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Wjec A Level Chemistry > 3.4 D-block > Flashcards

3.4 D-block Flashcards

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1
Q

What is a transition metal?

A

Element that possesses a partially filled d sub-shell as an atom or in its stable ions

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2
Q

Can d-block transition metals attain various oxidation states in their compounds?

A

Yes

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3
Q

How can d-block transition metals attain various oxidation states in their compounds?

A

The energy levels of the 4s and 3d sub-levels are very close which means different numbers of electrons can be gained or lost using similar amounts of energy

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4
Q

Common oxidation states of chromium

A

+3
+6

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5
Q

Common oxidation states of manganese

A

+2
+4
+7

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6
Q

Common oxidation states of iron

A

+2
+3

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7
Q

Common oxidation states of cobalt

A

+2
+3

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8
Q

Common oxidation states of copper

A

+1
+2

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9
Q

Colour of aqueous solutions of compounds containing Cr3+

A

Green

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10
Q

Colour of aqueous solution of compounds containing CrO4^2-

A

Yellow

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11
Q

Colour of aqueous solution of compounds containing Cr2O7^2-

A

Orange

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12
Q

Colour of aqueous solution of compounds containing MnO4^-

A

Purple

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13
Q

Colour of aqueous solution of compounds containing Co^2+

A

Pink

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14
Q

Colour of aqueous solution of compounds containing Fe^2+

A

Pale green

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15
Q

Colour of aqueous solution of compounds containing Fe^3+

A

Red-brown

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16
Q

Colour of aqueous solution of compounds containing Cu^2+

A

Pale blue

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17
Q

What is a ligand?

A

Small molecule or ion with a lone pair of electrons which can bond to a transition metal ion

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18
Q

How many ligands does a tetrahedral transition metal complex have?
What angle are these to eachother?

A

4
109.5 degrees

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19
Q

How many ligands does a octahedral transition metal complex have?
What angle are these to eachother?

A

6
90 degrees

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20
Q

Is a tetrahedral or octahedral transition metal complex more common?

A

Octahedral

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21
Q

When is a transition metal ion coloured

A

In complexes

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22
Q

What energy do d-orbitals in a transition metal ion have when there is no ligand?

A

Degenerate
The same

23
Q

What happens to the energy levels of d-orbitals of transition metals when a ligand approaches?

A

Energy of 3 of the d-orbitals become different to the other 2
3 of lower energy
2 of higher energy

24
Q

How does an electron in one of the d-orbitals move between the sets of orbitals of different energies?

A

It needs to gain sufficient energy which is absorbed in the form of light

25
Q

How many frequencies of light is absorbed as an electron gains energy in a d-orbital and why?

A

1
It corresponds to the energy gap between orbitals

26
Q

Which colour is seen after light is absorbed by an electron from a d-orbital?

A

The complementary colour is reflected
The colour seen is made up of the light frequencies that are NOT absorbed

27
Q

Colour of compounds containing ((Cu(H2O)6))^2+ and which region of the spectrum is absorbed

A

Pale blue
Light in red region is absorbed

28
Q

Colour of complexes containing ((Fe(H2O)6))^3+ and which region of the spectrum is absorbed

A

Yellow
Light in the purple region is absorbed

29
Q

Are all transition metal complexes coloured and why?

A

No
Electrons cannot move from lower to higher orbitals as they either have a full d sub-shell or an empty d-subshell

30
Q

Examples of colourless transition metal complexes

A

Copper(I) - full d sub-shell
Scandium(III) - empty d sub-shell

31
Q

What is a ligand exchange reaction

A

Where a ligand in a complex ion is replaced by a different one

32
Q

Why is concentrated hydrochloric acid used in ligand exchange reactions?

A

Provides a high concentration of chloride ions

33
Q

Why can less chloride ions fit around a complex ion than other ligands eg water molecules

A

Chloride ions are bigger than water molecules so there isn’t room to fit six around the central metal ion

34
Q

What happens if conc HCl is added to a solution containing ((Cu(H2O)6))^2+

A

6 water molecules are replaced by 4 chloride ions

35
Q

What happens if conc HCl is added to a solution containing ((Co(H2O)6))^2+

A

6 water molecules are replaced by 4 chloride ions

36
Q

Colour of ((Cu(H2O)6))^2+

A

Blue

37
Q

Colour of ((Cu(NH3)4(H2O)2))^2+

A

Royal blue

38
Q

Colour of ((Co(H2O)6))^2+

A

Pink

39
Q

Colour of ((CuCl4))^2-

A

Yellow-green

40
Q

Colour of ((CoCl4))^2-

A

Blue

41
Q

Homogenous transition metal catalysts

A

• same physical state as reactants
• use variable oxidation states to oxidise/reduce a reactant
• transition metal is returned to original oxidation state by a reaction with another molecule

42
Q

Examples of homogeneous transition metal catalysts

A

• Manganese(IV) oxide in decomposition of hydrogen peroxide
• Vanadium(V) oxide in the contact process, conversion of SO2 to SO3, vanadium(V) oxide is reduced from +5 to +4 and then reformed to original oxidation state

43
Q

Heterogenous transition metal catalyst

A

• different physical state to the reactants
• partially filled d-orbitals
• provides a solid surface for reactants to be adsorbed and brought closer for more opportunity to react
• molecules with lone pair of electrons can form coordinate bonds to the metal as there are available empty d-orbitals, this increases reactivity of species bonded to the metal

44
Q

Examples of heterogenous transition metal catalysts

A

• iron - Haber process
• nickel - hydrogenation of vegetable oil to form margarine

45
Q

What happens when NaOH(aq) is added to most transition metal ions

A

A coloured precipitate forma

46
Q

What does it mean if the precipitate of a transition metal ion dissolves on addition of excess NaOH(aq)

A

The transition metal is atmophoteric

47
Q

Cr3+ Solution colour
Observation after OH- is added
Observation after excess OH- is added

A

Green
Grey-green precipitate
Precipitate dissolves giving a deep green solution

48
Q

Fe2+ Solution colour
Observation after OH- is added
Observation after excess OH- is added

A

Pale green
Dark green precipitate
No change

49
Q

Fe3+ Solution colour
Observation after OH- is added
Observation after excess OH- is added

A

Yellow
Red-brown precipitate
No change

50
Q

Cu2+ Solution colour
Observation after OH- is added
Observation after excess OH- is added

A

Pale blue
Pale blue precipitate
No change

51
Q

Ionic equation when NaOH(aq) is added to a solution containing Cr3+

A

Cr3+(aq) + 3OH-(aq) —> Cr(OH)3(s)
Cr(OH)3(s) + 3OH-(aq) —> [Cr(OH)6]3-(aq)

52
Q

Ionic equation when NaOH(aq) is added to a solution containing Fe2+

A

Fe2+(aq) + 2OH-(aq) —> Fe(OH)2(s)

53
Q

Ionic equation when NaOH(aq) is added to a solution containing Fe3+

A

Fe3+(aq) + 3OH-(aq) —> Fe(OH)3(s)

54
Q

Ionic equation when NaOH(aq) is added to a solution containing Cu2+

A

Cu2+(aq) + 2OH-(aq) —> Cu(OH)2(s)

Wjec A Level Chemistry (19 decks)

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