Chemistry · Analytical Chemistry
Make a red cabbage pH indicator and test household liquids
Extract a natural indicator from red cabbage and rank household liquids from acid to base.
- DifficultyBeginner
- Estimated time1–3 hours
- BudgetUnder ₹250
- ClassClass 6–10
- TeamSolo or up to 2
- You needHousehold materials
Prerequisites: None
Original · by TechnifyedExperimentScience Fair ProjectBeginner friendlyLow costWell documented
Overview
Red cabbage contains anthocyanin, a pigment that turns red in acids, purple when neutral and green to yellow in bases. Boil the leaves, collect the purple liquid and use it to test liquids from your kitchen.
Why build this?
It gives a full colour scale with no lab chemicals, and you can check your results against real pH paper.
What you will learn
- What acids and bases are
- How an indicator shows pH by changing colour
- How to build and use a colour reference scale
- Why natural pigments respond to pH
Skills you will use
Safety
- Wear safety glasses and gloves, work in a ventilated place, label every container and wash your hands afterwards. Do not taste or smell chemicals directly, and do not mix chemicals beyond the steps given.
- Hot surfaces and liquids can burn. Use tongs or oven gloves and let things cool before touching them.
Materials and tools
- Half a red cabbage
- Hot water and a strainer
- Clear glasses or test tubes
- Lemon juice, vinegar, soda water, milk, soap solution, baking soda solution, detergent
- pH paper (optional)
Make it cheaper: Use hibiscus petals or beetroot if red cabbage is not available.
Step-by-step roadmap
Start
You will finish with: a colour chart of at least seven household liquids ordered by pH, with a photo of the lined-up glasses.
- 1
Prerequisites
Know this first: none. Then collect the 5 items in the materials list.
- 2
Learn
- What acids and bases are
- How an indicator shows pH by changing colour
- How to build and use a colour reference scale
- Why natural pigments respond to pH
- 3
Plan
Write your question, your hypothesis and the one thing you will change. Draw the table you will fill in before you start.
- 4
Build
- Chop the cabbage, pour hot water over it and leave for 15 minutes.
- Strain the purple liquid and let it cool.
- Pour 20 ml of indicator into each glass.
- Add a teaspoon of each test liquid to a separate glass and record the colour.
- Arrange the glasses from most red to most yellow-green.
- Check three of them with pH paper and label your scale with approximate pH values.
- 5
Test
Lemon juice and vinegar should turn it red or pink; baking soda should turn it blue-green; detergent green to yellow.
- 6
Document
Record every reading with its unit, photograph the setup and draw a graph of the result. Report structure
- 7
Present
Explain the question, the method and the graph in two minutes; keep the setup ready to demonstrate. Presentation structure · Viva questions
- 8
Publish
Share the report and photos with your class, a science fair or your school magazine.
Expected outcome
A colour chart of at least seven household liquids ordered by pH, with a photo of the lined-up glasses.
Other versions of this project
Beginner version
Test only lemon juice, water and baking soda and describe the three colours.
Advanced version
Make indicator paper by soaking and drying filter paper, and compare its sharpness with turmeric and hibiscus indicators.
Research version
Measure the colour of each sample from phone photos (RGB values) and plot hue against pH to make a quantitative scale.
Low-budget version
Use hibiscus petals or beetroot if red cabbage is not available.
Make this project better
- BasicTest only lemon juice, water and baking soda and describe the three colours.
- This projectMake a red cabbage pH indicator and test household liquids
- AdvancedMake indicator paper by soaking and drying filter paper, and compare its sharpness with turmeric and hibiscus indicators.
- ResearchMeasure the colour of each sample from phone photos (RGB values) and plot hue against pH to make a quantitative scale.
Ways to do this project
Text marked "You write this" is a prompt for your own work; everything else is specific to this project.
- Problem
- Which household liquids are acidic, neutral or basic, and how do they rank?
- Hypothesis
- If a liquid is acidic, then the cabbage indicator will turn red or pink; if basic, green or yellow.
- Variables
- Independent: liquid tested. Dependent: indicator colour. Controlled: indicator volume, amount of liquid added, lighting
Materials and procedure are in Materials and the Roadmap.
Observation table
| Liquid | Colour with indicator | pH paper value | Acid, neutral or base |
|---|---|---|---|
- Graph
- A colour strip with each liquid placed along a pH axis
- Results
- You write thisState what the graph shows in one or two sentences, with numbers.
- Conclusion
- You write thisSay whether the result supports your hypothesis and why you think so.
Display board
- Title and your name
- Question
- Hypothesis
- Materials
- Procedure (with photos)
- Data table and graph
- Conclusion
- What you would do next
Questions judges ask
- What is the pigment in red cabbage?
- Why does soap turn the indicator green?
- What is pH?
- What would you change if you did this again?
- What was your biggest source of error, and how did you reduce it?
- Where is this idea used in real life?
- Research question
- Which household liquids are acidic, neutral or basic, and how do they rank?
- Hypothesis
- If a liquid is acidic, then the cabbage indicator will turn red or pink; if basic, green or yellow.
- Variables
- Independent: liquid tested. Dependent: indicator colour. Controlled: indicator volume, amount of liquid added, lighting
- Methodology
- Measure the colour of each sample from phone photos (RGB values) and plot hue against pH to make a quantitative scale.
- Data collection
- You write thisSay what you will record, how many times, and how you will keep the records safe.
- Analysis
- A colour strip with each liquid placed along a pH axis
- Limitations
- You write thisList what could have affected the result: small sample, instrument limits, things you could not control.
Literature review
Find five to eight sources (your textbook, review articles, reports) and note what each says about your question. Group them by idea, not one after another, and end with what is still not known.
References
List every source you used in one style throughout (author, year, title, where it was published, link and the date you opened it).
Working as a team
Solo or up to 2. Suggested roles:
Report and presentation
Report structure
- Title and question
- Background: the science behind it
- Hypothesis
- Materials
- Method (steps, with a diagram or photo)
- Observations (table)
- Results (graph and calculation)
- Sources of error
- Conclusion
- What you would do next
- References
Presentation structure
- The question
- Why it matters
- The idea behind it
- Setup (photo)
- Method in three steps
- Results (one clear graph)
- What the result means
- Errors and limits
- Conclusion and next step
Viva questions
Try answering before you open each one.
What is the pigment in red cabbage?
Anthocyanin, which changes structure and colour with pH.
Why does soap turn the indicator green?
Soap solution is basic.
What is pH?
A scale from 0 to 14 that measures how acidic or basic a solution is; 7 is neutral.
Is this indicator as accurate as a pH meter?
No, it gives a range, not an exact value.
Resources
Source and attribution
Original
Written by Technifyed. Free to use for your own school or college project; write the report in your own words. Added 1 Oct 2026.
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