Module 5: Chapter 24 - Transition Elements Flashcards
1
Q
What are d-block elements?
A
D-block elements are located between group 2 and group 13 of the periodic table. All D-block elements highest energy electron is in a d-orbital
2
Q
What is common between all d-block elements?
A
All d-block elements:
* Are metallic, displaying the typical physical properties of metals
* Have high melting and boiling points
* are shiny in appearance
* Conduct both electricity and heat
3
Q
What are some uses of D-block elements?
A
- Coinage - Copper, silver, nickel, and zinc
- Construction - Iron and copper
- Aerospace - Titanium
4
Q
Explain what happens when d-block elements form ions
A
When d-block elements form ions, they lose the 4s electrons before losing any of the 3d electrons:
* When forming an atom, the 4s orbital fills before the 3d orbitals
* When forming an ion, the 4s orbital empties before the 3d orbitals
5
Q
What is a transition element?
A
A transition element is a d-block element that forms at least one ion with a partially filled d-orbital
6
Q
Which 2 d-block elements are not transition elements?
A
- Scandium
- Zinc
7
Q
Why is scandium a d-block element but not a transition element?
A
Scandium only forms the ion Sc³⁺ by the loss of two 4s electrons and one 3d electron:
* The electron configuration of Sc is 1s²2s²2p⁶3s²3p⁶3d¹4s²
* Sc³⁺ has an electronic configuration of 1s²2s²2p⁶3s²3p⁶
Therefore the only ion that Scandium forms has empty d-orbitals, so it does not form an ion with a partially filled d-orbital and is therefore not classified as a transition element
8
Q
Why is zinc a d-block element but not a transition element?
A
Zinc only forms the ion Zn²⁺ by the loss of two 4s electrons:
* The electron configuration of Zn is 1s²2s²2p⁶3s²3p⁶3d¹⁰4s²
* Zn²⁺ has an electronic configuration of 1s²2s²2p⁶3s²3p⁶3d¹⁰
Therefore the only ion that Zinc forms has full d-orbitals, so it does not form an ion with a partially filled d-orbital and is therefore not classified as a transition element
9
Q
What are the unique properties of transition metals?
A
- They form compounds in which the transition element has different oxidation states
- They form coloured compounds
- The element and their compounds can act as catalysts
10
Q
What colour are compounds of Titanium with an oxidation number of +3?
A
Purple
11
Q
What colour are compounds of Vanadium with an oxidation number of +2?
A
Violet
12
Q
What colour are compounds of Vanadium with an oxidation number of +3?
A
Green
13
Q
What colour are compounds of Vanadium with an oxidation number of +4?
A
Blue
14
Q
What colour are compounds of Vanadium with an oxidation number of +5?
A
Yellow
15
Q
What colour are compounds of Chromium with an oxidation number of +2?
A
Blue
16
Q
What colour are compounds of Chromium with an oxidation number of +3?
A
Technically pale purple however it mostly appears Green
17
Q
What colour are compounds of Chromium with an oxidation number of +6?
A
Orange
18
Q
What colour are compounds of Manganese with an oxidation number of +2?
A
Pale Pink
19
Q
What colour are compounds of Manganese with an oxidation number of +4?
A
Pink
20
Q
What colour are compounds of Manganese with an oxidation number of +6?
A
Green
21
Q
What colour are compounds of Manganese with an oxidation number of +7?
A
Purple
22
Q
What colour are compounds of Iron with an oxidation number of +2?
A
Pale Green
23
Q
What colour are compounds of Iron with an oxidation number of +3?
A
Yellow
24
Q
What colour are compounds of Cobalt with an oxidation number of +2?
A
Pink
25
What colour are compounds of Cobalt with an oxidation number of +3?
Green
26
What colour are compounds of Nickel with an oxidation number of +2?
Green
27
What colour are compounds of Copper with an oxidation number of +2?
Pale Blue
28
When are transition element compounds the strongest oxidising agent?
When they contain the transition element in its highest oxidation state
29
Why do transition elements form brightly coloured compounds?
The colour of the solid/solution is linked to the **partially filled d-orbitals** of the transition metal ion. The colour of a solution can vary with different oxidation states
30
What are 4 examples of transition element compounds acting as heterogeneous catalysts?
* The **haber process** for the manufacture of ammonia from the reaction between nitrogen and hydrogen. It is catalysted by a **finely divided iron catalyst**
* The **contact process** in the production of sulfur trioxide from the oxidation of sulfur dioxide. It is **catalysed by vanadium (V) oxide, V₂O₅(s)**
* The **hydrogenation of vegetable fats** in the manufacture of margarine. It is catalysed by a **nickel catalyst**
* The catalytic **decomposition of hydrogen peroxide** forming oxygen uses manganese (IV) oxide, **MnO₂(s) as the catalyst**
31
What is the equation for the catalytic decomposition of hydrogen peroxide?
2H₂O₂(aq) -> 2H₂O(l) + O₂(g)
| **MnO₂(s) as the catalyst**
32
What are 2 examples of a transition element compound acting as a homogeneous catalyst?
* The reaction between iodide ions and peroxodisulfate ion, S₂O₈²⁻, is catalysed by Fe²⁺(aq) ions
* The reaction of zinc metal with acids is catalysed by the presence of Cu²⁺(aq) ions
33
What is the 2 step mechanism and overall equation for the reaction between iodide ions and peroxodisulfate ion, S₂O₈²⁻?
**Fe²⁺(aq) reacts:** S₂O₈²⁻(aq) + Fe²⁺(aq) -> 2SO₄²⁻(aq) + Fe³⁺(aq)
**Fe²⁺(aq) regenerated:** Fe³⁺(aq) + 2I⁻(aq) -> I₂(aq) + Fe²⁺(aq)
**Overall equation:** S₂O₈²⁻(aq) + 2I⁻(aq) -> 2SO₄²⁻(aq) + I₂(aq)
34
What are complex ions?
A transition metal (or aluminium) ion bonded to ligands by coordinate bonds (dative covalent bonds)
35
How are complex ions formed?
A complex ion is formed when one or more molecules or negatively charged ions bond to a central metal ion
36
What is a ligand?
A molecule or ion that can donate a pair of electrons to the central metal ion to form a coordinate/dative covalent bond
37
What is the coordination number?
The coordination number indicates the number of coordinate bonds formed between the central metal ion and ligands
38
How do you represent the formula of a complex ion?
* The whole complex ion is enclosed in square brackets with the overall charge of the complex ion shown outside of the square brackets
* The ligand is inside round brackets with the number of ligands shown ourside the round brackets
39
How must you draw the structure of a complex ion?
* You must draw the 3D shape of the ion, including bond angles
* You must enclose the whole ion in square brackets and with the overall charge of the complex ion outside the brackets
40
What is the coordination number of the complex ion [Cr(H₂O)₆]³⁺?
6
41
What can be a ligand?
A ligand is any molecule or ion that can donate a pair of electrons to a central metal ion, this includes:
* Negative ions, e.g. Cl⁻, OH⁻
* Neutral molecules (**with lone pairs**), e.g. H₂O, NH₃,
42
What is a monodentate ligand?
A monodentate ligand is a ligand that is able to donate **one** pair of electrons to a central metal ion
43
What is a bidentate ligand?
A bidentate ligand is a ligand which is able to donate **two** pairs of electrons to a central metal ion
44
What are 2 examples of neutral monodentate ligands?
* Water
* Ammonia
45
What are 3 examples of monodentate ligand ions?
* Chloride
* Cyanide
* Hydroxide
46
What are 2 examples of bidentate ligands?
* 1,2-diaminoethane (frequently shortened to en)
* Ethandioate ion (oxalate ion)
47
What is the ethandioate (oxalate) ion?
48
Draw the structure of the complex ion [Co(NH₂CH₂CH₂NH₂)₃]³⁺
49
What does the shape of a complex ion depend on?
Its coordination number
50
What is the shape of a complex ion with a coordination number of 6?
Octahedral
51
What is the shape of a complex ion with a coordination number of 4?
* Tetrahedral
* Square planar
52
When would a complex ion with a coordination number of 4 form a tetrahedral shape and when would it form a square planar shape?
* The tetrahedral shape is by far the more common of the 2 shapes
* However, a **square planar** shape occurs in complex ions of **transition metals with eight d-electrons in the highest energy d-sub-shell**
53
What are the 3 commons transition metal (and their oxidation number) that form complex ions with a square planar shape?
* Plantinum (II)
* Palladium (II)
* Gold (III)
54
What is the bond angle of a square planar molecule?
90°
55
What does a square planar molecule look like?
56
Draw the structure of the complex ion [Mn(H₂O)₆]²⁺
57
Draw the structure of the complex ion [CoCl₄]²⁻
58
Draw the structure of the complex ion [Pt(NH₃)₄]²⁺
59
What does stereoisomerism in complex ions depend on?
For complex ions, the type of stereoisomerism depends on the number and the type of ligands that are attached to the central metal ion, and the shape of the complex:
60
When does stereoisomerism occur in complex ions?
* Some **four-coordinate and six-coordinate** complex ions containing **two different monodentate ligands** show **cis-trans** isomerism
* Some **six-coordinate** complex ions containing **monodentate and bidentate ligands** can show both **cis-trans and optical** isomerism
61
When does cis-trans stereoisomerism occur in complex ions?
In complex ions no C=C double bond is required for cis-trans isomerism, instead the shape of the complex holds in different orientations about the central metal ion:
* It can occur in some **square planar** and **octahedral** complex ions
62
Explain how cis-trans stereoisomerism occurs in square planar complexes:
cis-trans stereoisomerism occurs in square planar complexes which have **no more than two identical ligands attached to the central metal ion**. As the ligands are arranged in the same plane at the corners of a square with 90° bond angles, the cis-isomer will have the 2 identical groups adjacent to each other whereas the trans-isomer will have the 2 identical groups across from one another
63
What is the bond angle between the identical ligands for the cis-isomer of a square planar complex ion?
90°
64
What is the bond angle between the identical ligands for the trans-isomer of a square planar complex ion?
180°
65
Draw the 2 stereoisomers of the complex ion [Pd(NH₃)₂Cl₂]
66
Explain how cis-trans stereoisomerism occurs in octahedral complexes containing monodentate ligands:
Octahedral complexes containing four of one type of ligand and two of another type of ligand can display cis-trans isomerism. In the cis-isomer the pair of ligands will be adjacent to each other with their coordinate bonds separated by 90°, whereas in the trans-isomer the pair of ligands will be opposite across the central metal ion, with their coordinate bonds 180° apart
67
Draw the 2 stereoisomers for the complex ion [Co(NH₃)₄Cl₂]⁺
68
Explain how cis-trans stereoisomerism occurs in octahedral complexes containing bidentate ligands:
Octahedral complexes containing **exactly 2 bidentate ligands** can also show cis-trans isomerism depending on whether the identical ligands are adjacent or opposite to one another
69
Draw the 2 stereoisomers for the complex ion [Co(NH₂CH₂CH₂NH₂)₂Cl₂]⁺
70
When does optical isomerism occur in complex ions?
* Optical isomerism only occurs in octahedral complexes containing two or more bidentate ligands
* Only cis-isomers can form optical isomers (trans-isomers **cannot** form optical isomers)
71
Why can cis-isomers form optical isomers for complex ions?
In the cis-isomers there is no plane of symmetry, hence it can form non-superimposable mirror images and therefore optical isomers
72
Why can't trans-isomers form optical isomers for complex ions?
Trans-isomers contain a plane of symmetry, therefore its mirror image is is exactly the same as itself and can be superimposed. Therefore it cannot form optical isomers
73
Explain how optical isomerism can occur in octahedral complexes:
For cis-isomers with 2 or more bidentate ligand non-superimposable mirror images of the molecule can exist and therefore the display optical isomerism
74
Draw the 2 optical isomers of the cis-isomer of the complex ion [Co(NH₂CH₂CH₂NH₂)₂Cl₂]⁺
75
Draw the 2 optical isomers of the complex ion [Ru(NH₂CH₂CH₂NH₂)₃]²⁺
76
What is the role of cis-trans isomerism in medicine?
**cis-platin** can be used as an anti-cancer drug
77
What is the structure of cis-platin?
cis-[Pt(NH₃)₂Cl₂]
78
How does cis-platin (cis-[Pt(NH₃)₂Cl₂]) work as an anti-cancer drug?
Cis-platin can be used to inhibit tumour growth as it forms a platinium complex inside of a cell which binds to DNA and prevents the DNA of the cell from replicating and therefore cell division. Activation of the cell's own repair mechanism eventually leads to systematic cell death
79
What are the downsides of cis-platin?
cis-platin has many unpleasant side effects and can lead to kidney damage
80
What is a ligand substitution reaction?
A reaction in which one or more ligands in a complex ion are replaced by different ligands
81
What happens when copper(II) sulfate is dissolved in water?
The pale blue complex ion, [Cu(H₂O)₆]²⁺ is formed
82
What is the reaction when an excess of aqueous ammonia is added to a solution containing [Cu(H₂O)₆]²⁺?
[Cu(H₂O)₆]²⁺(aq) + 4NH₃(aq) -> [Cu(NH₃)₄(H₂O)₂]²⁺(aq) + 4H₂O(l)
83
Explain the reaction when an excess of aqueous ammonia is added to a solution containing [Cu(H₂O)₆]²⁺
Four ammonia ligands have replaced four of the water ligands to form [Cu(NH₃)₄(H₂O)₂]²⁺:
* A pale blue precipitate of Cu(OH)₂ is formed in the first stage of the reaction
* The Cu(OH)₂ precipitate then dissolves in excess ammonia to form [Cu(NH₃)₄(H₂O)₂]²⁺
The four NH₃ ligands are arranged in the same plane with the two H₂O ligands above and below
84
Describe and explain the observations for the reaction when an excess of aqueous ammonia is added to a solution containing [Cu(H₂O)₆]²⁺
* Initially there is a pale blue solution of [Cu(H₂O)₆]²⁺
* A pale blue precipitate of Cu(OH)₂ is formed in the first stage of the reaction
* The Cu(OH)₂ precipitate then dissolves in excess ammonia to form a dark blue solution of [Cu(NH₃)₄(H₂O)₂]²⁺
85
What is the reaction when an excess of concentrated hydrochloric acid is added to a solution containing [Cu(H₂O)₆]²⁺?
[Cu(H₂O)₆]²⁺(aq) + 4Cl⁻(aq) ⇌ [CuCl₄]²⁻(aq) + 6H₂O(l)
86
Explain the reaction when an excess of concentrated hydrochloric acid is added to a solution containing [Cu(H₂O)₆]²⁺
Six water ligands have been replaced by 4 chloride ligands. As the chloride ligands are larger in size than the water ligands, fewer chlrodie ligands can fit around the central Cu²⁺ ion, resulting in a change of coordination number from 6 to 4 and therefore a change in shape from octahedral to tetrahedral
87
Describe and explain the observations for the reaction when an excess of concentrated hydrochloric acid is added to a solution containing [Cu(H₂O)₆]²⁺
During the reaction the colour of the solution changes from a pale blue colour to a yellow colour. The green intermediate colour is not due to the formation of an intermediate species (as it is for the reaction in aqueous ammonia) but rather the blue and yellow solutions mixing
88
What happens when Chromium(III) potassium sulfate is dissolved in water?
The pale purple complex ion [Cr(H₂O)₆]³⁺ is formed
89
What is chrome alum?
Chromium(III) potassium sulfate
90
What is Chromium(III) potassium sulfate?
91
What happens when chromium (III) sulfate is dissolved in water?
The dark green complex ion [Cr(H₂O)₅SO₄]⁺ is formed
92
What is the reaction when an excess of aqueous ammonia is added to a solution containing [Cr(H₂O)₆]³⁺?
[Cr(H₂O)₆]³⁺(aq) + 6NH₃(aq) -> [Cr(NH₃)₆]³⁺(aq) + 6H₂O(l)
93
Explain the reaction when an excess of aqueous ammonia is added to a solution containing [Cr(H₂O)₆]³⁺
* Initially there is a pale purple solution containing [Cr(H₂O)₆]³⁺
* A grey-green precipitate of Cr(OH)₃ is formed
* The Cr(OH)₃ precipitate dissolves in excess ammonia to form the complex ion [Cr(NH₃)₆]³⁺
94
Describe and explain the observations for the reaction when an excess of aqueous ammonia is added to a solution containing [Cr(H₂O)₆]³⁺
* Initially there is a pale purple/violet solution containing [Cr(H₂O)₆]³⁺
* Upon the formation of Cr(OH)₃ it turns grey-green
* It then returns to a darker purple colour when [Cr(NH₃)₆]³⁺ has been formed
95
What is the structure of haemoglobin?
Haemoglobin contains four protein chains held together by weak intermolecular forces. Each protein chain contains a haem molecule within its structure. The central metal ion in a haem group is Fe²⁺ which can bind to oxygen gas
96
Explain the biochemical importance of iron in haemoglobin:
Haemoglobin is found in red blood cells. As blood passes through the lungs, the Fe²⁺ atom in the haem group of the haemoglobin bonds to oxygen forming a compound known as oxyhaemoglobin. The oxyhaemoglobin can then release the oxygen to body cells. The haemoglobin can also bond to carbon dioxide and carry it back to the lungs where it is exhaled.
However, carbon monoxide can also bind to the Fe²⁺ ion in haemoglobin forming a complex known as carboxyhaemoglobin. In this case a ligand substitution takes place in which the oxygen in haemoglobin is replaced by carbon monoxide. Carbon monoxide binds to haemoglobin much more strongly than oxygen, it is so strong that the process is irreversible. Therefore a small concentration of carbon monoxide can prevent a large proportion of haemoglobin carrying oxygen. If the concentration of carboxyhaemoglobin becomes too high, oxygen transport is prevented, leading to death.
97
What is a precipitation reaction?
A reaction in which two aquous solutions containing ions react together to form an insoluble ionic solid, called a precipitate
98
What do transition metal ions in aqueous solutions react with to form precipitates?
* Aqueous sodium hydroxide
* Aqueous ammonia
However, **some** of these precipitates may dissolve in an excess of sodium hydroxide or ammonia to form complex ions in solution
99
What are the observations of a solution of Cu²⁺ reacting with NaOH(aq)?
A **blue solution** reacts to form a **blue precipitate** of copper(II) hydroxide
The precipitate is insoluble in excess sodium hydroxide
100
What are the observations of a solution of Fe²⁺ reacting with NaOH(aq)?
A **pale green solution** reacts to form a **green precipitate** of iron(II) hydroxide
The 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)
101
What are the observations of a solution of Fe³⁺ reacting with NaOH(aq)?
A **pale yellow solution** reacts to form an **orange-brown precipitate** of iron(III) hydroxide
The precipitate is insoluble in excess sodium hydroxide
102
What are the observations of a solution of Mn²⁺ reacting with NaOH(aq)?
A **pale pink solution** reacts to form a **light brown precipitate** of manganese(II) hydroxide which darkens on standing in air
The precipitate is insoluble in excess sodium hydroxide
103
What are the observations of a solution of Cr³⁺ reacting with NaOH(aq)?
A **violet solution** reacts to form a **grey-green precipitate** of chromium(II) hydroxide
The precipitiate is soluble in excess sodium hydroxide forming a **dark green solution**
104
What are the equations of a solution of Cu²⁺ reacting with NaOH(aq)?
Cu²⁺(aq) + 2OH⁻(aq) -> Cu(OH)₂(s)
*which can also be written as:*
**[Cu(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Cu(OH)₂(H₂O)₄] + 2H₂O(l)**
105
What are the equations of a solution of Fe²⁺ reacting with NaOH(aq)?
Fe²⁺(aq) + 2OH⁻(aq) -> Fe(OH)₂(s)
*which can also be written as:*
**[Fe(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Fe(OH)₂(H₂O)₄] + 2H₂O(l)**
In air: Fe(OH)₂(s) -> Fe(OH)₃(s)
106
What are the equations of a solution of Fe³⁺ reacting with NaOH(aq)?
Fe³⁺ + 3OH⁻(aq) -> Fe(OH)₃(s)
*which can also be written as:*
**[Fe(H₂O)₆]³⁺(aq) + 3OH⁻(aq) -> [Fe(OH)₃(H₂O)₃] + 3H₂O(l)**
107
What are the equations of a solution of Mn²⁺ reacting with NaOH(aq)?
Mn²⁺(aq) + 2OH⁻(aq) -> Mn(OH)₂(s)
*which can also be written as:*
**[Mn(H₂O)₆]²⁺(aq) + 2OH⁻(aq) -> [Mn(OH)₂(H₂O)₄] + 2H₂O(l)**
108
What are the equations of a solution of Cr³⁺ reacting with NaOH(aq)?
Cr³⁺ + 3OH⁻(aq) -> Cr(OH)₃(s)
*which can also be written as: *
**[Cr(H₂O)₆]³⁺(aq) + 3OH⁻(aq) -> [Cr(OH)₃(H₂O)₃] + 3H₂O(l)**
In excess NaOH:
Cr(OH)₃(s) + 3OH⁻(aq) -> [Cr(OH)₆]³⁻(aq)
*which can also be written as:*
**[Cr(OH)₃(H₂O)₃] + 3OH⁻(aq) -> [Cr(OH)₆]³⁻(aq)**
109
What is the precipitation reaction of Cu²⁺ with ammonia?
In the first stage of the reaction a precipitation reaction takes place:
Cu²⁺(aq) + 2OH⁻(aq) -> Cu(OH)₂(s)
*which can also be written as:*
**[Cu(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Cu(OH)₂(H₂O)₄] + 2NH₄⁺**
**Cu(OH)₂ / [Cu(OH)₂(H₂O)₄] is a blue precipitate which dissolves in excess ammonia to form a deep blue solution with the formula [Cu(NH₃)₄(H₂O)₂]²⁺(aq)**
110
What is the precipitation reaction of Cr³⁺ with ammonia?
In the first stage of the reaction a precipitation reaction takes place:
Cr³⁺ + 3OH⁻(aq) -> Cr(OH)₃(s)
*which can also be written as:*
**[Cr(H₂O)₆]³⁺(aq) + 3NH₃(aq) -> [Cr(OH)₃(H₂O)₃] + 3NH₄⁺**
**Cr(OH)₃ / [Cr(OH)₃(H₂O)₃] is a green precipitate whcih dissolves in excess ammonia to form [Cr(NH₃)₆]³⁺(aq) which is a purple solution**
111
What is the precipitation reaction of Fe²⁺ with aqueous ammonia?
**[Fe(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Fe(OH)₂(H₂O)₄] + 2NH₄⁺(aq)**
It reacts in the same way as it would with aqueous sodium hydroxide, forming a precipitate of Fe(OH)₂(s). There is no further reaction with aqueous ammonia and so the precipitate does not dissolve
112
What is the precipitation reaction of Mn²⁺ with ammonia?
**[Mn(H₂O)₆]²⁺(aq) + 2NH₃(aq) -> [Mn(OH)₂(H₂O)₄] + 2NH₄⁺(aq)**
It reacts in the same way as it would with aqueous sodium hydroxide, forming a precipitate of Mn(OH)₂(s). There is no further reaction with aqueous ammonia and so the precipitate does not dissolve
113
What is the precipitation reaction of Fe³⁺ with ammonia?
**[Fe(H₂O)₆]³⁺(aq) + 3NH₃(aq) -> [Fe(OH)₃(H₂O)₃] + 3NH₄⁺(aq)**
It reacts in the same way as it would with aqueous sodium hydroxide, forming a precipitate of Fe(OH)₃(s). There is no further reaction with aqueous ammonia and so the precipitate does not dissolve
114
What are 6 redox reactions involving transition metals?
* Oxidation of Fe²⁺
* Reduction of Fe³⁺
* Oxidation of Cr³⁺
* Reduction of Cr₂O₇²⁻
* Disproportionation of Cu⁺
* Reduction of Cu²⁺
115
What is the equation and observations for the oxidation of Fe²⁺?
**5Fe²⁺(aq) + MnO₄⁻(aq) + 8H⁺(aq) -> Mn²⁺(aq) + 5Fe³⁺(aq) + 4H₂O(l)**
The solution containing MnO₄⁻ ions is purple and is decolourised by the Fe²⁺ ions to form a colourless solution containing Mn²⁺
116
What is the equation and observations for the reduction of Fe³⁺?
**2Fe³⁺(aq) + 2I⁻(aq) -> 2Fe²⁺(aq) + I₂(aq)**
The orange-brown Fe³⁺ ions are reduced to pale green Fe²⁺ ions. However, this colour change is obscured by the oxidation of iodide ions to form iodine, which has a brown colour
117
What is the equation and observations for the reduction of Cr₂O₇²⁻?
**Cr₂O₇²⁻(aq) + 14H⁺(aq) + 3Zn(s) -> 2Cr³⁺(aq) + 7H₂O(l) + 3Zn²⁺(aq)**
**Zn(s) + 2Cr³⁺(aq) -> Zn²⁺(aq) + 2Cr²⁺(aq)**
The orange dichromate ions are reduced to green chromium(III) ions. However, with an excess of zinc, the chromium(III) ions are reduced further to chromium(II), which is a pale blue colour
118
What is the equation and observations for the oxidation of Cr³⁺?
**2Cr³⁺ + 3H₂O₂ + 10OH⁻ -> 2CrO₄²⁻ + 8H₂O**
119
What is the equation and observations for the reduction of Cu²⁺?
**2Cu²⁺(aq) + 4I⁻(aq) -> 2CuI(s) + I₂(s)**
The pale blue solution turns brown with a white precipitate present (however the precipitate may be masked by the brown solution)
120
What is the equation and observations for the disproportionation of Cu⁺?
A brown precipitate of copper is formed together with a blue solution of copper(II) sulfate
## Footnote
Where the sulfuric acid is hot and dilute
121
How can you identify transition metal ions?
You can identify them through the observations of the precipitates formed in the reaction with aqueous sodium hydroxide
122
How can electrode potentials be used to explain redox reactions?
The more positive the Eθ value, the more likely the equilibrium is to shift to the right and cause the gain of electrons, resulting in the species undergoing reduction (good oxidising agent)
123
What is a use of hot alkaline hydrogen peroxide?
It is a powerful oxidising agent
124
Draw the complex and name the shape of [Fe(C₂O₄)₃]³⁻
Octahedral
125
Draw the complex and name the shape of [Co(CH₂NH₂NH₂CH₂)₂Cl₂]⁺
Octahedral
126
What colour is a solution of [CuCl₄]²⁻?
Yellow
127
What is the colour of a Titanium compound with the oxidation state of 2+?
Violet
128
What colour is a solution of [Cr(H₂O)₆]³⁺?
Purple
