St. Paul’s Secondary School Registration No. :BCh24

1. St. Paul’s Secondary School Registration No. :BCh24 開心漂白大發現 The Bleach File

2. Introduction • Types of Chlorine bleach: • 1. KAO Bleach • 2. Clorox Bleach • 3. No Frills Bleach • 4. LibY Bleach • Types of colour-safe bleach • 1. Vanish in-wash stain remover (colour-safe) • 2. KAO Liquid Wide Bleach.

3. Content • Working principles • Chemical content • Cleansing power towards different types of stains • Possible damages to cloth • Effect of mixing chlorine bleach and colour-safe bleach

4. Chemical Content and Working Principles of Chlorine Bleach and Colour-Safe Bleach: • Oxidizing power of the hypochlorous acid HOCl (aq) in chlorine bleaches • Oxidizing power of hydrogen peroxide H2O2 (aq) in colour-safe bleaches. • HOCl (aq) + D  H+ (aq) + Cl- (aq) + DO • H2O2 (aq) + D  H2O (l) + DO • Coloured Colourless

5. Investigation Experiment 1 Aim: To find out the active ingredient in chlorine bleaches and colour safe bleaches I )To test for ClO- in chlorine bleaches: Equation Involved: OCl-(aq) + Cl-(aq) + 2H+(aq) Cl2 (g) + H2O (l)

6. Testing of the gas evolved after mixing chlorine bleach with hydrochloric acid

7. (II) To test for H2O2 in colour safe bleaches: Equation involved: 2H2O2(aq) O2 (g) + 2H2O(l) • Results: • A gas was evolved • The glowing splint relighted, which suggests that the gas is oxygen.

8. Conclusion: • Active ingredients in chlorine bleaches • hypochlorite ions • Active ingredient in colour safe bleaches • hydrogen peroxide

9. Experiment 2 Aim: To determine the concentration of sodium hypochlorite in different brands of household chlorine bleaches.

10. S2O32-(aq) Diluted chlorine bleach, KI and H2SO4 To determine the concentration of sodium hypochlorite in different brands of household chlorine bleaches. Equations involved: 1) OCl-(aq) + 2I-(aq) + 2H+(aq) I2 (g) + Cl- (aq) + H2O (l) 2) I2 (aq) + 2S2O32-(aq) S4O62-(aq) + 2I-(aq) with starch added as indicator Titrated against S2O32-(aq) Starch added Colour change at end point: from blue to colourless

11. Greatest molarity of NaOCl Conclusion:

12. Best buy Price per mole of NaOCl ($) Brands of chlorine bleach

13. Experiment 3 Aim: To determine the concentration of hydrogen peroxide in different brands of colour-safe bleach

14. MnO4-(aq) Diluted colour-safe bleach To determine the concentration of hydrogen peroxide in different brands of colour-safe bleach. Equation involved: 6H+(aq) + 2MnO4-(aq) + 5H2O2(l) 5O2(g) + 2Mn2+(aq) + 8H2O (l) Colour change at end point: from colourless to pale pink

15. Highest molarity of H2O2 Best Buy Price per mole of H2O2 ($) Brands of colour safe bleach

16. Price of the bleaches per number of moles of active ingredients in chlorine bleaches and colour safe bleaches more expensive Price per mole of active ingredient ($) Chlorine bleaches Colour safe bleaches

17. Experiment 4 • Aim: • To investigate the cleansing power and possible damages to cloth of different chlorine/colour-safe bleaches. • Introduction: • Different kinds of cloths with different stains were soaked into different samples • Changes in textures and original colour of the fabrics, and the degree of removal of stains would be considered.

18. 1.Curry stain Purple cotton fabric Towel with curry stain with curry stain

19. 2.Dark Soy Sauce Stain Purple cotton fabric Towel with dark with dark soy sauce stain soy sauce stain

20. 3.Black Ink Stain Purple cotton fabric with black ink stain Towel with black ink stain

21. 4.Ketchup Stain Purple cotton fabric with ketchup stain Towel with ketchup stain

22. 5.Marker (Black) and Highlight Pen (Green) Stains Purple cotton fabric with marker and highlight pen stains Towel with marker and highlight pen stains

23. Analysis of Results: 1)  Curry Stain Kao bleached the curry stains most effectively. 2)  Black Ink Stain All the results were unsatisfactory. Colour-safe bleach bleached the black ink stain much better than chlorine bleaches.

24. Similar performance on 3)  Dark Soy Sauce Stain 4)  Ketchup Stain 5)  Marker and Highlight Pen Stains

25. 6.White cotton fabrics     One piece of white cotton fabric was dipped into each of the four different kinds of undiluted chlorine bleach for four days. Result: The pieces of white cotton fabric turned paler and thinner than the original sample. LibY Bleach No Frills Bleach KAO Bleach Clorox Bleach Original sample

26. 7.Coloured checked fabrics     One piece of coloured checked fabric was dipped into each of the two different kinds of colour-safe bleach for three days. Result: No obvious change in colour and texture.

27. Vanish Conclusion: The best stain remover:

28. Experiment 5 • Aim: • To investigate the consequences of mixing household chlorine bleach and colour-safe bleach • Questions in mind: • What will happen if household chlorine bleach is mixed with colour-safe bleach? • Will the effectiveness of the bleaching action be increased upon mixing?

29. Chlorine bleach Colour safe bleach

30. High density white foam was evolved • Heat was produced

31. The beaker of foam finally overflowed.

32. To collect the gas produced: - by displacement of water

33. Test result: The glowing splint relighted which shows that the gas was oxygen.

34. Conclusion: • Redox reaction happened between hydrogen peroxide andhypochlorite ion. • Equations involved: • OCl-(aq) + H2O2(l) Cl-(aq) + O2(g) + H2O(l) • (O.A.) (R.A.) • An exothermic reaction • The oxygen formed causes the formation of the high density white foam.

35. Recommendation: • Chlorine bleach and colour-safe bleach should be used separately.

36. Never mix them together Adding Chlorine Bleach A lot of foam and heat are produced Colour safe bleach

37. Do you know how to choose between chlorine bleach and colour safe bleach now?

38. St. Paul’s Secondary School Registration No. :BCh24 Group members: Ivy Yeung Vivien Chu Helen Kwai Maggie Chow Amelia Ho Teacher Advisors: Mrs. A. Lam Miss I. Lau

39. The End