Acids dissociate to varying degrees in water solution. Strong acids such as HCl quickly dissociate, losing protons, and weak acids dissociate only slightly. The pH of the solution, which is directly proportional to the degree of dissociation, can be measured to determine the strength of the acid, and can help identify the acid. Students determine the equilibrium constants of three acids and compare the data to known values to identify them. pH meter is required, but not included.