Determination of Dissolved Oxygen in a Water Sample Essay Example for Free

Determination of Dissolved Oxygen in a Water Sample EssayTo find out the oxygen content of a pissing sample by adding MnSO4 and alkaline KI into the re firmness of purpose. 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 oxygen content could be calculated.ResultTrial1Trial2Final burette reading (cm3)19.2638.4219.8238.35Initial burette reading (cm30.1019.500.7419.82Volume of Na2S2O3 added (cm3)19.1618.9219.0818.53Data being utilize for calculationCalculationNo of moles of Na2S2O3 used =2S2O32- + I2 S4O62- + 2I-No. of moles of I2 in 100 cm3 solution = = 1.18252Mn(OH)3 + 2I- + 6H+ I2 + 2Mn2+ + 6H2ONo. 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-3DiscussionReason of filling the whole volumetrical flaskDuring the experiment, the water sample was all owed to fill with the whole volumetric flask, this is because we have to prevent oxygen from turn from the air into the water sample.Reason of using a magnetic stirrerWhen conducting the experiment, insoluble manganese (III) hydroxide was formed. It would dissolve in potassium iodide so we have to use a magnetic stirrer to fastness up the reaction process. As a magnetic stirrer could stir the solution without spilling, it is very respectable 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 turn into the solution as the mouth of volumetric flask could still allow oxygen to diffuse in. notwithstanding one set of data could be used beside trials.