Chapter 18: The Representative Elements

The electrolysis of aqueous sodium chloride (brine) is an important industrial process for the production of chlorine and sodium hydroxide. In fact, this process is the second largest consumer of electricity in the United States, after the production of aluminium. Write a balanced equation for the electrolysis of aqueous sodium chloride (hydrogen gas is also produced).

Bacterial digestion is an economical method of sewage treatment. The reaction

$$\begin{gathered} {\text{5CO}}_{\text{2}}\text{(g) + 55N}{{\text{H}}_{\text{4}}}^{\text{+}}{\text{(aq) + 76O}}_{\text{2}}\text{(g)}\stackrel{Bacteria}{\to }{\text{C}}_5{\text{H}}_7{\text{O}}_2{{\text{N(s) + 54NO}}_2}^{\text{-}}{\text{(aq)52H}}_2{\text{O(I)+109H}}^{+}\text{(aq)} \\ BacterialTissue \end{gathered}$$

is an intermediate step in the conversion of the nitrogen in organic compounds into nitrate ions. What mass of bacterial tissue is produced in a treatment plant for every${\text{1.0×10}}^4\text{kg}$of wastewater containing${\text{3.0\% NH}}_{\text{4}}^{\text{+}}$ions by mass? Assume that 95% of the ammonium ions are consumed by the bacteria.

Phosphate buffers are important in regulating the$p\mathrm{H}$of intracellular fluids. If the concentration ratio of ${\text{H}}_{\text{2}}{\text{PO}}_{\text{4}}^{\text{-}}$to $\text{HP}{{\text{O}}_{\text{4}}}^{\text{2 -}}$in a sample of intracellular fluid is $\text{1.1: 1}$what is $p\mathrm{H}$the of this sample of intracellular fluid?

${\text{H}}_{\text{2}}\text{P}{{\text{O}}_{\text{4}}}^{\text{-}}\text{(aq)}\rightleftharpoons \text{HP}{{\text{O}}_{\text{4}}}^{\text{2 -}}{\text{(aq) +H}}^{\text{+}}\text{(aq)}$

${\mathit{K}}_{\mathit{a}}{\text{=6.2×10}}^{\text{-8}}$

It took 150. s for a current of 1.25 A to plate out 0.109 g

of metal from a solution containing its cations. Show

that it is not possible for the cations to have a charge

of +1.

Hydrogen gas is being considered as a fuel for automobiles. There are many chemical means for producing hydrogen gas from water. One of these reactions is

${\text{C(s) +H}}_{\text{2}}\text{O(g)}\to {\text{CO(g) +H}}_{\text{2}}\text{(g)}$

In this case the form of carbon used is graphite.

a. Calculate ${\text{ΔH}}^{°}$and${\text{ΔS}}^{°}$for this reaction using data from Appendix 4 .

b. At what temperature is${\text{ΔG}}^{°}\text{=0}$ for this reaction? Assumeanddo not depend on temperature.

Molten ${\text{CaCl}}_{\text{2}}$is electrolyzed for $8.00h$to produce $\mathrm{Ca}\left(s\right)$and data-custom-editor="chemistry" ${\text{Cl}}_{\text{2}}\text{(g)}$

a. What current is needed to produce$5.52\mathrm{kg}$of calcium metal?

b. If$5.52\mathrm{kg}$calcium metal is produced, what mass (inkg of${\text{Cl}}_{\text{2}}$is produced?

Calculate the solubility of$\text{Mg}(\text{OH}{)}_2\left({\mathit{K}}_{\text{sp}}{\text{=8.9×10}}^{\text{-12}}\right)$in an aqueous solution buffered at$\text{pH = 9.42}$ .

Which of the following statement(s) is(are) true?

a. The alkali metals are found in the earth’s crust in the form of pure elements.

b. Gallium has one of the highest melting points known for metals.

c. When calcium metal reacts with water, one of the products is ${\text{H}}_{\text{2}}\text{(g)}$.

d. When ${\text{AlCl}}_{\text{3}}$is dissolved in water, it produces an acidic solution.

e. Lithium reacts in the presence of excess oxygen gas to form lithium superoxide.

What is the hybridization of the underlined nitrogen atom in each of the following molecules or ions?

a. ${\mathrm{NO}}^{+}$

b. $N_2{O}_3\left(O_{2}N\underline{N}O\right)$

c. $\underline{N}{O}_2^{-}$

d.${\underline{N}}_2$

Nitrous oxide (${\text{N}}_{\text{2}}\text{O}$) can be produced by thermal decomposition of ammonium nitrate:

${\text{NH}}_{\text{4}}{\text{NO}}_{\text{3}}\text{(s)}\stackrel{\text{heat}}{\to }{\text{N}}_{\text{2}}{\text{O(g) + 2H}}_{\text{2}}\text{O(l)}$

What volume of ${\text{N}}_{\text{2}}\text{O(g)}$collected over water at a total pressure of $\text{94.0 kPa}$and${\text{22}}^{\text{o}}\text{C}$can be produced from thermal decomposition of ${\text{8.68 g NH}}_{\text{4}}{\text{NO}}_{\text{3}}$? The vapor pressure of water at${\text{22}}^{\text{o}}\text{C}$is$\text{22torr}$.