Dissociation Equations: HCl vs CH₃COOH
Cambridge IGCSE Chemistry (0620) · Strong & Weak Acids · Past Paper Style
Write the symbol equation to show the dissociation of hydrochloric acid in water.
💡 HCl is a strong acid — it fully dissociates. Use a single arrow (→).
Which arrow correctly represents the dissociation of hydrochloric acid?
💡 Think: does HCl fully or partially dissociate?
Explain why hydrochloric acid has a lower pH than ethanoic acid of the same concentration.
💡 Think about the number of H⁺ ions produced per molecule.
A student states: 'The dissociation of HCl produces two ions.' Write the full ionic equation showing these ions with correct state symbols.
💡 Include state symbols for EVERY species, including the reactant.
Evaluate each statement about HCl dissociation. Mark each as TRUE or FALSE.
HCl dissociates partially in water.
The equation HCl(aq) → H⁺(aq) + Cl⁻(aq) is correctly balanced.
The H⁺ ion produced is responsible for the acidic properties of the solution.
💡
Write the symbol equation to show the dissociation of ethanoic acid (CH₃COOH) in water.
💡 Ethanoic acid is a weak acid — it only partially dissociates. Use the reversible arrow ⇌.
What does the ethanoate ion (CH₃COO⁻) represent in the dissociation equation of ethanoic acid?
💡 Think about what remains after the acid donates its proton.
A student writes: CH₃COOH(aq) → H⁺(aq) + CH₃COO⁻(aq). Identify and correct the error.
💡 Look carefully at the arrow used.
A 0.1 mol/dm³ solution of ethanoic acid has a higher pH than 0.1 mol/dm³ hydrochloric acid. Explain this observation in terms of ions present.
💡 Focus on the relative concentrations of H⁺ ions in each solution.
Evaluate each statement about ethanoic acid dissociation. Mark each as TRUE or FALSE.
At equilibrium, most CH₃COOH molecules remain undissociated.
The pH of 0.1 mol/dm³ ethanoic acid equals 1.
Adding water to ethanoic acid shifts the equilibrium to the right, producing more H⁺.
💡
Explain the significance of the ⇌ symbol in the equation: CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq).
💡 Think about three things: direction, completeness, and what this tells us about the acid.
Compare the equations for HCl and CH₃COOH dissociation. What does the difference in arrows tell us about the strength of each acid?
💡 Discuss both arrows and link each to the degree of dissociation.
In the equation CH₃COOH(aq) ⇌ H⁺(aq) + CH₃COO⁻(aq), what does the right-pointing arrow represent?
💡 The ⇌ symbol contains TWO arrows. Focus on just the forward one.
A student says: 'The ⇌ in the equation means the reaction has stopped.' Is this correct? Explain your answer.
💡 Think about dynamic equilibrium — what is really happening at the molecular level?
Using the equations below, explain the difference between strong and weak acids. Include reference to the symbols used and the relative concentrations of H⁺ ions produced. [6 marks — Extended Writing]
💡 Structure your answer: (1) define strong/weak, (2) discuss the arrows, (3) discuss [H⁺], (4) discuss pH.
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