Question

Calculate the pH of a solution formed by mixing 250.0 ml of 0.15 mol L-1 NH4Cl with 200.0 ml of 0.12 mol L-1 NH₃. The Kb for NH₃ is 1.8 × 10-5.

1) 9.06
2) 4.74
3) 4.55
4) 9.26
5) 9.45

Answer 1

To calculate the pH of a solution formed by mixing NH4Cl and NH3, we can use the Henderson-Hasselbalch equation. First, calculate the concentrations of NH4+ and NH3 in the mixed solution. Then, plug the concentrations into the Henderson-Hasselbalch equation to calculate the pH. The pKa for NH3 can be found by taking the negative logarithm of its Kb value.

Step-by-step explanation:

To calculate the pH of a solution formed by mixing two solutions, we can use the Henderson-Hasselbalch equation. First, we need to calculate the concentrations of NH₄⁺ and NH₃ in the mixed solution. For NH₄⁺, we can use the molarity of the NH₄Cl solution. For NH₃, we need to calculate the molarity by dividing the moles of NH₃ by the volume of the mixed solution. Once we have the concentrations, we can plug them into the Henderson-Hasselbalch equation to calculate the pH.

The Henderson-Hasselbalch equation is: pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the NH₃ (NH₃ is the conjugate base) and [HA] is the concentration of the NH₄⁺ (NH₄⁺ is the weak acid).

In this case, the pKa for NH₃ is the negative logarithm of the Kb value, which is given as 1.8 × 10-5.

By plugging in the values, we can calculate the pH of the solution.