Chemistry The Science in Context

Thomas R. Gilbert

Chapter 4 Reactions in Solution: Aqueous Chemistry in Nature - all with Video Answers

Educators

Dilution of Adult-Strength Cough Syrup A standard dose of an over-the-counter cough suppressant for adults is $20.0 \mathrm{mL} .$ A portion this size contains $35 \mathrm{mg}$ of the active pharmaceutical ingredient (API). Your pediatrician says you may give this medication to your 6-year-old child, but the child may take only $10.0 \mathrm{mL}$ at a time and receive a maximum of 4.00 mg of the API. What is the concentration in $\mathrm{mg} / \mathrm{mL}$ of the adult-strength medication, and how many millimeters of it would you need to dilute to make 100.0 mL of child-strength cough syrup?

David Collins

Numerade Educator

03:55

Problem 31

The concentration of $\mathrm{Na}^{+}$ in seawater, $0.481 M,$ is higher than in the cytosol, the fluid inside human cells $(12 \mathrm{mM})$ How much water must be added to 1.50 mL of seawater to make the $\mathrm{Na}^{+}$ concentration equal to that found in the cytosol? Assume the volumes are additive.

Rocket Fuel in Drinking Water Near Las Vegas, NV, improper disposal of perchlorates used to manufacture rocket fuel has contaminated a stream that flows into Lake Mead, the largest artificial lake in the United States and a major supply of drinking and irrigation water for the American Southwest. The EPA has proposed an advisory range for perchlorate concentrations in drinking water of 4 to $18 \mu \mathrm{g} / \mathrm{L} .$ The perchlorate concentration in the stream averages $700.0 \mu \mathrm{g} / \mathrm{L},$ and the stream flows at an average rate of 161 million gallons per day
$(1 \mathrm{gal}=3.785 \mathrm{L})$
a. What are the formulas of sodium perchlorate and ammonium perchlorate?
b. How many kilograms of perchlorate flow from the Las Vegas stream into Lake Mead each day?
c. What volume of perchlorate-free lake water would have to mix with the stream water each day to dilute the stream's perchlorate concentration from 700.0 to
$4 \mu g / L ?$
d. since $2003,$ Maryland, Massachusetts, and New Mexico have limited perchlorate concentrations in drinking water to $0.1 \mu \mathrm{g} / \mathrm{L} .$ Five replicate samples were analyzed for perchlorates by laboratories in each state, and the following data $(\mu \mathrm{g} / \mathrm{L})$ were collected:
$$\begin{array}{ccc}
\mathrm{MD} & \mathrm{MA} & \mathrm{NM} \\
\hline 1.1 & 0.90 & 1.2 \\
\hline 1.1 & 0.95 & 1.2 \\
\hline 1.4 & 0.92 & 1.3 \\
\hline 1.3 & 0.90 & 1.4 \\
\hline 0.9 & 0.93 & 1.1 \\
\hline
\end{array}$$
Which of the labs produced the most precise analytical results?

David Collins

Numerade Educator

11:14

Problem 132

Acidic Mine Drainage Water draining from abandoned mines on Iron Mountain in California is extremely acidic and leaches iron, zinc, and other metals from the underlying rock (Figure $\mathrm{P} 4.132$ ). One liter of drainage contains as much as $80.0 \mathrm{g}$ of dissolved iron and $6 \mathrm{g}$ of zinc.
a. Calculate the molarity of iron and of zinc in the drainage.
b. One source of the dissolved iron is the reaction between water containing $\mathrm{H}_{2} \mathrm{SO}_{4}$ and solid $\mathrm{Fe}(\mathrm{OH})_{3} .$ Complete the following chemical equation, and write a net ionic equation for the process.
$$
2 \mathrm{Fe}(\mathrm{OH})_{3}(s)+3 \mathrm{H}_{2} \mathrm{SO}_{4}(a q) \rightarrow
$$
c. Sources of zinc include the mineral smithsonite, $\mathrm{ZnCO}_{3} .$ Write a balanced net ionic equation for the reaction between smithsonite and $\mathrm{H}_{2} \mathrm{SO}_{4}$ that produces $\mathrm{Zn}^{2+}(a q)$
d. One member of a class of minerals called ferrites is found to contain a mixture of zinc(II), iron(II), and iron(III) oxides. The generic formula for the mineral
is $\mathrm{Zn}_{x} \mathrm{Fe}_{1-x} \mathrm{O} \cdot \mathrm{Fe}_{2} \mathrm{O}_{3} .$ If acidic mine waste flowing
through a deposit of this mineral contains $80 \mathrm{g}$ of $\mathrm{Fe}$ and $6 \mathrm{g}$ of $\mathrm{Zn}$ as a result of dissolution of the mineral, what is the value of $x$ in the formula of the mineral in the deposit?
PICTURE CANT COPY

Nitrogen-Fixing Bacteria Bacteria found among the roots of legumes perform an important biological function, converting nitrogen to ammonia in a process known as nitrogen fixation. The electrons required for this redox reaction are supplied by transition metal-containing enzymes called nitrogenases. The unbalanced chemical equation for this process is $\mathrm{N}_{2}(g)+\mathrm{H}^{+}(a q)+\mathrm{M}^{2+}(a q) \rightarrow \mathrm{NH}_{3}(a q)+\mathrm{H}_{2}(g)+\mathrm{M}^{3+}(a q)$
where M represents a transition metal such as iron. Nitrification is a multistep process in which the nitrogen in organic and inorganic compounds is biochemically oxidized. Bacteria and fungi are responsible for a part of the nitrification process described by the reaction:
$$
\mathrm{NH}_{4}^{+}(a q)+\mathrm{M}^{3+}(a q) \rightarrow \mathrm{NO}_{2}^{-}(a q)+\mathrm{M}^{2+}(a q)
$$
a. What are the oxidation numbers of nitrogen in the reactants and products of each reaction?
b. Which compounds or ions are being reduced in each reaction?
c. Balance the equations in acidic solution.

Oluwapelumi Kolawole

Numerade Educator