Metals and alloys

Metals and alloys

1. Extracting copper

   • Impure copper can be purified in the lab using electrolysis cell.
   • Advantages of recycling copper are that:
     • it has a fairly low melting point so the energy cost to melt it is low
     • It reduces the need for mining, saving reserves and the environmental problems caused by mining
     • It keeps the cost of copper down
   • Disadvantages and problems of recycling copper are that:
     • the small amounts used in electrical equipment are difficult to separate
     • valuable 'pure' copper scrap must not be mixed with less pure scrap, such as solder.
     • less copper mined means fewer jobs
     • the actual separating process may produce pollution
     • a lot of copper is thrown away as it is difficult to persuade people to recycle it
   • in the purification of copper by electrolysis, an electrolyte of copper(2) sulfate solution is used.
   • The impure copper is the anode, and a sheet of pure copper is the cathode
     • The positive anode loses mass as the copper disolves
     • The negative cathode gains mass as pure copper is plated onto it.
   • The concentration of the copper(2) sulfate electrolyte stays the same because as the impure copper anode dissolves, pure copper is plated on to the cathode at the same rate.
   • At the anode, the Cu atoms lose electrons to form Cu2+ ions. This is called oxidation. The electron half equation is: Cu-2e->Cu2+
   • At the cathode, copper is plated when Cu2+ ions gain electrons. This is reduction. THe half equation is: Cu2++2e->Cu

2. Alloys

   • Alloys are mixtures containing at least one metal
   • Alloys have different properties and we match the alloy to the job we use it for. Examples include:
     • amalgam, which contains mercury (this is used for filling teeth)
     • Brass, which contains copper and zinc
     • Solder, which contains lead and tin
   • Some smart alloys return to their original shape after being heated to a certain temperature.
   • Nitinol (nickel-titanium) is a smart alloy which is used to make spectacle frames; it returns to its original shape after being bent if it is put into hot water.
   • Smart alloys are becoming more important as new ways to use them are found