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Module 1: Acid, Bases and Salts

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Strong and Weak Acid – Base and Acid Strength

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This video describes about strong and weak acids and bases.What makes an acid or base strong?If an acid dissociates completely, it is called as strong acid. For example, hydrochloric acid dissociates completely into a hydrogen ion and a chlorine ion.Strong acids are good proton donors and have weak conjugate base.Strong acids never reach equilibrium with their conjugate base and hence there is no acid dissociation constant for strong acids. Some examples of strong acids are hydrochloric acid, hydrobromic acid, hydroiodic acid and nitric acid.What makes an acid a weak acid is that it dissociates partially into a hydrogen ion and a conjugate base.For example, ethanoic acid dissociates partially in water to form ethanoic ion which is the conjugate base and a hydrogen ion. The equilibrium constant specific to weak acids otherwise known as acid dissociation constant, Ka is represented as the ratio of product of hydrogen ion concentration and conjugate base to the concentration of the acid molecule.Here are some examples of weak acids:All metal hydroxides are strong bases.Strong bases dissociate into hydroxyl ions completely when dissolved in water. Just like strong acids, strong bases too do not have a base dissociation constant, as they never reach equilibrium.For example, sodium hydroxide dissociates completely into sodium ion and hydroxyl ion.Some examples of strong bases are lithium hydroxide, sodium hydroxide and potassium hydroxide.Weak bases are those solutions where a small fraction of base molecules protonates into conjugate acid [HB+] and hydroxyl ions [OH-] when dissolved in water.For example, ammonia dissociates into ammonium ion and hydroxyl ion.The equilibrium constant specific to weak bases, otherwise known as base dissociation constant, Kb is represented as the ratio of product of hydroxyl ion concentration and conjugate acid to the concentration of base molecule.Some examples of weak bases are ethylamine, diethylamine and all bases related to ammonia.