Zinc Vs Copper

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In order to save expensive copper, penny coins, starting in 1983, were made of zinc with a thin layer of copper plated on the surface. If these coins are heated, the zinc will diffuse into the copper layer, producing a surface alloy of zinc and copper. These alloys are brasses. Not only does the zinc change the properties of copper, but also the color of the brasses changes with zinc content - reaching a golden yellow color at around 20% zinc and golden at 35-40% zinc. Copper also oxidizes when heated in air, producing a black layer of copper oxide (CuO). Thus when heated, there is a competition between the rate of oxidation (making the surface black) and the rate of diffusion (making the surface a golden-yellow color). Some of the zinc metal will be oxidized and enter solution as Zn+2 ions. Electrons can then be transferred from unreacted zinc metal to Zn+2 ions at the penny's copper surface. These newly reduced Zn metal atoms are deposited on the penny. Heating the zinc coated penny on a hot plate allows the zinc atoms to migrate into the copper surface. The result is an alloy, or solid solution, of zinc and copper known as brass. An alloy is a mixture (solution) of different types of atoms, generally metals. An alloy can have a variable composition, but a compound has a specific composition. The color of the post-1983…show more content…
The cell emf is also called the cell potential. The magnitude of the emf is a quantitative measure of the driving force or thermodynamic tendency for the reaction to occur. In general, the emf of a voltaic cell depends upon the substances that make up the cell as well as on their concentrations. Hence, it is common practice to compare standard cell potentials, symbolized by Eocell . These potentials correspond to cell voltages under standard state conditions-gases at 1 atm pressure, solutions at 1 M concentration, and temperature at
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