Ch5.3 Transition elements Flashcards
1
Q
Which 2 elements are exceptions to the Aufbau principle?
A
chromium and copper
2
Q
How is chromium an exception to the Aufbau principle?
A
- 3d and 4s orbitals all contain 1 unpaired e-
- 1s2 2s2 2p6 3s2 3p6 4s1 3d5
3
Q
How is copper an exception to the Aufbau principle?
A
- 3d orbital is filled completely leaving 4s half-filled
- 1s2 2s2 2p6 3s2 3p6 4s1 3d10
4
Q
Which electrons are lost first when ions are formed of the transition elements and why?
A
- 4s electrons are lost before the 3d electrons unlike in all other elements
- this is because, once filled, the 4s electrons have a slightly higher energy than the 3d electrons
5
Q
Define transition metal
A
a d block element that has an incomplete d-subshell as a stable ion
6
Q
What are the physical properties of transition metals?
A
- high density
- high melting and boiling points
- shiny in appearance (lustrous)
- conduct electricity
7
Q
What are the chemical properties of transition metals?
A
- have variable oxidation states
- transition metal compounds form coloured solutions in water
- catalysts
8
Q
Can transition metals form ions with more than one stable oxidation state?
A
Yes
- all of the transition metals in period 4 do this (Ti to Cu)
9
Q
Which compounds containing transition metals can act as strong oxidising agents?
A
- compounds containing a transition metal in a high oxidation state
eg. potassium manganate (VII) KMnO4
eg. potassium dichromate (VI)
K2Cr2O7
10
Q
Explain what is meant by the statement: compounds of transition metals can undergo disproportionation
A
- the transition metal species is both oxidised and reduced in the same reaction
11
Q
Explain why transition metal compounds are often coloured
A
- white light hits an object and part of the spectrum is absored by the object and the remaining is reflected which is the light we see
- as light hits a transition metal ion, the electrons become excited (energised) and if there are some partially filled d sub-shells available, they can move up an energy level
- as the electrons then drop back down, they release light energy which we see as colour
NOTE: a compound will only be coloured if the transition metal ion has partially filled d subshells
12
Q
Define catalyst
A
- a substance which speeds up a reaction by providing an alternative pathway with a lower activation energy and isn’t used up itself in the reaction
13
Q
Why are transition metals good catalysts?
A
- reactants are ADsorbed to the surface of a transition metal where it may gain or lose electrons and form an intermediate allowing a pathway with a lower activation energy
- the transition metals can vary in oxidation states and once the reaction has occurred, the products are DEsorbed and the transition metal remains unchanged
14
Q
What is the equation for hydrogen production?
A
Zn(s) + H2SO4(aq) –> ZnSO4(aq) + H2(g)
15
Q
What is the catalyst for the reaction for hydrogen production?
A
CuSO4 or Cu2+ ion
16
Q
What is the equation for the contact process?
A
2SO2 + O2 ⇌ 2SO3
17
Q
What is the catalyst for the reaction of the contact process?
A
V2O5 or V5+ ion
18
Q
What is the equation for oxygen production?
A
2H2O2 –> 2H20 + O2
19
Q
What is the catalyst for the reaction for oxygen production?
A
MnO2 or Mn4+ ion
20
Q
What is the equation for the Haber process?
A
N2 + 3H2 ⇌ 2NH3
21
Q
What is the equation for the hydrogenation of ethene?
A
C2H4 + H2 –> C2H6
22
Q
What is the catalyst for a catalytic converter?
A
Pt or Pd
23
Q
What is the catalyst for vitamin B12?
A
Co
24
Q
Define ligand
A
a molecule or ion that can donate a pair of electrons to the central transition metal ion to form a coordinate bond (dative covalent bond)
25
Define coordinate bond
a bond in which one of the bonded atoms provides both electrons for the covalent bond
26
State some features of ligands
- all ligands have at least one lone pair of electrons
- ligands can be neutral molecules or charged
27
What is a monodentate ligand?
- a ligand that donates just one pair of electrons to the central metal ion to form one coordinate bond
- eg. Cl- , OH- , CN- , NH3 , OH2 , SCN- (thiocyanate)
28
What is a bidentate ligand?
- a ligand that contains 2 atoms which donate a pair of electrons each to the central metal ion
- 2 coordinate bonds are formed per ligand
29
What is a multidentate ligand?
- a ligand that can form several coordinate bonds
- eg. EDTA 4- (ethylenediaminetetraacetic acid)
30
Describe a linear complex ion giving its bond angles and occurrence
- 2 bonding regions in straight line
- angle 180 degrees
- occurs in Ag+ complexes
31
Describe a tetrahedral complex ion giving its bond angles and occurrence
- 4 bonding regions spread as far apart as possible
- angle 109.5 degrees
- occurs with large ligands eg. Cl-
32
Describe a square planar complex ion giving its bond angles and occurrence
- 4 bonding regions spread as far apart as possible in a planar restriction
- angle 90 degrees
- occurs in Pt 2+ complexes
33
Describe an octahedral complex ion giving its bond angles and occurrence
- 6 bonding regions spread as far as possible
- angle 90 degrees
- most common occurrence
34
What are the 2 types of stereoisomerism?
- cis-trans / E-Z
- optical isomerism
35
What is stereoisomerism?
molecules or complexes with the same structural formula but with a different spatial arrangement of these atoms
36
What is cis-platin and how does it work?
- a very effective drug to fight cancer
- it works by binding to DNA and stopping replication and cell division
37
What is optical isomerism?
- optical isomers are non-superimposable mirror images of each other
38
What do ligand substitution reactions involve?
- a ligand in a complex ion being removed and replaced by another ligand
- common ligand substitution reactions involve the substitution of water molecules with another ligand
39
[Cu(H2O)6]2+ + NH3 (dropwise)
equation, colours, type of reaction
[Cu(H2O)6]2+ + 2NH3 --> [Cu(H2O)4(OH)2] + 2NH4+
[Cu(H2O)6]2+ is pale blue solution
[Cu(H2O)4(OH)2] is pale blue precipitate
hydrolysis reaction
ammonia acts as a base pulling a proton off two of the water ligands
40
[Cu(H2O)4(OH)2] + NH3 (excess after dropwise)
equation, colours, type of reaction
[Cu(H2O)4(OH)2] + 4NH3 --> [Cu(H2O)2(NH3)4]2+ + 2H2O + 2OH-
[Cu(H2O)4(OH)2] is a pale blue precipitate
[Cu(H2O)2(NH3)4]2+ is a deep blue solution
substitution reaction
adding NH3 in excess causes ligand exchange to occur
41
[Cu(H2O)6]2+ + NH3 (excess straight away/overall reaction)
equation, colours, type of reaction
[Cu(H2O)6]2+ + 4NH3 ⇌ [Cu(H2O)2(NH3)4]2+ + 4H2O
[Cu(H2O)6]2+ is a pale blue solutiion
[Cu(H2O)2(NH3)4]2+ is a deep blue solution
substitution reaction
42
[Cr(H2O)6]3+ + NH3 (dropwise)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 3NH3 --> [Cr(H2O)3(OH)3] + 3NH4+
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(H2O)3(OH)3] is a dark green precipitate
hydrolysis reaction
ammonia is acting as a base when it pulls protons from 3 of the water ligands
43
[Cr(H2O)3(OH)3] + NH3 (excess after dropwise)
equation, colours, type of reaction
[Cr(H2O)3(OH)3] + 6NH3 --> [Cr(NH3)6]3+ + 3H2O + 3OH-
[Cr(H2O)3(OH)3] is a dark green precipitate
[Cr(NH3)6]3+ is a purple solution
substitution reaction
(more likely to occur with conc NH3)
44
[Cr(H2O)6]3+ + 6NH3 (excess straight away/overall reaction)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 6NH3 ⇌ [Cr(NH3)6]3+ + 6H2O
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(NH3)6]3+ is a purple solution
substitution reaction
45
[Cu(H2O)6]2+ + conc HCl
equation, colours, type of reaction
[Cu(H2O)6]2+ + 4Cl- ⇌ [CuCl4]2- + 6H2O
OR
[Cu(H2O)6]2+ + HCl ⇌ [CuCl4]2- + 6H2O + 4H+
[Cu(H2O)6]2+ is a pale blue solution
[CuCl4]2- is a yellow solution
(often looks green instead of yellow because there is a mix of the blue and yellow solutions present)
46
[Cu(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Cu(H2O)6]2+ + 2OH- --> [Cu(H2O)4(OH)2] +2H2O
dropwise simple equation
Cu2+ + 2OH- --> Cu(OH)2
excess: no further reaction
[Cu(H2O)6]2+ is a pale blue solution
[Cu(H2O)4(OH)2] / Cu(OH)2 is a blue gelatinous precipitate
hydrolysis reaction
47
[Fe(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation [Fe(H2O)6]2+ + 2OH- --> [Fe(H2O)4(OH)2] + 2H2O
dropwise simple equation
Fe2+ + 2OH- --> Fe(OH)2
excess: no further reaction but precipitate darkens in time on the surface as it oxidises to [Fe(H2O)3(OH)3] (orange-brown precipitate)
[Fe(H2O)6]2+ is a pale green solution
[Fe(H2O)4(OH)2] / Fe(OH)2 is a dark green precipitate
hydrolysis reaction
48
[Fe(H2O)6]2+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Fe(H2O)6]2+ + 2NH3 --> [Fe(H2O)4(OH)2] + 2NH4+
excess: no further reaction but the precipitate darkens with time on oxidation to [Fe(H2O)3(OH)3]
[Fe(H2O)6]2+ is a pale green solution
[Fe(H2O)4(OH)2] is a dark green precipitate
hydrolysis reaction
49
[Fe(H2O)6]3+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Fe(H2O)6]3+ + 3OH- --> [Fe(H2O)3(OH)3] + 3H2O
dropwise simple equation
Fe3+ + 3OH- --> Fe(OH)3
excess: no further reaction
[Fe(H2O)6]3+ is a pale yellow solution
[Fe(H2O)3(OH)3] is an orange-brown precipitate
hydrolysis reaction
50
[Fe(H2O)6]3+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Fe(H2O)6]3+ + 3NH3 --> [Fe(H2O)3(OH)3] + 3NH4+
excess: no further reaction
[Fe(H2O)6]3+ is a pale yellow solution
[Fe(H2O)3(OH)3] is an orange-brown precipitate
hydrolysis reaction
51
[Mn(H2O)6]2+ + NaOH (dropwise vs excess)
equation, colours, type of reaction
dropwise full equation
[Mn(H2O)6]2+ + 2OH- --> [Mn(H2O)4(OH)2] + 2H2O
dropwise simple equation
Mn2+ + 2OH- --> Mn(OH)2
excess:
no further reaction but the precipitate darkens over time as it oxidises:
4Mn(OH)2 + O2 --> 2Mn2O3 + H2O
[Mn(H2O)6]2+ is a very pale pink solution
[Mn(H2O)4(OH)2] is a brown precipitate
hydrolysis reaction
52
[Mn(H2O)6]2+ + NH3 (dropwise vs excess)
equation, colours, type of reaction
dropwise
[Mn(H2O)6]2+ + 2NH3 --> [Mn(OH)2(H2O)4] + 2NH4+
excess:
no further reaction but the precipitate darkens over time as it oxidises:
4Mn(OH)2 + O2 --> 2Mn2O3 + H2O
[Mn(H2O)6]2+ is a very pale pink solution
[Mn(H2O)4(OH)2] is a brown precipitate
hydrolysis reaction
53
[Cr(H2O)6]3+ + NaOH (dropwise)
equation, colours, type of reaction
[Cr(H2O)6]3+ + 3OH- --> [Cr(H2O)3(OH)3] + 3H2O
[Cr(H2O)6]3+ is a pale purple solution but can look green due to impurities
[Cr(H2O)3(OH)3] is a dark green precipitate
hydrolysis reaction
54
[Cr(H2O)3(OH)3] + NaOH (excess after dropwise)
equation, colours, type of reaction
precipitate re-dissolves in excess hydroxide
[Cr(H2O)3(OH)3] + 3OH- --> [Cr(OH)6]3- + 3H2O
[Cr(H2O)3(OH)3] is a dark green precipitate
[Cr(OH)6]3- is a dark green solution
substitution reaction
55
What is the test for ammonium ions?
- add NaOH to NH4+ sample to make NH3 and H2O
- NH3 will turn damp red litmus paper blue
56
What is the test for carbonate ions?
- add HCl to sample
CO3 2- + 2H+ --> H2O + CO2
CO2 turns limewater cloudy when it's bubbled through
57
What is the test for sulphate ions?
- add HCl followed by BaCl2
Ba2+ + SO4 2- --> BaSO4
BaSO4 is a white precipitate
58
What is the test for halide ions?
- add nitric acid followed by silver nitrate
AgCl, AgBr or AgI formed
AgCl is white precipitate that dissolves in dilute or conc ammonia
AgBr is a cream precipitate that dissolves in just conc ammonia
AgI is a yellow precipitate that is insoluble in ammonia of any conc
59
How does haemoglobin relate to ligand substituution?
- haemoglobin is a complex protein of 4 polypeptide chains and each haemoglobin has 4 haem groups
- each haem group has an Fe2+ ion at its centre, oxygen can reversibly bind to the Fe2+ ion which allows oxygen to be transported around the body
60
Describe the stucture of the Fe2+ complex ion in haemoglobin
- there are 4 coordinate bonds between the Fe2+ ion and the nitrogen atoms in the haem structure
- a further coordinate bond is formed with globin protein
- the final coordinate bond is formed with an O2 molecule which is then transported
61
Describe and explain how CO is related to haemoglobin and ligand substitution
- CO and O2 can both bind to haemoglobin at the same place
- CO binds more strongly to the haemoglobin than O2
- if CO and O2 are both present in the lungs then CO will bind over O2 so there is less haemoglobin for O2 to bind to
- CO molecules can replace O2 molecules and they are both ligands so this is ligand substitution
- reaction of binding isn't reversible for CO
62
What happens to the body if CO and O2 are both present in the lungs at the same time?
- tissues are starved of O2 because it can't be transported
63
What symptoms can different concentrations of CO in the blood cause?
- low concs: headaches, nausea and potential suffocation
- high concs: fatal
64
How is CO formed?
- during incomplete combustion of carbon-containing fuels
- burning tobacco also releases CO which is why long-term smokers become short of breath
65
What are the physical properties of CO?
- colourless
- odourless
66
