A pH meter is a device that measures the pH of a solution by measuring the voltage between two electrodes submerged in the solution.pH is a measure of hydrogen ion concentration; a measure of the acidity or alkalinityof a solution. The pH scale usually ranges from 0 to 14. Aqueous solutions at 25°C with a pH less than seven are acidic, while those with a pH greater than seven are basic or alkaline. A pH level of is 7.0 at 25°C is defined as 'neutral' because the concentration of H3O+ equals the concentration of OH− in pure water.Very strong acids may have a negative pH, while very strong bases may have a pH greater than 14.