3) experimental procedure, part B.3. A solutuion of MnSO4 is added to fix the dissolved oxygen in the collected sample.
a) what is the meaning of the experission, "fix the dissolved oxygen," and why is it so important for the analysis of dissolved oxygen in a water sample?
b) only an approximate volume (~1mL) of MnSO4 is required for fixing the dissolved oxygen in the sample, explain why an exact volume is not crtical.
can any one help me to solve these questions?
2017-10-31 12:20 am
回答 (1)
2017-10-31 1:29 am
a)
The terms "fixed the dissolved oxygen" means that dissolved oxygen is converted to a compound that cannot escape away from the solution. To fix the dissolved oxygen, an excess of MnSO₄ solution and an excess of alkaline potassium iodide are added to the water sample, dissolved oxygen in the sample oxidizes manganese(II) ions to manganese(III) hydroxide precipitate in the alkaline medium.
8OH⁻(aq) + 4Mn²⁺(aq) + O₂(aq) + 2H₂O(l) → 4Mn(OH)₃(s)
The fixation of dissolved oxygen is important for the analysis of dissolved oxygen in water sample. Firstly, the dissolved oxygen cannot escape from the solution after fixation. Secondly, Dissolved oxygen is completely converted to Mn(OH)₃ quantitative. The amount of dissolved oxygen can be found by the determination of the amount of Mn(OH)₃.
b)
This is because MnSO₄ is in excess, while the dissolved oxygen is the limiting reactant.
The terms "fixed the dissolved oxygen" means that dissolved oxygen is converted to a compound that cannot escape away from the solution. To fix the dissolved oxygen, an excess of MnSO₄ solution and an excess of alkaline potassium iodide are added to the water sample, dissolved oxygen in the sample oxidizes manganese(II) ions to manganese(III) hydroxide precipitate in the alkaline medium.
8OH⁻(aq) + 4Mn²⁺(aq) + O₂(aq) + 2H₂O(l) → 4Mn(OH)₃(s)
The fixation of dissolved oxygen is important for the analysis of dissolved oxygen in water sample. Firstly, the dissolved oxygen cannot escape from the solution after fixation. Secondly, Dissolved oxygen is completely converted to Mn(OH)₃ quantitative. The amount of dissolved oxygen can be found by the determination of the amount of Mn(OH)₃.
b)
This is because MnSO₄ is in excess, while the dissolved oxygen is the limiting reactant.
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