Question

Why do acids change blue litmus to red?

Answer 1

Hint: Litmus is a water-soluble combination of several lichen-derived colours. It is frequently absorbed into filter paper to generate one of the first types of pH indicator, which is used to measure the acidity of materials. Litmus paper is a type of paper made from a water-soluble pigment found in lichens. It is used to determine the pH of a solution. Neutral litmus paper is also purple in appearance and becomes red in acidic and blue in alkaline circumstances.

Complete answer:
Litmus is a water-soluble colour combination derived from lichens, particularly Roccella tinctoria. It is frequently absorbed into filter paper to generate one of the first types of pH indicator, which is used to measure the acidity of materials.
Under acidic conditions, blue litmus paper turns red, whereas red litmus paper turns blue under basic (i.e. alkaline) conditions.
Blue litmus' pigment interacts with \[{{H}^{+}}\] ions and alters chemically, causing the bonds to 'tune' to reflect a longer wavelength of light, making it seem red to human eyes. When the pigment interacts with free hydrogen ions in acids, it absorbs blue to green wavelengths.
Otherwise, the identical pigment in the base interacts differently with \[O{{H}^{-}}\] ions and becomes 'tuned' to reflect the short wavelength, resulting in a blue appearance. After reacting with the hydroxyl ions in the base, it now absorbs the green and red wavelengths. A litmus paper is an indication used to identify an acidic material, as we all know. It alters the colour of the material as a result. The blue litmus paper is used to determine the acidity of a solution and becomes red in acidic conditions. It will not affect the colour of basic solutions. It will turn red under acidic circumstances and will not change colour in basic settings. If we use blue litmus paper as an indication, the strip of paper will remain blue.

Note:
Water-soluble gases that influence acidity or basicity can also be tested using wet litmus paper; the gas dissolves in the water and the resultant solution colours the litmus paper. Ammonia gas, for example, is alkaline and turns red litmus paper blue. The colour shift occurs throughout the pH range 4.5–8.3, with blue litmus paper turning red under acidic conditions and red litmus paper turning blue under basic or alkaline settings.