Question

Why can't the product of an acid reacting with water react with water and produce OH−

? Take the reaction below as an example:

H₂CO₃(aq) + H₂O(l) ↽−−⇀ HCO₃⁻ (aq) + H₃O⁺ (aq)
HCO₃⁻ (aq) + H2O(l) ↽−−⇀ CO₃²⁻ (aq) + H₃O⁺ (aq)

Why can't the CO₃²⁻ react with water (not H₃O⁺) and produce OH⁻ ions? If it can then why is the solution acidic and not basic?

PS. I am a high school student and would really appreciate a straightforward answer.

Answer 1

In the reaction between an acid and water, hydronium ions (H₃O⁺) are produced instead of hydroxide ions (OH⁻). The bicarbonate ion (HCO₃⁻) can act as an acid and donate a proton to water, forming H₃O⁺ ions. The reaction of CO₃²⁻ with water can produce OH⁻ ions, but the concentration of OH⁻ ions is very low compared to H₃O⁺ ions in this case, resulting in an acidic solution.

Step-by-step explanation:

An acid reacts with water to produce hydronium ions (H₃O⁺) and not hydroxide ions (OH⁻). In the reaction you provided, the product of the reaction between HCO₃⁻ and H₂O is H₃O⁺, not OH⁻.

This is because the bicarbonate ion acts as an acid and donates a proton to water, forming hydronium ions.

The CO₃²⁻ ion can react with water to produce OH⁻ ions, but this reaction is very weak. Additionally, the concentration of CO₃²⁻ ions is very low in the solution, so the contribution of OH⁻ ions from this reaction is negligible compared to the concentration of H₃O⁺ ions.

The solution is acidic because the concentration of H₃O⁺ ions is greater than the concentration of OH⁻ ions. In an acidic solution, the concentration of H₃O⁺ ions is higher, while in a basic solution, the concentration of OH⁻ ions is higher.