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Analysis of two Commercial Brands of Bleaching Solution

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Experiment 4 Analysis of two Commercial Brands of Bleaching Solution Objective To determine the concentrations of the active ingredients in 2 commercial bleaches. Introduction Sodium hypochlorite is usually found in bleaching solutions. It is the active ingredient of bleaching solutions. It bleaches by oxidation. When it is added to dye, the following reaction occurs: ClO- + dye ----------------> Cl- + (dye + O) If the oxidized form of the dye is colorless, then the color of the dye would fade away. In the presence of acid, the hypochlorite ions from the bleaching solution reacts with the iodine ions from potassium iodide in the following way: ClO- + 2I- + 2H+ --------->I2 + H2O + Cl- When sodium thiosulphate solution is added into this reacted solution, a further reaction occurs: I2 + 2S2O32- -------------->2I- + S4O62- This reaction could be used in titration to find out the number of moles of thiosulphate ions, thus the concentration of hypochlorite ions in the bleaching solution. Procedure 1. 10 cm3 of Kao Bleach was pipette into a volumetric flask. Distilled water was added until the meniscus reaches the graduation point. ...read more.


=8.041 X 10-4 moles of I2 in the reaction So, there are 8.041 X 10-4 moles of ClO- ions in the diluted solution. Concentration of ClO- in Kao bleach = 8.041 X 10-4 X 10 /10 X 1000 =0.8041M Conclusion The concentration of ClO- in Kao is 0.5899M while that of Clorox is 0.8041M. Discussion 1. When we add starch solution into the conical flask, the solution turns dark blue. After that, when we add a few drops of sodium thiosulphate, the colour of the solution would turn colourless. We must be careful when we are doing this step. This is because the starch-iodine complex does not show graduation of color change. We may get pass the end point easily. The readings would be inaccurate. 2. Dilute sulphuric acid is irritating. So we must be extra careful in using it. How did I use sulphuric acid more safely? I used a larger measuring cylinder to measure out the amount of sulphuric acid. The likeliness of spilling the acid would be lower. ...read more.


6. This is because before reaching the end point, starch solution will not show any signs of being close to the end point. Other indicators will. For example, if methyl orange is close to its end point, it will first change the color of the solution to orange. Then, the solution would turn back to its original colour. In this way, we will know that we are close to the end point and we would add the solution more slowly. However, similar characteristics could not be found when we use starch as an indicator. So, we may get pass the end point easily. This problem is solved by titrating the iodine solution without any indicator first. After the brown color of iodine vanishes, we know that we are very close to the end point. At this stage, adding starch solution can tell us whether there is still iodine in the solution. As we know that we are already very close to the end point, we would add the solution more slowly. It would be lees likely to shoot pass the end point. ...read more.

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