Learning focus
Develop precise chemical language, connect equations and practical observations, interpret periodic trends and apply salt-preparation rules to unfamiliar examples.
Ethanoic acid equation
Ethanoic acid dissociates partially: CH3COOH(aq) <=> H+(aq) + CH3COO-(aq). The ethanoate ion is the conjugate residue after the proton is donated. Most particles remain as CH3COOH at equilibrium.
Meaning of the reversible arrow
The equilibrium symbol shows that forward dissociation and reverse recombination occur. It does not imply equal concentrations. For a weak acid, the equilibrium position is mainly on the molecular side.
Particle interpretation
A particle diagram for a weak acid should contain many intact HA or CH3COOH molecules and relatively few H+ and anion particles. A strong acid at the same concentration should show almost only ions.
Reaction rate comparison
A weak acid may continue to dissociate as H+ ions are consumed during reaction. It can eventually react with the same stoichiometric quantity of a reactant as a strong monoprotic acid of the same concentration, while showing a slower initial rate because its initial H+ concentration is lower.
Practical or data skill
Use particle cards to represent partial dissociation and dynamic equilibrium. Remove H+ cards to model reaction and allow additional molecules to dissociate.
Examination tip
Partial dissociation does not mean that weak-acid molecules are physically diluted.
Review questions and suggested answers
Question 1
Write the ethanoic acid dissociation equation.
Suggested answer
CH3COOH(aq) <=> H+(aq) + CH3COO-(aq).
Question 2
Why is a reversible arrow used?
Suggested answer
Dissociation is partial and ions can recombine.
Question 3
Which particles are most numerous in a weak acid?
Suggested answer
Undissociated acid molecules.
