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.