VJC 2022 H2 Chem Prelim P2_ans_

1 © VJC 2022 9729/02/PRELIM/22 [Turn over CANDIDATE NAME CT GROUP VICTORIA JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 ……………………………………………….………….. …………………………….. CHEMISTRY 9729/02 Paper 2 Structured Questions Candidates answer on the Question Paper. 15 September 2022 2 hours Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and CT group in the space at the top of this page. Write in dark blue or black pen. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the space provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 / 25 2 / 13 3 / 12 4 / 19 5 / 6 Total / 75 This document consists of 18 printed pages.

2 © VJC 2022 9729/02/PRELIM/22 [Turn over 1 (a) The most common oxidation states of iron are +2 and +3. (i) Iron(II) and iron(III) both contain electrons in all five 3d orbitals. Sketch and label the shape of the following two 3d orbitals: • one 3d orbital from the lower energy level in an octahedral complex • one 3d orbital from the higher energy level in an octahedral complex Use the axes below. [2] • Lower energy level (in between axes) 3dxy 3dxz 3dyz • Higher energy level (on the axes) 3dx2-y2 3dz2 (ii) Explain why Fe2+(aq) ions are coloured, whereas Zn2+(aq) ions are colourless. • The degenerate 3d orbitals in Fe 2+ octahedral complex is split into 2 different energy levels due to the presence of water ligands. • d-d transition took place whereby a 3d electron from the lower energy level is promoted to the upper energy level by absorbing energy from the visible region of the electromagnetic spectrum. The colour seen is the complement of the colour absorbed. • Fe2+ has a partially-filled d subshell but Zn2+ has completely filled 3d subshell and so d-d transition whereby an electron is promoted from a lower energy level to a higher energy level is impossible. [3] lower energy level higher energy level z y x

3 © VJC 2022 9729/02/PRELIM/22 [Turn over (iii) Most naturally occurring samples of iron(II) oxide are found as the mineral w üstite. Wüstite has formula Fe20Ox. It contains bo