Understanding Universal Indicator Paper
Chemistry: Cambridge International GCSE Supplement, topic 7.1.11
Understanding Acids, Bases & Universal Indicator Paper
Universal indicator paper compares acidity, neutrality, or alkalinity by colour or pH. pH runs from 0 (strong acid) to pH 14 (strong base).
Characteristics of acids and bases
- Acids taste sour and feel rough.
- Bases taste bitter and feel slippery.
- Both acids and bases react differently with universal indicator paper.
- Acids increase hydrogen ion concentration in water.
- Bases decrease hydrogen ion concentration by releasing hydroxide ions.
What is universal indicator paper?
- Universal indicator paper changes colour based on pH level.
- It shows a range from red (acidic) to purple (alkaline).
- Scientists use it to measure the strength of acids and bases.
- The paper helps compare relative acidity and alkalinity quickly.
Using universal indicator paper
- Dip the paper into a solution of acid or base.
- Observe the colour change on the paper carefully.
- Match the colour with the pH chart provided.
- The pH scale runs from 0 to 14.
- pH 7 shows neutrality; lower than 7 shows acidity; higher than 7 shows alkalinity.
Interpreting pH and colour results
- Red or orange suggests high hydrogen ion concentration (strong acid).
- Yellow or green shows weak acids or neutral solutions (like pure water).
- Blue or purple means low hydrogen ion concentration (alkaline solution).
- The closer the pH to 0, the stronger the acid.
- The closer the pH to 14, the stronger the base.
Summary of key points
- Acids and bases show different colours on universal indicator paper.
- Colour corresponds to the hydrogen ion concentration and pH.
- Universal indicator paper offers a simple visual pH test.
- The pH scale helps compare relative acidity and alkalinity.
Test yourself on Understanding Universal Indicator Paper
What happens to the hydrogen ion concentration in water when an acid is present?