Test various substances with indicator solution and look for colour changes in this microscale class practical

In this experiment, students observe the colour changes that result from adding indicator solution to a variety of acidic and alkaline substances. They then use their observations to estimate the pH of each substance, determining its acidity or basicity.

The practical should take about 15 minutes.

Equipment

Apparatus

  • Eye protection
  • Student worksheet
  • Clear plastic sheet (eg ohp sheet)
  • Plastic pipettes

Chemicals

Note

Solutions should be contained in plastic pipettes. See the accompanying guidance on apparatus and techniques for microscale chemistry, which includes instructions for preparing solutions.

  • Sodium hydroxide, 1 mol dm–3
  • Hydrochloric acid, 1 mol dm–3
  • Sulfuric acid, 1 mol dm–3
  • Nitric acid, 1 mol dm–3
  • Sodium carbonate, 0.5 mol dm–3
  • Ammonia solution, 1 mol dm–3
  • Vinegar
  • Lemon juice
  • Household bleach (diluted 1:1 with water – see note 10 below)
  • Soap solution
  • Full-range indicator solution (diluted 1:1 with deionised water – see notes 11 and 12)

Health, safety and technical notes

  1. Read our standard health and safety guidance.
  2. Wear eye protection throughout (splash-resistant goggles to BS EN166 3).
  3. Hydrochloric acid, HCl (aq), 1 mol dm–3is low hazard – see CLEAPSS Hazcard HC047a and CLEAPSS Recipe Book RB043.
  4. Nitric acid, HNO3(aq), dilute 1 mol dm–3 is CORROSIVE – see CLEAPSS Hazcard HC067 and CLEAPSS Recipe Book RB061.
  5. Sulfuric acid, H2SO4(aq), 1 mol dm–3is an IRRITANT – see CLEAPSS Hazcard HC098a and CLEAPSS Recipe Book RB098.
  6. Sodium hydroxide solution, NaOH(aq), 1 mol dm–3 is CORROSIVE – see CLEAPSS Hazcard HC091a and CLEAPSS Recipe Book RB085.
  7. Sodium carbonate, Na2CO3.10H2O, 0.5 mol dm–3 is low hazard – see CLEAPSS Hazcard HC095A and CLEAPSS Recipe Book RB080.
  8. Vinegar, lemon juice and soap solution are all of low hazard.
  9. Ammonia solution, NH3(aq), 1 mol dm–3 is an IRRITANT – see CLEAPSS Hazcard HC006 and CLEAPSS Recipe Book RB006.
  10. A 1:1 dilution of bleach is an irritant and if mixed with acid can release toxic chlorine – see CLEAPSS Hazcard HC089.
  11. A 1:1 solution of universal indicator is (probably) flammable (depending on the formulation) – keep away from sources of ignition and see CLEAPSS Hazcard HC032.
  12. Full-range indicator is a solution in propanol (or methylated spirits) which has a low surface tension and spreads out if used neat. Adding water increases the surface tension while still keeping the indicator in solution.

Procedure

  1. Place a clear plastic sheet over the table on your worksheet.
  2. Put two drops of each solution in the appropriate box on the plastic sheet.
  3. Add one drop of full-range indicator to each solution.

Question

What conclusions can you draw from your observations?

Downloads

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Additional information

This resource is part of our Microscale chemistry collection, which brings together smaller-scale experiments to engage your students and explore key chemical ideas. The resources originally appeared in the book Microscale chemistry: experiments in miniature, published by the Royal Society of Chemistry in 1998.

© Royal Society of Chemistry

Health and safety checked, 2018