Babloo found something strange: his yellow turmeric stain turned red when soap touched it. And when he dipped a blue strip into lemon juice — it turned red too. Both are indicators doing their job — changing colour to reveal whether something is an acid or a base. This post explains every indicator you need to know for Class 7 CBSE.
An indicator is a substance that changes colour in the presence of an acid or a base, and is used to identify whether a substance is acidic, basic, or neutral.
Indicators are important because many acids and bases are dangerous to taste or touch directly. Instead of tasting a chemical, we use an indicator to test it safely. The colour change tells us everything we need to know. Not sure what acids and bases actually are? Read our simple explanation on what acids, bases, and salts are before continuing.
Litmus is a natural dye extracted from lichens. It is purple in its natural form but is used in two versions for testing:
Turmeric (haldi) is a yellow spice found in every Indian kitchen — and it is also a natural indicator.
China rose can be used to make a natural indicator solution by soaking the petals in water.
Now that you know how each indicator behaves, it helps to understand why acids and bases behave differently from each other. Read our post on the difference between acids and bases to get a clearer picture. You can also go through the complete Class 7 notes on acids, bases, and salts which covers indicators, neutralisation, and more in one place.
An indicator is a substance that changes colour in the presence of an acid or a base. It helps identify whether a substance is acidic, basic, or neutral without tasting it. Common indicators include litmus, turmeric, and China rose. To understand what acids and bases are, visit our post on acids, bases, and salts explained.
Litmus is a natural dye extracted from lichens. It is the most commonly used indicator. Blue litmus turns red in acids; red litmus turns blue in bases.
Turmeric turns red in basic solutions. It shows no colour change in acidic or neutral solutions — it stays yellow. This is why a turmeric stain on fabric turns red when washed with soap.
China rose indicator turns dark pink or magenta in acidic solutions and turns green in basic solutions. In neutral solutions, it stays pink.
Many acids and bases are dangerous or harmful if swallowed or even touched. Indicators allow us to test whether a substance is acidic or basic safely, just by observing a colour change. Want to practise what you have learned? Try the important questions on acids, bases, and salts for Class 7.