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Alevel Chemistry Edexcel > Topic 15 - Transition Metals > Flashcards

Topic 15 - Transition Metals Flashcards

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1
Q

What are transition metals?

A

d-block elements which can form one or more stable ions with incompletely-filled d-orbitals
-aka every d-block element except zinc and scandium

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2
Q

Why are zinc and scandium not transition metals?

A
  • zinc’s ion Zn2+ has a full d-subshell

- scandium’s ion Sc3+ has an empty d-subshell

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3
Q

Why do transition metals show variable oxidation number?

A

they can form ions by loosing electrons from their 4s or 3d subshells

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4
Q

What is a ligand?

A

a molecule/negative ion with a lone pair of electrons which can form a dative bond with the empty, available d-orbitals of a transition metal

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5
Q

What is a complex ion?

A

a central transition metal ion surrounded by ligands

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6
Q

What is the coordination number (of a complex ion)?

A

the number of molecules/atoms a transition metal can datively bond to
-aka number of ligands

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7
Q

How do you name complex ions?

A
  • number of ligands (di, tri, tetra, penta, hexa etc)
  • ligand (aqua, ammine, hydroxo, chloro, fluoro, cyano, etc)
  • name of transition metal (or latin for anionic complexes: chromate, ferate, cobaltate, aluminate, vandate, cuprate, etc)
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8
Q

What is a cationic complex?

A

a complex ion with a positive charge

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9
Q

What is an anionic complex?

A

a complex ion with a negative charge

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10
Q

What is a monodentate ligand?

A

a ligand with one long pair of electrons/that can form one dative bond
eg. Cl-, H20, CN-, NH3

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11
Q

What is a bidentate ligand?

A

a ligand with two long pairs of electrons/that can form two dative bonds
eg. NH2CH2CH2NH2 (1,2 diaminoethane)

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12
Q

What is a polydentate ligand?

A

a ligand with multiple long pairs of electrons/that can form multiple dative bonds
eg. EDTA2- (hexadentate ligand)

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13
Q

Where does the colour of transition metal ions and complex ions come from?

A

splitting of energy levels of the d-orbitals by ligands

  • repulsion between the 3d electrons and the ligand’s lone pair of electrons increases the energy of the transition metal’s d-orbitals
  • some d-orbitals rise in energy more than others, which creates a gap between the d-orbitals
  • a particular wavelength of light is absorbed, which promotes electrons within the d-orbitals
  • the complementary colour is reflected
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14
Q

Why do some aqueous transition metal ions and complex ions have a lack of colour?

A

no d-orbital electrons or d subshell is full so no electrons jump so no energy is absorbed

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15
Q

What could cause a change of colour in transition metal ions?

A
  • change in oxidation number
  • change in ligand
  • change in coordination number
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16
Q

How is haemoglobin an example of a complex ion?

A

it is an iron (II) complex containing a multidentate ligand

-ligand exchange rxn occurs when an oxygen molecule bond to haemoglobin it replaced with a carbon monoxide molecule

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17
Q

What is the colour of the vanadium ion with an oxidation number of +5 aka VO2 +?

A

yellow

18
Q

What is the colour of the vanadium ion with an oxidation number of +4 aka VO 2+?

A

blue

19
Q

What is the colour of the vanadium ion with an oxidation number of +3 aka V3+?

A

green

20
Q

What is the colour of the vanadium ion with an oxidation number of +2 aka V2+?

A

violet

21
Q

How can Cr2O7 2- be reduced to Cr3+ and then reduced further to Cr2+?

A

using zinc (as reducing agent) in dilute acid

22
Q

How can Cr3+ be oxidised to Cr2O7 2-?

A

using hydrogen peroxide in alkaline conditions followed by acidification

23
Q

2CrO4 2− + 2H+ ⇌

A

Cr2O7 2− + H2O

24
Q

What is observed when a little sodium hydroxide is added to chromium ions?

A

green solution changes to grey-green ppt

25
Q

What is observed when a little ammonia is added to chromium ions?

A

green solution changes to grey-green ppt

26
Q

What is observed when a little sodium hydroxide is added to iron(III) ions?

A

yellow solution changes to brown-red ppt

27
Q

What is observed when a little ammonia is added to iron(III) ions?

A

yellow solution changes to brown-red ppt

28
Q

What is observed when a little sodium hydroxide is added to iron(II) ions?

A

pale green solution changes to dark green ppt

29
Q

What is observed when a little ammonia is added to iron(II) ions?

A

pale green solution changes to dark green ppt

30
Q

What is observed when a little sodium hydroxide is added to cobalt ions?

A

pink solution changes to blue ppt

31
Q

What is observed when a little ammonia is added to cobalt ions?

A

pink solution changes to blue ppt

32
Q

What is observed when a little sodium hydroxide is added to copper ions?

A

blue solution changes to pale blue ppt

33
Q

What is observed when excess sodium hydroxide is added to chromium ions?

A

green solution changes to grey-green ppt changes to green solution (ppt dissolves)

34
Q

What is observed when excess ammonia is added to chromium ions?

A

green solution changes to grey-green ppt changes to purple solution (ppt dissolves)

35
Q

What is observed when excess ammonia is added to cobalt ions?

A

pink solution changes to blue ppt changes to pale brown solution (ppt dissolves)

36
Q

What is observed when excess ammonia is added to copper ions?

A

blue solution changes to pale blue ppt changes to dark blue solution (ppt dissolves)

37
Q

What could lead to a change in coordination number?

A

-large uncharged ligands (eg. H2O) being substituted with small, charged ligands (eg. Cl-)

38
Q

How does vanadium (V) oxide (V2O5) catalyse the contact process (SO2 + 1/2 O2 → SO3)?

A

acts as a heterozygous catalyst

  • sulfur dioxide (SO2) is oxidised to SO3 by vanadium oxide, which reduces it vanadium (IV) oxide (V2O4)
  • reduced catalyst is then oxidised back to vanadium (V) oxide
39
Q

What are the two reactions showing how vanadium (V) oxide acts as a catalyst in the contact process (SO2 + 1/2 O2 → SO3)?

A

V2O5 + SO2 → V2O4 + SO3

V2O4 + 1/2 O2 → V2O5

40
Q

How does a catalytic converter decrease carbon monoxide and nitrogen monoxide emissions from internal combustion engines?

A
  • carbon monoxide and nitrogen monoxide absorb to surface of catalyst
  • their bonds weaken
  • carbon dioxide and nitrogen dioxide desorb from the surface of the catalyst
41
Q

What are the reactions showing Fe2+ catalysing the reaction between I- and S2O8 2-?

A

S2O8 2- + 2I- → 2Fe3+ + 2SO4 -

2Fe3+ + 2I- → I2 + 2Fe2+

42
Q

What is autocatalysis?

A

when a product catalyses its own reaction

-as conc of product increases, the rate of rxn increases

Alevel Chemistry Edexcel (19 decks)

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