Experiment 39: Analysis of Commercial Bleach Purpose Introduction: Many commercial products are effective because they contain oxidizing agents. Some products that contain oxidizing agents are bleaches, hair coloring agents, scouring powders, and toilet bowl cleaners. The most common oxidizing agent in bleaches is sodium hypochlorite, NaClO (sometimes written NaOCl). Commercial bleaches are created by bubbling chlorine gas into a sodium hydroxide solution (remember this from your “funky redox rxns”?). Some of the chlorine is oxidized to the hypochlorite ion, ClO- and some is reduced to the chloride ion, Cl- (a disproportionation reaction).

The chemical equation for the process is: Cl 2 (g) + 2OH- (aq) ---> ClO - (aq) + Cl - (aq) + H 2 O Terms Oxidizing agent – transfers oxygen atoms or gains electrons Oxidized – to give electrons Reduced- compound gains electrons

The amount of hypochlorite ion (ClO - ) present in a solution of bleach can be determined by oxidation-reduction titration. One of the best methods is the iodine-thiosulfate titration procedure. Iodide ion, I-, is easily oxidized by almost any oxidizing agent (It has many electrons to lose!). In an acid solution, hypochlorite ions oxidize iodide ions to form iodine, I 2. The iodine that forms is then titrated with a standard solution of sodium thiosulfate.

The analysis takes place in a series of steps: 1.Acidified iodide ion is added to hypochlorite ion solution, and the iodide is oxidized to iodine. 2H + (aq) + HOCl(aq) + 2I - (aq) ---> Cl - (aq) + I 2 (aq) + H 2 O (l) Oxidizing agent reduced oxidized

3.The Iodine solution is titrated with a standard solution of thiosulfate ions, which reduces the iodine back to iodide ions: I 2 + (2S 2 O 3 ) > 2I - + (S 4 O 6 ) 2-

Part A Dilute 1M Na 2 S 2 O 3 to 0.05M Na 2 S 2 O 3 Pour 5 ml of 1M Na 2 S 2 O 3 into a 250 ml beaker Dilute with DI water until it reaches 100 ml This will create a 0.05M Na 2 S 2 O 3

Part A standardization of Na 2 S 2 O 3 Rinse and fill a buret with Na 2 S 2 O 3 Rinse and fill a second buret with 3 M KIO 3 Dispense 15 ml of KIO 3 solution into a 250 ml Erlenmeyer flask – Add to flask 25 ml of water – 3ml of 3M KI – 2ml of 3M H 2 SO 4

Part A begin titration Slowly add Na 2 S 2 O 3 When the solution turns a light yellow add 0.5ml of starch indicator, the solution will turn black Continue to add Na 2 S 2 O 3 until the solution reaches an endpoint (turns colorless) Calculate Molarity of Na 2 S 2 O 3 using the formula below as seen on page 481 lO S 2 O H + ---> l - + 3S 4 O H 2 O lO I H + ---> l - + 3I 2 + 3H 2 O

Calculations for standarization Moles of lO 3 -2 = (Molarity lO 3 -2 x volume of lO 3 -2 ) 6 Moles of lO 3 -2 = 1 moles of Na 2 S 2 O 3

Part B Determination of the oxidizing agent of bleach Fill buret with 0.05M Na 2 S 2 O 3 Add 0.5g of bleach into a 250ml flask Record the mass of the unknown bleach

Part B Determination of the oxidizing agent of bleach – To the flask add 25 ml of di water 3ml of 3M KI 2ml of 3 M H 2 SO 4 5 drops of 3 % ammonium molybdate It should turn a dark brown, if it does not call me over If it does immediately begin to titrate 2H + (aq) + HOCl(aq) + 2I - (aq) ---> Cl - (aq) + I 2 (aq) + H 2 O (l)

Part B begin titration Slowly add Na 2 S 2 O 3 to flask When the solution turns a light yellow add 0.5ml of starch, the solution will turn black\ Continue to add Na 2 S 2 O 3 until it turns clear I 2 + (2S 2 O 3 ) > 2I - + (S 4 O 6 ) 2-

Part B begin titration Calculate Moles of NaOCl using the formula below as seen on page 480 NaOCl + 2S 2 O H + ---> Cl - + S 4 O 6 + H 2 O

Calculations for % oxidizing agent (OCL) Moles of Na 2 S 2 O 3 = (Molarity Na 2 S 2 O 3 x volume of Na 2 S 2 O 3 ) 1 Moles of NaOCL = 2 moles of Na 2 S 2 O 3