Chemistry - Extracting Unreactive Metals (AQA Syllabus A)

Building materials, such as limestone or metals, is one area covered in GCSE Science. This is the second of seven quizzes on that topic - and the first of two on extracting metals from the ground - and it looks in particular at extracting unreactive metals.

Metals are one of the natural materials that can be found in the ground. The extraction of unreactive metals is considerably easier than getting more reactive metals like aluminium and magnesium from their ores. The least reactive, like gold and silver, occur 'native' which means that they exist as the metal itself. Extracting them is just a matter of chipping them out of the rocks. That does require some physical effort, but it does not involve the need for any chemical reactions.

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Metals a little higher than gold and silver occur as compounds, usually the oxide, and so they need to be chemically extracted (smelted). Where natural processes have concentrated these sufficiently, we say that we have an ore. Metals can be commercially extracted from these ores.

Luckily we can use other materials to help us! The non-metal carbon is more reactive than metals like iron (which we use to make steels) and copper (which we use for things like water pipes and electrical cables). This means that it is relatively cheap and easy to obtain these metals. Simply heating the unreactive metal oxide with carbon will reduce the metal, displacing it from the ore.

Carbon comes in many forms and, for smelting metals, it was originally charcoal that was used. In fact, the discovery of smelting was probably by pure accident. Some of the ores of copper are attractive and have been used for jewellery. Imagine, a few thousand years in the past, a piece of jewellery was accidentally dropped into a wood fire. When wood burns, it leaves a lot of carbon. When the fire was cold, the owner of the jewelery would have looked for it but have only found a lump of copper.

The next step would have been to use charcoal, which contains more carbon than the ashes of wood burnt on an open fire. The first furnaces that were used to smelt iron were powered by charcoal but eventually coke, made from coal, was found to be even more effective.

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  1. What is the special name given to the process of extracting iron from iron ore in a blast furnace?
    Smelting is also applied to any metal extraction process involving heat and producing the molten metal
  2. Why can gold be found in the Earth's crust in its native state?
    Silver can also be found native, even though it is more reactive than gold
  3. Which of the following statements is correct?
    In order to obtain any metal from its oxide it has to be reduced
  4. What is the main impurity in iron from a blast furnace?
    Iron straight from the blast furnace contains about 4% carbon, which makes it very brittle
  5. During the process of smelting, what happens to copper ore?
    Most metals are extracted from a metal oxide and copper is no exception. When oxygen is removed from a chemical, we say it has been reduced
  6. Carbon can be used to remove the oxygen from copper oxide to leave the copper. This contains impurities including carbon. How is this copper purified?
    The impure copper is used as the anode. Copper ions are attracted to the cathode but the impurities are not and simply drop to the bottom of the reaction vessel
  7. It is said that by the middle of the 21st century economical copper ores will have been used up. New ways of extracting copper from low-grade ores are being researched. One of these is called phytomining. What does phytomining involve?
    When the plants are burned, the ash is high in concentration of the copper ores. This could be used for other metals too as their best ores start to run out
  8. Another idea is to dump scrap iron into solutions of copper salts. How would this work?
    Iron is more reactive than copper and would displace it from solutions of its salts
  9. Bioleaching is yet another idea for getting metals that are less reactive than aluminium from very low grade ores and wastes. What organisms are used in this process?
    There are many advantages and disadvantages of bioleaching. The process is simpler and does not require complex equipment but it is much slower than conventional methods, meaning that it takes longer for a company to earn the money back that they spent on setting it up
  10. The most common ore of tin is cassiterite, a form of tin oxide with the formula SnO2. Which of the following is a balanced equation showing the extraction of tin from this ore?
    This question tests both whether you know that tin, an unreative metal, would be extracted using carbon, and your knowledge of balancing equations

Author: Kev Woodward

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