This practical is a good introduction to acids and alkalis. Pupils test a range of substances with universal indicator solution. The colour of the resultant solution is checked against a pH chart to determine if the substance is an acid or an alkali.
Equipment required (per set):
- Test tube holder
- Test tubes
- Dropper bottle of UI solution
- pH chart
- Spatula / stirrer
- Substances to test: limewater, vinegar, bicarbonate of soda, water, lemon juice, milk, milk of magnesia, dissolved indigestion tablet, saltwater, lemonade, mouthwash etc
- Pipette or dropper
- Deionised (distilled) water
The substances to be tested can vary as long as some acid and some alkali based liquids are included. Any acids or alkalis to be used (ethanoic acid for instance) do not need to be more than 0.5 mol.
Universal Indicator paper or solution should be used for this practical, not litmus. Litmus will not normally detect neutral solutions whereas UI will visibly show the differences between acids, alkalis and neutrals.
Students place a spatula of a solid or a few drops of a sample liquid into a test tube and then add half a tube of deionised (distilled) water. The liquid is mixed and a few drops of UI solution added. The colour of the resultant mixture is then compared to the pH chart. A table of acidic, alkali and neutral substances can then be created.