RI 2017 Y5 Promo Suggested Solutions

1 © Raffles Institution 9729/ Year 5 Promo /2017 RAFFLES INSTITUTION 2017 YEAR 5 H2 CHEMISTRY PROMOTION EXAMINATION S ECTION A 1 2 3 4 5 6 7 8 9 10 D D A D C B D B A A 11 12 13 14 15 16 C C B B D C 1 Answer: D relative molecular mass = weighted average mass of 1 molecule of the substance 1 12 x mass of 1 atom of carbon-12 S tudents need to find the option which most closely describes the above. A. Inc orrect. If only the relative isotopic mass of the most abundant isotope was considered for each atom, it will not be able to account for the mass of the different isotopes of the sam e el ement, which is required for the weighted average mass. B. Incorrect. The denominator should have been t he mass of 1 12 of one 12C atom. C. Incorrect. The denominator should have been the mass of 1 12 of 1 mole of 12C atoms. D. Correct. This option most accurately defines relative atomic mass. 2 Answer: D G2+ ion has the same number of electrons as PH3, i.e. G2+ ion has 18 electrons. So, G must have 20 electrons. As the 4s orbital will be filled before the 3d orbitals, the ground state electronic configuration of G will be 1s2 2s2 2p6 3s2 3p6 4s2. 3 Answer: A 1. Incorrect. Cu2O contains Cu+ ion. The ground state electronic configuration of Cu is 1s2 2s2 2p6 3s2 3p6 3d10 4s1. To f orm Cu+ ion, the electron will be removed from the 4s orbital. The ground state electronic configuration of Cu+ is 1s2 2s2 2p6 3s2 3p6 3d10. Cu+ ion does not have an unpaired d electron. 2. Incorrect . Zn(NO3)2 contains Zn2+ ion. The ground state electronic configuration Zn is 1s2 2s2 2p6 3s2 3p6 3d10 4s2. To f orm Zn2+ ion, the 2 electrons will be removed from the 4s orbital. The ground state electronic configuration of Zn2+ is 1s2 2s2 2p6 3s2 3p6 3d10. Zn2+ ion does not have an unpaired d electron. 3. Correct. Ti2(SO4)3 contains Ti3+ ion. The ground state electronic configuration of Ti is 1s2 2s2 2p6 3s2 3p6 3d2 4s2. To form Ti 3+, 2 electrons will be removed from the 4s orbital, followed by 1 electron from a 3d or bital. This document is copyrighted, please do not reproduce it without permission

2 © Raffles Institution 9729/ Year 5 Promo /2017 The ground state electronic configuration of Ti3+ is 1s2 2s2 2p6 3s2 3p6 3d1. Ti3+ ion has an unpaired d electron. H ence, only option 1 is correct. 4 Answer: D The actual bond length of N(1)≡N(2) (0.112 nm) in N2O is between that of N=N (0.120 nm) and N≡N (0.110 nm), which indicates that the N(1)≡N(2) bond in N2O is stronger than a N=N bond but weaker than a N≡N bond. Also, the actual bond length of N (2)→O (0.119 nm) in N 2O is between that of N –O (0.147 nm) and N=O (0.115 nm) , which indicates that the N(2) →O bond in N 2O is stronger than a N –O bond but weaker than a N=O bond. This is due to the delocalisation of the π electrons between N(1) and N(2) over the N(2)→O bond, which weakens the N(1)≡N(2) bond but strengthens the N(2)→O bond. 5 Answer: C amount of L = 0.058 46.