Question

What is the pH of a buffer that is 0.6 M HF and 0.2 M NaF? The Ka of HF is 6.8 Ã 10â4. What is the pH of a buffer that is:_______ a. 3.65b. 3.17c. 3.50d. 2.69

Answer 1

Answer:

The correct option is  d

Step-by-step explanation:

From the question we are told that

   The concentration of  HF  is  [HF] =  0.6 M

   The concentration of  NaF  is  $[NaF ] = 0.2 M$

   The Ka of  HF  is  $K_a = 6.8 *10^{-4}$

Generally HF(Hydrogen fluoride )  is ionized as follows  

      $HF_{(aq)} + H_2 O _{(l)} \rightleftharpoons H_3O^+ _{(aq) } + F^- _{(aq)}$  

Generally NaF(Sodium fluoride )  is ionized as follows  

       $NaF_{(aq)} + H_2 O _{(l)} \rightleftharpoons Na^+ _{(aq) } + F^- _{(aq)}$  

Generally the from Henderson-Hasselbalch equation the pH of the buffer is mathematically represented as

       $pH = pKa + log [\frac{[NaF ]}{HF} ]$

=>     $pH = -log(K_a) + log [\frac{[NaF ]}{HF} ]$

=>     $pH = -log(6.8 *10^{-4}) + log [\frac{[0.2 ]}{0.6} ]$

=>    $pH = 2.69$