Ethanoic acid (CH₃COOH), also known as acetic acid, reacts with water as a typical weak acid by donating a proton (H⁺) to water molecules.
When ethanoic acid is added to water, an acid-base reaction occurs where the ethanoic acid molecule loses a proton and the water molecule gains a proton. This process produces Hydroxonium ions (H₃O⁺) and Ethanoate ions (CH₃COO⁻).
The reaction can be represented by the following reversible equation:
CH₃COOH(aq) + H₂O(l) ⇌ CH₃COO⁻(aq) + H₃O⁺(aq)
Understanding the Reaction
This reaction is characterized by the following points:
- Weak Acid Behavior: Ethanoic acid is a weak acid, meaning it does not fully dissociate (break apart into ions) in water. Only a small fraction of ethanoic acid molecules donate their proton to water at any given time.
- Formation of Ions: The reaction leads to the formation of:
- Ethanoate Ion (CH₃COO⁻): The conjugate base of ethanoic acid, formed after the acid loses a proton.
- Hydroxonium Ion (H₃O⁺): Formed when a water molecule accepts a proton from the acid. These ions are responsible for the acidic properties of the solution.
- Reversible Equilibrium: The reaction is reversible, indicated by the double arrow (⇌). This means that while ethanoic acid reacts with water to form ions, the reverse reaction is also happening simultaneously. The ethanoate ions and hydroxonium ions react with each other to reform ethanoic acid and water.
- Equilibrium Position: As stated in the reference, the back reaction (Ethanoate ions and Hydroxonium ions reforming Ethanoic acid and water) is more successful than the forward one. This means the equilibrium lies primarily to the left, with the majority of the ethanoic acid remaining in its molecular form rather than dissociating into ions. This is why it is classified as a weak acid.
Products of the Reaction
The primary chemical species present in a solution of ethanoic acid in water are:
| Reactants | Products |
|---|---|
| Ethanoic acid | Ethanoate ion |
| Water | Hydroxonium ion |
And also significant amounts of unreacted ethanoic acid and water molecules.
In summary, when ethanoic acid reacts with water, it partially dissociates to form ethanoate ions and hydroxonium ions, establishing a dynamic equilibrium where the reformation of the acid and water from the ions is favoured.
