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Practicals

Rainbow Burette
AKA: pH Scale

Summary

A burette is filled with an acid, an alkali and UI solution. A rainbow of colours appears.

Operation

This demonstration is a very visual representation of the pH scale. Dilute hydrochloric acid and dilute sodium hydroxide solution are added to a standard burette with a little UI solution. Within a few seconds, a rainbow of colours should appear along the length of the tube.

Equipment required (per demo):

  • Standard burette
  • Burette clamp
  • Bung to fit burette
  • Hydrochloric acid (0.1 mol dm3) - Low hazard
  • Sodium hydroxide solution 0.1 mol-3 (Irritant)
  • Universal indicator solution (Highly flammable)

The following is a typical procedure...

The burette is clamped securely to a stand. The burette tap is closed and approximately 10cm3 of the sodium hydroxide solution is added to the burette followed by a few drops of universal indicator solution. The bung is inserted into the end of the burette and the tube is turned gently once to mix the two solutions.

Approximately 20 cm3 of hydrochloric acid is then added to the burette. The bung is replaced and the tube turned gently once to mix the acid with the other solutions. Re-clamp the burette and wait.

Within a few seconds a rainbow should start to appear around the centre of the tube. This may extend over time as the liquids mix.

Safety

 Caution

Wear eye protection.

The contents of this page are for information only. Please refer to CLEAPSS, SSERC or ASE safety advice and/or publications before undertaking any preparation, practical experiment or using any equipment featured on this site or any other.

Some experimentation may be required to get a full spectrum of colours. Adding a small amount of deionised water between the acid and the alkali may help to achieve a good green colour at the centre of the rainbow.