Chapter 16, Problem 1DE

(a)

Interpretation Introduction

To determine: The method of categorization of the sample as acidic or basic.

Answer to Problem 1DE

Solution: The method of categorization of the sample as acidic or basic is by using litmus paper.

Explanation of Solution

If the solution is acidic, it changes blue litmus paper into red and there is no change in color for red litmus paper.

If the solution is basic it changes red litmus paper into blue and there is no change in color for blue litmus paper.

Conclusion

The sample is categorized as acidic or basic by using litmus paper.

(b)

Interpretation Introduction

To determine: The method of categorization of the sample as weak acid or strong acid.

Answer to Problem 1DE

Solution: The method of categorization of the sample as weak acid or strong acid is titration.

Explanation of Solution

A strong acid and a weak acid can be differentiated by titrating them agianst a strong base like NaOH with the help of two acid-base indicators namely, methyl orange and phenolphthalein. The titre value is noted in both the cases.

When strong acid is titrated agianst a strong base, the same titre value is obtained for both the indicators. For tritration of weak acid and strong base, the color of indicator,methyl orange changes much earlier than the phenolphthalein and two different titre values are obtained.

Conclusion

Thus, the method of categorization of the sample as weak acid or strong acid is titration.

(c)

Interpretation Introduction

To determine: The value of $K_{\text{a}}$ for weak acid.

Answer to Problem 1DE

Solution: The value of $K_{\text{a}}$ for weak acid is determined by using $\text{p}{K}_{\text{a}}$ value.

Explanation of Solution

The $\text{p}{K}_{\text{a}}$ for the pure substance is equal to its $\text{pH}$ value.

The value of $\text{p}{K}_{\text{a}}$ is calculated by the formula,

$\text{p}{K}_{\text{a}}=-\log K_{\text{a}}$

Rearrange the above equation to calculate the value of $K_{\text{a}}$ .

$K_{\text{a}}=-\text{antilog}\text{p}{K}_{\text{a}}$

Conclusion

The value of $\text{p}{K}_{\text{a}}$ is used to determine $K_{\text{a}}$ .

(d)

Interpretation Introduction

To determine: The method of separation of salt of weak acid.

Answer to Problem 1DE

Solution: The method of separation of salt of weak acid is by using the immiscible organic solvent and water.

Explanation of Solution

Weak acids being organic in nature are more soluble in organic solvent.

For the separation of sodium salt of weak acid, the titrated mixture is dissolved in the mixture of immiscible organic solvent and water.

The salt being ionic preferred to dissolved in aqueous layer and weak acid preferred to dissolve in organic layer.

The aqueous layer is separated by separating funnel.

Conclusion

The salt of weak acid is separated by using the immiscible organic solvent and water.

(e)

Interpretation Introduction

To determine: The strength of the base and the $K_{\text{b}}$ value.

Answer to Problem 1DE

Solution: The strength of the base and the $K_{\text{b}}$ value is stated below.

Explanation of Solution

The strength of a base is determined by comparing $\text{pH}$ paper with $\text{pH}$ scale.

If the value of $\text{pH}$ of the solution is close to $14$ than it is a strong base and if the value of $\text{pH}$ of the solution is close to $7$ than it is a weak base.

The ${\text{pK}}_{\text{b}}$ for the pure substance is equal to its $\text{pH}$ value.

The value of ${\text{pK}}_{\text{b}}$ is calculated by the formula,

  ${\text{pK}}_{\text{b}}=-\log K_{\text{b}}$

Rearrange the above equation to calculate the value of ${\text{K}}_{\text{b}}$ .

$K_{\text{b}}=-\text{antilog}{\text{pK}}_{\text{b}}$

Conclusion

The strength of the weak base is determined by using $\text{pH}$ paper.