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Difficulty: MediumAlkaline Earth Metals: Calcium Extraction, Properties, and Compounds

Match each calcium-containing substance on the left with its correct chemical function or industrial preparation description on the right.

  • Calcium fluoride (CaF2\text{CaF}_2)Serves as a flux to lower the melting temperature of the electrolyte during the extraction of calcium.
  • Calcium oxide (CaO\text{CaO})Prepared by calcination of limestone and used as a basic drying agent for ammonia gas.
  • Calcium sulfate hemihydrate (CaSO4⋅12H2O\text{CaSO}_4\cdot\frac{1}{2}\text{H}_2\text{O})Formed by controlled heating of gypsum at 120∘C120^\circ\text{C} and sets hard upon rehydration.
  • Calcium hydroxide (Ca(OH)2\text{Ca(OH)}_2)Formed by slaking quicklime and used in aqueous solution to detect carbon(IV) oxide.

Answer

Calcium fluoride matches with serving as a flux in calcium extraction; Calcium oxide matches with calcination product of limestone used to dry ammonia; Calcium sulfate hemihydrate matches with partial dehydration product of gypsum; Calcium hydroxide matches with slaked lime used to detect carbon(IV) oxide.
Each calcium compound is correctly paired according to standard industrial practices and chemical properties: calcium fluoride lowers the electrolytic bath melting point; calcium oxide is a basic desiccant produced from limestone; calcium sulfate hemihydrate is formed by partially dehydrating gypsum; and slaked lime solution forms a precipitate with carbon(IV) oxide.

Step-by-Step Solution

1
Identify the industrial metallurgical role of calcium fluoride in calcium metal extraction.
Calcium fluoride acts as a flux in fused CaCl2\text{CaCl}_2 electrolysis to decrease the operating temperature.
Lowering the melting point improves electrical conductivity and reduces thermal energy consumption.
2
Analyze the industrial preparation and chemical nature of calcium oxide.
Thermal decomposition of CaCO3\text{CaCO}_3 yields basic CaO\text{CaO}, which does not react with basic gases like NH3\text{NH}_3.
Acidic drying agents such as concentrated H2SO4\text{H}_2\text{SO}_4 would react with ammonia, making basic quicklime the required choice.
3
Determine the formula and thermal origin of Plaster of Paris.
Controlled heating of gypsum yields calcium sulfate hemihydrate (CaSO4⋅12H2O\text{CaSO}_4\cdot\frac{1}{2}\text{H}_2\text{O}).
Heating at 120∘C120^\circ\text{C} drives off part of the water of crystallization without causing complete dehydration to anhydrous anhydrite.
4
Relate calcium hydroxide to its slaking reaction and analytical application.
Slaking CaO\text{CaO} produces Ca(OH)2\text{Ca(OH)}_2, whose aqueous solution forms an insoluble milky CaCO3\text{CaCO}_3 precipitate with CO2\text{CO}_2.
The reaction of dissolved calcium hydroxide with carbon(IV) oxide produces insoluble calcium trioxocarbonate(IV).

Key Concept

Chemical properties, industrial preparations, and extraction roles of calcium and its major compounds.
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Topics

Alkaline Earth Metals: Calcium Extraction, Properties, and Compounds

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