Answer:
4.07
Step-by-step explanation:
There is some info missing. I think this is the original question.
A solution is prepared at 25 °C that is initially 0.057 M in nitrous acid (HNO₂), a weak acid with Ka = 4.5 × 10⁻⁴, and 0.30 M in sodium nitrite (NaNO₂). Calculate the pH of the solution. Round your answer to 2 decimal places.
Nitrous acid is a weak acid and nitrite (coming from sodium nitrite) is its conjugate base. Together, the form a buffer system. We can calculate its pH using the Henderson-Hasselbach equation.
pH = pKa + log [base]/[acid]
pH = -log 4.5 × 10⁻⁴ + log 0.30/0.057
pH = 4.07