A pH meter is a scientific instrument that measures the hydrogen-ion activity in water-based solutions, indicating its acidity or alkalinity expressed as pH. The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode, and so the pH meter is sometimes referred to as a "potentiometric pH meter". The difference in electrical potential relates to the acidity or pH of the solution. Testing of pH via pH meters (pH-metry) is used in many applications ranging from laboratory experimentation to quality control.
781 pH/Ion Meter pH meter by Metrohm
5.739 pH/Ion at 23 °C temperature shown on photo. pH 7110 pH meter manufactured by inoLab
A simple pH meter
Soil pH meter
In chemistry, pH, also referred to as acidity or basicity, historically denotes "potential of hydrogen". It is a logarithmic scale used to specify the acidity or basicity of aqueous solutions. Acidic solutions are measured to have lower pH values than basic or alkaline solutions.
Test tubes containing solutions of pH 1–10 colored with an indicator
Lemon juice tastes sour because it contains 5% to 6% citric acid and has a pH of 2.2 (high acidity).