transition metals

Question 1

What does H2O2 act as

Answer 1

Oxidising agent

Question 2

How to oxidise transition metal complex

Answer 2

Standing in air or H2O2

Question 3

[Fe(H2O)6]2+ with little OH- or little NH3 reaction and colours

Answer 3

Deprotonation to [Fe(H2O)4(OH)2]

Pale green solution, green ppt

Question 4

[Cu(H2O)6]2+ with little OH- or little NH3 reaction and colours

Answer 4

Deprotonation to [Cu(H2O)4(OH)2]

Blue solution, blue ppt

Question 5

[Fe(H2O)6]3+ with little OH- or little NH3 reaction and colours

Answer 5

Deprotonation to [Fe(H2O)3(OH)3]

Yellow solution, orange ppt

Question 6

[Cu(H2O)6]2+ with excess NH3 and colours

Answer 6

Ligand exchange to [Cu(NH3)4(H2O)2]2+

Blue precipitate to deep blue solution

Question 7

Conversion of chromate (VI) to dichromate (VI)

Answer 7

Acid equilibrium

2CrO42− + 2H+ ⇌ Cr2O72− + H2O

Question 8

Chromate (VI) colour

Answer 8

Yellow

Question 9

Dichromate (VI) colour

Answer 9

Orange

Question 10

How far can zinc reduce dichromate (VI)

Answer 10

To Cr2+

Question 11

How to produce dichromate (VI) from Cr3+

Answer 11

Chromium (III) to chromate (VI) using H2O2.

Addition of acid

Question 12

Transition metal def

Answer 12

D-block elements that form one or more stable ions with incompletely-filled d-subshell.

Question 13

Ligand

Answer 13

Molecule or ion that forms co-ordinate bond with a transition metal by donating pair of electrons.

Question 14

Complex

Answer 14

Central metal atom or ion surrounded by ligands. Can be charged or neutral and denoted by square brackets

Question 15

How does transition metal form coloured soln

Answer 15

Electron transitions between d-orbitals split by ligands caused by absorption of visible light. Complementary colour shown.

Question 16

Why do some aqueous ions show no colour

Answer 16

Splitting so small/large that energy transition outside of VL range.
D subshell is full/empty therefore no electron transition possible

Question 17

What can cause colour changes in transition metals

Answer 17

Oxidation number (higher charge = greater splitting)
Ligand (stronger bond by ligand increases splitting)
Coordination number (change in splitting)

Question 18

Monodentate ligand and example

Answer 18

Only can donate one pair of electrons to metal centre at a time as only one pair points to metal centre. H2O, OH-, NH3.

Question 19

Why do complexes with 6 ligands form octahedral shape

Answer 19

Spread out to minimise electron repulsion

Question 20

Why do some transition metal ions form tetrahedral complexes

Answer 20

Larger ligands such as chloride have such great repulsion between them that it is unstable. Due to size and negative charge.

Question 21

Example of square planar complex

Answer 21

Cis-platin

Question 22

Why is cis-platin used and not trans-platin

Answer 22

Only cis-form is active in causing cell death

Question 23

Haem group structure

Answer 23

Multidentate ligand around Fe(II)

Question 24

Why is CO toxic

Answer 24

Oxygen molecule bound to haemoglobin replaced by CO. CO is a stronger ligand than O2 and remain bound even at low conc/

Question 25

Vanadate (V) formula and colour

Answer 25

VO2 + Yellow

Question 26

Vanadate (IV) formula and colour

Answer 26

VO 2+ Blue

Question 27

Vanadium (III) formula and colour

Answer 27

V3+ Green

Question 28

Vanadium (II) formula and colour

Answer 28

V2+ Violet but oxidises back to V3+

Question 29

Chelate effect

Answer 29

``` Multidentate ligands replace monodentate ligands as it introduces more disorder (higher S system) Ligand sub is feasible if exothermic (S surr will be +ve) if endothermic (and magnitude of S surr is less than S sys) ```

Question 30

Why do transition metals act as good catalyst

Answer 30

Can change oxidation state and engage in redox reactions

Question 31

Contact process (production of H2SO4) with vanadium (V) oxide

Answer 31

Overall reaction: 2SO2 + O2 -> 2SO3 1) 2SO2 + V2O5 -> 2SO3 + 2V2O4 2) 2V2O4 + O2 -> 2V2O5 Vanadium (V) oxide catalyst

Question 32

How does catalytic converter work

Answer 32

Adsorption of CO and NO molecules onto catalyst surface, weakening of chemical bonds and reaction, desorption of CO2 and N2 product molecules from surface. 2NO + 2CO -> N2 + 2CO2

Question 33

Fe2/3+ ions in reaction between I- and S2O8 2- ions

Answer 33

Both reactants negative so slow S2O8 2- + 2Fe2+ -> 2SO4 2- + 2Fe3+ 2Fe3+ + 2I- -> I2 + 2Fe2+

Question 34

Mn2+ ions in autocatalysing reaction between MnO4- and C2O4 2- 5C2O4 2- + 2MnO4 - + 16H+ -> 10CO2 + 2Mn2+ + 8H2O

Answer 34

5C2O4 2- + 2MnO4 - + 16H+ -> 10CO2 + 2Mn2+ + 8H2O 4Mn2+ + MnO4- + 8H+ -> 5Mn3+ + 4H2O 2Mn3+ + C2O4 2- -> 2CO2 + 2Mn2+

Question 35

[Co(H2O)6]2+ with little OH- or little NH3 reaction and colours

Answer 35

[Co(OH)2 (H2O)4] | Pink solution to blue precipitate (turns brown on standing)

Question 36

[Co(H2O)6]2+ with excess NH3 reaction and colours

Answer 36

[Co(OH)2 (H2O)4] to [Co(NH3)6] | Pink solution to blue precipitate that dissolves to form yellow-brown solution

Question 37

Cu2+ colour

Answer 37

Pale blue

Question 38

Co2+ colour

Answer 38

Pink

Question 39

Fe2+ colour

Answer 39

Pale green

Question 40

Fe3+ colour

Answer 40

Yellow

Question 41

Cr3+ colour

Answer 41

Green

Question 42

Cr2O7 2- colour

Answer 42

Orange

Question 43

Cr2+ colour

Answer 43

Blue

Question 44

CrO4 2- colour

Answer 44

Yellow

Question 45

Reducing Cr2O7 2-

Answer 45

Using zinc and dilute acid

Question 46

Amphoteric meaning

Answer 46

Reacts with both acids and bases

Question 47

Reaction of [Cr(OH)3 (H2O)3] with base and colours

Answer 47

To [Cr(OH)6]3- | Grey-green precipitate to dark green solution

Question 48

Reaction of [Cr(OH)3 (H2O)3] with acid and colours

Answer 48

[Cr(H2O)6]3+ | Grey green precipitate to green solution

Question 49

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

Answer 49

[CuCl4]2- Pale blue to yellow

Question 50

[Co(H2O)6]2+ with Cl-

Answer 50

[CoCl4]2- Pale pink to blue