colours of test tube reactions

Question 1

What happens when aqueous NaOH is added to hexaaqua iron(II) and hexaaqua copper(II)?

Answer 1

• OH-
• Fe
  
  • little - green ppt goes brown on standing, particularly on top
    
    • Fe(H₂O)(OH)₂ (s)
  • excess - no further change
• Cu
  
  • blue ppt
  • Cu(H₂O)₄ (OH)₂ (s)

Question 2

Why does [Fe(H₂O)₆] ²⁺(aq) go brown on standing?

Answer 2

• Fe(II) oxidised to Fe(III) by oxygen in the air
• presence of [Fe(H₂O)₅ (OH)]²⁺(aq)

Question 3

What happens when aqueous NH3 is added to hexaaqua iron(II) and hexaaqua copper(II)?

Answer 3

• Fe
  
  • green ppt goes brown on standing in air
• Cu
  
  • blue ppt
  • excess - deep blue soln
    
    • [Cu(H₂O)₂(NH₃)_4]²⁺

Question 4

What happens when aqueous CO₃^2- is added to hexaaqua iron(II) and hexaaqua copper(II)?

Answer 4

• Fe
  
  • green ppt of FeCO3
• Cu
  
  • blue-green ppt of CuCO3

Question 5

What happens when aqueous NaOH is added to hexaaqua iron(III) and hexaaqua aluminium(III)?

Answer 5

• Fe
  
  • brown ppt
  • may look orange brown
  • no further change in excess
• aluminium
  
  • white ppt
  • in excess forms a colourless soln
    
    • [Al(OH)4]-

Question 6

What happens when aqueous NH3 is added to hexaaqua iron(III) and hexaaqua aluminium(III)?

Answer 6

• Fe
  
  • brown ppt, may look orange-brown
• al
  
  • white ppt
• no further change in excess for either

Question 7

What happens when aqueous Na2CO3 is added to hexaaqua iron(III) and hexaaqua aluminium(III)?

Answer 7

• Fe
  
  • brown ppt may look range brown
  • CO2 evolved
• AL
  
  • white ppt
  • CO2 gas evolved

Question 8

What is the colour of hexaaqua iron(II)/iron(III)/Cu(II)/Al(III) solutions

Answer 8

• iron (II)
  
  • green
• copper (II)
  
  • blue soln
• Fe(III)
  
  • purple
  • may look yellow-brown due to some [Fe(H₂O)₅(OH)]²⁺
• Al(III)
  
  • colourless soln

Question 9

How are the vandium ions we need to know about produced?

Answer 9

• ammonium vandate is reduced by zinc metal under acidic conditions