Final answer:
The pH of the buffer solution after the addition of 0.0060 mol HCl to the diethylamine and diethylammonium chloride buffer is 3.20, indicating an acidic solution with an increase in the protonated species.
Step-by-step explanation:
The pH of the buffer solution after adding 0.0060 mol of HCl to a 1 L buffer solution containing 0.312M diethylamine and 0.231M diethylammonium chloride can be calculated using the Henderson-Hasselbalch equation:
pH = pKa + log ([base]/[acid])
Where pKa is the negative log of the K₁ value for diethylamine, which is 1.3 × 10−3 at 25°C, or 3.09. After adding 0.0060 mol HCl to the buffer, the concentration of diethylamine will decrease by 0.0060 M (since it reacts with HCl), and the concentration of diethylammonium chloride will increase by the same amount. We can calculate the new concentrations as follows:
- New concentration of diethylamine = 0.312 M - 0.0060 M = 0.306 M
- New concentration of diethylammonium chloride = 0.231 M + 0.0060 M = 0.237 M
Now apply these values to the Henderson-Hasselbalch equation:
pH = 3.09 + log (0.306/0.237)
pH = 3.09 + log (1.2915)
pH = 3.09 + 0.111
pH = 3.20
The solution after adding HCl remains acidic, with a pH of 3.20, lower than both the initial pH of the diethylamine buffer and the pKa value of diethylamine, indicating more protonated species (diethylammonium ions) are present after the addition of HCl.