Learning focus
Develop precise chemical explanations, connect observations to reactivity and structure, interpret industrial and environmental processes, and apply evidence to unfamiliar contexts.
Thermal decomposition
Limestone decomposes in the hot furnace: CaCO3 -> CaO + CO2. Calcium oxide is a basic oxide.
Removing silica
Silicon dioxide is an acidic impurity in the ore. It reacts with calcium oxide: CaO + SiO2 -> CaSiO3. Calcium silicate is the slag.
Separation
Molten slag is less dense than molten iron and forms an upper layer, allowing separate tapping. This is a chemical purification step followed by physical separation.
Uses and waste
Slag may be used in road construction or cement-related products, reducing waste. The exact commercial use depends on composition and standards.
High-value recall and connections
Essential recall: Write the limestone decomposition equation. CaCO3 -> CaO + CO2. What type of oxide is CaO? A basic oxide. Name the slag. Calcium silicate, CaSiO3. Practical connection: Arrange cards showing limestone decomposition, acid-base oxide reaction and density separation into the correct order. Examination connection: The impurity removed is silicon dioxide, and the slag is calcium silicate.
Practical or data skill
Arrange cards showing limestone decomposition, acid-base oxide reaction and density separation into the correct order.
Examination tip
The impurity removed is silicon dioxide, and the slag is calcium silicate.
Review questions and suggested answers
Question 1
Write the limestone decomposition equation.
Suggested answer
CaCO3 -> CaO + CO2.
Question 2
What type of oxide is CaO?
Suggested answer
A basic oxide.
Question 3
Name the slag.
Suggested answer
Calcium silicate, CaSiO3.
