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CHEM 146
Lab 6 Worksheet v1.3 |
1
Lab 6 Worksheet
GRADE ____ /25 p
Your name:
Your section:
Note:
great care must be exercised in accurately reading VNaOH, that is, the volume must be interpolated (estimated between the scale “tick marks”) to within 0.1 mL. Small errors in interpolating the volume can significantly impact the resulting pKa determination and molar mass calculations.
An unknown weak acid (
Weak Acid #1) is titrated with standardized NaOH (
0.5002 M NaOH) and gives the following weak acid titration (pH vs. VNaOH) and First Derivative (
d(pH)/d(VNaOH) vs.
VNaOH) curves:
First Derivative ()
1. From the curves,
what is the
VNaOH
(volume of titrant base)
at the endpoint for
Weak Acid #1?
2. For
Weak Acid #1,
what is the pKa?
3. For
Weak Acid #1,
what is the pH at the endpoint?
4. Assuming the mass of the weak acid used in the titration was 0.211 g,
what is the molar mass (
MHA) of Weak Acid #1
? Show all work. Clearly state all equations (symbolic mathematical expressions) used.
A
different
unknown weak acid (
Weak Acid #2) is titrated with standardized NaOH (
0.4477 M NaOH) and gives the following weak acid titration (pH vs. VNaOH) and First Derivative (
d(pH)/d(VNaOH) vs.
VNaOH) curves:
First Derivative ()
5. From the curves,
what is the
VNaOH
(volume of titrant base)
at the endpoint for
Weak Acid #2?
6. For
Weak Acid #2,
what is the pKa?
7. For
Weak Acid #2,
what is the Ka? Show all work.
8. Assuming the mass of the weak acid used in the titration was 0.117 g,
what is the molar mass (
MHA) of Weak Acid #2
? Show all work. Clearly state all equations (symbolic mathematical expressions) used.
