Nickel Complexes and the Octahedral Structure

Material Test tubes solution of nickel chloride hydrate [Ni(H20)6]Cl2, diluted ammonia solution, diluted sodium hydroxide solution. 

Procedure Gradually add, in portions, ammonia solution to the green-colored nickel chloride solution until the color turns violet. Show and compare a 3D-model for the octahedron structure of the hexa ammine complex. Slowly add sodium hydroxide solution (drop by drop) into the violet-colored solution, for comparison also to the green-colored nickel chloride solution. 

Observation The color of the solution changes from green, through several other colors, to violet. No precipitation appears from the violet solution after adding sodium hydroxide solution, this does however happen in the green solution. 

Problem In order to also obtain a solid substance which shows a regular octahedral complex, from pink colored cobalt(II) chloride hydrate the yellow colored ammine complex of cobalt(III) ions is formed [Co(NH3)6]3 +. However, the cobalt(II) chloride has to be oxidized with hydrogen peroxide - a cross-linkage to redox reactions (see Chap. 8) is possible. 

Material Beaker (250 ml), round flask (100 ml), measuring cylinder (50 ml), scales, hot plate, Buechner-funnel, suction support, water jet pump cobalt(II) chloride (CoCl2 6 H20), ammonium chloride (NH4C1), concentrated ammonia solution (25%), hydrogen peroxide solution (30%), active carbon granulates, ethanol. 

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