Determining the Strength of Acids and Bases

Determining the Strength of Acids and Bases Strong electrolytes are completely dissociated into ions in water. The acid or base molecule does not exist in aqueous solution, only ions. Weak electrolytes are incompletely dissociated. Here are definitions and examples of strong and weak acids and strong and weak bases. Strong Acids Strong acids completely dissociate in water, forming H and an anion. There are six strong acids. The others are considered to be weak acids. You should commit the strong acids to memory: HCl: hydrochloric acidHNO3: nitric acidH2SO4: sulfuric acidHBr: hydrobromic acidHI: hydroiodic acidHClO4: perchloric acid If the acid is 100 percent dissociated in solutions of 1.0 M or less, it is called strong. Sulfuric acid is considered strong only in its first dissociation step;  100 percent dissociation isnt true as solutions become more concentrated.   H2SO4 → H HSO4- Weak Acids A weak acid only partially dissociates in water to give H and the anion. Examples of weak acids include hydrofluoric acid, HF, and acetic acid, CH3COOH. Weak acids include: Molecules that contain an ionizable proton. A molecule with a formula starting with H usually is an acid.Organic acids containing one or more carboxyl group, -COOH. The H is ionizable.Anions with an ionizable proton (e.g., HSO4- → H SO42-).CationsTransition metal cationsHeavy metal cations with high chargeNH4 dissociates into NH3 H Strong Bases Strong bases dissociate 100 percent into the cation and OH- (hydroxide ion). The hydroxides of the Group I and Group II metals usually are considered to be strong bases. LiOH: lithium hydroxideNaOH: sodium hydroxideKOH: potassium hydroxideRbOH: rubidium hydroxideCsOH: cesium hydroxide*Ca(OH)2: calcium hydroxide*Sr(OH)2: strontium hydroxide*Ba(OH)2: barium hydroxide * These bases completely dissociate in solutions of 0.01 M or less. The other bases make solutions of 1.0 M and are 100 percent dissociated at that concentration. There are other strong bases than those listed, but they are not often encountered. Weak Bases Examples of weak bases include ammonia, NH3, and diethylamine, (CH3CH2)2NH. Like weak acids, weak bases do not completely dissociate in aqueous solution. Most weak bases are anions of weak acids.Weak bases do not furnish OH- ions by dissociation. Instead, they react with water to generate OH- ions.