Transition Metals Flashcards
Define transition metal
A transition metal is one which forms at least one stable ion with a partially filled d-sub-shell
Why is scandium not a transition metal?
It forms a Sc3+ ion with the configuration: 1S2 2S2 2P6 3S2 3P6
Sc3+ is the only ion formed and the d -sub shell is empty
Why is zinc not classified as a transition metal
Zn2+ is the only ion formed with a configuration of: 1s2 2s2 2p6 3s2 3p6 3d10
The d-sub shell is full
To make chromium more stable what is the expected configuration
1s2 2s2 2p6 3s2 3p6 4s1 3d5
So copper is more stable what is the expected electron configuration
1s2 2s2 2p6 3s2 3p6 4s1 3d10
What are the 4 key features of a transition elements
- They form complex ions
- They form coloured ions
- They have catalytic properties
- They have variable oxidation states
Define a coordinate bond
a shared pair of electrons which have both come from the same atom
Define a ligand
A molecule or ion with a lone pair of electrons which can form a coordinate bond with a central ion
Define a Bidente the ligand
Two atoms that each donate a pair of electrons
Define coordination number
The number of coordinate bonds around a central atom or ion
define complex ion
An atom or ion surrounded by ligands
What is the shape of Cis Platin, co-ord number and Pt oxidation state
What are the elements in it and draw the atom
Pt, NH3, Cl
Square planar
4
+2
What is the shape of Silver ammonia, co-ord number and Ag oxidation state
[Ag(NH3)2]+
Linear
2
+1
Which transition metal is the active part of toluene’s regent, write an equation of how it is formed by dissolving in ammonia
Agile + 2NH3 —> [Ag(NH3)2] + Cl-
When drawing a 3d complex ion where do the coordinate bonds always stem from
The atom with the lone pair of electrons
Eg: Cu—:NH3
State the shape, co-ord number and oxidation state of ni in [Ni(H2NCH2CH2NH2)3]2+
Octahedral
6
+2
What is EDTA4-
Hexadentate ligand, it form is an octahedral shape. It forms 6 coordinate bonds, 2 coordinate bonds from the N atom and 4 coordinate bonds from the O- atoms
Explain what EDTA4- is
Hexadentate ligand- occupies an octahedral shape
Can form 6 coordinate bonds, 2 coordinate bonds form form the N atoms and 4 coordinate bonds from the O- atoms
Show how [Cu(H2O)6]2+ can be converted into [Cu(H2O)2(NH3)4]2+
[Cu(H2O)6]2+ + 4NH3 —> [Cu(H2O)2(NH3)4]2+ + 4H2O
Show the reaction between [Cu(H2O)6]2+ and cyanide - what changes
[Cu(H2O)6]2+ + Cn- —> [Cu(H2O)5CN]+ + H2O
The charge of the complex
Show the reaction between [Cu(H2O)6]2+ and Cl- ions- what changes?
[Cu(H2O)6]2+ + 4Cl- —> [CuCl4]2- + 6H2O
Blue solution Yellow
Coordination number 6. Coordination number 4
octehedral. Tetrahedral
What shape are chlorocomplexes and why
Tetrahedral- chlorine ligand is too big to fit any more than 4Cl- ligands around the metal ion
When does the chelate effect occur
When the monodentate ligand is substituted by a bidentate or a multidentate ligand
What type of substitution occurs in this reaction
Include change in ligand, change in moles and entropy change
Between [Cu(H2O)6]2+ and 3H2NCH2CH2NH2
Is this reaction therefore thermodynamically favourable
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 = [Cu(H2NCH2CH2NH2)3]2+ + 6H2O
Bidentate substitution
Change in ligand: from mono-bi
4 moles to 7 moles
Large increase in delta S
Very thermodynamically favourable as the large increase in entropy ions the chelate effect
What type of substitution happens between [Co(NH3)6]2+ + EDTA4-
Change in ligand, number of moles on each side, entropy change, is it thermodynamically stable
Multidentate substitution
[Co(NH3)6]2+ + EDTA4- = [CoEDTA]2- + 6NH3
Mono-Multi
2 moles to 7 moles
Large increase in entropy so thermodynamically favourable
The three stages of why this reaction is thermodynamically favourable using the equation delta G= delta H-Tdelta S
[Cu(NH3)6]2+ + 3H2NCH2CH2NH2 = [Cu(H2NCH2CH2NH2)3]2+ + 6NH3
Stage one delta H:
Delta H is negligible as your make and break the same number of bonds and make and break the same types of bonds/ bonds with similar enthalpies
Stage 2 delta S:
Increase in entropy, increase in particles in solution from 4 to 7 moles
Stage 3 delta G:
delta G is negative because Tdelta S is greater than. DeltaH
Describe haemoglobin and its structure
-Used to transport oxygen around the body
- made up of central Fe2+ ion which has a coordination number of 6
- forms 4 bonds to a ring system called porphyrin
- these bonds re square planar, the 5th bond to the Fe2+ is called a globin, one more bond can form above the ring and this is for O2
Describe the coordinate bonds in haemoglobin
- 4 coordinate bonds between fe2+ and the N atoms in the haem structure
- 1 coordinate bond between the Fe2+ and the protein globin
- 1 coordinate bond between the Fe2+ and O2
Describe how O2 can be transported around the body and how CO2 can from coordinate bonds with Fe2+
O2: needs to break the coordinate bonds to release O2, so the CO2 molecule can form a coordinate bond to the Fe2+ ion to be transported back to the lungs
How does CO poisoning occur
Carbon monoxide permanently coordinates to the Fe2+ meaning that haemoglobin can no longer transport O2 around the body
Define stereoisomerism
Same structural formula, different arrangement of atoms in space
Describe the two isomers of octehedral complexes
If the 2 ligands are arranged opposite each other (180) then this is a trans isomer
If the 2 ligands are arranged next to each other (90) then it is a cis isomer
Describe isomerism in square planar complexes - show this cisplatin and transplatin
If alike ligands are opposite each other then it is trans
If alike ligands are next to each other then it is cis
When do optical isomers occur in complex ions
When at least 2 bidente ligands on the central ion and the cis isomer will showtical isomerism
What colours fall within low energy light and which fall within high energy light
Low-ROY- red orange yellow
High-BIV- blue indigo violet
What is the colour of KMNO4
What is the colour of CuSO4
KMNO4– Absorbs yellow and green components of white light- the remaining colours which are transmitted make it appear purple
CuSO4– absorbs red, orange,yellow,green components of white light, the remaining colours transmitted make CuSO4 look blue
Why are transition metal ions coloured
They have partially filled d-sub shells
In a pure transition metal atom all d-sub shells are of equal energy- known as the ground state
In transition metal compounds, the presence of other atoms causes the d-orbitals to have slightly different energies
Enables electrons to be excited from one d-orbital to another
When an electron moves from a lower energy d orbital to a higher energy d orbital the energy needed to make the transition is taken from white light
The colours that are reflected give the compound in colour
What is delta
The difference in energy between the d-sub shells
What are the two equations for delta E
Delta E= Hf
H= Planck constant- 6.626x10-34
F= frequency of light (hz)
Delta E= h C/l
H= Planck constant
C= speed of light
L= wavelength of light
What happens if a compound has a large delta E between d-sub shells
High energy light (VIB) will be absorbed to excite D electrons
Low energy (ROY) light is transmitted
This means the compound will appear red
What happens if a transition metal compound has a small delta E between d-sub shells
Low energy light (ROY) will be absorbed to excite d electrons
High energy light (BIV) is transmitted
Compound will appear blue/purple
What 4 things can change the colour of a complex ion
-coordination number
-type/number of ligands
-oxidation state
-shape of complex
Show the different colours for the different oxidation states of Vo
VO2 + yellow
VO2+ Blue
V3+ green
V2+ Violet
Why may some complexes appear colourless
Why is Zn colourless
Have no d electrons or a full d sub shell
- doesn’t absorb visible light. D sub shell not partially full- if no d-electrons visible light can’t be absorbed
How to use a colorimeter
- a solution of light shines light of a specific frequency through a solution of transition metal compound
Some of the light is absorbed by the sample and some of the light is transmitted by the sample
The transmitted light hits the detector which measures how much light has passed through the sample
The detector gives a reading for the amount of light which passed through the sample
What does each transmittance mean
1.0= all the light passed through the sample and none was absorbed
0.5= 50% of the light was transmitted and 50% of the light was absorbed by the compound
0.0= all the light was absorbed by the transition metal compound
Give a method to determine the unknown concentrations of a transition metal ion solution
- An appropriate ligand such as -SCN is added to the solution in order to intensify the colour
- A range of solutions of the same complex ion are made of known concentrations
- One at a time these are tested in a colorimeter and the transmission or absorbance in measured
- A graph is plotted of conc vs transmission and a line of best fit drawn
- The transmission/absorbance of the unknown solution is measured in a colorimeter and its concentration is determined by reading off the calibration curve
What should you do before taking a reading
Place a cuvette filled with water into the colorimeter and set to 0- removes absorbance due to solvent and ensures accuracy
How does a colorimeter work
A filter us used which only allows one colour of light through the sample
How to find the conc of an unknown sample using calibration curve
Measure absorbance for a range of known concentrations
Plot a graph for absorbance against concentration
Read the value of the concentration for the measured absorbance of the graph
What is a catalyst
A substances which increases the rate of a chemical reaction without being used up
How does a catalyst work
Provide an alternative reaction pathway with lower activation energy
Homogenous catalyst definition
Where the catalyst is in the same phase as the reactant
How does a heterogenous catalyst work
Reactants adsorb onto the surface on an active site
Reaction occurs on the surface of the catalyst
Products desorb from the surface of the catalyst
Heterogenous catalyst definition
Catalyst is in a different phase to the reactants
Catalyst are expensive so how do you make them more efficient
Increase the surface area
Spread the catalyst over an inert support medium
How can poisoning of a catalyst occur
Impurities can block the active site
This prevents reactants from adsorbing
Purifying rage reactants is the best way to prevent poisoning
Equation for making ammonium in the haber process
Catalyst by solid iron
N2+3H2= 2NH3
Making sulfuric acid in the contact process
Catalyst by solid vanadium oxide- V2O5
Step 1
SO2 + V2O5 = SO3 + V2O4
Step 2
2V2O4 + O2 =2V2O5
Overall reaction
2SO2 + O2 = 2SO3
Manufacture of methanol- two reactions, the first forming a mixture of synthesis gas
1- CH4 + H2O—> CO + 3H2
2. Catalyst by solid chromium oxide
CO+ 2H2–> CH3OH
The equation when the homogeneous peroxodisulfate (S2O82-) oxidise I- to I2
The uncatalysed reaction has a high Ea as the two negative ions repel eachother
S2O8 2- + 2I- —> 2SO4 2- + I2
Catalysed by Fe2+
1: 2Fe2+ + S2O8 2- —> 2SO4 2- + 2Fe3+
2: 2Fe3+ + 2I- —> I2 + 2Fe2+ (remade)
What is an auto catalyst
One of the producers of the reaction catalyses the reaction as it proceeds further
Mn2+ working as an auto catalyst
1: MnO4- + 4Mn2+ + 8H+ —> 5Mn3+ + 4H2O
2: C2O42- + 2Mn3+ —> 2CO2 + 2mn2+
Overall: C2O42- + 2Mn3+ —> 2CO2 + 2mn+
Describe the graph when the reaction of MNO4- is tracked using a colorimeter
The rate starts of slow as there is no catalyst initially
The two negatively charged reactants collide with a very high ea
Then as some Mn2+ is formed the state increases as the reaction becomes increasingly catalysed
The rate then decreases and levels off as the reactants get used up
Equation for Fe2+ to Fe3+ providing colour change
Fe2+ —> Fe3+ + e-
Green to brown
MnO4- to Mn2+ and colour change
MnO4- + 8H+ + 8e- —> Mn2+ + 4H2O
Purple to colourless
Cr2O72- to 2Cr3+ and colour change
6e- + 14H+ + Cr2O72- —> 2Cr3+ + 7H2O
Orange to green
Cr2O72- to Cr3+ and colour change
6e- + 14H+ + Cr2O72- —> 2Cr3+ + 7H2O
Orange to green
Suggest why the zinc and acid were added
Reduce only Fe3+ to Fe2+ ions
Explain why it was necessary to remove excess zinc
Zinc would react with MnO4-
State why an excess of hydrogen ions is added to the reaction mixture
To ensure that all the MnO4- reacts to form Mn2+
Suggest one property of an impurity that would cause the calculated mass of FeSO4.7H2O was greater than the actual mass of the sample that had been weighed out
Reducing agent so would react with more dichromate
State the colour change that occurs at the end point of this titration and give a reason for this colour change
Colourless —> pink
Just after endpoint, MnO4- is in excess of
Explain why incorrect value for the number of moles of iron chloride formed would have been obtained if the original solution had been titrated with potassium manganate
KMnO4 will also oxidise Cl-
