Read the pH scale
Below 7: acidic. Exactly 7: neutral. Above 7: alkaline. The usual school scale runs from 0 to 14. Universal indicator is red/orange/yellow in acids, green at neutral, and blue/purple in alkalis.
Lesson 4.7 · AQA Combined Science
pH and neutralisation
The ions that matter
Acids form H⁺ ions in water. Alkalis contain OH⁻ ions. During neutralisation these react to form water: H⁺ + OH⁻ → H₂O.
Measure and explain
Add a little universal indicator to a sample and compare the colour with its chart to estimate pH. A pH probe gives a numerical reading. Adding alkali to an acid makes pH rise towards 7; too much alkali takes it above 7. Diluting an acid with water moves its pH towards 7.
Remember
Acid: pH < 7. Neutral: pH 7. Alkali: pH > 7. H⁺ + OH⁻ → H₂O.
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