Materials: 2 ml manganese sulphate solution, 2 ml alkaline-iodine solution, 0.025M sodium thiosulphate solution, 2ml concentration sulphuric acid, starch solution
Procedure
1. When sampling water, care must be taken to ensure that a good representative sample of the water to be analyzed is obtained. For most purposes, this includes attention to dissolved gases. Therefore, the water sample should be taken in a clean bottle which must be filled to overflowing and tightly sealed with stopper without introduction of air. If the water is sampled from a tap, it must be allowed to run for at least 5 minutes prior to sampling. For this purpose, you may collect the water into a 1 L reagent bottle fitted with a stopper.
2. The stopper is removed carefully from the conical flask and 2 mL of the manganese sulfate solution is added, discharging the reagent from the tip of a pipette put well below the water surface. Stopper is replaced.
3. Similarly, 2 mL of the alkaline-iodide solution is introduced.
4. The stopper is placed in the bottle, be sure that no air becomes entrapped. Some overflow may occur. The content is mixed thoroughly by inversion and rotation. Manganese hydroxide is precipitated and will settled on standing.
5. When the precipitate has settled, 2 mL of concentrated sulfuric acid is introduced with the tip of the pipette well below the surface of the solution.
6. The stopper is replaced and mixed until the precipitate dissolves completely. The dissolved oxygen now liberates
