PH is dissolved in water, the pH will be greater than 7. A solution of a strong acid, such as hydrochloric acid, at concentration 1 mol dm has a pH of 0. A solution of a strong alkali, such as sodium hydroxide, at concentration 1 mol dm, has a pH of 14. Thus, measured pH values will lie mostly in the range 0 to 14, though negative pH values and values above 14 are entirely possible. Since pH is a logarithmic scale, a difference of one pH unit is equivalent to a tenfold difference in hydrogen ion concentration. <br> The pH
PH indicator frequently weak acids or weak bases. The general reaction scheme of a pH indicator can be formulated as: Here, HInd stands for the acid form and Ind for the conjugate base of the indicator. The ratio of these determines the color of the solution and connects the color to the pH value. pH indicators that are weak protolytes, the Henderson–Hasselbalch equation for them can be written as: The equation, derived from the acidity constant, states that when pH equals the p"K" value of the indicator, both species are present in a 1:1 ratio. If pH is above the p"K" value,