Chang Pui Chung Memorial School

2. Chang Pui Chung Memorial School Miss Soo May Kei Target group: S6 Student

3. Making Your Own Acid-Base Indicator TOPIC

4. Background knowledge: • Acid-base titration2) Chemical equilibrium (titration curve) Making Your Own Acid-Base Indicator

6. Work Schedule • Date:3 July, 2006 (3 hours) • Searching information and planning investigation • Writing the first page of proposal form Making Your Own Acid-Base Indicator

7. Work Schedule • Date: 6 July, 2006 (4 hours) • Discussing the first page of the proposal form with the students • Writing the proposal Making Your Own Acid-Base Indicator

8. Work Schedule • Date: 17 & 18 July, 2006 (6 hours) • Conducting the investigation 1) Making natural indicators 2) Choosing a suitable indicators for titration 3) Determining the concentration of oven cleaner Making Your Own Acid-Base Indicator

9. Work Schedule • Date: 19 July, 2006 (4 hours) • Organizing and analyzing data Making Your Own Acid-Base Indicator

10. Work Schedule • Date: 21 July, 2006 (3 hours) • Presenting the findings Making Your Own Acid-Base Indicator

11. END

12. How to extract the pigments from the plant materials? For cherries and grapes: Remove their peels For red cabbage, beet root and rose petal: Cut them into small pieces

13. Add some water to them and heat the mixtures using a heater

14. Filter the solutions using pieces of filter paper

15. Five plant indicator solutions are made! Red cherry Red cabbage

16. Beet root Red grape

17. Red rose petal Five natural indicators Back

18. When ≦ 1/10 pH ≦ pKIn + log 1/10 ≦ pKIn - 1 ≦ 8.15 When [Ph-(aq)] = [HPh(aq)], pH = pKIn = -log (7 x 10-10) = 9.15 When ≧ 10 pH ≧ pKIn + log 10 ≧ pKIn + 1 ≧ 10.15 Phenolphthalein

19. When 1/10 pH ≦ pKIn + log 1/10 ≦ pKIn - 1 ≦2.7 When [Me(aq)] = [HMe+(aq)], pH = pKIn = -log (2 x 10-4) = 3.7 When ≧ 10 pH ≧ pKIn + log 10 ≧ pKIn + 1 ≧ 4.7 Methyl orange

20. Acid-base Titrations Acid (CH3COOH or HCl) Oven cleaner (NaOH) + indicator

21. pH Titration Curves Strong Acid-Strong Base Titration Sharp change in pH at the equivalence point: 3-11

22. Strong Acid-Weak Base Titration Sharp change in pH at the equivalence point: 2-6

23. Weak Acid-Strong Base Titration Sharp change in pH at the equivalence point: 8-12

24. Weak Acid-Weak Base Titration NO Sharp change in pH at the equivalence point.

25. pH12 pH2 Results • Red cabbage showed different colours at different pH solutions.

26. pH12 pH2 • Red grapes showed insignificant colour change

27. pH12 pH2 • Red cherries also showed insignificant colour change.

28. pH12 pH2 • Red rose petals showed a lot of colour at different pH solution but less significant than red cabbage.

29. pH12 pH2 • Beet root showed a sharp colour change between pH 12 and pH 11

30. Colour of the indicators in different pH solutions

31. pH12 pH2 • Beet root showed a sharp colour change between pH 12 and pH 11 As it showed a sharp colour change at alkaline region, it is suitable for being used as indicatorin acid-base titration. Back

32. pH12 pH2 Freshly prepared beet root solution Over-night beet root solution pH12 pH2

33. Colour of the indicators (overnight and fresh beet root solution)in different pH solutions

34. Titration between HCl and oven cleaner (NaOH) using phenolphthalein and beet root as indicator

35. The concentration of NaOH in the oven cleaner with using different indicators Back