How acidic is it? The pH scale
Use universal indicator to measure the pH of seven household liquids, from lemon juice to limewater, and place each on the pH scale.
Core concept
The pH scale from 0 to 14 measures how acidic or basic a solution is
Topic: Acids, bases and salts
Some indicator: A substance that changes colour to show whether something is an acid or a base. All key words only tell you whether a substance is an acid: A substance that tastes sour, like lemon juice or vinegar. It turns blue litmus red. All key words or a base: The opposite of an acid, like soap or baking soda solution. It feels slippery and turns red litmus blue. All key words. Universal indicator is a mixture: Two or more substances mixed together, which can be separated again. All key words of several indicators, so it shows a whole range of colours. Each colour matches a number on the pH scale, which runs from 0 to 14. A pH below 7 is acidic, exactly 7 is neutral: Neither an acid nor a base, like pure water. All key words, and above 7 is basic (alkaline). The further from 7, the stronger the acid or base.
What you will learn
- Use universal indicator and a colour chart to find the pH of a solution.
- Classify solutions as acidic, neutral or basic from their pH.
- Compare how strongly acidic or basic different household liquids are.
Before you start
- Know that indicators change colour in acids and bases. Try "Natural indicators: acids and bases" first.
Materials
- Universal indicator
- Lemon juice, vinegar, milk, distilled water, baking soda solution, soap solution and limewater
Equipment
- 6 test tubes in a rack
- pH colour chart
Procedure
- Add a few drops of universal indicator to a test tube.
- Add one household liquid to the tube and stir.
- Match the colour to the pH chart: red (pH 1–2), orange (3–4), yellow (5–6), green (7), blue-green (8), blue (9–10), purple (11–14).
- Test as many liquids as you can and record each pH.
How this simulation is simplified
- Each liquid is shown at a typical pH value. Real samples vary slightly.
- The colour is read instantly after stirring, as with a pH meter reading.