Silver sulfide represented by the chemical formula Ag₂S ^[1] is a black crystalline powder that is soluble in nitric acid, sulfuric acid and alkali cyanide solutions. Ag₂S is insoluble in alcohol ^{[1, 5]}. It occurs in nature as the mineral argentite and is an ionic compound ^{[5, 6]}. It is very stable and doesn’t decompose easily except at an extremely high temperature or by the electrolysis of the molten compound ^[11].

Silver Sulfide Identification
CAS Number	21548-73-2 [1]
PubChem CID	30686 [2]
ChemSpider ID	145878 [3]
EC Number	244-438-2 [1]

Composition and Synthesis

Silver sulfide can be prepared by a reaction between silver and gaseous hydrogen sulfide. Hydrogen gas is released in the process.

2Ag + H₂S = Ag₂S + H₂

Our silverware tarnishes because of the above reaction. Air contains traces of hydrogen sulfide which causes the silver to tarnish forming silver sulfide. You can polish your silver utensils clean by rubbing them with a cloth and polishing compounds ^[7] It can be represented by the below reaction with aluminum that involves the reduction of silver sulfide to silver ^[13].

3Ag₂S + 2Al = 6Ag + Al₂S₃

Properties and Characteristics of Silver Sulfide

General Properties
Molar mass/molecular weight		248.804 g/mol [2]
Physical Properties
Color/appearance		Black powder [1]
Melting point/freezing point		845°C, 1553°F [1]
Boiling point		N/A [1]
Density		7.234 g cm-3 [1]
State of matter at room temperature (normal phase)		Solid [1]
Resistivity		0.1 – 10 ohm-m [14]
Chemical Properties
Solubility in water		Insoluble [5]
pH		<7 (acidic) [6]
Atomic Properties
Crystal structure	Orthogonal [4]
Band gap of nanoparticles	0.96 eV [10]

Prominent Reactions

Silver sulfide reacts with hydrochloric acid to produce silver chloride and hydrogen sulfide ^[9].

Ag₂S + 2HCl = 2AgCl + H₂S

It reacts with nitric acid to form silver sulfate, nitric oxide, and water ^[8].

3Ag₂S + 8HNO₃ = 3Ag₂SO₄ + 8NO + 4H₂O

Silver Sulfide Uses

1. The compound finds application in anti-microbial and anti-bacterial agents ^[4].
2. As a photosensitizer in photography ^[4].
3. As a lab reagent ^[4].
4. Inlaying in niello metalwork and ceramics ^[5].

Is It Dangerous

The compound is irritating to the eyes, skin, and respiratory system. Hence contact and inhalation should be avoided ^[4]. Ingestion is harmful as it may cause health hazards like irreversible pigmentation during metabolism ^[12].

Silver Sulfide (Ag₂S) Price

5 grams of the compound costs around $80 ^[8].

References
1. Silver Sulfide – Americanelements.com
2. Disilver Sulphide – Pubchem.ncbi.nlm.nih.gov
3. Silver Sulfide – Chemspider.com
4. Silver sulfide (Ag₂S) semiconductors – Azom.com
5. Silver (I) Sulfide – Chemicalbook.com
6. Is Silver Sulfide An Acid or Base? – Brainly.in
7. What is Silver Sulfide? – Chemical Formula & Uses – Study.com
8. Silver (I) Sulfide – Chemicalbook.com
9. Silver sulfide hydrochloric acid ag 2 s 2hcl 2agcl h – Coursehero.com
10. The structural and optical constants of Ag2S semiconductor nanostructure in the Far-Infrared – Ncbi.nlm.nih.gov
11. Chemical decomposition of silver sulfide? – Answers.yahoo.com
12. Exposure-Related Health Effects of Silver and Silver Compounds: A Review – Academic.oup.com
13. Finishing techniques in metalwork – Philamuseum.org
14. Silver and sulfur: case studies, physics and possible solutions- Pdfs.semanticscholar.org