Question

What will be the pH of a buffer solution prepared from 0.20 mol NH₃, 0.40 mol NH₄NO₃, and just enough water to give 1.00 L of solution?

a) pH < 7
b) pH = 7
c) pH > 7
d) Cannot be determined

Answer 1

The pH of the buffer solution prepared from 0.20 mol NH3 and 0.40 mol NH4NO3 in 1.00 L of solution is greater than 7, indicating that the solution is basic. Therefore, the correct answer is (c) pH > 7.

Step-by-step explanation:

The pH of a buffer solution prepared from 0.20 mol NH₃ (ammonia), 0.40 mol NH₄NO₃ (ammonium nitrate), and just enough water to give 1.00 L of solution can be determined using the Henderson-Hasselbalch equation:

pH = pKa + log ([A−]/[HA])

Where:

• pKa is the acid dissociation constant of the ammonium ion (NH₄+), which is 9.25.
• [A−] is the concentration of the base (NH₃) in moles per liter.
• [HA] is the concentration of the acid (NH₄+) in moles per liter.

Given the molarities of NH₃ and NH₄+, we have:

pH = 9.25 + log (0.20/0.40)

pH = 9.25 + log (0.5)

pH = 9.25 - 0.3010

pH = 8.949

The pH is greater than 7, indicating that the solution is basic. Therefore, the correct answer is (c) pH > 7.