SRJC H2 CHEM P2 QP

1 SRJC 9647/02/PRELIM/2014 Turn Over] SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS CHEMISTRY 9647/02 Preliminary Examination 22 August 2014 Paper 2 Structured Questions (SPA) 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 on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough work. Answer all questions in the space provided. You are advised to spend 30 minutes on question 1. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part questions. This document consists of 19 printed pages and 1 blank page For Examiner’s Use 1(P) /12 2 /20 3 /13 4 /12 5 /15 TOTAL P2 /72 For Examiner’s Use P1 /40 P2 /72 P3 /80 GRAND TOTAL /192 % GRADE

2 SRJC 9647/02/PRELIM/2014 Turn Over] Answer all questions in the space provided 1 Planning (P) Borax, also known as sodium tetraborate decahydrate, Na 2B4O5(OH)4.10H2O, is a controlled poison in Singapore and cannot be bought off the shelf. Borax dissolves slightly in water to form an alkaline solution: Na2B4O5(OH)4(s) ⇌ 2Na+(aq) + [B4O5(OH)4]2-(aq) [B4O5(OH)4]2-(aq) + 5H2O(l) ⇌ 4H3BO3(aq) + 2OH-(aq) The solubility product of borax at 30°C can be determined via volumetric analysis using hydrochloric acid solution. (a) Assuming that a cm3 of 0.500 mol dm -3 HCl is required for titrati ng 25.0 cm 3 of borax solution at 30°C, calculate the solubility product of borax (excluding units) in terms of a. [3] (b) Deduce the sign for ∆S for the dissolution of borax . Hence, predict whether this process will be more or less feasible at a higher temperature, given that ∆H is endothermic. ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… [2] For Examiner’s Use

3 SRJC 9647/02/PRELIM/2014 Turn Over] (c) The solubility of borax can also be defined as 30 g of solid that will dissolve in 100 g of water at 60°C. Other than volumetric analysis, write a plan to validate the above information. Your plan should also include  steps to prepare a saturated solution  steps to maintain the temperature throughout the experiment ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… For Examiner’s Use

4 SRJC 9647/02/PRELIM/2014 Turn Over] …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… …………………………………………………………………………………………..…… …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… …………………………………………………………………………………………..…… ………………………………………………………………………………………..……… [6] (d) Identify one potential safety hazard in either experiment (a) or (c) and state how you would minimise this risk. …………………………………………………………………………………………..…… ……………………………………………………………………….……………….……… [1] [Total: 12] For Examiner’s Use

5 SRJC 9647/02/PRELIM/2014 Turn Over] 2 Sodium and chlorine are two common elements on Earth. Elemental chlorine is commercially produced from brine, also known as concentrated sodium chloride, by electrolysis. The electrolysis of brine solution containing neutral litmus solution is carried out in the following apparatus using graphite electrodes. The colour changes of the litmus solutions around regions A and B were observed during the process. (a) (i) With the aid of the Data Booklet, account for the colours changes observed around regions A and B. Include balanced equations where appropriate. Region Observations Reason A Litmus solution first turned red, and then turned colourless B Litmus solution turned blue asbestos diaphragm brine solution with neutral purple litmus solution graphite electrodes For Examiner’s Use A B

6 SRJC 9647/02/PRELIM/2014 Turn Over] (ii) The asbestos diaphragm is a porous material that prevents the products from electrolysis from mixing. Write an equation to illustrate the reaction that will occur at room temperature when the diaphragm was removed after the electrolysis. ……………………………………………………………………….………………. (iii) Useful chlorine -containing products such as sodium chlorate( V) and chlorine dioxide may be obtained from further processing of the products in (a)(ii). By considering the numbers of bonding and non –bonding electron pairs, draw diagrams in the boxes below to show the likely shape of ClO3 – and ClO2. In your diagrams, state the shape and clearly indicate the respective bond angle values. chlorate(V) ion , ClO3 – Shape: …………………………. Bond angle: ……………………. chlorine dioxide, ClO2 Shape: …………………………. Bond angle: ……………………. [9] (b) Chlorine dioxide is an unstable gas which decomposes into chlorine gas and oxygen gas readily. (i) Write a balanced equation for this decomposition. ……………………………………………………………………….………………. For Examiner’s Use

7 SRJC 9647/02/PRELIM/2014 Turn Over] (ii) At a pressure of 1 atm and decomposition temperature of 40 C, calculate the volume of c hlorine gas formed when 150.0 g of chlorine dioxide is decomposed. (iii) Comparing between chlorine and chlorine dioxide gas, state and explain which gas deviates more from ideal gas behaviour. ……………………………………………………………………………………… ……………………………………………………………………….……………… ……………………………