Chemical Formula For Calcium Sulfide

Chemical Formula for Calcium Sulfide

Calcium sulfide is an ionic compound composed of calcium (Ca), a Group 2 alkaline earth metal, and sulfur (S), a Group 16 chalcogen. The chemical formula for calcium sulfide is CaS. This formula reflects the compound’s stoichiometry, where one calcium cation (Ca²⁺) is ionically bonded to one sulfide anion (S²⁻).

Structure and Bonding

Calcium sulfide adopts a crystalline structure similar to sodium chloride (NaCl), known as the rocksalt structure. In this arrangement, each Ca²⁺ ion is surrounded by six S²⁻ ions, and vice versa, forming a highly symmetric lattice stabilized by strong electrostatic forces between the oppositely charged ions.

Preparation of Calcium Sulfide

Calcium sulfide can be synthesized through several methods:
1. Direct Reaction of Elements:
Calcium and sulfur react at high temperatures (typically above 800°C) to form CaS:
[
\text{Ca} + \text{S} \rightarrow \text{CaS}
]
2. Reaction with Calcium Oxide (Quicklime):
Calcium oxide reacts with hydrogen sulfide (H₂S) gas to produce CaS and water:
[
\text{CaO} + \text{H}_2\text{S} \rightarrow \text{CaS} + \text{H}_2\text{O}
]
3. Thermal Decomposition of Calcium Sulfate (Gypsum):
At elevated temperatures, calcium sulfate (CaSO₄) reduces to CaS in the presence of carbon ©:
[
\text{CaSO}_4 + 2\text{C} \rightarrow \text{CaS} + 2\text{CO}_2
]

Properties of Calcium Sulfide

• Physical State: White to yellow solid, depending on impurities.
  
• Melting Point: ~2,500°C (decomposes before melting).
  
• Solubility: Insoluble in water but reacts with it to form calcium hydroxide (Ca(OH)₂) and hydrogen sulfide (H₂S):
  [
  \text{CaS} + 2\text{H}_2\text{O} \rightarrow \text{Ca(OH)}_2 + \text{H}_2\text{S}
  ]
  
• Reactivity: Reacts with acids to produce hydrogen sulfide gas, a toxic and flammable compound with a characteristic “rotten egg” odor.
  

Applications

Calcium sulfide has niche applications due to its unique properties:
- Luminophores: Used in phosphors for cathode ray tubes (CRTs) and fluorescent lamps.
- Desulfurization: Employed in the removal of sulfur impurities from fuels and gases.
- Chemical Synthesis: Serves as a precursor for other calcium compounds, such as calcium polysulfide.

Safety Considerations

• Toxicity: Calcium sulfide itself is relatively non-toxic, but its reaction with water or acids produces H₂S, which is highly toxic and potentially fatal in high concentrations.
  
• Handling: Requires proper ventilation and protective equipment to avoid inhalation of H₂S gas.