Q. 10.55 - An Introduction to General, Organic, and Biological Chemistry

Question

Which of the following represents a buffer system? Explain.

a. $\mathrm{NaOH}$ and $\mathrm{NaCl}$

b.  ${\mathrm{H}}_2{\mathrm{CO}}_3$ and ${\mathrm{NaHCO}}_3$

c.  $\mathrm{HF}$ and $KF$

d. $\mathrm{KCl}$ and $\mathrm{NaCl}$

Step-by-Step Solution

Answer

(Part a) The mixture $NaOH$and $NaCI$ $\&$ $KCI$ and $NaCI$are not a buffer systems.

(Part b) The mixture ${\mathrm{H}}_2{\mathrm{CO}}_3$ and ${\mathrm{NaHCO}}_3$ $\&$ $HF$ and $KF$ are a buffer systems.

Step 1- Introduction (Part a)

A buffer system is a solution that withstands changes in $pH$ when an acid or base is added. The acidic solution contains a high concentration of hydrogen ions  $(H +)$and has a  $pH$ value of less than $7$. The basic solution contains a high concentration of hydroxide ions $\left(OH\right)$ and has a pH value above $7.$ 

Step 2- Explanation (part a)

a.

 The solution of strong base and its salt is completely ionized. Therefore, the $NaOH$ and $NaCl$ solutions are not buffer systems. 

Step 3- Explanation (part b)

b.

The mixture contains weak acid $H_2 {CO}_3$ and its salt ${\mathrm{NaHCO}}_3$. Therefore, the solution of  $H_2 {CO}_3$and ${\mathrm{NaHCO}}_3$ is a buffer system. 

Step 4- Explanation (part c)

c.

 The mixture contains the weak acid $HF$ and its salt $KF.$ Therefore, the mixture of $HF$ and $KF$ is a buffer system. 

Step 5- Explanation (part d)

d.

Both substances are salts. The mixture does not contain weak acids. Therefore, a mixture of $KCl$ and $NaCl$ is not a buffer.