Determination of Chlorine and Iodine in Water

        To determine the amount of chlorine in tap water the buret was again filled with sodium thiosulfate and the initial volume was recorded. The beaker was filled with a 100 mL of bathroom water and .5 grams of KI and 2 mL of acetic acid was added and stirred until it dissolved. The solution was titrated and starch was again added once it lost its yellowish color, this turned the solution blue and the titration continued until it was clear. The final volume was recorded and volume used was found. The moles of thiosulfate was calculated by multiplying the molarity of thiosulfate by liters of thiosulfate, then to get moles of chlorine, moles of thiosulfate was divided by two because two moles of thiosulfate are required for each mole of chlorine, this was used to obtain the molarity of chlorine for bathroom water. This experiment was repeated an additional two times. The experiment was repeated with 4 iodine purification tablets dissolved in 2 liters of deionized water. The iodine water replaced the bathroom water in the last experiment, this was done three times.

                

Data:

Standardization of sodium thiosulfate solution

First standardization =     .000170 M x .0235 =3.995 10-6 mol KIO3  

399.5 10-6 mol KIO3 x 6 = 2.397 10-5 mol/.0235L=.001mol/liter thiosulfate

Second standardization =     .000170 M x .023 =3.91 10-6 mol KIO3  

399.5 10-6 mol KIO3 x 6 = 2.346 10-5 mol/.023L=.001mol/liter thiosulfate

Third standardization =     .000170 M x .021 =3.57 10-6 mol KIO3  

3.57 10-6 mol KIO3 x 6 = 2.142 10-5 mol/.021L=.001mol/liter thiosulfate

Concentration of iodine

#1    .001/.011=.091mol thiosulfate

.091mol/2=.045mol iodine

.045mol/.100=.455 molarity of iodine

#2    .001/.0115=.087mol thiosulfate

.087mol/2=.043mol iodine

.043mol/.100=.435 molarity of iodine

#3    .001/.0105=.095mol thiosulfate

.095mol/2=.047mol Iodine

.047mol/.100=.476 molarity of Iodine

Concentration chlorine

#1    .001/.002=.5mol thiosulfate

.5mol/2=.25mol chlorine

.25mol/.100=2.5 molarity of chlorine

#2    .001/.0035=.289mol thiosulfate

.289mol/2=.143mol chlorine

.143mol/.100=1.43 molarity of chlorine

#3    .001/.0035=.289mol thiosulfate

.289mol/2=.143mol chlorine

.143mol/.100=1.43 molarity of chlorine

Titration of tap water and Iodine solution

Conclusion:

The objectives of this lab were to standardize the sodium thiosulfate, because of microorganisms eating it the concentration changes over time and needs to be standardized each day it is used. The moles of KIO3 were found and from this moles and molarity of thiosulfate were calculated, the molarity was used for the rest of equations to measure chlorine in bathroom tap water and to measure iodine in water. The chlorine was reacted with KIO to form I2 which was titrated with the standardized sodium thiosulfate solution, the iodine turned the solution yellow which disappeared once all the iodine had reacted, and starch was added to give a blue color to see more clearly if all the iodine had reacted. The volume of sodium thiosulfate used in the titration was used to find the average molarity of iodine in the iodine treated water and the molarity of chlorine in the bathroom tap water. The molarity of the chlorine in the bathroom water was much higher than in the iodine water this may have been caused from titrating to much of the sodium thiosulfate because once we added the starch it did not turn blue this must have meant that all the iodine was already reacted because too much was added. When doing the standardizations they all had the exact same concentration so those were most likely right and with the iodine everything seemed to go correctly and the averages were similar but with the chlorine experiment each titration was over the correct amount of sodium thiosulfate which most likely caused this large error.