Silver Chloride
Properties
| State | Solid at room temperature |
| Color | White (darkens to gray-purple on light exposure) |
| Solubility | Insoluble in water (0.00019 g/100 mL at 25°C); soluble in ammonia and thiosulfate solutions |
| Melting Point | 455°C |
| Boiling Point | 1547°C |
About Silver Chloride
Silver chloride is a white ionic salt with the formula AgCl, a molar mass of 143.32 g/mol, and a solubility-product constant of 1.77 × 10^-10 at 25 °C — small enough that it precipitates almost quantitatively when chloride and silver(I) ions meet in solution. That precipitation is the textbook qualitative test for chloride ion: add silver nitrate to an unknown, watch a curdy white solid form, then confirm it's AgCl (and not AgBr or AgI) by its clean dissolution in dilute aqueous ammonia via the [Ag(NH3)2]+ diammine complex. The structure is rock-salt — same as NaCl — but with much weaker Ag-Cl ionic character because Ag+ is highly polarizing and the bond carries significant covalent contribution, which is why silver halides are dramatically less soluble than alkali-metal halides. AgCl darkens on light exposure to a purple-gray as photons promote electrons that reduce Ag+ to metallic silver clusters; this photochemistry was the foundation of early daguerreotype and calotype photography before silver bromide took over for its higher sensitivity. The most important modern application is the silver/silver-chloride electrode, the dominant reference electrode in laboratory pH meters, ion-selective electrodes, and biomedical recording (EKG, EEG, EMG): a silver wire coated with AgCl in contact with chloride solution gives a stable, reproducible, drift-free potential of +0.222 V vs SHE in saturated KCl.
Where you'll encounter it
If you've ever calibrated a pH meter or recorded an EKG, you've used a silver/silver-chloride reference electrode without thinking about the electrochemistry. The Ag/AgCl reference replaced the older saturated calomel electrode (SCE) because it doesn't contain mercury, gives equally stable potentials, and tolerates higher temperatures. Most disposable EKG patches stick to skin via a hydrogel containing chloride ions in contact with a silver-chloride coated stud — that's the half-cell that lets the recorder pick up the millivolt-scale heart signals without electrode polarization drifting the baseline. In a teaching lab, AgCl precipitation is the cleanest possible demonstration of Ksp: titrate Cl- against AgNO3 with chromate indicator (the Mohr method) and the endpoint shows up as a brick-red Ag2CrO4 precipitate the instant free Cl- runs out. The third niche is wound-care silver dressings, where slow AgCl release supplies bacteriostatic Ag+ to chronic wounds without the cytotoxicity of higher silver-nitrate concentrations.
Common Uses
- Silver/silver-chloride reference electrode in pH meters, ion-selective electrodes, and biomedical recording
- Disposable EKG, EEG, and EMG sensor pads with hydrogel chloride contact
- Qualitative chloride ion identification by curdy precipitate plus ammonia solubility test
- Mohr-method argentometric titration with chromate indicator for chloride quantification
- Photochromic glass lenses (alongside AgBr) for UV-darkening eyewear
- Silver-impregnated wound dressings for slow Ag+ release as bacteriostatic agent
Safety Information
GHS: Skin irritation Category 2 (H315), Eye irritation Category 2A (H319), Aquatic acute and chronic Category 1 (H400, H410). Acute oral toxicity is low because AgCl is so insoluble it releases minimal bioavailable Ag+. The clinical concern is argyria — a permanent slate-blue to gray skin discoloration from cumulative dermal silver-sulfide deposition seen in workers with chronic occupational silver exposure and in people who self-administer colloidal silver supplements. OSHA PEL for soluble silver compounds is 0.01 mg/m3 as Ag (8-hr TWA), and AgCl is treated under this limit. Environmental discharge of silver salts is regulated because Ag+ is acutely toxic to aquatic organisms at low parts-per-billion levels. Handle with nitrile gloves; recover silver from waste streams.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.