Litmus paper is one of the most well-known and oldest indicator papers. Litmus is a natural product, derived from lichens. By roll, 7 mm length and 5 m width.
Colour change occurs when moving from neutral to the acid or base range.
pH measuring range | 5.0 to 8.0 |
Transition | Acid ? neutral ? alkali |
Colour conversion | Red ? violet ? blue |