video from ChemToddler and explanation from wikipedia
A universal indicator is present in a water solution at pH = 14 (purple colour) while an acid is slowly added turning the solution colour to blue, green, yellow and finally red when the pH goes down to 0. The bottom part of the beaker solution goes slower to lower pH when at the top local acid conditions are always observed until an homogeneus pH is obtained
A Universal indicator is a pH indicator composed of a blend of several compounds that exhibits several smooth colour changes over a pH value range from 1-14 to indicate the acidity or basicity of solutions.
A universal indicator is typically composed of water, propan-1-ol, phenolphthalein sodium salt, sodium hydroxide, methyl red, bromothymol blue monosodium salt, and thymol blue monosodium salt.
The colours that indicate the pH of a solution, after adding a universal indicator are:
| pH range | Description | Colour | ||
|---|---|---|---|---|
| 0-3 | Strong acid | Red | ||
| 3-6 | Acid | Orange/Yellow | ||
| 7 | Neutral | Green | ||
| 8-11 | Base | Blue | ||
| 11-14 | Strong Base | Purple |
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