15.2 2 Reactions of cobalt and iron complexes

Question 1

sodium hydroxide+ hexaaquacobalt (II) ion

Answer 1

pink solution forms a blue precipitate
[Co(H2O)6]2+ +2OH- = [Co(H2O)4(OH)2]+H2O
Acid base reaction
when left to stand precipitate gradually turns pink

Question 2

aqueous ammonia + hexaaquacobalt(II) ion

Answer 2

same oberservations pink solution forms a blue preciptate
[Co(H2O)6]2+ +2NH3=[Co(H20)2(OH)2] +2NH4+
If use aqueous ammonia in excess preciptate dissolves to form a brown solution
[Co(H2O)2(OH)2]+6NH3=[Co(NH3)6]2+ + 4H2O +2OH-

Question 3

Brown solution of [Co(NH3)6]2+

Answer 3

Upon standing brown solution changes colour due to oxygen in the atmosphere
2+ to 3+ and yellow [Co(NH3)6]3+
resulting solution much darker than yellow due to other products

Question 4

concentrated hydrochloric acid slowly added to solution containg hexaaquacobalt(ii)

Answer 4

pink solution gradually changes to blue
[Co(H2O)6]2+ +4Cl-=[CoCl4]2- + 6H2O
change in coordination number

Question 5

aqueous sodium hydroxide is added to hexaaquairon (II) ion

Answer 5

pale green forms a green precipitate
[Fe(H2O)6]2+ +2OH-= [Fe(H2O)4(OH)2]+2H2O
Acid-base reaction

Question 6

aqueous ammonia is added to hexaaquairon (II) ion

Answer 6

[Fe(H2O)6]2+ +2NH3 = [Fe(H2O)4(OH)2] +2NH4+

pale green forms a green precipitate

Question 7

upon standing green preciptate

Answer 7

gradually changes to brown [Fe(H2O)3(OH)3] Triaaquatrihyroxoiron (III)

Question 8

Sodium hydroxide is added to solution containing hexaaquairon (III)

Answer 8

Yellow-brown solution forms a brown precipiate
[Fe(H2O)6]3+ +3OH-=[Fe(H2O)3(OH)3] +3H2O
Acid base reaction
no futher reactions

Question 9

aqueous ammonia is added to solution hexaaquairon(III)

Answer 9

[Fe(H2O)6]3+ 3NH3 = [Fe(H2O)3(OH)3] +3NH4+
Yellow brown solution forms a brown precipitate
no futher reactions