Q. 10.58 - An Introduction to General, Organic, and Biological Chemistry

Question

Consider the buffer system of hydrofluoric acid, HF, and its salt, NaF .

$\mathrm{HF}\left(aq\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)\rightleftarrows {\mathrm{H}}_3{\mathrm{O}}^{+}\left(aq\right)+{\mathrm{F}}^{-}\left(aq\right)$

a. The purpose of this buffer system is to:

            1. maintain [HF]

            2. maintain $\left[{\mathrm{F}}^{-}\right]$

            3. maintain $\mathrm{pH}$

b. The salt of the weak acid is needed to:

            1. provide the conjugate base

            2. neutralize added ${\mathrm{H}}_3{\mathrm{O}}^{+}$

            3. provide the conjugate acid

c. If ${\mathrm{OH}}^{-}$is added, it is neutralized by:

             1. the salt

             2. ${\mathrm{H}}_2\mathrm{O}$

             3. ${\mathrm{H}}_3{\mathrm{O}}^{+}$

d.  When${\mathrm{H}}_3{\mathrm{O}}^{+}$is  added, the equilibrium shifts in the direction of the:

             1. reactants

             2. products

             3. does not change

Step-by-Step Solution

Answer

(Part a)       The  purpose of  this buffer  system is maintain the pH of the solution.

(Part b)         1. To furnish the conjugate base for the acid.

            2. To compensate for the additional${\mathrm{H}}_3{\mathrm{O}}^{+}$

(Part c)      If ${\mathrm{OH}}^{-}$ is added ,it is neutralized by  ${\mathrm{H}}_3{\mathrm{O}}^{+}$

(Part d)       The  ${\mathrm{H}}_3{\mathrm{O}}^{+}$ is consumed when equilibrium shifted to reactants.

Step - 1 Introduction (Part a)

Buffer solution: 

                       A acetic base and its negative ion are found in a buffer solution. When tiny quantity of acid or base are added to a buffer, it should not change.

Step - 2 Given information ( part-a)

The hydrofluoric acid and sodium fluoride buffer system is as follows:

$\mathrm{HF}\left(aq\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}\left(aq\right)+{\mathrm{F}}^{-}\left(aq\right)$

Step - 3 Explanation (part-a)

• The buffer solution's $\mathrm{pH}$ remains constant.
• The goal of this buffer system is to keep a solution's $\mathrm{pH}$ constant. 

Step - 4 Given information (part-b)

• The weak acid's salt dissociates in this buffer environment, releasing the acid's conjugate base. 
• The conjugate base cancels out the extra  ${\mathrm{H}}_3{\mathrm{O}}^{+}$.

Step - 5 Explanation (part- b)

As a result, the weak acid salt is required for the following:

           1. To furnish the conjugate base for the acid.

           2. To compensate for the additional${\mathrm{H}}_3{\mathrm{O}}^{+}$.

Step - 6 Given information (part - c)

     When ${\mathrm{OH}}^{-}$ is added to the buffer system;

Step - 7 Explanation (part -c)

•    ${\mathrm{OH}}^{-}$is introduced into the buffer system, it is neutralized by ${\mathrm{H}}_3{\mathrm{O}}^{+}$

Step - 8 Given information (part-d)

• When acid or ${\mathrm{H}}_3{\mathrm{O}}^{+}$is added to the buffer system, the equilibrium moves in the direction of consumption of ${\mathrm{H}}_3{\mathrm{O}}^{+}$.

 

          $\mathrm{HF}\left(aq\right)+{\mathrm{H}}_2\mathrm{O}\left(l\right)\rightleftharpoons {\mathrm{H}}_3{\mathrm{O}}^{+}\left(aq\right)+{\mathrm{F}}^{-}\left(aq\right)$

Step - 9 Explanation (part- d)

 

   When the equilibrium moves to the reactants, the ${\mathrm{H}}_3{\mathrm{O}}^{+}$ is devoured.