Silver (Ag) Precipitates and Complexes

Required Training	Required PPE
UC Lab Safety Fundamentals	Lab coat, safety glasses/goggles, nitrile gloves
Equipment	Chemicals
Large evaporating dish	water
Large stir rod	0.1 M AgNO3
Stir plate	1 M NaHCO3
Clean white paper for a background	6 M NaOH
	1 M NaCl
	6 M NH4OH
	1 M KBr
	1M Na2S2O3
	KI

Procedure:

1. In a medium evaporating dish, mix 100 mL water with 3 mL of 0.1 M AgNO₃ and add in the order listed below while stirring:
2. Add 5 mL 1 M NaHCO₃ (mw=84) forming the white precipitate Ag₂CO₃
3. Add 3 mL 6 M NaOH (mw=40) forming the brown precipitate Ag₂O
4. Add 1 mL 1 M NaCl (mw=58) forming the white precipitate AgCl
5. Add 3 mL 6 M NH₄OH (mw=35) forming a clear solution
6. Add 0.5 mL 1 M KBr (mw=119) forming a white to light yellow precipitate AgBr
7. Add 1 mL 1M Na₂S₂O₃ (mw=248) forming a clear solution
8. Add 0.5 mL fresh, colorless KI (mw=166) to form a yellow precipitate AgI

Hazards:

Dispose of chemicals promptly to avoid a detonation/explosion hazard. Silver nitrate can stain skin black for days—If any solutions, especially the 6M bases, are spilled on one's self, wash the affected area for at least 15 minutes.

Discussion:

A precipitation reaction occurs when a precipitant causes a chemical to fall out of solution. The remaining solution is called a supernate or supernatant. A very important stage in precipitation is the onset of nucleation. The creation of a solid particle includes the formation of a solid-solution interface, which requires energy based on the relative surface energy of the solid and the solution. If this energy is not available, and not a nucleation site available, supersaturation occurs.

SOP:

Acutely Toxic Material – Silver Nitrate

Corrosive: Ammonium Hydroxide, Silver Nitrate, Sodium Hydroxide

Strong Oxidizer – Silver Nitrate

Disposal (by Storeroom):

This demo requires special waste disposal. Bring to storeroom for proper disposal