A-LevelChemistryChemical bonding9701/41 · May/June 2019 · Q19 Marks

Aqueous solutions of copper(II) salts contain the blue-coloured [Cu(H2O)6]²+ complex ion. Separate portions of this blue solution react with aqueous sodium hydroxide and with concentrated hydrochloric acid.

(a)Give the following information for each of these reactions. • reaction with aqueous sodium hydroxide ionic equation type of reaction colour and state of the copper-containing product • reaction with concentrated hydrochloric acid ionic equation type of reaction colour and state of the copper-containing product[6]
(b)Chloride ions can be identified using aqueous silver nitrate, AgNO3(aq). Ag+(aq) + Cl-(aq) → AgCl(s) 0.303 g of a chloride of sulfur is completely hydrolysed with water. All the chlorine atoms present in the chloride of sulfur are converted into chloride ions. The solution is diluted to 100.0 cm³. A 25.00 cm³ sample of this solution is titrated with 0.0500 mol dm⁻³ AgNO3(aq). The titration requires 22.40 cm³ of 0.0500 mol dm⁻³ AgNO3(aq). Calculate the empirical formula of the chloride of sulfur. Show all your working. empirical formula of chloride of sulfur =[3]

Mark scheme

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

M1 [Cu(H2O)6]2+ + 2OH- → Cu(OH)2 + 6H2O
M2 precipitation
M3 blue precipitate
M4 [Cu(H2O)6]2+ + 4Cl- → CuC142- + 6H2O
M5 ligand exchange / displacement / substitution / replacement
M6 yellow solution
M1 amount of Ag+ = 0.050 × 0.0224 = 1.12 × 10-3 mol (in 25 cm³) amount of Ag+ = 1.12 × 10−3 × 4 = 4.48 × 10–3 mol (in 100 cm³)
M2 amount of Cl- = 4.48 × 10–3 mol (in 100 cm³) mass of Cl- = 4.48 × 10−3 × 35.5 = 0.159 g (in 100 cm³) mass of S = 0.303 – 0.159 = 0.144 g (in 100 cm³) ecf
M3 moles of S = 0.144/32.1 = 4.49 × 10-3 molar ratio S: Cl 1:1 → SCl ecf

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.