However the volume increments should not be too small as there may be two or

# However the volume increments should not be too small

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can be added as it reaches the endpoint. However, the volume increments should not be too small as there may be two or more points of the straight line of the second derivative plot that passes zero and it may become vulnerable to experimental errors due to more volume measurements. Also, the volume increments should not be too large or there would not be enough points to make accurate results and graphs. The data gathered was then plotted so that one can clearly see the equivalence point. The first plotted graph was the normal titration curve. Shown in Figure 2 is the normal titration curve for trial 2. 0 10 20 30 40 50 60 0 2 4 6 8 10 12 14 Volume Titrant added (ml) pH 2

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Figure 2. Normal Titration Curve For this graph, the equivalence point can be seen at the corresponding volume of the curve’s inflection point where the pH change is highest. The preceding points are the pre-equivalence points where the pH values are acidic while the points following the inflection point are the post-equivalence points where the pH of the analyte is towards basic. Another graph used was the First Derivative plot where dpH/dV is a function of the average volume. Figure 3 shows the First derivative plot of trial 2. 0 5 10 15 20 25 30 0 1 2 3 4 5 6 V'/Ave. Volume titrant added (ml) dpH/dV Figure 3. First Derivative Plot This graph gives a clearer image for determining the equivalence point. Because the change in potential with respect to the added volume is highest at equivalence point, the graph will have a “spiked” curve and will peak at the corresponding volume. The pre- and post-equivalence points have almost equal changes in potential as certain volumes of titrant are added.
• Fall '17
• pH, potentiometric titration

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