Topic 24: Aqueous Chemistry

Question 1

Hexaaqua complexes

Answer 1

6 water molecules acting as ligands around a transition metal

Question 2

Fe^2+ and Fe^3+ hexaaqua solutions acidity difference why?

Answer 2

Fe^3+ much more acidic than Fe^2+
3+ smaller and higher charged than 2+ so more polarising. Strongly attracts electrons from O weakening the OH bonds which will release a H+ making it acidic.

Question 3

Fe^3+ in water equation

Answer 3

Hydrolysis
[Fe(H2O)6]^3+(aq) <===> [Fe(H2O)5(OH)]^2+ + H+

Question 4

M3+ adding OH- equations

Answer 4

[M(H2O)6]^3+(aq) + OH-(aq) —> [M(H2O)5(OH)]^2+(aq) + H2O(l)

[M(H2O)5(OH)]^2+(aq)
+ OH-(aq) —> [M(H2O)4(OH)2]^+(aq) + H2O(l)

[M(H2O)4(OH)2]^2+(aq) + OH-(aq) —> M(H2O)3(OH)3(s) + H2O(l)

Question 5

Mg2+ adding OH- equations

Answer 5

[M(H2O)6]^2+(aq) + OH-(aq) —> [M(H2O)5(OH)]^+(aq) + H2O(l)

[M(H2O)5(OH)]^+(aq)
+ OH-(aq) —> M(H2O)4(OH)2(s) + H2O(l)

Question 6

M^2+ with ammonia full eq’n

Answer 6

[M(H2O)6]^2+(aq) + 2NH3 —> M(H2O)4(OH)2(s) + 2NH4+

Question 7

M^3+ with ammonia full eq’n

Answer 7

[M(H2O)6]^3+(aq) + 3NH3 —> M(H2O)3(OH)3(s) + 3NH4+

Question 8

Fe^3+ and CO3^2-

Answer 8

DOESN’T FORM Fe₂(CO₃)₃ - doesn’t exsist???

Question 9

Fe^3+ and CO3^2- overall equation

Answer 9

2[Fe(H2O)6]^+3(aq) + 3CO3^2-(aq) —> 2Fe(H2O)3(OH)3 + 3CO2(g) + 3H2O(l)

Question 10

Fe^3+ and CO3^2- overall equation DERVIVED???

Question 11

Fe^2+ and CO3^2- overall equation

Answer 11

[Fe(H2O)6]^+2(aq) + CO3^2-(aq) —> FeCO3(s) + 6H2O(l)

Question 12

Fe^3+ in water colour

Answer 12

purple solution
may look yellow-brown due to some
[Fe(H2O)5(OH)]2+(aq)

Question 13

Fe^2+ in water colour

Answer 13

green solution

Question 14

Fe^2+ in OH- colour and in exess

Answer 14

green ppt goes brown on standing in
air
nvc in excess

Question 15

Fe^3+ in OH- colour and in excess

Answer 15

brown ppt (ppt may look
orange-brown)
nvc in excess

Question 16

Al3+ in water colour

Answer 16

[Al(H2O)6]^3+(aq)
colourless solution

Question 17

Chelation

Answer 17

Water ligands being replaces by bidentate or multidentate ligands

Question 18

Ammonia replacing water ligands in M2+

Answer 18

One at a time
[M(H2O)6]^2+ + NH3 <===> [M(NH3)(H2O)5]^2+ + H2O
AND SO ON AND SO ON LIKE 6 TIMES!!!!
Overall:
[M(H2O)6]^+2 + 6NH3 <===> [M(NH3)6]^2+ + 6H2O

Question 19

What else could happen during NH3 substitution?

Answer 19

Ammonia is a base so in solution forms OH- ppt may form and redissolve
[M(H2O)6]^2+(aq) + 2OH-(aq) —> M(H2O)4(OH)2(s) + 2H2O(l)

M(H2O)4(OH)2(s) + 6NH3(aq) <===> [M(NH3)6]^2+(aq) + 4H2O(l) + 2OH-(aq)

Question 20

hexaaqua complex of Cu2+ with excess NH3 equation

Answer 20

[Cu(H2O)6]2+ + 4NH3 <===> [Cu(NH3)4(H2O)2]^2+ + 4H2O

Question 21

hexaaqua complex of Cu2+ with excess NH3 explanation

Answer 21

Ammonia acts as a base removing protons from 2 of the water ligands producing ppt
Then the ppt dissolves as the ammonia has replaced both OH- and two H2O ligands

Question 22

hexaaqua complex of Cu2+ with little NH3 equation

Answer 22

[Cu(H2O)6]2+ + 2NH3 —> Cu(H2O)4(OH)2(s) + 2NH4+

Question 23

hexaaqua complex of Cu2+ with little NH3 colour

Answer 23

Blue ppt

Question 24

hexaaqua complex of Cu2+ with excess NH3 colour

Answer 24

Deep blue solution

Question 25

[Cu(NH3)4(H2O)2]^2+ shape

Answer 25

Octahedral - slightly distorted Water above and below NH3 like square planar CuO bonds longer so weaker than CuN bonds. Water poorer ligand.

Question 26

Shape of complex with Cl- ligands

Answer 26

Tetrahedral - coordination number 4 as too big to all fit around central metal ion

Question 27

Cu^+2 hexaaqua complex colour

Answer 27

Blue solution

Question 28

Cu2+ hexaaqua complex with OH- colour and in excess

Answer 28

Blue ppt Cu(H2O)(OH)2(s) nvc in excess

Question 29

Fe^2+ in NH3 and in excess colour

Answer 29

Fe(H2O)4(OH)2(s) Green ppt goes brown on standing in air nvc in excess

Question 30

Fe^3+ in NH3 and in excess colour

Answer 30

Fe(H2O)3(OH)3(s) brown ppt (ppt may look orange-brown) nvc in excess

Question 31

Fe^2+ in CO3^2- colour

Answer 31

FeCO3(s) green ppt

Question 32

Cu2+ in CO3^2- colour

Answer 32

CuCO3(s) blue-green ppt

Question 33

Fe^3+ in CO3^2- colour

Answer 33

Fe(H2O)3(OH)3(s) brown ppt (ppt may look orange-brown) and CO2 gas evolved

Question 34

Al^3+ and OH- and in excess colour

Answer 34

Al(H2O)3(OH)3(s) white ppt in excess [Al(OH)4]–(aq) colourless solution dissolves in excess

Question 35

Al3+ and NH3 colour and in excess

Answer 35

Al(H2O)3(OH)3(s) white ppt nvc in excess

Question 36

Al3+ in CO3^2- colour

Answer 36

Al(H2O)3(OH)3(s) white ppt and CO2 gas evolved

Question 37

Entropy in ligand substitution

Answer 37

Multidentate ligands are favoured as they displace multiple ligands meaning the number of species increases. This gives the reaction a positive entropy and so favouring the reaction.

Question 38

Cu2+ and Cl- colour and complex

Answer 38

[Cu(Cl)4]^-2 yellow - green

Question 39

Fe2+ and Cl colour and complex

Answer 39

[Fe(Cl)4]- yellow