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Chemistry Unit 5 > Transition metals > Flashcards

Transition metals Flashcards

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1
Q

Characteristic features of Transition metals

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

What allows them this is their incomplete d orbital

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2
Q

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

A
  • Electrons excited, so there’s a transition from ground state to excited state
  • Energy absorbed from visible light
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3
Q

Co-ordinate bond

A
  • A covalent bond
  • in which pair of electrons come from one atom
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4
Q

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

A
  • TM ions can accept electron pairs
  • O in H2O can donate pair
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5
Q

Why can CuCl colourless, but CuCl2 coloured?

A
  • 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
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6
Q

Bidentate ligand

A
  • 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
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7
Q

Naturally-occuring complex that contains iron

A
  • Haemoglobin
  • transports oxygen around body
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8
Q

Coordination number

A
  • no. of co–ordinate bonds
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9
Q

Multidentate ligand

A
  • a molecule than can donate many lone pairs to a metal ion in order to form co-ordinate bonds
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10
Q

Why can a molecule act as a ligand?

A
  • Have a lone pair
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11
Q

Name the ammonia complex used to distinguish aldehydes and ketones

A
  • Tollen’s reagent (diammine silver)
  • [Ag(NH3)2]+
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12
Q

Ligand

A
  • species which can donate a pair of electrons to a metal ion
  • acts as a lewis base
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13
Q

E=hf

A
  • 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
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14
Q

Most common shapes found in TM complexes

A
  • octahedral 90°
  • tetrahedral 109°
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15
Q

Autocatalysis

A
  • A product of the reaction acts as a catalyst.
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16
Q

How is Mn2+ involved in the reaction between C2O42- and KMnO4

A
  • Mn2+ is oxidised to Mn3+ by MnO4-
  • Mn3+ is reduced to Mn2+ by C2O42-
  1. MnO4- + 4Mn2+ + 8H+ → 5Mn3+ + 4H2O
  2. C2O42-– + 2Mn3+ → 2Mn2+ + 2CO2
17
Q

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

A
  • Poison attaches to surface, blocking active site
  • Purify reactants (remove impurities)
18
Q

Heterogenous catalyst

A

catalyst in a different phase from that of the reactants.

19
Q

Homogenous catalyst

A

catalyst in a same phase from that of the reactants.

20
Q

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

A
  • Poison is Sulphur
  • Poison is adsorbed onto active sites.
  • Poison is not desorbed.
21
Q

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

A
  • Pt, Pd or Rh
  • Deposited on a ceramic honeycomb ,
  • which increases the surface area of the catalyst.
22
Q

Why are W and Ag very poor catalysts?

A
  • 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
23
Q

Oxidising and Reducing agents

A
  • Oxidising agents gains electrons
  • Reducing agents lose electrons
24
Q

Steps in the mechanism of heterogenous catalysts

A
  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

​

25
Q

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

A
  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
26
Q

Explain the curve: MnO4- and C2O42-

A
  • 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
27
Q

Complex ion definition

A
  • TM bonded to 1 or more ligands
  • Which are co-ordinately bonded
28
Q

Why is solution X red

A
  • (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
29
Q

Why is CO toxic?

A
  • Because it bonds to the haemoglobin, forming carboxyhaemoglobon
  • CO has greater affinity
  • carboxy is more stable than oxy
  • Prevents oxygen being transported
30
Q

2 ways to maximise the efficiency of catalysts?

A
  • Use powder to increase surface area of catalyst
  • Remove catalyst poisons from reactants
31
Q

Why are inert mediums used for heterogenous catalysts

A
  • to maximize surface area
  • and minimise cost
32
Q

Define active site

A
  • where reactants are adsorbed onto a catalyst surface

Note:

  • if the surface area increases, the number of active sites also increases
33
Q

Explain how and why iron ions catalyse the reaction between iodide ions and S2O82– ions

A
  • Reaction 1 and 2 involving I- and S2O82-
  • 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
34
Q

Why is Fe3+ more acidic than Fe2+

A
  • [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
35
Q

Why is it possible to use a spectrometer to measure the reaction between MnO4- and C2O42-

A
  • Manganate(VII) ions are coloured (purple)
  • All other reactants and products are too faint to be detected
36
Q

Factors that affect the colour of a complex

A
  • Type metal
  • Oxidation state of the metal
  • Type of ligands
  • Co-ordination number
  • Shape
37
Q

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

A
  • Reaction may be too fast** and may become **uncontrollable
  • Explosion may occur

Chemistry Unit 5 (7 decks)

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