Procedure: 1. All instruments were washed by using deionised water. 2. 25cm3 of sodium thiosulphate solution was pipetted out and pour into a volumetric flask. 3. Deionised water was added to the graduation mark. Part A 1. Diluted sodium thiosulphate solution with unknown concentration was poured into the burette. 2. 25cm3 of standard 0.027M iodine solution was pipetted out and pour into a conical flask. 3. The iodine solution was titrated with sodium thiosulphate solution until it became pale yellow in …showed first 75 words of 515 total…

…showed last 75 words of 515 total…to carry out the experiment in a fume-cupboard. Secondly, as Cl2 gas will be formed at the moment when hydrochloric acid meet MnO2, in order to ensure no Cl2 gas will escape, which may cause a serious error in calculation, 25cm3 of KI will be added into MnO2 first before adding in Hydrochloric acid. So that all the Cl2 gas produced will react with I- and form I2, leading to an accurate answer during calculation.