Unit 3.4 - Chemistry of the d-block transition metals Flashcards
1
Q
What are all of the elements from scandium to zinc? What does this mean?
A
d-block elements
3d orbitals are being filled
2
Q
Transition metal
A
An element that possess a partially filled d sub-shell as an atom or in its stable ions
3
Q
Why are scandium and zinc not transition metals even though they’re d-block elements?
A
Scandium: 3d orbital is empty
Zinc: 3d orbital is full
So neither are partially full, which is the definition of a transition metal
4
Q
Which d-block elements are NOT transition metals?
A
Scandium and zinc
5
Q
Which level fills first, the 4s or 3d level?
A
4s level fills first
6
Q
Which orbital has the lowest amount of energy as the 3d level fills?
A
The energy of the 3d electrons is below that of the 4s electrons
7
Q
Which level are electrons removed from first and then afterwards when electrons are removed from scandium and zinc?
A
They’re removed first from the 4s level, and only then from the 3d level
8
Q
Where do we remove electrons from first in the transition elements and then afterwards when forming ions?
A
We remove the 4s electrons first, then the 3d electrons in the reverse order to that in which we filled them
9
Q
Cr3+ electronic configuration
A
1s^22s^22p^6s3^23p^63d^3
10
Q
General properties of the transition element
A
- Metals with closely packed structures
- Atomic radius decreases gradually = first ionisation energy increases gradually
- Strong metallic bonds = high melting points
- High densities + high tensile strengths
- Form alloys with one another readily
11
Q
How come transition elements are dense?
A
Closely packed structures
12
Q
Why does the first ionisation energy of the transition elements increase gradually?
A
As the atomic radius decreases gradually
13
Q
Why do the transition elements form strong metallic bonds?
A
As the 3d and 4s electrons are available for metallic bonding
14
Q
Why do the transition elements have high melting points?
A
Strong metallic bonds
15
Q
Why do the transition elements have high densities and high tensile strengths?
A
Have relatively small atomic radii and closely packed structures
16
Q
Why do the transition elements form alloys with one another readily?
A
As they have similar atomic radii
17
Q
Why does having similar atomic radii in transition elements mean that they can form alloys with one another readily?
A
Because there will be little disruption to the metal lattice when one atom is substitute for another
18
Q
Example of an alloy
A
Stainless steel
19
Q
What makes up stainless steel?
A
Fe/Cr
20
Q
What’s good about stainless steel and why is this the case?
A
Rusts slowly due to the chromium element
21
Q
Characteristic properties of the transition elements
A
- Variable oxidation states
- Catalysis
- Complex ion formation
22
Q
How many oxidation states can transition elements occur in in their compounds?
A
Two or more
23
Q
Most common oxidation states of transition elements
A
+2, +3
24
Q
Why do the transition elements have varying oxidation states?
A
The difference in energy between the 3d and the 4s electrons is relatively small (i.e - the ionisation energies of the 3d and 4s electrons are similar)
25
When do chromium and manganese form compounds in their highest oxidation states?
With oxygen and fluorine
26
Which elements can have the electronic structure of Argon and when does this occur?
Chromium and manganese form compounds in their highest oxidation states with oxygen and fluorine
They have the electronic structure of argon in these states
27
Which transition elements compounds form compounds in the highest oxidation states?
Chromium and manganese
28
What has happened to Cr6+ and Mn7+ for them to have the same electronic structure as argon?
Remove all of their electrons
29
Catalysts
Substances that increase the rate of a chemical reaction by providing an all active pathway with a lower activation energy
30
How do catalysts increase the rate of a chemical reaction?
By proving an alternative pathway with a lower activation energy
31
Why is the position of equilibrium unaffected with catalysts and what is the only thing that is affected?
The activation of both the forward and backward reaction are reduced
Only rate is affected
32
Why are catalysts so important in industry?
Reactions occur faster
Provides chemical reactions at lower temperatures = lowers the energy demand of a reaction
33
What are transition metals and their compounds important as?
Industrial catalysts
34
What type of catalysts do transition elements act as and how?
Surface catalysts
Provide active sites on their surface to facilitate the reaction
35
How come transition elements can act as surface catalysts that provide active sites on their surfaces?
As they have partially filled d-orbitals high enable them to form temporary bonds with reactant molecules
36
When is vanadium used as a catalyst?
Contact process = manufacture of sulphuric acid
37
When is iron used as a catalyst and in what state?
Fe/FeO
Haber process = manufacture of ammonia
38
When is nickel used as a catalyst?
Hydrogenation of C=C bonds in vegetable oils
39
Catalyst of the Haber process (manufacture of sulphuric acid)
Vanadium
40
Catalyst of the haber process
Iron Fe/FeO
41
Catalyst of the hydrogenation of C=C bonds in vegetable oils
Nickel
42
What is sulphuric acid used for in industry?
Car batteries
43
What is ammonia used for in industry?
Fertiliser
44
What are vegetable oils used for in industry?
To make margarine
45
Why can the transition elements act as catalysts in solution?
Because the transition metal may take part in a sequence of reaction stages and be left unchanged because of its ability to have more than one oxidation state
46
What can transition elements do due to their ability to have more than one oxidation state? Why?
Can act as catalysts in solution
May are part in a sequence of reaction stages and be left unchanged
47
Why isn’t it sustainable to use transition metals as catalysts and what is being done instead?
They have to be mined
Enzymes are being designed to take part in industrial processes instead
48
Area under a Maxwell-Boltzmann distribution
Area under the curve = total number of particles with specific energies
49
How do transition metals change oxidation states?
By gaining or losing electrons in d-orbitals
50
How can transition metals specifically speed up reactions?
By speeding up the transfer of electrons in d-orbitals
51
How do reactants react with transition elements when they act as catalysts?
Use vacant d-orbitals to form temporary bonds with catalyst which holds the reactant so that the reaction can take place
52
heterogeneous catalyst
A catalyst in a different physical state to the reactants
53
Homogenous catalyst
A catalyst in the same physical state to the reactants
54
Example of a heterogenous catalyst
Fe in the haber process
55
Example of a homogenous catalyst
Concentrated H2SO4 in esterification = all liquid
56
Zn2+ electronic structure
1s^22s^2sp^63s^23p^63d^10
57
Catalyst of Haber process
Iron
58
Catalyst of hydrogenation of oils/alkenes to form margarines
Nickel
59
Catalyst of polymerisation of ethane
Iron, cobalt
60
Catalyst of contact process
Vanadium (V) oxide
61
Haber process equation
N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
62
Polymerisation of ethane reaction
nCH2 = CH2 + H2 —> [-CH2-CH2-]n
63
Vanadium (V) oxide
V2O5
64
Contact process reaction
2SO2 + O2 —> 2SO3
65
Catalyst of production of nitric acid from ammonia
Platinum
66
Catalyst of the decomposition of hydrogen periodise
Manganese (IV) oxide
67
Decomposition of hydrogen perioxide reaction
2H2O2 —> 2H2O + O2
68
Reactions for the production of nitric acid from ammonia
4Nh3 + SO2 —> 4NO + 6H2O
2NO + O2 —> 2NO2 ⇌ N2O4
3NO2 + H2O —> 2HNO3 + NO
69
What is a complex ion?
Complexes are made up of a transition metal ion bonded to atoms or molecules which surround it (ligands)
70
What do ligands do with transition metal ions?
Form coordinate bonds/dative bonds
71
How are complex ions always written?
In square brackets
72
What do complex ions mostly have but not always?
Charges
73
Describe how a coordinate bond is formed between a transition metal ion and a ligand to form a complex ion
The transition metal has an empty orbital, and the ligand has a lone pair of electrons
The two atomic orbitals overlap to form a molecular orbital
A coorinate bond is formed between the ligand and the transition metal ion
74
Ligand
A small molecule or ion with a lone pair of electrons that can form a coordinate bond to a transition metal
75
Common ligands
H2O, NH3, Cl-, OH-, CN-
76
Complex
The combination of a transition metal ion and the ligands
77
Most common way of ligands being arranged around a transition metal ion
6 ligands arranges octahedral around the metal atom
78
Less common way of ligands being arranged around a transition metal ion
4 ligands arranged tetrahedrally
79
Angle in octahedrally arranged ligands around a metal atom
90
80
Angle in tetrahedrally arranged ligands around the metal atom
109.5
81
Which transition metal can be used to demonstrate the variation in transition metal complexesL
Copper
82
Which copper complexes are used to demonstrate the variation in transition metal complexes?
[Cu(H2O)6]2+
[CuCl4]2-
[Cu(H2O)2(NH3)4]^2+
83
Why are the structures and pooper ties of different copper complexes different even though they all contain Cu2+ ions?
Due to their different ligands
84
What are the most common complexes of aqueous solution of Cu2+ or Co2+?
[Cu(H2O)6]2+ and [Co(H2O)6]2-
85
Where do we draw the coorinate bond from in H2O and why?
From the oxygen
The lone pair of electrons is on the oxygen
86
How is the complex [Cu(H2O)2(NH3)4]2+ formed?
Addition of ammonia to a solution containing [Cu(H2O)6]2+ causes ammonia molecules to replace 2 water molecules
87
[Cu(H2O)2(NH3)4]2+ colour
Royal blue solution containing the ions
88
Shape of the [Cu(H2O)2(NH3)4]2+ complex
Octahedral, but as it contains 2 different ligands, there could be two different arrangements of ligands
89
Shape of [CuCl4]2- complexes
Tetrahedral
All 4 chlorides at 109.5 to each other
90
How are [CuCl4]2- complexes formed?
When copper (II) ions react with concentrated hydrochloric acid, which displaces water molecules
91
Why does a distinct colour change occur when [CuCl4]2- complexes are formedL
As the change in ligands and coordination geometry both contribute to changes in light absorbed
92
Steps to naming com0exes
1. State the number of ligands around the central atom
2. Name the ligands present
3. Name the cation
93
Word used for the number of ligands around the central atom, from 1 to 6
Mono
Di
Tri
Tetra
Penta
Hexa
94
Name for H2O ligand
Aqua
95
Name for NH3 ligand
Ammine
96
Name for OH- ligand
Hydroxy
97
Name for CN- ligand
Cyano
98
Name for Cl- ligand
Chloro
99
How do we name the cation in a complex if we have a neutral or cationionic (positive) complex?
Use the ordinary name of the metal (e.g - iron, copper)
100
How do we name the cation in a complex if we have an anionic (negative) complex?
Use the latinised name
101
Cr latinised name
Chromate
102
Fe latinised name
Ferrate
103
Zinc latinised name
Zincate
104
Pb latinised name
Plumbate
105
Mn latinised name
Manganate
106
Cu latinised name
Cuprate
107
Al latinised name
Aluminate
108
Sn latinised name
Stannate
109
Co latinised name
Cobaltate
110
Name for complex [Fe(CN)6]4-
Hexacyanoferrate (II)
111
Name and state where 3 transition metals are found as trace element in living systems
Iron = haemoglobin
Cobalt = spleen
Manganese = photosystems in photosynthesis
112
Name 3 important economic uses of transition metals
Catalysts
Fe = in the haber process to make ammonia
Iron = in the construction industry (steel)
113
How are most of the complex ions formed by transition metal ions?
Coloured
114
In what state only are transition metal atoms coloured and why?
In complexes
Ligands cause the colours
115
What cause the colour in transition metal complexes?
Ligands
116
[Cr(H2O)6]3+ colour
Dark green
117
[Fe(H2O)6]2+ colour
Pale green
118
[Fe(H2O)6]3+ colour
Yellow
119
[Cu(H2O)6]2+ colour
Bright blue
120
[Co(H2O)6]2+ colour
Pink
121
[CoCl4]2- colour
Blue
122
[CuCl4]2- colour
Yellow or green
123
Colour of an aqueous solution of compounds containing the ions Cr3+
Green
124
Colour of an aqueous solution of compounds containing the ions Co2+
Pink
125
Colour of an aqueous solution of compounds containing the ions Fe2+
Green
126
Colour of an aqueous solution of compounds containing the ions Fe3+
Yellow
127
Colour of an aqueous solution of compounds containing the ions Cu2+
Blue
128
Colour of an aqueous solution of compounds containing the ions CrO4^2-
Yellow
129
Colour of an aqueous solution of compounds containing the ions Cr2O7^2-
Orange
130
Colour of an aqueous solution of compounds containing the ions MnO4-
Purple
131
What colour is a transition metal complex without ligands?
Colourless
132
Why are Cu2+ complexes blue?
If white light (ordinary sunlight for example) passes through copper (II) sulphate solution, some wavelengths of light are absorbed by the solution.
Copper (II ions in solution absorb light in the red region of the spectrum
The light which passes through the solution and out of the other side will have all of the colours except for red
We see this mixture of wavelengths as pale blue (cyan)
It’s the blue light that’s transmitted that we can see
133
[Cu(H2O)6]2+
[CuCl4]2-
[Cu(h2O)2(NH3)4]2+
colours
blue
green
deep blue
134
what do different ligands in a complex ion cause?
different colours
135
hexa (6 coordinate bonds) complexes shape
oxtehedral
136
tetra (4 coorinate bonds) complexes shape
tetrahedral
137
what do ligand have a dramatic effect on when introduced around a metal ion?
on the orbitals of the atom
138
describe the orbitals of a transition metal without ligands
5 degenerate 3d orbitals with the same energy
139
how many types of d orbital are there?
5
140
what raises the energy of the d orbitals when ligands bond with a transition metal ion?
the repulsion between the electrons in the ligands and the electrons in the d orbitals of the metal ion
141
why don't the energies of the d orbitals raise by the same amount when when ligands bond with a transition metal ion?
because of the way the d orbitals are arranged in space
142
ways the d orbitals are split in octehedrals when ligands bond with the transition metal ion
2 d orbitals above (higher energy)
3 d orbitals below (lower energy)
143
ways the d orbitals are split in tetrahedrals when ligands bond with the transition metal ion
3 d oribitals above (higher energy)
2 d orbitals below (lower energy)
144
what does the size of the energy gap between the 2 split groups when ligands bond with a transition metal ion vary with?
the nature of the transition metal ion
its oxidation state
the nature of the ligands
145
what happens when white light is passed through a solution of ions?
some of the energy in the light is used to promote an electron from the lower set of orbitals into a space in the upper set
146
what does the presence of water molecules in hydrated copper (II) sulphate cause?
the splitting of d orbitals
147
describe the 3d orbitals of the Cu2+ ion before water is added
degenerate 3d orbitals
148
what happens to the orbitals of Cu2+ when water is added?
they split
149
what happens to blue light when passed through copper (II) sulfate solution?
is the only light that's transmitted
150
what does white light cause in the split d orbitals of a metal ion complex?
a transition between the lower split level and the higher split level
an electron is promoted to the higher level and the frequency left behind is the colour seen
151
why does the compled [Cu(H2O)6]2+ appear blue?
1. the water ligands cause the d-orbitals to split into 3 of lower energy and two of higher energy
2. electrons can move from the lower to higher energy level by absorbing a specific frequency of light
3. this corresponds to the energy gap E=hf
4. the light that isn't absorbed is the colour that is seen
5. therefore it appears blue as it absorbs all other colours apart from blue
152
equation for calculating the energy of 1 electron transmission
e=hf
or
E = hc/lambda
153
what do we need wavelength in?
metres
154
how do we go from J to kJmol-1?
divide by 1000
multiply by avogadro constant
155
why are some complexes colourless? give examples
copper complexes have an electronic configuration with a full d-sub shell (d10) which mains there is no empty orbitals to allow electrons to jump between energy levels (nowehere for electrons to go when the d orbitals split)
So, Cu (I) complexes do not absorb light in the visible region and appear colourless
Zn2+ is also colourless for the same reason
also Sc3+ is colourless
is has an empty d subshell, so there's no electrons to move between d orbitals
156
ions in complexes that cause them to be colourless
Cu (I)
Zn2+
Sc3+
157
colour of [Cu(H2O)6]2+
cyan/pale blue
158
how is [Cu(H2O)6]2+ formed from copper oxide and sulphuric acid?
neutralisation reaction
yields water
water can bind to copper to form [Cu(H2O)6]2+
cyan/pale blue colour appears
159
what can [Cu(H2O)6]2+ be formed from reacting?
copper oxide
sulphuric acid
160
Summarise why some complexes a colourless
Nowhere for electrons to go when absorbing frequencies of light in the visible region
161
Name 3 colourless complexes
Cu (I)
Zn (II)
Sc3+
162
Describe copper
Brownish-red metallic element
163
Why is copper so important? Give an example
One of the most widely used metals
(e.g - electrical wires)
164
Why is copper used for electrical wires?
Excellent conductor of electricity
165
Describe pure copper
Soft
166
What is pure copper good for and why?
Copper piping
Soft
167
How are alloys of copper different to pure copper?
Far harder and stronger
168
Two most important alloys of copper
Brass
Bronze
169
Brass alloy
Zinc and copper
170
Bronze alloy
Tin and copper
171
What do alloys of copper and pure copper have in common?
The alloys have corrosion resistance almost as goof as t\hat of pure copper
172
Which electron is lost first in transition metal ions?
4s electron
173
Describe copper (I) compounds
Not very stable
174
What can easily be oxidised to copper (II) and why?
Copper (I) compounds
Not very stable
175
What can copper (I) compounds be oxidised to and how?
To copper (II)
In many cases, by mere exposure to air
176
What are copper (I) compounds mostly?
Unstable
177
What can copper (I) compounds be formed as? Give an example
Insoluble compounds
e.g - copper (I) iodide, a white solid
178
Describe copper (I) iodide
White solid
179
How do copper (II) ion exist?
Not as simple ions in aqueous solution but as complex hydrated ions
180
Main copper complex ion present in aqueous solution
Hexaqua copper (II)
[Cu(H2O)6]^2+
181
Colour of [Cu(H2O)6]^2+
Blue
182
Different reactions of copper (II) ions to remember
With iodine ions
With aqueous sodium hydroxide
Ligand exchange reactions (aqueous ammonia and concentrated hydrochloric acid)
183
Example reaction for the reaction between copper (II) ions with iodide ions
Aqueous copper (II) sulfate and potassium iodide
184
What happens in the reaction between aqueous copper (II) sulfate and potassium iodide?
Copper (II) ions a reduced to copper (I) ions
185
What happens in the reaction between aqueous copper (II) sulfate and potassium iodide to the iodine?
Iodide ions are oxidised to iodine
186
How is copper (I) iodide formed?
As a white precipitate
187
What is the red-brown solution formed when copper (II) ions react with iodide ions?
Due to the iodine which reacts with excess iodide ions to form the soluble complex ion, I3-
188
What are the two colours formed during the reaction of copper (II) ions and iodide ions and why does this occur?
Copper (I) iodide is formed as a white precipitate
The red-brown solution is due to he iodine, which reacts with excess iodide ions to form the soluble complex ion, I3-
189
Equation for the reaction between copper (ii) ions and iodide ions
2Cu2+ + 4I- —> 2CuI + I2
190
What type of reaction is the reaction between copper (II) ions and iodide ions?
Redox
191
What do metallic cations normally act as in redox reactions?
Oxidising agents
192
What happens to iodide ions in the reaction between copper (II) ions and iodide ions?
Oxidised to iodine
193
What happens when sodium hydroxide and copper (II) ions are reacted in aqueous solution?
Gelatinous blue precipitate of copper (II) hydroxide is formed
194
When is a gelatinous precipitate of copper (II) hydroxide formed?
When sodium hydroxide and copper (II) ions react in aqueous solution
195
How do we know that copper (II) hydroxide is a basic hydroxide?
Precipitate is insoluble in excess alkali
196
What kind of hydroxide is copper (II) hydroxide?
Basic
197
What give experimental evidence that copper (II) hydroxide is a basic hydroxide?
Insoluble in excess alkali
Reacts with an acid to form a copper (II) salt
198
Equation for the reaction between copper (II) ions and aqueous sodium hydroxide
Cu2+ + 2OH- —> Cu(OH)2
199
What happens when a transition metal ion is exposed to a mixture of ligands?
Ligands can be exchanged to form a new complex
200
Example of a mixture of ligands
An aqueous solution containing chloride ion
201
Wha kind of processes are ligand exchange reactions?
Equilibrium processes
202
Why is knowing the concentration of metal ions and any possible ligands key to identifying the species that will be present in solution in ligand exchange reactions?
They’re equilibrium processes
203
What do processes being equilibrium processes allow us to do?
Identify the species that will be present in solution
204
What can we do with equilibrium processes?
Manipulate the side of the equilibrium point
205
What happens when the side of the equilibrium point is changes?
The colour alters
206
What is ammonia?
A weak alkali
207
What does ammonia solution contain and why?
Hydroxide ions
Ammonia is a weak alkali
208
What happens when concentrated ammonia solution is added to copper (II) ions in aqueous solution?
A blue precipitate of copper (II) hydroxide is initially formed
209
What happens when *excess* ammonia is added to copper (II) ions in aqueous solution?
A deep blue/royal blue solution is formed
210
Why is a deep blue solution formed when *excess* ammonia is added to copper (II) ions?
The ammonia molecules have complexed with the copper (II) ions
211
How much ammonia is added to copper (II) ions to form a blue precipitate?
Just a few drops
212
Describe the deep blue solution formed when excess ammonia reacts with copper (II) ions
Completely soluble
213
Equation for the reaction between copper (II) ions and ammonia
[Cu(H2O)6]^2+ + 4NH3 ⇌ [Cu(H2O)2(NH3)4]^2+ +2H2O
(Remember, it’s the complex ion that takes place here)
214
[Cu(H2O)6]^2+ name
Hexaqua copper (II)
215
[Cu(H2O)6]^2+ colour
Blue
216
[Cu(H2O)2(NH3)4]^2+ name
Diaqua tetramine copper (II)
217
[Cu(H2O)2(NH3)4]^2+ colour
Deep blue
218
Why is the reaction between copper (II) ions and ammonia an exchange reaction?
4 ammonia ligands replace 4 water ligands
219
Why is hydrochloric chosen to react with copper (II) ions?
A good source of chloride ions
220
What type of hydrochloric acid has to be added to copper (II) ions?
Concentrated
221
What happens when concentrated hydrochloric acid is added to copper (II) ions in exces?
Yellow-green solution is formed
222
Why is the reaction between hydrochloric acid and copper (II) ions an exchange reaction?
The water molecules have been replaced by chloride ions
223
Equation for the reaction between copper (II) ions and hydrochloric acid
[Cu(H2O)6]^2+ + 4Cl- ⇌ [CuCl4]^2- + 6H2O
224
[CuCl4]^2- name
Tetrachloro cuprate (II)
225
[CuCL4]^2- colour
Yellow-green
226
What are the two things that have swapped in the exchange reaction between copper (II) ions and hydrochloric acid?
Ligands
Geometry
227
How has geometry been swapped during the reaction between copper (II) ions and hydrochloric acid?
Octahedral to tetrahedral structure
228
What happens if we add water back to the reaction between concentrated sulphuric acid and copper (II) ions? Why?
Colour turns back blue
The position of equilibrium has shifted to the left
229
Why isn’t the blue colour as strong when you add water back to the reaction between concentrated hydrochloric acid and copper (II)?
Due to the dilution effect
230
Le Chatelier’s principle
When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change
231
What happens to the position of equilibrium if the concentration is increased on one side of an equation?
The position of equilibrium moves to the other side
232
What happens to the position of equilibrium if pressure is increased?
Position of equilibrium moves to the side of the equation with the least gaseous molecules (look at big numbers in front) and vice versa
233
What type of reactions does changing the pressure affect?
Reactions where gases are involved
234
What happens to the position of equilibrium if we add a catalyst and why?
Speeds up the rate of the forward and reverse reactions equally, so no effect on the position of equilibrium
(Although the state of equilibrium is established more quickly)
235
What happens to the position of equilibrium if we increase the temperature?
Equilibrium position moved in the endothermic (positive) direction (absorb the extra heat) and vice versa
236
Describe chromium
Grey
Metallic
Can take on a high polish
One of the transition elements
237
What are the oxidation states that chromium exists in?
+2
+3
+6
238
Describe the +2 oxidation state of chromium
Unstable in air
239
Describe the +3 oxidation state of chromium
Most stable state of chromium
240
Describe the +6 oxidation state of chromium
Found mainly with very electronegative elements such as oxygen
241
Examples where chromium is found with a +6 oxidation state?
Dichromate (VI)
Chromate (VI)
242
What is the dichromate (VI) ion in equilibrium with?
The chromate (VI) ion
243
How does chromate (VI) change into dichromate (VI)?
By adding acid
244
What happens when you add acid to chromate (VI)?
Changes into dichromate (VI)
245
How do you turn dichromate (VI) into chromate (VI)?
By adding alkali
246
What happens when you add alkali to dichromate (VI)?
Turns into chromate (VI)
247
Does the reaction of turning into dichromate (VI) from chromate (VI) and vice versa involve redox?
No
248
Equation of the reaction for the conversion of chromate (VI) into dichromate (VI)
2CrO4^2- + 2H+ (equilibrium) Cr2O7^2- + H2O
249
Colour of chromate (VI) ion
Yellow
250
Colour of dichromate (VI) ion
Orange
251
What is the dichromate (VI) ion in acidic solution?
A powerful oxidising agent
252
What happens when dichromate (VI) ions react with acidic solution?
Dichromate (VI) ions are reduced to chromium (III) ions
253
Two species which are readily oxidised by dichromate (VI) ions
1.) iron (II) ions
Fe^2+ —> Fe^3+
2.) ethanol
CH3CH2OH —> CH3CHO
254
Chromium (III) ions colour
Green
255
What’s the colour change when iron (II) ions are oxidised by dichromate (VI) ions?
The colour change is difficult to see owing to the formation of yellow iron (III) ions
256
Fe3+ ions colour
Yellow
257
Half equation for the reduction of the dichromate (VI) ion
Cr2O7^2- + 14H+ + 6e- —> 2Cr^3+ + 7H2O
258
Combine the half equation for the oxidation of iron (II) ions and the \oxidation of Fe2+ ions
Cr2O7^2- + 14H+ + 6e- —> 2Cr^3+ + 7H2O
Fe^2+ —> Fe^3+ + e- (x6)
Cr2O7^2- + 14H+ + 6Fe^2+ —> 2Cr^3+ + 6Fe^3+ + 7H2O
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How do chromium (III) ions exist?
Not as simple ions in aqueous solution but as complex hydrated ions
260
Main complex ion present in aqueous solution
[Cr(H2O)6]^3+
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[Cr(H2O)6]^3+ name
Hexaqua chromium (III)
262
With what type of ions does adding an excess of OH- dissolve the initial precipitate? Give an example
Amphoteric
e.g - Cr^3+ ions
263
Dichromate ion
Cr2O7^2-
264
Chromate ion
CrO4^2-
265
Example of a transition metal having variable oxidation states
Mn
+1 to +7
266
Why is copper a transition metal?
Copper atoms can form Cu2+ cations, which have incomplete d subshells
267
What do we mention when asked to give 3 properties of the d- block?
- form coloured ions
- catalysts
- variable oxidation states
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How could iron (III) oxide be chemically separated from aluminium oxide?
All aqueous NaOH, Al2O3 dissolves whilst Fe2O3 doesn’t
Filter off undissolved Fe2O3
269
Acid
Species that can donate a proton or accept an electron pair
270
Base
Species that can accept a proton or donate an electron pair
271
What makes an acid or base strong?
Completely ionised
272
What makes an acid or base weak?
Partially ionised
273
Why can transition metal complexes act as catalysts?
-variable oxidation states
-partially filled d-orbitals which enable them to form temporary bonds with the reactant molecules
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Precipitate formed with NaOH and Mg2+ or Pb2+
White
275
What happens when acids react with metal carbonates?
Gives CO2 gas
276
Grams in 1dm3
1000g
277
How many dm3 is 1000g?
1
278
How do we find an appropriate wavelength to find the concentration of something in an equilibrium mixture?
Find a wavelength absorbed by one but not the other
