Question

Calculate the pH of the buffer prepared by mixing 600cc of 0.6M NH₃ and 400cc of 0.5M NH₄Cl .

( Kb for NH₃ = 1.8 ×10⁵ )
A. 11.3
B. 9.5
C. 9
D. 5

Answer 1

The calculation of a buffer solution's pH with given concentrations of NH₃ and NH₄Cl can be done using the Henderson-Hasselbalch equation. The resulting pH is approximately 9.65.

Step-by-step explanation:

The student has asked about the calculation of the pH of a buffer solution. To calculate the pH of the buffer prepared by mixing 600 cc of 0.6 M NH₃ (ammonia) and 400 cc of 0.5 M NH₄Cl (ammonium chloride), use the Henderson-Hasselbalch equation:

pH = pKa + log ([Base]/[Acid])

NH₃ is the base and NH₄Cl provides the NH₄⁺, which is the conjugate acid. Ammonia’s pKa is 9.25. Calculate the moles of NH₃ and NH₄⁺:

• NH₃: 0.6 moles/L × 0.6 L = 0.36 mol
• NH₄Cl: 0.5 moles/L × 0.4 L = 0.20 mol

Using the Henderson-Hasselbalch equation:

pH = 9.25 + log (0.36/0.20) = 9.25 + log (1.8)

After calculating, the pH of the buffer solution is approximately 9.65, which means the solution is basic.