Measurement pH is an expression of acidity or alkalinity of a solution. It is measured on a scale of 1 to 14. Acids have a pH of 1 to 7,the lower the number, the stronger the acid. Some acids are weak like vinegar and some are strong like sulfuric acid. Bases have a pH of 7 to 14, the higher the number, the stronger the base.
Bases can be weak like milk of magnesia or strong like some oven cleaners.
Water is neutral, therefore it has a pH of 7. From a chemical point of view, pH is a measure of hydrogen ion activity. It is based on a log base 10 scale. The pH of a solution is usually measured using a pH meter, an electronic device with a probe that can be inserted into a solution of unknown pH. The probe contains an acidic aqueous solution enclosed by a special glass membrane that allows migration of hydrogen ions. If the unknown solution has a different pH from the solution in the probe, an electrical potential results.