Chemical Concept Demonstrated

• Transition metal chemistry

Demonstrations

Nickel

• Dissolve 1-1.5 g NiCl₂ in 40 mL concentrated HCL to form the yellow-green NiCl₆^4- complex ion.
• Decant NiCl₆^4- into 500 mL water to produce the blue-green Ni(H₂O)₆²⁺ complex ion.  Divide this solution into two portions: 350 mL and 175 mL.
• Add 1.5 g solid EDTA and about 45 mL 2 M NaOAc to the smaller portion of the Ni(H₂O)₆²⁺ complex to form the blue Ni(EDTA) complex.
• Add 30 mL concentrated NH₃ to the larger portion of the Ni(H₂O)₆²⁺ complex to form the blue Ni(NH₃)₆²⁺complex ion.   Divide this solution into two equal portions.
• Add a dilute aqueous solution of ethylene diamine to one portion of the Ni(NH₃)₆²⁺ complex to form a lavender complex for which the formula Ni(en)(NH₃)₄²⁺ has been proposed.
• Add a solution of dimethyl glyoxime in ethanol to the other portion of the Ni(NH₃)₆²⁺ complex to form the red Ni(DMG)₂ complex.

Cobalt

• Dissolve several grams of CoCl₂ in concentrated HCl to form the deep-blue CoCl₄^2- complex ion.  Pour some of this solution into water to form the pink Co(H₂O)₆²⁺ complex.  Divide this solution into three equal portions.
• Add a dilute aqueous solution of ethylene diamine to one portion of the CoCl₄^2- solution to form the brown Co(en)₃²⁺ complex.
• Add a solution of dimethyl glyoxime in ethanol to another portion of the CoCl₄^2- solution to form the orange-brown Co(DMG)₂ complex.
• Add concentrated NH₃ to the third portion of the CoCl₄^2- solution to form the blue Co(NH₃)₆²⁺ complex.

Iron

• Add an aqueous solution of KSCN drop by drop to an aqueous solution of the Fe³⁺ ion to form a mixture of the Fe(SCN)²⁺ and Fe(SCN)₂⁺ ions.

Chromium

• Dissolve a few grams of Cr(NO₃)₃ in 45 mL concentrated HCl and decant the resulting solution into 200 mL of water.  Divide the solution into two portions.
• Add a dilute aqueous solution of ethylene diamine to one portion of the Cr³⁺ solution to form the lavender Cr(en)₃³⁺ complex.
• Add concentrated NH₃ to the other portion of the Cr³⁺ solution to form a green solution of the Cr(NH₃)₆³⁺complex.
• Add a few drops of concentrated HCl to a yellow solution of the CrO₄^2- ion and note the change in the color of the solution to orange as the Cr₂O₇^2- ion is formed.
• Add concentrated NH₃ to the orange Cr₂O₇^2- solution and note the change in the color of the solution as the CrO₄^2- ion is formed.

Copper

• Prepare a saturated solution of the Cu²⁺ ion in concentrated HCl and note the green color of the solution due to the presence of the CuCl₄^2- ion.
• Pour 20 mL of the CuCl₄^2- ion solution into 200 mL of water and note the formation of the light blue Cu(H₂O)₆²⁺ complex.
• Add 6 M NH₃ drop by drop to a fresh solution of the Cu²⁺ ion until Cu(OH)₂ precipitates.
• Continue adding 6 M NH₃ until the solution turns the deep blue color of the Cu(NH₃)₄²⁺ ion.

Contributors

• Dr. George Bodner (Perdue University)