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

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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
RoughAccurate 1Accurate 2
Final volume0.0014.650.00
Initial volume35.2048.0033.50
Volume of ammonium hydroxide used (ml)35.0033.3533.50
Average volume of ammonium hydroxide used (ml) (33.35+33.50)/2 =33.43 (2 d.p.)

Table II:
Volume Titration
RoughAccurate 1Accurate 2
Final volume0.0014.0016.50
Initial volume33.2046.8549.40
Volume of ammonium hydroxide used (ml)33.2032.8532.90
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
RoughAccurate 1Accurate 2
Final volume0.000.000.00
Initial volume25.6025.1025.20
Volume of sodium hydroxide used (ml)25.6025.1025.20
Average volume of sodium hydroxide used (ml) (25.10+25.20)/2 =25.15(2 d.p.)

Table IV:
Volume Titration
RoughAccurate 1Accurate 2
Final volume0.008.0016.00
Initial volume5.6013.3021.20
Volume of sodium hydroxide used (ml)5.605.305.20
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)pHVolume of ammonium hydroxide (ml)pH 0.000.7320.501.73
0.501.0321.001.76
1.001.0421.501.79
1.501.0522.001.83
2.001.0622.501.87
2.501.0723.001.91
3.001.0823.501.95
3.501.0924.001.99
4.001.1124.502.05
4.501.1225.002.10
5.001.1325.502.17
5.501.1526.002.25
6.001.1626.502.33
6.501.1727.002.44
7.001.1927.502.60
7.501.2028.002.80
8.001.2228.503.16
8.501.2329.004.39
9.001.2529.506.69
9.501.2730.007.86
10.001.2930.508.13
10.501.3031.008.25
11.001.3231.508.34
11.501.3432.008.42
12.001.3532.508.48
12.501.3733.008.54
13.001.3933.508.59
13.501.4134.008.64
14.001.4334.508.68
14.501.4535.008.73
15.001.4735.508.76
15.501.4936.008.80
16.001.5136.508.82
16.501.5337.008.85
17.001.5537.508.88
17.501.5738.008.90
18.001.6038.508.91
18.501.6239.008.92
19.001.6439.508.94
19.501.6740.008.96
20.001.70
Figure 1: Graph of pH value against volume of ammonium hydroxide added

Table VI:
Volume of sodium hydroxide used (mL)pHVolume of sodium hydroxide used (mL)pH 0.002.8918.005.07
0.503.0318.505.11
1.003.3319.005.16
1.503.4519.505.20
2.003.6120.005.27
2.503.6820.505.33
3.003.7721.005.40
3.503.8521.505.47
4.003.9122.005.57
4.503.9722.505.66
5.004.0423.005.77
5.504.0923.505.93
6.004.1224.006.23
6.504.1724.506.62
7.004.2325.0010.23
7.504.0025.5011.01
8.004.3226.0011.27
8.504.3626.5011.40
9.004.3927.0011.53
9.504.4227.5011.62
10.004.4628.0011.68
10.504.4928.5011.73
11.004.5429.0011.79
11.504.5629.5011.82
12.004.6130.0011.85
12.504.6430.5011.89
13.004.6831.0011.91
13.504.7131.5011.94
14.004.7532.0011.95
14.504.7832.5011.98
15.004.8233.0012.00
15.504.8633.5012.01
16.004.8934.0012.04
16.504.9334.5012.05
17.004.9735.0012.06
17.505.02

Figure 2: Graph of pH value against sodium hydroxide added

Discussion:

In part 1 A of the experiment, which is the strong acid-weak...
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