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The Extraction Of Metals Notes

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Unit 2: 13 The Extraction of Metals

THE EXTRACTION OF METALS The occurrence of metals in the Earth's crust:

• Metals are found in the Earth's crust, the least reactive as their elements and the more reactive as metals oxides and sulfides.

• Rocks that contain a high enough percentage of metal to be extracted commercially are ores.

• Aluminium and iron are the most abundant metals in the Earth crust.

METHODS OF EXTRACTION

Most compounds are found as OXIDES OR SULFIDES. Sulfides are converted to oxides by ROASTING IN AIR

e.g. zinc sulfide + oxygen → zinc oxide + sulfur dioxide

2ZnS(s) + 3O2(g) → 2ZnO(s) + 2SO2(g) Roasting sulfide ores produces sulfur dioxide which leads to acid rain, however this can be collected and used to manufacture sulfuric acid.

The extraction of metals involves reduction. In these reactions, the metal ions gain electrons:

• Using hydrogen as the reducing agent (for tungsten)

• Electrolysis (aluminium from purified bauxite)

• Using a more reactive metal (titanium from TiO2 via TiCl4)

• Using carbon and carbon monoxide as the reducing agents (for extracting, iron, copper and manganese) Which method is used depends on;

1. the energy requirements - extraction uses large amounts of energy

2. the cost of the reducing agent - carbon (in the form of coke) is cheap and widely used but more reactive metals are more expensive

3. the metal purity required - the higher the required purity, the greater its cost.

Recycling metals: Recycling metals;
> saves resources (e.g. metal ores)
> creates less waster (e.g. mining waste)
> saves energy resources (less energy needed to recycle than to extract from ores)
> reduces air pollution (e.g. CO2 and SO2 and CO) However there are costs associated with sorting and transporting metals to be recycled. RECYCLE COPPER by reacting scrap copper with sulphuric acid or a specific enzyme to form solutions containing Cu2+(aq).
-The copper can be extracted by reaction with scrap iron. Cu2+(aq) + Fe(s) → Cu(s) + Fe2+(aq)

CHEMISTRY AS NOTES

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