A solution is prepared by dissolving 0.23 mol of nitrous acid and 0.27 mol of sodium nitrite in water sufficient to yield 1.00 L of solution.The addition of 0.05 mol of NaOH to this buffer solution causes the pH to increase slightly.The pH does not increase drastically because the NaOH reacts with the ________ present in the buffer solution.The K_a of nitrous acid is 4.5 × 10^-4. A) H₂O B) H₃O⁺ C) nitrite D) nitrous acid E) This is a buffer solution: the pH does not change upon addition of acid or base.

Question

Quizplus · Accepted Answer

A buffer solution resists changes in pH upon addition of small amounts of acid or base. It consists of a weak acid and its conjugate base or a weak base and its conjugate acid. In this case, nitrous acid and sodium nitrite are the weak acid/conjugate base pair in the buffer solution. When NaOH is added, it reacts with nitrous acid to form sodium nitrite and water as follows: NaOH + HNO2 → NaNO2 + H2O. This reaction consumes nitrous acid and shifts the equilibrium towards the undissociated form, hence the pH doesn't change drastically. So, the correct answer is D - nitrous acid.

A Solution Is Prepared by Dissolving 0