1. Initial Concentration of HCl:
* The initial pH of 4 corresponds to a hydrogen ion concentration ([H+]) of 10^-4 M (since pH = -log[H+]).
2. Moles of HCl Added:
* You added 0.003 moles of HCl to 1 L of solution, making the concentration of added HCl 0.003 M.
3. Total Moles of H+:
* Since HCl completely dissociates, the added HCl contributes 0.003 moles of H+ to the solution.
* The initial solution already contained 10^-4 moles of H+ per liter (calculated from the pH).
4. New Total Concentration of H+:
* Add the moles of H+ from the initial solution and the added HCl: (10^-4) + 0.003 = 0.0031 moles/L
5. New pH:
* Calculate the new pH using the formula: pH = -log[H+]
* pH = -log(0.0031) ≈ 2.51
Therefore, the new pH of the solution after adding 0.003 moles of HCl is approximately 2.51.
