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OCR A-Level Chemistry A > Chapter 24 - Transition Elements > Flashcards

Chapter 24 - Transition Elements Flashcards

D-block element, The formation and shapes of complex ions, Stereoisomerism in complex ions, Ligand substitution and precipitation, Redox and qualitative analysis.

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1
Q

What are the two special cases in the d-block in terms of electron configuration?

A

1) Chromium: 3d5 4s1 instead of 3d4 4s2. Half filled subshell
2) Copper: 3d10 4s1 instead of 3d9 4s2. Full subshell

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2
Q

Why do these special cases exist in the d block electron configurations?

A

A half filled and a fully filled d sub shell gives greater stability to these atoms.

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3
Q

What are transition elements?

A

D-block elements that form at least one ion with a partially filled d-orbital.

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4
Q

Which d-block elements are excluded from being transition elements?

A

Scandium and zinc. scandium forms a sc 3+ ion and zinc forms a Zn 2+ ion.

the zinc is empty and scandium is scant.

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5
Q

What are the properties of the transition elements?

A

1) transition elements form compounds with different oxidation states.
2) Form coloured compounds
3) Elements and compounds can act as catalysts

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6
Q

what are the colours of the various ions of iron?

A

iron 2+ - pale green

iron 3+ - yellow

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7
Q

What colours are the various ions of Chromium (Cr) ? what are the colours?

A

chromium/cr 3+ is green

chromium/cr 6+ is yellow / orange

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8
Q

What colours are the various ions of Copper?

A

Cu 2+ is blue

Cu + and Cu 3+ is colourless

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9
Q

table of common oxidation states and their colours?

A
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10
Q

What colour is potassium dichromate(VI)?

A

K2Cr2O7 is Orange

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11
Q

What colour is cobalt(II) chloride?

A

cobalt(II) chloride is Pink-purple

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12
Q

What colour is nickel(II) sulfate (NiSO₄) ?

A

NiSO₄ is Green

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13
Q

What colour is hydrated copper(II) sulfate?

A

Blue

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14
Q

What is the catalyst used in the Haber process?

A

an iron catalyst is used in the haber proccess.

N2 (g) + 3H2 (g) = 2NH3 (g)

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15
Q

What is the catalyst used in the production of sulfur trioxide for the manufacture of sulfuric acid?

A

Vanadium(V) oxide
V2O5

2SO2 (g) + O2 (g) = 2SO3

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16
Q

What is the catalyst used in hydrogenation?

A

Nickel

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17
Q

What is the catalyst used in the reaction of zinc metal with acids?

A

Cu 2+ ions are used as a catalyst in the reaction of zinc metal with acids : Zn (s) + H2SO4 = ZnSO4 (aq) + H2 (g)

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18
Q

What is the catalyst used in catalytic decomposition of hydrogen peroxide?

A

Manganese(IV) oxide
MnO2

2H202 (aq) = 2H2O (l) + O2

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19
Q

Define what a complex ion is

A

A complex ion is formed when ligands bond to a central transition metal ion.

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20
Q

Define coordination number

A

The number of coordinate bonds attached to the central metal ion.

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21
Q

Define what a ligand is

A

A molecule or ion that can donates a pair of electrons to the central transition metal ion to form a coordinate bond or dative covalent bond.

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22
Q

What is meant by a monodentate ligand?

A

A ligand that is able to donate one (hence mono) pair of electrons to a central metal ion.

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23
Q

Give 5 examples of common monodentate ligands and their charges

A
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24
Q

what is a bidentate ligand?

A

A bidentate (bi = two) ligand donates two pairs of electrons to the central metal ion

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25
Q

how is a complex ion shown?

A
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26
Q

Define denticity

A

The number of separate sites in a molecule or ion that can donate an electron pair to a transition metal ion.

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27
Q

What shape is created from a complex ion having a coordination number of 6?

A

an Octahedral shape is formed when it has a coordination number of six.

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28
Q

what is an octahedral shape?

A

an octahedral shape has:

1) the ligands arranged at the corners of the octahedron
2) bond angles of 90 degrees around the central metal ion

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29
Q

What shapes can be created from a complex ion having a coordination number of 4?

A

when there is a coordination number if 4 the shape is:
Tetrahedral
OR
Square planar

30
Q

When is a square planar shape formed in a complex ion?

A

When the transition metal in the complex ion has eight d-electrons in the highest energy d-sub-shell. e.g platinum (II) and palladium (II)

31
Q

What is stereoisomerism?

A

Same structural formula but a different arrangement of the atoms in space.

32
Q

What are the two types of stereoisomerism?

A

Cis-trans isomerism

Optical isomerism

33
Q

when does cis-trans isomerism exist in monodente square planar complexes? what is the general formula?

A

cis and trans isomers exist in square planar complexes with:

1) two molecules/ions of one monodentate ligand, X
2) two molecules/ions of another monodentate ligand Y

the general formula is [MX2Y2]n (n=charge)

34
Q

When can complex ions show cis-trans isomerism?

A

cis-trans isomers exist in square planar and octahedral complex ions.

35
Q

how does optical isomerism occur with both bidentate and monodentate ligands?

A

cis isomers of octohedral complexes have optical isomers if they have:

1) two molecules/ions of a bidentate ligand
2) two molecules/ions of a monodentate ligand

36
Q

how does cis-trans isomerism occur in octahedrals with monodentate ligands?

A

cis and trans isomers exist in in octahedral complxes with:

1) four molecules or ions of one monodentate ligand X
2) two molecules/ions of another mondentate ligand Y

the general formula is [MX4Y2]n (n=charge)

37
Q

When can complex ions show both types of stereoisomerism?

A

Six coordinate complex ions containing monodentate and bidentate ligands.

38
Q

What is optical isomerism?

A

Non-superimposable mirror images of each other.

Called enantiomers

39
Q

Define ligand substitution

A

Ligand substitution is a reversible reaction of a complex ion where One ligand in a complex ion is replaced by another ligand.

40
Q

Describe ligand substitution of aqueous copper(II) ions with ammonia, NH3

A

Four H2O molecules are replaced by ammonia (NH3) ligands, the solution turns from pale blue to dark blue.

[Cu(H2O)6] 2+ + 4NH3 = [Cu(NH3)4(H2O)2]2+ + 4H2O (l)
pale blue to dark blue

41
Q

Describe the ligand substitution of aqueous ammonia, NH3 with [Cr(H2O)6]3+ ?

A

six H2O molecules are replaced with six NH3 ligands to form [Cr(NH3)6}3+

the colour changes from violet to purple

[Cr(H2O)6]3+ + 6NH3 = [Cr(NH3)6}3+ + 6H2O
violet solution purple solution

42
Q

Describe ligand substitution of aqueous copper(II) ions with chloride ions

A

six H2O ligands are replaced by 4 chloride ions Cl- ligands. The solution starts out pale blue and moves to yellow on completion.

[Cu(H2O)6]2+ + 4Cl- = [CuCl4]2- + 6H2O

43
Q

Why does the solution of aqueous copper (II) ions reacting with chloride ions turn green as the reaction proceeds?

A

The yellow and blue solutions mixing gives a green colour.

44
Q

Why does the shape of the aqueous copper (II) ion change from octahedral to tetrahedral when it reacts with chloride ions?

A

Chloride ligands are larger in size than water ligands so fewer of them can fit around the Cu2+ ion.

45
Q

What is formed when chromium(III) potassium sulphate is dissolved in water? what’s the formula and colour?

A

The complex ion [Cr(H2O)6]3+ is formed.

A pale purple solution.

46
Q

What is formed instead when only chromium(III) sulphate is dissolved in water?

A

The complex ion [Cr(H2O)5SO4]+ is formed.

A green solution.

47
Q

Describe the reaction between [Cr(H2O)6]3+ and an excess of aqueous ammonia

A

A grey green precipitate of Cr(OH)3 is formed initially.
Cr(OH)3 dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+.
A purple solution.

48
Q

why is carbon monoxide bonding to haemoglobin so bad?

A

carbon monoxide can bond to haemoglobin but the process is irreversible as the bond is so strong. can lead to death.

49
Q

How does ligand substitution help with gas exchange in blood?

A

haemoglobin in red blood cells contain four protein chains

1) Each protein chain has a planar haem molecule within its structure
2) The Fe 2+ metal ion in haem bonds to a protien chain and water
3) the water can exchange for oxygen gas or CO2

Hb + O2 = HbO2

50
Q

What is a precipitation reaction?

A

a precipitation reaction is when Two aqueous solutions contain ions react together to form an insoluble ionic solid. (the precipitate)

51
Q

Describe the precipitation reaction of Fe2+ with OH and what is the equation?

A

Fe2+ + 2OH (OH- ions) = Fe(OH)2 (s)

pale green solution to green precipitate

52
Q

Describe the precipitation reaction of Fe3+ with OH and what is the equation?

A

Fe3+ + 3OH- = Fe(OH)3 (s)

pale yellow to orange-brown precipitate

53
Q

Describe the precipitation reaction of Mn2+ with OH and what is the equation?

A

Mn2+ + 2OH- = Mn (OH)2 (s)

pale pink solution to light brown precipitate

54
Q

Describe the precipitation reaction of Cr3+ with OH and what is the equation?

A

Cr3+ (aq) + 3OH- (aq) = Cr(OH)3 (s)

violet solution to green precipitate

55
Q

Describe the precipitation reaction of Cu2+ with NaOH and what is the equation?

A

Cu2+(aq)+2NaOH(aq)→ Cu(OH)2(s)+2Na+(aq)

pale Blue solution blue precipitate of copper(II) hydroxide.

Insoluble in excess NaOH.

56
Q

How do Cr3+ react with an excess of aqueous NaOH?

A

the hydroxide of Cr 3+ does dissolve in excess NaOH

Cr3+ =(NaOH (aq))= Cr(OH)3 (s) =excess NaOH=[Cr (OH)6] 3-
Violet solution green precipitate dark green solution

57
Q

How do Cu2+, Fe2+, Fe3+ and Mn2+ react with an excess of aqueous ammonia?

A

The hydroxides of Fe 2+,Fe 3+ and Mn2+ do not dissolve in excess NaOH

58
Q

What is the catalyst used in the reaction of zinc metal with acids?

A

Cu 2+ ions are used as a catalyst in the reaction of zinc metal with acids : Zn (s) + H2SO4 = ZnSO4 (aq) + H2 (g)

59
Q

how does Fe2+, Fe3+ and Mn 2+ react with excess NH3?

A

the hydroxides of Fe2+, Fe3+ and Mn2+ do not dissolve in excess NH3

60
Q

how do the hydroxides of Cu2+ and Cr2+ react with excess NH3?

A

the hydroxides of Cu2+ and Cr2+ do dissolve in excess NH3 (aq)

Cr 3+ (aq) = Cr(OH)3 (s) = [Cr(NH3)6]3+
violet solution green precipitate purple solution

Cu2+ = Cu(OH)2 (s) = [Cu(NH3)4(H2O)2]2+
pale blue solution blue preciptate dark blue solution

61
Q

what happens in the reavttion between Fe2+ ions and acidified magnate (VII) ions MnO4 - ?

A

MnO4 - (aq) + 8H+ (aq) + 5Fe2+ (aq) = Mn2+ (aq) + 5 Fe3+ (aq) + 4H2O (l)

purple to colourless

fe 2+ is oxidised to Fe3+
Mn is reduced from +7 in Mn04- to +2 in Mn2+

62
Q

what happens when Fe 3+ is added to iodine ions?

A

Fe3+ ions are reduced to Fe2+ ions by iodide ions I- (aq)

2Fe3+ + 2 I- (aq) = 2Fe2+ (aq) + I2 (aq)
yellow ornge pale green brown

Fe3+ is reduced to Fe2+
I- is oxidised to I2

63
Q

what happens when acidified dichromate (VI) ions (Cr2O7)2- are added to zinc metal?

A

Cr2O7 2- + 14H+ + 3Zn = 2Cr 3+ + 7 H2O (l) + 3Zn 2+
orange green
cr is reduced from +6 to 3+
zn is oxidsed from 0 to +2

64
Q

chromium(III) Cr3+ ions + hot alkaline hydrogen peroxide , H2O2?

A

2Cr3+ + 3H2O2 + 10 OH- = 2CrO4 2- (aq) + 8H2O

YELLOW SOLUTION

65
Q

(Cu 2+ ) + (iodide ions) I- = ?

A

2Cu2+ + 4I- = 2 CuI (s) + I2 (aq)

pale blue solution to a brown solution + white precipitate

66
Q

Cu2O + hot dilute sulferic acid = ?

A

Cu2O (s) + H2SO4 = Cu (s) + CuSO4 (aq) + H2O
red-brown solid brown solid and a blue solution

this is a disproportionation reaction :) as cu is both oxidised and reduced

67
Q

what are the tests for anions?

A
68
Q

you got this

A

don’t give up :)

69
Q

max is a sexy cunt

A

;)

70
Q

table

A

OCR A-Level Chemistry A (33 decks)

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