Bronsted-Lowry Acids and Bases

Active learning works for this topic because students need to visualize proton transfer, not just memorize definitions. Moving from static diagrams to dynamic role play and matching games helps them internalize the shifting identities of acids and bases during reactions.

• Year 12
• Chemistry
• 3 activities
• 15 min–25 min

Learning Objectives

1. Compare and contrast the Arrhenius and Bronsted-Lowry definitions of acids and bases.
2. Identify conjugate acid-base pairs in given chemical reactions.
3. Explain the amphiprotic nature of substances like water using the Bronsted-Lowry model.
4. Predict the direction of proton transfer in acid-base reactions based on conjugate pair strength.

Role Play

⏱ 20 min·Whole Class

Role Play: The Proton Handover

Students act as different molecules (e.g., HCl, H2O, NH3). One student holds a 'proton' (a ball) and must decide, based on their molecular identity, whether to donate it to another student, identifying the resulting conjugate pairs in the process.

Prepare & details

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

Facilitation Tip: During the Role Play, assign clear roles for H+ donors and acceptors, and require students to physically move between sides of the room as protons transfer to reinforce the direction of reactions.

Setup: Open space or rearranged desks for scenario staging

Materials: Character cards with backstory and goals, Scenario briefing sheet

• Apply
• Analyze
• Evaluate
• Social Awareness
• Self-Awareness

Think-Pair-Share

⏱ 15 min·Pairs

Think-Pair-Share: Amphiprotic Detectives

Pairs are given a list of ions like HCO3- and HPO42-. They must write two equations for each: one where it acts as an acid and one as a base, then share their reasoning with another pair to verify the conjugate pairs formed.

Prepare & details

Identify conjugate acid-base pairs in various chemical reactions.

Facilitation Tip: During the Think-Pair-Share, provide molecular diagrams with ionisable hydrogens highlighted so students can focus on bond polarity rather than guessing.

Setup: Standard classroom seating; students turn to a neighbor

Materials: Discussion prompt (projected or printed), Optional: recording sheet for pairs

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

Gallery Walk

⏱ 25 min·Small Groups

Gallery Walk: Conjugate Matching

Cards with various acids and bases are posted around the room. Students move in small groups to find and record the matching conjugate partner for each card, explaining the 'one proton difference' rule to their peers.

Prepare & details

Explain why some substances can act as both an acid and a base (amphiprotic).

Facilitation Tip: During the Gallery Walk, post reaction equations at different stations and have students physically match conjugate pairs using sticky notes to make abstract pairs concrete.

Setup: Wall space or tables arranged around room perimeter

Materials: Large paper/poster boards, Markers, Sticky notes for feedback

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

Teaching This Topic

Start by explicitly linking the new model to Year 10 Arrhenius knowledge to avoid a disconnect. Use analogies like a ‘hot potato’ game for proton transfer, but transition quickly to chemical equations so students practice identifying roles. Avoid overemphasizing memorization of examples; instead, prioritize repeated practice with unfamiliar acids and bases to build flexible understanding.

What to Expect

Successful learning looks like students confidently identifying acids, bases, conjugate pairs, and amphiprotic substances in new equations without prompting. They should also explain why proton transfer defines these roles, not molecular composition alone.

Watch Out for These Misconceptions

Common Misconception

During the Role Play activity, watch for students who treat all hydrogens as acidic. Redirect them by asking them to examine molecular structures and identify which hydrogen is bonded to an electronegative atom (e.g., oxygen or nitrogen) that can stabilize the negative charge after donation.

What to Teach Instead

During the Think-Pair-Share activity, provide a card with methane (CH4) and a card with hydrogen chloride (HCl). Ask students to compare the polarity of the bonds and explain why only HCl can donate a proton. Use their discussion to clarify that only ionisable hydrogens in polar bonds act as Bronsted-Lowry acids.

Common Misconception

During the Gallery Walk activity, watch for students who pair conjugate acids and bases by counting total hydrogens rather than tracking single proton differences.

What to Teach Instead

During the Gallery Walk activity, hand out a checklist that asks students to record the proton count for each species in the reaction and verify that conjugate pairs differ by exactly one proton. Circulate and prompt groups to explain their reasoning using the checklist.

Assessment Ideas

Quick Check

After the Role Play activity, display the reaction NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq) and ask students to individually write down the Bronsted-Lowry acid, base, conjugate acid, and conjugate base on a small whiteboard or paper. Collect and review responses to identify misconceptions before moving to the next activity.

Exit Ticket

After the Gallery Walk activity, give each student two chemical equations and ask them to circle the conjugate acid-base pairs and label each species as an acid or base. Collect the exit tickets to assess whether students can identify pairs and roles independently.

Discussion Prompt

During the Think-Pair-Share activity, pose the question: 'Why is the Bronsted-Lowry definition more useful than the Arrhenius definition for understanding reactions in non-aqueous solvents like liquid ammonia?' Have students discuss in pairs and then share their reasoning with the class, listening for explanations that mention proton transfer and solvent independence.

Extensions & Scaffolding

• Challenge: Provide a set of organic acids with multiple ionisable groups and ask students to predict all possible conjugate pairs for a given reaction.
• Scaffolding: Give students a partially completed table with acids and bases listed but missing conjugate partners; they fill in the gaps using molecular diagrams.
• Deeper exploration: Have students research and present on amphiprotic substances in biological systems, connecting proton transfer to enzyme function or amino acid behavior.

Key Vocabulary

Proton donor	A chemical species that donates a hydrogen ion (H+) in a reaction, characteristic of a Bronsted-Lowry acid.
Proton acceptor	A chemical species that accepts a hydrogen ion (H+) in a reaction, characteristic of a Bronsted-Lowry base.
Conjugate acid-base pair	Two species that differ by a single proton (H+), where one is the acid and the other is its conjugate base.
Amphiprotic	A substance that can act as either a Bronsted-Lowry acid (donate a proton) or a Bronsted-Lowry base (accept a proton) in different reactions.