It has a pH of 7 and also a pOH of 7, where the term pOH refers to the negative logarithm of the hydroxide ion concentration. Similarly, if a strong base solution contains 0.1 moles per liter of OH - ions, it has a pOH of 1. Most solutions have a pH between 0 and 14, and 7 is the neutral point. And since the scale is logarithmic, each unit change in pH represents 10 times as many ions in solution. A strong acid or base is one which dissociates completely when it dissolves in water.
Many solutions also contain mixtures of several acidic or basic substances.
In these cases, it is difficult to estimate the total amount of acid or base by measuring the pH, so this must be done by titration. As every high school chemistry student knows, acids react with bases to form water and salts. Therefore, an acid is titrated using a standard base, and visa versa . In water and wastewater analysis, the amount of acid needed to titrate a solution to a particular pH is a measure of the acid neutralizing capacity of that solution, and is referred to as the solution's alkalinity . In natural waters, the pH is most often controlled by the concentrations of carbonate, bicarbonate, and carbon dioxide, since these are products of respiration and fermentation.