Chemistry · Grade 12

Active learning ideas

Acid-Base Titrations & Equivalence Point

Active learning works well here because students often hold misconceptions about pH and equivalence points that are best corrected through direct observation and data collection. Handling real solutions in lab or simulations builds intuition about pH changes that lectures alone cannot provide.

• Ontario Curriculum Expectations
• HS-PS1-6

• 30–50 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Inquiry Circle
• 50 min · Pairs

Lab Investigation: Strong Acid-Strong Base Titration

Provide students with HCl solution of unknown concentration and standardized NaOH. Each pair uses a burette and pH probe to titrate 25 mL analyte, recording pH at 0.5 mL intervals. They plot the curve in real time using graphing software and identify the equivalence point.

Differentiate between the equivalence point and the half-equivalence point in a titration.

Facilitation Tip

In the Virtual Simulation: All Titration Types, pause the simulation at key points to prompt predictions about pH changes before revealing the next data point.

What to look for

Present students with three unlabeled titration curves (SA-SB, WA-SB, SA-WB). Ask them to label each curve with the correct titration type and briefly justify their choice by referencing the pH at the equivalence point and the presence or absence of a buffer region.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 02

• Inquiry Circle
• 30 min · Small Groups

Curve Analysis: Weak Acid-Strong Base

Distribute printed or digital titration curves for weak acid-strong base. In small groups, students mark half-equivalence and equivalence points, calculate pKa, and predict indicator suitability. Groups present findings to the class for peer review.

Predict the pH at the equivalence point for different types of acid-base titrations.

What to look for

Pose the question: 'If you are titrating a weak acid with a strong base, and your equivalence point is at pH 9.2, which of the following indicators would be most suitable: methyl orange (pH range 3.1-4.4), bromothymol blue (pH range 6.0-7.6), or thymol blue (pH range 8.0-9.6)?' Facilitate a discussion on why the chosen indicator's color change range must bracket the equivalence point pH.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 03

• Inquiry Circle
• 40 min · Pairs

Indicator Selection Challenge

Set up stations with sample titration curves and indicator lists. Pairs select and justify the best indicator for each curve type, testing color changes with pH buffers. They rotate stations and compile a class comparison chart.

Explain how to select an appropriate indicator for a given titration.

What to look for

Provide students with a scenario: 'You are performing a titration of a 0.10 M acetic acid solution with 0.10 M sodium hydroxide.' Ask them to: 1. Predict whether the pH at the equivalence point will be above, below, or equal to 7. 2. State the approximate pH at the half-equivalence point. 3. Name one indicator that would be suitable for this titration.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

Activity 04

• Inquiry Circle
• 35 min · Individual

Virtual Simulation: All Titration Types

Use PhET or similar software for whole class. Students individually simulate titrations, adjusting concentrations and strengths, then share curve screenshots in a shared document for discussion on pH trends.

Differentiate between the equivalence point and the half-equivalence point in a titration.

What to look for

Present students with three unlabeled titration curves (SA-SB, WA-SB, SA-WB). Ask them to label each curve with the correct titration type and briefly justify their choice by referencing the pH at the equivalence point and the presence or absence of a buffer region.

• Analyze
• Evaluate
• Create
• Self-Management
• Self-Awareness

A few notes on teaching this unit

Start with the Lab Investigation to ground the concept in concrete data, then use Curve Analysis to contrast curves systematically. Avoid rushing through calculations; instead, emphasize pattern recognition from plotted data. Research shows that students grasp equivalence points more deeply when they physically measure pH changes and discuss results in groups.

Successful learning looks like students correctly identifying titration types from curves, justifying choices based on pH at equivalence points and buffer regions. They should also select appropriate indicators and explain why pH range matters, demonstrating mastery of acid-base concepts through evidence.

---

Watch Out for These Misconceptions

• During Lab Investigation: Strong Acid-Strong Base Titration, watch for students assuming the equivalence point is always at pH 7 regardless of acid or base strength.

  Use the lab data to plot pH versus volume and ask students to identify the equivalence point pH directly from their curve, noting its proximity to 7 for this specific titration.

• During Curve Analysis: Weak Acid-Strong Base, watch for students confusing the half-equivalence point with the steepest part of the curve.

  Have students mark both points on their curves and explain why the half-equivalence point occurs in the buffer region before the steep rise at equivalence.

• During Indicator Selection Challenge, watch for students selecting indicators based on color preference rather than pH range.

  Provide indicator pH range cards at each station and require students to justify their choice using the equivalence pH from their titration data.

---

Methods used in this brief

• Inquiry Circle