Ligand substitution reactions

Question 1

What are two similarly sized ligands?

Answer 1

H2O and NH3

Question 2

What happens to the co-ordination number if the ligands are a similar size?

Answer 2

There will be no change

Question 3

What ligand is larger than H2O and NH3?

Answer 3

Cl-

Question 4

What happens to the co-ordination number when Cl- replaces H2O and NH3 in an octahedral complex?

Answer 4

Reduces from 6 to 4

Question 5

What happens to the shape if the complex when Cl- replaces H2O and NH3 in an octahedral complex?

Answer 5

changes from octahedral to tetrahedral

Question 6

What is a partial substitution of ligands?

Answer 6

Not all ligands are substituted for other ligands

Question 7

What is haemoglobin?

Answer 7

A protein found in blood that helps to transport oxygen around the blood

Question 8

What ions does haemoglobin contain?

Answer 8

Fe2+

Question 9

What co-ordination number do the Fe2+ ions in haemoglobin have?

Answer 9

6

Question 10

How many lone pairs does Fe2+ receive from nitrogen atoms?

Answer 10

4

Question 11

What is porphyrin?

Answer 11

A multi dentate ligand which the 4 nitrogen atoms are a part of

Question 12

Other than nitrogen, where do the other two lone pairs for the Fe2+ come from?

Answer 12

Globin (a protein)

Either an oxygen or a water molecule

Question 13

What happens to haemoglobin in the lungs?

Answer 13

The oxygen concentration is high so water ligands are substituted for oxygen molecules to form oxyhaemoglobin

Question 14

What happens to haemoglobin when it reaches the place where oxygen is needed?

Answer 14

The oxygen molecules are exchanged for water molecules

Question 15

How is carbon monoxide poisonous?

Answer 15

The water and oxygen molecules are substituted for carbon monoxide ligands, forming carboxyhaemoglobin , meaning the haemoglobin can’t carry oxygen anymore

Question 16

Which molecule binds most strongly to the iron, carbon monoxide, water or oxygen?

Answer 16

Carbon monoxide

Question 17

what two things is complex ion stability affected by?

Answer 17

Enthalpy change

Entropy change

Question 18

When is it hard for ligand exchange reactions to be reversed?

Answer 18

If the new complex is much more stable than the last

Question 19

What type of ligand forms a more stable complex than mono dentate?

Answer 19

Multidentate and bidentate

Question 20

How does enthalpy change during a ligand substitution reaction?

Answer 20

The enthalpy change is very small

Question 21

Why is the enthalpy change during a ligand substitution the way it is?

Answer 21

The strengths of the bonds being broken is often very similar to the strength of the new bonds being made

Question 22

What happens to the entropy when mono dentate ligands are substituted with multi dentate ligands? why?

Answer 22

Increases

Increases the number of particles

Question 23

What is the chelate effect?

Answer 23

Multidentate ligands always forming much more stable complexes than mono dentate ligands