Chemistry · 10th Grade

Active learning ideas

Arrhenius and Brønsted-Lowry Acid-Base Definitions

Active learning helps students move from memorizing definitions to applying them flexibly. This topic requires students to compare two frameworks, spot their limits, and justify when each is useful. Hands-on activities make those comparisons concrete and help students see why Bronsted-Lowry expands the Arrhenius view beyond water.

• Common Core State Standards
• STD.HS-PS1-2
• STD.CCSS.ELA-LITERACY.RST.9-10.4

• 20–45 min
• Pairs → Whole Class
• 4 activities

Activity 01

• Think-Pair-Share
• 20 min · Pairs

Think-Pair-Share: Which Definition Applies?

Give students a set of six reactions, some clearly Arrhenius (HCl in water producing H+ and OH-), some that only fit Bronsted-Lowry (NH3 acting as a base in a non-aqueous context). Students individually classify each reaction using one or both frameworks, then discuss their reasoning with a partner before whole-class debrief on where the models agree and where only Bronsted-Lowry applies.

Differentiate between Arrhenius and Brønsted-Lowry definitions of acids and bases.

Facilitation Tip

During the Think-Pair-Share, circulate and listen for students who initially confuse the definitions before they discuss in pairs.

What to look for

Provide students with the reaction HCl + H2O -> H3O+ + Cl-. Ask them to: 1. Identify the Arrhenius acid and base in this reaction. 2. Identify the Brønsted-Lowry acid, Brønsted-Lowry base, conjugate acid, and conjugate base. 3. Explain why the Brønsted-Lowry definition is more general.

• Understand
• Apply
• Analyze
• Self-Awareness
• Relationship Skills

Activity 02

• Concept Mapping
• 25 min · Pairs

Annotation Activity: Identify Conjugate Pairs

Students receive printed Bronsted-Lowry reaction equations and use colored pencils or highlighters to label the acid, base, conjugate acid, and conjugate base. Partners then check each other's labeling and discuss any disagreements. The visual annotation makes the proton transfer pathway explicit and reveals the conjugate relationship clearly.

Explain what defines a 'proton donor' and a 'proton acceptor' in a chemical reaction.

Facilitation Tip

For the Annotation Activity, provide colored pencils so students can trace proton transfers between conjugate pairs on printed reaction sheets.

What to look for

Present students with a list of substances (e.g., NaOH, H2SO4, NH3, CH3COOH). Ask them to classify each as an Arrhenius acid, Arrhenius base, Brønsted-Lowry acid, or Brønsted-Lowry base, and to justify their classifications.

• Understand
• Analyze
• Create
• Self-Awareness
• Self-Management

Activity 03

• Jigsaw
• 45 min · Small Groups

Jigsaw: Arrhenius vs. Bronsted-Lowry Case Studies

Expert groups each investigate one model using real reaction examples: Group A covers Arrhenius acids and bases, Group B covers Bronsted-Lowry proton donors and acceptors, Group C covers conjugate pairs, and Group D covers limitations of each model. Groups then share findings in mixed teams and collaboratively complete a comparison chart.

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

Facilitation Tip

In the Jigsaw, assign each group one case study so they become experts before teaching others during the Gallery Walk.

What to look for

Pose the question: 'When would you choose to use the Brønsted-Lowry definition over the Arrhenius definition?' Guide students to discuss scenarios involving non-aqueous solutions or reactions where proton transfer occurs without direct production of H+ or OH- in water.

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

Activity 04

• Gallery Walk
• 35 min · Small Groups

Gallery Walk: Reactions Under Both Lenses

Post five reaction scenarios around the room. At each station, students write whether the reaction fits the Arrhenius model, the Bronsted-Lowry model, or both, and identify the conjugate acid-base pair where applicable. A final station shows an example that Arrhenius cannot explain, prompting students to articulate the limitation in writing.

Differentiate between Arrhenius and Brønsted-Lowry definitions of acids and bases.

What to look for

Provide students with the reaction HCl + H2O -> H3O+ + Cl-. Ask them to: 1. Identify the Arrhenius acid and base in this reaction. 2. Identify the Brønsted-Lowry acid, Brønsted-Lowry base, conjugate acid, and conjugate base. 3. Explain why the Brønsted-Lowry definition is more general.

• Understand
• Apply
• Analyze
• Create
• Relationship Skills
• Social Awareness

A few notes on teaching this unit

Start with the Think-Pair-Share so students confront their initial assumptions. Move to annotation to practice identifying proton transfers, which builds the mental model needed for Bronsted-Lowry. Avoid rushing to the Bronsted-Lowry definition before students have tested the Arrhenius model on familiar reactions. Research shows that confronting misconceptions early and practicing transfer to new contexts improves long-term retention.

Students will explain when to use each definition, identify conjugate pairs, and argue why Bronsted-Lowry is more general. They will also critique the Arrhenius model and recognize water’s amphoteric role. Success looks like clear justifications in discussions, written answers, and gallery walk labels.

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Watch Out for These Misconceptions

• During Think-Pair-Share: Which Definition Applies?, watch for students who claim Arrhenius and Bronsted-Lowry are identical because they both use the term 'acid.' Redirect by asking them to test a reaction without water, such as NH3 reacting with HCl gas, and decide which definition still applies.

  Provide the NH3 + HCl reaction during the pair discussion. Ask students to label it under both models and note where Arrhenius cannot be used. Have pairs present their reasoning to the class to resolve the confusion.

• During Annotation Activity: Identify Conjugate Pairs, watch for students who treat water as a neutral solvent in every reaction. Redirect by asking them to trace the proton in reactions where water acts as an acid or base, such as with NH3 or HCl.

  Add a note on each reaction sheet: ‘Circle the proton donor and acceptor. Underline water if it is a participant.’ Require students to explain water’s role in their annotations before moving on.

• After Jigsaw: Arrhenius vs. Bronsted-Lowry Case Studies, watch for students who believe the conjugate base of a strong acid is strong. Redirect during the gallery setup by having each group post a mini-poster showing Ka and Kb values for HCl/Cl- and CH3COOH/CH3COO- pairs.

  Ask groups to calculate or look up Ka and Kb values for their assigned pairs. Have them add a line to their poster: ‘Strong acid → very weak conjugate base.’ Display posters during the Gallery Walk so students see the inverse relationship.

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Methods used in this brief

• Think-Pair-Share
• Concept Mapping
• Jigsaw
• Gallery Walk