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Title
Investigation of the suitability of indicators and instrumental detection of equivalence points in acid-base titration.
Objective
1. To understand the importance of choosing suitable indicators for detecting the end points of acid-base titrations.
2. To obtain titration curves for some acid-base titrations.
Materials and Method
(Please refer to the General Chemistry BPH2012 practical manual pg 4-5)

Results
Part I: Suitability of Indicators

A.Strong acid-weak base titration

1
2
Initial Burette Reading (mL)
19.50
17.00
Final Burette Reading(mL)
50.00
47.30
NH4OHused(mL)
30.50
30.30
Average Titre Volume (mL)

Table 1.1: Volume of 0.1M of NH4OH used to titrate 25mL of 0.1M of HCl using phenolphthalein as indicator.

1
2
Initial Burette Reading (mL)
25.00
18.50
Final Burette Reading (mL)
49.80
43.50
NH4OH used (mL)
24.80
25.00
Average Titre Volume (mL)

Table 1.2 : Volume of 0.1M of NH4OH used to titrate 25mL of 0.1M of HCl using screened methyl orange as indicator.

B. Weak acid-strong base titration

1
2
Initial Burette Reading (mL)
15.10
13.30
Final Burette Reading (mL)
40.30
38.70
NaOH used (mL)
25.20
25.40
Average Titre Volume (mL)

Table 2.1: Volume of 0.1M of NaOH used to titrate 25mL of 0.1M of acetic acid with phenolphthalein as indicator.

1
2
Initial Burette Reading (mL)
12.80
15.30
Final Burette Reading (mL)
15.30
17.60
NaOH used (mL)
2.50
2.30
Average Titre Volume (mL)

Table 2.2: Volume of 0.1M of NaOH used to titrate 25mL of 0.1M of acetic acid with screened methyl orange as indicator.

Part II: pH titration curves

A.Strong acid-weak base titration

Volume of NH4OH added (mL) pH reading

Volume of NH4OH added (mL) pH reading
0.0
1.18

18.0
2.82
0.5
1.19

18.5
3.27
1.0
1.19

19.0
4.21
1.5
1.20

19.5
5.19
2.0
1.21

20.0
6.32
2.5
1.22

20.5
7.43
3.0
1.25

21.0
7.87
3.5
1.27

21.5
8.48
4.0
1.29

22.0
8.60
4.5

References: [1] Chemical Education (Chemed) group at University of Wisconsin, 23 August 2009, revision date, ChemPaths Genchem Textbook: Indicators – phenolphthalein, [online] www.chemed.chem.wisc.edu/chempaths/GenChem_Textbook/ Madison. [2] Jim Clark, April 2009, Revision date. Titrations, [online] www.chemguide.co.uk. [3] Christine Chang, Kelly Cox, 2012, posted year, Titration curve of weak acid-strong base titration, [online] www.chemwiki.ucdavis.edu UC Davis, ChemWiki. [4] Ebbing DD & Gammon SD (2005). General Chemistry, 9th Edition, McGraw Hill.