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…show more content… Then, the pH increased again until pH 6.60. At equivalent point, the pH value increased critically. Beyond equivalent point, pH increased slowly again with addition of base. The equivalent point for this strong acid-weak base titration is pH 8.70.
The result obtained using acid-base indicators in strong acid-weak base titration (part 1A) showed that the end point obtained when using methyl orange is pH 8.50 and the end point obtained when using phenolphthalein is pH 8.62. Compare with the result obtained from the titration curve (figure 1), the end point for the both indicators were way too far to the equivalent point which is pH 5.60. For the weak acid-strong base titration (part 1B), the end point obtained when using phenolphthalein is pH 9.00 and the end point obtained when using methyl orange is pH 4.10. Comparing the results obtained to the titration curve (figure 2), the end point of phenolphthalein indicator is closer to the equivalent point compare to the methyl orange indicator. These results are not accurate compare to the theory of the titration. This may be due to systematic error and random error occurred throughout the experiment. One of the possible error is parallax error where we incorrectly positioning of the eye when reading the measurement at the burette. Besides, the burette and the pipette may be containing small amount of the distill water causing the acid or base diluted. The mixture of acid and base is not
