Site pages
Current course
Participants
General
18 February - 24 February
25 February - 3 March
4 March - 10 March
11 March - 17 March
18 March - 24 March
25 March - 31 March
1 April - 7 April
8 April - 14 April
15 April - 21 April
22 April - 28 April
2. Principle
|
When the solutions of manganese and alkaline iodide are added to the seawater sample, the following reactions normally take place. Manganese ion reacts with the hydroxide of the alkaline iodide to give Mn(OH)2. Mn(OH)2 reacts with the dissolved oxygen present in the water sample to give Mn(OH)3. In the presence of acid (above pH 1.5), Mn(OH)2 reacts with iodide to liberate iodine. The iodine liberated is titrated against Na2S2O3 to convert the iodine to iodide. The sequence of the above reactions are explained through the following formulae: Mn2+ + 2OH- Mn(OH)2 2 Mn(OH)2 + ½ O2 + H2O 2Mn(OH)3 2Mn(OH)3 + 3 I- + 6H+ 2Mn2+ + I-3 + 6 H2O 2S2O32- + I-3 S4O62- + 3I- Range of detection: up to 10 ml O2/1 |
Last modified: Monday, 5 December 2011, 7:45 AM