Analysis of Two Commercial Bleaches

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Date of experiment: 13/10/2010                         Name: Cheung Lap Kwan (6)

Po Leung Kuk Ngan Po Ling College 2010-2011

Form 6 Chemistry Laboratory Report

Title: Analysis of Two Commercial Bleaches

Introduction:

    Most of the commercial bleaches we can buy in the markets have the same main active ingredient, Sodium hypochlorite [sodium chlorate(I)]. If we want to estimate the actual amount of sodium hypochlorite in the bleach, we can do the titration in the laboratory.

    In this experiment, the active ingredient, sodium chlorate (I), is allowed to react with an excess of potassium iodide solution in the presence of hydrogen ion, liberating iodine. The chemical reaction is:

     ClO- (aq) +2 I- (aq)+ 2 H+       I2(aq) + H2O + Cl-(aq)

   The iodine produced is then titrated with standard sodium thiosulphate solution. Near the end-point during titration, we use starch solution as an indicator. This reaction we call”Iodometic titration”. The chemical reaction is:

     I2(aq) + 2 S2O32-(aq)        2 I-(aq) + S4O62-(aq)

    By taking and analysing the data of volume of standard sodium thiosulphate solution, we can estimate the amount of sodium hypochlorite in the target bleach.

Purposes: 

   

To analyse and compare two commercial bleaches, “Kao” Bleach and “Clorox” Bleach and then find out which one is cheaper upon their bleaching strength.

Apparatus and Reagents Used:

     

Apparatus used: 2 100ml beakers (One for “Kao” Bleach, one for “Clorox” Bleach),

                     2 25.0cm3 pipettes (Washed by deionized water first, then washed by bleaches),

                     2 10.0cm3 pipettes (Washed by deionized water first, then one was washed by potassium iodide solution, one was washed by sulphuric acid),

                     1 pipette filler,

                     2 250cm3 volumetric flasks (Washed by deionized water only),

                     1 conical flask (Washed by deionized water only),

                     1 burette (Washed by deionized water first, then washed by standard thiosulphate solution),

                     1 washing bottle (Filled with deionized water), and

                     1 dropper

                     

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     Reagents used: “Kao” Bleach,

“Clorox” Bleach,

1.0 M potassium iodide solution (KI),

1.0 M sulphuric acid (H2SO4),

Standard thiosulphate solution(S2O32-) with conc. = 0.05 M, and

Starch indicator

Chemical Reactions Involved:

     ClO- (aq) +2 I- (aq)+ 2 H+       I2(aq) + H2O + Cl-(aq)

I2(aq) + 2 S2O32-(aq)        2 I-(aq) + S4O62-(aq)

Procedures:

  1. Exactly 25.0 cm3 of one of the bleaches was pipetted into a clean 250 cm3 volumetric flask. The mark was made up by using deionized water. The flask was shook well. ...

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