Chemistry

Calcium Hydrosulfide

Calcium Hydrosulfide

Calcium hydrosulfide is the chemical compound with the formula Ca(HS)2 or CaH2S2. It is an inorganic chemical compound consisting of calcium cations (Ca²⁺) and hydrosulfide anions (HS⁻). It is formed from the reaction of calcium hydroxide or calcium carbonate with hydrogen sulfide:

Ca(OH)2 + 2 H2S → Ca(HS)2 + 2 H2O

CaCO3 + 2 H2S → Ca(HS)2 + H2O + CO2

It is a less commonly encountered compound compared to calcium sulfide (CaS) or calcium sulfate (CaSO₄), but it plays a role in certain industrial and geochemical processes.

Properties

  • Chemical formula: Ca(SH)2
  • Molar mass: 105.922383 g/mol
  • Appearance: Usually exists in solution; not commonly found in pure solid form
  • Solubility: Soluble in water, forming a strongly basic solution
  • Odor: Rotten egg smell (due to release of hydrogen sulfide, H₂S)
  • Stability: Unstable in air; decomposes easily to calcium sulfide (CaS) and H₂S gas
  • pH: Basic (due to hydrolysis of HS⁻ to OH⁻ and H₂S)
  • Toxicity: Toxic by inhalation due to H₂S; corrosive

Chemical Behavior

Reaction with acids: Ca(HS)2 + 2𝐻𝐶𝑙 → 𝐶𝑎𝐶𝑙2 + 2𝐻2𝑆↑

This reaction releases hydrogen sulfide gas, which is highly toxic and flammable.

Hydrolysis in water: 𝐻𝑆 +𝐻2𝑂 ⇌ 𝐻2𝑆 + 𝑂𝐻−

This equilibrium gives the solution a strong basic character.

Natural Occurrence

Calcium hydrosulfide does not occur naturally in a stable form. However, HS⁻ ions can be present in alkaline, anoxic environments (such as hot springs, deep-sea hydrothermal vents, or anaerobic sediments) where calcium and sulfide sources coexist.

Industrial Preparation

Commonly prepared by dissolving calcium sulfide (CaS) in water and saturating it with hydrogen sulfide (H₂S):

𝐶𝑎𝑆 + 𝐻2𝑆 → 𝐶𝑎(𝐻𝑆)2

Often used in pulp and paper industries (kraft process), tanning, and ore flotation.

Safety Considerations

  • Hydrogen sulfide release is a major hazard:
  • Flammable
  • Toxic (inhibits cellular respiration)
  • Must be handled in well-ventilated areas with appropriate PPE (personal protective equipment).