2.1.3 Turmeric as an Indicator

What is Turmeric Paper?

It is yellow paper made by dipping filter paper in turmeric paste .

Key Facts and Examples

• Turmeric paper can test basic substances only.

Example: Soap solution turns turmeric paper red

• Turmeric paper cannot differentiate between acidic and neutral substances .

Example: Lemon juice and water both keep turmeric paper yellow

• Basic substances turn turmeric paper from yellow to red .

Example: Baking soda solution, lime water turn turmeric red

• Olfactory indicators change odour in acidic or basic medium .

Example: Onion strips change smell with acids and bases

Activity 2.3: Preparing and Using Turmeric Paper

What you need:

• Turmeric (haldi)
• Petri dish or container
• Water
• Filter paper
• Dropper
• Samples from Activity 2.1

What to do:

• Step 1: Take a spoonful of turmeric in a petri dish or container and add a little water to make a paste
• Step 2: Carefully dip a piece of filter paper in the turmeric paste until it gets yellow colour
• Step 3: Take it out and allow it to dry
• Step 4: Cut this yellow paper into thin strips, which are used as 'turmeric paper'
• Step 5: Using a dropper, put a drop of each sample used in Activity 2.1, one by one, on separate pieces of turmeric paper
• Step 6: Record your observations

Observations

What you see:

Why this happens:

We have studied that turmeric contains natural pigments that react only with bases . This is why it can identify basic substances but cannot differentiate between acidic and neutral substances.

• Basic substances cause chemical change in turmeric pigment
• Acidic and neutral substances do not react with turmeric

Activity: Testing Olfactory Indicators

What you need:

• Finely chopped onions
• Container with lid
• Clean cotton cloth or filter paper strips
• Tamarind water
• Baking soda solution

What to do:

• Step 1: Take some finely chopped onions in a container, along with some strips of clean cotton cloth or filter paper
• Step 2: Tightly close the container and leave it overnight
• Step 3: Take two cotton cloth or filter paper strips from the container and check their odour
• Step 4: Keep them on a clean surface and put a few drops of tamarind water on one strip and a few drops of baking soda solution on the other
• Step 5: Allow the drops to spread on the strips
• Step 6: Check the odour again

Observations

What you see:

• Original onion smell on both cloth strips
• Tamarind water strip loses onion smell
• Baking soda strip loses onion smell
• Different final odours on each strip

Why this happens:

We have studied that olfactory indicators are substances whose odours change in acidic or basic medium . This is why onion-soaked strips smell different when treated with acids and bases.

• Onion compounds react with acids and bases
• Chemical reactions change odour molecules

Section Summary: Nature - Our Science Laboratory