PH Meter. pH is a measurable parameter between the values of 0 and 14, provided the concentration of the solution does not exceed 1M. Solutions with a pH<7 are acidic, whereas those with a pH>7 are alkaline. A pH meter is a device that measures the changes in the activity of hydrogen ions in a solution. What are acids and alkalis? According to the Arrhenius definition, acid is any substance that produces dissociated hydrogen (H + ) ions or hydronium ions H 3 O + when it is dissolved in water. A base is a substance that produces dissociated hydroxyl (OH - ) ions when it is dissolved in water. The concept of pH was proposed by the Danish chemist Søren Peder Lauritz Sørensen in 1909. The pH quantifies the H + ions in a solution. The notional definition of pH is logarithmic of the reciprocal of hydrogen ion activity, a H +, in a solution: Equation 1. The notational definition of pH expressed in mathematical terms. The pH is directly related to the proton ...