CH3CH2CH2CH2OH alcohol 74 97 CH3CH2COOH carboxylic acid 74 118 a) Predict whether hexane has a hig…
- Q7 · 2025 QCAA · Paper 2 · 4 marksChemical synthesisQUESTION 7 (4 marks) Contrast the operation of a hydrogen fuel cell under acidic conditions and a hydrogen fuel cell under alkaline conditions by completing the table. Hydrogen fuel cell Contrast Acidic conditions Alkaline conditions Electrolyte used Movement of ions Note: If you make a mistake, cancel it by ruling a single diagonal line through your work a…
- Q8 · 2025 QCAA · Paper 2 · 9 marksOrganic chemistryQUESTION 8 (9 marks) Haloalkanes are useful intermediates for making other organic compounds. 1-bromopropane KCN(ethanol) conc. NH3(ethanol) conc. NaOH(ethanol) heat/reflux heat heat/reflux Compound A Alkene NaOH(aq) heat/reflux Amine B Amine C Compound D a) Determine the structural formulas and IUPAC names for compounds A and D. [4 marks] Compound A IUPA…
- Q9 · 2025 QCAA · Paper 2 · 5 marksChemical equilibriumQUESTION 9 (5 marks) Yellow chromate ions (CrO4 −) are in equilibrium with orange dichromate ions (Cr2O7 2−) in an aqueous solution. −(aq) + 2H+(aq) Cr2O7 2−(aq) + H2O(l) 2CrO4 Yellow Orange Two experiments were conducted to investigate the effect of pH on the position of equilibrium. −] [H+] 2−] [CrO4 [Cr2O7 Kc at 25 °C (mol…
- Q1 · 2024 QCAA · Paper 1 · 1 markChemical equilibriumQUESTIONS 1–2 Questions 1–2 refer to hydrated copper sulfate and its decomposition when heated. Hydrated copper sulfate (CuSO4·H2O) decomposes to form copper sulfate (CuSO4) and water when heated. heat + CuSO4·H2O(s) CuSO4(s) + H2O(g) QUESTION 1 Which of the following is exchanged with the surrounding environment when CuSO4·H2O(s) is heated in a closed syste…
- Q2 · 2024 QCAA · Paper 1 · 1 markRedox and electrochemistryQUESTIONS 1–2 Questions 1–2 refer to hydrated copper sulfate and its decomposition when heated. Hydrated copper sulfate (CuSO4·H2O) decomposes to form copper sulfate (CuSO4) and water when heated. heat + CuSO4·H2O(s) CuSO4(s) + H2O(g) QUESTION 2 Determine the oxidation number of sulfur (S) in CuSO4·H2O. (A) + 8 (B) + 6 (C) − 2 (D) − 4
- Q3 · 2024 QCAA · Paper 1 · 1 markRedox and electrochemistryQUESTION 3 Identify which of the following is an essential component of an electrolytic cell. (A) voltmeter (B) salt bridge (C) power supply (D) standard hydrogen electrode (SHE)
- Q4 · 2024 QCAA · Paper 1 · 1 markPolymers and biomoleculesQUESTION 4 Identify which polymer contains a carbonyl (C= O) group. (A) polyester (B) polyethene (C) polypropene (D) polytetrafluorethene
- Q5 · 2024 QCAA · Paper 1 · 1 markAcids, bases and titrationQUESTION 5 Titration is a volumetric analysis method used to (A) measure the pH of an analyte. (B) determine the volume of a titrant. (C) calculate the concentration of an identified solution. (D) prepare a standard solution of known concentration and volume.
- Q6 · 2024 QCAA · Paper 1 · 1 markAcids, bases and titrationQUESTION 6 The equivalence point of an acid–base titration occurs when the (A) pH equals the pKa. (B) pH stops changing. (C) indicator changes colour. (D) titrant completely neutralises the analyte.
- Q7 · 2024 QCAA · Paper 1 · 1 markChemical synthesisQUESTION 7 Which option is a principle of green chemistry? (A) avoid chemical derivatives (B) decrease energy efficiency (C) prevent catalytic reactions (D) minimise atom economy
- Q8 · 2024 QCAA · Paper 1 · 1 markOrganic chemistryQUESTION 8 H H H O H C C C C O H H H H Determine the IUPAC name of the organic compound shown. (A) butanoic acid (B) butanone (C) butanol (D) butanal
- Q9 · 2024 QCAA · Paper 1 · 1 markPolymers and biomoleculesQUESTION 9 Polytetrafluorethene (PTFE) has a higher melting point than polypropene (PP) due to the (A) C– F bonds being non-reactive. (B) fluorine atoms forming stable C– F covalent bonds. (C) dispersion forces between closely packed fluorocarbon chains. (D) dipole–dipole interaction between fluorine and carbon atoms within the fluorocarbon chain.
- Q10 · 2024 QCAA · Paper 1 · 1 markAcids, bases and titrationQUESTION 10 The acid dissociation constant (Ka) represents the (A) pH of an acid solution. (B) strength of an acid solution. (C) concentration of an acid solution. (D) conjugate acid–base pairs of an acid solution.