Transition Metals

Question 1

Define ligand

Answer 1

A ligand is a molecule or ion that forms a coordinate bond with a transition metal by donating a pair of electrons

Question 2

Define complex

Answer 2

A complex is a central metal atom or ion surrounded by ligands

Question 3

Define coordination number

Answer 3

Number of coordinate bonds to the central metal atom or ion

Question 4

Define transition metals

Answer 4

A transition element is one that forms at least one stable ion with a partially filled d sub-shell

Question 5

What are the key features of transition metals

Answer 5

1 - form complex ions
2 - coloured ions
3- catalytic properties
4 - variable oxidation states

Question 6

Define coordinate bond

Answer 6

A shared pair of electrons which have both come from the same atom

Question 7

Give examples of monodentate ligands, bidentate ligands and multidentate ligands

Answer 7

Monodentate - H2O, NH3, Cl-, CN-

Bidentate - H2NCH2CH2NH2 (ethane - 1,2 - diamine) and C2O42- (ethanedioate)

Multidentate - EDTA4-

Question 8

Define monodentate, bidentate and multidentate ligand

Answer 8

Monodentate - Each ligand forms 1 coordinate bond
Bidentate - each ligand forms 2 coordinate bonds
Multidentate - each ligand forms 2 or more coordinate bonds

Question 9

What are the four common shapes which transition metals complexes form and give examples

Answer 9

Octahedral - 6 coordinate bonds - H2O and NH3 (e.g. [cu(H2O)6]
Tetrahedral - 4 coordinate bonds - Cl- (e.g.CuCl42-)
Square planar - 4 coordinate bonds - CN- [Ni(CN)4]2- OR cis platin (e.g. [Pt(Cl2)2(NH3)2]
Linear - 2 coordinate bonds - Ag (e.g. [Ag(NH3)2]+

Question 10

Show how the complex [Cu(H2O)6]2+ can be converted into [Cu(H2O)3(NH3)3]2+

Answer 10

[Cu(H2O)6]2+ + 3NH3 ————> [Cu(H2O)3(NH3)3]2+ + 3H2O

Question 11

What is the chelate effect

Answer 11

When a monodentate ligand is substituted by a bidentate ligand or a multidentate ligand

Question 12

Explain why this reaction is feasible when changing [Cu(NH3)6]2+ to [Cu(H2NCH2CH2NH2)3]2+

Answer 12

There are 4 moles on the left
There are 7 moles on the right
There has been an increase in entropy
Delta S is more positive
Delta H is zero as same number of bonds are being broken and formed

Question 13

Haemoglobin

Answer 13

O2 forms a coordinate bond to Fe2+ in haemoglobin enabling oxygen to be transported in the blood
CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin
This prevents O2 from bonding to the Fe2+, causing suffocation

Question 14

Stereoisomers

Answer 14

Same structural formula but different arrangement of atoms in space

Question 15

Cis and trans

Answer 15

Cis - same side - displays optical isomerism mirror image
Trans - opposite sides

Question 16

What does cis platin do

Answer 16

Binds to DNA in cancer cells and stops cell replication

Question 17

Why are transition metals coloured (example blue)

Answer 17

1 - Transition metals are coloured because they have partially filled d subshells
2 - These electrons absorb a specific amount of energy from visible light and transmit the rest of the colours
3 - These d subshells electrons become excited and move from ground stable state to unstable state
ROY is mostly absorbed
BIV is transmitted

Question 18

What is the energy for the different colours

Answer 18

SMALL E ROY - low energy - long wavelength
BIG E BIV - high energy - short wavelength

Question 19

What is delta E

Answer 19

Difference in energy between ground state and excited state

Question 20

What are the 2 equations for delta E

Answer 20

Delta E = hv
Delta E = h(c/wavelength)

H = plancks constant
V = frequency of light

Question 21

If there is a change to delta E it can change the colour of the compound. What things can change the colour

Answer 21

Change in ligand
Change in oxidation state
Change in coordination number
Change in shape

Question 22

Writing frame for if it is a red solution

Answer 22

If has a large delta E between d subshells
High energy light BIV will be absorbed to excite electrons
ROY is reflected
This means co pound will look red

Question 23

Key points of calorimetry

Answer 23

Measure absorbance for a range of known concentrations
Plot a graph of absorbance against concentration
Read the value of the concentration for the measured absorbance from the graph

Question 24

Heterogenous catalyst vs homogenous catalyst

Answer 24

Heterogenous - catalyst is in a different phase to the reactants
Homogenous - where the catalyst is in same phase as the reactants

Question 25

Mechanism for heterogenous catalysts

Answer 25

1) Reactants aDsorb (stick to) onto the surface of catalyst on active site
2) reaction occurs on the surface of that catalyst
3) Products desorb from the surface of the catalyst

Question 26

Homogenous catalyst example you need to know

Answer 26

S2O82- + 2I- ————> 2SO₄²- + I2

Reaction is catalysed by Fe2+ ions
Combine redox reactions for S2O8- ——> SO₄²- and Fe2+ ——> Fe3+
Step 1: S2O82- + 2FE2+ ————> 2SO₄²- + 2Fe3+

STEP 2: combine redox reaction for I- ———> I2 and Fe3+ ———> Fe2+
2I- + 2Fe3+ ———> I2 + 2Fe2+

Question 27

What is autocatalysis

Answer 27

Where one of the products of the reaction actually catalyses the reaction as it proceeds further.

Question 28

Autocatalysis example you just know

Answer 28

Combine redox reaction of MnO4- ———> Mn2+ and C2O42- ——> CO2
Uncatalysed reaction : 2MnO4- + 16H+ 5C2O42- ———> 2Mn2+ 8H2O + 10CO2

Mn2+ catalyse reaction in 2 step process. Initially rate is slow but as more catalyst produced the rate increases.

Step 1: combine the equation of MnO4- to Mn2+ and Mn2+ to Mn3+
4Mn2+ + MnO4- + 8H+ ———> 5Mn3+ +4H20
Mn2+ oxidised by MnO4- to Mn3+

Step 2: combine equation of Mn3+ to Mn2+ and C2O42- TO CO2
2Mn3+ + C2O42- ———> 2CO2 + 2Mn2+

Question 29

Describe the concentration vs time graph for autocatalysis of MnO4-

Answer 29

1- Rate starts off slow as there is no catalyst initially
2- The two negatively charged reactants collide with very high Ea
3 - Then as some Mn2+ is formed the rate increases as the reaction is being increasingly catalysed
4- The rate then decreases and levels off as the reactants get used up