SS - Iron and Transition Metals

Question 1

What 2 reactants must iron be exposed to, to rust?

Answer 1

Oxygen and Water

Question 2

Give the 2 half-equations and thus the overall reaction for the ionisation of iron when rusting

Answer 2

Fe (s) ⇌ Fe²⁺ (aq) + 2e⁻
2H₂O (l) + O₂ (g) + 4e⁻ ⇌ 4OH⁻ (aq)

2H₂O (l) + O₂ (g) + 2Fe (s) ⇌ Fe²⁺ (aq) + 4OH⁻ (aq)

Question 3

When iron rusts, what 2 precipitates are formed and how does the 1st become the 2nd?

Answer 3

Fe(OH)₂ is further oxidised to Fe(OH)₃

Question 4

Give the equation for the oxidation of Iron (II) hydroxide

Answer 4

2H₂O (l) + O₂ (g) + 4Fe(OH)₂ (s) → 4Fe(OH)₃ (s)

Question 5

What is the final product for the rusting of Iron?

Answer 5

Hydrated iron (III) oxide
Fe₂O₃∙xH₂O

Question 6

Name 2 ways of preventing rusting

Answer 6

• Coating the iron with a barrier to keep oxygen or water away
• Using a sacrificial metal

Question 7

Name a common sacrificial metal and describe how it prevents rusting

Answer 7

Zinc
Because the Zn/Zn²⁺ system has a more negative Eᶱ value than the Fe/Fe²⁺ system, meaning the zinc will be oxidised to Zn²⁺ ions in a preference to the ion
A coating of zinc is sprayed onto the object (galvanising) or blocks of zinc can be bolted to the iron (like on the hull of ships)

Question 8

Name a common alloy of iron

Answer 8

Steel

Question 9

Describe the 3 stages for the recycling of iron and steel

Answer 9

1) Iron and steel are separate from other recyclables by passing the mixture of materials under a magnet
2) The iron and steel are then cleaned by melting it in a furnace and blowing Oxygen through to burn off the impurities (e.g. Carbon). The temperature rises as the impurities are removed but this is controlled by adding more solid iron and steel to be recycled
3) After the impurities have been removed, carbon and other elements such as nickel, chromium or manganese may be added in controlled amount obtain steel with exactly the desired properties

Question 10

How are metals removed from their ores?

Answer 10

Reduction

Question 11

Give 3 methods in which metals can be extracted from their ores by reduction

Answer 11

1) Heating with Carbon
2) Reduction by a more reactive metal
3) Electrolysis

Question 12

Describe the method for extracting a metal from its ore with Carbon

Answer 12

The Carbon is oxidised to Carbon Monoxide and then to Carbon Dioxide, each time losing electrons and thus reducing the metal

Question 13

Give a positive and negative for using Carbon to extract metal from its ore

Answer 13

+ve - It’s a cheap method because there are lots of cheap sources of Carbon
-ve - It doesn’t work with reactive metals because the carbon isn’t a strong enough reducing agent

Question 14

Describe the method for extracting a metal from its ore by reducing it with a more reactive metal and give a disadvantage about the method

Answer 14

Very reactive metals (e.g. Sodium) are powerful reducing agents. They’re used in the extraction of metals like titanium.
In order get the pure metal, the metal compound is heated with sodium or magnesium
It is expensive due to the high cost of sodium metal

Question 15

Describe the method of extracting a metal from its ore by electrolysis and give a disadvantage about this method

Answer 15

An electric current is passed through the molten ore

1) The power supply draws electrons out of the metal in the impure lump, oxidising it to form positive ions
2) As the impure metal electrode is oxidised, any impurities fall to the bottom of the cell
3) The positive ions pass through the electrolyte (usually a solution of a salt and the metal) since they are attracted to the negative electrode
4) The negative electrode starts as a thin piece of pure metal (the same as being extracted). The metal ions receive electrons and are reduced when they arrive at the cathode, which adds to the pure metal electrode

This method is expensive since high temperatures are needed to melt the ore, and a lot of electricity is used

Question 16

In which block in the periodic table are transition elements found?

Answer 16

d-block

Question 17

Explain why Scandium and Zinc are not technically transition metals

Answer 17

The transition metals are compounds that form at least 1 stable ion where the compound has an incomplete d subshell.
Therefore, Scandium is not a transition metal, because it forms only Sc³⁺ ions with no d-electrons, and Zn is not a transition metal because it forms only Zn²⁺ ions with all the 3d electrons present.

Question 18

Define transition metal

Answer 18

A transition metal is a metal that can form at least one stable ion with an incomplete d-subshell

Question 19

Give the electron configuration for Chromium and explain why

Answer 19

1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵ 4s¹

One electron moves from the 4s subshell to the 3d shubshell since a full or half-full d-subshell is more stable

Question 20

Give the electron configuration for Copper and explain why

Answer 20

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s¹

One electron moves from the 4s subshell to the 3d shubshell since a full or half-full d-subshell is more stable

Question 21

When ions of transition metals are formed, which subshell electrons are removed first?

Answer 21

s electrons

Question 22

State 4 special chemical properties that transition elements have

Answer 22

1) They can form complex ions
2) They can exist in variable oxidation states
3) They form coloured ions
4) Transition metals and their compounds make good catalysts

Question 23

Give the 2 occurring oxidation states of Copper and state the colour of their aqueous solutions

Answer 23

+1 and +2

• Cu⁺ ions are unstable so disproportionate in aqueous solution: 2Cu⁺ → Cu²⁺ + Cu
• Cu²⁺ ions are pale blue in aqueous solution

Question 24

Explain why transition metals (such as iron) can exist in variable oxidation states

Answer 24

The 4s and 3d orbitals are all at very similar energy levels, so there isn’t much difference between the energy levels of 2 different ions that remove either 4s or 3d orbital electrons
Therefore, no single electronic configuration is the most stable, so several can exist - each with a different oxidation state

Question 25

Explain why transition metals and their compounds make good catalysts

Answer 25

Because they can change oxidation states by gaining or losing electrons within their d-orbitals, meaning they can transfer electrons to speed up reaction

Question 26

Give 3 examples of transition metals or their compounds being use as catalysts

Answer 26

1) Iron is the catalyst for the Haber process, to produce ammonia
2) Vanadium (V) Oxide, V₂O₅, is the catalyst used in the Contact process to make sulfuric acid
3) Nickel is the catalyst used to harden margarine

Question 27

What do aqueous transition metals form when NaOH is added?

Answer 27

A coloured precipitate

Question 28

Why is a coloured precipitate formed when NaOH is added to aqueous transition metal?

Answer 28

• Transition metal ions in aqueous solution form complex ions with the water
• Adding hydroxide ions removes H⁺ from the water ligands, taking away the positive charge - neutralising the complex ion
• A precipitate is formed because the neutralised complex ion is unable to dissolve in water

Question 29

Give the colour of Iron (II) ions in solution

Answer 29

Green

Question 30

Give the colour of Iron (III) ions in solution

Answer 30

Orange / Brown

Question 31

Give the colour of Copper (II) ions in solution

Answer 31

Pale Blue

Question 32

Give the equation and colour change for the addition of NaOH to a solution of Iron (II) ions

Answer 32

[Fe(H₂O)₆]²⁺ + 2OH⁻ → [Fe(H₂O)₄(OH)₂] + 2H₂O

Green solution → Green precipitate

Question 33

Give the equation and colour change for the addition of NaOH to a solution of Iron (III) ions

Answer 33

[Fe(H₂O)₆]³⁺ + 3OH⁻ → [Fe(H₂O)₃(OH)₃] + 3H₂O

Orange / Brown solution → Rust-brown precipitate

Question 34

Give the equation and colour change for the addition of NaOH to a solution of Copper (II) ions

Answer 34

[Cu(H₂O)₆]²⁺ + 2OH⁻ → [Cu(H₂O)₄(OH)₂] + 2H₂O

Pale blue solution → Blue precipitate

Question 35

Describe the 2 ways in which Ammonia can react with transition metals

Answer 35

1) A little NH₃ reacts in the same way as adding NaOH - removing H⁺ ions and forming a precipitate
2) When a large amount of NH₃ is added, the second reaction happens, where the precipitate dissolves causing a solution, because the NH₃ molecules can act as ligands

Question 36

Give the equations and colour changes for the reaction between aqueous Copper (II) ions and:

i) A little NH₃
ii) A lot of NH₃

Answer 36

i) [Cu(H₂O)₆]²⁺ + 2NH₃ → [Cu(H₂O)₄(OH)₂] + 2NH₄⁺
Pale blue solution → Blue precipitate

ii) [Cu(H₂O)₆]²⁺ + 4NH₃ → [Cu(NH₃)₄]²⁺ + 6H₂O
Pale blue solution → Intense blue solution

Question 37

Explain why transition metals are good homogeneous catalysts

Answer 37

Because they can change oxidation states easily

Question 38

Name and explain 2 conditions for a good heterogeneous catalyst

Answer 38

1) Attract reactant molecules strongly enough so that they are held to the surface long enough to react
2) Not attract the product molecules so strongly that they won’t be able to be able to desorb and block the catalyst from the fresh reactants