Whitley Prelim P2 Ans

1 WHITLEY SECONDARY SCHOOL SCIENCE DEPARTMENT PRELIMINARY EXAMINATIONS 2024 CHEMISTRY PAPER 2 (6092/02) SECONDARY 4 EXPRESS Setter: Mrs Ambikai Answers Qn Answers Marks / Remarks 1 (a) F [1] each (b) B (c) A (d) D (e) E 2 (a) A: Iron (II) carbonate B: Iron (II) oxide C: carbon dioxide D: sulfuric acid [1] each (b) FeO + 2H+  Fe2+ + H2O [1] (c) The iron (II) hydroxide was oxidised to form iron (III) hydroxide which is brown in colour [1] 3 (a) Non-metal. Boron shares electrons with fluorine to form covalent bonds. [1] (b) Boron does not have stable noble gas configuration It has only 6 electrons around it even after forming covalent bonds with fluorine [1] [1] (c) Low melting point. Boron trifluoride is a simple covalent molecule with weak intermolecular forces of attraction (or van der waals forces) which requires only a small amount of energy to be overcome. [1] [1] 4 (a) +3 +5 +2 +4 All correct: [2] 3 or 2 correct: [1] 1 correct: [0] (b) (i) Mn(NO3)2  MnO2 + 2NO2 [1] (ii) Manganese is oxidised and nitrogen is reduced As the oxidation state of Mn increases from +2 in Mn(NO3)2 to +4 in MnO2As the oxidation state of N is decreased from +5 in Mn(NO3)2 +4 in NO2. Hence it is a redox reaction. [1] [1] [1]

2 5 (a) The higher the air : fuel ratio, the lower is the concentration of carbon monoxide emitted by the car; When the air : fuel ratio is high, there are more oxygen available for complete combustion to take place; Thus more carbon dioxide is produced instead of carbon monoxide; [1] [1] [1] (b) More complete combustion takes place when the air : fuel ratio increases; More heat is produced causing the temperature to be very high; This causes more reaction between nitrogen and oxygen to take place to form oxides of nitrogen; [1] [1] [1] (c) Carbon dioxide is a greenhouse gas; and contributes to global warming. This has led to climate change resulting in: (any 2)  changes in rainfall patterns  heat waves  tropical storms  melting of polar ice caps [1] [1] [2] 6 (a) Monoatomic refers to a substance that consists of single atoms, not bonded to each other. [1] (b) Atoms of noble gases have a complete valence shell/stable electronic configuration and do not need to gain, lose or share electrons. [1] (c) Each of the noble gas have different boiling points. [1] (d) Neon has the smallest (relative) atomic mass / atoms have the smallest masses [1] [1] (e) 7 (a) Manganese, chromium, iron; Manganese is the most reactive as it displaces both iron and chromium from their compounds; Chromium is more reactive than iron as it displaces iron from its compound OR Iron is the least reactive as it is unable to displace both manganese and chromium from its compounds. [1] [1] [1] (b) Mn (s) + Fe2+(aq)  Mn2+(aq) + Fe (s) 1] for corre