Analysis of Chlorine in Commercial Bleaching Solutions

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Practical Report (Experiment 6)                                            F.6A Angel Chan (4)

Experiment 6 (28-11-08)

Analysis of Chlorine in Commercial Bleaching Solutions

Objective

To determine the molarities of sodium chlorate (I) in two brands of bleach solution by titration.

Theory

Reaction between chlorate (I) and iodide ions with the present of sulphuric acid:

CIO- (aq)   +  2I- (aq)   +  2H+ (aq)  →  Cl- (aq)   +  I2 (aq)  +  H2O(l)

Reaction between hypochlorite ions and iodine:

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

Procedures

  1. Determine the total volume of bleach in the commercial bottles provided.
  2. Note the price of the sample.
  3. Wash a 25.0 cm3 pipette with distilled water and then with the bleach solution.
  4. Pipette 25.0 cm3 of the bleach into a 250.0 cm3 of volumetric flask.
  5. Make up to the graduated mark of the volumetric flask.
  6. Stopper the flask and invert it several times in order to mix the contents well.
  7. Label the flask.
  8. Wash a burette with distilled water and then with standard sodium hypochlorite solution.
  9. Pour the sodium hypochlorite solution into the burette and ensure the tip of burette is filled.
  10. Record the initial burette reading.
  11. Pipette 25.0 cm3 of the diluted bleach into a conical flask.
  12. Add 10 cm3 of KI solution and 10 cm3 of 1 M sulphuric acid into the flask.
  13. Run the solution from the burette into the conical flask, swirling the flask all the time.
  14. Stop the titration when the colour of solution in the conical flask just becomes pale yellow.
  15. Add 3 cm3 of starch indicator.
  16. Run the solution slowly form the burette until the solution in the flask turns from dark blue to colourless.
  17. Record the final burette reading.
  18. Repeat steps(a)-(q) three more times.
  19. Repeat steps(a)-(r) with another brand of bleaching solution.
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Results

Brand Name of bleach : Clorox vs 0.1M Na2S2O3

Brand Name of bleach : Kao vs 0.1M Na2S2O3

Calculations

Clorox
No. of mole of S
2O32- = = 3.89 x 10-3 mol

By equation, no of moles of S2O32- : I2 = 2 : 1

∴ no. of moles of I2 liberated =  = 1.944 x 10-3 mol

By equation, no of moles of I2 : CIO- = 1 : 1

∴ no. of moles of CIO- = 1.944 x 10-3 mol

No. of mole of CIO- in the original bleach solution = 1.944 x 10-3 x  = 0.01944 ...

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