Easy Wins For An Open Evening

Rainbow Neutralisation Reaction

A neat little neutralisation reaction with a little of the wow factor everyone wants for open evening.

Remember: always take appropriate safety precautions when handling chemicals.

You will need:

• Sodium Hydroxide (NaOH) 0.5 mol dm^-3 (irritant)
• Hydrochloric Acid (HCl) 0.5 mol dm^-3
• Universal Indicator (flammable) and colour chart
• Glass tube around 60 cm × 1 cm diameter
• 2 × stoppers to fit tube
• Pipettes
• Goggles
• Clamp, boss and stand

Method:

1. Fill a beaker with 60 cm³ of tap water and add enough universal indicator for the solution to turn green. Mix the solution.
2. Stopper one end of the tube to make a watertight seal.
3. Add the universal indicator from step 1 to the tube, leaving around a 2 cm gap at the top.
4. Clamp the tube vertically.
5. Add 3 to 4 drops of hydrochloric acid to the top of the tube (the top of the liquid will turn red).
6. Stopper the top of the tube, carefully invert it and re-clamp it vertically.
7. Remove the (now top) stopper and add 3 to 4 drops of sodium hydroxide solution (the top of the liquid will turn purple).
8. Re-stopper the tube. Both ends of the tube are now stoppered.
9. Remove from the clamp stand and invert the tube 3 to 4 times.
10. Watch for the rainbow of colours to appear.