Acids, bases and indicators

O/L Science · G.C.E. Ordinary Level · Grades 10–11

Aim

To classify common solutions as acidic, neutral or basic using indicators.

Apparatus

• Test tubes and a rack
• Litmus, universal indicator, phenolphthalein
• Solutions (lime juice, vinegar, water, baking soda…)

Method

1. Pour a little of each solution into a test tube.
2. Dip blue and red litmus paper in it.
3. Add a few drops of universal indicator and note the colour.
4. Add a few drops of phenolphthalein.
5. Classify the solutions as acidic, neutral or basic by pH.

Conclusion

Acids (pH < 7) turn blue litmus red and universal indicator red or orange. Bases (pH > 7) turn red litmus blue and the universal indicator blue or purple; phenolphthalein is pink only in bases. Neutral solutions (pH 7) give green.