Question

iclicker question
what change will be caused by the addition of a small amount of hcl to a hf/naf buffer?
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
e. the fluoride ions will precipitate out of solution.

Explanation:

• In a HF/NaF buffer, the equilibrium is \(HF + H_2O

ightleftharpoons H_3O^+ + F^-\).

• When a small amount of HCl (which provides \(H_3O^+\)) is added, the \(H_3O^+\) will react with \(F^-\) (from NaF) according to the reaction \(H_3O^+ + F^-

ightarrow HF + H_2O\).

• As a result, the concentration of \(F^-\) (\([F^-]\)) decreases because it is consumed by the added \(H_3O^+\), and the concentration of HF (\([HF]\)) increases as it is formed from the reaction of \(F^-\) and \(H_3O^+\).

Answer:

D. \([F^-]\) will decrease and \([HF]\) will increase