pH is the measurement of free H+ ions in solution.
pH is a scale used to show an aqueous solution's acidity or alkalinity.
Solutions that have a high concentration of H+ ions (>10-7 mol/L) are said to be acidic and have a lower pH than alkaline, or basic, solutions.
Solutions that have a low concentration of H+ ions (<10-7 mol/L) are said to be basic, or alkaline, and have a higher pH than acidic solutions.
