Determination of Dissolved Oxygen in a Water Sample Essay

To find out the group O content of a water sample by adding MnSO4 and alkaline KI into the solving. Mn2+ was oxidized into Mn3+. Then Mn3+ was reduced back into Mn2+ and I- was oxidized to I2. The solution was titrated against sodium thiosulphate solution and the group O content could be calculated.Result exertion1Trial2Final burette reading (cm3)19.2638.4219.8238.35Initial burette reading (cm30.1019.500.7419.82 people of Na2S2O3 added (cm3)19.1618.9219.0818.53Data being used for calculationCalculationNo of moles of Na2S2O3 used =2S2O32- + I2 S4O62- + 2I-No. of moles of I2 in cytosine cm3 solution = = 1.18252Mn(OH)3 + 2I- + 6H+ I2 + 2Mn2+ + 6 pissNo. of moles of Mn(OH)3 in 100 cm3 solution = 1.1825 X 2 = 2.3654 Mn(OH)2 + O2 + 2 H2O 4 Mn(OH)3No. of moles of O2 in 100 cm3 solution = 2.365Oxygen content = 18.92 mg dm-3Discussion case of filling the whole volumetric flaskDuring the experiment, the water sample was allowed to fill with the whole volumetric flask, this is because we wear to prevent oxygen from dissolving from the air into the water sample.Reason of using a magnetic scaremongerWhen conducting the experiment, insoluble manganese (III) hydroxide was formed. It would dissolve in potassium iodide so we have to use a magnetic fluff uprer to speed up the reaction process. As a magnetic stirrer could stir the solution without spilling, it is very good to be used in this situation.Source of errorAs the manganese (II) sulphate and potassium iodide solution was added into the flask with over flowing. There will be loss of solution in this process. The chemicals added might be not enough and it will affect the experiment result.We cannot avoid oxygen in air from dissolving into the solution as the mouth of volumetric flask could still allow oxygen to diffuse in.Only one set of data could be used beside trials.