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A-Level Chemistry > Chapter 24 > Flashcards

Chapter 24 Flashcards

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1
Q

Physical properties of d block elements

A

High melting points and boiling points
Shiny in appearance
Conduct both electricity and heat

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2
Q

Transition elements

A

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

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3
Q

What two d block elements are not transition elements?

A

Scandium and zinc are d block elements but do not match the definition and are thus not classified as transition elements

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4
Q

Scandium

A

Only forms Sc3+ by loss of two 4s electrons and one 3d electron thus highest energy electron is in 3p subshell/orbital

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5
Q

Zinc

A

Only forms the Zn2+ ion by the loss of its two 4s electrons thus has a fully filled 3D subshell (full d-orbitals)

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6
Q

Properties of transition metals?

A

They form compounds in which the transition element has different oxidation states
They form coloured compounds
The elements and their compounds can act as catalysts

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7
Q

Variable oxidation states

A

Transition elements form compounds with more than one oxidation state - number of oxidation states increases across the transition elements series to manganese and then decreases - all of the transition elements form compounds with an oxidation number of +2

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8
Q

Species containing transition metal in highest oxidation state?

A

A strong oxidising agent

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9
Q

Potassium dichromate (vi)

A

Bright orange

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10
Q

Cobalt (ii) chloride

A

Pink-purple

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11
Q

Nickel (ii) Sulfate

A

Green

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12
Q

Copper (ii) Sulfate

A

Blue

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13
Q

What is colour of transition element solution linked to?

A

Partially filled d-orbitals of the transition metal ion - colour varies with different oxidation states

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14
Q

Fe 2+

A

Pale green

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15
Q

Fe 3+

A

Yellow

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16
Q

Cr 3+

A

Green

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17
Q

Cr +6

A

Yellow

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18
Q

Haber process

A

Manufacture of ammonia from nitrogen and hydrogen
CATALYSED BY A FINELY DIVIDED IRON CATALYST

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19
Q

Contact process

A

Sulfur trioxide from oxidation of sulfur dioxide - catalysed by vanadium oxide

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20
Q

Hydrogenation of vegetable fats in manufacture of margarine?

A

Uses nickel as the catalyst

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21
Q

Catalytic decomposition of hydrogen peroxide forming oxygen

A

Uses manganese oxide as the catalyst
2H2O2 -> 2H2O + O2

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22
Q

Example of homogenous catalysts

A

Catalyst is in the same physical state as the reactants - reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+ (aq) ions

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23
Q

Overall reaction homogenous catalyst

A

S2O82- (aq) + 2I- (aq) -> 2SO42- (aq) + I2 (aq)

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24
Q

When peroxodisulfate ions is carried out with a trace of starch

A

A blue-black colour forms ; if this experiment is repeated with a small a Fe2+ - blue black solution forms much more quickly demonstrating the catalytic action of transition metal ion

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25
Q

Fe2+ disulfate?

A

Forms Fe3+

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26
Q

Vital property of d-block elements?

A

Ability to form complex ions - blue solution is formed containing complex ion [Cu(H2O)6]2+

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27
Q

How can complex ions be formed?

A

Not restricted to d-block elements - other elements such as aluminium can also form complex ions

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28
Q

What is a ligand?

A

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

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29
Q

What is a ligand?

A

It is a molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond

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30
Q

What is a dative covalent bond/coordinate bond?

A

Special kind of covalent bond which is formed when one of the bonded atoms provides both of the electrons for the shared pair - coordination number indicates the number of coordinate bonds attached to the central metal ion

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31
Q

Overall charge of complex ion

A

Sum of the charges on the central metal ion and any ligands present

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32
Q

Water acting as a ligand?

A

Each water molecule donating a lone pair of electrons from the oxygen atom to the central metal ion to form a coordinate bond

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33
Q

Monodentate ligand

A

A ligand that is able to donate one pair of electrons to a central metal ion

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34
Q

Examples of monodentate ligands

A

Water/ammonia/halides/cyanide

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35
Q

Bidentate ligands

A

Donate two lone pairs of electrons to the central metal ion forming two coordinate bonds

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36
Q

Common bidentate ligands?

A

1,2 - diaminoethane and ethanedioate

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37
Q

1,2-diaminoethane

A

Each nitrogen atom donates a pair of electrons to the central metal ion forming a coordinate bond

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38
Q

Ethanedioate ion

A

Each negatively charged oxygen atom donates a lone pair of electrons to the central metal ion

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39
Q

6 coordinate complexes?

A

With coordination number 6 an octahedral shape is produced - bond angles around central ion being 90 degrees

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40
Q

Complexes with coordination number 4

A

Either tetrahedral or square planar

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41
Q

Tetrahedral shape

A

Common of the two shapes with bond angles of 109.5 around the central metal ion

42
Q

When does square planar shape occur?

A

Occurs in complex ions of transition metals with 8 d electrons in the highest energy d sub-shell ; platinum , palladium and gold fall in this category and tend to form square planar complexes

43
Q

Square planar

A

Ligands are arranged with two going out and two going in
90 degrees bond angle

44
Q

Platinum charge

A

2+

45
Q

Palladium charge

A

2+

46
Q

Gold charge

A

3+

47
Q

For complex ions type of stereoisomerism?

A

Depends on number and type of ligands that are attached to central metal ion
4 and 6 coordinate complex ions containing two different monodentate ligands show cis-trans isomerism
6 coordinate complex ions containing monodentate and bidentate ligands can show both cis trans and optical isomerism

48
Q

Cis trans isomerism in complex ions?

A

Cis-trans isomerism occurs in some square planar and octahedral complex ions

49
Q

Cis-trans isomerism square planar

A

Simplest example of cis-trans isomerism is found in 4 coordinate square planar complexes that have no more than two identical ligands attached to the central metal ion

50
Q

Cis square planar isomer?

A

Two identical groups are adjacent to each other - one going inside and one going outside (next to each other vertically)

51
Q

Trans isomer

A

Two identical groups are diagonally opposite each other - coordinate bonds are 180 degrees apart

52
Q

Cis-trans in monodentate ligands?

A

Octahedral complexes containing 4 of one type of ligand and two of another type of ligand also exist ast cis-trans isomers

53
Q

Cis [Co(NH3)4Cl2]+

A

Chloride ligands are next to each other - 90 degrees apart (different bonds - one in the plane and the other going out)

54
Q

Trans [Co(NH3)4Cl2]+

A

Chloride ligands are vertically opposite each other - 180 degrees apart - both ligands are in the same plane

55
Q

Colours of [Co(NH3)4Cl2]+

A

Cis = violet
Trans = green

56
Q

Bidentate ligands cis-trans stereoisomerism

A

THERE SHOULD BE TWO OF THE SAME LIGANDS NEXT TO EACH OTHER (DIFFERENT PLANES) - 90 DEGREES APART FOR CIS AND 180 FOR TRANS (SAME PLANE)

57
Q

Optical isomers

A

Non-superimposable mirror images of each other

58
Q

Optical isomers of octahedral complexes?

A

Only occurs in octahedral complexes containing two or more bidentate ligands
Can only form enantiomers of cis isomers

59
Q

Optical isomers

A

Can also be seen in complexes containing 3 bidentate ligands

60
Q

1,2-diaminoethane

A

Such a common bidentate ligand that it is often abbreviated to “en”

61
Q

Ligand substitution reaction

A

One ligand in a complex ion is replaced by another ligand

62
Q

Reactions of aqueous copper (ii) ions

A

Copper sulfate is dissolved in water and [Cu(H2O)6]2+ forms
This is a pale blue solution which changes colour to form a dark blue solution when 4NH3 is added and replaces 4 of the H2O ligands producing 4H2O as a by-product

63
Q

Breakdown of addition of 4NH3 to hexaaquacopper

A

Add the ammonia drop-wise to the solution
- pale blue precipitate of Cu(OH)2 is formed in the first stage of the reaction
- the precipitate then dissolves in excess ammonia to form a dark blue solution

64
Q

Ligand substitution with chloride ions?

A

Concentrated HCl can be used as a source of chloride ions - excess is added - the pale blue solution changes colour to form a yellow solution which is another example of a ligand substitution reaction as 6 water ligands have been replaced with 4 chloride ligands

65
Q

Observations of ligand substitution of chloride ions?

A

Intermediate green solution is formed but this is just the result of the yellow solution mixing with the blue solution to give a green colour as the reaction proceeds

66
Q

Hexaaquacopper to tetrachlorocopper?

A

Change in coordination number : 6 to 4
Change in colour : pale blue to yellow solution
Change in shape : octahedral to tetrahedral

67
Q

Reasoning behind number of chloride ligands?

A

They are larger in size/bulkier than water ligands so fewer chloride ligands can fit around the central Cu2+ ion

68
Q

What is chromium potassium Sulfate called?

A

Chrome alum

69
Q

When chromium potassium Sulfate is dissolved in water?

A

Complex ion [Cr(H2O)6]3+ is formed - this is pale purple solution

70
Q

When chromium iii Sulfate is dissolved in water?

A

Green solution containing chromium iii is formed - in this case it is the complex ion [Cr(H2O)5SO4]+ where ONE OF THE WATER LIGANDS IS REPLACED WITH SO4

71
Q

Oxidation state of chromium ions?

A

+3

72
Q

Equation for chromium ligand substitution reaction with ammonia?

A

[Cr(H2O)6]3+ + 6NH3 -> [Cr(NH3)6]3+ + 6H2O
Where hexaaquachromium is violet and turns purple

73
Q

Breakdown of reaction of ammonia with (cr(H2O)6) 3+

A

When the ammonia is added drop-wise to the chromium iii solution it takes place in two steps
STEP 1 : grey-green precipitate of cr(oh)3 is formed
STEP 2 : precipitate dissolves in excess ammonia to form the complex ion (cr(NH3)6)3+

74
Q

Carbon monoxide + Fe2+

A

Forms carboxyhaemoglobin - ligand substitution reaction takes place where the oxygen in haemoglobin is replaced by carbon monoxide as carbon monoxide binds to haemoglobin more strongly than oxygen so a small concentration of carbon monoxide can prevent a large proportion of haemoglobin molecules from carrying oxygen

75
Q

Carboxyhaemoglobin?

A

Bond is so strong that this process is irreversible

76
Q

Precipitation reaction

A

When two aqueous solutions containing ions react together to form an insoluble ionic solid called a precipitate

77
Q

Cu2+ reaction with NaOH

A

Blue solution forms a blue precipitate of copper hydroxide and PRECIPITATE IS INSOLUBLE IN EXCESS NAOH

78
Q

Fe2+ with NaOH

A

Pale green solution reacts to form a green precipitate of Iron (ii) hydroxide - precipitate is insoluble in excess sodium hydroxide but turns brown at its surface on standing in air as iron (ii) is oxidised to iron (iii)

79
Q

Fe3+ with NaOH

A

Pale yellow solution reacts to form an orange-brown precipitate of iron(iii) hydroxide - precipitate is insoluble in excess sodium hydroxide

80
Q

Mn2+ and NaOH

A

Pale pink solution reacts to form a light brown precipitate of manganese (ii) hydroxide which darkens on standing in air
PRECIPITATE IS INSOLUBLE IN EXCESS NAOH

81
Q

Reaction of Cr3+ with NaOH

A

Violet solution reacts to form a grey-green precipitate of chromium (iii) hydroxide
Precipitate is SOLUBLE IN EXCESS NAOH forming a dark green solution

82
Q

Chain of reaction Cr3+ and NaOH

A

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

83
Q

Copper hydroxide precipitate and ammonia?

A

Dissolves in excess ammonia to form a deep blue solution with the formula [Cu(NH3)4(H2O)2]2+

84
Q

Chromium hydroxide precipitate + ammonia

A

Chromium hydroxide is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ which is a purple solution

85
Q

Fe2+/Fe3+/Mn2+ + ammonia

A

All react with an excess of aqueous ammonia in the same way as they react with aqueous sodium hydroxide - forming precipitates of iron (ii and iii) hydroxide and manganese hydroxide - no further reaction with aqueous ammonia so these precipitates do not dissolve

86
Q

Fe2+ + MnO4- ions

A

Fe2+ is oxidised to Fe3+
MnO4- is reduced to Mn2+
Solution containing MnO4- is purple and is decolourised by Fe2+ ions to form a colourless solution containing Mn2+ ions

87
Q

Fe3+ to Fe2+

A

When a solution of Fe3+ reacts with iodide ions the orange brown Fe3+ ions are reduced to pale green Fe2+ ; this colour change is obscured by the oxidation of iodide ions to form iodine which has a brown colour

88
Q

2Fe3+ + 2I- -> 2Fe2+ + I2

A

2Fe3+ is orange brown
Fe2+ is pale green
I2 is brown

89
Q

Electrode potential for redox reactions?

A

More positive the electrode potential value - the more likely the species to undergo reduction and shift to the right, gaining electrons

90
Q

How are cr2o72- ions reduced to cr3+?

A

Orange to green colour - reduced by the addition of zinc - with an excess of zinc, chromium iii ions are reduced further to chromium ii which is pale blue colour

91
Q

Oxidation of cr3+ to cro42-

A

Hot alkaline hydrogen peroxide h2o2 is a powerful oxidising agent and can be used to oxidise chromium iii to chromium 6

92
Q

Overall equation for oxidation of cr3+ to cro42-

A

3H2O2 + 2Cr3+ + 10OH- -> 2CrO42- + 8H2O

93
Q

Reduction of Cu2+ to Cu+

A

When they react with excess iodide ions a redox reaction occurs and I- is oxidised to brown I2 while a white precipitate of copper iodide is also created

94
Q

Equation for reduction of cu2+ to cu+

A

2Cu2+ + 4I- -> 2CuI + I2 (s)
Pale blue
Copper iodide is a white precipitate
Iodine is brown

95
Q

Disproportionation of Cu+ ions

A

Solid copper (I) oxide reacts with hot dilute H2SO4 - a brown precipitate of copper is formed together with a blue solution of copper (ii) Sulfate

96
Q

Disproportionation of Cu+ ions equation

A

Cu2O + H2SO4 -> Cu + CuSO4 + H2O
Copper goes from +1 to + 2
-1 to 0

97
Q

Copper solid

A

Brown solid

98
Q

Copper Sulfate

A

Blue solution

99
Q

Ammonium ions + OH-

A

NH4- + OH- -> NH3 + H2O
Ammonia is evolved it will turn damp red litmus paper blue

100
Q

Halide ions solubility in NH3

A

Cl- soluble in dilute NH3
Br- soluble in concentrated nh3
I- insoluble in NH3

A-Level Chemistry (28 decks)

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