Acid-Base Equilibria

The molecular scene depicts the relative concentrations of ${\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}$  (purple) and ${\mathbf{\text{OH}}}^{\mathbf{\text{ - }}}$ (green) in an aqueous solution at ${\mathbf{25}}^{\mathbf{0}}\mathit{C}$. (Counter ions and solvent molecules are omitted for clarity.) 

(a) Calculate the pH. 

(b) How many  ${\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}$ ions would you have to draw for every ${\mathbf{\text{OH}}}^{\mathbf{\text{ - }}}$ ion to depict a solution of pH 4?

Polymers are not very soluble in water, but their solubility increases if they have charged groups. 

(a) Casein, a milk protein, contains many ${\mathbf{\text{COO}}}^{\mathbf{\text{ - }}}$ groups on its side chains. How does the solubility of casein vary with pH?

 (b) Histones are proteins essential to the function of DNA. They are weakly basic due to the presence of side chains with ${\mathbf{\text{ - NH}}}_{\mathbf{\text{2}}}$ and =NH groups. How does the solubility of a histone vary with pH?

Hemoglobin (Hb) transports oxygen in the blood:

${\mathbf{\text{HbH}}}^{\mathbf{\text{ + }}}{\mathbf{\text{(aq) + O}}}_{\mathbf{\text{2}}}{\mathbf{\text{(aq) + H}}}_{\mathbf{\text{2}}}{\mathbf{\text{O(l)nHbO}}}_{\mathbf{\text{2}}}{\mathbf{\text{(aq) + H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}\mathbf{\text{(aq)}}$

In blood, ${\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}$ is held nearly constant at ${\mathbf{\text{4×10}}}^{\mathbf{\text{ - 8}}}\mathbf{\text{M}}$ .

(a) How does the equilibrium position change in the lungs? 

(b) How does it change in O2-deficient cells? 

(c) Excessive vomiting may lead to metabolic alkalosis, in which [${\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}$] in blood decreases. How does this condition affect the ability of Hb to transport ${\mathbf{\text{O}}}_{\mathbf{\text{2}}}$ ?

 (d) Diabetes mellitus may lead to metabolic acidosis, in which [${\mathbf{\text{H}}}_{\mathbf{\text{3}}}{\mathbf{\text{O}}}^{\mathbf{\text{ + }}}$] in blood increases. How does this condition affect the ability of Hb to transport ${\mathbf{\text{O}}}_{\mathbf{\text{2}}}$?

Nitrogen is discharged from wastewater treatment facilities into rivers and streams, usually as ${\text{NH}}_{\text{3}}$ and ${\mathbf{\text{NH}}}_{\mathbf{4}}$ :
${\mathbf{\text{NH}}}_{\mathbf{\text{3}}}{\mathbf{\text{(aq) + H}}}_{\mathbf{\text{2}}}\mathbf{\text{O(l)}}\mathbf{\rightleftharpoons }{\mathbf{\text{NH}}}_{\mathbf{\text{4}}}^{\mathbf{\text{ + }}}{\mathbf{\text{(aq) + OH}}}^{\mathbf{\text{ - }}}\mathbf{\text{(aq)}}\mathbf{ }\mathbf{ }\mathbf{ }{\mathbf{\text{K}}}_{\mathbf{\text{b}}}{\mathbf{\text{ = 1.76×10}}}^{\mathbf{\text{ - 5}}}$

One strategy for removing it is to raise the pH and “strip” the ${\mathbf{\text{NH}}}_{\mathbf{\text{3}}}$ from solution by bubbling air through the water. 

(a) At pH=7.00, what fraction of the total nitrogen in solution is  ${\mathbf{\text{NH}}}_{\mathbf{\text{3}}}$, defined as  $\left[{\text{NH}}_{\text{3}}\right]\mathbf{\text{/}}\left(\left[{\text{NH}}_{\text{3}}\right]\text{ + }\left[\text{N}{{\text{H}}_{\text{4}}}^{\text{ + }}\right]\right)$ 

 (b) What is the fraction at pH 10.00 ? 

(c) Explain the basis of ammonia stripping.

Kevlar®, a polymeric aromatic amide, is synthesized from the monomers p-phenylenediamine (left) and terephthaloyl chloride (right). The polymer strands are initially aligned randomly, but they are dissolved and spun to give a lightweight, flexible product that is five times stronger than steel of the same weight

The first step in the reaction of an amine with an acid chloride is

(a) Describe this step in terms of a Lewis acid-base reaction. 

(b) Would you expect water or ammonia to react faster with an acid chloride? Explain