Determine the pH of a buffer solution prepared by dissolving 0.75 mol NH3 and 0.25 mol NH4Cl in 1.00 L of solution. (Kb NH3 = 1.8 x 10-5) (remember to find pKa!)Question 8Select one:a.4.27b.8.78c.9.73d.4.74
Question
Determine the pH of a buffer solution prepared by dissolving 0.75 mol NH3 and 0.25 mol NH4Cl in 1.00 L of solution. (Kb NH3 = 1.8 x 10-5) (remember to find pKa!)Question 8Select one:a.4.27b.8.78c.9.73d.4.74
Solution
To solve this problem, we need to use the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]). In this case, NH3 is the base (A-) and NH4+ is the acid (HA).
Step 1: Calculate pKa from Kb We know that Ka * Kb = Kw = 1.0 x 10^-14. We can rearrange this to find Ka = Kw / Kb = 1.0 x 10^-14 / 1.8 x 10^-5 = 5.56 x 10^-10. Then, we find pKa by taking the negative log of Ka, so pKa = -log(5.56 x 10^-10) = 9.25.
Step 2: Use the Henderson-Hasselbalch equation Now we can plug our values into the Henderson-Hasselbalch equation. The concentration of NH3 ([A-]) is 0.75 mol / 1.00 L = 0.75 M, and the concentration of NH4+ ([HA]) is 0.25 mol / 1.00 L = 0.25 M. So, pH = 9.25 + log(0.75/0.25) = 9.25 + log(3) = 9.25 + 0.48 = 9.73.
So, the pH of the buffer solution is 9.73, which corresponds to option c.
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