Shipwrecks, Corrosion and Conservation

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6: Option - Shipwrecks, Corrosion and Conservation

6.1: The chemical composition of the ocean implies its potential role as an electrolyte

Identify the origins of the minerals in oceans as:

leaching by rainwater from terrestrial environments

hydrothermal vents in mid-ocean ridges

Identify - recognise and name

There are 2 major sources of the salts in seawater:

Leaching by rain and ground water.

Dissolution of salts by water passing through hydrothermal vents.

LEACHING BY RAIN AND GROUND WATER

The main ions that are dissolved as rainwater percolates through the soil and makes its way into creeks and rivers are Na, Ca, Mg, Cl and SO4.

Water that seeps down into underground aquifers dissolves greater quantities of these ions and under certain conditions (slightly lower pH than normal) picks up significant amounts of Hydrogen Carbonate (by dissolving carbonate)

Small amounts of nitrate and phosphate are also dissolved: these result from decay of plant and animal matter.

Although leaching of salts from the ground is a natural process, it has been significantly increased by human activities such as clear felling of forests, land clearing for pastoral pursuits and cultivation for crop growing.

Some underground aquifers pick up high concentrations of sodium chloride (from the many salt deposits that exist there), and these carry large amounts of salt to the oceans.

HYDROTHERMAL VENTS

Mid-ocean ridges (often containing fissures or cracks in the rock) exist near the Earth's crust.

Seawater is able to percolate down these fissures and come close to ...

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...Results:

Different metals and their corrosion rate

Metal Observation at start Observation of metal after 3 days

Aluminium Silver and shiny No change

Tin Silver and shiny No change

Zinc Silver and shiny No change

Iron Silver and shiny A coating of rust formed on the nail

Brass Gold and shiny A coating of corrosion formed on the topside of the tack and some corrosion was seen in the water.

Stainless Steel Silver and shiny No change

Plan and perform a first-hand investigation to compare the effectiveness of different protections used to coat a metal such as iron and prevent corrosion

Compare - show how things are similar or different

Gather and process information to identify applications of cathodic protection, and use available evidence to identify the reasons for their use and the chemistry involved

Identify - recognise and name

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