Chang Pui Chung Memorial School Miss Soo May

Chang Pui Chung Memorial School Miss Soo May Kei Target group: S 6 Student

Background knowledge: 1) Acid-base titration 2) Chemical equilibrium (titration curve) Making Your Own Acid-Base Indicator

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

• 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

• 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

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

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

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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

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

• Filter the solutions using pieces of filter paper

• Five plant indicator solutions are made! Red cherry Red cabbage

Beet root Red grape

Red rose petal Five natural indicators Back

Phenolphthalein When ≦ 1/10 p. H ≦ p. KIn + log 1/10 ≦ p. KIn - 1 ≦ 8. 15 When [Ph-(aq)] = [HPh(aq)], p. H = p. KIn = -log (7 x 10 -10) = 9. 15 When ≧ 10 p. H ≧ p. KIn + log 10 ≧ p. KIn + 1 ≧ 10. 15

Methyl orange When 1/10 p. H ≦ p. KIn + log 1/10 ≦ p. KIn - 1 ≦ 2. 7 When [Me(aq)] = [HMe+(aq)], p. H = p. KIn = -log (2 x 10 -4) = 3. 7 When ≧ 10 p. H ≧ p. KIn + log 10 ≧ p. KIn + 1 ≧ 4. 7

Acid-base Titrations Acid (CH 3 COOH or HCl) Oven cleaner (Na. OH) + indicator

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

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

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

Weak Acid-Weak Base Titration NO Sharp change in p. H at the equivalence point.

Results • Red cabbage showed different colours at different p. H solutions. p. H 12 p. H 2

• Red grapes showed insignificant colour change p. H 12 p. H 2

• Red cherries also showed insignificant colour change. p. H 12 p. H 2

• Red rose petals showed a lot of colour at different p. H solution but less significant than red cabbage. p. H 12 p. H 2

• Beet root showed a sharp colour change between p. H 12 and p. H 11 p. H 12 p. H 2

Colour of the indicators in different p. H solutions p. H 2 p. H 3 p. H 4 p. H 5 p. H 6 p. H 7 p. H 8 p. H 9 p. H 10 1 2 3 4 5 1. red cabbage 3. red cherry 5. beet root 2. red rose petal 4. red grape p. H 11 p. H 12

• Beet root showed a sharp colour change between p. H 12 and p. H 11 p. H 12 p. H 2 As it showed a sharp colour change at alkaline region, it is suitable for being used as indicator in acid-base titration. Back

Freshly prepared beet root solution p. H 12 p. H 2 Overnight beet root solution p. H 12 p. H 2

Colour of the indicators (overnight and fresh beet root solution)in different p. H solutions p. H p. H 2 3 4 5 6 7 8 9 10 11 12 1 2 1. Overnight 2. Fresh

Titration between HCl and oven cleaner (Na. OH) using phenolphthalein and beet root as indicator Indicator Average volume of HCl required for the neutralization Phenolphth- Over-night Fresh beet alein beet root indicator 9. 68 cm 3 9. 58 cm 3 9. 10 cm 3

The concentration of Na. OH in the oven cleaner with using different indicators Indicator used phenolphthalein Over-night Fresh beet root solution Concentration of Na. OH in the oven cleaner 1. 936 M 1. 916 M 1. 820 M Back