<p> An Experiment on Nine Unknown Bottles (Extracted from American Chemical Society : Modern Experiments for Introductory College Chemistry, 1967) Possible Combinations of the Nine Bottles</p><p>2</p><p> l M M M M M M M</p><p>6 M M M M M C M 6 M 1 M M 6</p><p>9 3 1 </p><p>2 5 5 2 2 h 1 5 3 3 . . . . . t . . . . i 0 0 0 0 0 0 0 0 0 W</p><p>. d t a s</p><p>H O a N</p><p>M</p><p>6 . 0 l 3 3 4 I 3 2 O l 3 4 3 O C 2 2 r 3 O l l H O O K O S O C 2 O O O H 2 H 4 B l O C S S C O S N S N a I 2 2 a a 2 N a 2 a H C a g a a a N K N B N H H N N K N A N N - N l C a N</p><p>1 x x x x x x x x x 2 x x x x x x x x x 3 x x x x x x x x x 4 x x x x x x x x x 5 x x x x x x x x x 6 x x x x x x x x x 7 x x x x x x x x x 8 x x x x x x x x x 9 x x x x x x x x x 10 x x x x x x x x x 11 x x x x x x x x x 12 x x x x x x x x x 13 x x x x x x x x x 14 x x x x x x x x x 15 x x x x x x x x x 16 x x x x x x x x x 17 x x x x x x x x x 18 x x x x x x x x x 19 x x x x x x x x x 20 x x x x x x x x x 21 x x x x x x x x x 22 x x x x x x x x x</p><p>One of the Combinations and the Expected Results No. of bottle Chemical No. of bottle Chemical</p><p>1 KClO3 6 NaOH</p><p>2 H2O 7 H2SO4</p><p>3 BaCl2 8 NH4Cl 4 KI 9 NaBr</p><p>5 Na2S 1 (a) 1 + 7 + 2  No reaction (b) 1 + 7 + 4  I2 No (c) 1 + 7 + 9  Br2 2 (d) 2 + 4 + 7  No reaction reaction (e) 9 + 7 + 2  No reaction (f) I2 [from (b) + 7 + 1 (excess)  colorless solution 3 No No reaction reaction</p><p>4 No No No reaction reaction reaction</p><p>5 No No White No reaction reaction ppt. reaction</p><p>6 No No Cloudy No No reaction reaction reaction reaction</p><p>7 No No White No White ppt. + Heat reaction reaction ppt. reaction odour of evolved</p><p>H2S</p><p>8 No No No No Odour Odour No</p><p> reaction reaction reaction reaction of H2S of NH3 reaction</p><p>9 No No No No No reaction No No No reaction reaction reaction reaction reaction reaction reaction 1 2 3 4 5 6 7 8 9</p><p>Workshop on School-based Assessment</p><p>Skills to be assessed in GCE Science Subjects P – Planning I – Implementation A – Analysing evidence and drawing conclusions E – Evaluating evidence and procedures</p><p>Examples to illustrate how these skills can be assessment Example 1: Inorganic/Organic Qualitative Analysis (I & A) Carry out the tests outlined below on two compounds A and B, each of which contains one cation and one anion. Based on your results, suggest the cations and anions they contained.</p><p>Test Observation Inference To an aqueous solution of A, add NH3(aq) dropwise until in excess. To an aqueous solution of A, add acidified BaCl2(aq). Carry out a flame test on B. Mix aqueous solutions of A and B. Then add a few drops of starch solution to the mixture.</p><p>A: NH4Fe(SO4)2.12H2O(s); B: NaI(s) Example 2: Freezing Point Determination of an Organic Compound (I & E) 1. Heat compound D in a water bath until it melts. 2. Allow the molten D to cool while measuring its temperature to the nearest 0.5oC for every half-minute for 8 minutes. 3. Plot a cooling curve and read from your curve the freezing point of D. 4. Evaluate the method of freezing point determination. Suggest reasons why the method may not give an accurate value of the freezing point, and improvements to the method. D: palmitic acid C15H31CO2H Example 3: Planning an Experiment The following three compounds are colourless liquids: </p><p> cyclohexene propanone 2-bromopropane</p><p>You are required to plan a series of tests to distinguish the three compounds from one another. Your answer should include a brief description of each test and the expected observation. Notes; Marks will be awarded to the logical sequence of the tests and their effectiveness in identify/eliminate the compounds. Equations and quantities of reagents used and not required. If any of the compounds and/or reagents used in a test has a potential hazard, suggest the necessary safety precautions.</p>