Creating copper – a displacement reaction demonstration

Creating copper – a displacement reaction demonstration


Millions of tons of copper are extracted every year. It’s valued for its relatively high conductivity and low reactivity, making it ideal for use in, amongst other things, electrical wiring and piping for heating and drinking water. We can’t rely on just finding lots of copper lying around though; copper occurs naturally in the Earth’s crust as a range of compounds of copper with sulfur, oxygen and other elements. If there’s enough copper to make it worthwhile extracting the rock is known as an ore. We get to the copper in a type of reaction called reduction. Today we’ll be demonstrating this process with zinc. We start with some powered copper oxide and zinc. Masses, volumes and equipment lists can be downloaded from the EIC website (link beneath). The thoroughly mixed powders are laid out on a clean tin lid and shaped into a line or sausage shape. The end of the line can be lit with a roaring Bunsen. Now what happens next can depend on your supply of zinc. Sometimes at this scale the glow will need to be chased up the length of the line with the Bunsen. Other samples of zinc might get the reaction going under its own steam. Look out for the characteristic green colour in the flame from the copper. You can sometimes get, though, quite ‘sparky’ zinc, so the use of a safety screen is appropriate. Either way, make sure you practice ahead of time so you know what to expect from your stock. As the reaction cools it’s worth noting the presence of the yellow solid on the surface – a sign that zinc oxide is present. In terms of what’s happened in the reaction, the copper started in a compound with the oxygen – copper oxide. Zinc, a more reactive element sometimes said to have a higher activity, steals the oxygen away from the copper. The zinc is oxidised to zinc oxide and the copper in the copper oxide is reduced to the metal. Zinc oxide is thermochromic; it changes from a white solid to yellow on heating, as can be shown by heating a separate sample in a borosilicate tube. On cooling it returns to white and the same thing happens to the material on the surface of our freshly prepared block of copper. But how to get rid of the unreacted zinc and the zinc oxide? Placing in 2 molar hydrochloric acid for about 20 minutes brightens up the color significantly and it takes a much more ‘coppery’ appearance. When acids react with metal oxides, they form the metal compound known as a salt, and water. You can think about it as the zinc and hydrogen swapping places, or the oxygen and the chlorine swapping places. The copper conducts electricity, but for it to be useful in wiring we need the purity to be much higher. One way to accomplish this is through electrolysis. The copper from the impure block dissolves into solution as a current is passed through and moves through the solution as positively charged particles called ions. They themselves turn back into copper on the other electrode, which slowly builds up with the pure copper over time.

6 Comments

  1. Copper and I got a looooong history together.

    I remember being 14 and robbing pipes, wiring spools and boilers to sell to the scrap yard. Good times.

  2. if chemist can't do it. No one can. Tshirt, hoodies and mugs
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  3. Isn't Zinc being reduced because it is gaining electrons and isn't copper being oxidized because it is losing electrons? Please help!

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