Q. 10.56 - An Introduction to General, Organic, and Biological Chemistry

Question

Which of the following represents a buffer system? Explain.

a. $H_{3}P{O}_3$

b. ${\mathrm{NaNO}}_3$

c. ${\mathrm{HC}}_2{\mathrm{H}}_3{\mathrm{O}}_2\text{ and }{\mathrm{NaC}}_2{\mathrm{H}}_3{\mathrm{O}}_2$

d. $\mathrm{HCl}\text{ and }\mathrm{NaOH}$

Step-by-Step Solution

Answer

1. The mixture ${\mathrm{H}}_3{\mathrm{PO}}_3$,  and $\mathrm{HCl}\text{ and }\mathrm{NaOH}$ is not a buffer system.
2. The mixture ${\mathrm{HC}}_2{\mathrm{H}}_3{\mathrm{O}}_2\text{ and }{\mathrm{NaC}}_2{\mathrm{H}}_3{\mathrm{O}}_2$ is a buffer system.
3. The mixture contains  weak acid ${CH}_3 COONa$ and its salt .
4.  $\mathrm{HCl}\text{ and }\mathrm{NaOH}$which is not a sufficient condition for buffering.

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 $\left(OH\right)$ with a $pH$ value above $7$.

Step 2-Explanation (part a)

a. Weak acid $H_3 {PO}_4$ is not a sufficient buffer as it tends to increase the concentration of $H^{+.}$ Increase the ions.

Need a salt of weak acid. 

Step 2- Explanation (part b)

b. Salt ${NaNO}_3$ is not a good buffer as it tends to increase the concentration of ${NO}_3¯$.

Step 4- Explanation (part c)

c. The mixture contains weak acid ${CH}_3 COOH$ and its salt ${CH}_3 COONa$.

Therefore, the mixture of  ${CH}_3 COOH$and ${CH}_3 COONa$ is a buffer.

Step 5- Explanation (part d)

d. The mixture contains strong acid $HCl$ and strong base $NaOH$,

Step 6- Explanation (part d)

The mixture of HCl and NaOH is not a buffer system.