Class: BE210
Group: R3
Members:
FACILITATOR ..Tony Chen
TIME & TASK KEEPER
Luan Vo
SCRIBE
..Deepak Kollali
PRESENTER .Hughie Choe
Date: May, 2002
Abstract:
The values of pKa2 and pKa3 for phosphate salts were determined to
within 1% of literature values using titrations and the equal molar quantity
method, along with a Fisher Scientific Accumet Model 625 pH meter. Experimentally,
pKa3 was determined by extrapolation using the equal molar quantity method
and subsequent dilutions. pKa2 was accurately obtained two ways: the same
method employed in the determination of pKa3 and by plotting a pKa vs.
Sqrt(I) graph for the high ionic strength titrations (I=1.09 M to1.24 M).
The latter method yielded the smaller 95% confidence interval, but the
results were untrustworthy and may be a coincidence since the application
of the Debye-Hückel equation is not intended for ionic strengths greater
than 0.1 M. The final experimental value of pKa2 of phosphate salts
was found to be 7.243 ± 1.166 with 95% confidence and pKa3 was found
to be 12.265 ± 5.079 also with 95% confidence. The pKa2 and
pKa3 values had percent errors of 0.46% and 0.45%, respectively, to their
literature values of 7.21 and 12.32.