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Lecture

CHM110H5 Lecture Notes - Equilibrium Constant, Titration, Sodium Hydroxide


Department
Chemistry
Course Code
CHM110H5
Professor
Judith C Poe

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Lab 4 - Identification of an Unknown Acid by pH Titration
29 October 2012
5 November 2012

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Purpose: To experimentally determine, through titration, the Ka of an unknown acid in order to
find out what the acid is. This will be determined by finding the Ka for the following reaction:
HA + H2O <--> A-+H3O+
where
Ka = [A-][H3O+]/[HA]
From there, it will be compared with the Ka values of other acids.
Experimental Method: Refer to pages 68-70 in Course Manual for CHM110. In the beginning
of the titration of the unknown acid, 0.4 mL of NaOH was added for the first reading instead of
0.25 mL, and proceeded as described in the manual from there. Additionally, in the titration of
the unknown acid, the portion where NaOH was supposed to be added drop by drop was skipped.
Results:
Part 1:
Figure 1
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pH
Volume NaOH Added (mL)
Titration Curve for HCl
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Figure 2
Figure 3
Calculations:
1. pH at equivalence for HCl=7. Based on Figure 1, when pH =7, ≈25.9 mL of NaOH was added.
Vb = 0.0259 L
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pH
Volume NaOH Added (mL)
Titration Curve for Unkown Acid
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pH
V
Average Volume Interval
pH/V
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