NYJC 2021 H2 Chemistry 9729 P2

[Turn Over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 2 CANDIDATE NAME CLASS TUTOR’S NAME CHEMISTRY 9729/02 Paper 2 Structured Questions 01 September 2021 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name and class 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 in the spaces provided on the Question Paper. 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. For Examiner’s Use 1 /14 2 /16 3 /20 4 /25 Total /75 This document consists of 20 printed pages..

2 H2 Chemistry 9729/02 NYJC J2/2021 PRELIM. Answer all the questions in the spaces provided. 1 This is a question on the salts of magnesium. (a) Struvite, MgNH4PO4·6H2O, is a fertiliser mineral that can be obtained from wastewaters. It is a salt that contains two cations and one anion. (i) Draw a dot-and-cross diagram of MgNH4PO4. [2] (ii) Explain why MgNH4PO4 is only slightly soluble in water. …..………………………………………………………………………………………… ..…………………………………………………………………………………………… ….…………………………………………………………………………………………. …………………………………………………………………………………………. [1] (iii) Thermal decomposition of MgNH4PO4 produces an alkaline gas, water and a white powder of magnesium pyrophosphate, Mg2P2O7. Write an equation with state symbols for this reaction. …………………………………………………………………………………………. [1] (b) The value of the solubility products and melting points of some magnesium salts at 298 K are shown in Table 1.1. Table 1.1 salt value of solubility product melting point / oC magnesium chloride, MgCl2 714 magnesium hydroxide, Mg(OH)2 1.8 × 1011 350 magnesium phosphate, Mg3(PO4)2 4.0 × 1025 1184 In this question, give each of your numerical answers to two significant figures. Magnesium phosphate is widely used in medication to support the relaxation of muscles. This compound is used to prevent the cramping of muscles and vitamin E deficiency. (i) With an appropriate equation, define the lattice energy of magnesium phosphate. …..………………………………………………………………………………………… ..…………………………………………………………………………………………… …………………………………………………………………………………………. [2]

3 H2 Chemistry 9729/02 NYJC J2/2021 PRELIM. [Turn Over (ii) Suggest an explanation, in terms of structure and bonding, for the differ