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Qualitative analysis: tests for ions

Past-paper questions pack

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Questions are numbered; the mark schemes (the answer key) follow on separate pages so the question pages can be handed out alone. www.chemistryaleveltutor.com

OCR AS and A-level Chemistry past-paper questions since 2016 · 25 parts · mark schemes follow the questions · www.chemistryaleveltutor.com · Questions and mark schemes © OCR

1. June 2025 · Paper 1 · Q21(a)(ii) · 2 marks ·
(ii) Solutions of iron(II) sulfate, FeSO4, and copper(II) sulfate, CuSO4, can be distinguished by adding aqueous sodium hydroxide. Describe what would be observed when NaOH(aq) is added to each solution. Observation with FeSO4(aq) ............................................................ Observation with CuSO4(aq) ............................................................ [2]
2. June 2025 · AS Paper 1 · Q22(c) · 4 marks ·
(c) A group of students is provided with aqueous solutions of sodium chloride, sodium bromide and sodium iodide in three unlabelled bottles. Explain how the students can identify which bottle contains each aqueous solution using precipitation reactions and the solubility of any precipitate formed. Include an ionic equation in your answer. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [4]
3. June 2025 · Paper 3 · Q4(a)(ii) · 7 marks ·
(ii) Complete the flowchart by adding formulae in the boxes. ................. ................. white precipitate white precipitate Ag+(aq) Ba2+(aq) ................. ................. ................. acidic solution containing three ions Cl 2(aq)/H2O(I) H+(aq)/H2S(g) SO3 2–(aq) ................. ................. yellow solid colourless neutral liquid H+/Cr2O7 2–(aq) Ba2+(aq) green solution white precipitate [7]
4. June 2024 · AS Paper 1 · Q10 · 1 marks ·
10 An unknown compound is tested to identify whether it contains sulfate, carbonate or halide ions. What is the correct sequence of tests required? A carbonate, halide, sulfate B carbonate, sulfate, halide C halide, carbonate, sulfate D sulfate, carbonate, halide Your answer [1]
5. June 2024 · Paper 1 · Q13 · 1 marks ·
13 A student analyses a solution of a salt. The results are shown below. Test Observation Reaction with NaOH(aq) Green precipitate Reaction with Ba(NO3)2(aq) White precipitate What is the formula of the salt? A CuCl 2 B CuSO4 C FeCl 2 D FeSO4 Your answer [1]
6. June 2024 · AS Paper 2 · Q1(c)(iii) · 2 marks ·
(iii) Outline how you would test for the presence of NH4 + ions in a solution. Your answer should include observations. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [2]
7. June 2023 · Paper 1 · Q11 · 1 marks · AO2
11 A student adds aqueous potassium carbonate to one test tube and aqueous silver nitrate to a second test tube. The student adds dilute hydrochloric acid to each test tube. Which row has the correct observations? Aqueous potassium carbonate Aqueous silver nitrate A no change precipitate B no change no change C effervescence no change D effervescence precipitate Your answer [1]
8. June 2023 · AS Paper 2 · Q2(b)(i) · 2 marks · AO2
(b) A student has a 5.00 g mixture of sodium chloride, NaCl (s), and barium nitrate, Ba(NO3)2(s). The student also has a solution of sodium sulfate, Na2SO4(aq). The student uses the method below to determine the percentage by mass of NaCl (s) in the mixture. Step 1 Dissolve the 5.00 g mixture in distilled water. Step 2 Add an excess of Na2SO4(aq) to the solution. A precipitate of barium sulfate forms. Step 3 Filter off the precipitate, wash with water, and dry. Step 4 Weigh the dried precipitate. The molar mass of barium sulfate is 233.4 g mol–1. (i) Write an equation for the formation of barium sulfate in step 2. Include state symbols. ...................................................................................................................................... [2]
9. June 2023 · Paper 3 · Q4(c)(ii) · 3 marks · AO2
(ii) The student adds NaOH(aq) to the aqueous solution of Tutton’s salt and warms the mixture. A precipitate and a gas are formed. Write the formulae of the precipitate and gas and suggest a test that could confirm the identity of the gas. Formula of precipitate ....................................................................................................... Formula of gas .................................................................................................................. Test to confirm the identity of the gas ................................................................................ ........................................................................................................................................... ...................................................................................................................................... [3]
10. June 2023 · Paper 3 · Q4(c)(iii) · 2 marks · AO2
(iii) How could the student carry out a test-tube test to confirm the anion in the Tutton’s salt? ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
11. June 2022 · Paper 1 · Q21(b)(ii) · 1 marks · AO3
(ii) 10 cm3 of dilute sulfuric acid is added to 10 cm3 of the colourless solution of Ba(OH)2. Write an ionic equation, including state symbols, for the reaction. ...................................................................................................................................... [1]
12. June 2022 · AS Paper 1 · Q24(b) · 5 marks · AO3
(b) A student is supplied with aqueous solutions of ionic compounds B and C. Compound B is a chloride, bromide or iodide of a Group 1 element. Compound C is a chloride, bromide or iodide of a Group 2 element. The molar masses of B and C are both in the range 100–115 g mol–1. Use this information and test-tube tests to show how the student could identify the halide present in B and C and the formulae of B and C. Explain your reasoning. In your answer, include observations, colours and equations. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]
13. June 2022 · AS Paper 2 · Q2(b)(ii) · 2 marks · AO3
(ii) A student adds a few drops of dilute sulfuric acid to the colourless solution. Describe what the student would observe, and give the formula of the barium compound produced. Observation ....................................................................................................................... Formula of barium compound ........................................................................................... [2]
14. November 2021 · Paper 1 · Q15 · 1 marks ·
15 NH4Fe(SO4)2•12H2O is a hydrated ‘double salt’. A student analyses this double salt using test tube tests. Which row(s) gives/give correct result(s) for the stated test? Test Results 1 Reaction with cold NaOH(aq) Green precipitate 2 Reaction with Ba(NO3)2(aq) White precipitate 3 Reaction with warm NaOH(aq) Red-brown precipitate and an alkaline gas A 1, 2 and 3 B Only 1 and 2 C Only 2 and 3 D Only 1 Your answer [1]
15. November 2020 · Paper 1 · Q22(a) · 6 marks · AO3
22 (a)* B and C are compounds of two different transition elements. A student carries out test tube reactions on aqueous solutions of B and C. The observations of the student’s tests are shown below. Test B(aq) C(aq) NH3(aq) added dropwise green precipitate D grey-green precipitate E 1 excess NH3(aq) added no further change purple solution F HNO3(aq) no change no change 2 followed by Ba(NO3)2(aq) white precipitate G no change HNO3(aq) no change no change 3 followed by AgNO3(aq) no change white precipitate H Analyse the results to identify B to H, and construct ionic equations for the formation of products D to H. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
16. November 2020 · AS Paper 2 · Q1(c) · 6 marks · AO1, 2, 3
(c)* A student is provided with samples of three nickel compounds. One sample is nickel(II) bromide, another is nickel(II) sulfate and the third is nickel(II) carbonate. The student doesn’t know which sample is which. Describe the tests that the student could carry out to identify the anion (negative ion) in each sample, and write equations for any reactions. [6] ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... Additional answer space if required ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...................................................................................................................................................
17. June 2019 · AS Paper 1 · Q23(b) · 5 marks · AO3
(b) You are supplied with a sample of ammonium bromide. Describe simple tests that would identify the cation and anion present in ammonium bromide. Include reagents, expected observations and relevant equations. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]
18. June 2018 · Paper 1 · Q7 · 1 marks · AO2
7 Which statement about ammonium carbonate is not correct? A It reacts with Ba(NO3)2(aq) to form a white precipitate. B It effervesces with dilute nitric acid. C It release an alkaline gas with warm NaOH(aq). D It has the formula NH4CO3. Your answer [1]
19. June 2018 · AS Paper 1 · Q23(a)(ii) · 2 marks ·
(ii) At the end of the experiment, the student adds a few drops of aqueous sodium chloride to the reaction mixture in the polystyrene cup to test whether all the aqueous silver nitrate has reacted. Explain how the results would show whether all the aqueous silver nitrate has reacted. Include an equation with state symbols in your answer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
20. June 2017 · Paper 1 · Q8 · 1 marks ·
8 Four pairs of solutions are mixed. Which pair of solutions forms a white precipitate? A NH4Cl (aq) and NaOH(aq) B KBr(aq) and AgNO3(aq) C FeCl 3(aq) and NH3(aq) D Cr2(SO4)3(aq) and BaCl 2(aq) Your answer [1]
21. June 2017 · Paper 1 · Q17(d)(i) · 2 marks ·
(d) Two changes are described below. For each change, • write an equation, including state symbols, • state and explain how the entropy changes. (i) The reaction of aqueous barium nitrate with aqueous sodium sulfate. Full equation with state symbols ........................................................................................................................................... Explanation of entropy change .......................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
22. June 2017 · AS Paper 1 · Q22(b) · 5 marks ·
(b) B and C are ionic compounds of two different Group 1 elements. The molar masses of B and C are both approximately 140 g mol–1. A student dissolves B and C in water in separate test tubes and analyses the solutions. The observations are shown below. Observation Test B(aq) C(aq) Addition of HNO3(aq) bubbles no change followed by BaCl2(aq) no change white precipitate Use this information and the observations to identify the formulae of B and C. Explain your reasoning. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [5]
23. June 2017 · AS Paper 2 · Q1(b)(ii) · 2 marks ·
(ii) Describe the use of aqueous barium chloride in qualitative analysis. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2]
24. June 2016 · AS Paper 1 · Q11 · 1 marks ·
11 A student adds aqueous sodium carbonate to one test-tube and aqueous silver nitrate to a second test-tube. The student adds dilute sulfuric acid to each test-tube. Which row has the correct observations? Aqueous sodium carbonate Aqueous silver nitrate A no change precipitate B no change no change C effervescence no change D effervescence precipitate Your answer [1]
25. June 2016 · AS Paper 1 · Q23(c)(ii) · 1 marks · AO1
(ii) How would the appearance of the precipitates allow you to distinguish between chloride, bromide and iodide ions? Chloride ............................................................................................................................. Bromide ............................................................................................................................. Iodide ................................................................................................................................ [1]

Mark schemes

1. June 2025 · Paper 1 · Q21(a)(ii)
Mark scheme June 2025 Paper 1 Q21(a)(ii)
2. June 2025 · AS Paper 1 · Q22(c)
Mark scheme June 2025 Paper 1 Q22(c)
3. June 2025 · Paper 3 · Q4(a)(ii)
Mark scheme June 2025 Paper 3 Q4(a)(ii)
4. June 2024 · AS Paper 1 · Q10
Mark scheme June 2024 Paper 1 Q10
5. June 2024 · Paper 1 · Q13
Mark scheme June 2024 Paper 1 Q13
6. June 2024 · AS Paper 2 · Q1(c)(iii)
Mark scheme June 2024 Paper 2 Q1(c)(iii)
7. June 2023 · Paper 1 · Q11
Mark scheme June 2023 Paper 1 Q11
8. June 2023 · AS Paper 2 · Q2(b)(i)
Mark scheme June 2023 Paper 2 Q2(b)(i)
9. June 2023 · Paper 3 · Q4(c)(ii)
Mark scheme June 2023 Paper 3 Q4(c)(ii)
10. June 2023 · Paper 3 · Q4(c)(iii)
Mark scheme June 2023 Paper 3 Q4(c)(iii)
11. June 2022 · Paper 1 · Q21(b)(ii)
Mark scheme June 2022 Paper 1 Q21(b)(ii)
12. June 2022 · AS Paper 1 · Q24(b)
Mark scheme June 2022 Paper 1 Q24(b)
13. June 2022 · AS Paper 2 · Q2(b)(ii)
Mark scheme June 2022 Paper 2 Q2(b)(ii)
14. November 2021 · Paper 1 · Q15
Mark scheme November 2021 Paper 1 Q15
15. November 2020 · Paper 1 · Q22(a)
Mark scheme November 2020 Paper 1 Q22(a)
16. November 2020 · AS Paper 2 · Q1(c)
Mark scheme November 2020 Paper 2 Q1(c)
17. June 2019 · AS Paper 1 · Q23(b)
Mark scheme June 2019 Paper 1 Q23(b)
18. June 2018 · Paper 1 · Q7
Mark scheme June 2018 Paper 1 Q7
19. June 2018 · AS Paper 1 · Q23(a)(ii)
Mark scheme June 2018 Paper 1 Q23(a)(ii)
20. June 2017 · Paper 1 · Q8
Mark scheme June 2017 Paper 1 Q8
21. June 2017 · Paper 1 · Q17(d)(i)
Mark scheme June 2017 Paper 1 Q17(d)(i)
22. June 2017 · AS Paper 1 · Q22(b)
Mark scheme June 2017 Paper 1 Q22(b)
23. June 2017 · AS Paper 2 · Q1(b)(ii)
Mark scheme June 2017 Paper 2 Q1(b)(ii)
24. June 2016 · AS Paper 1 · Q11
Mark scheme June 2016 Paper 1 Q11
25. June 2016 · AS Paper 1 · Q23(c)(ii)
Mark scheme June 2016 Paper 1 Q23(c)(ii)