In chemistry, pH (/piːˈeɪtʃ/), historically denoting “potential of hydrogen” (or “power of hydrogen”) is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions. The pH scale is logarithmic and inversely indicates the concentration of hydrogen ions in the solution.