Investigation of the Suitability of Indicators and Instrumental Detection of Equivalence Points in Acid-Base Titrations

Objective: To understand the importance of choosing suitable indicators for detecting the end points of acid-base titrations. To obtain titration curves some acid-base titrations.

Materials and method:
As shown in page 2 and 3 in General Chemistry practical manual 2011.
Result:
Part 1: Suitability of Indicators Strong acid-weak base titration
Table I:
Volume Titration Rough Accurate 1 Accurate 2
Final volume 0.00 14.65 0.00
Initial volume 35.20 48.00 33.50
Volume of ammonium hydroxide used (ml) 35.00 33.35 33.50
Average volume of ammonium hydroxide used (ml) (33.35+33.50)/2 =33.43 (2 d.p.)

Table II:
Volume Titration Rough Accurate 1 Accurate 2
Final volume 0.00 14.00 16.50
Initial volume 33.20 46.85 49.40
Volume of ammonium hydroxide used (ml) 33.20 32.85 32.90
Average volume of ammonium hydroxide used (ml) (32.85+32.90)/2 =32.88 (2 d.p.)

Weak acid-strong base titration
Table III:
Volume Titration Rough Accurate 1 Accurate 2
Final volume 0.00 0.00 0.00
Initial volume 25.60 25.10 25.20
Volume of sodium hydroxide used (ml) 25.60 25.10 25.20
Average volume of sodium hydroxide used (ml) (25.10+25.20)/2 =25.15(2 d.p.)

Table IV:
Volume Titration Rough Accurate 1 Accurate 2
Final volume 0.00 8.00 16.00
Initial volume 5.60 13.30 21.20
Volume of sodium hydroxide used (ml) 5.60 5.30 5.20
Average volume of sodium hydroxide used (ml) (5.30+5.20)/2 =5.25 (2 d.p.)

(d.p. = decimal point)
Formula used to calculate the average volume of sodium hydroxide used (ml)
Average volume of sodium hydroxide used =(Accurate 1+Accurate 2)/2
Part 2: pH titration curves Strong acid-weak base titration

Table V:
Volume of ammonium hydroxide (ml) pH Volume of ammonium hydroxide (ml) pH
0.00 0.73 20.50 1.73
0.50 1.03 21.00 1.76
1.00 1.04 21.50 1.79
1.50 1.05 22.00 1.83
2.00 1.06 22.50 1.87
2.50 1.07 23.00