Mock Paper 3

CHEMISTRY 9729/03 Paper 3 Free Response Questions 2 hours READ THESE INSTRUCTIONS FIRST Write in dark blue or black pen. You may use an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. Answer all questions in the spaces provided on the Question Paper. If additional space is required, you should use the pages at the end of this booklet. The question number must be clearly shown. Section A Answer all questions. Section B Answer one question. The use of an approved scientific calculator is expected, where appropriate. The number of marks is given in brackets [ ] at the end of each question, or part question. Question 1 2 3 4 5 Total Marks scored Maximum Marks 22 15 23 20 20 80 This document consists a total of 30 printed pages and 3 blank pages.

Paper by @ijustloveh2chem 2 BLANK

Paper by @ijustloveh2chem 3 Section A: Answer all questions. 1 Nitrogen, being the most abundant element in our atmosphere, is an element with much research interest and many applications. (a) Apart from N2, there are a few other poly-nitrogen species that are discovered to be stable enough at room temperature. One of these poly-nitrogen species is N5+. N5+ has 5 nitrogen atoms arranged in a straight-chain. Only the sigma bonds of N5+ is shown in the structure below. Na—Nb—Nc—Nd—Ne Some data is presented in Table 1.1. Bond length of Na—Nb and Nd—Ne 110 pm Bond length of Nb—Nc and Nc—Nd 130 pm Bond angle of Na—Nb—Nc 168° Bond angle of Nb—Nc—Nd 111° Table 1.1 (i) State the principles of the Valence Shell Electron Pair Repulsion theory. [2] (ii) State the geometry at the atoms Nb, Nc and Nd that most suitably explains the data in Table 1.1. [1] (iii) By considering your answer in (ii) and data in Table 1.1, draw a dot-and-cross diagram of N5+. [2] (iv) State the oxidation state of each of the nitrogen atoms Na to Ne from your dot-and-cross diagram in (iii). [1] …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… ……………………………………………………………………………………………………………

Paper by @ijustloveh2chem 4 …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… …………………………………………………………………………………………………………… (b) The azide ion, N3-, is another poly-nitrogen species. The hypothetical salt [N5+] [N3-] has been postulated to be unstable at low temperatures. Some 2.267 mmol of [N5+] [SbF6-] was mixed with 2.267 mmol of CsN3 in SO2 at -196 °C. The mixture was warmed to -64 °C (the melting point of SO2), and a violent reaction started to take place