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

  • 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.

  • Sodium hydroxide, 1 mol dm–3
  • Hydrochloric acid, 1 mol dm–3
  • Sulphuric 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.
  4. Nitric acid, HNO3(aq), dilute 1 mol dm–3 is CORROSIVE.
  5. Sulfuric acid, H2SO4(aq), 1 mol dm–3is an IRRITANT.
  6. Sodium hydroxide solution, NaOH(aq), 1 mol dm–3 is CORROSIVE.
  7. Sodium carbonate, Na2CO3.10H2O, 0.5 mol dm–3 is low hazard.
  8. Vinegar, lemon juice and soap solution are all of low hazard.
  9. Ammonia solution, NH3(aq), 1 mol dm–3 is an IRRITANT.
  10. A 1:1 dilution of bleach is an irritant and if mixed with acid can release toxic chlorine.
  11. A 1:1 solution of universal indicator is (probably) flammable (depending on the formulation). Keep away from sources of ignition.
  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?

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