Acids turn blue litmus red. When blue litmus paper is placed in an acidic substance, it will turn red. However, if placed in a substance that is basic or neutral, it will remain blue.
What is the purpose of litmus paper?
The litmus paper gives a general indication of acidity or alkalinity. Under the acidic conditions, the blue paper turns red where the pH level is below 4.5. In contrast, the red paper does not change its colour under alkaline conditions where the pH level is above 8.3. Blue litmus doesn’t change its colour under alkaline conditions, while the red one doesn’t change its colour under acidic conditions.