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AS/A-Level Chemistry- Transition metals' reaction

Transition metals' reaction

· A-level Chemistry,Transition metal,coloured metal ions,reactions,ion identification

In A-Level Chemistry, ooking at the reactions with NaOH, NH3, CO32- and Cl-, we can identify these transition metal ions.

Aluminium Al3+

  • colourless as aqueous solution
  • white precipitate when reacting with NaOH/NH3: [Al(H2O)6]3+ +3OH- ⇨  Al(H2O)3(OH)3 +3H2O //   [Al(H2O)6]3++ 3NH3 ⇨ Al(H2O)3(OH)3 +2H2O+ 3NH4+
  • Excess NaOH: white precipitate dissolves into colourless solution   Al(H2O)3(OH)3  + OH- à      [Al(OH)4]3-+ 3H2O 
  • Excess NH3: white precipitate remains
  • white precipitate + effervescence with CO32-:   2[Al(H2O)6]3++  3CO32- ⇨   2[Al(H2O)3(OH)3]+ 3CO2 + 3H2O

Chromium III Cr3+

  • purple as aqueous solution
  • green precipitate when reacting with NaOH/NH3: [Cr(H2O)6]3++ 3OH- ⇨  Cr(H2O)3(OH)3 +3H2O //   [Cr(H2O)6]3++ 3OH-  ⇨  Cr(H2O)3(OH)3+ 2H2O+ 3NH4+
  • Excess NaOH: green precipitate dissolves into green solution  Cr(H2O)3(OH)3  + 3OH-  ⇨   [Cr(OH)6]3-+ 3H2O
  • Excess NH3:  green precipitate dissolves into purple solution  Cr(H2O)3(OH)3  + 6NH3 ⇨   [Cr(NH3)6]3++ 3H2O + 3OH- 
  • green precipitate + effervescence with CO32-:   2[Cr(H2O)6]3++  3CO32- ⇨   2[Cr(H2O)3(OH)3]+ 3CO2 + 3H2O

Cobalt II Co2+

  • pink as aqueous solution
  • blue precipitate when reacting with NaOH/NH3: [Co(H2O)6]2++ 2OH- ⇨  Co(H2O)4(OH)2 +2H2O //  Co(H2O)6]2++ 2OH- ⇨  Co(H2O)4(OH)2 +2H2O+ 2NH4+
  • Excess NaOH: blue precipitate remains
  • Excess NH3:  blue precipitate dissolves into pale yellow-brown solution   Co(H2O)4(OH)2 +  6NH3 ⇨   [Co(NH3)6]2++ 4H2O + 2OH-
  • pink precipitate with CO32-:   [Co(H2O)6]2++  CO32- ⇨    CoCO3+ 6H2O
  • blue solution with CL-:   [Co(H2O)6]2++  4Cl- ⇨  [CoCl4]2- + 6H2O

Copper II Cu2+

  • pale blue as aqueous solution
  • blue precipitate when reacting with NaOH/NH3: [Cu(H2O)6]2++ 2OH-  ⇨  Cu(H2O)4(OH)2 +2H2O //   [Cu(H2O)6]2++ 2OH- ⇨  Cu(H2O)4(OH)2 +2H2O+ 2NH4+
  • Excess NaOH: blue precipitate remains
  • Excess NH3:  blue precipitate dissolves into deep blue solution  Cu(H2O)4(OH)2 +4NH3   ⇨   [Cu(NH3)4(H2O)2]2++ 2H2O + 2OH-
  • blue-green precipitate+ effervescence with CO32-:  [Cu(H2O)6]2++  CO32- ⇨    CuCO3+ 6H2
  • yellow-green solution with Cl-:  [Cu(H2O)6]2++  4Cl- ⇨   [CuCl4]2- + 6H2O

Iron II Fe2+

  • pale green as aqueous solution
  • green precipitate when reacting with NaOH/NH3: [Fe(H2O)6]2++ 2OH- ⇨  Fe(H2O)4(OH)2 +2H2O //   [Fe(H2O)6]2++2OH- ⇨  Fe(H2O)4(OH)4 +2H2O+ 4NH4+
  • Excess NaOH: green precipitate remains
  • Excess NH3:  green precipitate remains
  • green precipitate + effervescence with CO32-:  [Fe(H2O)6]2++  CO32- ⇨    FeCO3+ 6H2O

Iron III Fe3+

  • purple as aqueous solution
  • yellow-brown precipitate when reacting with NaOH/NH3: [Fe(H2O)6]3++ 3OH- ⇨  Fe(H2O)3(OH)3 +3H2O // [Fe(H2O)6]3++ 3OH ⇨ Fe(H2O)3(OH)3 +2H2O+ 3NH4+
  • Excess NaOH: yellow-brown precipitate remains
  • Excess NH3:  yellow-brown precipitate remains
  • yellow-brown precipitate + effervescence with CO32-:  2[Fe(H2O)6]3++ 3CO32- ⇨    2[Fe(H2O)3(OH)3]+ 3CO2 + 3H2O

As a summary:

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Drafted by Eunice Wong (Chemistry)

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