Acetic acid (HC2H3O2) is the weak acid found in vinegar. What is the net ionic equation for the acid–base reaction that occurs when acetic acid and sodium hydroxide (NaOH) solutions are mixed?
A) HC2H3O2(aq) + OH– (aq) –––> C2H3O2 – (aq) + H2O(l)
B) H+ (aq) + OH– (aq) –––> H2O(l)
C) H3O + (aq) + OH– (aq) –––> 2H2O(l)
D) C2H3O2 – (aq) + H+ (aq) + Na+ (aq) + OH– (aq) ––––> Na+ (aq) + C2H3O2 – (aq) + H2O(l)
E) HC2H3O2(aq) + NaOH(aq) –––––> NaC2H3O2(aq) + H2O(l)
The Correct Answer and Explanation is :
The correct answer is A) HC2H3O2(aq) + OH–(aq) → C2H3O2–(aq) + H2O(l).
Explanation:
The reaction in question involves acetic acid (HC2H3O2) and sodium hydroxide (NaOH), which is a base. Acetic acid is a weak acid that only partially dissociates in solution, while sodium hydroxide dissociates completely into sodium (Na+) and hydroxide (OH-) ions in water.
When these two solutions are mixed, the hydroxide ion (OH–) from NaOH acts as a base and reacts with the acetic acid, which donates a proton (H+). The reaction is as follows:
- Acetic acid (HC2H3O2) dissociates in water to form acetate ions (C2H3O2–) and hydrogen ions (H+):
[
\text{HC}_2\text{H}_3\text{O}_2 (aq) \rightleftharpoons \text{H}^+ (aq) + \text{C}_2\text{H}_3\text{O}_2^- (aq)
] - Sodium hydroxide (NaOH) dissociates completely to form sodium ions (Na+) and hydroxide ions (OH–):
[
\text{NaOH} (aq) \rightarrow \text{Na}^+ (aq) + \text{OH}^- (aq)
] - The hydroxide ion (OH–) from NaOH reacts with the hydrogen ion (H+) from acetic acid to form water:
[
\text{H}^+ (aq) + \text{OH}^- (aq) \rightarrow \text{H}_2\text{O} (l)
] - The result is the formation of acetate ions (C2H3O2–) and water. Therefore, the net ionic equation is:
[
\text{HC}_2\text{H}_3\text{O}_2 (aq) + \text{OH}^- (aq) \rightarrow \text{C}_2\text{H}_3\text{O}_2^- (aq) + \text{H}_2\text{O} (l)
]
Why other options are incorrect:
- B) The reaction described is too general and represents the neutralization between a strong acid (H+) and a strong base (OH–), not involving the weak acid (acetic acid).
- C) Similar to B, this represents a strong acid–base neutralization reaction and doesn’t account for acetic acid specifically.
- D) This equation is overly complicated because the Na+ ion does not participate directly in the neutralization reaction, making it unnecessary.
- E) This is a molecular equation for the full reaction, which is not the net ionic equation, as it includes spectator ions (Na+).
Thus, the correct net ionic equation is A, as it shows the actual chemical species involved in the acid–base reaction, excluding spectator ions.