Universal Indicator
Summary: Universal indicator is a mixture of several indicators that changes colour across the full pH range (0–14). It is used to estimate the approximate pH of a solution by comparing the colour to a colour chart. Tags: igcse chemistry definition acids-bases indicators Created: 2026-07-14 Last Updated: 2026-07-23
Universal indicator is a mixture of several different indicators designed to produce a continuous range of colours across the full pH scale. Unlike single indicators (litmus, methyl orange, etc.) which only show one colour change, universal indicator can estimate the approximate pH value of a solution.
pH Colour Chart
| pH | Colour | Nature |
|---|---|---|
| 0–2 | Red | Strongly acidic |
| 3–4 | Orange | Weakly acidic |
| 5–6 | Yellow | Very weakly acidic |
| 7 | Green | Neutral |
| 8–9 | Blue | Weakly alkaline |
| 10–11 | Dark blue / Violet | Moderately alkaline |
| 12–14 | Purple / Violet | Strongly alkaline |
How to Use Universal Indicator
- Add a few drops of universal indicator solution to the test solution, OR dip universal indicator paper into the solution
- Observe the colour produced
- Compare the colour to the colour chart provided
- Read the approximate pH value from the chart
How It Compares Hydrogen Ion Concentration
The pH scale is logarithmic — each unit represents a 10× change in H⁺ concentration:
- pH 3 has 10× more H⁺ ions than pH 4
- pH 3 has 100× more H⁺ ions than pH 5
- pH 3 has 1000× more H⁺ ions than pH 6
Using universal indicator:
- Lower pH / red colours = higher H⁺ concentration = more acidic
- pH 7 / green = H⁺ and OH⁻ concentrations equal = neutral
- Higher pH / blue-purple colours = lower H⁺ concentration = more alkaline
Universal Indicator vs Other Indicators
| Indicator | What It Tells You | Precision |
|---|---|---|
| Universal indicator | Approximate pH value (0–14) | ±1 pH unit |
| Litmus | Acid OR alkali only (yes/no) | None |
| Methyl orange | Acid OR alkali only | None |
| pH meter / probe | Exact pH value | ±0.01 pH units |
Advantages and Disadvantages
Advantages:
- Quick and easy to use
- Gives an estimate of pH across the full range
- Inexpensive
Disadvantages:
- Only gives an approximate pH value (±1 unit)
- Cannot be used if the solution itself is coloured (masks the indicator colour)
- Less precise than a pH meter
Key Facts
- Universal indicator = mixture of several indicators → full colour range
- Can estimate pH from 0 to 14 using a colour chart
- Red/orange/yellow = acidic; green = neutral; blue/purple = alkaline
- Each pH unit = 10× change in H⁺ ion concentration
- Less precise than a pH meter but more informative than single indicators
See Also
This is a key term definition page — part of the IGCSE Chemistry (0620/0971) keyword glossary.