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A2 Chemistry 2 > Transition Metals and their Chemistry > Flashcards

Transition Metals and their Chemistry Flashcards

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1
Q

What is a simple definition of a transition metal?

A

An element between the s and p blocks of the periodic table

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2
Q

What is a better definition of a transition metal?

A

An element which forms one or more stable ions which have incompletely full d sub-shells

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3
Q

What are the general properties of transition metals?

A

Hard metals with high melting and boiling temperatures
Show more than one oxidation number in their compounds
Many show catalytic activity

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4
Q

Which are d block elements that are not transition metals?

A

Scandium and zinc

Second definition excludes them

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5
Q

Where are the first electrons lost from in transition metals?

A

Outer 4s subshell followed by the 3d subshell

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6
Q

How are the small fluctuations in the general trend of increasing ionisation energies explained?

A

Relative stability of full and half-full subshells

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7
Q

What can phytomining be used for?

A

Extract transition metals using plants from areas where they cannot be obtained economically by other methods

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8
Q

How is phytomining carried out?

A

Crops grow on soil containing metal
Plant is burned and energy used for electricity
Leaves bio-ore which is then smelted

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9
Q

What are the advantages and disadvantages of phytomining?

A

Bio-ores are almost sulphur free
Need less energy for smelting
Cause less acid rain pollution
Usually have higher metal content than mineral ores
‘Green’ alternative to mining low grade ores
Only commercially viable if the price of the metal being extracted remains high

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10
Q

What are general observations made on the transition metals from titanium to copper?

A

+1, +2, +3 are the most common
From titanium to chromium, +3 is the most common
From manganese onwards, +2 is the most common

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11
Q

What happens with very high oxidation numbers?

A

Involved in covalent bonding Mn2O7

Form polyatomic ions such as (CrO4)2-

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12
Q

What does changes in the colour of solution indicate?

A

A change in the oxidation number of the ion

When the 3d orbital is either empty of full, the solution is colurless

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13
Q

What is a simple explanation for explaining the colour of solution?

A

Due to electrons absorbing photons of certain frequencies of visible light
Energy of each of these photons matches the energy needed for one electron to jump from a lower to a higher energy orbital
Frequencies of visible light remaining after this absorption give the solution its colour

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14
Q

What sort of bonding is involved in complex ions?

A

Dative covalent (co-odinate) bonds

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15
Q

How are complex ions formed?

A

Small size results in high electron density which attract electron rich species
Central metal ion is surrounded by either anions or molecules that act as electron-pair donors
The electron-pair donors are called ligands

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16
Q

What does the number of ligands involved in a complex ion depend one?

A

Size of metal ion

Size of ligand

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17
Q

What is the charge of a complex ion?

A

Sum of the charge on the metal ion and the charge(s) of the ligands

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18
Q

What are anionic and cationic ion complexes?

A

Anionic - Attracted to anode during electrolysis

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19
Q

What is the co-ordination number?

A

Number of lone pairs attached to the metal ion

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20
Q

What are monodentate, bidentate and polydentate ligands?

A

Mono - join to the metal ion by one atom only
Bi - join to the metal atom by two atoms
Poly - attach to the metal ion by more than two atoms

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21
Q

What is 1,2-diaminoethane? Where are the lone pairs?

A

:NH2-CH2-CH2-H2N:

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22
Q

What is ethanedioate? Where are the lone pairs?

A

:O- :O-
C - C
=O =O

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23
Q

What is the charge of edta? Where are the lone pairs?

A

4-
Nitrogen and oxygens with single bonds
6 lone pairs

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24
Q

Give 3 biological examples that contain transition metals?

A

Chlorophyll, vitamin B12 and haemoglobin

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25
What does the shape of complex ions depend on? Give some examples of sorts of shape
Depends on number of electrons within the d orbital and the coordination number Linear, planar, tetrahedral, octohedral
26
What is the most common coordination number and what shape is it?
6 | Octohedral
27
What are the oxidation numbers of vandium? What are the colours?
V2+ +2 Purple V3+ +3 Green (VO)2+ +4 Blue (VO2)+ +5 Yellow
28
What must be taken into account when working out a suitable reducing agent?
The reaction involving the vandium species must have a more a more positive E standard (so it goes to the right) than the E standard of the reducing agent Activation energy and kinetic feasibility must also be taken into account
29
What does the stability of oxidation numbers depend on?
Arrangement of electron in the ions | Half-full of full subshells are more stable
30
How does copper (I) exist?
Unstable in aqueous solution | Exists at high temperatures, when insoluble and precipitated, in complexes
31
How do copper (I) compounds disproportionate in aqueous solution?
Cu2SO4 --> Cu(s) + CuSO4(aq)
32
How can copper (I) ions be stabilised in solution?
Adding conc HCl to form a complex | CuCl(s) + Cl-(aq) --> [CuCl2]- (aq)
33
How can copper (I) chloride be made?
Boil: [Cu(H2O)6]2+ +4Cl- -->[CuCl4]2- +6H2O Boil: [CuCl4]2- + Cu(s) --> 2[CuCl2]- [CuCl2]- + (cold water) --> CuCl(s) + Cl-
34
How is copper (I) iodide made?
Precipitated as a white solid when potassium iodide solution is added to copper (II) sulphate solution
35
How is copper (I) oxide made?
Precipitated as a red solid when alkaline solution of copper (II) sulphade is reduced be glucose?aldehyde Cu2+ complexed with 2,3-dihydroxybutanedioates to prevent precipitation of Cu(OH)2
36
What are the oxidation number and colour of chromium (II)?
Cr2+ pale blue in aqueous solution | Easily oxidised
37
What is the most stable oxidation number of chromium?
Cr3+ violet/blue-grey Hydrated gives green solution when involved in reactions as a ligand exhange often takes place Exhibits amphoteric characteristics [Cr(H2O)3(OH)3] + 3H+ --> [Cr(H2O)6]3+ [Cr(H2O)3(OH)3] + 3OH- --> [Cr(OH)6]3- +3H2O
38
What are chromium compounds often used as?
Green and yellow pigments, protective primers, tanning animal hides and to prevent the corrosion of metals
39
What is the highest oxidation number of chromium and what are the colours of its compounds?
+6 CrO3 Chromate ion (CrO4)2- bright yellow Dichromate (Cr2O7)2- orange
40
How does chromium oxide react with water?
CrO3(s) + H2O --> H2CrO4(aq)
41
How does the chromate (VI) and the dichromate (VI) ion exist in equilibrium?
(CrO4)2- +2H+ (Cr2O7)2- +H2O | Shifted to the right in acidic solution and the left in alkaline solution
42
Why are complex ions coloured?
Movement between partly filled d-orbitals (movement between 3d and other shells too large Ligands change the energy of an orbital as orbitals closer to the ligands have higher energy 'Splits' the orbitals into lower and higher energy orbitals Split occurs so that total energy of 3d is the same
43
What does crystal field theory show?
More electrons allow a greater combination of transitions therefore transition metal ions undergo changes of colour when the oxidation number changes
44
How is the Cr2+ ion stable? What does it look like?
In red-coloured chromium (II) ethanoate [Cr2(CH3CO2)4(H2O)2] See picture
45
How is [Cr2(CH3CO2)4(H2O)2] made?
Reducing Cr3+ compound using zinc to form blue solution Sodium ethanoate added to form bright red precipitate When exposed to air, it will be oxidised to Cr3+ and turn grey-green
46
How is [Cr2(CH3CO2)4(H2O)2] made in the lab?
When tap funnel is opened, HCl runs into flask Zn(s) +2HCl --> ZnCl2 + H2(g) H2 reduces orange dichromate (VI) to green chromium (II) then to blue chromium (II) (Cr2O7)2- + 6H+ + 4H2 --> 2Cr2+ + 7H2O Once turned blue, tap is closed and pressure builds up, forcing content into boiling tube and producing red precipitate 2Cr2+ + 4CH3COO- +2H2O --> [Cr2(CH3CO2)4(H2O)2]
47
Adding OH- to hexaaqua 2+ ions
[M(H2O)6]2+ + 2OH- --> [M(H2O)4(OH)2](s) + 2H2O | Acid base reaction
48
What is the exception for adding OH- to hexaaqua 2+ ions?
[Zn(H2O)6]2+ + 2OH- --> [Zn(H2O)4(OH)2](s) + 2H2O | [Zn(H2O)4(OH)2](s) + 2OH- --> [Zn(OH)4]2-
49
Adding OH- to hexaaqua 3+ ions
[Cr(H2O)6]3+ + 3OH- --> [Cr(H2O)3(OH)3](s) + 3H2O [Cr(H2O)3(OH)3](s) + 3OH- --> [Cr(OH)6]3- + 3H2O Smaller ion so more likely to polarise OH bond and break it, hence more likely to dissolve
50
What ions act as amphorteric hydroxides?
Zn2+ Al3+ Cr3+ ACID: [Cr(H2O)3(OH)3](s) + OH- [Cr(H2O)2(OH)4]- + H2O BASE: [Cr(H2O)3(OH)3](s) + H+ [Cr(H2O)4(OH)2]- + H2O
51
What initial reaction occurs when small amounts of ammonia added to hexaaqua 2+ and 3+ ions?
[M(H2O)6]2+ + 2NH3 --> [M(H2O)4(OH)2](s) + 2NH4+ [M(H2O)6]3+ + 3NH3 --> [M(H2O)3(OH)3](s) + 3NH4+ Acid-base reaction
52
What reaction occurs when ammonia acts is added in excess to hexaaqua 2+ ions?
[Cu(H2O)6]2+ + 4NH3 --> [Cu(NH3)4(H2O)2](s) + 4H2O Ligand exhange reaction Maximum of 4 ammonia ligands as it is slightly larger than H2O
53
Give 5 examples of transition metals acting as catalysts
TiCl3 in the polymerisation of ethene Iron in the Haber process (or rubidium which is more effective but more expensive) Vanadium in the Contact process Platinum gauze in the first stage of the Ostwald process Nickel in the hydrogenation of vegetable oils to make margarine
54
What is the Contact process?
Producing sulphur trioxide needed in the manufacture of sulphuric acid 2SO2(g) + O2(g) 2SO3(g)
55
How has the catalyst used in the Monsanto process developed?
Originally, cobalt and iodide co-catalyst used at 300C and 700 atm Rhodium/iodide used which presented some problems so iridium presented as alternative When used with ruthenium it is very active and reduces costs, CO2, drying columns and formation of by-products
56
What are the two types of catalysts?
Homogeneous- same phase as reactants | Heterogeneous- different phase from reactants
57
How does a heterogeneous reactant work?
Reactant molecules adsorbed onto surface of catalyst at active sites, weakening bonds between atoms Reduces energy needed to break reactant molecules apart and increases chance of successful collision If other molecules bind irreversibly, the catalyst is poisoned and will no longer work
58
Why are transition metals effective catalysts?
Exist in multiple oxidation states to provide alternative route
59
Why are catalysts finely divided?
Larger surface area allows more reactants to be adsorbed
60
What are the modern uses of transition metals?
Supra molecules Chemotherapy Photochromic lenses
61
How do photochromic lenses work?
Contain copper and silver halides which exist in equilibrium: Cu+(s) + Ag+(s) Cu2+(s) + Ag(s) In bright light, the equilibrium shifts and silver atoms are produced
62
How does chemotherapy work?
Uses chemicals to damage or destroy cancer cells, causing as little harm as possible to healthy tissue Many drugs damage DNA or proteins involved in cell division Cis-platin slows growth of cancer cells by binding to the DNA of nucleus and interfering with natural repair mechanisms
63
What alternatives are being developed to cis-platen?
Trans isomer which is used with other drugs to enhance effects without considerable damage Gold which is small enough to pass through the membranes, delivering the drug to its target Heat allows chemo dosage to be reduced whilst retaining same efficiency

A2 Chemistry 2 (5 decks)

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