Strong acidA strong acid is an acidic compound which ionizes completely or almost completely in aqueous solution. pH is the measure of acidity/base strength. It is defined well for aqueous solutions as the -log10(M[H+]) - the negative of the log (base 10) of the concentration of Hydrogen (or more accurately hydronium, H3O+) ions in soultion. Neutral pure water at STP has an equilibrium concentration of 1 hydronium ion per 10,000,000 water molecules (M = 10 ^-7 ) and thus has a pH of 7. Acidic materials have a pH lower than this and bases have a pH higher than this. The corresponing basic equivalents are the strong bases. Examples of strong acids: * Hydrochloric acid * Nitric acid * Sulphuric acid * Hydrobromic acid * Hydroiodic acid * Trichloro acetic acid * Perchloric acid Differentiating between the strength of the strong acids in aqueous solutions is impossible, because the concentration of hydrogen ions is always equal to the concentration of the acid. Only through replacing water with concentrated Acetic acid as a diluent one can observe and measure diference in the tendency to dissociate the proton ion, among the strong acids. (The analogical way to differentiate between strength of the strong bases is to use liquid ammonia as a diluent, instead of water).