Calculating the pH of Solutions

Learning Objectives

After completing this exercise, students will be able to:

• Calculate the pH of a solution containing strong and/or weak acids and/or bases.
• Assess the reasonableness of a calculated pH of an acid/base solution.

In this assignment, you will learn how to calculate the pH of a solution containing acids and/or bases.  The first step in calculating the pH of a solution is to identify what type of species are present.  Your solution could contain the following:

• Strong acid
• Strong base
• Weak acid
• Weak base
• Mixture of a strong and weak acid
• Mixture of a strong and weak base
• Mixture of a conjugate acid/base pair

Each group will be assigned one reaction mixture.  Your group’s job is to determine how to calculate the pH of the resulting solution and explain the process to the rest of the class.  The attached sheet has the group and mixture assignments.

Assignment Products:

1. Since we figured out the concentrations of all species present after the reaction, there is no need to explain that part of the problem.
2. Worked-out solution for calculating the pH.
3. Identify the type of solution resulting from the reaction. For example:  solution of a weak acid or mixture of a conjugate acid/base pair.
4. A handout to distribute to the class explaining how to calculate the pH of that type of solution. Handout should be no longer than the front and back of an 8.5” x 11” page.  Handout should be easy to read and follow.  The audience for the handout is the other students in the class, so consider what they already know and what requires explanation.
1. 5 minute presentation on how to calculate the pH of the solution. All members of the group must be prepared to make the presentation individually.

Group

Number

Group

Members

Group

Assignment

1

Calculate the pH of 20.0 mL of 0.150 M maleic acid.

2

Calculate the pH of the resulting solution when 20.0 mL of 0.150 M maleic acid is mixed with 10.00 mL of 0.100 M OH-.

3

Calculate the pH of the resulting solution when 20.0 mL of 0.150 M maleic acid is mixed with 30.00 mL of 0.100 M OH-.

4

Calculate the pH of the resulting solution when 20.0 mL of 0.150 M maleic acid is mixed with 40.00 mL of 0.100 M OH-.

5

Calculate the pH of the resulting solution when 20.0 mL of 0.150 M maleic acid is mixed with 60.00 mL of 0.100 M OH-.

6

Calculate the pH of the resulting solution when 20.0 mL of 0.150 M maleic acid is mixed with 75.00 mL of 0.100 M OH-.

Assignment Component

Score (points)

Type of solution

4

pH calculation

8

Handout Draft

4

Handout Final Draft

Organization/structure

4

Content

4

Presentation

4

Presentation

Organization/structure

4

Content

4

Presentation

4

Total

40

4 Exemplary

3 Proficient

2 Developing

1 Beginning

Organization, Structure

The message is logically and fully developed consistent with the constraints of the audience and the intent of the message; Is purposeful and coherent.

The message contains elements of logical development contains clear transitions has a recognizable flow of ideas.

The message lacks a logical organization is sometimes disjointed and/or awkward.

The message has no discernible organizational structure contains random, unconnected elements.

Content

The message is engaging. provides significant insight, or new information, or a useful perspective from the work.

The message is clear, accurate, and appropriate. provides insight, or enough information to make an informed decision.

The message is somewhat inaccurate or unclear. provides little insight or information.

The message is distorted or contains misinformation. confuses or misleads.

Presentation

The style and tone of the message enhances its effectiveness; the message has discernible style and elegance.

The style and tone of the message supports its effectiveness.

The style and tone of the message supports effectiveness in some aspects and undermines it in others.

The style and tone of the message undermines its effectiveness.