Have you ever wondered if everyday items could help us understand the chemical world around us? This activity explores how natural substances can act as indicators to tell us if something is an acid or a base.

Here's How We Do It

Part 1: Onion as an Indicator

1. Prepare your onion strips: Finely chop some onions and place them in a plastic bag with a few strips of clean cloth. Seal the bag tightly and leave it in the refrigerator overnight. These cloth strips will now be infused with onion's scent!
2. Smell check: Take two of these onion-infused cloth strips and note their initial scent.
3. Test time:
   • Place one strip on a clean surface and add a few drops of dilute hydrochloric acid (HCl) solution to it.
   • On the other strip, add a few drops of dilute sodium hydroxide (NaOH) solution.
4. Rinse and re-check: Gently rinse both cloth strips with water and smell them again.
5. Record your findings: Write down what you observe about the scent of each strip.

Part 2: Vanilla and Clove Oil as Indicators

1. Initial scent check: Take a small amount of dilute vanilla essence and clove oil and note their distinct odors.
2. Acid and base test:
   • In separate test tubes, place a few drops of dilute vanilla essence and clove oil.
   • Add dilute HCl solution to one set of test tubes.
   • Add dilute NaOH solution to another set of test tubes.
3. Record your findings: Observe and note any changes in the odor of the vanilla essence and clove oil in both the acidic and basic solutions.

What We Observed

Here's a summary of the fascinating changes we saw:

• Onion: Onions have a distinct smell because of compounds like sulphurous allium. When exposed to a base, this smell vanishes, but it remains unchanged in an acid.
• Vanilla Essence: Vanilla's pleasant scent, due to an aldehyde (a weak acid), disappears in a basic solution but stays strong in an acidic one.
• Clove Oil: The characteristic smell of clove oil cannot be detected in the presence of a base.