Ionic Equilibrium In Solution

Step 1: Calculate the moles of NaOH and HCl.
First, calculate the moles of NaOH and HCl:
Step 2: Determine the excess NaOH.
Since NaOH is in excess, subtract the moles of HCl from NaOH, and then calculate the pH based on the concentration of excess OH .
Step 3: Conclusion.
The final pH of the solution will be 12, as the excess OH makes the solution basic.
Final Answer:

Step 1: Henderson-Hasselbalch equation.
The pH of a buffer solution is calculated using the Henderson-Hasselbalch equation: Substituting the given concentrations and pH value, we find the result.

Step 2: Conclusion.
The pH of the buffer is 5.04, corresponding to option (4).

The solubility product indicates the solubility of the salts in solution. By comparing the ion product of each sulfide with its solubility product, we determine that CuS will precipitate because its ion product exceeds the solubility product, while MnS and FeS will not.