8.3 – Strong vs. Weak Acid & Base Titrations Topic 8 – Acids & Bases 8.3 – Strong vs. Weak Acid & Base Titrations

Strong and Weak Acids and Bases Objectives: Understand the difference between strong and weak acids and bases Complete an experiment to explore the difference in properties of strong/weak acids and bases

Strong and Weak Acids Strong Acids: HA(aq)  H+(aq) + A ̶ (aq) …..the acid fully dissociates into ions For example: HCl(aq)  H+(aq) + Cl ̶ (aq) Includes: hydrochloric, sulfuric, phosphoric, nitric Strong acids have weak conjugate bases Weak Acids: HA(aq)  H+(aq) + A ̶ (aq) …..the acid only partially dissociates into ions For example: HF(aq)  H+(aq) + F ̶ (aq) Includes: hydrofluoric, ethanoic, carbonic Weak acids have strong conjugate bases

Strong and Weak Bases Strong Bases: BOH(aq)  B+(aq) + OH ̶ (aq) …..the base fully dissociates into ions For example: NaOH(aq)  Na+(aq) + OH ̶ (aq) Includes: group (I) hydroxides, barium hydroxide Strong bases have weak conjugate acids Weak Bases: BOH(aq)  B+(aq) + OH ̶ (aq) …..the base only partially dissociates into ions For example: NH3(aq) + H2O(l)  NH4+(aq) + OH ̶ (aq) Includes: ammonia, amines Weak bases have strong conjugate acids

So what? The equilibrium has a profound effect on the properties of the acid/base Compared with strong acids of the same concentration, weak acids: Have lower electrical conductivity React more slowly pH is higher (less acid) Change pH more slowly when diluted However, they neutralise the same volume of alkali Weak bases follow a similar pattern

Strong Acid & Strong Base

Strong Acid & Weak Base

Weak Acid & Strong Base

Weak Acid & Weak Base

Compare Titration Curves

Simulation http://phet.colorado.edu/en/simulation/acid-base- solutions

Key Points Strong acids/bases dissociate fully into ions Weak acids/bases only partially dissociate, forming an equilibrium The strong/weak character has a significant effect on the chemical properties

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