Analysis of two commercial brands of bleaching solution Essay Example for Free

Analysis of two commercial-grade brands of bleaching solution EssayObjective To determine the concentrations of the active ingredients in 2 commercial bleaches. Introduction Sodium hypochlorite is usu onlyy 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, wherefore the color of the dye would fade away. In the presence of deadly, 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 employment 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 discolorise was pipette into a volumetric flask. Distilled water was added until the meniscus reaches the graduation point. 2. 25 cm3 of the titrated bleach was pipette into a conical flask. About 10 cm3 of potassium iodide and debauch sulphuric acid was added into the conical flask. 3.The solution was titrated with sodium thiosulphate solution until the brown colour of the iodine fades. 4. Starch solution was added into the conical flask, and the solution was further titrated until the brown colour of the stiffen-iodine complex turns to colourless. The volume of sodium thiosulphate solution required to reach the end point was recorded. 5. Steps 1 to 4 were repeated 3 more than times. 6. Steps 1 to 5 were repeated using Clorox Bleach. Data and Calculation Molarity of standard Na2S2O3 solution = 0. 05182M Brand A Kao Price $11. 9/ 1500ml tally 1 2 3 Final reading/cm3 26. 8 23. 1 25. 7 26. 0 Initial reading/ cm3.4. 1 0. 4 2. 9 3. 2 Volume of Na2S2O3 22. 7 22. 7 22. 8 22. 8 Average no. of moles of Na2S2O3 used in the titration 0. 05182 X (22. 7 + 22. 8 X 2)/3 X 0. 001 = 1. 180 X 10-3 moles So, in that respect are (1. 180 X 10-3 /2) =5. 90 X 10-4 moles of I2 in the reaction So, there are 5. 90 X 10-4 moles of ClO- ions in the diluted solution. minginess of ClO- in Kao bleach = 5. 90 X 10-4 X 10 /10 X 1000 =0. 5899M Brand B Clorox Price $21. 9/ 2840ml Trial 1 2 3 Final reading/cm3 33. 5 32. 4 32. 0 33. 2 Initial reading/ cm3 2. 7 1. 3 0. 9 2. 3 Volume of Na2S2O3 30. 8 31. 1 31. 1 30. 9 Average no. of moles of Na2S2O3 used in the titration0. 05182 X (30. 9+ 31. 1 X 2)/3 X 0. 001 = 1. 608 X 10-3 mole So, there are (1. 608 X 10-3 /2) =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 i nto the conical flask, the solution turns dark blue. after(prenominal) that, when we add a few drops of sodium thiosulphate, the colour of the solution would turn colourless. We must be diligent 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. 3. After I had done all the experiments, I found out that the tip of the pipette was blue. When I asked Mr. Leung, he said that the pipette could not be used anymore. Why? I could call up of 2 reasons.First, the broken tip of the pipette could cause danger when we are using the pipette. We would allow a higher chance of getting our finger cut. Second, the broken tip of the pipette may cause the solution to be carried to leak. So, it is unreliable. Answers to Study Question 1. (a) Amount of active ingredient in Kao 0. 5899 X (35. 5 + 16) = 30. 38 g /dm3 Amount of active ingredient in Clorox 0. 8041 X (51. 5) = 41. 41 g/dm3 (b) approach per gram of Kao (11. 9 X 1000/1500) /30. 38 = $0. 2611 per gram Cost per gram of Clorox (21. 9 X 1000/2840) / 41. 41 = $ 0. 186 per gram 2. As Clorox is of a lower price, it is the better buy.3. Adding potassium iodide in excess ensures that all chlorate ions have reacted. Only when all the chlorate ions have been reacted that the amount of iodine formed can fully reflect the amount of chlorate ions in the solution. This ensures that the volume of sodium thiosulphate used in the titration can be used to determine the number of moles of chlorate ions in the solution. 4. When an acid is added into a solution of chlorate and iodine ions, iodine would be liberated. The iodine can then be used in titration t o determine the amount of the chlorate ions. 5. The second way it may deteriorate is by decomposition by sunlight2H+ + 2ClO- - 2HCl + O2 The chlorate ions, under sunlight, spoil back to chlorine ions and the bleaching ability of the bleaching solution is reduced. 6. This is because before reaching the end point, starch solution will not show any signs of being dummy up 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 legitimate 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 poi nt. 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 promising to shoot pass the end point.