To determine the % by mass of manganese (IV) oxide in a solid sample. ( By Titration )

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 …

…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.