A-LevelChemistryAnalytical techniques9701/32 · May/June 2024 · Q314 Marks

3 FB 7 is an aqueous solution of a salt containing one cation and one anion, both of which are listed in the Qualitative analysis notes.

(a)(i)Carry out the following tests using a 1 cm depth of FB 7 in a test-tube for each test. Record your observations in Table 3.1. Table 3.1 test Test 1 Add aqueous barium chloride or aqueous barium nitrate. Test 2 Add aqueous sodium hydroxide, then transfer the mixture to a boiling tube and warm gently, then add a small piece of aluminium foil. Test 3 Add aqueous ammonia. observations[4]
(a)(ii)The results of the tests in Table 3.1 allow you to deduce one cation and two possible anions in FB 7. Deduce which ions may be present in FB 7. Give the formulae of the ions. cation ................................. anion ................................. or .................................[2]
(a)(iii)Describe a test to identify which of the possible anions is present in FB 7. Carry out your test. Record your observations and conclusion. test ...................................................................................................................................................................................................................................................... observations ...................................................................................................................................................................................................................................... conclusion ......................................................................................................................................................................................................................................[2]
(b)(i)FB 8 and FB 9 are solutions of Group 1 salts. Each contains one anion, both of which are listed in the Qualitative analysis notes. One of the anions contains oxygen but not nitrogen. The other anion is a halide. Carry out tests to identify the two anions. Record your tests and observations in a suitable form in the space below.[4]
(b)(ii)Use your observations in (b)(i) to complete Table 3.2 by identifying the formulae of the anions in FB 8 and FB 9. Table 3.2 FB 8 FB 9 anion[1]
(b)(iii)Write an ionic equation for a reaction observed in (b)(i) for one of the anions tested. Include state symbols.[1]

Mark scheme

Marking points from the official mark scheme (May/June 2024). The mark or mark type is shown in brackets.

[4] Test 1 • no (visible) change / no reaction / no ppt
[4] Test 2 • white ppt • soluble in excess • negative litmus test / litmus stays red / no change / no reaction • fizzing • gas / NH3 turns (damp red) litmus blue
[4] Test 3 • white ppt • soluble in excess
[4] Two points needed for each mark.
[2] M1 cation: Zn²⁺ after correct observations in Test 3
[2] M2 anions: NO2⁻ or NO3⁻ after correct ammonia gas observations in Test 2 with Al
[2] EITHER M1 add (a few drops of) (acidified aqueous) KMnO4/potassium manganate(VII) M2 no change or solution stays purple/pink AND anion is NO3⁻
[2] OR M1 add named mineral acid M2 no change/no bubbling / no brown gas / no blue solution AND anion is NO3⁻
[4] M1 table of results drawn with clear sections for test and for observations with each salt e.g. test as row-header and FB 8 and FB 9 as column-headers or vice versa
[4] M2 reagents are (aqueous) silver nitrate AND a named acid
[4] M3 + AgNO3(aq) FB 8: (pale) yellow ppt AND insoluble in (aqueous) NH3 AND white to brown ppt with FB 9 if tested
[4] M4 + named acid FB 9: effervescence / bubbling / fizzing AND gas / CO2 gives white ppt with limewater
[1] FB 8: I⁻ AND FB 9: CO3²⁻
[1] One of: Ag⁺(aq) + I⁻(aq) → AgI(s) 2H⁺(aq) + CO3²⁻(aq) → H2O(l) + CO2(g)
[1] equation must match observation from 3(b)(i)