Final answer:
The pH of a solution containing 0.72 M NH3 and 0.26 M NH4F is calculated using the Henderson-Hasselbalch equation, which relates the pH of a buffer solution to the concentration of the base and its conjugate acid and the pKa of the acid.
Step-by-step explanation:
To calculate the pH of a solution of 0.72 M NH3 (ammonia) and 0.26 M NH4F (ammonium fluoride), we need to consider the buffer solution formed by the weak base (NH3) and its conjugate acid (NH4+ from NH4F). This solution follows the Henderson-Hasselbalch equation, which is:
pH = pKa + log([Base]/[Acid])
In this case, ammonia is the base (NH3), and ammonium (NH4+) is the acid. To find pKa, we can use the relation pKa = -log(Ka), where Ka for NH4+ is 5.6 × 10-10. Using these values, we can solve for the pH of the buffer solution.
Note that the question provided involves a comparably similar system for which we know the Kb value of NH3 from the example of household ammonia where the pH is given as 11.612 at a 0.950 M concentration.
Using this, we can infer the Kb for NH3, and since pKb = -log(Kb), we can also find pKb and then pKa (since pKa + pKb = 14 for conjugate acid-base pairs). You can use these values along with the Henderson-Hasselbalch equation to calculate the pH of the given NH3/NH4F buffer system.