Hayley and Maeve joined Derek Shrubsol’s grade 10 class (Oak Bay High School) to measure dissolved oxygen in Bowker Creek (Feb. 7th, 2020).
The water samples were treated with manganous sulfate, potassium hydroxide, potassium iodide, and finally sulfuric acid. The initial precipitate of manganous hydroxide, Mn(OH)2, combines with the dissolved oxygen in the sample to form a brown precipitate, manganic hydroxide, MnO(OH)2. Upon acidification, the manganic hydroxide forms manganic sulfate which acts as an oxidizing agent to release free iodine from the potassium iodide. The iodine, which is stoichiometrically equivalent to the dissolved oxygen in the sample, was then titrated with sodium thiosulfate.
Images show some of the students completing this final titration. So, how much O2 was in the water? I will post the answer here when I have it. I hope they washed their hands – see Talen’s Bowker Creek E. coli survey in the ‘Classroom’ section of our Blogs page.