S.6 Chemestry Paper 1

Page 1 of 6 Apex Examination Council 0781170799 CANDIDATE’S NAME…………………………………………………………………….. SIGNATURE…………………………………………… PRE MOCK EXAMUNATIONS 2026 UGANDA ADVANCED CERTIFICATE OF EDUCATION CHEMISTRY PAPER 1 INSTRUCTIONS TO CANDIDATES This paper consists two sections A and B. It has 6 examination items. Section A has two compulsory items. Section B has two parts. Part I and part II. Answer one item from each part. Answer four items in all. Any additional item(s) answered will not be scored. Personal number Page 2 of 6 Apex Examination Council 0781170799 SECTION A Answer all questions in this section. ITEM 1 SCENARIO PhosGuard Industries manufacture phosphorus -derived reagents used in water treatment to remove heavy metal poisoning. Part of their continuous firing reactor line handles phosphorus(V) chloride (PCl₅) as an intermediate. The safety team performs gas phase equilibrium checks to ensure plant safety and downstream water treatment compatibility. A gas phase equilibrium test was carried out by introducing 3.60 moles of phosphorus(V) chloride into a rigid vessel of volume 2.00 dm³ at a given temperature. Analysis showed 1% dissociation according to: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) ΔH = +124 kJ mol⁻¹ Using this information, the equilibrium constant, Kc, can be determined. In a follow -up process optim ization test, the company introduces an additional 0.050 moles of chlorine gas (Cl₂) into the same system at the same temperature. A treatment test was carried out where 0.208 g of phosphorus(V) chloride (PCl₅) was completely hydrolysed in 1.00 dm³ of water, producing hydrochloric acid (HCl). The acid produced supplies chloride ions (Cl⁻), which are then used to react with lead(II) ions (Pb²⁺) in wastewater to form a precipitate. PCl₅(g) + 4H₂O(l) → H₃PO₄(aq) + 5HCl(aq) Pb²⁺(aq) + 2Cl⁻(a q) → PbCl₂(s) A sample of wastewater contains 0.020 mol dm⁻³ Pb²⁺ ions. You have been contacted for help. TASK As …