Carboxylic Acids Demystified

Overview

This lesson (lesson 9 of 20) introduces carboxylic acids as an organic functional group and links structure to properties and predictable reactions. It builds from earlier work on organic molecules and functional groups by focusing on the -COOH group, naming patterns, and reaction evidence.

Learning intentions

• WALT identify the carboxylic acid functional group in structural formulae.
• WALT relate the structure of carboxylic acids to their physical and chemical properties.
• WALT describe typical reactions of carboxylic acids using particle-level reasoning.
• WALT record observations and use them to explain reaction outcomes.

Success criteria

• I can point out the -COOH functional group and state its role in properties.
• I can match a carboxylic acid to a naming pattern (common or systematic) from a given structure.
• I can predict the likely reaction type (e.g., with alcohols to form esters; with carbonates to form CO₂).
• I can use evidence from observations to justify my reaction explanation.

Curriculum links

• Science capability: developing and using scientific knowledge through cause-and-effect links between structure and behaviour.
• Science capability: participating in science investigations by using fair testing and recording observations.
• Science capability: communicating in science by explaining results using appropriate chemistry language.
• NCEA internal investigation skills align with building a clear purpose, method, raw data, processing, interpretation, and reporting (foundation for later AS91187-style practical work).

Lesson structure (60 minutes)

1. 0–5 min · Retrieval hook. Teacher shows three quick structural sketches from previous functional-group work and asks students to identify the functional group present. Students respond on mini-whiteboards and explain one word for “how they knew”.

2. 5–15 min · Direct teach: structure → properties. Teacher introduces carboxylic acids using the general formula R–COOH and highlights what changes (R group) while the functional group stays the same. Students annotate a simple diagram and complete a guided “structure features” table (functional group, polarity idea, hydrogen bonding idea).

3. 15–25 min · Naming and recognising. Teacher models converting a drawn carbon chain into a carboxylic acid name (common examples such as ethanoic/methanoic; and “-oic acid” endings). Students work in pairs to name 4 structures and justify choices using the “must contain -COOH at the end” rule.

4. 25–42 min · Practical stations: reaction evidence. Teacher sets up three short stations with small quantities and clear safety instructions (goggles on, teacher supervision, no tasting). Students rotate in groups of 5, recording raw observations in a table: colour/odour changes (without identifying odours by sniffing), gas presence (where safe), temperature change (if applicable), and any precipitate formation.

Station A (carbonate + carboxylic acid): observe bubbling as CO₂ forms and identify “gas test” results only as directed by the teacher. Station B (acid + sodium hydrogencarbonate control vs carbonate variant): compare rate/extent to discuss how conditions affect reaction evidence. Station C (carboxylic acid + alcohol → ester smell/indicator evidence if your school uses a safe esterification demonstration): focus on “observable outcome + explanation”, not direct sniffing unless explicitly permitted with school procedure.

5. 42–52 min · Processing: from observations to explanation. Teacher prompts students to convert raw observations into pattern statements (e.g., “Acid produces gas with carbonates; ester formation gives a different observable outcome”). Students complete a CER-style response (Claim–Evidence–Reasoning) for one station, using particle-level language (bond changes; functional group driving the reaction).

6. 52–58 min · Whole-class share and misconception check. Teacher leads a short discussion: common misconceptions (e.g., “all organic molecules are acids”, “-COOH is just a carbonyl”). Students correct misconceptions using stems: “I used to think… now I know… because…”

7. 58–60 min · Exit ticket. Teacher gives a single question on paper: “Draw the functional group for a carboxylic acid and predict one reaction outcome with a carbonate.” Students hand in with a short justification sentence.

Resources

• Carboxylic acid structure cards (with and without -COOH)
• Student workbook/worksheet: functional group + naming tasks
• Station observation sheets with headings for raw data
• Goggles and appropriate lab safety equipment
• Practical station materials (selected to match your school’s safety procedures): acids, carbonate/hydrogencarbonate, suitable alcohol and demonstration setup/indicator as approved by your school
• Mini-whiteboards and markers
• CER sentence starters and chemistry word bank (acid, functional group, -COOH, ester, CO₂, gas, hydrogen bonding)

Assessment

• Formative checks: mini-whiteboard retrieval at the start and naming justifications during pair work.
• During stations: teacher circulates to check students record raw observations accurately (not just conclusions).
• Exit ticket: assess whether students can correctly identify -COOH and predict a reaction outcome with supporting reasoning.

Differentiation

• Support: provide sentence starters for CER and a worked example for naming; offer a checklist for what to record as “raw observation”.
• EAL/SEN: allow oral explanation to teacher before writing; provide bilingual word bank where available (acid, carboxylic acid, functional group, evidence).
• Extension: challenge students to propose how changing the R group might influence reaction rate or boiling point, and to suggest one controlled variable for a follow-up practical.
• Mixed grouping: place at least one confident student per station group, but rotate roles (recorder, measurer/observer, safety checker, reporter) so all contribute.