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Metal Extraction Concepts

Key Concepts

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Example 1

Question: A particular rock is known to contain iron minerals and calcium minerals.
On heating in a charcoal fire, the rock will ooze liquid iron.
Why doesn't the rock also ooze liquid calcium?

Response:

  1. Refer to the activity series of metals:

    potassium > calcium > sodium > magnesium > aluminium > zinc > iron > nickel > tin > lead > copper > silver > platinum > gold
  2. Determine which of the elements is more active (reactive).

    Calcium occurs before iron in the activity series so calcium is the more active metal.

  3. Infer the relative stability of the compounds each metal will form.

    More active metals form more stable compounds than less active metals.

    Calcium will form more stable compounds than iron.

  4. Infer the relative amount of energy required to extract each metal from its compound.

    The more stable the compound, the more energy is required to extract the metal from the compound.

    Calcium forms more stable compounds than iron, so it will require more energy to extract calcium from its compounds than to extract iron from its compounds.

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Example 2

Question: In some rivers in the world it is possible to "pan" for gold.
Sediment from the riverbed is placed in the pan along with some water.
The pan is swirled to float the lighter sediment in the water, and this water is then discarded.
More water is added to the pan then swirled again, and once more the water is discarded.
This continues until the very small pieces of dense gold can be picked out of the remaining sediment.
Why is it possible to pan for gold but not to pan for aluminium?

Response:

  1. Refer to the activity series of metals:

    potassium > calcium > sodium > magnesium > aluminium > zinc > iron > nickel > tin > lead > copper > silver > platinum > gold

  2. Determine which of the elements is more active (reactive).

    Aluminium occurs before gold in the activity series so aluminium is the more active metal.

  3. Infer the relative stability of the compounds each metal will form.

    More active metals form more stable compounds than less active metals.

    Aluminium will form more stable compounds than gold, indeed gold is so unreactive that it rarely forms compounds and is often found in nature as the uncombined element.

    Aluminium is so active (reactive) that it is only found in nature as compounds, never as the uncombined element.

  4. Since panning requires the metal to be in its elemental or native form, it is possible to pan for gold but it is not possible to pan for aluminium because aluminium will only be found in nature in compounds.

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Example 3

Question: A museum curator has been presented with a fine aluminium ring said to have been removed from the finger of an ancient Egyptian mummy.
Why would the museum curator believe this ring to be a fake ancient artefact?

Response:

Aluminium is a highly reactive metal.

It forms very stable compounds.

Because it forms very stable compounds it requires enormous amounts of energy to extract it from its ores.

Electricity can be used to supply the energy required to extract aluminium from its ores.

The ancient Egyptians would not have been able to supply enough energy (electricity) in order to extract the aluminium from its ores.

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