2021 MI Prelim H2 Chemistry P2 (9729_02) Answers

Class Adm No Candidate Name: This question paper consists of 17 printed pages and 1 blank page. 2021 Preliminary Exams Pre-University 3 H2 CHEMISTRY 9729/02 Paper 2 Structured Questions 16 Sep 2021 2 hours Candidates answer on the Question paper. Additional materials: Data Booklet READ THESE INSTRUCTIONS FIRST Do not turn over this question paper until you are told to do so Write your name, class and admission number on all the work you hand in. 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. The use of an approved scientific calculator is expected, where appropriate. A Data Booklet is provided. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. Question 1 2 3 4 5 6 Total Marks 13 7 18 13 9 15 75

2 Answer all questions in the spaces provided. 1 (a) Explain why the ions of Group 2 elements increase in size down the Group. [2] Although both nuclear charge and shielding effect increases, the distance between the valence electron and the nucleus increases. ; The electrostatic forces of attraction between the positive nucleus and the outermost electron decreases and valence electrons are pulled less closely. ; (b) Magnesium is a Group 2 element. Magnesium nitrate decomposes to form an oxide and two gases when heated strongly. (i) Write a balanced chemical equation, with state symbols, for the decomposition of magnesium nitrate. [1] 2 Mg(NO3)2 (s) ⟶ 2 MgO (s) + 4 NO2 (g) + O2 (g) (ii) Describe and explain the relative thermal stability of magnesium nitrate and barium nitrate. [2] Ba2+ ion is larger than Mg2+ ion while charge is the same, thus Ba2+ has a lower charge density and polarises NO3– less. ; N–O bond is weakened less and BaNO3 is more thermally stable. ; (iii) 2.0 g of magnesium nitrate was heated strongly with a non-luminous Bunsen flame until it was completely decomposed. On the same axes, sketch a graph showing the progress of reaction as 2.0 g of barium nitrate was strongly heated with the same Bunsen flame until it was completely decomposed. [1] Mg(NO3)2 mass of solid remaining / g 2.0 time Ba(NO3)2 less steep everywhere flatten and higher mass remaining

3 [Turn over (c) One of the products of the decomposition of Group 2 nitrates is the metal oxide. Metal oxides are ionic compounds with attractive forces existing within them that can be quantified by the lattice energy. (i) Using the following data and relevant data from the Data Booklet, construct a Born-Haber cycle