Untitled Document

Material
20 mL household bleach, 15 mL of 1 M potassium iodide solution, 15 mL of 1 M sulfuric acid, 100 mL standard sodium thiosulfate solution, approximately 0.1 M starch indicator solution, 90 mL distilled water, 250 mL volumetric flask, 2 x 20 mL pipettes, pipette filler, 3 x 100 mL conical flasks, 10 mL measuring cylinder, burette and stand, small funnel, white tile, safety glasses

Theory
Household bleach is manufactured by passing an electric current through brine, a concentrated solution of sodium chloride. Chlorine and sodium hydroxide are produced and react to form a mixture of sodium hypochlorite and sodium chloride:

The decolourising effect of bleach is due to the action of the hypochlorate ion (OCl^-) as an oxidant. The concentration of the sodium hypochlorate in a bleach is recorded as its ‘available chlorine'. The available chlorine is usually expressed on the label of the bottle of bleach as a percentage of weight/volume (w/v) or weight/weight (w/w)
In this analysis, the hypochlorite ion in a sample of bleach is reacted with an excess of iodide ions. Iodine is a product of the reaction:

The amount of iodine produced is then determined by titration with standard sodium thiosulfate solution:

Since starch turns blue in the presence of iodine, it is used as all indicator for this final reaction.

1	Record the brand of household bleach to be analysed and the manufacturer's specifications as to available chlorine content.
2	Use a pipette to dispense 20.00 mL of the bleach into a 250 mL volumetric flask. Use distilled water to make up the solution to the calibration line of the flask and mix thoroughly.
3	Using a pipette, transfer a 20.00mL volume of the diluted bleach solution to each of three 100 mL conical flasks.
4	Fill a burette with standard sodium thiosulphate solution. Record the initial volume of liquid in the burette and the concentration of the sodium thiosulphate solution.
5	To each flask, add about 5 mL of 1 M potassium iodide solution and aboul 5 mL of 1 M sulfuric acid. The solution will turn dark brown as iodine is formed.
6	Titrate each mixture with the sodium thiosulfate solution until the yellow-brown colour of the iodine has become pale, then add 1-2 mL of starch indicator solution. The solution will turn blue. Continue the titration until the blue colour just disappears. Record the final volume of liquid in the burette for each titration.