LF-13 · TEACHER LESSON PLAN

Red cabbage pH indicator lab

Use cabbage pigment to compare acidic, near-neutral and basic samples

ChemistryGrades 6–1030 min prep + 20 min testingHazard low; hot-water prep and household samplesNGSS MS-PS1-2

01 //

Driving question

START THE LESSON WITH THISHow does the kind of household liquid change the color of red-cabbage indicator?

02 //

Learning objectives

Students observe and record each sample's indicator color under the same lighting and compare it with the purple reference.
Students classify each tested liquid approximately as acidic, near neutral or basic from its observed color.
Students explain how cabbage pigment responds to different liquids while noting that color is an approximate indicator, not an exact pH measurement.

03 //

Standards

Dimension	Alignment
Performance expectation	MS-PS1-2Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. (Partial alignment: students compare the indicator's color before and after adding household liquids; color change is not among the properties the assessment boundary lists (density, melting point, boiling point, solubility, flammability, odor).)
Practices	SEP 4Analyze and interpret data.
Core idea	PS1.BIn a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants.
Crosscutting	PatternsMacroscopic patterns are related to the nature of microscopic and atomic-level structure.

Standards text paraphrased from nextgenscience.org. Alignment is partial; this hands-on activity does not cover every part of the performance expectation.

03A //

State standards crosswalk

Use the row as a planning crosswalk, then confirm local district pacing and grade placement. “Partial” labels describe a skill connection, not full mastery of the complete standard.

State	Verified standard	How this lesson aligns	Official source
California	CA NGSS MS-PS1-2	Partial connection: students analyze color observations after samples interact, but color is not one of the properties named in the assessment boundary.	Open standard ↗
Texas	Science.8.6(D)	Direct topic match: students compare acid and base behavior relative to the purple reference; the color test gives an approximate category, not a pH value.	Open standard ↗
Florida	SC.8.P.9.2	Partial connection: the investigation demonstrates an indicator color response, but does not distinguish physical from chemical changes using multiple lines of evidence.	Open standard ↗
New York	NYSSLS MS-PS1-2	Partial connection: students interpret a color change after interaction, but this short indicator test alone does not establish whether a new substance formed.	Open standard ↗
Pennsylvania	STEELS 3.2.6-8.D	Partial connection: students analyze color properties after liquids interact, but color change alone is insufficient evidence to determine that a chemical reaction occurred.	Open standard ↗

04 //

Materials and prep timeline

PER GROUP

Teacher-prepared cooled red-cabbage indicator: 10 mL in each of five cups
Five clear or white cups: four food-grade tests plus one purple reference
2 mL each of lemon juice, vinegar, plain water and baking-soda solution
One indicator dropper and one clean labeled dropper per test sample, labels, white paper and goggles

TEACHER ONLY

An adult uses red cabbage and hot water to prepare the indicator, strains it through a separate strainer and lets it cool before students handle it.
Use an adult-only pot for the hot-water preparation. Use only the listed food-grade samples and keep them in separate cups; do not bring household cleaners into this student activity.
Provide one student sheet per student and keep a purple reference cup for comparison.

CLASS-SIZE KIT PLANNER

One per-group kit contains every item in the team materials list above. Groups are balanced around the listed 3–4 students target.

Students	Groups	Per-group kits	Student sheets	Suggested group split
20	5	5 complete kits	20 copies	5 groups of 4
25	7	7 complete kits	25 copies	4 groups of 4 and 3 groups of 3
30	8	8 complete kits	30 copies	6 groups of 4 and 2 groups of 3

BEFORE CLASS · 30 MINPrepare indicator

Adult heats chopped cabbage in water, cools and strains the extract. Set out labeled, separate sample cups and fresh droppers.

0–4 MINPredict

Students predict possible color groups and review sample handling: observe only, do not taste, and never mix samples.

4–14 MINTest separately

Add the same indicator volume to each cup and a small, equal amount of one teacher-approved liquid. Use a clean labeled dropper for each sample.

14–18 MINCompare colors

Record colors promptly under the same light and compare each with the purple reference; classify the result approximately.

18–20 MINExplain limits

Connect the color pattern to cabbage pigment and explain why it does not provide an exact pH value.

04A //

Lab figures and data visuals

Reviewed article images support the lesson flow. Use the tables and student sheet to record actual observations; pictured patterns are not target results.

A labeled diagram compares approximate cabbage-indicator colors for lemon juice and vinegar, plain water, and baking-soda solution, with a clear warning that shades are not exact pH readings. — **Compare the pattern, not a number.**These are common illustrative shifts, not guaranteed results. Record the colors actually observed in your setup.

A teacher-prepared red-cabbage extract is strained into clear sample cups beside goggles and measured household test solutions. — **Make one batch for every comparison.**Keep extraction and sample volumes consistent, let the hot extract cool, and use clean droppers to avoid cross-contamination.

Separate clear sample cups show red-cabbage indicator color shifts beside a purple reference cup and clean droppers. — **Keep the comparison fair.**Use the same extract and sample volumes, separate cups and clean droppers, then record before classifying.

04B //

Printable shopping list

TEACHER PREP · Red cabbage pH indicator lab

Shopping and staging checklist

Multiply the per-group kit contents by the class-size planner. The teacher section includes teacher-provided materials and setup or safety notes.

PER-GROUP KITS

Teacher-prepared cooled red-cabbage indicator: 10 mL in each of five cups
Five clear or white cups: four food-grade tests plus one purple reference
2 mL each of lemon juice, vinegar, plain water and baking-soda solution
One indicator dropper and one clean labeled dropper per test sample, labels, white paper and goggles

TEACHER-PROVIDED MATERIALS + SETUP RULES

An adult uses red cabbage and hot water to prepare the indicator, strains it through a separate strainer and lets it cool before students handle it.
Use an adult-only pot for the hot-water preparation. Use only the listed food-grade samples and keep them in separate cups; do not bring household cleaners into this student activity.
Provide one student sheet per student and keep a purple reference cup for comparison.

QUANTITIES BY CLASS SIZE

Material	Per group kit	20 students	25 students	30 students
Cups, four food-grade test samples plus purple reference	5	25	35	40
Cooled red-cabbage indicator	50 mL	250 mL	350 mL	400 mL
Teacher prep: red cabbage, hot water, adult-only pot and strainer	Prepare a batch	Yield at least 250 mL	Yield at least 350 mL	Yield at least 400 mL
Lemon juice, vinegar and baking-soda solution	2 mL each	10 mL each	14 mL each	16 mL each
Separate clean droppers for the three test samples	3, plus 1 indicator dropper	15, plus 5 indicator droppers	21, plus 7 indicator droppers	24, plus 8 indicator droppers
White paper and label set	1 sheet and set	5 sheets and sets	7 sheets and sets	8 sheets and sets
Student sheets and goggles	1 per student	20	25	30

Prepare 5 kits for 20 · 7 kits for 25 · 8 kits for 30 students.

05 //

Lesson flow

Minutes	What happens
0–4	Engage Show the cooled purple indicator. Ask how color might change across household liquids; separate prediction from measured result.
4–7	Explore Label clear cups and place a purple reference under the same light. Review goggles, no tasting, clean droppers and no mixing.
7–14	Explore Add equal indicator amounts. Test lemon juice, vinegar, plain water and baking-soda solution in separate labeled cups, using a clean dropper for each. Household cleaners are not part of this activity.
14–18	Explain Record the resulting color and compare it with the reference. Red/pink commonly indicates an acidic sample, purple near neutral and blue/green a basic sample; shades depend on concentration and conditions.
18–20	Evaluate Use the color pattern to classify approximately. State that a calibrated pH strip or meter is needed for a more precise pH measurement.

06 //

Discussion questions

1. What did the purple reference help you compare?

SAMPLE ANSWERIt showed the starting indicator color under the same light. Each separately tested cup can be compared with it, but a color estimate does not give an exact pH.

2. Which tested liquids appeared acidic or basic?

SAMPLE ANSWERUse the recorded colors: vinegar and lemon juice often shift red/pink, plain water often remains closer to purple, and baking-soda solution often shifts blue/green. Record actual observations because shades can vary.

3. Why use the same amount of indicator and a clean dropper?

SAMPLE ANSWEREqual indicator volume makes the cups easier to compare. A clean, separate dropper helps prevent one sample from contaminating another.

4. Why is cabbage color not an exact pH measurement?

SAMPLE ANSWERThe pigment changes across a color range, and concentration, lighting, sample color and indicator preparation affect what students see. A calibrated pH strip or meter is more precise.

07 //

Common misconceptions

STUDENTS OFTEN SAY“A red color tells the exact pH number.”

BETTER IDEAThe indicator gives an approximate category or range; use a calibrated pH strip or meter for a more precise value.

STUDENTS OFTEN SAY“Every shade has one fixed meaning in every setup.”

BETTER IDEALighting, pigment concentration, liquid color and sample amount affect appearance, so compare under consistent conditions with a reference.

STUDENTS OFTEN SAY“A cleaner would make a stronger color, so I should add it.”

BETTER IDEAUse only the four listed food-grade samples, keep them separate, and record what the indicator actually shows.

08 //

Differentiation

SUPPORT

Place a purple reference and a simple red/pink–purple–blue/green color strip beside the cups.
Pre-label sample cups and match each to its own clean dropper; have an adult dispense the approved liquids.
Offer the frame: “Compared with purple, sample ___ became ___. This suggests ___, but the color is approximate.”

EXTEND

Compare a dilution series of one teacher-approved sample using equal indicator and total liquid volumes; record how the shade changes.
Repeat the color comparison under two lighting conditions and explain why a controlled light source improves comparison.
Compare the indicator's category with pH paper measurements collected by the teacher; explain mismatches and limits.

09 //

Assessment rubric

Criterion	Beginning	Developing	Secure
Observation	Leaves colors blank or guesses from the sample name.	Records colors but uses inconsistent lighting or omits the reference.	Records each observed color and compares it with the purple reference under common light.
Approximate classification	Labels exact pH values without evidence.	Classifies some samples but does not connect labels to observed colors.	Uses observed colors to classify approximately and avoids claiming exact pH.
Fair comparison	Combines samples or uses no consistent method.	Uses separate cups but omits a control such as indicator amount or dropper cleanliness.	Uses equal indicator amounts, separately labeled cups and clean droppers for each approved sample.
Explanation and safety	Misstates color as exact or ignores safe handling.	Names pigment or safety rules without connecting them to the method.	Explains pigment-based color change, measurement limits and the rule never to mix samples or cleaners.

10 //

Vocabulary

Indicator – A material that changes appearance in response to a condition such as acidity or basicity.
Anthocyanin – A plant pigment in red cabbage that can show different colors in different solutions.
Acidic – A solution category associated with pH below neutral.

Basic – A solution category associated with pH above neutral.
Neutral – A solution category near pH 7 in water-based comparisons.
Reference – A comparison standard, here the starting purple indicator color.

11 //

Safety, cleanup and troubleshooting

BEFORE STUDENTS TOUCH ANYTHING

An adult should prepare the cabbage extract with hot water and let it cool before students handle it. Wear goggles and do not taste any test sample.
Use only the listed small food-grade samples: lemon juice, vinegar, plain water and baking-soda solution. Keep samples in separate labeled cups and leave household cleaners out of the activity.

Troubleshooting: If no color shift is visible, confirm the extract is cooled and the liquid is added to its own clear cup under good light. Use fresh indicator and a clean dropper. If an unknown or unapproved product appears, do not test it; tell the supervising adult.