Ammonia is added to solutions of cobalt, nickel, and copper 2+ cations. First formation of the hydroxide precipitate is seen, then of the ammonia complex.
Đang xem: Ammonia with copper(ii) nitrate
|Co2+ + NH4OH → Co(OH)2(s)||blue ppt. (gives green mixture)|
|Cu2+ + NH4OH → Cu(OH)2(s)||blue ppt.|
|Ni2+ + NH4OH → Ni(OH)2(s)||green gel|
|Co(OH)2(s) + 6NH3 → Co(NH3)62+(aq)||brown complex|
|Cu(OH)2(s) + 4NH3 → Cu(NH3)42+(aq)||dark blue complex|
|Ni(OH)2(s) + 6NH3 → Ni(NH3)62+(aq)||blue complex|
Gloves Goggles 6 x 50mL beakers or 200mm test tubes in lighted rack, labeled in pairs as: Co2+, Cu2+, and Ni2+ 3 stir rods
Co(NO3)2.6H2O (cobaltous nitrate) Cu(NO3)2.2.5H2O (copper nitrate) Ni(NO3)2.
6H2O (nickel (II) nitrate) 3M or 6M NH4OH in a dropper bottle 15M NH4OH in a dropper bottle
Prior to Lecture (prep time 10 min.)
1. Prepare 0.1M solutions of the following:
Co(NO3)2.6H2O (cobaltous nitrate) MW = 291.05g/molCu(NO3)2.2.5H2O (copper nitrate) MW = 232.6g/molNi(NO3)2.
6H2O (nickel (II) nitrate) MW = 290.81g/mol
2. Assemble the following:
3M or 6M NH4OH in a dropper bottle15 M NH4OH in droppler bottleSix 50 mL beakers or 200mm test tubes in lighted rack, labeled in pairs as: Co2+, Cu2+, and Ni2+three stir rods goggles gloves
To Conduct Demonstration
Pour 0.1M solutions of Cu2+, Co2+, and Ni2+ into pairs of labeled beakers (to a depth of 1/2″) on an overhead projector or document projector, or into 200mm test tubes (to a depth of 1″) in a lighted rack.Add 3M or 6M NH4OH drop wise while stirring with the stir rod to one beaker or test tube of each pair. The solutions will become cloudy and change color due to the precipitation of metal hydroxides.Add 15M NH4OH with stirring to the same beaker or test tube. The precipitates will dissolve and darkly colored ammonia complexes will form. (Cobalt requires 6 times the cation volume to form the complex.) Use the other beakers or test tubes as references. Use watch glasses over the beakers or crystallizing dishes to contain the ammonia fumes.
Safety and Disposal