PH a pH of 7.3. This is clearly wrong as an acid solution should have a pH of less than 7. Treating the system as a mixture of hydrochloric acid and the amphoteric substance water, a pH of 6.89 results. A weak acid or the conjugate acid of a weak base can be treated using the same formalism. First, an acid dissociation constant is defined as follows. Electrical charges are omitted from subsequent equations for the sake of generality and its value is assumed to have been determined by experiment. This being so, there are three unknown concentrations, [HA], [H] and
PH of both ions. However the pH of the neutral NaCl solution will be slightly different from that of neutral pure water because the hydrogen and hydroxide ions' activity is dependent on ionic strength, so K varies with ionic strength. If pure water is exposed to air it becomes mildly acidic. This is because water absorbs carbon dioxide from the air, which is then slowly converted into bicarbonate and hydrogen ions (essentially creating carbonic acid). The United States Department of Agriculture Natural Resources Conservation Service, formerly Soil Conservation Service classifies soil pH ranges as follows: pH-dependent plant pigments that can be