A-LevelChemistryAnalytical techniques9701/31 · Oct/Nov 2019 · Q316 Marks

FA 5 is a salt that contains two different cations and a single anion from those listed in the Qualitative Analysis Notes.

(a)(i)Place a small spatula measure of FA 5 in a hard-glass test-tube and heat gently. Do not inhale the fumes. Record all your observations. [2][2]
(a)(ii)Pour a 4 cm depth of distilled water into a boiling tube. Add the remaining FA 5 and stir carefully until the solid has dissolved. This solution is FA 6. Carry out the following tests on FA 6 and record your observations. test To a 1 cm depth in a test-tube, add aqueous ammonia. To a 1 cm depth in a boiling tube, add aqueous sodium hydroxide, then warm the mixture. To a 1 cm depth in a test-tube, add aqueous barium nitrate or aqueous barium chloride, then add dilute hydrochloric acid or dilute nitric acid. [4][4]
(a)(iii)Identify the three ions in FA 5. FA 5 contains .............................................. , .............................................. and .............................................. . [2][2]
(b)A student carried out Qualitative Analysis tests on a hydrated salt, FA 7, and concluded that it contained the ions K⁺, Cr³⁺ and SO₄²⁻. The relative formula mass of FA 7 is 499.3. Determine the formula of FA 7. The formula of FA 7 is .............................................. . [2][2]
(c)(i)FA 8 is a solution containing a single cation and a single anion, both of which are listed in the Qualitative Analysis Notes. Carry out the following tests and record your observations. test To a 1 cm depth in a test-tube, add a few drops of aqueous acidified potassium manganate(VII), then add starch indicator. To a 1 cm depth in a test-tube, add aqueous sodium hydroxide. [2][2]
(c)(ii)Identify the two ions in FA 8. FA 8 contains .............................................. and .............................................. . [1][1]
(c)(iii)Suggest an additional test you could carry out to confirm the presence of the anion in FA 8. Carry out this test and record your result. [2][2]
(c)(iv)Give the ionic equation for the reaction you carried out using FA 8 and sodium hydroxide. Include state symbols. [1][1]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2019). The mark or mark type is shown in brackets.

[1] • melts / dissolves • condensation / moisture on the walls of the test-tube / steam produced • white smoke / fumes (NOT gas) • (gas) turns red litmus blue gas turns blue litmus red • white residue Award 1 mark for two correct observations from the list, award 2 marks for three or more correct observations. If both gas observations are given they must be in the correct order for both to be credited.
[1] NH3 White ppt and insoluble in excess
[1] NaOH White ppt and sol in excess Allow 1 mark for white ppt with both NH3 and NaOH
[1] hot NaOH Gas / NH3 (on warming) turns red litmus blue
[1] Ba2+ White ppt insoluble in acid / white ppt no reaction with acid Reject white ppt formed when acid added
[1] names or correct formulae
[1] NH4+, Al3+, SO42- Award 1 mark for two ions, award 2 marks for three ions.
[1] Any formula (involving all three ions) in which the charges on the ions cancel (e.g. K3Cr(SO4)3)
[1] KCr(SO4)2.12H2O
[1] Red-brown (allow yellow / yellow-brown / orange / orange-brown / brown) (solution) or KMnO4 / purple decolourises and turns blue-black / dark blue / black (on adding starch)
[1] Green ppt and insoluble in excess / turns brown (on standing) Reject grey-green
[1] Fe2+ / iron(II) and I-/iodide This mark is free-standing
[1] Uses silver nitrate and yellow ppt
[1] ppt insoluble in HNO3 or ppt insoluble in NH3 (nitric acid may be added initially)
[1] Fe2+(aq) + 2OH-(aq) → Fe(OH)2(s) ecf for Cr3+ / Cu2+ / Fe3+ or any other transition metal ion concluded in (ii).