5.3

Question 1

Transition metal definition

Answer 1

A transition metal is an element that has an incomplete d-sub-shell as a stable ion.

Question 2

What two metals are not transition elements in the d-block, and what are their ions’ electronic configurations?

Answer 2

Sc³+: 1s², 2s², 2p⁶, 3s², 3p⁶
Zn²+: 1s², 2s², 2p⁶, 3s², 3p⁶, 3d¹⁰

Question 3

How come transition metals have variable oxidation states?

Answer 3

Because the 3d and 4d energy levels are so close in energy, the 3d electrons can be lost when an atom forms are stable 2+ ion

Question 4

When are transition metals’ highest oxidation states found?

Answer 4

In strong oxygen agent compounds
For example, potassium manganate (VII) and potassium dichromate (VI)

Question 5

Molecular formulae of:
Potassium manganate (VII)
Potassium dichromate (VI)
Sodium Thiosulphate
Chromate

Answer 5

KMnO4 (purple)
K2Cr2O7 (orange)
S2O3²-
CrO4²- (yellow)

Question 6

How do we see colour?

Answer 6

The colour that we observe is a mix of the wavelengths of light not absorbed.

Question 7

What are the 2 methods of transition metals as catalysts?

Answer 7

A) adsorption and desorption
B) t.m. changes oxidation state then bind to reactants forming intermediates with lower activation energy

Question 8

Pros and cons of transition metal catalysts

Answer 8

Pros
Reduce time and energy needed for reactions

Cons
Can be toxic, must be handled with care, and disposal must be in such a way as not to cause pollution.

Question 9

Complex ion definition

Answer 9

A complex ion is a transition metal bonded to 1 or more ligands by coordinate bonds.

Question 10

Ligand definition

Answer 10

A ligand is a molecule or ion that can donate a pair of electrons to a transition metal to form a coordinate bond.

Question 11

Conditions for cis-trans isomerism in complex ions

Answer 11

Octahedral - 4 monodentate and 2 different monodentate ligands OR 2 bidentate and 2 monodentate ligands
Square planar - 2 monodentate and 2 different monodentate

Question 12

Conditions for optical isomerism in complex ions

Answer 12

Octahedral - 3 bidentate OR 2 bidentate and 2 monodenate OR 1 hexadentate

Question 13

5 reaction names and their transition metal catalysts

Answer 13

Contact process:
Vanadium (V) oxide, V2O5

Alkenes hydrogenation:
Nickel

Haber process:
Iron

Hydrogen production:
Copper (II)

Decomposition of H2O2:
Manganese (IV) oxide, MnO2

Question 14

Name a hexadentate ligand

Answer 14

EDTA

Question 15

What is EDTA used for?

Answer 15

Decreases concentration of metal ions in a solution by binding with them
Treats mercury or lead poisoning

Question 16

What is the name of the cancer treatment drug?

Answer 16

Cis-platin

Question 17

Describe cis-platin

Answer 17

PtCl2(NH3)2
Prevents cancer cell division

Question 18

Tetrahedral

Answer 18

109.5°

Question 19

Chloride exception

Answer 19

Tetrahedral as ions are too big and only 4 can fit

Question 20

Describe haemoglobin

Answer 20

FeN4 in octahedral shape with O2 bonded temporarly above and globin below
O2 is replaced with H2O when delivered
CO permanently bonds so can displace O2

Question 21

General precipitation ligand substitution reactions

Answer 21

[M(H₂O)₆]²⁺ (aq) + 2OH⁻ (aq) –> [M(H₂O)₄(OH)₂]²⁺ (s) + 2H₂O (l)

If NH₃ (aq), forms same precipitate but NH₄⁺

Question 22

Precipitation reactions colours

Answer 22

Fe²⁺: pale green → dark green
Fe³⁺: pale yellow → rusty brown
Mn²⁺: pale pink → brown
Cu²⁺: pale blue → blue
Cr³⁺: violet → green

Question 23

Cu²⁺ other reactions (vague)

Answer 23

+ Excess NH₃ (aq)
+ Hydrochloric acid (aq)

Question 24

Cu²⁺ and excess NH₃ (aq) reaction and colours

Answer 24

[Cu(H₂O)₆]²⁺ (aq) + 4NH₃ (aq) ⇄ [Cu(NH₃)₄(H₂O)₂]²⁺ (aq) + 4H₂O (l)
Pale blue sol. ⇄ Blue sol.

Question 25

Cu²⁺ and Hydrochloric acid reaction and colours

Answer 25

[Cu(H₂O)₆]²⁺ (aq) + 4Cl⁻ (aq) ⇄ [CuCl₄]²⁻ (aq) + 6H₂O (l) Pale blue sol. ⇄ Yellow sol.

Question 26

Cr³⁺ reactions (vague)

Answer 26

+ Excess NH₃ (aq) + Excess NaOH (aq) Oxidation to Cr⁶⁺

Question 27

Cr³⁺ and excess NH₃ (aq) reaction and colours

Answer 27

[Cr(H₂O)₆]³⁺ (aq) + 6NH₃ (aq) ⇄ [Cr(NH₃)₆]³⁺ (aq) + 6H₂O (l) Violet sol. ⇄ Purple sol.

Question 28

Cr³⁺ and excess NaOH (aq) reaction and colours

Answer 28

[Cr(H₂O)₆]³⁺ (aq) + 6OH⁻ (aq) → [Cr(OH)₆]³⁻ (aq) + 6H₂O (l) Violet sol. → Green sol.

Question 29

Cr³⁺ to Chromate (VI) reaction and colours

Answer 29

Alkaline conditions 2[Cr(OH)₆]³⁻ (aq) + 3H₂O₂ (aq) HEAT→ 2CrO₄²⁻ (aq) + 2OH⁻ (aq) + 8H₂O (l) Green sol. → Yellow sol.

Question 30

Chromate (III) to Chromate (VI)

Answer 30

2CrO₄²⁻ (aq) ⇄ Cr₂O₇²⁻ (aq) Yellow sol ⇄ Orange sol. --> +H⁺ <-- +OH⁻

Question 31

Which is more stable - Fe²⁺ or Fe³⁺?

Answer 31

Fe³⁺ due to the half filled d orbital (while Fe²⁺ is partially filled)

Question 32

How can the concentration of oxidising agents in a solution be found?

Answer 32

React unknown conc. oxidising agent (e.g. Cu²⁺) with potassium iodide. 2Cu²⁺ + 4I⁻ → 2CuI + I₂ Then titrate this with Sodium Thiosulphate (S₂O₃²⁻) to find [I₂] and calculate [Cu²⁺] 2S₂O₃²⁻ + I₂ → 2I⁻ + S₄O₆²⁻ Brown sol. → Pale yellow. The end-point is hard to see so we add starch solution. This turns the solution blue and changes the colour change to Dark blue sol. → Pale yellow sol.