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. AgCl is controlled under the same low occupational limit that applies to soluble silver compounds. 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. We deliberately do not publish occupational exposure limits or other regulatory thresholds: those values are revised over time and differ between jurisdictions, so the only correct source is the current SDS and the regulations that apply where you work.