Chapter 19, Problem 19.40P

Match the $\text{p}{K}_{\text{a}}$ values to the appropriate compound. $\text{p}{K}_{\text{a}}$ values: $0.28,1.24,2.66,2.86,$ and $3.12$. Compounds (a) ${\text{FCH}}_{\text{2}}\text{COOH}$; (b) ${\text{CF}}_{\text{3}}\text{COOH}$; (c) ${\text{F}}_{\text{2}}\text{CHCOOH}$; (d) ${\text{ICH}}_{\text{2}}\text{COOH}$; (e) ${\text{BrCH}}_{\text{2}}\text{COOH}$

Interpretation Introduction

(a)

Interpretation: The $\text{p}{K}_{\text{a}}$ value of the given compound is to be predicted.

Concept introduction: The $\text{p}{K}_{\text{a}}$ value is inversely related to the acidic strength of the compound. The major factors that contribute to the acidic strength are $\text{s}$ character, inductive effect and polarity. The high percentage of $\text{s}$ character increases the acidity. There are two types of inductive effects named as positive and negative inductive effect. Positive inductive effect lowers the acidic strength of the compounds, whereas negative inductive effect increases the acidic strength of the compounds.

Answer to Problem 19.40P

The $\text{p}{K}_{\text{a}}$ value of ${\text{FCH}}_{\text{2}}\text{COOH}$ is $2.66$.

Explanation of Solution

The given compound is ${\text{FCH}}_{\text{2}}\text{COOH}$. Fluorine is electron withdrawing group due to which its acidic strength is high and $\text{p}{K}_{\text{a}}$ value is low. Only one fluorine atom is present in the compound. Therefore, the $\text{p}{K}_{\text{a}}$ value of ${\text{FCH}}_{\text{2}}\text{COOH}$ is $2.66$.

Conclusion

The $\text{p}{K}_{\text{a}}$ value of ${\text{FCH}}_{\text{2}}\text{COOH}$ is $2.66$.

Interpretation Introduction

(b)

Interpretation: The $\text{p}{K}_{\text{a}}$ value of the given compound is to be predicted.

Concept introduction: The $\text{p}{K}_{\text{a}}$ value is inversely related to the acidic strength of the compound. The major factors that contribute to the acidic strength are $\text{s}$ character, inductive effect and polarity. The high percentage of $\text{s}$ character increases the acidity. There are two types of inductive effects named as positive and negative inductive effect. Positive inductive effect lowers the acidic strength of the compounds, whereas negative inductive effect increases the acidic strength of the compounds.

Answer to Problem 19.40P

The $\text{p}{K}_{\text{a}}$ value of ${\text{CF}}_{\text{3}}\text{COOH}$ is $0.28$.

Explanation of Solution

The given compound is ${\text{CF}}_{\text{3}}\text{COOH}$. Fluorine is highly electronegative due to which its acidic strength is high and $\text{p}{K}_{\text{a}}$ value is low.

The order of electronegativity among halogens is shown below.

$\text{I}<\text{Br}<\text{Cl}<\text{F}$

Three fluorine atoms are present in the compound. Therefore, the $\text{p}{K}_{\text{a}}$ value of ${\text{CF}}_{\text{3}}\text{COOH}$ is $0.28$.

Conclusion

The $\text{p}{K}_{\text{a}}$ value of ${\text{CF}}_{\text{3}}\text{COOH}$ is $0.28$.

Interpretation Introduction

(c)

Interpretation: The $\text{p}{K}_{\text{a}}$ value of the given compound is to be predicted.

Concept introduction: The $\text{p}{K}_{\text{a}}$ value is inversely related to the acidic strength of the compound. The major factors that contribute to the acidic strength are $\text{s}$ character, inductive effect and polarity. The high percentage of $\text{s}$ character increases the acidity. There are two types of inductive effects named as positive and negative inductive effect. Positive inductive effect lowers the acidic strength of the compounds, whereas negative inductive effect increases the acidic strength of the compounds.

Answer to Problem 19.40P

The $\text{p}{K}_{\text{a}}$ value of ${\text{F}}_{\text{2}}\text{CHCOOH}$ is $1.24$.

Explanation of Solution

The given compound is ${\text{F}}_{\text{2}}\text{CHCOOH}$. Fluorine is electron withdrawing group due to which its acidic strength is high and $\text{p}{K}_{\text{a}}$ value is low.

The order of electronegativity among halogens is shown below.

$\text{I}<\text{Br}<\text{Cl}<\text{F}$

Two fluorine atoms are present in the compound. Therefore, the $\text{p}{K}_{\text{a}}$ value of ${\text{F}}_{\text{2}}\text{CHCOOH}$ is $1.24$.

Conclusion

The $\text{p}{K}_{\text{a}}$ value of ${\text{F}}_{\text{2}}\text{CHCOOH}$ is $1.24$.

Interpretation Introduction

(d)

Interpretation: The $\text{p}{K}_{\text{a}}$ value of the given compound is to be predicted.

Concept introduction: The $\text{p}{K}_{\text{a}}$ value is inversely related to the acidic strength of the compound. The major factors that contribute to the acidic strength are $\text{s}$ character, inductive effect and polarity. The high percentage of $\text{s}$ character increases the acidity. There are two types of inductive effects named as positive and negative inductive effect. Positive inductive effect lowers the acidic strength of the compounds, whereas negative inductive effect increases the acidic strength of the compounds.

Answer to Problem 19.40P

The $\text{p}{K}_{\text{a}}$ value of ${\text{ICH}}_{\text{2}}\text{COOH}$ is $3.12$.

Explanation of Solution

The given compound is ${\text{ICH}}_{\text{2}}\text{COOH}$. Iodine is electron withdrawing group due to which its acidic strength is high and $\text{p}{K}_{\text{a}}$ value is low. Iodine is less electronegative as compared to fluorine.

The order of electronegativity among halogens is shown below.

$\text{I}<\text{Br}<\text{Cl}<\text{F}$

Only one iodine atom is present in the compound. Therefore, the $\text{p}{K}_{\text{a}}$ value of ${\text{ICH}}_{\text{2}}\text{COOH}$ is $3.12$.

Conclusion

The $\text{p}{K}_{\text{a}}$ value of ${\text{ICH}}_{\text{2}}\text{COOH}$ is $3.12$.

Interpretation Introduction

(e)

Interpretation: The $\text{p}{K}_{\text{a}}$ value of the given compound is to be predicted.

Concept introduction: The $\text{p}{K}_{\text{a}}$ value is inversely related to the acidic strength of the compound. The major factors that contribute to the acidic strength are $\text{s}$ character, inductive effect and polarity. The high percentage of $\text{s}$ character increases the acidity. There are two types of inductive effects named as positive and negative inductive effect. Positive inductive effect lowers the acidic strength of the compounds, whereas negative inductive effect increases the acidic strength of the compounds.

Answer to Problem 19.40P

The $\text{p}{K}_{\text{a}}$ value of ${\text{BrCH}}_{\text{2}}\text{COOH}$ is $2.86$.

Explanation of Solution

The given compound is ${\text{BrCH}}_{\text{2}}\text{COOH}$. The order of electronegativity among halogens is shown below.

$\text{I}<\text{Br}<\text{Cl}<\text{F}$

Bromine is more electronegative as compared to iodine. Therefore, the $\text{p}{K}_{\text{a}}$ value of ${\text{BrCH}}_{\text{2}}\text{COOH}$ is $2.86$.

Conclusion

The $\text{p}{K}_{\text{a}}$ value of ${\text{BrCH}}_{\text{2}}\text{COOH}$ is $2.86$.