Chapter 20

Aluminum Production What substance is electrolyzed in the industrial process to produce aluminum metal?

Write the oxidation and reduction half-reactions for a silver-chromium voltaic cell. Identify the anode, cathode, and the direction of electron flow

Corrosion Explain why water is necessary for the corrosion of iron.

Space Travel The space shuttle uses a \(\mathrm{H}_{2} / \mathrm{O}_{2}\) fuel cell to produce electricity. a. What is the reaction at the anode? At the cathode? b. What is the standard cell potential for the fuel cell?

Fuel Cells Explain how the oxidation of hydrogen in a fuel cell differs from the oxidation of hydrogen when it burns in air.

Copper Refining In the electrolytic refining of copper, what factor determines which piece of copper is the anode and which is the cathode?

Storage Batteries Lead-acid batteries and other rechargeable batteries are sometimes called storage batteries. What is being stored in these batteries?

Apply Suppose that you have a voltaic cell in which one half-cell is made up of a strip of tin immersed in a solution of tin (II) ions. a. How could you tell by measuring voltage whether the tin strip was acting as a cathode or an anode in the cell? b. How could you tell by simple observation whether the tin strip was acting as a cathode or an anode?

Hypothesize 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.

Analyze An earthen vessel was discovered in 1938 near Baghdad. This ancient vessel contained an iron bar surrounded by a copper cylinder, as shown in Figure 20.30 . When filled with an electrolyte such as vinegar, this vessel might have acted as a battery. a. Identify the cathode. b. Identify the anode. c. Calculate the standard cell potential of this battery.

Apply During electrolysis, an electrolytic cell releases bromine vapor and hydrogen gas. After electrolysis, the cell is found to contain a concentrated solution of potassium hydroxide. What was the composition of the cell before electrolysis began?

A battery is assembled using tin and mercury, which have the following reduction half-reactions: $$ \begin{array}{l}{\mathrm{Sn}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Sn}} \\\ {\mathrm{Hg}^{2+}+2 \mathrm{e}^{-} \rightarrow \mathrm{Hg}}\end{array} $$ a. Write a balanced equation for the cell's reaction. b. What is oxidized and what is reduced? Identify the oxidizing agent and the reducing agent. c. Which reaction occurs at the anode? At the cathode? d. What is the cell potential? Use Table 20.1 e. If sodium sulfate solution is in the salt bridge, in which direction do the sulfate ions move?

If the volume of a sample of chlorine gas is 8.2 \(\mathrm{L}\) at 1.2 atm and 306 \(\mathrm{K}\) , what volume will the gas occupy at STP? (Chapter 13\()\)

What is meant by solvation? Explain how this process is important for the dissolving of ionic salts in water. (Chapter 14)

Explain how the molarity of a solution is different from its molality. (Chapter 14)

Define the calorie. State how the calorie is related to the Calorie and the joule. (Chapter 15)

Explain why you would find an aluminum chair to be hotter to sit on than a wooden bench after each had been in the sunlight for the same amount of time. (Chapter 15)

What does a negative sign for the free energy of a reaction tell you about the reaction? $$ \left(\Delta G_{\text { system }}=\Delta H_{\text { system }}-T \Delta S_{\text { system }}\right)(\text { Chapter } 15) $$

According to the collision model of chemical reactions, how is it possible that two molecules can collide but not react? (Chapter 16)

List five factors that can affect the rate of a reaction. (Chapter 16)

The decomposition reaction \(\mathrm{A}_{2} \mathrm{B} \rightarrow 2 \mathrm{A}+\mathrm{B}\) proceeds to equilibrium at \(499^{\circ} \mathrm{C}\) . Analysis of the equilibrium mixture shows \(\left[\mathrm{A}_{2} \mathrm{B}\right]=0.855 \mathrm{mol} / \mathrm{L},[\mathrm{A}]=2.045 \mathrm{mol} / \mathrm{L},\) and \([\mathrm{B}]=1.026 \mathrm{mol} / \mathrm{L} .\) What is \(K_{\mathrm{eq}} ?(\text {Chapter } 17)\)

What is the solubility in mol/L of silver iodide, AgI. \(K_{\mathrm{sp}}\) for AgI is \(3.5 \times 10^{-17} .\) (Chapter 17\()\)

If you have a solution of a strong acid, is that the same as having a concentrated solution of the acid? Explain your answer. (Chapter 18)

What are the oxidation numbers for the elements in the ion \(\mathrm{PO}_{4}^{3-?}(\text { Chapter } 19)\)

Sunken Ships Study of the sunken ocean liner Titanic has opened the possibility that deterioration of the steel hull might be partly due to the presence of rusticle communities. Research how the biological activity of rusticle communities results in the oxidation of iron. Write an essay that describes the role of rusticle communities in the destruction of the Titanic.

Statue of Liberty Several years ago, the supporting structure of the Statue of Liberty became so corroded that it had to be replaced entirely. Find out what the structure was made of and why it corroded so badly. Write a report that explains the chemical processes involved and include a time line of the statue, starting in France before 1886.

Will NAD + oxidize \(\mathrm{Fe}^{2+}\) to \(\mathrm{Fe}^{3+}\) ? Explain your answer.