A buffer solution is 0.100 M in both HC7H5O2 and LiC7H5O2 and has a pH of 4.19. Which of the following pH values would you expect from the addition of a small amount of a dilute solution of a strong acid?
When a small amount of a strong acid is added to a buffer solution, the pH of the buffer solution is expected to decrease. This is because the added acid will react with the base component of the buffer (in this case, LiC7H5O2) to form the corresponding salt and water, thereby decreasing the concentration of the base and increasing the concentration of the acid.
Since the initial pH of the buffer solution is 4.19, which is less than 7, it indicates that the solution is acidic. Therefore, the addition of a strong acid would further decrease the pH. Among the given pH values, we would expect a decrease in pH to a value less than 4.19.
Therefore, the expected pH value would be either 3.7 or 3.9.
When a small amount of a strong acid is added to a buffer solution, it gets neutralized by the conjugate base present in the buffer, resulting in a slight change in the pH of the solution. In this case, the buffer consists of HC7H5O2 (acetic acid) and its conjugate base LiC7H5O2 (acetate).
Since the pH of the buffer is given as 4.19, we know that the acetic acid (HC7H5O2) is only partially ionized. At this pH, we can assume that most of the acetic acid is in the undissociated form (HA) and only a small fraction has dissociated into H+ ions and the acetate ion (A-). The conjugate base (acetate) will react with the added strong acid to maintain the pH.
When a strong acid is added, it will react with the acetate ions (A-) to form more acetic acid (HA) through the reaction:
A- + H+ -> HA
This reaction consumes H+ ions, resulting in a shift in equilibrium and a slight increase in pH.
Therefore, by adding a small amount of a dilute solution of a strong acid to the buffer, we would expect the pH of the buffer to increase slightly from its original value of 4.19. The exact pH increase would depend on the concentration of the strong acid added and the buffer capacity.