RVHS_H1_Chemistry_P1_Soln_2024

River Valley High School 2024 JC 2 H1 Chemistry 8873 Prelim Exam Paper 1 Worked Solutions 1 A The decomposition involves: n → p+ + e− where the newly-formed proton stays in the nucleus. As the proton number of the atom increases by 1 following the decomposition, the element will no longer be the same. Options B and D are eliminated. Option A involves an increase in proton number by 1 going from K to Ca, hence it is the correct answer. 2 C Option A: By definition, one mole of a substance contains exactly 6.02  1023 (or Avogadro number) elementary entities. Option A is incorrect because of the phrase “same number of atoms as there are in 12.000 g of carbon-12”. Option B: By definition, relative isotopic mass (Ar) is the mass of one mole of atoms of an isotope (of a certain element) relative to 1 12 the mass of one mole of 12C atoms. Option B is incorrect because in the formula given, the numerator used is “average mass of all isotopes of lithium”. Option C: By definition, relative atomic mass (Ar) is the average mass of one mole of atoms of an element relative to 1 12 the mass of one mole of 12C atoms. Note that some textbooks define relative atomic mass as “the average mass of one atom of an element relative to 1 12 the mass of one 12C atom”. Hence, option C is correct. Option D: By definition, relative molecular (Mr) mass is the average mass of one mole of molecules relative to 1 12 the mass of one mole of 12C atoms. Option D is incorrect because in the formula given, the numerator used is “average mass of one atom of E”.

3 A Statement 1: Correct According to Aufbau’s build up principle, in the ground state of an atom or ion, electrons fill atomic orbitals of the lowest available energy level before occupying higher-energy levels. Statement 2: Incorrect The order of filling the orbitals is 1s, 2s, 2p, 3s, 3p, 4s, 3d. Statement 3: Incorrect The shell with principal quantum number 2 only has 2s and 2p orbitals. Hence, it can hold a maximum of 8 electrons. 4 D A: Due to the overlap of unhybridised 2p orbitals, mobile delocalised electrons are found in the lattice structure. B: Each carbon atom forms 3 sigma bonds with 3 other carbon atoms. C: Instantaneous dipole-induced dipole interactions exist between each graphite plane. D: Conduction of electricity occurs due to the overlap of unhybridised 2p orbitals. The overlapping occurs perpendicular to the axis of the unhybridised 2p orbitals. 5 A A: There is an unpaired electron on N atom in NO2 molecule. B: The Cu+ ion has an electronic configuration of 1s2 2s2 2p6 3s2 3p6 3d10 4s0. C: The Li+ ion has an electronic configuration of 1s2 2s0. D: After heterolytic fission, Cl+ and Cl ions are formed, which do not have a single unpaired electron. 6 B When indicator P turns yellow, it means pH of solution is higher than 5. When indicator Q turns yellow, it means pH of solution is less than 5.7. Therefore, pH range of the soluti