Page 79 - Pharmaceutical_Analytical_Chemistry_1_Theoretical_Notes_Level_1
P. 79
Mansoura National University
Pharm D-Clinical Pharmacy Program Level 1 Pharm. Anal. Chem. 1 (PC 101)
How to predict the shape of the Titration Curve
Choice of Acid-Base Indicators
For accurate titrimetric method, the indicator should be
selected so as to make the titration error as small as
possible, which means that the indicator should be selected so
that it changes its color as close as possible to the
equivalence point.
To achieve that, the pH-range of the indicator
(i.e. pH-interval within which the indicator changes its color)
should fall in the vertical part of the titration curve which is the part marked by sharp
change of pH.
❖ The following three indicators are used as examples of different pH ranges:
{1} M.O. indicator [pH range in the acidic region (≈ 3.0 - 4.5)].
{2} Bromothymol blue indicator [pH range in the neutral region (≈ 6.0 – 7.6)].
{3} ph.ph. indicator [pH range in the basic range (≈ 8.5 - 10)].
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