We used the winkler method to determine the dissolved oxygen content in water.?

Question

i forgot what's supposed to happen when MnSO4 solution, NaOH-KI solution, conc H2SO4 and starch are added separately. i know one solution makes a brown precipitate and one turns the water black but which?! help please!!:)

Answer 1

The Winkler test is used to determine the level of dissolved oxygen in water samples. This metric is then used to estimate the biological activity in the water sample. An excess of Manganese(II) salt, iodide (I-) and hydroxide (OH-) ions are added to a water sample causing a white precipitate of Mn(OH)2 to form. This precipitate is then oxidized by the dissolved oxygen in the water sample into a brown Manganese precipitate. In the next step, a strong acid (either hydrochloric acid or sulphuric acid) is added to acidify the solution. The brown precipitate then convert the iodide ion (I-) to Iodine. The amount of dissolved oxygen is directly proportional to the titration of Iodine with a thiosulphate solution