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December 22, 2014

Homework Help: Chemistry Help Please

Posted by Sara on Wednesday, October 22, 2008 at 10:06am.

Titration of a Sample of Household bleaches:

The oxidizing agent in a household bleach is determined by placing 100 mL of distilled water in a 250 mL Erlenmeyer flask and adding 10 mL of the 10% (w/w) KI solution, swirling the contents of the flask to mix the solutions. Add an accurately measured 0.5 mL of your assigned bleach to the flask, and swirl. Then add 10 mL of 2 M H2S04 and proceed with the titration, using the standardized sodium thiosulfate solution. Add the starch indicator when the solution is pale yellow and continue the titration until the deep blue colour of the starch indicator disappear. Record the volume of thiosulfate solution used in the titration.

From the concentration and volume of the added sodium thiosulfate solution used to titrate the different brands of bleach, calculate the numbers of moles of the oxidizing agent presence, assuming it to be sodium hypochlorite, NaOCl. Use this to calculate the number of grams of sodium hypochlorite that was present in the 0.5 mL of bleach. Express the final result as the mass of sodium hypochlorite per 100 mL of bleach.

The sodium thiosulfate reacts with the sodium hypochlorite according to the following stoichiometric redox equations:

NaClO (aq) + 2H^+ + 2I- ---> I2 + Cl- +H2O + Na^+

Recall:

2S203^ 2- + I2- ---- > 2I- + S4O6 ^ 2-

B. Titration of household bleach: Javex

Calculated Concentration of Na2S2O3- 0.032400M

Trail #

1-Volume of bleach ( 0.5mL)
Volume of Na2S2O3 ( 53 mL)
= mass of NaOCl/100 mL bleach ________________?


2-Volume of bleach ( 0.5mL)
Volume of Na2S2O3 ( 55.4 mL)
= mass of NaOCl/100 mL bleach ________________?


Average mass of NaOCl/100 mL bleach ___________________?

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