Drag the paper into the beaker — watch it change color!
Red litmus paper turns blue in a basic (alkaline) solution.
Blue litmus paper turns red in an acidic solution.
In the real world, litmus paper is made from lichen — a natural organism. Scientists extract a dye called litmus from it and soak paper strips in the solution.
The chemistry behind it:
In acidic solutions (lots of H⁺ ions), the litmus dye molecule gains a proton
and shifts its light absorption to appear red.
In basic solutions (lots of OH⁻ ions), it loses a proton and appears
blue.
Key reaction:
HIn ⇌ H⁺ + In⁻
Red (acid) ⇌ Blue (base)