Part A- Interpreting the titration curve Use the titration curve to determine the equivalence points for the unknown acid, the volumes at 50% of the equivalence points, Ka1, and Ka2 for the unknown acid. Because we recorded the pH at about 1 mL increments, we will need to do some estimating of pH values. When doing the estimating, a good approach is to average the known values on either side of the point you want to estimate. There will be some error in our readings, but it should be small enough for our purposes. Identify the second equivalence point on the titration curve. Use the two volume measurements where the largest change in pH occurs. Take the average of these two volumes to find where the equivalence occurs. What is the volume needed to reach the second equivalence point? Identify the first equivalence point on the titration curve. The first equivalence point should occur at half the volume needed for the second equivalence point. Look for the largest pH change near this value, and take the average of the volumes above and below it. What is the volume of NaOH needed to reach the first equivalence point? Volume at 50% of the first equivalence point. Estimate the pH at 50% volume of the first equivalence point. This represents pKa1. What is the Ka1?
Part A- Interpreting the titration curve Use the titration curve to determine the equivalence points for the unknown acid, the volumes at 50% of the equivalence points, Ka1, and Ka2 for the unknown acid. Because we recorded the pH at about 1 mL increments, we will need to do some estimating of pH values. When doing the estimating, a good approach is to average the known values on either side of the point you want to estimate. There will be some error in our readings, but it should be small enough for our purposes. Identify the second equivalence point on the titration curve. Use the two volume measurements where the largest change in pH occurs. Take the average of these two volumes to find where the equivalence occurs. What is the volume needed to reach the second equivalence point? Identify the first equivalence point on the titration curve. The first equivalence point should occur at half the volume needed for the second equivalence point. Look for the largest pH change near this value, and take the average of the volumes above and below it. What is the volume of NaOH needed to reach the first equivalence point? Volume at 50% of the first equivalence point. Estimate the pH at 50% volume of the first equivalence point. This represents pKa1. What is the Ka1?
Chapter13: Titrations In Analytical Chemistry
Section: Chapter Questions
Problem 13.18QAP
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Transcribed Image Text:Part A - Interpreting the titration curve
Use the titration curve to determine the equivalence points for the unknown acid, the volumes at 50% of the equivalence points, Ka1, and
Ka, for the unknown acid. Because we recorded the pH at about 1 mL increments, we will need to do some estimating of pH values.
When doing the estimating, a good approach is to average the known values on either side of the point you want to estimate. There will
be some error in our readings, but it should be small enough for our purposes.
Identify the second equivalence point on the titration curve. Use the two volume measurements
where the largest change in pH occurs. Take the average of these two volumes to find where the
equivalence occurs. What is the volume needed to reach the second equivalence point?
Identify the first equivalence point on the titration curve. The first equivalence point should occur at
half the volume needed for the second equivalence point. Look for the largest pH change near this
value, and take the average of the volumes above and below it. What is the volume of NaOH
needed to reach the first equivalence point?
Volume at 50% of the first equivalence point.
Estimate the pH at 50% volume of the first equivalence point. This represents pKa1.
What is the Ka1?
Transcribed Image Text:Titration Curve for Unknoówn A
12
11.49
10.04
10
2.85
10
15
20
25
30
35
ml levels
pH levels
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