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Using Redox Titration to Analyze the Oxidizing Strength of Bleach Lab

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Introduction

Abhinav Jain Ms. O'Hanlon Chemistry HL Period 8 22nd November, 2009 Using Redox Titration to Analyze the Oxidizing Strength of Bleach Lab Data Collection and Processing: Volume of KIO3 = 10.00 cm3 = 0.01 dm3 Molarity of KIO3 = 0.005000 M Since M = n/v Moles of KIO3 = 0.01 dm3 � 0.005 m = 0.00005 moles KIO3 The following table shows values for standardization: (Trial) Titration 1 � 0.05 cm3 Titration 2 � 0.05 cm3 Titration 3 � 0.05 cm3 Start 0.00 15.50 30.70 End 15.50 30.70 46.00 Total 15.50 15.20 15.30 Average Titre value= (15.20 + 15.30)/2 = 15.25 cm3 = 0.01525 dm3 Uncertainty Propagation found later Qualitative Observations: The Sodium Thiosulfate was white and clumped up into rocks. When mixed with water, it dissolved easily. The Sodium Carbonate was white and very fine like iron filings and again, dissolved easily when mixed with water. In order to find the concentration of the Thiosulfate, we need to convert the moles of KIO3 into moles of S203 Looking at the following equations: IO3- (aq) + 5 I- (aq) + 6 H+ (aq) ...read more.

Middle

2 S203 2- (aq) + I2 (aq) 2 I- (aq) + S406 2- (aq) ClO- + 2I- + 2H+ H2O + I2 + Cl- The Hypochlorite to Iodine ratio is 1:1 And the Thiosulfate ratio to Iodine is 2:1 Therefore the Thiosulfate to Hypochlorite ratio is 2:1 Therefore, Hypochlorite moles = Thiosulfate moles/2 = 0.000403279 moles/2 = 0.000201639 moles Since there was a dilution of 1 to 10, the moles above need to be multiplied by 10 = 0.000201639 moles � 10 = 0.00201639 moles In order find the % by mass of the Hypochlorite, one needs to multiply the moles by (Molar mass of NaClO/mass average (Experimental) = 0.00201639 moles � (74.5/3.01) = 0.04990741245 � 100 = 4.990741245% Uncertainty Propagation: Uncertainty from massing scale = 0.02/3.01�100 = 0.66% Uncertainty from Volumetric Pipette = 0.04/25�100 = 0.16% Uncertainty from titration 1(Burette) = 0.05/15.25�100 = 0.33% Uncertainty from titration 2(Burette) = 0.05/20.05�100 = 0.25% Once of all of them have been added up, = 0.66 + 0.16 + 0.33 + 0.25 = 1.4% For relative uncertainty, 1.4% of 4.990741245% = 0.06987037743 % Conclusion and Evaluation: The experimental value obtained for the % by mass of the NaClO which is the oxidizing agent is 4.99%. ...read more.

Conclusion

This is because after the sodium Thiosulfate pentahydrate was poured down from the weighing boat, some visible particles could still be seen on the boat. Since more mass was measured then the actual mass used, this will mean our molar mass value will be high as our mass value will be too high. In order to improve this error, the acidic salt remaining on the weighing boat should have been washed down with distilled water giving us more accuracy. Instrumental Error It was assumed that all the hypochlorite was NaClO3 when in fact it could have included other impurities. This would have affected our final value because if we took into account a larger mass, that means our mass value would have been too high causing our percentage value to be low which was the case in this lab. A way to improve this would be to find out what other compounds were present in that bleach so that those values can be taken into account for. An overall improvement method to reduce random errors in this lab would be repetition of trials. Overall, this experiment was fairly accurate and precise resulting in not many errors overall. ...read more.

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