Lakmoepapier

Lakmoepapier, often translated as litmus paper, is a water-soluble paper used to test for acidity. It is dyed with a mixture of natural dyes from lichens, most famously Roccella tinctoria. When exposed to an acidic substance, lakmoepapier turns red. When exposed to a basic or alkaline substance, it turns blue. In neutral solutions, it remains its original purplish color.

The mechanism behind this color change relies on the presence of specific chemical compounds within the lichen dyes that undergo a structural change depending on the concentration of hydrogen ions (H+) in the solution. This change in structure alters how the dye absorbs and reflects light, resulting in the observable color change.

Lakmoepapier is a common and simple tool for qualitative pH testing. It is widely used in educational settings for basic chemistry experiments, in households for checking the pH of water or soil, and in some industrial processes for quick checks. It is important to note that lakmoepapier provides a general indication of acidity or alkalinity and does not give a precise pH value. For more accurate measurements, pH meters or universal indicator solutions are used. Its ease of use and low cost make it a valuable introductory tool for understanding acid-base chemistry.