Spectrophotometry
POTENTIOMETRIC DETERMINATION OF THE PURITY AND DSSOCIATION CONSTANT OF HYDROGEN PHTHALATE
Department of Chemical Engineering, College of Engineering
University of the Philippines, Diliman, Quezon City, Philippines
Date Due: September 20, 2013
Date Submitted: September 20, 2013
RESULTS AND DISCUSSION
An experiment was conducted to determine the purity of Hydrogen Phthalate sample and its dissociation constant. To perform the experiment with the utmost precision, equivalence point was determined using potentiometric determination.
Two methods exist for potentiometric determination exist: direct and indirect. Potentiometric techniques are often and effectively used when visual indicators are unavailable for titration. This is often more accurate compared to volumetric titration since pH meters are often more sensitive and dependable compared to visual indicators as visual indicators are highly dependent upon human judgement to declare whether the endpoint has been reached. This opens the experiment to the possibility of human error since minute changes in color cannot be easily determined by humans performing the titration. This however is more time consuming as one has to utilize smaller addition of titrant than necessary.
Potentiometry is often divided into two methods further: direct and indirect. Indirect titration works by using a pH meter to measure pH after every addition of the titrant. Direct potentiometry determines the potential of a cell by comparing a reference electrode at a constant concentration against the indicator electrode at different analyte concentrations. For the purposes of this experiment, indirect potentiometric titration was performed.
Std
1
2
3
Weight
0.2158
0.2058
0.202
Final
42.1
42.4
20.3
Initial
20.3
20.9
0
Vol
21.8
21.5
20.3
NaOH M
0.048473
0.046871
0.048726
Ave M
0.048023234
Table 1. Standardization data
Titrant used was sodium hydroxide which was standardized using 99.8 %
Department of Chemical Engineering, College of Engineering
University of the Philippines, Diliman, Quezon City, Philippines
Date Due: September 20, 2013
Date Submitted: September 20, 2013
RESULTS AND DISCUSSION
An experiment was conducted to determine the purity of Hydrogen Phthalate sample and its dissociation constant. To perform the experiment with the utmost precision, equivalence point was determined using potentiometric determination.
Two methods exist for potentiometric determination exist: direct and indirect. Potentiometric techniques are often and effectively used when visual indicators are unavailable for titration. This is often more accurate compared to volumetric titration since pH meters are often more sensitive and dependable compared to visual indicators as visual indicators are highly dependent upon human judgement to declare whether the endpoint has been reached. This opens the experiment to the possibility of human error since minute changes in color cannot be easily determined by humans performing the titration. This however is more time consuming as one has to utilize smaller addition of titrant than necessary.
Potentiometry is often divided into two methods further: direct and indirect. Indirect titration works by using a pH meter to measure pH after every addition of the titrant. Direct potentiometry determines the potential of a cell by comparing a reference electrode at a constant concentration against the indicator electrode at different analyte concentrations. For the purposes of this experiment, indirect potentiometric titration was performed.
Std
1
2
3
Weight
0.2158
0.2058
0.202
Final
42.1
42.4
20.3
Initial
20.3
20.9
0
Vol
21.8
21.5
20.3
NaOH M
0.048473
0.046871
0.048726
Ave M
0.048023234
Table 1. Standardization data
Titrant used was sodium hydroxide which was standardized using 99.8 %
References: [1]Harris, D. C. Quantitative chemical analysis. (8th ed.)(2010). [2] Skoog, D., West, D., Holler, F., & Crouch, S [3] Harvey, D. (2000). In Modern Analytical Chemistry. The Mc-Graw hill companies, Inc.