Reaction of Copper, Cu2+

Cu2+(aq) (pale blue) 1ons can be obtained b
Dissolving a solub1e copper (II) salt in water, for example solid copper (II) sulphate (pale blue).
Dissolving black CuO in an acid such as sulphuric acid.

Test Observation Notes
(a) Add dil HCl and warm Solution turns form light blue to yellow-green warming drives out some water and thus increases the concentration of Cl ligands, resulting in the formation of yellow complex. Ggreenish-yellow is caused by mixing of blue of Cu2+ and yellow of [CuCl4]2
Add conc HCl Solution turns from light blue to yellowish-green Chlorine ligands replace water ligands from the aqua complex
Add NaOH(aq) Pale blue ppt formed, insoluble in exess NaOH Precipitation of Cu2+ by OH ions

Add KI(aq) followed by;


(i) Na2S2O3


(ii) Starch solution

Solution turns pale blue to brown. white ppt is formed.

Brown colour disappears, leaving a white solid


blue black colour appears

2Cu2+(aq) + 4I → 2CuI(s) + I2(aq). CuI(white ppt)

Brown iodine is reduced to colourless iodide by sodium thiosulphate


This is a test to confirm the presence of iodine

Add NH3(aq) A blue ppt is formed soluble in xs ammonia to give a deep blue solution Cu(OH)2(s) is first precipitated. The ppt dissolves in xs ammonia to form a deep blue complex


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