RVHS_H1_Chemistry_P2_Soln_2024

River Valley High School 8873/02/PRELIMS/24 2024 Preliminary Examination [Turn over River Valley High School 2024 JC 2 H1 Chemistry 8873 Prelim Exam Paper 2 Suggested Solution 1 (a) (b) Shape: Trigonal pyramidal Bond angle: 107° Explanation: There are 3 bond pairs and one lone pair of electrons around the central S atom. The electron pairs are arranged as far apart as possible to minimise repulsion. (c) Dative bond is formed when the N atom donates a lone pair of electrons into an empty 1s orbital of an electron deficient H atom for sharing. As a result, the electron deficient H atom achieves a stable duplet configuration. (d) Ammonium sulfite has a higher boiling point than ammonia. Ammonium sulfite has a giant ionic lattice structure while ammonia has a simple covalent structure. More energy is needed to overcome the stronger electrostatic forces of attraction between NH 4+ and SO32− ions than the weaker hydrogen bonding between NH3 molecules.

2 River Valley High School 8873/02/PRELIMS/24 2024 Preliminary Examination 2 (a) Ca2+(g) + 2Cl–(g) → CaCl2(s) H = lattice energy (b) Ionic radius of Ca2+ = 0.099 nm Ionic radius of Mg2+ = 0.065 nm |𝐿𝐸| | 𝑞+𝑞− 𝑟+ + 𝑟−| Magnitude of lattice energy of MgC l2 is higher as the ionic radius of Mg 2+ is smaller than that of Ca2+ (and both ions have the same charge), resulting in a (stronger electrostatic force of attraction between Mg2+ and Cl– ions in MgCl2). (c) [Ca(H2O)6]2+ + H2O = [Ca(H2O)5(OH)]+ + H3O+ Ca2+ ions will polarise H2O molecule, causing partial hydrolysis to occur. This will cause a small amount of H+ to form, resulting in a solution of pH 6.5.

3 River Valley High School 8873/02/PRELIMS/24 2024 Preliminary Examination [Turn over (d) Amount of CaCO3 = 11.375 100.1 = 0.1136 mol Amount of HCl = 250 1000 × 2.00 = 0.5000 mol Hence, CaCO3 is limiting. Energy released = mcΔT = (250)(4.2)(1.58) = 1659 J = 1.659 kJ x = − 1.659 0.1136 = −14.6 kJ mol−1 (e) (i) To prevent the solution from spraying out of the conical flask due to bubbling. (ii) CaCO3  CO2 Mass loss = mass of CO2 produced = 0.1136 × 44.0 = 4.998 g = 5.00 g (iii) Rate = k[HCl] (iv)

4 River Valley High School 8873/02/PRELIMS/24 2024 Preliminary Examination (v) An increase in temperature will lead to a n increase in the average kinetic energy of reactant molecules. More particles will have energy greater than or equal to Ea. The frequency of effective collisions increases. Hence, the rate of reaction increases.

5 River Valley High School 8873/02/PRELIMS/24 2024 Preliminary Examination [Turn over 3 (a) Nanomaterial is a material with at least 1 dimension on nanoscale from 1 nm to 100 nm. (b) High tensile strength. It has strong covalent bonds between atoms in a giant network of carbon atoms. (c) It is due to the (black) colour of CNT materia