EJC Nov 2019 H1 Chemistry 8873 Paper 2 Suggested Solutions

* 0011376599402 * I IIIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIII IIII 2 Section A Answer all the questions in this section in the spaces provided. 1 ■ Deduce the symbol of this species and include its charge, if any, and its atomic and mass numbers. · l..::_ucLES & MOE 2019 � 8873/02/O/N/19 _J � (a) Define the term isotopes. Isotopes are atoms of the same element with the same number of protons but different ············· .. number of neutrons······· ........................... ............................................................................................... [1] (b) Compared to the isotope �He, a species has • 8 times as many neutrons, • 9 times as many electrons, • 13 more protons. 31 P3− · 15 ·············································· ............................... Note: atomic number, mass number and charge must all be included in one single symbol·····································:·························· [3] Working: Number of protons = 2 + 13 = 15 Hence, the unknown species is P. Number of electrons = 9(2) = 18 Hence, charge of unknown species = 3− Number of nucleons = 8(4−2) + 15 = 31

* 0011376599403 * I IIIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIIII IIII IIII 3 (c) The relative atomic mass of an element depends on the percentage abundance of each isotope present. (i) A sample of sulfur contains four isotopes, as shown in Table 1.1. Table 1.1 isotope relative percentage isotopic mass abundance I% 328 31.972 95.02 33s 32.971 0.75 343 33.968 4.21 363 35.967 0.02 Calculate the relative atomic mass of sulfur in this sample, giving your answer to two decimal places. (ii) Suggest why the relative atomic mass in the Periodic Table for nickel is lower than that for cobalt. ....................................................................................................................................... [1] (d) Nickel reacts with sulfur to form nickel(II) sulfide, NiS. State the electronic configurations of the nickel ion, Ni2+, and the sulfide ion, s2-. Ni2+ 1s2 .................................................................................................................................. . s2- 1 s2 .......... .................................... .............. ................. ...... ....... .......... .... .......................... . [2] [Total: 9] l.!,ucLES & MOE 2019 � 8873/02/O/N/19 [Tumov� Note: answer must be in 2 d.p. (as stated in the question) or no credit will be given A sample of cobalt contains primarily of the isotope 59Co, while in a sample of nickel, 58Ni is the isotope with the highest percentage abundance. 2s2 2p6 3s2 3p6 3d8 2s2 2p6 3s2 3p6

Na is oxidised as the oxidation number of Na increases from 0 in Na to +1 in Na2O. KNO3 is reduced as the oxidation number of N decreases from +5 in KNO3 to 0 in N2. Na → Na+ + e− 2NO3− + 10e− → N2 + 6O2− Note: species such as H2O, H+ and O2 sho