Extraction of Metals
From ZuluNotes - Free Leaving Cert Notes
There are two aspects to this section of the higher option: the study and extraction of strongly electropositive metals and the study of d-block metals.
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Strongly Electropositive Metals
From your chapter on electrochemistry, you should already be familiar with the electrochemical series and its applications. Elements near the top of the scale are very difficult to find naturally and the process of electrolysis is used to extract most of these. For your course, you need to be familiar with the extraction of sodium and aluminium.
Extraction of Sodium
- Used in street lighting
- Extracted using the Downs cell
- Calcium chloride added to lower melting point
- Large electric current
- Negative electrode: 2Na+ + 2e- gives 2Na
- Positive electrode: 2Cl- gives Cl2 + 2e-
- Carbon anode is used to prevent reaction between chlorine and steel
- Chlorine gas is an important by-product
Extraction of Aluminium
There are two parts to this process: the extraction of aluminium oxide from bauxite, and the electrolysis of Al2O3 to give pure aluminium.
Obtaining Al2O3 from bauxite
- The bauxite is crushed and mixed with water and hot sodium hydroxide
- The mixture is subjected to high heats and pressures to form sodium aluminate
- Flour is added to the mixture and the impurities are precipitated out
