2024 TMJC JC2 H2 Chemistry - Prelim P4 (Suggested Solutions)

Answer all questions in the spaces provided. 1 Investigation of some inorganic and organic reactions In this question, you will be investigating some inorganic and organic reactions by carrying out the stipulated tests. Carefully record your observations in Tables 1.1 and 1.2. Unless otherwise stated, the volumes given below are approximate and should be estimated rather than measured. (a) Organic analysis In this question, you will deduce the structure of an organic compound, FA 1. FA 1 has the molecular formula C4H8O2 with two functional groups present. Do not carry out the tests for which observations have been recorded. Do not use the Bunsen burner for heating in this part of the question. Instead, use the hot water provided. Table 1.1 tests observations (i) Place about 2 cm depth of aqueous sulfuric acid in a test-tube. To this test -tube, add about 1 cm depth of FA 1, followed by 1 drop of aqueous potassium manganate(VII). Warm the mixture in the hot water bath for two minutes.  Purple KMnO4 decolourises / turns colourless. (ii) Add 1 cm depth of aqueous silver nitrate to a test-tube. Then slowly add 1 cm depth of aqueous sodium hydroxide. Add aqueous ammonia slowly, with shaking, until the precipitate just dissolves. To this mixture, add about 1 cm depth of FA 1. Place the test-tube containing the mixture in the water bath for two minutes.  Black / b rown / grey ppt formed  Black / b rown / grey ppt dissolves to give a colourless solution  No silver mirror observed. (iii) Place about 1 cm depth of FA 1 in a test -tube. To this test -tube, add 2,4 -dinitrophenylhydrazine dropwise. Orange ppt. formed (iv) Place about 1 cm depth of FA 1 and add 8 drops of aqueous sodium hydroxide in a test -tube. Then, add aqueous iodine dropwise, until a permanent yellow / orange colour is obtained. Warm the mixture in the hot water bath for two minutes.  Brown / Orange solut ion decolourises.  Pale yellow ppt observed. (v) Place 1 cm depth of FA 1 in a test-tube. To this test-tube, cautiously add a small piece of anhydrous phosphorus pentachloride. Dense white fumes, which turns moist blue litmus paper red. [2] M1 M2 4 to 6 marking points – [M1] and [M2] 2 to 4 marking points – [M1] only Markers’ Comments o Some candidates were unfamiliar with the expected observations for these common reagents used in Organic Qualitative Analysis. o Many candidates omitted the observations that accompanied the preparation of Tollens’ reagent. Candidates also wrongly wrote “no observable change” for the negative Tollens’ reagent test, even though it was not permissible to write so.

2024 H2 Chemistry Paper 4 (Suggested Solutions) 2 Tampines Meridian Junior College 2024 JC2 Preliminary Examination H2 Chemistry (b) (i) Observations from (a)(ii) and (a)(iii) can be used to identify one of the functional groups present in FA 1. Identify the f