Understanding the Chemistry
* HNO₂ is a weak acid: It only partially ionizes in solution.
* NaNO₂ is the salt of its conjugate base: It provides the nitrite ion (NO₂⁻) which is the conjugate base of HNO₂.
* The presence of both the weak acid and its conjugate base creates a buffer solution: This solution resists changes in pH.
The Henderson-Hasselbalch Equation
We'll use the Henderson-Hasselbalch equation to calculate the pH of this buffer solution:
pH = pKa + log([conjugate base]/[acid])
1. Find the pKa of HNO₂:
* The pKa of nitrous acid (HNO₂) is approximately 3.14. You can find this value in a table of acid dissociation constants (Ka values).
2. Plug in the concentrations:
* [acid] = [HNO₂] = 0.16 M
* [conjugate base] = [NO₂⁻] = 0.50 M
3. Calculate the pH:
pH = 3.14 + log(0.50 / 0.16)
pH = 3.14 + log(3.125)
pH ≈ 3.14 + 0.49
pH ≈ 3.63
Therefore, the pH of the solution is approximately 3.63.
