demonstrations:testing_ph_indicators
Testing pH Indicators
Materials: ★★☆ Available in most school laboratories or specialist stores
Difficulty: ★☆☆ Can be easily done by most teenagers
Safety: ★★☆ Some safety precautions required to perform safely
Categories: Acids and Bases
Alternative titles:
Summary
This experiment investigates how different pH indicators change color across the acidic, neutral, and basic ranges.
Procedure
- Prepare a series of solutions with different pH values, ranging from strongly acidic to strongly basic.
- Select several pH indicators to test. Examples include litmus, universal indicator, phenolphthalein, methyl orange, bromothymol blue, and natural extracts such as red cabbage juice.
- Place small samples of each pH solution into test tubes or wells in a spotting tile.
- Add a few drops of an indicator to each solution and record the color observed.
- Repeat the process with the other indicators to compare results.
- Summarize findings in a table showing pH values and corresponding indicator colors.
Links
Chemistry Lesson | pH Indicator | Acid & Base Experiment | Science for Kids - Big Bang Academy Kids:
Variations
- Test natural indicators from foods such as beetroot, turmeric, blueberries, or hibiscus tea.
- Compare the sensitivity of synthetic versus natural indicators across different pH ranges.
- Use a digital pH probe to measure exact pH values and compare them to the indicator results.
Safety Precautions
- Wear safety goggles and gloves to protect against spills.
- Handle acids and bases with care; even dilute solutions can irritate skin and eyes.
- Avoid tasting or touching any chemicals or indicator solutions.
- Dispose of all solutions safely, flushing dilute samples down the sink with plenty of water.
Questions to Consider
- Why do different indicators show different colors at the same pH? (Because each indicator has its own unique transition range where its molecular structure changes.)
- How could using multiple indicators improve the accuracy of identifying a solution’s pH? (By covering overlapping pH ranges, giving a clearer estimate.)
- Why might natural indicators be less precise than laboratory-prepared indicators? (Natural extracts often contain mixtures of compounds, making the color changes less sharp.)
- What practical uses are there for pH indicators outside the classroom? (They are used in soil testing, swimming pool maintenance, medical diagnostics, and industrial processes.)