Final answer:
The percent ionization of formic acid in a solution changes depending on additional components in the solution. Without additions, it is initially 3.5%. The addition of sodium formate has little effect due to buffer action, whereas adding 0.200 M HCl significantly reduces the percent ionization, demonstrating the common ion effect.
Step-by-step explanation:
To determine the percent ionization of formic acid in solution, consider the given information. The initial concentration of formic acid is 0.150 M, and the pH of the solution without any additions is 2.28. If sodium formate is added to a final concentration of 0.100 M, the percent ionization of formic acid is not significantly changed because the formic acid and formate ion exist in a buffer equilibrium.
However, upon the addition of 0.200 M HCl, the scenario changes due to the common ion effect. The strong acid increases the concentration of H+, which drives the ionization equilibrium to the left according to Le Chatelier's principle. The percent ionization of formic acid decreases significantly when HCl is added to the system. This decrease can be calculated by determining the new concentration of HCO2− ions using the equilibrium constant expression and the initial concentrations.
A balanced equilibrium equation would be HCO2H ⇌ H+ + HCO2− for the ionization of formic acid. To determine the percent ionization, you take the concentration of HCO2−, divide by the initial concentration of HCO2H, and multiply by 100. This calculation shows that adding a strong acid like HCl can significantly reduce the percent ionization of formic acid.