Transition metals

Question 1

What is the definition of a transition metal?

Answer 1

An element which forms at least one stable ion with a partially filled subshell

Question 2

Why is scandium not a transition metal?

Answer 2

• The only ion formed is Sc3+
• The d subshell is empty

Question 3

Why is Zinc not a transition metal?

Answer 3

• The only ion formed is Zn2+
• The d subshell is full

Question 4

What are the 4 features of transition metals?

Answer 4

• Form complex ions
• Coloured ions
• Catalytic properties
• Variable oxidation states

Question 5

What is a ligand?

Answer 5

An ion or molecule with a lone pair of electrons which can form a coordinate bond with a transition metal ion

Question 6

What is a bidentate ligand?

Answer 6

A bidentate ligand has 2 atoms that each donate a lone pair of electrons

Question 7

What is the coordinate number?

Answer 7

The number of coordinate bonds a transition metal ion forms

Question 8

What is a complex ion?

Answer 8

A central atom or ion surrounded by ligands

Question 9

Describe the coordinate bonds that EDTA4- can form

Answer 9

Forms six coordinate bonds- 2 coordinate bonds from N and 4 coordinate bonds from O

Question 10

Explain why the reaction is thermodynamically favourable:
[Cu(NH3)6]2+ + 3H2NCH2CH2NH2 <=> [Cu(H2NCH2CH2NH2)3]2+ + 6NH3

Answer 10

Stage 1- H
- Delta H is negligible
- Make and break same number of bonds
- Make and break same type of bonds

Stage 2- S
- Increase in entropy
- Increase of moles in solution (from 4 to 7)

Stage 3- G
- G= H-TS
- G<0
- TS>H

Question 11

Why is CO toxic?

Answer 11

• Carbon monoxide permanently coordinates to Fe2+
• Hb can no longer transport oxygen around the body

Question 12

Explain when optical isomers occur in complex ions

Answer 12

• An octahedral complex has at least 2 bidentate ligands
• The Cis structure will have optical isomers

Question 13

Explain the energy of each wavelength of light

Answer 13

• ROY light = low energy
• BIV light = high energy

Question 14

What changes to transition metal ions can alter the colour of a compound?

Answer 14

• Change in ligands
• Change in oxidation state of metal
• Change in coordination number of complex
• Change in shape of complex

Question 15

Explain the process of using colorimetry to determine the unknown concentration of a transition metal ion solution

(5 marks)

Answer 15

• 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
• The absorbance of each is tested using a colorimeter
• A graph is plotted of conc vs transmision and line of best fit is drawn
• The absorbance of the unknown solution is measured in a colorimeter and its concentration is determined by reading off the calibration curve

Question 16

What is a catalyst?

Answer 16

• A substance which increases the rate of a chemical reaction
• Without being used up

Question 17

What is a heterogenous catalyst?

Answer 17

Where the catalyst is in a different phase to the reactants

Question 18

What is a homogenous catalyst?

Answer 18

Where the catalyst is in the same phase as the reactants

Question 19

Explain how heterogenous catalysts work

Answer 19

• Reactants adsorb onto the surface of the catalyst on an active site
• Reaction occurs on the surface of the catalyst
• Products desorb from the surface of the catalyst

Question 20

Give the equation for the Haber process and state what it is catalysed by

Answer 20

N2 + 3H2 <=> 2NH3

Catalysed by solid iron

Question 21

Give the equations of the 2 steps of the contact process and give the overall equation

Answer 21

Step 1:
SO2 + V2O5 => SO3 + V2O4
Step 2:
2V2O4 + O2 => 2V2O5

Overall reaction:
2SO2 + O2 => 2SO3

Question 22

Give the 2 equations of the manufacture of methanol

Answer 22

Formation of synthetic gas:
CH4 + H2O -> CO + 3H2

Then the following reaction is catalysed by solid Cr2O3:
CO + 2H2 -> CH3OH