Acids and Bases Lesson 4 Strong and weak

Acids and Bases - Lesson 4 Strong and weak acids and bases Main

Refresh � 100 cm 3 of a Na. OH solution of p. H 12 is mixed with 900 cm 3 of water. What is the p. H of the resulting solution? A. B. C. D. 1 3 11 13

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Lesson 4: 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: Na. OH(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: NH 3(aq) + H 2 O(l) �NH 4+(aq) + OH-(aq) � Includes: ammonia, amines � Weak bases have strong conjugate acids

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

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 � p. H is higher (less acid) � Change p. H more slowly when diluted � However, they neutralise the same volume of alkali � Weak bases follow a similar pattern

Experiment � Complete the experiment investigating strong/weak acids and bases � When you give explanations, focus on reasons in terms of the equilibrium rather than just ‘because it is strong/weak’

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