An ore is a naturally occurring rock that contains economically viable amounts of a metal.
Why do metals need to be extracted from their ores?
Metals are often found in nature as compounds, so they must be extracted to obtain them in their pure metallic form.
What determines the method used for metal extraction?
The method of extraction depends on the metal's reactivity, which can be predicted from its position in the electrochemical series.
What is the electrochemical series?
The electrochemical series is a list of metals arranged in order of their standard electrode potential (E°), indicating their reactivity.
Which metals are highly reactive and require electrolysis for extraction?
Highly reactive metals, such as potassium, sodium, and aluminium, require electrolysis for extraction.
What is the primary method used to extract aluminium?
Aluminium is extracted using electrolysis of molten aluminium oxide (Al₂O₃) dissolved in cryolite.
Why is cryolite used in the extraction of aluminium?
Cryolite lowers the melting point of aluminium oxide, reducing energy costs in the extraction process.
What is the half-equation at the cathode during aluminium extraction?
Al³⁺(l) + 3e⁻ → Al(l)
What is the half-equation at the anode during aluminium extraction?
2O²⁻(l) → O₂(g) + 4e⁻
Why do carbon electrodes in aluminium extraction need frequent replacement?
Oxygen formed at the anode reacts with carbon electrodes, forming carbon dioxide, which gradually wears them away.
Which metals are extracted using reduction with carbon?
Metals with moderate reactivity, such as iron, zinc, tin, and lead, are extracted using reduction with carbon.
What is the role of carbon in metal extraction?
Carbon acts as a reducing agent, removing oxygen from metal oxides to produce the pure metal.
Which industrial furnace is used for extracting iron?
The blast furnace is used for extracting iron from its ore.
What is the role of limestone in a blast furnace?
Limestone decomposes into calcium oxide, which reacts with impurities to form slag.
What is the overall reaction for the extraction of iron in a blast furnace?
Fe₂O₃(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)
What is the purpose of slag in iron extraction?
Slag removes impurities from the molten iron and floats on top of it.
How are unreactive metals like gold and silver extracted?
Unreactive metals are extracted by physical separation since they are often found in their native form.
How is mercury extracted from its ore?
Mercury is extracted by heating mercury(II) oxide, which decomposes into mercury metal and oxygen.
What is the definition of a reducing agent in metal extraction?
A reducing agent is a substance that donates electrons or removes oxygen from a compound during a chemical reaction.
What is the overall reaction for the extraction of aluminium?
2Al₂O₃(l) → 4Al(l) + 3O₂(g)
Explanation Questions
Why can’t highly reactive metals be extracted using carbon reduction?
Highly reactive metals have a strong affinity for oxygen and form stable oxides, making carbon reduction ineffective. Instead, electrolysis is required.
Why does electrolysis require molten or dissolved compounds?
Electrolysis requires free-moving ions to conduct electricity, which is only possible when the compounds are molten or dissolved.
Why is carbon monoxide used as a reducing agent in a blast furnace?
Carbon monoxide is a strong reducing agent that reacts with metal oxides to form pure metal and carbon dioxide.
How does the electrochemical series help determine the method of metal extraction?
Metals higher in the series require electrolysis, while those lower can be extracted using carbon reduction or direct heating.
Why does the temperature in a blast furnace need to be very high?
High temperatures ensure that the reduction reactions occur efficiently and that the extracted metal remains molten for easy collection.
Why is slag removed separately from molten iron?
Slag contains impurities removed from the ore and has a lower density, allowing it to be separated from the molten iron.
Why does gold not require extraction using chemical methods?
Gold is very unreactive and is usually found in its native form, so it can be physically separated from its ore.
What happens to the waste gases produced in a blast furnace?
Waste gases, such as carbon dioxide, are released or collected for industrial use, while hot air is recycled in the furnace.
How does the presence of impurities affect the extraction of metals?
Impurities can interfere with metal extraction and must be removed to produce pure metal. Slag formation helps in this process.
Why is aluminium more expensive to extract than iron?
Aluminium extraction requires electrolysis, which consumes large amounts of electrical energy, making it more expensive than carbon reduction used for iron.