Multiple Choice
Titration confirms an acetic acid solution to be 0.1 M. Calculate the pH. (acetic acid K a = 1.76 x 10-5 M).
2. Water
Titration
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Use the titration curve below.
What is the predominate species in the solution of phosphoric acid at pH = 5?
A
H3PO4
B
H2PO4-
C
HPO4-2
D
PO4-3
Verified step by step guidance1
Identify the relevant pKa values from the titration curve. For phosphoric acid, the pKa values are approximately 2.2, 7.2, and 12.7.
Determine the pH range in which the solution is buffered by each species. The predominant species at a given pH is the one that corresponds to the pKa value closest to that pH.
At pH = 5, compare this pH to the pKa values. The pH of 5 is between the first pKa (2.2) and the second pKa (7.2).
In the pH range between the first and second pKa, the predominant species is the one formed after the first deprotonation. For phosphoric acid, this is H2PO4⁻.
Conclude that at pH = 5, the predominant species in the solution of phosphoric acid is H2PO4⁻.
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