Chemistry · Ch 5 — Alkali and Alkaline Earth Metals
Important Compounds of Calcium: Quick Lime (CaO)
Important Compounds of Calcium: Quick Lime (CaO)
Preparation. Quick lime, CaO, is produced on a commercial scale by heating limestone in a lime kiln (Figure 5.10) over the temperature range 1070-1270 K: CaCO₃ ⇌ CaO + CO₂. Since this reaction is reversible, the carbon dioxide produced is continuously removed as it forms, which drives the reaction to completion.
Properties. Calcium oxide is a white, amorphous solid with a melting point of 2870 K.
- It absorbs both moisture and carbon dioxide on exposure to the atmosphere: CaO + H₂O → Ca(OH)₂ and CaO + CO₂ → CaCO₃.
- Adding a limited amount of water breaks up a lump of lime -- this process is called slaking of lime, and the product is slaked lime: CaO + H₂O → Ca(OH)₂.
- A mixture of quick lime (CaO) and sodium hydroxide is called soda lime.
- CaO combines with acidic oxides such as SiO₂ and P₄O₁₀, e.g. CaO + SiO₂ → CaSiO₃ and 6CaO + P₄O₁₀ → 2Ca₃(PO₄)₂. …
What this figure shows. A schematic cutaway of an industrial lime kiln: a mixture of limestone and coal (fuel) is fed in at the top, air is blown in near the base, waste gas (CO2) escapes from the top, and the finished quick lime (CaO) is drawn off at the bottom -- illustrating the continuous heating that drives CaCO3 → Ca …