A solution of nitrous acid and potassium nitrite acts as a buffer due to reactions that occur within the solution when a strong acid or a strong base is added.

(a) Write the net ionic equation for the reaction that occurs in this buffer to react away any added HCl (aq).

(b) Write the net ionic equation for the reaction that occurs in this buffer to react away any added NaOH (aq).

a. NO₂⁻ + H⁺ → HNO₂

b. HNO₂ + OH⁻ → NO₂⁻ + H₂O

Explanation:

A buffer is defined as an aqueous mixture of a weak acid and its conjugate base or vice versa.

The buffer of the problem is HNO₂/NO₂⁻ where nitrous acid is the weak acid and NO₂⁻ is its conjugate base.

a. When a acid is added to a buffer as the buffer of the problem, the conjugate base will react with the acid, to produce the weak acid, thus:

NO₂⁻ + HCl → HNO₂ + Cl⁻

Ionic equation is:

NO₂⁻ + H⁺ + Cl⁻ → HNO₂ + Cl⁻

In the net ionic equation, you avoid the ions that don't react, that is:

NO₂⁻ + H⁺ → HNO₂

b. In the same way, the weak acid will react with the strong acid producing water and the conjugate base, thus:

HNO₂ + NaOH → NO₂⁻ + H₂O + Na⁺

The ionic equation is:

HNO₂ + Na⁺ + OH⁻ → NO₂⁻ + H₂O + Na⁺

And the net ionic equation is:

HNO₂ + OH⁻ → NO₂⁻ + H₂O