Transition metals

Question 1

Characteristic features of Transition metals

Answer 1

• Coloured ions
• Can form complexes
• Variable oxidation states
• Catalytic activity

What allows them this is their incomplete d orbital

Question 2

Why are complex ions with partially filled d sub-levels coloured?

Answer 2

• Electrons excited, so there’s a transition from ground state to excited state
• Energy absorbed from visible light

Question 3

Co-ordinate bond

Answer 3

• A covalent bond
• in which pair of electrons come from one atom

Question 4

Why can co-ordinate bonds form between transition metal ions and water molecules?

Answer 4

• TM ions can accept electron pairs
• O in H2O can donate pair

Question 5

Why can CuCl colourless, but CuCl₂ coloured?

Answer 5

• Cu⁺ is present in CuCl
• Cu²⁺ is in CuCl₂
• Cu⁺ has a fully filled d sub–shell (1)
• Cu²⁺ has a partially filled d sub–shell (1)
• In Cu⁺ there is no absorbtion of light as electron transition not possible

Question 6

Bidentate ligand

Answer 6

• a molecule than can donate 2 lone pairs to a metal ion in order to form 2 co-ordinate bonds
• from 2 different atoms in a molecule

Question 7

Naturally-occuring complex that contains iron

Answer 7

• Haemoglobin
• transports oxygen around body

Question 8

Coordination number

Answer 8

• no. of co–ordinate bonds

Question 9

Multidentate ligand

Answer 9

• a molecule than can donate many lone pairs to a metal ion in order to form co-ordinate bonds

Question 10

Why can a molecule act as a ligand?

Answer 10

• Have a lone pair

Question 11

Name the ammonia complex used to distinguish aldehydes and ketones

Answer 11

• Tollen’s reagent (diammine silver)
• [Ag(NH₃)₂]⁺

Question 12

Ligand

Answer 12

• species which can donate a pair of electrons to a metal ion
• acts as a lewis base

Question 13

E=hf

Answer 13

• E is the energy absorbed by the excited electron to move from the ground to excited state
• h is Planck’s constant
• f is the frequency of light absorbed

Question 14

Most common shapes found in TM complexes

Answer 14

• octahedral 90°
• tetrahedral 109°

Question 15

Autocatalysis

Answer 15

• A product of the reaction acts as a catalyst.

Question 16

How is Mn²⁺ involved in the reaction between C₂O₄^2- and KMnO₄

Answer 16

• Mn²⁺ is oxidised to Mn³⁺ by MnO₄^-
• Mn³⁺ is reduced to Mn²⁺ by C₂O₄^2-

1. MnO₄^- + 4Mn²⁺ + 8H⁺ → 5Mn³⁺ + 4H2O
2. C₂O₄^2-– + 2Mn³⁺ → 2Mn²⁺ + 2CO₂

Question 17

Why does poisoning reduce the effectiveness of catalysts and how can it be minimised?

Answer 17

• Poison attaches to surface, blocking active site
• Purify reactants (remove impurities)

Question 18

Heterogenous catalyst

Answer 18

catalyst in a different phase from that of the reactants.

Question 19

Homogenous catalyst

Answer 19

catalyst in a same phase from that of the reactants.

Question 20

,Substance which poisons iron in the Haber process and how does it do it?

Answer 20

• Poison is Sulphur
• Poison is adsorbed onto active sites.
• Poison is not desorbed.

Question 21

Catalysts used in exhaust systems and how they’re made to maximise efficiency

Answer 21

• Pt, Pd or Rh
• Deposited on a ceramic honeycomb ,
• which increases the surface area of the catalyst.

Question 22

Why are W and Ag very poor catalysts?

Answer 22

• In W the adsorption is too strong so products not desorbed
• This means the Active sites are blocked
• In Ag the adsorption is too weak
• Reactants not held long enough for a reaction to occur

Question 23

Oxidising and Reducing agents

Answer 23

• Oxidising agents gains electrons
• Reducing agents lose electrons

Question 24

Steps in the mechanism of heterogenous catalysts

Answer 24

1. Reactants adsorb on the active site of the catalysts (surface)
2. Reactants must be correctly oritented
3. Bonds of the reactants weaken
4. Reactants combine, forming products which desorb from sufarce

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Question 25

2 Risks associated with using cisplatin for anticancer drugs and state how the adverse effects could be minimised

Answer 25

1. May lead to **_patient death_** as it kills normal cells 2. It may attach to DNA in normal cells,leading to hair loss * Use in very small amounts * Focus the application to the tumour

Question 26

Explain the curve: MnO₄^- and C₂O₄^2-

Answer 26

* Curve starts with shallow gradient (slow rate) * Because negative ions collide so Ea high * Curve gets steeper because autocatalyst (Mn²⁺) formed * Ea lowered because oppositely charged ions **_attract_** * The rate therefore **_increases_** * Curve levels out approaching time axis as **_MnO₄-**_ ions _**used up_**

Question 27

Complex ion definition

Answer 27

* TM bonded to 1 or more ligands * Which are co-ordinately bonded

Question 28

Why is solution X red

Answer 28

* (Frequencies of) Complementary colour to red is absorbed from the white light * electrons in d orbital excite as they gain the photon's energy * Red light that remains is transmitted and the colour is observed

Question 29

Why is CO toxic?

Answer 29

* Because it bonds to the haemoglobin, forming carboxyhaemoglobon * CO has greater affinity * carboxy is more stable than oxy * Prevents oxygen being transported

Question 30

2 ways to maximise the efficiency of catalysts?

Answer 30

* Use powder to increase surface area of catalyst * Remove catalyst poisons from reactants

Question 31

Why are inert mediums used for heterogenous catalysts

Answer 31

* to maximize surface area * and minimise cost

Question 32

Define active site

Answer 32

* where reactants are adsorbed onto a catalyst **_surface_** Note: * if the surface area increases, the number of active sites also increases

Question 33

Explain how and why iron ions catalyse the reaction between iodide ions and S₂O₈^2– ions

Answer 33

* Reaction 1 and 2 involving I- and S₂O₈^2- * 2 negative ions would repel leading high Ea * Positive Fe ions attract negative ions * (**Fe**) has a variable oxidation state * With iron ions, theres an alternative route to the reaction * One with a lower activation energy * Fe²⁺ is involved but regenerated

Question 34

Why is Fe³⁺ more acidic than Fe²⁺

Answer 34

* [Fe(H₂O)₆]³⁺⇒ [Fe(H₂O)₅OH]²⁺ + H⁺ * Fe³⁺ ion has higher charge density than Fe²⁺ * There's increased polarisation in the co-ordinatedly bonded water ligands * O—H bond weakens and H+ ion released

Question 35

Why is it possible to use a spectrometer to measure the reaction between MnO₄- and C₂O₄^2-

Answer 35

* Manganate(VII) ions are coloured (purple) * All other reactants and products are too faint to be detected

Question 36

Factors that affect the colour of a complex

Answer 36

* Type metal * Oxidation state of the metal * Type of ligands * Co-ordination number * Shape

Question 37

Explain why a combustion reaction shouldn't use a very good catalyst

Answer 37

* Reaction may be **_too fast**_ and may become _**uncontrollable_** * **_Explosion_** may occur