2. Properties of transition elements

Question 1

special chemical properties of transition elements

Answer 1

1. can exist in variable oxidation states e.g Fe2+ and Fe3+

2. form coloured ions e.g. Fe2+ ions are green and Fe3+ ions are yellow

Question 2

why do transition elements show variable oxidation states

Answer 2

energy levels of 4s and 3d subshells are very close together.
different numbers of electrons can be gained or lost using fairly similar amounts of energy

Question 3

Why do Transition elements and their compounds make good catalysts?

Answer 3

they can change oxidation states by gaining or loosing electrons from their D orbitals.
they can transfer electrons to speed up reactions.
Transition metals are also good at adsorbing substances onto their surface to lower the activation energy of reactions.

Question 4

What reaction does CuSO4 catalyse?

oxidation state of copper 2+

Answer 4

reaction of zinc with acids

Question 5

Equation where CuSO4(s) acts as a catalyst

oxidation state of copper 2+

Answer 5

Zn(s) + H2SO4(aq) —-> ZnSO4(aq) + H(g)

Question 6

What reaction does MnO2 catalyse?

oxidation state of Manganese 4+

Answer 6

decomposition og hydrogen peroxide

Question 7

Equation where MnO2(s) acts as a catalyst

oxidation state of Manganese 4+

Answer 7

2H2O2(aq) —-> 2H2O(l) + O2(g)

Question 8

What reaction does Fe catalyse?

oxidation state of iron 0

Answer 8

Haber process to produce ammonia

Question 9

Equation where Fe(s) acts as a catalyst

oxidation state of iron 0

Answer 9

N2(g) + 3H2(g) —-> 2NH3(g)

Question 10

Why are catalysts good for industry and environment?

Answer 10

allow reactions to happen faster and at lower temperatures and pressures
reducing energy useage

Question 11

Why do transition metal catalysts pose health risks?

Answer 11

many of the metals and their compounds are toxic

Question 12

How does long term exposure to copper pose health risks?

Answer 12

can damage liver and kidneys

Question 13

How does exposure to manganese pose health risks?

Answer 13

can cause psychiatric problems

Question 14

the 2 Formulas of transition elements in aqueous solutions?

Answer 14

[M(H2O)6}n+

M n+(aq) (as long as transition metal is only bonded to water)

Question 15

What do you get when you mix aqueous solution of transition element ions with aqueous sodium hydroxide (NaOH) OR aqueous ammonia (NH3)

Answer 15

a coloured hydroxide precipitate

Question 16

Copper II (2+)
reaction with sodium hydroxide

Answer 16

[Cu(H2O)6]2+(aq) + 2OH-(aq) -> Cu(OH)2(H2O)4 + 2H2O(l)
can also be written as
Cu2+(aq) + 2OH-(aq) -> Cu(OH)2(s)

Question 17

Copper II (2+)
reaction with ammonia

Answer 17

[Cu(H2O)6]2+(aq) + 2NH3(aq) -> Cu(OH)2(H2O)4 + 2NH4+(aq)

Question 18

Copper II (2+)
reaction with excess ammonia

Answer 18

Cu(OH)2(H2O)4 reacts further to form

[Cu(NH3)4(H2O)2]2+ (aq)

Question 19

Copper II (2+)

1. colour change with Ammonia/sodium hydroxide
2. colour change with excess ammonia

Answer 19

1. pale blue solution to a blue precipitate

2. dark blue

Question 20

Iron II (2+)
reaction with sodium hydroxide

Answer 20

[Fe(H2O)6]2+(aq) + 2OH-(aq) -> Fe(OH)2(H2O)4 + 2H2O(l)
can also be written as
Fe2+(aq) + 2OH-(aq) -> Fe(OH)2(s)

Question 21

Iron II (2+)
reaction with ammonia

Answer 21

[Fe(H2O)6]2+(aq) + 2NH3(aq) -> [Fe(OH)2(H2O)4] + 2NH4+(aq)

Question 22

Iron II (2+)
1. colour change with Ammonia/sodium hydroxide

Answer 22

1. pale green solution to a green precipitate which darkens on standing

Question 23

Iron III (3+)
reaction with sodium hydroxide

Answer 23

[Fe(H2O)6]3+(aq) + 3OH-(aq) -> Fe(OH)3(H2O)3 + 3H2O(l)
can also be written as
Fe3+(aq) + 3OH-(aq) -> Fe(OH)3(s)

Question 24

Irons III (3+)
reaction with ammonia

Answer 24

[Fe(H2O)6]3+(aq) + 3NH3(aq) -> [Fe(OH)3(H2O)3}(s) + 3NH4+(aq)

Question 25

Iron III (3+)
1. colour change with Ammonia/sodium hydroxide

Answer 25

1. yellow solution to an orange precipitate which darkens on standing

Question 26

Manganese II (2+)
reaction with sodium hydroxide

Answer 26

Mn(H2O)6 + 2OH-(aq) -> Mn(OH)2(H2O)4 + 2H2O
oxidation can be summarised by:
Mn(OH)2 + O2 -> 2Mn2O3 + 4H2O

Question 27

Manganese II (2+) 
reaction with ammonia

Answer 27

[Mn(H2O)6]2+(aq) + 2NH3(aq) -> Mn(OH)2(H2O)4 + 2NH4+(aq)

Question 28

Manganese II (2+)
1. colour change with ammonia/sodium hyrdroxide

Answer 28

1. pale pink solution to a pink/buff precipitate which darkens on standing

Question 29

Chromium (III) (3+)

reaction with sodium hydroxide

Answer 29

[Cr(H2O)6}3+(aq) + 3OH-(aq) -> Cr(OH)3(H2O)3 + 3H2O
Then
Cr(OH)3(H2O)3 + 3OH-(aq) -> [Cr(OH)6]3-(aq) + 3H2O

Question 30

Chromium (III) (3+)

reaction with ammonia

Answer 30

[Cr(H2O)6]3+(aq) + 3NH3(aq) -> Cr(OH)3(H2O)3 + 3NH4(aq)
Then
Cr(OH)3(H2O)3 + 6NH3(aq) -> [Cr(NH3)6]3+(aq) + 3H2O + 3OH-(aq)

Question 31

Chromium (III) (3+)

1. colour change with ammonia/sodium hyrdroxide
2. colour change with excess sodium hydroxide
3. colour change with excess ammonia

Answer 31

1. green solution to a grey/green precipitate
2. dark green solution
3. purple solution