Question

Suppose you have an alkaline buffer consisting of 0.2 M aqueous ammonia and 0.1 M ammonium chloride. What is the pH of the solution?

A) pH = 7

B) pH > 7

C) pH < 7

D) Cannot be determined with the given information

Answer 1

Using the Henderson-Hasselbalch equation with the given concentrations and the pKa of ammonium ion (9.25), the pH of the buffer solution is determined to be approximately 9.55, indicating that the solution is basic.

Step-by-step explanation:

The question is asking for the pH of a buffer solution consisting of 0.2 M aqueous ammonia (NH3) and 0.1 M ammonium chloride (NH4Cl). To determine the pH of this buffer solution, you need to use the Henderson-Hasselbalch equation:

\[pH = pKa + \log(\frac{\text{[base]}}{\text{[acid]}})\]

Ammonia is a weak base, and ammonium chloride is its conjugate acid. The pKa for the conjugate acid of ammonia (NH4+) is 9.25. Using the provided concentrations for ammonia (base) and ammonium chloride (conjugate acid) in the Henderson-Hasselbalch equation:

\[pH = 9.25 + \log(\frac{0.2}{0.1})\]

\[pH = 9.25 + \log(2)\]

\[pH = 9.25 + 0.3\]

\[pH \approx 9.55\]

Since the pH is greater than 7, the buffer solution is basic. Therefore, the correct answer is:

• B) pH > 7