Reactions of inorganic compounds in aq

Question 1

Lewis theory of acids

Answer 1

Electron pair acceptors in the formation of co-ordinate bonds

Question 2

Lewis theory of bases

Answer 2

Electron pair donors in the formation of co-ordinate bonds

Question 3

Why is the Lewis definition of acids wider than the Bronsted-Lowry one?

Answer 3

Bronsted-Lowry applies only to exchange of protons so compounds have to contain hydrogens

Question 4

Aqua ions

Answer 4

6 water molecules act as ligands bonding to the metal ion in an octahedral arrangement

Question 5

Why is Fe3+ (aq) acidic at all and why the difference with Fe2+(aq)?

Answer 5

The Fe3+ ion is both smaller and more highly charged than Fe2+, making it more strongly polarising. So in the [Fe(H2O)6]3+ ion the iron strongly attracts electrons from the oxygen atoms of the water ligands, thus weakening the O-H bonds in of the water molecules. This complex ion will then readily release an H+ making the solution acidic. Fe2+ is less polarising and hence less O-H bonds break in solution.

Question 6

Hydrolysis reaction

Answer 6

O-H bonds are broken and a new species are formed.

Question 7

How to distinguish between Fe2+ and Fe3+ in aq

Answer 7

[Fe(H2O)6]2+ = pale green
[Fe(H2O)6]3+ = pale brown
Add dilute alkali, which precipitates the hydroxides whose colours are more obviously different.

Question 8

Reactions with the base CO32-

Answer 8

In general, carbonates of transition metal ions in oxidation state +2 exist, while those of ions in the +3 state don’t

Question 9

2 Amphoteric hydroxides

Answer 9

Al(H2O)3(OH)3 + Cr(H2O)3(OH)3

Question 10

CrO42-

Answer 10

Yellow

Question 11

Cr2O72-

Answer 11

Orange

Question 12

How can water molecules acting as ligands be replaced by other ligands?

Answer 12

1. Other ligands form stronger co-ordinate bonds (better Lewis bases)
2. Present in higher conc. and an equilibrium is displaced

Question 13

[Co(H2O)4(OH)2]

Answer 13

Blue precpitate

Question 14

What happens if more conc. NH3 is added to [Co(H2O)4(OH)2]?

Answer 14

Both OH- and all 4 water ligands are replaced by ammonia because :

1. Ammonia is a better ligand than water
2. High conc. of ammonia displaces equilibria, displacing water and OH-

Question 15

Observations if more conc. NH3 is added to [Co(H2O)4(OH)2]

Answer 15

The blue precipitate dissolves to form a pale yellow solution which is oxidised by oxygen in air to a brown mixture with Co(III)

Question 16

[Cu(H2O)6]2+ + 4NH3

Answer 16

[Cu(NH3)4(H2O)2]2+ pale blue to very deep blue

Question 17

Shape of [Cu(NH3)4(H2O)2]2+

Answer 17

Octahedral, 4 NH3 square planar arrangement with H2O above and below. Cu-O bonds are longer and weaker than Cu-N

Question 18

[Cu(H2O)6]2+ + 4Cl-

Answer 18

[CuCl4] 2-, Pale blue replaced by yellow [CuCl4]2- -> co-ordinate number 6-> 4

Question 19

Chelation

Answer 19

Formation of complexes with multidentate ligands

Question 20

Why do multidentate ligands form more stable complexes than monodentate ligands?

Answer 20

Entropy change

Question 21

[Fe(H2O)6]2+

Answer 21

Pale green

Question 22

[Co(H2O)6]2+

Answer 22

Pink

Question 23

[Cu(H2O)6]2+

Answer 23

Pale blue

Question 24

[Al(H2O)6]3+

Answer 24

Colourless

Question 25

[V(H2O)6]3+

Answer 25

Green

Question 26

[Cr(H2O)6]3+

Answer 26

Pale green

Question 27

[Fe(H2O)6]3+

Answer 27

Yellow

Question 28

Deprotonation

Answer 28

The loss of a proton by a water ligand to form a hydroxo ligand

Question 29

Fe(OH)2

Answer 29

Green

Question 30

Co(OH)2

Answer 30

Blue

Question 31

Cu(OH)2

Answer 31

Pale Blue

Question 32

Al(OH)3

Answer 32

White

Question 33

Cr(OH)3

Answer 33

Green/grey

Question 34

Fe(OH)3

Answer 34

Brown

Question 35

Al(OH)63-

Answer 35

Colourless

Question 36

Cr(OH)63-

Answer 36

Green

Question 37

FeCO3

Answer 37

Green ppt 2+ / Brown ppt 3+

Question 38

CoCO3

Answer 38

Pink ppt

Question 39

CuCO3

Answer 39

Green-Blue ppt

Question 40

[Co(OH)2(H2O)4]

Answer 40

Blue ppt

Question 41

[Co(NH3)6]2+

Answer 41

Straw

Question 42

[Co(NH3)6]3+

Answer 42

Brown

Question 43

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

Answer 43

Dark Blue

Question 44

CoCl42-

Answer 44

Blue

Question 45

CuCl42-

Answer 45

Green/yellow

Question 46

The chelate effect

Answer 46

The entropy of the system thus increases, and multidentate complexes are therefore more stable than complexes involving monodentate ligands.

Question 47

VO2+

Answer 47

Yellow

Question 48

CrCO3

Answer 48

Pale green ppt

Question 49

CoCO3

Answer 49

Pink ppt

Question 50

AlCO3

Answer 50

White ppt

Question 51

3 changes to a transition-metal complex which result in a change in colour

Answer 51

1. Oxidation states
2. Ligands
3. Co-ordination number

Question 52

Outline a plan for experiments which would enable you to determine the conc. of a transition metal ion in a solution of unknown conc.

Answer 52

1. Add appropriate ligand to intensify colour
2. Make up solutions of known conc.
3. Measure absorption
4. Plot graph of results
5. Measure absorption of unknown + compare

Question 53

Linear complex formed when an excess of conc. HCl is added to silver chloride

Answer 53

[AgCl2]2-

Question 54

Reagents for VO2+ -> [V(H2O)6]2+

Answer 54

HCl, Zn

Question 55

Reagent for {Ag(NH3)2]+ -> Ag

Answer 55

Aldehyde

Question 56

Reagent for [Cr(H2O)6]3+ -> CrO42-

Answer 56

H2O2, NaOH

Question 57

Describe an experiment to show that vanadium has several oxidation states

Answer 57

1. Xs Zn, HCl
2. Absence of air
3. Colours seen
4. V(IV), V(III), V(II) seen

Question 58

2 equations to show that chromium (III) hydroxide is amphoteric

Answer 58

1. Cr(OH)3 + 3H+ -> [Cr(H2O)6]3+

2. Cr(OH)3 + 3OH- -> [Cr(OH)6]3-