The Theory behind the Experiment

NaClO, or bleach is a powerful oxidizing agent. We are doing an oxidation-reduction titration to determine the amount of hypochlorite ion present in a sample of commercial bleach. We add iodine ions to the bleach which oxidizes into elemental iodine. Iodine, in the presence of starch, forms a colored triiodide ion which we can see. We titrate the ion with thiosulfate ions back into iodide ions which are colorless. By knowning how much thiosulfate we used for the titration, we can calculate how much of the triiodide ions were present. From that we can calculate how much iodine was formed, how much iodide was oxidized, and, finally, how much hypochlorite we originally had in our bleach.

Sources of Error

Any volumetric transfers of our original solutions may contain errors.
Any errors in buret readings.
Adding too much iodine to the starch may form a complex that may not reversibly ionize.
Any errors in the preparation of the original reagent solutions.

48 Responses to “Experiment 10 – Analysis of a Commercial Bleach”
  1. Melanie Miller says:

    My partner and I did this experiment three times and every time we measured how much of the titrate was gone, it was 3.5. Yet, when i did the percent error after all the calculations we had a 95.4%. The errors that could have happened were adding to much starch or iodine. I could have also calculated the data wrong.

  2. Lacey Orcutt says:

    The first time i did this experiment my partner and i found out we over titrated because when i went to add the starch in it didnt ture black, but after doing it the other two times we found that the first time was still very close to the other two.

  3. Laurice Edualaine Harris says:

    My group did this experiment 4 times. On the first trial, we added too much Na2S2O3(we added like 3.5ml) when we added the starch, nothing happened so we decided to just get rid of the data. On our 2nd try, I forgot to add the HCl so that screwed us and we decided to get rid of the data (my bad, sorry guys…) On our third trial we finally got it right but we had 52.7% error. On our 4th trial we got 50.4% error. Our average % error was 51.4%

  4. Kris Krohn says:

    Although the three sets of data for this titration lab were all grouped very closely, our overall percent after calculating the average, was over 50%. This could have come from not using correct amounts of starch or iodine, or from our first trial where we over titrated. It is also possible that our data was calculated incorrectly, giving a skewed percent error.

  5. Nick Hensch says:

    We may have added too much of the thiosulfate when titrating and still got the color change, but the wrong amount of thiosulfate to use in the equations. This most likely caused our 52% error, but even after rechecking our math, we found no errors in our calculations.

  6. Justin Derby says:

    My partner and I did this experiment with an average titrating of 3.37. After calculating, we found out there was 2.32% of bleach which gave us a 7.2% error.

  7. Jess Mason says:

    thanks for the information!

  8. Alex Bendlage says:

    I found this blog to be very helpful. Instead of cramming to get the information needed to complete our labs in at the end of class, it is all present here and easy to get to. In this lab, my partner and i originally thought that we did a good job with the titrations, but when we did the calculations, we had over 50% error.

  9. Jess Mason says:

    i used this info to figure out what kind of error could have changed the results.

  10. Hanna Anderson says:

    I guess I typed my response in the wrong section of this blog so I’ll start over. My partner and I had problems titrating. We slowly let the drops of the solution out of the buret but we weren’t coordinated enough to stir at the same time so we over-titrated. This caused our readings of the buret for our first run through to be off from the second two readings. This probably caused our high percent error.

  11. Jackson Cover says:

    During the three times me and my partner did this experiement we recored the amount of titration we did. We had an average of 3.36 of solution. This gave us an error of 7.2%. the error could have occured by adding not enough acid or bleach. Transfer error is the most likely cause for the error.

  12. Jake Roman says:

    My partner and I seems have done well on the lab. We carefully measured out everything as close a possible. We ended with an error of 8.47%. The reasoning for this could have been the first trial we didn’t think the black from the starch would disappear so fast. This may be the reason our first trial was higher vol. than the rest.

  13. Jeremiah Herman says:

    In this experiment my partner and I had huge percent errors, way over fifty. This was weird because it seemed as if the titrations were going good but when we got to the end we did not have near enough, they were all low.

  14. Austin Bain says:

    We continued to have troubles with the titraition. We over titraited many times. This led to a higher percent error which was 54.7%

  15. Daniel Frey says:

    Each time my partners and I did this experiment, we got an error around 55%. The first time, which had the greatest error, we did not accurately read the buret. However, after the last two trials, which I had felt were performed accurately, and comparing results with other groups, I think that there must have been some error in the initial preparation of the solutions or the calculations themselves.

  16. Krystal Wilson says:

    Honestly, I enjoyed this lab because it involved careful procedures along with analysis. My partner and I repeated the titration three times in order to gather information to figure the average of our work. It was interesting to find that every repetition equaled the same (3.5). I thought that we had done very well, because when I calculated our percent error it equaled 1.88. One error that I thought we had was while we were titrating the bleach, we may have let our color get to yellow or not yellow enough. All-in-all, we were successful.

  17. Josh Vosatka says:

    Even though all three times we titrated and ended up with basically the same amount of difference between the readings, our percent error was pretty high at 52.4%. The first time we titrated our initial reading may have been off so i just ignored it, but either way, all three times were in the same ballpark. Our buret was leaking towrad the beginning, so that could have created some error.

  18. robby stagaul says:

    k this lab doesnt make sense at all- our error was over 100, so obviously something wasnt right. wut the buck

  19. Sarah Ritchie says:

    My partner and I did this experiment twice. The first time our solution turned clear but the second time went better. Our percent errors were high which could have resulted in using too much starch or we titrated our solution too much. I could have also done some of the calculations wrong.

  20. Dustin Duong says:

    During our experimentation my group had problems with titrating as a few times we added to much thiosulfate and the solution turned clear before we added the starch. We did, however, eventually become patient enough to complete the experiment with little percent error.

  21. Lindsay Schrader says:

    We had to redo our first experiment because we forgot to continually mix the solutions after adding the drops from the buret. Because of this, we over did it and missed the second step.

  22. Keith Flaherty says:

    My partner and I completed three titration trials where we got differences in readings from 3.4 to 4.1. We calculated that there was an average of 2.6% bleach in the commercial bleach that we tested. It was supposed to have 2.5% bleach. Our percent error was around 4%. One error could have been that we did not have exact measurements of the solutions which could have made our calculations a little off.

  23. Keegan Boyer says:

    Our error was caused by not measuring out the exact regents as what they were supposed to be.

  24. Ilise Schoenfeld says:

    I didnt mind this lab, just all of the calculations were a lot of trouble for my partner and I, so i think that is our biggest source of error. I think we were pretty efficient with the titration part of the lab…

  25. Melissa Casey says:

    My partner and I had the same problem that Melanie and her partner had. We completed the titration 3 times and for the trial 1 we got 4 and then 3.5 for the other 2 trials. Our percent error was 52%. I guess I don’t understand where we went wrong, becuase we followed all of the steps, but maybe the solid KI didn’t dissolve totally, or maybe we didn’t clean everything out properly before we went onto the next trial. I just find it odd that our percent error was that high. I double checked all of my calculation and still ended up with 52% error.

  26. Dan Winter says:

    Our first attempt at titrating in this lab was somewhat unsuccessful– upon stirring the mixture, the solution turned clear. We had titrated too far. This, of course, probably assisted in our 35.6% error. Each trial used between 4 and 4.75 mL of the titrating solution. Other error factors could have been in measuring the volumes to create our solutions.

  27. Spencer Partridge says:

    The First time we titrated the mixtyure turned clear after we had started to head over to the counter in order to put in the starch. Thus we had a really high source of error.

  28. Corey Moore says:

    My partners and I only had to do this lab three times to get the data we needed. We found our average titration to be abot 3.5. and .365 diluted M of bleach. Our first time running the lab we all believed we used to much to turn the liquid clear. Our percent error was about 53%.

  29. Brittny Pokorny says:

    our first two trials were completely off because we either didn’t add the HCl or added too much NaSO. But the next two were done correctly and we still had 45% error. Whatev.

  30. Samantha Watson says:

    2/3 trials were off so only one we were able to use. the other 2 made our percent error really high.

  31. Sami Cronin says:

    My lab partner and I did this experiment quite a few times, mainly because we had a hard time controlling the flow of Na2S2O3 into our flask, so we ended up with a clear solution quite a few times. This meant that when we finally did get it to stay yellow, it was probably a bit darker than it needed to be, but we were hesitant to add any more. That is probably one of our main sources of error, along with adding enough starch and cleaning the flask well between uses.

  32. Lucas Polaski says:

    My results were similar to Jeremiah’s. The titratiions seemd to go just fine and we did not go past the equalization point, but after the caculations were completed, our bleach concentration was much lower than the accepted value. this could be due to overdilution of the bleach solution or improper measuring on the account of my partner and I

  33. Jess Macauley says:

    If I did my calculations right, I’m pretty sure my partner and I got 2% error.

  34. Lindsay Screws says:

    My partners and I had some problems with our measuring and the buret but we ended up with an average of 3.105 which gave us about 24% error.

  35. Thomas Shatzer says:

    This lab was fun. My partner and i made onebig mistake at the beginning, and had to start over. We added water to the bleach to dilute it when we didnt need to. Other than that we had a nine percent error which probably resulted from going to fast.

  36. Katie Hoyum says:

    There was a good deal of error in our three titrations, but because one time we added too little sodium thiosulfate and the other two times we added too much, the average percent of error was only 14 percent.

  37. Emily Bajet says:

    basically, my partner and I had an average titration level of 3.5, which meant a 12% error. yay.

  38. Jordan Underwood says:

    This lab was interesting to say the least. Me and my partner thought we did good at the beginning but when i calculated the results we had a huge amount of error. i think its because we didnt let the KI solution and the bleach reach the yellow color and that messed up our later results.

  39. Jordan Underwood says:

    This lab was interesting to say the least. Me and my partner thought we did good at the beginning but when i calculated the results we had a huge amount of error. i think its because we didnt let the KI solution and the bleach reach the yellow color and that messed up our later results.

  40. Chuck Norris says:

    Me and my parter got 2% error. that is just awesome.

  41. Mike Miniaci says:

    My partner and I got 8.47% as our average percent error. I dont think we made any major errors during this experiment that I know of.

  42. Tanner Nash says:

    The blog is a good idea. Better to do it at home than cramming at the end of class. Gives us a chance to read over the info and see it for ourselves. Our group had some problem on the first titration but went well afterward with three similar readings during the three times tested.

  43. Jordan Ask says:

    My partner and I got a 2.5 % of bleach, which was about a 50 % error. The error had to of come from contamination of the flask we used, because we were careful with all the other steps.

  44. Kevin Wickham says:

    my partner and i got an average of 2.4% bleach. with a percent error of 7.3%. the firts titration i put a little to much in, about 3.5 mL. which mest with the averaging of the other two. also there may have been some inacurate messerments when getting the chemicals.

  45. Tim Olmstead says:

    I am late because I was gone friday but me and my partener had 14 percent error the first one didn’t do too great but the second two were really good

  46. Adam Koolbeck says:

    Thanks for the information. This lab seemed easy, but after doing it my percent error was huge.

  47. Craig Crowther says:

    After messing up two of the titrations my partner and i did one correct and the data that we got from it gave us over 50% error. this error could have occurred in measuring the chemicals or the speed at which we conducted this experiment. (this is posted late because i was not in school on friday)

  48. Daniel Frey says:

    Were we given different numbers for the actual percent bleach? It seems like some people were given 2.5 and others, like me, about 5. We were getting the same answers as other people with very small error were getting, but had a large error.

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