Chemistry · Grade 11

Active learning ideas

Arrhenius and Brønsted-Lowry Definitions

Active learning helps students grasp abstract acid-base models because concrete examples make invisible proton transfers visible. By sorting, role-playing, and comparing, students move beyond memorization to see how definitions apply in real reactions.

• Ontario Curriculum Expectations
• HS-PS1-2

• 20–35 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Jigsaw
• 30 min · Small Groups

Card Sort: Acid-Base Reactions

Prepare cards with chemical equations like HCl + H2O and NH3 + HCl. Students sort them into Arrhenius-only, Brønsted-Lowry-only, or both categories, then justify choices. Follow with whole-class share-out to refine understandings.

Compare the Arrhenius and Brønsted-Lowry definitions of acids and bases, highlighting their differences.

Facilitation Tip

During Card Sort: Acid-Base Reactions, circulate and ask each pair to justify one placement that might be controversial to surface misconceptions early.

What to look for

Provide students with a list of chemical formulas (e.g., HCl, NaOH, NH3, H2O). Ask them to classify each as an Arrhenius acid, Arrhenius base, or neither, and briefly justify their classification.

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

Activity 02

• Jigsaw
• 25 min · Pairs

Proton Transfer Role-Play

Assign students roles as molecules (e.g., HCl as acid, H2O as base). They act out proton donation and acceptance, forming conjugate pairs. Switch roles for multiple reactions and draw diagrams to record outcomes.

Identify conjugate acid-base pairs in a Brønsted-Lowry reaction.

Facilitation Tip

For Proton Transfer Role-Play, assign proton donors and acceptors roles so each student physically enacts their particle’s behavior in the reaction.

What to look for

Present the reaction: NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq). Ask students: 'According to the Brønsted-Lowry definition, which species is the acid and which is the base? Identify the conjugate acid-base pair. Why wouldn't this reaction be fully explained by the Arrhenius definition?'

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

Activity 03

• Jigsaw
• 35 min · Pairs

Comparison T-Chart Challenge

Provide a T-chart template. Pairs fill columns with definitions, examples, strengths, and limitations of each model, then add real-world applications. Groups present one unique insight to the class.

Explain why the Brønsted-Lowry definition is more inclusive than the Arrhenius definition.

Facilitation Tip

During Comparison T-Chart Challenge, require groups to include at least one example that breaks the other group’s model to force critical comparison.

What to look for

On an index card, have students write one sentence comparing the scope of the Arrhenius and Brønsted-Lowry definitions and one example of a conjugate acid-base pair from a reaction they have seen.

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

Activity 04

• Jigsaw
• 20 min · Individual

Conjugate Pair Hunt

List 10 reactions on worksheets. Students identify and label acids, bases, conjugates individually, then check with partners. Discuss edge cases like amphoteric substances.

Compare the Arrhenius and Brønsted-Lowry definitions of acids and bases, highlighting their differences.

Facilitation Tip

For Conjugate Pair Hunt, have students sketch particle-level diagrams on whiteboards to connect ion formation with proton transfers.

What to look for

Provide students with a list of chemical formulas (e.g., HCl, NaOH, NH3, H2O). Ask them to classify each as an Arrhenius acid, Arrhenius base, or neither, and briefly justify their classification.

• Understand
• Analyze
• Evaluate
• Relationship Skills
• Self-Management

A few notes on teaching this unit

Start with familiar examples like HCl and NaOH, then introduce NH3 in water to expose gaps in Arrhenius. Research shows alternating between concrete manipulatives and abstract definitions builds stronger mental models. Avoid over-relying on textbook definitions alone; let students test models against data.

Students will explain why some substances fit one definition but not the other, and identify conjugate pairs in reactions they analyze. They will also articulate the limitations of each model when given new examples.

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Watch Out for These Misconceptions

• During Card Sort: Acid-Base Reactions, watch for students who place ammonia in the Arrhenius base column without noting it fails in non-aqueous solvents.

  Ask them to test ammonia in the Brønsted-Lowry base pile and explain why it fits only when proton transfer is considered, not ion production alone.

• During Proton Transfer Role-Play, watch for students who claim conjugate pairs have equal strength because they appear symmetrical in the reaction.

  Have them assign roles to strong and weak acids in their skits and use their scripts to argue why conjugate pairs must differ in reactivity.

• During Comparison T-Chart Challenge, watch for students who ignore ions when discussing Brønsted-Lowry, treating protons as separate from the species.

  Direct them to circle all ions in their T-chart cells and trace how proton transfers create or consume those ions, forcing them to connect the ideas.

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Methods used in this brief

• Jigsaw