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Course: AP®︎/College Chemistry > Unit 8

Lesson 7: Acid–base titrations
Science
AP®︎/College Chemistry
Acids and bases
Acid–base titrations
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Acid–base titrations

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Problem

A sample of a weak acid, HA, is dissolved in distilled water and titrated with a solution of strong base. The pH curve for the titration is shown in the graph below.
A graph representing the change in p H by adding a base during titration. The x axis is labeled as ml of base added, with an interval from 0 to 60 and a scale of 10. The y axis is labeled as p H, with an interval from 0 to 14 and a scale of 2. The graphical representation starts at p H of 3 on the y axis and is represented by a curved line. This shows a gradual increase of p H value with adding the base until the graph reaches p H 6 after adding about 38 ml of base. The curved line becomes a straight line parallel to the y axis showing a sudden increase in the p H value to reach 11 at the 40 ml of base. The graph continues to show a gradual increase represented by a curved line to reach p H value of 12 at 60 ml of base.
Using the curve, estimate the pKa value for the acid.
Write your answer to the tenths place.
  • Your answer should be
  • an integer, like 6
  • a simplified proper fraction, like 3/5
  • a simplified improper fraction, like 7/4
  • a mixed number, like 1 3/4
  • an exact decimal, like 0.75
  • a multiple of pi, like 12 pi or 2/3 pi