In the discussion on the composition of air, mention is made of the fact that water vapor may have a concentration as high as 40,000 ppm. Calculate the partial pressure exerted by water vapor at this concentration. Assume that this represents a situation with 100% humidity. What temperature would be needed to achieve this value?

Silver ions have long been known to have biocidal properties. The increasing use of silver for this purpose has led to greater silver concentrations in waste water, and there has been several concern regarding it. However, recent studies revealed that the silver was largely put back into the environment as ${Ag}_2 {~S}$. The solubility of this sulfide is $1.4 \times 10^{-4} {~g} / {L}$.

(a) Calculate the $K_{\text {sp }}^{\prime}$ for ${Ag}_2 {~S}$.

(b) How does the solubility of ${Ag}_2 {~S}$ change as the pH decreases?

A 2010 article in Science magazine described "Sewage Treatment with Anammox." The authors noted that "Fixed nitrogen such as ammonium and nitrate [ions] should be removed [from sewage] to avoid toxic algal blooms in the environment." One approach to removing ammonium ions is to use ammonium-oxidizing (anammox) bacteria. Two (unbalanced) reactions that are involved are:

$$\begin{aligned} & {NH}_4{ }^{+}({aq})+{NO}_2{ }^{-}({aq}) \rightarrow {N}_2({~g})+{H}_2 {O}(\ell) \\ & {NH}_4{ }^{+}({aq})+{O}_2({~g}) \rightarrow {NO}_2{ }^{-}({aq})+{H}_2 {O}(\ell) \end{aligned}$$

Balance these two equations in acid solution.

Calculate the mass of Mg that could be obtained by the process described in previous study question from 1.0 L of seawater. To prepare 100. kg of Mg, what volume of seawater would be needed? (The density of seawater is 1.025 g/cm$^3$.)

Although there are a number of magnesium containing minerals, the commercial source of this metal is seawater. Treatment of seawater with Ca(OH)$_2$ gives insoluble Mg(OH)$_2$. This reacts with HCl to produce MgCl$_2$, which is dried, and the metal is obtained by electrolysis of the molten salt. Write balanced net ionic equations for the three reactions described here.

In any solution, there must be a balance between the positive and negative charges of the ions that are present. Use the data in Table 20.2 to determine how close to a balance of charge is achieved for the ions in seawater. (The table lists only the major ions in seawater, and the balance between positive and negative charge will only be approximate.)

The potential of a half-cell varies with concentration of reactants and products. For this reason, standard potentials are measured at 1M concentration. Maintaining a pressure of 1 atm is especially important in half-cells that involve gases as reactants or products. Suggest a reason why gas pressure is critical in these cells.

For the following exercises, use the given rational function to answer the question. The concentration C of a drug in a patient’s bloodstream t hours after injection in given by $C(t)=\frac{2 t}{3+t^{2}}.$ What happens to the concentration of the drug as t increases?

For the following exercise, use the given rational function to answer the question.
The concentration $C$ of a drug in a patient's bloodstream $t$ hours after injection in given by $C(t)=\frac{2 t}{3+t^2}$. What happens to the concentration of the drug as $t$ increases?

For the following question,

Use the given rational function to answer the question.

The concentration $C$ of a drug in a patient's bloodstream $t$ hours after injection in given by $C(t)=\frac{2 t}{3+t^2}$. What happens to the concentration of the drug as $t$ increases?

Suppose you have three solutions with different concentrations of particles. Relative to the concentration of particles in a cell, one solution is isotonic, oneis hypertonic, and one is hypotonic. Use this information to answer the next two questions.

Which solution has the highest concentration of water molecules?

The concentration of the Sn$^{2+}$ solution used in previous problem can be found by letting it react with a known amount of Fe$^{2+}$. What is the molar concentration of an Sn$^{2+}$ solution if 23.84 mL is required for complete reaction with 1.4855 g of Fe$_2$O$_3$?

The rate constant for the second-order reaction 2 NOBr $\to$ 2 NO + Br2 is 0.80/M·s at 10°C.
(a) Starting with a concentration of 0.086 M, calculate the concentration of NOBr after 22 s. (b) Calculate the half-lives when [NOBr]$_0$ = 0.072 M and [NOBr]$_0$=0.054 M.

If $t$ is in minutes since the drug was administered, the concentration, $C(t)$ in $\mathrm{ng} / \mathrm{ml}$, of a drug in a patient's bloodstream is given by

$$C(t)=20 t e^{-0.03 t} .$$

(b) What is the concentration of the drug in the body after 15 minutes? After an hour?