Consider the electrolytic procedure for purifying copper described in Figure 21.6. Suppose that a sample of copper contains the following impurities: $\mathrm{Fe}, \mathrm{Ag}, \mathrm{Zn}, \mathrm{Au}, \mathrm{Co}, \mathrm{Pt}$, and Pb . Which of the metals will be oxidized and dissolved in solution and which will be unaffected and simply form the sludge that accumulates at the bottom of the cell?