<P> A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH ( acidity or basicity ) of the solution can be determined visually . Hence , a pH indicator is a chemical detector for hydronium ions ( H O ) or hydrogen ions ( H ) in the Arrhenius model . Normally , the indicator causes the color of the solution to change depending on the pH . Indicators can also show change in other physical properties ; for example , olfactory indicators show change in their odor . The pH value of a neutral solution is 7.0 . Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic ( alkaline ) . As most naturally occurring organic compounds are weak protolytes , carboxylic acids and amines , pH indicators find many applications in biology and analytical chemistry . Moreover , pH indicators form one of the three main types of indicator compounds used in chemical analysis . For the quantitative analysis of metal cations , the use of complexometric indicators is preferred , whereas the third compound class , the redox indicators , are used in titrations involving a redox reaction as the basis of the analysis . </P>
<P> A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH ( acidity or basicity ) of the solution can be determined visually . Hence , a pH indicator is a chemical detector for hydronium ions ( H O ) or hydrogen ions ( H ) in the Arrhenius model . Normally , the indicator causes the color of the solution to change depending on the pH . Indicators can also show change in other physical properties ; for example , olfactory indicators show change in their odor . The pH value of a neutral solution is 7.0 . Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic ( alkaline ) . As most naturally occurring organic compounds are weak protolytes , carboxylic acids and amines , pH indicators find many applications in biology and analytical chemistry . Moreover , pH indicators form one of the three main types of indicator compounds used in chemical analysis . For the quantitative analysis of metal cations , the use of complexometric indicators is preferred , whereas the third compound class , the redox indicators , are used in titrations involving a redox reaction as the basis of the analysis . </P>
what ion causes the color of the indicator to change
what ion causes the color of the indicator to change
hydronium ions or hydrogen ions
hydronium ions or hydrogen ions