Calcium sulfide (CaS) structure, properties, production, uses

The calcium sulfide It is an inorganic solid formed by the element calcium (Ca) and the element sulfur (S), the chemical formula is CaS. It is a yellowish-white solid soluble in water, which is found in nature in some volcanoes and in some meteorites in the form of a mineral called oldhamite..

When CaS dissolves in water, it forms various compounds due to the sulfide ion S^two- becomes ion SH^- and OH ions are formed^-. The resulting solution is alkaline. This compound is used as a base for compounds that are luminescent or that produce visible light under certain conditions. These materials are also used in luminous paints.

CaS has been considered as a possible drug to treat heart and blood vessel problems such as hypertension or high blood pressure, which is a disease that affects a large part of the world's population.

With calcium sulfide other compounds such as calcium nitrate and calcium carbonate can be obtained. It must be handled with caution and in contact with the humidity of the atmosphere it can produce H_twoS which is very toxic.

Article index

• 1 Structure
• 2 Nomenclature
• 3 Physical properties
  • 3.1 Physical state
  • 3.2 Molecular weight
  • 3.3 Melting point
  • 3.4 Density
  • 3.5 Solubility
• 4 Chemical properties
  • 4.1 Aqueous solution
  • 4.2 Compounds present when dissolved in water
  • 4.3 Reaction with acids
  • 4.4 Other reactions
• 5 Obtaining
  • 5.1 Presence in nature
• 6 Uses
  • 6.1 In luminous materials
  • 6.2 In medicine
  • 6.3 In obtaining other compounds
  • 6.4 Other applications
• 7 Risks
• 8 References

Structure

Calcium sulfide is a highly ionic compound formed by a calcium ion Ca^two+ and a sulfide ion S^two-.

Crystallizes into a cubic structure like rock salt.

Nomenclature

• Calcium sulfide

Physical properties

Physical state

Yellowish-white crystalline solid, cubic crystals like those of sodium chloride.

Molecular weight

72.144 g / mol

Melting point

2528 ºC

Density

2.59 g / cm³

Solubility

Soluble in water. Insoluble in ethanol.

Chemical properties

Aqueous solution

As CaS dissolves in water, it separates into its calcium Ca ions. ^two+ and sulfur S^two-. The latter in water takes a proton and becomes the hydrosulfide ion SH^- releasing a hydroxyl ion OH^-.

S^two- + H_twoO ⇔ SH^- + Oh^-

Therefore, calcium sulfide CaS solutions are alkaline (have a basic pH) and do not have S ions.^two- but SH^-.

Only when a large amount of alkali such as sodium hydroxide NaOH is added to the solution does the equilibrium shift towards the formation of sulfide ions S^two-.

The SH^- can take another proton H⁺ from water, forming hydrogen sulfide, which is a very toxic compound.

SH^- + H_twoO ⇔ H_twoS + OH^-

For this reason, small amounts of H are formed in water._twoYes and when exposed to humidity in the environment, CaS gives off an unpleasant smell typical of hydrogen sulfide.

Compounds present when dissolved in water

The result of the reactions in water indicated above is that Ca (SH) is formed_two, Ca (OH)_two and Ca (SH) (OH).

CaS + H_twoO → Ca (SH) (OH)

Ca (SH) (OH) + H_twoO → Ca (OH)_two + H_twoS

Reaction with acids

The same reactions that occur in water cause CaS to react with acids forming H_twoS.

CaS + 2 HCl → CaCl_two + H_twoS

Other reactions

If a solution of calcium sulfide is heated with sulfur, the polysulfide ions S are obtained.₄^two- and S₃^two-.

If CaS is heated in dry air or pure oxygen the compound oxidizes to calcium sulphite CaSO₃ and then to calcium sulfate CaSO₄:

2 CaS + 3 O_two → 2 CaSO₃

2 CaSO₃ + OR_two → 2 CaSO₄

With oxidizing agents such as potassium chlorate KClO₃, potassium nitrate KNO₃ or lead dioxide PbO_two violent reactions occur.

Obtaining

Calcium sulfide can be prepared by calcining (heating to a very high temperature) the elements calcium (Ca) and sulfur (S) in an inert atmosphere, that is, no oxygen or water vapor, for example, are present..

Ca + S + heat → CaS

It can also be obtained by heating calcium sulfate CaSO₄ with charcoal:

Case₄ + 2 C → CaS + 2 CO_two

However, in the latter case a pure CaS is not obtained, as it reacts additionally with CaSO₄ forming CaO and SO_two.

CaS is also generated by burning coal waste.

Presence in nature

CaS is naturally present in the mineral oldhamite. This is a component of some meteorites and is important for scientific research carried out on the solar system..

Oldhamite is believed to have formed by condensation in the nebula that originated the solar system. It is also present in volcanoes.

In addition, calcium sulfide is produced naturally by the reduction of CaSO₄ (plaster) possibly due to the action of bacteria.

Applications

In luminous materials

One of the most widespread uses of calcium sulfide has been as a base for luminescent compounds. These are substances that emit visible light under certain circumstances..

In the luminescent compounds of CaS this acts as a base and activators are added to the structure such as chlorides of certain elements such as cerium (Ce³⁺) and europium (Eu^two+).

The material resulting from the union of the CaS and the activator is used for example in cathode ray tube screens that make up the old screens of computers or computers or old TV sets.

They are also used in current light-emitting diode, or LED, lamps. Light-Emitting Diodes).

These materials are also used in luminous paints and varnishes..

In medicine

Calcium sulfide has been considered in medical scientific studies as a drug to treat high blood pressure (high pressure in the arteries). This is a disease that affects the cardiovascular system of many people (heart and blood vessels).

CaS is considered a “donor” of H_twoS. This plays an important role in regulating the tone or strength of blood vessels, so the administration of CaS could be a possible remedy to treat hypertension.

In obtaining other compounds

Calcium sulfide makes it possible to prepare other compounds such as calcium nitrate Ca (NO₃)_two:

CaS + 2 HNO₃ → Ca (NO₃)_two + H_twoS

It has also been used to obtain calcium carbonate CaCO₃. To do this, an aqueous solution of CaS is subjected to carbonation with CO_two:

CaS + H_twoO + CO_two → H_twoS + CaCO₃

Other apps

Calcium sulfide is also used as a lubricant additive and as a flotation agent in mineral extraction..

Risks

Calcium Sulfide can cause skin, eye, and respiratory tract irritation. It must be handled with caution and with adequate safety equipment.

It is a very toxic compound for aquatic life, so it is dangerous for these environments.

References

1. Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
2. Lide, D.R. (editor). (2005). CRC Handbook of Chemistry and Physics. 85^th CRC Press.
3. Ropp, R.C. (2013). Group 16 (O, S, Se, Te) Alkaline Earth Compounds. Calcium Sulfide. In Encyclopedia of the Alkaline Earth Compounds. Recovered from sciencedirect.com.
4. Li, Y.F. et al. (2009). Calcium sulfide (CaS), a donor of hydrogen sulfide (H (2) S): a new antihypertensive drug? Med Hypotheses, 2009 Sep; 73 (3): 445-7. Recovered from ncbi.nlm.nih.gov.
5. House J.E. and House, K.A. (2016). Sulfur, Selenium, and Tellurium. Occurrence of Sulfur. In Descriptive Inorganic Chemistry (Third Edition). Recovered from sciencedirect.com.
6. U.S. National Library of Medicine. (2019). Calcium sulphide. Recovered from pubchem.ncbi.nlm.nih.gov.
7. De Beer, M. et al. (2014). Conversion of calcium sulphide to calcium carbonate during the process of recovery of elemental sulfur from gypsum waste. Waste Manag, 2014 Nov; 34 (11): 2373-81. Recovered from ncbi.nlm.nih.gov.