The change in pH of a solution upon the addition of an acid (such as HCl) can be calculated using the equation for the dissociation of the acid:
HCl + H2O → H3O+ + Cl-
Since HCl is a strong acid, it dissociates completely in water, meaning that all of the HCl molecules will be converted into H3O+ ions.
The initial concentration of H3O+ ions in the solution can be calculated as follows:
[H3O+] = 0.03 mol / 0.50 L = 0.06 M
The pH of a solution with a concentration of H3O+ ions can be calculated using the equation:
pH = -log[H3O+]
So, in this case:
pH = -log(0.06) = 1.22
Therefore, the change in pH after the addition of 0.03 mol of HCl to 0.50 L of solution would be a decrease to 1.22, which represents a significant decrease in solution acidity