The diamine silver complex is formed by reaction between silver and which chemical?

• A. Ammonium Hydroxide
• B. Hydrochloric Acid
• C. Sodium Hydroxide
• D. Acetic Acid

Answer: (A)

Ammonia acts as a ligand to silver ions, forming the diamine complex [Ag(NH3)2]+. In solution, silver ions bind two ammonia molecules, yielding Ag+ + 2 NH3 ⇌ [Ag(NH3)2]+. Ammonium hydroxide is the source of the ammonia in this context, creating the stable diamine complex used in silver-staining methods. This complex is soluble and readily reduced to metallic silver during development, which is essential for the staining reaction.

Using hydrochloric acid would produce silver chloride, which is poorly soluble; sodium hydroxide would precipitate silver as silver oxide/hydroxide; acetic acid would form silver acetate. None of these provide the diamine complex that the staining chemistry relies on.