Final answer:
The question is about calculating the pH of a buffer solution composed of HNO₂ and KNO₂. By using the Henderson-Hasselbalch equation and the given concentration and volume to find the moles of each component, one can determine the pH of the solution.
Step-by-step explanation:
The student is asking about the calculation of the pH of a buffer solution which is prepared by mixing HNO₂ (nitrous acid) with KNO₂ (potassium nitrite). The formula for calculating pH in this case utilizes the Henderson-Hasselbalch equation, which is pH = pKa + log([A-]/[HA]). The given values are: the concentration of HNO₂ is 1.40 M with a volume of 150 mL, the concentration of KNO₂ is 0.909 M with a volume of 111 mL, and the Ka of HNO₂ is 5.62e⁻⁴.
To proceed with the calculation, we need to find the moles of HNO₂ and KNO₂ by using their respective volumes and concentrations. After that, we apply the Henderson-Hasselbalch equation. The moles of HNO₂ (acid, HA) are found to be 1.40 M * 0.150 L = 0.210 mol, and the moles of KNO₂ (base, A-) are 0.909 M * 0.111 L = 0.1009 mol. Given that KNO₂ fully dissociates into K+ and NO₂-, we can simplify this to the ratio of NO₂- to HNO₂.
Applying the Henderson-Hasselbalch equation, the pKa is the negative logarithm of Ka, which is -log(5.62e⁻⁴) = 3.25. We then plug in the ratio of the base to the acid into the equation:
Using a calculator, this yields a pH value for the buffer which would then give the answer to the student's question.