Silver Cation: Properties, Reactions, Health and Environmental Effects

Posted on Mar 30, 2025 in Chemistry

Silver (Ag) is a white metal, malleable and ductile. It is insoluble in dilute hydrochloric and sulfuric acids but dissolves readily in nitric acid and concentrated sulfuric acid. Silver is almost always monovalent in its compounds, but divalent oxides, sulfur fluoride, and some coordination compounds containing divalent and trivalent silver are known. Although silver does not oxidize when heated, it can be oxidized chemically or electrolytically to form silver oxide or peroxide, a powerful oxidizing agent. For this reason, it is widely used as an oxidizing catalyst in the production of certain organic materials.

Ion Reactions of Silver (Ag+)

  1. Dilute Hydrochloric Acid

    A white precipitate of silver chloride (AgCl) is obtained, which darkens when exposed to light. The precipitate is insoluble in water and acids (including nitric acid) but soluble in dilute ammonium hydroxide due to the formation of the silver diammine complex ion ([Ag(NH3)2]+). It can be reprecipitated from the ammonia solution by adding dilute nitric acid or potassium iodide solution.

  2. Potassium Iodide Solution

    A yellow precipitate of silver iodide (AgI) is formed, insoluble in ammonium hydroxide solution but readily soluble in potassium cyanide and sodium thiosulfate.

  3. Potassium Chromate Solution

    A red precipitate of silver chromate (AgCrO4) is obtained, insoluble in dilute acetic acid but soluble in dilute nitric acid and ammonium hydroxide solution.

  4. Hydrogen Sulfide

    A black precipitate of silver sulfide (Ag2S) is produced, sparingly soluble in water (solubility: 1 × 10-5 g per liter) and ammonium hydroxide solution but soluble in dilute nitric acid when heated.

  5. Sodium Hydroxide Solution

    A precipitate of silver oxide (Ag2O) is obtained, insoluble in excess precipitant.

  6. Ammonium Hydroxide Solution

    A white precipitate forms initially, which transforms directly into brown silver oxide (Ag2O), soluble in excess reagent.

Silver Cation Effects on Health

Soluble silver salts, especially silver nitrate (AgNO3), are lethal at concentrations up to 2 g. Silver compounds can be slowly absorbed by body tissues, leading to bluish or blackish pigmentation of the skin (argyria).

  • Eye Contact: May cause severe damage to the cornea if the fluid comes into contact with the eyes.
  • Skin Contact: May cause skin irritation. Repeated contact with skin can cause allergic dermatitis.
  • Dangers of Swallowing: Moderately toxic. May cause stomach upset, nausea, vomiting, diarrhea, and narcosis. If material is swallowed and aspirated into the lungs, or if vomiting occurs, it can cause chemical pneumonitis, which can be fatal.
  • Organ Effects: Chronic overexposure to silver can cause kidney damage, eye damage, liver damage, anemia, and brain damage in laboratory animals.

Effect on the Environment

Generally, unbound silver is the most toxic form, while compounds that do not produce a significant concentration of unbound silver in water are many orders of magnitude less toxic. Because of silver’s tendency to form water-insoluble chemicals, the opportunity for an organism to be affected long-term is minimal. There is some evidence that certain shellfish gradually absorb silver, but the levels observed do not adversely affect these organisms.

Main Compound Forming the Silver Cation: Silver Nitrate

Silver nitrate (AgNO3) is an inorganic salt sold commercially in powder form. It is a yellowish-white powder but is usually used in solution.

Uses:

  • Cauterizing wounds
  • Treating calluses on the hands
  • Analysis of chloride
  • Detection of reducing sugars
  • Forming the silver mirror

Risks:

  • Ingestion: Highly toxic, may cause serious harm and even death.
  • Inhalation: Severe irritation, long-term effects unknown.
  • Skin: High concentrations are dangerous, causing burns that may result in skin discoloration. Always use gloves.
  • Eyes: Extremely dangerous, causes blindness.

Medical Applications:

Silver nitrate and silver itself are used as antiseptics and disinfectants applied topically. Also used as a cauterizing agent in bleeding ulcers or to harden cool surfaces. In cytochemistry, it was used to stain the rough endoplasmic reticulum.