- Structure
- Nomenclature
- Physical properties
- Physical state
- Molecular weight
- Melting point
- Density
- Solubility
- Chemical properties
- Aqueous solution
- Compounds present when dissolved in water
- Reaction with acids
- Other reactions
- Obtaining
- Presence in nature
- Applications
- In luminous materials
- In medicine
- In obtaining other compounds
- Other apps
- Risks
- References
The calcium sulfide is an inorganic solid element consisting of calcium (Ca) and element sulfur (S), of the chemical formula CaS. It is a water-soluble, yellowish-white solid, 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 2- becoming the SH - ion 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.
Calcium sulfide CaS has been found in some meteorites. Author: Родион Журавлёв. Source: Pixabay.
CaS has been considered as a possible medicine 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 2 S which is very toxic.
Structure
Calcium sulfide is a highly ionic compound formed by a calcium ion Ca 2+ and a sulfide ion S 2-.
It crystallizes into a cubic structure like rock salt.
Cubic crystal structure of calcium sulfide. Yellow = sulfur; white = calcium. Benjah-bmm27 / Public domain. Source: Wikimedia Commons.
Nomenclature
- Calcium sulphide
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 / cm 3
Solubility
Soluble in water. Insoluble in ethanol.
Chemical properties
Aqueous solution
When dissolved in water, CaS separates into its calcium Ca 2+ and sulfur S 2- ions. The latter in water takes a proton and becomes the hydrosulfide ion SH - releasing a hydroxyl ion OH -.
S 2- + H 2 O ⇔ SH - + OH -
Therefore, calcium sulfide CaS solutions are alkaline (they have a basic pH) and do not have S 2- ions 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 S 2- sulfide ions.
Calcium sulfide dissolves in water, forming other compounds. Author: Clker-Free-Vector-Images. Source: Pixabay.
SH - can take another H + proton from water, forming hydrogen sulfide, which is a very toxic compound.
SH - + H 2 O ⇔ H 2 S + OH -
For this reason, small amounts of H 2 S are formed in water 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) 2, Ca (OH) 2 and Ca (SH) (OH) are formed.
CaS + H 2 O → Ca (SH) (OH)
Ca (SH) (OH) + H 2 O → Ca (OH) 2 + H 2 S
Reaction with acids
The same reactions that occur in water cause CaS to react with acids, forming H 2 S.
CaS + 2 HCl → CaCl 2 + H 2 S
Other reactions
If a calcium sulfide solution is heated with sulfur, the polysulfide ions S 4 2- and S 3 2- are obtained.
If CaS is heated in dry air or pure oxygen the compound oxidizes to calcium sulphite CaSO 3 and then to calcium sulphate CaSO 4:
2 CaS + 3 O 2 → 2 CaSO 3
2 CaSO 3 + O 2 → 2 CaSO 4
With oxidizing agents such as potassium chlorate KClO 3, potassium nitrate KNO 3 or lead dioxide PbO 2 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 CaSO 4 with charcoal:
CaSO 4 + 2 C → CaS + 2 CO 2
However, in the latter case a pure CaS is not obtained, since it additionally reacts with CaSO 4 forming CaO and SO 2.
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.
Calcium sulfide CaS is in the mineral oldhamite, which has been found in some meteorites. Leon Hupperichs / CC BY-SA (https://creativecommons.org/licenses/by-sa/3.0). Source: Wikimedia Commons.
In addition, calcium sulfide is produced naturally by the reduction of CaSO 4 (gypsum), 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 (Ce 3+) and europium (Eu 2+).
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.
Old computer monitors had cathode ray tubes in which luminescent calcium sulfide compounds and activators are sometimes used. Author: Andreas160578. Source: Pixabay.
They are also used in current light-emitting diode, or LED (Light-Emitting Diodes) lamps.
LED lamp. Some may contain luminescent calcium sulfide compounds. No machine-readable author provided. APPER assumed (based on copyright claims). / CC BY-SA (http://creativecommons.org/licenses/by-sa/3.0/). Source: Wikimedia Commons.
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 2 S. It 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.
Calcium sulfide has been studied as a possible remedy for high blood pressure in the cardiovascular system in sick people. Author: Mohamed Hassan. Source: Pixabay.
In obtaining other compounds
Calcium sulfide makes it possible to prepare other compounds such as calcium nitrate Ca (NO 3) 2:
CaS + 2 HNO 3 → Ca (NO 3) 2 + H 2 S
It has also been used to obtain calcium carbonate CaCO 3. To do this, an aqueous solution of CaS is subjected to carbonation with CO 2:
CaS + H 2 O + CO 2 → H 2 S + CaCO 3
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
- Cotton, F. Albert and Wilkinson, Geoffrey. (1980). Advanced Inorganic Chemistry. Fourth Edition. John Wiley & Sons.
- Lide, DR (editor). (2005). CRC Handbook of Chemistry and Physics. 85 th CRC Press.
- Ropp, RC (2013). Group 16 (O, S, Se, Te) Alkaline Earth Compounds. Calcium Sulfide. In Encyclopedia of the Alkaline Earth Compounds. Recovered from sciencedirect.com.
- Li, YF 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.
- House JE and House, KA (2016). Sulfur, Selenium, and Tellurium. Occurrence of Sulfur. In Descriptive Inorganic Chemistry (Third Edition). Recovered from sciencedirect.com.
- US National Library of Medicine. (2019). Calcium sulphide. Recovered from pubchem.ncbi.nlm.nih.gov.
- 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.