Olfactory indicators : Onion, Vanilla essence and Clove oil in Acids, Bases and Salts – Class 10 Science Experiment

Chapter Name: Acids, Bases and Salts

Activity Name: Olfactory indicators : Onion, Vanilla essence and Clove oil in Acids, Bases and Salts

Activity Description:

This experiment aims to use three substances – onion, vanilla essence, and clove oil – as olfactory indicators to detect the presence of acids or bases. Olfactory indicators are substances that change their smell when they come into contact with acidic or basic solutions.

Required Items:

  1. Finely chopped onions
  2. Clean cloth
  3. Plastic bag
  4. Dilute hydrochloric acid (HCl)
  5. Dilute sodium hydroxide (NaOH)
  6. Distilled water
  7. Test tubes
  8. Clove oil
  9. Vanilla essence

Step by Step Procedure:

  1. Place the finely chopped onions in a plastic bag along with a clean cloth.
  2. Tightly tie up the bag and keep it overnight in the fridge.
  3. Use the cloth strips from the onions to test for acidity or basicity by checking their odour.
  4. Place two cloth strips on a clean surface.
  5. Put a few drops of dilute HCl on one strip and a few drops of dilute NaOH on the other.
  6. Rinse both strips separately with distilled water and again check their odour. Note the observations.
  7. Take some clove oil and vanilla essence.
  8. In one test tube, add dilute HCl, and in another test tube, add dilute NaOH.
  9. Add a drop of dilute vanilla essence to both test tubes and shake well.
  10. Check the odour of both test tubes and record your observations.
  11. Test the change of odour of clove oil with dilute HCl and dilute NaOH. Record your observations.

Experiment Observations:

  • The cloth strips soaked with onions might change their odour depending on whether they are exposed to an acidic or basic solution.
  • The odour of the cloth strip with dilute HCl might differ from the one with dilute NaOH after rinsing.


  1. Handle dilute HCl and dilute NaOH with care, as they are corrosive and can cause skin and eye irritation.
  2. Use small quantities of the acidic and basic solutions for testing.
  3. Keep the test area well-ventilated to avoid inhalation of strong odours.

Lesson Learnt from Experiment:

This experiment demonstrates that certain substances, such as onions, vanilla essence, and clove oil, can act as olfactory indicators and change their smell when exposed to acidic or basic solutions. The change in odour can help detect the presence of acids or bases.

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