Indicator Papers are dye-infused paper strips that are used to measure the level of acidity and alkalinity of a solution and are used to get an idea about the pH of a solution. Indicator paper comes in form of strips that have been dipped in a a halochromic chemical compound, which helps in visual determination of the magnitude of acidity and alkalinity of pH of the given solution. The universal paper indicators are laced with a solution of varied compounds that exhibit varied smooth color transitions on exposure to acidic and alkaline solutions over a pH range of 1 to 14.
Although there are various forms of indicator paper commercially available in the market, all of them have more or less the same formula
1) Usual chemical components of the solution dried on the paper consist of water, 1-Propanol and various salts of Sodium like Sodium Hydroxide, Phenolphthalein salt of Sodium as well as thymol and bromothymol monosodium salts
2) On exposure to an acidic or alkaline solution, the colors exhibited on the universal indicator paper strips vary between shades of red, orange, yellow, green, blue and violet or purple
3) The colors from red to yellow indicate that the test solution is acidic in nature and hues lying between shades of green and blue are indicative of basic nature of test solution