Penn State CHEM 113 Week 10 Post Lab Questions and Analysis

Complete all questions by handwriting the answers directly into your lab notebook. When answering

questions, be sure to fully explain your answers. For more detailed instructions, review the Claim,

Evidence, Reasoning video.

Section F-G. Titration of a Weak Acid with a Strong Base; Interpretation of Titration Curves and

Application to Buffer Systems

Q1.

Fall 2023

Q2.

Q3.

(a) Plot your data for the titration of acetic acid with sodium hydroxide directly on Figure 1 (page

81). Draw a smooth curve through the points. Cut out and tape this figure into your lab

notebook.

(b) On your experimental titration curve, label:

• The beginning of the titration (before any NaOH has been added) as point A.

• The equivalence point as point B.

• A point well past the equivalence point as point C.

NOTE: Data selected from the computer simulation show that the equivalence point pH is

8.31 and that it occurs after the addition of exactly 5 drops of 0.01 M NaOH.

(c) Label the pH at each point, A-C.

(d) Label the dominant species in solution at each point, A-C.

(e) Label the half-equivalence point and pka.

(f) Draw a box around the buffer region and label the two chemical species that form the buffer

system.

Does the pH at the equivalence point make sense? Explain your answer based on what the

dominant species are in the solution at that point.

Determine the K₂ for CH3COOH from your experimental titration data. How does this value

compare to the K₂ you determined from the computer-generated titration curve in ILQ1?/nQ4.

Report how many drops of NaOH you used to prepare your buffer solution and report the pH

measured for this buffer solution. Based on the titration curve in Figure 1 and your table from

ILQ2, is this the pH that you expected? Explain.

Section H. Dilution of Buffers

Q5.

Q6.

Use the Claim, Evidence, Reasoning method to explain the effect of dilution on the pH of

buffers.

Use the Claim, Evidence, Reasoning method to explain the effect of dilution on buffer capacity.

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