Chapter 19

What is the potential of a cell made up of \(\mathrm{Zn} / \mathrm{Zn}^{2+}\) and \(\mathrm{Cu} / \mathrm{Cu}^{2+}\) half-cells at \(25^{\circ} \mathrm{C}\) if \(\left[\mathrm{Zn}^{2+}\right]=0.25 \mathrm{M}\) and \(\left[\mathrm{Cu}^{2+}\right]=0.15 \mathrm{M} ?\)

Calculate the standard potential of the cell consisting of the \(\mathrm{Zn} / \mathrm{Zn}^{2+}\) half-cell and the SHE. What will the emf of the cell be if \(\left[\mathrm{Zn}^{2+}\right]=0.45 \mathrm{M}, \mathrm{P}_{\mathrm{H}_{2}}=2.0 \mathrm{~atm}\), and \(\left[\mathrm{H}^{+}\right]=1.8 \mathrm{M} ?\)

What is the emf of a cell consisting of a \(\mathrm{Pb}^{2+} / \mathrm{Pb}\) half-cell and a \(\mathrm{Pt} / \mathrm{H}^{+} / \mathrm{H}_{2}\) half-cell if \(\left[\mathrm{Pb}^{2+}\right]=0.10 \mathrm{M}\) \(\left[\mathrm{H}^{+}\right]=0.050 \mathrm{M},\) and \(\mathrm{P}_{\mathrm{H}_{2}}=1.0 \mathrm{~atm} ?\)

Explain the differences between a primary galvanic cell-one that is not rechargeable- and a storage cell (for example, the lead storage battery), which is rechargeable.

Discuss the advantages and disadvantages of fuel cells over conventional power plants in producing electricity.

The hydrogen-oxygen fuel cell is described in Section 19.6 . (a) What volume of \(\mathrm{H}_{2}(g)\), stored at \(25^{\circ} \mathrm{C}\) at a pressure of 155 atm, would be needed to run an electric motor drawing a current of \(8.5 \mathrm{~A}\) for \(3.0 \mathrm{~h} ?\) (b) What volume (liters) of air at \(25^{\circ} \mathrm{C}\) and \(1.00 \mathrm{~atm}\) will have to pass into the cell per minute to run the motor? Assume that air is 20 percent \(\mathrm{O}_{2}\) by volume and that all the \(\mathrm{O}_{2}\) is consumed in the cell. The other components of air do not affect the fuel-cell reactions. Assume ideal gas behavior.

Steel hardware, including nuts and bolts, is often coated with a thin plating of cadmium. Explain the function of the cadmium layer.

"Galvanized iron" is steel sheet that has been coated with zinc; "tin" cans are made of steel sheet coated with tin. Discuss the functions of these coatings and the electrochemistry of the corrosion reactions that occur if an electrolyte contacts the scratched surface of a galvanized iron sheet or a tin can.

Tarnished silver contains \(\mathrm{Ag}_{2} \mathrm{~S}\). The tarnish can be removed by placing silverware in an aluminum pan containing an inert electrolyte solution, such as \(\mathrm{NaCl}\). Explain the electrochemical principle for this procedure. [The standard reduction potential for the half- cell reaction \(\mathrm{Ag}_{2} \mathrm{~S}(s)+2 e^{-} \rightarrow 2 \mathrm{Ag}(s)+\mathrm{S}^{2-}(a q)\) is \(-0.71 \mathrm{~V} .]\)

How does the tendency of iron to rust depend on the \(\mathrm{pH}\) of solution?