halide ions with silver nitrate

• This reaction is used as a test to identify which halide ion is present. The test solution is made acidic with nitric acid, and then silver nitrate solution is added dropwise
• The role of nitric acid added before silver nitrate is to react with any carbonates present to prevent formation of the white precipitate silver carbonate, giving a false positive result for chloride ions
• Chlorides produce a white precipitate

  • Ag+ (aq) + Cl - (aq) -----> AgCl(s)
• Bromides produce a cream precipitate

  • Ag+ (aq) + Br- (aq) ----> AgBr(s)
• Iodides produce a pale yellow precipitate

  • Ag+ (aq) + I- (aq) ----> AgI(s)
• The silver halide precipitates can be treated with dilute or concentrated ammonia solution to help differentiate between them if the colours look similar
• silver chloride precipitate redissolves when dilute aqueous ammonia is added
• silver bromide precipitate will not redissolve when dilute aqueous ammonia is added

  BUT

  silver bromide precipitate will redissolve when concentrated aqueous ammonia is added
• silver iodide precipitate will NOT redissolve when either concentrated or dilute aqueous ammonia is added