MCAT General Chemistry Question 142: Answer and Explanation
Home > MCAT Test > MCAT general chemistry practice tests
Test Information
- Use your browser's back button to return to your test results.
- Do more MCAT general chemistry practice tests.
Question: 142
7. Question below refer to the titration curve of acid X shown below:
What is the approximate value of pKa1?
- A. 1.9
- B. 2.9
- C. 3.8
- D. 4.1
Correct Answer: A
Explanation:
The first pKa in this curve can be estimated by eye. It is located halfway between the starting point (when no base had yet been added) and the first equivalence point (the first steep portion of the graph, around 15 mL). This point is at approximately 7-8 mL on the x-axis, which corresponds to a pH of approximately 1.9. Notice that this region experiences very little change in pH, which is the defining characteristic of a buffer region.