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Gold

Learning objectives

Students will reinforce their understanding of the reactivity series and use it to identify ancient artefacts.

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Curriculum link

� 9f patterns of reactivity - identify some metals that corrode readily and some that do not; make connections between reactivity of metals and aspects of their use.
� 9e reactions of metals and metal compounds – identify evidence that indicates that a chemical reaction has taken place.

Running the activity

Suggested time: 20 minutes.

Possible starter:
Show page 1 – either projected or as an OHT. Let students read the news story.

Main activity:
Show page 2. This page must be shown in colour, as it has pictures of six ancient artefacts, each made from a different metal. Tell students that they will be identifying the metals that the artefacts are made from . . . But first they must solve the puzzle on page 3 to put the six metals of the artefacts in order of reactivity. When students have worked out the order of reactivity (aluminium, iron, lead, copper, silver, gold), ask them, in groups, to identify the metals on page 2. They will need to look at the colours of the metals, as well as the extent to which they have corroded – the more reactive the metal, the more corroded it is. Then tell students to plan exactly what to tell the teenagers who found the artefacts in order that they are ready for their TV appearance.

The metals are:
Soft drinks can – aluminium (aluminium is very reactive, but it appears inert as its surface is covered in a layer of unreactive aluminium oxide.
Plate – silver (it is only very slightly corroded as silver is the second least reactive metal of those being considered)
Sword – iron (it is rust coloured, and very corroded since iron is the second most reactive of the metals being considered)
Coins – copper (they are copper coloured and slightly corroded with green 'verdigris' on their surface)
Bracelet – gold (it has not corroded at all – gold is the least reactive of the metals being considered)
The final picture is a Roman 'curse' made out of lead. Roman people used to scratch curses onto small pieces of lead. The lead is quite heavily corroded, as lead is one of the more reactive metals being examined today.

Some students might be interested to know about the workings of a metal detector:
The machine is switched on, and the 'search head' is slowly swept across the ground in front as you walk. When an audible signal is heard in the earpiece, stop! Advanced models will display the metal type, and its depth.

Current oscillates fast in the outer coil in the 'search head'. So a magnetic field goes in and out of the ground. Any metals will have a flow of current induced by the magnetism. This makes its own magnetic field, detectable by the inner coil in the search head, a bit later than the original current. The time difference is called the 'phase shift'. Excellent conductor metals, such as copper, silver, gold, give longer 'phase shifts'. And the thicker they are the better.

Plenary:
Ask some groups to tell the class what they plan to tell the teenagers.

Possible extension:
� researching types of detectors. (This links to Unit 9I Energy and Electricity, in which pupils should be able to describe an electrical generator)
� burying metals for a term, and checking the corrosion effects of the soil.

Web links

News links

The Guardian

See this article for the Guardian's report of the find.

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