🎯 Objective
Study the effect on pH of acetic acid solution when sodium acetate (common ion: CH₃COO⁻) is added.
Theory
Equilibrium
CH₃COOH ⇌ H⁺ + CH₃COO⁻
Common Ion Effect
Adding CH₃COO⁻ introduces an ion already present in the equilibrium. Use Le Chatelier's
principle to predict which way it shifts — decide yourself before adding the salt.
Henderson Equation
pH = pKa + log([A⁻]/[HA])
⚠️ Safety
- Acetic acid is corrosive and has a pungent, irritating vapour — avoid skin/eye contact and inhaling fumes; wear goggles.
- Handle sodium acetate as a mild irritant; do not taste any solution.
- Use a proper pH meter or indicator paper — never a mouth pipette to transfer solutions.
- Wipe up spills promptly and wash hands after the experiment.
🔮 Predict before you experiment
You start with 0.1 M acetic acid, CH₃COOH ⇌ H⁺ + CH₃COO⁻. Predict what adding solid CH₃COONa (a source of the common ion CH₃COO⁻) will do, then lock it to unlock the salt buttons.
pH Meter
2.87
0 (Acidic)
7 (Neutral)
14 (Basic)
Equilibrium State
CH₃COOH
⇌
H⁺ +
CH₃COO⁻
At equilibrium
H⁺ H⁺ H⁺
0.1 M CH₃COOH
No salt added
Add Sodium Acetate (CH₃COONa)
📊 Observations
| [CH₃COONa] | pH |
|---|---|
| 0 M | 2.87 |
Lab Notebook
Observations will appear here...