Chapter 24 Flashcards
1
Q
Where are the D-Block elements located?
A
Between group 2 and group 13. Across the periodic table from scandium to zinc.
2
Q
Which subshell has the highest energy?
A
The 3d subshell has the highest energy and electrons are added to just 3d orbitals.
3
Q
Give me the properties of the d-block elements?
A
As they are all metallic:
They have a high melting point, boiling point, shiny and can conduct heat and electricity.
4
Q
What happens when forming an atom?
A
The 4S orbital field before the 3D orbitals
5
Q
Why is chromium and copper different?
A
As chromium has a half filled d5 sub shell and copper has a fully filled d10 subshell which gives additional stability of chromium and copper atoms.
6
Q
What is the electron configuration for chromium and copper?
A
Cr - 3d5 4s1
Cu - 3d10 4s1
7
Q
What happens when forming an ion?
A
The 4S orbital empties before the 3D orbitals
8
Q
What is a D-Block element?
A
It is an element where the highest energy electrons are in the D orbitals. Scandium (3d1 4s2) through to zinc (3d10 4s2) are all the block elements.
9
Q
What are transition metals?
A
They are defined d-block elements that form at least one ion with a partially filled the sub shell.
10
Q
Which metals don’t fit the definition of a transition metal?
A
Scandium and zinc
11
Q
Why does Scandium not fit the definition?
A
- It only forms Sc 3+ ions
- Sc 3+ is [Ar]
- The d-subshell is empty (no electrons in the subshell)
12
Q
Why does Zinc not fit the definition?
A
- It only forms Zn 2+ ions
- Zn 2+ is [Ar] 3d10
- The d-subshell is completely full
13
Q
What are the 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.
14
Q
Explain the variable oxidation state?
A
Transition elements form compounds with more than one oxidation state e.g iron forms two chlorides: iron (II) Chloride, FeCl2 and iron (III) chloride, FeCl3
15
Q
What does the oxidation state number increase and decrease ?
A
Across the series to manganese and then decreases.
16
Q
Which oxidation state is very common?
A
+2 as it coordinates with the loss of the 4s electrons
17
Q
What are the solid compounds dissolved in to produce coloured solutions?
A
water
18
Q
What does the colour of the solution link to?
A
The partially filled the orbitals of the transition metal ion this colour varies with different oxidation states
19
Q
What colour is potassium dichromate?
A
Bright orange
20
Q
What colour is cobalt chloride?
A
Blue
21
Q
What colour is nickel (III) sulphate
A
Green
22
Q
What colour is hydrated copper (II) sulphate?
A
Blue
23
Q
What colour is iron (II)?
A
Pale green
24
Q
What colour is iron (III)
A
Yellow
25
What colour is Cr (III)
Green
26
What colour is Cr (VI)
Yellow or orange
27
What is a catalyst?
It is a substance which increases the rate of a chemical reaction without undergoing permanent change it provides an alternative reaction pathway with a lower activation energy.
28
What is a heterogeneous catalyst?
A catalyst with a different physical state to the reactants
29
Give an example of a heterogeneous catalyst?
The hydrogenation of vegetable fats in the manufacture of margarine uses nickel as its catalyst
30
Give the steps of heterogeneous catalysis?
1. Adsorption - reactant molecules form weak bonds to the catalyst surface
2. Bonds break in the reactants
3. Bonds in the products form
4. Products desorbs from the catalyst surface
31
What is a homogeneous catalyst?
A catalyst with the same physical state as the reactants.
32
Give an example of a homogeneous catalyst?
S2O8 2- + 2I- --> 2SO4 2- + I2 is catalysed by Fe 2+ or Fe 3+
1. 2Fe 3+ + S2O8 2- --> 2Fe 3+ + 2SO4 2-
2. 2Fe 3+ + 2I- --> 2Fe 2+ + I2
these combine to give the overall equation
33
What is a complex ion?
A complex ion if formed when one or more molecules or negative ions bond to a central metal ion. These molecules or negative ions are known as ligands. The overall charge can be +, - or neutral.
34
What is a ligand?
A molecule or ion which donates a pair of electrons to a central metal ion to form a coordinate bond/dative covalent bond (both electrons for the shared pair are provided by the same atom)
35
What does the coordination number indicate?
The number of coordinate bonds attached to the central metal ion. The shape of a complex ion depends on its coordination number.
36
What is the most common coordination number?
Six and four
37
What is the complex ion when copper sulphate forms a blue solution when dissolved in water?
[Cu (H2O)6] 2+
Ligand = H2O
Coordination number = 6
Bond angle = 90 degrees
38
What shape do six coordinate complexes have?
Octahedral shape
39
How is a complex ion represented?
In its formula the complex ion is enclosed by square brackets with the overall charge shown outside the brackets. The overall charge of the complex ion is the sum of the charges on the central metal metal iron and any ligands present.
40
Why are square brackets used?
To group all the parts of the complex ions together
41
How is the ligand shown?
Inside round brackets, the number of ligands are shown outside the round brackets.
42
How is [Cr(H2O)6 ] 3+ formed?
When CrCl3 . 6H2O is dissolved in water. Cr 3+ is the central metal ion and water is the ligand donating a lone pair of electrons from the oxygen to the central metal ion to form a coordinate bond. The coordination number is 6 as there are 6 coordinate bonds around the central metal ion.
43
What are monodentate ligands?
A ligand which donates one pair of electrons to the central atom.
44
What charge a does a water ligand have?
neutral
45
What charge a does a ammonia ligand have?
neutral
46
What charge a does a chloride ligand have?
-1
47
What charge a does a cyanide ligand have?
-1
48
What charge does a hydroxide ligand have?
-1
49
What are biodentate ligands?
A biodentate ligand donatse two pairs of electrons from different atoms to the central metal atom forming 2 coordinate bonds.
50
In biodentate ligands what does not correspond the coordination number of complexes?
The number of ligands
51
What are the shapes of four coordinate complexes?
Tetrahedral and square planar
52
Describe tetrahedral complexes?
- most common
| - bond angle = 109.5 around the central metal
53
Describe square planar complexes?
- occurs in complex ions of transition metals with 8d electrons in the highest d-sub shell.
- e.g platinum (II), palladium (II), gold (III)
54
What shape is a 6 coordinate complex?
Octahedral
55
Describe octahedral complex?
- bond angle 90
| - e.g MnSO4 dissolves in water forming the complex ion [Mn(H2O)6] 2+ creating 90 bond angles.
56
What are stereoisomers?
They have the same structural formula but different arrangement of atoms in space.
57
What two types of stereoisomerism do complex ions display?
- cis-trans isomerism
| - optical isomerism
58
What does the type of stereoisomerism depend on?
The number and type of ligands attached to the central metal ion and the shape of the complex.
59
What show cis-trans isomerism?
Some 4 and 6 coordinate complex ions which contain two different monodentate ligands.
60
What show cis-trans and optical isomerism?
Some 6 coordinate complexes which contain monodentate and bidentate ligands
61
What is not present in complex ions?
A double bond so the shape of the complex holds the groups in the correct orientation.
62
Where does cis-trans isomerism occur?
In some square planar and octahedral complexes (when there's 2 different monodentate ligands)
63
What are optical isomers?
Non super imposable mirror images of each other
64
Where does optical isomerism occur?
In some octahedral complexes when there's 3 bidentate ligands.
65
What isomerism does bidentate ligands show?
Cis-trans isomerism
66
What isomerism does [Co(NH2CH2CH2NH2)2Cl2]+ show?
Cis-trans and optical isomerism
| It occurs in octahedral complexes with 2 bidentate ligands and 2 monodentate ligands.
67
What is a precipitate reaction?
When two aqueous solutions containing ions react together to form an insoluble ionic solid called a precipitate.
68
What do all aqueous transition metal ions react with?
Aqueous sodium hydroxide and aqueous ammonia to form precipitates. Some of these precipitate will dissolve in excess of sodium hydroxide to form complex ions in solution.
69
What do all transition metals have in aq solution?
6 water ligands
70
What colour is [Cu(H2O)6]2+?
BLUE
71
What colour is Cu(OH)2?
BLUE PRECIPITATE
72
What colour is [Fe(H2O)6]2+?
PALE GREEN
73
What colour is Fe(OH)2?
GREEN PRECIPITATE
74
What happens if the iron precipitate was left standing in air?
The precipitate would turn brown on the surface as Fe 2+ is oxidised.
75
What colour is [Fe(H2O)6]3+?
PALE YELLOW
76
What colour is Fe(OH)3?
ORANGE-BROWN PRECIPITATE
77
What colour is [Cr(H2O)6]3+?
VIOLET
78
What colour is Cr(OH)3?
GREEN PRECIPITATE
79
When the precipitate is left standing which metal hydroxides are insoluble in excess sodium hydroxide?
All are insoluble apart from Cr(OH)3, which redissolves to form a DARK GREEN SOLUTION
80
What colour is [Cr(H2O)6]3-?
DARK GREEN SOLUTION
81
What is formed when chromium (III) potassium sulphate is dissolved in water?
[Cr (H2O)6]3+, which is a pale purple solution
82
What colour is [Cr(H2O)6]3+?
VIOLET
83
What colour is [Cr(NH3)6]3+?
PURPLE
84
What happens to the [Cr(H2O)6]3+?
It takes place in ligand substitution with excess ammonia to form [Cr(NH3)6]3+. When NH3 is added:
1. A green/grey precipitate of Cr(OH)3 is formed
2. The Cr(OH)3 precipitate dissolves in excess ammonia to form [Cr(NH3)6]3+
85
What is a ligand substitution reaction?
It is when one ligand in a complex ion is replaced by another ligand.
86
What happens when aqueous copper (II) ions dissolve in water?
A pale blue complex ion [Cu(H2O)6]2+ is formed
87
What happens to the [Cu(H2O)6]2+ when NH3 is added dropwise?
[Cu(NH3)4(H2O)2]2+ is formed which is DARK BLUE and a trans isomer. 4H2O is also formed.
88
What replaces 4H2O molecules in [Cu(H2O)6]2+?
Ammonia
89
What complex shapes do [Cu(H2O)6]2+ and [Cu(NH3)4(H2O)2]2+ have?
Tetrahedral
90
What colour is [Cu(H2O)6]2+?
PALE BLUE (octahedral)
91
What happens to [Cu(H2O)6]2+ when 4Cl- is added?
[CuCl4]2- is formed which is a tetrahedral complex which is YELLOW. The 6 water ligands have been replaced with 4 chloride ligands.
Concentrated HCl is added
92
If water is added to the yellow solution of [CuCl4]2-?
A blue solution will form but in a more dilute and paler form.
93
Why does the coordination number change from 6 to 4?
As Cl- are larger ligands than H2O fewer can fit around the central Cu2+
94
What would happen if ammonia was added drop wise?
If it was added to any aqueous transition metal ions you would first observe the formation of a metal hydroxide precipitate
95
What would happen if you kept adding NH3 to Cu(OH)2 and Cr(OH)3?
They would redissolve to form their complex ions.
[Cu(H2O)6]2+ --> Cu(OH)2 --> [Cu(NH3)4(H2O)2]2+
[Cr(H2O)6]3+ --> Cu(OH)3 --> [Cu(NH3)4(H2O)2]3+
96
Which metal hydroxides don't dissolve in excess aqueous ammonia?
Fe(OH)2, Fe(OH)3 and Mn(OH)3
97
What colour can chromium be?
Green or violet
98
What is the complex ion for chromium to be violet?
[Cr(H2O)6]2+
99
What happens when chromium sulphate dissolves in water?
It forms [Cr(H2O)5SO4]+ where 1 H2O ligand is replaced by SO4 2- which appears green
100
What is cis- platin used in?
cancer treatment
101
What are the chloride ligands replaced with in cis-platin?
Water ligands
102
How does cis platin work?
Adjacent guanine bases in the DNA helix can use the lone pairs of the nitrogen to replace the water ligands forming coordinate bonds to the platinum another ligand substitution reaction this kinks the helix preventing the DNA from locating and cell division.
103
What is trans-platin?
It is inactive as the geometry won't allow the DNA to bind in the same way.
104
What does haemoglobin contain?
Four protein chains which are held together by weak intermolecular forces. Each protein chain has a haem molecule with iron(II) being the central metal ion in the Haem group.
105
Describe how oxygen binds to haemoglobin?
So blood passes through the lungs and oxygen bonds to the haemoglobin due to the fact there is increased oxygen pressure. The oxygen is transported around the body and is released to body cells as well as forming a complex with carbon dioxide which is transported to the lungs released and exhaled.
106
Why is carbon monoxide toxic?
It replaces oxygen in like in substitution which forms carboxyl-haemoglobin. Carbon monoxide binds more strongly than oxygen so the process is irreversible it causes death as oxygen transport is prevented.
107
What happens in the process when Fe2+ is oxidised to Fe3+ ?
A redox reaction between Fe 2+ and MnO4- in acidic conditions is used for a redox titration (self indicating, pale pink endpoint when assuming MnO4- is in the burette)
Fe 2+ is oxidised to Fe3+ Fe 2+ ---> Fe 3+ + e-
MnO4- is reduced to Mn 2+
MnO4- + 5e- + 8H+ --> Mn 2+ + 4H2O
MnO4- = purple
Mn 2+ = colourless
108
What happens in the process when Fe3+ is reduced to Fe2+ ?
Fe 3+ reacts with I-, the orange-brown Fe3+ is reduced to Fe2+ a pale green colour. The colour change is observed by the oxidation of iodide ions to form I2 which has a brown colour
Fe3+ is reduced to Fe 2+ Fe3+ + e- --> Fe2+
I- is oxidised to I2 2I --> I2 + 2e-
2Fe3+ + 2I- ---> 2Fe2+ +I2
orange-brown. pale green
109
What happens in the process when Cu2+ is reduced to Cu+ ?
Cu2+ is reduced to Cu+ (in the form of CuI precipitate)
I- is oxidised to I2
Cu 2+ + 2I --> CuI + 1/2 I2
pale blue white precipitate
110
What happens in the process when Cr3+ is oxidised to CrO4 2- ?
Cr3+ is mixed with hot alkaline H2SO4
- Cr3+ is oxidised to CrO4 2-
Cr3+ +8OH ---> CrO4 2- +3e- +4H2O
- H2O2 is reduced to OH H2O2 + 2e- ---> 2OH-
3H2O2 + 2Cr3+ +10OH- --> 2CrO4 2- +8H2O
HYDROGEN PEROXIDE IS A POWERFUL OXIDISING AGENT
111
What happens in the process when Cr2O7 2- is reduced to Cr3+ ?
Dichromate ions (IV) Cr2O7 2- has an orange colour and Cr 3+ has a green colour. Acidified dichromate ions can be reduced to Cr 3+ by the addition of zinc.
-Zinc is oxidised to Zn 2+ Zn --> Zn 2+ +2e-
- Cr2O7 2- is reduced to Cr 3+
Cr2O7 2- + 6e- + 14H+ --> 2Cr 3+ + 7H2O
Cr2O7 2- + 3Zn + 14H+ --> 2Cr 3+ +3Zn2+ + 7H2O
orange green
with excess Zn; Cr3+ is reduced further to Cr2+ (pale blue) - Cr 3+ + e- --> Cr 2+
Zn + 2Cr 3+ --> Zn 2+ + 2Cr 2+
green. pale blue
Zn is a powerful reducing agent and can reduce:
Cr2O7 2- --> Cr 3+ --> Cr 2+
Therefore CrO4 2- can be reduced to Cr 2+
112
Describe the disproportionation of Cu+ ions.
When solid copper (I) oxide reacts with hot dilute sulphuric acid a brown precipitate of copper is formed in a blue solution of copper (II) sulphate. The copper (I)ions have simultaneous been oxidised and reduced in this reaction – disproportionation.
113
How do you identify the transition metal ions?
They use sodium hydroxide and the colour of the metal hydroxide precipitate formed is used to identify these ions.
114
Which metal hydroxides form a green precipitate?
- Fe(OH)2
| - Cr (OH)3 - soluble in excess NaOH producing a dark green colour
115
What would happen if you used ammonia to identify the hydroxides?
- the blue precipitate of Cu(OH)2 would redissolve to give a dark blue solution containing
[Cu (NH3)4 (H2O)2] 2+
- the green precipitate of Cr(OH)3 would redissolve to give a purple solution of [Cr(NH3)6] 3+
116
How can you identify if ammonia is present?
NaOH is heated gently, and damp pH paper is held at the neck of the tube with it turning blue.
NH4+ +OH- --> NH3 + H2O
NH3 vapour would rise and redissolve on the surface of the paper which will turn blue.
117
How is carbonate ions identified?
- Dilute nitric acid is added
- Observation; effervescence
2H+ +CO3 2- --> CO2 + H2O
118
Why is nitric acid the best acid to use when identifying carbonate ions?
As nitrate ions don't interfere with any subsequent tests.
119
How is sulphate ions identified?
- Add Ba 2+
- Observation : white precipitate
- Ba 2+ + SO4 2- --> BaSO4
120
Why is the sulphate test after the carbonate test?
Carbonate ions also react with Ba2+ to give a white precipitate of barium carbonate so this test is carried out after the carbonate test so that you can reach and on ambiguous conclusion.
121
What acid can be used?
BaCl2 and Ba(NO3)2 can be used but if there is a subsequent test then Ba(NO3)2 is used.
122
How is halide ions identified?
Ag+ is added and a precipitate of AgX is formed. The precipitate colour and solubility is recorded.
Ag+ + X- --> AgX
Cl- --> white precipitate and soluble in dilute and conc NH3
Br - --> cream precipitate and soluble in conc NH3
I- --> yellow precipitate and insoluble in NH3
123
Why is the halide ion test after the carbonates and sulphate test?
Carbonate and sulphate also reacts with Ag+ to give a white precipitate of silver carbonate and silver sulphate so the test is carried out afterwards so that you can reach an unambiguous conclusion.
