24.4 ligand substitution and precipitation

Question 1

what is ligand substitution?

Answer 1

when one ligand in a complex ion is replaced by another ligand

Question 2

what happens when copper (II) sulfate is dissolved in water?

Answer 2

[Cu(H 2O) 6] 2+ is formed

Question 3

what colour is [Cu(H 2O) 6]2+?

Answer 3

pale blue

Question 4

what happens when excess ammonia is added to [Cu(H2O)6]2+?

Answer 4

Question 5

what colour is [Cu(NH3)4 (H2O)2]2+ ?

Answer 5

dark blue

Question 6

how is the ammonia added to the [Cu(H20)6]2+ ?

Answer 6

dropwise

Question 7

what intermediate is formed when ammonia is added dropwise to [Cu(H20)6]2+ ?

Answer 7

Cu(OH)2

Question 8

what colour precipitate is Cu(OH)2 ?

Answer 8

pale blue

Question 9

what are the colour changes in the ligand substitution in [Cu(H2O)6]2+ ?

Answer 9

Question 10

what are the shapes of [Cu(H2O)6]2+ and [Cu(H2O)2 (NH3)4]2+ ?

Answer 10

octahedral

Question 11

what happens when HCl is added dropwise to [Cu (H20)6]2+ ?

Answer 11

Question 12

what is the colour of [Cu(H20)6]2+ ?

Answer 12

Question 13

what is the colour of [CuCl4]2- solution?

Answer 13

yellow

Question 14

why is there a change in shape from octahedral to tetrahedral?

Answer 14

chloride ligands are larger than water ligands so only 4 chlorine molecules can fit in

therefore the coordination number changes from 6 to 4

Question 15

what kind of reaction is ligand substitution with Cl- ions?

Answer 15

a reversible reaction

Question 16

what would happen if the concentration of water was increased in this equation?

Answer 16

the EQ will shift to the left to form some [Cu(H20)6]2+ which reacts with the remaining [CuCl4]2- to form a pale green solution

this is because yellow and blue are mixed

Question 17

steps of ligand substitution with chloride ions?

Answer 17

1. [Cu(H20)6]2+ reacts with HCl to form [CuCl4]2-
2. this forms a yellow solution
3. when H2O is added then the EQ shifts left and a pale green solution forms

Question 18

what are the colour changes in ligand substitution with chloride ions?

Answer 18

Question 19

what is formed when chrome alum is dissolved in water?

Answer 19

[Cr(H2O)6] 3+

Question 20

what colour is [Cr(H2O)6] 3+ ?

Answer 20

violet

Question 21

what happens when NH3 is added dropwise to [Cr(H2O)6] 3+ ?

Answer 21

Question 22

what colour is [Cr(NH3)6] 3+ ?

Answer 22

purple

Question 23

what shape are both [Cr(H2O)6] 3+ and [Cr(NH3)6] 3+ ?

Answer 23

octahedral

Question 24

what are the colour changes in the reaction if ammonia with chromium (III) ions?

Answer 24

Question 25

what intermediate is formed when [Cr(H2O)6] 3+ reacts with excess ammonia dropwise?

Answer 25

Cr(OH)3 is formed

Question 26

what colour is Cr(OH)3 ?

Answer 26

grey-green

Question 27

what is a precipitation reaction?

Answer 27

when two aqueous solutions containing ions react together to form an insoluble ionic solid (a precipitate)

Question 28

what ions do not dissolve in excess NaOH in a precipitation reacion?

Answer 28

Cu2+
Fe2+
Fe3+
Mn2+

Question 29

what ion does NaOH provide?

Answer 29

OH-

Question 30

Cu2+ + 2OH-

aqueous and blue

Answer 30

Cu(OH)2

solid and blue

Question 31

Fe 2+ + 2OH-

aqueous and green

Answer 31

Fe(OH)2

solid and green

Question 32

what happens when Fe(OH)2 reacts with air?

Answer 32

Fe(OH)3 forms

orange brown solid

Question 33

Fe 3+ + 3OH-

aqueous and yellow

Answer 33

Fe(OH)3

solid and orange-brown

Question 34

Mn2+ + 2OH-

aqueous and pink

Answer 34

Mn(OH)2

solid and light-brown

Question 35

what ion does dissolve in NaOH?

Answer 35

Cr3+

Question 36

Cr3+ + 3OH-

aqueous and violet

Answer 36

Cr(OH)3

solid and green

Question 37

Cr(OH)3 + 3OH-

solid and green

Answer 37

[Cr(OH)6] 3-

aqueous and dark green

Question 38

what ions are soluble in NH3?

Answer 38

Cr3+
Cu2+

Question 39

what ions are insoluble in NH3?

Answer 39

Fe2+
Fe3+
Mn2+