2019 TJC H2 Chem Prelim P2 QP

1 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 CANDIDATE NAME CIVICS GROUP / CENTER NUMBER S INDEX NUMBER CHEMISTRY 9729/02 Paper 2 Structured Questions 28 August 2019 2 hours Candidates answer on the Question Paper. Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your Civics Group, centre number, index number and name 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. This document consists of 20 printed pages For Examiner’s Use 1 /7 2 /10 3 /10 4 /14 5 /20 6 /14 Total / 75 PRELIMINARY EXAMINATIONS HIGHER 2

2 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 1 (a) The table below shows the first, second and third ionisation energies of some elements in the Periodic Table. Element First Ionisation energy (kJ mol-1) Second Ionisation energy (kJ mol-1) Third Ionisation energy (kJ mol-1) Ca 590 1150 4940 Mn 716 1510 3250 Fe 762 1560 2960 Co 757 1640 3230 Ni 736 1750 3390 (i) Explain why the first and second ionisation energies of the transition metals are relatively invariant. [2] (ii) Write the electronic configurations of Ca and Fe atoms at ground state. Explain the differences in the values of the third ionisation energies between iron and calcium. [2]

3 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 (b) Calcium cyanamide, CaCN2, is used as a fertiliser in agriculture. Through hydrolysis in the presence of carbon dioxide, calcium cyanamide produces cyanamide, NH2CN. Cyanamide can be extracted by organic solvents. (i) Draw the dot–and–cross diagram for the cyanamide molecule, NH2CN. [1] (ii) With reference to structure and bonding, deduce whether CaCN2 has a higher or lower melting point as compared to NH2CN. [2] [Total: 7] 2 A saturated solution of magnesium methanoate, Mg(HCO 2)2, has a solubility of approximately 143 g dm–3 at room temperature. The exact solubility can be determined by titrating magnesium methanoate solution against a standard potassium manganate(VII) solution. During the titration, the methanoate ion, H CO2–, is oxidised to carbon dioxide while the manganate(VII) ion, MnO4–, is reduced to Mn2+. (a) (i) Write the overall equation for the reaction between HCO2– and MnO 4– under acidic conditions. [1]

4 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 (ii) Calculate the approximate concentration of HCO2– ions present in the saturated solution. [1] (iii) The titre value from titrating 25.0 cm 3 of saturated magnesium methanoate solution against 0.0500 mol dm–3 potassium manganate(VII) solution is found to be too high. Describe the steps to prepare a suitable solution of magnesium methanoate from the saturated solution. Your plan should include details of quantities measured and apparatus used. [3]

5 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 (b) An industrial chemist introduced 2 atm of carbon dioxide and 2 atm of hydrogen gas into a 1 dm3 container at 300 K. The temperature is then raised to 900 K, at which the Kp is 0.641. CO2(g) + H2(g) ⇌ H2O(g) + CO(g) H < 0 (i) Calculate the partial pressure of H2 present at equilibrium at 900 K. [3] (ii) Explain if the Kp value at 300 K is higher or lower than 0.641. [2] [Total: 10]

6 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 3 (a) Sulfur tetrachloride decomposes to sulfur dichloride and a gas that bleaches litmus. (i) Using the VSEPR theory, deduce and draw the shape of SCl2. Give a value for the bond angle. [3] Shape : ___________________ Bond angle : _______________ (ii) State whether the bond angle of SCl2 is expected to be larger or smaller than SF2. Explain your answer. [1]

7 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 (b) (i) There are two possible molecular arrangements for SCl4 with different relative stabilities. Draw these two molecular arrangements in the boxes below, showing clearly the shape around the central atom. [2] (I) (II) (ii) Apply the principles of the VSEPR theory to discuss the relative s tabilities of molecular arrangements (I) and (II). [1] (c) SCl4 combines with BCl3 to give X with the composition by mass: S, 11.0% ; B, 3.7%. (i) Derive the empirical formula of X. [1]

8 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 (ii) Draw a likely structure of X, showing clearly the shape around the central atom(s). State the type of bond formed when SCl4 and BCl3 combine to form X. [2] Type of bond : _____________________ [Total: 10]

9 [Turn over DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN DO NOT WRITE IN THIS MARGIN 9729 / TJC Prelim / 2019 4 (a) Hydrogen halides are acids resulting from the chemical reaction of hydrogen with one of the halogens. (i) Briefly explain the trend in the boiling point for hydrogen chloride, hydrogen bromide and hydrogen iodide. [2] (ii) By quot