Blast Furnace: Slag Chemistry
Cambridge IGCSE Chemistry 0620 · 15 Questions · 26 Marks Total
EXAMINER SAFETY NOTE
The blast furnace operates at temperatures up to 2000 °C. Molten iron (~1500 °C) and molten slag are both extremely hazardous. Industrial workers use shielded tapping equipment. Never attempt to simulate these reactions in a school laboratory.
Section A
5 Questions
8 marks
Section B
5 Questions
8 marks
Section C
5 Questions
10 marks
Section A: Limestone Decomposition
5 questions · 8 marks
Write the symbol equation, including state symbols, for the thermal decomposition of limestone in the blast furnace.
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State the type of reaction that occurs when limestone is heated strongly in the furnace.
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Give two conditions required for the thermal decomposition of limestone to occur.
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Name the gas produced when limestone thermally decomposes.
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Explain why limestone is added to the blast furnace, rather than simply heating the iron ore alone.
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Section B: Removing Impurities & Slag
5 questions · 8 marks
Name the main non-metallic impurity found in iron ore that must be removed during iron extraction.
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Write the symbol equation, including state symbols, for the formation of slag in the blast furnace.
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Give the chemical name and formula of slag.
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Describe the physical state of slag inside the blast furnace and explain how this property allows it to be separated from molten iron.
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Suggest one large-scale industrial use of slag after it has been removed from the blast furnace.
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Section C: Acid–Base Chemistry
5 questions · 10 marks
State the type of chemical reaction that occurs when calcium oxide reacts with silicon dioxide.
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Explain, using the concepts of acidic and basic oxides, why calcium oxide reacts with silicon dioxide.
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Classify each of the following as either an acidic oxide or a basic oxide: (i) SO₃ (ii) MgO (iii) P₄O₁₀
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A student claims: 'The formation of slag in the blast furnace is just like a neutralisation reaction in aqueous solution.' Evaluate this statement, identifying ONE similarity and ONE difference between the two types of neutralisation.
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The diagram below represents a simplified blast furnace. Using your knowledge of slag chemistry: (a) Label the raw material that acts as a flux. [1] (b) Write the equation for its decomposition inside the furnace. [1] (c) State the temperature zone (top, middle, or bottom) where slag formation occurs, and explain why. [1]
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🔑 Key Equations Summary
Limestone Decomposition
CaCO₃(s) → CaO(s) + CO₂(g)
Slag Formation (Neutralisation)
CaO(s) + SiO₂(s) → CaSiO₃(l)
basic oxide + acidic oxide → salt
Cambridge IGCSE Chemistry 0620 · Topic 9.6 · Blast Furnace
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