Acid concentration refers to the amount of acid present in a solution, usually measured in moles per liter (Molarity).
This is a measure of the concentration of a solute in a solution, or of any chemical species in terms of amount of substance in a given volume.
pH Scale: A logarithmic scale used to specify the acidity or basicity/alkalinity of an aqueous solution.
Hydronium Ion Concentration: The number of hydronium ions (H3O+) per unit volume; it's directly related to pH and acid strength.