Copper(II) Chloride (CuCl2)
Copper(II) Chloride, also known as Cupric Chloride, forms a blue-green, orthorhombic, crystalline structure in the dihydrated state and can be used as (amongst other things)a flame colorant, oxidizing agent, and mild Lewis acid.
Copper(II) Chloride is highly soluble in water and will produce a blue solution, but when concentrated the CuCl2 aqueous solution will turn dark green.
In its anhydrous state, CuCl2 is brown; however Copper(II) Chloride Dihydrate (CuCl2 • 2 H2O) is light blue. Anhydrous Copper Chloride is hygroscopic and will readily absorb moisture out of the air to form the Dihydrate. By heating the hydrated Copper Chloride, one can drive off the water (in the form of steam) from the CuCl2 • 2 H2O crystals and form anhydrous Copper(II) Chloride.
The pictures below shows the color change exhibited by Copper Chloride over a 7 day period as anhydrous CuCl2 slowly absorbs water from the air to become CuCl2 • 2 H2O.
The last picture shows the contrast in the color of anhydrous versus the hydrated form of Copper(II) Chloride.
Hydration of Copper(II) Chloride
The low reactivity of Copper relative to other metals allows Copper salts (such as CuCl2) to act as oxidizing agents at times, especially in the presence of reducing agents (Aluminum metal for example). Copper Chloride can oxidize other metals, forming their Chloride salt, while being reduced to Copper metal in the process.
The video and pictures below depict the reaction between anhydrous Copper(II) Chloride and Aluminum powder.
The Aluminum Chloride produced during the reaction sublimes in the process.
|A 40 gram mixture of anhydrous CuCl2 and Aluminum powder react giving off thick, multi-colored (purple, yellow, and white), fumes.|
Copper(II) Chloride is also an effective flame colorant, able to turn flames vivid green and blue colors.
Left: Copper(II) Chloride colors a cool ethanol flame a vivid green.
Right: A very hot, butane flame is colored a bright blue by Copper(II) Chloride.