Interaction | Reaction | Process     Data Page

When excess hydroxide is added to a solution of pink hexaaquacobalt(II) ion, the complex cation acts as a Brønsted acid and loses two protons giving a precipitate of blue tetraaquadihydroxycobalt(II) and two waters. (Only two moles of hydroxide are used.)

On standing in air the blue ppt. turns pink and then brown.

[Co(H2O)6]2+
  +  
6
NaOH(aq)
         

Co(H2O)4(OH)2
Co(OH)2
  +  
2
Na+
  +  
2
H2O
  +  
4
NaOH(aq)
Reactant Page Go To Go To
Hexaaquacobolt(II) ion     Reactions Using    Reactions Forming
Sodium hydroxide solution     Reactions Using    Reactions Forming
Tetraaquadihydroxycobalt(II)     Reactions Using    Reactions Forming
Sodium ion     Reactions Using    Reactions Forming
Water     Reactions Using    Reactions Forming
Sodium hydroxide solution     Reactions Using    Reactions Forming

Interaction, Reaction, Process defined as:
British A-Level Chemistry: A2
Precipitation
Proton transfer: Brønsted reaction

© Mark R. Leach 1999 –

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