pH, POH, and Percent Dissociation

Grade 11 · Chemistry

Semester 1 | Period 3 | Week 14

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Subject: Chemistry

Semester: 1

Period: 3

Week: 14

School Name:
Teacher’s Name:
Subject: Chemistry
Grade Level: Grade 11
Week & Period: Week 14, Period III
Date:

Topic: pH, pOH, and Percent Dissociation
Sub-topic:

  • pH and pOH calculations
  • Percent dissociation of acids and bases

 

Learning Objectives
By the end of the lesson, learners should be able to:

  1. Calculate the pH and pOH of solutions
  2. Explain the pH scale and its relevance
  3. Calculate percent dissociation of weak acids and bases

 

Previous Knowledge
Learners are familiar with the concept of acids, bases, and electrolytic dissociation from the previous lesson.

Instructional Materials:

  • pH scale chart
  • Calculators
  • Sample acids and bases with given concentrations
  • Formula sheets

 

Anticipation (Warm-Up) – 5 minutes
Pose the question: “How can we measure the strength of an acid?” Discuss student answers and introduce the concept of pH and dissociation.

 

Building Knowledge (Main Lesson) – 25 minutes

  1. pH and pOH Calculations
    • pH = -log[H⁺]
    • pOH = -log[OH⁻]
    • Relationship: pH + pOH = 14
    • H⁺ and OH⁻ concentration from molarity
  2. The pH Scale:
    • Ranges from 0 to 14
    • Acidic (<7), Neutral (=7), Basic (>7)
    • Visual illustration on a chart
  3. Percent Dissociation:
    • Formula: % dissociation = ([H⁺] dissociated / initial [HA]) × 100
    • Use examples of weak acids like acetic acid

 

Learners’ Activities:

  • Calculate pH and pOH for sample problems
  • Use pH strips to test acidity of household substances
  • Calculate percent dissociation from given data

 

Consolidation (Review and Assessment) – 10 minutes

  • Solve 2 pH/pOH problems as classwork
  • Oral quiz: Ask students to identify if a solution is acidic/basic given its pH

 

Homework / Assignment:

  1. Calculate the pH of a 0.01M HCl solution.
  2. Find the percent dissociation of a 0.2M acetic acid solution where [H⁺] = 0.01M
  3. Write short notes on the significance of the pH scale.

Notes – Detailed and Explained

pH and pOH are logarithmic measures of hydrogen ion and hydroxide ion concentrations. A low pH means high acidity; a high pH indicates alkalinity.

Percent Dissociation measures the degree to which an acid or base ionizes in water. Strong acids/bases dissociate completely (near 100%), while weak ones dissociate partially (much less than 100%).

pH Scale: The logarithmic nature means each pH unit reflects a tenfold change in H⁺ concentration. A pH of 3 is 10 times more acidic than a pH of 4.

 

Expanded Notes / Instructions:

  • Link pH changes to biological systems (e.g., blood pH)
  • Reinforce base 10 logarithms with math review if needed
  • Provide scaffolds for students with math difficulties

 

Inclusive / Differentiation:

  • Use visuals like colored pH strips for tactile learners
  • Pair weak and strong students to work through problems

Teacher’s Reflection (Post-Lesson Questions):

  • Were students able to relate pH values to acidity/basicity?
  • Did the class struggle with logarithmic operations?
  • Who may need more support with percent dissociation?