Question

"What change will be caused by the addition of a small amount of HCL to a HF/NaF buffer?

H+ + F- → HF

a. [H3O+] will increase significantly.
b. [F-] and [H3O+] will both increase.
c. [HF] will decrease and [F-] will increase.
d. [F-] will decrease and [HF] will increase.

Answer 1

The addition of HCl to a HF/NaF buffer decreases the concentration of F- and increases the concentration of HF, while the pH remains relatively stable due to the buffer's capacity to neutralize added acid.

Step-by-step explanation:

When a small amount of HCl is added to a HF/NaF buffer, the H+ ions from HCl will react with F- ions to form HF according to the reaction H+ + F- → HF. This reaction will use up some of the free fluoride ions (F-), thus decreasing their concentration, while the concentration of HF will increase because HF is being formed.

In a buffer system such as this, the pH does not change significantly because the added acid reacts with the base component of the buffer. In the case of the HC2H3O2/NaC2H3O2 buffer, when OH- ions are added, they react with HC2H3O2 to form water (H2O) and the acetate ion (C2H3O2-), preventing a significant pH change. The same principle applies to the HF/NaF buffer with the addition of HCl.