Chapter 19, Problem 19.120P

(a)

Interpretation Introduction

Interpretation:

Glycine dissolved in pure water whether will have a protonated $COOH$ group and an unprotonated $N{H}_2$ group has to be determined. 

Concept Introduction:

Dissociation constant of acid:

An acid dissociation constant $\left(K_a\right)$ is a quantitative measure of the strength of an acid in solution. 

Dissociation constant of base:

A base dissociation constant $\left(K_b\right)$ is a quantitative measure of the strength of a base in solution. 

Zwitterion:

This term is used mostly in case of amino acids. Zwitterion is a molecule with two or more functional groups, of which at least one has a positive and one has a negative electrical charge and the net charge of the entire molecule is zero. 

(b)

Interpretation Introduction

Interpretation:

$\left[{}^{+}{\text{NH}}_3{\text{CH}}_2{\text{COO}}^{-}\right]/\left[{}^{+}{\text{NH}}_3{\text{CH}}_2\text{COOH}\right]$ ratio has to be determined at $\text{pH 5}\text{.5}\text{.}$

Concept Introduction:

Henderson-Hasselbalch Equation:

The Henderson-Hasselbalch Equation can be written for any conjugate acid–base pair as given bellow,

$pH=p{K}_a+\log \left(\frac{\left[Base\right]}{\left[Acid\right]}\right)$

Where,

$\begin{array}{l}\text{pH}\text{=}\text{-log}\left[{\text{H}}_{\text{3}}{\text{O}}^{\text{+}}\right]\\ \\ {\text{pK}}_{\text{a}}\text{=}{\text{-logK}}_{\text{a}}\\ \\ {\text{K}}_{\text{a}}\text{=}\text{Dissociation constant}\text{of}\text{acid}\\ \\ \left[\text{Base}\right]\text{=}\text{Concentration of base}\\ \\ \left[\text{Acid}\right]\text{=}\text{Concentration of acid}\end{array}$

(c)

Interpretation Introduction

Interpretation:

Structure of lysine at $pH1$, physiological $pH$$\left(\sim 7\right)$ and $pH13$ has to be determined. 

Concept Introduction:

Acidic $\text{pH}$ means $H^{+}$ ions are available.  In other words, the concentration of $H^{+}$ ion is more.  So the base present in the system will be protonated. 

Basic $\text{pH}$ means the concentration of $H^{+}$ ion is less, the concentration of $O{H}^{-}$ ion is more.  So the acid present in the system will be deprotonated. 

Physiological $pH$$\left(\sim 7\right)$ means neutral.  The concentration of $H^{+}$ ion and $O{H}^{-}$ ion are same.  At such condition zwitterion will be formed. 

Zwitterion:

This word is used mostly in case of amino acids.  Zwitterion is a molecule with two or more functional groups, of which at least one has a positive and one has a negative electrical charge and the net charge of the entire molecule is zero. 

(d)

Interpretation Introduction

Interpretation:

The structure of glutamic acid at $\text{pH 1}$, physiological $pH$$\left(\sim 7\right)$ and $pH13$ has to be identified from the given options. 

Concept Introduction:

Acidic $\text{pH}$ means $H^{+}$ ions are available.  In other words, the concentration of $H^{+}$ ion is more.  So the base present in the system will be protonated. 

Basic $\text{pH}$ means the concentration of $H^{+}$ ion is less, the concentration of $O{H}^{-}$ ion is more.  So the acid present in the system will be deprotonated. 

Physiological $pH$$\left(\sim 7\right)$ means neutral. The concentration of $H^{+}$ ion and $O{H}^{-}$ ion are same. At such condition zwitterion will be formed.

Zwitterion:

This term is used mostly in case of amino acids.  Zwitterion is a molecule with two or more functional groups, of which at least one has a positive and one has a negative electrical charge and the net charge of the entire molecule is zero.