Chem4 Flashcards
What is the primary ore used in aluminum extraction and its chemical formula?
Bauxite, with the chemical formula Al₂O₃.
Why is cryolite (NaAlF₆) added to the mixture during aluminum extraction?
It acts as a solvent for bauxite, allowing the aluminum oxide to dissolve for electrolysis.
What role does fluorspar (CaF₂) play in aluminum extraction?
It acts as a flux, reducing the mixture’s melting point from 2045°C to 950°C, saving energy.
What material is used for the anode in aluminum extraction, and what happens there?
Graphite bars; oxidation occurs, producing O₂ gas:
Al₂O₃ → 2Al³⁺ + 3O²⁻ → 3/2O₂ + 6e⁻.
What material is used for the cathode, and what forms there?
An iron container lined with graphite; molten aluminum (Al) deposits via reduction:
2Al³⁺ + 6e⁻ → 2Al(l).
Write the total reaction for aluminum extraction.
2Al³⁺ + 3O²⁻ → 2Al(l) + ³⁄₂O₂(g).
Why do graphite anodes need periodic replacement?
Oxygen reacts with graphite, forming CO/CO₂ gases, eroding the bars:
2C(s) + ³⁄₂O₂(g) → CO(g) + CO₂(g).
What modern alternative improves upon cryolite in aluminum extraction?
A mixture of Na, Ca, and Al fluoride salts—lower melting point and density.
How does the modern fluoride salt mixture improve efficiency?
- Lower melting point saves energy.
- Lower density eases molten aluminum separation.
Where does metal deposition occur in all electrolysis experiments?
At the cathode (reduction site).
What gas evolves at the anode during aluminum extraction?
Oxygen gas (O₂).
Why is the high melting point of pure Al₂O₃ a problem?
Melting it alone requires excessive energy (2045°C); cryolite/fluorspar reduce this to 950°C.
