Chemistry - Extracting Reactive Metals (AQA Syllabus A)

In GCSE Science students will look at some of the materials used in building, such as limestone or metals. This is the third of seven quizzes on that topic - and the second of two on extracting metals from the ground - and it looks in particular at extracting reactive metals.

The rocks of the Earth's crust contain metals in the form of metal compounds like iron oxide and aluminium oxide. These are often mixed with other substances and where they occur in a high enough concentration, we call them ores. An ore is a rock from which a metal can be extracted economically.

Ores are mined from the ground on a large scale. They often need to be concentrated even more before the metal is extracted and purified. The economics of using a particular ore may change over time. For example, as a metal becomes rarer, an ore that only has a low concentration of the metal may be used when it was previously considered too expensive to mine.

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Many ores are the oxides of a metal and when metal oxides are reduced (have their oxygen removed), the metal is left. How this is done depends on the reactivity of the metal. The extraction of reactive metals like aluminium is usually carried out by using electrolysis. That is relatively easy nowadays, there is plenty of electricity available and so aluminium is a commonly used metal.

But this wasn't always the case. Aluminium ore is extremely difficult to melt and before the 'easy' method of melting it had been discovered, the only way of producing aluminium was to displace it from its compounds using an even more reactive metal. So only very rich people could afford things made from aluminium - in fact one of the ways that they showed off their wealth in the middle of the nineteenth century was to provide dinner guests with cutlery made from aluminium instead of silver!

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  1. What is an ore?
    Ores of reactive metals need to be purified before they can be reduced
  2. What is the usual method of extracting a reactive metal from its purified ore?
    The ore needs to be molten in order for it to conduct electricity
  3. What is the correct order of these sentences which briefly describe the process used to extract a reactive metal like aluminium?

    1. Electrodes are placed into the molten ore.
    2. The ore is purified and melted.
    3. The molten metal can be tapped off and cast into ingots.
    4. The metal ions are deposited as molten aluminium.
    Once the ingots have cooled and solidified, they can be shaped into useful objects or melted and mixed with other metals to make alloys
  4. Why do the ores of reactive metals need to be molten during the extraction process?
    Metal compounds are ionically bonded so electricity can only pass through if they are in liquid form or dissolved in water. Dissolving them in water is no good as reactive metals will react with water so the only option is to melt the ore
  5. During the electrolysis of a reactive metal ore, which electrode attracts the metal ions?
    Metal ions are positively charged and therefore are always attracted to the cathode which is the negative electrode. There is no such thing as a neutral electrode
  6. Why can you not obtain group I and group II metals by heating their oxide with carbon?
    Carbon is used to displace metals from their ores so if the metal is more reactive than carbon, the carbon will not be able to displace it
  7. Titanium is a stronger and lighter metal than iron. Apart from the fact that iron is more abundant in the Earth's crust, why do we not use it instead?
    Like aluminium, titanium forms a thin oxide coating that protects it from further corrosion
  8. To extract titanium, the ore (titanium dioxide) is converted to titanium chloride which is then reacted with magnesium at 800oC. The magnesium combines with the chloride, leaving the titanium metal on its own. The reaction of magnesium with the titanium chloride is an example of what sort of reaction?
    The extraction of titanium needs to take place away from oxygen and so it is carried out in an argon atmosphere
  9. What does the displacement reaction of magnesium with the titanium chloride tell you about titanium and magnesium?
    Since magnesium displaces titanium form titanium chloride, magnesium must be more reactive than titanium
  10. Which of the following metals could also be used to displace titanium from its chloride?
    It is likely that you don't know where titanium fits in the reactivity series but that doesn't matter. You know from question 8 that magnesium works, so all you need to do is to look at the list of possible answers for a metal higher than magnesium in the reactivity series. Examiners will sometimes throw in questions like this to check how much you really understand about the subject, rather than just testing your knowledge of facts

Author: Kev Woodward

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