2021 DHSH2 Prelim Paper 1_Worked Solutions

2021 Y6 Preliminary Examination H2 Chemistry 9729 Paper 1 Suggested Solutions ã DHS Chemistry Unit Page 1 of 6 Answer Key 1 2 3 4 5 6 7 8 9 10 C D B D B C C A D C 11 12 13 14 15 16 17 18 19 20 B B C A C A D D B C 21 22 23 24 25 26 27 28 29 30 A B A D C A D B A C 1 C No. of electrons in Re3+75187 = 75 – 3 = 72 No. of neutrons in Re3+75187 = 187 – 75 = 112 Calculate the number of electrons and neutrons in each ion and compare to that of Re3+75187.This ion should have 72 electrons and 112 neutrons. O A No. of electrons in 182W2+ (Z = 74) = 74 – 2 = 72 No. of neutrons in 182W3+ = 182 – 74 = 108 (≠ 112) O B No. of electrons in 186W+ (Z = 74) = 74 – 1 = 73 (≠ 72) No. of neutrons in 186W+ = 186 – 74 = 112 P C No. of electrons in 188Os4+ (Z = 76) = 76 – 4 = 72 No. of neutrons in 188Os4+ = 188 – 76 = 112 O D No. of electrons in 189Os3+ (Z = 76) = 76 – 3 = 73 (≠ 72) No. of neutrons in 189Os3+ = 189 – 76 = 113 (≠ 112) 2 D The largest increase in successive ionisation energies (IE) occur between 9th and 10th IE. This implies that the 10th electron is removed from an inner shell. Since Z ≤ 20, only s and p subshells exists. Hence, each shell can only accommodate up to a maximum of 8 electrons. This would imply that the 2nd to 9th electron also lies in another inner shell. There will be only one electron in the valence shell. This element therefore belongs to Group 1 (either Na or K). O A The element belongs to Group 1 since it has only one electron in the valence shell. O B There is insufficient data to conclude that the element lies in the third period. Since Z ≤ 20, this Group 1 element can be in the fourth period. O C As a Group 1 element, the 6th and 7th electrons are removed from the same p-subshell. P D There is a large electronegativity difference between the Group 1 element and oxygen (Group 16). Hence, the compound formed will be ionic in nature. 3 B O A BeCl2 is linear while SO2 is bent. P B Both CO2 and I3− are linear. O C NO3− is trigonal planar while PH3 is trigonal pyramidal. O D PO43− is tetrahedral while SF4 is see-saw. Be ClCl S OO C OO II I N OO O P H H H P O OO O 3 S F F F F

Dunman High School 2021 Y6 Preliminary Examination – H2 Chemistry 9729/01 Solutions ã DHS Chemistry Unit Page 2 of 6 4 D O A In giant molecular structures, the lattice of atoms are held together by strong covalent bonds. O B Ionic bonding is non-directional. Each cation is electrostatically attracted to any anion, not necessarily to the anion to which electrons were transferred. O C In giant metallic structures, only valence electrons are delocalised within the metal lattice. P D Simple molecular structures are held together by weak intermolecular forces of attraction such as instantaneous dipole-induced dipole (id-id) interactions, permanent dipole-permanent dipole interactions and hydrogen bonding. 5 B Based on the mole ratio, CH3OH is the limiting reagen