science education section, edb. miss soo may kei target group: s6 student
TRANSCRIPT
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
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
Phenolphthalein
When [Ph-(aq)] = [HPh(aq)],
pH = pKIn
= -log (7 x 10-10)
= 9.15
When 1/10≦
pH pK≦ In + log 1/10
≦ pKIn - 1
≦ 8.15
When 10≧
pH pK≧ In + log 10
≧ pKIn + 1
≧ 10.15
[HPh(aq)]
(aq)][Ph
When [Me(aq)] = [HMe+(aq)],
pH = pKIn
= -log (2 x 10-4)
= 3.7
When 1/10
pH pK≦ In + log 1/10
≦ pKIn - 1
≦2.7
(aq)][HMe
[Me(aq)]
When 10≧
pH pK≧ In + log 10
≧ pKIn + 1
≧ 4.7
(aq)][HMe
[Me(aq)]
Methyl orange
Strong Acid-Strong Base TitrationStrong Acid-Strong Base Titration
Sharp change in pH at the equivalence point: 3-11
Sharp change in pH at the equivalence point: 3-11
pH Titration Curves
Sharp change in pH at the equivalence point: 2-6
Sharp change in pH at the equivalence point: 2-6
Strong Acid-Weak Base TitrationStrong Acid-Weak Base Titration
Sharp change in pH at the equivalence point: 8-12
Sharp change in pH at the equivalence point: 8-12
Weak Acid-Strong Base TitrationWeak Acid-Strong Base Titration
NO Sharp change in pH at the equivalence point.
NO Sharp change in pH at the equivalence point.
Weak Acid-Weak Base TitrationWeak Acid-Weak Base Titration
• Red rose petals showed a lot of colour at different pH solution but less significant than red cabbage.
pH12 pH2
Colour of the indicators in different pH solutions
pH2
pH3
pH4
pH5
pH6
pH7
pH8
pH9
pH10
pH11
pH12
1
2
3
4
5
1.red cabbage 2.red rose petal
3.red cherry 4.red grape
5.beet root
• Beet root showed a sharp colour change between pH 12 and pH 11
Back
pH12 pH2
As it showed a sharp colour change at alkaline region, it is suitable for being used as indicator in acid-base titration.
Colour of the indicators (overnight and fresh beet root
solution)in different pH solutionspH 2
pH3
pH4
pH5
pH6
pH7
pH8
pH9
pH10
pH11
pH12
1
2
1.Overnight 2.Fresh
Indicator Phenolphth-alein
Over-night beet root indicator
Fresh beet root
indicator
Average volume of HCl required for the neutralization
9.68cm3 9.58cm3 9.10cm3
Titration between HCl and oven cleaner(NaOH) using phenolphthalein and beet root as indicator