A-LevelChemistryAnalytical techniques9701/32 · May/June 2025 · Q313 Marks

Solutions FB 7 and FB 8 each contain one cation and one anion. All of the ions are listed in the Qualitative analysis notes.

(a)(i)Carry out the following tests and record your observations in Table 3.1. Use a 1 cm depth of FB 7 or FB 8 in a test-tube for each test. Table 3.1 test Test 1 Add an equal volume of aqueous potassium iodide, then add excess aqueous sodium thiosulfate (aq). Test 2 Add a small spatula measure of zinc powder. Leave the mixture to stand. Test 3 Add a few drops of aqueous silver nitrate. Test 4 Add aqueous ammonia. observations FB 7 FB 8 [6][6]
(a)(ii)Deduce the formula of FB 8. FB 8 is ................................. [1][1]
(a)(iii)For FB 8, state the numbers of all the tests from Table 3.1 that involve a redox reaction. [1][1]
(a)(iv)Give the ionic equation for one of the reactions in Test 4. Include state symbols. [1][1]
(b)(i)Carry out tests to identify the anion in FB 7. The anion does not contain sulfur. Record your tests and observations in a suitable form in the space below. You must use a boiling tube if any liquid is heated. [3][3]
(b)(ii)Deduce the formula of FB 7. FB 7 is ................................. [1][1]

Mark scheme

Marking points from the official mark scheme (May/June 2025). The mark or mark type is shown in brackets.

[6] FB7 is Cu(NO3)2; FB8 is FeCl3 2 * = 1 mark (round down). Max. 6 marks 2 x highlighted boxes = 1 * Test 1 FB 7: Brown colour (ignore state) * Test 1 FB 8: Brown/red-brown solution (forms) *
Test 1 FB 7 then add excess: white ppt (formed)*, ppt soluble in excess / solution turns colourless*
Test 1 FB 8 then add excess: turns colourless / goes (pale) yellow / pale pink*
Test 2 FB 7: Pink / brown / black solid*
Test 2 FB 7 then leave: solution turns paler blue / colourless *
Test 2 FB 8: Fizzing / effervescence *
Test 2 FB 8 then leave: (gas) pops with lighted splint *
Test 3 FB 7: no change / no ppt / no reaction AND
Test 3 FB 8: ppt forms *
Test 4 FB 7: (pale) blue ppt * soluble in excess * deep / dark blue solution formed / in excess *
Test 4 FB 8: brown / red-brown / rust ppt AND insoluble in excess (NH3) *
[1] FB 8 is FeCl3
[1] Tests 1 AND 2 (are redox)
[1] One equation from: • Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s) • Cu²⁺(aq) + 4NH₃(aq) → [Cu(NH₃)₄]²⁺(aq) • Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)
[3] M1 Add (excess) NaOH to FB 7 AND heat AND add aluminium
[3] M2 Gas / ammonia / fizzing turns (damp red) litmus blue
[3] M3 Add (acidified) KMnO4 AND remains purple / no change / not decolorised OR Add specified (dilute) mineral acid AND no change / no fizzing / no brown gas
[1] FB 7 is Cu(NO3)2

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