A-Level Colours

• [Cu(H2O)6]2+

  Pale blue solution

  
• Cu(OH)2


  Pale blue ppt

  
• [Cu(NH3)4(H2O)2]2+

  Dark blue

  
• [CuCl4]2-

  Yellow solution

  
• Why is there a green intermediate formed when concentrated hydrochloric acid is added drop-wise to [Cu(H2O)6]2+

  The green still consists of [CuCl4]2- a yellow colour that is mixed with the blue solution (unreacted [Cu(H2O)6]2+). the green is as a result of not all Cu(H2O)6]2+ reacting

  
• Blue + Yellow ->


  Green

  
• [Cr(H2O)6]3+

  Violet solution

  
• [Cr(H2O)5 SO4]+

  Green

  
• [Cr(H2O)5 Cl]2+

  Green

  
• [Cr(NH3)6]3+


  Purple solution

  
• Cr(OH)3


  Grey-green precipitate

  
• Cu2+


  Blue

  
• Fe2+


  Pale green

  
• Fe3+


  Pale yellow

  
• Mn2+


  Pale pink

  
• Cu(OH)2 (Cu2+ + NaOH)


  Pale blue ppt

  
• Fe(OH)2(Fe2+ + NaOH)

  Green ppt

  
• Fe(OH)3(Fe3+ + NaOH)

  Orange-brown ppt

  
• Mn(OH)2(Mn2+ + NaOH)

  Pale brown ppt

  
• [Cr(OH)6]3-

  Dark green solution

  
• Reduction of Fe3+ to Fe2+ (using I-)

  Orange-brown -> pale-green

  
• Cr2O72- to Cr3+

  Orange -> green
• Cr3+ to Cr2+

  Green -> pale blue
• CrO4 2-

  Yellow

  
• Cu2+ to Cu+

  Blue -> colourless
• Test for ammonium ions (revision)

  add sodium hydroxideheat gentlyred litmus paper turns blue
• Test for sulfate ions SO4 2- (revision)

  Add Ba2+ (aq) ionsWhite ppt is formed in presence
• Test for halide ions Cl-, Br-, I- (revision)

  Add Ag+ (aq) ionsCl-: white ppt, soluble in dilute ammoniaBr-: cream ppt, soluble in conc. ammoniaI-: yellow ppt, insoluble in ammonia