In 1923, J.N. Bronstead and J.M. Lowry, working separately, proposed the definition that an acid is a substance that can donate a proton to another substance, and a base is a substance that can accept a proton from another substance. Strong acids would therefore increase the hydrogen ion concentration of a solution, and strong bases would increase the hydroxide concentration of a solution. The measurement of pH is a simplified way to express the hydrogen ion and hydroxide concentration of acids and bases. Using the pH scale, a solution with a pH of 7 is neutral, below 7 is acidic, and above 7 is basic. pH paper is one of the indicators used to measure the pH of solution; the paper changes color for known pH ranges. The pH paper, however, only determines relative ranges; a pH meter, an electronic instrument, is preferred for a more precise measurement of pH. This module simulates the measurement of pH for acids and bases with pH paper as the indicator. The calculated numerical value of pH is also displayed.
HCl hydrochloric acid HF hydrofluoric acid HCN hydrocyanic acid HNO2 nitrous acid HOC6H5 phenol HOAc acetic acid NH3 ammonia NaOH sodium hydroxide (CH3)3N trimethylamine (CH3)2NH2 dimethylamine (CH3)NH2 methylamine C6H5NH2 aniline C5H5N pyridine